Alysha Ann Reinard

Fast ejecta during the ascending phase of solar cycle 23: ACE observations, 1998–1999

We discuss fast ejecta observed at 1 AU during a period of increasing solar activity from February 5, 1998, to November 29, 1999. “Fast ejecta” are transient, noncorotating flows that move past the Earth during a day or more, with a maximum speed >600 km s−1. We identify two classes of fast ejecta at 1 AU: (1) magnetic clouds, whose local magnetic structure is that of a flux rope; and (2) “complex ejecta,” which are not flux ropes and have disordered magnetic fields. Nearly equal numbers of magnetic clouds and complex ejecta were found: four and five, respectively. The complex ejecta had weaker magnetic fields and higher proton temperatures than the magnetic clouds on average. The average β for the complex ejecta (0.25 ± 0.09) was larger than that for the magnetic clouds (0.06 ± 0.04). The complex ejecta and magnetic clouds had comparable speeds on average, namely, 558 ± 80 and 500 ± 63 km s−1, respectively. Using the duration of the stream and that of the counterstreaming electrons to measure the ejecta, the average time for the complex ejecta to move past ACE was 3 days, which is more than twice that for the magnetic clouds. All of the magnetic clouds contain some material with a high a/proton density ratio (>8%) and a density ratio of O7+/O6+ > 1. However, three of the five complex ejecta did not contain material with O7+/O6+ > 1, although four of the complex ejecta contained material with O7+/O6+ > 1. All of the magnetic clouds caused geomagnetic storms. Three complex ejecta produced no geomagnetic storms. The other two complex ejecta produced geomagnetic storms indirectly: one by driving a shock into the rear of a magnetic cloud and the other by amplifying southward fields in its leading edge and interaction region. Most of the magnetic clouds were associated with a single solar source, but nearly all of the complex ejecta could have had multiple sources. We find evidence in the solar observations that some of the complex ejecta could have been produced by the interaction of two or more coronal mass ejections (CMEs). At least three CMEs might have interacted to produce a large complex ejection that arrived at 1 AU on May 4, 1998. This complex ejection was overtaking and interacting with a magnetic cloud. We discuss several hypotheses concerning the structures and origins of complex ejecta, including the likely possibility that some complex ejecta are formed by a series of interacting CMEs of various sizes.

Coronal Mass Ejection-Associated Coronal Dimmings

We report on a statistical analysis of 96 CME-associated EUV coronal dimmings between 1998 and 2000. We investigate the size and location of the events and characterize how these events evolve with time. The durations typically range from 3 to 12 hr. The dimmings appear most frequently within the belt of active regions (20°-50° latitude). Dimming events are generally symmetric in latitude and longitude with some tendency to be broader in latitude. The temporal profiles of most events are characterized by a sharp rise and a gradual recovery. Although the majority of cases are well fit by a single recovery slope, a large minority of events have a two-part decay with an initial decaying slope that is similar in magnitude to the rising slope and a secondary, flatter, decay lasting several hours.

EVIDENCE THAT TEMPORAL CHANGES IN SOLAR SUBSURFACE HELICITY PRECEDE ACTIVE REGION FLARING

We report on the analysis of subsurface vorticity/helicity measurements for flare producing and quiet active regions. We have developed a parameter to investigate whether large, decreasing kinetic helicity density commonly occurs prior to active region flaring. This new parameter is effective at separating flaring and non-flaring active regions and even separates among C-, M-, and X-class flare producing regions. In addition, this parameter provides advance notice of flare occurrence, as it increases 2-3 days before the flare occurs. These results are striking on an average basis, though on an individual basis there is still considerable overlap between flare associated and non-flare associated values. We propose the following qualitative scenario for flare production: subsurface rotational kinetic energy twists the magnetic field lines into an unstable configuration, resulting in explosive reconnection and a flare.

THE RELATIONSHIP BETWEEN CORONAL DIMMING AND CORONAL MASS EJECTION PROPERTIES

Coronal dimmings are closely related to the footpoints of coronal mass ejections (CMEs) and, as such, offer information about CME origins and evolution. In this paper, we investigate the relationship between CME and dimming properties. In particular, we compare CME quantities for events with and without associated dimmings. We find that dimming-associated CMEs, on average, have much higher speeds than non-dimming-associated events. In fact, CMEs without an associated dimming do not appear to travel faster than 800 km s–1, i.e., the fast solar wind speed. Dimming-associated events are also more likely to be associated with flares, and those flares tend to have the highest magnitudes. We propose that each of these phenomena is affected by the energy available in the source region. Highly energetic source regions produce fast CMEs that are accompanied by larger flares and visible dimmings, while less energetic source regions produce slow CMEs that are accompanied by smaller flares and may or may not have dimmings. The production of dimmings in the latter case may depend on a number of factors including initiation height of the CME, source region magnetic configuration, and observational effects. These results have important implications for understanding and predicting CME initiations.

Analysis of Interplanetary Coronal Mass Ejection Parameters as a Function of Energetics, Source Location, and Magnetic Structure

We describe a study of how ICME parameters vary as function of source location, associated flare magnitude, and magnetic structure. The strongest compositional enhancements are found to occur in events originating in central longitudes of the Sun, those with large associated flares, and those that are identified as magnetic clouds. In situ velocity is highest for events associated with large flares. Density has a strong negative correlation with associated flare size, but no strong trend with source longitude or magnetic cloud structure. Temperature is lower than expected for events originating in central longitudes, events associated with large flares, and for magnetic clouds. Total magnetic field is highest for events originating in central longitudes and for magnetic clouds. Combining these results, we suggest that ICMEs may have a basic structure consisting of a core (or cores) of magnetic cloud plasma and compositional signatures that are modulated by CME energetics, surrounded by an envelope with weaker signatures. If this core/envelope scenario is proven to be valid, that suggests that a larger percentage of energetic ICMEs may contain enhanced composition that is not detected by the current single track observations.

IONIC COMPOSITION STRUCTURE OF CORONAL MASS EJECTIONS IN AXISYMMETRIC MAGNETOHYDRODYNAMIC MODELS

We present the ionic charge state composition structure derived from axisymmetric MHD simulations of coronal mass ejections (CMEs), initiated via the flux-cancellation and magnetic breakout mechanisms. The flux-cancellation CME simulation is run on the Magnetohydrodynamics-on-A-Sphere code developed at Predictive Sciences, Inc., and the magnetic breakout CME simulation is run on ARC7 developed at NASA GSFC. Both MHD codes include field-aligned thermal conduction, radiative losses, and coronal heating terms which make the energy equations sufficient to calculate reasonable temperatures associated with the steady-state solar wind and model the eruptive flare heating during CME formation and eruption. We systematically track a grid of Lagrangian plasma parcels through the simulation data and calculate the coronal density and temperature history of the plasma in and around the CME magnetic flux ropes. The simulation data are then used to integrate the continuity equations for the ionic charge states of several heavy ion species under the assumption that they act as passive tracers in the MHD flow. We construct two-dimensional spatial distributions of commonly measured ionic charge state ratios in carbon, oxygen, silicon, and iron that are typically elevated in interplanetary coronal mass ejection (ICME) plasma. We find that the slower CME eruption has relatively enhanced ionic charge states and the faster CME eruption shows basically no enhancement in charge states—which is the opposite trend to what is seen in the in situ ICME observations. The primary cause of the difference in the ionic charge states in the two simulations is not due to the different CME initiation mechanisms per se. Rather, the difference lies in their respective implementation of the coronal heating which governs the steady-state solar wind, density and temperature profiles, the duration of the connectivity of the CME to the eruptive flare current sheet, and the contribution of the flare-heated plasma associated with the reconnection jet outflow into the ejecta. Despite the limitations inherent in the first attempt at this novel procedure, the simulation results provide strong evidence in support of the conclusion that enhanced heavy ion charge states within CMEs are a direct consequence of flare heating in the low corona. We also discuss future improvements through combining numerical CME modeling with quantitative ionic charge state calculations.

White-light Observations of Solar Wind Transients and Comparison with Auxiliary Data Sets

This paper presents results utilizing a new data processing pipeline for STEREO/SECCHI. The pipeline is used to identify and track 24 large- and small-scale solar wind transients from the Sun out to 1 AU. This comparison was performed during a few weeks around the minimum at the end of Solar Cycle 23 and the start of Cycle 24 (2008 December to 2009 January). We use coronagraph data to identify features near the Sun, track them through HI-2A, and identify their signatures with in situ data at the Earth and STEREO-B. We provide measurements and preliminary analysis of the in situ signatures of these features near 1 AU. Along with the demonstration of the utility of heliospheric imagers for tracking even small-scale structures, we identify and discuss an important limitation in using geometric triangulation for determining three-dimensional properties.

STUDY OF THE RECURRING DIMMING REGION DETECTED AT AR 11305 USING THE CORONAL DIMMING TRACKER (CoDiT)

We present a new approach to coronal dimming detection using the COronal DImming Tracker tool (CODIT), which was found to be successful in locating and tracking multiple dimming regions. This tool, an extension of a previously developed coronal hole tracking software, allows us to study the properties and the spatial evolution of dimming regions at high temporal and spatial cadence from the time of their appearance to their disappearance. We use Solar Dynamics Observatory/Atmospheric Imaging Assembly 193 A wavelength observations and Helioseismic and Magnetic Imager magnetograms to study dimmings. As a demonstration of the detection technique we analyzed six recurrences of a dimming observed near AR 11305 between 2011 September 29 and October 2. The dimming repeatedly appeared and formed in a similar way, first expanding then shrinking and occasionally stabilizing in the same location until the next eruption. The dimming areas were studied in conjunction with the corresponding flare magnitudes and coronal mass ejection (CME) masses. These properties were found to follow a similar trend during the observation period, which is consistent with the idea that the magnitude of the eruption and the CME mass affect the relative sizes of the consecutive dimmings. We also present a hypothesis to explain the evolution of the recurrent single dimming through interchange reconnection. This process would accommodate the relocation of quasi-open magnetic field lines and hence allow the CME flux rope footpoint (the dimming) to expand into quiet-Sun regions. By relating the properties of dimmings, flares, and CMEs we improve our understanding of the magnetic field reconfiguration caused by reconnection.

COMPOSITION STRUCTURE OF INTERPLANETARY CORONAL MASS EJECTIONS FROM MULTISPACECRAFT OBSERVATIONS, MODELING, AND COMPARISON WITH NUMERICAL SIMULATIONS

We present an analysis of the ionic composition of iron for two interplanetary coronal mass ejections (ICMEs) observed on 2007 May 21-23 by the ACE and STEREO spacecraft in the context of the magnetic structure of the ejecta flux rope, sheath region, and surrounding solar wind flow. This analysis is made possible due to recent advances in multispacecraft data interpolation, reconstruction, and visualization as well as results from recent modeling of ionic charge states in MHD simulations of magnetic breakout and flux cancellation coronal mass ejection (CME) initiation. We use these advances to interpret specific features of the ICME plasma composition resulting from the magnetic topology and evolution of the CME. We find that, in both the data and our MHD simulations, the flux ropes centers are relatively cool, while charge state enhancements surround and trail the flux ropes. The magnetic orientations of the ICMEs are suggestive of magnetic breakout-like reconnection during the eruption process, which could explain the spatial location of the observed iron enhancements just outside the traditional flux rope magnetic signatures and between the two ICMEs. Detailed comparisons between the simulations and data were more complicated, but a sharp increase in high iron charge states in the ACE and STEREO-A data during the second flux rope corresponds well to similar features in the flux cancellation results. We discuss the prospects of this integrated in situ data analysis and modeling approach to advancing our understanding of the unified CME-to-ICME evolution.

Comparison between average charge states and abundances of ions in CMEs and the slow solar wind

We present results from a comparison of CME and slow solar wind ejecta detected at the ACE spacecraft in 1998 and 1999. CME events were identified based on the observation of counterstream ing halo electrons from SWEPAM data. We discuss the compositional signatures in the framework of a recent model of the coronal magnetic field by Fisk and Schwadron [1]. We conclude that slow solar wind and CMEs have a common source in the corona, presumably coronal loops. The largest amount of fractionation is found in helium and in charge state composition. The former is related to collisional effects in the corona and the latter is attributed to the anomalous heating and propagation properties of some CMEs.