Summary
There are continuing efforts to refine our understanding of the association between Polar Mesospheric Clouds (PMCs) and Polar Mesosphere Summer Echoes (PMSEs). These layered phenomena of the high-latitude summer mesopause region are revealing important details on physical conditions at extremely low atmospheric temperatures and pressures, as well as dynamical processes ranging in scale from gravity waves to inter-hemispheric circulation. The first simultaneous common-volume observations of PMC and PMSE by lidar and radar in the southern hemisphere were made at Davis station (68.6°S, 78.0°E) during the 2005/06 austral summer. From 349 hours of Rayleigh lidar operation, PMC were detected during 21 hours (6% occurrence probability). PMSE were simultaneously observed during 41% of the PMC events. During coincident events, PMCs were generally seen overlapping with the lower borders of PMSE regions. The PMCs were narrower in vertical extent than the PMSEs, with overall mean root-mean-square thicknesses of 0.46±0.02 km and 1.61±0.09 km respectively (one standard error in the mean quoted). Both phenomena exhibited diurnal variations in occurrence, height and intensity. At Davis, the mean centroid heights of coincident PMCs and PMSEs were 83.97±0.10 km and 85.31±0.14 km respectively. While the difference in centroid height between the two phenomena (approximately 1.3 km) is similar to that seen in the NH, the individual mean values are approximately 1 km higher at Davis than for near-conjugate NH latitudes. This paper presents a summary of the Davis observations, and a discussion of the centroid height difference in PMC and PMSE distributions in terms of the asymmetry in summer mesopause frost point regions between the northern and southern hemispheres revealed by the Aura satellite.