Cloud Effect on Temperature Profiles from Microwave Measurements

In this study, we address the characterization of clouds and its inclusion in microwave retrievals in order to study its effect on tropospheric temperature profiles measured by TEMPERA radiometer. TEMPERA retrieves atmospheric temperature profiles by measuring emitted radiation of molecular oxygen at 60 GHz. It is the first ground-based microwave radiometer that allows to obtain temperature profiles in the troposphere and stratosphere at the same time. In order to characterize the clouds a multi-instrumental approach has been performed at the aerological station of MeteoSwiss in Payerne (Switzerland). Cloud base altitudes were detected using ceilometer measurements while the integrated liquid water (ILW) was measured by a HATPRO radiometer. Additional cloud information was obtained from a co-located cloud camera and using an automatic partial cloud amount detection algorithm (APCADA). All this information has been used to characterize the clouds by means of a Liquid Water Content (LWC) profile. Different LWC profiles (shapes and values) have been tested in order to find the best cloud characterization depending on cloud type, altitude and ILW. Microwave temperature profiles have been obtained incorporating this liquid water profile in the inversion algorithm and they have been evaluated against retrievals without considering clouds, in order to assess the liquid water effect on microwave measurements. The results have been compared with the temperature profiles from radiosondes which are launched twice a day at this station. Two years of data have been analyzed and almost 300 non-precipitating cloud cases were studied. The statistical analysis carried out over all the cases evidenced that temperature retrievals improved in most of the cases when clouds were incorporated in the inversion algorithm.