Ahmad Alharbi

Gather.town id
SP006
Poster Title
Variability of Mg II h&k Lines in the Quiet Sun
Institution
University of Glasgow
Abstract (short summary)
It is critical to determine the solar disk's radiation in Mg II lines, e.g. to evaluate the radiation incident on solar chromospheric structures such as spicules or prominences, and to comprehend the radiation emitted by these structures in these lines. The aim of this project is to investigate the spatial and temporal variability of the Mg II h&k (2803.53 and 2796.35, respectively) lines in solar observations. Additionally, we seek to derive information on the spectral features of the Mg II h&k lines in the quiet sun at the centre of the sun. We present a novel approach for automatically determining the positions of k1v, k2v, k3, k2r, and k1r, as well as h1v, h2v, h3, h2r, and h1r, in the line profiles obtained by IRIS at the quiet sun centre. In this poster, we will address the variation in the spectral characteristics of the Mg II h&k lines in the quiet sun at the sun centre.
Plain text (extended) Summary
The aim of this project is to investigate the spatial and temporal variability of the Mg II h&k lines in the
Quiet Sun. Mg II ions provide a variety of spectral lines of substantial diagnostic potential in the solar
atmosphere, particularly between the upper photosphere and the upper chromosphere.
In this work we seek to derive information on the spectral features of the Mg II h&k lines in the quiet sun
at the centre of the sun. We present a novel approach for automatically determining the positions of the
outer minima in the red and blue wings (k1r, h1r, k1v, h1v), line emission peaks in the red and blue sides
(k2r, h2r, k2v, h2v), and the central absorption cores (k3, h3) in the spectroscopic observations obtained
by IRIS at quiet sun centre. Figure 1 shows an example of an IRIS spectrum of the Mg II h&k lines at
2796 and 2803 Å at Sun's centre, with labels indicating these spectral features
To do this, we first calculate all the differences in intensity and use the sign of all these values. We then
take the difference in sign between every two consecutive points to find the turning points. If the
difference in the sign between two consecutive points is positive, it is a local minimum, while if the
difference in the sign is negative, it is a local maximum. Given that this method will determine all the
local minima or maxima while we need to determine only five points for any of the h or k line, we
exclude peaks with a difference in intensity of less than one-third of the standard deviation. Figure 2
shows the result of our algorithm on two example line profiles.
After analysing a full raster, we plot histograms for (k1v, k2v, k3, k2r, and k1r) and (h1v, h2v, h3, h2r,
and h1r), and fitted them with a Gaussian distribution. We found that the wavelength histograms are
relatively well described by Gaussian distributions, while the intensity histograms are clearly
asymmetrical. Figure 3 shows the results for a single raster for the k line only.
The spread in wavelengths is clearly larger for k1v and k1r, which is expected because of the lower
intensities and greater difficulty to identify these features. As noted by other authors, the wavelength
histograms in k3 will provide information on the velocities in the upper chromosphere, while intensity
histograms in k3 can give an indication of the transition region height, where these features are formed.
The spread and differences in k2v and k2r histograms suggest variations in temperature and velocities of
the chromospheric regions where these peaks are formed. The intensity histograms will allow us to
explore the relative contributions of different quiet Sun features to the total emission in the Mg II lines.
This preliminary analysis on a single IRIS raster demonstrates there is a wealth of information that can be
obtained from the complex Mg II line profile shapes by studying their key features automatically. We are
now working on applying this code to all quiet Sun rasters obtained between 2014 and 2021 to investigate
the temporal variation of Mg II h&k lines, and we will subsequently explore the centre-to-limb variations.
Eventually, characterising the temporal and spatial variability of Mg II emission in the solar atmosphere
will allow to probe the variations of physical conditions where the h and k lines are formed and assess the
impact these variations may have on chromospheric structures illuminated by the Sun's radiation in these
lines.
URL
a.alharbi.5@research.gla.ac.uk