Analysis of current intensification in the Northwest Mediterranean shelf

• Occasional flow intensifications on the NW Mediterranean shelf are analysed.
• Main causes are sustained winds from the NE–SE combined with the shelf narrowing.
• Sporadic presence of coastal trapped waves is found, and contributes to flow pulses.
• Link between pulses and climatic indices suggests further increase of pulse occurrence.

Flow intensification episodes lasting more than 12 h are observed occasionally at different locations along the Northwestern Mediterranean coast. In the last years, these pulses have hindered ship operations outside the Barcelona harbour, thus attracting the attention of the port authorities. In this paper, the strongest intensification events in the Barcelona coast area are quantified and characterized in order to identify the mechanisms which generate them. For this, current, sea level and meteorological measured and modelled data, at local and regional scale, are analysed. The results show that the flow accelerations are due to the combination of a narrow coastal shelf and the prevalence of a strong and sustained wind from the NE to SE. The synoptic atmospheric conditions that lead to this meteorological scenario are described. For one of the events, the presence and contribution to the current fluctuations of a coastal trapped wave, likely generated at the Eastern edge of the Gulf of Lions shelf, and other factors such as a freshwater discharge are also identified and discussed.