89th American Meteorological Society Annual Meeting

Monday, 12 January 2009: 2:00 PM
Lightning and radar observations of Hurricane Rita landfall
Room 131A (Phoenix Convention Center)
Bradley G. Henderson, LANL, Los Alamos, NM; and D. M. Suszcynsky, K. C. Wiens, C. A. Jeffery, and R. E. Orville
Poster PDF (197.6 kB)
Hurricane Rita made landfall near the Texas-Louisiana border at approximately 7:40 GMT on 24 September 2005. Hurricanes are not normally strong lightning producers, but at this time, Rita experienced strong updrafts and significant lightning activity. Radar reflectivity data from the Houston WSR-88D station plainly show the prominent updraft feature with echoes reaching 55-60 dBZ. Radar temporal reflectivity contours demonstrate moderate convective development with a strong surge at landfall. Georeferenced Very High Frequency (VHF) data from the Houston LDAR II network [Ely et al., 2006] show that the lightning events lie in distinct vertical columns coincident with the region of strongest convection. These features appear to be concentrated in the northern section of the hurricane eyewall. The peak VHF lightning rate occurred at the time of Rita landfall. GOES IR image data of the events do not plainly show a growing updraft, presumably due to masking of the convective activity below by cirrus blowoff.

In this paper, we present the temporal evolution of Rita's landfall. We suggest that the convective updraft and lightning associated with landfall mark a transition between oceanic hurricane dynamics and continental thunderstorm dynamics as a result of the rapid changes in water vapor, temperature, and wind profiles as the hurricane moved onto shore. Lightning is a direct consequence of the electrification and breakdown processes that take place during the convective stages of thunderstorm development. As Rita makes landfall, the eye shows signs of collapse, and overhead infrared imagery from the GOES satellite depict billowing features that are more typically seen in land-based thunderstorms. In addition to the LDAR II lightning data, we present Very-Low Frequency (VLF) lightning data recorded by the Los Alamos Sferic Array (LASA). VLF can discriminate between lightning types, and in the LASA data, Rita landfall lightning activity was dominated by Narrow Bi-polar Events (NBEs)---high-energy, high-altitude, compact intra-cloud discharges. The opportunity to locate NBE lightning sources in altitude may be particularly useful in quantifying the vertical extent (strength) of the convective development and in possibly deducing vertical charge distributions.

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