VARIABILITY OF MOISTURE IN THE UPPER TROPOSPHERE AS INFERRED FROM TOVS SATELLITE-OBSERVATIONS AND THE ECMWF MODEL ANALYSES IN 1989

Large-scale variability of moisture in the upper troposphere is examin ed using TIROS (Television Infrared Observation Satellite) Operational Vertical Sounder (TOVS) satellite observations and ECMWF model analys es from 1989 in the latitude band from 40 degrees N to 40 degrees S. T o compare these dissimilar datasets, upwelling radiances were computed for the 6-7-mu m water vapor band from the ECMWF temperature and mois ture analyses, and these computed radiances were compared to the corre sponding TOVS satellite observations. The ECMWF-based radiances reprod uce the general locations and seasonal cycle of the TOVS-observed mois ture features, particularly after an improved convective parameterizat ion scheme was adopted by ECMWF in May 1989. However, the ECMWF analys is scheme still results in much milder lateral moisture gradients and seasonal contrasts than indicated by the TOVS observations. Seasonally , the upper troposphere in each hemisphere dries in winter and moisten s in summer, but there are regions in each hemisphere that run counter to this seasonal trend, apparently depending on continental- and mons oon-scale dynamics. Dynamically, the TOVS-observed regions of signific ant subtropical dryness are correlated with persistent subsidence indi cated by ECMWF 300-mb vertical velocity analyses. The TOVS radiance ob servations indicate large variations in space and time of the upper-tr opospheric moisture field, which are not fully captured by the ECMWF a nalyses.