Dec 1, 2009

The Great 2006 Heat Wave over California and Nevada: Signal of an Increasing Trend

Alexander Gershunov
AMS Journal of Climate
  • States that most of the great California–Nevada heat waves can be classified into primarily daytime or nighttime events depending on whether atmospheric conditions are dry or humid
  • States that a rash of nighttime-accentuated events in the last decade was punctuated by an unusually intense case in July 2006, which was the largest heat wave on record (1948–2006)
  • States that there is generally a positive trend in heat wave activity over the entire region that is expressed most strongly and clearly in nighttime rather than daytime temperature extremes
  • States that this trend in nighttime heat wave activity has intensified markedly since the 1980s and especially since 2000
  • States that the two most recent nighttime heat waves were also strongly expressed in extreme daytime temperatures
  • States that circulations associated with great regional heat waves advect hot air into the region, and that this air can be dry or moist, depending on whether a moisture source is available, causing heat waves to be expressed preferentially during day or night
  • States that a remote moisture source centered within a marine region west of Baja California has been increasing in prominence because of gradual sea surface warming and a related increase in atmospheric humidity
  • States that a prolonged stream of moisture from this southwestern source added to the very strong synoptic dynamics during the 2006 heat wave, and, despite the heightened humidity, an environment in which afternoon convection was suppressed, keeping cloudiness low and daytime temperatures high
  • Discusses the relative contributions of these factors and possible relations to global warming are discussed