Simulations of Coastal Atmospheric Dynamics and Transport Processes

Sammanfattning: The marine atmosphere can be highly variable in space and time, and the coastal terrain plays a crucial role in influencing its properties. These, in turn, determine the atmospheric transport in the coastal zone.The rapid collapse of a cloud-topped Marine Atmospheric Boundary Layer (MABL) is studied using aircraft observations of the same, made off the south-eastern coast of Sweden, and mesoscale atmospheric model simulations. The study reveals distortion of the vertical turbulent eddy structure due to the rapid evolution, a new mode of initiation of low-level wind jet due to the collapse, as well as how the jet strength and location are affected by the blocking by coastal terrain. Marine atmospheric variability and the coastal terrain continue to play a central role in the rest of the thesis focussing on coastal atmospheric transport. A Lagrangian Random Particle dispersion model (LAP) is developed and used to quantify this transport. Dispersion calculations using particle models are subject to errors and uncertainties. A method to characterize these is proposed and used with the LAP model, with three different turbulence parameterizations. Simulated dispersion is shown to agree well with measurements from a field program.The LAP model, in conjunction with Mesoscale Model 5 (MM5) simulations, is applied to examine the inland transport of marine air along the California coast during a period of dramatic and rare wind rotation in June 1996. The impact of this wind field rotation on the spatial structure of marine air penetration, blocking by the coastal terrain, and the diurnal impact on penetration are revealed. A simple method of quantification of marine air transport using the particle model is proposed and shows interesting features of penetration. During the commonly seen northerly winds along the California coast during summer, the air flow is considered dynamically blocked by the terrain. Marine air transport during five such typical days of June 1996 is examined using MM5 and LAP model simulations. A significant amount of cross-coast transport is shown to occur on all the days at specific coastal locations. Diurnal enhancement of the transport, as well as daily variations in the same are also revealed.