Some Ideas For Future Reanalysis Efforts
John Lanzante
The Problem
- Time series used for studying long-term climate often contain artificial inhomogeneities, especially jumps at times when measuring instruments are replaced. A striking example occurred at Calcutta, India in 1968. Many other such cases can be found, although typically they are not as extreme.
- The difficulties are greater for radiosonde than surface or satellite data. The obstacles include:
- Historical documentation of changes in instruments or measurement practices is often incomplete, ambiguous or erroneous.
- The magnitudes of artificial inhomogeneities are often comparable to those of real climate variability, complicating the distinction between the two.
- Instrument changes are controlled at the country or station level; sometimes changes affect a large, contiguous area, hampering efforts to use “buddy-checks” of neighboring stations; in other instances changes occur at different times at each station, greatly magnifying the number of inhomogeneities which must be identified.
- The sparseness of the upper-air station network makes use of “buddy-checks” of neighboring stations more problematic.