Assessment of wind products obtained from multiple microwave scatterometers over the China Seas

Sea surface winds （SSWs） are vital to many meteorological and oceanographic applications, especially for regional study of short-range forecasting and Numerical Weather Prediction （NWP） assimilation. Spaceborne seatterometers can provide global ocean surface vector wind products at high spatial resolution. However, given the limited spatial coverage and revisit time for an individual sensor, it is valuable to study improvements of multiple microwave scatterometer observations, including the advanced scatterometer onboard parallel satellites MetOp-A （ASCAT-A） and MetOp-B （ASCAT-B） and microwave scatterometers aboard Oceansat-2 （OSCAT） and HY-2A （HY2-SCAT）. These four scatterometer-derived wind products over the China Seas （0°-40°N, 105°-135°E） were evaluated in terms of spatial coverage, revisit time, bias of wind speed and direction, after comparison with ERA-Interim forecast winds from the European Centre for Medium-Range Weather Forecasts （ECMWF） and spectral analysis of wind components along the satellite track. The results show that spatial coverage of wind data observed by combination of the four sensors over the China Seas is about 92.8% for a 12-h interval at 12：00 and 90.7% at 24：00, respectively. The analysis of revisit time shows that two periods, from 5：30-8：30 UTC and 17：00-21：00 UTC each day, had no observations in the study area. Wind data observed by the four sensors along satellite orbits in one month were compared with ERA-Interim data, indicating that bias of both wind speed and direction varies with wind speed, especially for speeds less than 7 m/s. The bias depends on characteristics of each satellite sensor and its retrieval algorithm for wind vector data. All these results will be important as guidance in choosing the most suitable wind product for applications and for constructing blended SSW products.

Sea surface winds(SSWs) are vital to many meteorological and oceanographic applications,especially for regional study of short-range forecasting and Numerical Weather Prediction(NWP) assimilation. Spaceborne scatterometers can provide global ocean surface vector wind products at high spatial resolution. However,given the limited spatial coverage and revisit time for an individual sensor,it is valuable to study improvements of multiple microwave scatterometer observations,including the advanced scatterometer onboard parallel satellites Met Op-A(ASCAT-A) and Met Op-B(ASCAT-B) and microwave scatterometers aboard Oceansat-2(OSCAT) and HY-2A(HY2-SCAT). These four scatterometer-derived wind products over the China Seas(0°–40°N,105°–135°E) were evaluated in terms of spatial coverage,revisit time,bias of wind speed and direction,after comparison with ERA-Interim forecast winds from the European Centre for Medium-Range Weather Forecasts(ECMWF) and spectral analysis of wind components along the satellite track. The results show that spatial coverage of wind data observed by combination of the four sensors over the China Seas is about 92.8% for a 12-h interval at 12:00 and 90.7% at 24:00,respectively. The analysis of revisit time shows that two periods,from 5:30–8:30 UTC and 17:00–21:00 UTC each day,had no observations in the study area. Wind data observed by the four sensors along satellite orbits in one month were compared with ERA-Interim data,indicating that bias of both wind speed and direction varies with wind speed,especially for speeds less than 7 m/s. The bias depends on characteristics of each satellite sensor and its retrieval algorithm for wind vector data. All these results will be important as guidance in choosing the most suitable wind product for applications and for constructing blended SSW products.