Winter/summer transition in the Antarctic mesopause region

Abstract

A new set of temperature data with unprecedented resolution and accuracy has been obtained from Fe lidar measurements at Davis, Antarctica (69∘S). Here we concentrate on the months of the winter/summer transition (November to February) where we have collected a total of 1305 hours of observations in the three seasons 2010/2011, 2011/2012, and 2012/2013. The temporal development of temperatures around the mesopause in 2012/2013 is rather similar to the northern hemisphere (NH), whereas the other seasons are significantly different, exhibiting, e.g., an unusual higher and colder mesopause around solstice (‘elevated summer mesopause’, ESM). During this exceptional period mean daily mesopause heights and temperatures are approximately 92.0±0.5 km and 125 K, respectively. The seasonal variation of temperatures in the mesopause region is closely related to the circulation in the stratosphere which exhibits an early (late) vortex breakdown in 2012/2013 (2010/2011). The situation is more complicated in 2011/2012. The early (late) transition in the mesopause region is accompanied by an early (late) appearance of polar mesosphere summer echoes (PMSE). Zonal winds as measured by an MF radar also show systematic differences with westward winds reaching up to very high altitudes (nearly 100 km) for the late transition in 2010/2011 and to more common heights (∼90km) for the early transition in 2012/2013. A mesopause being higher and colder compared to the NH (as occasionally observed at Davis) cannot be achieved by standard models. More sophisticated characterization of gravity wave forcing might be required.