Relation between Thermal and Magnetic Properties of Active Regions as a Probe of Coronal Heating Mechanisms

Yashiro, S.; Shibata, Kazunari

doi:10.1086/319486

Cited by 29 publications

(35 citation statements)

References 23 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…It is also lower than the index of 1.0 obtained by Schrijver & Aschwanden (2002) from simulations of solar and stellar soft X-ray emission, and the index of 0.9 obtained by Yashiro & Shibata (2001) based on data from the Yohkoh Soft X-ray Telescope. The difference between the result of this paper and the global analysis of Fludra & Ireland (2008) of the same O V spectral line can be explained by the fact that the global analysis does not separate the time variable and quasi-static heating.…”

Section: Coronal Heatingcontrasting

confidence: 65%

Radiative and magnetic properties of solar active regions

Fludra

Warren

2010

A&A

View full text Add to dashboard Cite

Context. Global relationships between the photospheric magnetic flux and the extreme ultraviolet emission integrated over active region area have been studied in a previous paper by Fludra & Ireland (2008, A&A, 483, 609). Spatially integrated EUV line intensities are tightly correlated with the total unsigned magnetic flux, and yet these global power laws have been shown to be insufficient for accurately determining the coronal heating mechanism owing to the mathematical ill-conditioning of the inverse problem. Aims. Our aim is to establish a relationship between the EUV line intensities and the photospheric magnetic flux density on small spatial scales in active regions and investigate whether it provides a way of identifying the process that heats the coronal loops. Methods. We compare spatially resolved EUV transition region emission and the photospheric magnetic flux density. This analysis is based on the O V 62.97 nm line recorded by the SOHO Coronal Diagnostic Spectrometer (CDS) and SOHO MDI magnetograms for six solar active regions. The magnetic flux density φ is converted to a simulated O V intensity using a model relationship I(φ, L) = Cφ δ L λ , where the loop length L is obtained from potential magnetic field extrapolations. This simulated spatial distribution of O V intensities is convolved with the CDS instrument's point spread function and compared pixel by pixel with the observed O V line intensity. Parameters δ and λ are derived to give the best fit for the observed and simulated intensities. Results. Spatially-resolved analysis of the transition region emission reveals the complex nature of the heating processes in active regions. In some active regions, particularly large, local intensity enhancements up to a factor of five are present. When areas with O V intensities above 3000 erg cm −2 s −1 sr −1 are ignored, a power law has been fitted to the relationship between the local O V line intensity and the photospheric magnetic flux density in each active region. The average power index δ from all regions is 0.4 ± 0.1 and λ = −0.15 ± 0.07. However, the scatter of intensities in all regions is significantly greater than ±3σ from the fitted model. We therefore determine for the first time an empirical lower boundary for the I OV − φ relationship that is the same for five active regions. We postulate that it represents a basal heating. Because this boundary is present in the spatially-resolved data, this is compelling proof that the magnetic field is one of the major factors contributing to the basal component of the heating of the coronal plasma. We discuss the implications for the diagnostics of the coronal heating mechanism.

show abstract

Section: Coronal Heatingcontrasting

confidence: 65%

Radiative and magnetic properties of solar active regions

Fludra

Warren

2010

A&A

View full text Add to dashboard Cite

show abstract

“…Pres & Phillips (1999) showed how a temporal evolution of the total Fe XII 195 Å flux in SOHO-EIT of a coronal bright point matches that of the total magnetic flux. Yashiro & Shibata (2001) analysed soft X-ray emission from the Yohkoh SXT telescope, refining the analysis of Golub et al (1980) to derive the dependence of the thermal energy and pressure on Φ and B, respectively. Fludra et al (2002) presented for the first time relationships between the EUV spectral lines from the SOHO Coronal Diagnostic Spectrometer and the magnetic flux in active regions.…”

Section: Introductionmentioning

confidence: 99%

Radiative and magnetic properties of solar active regions

Fludra¹,

Ireland²

2008

A&A

View full text Add to dashboard Cite

Context. The relationships between the photospheric magnetic flux and either the X-ray or extreme ultraviolet emission from the solar atmosphere have been studied by several authors. Power-law relations have been found between the total magnetic flux and X-ray flux or intensities of the chromospheric, transition region, and coronal emission lines in solar active regions. These relations were then used to infer the mechanism of the coronal heating. Aims. We derive accurate power laws between EUV line intensities and the total magnetic flux in solar active regions and discuss their applications. We examine whether these global power laws are capable of providing the diagnostics of the coronal heating mechanism.Methods. This analysis is based on EUV lines recorded by the Coronal Diagnostic Spectrometer (CDS) on SOHO for 48 solar active regions, as they crossed the central meridian in years 1996-1998. Four spectral lines are used: He I 584.3 Å (3 × 10 4 K), O V 629.7 Å (2.2 × 10 5 K), Mg IX 368.06 Å (9.5 × 10 5 K), and Fe XVI 360.76 Å (2.0 × 10 6 K). In particular, the Fe XVI 360.76 Å line, seen only in areas of enhanced heating in active regions or bright points, has not been used before for this analysis. Results. Empirical power laws are established between the total active region intensity in the lines listed above and the total magnetic flux. We demonstrate the usefulness of some spatially integrated EUV line intensities, I T , as a proxy for the total magnetic flux, Φ, in active regions. We point out the approximate, empirical nature of the I T − Φ relationships and discuss the interpretation of the global power index. Different power index values for transition region and coronal lines are explained by their different dependence on pressure under the assumption of hydrostatic loop models. However, the global power laws are dominated by the size of the active regions, and we demonstrate for the first time the difficulties in uniquely relating the power index in the global I T − Φ relationship to the power index for individual loops and comment on results obtained by other authors. We caution against using global power laws to infer the coronal heating mechanism without a detailed knowledge of the distributions of the magnetic flux densities and instrumental response as a function of temperature. Despite these uncertainties, we show that the intensities of the transition region lines in individual loops depend on the photospheric magnetic flux density, φ, through I tr ∝ φ δt , δ t < 1, and the coronal line Fe XVI, I Fe ∝ φ δc , δ c > 1, and under the assumption of hydrostatic loops we can place a constraint on the coronal heating models, obtaining the volumetric heating rate, E H (erg cm −3 s −1 ), E H ∝ φ γ , where 0.6 < γ < 1.1.

show abstract

“…Several authors (Rosner, Tucker, & Vaiana 1978;Serio et al 1981;Golub et al 1980;Porter & Klimchuk 1995;Kano & Tsuneta 1995;Aschwanden et al 2000;Yashiro & Shibata 2001) have determined how coronal plasma parameters (temperature or pressure) depend on the loop length or magnetic field strength in active regions (ARs). The aim has generally been to combine the observations with theoretical scaling laws from quasi-steady loop models to test the validity of these models or derive scaling laws for the heating rate and thereby constrain coronal heating theories.…”

Section: Introductionmentioning

confidence: 99%

The Long‐Term Evolution of AR 7978: The Scalings of the Coronal Plasma Parameters with the Mean Photospheric Magnetic Field

Driel-Gesztelyi

Démoulin

Mandrini

et al. 2003

ApJ

View full text Add to dashboard Cite

We analyze the evolution of the fluxes observed in X-rays and correlate them with the magnetic flux density in active region (AR) NOAA 7978 from its birth throughout its decay, for five solar rotations. We use Solar and Heliospheric Observatory Michelson Doppler Imager (MDI) data, together with Yohkoh Soft X-Ray Telescope (SXT) and Yohkoh Bragg Crystal Spectrometer (BCS) data, to determine the global evolution of the temperature and the emission measure of the coronal plasma at times when no significant brightenings were observed. We show that the mean X-ray flux and derived parameters, temperature and emission measure (together with other quantities deduced from them, such as the density and the pressure), of the plasma in the AR follow power-law relationships with the mean magnetic flux density ( " B B). The exponents (b) of these power-law functions (a " B B b ) are derived using two different statistical methods, a classical least-squares method in log-log plots and a nonparametric method, which takes into account the fact that errors in the data may not be normally distributed. Both methods give similar exponents, within error bars, for the mean temperature and for both instruments (SXT and BCS); in particular, b stays in the range [0.27, 0.31] and [0.24, 0.57] for full-resolution SXT images and BCS data, respectively. For the emission measure, the exponent b lies in the range [0.85, 1.35] and [0.45, 1.96] for SXT and BCS, respectively. The determination of such power-law relations, when combined with the results from coronal heating models, can provide us with powerful tools for determining the mechanism responsible for the existence of the high-temperature corona.

show abstract

Relation between Thermal and Magnetic Properties of Active Regions as a Probe of Coronal Heating Mechanisms

Cited by 29 publications

References 23 publications

Radiative and magnetic properties of solar active regions

Radiative and magnetic properties of solar active regions

Radiative and magnetic properties of solar active regions

The Long‐Term Evolution of AR 7978: The Scalings of the Coronal Plasma Parameters with the Mean Photospheric Magnetic Field

Contact Info

Product

Resources

About