  Hand-drawn synoptic maps from the Meudon Observatory (1919 onwards) and the
McIntosh archive (1967 onwards) are two important sources of long-term,
manually recorded filament observations. In this study, we calibrate the Meudon
maps and subsequently identify filaments through an automated method. We
extract physical parameters from this filament database and perform a
comparative study of their long-term evolution focusing on the cotemporal
period of McIntosh and Meudon observations. The spatio-temporal evolution of
filaments manifests in the form of a filament butterfly diagram, indicating
further that they are intimately related to the large-scale solar cycle.
Physical descriptors such as the number and length of filaments, which are
tracers of solar surface magnetic field, have cycles which are phase-locked
with the 11 year sunspot cycle. The tilt angle distribution of filaments - both
near or distant from active region locations - indicates that their origin is
due to either large-scale surface magnetic field or inter-active region field
evolution. This study paves the way for constructing a composite series of
hand-drawn filament data with minimal gaps stretching the time span of solar
filament observations to a century. On the one hand, this would serve as useful
constraints for models of magnetic field emergence and evolution on the Sun's
surface over multiple solar cycles, and on the other hand, this filament
database may be used to guide the reconstruction of filament-prominence
associated eruptive events before the space age

Solar and Stellar Astrophysics