Detection of polar stratospheric clouds with ERS-2/GOME data

Abstract

Based on radiative transfer calculations, it is studied whether polar stratospheric clouds (PSCs) can be detected by the new Global Ozone Monitoring Experiment (GOME) on board the second European Research Satellite (ERS-2) planned to be launched in 1995. It is proposed to identify PSC-covered areas by use of an indicator, the Normalized Radiance Difference (NRD), which relates the difference of two spectral radiances at 0.515 µm and 0.67 µm to one radiance measured in the centre of the oxygen A-band at 0.76 µm. Simulations are carried out for two solar zenith angles, <Theta>=78.5° and <Theta>=86.2°. They indicate that, in presence of PSCs and with increasing solar zenith angles above <Theta>=80°, the NRD decrease to values clearly below those derived under conditions of a cloud-free stratosphere. Results for <Theta>=86.2° show that the method is successful independent of existing tropospheric clouds, of different tropospheric aerosol loadings, and of surface albedos. Results for <Theta>=78.5° illustrate that PSC detection under conditions of smaller solar zenith angles <Theta><80° needs additional information about tropospheric clouds.