Investigating the impact of the vertical structure of the atmospheric boundary layer and the surface heterogeneities on the development of the valley and coastal breezes (the WINDABL project).

Thermally driven winds (breezes) are mesoscale diurnal/nocturnal wind circulations initiated by surface temperature gradients in areas with contrasting surfaces when weak and fair-weather synoptic conditions dominate. The characteristics of the breezes depend on the strength of the surface temperature gradient, but also on the interaction with other winds of different spatio-temporal scales, such as the background winds (of low-moderate intensity). Besides, the thermodynamic vertical profile of the atmospheric boundary layer (ABL) can also impact the breeze characteristics. In this context, some recent modelling experiments have shown how the vertical structure of the pre-existing ABL is a key factor that controls the impact of specific surface changes on the breeze characteristics. This issue motivated the development of the WINDABL project* to further investigate this finding through an observational and modelling strategy.

In this work, we present the methodology carried out for the observational part of the project, which consisted of the installation of meteorological (and surface energy balance) stations at strategic locations for the long-term monitoring of breezes and the launching of atmospheric soundings during intensive observation periods characterised by breeze conditions. This strategy was developed both at a coastal and a mountainous (valley) area. The former corresponds to the northern part of the Gulf of Cádiz (southwestern Iberian Peninsula coast) and the latter to the Vallée d’Aure, on the Northern side of the Pyrenees.

We also present some first results obtained from the analysis of the data of the different towers and from 26 radiosoundings launched during 8 different breeze events that allow to highlight the breezes characteristics during contrasting background winds and different ABL thermodynamic vertical structure at both locations. The results indicate how the contrasting synoptic conditions lead to important differences in the variables observed near the surface. As an example, we show how the formation hour, the duration and the degree of impact on the surface variables of the daytime marine breezes display a totally different behaviour depending on the pre-existing synoptic conditions.

* The WINDABL project (PR2022-055) is a project to impulse the career of young researchers funded by the University of Cádiz (Spain) (Plan Propio). The field activities of this project were developed in collaboration with the MOSAI project (Model and Observation for Surface-Atmosphere Interactions, https://mosai.aeris-data.fr/)  and with the LATMOS-i project (Land-ATMOSphere interactions in a changing environment: How do they impact on atmospheric-boundary-layer processes at the meso, sub-meso and local scales in mountainous and coastal areas?) (PID2020-115321RB-I00, funded by MCIN/AEI/ 10.13039/501100011033).