Tidal variations as a factor influencing sea breezes

Sea breezes are mesoscale atmospheric circulations that develop in coastal areas due to the thermal contrast between land and sea, with relevant environmental and socio-economic impacts, such as pollutant dispersion or thermal comfort, among others. While their dependence on synoptic conditions and land–sea thermal gradients has been widely studied, the potential influence of tidal variability has received much less attention.

This study focuses on the role of tidal variations in the formation and modulation of sea breeze events using observational data from a coastal site. Measurements from a shoreline weather station equipped with a 3D sonic anemometer are combined with tidal forecasts obtained using the Tidex2020 software.

Sea breeze events are identified using an objective algorithm adapted from previous studies and subsequently classified into two main groups: those initiating during the rising tide phase (flood) and those beginning during the falling tide phase (ebb). This classification ensures that flood events are preceded by low-tide conditions and ebb events by high-tide conditions. 

Results show a higher frequency of flood events than ebb ones. As expected, sonic anemometer data demonstrate that flood events exhibit higher sensible heat flux (SH) values in the hours preceding breeze onset due to the increased intertidal area exposed during the preceding ebb tides, which could favour the needed conditions for sea breezes development. Regarding wind speed, breezes developing under high-tide conditions (flood events) tend to reach higher wind speeds than those developing under low-tide conditions (ebb events), which could be associated with the different surface roughness and land–sea thermal contrast near the shoreline in both types of events. In this presentation, we will discuss all these factors influencing the breeze development, as well as the additional effect of the current direction in comparison to the wind direction, which also affects the surface roughness of the sea surface (waves formed).