. It is well known that the ionosphere plays a role in determining the global state of the magnetosphere. The ionosphere allows magnetospheric currents to close, thereby allowing magnetospheric convection to occur. The amount of current which can be carried through the ionosphere is mainly determined by the ionospheric conductivity. This paper starts to quantify the nonlinear relationship between the ionospheric conductivity and the global state of the magnetosphere. It is found that the steady-state magnetosphere acts neither as a current nor as a voltage generator; a uniform Hall conductance can influence the potential pattern at low latitudes, but not at high latitude; the EUV generated conductance forces the currents to close in the sunlight, while the potential is large on the nightside; the solar generated Hall conductances cause a large asymmetry between the dawn and dusk potential, which effects the pressure distribution in the magnetosphere; a uniform polar cap potential removes some of this asymmetry; the potential difference between solar minimum and maximum is ∼11%; and the auroral precipitation can be related to the local field-aligned current through an exponential function. Key words. Ionosphere (ionosphere-magnetosphere interactions; modelling and forecasting; polar ionosphere)

/pdf/ionospheric-control-of-the-magnetosphere-conductance-2n6mgn0pzu.pdf

Ionospheric control of the magnetosphere: conductance

Electric-field-penetration events have been identified using F-region vertical-drift measurements obtained in the October 6-13, 1984 period by the Jicamarcan incoherent-backscatter radar and corresponding h-prime F measurements from ionosondes at Fortaleza, Cachoeira Paulista, and Dakar. Predictions made using the Rice Convection Model for the pattern, strength, and duration of the low-latitude electric field occurring in response to an increasing high-latitude convection agree with observations. The observed 1-2 h duration of the low-latitude response to decreased convection can be explained by the fossil-wind theory of Richmond (1983).

Penetration of high latitude electric fields effects tolow latitude during Sundial 1984

[1] It is well known that the interplanetary electric field can penetrate to the low-latitude ionosphere. It is generally believed that the penetration of electric fields can last only for ∼30 min because of the shielding effect in the ring current. In this paper we present the observations of the dayside ionospheric electric field enhancements at middle and low latitudes in association with reorientations of the interplanetary magnetic field (IMF). In six cases, the eastward electric field in the dayside equatorial ionosphere, measured by the Jicamarca incoherent scatter radar, was enhanced for 2–3 hours after the IMF turned southward and remained continuously southward. In one case the eastward electric field in the dayside midlatitude ionosphere, measured by the Millstone Hill incoherent scatter radar, was continuously enhanced for ∼10 hours during southward IMF. Since Millstone Hill is close to the equatorward boundary of the auroral zone during magnetic storms, the penetration electric field there may be different from that at the equatorial ionosphere. The most striking feature of the measurements is that the enhancements of the ionospheric electric field can last for many hours without significant decay. The electric field enhancements in the middle- and low-latitude ionosphere are closely related to magnetic activity and occur during the main phase of magnetic storms. The observations show that the interplanetary electric field can continuously penetrate to the low-latitude ionosphere without shielding for many hours as long as the strengthening of the magnetic activity is going on under storm conditions.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2005JA011202

Long‐duration penetration of the interplanetary electric field to the low‐latitude ionosphere during the main phase of magnetic storms

A record of the geomagnetic field on the ground sometimes shows smooth daily variations on the order of a few tens of nano teslas. These daily variations, commonly known as Sq, are caused by electric currents of several $\upmu \mbox{A}/\mbox{m}^{2}$
 flowing on the sunlit side of the E-region ionosphere at about 90–150 km heights. We review advances in our understanding of the geomagnetic daily variation and its source ionospheric currents during the past 75 years. Observations and existing theories are first outlined as background knowledge for the non-specialist. Data analysis methods, such as spherical harmonic analysis, are then described in detail. Various aspects of the geomagnetic daily variation are discussed and interpreted using these results. Finally, remaining issues are highlighted to provide possible directions for future work.

/pdf/sq-and-eej-a-review-on-the-daily-variation-of-the-2vlnpg7jur.pdf

Sq and EEJ—A review on the daily variation of the geomagnetic field caused by ionospheric dynamo currents

[1] This paper describes the coupling of BATS-R-US (Block Adaptive Tree Solar-wind Roe-type Upwind Scheme), a magnetohydrodynamics (MHD) code representing the Earth's global magnetosphere and its coupling to the ionosphere and solar wind, and the Rice Convection Model (RCM), which represents the inner magnetosphere and its coupling to the ionosphere. The MHD code provides a time-evolving magnetic field model for the RCM as well as continuously updated boundary conditions for the electric potential and plasma. The RCM computes the distribution functions of inner magnetospheric particles, including transport of inner plasmasheet and ring current particles by gradient/curvature drifts; it thus calculates more accurate inner magnetospheric pressures, which are frequently passed to the MHD model and used to nudge the MHD values. Results are presented for an initial run with the coupled code for the case of uniform ionospheric conductance with steady solar wind and southward interplanetary magnetic field (IMF). The results are compared with those for a run of the MHD code alone. The coupled-code run shows significantly higher inner magnetospheric particle pressures. It also exhibits several well-established characteristics of inner magnetospheric electrodynamics, including strong region-2 Birkeland currents and partial shielding of the inner magnetosphere from the main force of the convection electric field. A sudden northward turning of the IMF causes the ring current to become more nearly symmetric. The inner magnetosphere exhibits an overshielding (dusk-to-dawn) electric field that begins about 10 min after the northward turning reaches the magnetopause and lasts just over an hour.

/pdf/coupling-of-a-global-mhd-code-and-an-inner-magnetospheric-3v8r3da61s.pdf

Coupling of a global MHD code and an inner magnetospheric model: Initial results

[1] The Magnetosphere-Thermosphere-Ionosphere-Electrodynamics General Circulation model of Peymirat et al. [1998] is used to investigate ionospheric-wind-dynamo influences on low-latitude ionospheric electric fields during and after a magnetic storm. Simulations are performed with time-varying polar cap electric potentials and an expanding and contracting polar cap boundary. Three influences on equatorial electric fields can be of comparable importance: (1) global winds driven by solar heating; (2) direct penetration of polar cap electric fields to the equator that are partially shielded by the effects of Region-2 field-aligned currents; and (3) disturbance winds driven by high-latitude heating and ion-drag acceleration. The first two influences tend to have similar magnetic local time (MLT) variations in a steady state, while the disturbance-wind influence tends to have the opposite MLT variations. The nighttime disturbance winds at upper midlatitudes that affect the global ionospheric wind dynamo are predominantly westward after the simulated magnetic storm. The nighttime winds drive an equatorward dynamo current that tends to charge the low-latitude ionosphere positively around midnight, which can lead to reductions or reversals of the normal equatorial night-side east-west electric fields. The simulations partly support the theories of the so-called “disturbance dynamo” [Blanc and Richmond, 1980] and “fossil wind” [Spiro et al., 1988], both of which predict long-lasting disturbances in the equatorial eastward electric field associated with magnetic storms. However, the simulations do not support the element of fossil wind theory that links the disturbance-wind influence on equatorial electric fields to polar cap contraction following the storm. The simulations show a stronger wind-produced enhancement of steady state shielding than predicted by the model of Forbes and Harel [1989], due to the fact that the disturbance winds extend well equatorward of the Region-2 currents.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2002JA009758

Long-lasting disturbances in the equatorial ionospheric electric field simulated with a coupled magnetosphere-ionosphere-thermosphere model

The penetration of the electric field and associated magnetic perturbations from high latitudes to low latitudes is studied with the Magnetosphere-Thermosphere-lonosphere-Electrodynamics General Circulation Model (MTlEGCM) of Peymirat et al. [1998] in response to variations of the polar cap potential drop. For a sudden decrease of the polar cap potential of ∼ 40 kV, the model reproduces the well-known overshielding phenomenon corresponding to a sudden reversal of the low-latitude electric field. For quasi-periodic oscillations of the polar cap potential drop of ∼ 40 min period, the model predicts that the poleward electric field and the eastward Hall current in the auroral zone lag slightly in phase (< 1 min), while the eastward electric field and current at the magnetic equator are advanced slightly in phase, with respect to the potential-drop oscillations. These phase differences are interpreted as the consequence of the succession of shielding and overshielding episodes induced by the response of the region-2 field-aligned currents to the polar cap variations. The phase differences among the polar cap potential and the auroral and equatorial electric fields and currents increase with the plasma sheet pressure. The amplitude of the associated magnetic perturbations is very dependent on the distribution of the potential along the polar cap boundary. The model predictions are tested against the observations of Kobea et al. [this issue] for two events, one representing simple overshielding and the other associated with polar cap potential oscillations. The model underestimates the decay time of the magnetic perturbations by a factor of 2 during the overshielding event, and the model gives results compatible with the observations during the second event. The disagreements may be due to limitations of the model and uncertainties of the input parameters.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2000JA000057

Electrodynamic coupling of high and low latitudes: Simulations of shielding/overshielding effects

The penetration of disturbance electric fields from the polar region to the magnetic equator on the dayside of the Earth is examined with geomagnetic data on May 27, 1993. First, we examine a dayside equatorial disturbance that followed the rapid recovery of magnetic activity from a storm and that has the characteristics of overshielding caused by persistent region-2 field-aligned currents. It lasted *0 3 hours. Second, we analyze a series of fluctuations with periods of 25-75 min, to determine the variations of amplitude and phase with magnetic latitude and magnetic local time. The fluctuations were highly coherent at all latitudes between the magnetic equator and the auroral zone, but the coherency decreasedin the polar cap. A northward fluctuation at the equator during midday hours accompanied auroral zone fluctuations that were southward before noon, eastward around noon, and northward after noon. The amplitudes decreased away from the auroral zone toward midlatitudes but were amplified under the equatorial electrojet. No detectablep hased ifferencesa re found, indicating that any temporal lags which might be inducedb y persistencein the region-2f ield-alignedc urrentsa re less than i min for fluctuations having periods like those examined here. A synoptic inversion analysis of the high-latitude magnetic data to estimate the time-varying high-latitude electric potential patterns shows that fluctuations of the high-latitude east-west potential gradient tended to be concentrated around midday, where they were in phase with fluctuations in the midday east-west potential gradient at the magnetic equator.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2000JA000058

Electrodynamic coupling of high and low latitudes: Observations on May 27, 1993

A new simulation model of the thermosphere, the ionosphere, and the magnetosphere is presented. This model, which we call the magnetosphere-thermosphere-ionosphere electrodynamics general circulation model (MTIE-GCM), calculates the three-dimensional structure of the thermosphere and the ionosphere, the two-dimensional magnetospheric plasma convection in the equatorial plane of the magnetosphere, and the couplings among the thermosphere, the ionosphere, and the magnetosphere. The electrodynamic couplings induced by the auroral precipitation, the region 2 field-aligned currents, and the neutral winds are self-consistently computed. The major drawback of the model is the use of a dipole magnetic field in the magnetosphere such that we do not expect to reproduce observations exactly but rather to predict only correct orders of magnitude. The MTIE-GCM is run for solar maximum conditions and moderate magnetic activity in a sample case, where the electric potential is imposed in the polar cap but calculated everywhere else, to study the electrodynamic couplings occurring at high latitudes. The neutral winds increase the north–south component and decrease the east–west component of the ionospheric electric field, corresponding to an enhancement of the shielding effect by 10%. The region 2 field-aligned currents and the distribution of the magnetospheric pressure present smaller modifications, suggesting that the magnetosphere acts partly as a current generator. However, the results could possibly be different if the polar cap electric potential were allowed to change due to the neutral winds.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/98JA01235

A magnetosphere-thermosphere-ionosphere electrodynamics general circulation model

[1] The influence of the ionospheric wind dynamo on the steady state electrodynamic interaction between the ionosphere and the inner magnetosphere is evaluated with the Magnetosphere-Thermosphere-Ionosphere Electrodynamics General Circulation Model (MTIE-GCM) of Peymirat et al [1998] Two types of interaction between the solar wind–magnetosphere (SWM) dynamo and the ionospheric dynamo are considered: either the SWM dynamo is a voltage generator imposing a fixed electric potential in the polar cap or it is a hybrid current/voltage generator such that the electric potential in the polar cap results from the combined action of the SWM and ionospheric dynamos The following results are found (1) The dynamo effect of winds that are accelerated by the high-latitude ion convection increases the meridional electric field in the auroral zone but reduces the potential variation around the Auroral Zone Equatorial boundary (AZEQ) and the plasma pressure in the nightside magnetosphere close to the Earth, corresponding to an enhancement of the shielding effect produced by Region 2 field-aligned currents The magnitudes of the wind-induced effects are on the order of 10% for the shielding potential and 20% for the plasma pressure reduction (2) The wind-induced reduction of magnetospheric plasma pressure near the Earth is ∼4 times larger for a doubling of the plasma source density in the tail (3) The relative influence of winds on shielding is similar for polar cap potential drops of 30 kV and 70 kV (4) When the wind is allowed to influence the polar cap potential, it increases the potential drop along the polar cap boundary by ∼10% but does not modify the net influence on the shielding potential along AZEQ (5) The influence of the neutral winds set up by the high-latitude convection is restricted to the auroral zone

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2001JA900106

C. Peymirat

Papers

Long-lasting disturbances in the equatorial ionospheric electric field simulated with a coupled magnetosphere-ionosphere-thermosphere model

Electrodynamic coupling of high and low latitudes: Simulations of shielding/overshielding effects

Electrodynamic coupling of high and low latitudes: Observations on May 27, 1993

A magnetosphere-thermosphere-ionosphere electrodynamics general circulation model

Neutral wind influence on the electrodynamic coupling between the ionosphere and the magnetosphere