We have revisited the ideal MHD interchange instability for the case of the nonaligned gradients of the plasma pressure p and unit magnetic flux tube volume V, i.e., the background field-aligned current (FAC) included. Several possibilities of a directional difference between ∇p and ∇V in the Earth's plasma sheet are considered. The growth of an interchange perturbation leading to the pressure-gradient-driven FAC striation is illustrated through numerical simulation in a simple model of the nightside region 1 FAC by Karty et al. <1984> and Yang et al. <1994>. It is shown that the FAC is being striated by the interchange process on a timescale from minutes to tens of minutes. The application to the quiet time discrete arc formation is discussed.