Konstantin Kabin

The interaction between the magnetosphere of Saturn and Titan's ionosphere

A three-dimensional (3-D) multi-species magnetohydrodynamic model was used to study the interaction of Titans ionosphere and Saturns magnetosphere. The three generic species which were considered are light (e.g., H + , H 2 + , and H 3 + ), medium (e.g., N + and CH 5 + ), and heavy (e.g., N 2 + and HCNH + ) ion species. The effects of exospheric mass loading, major chemical reactions, and ion-neutral collisions were considered. The upstream parameters were selected to be the nominal values for the case when Titan is in the magnetosphere of Saturn. The simulation results are compared with Voyager measurements as well as related model calculations. The 3-D three-species model results reproduce reasonably well the global features such as magnetic barrier, magnetotail, and the distributions of the major ionospheric species. The outward escape flux of the major ionospheric species (i.e., the heavy ion species) from the tail is calculated to be approximately 6.5 × 10 24 s -1 .

Interaction of the Saturnian magnetosphere with Titan: Results of a three‐dimensional MHD simulation

The results of our three-dimensional multiscale magnetohydrodynamic (MHD) model describing the interaction of Saturns magnetosphere with Titans upper atmosphere and exosphere are presented. The effects of a conducting ionosphere, exospheric mass loading and ion-neutral charge exchange are taken into consideration. Because the ion gyroradius, in general, is not small compared to the radius of Titan the MHD approximation is not strictly applicable. However, it is still useful for the understanding of the general large-scale features of the magnetospheric interaction. The upstream parameters are set for the typical case when Titan is inside the Saturnian magnetosphere. Although Titan certainly does not have a strong intrinsic magnetic field, some observed structures in Titans wake might be explained by assuming the existence of a small intrinsic magnetic field. Thus we also considered the possibility that Titan has a small intrinsic dipole moment. The results of the simulations are compared with Voyager measurements and provide estimates of the total mass loading and the rate of ion-neutral charge exchange. The simulation results reproduce the overall behavior of the observations, but it is clear that non-MHD effects also play a role in the interaction between Saturns magnetosphere and Titan.

DUST-GAS INTERRELATIONS IN COMETS: OBSERVATIONS AND THEORY

The development of the expanding atmosphere from the evaporating cometary nucleus has traditionally focused on observing and modeling the separate development of two distinct components, gas and dust,which are coupled dynamically with one another at distances out to a few tens of cometary radii. In the last decade or so, however, direct evidence from observations and suggestions from theory suggest that the dusty-gas coma is a tightly coupled system where material is transferred between the solid and gaseous phase as an important integral part of the basic development of the coma.Comet Hale-Bopp (C/1995 O1) was discovered far from the sun and is the largest and most productive comet, in the sense of release of gas and dust in modern times. This has permitted observations to be made over an unprecedented range of heliocentric distance. This paper presents a review of a range of important issues regarding interrelations between dust and gas in comets, a description of the gas and dust environment for Hale-Bopp, and a summary of the preliminary results from Hale-Bopp which are relevant to these issues. Particular topics include dusty-gas models, dust fading and fragmentation, the role of dust and gas jets, the day/night distribution of gas and dust, and extended sources of gas.

Analysis of the 3-D shape of the terrestrial bow shock by interball/magion 4 observations

Abstract Location and shape of the terrestrial bow shock are analyzed using MAGION 4 (sub satellite of INTERBALL 1) crossings of this boundary and upstream solar wind parameters measured by the WIND spacecraft. Different crossing points were mapped to the Sun — Earth line and to the terminator plane using an analytical model of the planetary bow shock previously developed for the Martian bow shock investigation. Analysis of the subsolar bow shock position as a function of Alfvenic Mach number ( M a ) revealed fine effect that this boundary tends to approach the Earth when M a is decreasing for field-aligned flow of the solar wind, while for non field-aligned flow the bow shock moves away from the planet. Asymmetry of the terrestrial bow shock in the terminator plane is found for non field-aligned flow with anisotropic Friedrichs diagrams.

Wind observations of the terrestrial bow shock: 3-D shape and motion

Between late 1994 and early 2001 the Wind orbiter, generally targeted to stay in the solar wind, passed through the Earth’s magnetosphere ∼50 times. About 450 distinct bow shock crossings were collected during the inbound and outbound bracketing each Wind perigee. These crossings and corresponding vectorial upstream solar wind measurements by the Wind MFI and SWE instruments are used to study the 3-D shape of the bow shock and its motion. Mapping of bow shock crossings to the Sun-Earth line and to the terminator plane is realized using a recent analytical model of the planetary bow shock. The asymmetry of the terrestrial bow shock in the terminator plane is studied as a function of Friedrichs diagram anisotropy. Analysis of the subsolar bow shock position as a function of Alfvenic Mach number Ma during intervals of magnetic field aligned solar wind flow shows that the shock tends to approach the Earth when Ma is decreasing, while for non field-aligned flows bow shock moves from the planet.

Titan's magnetic wake: Atmospheric or magnetospheric interaction

We compare the magnetic field topology in the Titan wake to an idealized picture of magnetic field lines draping about a conductive nonmagnetic obstacle. It is shown that in the inner part of the wake the magnetic field picture differs significantly from that expected for an idealized draping: The transverse magnetic field component rotates by 90° as compared with the direction of the upstream transverse magnetic field. Another difference is the existence of a deep magnetic field minima separating the inner and outer parts of the wake. Transverse magnetic field rotation can be explained neither by temporal changes in the upstream magnetic field nor by reconnection processes in the wake. We find that this behavior of the transverse magnetic field can be explained at least qualitatively if one assumes the existence of a small intrinsic magnetic field of Titan. An effective magnetic dipole of 1021 G cm3 can account for the observed topology of the Titan magnetic wake. The origin of this field may be related to a residual magnetization of Titans crust or to induction in a conducting ionosphere of the satellite. We present results of MHD simulations which support the above theoretical conclusion.

On Europa's magnetospheric interaction: A MHD simulation of the E4 flyby

The global three-dimensional interaction of Europa with the Jovian magnetosphere is modeled by using a complete set of ideal magnetohydrodynamic (MHD) equations. The model accounts for exospheric mass loading, ion-neutral charge exchange, recombination, and a possible intrinsic dipole magnetic field of Europa. The single-fluid MHD equations are solved by using a modern, finite volume, higher-order, Godunov-type method on an adaptively refined unstructured grid, which allows detailed modeling of the region near Europa while still resolving both the upstream region and the satellites wake. The magnetic field and plasma density measured during Galileos E4 flyby of December 19, 1996, are reproduced reasonably well in the simulation. We find the agreement between the data and our model particularly convincing if we assume that the plasma velocity during the E4 flyby deviated from the nominal corotation direction by approximately 20P. Evidence from the Galileo energetic particle detector also supports this assumption. In this case, we can fit the data using a dipole with orientation close to that of an induced dipole arising from the interaction of a hypothetical conducting subsurface layer on Europa with the periodically changing magnetic field of Jupiter. However, the magnitude of the dipole in our model is somewhat smaller (70%) than that suggested by Khurana et al. [1998]. The total mass loading and ion-neutral charge exchange rates are consistent with the estimates of Europas atmosphere and ionosphere.

Io's Magnetospheric Interaction: An MHD Model with Day-Night Asymmetry

Abstract In this paper we present the results of an improved three-dimensional MHD model for Ios interaction with Jupiters magnetosphere. We have included the day-night asymmetry into the spatial distribution of our mass-loading, which allowed us to reproduce several smaller features of the Galileo December 1995 data set. The calculation is performed using our newly modified description of the pick-up processes that accounts for the effects of the corotational electric field existing in the Jovian magnetosphere. This change in the formulation of the source terms for the MHD equations resulted in significant improvements in the comparison with the Galileo measurements. We briefly discuss the limitations of our model and possible future improvements.

Velocity distributions of energetic atoms in planetary exospheres from dissociative recombination

[1] A kinetic theory description of translational energetic atoms in the upper planetary atmosphere is presented. A new analytical result for the velocity distribution of the products of reactive collisions is described. Our calculation takes into account different temperatures of the reactants and arbitrary dependence of the cross section on the relative velocity of the colliding particles. The final result is applied to the production of hot oxygen and carbon by dissociative recombination of O + 2 and CO + , respectively. The nascent distribution of hot atoms generated in this way is compared with the earlier Monte Carlo calculations. We use the Boltzmann equation to study the thermalization of the hot oxygen via collisions with the thermal oxygen population. The results of this calculation demonstrate quasi-steady state velocity distribution of high-energy oxygen atoms near the exobase of Venus for daytime conditions.

GLOBAL MHD SIMULATIONS OF SPACE PLASMA ENVIRONMENTS: HELIOSPHERE, COMETS, MAGNETOSPHERES OF PLANETS AND SATELLITES

Magnetohydrodynamics (MHD) provides an approximate description of a great variety of processes in space physics. Accurate numerical solutions of the MHD equations are still a challenge, but in the past decade a number of robust methods have appeared. Once these techniques made the direct solution of MHD equations feasible, a number of global three-dimensional models were designed and applied to many space physics objects. The range of these objects is truly astonishing, including active galactic nuclei, the heliosphere, the solar corona, and the solar wind interaction with planets, satellites, and comets. Outside the realm of space physics, MHD theory has been applied to such diverse problems as laboratory plasmas and electromagnetic casting of liquid metals. In this paper we present a broad spectrum of models of different phenomena in space science developed in the recent years at the University of Michigan. Although the physical systems addressed by these models are different, they all use the MHD equations as a unifying basis.