Submitted Abstracts

There are 131 abstracts


Motions Near and Above the Solar Surface captured in the SDO Era

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Presentation Type: Oral

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

Abstract:

Since its launch in 2010, the Solar Dynamics Observatory has helped make rapid progress in the detection, identification, characterization and understanding of dynamic motions near and above the solar surface, ranging from the photosphere through to the outermost extremities of the solar corona. The ability to capture a variety of solar features through optical and extreme-ultraviolet filters at high spatial and temporal resolutions has allowed for unprecedented studies of both large- and small-scale phenomena, including those present in sunspot umbrae/penumbrae, filaments, plumes and coronal loops. Here I will outline some of the landmark publications that have employed crucial SDO observations, before highlighting some of the most recent results concerning dynamic phenomena in our Sun’s atmosphere.




Dynamic Evolution of Coronal Magnetic Field via the MHD-DARE Numerical Model

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Presentation Type: Oral

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

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We present a self-consistent numerical simulation to show how a solar eruption (including a flare) is initiated in a non-potential magnetic flux emerging region using our MHD-DARE (Data-driven Active Region Evolution) model, driven directly by the measured AR vector magnetograms from SDO/HMI. Specifically, we carried out a simulation of the 3D coronal magnetic field, starting from a nearly potential, quasi-equilibrium initial state and following the dynamic evolution for a long duration (~2 days in physical time), leading to a catastrophic eruption. During the whole process, the observed sequence of SDO/HMI vector magnetograms was applied as part of the time-dependent bottom boundary conditions. We show that the field morphology resembles the sequence of the corresponding EUV images from SDO/AIA, in addition to the successful match of the timing of the flare onset. We will also show additional simulations of eruptive or non-eruptive events with or without the presence of magnetic flux ropes. We discuss the possible scenarios of the source and dynamics of solar eruptions involving magnetic flux ropes.




Data Constrained Coronal Mass Ejections in A Global Magnetohydrodynamics Model

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Presentation Type: Poster

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

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We present a first-principles-based coronal mass ejection (CME) model suitable for both scientific and operational purposes by combining a global magnetohydrodynamics (MHD) solar wind model with a flux rope-driven CME model. Realistic CME events are simulated self-consistently with high fidelity and forecasting capability by constraining initial flux rope parameters with observational data from GONG, SDO/HMI, SOHO/LASCO, and STEREO/COR. We automate this process so that minimum manual intervention is required in specifying the CME initial state. With the newly developed data-driven Eruptive Event Generator Gibson-Low (EEGGL), we present a method to derive Gibson-Low (GL) flux rope parameters through a handful of observational quantities so that the modeled CMEs can propagate with the desired CME speeds near the Sun. A test result with CMEs launched with different Carrington rotation magnetograms are shown. Our study shows a promising result for using the first-principles-based MHD global model as a forecasting tool, which is capable of predicting the CME direction of propagation, arrival time, and ICME magnetic field at 1 AU.




Pre-Eruption Oscillations in Quiescent Filament Observed in AIA 171 \AA

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Presentation Type: Oral

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

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A large quiescent filament located near the south-west limb of the Sun underwent an eruption on 14 August 2013. Shortly before the eruption two flares occur in NOAA Active Region (AR) 11817, located near the filament. The temporal and spatial proximity suggests that the flares caused the filament to erupt. However, there is no extreme ultraviolet (EUV) wave or ejection which seemed to cause this. We use 171 \AA images for over two days before the eruption from Atmospheric Imaging Assembly (AIA) on board Solar Dynamics Observatory (SDO) to investigate this event. We observe oscillations in the western portion of the quiescent filament almost 40 hours prior to eruption, but not so much in the eastern portion. For several hours prior to eruption, the western portion is seen to undergo a slow rise. Subsequently, it is this western portion which erupts, while the eastern portion does not. We also use Helioseismic and Magnetic Imager (HMI) to study changes in the active region, and find that along with a continuous emergence of magnetic flux in the region, there was also a migration of polarity producing a large shear. We make use of the hmi.sharp to determine shear in the active region. We suggest that the oscillations are a result of natural perturbation, and the flares acted as a destabilising factor which resulted in the eruption.




On the Formation Mechanism of A Long-lived Polar Crown Cavity

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Presentation Type: Oral

Session: Session 4: The Evolution of Active Regions

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We report the study of the longest-lived polar crown cavity of Solar Cycle 24th observed in the year 2013 and propose a physical mechanism to explain the sustained existence. We used high temporal and spatial resolution observations from the Atmospheric Imaging Assembly (AIA) and the Helioseismic Magnetic Imager (HMI) instruments on board the Solar Dynamics Observatory (SDO) to explore the structure and evolution. We examined the circumpolar cavity in great detail from March 21, 2013, till October 31, 2013, while it existed for more than one year. Our study suggests two necessary conditions to form a long stable circumpolar cavity or any polar crown cavity. First, the underlying polarity inversion line (PIL) of the circumpolar cavity is formed between the trailing part of dozens of decayed active regions distributed in different longitudes and the unipolar magnetic field in the polar coronal hole. Second, the long life of the cavity is sustained by the continuing flux cancellation along the polarity inversion line. The flux is persistently transported toward the polar region through surface meridional flow and diffusion, which also leads to the shrinking of the polar coronal hole. Comparing with the existing theory of the formation of polarity inversion lines, we introduce a new category named as “Diffused trailing flux and polar coronal hole interaction region” to explain the polar crown cavity. The existence of such region also helps explain the process of polar reversal, which provides insight into the solar cycle.




The discovery of an electron current at Earth's McIlwain L=6

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Presentation Type: Oral

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

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The Large Yield RAdiometer (LYRA) is an ultraviolet solar radiometer on-board ESA's PROBA2 micro-satellite. Since its launch in 2009 to an altitude of 735km, one of the most peculiar and intriguing results of LYRA is the detection of short, strong, bursts that do not directly correlate with solar coronal events, nor with pointing of the instrument to Earth's upper atmosphere, but correlate well with high a_p index on Earth's surface and the crossing by the satellite of the L=6 shell. Very similar detections were more recently made by the Energetic Particles Telescope (EPT) on board the PROBA-V micro-satellite, establishing the identification of the detections as relativistic electrons of the 2.4-8 MeV energy range. Several attributes of those detections, including their dependency to various space weather indexes (ap, D_st, etc), their geographical distribution, a dawn/dusk asymmetry and others will be presented. Open questions related to the discovery of this phenomenon will also be discussed.




Determining ICME Magnetic Field Orientation with the ForeCAT In Situ Data Observer

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Presentation Type: Oral

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

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CMEs drive the strongest space weather events at Earth and throughout the solar system. At Earth, the amount of southward magnetic field in a CME is a major component in determining the severity of an impact. We present results from ForeCAT (Forecasting a CME’s Altered Trajectory, Kay et al. 2015), which predicts the deflection and rotation of CMEs based on magnetic forces determined by the background magnetic field. Using HMI magnetograms to reconstruct the background magnetic field and AIA images to constrain the early evolution of CMEs, we show that we can reproduce the deflection and rotation of CMEs observed in the corona. Using this CME location and orientation from ForeCAT results and a simple force-free flux rope model we show that we can reproduce the in situ magnetic profiles of Earth-impacting CMEs. We compare these results with the in situ profiles obtained assuming that no deflection or rotation occurs, and find that including these nonradial effects is essential for accurate space weather forecasting.




Estimating and Separating Noise from AIA Images

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Presentation Type: No Preference

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

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All digital images are corrupted by noise and SDO AIA is no different. In most solar imaging, we have the luxury of high photon counts and low background contamination, which when combined with carful calibration, minimize much of the impact noise has on the measurement. Outside high-intensity regions, such as in coronal holes, the noise component can become significant and complicate feature recognition and segmentation. We create a practical estimate of noise in the high-resolution AIA images across the detector CCD in all seven EUV wavelengths. A mixture of Poisson and Gaussian noise is well suited in the digital imaging environment due to the statistical distributions of photons and the characteristics of the CCD. Using state-of-the-art noise estimation techniques, the publicly available solar images, and coronal loop simulations; we construct a maximum-a-posteriori assessment of the error in these images. The estimation and mitigation of noise not only provides a clearer view of large-scale solar structure in the solar corona, but also provides physical constraints on fleeting EUV features observed with AIA.




Subsurface Zonal and Meridional Flows from SDO/HMI

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Presentation Type: Oral

Session: Session 1: Motions Inside the Sun

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We study the solar-cycle variation of the zonal and meridional flows in the near-surface layers of the solar convection zone from the surface to a depth of about 16 Mm. The flows are determined from SDO/HMI Dopplergrams using the HMI ring-diagram pipeline. The zonal and meridional flows vary with the solar cycle. Bands of faster-than-average zonal flows together with more-poleward-than-average meridional flows move from mid-latitudes toward the equator during the solar cycle and are mainly located on the equatorward side of the mean latitude of solar magnetic activity. Similarly, bands of slower-than-average zonal flows together with less-poleward-than-average meridional flows are located on the poleward side of the mean latitude of activity. Here, we will focus on the variation of these flows at high latitudes (poleward of 50 degree) that are now accessible using HMI data. We will present the latest results.




Temporal Changes of pModes Properties Derived from Nearly 20 Year of Observations

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Presentation Type: Poster

Session: Session 1: Motions Inside the Sun

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I present a detailed comparison of the temporal changes of the characteristics of the low and intermediate p-modes oscillations derived from nearly 20 years of observations acquired from three instruments: GONG, MDI and HMI. These characteristics were estimated using three quite different data reduction pipe-lines. The comparisons are both at the level of mode characteristics (frequency, linewidth, amplitude and asymmetry) and at the level of inferred properties of the solar interior (i.e., changes in the solar internal rotation), and for co-eval observations.