Understanding the microphysics (size, shape, velocity) of heavy precipitation is important for scientists to accurately estimate rainfall rate and for improving these parameterizations in models that predict weather. Between May and June, the ARM Southern Great Plains (SGP) site is hosting a joint field campaign for scientists from the National Center for Atmospheric Research (NCAR), the National Oceanic and Atmospheric Administration (NOAA), and the University of Oklahoma that involves daily precipitation measurements using a video disdrometer. A disdrometer is an instrument used to measure the drop size distribution and velocity of falling precipitation. Some disdrometers can distinguish between rain and graupel (solid precipitation such as hail, sleet, and snow pellets). Newer disdrometers that use microwave or laser technologies are sensitive enough to analyze individual snowflakes.
In late April, an NCAR 2D video disdrometer was installed at Kessler Farm near SGP’s Purcell Boundary Facility, next to a disdrometer used by NOAA’s National Severe Storms Laboratory (NSSL). In addition to the surface observation area, the Purcell Boundary Facility provides scientists with the internet connection, power, and workspace needed to record their research. Goals of this 2-month campaign are to accurately measure characteristics of precipitating particles using 2D video disdrometer technology.
The National Weather Service uses 2D video disdrometers for dual-polarization measurements. Polarization measurements are important for discriminating between radar signals that bounce off of symmetrical versus irregular shapes (i.e., rain drops versus snow or ice crystals). The Weather Service radars (WSR-88Ds) will be upgraded with dual-polarization capability in the next five to seven years, which will provide polarization radar measurements and allow scientists to remotely study precipitation microphysics from instruments located throughout the United States. Accurate in-situ measurements are important for verifying and understanding polarization radar capabilities. Disdrometer observations obtained during the field campaign will be used to verify polarimeter radar measurements from an NSSL dual-polarization radar located about 30 km away, in the same field of view. In addition, the data will be used to develop data retrieval algorithms, to study rain microphysics, and to derive improved parameterization schemes for National Weather Prediction models.