[Seminar] Dr. Young-Ha Kim

Transient dynamics of gravity waves and its representation in a global mode

In recent decades, climate modeling studies have shown that the proper representation of the stratospheric circulation in models is required to reliably simulate the tropospheric climate and variability on seasonal to longer-time scales. Current-day global models include the mesosphere in their domains to fully resolve the stratospheric circulation, thereby demanding realistic parameterization of subgrid-scale (mesoscale) gravity waves, a key process that controls the middle atmospheric circulation. Traditionally, all existing gravity wave parameterizations have commonly been using several underlying assumptions to efficiently describe the wave processes. One of such assumptions is to diagnose the processes as if the waves reach the model top instantaneously once they are generated in the troposphere. This so-called steady-state assumption does not allow the waves to experience temporal variations of the background flow and to timely exchange their momentum with the flow. Given that it takes several hours to days for the waves to travel to the mesosphere, it is required to assess the reality of this assumption. In this talk, a prognostic model of gravity waves, which has recently been developed to simulate the transient propagation of waves, will be introduced, and the effect of the transient dynamics will be presented using this model as a subgrid-scale parameterization in the German operational atmosphere model (ICON). We focus particularly on the intermittency of simulated gravity waves and its comparison to the observations as well as on the modeled middle atmospheric circulation. In addition, a new finding of interaction between gravity waves and large-scale equatorial waves in the stratosphere, simulated using the same model, will be reported.