Extended Abstract (2.0M)12.4
Strong wind shears in stratiform precipitation observed with weather radar
Valery Melnikov, University of Oklahoma/CIMMS, Norman, OK; and R. J. Doviak
Radar observations of strong wind shears in stratiform precipitation are presented. In 87%, spectrum widths larger than 4 m/s (derived gust velocities exceed 6.1 m/s) are measured; derived wind shears exceed 40 m/s/km. Layers of extremely large spectrum width (exceeding 10 m/s) often exhibit wavy spatial patterns. To observe such layers with weather radar, special volume coverage with elevation increment of 0.12 deg has been designed for the WSR-88D KOUN (Norman, OK). Using this coverage several cases with exceptionally large widths 15-17 m/s located near the ground have been studied. Maximal wind shears in these layers reached 60 m/s/km. Low level strong wind shears are dangerous for flights. The data show that the wind shears in stratiform precipitation can reach values typical for thunderstorms.
Three schemes of wind shear estimation are discussed: 1) estimation based on the difference of the Doppler velocities at the radar beams adjacent in elevation, 2) difference of the Doppler velocities along a single beam, and 3) spectrum width measurements. Advantages and pitfalls of the schemes are demonstrated. It is shown that spectrum width measurements provide most reliable estimations of the low-level wind shears. Fluctuations of vertical wind velocities that cause airplane shocks are derived for the wavy shear layers.
Session 12, Radar
Thursday, 24 January 2008, 1:30 PM-3:00 PM, 226-227
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