Abstract
A significant inter-annual decrease in polar mesosphere ice-particles, i.e., PMSE and PMC, during 2010–2011 is compared with earlier austral summers, in particular with 2009–2010. The first IAP iron lidar temperature measurement at Davis (68.6°S), Antarctica from 14 December 2010 are used to assess thermal effects of atmospheric processes on the mesopause region. We report low average temperatures of ∼125K measured by Fe-lidar near 90km when the PMSE season commenced, whereas temperatures were warmer in 2010–2011 compared to 2009–2010 at altitudes where PMSE normally occur (around 86km). Summer mesopause region temperature anomalies are derived using Aura MLS records. We reveal that the late break-down of the Antarctic stratospheric polar vortex on 5 January 2010, coupled with enhanced early summer mesospheric zonal wind field, provide a barrier to upward propagation of atmospheric gravity waves to be the main mechanism for the observed warm early summer season below the mesopause. The mesopause in 2010–2011 was unusually high and cold. We conclude that the timing of the annual break-down of the southern polar stratospheric vortex as manifest in zonal winds at 30hPa impacts mesosphere temperature and ice-particle formation early in the austral summer.
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