International comparison of satellite winds - An update

Winds obtained from geostationary satellites (mainly GMS and GOES East and West) are compared with one another and with rawinsonde winds, the comparisons serving as a periodic quality check of satellite cloud motions (or winds) set up by the Coordination for Geostationary Meteorological Satellites. Differences were determined between colocated cloud motions observed by adjacent satellites in areas of overlapping coverage (Type 1) and between colocated rawinsondes and cloud motions within the field of view of each individual satellite (Type 2). Among colocated satellite winds (Type 1), rms vector differences of high clouds rarely exceed 10 mps and of low clouds, 6 mps. Among colocated cloud and balloon vectors (Type 2), however, rms vector differences are large. At high levels, differences range from 12 to 40 mps for GMS winds and from 10 to 19 mps for GOES winds. The greater disagreement of satellite winds with rawinsonde winds than with each other is attributed in large part to error in the assignment of cloud height, especially in the presence of strong vertical shear and to a lesser extent on time differences between cloud and balloon measurements.