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

Abstract

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.

Seasonal and Interannual Variation of Mesospheric Gravity Waves Based on MF Radar Observations over 15 Years at Syowa Station in the Antarctic

“…Lübken et al (2014) showed that the timing of the zonal wind decrease associated with the stratospheric polar vortex breakdown in spring was consistent with the onset of polar mesospheric clouds (PMC), and the temperature decrease around the mesopause. These authors proposed that the simultaneous changes in the two separate height regions could be explained by an increase in the eastward forcing by GWs that can propagate into the mesosphere after the stratospheric winds have weakened; however, they did not show observational evidence of the GW modulation.…”

Using polar mesosphere summer echoes and stratospheric/mesospheric winds to explain summer mesopause jumps in Antarctica

“…In subsection 4.2 we will use these observations to provide an explanation for the unique temporal variation of the mesopause at Antarctic latitudes. Note that some related observations have been published before (Kirkwood et al, 2008;Karlsson et al, 2011;Benze et al, 2012;Morris et al, 2012;Lübken et al, 2014;Viehl et al, 2015).…”

“…High resolution temperature measurements by resonance lidar have recently revealed that in mid summer at Davis (69 • S) the altitude of the mesopause increases within a few days and its temperature decreases substantially compared to the standard northern hemisphere values of 88 km and 130 K, respectively (Lübken, 1999;Lübken et al, 2014Lübken et al, , 2015. Model results indicate that this phenomenon is related to the circulation in the stratosphere coupled to the mesosphere by the transmission of gravity waves (see, e.g., Becker et al, 2015).…”

Frequency spectra and vertical profiles of wind fluctuations in the summer Antarctic mesosphere revealed by MST radar observations

“…Kirkwood et al . [] and subsequent studies [e.g., Lübken et al ., ] indicated that the PMSE detection in the SH usually starts at high altitudes and descends gradually with time. Such a feature is observed in the 2014/2015 and 2015/2016 seasons but not in 2013/2014.…”