Disturbance Dynamo Effects Observed in the Low-Latitude Ionosphere by IMAGE FUV

T.J. Immel, H.U. Frey, S.B. Mende, B.G. Fejer, and J.L. Burch


The stormtime disturbance dynamo is generated in the hours after the onset of
magnetic activity. Its effects advance from high to low latitudes as
thermospheric disturbance winds propagate equatorward from the auroral zones.
With the increase in westward winds at middle latitudes from coriolis-slowed
equatorward winds comes an additional electric field as plasma is dragged across
field lines in the same direction. The resultant current produces an additional
redistribution of charge and an eastward polarization current. These electric
fields influence the low-latitude ionosphere by slowing or reversing the
downward and eastward drift of the nighttime F-layer plasma. The efficiency of
the disturbance dynamo fields in affecting the vertical and meridional drifts of
the plasma varies with both local time and latitude. The IMAGE-FUV observations
at 135.6 nm provide a unique perspective on these effects through the retrieval
of velocities of plasma bubbles in the equatorial ionospheric anomaly.
Comparisons to the characterization of both zonal and vertical disturbance
dynamo effects measured with the Jicamarca radar yields similarities and some
differences. We describe the sometimes differing results, with the goal of
better understanding the dynamo effects in the low latitude ionosphere.

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Global Aspects of Magnetosphere-Ionosphere Coupling, 2006 Yosemite Workshop, 
Yosemite National Park, CA, USA, 7-10 February 2006