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Meteorology

Masters theses

Here is a list of currently available topics for Masters theses in the Meteorology group. As a Masters student you are always invited to talk to us about your own ideas for a thesis topic.

How well do weather forecast models simulate precipitation variability at the sub-hourly time scale?

Precipitation from weather forecasting models typically provide data every hour or less, while the actual rain shower that hits you on the way home may only last some minutes. The central question of this thesis is, how do modelled and observed rainfall time characteristics compare? We have new high-resolution rainfall and precipitation phase instrumentation in place at GFI, measuring at 1 min resolution. The purpose of this thesis is to investigate the observed short-term precipitation statistics with simulations from the current operational AROME model run at Met Norway at  as sub-hour resolution obtained from operational weather forecast models. A possible result of this Masters thesis is to develop a more useful way to communicate precipitation forecasts.

Relevant literature: The AROME forecast model (Seity et al., 2011). Precipitation variability from MRR and Disdrometer (Jaffrain et al., 2011)

Contact: Harald Sodemann (Numerical Modeling, Atmospheric Water Cycle)

 

Origin of moisture observed from aircraft measurements of an atmospheric river near Iceland

Moisture is often transported along frontal regions of extratropical cyclones. In a vertically integrated perspective, the total column water appears to flow poleward similar to a river, therefore these features are sometimes called Atmospheric Rivers (ARs). In September and October 2016, aircraft measurements during the international NAWDEX/NEAREX/EPATAN campaign near Iceland sampled ARs during 3 cases. The task within this Masters thesis will be to simulate the moisture transport during a selected event with a mesoscale numerical weather prediction model equipped with water vapour source tracers. The sources, structure and evolution will be compared to aircraft measurements and satellite imagery, to investigate how moisture is "handed over" from one cyclone to another.

Relevant literature: Moisture transport in Atmospheric Rivers (Ralph et al., 2011). Sources of water vapour in Atmospheric Rivers (Sodemann and Stohl, 2013).

Contact: Harald Sodemann (Numerical Modeling, Atmospheric Water Cycle)

 

Evaporation "hot spots" and the Deuterium excess signature in high-resolution climate models

The atmospheric water cycle is a key component of weather forecasting and climate models. This work is about identifying the regions where strong latent heat flux, or evaporation occurs, and how this affects the Deuterium excess, a stable isotope indicator of evaporation conditions. We have 6-hourly data from several current climate models which allow to compare how the evaporation process is simulated in each of them. A possible outcome of the work is to better understand where uncertainties in the water cycle of models are located, and how we can use additional measurements to improve them.

Relevant literature: Deuterium excess in the global water cycle (Pfahl and Sodemann, 2014). The NorESM climate model's water cycle (Bentsen et al., 2012).

Contact: Harald Sodemann (Numerical Modeling, Atmospheric Water Cycle)

 

Moisture source variability during periods of low predictability

The aim of this thesis is to investigate what role moist processes play during periods of low predictability. A moisture source identification is applied to data from the ECMWF 51-member ensemble to examine the variability of moisture sources and transport in each member. A keen interest in learing and applying ensemble methods as well as advanced atmospheric diagnostics based on backward trajectories are needed for this project.

Relevant literature: The moisture source diagnostic of Sodemann et al. (2008). Application of the moisture source perspective to Central Europe (Sodemann and Zubler, 2010). Measuring uncertainty in the ECMWF ensemble prediction system (Buizza et al, 1999)

Contact: Harald Sodemann (Numerical Modeling, Atmospheric Water Cycle)

 

Validation of remotely sensed wind profiles against radiosoundings

The marine atmospheric boundary layer is in the altitudes relevant for state-of-the-art and future expected wind turbines (0-300 m) not yet well understood. To improve our understanding of the complex interaction between wind shear, atmospheric stability and turbulence characteristics offshore, the offshore measurement campaign OBLEX-F1 (Offshore Boundary Layer Experiment at FINO1) has been initiated. It is an intensive observational campaign within the German Bight and is carried out by NORCOWE and several international partner institutions. The data from the experiment allows for an intensive and detailed study of the marine atmospheric boundary layer under various synoptic conditions.
Within this master project, wind profiles from a scanning lidar system (Leosphere WindCube 100S) should be validated against radiosoundings from two sites in the vicinity, Schleswig and Norderney. It will include a  statistical analysis of the observed differences as function of the synoptic situation, in particular wind speed, wind direction, and atmospheric stability.
More information on the project can be found here.

Contact: Joachim Reuder (Boundary layer meteorology, Energy meteorology)

 

The importance of longwave radiation flux divergence on stable boundary layer development

Radiation divergence is often assumed negligible in investigations of the atmospheric boundary layer. While this assumption might be applicable for many typical conditions, e.g. convective or near-neutral boundary layers, it might be often violated in the case of the stable boundary layer (SBL). Based on radiation measurements at two levels (1 m and 7 m) and eddy covariance measurements at 3 levels of a 10 m mast during a field campaign in February 2018 (Hailuoto, Finland) as part of the ISOBAR project (https://isobar2018campaign.w.uib.no/) the proposed master thesis will investigate the effect of radiative flux divergence close to the ground on turbulence and thus on structure and dynamics of the SBL.   

Advisors: Joachim Reuder, Stephan Kral

 

Turbulence estimates from lidar measurements  

Lidar wind profilers are widely used for the measurement of wind profiles in 10 range bins distributed over the lowest 200-300 m of the atmosphere with an already rather high temporal resolution of 1 Hz. Based on the measurement principle of pulsed lidar systems, analyzing the backscatter information of typically 10.000 lidar pulses for the determination of the 1 second average values, the raw data should, however, contain additional information on atmospheric turbulence at the chosen measurement heights of the lidar system. The master project aims to analyze the spectral broadening in the backscattered lidar signal of different available data sets for an categorization and qualitative description of changes of the turbulence structure with altitude under different atmospheric (stability) conditions. In case of interest the work can also include a targeted field campaign to compare and validate the observed spectral broadening against turbulence parameters measured by a sonic anemometer on a meteorological mast.        

Advisors: Joachim Reuder, Stephan Kral

 

Roughness length and flux footprints for the Hailuoto campaign from high resolution RPAS based photogrammetry

Intensive turbulence measurements have been performed during the Hailuoto-II campaign in Finland in February 2018 as part of the ISOBAR research project on stable boundary layers (https://isobar2018campaign.w.uib.no/). The appropriate analysis of those turbulence measurements and the corresponding accuracy of the observed fluxes of sensible and latent heat are strongly dependent on a reliable information of the surface characteristics upstream of the measurement mast. The master project will use a photogrammetry data sets taken from a Remotely Piloted Aircraft System (RPAS) with a horizontal resolution of better than 5 cm and a height resolution of around 1 cm, to estimate a wind direction dependent characterization of the relevant surface conditions around the eddy-covariance measurement site.             

Advisors: Joachim Reuder, Stephan Kral

 

What are the Atmospheric Ingredients for large-scale Sea-Ice Break-Up Events?

Extratropical cyclones moving from the mid-latitudes into the Arctic Ocean sometimes have a devastating effect on the sea-ice cover. They bring warm and moist air masses into the Central Arctic and are typically associated with strong winds that can fracture the ice-cover over large regions. Although these events typically only last a few days, they likely play a climatological role. It is known that intense cyclones receive an important amount of their energy from diabatic processes, such as latent heat release during cloud and rain formation. For arctic cyclones the importance of this process is still unknown but might be of particular relevance as fractures in sea-ice expose the comparatively warm Arctic Ocean to the atmosphere, leading to extreme heat fluxes that can fuel the cyclone. This Master thesis project will look at the importance of these diabatic effects for a cyclone leading to a large-scale sea-ice break-up using a mesoscale atmospheric model and sea-ice boundary conditions from a state-of-the art sea-ice model, which is developed locally in Bergen at the Nansen Environmental and Remote Sensing Center. By systematically varying the initial humidity as well as heat fluxes, this Master’s project will find the importance of both the local fluxes as well as the transported moisture in the evolution of the cyclone and its feedback on the sea-ice break-up.

Advisors: Thomas Spengler (Atmospheric Dynamics) and Clemens Spensberger

 

Characteristics of Extreme Storms impacting Norway

The most intense cyclones hitting Norway during winter in the period 1979-2017 will be identified using a cyclone track database as well as land-based wind and precipitation observations. The tracks of the cyclones will then be used to assess what kind of development these cyclones underwent during their genesis and intensification, pinpointing the pertinent and most dominant processes contributing to the cyclone intensity. Particular focus will be on the role the jet stream as well as the sea surface temperature along the path of the cyclone, as well as the contribution of moist diabatic processes and surface fluxes. The overall goal is to identify possible development pathways and conducive conditions for these extreme cyclones to occur. Additional focus will be on the interannual variability of these storms and its association with large-scale weather patterns such as the North Atlantic Oscillation. The results will help us understand the necessary ingredients for extreme cyclone development affecting Norway in the current climate. Depending on the findings, it might be possible to make inferences about the future occurrence of these extreme storms in the vicinity of Norway.

Advisors: Thomas Spengler (Atmospheric Dynamics), Leonidas Tsopouridis (PhD student), and Clemens Spensberger

 

Response of Extratropical Cyclones to an Environment in a Changed Climate

Recent studies investigated the development of extratropical cyclones, where the authors varied environmental variables, such as temperature, stratification and humidity. The motivation for these sensitivity experiments is to improve our understanding of the development of extratropical cyclones in a future climate, where we know that the temperature, stratification and humidity will be altered. Several of these studies, however, had some pitfalls in their experimental setup. Here, we propose idealized simulations with a model tool developed at GFI, where we will study the response of differently initialized extratropical cyclones to variations in the aforementioned environmental parameters. Particular focus will be on understanding the role of latent heat release on the dynamic and thermodynamic development and nature of these cyclones. Special focus will on the response with respect to cyclones of different size, as cyclones are expected differently to changes in their environment dependent on their size. The study will lead to a better understanding of how mid-latitude cyclones might respond to a changing environment associated with climate change.

Advisors: Thomas Spengler (Atmospheric Dynamics) and Hai Bui (Postdoc)

 

Influence of Sea Surface Temperature on Storm Tracks

The effect of the sea surface temperature (SST), in particular SST fronts along the midlatitude western boundary current, on storm tracks is a matter on ongoing debate. Climatologically, storm tracks are collocated with the SST fronts in the western Atlantic and western Pacific and genesis of strong storms often occurs along these SST fronts. However, it is still unclear if the strength of the SST front or the absolute value of the SST itself has the primary influence on the strength and development of extratropical cyclones. Here, we propose to address this controversy using three different runs with a climate model: one control simulation, and two simulations where the SST front over respectively the Gulf Stream region and the Kuroshio region has been smoothed. Preliminary results using the smoothed Gulf Stream simulation show that the baroclinicity is increased (decreased) at location where the SST gradient is increased (decreased). These findings will be supported by data from idealised cyclone development simulations with different configurations for both the strength SST front and the absolute value of the SST. Different measures of baroclinicity will be compared with storm intensity and storm track measures for both the climate and idealized simulations.

Advisors: Thomas Spengler (Atmospheric Dynamics) and Chris Weijenborg (Postdoc)

 

Sensitivity of Midlatitude Cyclone Development to Future Climate Environments

Our current understanding of how midlatitude cyclones and their intensity will change in a future climate remains limited. Parameters like static stability, tropopause height, and horizontal temperature gradients will all be affected by climate change. In this master project, we will use a conceptual model where the aforementioned parameters can be modified to represent future changes in climate. From different model runs, we will test how the growth rate, the horizontal scale, and the structure of midlatitude cyclones will change. The model is modified from the classical Eady model and is highly idealised, making it easier to understand the response to modified parameters. Focus will be on understanding the concept of the impacts from a changing climate, rather than representing the future climates in a complex and more realistic model.

Advisors: Thomas Spengler (Atmospheric Dynamics) and Kristine Flacké Haualand (PhD student)

 

Limits of Predictability of Extratropical Cyclone Development associated with the Structure of the Tropopause

Several recent studies on the predictability of extratropical cyclone development point to the sensitivity of the forecasts to the accurate representation of the tropopause. In particular, the sharpness of the vertical shear and stratification is often underestimated in operational weather forecasting models due to vertical model resolution or poor initial conditions based on insufficient observations to constrain the analysis. While it has been pointed out that there is an effect of this misrepresentation of the tropopause, it has not been sufficiently quantified how large the effect of certain deficiencies in representation of the wind or vertical stratification really is. In this Master thesis, we will use an idealized model based on the Eady problem, where we can modify the stratification and vertical wind shear to mimic different structures of the tropopause. The goal is to assess sensitivities of extratropical cyclone growth with respect to varying wind shear and stratification in the tropopause region. Results from this study will indicate how sensitive forecasts might be given certain deficiencies in the representation of the tropopause and thereby indicate associated predictability issues.

Advisors: Thomas Spengler (Atmospheric Dynamics) and Kristine Flacké Haualand (PhD student)

 

Role of Cold Air Outbreaks in Atmosphere-Ocean-Ice Interactions in a coupled mixed layer Model

Cold air outbreaks play a crucial role in the air-sea heat exchange in the higher latitudes. However, we still lack some basic understanding about the sensitivities of these phenomena to latent heating and the role of coupling to the ocean. To further explore these sensitivities, we coupled a moist convective atmospheric boundary layer model with an ocean mixed layer model to investigate the response of moist convection as well as ocean mixing during cold air outbreaks. The model yields a two-dimensional steady state for a cold air outbreak downstream of an ice edge. The atmospheric model is based on the equations for liquid water potential temperature and total water mixing ratio, the oceanic model on those for temperature and salinity.

Using this model, a variety of coupled and uncoupled solutions with different resolutions and sea ice concentrations can be assessed. Varying sea ice concentration and resolution alters the distribution and intensity of the air-sea heat exchange with ramifications for mixed layer depths in both the atmosphere and ocean. The obtained results will have implications for numerical weather prediction and climate models, in particular regarding model resolution and the degree of coupling for the representation of air-sea interaction during cold air outbreaks. Furthermore, the model can be used to assess the hydrological cycle in cold air outbreaks, yielding important insights into the role of evaporation and precipitation in cold air outbreaks.

Advisors: Thomas Spengler (Atmospheric Dynamics) and Clemens Spensberger (Researcher)