A comparison of satellite-retrieved parameters with mesoscale model analyses

Abstract

A scheme to retrieve quantitative products from radiances recorded by the AVHRR (Advanced Very High Resolution Radiometer) on NOAA satellites over the same area as the Meteorological Office mesoscale model is outlined. Satellite products and model fields are both averaged over fifth of a degree latitude/longitude grid squares. Results for one satellite overpass over the British Isles on 21 June 1986 are described in detail. Fields of surface temperature over land and sea, fractional cloud cover and cloud top temperature retrieved from the AVHRR data are compared with the corresponding model-analysed fields nearest in time to the satellite overpass. The AVHRR and model sea surface temperatures are in reasonable agreement (∼0.7K), although the satellite data provide the more detailed field. The satellite land surface brightness temperatures could not be easily compared with the model ground temperatures as the former are radiative skin temperatures whereas the latter are related to screen temperatures and near-surface lapse rates. Differences of up to 10 K are noted in clear sky situations. The satellite and model fractional cloud cover fields are in reasonable agreement though the satellite fields did highlight one or two areas where the model analysis is in error. This is mainly in areas devoid of conventional observations. Fields of satellite cloud top temperatures show more detail and are more realistic than the corresponding model fields. This is not surprising as cloud top temperatures cannot be easily inferred from the surface observations analysed by the model. Satellite products, such as the ones described here, could in the future be used operationally to improve mesoscale or regional model analyses.