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Chuixiang Yi

fact that the momentum flux throughout the canopy must be downward. This is a well-known problem with countergradient momentum transport. Similarly, many observations have demonstrated that all gradient-diffusion schemes including momentum, mass, and heat fail completely within canopy ( Denmead and Bradley 1985 ). c. The spatial-average scheme and simplified governing equation As discussed above, the mixing length ℓ is not appropriate to use as the length scale within canopy. The drag exerted on

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Callum J. Shakespeare and Andrew McC. Hogg

( St. Laurent and Garrett 2002 ; Kunze 2017 ). However, not all the small-scale internal tide dissipates in the deep ocean and little attention has been given to the waves that escape this region and propagate into the upper ocean. Waves which span the ocean depth are potentially important, since small-scale internal tides are also associated with vertical fluxes of momentum that can act to accelerate the local flow when the waves dissipate, thereby driving the upper ocean. The momentum transport

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Tiffany A. Shaw, Michael Sigmond, Theodore G. Shepherd, and John F. Scinocca

correctly to climate perturbations; there is a need to ensure that their responses to climate perturbations are physical. Unphysical sensitivities and feedbacks from parameterizations need to be identified and minimized. In the case of the parameterization of gravity wave drag (GWD), Shepherd and Shaw (2004) argued that momentum conservation is a key physical constraint, and that nonconservation can lead to spurious downward influence from a middle-atmospheric radiative perturbation. In the context of

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François Lott, Olivier de Viron, Pedro Viterbo, and François Vial

1. Introduction Over the last four decades, the budget of atmospheric angular momentum (AAM) has been the subject of many studies. For geodesists, this interest follows that, for nearly all periodicities, changes in AAM correspond to changes in the parameters of the earth’s rotation ( Barnes et al. 1983 ). For climatologists, this interest follows that the AAM varies with planetary-scale tropical oscillations affecting the climate at intraseasonal ( Madden 1987 ; Hendon 1995 ) and interannual

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Jaclyn N. Brown, J. Stuart Godfrey, and Russell Fiedler

1. Introduction The pressure gradient and wind stress are considered the dominant forces in the equatorial Pacific Ocean. Zonally they determine the slope of the thermocline and the Equatorial Undercurrent (EUC). They also describe the meridional tropical cells that form from the poleward surface Ekman flow overlying a return equatorward geostrophic flow. To understand these balances, the horizontal zonal momentum equation (ZME) is often used: where Fr V and Fr H are the zonal forces per unit

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Ru Chen, James C. McWilliams, and Lionel Renault

balances, hence climate and productivity as well (e.g., Pierce et al. 2000 ; Thomson and Krassovski 2010 ; Meinvielle and Johnson 2013 ). The CUC and its transport vary significantly over weeks and seasons to decades (e.g., Marchesiello et al. 2003 ; Collins et al. 2004 ; Meinvielle and Johnson 2013 ; Thomson and Krassovski 2015 ). Our purpose here is to assess the governors of the CUC transport and its variability from a momentum perspective. Assessing the mechanisms of the CUC origin is useful

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Tsung-Lin Hsieh, Chiung-Yin Chang, Isaac M. Held, and Pablo Zurita-Gotor

1. Introduction The convergence of eddy momentum flux toward the jet in the midlatitude atmosphere is one of the most fundamental questions in the study of the general circulation. The classical explanation relies on the midlatitudes being the source of eddies that then propagate or migrate poleward and especially equatorward, so that the dissipation of the eddies is displaced in latitude from their source. From the general perspective of pseudomomentum (i.e., wave activity) conservation, the

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Erik N. Rasmussen and Jerry M. Straka

tornado in which angular momentum generally increases with increasing radius and a certain degree of axisymmetry is maintained. The angular momentum budget of this TC is analyzed, and its evolution is interpreted in the context of near-ground virtual potential temperature changes, reflectivity changes, and the evolution of the swirl at somewhat larger scales than the tornado cyclone. The angular momentum budget analysis is described in section 2 , and evolution is summarized for each phase of tornado

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Xiaoliang Song, Xiaoqing Wu, Guang Jun Zhang, and Raymond W. Arritt

1. Introduction The importance of convective momentum transport (CMT) in the atmospheric general circulation was recognized in the 1970s. Houze (1973) evaluated the momentum budget using observational data and found that the magnitude of CMT was comparable to other terms in the angular momentum budget. Using the Global Atmospheric Research Program (GARP) Atlantic Tropical Experiment (GATE) phase III data, Stevens (1979) estimated the momentum budget of a composite synoptic-scale tropical

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David P. Marshall and Helen R. Pillar

1. Introduction When a force is applied to a Boussinesq fluid, such as the ocean, fluid parcels are accelerated both locally, by the applied force, and nonlocally, by the pressure gradient forces established to maintain nondivergence of the resultant motion and to satisfy the kinematic boundary condition. The net acceleration can be represented through a “rotational force” in the rotational component of the momentum equation. To illustrate this point, consider the effect of a zonal force that

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