SH12A-01
Tracking the 3-D Structure of an Erupting Filament With the STEREO/SECCHI EUVI
On 2007 May 19, the STEREO/SECCHI EUVI observed an erupting filament that was associated with a CME. The stereoscopic observations in both He II and Fe IX allow a detailed study of the 3-D geometry and dynamics of the filament as it erupts. Deconvolution of the EUVI imagery with the instrument point spread function enhances image contrast and detail, and improves the accuracy of the 3-D analysis. The quantitative results of such an analysis may lead to a better understanding of the early CME process.
SH12A-02
Relation between Coronal Mass Ejection, Type II Radio Burst, and EUV Wave during the 2008 March 25 STEREO Event
STEREO and SOHO observations of the March 25, 2008 coronal mass ejection (CME) provide an excellent opportunity to study its early evolution from multiple view points. The CME was fast (980 km/s) and wide (112 degrees) from the east limb of the Sun as viewed by SOHO. The STEREO spacecraft were separated by about 50 degrees, so the CME was a disk event for the STEREO-behind spacecraft and a behind-the-limb event for STEREO-ahead. The CME was associated with a well defined EUV wave as observed by the STEREO/EUVI instrument, a metric type II burst, and a multi-component type II burst observed by the STEREO/WAVES and Wind/WAVES instruments. One of the important aspect of this CME is that it was well observed by STEREO/SECCHI inner coronagraph (COR1) when the metric type II burst was in progress, so we are able to obtain the shock height with respect t the CME. This enabled us to infer the connection the coronal shock driven by the CME (inferred from type II burst) and the EUV wave. It appears that the EUV wave steepened into a shock and produced the type II burst. The multiple components of the type II burst were not harmonically related, so we examined the circumstances of the eruption. CME was ejected in the region between two streamers, so the CME-driven shock is likely to simultaneously encounter high and low- density regions of the corona, thus producing type II bursts at widely separated frequencies. This paper summarizes these observations and explains how the CME, type II radio burst, and EUV waves all fit together.
SH12A-03
Comprehensive STEREO Observations of the 2008 February 4 CME
Thanks to the two Heliospheric Imagers that are part of STEREO's SECCHI instrument package, the two STEREO spacecraft are the first that are capable of following a CME continuously from the Sun all the way to 1 AU, where the PLASTIC and IMPACT instruments on the spacecraft can then also provide in situ information on the CME, assuming it hits one of the the two satellites. We present the first kinematic study of a CME that has been observed in such a comprehensive manner. The event begins on 2008 February 4 and is successfully tracked by STEREO-A to 1 AU where it hits STEREO-B on February 7. This is therefore a good example of STEREO's capability for one satellite (STEREO-A in this case) to observe a white-light CME front hitting the other satellite (STEREO-B in this case) at the same time as that second satellite is measuring the CME properties in situ.
SH12A-04
Observations and analysis of the April 9, 2008 CME using STEREO, Hinode TRACE and SoHO data
On April 9, 2008 a CME originating from an active region behind the limb was well-observed by STEREO, Hinode, TRACE and SoHO. Several interesting features connected to this eruption were observed. (1) The interaction of the CME with open field lines from a nearby coronal hole appeared to cause an abrupt change in the direction of the CME ejecta. (2) The prominence material was heated, as evidenced by a change from absorption to emission in the EUV wavelengths. (3) Because the active region was behind the limb, the X-Ray Telescope on Hinode was able to take long enough exposure times to observe a faint current- sheet like structure, and it was able to monitor the dynamics of the plasma surrounding this structure. This event is also being studied in the context of activity that occurred during the Whole Heliosphere Interval (WHI).
SH12A-05
Conservation of open solar magnetic flux and the floor in the heliospheric magnetic field
The near-Earth heliospheric magnetic field intensity, |B|, exhibits a strong solar cycle variation, but returns to the same "floor" value each solar minimum. The current minimum, however, has seen |B| drop below previous minima, bringing in to question the existence of a floor, or at the very least requiring a re-assessment of its value. In this study we assume heliospheric flux consists of a constant open flux component and a time-varying contribution from CMEs. In this scenario, the true floor is |B| with zero CME contribution. Using observed CME rates over the solar cycle, we estimate the "no-CME" |B| floor at ~4.2± 0.5 nT, lower than previous floor estimates and below |B| observed this solar minimum. We speculate that the drop in |B| observed this minimum may be due to a persistently lower CME rate than the previous minimum, though there are large uncertainties in the supporting observational data.
SH12A-06
Multipoint Analysis of Meso-scale Structures in the Ambient Solar Wind: STEREO-A, -B, and L1 Observations
We explore sources of apparent time-dependence of meso-scale structures (those lasting two to three days and less) in the ambient solar wind through analysis of measurements from STEREO-A, -B, and L1 spacecraft (WIND, ACE, and SOHO). In early 2008, stable corotating interaction regions and high-speed streams provided excellent boundaries and features for co-registering the large-scale, corotating solar wind observed by several heliospheric spacecraft separated in solar orbital phase near 1 AU. During this period, STEREO-B (located 23 degrees behind the Earth in heliographic longitude) first observed the large-scale corotating stream structures, followed by the WIND, ACE, and SOHO spacecraft at Earth, then finally by STEREO-A (located 22 degrees ahead of the Earth in heliographic longitude). Conspicuous similarities in the macro-scale solar wind flow dominate the comparison between spacecraft observations and permit us to time-adjust the observed flow features reasonably well by assuming a simple corotating solar wind source. While the co-registered, large-scale solar wind structure agrees well, mesoscale flow features can exhibit large measured differences at the various spacecraft. We focus on one such interesting feature which exhibits apparent time dependence. Though this few-day-long, significant flow speed event is observed by the PLASTIC experiments on both STEREO-A and STEREO-B, it is not seen at the L1 spacecraft which the STEREO spacecraft bracket in space and time. We explore potential sources of the apparent time dependence of this meso-scale feature. Latitudinal differences in the multipoint measurements is one source that could account for the apparent mesoscale flow structure variability. We also explore explicit time variation of the solar wind's source, by analyzing relevant coronal holes observed simultaneously by the STEREO spacecraft imagers. This event and analysis underscores that multipoint heliospheric observations and analysis reveals the existence of mesoscale structure in the solar wind and can be used to constrain its possible source(s).
SH12A-07
Numerical Study of Interchange Reconnection Associated with CMEs
We present preliminary results from a new project to numerically investigate the role of interchange reconnection in the long-term evolution of the heliospheric magnetic field. We use the BATS-R-US model (U. of Michigan) to follow the detailed interaction between the magnetic field of CMEs and the ambient field. In particular, we use high-resolution simulations to track the interchange reconnection processes as the CME propagates away from the Sun. In the course of the project, we plan to simulate real CME events and compare the field evolution with in-situ measurements. We also plan to simulate idealized CMEs in order to investigate how the flux-rope orientation and the distance from coronal holes affect the change in the global field. The goal of this project is to better understand the role of the heliospheric flux in the evolution of the solar magnetic field and the solar cycle.
SH12A-08
Interplanetary Coronal Mass Ejection speeds and temperatures relative to the background solar wind observed at ACE, WIND, and STEREO
When examining ACE ICMEs compared to the background solar wind conditions over the solar cycle, we found 2 key results: 1) Most ICMEs have speeds within the one standard deviation of the background wind speed, and ICME speeds generally track the variations in the background wind speed. 2) Even though the proton temperature and proton speed in the background wind are well correlated and the ICME speed generally follows the background wind speed, the ICME temperature does not follow the ICME speed. Instead the temperature of most of the ICMEs is low and has no significant trend with time. Three possibilities to explain the correlation between the ICME and background wind speed are: 1) The CME launch speeds change over the solar cycle as the solar wind speed changes; 2) The speed is closer to the background speed when ACE crosses on the edge of a CME; 3) As CMEs propagate their interaction with the background wind causes fast CMEs to slow and slow ones to speed up. These possibilities can be tested by comparing ACE, WIND, and STEREO in situ measurements, and by comparing the trend in the published speeds determined from remote observations of CMEs with the trend in the ICME speeds. Although fully understanding how the low ICME temperatures develop, and why the temperatures are uncorrelated with the background wind conditions is not straightforward, we will develop expected temperature formulas to assist in identify ICMES in the STEREO data and explore how much the temperature relative to the expected temperature varies across the ICME to determine if the anomalously low temperatures are spatially confined within the ICMEs. Our initial comparisons between ACE and STEREO ICME data indicate the ratio of the temperature to the expected temperature and the proton beta can be significantly different from one spacecraft to another across a given ICME.