Propagation of BBFs and Dipolarization Fronts in the Global MHD simulation of February 27, 2009 Substorm

Details Propagation of BBFs and Dipolarization Fronts in the Global MHD simulation of February 27, 2009 Substorm Propagation of BBFs and Dipolarization Fronts in the Global MHD simulation of February 27, 2009 Substorm

Dec 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsm41a1856g&link_type=abstract

American Geophysical Union, Fall Meeting 2010, abstract #SM41A-1856

Physics

[2723] Magnetospheric Physics / Magnetic Reconnection, [2753] Magnetospheric Physics / Numerical Modeling, [2760] Magnetospheric Physics / Plasma Convection, [2790] Magnetospheric Physics / Substorms

Scientific paper

A global MHD simulation has been performed to investigate the THEMIS substorm on February 27, 2009. During this substorm the conjugated observations from the space and on the THEMIS ground observatories are available. The location and time of this substorm onset can be determined based on these observations. The initial auroral brightening is found at around 07:49 UT in the field of view of Fort Smith station (FSMI), with a pre-existing auroral arc located equatorward. A couple minutes later, the in situ observations recorded a sharp dipolarization front sunward passing through THEMIS spacecraft, which travels almost 10 RE in the magnetotail. In this study our global MHD model, i.e., OpenGGCM, driven by the real-time solar wind/IMF conditions, is able to reproduce the key features of these substorm signatures, including the auroral breakup at FSMI with the same onset time as the observations, and a strong earthward Bursty Bulk Flow (BBF) and dipolarization fronts that cause the substorm onset signatures. It is found in the simulation that the auroral breakup is caused by the strong flow shear and the flow vortices which form as the BBF moves earthward. Investigation of the tail BBF and its dipolarization front (DF) reveals that the bipolar change of the Bz component ahead of the DF can be produced by the interaction between two distinct plasmas from separate X lines: the anti-sunward moving southward flux tubes in the tailward flows emanating from an inner magnetic reconnection region, and the sunward traveling dipolarized tubes within the front of a strong earthward BBF that originates in a mid-tail reconnection region. The rebound and oscillations of the intruding BBF reported by the recent THEMIS observations are also seen in the simulation when the BBF encounters the high-pressure inner magnetosphere.

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