Preliminary estimation of horizontal fluxes of cloud liquid water in relation to subtropical moisture budget studies employing ISCCP, SSMI, and GEOS-1/DAS data sets

Special Sensor Microwave/Imager (SSM/I) retrievals of cloud liquid water, I nternational Satellite Cloud Climatology Project (ISCCP) cloud estimates, a nd winds from the Goddard EOS (GEOS-1/DAS) assimilation are employed to eva luate vertically integrated cloud liquid water (CLW) transport for 1992. Fi rst, GEOS-1/DAS multiyear data are used to confirm an earlier finding of a paradoxical net moisture sink over the Arabian-Iraqi desert [Alpert and Sha y-El, 1993]. The negative vertically integrated moisture flux divergence ov er this region is balanced mainly by the negative incremental analysis upda tes (IAU) of moisture. Moisture fluxes reveal strong convection but without precipitation in a shallow Hadley-type cell. Vertical profiles indicate th at the moisture removal process is associated with middle and high clouds a nd probably with CLW flux divergence. The CLW fluxes are estimated explicit ly and globally from ISCCP and SSM/I by using linear regression methods. Ar eas of significant CLW divergence are found over the eastern coasts of both the United States and Asia, in the vicinity of the Gulf Stream and Kuroshi o currents, as earlier conjectured by Peixoto [1973]. In both the Arabian-I raqi desert and over the Sahara, divergence of a vertically integrated CLW flux opposes the convergence of a vertically integrated horizontal moisture flux, thus explaining at least partially the paradoxical net sink and sour ce in these regions. However, the magnitude of the annual CLW flux estimate s as calculated here is, in general, too small to play any significant role in the vertically integrated water budget, except perhaps along coastal re gions and over dry subtropical deserts where precipitation minus evaporatio n is relatively small.