Gravity waves generated during magnetic substorms
01 Nov 1970-Journal of Atmospheric and Solar-Terrestrial Physics (Pergamon)-Vol. 32, Iss: 11, pp 1793-1805
TL;DR: In this paper, wind and temperature data obtained in the F -region from incoherent scatter, show strong oscillations of the ion temperature and velocity with period of some 2 hours These oscillations can be interpreted as due to atmospheric gravity waves travelling Southwards.
About: This article is published in Journal of Atmospheric and Solar-Terrestrial Physics.The article was published on 1970-11-01. It has received 113 citations till now. The article focuses on the topics: Gravity wave & Atmospheric wave.
Citations
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TL;DR: The theoretical and observational evidence concerning the global propagation of atmospheric gravity waves is reviewed in this article, with special emphasis on the waves generated in the auroral zones, and it is concluded that the only natural sources of large-scale TIDs are in the ionospheric zones.
392 citations
TL;DR: In this article, the authors review the theory of acoustic-gravity waves, the interaction of such waves with the ionosphere, the experimental support for the existence of acoustic gravity waves in the upper atmosphere, and the role played by acoustic gravity wave in thermospheric dynamics.
Abstract: In this paper we review the theory of acoustic-gravity waves, the interaction of such waves with the ionosphere, the experimental support for the existence of such waves in the upper atmosphere, and the role played by acoustic-gravity waves in thermospheric dynamics. After a thorough discussion on the properties of acoustic-gravity waves in an ideal isothermal atmosphere, the effects produced by horizontal winds, sharp boundary discontinuities, and dissipative processes are discussed. The generation of these waves by stationary or moving sources is then treated. It is shown that the atmospheric response to a stationary impulse source can be described by the emission of three waves: acoustic, buoyancy, and gravity. These discussions are then followed by reviewing propagation effects in a realistic atmosphere for both free waves and guided waves. Recent numerical results are given. When acoustic-gravity waves propagate through the ionosphere, interaction between the wave and the ionosphere will take place. The physical processes involved in such an interaction are examined.
365 citations
TL;DR: In this article, a computer model is used to simulate the winds and temperature variations in the thermosphere which result from auroral region electric currents during a large isolated magnetic substorm.
Abstract: A computer model is used to simulate the winds and temperature variations in the thermosphere which result from auroral region electric currents during a large isolated magnetic substorm. A disturbance propagates with a speed of 750 m/s poleward and equatorward, with an amplitude of about 200 m/s in the north-south velocity and about 100 K in the temperature at 400-km altitude. The amplitude decays relatively little before the disturbance reaches the equator. The time history of the disturbance is roughly that of a single sinusoid whose period increases with horizontal distance from the source and with decreasing altitude. East-west winds of over 400 m/s at 400-km altitude are created in the auroral region itself by the ion drag mechanism. The spatial distribution of these ion drag winds is significantly affected by momentum convection, so that a simple interpretation in terms of local ion drag forces is generally not sufficient. A residual electric field of about 5 mV/m remains after the substorm source is turned off, due to the dynamo effect of the ion drag winds. Vertical velocities up to about 40 m/s are produced inside the auroral region, primarily by the fact that the heated air is more buoyant than the air outside. Comparison of our simulation with numerous observations shows generally good agreement.
315 citations
TL;DR: In this paper, the authors examined large-scale gravity waves in the thermosphere and their ability to transfer energy from high to low latitudes during magnetic disturbances, assuming that the gravity wave source is either the Lorentz force of auroral electrojet currents or a heat input due to energetic particle precipitation or to Joule heating.
Abstract: This is the first in a series of papers examining large-scale gravity waves in the thermosphere and their ability to transfer energy from high to low latitudes during magnetic disturbances. The gravity wave source is assumed to be either the Lorentz force of auroral electrojet currents or else a heat input due to energetic particle precipitation or to Joule heating. It is pointed out that the characteristic vertical width of the gravity wave source should usually lie between 2 and 4 pressure scale heights, placing constraints on the vertical wavelengths and horizontal velocities of the generated waves. A simplified analytic model of small-amplitude wave generation by a current source shows how wave energy production depends on the temporal and spatial dimensions of the source, on the electric field strength, and on the electron density enhancement. The steep thermospheric temperature gradient in the vicinity of the source altitude strongly influences the properties of upward and downward propagating waves compared with waves generated in an isothermal atmosphere. Waves produced by the Lorentz force of Hall currents, by the Lorentz force of Pedersen currents, and by Joule heating are influenced quite differently by this temperature gradient. Because upgoing waves above the source are combinations of waves originally launched upward and waves originally launched downward but reflected around 110 km altitude, the mean effective source altitude is about 110 km for the far field response in the thermosphere. Large-scale traveling ionospheric disturbances observable at middle latitudes are most likely produced primarily by Pedersen, rather than Hall, currents. The temperature structure of the thermosphere generally causes gravity wave packets to refract upward; waves traveling with a horizontal component of velocity faster than 250 m/s and with an initial downward component of group velocity will always be reflected upward in the lower thermosphere. The effects of viscosity, heat conduction, and Joule dissipation tend to filter out shorter-period and slower moving waves from observation points at some distance from the source, so that only long-period fast moving waves can reach low latitudes from an auroral source. For example, a wave with a 94-min period moving horizontally at 605 m/s is largely dissipated by the time it has traveled 4000 km from a typical auroral source. A numerical simulation using a fairly realistic thermospheric model illustrates many of the points described from analytic considerations.
261 citations
TL;DR: In this paper, the properties and physics of density perturbations are reviewed and applied to the upper atmosphere of the terrestrial gas envelope above about 100 km altitude, where the energy budget of this outer gas layer is partly controlled by the dissipation of solar wind energy.
Abstract: The upper atmosphere constitutes the outer region of the terrestrial gas envelope above about 100 km altitude. The energy budget of this outer gas layer is partly controlled by the dissipation of solar wind energy. Since this energy input is largely irregular, the resulting density changes are considered as perturbations. The properties and physics of such density perturbations are reviewed here. Besides being an important link in the complex chain of solar-terrestrial relations, such disturbances are also of practical interest because they affect the orbits of satellites and space stations and are responsible for ionospheric disturbance effects.
119 citations
References
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TL;DR: Auroral electrojet index and universal time variations, discussing polar disturbance statistics are discussed in this paper, where the authors also discuss the effect of time variations on polar disturbances and their correlation.
Abstract: Auroral electrojet index and universal time variations, discussing polar disturbance statistics
741 citations
TL;DR: In this paper, the energy that is deposited in the ionosphere by internal atmospheric gravity waves propagating upward from below is assessed on the basis of recent observational data, and the implied heating rates are found to range from 10°K/day (near the 95-km level) to 100°K / day (near 140 km), and they therefore compete with solar radiation as the primary source of heating in ionospheric E region.
Abstract: The energy that is deposited in the ionosphere by internal atmospheric gravity waves propagating upward from below is assessed on the basis of recent observational data. The implied heating rates are found to range from 10°K/day (near the 95-km level) to 100°K/day (near 140 km), and they therefore compete with solar radiation as the primary source of heating in the ionospheric E region. The tidal input may be comparable, but its height of deposition is more difficult to assess. The residual wave energy that reaches the F region carries a flux that may exceed 10−4 watt/m2, and so it may play a significant role in determining the heat budget of these higher levels. The waves should be accompanied by reversible temperature fluctuations of ±10°K and more, low in tne E region, and they may therefore account for irregular temperature structure that has been reported.
212 citations
TL;DR: In this paper, the average time delay between the peak of the geomagnetic perturbation and that of the atmosphere is 6.7±0.3 hours, and for latitudes smaller than 25° (average: 25°) it is 7.2± 0.5 hours.
Abstract: The density variations that accompany geomagnetic disturbances have been studied by analyzing the drag of three satellites with high orbital inclination (Injun 3, Explorer 19, and Explorer 24) and one with moderate inclination (Explorer 17). The average time delay between the peak of the geomagnetic perturbation and that of the atmosphere is 6.7±0.3 hours. While there seems to be no significant dependence on the time delay on the intensity of the perturbation and on the geographic location with respect to the sun, there appears to be some dependence on latitude. For latitudes greater than 55° (average: 65°) the mean time delay is 5.8±0.5 hours, and for latitudes smaller than 55° (average: 25°) it is 7.2±0.3 hours. All three high-inclination satellites give consistently smaller delay times at high latitudes. The observed density changes are interpreted as being caused by changes in temperature. For smaller perturbations (Kp < 5) the temperature T shows a nearly linear dependence on Kp, and for latitudes lower than 55° the rate of change ΔT/ΔKp is about 28°. For latitudes above 55° (average: 65°) ΔT/ΔKp seems to be about 15–25% greater. For more intense disturbances (Kp ≥ 5), ΔT/ΔKp is systematically larger, confirming the nonlinearity of the relation between T and Kp, when considered over its total range; there is also a good indication that some atmospheric perturbations are enhanced in the auroral zones more than others.
120 citations
TL;DR: In this paper, it is suggested that auroral zone perturbations are a possible generating mechanism for atmospheric gravity waves which then propagate in a southeasterly direction over great circle paths exceeding 5000 km and are manifested as large TIDs observed by the Boulder scan-backscatter sounder.
60 citations