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Wayne R. Sand

Abstract

This study relates data gathered during the penetration of hailstorms between 4.9 and 6.7 km MSL by an armored T-28 aircraft to detailed radar data of the hailstorms penetrated. These data recorded by the T-28 data system are combined with observations made by the author while piloting the T-28 through hailstorms. The radar data from the National Hail Research Experiment CPR-2 are specially prepared as Constant Altitude Plan Position Indicator (CAPPI) displays and vertical sections along the aircraft track for comparison with the data gathered by the aircraft system and pilot's observations.

The results indicate that significant updrafts are frequently found well ahead of the high radar reflectivity zones. The updrafts are found to be relatively smooth while the high radar reflectivity zones are found to be very turbulent. Significant quantities of supercooled liquid water are found in the updraft regions. Significant airframe icing is found in the strong updrafts with the most severe icing along the edges of the updrafts. The high reflectivity zones are found to contain almost exclusively ice. Hail is more frequently found in the area of strong reflectivity but small hail is found outside the 40 dBZ contour.

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August H. Auer Jr. and Wayne Sand

Abstract

During the summers of 1964 and 1965, the Colorado State University Hail Suppression Research Project made updraft measurements beneath the base of cumulus and cumulonimbus clouds in northeastern Colorado. Analysis of the data reveals that the average maximum updraft appears to be located in the right-front quadrant of the radar echo. For heavily precipitating cumulonimbus clouds, this average maximum updraft exceeded 6 m sec−1. There is also a proportional increase in the magnitude of the updrafts relative to the amount of precipitation falling from the cloud. Average updrafts of all measurements on moderately and heavily precipitating cumulonimbi were 2.5 m sec−1 and 3.8 m sec−1, respectively. Much stronger updrafts can be expected on the common boundaries of converging cumulonimbus clouds. Updrafts appear to exhibit laminar flow characteristics with turbulence found upon entering and leaving the strong updraft regions. Smooth steady updrafts may exist for an hour or more, indicating that the more intense thunderstorms possess a steady-state phase. During this steady-state phase, areas of scud cloud were normally found in the areas of strongest updrafts. From a limited study, no apparent correlations were found between maximum updrafts observed and certain environmental parameters.

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Thomas G. Kyle, Wayne R. Sand, and D. J. Musil

Abstract

Twelve thunderstorm updrafts were analyzed in detail and a composite average derived. The updrafts were normalized in width and maximum intensity so they could he compared on the same scale. The composite average was compared with the Gaussian and the polynomial curves frequently used by modelers to describe some updraft characteristics. The composite average was also compared with an axially symmetric jet model. Favorable results were found in all three cases with good results in the case of the axially symmetric jet model. The relationship between updraft width and maximum vertical velocity is almost linear for smaller updrafts, but deviates from linear for the wider updrafts. It was found that a sensible temperature excess exists in the updrafts at the altitude where measurements were taken (5.0 to 6.2 km).

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Wayne R. Sand, William A. Cooper, Marcia K. Politovich, and Donald L. Veal

Abstract

The characteristics of clouds which have led to airframe icing on an instrumented Beechcraft Super King Air are summarized. The icing encounters occurred at altitudes from 0–8000 m MSL, in summer and winter, in stratiform and cumuliform clouds, and at temperatures from 0 to −30°C. The characteristics of icing encounters in different areas and in different seasons are compared. The fraction of measurements exceeding various threshold values of liquid water content, average liquid water content over a given distance, volume-median droplet diameter, droplet concentration, ice crystal concentration, and potential ice accumulation are given. The effects of these cloud characteristics on aircraft performance were measured by comparing the rate of climb of the aircraft with ice to the rate of climb for the clean aircraft under the same conditions. Most icing encounters led to a reduction in the rate of climb that increased linearly with the path integral of the supercooled liquid water content. The volume-median diameter had little correlation with changes in performance. Some potentially hazardous conditions, which decreased the rate of climb capability of this aircraft by 7–9 m s−1, are also discussed.

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Roy Rasmussen, Marcia Politovich, John Marwitz, Wayne Sand, John McGinley, John Smart, Roger Pielke, Steve Rutledge, Doug Wesley, Greg Stossmeister, Ben Bernstein, Kim Elmore, Nick Powell, Ed Westwater, B. Boba Stankov, and Don Burrows

Field studies in support of the Winter Icing and Storms Project (WISP) were conducted in the Colorado Front Range area from 1 February to 31 March 1990 (WISP90) and from 15 January to 5 April 1991 (WISP91). The main goals of the project are to study the processes leading to the formation and depletion of supercooled liquid water in winter storms and to improve forecasts of aircraft icing. During the two field seasons, 2 research aircraft, 4 Doppler radars, 49 Mesonet stations, 7 CLASS sounding systems, 3 microwave radiometers, and a number of other facilities were deployed in the Front Range area. A comprehensive dataset was obtained on 8 anticyclonic storms, 16 cyclonic storms, and 9 frontal passages.

This paper describes the objectives of the experiment, the facilities employed, the goals and results of a forecasting exercise, and applied research aspects of WISP. Research highlights are presented for several studies under way to illustrate the types of analysis being pursued. The examples chosen include topics on anticyclonic upslope storms, heavy snowfall, large droplets, shallow cold fronts, ice crystal formation and evolution, and numerical model performance.

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