Exploring the Sun - Climate Link

Behera, Abhinna Kumar (2014) Exploring the Sun - Climate Link. Masters thesis, Indian Institute of Science Education and Research Kolkata.

PDF (MS dissertation of Abhinna Kumar Behera) Abhinna_Kumar_Behera.pdf - Submitted Version Restricted to Repository staff only Download (6MB)

Abstract

The varying magnetic field of Sun and the sunspot cycle modulate Sun’s energy output and the heliospheric open flux. The former is the primary energy input into the global climate system and the later may be relevant for climate due to its modulation effect on cosmic rays. It is the sole reason behind the formation of the cloud, winds and water currents in ocean, sea, etc. Hence, it will be quite reasonable to identify this “Sun - Climate Link” by focusing on the short term and long term changes, that occurs in Sun and Earth’s atmosphere. The connection in between solar activity and global climate, is the main theme of our work and to find out this connection, we have employed Wavelet Transform. The periodic behavior of solar activity has been studied to a great extent; the multi-scale characterization of the sunspot numbers and the global temperature anomalies, reveals clear signature of self-similarity, complex scaling behavior and periodicity. Using generalized Hurst exponent, we have quantified the self-similar nature and to capture the transient behavior present in the solar activity, we have used scale dependent varying window. Using Morlet wavelet function, the optimal time-frequency localization has been shown as it is very necessary to focus on the cyclic behavior of solar activity, which is best observed as the formation of sunspot numbers everyday. The sunspot numbers, spanning over 400 years, is a direct proxy for varying solar magnetic field as sunspots constitute strongly magnetized, visibly dark regions on the Sun. We utilize this recorded data for studying the Sun - Climate link. We divide the time series used into three periods: Maunder Minima + pre-industrial (1610 - 1815), post Maunder Minima + pre-industrial (1715 - 1815) and industrial (1815-2013) periods in order to correlate solar activity with climate changes by segregating the Maunder minima effect and the anthropogenic effect. To focus on long-term climate relevant trends, we have removed the well-known 11 year periodicity by taking the decadal average of both sunspot numbers and temperature anomalies. The work explores the phase relationship between temperature anomalies and sunspot numbers and observed this with the changes in the correlation coefficients, calculated on decadal basis. The sunspot numbers that are available, span since 1610 - 2013 and we confront this with the northern hemisphere temperature anomalies over the same period.

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