Solar Soft X-ray Irradiance Variability, I: Segmentation of Hinode/XRT Full-Disk Images and Comparison with GOES (1 – 8 Å) X-Ray Flux

Abstract

It is of great interest and importance to study the variabilities of solar EUV, UV and X-ray irradiance in heliophysics, in Earth's climate, and space weather applications. A careful study is required to identify, track, monitor and segment the different coronal features such as active regions (ARs), coronal holes (CHs), the background regions (BGs) and the X-ray bright points (XBPs) from spatially resolved full-disk images of the Sun. Variability of solar soft X-ray irradiance is studied for a period of 13 years (February 2007-March 2020, covers Solar Cycle 24), using the X-Ray Telescope on board the Hinode (Hinode/XRT) and GOES (1 -8 Å). The full-disk X-ray images observed in Al_mesh filter from XRT are used, for the first time, to understand the solar X-ray irradiance variability measured, Sun as a star, by GOES instrument. An algorithm in Python has been developed and applied to identify and segment coronal X-ray features (ARs, CHs, BGs, and XBPs) from the full-disk soft X-ray observations of Hinode/XRT. The segmentation process has been carried out automatically based on the intensity level, morphology and sizes of the X-ray features. The total intensity, area, and contribution of ARs/CHs/BGs/XBPs features were estimated and compared with the full-disk integrated intensity (FDI) and GOES (1 -8 Å) X-ray irradiance measurements. The XBPs have been identified and counted automatically over the full disk to investigate their relation to solar magnetic cycle. The total R. Kariyappa

Solar Soft X-Ray Irradiance Variability, II: Temperature Variations of Coronal X-Ray Features

“…It has been observed and reported earlier that the XBPs show a high variability in their temperature and that the average temperature ranges from 1.1 MK to 3.4 MK (Kariyappa et al, 2011). Considering the high temperature and a large number of XBPs present over the full-disk at any time, the XBPs contribute significantly to total intensity (Adithya et al, 2021) and temperature variability of the full-disk and to the heating of the corona at the sites of XBPs. The temperature values and their variations of all the features suggest that the features show a high variability in their temperature and that the heating rate of the emission features may be highly variable on solar cycle timescales.…”

“…In addition they investigated and discussed in detail the role of magnetic field on EUV & UV irradiance variability by comparing SWAP and AIA images with SDO/HMI magnetograms. Recently (Adithya et al, 2021), Paper I hereafter, have segmented the soft X -ray images obtained by Hinode/XRT for the period 2007 to 2020 and studied the total intensity of individual features and their contribution full-disk intensity values. The segmentation maps of the individual features observed with two filters will be used to derive the temperature maps by filter ratio method.…”