Aspects of magnetopause/magnetosphere response to interplanetary discontinuities, and features of magnetopause Kelvin-Helmholtz waves

• Autores: Farrugia, C. J.; Gratton, Fausto Tulio Livio
• Año de publicación: 2011
• Idioma: inglés
• Tipo de recurso: artículo
• Materia: INTERPLANETARY DISCONTINUITIES; KELVIN-HELMHOLTZ INSTABILITY; VORTEX SHEETS
• Institución: Consejo Nacional de Investigaciones Científicas y Técnicas

We describe (i) perturbations of the magnetopause/magnetosphere elicited by an interplanetary discontinuity and (ii) the production of Kelvin-Helmholtz waves on the magnetopause. These are two large topics, so for reasons of space we combine both features in a single data example, supporting the observations by theory. Correspondingly, the observations, made by ACE, consist of an interval in which a current sheet is followed by a period of strongly northward IMF. In view of recent attention directed at the effect of variations of the azimuthal component of the solar wind velocity on the magnetosphere, we chose a current sheet (CS) across which the east-west components of both field and flow vectors change polarity. A two-stage response is evident in the records of Cluster, outbound at the dusk terminator at 27° MLAT: (i) Four cycles of large-amplitude, ~3min oscillations during which the spacecraft sample alternately the cold, dense magnetosheath and the hot and tenuous magnetosphere plasmas. We argue that these motions are likely due to tangential stresses applied to the magnetopause. (ii) Soon thereafter the oscillatory character changes dramatically, and ~80s small-amplitude undulations appear which we argue to be magnetopause surface waves. Applying linear MHD theory we show these waves are due to a locally Kelvin-Helmholtz unstable boundary. As input parameters, we take values during the preceding large oscillations at the same magnetopause locale. An aspect of the non-linear phase of this instability is illustrated by a numerical simulation: the reduced duration of the evolution into large vortices by a strong initial perturbation.
Fil: Farrugia, C. J.. University Of New Hampshire; Estados Unidos
Fil: Gratton, Fausto Tulio Livio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física del Plasma. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física del Plasma; Argentina. Pontificia Universidad Católica Argentina "Santa María de los Buenos Aires". Facultad de Ciencias Fisicomatemáticas e Ingeniería; Argentina