A diabatic Lagrangian technique for the analysis of convective storms

This study reports the design and testing of a new diabatic Lagrangian technique for the analysis of potential temperature, water vapor and cloud water mixing ratios, and virtual buoyancy in convective storms. Predicated on the availability of a complete, 4-D wind and reflectivity analysis of a subject storm, the Lagrangian analysis first calculates backward air trajectories from analysis gridpoints into the storm environment. After initializing each back-trajectory using an environmental sounding, the Lagrangian analysis then calculates time-dependent microphysical moistening-evaporation and diabatic heating-cooling changes in the forward trajectory direction. By integrating the field of trajectories forward in time back to the respective originating analysis gridpoints, the diabatic Lagrangian analysis thus obtains the 3-D fields of temperature, vapor, and cloud content at any given analysis time. Rain and graupel contents for calculating evaporation, melting, and other microphysical tendencies following the individual air trajectory motions are estimated from the local (Lagrangian) radar reflectivity. For simplicity in this preliminary study, a 1-moment version of the Lin-Farley-Orville (LFO) microphysical parameterization (Gilmore et al. 2004s) is used to calculate the parameterized heating/cooling and water substance tendencies.

The diabatic Lagrangian analysis is demonstrated for the case of a simulated supercell storm and for the 9 June 2009 supercell storm observed during VORTEX2. The modeled wind and reflectivity fields are obtained from the simulated 22 May 1981 Binger, OK supercell (Ziegler et al. 2010), while the observed wind and reflectivity fields are obtained from a series of wind syntheses incorporating up to 5 Doppler radars (i.e., combining data from the SR1, SR2, NOXP, and DOW6 mobile radars with the Dodge City WSR-88D) from the 9 June 2009 Greensburg, KS supercell case during the Verification of the Origins of Rotation in Tornadoes Experiment (Second Phase) or VORTEX2. The diabatic Lagrangian analysis compares favorably with the known output buoyancy and water substance fields in the simulated storm case and with surface in-situ mobile mesonet and Sticknet observations in the 9 June 2009 supercell case.