Birds Mimicking Microbursts on June 2, 1990 in Orlando, Florida
MASSACHUSETTS INST OF TECH LEXINGTON LINCOLN LAB
Pagination or Media Count:
During 1990 and 1991, the Terminal Doppler Weather Radar TDWR testbed collected Doppler radar measurements in Orlando, Florida in support of the TDWR Project. The main focus of the project is to develop algorithms that automatically detect wind shears such as microbursts anti gust fronts. While the primary goal of the TDWR is to detect scattering from raindrops, the sensitivity of the system allows for the detection of biological echoes as well. Previous research has shown that under certain conditions the scattering from birds and insects will lead to divergent signatures that mimic microbursts. This type, of pattern has been documented in Alabama Rinehart, 1986, Illinois Larkin and Quine, 1989, and Missouri Evans, 1990. In the Alabama and Illinois events, a divergent pattern similar to a microburst was produced when a large number of birds departed in the early morning hours from an overnight roosting site. On 2 June 1990 in Orlando, Florida, there were 11 surface divergent signatures similar to microbursts detected by the TDWR testbed radar. The maximum differential velocity of these events ranged from 11 to 36 ms, while the maximum reflectivity varied from 0 to 44 dBz. There was light rain in the area and low-reflectivity returns aloft however, the reflectivity wag more. like low-reflectivity microbursts in Denver than high-reflectivity microbursts that generally are observed in Orlando. These divergences were not detected by the microburst algorithm since the TDWR site adaptation parameters have been adjusted to avoid issuing alarms for signatures such as those on 2 June. Detailed investigation was conducted of two events to verify that these were not actual microbursts. bird burst, dry microburst, stipple, outflow prediction, reflectivity asymmetry, forcing mechanisms.
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