The growth of the planetary boundary layer at a coastal site: a case study

A lidar system is used to determine the diurnal evolution of the planetary boundary-layer (PBL) height on a summer day characterised by anticyclonic conditions. The site is located on a peninsular site some 15 km distant from the sea in south-east Italy. Contrary to expectations, the PBL height, after an initial growth consequent to sunrise, ceases to increase about two hours before noon and then decreases and stabilises in the afternoon. The interpretation for such an anomalous behaviour is provided in terms of trajectories of air parcels towards the lidar site, which are influenced by the sea breeze, leading to a transition from a continental boundary layer to a coastal internal boundary layer. The results are analysed using mesoscale numerical model simulations and a simple model that allows for a more direct interpretation of experimental results