Abstract
The temporal and spatial distribution of lightning strikes varies across California and has a differential effect on lightning fire ignitions. We analyzed 16 years of lightning strike data obtained from the National Lightning Detection Network to determine how the distribution of lightning strikes was affected by geography, topography, and large-scale weather patterns. Although there were significant differences in the number and density of strikes among bioregions, the annual, monthly, and hourly patterns were similar. The number of strikes increased with elevation. Strike polarity varied by month, and mean peak positive current, mean peak negative current, and number of return strokes per strike varied by bioregion. Weather patterns associated with lightning included strengthened high pressure cells stationed over the western United States that deploy moist monsoonlike air masses and promote rising motions, especially over mountain features. Understanding the variation in lightning strike distributions provides insight into the role of fire in different bioregions of the state and aids in the prediction of wildland fire occurrence.
Highlights
The role fire plays in an ecosystem is dependent on the simultaneous occurrence of an ignition source, sufficient fuel to carry the fire, and weather conditions conducive for burning
In a study of thunderstorms and lightning fires in California, Palmer (1917) found that the number of lightning fires varied across the state, with the mountainous regions receiving more than the coastal regions
Months with high numbers of lightning occurrences in Sierra Nevada are accentuated when anomalously high geopotential heights were positioned over the Pacific northwest; those with high numbers of lightning strikes in the Mojave region are associated with a broad center of anomalously high geopotential heights over the northwest and the intermountain west, and those with high numbers of lightning strikes in the southern California San Jacinto Mountain region are associated with positive 700 hPa height anomalies extending from the Pacific northwest down to the central California and Nevada
Summary
Time, and location, the combined van Wagtendonk and Cayan: Temporal and Spatial Distribution of Lightning Page 37 system provided polarity, mean peak current in kiloamps (kA), and number of return strokes. Recent observational evidence indicates that, since the mid-1980s, warmer spring and summer temperatures have caused earlier snowmelt van Wagtendonk and Cayan: Temporal and Spatial Distribution of Lightning Page 38 and drier landscapes and have allowed wildfires to start earlier, last longer, and become larger in middle elevation forests of the western United States (Westerling et al 2006). Our objective was to determine the effect of geography, topography, and largescale weather patterns on the temporal and spatial distribution of lightning strikes and lightning strike characteristics
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