摘要：Aims. Although the temporal evolution of active regions (ARs) is
relatively well understood, the processes involved continue to be the subject of
investigation. We study how the magnetic field of a series of ARs evolves with time to
better characterise how ARs emerge and disperse.
Methods. We examined the temporal variation in the magnetic field
distribution of 37 emerging ARs. A kernel density estimation plot of the field
distribution was created on a log-log scale for each AR at each time step. We found that
the central portion of the distribution is typically linear, and its slope was used to
characterise the evolution of the magnetic field.
Results. The slopes were seen to evolve with time, becoming less steep
as the fragmented emerging flux coalesces. The slopes reached a maximum value of
~−1.5 just before the time of maximum flux
before becoming steeper during the decay phase towards the quiet-Sun value of
~−3. This behaviour differs significantly
from a classical diffusion model, which produces a slope of −1. These results suggest that simple
classical diffusion is not responsible for the observed changes in field distribution, but
that other processes play a significant role in flux dispersion.
Conclusions. We propose that the steep negative slope seen during the
late-decay phase is due to magnetic flux reprocessing by (super)granular convective cells.
