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This paper investigates the North–South (N–S) as well as East–West (E–W) distribution and asymmetry in Soft X-ray flares (SXR) activity during the period 1976–2019 which corresponds to solar cycles 21–24. Our results reveal that, cycles 21, 22 and 23 are dominated by southern hemisphere and the cycle 24 is also found to be southern hemisphere dominated using soft X-ray flares data. The cumulative plot indicates a slight excess of X-ray flare events in the southern hemisphere during solar cycles 21, 23 and 24. A significant excess of flare events in the southern hemisphere has been observed in the cumulative plot during cycle 22. The most prolific latitude band in the N–S distribution is the 10°–20° which produced maximum number of soft X-ray flares over solar cycles 21, 22, 23 and 24 whereas no such longitudinal band is observed in the E–W distribution. The time-latitude plot of SXR flares is also constructed to study the behaviour of N–S distribution. It is also revealed in current work that the occurrence (number) of M and X class flares is showing a declining trend since solar cycle 21 till solar cycle 24 thereby violating the Gnevyshev-Ohl (G-O) rule. A significant eastern dominance is being observed till solar cycle 23 but the predominance shifted to western hemisphere during cycle 24. Our analysis reveals that the North–South asymmetry is highly significant in comparison to East–West asymmetry. [ABSTRACT FROM AUTHOR]

The Mg II core-to-wing ratio (c/w ratio) data is used to derive the solar extreme UV emission which brings a vital role in the creation of the Earth's ionosphere region. A continuous Mg II c/w ratio data has scientific importance towards the analysis of the earth's climate as well as for the solar chromosphere region. Various instruments of ESA and NASA satellites such as SUSIM, SOLSTICE, GOME, NOAA9, NOAA11 etc. measure Mg II c/w ratio data at different time scales but still some missing measurements are being reported. To fill those missing gaps, the current investigation has used the correlation analysis technique between Mg II and other solar indices separately. Our result establishes a highest correlation with 10.7 cm (2800 MHz) radio flux (F10.7) data in comparison to other solar indices during solar cycle 22 and 23. But for phase-wise correlation analysis, the correlation coefficient shows varying behavior during declining and rising phase of each solar cycle due to hysteresis of magnetic field inside the Sun. Also, the correlation coefficient of the linear regression model for Coronal Index vs. Mg II has a higher value than 10.7 cm radio flux vs. Mg II during maximum phase of each solar cycle. In the present investigation, the composite Mg II c/w ratio data is computed using a linear regression model with strongly correlated solar index data depending on time frame analysis of each solar cycle to achieve better correlation. Finally, a correlation analysis is also being performed between the computed composite Mg II c/w ratio and Bremen composite data and a fair correlation around 0.98 has been found. The computed series is also validated with other long-range solar indices data to verify different long-range trends that can reflect the actual nature of the Sun's chromosphere region. [ABSTRACT FROM AUTHOR]