Magnetic field evolution around a fast-moving pore emerging from the quiet Sun

Abstract

Context. Solar pores are intense concentrations of magnetic fields on the solar surface and plasma flows have always played a key role in spurring the evolution of the pores. Aims. In this study, we present the evolution of the magnetic field and plasma velocity around a fast-moving pore. The target pore expands into the quiet Sun area with a sufficiently fast speed after its emergence, while the background magnetic fields around the pore are simple. These characteristics provide us with an excellent opportunity to study the interaction between plasma motions and ambient magnetic fields. Methods. We analyzed the Helioseismic and Magnetic Imager (HMI) vector magnetograms with a pixel size of 0.5″ and a temporal cadence of 12 min across a duration of 11 h. We also adopted he HMI dopplergrams present the line-of-sight velocities. The horizontal flow fields were obtained using the Differential Affine Velocity Estimator for Vector Magnetograms method. Results. Pure horizontal magnetic fields are generated in the moving frontwards when the pore is subject to fast movement. The generated magnetic fields occur outside the emerging site and thus can be ruled out as the emerging flux from the interior. Instead, they are highly correlated with the broader downflows and expanding horizontal plasma motions in front of the pore. A magnetic gap can be observed between the magnetic fields inside and outside the pore. The temporal evolution of the generated magnetic fields is related to the speed of the pore, which is also distinguished from the original fields within the pore. Conclusions. The observations suggest that the plasma flows driven by the fast proper motion of the pore compress and stretch the local magnetic field to a horizontal non-radial direction, ultimately leading to the magnetic field amplification in the front part of the moving pore.