Mika Rantanen defends his PhD thesis
On Friday 24th April, Mika Rantanen will defend this PhD thesis "Diagnostic Studies of Extratropical Cyclones in the Present and Warmer Climate". The opponent is Prof. Heini Wernli from ETH Zurich and the Custos is Prof. Heikki Järvinen from the University of Helsinki.

The PhD thesis contains 4 papers.  Both idealised simulations and numerical simulations of real weather events were analysed in the series of papers. In the first paper, a diagnostic method was developed to analyse the physical causes of vertical motion, geopotential height tendency and relative vorticity tendency within extratropical cyclones. This method was then applied in the second paper where idealised extra-tropical storms were simulated in different background environemental conditions. These conditions were selected to mimic likely changes to our future climate - the effect of uniform warming and changes to the large-scale North-South temperature gradient were investigated. Warming the atmosphere was found to decrease the kinetic energy of the cyclone, which is linked both to a weaker capability of the storm to exploit the available potential energy of the zonal mean flow, and less efficient production of eddy kinetic energy in the wave. In the third paper, the diagnostic method was applied to a real storm which underwent extra-tropical transition where it showed that diabatic processes such as condensation and associated latent heat release were critical in the strengthening of the storm. In the last paper, another idealised modelling approach was taken. 10-year simulations were performed with an aqua-planet and how the most extreme storms changed with a uniform warming of 4K was investigates. The main result of this last paper was that extreme storms did not get any stronger but they had much more precipitaiton associated with them and that this precipitaiton occured farther from the cyclone centre.

Read the thesis here: http://urn.fi/URN:ISBN:978-952-336-106-5