Ionospheric Pedersen Conductivity Research Articles

Joule Heating rate at high-latitudes by Swarm and ground-based observations compared to MHD simulations

We compare Joule Heating rates as derived from ground-based magnetic field and all-sky camera data, from Low Earth Orbit satellite data (ESA Swarm) and from a MHD simulation (GUMICS-5) with each other in a case study of an auroral arc system. The observational estimates of Joule Heating rates provide information on regional scales and with high spatial resolution (10–100 km). Their comparison with global MHD results is conducted for a quiet time interval of a few minutes, just before a magnetic substorm. Analysis of the ground-based observations yields electric field with dominating North-South component pointing towards the arcs and having maxima values in the range 20–35 V/km. Combining these values with Pedersen conductance estimates from optical data (5–10 S) yields Joule Heating rates in the range 2.5–3.5 mW/m2. Swarm electric field measurements are consistent in their direction and intensity with the ground-based estimates. They also show that heating is increased particularly in the region where the conductance is low. The total amount of Joule heating in the area between the Swarm A and C satellite footprints while crossing the all-sky camera field of view is estimated to be 46 MW and the total amount energy dissipation during the 80 s overflight is around 3.6 GJ (1000 kWh). GUMICS-5 estimate of the peak Joule Heating in the magnetic local time sector of the arc system is smaller than that from the ground-based data with a factor of 2.9. Comparisons of GUMICS-5 results with Space Weather Modeling Framework (SWMF), shows that the latter gives on average larger heating rates being thus more consistent with our regional observations. However, both MHD-codes yield smaller Joule Heating rates around the time of the arcs and during the following substorm than the CTIP-e code. CTIP-e has a more detailed description of ionosphere-thermosphere interactions than the MHD-codes and its convection electric field is enhanced with a randomly varying additional component mimicking small scale structures. GUMICS-SWMF comparisons of global Joule Heating patterns in the Northern polar area reveal that the two simulations have significant differences in their spatial distribution of heating rates. Main cause for these deviations is the difference in the derivation of ionospheric Pedersen conductance. Our results emphasize the fact that future estimates of the global energetics in the magnetosphere–ionosphere–thermosphere system require better knowledge on ionospheric conductivities, both by new measurement concepts and by better understanding on the background physics controlling conductivity variations.

Ionospheric Conductances Due To Electron and Ion Precipitations: A Comparison Between EISCAT and DMSP Estimates

AbstractEnergetic particle precipitation is the major source of electron production that controls the ionospheric Pedersen and Hall conductances at high latitudes. Many studies use empirical formulas to estimate conductances. The particle precipitation spectra measured by the Defense Meteorological Satellite Program (DMSP) Special Sensor J are often used as the input to the empirical formulas. In this study, we evaluate the empirical formulas of ionospheric conductances during four different types of auroral precipitation conditions based on 63 conjugate events observed by DMSP and EISCAT. The conductances calculated from the DMSP data with the empirical formulas are compared with those based on EISCAT measurements with the standard equations. The best correlation between these two is found when the empirical Robinson formulas (Robinson et al., 1987, https://doi.org/10.1029/ja092ia03p02565) are used in the presence of diffuse electron precipitation without ions. In the presence of ion precipitation, the correlation coefficients are smaller, but the correlation improves when the Galand formulas (Galand & Richmond, 2001, https://doi.org/10.1029/1999ja002001) are used to estimate the contribution of ion precipitation to the conductances. We also found that pure ion precipitation can cause the increase of conductances up to 2–7 S for Pedersen and 2.5–10 S for Hall conductances, which is positively correlated with the auroral electrojet index. Overall, the empirical formulas applied to the DMSP particle spectra underestimate the ionospheric conductances.

Role of ionospheric Pedersen conductance and its gradient in field-aligned currents

Field-aligned current (FAC) is one of the most important aspects in the coupling of magnetosphere and the ionosphere. This paper presents a systematic numerical study of the magnetospheric and ionospheric influences on the evolution and modification of FACs, with focus on the role of ionospheric Pedersen conductance and its gradient. FACs are typically generated in the magnetosphere and are carried into the ionosphere by Alfvén waves. During their reflection from the ionosphere, these FACs are modified. The nature of modifications depends on the magnitude and distribution of ionospheric Pedersen conductance. A uniform ionosphere, having a high Pedersen conductance, enhances such a magnetospheric FAC strongly. For conductance-gradients perpendicular to the wave-polarization, FACs are generated after the reflection of simple Alfvénic perturbations, which are not carrying any FACs. A suitable arrangement of ionospheric Pedersen conductance can create a pair of antiparallel FACs, with consequent generation of a strong Pedersen current at the ionospheric boundary. For conductance-gradients along the polarization of the wave, the steady state velocity perturbation assumes an average value of the imposed Pedersen conductance over the entire region after reflection from the ionosphere. This configuration is comparable to the situation where the Cowling conductance operates.

Formation of a Displaced Plasma Wake at Neptune's Moon Triton

AbstractA prominent feature of the interaction between a planetary moon and its magnetospheric environment is the formation of a wake cavity in the downstream hemisphere, characterized by a significant decrease of the incident plasma density. Using an analytical model of Triton's sub‐Alfvénic interaction with Neptune's magnetosphere, we demonstrate that this moon's wake may be rotated away from its downstream hemisphere into a region that would be accessible to the undisturbed upstream flow. Due to the strong tilt of Neptune's magnetospheric field and the low Alfvénic Mach number of the plasma, one of Triton's Alfvén wings can penetrate into the upstream region and intercept the impinging plasma long before it reaches the moon. The interaction with this upstream wing causes the flow to be deflected toward Triton at a steep angle before being absorbed, thereby generating a wake cavity that is significantly displaced with respect to the moon's geometric plasma shadow. Along the downstream‐facing wing, the flow is deflected away from Triton and therefore unable to refill the displaced wake. Since the ionospheric Pedersen conductance greatly exceeds the Alfvén conductance, this asymmetric flow deflection is particularly intense at Triton: when the plasma encounters the wings, it is channeled toward or away from the moon along the axes of the wing tubes. The deflection of the streamlines away from their upstream direction peaks in the range of plasma parameters found along Triton's orbit. Therefore, the displaced wake may be a persistent feature of this moon's plasma interaction and observable during future flybys.

Role of Ionospheric Pedersen Conductance and its Gradient in Field-Aligned Currents

Field-aligned current (FAC) is one of the most important aspects in the coupling of magnetosphere and the ionosphere. This paper presents a systematic numerical study of the magnetospheric and ionospheric influences on the evolution and modification of FACs, with focus on the role of ionospheric Pedersen conductance and its gradient. FACs are typically generated in the magnetosphere and are carried into the ionosphere by Alfven waves. During their reflection from the ionosphere, these FACs are modified. The nature of modifications depends on the magnitude and distribution of ionospheric Pedersen conductance. A uniform ionosphere, having a high Pedersen conductance, enhances such a magnetospheric FAC strongly. For conductance-gradients perpendicular to the wave-polarization, FACs are generated after the reflection of simple Alfvenic perturbations, which are not carrying any FACs. A suitable arrangement of ionospheric Pedersen conductance can create a pair of antiparallel FACs, with consequent generation of a strong Pedersen current at the ionospheric boundary. For conductance-gradients along the polarization of the wave, the steady state velocity perturbation assumes an average value of the imposed Pedersen conductance over the entire region after reflection from the ionosphere. This configuration is comparable to the situation where the Cowling conductance operates.

Swarm Observations of Dawn/Dusk Asymmetries Between Pedersen Conductance in Upward and Downward Field‐Aligned Current Regions

AbstractThe locations of region 1 and 2 field‐aligned current systems were determined using fluxgate magnetometer measurements from 875 dawn‐dusk passes of the Swarm A satellite. Within each field‐aligned current region, the ionospheric Pedersen conductance was derived from the newly corrected Swarm electric and magnetic field measurements. The Pedersen conductances are generally consistent with photoionization models. However, we show that the in situ method of determining Pedersen conductance allows for a more complete description of magnetosphere‐ionosphere coupling and should be used in future studies when possible. We show that, overall, the Pedersen conductance is larger in the upward current region than in the downward region by ∼0.6 S on the dawn side of the Earth. Meanwhile, the dusk side Pedersen conductance is equivalent in both current regions. We attribute this asymmetry to dawn side energetic electron precipitation, commonly associated with substorm electron injections from the magnetotail.

Role of the Ionospheric Conductance Profile in Sub‐Alfvénic Moon‐Magnetosphere Interactions: An Analytical Model

AbstractWe develop an analytical model of the Alfvén wings generated by the interaction between a moon's ionosphere and its sub‐Alfvénic magnetospheric environment. Our approach takes into account a realistic representation of the ionospheric Pedersen conductance profile that typically reaches a local minimum above the moon's poles and maximizes along the bundle of magnetospheric field lines tangential to the surface. By solving the equation for the electrostatic potential, we obtain expressions for various quantities characterizing the interaction, such as the number flux and energy deposition of magnetospheric plasma onto the surface, the spatial distribution of currents within the Alfvén wings and associated magnetic field perturbations, as well as the Poynting flux transmitted along the wings. Our major findings are: (a) Deflection of the magnetospheric plasma around the Alfvén wings can reduce the number flux onto the surface by several orders of magnitude. However, the Alfvénic interaction alone does not alter the qualitative shape of the “bullseye”‐like precipitation pattern formed without the plasma interaction. (b) Due to the deflection of the upstream plasma, the energy deposition onto the moon's exosphere achieves its minimum near the ramside apex and maximizes along the flanks of the interaction region. (c) Even when the ionospheric conductance profile is continuous, the currents along the Alfvén wings exhibit several sharp jumps. These discontinuities generate spikes in the magnetic field that are still observable at large distances to the moon. (d) The magnitude and direction of the wing‐aligned currents are determined by the slope of the ionospheric conductance profile.

Constraining the Temporal Variability of Neutral Winds in Saturn's Low‐Latitude Ionosphere Using Magnetic Field Measurements

AbstractThe Cassini spacecraft completed 22 orbits around Saturn known as the “Grand Finale” over a 5 months interval, during which time the spacecraft traversed the previously unexplored region between Saturn and its equatorial rings near periapsis. The magnetic field observations reveal the presence of temporally variable low‐latitude field‐aligned currents which are thought to be driven by velocity shears in the neutral zonal winds at magnetically conjugate thermospheric latitudes. We consider atmospheric waves as a plausible driver of temporal variability in the low‐latitude thermosphere, and empirically constrain the region in which they perturb the zonal flows to be between ±25° latitude. By investigating an extensive range of hypothetical wind profiles, we present and analyze a timeseries of the modeled velocity shears in thermospheric zonal flows, with direct comparisons to empirically inferred angular velocity shears from the Bϕ observations. We determine the maximum temporal variability in the peak neutral zonal winds over the Grand Finale interval to be ∼350 m/s assuming steady‐state ionospheric Pedersen conductances. We further show that the ionospheric currents measured must be in steady‐state on ∼10 min timescales, and axisymmetric over ∼2 h of local time in the near‐equatorial ionosphere. Our study illustrates the potential to use of magnetospheric datasets to constrain atmospheric variability in the thermosphere region.

The Case for Improving the Robinson Formulas

AbstractAuroral particle precipitation is the main source of ionization on the nightside, making it a critical factor in geospace physics. This magnetosphere‐ionosphere linkage directly contributes to, even controls, the nonlinear feedback within this coupled system. One study has dominated our understanding of this connection, presenting a pair of equations relating auroral particle precipitation to ionospheric Pedersen and Hall conductance, the famous Robinson formulas. This Commentary examines the history of the development and usage of the Robinson formulas and the recent studies exploring corrections and expansions to it. The conclusion is that more work needs to be done; the space physics research community should take up the task to develop improvements and enhancements to better quantify the connection of auroral precipitation to ionospheric conductance.

Ionospheric Modulation by Storm Time Pc5 ULF Pulsations and the Structure Detected by PFISR‐THEMIS Conjunction

AbstractWe investigate a significant duskside ionospheric density modulation in the Pc5 frequency band and related spatial structures during the storm on 28 May 2017. We take advantage of 3‐D ionospheric observations by the PFISR and simultaneous magnetospheric in situ observations. Inversion of the density suggests that the Pc5 pulsations modulated precipitating electrons over a broad range of energies (~5–500 keV). Such strong electron precipitation likely caused a significant density modulation rate of ~8 and ionospheric Pedersen and Hall conductances to vary rapidly and peaked at ~70–100 S. The reflection coefficient was also substantially modulated between 0.5 and 0.9. Moreover, the observations by the multibeam PFISR and THEMIS E both reveal that the Pc5 pulsations propagated westward in the duskside region. It suggests that quasiperiodic activities in the nightside and subsequent duskward drifts were likely the source of the duskside Pc5 pulsations.

Flow Velocity and Field‐Aligned Current Associated With Field Line Resonance: SuperDARN Measurements

AbstractThis study presents observations of the two‐dimensional velocities and field‐aligned currents of magnetospheric field line resonances. Knowledge of the two‐dimensional plasma flows is essential for determining the field‐aligned current structure of the field line resonance and for understanding the role that field line resonances play in the generation of some auroral arc forms. In this work the full velocity vectors are determined from a high‐resolution fit to the Super Dual Auroral Radar Network (SuperDARN) line‐of‐sight data. Two discrete field line resonance events are presented, one at 4.0 mHz (4‐ to 5‐min period) and the other at 0.6 mHz (30‐min period). Band‐pass filtering the north‐south and east‐west components of the total convection velocity vectors reveals the two‐dimensional velocity field specific to an individual field line resonance. The field line resonance velocities exhibit periodic vorticity, which correspond to periodic poleward moving bands of enhanced field‐aligned current. Assuming a constant ionospheric Pedersen conductance of 10 S, peak field‐aligned current values are estimated to be 2–4 μA/m2. The field‐aligned currents alternate between upward and downward directed and peak in magnitude ~0.5–1° poleward and/or equatorward of the peak in field line resonance flow velocity. A Swarm satellite overpass occurs directly over the 0.6‐mHz field line resonance. The SuperDARN field‐aligned current profile along the Swarm trajectory is found to be similar in magnitude and structure to that determined from Swarm‐A and Swarm‐C in situ measurements.

Auroral radio emission from ultracool dwarfs: a Jovian model

A number of fast-rotating ultra cool dwarfs (UCDs) emit pulsed coherent radiation, attributed to the electron cyclotron maser instability, a phenomenon that occurs in the solar system at planets with strong auroral emission. In this paper we examine magnetosphere-ionosphere coupling currents in UCDs, adopting processes used in models of Jovian emission. We consider the angular velocity gradient arising from a steady outward flux of angular momentum from an internal plasma source, as analogous to the jovian main oval current system, as well as the interaction of a rotating magnetosphere with the external medium. Both of these mechanisms are seen in the solar system to be responsible for the production of radio emission. We present the results of an investigation over a range of relevant plasma and magnetosphere-ionosphere coupling parameters to determine regimes consistent with observed UCD radio luminosities. Both processes are able to explain observed UCD luminosities with ionospheric Pedersen conductances of ~1-2 mho, either for a closed magnetosphere with a plasma mass outflow rate of ~10$^5$ kg/s, i.e. a factor of ~100 larger than that observed at Jupiter's moon Io, or for a dwarf with an open magnetosphere moving through the interstellar medium at ~50 km/s and a plasma mass outflow rate of ~1000 kg/s. The radio luminosity resulting from these mechanisms have opposing dependencies on the magnetic field strength, a point which may be used to discriminate between the two models as more data become available.

Role of finite ionospheric conductivity on toroidal field line oscillations in the Earth's magnetosphere—Analytic solutions

AbstractAn analytic solution has been formulated to study the role of ionospheric conductivity on toroidal field line oscillations in the Earth's magnetosphere. The effect of ionospheric conductivity is addressed in two limits, viz, (a) when conductance of Alfvén wave is much different from ionospheric Pedersen conductance and (b) when conductance of Alfvén wave is close to the ionospheric Pedersen conductance. In the former case, the damping is not significant and standing wave structures are formed. However, in the latter case, the damping is significant leading to mode translation. Conventionally, “rigid‐end” and “free‐end” cases refer to eigenstructures for infinitely large and vanishingly small limit of ionospheric conductivity, respectively. The present work shows that when the Pedersen conductance overshoots (undershoots) the Alfvén wave conductance, a free‐end (rigid‐end) mode gets transformed to rigid‐end (free‐end) mode with an increase (decrease) in harmonic number. This transformation takes place within a small interval of ionospheric Pedersen conductance around Alfvén wave conductance, beyond which the effect of conductivity on eigenstructures of field line oscillations is small. This regime of conductivity limit (the difference between upper and lower limits of the interval) decreases with increase in harmonic number. Present paper evaluates the damping effect for density index other than the standard density index m = 6, using perturbation technique. It is found that for a small departure from m = 6, both mode frequency and damping rate become a function of Pedersen conductivity.

An analytical model of sub‐Alfvénic moon‐plasma interactions with application to the hemisphere coupling effect

AbstractWe develop a new analytical model of the Alfvén wing that is generated by the interaction between a planetary moon's ionosphere and its magnetospheric environment. While preceding analytical approaches assumed the obstacle's height‐integrated ionospheric conductivities to be spatially constant, the model presented here can take into account a continuous conductance profile that follows a power law. The electric potential in the interaction region, determining the electromagnetic fields of the Alfvén wing, can then be calculated from an Euler‐type differential equation. In this way, the model allows to include a realistic representation of the “suspension bridge”‐like conductance profile expected for the moon's ionosphere. The major drawback of this approach is its restriction to interaction scenarios where the ionospheric Pedersen conductance is large compared to the Hall conductance, and thus, the Alfvénic perturbations are approximately symmetric between the planet‐facing and the planet‐averted hemispheres of the moon. The model is applied to the hemisphere coupling effect observed at Enceladus, i.e., to the surface currents and the associated magnetic discontinuities that arise from a north‐south asymmetry of the obstacle to the plasma flow. We show that the occurrence of this effect is very robust against changes in the conductance profile of Enceladus' plume, and we derive upper limits for the strength of the magnetic field jumps generated by the hemisphere coupling effect. During all 11 reported detections of the hemisphere coupling currents at Enceladus, the observed magnetic field jumps were clearly weaker than the proposed limits. Our findings are also relevant for future in situ studies of putative plumes at the Jovian moon Europa.

A simulation study of Io-related Jovian decametric radiation: Control factor of occurrence probability

[1] Io-Jupiter interaction leads to auroral emissions and Jovian decametric radiations (Io-DAM). The longitudinal distribution of the Io-DAM occurrence probability has been considered to be controlled by the footprint magnetic intensity of each hemisphere. Recent observations revealed that the brightness of the main auroral spot is mainly modulated by Io's magnetic latitude. In the present study, we propose that the Io-DAM occurrence probability is controlled by the north-south asymmetry of the footprint magnetic intensity, in addition to Io's magnetic latitude. Hall magnetohydrodynamic equations are solved in the corotating meridional plane, which includes the Jovian ionosphere of finite thickness. We assume that the ionospheric Pedersen conductance is inversely proportional to the footprint magnetic intensity; the conductance is nearly the same for both ionospheres at a longitude of 290°, while twice higher for the south than for the north at a longitude of 110°. Above the northern ionosphere, the parallel current density further than 20° downstream of the main spot is estimated to be 1.5–2.0 times larger for 290° than for 110°. This indicates that if the Io-DAM lead angle is large, the suppressed Io-DAM occurrence probability for the northern hemisphere around 110° would be caused by the north-south asymmetry of the footprint magnetic intensity. A large current density conducted into the south around 110° would be the source of the Io-D component, radiated from the southern hemisphere. The observed brightness of the Io-related auroras is discussed in the context of the intensity of the parallel current density.

Characterizing the limitations to the coupling between Saturn's ionosphere and middle magnetosphere

Observations of Saturn's ultraviolet and infrared aurora show structures that, when traced along the planetary magnetic field, map to the inner, middle, and outer magnetosphere. From low to high latitudes the structures seen in the UV are the Enceladus footprint, which maps to an equatorial radius of 4 RS (Saturn radii); a diffuse emission that maps to a broad equatorial region from 4–11 RS on the nightside; and a bright ring of emission that maps to ∼15 RS. With the exception of the Enceladus spot, the magnetospheric drivers for these auroral emissions are not yet fully understood. We apply a 1D spatial, 2D velocity space Vlasov solver to flux tubes mapping from equatorial radii of 4, 6, 9, and 13 RS to Saturn's southern atmosphere. The aim is to globally characterize the field‐aligned potential structure and plasma density profiles. The ionospheric properties ‐ the field‐aligned current densities at the ionospheric boundary, energy intensity profiles and fluxes of the electrons precipitating into the ionosphere ‐ are also determined. We then couple our results to an ionospheric model to calculate the Pedersen conductances at the foot of the relevant flux tubes. We find that for a zero net potential drop between the ionosphere and magnetosphere, there exists a sharp potential drop at ∼1.5 RS along the magnetic field line as measured from the planetary center. The strength of this potential drop is approximately equal to that of the ambipolar potential resulting from the centrifugal confinement of the heavy, cold magnetospheric ion population. We also find that the ionospheric properties respond to changes in the magnetospheric plasma population, which are reflected in the nature of the precipitating electron population. For the flux tube mapping to 9 RS (−70°), the incident electron energy flux into the ionosphere resulting from a magnetospheric plasma population with a small fraction of hot electrons is an order of magnitude less than that inferred from observations, implying that significant high‐latitude field‐aligned potentials (up to 1.5 keV) may exist in the saturnian magnetosphere. Calculated ionospheric Pedersen conductances range from 3.0–18.9 mho, and are thus not expected to limit the currents flowing between the ionosphere and magnetosphere.

Effects of finite plasma pressure on centrifugally driven convection in Saturn's inner magnetosphere

We have previously shown simulation results for centrifugally driven plasma convection in Saturn's inner magnetosphere (2 < L < 12) using the Rice Convection Model, including a continuously active distributed plasma source, and the effects of the Coriolis force and the pickup current. These simulations result in a quasi‐steady state, in which fast, narrow inflow channels alternate with slower, wider outflow channels, consistent with Cassini Plasma Spectrometer observations. These previous simulations, however, did not include the plasma pressure. We investigate here the effects of finite plasma pressure and the associated gradient‐curvature drift current by giving the cold plasma a finite temperature. Our simulations confirm the theoretical expectation that a finite plasma pressure produces a force in the positive radial direction, the same direction as the centrifugal force, and acts as an additional driver of plasma convection. Our simulations also confirm that the radial velocities can be reduced (to keep them within observational constraints) by increasing the assumed ionospheric Pedersen conductance (also within observational constraints).

Nonlinear dispersive scale Alfvén waves inmagnetosphere-ionosphere coupling: Physical processes and simulation results

Dispersive Alfven waves (DAWs) have been demonstrated to play a significant role in auroral generation of the magnetosphere-ionosphere coupling system. Starting from a two fluid reduced MHD model, we summarize the frequency, temporal and spatial characteristics of magnetospheric DAWs. Then, the nonlinear kinetic and inertial scale Alfven waves are studied, and we review some theoretical aspects and simulation results of dispersive Alfven waves in Earth’s magnetosphere. It is shown that dispersive standing Alfven waves can generate the field-aligned currents which transport energy into the auroral ionosphere, where it is dissipated by Joule heating and energy lost due to electron precipitation. The Joule dissipation can heat the ionospheric electron and produce changes in the ionospheric Pedersen conductivity. As a feedback, the conducting ionosphere can also strongly affect the magnetospheric currents. The ponderomotive force can cause the plasma to move along the field line, and generate ionospheric density cavity. The nonlinear structuring can lead to a dispersive scale to accelerate auroral particle, and the Alfven waves can be trapped within the density cavity. Finally, we show the nonlinear decay of dispersive Alfven waves related to two anti-propagating electron fluxes observed in the auroral zone.

Magnetosphere‐ionosphere coupling at Jupiter: A parameter space study

Jupiter's main auroral emission is a signature of the current system that transfers angular momentum from the planet to radially outward moving Iogenic plasma. Ray et al. (2010) developed a steady state model of this current system which self‐consistently included the effects of a field‐aligned potential, Φ∥, and an ionospheric conductance modified by precipitating electrons. The presented parameter space study extends their model to explore how variations in the auroral cavity density and temperature, magnetospheric mass loading rate, and background ionospheric Pedersen conductance affect the current system and resulting auroral emission. We show that while the solutions found by Ray et al. (2010) vary with changes in the system parameters, the gross general trends remain similar to the original solutions. We find that, for an outer constraint of I100 = 86 MA, the high‐latitude electron temperature and density have a lower limit of ∼1.5 keV and an upper limit of ∼0.01 cm−3, respectively, in order for solutions to be consistent with observations of Jupiter's auroral emission. For increases in the radial mass transport rate and an outer constraint of = 75 kV the auroral emission brightness increases.

Magnetosphere-ionosphere coupling in Jupiter's middle magnetosphere: Computations including a self-consistent current sheet magnetic field model

In this paper we consider the effect of a self-consistently computed magnetosdisc field structure on the magnetosphere-ionosphere coupling current system at Jupiter. We find that the azimuthal current intensity, and thus the stretching of the magnetic field lines, is dependent on the magnetosphere-ionosphere coupling current system parameters, i.e. the ionospheric Pedersen conductivity and iogenic plasma mass outflow rate. Overall, however, the equatorial magnetic field profiles obtained are similar in the inner region to those used previously, such that the currents are of the same order as previous solutions obtained using a fixed empirical equatorial field strength model, although the outer fringing field of the current disc acts to reverse the field-aligned current in the outer region. We also find that, while the azimuthal current in the inner region is dominated by hot plasma pressure, as is generally held to be the case at Jupiter, the use of a realistic plasma angular velocity profile actually results in the centrifugal current becoming dominant in the outer magnetosphere. In addition, despite the dependence of the intensity of the azimuthal current on the magnetosphere-ionosphere coupling current system parameters, the location of the peak field-aligned current in the equatorial plane also varies, such that the ionospheric location remains roughly constant. It is thus found that significant changes to the mass density of the iogenic plasma disc are required to explain the variation in the main oval location observed using the Hubble Space Telescope.