Exploring the Global Response of the Sun-Heliosphere-Magnetosphere-Ionosphere-Atmosphere System I
Presiding: J U Kozyra, University of Michigan; N A Schwadron, Southwest Research Institute
SA11A-01 INVITED 08:30h
The October 28, 2003 and Nov 7, 2004 CME Events: A Data-Driven MHD Model and Comparative Impact Scenarios
In the "Halloween Epic" of late October and early November of 2003, active regions 10484, 10486, and 10488 produced some of the most intense flare activity, powerful CMEs and associated geomagnetic storms during Solar Cycle 23. While each of these regions was remarkable in size and magnetic complexity, AR 10486 -- the largest sunspot group observed since November 1990 -- was by far the most significant. This active region maintained its extreme size, complex magnetic structure, and great eruption potential during its entire transit across the visible solar disk. Of the twelve major events that produced X-class flares, three stand out as defining events: the X17.2 event on Oct 28, the X8.3 event on Nov 2, and the X28+ event on Nov 4. In this paper, we present a recent numerical effort to model the Halloween Event from Oct 28, which was associated with an erupting prominence in AR 10486. We developed a data-driven MHD model of the solar eruption, and we studied the onset and dynamics of the CME and related shock wave in the low corona and interplanetary space. In our model, we adopted high-resolution magnetic data from MDI onboard SoHO to set a realistic boundary condition for the radial magnetic field at the Sun. The CME is triggered by slowly evolving the boundary conditions for the coupled tangential magnetic field and tangential plasma velocity at the solar surface up to a point when the MHD equilibrium of the prominence with the surrounding coronal field is no longer attainable. As a result of the loss of mechanical equilibrium, the prominence erupts, resembling a CME. We also compare interplanetary characteristics of the Oct 28, 2003 and Nov 7, 2004 events, considering a variety of CME impact scenarios by tracking different angular positions in the simulated CME.
SA11A-02 INVITED 08:50h
Bimodal Solar Wind-Magnetosphere-Ionosphere Coupling
Regarding its coupling to the solar wind, the magnetosphere-ionosphere system appears to be schizophrenic. That is, it seems to manifest two modes with contradictory qualities, modes that alternate depending on solar wind conditions. Normal conditions elicit the normal mode (aka the solar wind-dominated mode). But extreme conditions bring out the un-normal mode (aka the ionosphere-dominated mode). This talk emphasizes the un-normal, ionosphere-dominated mode, which makes its presence during great magnetic storms. Then the magnetosphere-confining Chapman-Ferraro current system fades away to be replaced by the region 1 currents system which links the now dominant ionosphere to the whole of geospace out to and including the bow shock. Dst no longer responds to the ram pressure of the solar wind. The electrical potential across the polar cap stops growing as solar wind driving strengthens. Instead, it becomes bound to ionospheric conductance, which as the storm intensifies transforms under local instability. The ionosphere appears to lose its grip on magnetospheric convection, although this is not certain. The plasmasphere is stripped away, most likely to feed (by global circulation) an intensifying ring current. The outer magnetosphere begins a series of slow, macroscale convulsions. Huge parallel potentials possibly develop in the magnetosphere's outer regions, reacting against the ionosphere's domination. Compared to the solar wind-dominated magnetosphere, the ionosphere-dominated magnetosphere is comparatively unknown and, so, provides opportunities for significantly advancing our understanding of the coupled solar wind-magnetosphere-ionosphere system.
SA11A-03 09:10h
Solar Wind Excitation of Magnetospheric ULF Waves
We use global simulations of the magnetosphere-ionosphere system to investigate how the solar wind and the interplanetary magnetic field couple ULF wave energy into the magnetosphere, how the energy is converted and travels into the ionosphere, and how these processes depend on parameters like the wave frequency and the dipole tilt. We find that (i) SW density fluctutions couple more efficiently to the magnetosphere than IMF fluctuations, (ii) fluctuations are more effectively coupled to the magnetosphere during northward IMF, (iii) fluctuations are are more effectively coupled to the magnetosphere during solstice compared to equinox, (iv) the primary entry channels for the wave energy are the cusps, but there can also be other hot spots in the ionosphere that receive disproportionate amounts of wave power, and (v) there is a distinct difference between the small amplitude regime which causes a linear response, and the large amplitude regime which leads to non-linear phenomena such as line broadening and harmonics.
SA11A-04 09:25h
The Cusps from Magnetosheath to Ionosphere
The magnetospheric cusps are persistent, yet dynamic features of the magnetosphere, and an important conduit between solar wind and ionospheric plasma populations. Mid- and high-altitude data from Cluster, along with low-altitude DMSP data, ACE solar wind data, and ground-based SuperDARN convection data are combined in order to synthesize an overall picture of the particle transport through the cusps. Solar wind parameters affect the nature and position of plasma entry at the magnetopause, as well as the position and characteristics of the cusp region. High altitude cusp and magnetosheath data from Cluster are utilized during dayside apogee, while mid-altitude cusp data are sampled during periods of dayside perigee. The multiple Cluster satellites enable temporal and spatial features to be distinguished, allowing direct comparisons with the more instantaneous low-altitude crossings of the DMSP spacecraft. Over 100 Cluster/DMSP magnetic conjunctions in the cusps have been identified between 2001 and 2004, from which two events representing the two Cluster altitude regimes have been selected. Global convection patterns derived from SuperDARN data further place events into an overall context. Together, these various data sets describe a pathway from the Sun to the Earth that constitutes an important source of mass, momentum, and energy transport into the Earth's magnetosphere.
SA11A-05 09:40h
Atmospheric Effects of Coronal Holes and Powerful High-Speed Solar Wind Streams in 2003 Observed by the TIMED Spacecraft
Recurrent and powerful high speed streams were responsible for driving a large portion of the magnetic activity during the year 2003. High speed streams in this year were among the most geoffective of the entire solar cycle due both to their long-durations (10's of days) and high velocities. In addition, the polar coronal holes, that provided the source of the high speed streams, also contributed to a significant variation in solar EUV radiation by covering a large fraction of the solar disc each rotation. The TIMED spacecraft with ground-based collaborators made comprehensive measurements of the atmospheric response to these strong, long-duration energy inputs. Initial analysis indicates an interesting coupling between variations in the EUV radiation and solar wind inputs in producing the atmospheric response. The decrease in solar EUV (due to the presence of the coronal hole on the solar disc) begins to precondition the atmosphere several days before the fast coronal hole wind hits the Earth, causing the atmosphere to cool and increasing the O/N2 ratio. Long intervals of recurrent substorm activity triggered by the high speed streams deposit energy in this preconditioned atmosphere. Models indicate that the effects of magnetic activity penetrate deeper in altitude and lower in latitude in such a cooler atmosphere. In addition, enhancements in NO and other changes in atmospheric chemistry driven by the recurrent long-duration substorm activity may not recover before the next high speed stream hits, making for weeks long perturbations. There are also indications that mesospheric tides may be modulated in some way by the high speed stream inputs.