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Topics for master theses in the theory group

Bei Interesse an Masterarbeiten im Lehrstuhl für Theoretische Meteorologie bitte bei Prof. G. Craig, Prof. T. Birner, Priv.Doz. T. Janjic oder Dr. C. Keil nachfragen. Nachfolgend eine Auswahl derzeit offener Themen:

Dynamics-transport coupling in the stratosphere

The stratospheric circulation is projected to change in response to a warming climate. A changing circulation can impact the transport of trace gases (ozone, water vapor and ozone destroying substances) in the middle and upper atmosphere. The project will focus on developing a better understanding of the dynamics-transport coupling in the stratosphere.

Changes in the large-scale stratospheric dynamics and transport of trace gases will be investigated using a combination of theory, observations and numerical modeling. Key topics of investigation will be the subseasonal to climatological impact of stratospheric dynamical processes on the global distribution of tracers in the stratosphere. A hierarchy of climate models will be used.

For more detailed information please contact Aman Gupta or Thomas Birner.

Large-scale impacts of convective clouds

Although convective clouds are much smaller than large-scale weather systems, they can be a major source of error in weather forecasts because errors grow rapidly. Studying this error growth requires large ensembles of forecasts to accurately represent the many ways that the weather situation can develop. The aim of this project is to develop a simple numerical model that can represent the error growth processes, but is inexpensive to run in large ensembles. Different model formulations will be designed, programmed in Python and evaluated using advanced verification measures.

For more detailed information please contact George Craig.

Stratosphere-troposphere and climate dynamics

Topics broadly in the area of stratosphere-troposphere and climate dynamics are available upon request. Recent research topics in our group include: variability and long-term trends in the width of the tropical belt, processes that govern the temperature structure of the tropical tropopause layer, the dynamics of sudden stratospheric warmings and their coupling to the troposphere, transport processes in the upper troposphere / lower stratosphere. Interested candidates are asked to look through research topics on our group's website, in particular our recent publications: https://www.meteo.physik.uni-muenchen.de/~Thomas.Birner/pubs.html.

For more detailed information please contact Thomas Birner.

Assimilation of cloud information

The assimilation of cloud-related observations is challenging as traditional error metrics (e.g. RMS error) are not really suitable for the evaluation of intermittent fields as clouds or precipitation (double penalty problem). To overcome this deficiency, various feature-based scores have been developed for the verification of forecast precipitation fields, but these scores have not yet been applied in the context of data assimilation.

The goal of this thesis ist to test the use of feature-based metrics for the assimilation of cloud-affected satellite observations in the emsemble data assimilation system KENDA for the regional weather forecast model COSMO-DE. Different approaches shall be tested in an idealized setup of KENDA that is used by several people in the HErZ data assimilation group.

Contact: Leonhard Scheck

Tropospheric moisture variability and the development of tropical convection

Observations and high-resolution numerical simulations both show that tropospheric humidity affects the development of deep moist convection, with a drier troposphere typically limiting or delaying the apparition of the deepest clouds. This phenomenon is generally explained by the fact that a dry environment can quickly erode the cloud core through lateral mixing (called entrainment). Although convective cloud parameterizations usually account for entrainment, the influence of environmental humidity is generally not well captured, in part because the host model (typically a weather prediction or climate model) cannot resolve all the small spatial humidity fluctuations.

In this project, a Cloud Resolving Model (CRM) operating at about 100m resolution will be used to examine the connections between the development of deep clouds and small scale moisture fluctuations in the free troposphere. The analysis of high-resolution model data should constitute the first step towards a parameterization of convection that could explicitly account for unresolved moisture variability.

Contact: Julien Savre

Applicability of lossy compression methods to meteorological applications

The storage space requirements for output of numerical weather and climate prediction is growing faster than the cost of storage space is decreasing. Model resolution is continuously increased to overcome issues with parameterized physical processes like convection. At the same time the ensemble size (e.g. the number of model runs performed to create one forecast) is also increased to improve the assessment of uncertainty within the forecast. Both in combination results in really big data sets that are not only difficult to process but also very expensive to store.

One way to reduce the amount of output is to rely more on online diagnostics and not to save large fractions of the output. While this approach appears promising in operational setups of weather services, it is only a partial solution in research. Visualization of arbitrary aspects of a model run would no longer be possible and experiments would have to be carried out again if changes are made to the online diagnostic.

Another way is to store model output with reduced precision. File formats currently in use support only lossless compression or if lossy compression is possible only spatial correlation between neighboring data points is used (e.g., JPEG compression). The temporal correlation is ignored. In contrast, video compression algorithms are essentially based on the temporal correlation between successive time steps. Without reducing the quality, this results in a compression ratio that is by one order of magnitude higher than that of individual images. Central ideas of video compression should be directly transferable to the compression of model output. Examples are differential coding (only differences between time steps are stored) and motion compensation (for unchanged but moved parts of an image only a displacement vector is stored). On the other hand, assumptions about the perception by the human eye are not applicable (e.g., changes in brightness and color are not equally important).

The following questions should be addressed in this thesis:
Which compression algorithms are best suited for meteorological model output? Candidates are video compression and general purpose algorithms. The plan is not to develop new algorithms, but to asses existing ones.
What are the characteristics of errors produced by the analyzed algorithms?
Which degree of compression is acceptable for a set of different meteorological applications?

Contact: Robert Redl

Investigation of tropical predictability in simulations using a stochastic convection scheme

In a series of model experiments (ICON) a stochastic convection scheme has been used to investigate the limits of atmospheric predictability that originate from the fast error growth that happens in moist convection and the spreading of this error upscale. However, although global simulations were performed this analysis has been restricted to the midlatitudes.

The main idea behind this master thesis is to first re-apply the diagnostics that were used before to the tropics in addition with a basic evaluation of model performance and biases. In a second step diagnostics and phenomena that are specific to the tropics (eg. Kelvin waves, MJO) should be considered and their role in the error growth process could be investigated.

This project requires interest in dynamical meteorology and modeling as well as a substantial amount of data analysis using python.

Further reading:
Selz, 2019: Estimating the intrinsic limit of predictability using a stochastic convection scheme. (dataset description, midlatitude analysis)
Judth, 2020: Atmospheric Predictability of the Tropics, Middle Latitudes, and Polar Regions Explored through Global Storm-Resolving Simulations (Investigation of tropical predictability with a high-res model)

Contact: Tobias Selz or George Craig

Feedbacks between the large-scale circulation and ozone in CO2-driven climate change simulations

Increasing greenhouse gas concentrations drive thermodynamical temperature changes in the atmosphere, which in turn lead to changes of the large-scale circulation. In the stratosphere, the hemisphere-wide mean meridional circulation (the Brewer-Dobson circulation) is strengthening due to GHG increases. This strengthened circulation leads to changes in the distribution of trace gases, like stratospheric ozone. Because ozone is a radiatively active gas, the changed ozone distribution causes temperature changes, that might again modify the circulation response to GHG forcing.

In the proposed project, it shall be investigated how the circulation-induced changes in ozone concentrations might feed back onto the circulation. To do so, simulations with the chemistry-climate model EMAC will be analyzed, which are representing pre-industrial climate conditions and climate conditions under quadrupled CO2 concentrations. By contrasting simulations in which ozone is adapting to the changed climate with simulations in which ozone is held fixed at the pre-industrial level, the effects of ozone changes on circulation changes are quantified.

The master student will join the young investigators group MACClim („The role of the middle atmosphere in a changing climate“), that is a joint project between MIM at LMU Munich and the DLR Institute for Atmospheric Physics in Oberpfaffenhofen.

For further information, contact: Hella Garny / Roland Eichinger


Further themes are possible, please talk to Prof. G. Craig, Prof. T. Birner, Priv.Doz T. Janjic or Dr. C. Keil.