Submitted Abstracts

There are 131 abstracts


Statistical Analysis of Small-Scale Magnetic Flux Emergence Patterns: A Useful Subsurface Diagnostic?

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Presentation Type: Poster

Session: Session 1: Motions Inside the Sun

Abstract:

While sunspots follow a well-defined pattern of emergence in space and time, small-scale flux emergence is assumed to occur randomly at all times in the quiet Sun. HMI’s full-disk coverage, high cadence, spatial resolution, and duty cycle allow us to probe that basic assumption. Some case studies of emergence suggest that temporal clustering on spatial scales of 50–150 Mm may occur. If clustering is present, it could serve as a diagnostic of large-scale subsurface magnetic field structures. We present the results of a manual survey of small-scale flux emergence events over a short time period, and a statistical analysis addressing the question of whether these events show spatio-temporal behavior that is anything other than random.




The Efffect of Image Apodization on Global Mode Parameters and Rotational Inversions

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Presentation Type: Poster

Session: Session 1: Motions Inside the Sun

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It has long been known that certain systematic errors in the global mode analysis of data from both MDI and HMI depend on how the input images were apodized. Recently it has come to light, while investigating a six-month period in f-mode frequencies, that mode coverage is highest when B0 is maximal. Recalling that the leakage matrix is calculated in the approximation that B0=0, it comes as a surprise that more modes are fitted when the leakage matrix is most incorrect. It is now believed that the six-month oscillation has primarily to do with what portion of the solar surface is visible. Other systematic errors that depend on the part of the disk used include high-latitude anomalies in the rotation rate and a prominent feature in the normalized residuals of odd a-coefficients. Although the most likely cause of all these errors is errors in the leakage matrix, extensive recalculation of the leaks has not made any difference. Thus we conjecture that another effect may be at play, such as errors in the noise model or one that has to do with the alignment of the apodization with the spherical harmonics. In this poster we explore how differently shaped apodizations affect the results of inversions for internal rotation, for both maximal and minimal absolute values of B0.




Quantitative estimation of the energy flux during an explosive chromospheric evaporation in a white light flare kernel observed by Hinode, IRIS, SDO, and RHESSI

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Presentation Type: Poster

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

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An X1.6 flare occurred at the AR 12192 on 2014 October 22 at14:02 UT was observed by Hinode, IRIS, SDO, and RHESSI. We analyze a bright kernel which produces a white light (WL) flare with continuum enhancement and a hard X-ray (HXR) peak. Taking advantage of the spectroscopic observations of IRIS and Hinode/EIS, we measure the temporal variation of the plasma properties in the bright kernel in the chromosphere and corona. We found that explosive evaporation was observed when the WL emission occurred, even though the intensity enhancement in hotter lines is quite weak. The temporal correlation of the WL emission, HXR peak, and evaporation flows indicate that the WL emission was produced by accelerated electrons. To understand the white light emission processes, we calculated the deposited energy flux from the non-thermal electrons observed by RHESSI and compared it to the dissipated energy estimated from the chromospheric line (Mg II triplet) observed by IRIS. The deposited energy flux from the non-thermal electrons is about 3.1 × 1010erg cm−2 s−1 when we consider a cut-off energy 20 keV. The estimated energy flux from the temperature changes in the chromosphere measured from the Mg II subordinate line is about 4.6−6.7×109erg cm−2 s−1, ∼ 15−22% of the deposited energy. By comparison of these estimated energy fluxes we conclude that the continuum enhancement was directly produced by the non-thermal electrons.




Influence of the Sun on the Space Weather Conditions: Cycle 24 Observations from 1 AU to Mars

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Presentation Type: Oral

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

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Motivated by future crewed missions to Mars, there is a growing need to advance our knowledge of the heliospheric conditions between the Earth (~1 AU) orbit and Mars (~1.5 AU) orbit locations. Comparative conditions at these locations are of special interest since they are separated by the interplanetary region where most solar wind stream interaction regions develop. These regions alter the propagation of solar-heliospheric disturbances, including the interplanetary CME-driven shocks that create the space radiation (via solar energetic particles) that are hazardous to humans. Although the deep Cycle 23 minimum and the modestly active Cycle 24 maximum have produced generally weaker solar events and heliospheric conditions, observations from solar and planetary missions during the SDO era provide a unique opportunity to study how and to what extent the solar eruptive events impact the local space environments at Earth (and/or STEREO-A) and Mars, and for a given solar-heliospheric event period how the geospace and near-Mars space conditions compare and contrast with one another. Such observations include those from SDO, L1 observers (ACE,WIND,SOHO) and STEREO-A at 1 AU, and Mars Express, MSL, and MAVEN at ~1.5 AU. Using these observations, we will highlight a number of Cycle 24 space weather events observed along the 1-AU orbit (at Earth and/or STEREO-A) and Mars that are triggered by CMEs, SEPs, flares, and/or CIRs. Numerical 3D simulations from WSA-Enlil-cone will also be presented to provide global context to the events discussed.




Direct imaging of a classical solar eruptive flare

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Presentation Type: Oral

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

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Solar flares are the most energetic events in the solar system that have a potential hazard on Earth. Although a standard model for the eruptive flare accompanied by a coronal mass ejection has been outlined and elaborated for decades, some key aspects are still under debate, such as what drives the eruption, what is the role of magnetic reconnection, and how the flare loops evolve. Here we present an excellent event exhibiting nearly all the key elements involved in the standard flare model. Using extreme-ultraviolet imaging observations, we detect the unambiguous rise and eruption of a magnetic flux rope, solid evidence for magnetic reconnection, and evident slipping and rising motions in flare loops. Modeled coronal magnetic field supports the interpretation of a pre-existing flux rope that persists after the eruption with reduced twist. This flare, from the observational view, shows a clear and comprehensive picture of how a classical solar eruptive flare occurs and evolves, and helps to clarify some of the controversial topics in the standard flare model.




Are Dynamical Sources Essential for the Production of the Ambient Solar Wind?

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Presentation Type: Oral

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

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At a basic level, the large structure of the solar corona and its connection to the solar wind has been known for many years. In the classic (near-solar minimum) picture, the slow solar wind is associated with the streamer belt at low latitudes, while the fast solar wind arises from coronal holes at higher latitudes. At a deeper level, important aspects of this connection still puzzle us. One such controversy is the origin of the slow solar wind. One group of theories assume that the slow wind primarily arises quasi-statically from regions of large expansion factor near the boundaries of coronal holes, while a contrasting set of theories argue that the slow solar wind is primarily dynamic in origin and involves the reconnection and exchange of open and closed fields. In this talk, we describe evidence for both sets of theories, and ongoing and future work that may help to resolve this question. Work supported by NASA, NSF and AFOSR.




Modeling the Energization and Eruption of Flux Ropes and Sheared Arcades

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Presentation Type: Oral

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

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Solar magnetic eruptions are dramatic sources of solar activity, and dangerous sources of space weather hazards. Observations of the solar photosphere and overlying atmosphere by the Solar Dynamics Observatory have given us new views, measurements, and modeling constraints for understanding these eruptions. This presentation will review the current state of the art in modeling the energization and eruption of sheared magnetic arcades and of magnetic flux ropes in the corona, and will review the critical role that observations play in the motivation, development, and application of these models.




The Thermodynamics of Coronal Jets and Their Contribution to the Solar Wind

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Presentation Type: Oral

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

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Coronal (or X-ray) jets are transient, collimated plasma eruptions that are observed low in the corona in EUV and soft X-ray bands. It is widely accepted that they are triggered by reconnection between closed and open magnetic fields, but their detailed formation mechanisms are still under debate. Since coronal jets are often seen to extend to several solar radii, it has been suggested that they may contribute to powering the solar wind, but the amount of this contribution remains largely uncertain. Here we present the first MHD simulations of coronal jets that include the solar wind and a realistic description of the energy transfer in the corona ("thermodynamic MHD"). The evolution in our model is driven by the emergence of a magnetic flux rope into an open magnetic field. We find different types of jets in our simulations, and discuss their respective formation mechanisms, morphologies, and emission properties. We also analyze their energy and mass contributions to the solar wind, and compare them with existing estimations obtained from observations.




What Produce Energetic Flares with X-Shaped Ribbons on the Outskirts of Solar Active Region?

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Presentation Type: Oral

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

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Typical solar flares display two quasi-parallel, bright ribbons on the chromosphere. In between is the polarity inversion line separating concentrated magnetic fluxes of opposite polarities in active regions (ARs). Intriguingly a series of flares exhibiting X-shaped ribbons occur at the similar location on the outskirts of NOAA AR 11967, where magnetic fluxes are scattered, yet three of them are alarmingly energetic. The X shape is similar in UV/EUV with hard X-ray emission projected in the center, which cannot be accommodated in the standard flare model. Mapping out magnetic connectivities in potential fields, we found that the X morphology is dictated by the intersection of two quasi-separatrix layers, i.e., a hyperbolic flux tube (HFT), within which a separator connecting a double null is embedded. This topology is not purely local but regulated by fluxes and flows over the whole AR. The nonlinear force-free field model suggests the formation of a current layer at the HFT, where the current dissipation can be mapped to the X-shaped ribbons via field-aligned heat conduction. These results highlight the critical role of structural skeletons in 3D magnetic reconnection.




Joint SDO and IRIS Observations of a Novel, Hybrid Prominence-Coronal Rain Complex

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Presentation Type: Oral

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

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Solar prominences and coronal rain are intimately related phenomena, both involving cool material at chromospheric temperatures within the hot corona and both playing important roles as part of the return flow of the chromosphere-corona mass cycle. At the same time, they exhibit distinct morphologies and dynamics not yet well understood. Quiescent prominences consist of numerous long-lasting, filamentary downflow threads, while coronal rain is more transient and falls comparably faster along well-defined curved paths. We report here a novel, hybrid prominence-coronal rain complex in an arcade-fan geometry observed by SDO/AIA and IRIS, which provides new insights to the underlying physics of such contrasting behaviors. We found that the supra-arcade fan region hosts a prominence sheet consisting of meandering threads with broad line widths. As the prominence material descends to the arcade, it turns into coronal rain sliding down coronal loops with line widths 2-3 times narrower. This contrast suggests that distinct local plasma and magnetic conditions determine the fate of the cool material, a scenario supported by our magnetic field extrapolations from SDO/HMI. Specifically, the supra-arcade fan (similar to those in solar flares; e.g., McKenzie 2013) is likely situated in a current sheet, where the magnetic field is weak and the plasma-beta could be close to unity, thus favoring turbulent flows like those prominence threads. In contrast, the underlying arcade has a stronger magnetic field and most likely a low-beta environment, such that the material is guided along magnetic field lines to appear as coronal rain. We will discuss the physical implications of these observations beyond prominence and coronal rain.