SOT: vector magnetic field measurements in the photosphere and clues to the field orientation in the chromosphere.
XRT: high resolution images showing coronal field geometry at all coronal temperatures
EIS: morphology and temperature of all visible structures within the active region
We would like to request the observations for a Hinode active region coordination demonstration. In addition, this HOP will obtain valuable data for a test of another sort, namely non-linear force-free field extrapolation to produce credible coronal vector magnetic field estimates from Hinode observations.
Hopeful of increasing frequency of active region targets, we request a short observation to demonstrate coordination between instruments for the upcoming increase in cycle 24 active region targets. This observation has ONE goal: demonstrate the Hinode observatory will produce a scientifically useful dataset that incorporates the power of each instrument for these highly valuable targets of opportunity. This dataset will be used for another evaluation non-linear force-free field extrapolations of coronal fields. This was requested by the NLFF group led by Karel Schrijver at LMSAL. Recent results of the NLFF group using Hinode data can be found in http://arxiv.org/abs/0902.1007. An excerpt from the abstract of that paper follows.
“Nonlinear force-free field (NLFFF) models are thought to be viable tools for investigating the structure, dynamics and evolution of the coronae of solar active regions. In a series of NLFFF modeling studies, we have found that NLFFF models are successful in application to analytic test cases, and relatively successful when applied to numerically constructed Sun-like test cases, but they are less successful in application to real solar data. Different NLFFF models have been found to have markedly different field line configurations and to provide widely varying estimates of the magnetic free energy in the coronal volume, when applied to solar data. NLFFF models require consistent, force- free vector magnetic boundary data. However, vector magnetogram observations sampling the photosphere, which is dynamic and contains significant Lorentz and buoyancy forces, do not satisfy this requirement, thus creating several major problems for force-free coronal modeling efforts. In this article, we discuss NLFFF modeling of NOAA Active Region 10953 using Hinode/SOT-SP, Hinode/XRT, STEREO/SECCHI-EUVI, and SOHO/MDI observations, and in the process illustrate the three such issues we judge to be critical to the success of NLFFF modeling: (1) vector magnetic field data covering larger areas are needed so that more electric currents associated with the full active regions of interest are measured, (2) the modeling algorithms need a way to accommodate the various uncertainties in the boundary data, and (3) a more realistic physical model is needed to approximate the photosphere-to-corona interface in order to better transform the forced photospheric magnetograms into adequate approximations of nearly force-free fields at the base of the corona.”
A small to medium-sized AR close to central meridian is the requested target. It must have sunspots and must not be evolving very rapidly when observed. Since the NLFF extrapolations require vector measurements of the boundary conditions at every position where field lines from the AR intersect the solar surface, large area coverage is needed. In addition, since the fields in the photosphere are not completely force-free, any additional observations we can collect to indicate the chromospheric field directions are needed, such as H-alpha images. XRT and EIS images are needed to show the loop geometry in the corona for comparison with the extrapolations. TRACE and STEREO EUVI images will also be used if available.
The HOP 100 science team will work together to calibrate, combine and analyze the data. We will provide the Level 2 measurements, internally coaligned, to the NLFF team and anyone else interested within 2 months of collection of a satisfactory observation. |
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