Characterization of the marine‐air intrusion “Marinada” in the eastern Ebro sub‐basin through observations and mesoscale modelling

The eastern Ebro basin is composed of an extensive irrigated plain, surrounded by rainfed slopes and wooden mountain ranges and open to the west to the agricultural western Ebro basin. The sea breeze generated at the coast is able to surmount the Catalan Pre-coastal Range through its lowest heights, reaching the basin by its easternmost part. It is a well‐known feature in the region, called Marinada.

A network of Automatic Weather Stations from the Catalan Meterological Service is used here to analyse a period of 19 years (2003–2021). A filtering procedure is developed which selects the events when the Marinada is present, based on detecting clear sky, weak wind conditions and the wind direction from the coast in the afternoon. The analysis of these days show that the Marinada propagates along the basin in the afternoon meanwhile observations of the specific humidity show a sudden increase as the temperature cools down, resulting on a cold and humid advection. It is also found that the timing of the arrival of the Marinada depends on the mesoscale/synoptical circulations already present in the region (westerlies or a thermal low).

Two Marinada events during the LIAISE experimental field campaign during summer 2021 (one with the predominance of westerlies and the other with a thermal low) are further analysed using the MesoNH model. Mesoscale simulations over the Ebro river basin are made at 2km resolution in the horizontal and 4m in the vertical (stretched with height). The initial and lateral boundary conditions are taken from the ECMWF model. Turbulence, radiation and surface parameterizations are taken to properly reproduce the phenomenon. It is shown that the Marinada is a fall wind, generated by a cool marine air mass advected over the Catalan Pre-coastal Range by the action of the sea breeze and the upslope wind. The characteristics and dynamics of the Marinada depend on the synoptical situation. For instance, under thermal low conditions the Marinada is initiated earlier and it is more intense than for the westerlies case. Results also highlight the importance of representing the surface features in the model (such as the irrigation processes) to properly capture the observations of the propagation of the Marinada inland.