I: Active-region Loops,
Mike Marsh & Aveek Sarkar (11)

Last Updated Fri Dec 5 16:24:42 2008

1: Markus J. Aschwanden (aschwanden@lmsal.com), Lockheed Martin, Solar & Astrophysics Lab. [E]
[soi] Title: Heating and Cooling of Coronal LoopsAbstract: The physical evolution of impulsively-heated coronal loops and their subsequent cooling is now explored in great detail, using multi-wavelength data in soft X-rays and EUV, in particular with HINODE/EIS, XRT, STEREO/EUVI, TRACE, and RHESSI. With stereoscopic triangulation we can reconstruct the 3D geometry of active regions with unprecedented detail, comprising up to 100,000 loops per active region, using the "Instant Stereoscopic Tomography of Active Region" (ISTAR) method. Using some newly developed analytical approximations of the density n(s,t) and temperature evolution T(s,t) of impulsively-heated coronal loops we are now able to reproduce the observed evolution of light curves in soft X-rays, hard X-rays, and EUV, and to quantify their non-equilibrium dynamics with a self-consistent model of their hydrodynamic evolution.
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2: Sofiane Bourouaine (bourouaine@mps.mpg.de), Max-Planck Institute for Solar System Research, Katlenburg-Lindau [I]
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[poster] We model a coronal loop as a bundle of seven separate strands or filaments. Each of the loop strands used in the model can independently be heated by Alfv\'{e}n/ion cyclotron waves via wave-particle interactions described by the quasi-linear treatment of the Vlasov equation. The Alfv\'{e}n waves are assumed to penetrate the strands from their footpoints with different energy inputs. As a result, different heating profiles occur within each strand, and this differential heating leads to a varying cross-field temperature in the total coronal loop. The simulated TRACE/SXT observation of this model loop implies flat temperatures, e.g., one from the 171:195 ratio and the other for the 171:284 ratio. We showed that, the flatness in the temperature profiles is a consequence of coronal loop consists of, filaments having approximate values of electron density and differenttemperatures distributed over an interval ranges between 0.8 MK (or less) to 1.5 MK (or more). This result can maintain even in case when the loop consists of small number of filaments that form a discrete loop structure. Therefore, the flat ratios often obtained in observed TRACE loops can be a signature that these loops are multithermal and have small cross-field density variation.
3: George Doschek (gdoschek@ssd5.nrl.navy.mil), Naval Research Laboratory [C]
[soi] I am interested in the physics of active region loops and am using EIS raster spectra to determine the physical conditions in the loops. My group is also pursuing this topic. I am in addition interested in sources of the solar wind in active regions and have recently published an ApJ paper on that topic, again based on EIS spectra.
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4: Mike Marsh (), University of Central Lancashire [I]
[soi] Interested in coronal loops from both modelling and observational perspectives.
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5: Helen Mason (hm11@damtp.cam.ac.uk), University of Cambridge [C]
[soi] The Cambridge (UK) group (Mason, Tripathi, Del Zanna and Chifor) has run a series of Hinode/EIS campaigns to study active regions. These have focused on determining the plasma parameters (electron density, EM, flows, filling factors) in active regions. Several data sets were obtained in the initial phase of Hinode operations. Analyses have been carried out on individual loops, the 'moss' regions at the foot points of hot loops, and of the micro-flaring activity in the core of active regions.
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6: Richard Nightingale (nightingale@lmsal.com), Lockheed Martin Solar & Astrophysics Lab. [F]
[soi] soi: I am interested in coronal loops, rotating sunspots, their inter-connection, and loop heating.
[poster] Title: High-Resolution Measurements of Electron Temperature, Density, and Width Profiles of 234 Coronal Loops in the Non-Equilibrium Cooling Phase [Authors: Markus J. Aschwanden & Richard W. Nightingale] Abstract: We measure the profiles of the electron temperature T_e(s), the electron density n_e(s), and loop widths w(s) of 234 coronal loops from triple-filter TRACE data. We model also the loop geometry with a semi-circular model in order to measure the unprojected full loop length L and the inclination angle theta of the loop plane to the vertical, which are both required to apply loop scaling laws and hydrodynamic models. The statistics of the measured loop parameters are: electron temperatures T_e = 1.18 ± 0.30 MK, electron densities n_e = 10^(9.0±0.2) cm^(-3), loop widths w = 1.44 ± 0.33 Mm, loop lengths L = 56 ± 47 Mm, fraction of detected loop lengths L_det/L = 0.67 ± 0.23, and loop inclination angles \theta = 22 ± 18 deg. From these parameters we determine the average overpressure of these loops with respect to the equilibrium RTV law, q = p/p_RTV and find that 86% of the loops exhibit an overpressure (up to q < 30), 9% an underpressure, and only about 5% are consistent with RTV. We interpret the observed overpressure as a natural consequence of the non-equilibrium cooling phase. Applying a non-equilibrium scaling law we predict that the loops were heated to soft X-ray temperatures up to T_e < 15 MK prior to their cooling to EUV wavelengths. For the loop lifetimes we find an approximate scaling of t_life ~ 10 (L/10 Mm)^2 min, with a median lifetime of 7 hours for our sample of TRACE loops. This study postulates a paradigm shift from equilibrium models to non-equilibrium models in the loop cooling phase, which is dominantly observed in EUV wavelengths.
7: Hardi Peter (peter@kis.uni-freiburg.de), Kiepenheuer Institut fur Sonnenphysik [H]
[soi] My main interest is in the structure, dynamics and heating of the corona. Naturally this implies I am most interested in the AR loops working group. What are these loops, how do they change, how do loops intact, and do loops keep their identity? Are rather simple 1D models adequate to understand them, and is a MHD-type description sufficient? Understanding the corona implies also to understand the chromosphere. I think it is still unclear how the corona and the chromosphere are interconnected. What role do dynamic chromospheric phenomena play for the corona. Is the corona a mere hot end of the chromosphere, the heating and dynamics of the corona only an imprint of the chromospheric activity? Or is the corona an object by its own, with a (not yet well) defined interface to the corona?
[poster] The structure and dynamics of a box in a stellar corona are be modeled employing a 3D MHD model for different levels of magnetic activity. In these models we account for the mass, momentum and energy balance including heat conduction and radiative losses. The heating is through current dissipation in the corona driven by photospheric motions (flux braiding). The models include a synthesis of EUV and X-ray emission to allow a direct comparison to observations with e.g. SUMER/SOHO or EIS/Hinode. Depending on the setup at the lower boundary, i.e. depending on the surface magnetic field, we obtain radically different coronae. In one case the corona look pretty much like the active region solar corona with long loops following the magnetic field (bLoops). If increase the complexity of the surface magnetic field, we find that we still see loop-like structures in EUV intensities, but these do not outline magnetic field lines. Instead these iLoops are a projection effect because the coronal emission originates from a corrugated surface. These iLoops, not outlining magnetic field lines, could be a good explanation for the numerous small loops seem above the network in the quiet Sun, and they might also be of importance in the coronae of more active, and presumably magnetically more complex, stars.
8: Aveek Sarkar (), University of Central Lancashire [I]
[soi] Interested in coronal loops from both modelling and observational perspectives.
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9: Ignacio Ugarte-Urra (iugarte@ssd5.nrl.navy.mil), Naval Research Laboratory [G]
[soi] I am interested in how coronal loops form and evolve. I have studied loop evolution using EIS and XRT on board Hinode. Lately, in this context, I have investigated the diagnostic capabilities of EIS slot imaging.
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10: Peter Young (peter.young.ctr.uk@nrl.navy.mil), GMU/NRL [G]
[soi] I am interested in the properties of different types of loop structures in active regions. I will present some results from the Hinode/EIS instrument, in particular the relation of velocity and line width to line intensity; temporal properties from high cadence sit-and-stare observations; and density results from a range of ions.
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11: Pia Zacharias (pia@kis.uni-freiburg.de), Kiepenheuer Institut fur Sonnenphysik, Freiburg, Germany [H]
[soi] I am a third year PhD student working on the spectral analysis of three-dimensional MHD models of the solar corona above an active region embedded in the network. Emission line intensities, Doppler shifts and line widths are synthesized from the simulation data to allow detailed comparison to observations. I am interested in the morphology and dynamics of loop-like structures in 3D. My work focuses among others on the formation and evolution of Doppler shifts synthesized from the MHD model and on how the observed structures relate to the magnetic field topology. Individual magnetic fieldlines are traced in the simulation box and their physical properties are analyzed on a statistical basis.
[poster] We study EUV emission line spectra derived from 3D MHD models of structures in the corona, in particular of an active region surrounded by a strong chromospheric network. The 3D MHD models account properly for the energy balance, especially for heat conduction and radiative losses. This allows us to reliably synthesize the profiles of EUV emission lines observable with current EUV spectrometers, e.g. SUMER/SOHO and EIS/Hinode. We investigate the temporal evolution of intensities and Doppler shifts of the EUV emission lines synthesized from these models. This is of major interest for the underlying mechanism of the heating of the solar corona, i.e. dissipation of currents in the corona driven by photospheric motions (flux braiding). In this numerical experiment we explore the effects of increased magnetic activity on the synthesized Doppler shifts. We predict maximum redshifts at higher temperatures than those found for the quiet Sun.

Second Choice

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