Distinguishing Elevated from Surface-Based Convection Using Convergence Columns Identified from Dual-Polarization Doppler Radar Data

This paper presents a novel use of dual-polarization Doppler radar data to identify updraft characteristics of convective storms. In this work convergence columns are used to distinguish a case of elevated convection from one of surface-based convection. Convergence columns are areas of contiguous convergence found from a three-dimension grid of convergence values derived from radial velocity fields. ZDR columns are identified in the mid-levels as indicators of precipitation growth in the updraft and these are used to anchor columns of convergence.

The inversion that defined the convection as elevated was directly observed by in situ soundings taken as part of the PRECIP project (IOP 1). The observations show that the updraft of the elevated convection depicted by the convergence column originates above the surface whereas that of the surface based cell is apparent in the lowest elevation observed by the radar. Convergence is reduced beneath the inversion associated with the elevated convective event compared to the lower levels of the surface-based event. In addition, it can be seen that the convergence column of the surface-based convection is more upright than that of the elevated convection. Furthermore, there are indications that the radar derived convergence product can be used to classify convective type on a cell-by-cell basis and that transitions of cells from one convective type to another can be observed.