Wednesday, 13 January 2016
This study examines the spatial and seasonal climatology (2004-2010) of the cloud-to-ground (CG) lightning flash peak current (Ip) across four US coastal regions, encompassing parts of the Gulf of Mexico (region 1), the Florida panhandle (region 2), Lake Michigan (region 3) and part of the Mid-Atlantic US (region 4). Its goal is to investigate the hypothesis that sodium chloride (NaCl) enhances the oceanic negative polarity CG (-CG) Ip magnitudes. Cross-sections of negative peak current (denoted as –Ip) along the oceanic-continental boundary of regions 1, 2 and 4 demonstrate a monotonic reduction by 2-2.5 kA. However, there is no similar reduction observed across the continental-fresh water boundary (region 3), and the positive peak current (+Ip) exibits no similar reduction across any boundary. The latitudinal and seasonal variation of -Ip across region 1 reveals a markedly consistent behavior. In particular, the -Ip amplitude maximum is observed during the summer months and decreases with increasing latitudes. This trend vanishes approximately 100 km inland from the Gulf of Mexico coastline. The longitudinal and seasonal variation of -Ip across region 4 does not exhibit a similar amplitude dependence on the respective longitudes (i.e., west-east), although the oceanic -Ip still exhibits its higher magnitudes during the summer months. We speculate that the increasing evaporation and convective mixing over lower latitudes are the driving forces that enhance the atmospheric NaCl concentration, leading to the higher thundercloud potentials and larger -Ip.
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