A New Way to Simulate the Polarimetric Radar Signatures of Melting Layers

Melting layers contain complex microphysical processes which largely influence the precipitation systems. They usually manifest as bright bands in radar observations, Most radar forward operators embed in numerical weather models showed a limited capacity to simulate melting layers because bulk microphysics schemes (BMPs) neglect the melting state of particles to reduce the computational complexity. To present polarimetric simulations closer to observations, a new melting layer simulation algorithm was proposed for radar forward operators. The new simulator was tested using three double-moment schemes (i.e., Morrison, NSSL, WDM6) for the simulations of Typhoon Hato (2017). Compared with polarimetric radar observations, it was found that the peak and thickness of the simulated bright bands were overestimated in the Morrison and NSSL scheme and underestimated in WDM6 in the conventional simulator. The new simulator significantly improved the simulation of melting layers in three schemes, by simulating a more realistic evolution of particle size distribution of melting particles. Furthermore, liquid drops and melting particles were allowed to coexist in melting layers, which brought the simulation more consistency with observations. The new simulator digs deeply into microphysical factors influencing polarimetric simulations, providing valuable insights for better understanding the polarimetric signatures of mixed-phase clouds. A forward operator with improved capability to represent melting particles will also help us to develop better optimization-based radar retrieval methods for precipitation with mixed-phase processes.