Low-Level Cloud Motion Winds from Meteosat High-Resolution Visible Imagery

Abstract

Low-level wind fields over the Atlantic have been derived from clouds in Meteosat high-resolution visible images experimentally with one production cycle per day over a period of more than 1 yr. The cloud motion winds from VIS imagery (VIS-CMW) use a template size of 32 32 VIS pixels, corresponding to about 80 km 80 km at the subsatellite point, which is four times better than for the corresponding IR (infrared window) winds (160 km 160 km). The yield is increased through the better spatial resolution of the VIS images and a better contrast between cloud and ocean surface, which effectively leads to an increase in wind vectors by a factor of 6. This implies a much better description of the low-level atmospheric flow by the VIS-CMW as compared to IR winds. The impact of the new VIS-CMW has been tested with a data assimilation experiment at the European Centre for Medium-Range Weather Forecasts, and small positive improvements have been found. The mean vector rms difference versus the verifying analysis shows improvement by up to 15% over some areas of the Atlantic Ocean. Comparisons of the short-term forecast using VIS cloud motion winds with independent scatterometer surface winds confirm the small improvements.