Recent Advances in the Study of Upward Field‐aligned Currents Generated Near the Earth's Magnetopause Boundary

Sheared plasma flows in the boundary layer have been associated with field‐aligned currents (FACs) and particle precipitation. While the currents are generated by the potential difference across the magnetopause, the ionosphere plays a key role in controlling the currents. A magnetosphere‐ionosphere coupling model based on a Vlasov equilibrium solution for the generator is discussed. A simple analytical theory based on velocity shear generator and a quasi‐stationary magnetosphere‐ionosphere coupling model are reviewed. The comparisons of the theory with DMSP upward afternoon R1 FAC density (J ||) and FAC width (Λ) that are located at the low‐latitude boundary layer (LLBL) show remarkably good scaling of R1 with solar wind and ionospheric parameters. It is found that Λ ∼ n sw −0.5 and Λ ∼ L when Λ/L < 5 where L is the auroral electrostatic scale length. The average LLBL thickness (Δm) is inferred to be around 3000 km, which appears to have weak dependence on Vsw. J || has dependencies on Δm, Σ p , n sw , and V sw . The analytical theory provides a simple way to organize data and to infer boundary layer structures from ionospheric data. The calculated and observed J || are in good agreement. Excluding data from noon, log(J ||,max_cal) = (0.96 ± 0.04) log(J ||_obs) + (0.03 ± 0.01) where J ||,max_cal = calculated J ||,max and J ||_obs = observed J ||.