Temperature Decadal Change over Polar Region as seen from TOVS and NCEP Reanalysis

    Ever since the NCEP/NCAR reanalysis data set is available to the public, it has been widely used for various studies over different time and space scales. Over the arctic region, however, the amount of actual upper-air data are very sparse, and because of the lack of observations, it is uncertain how well the reanalysis reproduce the actual atmospheric structure in the central Arctic.

     A new major research tool to study the Arctic atmosphere in the 1980s and 1990s is the TOVS Polar Pathfinder(Path-P) satellite data set (Francis and Schweiger, 2000). We compare the reanalysis with this TOVS Path_P data set. These data provide temperature and moisture at ten/five standard pressure levels on a 100x100km grid north of 60^oN on daily bases. This data set is the first of itskind which can diagnose atmospheric characteristics across the Arctic basin in a consistent manner and with good horizontal resolution.We emphasize the temperature decadal changes from the two data sets over the Arctic region for the past 20 years. We computed the monthly means for each decade from 1989 to 1998 and from 1980 to 1988. Then the decadal change is defined as the differences between these two means.

    Compared with the 1980s, in 1990s,we see cooling in the upper layers (above 300hPa) and warming in the lower atmosphere. Both TOVS and NCEP reanalysis show very similar patterns, however the magnitude of the change differs, either cooling in the upper layers or warming at the lower levels from the NCEP/NCAR reanalysis is not as strong as shown in TOVS analysis.

     Based on TOVS analysis, the warming in the lower levels spans from March to September, with the strongest warming shown in April. The April warming also has a deep signature which goes to as high as 400hpa, while in the other months the warming is limited to below 700 hpa. NCEP/NCAR reanalysis also present similar warming signature in April vertically, but its 850hpa warming is weaker by about 1^oK, while at 400hpa the strength is the same as in TOVS. Inthe lower levels, the NCEP/NCAR reanalysis show shorter time period of warming, and much stronger cooling year around.