Global structure and seasonal and interannual variability of the migrating diurnal tide seen in the SABER/TIMED temperatures between 20 and 120 km

摘要

The present paper is focused on the global spatial (altitude and latitude) structure and seasonal and interannual variability of the migrating diurnal tide derived from the Sounding of the Atmosphere using Broadband Emission Radiometry/Thermosphere-Ionosphere-Mesosphere-Energetics and Dynamics (SABER/TIMED) temperature measurements for 6 full years (January 2002 to December 2007). The tidal results are obtained by a new analysis method where the tides (migrating and nonmigrating) and the planetary waves (zonally traveling and stationary) are simultaneously extracted from the satellite data. It has been found that above 70 km height the SABER migrating diurnal tide reflects mainly the distinctive features of the first symmetric propagating (1,1) mode, while below this height it reflects the features of the first symmetric trapped (1,?2) mode. The trapped component amplifies near 50 km, and its phase is close to ～1600 LT. The seasonal behavior of the diurnal tide over the equator is dominated by semiannual variation with a primary maximum in February–March (18 K, average amplitude for 6 years) and a secondary maximum in August–September (15 K). The tidal amplitude grows rapidly in the mesosphere/lower thermosphere; however, it undergoes some decay near ～90 km, defining ubiquitous double-peaked vertical structure. A very rapid reduction in amplitude is detected at heights near 115 km; however, above this level the diurnal tide amplifies again. The vertical wavelength of the propagating diurnal tide is ～20 km over the equator; at middle latitudes it is not very different from that over the equator, but its magnitude depends on the season. In the winter it is longer than that in summer. The interannual variability of the diurnal tide indicates a clear correlation with the stratospheric quasi-biennial oscillation.