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  • 1
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    Delineating mid- and low-level water vapor patterns in pre-convective environments using VAS moisture channels (1984)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Infrared and visible imagery from VAS are used to delineate mid- and lower-tropospheric moisture fields for a variety of severe storm cases in the southern and central United States. The ability of sequences of images to isolate areas of large negative vertical moisture gradients and apparent convective instability prior to the onset of convective storms is assessed. A variety of image combination procedures are used to deduce the stability fields which are then compared with the available radiosonde data. The results for several severe storm cases indicate that VAS can detect mid- and low-level mesoscale water vapor fields as distinct radiometric signals. The VAS imagery shows a strong tendency for thunderstorms to develop along the edges of bands of midlevel dryness as they overtake either preexisting or developing low-level moisture maxima. Image sequences depict the speed with which deep moist and dry layers can develop and move.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Monthly Weather Review (ISSN 0027-0644); 112; 2178-219
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Use of the VAS for analysis of a prethunderstorm environment (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The information content of the VAS radiances can be converted to meteorological parameters useful for analyzing a severe weather environment. The method by which the VAS variances are converted to vertical profiles of temperature, dewpoints, and equivalent potential temperature involves a basic regression technique using the most local radiosonde data available for establishing a correlation matrix. The results indicate that mesoscale features apparent within images of the radiances can be converted to usable temperature and moisture fields using regression when surface temperature and dewpoint observations are included within the total data base. In addition, results indicate that surface data are very important for better defining lower tropospheric structure that the VAS radiances alone cannot properly resolve. Analyses of these retrievals distinctly show mesoscale structure in the temperature and moisture fields derived with VAS radiances collected every 3 hours, and 0000 GMT. The retrievals capture the moisture structure. More important, convective instability is clearly detected immediately before the onset of convection. The results indicate that the VAS is capable of providing valuable mesoscale information suitable for analyzing a preconvective environment that is generally clear.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: VISSR Atmospheric Sounder (VAS) Res. Rev.; p 9
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  • 3
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    Diagnosing convective instability using VAS data (1983)
    In:  Other Sources
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    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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  • 4
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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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  • 5
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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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  • 6
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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
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    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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  • 7
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    A simple Lagrangian forecast system with aviation forecast potential (1983)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: A trajectory forecast procedure is developed which uses geopotential tendency fields obtained from a simple, multiple layer, potential vorticity conservative isentropic model. This model can objectively account for short-term advective changes in the mass field when combined with fine-scale initial analyses. This procedure for producing short-term, upper-tropospheric trajectory forecasts employs a combination of a detailed objective analysis technique, an efficient mass advection model, and a diagnostically proven trajectory algorithm, none of which require extensive computer resources. Results of initial tests are presented, which indicate an exceptionally good agreement for trajectory paths entering the jet stream and passing through an intensifying trough. It is concluded that this technique not only has potential for aiding in route determination, fuel use estimation, and clear air turbulence detection, but also provides an example of the types of short range forecasting procedures which can be applied at local forecast centers using simple algorithms and a minimum of computer resources.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Conference on Aerospace and Aeronautical Meteorology; Jun 06, 1983 - Jun 09, 1983; Omaha, NE
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    NASA TECHNICAL REPORTS
  • 8
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    An interactive meteorological display and analysis system (1983)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The GEMPAK system, a general meteorological software package being developed at NASA/Goddard Space Flight Center to support mesoscale meteorological research programs, is described. The primary purpose of the system is to provide analysis support and data integration techniques for conventional and satellite derived data sets. Current capabilities of the system range from data listing and editing to interactive objective analysis procedures and coordinate transformations. Output graphics use a graphics subroutine package designed to support meteorological plotting functions. A flexible diagnostics package is currently under development.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Conference on Aerospace and Aeronautical Meteorology; Jun 06, 1983 - Jun 09, 1983; Omaha, NE
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  • 9
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    Techniques for diagnosing mesoscale phenomena affecting aviation using VAS satellite data (1983)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: A major advance in geostationary satellite observations occurred recently with the inclusion of an experimental instrument aboard the latest Geostationary Operational Environmental Satellites (GOES). This instrument, called the Visible Infrared Spin-Scan Radiometer (VISSR) Atmospheric Sounder (VAS), permits simultaneous observations of the atmosphere in up to 12 infrared channels, in addition to the visible image. In the present investigation, particular emphasis is placed on the ability of VAS imagery and derived soundings to delineate isolated, meso-scale regions of convective instability. The results of the investigation point to the ability of the VAS instrument to delineate meteorologically meaningful patterns of low-level moisture and mid-level dryness and to the utility of the image overlay procedure for isolating, in real time, regions of convective potential, at time and space scales unresolvable using radiosonde data alone.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Conference on Aerospace and Aeronautical Meteorology; Jun 06, 1983 - Jun 09, 1983; Omaha, NE
    Format: text
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  • 10
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    The use of VAS satellite data in weather analysis, prediction and diagnosis (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-07-27
    Description: Imagery available with the Goes satellite visible-IR spin-scan radiometer (VISSR) atmospheric sounders (VAS) are examined in terms of mid- and low-tropospheric moisture sensing and mesoscale soundings. The VAS can be operated in a Dwell Sounding mode (DS) involving preprogrammed scanning of a specific area using any number of combinations of 12 channels between 4-15 microns. A second, multi-spectral imaging mode (MSI) comprises operation of two IR channels simultaneously when time constraints are in effect. Case studies are presented to demonstrate the effectiveness of VAS imagery for characterizing mesoscale moisture conditions when identifying severe storms. The moisture patterns of the upper and lower troposphere are made visible, and a 6.7 micron channel image can be overlaid on a low level moisture field to delineate fields of potential instability.
    Keywords: METEOROLOGY AND CLIMATOLOGY
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