Physics
Scientific paper
Jan 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006adspr..38.1615p&link_type=abstract
Advances in Space Research, Volume 38, Issue 8, p. 1615-1625.
Physics
2
Scientific paper
We have investigated the population of the magnetosphere by ionospheric O+ ions from the dayside during the first 8 h of the September 24 25, 1998 magnetic storm by tracing ion trajectories from the ionosphere in time-dependent electric and magnetic fields obtained from a three-dimensional global magnetohydrodynamic (MHD) simulation of the magnetosphere during this storm event. The MHD simulation used WIND data upstream of Earth as input for this storm that began at 2345 UT on September 24, 1998, when a magnetic cloud impacted Earth’s magnetosphere. Ions were launched from both hemispheres on the dayside, in a region extending from 11 to 13 MLT and from 70° to 85° invariant latitude at five minute intervals, beginning 2 h before storm onset and extending to 8 h after the storm commenced. Ions were launched with energies that reflected the effects of ion energization along field lines during this event (e.g. [Cladis, J.B., Collin, H.L., Lennartsson, O.W., Moore, T.E., Peterson, W.K., Russell, C.T., 2000. Observations of centrifugal acceleration during compression of magnetosphere. Geophys. Res. Lett. 27, 915.]), as these effects were not a priori included in the MHD simulation of the event. The ion launch rate was dynamically normalized to observations by using the [Pollock Jr., C.J., Chappell, C.R., Gurnett, D.A., 1990. A survey of upwelling ion event characteristics. J. Geophys. Res. 95, 18 969.] and [Moore, T.E., Peterson, W.K., Russell, C.T., Chandler, M.O., Collier, M.R., Collin, H.L., Craven, P.D., Fitzenreiner, R., Giles, B.L., Pollock, C.J., 1999. Ionospheric mass ejection in response to a CME. Geophys. Res. Lett. 26, 2339.] relationship between the standard deviation of solar wind dynamic pressure and dayside O+ outflow. We found that ionospheric O+ ions had access to the plasma sheet beyond a radial distance of 10 RE before the storm, but gained access to the near-Earth region and partial ring current soon after the sudden commencement. In addition, significant changes to the magnetospheric configuration caused by the variations in solar wind dynamic pressure, most notably the two pressure peaks at 2345 and ˜0145 UT resulted in a relative absence of O+ ions from the magnetotail extending from ˜0140 to ˜0300 UT. After 0300 UT, and for the next hour, the O+ density in the plasma sheet increased to >1 cm-3, and O+ was more abundant in the magnetotail compared even to the period immediately following the storm commencement.
Abdalla Maha Ashour
El-Alaoui Mostafa
Peroomian Vahé
Zelenyi Lev M.
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