School of Meteorology (Defense)


Blake J. Allen
OU School of Meteorology

25 June 2014, 10:00 AM

National Weather Center, Room 5930
120 David L. Boren Blvd.
University of Oklahoma
Norman, OK

Total lightning observations that will soon be available from the GOES-R Geostationary Lightning Mapper (GLM) have the potential to be useful in the initialization of numerical weather models, particularly in areas where other types of observational data, especially radar data, are sparse. Previous studies have shown promise in using total lightning data for this purpose, but have been limited mainly to nudging-type schemes to help initialize and maintain convection. To further explore how effectively the assimilation of such data can aid in modulating convective strength and in producing more detailed storm characteristics, this study used the Ensemble Kalman Filter (EnKF) to assimilate pseudo-GLM observations into a storm-scale model with 1 km horizontal grid spacing for three real-data cases. These cases include an isolated, non-severe storm (June 6, 2000), the tornadic Moore - Oklahoma City May 8, 2003 supercell, and a non-tornadic supercell (July 5, 2000).

In each case, pseudo-GLM observations were created from ground-based lightning mapping array data by generating flash extent densities with a resolution approximately equal to the resolution of the GLM at its nadir. These psuedo-observations were then assimilated to produce analyses of each storm, and tests were done to examine 1.) The effectiveness of different EnKF observation operator relationships, with a focus on relationships between graupel volume and total flash rates; 2.) The utility of temporally averaging observations over a range of different time periods to smooth short time-scale variations in flash rates and to lower the computational cost of the assimilation process; 3.) Different methods of triggering convection in the initially horizontally homogeneous model.

The best results were obtained using observation operators based on graupel volume and graupel mass, while an observation operator utilizing non-inductive charging rate performed less well. The highest temporal resolution pseudo-GLM data tested (1-minute) produced superior results when compared with temporally averaged data. Finally, a newly modified method of initially triggering convection improved the reproduction of the early reflectivity structure in the June 6, 2000 case and improved reproduction of the mesocyclone path in the May 8, 2003 case.

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School of Meteorology (Defense) Seminar Series website