Dynamical response of the magnetosphere‐ionosphere system to a solar wind dynamic pressure oscillation

Abstract

[1] On 28 February 1998, four quasi-periodic pressure pulses with an amplitude of a few nPa detected by ACE gave rise to periodic compressions of the magnetosphere with period of about 14 min. In concert with periodic compressed and expanded states of the magnetosphere forced directly by the pressure variation, a coherent geomagnetic field fluctuation with the same period appeared on a global scale and was recorded at stations located from polar to equatorial regions. Most ground-level geomagnetic field signatures on the dayside can be interpreted as the result of a global ionospheric current system, like the global Pc5 event examined by Motoba et al. [2002]. In the afternoon polar ionosphere covered with the dense magnetometer stations, a vortical current structure associated with pressure-induced field-aligned currents (FACs) is centered at 72°± 1°and consists of a counterclockwise (clockwise) vortex in response to positive (negative) changes of solar wind pressure oscillation. Although the vortical current signatures are unclear in the morning sector, each afternoon vortex could pair with the morning one with opposite rotation. During this event, the interplanetary magnetic field (IMF) remained steady with a strong southward orientation (À10 nT or less). In addition to the pressureinduced FAC system, the steady southward IMF drives the dayside Region 1 (R1) current system, resulting in the familiar large-scale two-cell convection pattern in the ionosphere observed by SuperDARN radars. The SuperDARN convection patterns indicated that the ionospheric convection reversal boundary (CRB) in the afternoon was located in the range of 73°$ 77°N around 15 MLT. The ionospheric footprint of the pressure-induced FAC in the afternoon was found to be 1.5°± 1.1°$ 4.0°± 1.4°e quatorward of the CRB. This suggests that the pressure-induced FAC is started inside the R1 current system originating from the outer magnetospheric boundary layer. We argue that the paired FAC system responsible for the global geomagnetic fluctuations on the ground arises from the oscillatory large-scale dynamical convection originating well inside the closed field lines in direct response to the quasi-periodic pressure variations, not from the localized undulations on the magnetopause nor from global eigenmode oscillations of the magnetospheric cavity.

Magnetospheric vortices and their global effect after a solar wind dynamic pressure decrease

“…Fujita et al [] suggested in their simulation study that the convection pattern in the ionosphere in their second main impulse phase is directly connected to the Region 2 current in the case of the negative impulse. A connection between the magnetosphere and the ionosphere by FACs was discussed by Motoba et al [] and Fujita et al []. From our simulation results, we find two major vortices in the plasma sheet, one in the dawn and the other in the dusk, each with a different rotation sense (counterclockwise in the dawn and clockwise in the dusk when viewed from the north).…”

Global Ionospheric Current System Associated With Penetration Electric Field and New Mechanism for the Generation of Dayside Westward Electric Field at Low Latitudes During Northward IMF

“…The excellent agreement in V i and ∆ H (Figure e) indicates that the magnetic perturbations are also caused by the corresponding perturbations in the IMF. Therefore, magnetic perturbations at a single station can be used to represent the perturbations caused by the IMF/solar wind, as done in many previous studies (e.g., Kikuchi et al, , ; Motoba et al, ; Nishida, , ).…”

Dayside magnetospheric and ionospheric responses to solar wind pressure increase: Multispacecraft and ground observations

“…Motoba et al . [] also believed that the ionospheric convection associated with the MI signature is closely coupled with the magnetospheric convection. By simulation, Slinker et al .…”