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Robert A. Cohen and Carl W. Kreitzberg

Abstract

Distinct airstreams, separated by sharp boundaries, are present in numerical weather simulations and can be used to identify characteristic structures in baroclinic storms. To allow objective comparisons between different analyses, a rigorous treatment of airstream boundaries is performed based upon a numerical procedure in which the uncertainty of individual trajectory paths is related to the strength of an airstream boundary, as defined and quantified herein. The properties of the procedure are then investigated via application to a numerical simulation of the ERICA IOP 4 storm. The work not only provides the necessary framework within which future analyses of airstreams can be interpreted but also provides insights into quantitative properties of atmospheric flows.

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Donald J. Perkey, Kevin N. Young, and Carl W. Kreitzberg

Newspapers, television, and newsweeklies contained numerous articles proclaiming drought conditions during 1980 and 1981. This study investigates the causes and consequences of the drought as it affected eastern Pennsylvania. Precipitation data indicate below-average amounts during this period, while temperature records show above-average values. These values show that a meteorological drought did occur in this region during 1980 and 1981. However, meteorological factors were only part of the cause of the region's water shortage.

In addition to analyzing the drought's meteorological origin, this study probes the anthropogenic and regional social-political causes and impacts of the water shortage. Although regional water storage facilities are adequate when below-average precipitation amounts occur in very local areas, they are not adequate when below-average amounts occur over larger regions. This inadequacy is compounded when demands such as the needs of other political regions and the river-basin ecological system are included in addition to the primary region's industrial and domestic water requirements. Thus, this paper illustrates some of the complexities involved in trying to prepare for the normal fluctuations in a climatic variable such as precipitation amount.

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Paul J. Neiman, M. A. Shapiro, Evelyn G. Donall, and Carl W. Kreitzberg

Abstract

On 25–27 January 1988, the National Oceanic and Atmospheric Administration's Wave Propagation Laboratory, Drexel University, and the Office of Naval Research carried out a combined pre-ERICA research aircraft investigation of a major marine cyclone moving northeastward over the Canadian Maritime Provinces. Flight-level and dropwindsonde observations documented the diabatic modification of the cyclone's warm sector marine boundary layer (MBL) as it moved out over cold underlying water. These observations and results from the Blackadar one-dimensional boundary layer model both show that heat fluxes were directed downward from the warm sector MBL into the cold ocean. Vertical gradients of these downward heat fluxes diabatically cooled the lower portion of the warm sector MBL and generated large static stability within the entire layer. The increase in stable stratification allowed large vertical wind shear to exist within this layer and strong wind speeds to exist at its top. The increase in static stability within the warm sector MBL acted to concentrate isentropic potential vorticity in this layer, but these changes also weakened the horizontal gradients of temperature, moisture, and wind velocity within the adjacent warm- and cold-frontal zones at the surface.

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Richard Rotunno, Leonard J. Pietrafesa, John S. Allen, Bradley R. Colman, Clive M. Dorman, Carl W. Kreitzberg, Stephen J. Lord, Miles G. McPhee, George L. Mellor, Christopher N. K. Mooers, Pearn P. Niiler, Roger A. Pielke Sr., Mark D. Powell, David P. Rogers, James D. Smith, and Lian Xie

U.S. Weather Research Program (USWRP) prospectus development teams (PDTs) are small groups of scientists that are convened by the USWRP lead scientist on a one-time basis to discuss critical issues and to provide advice related to future directions of the program. PDTs are a principal source of information for the Science Advisory Committee, which is a standing committee charged with the duty of making recommendations to the Program Office based upon overall program objectives. PDT-1 focused on theoretical issues, and PDT-2 on observational issues; PDT-3 is the first of several to focus on more specialized topics. PDT-3 was convened to identify forecasting problems related to U.S. coastal weather and oceanic conditions, and to suggest likely solution strategies.

There were several overriding themes that emerged from the discussion. First, the lack of data in and over critical regions of the ocean, particularly in the atmospheric boundary layer, and the upper-ocean mixed layer were identified as major impediments to coastal weather prediction. Strategies for data collection and dissemination, as well as new instrument implementation, were discussed. Second, fundamental knowledge of air–sea fluxes and boundary layer structure in situations where there is significant mesoscale variability in the atmosphere and ocean is needed. Companion field studies and numerical prediction experiments were discussed. Third, research prognostic models suggest that future operational forecast models pertaining to coastal weather will be high resolution and site specific, and will properly treat effects of local coastal geography, orography, and ocean state. The view was expressed that the exploration of coupled air-sea models of the coastal zone would be a particularly fruitful area of research. PDT-3 felt that forecasts of land-impacting tropical cyclones, Great Lakes-affected weather, and coastal cyclogenesis, in particular, would benefit from such coordinated modeling and field efforts. Fourth, forecasting for Arctic coastal zones is limited by our understanding of how sea ice forms. The importance of understanding air-sea fluxes and boundary layers in the presence of ice formation was discussed. Finally, coastal flash flood forecasting via hydrologic models is limited by the present accuracy of measured and predicted precipitation and storm surge events. Strategies for better ways to improve the latter were discussed.

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