Walt Petersen

WRF Simulations of the 20–22 January 2007 Snow Events over Eastern Canada: Comparison with In Situ and Satellite Observations

Abstract One of the grand challenges of the Global Precipitation Measurement (GPM) mission is to improve cold-season precipitation measurements in mid- and high latitudes through the use of high-frequency passive microwave radiometry. For this purpose, the Weather Research and Forecasting model (WRF) with the Goddard microphysics scheme is coupled with a Satellite Data Simulation Unit (WRF–SDSU) to facilitate snowfall retrieval algorithms over land by providing a virtual cloud library and corresponding microwave brightness temperature measurements consistent with the GPM Microwave Imager (GMI). When this study was initiated, there were no prior published results using WRF at cloud-resolving resolution (1 km or finer) for high-latitude snow events. This study tested the Goddard cloud microphysics scheme in WRF for two different snowstorm events (a lake-effect event and a synoptic event between 20 and 22 January 2007) that took place over the Canadian CloudSat/Cloud-Aerosol Lidar and Infrared Pathfinder Sat...

POTENTIAL ROLE OF DUAL- POLARIZATION RADAR IN THE VALIDATION OF SATELLITE PRECIPITATION MEASUREMENTS Rationale and Opportunities

Abstract Dual-polarization weather radars have evolved significantly in the last three decades culminating in operational deployment by the National Weather Service. In addition to operational applications in the weather service, dual-polarization radars have shown significant potential in contributing to the research fields of ground-based remote sensing of rainfall microphysics, the study of precipitation evolution, and hydrometeor classification. Microphysical characterization of precipitation and quantitative precipitation estimation are important applications that are critical in the validation of satellite-borne precipitation measurements and also serve as valuable tools in algorithm development. This paper presents the important role played by dual-polarization radar in validating spaceborne precipitation measurements. Examples of raindrop size distribution retrievals and hydrometeor-type classification are discussed. The quantitative precipitation estimation is a product of direct relevance to spa...

The Midlatitude Continental Convective Clouds Experiment (MC3E)

AbstractThe Midlatitude Continental Convective Clouds Experiment (MC3E), a field program jointly led by the U.S. Department of Energy’s Atmospheric Radiation Measurement (ARM) Program and the National Aeronautics and Space Administration’s (NASA) Global Precipitation Measurement (GPM) mission, was conducted in south-central Oklahoma during April–May 2011. MC3E science objectives were motivated by the need to improve our understanding of midlatitude continental convective cloud system life cycles, microphysics, and GPM precipitation retrieval algorithms. To achieve these objectives, a multiscale surface- and aircraft-based in situ and remote sensing observing strategy was employed. A variety of cloud and precipitation events were sampled during MC3E, of which results from three deep convective events are highlighted. Vertical structure, air motions, precipitation drop size distributions, and ice properties were retrieved from multiwavelength radar, profiler, and aircraft observations for a mesoscale convec...

Drop Shapes and Fall Speeds in Rain: Two Contrasting Examples

AbstractTwo rain events are analyzed using two collocated 2D-video disdrometers (2DVD) and a C-band polarimetric radar at 15-km distance. Both events had moderate-to-intense rainfall rates, but the second event had an embedded convective line. For the first event, the fall speed distribution for a given drop diameter interval showed a narrow and symmetric distribution with a mode at the expected value; the second event produced a wider distribution with a significant skewness toward lower fall speeds. The “slower” drops in the second event were detected while the convective line was directly over the 2DVD site. Drop shape information from the two 2DVD instruments showed that, during the passage of the convection line, around 30%–40% of the drops did not have an axis of rotational symmetry, whereas for event 1, it was only 5%. The implications are that for event 1 the dominant mode of drop oscillation is the axisymmetric mode, and that within the convective line of event 2 other fundamental modes were freq...