Sunday, 22 January 2012
An Examination of the Relationship Between Lightning and Rainfall Over Oceanic Regions Using the Global Lightning Detection (GLD360) Network
Hall E (New Orleans Convention Center )
Despite advancements in modern observation technologies, it remains difficult to retrieve meteorological data across the earth's vast ocean basins with sufficient spatial and temporal frequency to facilitate accurate weather reporting and forecasting. Remote sensing techniques provide spatial continuity (e.g. geostationary GOES satellites) but fail to capture the finer structures of convective features. Polar orbiting satellites provide high resolution imagery of internal structures of convective clouds but their generally large orbit inclination angles limit coverage over any one location to approximately two times per day. Recent research has illuminated the potential for long-range lightning detection technologies to provide observations across portions of the earth's surface historically void of data (e.g. oceanic regions). Pessi et al. (2009) compared very-low frequency (VLF) emissions from lightning flashes, termed ‘sferics', detected by the Pacific Lightning Detection network (PacNet) to satellite derived quantities such as near surface rain rate and maximum reflectivity over a portion of the central North Pacific Ocean. To date, VLF detectors have been installed world-wide leading to the advent lightning detection on a global scale. This study utilizes data from the more advanced Global Lightning Detection Network (GLD360) in conjunction with the Tropical Rainfall Measuring Mission's precipitation radar (TRMM PR) over the western North Pacific Ocean – a region noted for its tendency to support tropical and extratropical cyclogensis – to derive a similar result. Logarithmic fits best suit the data over the range of approximately 40-46 dBZ for the domains of normalized flash count and maximum-observed flash current respectively (0.5° x 0.5° grid spacing). Newly developed data processing algorithms from TRMM (version 7 2A23 and 2A25 products) and GLD360 became available in May 2011 and the improved location accuracy (LA) of this data set produced a qualitatively similar result with minor variation in reflectivity range sensitivity. Although preliminary, the results presented herein suggest that a robust relationship exists between the normalized flash count/maximum flash current from GLD360 and the maximum reflectivity as observed by TRMM PR over oceanic regions. The major implication is that long-range lightning flash observations can be used to infer intensity changes and development in convectively active regions. Furthermore, numerical weather prediction would benefit from ingesting such data as it could lead to more accurate model initialization.
Reference: Pessi, A., S. Businger, K. L. Cummins, N. W. S. Demetriades, M. Murphy, and B. Pifer, 2009: Development of a Long-Range Lightning Detection Network for the Pacific: Construction, Calibration, and Performance. Journal of Atmospheric and Oceanic Technology, 26, 145-166.