Wirbelstürme im Mittelmeer.

Nissen, Cara (2012) Wirbelstürme im Mittelmeer. (Bachelor thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 36 pp.

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Abstract

Two time slice experiments (1959-1990 (20C) and 2069-2100 (21C) respectively) of the ECHAM5 model were performed and the results served as the basis for the analysis of storms in the Mediterranean Sea in this thesis. The goal is to investigate potential changes of the simulated storms under climate change as well as to elaborate differences between the identified "tropcial like" cyclones and true tropical systems. The analysis of the genesis positions and tracks of all simulated storms reveals two main genesis regions, one in the northwestern and a second in the southeastern Mediterranean Sea. Most of the systems move eastwards from where they developed. Both for genesis positions and tracks, no change is observed under climate change. In a frequency distribution of the maximum intensities of the storms, a statistically significant decrease of high maximum intensities is found for all the storms. A criterion found in the literature helping identifying true tropical cyclones is varied and applied to the data set. A decrease of 30% to 50% in the number of the "tropical like" storms can be found between 20C and 21C. No statistically significant changes in the frequency distribution of the maximum intensity is observed. Problems using the criterion are identified giving indications for how the criterion should be modified for "tropical like" cyclones in the Mediterranean Sea. It should hence take into account that the "tropical like" cyclones only develop a warm core in certain vertical levels and during certain time steps. A possible approach is considering the increase in temperature anomaly between certain height levels. This study reveals that the storms identified by the 554-criterion (minimum value in relative vorticity in 850 hPa (in 10-5 s-1), minimum decrease of relative vorticity between 850 hPa and 250 hPa (in 10-5 s-1) as well as the minimum number of time steps the first two named criteria have to be consecutively fulfilled) show an increase in temperature anomaly between 700 hPa and 400 hPa 2.5-times magnified compared to those storms not showing any decrease in relative vorticity between 850 hPa and 250 hPa The simulated genesis positions of the "tropical like" cyclones show a decrease in the number of systems in the central Mediterranean Sea in 21C compared to 20C. The analysis of the atmospheric wind shear and stability conditions don't give any clear explanation for that. A more detailed analysis of the atmospheric conditions for any particular season has to be performed to find more distinct correlations. In this study, besides differences in the warm core, further differences between "tropical like" cyclones and true tropical systems are found in the maximum attained wind speeds, the ,, radius of maximum winds" and the genesis date of the systems.

Document Type: Thesis (Bachelor thesis)
Thesis Advisor: Latif, Mojib and Martin, Thomas
Subjects: Course of study: BSc Physics of the Earth System
Research affiliation: OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-ME Maritime Meteorology
Date Deposited: 10 Jan 2013 11:38
Last Modified: 03 Aug 2023 08:20
URI: https://oceanrep.geomar.de/id/eprint/19964

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