Quantifying the Effects of Radar Resolution on a Warm Rain Retrieval

Abstract:

In order to understand the life cycle and radiative impact of warm clouds, it is important to be able to detect and measure their precipitation. Due to the ubiquity of these clouds, particularly over the oceans, spaceborne radar is key to obtaining this information. Acquiring high fidelity measurements of precipitation from space is challenging, however, due to requirements of high radar sensitivity and the necessity of measuring close to the surface. In planning such a measurement, a number of tradeoffs exist in instrument design, particularly with regard to sampling and resolution. Non uniform beam filling increases uncertainty in a radar measurement as the instrument footprint becomes larger, while choices impacting vertical resolution affect the ability to sample within shallow clouds and notably between cloud base and the surface, where the surface return can mask out falling precipitation with low reflectivity.

Here we will present results of an observing system simulation experiment (OSSE), designed to explore the range of possibilities in spaceborne radar measurements of warm rain. Utilizing a high resolution model in combination with instrument simulators as our ‘observations’ we use a simple retrieval to estimate rain water content in and below shallow clouds. We evaluate the performance of the retrieval given a range of choices in horizontal and vertical resolution in order to quantify the tradeoffs in designing a spaceborne radar for this task.