Constructing a Temporal and Spatial Record of Lightning Strikes in Arctic Alaska: Discerning between increased strike frequency and increased detection capability

Previous published explorations of the relation between contemporary wildfire and lightning in Alaska have focused largely on the central boreal forest. Following the long duration (3 month), large extent (100,000 ha) 2007 Anaktuvuk River Fire on the North Slope of Alaska, some have questioned whether changes in summertime temperatures in that region have affected convective storms and the frequency of lightning strikes. Investigations of strike frequency rely on sensor networks that have progressively increased their detection capabilities by the addition of new stations or the installations of more sensitive instrumentation. Distinguishing whether North Slope lightning strikes have become more frequent requires isolating the bias of the increased detection capability of the Alaska Lightning Detection System (ALDS) between the years 1988 and 2010. Numerous methods are applied to remove this bias. Attempts are made to use only records collected from a select few legacy stations that were operational during the duration of the record. Given the history of network improvements, I have also sought to identify step-wise increases in detection and calibrate past records to reflect modern detection capabilities. Regardless of the method to remove the bias, it is clear that the timing, frequency and location of strikes have changed over the 22 years of record. I use the center time analysis (the date when half of the annual strikes have occurred) to explore if lightning is persisting later into the summer season when the tundra is drier and more apt to burn. Though the data from the whole state show a weak trend toward an earlier center time, the North Slope data lack a trend toward either earlier or later center time. It is clear that for most years, the center time is later on the North Slope than for the whole state. Following bias removal, the frequency of strikes has clearly increased starting in the summer of 2002 with the largest number of strikes occurring in 2007. Further comparison of strike frequency and timing with North Slope meteorological conditions will provide insight into the sensitivity of the region to more large magnitude tundra fires. Though vegetation recovery at burned sites appears to be more rapid than anticipated, the thermal disturbance fire generates can have long lasting impacts on active layer dynamics, hillslope stability and the generation and persistence of thermal erosion features.