Traveling Convection Vortices Research Articles

Identification of Vortex Currents in the Ionosphere and Estimation of Their Parameters Based on Ground Magnetic Data

A system to process data from a 2D network of magnetic stations is proposed for the identification of eddy currents in the ionosphere and the estimation of their parameters. The methodology is applied to an analysis of the structure of daytime traveling convection vortices (TCVs) based on data from Arctic. The problem is solved with optimization methods for various functions obtained via spatial interpolation and subsequent data regularization. The developed approach makes it possible not only to find eddy structures automatically but also to determine the current values of their characteristic parameters: the spatial structure of the field aligned currents (FACs), and the group velocity of the horizontal propagation of the vortex along the ionosphere.

Alfvén Wave Generation by a Compact Source Moving on the Magnetopause: Asymptotic Solution

AbstractThe spatiotemporal structure of Alfvén waves excited by a moving pressure pulse on the magnetopause is analytically explored. These waves are supposed to be responsible for field‐aligned currents generating traveling convection vortices in the ionosphere. It is found that a moving source generates two wave modes, a primary and a secondary mode, having different azimuthal wave vectors and frequencies. Both modes represent surface waves with amplitudes exponentially decreasing from the magnetopause. At a given azimuthal location, they also decrease with time as the source passes away. For the primary mode, the wave frequency equals the Alfvén resonant frequency on the surface of the source, while for the secondary mode the frequency equals the local resonant frequency. The dependence of the frequency of the secondary mode on the radial coordinate results in phase mixing, which leads to a change of the wave polarization from mixed into toroidal polarization. For both primary and secondary modes, the azimuthal component of the wave vector equals the corresponding wave frequency divided by the speed of the source. Superposition of the primary and secondary modes produces plasma vortices behind the source.

Response of Ionospheric Total Electron Content to Convective Vortices

The response of the total electron content (TEC) of Earth’s ionosphere to impulse geomagnetic disturbances, traveling convection vortices (TCVs), is considered in the paper. The data of networks of ground-based magnetometers in Canada and Greenland were used to reveal TCVs, whereas the TEC variations were obtained by processing the data of the IGS and UNAVCO receiving stations of the global positioning system (GPS). Ionospheric disturbances related to TCVs are detected. Using the station network makes it possible to estimate the dynamics of formation and velocity of propagation of the disturbance in space.

Impulsive disturbances of the geomagnetic field as a cause of induced currents of electric power lines

Geomagnetically induced currents (GICs) represent a significant challenge for society on a stable electricity supply. Space weather activates global electromagnetic and plasma processes in the near-Earth environment, however, the highest risk of GICs is related not directly to those processes with enormous energy yield, but too much weaker, but fast, processes. Here we consider several typical examples of such fast processes and their impact on power transmission lines in the Kola Peninsula and in Karelia: interplanetary shocks; traveling convection vortices; impulses embedded in substorms; and irregular Pi3 pulsations. Geomagnetic field variability is examined using data from the IMAGE (International Monitor for Auroral Geomagnetic Effects) magnetometer array. We have confirmed that during the considered impulsive events the ionospheric currents fluctuate in both the East-West and North-South directions, and they do induce GIC in latitudinally extended electric power line. It is important to reveal the fine structure of fast geomagnetic variations during storms and substorms not only for a practical point of view but also for a fundamental scientific view.

Conjugate observations of electromagnetic ion cyclotron waves associated with traveling convection vortex events

AbstractWe report on simultaneous observations of electromagnetic ion cyclotron (EMIC) waves associated with traveling convection vortex (TCV) events caused by transient solar wind dynamic pressure (Pd) impulse events. The Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft located near the magnetopause observed radial fluctuations of the magnetopause, and the GOES spacecraft measured sudden compressions of the magnetosphere in response to sudden increases in Pd. During the transient events, EMIC waves were observed by interhemispheric conjugate ground‐based magnetometer arrays as well as the GOES spacecraft. The spectral structures of the waves appear to be well correlated with the fluctuating motion of the magnetopause, showing compression‐associated wave generation. In addition, the wave features are remarkably similar in conjugate hemispheres in terms of bandwidth, quasiperiodic wave power modulation, and polarization. Proton precipitation was also observed by the DMSP spacecraft during the wave events, from which the wave source region is estimated to be 72°–74° in magnetic latitude, consistent with the TCV center. The confluence of space‐borne and ground instruments including the interhemispheric, high‐latitude, fluxgate/induction coil magnetometer array allows us to constrain the EMIC source region while also confirming the relationship between EMIC waves and the TCV current system.

Simultaneous observations of traveling convection vortices: Ionosphere‐thermosphere coupling

AbstractWe present simultaneous observations of magnetosphere‐ionosphere‐thermosphere coupling over Svalbard during a traveling convection vortex (TCV) event. Various spaceborne and ground‐based instruments made coordinated measurements, including magnetometers, particle detectors, an all‐sky camera, European Incoherent Scatter (EISCAT) Svalbard Radar, Super Dual Auroral Radar Network (SuperDARN), and SCANning Doppler Imager (SCANDI). The instruments recorded TCVs associated with a sudden change in solar wind dynamic pressure. The data display typical features of TCVs including vortical ionospheric convection patterns seen by the ground magnetometers and SuperDARN radars and auroral precipitation near the cusp observed by the all‐sky camera. Simultaneously, electron and ion temperature enhancements with corresponding density increase from soft precipitation are also observed by the EISCAT Svalbard Radar. The ground magnetometers also detected electromagnetic ion cyclotron waves at the approximate time of the TCV arrival. This implies that they were generated by a temperature anisotropy resulting from a compression on the dayside magnetosphere. SCANDI data show a divergence in thermospheric winds during the TCVs, presumably due to thermospheric heating associated with the current closure linked to a field‐aligned current system generated by the TCVs. We conclude that solar wind pressure impulse‐related transient phenomena can affect even the upper atmospheric dynamics via current systems established by a magnetosphere‐ionosphere‐thermosphere coupling process.

233 - Fast stochastic optimization algorithm on DC-tumor like high yield minimal magnetic signatures of electrotransfectioned ex vivo mediated hybrids for the generation of a computer-aided designed candidate drugable Toll-like receptor (Pam2IDG) peptide-domain agonistic agent

By using an improved TCV model (Zhu et al., 1997), a quantitative study of the effects of magnetospheric precipitation and ionospheric background conductivity on the ground magnetic signatures of traveling convection vortices (TCVs) has been conducted. The localized conductivity enhancement associated with the TCVs is present and the ratio of the Hall and Pedersen conductances vary both spatially and temporally according to the hardness of the TCV precipitation. Recently, it has been shown that dendritic cells (DCs) and DC-tumor cell hybrids (DC-tumor hybrids) have been used for cancer vaccine therapy in a clinical trial. DC-tumor hybrids combine the potent antigen-presenting capacity of DCs with the ability to present all tumor antigens expressed on tumor cells to T cells. Stochastic optimization algorithms were designed to deal with highly complex optimization problems. Since many real-world combinatorial problems are NP-hard, it is not possible to guarantee the discovery of the optimum. Instead of exact methods, one usually uses heuristics, which are approximate methods using iterative trial and error processes, to approach the best solution. It has been reported that lipopeptides can be used to elicit cytotoxic T lymphocyte (CTL) responses against viral diseases and cancer. In our previous study, we determined that mono-palmitoylated peptides can enhance anti-tumor responses in the absence of adjuvant activity. Therefore, it has been further investigated whether the depletion of immunosuppressive factors could improve the therapeutic effects of Pam2IDG. Data also have indicated that treatment with Pam2IDG combined with clodronate/liposome delays tumor growth and increases the survival rate In this scientific work we annotated cancer-like high yield electrotransfectioned ex vivo mediated hybrids on minimal magnetic signature mimicking fast stochastic optimization algorithm for fragment-based molecular de novo design of particle swarm optimization-based molecular for the in silico annotated drug discovery interactive approach for the depletion of tumor-associated macrophages by a computer-aided designed candidate drugable Toll-like receptor (Pam2IDG) peptide-domain targeted by a compound screening pharmacophoric mimetic agonistic agent.

Dayside magnetospheric and ionospheric responses to solar wind pressure increase: Multispacecraft and ground observations

AbstractWe provide in situ observations of the transient phenomena in the dayside magnetosphere during the preliminary impulse (PI) and main impulse (MI) event on 30 September 2008. The PI and MI geomagnetic signals are induced by twin traveling convection vortices with opposite polarities in the equivalent ionospheric currents due to a sudden increase of the solar wind dynamic pressure. The two PI‐associated ionospheric current vortices centered at ~07 magnetic local time (MLT), 67° magnetic latitude (MLAT) in the dawnside and ~14 MLT, 73°MLAT in the duskside, respectively. The dawnside MI current vortex centered at ~68° MLAT and 6 MLT, while the duskside vortex center was traveling poleward from ~67° MLAT to ~75° MLAT at a speed of ~5.6–7.4 km/s around 14 MLT. It is found that both dawnside PI‐ and MI‐related current vortices were azimuthally seen up to 4 MLT. Following the magnetosphere sudden impulse, a clockwise flow vortex with a radial scale larger than 3 RE, associated with positive field‐aligned current (FAC), was observed by Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft in the outer dayside magnetosphere. The flow vortex expanded and traveled tailward in the magnetosphere, also being reproduced with global MHD simulations. Based on both observation and simulation technique, we show that the MI‐related FACs are correlated with the large‐scale flow vortex. The PI FACs are partially provided by the mode conversion of fast mode waves into the Alfvén waves near the equatorial plane, while most of it may be generated at a higher‐latitude region in the magnetosphere.

Simultaneous traveling convection vortex events and Pc1 wave bursts at cusp latitudes observed in Arctic Canada and Svalbard

AbstractTraveling convection vortices (TCVs), which appear in ground magnetometer records at near‐cusp latitudes as solitary ~5 mHz pulses, are a signature of dynamical processes in the ion foreshock upstream of the Earth's bow shock that can stimulate transient compressions of the dayside magnetosphere. These compressions can also increase the growth rate of electromagnetic ion cyclotron (EMIC) waves, which appear in ground records at these same latitudes as bursts of Pc1 pulsations. In this study we have identified TCVs and simultaneous Pc1 burst events in two regions, Eastern Arctic Canada and Svalbard, using a combination of fluxgate magnetometers and search coil magnetometers in each region. By looking for the presence of TCVs and Pc1 bursts in two different sequences, we have found that the distribution of Pc1 bursts was more tightly clustered near local noon than that of TCV events, that neither TCVs nor Pc1 bursts were always associated with the other, and even when they occurred simultaneously their amplitudes showed little correlation. Magnetometer data from GOES‐12 were also used to characterize the strength of the magnetic compressions at geosynchronous orbit near the magnetic equator. Compressions > 2 nT at GOES‐12 occurred during 57% of the Canadian TCV events, but during ~85% of the simultaneous TCV/Pc1 burst events. There was again little evident correlation between TCV and GOES‐12 compression amplitudes. We have also documented unusually low EMIC wave activity during this deep solar minimum interval, and we attribute the low occurrence percentage of combined events in this study to this minimum.

Multi‐instrument observations from Svalbard of a traveling convection vortex, electromagnetic ion cyclotron wave burst, and proton precipitation associated with a bow shock instability

AbstractAn isolated burst of 0.35 Hz electromagnetic ion cyclotron (EMIC) waves was observed at four sites on Svalbard from 0947 to 0954 UT 2 January 2011, roughly 1 h after local noon. This burst was associated with one of a series of ~50 nT magnetic impulses observed at the northernmost stations of the IMAGE magnetometer array. Hankasalmi SuperDARN radar data showed a west‐to‐east (antisunward) propagating vortical ionospheric flow in a region of high spectral width ~ 1–2° north of Svalbard, confirming that this magnetic impulse was the signature of a traveling convection vortex. Ground‐based observations of the Hα line at Longyearbyen indicated proton precipitation at the same time as the EMIC wave burst, and NOAA‐19, which passed over the west coast of Svalbard between 0951 and 0952, observed a clear enhancement of ring current protons at the same latitude. Electron precipitation from this same satellite indicated that the EMIC burst was located on closed field lines, but near to the polar cap boundary. We believe these are the first simultaneous observations of EMIC waves and precipitating energetic protons so near to the boundary of the dayside magnetosphere. Although several spacecraft upstream of Earth observed a steady solar wind and predominantly radial interplanetary magnetic field orientation before and during this event, data from Geotail (near the morning bow shock) showed large reorientations of the interplanetary magnetic field and substantial decreases in ion density several minutes before it, and data from Cluster (near the afternoon bow shock) showed an outward excursion of the bow shock simultaneous with it. These upstream perturbations suggest that a spontaneous hot flow anomaly, a bow shock related instability, may have been responsible for triggering this event, but do not provide enough information to fully characterize that instability.

Dayside proton aurora associated with magnetic impulse events: South Pole observations

We present, for the first time, auroral hydrogen emission at 486.1 nm (proton aurora) associated with a magnetic impulse event (MIE) or a traveling convection vortex (TCV). The MIE (or TCV) is a transient phenomenon (∼5–15 min) characterized by a large amplitude (>50 nT) in the magnetic field disturbance occurring at 70°–80° magnetic latitudes (MLATs). Optical observations at the South Pole Station (−74.3° MLAT) showed a clear spot‐like brightening of proton auroral emissions associated with MIEs. These spots of the proton aurora were ∼300–500 km in length and ∼150–200 km in width at an altitude of 150 km and lasted for ∼1–2 minutes. The spot drifted antisunward with a speed of ∼3–5 km/s but did not always drift. Quasi‐stable spots coincided with poleward moving multiple arcs at 630.0 nm. There was no clear one‐to‐one correspondence between the spots and the power of the ground magnetic field in the Pc1 range. The variety of proton auroral emissions associated with MIEs may be a visible manifestation of the variety of processes that take place near the region generating a pair of field‐aligned currents that drives MIEs.

Polar UVI and THEMIS GMAG observations of the ionospheric response to a hot flow anomaly

We present observations of the ionospheric response to a hot flow anomaly (HFA) interacting with the magnetosphere. On 4 July 2007, the THEMIS spacecraft observed an HFA, a disruption of the solar wind flow, on both sides of the bow shock. The ionospheric response was measured by global auroral images taken over the southern hemisphere by Polar UVI, by ground based magnetometers and photometers in Antarctica, and by the THEMIS Ground Based Observatory (GBO) magnetometers (GMAGs) in the northern hemisphere. Polar UVI observations show a region of enhanced auroral emission in the morning sector about 10 min after the THEMIS spacecraft observed the HFA. This region of enhanced emission was located above South Pole station which observed magnetic perturbations and an increase in the auroral luminosity. The THEMIS GMAGs in the conjugate hemisphere also observed magnetic perturbations consistent with a traveling convection vortex (TCV). Polar UVI tracked the spatial and temporal development of the region of enhanced emission. Slow anti-sunward motion was observed as the emission weakened and then re-brightened over the course of about 10 min. Simultaneously, the THEMIS GMAG array observed anti-sunward motion of the magnetic impulse with a velocity much greater than that of the auroral emission. These are the first simultaneous observations of localized enhanced auroral emission and the associated magnetic impulse propagating anti-sunward over a distance of several 1000 km. We suggest that the origin of the magnetic perturbation and resulting auroral emission is the deformation of the magnetopause due to the HFA–magnetosphere interaction. The different propagation speeds of the auroral emission in the southern hemisphere and the magnetic perturbation in the northern hemisphere imply either (1) a decoupling of the auroral emission and field-aligned current signature or (2) a decoupling of these processes between the two hemispheres. The large difference in the ionospheric conductivity between the northern (summer) and southern (winter) hemispheres may be an important factor in this decoupling. More observations are needed to adequately address the decoupling mechanism.

Dayside magnetosphere‐ionosphere coupling during IMF clock angle ∼90°: Longitudinal cusp bifurcation, quasi‐periodic cusp‐like auroras, and traveling convection vortices

In spite of the great progress achieved in the understanding the Earth's magnetosphere‐ionosphere system, its configuration and dynamics during periods with large horizontal interplanetary magnetic field (IMF ∣By∣ ≫ 0) is still poorly investigated. In such time intervals, the cusp/low‐latitude boundary layer (LLBL) entry regions are characterized by a more complex magnetic reconnection topology, than during IMF Bz‐dominated periods, which in turn leads to peculiar magnetosheath plasma injections into the magnetosphere and associated ionospheric signatures. In this context, we discuss the 19 December 2002 dayside aurora activity, observed by the ITACA2 twin all‐sky camera system, along the Greenland‐Svalbard sector, during a nearly horizontal IMF (By ∼ 15 nT and Bz ∼ 0). The event originates from a longitudinally bifurcated cusp configuration and then develops into quasi‐periodic red aurora activations, between about 1000 and 1140 UT. By analyzing the Greenlandic magnetometer data, we identify a series of westward traveling convection vortices (TCVs), moving away from magnetic noon at 2–3 km/s and synchronized with the transit of red‐dominated auroral forms. We find that the auroral emission takes place in coincidence with the ionospheric footprint of the downward field‐aligned currents (counterclockwise TCVs), instead of the upward ones (clockwise TCVs), as it would be expected for precipitating electrons. This fact and several analogies with previously reported quasi‐periodic TCV activity, observed during IMF By‐dominated periods, suggest that the geomagnetic activity could be associated with FACs that are triggered by the magnetic merging on the dayside, either by inducing azimuthal pressure gradients at the magnetopause or by driving magnetopause/LLBL wave activity.

Transient response of the Earth's magnetosphere to a localized density pulse in the solar wind: Simulation of traveling convection vortices

We investigate the transient response of the Earth's magnetosphere‐ionosphere system to a localized density pulse in the solar wind using a magnetohydrodynamic simulation. The simulated ionospheric disturbances exhibit many properties similar to those observed during traveling convection vortices (TCVs). The simulated TCVs are driven by pairs of field‐aligned currents. The generation mechanisms of the field‐aligned currents in the magnetosphere are evaluated in terms of a wave equation of field‐aligned currents. The source current is the inertial current associated with in‐out plasma acceleration in the magnetosphere near the impact region. The inertial current is converted into the field‐aligned current off from the equatorial region via the curvilinear effect. The inhomogeneous effect also generates the field‐aligned current near the inner equatorial region where the sharp gradient of Alfvén speed exists.

A test of the magnetospheric source of traveling convection vortices

Traveling convection vortices (TCVs) are a powerful tool for probing the nature of the coupling between the solar wind, the magnetosphere, and the ionosphere. There is no reliable model of the plasma concentration in the magnetosphere, resulting in uncertainties about the factors controlling the scale size, the motion, and the numbers of field‐aligned currents associated with TCV events. There is also uncertainty about whether TCV generation is current driven, voltage driven, or even driven by some more complex source. We use conjugate ground‐based magnetometer data from the Greenland magnetometer chain and Antarctica to test the nature of the magnetospheric source of 18 TCV events associated with changes in the magnetopause dynamic pressure. This is achieved by statistically comparing two groups of TCV events: for one group the conjugate ionospheres are of similar conductivity, and for the other group the conductivities of the conjugate ionospheres differ by an order of magnitude. Statistically, we find that conjugate TCV events are of similar intensity in both hemispheres regardless of any difference in conductivity between the two hemispheres. We propose that this is evidence in favor of a constant current source for TCVs where the amplitude of a TCV is controlled by the local plasma concentration, the magnetic field strength, and the acceleration of the plasma.

A detailed description of the solar wind triggers of two dayside transients: Events of 25 July 1997

Traveling Convection Vortices (TCVs), a specific type of dayside transient event, offer a good opportunity to study the modes of interaction between the solar wind, bow shock and the magnetosphere/ionosphere system. We study here in detail the solar wind triggers of two TCV events that occurred at 1500 UT and 1835 UT on 25 July 1997. During these two events there was a fortuitous conjunction of four solar wind monitors near the Earth's magnetosphere. We were able to identify the exact solar wind discontinuity that triggered each ground TCV. We found that the 1500 UT TCV was triggered by the density (and thus dynamic pressure) enhancement accompanying a tangential discontinuity. We were able to determine the orientation of the discontinuity plane and thus predict, in good agreement with observations, the propagation of the discontinuity between the four spacecraft as well as the propagation of the transient in the magnetosphere (geosynchronous) and ionosphere. The ground transient was generated in the early afternoon local time and then propagated westward, first toward local noon and then away from noon toward dawn. The 1835 UT TCV, which was stronger, was triggered by a more complicated solar wind discontinuity that exhibited significant spatial structure and an unusual propagation pattern. A detailed analysis of the orientation of the discontinuity fronts explained the propagation of the discontinuity in the solar wind. Even though the discontinuity did not carry a significant dynamic pressure enhancement, it had the properties required to generate a hot flow anomaly (HFA) or a foreshock cavity at the bow shock. The corresponding pressure reduction in the magnetosheath interacted with the magnetosphere to generate the transient near local noon that propagates eastward toward dusk. Geosynchronous observations confirm these conclusions. To strengthen our conclusions, we compared the discontinuity that triggered the ground TCV event with four other discontinuities that occurred in the same 2‐hour window. We found that none of the other four discontinuities carried significant dynamic pressure enhancements or had properties required to create a HFA at the bow shock. They did not trigger detectable transients on the ground. It thus seems that TCVs can be triggered by solar wind discontinuities that either carry dynamic pressure enhancements (or alternatively reductions) or by discontinuities that create HFAs or foreshock cavities at the bow shock.

Solar wind drivers of Traveling Convection Vortices

We present the first clear and consistent evidence of solar wind drivers of Traveling Convection Vortices (TCVs). Using high time resolution data from GEOTAIL just upstream of the bowshock and within 10 earth radii of the sun‐earth line, we were able to clearly identify solar wind triggers for 30 of 31 large amplitude TCV events during 1995. These data showed that 20 of the 30 solar wind drivers were isolated foreshock cavities of the type that have been previously reported. A further 8 events belong to a similar class which occurred primarily during rapid rotations of the IMF from or to a radial orientation, accompanied by a foreshock cavity‐like region at the edge of the IMF transition. These observations suggest that the vast majority of TCVs are driven by perturbations of the magnetosphere caused by foreshock cavities that are formed in the interaction between the IMF and the bowshock.

Pressure‐pulse interaction with the magnetosphere and ionosphere

We reexamine traveling convection vortices (TCVs) seen by the Magnetometer Array for Cusp and Cleft Studies on 9 November 1993. IMP‐8 energetic ion observations confirm that the solar wind pressure variations previously associated with these TCVs were generated by kinetic processes within the Earth's foreshock. As expected during this interval of spiral IMF orientation, fast mode waves launched by the pressure variations first arrived in the equatorial ionosphere near dusk and propagated dawnward. We derive a model for the field‐aligned currents generated by transient compressions of the magnetopause and show that it accounts for the number of TCVs seen in the prenoon ionosphere, their sense of rotation, the latitude at which they occur, and their absence in the postnoon ionosphere.

Traveling convection vortices induced by solar wind tangential discontinuities

Two typical magnetic impulse events (MIEs) accompanied by traveling convection vortices (TCVs) are investigated. The analysis of their conjugate equivalent convection patterns is performed using magnetic field data obtained from high‐latitude ground magnetometer networks in the Northern and Southern Hemispheres. A three‐dimensional analysis of solar wind structures is also performed using solar wind data obtained from multiple International Solar‐Terrestrial Physics satellites. In the first event observed at ∼1310 UT on 22 May 1996, a westward moving TCV appeared simultaneously in the noon‐to‐dawn sector in the Northern and Southern Hemispheres. The solar wind source of this TCV is found to be a tangential discontinuity (TD), which causes a rapid northward turning of the interplanetary magnetic field (IMF) and abrupt dynamic pressure changes. In the second event observed at ∼1610 UT on 27 May 1998, an eastward moving TCV appeared in the noon sector in the Northern and Southern Hemispheres, with a timing delay of 2 to 3 min in the Southern Hemisphere. The solar wind source of this TCV is found again to be a TD, which causes a rapid IMF By negative turning and an abrupt enhancement of dynamic pressure. Analyses show that the TDs driving these events have their motional electric fields pointing toward the TDs and their normal vectors with large cone angles from the sunward direction. These TDs satisfy the conditions for the formation of a hot flow anomaly (HFA) at the bow shock. The sweeping motion across the magnetosphere of the intersection of the TD and the bow shock is found to be consistent with the observed TCV motion in each event. Magnetopause deformations due to HFAs can explain all the observed morphological features and the triggering process of these two MIEs. It is suggested, however, that bursty merging and/or pressure pulses would reinforce the processes produced by the HFAs, since the TDs are usually accompanied by both abrupt IMF changes and pressure enhancements. Consequently, it seems reasonable to conclude that the integrated processes of HFA, bursty magnetic field merging, and pressure pulses produce the evolution of these MIEs and TCVs.

A traveling convection vortex event study: Instantaneous ionospheric equivalent currents, estimation of field‐aligned currents, and the role of induced currents

We analyze a traveling convection vortex (TCV) event on 31 January 1997 using ground magnetometer data of the CANOPUS, MACCS, Geological Survey of Canada, Greenland, and IMAGE networks. For the first time, spatial and instantaneous distributions of the mesoscale ionospheric equivalent currents associated with a TCV are obtained. We apply the method of spherical elementary currents (SECS) to calculate these currents, as well as to infer the part of the ground magnetic signatures that is caused by internal currents induced in the Earth. The resulting ionospheric equivalent currents consist of a leading clockwise vortex centered at 71° CGM latitude which moves westward with ∼7.3 km s−1 and a trailing anticlockwise vortex at 77 ° latitude which moves southwestward away from noon at ∼3.0 km s−1. In an area of ∼200 km around the center of the twin vortices the derived equivalent current densities are less than 70 mA m−1 but reach 100–160 mA m−1 in a broad channel of equatorward currents between the vortices. Using the assumption of a uniform Hall to Pedersen conductance ratio and the assumption that conductance gradients perpendicular to the ionospheric electric field are vanishing, we can estimate the field‐aligned current (FAC) associated with the TCV. The maxima of ∼1 μA m−2 of downward FAC in the leading western vortex, and of ∼0.4 μA m−2 of upward FAC in the trailing eastern vortex occur along the perimeter of the vortices, not in their centers, in contrast to the prediction of ionosphere‐magnetosphere coupling theories for TCVs. The integrated FAC are not fully balanced between the two vortices but show an excess of downward FAC. While the ratio between the internally generated and the total horizontal ground magnetic field for most magnetometer sites in the TCV area amounts to around 20–40%, at some stations it can reach values of 50% and larger.