Diffusion at the Earth magnetopause : enhancement by Kelvin-Helmholtz instability

• Published in: Annales geophysicae (1988) Vol. 25; no. 1; pp. 271 - 282
• Main Authors: SMETS, R, BELMONT, G, DELCOURT, D, REZEAU, L
• Format: Journal Article
• Language: English
• Published: Katlenburg-Lindau European Geophysical Society 01.01.2007; European Geosciences Union; Copernicus Publications
• Subjects: Earth Sciences; Earth, ocean, space; Exact sciences and technology; External geophysics; Ocean, Atmosphere; Physics of the high neutral atmosphere; Physics of the ionosphere; Physics of the magnetosphere; Sciences of the Universe; Interplanetary magnetic field; tangential discontinuities; models; Magnetic reconnection; cusp; efficiency; Kelvin Helmholtz instability; thickness; Larmor radius; boundary layer; Shear flow; Magnetosheath; Magnetopause; solar wind; and boundary layers; Magnetosheath; Solar wind- magnetosphere interactions; magnetosphere; Finite Larmor radius; Magnetospheric physics (Magnetopause; Distribution function; Magnetic field reversal; Diffusion; Hybrid simulation
• ISSN: 0992-7689; 1432-0576; 1432-0576
• DOI: 10.5194/angeo-25-271-2007

Using hybrid simulations, we examine how particles can diffuse across the Earth's magnetopause because of finite Larmor radius effects. We focus on tangential discontinuities and consider a reversal of the magnetic field that closely models the magnetopause under southward interplanetary magnetic field. When the Larmor radius is on the order of the field reversal thickness, we show that particles can cross the discontinuity. We also show that with a realistic initial shear flow, a Kelvin-Helmholtz instability develops that increases the efficiency of the crossing process. We investigate the distribution functions of the transmitted ions and demonstrate that they are structured according to a D-shape. It accordingly appears that magnetic reconnection at the magnetopause is not the only process that leads to such specific distribution functions. A simple analytical model that describes the built-up of these functions is proposed.