LARGE-SCALE CLOUD FEATURES DURING JANUARY 1993 IN THE NORTH-ATLANTIC OCEAN AS DETERMINED FROM SSM I AND SSM/T2 OBSERVATIONS/

Satellite microwave (special sensor microwave/imager (SSM/I) and speci al sensor microwave water vapor sounder (SSM/T2)) data are used to stu dy the large-scale cloud and precipitation features during January 199 3 in the North Atlantic (30 degrees-80 degrees N, 80 degrees W-30 degr ees E). Modification and validation of existing retrieval algorithms a re made so that these algorithms are more suitable for high-latitude s ituations. A new algorithm for atmospheric ice/snow retrieval using SS M/T2 data is developed. Although no direct validation has been conduct ed, the retrieved large-scale ice water path distribution compares wel l with a snowfall frequency climatology derived from shipboard present -weather reports. Monthly mean distributions of water vapor path, liqu id water path, ice water path, and rainfall rate are investigated in r elation to sea surface temperature. The results show that the magnitud e of precipitable water is highly correlated with the absolute value o f sea surface temperature. The largest values of liquid water path and rainfall are found over the Gulf Stream. Snowfall is greatest off the east coast of Canada, which is thought to correspond to the shallow c onvection associated with cold air outbreaks from the continent. Fresh water flux (precipitation minus evaporation) retrieved from satellite data show that rainfall and evaporation are almost in balance in the middle of North Atlantic (40 degrees-60 degrees N, 50 degrees-10 degre es W), while rainfall is larger than evaporation north of this region, and evaporation is larger than rainfall to the south. Also, high valu es of fresh water fluxes are found along the Gulf Stream. Strong corre lation was found between northward water vapor transport across 60 deg rees N parallel and the cloud and precipitation properties in the Gree nland Sea, implying that horizontal water vapor transport from lower l atitudes plays an important role in the cloud development in this regi on.