Submitted Abstracts

There are 131 abstracts


The SDO AIA and HMI archive at MEDOC

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Presentation Type: Poster

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

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MEDOC, created as the European data and operations center for SoHO, hosts also data from STEREO, SDO, and various other solar physics missions. The SDO archive at MEDOC represents more than 250TB of data, and covers the full length of the mission. It includes aia.lev1 data at a minimum cadence of 60s in the EUV channels (12s at specific periods of interest), and most of the 720s-cadence HMI series. It is complemented by a database of DEM maps derived from AIA, that will be presented at the mini-workshop on thermal diagnostics. MEDOC provides a reliable, convenient, and fast (especially for European users) access to these SDO data, by a web interface and webservices. We also provide IDL and Python clients to these webservices, allowing complex queries and automated analyses on large datasets to be made.




Automated detection, characterization, and tracking of filaments from SDO data

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Presentation Type: Poster

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

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Thanks to the cadence and continuity of AIA and HMI observations, SDO offers unique data for detecting, characterizing, and tracking solar filaments, until their eruptions, which are often associated with coronal mass ejections. Because of the requirement of short latency when aiming at space weather applications, and because of the important data volume, only an automated detection can be worked out. We present the code "FILaments, Eruptions, and Activations detected from Space" (FILEAS) that we have developed for the automated detection and tracking of filaments. Detections are based on the analysis of AIA 30.4 nm He II images and on the magnetic polarity inversion lines derived from HMI. Following the tracking of filaments as they rotate with the Sun, filament characteristics are computed and a database of filaments parameters is built. We are currently building a database of filament detections by this code, covering the full SDO mission, and that will be made available to the community.




Energetic characterisation and statistics of solar coronal brightenings

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Presentation Type: Oral

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

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To explain the high temperature of the corona, much attention has been paid to the distribution of energy in dissipation events. Indeed, if the event energy distribution is steep enough, the smallest, unobservable events could be the largest contributors to the total energy dissipation in the corona. Previous observations have shown a wide distribution of energies but remain inconclusive about the precise slope. Furthermore, these results rely on a very crude estimate of the energy. On the other hand, more detailed spectroscopic studies of structures such as coronal bright points do not provide enough statistical information to derive their total contribution to heating. We aim at getting a better estimate of the distributions of the energy dissipated in coronal heating events using high-resolution, multi-channel EUV data. To estimate the energies corresponding to heating events and deduce their distribution, we detected brightenings in five EUV channels of SDO/AIA. We combined the results of these detections and used maps of temperature and emission measure derived from the same observations to compute the energies. We obtain distributions of areas, durations, intensities, and energies (thermal, radiative, and conductive) of events. These distributions are power laws and we also find power-law correlations between event parameters. The energy distributions indicate that the energy from a population of events like the ones we detect represents a small contribution to the total coronal heating, even when extrapolating to smaller scales. The main explanations for this are how heating events can be extracted from observational data, and the incomplete knowledge of the thermal structure and processes in the coronal plasma attainable from available observations.




GAIA-DEM: a database providing AIA/SDO DEM maps

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Presentation Type: Oral

Session: Session 4: The Evolution of Active Regions

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The Gaussian AIA DEm Maps (GAIA-DEM) database at MEDOC (IAS) provides through a simple and intuitive web interface DEM inversions of the SDO/AIA data, computed every 30min. The Gaussian approximation is used to describe the main features of the true DEM(log T) by its first moments. For each date, maps of the three Gaussian fit parameters (central temperature, total emission measure and Gaussian width) and of the chi^2 are available in FITS format. Users can preview the maps before downloading them. In addition, users can display the initial SDO/AIA images using Helioviewer, and query the database through webservices accessible from IDL and Python clients. This presentation is for the "Thermal Diagnostics with SDO/AIA" mini-workshop.




Mass Diagnostics of Eruptive Filament Material

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Presentation Type: Oral

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

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Filament eruptions are not only breathtakingly beautiful, but also key to our understanding of the variable environment which is the solar atmosphere. From the distribution of the material and internal density structure, it is possible to learn about the associated magnetic field which drives the transient activity in the corona, and knowledge of the total mass can answer questions regarding the kinetic energy of coronal mass ejections (CMEs). My research centers around the development of a technique which uses multi-wavelength EUV images from SDO/AIA to determine the mass of any plasma which appears in absorption, as filaments and associated eruptions frequently do. This method is being continuously developed to not only increase the accuracy of results, but also to widen its applicability to a broader spectrum of data (figuratively and literally). I show how I have successfully examined several events using this technique, particularly focusing on partially failed eruptions. I also demonstrate how is possible to use these results to further analyse the material, for example, by constraining numerical experiments which aim to recreate observed plasma instability.




An comprehensive time-distance measurement of deep meridional flow and its temporal variation

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Presentation Type: Oral

Session: Session 1: Motions Inside the Sun

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We report our latest results on the Sun’s deep solar meridional-flow measurements by time-distance helioseismology technique using 6 years of SDO/HMI Doppler-velocity data. Determination of the meridional flow by time-distance helioseismology depends on a precise measurement of the flow-induced travel-time shifts of acoustic waves traveling in the solar interior. To resolve the weak travel-time-shift signals due to deep meridional flow, we need a high signal-to-noise ratio and a robust removal of the center-to-limb (CtoL) effect, which dominates the travel-time shifts. Here we perform an ultimately comprehensive measurement that tracks acoustic waves between any two points on solar surface. The travel-time shifts are composed of CtoL effect, which is a function of disk-centric distances, and contribution from the flow component parallel to wave traveling direction, which is a function of latitude and orientation. Assuming these two effects are independent, we can derive the CtoL effect and meridional-flow contributions by solving a set of linear equations in a least-square sense. We show the solved CtoL effect and the inversion results for the solar meridional flow, and analyze the annual variation of meridional flow from May 2010 to Apr 2016.




Emergence of magnetic flux generated in a solar convective dynamo

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Presentation Type: Oral

Session: Session 4: The Evolution of Active Regions

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We present a realistic numerical model of sunspot and active region formation through the emergence of flux tubes generated in a solar convective dynamo. The magnetic and velocity fields in a horizontal layer near the top boundary of the solar convective dynamo simulation are used as a time-dependent bottom boundary to drive the radiation magnetohydrodynamic simulations of the emergence of the flux tubes through the upper most layer of the convection zone to the photosphere. The emerging flux tubes interact with the convection and break into small scale magnetic elements that further rise to the photosphere. At the photosphere, several bipolar pairs of sunspots are formed through the coalescence of the small scale magnetic elements. The sunspot pairs in the simulation successfully reproduce the fundamental observed properties of solar active regions, including the more coherent leading spots with a stronger field strength, and the correct tilts of the bipolar pairs. These asymmetries originate from the intrinsic asymmetries in the emerging fields imposed at the bottom boundary, where the horizontal fields are already tilted. The leading sides of the emerging flux tubes are up against the downdraft lanes of the giant cells and strongly sheared downward. This leads to the stronger field strength of the leading polarity fields. We find a prograde flow in the emerging flux tube, which is naturally inherited from the solar convective dynamo simulation. The prograde flow gradually becomes a diverging flow as the flux tube rises. The emerging speed is similar to upflow speed of convective motions. The azimuthal average of the flows around a (leading) sunspot reveals a predominant down flow inside the sunspots and a large-scale horizontal inflow at the depth of about 10 Mm. The inflow pattern becomes an outflow in upper most convection zone in the vicinity of the sunspot, which could be considered as moat flows.




A Survey of Sunquake Events in Solar Cycle 24

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Presentation Type: Poster

Session: Session 1: Motions Inside the Sun

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Sunquake events are transient acoustic emissions caused by solar flares. Many past efforts have used helioseismic holography method, which employs a theoretical Green's Function for quiet Sun, to reconstruct acoustic sources caused by flares. In this work, rather than a theoretical Green's Function based on a quiet-Sun model, we use an observational Green's Function constructed from time-distance measurements of outgoing waves from sunspots regions, to reconstruct acoustic emissions during solar flares. This is expected to give a better-determined sunquake location and timing. We apply this newly developed analysis method on 50 strongest solar flares observed by the SDO/HMI during the solar cycle 24, and study both the temporal and spatial relations among sunquake events, white-light enhancements and Doppler-velocity anomalies caused by the flares. Based on these studies, we discuss what causes sunquake events and why only a small fraction of flares are associated with sunquakes.




Investigation of the role of magnetic cancellation in triggering solar eruptions in NOAA AR12017

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Presentation Type: Poster

Session: Session 4: The Evolution of Active Regions

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During its evolution, NOAA AR12017 was the source of 3 Coronal Mass Ejections (CMEs) and a multitude of energetic flares. In its early stages of its evolution it appeared to emerge as a single bipole, which was followed by the emergence of a smaller (secondary) bipole near its pre-existing leading polarity, forming a new polarity inversion line (PIL) between the non-conjugated opposite polarities as well as an evolving magnetic topology in the solar corona. Using photospheric magnetic field observations from SDO/HMI, spectra and imaging from IRIS covering the photosphere and transition region, coronal observations from SDO/AIA and flare centroids from RHESSI, we investigate the cause(s) of activity associated with the new PIL. The time range of the observations spans several hours prior and up to the time of the X1.0 flare (associated with a CME eruption). Continuous photospheric cancellation correlates with flaring activity in the X-rays right at the new PIL, which suggests that cancellation is dominant mechanism for the activity of this extremely flare-productive AR.




8 years of Solar Spectral Irradiance Variability Observed from the ISS with the SOLAR/SOLSPEC Instrument

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Presentation Type: Poster

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

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Accurate measurements of Solar Spectral Irradiance (SSI) are of primary importance for a better understanding of solar physics and of the impact of solar variability on climate (via Earth's atmospheric photochemistry). The acquisition of a top of atmosphere reference solar spectrum and of its temporal and spectral variability during the unusual solar cycle 24 is of prime interest for these studies. These measurements are performed since April 2008 with the SOLSPEC spectro-radiometer from the far ultraviolet to the infrared (166 nm to 3088 nm). This instrument, developed under a fruitful LATMOS/BIRA-IASB collaboration, is part of the Solar Monitoring Observatory (SOLAR) payload, externally mounted on the Columbus module of the International Space Station (ISS). The SOLAR mission, with its actual 8 years duration, will cover almost the entire solar cycle 24. We present here the in-flight operations and performances of the SOLSPEC instrument, including the engineering corrections, calibrations and improved know-how procedure for aging corrections. Accordingly, a SSI reference spectrum from the UV to the NIR will be presented, together with its variability in the UV, as measured by SOLAR/SOLSPEC for 8 years. Uncertainties on these measurements and comparisons with other instruments will be briefly discussed.