Finding Magnetospheric Dynamics with Observed Imbalances in Earth’s Open and Closed Magnetic Flux

Earth’s magnetosphere is an unstable system. We observe this in many aspects of the system, for example, substorms. A key indicator of the state of the system is the amount of open magnetic flux and the rate at which it is changing. These measures are intimately tied to the driving of the system (i.e. dayside reconnection) but also, the response of the system (i.e. nightside reconnection). When they become imbalanced, extraordinary phenomena such as substorms can dominate magnetospheric dynamics. Understanding when and how these imbalances occur is therefore a key to understanding our magnetosphere.

 

Using auroral data from the IMAGE (Imager for Magnetopause-to-Aurora Global Exploration) spacecraft, we calculate the amount of magnetic flux in the open region of the magnetosphere and the amount of flux in the auroral region. The open flux is indicative of the amount of flux which is convecting towards the nightside and the closed flux in the auroral region is indicative of the amount of magnetic flux which is convecting towards the dayside. Together, the two quantities tell us how much of the magnetosphere is convecting. By investigating the timing of the peaks and troughs in these timeseries, we evaluate when the system is unstable and when day- and nightside reconnection occurs. We study these timeseries statistically and the relation between their peaks and troughs.

 

Overall, and over long timescales, a balance between day- and nightside reconnection must exist because the amount of magnetic flux in the magnetosphere is finite. On timescales of minutes to 100s of minutes however, we find that imbalances occur. We observe that the magnetosphere can become imbalanced on timescales from minutes to ~3 hours, with the median timescale being 24 minutes. Without consideration of any driving parameter or any other dataset and by simply investigating statistically the convecting magnetic flux content, we find two distinct statistical distributions: one where dayside reconnection is dominant and one where nightside reconnection is dominant. We find that the two show differences in their statistical behaviour, indicating that nightside flux closure can be up to 4 times higher than flux opening.