Earth Science: Ground Validation Of Precipitation Models
Posted on Apr 5, 2021 by NASA
Quantifying the Earth's hydrological cycle, and in particular precipitation, is perhaps one of the most challenging problems facing atmospheric scientists today, and is critical to any worthy assessment of climate variability/change. NASA plays a key role in mitigating these issues via provision of platforms, instruments and scientific expertise for observing the water cycle from space. As such, NASAs Precipitation Measurement Mission (PMM) Science Team, including the NASA-JAXA Global Precipitation Measurement (GPM) Mission, launched in February 2014, are continually developing and improving satellite-based precipitation retrieval algorithms. These algorithms employ multi-frequency combinations of active (ie, radar) and passive microwave (PMW) sensors to quantify the 3-D distribution of precipitation in the Earth's troposphere.
PMW measurements are affected by emission and scattering by a diverse mixture of precipitation particle types and sizes throughout the atmospheric column, and by the variable emission properties of the Earth's land surfaces. Radar measurements are also affected by the range profile of cloud and precipitation hydrometeors in the atmospheric column. As such, complex combinations of observed and modeled precipitation particle physics (numbers, sizes, shapes, phases) and radiative transfer modeling enter into the realm of space-borne precipitation algorithm development. These algorithms require detailed ground validation from a combination of state of the art instruments such as multi-frequency polarimetric radar, disdrometer, and profiler measurements. Complementing the ground based observations (and mitigating their limitations to some extent) cloud resolving models such as the Weather Research and Forecast model (WRF) are used to test new precipitation retrieval algorithms, mitigate satellite orbit sampling biases, and subsequently to integrate the precipitation estimates with land surface/hydrological models. Hence from an integrated perspective, basic atmospheric weather prediction model microphysics and prognosticated precipitation fields must also be validated with similar ground observations.
Research objectives in this will leverage data collected from a robust instrumentation network currently operated at GSFC and WFF. The research will target retrievals of particle size distribution and phase information (with attendant errors) in the full troposphere from ground based multi-frequency radar and disdrometer data. These analyses would be accompanied by comparison to precipitation data collected by coincident GPM satellite overpasses and current high-resolution WRF simulations of precipitation over instrumented locations. In this way biases in both models and space-borne observations can be identified and corrected and ground validation methodologies refined in support of the NASA GPM mission. Work with David Wolff will be carried out at Wallops Flight Facility in Wallops, Virginia. Work with Gerry Heymsfield and Robert Meneghini would be carried out at NASA GSFC in Greenbelt, Maryland.