The coupling of global fast MHD waves to resonant Alfv\u00e9n waves in the Earth\u2019s magnetosphere has been studied for over 4 decades (Southwood, 1974). The process has been used to explain observations in solar coronal loops (Goossens et al., 2002), other planetary magnetospheres (Mars, Jupiter and Saturn – Cramm et al., 1998; Glassmeier et al., 1989; Khurana and Kivelson, 1989; Russell, 1989) and even neutron star magnetospheres (Rezania and Samson, 2005). Alfv\u00e9n waves play a key role in magnetosphere-ionosphere coupling and auroral processes, as well as particle acceleration (associated with strong field aligned currents) and transport of energy. Until recently the most sophisticated theory was 2D, so strictly only applied to, for example, axisymmetric magnetospheres. Recently three Team members have performed simulations of Alfv\u00e9n resonances in 3D. The results are strikingly different to 2D theory, and are expected to catalyze a re-evaluation of resonant wave coupling in real life. For example, in 3D Alfv\u00e9n resonances can cross L-shells and have a different polarization angle compared to 2D. Any non-axisymmetric planetary
magnetosphere can exhibit 3D Alfv\u00e9n resonances. The Earth, with its variety of ground-based observations and satellite mission makes it the ideal setting to search for the first ever observation of a 3D Alfv\u00e9n resonance. The search will focus on regions where the magnetosphere is most non-axisymmetric, either due to density plumes (in the afternoon) or field lines being distended due to the global convection cycle. There are many important applications of standing Alfv\u00e9n waves, such as radiation belt particle interactions, ionospheric heating, auroral dynamics (Lessard et al., 1999; Mann et al., 2013; Degeling et al., 2018), which are beyond the scope of the present team. We will, however, demonstrate the efficacy of these ideas by
remote sensing of plasma density. Specifically, we shall focus on (i) identifying signatures of 3D Alfv\u00e9n resonances in simulations, (ii) develop software to search for these in data sets, (iii) produce maps of 3D resonance properties to highlight the potential impact in related research areas, (iv) apply this knowledge to improve remote sensing of plasma density using 3D Alfv\u00e9n waves and to understand the modification of Alfv\u00e9n resonance signatures in ground magnetometer data by the overlying ionosphere.<\/p>\n","protected":false},"excerpt":{"rendered":"
The coupling of global fast MHD waves to resonant Alfv\u00e9n waves in the Earth\u2019s magnetosphere has been studied for over 4 decades (Southwood, 1974). The process has been used to explain observations in solar coronal loops (Goossens et al., 2002), … Continue reading