H. Aceves,1 M. Reyes–Ruiz,1 and C. E. Chávez1,2
1 Instituto de Astronomía, Universidad Nacional Autónoma de Mexico, Apdo. Postal 106, 22830 Ensenada, B. C., México. (aceves@astrosen.unam.mx, maurey@astrosen.unam.mx, carlosepech@astrosen.unam.mx).
2 Facultad de Ingeniería Mecánica y Eléctrica, Universidad Autónoma de Nuevo León, Av. Universidad S/N, 66451 San Nicolás de los Garza, Nuevo León, Mexico.
Received 2011 August 11.
Accepted 2012 January 28.
RESUMEN
Se estudian los efectos que las fluctuaciones magneticas turbulentas tienen sobre la dinámica de iones pickup de O+ en las regiones polares magnéticas de la ionofunda de Marte. En particular estudiamos su efecto en los perfiles de velocidad promedio como función de la altitud sobre los polos, con el fin de comparar con datos reciente del Mars Express que indican que su velocidad promedio es pequeña y esencialmente en la dirección antisolar. Se encuentra que, aunque las fluctuaciones magnóeticas ocasionan desviaciones del simple movimiento de arrastre girotroópico, incluso amplitudes de fluctuación más grandes que las medidas no son capaces de reproducir los perfiles verticales de velocidad de los iones de O+. Concluimos que otro mecanismo físico, diferente a uno puramente de dinámica de partículas cargadas, esta actuando sobre estos iones en el terminador marciano. Una posibilidad es que exista una interacción de tipo viscoso entre el viento solar y la ionosfera marciana a bajas altitudes.
ABSTRACT
We study some of the effects that magnetic turbulent fluctuations have on the dynamics of pickup O+ ions in the magnetic polar regions of the Mars ionosheath. In particular we study their effect on the bulk velocity profiles of ions as a function of altitude over the magnetic poles, in order to compare them with recent Mars Express data; that indicate that their average velocity is very low and essentially in the anti–sunward direction. We find that, while magnetic field fluctuations do give rise to deviations from simple E × B–drift gyromotion, even fluctuation amplitudes much greater than those of in situ measurements are not able to reproduce the vertical velocity profile of O+ ions. We conclude that other physical mechanisms, different from a pure charged particle dynamics, are acting on pickup ions at the Martian terminator. One possibility is a viscous–like interaction between the Solar Wind and the Martian ionosphere at low altitudes.
Key Words: acceleration of particles — magnetic fields — methods: numerical — planets and satellites: individual (Mars) — turbulence.
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]]> ACKNOWLEDGMENTS
This research was funded by Universidad Nacional Autónoma de México-PAPIIT Research Projects IN121406 and IN109710, and Conacyt Projects 25030 and 60354.
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