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  • 11
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    Diagnosing convective instability using VAS data (1983)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: The utility of combining visible and various infrared images from the VAS to produce a forecasting tool, that can be available on a near real time basis, to predict severe weather development is shown. Areas where dry air in the midtroposphere overlays substantial moisture at low levels are used to diagnose mesoscale regions that have the potential for being convectively unstable before the onset of severe convection. Specifically, 6.7 micron water vapor imagery, used for isolating regions of substantial midlevel dryness, are combined with images of low level clouds or with split-window low level moisture images to delineate regions that have the potential for convective instability. In areas where scattered low level clouds are present, computer generated, color image combinations are used to isolate those warm, low level clouds that are in potential convectively unstable environments from clouds that exist under a deeply moist atmosphere. In clear regions, the split window technique is used for delineating areas of substantial boundary layer moisture. These images are again computer overlayed by the midlevel dryness to produce a color coded image of potential convective instability.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: VISSR Atmospheric Sounder (VAS) Res. Rev.; p 7
    Format: text
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  • 12
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    Ozone, jet streaks and severe weather (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Data from three independent observing platforms are synthesized to study the role of jet streaks in severe weather. The three data types are: conventional radiosondes; 6.7 micron water vapor imagery from the GOES satellite; and total ozone imagery from Nimbus 7. Diagnoses are then made of potential vorticity, mid-tropospheric moisture, and total ozone at and below the level of jet streaks. Potential vorticity and total ozone distributions are both tracers of stratospheric air. Theoretically, both should respond to the transverse, vertical circulations expected in the vicinity of jet streaks. Both should increase due to the sinking above the left front quadrant of the streaks. Moisture, on the other hand, increases in the ascent under the left front quadrant. This study shows striking agreement between the three parameters independently observed from three different observing platforms. Moreover, the three severe weather case studies suggest a unique distribution of ozone, potential vorticity, and mid-tropospheric moisture relative to a jet streak. This, in turn, led to the creation of a new ozone/jet streak model which shows that the total ozone distribution provides a signature in the vicinity of jet streaks and permits identification of areas most likely to experience severe weather at a later time. The value of such observations to operational forecasting is discussed.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Scientific and Operational Requirements for TOMS Data; p 20
    Format: application/pdf
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  • 13
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    Advective forecasts of VAS imagery for use in anticipating convective destabilization (1984)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Wind field forecasts, based on data from the Visible Atmospheric Sounder (VAS) instrument on board the most recent GOES satellite, are described. The forecasts were used to generate a series of water vapor images for the Central U.S. according to an isentropic prediction scheme. The ability of VAS imagery to detect regions of mesoscale convective instability was contrasted with data from a 9-12 hr advective forecast and the results are discussed. It is shown that the VAS imagery was free from masking by convective outflows and lends itself to repeated applications for updating throughout the day. The incorporation of surface data into the VAS forecast is recommended in order to identify areas of persistent moisture convergence. Some examples of the VAS imagery are provided.
    Keywords: METEOROLOGY AND CLIMATOLOGY
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  • 14
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    Short-range forecasting and nowcasting, using a simple, isentropic prediction model (1989)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A numerical advection model which can be run on a local computer in a real-time forecast environment is described. This isentropic forecast model provides the local forecast office with easy access to temporally and spatially detailed estimates of atmospheric temperature, moisture, and wind field changes between 12-h rawinsonde observations. Case studies are presented based on the use of the model to predict the preconvective environment in spring and summer situations. Short-term forecasts of midtropospheric static stability patterns and stability index changes are traced for several severe storm events with and without the inclusion of surface data observed during the day. Forecast images of VAS low- and midlevel moisture fields and vertical moisture gradients are compared with the observations to determine the utility of the combined model/VAS imagery as a nowcasting guide.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Weather and Forecasting (ISSN 0882-8156); 4; 5-23
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  • 15
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    Factors which influence the development of a low-level jet and coastal cyclogenesis (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Mesoscale model simulations were run to examine the mechanisms which generate a low-level jet (LLJ) and the sea-level pressure decrease (SLPD) associated with secondary cyclogenesis along the East Coast of the U.S. Data collected during the Presidents' Day cyclone of February 18-19, 1979 are reviewed, including the behavior of the LLJ preceding cyclogenesis. The simulations covered adiabatic conditions, the absence and presence of latent heating, and the inclusion of all physical parameters with and without computations of boundary layer phenomena, 60-km grid-scale precipitation, and convective precipitation. The results indicate that synergistic reactions among the LLJ, latent heat release, jet-induced circulation, and boundary layer processes are necessary to account for secondary cyclogenesis and the accompanying rapidly evolving mass, momentum and moisture fields.
    Keywords: METEOROLOGY AND CLIMATOLOGY
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  • 16
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    The use of a simplified isentropic model for short-term aviation forecasting (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A simple, multiple-layer, isentropic potential vorticity forecast model is described for predicting short-term atmospheric changes between 12-hourly radiosonde observations. The model and the model initialization technique are described, and a case study with both convection and strong horizontal wind shear is discussed. The wind and stream function field forecasts and the forecast areas of convective instability are constrasted with observational results to assess the model's strengths and weaknesses. Excellent agreement is obtained between model predictions and observations.
    Keywords: METEOROLOGY AND CLIMATOLOGY
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  • 17
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    Spectral scales in the atmospheric boundary layer (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Wind data taken from 10 levels between 18 and 305 m were examined to determine the properties of atmospheric turbulence within and above the atmospheric surface layer into the PBL. The samples were averaged over 40 min intervals, with all periods of rain, fog, and other disturbances being eliminated from the 16 days of monitoring. Turbulence spectra were calculated using a fast Fourier transformation. The tower was located in rolling terrain covered with pine forests, waist-high scrub, and cultivated fields. Results are presented for the wavelength and Eulerian length scales, considering the neutral, stable, and unstable PBL. Correlation coefficients were found between velocity fluctuations and wavelengths for the stability classes. Good agreements were found for measured and computed spectra in all but unstable conditions.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Applied Meteorology; 21; Nov. 198
    Format: text
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  • 18
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    The computation of isentropic atmospheric trajectories using a 'discrete model' formulation (1979)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: An explicit technique for calculating atmospheric trajectories is presented as an alternative method to the standard implicit scheme of Danielsen (1961). The technique uses the inviscid equations of motion and the discrete model formulation derived by Greenspan (1972, 1973) to compute trajectories on isentropic surfaces, assuming adiabatic flow. The discrete model formulation is designed specifically for a Lagrangian system and objectively accounts for the geostrophic departures, local psi-tendencies, and the subsequent accelerations along the entire length of the trajectory. Application of the discrete formulation to a diagnostic case study yielded favorable results.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Monthly Weather Review; 107; May 1979
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  • 19
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    The Presidents' Day cyclone of 18-19 February 1979 - Synoptic overview and analysis of the subtropical jet streak influencing the pre-cyclogenetic period (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A detailed examination is undertaken of the subtropical jet (STJ) streak revealed by an analysis of the Presidents' Day cyclone of February 18-19, 1979. During its 24 h period, the STJ's flow became increasingly supergeostrophic and apparently unbalanced, while ageostrophic wind speeds increased to more than 30 m/sec in association with a significant cross-contour component, directed toward lower values of the Montgomery streamfunction, as the flow along the STJ became more divergent with time. These phenomena are linked to the increasing confluence in the entrance region of the jet streak and the decreasing wavelength of the trough-ridge system in which the jet streak was embedded. The upper level divergence and upward vertical motion near the axis of the STJ are found to be important factors in the development of the cyclone's first area of heavy snow.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Monthly Weather Review (ISSN 0027-0644); 112; 31-55
    Format: text
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  • 20
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    A model for the simulation of atmospheric turbulence (1976)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: A method that produces realistic simulations of atmospheric turbulence is developed and analyzed. The procedure makes use of a generalized spectral analysis, often called a proper orthogonal decomposition or the Karhunen-Loeve expansion. A set of criteria, emphasizing a realistic appearance, a correct spectral shape, and non-Gaussian statistics, is selected in order to evaluate the model turbulence. An actual turbulence record is analyzed in detail, providing both a standard for comparison and input statistics for the generalized spectral analysis. The simulation utilizes the eigenfunction-expansion procedure to produce preliminary time histories of the three velocity components simultaneously. It is found that important cross-statistical features are reasonably well-behaved.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Applied Meteorology; 15; June 197
    Format: text
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