Sammendrag
Polar cap patches are regions of enhanced plasma density, seen to drift fromthe sunlit ionosphere
on the day side, over the polar cap, and into the night side Auroral oval. The patches are related
to substorm activity and reconnection processes in Earth’s magnetic tail.
The fact that the patches crosses the open-closed field line boundary (OCB) and goes into
the poleward edge of the aurora, can be used as an indicator of the night side merging gap, and
the ongoing reconnection processes in the tail.
A statistics of the occurrence of polar cap patch OCB crossings at the night side and its
dependence on IMF By are made using data from Meridian scanning photometer (MSP) and
All-sky camera (ASI) in Ny- Ålesund, Svalbard. This statistics can give indications of the positioning
of the night side merging gap and it’s IMF By dependence.
Polar cap patches was found to cross the night side OCB over Svalbard in the interval 18:30
– 04:50 MLT with an average of 23:25 MLT, more than half an our before magnetic midnight.
The changes in IMF By seems to be able to move the area where patches crosses the OCB by
∼ 1 hour MLT.