Abstract:
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 the McIntosh and Meudon observations. The spatiotemporal evolution of filaments
manifests in the form of a filament butterfly diagram, further indicating that they are intimately related to the largescale solar cycle. Physical descriptors such as the number and length of filaments, which are tracers of the solar
surface magnetic field, have cycles which are phase locked with the ∼11 yr sunspot cycle. The tilt-angle
distribution of filaments—both near to 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 over the time span of
solar filament observations up to a century. On the one hand, this would serve as a useful constraint 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.
