Simulations of radar signals on the basis of cloud model results - deep convection conditions

Simulation of observed radar returns is one of the tools for validating a new cloud microphysics code by H. Morrison and W.W. Grabowski. The code includes a two-moment bulk warm rain scheme and two-moment ice microphysics scheme with prognostic rime mass fraction. Both the simulator and the cloud model share the following set of assumptions. Three general types of particles are taken into account: cloud droplets, drizzle drops and ice crystals; particles are characterised by modified gamma size distribution (in case of rain drops it becomes exponential); and particles are described in terms of mass and area to dimension relationships. Liquid particles are assumed to be spherical and ice crystals are treated as spheres, dense non-spherical particles, graupel or aggregates, depending on their size and rimed mass fraction. Simulator input consists of particle number concentrations, mixing ratios (for ice crystals separate mixing ratios for mass grown by riming and water vapour deposition are employed), temperature and relative humidity profiles. Pre-calculated look up tables containing particle scattering properties (radar reflectivity and attenuation) as functions of input parameters are used in order to speed up the code. The simulator is applied to deep convection conditions observed during the Tropical Warm Pool International Cloud Experiment, Darwin, Australia, January - February 2006. The simulation results are compared to data collected by the millimeter wavelength cloud radar (MMCR) situated in Darwin, Australia - one of the measurement sites of the Atmospheric Radiation Measurement program.