Evidence for particle injection as the cause of Dst reduction during HILDCAA events

Details Evidence for particle injection as the cause of Dst reduction during HILDCAA events Evidence for particle injection as the cause of Dst reduction during HILDCAA events

Jan 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004jastp..66..177s&link_type=abstract

Journal of Atmospheric and Solar-Terrestrial Physics, Volume 66, Issue 2, p. 177-186.

Physics

15

Hildcaa, Ring Current, Dst, Energetic Protons

Scientific paper

The Earth's magnetic field at the equator, as monitored by the Dst index, can stay below its quiet day value for days. This can happen after storms resulting in a very slow recovery of the Dst index, or it can happen in the absence of a storm. Such ``anomalous'' behavior of the Dst recovery is observed during times showing continuous auroral activity called High Intensity Long Duration Continuous AE Activity (HILDCAA) (Planet. Space Sci. 35 (1987) 405). The Dst is mostly attributed to the ring current (RC), but it also depends on other current systems in the magnetosphere such as magnetopause, tail and auroral currents. It is well established that the magnetic effect of the RC is proportional to the energy content of the charged particles generating it (J. Geophys. Res. 64 (1959) 2239; 71 (1966) 3125). It is thus of interest to determine if the reduction of the Dst during HILDCAAs is due to an increased RC or/and can be accounted for by an increase or a relocation of other current systems.
This paper considers the injection of electrons and protons into the auroral and subauroral zone for four cases exhibiting HILDCAA activity. The total energy flux of the ions into the midnight/evening quadrant gives a good estimate of the energy injection into the RC (J. Geophys. Res. 107 (2002) 149). This injection, if it occurs during the recovery phase of a storm, prolongs the final decay of the Dst to quiet day values, and if it occurs during times without storms the injection can maintain Dst at more or less constant negative values for days. The ion injection into the RC is sufficient to account for the reduced Dst index during HILDCAAs. It is determined that the HILDCAA events are associated with a low-level injection of protons into the outer portion of the RC above L equal 4. The HILDCAA events are thus not due to plasma sheet current intensifications or earthward motion of this current. The prolonged low-level ion injection is associated with fluctuations in the Bz component of the solar wind magnetic field giving rise to magnetic field line merging on the front side of the magnetosphere (Planet. Space Sci. 35 (1987) 405). The duration of the Bz negative phases are not long enough to drive a magnetic storm.

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