The Growth of the Planetary Boundary Layer at a Coastal Site: a Case Study

Abstract

A lidar system is used to determine the diurnal evolution of the planetary boundary layer (PBL) height on a summer day characterized by anticyclonic conditions. The site is located some 15 km distant from the sea, on a peninsula in south-east Italy. Contrary to expectations, the PBL height, after an initial growth consequent to sunrise, ceases to increase about 2 h before noon and then decreases and stabilizes in the afternoon. An interpretation of such 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 analyzed using mesoscale numerical model simulations and a simple model that allows for a more direct interpretation of experimental results.

Contrasting Air Mass Advection Explains Significant Differences in Boundary Layer Depth Seasonal Cycles Under Onshore Versus Offshore Flows

“…Both rawinsonde sites at San Diego and Oakland are characterized by urban hotspots which likely trigger high summer time BLDs under offshore flow. These results cumulatively explain that, under onshore flows, the impact of MBL on the BLD over coastal sites is substantial, consistent with previous findings (e.g., De Tomasi et al, ; Melas et al, ).…”

Thermal Structure of a Coastal–Urban Boundary Layer

“…However, their applicability in coastal-urban environments is questionable. While very few experiments have been conducted to investigate coastal-urban interactions, Mestayer et al (2005) have observed the variation of the boundary-layer height during sea-breeze events in Marseille during the ESCOMPTE campaign, noting that the sea breeze tends to weaken boundary-layer development (Lemonsu et al 2006) despite the increasing insolation as the day progresses into the afternoon; a similar behaviour was also found by De Tomasi et al (2011) in Lecce, Italy. We do not refer to these experiments to provide an exhaustive list of urban boundary-layer studies, but to emphasize the fact that very few observations exist on the thermal characteristics of the urban boundary layer (Barlow 2014).…”

“…While relatively few surface parameters are required to estimate the vertical structure of the boundary layer over homogeneous terrain, the high degree of surface heterogeneity and the influence of the sea breeze in coastal-urban zones require knowledge of the flow history (De Tomasi et al 2011). In New York City, observations of urban heat islands and cool islands (Gaffin et al 2008;Meir et al 2013) cannot be solely explained using surface characteristics.…”

The role of subsidence in a weakly unstable marine boundary layer: a case study

“…The impact of these subgrid-scale motions on grid-scale variables is relevant, particularly in the low levels, where they may significantly alter the atmospheric status through mixing. Especially in situations with strong spatial inhomogeneities (e.g., at the land-sea transition zone, where the structure of the ABL flow is more complex due to the abrupt changes in the surface roughness or thermal forcing) and rapid temporal variations, mesoscale models are not able yet to simulate the structure of PBL in all its complexity (De Tomasi et al, 2011), with significant discrepancies among different parametrization schemes. Generally, sub-grid fluxes are parametrized using two categories of closure schemes (Shin and Hong, 2011).…”