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Author: Roger M. Wakimoto
Publisher:
ISBN:
Category : Aerodynamics
Languages : en
Pages : 258
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Book Description
This dissertation investigates the thunderstorm gust front with the aid of Project NIMROD data. The main goal is to present the time dependent solution of the gust front. RHI and VAD cross sections of reflectivity and Doppler velocity were constructed for different three minute radar scans to determine the vertical structure. These analyses revealed that the life cycle of the gust front could be divided into four stages: 1) the formative stage; 2) the early mature stage; 3) the late mature stage; and 4) the dissipation stage. A new finding was a horizontal roll detected in the reflectivity patterns during stages II and III. This phenomenon was called a "precipitation roll." Rawinsonde launchings revealed the thermodynamic structure of the gust front. The cold air layer was found to correspond closely to the observed surface pressure rise. Calculations confirmed that the collision of two fluids produced nonhydrostatic pressure forces at the leading edge of the outflow. A dry, cool layer at the top of the gust front was a result of the low level outflow that was lifted vertically at the frontal boundary and advected back by the circulation within the bead of the gust front. The equation for the propagation speed of a density current was confirmed to accurately predict the movement of the gust front, thus disproving the theory that the gust front is an advecting phenomenon. Comparisons are made between the gust front and the "downburst" to emphasize their different nature.
Author: Roger M. Wakimoto
Publisher:
ISBN:
Category : Aerodynamics
Languages : en
Pages : 258
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Book Description
This dissertation investigates the thunderstorm gust front with the aid of Project NIMROD data. The main goal is to present the time dependent solution of the gust front. RHI and VAD cross sections of reflectivity and Doppler velocity were constructed for different three minute radar scans to determine the vertical structure. These analyses revealed that the life cycle of the gust front could be divided into four stages: 1) the formative stage; 2) the early mature stage; 3) the late mature stage; and 4) the dissipation stage. A new finding was a horizontal roll detected in the reflectivity patterns during stages II and III. This phenomenon was called a "precipitation roll." Rawinsonde launchings revealed the thermodynamic structure of the gust front. The cold air layer was found to correspond closely to the observed surface pressure rise. Calculations confirmed that the collision of two fluids produced nonhydrostatic pressure forces at the leading edge of the outflow. A dry, cool layer at the top of the gust front was a result of the low level outflow that was lifted vertically at the frontal boundary and advected back by the circulation within the bead of the gust front. The equation for the propagation speed of a density current was confirmed to accurately predict the movement of the gust front, thus disproving the theory that the gust front is an advecting phenomenon. Comparisons are made between the gust front and the "downburst" to emphasize their different nature.
Author: United States. Thunderstorm Project
Publisher:
ISBN:
Category : Meteorology in aeronautics
Languages : en
Pages : 308
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Book Description
Author:
Publisher:
ISBN:
Category : Meteorology
Languages : en
Pages : 932
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Book Description
Author: Roger M. Wakimoto
Publisher:
ISBN:
Category :
Languages : en
Pages : 23
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Book Description
Author: Kenneth E. Mitchell
Publisher:
ISBN:
Category : Fronts (Meteorology)
Languages : en
Pages : 124
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Book Description
Author:
Publisher:
ISBN:
Category : Storms
Languages : en
Pages : 632
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Book Description
Author: Keith L. Seitter
Publisher:
ISBN:
Category : Atmospheric turbulence
Languages : en
Pages : 40
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Book Description
The thunderstorm gust front is an important feature for both the maintenance and initiation of storms. Previous studies have shown that the thunderstorm outflow producing the gust front can be treated as an atmospheric density current to a good approximation. In this study, a new version of the density current speed equation, based on the surface pressure rise, is derived. This equation is shown to give much better results than other commonly used forms when applied to twenty previously reported gust front observations. A two-dimensional numerical model is used to investigate the dynamics of atmospheric density currents. Simulations with this model show the effects of the environmental wind relative to the storm and the wind shear on the propagation of the gust front and the depth of the thunderstorm outflow. The results of these simulations are discussed in terms of the conditions necessary for the gust front to remain in a position that is beneficial for the maintenance of the storm. Moist processes are included in the model and simulations are made to investigate atmospheric density current propagation through a moist atmosphere. The lifting that occurs during gust front passage is calculated and it is found that even when this lifting is sufficient to bring moist parcels above their level of free convection; deep convection is prohibited by other aspects of the circulation. The generation of an arc cloud by the gust front is found to result in a less intense and slower gust front compared to an outflow that did not produce an arc cloud. This result is interpreted in terms of the gust front speed equation based on the surface pressure rise.
Author: R. C. Goff
Publisher:
ISBN:
Category : Aircraft
Languages : en
Pages : 142
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Book Description
Strong wind changes and turbulence encountered by aircraft arriving or departing an airport constitute hazards to safe flight. Most serious encounters are thunderstorm outflow related. The gust front structure as observed by Doppler radar, standard weather radar, a 461 m meteorologically instrumented tower, aircraft and other observations is presented. Gust front evolution as observed with a severe thunderstorm is shown. Turbulence and multiple surges are discussed. (Author).
Author: United States. Federal Aviation Administration. Systems Research and Development Service
Publisher:
ISBN:
Category : Thunderstorms
Languages : en
Pages : 122
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Book Description
Author: Jean Theodore Lee
Publisher:
ISBN:
Category : Atmospheric turbulence
Languages : en
Pages : 43
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Book Description
The 1980 Spring Observation Program extended from April 15 to June 19 at the National Severe Storms Laboratory, Norman, Oklahoma. Aircraft, rawinsonde network, mesoscale surface network, low-level wind shear alert system at Will Rogers World Airport, 444 m instrumented tower and satellite observations augmented a conventional weather radar and a new, dual Doppler weather radar system to obtain concurrent data on weather hazards to aircraft. Storm days and data acquired are detailed. An objective for the spring program was to determine the characteristics and detectability of turbulence, wind shear and other aircraft operational weather hazards using indirect (radar) probes. The South Dakota School of Mines T-28 aircraft and the National Aeronautics and Space Administration's F-106 aircraft made thunderstorm penetrations during Doppler radar and lightning operations. Data obtained are discussed, and the analysis of a turbulence case and two gust front cases are presented. These indicate the Doppler radar's potential use to detect and dimensionalize aviation weather hazards both in-cloud and in optically clear air. These studies and additional ones now in progress will provide material for guideline development as to siting and uses of the Next Generation Radar (NEXRAD) in aviation-related situations. (Author).
