Evaluation of the Upper-Tropospheric Moisture Climatology in a General Circulation Model Using TOVS Radiance Observations

Abstract

TOVS satellite observations are used to evaluate the upper-tropospheric (400?200 mb) moisture distribution simulated by the GLA GCM in a 10-yr (1979?1988) integration produced for the Atmospheric Model Inter-comparison Project, in which several models participated worldwide. The simulated moisture fields show remarkable success in duplicating the large-scale structure and seasonal features in the observations, but they show insufficient contrast between very dry and very moist regions. The simulation generally does well in northern summer (June?July?August) but worse in northern winter. This is consistent with deficiencies in the annual cycle of moist convection so that convective rain stays too close to the equator in northern winter. The related misplacement of convective activity associated with the Asian monsoon produces discrepancies in the moisture over much of the Eastern Hemisphere. The simulation also shows a too weak moisture response to interannual fluctuations in the sea surface temperature, even for the large El Niño episode of 1983. These results indicate that deficiencies in modeling oceanic convection may be in part responsible for errors in the simulated upper-tropospheric moisture patterns.