Waves with period near 3 days in the equatorial mesosphere and lower thermosphere over Ascension Island

A meteor radar was deployed on Ascension Island (8°S, 14°W) in the equatorial mid-Atlantic in 2001. Routine operation started in October of that year. The radar has been used to measure horizontal winds in the equatorial mesosphere/lower thermosphere (MLT) region over the interval October 2001-October 2002. Here, we present results concerning atmospheric waves with periods between ∼2 and 4 days-a period range which includes 3-day, planetary-scale, ultra-fast Kelvin waves. The observations reveal that in this period range, the wave field is highly variable and, although it displays clear signatures of ultra-fast Kelvin waves, such waves are intermittent and make a relatively minor contribution to the total wave activity at periods near 3 days during this year.