Spaceborne precipitation radar simulation from a global cloud resolving model

Abstract:

The ability of spaceborne radars to detect and measure clouds and precipitation globally is affected by their inherent sensitivity limits, by attenuation of the microwave radiation in the atmosphere, and by variability of the precipitation over scales smaller than the radar footprint. Effective design of radars and the interpretation of their measurements require that the influence of these phenomena on their performance be quantified. Such quantification is hindered by the incompleteness of the existing reference measurements.

Simulation of radar observations from atmospheric models can be used as an alternative to direct measurements, but most models either operate on a local scale and are thus not globally representative, or else are too coarse in their resolution to simulate sub-footprint scale phenomena. This gap is currently being bridged by global cloud resolving models, which simulate the entire atmosphere at scales approaching that of individual clouds. We have simulated spaceborne radar measurements globally from a run of the Nonhydrostatic Icosahedral Atmospheric Model (NICAM) at a resolution of 800 m.

A radar single scattering model was developed for each of the five NICAM cloud and precipitation particle classes: cloud ice, cloud water, rain, snow and graupel, retaining consistency with the model microphysics assumptions. Additionally, regions with melting snowflakes were considered separately, as they have a pronounced effect on radar observations. The results of the single scattering calculations were then used in a time-dependent radiative transfer model in order to simulate attenuation and multiple scattering effects. Finally, the simulated observations were spatially averaged to reproduce the effect of a radar footprint larger than a single grid point. Using this approach, we can estimate the performance of various radar configurations in current and future Earth observing satellite missions.