Spatial Extent of the Magnetic Influence of an Active Region on the Solar Atmosphere

Solar activity can be witnessed in the form of sunspots and active regions, where the magnetic field is enhanced by up to a factor of 1000 as compared to that of the quiet Sun. In addition, solar activity manifests itself in terms of flares, jets, coronal mass ejections and the production of highly energetic particles. All these processes are governed by the solar magnetic field. Here we study the spatial reach of the influence of the magnetic field of active regions on the photosphere and in the solar corona. An active region is modelled by a magnetic dipole located under the photosphere. This simplified description allows us to study the spatial influence of an active region in the solar atmosphere in a rough but easy way. We find that the area of influence of the magnetic field of an active region on the solar atmosphere increases with both the maximum strength of the magnetic field in the active region and the depth of the dipole under the photosphere. For a typical active region, the magnetic field can be neglected for distances beyond ca. 700 Mm on the photosphere and two solar radii in the solar corona.