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Long-term Study of the Sun and Its Implications to Solar Dynamo Models

The Sun shows a wide range of temporal variations, from a few seconds to decades and even centuries, broadly classified into two classes short-term and Long-term. The solar dynamo mechanism is believed to be responsible for these global changes happening in the Sun. Hence, many dynamo models have been proposed to explain the observed behaviour of the Sun. This thesis is primarily focused on studying the \lt\ variation of the Sun and provides various inputs to the solar dynamo models. With a renewed interest in the subject, several automatic techniques have been developed for extensive data analysis as applied to long-term datasets and presented in this thesis. This approach provides better consistency and eliminates human subjectivity, which has been a normal practice in the past. The variation of penumbra to umbra area ratio, q, observed here, will provide constraints in sunspot simulations. In addition, the absence of any difference in the behaviour of small and big spots does not support the idea of the global and local dynamo. Two classes of BMRs observed in the magnetograms further verify this behaviour. The importance of the NSSL is not studied so well in the context of solar dynamo models, but it will be worth waiting to see its significance for understanding solar dynamo. Finally, the indication of tilt quenching presented here needs to be further verified using the more comprehensive data set, including stronger cycles.