  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.
