VORTEX2: Multiscale Analyses of Tornadic Storms Using Multiparameter Mobile Radars

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Intellectual merit: The Verification of Origins of Rotation in Tornadoes Experiment #2 (VORTEX 2) is a multi-scale investigation of factors that lead to tornadogenesis. VORTEX 2 is a follow on to VORTEX 1 whose field phase was conducted during the Spring of 1994 and 1995. The VORTEX 1 advanced knowledge of the kinematic structures of tornadic and nontornadic storms and provided some hints as to the sensitivity of the evolution of supercell storms and tornadogenesis to very fine spatial scale heterogeneity. The VORTEX 2 community intends to extend and build upon the results of VORTEX 1. The research supported under this proposal addresses the stormscale circulations, and thermodynamic and precipitation variability that affect the development and distribution of vorticity in tornadic storms. The primary data set common to these research objectives are Doppler and polarimetric radar observations over the entire breadth and depth of the parent tornadic storm and its immediate environment. C-band radars, with their ability to both penetrate heavy precipitation and sense the clear-air inflow associated with supercell storms, are required. Although the Principal Investigators will cover the entire depth of the storm with two C-bands, frequent coordinated sampling of the lowest 3 kilometers will be made with a X-band dual-polarimetric radar to examine the microphysics and dynamics of the rear-flank downdraft and angular momentum beneath the mesocyclone. These three radars will be tightly coordinated to provide the storm-scale circulation and precipitation structure needed to place finer-scale observations from other instruments into the context of larger-scale storm and environmental flow. The scientific objectives of this research are to study: (i) vorticity dynamics associated with low-level rotation in supercells, (ii) the role of angular momentum transfer on tornadogenesis (iii) precipitation and thermodynamics of the rear-flank downdraft, (iv) the impact of environmental heterogeneity (including boundaries) on storm evolution, (v) the role of cell mergers on tornadogenesis, (vi) the evolution of polarimetric signatures within tornadic and non-tornadic supercells, and (vii) improvements in the analysis and forecasting of tornadic storms through the use of ensemble Kalman-filtering data assimilation. Broader impacts: According to the 1997 Workshop on Societal and Economic Impacts of Weather, tornadic storms account for about 73 fatalities each year and have an average economic impact of about $700M. While lead times associated with tornado warnings have increased with the National Weather Service (NWS) Doppler modernization and forecaster training program, false alarm rates have essentially remained flat. The lack of improvement in false alarms reflects lack of understanding of the physical processes that can cause or limit tornadogenesis. The research conducted here will improve fundamental knowledge, enabling better conceptual models and improved forecasting ability. The improved data assimilation and numerical weather prediction techniques will aid forecasters in their efforts to better warn the public. The independent dual-polarization and multiple-Doppler derived wind fields will aid in storm process and model validation studies. The dual-polarization data will provide an early indication of polarimetric signatures associated with tornadogenesis, if they exist, which will maximize the benefit of the dual-polarimetric upgrade of the NWS operational radar network. The datasets will also be used in university classes from freshman orientation to graduate level term projects. Computer-based teaching modules will be developed and made available to the community.