Abstract:
Kodaikanal Solar Observatory (KoSO) possesses one of world’s longest and
homogeneous records of sunspot observations that span more than a
century (1904–2017). Interestingly, these observations (originally recorded in
photographic plates/films) were taken with the same setup over this entire
time period which makes this data unique and best suitable for long-term
solar variability studies. A large part of this data, between 1921–2011, were
digitized earlier and a catalog containing the detected sunspot parameters
(e.g., area and location) was published in Mandal et al. (2017). In this article, we
extend the earlier catalog by including new sets of data between 1904–1921
and 2011–2017. To this end, we digitize and calibrate these new datasets
which include resolving the issue of random image orientation. We fix
this by comparing the KoSO images with co-temporal data from Royal
Greenwich Observatory. Following that, a semi-automated sunspot detection
and automated umbra detection algorithm are implemented onto these
calibrated images to detect sunspots and umbra. Additionally, during this
catalog updation, we also filled data gaps in the existing KoSO sunspot catalog
(1921–2011) by virtue of re-calibrating the “rouge” plates. This updated sunspot
area series covering nearly 115 years (1904–2017) are being made available to
the community and will be a unique source to study the long term variability
of the Sun.
