Lightning Climatology: Median Peak Current Increase Along the U.S. Coast

Climatological studies of cloud-to-ground (CG) lightning have discovered interesting features across the United States. One such feature that has been noted in previous research is a sharp increase in the median negative peak currents along the U.S. coasts. The values over the ocean are consistently higher than over land with a rapid increase of approximately 4kA at the coastline. The median positive peak currents also show an increase offshore. However, there is no distinct change at the coastline. One explanation for this observation is the higher conductivity of the salt water decreases the attenuation of the electromagnetic signal of the CG flashes over the water. This would lead to a flash that would appear stronger to the NLDN sensors. However, there is a problem with this hypothesis. If the attenuation explanation is correct, the same sharp transition at the coastline should be seen in the positive peak current. A possible explanation for the absence of the sharp coastline increase in the positive peak currents is due to intracloud flashes, which are detected as weak positive CG flashes and contaminate the dataset. To minimize contamination all positive flashes below 10kA are omitted. However, this cutoff can also remove weak positive CG flashes and leave strong intracloud flashes in the dataset. Analyses of the peak currents for selected locations along the U.S. coasts are performed to determine the validity of this hypothesis.