Differences and Similarities between Extratropical Cyclones during Summer and Winter

Sammanfattning: Extratropical cyclones (ETC) are synoptic scale low pressure systems, which have a large impact on the weather in the mid latitudes. These low pressure systems usually develop during several days and are connected to fronts. Thus, they can bring cloudiness, rain and even severe weather including strong winds. Extratropical cyclogenesis occur in regions of baroclinic instability and is thus a result of the interaction between several physical processes at different levels in the troposphere. The aim of this study is to investigate differences and similarities between ETCs during summer and winter. The ETCs of interest begin their development in the North Atlantic Ocean, and subsequently approach the western parts of Europe. The data used were obtained from the GFS model analysis weather maps and provided information regarding e.g. the pressure at different levels in the troposphere, equivalent potential temperature and 300 hPa wind. ETCs were found to develop more frequently during winter, and also showed a considerably lower pressure than in summer due to higher baroclinic instability. Additionally, the lifetime were found to be similar during the two seasons whereas the distance covered during development were longest in winter. Finally, two case studies of extratropical cyclogenesis were performed and analyzed by physical interpretation of the quasi-geostrophic omega and height tendency equation.