[1] A new characteristic of the austral summer polar mesopause as revealed by ground-based radar and satellite temperature measurements is reported, that is linked to inter-annual variability of the low-latitude easterly wind jet. Four consecutive seasons of polar mesosphere summer echoes (PMSE) and mesosphere temperature observations above Davis, Antarctica (68.6°S) show a mid-January diminution in PMSE occurrence rate that coincides with a minor mesopause warming of several degrees. Spectral analyses of PMSE, Aura Microwave Limb Sounder (MLS) temperatures and radar meridional winds show the presence of ∼4–5-day planetary waves (PWs) throughout the austral summer in the polar upper mesosphere together with enhanced ∼2-day PW activity from mid-January to mid-February. Analysis of MLS temperatures show that the ∼2-day PWs have zonal wavenumbers (S) with both westward (S = −2, −3) and eastward (S = +2, +3) components. Although displaying some inter-annual variation in the peak onset time, the mid-January mesopause warming coincides with a weakening of the equatorward meridional wind above Davis and enhancement of low-latitude 2-day PW activity. ; Ray J. Morris, Andrew R. Klekociuk, and David A. Holdsworth