1.  学术报告：The seasonal variation of the diurnal thermal tide - from meteor radar, TIMED observations and WACCM4 | | 时间：9月16日（星期五）上午9：00
地点：行政科研楼1514室
报告人：Lu Xian博士（美国伊利诺伊大学 UIUC）
摘要：The seasonal variability of the diurnal tide in the mesosphere and lower thermosphere (MLT) over Maui, HI (20.7◦N, 156.3◦W) is investigated using meteor radar horizontal wind measurements from years 2002 to 2007. The semiannual oscillation (SAO) of tidal amplitudes is dominant above ∼88 km, with amplitudes at equinoxes 2-3 times larger than at solstices. Below 88 km, the annual oscillation (AO) dominates and its magnitude is smaller than the SAO. The AO dominates in the phase variation of the diurnal tide, which advances in winter and lags in summer as compared with equinoxes. The vertical wavelength also has a noticeable seasonal variation with shorter vertical wavelengths found at equinoxes. The reconstructed diurnal tide from the TIDI and SABER measurements is compared with the meteor radar observation and a consistency is found in the seasonal variation of the tidal amplitude. Based on the TIDI and SABER measurements, the migrating diurnal tide (DW1) is the dominant tidal component while three other nonmigrating tides, DW2, DS0 and DE3, are non-negligible. The seasonal variation of the diurnal tide is well captured by the Global Scale Wave Model and the Whole Atmosphere Community Climate Model (WACCM) while important discrepancies still exist.
The WACCM is used to investigate the mechanisms causing the seasonal variability of the diurnal tide. The radiative heating due to the radiative heating by water vapor is important to determining the SAO of the tidal amplitude. The tidal heating is more symmetric at equinox and stronger (1,1) Hough mode is excited, which is the dominant mode in the MLT region. The superposition of the (1,1) and (1,2) Hough modes are responsible for the inter-hemispheric differences and AO of the tidal phase.
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