Romana Ratkiewicz

Acceleration of the High Speed Solar Wind in Coronal Holes

We outline a theory for the origin and acceleration of the fast solar wind as a consequence of network microflares releasing a spectrum of high frequency Alfvén waves which heat (by cyclotron absorption) the corona close to the Sun. The significant features of our model of the fast wind are that the acceleration is rapid with the sonic point at around two solar radii, the proton temperatures are high (~ 5 million degrees) and the minor ions are correspondingly hotter, roughly in proportion to their mass. Moreover we argue that since the energy flux needed to power the quiet corona in closed field regions is about the same as that needed to drive the fast solar wind, and also because at deeper levels (< 2 × 105 K) there is no great difference in the properties of supergranules and network in closed and open field regions, the heating process (i.e., dissipation of high frequency waves) must be the same in both cases.

THE EFFECTS OF LOCAL INTERSTELLAR MAGNETIC FIELD ON ENERGETIC NEUTRAL ATOM SKY MAPS

We study the effects of the strength and direction of the local interstellar magnetic field (ISMF) on the heliosphere geometry that generates the locus of points associated with the position of the IBEX ribbon of energetic neutral atoms. MHD heliosphere models are run for a variety of ISMF parameters to specifically study the correlation between locations of maxima of the ISMF magnitude along the field lines and places where the local ISMF B is perpendicular to radial vectors r from the Sun, i.e., B ? r = 0. The study confirms the existence of a strong physical relationship between the ribbon and the ISMF.

IBEX RIBBON: WHAT COULD IT TELL ABOUT THE LOCAL INTERSTELLAR MAGNETIC FIELD?

We show that the shape of the IBEX Ribbon can be reproduced assuming energetic neutral atoms originate in regions beyond the heliopause where the interstellar magnetic field is the strongest and perpendicular to radial directions from the Sun. The best fit to the observed ribbon was obtained for the local interstellar magnetic field B ? = 3.0 ? 1.0 ?G pointing from ecliptic/galactic coordinates (?, ?)/(l, b) = (225? ? 5?, 35? ? 5?)/(27? ? 5?, 51? ? 5?) close to the apparent ribbon center (?, ?)/(l, b) = (221?, 39?)/(33?, 55?). The geometrical considerations presented below should prove useful in identifying the mechanism of ribbon formation.

Structure of the heliospheric current sheet from plasma convection in time-dependent heliospheric models

Context. The heliospheric current sheet is a plasma layer dividing the heliosphere into the regions of different magnetic field polarity. Since it is very thin compared to the size of the system, it is difficult to incorporate into the numerical models of the heliosphere. Because of the solar magnetic field reversals and the diverging and slowing down plasma flow in the outer heliosphere, the heliospheric current sheet is expected to have a complicated structure, with important consequences for transport processes in the heliosheath. Aims. We determine the shape and time evolution of the current sheet in selected time-dependent 3-D models of the heliosphere, assuming that the heliospheric current sheet is a tangential discontinuity convected by the plasma flow. Methods. We have derived the shape of the heliospheric current sheet at a given time by following the plasma flow lines originating at the neutral line on the source surface surrounding the Sun. The plasma flow was obtained from numerical MHD or gas-dynamical solutions. Results. The large-scale structure of the magnetic field polarity regions and the heliospheric current sheet in time-dependent asymmetric models of the heliosphere differs from the results obtained in simpler models. In particular, in the forward heliosheath it is characterized by secondary folds in the heliospheric current sheet that are caused by the solar wind latitudinal variation over the solar cycle. We present examples illustrating some cases of interest: a “bent” current sheet, and the HCS structure during the magnetic field reversal at the solar maximum. We also discuss the evolution of the magnetic polarity structure in the region close to the heliopause.

Effects of interstellar magnetic field B and constant flux of neutral H on the heliosphere

[1] A treatment showing that the local interstellar medium (LISM) bow shock (BS) may exist and the heliosphere is tilted has recently been given by Ben-Jaffel et al. [2000] and used in an attempt to interpret combined Voyager UVS data and Hubble Space Telescope spectra of the Ly α sky background emission as plausible evidence for the existence of BS. However, the authors stressed the need for a more accurate description of the interface region in order to interpret the available data confidently. In this paper we use a more sophisticated Three-Dimensional Time-Dependent Magnetohydrodynamic with Neutral Particles (3DT MHD + N) model of the interaction between the solar wind and the interstellar medium with LISM neutral particles included. We report a parametric study of the effect of the LISM magnetic field strength and inclination angle in the presence of the neutral H atoms on the heliosphere and the heliospheric boundary. Ninety model cases that have been analyzed facilitate in building a diagnostic tool either to interpret archive data on the sky background radiation field or to stimulate new observations related to the interface, observations that may capture some of the fine structure revealed by the new model. Because the inclination angle and strength of the interstellar magnetic field induce unambiguous signatures in the heliospheric structure, our model calculations may serve as a lever to constrain the nature of the LISM from observational data.

Comparison of Heliospheric Models with Observations of the Voyager and IBEX Spacecraft

Results of modeling the heliosphere are compared with observations of the Voyager spacecraft and the IBEX mission simultaneously. The MHD solutions are tested against observational data for different strengths and orientations of the local interstellar magnetic field (LIMF) used in the simulations for asymmetric magnetized solar wind flow. We show that the model reproduces approximately the position of the IBEX ribbon and the termination shock crossing distance for Voyager 2, when the LIMF vector lies in the proximity of the hydrogen deflection plane with the inclination angle to the local interstellar flow equal to 39° ± 9° and its magnitude is 2.4 ± 0.3 μG. In ecliptic coordinates this solution corresponds to the LIMF vector pointing from (longitude, latitude) = (227° ± 7°, 35° ± 7°).

ADVECTIVE TRANSPORT OF INTERSTELLAR PLASMA INTO THE HELIOSPHERE ACROSS THE RECONNECTING HELIOPAUSE

We discuss results of magnetohydrodynamical model simulations of plasma dynamics in the proximity of the heliopause (HP). The model is shown to fit details of the magnetic field variations observed by the Voyager 1 spacecraft during the transition from the heliosphere to the local interstellar medium (LISM). We propose an interpretation of magnetic field structures observed by Voyager 1 in terms of fine-scale physical processes. Our simulations reveal an effective transport mechanism of relatively dense LISM plasma across the reconnecting HP into the heliosphere. The mechanism is associated with annihilation of magnetic sectors in the heliospheric plasma near the HP.

Questions about effects of interplanetary and interstellar magnetic fields on the heliospheric interface

In this paper we discuss configurations of the heliospheric interface shaped by the influence of both the uniform interstellar and the interplanetary (Parker model — Archimedean spiral) magnetic fields in the presence of the neutral particles. Magnetic fields strongly affect the structure and the shape of the heliospheric interface, which becomes asymmetric for any configuration of the interstellar magnetic field (ISMF), for the case where the interplanetary magnetic field (IMF) is included. In particular, the interstellar magnetic field lines may merge with interplanetary magnetic field lines of opposite direction at the heliopause. This may possibly cause a reconnection of the magnetic field lines at the heliopause.

The Termination Shock and Beyond: MHD Modeling

The 3D MHD models of the solar wind — interstellar plasma interaction including, in a self‐consistent way, interactions of various populations of plasma and neutral particles should be ready to confront their results with the forthcoming data that will be obtained from space missions. In the near future, predictions made by sophisticated theoretical models should help refine the goals and optimize the capabilities of the instruments that will explore the far heliosphere and the LISM. In this paper we are giving a short survay of the MHD models and point out the problems, which need to be solved in the near future. As the example we show our recent numerical results with the simple model of the current sheet.

The local interstellar magnetic field predictions from the MHD model and VOYAGERS’ data

The termination shock (TS) crossings by Voyager 1 (V1) and Voyager 2 (V2) revealed the asymmetry of the heliosphere. Crossings took place at distances 94 AU and 84 AU, respectively, in two different times, on December 16, 2004—V1, and on August 30, 2007—V2. However both occurred on the declining phase of the previous 11‐year solar cycle. The asymmetry may result from the solar wind dynamic pressure asymmetry or from the shock motion or from the local interstellar magnetic field (LIMF) asymmetric pressure. The question arises: if the interstellar magnetic field were the only factor responsible for the measured asymmetries, is it possible to find such a shape of the TS, which would reflect the real positions of V1 and V2 when they crossed the shock? Using our 3D MHD time dependent code we simulate the heliosphere/interstellar medium interactions for several different combinations of physical parameters in an attempt to answer this question. The results obtained places a substantial constraint on the orienta...