Radar observations of longitudinal variability of tidal/planetary waves and mean motions in the tropical mesosphere

During the summer of 1995, two MP radars located at Hawaii and Puerto Rico were in operation to measure mesospheric motions. We use the data obtained at the two sites to study the longitudinal variability of mean winds, plane tary waves, and tides. On average the winds at Puerto Rico were more westwa rd and equatorward than those at Hawaii. Quasi 2-day planetary wave activit y was evident most of the time from June 28 to July 25. The quasi 2-day wav e had a zonal wave number (m) of 3 during one occasion and 4 during another , and the periods of the two planetary waves were 56 and 48 hours, respecti vely. The diurnal tide at Puerto Rico was stronger than that at Hawaii abov e 86 km, and the semidiurnal tide at Hawaii was strongly damped in the alti tude range of 90-98 km. Both the semidiurnal and the diurnal tides were app arently modulated by longer-period waves, which was perhaps the most import ant factor in accounting for their large spatial and temporal variability. The phase difference at the two sites deviates considerably from the expect ation of purely migrating tides.