Observed and simulated influence of rainy-region SST on the tropical upper tropospheric humidity (UTH)
Hui-Wen Chuang, Univerisity of Michigan, Ann Arbor, MI; and X. Huang
Tropical deep convections play a key role in vertically transporting moisture from the boundary layer to the upper troposphere. In this study we investigate how the variations of SST over the tropical deep convective regions (rainy-region SST) affect the interannual variations of tropical UTH at different pressure levels. Interannual anomalies of UTH profiles are separately derived from ECMWF ERA-40 reanalysis and AIRS retrievals. Rainy-region SST is derived from the observed SST and GPCP pentad-resolution dataset. For comparison, simulated anomalies from the GFDL AM2 AMIP run and GFDL coupled-GCM (CM2) 100-year run are analyzed. While the variation of UTH in the AM2 and CM2 closely follows the constant relative humidity hypothesis, the relative humidity between 250-400 mb in AIRS retrievals (ECMWF) is noticeably decreasing (increasing) as temperature increases. When the inner tropical (15S-15N) rainy-region SST is used instead of the mean SST, the correlations between UTH (250-450mb) anomalies and surface temperature anomalies are improved by 10.9% for ECMWF and by 20.5% for AIRS, but decreased by 10.69% for AM2 and 3.65% for CM2 simulations. This result indicates that the GFDL GCM has difficulties in capturing observed influence of rainy-region SST on the UTH. The vertical structure of such correlations and their connections with deep convection maximum outflow level are further discussed.
Session 7A, Global dynamics and processes - II
Tuesday, 13 January 2009, 3:30 PM-5:45 PM, Room 129A
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