Polarimetric Thermodynamic Retrievals in the Melting Layer: One-Dimensional Spectral Bin Model Simulations

Retrievals of latent heating rates are a primary objective in the atmospheric science community due to their important dynamical consequences across all spatial and temporal scales. Much of the focus has centered on mesoscale convective systems (MCSs) and the different heating profiles typical of their convective and stratiform portions. In the stratiform portion, the archetypal heating profile features warming above the freezing level due to deposition and cooling at and below the freezing level due to melting and/or evaporation. These profiles are typically scaled according to simple reflectivity-based parameters such as the “bright band”, which has long been known to be a consequence of melting hydrometeors.

In this study, the potential for dual-polarization radar to aid thermodynamic retrievals in the melting portion of stratiform precipitation is explored. A one-dimensional Lagrangian spectral bin model is employed that includes the melting, evaporation, and sublimation of snow aggregates with variable riming fractions for a prescribed temperature and moisture profile. Building off past versions of the model, environmental feedbacks of temperature and moisture have been incorporated. The reflectivity Z, differential reflectivity Z_DR, and specific differential phase shift K_DP are calculated using Rayleigh scattering equations at S band and compared to the cooling rates associated with various microphysical processes as well as to quasi-vertical profiles of radar observations in stratiform precipitation. In particular, the potential for diabatic cooling to produce sudden downward excursions (“sagging”) of the bright band is investigated.