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John McCarthy

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John McCarthy

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John McCarthy

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The one-dimensional cumulus dynamics model of Simpson and Wiggert has been applied to a large set of southern plains summer soundings to determine the seeding potential in terms of cloud growth and tower precipitation production. A 25% increase in height is predicted on 22% of the days, while a 50% increase is expected on about 7% of the days. The water fallout from the tower is seen to increase by 25% on 37% of the days. It was not possible to determine the precipitation on the ground as a part of the model calculation. Cloud size varies inversely with the model entrainment rate, whose complicated relationship to seedability is analyzed in detail.

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John McCarthy

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Equations are developed which describe 1) the airborne temperature instrumentation response to an arbitrary ambient temperature profile, for a two-term exponential system; and 2) a numerical scheme which corrects the sensor data for this lag. When in-cloud temperature fluctuations are of the same order as the instrument fidelity, as in some cumulus cloud penetrations, serious discrepancies may result between the ambient profile and the sensor response, making a correction desirable.

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John McCarthy

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This research is concerned with the verification of an expression which relates the entrainment rate in a cumulus cloud to the diameter of that cloud, where the entrainment rate is defined as the fractional increase in cloud mass due to mixing with the environment, per unit height. A series of airplane penetrations of relatively small cumulus clouds, conducted during the summer of 1971, was used as a data base for making Stommel entrainment calculations. When a stratification of 23 cloud passes was analyzed, a strong inverse diameter dependence on the mixing rate was evident. For six cloud passes that were described as vigorously growing, well-defined, single isolated towers, the inverse relation was even stronger, and could be expressed by E=0.3/R, where E is the entrainment rate and R the radius; the expression has a correlation coefficient of 0.85.

There was a strong indication that the cumulus clouds studied were best described as the end result of an evolution of a series of starting plumes, rather than as purely plume or bubble elements. Failure to find a primary cloud core beneath the main cloud cap, the evaluation of the entrainment parameter value as between bubble and plume values, and evidence of thermal-induced self-modification of the environment suggested the mixed thermal-plume nature of the cumulus clouds under study.

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Randall R. Bensch and John McCarthy

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The low-level airflow and thermodynamic features of an Oklahoma hailstorm are explored using single-Doppler radar data and research aircraft measurements. Cloud structures at the base of the hailstorm are matched with the airflow in that part of the thunderstorm. A distinct discontinuity in the thermodynamic properties of the air reveals the existence of an outflow boundary in the form of a weak gust front. The nature of the airflow in the area of the gust front indicates that much of the inflow air is ascending over the gust frontal surface as it enters the storm updrafts.

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Peter H. Hildebrand and John McCarthy

A workshop was held at the National Center for Atmospheric Research (NCAR) during February of 1982 to consider the scientific needs for research aircraft in the next decade and the impacts of these needs upon the fleet of aircraft that the Research Aviation Facility (RAF) supports for the atmospheric sciences research community. The workshop was attended by a group of atmospheric scientists who represented the major research interests supported by RAF. The attendees discussed scientific priorities for research in the next 10 years, the types of new instrumentation expected within the next decade, and the operational requirements and aircraft fleet that would be required to serve these scientific goals.

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Diane E. Ziegler and John McCarthy

Instrumented research aircraft data quality during Project SESAME ‘79 is examined in a series of tower fly-bys designed to compare temperature and static pressure measurements with reference values obtained from sensors located on the towers. Aircraft studied included an NCAR Queen Air and Sabreliner, and the South Dakota T-28. Measurements indicate that the quality of data was within acceptable limits. A discussion of data quality assessment philosophy is given, along with specific means of identifying real and potential sources of error.

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Steven E. Koch and John McCarthy

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Data from the National Severe Storms Laboratory surface mesonetwork are objectively analyzed to give insight into processes that contributed to the development of three tornadic mesoconvective systems near the 8 June 1974 Oklahoma dryline. Storm cells constituting each of the systems form over recurring zones of convergence within 20 km of the dryline. Different mechanisms appear to force the individual convergence zones.

Storms of the first system appear simultaneously only after the establishment of a pressure trough just cast of a zone of convergence 15 km east of the dryline. The convergence zone intensifies and progresses eastward with the storms; meanwhile, a second convergence zone appears at the dryline in response to apparent storm-induced pressure systems trailing the storms. The fact that deep convection did not occur over the second zone is attributed to static stabilization caused by mesoscale unsaturated downdrafts in the upper troposphere. Storms of the second system develop in a consecutive manner over a third set of convergence anomalies that originally appeared at the dryline and subsequently propagated northeastward. These propagating disturbances have gravity wave characteristics. Formation of the third system, a solid squall line, is related to a frontogenetic circulation about a progressing cold front as it encountered the abundant moisture present at the stalled dryline.

It is concluded that precursor conditions to severe convective occurrences can be determined from surface mesoscale analysis and, moreover, provide considerable insight into mechanisms that produce low-level convergence.

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John McCarthy and Steven E. Koch

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A study is made of the 8 June 1974 Oklahoma dryline and tornado outbreak case, using data synthesis 1) to fit existing concepts on dryline structure and behavior to this case, and 2) to identify processes contributing to moisture convergence along the dryline. The dryline undergoes a major transformation in structure (from sloped to slopeless) during the day, as implied from mesoscale (10–100 km) and subsynoptic scale (100–1000 km) analysis of virtual potential temperature fields. Mesoscale examination of dryline movement reveals the presence of wavelike perturbations which propagate along the dryline, irregardless of its slope, and contribute more to its eastward progression than does the downward slope of the terrain.

All but one of 22 tornadoes reported in Oklahoma on this date were associated with thunderstorms that formed within a subsynoptic moisture convergence region at the dryline in central Oklahoma. Results indicate a downward transport of southwesterly momentum through a well-developed mixed-layer west of the dryline and isallobaric effects at the dryline contributed to the buildup of convergence.

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