SH23B-01
Synthetic Radio Maps of CMEs up to 24 Solar Radii Heliocentric Distance
We present numerical MagnetoHydroDynamic (MHD) simulations of coronal mass ejections (CMEs) and plasma simulations of radio emission from the CME-driven shocks. The simulations correspond to an idealized system, where rotational symmetry around the rotation axis of the Sun is assumed. So the CME has a flux rope structure that extends like a torus around the symmetry axis, i.e. no geometrical effects due to a connection of footpoints of the flux rope with the solar surface are considered. The CME-driven shock extends to an almost spherical shape during the temporal evolution of the CME. We find that our simulations can reproduce the dynamic spectra of coronal radio type II bursts, where the frequency drift rates correspond to the CME-driven shock speeds. We find further, that the CME-driven shock is an effective radio emitter at metric wavelengths, when the CME has reached a heliocentric distance of about two solar radii (R\odot). Towards the center of the CME, where the plasma emission frequency drops significantly due to an over expansion of the core of the CME, the emission is eclipsed for a fixed frequency radio receiver. We apply our simulation results to explain the radio images of type II bursts obtained by radio heliographs, in particular to the banana-shaped images of radio sources associated with fast CMEs. The shock at the rear part of the CME can become an effective radio emitter, where reconnection of magnetic field lines leads to enhanced gradients of magnetic fields. Yet, this emission is usually at lower frequencies than that at the shock front. We apply our kinetic and analytic model of plasma radiation further to MHD simulations of CMEs in 3D. The differences between the 3D and 2D cases are discussed.
SH23B-02
Impulsive Dynamics of Coronal Mass Ejections
Coronal mass ejections (CMEs) are a magnetic eruptions that carry 1023 Wb of magnetic flux and 1015\-- 16~g of material into interplanetary space with a kinetic energy of 1031\--32 ergs and represent the dominant source of non-recurrent geomagnetic storms. Quantifying and understanding CME kinematics is fundamental for testing theoretical models of CME propagation. We propose a heuristic Newtonian model for quantifying impulsive CME dynamics and investigate CMEs observed by Large Angle Spectrometric Coronagraph (LASCO) augmented with observations of eruptive prominences observed by the Extreme Ultraviolet Imaging telescope (EIT), Nobeyama Radioheliograph (NRoH), Big Bear Solar Observatory (BBSO), and Kanzelhöehe Solar Observatory (KSO). Work supported by NASA and ONR.
SH23B-03
Exploring the solar origin of interplanetary magnetic flux ropes
In this study, we explore the solar origin of interplanetary magnetic flux ropes observed as Magnetic Clouds (MCs) at 1~AU, namely, whether flux ropes are primarily created by magnetic reconnection in the Sun's corona at the onset of Coronal Mass Ejections, or have emerged from below the photosphere and are pre-existing before the eruption. We compared the magnetic flux in toroidal (total flux) and poloidal (total twist) components in the MC with the total reconnected flux measured from flare and magnetic field observations at the source region of the MC. We find that the poloidal MC flux and reconnection flux are scaled and correlated in a dozen events with suitable solar and interplanetary observations. The result suggests that flux ropes may be primarily created by low-corona reconnection on the Sun in these events. We also discuss interaction between flux ropes and large-scale coronal magnetic field upon eruption.
SH23B-04
Relationship between Halo Coronal Mass Ejections, EIT Flare Arcades, Coronal Neutral Line and Magnetic Clouds
Coronal mass ejections (CMEs) are the most important solar drivers of geomagnetic storms. Their interplanetary counterparts, interplanetary CMEs (ICMEs), can be detected in-situ, for example, by ACE and Wind spacecraft. An ICME usually exhibits a complex structure that very often includes a magnetic cloud (MC), which is thought to be a magnetic flux rope, capable of providing prolonged periods of southward interplanetary magnetic field at 1 AU. The magnitude of the storm depends, in general, on the orientation and intensity of the magnetic field in the ejecta. In this presentation we will discuss how the size of the geomagnetic storm can be predicted from coronagraph images. There is observational evidence that the orientation of a halo CME elongation corresponds to the orientation of the underlying flux rope, while the intensity of the magnetic field in an ejecta seems to be related to the CME speed. Here we compare orientation angles of elongated LASCO halo CMEs, EIT flare arcades (post flare loop system), the local tilt of the heliospheric current sheet and the corresponding MCs. We report that i) for about 64% of CME-ICME events, a good correspondence was found between the orientation angles of CMEs and MC; ii) 20 out of 25 CMEs (80%) were oriented along the axis of the corresponding EIT flare arcade; and iii) 19 out of 25 (76%) of CMEs are co- aligned with the heliospheric current sheet at 2.5 solar radii. In the final part of the presentation we will discuss the applications of our findings to CME modeling, space weather forecast and possible future studies. http://www.bbso.njit.edu/~vayur/
SH23B-05
Variations in the GCR Flux Associated with Heliospheric Transient Structures Near the August 20, 2006 Forbush Decrease
On August 20, 2006 a Forbush decrease observed at Polar in the Earth's magnetosphere was also seen at the INTEGRAL spacecraft outside the magnetosphere during a very active time in the solar wind. Data from Polar HIST and from INTEGRAL's Ge detector saturation rate (GEDSAT), which measures the GCR background with a threshold of ~200 MeV, show similar, short-period GCR variations in and around the Forbush decrease. The solar wind magnetic field and plasma conditions during this time reveals three interplanetary shocks present in the days leading up to and including the Forbush decrease. The first two shocks are driven by interplanetary coronal mass ejections (ICMEs) and the last one by a high-speed stream. However, the solar wind following these shocks and during the Forbush decrease is not particularly geoeffective. The Forbush decrease, which begins at ~1200 UT on August 20, 2006 is the largest intensity change during this active time, but there are many others on a variety of timescales. Looking at more than 14 consecutive hours of INTEGRAL and Polar data on August 21, 2006 shows great similarities in the time history of the measurements made aboard the two satellites coupled with differences that must be due to GCR variability on a scale size of the order or less than their separation distance. Despite the spacecraft separation of over 25 Re, many of the larger intensity fluctuations remain identical at both satellites. Autocorrelation and power spectral analyses have shown these are not ar-n processes and that these fluctuations are statistically significant. Such analyses can be done with high confidence because both detectors aboard Polar and INTEGRAL have large geometric factors that generate high count rates on the order of 1000 particles per spin, ensuring rigorous, statistically significant samples.
SH23B-06
Photospheric Flows and Flares/CMEs: A Progress Report
Coupling between magnetic fields in the solar photosphere and corona implies that flows at the photosphere --- the only atmospheric layer where the magnetic field is routinely measured --- can inject magnetic energy and helicity into the coronal field. Fluxes of magnetic energy and helicity into the corona might play an important role in flares and coronal mass ejections (CMEs). Some flow patterns --- including shear flows, converging flows, and rotational flows --- have been proposed as particularly important processes leading to flares and CMEs. How common are these flow patterns? Which flows, if any, are statistically associated with flares and CMEs? To answer these questions and others, we have estimated photospheric flows using sequences of full-disk, MDI magnetograms, with a nominal 96-minute cadence, from more than 60 active regions. Our active region sample includes both regions that produced many flares and CMEs, and regions that produced little activity. Our analysis is not yet complete, but we present a progress report here.