Submitted Abstracts

There are 131 abstracts


Flare-associated Fast-mode Coronal Wave Trains Detected by SDO/AIA: Recent Observational Advances

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Presentation Type: No Preference

Session: Session 2: Motions Near and Above the Solar Surface

Abstract:

Quasi-periodic Fast Propagating wave trains (QFPs) are new observational phenomena discovered by SDO/AIA in extreme ultraviolet (EUV). They were interpreted as fast-mode magnetosonic waves using MHD modeling, and also found to be closely related to quasi-periodic pulsations in solar flare emission ranging from radio to X-ray wavelengths. The significance of QFPs lies in their diagnostic potential (and possibly in flare energy transport), because they can provide critical clues to flare energy release and serve as new tools for coronal seismology. In this presentation, we report recent advances in observing QFPs. In particular, using differential emission measure (DEM) inversion, we found clear evidence of heating and cooling cycles that are consistent with alternating compression and rarefaction expected for magnetosonic wave pulses. We also found that different local magnetic and plasma environments can lead to two distinct types of QFPs located in different spatial domains with respect to their accompanying coronal mass ejections (CMEs). More interestingly, from a statistical survey of over 100 QFP events, we found a preferential association with eruptive flares rather than confined flares. We will discuss the implications of these results and the potential roles of QFPs in coronal heating, energy transport, and solar eruptions.




Evolution and Distribution of Electric Currents in Solar Active Regions

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Presentation Type: Poster

Session: Session 5: Studies of Solar Eruptive Events (SEEs)

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It is now well established that solar eruptions are powered by the free energy stored in electric currents in the corona, but it remains an open question to which degree those currents are neutralized (i.e., shielded by return currents). While the degree of current neutralization appears to be closely related to the capability of active regions to produce eruptions, this relationship has not yet been investigated. In this work, we use HMI vector magnetic field data to study evolution and distribution of electric currents in several selected active regions, and further explore difference in quiet and eruptive active regions. We will also place a discussion on whether current-neutralization affects onset of CMEs.




Understanding the Physical Nature of Coronal "EIT Waves"

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Presentation Type: Poster

Session: Session 5: Studies of Solar Eruptive Events (SEEs)

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For almost 20 years the physical nature of globally-propagating waves in the solar corona (commonly called "EIT waves") has been controversial and subject to debate. Additional theories have been proposed throughout the years to explain observations that did not fit with the originally proposed fast-mode wave interpretation. However, the incompatibility of observations made using the Extreme-ultraviolet Imaging Telescope (EIT) on the Solar and Heliospheric Observatory with the fast-mode wave interpretation have been challenged by differing viewpoints from the Solar Terrestrial Relations Observatory spacecraft and higher spatial/temporal resolution data from the Solar Dynamics Observatory. In this paper, we reexamine the theories proposed to explain "EIT waves" to identify measurable properties and behaviours that can be compared to current and future observations. Most of us conclude that "EIT waves" are best described as fast-mode large-amplitude waves/shocks, which are initially driven by the impulsive expansion of an erupting coronal mass ejection in the low corona.




Measuring the magnetic field of a trans-equatorial loop system using coronal seismology

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Presentation Type: Oral

Session: Session 2: Motions Near and Above the Solar Surface

Abstract:

First observed by SOHO/EIT, "EIT waves" are strongly associated with the initial evolution of coronal mass ejections (CMEs) and after almost 20 years of investigation a consensus is being reached which interprets them as freely-propagating waves produced by the rapid expansion of a CME in the low corona. An "EIT wave" was observed on 6 July 2012 to erupt from active region AR11514 into a particularly structured corona that included multiple adjacent active regions as well as an adjacent trans-equatorial loop system anchored at the boundary of a nearby coronal hole. The eruption was well observed by SDO/AIA and CoMP, allowing the effects of the "EIT wave" on the trans-equatorial loop system to be studied in detail. In particular, it was possible to characterise the oscillation of the loop system using Doppler velocity measurements from CoMP. These Doppler measurements were used to estimate the magnetic field strength of the trans-equatorial loop system via coronal seismology. It was then possible to compare these inferred magnetic field values with both extrapolated magnetic field values from a Potential Field Source Surface extrapolation as well as the direct measurements of magnetic field provided by CoMP. These results show that the magnetic field strength of loop systems in the solar corona may be estimated using loop seismology.




Coronal Holes and Magnetic Flux Ropes Interweaving Solar Cycles

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Presentation Type: Oral or ePoster

Session: Session 3: Solar Magnetic Variability and the Solar Cycle

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Coronal holes, dark patches observed in solar observations in extreme ultraviolet and x-ray wavelengths, provide an excellent proxy for regions of open magnetic field rooted near the photosphere. Through a multi-instrument approach, including SDO data, we are able to stitch together high resolution maps of coronal hole boundaries spanning the past two solar activity cycles. These observational results are used in conjunction with models of open magnetic field to probe physical solar parameters. Magnetic flux ropes are commonly defined as bundles of solar magnetic field lines, twisting around a common axis. Photospheric surface flows and magnetic reconnection work in conjunction to form these ropes, storing magnetic stresses until eruption. With an automated methodology to identify flux ropes within observationally driven magnetofrictional simulations, we can study their properties in detail. Of particular interest is a solar-cycle length statistical description of eruption rates, spatial distribution, magnetic orientation, flux, and helicity. Coronal hole observations can provide useful data about the distribution of the fast solar wind, with magnetic flux ropes yielding clues as to ejected magnetic field and the resulting space weather geo-effectiveness. With both of these cycle-spanning datasets, we can begin to form a more detailed picture of the evolution and consequences of both sets of solar magnetic features.




Successive CMEs, Particle Acceleration and Geo-Effective Events

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Presentation Type: Oral

Session: Session 7: Space Weather at the Earth and other Planets

Abstract:

Series of coronal mass ejections (CMEs) may be associated with sympathetic, homologous or unrelated eruptions. Previous works have shown that the presence of a previous CME before a fast, wide and western limb CME increases the likelihood of having a large solar energetic particle events. In addition, successive CMEs can now be tracked through coronagraphs and heliospheric imagers and their interaction studied. Such interacting CMEs often result in strong geo-effects. Here, we present some coronal and heliospheric observations of successive CMEs and discuss which kind of eruptions results in more geo-effective CMEs.




Large-Amplitude Oscillations in Prominences

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Presentation Type: Oral

Session: Session 6: Atmospheric Dynamics and Sources of the Solar Wind

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Large-amplitude oscillations in prominences are among the most spectacular phenomena of the solar atmosphere. Such an oscillations involve motions with velocities above 20 km/s, and large portions of the filament that move in phase. These are triggered by energetic disturbances as flares and jets. The AIA/SDO instrument offers an unprecedented view of the processes that trigger the oscillations and the subsequent dynamics. These oscillations are an excellent tool to probe the not directly measurable filament morphology. In addition, the damping of these motions can be related with the process of evaporation of chromospheric plasma associated to coronal heating. In these talk I will review recent observational and theoretical progress on large-amplitude seismology on prominences.




The New SDO/EVE Coronal Dimming Catalog

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Presentation Type: Poster

Session: Session 5: Studies of Solar Eruptive Events (SEEs)

Abstract:

Coronal dimmings are hours-long voids in the solar corona that can be indicative of plasma density depletion from CMEs. Much prior work has established the theoretical case for this link – tying the emission measure to the mass of the departing CME. These studies have always relied primarily on spectral images of the corona (e.g., SDO/AIA). Our recent work has demonstrated that coronal dimming is observable with irradiance data using SDO/EVE, which can provide higher temperature resolution than relatively broadband spectral imagers. We extend our prior studies which focused on a handful of events to the entire 4 history of SDO/EVE/MEGS-A data, which includes hundreds to thousands of events. We characterize the dimming light curves in terms of dimming depth and slope and compare this statistically sized sample to CME masses and speeds determined with SOHO/LASCO coronagraph data in the CDAW catalog. We will present preliminary statistics on this new extensive dimming catalog and its comparison to the CDAW CME catalog.




Inferring Magnetic Fields and Electron Densities from Coronal Seismology

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Presentation Type: Oral

Session: Session 2: Motions Near and Above the Solar Surface

Abstract:

The solar corona oscillates at many different spatial sizes and temporal size scales. However, much remains unknown about many of these oscillations: they are intermittent for unknown reasons; appear on some coronal features and not on others; and may, or may not, be magnetohydrodynamic (MHD) wave modes. Using a series of automated oscillation detection routines, we extract space-time-density maps from a quagmire of oscillating loops. From these data products, we extract coronal magnetic fields and densities in order to to differentiate between potential excitation mechanisms and between potential damping mechanisms. The spread of periods, amplitudes, and damping times, allow us to map the spatial distribution of these parameters. Initial periods of P~300-500s, result in inferred coronal magnetic field of B~20G-50G. The decrease in the oscillation period of the loop position corresponds to a drop in number density inside each coronal loop, as predicted by MHD. As the the period drops below a threshold of P~300s, our MHD model cannot explain the sudden observed decrease in both period and density and so a secondary dissipation mechanism must occur at this point in time and space.




Quasi-Periodic Pulsations in Hydrogen Emission During Solar Flares

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Presentation Type: Oral

Session: Session 5: Studies of Solar Eruptive Events (SEEs)

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There have been increasing reports of quasi-periodic pulsations (QPPs) during solar flares in the literature recently. These recurrent variations in intensity have been detected over a wide range of wavelengths, most prevalently in X-rays and radio waves. The nature of these pulsations is still in dispute but they are widely agreed to be evidence for either a form of periodic driver of nonthermal electrons (such as magnetic reconnection) or magnetohydrodynamic oscillations. Flare observations of QPPs at EUV wavelengths have been scarce in recent years, and those in the literature are often derived from broadband measurements leaving some ambiguity as to whether the periodic behavior was occurring in the line(s) or the continuum. Here we present evidence for synchronous QPPs in the Lyman continuum (from SDO/EVE) and the Lyman-alpha line (from GOES/EUVS) during the well-studied 15 February 2011 X-class flare. The data were detrended using a Savitzky-Golay filter to reveal a periodicity of 2-3 minutes during the impulsive phase. Similar values were found in the SDO/AIA 1600A and 1700A channels despite being saturated, although no such evidence was found in the higher order Lyman lines (Lyman-beta, Lyman-gamma, Lyman-delta, etc). The formation temperature of the Lyman series of hydrogen suggests this emission is coming from the chromospheric footpoints, implying a quasi-periodic heating response due to a bursty energy release mechanism in the corona.