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Abstract
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.
Abstract
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.
Abstract
Airborne foil impactor measurements in Atlantic Hurricane Ginger (1971) show a raindrop size spectrum which is well represented by an exponential relation of the Marshall-Palmer type. No difference was observed between the spectral characteristics of the rainbands and those of the eyewall, but some dependence of the slope-rainfall rate relation on rainwater content was noted.
Abstract
Airborne foil impactor measurements in Atlantic Hurricane Ginger (1971) show a raindrop size spectrum which is well represented by an exponential relation of the Marshall-Palmer type. No difference was observed between the spectral characteristics of the rainbands and those of the eyewall, but some dependence of the slope-rainfall rate relation on rainwater content was noted.
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.
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.
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.
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-, 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
Fluctuations of temperature, horizontal velocity and vertical velocity were measured at scales from 50 m to 5 cm with airborne hot-film anemometers at altitudes of 150 and 900 m in clear air, and in subcloud air with and without rainfall. Although nearly inertial subrange spectral behavior was often present at scales smaller than 20 m, significant regions existed where inertial behavior did not appear until scales smaller than a few meters were reached. The energy dissipation rate varied intermittently by two orders of magnitude or more over scales ranging from 100 m to several kilometers. High Reynolds number intermittency effects were observed in the temperature spectra. In an anomalous region, here called a “dry hole,” the microstructure of the velocity and temperature fields was radically different from that of the surrounding environment. Spectral intensity decreased by an order of magnitude and spectral shape was definitely non-inertial. Despite these changes, the probability distribution of the energy dissipation seemed to remain close to log-normal as did the distribution in the surroundings.
Abstract
Fluctuations of temperature, horizontal velocity and vertical velocity were measured at scales from 50 m to 5 cm with airborne hot-film anemometers at altitudes of 150 and 900 m in clear air, and in subcloud air with and without rainfall. Although nearly inertial subrange spectral behavior was often present at scales smaller than 20 m, significant regions existed where inertial behavior did not appear until scales smaller than a few meters were reached. The energy dissipation rate varied intermittently by two orders of magnitude or more over scales ranging from 100 m to several kilometers. High Reynolds number intermittency effects were observed in the temperature spectra. In an anomalous region, here called a “dry hole,” the microstructure of the velocity and temperature fields was radically different from that of the surrounding environment. Spectral intensity decreased by an order of magnitude and spectral shape was definitely non-inertial. Despite these changes, the probability distribution of the energy dissipation seemed to remain close to log-normal as did the distribution in the surroundings.
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.
Abstract
An automated cloud-edge detection algorithm was developed and extensively tested. The algorithm uses in situ cloud physics data measured by a research aircraft coupled with ground-based weather radar measurements to determine whether the aircraft is in or out of cloud. Cloud edges are determined when the in/out state changes, subject to a hysteresis constraint. The hysteresis constraint prevents isolated transient cloud puffs or data dropouts from being identified as cloud boundaries. The algorithm was verified by detailed manual examination of the dataset in comparison to the results from application of the automated algorithm.
Abstract
An automated cloud-edge detection algorithm was developed and extensively tested. The algorithm uses in situ cloud physics data measured by a research aircraft coupled with ground-based weather radar measurements to determine whether the aircraft is in or out of cloud. Cloud edges are determined when the in/out state changes, subject to a hysteresis constraint. The hysteresis constraint prevents isolated transient cloud puffs or data dropouts from being identified as cloud boundaries. The algorithm was verified by detailed manual examination of the dataset in comparison to the results from application of the automated algorithm.
Abstract
Electric-field measurements made in and near clouds during two airborne field programs are presented. Aircraft equipped with multiple electric-field mills and cloud physics sensors were flown near active convection and into thunderstorm anvil and debris clouds. The magnitude of the electric field was measured as a function of position with respect to the cloud edge to provide an observational basis for modifications to the lightning launch commit criteria (LLCC) used by the U.S. space program. These LLCC are used to reduce the risk that an ascending launch vehicle will trigger a lightning strike that could cause the loss of the mission or vehicle. Even with fields of tens of kV m−1 inside electrically active convective clouds, the fields external to these clouds decay to less than 3 kV m−1 within 15 km of cloud edge. Fields that exceed 3 kV m−1 were not found external to anvil and debris clouds.
Abstract
Electric-field measurements made in and near clouds during two airborne field programs are presented. Aircraft equipped with multiple electric-field mills and cloud physics sensors were flown near active convection and into thunderstorm anvil and debris clouds. The magnitude of the electric field was measured as a function of position with respect to the cloud edge to provide an observational basis for modifications to the lightning launch commit criteria (LLCC) used by the U.S. space program. These LLCC are used to reduce the risk that an ascending launch vehicle will trigger a lightning strike that could cause the loss of the mission or vehicle. Even with fields of tens of kV m−1 inside electrically active convective clouds, the fields external to these clouds decay to less than 3 kV m−1 within 15 km of cloud edge. Fields that exceed 3 kV m−1 were not found external to anvil and debris clouds.
Abstract
The accuracy and availability of data from a network of 915-MHz boundary layer wind profilers operated by the U.S. Air Force on the Eastern Range are assessed using an automated quality control (QC) algorithm developed by the authors. The accuracy and reliability of the automated algorithm is assessed using the results of an extensive manual examination of the same data used for the assessment of the instruments. The details of the automated algorithm and the manual screening process are provided.
Data were collected over a 647-day period from five profilers configured to produce one profile every 15 min, resulting in about 200 000 measurements. The results indicate that the instruments provide reliable, accurate data except when maintenance problems or heavy precipitation are present. Precipitation affected as much as 25% of the measurements in the dataset. The automated QC algorithm proved extremely effective in identifying unacceptable data. Only 0.03% of the data passing automated QC were identified as bad by manual review. While some valid data were identified as bad, the automated algorithm appears to provide exceptional performance for use in automated operational assimilation of boundary profiler data for model initialization and data visualization.
Abstract
The accuracy and availability of data from a network of 915-MHz boundary layer wind profilers operated by the U.S. Air Force on the Eastern Range are assessed using an automated quality control (QC) algorithm developed by the authors. The accuracy and reliability of the automated algorithm is assessed using the results of an extensive manual examination of the same data used for the assessment of the instruments. The details of the automated algorithm and the manual screening process are provided.
Data were collected over a 647-day period from five profilers configured to produce one profile every 15 min, resulting in about 200 000 measurements. The results indicate that the instruments provide reliable, accurate data except when maintenance problems or heavy precipitation are present. Precipitation affected as much as 25% of the measurements in the dataset. The automated QC algorithm proved extremely effective in identifying unacceptable data. Only 0.03% of the data passing automated QC were identified as bad by manual review. While some valid data were identified as bad, the automated algorithm appears to provide exceptional performance for use in automated operational assimilation of boundary profiler data for model initialization and data visualization.
