Gravity-waves impact on ice clouds in the tropopause region (GW-ICE) / GW-TP -Modification of gravity waves propagating across the tropopause (GW-TP)

Peter Spichtinger, Universität Mainz
Ulrich Achatz, Goethe Universität Frankfurt
Andreas Dörnbrack, DLR Oberpfaffenhofen
Rupert Klein, Freie Universität Berlin

PhD students:
Niclas Ehlert, Uni Mainz; Christopher Pütz, Freie Universität Berlin; Vera Bense, Uni Mainz; Sonja Gisinger, DLR Oberpfaffenhofen;

For the second Phase of the Research Unit, the project GW-TP has been replaced by the project GW-ICE

Summary GW-ICE: - Gravity-waves impact on ice clouds in the tropopause region (GW-ICE)
Gravity waves constitute an important component of the atmosphere system. They influence the vertical momentum and energy transport and thus contribute crucially to circulations in the atmosphere. Gravity waves are excited mostly in the troposphere and propagate through the tropopause region into the higher atmosphere. During the propagation their properties might be changed. Additionally, gravity waves induce high vertical velocities and therefore influence the formation and evolution of ice clouds in the tropopause region. In this project the interaction between gravity waves and ice clouds will be investigated. For this purpose we will use the WKB model, which was developed in the first phase of MS-GWaves. This model will be extended by ice cloud physics and further will be used for the investigation of interactions of gravity waves and ice clouds. Additionally, gravity wave-induced ice clouds will be simulated using a large eddy simulation (LES) model. Possible feedbacks of ice clouds to tropopause dynamics by diabatic effects will also be investigated. The radiative effect of simulated ice clouds (WKB or LES model) will be investigated using a radiative transfer model. Thus, we will be able to estimate the impact of gravity waves on ice clouds and their radiative forcing. We will also estimate feedbacks of ice clouds to tropopause dynamics and will give a better estimate of the radiative forcing of gravity wave-induced ice clouds.

Summary: GW-TP - Modification of gravity waves propagating across the tropopause (GW-TP)
The tropopause region has a potentially crucial impact on vertically propagating gravity waves. In this region static stability (N) and horizontal wind (U) change significantly, leading to wave propagation or (partial) reflection depending on the pertinent flow regime. In addition, non-linear effects, such as wave generation by shear instabilities, are likely to arise. Because of the strong gradients of N and U, the tropopause region has its own dynamical characteristics. Thus, we expect that gravity waves induce variations in the tropopause region. However, since detailed observations and—in particular--systematic theoretical investigations are lacking thus far, current understanding of these processes is limited. As a consequence, solid parameterisations for propagating waves through the tropopause are not available.