Hemispheric Asymmetry of Annual/Semi-Annual Oscillations in Mesospheric Neutral Winds and Pressure Between Northern and Southern High Latitude Regions

Abstract

We present oscillating features from long-term neutral wind (meteor radar) and pressure (microwave limb sounder) measurements at Esrange (67°N, 20°E, 2007–2018) in the northern hemisphere and King Sejong Station (KSS; 62°S, 58°W, 2007–2017) in the Southern Hemisphere using the Lomb-Scargle periodogram and wavelet analysis. In zonal winds and pressure, we estimated the height profiles for the amplitude ratio between annual oscillation (AO) and semi-annual oscillation (SAO) at both sites. Over KSS, the ratio indicates that SAO increases with altitude, whereas AO decreases, with SAO becoming the dominant oscillating component at around 90 km. However, the ratio mostly remains constant with an altitude due to the steady formation of a westward wind field throughout the height in summer. More intensive gravity wave activity over KSS drives meridional residual circulation in summer mesopause, creating a more powerful SAO signature above 90 km.

Keywords

• mesospheric neutral winds/pressures
• annual oscillation
• semi-annual oscillation
• hemispheric asymmetry