Comparison of the simulated microwave cloudy radiances using ARTS and RTTOV-SCAT

P. SALIO; C. PRIGENT; P. ERIKSSON; GALLIGANI, VICTORIA SOL

Darmstadt

Conferencia; 21st. International TOVS Study Conference; 2017

Radiative transfer models are used in numerical weather prediction (NWP) as observation operators during assimilation. In order to assimilate passive microwave radiances in an all-sky scenario, an improvement in our understanding of the scattering properties of frozen hydrometeors is essential. At high microwave frequencies, frozen hydrometeors significantly scatter radiation, and the relationship between radiation and hydrometeor populations becomes very complex. The main difficulty in cloudy microwave remote sensing is correctly characterizing this scattering signal due to the complex and variable nature of the size, composition and shape of frozen hydrometeors. These problems make it hard to assimilate microwave observations in NWP models, particularly in situations where scattering effects are most important, like deep-convective areas, over land surfaces or in moisture sounding channels. In the present study, the performance of the very fast radiative transfer for television operational vertical sounder (RTTOV) and its scattering package, RTTOV-SCATT, is compared with the research radiative transfer model, the Atmospheric Radiative Transfer Simulator (ARTS). In RTTOV-SCATT, the bulk optical properties for hydrometeor species are taken from pre-calculated look-up tables, while in ARTS, the bulk optical properties can be defined by the user. In the present study, different real atmospheric scenarios are used to compare the first-guess (FG) departure for both clear and cloudy sky conditions of the GPM microwave imager GMI, with consistency in the input bulk optical cloud properties. In the context of the upcoming launch of the Ice Cloud Imager (ICI) onboard Metop-SG satellites, the present study also compares the performance of RTTOV and ARTS in the sub-millimeter frequencies.