A New Cloud Ice Microphysical Parameterization Developed from CALIOP/CloudSat for Numerical Weather Prediction

We describe and evaluate a new cloud ice microphysical parameterization based on CALIOP/CloudSat satellite-based retrievals for use with the NAVy Global Environmental Model (NAVGEM) system. NAVGEM is a single-moment numerical weather prediction model, meaning that the ice water content (IWC) resolved at any model bin is related to the ice cloud effective radius (R_e) as a function of temperature in order to conduct corresponding radiative transfer calculations. Currently, the relationship in operational NAVGEM is described by Wyser (1998) for cirrus clouds based on historical airborne measurements. As such, glaciated ice, for which NAVGEM physics cannot distinguish relative to cirrus cloud ice, are not necessarily well represented. Further, in situ aircraft measurements pre-2007 are likely to have been impacted ice crystal shattering effects due to limited sensor probe designs that caused size-aliasing issues in the datasets. The new parameterization relates R_e to IWC and temperature using four years of the joint CALIOP/CloudSat 2C-ICE product.

We find from these data that R_e is reasonably well correlated with temperature (r ~ 0.70) and does not exhibit a strong latitudinal signal. Polynomial expressions are defined based on the 2C-ICE data for R_e(IWC,T) at different temperature ranges. Once these expressions are integrated into NAVGEM, an experiment is conducted to test the impacts of the new parameterization. NAVGEM is run for two months (with a two-week spin-up) using the current model state (control run) and the new parameterization. Model analyses and forecasts are scored relative to the ECMWF reanalysis along with a NAVGEM self-analysis for a variety of parameters (e.g., air temperature and geopotential height). Significant improvements (> 1 delta) are shown for most of the forecast cycle, especially in the tropics. However, significant negative model changes are found at the 120 h timestep, and via self-analysis. Plans and efforts to harness the power of remote sensing observations to better inform regional and global models of ice cloud microphysical properties will be discussed.