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Solar Atmosphere (solar + atmosphere)
Selected AbstractsA chromospheric dark-cored fibril in Ca II IR spectraASTRONOMISCHE NACHRICHTEN, Issue 6 2010C. Beck Abstract We investigate the thermodynamical and magnetic properties of a "dark-cored" fibril seen in the chromospheric Ca II IR line at 854.2 nm to determine the physical process behind its appearance. We analyse a time series of spectropolarimetric observations obtained in the Ca II IR line at 854.2 nm and the photospheric Fe I line at 630.25 nm. We simultaneously invert the spectra in both wavelength ranges with the SIR code to obtain the temperature and velocity stratification with height in the solar atmosphere and the magnetic field properties in the photosphere. The structure can be clearly traced in the line-of-sight (LOS) velocity and the temperature maps. It connects from a small pore with kG fields to a region with lower field strength. The flow velocity and the temperature indicate that the height of the structure increases with increasing distance from the inner footpoint. The Stokes V signal of 854.2 nm shows a Doppler-shifted polarization signal with the same displacement as in the intensity profile, indicating that the supersonic flow seen in the LOS velocity is located within magnetized plasma. We conclude that the chromospheric dark-cored fibril traces a siphon flow along magnetic field lines, driven by the gas pressure difference caused by the higher magnetic field strength at the inner footpoint. We suggest that fast flows guided by the magnetic field lead to the appearance of "dark-cored" fibrils in intensity images. Although the observations included the determination of the polarization signal in the chromospheric Ca II IR line, the signal could not be analysed quantitatively due to the low S/N. Chromospheric polarimetry will thus require telescopes of larger aperture able to collect a sufficient number of photons for a reliable determination of polarization in deep and only weakly polarized spectral lines (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The origin of cutoff frequencies for torsional tube waves propagating in the solar atmosphereASTRONOMISCHE NACHRICHTEN, Issue 6 2010R. Hammer Abstract Torsional waves supported by magnetic flux tubes have long been thought to bear a high potential for supplying energy and momentum to the upper solar atmosphere, thereby contributing to its heating and to the driving of dynamic events like spicules. This hope rested on the belief that their propagation is not impeded by cutoff restrictions, unlike longitudinal and kink waves. We point out that this applies only to thin, isothermal tubes. When they widen in the chromosphere, and as a result of temperature gradients, cutoff restrictions arise. We compare them to recent observational reports of such waves and of vortex motions and find that their long period components are already affected by cutoff restrictions. An observational strategy is proposed that should permit the derivation of better information on vortex flows from off-center observations with next generation telescopes (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Advanced Technology Solar Telescope: A status reportASTRONOMISCHE NACHRICHTEN, Issue 6 2010S.L. Keil Abstract Magnetic fields control the inconstant Sun. The key to understanding solar variability and its direct impact on the Earth rests with understanding all aspects of these magnetic fields. The Advanced Technology Solar Telescope (ATST) has been design specifically for magnetic remote sensing. Its collecting area, spatial resolution, scattered light, polarization properties, and wavelength performance all insure ATST will be able to observe magnetic fields at all heights in the solar atmosphere from photosphere to corona. After several years of design efforts, ATST has been approved by the U.S. National Science Foundation to begin construction with a not to exceed cost cap of approximately $298M. Work packages for major telescope components will be released for bid over the next several months. An application for a building permit has been submitted (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Instrument and data analysis challenges for imaging spectropolarimetryASTRONOMISCHE NACHRICHTEN, Issue 6 2010C. Denker Abstract The next generation of solar telescopes will enable us to resolve the fundamental scales of the solar atmosphere, i.e., the pressure scale height and the photon mean free path. High-resolution observations of small-scale structures with sizes down to 50 km require complex post-focus instruments, which employ adaptive optics (AO) and benefit from advanced image restoration techniques. The GREGOR Fabry-Pérot Interferometer (GFPI) will serve as an example of such an instrument to illustrate the challenges that are to be expected in instrumentation and data analysis with the next generation of solar telescopes (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] On the observation of traveling acoustic waves in the solar atmosphere using a magneto-optical filterASTRONOMISCHE NACHRICHTEN, Issue 3-4 2007M. Haberreiter Abstract In contrast to low-frequency waves that are trapped in the cavity of the Sun, high-frequency waves can travel freely in the solar atmosphere. By modelling the observed intensity signal in the red and blue wings of K I 7699 Å and Na I 5890 Å, we aim to better understand the measurements carried out with the Magneto-Optical Filter at Two Heights (MOTH) experiment. We model the observed intensity signal with radiative transfer calculations carried out with the COde for Solar Irradiance (COSI). Furthermore, we derive the formation height of the lines in order to analyze to what extent the contribution functions are modulated by the acoustic waves. We find a phase lag between the red and blue filter for acoustic waves with a frequency above ,7 mHz and conclude that a frequency dependent data analysis is required for higher frequencies. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Short-period waves in the solar atmosphereASTRONOMISCHE NACHRICHTEN, Issue 4 2003M. Wunnenberg No abstract is available for this article. [source] Magnetic reconnection in the solar atmosphere: from proposal to paradigmASTRONOMY & GEOPHYSICS, Issue 3 2010Peter Cargill Meeting report On 13 November 2009, the RAS hosted a discussion meeting to commemorate the formal retirement of Prof. Eric Priest. Here Peter Cargill, Clare Parnell, Philippa Browning, Ineke de Moortel and Alan Hood examine how magnetic reconnection has evolved over the past 50 years from an important but controversial proposal, to a general paradigm. [source] | ||||||||||