Tracking Streamer Blobs Into the Heliosphere

In this paper, we use coronal and heliospheric images from the STEREO spacecraft to track streamer blobs into the heliosphere and to observe them being swept up and compressed by the fast wind from low-latitude coronal holes. From an analysis of their elongation/time tracks, we discover a 'locus of enhanced visibility' where neighboring blobs pass each other along the line of sight and their corotating spiral is seen edge on. The detailed shape of this locus accounts for a variety of east-west asymmetries and allows us to recognize the spiral of blobs by its signatures in the STEREO images: In the eastern view from STEREO-A, the leading edge of the spiral is visible as a moving wavefront where foreground ejections overtake background ejections against the sky and then fade. In the western view from STEREO-B, the leading edge is only visible close to the Sun-spacecraft line where the radial path of ejections nearly coincides with the line of sight. In this case, we can track large-scale waves continuously back to the lower corona and see that they originate as face-on blobs.Comment: 15 pages plus 11 figures; figure 6 shows the 'locus of enhanced visibility', which we call 'the bean'. (accepted by ApJ 4/02/2010

Observations of Detailed Structure in the Solar Wind at 1 AU with STEREO/HI-2

Heliospheric imagers offer the promise of remote sensing of large-scale structures present in the solar wind. The STEREO/HI-2 imagers, in particular, offer high resolution, very low noise observations of the inner heliosphere but have not yet been exploited to their full potential. This is in part because the signal of interest, Thomson scattered sunlight from free electrons, is ~1000 times fainter than the background visual field in the images, making background subtraction challenging. We have developed a procedure for separating the Thomson-scattered signal from the other background/foreground sources in the HI-2 data. Using only the Level 1 data from STEREO/HI-2, we are able to generate calibrated imaging data of the solar wind with sensitivity of a few times 1e-17 Bsun, compared to the background signal of a few times 1e-13 Bsun. These images reveal detailed spatial structure in CMEs and the solar wind at projected solar distances in excess of 1 AU, at the instrumental motion-blur resolution limit of 1-3 degree. CME features visible in the newly reprocessed data from December 2008 include leading-edge pileup, interior voids, filamentary structure, and rear cusps. "Quiet" solar wind features include V shaped structure centered on the heliospheric current sheet, plasmoids, and "puffs" that correspond to the density fluctuations observed in-situ. We compare many of these structures with in-situ features detected near 1 AU. The reprocessed data demonstrate that it is possible to perform detailed structural analyses of heliospheric features with visible light imagery, at distances from the Sun of at least 1 AU.Comment: Accepted by Astrophysical Journa

Solar Wind Drag and the Kinematics of Interplanetary Coronal Mass Ejections

Coronal mass ejections (CMEs) are large-scale ejections of plasma and magnetic field from the solar corona, which propagate through interplanetary space at velocities of $\sim$100--2500~km~s$^{-1}$. Although plane-of-sky coronagraph measurements have provided some insight into their kinematics near the Sun ($<$32~R$_\odot$), it is still unclear what forces govern their evolution during both their early acceleration and later propagation. Here, we use the dual perspectives of the Solar TErrestrial RElations Observatory (STEREO) spacecrafts to derive the three-dimensional kinematics of CMEs over a range of heliocentric distances ($\sim$2--250\,R$_{\odot}$). We find evidence for solar wind (SW) drag-forces acting in interplanetary space, with a fast CME decelerated and a slow CME accelerated towards typical SW velocities. We also find that the fast CME showed linear ($\delta=1$) dependence on the velocity difference between the CME and the SW, while the slow CME showed a quadratic ($\delta=2$) dependence. The differing forms of drag for the two CMEs indicate the forces and thus mechanism responsible for there acceleration may be different

The Temperature-Dependent Nature of Coronal Dimmings

The opening-up of the magnetic field during solar eruptive events is often accompanied by a dimming of the local coronal emission. From observations of filament eruptions recorded with the Extreme-Ultraviolet Imager on STEREO during 2008-2009, it is evident that these dimmings are much more pronounced in 19.5 nm than in the lower-temperature line 17.1 nm, as viewed either on the disk or above the limb. We conclude that most of the cooler coronal plasma is not ejected but remains gravitationally bound when the loops open up. This result is consistent with Doppler measurements by Imada and coworkers, who found that the upflow speeds in a transient coronal hole increased dramatically above a temperature of 1 MK; it is also consistent with the quasistatic behavior of polar plumes, as compared with the hotter interplume regions that are the main source of the fast solar wind. When the open flux reconnects and closes down again, the trapped plasma is initially heated to such high temperatures that it is no longer visible at Fe IX 17.1 nm. Correspondingly, 17.1 nm images show a dark ribbon or ``heat wave'' propagating away from the polarity inversion line and coinciding with the brightened Fe XV 28.4 nm and Fe XII 19.5 nm post-eruptive loops and their footpoint areas. Such dark ribbons provide a clear example of dimmings that are not caused by a density depletion. The propagation of the ``heat wave'' is driven by the closing-down, not the opening-up, of flux and can be observed both off-limb and on-disk.Comment: 5 figures, movies are available online on the ApJL websit

A synoptic view of solar transient evolution in the inner heliosphere using the Heliospheric Imagers on STEREO

By exploiting data from the STEREO/heliospheric imagers (HI) we extend a well-established technique developed for coronal analysis by producing time-elongation plots that reveal the nature of solar transient activity over a far more extensive region of the heliosphere than previously possible from coronagraph images. Despite the simplicity of these plots, their power in demonstrating how the plethora of ascending coronal features observed near the Sun evolve as they move antisunward is obvious. The time-elongation profile of a transient tracked by HI can, moreover, be used to establish its angle out of the plane-of-the-sky; an illustration of such analysis reveals coronal mass ejection material that can be clearly observed propagating out to distances beyond 1AU. This work confirms the value of the time-elongation format in identifying/characterising transient activity in the inner heliosphere, whilst also validating the ability of HI to continuously monitor solar ejecta out to and beyond 1A

UA37/34 Biographical Sketch of James Wigtil

Biographical sketch of James Wigtil, thirteenth president of the Association for Specialists in Group Work written by Vernon Sheeley and annotated by James Wigtil

Comprehensive Observations of a Solar Minimum CME with STEREO

We perform the first kinematic analysis of a CME observed by both imaging and in situ instruments on board STEREO, namely the SECCHI, PLASTIC, and IMPACT experiments. Launched on 2008 February 4, the CME is tracked continuously from initiation to 1 AU using the SECCHI imagers on both STEREO spacecraft, and is then detected by the PLASTIC and IMPACT particle and field detectors on board STEREO-B. The CME is also detected in situ by ACE and SOHO/CELIAS at Earth's L1 Lagrangian point. The CME hits STEREO-B, ACE, and SOHO on 2008 February 7, but misses STEREO-A entirely. This event provides a good example of just how different the same event can look when viewed from different perspectives. We also demonstrate many ways in which the comprehensive and continuous coverage of this CME by STEREO improves confidence in our assessment of its kinematic behavior, with potential ramifications for space weather forecasting. The observations provide several lines of evidence in favor of the observable part of the CME being narrow in angular extent, a determination crucial for deciding how best to convert observed CME elongation angles from Sun-center to actual Sun-center distances.Comment: 27 pages, 10 figures, AASTEX v5.2, accepted by Ap

Synergy Recognition: Do CFOs with Investment Banking Backgrounds Make More Acquisitions Than Their Peers?

Numerous academic studies point out the detrimental effects of large acquisitions on the performance of acquirers, often concluding that companies rarely recognize the revenue and cost synergies that they hope to attain with an acquisition. Concurrently, a number of finance professionals propose that investment bankers tend to maintain extreme optimism about the value of acquisitions. Thus, in study I ask the following research question: Are individuals with work experience in investment banking more likely to participate in M&A activity than their non-banking peers? Specifically, I test whether the executives (specifically CFOs) of publicly traded technology companies with investment banking work experience are more likely to make acquisitions than their peers who have never worked in transaction advisory. I predict that CFOs with backgrounds in investment banking are more likely to participate in M&A activity due to the confidence they possess in their ability to realize merger synergies. I find evidence indicating that firms with CFOs with work experience in the investment banking industry make more acquisitions than firms that have CFOs with no investment banking work experience. That is, CFOs with investment banking work experience make twice as many acquisitions as firms that have CFOs with no investment banking experience

Moral Virtue as a Requisite for Illumination in the Platonic Tradition

This paper traces the development of the idea that we must cultivate moral virtue in order to attain some degree of illumination regarding the nature of reality. I use the term “illumination” to cover a range of meanings intended by the philosophers I discuss, such as the “acquisition of wisdom” (Phaedo, 65a), the “sight” of divine beauty (Symposium, 210d–212b), or a mystical experience involving God or divine reality. Although this theme appears in many texts from the Platonic tradition, I focus on three major stages of its development. First, I show how Plato provides the basic framework of the idea that moral virtue is necessary for illumination, especially in his Phaedo and Symposium. Then, I explain how Plotinus synthesizes and substantially develops Plato’s discussions of this idea. Finally, I discuss the Cappadocian Fathers’ (Basil of Caesarea, Gregory of Nyssa, and Gregory Nazianzen) Christianization of this Platonic theme. In other words, Plotinus develops the basic framework of this argument first set forth by Plato, and the Cappadocians then adapt and modify Plotinus’ views to fit their Christian commitments