Lightning Frequency

I'll beat the lightning theme to death one last time today. In the last few weeks, I have added lightning-themed posts, here, here, and here. In today's post, I took the 1,884,764 lightning strikes in the BLM lightning archive (1986-2010) and computed a density of strikes. To do this, I created a raster grid of Alaska where each cell is 10 square miles. The GIS software then counted the number of lightning strikes that occurred in each cell and divided by 27 (years) and then by 10 (square miles per grid cell). The resultant map shows the frequency of cloud-to-ground lightning strikes. Figure 1 shows the raw computation of lightning frequency. For visual purposes, I ran a 3x3 mean filter across the data to remove a lot of the noisiness in the map. Figure 2 shows a smoother, more aesthetically pleasing representation of lightning frequency.

The lightning data is fairly similar to the thunderstorm climatology map that NOAA produced in their 1976 report on thunderstorm climatology in Alaska. Their report showed the greatest density in the Fortymile Country whereas the BLM's lightning data indicates the area immediately east of Fairbanks has the highest density of lightning strikes.

Figure 1. Raw number of lightning strikes per square mile in Alaska (1986-2012). Grid cells are 10 square miles.

Figure 2. Smoothed number of lightning strikes per square mile in Alaska (1986-2012). Grid cells are 10 square miles and the data were smoothed using a 3x3 mean filter.

Figure 3. Figure 7 from 1976 NOAA report on thunderstorm climatology in Alaska.