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 special sensor microwave water vapor sounder (SSM/T2)) data are used to study the large-scale cloud and precipitation features during January 1993 in the North Atlantic (30 degrees-80 degrees N, 80 degrees W-30 degrees E). Modification and validation of existing retrieval algorithms are made so that these algorithms are more suitable for high-latitude situations. A new algorithm for atmospheric ice/snow retrieval using SSM/T2 data is developed. Although no direct validation has been conducted, the retrieved large-scale ice water path distribution compares well with a snowfall frequency climatology derived from shipboard present-weather reports. Monthly mean distributions of water vapor path, liquid water path, ice water path, and rainfall rate are investigated in relation to sea surface temperature. The results show that the magnitude of precipitable water is highly correlated with the absolute value of 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 convection 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 degrees W), while rainfall is larger than evaporation north of this region, and evaporation is larger than rainfall to the south. Also, high values of fresh water fluxes are found along the Gulf Stream. Strong correlation was found between northward water vapor transport across 60 degrees N parallel and the cloud and precipitation properties in the Greenland Sea, implying that horizontal water vapor transport from lower latitudes plays an important role in the cloud development in this region.