Formation, lifetime and climate impact of cirrus clouds and their interaction with dynamics using detailed cloud resolving models and ECHAM5

Investigations using box models and cloud-resolving models

The formation and life cycle of cirrus clouds is investigated using box models and large eddy simulations including a detailed ice microphysics scheme. The main focus is on the feedback between mesoscale dynamics and cirrus clouds. Here, different dynamical regimes are investigated, as orographic waves as a trigger for cirrus cloud formation (see movie) or convection inside ice-supersaturated layers. In addition, we investigate the competition of different ice nucleation mechanisms; including potential anthropogenic influences.

The formation and evolution of orographic cirrus clouds is shown in this movie. Colours indicate relative humidity over ice, grey lines show isentropes (i.e. approximately streamlines of the flow) and ice water content is denoted by white isolines.

Cirrus clouds in the general circulation model (GCM) ECHAM

Since the global net effect of cirrus clouds is highly uncertain, the representation of cirrus clouds in the ECHAM5 GCM is also a focus of our work. We are working on including the impact of mesoscale dynamics on cirrus clouds in the ECHAM5 GCM for a better representation of cirrus clouds. Recently, orographic cirrus clouds were included into the ECHAM5, leading to a more physical representation of cirrus clouds (Joos et al., 2008).

Global distribution of in cloud ice crystal number concentration (in cm^-3) in the upper troposphere (165-285 hPa) for (left) the simulation with the standard ECHAM and (right) the simulation with the newly developed coupling of gravity wave drag and ice microphysics in order to represent orographic cirrus correctly (from Joos et al., 2008).