Hot Plasma Pressure Research Articles

Ganymede's Auroral Footprint Latitude: Comparison With Magnetodisc Model

AbstractVariations of Ganymede's auroral footprint locations are presented based on observations by the Hubble Space Telescope in 2007 and 2016. The poleward and equatorward shifts of Ganymede's footprint could be influenced by the mass outflow rate from Io and the solar wind compression, as the internal and external factors respectively. We compare our results with Ganymede's footprint mapping based on the magnetodisc model. The mapped footprint in Jupiter's ionosphere shifts equatorward with increased hot plasma parameter, Kh, which is associated with hot plasma pressure. We analyzed the effect of cold plasma number density (Nc), related to the mass outflow rate and connected to the material produced by Io. The results show that the magnetic footprint is shifted equatorward by 0.37° when the mass outflow rate is increased from 800–2,000 kg s−1. Iogenic plasma has a strong influence on the stretching of the magnetic field lines in Jupiter's middle magnetosphere, causing the equatorward shift of Ganymede's footprint. For external factors, Ganymede's footprint shifted poleward by 0.62° under the influence of solar wind compression while the mass outflow is kept constant at 1,000 kg s−1. We present similar locations of Ganymede's footprint based on the field lines mapped as a result of the compensation between an increase of Kh and the solar wind compression. Overall, the location of Ganymede's auroral footprint corresponds with the mass loading rate from Io and the solar wind dynamic pressure.

An Enhancement of Jupiter's Main Auroral Emission and Magnetospheric Currents

AbstractWe present observations of Jupiter's magnetic field and plasma obtained with the NASA Juno spacecraft during February 2018, along with simultaneous Hubble Space Telescope (HST) observations of the planet's auroras. We show that a few‐day transient enhancement of the azimuthal and radial magnetic fields and plasma temperature was coincident with a significant brightening of Jupiter's dawn‐side main auroral emission. This presents the first evidence of control of Jupiter's main auroral emission intensity by magnetosphere‐ionosphere coupling currents. We support this association by self‐consistent calculation of the magnetosphere‐ionosphere coupling and radial force balance currents using an axisymmetric model, which broadly reproduces the Juno magnetic field and plasma observations and the HST auroral observations. We show that the transient enhancement can be explained by increased hot plasma pressure in the magnetosphere together with increased iogenic plasma mass outflow rate. Overall, this work provides important observational and modeling evidence revealing the behavior of Jupiter's giant magnetosphere.

A Self‐Regulating Equilibrium Magnetopause Model With Applications to Saturn

AbstractWe describe a new method of constructing an equilibrium magnetopause surface based on the pressure balance between external and internal pressure sources. Details are given for every step of the procedure, including the initial pressure balance condition (which determines magnetopause morphology), the related underlying assumptions, and the final optimized magnetopause surface. Our method produces a final equilibrium magnetopause surface that satisfies the local balance between the solar wind dynamic pressure and planetary magnetic pressure with an error no greater than 1%. We also discuss the contribution of hot plasma pressure and equatorial ring currents and their effects on magnetopause morphology. For each optimized magnetopause boundary, we give coefficients for fitted polynomial approximations to allow simple and accurate reproductions for practical applications. We specifically discuss the potential application to the modeling of Saturn's magnetopause and describe how the equilibrium magnetopause model can be used to estimate the compressibility of the boundary.

A model of force balance in Jupiter's magnetodisc including hot plasma pressure anisotropy

AbstractWe present an iterative vector potential model of force balance in Jupiter's magnetodisc that includes the effects of hot plasma pressure anisotropy. The fiducial model produces results that are consistent with Galileo magnetic field and plasma data over the whole radial range of the model. The hot plasma pressure gradient and centrifugal forces dominate in the regions inward of ∼20 RJ and outward of ∼50 RJ, respectively, while for realistic values of the pressure anisotropy, the anisotropy current is either the dominant component or at least comparable with the hot plasma pressure gradient current in the region in between. With the inclusion of hot plasma pressure anisotropy, the ∼1.2 and ∼2.7° shifts in the latitudes of the main oval and Ganymede footprint, respectively, associated with variations over the observed range of the hot plasma parameter Kh, which is the product of hot pressure and unit flux tube volume, are comparable to the shifts observed in auroral images. However, the middle magnetosphere is susceptible to the firehose instability, with peak equatorial values of βh∥e−βh⊥e≃1 − 2, for Kh=2.0 − 2.5 × 107 Pa m T−1. For larger values of Kh,βh∥e−βh⊥e exceeds 2 near ∼25 RJ and the model does not converge. This suggests that small‐scale plasmoid release or “drizzle” of iogenic plasma may often occur in the middle magnetosphere, thus forming a significant mode of plasma mass loss, alongside plasmoids, at Jupiter.

A combined model of pressure variations in Titan's plasma environment

AbstractIn order to analyze varying plasma conditions upstream of Titan, we have combined a physical model of Saturn's plasma disk with a geometrical model of the oscillating current sheet. During modeled oscillation phases where Titan is farthest from the current sheet, the main sources of plasma pressure in the near‐Titan space are the magnetic pressure and, for disturbed conditions, the hot plasma pressure. When Titan is at the center of the sheet, the main sources are the dynamic pressure associated with Saturn's cold, subcorotating plasma and the hot plasma pressure under disturbed conditions. Total pressure at Titan (dynamic plus thermal plus magnetic) typically increases by a factor of up to about 3 as the current sheet center is approached. The predicted incident plasma flow direction deviates from the orbital plane of Titan by ≲10°. These results suggest a correlation between the location of magnetic pressure maxima and the oscillation phase of the plasma sheet. Our model may be used to predict near‐Titan conditions from “far‐field” in situ measurements.

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.

Influence of hot plasma pressure on the global structure of Saturn’s magnetodisk

Using a model of force balance in Saturn's disk‐like magnetosphere, we show that variations in hot plasma pressure can change the magnetic field configuration. This effect changes (i) the location of the magnetopause, even at fixed solar wind dynamic pressure, and (ii) the magnetic mapping between ionosphere and disk. The model uses equatorial observations as a boundary condition—we test its predictions over a wide latitude range by comparison with a Cassini high‐inclination orbit of magnetic field and hot plasma pressure data. We find reasonable agreement over time scales larger than the period of Saturn kilometric radiation (also known as the camshaft period).

Medium-scale splitting of outflowing field-aligned currents and kappa distribution of magnetospheric ions

The medium-scale (50–200 km in the projection onto ionospheric altitudes) splitting of the field-aligned currents flowing out of the ionosphere has been considered in the case when the approximation of the distribution function of hot magnetospheric ions by the kappa distribution is taken into account. It was assumed that the condition of magnetostatic equilibrium and isotropy of hot magnetospheric plasma pressure is satisfied in the magnetosphere. The theoretical parameter of magnetospheric plasma hot stratification has been obtained for the case of ion kappa distribution. The parameter characterizes the number of structures into which the band of the field-aligned current flowing out of the ionosphere is split. The theoretical predictions have been compared with the observations on the Intercosmos-Bulgaria-1300 and Aureol-3 satellites. It has been indicated that the number of measured structures is in better agreement with that of the theoretically predicted structures in 70% of cases if the non-Maxwellian tails of ion distribution functions are taken into account.

Numerical simulation of the Io‐torus‐driven radial plasma transport

A series of six axis symmetric equilibrium models for Jupiter's inner magnetosphere was constructed, upon which the motion of an Io‐torus‐generated, mass overloaded magnetic flux tube on a meridian plane of the inner Jovian magnetosphere was studied numerically via magnetohydrodynamics approach. The flux tube is represented as a one‐dimensional filament, while the Jovian magnetosphere is represented as a two‐dimensional stationary medium. With only cold plasma included in the model, such heavy filament is unstable. However, when both cold and hot plasma are included in the models, the heavy filament is stabilized by the huge thermal pressure gradient for the Voyager period. For the Galileo period, the situation is less definitive because there is no observation‐based hot plasma pressure data available within 6.75 Jovian radii (RJ). Nevertheless, our simulations in two models suggested that even with both cold and hot plasma included in the models, the heavy filament is still unstable for this period. The filament moves outward toward the middle and/or outer magnetosphere due to the interchange instability. The mass elements in the unstable filament are propelled along its length by the centrifugal force toward the equatorial plane. This filament tends to be more stretched in the outward direction than its neighbors as time elapses. The outward moving speed of the filament within 7.1 RJ is comparable with the Galileo spacecraft's observation in the Io torus on 7 December 1995.

Investigations of the hot plasma pressure gradients and the configuration of magnetospheric currents from interball

One of the main aspects of the multi satellite INTERBALL program is connected with the experimental determination of the hot plasma pressure distribution inside the magnetosphere and the solution of the well known problem of the inner magnetosphere substorm onset. The main results of the experimental observations, the structure of high latitude currents and the modeling of the magnetospheric processes are discussed. Observations of particles in a wide energy range from tens of eV to Mev energies give the possibility to construct the full distribution function and to calculate plasma pressure. Quiet time plasma pressure profiles show the regularity and the increase of the pressure with the decrease of the geocentric distance. The observed region of plasma pressure plateau means the existence of nearly zero transverse and field-aligned current regions. The existence of such a region gives the possibility to explain the observed gap between Region 1 and Region 2 currents. Investigations of the fluctuations of the plasma bulk velocity inside the plasma sheet support the existence of plasma sheet turbulence. The existence of plasma sheet turbulence explains the inner magnetosphere substorm onset as only stable before substorm plasma region can become unstable. The introduction of the turbulent transport in the model of the plasma sheet and the theory of the plasma sheet with medium-scale turbulence are discussed

Hot plasma pressure variations on the geostationary orbit on the base of Gorizont satellite data

Plasma and energetic particles pressure distribution is studied using data from the plasma and energetic particle experiment (0.1 – 133 keV) onboard the Gorizont-35 geostationary satellite for the period from 11 to 25 March 1992. The analysed period consists of relatively quiet time, small geomagnetic storms, SC and the time of the northern orientation of the IMF. The calculations show that the basic contribution to the total particle pressure was made by ions at the energy from 0.1 to 12.4 keV. The derived average value of the calculated pressure (∼1 nPa) points to the important role of the geostationary orbit plasma population in the formation of the magnetosphere pressure balance and of the near-Earth magnetic field distortion.

Multiple inverted‐V structures and hot plasma pressure gradient mechanism of plasma stratification

A mechanism of plasma stratification within the inner plasma sheet is discussed. It is suggested that plasma pressure is isoptropic and particle motion is unmagnetized for the spatial scales in which the structures are formed. The solution of the magnetosphere‐ionosphere interaction problem shows that upward field‐aligned current may split into separate structures. The number of structures formed is determined by a parameter which depends on upward field‐aligned current density, field‐aligned current band width, hot magnetospheric ion temperature, and height‐integrated Pedersen ionospheric conductivity. The Intercosmos‐Bulgaria‐1300 satellite base data has been used to identify events of multiple inverted‐V structures. It is shown that the hot stratification plasma mechanism offers a good description of the number of observed structures.

Azimuthal hot plasma pressure gradients and dawn-dusk electric field formation

Abstract The effects of hot plasma pressure gradients in the high latitude magnetosphere are analysed. It is shown that such a mechanism may in fact be responsible for Region 1 field-aligned currents and for the dawn-dusk electric field. The estimated azimuthal gradients in the plasma pressure may account for the observed field-aligned currents and also give the opportunity to determine the day-night plasma pressure changes along isosurfaces of magnetic flux tube volume. These pressure changes are then compared with experimentally measured pressure distribution and it is shown that the day-night plasma change, in the high latitude magnetosphere, may be high enough to sustain Region 1 currents. The closure of these currents in the high latitude magnetosphere may in turn be responsible for the dawn-dusk electric field and the dawn-dusk potential drop in the inner plasma sheet regions. The influence of the IMF on the magnetostatically equilibrium inner magnetospheric currents may qualitatively explain the IMF control of the dawn-dusk electric field and magnetospheric activity.

The magnetostatic equilibrium in high latitude magnetosphere and the selection of coordinate system for high latitude processes description

The coordinate system employing isosurfaces of magnetic flux tube volume as the coordinate surfaces was used for the reconstruction of azimuthal magnetospheric plasma pressure gradients on a basis of the data of large scale field aligned currents distribution and the Tsyganenko magnetic field models. The integral plasma pressure changes are compared with the satellite measurements of plasma pressure. It was shown that Region I and Region II currents can be maintained by azimuthal hot plasma pressure gradients. The localization of the Region I currents in the inner magnetosphere creates the mechanism of dawn-dusk electric field formation which does not require the reconnection or viscous interaction of the solar wind with the magnetosphere.

An empirical model of the Venusian outer environment 1. The shape of the dayside solar wind‐atmosphere interface

Solar wind plasma and magnetic field data and ionospheric data obtained from the Pioneer Venus orbiter are considered. It is shown that the variation of the magnetic field pressure within the magnetic barrier is similar to that expected for the solar wind pressure variations along an obstacle's boundary when a more realistic approximation of the shape of the ionosphere is included. Simultaneous solar wind pressure, ionospheric pressure, and magnetic barrier pressure data show that the ionospheric pressure below the ionopause is approximately equal to the solar wind pressure. The magnetic barrier pressure is equal to approximately 2/3 to 3/4 of both the solar wind pressure and the ionopsheric pressure. Estimates of the hot plasma pressure contribution to the total pressure within the magnetic barrier vary from 1/4 to 1/3. Just below the ionopause the ionospheric pressure deviations from the mean ionospheric pressure are significant especially below ∼400 km and appear to be indicative of the adjustment of the ionospheric structure to changing solar wind conditions. A first‐order model of the ionopause pressure variations as a function of height and solar‐zenith angle is suggested. This model provides an estimate of an ‘instant’ ionopause profile for the given solar wind conditions. The mean and ‘instant’ shapes of the ionopause do not appear to correspond to the estimates obtained from ionospheric pressure equilibrium for a given H/r0.

The role of hot plasma in magnetospheric convection

Several authors have shown that the presence of hot plasma in the magnetosphere can severely modify an imposed convection pattern and even prevent its penetration to low latitudes. Here with the aid of simple theoretical models we argue that the important parameters governing such effects are the hot plasma pressure, its number density, and the ionospheric conductivity. A result of this is that a fluid description of the phenomenon can be given. Changes in convection naturally give rise to east-west pressure gradients near the ring current inner edge, and these give rise to east-west flows, which cause the shielding effect. We show that plasma compressional energy is lost in Joule dissipation in the ionosphere in these flows which are rapidly set up on the nightside. On the dayside the process is slower, but we conclude that the dayside conductivity is the parameter controlling final ring current penetration. In the long time limit the fluid approximation breaks down, and we qualitatively discuss the development of steady state flow patterns and the effects of collisionless plasma behavior in this limit.