IMF Control of Auroral Dynamics during a Magnetic Storm


Lewis, W.S., Burch, J.L., Retherford, K.D., Mende, S.B., Frey, H.U., Immel, T.J., Murphree, J.S.


The Far Ultraviolet Imager system on the IMAGE satellite obtains separate images of the proton
and electron auroras. Previous experiments have shown that following the passage of
interplanetary shocks, auroral activity typically progresses from near noon to near midnight in a
period of a few minutes. As shown by IMAGE-FUV, the proton auroras are more intense in the
dusk sector following the shock while the electron auroras are more intense near midnight.
However, once substorm activity begins, the two types of aurora generally show the same
morphology. In a particular case, on September 25, 2001, a shock was followed by several large
substorms. Throughout this time period, IMF By remained strongly negative. As a result, a
super-rotation of all auroral forms, oval as well as polar cap, was observed. This continuous
counterclockwise motion maintained an angular velocity of 1-2 degrees per minute throughout
the event. Co-incident with the arrival of a second shock, By rotated to near 0, and the auroral
rotation stopped. During the event, localized bright aurora indicative of a reconnection region
was observed in the cusp, while a second bright auroral spot moved from the nightside across
the polar cap and back to the cusp region. Its motion in local time corresponded with cusp
motions that were correlated with changes in By such that both spots moved simultaneously
either westward or eastward. This second spot is possibly associated with a neutral line that is
located far down the tail and moves along the boundary of a magnetospheric lobe cell as the
event progresses. 
		   
_______________
Fall 2002 Meeting of the American Geophysical Union
San Francisco, CA, USA, 6-10 December 2002