24th Conference on IIPS


Mobile Micro Rain Radar deployments in North Carolina

Jessica L. Proud, Renaissance Computing Institute, Chapel Hill, NC

The Micro Rain Radar (MRR) 1 is a compact, vertically pointed radar that is designed to measure the vertical profiles of drop size distributions. From the drop size distributions, several parameters can be derived, including the characteristic fall velocity resolved into 30 range gates, the liquid water content, the rain rate, and reflectivity. It operates at a frequency of 24.1 GHz FM-CW and has a transmit power of 50 mW. The radar system consists of an antenna dish, radar, receiver unit, and a RS-232 data transmission interface. The MRR detects very small amounts of precipitation that are below the threshold of conventional rain gauges. Also, the MRR provides information for now-casting of precipitation, as it detects the start of rain or snow from ground level up to 6 km above the radar anywhere from several minutes to more than two hours before the onset of rain or snow at ground level. Another use for the radar is that it can show, particularly on reflectivity and fall velocity data plots, the height of the bright band above the ground that designates the freezing level during winter storm events. The ability to detect this important upper air feature was one main reason for acquiring a MRR for North Carolina, as western and central areas of the state can experience very high impact ice storms. These storms can result in huge power outages and road closures. For example, during an early winter ice storm during which about 2.5 cm of freezing rain fell in 2002, over 1.3 million people were without power and roads were closed for over two weeks 2. This storm resulted in 43 counties being declared federal disaster areas and power companies were stranded west of the most heavily impacted areas due to a lack of data that may have helped in forecasting and now-casting. One way to help alleviate such situations is to collect more upper air data that may help forecasters make more informed forecasts and now-casts. To address the need for more upper air data, a MRR was purchased by RENCI (Renaissance Computing Institute) 3 so that the functionality of the radar could be tested. One unique feature of the RENCI MRR is that it is mounted on a small trailer to allow it to be easily transportable. This mobility allows the radar to be moved to various locations around the state as determined by an approaching weather event. The trailer has a leveling system so that the radar is always vertical when sampling, an enclosure and dome to protect the radar during transport, and an onboard computer. The trailer also includes a camera, a new, compact weather station called the Vaisala Weather Transmitter WXT510 that measures six variables, an infrared temperatures sensor to measure the temperature of the ground, and a GPS to determine the location and elevation of the radar. All data collected on the trailer (e.g. MRR and weather station data) is sent back to RENCI real-time using wireless broadband. During one winter weather event in February 2007, data collected by the MRR clearly shows snow at upper levels (1900 m) evaporating before it hit the ground, as well as the slow descent of the snow to the ground over a two hour period as the dry layer dissipated. This is shown from 0500-0800 UTC on the figure below, which shows a reflectivity plot of height versus time. The data also shows the snow to sleet to rain phase shifts aloft (~1600 m) over time (see figure below from 1130-1330 UTC). Finally, since the nearest WSR-88D radar overshoots the area the data was collected in by nearly 3 km, the MRR allowed forecasters at a remote location to more directly observe precipitation intensity and type at the MRR site. With this data, forecasters could better determine what may happen as the storm evolved. Data collected during events is sent real-time and automatically to a public RENCI web site so that it is easily downloadable and can be used and viewed by others such as the National Weather Service (NWS). In addition to winter weather events, the mobile MRR is currently deployed along the southeastern coast of North Carolina in anticipation of a tropical event. Data collected during a tropical event from the MRR would provide information such as the current rain rate as well as the rain rate at which the MRR attenuates. Also, the MRR will be used to improve the Z-R relationship of the NWS radar that samples the southeastern part of North Carolina. If after testing the radar it is found to be valuable in forecasting and now-casting in winter weather, tropical storms, and other warm precipitation events, we will explore deploying a mesh of MRR radars across the state. 1 Manufactured by Metek GmbH and distributed by Bristol Industrial and Research Associates Ltd. (Biral) 2 Federal Emergency Management Association: “Federal Disaster Funds Authorized For North Carolina To Aid Local Government Ice Storm Recovery,” December 12, 2002. 3 RENCI is a North Carolina state organization that is a joint venture of the University of North Carolina Chapel Hill, North Carolina State University, and Duke University. RENCI works to use technology in to solve multidisciplinary problems in North Carolina.

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Session 9A, Radar IIPS and Applications, Part II (Continued)
Thursday, 24 January 2008, 3:30 PM-5:15 PM, 206

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