Cloud-to-Ground Lightning Characteristics, 1989-2000: West Coast Percent Positive Anomaly

In the period from 1989 to 2000, the National Lightning Detection Network recorded over 250 million cloud-to-ground (CG) lightning flashes. Climatological analysis of the cloud-to-ground flashes, in the form of lightning flash density and percentage of positive polarity maps, reveal significant geographical variations. In the Pacific Coastal region of the United States, the prominent variation observed is the high percentage of positive CG flashes. The high percentage (~50%\)) dominates the coastline and just offshore, which is up to five times greater than percent positive values along any other U.S. coastline. The values of percent positive decrease drastically a few kilometers inland, which coincides with a dramatic increase in the total (positive and negative) CG lightning flash density and increase in average elevation. Seasonal analysis of CG characteristics shows that the region with a high percent of positive CG's has very little variation in the total number of CG's. This is unlike the rest of the US, which tends to have a distinct maximum in the warm season. The highest percent of positive CG flashes along the Pacific Coast has a maximum in the winter season and a minimum in summer. This min / max pattern is also seen in other parts of the U.S., but the values along the Pacific tend to be much greater. Three meteorological variables that previous researchers have determined affects the percentage of positive CG's are: environmental instability, vertical wind shear, and the height of the charge separation process. This study conducts a statistical analysis to determine how each of these variables contributes to the Pacific Coast anomaly.