Magnetic and velocity fields over active regions

Abstract

In order to understand the nature of dynamics over an active region (AR) , it is necessary to study the velocity and magnetic fields simultaneously. We present the preliminary results from our analysis of spectropolarimetric observations of active region NOAA-8426 over two days. These observations were done using Advanced Stokes Polarimeter (ASP) instrument of HAO-NSO (Elmore et al. 1992, Lites 1996) with the Richard Dunn Vacuum Tower Telescope, USA. The line-of-sight (LOS) magnetic field information is derived using least squares fitting of the Stokes-V profiles, in a weak field approximation. Simultaneous LOS velocity information over these AR is obtained in two ways: (i) Zero-crossing (ZC) velocities using Stokes-V profiles, and (li) centre of gravity (COG) velocities using Stokes-I profiles. The former corresponds to the magnetised plasma whereas the latter to the gross plasma over the AR. Average relative velocities of isolated polarity regions of the AR are presented in this paper.