Context. Active longitudes (ALs) are proposed behavioural patterns on the Sun, whereby certain solar phenomena tend
to appear at preferred longitudes, with these longitudes shifting over time on a scale of a few Carrington Rotations
(CRs). The existence of ALs remains a topic of debate, largely due to our limited understanding of their origin, evolution,
and physical significance.
Aims. This study aims to provide support and further evidence towards the existence of ALs by utilising longer-term
sunspot and solar flare datasets. As part of this effort, an artificial test dataset for control was also constructed in which
the longitudes of sunspots were randomised, allowing a direct comparison with the observational data.
Methods. Kernel density estimation (KDE) was employed to search for longitudinal groupings of sunspot groups and
flares on synoptic maps. Furthermore, we explored larger-scale structures by applying a 2D KDE to the peaks of the
1D KDEs (longitude as a function of CR). Finally, we generate artificial solar cycles by simulating sunspots with
randomised properties, most notably assigning longitudes from a uniform distribution.
Results. Distinguishable features were identified in the 2D KDEs, showing that during certain periods of the solar cycle,
a specific longitude range may exhibit heightened activity, which can later switch off entirely, and a new one can appear
∼180◦
away, consistent with the AL’s flip-flop effect. Although our randomised datasets also exhibited active longitudes
in their 2D KDEs, these differed notably from the observed patterns: inactive longitudes were less pronounced, and
active patches appeared shorter-lived and more numerous. We also identified a parameter for a qualitative comparison:
the number of KDE peaks (in the 1D KDE) per number of CRs in a solar cycle. This indicator shows a markedly
different distribution between the randomised and observed datasets, confirmed by a Cucconi test p-value of 0.0177.
CORE (COnnecting REpositories)
CORE (COnnecting REpositories)