The Atmospheric Dynamics group offers a broad range of Bachelor and Master topics in the fields of atmospheric dynamics, its numerical analyses, and prediction at many scales. The topics are derived from the current research interests of the group, which encompass the following interrelated themes central to modern meteorology:
- Waves in the atmosphere and their role in the weather and climate formation
- Climate modelling and climate change
- Extreme weather events
- Earth’s energy cycle and energy pathways in the atmosphere
- Analysis of the weather patterns
- Predictability, model errors, and biases
- Mathematical aspects of atmospheric dynamics
In our work, we combine statistical methods and novel diagnostics approaches. Typically, MS/Ba research is based on observation and analysis data and a hierarchy of numerical models, with complexity ranging from toy models to full-scale climate models. For mathematically-minded students, a number of problems coalescing meteorology with geometry, analysis, and statistics is available. Below is aninexhaustive list of proposed master thesis topics. For other topics and your idea, come to discuss.
Bachelor topics/Bachelor-Arbeiten (Richard Blender):
Extreme events in data and models
The public interest in meteorological events largely focuses on particularly intense phenomena that are associated with corresponding damage. Statistically speaking, these are very large deviations from the normal state, such as strong winds, high or low temperatures and intensive precipitation. If additionally time scales are taken into account, there is an abundance of possible causes of damage. Bachelor's theses are offered, in which the statistical properties of extremes are calculated and possible correlations with external factors are estimated.
Cyclone tracks in the middle latitudes
The cyclones in the mid-latitudes are sometimes associated with very heavy rainfall and storms. At the same time, their fluctuations are responsible for natural climate variability in the mid-latitudes. The cyclone tracks are influenced by large-scale conditions and may change in a warmer climate. In the bachelor theses, trajectories are determined from existing data, statistical properties such as spatial distributions, temporal correlations and large-scale connections.
Climate variability on long time scales
Climate fluctuations are found on time scales from decades to millennia. The causes of these fluctuations are usually be found in compartments that have processes on the corresponding time scales. Knowing these variabilities is crucial to assess anthropogenic climate changes. Climate models should be able to reflect observed fluctuations.
1. Interaction of inertia-gravity waves and the balanced flow on the sphere
Inertia-gravity waves appear at many scales in the atmosphere and ocean. In the extratropics, inertia-gravity waves (IG) are important ingredient of subsynoptic dynamics and they are generated by the interaction of the flow with orography, by surface and boundary layer processes, by tropospheric moist convection and by imbalance of synoptic jets. In the tropics, the primary source of IG waves is the convective heating and tropical IG waves appear at all spatial scales. In this project, we shall employ a new numerical model to study interactions between the propagating IG waves and the background balanced flow. The model solves global nonlinear shallow-water equations on the sphere for the IG and Rossby wave amplitudes.
Supervisors: Sergyiy Vasylkevych and Nedjeljka Žagar
2. Equatorial waves and the Rossby wave source
Two wave solutions exist near the equator that are absent in the extratropical atmosphere: the Kelvin wave (KW) and mixed Rossby-gravity (MRG) waves. These waves fill the frequency gap between the Rossby and inertia-gravity waves that is present in the midlatitudes. Depending on their vertical scale and the zonal wavenumber, the MRG and Kelvin waves have characteristics similar to either equatorial Rossby or inertia-gravity waves. Excited by latent heat release in deep tropical convection, they propagate through the equatorial waveguide, communicate effects of the heat sources far away along the equator and through their vertical energy and momentum transport they play an important role for the general circulation. In this project, we shall perform numerical simulations to quantify the contributions of these waves to the anomalous vorticity sources in the subtropics.
Supervisors: Nedjeljka Žagar and Frank Lunkeit
3. Where is the central latitude of ITCZ?
The Glossary of the American Meteorological Society defines the intertropical convergence zone (ITCZ) as “an axis, or a portion thereof, of the broad trade wind current of the Tropics. The axis is the dividing line between the southeast trades and the northeast trades and it is collocated with the ascending branch of the Hadley cell.” In research practice the ITCZ has usually been defined by the narrow belt of (proxy) observations of deep tropical convection, i.e., by the location of precipitation maxima above a certain threshold, by the surface wind convergence or by the zero crossing of the average meridional wind in the boundary layer. In this master thesis we will estimate the central latitude of ITCZ by evaluating the vertical velocity associated with the horizontal wind convergence in reanalysis data and its comparison with the precipitation maxima. Collocation properties of precipitation maxima and the latitude of strongest vertical motions will be discussed for different land and ocean regions.
Supervisor: Nedjeljka Zagar
4. Growth of forecast errors in the tropics
Many studies of the growth of errors in forecasts have focused on the quasi-geostrophic dynamics and often considered the error-free large-scale initial state. In contrast, the global operational numerical weather prediction and ensemble prediction systems are characterized by significant analysis uncertainties at large scales, especially in the tropics. In fact, data suggests that the larger the scale, the greater the initial uncertainties. In this project, we shall employ a simplified numerical model to study how initial state errors in inertia-gravity wave component of the tropical circulation affect the growth of forecast errors.
Supervisors: Nedjeljka Žagar and Sergiy Vasylkevych
5. Rossby wave variability
General circulation models (GCMs) simulate the spectrum of variability from weather to decadal time scales across many spatial scales. Temporal variability can be split among various time scales, variables and regions whereas details of the spatial spectrum associated with certain temporal frequency can be described as a combination of “preferred” patterns. Using the MODES (https://modes.cen.uni-hamburg.de) decomposition of reanalyses and climate model simulations into many scales, we shall investigate horizontal and vertical shifts in weather patterns - Rossby wave variability in midlatitudes.
Supervisor: Nedjeljka Žagar
6. Modelling the climate of Amasia
On very long time scales, continental drift effects the Earth and its climate system together with changes in the orbital parameters, etc. Recently it has been speculated that a supercontinent (Amasia) will form
over the North Pole in about 50 to 200 million years (Nature 482, 208-211, 2012). This project will use a climate model of intermediate complexity (PlaSim) to analyse the climate system of this future planet
Earth. The work will focus on particular aspects depending on the
interest of the student.
Supervisor: Frank Lunkeit
7. Sensitivity of tropical wave circulation to cumulus parameterization
Atmospheric circulation, tropical waves, cumulus parameterizations
The parameterization of moist (cumulus) convection is a crucial part of climate models. Various schemes have been proposed based on assumptions made about the dominant mechanisms. The particular choice of the parameterization scheme may have a significant effect on the simulated climate, in particular on the characteristics of tropical waves. This project will use a climate model of intermediate complexity (PlaSim) in an idealized setup to compare the effect of different cumulus parameterization schemes on tropical waves. A diagnostic Tool (MODES, https://modes.cen.uni-hamburg.de) will be applied to decompose the circulation, and to analyse the contribution of different wave types.
Supervisors: Frank Lunkeit and Nedjeljka Žagar
8. Understanding North Atlantic midwinter suppression in state-of-the-art climate simulations
We propose here a model study of the midwinter suppression in the Northern Atlantic, analysing an ensemble of CMIP model simulations over the historical period. We will first verify the existence of the relatively well understood Pacific midwinter suppression, comparing several indices of baroclinic activity in the mid-latitudinal storm track belt and studying the relation with the seasonality of Arctic and subptropical tropospheric temperatures. With this knowledge, we will focus on the North Atlantic sector, to assess whether the suppression exists in models and if the mechanisms of suppression are comparable with the Northern Pacific. We will then adopt a similar analysis on the study of future climate projections, after carefully selecting the models that better sample this mode of variability.
Supervisors: Richard Blender
9. How Aeolus observations improve the global weather forecasts?
Master topics are offered in relation to Aeolus satellite, the first satellite mission measuring the global wind profiles, https://www.esa.int/Applications/Observing_the_Earth/Aeolus.
The satellite was launched on 22 August 2018 and its observations are already contributing to global weather forecasts. DWD and ECMWF use data operationally and they have shown a positive impact of Aeolus on the initial conditions for weather forecast (analyses) and on the forecasts. The effect has been especially important in recent months due to the major cut in wind observations by aircrafts.
We invite students to join the ongoing work on understanding how Aeolus improves the representation of various processes in weather analyses and forecasts.
Supervisor: Nedjeljka Žagar