Interannual variability of mesopause zonal winds over Ascension Island: Coupling to the stratospheric QBO

Zonal-wind measurements obtained between October 2001 and July 2011 with the SKiYMET meteor radar located at Ascension Island (8 degrees S, 14 degrees W) have been used to study the interannual variability at meteor ablation altitudes (approximately 78-100 km) and its coupling to the stratospheric quasi-biennial oscillation (QBO). An upper mesospheric QBO (MQBO) with a period of 27.5 months has been detected throughout the observational period. The MQBO is found to be out-of-phase with the stratospheric QBO (SQBO) at 15-20 hPa and in-phase compared to 70 hPa, whereas no significant zero time-lag correlation exists between the long-term mesospheric zonal winds and the SQBO at 40-50 hPa. The MQBO magnitude is found to be 4.1+/-0.7 m/s at 88 km. No significant change in MQBO magnitude is found throughout the altitude range under consideration. It was found that the MQBO signal is mainly carried around the March equinox, although the MQBO signal is present throughout most of the year, although less pronounced, at the lower altitudes as well. No observational evidence was found that the MQBO, between approximately 78-100 km, plays a role in the interhemispheric ducting of the quasi-16 day wave.