Mechanisms responsible for asymmetric aurora between the conjugate hemispheres

• Published in: Journal of Geophysical Research: Space Physics
• Main Author: Reistad, Jone Peter
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: The University of Bergen 2016
• Subjects: Bergen; Birkeland; aurora australis
• Online Access: https://hdl.handle.net/1956/12121

The work presented in this thesis is part of ongoing research within one of the research groups at the Birkeland Centre for Space Science (BCSS) at the Department of Physics and Technology, University of Bergen. Members of this group have earlier found that the two hemispheres can exhibit large asymmetries in the auroral display, contrary to what have usually been assumed. The group at BCSS is focusing on aspects of the solar wind - magnetosphere - ionosphere interactions that can lead to a different outcome in the two polar hemispheres in terms of e.g. convection speeds, magnetic field perturbations, electric currents, and auroral emissions. As a part of this ongoing effort, this thesis investigates two mechanisms proposed to be important in creating north-south asymmetries in the auroral display. To do this, simultaneous images from space of both the aurora borealis and the aurora australis are used to identify periods and regions when asymmetric aurora occurs. During the work on this thesis, a systematic search was performed resulting in the hitherto largest dataset of such simultaneous global imaging of the Earth’s dual auroras. In Paper I [Reistad et al., 2013] we find that non-conjugate aurora, being features only visible, or significantly brighter in one hemisphere, is rather common during active auroral displays. Furthermore, we found that 10 out of 15 identified non-conjugate features were consistent with at least one of the two mechanisms investigated in detail in this thesis. Two mechanisms has been investigated in detail to learn more about their importance. In Paper II [Reistad et al., 2014] we find that the poleward part of the dusk side auroral oval in the northern hemisphere is on average brighter when the Interplanetary Magnetic Field (IMF) is pointing away from the Sun, compared to when IMF is pointing toward the Sun, during southward directed IMF. The opposite result is found when looking at the dusk side auroral oval in the southern hemisphere. We interpret the results as a possible effect of the ...