Preprints
https://doi.org/10.5194/os-2021-72
https://doi.org/10.5194/os-2021-72

  09 Aug 2021

09 Aug 2021

Review status: this preprint is currently under review for the journal OS.

Untangling the Mistral and seasonal atmospheric forcing driving deep convection in the Gulf of Lion: 2012–2013

Douglas Keller Jr.1, Yonatan Givon2, Romain Pennel1, Shira Raveh-Rubin2, and Philippe Drobinski1 Douglas Keller Jr. et al.
  • 1LMD/IPSL, École Polytechnique, Institut Polytechnique de Paris, ENS, PSL Research University, Sorbonne Université, CNRS, Palaiseau, France
  • 2Department of Earth and Planetary Sciences, Weizmann Institute of Science, Rehovot, Israel

Abstract. Deep convection in the Gulf of Lion is believed to be primarily driven by the Mistral winds. However, our findings show that the seasonal atmospheric change provides roughly 2/3 of the buoyancy loss required for deep convection to occur, for the 2012 to 2013 year, with the Mistral supplying the final 1/3. Two NEMOMED12 ocean simulations of the Mediterranean Sea were run for the Aug. 1st, 2012 to July 31st, 2013 year, forced with two sets of atmospheric forcing data from a RegIPSL coupled run within the Med-CORDEX framework. One set of atmospheric forcing data was left unmodified, while the other was filtered to remove the signal of the Mistral. The Control simulation featured deep convection, while the Seasonal did not. A simple model was derived, relating the anomaly scale forcing (the difference between the Control and Seasonal runs) and the seasonal scale forcing to the ocean response through the Stratification Index. This simple model revealed that the Mistral's effect on buoyancy loss depends more on its strength rather than its frequency or duration. The simple model also revealed that the seasonal cycle of the Stratification Index is equal to the net surface heat flux over the course of the year, with the stratification maximum and minimum occurring roughly at the fall and spring equinoxes.

Douglas Keller Jr. et al.

Status: open (until 16 Oct 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on os-2021-72', Anonymous Referee #1, 16 Sep 2021 reply

Douglas Keller Jr. et al.

Douglas Keller Jr. et al.

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Short summary
The Mistral winds were believed to be the primary source of cooling of the Gulf of Lion, leading to deep convection in the region, a process that mixes the ocean column from the sea floor to the sea surface. However, we have found that the seasonal atmospheric changes, and not only the Mistral winds, significantly cool the Gulf of Lion waters to cause deep convection, contributing roughly 2/3 of the required cooling with the Mistral winds contributing the final 1/3.