Sounding‐rocket observation of O II 83.4‐nm emission over the polar ionosphere

Results of recent satellite observations indicate that a large amount of O + are escaping from the terrestrial ionosphere into the magnetosphere. However, either the global distribution or the temporal variation of such O + escape has not been understood well yet. A 2‐Dimensional observation of oxygen ion emission (e.g., O II 83.4 nm) provides crucial information on the oxygen escape processes. In order to establish the basic technology required for such a 2‐D (i.e., imaging) observation, we have developed an eXtreme Ultra‐Violet (XUV) sensor sensitive to the O II 83.4‐nm emission. In this study we present recent results of the observation of O + ion escape from the ionosphere in the polar cap region using our XUV sensor carried by the sounding rocket SS‐520‐2. The XUV sensor successfully obtained an altitudinal profile of the intensity of the O II emission from 150 km through 1100 km of altitudes and detected 5–6 Rayleighs of the O II emission from the uppermost part of the ionosphere. The observation suggests that O + ions convected from the cusp/cleft region exist over the polar ionosphere.