Tornadic mesocyclone wind retrievals from radar observations

A variational method is developed to retrieve three-dimensional vortex winds of tornadic mesocyclones from radar observations. This method has the following features: (i) The vortex center is estimated as a continuous function of time and height in the four-dimensional space from radar observations. (ii) The retrieval domain is co-centered and moving with the slantwise vortex core at each vertical level. (iii) Vortex-flow-dependent background error covariance functions are formulated for the streamfunction and velocity potential with the mass continuity equation and boundary conditions satisfied automatically. The method has been tested with simulated radar observations for idealized mesocyclones and is being applied to real radar observations collected from the operational KTLX and TOKC as well as the phased-array radar at the National Weather Radar Testbed for the EF5 tornadic mesocyclone that struck Moore in Oklahoma on 20 May 2013. The retrieved three-dimensional vortex winds reveal highly curved areas of strong updraft and downdraft around the slantwise vortex core, and the vortex core is found to become increasingly vertical as the vortex intensifies. Retrieved vortex wind fields will be represented at the conference to show their complex structures at different vertical levels (from z = 0 to 5 km) and time evolutions.