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DAVID W. STUART

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DAVID W. STUART

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David W. Stuart

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Three subjective and two objective analysis techniques were employed to prepare height data for a synoptic case over North America. These heights were used as input to a ten-level quasi-geostrophic model for computation of omegas (vertical velocities in pressure coordinate system) over a grid 2° latitude square. Using a subjective analysis prepared by F. Sanders as a standard, all the techniques gave synoptically acceptable patterns locating the 500-mb low center within one grid square with the intensity within ±20 m. The average height differences at each level for each technique never exceeded 11 m. One subjective and one objective technique did slightly better than the others for the height field.

Comparison of the quasi-geostrophic omegas with the Sanders' values shows good agreement for all analysis techniques for the broad scale rising and sinking centers and zero lines. The 500-mb centers are located within one grid interval with the main central values generally within 10–20% of the Sanders' value. Areas enclosed by a given omega isopleth show even better agreement. Overall the subjective analysis prepared by the team of Johnson, Golden, Hudson and Cotter (JGHC) agrees best with the Sanders' results, but the results via Inman's Objective Height Analysis (HOBAN) were quite close.

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David W. Stuart

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The quasi-geostrophic omega equation is employed to perform a diagnostic case study of the baroclinic structure of a developing system. The model employs height data at ten pressure levels to obtain the vertical motion along with the divergence and twisting terms at four pressure levels all evaluated in a fairly objective manner. Results are presented for one synoptic time prior to the development of a cut-off low of the Nevada type. These clearly show the scale and magnitude of the baroclinic features and the relative importance of the twisting and divergence terms for producing vorticity changes on a moving parcel. These results suggest a possible sequence of events leading to the cut-off low and the type of detail that filtered prediction models should employ to allow us to evaluate completely the ability of filtered models to handle mid-tropospheric development.

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Rebecca Jo Meitín and David W. Stuart

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As a part of the Second Coastal Upwelling Experiment along the Oregon Coast in summer 1973, extensive thermodynamic data were gathered in a mesoscale area. These data were examined in relation to the marine inversion at seven stations along a line from Salem, Ore., to a point 22 n mi off the coast, or a distance of approximately 65 n mi. The structure of the inversion was examined via time sections of temperature and potential temperature at each station, and cross sections along the line for selected times during the intensive period. Limited time and cross sections of relative humidity were also examined. The inversion seemed to respond to even weak synoptic-scale changes, rising with low-level convergence and lowering with subsidence in high-pressure regions. It was also found that the marine inversion had a more complex structure than a single stable layer.

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Jefrey D. Hawkins and David W. Stuart

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Temporal and spatial variations in the structure of the lower atmosphere off Oregon's central coast are studied. The response of the wind and thermal fields to a synoptic-scale realignment aloft that causes a rapid shift from surface southerly to northerly winds is detailed. The effects and importance of the infrequent southerlies on the marine inversion, sea breezes and upwelling is also investigated.

A vast array of meteorological and oceanographic observations were measured by aircraft, land stations, buoys and ships during the first Coastal Upwelling Experiment I (CUE-I). The winds, air and water temperature, and currents from the surface ocean layer to 1.5 km are compared during 16–29 August 1972. The period of southerly surface winds created a warm moist lower atmosphere, weak sea breezes, and brought about a cessation to previous upwelling. In contrast, northerlies and ridging aloft produced a distinct marine inversion, strong sea breezes, and an upwelling event. The marked changes reveal the potential effect summer southerlies have on coastal Oregon's air-sea environment.

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DAVID W. STUART and CDR. THOMAS H. R. O'NEILL

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Results of tests for the optimum over-relaxation coefficients in the numerical relaxation of the omega equation are presented. One case considers a strong upper-level development for tests on a fixed grid using one-, two-, and three-dimensional forms of the omega equation. In the other case of a “classical storm” the omega equation is relaxed in its three-dimensional form using several different horizontal grids.

For the one- and two-dimensional tests, the relaxation scheme agreesv ery well with theory. In the three-dimensional tests, the observed over-relaxation coefficients are found to be less than the values given by the theory for all grid sizes considered. A sharp cut-off is found to occur shortly after the optimum over-relaxation value is reached regardless of the number of dimensions of the equation or the size of the grid.

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Kenneth H. Brink, David W. Stuart, and John C. Van Leer

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Coordinated meteorological and oceanographic (CTD) measurements were made near Point Conception, California, during March–April 1981. The goal of the observations was to study coastal upwelling and the local characteristics of the assumed wind driving. Results showed substantial topographically-induced spatial structure in the near-surface winds, with weaker winds generally occurring within the Santa Barbara Channel. The 1981 “spring transition” event was monitored by mews of hydrographic and sea level measurements. The details of the event suggest that it was not entirely driven by lead wind stress. The mean sea surface temperature pattern suggests the existence of an upwelling center between Points Arguello and Conception. The individual sea surface temperature charts are all dominated by patchiness on a scale of 5–15 km. The nature of these structures is not well understood, but on the one occasion when a patch was isolated by a CTD survey, its structure penetrated to at 1east 50 db.

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John Coll, David K. Woolf, Stuart W. Gibb, and Peter G. Challenor

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The roughness of the seas is rarely mentioned as a major factor in the economic or social welfare of a region. In this study, the relationship between the ocean wave climate and the economy of the Western Isles of Scotland is examined. This sparsely populated region has a high dependency on marine activities, and ferry services provide vital links between communities. The seas in the region are among the roughest in the world during autumn and winter, however, making maintenance of a reliable ferry service both difficult and expensive. A deterioration in wave and wind climate either in response to natural variability or as a regional response to anthropogenic climate change is possible. Satellite altimetry and gale-frequency data are used to analyze the contemporary response of wave and wind climate to the North Atlantic Oscillation (NAO). The sensitivity of wave climate to the NAO extends to ferry routes that are only partially sheltered and are exposed to ocean waves; thus, the reliability of ferry services is sensitive to NAO. Any deterioration of the wave climate will result in a disproportionately large increase in ferry-service disruption. The impacts associated with an unusually large storm event that affected the region in January 2005 are briefly explored to provide an insight into vulnerability to future storm events.

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Sarah A. Tessendorf, Roelof T. Bruintjes, Courtney Weeks, James W. Wilson, Charles A. Knight, Rita D. Roberts, Justin R. Peter, Scott Collis, Peter R. Buseck, Evelyn Freney, Michael Dixon, Matthew Pocernich, Kyoko Ikeda, Duncan Axisa, Eric Nelson, Peter T. May, Harald Richter, Stuart Piketh, Roelof P. Burger, Louise Wilson, Steven T. Siems, Michael Manton, Roger C. Stone, Acacia Pepler, Don R. Collins, V. N. Bringi, M. Thurai, Lynne Turner, and David McRae

As a response to extreme water shortages in southeast Queensland, Australia, brought about by reduced rainfall and increasing population, the Queensland government decided to explore the potential for cloud seeding to enhance rainfall. The Queensland Cloud Seeding Research Program (QCSRP) was conducted in the southeast Queensland region near Brisbane during the 2008/09 wet seasons. In addition to conducting an initial exploratory, randomized (statistical) cloud seeding study, multiparameter radar measurements and in situ aircraft microphysical data were collected. This comprehensive set of observational platforms was designed to improve the physical understanding of the effects of both ambient aerosols and seeding material on precipitation formation in southeast Queensland clouds. This focus on gaining physical understanding, along with the unique combination of modern observational platforms utilized in the program, set it apart from previous cloud seeding research programs. The overarching goals of the QCSRP were to 1) determine the characteristics of local cloud systems (i.e., weather and climate), 2) document the properties of atmospheric aerosol and their microphysical effects on precipitation formation, and 3) assess the impact of cloud seeding on cloud microphysical and dynamical processes to enhance rainfall. During the course of the program, it became clear that there is great variability in the natural cloud systems in the southeast Queensland region, and understanding that variability would be necessary before any conclusions could be made regarding the impact of cloud seeding. This article presents research highlights and progress toward achieving the goals of the program, along with the challenges associated with conducting cloud seeding research experiments

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