Magnetic field depression at the Earth's surface during energetic neutral atom emission fade-out in the inner magnetosphere

Details Magnetic field depression at the Earth's surface during energetic neutral atom emission fade-out in the inner magnetosphere Magnetic field depression at the Earth's surface during energetic neutral atom emission fade-out in the inner magnetosphere

Jun 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011jgra..11606220n&link_type=abstract

Journal of Geophysical Research, Volume 116, Issue A6, CiteID A06220

Physics

Magnetospheric Physics: Ring Current, Magnetospheric Physics: Magnetic Storms And Substorms (4305, 7954), Magnetospheric Physics: Magnetosphere: Inner, Magnetospheric Physics: Energetic Particles: Trapped, Magnetospheric Physics: Plasma Convection (2463)

Scientific paper

Using data from the high-energy neutral atom (HENA) imager onboard the IMAGE satellite, we examined the relation between the SYM-H index and the ring current energy during a storm main phase. The energy range of the energetic neutral atom (ENA) flux data used here is 16-120 keV for hydrogen and <180 keV for oxygen. From the data for the period 2000-2002, we selected 24 storm main phase events during which the IMAGE satellite was located at a geomagnetic latitude of ≥45° and a geocentric distance of ≥6 RE. According to the Dessler-Parker-Sckopke (DPS) equation, the ring current energy is expected to increase as the SYM-H index decreases. When the ENA energy flux is superimposed as a function of the SYM-H index for all 24 events, their overall correlation is negative; that is, the relation between the ENA energy flux and the SYM-H index is generally consistent with the DPS equation. However, an analysis of individual events showed only 10 events (42%) in which the ENA energy flux was negatively correlated with the SYM-H index (negative correlation events). There were 10 events showing no clear correlation between the ENA energy flux and the SYM-H index (no correlation events) and 4 events which contradicted the DPS equation (positive correlation events). In the superimposed plot, we noted that a smooth curve can be drawn for an upper limit of the data distribution, and data from the no correlation or positive correlation events create downward branches in the distribution. These observational results are not explained by the conventional DPS equation but by the “generalized” DPS equation, which includes a term representing energy stored in the stretched magnetic field. We can reasonably presume that the stretched magnetic field prevents energetic particles from being injected into the ring current. From the generalized DPS equation, we conclude that the total (kinetic and magnetic) energy stored in the stretched field and ring current loss mechanisms are important for understanding the relation between the ground magnetic field variation and ring current energy variation.

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