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Joakim Kjellsson, Kristofer Döös, Frédéric B. Laliberté, and Jan D. Zika

1. Introduction The atmospheric general circulation forms as a response to differential solar heating and oceanic heat transport, acting to redistribute energy from warm regions to cold regions, mainly through the exchange of dry static energy (DSE) and latent heat (LH) ( Trenberth and Stepaniak 2003a ). The geographical distribution of these exchanges dictates, among other climatic features, global patterns of precipitation and evaporation ( Muller and O’Gorman 2011 ). The atmospheric

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Olivier Pauluis, Arnaud Czaja, and Robert Korty

1. Introduction The global atmospheric circulation redistributes energy and entropy from equatorial regions to higher latitudes. This is accomplished by a combination of a poleward flow of high energy and high entropy air parcels and an equatorward return flow of parcels with lower energy and entropy content. Because of the turbulent nature of the atmosphere, individual parcel trajectories vary widely, and the circulation can only be described in an averaged sense. A key issue arises from the

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Bo Christiansen

1. Introduction The structure of the low-frequency atmospheric circulation in the extratropics is a subject of continuous interest. A far-reaching hypothesis suggests the existence of multiple circulation regimes. If this hypothesis is proven right it may have important consequences for both long-range weather forecasting and the understanding of climate variability and climate change ( Palmer 1999 ). However, the existence of atmospheric circulation regimes is still controversial. Some data

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Bingyi Wu

are generally used to characterize Arctic warming and AA. However, SATs are strongly influenced by the external forcing, such as sea ice concentrations (SICs) and surface sea temperatures (SSTs). Thus differences in SATs between the Arctic and the midlatitudes may exaggerate the thermal contrast of atmospheric circulation in the middle and lower troposphere. The updated study also indicated that warming in the lower troposphere associated with AA is not a direct driver of anomalous midlatitude

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Claude Frankignoul, Nathalie Sennéchael, Young-Oh Kwon, and Michael A. Alexander

1. Introduction Observational evidence that extratropical sea surface temperature (SST) anomalies have an influence on the large-scale atmospheric circulation during certain seasons has been found in the North Atlantic ( Czaja and Frankignoul 1999 , 2002 ; Rodwell and Folland 2002 ) and the North Pacific ( Liu et al. 2006 ; Frankignoul and Sennéchael 2007 , hereafter FS07 ). These air–sea interactions are highly relevant to the short-term climate predictability, as the SST anomalies tend to

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William B. Rossow, Yuanchong Zhang, and George Tselioudis

atmosphere–ocean circulations is primarily mediated by water processes: evaporative cooling of the surface and precipitation heating of the atmosphere. The latter is produced by the atmospheric motions themselves, which also produce clouds that alter the radiation exchanges. Together, precipitation and the cloud-induced radiation changes feed back on the general circulation. We can only observe the final result of the simultaneous action of all these processes and we cannot observe the circulation

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Wenchang Yang, Richard Seager, and Mark A. Cane

; Fu and Wang 1999 ). Despite the success in simulating the general features of the tropical circulation, this type of simple tropical atmospheric circulation model has been challenged because the nonlinear advection terms have been totally ignored and large Rayleigh friction coefficients have to be applied in order to obtain realistic simulations. Diagnostics of the observational circulation confirmed the suitability of a linear approximation of the surface wind momentum dynamics ( Zebiak 1990

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Ying Li, David W. J. Thompson, and Sandrine Bony

1. Introduction Accurate simulations of the atmospheric general circulation are a necessary condition for interpreting climate variability and predicting the climate response to external forcings. However, climate models exhibit a wide range of biases in their simulations of the current climate, and a major source of such biases stems from cloud processes and their role in the general circulation (e.g., Möbis and Stevens 2012 ; Ceppi et al. 2012 ; Oueslati and Bellon 2013 ; Stevens and Bony

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Qigang Wu, Jing Zhang, Xiangdong Zhang, and Wei Tao

(2012) shows that SLP at the center of the BSH varies on a decadal time scale based on intensity and location of the summer BSH; since the late 1990s, there has been a trend toward a stronger summer BSH. Stegall and Zhang (2012) have found that, along with the changed atmospheric circulation over the Chukchi and Beaufort Seas, there have been increasing trends in areal-averaged monthly mean and 95th percentile wind speeds from July through November. There are also many papers on wind regimes

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Edwin P. Gerber, Sergey Voronin, and Lorenzo M. Polvani

the fluctuation–dissipation relationship, a model with poor internal variability cannot be expected to exhibit the correct response to perturbed climate forcing . 5. Conclusions We have proposed that a new diagnostic be computed for validating simple atmospheric general circulation models within the HS94 framework. The HS94 test was originally designed to compare different numeric schemes, but in recent years primitive equation models with HS94 -like forcings have been used in climate

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