Study of the physical mechanisms during sea breeze events in the Mallorca island through observations and simulations

The physical mechanisms that take place under sea-breeze (SB) conditions in the island of Mallorca (western Mediterranean Sea) are analysed through the inspection of data from automatic weather stations (AWS) from the Spanish Meteorological Agency (AEMET) during the period 2009–2022. Hourly satellite-derived land-surface and sea-surface temperatures (LST and SST, respectively) are used to compute the surface temperature difference (LST–SST) in the three main basins. Besides, a method (Grau et al, 2020) is taken to select the SB events in the three main basins using data from AWS during the warm months of the year (from April to September). Results from the statistical analysis of the selected SB events show that the ranges of the temperature difference change in the three main basins pointing to the presence of other physical mechanisms in the setup of the sea breeze and the propagation of the sea-breeze front. It is found that there are differences in the SB features of the three basins (maximum wind speed, initiation and duration of the SB). Besides, in general SB conditions are not simultaneously met in the three basins, but when they do they can interact strongly.

To check if models are able to capture these observed physical mechanisms, data from the Copernicus regional reanalysis for Europe (CERRA) are taken. The features of the selected SB events obtained from the data analysis are compared to those obtained by the model at 5km spatial resolution. It is found that the thermal gradient is well captured by the model but a misrepresentation of the topography and other surface features might be the responsible of the differences between model and observations.

The representation by numerical models of some selected SB events are further analysed through mesoscale simulations made with the MesoNH model. Three nested domains are taken (horizontal resolutions of 5km, 1km and 250m) and the inner one is centered in the studied basin. The vertical resolution is 3m at the surface and stretched above. For a particular basin, the SB interacts with the already present locally-generated winds within the same basin but also with the SB generated in the other basins. Simulations clearly show that the SB is a cold and humid advection that interacts with the surface energy balance terms once it propagates inland.