SEASONAL-VARIATION OF GLOBAL SURFACE PRESSURE AND WATER-VAPOR

Previous studies have shown that the seasonal variation of global-mean surface pressure (p(s)) results from variation of global-mean water v apor pressure (p(w)). The current study, employing the global data gen erated by Version 1 of the Goddard Earth Observing System (GEOS-1) Dat a Assimilation System, shows that seasonal variations of regional p(s) and p(w) tend to be out of phase (particularly in the subtropics of t he two hemispheres) and that the magnitude of the former variation is generally much larger than that of the latter. The seasonal variations of these two quantities are maintained by airmass and water vapor tra nsports by the global divergent circulation, which is driven by the la tent heat released by cumulus convection over the water vapor sink, as the ''water mass forcing'' mechanism predicted. Since p(w) and p(s) a re used often in depicting the climate system, assessments of climate change in terms of the global-mean and regional variations of these tw o variables should be interpreted with caution.