Radiation fog, gravity waves and their interactions with turbulence in the atmospheric boundary layer

Abstract

This thesis deals with the study of two atmospheric phenomena that normally appear in the stable boundary layer (SBL): radiation fog and gravity waves (GWs), processes that are still not well understood. Therefore, their representation in the numerical weather prediction (NWP) models is one of the current challenges for the meteorological modelling. Thus, the main objective of this thesis is to gain knowledge about these phenomena, with especial emphasis to their interactions with turbulence in the SBL. The work starts with sensitivity experiments of the WRF (Weather Research and Forecasting) mesoscale model, in order to determine the most appropriate physical options for the simulation of fog. Subsequently, radiationfog forecasting is addressed through two different approaches: numerical modelling (WRF) and statistical methods (M14, Menut et al. (2014)). These two methods are evaluated and compared at two contrasting experimental sites. Finally, new methods for the fog-top height estimation are presented. This variable is usually unknown or subjected to expensive or not-always accessible data. The estimation offered in this thesis is based on turbulent surface measurements (friction velocity and heat flux). Regarding GWs, on the one hand, a comprehensive observational analysis of near-monochromatic GWs propagated in a duct layer is presented, being difficult to have the chance of analysing a case like this in the real atmosphere. On the other hand, the physical mechanisms governing smaller-scale GWs and drainage flows are elucidated, analysing in detail the interactions of these phenomena with the turbulence in the SBL, which is one of the main current challenges in micrometeorological studies