Substorm-associated large-scale magnetic field changes in the magnetotail: a prerequisite for "magnetotail deflation" events

Abstract

Abstract. An attempt is made to search for a critical condition in the lobe magnetic field to initiate large-scale magnetic field changes associated with substorm expansions. Using data from ISEE-1 for 1978, sudden decreases in the lobe magnetic field accompanied by magnetic field dipolarizations are identified. In this study, such events are designated as the magnetotail deflation. The magnetic field component parallel to the equatorial plane, B E , is normalized to a fixed geocentric distance, B EN , and is corrected for the compression effect of the solar wind dynamic pressure, B EN C . It is shown that the B EN C value just prior to a magnetotail deflation correlates well with the Dst index; B EN C = 37.5 − 0.217 Dst 0 , where Dst 0 denotes the Dst value corrected for the solar wind dynamic pressure. This regression function appears to delineate the upper limit of B EN C values, when they are sorted by the Dst 0 index. On the basis of this finding it is suggested that a prerequisite condition for magnetotail deflations must exist in the magnetosphere.

Extreme Geomagnetic Storms – 1868 – 2010

“…The SSC observed at Earth 35 minutes later is apparently caused by In compiling the list of associated ESP events in this work, we also verified our results by extensively cross-checking and enhancing the list with ESP events that have been identified in the literature for both the recent Solar Cycle 23 and earlier periods in the space era (e.g. Klecker et al, 1981;van Nes, Roelof, and Reinhard, 1984a;van Nes et al, 1984b;Beeck and Sanderson, 1989;Kallenrode, 1995;Huttunen-Heikinmkaa and Valtonen, 2009;Mäkelä et al, 2011). Table 5 includes information on ESP occurrence for the extreme storms that occurred after 1973.…”

“…Several studies have shown a relation between this expansion and the Dst index (Meng, 1984;Feldstein et al, 1997). The physical cause of this relation is not completely understood, but it has been suggested that the enhanced ring current during geomagnetic storms could alter the magnetic field geometry of the near-Earth magnetotail, delaying substorm onset until the open flux content of the magnetosphere grows unusually large (Nakai and Kamide, 2003;Milan, Boakes, and Hubert, 2008;Milan et al, 2009).…”

Influences on the radius of the auroral oval

“…We interpret the increase in oval radius during storms as a stabilization of the magnetotail to the onset of reconnection and substorms by the magnetic perturbation associated with the westward-directed ring current (see also Nakai and Kamide, 2003;Milan et al, 2008Milan et al, , 2009. Inside the ring current region a negative B Z perturbation is produced, measured at the surface of the Earth as the negative Sym-H perturbation.…”

“…Before this, Meng (1982Meng ( , 1984 and Yokoyama et al (1998), amongst others, showed a link between the latitude of the auroral oval and D st , another measure of ring current intensity. As suggested by Nakai and Kamide (2003), and reiterated by Milan et al (2008), the enhanced ring current found during geomagnetic storms could alter the magnetic field geometry of the nearEarth magnetotail, delaying substorm onset until the open flux content of the magnetosphere grows unusually large. This would naturally explain the observation of aurora at low latitudes during periods of intense geomagnetic disturbance, particularly geomagnetic storms.…”

The Sun’s Strange Behavior: Maunder Minimum or Gleissberg Cycle?

“…At the magnetopause the most important parameters are the rate at which B z is brought to the magnetopause. In the tail, the ring current plays an important role in allowing the tail fields to reconnect and join the closed magnetic field region (Siscoe 1978;Silverman and Feynman, 1980;Nakai and Kamida, 2003;Milan et al 2009a;Milan, 2009b). Thus both the solar wind magnetosphere coupling and the ring current intensity control the size of the auroral oval (Milan et al, 2009a).…”