Formation of Secondary Structures Associated With the Gradient Drift Instability in the High‐Latitude Ionosphere

Abstract The gradient drift instability (GDI) commonly occurs in the high‐latitude ionosphere and is widely recognized for producing elongated striation structures. While previous studies have established the linear growth and primary nonlinear development of striations, the formation of secondary structures remains not fully understood. Using two‐dimensional numerical simulations, we show that smaller branch structures evolve asymmetrically on the sides of striations when either the background electric field or the wave vector has a component along the density gradient. Our results indicate that in the linear stage, the electric field in the direction of density gradient modifies the effective growth rate by altering the wave vector orientation. In the nonlinear stage, electric field and wave vector direction coupling govern the emergence of branch structure, with electric field dominating when its effect opposes that of the wave vector. These results highlight the critical roles of electric field and wave vector orientation in generating secondary GDI structures.