Microburst Wind Structure and Evaluation of Doppler Radar for Wind Shear Detection.

Doppler weather radar data from the Joint Airport Weather Studies JAWS Project are used to determine the horizontal and vertical structure of airflow within microbursts. Typically, the associated downdraft is about 1 km wide and begins to spread horizontally at a height below 1 km. The median time is 5 min from initial divergence at the surface to maximum different wind velocity across the microburst. The height of maximum differential velocity is 75 m. The median velocity different is 22 ms over an average distance of 3.1 km. The outflow is assymetric, averaging twice as strong along the maximum shear axis compared to the minimum axis. Doppler radar could be an effective means for identifying microbursts and warning aircraft of wind shear hazards. For microburst detection such a radar must be able to measure wind velocities in clear air as well as heavy rain and hail. Scan update rates should be approximately every 2 min and the lowest few hundred meters of the atmosphere must be observed. Ground clutter must be considerably reduced from levels typically obtained with present Doppler radars.