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Abstract The turbulent ocean surface boundary layer (OSBL) shoals during daytime solar surface heating, developing a diurnal warm layer (DWL). The DWL significantly influences OSBL dynamics by trapping momentum and heat in a shallow near‐surface layer. Therefore, DWL depth is critical for understanding OSBL transport and ocean‐atmosphere coupling. A great challenge for determining DWL depth is considering wave‐driven Langmuir turbulence (LT), which increases vertical transport. This study investigates observations with moderate wind speeds (4–7 m/s at 10 m height) and swell waves for which breaking wave effects are less pronounced. By employing turbulence‐resolving large eddy simulation experiments that cover observed wind, wave, and heating conditions based on the wave‐averaged Craik‐Lebovich equation, we develop a DWL depth scaling unifying previous approaches. This scaling closely agrees with observed DWL depths from a year‐long mooring deployment in the subtropical North Atlantic, demonstrating the critical role of LT in determining DWL depth and OSBL dynamics.
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This content will become publicly available on June 1, 2026
The Response of Large Diurnal Warm Layers to Short-Term Variability in Solar and Wind Forcing: Observations and Physical Modeling
Abstract In conditions of low winds and high insolation, near-surface stratification develops in the ocean that is typically referred to as a diurnal warm layer (DWL). These layers can have a substantial effect on sea surface temperature and air–sea fluxes yet are rarely accounted for in modern global models due to their small vertical scale. Here, we present collocated measurements of vertical temperature and turbulence structures in large DWLs made from a Lagrangian float featuring a robotic lead screw temperature/salinity (T/S) profiler and pulse-to-pulse coherent ADCP as well as a comprehensive suite of meteorological observations above the ocean surface, yielding novel observations of the response of large DWLs to variability in wind and solar forcing at subhourly time scales. Comparison between the observations and a hierarchy of upper-ocean models reveals the importance of an accurate solar heating parameterization and suggests a modification to the critical bulk Richardson number used by default in theK-profile parameterization. Comparison to a simple scaling for DWL evolution highlights its potential as a means of incorporating DWL effects into global-scale modeling, and a new extension to the scaling is developed to remedy its inaccuracy in cases of wind decrease. None of the models tested are able to reproduce the observed response to sudden insolation loss on one of the stations. Significance StatementThis study presents measurements of warm layers of water that can develop on the ocean surface on a calm, sunny day. These layers are widespread in the ocean and change the relationship between the ocean and the atmosphere, but they are hard to include in large models because they are so shallow. By comparing first-of-their-kind observations of these warm layers made by our drifting buoy with several types of physical models, we improve our understanding of them and chart a realistic path toward their inclusion in global models.
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- Award ID(s):
- 2049546
- PAR ID:
- 10615111
- Publisher / Repository:
- AMS
- Date Published:
- Journal Name:
- Journal of Physical Oceanography
- Volume:
- 55
- Issue:
- 6
- ISSN:
- 0022-3670
- Page Range / eLocation ID:
- 771 to 786
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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