Three-Dimensional Air Circulation in a Squall Line from Airborne Dual-Beam Doppler Radar Data: A Test of Coplane Methodology Software

Abstract

The detailed structure of a tropical squall line observed in central Florida was investigated from an airborne dual-beam Doppler radar, pointing respectively fore and aft. This allowed dual-Doppler observations from a straight flight path in a way similar to the coplane sampling technique proposed for two ground-based Doppler radars and for which the authors had developed an elaborate method in order to obtain a reliable wind estimation. The application of this analysis method to the airborne dual-beam radar observations is discussed, along with the basic requirements due to the specific airborne data sampling. The retrieved three-dimensional airflow structures within the convective part of the squall line are found to be quite consistent with those previously documented from ground-based radars, such as the convective-scale downdrafts sustaining a well-marked rear-to-front flow or the convective updrafts associated with the front-to-rear flow at mid-to-upper levels and that detrain into the rear part of the squall-line system. Moreover, it is found that the coplane analysis provides a more regular description of the airflow than the conventional Cartesian analysis. The suitability of the coplane approach is also examined by quantifying the uncertainty due to geometric errors that affect the accuracy of the beam pointing.