Abstract

The Sun's activity cycle governs the radiation, particle and magnetic flux in the heliosphere creating hazardous space weather while the decadal-scale variations define space climate and force the terrestrial atmosphere. Predicting the solar cycle variations is challenging because of the unpredictable variations of parameters involved. Thus study in variations of solar activity is important for understanding the underlying mechanism involved and for predicting the level of activity in view of the activity impact on space weather and global climate. By using the observed data of solar parameters viz. sunspot numbers, F 10.7cm index and Lyman alpha index recorded for last seventy years (1947 - 2017) and applying the Hodrick Prescott filtering method to bifurcate each time series into cyclic and trend parts, we have predicted the trend of solar activities for solar cycles 25 & 26. During the analysis, the cyclic part of each time series was used to analyze the persistence while the trend part was used to obtain the input data for the study of future predictions. Further, the cyclic component of each parameter was analyzed by using the rescaled range analysis and the value of Hurst exponent was obtained for sunspot numbers, F10.7cm index and Lyman alpha index as 0.90, 0.93 and 0.96 respectively. By using the simplex projection analysis on the values of amplitude and phase of the trend component of each time series, we have reconstructed the future time series representing solar cycles 25 and 26. When extrapolated further in time, the reconstructed series provided the maximum values of sunspot numbers as 89±9 and 78±7; maximum values of F10.7 cm index were 124±11 and 118±9 and Lyman alpha index were 4.61±0.08 and 4.41±0.08 respectively for solar cycles 25 and 26. During analysis, we found that the solar cycle 25 will start in the year 2021 (January) and will last till 2031 (February) with its maxima in year 2024 (February) while the solar cycle 26 will start in the year 2031 (March) with its maxima in 2036 (June) and will last till the year 2041 (February).We have also compared the activities of solar cycles 5 & 6 (Dalton minima periods) to solar cycles 25 and 26 and have inferred that the other solar minimum is underway. This is a clear indication of substantial weakening trend in solar activity which may lead to the speculation of other minima and cooling global climate.