Anticipating STEREO: Addressing Issues in Coronal and Heliospheric Physics I
Presiding: D Alexander, Rice University; G Fisher, Space Sciences Laboratory, University of California, Berkeley
SH51D-01 INVITED 08:30h
STEREO Views of Solar Energetic Particle Events: New Light on old Controversies
The launch of STEREO in early 2006 will provide the multipoint measurements of the solar wind and solar energetic particles (SEPs) that are complemented by stereo images of coronal processes and CMEs. As the STEREO spacecraft separate, their new points of view hold promise for resolving anumber of controversial questions about the acceleration and transport of SEP events. Examples include: (a) What is the relative contribution of shock and flare-accelerated particles? How does it happen that most large SEP events during solar cycle 23 appeared to include both shock and flare-accelerated particles in the same event? (b) Why is there typically a 5-10 minute delay between the electromagnetic signatures of SEP events and the inferred release of SEP electrons at the Sun based on their arrival times at Earth? (c) What are the seed particles for SEP events? It used to be assumed that CME-driven shocks accelerate solar wind, but composition studies suggest that several suprathermal populations are often more important. (d) How does shock acceleration vary from the nose of the shock to its flanks? Do such variations help account for the variability of SEP spectra? (e) What fraction of the CME kinetic energy goes into accelerated particles? Initial comparisons suggest that SEPs may extract as much as 10%-20% of the CME kinetic energy. This talk will discuss examples of how multipoint in situ and remote sensing observations from STEREO, along with near-Earth observations, can help resolve these and other issues. This work was supported by NASA under NAS5-00133, NAG5-12929, and NNG04GB55G.
SH51D-02 08:52h
Coronal and Heliospheric Science Opportunities with the SECCHI Heliospheric Imager
The Heliospheric Imager (HI) is part of the SECCHI suite of instruments on-board the two STEREO spacecrafts. The two HI instruments will provide stereographic image pairs of solar coronal plasma and coronal mass ejections (CME) over a wide field of view (85 degrees), with an inner field limit of approximately 13 solar radii. These observations compliment the 15 solar radii field of view of the solar corona obtained by the other SECCHI instruments to provide unbroken coverage of the solar corona and heliosphere from the Sun to the Earth. The as-built characteristics of the HI will be presented along with the current data reduction and analysis approach. The constraints that HI observations place on models of CME propagation in the interplanetary medium will be discussed.
SH51D-03 INVITED 09:07h
STEREO WAVES Capabilities for Studying Initiation and Early-time Dynamics of Solar Eruptions
In 2006, NASA will launch the twin STEREO spacecraft from Kennedy Space Center into a pair of heliocentric orbits near 1 AU such that the spacecraft will move away from Earth (ahead and behind) at about 22 degrees per year. The purposes of the STEREO Mission are to understand the causes and mechanisms of coronal mass ejection (CME) initiation and to follow the propagation of CMEs through the heliosphere. Additionally, STEREO will study the mechanisms and sites of solar energetic particle (SEP) acceleration and determine 3-D time-dependent traces of the magnetic topology, temperature, density and velocity of the solar wind between the sun and Earth. To accomplish these goals, each STEREO spacecraft will be equipped with set of optical and particles and fields instruments including the STEREO WAVES (SWAVES) instrument which will use radio waves to track the location of CME-driven shocks (via type II bursts) and the 3-D topology of open field lines along which energetic particles flow (via the ubiquitous type III bursts). Type II bursts very often commence with a series of special type III bursts (called SA or type III-L bursts) that likely coincide with CME liftoff time, thus SWAVES should be able to determine this time to within 15 sec. It is also known that the occurrence of SEP events is usually accompanied by type II radio bursts at decametric wavelengths as well as strong type III bursts at all wavelengths. SWAVES will be able to determine the initiation of these bursts to within 15 sec, and from the simultaneous measurements from the two spacecraft, should be able to triangulate their source locations. The utility of radio observations and the capabilities of SWAVES will be illustrated by showing a number of examples using the similar Wind WAVES instrument in combination with SOHO coronagraph and RHESSI high energy X-ray/gamma ray observations.
SH51D-04 09:29h
Observations of Magnetic Restructuring during the Development of Coronal Mass Ejections
Using a multiwavelength approach during the period 1996-2003, we investigate the different scenarios for the onset and development of Corona Mass Ejections (CMEs). We developed a daily patrol which includes the radio emission measured by the Nancay Radioheliograph and the spectra obtained by the Nancay DAM array, by WAVES aboard SOHO and by various spectrographs operating in the dm-m domain. We identify the multi loops systems that participate in the eruption process. Through this data analysis, we identify the coronal regions of magnetic field interaction leading to the restructuring of the corona and the development of CMEs. We first concentrate on about 30 fast CMEs (greater than 700 km/s) which include narrow mini-CMEs as well as wide CMEs. We show that their development result from successive sequences (even for the mini CMEs) that are associated with abrupt modifications in the radio emission and the onset of new emitting sources at positions covering some portion of the solar disk, very large in the case of wide CMEs. We secondly focuss on the study of complex type III-like events detected by WAVES at 1MHz. These events present a close association with wide CMEs. We trace the progression of these events from the low corona to the interplanetary medium. Most of the accelerated electrons originate from several distinct regions of interactions between shocks and coronal structures. We anticipate that, for this class of type III-like events which often last more than 20 minutes, distinct electron beams originating at diffent times during the progression of these events, will be measured by the two spacecrafts of the STEREO mission.
SH51D-05 09:44h
3D mapping of temperatures, densities and filling factors in the corona with STEREO
The solar community will soon have the unprecedented opportunity to combine both white-light and EUV/X-ray data from 3 simultaneous viewpoints. A new framework is presented that uses all available data for simultaneous determination of 3D temperatures and densities at macro-scales, and multi-thermal distributions and filling factors at micro-scales. The method is based on the combination of standard differential emission measure (DEM) techniques and solar rotational tomography (SRT), which we refer to as differential emission measure tomography (DEMT). DEMT retains the full 3D spatial resolution of SRT while simultaneously providing information about unresolved multi-thermal structures, as is customary with DEM. When combined with white-light tomography, DEMT will allow determination of filling factors, thus giving the community access to a vast amount of 3D information about the state of the corona at a broad range of spatial scales. DEMT simulations using the Atmospheric Imaging Assembly (AIA) bandpasses are presented, and implications for STEREO are discussed.