Nighttime Geomagnetic Response to Jumps of Solar Wind Dynamic Pressure: A Possible Cause of Québec Blackout in March 1989

Updated summaries of the August 1972 and March 1989 space weather events have been constructed. The features of these two events are compared to the Carrington 1859 event and a few other major space weather events. It is concluded that solar active regions release energy in a variety of forms (X‐rays, EUV photons, visible light, coronal mass ejection (CME) plasmas and fields) and they in turn can produce other energetic effects (solar energetic particles (SEPs), magnetic storms) in a variety of ways. It is clear that there is no strong one‐to‐one relationship between these various energy sinks. The energy is often distributed differently from one space weather event to the next. Concerning SEPs accelerated at interplanetary CME (ICME) shocks, it is concluded that the Fermi mechanism associated with quasi‐parallel shocks is relatively weak and that the gradient drift mechanism (electric fields) at quasi‐perpendicular shocks will produce harder spectra and higher fluxes. If the 4 August 1972 intrinsic magnetic cloud condition (southward interplanetary magnetic field instead of northward) and the interplanetary Sun to 1 au conditions were different, a 4 August 1972 magnetic storm and magnetospheric dawn‐to‐dusk electric fields substantially larger than the Carrington event would have occurred. Under these special interplanetary conditions, a Miyake et al. (2012), https://doi.org/10.1038/nature11123‐like extreme SEP event may have been formed. The long duration complex 1989 storm was probably greater than the Carrington storm in the sense that the total ring current particle energy was larger.

Section: Power Failures and Intense Auroral Currentsmentioning

confidence: 99%

Review of the August 1972 and March 1989 (Allen) Space Weather Events: Can We Learn Anything New From Them?

Tsurutani,

Sen,

Hajra

et al. 2024

The Influence of Ionospheric Conductance on Magnetospheric Convection During the Southward IMF

Zhu,

Dai,

Wang

et al. 2024

Magnetospheric convection is a fundamental process in the coupling of the solar wind, magnetosphere, and ionosphere. Recent studies have shown that dayside magnetopause reconnection drives magnetospheric convection, progressing from the dayside to the nightside within approximately 10–20 min in response to southward turning of the interplanetary magnetic field. In this study, we use global magnetohydrodynamic (MHD) simulations to investigate the influence of ionospheric conductance on dayside‐driven convection. We conduct three simulation runs: two with normal ionospheric conductance and one with nearly infinite conductance. The temporal and spatial pattern of magnetospheric convection largely remain consistent across all three simulation runs. Comparing the results, we observe a reduction of 20% in magnetospheric convection and a 30% increase of ionospheric Region 1 field‐aligned current (FAC) and Pedersen current in the run with nearly infinite conductance, compared to the normal conductance model. The results indicate that ionospheric conductance does not affect the response time of enhanced magnetospheric convection to the solar wind. We suggest that the 10–20 min timescale for establishing magnetospheric convection corresponds to the anti‐sunward drag of reconnected magnetic field lines from the sub‐solar point to the flank magnetopause. In cases of larger ionospheric conductance, the ionosphere footprints of dragged field lines become more stationary, potentially resulting in larger Region 1 FAC and ionosphere Pedersen current. A larger Pedersen current is associated with stronger sunward J × B force in the ionosphere, which corresponds to a stronger anti‐sunward force in the magnetosphere, thereby reducing sunward convection of closed field lines.

Generation of Field‐Aligned Currents in Response to Sudden Enhancement of Solar Wind Dynamic Pressure

Zhang,

Ebihara,

Tanaka

2024

We investigated the generation of field‐aligned currents (FACs) in response to the sudden enhancement of the solar wind dynamic pressure by tracing backward in time a packet of the Alfvén wave in the global magnetohydrodynamic (MHD) simulation. The generation region is identified from three perspectives, including the continuity of the current, the energy conservation and the time rate of change in the FACs. The generation mechanism is found to be related with the tailward motion of the compressional wave, which is excited when the magnetopause is compressed due to the solar wind dynamic pressure pulse. The compressional wave with a high magnetic pressure center interacts with the Earth's dipole field and forms a protruding part of the wavefront near the equatorial plane. The leading edge of the merged magnetic pressure that pertains to the compressional wave and the Earth starts to generate preliminary impulse (PI) FACs off the equator, as the magnetic pressure force accelerates the plasma and magnetic field lines are bent (FAC dynamo 1). Main impulse (MI) FACs are generated behind the leading edge in the equatorial plane due to the enhanced magnetic tension force (FAC dynamo 2). Magnetic field lines would be extremely curved during the passage due to the increasing magnetic tension force. The polarity of PI FACs is decided by the parallel vorticity of plasma flow, and MI FACs are the result of enhanced perpendicular currents together with the plasma flow in the equatorial plane.