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A simple model of complex cusp ion dispersions during intervals of northward interplanetary magnetic field

During northward IMF intervals, cusp ion energy‐latitude dispersions observed by POLAR's TIMAS instrument often have two components. One dispersion decreases in energy with decreasing latitude. The second appears to split from the first and increases in energy as the equatorward edge of the cusp is approached. We present a simple model representing particle entry resulting from reconnection poleward of the cusp. We qualitatively show that split dispersions may arise on reconnected field lines which accelerate as they contract sunward into regions of lower magnetosheath flow velocity. The velocity filter effect produces the first dispersion by spreading particles entering near the reconnection site across a range of latitudes. The second, increasing energy dispersion, results from particles crossing the magnetopause at later times and lower latitudes. These particles are accelerated to higher energies due to the increased contraction speed of reconnected field lines at these latitudes.