On the impact of the extratropical tropopause inversion layer on coupled troposphere-stratosphere dynamics

Abstract:

The extratropical tropopause inversion layer (TIL) is a layer of enhanced stratification just above the local tropopause. Recent studies have suggested that the TIL may play a role in the propagation (and perhaps even generation) of planetary waves into the lower stratosphere. This is because the TIL tends to enhance the tropopause-level wave-guide, allowing for easier propagation of the tropospheric waves into the stratosphere. These waves then break in the stratosphere and can decelerate the stratospheric polar vortex, sometimes leading to sudden stratospheric warming events (SSWs). The TIL can also affect the downward impact following SSWs or other stratospheric anomalies. To assess the impact of the TIL on the two-way stratosphere-troposphere coupling as well as the general tropospheric dynamics, we use an idealized dry dynamical core general circulation model with varying TIL strengths. The model generates a weak TIL on its own; by imposing a specifically designed heating profile we are able to effectively control the TIL strength of our model simulations. Our experiments reveal that stronger TILs tend to be associated with more frequent SSWs, consistent with the above mentioned suggestions of recent studies. It also reveals potential changes to tropospheric baroclinic life cycles as well as a somewhat weaker tropospheric response to those SSWs associated with stronger TIL.