Sensitivity analysis and metamodels for the bulk parametrization of turbulent air–sea fluxes

Pelletier, Charles; Lemarié, Florian; Blayo, Éric

doi:10.1002/qj.3233

Cited by 6 publications

(5 citation statements)

References 31 publications

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“…However, this simple analytical development does not consider the wind response to the CFB that will partly counteract the stress response (Renault et al, 2016b). Additionally, as shown by Pelletier et al (2018), C D can also be impacted by the CFB, but its response strongly depends on the bulk formula used.…”

Section: Analytical Analysismentioning

confidence: 99%

On the implementation and consequences of the oceanic currents feedback in ocean–atmosphere coupled models

2019

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The Current FeedBack (CFB) to the atmosphere simply represents the influence of the surface oceanic currents on near-surface wind and surface stress. As the CFB has a significant influence on the oceanic circulation, it is crucial to implement it properly in a coupled Ocean-Atmosphere model. In this study, we first detail the modifications to be implemented into atmospheric models to account for the CFB. In the computation of air-sea fluxes, the relative winds, i.e., the difference between the near-surface winds and the surface oceanic currents, instead of absolute winds have to be used (Modification M1). However, because of the implicit treatment of the bottom boundary condition in most atmospheric models, the use of relative winds also involves a modification of the tridiagonal problem associated with the discretization of the vertical turbulent viscosity (Modification M2). Secondly, we show both analytically and using global coupled simulations that omitting M2 leads to a large underestimation of the surface stress curl response to the CFB and, subsequently, of the coupling coefficient between mesoscale surface stress curl and surface current vorticity. As a consequence, the dampening of the mesoscale activity induced by the CFB is strongly reduced (by a minimum a factor of 2 or more). The practical implementation of the CFB must be done carefully in the atmospheric component of a coupled model in order to avoid a large underestimation of the CFB effect on the oceanic circulation.

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Section: Analytical Analysismentioning

confidence: 99%

On the implementation and consequences of the oceanic currents feedback in ocean–atmosphere coupled models

2019

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“…However, both ocean and atmosphere models include parameterizations that are potentially not differentiable. This is, for instance, the case of the bulk formulas used to compute the turbulent fluxes at the air-sea interface (e.g., Pelletier et al, 2018). A first step is thus to test the convergence when coupling realistic models.…”

Section: The Schwarz Iterative Methodsmentioning

confidence: 99%

“…The parameters of the atmospheric model allow us to exactly reproduce the atmosphere of IPSL-CM5A2-LR when the atmosphere is run in stand-alone mode. In the ocean, the sea ice model LIM3 is used with one category of ice (IPSL-CM6-LR uses five ice categories based on ice thickness; see Rousset et al, 2015, for more details on LIM3 in the mono-category). The land surface model ORCHIDEE was removed to simplify and speed up the implementation of the Schwarz algorithm.…”

Section: The Schwarz Iterative Methodsmentioning

confidence: 99%

A Schwarz iterative method to evaluate ocean–atmosphere coupling schemes: implementation and diagnostics in IPSL-CM6-SW-VLR

et al. 2021

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Abstract. State-of-the-art Earth system models, like the ones used in the Coupled Model Intercomparison Project Phase 6 (CMIP6), suffer from temporal inconsistencies at the ocean–atmosphere interface. Indeed, the coupling algorithms generally implemented in those models do not allow for a correct phasing between the ocean and the atmosphere and hence between their diurnal cycles. A possibility to remove these temporal inconsistencies is to use an iterative coupling algorithm based on the Schwarz iterative method. Despite its large computational cost compared to standard coupling methods, which makes the algorithm implementation impractical for production runs, the Schwarz method is useful to evaluate some of the errors made in state-of-the-art ocean–atmosphere coupled models (e.g., in the representation of the processes related to diurnal cycle), as illustrated by the present study. IPSL-CM6-SW-VLR is a low-resolution version of the IPSL-CM6 coupled model with a simplified land surface model, implementing a Schwarz iterative coupling scheme. Comparisons between coupled solutions obtained with this new scheme and the standard IPSL coupling scheme (referred to as the parallel algorithm) show large differences after sunrise and before sunset, when the external forcing (insolation at the top of the atmosphere) has the fastest pace of change. At these times of the day, the difference between the two numerical solutions is often larger than 100 % of the solution, even with a small coupling period, thus suggesting that significant errors are potentially made with current coupling methods. Most of those differences can be strongly reduced by making only two iterations of the Schwarz method, which leads to a doubling of the computing cost. Besides the parallel algorithm used in IPSL-CM6, we also test a so-called sequential atmosphere-first algorithm, which is used in some coupled ocean–atmosphere models. We show that the sequential algorithm improves the numerical results compared to the parallel one at the expanse of a loss of parallelism. The present study focuses on the ocean–atmosphere interface with no sea ice. The problem with three components (ocean–sea ice–atmosphere) remains to be investigated.

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“…This is for instance the case of the bulk formulas used to compute the turbulent fluxes at the air-sea interface (e.g. Pelletier et al, 2018). A first step is thus to test the convergence when coupling realistic models.…”

Section: The Schwarz Iterative Methodsmentioning

confidence: 99%

A Schwarz iterative method to evaluate ocean- atmosphere coupling schemes. Implementation and diagnostics in IPSL-CM6-SW-VLR

Marti¹,

Nguyen²,

Braconnot³

et al. 2020

Preprint

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Abstract. State-of-the-art Earth System models, like the ones used in the CMIP6 intercomparison project, suffer from temporal inconsistencies at the ocean-atmosphere interface. Indeed, the coupling algorithms generally implemented in those models do not allow for a correct phasing between the ocean and the atmosphere, and hence between their diurnal cycles. A possibility to remove these temporal inconsistencies is to use an iterative coupling algorithm based on Schwarz methods. Despite the fact that the computational cost is large compared to standard coupling methods, which makes the method impractical as is for production runs, Schwarz algorithms are useful to evaluate some of the errors made in state-of-the-art ocean-atmosphere coupled models (e.g. in the representation of the processes related to diurnal cycle), as illustrated by the present study. A new coupling scheme based on such iterative method has been implemented in the IPSL coupled model. Comparisons between coupled solutions obtained with this new scheme and the standard IPSL coupling scheme show large differences at sunrise and sunset, when the external forcing (insolation at top of atmosphere) has the fastest pace of change. At these times of the day, the difference between the two numerical solutions is often larger than 100 % of the solution, even with a small coupling time step, thus suggesting that significant errors are potentially made with current coupling methods. Most of those differences can be strongly reduced by making only two iterations of the Schwarz method which leads to a doubling of the computing cost. A thorough design of the first guess to initialize the iterative process may yield a solution that reduces the error with only one iteration. The present study focuses on the ocean-atmosphere interface, with no sea-ice. The problem with three components (ocean/sea-ice/atmosphere) remains to be investigated.

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Sensitivity analysis and metamodels for the bulk parametrization of turbulent air–sea fluxes

Cited by 6 publications

References 31 publications

On the implementation and consequences of the oceanic currents feedback in ocean–atmosphere coupled models

On the implementation and consequences of the oceanic currents feedback in ocean–atmosphere coupled models

A Schwarz iterative method to evaluate ocean–atmosphere coupling schemes: implementation and diagnostics in IPSL-CM6-SW-VLR

A Schwarz iterative method to evaluate ocean- atmosphere coupling schemes. Implementation and diagnostics in IPSL-CM6-SW-VLR

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