The interplanetary (IP) shock is a kind of strong discontinuity, which can bring about significant variations of solar wind parameters during a short time interval, introducing perturbations into the geospace environment. Therefore, intensive research on the geoeffectiveness of the IP shock is essential to the magnetospheric studies and space weather prediction.
In the magnetosphere, although the dayside is always compressed by the impingement of IP shocks, magnetic field on the nightside may either increase or decrease according to satellite observations and MHD simulations. On the ground, the signature of geomagnetic sudden impulse (SI) at higher latitudes has two-phase bipolar variations: preliminary impulse (PI) and main impulse (MI). Traditionally, geomagnetic field variations on the ground and magnetospheric magnetic field responses (especially on the nightside) are separated topics in observational studies. The relationship between them has scarcely been studied.
Recently, Dr. Sun Tianran and Wang Chi from the State Key Laboratory of Space Weather, the National Space Science Center(NSSC), in cooperation with Russian scientist Dr. V. A. Pilipenko, revealed that although the two phenomena occur at largely separated locations, they are physically related and can form a response chain after the shock arrival. Based on the global PPMLR MHD code, the whole response process was studied in detail. Specifically, the region where the magnetic field decreases in the nightside magnetosphere is a dynamo, powering the transient field-aligned currents (FACs). These FACs further generate a pair of ionospheric current vortex, leading to MI variations on the ground. Therefore, the intrinsic physically related chain response was reported, and thus the magnetospheric SI and ground SI were linked together.
This work was published on the Journal of Geophysical Research (JGR)---Space Physics.
Link: http://onlinelibrary.wiley.com/doi/10.1002/2014JA020754/abstract
Citation: Sun, T. R., C. Wang, J. J. Zhang,V. A. Pilipenko, Y. Wang, and J. Y.Wang (2015), The chain responseof the magnetospheric and groundmagnetic field to interplanetary shocks,J. Geophys. Res. Space Physics, 120,157–165, doi:10.1002/2014JA020754.
Figure. Schematic plot of the current flow generated from the dynamos in the magnetic field decreasing regions. Contours of magnetic field variations areshown in the equatorial plane, with the red/blue regions illustratingthe positive/negative response regions, respectively. The blue curve is the current flow connecting the MI-related FAC and the negative response region.
