Backlinks: Dependence of substorm type and solar-wind energy coupling

Coauthors: Maria-Theresia Walach, Kyle Murphy, Colin Forsyth, David Sibeck

Storyline

Geomagnetic activity can be categorized into events that have similar characteristics like substorms, steady magnetospheric convection, and geomagnetic storms. Within substorms, further distinctions can be made, based on the number of immediate substorms before and after it. One major question is how much of the differences in these forms of magnetic activity are due to solar wind driving, and how much of it is due to intrinsic magnetospheric phenomena. In order to answer this question, we explore how solar wind driving differs between these events. In particular, we find that isolated multi-onset substorms are mainly caused by high solar-wind-driving after the first onset in comparison to single-onset substorms. More curiously, because of the temporal correlation in solar wind parameters, there is a statistically discernable increase in solar wind driving before onset for multi-onset substorms of the same strength as single-onset substorms. This suggests that the ionospheric response might be different for multi-onset substorms of the same strength as single-onset substorms. In fact, we find that auroral electrojet response is considerably different for different magnetospheric activity types of similar strengths. The strengths of the magnetic activity are determined based on the auroral electrojet currents flowing in the polar regions (or ring currents). The strengths of the electrojets saturate at high driving, however, there is substantial non-linearity during low solar wind electric fields. The state of the magnetosphere-ionosphere system or its response function is different during each of these categories of events.

Questions

1. How does substorm driving vary before and after the onset of different categories of substorms?
2. How does the substorm driving vary for storms, substorms, and SCM?
3. How does the auroral electrojet response vary for different categories of substorms (or SMCs, Storms, outside these categories)?
4. What can the answers to the above questions tell us about the magnetosphere-ionosphere system, its state, or response?
5. How can SMILE/ STORM benefit from this knowledge?

Figures

Q1. Fig 1a. : Distribution of substorm categories of similar strength with driving electric field. [It's not super clear how best to define strength. Right now I use min AL. But perhaps we should use the amount of energy pumped into the system? or some other error-free metric. ] The AL value is prone to substantial error (we need to quantify that error, and see if there are methods to reduce it. The plot has AL as a conditional variable.

Some new findings to be explored further:

• [ ] Kolmogorov-Smrinov test suggests that the distributions of single-onset and multi-onset substorms are the same up until 30 minutes before the onset! And they diverge substantially close to 30 minutes. [This 30 minutes might be close to the width of the autocorrelation function(?)]

• [ ] Furthermore, the distribution of single-onset substorms after the onset matches with the distribution of multi-onset 30 minutes before onset! [Need to check into this, and its implications.]

Q1. Fig 1b Correlation between post-onset and pre-onset driving for both single-onset and muti-onset substorms.