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SNOW-ONE-A and B Characterization Measurements and Data Analysis
Report Number: AFGL TR 83-0256
Author(s): Berthel, R. O.; Plank, V. G.; Main, B. A.
Corporate Author: Air Force Geophysics Laboratory
Publication Date: 9/20/1983
Pages: 60
Project: 0
Task: 0
AD Number: ADA141245
Photo Enhancement: Not Needed
Abstract Text:
To make realistic estimates of precipitable hydrometeors, meteorological modeling requires valid inter-relationships for the paramerization of mass concentrations, precipitation rates, fall velocities, number densities, etc. In response to these needs, AFGL has initiated a modest effort with objectives of defining such relationships and providing the means to verify model outputs. Measurements documenting the characteristics of naturally falling snow were obtained during the SNOW-ONE-A and SNOW-ONE-B field experiments. These consist of data acquired by three unique instruments: a snow-rate meter (SRM), a fall-velocity indicator (FVI), and a snow-structure recorder (SSR). This report describes the results of our participation in these field programs. Snow rates, particle-fall velocities, and snow-crystal information are presented. Correlations between snow rate and electro-optical transmittance/attenuation and mass-concentration measurements are illustrated. Relationships of fall velocity with snow-crystal size from analyzed data are given along with a method of determining fall velocity through knowledge of snow rate and liquid-water content. The data obtained during these two field experiments indicate that it may be possible to define mathematical relationships between precipitation rate and mass concentration and between fall velocity and snowflake size for broad categories of snow types.
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Tactical Visibility Meter
Report Number: AFGL TR 83-0256
Author(s): Moroz, Eugene Y.; Jacobs, Leo P.
Corporate Author: Air Force Geophysics Laboratory
Publication Date: 10/24/1983
Pages: 55
Project: 0
Task: 0
AD Number: ADA141286
Photo Enhancement: Incomplete
Abstract Text:
Accurate and timely visibility information is required by the Air Weather Service in support of Air Force tactical bare-base operations. The Air Force Geophysics Laboratory (AGGL) undertook a program to develop a tactical visibility meter (TVM) to satisfy this requirement. A prototype meter was designed and fabricated by Wright & Wright, Inc., Oak Bluffs, Mass. The meter measures the atmospheric scattering coefficient in the forward direction. Visibility is inferred from the measurement. The operation of the prototype meter was successfully demonstrated by AFGL in tests conducted at its Weather Test Facility, Otis AFB, Mass. In the next phase of the development, Wright & Wright, Inc., was tasked to design and fabricate a cost-effective preproduction version of the TVM. This report describes the current development, test, and evaluation of the TVM.
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Numerical Simulation of Thunderstorm Gust Fronts
Report Number: AFGL TR 83-0329
Author(s): Seitter, K. L.
Corporate Author: Air Force Geophysics Laboratory
Publication Date: 12/13/1983
Pages: 34
Project: 0
Task: 0
AD Number: ADA141214
Photo Enhancement: Not Needed
Abstract Text:
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.
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