Abstract
AbstractReal midlatitude meteorological cases are simulated over western Europe with the cloud mesoscale model Méso-NH, and the outputs are used to calculate brightness temperatures at microwave frequencies with the Atmospheric Transmission at Microwave (ATM) radiative transfer model. Satellite-observed brightness temperatures (TBs) from the Advanced Microwave Scanning Unit B (AMSU-B) and the Special Sensor Microwave Imager (SSM/I) are compared to the simulated ones. In this paper, one specific situation is examined in detail. The infrared responses have also been calculated and compared to the Meteosat coincident observations. Overall agreement is obtained between the simulated and the observed brightness temperatures in the microwave and in the infrared. The large-scale dynamical structure of the cloud system is well captured by Méso-NH. However, in regions with large quantities of frozen hydrometeors, the comparison shows that the simulated microwave TBs are higher than the measured ones in the window channels at high frequencies, indicating that the calculation does not predict enough scattering. The factors responsible for the scattering (frozen particle distribution, calculation of particle dielectric properties, and nonsphericity of the particles) are analyzed. To assess the quality of the cloud and precipitation simulations by Méso-NH, the microphysical fields predicted by the German Lokal-Modell are also considered. Results show that in these midlatitude situations, the treatment of the snow category has a high impact on the simulated brightness temperatures. The snow scattering parameters are tuned to match the discrete dipole approximation calculations and to obtain a good agreement between simulations and observations even in the areas with significant frozen particles. Analysis of the other meteorological simulations confirms these results. Comparing simulations and observations in the microwave provides a powerful evaluation of resolved clouds in mesoscale models, especially the precipitating ice phase.
Highlights
A strong need is emerging to have accurate radiative transfer simulations from realistic cloudy and rainy scenes at high microwave frequencies
The results from a representative case over western Europe are described in details in this paper and compared to the corresponding microwave observations from two microwave instruments, Sensor Microwave Imager (SSM/I) and Advanced Microwave Scanning Unit (AMSU), between 19 and 190 GHz
The radiative transfer code at Microwave (ATM) has been adapted to benefit from a detailed description of the hydrometeor properties as simulated by the Méso-NH microphysical scheme
Summary
A strong need is emerging to have accurate radiative transfer simulations from realistic cloudy and rainy scenes at high microwave frequencies. Simulations of realistic radiances of cloudy and rainy situations are strongly required at high microwave frequencies, implying that representative cloud model outputs along with accurate radiative transfer (RT) models exist. Wiedner et al (2004) directly compare radiative transfer simulation derived from mesoscale cloud model outputs with observations from TMI for two tropical situations. Most efforts on the analysis of cloudy and rainy situations in the microwave have been motivated by TRMM and, as a consequence, have concentrated on tropical latitudes and frequencies below 100 GHz. In this study, we propose to examine midlatitude cases with frequencies up to 190 GHz, using the same radiative transfer code and mesoscale cloud model as in Wiedner et al (2004).
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