Seasonal and quasi-biennial variations in the migrating diurnal tide observed by Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics (TIMED)

There are strong quasi-biennial oscillation (QBO) signatures in the amplitude of the diurnal tidal temperature in the tropical region and in the wind near ±20°. The magnitude of the QBO in the diurnal tidal amplitude reaches about 3 K in temperature and about 7 m/s (Northern Hemisphere) and 9 m/s (Southern Hemisphere) in meridional wind.

The period of the diurnal tide QBO is around 24 - 25 months in the mesosphere but is quite variable with altitude in the stratosphere. Throughout the mesosphere, the amplitude of the diurnal tide reaches maximum during March/April of years when the QBO in lower stratospheric wind is in the eastward phase. Because the tide shows amplification only during a limited time of the year, there are not enough data yet to determine whether the tidal variation is truly biennial (24-month period) or is quasi-biennial.