Global thermospheric atomic oxygen variations observed with the WIND Imaging Interferometer (WINDII): Wave 4 at low and high latitudes

The O(S-1) 557.7 nm atomic oxygen emission as observed in the daytime at 250 km altitude by the WINDII instrument on the UARS satellite is presented as a means of determining atomic oxygen concentrations there. This offers to fill a gap lying between the well-studied MLT region and the upper thermosphere at 400 km. At 250 km the O(S-1) emission is dominantly produced by the impact of photoelectrons on atomic oxygen, so that atomic oxygen number densities may be determined simply by dividing the observed volume emission rate by the solar flux. Day-by-day plots of the derived atomic oxygen concentrations are seen to track both the solar flux and Kp, showing reasonable consistency with NRLMSISE-00 values. One of the important issues of this region is the influence on it of the DE3 nonmigrating tide produced by deep tropical convection in the troposphere. At 250 km the resulting wave 4 pattern is seen at the equator in this emission, apparently the result of bunching of smaller-scale N-S elongated features, oriented in the NE to SW direction. Although absent at midlatitudes, the wave 4 appears strongly at high latitudes; the first time this has been reported. As this is not predicted by existing models it presents a challenge for further study. In a polar map of the emission rate the primary features are a wave 1 pattern on which large scale spiral structures are superposed, suggesting transport of atomic oxygen out of the polar cap.