Spotlight

Understanding the evolution of the solar magnetic field is an integral part of space physics. Solar activity, space weather, and solar irradiance, among other things, depend on the structure of the magnetic field. Continuous direct magnetographic observations of the magnetic field in the photosphere, which is the visible surface of the Sun, have been conducted since the 1970s. The large-scale evolution of the photospheric magnetic field follows a 22-year cycle, during which the polarity of the field changes twice. This means that we have direct observations of only a few magnetic cycles. This severely limits our ability to study and understand the long-term evolution of the solar magnetic field.

Surface flux transport simulations can be used to complement the observations. They take photospheric active regions, where strong magnetic field emerges through the solar surface, and simulate the transport and diffusion of the emerged magnetic flux on the solar surface to reconstruct the whole photospheric magnetic field. Active regions can be taken from magnetographic observations or reconstructed from other observations, such as sunspot observations, which have been routinely conducted significantly longer than magnetographic observations.

In this talk I present the basics of surface flux transport simulations and a method to reconstruct the photospheric magnetic field over the past century from observations of sunspots and the chromospheric calcium II K spectral line. I also discuss the properties of the reconstruction and the connection of the reconstruction to space weather and solar irradiance.

About Dr. Iiro Virtanen