INFINA (EX INFIP)   05545
INSTITUTO DE FISICA INTERDISCIPLINARIA Y APLICADA
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
The stability of supersonic magnetohydrodynamic flows with velocity shear.
Autor/es:
GNAVI, G.; GRATTON, F. T.; FARRUGIA, C. J.
Lugar:
Mendoza, Argentina
Reunión:
Congreso; FLUIDOS-2006, IX Reunión sobre Recientes Avances en Física de Fluidos y sus Aplicaciones; 2006
Institución organizadora:
Facultad de Ingenier¨ªa, U N Cuyo
Resumen:
A variety of different physical regimes are observed during spacecraft crossings of the low latitude boundary layer of the magnetopause (MP) flanks. A theoretical analysis of the linear stability of velocity shear flows, performed with continuous profiles of the magnetohydrodynamic fields B, V, T, and ¦Ñ, shows that the Kelvin-Helmholtz (KH) mechanism is significantly affected by plasma compressibility when the flow velocity becomes supersonic, as in the case of the MP flanks. The analysis also brings into light the efficacy of the interplanetary magnetic field in the control of the instability. It is noted that the use of a simplified model like the tangential discontinuity can miss the KH instability altogether, which emphasizes the importance of observations in situ to input realistic features into the models employed for the stability analysis. The action of compressibility on the KH growth rate is a strong function of the ratio of densities across the transition, and in addition the efficiency of the stabilizing effects, magnetic shear and plasma compressibility depends on the local values of the Mach and Alfv¨¦nic Mach numbers, and on the angles between B and V across the boundary layer. These factors vary over the MP and depend on the changing conditions of the solar wind. A selection of significant examples show the sensitivity of the KH excitation on particular features of two different boundary layer models, which connect the same set of asymptotic values of the physical quantities on both sides of the boundary layer. Work supported by Argentinean grants UBACYT X291/04 y CONICET PIP 5291/05, and NASA grants NAG 5-13166, NAG5-12189.