Atmospheric gravity waves launched by auroral currents
TL;DR: In this article, a model calculation is performed by which the magnitude and form of the anticipated atmospheric wave train may be assessed, and both are found to be consistent with observations already recorded, but the question as to whether the Lorentz force or the Joule dissipation is the more important exciting agency provided by the current, is left unanswered because of present uncertainties connected with the nature of the current itself.
About: This article is published in Planetary and Space Science.The article was published on 1970-04-01. It has received 179 citations till now. The article focuses on the topics: Atmospheric wave.
Citations
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TL;DR: A review of theoretical and observational results describing atmospheric gravity wave (AGW)/traveling ionospheric disturbance (TID) phenomena at high latitudes is presented in this paper.
Abstract: A review of theoretical and observational results describing atmospheric gravity wave (AGW)/traveling ionospheric disturbance (TID) phenomena at high latitudes is presented. Some recent experimental studies of AGW's using the Chatanika incoherent scatter radar and other geophysical sensors are reported. Specifically, the following features are described in detail: (1) cause/effect relations between aurorally generated AGW's and TID's detected at mid-latitudes, including probable ‘source signature’ identification, (2) AGW source phenomenology, particularly a semiquantitative assessment of the relative importance of Joule heating, Lorentz forces, intense particle precipitation, and other mechanisms in generating AGW's, and (3) detection of TID's in the auroral ionosphere. Several instances of F region electron density, temperature, and plasma periodicities accompanied by horizontal plasma velocities which were consistent with theoretical AGW/TID models are documented.
640 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
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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
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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
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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
References
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TL;DR: In this paper, the proper interpretation of irregular motions in the upper atmosphere has been investigated by a variety of techniques, but their proper interpretation has yet to be established. But their proper meaning has not yet been established.
Abstract: Irregularities and irregular motions in the upper atmosphere have been detected and studied by a variety of techniques during recent years, but their proper interpretation has yet to be established...
1,886 citations
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TL;DR: In this paper, a model of an arc is presented in which the height variation of the auroral ionization is taken into account and vertical currents are allowed to flow in the arc, and the electric field or wind velocity field required to drive the currents is computed for two different cases: in one, the current flow between the ionosphere and the outer magnetosphere is assumed to be limited and electric fields occur along the magnetic field lines in the magnetosphere; in the other, the conductivity along the field lines is assumed that are perfect.
Abstract: Certain observations indicate that the auroral electrojets are confined to the auroral arcs. A model of an arc is presented in which the height variation of the auroral ionization is taken into account and vertical currents are allowed to flow. The current flow in the arc is investigated, and the electric field or wind velocity field required to drive the currents is computed for two different cases: in one, the current flow between the auroral-zone ionosphere and the outer magnetosphere is assumed to be limited and electric fields occur along the magnetic field lines in the magnetosphere; in the other, the conductivity along the field lines is assumed to be perfect. In the first case the electrojets are probably driven by a longitudinal electric field in the magnetosphere. In the second case the driving electric field must be a meridional field in order to explain the observations, and strong sheet currents must flow along the field lines that connect the auroral ionosphere to the outer magnetosphere.
512 citations
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TL;DR: In this article, a perturbation treatment is used to determine the nature and magnitude of the effects of internal atmospheric gravity waves on the ambient rates of production, chemical loss, and motion of the ionization.
337 citations
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TL;DR: In this article, a network of CW Doppler sounders was used to detect ionospheric motions observed with a network-of-CW Dopplers. The motions of each type are attributed to various kinds of atmospheric waves that interact with the ionosphere.
293 citations
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TL;DR: In this paper, the authors used homogeneous wave guide theory to derive dispersion curves, vertical pressure distributions, and synthetic barograms for atmospheric waves, and found that the major features on barograms are due to dispersion; superposition of several modes is needed to explain observed features.
Abstract: Homogeneous wave guide theory is used to derive dispersion curves, vertical pressure distributions, and synthetic barograms for atmospheric waves. A complicated mode structure is found involving both gravity and acoustic waves. Various models of the atmosphere are studied to explore seasonal and geographic effects on pulse propagation. The influence of different zones in the atmosphere on the character of the barograms is studied. It is found that the first arriving waves are controlled by the properties of the lower atmospheric channel. Comparison of theoretical results and experimental data from large thermonuclear explosions is made in the time and frequency domains, and the following conclusions are reached: (1) The major features on barograms are due to dispersion; (2) superposition of several modes is needed to explain observed features; (3) scatter of data outside the range permitted by extreme atmospheric models shows the influence of winds for A1; wind effects and higher modes are less important for A2 waves. A discussion is included on atmospheric terminations and how these affect dispersion curves.
163 citations