A comparison of regional trends in 1979-1997 depth-averaged tropospheric temperatures

This study examines regional temperature trends during the period 1979-1997 from the Microwave Sounding Unit (MSU) 2r satellite measurements and compa res them with the same trends in depth-averaged tropospheric temperatures d erived from the National Center for Environmental Prediction (NCEP) reanaly sis, in an attempt to determine whether regional trends exist which are lar ger than known inhomogeneities in the data. Large, statistically significan t regional trends were found in both the NCEP and the MSU data that are of both signs and have larger magnitude than documented biases in the data. Th e datasets have overall agreement on the location and strength of these sig nificant regional trends at mid and high latitudes but agreement decreases in the tropics. A global annual average of the significant regional trends with larger ampl itudes than reported data biases and areally weighted over the globe yields - 0.02 degrees C over the 19-year period of the record in the MSU 2r Versi on C dataset, and - 0.05 degrees C/19 years in the NCEP data in the 1000-50 0 mb layer, increasing the bias threshold by as much as five times still re sults in an average cooling in both datasets. Subjecting the surface temperature record to the same regional analysis yie lds a regionally significant trend of 0.17 degrees C/19 years, approximatel y halving the trend obtained when all regions, regardless of significance, are considered. In addition, many regions with significant warming trends i n the surface network occur in areas with limited observations over oceans and are not confirmed by the other datasets. Discrepancies between signific ant regional trends in the surface record and the upper-air observations ar e not systematic. In no case are regionally significant, tropical, warming trends at the surface magnified at higher levels in the MSU and NCEP tropos pheric data. In the case of the NCEP reanalysis, both warming and cooling t rends on average become larger, more significant, and cover larger areas in shallower tropospheric layers. These results suggest that the disparity between global trends in satellite /rawinsonde/reanalysis datasets and those of the surface record are not sim ply the result of large-scale changes in the vertical structure of the atmo sphere or to large-scale biases in the satellite observations, but instead are linked to processes which are regional in nature. Copyright (C) 2000 Ro yal Meteorological Society.