Simulations of Global Hurricane Climatology, Interannual Variability, and Response to Global Warming Using a 50-km Resolution GCM

Abstract

A global atmospheric model with roughly 50-km horizontal grid spacing is used to simulate the interannual variability of tropical cyclones using observed sea surface temperatures (SSTs) as the lower boundary condition. The model’s convective parameterization is based on a closure for shallow convection, with much of the deep convection allowed to occur on resolved scales. Four realizations of the period 1981–2005 are generated. The correlation of yearly Atlantic hurricane counts with observations is greater than 0.8 when the model is averaged over the four realizations, supporting the view that the random part of this annual Atlantic hurricane frequency (the part not predictable given the SSTs) is relatively small (<2 hurricanes per year). Correlations with observations are lower in the east, west, and South Pacific (roughly 0.6, 0.5, and 0.3, respectively) and insignificant in the Indian Ocean. The model trends in Northern Hemisphere basin-wide frequency are consistent with the observed trends in the International Best Track Archive for Climate Stewardship (IBTrACS) database. The model generates an upward trend of hurricane frequency in the Atlantic and downward trends in the east and west Pacific over this time frame. The model produces a negative trend in the Southern Hemisphere that is larger than that in the IBTrACS. The same model is used to simulate the response to the SST anomalies generated by coupled models in the World Climate Research Program Coupled Model Intercomparison Project 3 (CMIP3) archive, using the late-twenty-first century in the A1B scenario. Results are presented for SST anomalies computed by averaging over 18 CMIP3 models and from individual realizations from 3 models. A modest reduction of global and Southern Hemisphere tropical cyclone frequency is obtained in each case, but the results in individual Northern Hemisphere basins differ among the models. The vertical shear in the Atlantic Main Development Region (MDR) and the difference between the MDR SST and the tropical mean SST are well correlated with the model’s Atlantic storm frequency, both for interannual variability and for the intermodel spread in global warming projections.

Spatiotemporal dynamics of global drought

“…This analysis draws a parallel with tropical cyclone studies, in which the densities and directions of their tracks have been analyzed in the world's oceans [Zhao et al, 2009].…”

Downscaling CMIP5 climate models shows increased tropical cyclone activity over the 21st century

“…The ocean component of the intensity model requires ocean mixed layer depth and sub mixed layer thermal stratification; in the simulations described here, we use present-day climatology for both these quantities. Thus, the effect of global warming on the thermal (11,19) and the regional downscaling model of Knutson et al (20), which was also driven by NCAR/NCEP reanalysis data. The technique captures well the observed spatial and seasonal variability of tropical cyclones around the globe, as well as the effects of such climate phenomena as El Nino Southern Oscillation (ENSO) and the Atlantic Meridional Mode (9).…”

“…A clear advantage of direct simulation is that it requires no additional assumptions or model applications (other than the detection algorithm). An important limitation of this approach is that it severely underresolves tropical cyclones, resulting in a substantial truncation of the intensity spectrum of simulated storms, even at 50-km grid spacing (11), and usually produces fewer events than observed (12).…”

A decadally-resolved paleohurricane record archived in the late Holocene sediments of a Florida sinkhole

“…Changes in the intensity distribution of hurricanes occurring in concert with changes in storm frequency could cause the frequency of storm deposits in sites with different flooding susceptibilities to diverge. Numerical modeling of late 21 st century hurricane climatology has suggested that declines in overall Atlantic hurricane frequency could occur simultaneously with a broadening of the intensity distribution of hurricanes leading to fewer but more intense storms , Gualdi et al 2008, Knutson et al 2008, Zhao et al 2009, Bender et al 2010). However, recent warming and increased hurricane frequency in the Atlantic has purportedly been accompanied by a disproportionate increase in the occurrence of intense hurricanes (Emanuel 2005, Webster et al 2005, Hoyos et al 2006.…”