Retrieval of Horizontal Wind Field and Mesoscale Vertical vorticity in Stratiform Precipitation by Conical Scannings with Two Doppler Radars

Abstract

Stratiform precipitations associated with fronts and squall lines are commonly observed by means of a single Doppler radar operating conical scannings. The data analysis is frequently the Velocity Azimuth Display—or VAD—methodelogy. This method directly yields, at each altitude, the horizontal wind vector at the center of the circle scanned by each radar gate, as well as its divergence and its stretching and shearing deformations at the circle scale. Also obtained are the terminal fall velocity of the hydrometeors, and, indirectly, the vertical velocity by integration of the air continuity equation. This paper deals with the case of two Doppler radars (spaced about 30 km apart) simultaneously operating conical scannings of stratiform precipitations. It is shown how a very simple extension of VAD analysis and its application to double radar yields the first derivatives of the horizontal wind and the mesoscale vertical vorticity. This new method, hereafter referred to as DVAD—or double VAD—analysis, is then illustrated by results gathered in the stratiform anvil at the rear of a tropical squall line observed during the “COPT 81” experiment.