Tropical Cool-Skin and Warm-Layer Effects and Their Impact on Surface Heat Fluxes

Yunwei Yan aKey Laboratory of Marine Hazards Forecasting, Ministry of Natural Resources, Hohai University, Nanjing, China
bState Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, MNR, Hangzhou, China

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Xiangzhou Song aKey Laboratory of Marine Hazards Forecasting, Ministry of Natural Resources, Hohai University, Nanjing, China

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Guihua Wang cDepartment of Atmospheric and Oceanic Sciences and Institute of Atmospheric Sciences, Fudan University, Shanghai, China

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Xiaojing Li bState Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, MNR, Hangzhou, China

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Abstract

Cool-skin and warm-layer effects are important phenomena in the ocean–atmosphere system. Here, we study tropical cool-skin and warm-layer effects and their impact on surface heat fluxes using the methods proposed by Fairall et al. in 1996, i.e., the F96 cool-skin scheme and the combined warm-layer method. The results reveal strong cool-skin effects (∼−0.3 K) in the Indo-Pacific warm pool, but weak effects in the equatorial Pacific and Atlantic cold tongues. The spatial pattern of the cool-skin effect is determined by the difference in the specific humidity between the sea and air. The warm-layer effect is strong (∼0.25 K) in both the warm pool and cold tongues but weak in the trade wind regions and exhibits a spatial pattern that is inversely related to the surface wind speed. In the tropics, the cool-skin effect causes an average reduction of 11.0 W m−2 in the heat loss from the ocean to the atmosphere, while the warm-layer effect causes an increase of 6.0 W m−2. With respect to the F96 cool-skin scheme, four common wind-speed-dependent empirical models could not fully capture the spatial distribution of the cool-skin effect. A new empirical model that depends on the sea–air humidity difference is proposed to overcome this problem. Compared to the combined warm-layer method, when only the F96 warm-layer scheme is applied, the effect is underestimated at both low and high wind speeds. These new findings improve our understanding of the cool-skin and warm-layer effects and provide insights into their parameterization schemes.

Significance Statement

The aim of this study is to improve our understanding of tropical cool-skin and warm-layer effects and to examine their impact on surface heat fluxes. In addition, we evaluate the parameterization schemes for these effects to provide insights into their improvement in ocean–atmosphere coupled models. Our results indicate that the sea–air humidity difference is likely the most important factor influencing the tropical cool-skin effect. As a result, a new empirical model that depends on the sea–air humidity difference is proposed. Furthermore, we find that existing diagnostic models underestimate the impact of the warm-layer phenomenon on the ocean–atmosphere system. Therefore, it is necessary to develop an improved parameterization scheme, especially as synchronous near-surface temperature measurements become available.

© 2023 American Meteorological Society. This published article is licensed under the terms of the default AMS reuse license. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

Corresponding author: Yunwei Yan, yunwei.yan@hhu.edu.cn

Abstract

Cool-skin and warm-layer effects are important phenomena in the ocean–atmosphere system. Here, we study tropical cool-skin and warm-layer effects and their impact on surface heat fluxes using the methods proposed by Fairall et al. in 1996, i.e., the F96 cool-skin scheme and the combined warm-layer method. The results reveal strong cool-skin effects (∼−0.3 K) in the Indo-Pacific warm pool, but weak effects in the equatorial Pacific and Atlantic cold tongues. The spatial pattern of the cool-skin effect is determined by the difference in the specific humidity between the sea and air. The warm-layer effect is strong (∼0.25 K) in both the warm pool and cold tongues but weak in the trade wind regions and exhibits a spatial pattern that is inversely related to the surface wind speed. In the tropics, the cool-skin effect causes an average reduction of 11.0 W m−2 in the heat loss from the ocean to the atmosphere, while the warm-layer effect causes an increase of 6.0 W m−2. With respect to the F96 cool-skin scheme, four common wind-speed-dependent empirical models could not fully capture the spatial distribution of the cool-skin effect. A new empirical model that depends on the sea–air humidity difference is proposed to overcome this problem. Compared to the combined warm-layer method, when only the F96 warm-layer scheme is applied, the effect is underestimated at both low and high wind speeds. These new findings improve our understanding of the cool-skin and warm-layer effects and provide insights into their parameterization schemes.

Significance Statement

The aim of this study is to improve our understanding of tropical cool-skin and warm-layer effects and to examine their impact on surface heat fluxes. In addition, we evaluate the parameterization schemes for these effects to provide insights into their improvement in ocean–atmosphere coupled models. Our results indicate that the sea–air humidity difference is likely the most important factor influencing the tropical cool-skin effect. As a result, a new empirical model that depends on the sea–air humidity difference is proposed. Furthermore, we find that existing diagnostic models underestimate the impact of the warm-layer phenomenon on the ocean–atmosphere system. Therefore, it is necessary to develop an improved parameterization scheme, especially as synchronous near-surface temperature measurements become available.

© 2023 American Meteorological Society. This published article is licensed under the terms of the default AMS reuse license. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

Corresponding author: Yunwei Yan, yunwei.yan@hhu.edu.cn

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