Retrieval of Kinematic Fields from Dual-Beam Airborne Radar Data Gathered in Circular Trajectories during the FASTEX Experiment

Abstract

The present paper describes the vertical structure of the wind field obtained by analysis of ?purls,? that is, circular trajectories regularly performed by airborne dual-beam Doppler radars within the FASTEX frontal cyclones. Kinematic information on these systems are obtained using a new analysis scheme named DAVAD (Dual-Beam Antenna Velocity Azimuth Display). Using this scheme, it is possible to obtain the mesoscale wind field and its first-order derivatives, that is, the horizontal divergence (thus the vertical velocity), the stretching and shearing deformations, and the vertical component of vorticity. A unique advantage of this analysis is that it also provides a direct estimate of the terminal fall velocity of the hydrometeors. All these parameters are crucial for validation and initialization of mesoscale and large-scale models. The capabilities of this method and the best conditions for its application are assessed through simulations. Finally, an example of application of the scheme on the secondary low observed during the Fronts and Atlantic Storm Track Experiment (FASTEX) Intensive Observation Period (IOP) 12 is discussed. Results of purl processing using DAVAD are being included in the FASTEX database.