Title: Ion
loss on Mars caused by the Kelvin-Helmholtz instability
Author(s): Penz
T, Erkaev NV, Biernat HK, Lammer H, Amerstorfer UV, Gunell H, Kallio E,
Barabash S, Orsini S, Milillo A, Baumjohann W
Source: PLANETARY
AND SPACE SCIENCE 52 (13): 1157-1167 NOV 2004
Document Type: Article
Language: English
Abstract: Mars
Global Surveyor detected cold electrons above the Martian ionopause,
which can be interpreted as detached ionospheric plasma clouds. Similar
observations by the Pioneer Venus Orbiter electron temperature probe
showed also extreme spatial irregularities of electrons in the form of
plasma clouds on Venus, which were explained by the occurrence of the
Kelvin-Helmholtz instability. Therefore, we suggest that the
Kelvin-Helmholtz instability may also detach ionospheric plasma clouds
on Mars. We investigate the instability growth rate at the Martian
ionopause resulting from the flow of the solar wind for the case where
the interplanetary magnetic field is oriented normal to the flow
direction. Since the velocity shear near the subsolar point is very
small, this area is stable with respect to the Kelvin-Helmholtz
instability. We found that the highest flow velocities are reached at
the equatorial flanks near the terminator plane, while the maximum
plasma density in the terminator plane appears at the polar areas. By
comparing the instability growth rate with the magnetic barrier
formation time, we found that the instability can evolve into a
non-linear stage at the whole terminator plane but preferably at the
equatorial flanks. Escape rates of O+ ions due to detached plasma
clouds in the order of about 2 x 10(23)-3 x 10(24) s(-1) are found.
Thus, atmospheric loss caused by the Kelvin-Helmholtz instability
should be comparable with other non-thermal loss processes. Further, we
discuss our results in view of the expected observations of heavy ion
loss rates by ASPERA-3 on board of Mars Express. (C) 2004 Elsevier Ltd.
All rights reserved.
Author Keywords: Mars;
magnetohydrodynamics; instabilities; atmospheric loss
KeyWords Plus: SOLAR-WIND
INTERACTION; MAGNETIC-FIELD; VENUS IONOPAUSE; LARMOR RADIUS; MHD;
IONOSPHERE; PLASMA; MODEL; SIMULATION; MAGNETOPAUSE
Addresses: Penz
T (reprint author), Graz Univ, Inst Theoret Phys, Univ Pl 5, Graz,
A-8010 Austria
Graz Univ, Inst Theoret Phys, Graz, A-8010 Austria
Graz Univ, Inst Geophys Astrophys & Meteorol, Graz, A-8010 Austria
Austrian Acad Sci, Inst Space Res, Graz, A-8042 Austria
Russian Acad Sci, Inst Computat Modelling, Krasnoyarsk, 660036 Russia
Swedish Inst Space Phys, Kiruna, SE-98128 Sweden
Finnish Meteorol Inst, Helsinki, FIN-00101 Finland
CNR, Inst Fis Spazio Interplanetaro, Rome, I-00133 Italy
Publisher: PERGAMON-ELSEVIER
SCIENCE LTD, THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB,
ENGLAND
Subject Category: ASTRONOMY
& ASTROPHYSICS
IDS Number: 873VW
ISSN: 0032-0633