Global structures of the DE3 tide

Researchers from LAGEO , the Institute of Atmospheric Physics, has shown that the DE3 tide can propagate up to above 110 km height and exhibits 2-year cycle oscillation. Among all the diurnal tides in the upper atmosphere, this tide is the most prominent component other than the migrating diurnal tide. Moreover, its importantance has been highlighted in recent years as it is considered as a main mechanism responsible for the generation of a typical ionospheric disturbance, implying its involvement into the ionospheric dynamo. But before the launch of US satellite mission, TIMED, the observation of this tide has been confined below 100 km height and only annual variation has been reported. The result by Chen Zeyu and Lu Daren has been published online December 14, 2008, in Chinese Science Bulletin.

By using the temperature measurements taken by the TIMED mission during which reliable temperatures at the heights above 100 km are first available, the tidal signal during 2002—2006 was delineated. The researchers further applied Hough Mode Decomposition (HMD) to the tidal signal, and found that the DE3 tide is most predominated by two leading propagating Hough modes, i.e., (3, 3) and (3, 4) modes. As the Hough modes are the solutions to a classical tidal equation, the application of HMD not only simplifies the investigation procedure, but also puts the HMD results on physical bases.

The researchers observed that the (3, 3) mode exhibits annual unimodal distribution with the maximal amplitude occurring at 110 km in late summer (around July each year). Moreover, characteristic 2-year cycle oscillation is observed in the (3, 3) mode, which suggests that the tide undergoes the same type inter-annual variation. With the help of this information, the 2-year cycle variation of the DE3 tide was observed by the authors. For example, this paper shows clearly that at the equator, the DE3 tidal amplitude exhibits two substantially enhanced activities with maximal amplitude exceeding 12 K in 2002 and 2004, respectively.

The main conclusion drawn by the researchers is that the tidal activity can propagate to lower thermosphere, which is indicated by the amplitude maximum at 110 km height, and it undergoes inter-annual variation of 2-year cycle. The research is supported by the Knowledge Innovation Project of the Chinese Academy of Sciences and the National Natural Science Foundation of China .

Reference: Chen Z Y, Lu D R. Global structures of the DE3 tide. Chin. Sci. Bull., 2009, , doi:10.1007/s11434-008-0585-x...