Engineering topics

Kopp, F. J.

Publications and source records attributed to Kopp, F. J..

7 records

NASA NTRS1989

Multiparameter radar study of a microburst - Comparison with model results

Radar observations and model results are used to investigate the microphysical evolution of an isolated, intense storm observed on July 20, 1988 during the Microburst and Severe Thunderstorm experiment. The storm grew to a height of 14 km and upon collapsing, produced heavy rain, pea-sized hail, and a microburst at the surface. The radar observations indicate that the initial precipitation development was by collision-coalescence. As the storm intensified, accretional growth became dominant leading to rapid precipitation development. Radar-derived rainfall rates peaked around 150 to 190 mm/h. Each morning during the experiment, a two-dimensional, time-dependent cloud model, initialized with the morning sounding, was run. The model results from the July 20 sounding are compared to the radar observations. Good agreement is shown in some aspects of the storm development, although the numerical simulation predicted a more vigorous storm than actually developed.

Tuttle, John D.↗

NASA NTRS1989

The primary cloud physics mechanisms of microburst formation

Several atmospheric soundings have been used as initial conditions in the Institute of Atmospheric Sciences' two-dimensional, time-dependent cloud model and resulted in a wide range of microbursts, some very wet and some nearly dry. Observations confirm the occurrence of at least three of the microbursts and give good comparisons of the intensity, upper-level convergence, downdraft, and other microburst characteristics. The effects of the liquid and ice microphysics are examined quantitatively. Precipitation loading, graupel/hail melting, and rain evaporation are all shown to be important. Evaporation and milting are, in general, the most dominant effects.

Orville, H. D.↗

NASA NTRS1988

On the microphysics of microbursts

The effects on microbursts of precipitation loading, and cooling of the downdraft due to graupel/hail melting and rain evaporation, were studied, using numerical models. The results for the microburst index indicate a low value for the weak microburst and a higher value for the strong microburst. The relative magnitude of the various terms indicate the importance of the microphysical processes. For the dry microburst the evaporation and loading effects are comparable (1.56 and 1.75 respectively) but 5 to 6 times the magnitude of the melting effect. For a wet, tropical microburst, the loading and melting terms are most important. The intermediate Denver case shows loading as the largest term, followed by evaporation and melting.

Orville, H. D.↗

NASA NTRS1985

Mesoscale-cloud scale simulation of convective response

The importance of mesoscale moisture information in the forecasting of weather events is being studied. A test is being prepared with the March 6, 1982 Vertical Atmospheric Sounder/Atmospheric Variability Experiment (VAS/AVE) case study to be run on the sub-synoptic scale model (SSM). Intracomparison of three carefully designed simulations should isolate the role of mesoscale information in the initial conditions for both moisture and vertical motion. Three simulations will be made for the period 1200Z 6 March to 0000Z 7 March starting with the regular synoptic time data of 1200Z. The distinction between the three cases arises from data manipulation at 1800Z midway through the forecast period. Comparison of results for the 1800Z to 0000Z time period will give the information desired.

Kopp, F. J.↗

NASA NTRS1985

Numerical simulation of convective response to mesoscale forcing

A two-dimensional mesoscale model was used to initialize a two-dimensional cloud model with both mesoscale thermodynamic and dynamic information utilized in the initialization. The Mesoscale-cloud mdoel linkage was used to examine differential convective response due to mesoscale variations for the April 24, 1982 Atmospheric Variability Experiment-Vertical Atmospheric Sounder (AVE-VAS), Case 4. On this day both data analyses and mesoscale model simulations indicated strong variations in thermodynamic and dynamic structure across the panhandle of Texas where a moderately strong convective line formed. Using the cloud model, the current research has shown a preferred area for strong convection to occur due to concomitant mesoscale convergence and mesoscale destabilization of the atmosphere.

Mcnider, R. T.↗

NASA NTRS1985

Simulation of mesoscale convective response

Results are reported from a transfer of thermodynamic and dynamic data downscale from a two-dimensional mesoscale model to a two-dimensional cloud model and a subsequent examination of the differential convective response of the cloud model to a mesoscale structure. The mesoscale model included a high resolution PBL formulation, with convective forces expressed in a profile of exchange coefficients over the height of the PBL and the magnitude of the surface heat flux. Account was also taken of forcing by long- and short-wave radiation, surface forcing by the surface energy budget, the terrain shape, and possible wave reflection at the top boundary. The slab-symmetric cloud model possessed subgrid-scale features, five types of moisture terms, and a subroutine for accretion processes. The mesoscale environment was observed to have a significant impact on convective response, i.e., the vertical velocity and the cloud water. Various factors which were not included in the study and which must be considered are discussed.

Mcnider, R. T.↗

NASA NTRS1984

Cloud scale influences on mesoscale precipitation patterns

A two dimensional time dependent finite difference grid cloud model is discussed. The model simulates atmospheric motions, potential temperature, water vapor, cloud liquid, cloud ice, rain and small hail. Lateral boundary conditions are open allowing flow in and out of the model domain. Various amounts of convergence were simulated to test the effects on cloud initiation and development. Soundings were run and results discussed.

Kopp, F. J.↗