Astrophysics and Space Sciences Transactions www.astrophys-space-sci-trans.net 1810-6528 1810-6536 5 1 2009 10.5194/astra-5-39-2009 http://www.astrophys-space-sci-trans.net/5/39/2009/ http://www.astrophys-space-sci-trans.net/5/39/2009/astra-5-39-2009.html http://www.astrophys-space-sci-trans.net/5/39/2009/astra-5-39-2009.pdf 39 42 2009-09-11 Shear driven waves in the induced magnetosphere of Mars: parameter dependence U. V. Amerstorfer ute.amerstorfer@oeaw.ac.at H. Gunell N. V. Erkaev H. K. Biernat Space Research Institute, Austrian Academy of Sciences, Schmiedlstr. 6, 8042 Graz, Austria Department of Physics, West Virginia University, Morgantown, WV 26506-6315, USA Institute of Computational Modelling, Russian Academy of Sciences, 660036 Krasnoyarsk-36, Russia Low frequency oscillations in the plasma in the induced magnetosphere of Mars were recently measured by the Mars Express spacecraft. Velocity shear was observed, and the plasma was shown to be Kelvin-Helmholtz unstable. In this paper we examine the effects on the frequency and growth rate of the instability when the parameters are varied around the observed values. It is found that if the velocity shear is increased by decreasing the velocity on the low velocity side, i.e. close to the planet, the growth rate increases, while a frequency consistent with the observations can be maintained. When finite Larmor radius effects are included, the growth rate depends on the direction of the vorticity and in the maximum case it is seen to increase substantially, up to a factor of 50, for narrow shear layers. This does also increase the frequency of the oscillations to a large extent. Amerstorfer, U V., Erkaev, N V., Langmayr, D., and Biernat,~H K.: On Kelvin Helmholtz instability due to the solar wind interaction with unmagnetized planets, Planet. Space Sci., 55, 1811–1816, \doi10.1016/j.pss.2007.01.015, 2007. Arshukova, I L., Erkaev, N V., Biernat, H K., and Vogl, D F.: Interchange instability of the Venusian ionopause, Adv. Space Res., 33, 182–186, \doi10.1016/j.asr.2003.04.015, 2004. Baranov, V B., Fahr, H J., and Ruderman, M S.: Investigation of macroscopic instabilities at the heliopause boundary surface, Astron. Astrophys., 261, 341–347, 1992. Biernat, H., Erkaev, N., Amerstorfer, U., Penz, T., and Lichtenegger, H.: Solar wind flow past Venus and its implications for the occurrence of the Kelvin-Helmholtz instability, Planet. Space Sci., 55, 1793–1803, \doi10.1016/j.pss.2007.01.006, 2007. Brace, L H., Theis, R F., and Hoegy, W R.: Plasma clouds above the ionopause of Venus and their implications, Planet. Space Sci., 30, 29–37, \doi10.1016/0032-0633(82)90069-1, 1982. Braginskii, S I.: Transport Processes in a Plasma, in: Reviews of\vadjust Plasma Physics, edited by Leontovich, M A., 1, 205–311, Consultants Bureau, New York, 1965. Espley, J R., Cloutier, P A., Brain, D A., Crider, D H., and Acuña,~ M H.: Observations of low-frequency magnetic oscillations in the Martian magnetosheath, magnetic pileup region, and tail, J. Geophys. Res., 109, A07 213, \doi10.1029/2003JA010193, 2004. Gunell, H., Amerstorfer, U V., Nilsson, H., Grima, C., Koepke,~M., Fränz,~ M., Winningham,~J D., Frahm,~R A., Sauvaud,~J.-A., Fedorov,~A., Erkaev,~N V., Biernat,~H K., Holmström,~M., Lundin,~R., and Barabash,~S.: Shear driven waves in the induced magnetosphere of Mars, Plasma Phys. Contr. F., 50, 074 018, \doi10.1088/0741-3335/50/7/074018, 2008. Huba, J D.: The Kelvin–Helmholtz instability: Finite Larmor radius magnetohydrodynamics, Geophys. Res. Lett., 23, 2907–2910, 1996. Lundin, R., Barabash, S., Andersson, H., Holmström, M., Grigoriev, A., Yamauchi, M., Sauvaud, J.-A., Fedorov, A., Budnik, E., Thocaven, J.-J., Winningham, D., Frahm, R., Scherrer,~J., Sharber,~J., Asamura,~K., Hayakawa,~H., Coates,~A., Linder,~D R., Curtis,~C., Hsieh,~K C., Sandel,~B R., Grande,~M., Carter,~M., Reading,~D H., Koskinen,~H., Kallio,~E., Riihela,~P., Schmidt,~W., Säles,~T., Kozyra,~J., Krupp,~N., Woch,~J., Luhmann,~J., McKenna-Lawler,~S., Cerulli-Irelli,~R., Orsini,~S., Maggi,~M., Mura,~A., Milillo,~A., Roelof,~E., Williams,~D., Livi,~S., Brandt,~P., Wurz,~P., and Bochsler,~P.: Solar Wind-Induced Atmospheric Erosion atMars: First Results from ASPERA-3 on Mars Express, Science, 305, 1933–1936, \doi10.1126/science.1101860, 2004. Penz, T., Erkaev, N V., Biernat, H K., Lammer, H., Amerstorfer,~U V., Gunell,~H., Kallio,~E., Barabash,~S., Orsini,~S., Milillo,~A., and Baumjohann,~W.: Ion loss on Mars caused by the Kelvin–Helmholtz instability, Planet. Space Sci., 52, 1157–1167, \doi10.1016/j.pss.2004.06.001, 2004. Penz, T., Arshukova, I L., Terada, N., Shinagawa, H., Erkaev, N V., Biernat, H K., and Lammer, H.: A comparison of magnetohydrodynamic instabilities at the Martian ionopause, Adv. Space Res., 36, 2049–2056, \doi10.1016/j.asr.2004.11.039, 2005. Russell, C T., Luhmann, J G., Elphic, R C., Scarf, F L., and Brace,~L H.: Magnetic field and plasma wave observations in a plasma cloud at Venus, Geophys. Res. Lett., 9, 45–48, 1982. Winningham,~J D., Frahm,~R A., Sharber,~J R., Coates,~A J., Linder,~D R., Soobiah,~Y., Kallio,~E., Espley,~J R., Lundin,~R., Barabash,~S., Holmström,~M., Andersson,~H., Yamauchi,~M., Grigoriev,~A., Scherrer,~J R., Jeffers,~S J., Kataria,~D O., Kozyra,~J U., Luhmann,~J G., Roelof,~E C., Williams,~D J., Livi,~S., Curtis,~C C., Hsieh,~K C., Sandel,~B R., Koskinen,~H., Säles,~T., Riihelä,~P., Schmidt,~W., Grande,~M., Carter,~M., Sauvaud,~J.-A., Fedorov,~A., Thocaven,~J.-J., McKenna-Lawler,~S., Orsini,~S., Cerulli-Irelli,~R., Maggi,~M., Wurz,~P., Bochsler,~P., Krupp,~N., Woch,~J., Fränz,~M., Asamura,~K., and Dierker,~C.: Electron oscillations in the induced martian magnetosphere, Icarus, 182, 360–370, \doi10.1016/j.icarus.2005.10.033, 2006. Wolff, R S., Goldstein, B E., and Yeates, C M.: The onset and development of Kelvin-Helmholtz instability at the Venus ionopause, J.\ Geophys. Res., 85, 7697–7707, 1980.