Abstract
Ionospheric convection patterns from the Super Dual Auroral Radar
Network are used to determine the trajectories, transit times and decay
rates of three polar cap patches from their creation in the dayside
polar cap ionosphere to their end of life on the nightside. The first
two polar cap patches were created within 12 minutes of each other and
travelled through the dayside convection throat, before entering the
nightside auroral oval after 104 and 92 minutes, respectively. When the
patches approached the nightside auroral oval, an intensification in the
poleward auroral boundary occurred close to their exit point, followed
by a decrease in the transit velocity. The airglow decay rates of
patches 1 and 2 were found to be ≈0.6% and ≈0.9% per minute,
respectively. The third patch decayed completely within the polar cap
and had a lifetime of only 78 minutes. After a change in drift
direction, patch 3 had a radar backscatter power half-life of 4.23
minutes, which reduced to 1.80 minutes after a stagnation, indicating a
variable decay rate. 28 minutes after the change in direction, and 16
minutes after stagnation, patch 3 completely disintegrated. We relate
this rapid decay to increased frictional heating, which speeds up the
recombination rate. Therefore, we suggest that the stagnation of a polar
cap patch is a main determinant to whether or not a polar cap patch can
exit through the nightside auroral oval.