Submitted Abstracts

There are 131 abstracts


EUV Cross-Calibration Strategies for the GOES-R SUVI

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Presentation Type: No Preference

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

Abstract:

The challenges of maintaining calibration for solar EUV instrumentation is well-known. The lack of standard calibration sources and the fact that most solar EUV telescopes are incapable of utilizing bright astronomical EUV sources for calibration make knowledge of instrument performance quite difficult. In the recent past, calibration rocket underflights have helped establish a calibration baseline. The EVE instrument on SDO for a time provided well-calibrated, high spectral resolution solar spectra for a broad range of the EUV, but has suffered a loss of coverage at the shorter wavelengths. NOAA's Solar UltraViolet Imager (SUVI), a solar EUV imager with similarities to SDO/AIA, will provide solar imagery over nearly an entire solar cycle. In order to maintain the scientific value of the SUVI's dataset, novel approaches to calibration are necessary. Here we demonstrate a suite of methods to cross-calibrate SUVI against other solar EUV instruments through the use of proxy solar spectra.




The Compound and Homologous Eruptions from AR 11429

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Presentation Type: Poster

Session: Session 4: The Evolution of Active Regions

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We present the study of compound eruptions from NOAA AR 11429 on 10 March 2012, which produced three flares within one hour. We observed three coronal flux structures prior to the eruption, located very near to each other and along the same Polarity Inversion Line (PIL). We analyzed that the first flare, due to the interaction of first flux structure and overlying field, reduce the overlying magnetic pressure and led to the eruption of second flux structure and subsequently the eruption of the third flux structure. The three flux structures were formed by the flux cancellation process and were the part of the same core flux system. The flux cancellation along the PIL, after March 9, resulted in the increase of non-potentiality of the magnetic field and non-potential energy, which led to homologous eruption on March 10.




How calibration and reference spectra affect the accuracy of absolute soft X-ray solar irradiance measured by the SDO/EVE/ESP during high solar activity

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Presentation Type: No Preference

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

Abstract:

The Extreme ultraviolet Spectrophotometer (ESP), one of the channels of SDO’s Extreme ultraviolet Variability Experiment (EVE), measures solar irradiance in several EUV and soft x-ray (SXR) bands isolated using thin-film filters and a transmission diffraction grating, and includes a quad-diode detector positioned at the grating zeroth-order to observe in a wavelength band from about 0.1 to 7.0 nm. The quad diode signal also includes some contribution from shorter wavelength in the grating’s first-order and the ratio of zeroth-order to first-order signal depends on both source geometry, and spectral distribution. For example, radiometric calibration of the ESP zeroth-order at the NIST SURF BL-2 with a near-parallel beam provides a different zeroth-to-first-order ratio than modeled for solar observations. The relative influence of “uncalibrated” first-order irradiance during solar observations is a function of the solar spectral irradiance and the locations of large Active Regions or solar flares. We discuss how the “uncalibrated” first-order “solar” component and the use of variable solar reference spectra affect determination of absolute SXR irradiance which currently may be significantly overestimated during high solar activity.




The Extreme Ultraviolet Monitor (EUVM) on MAVEN: Observations of the EUV Irradiance from Mars

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Presentation Type: No Preference

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

Abstract:

Launched in November 2013 and arriving at Mars in September 2014, Mars Atmosphere and Volatile Evolution (MAVEN) mission has made nearly two years of observations of the atmosphere, near space environment, and solar and space weather drivers at Mars. Included in the complement of instruments on MAVEN is the Extreme Ultraviolet Monitor (EUVM), which measures the absolute solar irradiance in three bandpasses (0.1-7 nm, 17-22 nm, and 121-122 nm) every one second while pointed at the Sun. The EUVM data products include the calibrated irradiances in the three bands (Level 2) at measured cadence and a modeled full spectrum from 0-190 nm in 1-nm bins at daily and 1-minute cadences. Much of the MAVEN mission so far has been observing a different face of the Sun than Earth. We will present an overview of the EUVM observations at Mars so far, including variability from solar cycle, solar rotations, flares, and planetary orbit and describe how to access the MAVEN data.




Extreme Ultraviolet Irradiance of the Early Sun

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Presentation Type: No Preference

Session: Session 8: The Sun as a Star

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Knowledge of the irradiance of the Sun in the EUV over the age of the solar system helps unravel the evolution of planetary atmospheres. In particular, the primary objective of the NASA Mars Atmosphere and Volatile Evolution (MAVEN) mission is to understand how our nearest neighbor lost its early, thicker and wetter atmosphere with the solar EUV being one of the primary drivers of atmospheric escape. To allow for a better estimate of the early Sun’s EUV output, the calibrated solar EUV spectral irradiance measurements of TIMED-SEE and SDO-EVE are put in context with measurements of sun-like stars of differing ages.




Long-period Intensity Pulsations as the Manifestation of the Heating Stratification and Timescale in Coronal Loops

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Presentation Type: Oral

Session: Session 4: The Evolution of Active Regions

Abstract:

In solar coronal loops, thermal non-equilibrium (TNE) is a phenomenon that can occur when the heating is both highly-stratified and quasi-constant. Unambiguous observational identification of TNE would thus permit to strongly constrain heating scenarios. Up to now, while TNE is the standard interpretation of coronal rain, it was not believed to happen commonly in warm coronal loops. Recently, the detection of long-period intensity pulsations (periods of several hours) has been reported with SoHO/EIT. This phenomenon appears to be very common in loops (Auchère et al. 2014). In Froment et al. 2015, three intensity-pulsation events studied with SDO/AIA, show strong evidence for TNE in warm loops. We use realistic loop geometries from LFFF extrapolations for one of these events are used as input to a 1D hydrodynamic simulation of TNE. A highly-stratified heating function is chosen to reproduce the observed period of pulsation and temperature of the loops. With these conditions, the heating function has to be asymmetric. The magnetic topology of the LFFF extrapolations points to the presence of sites of preferred reconnection at one footpoint, supporting the presence of asymmetric heating. We compared the properties of the simulated loop with the properties deduced from observations. We found that the 1D hydrodynamic simulation can reproduce the large temporal scale intensity properties of the pulsating loops (Froment et al. 2016, submitted). This simulation further strengthen the interpretation of the observed pulsations as signatures of TNE. This implies that the heating for these loops is highly-stratified and that the frequency of the heating events must be high compared to the typical cooling time.




Mini-CME eruptions in a flux emergence event in a coronal hole environment

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Presentation Type: Oral

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

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Small scale jets are observed to take place at the interface between the open magnetic field in coronal holes and bipolar magnetic field concentrations. A fraction of these shows an eruptive behavior, where a combination of cold dense and hot light plasma has been observed to propagate out along the jet region, combining traditional jets with what looks like the eruption of mini-CMEs. Here we discuss a simple model scenario for the explosive energy release process that leads to a mixture of hot and cold plasma being accelerated upwards simultaneously. The model explains both the typical steady state inverted-Y jet and the subsequent mini-CME eruptions found in blowout jets. The numerical experiment consists of a buoyant unstable flux rope that emerges into an overlying slanted coronal field, thereby creating a bipolar magnetic field distribution in the photosphere with coronal loops linking the polarities. Reconnection between the emerged and preexisting magnetic systems including the launching of a classical inverted-Y jet. The experiment shows that this simple model provides for a very complicated dynamical behavior in its late phases. Five independent mini-CME eruptions follow the initial near steady-state jet phase. The first one is a direct consequence of the reconnection of the emerged magnetic flux, is mediated by the formation of a strongly sheared arcade followed by a tether-cutting reconnection process, and leads to the eruption of a twisted flux rope. The final four explosive eruptions, instead, are preceded by the formation of a twisted torus-like flux rope near the strong magnetic concentrations at the photosphere. As the tube center starts emerging an internal current sheet is formed below it. This sheet experiences a tether cutting process that provides the important upwards kick of the newly formed mini-CME structure. As the fast rising cold and dense tube interacts with the overlying magnetic field, it reconnects at different spatial locations, either through a null region or through a local strong shear region without nulls. The restructuring of the magnetic field lines generate magneto-acoustic waves that transport twist and cold plasma out along the less stressed parts of the newly reconnected field lines. The emphasis of the talk will be on the physical forces responsible for the initial flux tube rising and the effects and reasons for the following destruction of the mini-CMEs.




The Complex Solar Polarity Reversal during Cycle 24

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Presentation Type: Oral

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

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The polarity reversal at solar poles is an important event with important implications for solar magnetism, the polarity of interplanetary coronal mass ejections, and even cosmic ray modulation. The poles often do not reverse simultaneously. During the several recent cycles, the north pole reversed first, followed by the south. During cycle 24, this trend has been broken in that the south pole reversed first. The polarity reversal is typically marked by the cessation of high-latitude eruptive activities such coronal mass ejections and prominence eruptions. Even though polar prominences started appearing as early as 2011, the reversal in the north was completed only by the end of 2015. On the other hand the south polar region behaved as in previous cycles and reversed over a shorter time scale, about a year before the reversal in the north. By combining prominence eruption detected automatically (Nobeyama Radioheliograph and SDO), the polar microwave brightness (Nobeyama Radioheliograph), and the magnetic butterfly diagram (SDO and NSO) we show that the complexity can be attributed to the emergence of active regions that violated the Hale polarity rule and Joy’s law. The extended period of near-zero field in the north polar region should result in very weak and delayed sunspot activity in the northern hemisphere in cycle 25, the southern hemispheric activity should start early; the amplitude will depend on how the south polar fields will evolve in the declining phase of cycle (24).




The Evolution of Active Regions

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Presentation Type: Oral

Session: Session 4: The Evolution of Active Regions

Abstract:

The solar corona is a highly dynamic environment which exhibits the largest releases of energy in the Solar System in the form of solar flares and coronal mass ejections. This activity predominantly originates from active regions, which store and release free magnetic energy and dominate the magnetic face of the Sun. Active regions can be long-lived features, being affected by the Sun’s convective flows, differential rotation and meridional flows. The Sun’s global coronal field can be seen as the superposed growth and subsequent diffusion of all previously formed active regions. This talk will look at active regions as an observable product of the solar dynamo and will discuss the physical processes that are at play which lead to the storage and release of free magnetic energy. What happens to flux that emerges into the corona so that it goes down an evolutionary path that leads to dynamic activity? And how does this activity vary with active region age? When an active region reaches the end of its lifetime, his much of the magnetic flux is recycled back into subsequent solar cycles? The current status of observations and modelling will be reviewed with a look to the future and fundamental questions that are still be be answered.




Filamentary Oscillations in the Penumbra of Sunspots

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Presentation Type: Oral

Session: Session 4: The Evolution of Active Regions

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The issue of long-term (on scales of several hours to days) morphological changes in sunspots, and particularly the possible existence of apparent rotational motions and oscillations, has drawn attention since the early 20th century. This kind of study requires data with high spatial resolution and good temporal sampling and coverage. The HMI instrument on board the Solar Dynamics Observatory routinely measures the full magnetic field vector in sunspots and allows us to track them with consistent image quality and high cadence during their entire disk passage. It is the ideal instrument to analyze the evolution of sunspots, and in particular the azimuthal component of the penumbral magnetic field. We carried out an analysis (Griñón-Marín et al. 2016 -Submitted-) looking for torsional oscillations in the penumbra of sunspots that led to no evidence of this kind of oscillation in the 25 sunspots analyzed. However, we detected filamentary-like oscillations in some areas of the penumbra with periods of several hours. In this contribution I will show their morphological analysis and discuss the possible sources for such oscillations.