Structure of Dayside Polar Cusp Precipitation during the Northward Interplanetary Magnetic Field

The unique trajectories of DMSP spacecraft relative to a dayside polar cusp are considered. They allow the cusp precipitation to be characterized in different longitudinal sectors for short time intervals of 2–3 min. The latitudinal widths of a cusp depend on the magnetic local time (MLT) and differ considerably in the pre- and after-noon sectors. A large-scale trend in ion energy fluxes upon a change in MLT can be observed in a cusp, along with smaller variations in energy fluxes having longitudinal dimensions of ~100–150 km. The latitudinal widths of a cusp are determined mainly by the solar wind dynamic pressure ( Psw ). The width of a cusp is 2.0°–2.5° of latitude at Psw = 17–19 nPa and only ~0.3° at Psw ≈ 1.0 nPa.