Nikolai Kruetzmann
Complexity Analysis of Geophysical Systems
Nikolai Kruetzmann, Department of Physics & Astronomy
Supervisors 
Dr. Adrian McDonald, Department of Physics & Astronomy
Dr. Wolfgang Rack, Gateway Antarctica
Dr. Steve George, Department of Geography
This project aims to utilise recently developed methods from the science of complex systems for studying and analysing the Earth's atmosphere, cryosphere, and potentially other geophysical domains.
The starting point of this project will be the Rényi entropy (RE) statistical measure, which was previously established as a useful tool for identifying atmospheric transition regions associated with barriers to horizontal mixing (Kruetzmann et al., 2008). Having successfully applied this measure to data from climate-model simulations, the first goal of the PhD project will be to use the RE measure to study the properties and behaviour of mixing barriers in more detail using satellite observations. One such barrier is the Antarctic polar vortex, a strong circumpolar stratospheric wind that occurs every Austral winter and spring. It separates the cold polar air masses from more temperate mid-latitude air, and thereby creates the extremely cold conditions, which lead to the formation of the ozone hole in spring. Accordingly, understanding this transition region is essential for predicting Antarctic ozone chemistry.
Given that many geophysical processes exhibit enhanced complexity at transition regions, it seems natural to examine a range of geophysical systems using the RE measure. Hence, this PhD research aims to extend the application of the RE methodology to other geophysical systems, and particularly to the cryosphere. In snow and ice, transition regions can be associated with internal layers created by changes in the ambient conditions at the time of deposit. By identifying and tracing internal layers in ground penetrating radar (GPR) measurements of the Antarctic snow cover, the layers can be used to measure snow accumulation over time. This is particularly relevant for determining the Antarctic mass balance, as the areal coverage can be greatly expanded from the common, but unrepresentative, point measurements, e.g. firn-core drilling or snow pits. However, conventional signal processing methods have major shortcomings in identifying the layers observed in GPR data. This project aims to use the RE and other complexity measures to better identify the transitions between different snow and ice layers, which will improve our understanding of the spatial variability of the Antarctic snow cover. Funding and logistic support for the acquisition of the GPR measurements has been secured in the form of the Christchurch City Council Antarctic Scholarship 2008. Additionally, this data and its analysis will contribute to the validation of the Cryosat-2 satellite (launch date in 2009). The combination of modern remote sensing technology with innovative analysis techniques will allow a large-scale analysis of the cryosphere in unprecedented detail.
Publications
Krützmann, N. C.; McDonald, A.J.; George, S.E. (2008). Quantitative Identification of Mixing Barriers in Chemistry-Climate-Model Simulations using Rényi Entropy. Geophysical Research Letters 35(6), L06806, doi:10.1029/2007GL032829.