Pinching of field-aligned currents as a possible mechanism for the formation of raylike auroral forms

Consideration is given to the case of a sheetlike field-aligned current flowing in a strong magnetic field and in a dense background plasma. Under certain conditions (connected with the current sheet thickness), the current sheet is divided into 'fibers' at ionospheric heights; the characteristic transverse scale of these fibers is determined. The division mechanism does not have a threshold and may be connected with current and field turbulence in auroral conditions; in particular, it may be connected with the division of a homogeneous arc into rays in the process of aurora activation.