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Millimeter/sub-millimeter wave observations for chromospheric science

Author(s): Masumi Shimojo and ALMA project

Institution(s): ALMA Project Office, National Astronomical Observatory of Japan

Abstract:

Except flares, the mm/sub-mm waves come from the lower chromosphere, and the emission mechanism of the waves is thermal emission from optically thick layer. The fact has been known from 1970’s. However, the spatial resolved observation in the wavelength range is very rare, because most telescopes for mm/sub-mm wave observation do not have the capability of solar observations and solar interferometric observations require many antennas for resolving phenomena with short lifetime. The Atacama Large Millimeter/sub-millimeter Array (ALMA) is the largest interferometer in the world for astronomical observations in mm/sub-mm wavelength. ALMA is constructed by 66 antennas and the highest spatial resolution reaches 0.04 arcsec@100GHz / 0.005 arcsec@900GHz, when ALMA starts the full operation phase (~ 2013). Although the ALMA project is the huge international astronomical project, it is not known well that ALMA has the capability to observe the Sun. At the end of 2010, ALMA project started the scientific verification activity for solar observation by ALMA and we performed two observing campaigns for verifying solar observations in May and December 2011. In the paper, we present the progress of verification activities for ALMA solar observations and discuss the chromospheric science using ultra-high spatial resolution data obtained by ALMA.




Photospheric Magnetic Fields from Magneto-Convection Simulations

Author(s): Robert F. Stein (1), Aake Nordlund (2), Dali Georgobiani (1)

Institution(s): (1) Michigan State University, (2) Niels Bohr Institute

Abstract:

We present the properties of photospheric magnetic fields from magneto-convection simulations and as they would be observed by Hinode, for both quiet Sun and plage regions. This will include statistical properties, morphology, Stokes spectra, energy fluxes and correlations with convection dynamics. The rate of flux emergence will be discussed as a constraint on model parameters.




Scaling laws for quiet-sun magnetic fields

Author(s): Jan Stenflo

Institution(s): ETH Zurich

Abstract:

The structuring of solar magnetic fields continues down to scales that are several orders of magnitude smaller than the scales that can currently be resolved. While the kG type flux tubes that can be explained in terms of the convective collapse mechanism have typical sizes in the range 10-70 km, the "hidden" flux of tangled fields that is revealed by the Hanle effect resides at still smaller scales. We have used a Hinode SOT/SP data set for the disk center of the quiet Sun to derive the kinetic and magnetic energy spectra in the resolved domain, and have used Hinode line-ratio data in combination with constraints from the Hanle effect to derive how the magnetic energy spectrum needs to be continued all the way down to the magnetic dissipation limit such that the combined constraints become satisfied. Special attention is paid to the effects of polarimetric noise and the modulation transfer function of the telescope. We find an approximate equipartition between kinetic and magnetic energy with power-law behavior in the range 200 - 1000 km. Below this scale the character of the energy spectrum changes, because it becomes dominated by the contribution from the kG flux tubes in the range 10 - 200 km. The spectrum then needs to be continued downwards to the dissipation limit (between 10 and 100 m) in a way that can explain the Hanle effect observations. We describe how the energy spectrum relates to the probability density functions for the flux densities and field strengths and to the cancellation function that describes the scaling of the average unsigned flux density.




Recurrent Eruptions in a Quadrupolar Magnetic Configuration Observed by SDO

Author(s): Sun, Xudong; Hoeksema, Todd; Liu, Yang; Hayashi, Keiji

Institution(s): HEPL, Stanford University

Abstract:

The active region AR11158 generated the first X-class flare of the current solar cycle as well as over a dozen CMEs over the course of a few days. Interestingly, most of these CMEs originated from a complex quadrupolar magnetic configuration on the eastern side rather than the center of the region where a major filament situated. A couple of pores emerged relatively late during the AR development but rapidly altered the magnetic connectivities, accumulating a large amount of electric current and free energy at the eruption site. HMI vector magnetograms and a non-linear force-free field extrapolation are used to explore the coronal field structures that favor the subsequent eruptions. AIA observation of the brightening flare loops and footpoint pairs provides further evidence for the interpretation.




Observation of Dynamic Features of Current Sheet Associated with 2010 August 18 Solar Flare

Author(s): Takasao, S. (1), Asai, A. (2) Isobe, H. (2), and Shibata, K. (1)

Institution(s): (1) Kwasan and Hida Obserbatories, Kyoto University, (2) Unit of Synergetic Studies for Space, Kyoto University

Abstract:

We report the simultaneous extreme-ultraviolet observation of magnetic reconnection inflow and outflow in a flare on 2010 August 18 observed by SDO/AIA. We found that during the rise phase of the flare, some plasma blobs appeared in a sheet structure above hot loops. The plasma blobs were ejected bidirectionally along the sheet structure (i.e. reconnection outflow). Simultaneously, bright threads visible in the extreme-ultraviolet images moved toward the sheet structure (i.e. reconnection inflow). Using the velocities of the inflow and outflow, we estimated the non-dimensional reconnection rate and found it varies during this period from 0.20 to 0.055. We also found that the plasma blobs in the sheet structure collided and possibly merged with each other before they were ejected from the sheet structure. From these observational results, we hypothesize that the sheet structure is the current sheet and that these plasma blobs are plasmoids or magnetic islands. This observational report could be important for understanding the dynamics of the reconnection region.




Using 3D MHD realistic simulations of the solar corona to test plasma diagnostics

Author(s): Testa, P (1), De Pontieu, B. (2), Martinez-Sykora, J. (2,3), Hansteen, V. (3), Carlsson, M. (3)

Institution(s): (1) Harvard-Smithsonian Center for Astrophysics; (2) LMSAL; (3) Univ. of Oslo

Abstract:

We synthesize coronal images and spectra from advanced 3D MHD simulations obtained from the state-of-the art Bifrost code, and explore how well they reproduce coronal observations with SDO/AIA and Hinode/EIS. We apply standard diagnostic techniques (e.g., density, and temperature diagnostics) to the synthetic observations and investigate how accurately the derived physical information matches the plasma parameters of the model. We discuss the limitations of the diagnostics and their implications.




The mass cycle between the chromosphere and the corona/solar wind

Author(s): Hui Tian

Institution(s): High Altitude Observatory, National Center for Atmospheric Research

Abstract:

The plasma is not static but flows almost everywhere above the chromosphere. EUV and FUV spectroscopy reveals a lot of information of these mass flows, and thus enhances our understanding of coronal heating and solar wind origin. Through a single Gaussian fit to line profiles, emission lines formed in the transition region (TR) are usually found to exhibit ubiquitous redshifts. While coronal lines show predominant blueshifts in coronal holes (CHs), quiet-Sun (QS) network boundaries and active region (AR) edges. However, careful scrutiny of the line profiles indicates that they are obviously enhanced in the blue wings, suggesting the presence of a secondary high-speed upflow component besides the primary component. Meanwhile, imaging observations of HINODE/SOT and SDO/AIA clearly reveal ubiquitous episodic high-speed outflows in the form of type-II chromospheric spicules and propagating coronal disturbances (PDs). It has been suggested that the secondary component is associated with the type-II spicules and PDs, although further detailed investigations are needed to reach a solid conclusion. Moreover, recent AIA observations reveal slow downflows in cool passbands, which may represent the cooling of the previously heated plasma and should be embedded in TR line profiles. These heating upflows and cooling downflows are natural results of the mass cycling between the chromosphere and corona/solar wind, and their different relative intensities at different temperatures are likely to be responsible for the well-known temperature dependence of TR Doppler shift. So far various double Gaussian fit algorithms and red-blue asymmetry analysis techniques have been applied to coronal line profiles to derive parameters of the upflow component. However, an unambiguous decomposition of different components are still not possible by using data acquired by current spectrographs. The IRIS instrument, with a very small instrumental width and high spectral, temporal and spatial resolutions, might be able to unambiguously decompose different emission components in this continuous mass cycling process.




Spectroscopic observations of coronal mass ejections, coronal dimming and EUV jets

Author(s): Hui Tian, Scott W. McIntosh

Institution(s): High Altitude Observatory, National Center for Atmospheric Research

Abstract:

Solar eruptions, particularly coronal mass ejections (CMEs) and extreme-ultraviolet (EUV) jets, have rarely been investigated with spectroscopic observations. We analyze several data sets obtained by the EUV Imaging Spectrometer onboard Hinode and find various types of flows during CMEs and jet eruptions. CME-induced dimming regions are found to be characterized by significant blueshift and enhanced line width by using a single Gaussian fit. While a red-blue (RB) asymmetry analysis and a RB-guided double Gaussian fit of the coronal line profiles indicate that these are likely caused by the superposition of a strong background emission component and a relatively weak (~10%) high-speed (~100 km s−1) upflow component. This finding suggests that the outflow velocity in the dimming region is probably of the order of 100 km s−1, not ~20 km s−1 as reported previously. Density and temperature diagnostics of the dimming region suggest that dimming is primarily an effect of density decrease rather than temperature change. The mass losses in dimming regions as estimated from different methods are roughly consistent with each other and they are 20%-60% of the masses of the associated CMEs. With the guide of RB asymmetry analysis, we also find several temperature-dependent outflows (speed increases with temperature) immediately outside the (deepest) dimming region. These outflows may be evaporation flows which are caused by the enhanced thermal conduction or nonthermal electron beams along reconnecting field lines, or induced by the interaction between the opened field lines in the dimming region and the closed loops in the surrounding plage region. In an erupted CME loop and an EUV jet, profiles of emission lines formed at coronal and transition region temperatures are found to exhibit two well-separated components, an almost stationary component accounting for the background emission and a highly blueshifted (~200 km s−1) component representing emission from the erupting material. The two components can easily be decomposed through a double Gaussian fit and we can diagnose the electron density, temperature and mass of the ejecta. Combining the speed of the blueshifted component and the projected speed of the erupting material derived from simultaneous imaging observations, we can calculate the real speed of the ejecta.




On the importance of Global Events in Destabilizations of the Solar Atmosphere

Author(s): Alan Title

Institution(s): Lockheed Martin Advanced Technology Center

Abstract:

A large segment of solar research has focused on structures that give rise to violent events- flares and coronal mass ejections (CME’s). This has placed emphasis on the development of active regions and filament channels with foci on energy build up and triggering. At the same time there have existed controversies about sympathetic flares, stealth CME’s, and whether there can be CME’s without flares. The operation of the Solar Dynamic Observatory, which collects full Sun line-of-sight and vector magnetograms field maps as well as full-Sun images in a range of wavelengths in the UV and EUV on a 12 second cadence 24/7, is now demonstrating that many violent solar events are connected. Recent simulations have suggested how the remote destabilizations occur. Maps of the Sun’s magnetic topology show both the paths and the bounds of some of the instabilities. It is clear that we are in early stages of understanding of some of probably many mechanisms for destabilization. It is also clear that an understanding of the consequences of magnetic topologies are now, and will in the future be, a rich research topic. Movies of solar events and corresponding simulations will be shown.




Constraints on coronal magnetic fields from observations of visible and IR emission lines

Author(s): Steven Tomczyk

Institution(s): HAO/NCAR

Abstract:

Information on the strength and direction of coronal magnetic fields can be obtained from the observation of the polarization of visible and IR emission lines. These observations are confined to the corona above the solar limb and integrated along the line-of-sight. A wealth of information is also available through the analysis of the waves that permeate the corona as observed in line-of-sight velocity measurements. I will present an overview of the strengths and weaknesses of techniques for extracting information on coronal magnetism from these sources, and present an assessment for future progress in this area.





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Last Updated on Tuesday, 24 January 2012 13:45