OpenGGCM Simulation of Ballooning and Axial MHD Mode at Substorm Onset (Invited)

Details OpenGGCM Simulation of Ballooning and Axial MHD Mode at Substorm Onset (Invited) OpenGGCM Simulation of Ballooning and Axial MHD Mode at Substorm Onset (Invited)

Dec 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsm54b..04r&link_type=abstract

American Geophysical Union, Fall Meeting 2010, abstract #SM54B-04

Physics

[2704] Magnetospheric Physics / Auroral Phenomena, [2753] Magnetospheric Physics / Numerical Modeling, [2764] Magnetospheric Physics / Plasma Sheet, [2790] Magnetospheric Physics / Substorms

Scientific paper

It is generally accepted that magnetic reconnection is the main mechanism that dissipates power during a substorm. It is less clear, however, whether the beginning of magnetic reconnection in the magnetotail also signifies the onset of the substorm expansion phase itself, i.e., whether the "outside-in" scenario applies, or if a different process happens first closer to Earth that triggers the reconnection onset in the magnetotail, i.e., the "inside-out" scenario. Global MHD simulations have generally supported the "outside-in" scenario. However, ideal MHD instabilities that could possibly trigger tail reconnection may have been missed due to coarse numerical resolution or due to other numerical effects. Here, we present results from an OpenGGCM simulation of the March 23, 2007 substorm that clearly shows growth of the ballooning mode as suggested by our earlier analysis (Zhu et al., 2009), as well as growth of an ideal-like instability that is purely axial and was previously reported by Siscoe et al. (2009). Both instabilities occur simultaneously and are immediately followed by reconnection onset. The simulations results are in accordance with recent Geotail observations of ballooning with a wavelength of approximately 0.5 RE, and the time scales agree with that of the explosive growth phase. The exact relation between the three instabilities, i.e., ballooning, the axial mode, and tearing, is not entirely clear yet; however, having demonstrated that the OpenGGCM reproduces all of them, they can now be analyzed in more detail. Furthermore, we present the expected auroral signature of these processes, which will allow for a more detailed comparison of the simulation results with ground based imagers.

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