We investigate magnetic data showing the presence of field-aligned magnetosphere-ionosphere coupling currents on 31 Cassini passes across Saturn's southern postmidnight auroral region. The currents are strongly modulated in magnitude, form, and position by the phase of the southern planetary period oscillations (PPOs). PPO-independent currents are separated from PPO-related currents using the antisymmetry of the latter with respect to PPO phase. PPO-independent downward currents~1.1 MA per radian of azimuth flow over the polar open field region indicative of significant plasma subcorotation are enhanced in an outer plasma sheet layer of elevated ionospheric conductivity carrying~0.8 MA rad À1and close principally in an upward directed current sheet at~17°-19°ionospheric colatitude carrying 2.3 MA rad À1 that maps to the outer hot plasma region in Saturn's magnetosphere (equatorial rangẽ 11-16 Saturn radii (R S )) colocated with the UV oval. Subsidiary downward and upward currents~0.5 MA rad À1 lie at~19°-20.5°colatitude mapping to the inner hot plasma region, but no comparable currents are detected at larger colatitudes mapping to the cool plasma regime inside~8 R S . PPO-related currents at~17.5°-20°colatitude overlap the main upward and subsidiary downward currents and carry comparable rotating upward and downward currents peaking at~1.7 MA rad À1 . The overall current layer colatitude is also modulated with 1°amplitude in the PPO cycle, maximum equatorward adjacent to the peak upward PPO current and maximum poleward adjacent to peak downward PPO current. This phasing requires the current system to be driven from the planetary atmosphere rather than directly from the magnetosphere.

We investigate the magnetic perturbations associated with field‐aligned currents observed on 34 Cassini passes over the premidnight northern auroral region during 2008. These are found to be significantly modulated not only by the northern planetary‐period oscillation (PPO) system, similar to the southern currents by the southern PPO system found previously, but also by the southern PPO system as well, thus providing the first clear evidence of PPO‐related interhemispheric current flow. The principal field‐aligned currents of the two PPO systems are found to be co‐located in northern ionospheric colatitude, together with the currents of the PPO‐independent (subcorotation) system, located between the vicinity of the open‐closed field boundary and field lines mapping to ~9 Saturn radius (Rs) in the equatorial plane. All three systems are of comparable magnitude, ~3 MA in each PPO half‐cycle. Smaller PPO‐related field‐aligned currents of opposite polarity also flow in the interior region, mapping between ~6 and ~9 Rs in the equatorial plane, carrying a current of ~ ±2 MA per half‐cycle, which significantly reduce the oscillation amplitudes in the interior region. Within this interior region the amplitudes of the northern and southern oscillations are found to fall continuously with distance along the field lines from the corresponding hemisphere, thus showing the presence of cross‐field currents, with the southern oscillations being dominant in the south, and modestly lower in amplitude than the northern oscillations in the north. As in previous studies, no oscillations related to the opposite hemisphere are found on open field lines in either hemisphere.

The magnetospheric magnetic field is highly time‐dependent and may have explosive changes (magnetospheric substorms and geomagnetic storms) accompanied by significant energy input into the magnetosphere. However, the existing stationary magnetospheric models can not simulate the magnetosphere for disturbed conditions associated with the most interesting magnetospheric physics events (intensive auroras, particle injection in the inner magnetosphere, and precipitations at the high latitudes, etc.). We propose a method for constructing a nonstationary model of the magnetospheric magnetic field, which enables us to describe the magnetosphere during the disturbances. The dynamic changes of the magnetosphere will be represented as a sequence of quasistationary states. The relative contributions to the Dst index by various sources of magnetospheric magnetic field are considered using a dynamic model of the Earth's magnetosphere. The calculated magnetic field is obtained by using the solar wind and geomagnetic activity empirical data of the magnetic storm of March 23–24, 1969 and the magnetic disturbance of July 24–26, 1986. The main emphasis is on the current system of the magnetospheric tail, the variations of which enable a description of the fast changes of Dst.

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[1] We propose a simple illustrative axisymmetric model of the plasma flow and currents in Jupiter's polar ionosphere which are due both to internal magnetospheric plasma processes and the solar wind interaction. The plasma flow in the model is specified using a combination of observations, previous modeling, and theory, and the ionospheric and field-aligned currents are then calculated. With increasing latitude, the model represents conditions in the inner, middle, and outer magnetosphere on closed field lines and on open field lines mapping to the tail lobes. The model allows us to address three important topics, concerned with the closure of the upward field-aligned currents flowing in the middle magnetosphere region, the energy transfers from planetary rotation to polar upper atmosphere heating and to the magnetosphere, and the relative significance of auroral processes associated with the boundary of open field lines (and hence with the solar wind interaction) and with the middle magnetosphere. It is shown in particular that the energy transfers to the polar upper atmosphere and magnetosphere are of order hundreds of TWeach and that discrete auroral precipitation is expected both at the boundary of open field lines and in the middle magnetosphere, though being dominated by the latter. While the initial calculations assume for simplicity a constant ionospheric conductance, we also present a development of the model in which the conductance is self-consistently increased in regions of upward field-aligned current by the precipitation of accelerated electrons. It is shown that this feedback acts to spread the upward current in the region equatorward of the open field line boundary, thus reducing the energy flux and total power of precipitating auroral electrons in this region. At the same time it concentrates the upward current in the equatorward part of the middle magnetosphere, thereby increasing the energy flux and total power of precipitating electrons in this region.

Abstract. This paper presents a global model of the Jovian magnetosphere which is valid not only in the equatorial plane and near the planet, as most of the existing models are, but also at high latitudes and in the outer regions of the magnetosphere. The model includes the Jovian dipole, magnetodisc, and tail current system. The tail currents are combined with the magnetopause closure currents. All inner magnetospheric magnetic field sources are screened by the magnetopause currents. It guarantees a zero normal magnetic field component for the inner magnetospheric field at the whole magnetopause surface. By changing magnetospheric scale (subsolar distance), the model gives a possibility to study the solar wind influence on the magnetospheric structure and auroral activity. A dependence of the magnetospheric size on the solar wind dynamic pressure p sw (proportional to p −0.23 sw ) is obtained. It is a stronger dependence than in the case of the Earth's magnetosphere (p −1/6 sw ). The model of Jupiter's magnetospheric which is presented is a unique one, as it allows one to study the solar wind and interplanetary magnetic field (IMF) effects.

Weak intrinsic magnetic dipole moments of tidally locked close-in giant exoplanets ("hot Jupiters") have been shown in previous studies to be unable to provide an efficient magnetospheric protection for their expanding upper atmospheres against the stellar plasma flow, which should lead to significant non-thermal atmosphere mass loss. The present work provides a more complete view of the magnetosphere structure of "hot Jupiters," based on a paraboloid magnetospheric model (PMM). Besides the intrinsic planetary magnetic dipole, the PMM considers among the main magnetic field sources also the electric current system of the magnetotail, magnetopause currents, and the ring current of a magnetodisk. Due to the outflow of ionized particles from the hydrodynamically expanding upper atmosphere, "hot Jupiters" may have extended magnetodisks. The magnetic field produced by magnetodisk ring currents dominates above the contribution of an intrinsic magnetic dipole of a "hot Jupiter" and finally determines the size and shape of the whole magnetosphere. A slower-than-the-dipole-type decrease of the magnetic field with the distance forms the essential specifics of magnetodisk-dominated magnetospheres of "hot Jupiters." This results in their 40%-70% larger scales compared to those traditionally estimated by only the planetary dipole taken into account. Therefore, the formation of magnetodisks has to be included in the studies of the stellar wind plasma interaction with close-in exoplanets, as well as magnetospheric protection for planetary atmospheres against non-thermal escape due to erosion by the stellar plasma flow.

[1] A re-scaling of a recent model of Jupiter's magnetosphere incorporating ring current, magnetopause, and tail current systems is used as a starting-point for modeling Saturn's magnetospheric field. The model is compared with observations obtained by Cassini during its Saturn orbit insertion fly-through of Saturn's magnetosphere, and is shown to give a good description. Comparison of ring current parameters obtained on the inbound and early outbound passes, when the magnetosphere was expanded due to low solar wind pressure, with those obtained by Voyager-1 under more usual conditions, and by Pioneer-11 when the magnetosphere was compressed, suggests that the ring current magnetic moment increases with system size. The effect is proposed to be due to radial stress balance conditions in a rapidly rotating magnetosphere, and has consequences for the dependence of magnetosphere size on solar wind pressure. Citation: Alexeev, I. I., V. V. Kalegaev,