Wave-particle interactions in the terrestrial magnetosphere
thesisposted on 15.12.2014, 10:41 by Lisa Baddeley
This thesis examines small scale poloidal mode magnetohydrodynamic waves which have an energy generation mechanism internal to the magnetosphere in the form of unstable particle populations. The energy from these particles is fed into a resonant wave mode and, ultimately, dissipated in the terrestrial ionosphere. By analysing Ion Distribution Functions (IDFs) the statistical occurrence of the driving magnetospheric particle populations is presented. Results indicate that the dominant driving particle populations are those of ~10 - 40 keV protons. The free energy of the particles has been quantified, revealing the dominance of the lower energy particle populations. The majority of unstable low energy protons contain > 1010 J of free energy in comparison to the higher energy protons which contain < 109 J. Using this method, one event, using conjugate ionospheric - magnetospheric data is examined and compared to a similar conjugate event of a rare subset of small scale waves called Giant Pulsations (Pgs). The available free energy is compared to the energy dissipated into the conjugate ionospheres. Estimates of the energy at the source and sink reveal that ~ 1010 J is transferred for the first event. Pgs are shown to transfer ten times this energy. The statistical study reveals that 1010 J is frequently available from unstable IDFs but 1011 J is not, thus providing an exploration for both the rarity of Pgs and the ubiquity of other small scale waves. Observations also suggest that drawn sector waves are driven by the drift-bounce resonance mechanism, while in the dark sector waves are driven by both drift and drift-bounce resonance mechanisms. Additionally, ionospheric observations indicate that the occurrence of small scale pulsations could be more abundant than previously thought. This implies that the quantity of energy being transported round the magnetospheric cavity and into the ionosphere via wave-particle interactions has previously been underestimated.