Dynamic effects of aurora-generated gravity waves on the mid-latitude ionosphere
TL;DR: In this article, a brief review of aurora-generated large-scale traveling ionospheric disturbances is given, and results of numerical simulations of one such event are presented. But the results of simulations are limited to the case of the 18 September 1974 event.
About: This article is published in Journal of Atmospheric and Solar-Terrestrial Physics.The article was published on 1979-07-01. It has received 53 citations till now. The article focuses on the topics: Ionospheric heater & Thermosphere.
Citations
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TL;DR: In this paper, four numerical simulations have been performed, at equinox, using a coupled thermosphere-ionosphere model, to illustrate the response of the upper atmosphere to geomagnetic storms.
Abstract: Four numerical simulations have been performed, at equinox, using a coupled thermosphere-ionosphere model, to illustrate the response of the upper atmosphere to geomagnetic storms. The storms are characterized by an increase in magnetospheric energy input at high latitude for a 12-hour period; each storm commences at a different universal time (UT). The initial response at high latitude is that Joule heating raises the temperature of the upper thermosphere and ion drag drives high-velocity neutral winds. The heat source drives a global wind surge, from both polar regions, which propagates to low latitudes and into the opposite hemisphere. The surge has the character of a large-scale gravity wave with a phase speed of about 600 m/s. Behind the surge a global circulation of magnitude 100 m/s is established at middle latitudes, indicating that the wave and the onset of global circulation are manifestations of the same phenomena. A dominant feature of the response is the penetration of the surge into the opposite hemisphere where it drives poleward winds for a few hours. The global wind surge has a preference for the night sector and for the longitude of the magnetic pole and therefore depends on the UT start time of the storm. A second phase of the meridional circulation develops after the wave interaction but is also restricted, in this case by the buildup of zonal winds via the Coriolis interaction. Conservation of angular momentum may limit the buildup of zonal wind in extreme cases. The divergent wind field drives upwelling and composition change on both height and pressure surfaces. The composition bulge responds to both the background and the storm-induced horizontal winds; it does not simply rotate with Earth. During the storm the disturbance wind modulates the location of the bulge; during the recovery the background winds induce a diurnal variation in its position. Equatorward winds in sunlight produce positive ionospheric changes during the main driving phase of the storm. Negative ionospheric phases are caused by increases of molecular nitrogen in regions of sunlight, the strength of which depends on longitude and the local time of the sector during the storm input. Regions of positive phase in the ionosphere persist in the recovery period due to decreases in mean molecular mass in regions of previous downwelling. Ion density changes, expressed as a ratio of disturbed to quiet values, exhibit a diurnal variation that is driven by the location of the composition bulge; this variation explains the ac component of the local time variation of the observed negative storm phase.
777 citations
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
TL;DR: In this paper, the effects of the St Patrick's Day storm of 2015, with its ionospheric response at middle and low latitudes, were analyzed using global and regional electron content, and the results showed that the American region exhibits the most remarkable increase in vertical total electron content (vTEC), while in the Asian sector, the largest decrease in vTEC is observed.
Abstract: This paper presents a study of the St Patrick's Day storm of 2015, with its ionospheric response at middle and low latitudes. The effects of the storm in each longitudinal sector (Asian, African, American, and Pacific) are characterized using global and regional electron content. At the beginning of the storm, one or two ionospheric positive storm effects are observed depending on the longitudinal zones. After the main phase of the storm, a strong decrease in ionization is observed at all longitudes, lasting several days. The American region exhibits the most remarkable increase in vertical total electron content (vTEC), while in the Asian sector, the largest decrease in vTEC is observed. At low latitudes, using spectral analysis, we were able to separate the effects of the prompt penetration of the magnetospheric convection electric field (PPEF) and of the disturbance dynamo electric field (DDEF) on the basis of ground magnetic data. Concerning the PPEF, Earth's magnetic field oscillations occur simultaneously in the Asian, African, and American sectors, during southward magnetization of the B z component of the interplanetary magnetic field. Concerning the DDEF, diurnal magnetic oscillations in the horizontal component H of the Earth's magnetic field exhibit a behavior that is opposed to the regular one. These diurnal oscillations are recognized to last several days in all longitudinal sectors. The observational data obtained by all sensors used in the present paper can be interpreted on the basis of existing theoretical models.
167 citations
TL;DR: In this article, the ionospheric and thermospheric response to a geomagnetic storm has been a challenge for many decades, due largely to the complex interactions between the plasma and neutral species.
Abstract: Unraveling the ionospheric and thermospheric response to a geomagnetic storm has been a challenge for many decades, due largely to the complex interactions between the plasma and neutral species. Geomagnetic storm sources to the upper atmosphere are caused by an increase in the convective electric field and auroral precipitation, that give rise to Joule heating, the primary driver of global atmospheric change. Driven by the impulsive energy input, wave surges propagate and interact globally, and are dependent on Universal Time (UT) and the time history of the source. There is a strong preference for surges to maximize on the nightside and in the longitude sector adjacent to the magnetic pole. Equatorward wind surges drive the plasma upwards and can initiate a positive ionospheric change. The divergent nature of the wind field causes upwelling and changes to the neutral composition that can be transported by the storm and background wind fields. Negative ionospheric phases result from increased molecular species. Ionosondes have recorded the apparently chaotic ionospheric response for more than 50 years, but it is only recently that local time (LT) and seasonal dependencies have been quantified. Numerical models have shed light on the physical processes; the LT response is caused by the diurnal wind field migration of the composition bulge, and the seasonal dependence is controlled through the transport of the bulge by the summer-to-winter prevailing circulation. Neutral density changes and satellite airglow observations support this basic concept. At low latitudes, electrodynamic changes are initiated by penetration of magnetospheric fields followed by rapid shielding. After shielding, the electrodynamics is forced by dynamo action of the disturbed neutral atmosphere, driving a sequence of equatorial plasma drifts for more than a day. The precise mechanisms responsible for this equatorial response have yet to be defined, but it is tempting to associate the time-scales with those of the global dynamical and composition response of the neutral atmosphere. Despite an increase in our understanding of the causes of the mid-latitude ionospheric response, simulation of a real storm has yet to confirm theory. We are limited by accurate knowledge of the source function, and by the lack of comprehensive data coverage of both the neutral and ionospheric parameters. Both are needed before theory and models can be thoroughly tested.
144 citations
TL;DR: In this paper, the authors investigated the idea that both phenomena are caused by traveling atmospheric disturbances (TADs) and concluded that TADs are responsible for both positive ionospheric storms at middle latitudes and the geomagnetic activity effect at low latitudes.
Abstract: Anomalous increases of the ionization density at middle latitudes (positive ionospheric storms) and anomalous increases of the neutral gas density at low latitudes (the geomagnetic activity effect) are prominent features of upper atmospheric storms. The present study investigates the idea that both phenomena are caused by traveling atmospheric disturbances (TADs). According to theory, such TADs are generated during magnetic substorm activity and propagate with high velocity from polar to equatorial latitudes. To examine the above hypothesis, magnetic, ionospheric, and neutral atmospheric data are compared for five different disturbance events. These case studies demonstrate that (1) there is a good temporal correlation between magnetic substorm activity at high latitudes, daytime positive ionospheric storms at middle latitudes, and the geomagnetic activity effect at low latitudes; (2) the initial phase of positive ionospheric storms propagates with high velocity toward lower latitudes; (3) this velocity is roughly consistent with the time lag of the geomagnetic activity effect at low latitudes; (4) the ionospheric disturbance is a conjugate phenomenon of global extent; and (5) it cannot be explained as an electric field effect. In summary, our data are fully consistent with the idea that TADs are responsible for both positive ionospheric storms at middle latitudes and the geomagnetic activity effect at low latitudes.
136 citations
References
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01 Jan 1975
TL;DR: In this paper, the authors propose a method to solve the problem of how to find the shortest path between two points of interest in a set of images. Index Reference Record created on 2004-09-07, modified on 2016-08-08
Abstract: Note: Bibliogr. : p. 423-440. Index Reference Record created on 2004-09-07, modified on 2016-08-08
604 citations
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 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
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