The radar simulator: Deriving the radar signal using the cloud model output

We present an approach to simulate cloud radar signals on the basis of cloud model output, the radar simulator. The simulator is being developed to aid validation of the cloud model. The cloud model applies double-moment bulk warm-rain and ice schemes developed by Morrison and Grabowski.^{1, 2} As an input, the simulator uses profiles of the mixing ratios and number concentrations of cloud droplets, rain/drizzle drops, and ice crystals, as well as the air temperature. For the ice crystals, the rimed mass fraction predicted by the ice scheme is also used. The simulator applies precomputed look-up tables containing scattering properties of cloud and precipitation particles, such as reflectivities, extinction and absorption coefficients. For each grid point, the coefficients are integrated over particle size distributions and summed over hydrometeor types. Consistent with assumptions in the cloud model microphysical scheme, modified gamma size distributions are assumed for cloud droplets and ice crystals, whereas the exponential Marshall-Palmer size distribution is assumed for the rain/drizzle drops. Application of the radar simulator to a simulation of clouds observed during the TWP-ICE campaign over northern Australia is presented.