Major Climate Variability and Natural Factors in Boreal Winter
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Pure and Applied Geophysics
Major Climate Variability and Natural Factors in Boreal Winter INDRANI ROY1 Abstract—The role of natural factors, mainly solar 11-year cyclic variability and volcanic eruptions on two major modes of climate variability the North Atlantic Oscillation (NAO) and El Nin˜o Southern Oscillation (ENSO) are studied for about the last 150 years period. The NAO is the primary factor to regulate Central England Temperature (CET) during winter throughout the period, though NAO is impacted differently by other factors in various time periods. Solar variability during 1978–1997 indicates a strong positive in-phase connection with NAO, which is different in the period prior to that. Such connections were further explored by known existing mechanisms. Solar NAO lagged relationship is also shown not unequivocally maintained but sensitive to the chosen times of reference. It thus points towards the previously known mechanism/relationship related to the Sun and NAO. This study discussed the important roles played by ENSO on global temperature; while ENSO is influenced strongly by solar variability and volcanic eruptions in certain periods. A strong negative association between the Sun and ENSO is observed before the 1950s, which is positive though statistically insignificant during the second half of the twentieth century. The period 1978–1997, when two strong eruptions coincided with active years of strong solar cycles, the ENSO and volcano suggested a stronger association. That period showed warming in the central tropical Pacific while cooling in the North Atlantic with reference to various other anomaly periods. It indicates that the mean atmospheric state is important for understanding the connection between solar variability, the NAO and ENSO and associated mechanisms. It presents critical analyses to improve knowledge about major modes of variability and their roles in climate and reconciles various contradictory findings. It discusses the importance of detecting solar signal which needs to be robust too. Keywords: Solar cyclic variability, NAO, ENSO, volcanic eruptions, multiple linear regression.
Abbreviations AOD Aerosol optical depth CET Central England Temperature CMIP5 Coupled Model Inter-comparison Project 5
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00024-020-02522-z) contains supplementary material, which is available to authorized users. 1
IRDR, University College London (UCL), London, UK. E-mail: [email protected]
ENSO EOF GCR NAO NH RCP SH SSN SST SLP UV
El Nin˜o Southern Oscillation Empirical Orthogonal Function Galactic cosmic ray North Atlantic Oscillation Northern hemisphere Representative concentration pathway Southern hemisphere Sunspot number Sea surface temperature Sea level pressure Ultra violet
1. Introduction The Sun is the main source of energy of the earth, but the level of scientific understanding relating to its influences on climate is still low (IPCC 2013). Regarding energy output, there is only a 0.1% change
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