Cirrus clouds during a Rossby Wave Breaking event

Master project suitable for master studies in
Atmosphere and Climate Science/Computational Sciences and Engineering/Earth Sciences/Environmental Sciences/Physics

Background:

Clouds are one of the most unknown components of the climate system. Cirrus clouds, consisting exclusively of ice crystals and occurring in the tropopause region, can contribute either to a net warming or a net cooling, depending on their microphysical properties. While the ice mass concentration (i.e. ice water content) is mainly determined by the environmental conditions (temperature and humidity) ice crystal number concentration is strongly influenced by the local dynamics. It is commonly assumed that large-scale dynamics is an important trigger for cirrus cloud formation and evolution. Especially, a significant impact of warm fronts associated with low-pressure systems is often assumed. However, the direct link between large-scale dynamics and cirrus clouds is still unclear. For a better understanding we have to investigate the properties of dynamics and cirrus clouds for establishing a proper link. There are some indications that cirrus clouds are sometimes associated with Rossby Wave Breaking (RWB) events.  These waves are present in the mid latitude atmosphere, leading to the formation of high- and low-pressure systems.

Concept:

Since the mechanism how RWB events could influence cirrus clouds is not clear, a case study of a RWB event with simultaneously observed cirrus clouds will be carried out. Cirrus clouds were measured by a ground-based Lidar at Kühlungsborn, Germany, on February 25th, 2008. Additionally, radiosonde data are available for in situ information of temperature, pressure and humidity as well as wind fields. For identifying large-scale structures and 3D information about meteorological variables, meteorological analyses/reanalyses from the European Centre of Medium-Range Weather Forecasts (ECMWF) are available. This data set can be also used as input for trajectory calculations in order to obtain information about the mean airflows and possible cloud formation events. Last but not least, satellite images from different platforms are available for identifying clouds and cloud structures from space. The main concept of the project is to combine the different data sets in order to obtain a conclusive picture about the formation and evolution of the measured cirrus clouds during this RWB event.

Master project:

As stated above the main task is to combine the existing data set to a conclusive picture about the life cycle of the measured cirrus cloud. In addition, a Lagrangian point of view should be introduced. For this purpose, trajectory calculations with the LAGRangian ANalysis TOol (LAGRANTO) will be carried out. These trajectories then will be used as input for a simple box model including ice microphysics. Using this box model in combination with the Eulerian data sets will enable us to study the life cycle of cirrus clouds in RWB events more precisely. The box model and the trajectory tool LAGRANTO are available and are intensively used for cirrus cloud studies. The final goal would be a better understanding of the life cycle of cirrus clouds in RWB events.

This work is collaboration with PD Dieter Peters (IAP Kühlungsborn, Germany) and Dr. Andreas Dörnbrack (DLR Oberpfaffenhofen, Germany).

Requirements:
•    (Basic) Knowledge of a higher programming language (MATLAB, FORTRAN etc.)
•    (Basic) Knowledge in cloud physics and atmospheric dynamics


Contact:
Dr. Peter Spichtinger
Institute for Atmosphere and Climate Science
Universitaetstrasse 16, CHN O16.2
8092 Zurich
Tel.: 044/63 27315
Email: peter.spichtinger@env.ethz.ch