The Direct Cloud-free Longwave Radiative Effect of Saharan Dust as observed by the Geostationary EarthRadiation Budget (GERB) Experiment

摘要

The Geostationary Earth Radiation Budget (GERB) instruments flying on the Meteosat Second Generation (MSG) series of satellites provide a unique tool with which to monitor the diurnally resolved evolution of the top of atmosphere broad-band radiation fields. In addition, coincident narrow band observations from the Spinning Enhanced Visible and InfraRed Imager (SEVIRI) instruments, also flying on the MSG platforms, can be used to provide information about the key atmospheric parameters that influence these broad-band radiative fluxes. One such parameter which can cause a large radiative perturbation, and is commonly seen within the GERB field of view is airborne Saharan dust. In this paper we briefly recap the algorithms that we have developed to identify and quantify Saharan dust loading over North Africa and Arabia using the SEVIRI observations, and to simultaneously diagnose the cloud-free longwave dust direct radiative effect (LW DRE) from GERB. Focussing on spring and early summer 2006, we obtain initial estimates of the regional mean aerosol optical depth at 0.67 (τ_(067)) and LW DRE of 0.5 ± 0.1 and 12 ± 4 W m~(-2) respectively. The corresponding dust longwave radiative efficiency is calculated to be 24 ± 4 W m~(-2) per unit τ_(067).