Miyakoda, Kikuro, Annalisa Cherchi, A Navarra, S Masina, and Jeff J Ploshay, February 2012: ENSO and its effects on the atmospheric heating processes. Journal of the Meteorological Society of Japan, 90(1), DOI:10.2151/jmsj.2012-103. Abstract
El Ni˜no-Southern Oscillation (ENSO) is an important air-sea coupled phenomenon that plays a dominant role in the
variability of the tropical regions. Observations, atmospheric and oceanic reanalysis datasets are used to classify ENSO
and non-ENSO years to investigate the typical features of its periodicity and atmospheric circulation patterns. Among
non-ENSO years, we have analyzed a group, called type-II years, with very small SST anomalies in summer that tend
to weaken the correlation between ENSO and precipitation in the equatorial regions. A unique character of ENSO is
studied in terms of the quasi-biennial periodicity of SST and heat content (HC) fields over the Pacific-Indian Oceans.
While the SST tends to have higher biennial frequency along the Equator, the HC maximizes it into two centers in the
western Pacific sector. The north-western center, located east of Mindanao, is strongly correlated with SST in the NINO3
region. The classification of El Ni˜no and La Ni˜na years, based on NINO3 SST and north-western Pacific HC respectively,
has been used to identify and describe temperature and wind patterns over an extended-ENSO region that includes the
tropical Pacific and Indian Oceans.
The description of the spatial patterns within the atmospheric ENSO circulation has been extended to tropospheric
moisture fields and low-level moisture divergence during November–December–January, differentiating the role of El
Ni˜no, when large amounts of condensational heat are concentrated in the central Pacific, from La Ni˜na that tends to
mainly redistribute heat to Maritime Continents and higher latitudes. The influence of the described mechanisms on
equatorial convection in the context of the variability of ENSO on longer timescales for the end of the 20th century is
questioned. However, the inaccuracy of the atmospheric reanalysis products in terms of precipitation and the shorter time
length of more reliable datasets hamper a final conclusion on this issue.
Yang, S, K M Lau, S-H Yoo, J L Kinter, Kikuro Miyakoda, and Chang-Hoi Ho, November 2004: Upstream subtropical signals preceding the Asian summer monsoon circulation. Journal of Climate, 17(21), DOI:10.1175/JCLI3192.1. Abstract
In this study, the authors address several issues with respect to the antecedent signals of the large-scale Asian summer monsoon that were earlier identified by Webster and Yang. In particular, they revisit the changes in the subtropical upper-tropospheric westerlies preceding the monsoon, depict the detailed structure of the monsoon's antecedent signals, and investigate the physical processes from the signals to the monsoon. They also explore the teleconnection of these signals to various large-scale climate phenomena and emphasize the importance of the upstream location of the signals relative to the Tibetan Plateau and the monsoon.
Before a strong (weak) Asian summer monsoon, the 200-mb westerlies over subtropical Asia are weak (strong) during the previous winter and spring. A significant feature of these signals is represented by the variability of the Middle East jet stream whose changes are linked to the Arctic Oscillation, North Atlantic Oscillation, El Nino-Southern Oscillation, and other climate phenomena. When this jet stream intensifies and shifts southeastward, cold air intrudes frequently from eastern Europe into the Middle East and southwestern Asia. As a result, in subtropical Asia, snow and precipitation increase, the ground wetness increases, and surface temperature decreases. A strengthening Middle East jet stream is also accompanied by increases in both stationary wave activity flux and higher-frequency eddy activities. The Tibetan Plateau acts to block these westerly activities propagating eastward and increase the persistence of the low-temperature anomalies, which in turn prolongs the atmospheric signals from winter to spring.
A strong link is found between the persistent low-temperature anomalies and the decrease in geopotential height over southern Asia, including the Tibetan Plateau, in spring. The latter indicates a late establishment of the South Asian high, and implies a delay in the atmospheric transition from winter to summer conditions and in the development of the summer monsoon. The preceding scenario for a strong Middle East jet stream and a weaker Asian monsoon can be applied accordingly for the discussion of the physical processes from a weak jet stream to a strong monsoon.
The current results of the relationship between the extratropical process and Asian monsoon resemble several features of the tropical-extratropical interaction mechanism for the tropospheric biennial oscillation (TBO). While the role of tropical heating is emphasized in the TBO mechanism, compared to the variability of the sea surface temperature related to El Nino-Southern Oscillation, the extratropical process examined in this study is more strongly linked to the Asian summer monsoon.
Miyakoda, Kikuro, J L Kinter, and S Yang, October 2003: The role of ENSO in the south Asian monsoon and pre-monsoon signals over the Tibetan plateau. Journal of the Meteorological Society of Japan, 81(5), 1015-1039. Abstract
El Nino and the Southern Oscillation (ENSO), and the South Asian (SA) summer monsoon interact with each other. In a previous paper, the process from the SA-monsoon to ENSO was discussed. In this paper, the process from ENSO to the monsoon is described.
As the consequence of ENSO events, a set of characteristic distributions of the temperature, wind and moisture is formed over the central and eastern Pacific Ocean. The anomalies of these fields are characterized by a "butterfly pattern" above the 500 hPa level, and a "horseshoe pattern" below 500 hPa. The patterns begin to appear in the winter, and influence the SA-monsoon in the following spring and summer. The distinct pattern of the butterfly shape may be explained by the extended Matsuno-Gill type dynamics, because the Pacific sector is dominated by the ENSO heating.
On the other hand, the Indian sector is characterized by the land-sea monsoon circulation. It is important to note that the anomaly components of this local circulation are controlled largely by ENSO. The air temperature anomaly of the layer between 200 and 500 hPa moves westward in the latitude belt of 20degrees-35degreesN over the Asian sector, which is associated with the butterfly pattern in the Pacific sector. During this migration, the signal provides a precursory background over the Tibetan Plateau in April-May-June at its peak, setting the stage for the initiation of the SA-monsoon. Another signal emanates also from the tropical Pacific to the Indian sector, in May-June-July at its peak, in conjunction with the horseshoe pattern of the sea surface temperature in particular. These signals emanate from the eastern part of the ENSO region, contribute to the establishment of the thermal contrast anomalies between land and ocean, and the anomalous wind system over the Indian sector, including the upward motion over the Indian subcontinent. The EOF (empirical orthogonal function) analysis of the sea surface temperature in the broader NINO3 region (15degreesN-15degreesS, 150degreesW-90degreesW) indicates that the two leading modes well represent the fields of horizontal wind and temperature for the Pacific sector (the first mode) as well as the Indian sector (the second mode).
Finally, the features associated with the 1976 climate shift are discussed. In the process from the SA-monsoon to ENSO, the mode of connection changed dramatically circa 1976; however, in the process from ENSO to the monsoon, the mode is almost the same before and after 1976. The reason for this asymmetry, in the change of the relationship, is discussed.
Kinter, J L., Kikuro Miyakoda, and S Yang, May 2002: Recent change in the connection from the Asian monsoon to ENSO. Journal of Climate, 15(10), 1203-1215. Abstract
The Asian monsoon and El Nino-Southern Oscillation (ENSO) are known to interact with each other. In this paper, four primary indices (the Indian monsoon rainfall index, the Webster and Yang monsoon index, the tropical-wide oscillation index, and the Southern Oscillation index) that characterize the temporal variation of these complex, chaotic and quasi-oscillatory phenomena are used to assess the action from the Asian monsoon to ENSO, that is, the linkage between the strong/weak monsoon and La Nina/El Nino. The evolution of the four previously documented indices and other auxiliary data over a 43-yr period is examined using the observed database and the reanalysis of the National Centers for Environmental Prediction. The Asian monsoon and ENSO intersect in a common area, namely, the warm pool in the western tropical Pacific. This region (e. g., 10degreesS-5degreesN, 110degrees-170degreesE) is located at the longitudinally central portion of the Walker circulation and also the equatorial end of the Indo-Pacific meridional overturning cell that is part of the zonal mean Hadley circulation. In recent decades, the connection between the monsoon and ENSO has changed considerably. This change is related to the atmospheric circulation over the entire North Pacific Ocean, which entered a new regime in about 1976. Before 1976, the correlations among the four primary indices, and those between the indices and the Nino-3 index of sea surface temperature, were strong. In recent decades, the ocean temperature in the entire North Pacific became considerably colder. The lower-tropospheric winds became simultaneously more cyclonic over the North Pacific. ENSO is now related to atmospheric fluctuations both in the Indian sector and in northeastern China. The western North Pacific monsoon in the vicinity of the Philippine Islands (9degrees-19degreesN, 139degrees-141degreesE) may play an important role together with the off-equatorial ocean heat content in a larger region (5degrees-15degreesN, 135degrees-170degreesE) in maintaining or even increasing ENSO activities.
Miyakoda, Kikuro, A Navarra, and M N Ward, October 1999: Tropical-wide teleconnection and oscillation. II: The ENSO-monsoon system. Quarterly Journal of the Royal Meteorological Society, 125(560), 2937-2963. Abstract
Two teleconnection indices, discussed in Part I, i.e. the Tropical-wide Oscillation Index (TOI) and the Walker circulation Index (WAI), are applied to the analysis of the ENSO-monsoon (El Nino Southern Oscillation-Asian monsoons) system. The first hypothesis presented in Part I was that the TOI for July-August-September (JAS) is closely related to the Indian summer monsoon index as well as the Southern Oscillation Index. As a result, the TOI represents the lead-lag characteristics of the tropical circulation variability over the eastern hemisphere (45 degrees E-170 degrees E) and simultaneously its interaction with the ENSO over the equatorial Pacific. The second hypothesis was that there are two types of connection between the ENSO and Asian monsoons: type I with distinct connection in space and time, and type II without connection. The WAI provides a measure for this connection. This idea is supported by comparisons of observed and model teleconnection structures in Part I.
Part II investigates these relations further. Time-lag correlations are calculated between the key indices and atmospheric variables over the equatorial Indo-Pacific Oceans. If type II years, derived by the WAI, are removed from the 34-year time series, correlations between the TOI and these variables increase appreciably, now showing clearly the biennial character. The analysis identifies a sequence of events involving biennial oscillation of the ENSO-monsoon system from approximately JAS(-1) to JAS(0), followed by intensification of the ENSO from JAS(0) to November-December-January(+1). The ENSO-monsoon oscillation system is not sinusoidal but skewed.
To show the geographical patterns associated with the above sequence of events, planar maps are presented of the lag correlation between the observed TOI(JAS) and (i) Vertical velocity at the 500 hPa level, (ii) precipitation, (iii) sea surface temperature (SST), and (iv) atmospheric sea level pressure. Distinct geographical distributions of the ENSO-monsoon oscillation emerge in both the observations and model data. One pattern is characterized by a horseshoe shape over the Pacific, which is generally symmetric around the equator, but with geographical differences depending on location in the lag sequence. The other pattern is a see-saw shape, primarily a standing oscillation located in the eastern South Pacific and the Indian Oceans, resembling the sea-level-pressure pattern found by Trenberth and Shea. Applying the lead-lag relationship, it is demonstrated that the SST over the central Pacific four months ahead can be projected, based on the TOI(JAS). Conversely, the intensity of the Indian monsoon rainfall for non-type II years can be projected 15 months ahead by the SST over the eastern Pacific Ocean. This indicates that the ENSO-monsoon oscillation system is quasi-periodic, as opposed to irregular, with a two-year cycle; this is clearly revealed with the removal of type II years.
Navarra, A, M N Ward, and Kikuro Miyakoda, October 1999: Tropical-wide teleconnection and oscillation. I: Teleconnection indices and type I/type II states. Quarterly Journal of the Royal Meteorological Society, 125(560), 2909-2935. Abstract
The tropical oscillation of the ENSO-monsoon (EI Nino Southern Oscillation-Asian monsoons) system is studied based on 34-year simulations of an atmospheric general-circulation model with specified sea surface temperature (SST), together with some observed data for the same period. In particular, two indices are studied: the first is the generalized index of Indian monsoon rainfall (IMR), and the other is an index by which the interaction/non-interaction between the ENSO and the Indian monsoon system is assessed.
In order to examine the validity of the first index, the Indian subcontinent and the near-equatorial western Pacific were selected as two key locations. They correspond, approximately, to the dominant regions in the first empirical orthogonal function of precipitation, for boreal summer and winter, respectively. These two regions form the western rim of a 'horseshoe' teleconnection pattern in their respective seasons. The time coefficients of empirical orthogonal function mode I in the two seasons are taken as the key indices which are referred to as the Tropical-wide Oscillation Index (TOI).
Having defined the spatial patterns in both seasons, the lead-lag teleconnection structure associated with the ENSO-monsoon system is studied; the result is that the TOI for boreal summer is more useful than the TOI for boreal winter for identifying the lead-lag nature of the ENSO-monsoon. The new index is then related to traditional indices like the IMR and the Southern Oscillation Index, but proves to be a more comprehensive index for lead-lag correlations with key variables, while the latter, the TOI for winter, has no precursory signal for the Indian monsoon for the following summer.
The second index is the Walker circulation Index (WAI), which represents the eastward/westward shift of the updraught region of the Walker circulation. It is proposed that the WAI can usefully distinguish between years when the ENSO-monsoon oscillation operates (type I) and years when it does not (type II). If the SST in the key region has a climatologically close-to-normal condition, the slate of the coupled equatorial system is in type II. On the other hand, if the deviation from climatology is large, the tropical-wide oscillation will continue to be active; these years are type I. Elimination of the type II years from the data significantly enhances the time-lagged correlations between the TOI and some key variables, such as SST. As a result, the biennial oscillation becomes clearer.
Miyakoda, Kikuro, Jeff J Ploshay, and Anthony Rosati, 1997: Preliminary study on SST forecast skill associated with the 1982/83 El Niño process, using coupled model data assimilation. Atmosphere-Ocean, 35(1), 469-486. Abstract PDF
A previous study by Rosati et al. (1997) has concluded that the specification of an adequate thermocline structure along the equatorial Pacific ocean is most crucial for El Niño forecasts. In that paper, the oceanic initial condition was generated by a data assimilation (DA) system (Derber and Rosati, 1989). However, the initial condition for the atmospheric part was taken from the National Meteorological Center's (NMC) operational analysis, which was simply attached to the oceanic part for the coupled model forecasts.
In the present paper, both the atmospheric and oceanic initial conditions are generated by a coupled DA system applied to a coupled air-sea general circulation model (GCM). The assimilation for the ocean is performed by the same system as mentioned above, in which the SST (sea surface temperature) and the subsurface temperatures are injected into a 15 vertical level oceanic GCM. The upper boundary condition, such as surface wind stress, is specified by the atmospheric DA. The assimilation for the atmosphere is performed by the continuous injection method of Stern and Ploshay (1992), using an 18 vertical level atmospheric GCM. The lower boundary condition, such as SST, is specified by the oceanic DA. The coupled model assimilations are carried out by switching the DA processes alternately every 6 hours between the ocean and the atmosphere.
The emphases of this study are: firstly, the effect of coupled air-sea model DA on the performance of subsequent forecsts; secondly, the impact of the coupled assimilation on improvement of the "spin-up" behavior of forecasts, i.e., to see whether a smooth start to the forecast is achieved by the coupled model DA process; and thirdly, investigation of the effect that the "spring barrier" has on predictability in the coupled GCM system. Preliminary results indicate that, in order to answer these questions, ensemble forecasts are necessary. Besides, the coupled assimilation could be important in improving the overall behavior of El Niño and La Niña forecasts.
A coupled atmosphere-ocean GCM (general circulation model) has been developed for climate predictions on seasonal to interannual timescales. The atmosphere model is a global spectral GCM T30L18 and the ocean model is global on a 1 degree grid. Initial conditions for the atmosphere were obtained from National Meteorological Center (now known as the National Centers for Environmental Prediction) analyses, while those for the ocean came from three ocean data assimilation (DA) systems. One system is a four-dimensional DA scheme that uses conventional SST observations and vertical temperature profiles inserted into the ocean model and is forced from winds from an operational analysis. The other two initialization schemes are based on the coupled model, both nudging the surface temperature toward observed SSTs and one nudging surface winds from an operational analysis. all three systems were run from 1979 to 1988, saving the state of the ocean every month, thus initial conditions may be obtained for any month during this period. The ocean heat content from the three systems was examined, and it was found that a strong lag correlation between Niño-3 SST anomalies and equatorial thermocline displacements exists. This suggests that, based on subsurface temperature field only, eastern tropical Pacific SST changes are possibly predictable at lead times of a year or more. It is this "memory" that is the physical basis for ENSO predictions.
Using the coupled GCM, 13-month forecasts were made for seven January and seven July cases, focusing on ENSO (El Niño-Southern Oscillation) prediction. The forecasts, whose ocean initial conditions contained subsurface thermal data, were successful in predicting the two El Niño and two La Niña events during the decade, whereas the forecasts that utilized ocean initial conditions from the coupled model that were nudged toward surface wind fields and SST only, failed to predict the events. Despite the coupled model's poor simulation of the annual cycle in the tropical Pacific, the ENSO forecasts from the full DA were remarkably good.
This study evaluates simulations of the East Asian winter monsoon in eight GCMs that participated in the Atmospheric Model Intercomparison Project (AMIP). In addition to validating the mean state of the winter monsoon, the cold surge and its transient properties, which includes the frequency, intensity, preferred propagation tracks, and the evolution patterns of the surges, are examined. GCM simulated temporal distribution of the Siberian high and cold surges is also discussed. Finally, the forcing of the cold surges on the tropical surface wind and convection, along with their interannual variation is analyzed. The mean state of the winter monsoon is generally portrayed well in most of the models. These include the climatological position of the Siberian high, the 200 hPa divergent center, and the large-scale wind patterns at the surface and the 200 hPa. Models display a wide range of skill in simulating the cold surge and its transient properties. In some of the models, the simulated cold surge trajectory, intensity, frequency, propagation patterns and source regions are in general agreement with those from the observed while in others, the models cannot adequately capture these observed characteristics. The temporal distribution of the Siberian high and cold surges were realistically reproduced in most GCMs. Most models were able to simulate the effect of the cold surges on the tropical surface wind, although a few models unrealistically generated subtropical southerly wind in the mid-winter. The relationship between cold surges and the tropical convection was not satisfactorily simulated in most models. The common discrepancies in the winter monsoon simulation can be attributed to many factors. In some models, the reason is directly related to the improper location of the large-scale convective center near the western Pacific. The satisfactory simulations of the monsoon circulation and the cold surges are partly due to the topographical characteristics of the East Asian continent, i.e., the Tibetan Plateau to the west and the oceans to the east. The correct simulation of the internnual variation of the surface wind near the South China Sea (SCS) and the maritime continent is a demanding task for most of the models. This will require adequate simulations of many aspects, including tropical convection, the Siberian cold dome, the extratropical-tropical linkage, and the air-sea interaction. The discrepancies noted here furnish a guide for the continuing improvement of the winter monsoon simulations. Improved simulations will lead to an adequate delineation of the surface wind and convection near the maritime continent, which is essential for portraying the winter monsoon forcing in a coupled model.
Zhang, Y, Kikuro Miyakoda, and Richard T Wetherald, et al., 1997: In GCM simulated East Asian winter monsoon: Results from eight AMIP models, PCMDI Report No. 39, Livermore, CA, PCMDI, 49 pp. Abstract
This paper evaluates simulations of the East Asian winter monsoon in eight GCMs that participated in the Atmospheric Model Intercomparison Project (AMIP). In addition to validating the mean state of the winter monsoon, the cold surge and its transient properties, which includes the frequency, intensity, preferred propagation tracks, and the evolution patterns of the surges, are examined. GCM simulated temporal distribution of the Siberian high and cold surges is also discussed. Finally, the forcing of the cold surges on the tropical surface wind and convection, along with their interannual variation is analyzed.
The mean state of the winter monsoon is generally portrayed well in the models considered. These include the climatological position of the Siberian high, the 200 hPa divergent center, and the large-scale wind patterns at the surface and 200 hPa. Models display a wide range of skill in simulating the cold surge and its transient properties. In some of the models, the simulated cold surge trajectory, intensity, frequency, propagaton patterns and source regions are in general agreement with those from the observed. While in others, the models cannot adequately capture these observed characteristics. The temporal distribution of the Siberian high and cold surges are realistically reproduced in most GCMs. Most models were able to simulate the effect of the cold surges on the tropical surface wind, although a few models unrealistically generated subtropical southerly wind in the mid-winter.
The common discrepancies in the winter monsoon simulation can be atttributed to many factors. In some models, the inadequate resolution and the improper locations of the tropical convection are the most notable reasons. The satisfactory simulations of the monsoon circulation and the cold surges are partly due to the topographical characteristics of the East Asian continent, i.e., the Tibetan Plateau to the west and the oceans to the east. The correct simulation of the interannual variation of the surface wind near the South China 9Sea (SCS) and the maritime continent is a demanding task for most of the models. This will require adequate simulations of many aspects, including tropical convection, the Siberian cold dome, the extratropical-tropical linkage, and the air-sea interaction.
The discrepancies noted here furnish a guide for the continuing improvement of the winter monsoon simulations. Improved simulations will lead to an adequate delineation of the surface wind and convection near the maritime continent, which is essential for portraying the winter monsoon forcing in a coupled model.
Rosati, Anthony, Richard G Gudgel, and Kikuro Miyakoda, 1996: Global ocean data assimilation system In Modern Approaches to Data Assimilation in Ocean Modeling, The Netherlands, Elsevier Science Publishers, 181-203. Abstract
A global oceanic four-dimensional data assimilation system has been developed for use in initializing coupled ocean-atmosphere general circulation models and also to study interannual variability. The data inserted into a high resolution global ocean model consists only of conventional sea surface temperature observations and vertical temperature profiles. The data are inserted continuously into the model by updating the model's temperature solution every timestep. This update is created using a statistical interpolation routine applied to all data in a 30-day window for three consecutive timesteps and then the correction is held constant for nine timesteps. Not updating every timestep allows for a more computational efficient system without affecting the quality of the analysis.
The data assimilation system was run over a ten year period from 1979-1988. The resulting analysis product was compared with independent analysis including model derived fields like velocity. The large scale features seem consistent with other products based on observations. Using the mean of the ten-year period as a climatology, the data assimilation system was compared with the Levitus climatological atlas. Looking at the sea surface temperature and the seasonal cycle, as represented by the mixed layer depth, the agreement is quite good, however, some systematic differences do emerge.
Special attention is given to the tropical Pacific examining the El Niño signature. Two other assimilation schemes based on using Newtonian nudging of SST, are compared to the full data assimilation system. The heat content variability in the data assimilation seemed faithful to the observations. Overall, the results are encouraging, demonstrating that the data assimilation system seems to be able to capture many of the large scale general circulation features that are observed, both in a climatological sense and in the temporal variability.
Gleckler, Peter J., Kikuro Miyakoda, and William F Stern, et al., 1995: Cloud-radiative effects on implied oceanic energy transports as simulated by atmospheric general circulation models. Geophysical Research Letters, 22(7), 791-794. Abstract PDF
This paper summarizes the ocean surface net energy flux simulated by fifteen atmospheric general circulation models constrained by realistically-varying sea surface temperatures and sea ice as part of the Atmospheric Model Intercomparison Project. In general, the simulated energy fluxes are within the very large observational uncertainties. However, the annual mean oceanic meridional heat transport that would be required to balance the simulated surface fluxes is shown to be critically sensitive to the radiative effects of clouds, to the extent that even the sign of the Southern Hemisphere ocean heat transport can be affected by the errors in simulated cloud-radiation interactions. It is suggested that improved treatment of cloud radiative effects should help in the development of coupled atmosphere-ocean general circulation models.
Miyakoda, Kikuro, Joseph J Sirutis, Anthony Rosati, C Tony Gordon, Richard G Gudgel, William F Stern, Jeffrey L Anderson, and A Navarra, 1995: Atmospheric parameterizations in coupled air-sea models used for forecasts of ENSO In Proceedings of the International Scientific Conference on the Tropical Ocean Global Atmosphere (TOGA) Programme, WCRP-91, WMO/TD No. 717, Geneva, Switzerland, World Meteorological Organization, 802-806. Abstract
In order to investigate the feasibility of seasonal forecasts, a prediction system is developed. Here the main theme is the study of atmospheric physics parameterization for coupled air-sea modeling. The oceanic GCM uses 1 degree global grid with a finer resolution in the equatorial belt. The atmospheric GCM has the spectral T30 representation, which includes all of the usual physics parameterizations. Using a first version of the model (Coupled Model I) and a set of appropriate initial conditions, the capability of El Niño and La Niña forecasting with a 13 month lead time was tested, resulting in successful forecasts of the 1982/83 and 1988/89 events (Rosati et al., 1995b). However, longer runs of this system have revealed a sizable systematic error in simulations with a tendency to cool most of the world ocean, particularly the western tropical Pacific, and also without an adequate annual cycle of the SST in the eastern tropical Pacific.
In order to improve some of these features, particularly the ENSO phenomena, various versions of the atmospheric parameterizations and mountain representation are incorporated into the atmospheric GCM, and the model simulations are examined. The experiments are divided into two steps: one is with the uncoupled atmospheric model, and the other is with the coupled model. In the first step, five year simulations are carried out with the observed SST prescribed, and the results are compared with observations, which enables one to make the critical validation of the model. The second step is to couple the atmospheric and oceanic models, and integrate them from a January 1982 initial condition for 7 years, and also for another initial condition, i.e., January, 1988 for 13 months.
Compared with the boundary forced simulation, the coupling process introduces more degree of freedom, with increase of the sensitivity as well as the complexity considerably. In particular, the El Niño simulation is sensitive to any change of physics. For this reason, the objective of the simulation is focused only on the equatorial Pacific process and secondly the Indian monsoon, as opposed to the overall improvement of the general circulation. In other words, the approach is close to that of mechanistic modeling with specific targets rather than that of a GCM with broader objectives. The research is proceeding in two directions. One is: investigating the model's sensitivity for El Niño and La Niña processes to variation in a coupling parameter. The second is: after a number of trial-and-error experiments on various combinations of the parameterizations, the second atmospheric model, i.e., Model II, is selected. It is shown that Coupled Model II performs substantially better in some aspects but worse in other aspects than Coupled Model I. The improvement is found in the SST: warming occurs not only over the equatorial Pacific but also over the whole globe. The SST increase is achieved by the strong effect of the cumulus convection. On the other hand, some deficiencies remain the same in both models, i.e., the large positive errors of the SST in the eastern oceans, the lack of an annual cycle of the SST in the eastern equatorial Pacific, and the failure in forecast of the second El Niño. In summary, the prediction of the Southern Oscillation has been achieved by the two models for a full first cycle but not for the second cycle .
A global oceanic four-dimensional data assimilation system has been developed for use in initializing coupled ocean-atmosphere general circulation models and also to study interannual variability. The data inserted into a high-resolution global ocean model consist of conventional sea surface temperature observations and vertical temperature profiles. The data are inserted continuously into the model by updating the model's temperature solution every time step. This update is created using a statistical interpolation routine applied to all data in a 30-day window for three consecutive time steps and then the correction is held constant for nine time steps. Not updating every time step allows for a more computationally efficient system without affecting the quality of the analysis.
The data assimilation system was run over a 10-yr period from 1979 to 1988. The resulting analysis product was compared with independent analysis including model-derived fields like velocity. The large-scale features seem consistent with other products based on observations. Using the mean of the 10-yr period as a climatology, the data assimilation system was compared with the Levitus climatological atlas. Looking at the sea surface temperature and the seasonal cycle, as represented by the mixed-layer depth, the agreement is quite good, however, some systematic differences do emerge.
Special attention is given to the tropical Pacific examining the El Niño signature. Two other assimilation schemes based on the coupled model using Newtonian nudging of SST and then SST and surface winds are compared to the full data assimilation system. The heat content variability in the data assimilation seemed faithful to the observations. Overall, the results are encouraging, demonstrating that the data assimilation system seems to be able to capture many of the large-scale general circulation features that are observed, both in a climatological sense and in the temporal variability.
Assuming that SST provides the major lower boundary forcing for the atmosphere, observed SSTs are prescribed for an ensemble of atmospheric general circulation model (GCM) simulations. The ensemble consists of 9 "decadal" runs with different initial conditions chosen between 1 January 1979 and 1 January 1981 and integrated about 10 years. The main objective is to explore the feasibility of seasonal forecasts using GCMs. The extent to which the individual members of the ensemble reproduce the solutions of each other (i.e., reproducibility) may be taken as an indication of potential predictability. In addition, the ability of a particular GCM to produce realistic solutions, when compared with observations, must also be addressed as part of the predictability problem.
A measure of reproducibility may be assessed from the spread among ensemble members. A normalized spread index, can be defined at any point in space and time, as the variability of the ensemble normalized by the climatological seasonal variability. In the time mean it is found that the reproducibility is significantly below unity for certain regions. Low values of the spread index are seen generally in the Tropics, whereas the extratropics does not exhibit a high degree of reproducibility. However, if one examines plots in time of seasonal mean for the U.S. region, for example, it is found that for certain periods this index is much less than unity, perhaps implying "occasional potential predictability." In this regard, time series of ensemble mean soil moisture and precipitation over the United States are compared with corresponding observations. This study reveals some marginal skill in simulating periods of drought and excessive wetness over the United States during the 1980s (i.e., the droughts of 1981 and 1988, and the excessive wetness during the 1982/83 El Niño). In addition, by focusing on regions of better time-averaged reproducibility - that is, the southeast United States and northeast Brazil - a clearer indication of a relationship between good reproducibility and seasonal predictability seems to emerge.
Stern, William F., and Kikuro Miyakoda, 1995: Interannual variability and reproducibility from multiple GCM simulations In Proceedings of the 19th Annual Climate Diagnostics Workshop, Springfield, VA, NTIS, 92-95.
Miyakoda, Kikuro, Anthony Rosati, and Richard G Gudgel, 1994: Air-sea coupling experiments: ENSO forecasting. Part I In Proceedings of the 18th Annual Climate Diagnostics Workshop, U. S. Dept. of Commerce/NOAA/NWS, 153-156.
Rosati, Anthony, Kikuro Miyakoda, and Richard G Gudgel, 1994: Air-sea coupling experiments: ENSO forecasting. Part II In Proceedings of the 18th Annual Climate Diagnostics Workshop, U. S. Dept. of Commerce/NOAA/NWS, 358-361.
The reanalysis of FGGE [First GARP (Global Atmospheric Research Program) Global Experiment] data for 128 days during two special observing periods has been performed, using an improved data-assimilation system and the revised FGGE level II dataset. The data-assimilation scheme features forward continuous (in time) data injection in both the original and the new systems. However, the major revisions in the new system include a better first guess and a more efficient dynamical balancing for the assimilation of observed data. The results of the implementation of this system are assessed by intercomparisons among the new FGGE analysis of other institutions such as ECMWF (European Centre for Medium-Range Weather Forecasts) and NMC (National Meteorological Center, Washington, D.C.), and also the original GFDL (Geophysical Fluid Dynamics Laboratory) analysis. The quality of the new GFDL analysis is now comparable to those of the other two institutions. However, the moisture analysis appears to be appreciably different, suggesting that the cumulus convection parameterizations and the boundary-layer moisture fluxes in the models are responsible for this discrepancy.
A detailed investigation of the results has been carried out by comparing the analyses with radiosonde observations. This verification reveals that temperature and wind differences have been reduced considerably from the original to the new GFDL analysis; they are now competitive with those of ECMWF and NMC, while with regard to the geopotential height, differences of the GFDL reanalysis are larger than the original GFDL as well as the ECMWF and the NMC. A comparative study is also made with UCLA analyses over Asia in connection with the Indian monsoon. The results indicate that the qualities of both analyses are comparable. The capability of representing Madden-Julian oscillations in the reanalysis and in the ECMWF and old GFDL analysis is investigated by comparing with satellite observations. It is revealed that these oscillations are successfully reproduced by the new analysis; however, the agreement with the satellite data is not quite satisfactory. The utilization of satellite-observed wind (satobs) and aircraft data (aireps) in the data assimilation needs particular care. It appears that the quality control of these data in the GFDL reanalysis is too restrictive; in other words, the toss-out criterion of wind data is too small. A consequence of the failure to accept some single-level data turns out to be a fairly large discrepancy in representing the maximum wind speed in the analysis. It is also discussed that the current forward continuous-injection scheme is not adequate to obtain diabatic quantities for the archive.
Miyakoda, Kikuro, and Joseph J Sirutis, 1990: Subgrid scale physics in 1-month forecasts. Part II: Systematic error and blocking forecasts. Monthly Weather Review, 118(5), 1065-1081. Abstract PDF
The capability of blocking prediction is investigated with respect to four models of different subgrid scale parameterization packages, which were described in Part 1. In order to assess the capability, blocking indices are defined, and threat and bias scores are set up for the predicted blocking index against the observation. Applying this evaluation scheme to the dataset of one-month forecasts for eight January cases, we conduct a study on the performance of blocking simulation.
First, it is immediately disclosed that the systematic biases in this forecast set are overwhelmingly large, so that the blocking index has to be adjusted to this bias. One of the major issues, suggested by Tibaldi and Molteni, is whether the systematic bias is generated by the failure of blocking forecasts. Overall, this study supports this assertion, despite the different definitions of blocking. The study also reveals that the A-model is inferior to the other three models, such as the E-model, with regard to blocking forecasts. The reason for this is that the E-model, for example, which includes turbulence closure parameterization, appears to provide an adequate conversion of low-frequency eddy potential to kinetic energy, and thereby produces a more reasonable amount of standing eddies related to the persistent ridges. It is also pointed out that the blocking activity in the winter Northern Hemisphere is manifested by a distinct subpolar peak in the meridional distribution of standing eddy kinetic energy. The E-model tends to generate a well-defined peak of this energy distribution. All models are deficient in expanding the zonal mean westerlies to higher latitudes, particularly the A-model. In this connection, a hypothesis is postulated on a precondition for blocking: the upstream westerlies prior to the onset have to be displaced relatively at lower latitude. In the successful cases of blocking forecasts, the upstream westerlies at 40° - 60°N are relatively weaker than those in the unsuccessful cases.
Miyakoda, Kikuro, Joseph J Sirutis, Anthony Rosati, and J Derber, 1990: Experimental forecasts with an air-sea model: Preliminary results In Air-Sea Interaction in Tropical Western Pacific, Beijing, China, China Ocean Press, 417-432. Abstract
An air-sea model has been applied to the seasonal forecasting problem for a single case beginning 1 October 1979. The model consists of an atmospheric model and a global 1° x 1° resolution oceanic model, with a higher latitudinal resolution in the equatorial zone. The initial conditions are obtained by the 4-dimensional data assimilation system for the atmosphere and the ocean. The experiments reveal that strong air-sea interaction is evident, manifested in a close connection between the predicted sea temperature and the sea level pressure anomaly patterns. There is a certain degree of predictive skill up to 5 months for the ocean and beyond 9 months for the atmosphere. However, the systematic bias in the sea temperature prediction is pronounced.
Sirutis, Joseph J., and Kikuro Miyakoda, 1990: Subgrid scale physics in 1-month forecasts. Part I: Experiment with four parameterization packages. Monthly Weather Review, 118(5), 1043-1064. Abstract PDF
Four packages of subgrid scale (SGS) physics parameterization are tested by including them in a general circulation model and by applying the four models to 1-month forecasts. The four models are formulated by accumulatively increasing the elaboration and the sophistication of the physics. The first is the reference model (the A-physics); the second model (the E-physics) uses the Monin-Obukhov similarity theory for the fluxes of surface boundary layer, the turbulence closure scheme for the fluxes in the entire atmosphere, and subsurface soil heat conduction; the third model (the F-physics) replaces the cumulus parameterization by the Arakawa-Schubert method; and the fourth model (the FM-physics) enhances the SGS orography. One-month integrations are performed for eight January cases, with each case consisting of three different forecasts. Originally, the forecast performance was expected to be a stepwise improvement with the elaboration of the SGS physics from the A to the FM, but the forecast results do not show up in such a simple way. The impact of these processes on the 1-month integration is subtle and yet significant. The superiority of the F-model over the A- and the E-models is evident in the last 10 days of the 1-month forecasts, though the performance of the E-model is consistently good, in comparison with the other models, in terms of root-mean-square (rms) error of geopotential height. It is likely that 80% condensation criterion in the E (instead of 100%) is at least partly responsible for the forecast deterioration in the last 10 days, compared with the F. The FM-model gives the lowest rms error, but the predicted transient eddies are extremely low, probably due to the excessively enhanced orography. The simulated global precipitation patterns are presented for the different models, and the drawbacks are discussed. The F- and the FM-models produce spatially smooth distribution of tropical rainfall. The 30-day forecast performance appears to be more sensitive to the initial conditions, rather than the SGS physics. The systematic errors in all of the models are substantial in magnitude, though they vary with the SGS physics.
Miyakoda, Kikuro, and Joseph J Sirutis, 1989: A proposal of moist turbulence closure scheme, and the rationalization of Arakawa-Schubert cumulus parameterization. Meteorology and Atmospheric Physics, 40, 110-122. Abstract
Subgrid-scale parameterizations related to moist process are discussed. In the first half of the paper, a turbulence closure scheme, including the effect of condensation, is proposed. In this parameterization, the subgrid-scale transfer is limited within a single vertical layer of a model per each time step, and the specification of condensation is of yes-or-no type. Therefore, the scheme is suited for a mesoscale circulation model.
In the second half of this paper, the bounded derivative method of Kreiss (1980) is applied to the formulation of parameterizations. One example is the derivation of various hierarchical versions in turbulence closure schemes, such as Mellor and Yamada (1974). Another example is an interpretation of the key assumption in Arakawa-Schubert (1974) theory of cumulus convection, i.e., the equilibrium of "cloud-work function".
Sirutis, Joseph J., and Kikuro Miyakoda, 1989: Forecast experiments of the 1982-83 El Niño with a coupled air-sea model In Proceedings of the 14th Annual Climate Diagnostics Workshop, Springfield, VA, NTIS, 35-40.
Navarra, A, and Kikuro Miyakoda, 1988: Anomaly general circulation models. Journal of the Atmospheric Sciences, 45(9), 1509-1530. Abstract PDF
Anomaly models based on a spectral general circulation model (GCM) are formulated and applied to a study of low-frequency atmospheric variability in the extratropics, and long-range forecasting research. A steady linear version of the anomaly model is treated by a matrix method. This model consists of nine vertical levels, 15 wave rhomboidal truncation, primitive equation system, and a fixed basic state, which is three-dimensionally variable. The matrix to be handled is extremely large, but can be solved using Krylov's technique. The solutions represent various teleconnection patterns known in the observed atmosphere. The sensitivity of the response of this anomaly model to zonal variability of the temporally fixed basic fields and to the geographical position of tropical heatings is investigated. The solutions of the steady linear anomaly model are compared with those of the original GCM, revealing that there are a few similarities among the solutions, but considerable discrepancies are also evident. A time-dependent nonlinear anomaly model is applied to further investigate the discrepancy. It appears that transient eddies are crucial for explaining the disagreement, although the study with the time-dependent anomaly model is preliminary.
A noteworthy aspect of the overall approach is that the anomaly models are derived, with only small modifications, from the full GCM, and therefore, their relationship can be readily investigated. It is concluded that the steady linear model may be used as a diagnostic tool for investigating the characteristics of the full GCM and the dynamics of a particular state of the atmosphere. However, caution is needed when there is a significant role played by transient eddies, and in the treatment of tropical Rayleigh friction.
A general circulation model (GCM) of the ocean that emphasizes the simulation of the upper ocean has been developed. This emphasis is in keeping with its future intent, that of an air-sea coupled model. The basic model is the primitive equation model of Bryan and Cox with the additions, of optional usage, of the Mellor-Yamada level 2.5 turbulence closure scheme and horizontal nonlinear viscosity. These modifications are intended to improve the upper ocean simulations, particularly sea surface temperature and heat content. The horizontal grid spacing is 1° latitude x 1° longitude and is global in domain. The equatorial region between 10°N and 10°S is further refined in the north-south direction to 1/3° resolution. There are 12 vertical levels, with six levels in the top 70 m. The model incorporates varying bottom topography.
Prior to coupling the ocean model to an atmospheric GCM, experiments have been carried out to determine the ocean GCM's performance using atmospheric forcing from observed data. The data source was the National Meteorological Center twice daily 1000 mb analysis for winds, temperature, and relative humidity for 1982 and 1983. From these data, wind stress and total heat flux were calculated from bulk formulas and used as surface boundary conditions for the ocean model.
The response of the ocean GCM to mixing parameterization schemes and frequency of atmospheric forcing have been examined. In particular, the use of constant eddy coefficients for both horizontal and vertical mixing (A-model) versus nonlinear horizontal viscosity and turbulence closure schemes (E-model) have been examined, along with comparisons of monthly mean versus 12-hourly forcing. It was found that, in general, the E-physics produces a more realistic mixed-layer structure as compared to A-physics. Using the monthly mean values produces sea surface temperatures that are too warm, presumably because the evaporative flux, which is proportional to the wind speed, is underestimated. The 12-h forcing improves appreciably both the A and E model since the heat flux is better represented; the E-case shows an even greater improvement due to its sensitivity to wind stirring. The near surface heat budget, along with more traditional variables, is examined for a short period during the 1982-83 El Niño event. These results are encouraging considering the many possible sources of error, including those in forcing data, initial conditions, radiative fluxes, and bulk exchange coefficients.
Stern, William F., and Kikuro Miyakoda, 1988: Systematic errors in GFDL's extended range prediction spectral GCM In Workshop on Systematic Errors in Models of the Atmosphere, CAS/JSC Working Group on Numerical Experimentation, Report No. 12, WMO/TD No. 273, World Meteorological Organization, 78-85.
Miyakoda, Kikuro, 1986: Assessment of results from different analysis schemes In International Conference on the Results of the Global Weather Experiment and Their Implications for the World Weather Watch, GARP Publications Series No. 26, (Volume 1), WMO/TD No. 107, World Meteorological Organization, 217-253. Abstract
Associated with GARP activities, two kinds of data assimilation methods have been developed, i.e., the intermittent and the continuous schemes. These schemes include two focal points, i.e., the spatial interpolation technique and the initialization procedure. A great deal of progress has been made on the former aspect in terms of the optimum interpolation analysis. In particular, the multivariate optimum interpolation has been widely used. For the intermittent scheme of data assimilation, the multivariate version is instrumental for incorporating various sources of observed data. For the second aspect, the normal mode initialization has been devised, which turned out to be a breakthrough for obtaining the dynamical balance between the mass fields and winds. Yet the decision to use this procedure depends upon the philosophy of the analysis. The observed data contain a fair amount of dynamically unbalanced components both real and spurious, and it is difficult if not impossible, to distinguish between them. In this situation, it is optional to apply the dynamical balance to the variables in the resulting analysis.
The tropical analysis presents a unique problem. Part of the reasons for this is the sparcity of data, but the real reason is the dominance of cumulus convection and gravity modes. Cumulus convection is frequently associated with Kelvin waves. Therefore, if a large portion of these waves is suppressed in the analysis, a sufficient amount of condensation cannot be expected in the subsequent forecast. Cumulus convection is affected appreciably by the sea surface temperature in the tropics. For these reasons, the tropical analyses are influenced by the quality of the GCM's convection scheme and by the specified sea surface temperature.
In connection with the FGGE data set, a number of comparisons have been made, for example, Kung, Chen, Baumhefner, Rosen et al., Lau, and Hollingsworth et al. In this paper, it is attempted to review these comparisons. Assessment of data assimilation schemes is not straightforward. Evaluation consists of many items, i.e., the degree of data fitting, the accurate representation of inidividual storm structure, the adequate inclusion of general circualtion features, and the impact on the subsequent forecasts. Depending on which of these aspects is emphasized determines the type of analysis. Data assimilation schemes, in various centers, have evolved considerably in the last 5 years. The results of recent analyses for January 1980, 81, 82, and 83 at GFDL, NMC, and ECMWF have been applied to monthly forecast studies for 8 January cases from 1977 to 1983.
Even for seasonal forecasts, data assimilation must be thought of as an essential component. It will be necessary to use an air-sea-land coupled GCM that will innovatively incorporate observed sea surface temperatures and satellite data. However, in considering forecasts on time scales of a season one cannot ignore the effects of the model's own climate drift.
This is the report of the 30-day forecast experiment conducted at GFDL. The first part is a summary of 8 January case studies, using a finite difference GCM without the anomalous boundary forcings of sea surface temperature (SST). The experiment reveals that the forecast skill of 10-day mean variables is marginal at the end of a month, but that the removal of systematic bias (climate drift) from the original forecasts raises the skill scores appreciably, producing useful one-month prognoses. However, the climate drift is alarmingly large; for example, the forecast error for the 500 mb geopotential height due to the drift is 64% of the total root mean square error. The second part of the paper discusses the forecasts incorporating the observed SST instead of the climatological SST. A series of forecasts was carried out for the most dramatic El Niño event of January 1983. In this study, forecasts were improved for the tropics by using the observed SST, whereas the impact for the extratropics was not beneficial. Four possible causes for the adverse effect of tropical SST were examined, i.e., the cumulus parameterization, the accuracy of SST, the initialization, and the tropical land surface condition. Preliminary investigations suggest that the forecast tropical divergence fields are quite different from those observed, in particular with respect to the components of large scale divergence associated with the 40-50 day oscillation. It is likely that the current initialization of the GFDL forecast system is deficient in treating this distinct tropical oscillation.
A series of one-month forecasts were carried out for eight January cases, using a particular prediction model and prescribing climatological sea-surface temperature as the boundary condition. Each forecast is a stochastic prediction that consists of three individual integrations. These forecasts start with observed initial conditions derived from datasets of three meteorological centers. The forecast skill was assessed with respect to time means of variables based on the ensemble average of three forecasts. The time of space filter is essential to suppress unpredictable components of atmospheric variabilities and thereby to make an attempt at extending the limit of predictability. The circulation patterns of the three individual integrations tend to be similar to each other on the one-month time scale, implying that forecasts for the 10 day (or 20 day) means are not fully stochastic.The overall results indicate that the 10-day mean height prognoses resemble observations very well in the first ten days, and then start to lose similarity to real states, and yet there is some recognizable skill in the last ten days of the month. The main interests in this study are the feasibility of one-month forecasts, the adequacy of initial conditions produced by a particular data assimilation, and the growth of stochastic uncertainty. An outstanding problem turns out to be a considerable degree of systematic error included in the prediction model, which is now known to be "climate drift". Forecast errors are largely due to the model's systematic bias. Thus, forecast skill scores are substantially raised if the final prognoses are adjusted for the model's known climatic drift.
Stern, William F., R T Pierrehumbert, Joseph J Sirutis, Jeff J Ploshay, and Kikuro Miyakoda, 1986: Recent developments in the GFDL extended-range forecasting system In Short- and Medium-Range Numerical Weather Prediction, Collection of papers presented at the WMO/IUGG NWP Symposium, World Meteorological Organization, 359-363. Abstract
An assessment is made of the areas of focus for improving extended-range forecasting. Two topics currently being researched involve the reduction of systematic error by improving a GCM's accuracy and the refinement of the transition between the data assimilation phase and the forecasting phase.
Subgrid-scale orographic parameterizations have been the subject of recent model improvement activities. Results are shown for an envelope orography with an N48L9 gridpoint model and using a mountain gravity wave drag scheme with an R42L18 spectral model. In both cases there is an encouraging reduction in the systematic errors.
Proper initialization of tropical features, i.e., 40-50 day waves, may be crucial for extended-range predictions in the extra-tropics as well as the tropics. Using a continuous data assimilation scheme the 40-50 day oscillations in the tropics appear to be well maintained from the assimilation to the forecast phase. However, the assimilation system underestimates precipitation and evaporation rates.
Daley, R, Jeff J Ploshay, and Kikuro Miyakoda, et al., 1985: Objective analysis and assimilation techniques used for the production of FGGE IIIb analyses. Bulletin of the American Meteorological Society, 66(5), 532-538. Abstract
A set of tables has been prepared which allows side-by-side comparison of the characteristics of six data assimilation systems (ECMWF, GFDL, GLAS, NMC, FSU, and NEPRF) used to produce FGGE IIIb analyses.
Miyakoda, Kikuro, Joseph J Sirutis, and Jeff J Ploshay, 1985: Monthly forecast experiment: preliminary report In Numerical Long-Range Forecast Evaluation Numerical Long-Range Forecasting Errors Monthly Forecasts, Washington, DC, National Academy Press, 292-296. Abstract
An experiment on monthly forecasts with eight winter cases was conducted by using a 1980 general circulation model that incorporates a set of subgrid-scale physics characterized by Mellor-Yamada turbulence closure (hierarchy level 2.5), the Monin-Obukhov parameterization for the layer next to the ground surface, Manabe's cumulus parameterization, and the soil heat conduction. The cases are for January from 1977 to 1983; they include the extraordinarily severe winter of 1977 and the most pronounced El Niño year of 1983. Graphs show correlation coefficients of 500-mb geopotential height anomalies (the deviation from climatology) and of the 1000-mb geopotential height anomalies between the predictions and observations for the Northern Hemispheric domain (90-25 degrees N). The study indicates that the 10- or 20- day height prognoses resemble the observations well in the first 10 days and then rapidly lose the similarity; yet there is some recognized skill, although marginal in the last 10 or 20 days of the month. The skill scores for the 1000-mb level are consistently better than those for the 500-mb level. This feature appears opposite to that for the daily weather forecasts and may suggest how forecast errors propagate in the vertical.
This is a progress report and follow-up of "Three cases of one-month GCM forecasts" (Caverly, et al., 1981). Each case includes an ensemble of three individual integrations, starting with three different initial conditions produced at GFDL, NMC, and ECMWF and prescribing the climatological sea surface temperature as the lower boundary condition. Monthly forecasts with the N48L9-F model and examples of verification statistics are presented. The experiment with four winter cases indicates that there is some skill in the mean height prognosis.
Miyakoda, Kikuro, and Anthony Rosati, 1984: Variation of sea surface temperature in 1976 and 1977, Pt. 2: Simulation with mixed layer models. Journal of Geophysical Research, 89(C4), 6533-6542. Abstract PDF
In connection with a study of the extreme weather events over the North American continent in January 1977, analyses were performed to investigate characteristic properties of spatial and temporal variations of sea surface temperature for the years 1976 and 1977 by using the world distribution of sea surface temperature described in the accompanying paper, Pt. 1. The time evolutions of ocean temperature patterns for these years are displayed by latitudinal distribution diagrams of sea surface temperature and by longitude-time (Hovmoller) diagrams. Gill-Turner's integral model and Mellor-Durbin's turbulence closure model of the mixed layer were applied to calculate the sea surface temperature anomaly in the Northern Hemisphere by using realistic atmospheric forcing. An increase of time variability of the external forcing leads to an appreciably improved simulation of the sea surface temperature anomaly fields. Both models gave reasonable predictions for <> 5 months in wintertime if the realistic external forcings were specified.
January 1977 was a month noted for its extraordinary weather over North America. The winter was dominated by two persistent large amplitude ridges positioned over the west coast of North America and the Icelandic region of the Atlantic Ocean. A very intense trough reached deep into the eastern United States and caused one of the coldest Januaries on record. One-month integrations of various GCMs were conducted in order to test their ability to simulate this blocking event. Reasonably high resolution finite difference and spectral models available at GFDL were used. Each GCM was integrated from three different analyses of the initial conditions. For some models, a fairly accurate forecast was obtained and considerable skill was recognized in the simulation of the 30-day evolution in terms of the 5-day or 10-day mean flow fields, including the period of record breaking coldness over the eastern United States. The main conclusion is that proper treatment of the subgrid-scale processes as well as sufficient spatial resolution are essential for the simulations of this phenomenon as an initial value problem. Weak zonal wind poleward of about 40 degrees N and upstream of the blocking ridge appears to be crucial for the successful simulation of the sustained blocking ridge.
Ploshay, Jeff J., Robert K White, and Kikuro Miyakoda, 1983: FGGE Level III-B Daily Global Analyses Part I (Dec 1978 - Feb 1979), NOAA Data Report ERL GFDL-1, Rockville, MD: NOAA, 278 pp.
Ploshay, Jeff J., Robert K White, and Kikuro Miyakoda, 1983: FGGE Level III-B Daily Global Analyses Part II (Mar 1979 - May 1979), NOAA Data Report ERL GFDL-2, Rockville, MD: NOAA, 285 pp.
Ploshay, Jeff J., Robert K White, and Kikuro Miyakoda, 1983: FGGE Level III-B Daily Global Analyses Part III (Jun 1979 - Aug 1979), NOAA Data Report ERL GFDL-3, Rockville, MD: NOAA, 285 pp.
Ploshay, Jeff J., Robert K White, and Kikuro Miyakoda, 1983: FGGE Level III-B Daily Global Analyses Part IV (Sept 1979 - Nov 1979), NOAA Data Report ERL GFDL-4, Rockville, MD: NOAA, 282 pp.
Caverly, R, Kikuro Miyakoda, and L Umscheid, 1982: Three cases of one-month GCM forecasts In Proceedings of the Sixth Annual Climate Diagnostics Workshop, Washington, DC, NOAA/Geophysical Fluid Dynamics Laboratory, 292-299.
Miyakoda, Kikuro, and J-P Chao, 1982: Essay on dynamical long-range forecasts of atmospheric circulation. Journal of the Meteorological Society of Japan, 60(1), 292-307. Abstract PDF
The feasibility of monthly and seasonal forecasts is considered. The gross features of departures of meteorological variables from climatology (anomalies) are the targets of forecasts, and the anomalies can be divided into two modes, i.e., free modes and forced modes. The free modes are the anomalies that are predicted under the specification of climatological external forcings for the surface temperature, that are free from the anomalous forcings, whereas, the forced modes are the anomalies that correspond to the anomalous components of external forcings. The GCM (general circulation model) is, in some cases, capable of predicting the free mode at least one month ahead (particularly, the most extraordinary blocking event in January, 1977), and is, in other cases, marginal. However, the capability could be increased further by improving the GCM. In addition, recent studies have revealed that there are growing evidences for the feasibility of prediction of forced modes over the United States through the teleconnection process from the sea surface temperature anomalies over the equatorial Pacific.
Yet the GCM approach is expensive and may be limited in improving mathematical accuracy, to a satisfactory extent. As a remedy, the possibility of anomaly models are being investigated.
Miyakoda, Kikuro, and Anthony Rosati, 1982: The variation of sea surface temperature in 1976 and 1977, 1: The data analysis. Journal of Geophysical Research, 87(C8), 5667-5680. Abstract PDF
To study the spatial distribution of the sea surface temperature (SST) for the years of 1976 and 1977, ship and satellite data at 1 degree quadrangles were collected. Two points were investigated: (1) the difference of monthly mean SST data between the two sources, and (2) map analyses over the globe. The study shows that without satellite data, an adequate coverage of world ocean is not possible and that there is a large difference in values between the ship and satellite data. The standard deviation of the difference between the satellite and merchant ship SST data for monthly and 1 degree quadrangle mean was plus or minus 1.49 degrees C, where the sampling errors were not subtracted. Using these data, analyses were created and compared with independent analyses. The comparisons included large-scale analyses and two small-scale analyses. Attention was focussed specially on (1) the utility of the satellite SST data and (2) the data quality control. The large-scale analyses agreed well with the independent analyses. However, both of the small-scale analyses did not compare well.
The GATE analysis was repeated utilizing the full GATE data set in the delayed mode and a revised four-dimensional analysis procedure. The reulting maps were compared with maps of other authors. Based on the new analysis, macroscale circulation features for the tropical African continent and Atlantic Ocean region were calculated, and other characteristic phenomena of this area were investigated. The easterly waves, in particular, were studied with respect to their formation, propagation, associated condensation, and possible conversion to hurricanes. It was possible to trace nine distinct easterly waves throughout their entire life history, and the analyzed tracks of these easterly waves agreed quite well with the subjective analyses of Sadler and Oda (1978). The time sequences of precipitation over the GATE A/B-array obtained by the present analysis and by satellite estimates were compared with some success.
Miyakoda, Kikuro, and R F Strickler, 1981: Cumulative results of extended forecast experiment. III: Precipitation. Monthly Weather Review, 109(4), 830-842. Abstract PDF
A diagnostic analysis and an appraisal of the precipitation calculation by the GFDL (Geophysical Fluid Dynamics Laboratory) 1967 version prediction model are presented, using two-week forecasts of 12 January and 12 July cases. The geographical distribution of predicted rainfall, moisture and snow over the Northern Hemisphere and the contiguous United States was investigated in comparison with climatological maps published by other authors. The agreement of precipitation and dew-point temperature is marginal. The major causes for the deficiencies are 1) a specification of excessive soil moisture over land, 2) probably an improper treatment of moisture diffusion associated with topography, and 3) an inadequate rain generation process in the model. However, the predicted snow distribution over the United States was reasonable.
Miyakoda, Kikuro, G D Hembree, and R F Strickler, 1979: Cumulative results of extended forecast experiments II: Model performance for summer cases. Monthly Weather Review, 107(4), 395-420. Abstract PDF
Two-week experimental forecasts were carried for 12 July cases with a nine vertical level, 270 km grid-size hemipheric model, and the results were examined statistically. The solutions studied were the stationary (10-day average) and transient components of the general circulation; in particular, the ensemble mean of temperature, zonal wind and eddy kinetic energy; and the hemispheric maps of ensemble mean height fields. The predictive ability of this model was examined by comparing the results with observation and calculating statistical scores such as standard deviation, correlation coefficient and horizontal gradient (S1) score for 1000, 500 and 50 mb geopotential height verified against the NMC (National Meteorological Center) analysis. The results were also analyzed in terms of zonal wavenumbers of geopotential. So far as this model (1967 version) is concerned, the predictability in the lower atmosphere seems to decay more rapidly in July than in January; the planetary-scale waves were better predicted. The simulation of the summer stratosphere is very poor with the nine-level vertical reolution. The prediction was also compared with that of a spectral model of comparable horizontal and vertical resolution.
Miyakoda, Kikuro, R F Strickler, and J Chludzinski, 1978: Initialization with the data assimilation method. Tellus, 30, 32-54. Abstract
The initial conditions generated by data assimilation technique with a general circulation model were evaluated. Two types of dynamic initialization, i.e., "the forward adjustment" and "the forward-backward adjustment," were tested using the real data produced by the NMC objective analysis. The degree of balance in the initial condition was examined in terms of the smoothness in the development of the rate of precipitation, angular momentum, and kinetic energy during the starting period of the prediction. The quality of the initialization was, however, appraised by the performance of the subsequent prediction. For the forward adjustment, various types of schemes of data insertion were studied with regard to the amount of shock produced and the degree of faithfulness of the injected data. In dealing with forward-backward processes, one difficult problem is how to design a reversible algorithm. An approximate method is presented for maintaining the reversibility in a system which includes kinetic energy dissipation, radiation, and the moist heating. In addition, the question is discussed as to which physical processes of the model must by included for the forward-backward initialization. It is found that the dynamic initialization using the forward-backward data assimilation produces predicitons that are, in some ways, better than those from the static or conventional initialization. However, for the forward data assimilation the predictions are consistently worse than those from the static initialization.
Miyakoda, Kikuro, and Joseph J Sirutis, 1977: Comparative intergrations of global models with various parameterized processes of subgrid-scale vertical transports: Description of the parameterizations. Beiträge zur Physik der Atmosphäre, 50, 445-487. Abstract
The effects of the parameterization of the vertical eddy transport on the general circulation were studied comparatively by including various schemes in a global finite difference model. Models with different combinations of parameterization schemes for the surface layer transfer, the planetary boundary layer processes and the cumulus convection were discussed. For the surface layer, two versions of the treatments were considered; they are Prandtl's aerodynamical method and the Monin-Obukhov version for constant-flux layer, which includes the effect related to the Richardson number. For the turbulent transfer processes in the rest of the PBL as well as the free atmosphere, the mixing length approach for neutral thermal stratification, the Mellor-Yamada's turbulence closure models, and the mixed layer method of Randall-Arakawa are included. For the ensemble cumulus convection, one scheme is the moist convective adjustment of Manabe et al. (1965) and the other is the scheme based on the recent theory of Arakawa et al. (1974).
The preliminary numerical results of these experiments have revealed that the turbulent closure model of a certain hierarchy level performed satisfactorily, and that the resulting vertical structure of tropical cumulus clouds and the horizontal rain distribution were different between the UCLA version of cumulus convection and the moist convective adjustment. The UCLA scheme of cumulus convection produced a deeper penetrative convection than the moist convective adjustment, and the distribution of rainfall relative to trough and ridge of tropical trade wind easterlies was also different between the two schemes.
Miyakoda, Kikuro, and Anthony Rosati, 1977: One-way nested grid models: The interface conditions and the numerical accuracy. Monthly Weather Review, 105(9), 1092-1107. Abstract PDF
Tests of several interface conditions in a one-way nested grid model were undertaken, where the ratio of grid size for the coarse mesh in the large domain and the fine mesh in the small domain was 4:1. The interface values for all parameters are specified by the solutions of the larger domain model, although they are modified in some cases. Scheme A includes "a boundary adjustment" and the consideration of mountain effect for the surface pressure along the interface. Scheme B uses, in addition to Scheme A, a "radiation condition" at the outward propagation boundaries. Scheme C uses viscous damping along five rows adjacent to the border lines in addition to Scheme A. The solutions for the fine-mesh models obtained by these schemes are compared quantitatively with the solution of a control model. The results show how quickly the effect at the interface propagates into the interior. The proper treatment of the mountain effect on the surface pressure along the interface, and the boundary adjustment are important for obtaining reasonable solutions. Schemes A, B, and C are all acceptable, though not entirely satisfactory. Scheme B was useful in reducing the false reflection at the interface. Scheme C gave smooth fields of predicted variables, but false reflection sometimes occurred. A combination of these conditions optimally chosen was applied to a 34 km mesh model for a domain covering the whole mainland of the United States. The resulting maps of the time integration show the formation of a front and the detailed structure of intense rainbands associated with the front.
Miyakoda, Kikuro, L Umscheid, D H Lee, Joseph J Sirutis, R Lusen, and F Pratte, 1976: The near-real-time, global, four-dimensional analysis experiment during the GATE period, Part I. Journal of the Atmospheric Sciences, 33(4), 561-591. Abstract PDF
Global upper air and surface data for the entire GATE period from 15 June to 24 September 1974, were collected by the Data Assimilation Branch of NMC and mailed to GFDL. After processing these data, a four-dimensional analysis technique was applied for the entire GATE period, using a global numerical model. For a selected period, several different versions of the data processing scheme were tested. The resulting analyses were compared with each other and with the objective analysis of NMC in Washington, DC, and ANMRC in Melbourne. Overall, the analyses for the extratropics were satisfactory for the Northern Hemisphere, and to a lesser extent, for the Southern Hemisphere, though flow patterns are somewhat excessively smoothed. The analyses for the tropics were not of the same quality as those for the erxtratropics, and yet they were much improved compared with those of several years ago. A noteworthy point is that tropical cyclones were successfully represented in several cases.
Miyakoda, Kikuro, 1974: Numerical weather prediction. American Scientist, 62(5), 564-574.
Miyakoda, Kikuro, J C Sadler, and G D Hembree, 1974: An experimental prediction of the tropical atmosphere for the case of March 1965. Monthly Weather Review, 102(8), 571-591. Abstract PDF
A two-week prediction was made, applying a general circulation model on Kurihara's grid to an observed data set. The maps for the basic meteorological elements at 10 vertical levels for 5 days in March 1965 were analyzed manually with the aid of nephanalysis charts This report discusses the forecast results selectively for the tropical areas only. The predicted wind, temperature, precipitation were compared, whenever possible, with the observed data including satellite cloud pictures. The main objective was to attempt a tropical forecast for a case study, and to obtain a crude idea, based on one sample, about the feasibility of predicting tropical weather systems. Some capability in the prediction of the tropical atmosphere is evident for about 3 days, in particular for the upper troposphere, but the prediction needs considerable improvement for the lower troposphere as well as for the stratosphere.
Miyakoda, Kikuro, 1973: Cumulative results of testing a meteorological-mathematical model: The description of the model. Proceedings of the Royal Irish Academy, 73A(9), 99-130. Abstract
series of two-week forecasts were made to a reasonable extent of success by an atmospheric general circulation model. The model is hemispheric, and has the grid size of about 270 km at mid-latitude, and 9 levels in the vertical, including the boundary layer, the troposphere and the middle stratosphere. The effects of radiation, water vapour and its phase change, evaporation, sensible heat flux and subgrid-scale turbulence effect are incorporated. The distribution of oceans and continents, the mountains, the sea surface temperature and the snow coverage are specified. These characteristics of the model have been described elsewhere only in fragmentary or obscure form. The purpose of this paper is, therefore, to portray in some detail these model's profile, including the basic equations, the Reynolds stress, the water vapour processes as well as the finite difference equations. Also the energy equation in finite difference form is derived.
Miyakoda, Kikuro, and L Umscheid, 1973: Effects of an equatorial "wall" on an atmospheric model. Monthly Weather Review, 101(8), 603-616. Abstract PDF
The effect of an artificial lateral boundary (the wall) at the Equator on a simulated atmospheric circulation was studied numerically. By comparing the solutions of two 30-day integrations of a global model with and without the wall, we found that the discrepancies of the wind and temperature at the middle and high latitudes became appreciable at approximately 8 days and serious at approximately 12 days. This suggests that the wall (hemispheric) model may be applied as a forecast model for a maximum of about 12 days. The disagreement in the wind between the two cases starts just below the tropopause level at the Equator and spreads toward the higher latitudes. Eventually, the middle latitudes respond to this equatorial effect, and the disagreement is amplified to the natural variability level. Insertion of the wall considerably increases the condensation of water vapor in the Tropics for the winter hemisphere; the reverse is true for the summer hemisphere. The result is that, in the winter hemisphere, the tropical troposphere and the stratosphere are cooler and the higher latitude troposphere is warmer in the wall case than in the control case. The opposite is true for the summer hemisphere.
Gordon, C T., L Umscheid, and Kikuro Miyakoda, 1972: Simulation experiments for determining wind data requirements in the tropics. Journal of the Atmospheric Sciences, 29(6), 1064-1075. Abstract PDF
Numerical simulation experiments are performed with a 9-level global general circulation model to help determine how much wind data in the tropics are needed for the reconstruction of meteorological fields. Prediction runs are updated every 12 hr with hypothetical data generated from the same model.
It is found that the asymptotic root mean square (rms) wind errors in the tropics, particularly in the 11S-11N "equatorial" latitude belt, fail to meet the GARP data requirements for the FGGE if surface pressure and temperature data alone are used for updating. The addition of tropical wind data at just two vertical levels leads to a significant, but insufficient, reduction of rms wind errors within the "tropics" (26S-26N); the largest errors remain near the equator. However, these errors become acceptably small if wind data are inserted at all 9 levels within the equatorial region. Another result is that insertion of tropical wind data at just two levels has a sizable influence upon wind errors even in the extratropics.
A critique of some implicit assumptions made in simulation experiments of the type we have performed is included.
Miyakoda, Kikuro, G D Hembree, R F Strickler, and I Shulman, 1972: Cumulative results of extended forecast experiments: I. Model performance for winter cases. Monthly Weather Review, 100(12), 836-855. Abstract PDF
A series of 2-week predictions were made with a general circulation model for 12 winter cases selected from the period 1964-69. All were January cases. The same prediction model-the most sophisticated and probably the most realistic model of those we tested in 1967-was used throughout. The model was hemispheric and had an N=40 grid (grid size of about 270 km at midlatitudes) with nine vertical levels. A detailed description of the model's performance is attempted by making statistical analyses of the forecast results compared with observed data. The analyses also provide useful insight into the dynamical behavior of the long waves in the middle latitude zone. The verification study reveals the practical limit of predictablility with the 1967 version of the Geophysical Fluid Dynamics Laboratory model. For example, the correlation coefficient between prediction and observation of the 500-mb geopotential deviation from January normal stays above zero until the 10th day. A spectral study of the planetary and cyclone waves was also made. The behavior of the ultralong wave in this model is disappointing, but cyclone waves are reasonably well predicted until the eighth day.
Delsol, F, Kikuro Miyakoda, and R H Clarke, 1971: Parameterized processes in the surface boundary layer of an atmospheric circulation model. Quarterly Journal of the Royal Meteorological Society, 97, 181-208. Abstract
A general circulation model is modified successively by adding five new features in the lower boundary layer; namely, (i) a different roughness parameter over land and sea, (ii)a Monin-Obukhov type treatment of the turbulent transfer process in the constant-flux layer, (iii) a Richardson number dependent parameterization for Ekman layer process, (iv) a diurnal variation of insolation, and (v) heat conduction into the soil. To assess the effect of each, the experiments are repeated by gradually increasing the complexity of the model. The circulation model has relatively low horizontal grid resolution and 9 vertical levels, and it is applied to a winter case for 14 day predictions. The results indicate that the sophistication of the boundary layer physics does not produce a particularly large effect on the synoptic scale prediction until about 7 days. Its effect may become large after 10 days. One noteworthy result is that the effect of the diurnal variation of insolation is not great for the free atmosphere but an influence is effectively transferred in the vertical, if the Richardson number dependent parameterization for the Ekman layer process is incorporated. The entire study is a preliminary test, the purpose of which is to determine the relative magnitude of each effect. A detailed comparison with observed data was not attempted.
Miyakoda, Kikuro, R W Moyer, H Stambler, R H Clarke, and R F Strickler, 1971: A prediction experiment with a global model of the Kurihara-grid. Journal of the Meteorological Society of Japan, 49, 521-536. Abstract
A general circulation model with the global grid system proposed by Kurihara was used to make a two-week forecast. The general characteristics of the model are: 9 vertical levels, a grid interval of approximately 220 km, orography, land-sea distribution, radiation, water vapor and convective adjustment. Data were collected from various regional data centers, and the maps were analyzed manually. The predicted results are compared with independent predictions for each hemisphere, using a hemispheric model of stereographic mapping, and also compared with observed data, where available. On the whole, the model's performance was somewhat inferior to that of a hemispheric model with comparable physics and grid resolution, due to excessive truncation error. Yet some advantage of the global prediction over the hemispherical predictions was recognized, particularly in the tropics and also in the middle latitudes. For example, it predicted the latitudinal position of the subtropical jet more correctly.
Miyakoda, Kikuro, R F Strickler, C J Nappo, P L Baker, and G D Hembree, 1971: The effect of horizontal grid resolution in an atmospheric circulation model. Journal of the Atmospheric Sciences, 28(4), 481-499. Abstract PDF
Truncation error of the numerical solution in a circulation model is still one of the most serious sources of error for the extended-period prediction. Different grid intervals are taken and the behavior of the solution is studied empirically. The meshes for the hemipsheric domain are N = 20, 40 and 80, where N is the number of grid points between the pole and the equator on the stereographic projection map. Analysis revealed that finer meshes provide clearly better solutions even for the planetary-scale mode, and the N = 80 solution is definitely different from the N = 40 beyond about 6 days. Further comparisons were made to see if the N = 80 solution is actually closer to observation. The results were encouraging. Promise is seen for improvement in the forecast to about 10 days. The inclusion of subgrid-scale eddy viscosity, which seems to be necessary, when applying a grid to the flow field, is also examined.
Miyakoda, Kikuro, and O Talagrand, 1971: The assimilation of past data in dynamical analysis. I. Tellus, 23(4-5), 310-317. Abstract
A method is presented to reduce the error in meteorological data analysis by using observations taken prior to analysis time, extrapolating them to the present time with the prediction equations, and mixing them with the present observation data. The equations can be non-linear, irreversible, and three-dimensional in space. The time span of the extrapolated data is several days. One-dimensional linear as well as two-dimensional non-linear vorticity equations are treated as examples. The best estimate of the analyzed field is the linear combination of a number of the predicted solutions from the past data with weights included that depend on predictability decay as functions of the data's age.
Talagrand, O, and Kikuro Miyakoda, 1971: The assimilation of past data in dynamical analysis. II. Tellus, 23(4-5), 318-327. Abstract
Systems for continuous data assimilation are presented and discussed. The balanced barotropic equation is used as an example of a dynamical (evolution) equation. In the first method, geopotential height data are assimilated into the model's computation, as the data becomes available, without any modification. It turns out that this leads to intolerable growth of error, suggesting the necessity of filtering the input information or alleviating discrepancies between the newly injected data and the prediction fields. In the second method, an optimal assimilation is attempted by applying adequate weights to the input data, which minimize statistically the mean-square difference between the estimate and the true solution. The analysis result is acceptable. But the magnitude of the error reduction is comparable to that of the previous synthesis analysis discussed in Part I of this paper. In the assimilation process we employed, the quality of the analysis seems to be determined by the characteristics of the measurements, i.e., density, distribution and magnitude of error, and also by the rate of inherited error growth in the dynamical prediction.
Miyakoda, Kikuro, R F Strickler, and G D Hembree, 1970: Numerical simulation of the breakdown of a polar-night vortex in the stratosphere. Journal of the Association for Computing Machinery, 27(1), 139-154. Abstract PDF
With a 9-level general circulation model, an attempt was made to simulate numerically the breakdown of the circumpolar vortex in the winter stratosphere for the case of March 1965. The marching computations were started 2 and 5 days prior to the breakdown. The simulation of the vortex elongation and destruction was, to a certain extent, successful, but the split vortex in the prediction erroneously merged again after 8 days. The sudden warming was not simulated at all. The development of the Aleutian high associated with the vortex breakdown was not well computed. Studies are made on zonally averaged quantities pertaining to the tropospheric and stratospheric circulations and their coupling. The increase of eddy kinetic energy at the time of the amplification of zonal wavenumber 2 is discussed both for the numerical simulation and for the observed fields. It is reconfirmed that the eddy kinetic energy in the stratosphere is primarily supplied from below in the form of vertical flux of geopotential. The propagation of wave energy takes place through a rather narrow zonal belt at high latitude. A possible relation between the stratospheric vortex destruction and the tropospheric process of meandering westerlies is discussed in terms of vertical transmission of wave energy.
Smagorinsky, Joseph, Kikuro Miyakoda, and R F Strickler, 1970: The relative importance of variables in initial conditions for dynamical weather prediction. Tellus, 22(2), 141-157. Abstract
Tests were made to evaluate the relative importance of large errors in some of the variables formally required to specify initial conditions for the time integration of the hydro-thermodynamic equations for the atmospheric motion. The prime purpose was to analyze the adjustment process immediately following the initial disturbance. The variables selected were the surface pressure, the water vapor, the boundary layer temperature, and the boundary layer wind. It is likely that these quantities are not individually nor possibly even collectively essential to the definition of initial conditions because of dynamic coupling. The experiments showed that the predictions appear almost the same after about six hours irrespective of the initial values of these quantities. But after several days, the subsequent error behaves similar to the growth noted in predictability experiments.
Miyakoda, Kikuro, Joseph Smagorinsky, R F Strickler, and G D Hembree, 1969: Experimental extended predictions with a nine-level hemispheric model. Monthly Weather Review, 97(1), 1-76. Abstract PDF
Two-week predictions were made for two winter cases by applying the Geophysical Fluid Dynamics Laboratory high-resolution, nine-level, hemispheric, moist general circulation model. Three versions of the model are discussed: Experiment 1 includes the orography but not the radiative transfer or the turbulent exchange of heat and moisture with the lower boundary; Experiment 2 accounts for all of these effects as well as land-sea contrast; Experiment 3 allows, in addition, the difference in thermal properties between the land-ice and sea-ice surfaces, as well as an 80% relative humidity condensation criterion reduced from the 100% criterion in Experiments 1 and 2.
The computed results are compared with observed data in terms of the evolution of individual cyclonic and anticyclonic patterns, the zonal mean structure of temperature, wind, and humidity, the precipitation over the United States, and the hemispheric energetics.
The forecast near sea level was considerably improved in Experiments 2 and 3 over Experiment 1. The experiment succeeded in forecasting the birth of second and third generation extratropical cyclones and their behavior thereafter. The hemispheric sum of precipitation was increased five times in Experiment 2 over that in Experiment 1, and even more in Experiment 3, the greatest contribution occurring in the Tropics. Two winter cases were considered. The correlation coefficients between the observed and the forecast patterns for the change of 500-mb geopotential height from the initial time remained above 0.5 for 13 days in one case and for 9 days in the other.
There are, however, several defects in the model. The forecast temperature was too low. In the flow pattern the intensities of the Highs and Lows weakened appreciably after 6 or 8 days, reflecting the fact that the forecast of eddy kinetic energy was less than the observed. On the other hand, the intensity of the tropospheric westerlies was too great.
Miyakoda, Kikuro, and R W Moyer, 1968: A method if initialization for dynamical weather forecasting. Tellus, 20(1), 115-128. Abstract
A new technique to solve the balance of equations for a given geopotential field is tested. The non-filtered thermo-hydrodynamical equations are used as the basis, and the balance solution is obtained iteratively by filtering out the high-frequency modes through the use of the Euler-backward time differencing scheme.
The merit of this technique as compared to conventional methods is that equations which include complicated processes, such as friction or heating, can be treated without difficulty, and that the balanced solution thus obtained appears completely consistent with the prognostic equations. Furthermore, it is no longer necessary to artificially modify the observed geopotential as in conventional schemes, so as to meet the ellipticity condition of the differential equations.
Syono, S, Kikuro Miyakoda, Syukuro Manabe, T Matsuno, S Murakami, and Y Okuta, 1959: Broad-scale and small-scale analyses of a situation of heavy precipitation over Japan in the last period of Baiu Season, 1957. Japan Journal of Physics, 2(2), 59-103.
Kombayashi, M, Kikuro Miyakoda, M Aihara, Syukuro Manabe, and K Katow, 1955: The quantitative forecast of precipitation with the numerical prediction method. Journal of the Meteorological Society of Japan, 33(5), 205-216.
Syono, S, K Gambo, Kikuro Miyakoda, M Aihara, Syukuro Manabe, and K Katow, 1955: Report on the numerical prediction of the 500-mb contour height change with double Fourier series method. Journal of the Meteorological Society of Japan, 33(3), 133-139.
