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Leighton A. Regayre, Kirsty J. Pringle, Lindsay A. Lee, Alexandru Rap, Jo Browse, Graham W. Mann, Carly L. Reddington, Ken S. Carslaw, Ben B. B. Booth, and Matthew T. Woodhouse

1. Introduction Aerosols affect Earth’s climate by absorbing and scattering solar and terrestrial radiation ( Twomey 1977 ; Boucher et al. 2013 ). The cloud albedo effect (CAE) ( Boucher et al. 2013 ), characterized by a decrease in cloud drop effective radius that results from an increase in cloud droplet number concentration for a given amount of liquid water ( Twomey 1977 ), is the largest component of the aerosol–cloud interaction. Uncertainty in the magnitude of CAE forcing remains the

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Pedro N. DiNezio, Lewis J. Gramer, William E. Johns, Christopher S. Meinen, and Molly O. Baringer

between these seasonal changes and variations in wind forcing over the North Atlantic has been extensively studied ( Schott and Zantopp 1985 ; Lee et al. 1985 ; Lee and Williams 1988 ). Most observational studies agree with the model results of Anderson and Corry (1985a , b) , Fanning et al. (1994) , and Greatbatch et al. (1995) , identifying local and remote along-isobath wind stress forcing as a driving mechanism for annual and higher-frequency variability, while modeling studies by Böning et

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L. J. Gray, S. T. Rumbold, and K. P. Shine

discrepancy between the 11-yr SC estimates from the SSU/MSU and the National Centers for Environmental Prediction (NCEP)–National Center for Atmospheric Research (NCAR) and 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) reanalyses. An additional output from the above calculations is the radiative forcing at the tropopause, which includes the so-called instantaneous radiative forcing due to the changes in irradiance and ozone, and also the effect of the FDH

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Xuebin Zhang, Bruce Cornuelle, and Dean Roemmich

wind forcing in the western and central equatorial Pacific (e.g., Zhang and McPhaden 2006 , hereafter ZM06 ). Because the remote wind forcing plays a dominant role in ENSO-related SST variations in the eastern equatorial Pacific (e.g., Rasmusson and Carpenter 1982 ; Harrison and Larkin 1998 ; Wang and Picaut 2004 ), local wind forcing in the eastern equatorial Pacific and associated physical processes were often neglected in previous studies. However, local wind forcing may also vary on ENSO

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Marius Bickel, Michael Ponater, Lisa Bock, Ulrike Burkhardt, and Svenja Reineke

et al. 2016 ). CO 2 emissions from fuel burning and several non-CO 2 effects contribute to the total radiative forcing of aviation with comparable magnitude. Indirect climate effects of aircraft aerosol emissions are potentially large (e.g., Gettelman and Chen 2013 ; Zhou and Penner 2014 ; Righi et al. 2016 ; Penner et al. 2018 ) but have remained highly uncertain due to open issues in our knowledge of aerosol–cloud interactions ( Kärcher 2017 ; Kärcher 2018 ). In contrast, the level of

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Martin Claus, Richard J. Greatbatch, Peter Brandt, and John M. Toole

forcing terms for the EDJs via the nonlinear interaction of intraseasonal Yanai waves ( Ascani et al. 2015 ), which are independent of the EDJs. It follows that the nonlinear terms in the zonal momentum budget can be parameterized as a dissipation and forcing in a linear model of the EDJs. Regardless of the actual driving mechanism, the EDJs must be maintained over a considerable depth range while they propagate vertically. This becomes apparent from an estimate of the effective lateral diffusivity

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Sang-Ik Shin, Prashant D. Sardeshmukh, and Robert S. Webb

oceans. A map of such sensitivities may also be interpreted as the “optimal” tropical SST forcing pattern of North American drought. The GCMs used were the National Center for Atmospheric Research (NCAR) atmospheric GCM community climate model version 3 (CCM3; Kiehl et al. 1998 ) and the Max Planck Institute for Meteorology (MPIM) atmospheric GCM ECHAM5 ( Roeckner et al. 2003 ). As a measure of drought, we employed the widely used Palmer drought severity index (PDSI; Palmer 1965 ), which is based

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M. J. Woodage and S. Woodward

requirements; however, the atmospheric component of the U.K. High-Resolution Global Environmental Model (HiGEM) with horizontal resolution of 1.25° longitude × 0.83° latitude has been used for such experiments and has been shown to produce realistic simulations of the mineral dust aerosol distribution and its associated radiative forcing ( Woodage et al. 2010 ). The question of the sign and magnitude of radiative forcing due to dust has been addressed by many authors. In one of the earliest papers

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Kettyah C. Chhak, Andrew M. Moore, and Ralph F. Milliff

1. Introduction At middle and high latitudes, the stochastic component of wind forcing associated with atmospheric “weather” on synoptic time scales is comparable in magnitude to the wind forcing associated with the seasonal cycle ( Willebrand 1978 ; Chave et al. 1991 ; Samelson and Shrayer 1991 ), and observations reveal that the stochastic component exerts considerable influence on the ocean circulation (e.g., DeRycke and Rao 1973 ; Niiler and Koblinsky 1989 ; Brink 1989 ; Koblinsky et

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Sarah M. Kang, Isaac M. Held, Dargan M. W. Frierson, and Ming Zhao

1. Introduction It is often assumed that the position of the ITCZ in the tropics is controlled by tropical mechanisms ( Xie 2004 ). However, there is paleoclimatic and modeling evidence that one can alter the position of the ITCZ by perturbing the thermal forcing in the extratropics, with the ITCZ moving away from a cooled hemisphere or toward a warmed hemisphere. For example, Koutavas and Lynch-Stieglitz (2004) find that the marine ITCZ in the eastern Pacific is displaced southward when the

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