Evolution of the current system during solar wind pressure pulses based on aurora and magnetometer observations

Abstract

We investigated evolution of ionospheric currents during sudden commencements using a ground magnetometer network in conjunction with an all-sky imager, which has the advantage of locating field-aligned currents much more accurately than ground magnetometers. Preliminary (PI) and main (MI) impulse currents showed two-cell patterns propagating antisunward, particularly during a southward interplanetary magnetic field (IMF). Although this overall pattern is consistent with the Araki (solar wind sources of magnetospheric ultra-low-frequency waves. Geophysical monograph series, vol 81. AGU, Washington, DC, pp [183][184][185][186][187][188][189][190][191][192][193][194][195][196][197][198][199][200] 1994. doi:10.1029/GM081p0183) model, we found several interesting features. The PI and MI currents in some events were highly asymmetric with respect to the noonmidnight meridian; the post-noon sector did not show any notable PI signal, but only had an MI starting earlier than the pre-noon MI. Not only equivalent currents but also aurora and equatorial magnetometer data supported the much weaker PI response. We suggest that interplanetary shocks impacting away from the subsolar point caused the asymmetric current pattern. Additionally, even when PI currents form in both pre-and post-noon sectors, they can initiate and disappear at different timings. The PI currents did not immediately disappear but coexisted with the MI currents for the first few minutes of the MI. During a southward IMF, the MI currents formed equatorward of a preexisting DP-2, indicating that the MI currents are a separate structure from a preexisting DP-2. In contrast, the MI currents under a northward IMF were essentially an intensification of a preexisting DP-2. The magnetometer and imager combination has been shown to be a powerful means for tracing evolution of ionospheric currents, and we showed various types of ionospheric responses under different upstream conditions.

Impacts of Magnetosheath High‐Speed Jets on the Magnetosphere and Ionosphere Measured by Optical Imaging and Satellite Observations

“…This auroral behavior is similar to the “shock aurora”, which is the response to interplanetary shocks/sudden commencements (SCs). For “shock aurora”, the diffuse aurora and discrete aurora are considered to be signatures corresponding signatures of the currents during preliminary impulse and main impulse (Motoba et al, ; Nishimura et al, ). Recent studies have shown that the foreshock transients can provide geospace effects similar to interplanetary shocks/SCs as described in the introduction section (Engebretson et al, ; Wang et al, 2018).…”

Dayside Magnetospheric and Ionospheric Responses to a Foreshock Transient on 25 June 2008: 2. 2‐D Evolution Based on Dayside Auroral Imaging

“…We calculated equivalent horizontal current distributions using magnetometer data available through SuperMAG. The method is described in Nishimura et al [2016]. Here, generators of FACs are in the magnetosphere, and the two ionospheres are the load of the electrical circuit.…”

Large‐Scale Traveling Ionospheric Disturbances Origin and Propagation: Case Study of the December 2015 Geomagnetic Storm

“…These processes produce favorable conditions for development of the ion‐cyclotron instability and scattering of the energetic particles into the loss cone (e.g., Zhang et al, ). In this case energetic particle precipitation can be a major source of ionization in the auroral ionosphere, leading to development of ionospheric irregularities (seen on Figure c), contribute significantly to the electrical conductance (e.g., Galand & Richmond, ) and further modifications of ionospheric currents (e.g., Nishimura et al, ). At that time, the AMPERE observations show an increase in the FACs magnitude (see Figure d).…”