P8A.9 Mobile Micro Rain Radar (MRR) deployment in North Carolina

Tuesday, 7 August 2007
Halls C & D (Cairns Convention Center)
Jessica L. Proud, Renaissance Computing Institue, Chapel Hill, NC; and K. Galluppi

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, and the rain rate. 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 start 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 chief 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 one inch of freezing rain fell in 2002, over 1.3 million people were without power and roads were closed for over two weeks (FEMA, 2003). 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)2 so that the functionality of the radar could be tested. If after testing the radar is found to be valuable in forecasting and now-casting in both winter weather and warm precipitation events, we may explore deploying a mesh of MRR radars across the state.

The Renci MRR 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 an automatic leveling system so that the radar is always vertical when sampling, an enclosure and dome to protect the radar during transport, and other instruments to detect weather variables at the ground. Although this trailer was not fully built-out this past winter, the MRR was still used during a few winter weather events. During one significant event, data collected by the MRR clearly showed 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. The data also showed the snow to sleet to rain phase shifts aloft (~1600 m) over time. 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.

Data collected during events is sent automatically and near real-time to a Renci ftp site so that it is easily downloadable and can be used and viewed by others such as the National Weather Service. Currently, a real-time web site with MRR observations, as well as other data such as surface observations and skew-t diagrams, is being designed so that relevant data can be viewed easily at one site. In addition to winter weather events, the mobile MRR will be deployed during the upcoming spring and summer to observe rain events.

1Manufactured by Metek GmbH and distributed by Bristol Industrial and Research Associates Ltd. (Biral)

2Renci is a joint venture of the University of North Carolina Chapel Hill, North Carolina State University, and Duke University and is a statewide virtual organization. Renci works to advance information technology in the state of North Carolina by applying technological expertise and the world's best computing, networking and data resources to multidisciplinary problems.

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