First observations of Southern Hemisphere polar mesosphere winter echoes including conjugate occurrences at ∼69°S latitude

Abstract

[1] We present the first account of polar mesosphere winter echoes (PMWE) observed from the Southern Hemisphere (SH), using measurements from Davis, Antarctica (68.6°S; 78.0°E). PMWE were observed by mesosphere-stratosphere-troposphere (MST) radar during solar proton events (SPEs) and auroral substorms. We supplement the MST radar measurements with profiles of temperature and turbulent velocity from co-located Rayleigh lidar and medium frequency (MF) radar, respectively, as well as temperature data from the Microwave Limb Sounder (MLS) onboard the Aura satellite. We establish that SH PMWE exhibit similar characteristics to their well-studied northern hemisphere counterpart. Significantly our observations reveal that these radar echoes in the lower mesosphere (∼50–80 km) can occur year-round, and on occasions simultaneously in both hemispheres. We report the seasonal occurrence distribution of SH PMWE is linked to the seasonal distribution of atmospheric turbulence in the lower mesosphere. We hypothesise that given sufficient turbulent velocities in the neutral atmosphere and co-located gradients in electron density, PMWE can occur throughout the year. However they are more likely in winter when turbulent velocities in the lower mesosphere maximise.