Major Climate Variability and Natural Factors in Boreal Winter

The role of natural factors, mainly solar 11-yearcyclic variability and volcanic eruptions on two major modes ofclimate variability the North Atlantic Oscillation (NAO) and ElNino Southern Oscillation (ENSO) are studied for about the last150 years period. The NAO is the primary factor to regulateCentral England Temperature (CET) during winter throughout theperiod, though NAO is impacted differently by other factors invarious time periods. Solar variability during 1978-1997 indicatesa strong positive in-phase connection with NAO, which is differentin the period prior to that. Such connections were further exploredby known existing mechanisms. Solar NAO lagged relationship isalso shown not unequivocally maintained but sensitive to thechosen times of reference. It thus points towards the previouslyknown mechanism/relationship related to the Sun and NAO. Thisstudy discussed the important roles played by ENSO on globaltemperature; while ENSO is influenced strongly by solar variabilityand volcanic eruptions in certain periods. A strong negative associationbetween the Sun and ENSO is observed before the 1950s,which is positive though statistically insignificant during the secondhalf of the twentieth century. The period 1978-1997, when twostrong eruptions coincided with active years of strong solar cycles,the ENSO and volcano suggested a stronger association. Thatperiod showed warming in the central tropical Pacific while coolingin the North Atlantic with reference to various other anomalyperiods. It indicates that the mean atmospheric state is importantfor understanding the connection between solar variability, theNAO and ENSO and associated mechanisms. It presents criticalanalyses to improve knowledge about major modes of variabilityand their roles in climate and reconciles various contradictoryfindings. It discusses the importance of detecting solar signal whichneeds to be robust too.