SA41B-01 INVITED 08:00h
Causes and Effects of Superstorms Associated With the Magnetic Field in the Corona and the Heliosphere
The emergence of three strong active regions late last fall altered the configuration of the solar corona and launched major disturbances that were felt throughout the heliosphere. The effects of the superstorms were dramatic and far reaching, but did they permanently disrupt the morphology of the heliospheric magnetic field? The role such major active regions play in the solar-cycle evolution of coronal structure and the location of the heliospheric current sheet will be investigated.
SA41B-02 08:15h
Response of the Electron Density in the Solar Corona to Extreme Solar Events
We present the results of a study aimed at investigating the response of the three-dimensional solar corona to the extreme solar events of October and November 2003. Three-dimensional images of the electron density ($N_e$) in the solar corona between 1.1 and 2.7 $R_{\odot}$ are formed from polarized brightness (pB) coronagraph measurements by the process of solar rotational tomography. Since each pixel of a coronagraph image represents a line of sight (LOS) integration of $N_e$, an inversion of the LOS measurements is required to reconstruct $N_e$. Solar rotational tomography exploits the Sun's rotation to combine a set of coronagraph images each measured at a different view angle to perform the required inversion and form the three-dimensional image of $N_e$. In this work, we focus on ground-based measurements obtained from the Mark-IV K-Coronameter at the Mauna Loa Solar Observatory (MLSO). The response of the corona to the extreme solar events is studied by comparing the $N_e$ reconstructions determined at periods before, during, and after the onset of the superstorms.
SA41B-03 INVITED 08:30h
High-Energy Solar Particle Events: Constraints on Diffusive Shock Acceleration Theory
The physics of the acceleration of solar-energetic particles (SEPs) to energies as high as several GeV are discussed in the context of diffusive shock acceleration. Superstorms that produce high-energy solar cosmic rays provide important constraints on the possible sources of these particles and on the acceleration time scale. The time scale for acceleration depends strongly on the topology of the magnetic field and plasma flow speed. On the one hand, theoretical predictions for this time scale can range over several orders of magnitude. On the other hand, it can be shown that, very generally, low-energy particles can be accelerated to several GeV in time scales shorter than a few minutes by nearly perpendicular shocks. This will be discussed in detail in this talk. The results from new simulations of test-particles encountering shocks moving through a medium containing large-scale (much larger than the particle gyroradii) magnetic field turbulence will be presented. Also, there have been new interpretations of observations of the charge state of SEPs and its dependence on energy that point to the importance of acceleration by nearly perpendicular shocks. These will also be discussed.
SA41B-04 08:45h
Space Weather Modeling Framework: An Overview and Application to the October 29, 2003 Storm
The University of Michigan's Space Weather Modeling Framework (SMWF) aims at providing framework for physics based space weather simulations, as well as for various space physics applications. The SWMF combines numerical models of the Solar Corona, Inner Heliosphere, Solar Energetic Particles, Global Magnetosphere, Inner Magnetosphere, Radiation Belts, Ionosphere and Upper Atmosphere into a parallel, high performance model. We present SWMF results from the October 29, 2003 storm, in which the global magnetosphere (BATSRUS), inner magnetosphere (RCM), ionospheric electrodynamics, and upper atmospheric models (GITM) are run together driven by data from the upstream ACE satellite. We will present comparisons between the simulation results and data from different magnetospheric satellites. We will further present model comparisons between the global magnetosphere run with and without the inner magnetosphere coupling.
SA41B-05 09:00h
Formation of the new radiation belt during October-November storms 2003
Stochastic acceleration and loss of MeV electrons during October-November storms 2003 is required to explain the rapid loss and the formation of a new radiation belt in the "slot " region, near L=3. The compression of plasmasphere during the main phase of the storm down to L=2.2 creates preferential conditions for local acceleration. Filling of the slot region of the radiation belts is modeled with a 2D pitch-angle, energy diffusion code. We find that the pitch angle distributions rapidly attain equilibrium shapes. Energy dependent lifetimes are on the scale of a day for MeV electrons and on the scale of a few hours for 10-100 keV electron population, which provides a source for chorus emissions. We show that the energy diffusion driven by whistler mode waves is capable of accelerating electrons up to energies of 3 MeV on the time scales of few days which is consistent with HEO and SAMPAX observations.
SA41B-06 09:15h
Extreme Solar Wind Conditions and Extreme Response of the Earth's Magnetosphere
To a very large extent, the solar wind controls magnetospheric activity, so that measurements of the solar wind upstream of the Earth can be used to predict the geomagnetic activity. We have developed a model to predict the Dst index based on available solar wind and ground magnetic field measurement. We will show that the model works under extreme solar wind conditions, such as the intervals of October-November 2003 and the Carrington Event (September 1859), a superstorm associated with extreme solar wind conditions, which, however, were not measured, and discuss the implications. For Carrington Event the model predicts a Dst of about -1800 nT based on the inferred solar wind speed of about 1780 and an interplanetary magnetic field z-component of about -70 nT. Thus within the context of the model the extreme response of the magnetosphere previously inferred by Tsurutani et al. [2003] is the normal response of the magnetosphere to the extreme solar wind conditions inferred by Siscoe [2004] for this event. In addition, we demonstrate by examples that the model prediction can be used to infer or confirm a solar wind parameter, such as solar wind speed, in cases when it was not measured or not measured well. Tsurutani et al. [2004]: Tsurutani, B. T., W. D. Gonzalez, G. S. Lakhina, and S. Alex, The Super Magnetic Storm of September 1-2, 1859, J. of Geophysical Physics, 108 (A7), 1268, DOI 10.1029/2002JA009504, 2003. Siscoe [2004]: Siscoe, G., 1859 Storm, IMF, IEF, TPP, & Dst, presented at Spring AGU, Montreal, May 17-21, 2004.
http://lasp.colorado.edu/~lix/
SA41B-07 INVITED 09:30h
Magnetospheric and Ionospheric Electric Fields During Superstorms
In the strongest magnetic storms, magnetospheric and ionospheric electric fields develop in ways that clearly differ from linear extrapolations from normal behavior. We will review observations and possible theoretical explanations of several specific superstorm-electric-field phenomena that have received considerable research attention recently. The observed polar-cap potential drop saturates at 200-250 kV, rather than increasing linearly with the solar-wind electric field, and the observed potential drops are in remarkably good agreement with a simple analytic theory (Hill-Siscoe model). Apparently the intense magnetosphere-ionosphere currents deform the magnetic field and flow near the dayside magnetopause, reducing the reconnection rate. Mass-loading and field-aligned potential drops may also play a role. Details are being investigated using global MHD simulations. Superstorms give rise to a very different phenomenon near the equatorward edge of the nightside auroral zone, where strong electric-field regions called SubAuroral Polarization Streams (SAPS) are observed. The corresponding fast magnetospheric flows affect plasmaspheric erosion and ring-current injection. Strong magnetospherically generated electric fields penetrate to the equatorial ionosphere, causing massive uplift of the F-layer on the day side and near dusk. SAPS and equatorial penetration events affect the structure of the mid- and low-latitude ionosphere and apparently have dramatic effects on Total Electron Content observed by GPS.