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Author: Alan R. Bohne
Publisher:
ISBN:
Category : Atmospheric turbulence
Languages : en
Pages : 68
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Book Description
Theoretical investigations are undertaken to relate intensity of turbulent air motion to Doppler radar spectrum mean and variance in precipitation environments. Examples of theoretical radar derived turbulence power density spectra and total precipitation motion variance show that effects due to imperfect particle response are significant for turbulence scale lengths less than 250 m. Doppler spectrum variance and estimated eddy dissipation rate (epsilon) are found strongly dependent upon precipitation environment for ranges less than about 20 km, and for cases where the turbulence outer scale length (lambda) is less than 0.5 km. They are also found to be essentially independent of lambda when the maximum pulse volume dimension is less than 1/2 lambda, and independent of range but strongly dependent on lambda at ranges where the maximum pulse volume dimension is greater than lambda. Estimation of epsilon by radar is shown to be unreliable until a method of remotely determining lambda is found. Nevertheless, classification of turbulence severity (index = cube root of epsilon is possible with only a reasonable guess of lambda. Analyses of aircraft/gust velocity data indicate that thunderstorm turbulence is localized into discrete patches, and that such localization must be accounted for when aircraft gust velocity data undergo power spectrum analysis.
Author: Alan R. Bohne
Publisher:
ISBN:
Category : Atmospheric turbulence
Languages : en
Pages : 68
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Book Description
Theoretical investigations are undertaken to relate intensity of turbulent air motion to Doppler radar spectrum mean and variance in precipitation environments. Examples of theoretical radar derived turbulence power density spectra and total precipitation motion variance show that effects due to imperfect particle response are significant for turbulence scale lengths less than 250 m. Doppler spectrum variance and estimated eddy dissipation rate (epsilon) are found strongly dependent upon precipitation environment for ranges less than about 20 km, and for cases where the turbulence outer scale length (lambda) is less than 0.5 km. They are also found to be essentially independent of lambda when the maximum pulse volume dimension is less than 1/2 lambda, and independent of range but strongly dependent on lambda at ranges where the maximum pulse volume dimension is greater than lambda. Estimation of epsilon by radar is shown to be unreliable until a method of remotely determining lambda is found. Nevertheless, classification of turbulence severity (index = cube root of epsilon is possible with only a reasonable guess of lambda. Analyses of aircraft/gust velocity data indicate that thunderstorm turbulence is localized into discrete patches, and that such localization must be accounted for when aircraft gust velocity data undergo power spectrum analysis.
Author: Alan R. Bohne
Publisher:
ISBN:
Category : Atmospheric turbulence
Languages : en
Pages : 0
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Book Description
Theoretical investigations are undertaken to relate intensity of turbulent air motion to Doppler radar spectrum mean and variance in precipitation environments. Examples of theoretical radar derived turbulence power density spectra and total precipitation motion variance show that effects due to imperfect particle response are significant for turbulence scale lengths less than 250 m. Doppler spectrum variance and estimated eddy dissipation rate (epsilon) are found strongly dependent upon precipitation environment for ranges less than about 20 km, and for cases where the turbulence outer scale length (lambda) is less than 0.5 km. They are also found to be essentially independent of lambda when the maximum pulse volume dimension is less than 1/2 lambda, and independent of range but strongly dependent on lambda at ranges where the maximum pulse volume dimension is greater than lambda. Estimation of epsilon by radar is shown to be unreliable until a method of remotely determining lambda is found. Nevertheless, classification of turbulence severity (index = cube root of epsilon is possible with only a reasonable guess of lambda. Analyses of aircraft/gust velocity data indicate that thunderstorm turbulence is localized into discrete patches, and that such localization must be accounted for when aircraft gust velocity data undergo power spectrum analysis.
Author: Alan R. Bohne
Publisher:
ISBN:
Category : Atmospheric turbulence
Languages : en
Pages : 68
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Book Description
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 28
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Book Description
A thunderstorm turbulence detection test bed was developed at the Federal Aviation Administration (FAA) Technical Center by the Massachusetts Institute of Technology, Lincoln Laboratory. This consists of a system to measure and process Doppler radar parameters, and an FAA aircraft instrumented to measure turbulence concurrently with the radar observations. The test bed is being used to investigate the relationship between radar-and aircraft-measured turbulence. Radar measurements of the Doppler spectrum width and aircraft measurements of airspeed fluctuations and center-of-gravity normal accelerations were converted to the cube root of epsilon (cube root of the turbulence dissipation factor) for comparison. Several data collections were made during the summer of 1980. Results of data analysis showed that the major turbulence sequences experienced by the aircraft were essentially reflected by the radar. However, Linear correlation coefficients between radar and aircraft the the cube root of epsilon were only about 0.5. The low correlations are considered to be due to differences in response to turbulence by the two measuring systems, deficiencies in the radar processing, and radar data interpolation errors between the 80-second radar scans. In a more practical analysis, radar-measured turbulence, classified into ranges of light, moderate, and severe turbulence, showed a potentially useful relationship to aircraft turbulence. The predictive value was enhanced by consideration of radar reflectivity factor as a screening variable.
Author: Robert K. Crane
Publisher:
ISBN:
Category :
Languages : en
Pages : 60
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Book Description
A procedure was developed to detect hazardous regions within thunderstorms using weather radar data. The procedure is based upon the hypothesis that convective turbulence occurs within 2-3 km of relative radar reflectivity maxima (cells). The hypothesis was tested using a limited set of simultaneous aircraft radar data. Good agreement was found between the observed regions of convective turbulence and the cell locations determined by radar. The viability of the hazard detection hypothesis as a basis for automatic warning and forecast depends upon the reliability of the cell detection and tracking algorithms. Analysis of precision radar data revealed that the cells are small in area extent, have a detection probability in excess of 0.9 using multiple radar scans, and are readily tracked for periods between 10 and 20 minutes. The characteristics of radar systems for acquiring data to support cell detection, are discussed. The role of Doppler spectral data is explored, and it is found that practical limitations on radar beamwidth hamper direct observation of turbulence on the scale size hazardous to aircraft. (Author).
Author: United States. Air Force. Wright Air Development Division
Publisher:
ISBN:
Category :
Languages : en
Pages : 60
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Book Description
Author: R. K. Crane
Publisher:
ISBN:
Category : Doppler radar
Languages : en
Pages : 139
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Book Description
This report documents the development and testing of a viable aircraft hazard detection scheme which operates as well employing conventional radar data as it does employing Doppler radar data. The detection scheme was evaluated using aircraft penetrations into the most turbulent regions of hail storms. These regions are of interest when verifying that turbulence can be detected but are not optimum for evaluating the detection technique under realistic operating conditions. If, in the latter case, higher false alarm rates can be expected, more development will be necessary to utilize more effectively the available information before the hazard detection procedure can be incorporated into an air traffic control environment. The recommended program to develop the automatic hazard detection system include: refine the cell and cluster detection algorithms to reduce the effect of the statistical uncertainties in the estimation of velocity perturbations; refine the cell significance algorithms using cell age location in the development pattern, apparent vertical transport of horizontal momentum and similar parameters to provide and indication of the intensity of the turbulence; and develop a graphical display of the cell, cluster and contour data that can be provided both to meteorologists for the development of short range forecasts.
Author: David Atlas
Publisher:
ISBN:
Category : Radar
Languages : en
Pages : 16
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Book Description
Author: Pravas Mahapatra
Publisher: IET
ISBN: 9780852969373
Category : Science
Languages : en
Pages : 484
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Book Description
Focusing on radar-based surveillance, this book has been written to provide a comprehensive introduction to the science, sensors and systems that form modern aviation weather surveillance systems.
Author: J. K. Thompson
Publisher:
ISBN:
Category : Radar meteorology
Languages : en
Pages : 16
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Book Description
An analysis of data obtained from the 1947 Ohio operations of the U.S. Weather Bureau thunderstorm project indicates that the magnitude and intensity of gusts encountered in air-mass and frontal thunderstorms may be considerably reduced by avoiding storm areas indicated by ground radar of a 10-centimeter wavelength. The analysis also indicates that the ground radar used becomes more effective for turbulence avoidance as the flight altitude is increased up to 25,000 feet and is least effective at 6,000 feet.
