Coastal winds in the Gulf of Cádiz (southwestern Iberian Peninsula): insights from observations and models

Winds in coastal areas are particularly complex due to the drastic change of roughness and thermal properties between the sea and the land areas. Besides, the coastal topography, the shoreline irregularities, the surface state (land cover/use, soil moisture, sea surface temperature (SST), wind waves), and the interactions with the upper parts of the atmospheric boundary layer (ABL) add more complexity to the final characteristics of the surface winds of these regions.

Among coastal winds, coastal breezes are especially common thermally driven flows formed in mid-latitude regions under fair-weather synoptic conditions. Under these situations, the thermal gradient between the sea and the ocean becomes more important, generating pressure gradient forces that lead to onshore winds during the daytime and offshore during the night. The impacts of these winds are broad and varied: they transport humidity, pollutants, and other physical properties in these regions; they can initiate convection (and even trigger the formation of storms), and they also drive the surface coastal currents, among others. From a societal point of view, the coastal breezes are crucial for the wind power industry, air-quality forecasts, maritime sports, and simply for the refreshing impact they cause, an aspect especially important in some areas commonly affected by extreme maximum temperatures and heat waves. Therefore, a correct understanding of the physical characteristics of the coastal breezes is a needed step to correctly forecast them and to be able to investigate their future trends.

In this work, we present an observational analysis of the coastal breezes observed in the Gulf of Cádiz. We highlight some differences found between the breezes formed at the sea and at the land areas from observational measurements. Besides, we use the mesoscale Weather Research and Forecasting (WRF) model to simulate key case studies, showing how the interaction with the background synoptic wind is very important for the final characteristics that the breezes have. Related to this, we have observed how the effect of the changes in the surface (SST, soil moisture) on the breeze’s characteristics depend on the wind vertical profile (background wind). That is, surface changes impact the ABL mixing and the momentum transfer from higher levels, which seems to be the main mechanism that impact the breezes at lower levels, even more than the surface thermal gradient effect.