Earth and Atmospheric Sciences, Department of
Date of this Version
10-2009
Abstract
The meteorological impact on wildfire activity in the North American boreal forest during the fire seasons of 2000 – 2006 is statistically analyzed through an integration of the following data sets: the MODerate Resolution Imaging Spectroradiometer (MODIS) level 2 fire products, the 3-hourly 32-km gridded meteorological data from North American Regional Reanalysis (NARR), the instantaneous lightning data collected by the Canadian Lightning Detection Network (CLDN), and the Alaska Lightning Detection Network (ALDN). Positive anomalies of the 500 hpa geopotential height field, convective available potential energy (CAPE), number of cloud-to-ground lightning strikes, and the number of consecutive dry days are found to be statistically important to the monthly variation of MODIS fire counts in portions of Canada and the entirety of Alaska. It is revealed that dry lightning strikes account for only 20% of the total lightning strikes, but they are associated with (and likely cause) 40% of the MODIS observed fire counts in the Alaskan and Canadian boreal forest regions. Analysis of fire occurrence patterns in two sub-regions of the North American boreal forest shows that a higher probability for dry lightning occurs only when 500 hPa geopotential heights are above ~5700 meters and CAPE values are near the maximum observed level, underscoring the importance of low-level instability to the boreal fire weather indices. In contrast, the higher probability for wet lightning is spread over a large range of CAPE values. Locations with a high percentage of dry strikes commonly experience an increased number of fire counts, while the mean number of fire counts per dry strike is more than 50% higher in western boreal forest, suggesting a geographic and possible topographic influence. Furthermore, the combination of at least 10 dry strikes per grid and at least 10 consecutive dry days is found to be an important threshold to increase fire activity.
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Comments
A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Geosciences, Under the Supervision of Professor Jun Wang. Lincoln, Nebraska: October, 2009
Copyright 2009 David Peterson.
A revised version of this document was published in Atmospheric Chemistry and Physics 10 (2010):6873–6888; doi:10.5194/acp-10-6873-2010 http://www.atmos-chem-phys.net/10/6873/2010/