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George Fisher   Submitted: 2008-05-21 14:31

In Paper I, we introduced and tested a method for predicting solar active region coronal emissions using magnetic field measurements and a chosen heating relationship. Here, we apply this forward-modeling technique to 10 active regions observed with the Mees Solar Observatory Imaging Vector Magnetograph and the Yohkoh Soft X-ray Telescope. We produce synthetic images of each region using four parameterized heating relationships depending on magnetic field strength and geometry. We find a volumetric coronal heating rate (dEH/dV , not to be confused with dEH/dA quoted by some authors) proportional to magnetic field and inversely proportional to fieldline loop-length (BL-1) best matches observed coronal emission morphologies. This parameterization is most similar to the steady-state scaling of two proposed heating mechanisms: van Ballegooijen?s ?current layers? theory, taken in the AC limit, and Parker?s ?critical angle? mechanism, in the case where the angle of misalignment is a twist angle. Although this parameterization best matches the observations, it does not match well enough to make a definitive statement on the nature of coronal heating. Instead, we conclude that (1) the technique requires better magnetic field measurement and extrapolation techniques than currently available, and (2) forward-modeling methods that incorporate properties of transiently heated loops are necessary to make a more conclusive statement about coronal heating mechanisms.

Authors: Lundquist L. L., Fisher G. H., Metcalf T. R., Leka K. D., McTiernan J. M.
Projects: None

Publication Status: ApJ (accepted)
Last Modified: 2008-09-23 21:01
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George Fisher   Submitted: 2008-05-21 14:24

We present a method for simulating coronal emissions from solar active regions using observed photospheric magnetograms and an assumption about the coronal heating mechanism as input. The method invokes a ?quasi-force-free? (minimized Lorentz force) coronal magnetic solution and a steady-state energy balance model solved along fieldlines. Coronal heating is included using parameterized approximations relating the heat deposited to properties of the magnetic field. We use calculated temperatures and densities to predict emissions and compare to observations from the Yohkoh Soft X-ray satellite. We use NOAA active region 8210 to test the model?s sensitivities. We find predicted intensities and emission morphologies change little with different assumptions for the coronal magnetic field. We test methods for calculating the proportionality constant in a heating scale relationship and find filling factors of ∼ 1-5x10-2 are needed to match temperature in the cases considered. We investigate the effect of heating scale height, finding that loop-top heating improves temperature predictions but decreases success of the emission morphology prediction. Footpoint heating has the opposite effect. Overall, our model produces relatively robust results for a wide range of assumptions. Yet the results are highly sensitive to the input coronal heating parameterization, making our method a powerful approach for discriminating between heating mechanisms. Nevertheless, we find substantial discrepancies between our synthetic emissions and observed emissions. We investigate sources of discrepancy and suggest that improved magnetic field extrapolations and dynamic heating are necessary to improve simulations.

Authors: Lundquist L. L., Fisher G. H., McTiernan J. M.
Projects: None

Publication Status: ApJ Supplements (accepted)
Last Modified: 2008-09-23 21:01
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