Observations of plasma density structures in association with the passage of traveling convection vortices and the occurrence of large plasma jets

Abstract. We report important results of the first campaign specially designed to observe the formation and the initial convection of polar cap patches. The principal instrumentation used in the experiments comprised the EISCAT, the Sondrestrom, and the Super DARN network of radars. The experiment was conducted on February 18, 1996 and was complemented with additional sensors such as the Greenland chain of magnetometers and the WIND and IMP-8 satellites. Two different types of events were seen on this day, and in both events the Sondrestrom radar registered the formation and evolution of large-scale density structures. The first event consisted of the passage of traveling convection vortices (TCV). The other event occurred in association with the development of large plasma jets (LPJ) embedded in the sunward convection part of the dusk cell. TCVs were measured, principally, with the magnetometers located in Greenland, but were also confirmed by the line-of-sight velocities from the Sondrestrom and SuperDARN radars. We found that when the magnetic perturbations associated with the TCVs were larger than 100 nT, then a section of the high-latitude plasma density was eroded by a factor of 2. We suggest that the number density reduction was caused by an enhancement in the O+ recombination due to an elevated Ti, which was produced by the much higher frictional heating inside the vortex. The large plasma jets had a considerable (>1000 km) longitudinal extension and were 200-300 km in width. They were seen principally with the Sondrestrom, and SuperDARN radars. Enhanced ion temperature (Ti) was also observed by the Sondrestrom and EISCAT radars. These channels of high Ti were exactly collocated with the LPJs and some of them with regions of eroded plasma number density. We suggest that the LPJs bring less dense plasma from later local times. However, the recent time history of the plasma flow is important to define the depth of the density depletion. Systematic changes in the latitudinal location and in the intensity of the LPJs were observed in the 2 min time resolution data of the SuperDARN radars. The effect of the abrupt changes in the LPJs location is to create regions containing dayside plasma almost detached from the rest of the oval density. One of these density features was seen by the Sondrestrom radar at 1542 UT. The data presented here suggest that two plasma structuring mechanisms (TCVs and LPJs) can act tens of minutes apart to produce higher levels of density structures in the near noon F-region ionosphere.Key words. Ionosphere (ionospheric irregularities) · Magnetospheric physics (electric fields; polar cap phenomena)

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The Auroral Substorm

Convection and Substorms ◽

10.1093/oso/9780195085297.003.0015 ◽

1996 ◽

Author(s):

Charles F. Kennel

Keyword(s):

Electric Fields ◽

Large Scale ◽

Time Development ◽

Local Times ◽

Space Resolution ◽

Auroral Activity ◽

Auroral Substorm ◽

The Many ◽

The One ◽

Cosmic Noise

Around the time the steady convection model was being developed, Akasofu (1964) was arranging ground-based magnetometer and all-sky camera observations of the complex time dependence of nightside auroral activity into the central phenomenological conception of tune-dependent magnetospheric physics—the auroral substorm. In this chapter, we assemble a description of a substorm from modern observations. We will see that observations of electric fields, auroral X rays, cosmic noise absorption, ionospheric density, and geomagnetic micropulsations have also been successfully ordered by the substorm paradigm. At the same time, it will become clear that each individual substorm has its own irreducible individuality, and that our summary description is really a list of effects that anyone thinking about substorms ought to consider. No real substorm will look exactly like the one described here. Spacecraft observations of auroral light, precipitation, currents, and fields from polar orbit have held out high promise for unified understanding of the development of the auroral substorm around the entire oval. Without truly global auroral observations, it would be difficult to establish decisive contact with observations of large-scale convection and the associated changes in magnetospheric configuration. Despite the high promise and the many other successes of spacecraft observations of the aurora, synthetic understanding of the time development of the auroral substorm at all local times, dayside and nightside, evening and dawn, has been slow in emerging, perhaps because a stringent combination of field of view, sensitivity, space and time resolution, and multispectral capability is required. One needs images of the whole oval with sufficient space resolution to identify important arc structures (50-100 km or better) in a temporal sequence that can articulate the evolution of activity on better than the 10-minute time scale on which polar cap convection develops. Only recently has it been possible to observe auroral activity at all local tunes around the auroral oval simultaneously and follow its time development from the beginning of the growth phase until well into the expansion phase. This amplification of the original paradigm is the subject of Sections 12.2 and 12.3.

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A statistical study of ion frictional heating observed by EISCAT

Annales Geophysicae ◽

10.1007/s00585-997-1399-x ◽

1997 ◽

Vol 15 (11) ◽

pp. 1399-1411 ◽

Cited By ~ 10

Author(s):

J. A. Davies ◽

M. Lester ◽

I. W. McCrea

Keyword(s):

Geomagnetic Activity ◽

Large Scale ◽

Frictional Heating ◽

Selection Criterion ◽

Ion Temperature ◽

F Region ◽

Diurnal Distribution ◽

Statistical Survey ◽

Uhf Radar ◽

The Imf

Abstract. Results of a statistical survey of F-region ion frictional heating are presented, a survey which is based on over 4000 h of common programme observations taken by the European incoherent scatter (EISCAT) UHF radar facility. The criterion adopted in this study for the identification of ion frictional heating was that defined by McCrea et al., requiring an enhancement in the F-region field-parallel ion temperature exceeding 100 K over two consecutive integration periods, which was itself based on a selection criterion for frictional heating derived for the study of high-latitude F-region ion temperature observations from the Atmospheric Explorer-C satellite. In the present study, the diurnal distribution of ion frictional heating observed by EISCAT is established and, furthermore, its dependence on geomagnetic activity and the orientation of the interplanetary magnetic field (IMF) is investigated; results are interpreted with reference to corresponding distributions of enhanced ion velocity, again derived from the extended set of EISCAT UHF common programme observations. The radar, due to its location relative to the large-scale convection pattern, observes ion frictional heating principally during the night, although preferentially during the post-midnight hours where there is reduced coupling between the ion and neutral populations. There is an increased preponderance of frictional heating during intervals of high geomagnetic activity and for a southward z component of the IMF and, moreover, evidence of asymmetries introduced by the y component of the IMF.

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The response of the thermosphere and ionosphere to magnetospheric forcing

Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences ◽

10.1098/rsta.1989.0029 ◽

1989 ◽

Vol 328 (1598) ◽

pp. 139-171 ◽

Cited By ~ 28

Keyword(s):

Electric Fields ◽

Plasma Density ◽

Large Scale ◽

Data Sets ◽

Polar Regions ◽

Ionospheric Model ◽

Plasma Convection ◽

Geomagnetic Disturbances ◽

F Region ◽

Wide Range

During the past six years, rapid advances in three observational techniques (groundbased radars, optical interferometers and satellite-borne instruments) have provided a means of observing a wide range of spectacular interactions between the coupled magnetosphere, ionosphere and thermosphere system. Perhaps the most fundamental gain has come from the combined data-sets from the NASA Dynamics Explorer ( DE ) Satellites. These have unambiguously described the global nature of thermospheric flows, and their response to magnetospheric forcing. The DE spacecraft have also described, at the same time, the magnetospheric particle precipitation and convective electric fields which force the polar thermosphere and ionosphere. The response of the thermosphere to magnetospheric forcing is far more complex than merely the rare excitation of 1 km s -1 wind speeds and strong heating; the heating causes large-scale convection and advection within the thermosphere. These large winds grossly change the compositional structure of the upper thermosphere at high and middle latitudes during major geomagnetic disturbances. Some of the major seasonal and geomagnetic storm-related anomalies of the ionosphere are directly attributable to the gross windinduced changes of thermospheric composition; the mid-latitude ionospheric storm ‘negative phase’, however, is yet to be fully understood. The combination of very strong polar wind velocities and rapid plasma convection forced by magnetospheric electric fields strongly and rapidly modify F-region plasma distributions generated by the combination of local solar and auroral ionization sources. Until recently, however, it has been difficult to interpret the observed complex spatial and timedependent structures and motions of the thermosphere and ionosphere because of their strong and nonlinear coupling. It has recently been possible to complete a numerical and computational merging of the University College London (UCL) global thermospheric model and the Sheffield University ionospheric model. This has produced a self-consistent coupled thermospheric-ionospheric model, which has become a valuable diagnostic tool for examining thermospheric-ionospheric interactions in the polar regions. In particular, it is possible to examine the effects of induced winds, ion transport, and the seasonal and diurnal U.T. variations of solar heating and photoionization within the polar regions. Polar and high-latitude plasma density structure at F-region altitudes can be seen to be strongly controlled by U.T., and by season, even for constant solar and geomagnetic activity. In the winter, the F-region polar plasma density is generally dominated by the effects of transport of plasma from the dayside (sunlit cusp). In the summer polar region, however, an increase in the proportion of molecular to atomic species, created by the global seasonal circulation and augmented by the geomagnetic forcing, controls the plasma composition and generally depresses plasma densities at all U.Ts. A number of these complex effects can be seen in data obtained from ground-based radars, Fabry-Perot interferometers and in the combined DE data-sets. Several of these observations will be used, in combination with simulations using the UCL-Sheffield coupled model, to illustrate the major features of large-scale thermosphere-ionosphere interactions in response to geomagnetic forcing.

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High-latitude ionospheric response to co-rotating interaction region- and coronal mass ejection-driven geomagnetic storms revealed by GPS tomography and ionosondes

Proceedings of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rspa.2010.0080 ◽

2010 ◽

Vol 466 (2123) ◽

pp. 3391-3408 ◽

Cited By ~ 11

Author(s):

D. Pokhotelov ◽

P. T. Jayachandran ◽

C. N. Mitchell ◽

M. H. Denton

Keyword(s):

Solar Wind ◽

Coronal Mass Ejection ◽

Plasma Density ◽

Large Scale ◽

Geomagnetic Storms ◽

Interaction Region ◽

Electron Content ◽

Polar Cap ◽

Total Electron ◽

Mass Ejection

Positive ionospheric anomalies induced in the polar cap region by co-rotating interaction region (CIR)- and coronal mass ejection (CME)-driven geomagnetic storms are analysed using four-dimensional tomographic reconstructions of the ionospheric plasma density based on measurements of the total electron content along ray paths of GPS signals. The results of GPS tomography are compared with ground-based observations of F region plasma density by digital ionosondes located in the Canadian Arctic. It is demonstrated that CIR- and CME-driven storms can produce large-scale polar cap anomalies of similar morphology in the form of the tongue of ionization (TOI) that appears on the poleward edge of the mid-latitude dayside storm-enhanced densities in positive ionospheric storms. The CIR-driven event of 14–16 October 2002 was able to produce ionospheric anomalies (TOI) comparable to those produced by the CME-driven storms of greater Dst magnitude. From the comparison of tomographic reconstructions and ionosonde data with solar wind measurements, it appears that the formation of large-scale polar cap anomalies is controlled by the orientation of the interplanetary magnetic field (IMF) with the TOI forming during the periods of extended southward IMF under conditions of high solar wind velocity.

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Observations of the generation of eastward equatorial electric fields near dawn

Annales Geophysicae ◽

10.5194/angeo-32-1169-2014 ◽

2014 ◽

Vol 32 (9) ◽

pp. 1169-1175 ◽

Cited By ~ 11

Author(s):

M. C. Kelley ◽

F. S. Rodrigues ◽

R. F. Pfaff ◽

J. Klenzing

Keyword(s):

Electric Field ◽

Electric Fields ◽

Plasma Density ◽

Large Scale ◽

Field Measurements ◽

Equatorial Ionosphere ◽

Winter Solstice ◽

The Pacific ◽

Density Perturbations ◽

Forecasting System

Abstract. We report and discuss interesting observations of the variability of electric fields and ionospheric densities near sunrise in the equatorial ionosphere made by instruments onboard the Communications/Navigation Outage Forecasting System (C/NOFS) satellite over six consecutive orbits. Electric field measurements were made by the Vector Electric Field Instrument (VEFI), and ionospheric plasma densities were measured by Planar Langmuir Probe (PLP). The data were obtained on 17 June 2008, a period of solar minimum conditions. Deep depletions in the equatorial plasma density were observed just before sunrise on three orbits, for which one of these depletions was accompanied by a very large eastward electric field associated with the density depletion, as previously described by de La Beaujardière et al. (2009), Su et al. (2009) and Burke et al. (2009). The origin of this large eastward field (positive upward/meridional drift), which occurred when that component of the field is usually small and westward, is thought to be due to a large-scale Rayleigh–Taylor process. On three subsequent orbits, however, a distinctly different, second type of relationship between the electric field and plasma density near dawn was observed. Enhancements of the eastward electric field were also detected, one of them peaking around 3 mV m−1, but they were found to the east (later local time) of pre-dawn density perturbations. These observations represent sunrise enhancements of vertical drifts accompanied by eastward drifts such as those observed by the San Marco satellite (Aggson et al., 1995). Like the San Marco measurements, the enhancements occurred during winter solstice and low solar flux conditions in the Pacific longitude sector. While the evening equatorial ionosphere is believed to present the most dramatic examples of variability, our observations exemplify that the dawn sector can be highly variable as well.

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Particle Energization in Relativistic Plasma Turbulence: Solenoidal versus Compressive Driving

The Astrophysical Journal ◽

10.3847/1538-4357/ac222e ◽

2021 ◽

Vol 922 (2) ◽

pp. 172

Author(s):

Vladimir Zhdankin

Keyword(s):

Particle Acceleration ◽

Electric Fields ◽

Large Scale ◽

High Energy ◽

Particle Energy ◽

Density Fluctuations ◽

Driving Mechanism ◽

Ion Temperature ◽

Driving Mechanisms ◽

Particle Energization

Abstract Many high-energy astrophysical systems contain magnetized collisionless plasmas with relativistic particles, in which turbulence can be driven by an arbitrary mixture of solenoidal and compressive motions. For example, turbulence in hot accretion flows may be driven solenoidally by the magnetorotational instability or compressively by spiral shock waves. It is important to understand the role of the driving mechanism on kinetic turbulence and the associated particle energization. In this work, we compare particle-in-cell simulations of solenoidally driven turbulence with similar simulations of compressively driven turbulence. We focus on plasma that has an initial beta of unity, relativistically hot electrons, and varying ion temperature. Apart from strong large-scale density fluctuations in the compressive case, the turbulence statistics are similar for both drives, and the bulk plasma is described reasonably well by an isothermal equation of state. We find that nonthermal particle acceleration is more efficient when turbulence is driven compressively. In the case of relativistically hot ions, both driving mechanisms ultimately lead to similar power-law particle energy distributions, but over a different duration. In the case of nonrelativistic ions, there is significant nonthermal particle acceleration only for compressive driving. Additionally, we find that the electron-to-ion heating ratio is less than unity for both drives, but takes a smaller value for compressive driving. We demonstrate that this additional ion energization is associated with the collisionless damping of large-scale compressive modes via perpendicular electric fields.

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Mechanisms and Evolution of Geoeffective Large-Scale Plasma Jets in the Magnetosheath

Universe ◽

10.3390/universe7050152 ◽

2021 ◽

Vol 7 (5) ◽

pp. 152

Author(s):

Alexei V. Dmitriev ◽

Bhavana Lalchand ◽

Sayantan Ghosh

Keyword(s):

Large Scale ◽

Spatial Scales ◽

Time History ◽

Plasma Jets ◽

Magnetic Data ◽

Transient Effects ◽

The Earth ◽

History Of ◽

Statistical Survey ◽

Upstream Solar Wind

Geoeffective magnetosheath plasma jets (those that interact with the magnetopause) are an important area of research and technology, since they affect the “space-weather” around the Earth. We identified such large-scale magnetosheath plasma jets with a duration of >30 s using plasma and magnetic data acquired from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) multi-spacecraft experiment during the years 2007 to 2009. We present a statistical survey of 554 of such geoeffective jets and elaborate on four mechanisms for the generation of these jets as the upstream solar wind structures of tangential discontinuities (TDs), rotational discontinuities (RDs), the quasi-radial interplanetary magnetic field (rIMF) and the collapsing foreshock (CFS) interrupting the rIMF intervals. We found that 69% of the jets are generated due to the interaction between interplanetary discontinuities (TD: 24%, RD: 25%, CFS: 20%) with the bow shock. Slow and weak jets due to the rIMF contributed to 31% of these jets. The CFS and rIMF were found to be similar in their characteristics. TDs and RDs contributed to most of the fast and powerful jets, with large spatial scales, which might be attributed to transient effects in the travelling foreshock.

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Ion and neutral temperature distributions in the E-region observed by the EISCAT Tromsø and Svalbard radars

Annales Geophysicae ◽

10.5194/angeo-20-1415-2002 ◽

2002 ◽

Vol 20 (9) ◽

pp. 1415-1427 ◽

Cited By ~ 7

Author(s):

S. Maeda ◽

S. Nozawa ◽

M. Sugino ◽

H. Fujiwara ◽

M. Suzuki

Keyword(s):

Heat Transport ◽

Frictional Heating ◽

Soft Particle ◽

Ion Temperature ◽

Polar Cap ◽

Low Latitude ◽

Neutral Temperature ◽

Defense Meteorological Satellite Program ◽

E Region ◽

Uhf Radar

Abstract. Simultaneous Common Program Two experiments by the EISCAT UHF radar at Tromsø and the EISCAT Svalbard radar at Longyearbyen from 00:00 to 15:00 UT on 22 September 1998 and 9 March 1999 have been utilized to investigate distributions of the ion and neutral temperatures in the E-region between 105 and 115 km. During the experiments, soft particle precipitations in the dayside cusp were observed over the Svalbard radar site by the Defense Meteorological Satellite Program (DMSP) F11 satellite. It is found that the dayside electric field in the regions of the low-latitude boundary of the polar cap and the cusp was greater and more variable than that in the auroral region. The ion temperature, parallel to the geomagnetic field at Longyearbyen, was higher than that at Tromsø during the daytime from 06:00 to 12:00 UT. The steady-state ion energy equation has been applied to derive neutral temperature under the assumption of no significant heat transport and viscous heating. The estimated neutral temperature at Longyearbyen was also higher than that at Tromsø. The ion and neutral energy budget was discussed in terms of the ion frictional heating and the Joule heating. The results indicate two possibilities: either the neutral temperature was high in the low latitude boundary of the polar cap and the cusp, or the heat transport by the polar cap neutral winds toward the dayside sector was significant.Key words. Ionosphere (auroral ionosphere; ionosphere–atmosphere interactions; polar ionosphere)

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Studying the dynamics of electric currents and polar caps in ionospheres of two hemispheres during the August 17, 2001 geomagnetic storm

Solar-Terrestrial Physics ◽

10.12737/stp-52201903 ◽

2019 ◽

Vol 5 (2) ◽

pp. 15-27

Author(s):

Сергей Лунюшкин ◽

Sergey Lunyushkin ◽

Владимир Мишин ◽

Vladimir Mishin ◽

Юрий Караваев ◽

...

Keyword(s):

Magnetic Storm ◽

Geomagnetic Storm ◽

Electric Fields ◽

Large Scale ◽

Hall Current ◽

Auroral Oval ◽

Polar Cap ◽

Advanced Technique ◽

Current Function ◽

Polar Caps

The magnetogram inversion technique (MIT), developed at ISTP SB RAS more than forty years ago, has been used until recently only in the Northern Hemisphere. In recent years, MIT has been improved and extended to make instantaneous calculations of 2D distributions of electric fields, horizontal and field-aligned currents in two polar ionospheres. The calculations were carried out based on one-minute ground-based geomagnetic measurements from the worldwide network of stations in both hemispheres (SuperMAG). In this paper, this extended technique is used in the approximation of uniform ionospheric conductance and is applied for the first time to calculations of equivalent and field-aligned currents in two hemispheres through the example of the August 17, 2001 geomagnetic storm. We have obtained the main and essential result: the advanced MIT-ISTP can calculate large-scale distributions of ionospheric convection and FACs in the Northern (N) and Southern (S) polar ionospheres with a high degree of expected hemispheric similarity between these distributions. Using the said event as an example, we have established that the equivalent and field-aligned currents obtained with the advanced technique exhibit the expected dynamics of auroral electrojets and polar caps in two hemispheres. Hall current intensities in polar caps and auroral electrojets, calculated from the equivalent current function, change fairly synchronously in the N and S hemispheres throughout the magnetic storm. Both (westward and eastward) electrojets of the N hemisphere are markedly more intense than respective electrojets of the S hemisphere, and the Hall current in the north polar cap is almost twice as intense as that in the south one. This interhemispheric asymmetry is likely to be due to seasonal conductance variations, which is implicitly contained in the current function. From FAC distributions we determine auroral oval boundaries and calculate magnetic fluxes through the polar caps in the N and S hemispheres. These magnetic fluxes coincide with an accuracy of about 5 % and change almost synchronously during the magnetic storm. In the N hemisphere, the magnetic flux in the dawn polar cap is more intense that that in the dusk one, and vice versa in the S hemisphere. These asymmetries (dawn–dusk and interhemispheric) in the polar caps are consistent with the theory of reconnection for IMF By>0 and with satellite images of auroral ovals; both of these asymmetries decrease during the substorm expansion phase.

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THEMIS satellite observations of hot flow anomalies at Earth's bow shock

Annales Geophysicae ◽

10.5194/angeo-35-443-2017 ◽

2017 ◽

Vol 35 (3) ◽

pp. 443-451 ◽

Cited By ~ 9

Author(s):

Christina Chu ◽

Hui Zhang ◽

David Sibeck ◽

Antonius Otto ◽

QiuGang Zong ◽

...

Keyword(s):

Solar Wind ◽

Energy Density ◽

Temperature Increase ◽

Time History ◽

Bow Shock ◽

Local Times ◽

Kinetic Energy Density ◽

Ion Temperature ◽

Wide Range ◽

Earth’S Bow Shock

Abstract. Hot flow anomalies (HFAs) at Earth's bow shock were identified in Time History of Events and Macroscale Interactions During Substorms (THEMIS) satellite data from 2007 to 2009. The events were classified as young or mature and also as regular or spontaneous hot flow anomalies (SHFAs). The dataset has 17 young SHFAs, 49 mature SHFAs, 15 young HFAs, and 55 mature HFAs. They span a wide range of magnetic local times (MLTs) from approximately 7 to 16.5 MLT. The largest ratio of solar wind to HFA core density occurred near dusk and at larger distances from the bow shock. In this study, HFAs and SHFAs were observed up to 6.3 RE and 6.1 RE (Earth radii), respectively, upstream from the model bow shock. HFA–SHFA occurrence decreases with distance upstream from the bow shock. HFAs of the highest event core ion temperatures were not seen at the flanks. The ratio of HFA ion temperature increase to HFA electron temperature increase is highest around 12 MLT and slightly duskward. For SHFAs, (Tihfa∕Tisw)/(Tehfa∕Tesw) generally increased with distance from the bow shock. Both mature and young HFAs are more prevalent when there is an approximately radial interplanetary magnetic field. HFAs occur most preferentially for solar wind speeds from 550 to 600 km s−1. The correlation coefficient between the HFA increase in thermal energy density from solar wind values and the decrease in kinetic energy density from solar wind values is 0.62. SHFAs and HFAs do not show major differences in this study.

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