A bias in the satellite‐observed low‐level cloud motion winds over the central tropical Pacific

Abstract

Island wind data from the central tropical Pacific are compared with satellite‐observed low‐level cloud motion winds over the same area during 1976–1980. The purpose of the comparison is to investigate the effect of gaps in the satellite wind series. It is found that the distribution of the gaps is such that the resulting time series is biased from the complete time series because of undersampling of the strongest westerly and northerly wind anomalies. This bias is strong enough, at least in this geographical region, to cause difficulties in estimating accurate mean fields from the cloud motion winds alone. The gaps leading to this bias occur on time scales of days to weeks and are most common during the northern hemisphere winter. Further, the gaps can be attributed to the presence of heavy, high cloud cover typical of strong convective events. The bias follows from the fact that the wind anomalies are also strongest at these times.