Minor ion composition in the polar ionosphere

Ion composition measurements from the EXOSD Suprathermal Ion Mass Spectrometer (SMS) are presented. Ions other than H + , notably O + , He + , O ++ N + and N ++ , are found to constitute a significant (>0.1) and at times dominant (>0.5) component of the thermal ion population in the high‐altitude polar ionosphere. Their relative abundance and occurrence are highly variable. Ion flux ratios in the range of 0.1–0.5 are typical for 0 + /H + , 0.1–0.3 for He + /H + , 0.1–0.3 for 0 ++ /O + , and 0.05–0.1 for N ++ /N + . Our observations show that (1) ions other than H + , notably He + , O + , O ++ and N + , often constitute a significant component (>0.1) of the thermal ion population in the high‐altitude polar ionosphere; (2) doubly charged oxygen and nitrogen (O ++ and N ++ ) are sometimes present with fluxes up to 0.1 of the singly‐charged (O + and N + ) ion fluxes; and (3) the He + and O ++ fluxes are sometimes comparable to the H + and O + fluxes.