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3D-Stereoscopic Analysis of Solar Active Region Loops: View all abstracts by submitter

Markus J Aschwanden   Submitted: 2000-01-25 14:02

In this paper we study the three-dimensional (3D) structure of hot (Teapprox 1.5-2.5 MK) loops in solar active region NOAA 7986, observed on 1996 August 30 with the {sl Extreme-ultraviolet Imaging Telescope (EIT)} onboard the {sl Solar and Heliospheric Observatory (SoHO)}. This complements a first study (Paper I) on cooler (Teapprox 1.0-1.5 MK) loops of the same active region, using the same method of {sl Dynamic Stereoscopy} to reconstruct the 3D geometry. We reconstruct the 3D-coordinates x(s), y(s), z(s), the density n_e(s), and temperature profile Te(s) of 35 individual loop segments (as a function of the loop coordinate s) using EIT 195 ang and 284 ang images. The major findings are: (1) All loops are found to be in hydrostatic equilibrium, in the entire temperature regime of Te=1.0-2.5 MK; (2) The analyzed loops have a height of 2-3 scale heights, and thus only segments extending over about one vertical scale height have sufficient emission measure contrast for detection; (3) The temperature gradient over the lowest scale height is of order dT/dsapprox 1-10 K/km; (4) The radiative loss rate is found to exceed the conductive loss rate by about two orders or magnitude in the coronal loop segments, implying that the loops cannot be in quasistatic equilibrium, since standard steady-state loop models show that radiative and conductive losses are comparable; (5) A steady-state could only be maintained if the heating rate EH matches exactly the radiative loss rate in hydrostatic equilibrium, requiring a heat deposition length {lambda}_H of the half density scale height lambda. (6) We find a correlation of p propto L-1 between loop base pressure and loop length, which is not consistent with the scaling law predicted from steady-state models of large-scale loops. - All observational findings indicate consistently that the energy balance of the observed EUV loops cannot be described by steady-state models.

Authors: Aschwanden,M.J., Alexander,D., Hurlburt,N., Newmark,J.S.,Neupert,W.M., Klimchuk,J.A., and G.A.Gary

Publication Status: 1999, ApJ 515, 842-867
Last Modified: 2000-08-31 08:27
Go to main E-Print page  Quadrupolar Magnetic Reconnection in Solar Flares: I. 3D Geometry inferred from Yohkoh Observations
  Exact Solutions for Reconnective Magnetic Annihilation
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