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Volland, H.

Publications and source records attributed to Volland, H..

At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

The problem of the boundary conditions in thermosphere dynamics.

A simple analytic solution for the generation and propagation of tidal waves at thermospheric heights is presented. It is used to show that a unique solution of tidal wave propagation within the thermosphere depends on the boundary conditions of the model, and that radiation conditions lead to such a unique solution.

Volland, H.↗
NASA NTRS1972

Magnetic storm characteristics of the thermosphere

Energy and diffusive mass transport associated with the thermospheric circulation are considered in a self-consistent, though mathematically relatively simple form to describe in a three-dimensional two-constituent model magnetic storm characteristics in composition (N2, O, and He), temperature and mass-density. It is shown that during disturbed conditions the latitudinal variations of composition and gas temperature T sub g reflect the local nature of the magnetic storm heat input assumed to be primarily confined to the auroral zones. Thereby T sub g and N2 increase, He decreases and O remains constant through the auroral zones at exospheric heights (due to the superposition of temperature and diffusion effects) in agreement with OGO-6 mass spectrometer measurements. In contrast, the magnetic storm response in the total mass density is characterized by a strong world-wide component and a relatively insignificant increase toward the poles with the density peak occurring between two (poles) and eight (equator) hours after the maximum energy input, in substantial agreement with satellite drag data.

Mayr, H. G.↗
NASA NTRS1972

A numerical study of a three dimensional spherical thermospheric density and wind model

Numerical calculations of the generation and propagation of the two important fundamental symmetric tidal wave modes - the diurnal mode (1, 1, 1,) and the semidiurnal mode (2, 2, 2) - were performed applying a realistic model thermosphere and taking into account heat conduction and the temporally and spatially varying ion-neutral collision number. Both wave modes are predominantly generated by the solar EUV heat input. It is shown that the latitude structure of the (1, 1, 1)-mode which is identical with the Hough function(1, -1) within the lower non-dissipative atmosphere degenerates into the spherical function P sub 1, 1 at thermospheric heights. The pressure field of this mode constitutes the observed pressure bulge of the thermosphere, the diurnal component of which peaks at 15 h L. T. The electric polarization field of the geomagnetic Sq current generates a significant fraction of this wave mode at F layer heights. This wave component shifts the total horizontal wind system to earlier times by about 1 hour in agreement with ionospheric observations. The latitude structure of the (2, 2, 2) mode is identical with the Hough function (2, 2) within the lower non-dissipative atmosphere. It degenerates to the spherical function P sub 2, 2 at thermospheric heights.

Volland, H.↗
NASA NTRS1972

A two component model of the diurnal variations in the thermospheric composition

A self-consistent, two-dimensional, two-component diffusion model is presented to describe the diurnal component of thermosphere dynamics. In the regions where oxygen and helium are the minor constituents, diffusion is shown to increase the amplitudes of these constituents and to advance the times of their diurnal maxima by several hours with respect to the gas temperature and the major species. Both effects are in basic agreement with satellite observations. The diffusion process is relatively insignificant for temperature, total mass density, and wind fields. The magnitude of the temperature-density phase delay is discussed with respect to its dependence on the electron density distribution.

Mayr, H. G.↗
NASA NTRS1972

Diffusion model for the phase delay between thermospheric density and temperature.

Consideration of a two-dimensional time-dependent model in which the thermosphere dynamics is excited by the UV heat input within the thermosphere, showing that the wind-induced variations in the diurnal component of atomic oxygen dominate over its temperature-induced variations up to 200 km. The assumption of diffusive equilibrium is therefore in general not valid for O within the lower thermosphere. The effect of the diurnal wind circulation is to redistribute O so that the diurnal variations in the forbidden O/forbidden N2 and forbidden O/forbidden O2 ratios are damped by about 20%, thus contributing to the maintenance of the nighttime F2 region, and the maximum in the diurnal variation of O is shifted by one to two hours away from the temperature maximum toward noon, thus contributing significantly to the temperature-density time lag at thermospheric heights above 200 km, where O becomes the major constituent.

Mayr, H. G.↗
NASA NTRS1972

Magnetic storm effects in the neutral composition.

Demonstration that the thermospheric wind circulation excited during magnetic storms, presumably by Joule heating within the auroral zone, is an effective mechanism for removing atomic oxygen at high latitudes. Wind-induced variations in O exceed the temperature effects up to 250 km. The calculated depletion is most pronounced at around 180 km, where the density can decrease by as much as a factor of two, consistent with the observed storm time variations in the ionosphere. At higher altitudes, this effect is canceled by the thermal expansion in atomic oxygen, thus explaining the negligible response in the concentration of this atmospheric constituent under disturbed conditions, when N2 increased by as much as a factor of ten.

Mayr, H. G.↗
NASA NTRS1971

Semiannual variations in the neutral composition.

Meteor trail observations of the meridional mesospheric wind field are analyzed in terms of spherical harmonics, showing a predominance in the P3 term for the semiannual component. This suggests two heat sources for the semiannual variations. One that peaks at the equator is associated with the semiannual migration of the sun between the two hemispheres. A second heat input of greater magnitude that peaks at high latitudes is presumably related to auroral heating associated with the semiannual component in the occurrence of magnetic storms. The wind circulation, consistent with these sources, is shown to cause a semiannual redistribution of the minor constituent O in the lower thermosphere with the effects of decreasing the ratios of O/N2 and O/O2 at high latitudes and of enhancing these ratios at mid to low latitudes during equinox.

Mayr, H. G.↗
NASA NTRS1971

The problem of uniqueness in thermosphere dynamics

The unique solution of tidal wave propagation within the thermosphere depends on the boundary conditions of the model. It is shown that the radiation condition leads to such a unique solution. Any other boundary values give rise to deviations from the physical solution with unrealistic physical parameters in the environment of the boundaries. The thickness of these boundary layers with unrealistic solutions is a few scale heights below the upper boundary of the model and a few tens of scale heights above the lower boundary of the model.

Volland, H.↗
NASA NTRS1971

A model for the temperature and composition effects in the semiannual variations of the thermospheric density

A model is proposed in which latitudinal variations in composition and temperature are used to interpret the semiannual effect in the thermospheric density. Two heat sources are postulated for the semiannual circulation: one at high latitudes associated with the semiannual component in the occurance of magnetic storms and a second weaker one that peaks at the equator associated with the semiannual migration between both hemispheres. Depending on the relative magnitude of these sources, the latitude regions in which composition and temperature effects dominate vary. The temperature effects however should be expected weakest at low to mid latitudes where the relative concentration of atomic oxygen is enriched during equinox. At high latitudes the semiannual temperature component would peak, associated with an oxygen depletion in the lower thermosphere during equinox. In combining these features it is shown that the total atmospheric density could still exhibit a relatively small latitude dependence in the semiannual component with the tendency to decrease at high latitudes, in agreement with observations.

Mayr, H. G.↗