Submitted Abstracts

There are 131 abstracts


The Analysis of Magnetic Field Vector in AR 11263 Based on SDO Data

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Presentation Type: Oral

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

Abstract:

Configuration changes of complex magnetic field could trigger flares. Using magnetic field data obtained from SDO-HMI we analyzed the dynamics of magnetic field configuration in active regions. We tried to employ the idea of Moore et al. (2012) that the direction of magnetic field lines which aligned themselves to the neutral line could trigger flare. Using the VAPOR software, we analyzed the magnetic field changes in AR 11263 before the flare explosions, especially changes in direction and the value of the magnetic field. The results of our investigation is that there were some changes of magnetic flux direction in which the closer the time of explosion, the smaller the angle subtended by the flux with the plane of reference of the neutral line. Keywords: flares – magnetic field change – neutral lines – deviation of tangential components




The Source of the Slow Wind and the Origin of its Dynamics

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Presentation Type: Oral

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

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The origin of the slow solar wind has long been one of the major unsolved problems in solar physics. Recently, we have proposed the S-Web model in which the slow wind originates from a dense web of separatrices and quasi-separatrix layers that form the boundary between open and closed magnetic flux in the corona. The large-scale dynamics of the photosphere and corona drive this S-Web, causing closed field plasma to be released onto open field lines, which is observed in the heliosphere as the slow wind. The S-Web model, therefore, predicts that both the source and variability of the slow wind are due to the dynamics of the open-closed magnetic field boundary. We argue that two main processes drive these dynamics: photospheric motions and thermal nonequilibrium. We present simulations showing the form of the variability expected from the S-web dynamics and discuss the implications of our calculations for understanding the observed properties of the slow wind and especially for interpreting SDO observations of coronal hole evolution. This work was supported by the NASA LWS Program.




The Global Energetics of Solar Flares and CMEs

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Presentation Type: Oral

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

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We present statistical results of a global flare energetics project, in which the mass, the kinetic energy, and the gravitational potential energy of coronal mass ejections (CMEs) is measured in 399 M and X-class flare events observed during the first 3.5 yrs of the Solar Dynamics Observatory (SDO) mission, using a new method based on the EUV dimming effect. The EUV dimming is modeled in terms of a radial adiabatic expansion process, which is fitted to the observed evolution of the total emission measure of the CME source region. The model derives the evolution of the mean electron density, the emission measure, the bulk plasma expansion velocity, the mass, and the energy in the CME source region. The EUV dimming method is truly complementary to the Thomson scattering method in white light, which probes the CME evolution in the heliosphere at r >2 R_sun, while the EUV dimming method tracks the CME launch in the corona. We compare the CME parameters obtained in white light with the LASCO/C2 coronagraph with those obtained from EUV dimming with AIA) onboard SDO for all identical events in both data sets. We investigate correlations between CME parameters, the relative timing with flare parameters, frequency occurrence distributions, and the energy partition between magnetic, thermal, non-thermal, and CME energies. CME energies are found to be systematically lower than the dissipated magnetic energies, which is consistent with a magnetic origin of CMEs.




Fourier and Wavelet Analysis of Coronal Time Series

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Presentation Type: Poster

Session: Session 4: The Evolution of Active Regions

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Using Fourier and wavelet analysis, we critically re-assess the significance of our detection of periodic pulsations in coronal loops. We show that the proper identification of the frequency dependence and statistical properties of the different components of the power spectra provies a strong argument against the common practice of data detrending, which tends to produce spurious detections around the cut-off frequency of the filter. In addition, the white and red noise models built into the widely used wavelet code of Torrence \& Compo cannot, in most cases, adequately represent the power spectra of coronal time series, thus also possibly causing false positives. Both effects suggest that several reports of periodic phenomena should be re-examined. The Torrence \& Compo code nonetheless effectively computes rigorous confidence levels if provided with pertinent models of mean power spectra, and we describe the appropriate manner in which to call its core routines. We recall the meaning of the default confidence levels output from the code, and we propose new Monte-Carlo-derived levels that take into account the total number of degrees of freedom in the wavelet spectra. These improvements allow us to confirm that the power peaks that we detected have a very low probability of being caused by noise.




Thermal Non-Equilibrium Revealed by Periodic Pulses of Random Amplitudes in Solar Coronal Loops

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Presentation Type: Poster

Session: Session 4: The Evolution of Active Regions

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We recently detected variations in extreme ultraviolet intensity in coronal loops repeating with periods of several hours. Models of loops including stratified and quasi-steady heating predict the development of a state of thermal non-equilibrium (TNE): cycles of evaporative upflows at the footpoints followed by falling condensations at the apex. Based on Fourier and wavelet analysis, we demonstrate that the observed periodic signals are indeed not signatures of vibrational modes. Instead, superimposed on the power law expected from the stochastic background emission, the power spectra of the time series exhibit the discrete harmonics and continua expected from periodic trains of pulses of random amplitudes. These characteristics reinforce our earlier interpretation of these pulsations as being aborted TNE cycles.




Impact of Magnetic Carrington Synoptic and Spatial Variance Maps in Modeling of the Corona and Solar Wind

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Presentation Type: Oral

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

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Synoptic maps derived from the measured photospheric solar longitudinal magnetic field are routinely used to drive coronal and heliospheric models. The recent development of spatial variance maps has provided an additional resource to better understanding the limitation of these models. In addition, measurements of the vector magnetic field are now available from different instruments (e.g. SDO/HMI, SOLIS/VSM) and can be used to compute synoptic maps of the true radial field. However, due to the low sensitivity of these measurements in regions of weak magnetic field, the adoption of these maps has been very limited. An effort is underway at NSO to merge both longitudinal and vector measurements together and derive more reliable synoptic maps of the radial field. An even more ambitious project is ongoing to produce also the first radial synoptic maps derived from SOLIS/VSM chromospheric measurements. Validation and diagnostic capability of these products will be discussed.




Two-scale Analysis of Solar Magnetic Helicity

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Presentation Type: Oral

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

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The solar magnetic helicity has opposite signs not only in the two hemispheres, but also at large and small length scales. The latter can be detected by computing magnetic helicity spectra, but this must be done separately in each hemisphere. Here we utilize a two-scale method from mean-field dynamo theory that allows us to compute magnetic helicity spectra as a function of two different wavenumbers: one corresponding to rapidly varying scale and one corresponding to a slowly varying one. We generalize this method to spherical harmonics and compute in that way global magnetic helicity spectra for that part of the field that shows a global dipolar symmetry. We present results from simple one-dimensional model calculations, three-dimensional dynamo simulations, and the two-dimensional magnetic field from synaptic vector magnetograms.




Seismology tools for studying the solar-stellar connection

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Presentation Type: Oral

Session: Session 8: The Sun as a Star

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Our knowledge of the Sun directly informs our understanding of stellar structure and evolution. For decades helioseismology has been a useful tool for characterising the Sun’s internal structure and dynamics. Helioseismology has also been used to study the Sun’s magnetic activity cycle and the impact of magnetic fields on the solar interior. More recently, missions such as Kepler and CoROT have provided high quality asteroseismic data for a large number of stars. I will discuss the synergies between helioseismology and asteroseismology of solar-like stars describing what we can learn about stars from the Sun and how observations of other stars are helping to establish just how typical a star the Sun is.




Doppler speeds of the hydrogen Lyman lines in solar flares from EVE

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Presentation Type: Oral

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

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The hydrogen Lyman lines provide important diagnostic information about the dynamics of the chromosphere, but until recently there have been few systematic studies of their variability during flares. We investigate Doppler shifts in these lines in several flares, and use these to calculate plasma speeds. We use spectral data from the Multiple EUV Grating Spectrograph B (MEGS-B) detector on board the Extreme-Ultraviolet Variability Experiment (EVE) instrument on the Solar Dynamics Observatory. MEGS-B obtains full-disk spectra of the Sun at a resolution of 0.1nm in the range 37-105nm, which we analyse using three independent methods. The first method performs Gaussian fits to the lines, and compares the quiet-Sun centroids with the flaring ones to obtain the Doppler shifts. The second method uses cross-correlation to detect wavelength shifts between the quiet-Sun and flaring line profiles. The final method calculates the “center-of-mass" of the line profile, and compares the quiet-Sun and flaring centroids to obtain the shift. In a study of 6 flares we find signatures of both upflow and downflow in the Lyman lines, with speeds of around 10 km s^−1 in the line profiles that have not undergone pre-flare subtraction, and speeds in the flare-excess profiles of around 30 km s^−1 . We include analysis of AIA images of these events in order to understand potential contributions from material ejections, and find that not all upflows can be explained by ejecta. We discuss current and future attempts at modelling these line profiles.




Towards the automatic detection and analysis of sunspot rotation

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Presentation Type: No Preference

Session: Session 4: The Evolution of Active Regions

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Torsional rotation of sunspots have been noted by many authors over the past century. Sunspots have been observed to rotate up to the order of 200 degrees over 8-10 days, and these have often been linked with eruptive behaviour such as solar flares and coronal mass ejections. However, most studies in the literature are case studies or small-number studies which suffer from selection bias. In order to better understand sunspot rotation and its impact on the corona, unbiased large-sample statistical studies are required (including both rotating and non-rotating sunspots). While this can be done manually, a better approach is to automate the detection and analysis of rotating sunspots using robust methods with well characterised uncertainties. The SDO/HMI instrument provide long-duration, high-resolution and high-cadence continuum observations suitable for extracting a large number of examples of rotating sunspots. This presentation will outline the analysis of SDI/HMI data to determine the rotation (and non-rotation) profiles of sunspots for the complete duration of their transit across the solar disk, along with how this can be extended to automatically identify sunspots and initiate their analysis.