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Aneesh C. Subramanian, Markus Jochum, Arthur J. Miller, Raghu Murtugudde, Richard B. Neale, and Duane E. Waliser

, doi:10.1029/2002GL016734 . Gregory , D. , R. Kershaw , and P. M. Inness , 1997 : Parametrization of momentum transport by convection. II: Tests in single-column and general circulation models . Quart. J. Roy. Meteor. Soc. , 123 , 1153 – 1183 . Hendon , H. H. , and M. Wheeler , 2008 : Some space–time spectral analyses of tropical convection and planetary-scale waves . J. Atmos. Sci. , 65 , 2936 – 2948 . Hendon , H. H. , M. Wheeler , and C. Zhang , 2007 : Seasonal

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Jenny Lindvall, Gunilla Svensson, and Cecile Hannay

biogeochemical systems are mainly through near-surface variables. Thus, it is of interest to evaluate them in order to assess biases and possible model deficiencies. Few studies that evaluate the performance of planetary boundary layer (PBL) parameters in GCMs are found in the literature. Some very early studies include Boer et al. (1991) and Randall et al. (1992) . At the time of these intercomparisons, most models did not resolve the diurnal variation in solar insolation and only had a few vertical grid

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Gerald A. Meehl, Julie M. Arblaster, Julie M. Caron, H. Annamalai, Markus Jochum, Arindam Chakraborty, and Raghu Murtugudde

with the planetary-scale monsoon are influenced by slowly varying boundary conditions. Of all the boundary forcing elements, ENSO-related SST anomalies are perhaps the dominant forcing element of monsoon interannual variations (e.g., Sikka 1980 ; Webster and Yang 1992 ). However, for atmospheric models (run with observed SSTs) to capture the ENSO–monsoon association, a realistic simulation of mean monsoon precipitation is a necessary ingredient ( Meehl and Arblaster 1998 ; Sperber and Palmer

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Alicia R. Karspeck, Steve Yeager, Gokhan Danabasoglu, Tim Hoar, Nancy Collins, Kevin Raeder, Jeffrey Anderson, and Joseph Tribbia

neighboring regions if the model does not capture the correct placement of eddies and meanders. In the midlatitudes, adjustments to the depth of the eastern boundary thermocline at the beginning of the assimilation improve the representation of coastal upwelling. Over multiple years, however, these initial adjustments propagate westward across the basin as planetary Rossby waves, which can degrade both the mean and variability (not shown). These features become increasingly difficult for the assimilation

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Stephen Yeager, Alicia Karspeck, Gokhan Danabasoglu, Joe Tribbia, and Haiyan Teng

1. Introduction Society would benefit tremendously if climate scientists could produce reliable forecasts, years to decades in advance, of changes in regional hurricane activity, rainfall, or the likelihood of extreme events such as severe heat waves. In the relatively new field of decadal climate prediction, work is under way to assess the feasibility of using coupled general circulation models (CGCMs) to generate such forecasts, but significant scientific challenges must be overcome if this

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Synte Peacock

8.5) scenario, how the fractional area of land in North America covered by events that would be considered extreme in today’s climate increases dramatically toward the end of the twenty-first century. For example, 4σ–6σ events are never seen in the model before the year 2000; yet, by the end of the twenty-first century, these events typically cover more than 20% of the area of North America in the summer (note that the Russian heat wave of 2010 was considered a 3σ event; J. Hansen et al. 2012

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