A Climatology of Heat Waves from a Multimillennial Simulation

Abstract

A 10 000-yr unforced simulation with the Commonwealth Scientific and Industrial Research Organisation (CSIRO) Mark 2 coupled global climatic model has been used to investigate the occurrence of heat waves over the globe. Results are presented for both seasonal (summer mean) and daily heat waves. Geographical distributions of the occurrence rates of these heat waves are shown for various magnitudes of surface temperature anomalies. The heat waves have specific geographical preferences with regions where relatively frequent, intense, and long-lasting heat waves occur. Time series over all 10 000 yr of the heat waves for the selected model grid boxes illustrate the differing temporal variabilities at these locations, as well as identifying the occurrences of extreme heat waves. To this end, the observed European heat wave of 2003 was simulated remarkably well in its overall characteristics; it occurs once in this simulation. Heat waves for various continental locations are shown to occur as isolated spatial and temporal events, and not as part of larger-scale systems over continental-size domains, suggesting stochastic forcing as a contributor to the initiation of the heat waves. Regional plots of selected heat waves at monthly intervals illustrated the considerable spatial variability, progression, and variation in the intensity of the heat waves. Comparison of year-long daily surface temperature anomalies for heat-wave years for simulated and observed conditions at individual model grid boxes indicated substantial agreement, while spatial plots permitted the progress of a short-term heat wave over the United States to be followed. Multidecadal time series plots of intense heat waves also showed basic similarities between the simulation and observations, despite the brevity of the latter. The simulated time series suggest that more extreme heat waves than currently are observed, owing to the brevity of the observations, may be a possibility as a consequence solely of natural variability. An examination of the physical processes associated with a heat wave showed mutually consistent climatic relationships, such that a heat wave was associated with reduced rainfall and consequently reduced soil moisture content, evaporation, and cloud cover, and increased insolation at the surface. These combined changes created the surface temperature increase intrinsic to the heat wave. All heat waves examined for different regions experienced negative rainfall anomalies prior to a heat wave. The cause of these rainfall anomalies was not readily apparent. While an ENSO influence on heat waves is shown to exist in the simulation, not all ENSO events produce heat waves, suggesting that stochastic influences may determine when a major heat wave occurs in conjunction with these events. The limitations of the adequacy of the model ENSO may, however, have had an influence in this regard.

Climatic characteristics of heat waves and their simulation in plant experiments

“…We only consider the period from 15 March until 15 October as we are most interested in heat waves during the growing season. Furthermore, warm spells during winter are thought to differ fundamentally from warm spells during the rest of the year (Hunt, 2007).…”

Frequency of marine heatwaves in the North Atlantic and North Pacific since 1950

“…We use 65 years of reconstructed SST data in the Northern Hemisphere where two case study heatwaves have occurred, the 2012 northwest Atlantic [Mills et al, 2013] and 2013-2014 northeast Pacific marine heatwaves [Bond et al, 2015]. These ocean regions are climatically important, as they are influenced by slow-varying modes of intrinsic climate variability [Deser et al, 2010;Hartmann, 2015].…”

“…These events have been referred to as marine heatwaves and have been described as regions of large-scale and persistent positive sea surface temperature (SST) anomalies [Pearce et al, 2011]. Well-known marine heatwaves have occurred in the Mediterranean Sea [Black et al, 2004;Olita et al, 2007], off Western Australia [Pearce and Feng, 2013], in the northwest Atlantic [Mills et al, 2013;Chen et al, 2014Chen et al, , 2015, and in the northeast Pacific [Bond et al, 2015;Hartmann, 2015]. Like heatwaves on land, marine heatwaves are likely to become more frequent and intense under continued anthropogenic warming assuming fixed temperature thresholds [Solomon et al, 2007].…”

Quantifying the Impact of Excess Moisture From Transpiration From Crops on an Extreme Heat Wave Event in the Midwestern U.S.: A Top‐Down Constraint From Moderate Resolution Imaging Spectroradiometer Water Vapor Retrieval

“…where H is the Jacobian matrix for projecting the state vectors onto the observational space, y o is the observations (water vapor columns), R is the covariance matrix of the observations, and E is the spatial localization computed from the physical distance of observations from the model grid (discussed later). R is (Hong & Lim, 2006); YSU = Yonsei University (Hong, Noh, & Dudhia, 2006); KF = Kain-Fritsch (Kain, 2004); RRTMG = The Rapid Radiative Transfer Model for Global models.…”

“…Anthropogenic activities may contribute to the severity of such events. While a regional oscillation in climate over a course of year can result from major climatic drivers such as the El Niño‐Southern Oscillation (ENSO), not all ENSO events are found to be conducive to an extreme event (Hunt, 2007). Similarly, the response of heat waves to anthropogenic forcing can manifest itself in nonstationary extremes that can hardly be disentangled from natural variabilities.…”