Solar Cycle Variations of the Magnetosphere: Causes and Consequences III
Presiding: M W Liemohn, University of Michigan; R L McPherron, Institiute of Geophysics and Planetary Physics, University of California, Los Angeles
SM44A-01 15:30h
Simulations of Solar Minimum and Solar Maximum Multi-dip Storms
The ring current represents the essential element of all geomagnetic storms; however, what mechanisms are important for the acceleration and loss of energetic particles during stormtime and how they relate to the solar wind drivers are not well understood. We use our global physics-based model to simulate ring current evolution during several large multi-dip storms that occurred during solar minimum, the rising phase of the solar cycle, and solar maximum conditions: the October 18, 1995 magnetic cloud, and the complex ejecta in early May 1998 and in October 21-25, 2001. We compare these storms in terms of ring current injection, morphology, role of dense plasma sheet, ion composition, and relative importance of particle loss mechanisms. We investigate the effect of varying solar activity, as reflected in near-Earth interplanetary conditions, on ring current evolution and how large geomagnetic storms form.
SM44A-02 15:50h
A statistical comparison of ion bulk properties at geosynchronous orbit during moderate and intense geomagnetic storms at solar minimum and maximum
Geosynchronous orbit plasma observations by the LANL MPAs before and during 42 intense storms and 111 moderate storms at solar minimum (January, 1995 - June, 1997) and at solar maximum (July, 1999 - June, 2002) are collected, categorized, and analyzed through the superposed epoch technique. The storms are defined by the pressure corrected Dst (Dst*). IMF southward Bz (Bs ) from the Wind and ACE spacecrafts is also included in this study. The similarities and differences among the average variations of IMF Bs, four channel fluxes (with energies ~30 keV, ~18 keV, ~7 keV, and ~1 keV) and several derived bulk properties of ions at geosynchronous orbit, and Dst* in the four storm categories are examined. It is found that both IMF Bs and plasma sheet density determine the intensity of the storm-time ring current. At geosynchronous orbit, hot-ion fluxes, density, and temperature vary with local time and are enhanced in high geomagnetic activity. It is also shown that hot ions are nearly isotropic in the central plasma sheet during storms. On the nightside, the storm-time temperature of hot ions at solar minimum is higher than that at solar maximum.
http://www-personal.engin.umich.edu/~jichunz/
SM44A-03 16:10h
The storm-time plasma sheet at geosynchronous orbit : CME- and CIR-dominated solar wind
The plasma sheet provides the primary source population for the storm-time ring current, and characteristic storm signatures are produced by the plasma sheet penetrating deep into the inner magnetosphere. Geosynchronous orbit offers an excellent vantage point from which to monitor the plasma sheet population that ultimately becomes the storm-time ring current. For well over a complete solar cycle, Los Alamos has been fielding magnetospheric plasma analyzers at geosynchronous orbit, creating an extensive multi-point database of plasma sheet conditions. Previous statistical analyses of these data have revealed important information about the access that the plasma sheet has to the inner magnetosphere. More recently, we have performed superposed epoch studies of the variation of plasma sheet properties as a function of storm phase. In the current study, we examine the storm-time behaviour for storms sorted according to the likely solar wind driver, i.e., CME-driven and CIR high-speed-stream-driven, and according to the phase of the solar cycle. We compare the geosynchronous data with data from the MENA instrument on-board the IMAGE satellite to investigate the global distribution of energetic ions in the inner magnetosphere during such events.
SM44A-04 INVITED 16:25h
Solar Cycle Variations Observed in the High-Latitude Ionosphere
We have prepared an 11 year record of the high-latitude ionospheric environment using the AMIE data assimilation technique driven primarily by ground magnetometers. Using this data set we examine the difference in the response of the high-latitude ionosphere to similar input events as identified by IMF Bz, By, V, and density profiles. We look at the effect of the phase of the solar cycle, season, and other long time scale variations. We present the results as identified modes of the ionosphere and discuss the evolution from one to another over the scale of a solar cycle.
SM44A-05 16:45h
Solar-cycle variations of polar wind and thermal ion outflows: Akebono observations and implications on magnetosphere-ionosphere coupling
Significant long-term variations are present in magnetospheric plasma composition, which result from solar-cycle variations in the coupling between the magnetosphere and the ionosphere, in particular ionospheric ion outflow to the magnetosphere. We present Akebono observations of solar-activity dependences of the lowest-energy components of ion outflow - H+ and O+ polar wind and thermal ion flows. These observations spanned a solar cycle, and covered a wide range of altitudes (1500-8500 km) and invariant latitudes (>60° ILAT) in the polar ionosphere and a variety of geomagnetic activity conditions. At low altitudes, the averaged H+ and O+ ion velocities increase with altitude at a larger rate at solar minimum than at solar maximum. In contrast, the situation is reversed at high altitudes. This may suggest that the polar wind and related thermal ion outflows correlate differently with solar activity at low and high altitudes, and that the dominant ion acceleration process may be different in different altitude regions. We consider geophysical processes that may contribute to the observed solar activity dependences, including the possible contributions of photoelectrons and elevated electron temperatures to the ambipolar electric field that drives the polar wind.