SH23A-01 13:40h
Propagation of the 12 May 1997 ICME in Evolving Solar Wind Structures
We simulate the 12 May 1997 interplanetary coronal mass ejection (ICME) event with a numerical 3-D magnetohydrodynamic (MHD) model, in which the background solar wind is determined from the SAIC and WSA coronal models, and the transient disturbance from the so-called cone model. We launch the same ICME-like, over-pressured plasma cloud into the background solar wind derived from various models including daily-updated coronal maps. We found that improved agreement with the observations is achieved when the maps are artificially modified to simulate the rapid displacement of one of the coronal hole boundaries after the CME eruption. We illustrate that multi-point temporal profiles of solar wind parameters and multi-perspective synthetic white-light images can be used to differentiate between various event scenarios that might be otherwise difficult to distinguish using single-point observations only.
SH23A-02 13:55h
What did we Learn About CMEs From the ISEE-3 Mission (of Relevance to the Stereo Mission)
ISEE-3 was launched in 1978 into a halo orbit around the L1 point. It was subsequently renamed ICE and sent on a journey around the Sun ahead of the earth in an orbit similar to that which one of the Stereo spacecraft will follow. ISEE-3 contained a comprehensive particles and fields instrumentation package, in many ways resembling the particles and fields packages of the Stereo mission. In this paper we discuss some results from the particle experiments which may have relevance to the upcoming Stereo mission. We will show observations of such aspects as particle time-intensity profiles, spectra, and anisotropies. We will discuss the relation with shock characteristics and also wave-particle interactions for the different type of particle events observed. We discuss the implications for the forthcoming Stereo mission.
SH23A-03 14:10h
FLAREs, CMEs and STEREO MISSION
A recent study of Cane et al. [2003] showed that in some intense SEP events, the ion time-intensity profiles exhibit two peaks, with an earlier one having a high $Fe/O$ and a later one having a low $Fe/O$ ratio. They suggested that these two-component events are due to CMEs and their accompanying flares occuring together, with the first peak being flare-related and the second peak being CME-driven shock related. We develop a model which examines particle accleration and transport when both flares and CM-driven shocks are present. Time-intensity profiles for three different scenarios: a pure shock case, a pure flare case and a shock-flare-mixed case are studied. Using reasonable estimates of the relative timing between CMEs and associated flares, we find that a large portion of the flare accelerated material is subject to absorption and re-acceleration by the CME-driven shock. Consequently, the time intensity profile for the shock-flare-mixed case shows an initial rapid increase, owing to particles accelerated at the flare site and followed by a plateau similar to that of a pure shock case. Furthermore, depending on the longitude of the spacecraft (whether it is well connected to the CME-driven shock only or the flare only or both), the same shock-flare-mixed event may exhibit different behaviors. The STEREO mission, which is scheduled to launch dual spacecraft in early 2005, will provide an excellent opportunity to study in further details of the relationship between solar flares and CMEs.
SH23A-04 14:25h
Diagnostics of Solar Wind Processes Using the Total Perpendicular Pressure
The sum of thermal and magnetic pressure, the total pressure perpendicular to the magnetic field, is a very useful diagnostic of processes in the solar wind. Most notably total pressure has been used to study pressure-balanced structures in which the sum of the thermal and magnetic pressure is constant despite the changes in the constituents of the pressure, namely the densities and temperatures of the plasma species and the magnetic field. Such structures occur when magnetic field lines are relatively straight and exert no curvature force on the plasma, when pressure differences have equilibrated through propagating compressional waves, and the plasma is at rest relative to the surrounding solar wind flow. At times these conditions do not ensue. In stream-stream interactions a pressure gradient exists that accelerates the slower flow and decelerates the more rapid flow. Surrounding an expanding magnetic flux rope, which often lies at the heart of an ICME, there should also be a pressure gradient. The nature of this pressure gradient is very different than those at fast-slow stream interfaces. We show how this one parameter helps classify various solar wind structures and enables us to learn more about the geometry of ICMEs.
SH23A-05 14:40h
Radio-quiet Fast Coronal Mass Ejections
Coronal mass ejections (CMEs) drive shocks in the interplanetary medium that produce type II radio emission. These CMEs are faster and wider on the average, than the general population of CMEs. However, when we start from fast (speed $>$ 900 km/s) and wide (angular width $>$ 60 degrees), more than half of them are not associated with radio bursts. In order to understand why these CMEs are radio quiet, we collected all the fast and wide (FW) CMEs detected by the Solar and Heliospheric Observatory (SOHO) mission's Large Angle and Spectrometric Coronagraph (LASCO) and isolated those without associated type II radio bursts. The radio bursts were identified in the dynamic spectra of the Radio and Plasma Wave (WAVES) Experiment on board the Wind spacecraft. We also checked the list against metric type II radio bursts reported in Solar Geophysical Data and isolated those without any radio emission. This exercise resulted in about 140 radio-quiet FW CMEs. We identified the source regions of these CMEs using the Solar Geophysical Data listings, cross-checked against the eruption regions in the SOHO/EIT movies. We explored a number of possibilities for the radio-quietness: (i) Source region being too far behind the limb, (ii) flare size, (iii) brightness of the CME, and (iv) the density of the ambient medium. We suggest that a combination of CME energy and the Alfven speed profile of the ambient medium is primarily responsible for the radio-quietness of these FW CMEs.
http://cdaw.gsfc.nasa.gov
SH23A-06 14:55h
Predictions for STEREO: Dynamic Spectra and Source Regions of Type II Radio Bursts
The source regions of type II radio bursts lie upstream of high Mach number shocks. Evidence exists that the shocks are rippled, resulting in many emitting regions over the global shock surface. Goals of the upcoming STEREO mission include determining the precise three dimensional structure and location of these emitting regions, as well as investigating propagation and beaming effects. Here we present theoretical predictions from a new analytic, semi-quantitative model of interplanetary type II radio bursts, which involves electron reflection and acceleration at a shock moving through the inhomogeneous solar wind, beam formation upstream of the shock via time-of-flight effects, Langmuir wave growth driven by the electron beams, and the conversion of Langmuir waves into freely propagating radiation by nonlinear wave-wave processes. Two sets of predictions are presented for observations by the two, widely separated STEREO spacecraft: (1) dynamic spectra, and (2) images of the macroscopic source region. Both show the importance of solar wind inhomogeneities and varying observer location.
SH23A-07 15:10h
Direction Finding Capabilities with the Stereo SWAVES Instrument
The WAVES instrument onboard the 3 axis stabilized STEREO spacecraft is composed of a set of 3 monopole antennas connected to a radio receiver. The receiver measures spectral and cross-spectral power densities on one, two or three antennas in the frequency range between 10 kHZ and 16 MHz. This package will therefore have direction finding (DF) capabilities, allowing to determine the direction of arrival of an incoming wave, its flux and polarization properties. A DF analytical model has been recently developed and applied to the CASSINI/RPWS data in order to perform DF on localized Jovian radio-emmission (Cecconi et al., xxx) We present an extension of this latter model for extended solar radio emmission such as type III and type II bursts, produced respectively by subrelativistic electrons travelling outward along open magnetic field lines to lower densities in the IPM and by solar wind electrons accelerated by transient shocks moving outward from the Sun to the IPM.
SH23A-08 15:25h
HERSCHEL Suborbital Program: 3-D Applications for the STEREO Mission
The HERSCHEL (HElium Resonance Scatter in the Corona and HELiosphere) Suborbital Program is an international collaborative program between a consortium of Italian Universities & Observatories led by Dr. E. Antonucci (and funded by the Italian Space Agency, ASI), the French IAS (funded in part by CNES) and the Solar Physics Branch of NRL (by NASA SEC and the Office of Naval Research). HERSCHEL will: investigate the slow and fast solar wind, determine the helium distribution and abundance in the corona, and test solar wind acceleration models; by obtaining simultaneous observations of the electron, proton and helium solar coronae. HERSCHEL will also establish proof-of-principle for the Ultra-Violet Coronagraph, which is in the ESA Solar Orbiter Mission baseline. The HERSCHEL launch date has been linked to the STEREO launch date to allow coordinated science between the two missions. One aspect of this scientific coordination is establishing the 3-D structure of the inner corona. HERSCHEL provides a third viewpoint for the inner corona covered by the A&B STEREO SECCHI COR-1. HERSCHEL is the only scheduled, space-based asset that could provide this third viewpoint for the critical inner corona viewed by STEREO COR-1 (although lower resolution, ground-based cononagraphs will make a contribution). A third viewpoint dramatically increases one's ability to establish the 3-D structure of an optically thin object (e.g. the metric in Fig. 7 of Davila 1994, ApJ 423, 871). HERSCHEL will provide at least a snapshot of that viewpoint, plus a wide range of additional information on the H and He composition of the inner corona.