Long-term variations of atmospheric wave activity in the mesosphere and lower thermosphere region over the equatorial Pacific

Abstract

We have analyzed long-term variations of the wind velocity variance of ultra-fast Kelvin (UFK) waves (3.0–3.8 d) and gravity waves in two wave period ranges; 30–35 h (0.7–0.8 c/d) and 8–11 h (2.1–2.9 c/d), in the equatorial mesosphere and lower thermosphere region using meteor wind radar (MWR) observations in Jakarta (JKT) (6°S 107°E) from November 1992 to June 1998, as well as two medium frequency (MF) radars at Christmas Island (2°N 157°W) and Pontianak (0.03°N 109°E) from January 1996 to July 1997. The long-term variations of the wind variance of these waves at JKT showed enhancements twice a year in 1993–1995, mostly coinciding with the westward wind phase of MSAO or the transition period of MSAO from eastward to westward wind. The activity of both UFK and gravity waves became significantly weak in 1996–1997. In particular, the UFK wave variance became simultaneously smaller at JKT and the two MF radar sites, indicating that this peculiar event had a global scale.