Abstract
The Community Microwave Emission Modelling platform (CMEM) has been developed by the European Centre for Medium-Range Weather Forecasts (ECMWF) as the forward operator radiative transfer model for low frequency passive microwave brightness temperatures (TB). It is used at ECMWF for L-band TB monitoring over snow free areas. In this paper, upgrades to CMEM are presented in order to explore forward modelling in snow-covered areas for coupled land-atmosphere numerical weather prediction systems. The upgrades enable to use CMEM on an extended range of frequencies and the Helsinki University of Technology multi-layer snow emission model is implemented. Offline CMEM experiments are evaluated against AMSR2 (Advanced Microwave Scanning Radiometer 2) observations showing that simulated TB is improved when using a multi-layer snow scheme, compared to a single-layer scheme. The improvements mainly result from a better representation of snow characteristics in the multi-layer snowpack model. CMEM is also evaluated in the Integrated Forecasting System and coupled to RTTOV (Radiative Transfer for TOVS). The numerical results show improved simulated TB at low frequency V polarization over snow-covered area compared to a configuration using emissivity atlas. Degradations at frequencies higher than 20 GHz indicate that further improvements are required in the emissivity and snowpack properties modelling.
Highlights
The surface emissivity is critical for the assimilation of surface-sensitive satellite microwave data over land
This study investigated the usage of Community Microwave Emission Modelling platform (CMEM) to estimate land surface emissivity over snow-covered areas
The Helsinki University of Technology (HUT) multi-layer snow emission model and new parameterizations, which allow for expansion of the target frequency, were implemented in CMEM
Summary
The surface emissivity is critical for the assimilation of surface-sensitive satellite microwave data over land. CMEM (Community Microwave Emission Modelling platform) is the ECMWF radiative transfer model developed for low frequency passive microwave brightness temperature observation monitoring and data assimilation. It is currently used at ECMWF as the Soil Moisture and Ocean Salinity (SMOS) forward operator to simulate L-band brightness temperatures [8,9]. In order to explore the performances of CMEM for a larger range of microwave frequencies in an operational-like environment, coupled experiments are conducted in the full IFS system, with CMEM interfaced to the observation operator Radiative Transfer for TOVS (RTTOV [15,16]) In this configuration, RTTOV replaces the atmospheric module of CMEM and CMEM provides surface emissivity and effective temperature as input to RTTOV.
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