Energetic atomic and molecular ions of ionospheric origin observed in distant magnetotail flow‐reversal events

Abstract

Energetic atomic (O+1 and N+1) and molecular (O2+1, NO+1, and N2+1) ions of ionospheric origin were observed in Earth's magnetotail at X ∼ −146 RE during two plasma sheet sunward/tailward flow‐reversal events measured by instruments on the GEOTAIL spacecraft. These events were associated with concurrent ground‐measured geomagnetic disturbance intensification at auroral‐ and mid‐latitudes (Kp = 7−). Energetic ions in the sunward‐component and tailward flows were from both the solar wind and ionosphere. Plasma and energetic ions participated in the flows. During tailward flow, ionospheric origin ion abundance ratios at ∼200–900 km/s in the rest frame were N+1/O+1 = ∼25–30% and (O2+1, NO+1, and N2+1) /O+1 = ∼1–2%. We argue that tailward flow most likely initiated ∼80–100 RE tailward of Earth and molecular ions were in the plasma sheet prior to geomagnetic intensification onset.