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Sarah Strazzo, James B. Elsner, Timothy LaRow, Daniel J. Halperin, and Ming Zhao


Of broad scientific and public interest is the reliability of global climate models (GCMs) to simulate future regional and local tropical cyclone (TC) occurrences. Atmospheric GCMs are now able to generate vortices resembling actual TCs, but questions remain about their fidelity to observed TCs. Here the authors demonstrate a spatial lattice approach for comparing actual with simulated TC occurrences regionally using observed TCs from the International Best Track Archive for Climate Stewardship (IBTrACS) dataset and GCM-generated TCs from the Geophysical Fluid Dynamics Laboratory (GFDL) High Resolution Atmospheric Model (HiRAM) and Florida State University (FSU) Center for Ocean–Atmospheric Prediction Studies (COAPS) model over the common period 1982–2008. Results show that the spatial distribution of TCs generated by the GFDL model compares well with observations globally, although there are areas of over- and underprediction, particularly in parts of the Pacific Ocean. Difference maps using the spatial lattice highlight these discrepancies. Additionally, comparisons focusing on the North Atlantic Ocean basin are made. Results confirm a large area of overprediction by the FSU COAPS model in the south-central portion of the basin. Relevant to projections of future U.S. hurricane activity is the fact that both models underpredict TC activity in the Gulf of Mexico.

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Yohei Yamada and Masaki Satoh

global warming do not exhibit a robust response. Zelinka and Hartmann (2010) showed that the combined mean of the 15 climate models for the A2 scenario of International Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) caused a decrease in the amount of upper clouds in the tropics (see also Zelinka et al. 2012b ). However, Collins and Satoh (2009) and Satoh et al. (2012a) recently argued that the amount of upper clouds might be increased under global warming conditions by using a

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Young-Kwon Lim, Siegfried D. Schubert, Oreste Reale, Myong-In Lee, Andrea M. Molod, and Max J. Suarez

convective precipitation ( Fig. 15c ). The results show that both total and large-scale precipitation increase noticeably over the tropics for ExpA, whereas there is a substantial reduction in convective precipitation. In contrast, for ExpB (the right panels) there is only a very small change in total precipitation over the tropics ( Fig. 15d ), while the large-scale precipitation over the TC genesis region increases slightly ( Fig. 15e ) along with a decrease in convective precipitation ( Fig. 15f

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Enrico Scoccimarro, Silvio Gualdi, Gabriele Villarini, Gabriel A. Vecchi, Ming Zhao, Kevin Walsh, and Antonio Navarra

evaporation rate over the tropics ( Fig. 9 , green and red lines, respectively) due to the increase in saturated water vapor pressure at the surface. The 2-K increase in SST leads to a net increase of the evaporation rate ( E ). This can be easily explained considering that E is proportional to the difference between saturated water vapor at the surface ( e s ) and water vapor pressure of the lower tropospheric layers ( e a ), and that e s depends on surface temperature following an exponential law

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Chao Wang and Liguang Wu

the relative SST warming pattern, not the magnitude of SST warming, can influence large-scale circulations in warming scenarios (e.g., Vecchi and Soden 2007b , hereafter VS07 ; Johnson and Xie 2010 ). Following VS07 , the relative SST is defined as the anomalous SST relative to the global tropics 20°S–20°N. Our purpose of using the relative SST is to remove the different warming magnitudes in various projection periods and scenarios, and emphasize the influences of the relative SST warming on

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Gabriele Villarini, David A. Lavers, Enrico Scoccimarro, Ming Zhao, Michael F. Wehner, Gabriel A. Vecchi, Thomas R. Knutson, and Kevin A. Reed

that it is real—to future work. These results add to an expectation that greenhouse gas–induced tropical warming should lead to an increase in rainfall rates of individual TCs (e.g., Knutson and Tuleya 2004 ; Knutson et al. 2010 , 2013 ). Current-generation GCMs project, under a wide range of projected twenty-first century forcing scenarios, a robust warming of the tropics and tropical cyclone basins over the twenty-first century (e.g., Zhao et al. 2009 ; Vecchi and Soden 2007 ; Villarini and

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John G. Dwyer, Suzana J. Camargo, Adam H. Sobel, Michela Biasutti, Kerry A. Emanuel, Gabriel A. Vecchi, Ming Zhao, and Michael K. Tippett

in climate model simulations) shifted to later in the calendar year in response to increased boreal summer insolation ( Korty et al. 2012 ). Our interest in the possibility of greenhouse gas–induced changes in tropical cyclone seasonality stems from global climate model (GCM) projections of changes in the annual cycles of other climate variables in response to increasing greenhouse gases. In the tropics and subtropics, the World Climate Research Programme’s (WCRP’s) Coupled Model Intercomparison

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Anne S. Daloz, S. J. Camargo, J. P. Kossin, K. Emanuel, M. Horn, J. A. Jonas, D. Kim, T. LaRow, Y.-K. Lim, C. M. Patricola, M. Roberts, E. Scoccimarro, D. Shaevitz, P. L. Vidale, H. Wang, M. Wehner, and M. Zhao

tropical cyclones per year, while GSFC_E and GISS_E have only around 6 tropical cyclones per year. In observations, more than half of the tropical cyclones (52%) are members of clusters 1 and 2, which form over higher latitudes (north of 20°N) and will be called here the northernmost tropical cyclones. In contrast, tropical cyclones in clusters 3 and 4 typically have genesis locations in the deep tropics (south of 20°N) and will be called here the southernmost tropical cyclones. As explained in

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Hamish A. Ramsay, Savin S. Chand, and Suzana J. Camargo

environmental fields, such as PI, midlevel saturation deficit and relative humidity, and deep-layer vertical wind shear (i.e., the absolute value of the vector wind difference between 850 and 200 hPa) were also analyzed to provide physical interpretation of the statistical changes. Broadly speaking, all models show increases in PI over the tropics for the two SST warming scenarios (p2K and p2K2CO2) and typically a slight decrease in PI when the SST is held fixed and the carbon dioxide doubled (2CO2), in

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Hui Wang, Lindsey Long, Arun Kumar, Wanqiu Wang, Jae-Kyung E. Schemm, Ming Zhao, Gabriel A. Vecchi, Timothy E. Larow, Young-Kwon Lim, Siegfried D. Schubert, Daniel A. Shaevitz, Suzana J. Camargo, Naomi Henderson, Daehyun Kim, Jeffrey A. Jonas, and Kevin J. E. Walsh

heating. In the tropics, precipitation associated with deep convection is a good indicator of tropical heating in the atmosphere. Similar to Wang et al. (2012) , the composites of ASO season precipitation anomalies over the tropical Pacific are used to illustrate and verify the changes in tropical heating, as shown in Fig. 10 . In both observations and the MME mean of the GCM simulations, associated with EP El Niño ( Figs. 10a,d ), there are positive precipitation anomalies across the central and

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