Accuracy of 404-MHz radar profilers for detection of low-level jets over the central United States

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 raw insonde and radar profiler data were time matched, producing 2614 paired ob servations over a 2-yr period. These observations were used to determine th e impacts of the height of the first profiler range gate (500 m) and contam ination of the hourly data by migrating birds on the ability of the profile r to accurately diagnose LLJ events. The profilers tend to underrepresent b oth 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, i ncreasing 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 approximat ely 2-2.5 m(2) s(-2) is suggested as an effective compromise between maximi zing threat score and probability of detection while maintaining a low fals e alarm rate.