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Aditi Sheshadri, R. Alan Plumb, and Daniela I. V. Domeisen

coupling during spring onset . J. Climate , 19 , 4891 – 4901 . Fogt , R. L. , J. Perlwitz , A. J. Monaghan , D. H. Bromwich , J. M. Jones , and J. G. Marshall , 2009 : Historical SAM variability. Part II: Twentieth-century variability and trends from reconstructions, observations, and the IPCC AR4 models . J. Climate , 22 , 5346 – 5365 . Gerber , E. P. , and L. M. Polvani , 2009 : Stratosphere–troposphere coupling in a relatively simple AGCM: The importance of

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J. G. Esler and N. Joss Matthewman

opposite in sense to the upper vortex. The sense of the vortex displacement at each level is generally fixed relative to the earth’s surface. Dynamical studies have primarily attributed the cause of SSWs to Rossby waves emanating from the troposphere, following the pioneering mechanistic model experiments of Matsuno (1971) . Tung and Lindzen (1979) subsequently argued that, for a given stationary (Rossby wave) forcing, a large SSW-like response will result only if a linear free-traveling Rossby wave

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Ariaan Purich and Seok-Woo Son

. Climate , 14 , 2238 – 2249 . Marshall , G. , 2003 : Trends in the Southern Annular Mode from observations and reanalyses . J. Climate , 16 , 4134 – 4143 . McLandress , C. , T. Shepherd , J. Scinocca , D. Plummer , M. Sigmond , A. Jonsson , and M. Reader , 2011 : Separating the dynamical effects of climate change and ozone depletion. Part II: Southern Hemisphere troposphere . J. Climate , 24 , 1850 – 1868 . Meehl , G. A. , C. Covey , T. Delworth , M. Latif , B

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Justin Bandoro, Susan Solomon, Aaron Donohoe, David W. J. Thompson, and Benjamin D. Santer

et al. 2006 ; Orr et al. 2012 ) and radiative ( Grise et al. 2009 ) mechanisms to explain this deep coupling in circulation between the stratosphere and troposphere ( Thompson and Wallace 2000 ; Jones and Widmann 2003 ; Thompson et al. 2005 ), where the tropospheric response lags the springtime ozone loss and maximizes in the austral summer. Although the role of the different proposed mechanisms remain uncertain, it is clear that changes in the stratospheric polar vortex are coupled to

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Martin Charron, Saroja Polavarapu, Mark Buehner, P. A. Vaillancourt, Cécilien Charette, Michel Roch, Josée Morneau, Louis Garand, Josep M. Aparicio, Stephen MacPherson, Simon Pellerin, Judy St-James, and Sylvain Heilliette

2010 ; Douville 2009 ). On the medium-range forecasting (or 2 week) time scale, knowledge of the stratospheric state can also improve the quality of tropospheric forecasts ( Christiansen 2001 , 2005 ; Baldwin et al. 2003 ; Zhou et al. 2002 ; Charlton et al. 2004 ). However, mechanisms to explain the stratospheric impact on the troposphere are still in dispute ( Charlton et al. 2005 ). At the same time that advances in understanding stratosphere–troposphere coupling were being made, new

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Gui-Ying Yang, Brian Hoskins, and Lesley Gray

has also been shown that the connection between the waves and convection varies with season and the wave type, with the Kelvin and R1 waves in winter having the strongest connection with convection. On average, convective signals have smaller phase speeds than those of the lower-stratospheric waves and the convective coupling is much less significant than that in the troposphere (see YHS 07a , b , c ). This indicates that, in general, when convectively coupled equatorial waves propagate

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Lon L. Hood and Boris E. Soukharev

troposphere–ocean response to 11-yr solar forcing is characterized further by carrying out MLR analyses of Hadley Centre SLP data during NH winter over the ~1880–2009 period. For comparison, corresponding ENSO regression coefficients are also calculated for zonal mean ozone, temperature, and SLP, expressed as the response to a −1 unit change in the Niño-3.4 index. In section 5 , the reality of the SLP solar response and the hypothesis of dynamical coupling to the tropical lower-stratospheric response are

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Charles McLandress, Theodore G. Shepherd, M. Catherine Reader, David A. Plummer, and Keith P. Shine

1. Introduction Halocarbons are potent greenhouse gases (GHGs) because they interact strongly with infrared radiation in the 8–13- μ m atmospheric window. Present-day concentrations of halocarbons are optically thin. In clear skies, this allows outgoing infrared radiation emitted by the surface and lower troposphere to reach the middle and upper troposphere where it is absorbed and re-emitted at a lower temperature, causing a net convergence of radiative flux, and hence warming. The warming

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Edwin P. Gerber and Seok-Woo Son

. Res. Atmos. , 118 , 5029 – 5060 , doi: 10.1002/jgrd.50316 . Farman , J. C. , B. G. Gardiner , and J. D. Shanklin , 1985 : Large losses in total ozone in Antarctica reveal seasonal CLO x /NO x interaction . Nature , 315 , 207 – 210 , doi: 10.1038/315207a0 . Garfinkel , C. I. , D. W. Waugh , and E. P. Gerber , 2013 : The effect of tropospheric jet latitude on coupling between the stratospheric polar vortex and the troposphere . J. Climate , 26 , 2077 – 2095 , doi: 10

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Gabriele Villarini and Gabriel A. Vecchi

Abstract

This study focuses on the statistical modeling of the power dissipation index (PDI) and accumulated cyclone energy (ACE) for the North Atlantic basin over the period 1949–2008, which are metrics routinely used to assess tropical storm activity, and their sensitivity to sea surface temperature (SST) changes. To describe the variability exhibited by the data, four different statistical distributions are considered (gamma, Gumbel, lognormal, and Weibull), and tropical Atlantic and tropical mean SSTs are used as predictors. Model selection, both in terms of significant covariates and their functional relation to the parameters of the statistical distribution, is performed using two penalty criteria. Two different SST datasets are considered [the Met Office’s Global Sea Ice and Sea Surface Temperature dataset (HadISSTv1) and NOAA’s extended reconstructed SST dataset (ERSSTv3b)] to examine the sensitivity of the results to the input data.

The statistical models presented in this study are able to well describe the variability in the observations according to several goodness-of-fit diagnostics. Both tropical Atlantic and tropical mean SSTs are significant predictors, independently of the SST input data, penalty criterion, and tropical storm activity metric. The application of these models to centennial reconstructions and seasonal forecasting is illustrated.

The sensitivity of North Atlantic tropical cyclone frequency, duration, and intensity is examined for both uniform and nonuniform SST changes. Under uniform SST warming, these results indicate that there is a modest sensitivity of intensity, and a decrease in tropical storm and hurricane frequencies. On the other hand, increases in tropical Atlantic SST relative to the tropical mean SST suggest an increase in the intensity and frequency of North Atlantic tropical storms and hurricanes.

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