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Manuel Pulido and John Thuburn

circulation from the summer to the winter hemisphere. This circulation explains the high temperatures observed in the winter mesosphere. Lindzen (1981) realized that an isotropic gravity wave spectrum generated at tropospheric levels would be filtered in a systematic way by the background wind in the middle atmosphere leading to a systematic forcing by gravity waves in the upper stratosphere and lower mesosphere. The seasonal variation of gravity wave drag (GWD) produced by gravity wave filtering deduced

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Peter Hitchcock, Theodore G. Shepherd, and Shigeo Yoden

1. Introduction Radiative transfer plays an important role in damping temperature perturbations in the middle atmosphere. In general, this damping is a nonlocal process in which heat is transferred to and from remote levels of the atmosphere and the surface and radiated away to space. This process is also nonlinear, mostly as a result of the nonlinear dependence of radiated power on temperature. In the mesosphere, molecular collisions occur sufficiently infrequently that local thermodynamic

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Charles McLandress and Theodore G. Shepherd

seen in surface pressure and storm tracks. Thus, possible changes in SSWs resulting from climate change would have an effect on ozone recovery and on Arctic ozone more generally. Because chemistry climate models (CCMs) are the only tools available for predicting the future evolution of climate change and ozone recovery in the middle atmosphere, it is important that they be able to get the SSWs right. Charlton et al. (2007) intercompared six stratosphere-resolving models and found that most

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Ryosuke Yasui, Kaoru Sato, and Yasunobu Miyoshi

1. Introduction Sudden stratospheric warming (SSW) events often occur in the polar region in Northern Hemisphere (NH) winter. This is a phenomenon in which a meridional circulation in the stratosphere is driven by stationary Rossby wave (RW) forcing, resulting in adiabatic heating in the polar stratosphere and adiabatic cooling in the equatorial stratosphere (e.g., Matsuno 1971 ). Interhemispheric coupling (IHC) of the middle atmosphere, which is described by an anticorrelation between the

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Andrew Orr, Peter Bechtold, John Scinocca, Manfred Ern, and Marta Janiskova

1. Introduction The middle atmosphere is dominated by a westerly jet in the winter hemisphere, an easterly jet in the summer hemisphere, and a meridional circulation comprised of upwelling in the tropics and downwelling over the winter pole, referred to as the Brewer–Dobson circulation ( Brewer 1949 ). The Brewer–Dobson circulation is a mechanically driven circulation arising from midlatitude wintertime wave drag in the stratosphere associated primarily with the dissipation of planetary

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Simon P. Alexander, Kaoru Sato, Shingo Watanabe, Yoshio Kawatani, and Damian J. Murphy

1. Introduction Despite their relatively small scale, gravity waves are an important component of the atmospheric general circulation because they transfer momentum upward from tropospheric sources to the middle atmosphere. The gravity wave drag generated upon breaking closes the mesospheric jet and induces a summer-to-winter-pole mesospheric circulation ( Haynes et al. 1991 ; Garcia and Boville 1994 ). Gravity waves, together with planetary waves, drive the winter polar stratosphere away from

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Chengyun Yang, Tao Li, Anne K. Smith, and Xiankang Dou

midlatitude troposphere, a signature of the MJO extending into the middle atmosphere might be expected. However, up to now, the response of the Southern Hemisphere (SH) middle atmosphere to the MJO has not been well studied. The MJO is, on average, weaker during the austral winter than the boreal winter ( Wang and Rui 1990 ; Hendon and Salby 1994 ). However, variability in the middle atmosphere is also weaker in the austral winter than in the boreal winter so the MJO-induced variation has the potential

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H. Luce, T. Takai, T. Nakamura, M. Yamamoto, and S. Fukao

retrieved from inelastic atmospheric backscatter light by water vapor molecules. At Shigaraki Middle- and Upper-Atmosphere (MU) Observatory, a Rayleigh–Mie–Raman (RMR) lidar has been operating for measuring, in addition to humidity profiles, temperature, optical properties (backscatter and extinction coefficients) of aerosol, and cirrus cloud particle properties in the troposphere ( Behrendt et al. 2004 ). Upon appropriate calibration, the Raman lidar set up at Shigaraki provides vertical profiles of

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Kaoru Sato, Satoshi Tateno, Shingo Watanabe, and Yoshio Kawatani

much different from that expected by radiation: the summer polar upper mesosphere is the coldest place in the earth’s atmosphere because of the upward motion, leading to the formation of polar mesospheric clouds. The polar stratospheric clouds that appear in the polar winter are confined to the cold lower stratosphere because the middle and upper stratosphere in winter is warm owing to the downward motion. Gravity waves are primary waves that drive the meridional circulation in the summer and

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Fabrizio Sassi, R. R. Garcia, D. Marsh, and K. W. Hoppel

1. Introduction Coupled atmosphere–ocean climate models, and in particular most of those that have been used in the Intergovernmental Panel on Climate Change (IPCC) reports, typically have a poorly resolved middle atmosphere, and chemical composition is for the most part specified ( Solomon et al. 2007 ). These models cannot represent ozone depletion or the complex couplings associated with changes of chemical composition and their effects on the dynamical and thermal structure of the middle

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