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Tammy M. Weckwerth and David B. Parsons

variations of several grams per kilogram can be concentrated in a few kilometers. Prior to the project, drylines were believed to be the primary surface-based forcing mechanism in the region for new convection forming as synoptic features approached (e.g., Rhea 1966 ). The local topographic variations are small and generally not critical to the triggering of convection, although the Texas Caprock area does exhibit an increased frequency of convection. The region has a nocturnal precipitation maximum (e

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Peter Jan van Leeuwen

1970 ). This equation is solved approximately by solving an ensemble of stochastic partial differential equations. The stochastic terms in these equations represent unknown external and internal terms (or factors) in the model. Unknown terms in external forcing and in the model equations are incorporated by adding random numbers, drawn from a known error density, to the model equations. It is also possible to multiply parts of the model equations by unknown factors, sometimes called multiplicative

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Robert A. Houze Jr.

equator because the Coriolis force is too weak for low-level convergence to be able to generate relative vorticity. 2 Gray (1968) found that genesis regions not only are located off the equator, where the Coriolis force is nonzero, but also have higher-than-average relative vorticity of the surface wind field and temperature stratification that is at least moderately conditionally unstable, and weak vertical shear of the horizontal wind. The strong background positive vorticity helps to trap energy

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Roland A. Madden and Paul R. Julian

convection moves from the Indian to the Pacific Ocean. This agrees with our conclusions. However, their work indicated that the singularrole of surface frictional stresses that we proposed isnot correct during northern winter. At that time, theyshowed that surface wind stresses over the central Pacific are nearly out-of-phase with AAM. If they werethe only driving force, the wind stresses would lead theAAM by 0.25 cycles. We computed the coherence andphase between AAM and the torque due to surfacewind

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T. N. Krishnamurti

planetary scaleheat sources in the generation of the eddy availablepotential energy. These in turn were converted to thestrong planetary scale motions via east-west overturnings. A key element in the planetary scale generationTABLE 2. List of useful symbols.xA.B.K,K,,,Kv, K~,,Kxzonal velocitymeridional velocityvertical velocitypotential temperaturespecific humiditystreamfunctionsvelocity potentialenergy exchange from A to Bkinetic energyfrictional force per unit mass of airof eddy available potential

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Robert Wood

subtropics. The hemispheric asymmetry in seasonality is caused by greater orographic forcing from the elevated continent to the east for the southern sheets ( Richter and Mechoso 2004 , 2006 ). Fig . 6. (a) Seasonal amplitude (maximum − minimum coverage), and (b) month of maximum stratocumulus cover. Locations with no reports, or where the seasonal amplitude of stratocumulus cover is less than 2.5% are not shown. Data are from the combined land–ocean cloud atlas database ( Hahn and Warren 2007 ). There

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William M. Frank

PARAMETERIZATION From the above scale arguments it can be seen thatthe design ofa parameterization scheme must dependheavily upon the nature of the circulation to be modelled. For example, often the problem is to model theslowly varying rotational flow of a dynamically largesystem (region III). The stiffness of the flow in sucha system inhibits the ability of embedded convectiveor mesoscale systems to drive the large-scale divergence and thereby to enhance their own forcing.There is a tendency for the

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Volkmar Wirth, Michael Riemer, Edmund K. M. Chang, and Olivia Martius

and E have been created during that time. c. Different types of RWPs and their propagation There are different types of RWPs associated with different temporal and spatial scales, different types of forcing, and specific properties of the background flow. Sometimes an RWP is little more than an individual trough or ridge ( Sanders 1988 ); sometimes an RWP may span a substantial part of the globe ( Branstator 2002 ). Some RWPs propagate along great circles, while others are ducted in the zonal

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Kuo-Nan Liou

numerical models. - The physical fundamentals and parameterizationfor the formation of cirrus clouds need to be developedin conjunction with large-scale weather and climatemodels. In addition, the manner in which the ice content is generated in the model should be connected tothe radiative transfer calculations. The aforementionedcloud and cloud radiative data may then be used toverify and tune the cirrus cloud model developed. Acknowledgments. This research was supported bythe Air Force

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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

cyclone constitutes an external forcing with persistent structure to the midlatitude wave. This idea is in marked contrast to traditional initial-value studies of baroclinic development, in which the initial perturbations are embedded in the midlatitude flow and are thus not an external forcing (e.g., Simmons and Hoskins 1979 ; Hakim 2000 ). 2) Evolution of the upstream trough ET may also influence the upstream trough, which may experience modifications of its shape, meridional extension, and

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