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studium:themen_fuer_masterarbeiten_theo [2018/06/29 08:54]
keil [Sudden stratospheric warmings and stratosphere-troposphere coupling]
studium:themen_fuer_masterarbeiten_theo [2020/06/04 08:30] (aktuell)
tobias.selz [Investigation of tropical predictability in simulations using a stochastic convection scheme]
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 ===== Topics for master theses in the theory group ===== ===== Topics for master theses in the theory group =====
  
-====Sudden stratospheric warmings ​and stratosphere-troposphere ​coupling====+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: 
 +\\ 
 + 
 +====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.  
 + 
 +/**
  
 The stratospheric circulation in winter is dominated by a strong cyclonic vortex over the pole. This polar vortex is caused by radiative cooling due to polar night. However, upward propagating planetary waves frequently perturb the vortex in terms of both position and strength. For sufficiently strong planetary wave forcing, these disturbances can grow enough to destroy the polar vortex as a well-organized entity. These abrupt transitions in the hemispheric-scale stratospheric circulation are usually associated with a strong warming of the polar stratosphere and are thus often called //​[[https://​www.meteorologie.lmu.de/​~Thomas.Birner/​ssw.html | sudden stratospheric warmings (SSWs)]]//. Furthermore,​ SSWs tend to produce circulation anomalies at the surface. The stratospheric circulation in winter is dominated by a strong cyclonic vortex over the pole. This polar vortex is caused by radiative cooling due to polar night. However, upward propagating planetary waves frequently perturb the vortex in terms of both position and strength. For sufficiently strong planetary wave forcing, these disturbances can grow enough to destroy the polar vortex as a well-organized entity. These abrupt transitions in the hemispheric-scale stratospheric circulation are usually associated with a strong warming of the polar stratosphere and are thus often called //​[[https://​www.meteorologie.lmu.de/​~Thomas.Birner/​ssw.html | sudden stratospheric warmings (SSWs)]]//. Furthermore,​ SSWs tend to produce circulation anomalies at the surface.
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 In this Master project we will explore the dynamical evolution leading up to and following SSW events based on meteorological reanalysis data and climate model output. In this Master project we will explore the dynamical evolution leading up to and following SSW events based on meteorological reanalysis data and climate model output.
  
-For more detailed information please contact Thomas Birner. ​+**/
  
 ====Assimilation of cloud information==== ====Assimilation of cloud information====
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 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. 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: ​Martin Weissmann, ​Leonhard Scheck+Contact: Leonhard Scheck
 ====Tropospheric moisture variability and the development of tropical convection==== ====Tropospheric moisture variability and the development of tropical convection====
  
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     ​     ​
 Contact: Julien Savre 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
 +
 +\\
 +
 +Further themes are possible, please talk to Prof. G. Craig, Prof. T. Birner, Priv.Doz T. Janjic or Dr. C. Keil.
 +\\
 + 
 +/**
  
 ====Predictability of convection in a very big ensemble==== ====Predictability of convection in a very big ensemble====
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 Contact: George Craig, Christian Keil Contact: George Craig, Christian Keil
- 
-==== 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 
-\\ 
- 
-Further themes are possible, please talk to Prof. G. Craig, Dr. C. Keil or Dr. M. Weissmann. 
-\\ 
-  
-/** 
-Bei Interesse an **Masterarbeiten** im Lehrstuhl für Theoretische Meteorologie bitte bei Prof. G. Craig, Dr. C. Keil oder Dr. M. Weissmann nachfragen. ​ 
-\\