Local and Global Drivers of the Mesopause

The drivers of the southern summer mesopause are investigated through a series of simulations using the Kühlungsborn Mechanistic General Circulation Model (KMCM) compared to lidar and radar observations from 2010 to 2013, which were presented in Lübken et al., JGR (2015). In general, the simulations before and during the breakdown of the polar jet agree quite well with the observations in terms of mesospheric winds and mesopause jumps, i.e., cooling and altitude changes. After the breakdown, the agreement is less good, as the mesopause response is more pronounced in the simulations than in the observations.

In my presentation, I will discuss the reason for the qualitative differences during the summer, namely the interaction between gravity wave activity and the two different mechanisms responsible for the jumps. These are 1)  the breakdown of the jet stream in November or December (allowing gravity waves from the lower atmosphere to propagate into the mesopause) and 2), the manifestation of interhemispheric coupling triggered by the warming of the northern winter stratosphere (which modifies the temperature gradient between the equatorial and polar regions). I will finish with an explanation for the differences between observations and simulations in the latter case due to a shift in the most cooled region relative to the mesopause.