A study of variations of solar spectral irradiance (SSI) in the wave-length
ranges 121.5 nm-300.5 nm for the period 1981-2009 is presented. We used
various data for ultraviolet (UV) spectral lines and international sunspot
number (ISSN) from interactive data centers such as SME (NSSDC), UARS
(GDAAC), SORCE (LISIRD) and SIDC, respectively. We reduced these data by
using the MATLsoftware package. In this respect, we revealed negative
correlations of intensities of UV (289.5 nm-300.5 nm) spectral lines
originating in the solar chromosphere with the ISSN index during the
unusually prolonged minimum between the solar activity cycles (SACs) 23 and
24. We also compared our results with the variations of solar activity
indices obtained by the ground-based telescopes. Therefore, we found that
plage regions decrease while facular areas are increasing in SAC 23. However,
the decrease in plage regions is seen in small sunspot groups (SGs), contrary
to this, these regions in large SGs are comparable to previous SACs or even
larger as is also seen in facular areas. Nevertheless, negative correlations
between ISSN and SSI data indicate that these variations are in close
connection with the classes of sunspots/SGs, faculae and plage regions.
Finally, we applied the time series analysis of spectral lines corresponding
to the wavelengths 121.5 nm-300.5 nm and made comparisons with the ISSN data.
We found an unexpected increase in the 298.5 nm line for the Fe II ion. The
variability of Fe II ion 298.5 nm line is in close connection with the
facular areas and plage regions, and the sizes of these solar surface indices
play an important role for the SSI variability, as well. So, we compared the
connection between the sizes of faculae and plage regions, sunspots/SGs,
chemical elements and SSI variability. Our future work will be the
theoretical study of this connection and developing of a corresponding model.
Solar spectral irradiance variability of some chromospheric emission lines through the solar activity cycles 21-23
