Evidence on a Class of Azimuthally Propagating Dipolarization Structures
in the Earth's Magnetosphere from 4 to 30 Re
We report observational evidence for a class of coherent magnetic
dipolarization structures that are long lived and radially extensive.
The reported dipolarization structures, a subset of general
dipolarizations, typically remain coherent over 20-30 min in real time,
3-6 hours in MLT, and 10-20 Re in radial distance. Arrays of more than
three spacecraft in non-collinear geometry are used to determine the
propagation vector, including both the normal speed and direction, of
such dipolarizations in the equatorial plane. The determined azimuthal
propagation is ~3 deg/min, which corresponds to
~50 km/s at 6.6 Re. This speed is consistent with those
obtained from two azimuthally separated spacecraft in previous works.
Further analysis suggests that these azimuthally propagating
dipolarizations (APDs) are often finger-like in shape, ranging from 5 to
20 Re in length and several Re in width. The reported APD may accompany
the earthward flow channel and dipolarizing flux bundle (DFB).