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Accuracy of 404-MHz Radar Profilers for Detection of Low-Level Jets over the Central United States

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  • 1 Department of Agronomy, Iowa State University, Ames, Iowa
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Abstract

The authors have evaluated the performance of operational hourly data from a NOAA Wind Profiler Network 404-MHz radar profiler for detecting low-level jet (LLJ) events in the central United States. Independent, collocated rawinsonde and radar profiler data were time matched, producing 2614 paired observations over a 2-yr period. These observations were used to determine the impacts of the height of the first profiler range gate (500 m) and contamination of the hourly data by migrating birds on the ability of the profiler to accurately diagnose LLJ events. The profilers tend to underrepresent both the strength and frequency of occurrence of the LLJ. It was found that about 50% of LLJ events with wind speed maxima below 500 m were detected, increasing to 70%–80% for events having their wind speed maxima above 500 m. To reduce contamination by migrating birds when using profilers to detect the LLJ, a second-moment filtering technique with a threshold of approximately 2–2.5 m2 s−2 is suggested as an effective compromise between maximizing threat score and probability of detection while maintaining a low false alarm rate.

Corresponding author address: Dr. Chad J. Daniel, 3010 Agronomy Hall, Iowa State University, Ames, Iowa 50011.

cdaniel@iastate.edu

Abstract

The authors have evaluated the performance of operational hourly data from a NOAA Wind Profiler Network 404-MHz radar profiler for detecting low-level jet (LLJ) events in the central United States. Independent, collocated rawinsonde and radar profiler data were time matched, producing 2614 paired observations over a 2-yr period. These observations were used to determine the impacts of the height of the first profiler range gate (500 m) and contamination of the hourly data by migrating birds on the ability of the profiler to accurately diagnose LLJ events. The profilers tend to underrepresent both the strength and frequency of occurrence of the LLJ. It was found that about 50% of LLJ events with wind speed maxima below 500 m were detected, increasing to 70%–80% for events having their wind speed maxima above 500 m. To reduce contamination by migrating birds when using profilers to detect the LLJ, a second-moment filtering technique with a threshold of approximately 2–2.5 m2 s−2 is suggested as an effective compromise between maximizing threat score and probability of detection while maintaining a low false alarm rate.

Corresponding author address: Dr. Chad J. Daniel, 3010 Agronomy Hall, Iowa State University, Ames, Iowa 50011.

cdaniel@iastate.edu

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