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Avery, S. K.

Publications and source records attributed to Avery, S. K..

14 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Empirical wind model for the middle and lower atmosphere. Part 2: Local time variations

The HWM90 thermospheric wind model was revised in the lower thermosphere and extended into the mesosphere and lower atmosphere to provide a single analytic model for calculating zonal and meridional wind profiles representative of the climatological average for various geophysical conditions. Local time variations in the mesosphere are derived from rocket soundings, incoherent scatter radar, MF radar, and meteor radar. Low-order spherical harmonics and Fourier series are used to describe these variations as a function of latitude and day of year with cubic spline interpolation in altitude. The model represents a smoothed compromise between the original data sources. Although agreement between various data sources is generally good, some systematic differences are noted. Overall root mean square differences between measured and model tidal components are on the order of 5 to 10 m/s.

Hedin, A. E.↗
NASA NTRS1993

Empirical wind model for the middle and lower atmosphere. Part 1: Local time average

The HWM90 thermospheric wind model was revised in the lower thermosphere and extended into the mesosphere and lower atmosphere to provide a single analytic model for calculating zonal and meridional wind profiles representative of the climatological average for various geophysical conditions. Gradient winds from CIRA-86 plus rocket soundings, incoherent scatter radar, MF radar, and meteor radar provide the data base and are supplemented by previous data driven model summaries. Low-order spherical harmonics and Fourier series are used to describe the major variations throughout the atmosphere including latitude, annual, semiannual, and longitude (stationary wave 1). The model represents a smoothed compromise between the data sources. Although agreement between various data sources is generally good, some systematic differences are noted, particularly near the mesopause. Root mean square differences between data and model are on the order of 15 m/s in the mesosphere and 10 m/s in the stratosphere for zonal wind, and 10 m/s and 4 m/s, respectively, for meridional wind.

Hedin, A. E.↗
NASA NTRS1989

The meteor radar as a tool for upper atmosphere research

Meteor radar provide measurements of the upper mesosphere and lower thermosphere neutral wind field by using the reflection of electromagnetic waves from meteor trails. These radars are relatively inexpensive and provide an excellent means of monitoring the mean winds and tides in the 80 to 100 km region. Recently new techniques were developed to detect meteor echoes from other ground based radar systems operating in the HF/VHF frequency range. The meteor echo information augments the data that are routinely collected by these radars. These new techniques are discussed.

Avery, S. K.↗
NASA NTRS1987

Meteor detection on ST (MST) radars

The ability to detect radar echoes from backscatter due to turbulent irregularities of the radio refractive index in the clear atmosphere has lead to an increasing number of established mesosphere - stratosphere - troposphere (MST or ST) radars. Humidity and temperature variations are responsible for the echo in the troposphere and stratosphere and turbulence acting on electron density gradients provides the echo in the mesosphere. The MST radar and its smaller version, the ST radar, are pulsed Doppler radars operating in the VHF - UHF frequency range. These echoes can be used to determine upper atmosphere winds at little extra cost to the ST radar configuration. In addition, the meteor echoes can supplement mesospheric data from an MST radar. The detection techniques required on the ST radar for delineating meteor echo returns are described.

Avery, S. K.↗
NASA NTRS1985

Data Descriptions and Vertical Structure Plots for Mean, Diurnal, and Semidurnal Components of Eastward and Northward (ordered by Latitude). Mean Winds and Tides over Poker Flat, Alaska (65 Deg N, 147 Deg W), During November 1981

The mean zonal and meridional winds and the amplitude and phase structures for the tidal harmonics for the month of November, 1981 are given. The mean winds are weak westerlies and weak southerlies. The westerlies are approximately 10 ms (-1) lower than those during November 1980 and 1982. The diurnal amplitudes are small in both the zonal and meridional wind components. The diurnal phase structures are characteristic of a propagating wave having a ertical wavelength of approximately 50 km. The semidiurnal tidal harmonic amplitudes are slightly larger than the diurnal amplitudes. However, the phase structures are different for the zonal and meridional components. The meridional phase structure appears evanescent. The zonal phase structure has a phase reversal at 88 km with downward phase progression below that level and upward phase progression above that level. The vertical wavelength is roximately 12 km. This short vertical wavelength occurs during other months of the year but longer wavelengths are more common.

Avery, S. K.↗
NASA NTRS1984

Interpolation problems in meteor radar analysis, part 7.6A

Meteor echoes come from random points in the observation volume, and are irregularly spaced in time. This precludes the use of fast fourier transformations (FFT) techniques on the raw data to give the spectrum of waves that are present. One way around this obstacle is to restrict our interest to a particular class of waves, and fit a corresponding model to the raw data. It is assumed that there is no horizontal variation across the observation volume for tides, but in the vertical this is certainly not the case. If, in addition, we are interested in other types of waves which may be present and whose periods are unknown, then examining the raw line-of-sight velocities does not tell us how to modify the model, since the line-of-sight direction is not fixed. This is the motivation for interpolation. Interpolation takes a temporal series of line-of-sight velocities, and transforms it to a temporal series of wind velocities for each orthogonal direction. The velocities along a given direction can then be examined readily for any waves in addition to tides.

Tetenbaum, D.↗
NASA NTRS1984

Data base management: MSTRAC (keynote paper), part 8

Technical Aspects of MST radars were discussed. The name of the group is MST Radar Coordination (MSTRAC). The geophysical parameters to be included in the sample data tapes were determined. It was suggested that MSTRAC compile a catalog of existing data at each of the facilities. It is found that: (1) there is a community of interested users for MST data; (2) the initial responses from observatories indicates that interest in MSTRAC is not overwhelming, probably because of time involved; and (3) the program needs reassessment.

Avery, S. K.↗
NASA NTRS1984

The transport of nitric oxide by the mean circulation and planetary waves

The effects of planetary waves on atmospheric nitric oxide (NO) concentration were investigated using a time-dependent numerical model. The model is used to calculate planetary wave and zonal mean winds, which in turn are used to calculate mean and perturbation NO distribution. The time-dependent model is used to determine equilibrium NO distributions resulting from time-dependent lower boundary planetary wave forcings. The factors which contribute to the zonal mean NO concentration are examined. NO chemistry is modelled using a simplified source sink approach. Changes in the initial NO distribution which result from the addition of planetary-wave winds are described. Planetary waves are found to induce a wavelike structure in the NO distribution which resembles that derived from observational data. These waves affect the NO concentration through wave-induced changes in the mean meridional circulation and through the NO perturbation induuced by the wave winds themselves.

Jones, G. A.↗
NASA NTRS1983

Meteorological and dynamical requirements for MST radar networks: Waves

Studies of wave motions using the MST radar have concentrated on single station time series analyses of gravity waves and tides. Since these radars collect high time resolution data they have the potential to become a significant tool for mesoscale research. In addition, radars are operated almost continuously unattended and, consequently, data sets are available for analyzing longer period wave motions such as tides and planetary scale waves. Although there is much to learn from single station data, the possibilities of new knowledge from a network of radars is exciting. The scales of wave motions in the atmosphere cover a broad range. Consequently the choice of a radar network depends to a large extent on the types of wave motions that are studied. There are many outstanding research problems that would benefit from observations from a MST radar network. In particular, there is a strong need for measurements of gravity wave parameters and equatorial wave motions. Some of the current problems in wave dynamics are discussed.

Avery, S. K.↗
NASA NTRS1983

Techniques for studying gravity waves and turbulence: Horizontal, vertical and temporal resolution needed

One of the most important atmospheric measurements that is needed is a measure of the gravity-wave spectrum. The MST radar has been investigated as means to measure the temporal resolution required to determine gravity-wave oscillations. The required vertical and horizontal resolution is dependent on the particular part of the gravity wave spectrum that is analyzed. Horizontal spacing is also discussed.

Avery, S. K.↗
NASA NTRS1983

The response of stationary planetary waves to tropospheric forcing

The lower boundary forcing of airflow over topography, and the internal forcing that results from the geographical distribution of diabatic heating, are studied in light of a steady state, linear, quasi-geostrophic model of stationary waves on a sphere. The lower boundary vertical motions forced by airflow over topography depend on whether the horizontal deflection of airflow around topographic features is taken into account, the level of the wind profile at which flow over topography is assumed to take place, and the topographic data set that was used in the forcing formulation. The lower boundary forcing is taken to be given by the observed stationary planetary wave in lower boundary geopotential height, and the internal forcing is computed using the planetary wave propagation equation on the observed wave structure.

Alpert, J. C.↗
NASA NTRS1982

The transport of nitric oxide in the upper atmosphere by planetary waves and the zonal mean circulation

A time-dependent numerical model was developed and used to study the interaction between planetary waves, the zonal mean circulation, and the trace constituent nitric oxide in the region between 55 km and 120 km. The factors which contribute to the structure of the nitric oxide distribution were examined, and the sensitivity of the distribution to changes in planetary wave amplitude was investigated. Wave-induced changes in the mean nitric oxide concentration were examined as a possible mechanism for the observed winter anomaly. Results indicate that vertically-propagating planetary waves induce a wave-like structure in the nitric oxide distribution and that at certain levels, transports of nitric oxide by planetary waves could significantly affect the mean nitric oxide distribution. The magnitude and direction of these transports at a given level was found to depend not only on the amplitude of the planetary wave, but also on the loss rate of nitric oxide at that level.

Jones, G. A.↗