Long-Term Variation of the Corona in Quiet Regions

Kamio, S.; Mariska, J. T.

doi:10.1007/s11207-012-0014-9

Cited by 12 publications

(31 citation statements)

References 16 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This result is contrary to earlier claims (e.g. : Kamio & Mariska 2012). Since both the centre-to-limb function and the widths of the radiance distributions do not depend on the radiometric calibration of the data, we are confident that our results point to truly constant properties of the quiet Sun during the activity cycle.…”

Section: Discussioncontrasting

confidence: 99%

“…7, could be still be compatible with a variability of the QS median radiance (but not of the width of the distribution) during the maximum of solar activity. However, such a variability would be rather small -of the order at most of 0.1-0.2 dex for the Mg  625 Å line; the variation found by Kamio & Mariska (2012) is of the order of a factor between 2 and 5 for lines of similar formation temperature (like the Fe  180 Å line) or hotter lines. In any case, our data for Mg  clearly show that the median radiance settles to a constant value by the end of 2004, which is much earlier that the Hinode measurements.…”

Section: Variability Of Quiet Sun Radiances During the Activity Cyclementioning

confidence: 93%

“…Another problem in the Kamio & Mariska (2012) results is related to their radiometric calibration, which is now known to be at fault. Del Zanna (2013) produced a completely new Hinode EIS calibration and applied it to a careful selection of the same dataset used by Kamio & Mariska (2012) in their analysis. The Del Zanna (2013) results are that the quiet Sun radiances in lines formed at or below 1 MK do not change, which agree with the present results.…”

Section: Variability Of Quiet Sun Radiances During the Activity Cyclementioning

confidence: 99%

See 2 more Smart Citations

The EUV spectrum of the Sun: SOHO CDS NIS radiances during solar cycle 23

Andretta

Zanna

2014

A&A

View full text Add to dashboard Cite

For the first time, we present and discuss EUV radiances of the solar transition region (TR) and corona obtained during a solar cycle. The measurements were obtained with the SOHO/coronal diagnostic spectrometer (CDS) during the period from 1996 to 2010. We find that limb-brightening significantly affects any characterisation of the solar radiances. We present the limb-brightening function for the main lines and find that it does not change measurably during the cycle. We confirm earlier findings that the radiance histogram of the cooler lines have a well defined, log-normal quiet-Sun component, although our results differ from previous ones. The width of the lowest-radiance log-normal distribution is constant along the cycle. Both the analysis of the centre-to-limb variation and of the radiance statistical distribution point to a constant quiet Sun emission along solar cycle 23. Lines formed above 1 MK are dramatically affected by the presence of active regions, and indeed, no "quiet Sun" region can be defined during periods of maximum activity. Much of the irradiance variability in lines formed below 1.5 MK is due to a change in the emitting area. For hotter lines, the emitting area saturates to almost 100% of full solar disk at the maximum of activity, while simultaneously the emission due to active regions increases by more than an order of magnitude. We show that structures around active regions, sometimes referred to as dark halos or dark canopies, are common and discuss their similarities and differences with coronal holes. In particular, we show how they are well visible in TR lines, contrary to coronal holes.

show abstract

Section: Discussioncontrasting

confidence: 99%

Section: Variability Of Quiet Sun Radiances During the Activity Cyclementioning

confidence: 93%

Section: Variability Of Quiet Sun Radiances During the Activity Cyclementioning

confidence: 99%

See 1 more Smart Citation

The EUV spectrum of the Sun: SOHO CDS NIS radiances during solar cycle 23

Andretta

Zanna

2014

A&A

View full text Add to dashboard Cite

show abstract

“…We use QS observations. There are no Si vii lines in the SW channel, but Kamio & Mariska (2012) and Mariska (2013) suggested the use of the Si vii 275.3 Å vs. Fe viii 185.2 Å ratio to monitor the relative sensitivity of the LW/SW channels. We will discuss this issue below.…”

Section: Silicon and Sulfur Linesmentioning

confidence: 99%

“…This ratio was used by Kamio & Mariska (2012) and Mariska (2013) to argue that both SW and LW channels had the same decrease in sensitivity. Other ratios such as the 278.4/196 Å show similar behaviour.…”

Section: Sw/lw Ratios and Long-term Correctionmentioning

confidence: 99%

A revised radiometric calibration for the Hinode/EIS instrument

Zanna¹

2013

A&A

View full text Add to dashboard Cite

An assessment of the in-flight radiometric calibration of the Hinode EUV Imaging Spectrometer (EIS) is presented. This is done with the line ratio technique applied to a wide range of observations of the quiet Sun, active regions, and flares from 2006 until 2012. The best diagnostic lines and the relevant atomic data are discussed in detail. Radiances over the quiet Sun are also considered, with comparisons with previous measurements. Some departures in the shapes of the ground calibration responsivities are found at the start of the mission. These shapes do not change significantly over time, with the exception of the shorter wavelengths of the EIS short-wavelength (SW) channel, which shows some degradation. The sensitivity of the SW channel at longer wavelengths does not show significant degradation, while that of the long-wavelength (LW) channel shows a significant degradation with time. By the beginning of 2010 the responsivity of the LW channel was already lower than the values measured on the ground by a factor of two or more. A first-order correction is proposed. With this correction, the main ratios of lines in the two channels become constant to within a relative 20%, and the He ii 256 Å radiances over the quiet Sun also become constant over time. This correction removes long-standing discrepancies for a number of lines and ions, in particular those involving the strongest Fe x, Fe xiii, Fe xiv, Fe xvii, and Fe xxiv lines, where discrepancies of factors of more than two were found. These results have important implications for various EIS science analyses, in particular for measurements of temperatures, emission measures and elemental abundances.

show abstract