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Tammy M. Weckwerth and David B. Parsons

1. Introduction Accurate, high-resolution, three-dimensional moisture measurements are critical, yet largely unavailable, for many atmospheric science applications (e.g., Weckwerth et al. 1999 ). For example, several national study groups ( National Research Council 1998 ; Emanuel et al. 1995 ; Dabberdt and Schlatter 1996 ) have suggested that a critical factor limiting the prediction of convective precipitation is the measurement uncertainty in the high-resolution distribution of water

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David M. Schultz and Philip N. Schumacher

upright convection) and slantwise convection. These three ingredients of instability, moisture, and lift are explored further in this article: section 3 reviews the calculation of symmetric instability and section 4 discusses moisture and lift, specifically the relationship between MSI and frontogenesis. In section 5 , the implications for the coexistence of instabilities to both moist gravitational and slantwise convections are examined, including a discussion of the structure, evolution

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Robert Wood

sharpen the temperature inversion immediately above the cloud top, which can be as strong as 10–20 K in just a few vertical meters ( Riehl et al. 1951 ; Riehl and Malkus 1957 ; Neiburger et al. 1961 ; Roach et al. 1982 ). Longwave cooling is the main driver of the overturning convective circulations that constitute the key dynamical elements of these clouds ( Lilly 1968 ). Turbulence homogenizes the cloud-containing layer, frequently couples this layer to the surface source of moisture that

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John Molinari and Michael Dudek

. A model that allowedcondensation only upon grid-scale saturation wouldfail to reproduce this heat source. (iii) Large vertical fluxes of heat, moisture, andother quantities by cumulus convection occur on scalesunresolvable by hydrostatic model grids. A model thatdid not implicitly include such subgrid-scale sourceterms could not accurately predict grid-scale evolutionwhen convection was active. The sum of net condensation heating (or moistening) in the column [(ii) above] and convective

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Andrew Staniforth and Jean Côté

a mistaken belief that semi-Lagrangian schemes are only good for smooth flows. Theirfindings clearly show that this is not the case. In a similar vein, Ritchie (1985) argued that the localizationof errors to the regions where the gradients are strongestwhen semi-Lagrangian advection is used is a desirableproperty that may be advantageously exploited for thetreatment of moisture transport in NWP models, sincelarge local gradients frequently occur in moisture fields(e.g., at fronts). He reported

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Julia H. Keller, Christian M. Grams, Michael Riemer, Heather M. Archambault, Lance Bosart, James D. Doyle, Jenni L. Evans, Thomas J. Galarneau Jr., Kyle Griffin, Patrick A. Harr, Naoko Kitabatake, Ron McTaggart-Cowan, Florian Pantillon, Julian F. Quinting, Carolyn A. Reynolds, Elizabeth A. Ritchie, Ryan D. Torn, and Fuqing Zhang

moves poleward and starts to interact with the midlatitude flow ( Fig. 1a ). This results in the formation of a jet streak ( Fig. 1b ) and a poleward deflection of the jet near the transitioning cyclone in conjunction with the development of a ridge–trough couplet ( Fig. 1b ). At the same time, a region of enhanced moisture flux—a so-called atmospheric river ( Zhu and Newell 1998 )—forms ahead of the downstream trough. The ridge–trough couplet continues to amplify, a new cyclone develops farther

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Dayton G. Vincent

,.:~ .~ ~~:~'~ ... ~ ~.. ~ .'~ ..~ :~~:.~?? _~::~?? .?.~~ /: o ;~0 ~$?OE IZtO I-~ 180 IS'O I,,~ V ' ~1 FIG. 1. Schematic view of the main convergence zones, the ITCZand SPCZ, along with the annual mean sea level pressure contoursand surface wind streamlines. (Extracted from Trenberth 1991a.) 'of low-level moisture convergence, between the predominantly northeasterly flow west of the eastern Pacific subtropical

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T. N. Krishnamurti

the monsoon circulations. This experiment strongly suggests the need for a careful determination of the initial heat source in the monsoonprediction problem.4. Apparent heating and moistening Yanai et al.'s (1973) definition of the apparent heatsource Q~ and the apparent moisture sink Q2 providesa powerful tool for diagnostic studies of the atmosphere.Figure 7a-d illustrates Luo and Yanai's (1984) estimates of Q~ and Q2 over four relevant regions; theseare over the western and eastern regions

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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

. However, the ageostrophic circulation required to maintain geostrophic balance would include subgrid-scale transports as well as resolved ageostrophic transport. In the presence of moisture, the static stability is reduced by latent heating. This reduction of stability could be expressed, neglecting the condensate loading term in the buoyancy, by replacing the potential temperature θ with the equivalent potential temperature in saturated regions. In the presence of moist instability, would then

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Zhiyong Meng and Fuqing Zhang

implemented at the University of Washington in January 2005 ( Torn and Hakim 2008a ). The 2-yr performance of this system was found to have slightly larger errors of wind and temperature fields, but smaller errors in moisture in comparison to deterministic output of different operational forecast models ( Fig. 2 ). Fig . 2. The performance of a quasi-operational WRF-EnKF system implemented at the University of Washington in comparison to selected operational forecasts in terms of RMS error (solid) and

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