Springtime transition in lower thermospheric atomic oxygen

Abstract

Abstract. Observations from three optical ground stations and the wind imaging interferometer on the upper atmosphere research satellite have been combined to describe a "springtime transition" in atomic oxygen. At each station the transition is characterized by a rapid 2-day rise in the night-time oxygen airglow emission rate by a factor of between 2 and 3, with a subsequent decrease by a factor of about 10 in the same period of time. This latter state of extremely weak oxygen airglow indicates a depletion of atomic oxygen that persists for many days. The characteristic signature is similar at both mid-latitude and high-latitude stations and is also observed in the hydroxyl airglow, except that immediately following the enhancement, the hydroxyl emission rate does not fall below the value it had before the event. Airglow rotational temperatures behave coherently with the emission rate. WINDII data show that the airglow emission rate perturbation is a planetary scale feature associated with strong vertical motions and that the event may be associated with the winter-tosummer zonal wind reversal. Data from the northern springtimes of 1992 and 1993 are reported upon in detail, with additional data from 1995 to confirm the persistence of the phenomenon.

First Ground Observations of OI5577 Green Line Emission over the Taiwan Area

“…In general, analysis shows a maximum during autumn and minimum near the spring equinox, but the detailed behavior strongly depends on the latitude. Latitudinal dependence indicates that the emission rate increases with latitude and this result has been confirmed in many other reports (e.g., Donahue et al 1973;Cogger et al 1981;Shepherd et al 1999). However, investigations of daily variation of OI5577 do not show clear characteristics pertaining to maxima or minma during daily observation.…”

Effects of solar cycle variations on oxygen green line emission rate over Kiso, Japan

“…During March to August i.e., during spring equinox and summer, there is an increasing trend in the emission rate as the night progresses and the opposite is seen during September to October i.e., during vernal equinox, where the emission rate is showing a decreasing trend. We know that the green line emission is greatly in uenced by the dynamical processes, especially the tides (Shepherd et al, 1995(Shepherd et al, , 1999Ward, 1999). Generally, a minimum is seen during midnight over the equator, while the mid-latitudes experience a maximum.…”

Quiet time F2-layer disturbances: seasonal variations of the occurrence in the daytime sector

“…1, right panels) can be related, on the one hand, with the maximal occurrence of geomagnetic disturbances (of low intensity as well) during equinoctial periods (Roosen, 1966). On the other hand, this effect can be related to the equinoctial transition in atomic oxygen abundance (Shepherd et al, 1999;Shiokawa and Kiyama, 2000;Mikhailov and Schlegel, 2001). The most probable reason for such variations is a change in the global circulation pattern accompanied by vertical motions inferred from observations at E-region heights (e.g.…”

“…Therefore, the tendency of the highand middle-latitude positive Q-disturbances to cluster around equinoxes can be related, on the one hand, to the maximal occurrence of geomagnetic disturbances (of low intensity as well) during equinoctial periods. On the other hand, this effect can be related to the equinoctial transition in atomic oxygen abundance (Shepherd et al, 1999;Shiokawa and Kiyama, 2000;Mikhailov and Schlegel, 2001). …”