Temporal variation of solar flare index during solar cycles 21–24

The present investigation attempts to quantify the temporal variation of Solar Flare Index(SFI)with other activity indices during solar cycles 21-24 by using different techniques such as linear regression,correlation,cross-correlation with phase lag-lead,etc.Different Solar Activity Indices(SAI)considered in this present study are Sunspot Number(SSN),10.7 cm Solar Radio Flux(F10.7),Coronal Index(CI)and MgⅡCore-to-Wing Ratio(MgⅡ).The maximum cycle amplitude of SFI and considered SAI has a decreasing trend from solar cycle 22,and cycle 24 is the weakest solar cycle among all other cycles.The SFI with SSN,F10.7,CI and MgⅡshows hysteresis during all cycles except for solar cycle 22 where both paths for ascending and descending phases are intercepting each other,thereby representing a phase reversal.A positive hysteresis circulation exists between SFI and considered SAI during solar cycles 22 and 23,whereas a negative circulation exists in cycles 21 and 24.SFI has a high positive correlation with coefficient values of 0.92,0.94,0.84 and 0.81 for SSN,F10.7,CI and MgⅡrespectively.According to crosscorrelation analysis,SFI has a phase lag with considered SAI during an odd-number solar cycle(solar cycles21 and 23)but no phase lag/lead during an even-numbered solar cycle(solar cycles 22 and 24).However,the entire smoothed monthly average SFI data indicate an in-phase relationship with SSN,F10.7 and MgⅡ,and a one-month phase lag with CI.The presence of those above characteristics strongly confirms the outcomes of different research work with various solar indices and the highest correlation exists between SFI and SSN as well as F10.7 which establishes that SFI may be considered as one of the prime activity indices to interpret the characteristics of the Sun’s active region as well as for more accurate short-range or long-range forecasting of solar events.     

Crustal accretion and metamorphism of Mesoarchean granulites in Palghat-Cauvery Shear Zone,Southern India

This work provides unequivocal evidence of the existence of Mesoarchean granulite facies metamorphic event in the Palghat-Cauvery Shear Zone (PCSZ) of South India. Charnockite samples from two prominent hills at Kollaimalai (KM) and Pachchaimalai (PM) as well as from two quarries within the Bhavani Shear Zone (BSZ) have been analyzed for their Sm-Nd and Rb-Sr ages to investigate the existence or otherwise of the Archean granulite facies events within the PCSZ. The Rb-Sr whole-rock isochron ages for massive charnockites from both the hills appear to be contemporaneous at 2.9 Ga with the initial Sr isotopic ratios of 0.7012 and 0.7014, respectively. However, the Rb-Sr data for whole-rock samples of basic granulites from one of the quarries within the BSZ indicate open system behavior, while the charnockites from the other quarry have insufficient spread in ⁸⁷Rb/⁸⁶Sr ratios and do not yield any isochron. The Sm-Nd data, on the other hand, do not distinguish between the massive charnockite and the lowland charnockite and yield Depleted Mantle model ages in the range 2.98±0.3 Ga for all of them. The ɛ^T _CHUR for all of these rocks are highly positive. Both the Sr isotopic ratios and positive ɛ^T _CHUR values for these rocks strongly suggest a mantle source for all of them. An upper age limit of ∼3.28 Ga may be assigned to the crustal accretion of the protolith of all these rocks on the basis of their Nd model ages. The Rb-Sr isochron ages of 2.9 Ga for the two massifs could be the age of granulite facies metamorphism. Thus, the metamorphism in the KM and PM Hills took place within ∼100 Ma of crustal accretion of these rocks and probably was part of the same geological event of crust formation and metamorphism. The open system behavior with respect to Rb-Sr isotopes in the basic granulite from Bhavani is possibly due to the migration of Sr isotopes, triggered during the later shearing of these rocks.