Storm-time magnetospheric currents inferred from mid-latitude geomagnetic field variations.

Abstract

Both D and H components of geomagnetic field data from 10 mid-latitude stations are used to examine the storm-time magnetospheric current system by deriving the longitudinally symmetric and asymmetric components of the fields. The asymmetry in D component suggests that net downward and upward field-aligned currents exist in the morning sector and from the evening to the early morning sector, respectively, when the IMF is southward. It also suggests the appearance of a net downward current in the afternoon sector at the developing stage of the storm-time ring current. These suggestions are confirmed by Magsat observation over the ionosphere since the direction of disturbances over the ionosphere is not the opposite but the same as that on the ground. This downward current signature co-exists with that of the morning sector during the southward IMF, suggesting that two different current systems co-exist at the developing phase of the ring current. One is the so-called partial ring current system whereas the other is the current system controlled by the IMF-Bz. A systematic phase shift of asymmetry in local time is seen in the dusk-side H but not in the D component, indicating that the contribution from westward drifting ring current particles can not be neglected as a cause for the H component asymmetry.

Interplanetary and Geomagnetic Consequences of Interacting CMEs of 13 – 14 June 2012

“…Then the second CME at 21:40 UT on 16 June probably pierces through the first one creating a small region where the density falls off very rapidly. The two peaks in SYM-H (Iyemori, 1990) at 22:40 UT on 16 June and at 01:05 UT on 17 June interspersed by a dip probably correspond to the arrival of the faster CME in which a rarefied region is embedded. The estimated speeds of two shocks marked as S1 and S2 were 450 and 485 km s −1 , respectively.…”

Wavelet-based multiscale analysis of geomagnetic disturbance

“…It is the oneminute high-resolution version of Dst, derived using data from magnetic observatories close enough to the magnetic equator, so as not to be influenced by auroral current systems. The SYM-H index provides an excellent measure of the large-scale behaviour of the ring current and magnetic storm dynamics (see Iyemori, 1990). Figure 7 shows the boundaries between antipersistent/persistent behaviour reflected by the scaling exponent β(t).…”

The ring current: a short biography

“…In 1969 IAGA officially sanctioned the use of Dst as a measure of the stormtime ring current. Recently a new index, called Sym H, has been developed, which uses averaged data from 6 stations reported at a 1-min cadence (Iyemori, 1990). In most applications Sym H can be treated as a high-resolution version of Dst, albeit with reduced absolute accuracy (Wanliss and Showalter, 2006).…”

“…Still, they were unable to explain why auroral displays should affect compass directions. A century and a half would pass before Kristian Birkeland (1867-1917 indicated for reference (Iyemori, 1990 [Birkeland, 1908]. Times of the SSC (near mid-day on 20 November), the main and recovery phases are indicated for reference (Iyemori, 1990).…”