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Potential for diagnostics with IRIS and Mg II lines

Author(s): Tiago M. D. Pereira, Mats Carlsson, Jorrit Leenaarts, Han Uitenbroek, Bart De Pontieu, Juan Martinez-Sykora,

Institution(s): NASA/ARC, University of Oslo, National Solar Observatory, LMSAL

Abstract:

The IRIS mission will open up a new window into the solar chromosphere and transition region. An important diagnostic that IRIS will bring is the Mg II H and K lines. Radiation from these lines is believed to be come from a wide range of formation depths, from the higher photosphere to the onset of the transition region. With a complex formation mechanism, Mg II H and K suffer from departures from LTE and partial redistribution (PRD). In this preliminary analysis we will look into the potential for diagnostics of Mg II H and K. Using a new parallel version of the RH code we synthesised Mg II H and K spectra from 3D rMHD simulations of the solar atmosphere. We will discuss the relevance of several approximations on the final observables, and will compare the Mg II H and K filtergrams with those of Ca II H, a robust chromospheric diagnostic line widely used with Hinode/SOT/BFI.




Coronal hole boundaries and the slow solar wind from Hinode/EIS/XRT/SOT and SUMER/SoHO

Author(s): M. S. Madjarska, Zh. Huang, J. G. Doyle and S. Subramanian

Institution(s): Armagh Observatory

Abstract:

We present a statistical study on outflows at coronal hole boundaries and inside coronal holes and discuss their role in the slow solar wind formation in the low solar corona. The outflows are studied in XRT/Hinode image data taken with the Al_poly filter using an automatic identification method. A spectroscopic analysis is made using EIS and SUMER data of spectral lines with formation temperatures in the range from 10 000 K to 12 MK. The derived plasma parameters of about 60 phenomena will be reported. The longitudinal magnetic field data for each feature falling in the SOT/Hinode field-of-view (more than 25) are studied using a magnetic feature tracking procedure and a visual inspection. The mechanism of the outflow formation and acceleration will be discussed.




Non-Linear Force-Free Modeling of Solar Corona With The Aid of Coronal Loops

Author(s): A. Malanushenko, M. DeRosa, C. Schrijver, M. S. Wheatland, S. Gilchrist

Institution(s): MSU/LMSAL, LMSAL, Univ. of Sydney

Abstract:

Accurate models of the coronal magnetic field are vital for understanding and predicting solar activity and are therefore of the greatest interest for solar physics. As no reliable measurements of the coronal magnetic field exists at present, the problem of constructing field models is typically viewed as a boundary value problem. The construction of realistic field models requires knowledge of the full vector of magnetic field at the boundaries of the model domain; vector magnetograms are, however, measured in the non force-free photosphere and their horizontal components are subject to large uncertainties. Even if an uncertainty-free vector magnetogram at the top layer of the chromosphere was known, the problem remains an extremely challenging non-linear problem. There are various methods for pre-processing vector magnetograms and using them to construct models of the coronal field. The success of these models is often judged based on how close its field lines correspond to the observed coronal loops, which are believed to follow lines of the coronal magnetic field. At present, the correspondence between coronal loops and magnetic field lines of many models based on the vector magnetograms is far from perfect (DeRosa et. al., 2009). The estimates of free energy in the field as well as distribution of the magnetic currents through the volume could be dramatically different for different models used (Schrijver et. al., 2008). This testifies to the need of a completely new approach to this problem. We present such an approach and demonstrate its results based on AIA and HMI data. We have developed a way to use coronal loops as a constraint for magnetic modelling; the field is therefore constructed to match coronal loops. We found that when tested on known magnetic fields the new method is able to reproduce overall shape of the field lines, large-scale spatial distribution of the electric currents and measure up to 60% of the free energy stored in the field. This was achieved with as little as line-of-sight magnetogram and less than hundred of synthetic "loops", that is, lines of magnetic fields projected onto a plane of the sky. We found that line-of-sight HMI magnetograms and spatial resolution of the AIA instrument combined with the amount of filters available are more than sufficient for obtaining such data. We briefly describe this new method and demonstrate reconstructions of the coronal magnetic field obtained using AIA and HMI data. We evaluate how well it reproduces coronal features and how much energy and helicity estimates fluctuate with time for a stable non-flaring active region, thus establishing the reliability of the new method.




Importance of the partial ionization in the chromosphere using 2D radiative-MHD simulations

Author(s): Juan Martinez-Sykora, Bart De Pontieu, Viggo H. Hansteen

Institution(s): Lockheed Martin Solar and Astrophysics Lab.

Abstract:

The bulk of the solar chromosphere is weakly ionized and interactions between ionized particles and neutral particles will have significant consequences for the thermodynamics of the chromospheric plasma. We investigate the importance of introducing neutral particles into the MHD equations using numerical 2.5D radiative MHD simulations obtained with the Bifrost code. The models span the solar atmosphere from upper layers of the convection zone to the low corona, and solve the full MHD equations with non-grey and non-LTE radiative transfer and thermal conduction along the magnetic field. The effects of partial ionization are implemented using the generalized Ohm's law, i.e., we consider the effects of the Hall and ambipolar diffusion in the induction equation. The ohmic, Hall, and ambipolar diffusivities show variations of several orders of magnitude in the chromosphere. These strong variations of the various magnetic diffusivities are absent and significantly underestimated when using the semi-empirical VAL-C model as a basis for estimates. We find that in the chromosphere, the ambipolar diffusion is of the same order of magnitude or even larger than the numerical diffusion used to stabilize our code. As result of this, we can study the effects of it in the simulations. The ambipolar diffusion produces strong impact on the chromosphere changing the thermal properties, dynamics and magnetic field evolution.




Spectroscopic Diagnostics with IRIS

Author(s): H.E. Mason and G. Del Zanna

Institution(s): University of Cambridge

Abstract:

This talk will review the spectroscopic diagnostics available in the IRIS wavelength bands, built on the previous heritage of observations in the 1330-1410A wavelength band. Consideration will be given to the accuracy of available atomic data in CHIANTI and the relevant atomic processes. Ways in which the IRIS data could be used to complement observations from other observatories (SDO and Hinode) will be explored with a view to probing the energy transport and dissipation in the solar atmosphere.




Observational Evidence of Magnetic Waves in the Solar Atmosphere

Author(s): Scott W. McIntosh

Institution(s): HAO/NCAR

Abstract:

The observational evidence in supporting the presence of magnetic waves in the outer solar atmosphere is growing rapidly - we will discuss recent observations and place them in context with salient observations made in the past. While the clear delineation of these magnetic wave "modes" is unclear, much can be learned about the environment in which they originated and possibly how they are removed from the system from the observations. Their diagnostic power is, as yet, untapped and their energy content (both as a mechanical source for the heating of coronal material and acceleration of the solar wind) remains in question, but can be probed observationally - raising challenges for modeling efforts. We look forward to the IRIS mission by proposing some sample observing sequences to help resolve some of the zoological issues present in the literature.




Estimating the (Dark) Energy Content of the Solar Corona

Author(s): Scott W. McIntosh & Bart De Pontieu

Institution(s): HAO/NCAR & LMSAL

Abstract:

Exploiting the recent discovery of ubiquitous low-frequency (3-5mHz) Alfvénic waves in the solar chromosphere (with Hinode/SOT), and corona (with the ground-based CoMP and SDO/AIA) we report on the Alfvénic wave energy content of the corona using a blend of observational data and a simple forward model of Alfvénic wave propagation. We explore the apparent discrepancy in the resolved coronal Alfvénic wave amplitude (~0.5km/s) measure by CoMP compared to those of the Hinode and SDO near the limb (~20km/s).We see that the temporal invariance of the CoMP coronal non-thermal line widths ably capture the presence of the hidden, or dark, energy content in the corona. Exploiting the fact that the magnetic field permeating the corona is ubiquitously carrying Alfvénic motions of non-negligible amplitude we construct a simple model of wave propagation using the SOT and AIA measurements as strong constraints. This model reproduces the key spectroscopic measurements of the CoMP observations and allows us to place preliminary constraints on the impact of the coronal magnetic filling factor, the input wave spectrum, the dissipation on the wave motions observed, in addition to their energy content.




Global MHD Models of the Corona and Solar Wind

Author(s): Z. Mikic, J. A. Linker, R. Lionello, P. Riley, V. S. Titov, and T. Torok

Institution(s): Predictive Science, Inc.

Abstract:

Magnetohydrodynamic (MHD) models are useful in understanding the properties of the global solar corona. They typically use measured photospheric magnetic fields and an empirical specification of coronal heating. Comparisons of simulated EUV and X-ray emission from such models with observations (such as SOHO/EIT, Hinode/XRT, STEREO/EUVI, and SDO/AIA) can provide a tight constraint on coronal heating models. We will describe how these models can be used to improve our understanding of the process that heats the corona.




Magnetic flux emergence into the atmosphere: 3D numerical models.

Author(s): Fernando Moreno-Insertis

Institution(s): Instituto de Astrofisica de Canarias

Abstract:

The emergence of magnetic flux from the solar interior is one of the fundamental processes that shape the solar photosphere, chromosphere and corona. Taking place on a bewildering range of space- and timescales, it has defied detailed understanding for a long time, among other things due to insufficient observational and computing/modeling power. With the current golden age of solar space missions and with the advent of Petaflop massively parallel computing, the situation is quickly improving. Recent 3D numerical experiments are able to follow the emergence of small to intermediate bipolar regions from the topmost thousands of km below the surface into the low atmosphere and the corona. Some of those models include the simultaneous solution of the MHD and radiation transfer problems, with the divergence of the radiation flux then being used as entropy source in the plasma physics problem. In all cases, post-facto spectral synthesis based on the computed data permits comparison with observational data in the visible/IR, EUV and X-ray ranges. The interaction between theory and observation is thus reaching an excellent level and it must be strengthened for the benefit of future solar physics research. In this lecture, a review of recent modeling efforts of flux emergence processes will be provided. Although with a theoretical bias, the lecture will also provide results concerning the comparison with observations. A number of shortcomings of the current modeling capabilities will be discussed.




Observations from the HRTS-9 Rocket in the NUV Passband of the IRIS Mission

Author(s): Jeff Morrill (1) , Clarence Kornedyke (1) , Donald McMullin (2), Linton Floyd (3)

Institution(s): (1) Naval Research Laboratory, Washington DC 20375, (2) Space Systems Research Corp., Alexandra VA 22314, (3) Interferometrics, Chantilly, VA 20151

Abstract:

The HRTS-9 rocket flew in April 1995 and observed several solar surface features on the western solar disk. The HRTS-9 spectrograph was modified to observe a 180 A wide portion of the solar spectrum near MgII at 2800 A. Also, a slit-jaw camera observed a 400 x 900" region around the 960" long x 1" wide spectrograph slit in five passbands, specifically,1540A (Si I), 1550A ( C IV), 1560A ( C I), 1600A, and images of H-alpha. During the flight, the slit was pointed at various features including the quiet sun near disk center and the limb, active regions, and a sunspot. At the end of the flight, the pointing was fixed and a slit scanning mechanism was used to collect a series of spectra that span about 45". From this data set spectral images at specific wavelengths in the 2765 to 2885A range can be generated and compared to the broadband images at shorter wavelengths. For example, preliminary spectral images in the MgII k line show evidence of loop structures similar to those seen in C IV. Our previous efforts with this data set has focused on the impact these radiance observations near MgII have on solar spectral irradiance studies. These topics include examining the sources of solar irradiance variability, the center-to-limb variability of the quiet sun, and the relationship between the MgII intensity and the photospheric magnetic field. In light of the upcoming IRIS Explorer mission, we are turning our attention to those science goals in order to anticipate and support potential observations by the IRIS NUV spectrograph channel. In this presentation we present an overview of the available observations, previous results as well as discuss our ongoing analysis and preliminary spectral images of features in the region near MgII. Work sponsored by NASA.





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Last Updated on Tuesday, 24 January 2012 13:45