Vertical profile retrievals with warm-rain microphysics using the ground-based microwave radiometer operated by the Hong Kong Observatory

•Vertical profile retrieval algorithm with absorption from rain is developed.•Warm rain microphysics is incorporated.•Rain water content is estimated based on radar reflectivity.•Average error of retrieved temperature ≤ 1 °C for the bottom 2000 m of profile

We present the formulation of a variational-method-based retrieval algorithm for a ground-based microwave radiometer. Absorption by air, water vapor, cloud liquid water and rain water are incorporated into the formulation. The absorption of microwave radiation by air is calculated using a line-by-line method, while that by liquid water is calculated using an empirical formula that models the complex refractive index of liquid water. The root-mean-squared error of the retrieved temperature was no more than 1 °C in the lowest 2000 m of the profiles based on the 1-year verification data. The absorption of microwave radiation by rain water is important for improving the accuracy of the retrieval profiles during rainy conditions.