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Tammy M. Weckwerth and David B. Parsons

lifted air parcels to their LCL prior to the interaction of the two boundaries, priming the intersection region for deep convection. Convection does not always develop at frontal–dryline merger or intersection locations, however. In a severe squall-line case study, initiation did not occur at the intersection between a cold front and dryline. Koch and Clark (1999) observed the development of a gravity current at the leading edge of the cold front. This produced a bore that propagated ahead on the

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Richard A. Anthes

weatherprediction models in middle latitudes. The current skill of limited-area models is summarized through theuse of conventional measures of verification such as S~ scores, root-mean-square errors and correlationsbetween forecast and observed changes. Additional measures of verification, which measure the skill orrealism of regional models in reproducing atmospheric structure on those scales, are discussed. Use of auniform set of verification measures such as those discussed here would facilitate model

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Scott R. Fulton, Paul E. Ciesielski, and Wayne H. Schubert

nonlinear problems and boundary conditions. Multigrid applications, current research, andavailable software are also discussed. CONTENTS1. Introduction2. Classical methods a. Gaussian elimination b. Point iterative methods c. ADI method d. Discussion3. Basic multigrid concepts a. Analysis of relaxation b. A two-grid method c. A multigrid method4. Survey ofmultigrid techniques a. Relaxation schemes b. Grids c. Grid transfers d. Control algorithms 1) Cycling algorithms 2) Full

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Robert A. Houze Jr.

resulting concentrated positive vorticity upward to produce a convective-scale positive vorticity perturbation that extends from low to midlevels. These “vortex hot towers” operate without strong downdrafts and spreading density currents. The subcloud boundary layer in the developing depression is therefore not diluted by downward transport of lower- θ e air. All of these properties are positive contributors to the intensification of a depression, especially in the lower troposphere. The convective

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Robert Wood

oceans where their mean coverage is typically 25%–40%. Over land, the regions with the highest stratocumulus cover are chiefly in the midlatitudes and in the coastal hinterlands adjacent to eastern boundary currents. However, the south and east of China is notable for being the only subtropical continental region with a high coverage of stratocumulus. The western sides of the major ocean basins, the developed trade winds, and the arid continental regions have the lowest coverage of stratocumulus, but

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P. L. Houtekamer and Fuqing Zhang

investigated in the 1980s and early 1990s (e.g., Ghil et al. 1981 ; Cohn and Parrish 1991 ; Daley 1995 ). One unsolved problem, aimed at an application with a realistic high-dimensional atmospheric forecast model, was how to obtain an appropriate low-dimensional approximation of the background error covariance matrix for a feasible implementation on a computational platform. The use of random ensembles currently seems to be the most practical way to address the issue. The use of Monte Carlo experiments

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Zhiyong Meng and Fuqing Zhang

-area models (LAMs), which is the focus of the current review. 1 The first LAM application of the EnKF was found in Snyder and Zhang (2003) and Zhang et al. (2004) , where synthetic radar data was assimilated into a cloud model. Those two studies demonstrated that the EnKF analysis can faithfully approximate the truth in terms of both dynamic and thermodynamic variables of a supercell storm ( Fig. 1 ). Fig . 1. The performance of a convective-scale EnKF in assimilating radar radial velocity for

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David M. Schultz

has been attributed to surface friction (e.g., Simpson 1972 ; Mitchell and Hovermale 1977 ) and would also appear to be relevant to cold fronts acting like density currents. Indeed, Simpson (1972) attributed the overhanging nose to the no-slip lower-boundary condition, allowing the overrunning of lighter prefrontal air by the denser postfrontal air. This produces a thin layer of prefrontal fluid that is transported underneath the cold air. The lobe-and-cleft structure at the head of a density

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William M. Frank

research into the nature of atmospheric convection andscale interactions in cumulus regimes. A major goal of these efforts has been to advance the state of the artin cumulus parameterization. This paper briefly reviews the cumulus parameterization problem in terms offundamental principles, goals and dynamic constraints as they apply to parameterization in mesoscale andlarger scale numerical models. Several popular current schemes are discussed in terms of their relationshipsto these overall aspects of

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Markus Gross, Hui Wan, Philip J. Rasch, Peter M. Caldwell, David L. Williamson, Daniel Klocke, Christiane Jablonowski, Diana R. Thatcher, Nigel Wood, Mike Cullen, Bob Beare, Martin Willett, Florian Lemarié, Eric Blayo, Sylvie Malardel, Piet Termonia, Almut Gassmann, Peter H. Lauritzen, Hans Johansen, Colin M. Zarzycki, Koichi Sakaguchi, and Ruby Leung

implicitly assumed that , which can lead to significant errors in the estimation of air–sea fluxes. By construction, the asynchronous coupling is expected to mitigate this latter issue since boundary data averaged in time are exchanged over a time interval usually much larger than the dynamical time step. However, the asynchronous coupling algorithm also suffers from a synchronicity issue. Indeed, the oceanic state used on comes from the previous time window and not the current time window. The

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