Free Access
Volume 579, July 2015
Article Number A73
Number of page(s) 10
Section The Sun
Published online 30 June 2015

Online material

Appendix A: The influence of clouds on the calculation of the area

In Sect. 2.3 we examined the effect of changing seeing conditions, i.e. clouds. We modelled the clouds as having two effects, namely a decrease of the intensity due to scattering, and a smoothing over pixels also due to scattering. The decrease in intensity due to clouds is 10% of the pixel value and the pixels are linearly smoothed over the neighbouring pixels only. This cloud was then turned on and off in a periodic fashion. The visual result can be seen in Fig. A.1. The result is as expected, the image looks blurry when compared to the non-cloudy image, i.e. Fig. 1. However, does this have an effect on the thresholding routine determining the area of the pore? The result can be seen in Fig. A.2. One can clearly see that clouds have a major impact on the thresholding routine. We tried to remedy this, but the smoothing over pixels is very hard to correct for. We realise that the clouds employed are unrealistic in the sense that they spontaneously appear in the entire FOV and that they are periodic. However the fact that clouds spontaneously appear is not a real concern since the small viewing aperture results in an almost immediate the cloud cover. Clouds are non-periodic but even one cloud is enough to deteriorate the data at that time. This is the reason that we decided to discard certain time intervals in the observations.

thumbnail Fig. A.1

One slice from the data set representing a magnetic pore in the solar photosphere with a cloud introducing seeing effects. The colour scale is the intensity.

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thumbnail Fig. A.2

Area of the simulated magnetic pore based on the thresholding routine. Left: area without cloud effects. Right: area with cloud effects.

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© ESO, 2015

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