SR/SSD 98-27

6-1-98

Technical Attachment

LISDAD Lightning Observations During the 22-23 February 1998
Central Florida Tornado Outbreak

Steven Goodman and Ravi Raghavan
Global Hydrology and Climate Center*
Huntsville, Alabama

A series of violent tornadoes caused multiple fatalities in Central Florida during the late evening and early morning hours of 22-23 February, 1998. The lightning time history of these storms was captured during the on-going ground validation campaign supporting the Lightning Imaging Sensor (LIS) experiment on the Tropical Rainfall Measuring Mission (TRMM). The ground validation campaign is a collaborative experiment that began in 1997 and involves scientists at the GHCC, MIT/Lincoln Laboratories, and the NWS Forecast Office at Melbourne, FL (Raghavan et. al., 1997).

The Lightning Imaging Sensor Data Applications Display (LISDAD) is a workstation that ingests and displays real-time data from the Melbourne WSR-88D Doppler radar, cloud-to-ground lightning flash information from the National Lightning Detection System (NLDN), and total lightning (in-cloud and ground flashes) from the NASA KSC Lightning Detection and Ranging (LDAR) system. Time histories of storm parameters such as maximum radar reflectivity, cloud top height, storm motion, and flash rates can be generated in real-time for selected storms of interest. These data are used in studies of the relationships between the observed lightning, and the storm structure and morphology.




Figure 1. LDAR lightning flashes (cyan) and NLDN ground strikes (blue) superimposed
on a radar reflectivity map of a tornadic storm at 05:00 UTC 23 Feb 98. Storm cell 8 is located in Seminole County north of the Orlando International Airport (MCO) approximately 100 km northwest (310° azimuth) of the Melbourne radar. Range rings from the radar are in 20 km intervals. Storm cell ID's are shown next to each storm.



Figure 2. Radar reflectivity map of a tornadic storm at 05:00 UTC 23 Feb 98 with NLDN ground strikes (blue). The large circles encompassing each storm indicate the radius of uncertainty in LDAR flash location (which is a function of the distance of the lightning from the LDAR antennas at KSC). The storm motion vectors and speed are shown next to each storm being tracked.

Figures 1 and 2 show the second major supercell storm, which contained a mesocyclone, moving through Seminole County. The extreme flash rate shown in Figure 1 is a recurring signature in a number of severe storms observed during the validation experiment in the past year. In a recent study on the feasibility of GOES lightning mapping from geosynchronous orbit, it is estimated that these lightning burst signatures could provide an average of 9 minutes additional lead time to severe storm warnings currently issued on the basis of radar signatures alone (Table 1). In the Florida storm outbreak, there was advance warning of the tornadic storms. However, the Florida storms, as with many Southeast storm outbreaks, occurred under the cover of darkness, when the NWS is deprived of valuable spotter reports and the rapid scan visible imagery that can help during the day. The lightning detection capability is a tool that operates day and night, and thus, is potentially important in such situations.

LDAR source locations are computed using a processor at KSC and transmitted along with reception time to the Melbourne WFO via wide-band telephone line. The LISDAD processor groups these sources into flashes on the basis of time-space proximity: the grouping algorithm applies a tolerance window of approximately 300 ms in time and 5 km in space. The plan projection of the centroids of these flash groups is computed and used as the basic lightning unit for subsequent processing and display. Figure 3 shows a summary image of all the LDAR lightning during the storm. An MPEG movie of the LDAR lightning flashes over 5 minute intervals as the storms move across central Florida. The density of lightning channel sources is shown in the x-y and y-z projections at the top and right hand side of Figure 3 and in the movie.

The LIS validation experiment is funded by NASA Headquarters. The LISDAD display system was recently upgraded through the MSFC Space Science Lab Research Investment Fund.


Related links on this tornadic episode:
MLB Synopsis: http://sunmlb.nws.fit.edu/wbstorms/3meso.html
NSSL Radar summary: http://whirlwind100.nssl.noaa.gov/~gordon/osf/23feb98/23feb98.html

References:

Raghavan, R., S. Goodman, P. Meyer, B. Boldi, A. Matlin, M. Weber, E. Williams, D. Sharp, S. Hodanish, J. Madura, and C. Lennon, "A Real-time Examination of the Incremental Value of Lightning Data in Diagnosing Convective Storm Characteristics,"Preprints, Seventh International Conference on Aviation, Range & Aerospace Meteorology, Long Beach, CA, American Meteorological Society, 1997.

Weber, M. E., E. R. Williams, M. M. Wolfson, and S. J. Goodman, An Assessment of the Operational Utility of a GOES Lightning Mapping Sensor, Project Report NOAA-18, MIT Lincoln Laboratory, Lexington, MA, 13 February 1998, 108 pp.