Ultra-low frequency waves in the magnetosphere
thesisposted on 15.02.2010, 09:59 by Lasse Boy Novock Clausen
Ultra-low frequency waves, i.e. pulsations between 0.1 and 1,000 mHz, are an inherent feature of space plasmas. These plasmas are largely collisionless and hence waves play an important role as an agent to transfer energy, mass and momentum. This work explores some of the wave's features in the Earth's magnetosphere using several different measurement techniques located in different regions. The first of the three case studies presented describes results from an experiment involving an ionospheric heating facility located on Svalbard. The SPace Exploration by Active Radar (SPEAR) facility periodically changed the ionospheric conductivities, superimposing a AC component on a background DC current. Thus the heated patch acted as a giant virtual antenna, emitting Alfvén waves which were detected by ground-based magnetometers in the vicinity of the heater. The following two case studies investigate naturally occurring waves, using both space- and ground-based instruments. In both cases waves generated at the bow shock penetrated into the magnetospheric cavity where they interacted with the local plasma and magnetic field. Whereas in the first case the propagation path of one individual wave packet is analysed, the last data chapter discusses the generation of Alfvénic continuum by upstream generated waves.