Field-aligned Current Intensity Research Articles

Juno Observations Set New Constraints on the Electrodynamic Interaction Between Io and Jupiter.

Juno's highly elliptical polar orbits provide unprecedented in-situ observations of the electrodynamic interaction between Jupiter and its volcanic moon Io. These observations occur in regions never sampled before both near Io's orbit and near Jupiter's ionosphere and at distances between the two. Magnetic field data obtained during multiple traversals of magnetic field lines mapping to Io's orbit reveal remarkably rich and complex magnetic signatures near flux tubes connected to Io's orbital position. Here we present a methodology to model the distribution of currents along Io's flux tube (IFT) and Alfvén wings in such a way as to match the magnetic field signature observed during Juno's traversals of the IFT and Alfvén wings downstream of Io. We obtain the location, size and morphology of the current-carrying region as well as the distribution of currents within the IFT and Alfvén wings. The observed field-aligned currents exhibit strong filamentation, with upward and downward currents splitting into secondary cells rather than forming uniform structures. Additionally, there is a strong correlation between total field-aligned current intensity, particle energy flux, and Poynting flux, indicating efficient energy transfer and coupling in the Jupiter-Io system. Using all of Juno's traversals up to perijove (PJ) pass 42, we estimate the strength of the interaction with regards to distance along Io's extended tail, Io's position in the plasma torus and the magnetic field intensity at the footprint in Jupiter's ionosphere, illuminating the interaction of Jovian magnetospheric plasma with Io and setting important constraints in the Io-Jupiter interaction.

Correlation analysis of field-aligned currents from the magnetic measurements of GRACE follow-on mission

In this study we performed a detailed analysis on the scale-size of field-aligned currents (FACs) at auroral latitudes, using the well-calibrated magnetic data from the non-dedicated magnetic field mission, Gravity Recovery and Climate Experiment Follow-On (GRACE-FO). With two spacecraft following each other, the GRACE-FO provides a good opportunity to identify the variation of FACs with different scale lengths. The results show that the auroral FACs can be classified into two groups: the small-scale ones, shorter than some tens of kilometers, dominated by kinetic Alfvén waves, are quite dynamic; and the large-scale ones, typically larger than 150 km, can be considered as quasi-static and persist longer than 1 min. The GRACE-FO observations also reveal that the small-scale FACs at the same location sometimes can persist over 25 s, e.g., around dusk and dawn hours, which is longer than the typical persistent period (10 s) of kinetic Alfvén waves as earlier reported. The FAC structures show clear magnetic local time dependence, with higher correlations between the spacecraft around dusk and dawn hours; lower correlations are found around midnight and lowest correlations around noon, implying that the small-scale FACs most frequently appear at the noon cusp region. Slightly better correlations of FACs between two spacecraft are found during local summer, and such seasonal dependence is dominated by the correlations of small-scale FACs at noon. However, further analysis shows that the small-scale FACs at noon have largest occurrence and intensity during local summer, which reveals that when interpreting the cross-correlation analysis the intensity of FACs needs to be taken into account.Graphical

Dynamics of field-aligned currents in two hemispheres during a magnetospheric storm from magnetogram inversion technique data

We continue to study the physical processes occurring during the August 17, 2001 magnetospheric storm by analyzing the dynamics of the intensity of field-aligned currents (FACs) in Iijima—Potemra Region 1 in the polar ionospheres of the two hemispheres, using the modernized magnetogram inversion technique. The results obtained on the dynamics of two types of FAC asymmetry (dawn-dusk and interhemispheric), as well as the previously obtained regularities in the behavior of Hall currents and the polar cap boundaries depending on the large azimuthal component of the interplanetary magnetic field (IMF), observed during the storm, and the seasonal behavior of the conductivity are consistent with the open magnetosphere model and with satellite observations of auroras in two hemispheres. We have shown that the weakening of the asymmetry of two types in the FAC distribution during substorms in the storm under study occurs almost completely in the winter hemisphere and is much weaker in the summer one. We associate this phenomenon with the predominance of the effect of long-term exposure to the azimuthal IMF component in the sunlit polar ionosphere of the summer hemisphere over the substorm symmetrization effect of the night magnetosphere. A symmetrization effect of the polar cap and FACs, created by the solar wind pressure pulse at the end of the storm, is observed. We propose a qualitative explanation of this effect.

Динамика продольных токов в двух полушариях Земли в ходе магнитосферной бури по данным техники инверсии магнитограмм

We continue to study the physical processes occurring during the August 17, 2001 magnetospheric storm by analyzing the dynamics of the intensity of field-aligned currents (FACs) in Iijima—Potemra Region 1 in the polar ionospheres of the two hemispheres, using the modernized magnetogram inversion technique. The results obtained on the dynamics of two types of FAC asymmetry (dawn-dusk and interhemispheric), as well as the previously obtained regularities in the behavior of Hall currents and the polar cap boundaries depending on the large azimuthal component of the interplanetary magnetic field (IMF), observed during the storm, and the seasonal behavior of the conductivity are consistent with the open magnetosphere model and with satellite observations of auroras in two hemispheres. We have shown that the weakening of the asymmetry of two types in the FAC distribution during substorms in the storm under study occurs almost completely in the winter hemisphere and is much weaker in the summer one. We associate this phenomenon with the predominance of the effect of long-term exposure to the azimuthal IMF component in the sunlit polar ionosphere of the summer hemisphere over the substorm symmetrization effect of the night magnetosphere. A symmetrization effect of the polar cap and FACs, created by the solar wind pressure pulse at the end of the storm, is observed. We propose a qualitative explanation of this effect.

Dynamics of the field-aligned currents distribution asymmetry during substorms in the equinox season

We continue to study the physical processes occurring during the August 17, 2001 magnetospheric storm by analyzing the dynamics of the intensity of field-aligned currents (FACs) in Iijima—Potemra Region 1 in the polar ionospheres of two hemispheres, using the modernized magnetogram inversion technique. The results obtained on the dynamics of the FAC asymmetry of two types (dawn–dusk and interhemispheric), as well as the previously obtained regularities in the behavior of Hall currents and polar cap boundaries depending on the large azimuthal component of the interplanetary magnetic field (IMF), observed during the storm, and the seasonal behavior of the conductivity are consistent with the open magnetosphere model and with satellite observations of auroras in two hemispheres. We have shown that the weakening of the asymmetry of two types in the FAC distribution during substorms in the storm under study occurs almost completely in the winter hemisphere and is much weaker in the summer one. We associate this phenomenon with the predominance of the effect of long-term exposure to the azimuthal IMF component in the sunlit polar ionosphere of the summer hemisphere over the substorm symmetrization effect of the night magnetosphere. A symmetrization effect of the polar cap and FACs, created by the solar wind pressure pulse at the end of the storm, is observed. We propose a qualitative explanation of this effect.

Динамика асимметрии распределения продольных токов во время суббурь в сезон равноденствия

We continue to study the physical processes occurring during the August 17, 2001 magnetospheric storm by analyzing the dynamics of the intensity of field-aligned currents (FACs) in Iijima—Potemra Region 1 in the polar ionospheres of two hemispheres, using the modernized magnetogram inversion technique. The results obtained on the dynamics of the FAC asymmetry of two types (dawn–dusk and interhemispheric), as well as the previously obtained regularities in the behavior of Hall currents and polar cap boundaries depending on the large azimuthal component of the interplanetary magnetic field (IMF), observed during the storm, and the seasonal behavior of the conductivity are consistent with the open magnetosphere model and with satellite observations of auroras in two hemispheres. We have shown that the weakening of the asymmetry of two types in the FAC distribution during substorms in the storm under study occurs almost completely in the winter hemisphere and is much weaker in the summer one. We associate this phenomenon with the predominance of the effect of long-term exposure to the azimuthal IMF component in the sunlit polar ionosphere of the summer hemisphere over the substorm symmetrization effect of the night magnetosphere. A symmetrization effect of the polar cap and FACs, created by the solar wind pressure pulse at the end of the storm, is observed. We propose a qualitative explanation of this effect.

Estimation of the contributions of conductance and electric field to the intensity of field-aligned currents in the night polar ionosphere during substorm expansion phase

Based on the output data of the magnetogram inversion technique, we analyze the dynamics of the Pedersen ionospheric currents and field-aligned currents (FACs) in the night mesoscale cells of the three main large-scale Iijima and Potemra Regions (R1, R2 and R0) during the expansion phase of the summer and winter substorms. FACs play a key role in the ionosphere-magnetosphere interaction. The continuity equation for the electric current density contains two types of possible feedback within the electric circuit parts that connect Pedersen currents and FACs in each cell. Pedersen ionospheric conductivity is dominant to Type 1, and the electric field dominates in Type 2 feedback. This paper studies both types of physical feedback in mesoscale cells of downward and upward FACs on the night side of the polar ionosphere from the data of two selected substorms of the summer and winter seasons in the northern hemisphere.

Specific Features of the Distributions of the Hall Currents and Magnetic Field of Pс4 Pulsations

The distributions of the intensities and directions of the Hall currents in the ionosphere have been determined by the given coordinates and intensities of magnrtospheric field-aligned currents (FAC). The examples of distributions calculated for three FAC show that the coincidence of specific features of the field of the Hall currents and the magnetic field on the ground level near the points of their projections is explained by the induction character of the formation of the Hall current. This makes possible to estimate the number, location, and intensity of field-aligned currents with experimentally constructed magnetic pulsation field distributions under the condition that the distances between the sources are larger than the ionospheric height. The presented solution of the equations for the field-lines and isolines of the Hall current intensity shows that the arcs of these curves are locally generated by a pair of equivalent field-aligned currents.

Positive and negative feedbacks in the magnetosphere-ionosphere coupling

We study dynamics of field-aligned currents (FACs) during the expansion phase (EP) of two selected summer and winter substorms, by applying the magnetogram inversion technique (MIT) to the data of the world network of ground-based stations. The empirical MIT data and the modified Iijima and Potemra (I-P) model are presented. It is supposed a sharp increase in the upward FAC in I-P Region 1 and associated upward inter-hemispheric current in the dusk sector of the summer hemisphere during EP – in correspondence with theoretical models. Simultaneously (relative to the substorm onset time), and with the same value range, the downward inter-hemispheric current should enhance in the conjugate sector of the winter hemisphere. This FACs restructuring scenario in two hemispheres may clarify some of the unresolved issues in substorm physics. E.g., we describe the strong seasonal variation in the magnetic and auroral activity that is practically absent or unknown in literature even for the Northern hemisphere. Trying to answer this and other questions debated in literature, we study and describe strong feedbacks between the intensity of night FACs flowing in/out of each hemisphere, on the one hand, and the ionosphere conductivity or electric field, on the other. These magnetosphere-ionosphere feedbacks cause, in particular, the above inter-hemispheric currents and consequences prior and during the EP of the addressed substorms.

Relationship between PC index and magnetospheric field-aligned currents measured by Swarm satellites

The relationship between the magnetospheric field-aligned currents (FAC) monitored by the Swarm satellites and the magnetic activity PC index (which is a proxy of the solar wind energy incoming into the magnetosphere) is examined. It is shown that current intensities measured in the R1 and R2 FAC layers at the poleward and equtorward boundaries of the auroral oval are well correlated, the R2 currents being evidently secondary in relation to R1 currents and correlation in the dawn and dusk oval sectors being better than in the noon and night sectors. There is evident relationship between the PC index and the intensity of field-aligned currents in the R1 dawn and dusk layers: increase of FAC intensity in the course of substorm development is accompanied by increasing the PC index values. Correlation between PC and FAC intensities in the R2 dawn and dusk layers is also observed, but it is much weaker. No correlation is observed between PC and field-aligned currents in the midnight as well as in the noon sectors ahead of the substorm expansion phase. The results are indicative of the R1 field-aligned currents as a driver of the polar cap magnetic activity (PC index) and currents in the R2 layer.

Local time resolved dynamics of field‐aligned currents and their response to solar wind variability

AbstractUsing 10 years of CHAMP measurements condensed into the empirical model of field‐aligned currents through empirical orthogonal function analysis, the dynamics of field‐aligned currents (FACs) is modeled and studied in separate magnetic local time (MLT) sectors. We investigate the distributions of FAC intensity and latitude and evaluate their predictability in terms of geospace parameters which are ranked according to their relative importance measured by a multivariate regression procedure. The response time to changes in solar wind variables is studied in detail and found to be much shorter for dayside FACs than on the nightside (15–25 min versus 35–95 min). Furthermore, dayside FACs can be parameterized more accurately: R2 values maximize greater than 0.7 for FAC latitude and greater than 0.3 for FAC intensity, whereas the corresponding values on the nightside are smaller than 0.3 and 0.15, respectively. The results support the separation between directly driven coupling processes acting on the dayside and unloading processes controlling the nightside. In addition, the MLT‐resolved standardized regression coefficients suggest that (1) FAC latitude is affected most significantly by the transpolar potential, substorm evolution, solar activity as represented by the F10.7 index and its square, and the dipole tilt; (2) Region‐1/2 current intensity is controlled most efficiently by substorm evolution, IMF Bz and IMF By; and (3) cusp current intensity is influenced by conductivity, IMF By and their cross item.

Field‐aligned currents during the extreme solar minimum between the solar cycles 23 and 24

AbstractThe solar minimum between solar cycles 23 and 24 was unusually long and deep. The upward region‐1 (R1) field‐aligned current (FAC) response to this extreme solar minimum was investigated using Defense Meteorological Satellite Program observations. The solar cycle responses on the dayside are different than those on the nightside. The field‐aligned current density (J//) on the dayside, at 12–17 magnetic local time (MLT), peaks in the declining phase of the solar cycle, in 2003, when the solar wind speed also peaks, whereas J// on the nightside, at 18–23 MLT, appears insensitive to the solar cycle. In 1995–2010, J// at 15–17 MLT reaches the lowest value during the extreme solar minimum in 2009, when the solar wind speed also reaches the lowest value. At 12–17 MLT, R1 is located mostly on open field lines or at the boundary layer, where the current is driven mostly by the velocity shear at the magnetopause boundary. However, on the nightside, R1 is located mostly on the closed field lines where J// is not driven directly and immediately by the solar wind. The nightside current width (Λ) exhibits a solar cycle effect such that Λ is smaller at the solar minimum and smallest in 2009. However, the dayside Λ exhibits little solar cycle effect. As a result, the FAC intensity (latitudinally integrated J//) exhibits a solar cycle variation at all local times and the FAC intensity is lower during the extreme solar minimum than that of the previous solar minimum.

A high‐resolution model of field‐aligned currents through empirical orthogonal functions analysis (MFACE)

Ten years of CHAMP magnetic field measurements are integrated into MFACE, a model of field‐aligned currents (FACs) using empirical orthogonal functions (EOFs). EOF1 gives the basic Region‐1/Region‐2 pattern varying mainly with the interplanetary magnetic fieldBz component. EOF2 captures separately the cusp current signature and By‐related variability. Compared to existing models, MFACE yields significantly better spatial resolution, reproduces typically observed FAC thickness and intensity, improves on the magnetic local time (MLT) distribution, and gives the seasonal dependence of FAC latitudes and the NBZ current signature. MFACE further reveals systematic dependences on By, including 1) Region‐1/Region‐2 topology modifications around noon; 2) imbalance between upward and downward maximum current density; 3)MLT location of the Harang discontinuity. Furthermore, our procedure allows quantifying response times of FACs to solar wind driving at the bow shock nose: we obtain 20 minutes and 35–40 minutes lags for the FAC density and latitude, respectively.

Sawtooth substorms generated under conditions of the steadily high solar wind energy input into the magnetosphere: Relationship between PC, AL and ASYM indices

Periodicity in occurrence of magnetic disturbances in polar cap and auroral zone under conditions of steady and powerful solar wind influence on the magnetosphere is analyzed on the example of 9 storm events with distinctly expressed sawtooth substorms (N=48). Relationships between the polar cap magnetic activity (PC-index), magnetic disturbances in the auroral zone (AL-index) and value of the ring current asymmetry (ASYM index) were examined within the intervals of the PC growth phase and the PC decline phase inherent to each substorm. It is shown that the substorm sudden onsets are always preceded by the PC growth and that the substorm development does not affect the PC growth rate. On achieving the disturbance maximum, the PC and AL indices are simultaneously fall down to the level preceding the substorm, so that the higher the substorm intensity, the larger is the AL and PC drop in the decline phase. The ASYM index increases and decreases in conformity with the PC and AL behavior, the correlation between ASYM and PC being better than between ASYM and AL. Level of the solar wind energy input into the magnetosphere determines periodicity and intensity of disturbances: the higher the coupling function EKL, the higher is substorm intensity and shorter is substorm length. Taking into account the permanently high level of auroral activity and inconsistency of aurora behavior and magnetic onsets during sawtooth substorms, the conclusion is made that auroral ionosphere conductivity is typically high and ensures an extremely high intensity of field-aligned currents in R1 FAC system. The periodicity of sawtooth substorms is determined by recurrent depletions and restorations of R1 currents, which are responsible for coordinated variations of magnetic activity in the polar cap and auroral zone.

Events of August 2, 2002: Features of substorm field-aligned currents

A model of alignment of the field-aligned current generator system in the disturbed magnetosphere is proposed. It has been found that Pedersen currents in the disturbed ionosphere of the auroral oval are meridional. They connect oppositely directed field-aligned currents (FACs) of two adjacent Iijima and Potemra (IP) regions. This supplements the dominant concept of currents in the literature, in which a substorm current wedge plays a major role. During the considered substorm, graphs have been obtained of changes in FAC intensities in each of the three Iijima and Potemra regions of the Northern Hemisphere. These new data suggest that during a disturbance, the Region 1 FAC and the sum of regions 2 and 0 FACs remain equal. The equality means that these three generators form a unified system. Inequalities of intensities between two FACs of different sign simultaneously observed in the dawn and dusk sectors have also been detected in each IP region. A conceptual model is proposed for the formation of this dawn-dusk asymmetry. In the model, in addition to FACs that close up in the ionosphere of the Northern Hemisphere, FACs connecting the two hemispheres are also presented. The conclusion is justified that the global magnetospheric dynamo operates as a voltage generator under relatively quiet (average) conditions, as during storms.

The generator system of field-aligned currents during the April 06, 2000, superstorm

Using ground-based magnetometer data of the April 6–7, 2000, superstorm, we obtained maps of ionospheric and field-aligned currents (FACs). Based on these, we deduced the electrical circuit of the disturbed magnetosphere/ionosphere and a conceptual model of its magnetospheric generators, which supply both hemispheres. This model implies that the generator system creates primarily the Region-1 FACs of Iijima and Potemra at both hemispheres, while the Region-2 and Region-0 FACs form by spreading of the Region-1 currents through the ionosphere. This conclusion is supported by observations. A second prediction of this model turns out to be the following hypothesis, which is also based on the new empirical data. The Region-2 FAC of the dawn side in the Northern Hemisphere is connected with the global dynamo via the asymmetric ring current of the inner magnetosphere, DRP-1. Coming with the DRP-1 into the dusk side, the Region-2 FAC then splits and connects with the dusk side ionosphere of both hemispheres. This way a part of the dawn side Region-1 current becomes connected with the dusk side dynamo of the opposite hemisphere. The intensity of Region-2 and Region-1 FACs of the dusk side is therefore smaller than on the dawn side of this hemisphere, provided that the conductivity in the magnetically conjugated Region-2 ionosphere is larger than the local. Similarly, the dawn–dusk asymmetry of the FAC intensities may also be caused by an inequality of magnetic field and/or pressure gradient in the northern and southern halves of the plasma sheet where DRP-1 flows. The predicted dawn–dusk asymmetry according to such a model is supported by the observations and appears causally connected with an asymmetry between the hemispheres. This conclusion opens a new approach to study these kinds of FAC asymmetries. Further analysis led to the additional conclusion, that the global magnetospheric dynamo works as a voltage generator both during relatively quiet (average) conditions as well as under strong disturbance conditions.

Spatial distribution of average vorticity in the high‐latitude ionosphere and its variation with interplanetary magnetic field direction and season

We present a technique to measure the magnetic field‐aligned vorticity of mesoscale plasma flows in the F region ionosphere using line‐of‐sight velocity measurements made by the Super Dual Auroral Radar Network (SuperDARN). Vorticity is often used as a proxy for magnetic field‐aligned current (FAC) intensity in the ionosphere but also provides information about turbulent processes in the ionosphere and magnetosphere. Using 6 years (2000–2005 inclusive) of vorticity measurements made by six SuperDARN radars in the Northern Hemisphere, we have compiled, for the first time, maps of average vorticity across the northern polar ionosphere. These maps have been subdivided according to different seasonal and interplanetary magnetic field (IMF) conditions. The variations in the morphology of the vorticity maps with IMF direction match very closely those seen in maps of average FAC intensity (determined using different methods and instrumentation), suggesting that vorticity is a good proxy for FAC in an averaged sense. The variations in the morphology of the vorticity maps with season show differences from those seen in the FAC maps, illustrating that ionospheric conductance plays a major role in determining the differences between measurements of vorticity and FAC.

Comparison of simulated and observed large-scale, field-aligned current structures

Abstract. Recently, a model of large-scale, field-aligned current (FAC) structures, based on zero-frequency MHD surface wave (SW) modes that can emerge from the solar wind-Earth's magnetosphere interaction, has been proposed. The FAC polarity and intensity distribution are quantified as a function of the solar wind parameters and the interplanetary magnetic field (IMF) magnitude that enter as input parameters. Besides, there are input parameters intrinsic to the Earth's magnetosphere – the size of the polar cap and the boundary regions and their plasma density variations. Influence of the IMF By component on the FAC structure is examined here. Depending on the IMF By magnitude, the predicted six-cell FAC structure tends to evolve in a spiral-like fashion. This large-scale FAC model is compared with experimental evidences and empirical FAC models based on DE-2 satellite data and high-precision Oersted and Magsat satellite magnetometer data. Among the various achievements of these long-term satellite measurements, an observation/discovery of a ground-based state of FACs which includes a pair of large-scale FACs in the polar cap under both positive and negative IMF Bz has been pointed out. The FAC pattern is qualitatively and quantitatively consistent with experimental data for both polar cap FAC and Region 1 and Region 2 FAC systems.

Field-aligned currents observed by CHAMP during the intense 2003 geomagnetic storm events

Abstract. This study concentrates on the characteristics of field-aligned currents (FACs) in both hemispheres during the extreme storms in October and November 2003. High-resolution CHAMP magnetic data reflect the dynamics of FACs during these geomagnetic storms, which are different from normal periods. The peak intensity and most equatorward location of FACs in response to the storm phases are examined separately for both hemispheres, as well as for the dayside and nightside. The corresponding large-scale FAC peak densities are, on average, enhanced by about a factor of 5 compared to the quiet-time FACs' strengths. And the FAC densities on the dayside are, on average, 2.5 times larger in the Southern (summer) than in the Northern (winter) Hemisphere, while the observed intensities on the nightside are comparable between the two hemispheres. Solar wind dynamic pressure is correlated with the FACs strength on the dayside. However, the latitudinal variations of the FACs are compared with the variations in Dst and the interplanetary magnetic field component Bz, in order to determine how these parameters control the large-scale FACs' configuration in the polar region. We have determined that (1) the equatorward shift of FACs on the dayside is directly controlled by the southward IMF Bz and there is a saturation of the latitudinal displacement for large value of negative Bz. In the winter hemisphere this saturation occurs at higher latitudes than in the summer hemisphere. (2) The equatorward expansion of the nightside FACs is delayed with respect to the solar wind input. The poleward recovery of FACs on the nightside is slower than on the dayside. The latitudinal variations on the nightside are better described by the variations of the Dst index. (3) The latitudinal width of the FAC region on the nightside spreads over a wide range of about 25° in latitude.

Comparison of large‐scale field‐aligned currents under sunlit and dark ionospheric conditions

The present study statistically compares large‐scale field‐aligned currents (FACs) under sunlit and dark ionospheric conditions. A total of ∼74,000 auroral oval crossings are selected from magnetic field measurements from the DMSP F7 and F12 to F15 satellites. For the dayside FAC it is reconfirmed that both current intensity and density are statistically larger in the illuminated events than in the unilluminated events. As for the nightside FAC, in contrast, a few important features become clear for the first time, which can be summarized as follows: (1) At 20 ≤ MLT < 02 both R1 and R2 intensities tend to be larger when the ionosphere is dark than when it is sunlit. (2) Although dependence on the ionospheric condition is less clear for the FAC density, a systematic preference of the occurrence of strong FACs for the dark ionosphere can be found for both R1 and R2 currents in the dusk‐to‐premidnight (16 ≤ MLT < 22) sector and for the R1 current in the postmidnight sector (00 ≤ MLT < 02). (3) For both FAC intensity and density the difference between the illuminated and unilluminated events tends to increase with increasing geomagnetic activity as measured by the IMF BZ component. Result 1 can be partially explained in terms of the interhemispheric asymmetry of the magnetospheric configuration, which, however, should not affect the FAC density. Therefore result 2 strongly suggests that the solar‐induced conductivity controls the M‐I coupling in a different way in certain nightside MLT sectors than in dayside sectors.