A Model Study of Heat Waves over North America: Meteorological Aspects and Projections for the Twenty-First Century

Abstract

The characteristics of summertime heat waves in North America are examined using reanalysis data and simulations by two general circulation models with horizontal resolution of 50 and 200 km. Several “key regions” with spatially coherent and high amplitude fluctuations in daily surface air temperature are identified. The typical synoptic features accompanying warm episodes in these regions are described. The averaged intensity, duration, and frequency of occurrence of the heat waves in various key regions, as simulated in the two models for twentieth-century climate, are in general agreement with the results based on reanalysis data. The impact of climate change on the heat wave characteristics in various key regions is assessed by contrasting model runs based on a scenario for the twenty-first century with those for the twentieth century. Both models indicate considerable increases in the duration and frequency of heat wave episodes, and in number of heat wave days per year, during the twenty-first century. The duration and frequency statistics of the heat waves in the mid-twenty-first century, as generated by the model with 50-km resolution, can be reproduced by adding the projected warming trend to the daily temperature data for the late twentieth century, and then recomputing these statistics. The detailed evolution of the averaged intensity, duration, and frequency of the heat waves through individual decades of the twentieth and twenty-first centuries, as simulated and projected by the model with 200-km resolution, indicates that the upward trend in these heat wave measures should become apparent in the early decades of the twenty-first century.

North American extreme temperature events and related large scale meteorological patterns: a review of statistical methods, dynamics, modeling, and trends

“…Eastern events While the large-scale meteorological patterns associated with heat waves in the eastern US have not yet seen much study, they have been examined for the Northeast and Central US Gulf Coast in Lau and Nath (2012) and for piedmont North Carolina by Chen and Konrad (2006). For both the Northeast and Gulf Coast, Lau and Nath found a mid-level ridge centered over the region as part of a wave train and precipitation deficits, broadly similar to the results for the Midwestern regions.…”

“…Midwest events Heat waves affecting the Midwest have anticyclonic flow at mid-levels, either as a closed anticyclone or as a strong ridge (Klein 1952;Karl and Quayle 1981;Namias 1982;Chang and Wallace 1987;Lyon and Dole 1995;Kunkel et al 1996;Livezey and Tinker 1996;Palecki et al 2001;Meehl and Tebaldi 2004;Lau and Nath 2012;Loikith and Broccoli 2012;Teng et al 2013), with associated clear skies allowing maximum solar heating of the surface as well as adiabatic warming from subsidence.…”

“…For at least some events, the continental anticyclonic flow at mid-levels is part of a larger pattern of anomalies with remote centers over the Pacific and Atlantic (Namias 1982;Chang and Wallace 1987;Livezey and Tinker 1996;Lau and Nath 2012;Loikith and Broccoli 2012;Teng et al 2013), with some suggestion that the anomalies are generated in the Pacific (Namias 1982; Lyon and Dole 1995;Livezey and Tinker 1996;Teng et al 2013), with possible predictability (Teng et al 2013). Teng et al (2013) have noted the similarity of the circulation pattern to a Rossby wave number 5 wave train in the jet stream waveguide.…”

“…Studies of the surface flow have been less common, but negative SLP anomalies have been noted (Chang and Wallace 1987;Lau and Nath 2012;Loikith and Broccoli 2012), and Lau and Nath (2012) have shown anomalous southerly (or southwesterly) flow at the surface, consistent with strong horizontal warm advection. The regional-scale flow also interacts with local mechanisms, particularly the Urban Heat Island (UHI) effect (Kunkel et al 1996;Palecki et al 2001).…”

“…The regional-scale flow also interacts with local mechanisms, particularly the Urban Heat Island (UHI) effect (Kunkel et al 1996;Palecki et al 2001). Another common element identified in several studies is the presence of drought (Chang and Wallace 1987;Karl and Quayle 1981;Namias 1982;Lyon and Dole 1995) as well as simultaneous precipitation deficits (Lau and Nath 2012).…”