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A Code for Automated Tracing of Coronal Loops Approaching Visual Perception  

Markus J. Aschwanden   Submitted: 2009-10-21 15:45

Here we develop a new numeric code with automated pattern recognition, customized for tracing of coronal loops, which for the first time breaks even with the results of visual tracing. The used method is based on oriented-directivity tracing of curvi-linear features, but in contrast to other general pattern recognition algorithms, it is customized to solar EUV and SXR images by taking advantage of the specific property that coronal loops have large curvature radii compared with their widths. We evaluate the performance of this new code by comparing the cumulative distribution of loop lengths, the median and maximum loop lengths, the completeness of detection, and the congruency of the detected patterns with other numeric codes and visual tracings. We find that the new code closely approaches the results of visual perception and outperforms the other existing numeric codes. This algorithm is useful for the 3D reconstruction of the geometry, motion, and oscillations of coronal loops, with single or stereoscopic spacecraft, as well as for modeling of the loop hydrodynamics and the coronal magnetic field.

Authors: Markus J. Aschwanden
Projects: TRACE

Publication Status: Solar Physics, (subm. 2009 Oct 20)
Last Modified: 2009-10-22 02:04
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4D-Modeling of CME Expansion and EUV Dimming Observed with STEREO/EUVI  

Markus J. Aschwanden   Submitted: 2009-06-08 11:24

This is the first attempt to model the kinematics of a CME launch and the resulting EUV dimming quantitatively with a self-consistent model. Our 4D-model assumes self-similar expansion of a spherical CME geometry that consists of a CME front with density compression and a cavity with density rarefaction, satisfying mass conservation of the total CME and swept-up corona. The model contains 12 free parameters and is fitted to the 2008 March 25, 18:30 UT, CME event observed with STEREO/A and B. Our model is able reproduce the observed CME expansion and related EUV dimming during the initial phase from 18:30 UT to 19:00 UT. The CME kinematics can be characterized by a constant acceleration (i.e., a constant magnetic driving force). While the observations of EUVI/A are consistent with a spherical bubble geometry, we detect significant asymmetries and density inhomogeneities with EUVI/B. This new forward-modeling method demonstrates how the observed EUV dimming can be used to model physical parameters of the CME source region, the CME geometry, and CME kinematics.

Authors: Markus J. Aschwanden
Projects: STEREO

Publication Status: Annales Geophysicae (accepted 2009-Aug-13, in press)
Last Modified: 2009-08-13 08:38
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Solar Image Processing Techniques with Automated Feature Recognition (Invited Review)  

Markus J. Aschwanden   Submitted: 2009-05-26 08:56

We present a comprehensive and systematic overview of image processing techniques of solar data that use automated feature detection algorithms. We discuss the aspects of: (1) image pre-processing procedures; (2) automated detection of spatial features; (3) automated detection and tracking of temporal features (events); and (4) post-processing tasks, such as visualization of solar imagery, cataloguing, statistics, theoretical modeling, prediction and forecasting. For each aspect we highlight the most recent developments and science results. We conclude with an outlook on future trends.

Authors: Markus J. Aschwanden
Projects: TRACE

Publication Status: Solar Phyiscs, Special Issue: Solar Image Processing, (accepted 2009-Oct-20, in press)
Last Modified: 2009-10-22 14:09
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First Measurements of the Mass of Coronal Mass Ejections from the EUV Dimming Observed with STEREO EUVI A+B Spacecraft  

Markus J. Aschwanden   Submitted: 2009-04-03 17:21

The masses of Coronal Mass Ejections (CMEs) have traditionally been determined from white-light coronagraphs, based on the Thomson scattering of electrons, which depends on the (generally unknown) angle of the CME propagation direction. Here we develop a new method of measuring CME masses from the EUV dimming seen with EUV imaging telescopes in multiple temperature filters. As a test we investigate 8 CME events with previous mass determinations from STEREO/COR2, of which 5 cases are fully detected with EUVI, 2 partially, and 1 not, using an automated multi-wavelength detection code. We find CME masses in the range of m_CME = (2-7) x 10^15 g. The agreement between the two EUVI/A and B spacecraft is m_A/m_B =1.3 +/- 0.6 and the consistency with white-light measurements by COR2 is m_EUVI/m_COR2 = 1.1+/-0.3. The consistency between EUVI and COR2 implies no significant mass backflows (or inflows) at r < 4 R_sun and adequate temperature coverage for the bulk of the CME mass in the range of T = 0.5-3.0 MK. The temporal evolution of the EUV dimming allows us also to model the evolution of the CME density n_e(t), volume V(t), height-time h(t), and propagation speed v(t) in terms of an adiabatically expanding self-similar geometry. We determine e-folding EUV dimming times of 1.3+/-1.4 hr. We test the adiabatic expansion model in terms of the predicted detection delay (0.7 hr) between EUVI and COR2 for the fastest CME event (2008-Mar-25) and find good agreement with the observed delay ( 0.8 hr).

Authors: Aschwanden,M.J., Nitta,N.V., Wuelser,J.P., Lemen,J.R., Sandman,A., Vourlidas,A., Colaninno,R.C.
Projects: STEREO

Publication Status: ApJ, subm. 2009 Apr 3
Last Modified: 2009-04-04 09:20
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The 3D Geometry, 3D Motion, and Hydrodynamics of Oscillating Coronal Loops  

Markus J. Aschwanden   Submitted: 2009-01-31 12:19

We transition from two-dimensional (2D) imaging observations of kink-mode loop oscillations in the solar corona to three-dimensional (3D) reconstructions by exploring two new methods: (1) De-projection of 2D loop tracings using the strategy of curvature maximization in 3D space, based on the assumption of force-free magnetic fields; and (2) stereoscopic triangulation of epipolar loop coordinates using coaligned images from the STEREO EUVI/A and B spacecraft. Both methods reveal new features of oscillating loops: non-circularity, non-planarity, and helical geometries. We extend the 3D reconstruction techniques into the time domain and find indications of circularly polarized (torsional) kink-mode oscillations, in contrast to linearly polarized modes assumed previously. We discuss also hydrodynamic effects of coronal loops in non-equilibrium state that are essential for the detection and modeling of kink-mode oscillations.

Authors: Markus J. Aschwanden
Projects: STEREO

Publication Status: Space Science Reviews, Topical Issue on Coronal Seismology, (subm, Jan-31,2009)
Last Modified: 2009-02-01 10:17
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Hydrodynamic Modeling of Coronal Loops with Hinode and STEREO  

Markus J. Aschwanden   Submitted: 2009-01-08 16:54

The hydrodynamic evolution of impulsively-heated coronal loops and their subsequent cooling can now be modeled with multi-wavelength imaging instruments in soft X-ray (SXR) and extreme ultraviolet (EUV) wavelengths. Using analytical approximations to the hydrodynamic evolution of the density n(s,t) and temperature T(s,t) of an impulsively-heated loop (as a function of the loop length coordinate s and time t) we show an example how lightcurves observed with HINODE/XRT, EIS, GOES, and STEREO/EUVI can be modeled with a forward-fitting method in order to infer the maximum heating rate, the heating duration, and the cooling time of a heated loop during a small B1-class flare on 2007-Feb-01, previously analyzed by Warren et al. (2007).

Authors: Aschwanden M.J.
Projects: Hinode/EIS

Publication Status: Astronomical Society of the Pacific Conference Series, Beyond Discovery - Toward Understanding, Second Hinode Science Meeting, 29 Sept - 3 Oct 2008, Boulder, Colorado, USA, (eds. M.Cheung, B.Lites, T.Magara, J.Mariska, and K.Reeves), Vol ..., (subm., 2009 Jan 8)
Last Modified: 2009-01-09 09:37
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First 3D Reconstructions of Coronal Loops with the STEREO A+B Spacecraft: III. Instant Stereoscopic Tomography of Active Regions  

Markus J. Aschwanden   Submitted: 2008-12-17 15:15

Here we develop a novel 3D reconstruction method of the coronal plasma of an active region by combining stereoscopic triangulation of loops with density and temperature modeling of coronal loops with a filling factor equivalent to tomographic volume rendering. Because this method requires only a stereoscopic image pair in multiple temperature filters, which are sampled within $approx 1$ minute with the recent STEREO/EUVI instrument, this method is about 4 orders of magnitude faster than conventional solar rotation-based tomography. We reconstruct the 3D density and temperature distribution of active region NOAA 10955 by stereoscopic triangulation of 70 loops, which are used as a skeleton for a 3D field interpolation of some 7000 loop components, leading to a 3D model that reproduces the observed fluxes in each stereosocpic image pair with an accuracy of a few percent (of the average flux) in each pixel. With the stereoscopic tomography we infer also a differential emission measure (DEM) distribution over the entire temperature range of $Tapprox 10^4-10^7$, with predictions for the transition region and hotter corona in soft X-rays. The tomographic 3D model provides also large statistics of physical parameters. We find that the EUV loops with apex temperatures of $T_m lapprox 3.0$ MK tend to be super-hydrostatic, while hotter loops with $T_m approx 4-7$ MK are near-hydrostatic. The new 3D reconstruction model is fully independent of any magnetic field data and is promising for future tests of theoretical magnetic field models and coronal heating models.

Authors: Markus J. Aschwanden, Jean-Pierre Wuelser, Nariaki V. Nitta,
Projects: STEREO

Publication Status: ApJ 695 (2009 April 1 issue), on-line 12-29
Last Modified: 2009-03-30 12:37
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Solar Flare and CME Observations with STEREO/EUVI  

Markus J. Aschwanden   Submitted: 2008-12-04 09:26

STEREO/EUVI observed 185 flare events (detected above the GOES-class C1 level or at >25 keV with RHESSI) during the first two years of the mission (Dec 2006 - Nov 2008), while coronal mass ejections (CME) were reported in about a third of these events. We compile a comprehensive catalog of these EUVI-observed events, containing the peak fluxes in soft X-rays, hard X-rays, and EUV, as well as a classification and statistics of prominent EUV features: 79 % show impulsive EUV emission (coincident with hard X-rays), 73 % show delayed EUV emission from postflare loops and arcades, 24 % represent occulted flares, 17 % exhibit EUV dimming, 5 % show loop oscillations or propagating waves, and at least 3 % show erupting filaments. We analyze an example of each EUV feature by stereoscopic modeling of their 3D geometry. We find that impulsive EUV emission indicates compression of cold coronal plasma during the flare energy release, in contrast to the delayed postflare EUV emission that results from cooling of the soft X-ray emitting flare loops. Occulted flares allow us to determine CME-related coronal dimming uncontaminated from flare-related EUV emission. From modeling the time evolution of EUV dimming we can accurately quantify the initial expansion of CMEs and determine their masses. Further we find evidence that coronal loop oscillations are excited by the rapid initial expansion of CMEs. These examples demonstrate that stereoscopic EUV data provide powerful new methods to model the 3D aspects in the hydrodynamics of flares and kinematics of CMEs.

Authors: Aschwanden,M.J., Wuelser,J.P., Nitta,N.V., and Lemen,J.R.
Projects:

Publication Status: Solar Physics, Topical Issue on STEREO Results during the Solar Minimum, (subm. 2008 Dec 4; accepted 2009 Mar 27)
Last Modified: 2009-04-11 08:24
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Markus J. Aschwanden   Submitted: 2008-09-02 14:16

Coronal loops that exhibit kink-mode oscillations have generally been assumed to have a constant density and temperature during the observed time interval. Analyzing their intensities in an EUV waveband, however, clearly shows that their brightness varies in a way that is consistent with a temperature cooling through the EUV passband, which limits their detection time, observed damping time, and number of observable periods. We study kink-mode oscillations of eight loops observed during the so-called ``harmonica event'' on 2001-Apr-15, 21:58-22:27 UT in 171 ang . We find loop densities of $n_e=1.4pm0.6 imes 10^9$ cm$^{-3}$, loop widths of $w=2.0pm2.6$ Mm, and e-folding cooling times of $ au_{cool}=17pm7$ min, when they cool through the peak temperature $T=0.95$ MK of the 171 ang band. We conclude that oscillations of a single loop can not be detected longer than 10-20 min in one single filter and appropriate light curve modeling is necessary to disentangle the subsequent oscillation phases of multiple near-cospatial loops.

Authors: Markus J. Aschwanden and Jaume Terradas
Projects: TRACE

Publication Status: ApJ Lett. (accepted, Sept 1, 2008; in press)
Last Modified: 2008-09-03 07:49
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The Effect of Radiative Cooling on Coronal Loop Oscillations  

Markus J. Aschwanden   Submitted: 2008-09-02 14:16

Coronal loops that exhibit kink-mode oscillations have generally been assumed to have a constant density and temperature during the observed time interval. Analyzing their intensities in an EUV waveband, however, clearly shows that their brightness varies in a way that is consistent with a temperature cooling through the EUV passband, which limits their detection time, observed damping time, and number of observable periods. We study kink-mode oscillations of eight loops observed during the so-called ``harmonica event'' on 2001-Apr-15, 21:58-22:27 UT in 171 ang . We find loop densities of n_e=(1.4+/-0.6) x 10^9 cm^-3, loop widths of w=2.0 +/- 2.6 Mm, and e-folding cooling times of t_cool=17 +/- 7 min, when they cool through the peak temperature T=0.95 MK of the 171 A band. We conclude that oscillations of a single loop can not be detected longer than 10-20 min in one single filter and appropriate light curve modeling is necessary to disentangle the subsequent oscillation phases of multiple near-cospatial loops.

Authors: Markus J. Aschwanden and Jaume Terradas
Projects: TRACE

Publication Status: ApJ 686, L127-L130
Last Modified: 2008-12-02 09:30
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New Aspects on Particle Acceleration in Solar Flares from RHESSI Observations  

Markus J. Aschwanden   Submitted: 2008-05-16 17:16

In this review we highlight a number of recent RHESSI observations that are directly relevant to the study of particle acceleration processes in solar flares. Many observations confirm our basic standard models of acceleration in various types of coronal magnetic reconnection regions, but reveal a number of unexpected features that either require more detailed magnetic, hydrodynamic, and kinetic modeling or rethinking in terms of alternative models.

Authors: Markus J. Aschwanden
Projects: RHESSI

Publication Status: Asian Journal of Physics, Special Issue on Flare Phenomena, (ed. Rajmal Jain), subm. 16 may 2008
Last Modified: 2008-09-23 21:01
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Markus J. Aschwanden   Submitted: 2007-12-24 13:07

The physical state of coronal loops is often studied with scaling laws that are derived from an equilibrium solution of the energy balance equation, which equates heating to the losses by radiation and thermal conduction, such as the RTV law ($n_e propto T_{max}^2/L$), or the generalization by Serio. Recent analysis of EUV data in the temperature range of $Tapprox 1-2$ MK, however, exhibit an unexplained overpressure up to a few orders of magnitude compared with these stationary equilibrium models. In this Letter we show that this overpressure can naturally be explained by the non-stationary cooling process alone, in the absence of any heating, which has a scaling of $(n/n_p) approx (T/T_p)^{1/2}$ and even allows to determine the peak density $n_p$ and temperature $T_p lapprox T_{max}$ to which the loop was heated before onset of the cooling phase.

Authors: Markus J. Aschwanden
Projects: TRACE

Publication Status: ApJ Letter (subm., Dec 24, 2007)
Last Modified: 2007-12-25 08:38
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Markus J. Aschwanden   Submitted: 2007-12-24 13:07

The physical state of coronal loops is often studied with scaling laws that are derived from an equilibrium solution, where the heating rate balances the loss rates by radiation and thermal conduction. Recent analysis of EUV data at temperatures of $T_1 approx 1.0$ MK, however, exhibit huge overpressures (or overdensities) $q_1$ up to a few orders of magnitude for long loops, compared with stationary equilibrium models. This overpressure can naturally be explained by the non-stationary cooling process alone, in the absence of any heating, which follows approximately the {sl Jakimiec scaling} of $T(t) propto n(t)^2$. In this Letter we show that the observed overpressure $q_1=n_1/n_0$ (with respect to the RTV density $n_0 propto T_1^2/L$) can be used as a new diagnostic to determine the peak density, $n_p approx n_0 q_1^{4/3}$, and peak temperature, $T_p approx T_1 q_1^{2/3}$, to which the loop was heated before onset of the cooling phase. This new non-equlibirum scaling law provides soft X-ray predictions based on EUV observations.

Authors: Markus J. Aschwanden
Projects: TRACE

Publication Status: ApJ Letter (revised, Version 2008 jan 9)
Last Modified: 2008-01-09 12:10
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Markus J. Aschwanden   Submitted: 2007-12-24 13:06

The physical state of coronal loops is often studied with scaling laws that are derived from an equilibrium solution of the energy balance equation, which equates heating to the losses by radiation and thermal conduction, such as the RTV law ($n_e propto T_{max}^2/L$), or the generalization by Serio. Recent analysis of EUV data in the temperature range of $Tapprox 1-2$ MK, however, exhibit an unexplained overpressure up to a few orders of magnitude compared with these stationary equilibrium models. In this Letter we show that this overpressure can naturally be explained by the non-stationary cooling process alone, in the absence of any heating, which has a scaling of $(n/n_p) approx (T/T_p)^{1/2}$ and even allows to determine the peak density $n_p$ and temperature $T_p lapprox T_{max}$ to which the loop was heated before onset of the cooling phase.

Authors: Markus J. Aschwanden, Nariaki Nitta, Jean-Pierre Wuelser, and James Lemen
Projects: None

Publication Status: ApJ Letter (subm., Dec 24, 2007)
Last Modified: 2007-12-24 13:06
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Markus J. Aschwanden   Submitted: 2007-12-19 15:59

Using the stereoscopically derived 3D geometry of 30 loops observed with STEREO/EUVI (described in Paper I), we determine here the electron density profiles $n_e(s)$ and electron temperature profiles $T_e(s)$ from a triple-filter analysis of the stereoscopic images taken in the wavelengths of $lambda=$ 171, 195, and 284 ang . The statistical results of our analysis of 7 complete loops are: observed loop widths $w_{obs}=2.6pm 0.1$ Mm, corresponding to effective loop widths of $w=1.1pm0.3$ Mm if corrected for the instrumental point-spread function, loop flux ratios $f_{loop}/f_{total} = 0.11 pm 0.04$, mean loop (DEM peak) temperatures $T_p=1.1 pm 0.2$ MK, DEM temperature gaussian widths $sigma_{DEM}=0.35pm 0.04$ MK, temperature variations along loops $sigma_T/T_p=0.24 pm 0.05$, (resolution-corrected) loop base densities $n_e=(2.2 pm 0.5) imes 10^{9}$ cm$^{-3}$, loop lengths of $L=130 pm 67$ Mm, and all quantities are found to agree between STEREO/A and B within a few percent. The temperature profiles $T(s)$ along loops are found to be nearly constant, within the uncertainties of the background subtraction. The density profiles $n_e(s)$ are consistent with hydrostatic loops, $n_e(h)=n_{base} exp(-h/lambda_T)$, predicted by the temperature scale heights $lambda_T$, using the stereoscopically measured height profiles $h(s)$. The stereoscopic 3D reconstruction allows us for the first time to accurately measure the loop length $L$ and to test loop scaling laws. We find that the observations are not consistent with the RTV scaling law (based on a uniform heating function), but are more consistent with Serio's scaling (adapted for footpoint heating) with heating scale heights in the range of $s_H approx 5-10$ Mm, which corroborates earlier EIT and TRACE results.

Authors: Markus J. Aschwanden, Nariaki Nitta, Jean-Pierre Wuelser, and James Lemen
Projects: STEREO

Publication Status: ApJ (in press, accepted March 4, 2008)
Last Modified: 2008-03-04 14:49
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Markus J. Aschwanden   Submitted: 2007-12-19 15:59

Using the stereoscopically derived 3D geometry of 30 loops observed with STEREO/EUVI (described in Paper I), we determine here the electron density profiles $n_e(s)$ and electron temperature profiles $T_e(s)$ from a triple-filter analysis of the stereoscopic images taken in the wavelengths of $lambda=$ 171, 195, and 284 ang . The statistical results of our analysis of 7 complete loops are: observed loop widths $w_{obs}=2.6pm 0.1$ Mm, corresponding to effective loop widths of $w=1.1pm0.3$ Mm if corrected for the instrumental point-spread function, loop flux ratios $f_{loop}/f_{total} = 0.11 pm 0.04$, mean loop (DEM peak) temperatures $T_p=1.1 pm 0.2$ MK, DEM temperature gaussian widths $sigma_{DEM}=0.35pm 0.04$ MK, temperature variations along loops $sigma_T/T_p=0.24 pm 0.05$, (resolution-corrected) loop base densities $n_e=(2.2 pm 0.5) imes 10^{9}$ cm$^{-3}$, loop lengths of $L=130 pm 67$ Mm, and all quantities are found to agree between STEREO/A and B within a few percent. The temperature profiles $T(s)$ along loops are found to be nearly constant, within the uncertainties of the background subtraction. The density profiles $n_e(s)$ are consistent with the gravitational stratification of hydrostatic loops, $n_e(h)=n_{base} exp(-h/lambda_T)$, defined by the temperature scale heights $lambda_T$ and stereoscopically measured from the height profiles $h(s)$. The stereoscopic 3D reconstruction allows us for the first time to accurately measure the loop length $L$ and to test loop scaling laws. We find that the observations are not consistent with equilibrium solutions, but rather display the typical overpressures of loops that have been previously heated to higher temperatures and cool down in a non-equilibrium state, similarly to earlier EIT and TRACE measurements.

Authors: Markus J. Aschwanden, Nariaki Nitta, Jean-Pierre Wuelser, and James Lemen
Projects: STEREO

Publication Status: ApJ (in press, accepted March 4, 2008)
Last Modified: 2008-03-04 14:52
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Markus J. Aschwanden   Submitted: 2007-12-19 15:59

Using the stereoscopically derived 3D geometry of 30 loops observed with STEREO/EUVI (described in Paper I), we determine here the electron density profiles $n_e(s)$ and electron temperature profiles $T_e(s)$ from a triple-filter analysis of the stereoscopic images taken in the wavelengths of $lambda=$ 171, 195, and 284 ang . The inference of the density and temperature at a given loop position $s$ is defined by the background-subtracted loop cross-section profiles $f_{lambda,loop}(x) = f_{lambda,total}(x) - f_{lambda,back}(x)$ in perpendicular direction $x$ to the loop, which crucially depend on the definition of the background profiles $f_{lambda,back}(x)$, often amounting to $gapprox 90\%$ of the total flux. Since this crucial aspect is the main limitation in the accuracy of inferring temperature and density parameters and has been treated inappropriately in many previous studies, we investigate up to 10 different background-subtraction methods here and test their self-consistency from the dual stereoscopic line-of-sights. The statistical results of our analysis of 7 complete loops are: observed loop widths $w_{obs}=2.6pm 0.1$ Mm, corresponding to effective loop widths of $w=1.1pm0.3$ Mm if corrected for the instrumental point-spread function, loop flux ratios $f_{loop}/f_{total} = 0.11 pm 0.04$, mean loop (DEM peak) temperatures $T_p=1.1 pm 0.2$ MK, DEM temperature gaussian widths $sigma_{DEM}=0.35pm 0.04$ MK, temperature variations along loops $sigma_T/T_p=0.24 pm 0.05$, (resolution-corrected) loop base densities $n_e=(2.2 pm 0.5) imes 10^{9}$ cm$^{-3}$, loop lengths of $L=130 pm 67$ Mm, and all quantities are found to agree between STEREO/A and B within a few percent. The temperature profiles $T(s)$ along loops are found to be nearly constant, within the uncertainties of the background subtraction. The density profiles $n_e(s)$ are consistent with hydrostatic loops, $n_e(h)=n_{base} exp(-h/lambda_T)$, predicted by the temperature scale heights $lambda_T$, using the stereoscopically measured height profiles $h(s)$. The stereoscopic 3D reconstruction allows us for the first time to accurately measure the loop length $L$ and to test loop scaling laws. We find that the observations are not consistent with the RTV scaling law (based on a uniform heating function), but are more consistent with Serio's scaling (adapted for footpoint heating) with heating scale heights in the range of $s_H approx 5-10$ Mm, which corroborates earlier EIT and TRACE results.

Authors: Markus J. Aschwanden, Nariaki Nitta, Jean-Pierre Wuelser, and James Lemen
Projects: STEREO

Publication Status: ApJ (in press, accepted March 4, 2008)
Last Modified: 2008-03-04 14:48
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Markus J. Aschwanden   Submitted: 2007-11-01 09:16

We present the first triangulation and 3D reconstruction of coronal loops, using the EUVI telescopes of the two STEREO A and B spacecraft. This first triangulation of coronal loops is performed in an active region, observed with STEREO A and B on 2007 May 9 with a spacecraft separation angle of alpha_sep=7.3 deg, at a wavelength of 171 A . We identify 30 loop structures (7 complete loops and 23 partial segments) and compute their 3D coordinates [x, y, z], [the full 3D coordinates are available as an electronic file]. We quantify the height range, the stereoscopic height measurement errors, the loop plane inclination angles, and the coplanarity and circularity of the analyzed loops. The background of the active region shows also ``moss'' features, for which we determine a mean height of h_{moss} ~ 4 Mm. The knowledge of the exact 3D geometry of a loop with respect to the observers line-of-sight has important consequences for determining the correct vertical density scale height (used in hydrostatic models), the aspect angle of loop cross-sections (used in inferring electron densities from optically thin emission measures), the absolute flow speeds (used in siphon flow models), the correct loop length (used in loop scaling laws), as well as the 3D vectors of the coronal magnetic field (used in testing theoretical magnetic field extrapolation models). The hydrodynamic and magnetic modeling of the analyzed loops will be described in subsequent papers.

Authors: Markus J. Aschwanden, Jean-Pierre Wuelser, Nariaki Nitta, Jim Lemen
Projects: STEREO

Publication Status: ApJ (to be submitted), Version 2007 Nov 1
Last Modified: 2007-11-08 14:09
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Markus J. Aschwanden   Submitted: 2007-11-01 09:16

We present the first triangulation and 3D reconstruction of coronal loops, using the EUVI telescopes of the two STEREO A and B spacecraft. This first triangulation of coronal loops is performed in an active region, observed with STEREO A and B on 2007 May 9 with a spacecraft separation angle of alpha_sep=7.3 deg, at a wavelength of 171 A . We identify 30 loop structures (7 complete loops and 23 partial segments) and compute their 3D coordinates [x, y, z], [the full 3D coordinates are available as an electronic file]. We quantify the height range, the stereoscopic height measurement errors, the loop plane inclination angles, and the coplanarity and circularity of the analyzed loops. The background of the active region shows also ``moss'' features, for which we determine a mean height of h_{moss} ~ 4 Mm. The knowledge of the exact 3D geometry of a loop with respect to the observers line-of-sight has important consequences for determining the correct vertical density scale height (used in hydrostatic models), the aspect angle of loop cross-sections (used in inferring electron densities from optically thin emission measures), the absolute flow speeds (used in siphon flow models), the correct loop length (used in loop scaling laws), as well as the 3D vectors of the coronal magnetic field (used in testing theoretical magnetic field extrapolation models). The hydrodynamic and magnetic mo

Authors: Markus J. Aschwanden, Jean-Pierre Wuelser, Nariaki Nitta, Jim Lemen
Projects: STEREO

Publication Status: ApJ (to be submitted), Version 2007 Nov 1
Last Modified: 2007-11-01 19:49
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Markus J. Aschwanden   Submitted: 2007-11-01 09:15

We present the first triangulation and 3D reconstruction of coronal loops, using the EUVI telescopes of the two STEREO A and B spacecraft. This first triangulation of coronal loops is performed in an active region, observed with STEREO A and B on 2007 May 9 with a spacecraft separation angle of alpha_sep=7.3 deg, at a wavelength of 171 A . We identify 30 loop structures (7 complete loops and 23 partial segments) and compute their 3D coordinates [x, y, z], [the full 3D coordinates are available as an electronic file]. We quantify the height range, the stereoscopic height measurement errors, the loop plane inclination angles, and the coplanarity and circularity of the analyzed loops. The background of the active region shows also ``moss'' features, for which we determine a mean height of h_{moss} ~ 4 Mm. The knowledge of the exact 3D geometry of a loop with respect to the observers line-of-sight has important consequences for determining the correct vertical density scale height (used in hydrostatic models), the aspect angle of loop cross-sections (used in inferring electron densities from optically thin emission measures), the absolute flow speeds (used in siphon flow models), the correct loop length (used in loop scaling laws), as well as the 3D vectors of the coronal magnetic field (used in testing theoretical magnetic field extrapolation models). The hydrodynamic and magnetic mo

Authors: Markus J. Aschwanden, Jean-Pierre Wuelser, Nariaki Nitta, Jim Lemen
Projects: STEREO

Publication Status: ApJ (in preparation)
Last Modified: 2007-11-01 09:15
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Abstracts by Author
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