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Francis J. Merceret

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Microscale horizontal velocity fluctuation measurements in Hurricane Caroline (1975) show that except in the eye, turbulent energy dissipation does not vary systematically with wind speed or altitude. Inertial subrange-shaped spectra are found below cloud base and slightly above it. At higher altitudes, some deviation from that shape may occur. The amount of energy dissipated within the body of the storm is slightly larger than that dissipated at the surface in accord with earlier estimates by residuals. The dissipation is highly intermittent with a log-normal cumulative probability distribution.

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Francis J. Merceret

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Francis J. Merceret

Abstract

Conventional techniques for determining which features of hurricanes govern their distribution of kinetic energy dissipation rate (ε) fail to yield significant correlations because of the high random variability of ε. Spectral analysis of the time series of the logarithm of ε, however, shows several distinct features which may be tentatively identified with specific aspects of the storm circulation. In particular, cloud-scale, cloud-cluster-scale and rainband-scale peaks occur in the power spectrum of log10ε.

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Francis J. Merceret

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Francis J. Merceret

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Francis J. Merceret Jr.

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Francis J. Merceret

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Francis J. Merceret

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The coherence between vertical wind profiles separated by a time lag is measured as a function of vertical scale from Doppler radar wind profiler data. Each profile covers altitudes from 6811 m to 16 261 m and is Fourier transformed over a vertical wavenumber (inverse scale) range from 0 to 3.33 × 10−3 m−1. Time lags between profiles of 0.083, 0.25, 0.5, 1.0, and 2.0 h are used. A correction for instrument noise is derived and is applied to the results. An empirical formula for the coherence as a function of lag and scale is presented and evaluated. The “coherence time” is defined as the value of time lag beyond which the coherence decays below a chosen value at a given scale. A relation between coherence time and vertical scale is derived. This relation provides a measure of the lifetime of wind features in the midtroposphere as a function of their vertical scale for application to space vehicle wind loads.

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Francis J. Merceret

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Extensive flight tests during GATE showed hot-film anemometry to be a useful tool for the airborne measurement of atmospheric turbulence in clear air and in subcloud rain, but not within clouds. Root-mean-square noise values lower than 0.08 ms−1 for velocity and 0.03°C for temperature were obtained over the scale range of 50 m to 4 cm at altitudes from 16 to 2000 m. Spectra of U′, W′ and θ were obtained over the same range with roughly 1 dB accuracy. Dissipation rates could be determined to within ±30%. Cross-component contamination was too large to permit reliable cross spectra to be obtained. It is suggested that an upgraded system could significantly reduce such contamination and improve the overall accuracy and signal-to-noise ratio.

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Francis J. Merceret

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The statistical distribution of the magnitude of the vector wind change over 0.25-, 1-, 2-, and 4-h periods based on data from October 1995 through March 1996 over central Florida is presented. The wind changes at altitudes from 6 to 17 km were measured using the Kennedy Space Center 50-MHz Doppler radar wind profiler. Quality controlled profiles were produced every 5 min for 112 gates, each representing 150 m in altitude. Gates 28 through 100 were selected for analysis because of their significance to ascending space launch vehicles. The distribution was found to be lognormal. The parameters of the lognormal distribution depend systematically on the time interval. This dependence is consistent with the behavior of structure functions in the f 5/3 spectral regime. There is a small difference between the 1995 data and the 1996 data, which may represent a weak seasonal effect.

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