Large‐scale analysis and forecast experiments with wind data from the Seasat A scatterometer

Abstract

A series of data assimilation experiments is performed to assess the impact of Seasat A satellite scatterometer (SASS) wind data on Goddard Laboratory for Atmospheric Sciences (GLAS) model forecasts. The SASS data are dealiased as part of an objective analysis system utilizing a three‐pass procedure. The impact of the SASS data is evaluated with and without temperature soundings from the NOAA 4 Vertical Temperature Profile Radiometer (VTPR) instrument in order to study possible redundancy between surface wind data and upper air temperature data. In the northern hemisphere the SASS data are generally found to have a negligible effect on the forecasts. In the southern hemisphere the forecast impact from SASS data is somewhat larger and primarily beneficial in the absence of VTPR data. However, the inclusion of VTPR data effectively eliminates the positive impact over Australia and South America. This indicates that SASS data can be beneficial for numerical weather prediction in regions with large data gaps, but in the presence of satellite soundings the usefulness of SASS data is significantly reduced.

Applications of scatterometer winds in coastal areas

“…Several studies have been made of the use of scatterometer data in weather forecast models (Cane et al 1981, Baker et al 1984, Anderson et al 1987 and in wave models (Janssen et al 1987) but all focus on the global scale. Generally, it is found that where in situ data are plentiful then the inclusion of scatterometer data has little impact but noticeable improvements occur in the data-sparse southern hemisphere.…”

An introductory review of the measurement of ocean surface wind vectors with a satellite radar scatterometer

“…The results of Baker et al (1984) show less of a quantifiable advantage due to the inclusion of SASS data in the forecast surface pressure and tropospheric wind fields than do those of Cane et al (1981), but in both studies the benefit was greatest in the Southern Hemisphere where conventional data are very sparse. Duffy et al (1984) compare 72 hour forecasts, from the U.S. Navy forecast model, derived with and without SEASAT scatterometer data.…”

“…It is contended that a study along these lines is a necessary follow-on to the reported work of Cane et al (1981), Baker et al (1984 and Duffy et al (1984), in readiness for evaluating the actual ERS-I-and N-ROSS-derived winds in the operational weather forecasting process. It should be noted that the problem of aliasing of wind direction will be less in the ERS-I and N-ROSS scatterometerdata because ofthe triple antenna configurations to be used (Duchossois 1983, Sherman 1984.Also the atmospheric temperature profiles, derived from the TOYS instrumentation on the NOAA satellite, are much improved on those of the VTPR.…”

“…These are by Cane et al (1981), Baker et al (1984) and Duffy et al (1984. Cane et al (1981) used simulated scatterometer data in forecast experiments for the month of February 1976.…”

“…Real SASS data from early September 1978 were used by Baker et al (1984). They employed an objective de-aliasing scheme to resolve the directional ambiguity (as would be the case in an operational forecasting procedure), but it was sometimes found necessary to apply a 'subjective enhancement' of the SASS wind field, especially near the centre of cyclones.…”