Physics Department Seminar University of Alaska Fairbanks

J O U R N A L    C L U B

Dipolarization initiated by Cowling electrojet current loop substantiated by THEMIS observations of a substorm on March 1, 2008
Joe Kan
Professor and Dean Emeritus, Physics Dept/GI UAF




We present THEMIS observations of a substorm on March 1, 2008 to substantiate the global M-I coupling substorm model that initiates dipolarization by the Cowling electrojet current loop (CECL). The Cowling electrojet is intensified by the induced equatorward E-field measured by Mozer (1971) driven by the earthward convection that is enhanced by the NEXL observed at X ~ −15 RE. Divergence of the Cowling electrojet launches Alfvén waves to form the time-dependent CECL, which then initiates the dipolarization as proposed by Kan (2007). Predictions of the CECL model include: (I) Brightening of the substorm onset preceded the dipolarization onset by ~80 ± 3 sec. This is consistent with the Alfvén travel time from the ionospheric footprint to the THEMIS-D in the neutral sheet estimated at ~80.3 sec based on the AM02 field model (Kubyshkina et al., 2009). (II) The substorm onset arcs are imbedded in the Cowling electrojet channel and connected by field lines to the dipolarization region. This is consistent with the observations that the Cowling electrojet peaked around ~67deg-68deg geomagnetic latitudes and extended from ~20 to ~02 MLT, which overlaps the substorm onset arcs and the footprints of THEMIS-D and -E satellites.


Friday, 11 Feb 2011

Globe Room, Elvey Building

3:45 PM