On the accuracy of RTTOV-SCATT for radiative transfer in all-sky conditions

GALLIGANI, VICTORIA; PATRICK ERIKSSON; ALAN GEER; VASILEIOS BARLAKAS

Conferencia; International TOVS Study Conferences (ITSC) XXIII; 2021

With the emergence of a new generation of microwave instruments and, especially, the Ice Cloud Imager (ICI) covering frequencies between 183 and 664 GHz, it is necessary to evaluate the performance of the fast scattering solver of Radiative Transfer for TOVS (RTTOV-SCATT). Thus, we compare RTTOV-SCATT with the reference quality model ARTS (Atmospheric Radiative Transfer Simulator), with a special emphasis on ICI. Results are also presented on the basis of the Advanced Microwave Sounding Unit A (AMSUA) and the Microwave Humidity Sounder(MHS). Simulations are conducted for (a) simple yet realistic cloudy conditions and (b) idealized scenarios that are designed to identify the limitations of RTTOV-SCATT. Under typical cloudy conditions, a rather good agreement is found between the two models for all sensors, with RTTOV-SCATT producing brightness temperatures that can differ by about ±4-10 K, strongly depending on the channel?s frequency and the level of extinction. However, the comparison reveals that, for largeviewing angles (above 55 o ), high values of the optical thickness (deep convective systems), and strongly peaked phase functions (linked to high frequencies), the two-stream solution of RTTOV-SCATT is less accurate; the disagreement between the models exceeds 20 K.