Current understanding of magnetic storms: Storm‐substorm relationships

Abstract

Abstract. This paper attempts to summarize the current understanding of the storm/substorm relationship by clearing up a considerable amount of controversy and by addressing the question of how solar wind energy is deposited into and is dissipated in the constituent elements that are critical to magnetospheric and ionospheric processes during magnetic storms. (1) Four mechanisms are identified and discussed as the primary causes of enhanced electric fields in the interplanetary medium responsible for geomagnetic storms. It is pointed out that in reality, these four mechanisms, which are not mutually exclusive, but interdependent, interact differently from event to event. Interplanetary coronal mass ejections (ICMEs) and corotating interaction regions (CIRs) are found to be the primary phenomena responsible for the main phase of geomagnetic storms. The other two mechanisms, i.e., HILDCAA (high-intensity, long-duration, continuous auroral electrojet activity) and the so-called RussellMcPherron effect, work to make the ICME and CIR phenomena more geoeffective. The solar cycle dependence of the various sources in creating magnetic storms has yet to be quantitatively understood.

Space Storms and Space Weather Hazards

“…Gonzalez et al (1998) have shown that there is a statistical relationship between the peak magnetic field magnitude within an ICME at 1 AU and its velocity (Fig. 10).…”

“…Several studies have addressed the issue, without however achieving conclusive evidence (e.g., Kamide, 1992;Kamide and Allen, 1997;Daglis et al, 1998;Kamide et al, 1998a;Daglis, 2000;Daglis et al, 2000). Studies opposing the "Chapman-Akasofu paradigm" have claimed that substorm occurrence is incidental to the main phase of storms, and that ion transport into the ring current is accomplished solely by enhanced largescale convection electric fields, with no contribution from substorms at all.…”

“…Yearly averaged sunspot number (heavy trace) for the interval 1972-1996 is also shown. After Kamide et al (1998). Figure 11.…”

“…Using the Dst index, Yokoyama and Kamide (1997) and Kamide et al (1998) examined statistically more than 1200 geomagnetic storms, from weak to intense, spanning over three solar cycles. It is surprisingly found that for more than 50% of intense magnetic storms, the main phase undergoes a two-step growth.…”

Variability of Geomagnetic Field with Interplanetary Magnetic Field at Low, Mid and High Latitudes

“…During the reconnection process efficient transfer of energy takes place from solar wind into magnetosphere as well as huge fluxes of charged particles enter the magnetosphere. These charged particles are deflected by the magnetic field of earth and circulate around the earth at a height of about 2 -7 R E (Earth Radii) [12], constituting a belt of current around earth, known as the ring current [13,14]. In addition some particles reach the high latitudinal ionosphere where they also develop other current system.…”