Rain Attenuation Estimation with the Numerical Weather Prediction Model WRF: Impact of Rain Drop Size Distribution for a Temperate Climate

Frequencies at and above K/Ka band are required for the deployment of (very) high throughput satellites. Yet, radio-links at those frequencies are strongly affected by tropospheric constituents, especially rain. The knowledge of the signal attenuation due to rain comes from dedicated propagation experiments with satellite beacons. Numerical Weather Prediction models could act as an alternative source of rain information, but the validation of their performances against beacon data remains incomplete, notably with respect to the local climatology. This work studies the rain attenuation predicted with the Weather Research and Forecasting (WRF) model 4.0.3 initialized with ERA-5 data, tests nine microphysics schemes, either single- or double-moment, and adapts rigorously the electromagnetic model to their assumed rain drop size distributions. Results are compared over three months in Toulouse, in a temperate region, at both 20.2 and 39.4 GHz, and a strategy is outlined to select the best parametrizations from the error metrics.