Global structure, seasonal and interannual variability of the migrating semidiurnal tide seen in the SABER/TIMED temperatures (2002–2007)

Abstract. The present paper is focused on the global spatial (altitude and latitude) structure, seasonal and interannual variability of the migrating semidiurnal tide derived from the SABER/TIMED temperature measurements for 6 years (January 2002–December 2007). The tidal results are obtained by a new analysis method where the tides (migrating and nonmigrating) and the planetary waves (zonally travelling and stationary) are simultaneously extracted from the satellite data. The strongest migrating semidiurnal tide has been derived at tropical latitudes (±20–30°) where it revealed significant amplification between May and August in the lower thermosphere of both hemispheres. On the average, the semidiurnal temperature tide is stronger in the SH (32 K) than that in the NH (30 K) and the tidal amplitudes at 110 km height are nearly a factor of 5 larger than those at 90 km. The migrating semidiurnal tide in both hemispheres revealed remarkable seasonal behavior at the altitude where it maximizes, ~110 km in the NH and ~115 km in the SH, indicating repeatable each year maxima exactly in May–June and August. However, while the main maximum in the NH is that in August, in the SH it is that in May. The vertical wavelengths indicated seasonal variability being larger in summer (~38–50 km) than in winter (~25–35 km). The seasonal behavior of the semidiurnal tide in the middle latitudes (±40°) is dominated by annual variability with a winter maximum in the upper mesosphere (90 km) of both hemispheres and summer one in the lower thermosphere (110 km). The NH summer maximum (June and August peaks) is much stronger than that in the SH (November and March peaks) having amplitudes of ~23 K and ~13–15 K respectively. The vertical wavelengths at both hemispheres indicated slight seasonal changes and a mean vertical wavelength of ~35 km is observed during most of the year. The interannual variability of the semidiurnal tide in the midlatitude lower thermosphere is at least partly connected with the stratospheric QBO as this effect is stronger in the NH.