Coronal magnetic arcades with a helical structure

A family of force-free magnetic fields, describing multipolar magnetic arcades is described. The family allows for twisted magnetic ropes, where magnetic field lines have a helical shape. These helical structures are specific to filament channels of active regions. In their structure, arcades belong to normal-polarity fields and correspond to prominences of active regions according to available observational data. A potential field is found that is external with respect to an arcade. The constructed force-free fields can be used to further develop the MHD model of filaments that takes into account the gas pressure gradient and gravity.