The Quasi 16-day Waves in the Mesosphere and Lower Thermosphere at Wuhan

Data observed by the Wuhan meteor radar(20 February 2002-10 November 2003) have been used to study the quasi 16-day oscillations in the mesosphere and lower thermosphere(MLT),which is a type of planetary wave with period ranges from 12 to 20 days.The results show that the zonal components are generally stronger than the meridional components.(1) In the year of 2002 and 2003,the largest amplitudes appear in early autumn(10 September-10 October) when the zonal background winds are eastward.The largest amplitude value derived from the Lomb-Scargle(L-S) periodograms is about 16 m/s.A second maximum appears in the summer of 2002,but not in the summer of 2003.There are no strong wave activities in the winter months of both years.(2) In 2002,the 16 day waves are strong from 86 to 98km with the maximum at about 90km to 94km,but they are strong at lower altitudes in 2003.The energy of the 16-day wave propagates upward in autumn,which means the wave originate from lower atmosphere,but the direction of wave energy propagation is downward in summer of 2002,which means the 16-day waves may propagate from the southern hemisphere.