October 1995 magnetic cloud and accompanying storm activity: Ring current evolution

Abstract

Abstract. The passage at Earth of the October 1995 magnetic cloud and the high-speed corotating stream overtaking it, monitored by the Global Geospace Science (GGS) spacecraft Wind, caused two consecutive geomagnetic storms: a major one during the strong B• < 0 nT phase of cloud passage and a moderate one during the intermittent Bz < 0 activity in the fast corotating stream. Large dynamic pressure changes were observed in the sheath region ahead of the cloud and in the cloud-stream interface region at its rear, resulting in substantial corrections to the measured Dst index. A burst of superdense plasma sheet extending over -•2 hours in local time was observed at geostationary orbit during the second storm. We simulate the ring current development during this storm period using our kinetic model and calculate the magnetic field perturbation caused by the ring current. The plasma inflow on the nightside is modeled throughout the investigated period using data measured at geosynchronous orbit. The modeled Dst index is compared with the observed D st values corrected for magnetopause and telluric currents. The temporal evolution of the ring current H + and O + distribution functionsis computed, considering losses due to charge exchange, Coulomb collisions, and ion precipitation. We find that (1) the storm time enhancement of the plasma sheet ion population contributed significantly to the ring current buildup; (2) an additional -•12 nT decrease in Dst is achieved when the symmetry line of the plasma convection paths is rotated eastward from the dawn-dusk direction with 3 hours during the first storm; (3) the major loss process is charge exchange, followed by Coulomb collisions and ion precipitation; (4) however, the energy losses due to ion precipitation increase monotonically during the more active periods, reaching the level of Coulomb losses at peak storm intensity. We argue that the losses due to ion precipitation considered in this study are closely related to the enhanced convection electric field, which in our model is parameterized with the planetary Kp index. Correspondingly, we find that (5) there is a very good correlation between the variations in time of this index and the magnitude of the ion precipitation losses.

Ionospheric and boundary contributions to the Dessler-Parker-Sckopke formula for &lt;i&gt;Dst&lt;/i&gt;

“…(56) may be compared to that used in most previous studies (e.g. Burton et al, 1975;McPherron, 2000, 2002;McPherron and O'Brien, 2001;Liemohn et al, 2001Liemohn et al, , 2002Jordanova et al, 1998Jordanova et al, , 2003Siscoe et al, 2005a,b):…”

“…Second, the use of the theorem for studying magnetospheric and geomagnetic-storm dynamics, in particular for predicting Dst time series on the basis of solar-wind and other inputs, is a separate topic and constitutes an extensive field of research in its own right (e.g. Burton et al, 1975;McPherron, 2000, 2002;McPherron and O'Brien, 2001;Liemohn et al, 2001Liemohn et al, , 2002Jordanova et al, 1998Jordanova et al, , 2003Siscoe et al, 2005a,b, and many others); elsewhere (Vasyliūnas, 2006) I discuss how the magnetotail term derived here affects some prediction equations for Dst.…”

Transport and loss of the inner plasma sheet electrons: THEMIS observations

“…It is thought that the injected energetic ions contribute to the evolution of the ring current population, and many ring current simulations have used the plasma sheet properties as boundary conditions for the calculations [e.g., Jordanova et al, 1998Jordanova et al, , 2006Ebihara et al, 2002]. The energetic electrons of the plasma sheet are also important because they play a significant role in the seed population of relativistic electrons in the radiation belts [e.g., Miyoshi et al, 2003Miyoshi et al, , 2007.…”

Plasma sheet access to the inner magnetosphere

“…The same mechanism on a grander scale is invoked for storm time particle injections and increases of the ring current, which can capture large portions of the near-Earth plasma sheet onto closed drift paths. For this reason many ring current or inner magnetospheric transport codes [Jordanova et al, 1998; Bourdarie et al, 1997] use the plasma sheet as an outer boundary condition (often based on Los Alamos geosynchronous data).…”