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M. Biasutti, I. M. Held, A. H. Sobel, and A. Giannini

models (GCMs). Recently, different atmospheric GCMs ( Folland et al. 1986 ; Giannini et al. 2003 ; Tippett and Giannini 2006 ; Lu and Delworth 2005 ; Hoerling et al. 2006 ), forced with the historic time series of global sea surface temperatures (SSTs), have been able to reproduce the main outlines of the twentieth-century Sahel pluvials and droughts, thus demonstrating that oceanic forcing has been the dominant driver of rainfall variability in this region. It appears that land surface and

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Leon D. Rotstayn, Mark A. Collier, Drew T. Shindell, and Olivier Boucher

1. Introduction Aerosol effects on climate are highly uncertain; even in the global mean, effective radiative forcing (ERF) caused by anthropogenic aerosols has a 5%–95% uncertainty range of −0.1 to −1.9 W m −2 , according to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR5; Boucher et al. 2013 ). Because aerosol forcing is so uncertain, it is difficult to use observations to constrain other critical properties of the climate system, such as transient

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Robert J. Allen and Charles S. Zender

forcings ( Shindell et al. 1999 ; Feldstein 2002 ; Gong et al. 2002 ). Several such external forcings have been identified, although no dominant mechanism has been clearly established. Atmospheric general circulation model (AGCM) simulations have showed that much of the multiannual to multidecadal variability of the NAO, as well as the late-twentieth-century trend, is related to North Atlantic SSTs ( Rodwell et al. 1999 ; Robertson et al. 2000 ). AGCMs have also showed that warming of tropical SSTs

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Edmund K. M. Chang

1. Introduction It is well known that the climate of the earth is not zonally symmetric. Since the forcing at the top of the atmosphere is zonally symmetric when averaged over a day or longer, the zonal asymmetries in the earth’s climate must be forced by zonal asymmetries in the lower boundary. Zonal asymmetries in the lower boundary include asymmetries in land–ocean distribution, and asymmetries in the location of mountains. Together, these asymmetries give rise to asymmetrical distribution

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Linda Forster, Claudia Emde, Bernhard Mayer, and Simon Unterstrasser

1. Introduction The global radiative forcing (RF) of line-shaped contrails and contrail cirrus calculated by general circulation models (GCMs) exhibits a high level of uncertainty. These uncertainties arise mainly from the radiative transfer models used to calculate the contrail RF as well as from the contrail parameterization and its inherent assumptions employed to represent contrail properties for large grid boxes rather than for individual contrails. A recent study by Frömming et al. (2011

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Benjamin M. Sanderson, R. Knutti, T. Aina, C. Christensen, N. Faull, D. J. Frame, W. J. Ingram, C. Piani, D. A. Stainforth, D. A. Stone, and M. R. Allen

fitting algorithm used in Stainforth et al. (2005) . b. Data preparation We seek a smooth fit to the simulated climatology and likely response to greenhouse gas forcing, both as functions of model parameters. The data required to train this emulation are taken from the first climate prediction .net ensemble of climate models, those experiments conducted with perturbed atmospheric parameters only. After filtering, an N member subset of models remains for use in this analysis (where N is 6096). The

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Richard Justin O. Small, Simon P. de Szoeke, and Shang-Ping Xie

MSD are presented in section 4 . The effect of diabatic heating anomalies on the evolution of the MSD is described in section 5 . Then section 6 investigates the relative importance of remote versus local diabatic forcing to the MSD. This is followed in section 7 by a discussion of how the present results relate to previous studies, and section 8 presents the conclusions. 2. Data and model a. Observations and reanalysis 1) Precipitation Measurements of precipitation vary greatly between

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Igor Kamenkovich, Pavel Berloff, and Joseph Pedlosky

of the North Atlantic circulation, the model includes idealizations, which are intended to make calculations possible and to simplify the analysis. The task of identifying the role of eddies in the near-equilibrium state has to rely on the analysis of the eddy flux convergences. These convergences can be tentatively interpreted as internally generated eddy forcing that maintains or resists the jetlike anomalies in, for example, the vorticity and buoyancy equations. The action of the eddy

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Peter Knippertz and Andreas H. Fink

and the dynamics of an intense and widespread dry-season precipitation event in tropical West Africa in January 2004 and its relation to forcing from the extratropics. The abundant rainfall had large impacts on human activities in several West African countries. The event was accompanied by intense precipitation over the Algerian and Libyan Sahara and by dust storms over northeastern Africa. Besides analysis, satellite, and synoptic station data, high-resolution observations from a field site in

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Bjorn Stevens and Stephanie Fiedler

Stevens (2015 , hereinafter S15) used three lines of reasoning to argue that present-day effective aerosol radiative forcing is very likely less negative than −1 W m −2 . The most quantitative bound arose from the logic that if one wishes to maintain that some component of the warming in the first half of the twentieth century was anthropogenic in origin, then this bounds to have a smaller magnitude than other positive forcings over the same time period. By adopting a simple model that

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