Nature of Axial Tail Instability and Bubble-Blob Formation in Near-Earth Plasma Sheet*

Details Nature of Axial Tail Instability and Bubble-Blob Formation in Near-Earth Plasma Sheet* Nature of Axial Tail Instability and Bubble-Blob Formation in Near-Earth Plasma Sheet*

Dec 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsm14b..06z&link_type=abstract

American Geophysical Union, Fall Meeting 2011, abstract #SM14B-06

Physics

[2723] Magnetospheric Physics / Magnetic Reconnection, [2752] Magnetospheric Physics / Mhd Waves And Instabilities, [2764] Magnetospheric Physics / Plasma Sheet, [2790] Magnetospheric Physics / Substorms

Scientific paper

Previous global MHD simulations of substorm events have identified the dynamic presence of an axial tail instability with dawn-dusk symmetry in the near-Earth plasma sheet as a major cause of the initial loss of MHD equilibrium on closed field lines prior to the subsequent magnetic reconnection and substorm expansion onset processes [Raeder et al. 2010; Siscoe et al. 2009]. In this work, energy principle analysis indicates that a two-dimensional thin current sheet configuration in the magnetotail is typically stable to the axial mode within the framework of ideal MHD model. Linear resistive MHD calculations find axial tail instabilities on closed field lines in the generalized Harris sheet configurations. The properties of these instabilities are similar to the axial tail modes observed in the global MHD simulations. The axial tail mode is unstable in regimes of low Lundquist number and regions with small normal component of magnetic field. Mode growth and structure show both similarities and differences in comparison to the linear resistive tearing mode of a one-dimensional Harris sheet. Unlike the conventional tearing mode of Harris sheet, the linear axial tail instability does not involve any reconnection process. Instead, the nature of the mode is dominantly an interchange or slippage process among neighboring flux tubes as facilitated by dissipations such as resistivity. The formation of bubble-blob pairs in pressure and entropy distributions in the near-Earth plasma sheet is shown to be a natural component as well as consequence of this axial instability process. *Supported by NSF grants AGS-0902360 and PHY-0821899. REFERENCES: Raeder, J., P. Zhu, Y. Ge, and G. Siscoe (2010), Open Geospace General Circulation Model simulation of a substorm: Axial tail instability and ballooning mode preceding substorm onset, J. Geophys. Res., 115, A00I16, doi:10.1029/2010JA015876. Siscoe, G. L., M. M. Kuznetsova, and J. Raeder (2009), Search for an onset mechanism that operates for both CMEs and substorms, Ann. Geophys., 27, 31413146.

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