Isothermal Bias of the "Filter Ratio" Method for Observations of Multithermal Plasma

Weber, Mark; Schmelz, J. T.; DeLuca, E. E.; Roames, J. K.

doi:10.1086/499125

Cited by 40 publications

(36 citation statements)

References 19 publications

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“…When the temperature is between 0.8 and 1.5 MK as determined via the EM Loci method, the narrowband filter ratio is found to agree. However, in agreement with Weber et al (2005), the temperature is found to be 1.1Y1.4 MK for positions/times when the spectral data are not consistent with a single temperature. Often the peaks of the cross sections of the loops, as shown in Aschwanden & Nightingale (2005), are offset in the two passbands.…”

Section: Discussion Of the Resultssupporting

confidence: 72%

“…The TRACE observations received much attention as a result of the dramatically enhanced spatial and temporal capabilities compared to previous EUV and X-ray instruments (Schrijver et al 1999). However, in an effort to analyze the newfound wealth of data, inaccurate techniques were used to determine temperature and then infer density from the TRACE data, as pointed out by Martens et al (2002) and Weber et al (2005). This has led to much heated debate over the actual temperature and densities of coronal loops.…”

Section: Introductionmentioning

confidence: 99%

“…Several authors, including Lenz et al (1999), Aschwanden et al (2000), Testa et al (2002), Winebarger et al (2003), and numerous others, have relied solely on filter ratios to determine temperature along coronal loops. Martens et al (2002) and Weber et al (2005) both showed that this approach often results in an inaccurate measurement, since the isothermal assumption required for the filter ratio technique did not match the differential emission measure curves from spectroscopic observations of the EUV emission from active regions. When using filter ratios there is little opportunity for observations to show an inconsistency with the isothermal assumption.…”

Section: Introductionmentioning

confidence: 99%

“…This is certainly true when only two filters are available, as is often the case for TRACE. When more than two filters are available the additional constraint(s) can further restrict the temperature (see Weber et al 2005 for details).…”

Section: Introductionmentioning

confidence: 99%

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Active Region Loops: Temperature Measurements as a Function of Time from JointTRACEandSOHOCDS Observations

Cirtain

Zanna

DeLuca

et al. 2007

ApJ

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In this paper, we aim to quantitatively investigate the structure and time variation of quiescent active region loop structures. We coordinated a joint program of observations (JOP 146) using TRACE, to obtain high-cadence EUV images, and SOHO CDS, to obtain spectroscopic data. Loop intensities are used to determine temperature as a function of time for a single loop, taking full account of the background emission. In many locations, the emission measure loci are consistent with an isothermal structure. However, the results indicate significant changes in the loop temperature (between 1 and 2 MK) over the 6 hr observing period. It is possible that the loop structures are composed of multiple, independently heated strands with sizes less than the resolution of the imager and spectrometer.

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Section: Discussion Of the Resultssupporting

confidence: 72%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Active Region Loops: Temperature Measurements as a Function of Time from JointTRACEandSOHOCDS Observations

Cirtain

Zanna

DeLuca

et al. 2007

ApJ

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“…The effects of plasma multithermality are discussed in Reale et al (2007) and for TRACE in e.g. Weber et al (2005) and Schmelz et al (2007b). We return to the assumption of isothermal plasma in Sect.…”

Section: Temperature Diagnostic Using Cifrmentioning

confidence: 99%

Is it possible to model observed active region coronal emission simultaneously in EUV and X-ray filters?

Dudík

Dzifčáková

Karlický

et al. 2011

A&A

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Aims. We investigate the possibility of modeling the active region coronal emission in the EUV and X-ray filters using one, universal, steady heating function, tied to the properties of the magnetic field. Methods. We employ a simple, static model to compute the temperature and density distributions in the active region corona. The model allows us to explore a wide range of parameters of the heating function. The predicted EUV and X-ray emission in the filters of EIT/SOHO and XRT/Hinode are calculated and compared with observations. Using the combined improved filter-ratio (CIFR) method, a temperature diagnostic is employed to compare the modeled temperature structure of the active region with the temperature structure derived from the observations. Results. The global properties of the observations are most closely matched for heating functions scaling as B 0.7−0.8 0 /L 0.5 0 that depend on the spatially variable heating scale-length. The modeled X-ray emission originates from locations where large heating scale-lengths are found. However, the majority of the loops observed in the 171 and 195 filters can be modeled only by loops with very short heating scale-lengths. These loops are known to be thermally unstable. We are unable to find a model that both matches the observations in all EUV and X-ray filters, and contains only stable loops. As a result, although our model with a steady heating function can explain some of the emission properties of the 171 and 195 loops, it cannot explain their observed lifetimes. Thus, the model does not lead to a self-consistent solution. The performance of the CIFR method is evaluated and we find that the diagnosed temperature can be approximated with a geometric mean of the emission-measure weighted and maximum temperature along the line of sight. Conclusions. We conclude that if one universal heating function exists, it should be at least partially time-dependent.

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On Solving the Coronal Heating Problem

2006

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Abstract.The question of what heats the solar corona remains one of the most important problems in astrophysics. Finding a definitive solution involves a number of challenging steps, beginning with an identification of the energy source and ending with a prediction of observable quantities that can be compared directly with actual observations. Critical intermediate steps include realistic modeling of both the energy release process (the conversion of magnetic stress energy or wave energy into heat) and the response of the plasma to the heating. A variety of difficult issues must be addressed: highly disparate spatial scales, physical connections between the corona and lower atmosphere, complex microphysics, and variability and dynamics. Nearly all of the coronal heating mechanisms that have been proposed produce heating that is impulsive from the perspective of elemental magnetic flux strands. It is this perspective that must be adopted to understand how the plasma responds and radiates. In our opinion, the most promising explanation offered so far is Parker's idea of nanoflares occurring in magnetic fields that become tangled by turbulent convection. Exciting new developments include the identification of the "secondary instability" as the likely mechanism of energy release and the demonstration that impulsive heating in subresolution strands can explain certain observed properties of coronal loops that are otherwise very difficult to understand. Whatever the detailed mechanism of energy release, it is clear that some form of magnetic reconnection must be occurring at significant altitudes in the corona (above the magnetic carpet), so that the tangling does not increase indefinitely. This article outlines the key elements of a comprehensive strategy for solving the coronal heating problem and warns of obstacles that must be overcome along the way.

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Isothermal Bias of the "Filter Ratio" Method for Observations of Multithermal Plasma

Cited by 40 publications

References 19 publications

Active Region Loops: Temperature Measurements as a Function of Time from JointTRACEandSOHOCDS Observations

Active Region Loops: Temperature Measurements as a Function of Time from JointTRACEandSOHOCDS Observations

Is it possible to model observed active region coronal emission simultaneously in EUV and X-ray filters?

On Solving the Coronal Heating Problem

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