Using the mesosphere-stratosphere-troposphere radar at Poker Flat, Alaska, the long-period waves (greater than 1.5 but less than 36 days) in the troposphere/lower stratosphere and mesosphere were analyzed for the first 340 days of 1984. A 16-day wave was significant the whole year in all regions resolved by the radar and had maxima in the winter lower stratosphere, consistent with the (1,3) Rossby normal mode. Contrary to the theory of the (1,3) normal mode, the observed 16-day wave had a maximum in the summer mesosphere. Two possible explanations are given: (1) The 16-day wave was generated in the winter hemisphere, then proprogated vertically and toward the summer polar following the westerly mean winds and (2) gravity waves from the summer troposphere modulated by the 16-day tropospheric wave propagated vertically into the mesosphere where the resulting momentum deposition varied in a 16-day cycle. The period of the 16-day wave varied from 12 to 19 days in the summer mesosphere. The quasi 2-day period in the high summer mesopshere migrated from about 51 to 47 hours over midsummer to midautum. ¿American Geophysical Union 1992