Lightning in the North American Monsoon: An Exploratory Climatology

The temporal and spatial distributions of the North American Monsoon have been studied previously with rainfall and satellite data. In the current study, the monsoon is examined with lightning data from Vaisala's Global Lightning Dataset GLD360 and National Lightning Detection Network. GLD360 has been operating for over three years and provides sufficient data to develop an exploratory climatology with minimal spatial variation in detection efficiency and location accuracy across the North American monsoon region. In addition, GLD360 provides continuous coverage in both time and space. About 80% of the strokes detected by GLD360 are cloud-to-ground. This paper will focus on the seasonal, monthly, weekly, and diurnal features of the lightning activity in the monsoon from Mazatlán north-northwest to northern Arizona and New Mexico. It is shown that the lightning frequency increases quickly during the middle weeks of June. Increased stroke activity moves from the east and southeast toward the coast of the Gulf of California (Sea of Cortez). Lightning then increases dramatically to a maximum in July and August. The highest stroke densities observed in Mexico approach those observed by GLD360 in several other parts of the world. In addition to furthering the understanding of the monsoon's temporal and spatial evolution, lightning is important in itself because it poses a threat to human safety, initiates wildfires, and causes interruptions to utilities, communications infrastructure, and mining operations. Furthermore, the continuous spatio-temporal coverage of GLD360 observations can be utilized, together with a suitable lightning-rainfall relationship, to provide precipitation estimates in data-sparse areas such as the Sierra Madre.