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K. S. Gage

Abstract

The observational evidence for k −5/3 law behavior in the atmospheric kinetic energy spectrum is reviewed. This evidence includes the results of atmospheric wind variability studies and the observed scale dependence of atmospheric dispersion. It is concluded that k −5/3 law behavior for time and space scales greater than those that can be three-dimensionally isotropic is probably a manifestation of the two-dimensional reverse-cascading energy inertial range.

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K. S. Gage and J. L. Green

Abstract

A technique is presented which enables an estimate of the atmospheric temperature profile from atmospheric stability measurements made by vertically looking VHF radars. The determination of the tropopause height leads to a most probable temperature at the tropopause for a given station and season. Measurements of atmospheric stability permit the temperature profile to be constructed from the tropopause upward. The profile can be continued to the surface simply by assuming a uniform lapse rate between the surface and the tropopause. We illustrate the technique with observations from the Sunset VHF radar located near Boulder, Colorado.

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G. D. Nastrom and K. S. Gage

Abstract

A statistical analysis of vertical air motion has been performed for data taken in the 3-20 km altitude range by the Poker Flat MST radar during the period September 1979-January 1982. The variability of vertical velocities is analyzed as a function of season, time of day and synoptic weather conditions. The overall frequency distribution of vertical velocities can be approximated by the sum of two normal distributions: one with variance about 10 times larger than the other. The variability of vertical velocity at all levels is found to correlate most closely with horizontal wind speed at 700 mb on a day-to-day basis. The total variance is larger in summer than in winter at all hours of the day and especially during the afternoon hours. A statistically significant diurnal variation of vertical motions is found during summer with amplitude in the midtroposphere near 2 cm s−1. Interpreting the vertical wind variability as a manifestation of vertically propagating waves, we compare the intensity here with earlier studies of turbulence variations. These comparisons show a plausible link between the intensity of turbulence at jet stream altitudes and the production of waves near the surface.

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K. S. Gage and W. L. Clark

Abstract

Sensitive Doppler radars have recently been developed that can routinely observe wind in the free atmosphere up to stratospheric heights. One of these, the 40 MHz Sunset radar, was used to observe the three-dimensional wind field associated with a polar front jet stream near Boulder on 15–16 April 1976. The south wind, which was the strongest component (of the wind), was sampled about once a minute for over 14 h over altitudes ranging from 5 to 13 km MSL at 1 km intervals. The temporal variability of the south wind at each height is presented along with the average variability for all heights over the 14 h period. The average variability closely follows a 1/3 power law at least out to 4 h lag time. Since the 1/3 power law is consistent with inertial range turbulence theory, and since turbulence cannot possibly be three-dimensionally isotropic on these scales, it is suggested that the observations might be interpreted as evidence for a two-dimensional, −5/3 inertial range.

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K. S. Gage and B. B. Balsley

In the past few years, sensitive Doppler radars have been used to probe the clear atmosphere from the boundary layer up to stratospheric altitudes. Routine Doppler radar observations are now attainable over a wide range of frequencies at virtually all altitudes in this height range. Although a number of these systems operate at UHF (300–3000 MHz), sensitive Doppler radars have recently been developed that operate at VHF (30–300 MHz). These new systems employ large, inexpensive antennas constructed of phased arrays of dipole elements. This paper surveys recent developments in the use of both VHF and UHF Doppler radars for probing the clear atmosphere and presents design considerations for new radar systems.

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K. S. Gage and W. H. Jasperson

Abstract

The results of an analysis of the variability of the atmospheric wind field below 5 km is presented for a limited sample of high-resolution wind profiles. The wind was measured by tracking balloons utilizing the Control Data METRAC positioning system installed at St. Cloud, Minnesota. Balloons were launched sequentially 30 min apart for a period of 7 h during the afternoon of 31 March 1976. The wind, averaged over 100 m intervals, was analyzed for temporal variability for lags τ up to 240 min. Temporal variability of the wind at individual altitudes on this day did not support any unique power law. However, when the variability statistics at all levels were combined the averaged variability was consistent with the τ power law.

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K. S. Gage and G. D. Nastrom

Abstract

This paper contains a theoretical interpretation of the wavenumber spectra of wind and temperature obtained from an analysis of data from over 6900 flights during the Global Atmospheric Sampling Program. The spectra cover scales ranging from 3 km to nearly 10 000 km. Major features of the observed spectra are found to be in general agreement with expectations from theoretical models of quasi two-dimensional turbulence. Kinetic energy spectra are remarkably universal, and temperature spectra adjust as required for equipartition between the two horizontal components of kinetic energy and potential energy. The observed wavenumber spectra agree closely in magnitude and shape with frequency spectra obtained independently, and this agreement supports the validity of the Taylor transformation; conversely, because the Taylor transformation works, it suggests the disturbances are turbulence rather than dispersive waves.

The GASP spectra are compared in a general way with recently proposed internal wave spectral models which have been advanced to account for the mesoscale spectrum of atmospheric motions. However, these model spectra are scaled to the frequency spectrum of horizontal velocities which must be Doppler shifted if they are indeed due to waves. It is argued that these spectral models are inconsistent with the non-Doppler shifted spectrum of waves needed to compare with the aircraft wavenumber spectrum presented here. We advocate in future studies employing a non-Doppler shifted internal wave model which could be based on the low-wind frequency spectrum of vertical motions.

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K. S. Gage and J. L. Green

Abstract

The relationship between the magnitude of backscattered power observed at vertical incidence by a VHF radar is related to atmospheric stability in accordance with the recently developed Fresnel scattering model. Utilizing the Fresnel scattering model, tropopause height can be determined objectively from the observed vertical profile of backscattered power. The method is demonstrated with observations from the Sunset VHF radar. A preliminary error analysis shows that the technique is potentially capable of determining tropopause heights within about 300 m of the tropopause heights determined from radiosonde soundings.

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G. D. Nastrom and K. S. Gage

Abstract

Atmospheric wavenumber spectra of wind and temperature have been obtained from over 6000 commercial aircraft flights made during the Global Atmospheric Sampling Program. Temperature and velocity spectra are approximately the same shape over the range of wavelengths 2.6 to 104 km. Spectral slopes are close to −5/3 in the range 2.6 to 300–400 km and are independent of latitude, season and location in the troposphere or stratosphere. At larger scales, spectral slopes steepen considerably and approach −3. It is found that spectral amplitudes of wind and temperature have log-normal frequency distributions Spectral amplitudes in the range 2.6 to 400 km vary somewhat with latitude, season and location in the troposphere or stratosphere. Temperature spectral magnitude varies more than velocity spectral magnitude, and is largest in the stratosphere and winter troposphere and smallest in the tropical troposphere. Meridional velocity spectral amplitude varies only slightly from the troposphere to the stratosphere but doe show a significant variation with latitude being smallest in the tropics. Zonal velocity spectral amplitude varies with latitude considerably less than the meridional velocity spectral amplitude. The seasonal variation of spectral amplitude is about the same at meridional for meridional and zonal velocities, with smallest values observed during summer.

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B. B. Balsley and K. S. Gage

The application of clear-air radars to operational wind profiling is considered. Several alternative techniques for determining atmospheric winds from radars are surveyed and, in light of the current interest in operational applications, the current status of the techniques is summarized and the need for more research and development knowledge before defining any final system configuration stressed. Finally, some possibilities for portable automated systems of the future are suggested.

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