Semiannual oscillation, annual oscillation, quasibiennial oscillation, and solar cycle variation of the OH airglow emission in the mesopause region

The vertically integrated emission rate, centroid altitude, peak emission rate, and peak height of the hydroxyl (OH) airglow were calculated from Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED)/Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) observations to study the seasonal and interannual variations in the intensity and location of the OH emission. The emission rate is inversely proportional to the height of the emission, with the semiannual oscillation dominating at low latitudes and the annual oscillation dominating at higher latitudes. The OH emission is modulated by the quasibiennial oscillation at the equator, and the quasibiennial oscillation signal is weak at other latitudes. We represented the vertical transport of atomic oxygen by using atomic oxygen concentrations obtained from a global atmospheric model, the Specified Dynamics Whole Atmosphere Community Climate Model with thermosphere and ionosphere eXtension simulations. Compared with the amplitudes of the migrating diurnal tide (DW1) calculated from temperature data observed by TIMED/SABER, we found that both the vertical transport of atomic oxygen and DW1 amplitudes in the equatorial region exhibit semiannual oscillation and quasibiennial oscillation, which have a strong correlation with the variations in the amplitude and phase of semiannual oscillation and quasibiennial oscillation in OH emission. It is likely that the DW1 affects the vertical transport of atomic oxygen that is involved in the reaction to produce O₃, thus affecting the OH emission. We analyzed the relationship between OH emission and solar activity by using the solar radio flux at 10.7 cm as a proxy for solar activity. The results showed that the OH emission is well correlated with solar activity, and the modulation of OH emission by solar activity has a significant latitudinal variation. The small correlation between emission height and solar activity indicates that solar activity modulates OH emission mainly through chemical rather than dynamic processes.