A case‐study of the coupled ocean–atmosphere response to an oceanic diurnal warm layer

Brilouet, Pierre‐Etienne; Redelsperger, Jean‐Luc; Bouin, Marie‐Noëlle; Couvreux, Fleur; Brossier, Cindy Lebeaupin

doi:10.1002/qj.4007

Cited by 7 publications

(19 citation statements)

References 137 publications

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“…The simulated SST has a warm bias (+0.2 • C) of similar amplitude as that in the ocean forced case (+0.2 • C). The warming trend probably results from a lack of nighttime mixing in the case of strong upper-ocean stratification as shown in Brilouet et al (2021).…”

Section: Impact Of the Couplingmentioning

confidence: 97%

“…We therefore decided to develop a more local AOSCM forcing based on the R/V Revelle data. This case study has been developed in the context of the French research project COCOA and has been used in several studies (Brilouet et al, 2021). The ship's location at the Equator implies possible strong large-scale advection, which needs to be quantified for forcing the AOSCM.…”

Section: Selected Period and Locationmentioning

confidence: 99%

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Assessment of the sea surface temperature diurnal cycle in CNRM-CM6-1 based on its 1D coupled configuration

et al. 2022

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Abstract. A single-column version of the CNRM-CM6-1 global climate model has been developed to ease development and validation of the boundary layer physics and air–sea coupling in a simplified environment. This framework is then used to assess the ability of the coupled model to represent the sea surface temperature (SST) diurnal cycle. To this aim, the atmospheric–ocean single-column model (AOSCM), called CNRM-CM6-1D, is implemented in a case study derived from the CINDY2011/DYNAMO campaign over the Indian Ocean, where large diurnal SST variabilities have been well documented. Comparing the AOSCM and its uncoupled components (atmospheric SCM and oceanic SCM, called OSCM) highlights the fact that the impact of coupling in the atmosphere results from both the possibility to take into account the diurnal variability of SST, which is not usually available in forcing products, and the change in mean state SST as simulated by the OSCM, with the ocean mean state not being heavily impacted by the coupling. This suggests that coupling feedbacks in the 3D model do not arise from the coupling of ocean and atmosphere vertical column physics but are more due to the large-scale dynamics resolved by the 3D model. Additionally, a sub-daily coupling frequency is needed to represent the SST diurnal variability, but the choice of the coupling time step between 15 min and 3 h does not impact the diurnal temperature range simulated much. The main drawback of a 3 h coupling is delaying the SST diurnal cycle by 5 h in asynchronous coupled models. Overall, the diurnal SST variability is reasonably well represented in CNRM-CM6-1 with a 1 h coupling time step and the upper-ocean model resolution of 1 m. This framework is shown to be a very valuable tool to develop and validate the boundary layer physics and the coupling interface. It highlights the interest to develop other atmosphere–ocean coupling case studies.

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Section: Impact Of the Couplingmentioning

confidence: 97%

Section: Selected Period and Locationmentioning

confidence: 99%

Assessment of the sea surface temperature diurnal cycle in CNRM-CM6-1 based on its 1D coupled configuration

et al. 2022

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“…The main prerequisite for resolving DWLs in ocean simulations is high vertical resolution of the upper oceanic layers (cf. Brilouet et al (2021)). The introduction of the z* ocean coordinate into the ICON model (detailed in Singh and Korn (in preparation)) allows running global experiments with an unprecedented vertical resolution.…”

Section: Methodsmentioning

confidence: 99%

“…(2022), a single column coupled model has been considered, while in Brilouet et al. (2021), a one column ocean model has been coupled to an atmospheric large‐eddy simulation model integrated over a limited area. Both experiments are based on or validated with the data from the Dynamics of the Madden Julian Oscillation (DYNAMO) campaign, during which diurnal SST differences of several Kelvin were observed.…”

Section: Introductionmentioning

confidence: 99%

Impact of Diurnal Warm Layers on Atmospheric Convection

2023

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Diurnal sea surface temperature (SST) anomalies and their interplay with the atmosphere and in particular with the diurnal cycle of convection have been an object of study for many decades. In this study, we investigate this connection for the first time using simulations that can explicitly resolve both the diurnal temperature variations in the ocean and convection in the atmosphere on a global scale.Diurnal variations in SST have already been described in Sverdrup et al. (1942). Since then, there have been numerous studies describing the physics and the conditions of appearance of diurnal SST variations, the seminal work by Price et al. (1986) being the first detailed description of this phenomenon. Under low-wind conditions and with sufficient insolation, a stable near-surface layer forms during the day in the upper layers of the ocean (until the depth of O(10 m)) that leads to a surface warming of up to 5 K (see Wick and Castro (2020)). In the absence of solar radiation during the night, the stratification dissolves as vertical turbulent mixing takes overhand, until a homogeneous mixed layer is restored. The physics of this phenomenon is described in detail in a monograph by Soloviev and Lukas (2013). This stratified, warm layer is known as diurnal warm layer (DWL) and it is ubiquitous in all latitudes, causing SST fluctuations of 0.2 K or more in the entire Northern hemisphere and beyond during boreal summer (see Gentemann et al. (2003)). A comprehensive discussion of its definition and properties can be found in a review by Kawai and Wada (2007). In particular, the authors of the review point out that the presence of DWLs in observations as well as in single column simulations leads to stronger latent and sensible heat fluxes. As surface fluxes connect the surface to the atmospheric boundary layer and since changes in boundary layer properties affect the development of convection, the question of the impacts of DWLs on atmospheric convection arises.Investigating this question in models requires both fine enough vertical resolution in the ocean, to resolve DWLs, and fine enough horizontal grid spacing in the atmosphere, to resolve atmospheric convection. With the development of deca-to kilometer scale simulations in a coupled configuration (Hohenegger et al. ( 2023)) such investigations are becoming possible. Prominent among the newest studies are the papers by Voldoire et al. (2022) and Brilouet et al. (2021). In Voldoire et al. (2022), a single column coupled model has been considered, while

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“…The simulated SST has a warm bias (+0,2°C), of similar amplitude to that in the ocean forced case (+0,2°C). The warming trend probably results from a lack of nighttime mixing in the case of strong upper ocean stratification as shown in Brilouet et al (2021).…”

Section: Impact Of the Couplingmentioning

confidence: 97%

Assessment of the sea surface temperature diurnal cycle in CNRM-CM6-1 based on its 1D coupled configuration

Voldoire

Roehrig

Giordani

et al. 2021

Preprint

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Abstract. A single column version of the CNRM-CM6-1 global climate model has been developed to ease development and validation of the boundary layer physics and air-sea coupling in a simplified environment. This framework is then used to assess the ability of the coupled model to represent the sea surface temperature (SST) diurnal cycle. To this aim, the atmospheric-ocean single column model (AOSCM), called CNRM-CM6-1D, is implemented on a case study derived from the Cindy-Dynamo field campaign over the Indian Ocean, where large diurnal SST variabilities have been well documented. Comparing the AOSCM and its uncoupled components (atmospheric SCM and oceanic SCM, called OSCM) highlights that the impact of coupling in the atmosphere results both from the possibility to take in to account the diurnal variability of SST, not usually available in forcing products, and from the change in mean state SST as simulated by the OSCM, the ocean mean state not being heavily impacted by the coupling. This suggests that coupling feedbacks are more due to advection processes in the 3D model than to the model physics. Additionally, a sub-daily coupling frequency is needed to represent the SST diurnal variability but the choice of the coupling time-step between 15 min and 3 h does not impact much on the diurnal temperature range simulated. The main drawback of a 3-h coupling being to delay the SST diurnal cycle by 5 h in asynchronous coupled models. Overall, the diurnal SST variability is reasonably well represented in the CNRM-CM6-1 with a 1 h coupling time-step and the upper ocean model resolution of 1 m. This framework is shown to be a very valuable tool to develop and validate the boundary layer physics and the coupling interface. It highlights the interest to develop other atmosphere-ocean coupling case studies.

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A case‐study of the coupled ocean–atmosphere response to an oceanic diurnal warm layer

Cited by 7 publications

References 137 publications

Assessment of the sea surface temperature diurnal cycle in CNRM-CM6-1 based on its 1D coupled configuration

Assessment of the sea surface temperature diurnal cycle in CNRM-CM6-1 based on its 1D coupled configuration

Impact of Diurnal Warm Layers on Atmospheric Convection

Assessment of the sea surface temperature diurnal cycle in CNRM-CM6-1 based on its 1D coupled configuration

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