Preprints
https://doi.org/10.5194/egusphere-2024-1146
https://doi.org/10.5194/egusphere-2024-1146
25 Apr 2024
 | 25 Apr 2024
Status: this preprint is open for discussion.

North Atlantic Subtropical Mode Water properties: Intrinsic and atmospherically-forced interannual variability

Olivier Narinc, Thierry Penduff, Guillaume Maze, Stéphanie Leroux, and Jean-Marc Molines

Abstract. This study investigates the contributions of the ocean’s chaotic intrinsic variability (CIV) and atmospherically-forced variability on the interannual fluctuations of the North Atlantic Eighteen Degree Water (EDW) properties. Utilizing a 1/4° regional 50-member ocean/sea-ice ensemble simulation driven by an original surface forcing method and perturbed initially, the forced variability of EDW properties is estimated from ensemble mean fluctuations, while CIV is determined from deviations around the ensemble mean within each member. The model successfully captures the main features of EDW, showing good agreement with observation-based ARMOR3D data in terms of location, seasonality, mean temperature and volume, and interannual variance of its main properties. CIV significantly impacts EDW, explaining 10–13 and 28–44 % of the interannual variance of its geometric and thermohaline mean properties, respectively, with a maximum imprint on EDW temperature. Observed and simulated intrinsic-to-total variance ratios are mostly consistent, dispelling concerns about a signal-to-noise paradox. This study also illustrates the advantages of ensemble simulations over single simulations in understanding oceanic fluctuations and attributing them to external drivers, while also cautioning against overreliance on individual simulations assessments.

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Olivier Narinc, Thierry Penduff, Guillaume Maze, Stéphanie Leroux, and Jean-Marc Molines

Status: open (until 20 Jun 2024)

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Olivier Narinc, Thierry Penduff, Guillaume Maze, Stéphanie Leroux, and Jean-Marc Molines
Olivier Narinc, Thierry Penduff, Guillaume Maze, Stéphanie Leroux, and Jean-Marc Molines

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Short summary
This study examines how the ocean's chaotic variability and atmospheric fluctuations affect yearly changes in North Atlantic Eighteen Degree Water (EDW) properties, using an ensemble of realistic ocean simulations. Results show that while yearly changes in EDW properties are mostly paced by the atmosphere, a notable fraction of these changes are random in phase. This study also illustrates the value of ensemble simulations over single runs in understanding oceanic fluctuations and their causes.