Submitted Abstracts

There are 131 abstracts


A Method For Finding Solar Flares Jointly Observed by Multiple Instruments

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Presentation Type: Poster

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

Abstract:

Our current fleet of space-based solar observatories offer us a wealth of opportunities to study solar flares over a range of wavelengths, and the greatest advances in our understanding of flare physics often come from coordinated observations between different instruments. However, finding or keeping track of which flares have been observed by specific combinations of instruments can be cumbersome and time consuming. To alleviate this issue, and provide access to a broader range of flaring events observed by GOES, RHESSI, Hinode (EIS, SOT, and XRT), SDO/EVE (MEGS-A and MEGS-B), and IRIS, a new interface has been developed and incorporated into SSWIDL (IDL> solar_flare_finder). This tool allows the user to search for solar flares that have been observed by a chosen combination of instruments in order to answer a specific science question. The user can also narrow their search by GOES class, location on the solar disk, maximum energy observed by RHESSI, etc. The routine searches a pre-generated lookup table to instantly return a list of events conforming to the user’s specifications, along with a (downloadable) plot of the flare lightcurves (GOES and RHESSI) with the timing of longer wavelength observations overlaid. A RHESSI quicklook image is also shown along with the pointing information of other instruments. Future improvements to the solar_flare_finder service will include adding flares that were not observed by RHESSI, adding additional instruments (e.g. Fermi, NoRH, GOES/EUVS, etc), and direct access to the data itself. This tool also enables us to determine how many flares have been co-temporally and co-spatially observed by various combinations of instruments over the current solar cycle. We present and discuss these statistics.




Solar Acoustic Oscillations Observations in SDO AIA and HMI around AR 12192

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Presentation Type: Poster

Session: Session 4: The Evolution of Active Regions

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Solar flares are dynamic objects occurring randomly and yet unannounced in nature. In order to find an efficient detection method, we require a greater breadth of knowledge of the system. One such mode is to observe flares in different frequency bands at different depths and study their temporal evolution through the flaring event. In this project we obtain acoustic observations of an X3 flare occurring on October 24, 2014 at 21:41UT. We employ the study of active regions, near sunspots, in which flaring activity is taking place. Our wavelet analysis utilizes time series data to create Fourier power spectra of individual pixels spatially resolved around the flare region, to study the frequency bands. In order to study the power distribution in regions around the flare and compare the measurements to magnetograms to search for any correlation, we combine observations of oscillations in three SDO AIA wavelengths: the 1600Å, 1700 Å and 304Å, and combine them with HMI data. We then study how the frequency distribution evolves temporally by constructing a Power Map Movie (PMM) of the regions. From these PMMs we can partition sub-regions in our main flaring region and take a survey of the oscillations for each frequency band.




Babcock Redux: An Amendment of Babcock’s Schematic of the Sun’s Magnetic Cycle

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Presentation Type: Oral

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

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We amend Babcock’s original scenario for the global dynamo process that sustains the Sun’s 22-year magnetic cycle. The amended scenario fits post-Babcock observed features of the magnetic activity cycle and convection zone, and is based on ideas of Spruit & Roberts (1983) about magnetic flux tubes in the convection zone. A sequence of four schematic cartoons lays out the proposed evolution of the global configuration of the magnetic field above, in, and at the bottom of the convection zone through sunspot Cycle 23 and into Cycle 24. Three key elements of the amended scenario are: (1) as the net following-polarity magnetic field from the sunspot-region -loop fields of an ongoing sunspot cycle is swept poleward to cancel and replace the opposite-polarity polar-cap field from the previous sunspot cycle, it remains connected to the ongoing sunspot cycle’s toroidal source-field band at the bottom of the convection zone; (2) topological pumping by the convection zone’s free convection keeps the horizontal extent of the poleward-migrating following-polarity field pushed to the bottom, forcing it to gradually cancel and replace old horizontal field below it that connects the ongoing-cycle source-field band to the previous-cycle polar-cap field; (3) in each polar hemisphere, by continually shearing the poloidal component of the settling new horizontal field, the latitudinal differential rotation low in the convection zone generates the next-cycle source-field band poleward of the ongoing-cycle band. The amended scenario is a more-plausible version of Babcock’s scenario, and its viability can be explored by appropriate kinematic flux-transport solar-dynamo simulations. A paper of the above title and authors, giving a full description of the solar dynamo scenario of this abstract, is available at http://arxiv.org/abs/1606.05371. This work was funded by the Heliophysics Division of NASA's Science Mission Directorate through the Living With a Star Targeted Research and Technology Program and the Hinode Project.




A class of three-dimensional MHD models for Coronal Bright Points

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Presentation Type: Oral

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

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The coronal bright points (CBPs) are classical features in solar physics: their first detection, in X Rays, dates back to almost half a century ago. They are also observed in the EUV, have lifetimes in a wide range between several minutes and a few days, and typical size $20$ to $30$ arc seconds. The recent space missions (like SDO) have provided a wealth of detailed information about their structure and time evolution. The CBPs seem to be related in many/most cases to processes of magnetic cancellation. The classical theoretical model by Priest et al (1994) explains a number of their features by way of the convergence of opposite-sign magnetic polarities in the photosphere, with ensuing reconnection of the overlying structures in the corona. That model is essentially 2D and, therefore, has clear limitations concerning the mutual photospheric motion of the two polarities. Also, it cannot study the complicated magnetic topology and reconnection patterns associated with three-dimensional null points in an evolving magnetic configuration. In this lecture we present first results of a project of three-dimensional modeling of the evolution of null-point structures overlying network-like magnetic configurations that can plausibly lead to the creation of hot regions in the corona, possibly observable as bright points in the EUV or X-Rays. Our model includes the time evolution of the plasma and magnetic structures from the lower atmosphere to the corona. It is strongly idealized, in that no radiation transfer, thermal conduction, nor partial ionization effects are included. The model solves the compressible MHD equations with, in particular, the electrical current and Lorentz force evolving in a self-consistent manner: no limitation to potential nor force-free structures is imposed. In this lecture, the focus will be set on the basic physical magnetohydrodynamical phenomena taking place in the different levels and regions of the atmosphere included in the model, rather than on providing observational proxies for comparison with satellite data.




The Photospheric Footprints of Coronal Hole Jets

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Presentation Type: Oral

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

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Coronal jets are transient, collimated ejections of plasma that are a common feature of solar X-ray and EUV image sequences. Of special interest are jets in coronal holes due to their possible contribution to the solar wind outflow. From a sample of 35 jet events I will investigate the photospheric signatures at the footpoints of these jets. White light images from the HMI on board SDO are used to derive the plane-of-sky flow field using local correlation tracking, and HMI magnetograms show the development of the magnetic flux. Both the evolution of the magnetic field and flows allow one to study the photospheric driver of these jets. One particularly interesting example demonstrates that the untwisting jet involves a tiny filament whose eruption is most likely triggered by the emergence of a small magnetic bipole close to one of its legs.




Advances on Our Understanding of Solar Cycle Propagation and Predictability

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Presentation Type: Oral

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

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As solar cycle 24 winds down and we start looking forward to the coming cycle 25, we are steadily approaching the time in which a new host of solar cycle predictions will be made. The point of this talk is to highlight some of the most important advances in our understanding of cycle propagation and its predictability (made since the last round of cycle predictions). In particular, this presentation will focus on theoretical and observational evidence in favor of a dynamo that relies on active region emergence and decay for its operation, and on evidence of a causal disconnection that takes place between one cycle and the next (making inter-cyclic prediction difficult)




Stealth CMEs and Stealthy Geomagnetic Storms

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Presentation Type: Poster

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

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We sometimes encounter coronal mass ejections (CMEs) whose low coronal signatures are apparently missing, especially when viewed on the disk. They are called stealth CMEs, which are usually slow and diffuse. Some of them result in medium geomagnetic storms. Similarly, there are orphan interplanetary CMEs (ICMEs) that lack a parent CME in coronagraph data but could cause geomagnetic storms when strong and sustained southward magnetic field is present. In addition, some geomagnetic storms may be attributable to a fast solar wind and stream interaction region, but it is often hard to rule out a trace of ICME (coming from a solar eruption) in in situ data. These events present a major challenge not only in heliophysics research but also in space weather prediction. We summarize our recent attempt to understand the origins of stealth CMEs and stealthy geomagnetic storms, making extensive use of SDO/AIA data in comparison with SOHO/LASCO and STEREO/EUVI/COR data. In situ data from Wind, ACE and STEREO are also examined. We discuss the relations of these events with coronal holes and sector boundaries.




The Cool Surge Following Flux Emergence in a Radiation-MHD Experiment

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Presentation Type: Oral

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

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Cool and dense ejections, typically Hα surges, often appear alongside EUV or X-ray coronal jets as a result of the emergence of magnetized plasma from the solar interior. Idealized numerical experiments explain those ejections as being indirectly associated with the magnetic reconnection taking place between the emerging and preexisting systems. However, those experiments miss basic elements that can importantly affect the surge phenomenon. In this paper we study the cool surges using a realistic treatment of the radiation transfer and material plasma properties. To that end, the Bifrost code is used, which has advanced modules for the equation of state of the plasma, photospheric and chromospheric radiation transfer, heat conduction, and optically thin radiative cooling. We carry out a 2.5D experiment of the emergence of magnetized plasma through (meso) granular convection cells and the low atmosphere to the corona. Through detailed Lagrange tracing we study the formation and evolution of the cool ejection and, in particular, the role of the entropy sources; this allows us to discern families of evolutionary patterns for the plasma elements. In the launch phase, many elements suffer accelerations well in excess of gravity; when nearing the apex of their individual trajectories, instead, the plasma elements follow quasi-parabolic trajectories with accelerations close to the solar gravity . We show how the formation of the cool ejection is mediated by a wedge-like structure composed of two shocks, one of which leads to the detachment of the surge from the original emerged plasma dome.




HMI Data Corrected for Stray Light Now Available

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Presentation Type: Poster

Session: Session 4: The Evolution of Active Regions

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The form of the point spread function (PSF) derived for HMI is an Airy function convolved with a Lorentzian. The parameters are bound by observational ground-based testing of the instrument conducted prior to launch (Wachter et al., 2012), by full-disk data used to evaluate the off-limb behavior of the scattered light, as well as by data obtained during the Venus transit. The PSF correction has been programmed in both C and cuda C and runs within the JSOC environment using either a CPU or GPU. A single full-disk intensity image can be deconvolved in less than one second. The PSF is described in more detail in Couvidat et al. (2016) and has already been used by Hathaway et al. (2015) to forward-model solar-convection spectra, by Krucker et al. (2015) to investigate footpoints of off-limb solar flares and by Whitney, Criscuoli and Norton (2016) to examine the relations between intensity contrast and magnetic field strengths. In this presentation, we highlight the changes to umbral darkness, granulation contrast and plage field strengths that result from stray light correction. A twenty-four hour period of scattered-light corrected HMI data from 2010.08.03, including the isolated sunspot NOAA 11092, is currently available for anyone. Requests for additional time periods of interest are welcome and will be processed by the HMI team.




MHD Waves at Umbral-Penumbral Boundary Observed with Hinode/SOT-SP and SDO/HMI

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Presentation Type: Poster

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

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The conversion of p-modes and other perturbations in the near-surface layers into MHD waves that can propagate along and across magnetic field lines is a topic of interest for energy transport. The photospheric signatures of MHD waves are weak due to low amplitudes at the beta=1 equipartion level where mode-conversion occurs. We report on oscillations observed with Hinode SOT/SP and HMI in which we have time series for sunspots 12186 (11.10.2014) and 12434 (17.10.2015). In the Milne-Eddington inversion results from SP, oscillations in the inclination angle and velocity are found at the umbral-penumbral boundary with ~5 minute periods. HMI data also shows distinct umbral-penumbral boundary oscillations consistent with the SP data. We discuss surface versus body modes that might explain these observations.