Tropical upper tropospheric motion field

Abstract

Upper tropospheric cloud motion vectors and commercial aircraft wind reports have enabled a detailed definition of the motion field. These two data sets have enhanced our observational capability since the launch of 4 to 5 geostationary satellites around the globe and the implementation of the ASDAR program. A sample is illustrated of recent commercial aircraft wind reports at the 300, 250, and 200 mb surfaces over parts of the Pacific Ocean, North America, and Atlantic Ocean. This data coverage is impressive. The rms difference between these data and those obtained from rawinsonde ascents (colocated) is around + or - 4 m/s. In a recent study of the cloud winds, from geostationary satellites, Johnson (1984) noted almost 15 m/s vector wind differences between estimates from GMS, GOES, and METEOSAT with respect to the rawinsonde observations. These results are illustrated based on the assessment of Johnson (1984). Overall, the commercial aircraft winds are the more accurate of these two observing systems. However, it is apparent that because of the sparcity of airline routes across southern oceans, one has to rely rather heavily on the cloud winds as a primary data source over the tropical southern oceans. The operational rawinsonde coverage over the tropics is generally very poor. The overall data coverage based primarily on the collections at the ECWMF are shown.