[P-EM05_2AM1] Characteristics of atmospheric waves in the mesosphere-lower thermosphere (MLT)

[PEM05-04] Long-term observations of MLT zonal wind variations in relation to stratospheric zonal winds over low-latitudes

*Kishore kumar GRANDHI¹, Kishore kumar KARANAM², Werner SINGER¹, Christoph ZULICKE¹, Gurubaran S³, Baumgarten GERD¹, Geetha RAMKUMAR², Sathishkumar S⁴, Markus RAPP⁵ (1.Leibniz Institute of Atmospheric Physics, University of Rostock, Kuhlungsborn, Germany, 2.Space Physics Laboratory, Vikram Sarabhai Space Center, Trivandrum, India, 3.Indian Institute of Geomagnetism, Navi Mumbai, India, 4.Equatorial Geophysical Research Laboratory, Indian Institute of Geomagnetism, Tirunelveli, India, 5.German Aerospace Center Institute of Atmospheric Physics (IPA), Oberpfaffenhofen, Wessling, Germany)

Keywords:MLT winds, MSAO, Meteor radar, MF radar, QBO

Long-term observations from medium-frequency and meteor radars (1993-2012) and rocket soundings (1979-1990 and 2002-2007) are used to study mesosphere lower thermosphere (MLT) zonal wind variations in relation to the stratospheric winds over Northern low-latitudes. The combined dataset provide a complete height profile of amplitude of semiannual oscillation (SAO) up to 100 km, with an exception around 75-80 km. The SAO signal has maxima around 50 km and 82 km and a minimum around 65 km. The MLT zonal winds show remarkable inter-annual variability during spring equinox and much less during fall equinox. Zonal wind mesospheric spring equinox enhancements (MSEE) appear with a periodicity of 2-3 years suggesting a modulation by the quasi-biennial oscillation, which we identified with the strength of stratospheric westward winds. Out of 20 years of observations, the stratospheric westward winds are strong during 11 years (non-MSEE) and weak during 9 years. Six of these years show large MLT winds (MSEE) and 3 years (1999, 2004 and 2006) show small MLT winds (missing-MSEEs). These unexpected small winds occur in years with global circulation anomalies as identified with strong sudden stratospheric warmings and an early spring transition of zonal winds, along with a minor enhancement in the tidal amplitudes.