Magnetic local time variation and scaling of poleward auroral boundary dynamics

Abstract

The balance of dayside and nightside reconnection processes within the Earth's magnetosphere and its effect on the amount of open magnetic flux threading the ionosphere is well understood in terms of the expanding-contracting polar cap model. However, the nature and character of the consequential fluctuations in the polar cap boundary are poorly understood. By using the poleward auroral luminosity boundary (PALB), as measured by the FUV instrument of the IMAGE spacecraft, as a proxy for the polar cap boundary, we have studied the motion of this boundary for more than 2 years across the complete range of magnetic local time. Our results show that the dayside PALB dynamics are broadly self-similar on timescales of 12 min to 6 h and appear to be monofractal. Similarity with the characteristics of solar wind and interplanetary magnetic field variability suggests that this dayside monofractal behavior is predominantly inherited from the solar wind via the reconnection process. The nightside PALB dynamics exhibit scale-free behavior at intermediate time scales (12-90 min) and appear to be multifractal. We propose that this character is a result of the intermittent multifractal structure of magnetotail reconnection.

An Empirical Orthogonal Function Reanalysis of the Northern Polar External and Induced Magnetic Field During Solar Cycle 23

“…This is because while the magnetopause reconnection is directly driven by the IMF, as discussed above, the magnetotail reconnection has a more complex relationship in which near‐Earth reconnection is controlled in a similar way to the DP1 equivalent current system, occurring at substorm onset, and distant tail reconnection is possibly correlated with the IMF at long lag. Thus, DP2EC is not expected to have a direct correlation with the IMF and be uncorrelated with it on time scales longer than the magnetotail response time to the IMF (Longden et al, ).…”

Effects of the interplanetary magnetic field on the location of the open‐closed field line boundary

“…The open‐closed field line boundary(OCB) is the interface between geomagnetic field lines that are open to solar wind and closed onto the opposite hemisphere [e.g., Lockwood , ; Rae et al , ; Kabin et al , ]. The location of the OCB connects closely to the most important dynamic processes in the Earth's magnetosphere, such as the large‐scale magnetosphere convection and magnetic reconnection at the magnetopause/magnetotail [e.g., Siscoe and Huang , ; Hubert et al , ; Lester et al , ; Milan et al , ; Milan , ; Aikio et al , ; Longden et al , ]. The study of shape and location of the OCB is not only important to estimate the total open magnetic flux which is a fundamental indicator of the total magnetic energy in the solar wind‐magnetosphere‐ionosphere coupling system but also to provide information of the magnetic reconnection location and rate.…”

Ionospheric Boundaries Derived From Auroral Images

“…Longden et al. (2014) used these data to study the local time variation and scaling of poleward auroral boundary dynamics. Mooney et al.…”

“…Subsequent studies have shown the usefulness of this original data set. Longden et al (2014) used these data to study the local time variation and scaling of poleward auroral boundary dynamics. Mooney et al (2020) used the data set to study the spatio-temporal variation of the OCB through the substorm cycle.…”