Global Water Vapor Flux and Maintenance during FGGE

Abstract

The relative humidity, temperature and wind fields generated by the First Global GARP Experiment (FGGE) III-b analysis of the Geophysical Fluid Dynamics Laboratory (GFDL) are used to examine the global precipitable water distribution, and the water vapor transport and maintenance for two extreme seasons of atmospheric circulation, i.e., December?February and June?August 1979. It has been observed that the major water vapor content exists in tropical areas, especially over three regions: equatorial Africa, the northern part of South America, and equatorial western Pacific in December-February; equatorial Africa, Central America and the northern part of South America, and monsoon areas in June-August. The water vapor transport was analyzed to explore how the high water vapor content of these areas is maintained by the large-scale atmospheric circulation. It is concluded that 1) the nondivergent stationary mode describes most of the atmospheric water vapor transport; 2) the stationary divergent modes, mainly the local Hadley and Walker circulations, are responsible for the local maintenance of the high water vapor content over three tropical areas; and 3) the divergent transient modes, essentially the cyclone systems, transport poleward an important portion of water vapor along the storm tracks in midlatitudes of both hemispheres and two major cloud bands in the Southern Hemisphere.