High time-resolution observations of periodic frictional heating associated with a Pc5 micropulsation

Abstract

Geomagnetic micropulsations are fluctuations of the Earth's magnetic field on time-scales ranging from a few seconds to several minutes and with amplitudes varying between a few and several hundred nanotesla. In the inner magnetosphere, where the Earth's magnetic field lines are closed, the oscillations can adopt a standing wave pattern with a scale size comparable to the dimensions of the magnetospheric cavity. These hydromagnetic waves constitute one of the primary mechanisms for the transfer of energy from the outer regions of the magnetosphere to the high-latitude ionosphere during geomagnetic substorms. In the ionosphere, Joule heating is thought to be the dominant damping process for the pulsations and the rate of energy dissipation during a typical event¹ is of the order of 10⁹ W. By means of the EISCAT (European Incoherent Scatter) radar facility it has been possible to measure directly the ionospheric ion-temperature and ion-velocity fluctuations during a micropulsation. The relationship predicted by the theory of Joule heating for these two parameters is confirmed in detail by the high time-resolution results reported here.