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David E. Waco

Abstract

Chi-square and Kolmogorov-Smirnov statistical tests are applied to distributions of wind and temperature variables measured in conjunction with Project HICAT U-2 flights from worldwide locations. A distinction is made between turbulent and nonturbulent situations. Turbulence is found to occur in layers that exhibit either large decreases in temperature with height or strong vertical wind shears. Turbulent outnumbered nonturbulent cases nearly 4 to 1 for Richardson numbers <15.

A high correlation exists between the magnitudes of in-flight measured temperature variations and the sum of the gust velocity components. Examples of time histories show that the high correlation does not reflect complexities of the temperature change for individual turbulence encounters.

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David E. Waco

Abstract

A specially instrumented NASA B-57B Canberra, capable of measuring turbulence velocities, winds and temperatures, flew several data runs on 26 March 1975 at 13 km altitude, east of the Sierra Nevada mountains of California. An area of light to moderate clear air turbulence extended for 120 km and contained zones of more intense turbulence. One zone, 10–20 km wide, occurred in a warm region centered over Death Valley. Significant variations of meteorological parameters included a wind shift of 13 m s−1 and 40° in 7 km, temperature changes of 3.5–5°C in 0.02 to 0.12 km, and variations in the mean vertical turbulence velocity of 3–4 m s−1 over distances of 15–25 km. The turbulence apparently originated after atmospheric waves had formed along show interfaces where low-velocity stratospheric air descended into a region of strong winds above Death Valley. The waves were amplified and broke down into turbulence when large vertical shear reduced the Richardson number below the critical value.

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David E. Waco

Abstract

Data obtained from U-2 HICAT flights were used to relate the magnitudes of horizontal temperature changes to flight conditions. The empirical findings can be used in estimating the effectiveness of aircraft-borne sensors which rely on temperature measurements for the remote detection of clear air turbulence.

Gust velocity changes of at least 20 ft sec−1 occurred in all but one of 68 turbulence encounters in which temperature changes were 3C or higher, and in only 13 of 97 cases with changes of less than 1C. Although short-period temperature variations were generally small during smooth flight and increased in magnitude during rougher flight, exceptions were noted. Large horizontal temperature changes were observed during smooth flight in the vicinity of severe turbulence and during occasional flights where the temperature changed appreciably over shallow vertical layers. Small changes were sometimes noted during moderate turbulence when the vertical temperature structure was nearly isothermal.

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DAVID E. WACO

Abstract

Horizontal and vertical temperature variations along with true gust velocity measurements of atmospheric turbulence were obtained above hurricane Beulah (1967) by an instrumented U–2. The U–2 flight was part of the U.S. Air Force High Altitude Clear Air Turbulence program. Pertinent findings include: (1) location of the tropopause just above the cloud tops at 54,000 ft (100 mb) with a temperature of −86°C, 12°C lower than the mean; (2) a vertical temperature rise of 11°C in a few hundred feet just above the tropopause; (3) horizontal temperature changes up to 7°C and smooth flight conditions in the stable layer above the cloud tops; and (4) small temperature fluctuations and generally turbulent conditions at cloud top level.

Aircraft measured winds, although questionable as to their exact directions and speeds, indicated that the flow was weak and anticyclonic near Beulah's top, becoming increasingly anticyclonic above.

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