Winter/summer mesopause temperature transition at Davis (69°S) in 2011/2012

Kurzfassung

We present quasi-continuous measurements of temperature profiles in the Southern Hemisphere mesopause region during the transition from winter to summer conditions in 2011/2012. In a period of 120 days around solstice, we have performed iron lidar observations at Davis (69°S), Antarctica, for a total of 736 h. The winter/summer transition is identified by a downward shift of the mesopause which occurs on 8 November 2011. Soon after transition, mesopause heights and temperatures are similar to the Northern Hemisphere (NH) colatitude summer (88 km, 130 K). Around solstice, the mesopause is elevated for several days by 4–5 km and is colder than typical NH temperatures by 10 K. In this period individual profiles show temperatures as low as 100 K. The occurrence of polar mesosphere summer echoes is closely connected to low temperatures. Below 88 to 90 km and in the main summer season of 2011/2012 temperatures at Davis are generally warmer compared to the NH by 5–15 K, whereas temperatures are generally colder above 90 km. The winter/summer transition and the first appearance of polar mesosphere summer echoes are strongly correlated to maximum zonal winds in the stratosphere which constrain gravity waves with eastward momentum reaching the mesosphere. At the breakdown of the stratospheric vortex around solstice, the mesopause is higher and, surprisingly, colder than normal.