Analyzing vortex winds in radar observed tornadic mesocyclones for nowcast applications

A computationally efficient method is developed to analyze the vortex wind fields of radar observed mesocyclones. The method has the following features: (i) The analysis is performed in a nested domain over the mesocyclone area on the conical surface of radar scan. (ii) The background error correlation function is formulated with a desired vortex-flow-dependence in the cylindrical coordinates co-centered with the mesocyclone. (iii) The square root of the background error covariance matrix is derived analytically to pre-condition the cost-function and thus enhance the computational efficiency. Using this method, the vortex wind analysis can be performed efficiently either in a stand-alone fashion or as an additional step of targeted fine-scale analysis in the existing radar wind analysis system developed for nowcast applications. The effectiveness and performance of the method will be demonstrated by movies of analyzed wind fields for the tornadic mesocyclones observed by operational radars in Oklahoma on 24 May 2011 and 20 May 2013. The method is currently being extended to analyze three-dimensional vortex winds from either single-Doppler or multi-Doppler scans of mesocyclones. Progress in this direction will be also reported at the conference.