Long-term tendencies in the mesosphere/lower thermospheremean winds and tides as observed by medium-frequencyradar at Tirunelveli (8.7°N, 77.8°E)

摘要

The present study examines changes in monthly mean winds and tides observed byMF radar at Tirunelveli (8.7°N, 77.8°E) for the years 1993-2007 with respect to long-termvariabilities, namely, the stratospheric quasi-biennial oscillation (QBO), the El Nifio-Southern Oscillation (ENSO), the solar cycle (SC), and the long-term trends, usingregression analysis. Both zonal and meridional winds show negative QBO response in thealtitude region 84-94 km and negative ENSO response (-1 m s-1 per Southern OscillationIndex) above 90 km. However, only the latter show a notable positive SC response.The response of meridional diurnal tide is positive to ENSO (above 90 km) andstratospheric QBO and is negative to SC. The tides in both wind components showpositive trends. The meridional winds show a significant negative trend (0.3 m s-1 yr-I).Further, monthly variations of the responses of mean winds and tides to QBO, ENSO, andSC are presented and discussed.