The intensity contrast of solar photospheric faculae and network elements

Ortiz, A.; Domingo, V.

doi:10.1051/0004-6361:20053869

Cited by 22 publications

(76 citation statements)

References 42 publications

(46 reference statements)

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“…Firstly, this is the only strong evidence for a dependence of local properties of the magnetic features on the global cycle. E.g., the facular contrast does not depend on solar cycle phase (Ortiz et al 2006). Secondly, such a confirmation appears timely in the light of the recent paper by Norton & Gilman (2004), who reported a smooth decrease in umbral brightness from early to mid phase in solar cycle 23, reaching a minimum intensity around solar maximum, after which the umbral brightness increased again, based on the analysis of more than 650 sunspots observed with the MDI instrument.…”

Section: Introductionmentioning

confidence: 51%

Properties of sunspots in cycle 23

Mathew

Pillet²,

Solanki

et al. 2007

A&A

100

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Aims. In this paper we investigate the dependence of umbral core brightness, as well as the mean umbral and penumbral brightness on the phase of the solar cycle and on the size of the sunspot. Methods. Albregtsen & Maltby (1978, Nature, 274, 41) reported an increase in umbral core brightness from the early to the late phase of solar cycle from the analysis of 13 sunspots which cover solar cycles 20 and 21. Here we revisit this topic by analysing continuum images of more than 160 sunspots observed by the MDI instrument on board the SOHO spacecraft for the period between 1998 March to 2004 March, i.e. a sizable part of solar cycle 23. The advantage of this data set is its homogeneity, with no seeing fluctuations. A careful stray light correction, which is validated using the Mercury transit of 7th May, 2003, is carried out before the umbral and penumbral intensities are determined. The influence of the Zeeman splitting of the nearby Ni I spectral line on the measured "continuum" intensity is also taken into account. Results. We did not observe any significant variation in umbral core, mean umbral and mean penumbral intensities with solar cycle, which is in contrast to earlier findings for the umbral core intensity. We do find a strong and clear dependence of the umbral brightness on sunspot size, however. The penumbral brightness also displays a weak dependence. The brightness-radius relationship has numerous implications, some of which, such as those for the energy transport in umbrae, are pointed out.

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Section: Introductionmentioning

confidence: 51%

Properties of sunspots in cycle 23

Mathew

Pillet²,

Solanki

et al. 2007

A&A

100

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“…We find that at low magnetic flux the contrast first decreases with increasing flux before it starts increasing at higher average field strength (see Sect. 4), which is not observed at lower resolution (e.g., Ortiz et al 2006). The initial decrease is due to the fact that the magnetic field has a tendency to live in intergranular lanes.…”

Section: Modeling Magnetic Brightening In the Quiet Sunmentioning

confidence: 88%

“…3.2) requires the inclusion of a field component that does not contribute to brightness. At lower resolution, such as the MDI observations used by Ortiz et al (2006), the fishhook feature becomes too indistinct to be used in this way.…”

Section: Intrinsically Weak Magnetic Fieldsmentioning

confidence: 99%

The brightness of magnetic field concentrations in the quiet Sun

Schnerr

Spruit

2011

A&A

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In addition to the "facular" brightening of active regions, the quiet Sun also contains a small scale magnetic field with associated brightenings in continuum radiation. We measure this contribution of quiet regions to the Sun's brightness from high spatial resolution (0 . 16-0 . 32) observations of the Swedish 1-m Solar Telescope (SST) and Hinode satellite. The line-of-sight magnetic field and continuum intensity near Fe i 6302.5 Å are used to quantify the correlation between field strength and brightness. The data show that magnetic flux density contains a significant amount of intrinsically weak fields that contribute little to brightness. We show that with data of high spatial resolution a calibration of magnetic flux density as a proxy for brightness excess is possible. In the SST data, the magnetic brightening of a quiet region with an average (unsigned) flux density of 10 G is about 0.15%. In the Hinode data, and in SST data reduced to Hinode resolution, the measured brightening is some 40% lower. With appropriate correction for resolution, magnetic flux density can be used as a reliable proxy in regions of small scale mixed polarity. The measured brightness effect is larger than the variation of irradiance over a solar cycle. It is not clear, however, if this quiet Sun contribution actually varies significantly.

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“…More recent photometric imaging supports this correlation for the small magnetic elements of the quiet network, but shows that the contrast of larger plage elements in active network and active region plage is negative near disk center, positive near the limb, and vanishes at intermediate heliocentric angle (e.g., Moran et al 1992;Zirin & Wang 1992;Lawrence et al 1993;Topka et al 1997;Sobotka et al 2000;Ortiz et al 2006). In fact, plage area measurements include even pores and spots that are dark at all heliocentric angles (W. Marquette 1992, private communication; Tlatov et al 2009).…”

Section: Introductionmentioning

confidence: 93%

Dimming of the Mid-20th Century Sun

Foukal

2015

ApJ

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Area changes of photospheric faculae associated with magnetic active regions are responsible for the bright contribution to variation in total solar irradiance (TSI). Yet, the 102-year white light (WL) facular record measured by the Royal Greenwich Observatory between 1874 and 1976 has been largely overlooked in past TSI reconstructions. We show that it may offer a better measure of the brightening than presently used chromospheric proxies or the sunspot number. These are, to varying degrees, based on magnetic structures that are dark at the photosphere even near the limb. The increased contribution of the dark component to these proxies at high activity leads to an overestimate of solar brightening around peaks of the large spot cycles 18 and 19. The WL facular areas measure only the bright contribution. Our reconstruction based on these facular areas indicates that TSI decreased by about 0.1% during these two cycles to a 20th century minimum, rather than brightening to some of the highest TSI levels in four centuries, as reported in previous reconstructions. This TSI decrease may have contributed more to climate cooling between the 1940s and 1960s than present modeling indicates. Our finding adds to previous evidence that such suppression of solar brightening by an increased area of dark flux tubes might explain why the Sun is anomalously quiet photometrically compared to other late-type stars. Our findings do not change the evidence against solar driving of climate warming since the 1970s.

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The intensity contrast of solar photospheric faculae and network elements

Cited by 22 publications

References 42 publications

Properties of sunspots in cycle 23

Properties of sunspots in cycle 23

The brightness of magnetic field concentrations in the quiet Sun

Dimming of the Mid-20th Century Sun

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