On the seasonal variation of electric and magnetic turbulence at high latitudes

Abstract

High‐pass filtered field measurements from the low‐altitude polar‐orbiting Dynamic Explorer 2 (DE2) spacecraft are used to investigate seasonal variation in the high‐latitude electric and magnetic fields on the scales from 3.8 km to 100 km. It is shown that the seasonal asymmetry has an opposite sense for the electric and magnetic components. The electric fields are by factor 3 enhanced and the magnetic fields are by factor 1.5 reduced under winter conditions as compared to summer conditions. The effect persists at very high polar latitudes, where the magnetic field lines are strongly stretched or open, so that the time required for the Alfvén‐wave communication between the ionosphere of summer and winter hemispheres is very large (>1 hour) or infinite. In this case, the earlier interpretations of the seasonal effect, which suggest that the magnetospheric generator of the turbulent fields is linked by the field‐aligned currents (FACs) to the high‐latitude ionosphere of both hemispheres, may be not applicable. A new explanation is proposed, in which it is assumed that the FACs from the generator region close through the Pedersen current in the ionosphere of only one hemisphere, either wintertime or summertime, and through the inertial current in the front of an outgoing Alfvén wave. It is demonstrated that the values of conductances derived within such an assumption are in a reasonable agreement with observations.