Browsing by Subject "Extra-tropical cyclones"

The purpose of this master's thesis is 1) to determine the meteorological structure and evolution of extra-tropical cyclones that develop in an idealized aqua-planet simulation, which utilizes a newly developed way to represent the large-scale initial state of the atmosphere; and 2) to examine the Lorenz energy cycle of this simulation. The simulation is run with the OpenIFS numerical weather model for 15 days, and the Lorenz energy cycle terms are computed for each time step of the simulation over a volume of the atmosphere, which extends from the 1000-hPa pressure surface to the 200-hPa pressure surface between 30 N and 75 N. The intensity of cyclones is evaluated with the TRACK program. In general, the simulation produces text-book type realistic cyclones whose structures resemble those of the Norwegian cyclone model. Cyclones which form upstream of the firstly developing original cyclone are smaller and less intense than the ones which form downstream of it. The most intense cyclone is the first cyclone which develops downstream of the original cyclone. None of the cyclones undergo their full life-cycle and therefore the simulation could be run for more than 15 days in the future. Over the course of the simulation, the available potential energy of the zonal mean flow decreases due to conversion to eddy available potential energy by a northward meridional heat flux. Vertical heat flux acts to inhibit this energy conversion, but its effect is minor. Eddy available potential energy is converted to eddy kinetic energy by the rising of warm air and the sinking of cold air within the developing cyclones and anticyclones. Eddy kinetic energy is converted to the kinetic energy of the zonal mean flow by momentum fluxes of the zonal wind component. The kinetic energy of the zonal mean flow is converted back to the available potential energy of the mean flow by the mean meridional overturning. In addition, friction dissipates the kinetic energy of the eddies and the zonal mean flow. Overall, the results of this thesis show that Lorenz energy cycle terms can be computed for an idealized aqua-planet simulation and that the computed terms can be used as diagnostics for evaluating the development of extra-tropical cyclones.