Astrophysics and Space Sciences Transactions www.astrophys-space-sci-trans.net 1810-6528 1810-6536 2 2 2006 10.5194/astra-2-63-2006 http://www.astrophys-space-sci-trans.net/2/63/2006/ http://www.astrophys-space-sci-trans.net/2/63/2006/astra-2-63-2006.html http://www.astrophys-space-sci-trans.net/2/63/2006/astra-2-63-2006.pdf 63 72 2006-11-29 Are heliospheric flows magnetic line- or flux-conserving? D. H. Nickeler nickeler@asu.cas.cz M. Karlický Astronomical Institute Ondřejov AV ČR, Czech Republic This article discusses and tests the validity of the frozen in magnetic field paradigm (or 'ideal magnetohydrodynamics (MHD) constraint') which is usually adopted by many authors dealing with heliospheric physics. To show the problem of using ideal MHD in such a counterflow configuration like the heliosphere, we first recapitulate the basic concepts of freezing-in of magnetic fields, respectively magnetic topology conservation and its violation (= magnetic reconnection) in 3-D, already done by other authors with different methods with respect to derivations and interpretations. Then we analyse different heliospheric plasma environments. As a model of the stagnation region/stagnation point in front of the heliospheric nose, we present and discuss the general solution of the ideal MHD Ohm's law in the vicinity of a 2-D stagnation point, which was found by us. We show that ideal MHD either leads necessarily to a diverging magnetic field strength in the vicinity of such a stagnation point, or to a vanishing mass density on the heliopause boundaries. In the case that components of the electric field parallel to the magnetic field do not exist due to the chosen form of the non-ideal Ohm's law, it is always possible to formulate the transport equation of the magnetic field as a modified ideal Ohm's law. We find that the form of the Ohm's law which is often used in heliospheric physics (see e.g. Baranov and Fahr, 2003), is not able to change magnetic topology and thus cannot lead to magnetic reconnection, which necessarily has to occur at the stagnation point. The diverging magnetic field, for instance, implies the breakdown of the flux freezing paradigm for the heliosphere. Its application, especially at the heliospheric nose, is therefore rather doubtful. We conclude that it is necessary to search for an Ohm's law which is able to violate magnetic topology conservation. Baranov, V. B., and Fahr, H.-J.: On nonideal MHD properties of the partially ionized interstellar gas, J. Geophys. Res., 108, 1110–1111, 2003. Contopoulos, J.: General Axissymmetric Magnetohydrodynamic Flows: Theory and Solutions, Astrophys. J., 460, 185–198, 1996. Cowling, T G.: Magnetohydrodynamics, Adam Hilger Ltd., Rank Precision Industries, 1976. Dreher, J.: Numerical investigations of magnetic reconnection at the Earth's magnetopause in the frame of Hall-MHD, dissertation (in german), Univ. of Bochum, 1997. Florinski,~V. and Zank,~G P.: Comment on \lq On nonideal MHD properties of the partially ionized interstellar gas\rq by V B Baranov and H.-J Fahr, J.\ Geophys. Res., 108, 4-1–4-3, 2003. Freidberg, J. P.: Ideal Magnetohydrodynamics, Plenum Press, New York, 1987. \vadjust D'haeseleer,~W D., Hitchon,~W N G., Callen,~J D., and Shohet,~J L.: Flux coordinates and magnetic field structures, Springer-Verlag, Berlin Heidelberg, 1991. Kulikovskii, A. G. and Lyubimov, G. A.: Magnetohydrodynamics, Addison-Wesley-Longman, Reading, Mass., 1965. Newcomb, W. A.: Motion of magnetic lines of force, Ann. Phys., 3, 347–385, 1958. Nickeler, D. H. and Fahr, H.-J.: Two dimensional stationary resistive MHD flows: Borderline to magnetic reconnection solutions, Adv. Space Res., 37, 1292–1294., 2006. Nickeler,~D H., Goedbloed,~J P., and Fahr,~H.-J.: Stationary field aligned MHD flows at astropauses and in astrotails, Astron. Astrophys., 454, 797–810, 2006. Priest, E. and Forbes, T.: Magnetic Reconnection, Cambridge University Press, Cambridge, 2000. Priest,~E., Hornig,~G., and Pontin,~D I.: On the nature of Three-Dimensional Magnetic Reconnection, J. Geophys. Res., 108, 6–1, 2003. Ratkiewicz, R., Grygorczuk, J., and Ben-Jaffel, L.: Questions about effects of interplanetary and interstellar magnetic fields on the heliospheric interface, in: AIP Conf. Proc. 719: Physics of the outer Heliosphere: 3rd Intern. ISSP Conf., edited by Florinski,~V., Pogorelov,~N V., and Zank,~G P., 93–98, 2004. Schindler, K., and Hesse, M.: General Magnetic Reconnection, Parallel electric fields, and Helicity, J. Geophys. Res., 93, 5547–5557, 1988. Schlüter, A.: Ionized gas in a magnetic field, Electromagnetic Phenomena in Cosmical Physics, Proceedings from IAU Symposium no. 6, edited by Lehnert, B., intern. Astron. Union, Symp. no. 6, Cambridge Univ. Press, 71–80, 1958. Stern, D. P.: The motion of magnetic field lines, Space Sci. Rev., 6, 147–173, 1966. Titov, V. S. and Hornig, G.: Magnetohydrodynamic flows sustaining stationary magnetic nulls, Phys. of Plasmas, 7, 3542–3550, 2000.