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- Author or Editor: Francis J. Merceret x
- Journal of Applied Meteorology and Climatology x
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Abstract
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.
Abstract
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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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.
Abstract
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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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.
Abstract
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.
Abstract
The statistical distribution of the magnitude of the vector wind change over 0.25-, 0.5-, 1-, and 2-h periods based on central Florida data from November 1999 through August 2001 is presented. The distributions of the 2-h u and υ wind-component changes are also presented for comparison. The wind changes at altitudes from 500 to 3000 m were measured using the Eastern Range network of five 915-MHz Doppler radar wind profilers. Quality-controlled profiles were produced every 15 min for up to 60 gates, each representing 101 m in altitude over the range from 130 to 6089 m. Five levels, each constituting three consecutive gates, were selected for analysis because of their significance to aerodynamic loads during the space-shuttle-ascent roll maneuver. The distribution of the magnitude of the vector wind change is found to be lognormal, consistent with earlier work in the midtroposphere. The parameters of the distribution vary with time lag, season, and altitude. The component wind changes are symmetrically distributed, with near-zero means, but the kurtosis coefficient is larger than that of a Gaussian distribution.
Abstract
The statistical distribution of the magnitude of the vector wind change over 0.25-, 0.5-, 1-, and 2-h periods based on central Florida data from November 1999 through August 2001 is presented. The distributions of the 2-h u and υ wind-component changes are also presented for comparison. The wind changes at altitudes from 500 to 3000 m were measured using the Eastern Range network of five 915-MHz Doppler radar wind profilers. Quality-controlled profiles were produced every 15 min for up to 60 gates, each representing 101 m in altitude over the range from 130 to 6089 m. Five levels, each constituting three consecutive gates, were selected for analysis because of their significance to aerodynamic loads during the space-shuttle-ascent roll maneuver. The distribution of the magnitude of the vector wind change is found to be lognormal, consistent with earlier work in the midtroposphere. The parameters of the distribution vary with time lag, season, and altitude. The component wind changes are symmetrically distributed, with near-zero means, but the kurtosis coefficient is larger than that of a Gaussian distribution.
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Velocity spectra obtained from a hot-film anemometer and a gust probe on board the NOAA DC-6 (39C) during a research mission into Hurricane Eloise 1975 are compared at common frequencies. The spectra compare reasonably well, thus justifying some confidence in measurements acquired from the individual instruments.
Abstract
Velocity spectra obtained from a hot-film anemometer and a gust probe on board the NOAA DC-6 (39C) during a research mission into Hurricane Eloise 1975 are compared at common frequencies. The spectra compare reasonably well, thus justifying some confidence in measurements acquired from the individual instruments.
Abstract
The National Hurricane Research Laboratory has developed and flight tested a new airborne liquid water meter for cloud physics measurements. The sensor is maintained at constant temperature rather than at constant current, and the operating temperature is held well below the in-situ boiling point. These two changes from previous instruments, such as the popular Johnson-Williams meter, permit accurate response over a wider range of drop sizes and finer spatial resolution. Flight tests on NOAA Research Flight Facility aircraft showed the new unit to be more sensitive, more stable, and more rapidly responding than the J-W and Levine instruments presently on board.
Abstract
The National Hurricane Research Laboratory has developed and flight tested a new airborne liquid water meter for cloud physics measurements. The sensor is maintained at constant temperature rather than at constant current, and the operating temperature is held well below the in-situ boiling point. These two changes from previous instruments, such as the popular Johnson-Williams meter, permit accurate response over a wider range of drop sizes and finer spatial resolution. Flight tests on NOAA Research Flight Facility aircraft showed the new unit to be more sensitive, more stable, and more rapidly responding than the J-W and Levine instruments presently on board.
