Jul 2026· Proceedings of the National Academy of Sciences of the United States of America· Vol 123 30, pp.
e2605662123
· 0 citations· 8 references
Medicine
Abstract
Current understanding of the role of ocean variability in air-sea exchange is constrained to large and mesoscale dynamics. Oceanic fronts and filaments with horizontal spatial scales of order 0.1 to 10 km-denoted submesoscale-are challenging to observe due to their fast-evolving flow and small spatiotemporal scales of variability. Observations investigating the air-sea fluxes at the submesoscale have shown substantial fluxes of heat, moisture, and momentum, affecting the structure of the overlying atmosphere. Here, modulations of the turbulent atmospheric boundary layer driven by ocean temperature anomalies are investigated using submesoscale-resolving ship and airborne measurements, providing in situ evidence of the atmospheric response to ocean submesoscale temperature variability. Observations suggest near-surface turbulent mixing driven by strong air-sea fluxes of heat and momentum, modifying the vertical structure of the planetary boundary layer. Linear regression coefficients between wind speed and sea surface temperature anomalies reveal a response similar in magnitude to that seen at larger scales, with an integrated change of 0.23 m s-1 °C-1, but occurring over smaller length-scales, implying sharper gradients. Lagged correlations and scaling analysis imply a combined influence of horizontal advection and vertical turbulent mixing of momentum in the atmosphere, previously only described by numerical simulations. Observed cross-frontal wind divergences over the lower 200 m suggest coherent circulations with vertical velocities of order 1 cm s-1. These observations confirm the rapid adjustment of the marine boundary layer to submesoscale ocean temperature variability and the importance of submesoscale-driven air-sea fluxes in changing the properties of the lower atmosphere, processes not resolved in most forecasting and prediction models.
A large share of energy within the global oceans lies within the mesoscale range, (100 km), where very large dynamic and thermodynamic variability has been observed. We address how the marine atmospheric boundary layer (MABL) in a trade‐wind region adapts to fast and spatially varying sea‐surface temperature (SST) structures, with a focus on changes in behaviour as a function of spatial scales. High‐resolution atmospheric simulation data indicate that, at scales smaller than 1000 km, the effects of enhanced entrainment of dry free tropospheric air overcome those of surface evaporation over warm SST anomalies. This is supported by computations from a conceptual bulk model, which confirm two different responses in MABL temperature and specific humidity: an increase in the forcing SST warms the MABL and reduces its humidity content slightly. Locally, this behaviour suppresses the surface sensible heat flux (SHF) and enhances the surface latent heat flux (LHF), as observed recently with in situ, satellite, and numerical modelling data. At larger scales, instead, the MABL is more in equilibrium with the ocean surface and the sensitivity of turbulent fluxes to the underlying SST anomalies is significantly smaller. The scale dependence of the LHF variability is analysed with a linear scale decomposition method. SST is found to be the primary driver of LHF variability when scales smaller than about 1000 km are resolved, whereas atmospheric variability takes the lead for larger scales. Despite the effects on the mean LHF being small, the link between SST and LHF variability potentially has important implications for atmospheric shallow mesoscale circulations, which remain to be explored.
Alessandro Storer, M. Borgnino, C. Pasquero et al.· Quarterly Journal of the Roy...· 0 citations
Mesoscale eddies in the Southern Ocean extend from the surface to the deep ocean and contribute to regional and global ocean heat budgets. However, sparse in situ observations have limited estimates of eddy meridional heat transport (EMHT) to the near surface, leaving deep-ocean processes poorly understood. Here we quantify deep eddy kinetic energy (EKE) and EMHT using Argo observations. We find that deep EMHT reaches at least the same order of magnitude as surface transport, despite deep EKE being only one-fifth of surface levels. Float observations and sensitivity experiments reveal that, relative to mean-flow transport alone, deep EMHT extends the meridional movement of subtropical warm waters towards Antarctica by over ten degrees of latitude. About 60% of this deep transport originates from the Indian Ocean sector. These findings provide observational evidence that mesoscale eddies can modulate deep Southern Ocean heat redistribution, with potential implications for Antarctic climate.
Tongya Liu, Xiaoming Zhai, Qingyou He et al.· Nature Communications· 0 citations
Direct observations of coherent turbulent structures at the base of the ocean surface boundary layer are rare. Here, we present a unique dataset from a drifting thermistor chain that captured temperature structures associated with mixed layer and transition layer turbulence. Following a storm with wind speeds up to 15 m s
−1
, the mixed layer deepened from 35 to 45 m depth over 6 days. Within the transition layer we observe temperature fluctuations indicative of shear-driven turbulence, including features consistent with Kelvin-Helmholtz and Holmboe instabilities. We examine the size and frequency of these structures in the context of the surface forcing, identifying four distinct regimes based on wind, wave, and surface heat flux magnitude. Thorpe scale–based estimates of entrainment velocity align with the observed mixed layer deepening when averaged over the upper portion of the transition layer. This rare observational dataset offers new insight into the mechanisms controlling mixing at the base of the mixed layer and provides a valuable benchmark for future numerical studies of stratified turbulence that resolve turbulent overturns.
A. Andriatis, Matthew H. Alford, Andrew J. Lucas et al.· Journal of Physical Oceanogr...· 0 citations
Coherent surface ocean temperature and velocity structures, with scales spanning 10–100 km, induce surface wind stress anomalies that generate near-surface vertical velocities through Ekman dynamics. These wind–front interactions are known as Thermal (TFB) and Current (CFB) feedbacks. Their relative contributions to ocean vertical velocities and their variability across scales remain underexplored. This study decomposes and attributes Ekman vertical velocity variability to TFB and CFB at
O
(100) km and
O
(10) km scales using output from a global 4–6 km ocean–atmosphere coupled simulation, focusing on the California Current System. Total Ekman velocities are decomposed into a linear component associated with wind stress curl and a nonlinear component involving ocean vorticity derivatives. At 30–200 km scales, TFB and CFB contribute similarly to the linear component, which is comparable in magnitude to the nonlinear term (
O
(1–5) m day
−1
in instantaneous value). At <30 km scales, nonlinear Ekman velocities exceed linear terms by an order of magnitude, reaching instantaneous values of
O
(10–50) m day
−1
and matching the total near-surface vertical velocities. The decomposition reveals that the nonlinear enhancement is driven by ocean vorticity gradients at <30 km scales. These results emphasize the importance of resolving small-scale wind–front interactions and ocean surface features that modulate upper-ocean vertical velocities, demonstrating, as a first step, the potential to infer subsurface vertical motions from surface measurements and Ekman dynamics. However, such inferences should be interpreted with caution where the surface Rossby number exceeds unity.
Yue Bai, Andrew F. Thompson, A. B. Villas Bôas et al.· Journal of Physical Oceanogr...· 0 citations
Thermal tides on Venus have been extensively studied near the cloud tops, where their three‐dimensional structure and contribution to the atmospheric momentum budget have been characterized from temperature and wind fields. However, their downward propagation and influence within the deep atmosphere remain uncertain, and their behavior in the deep atmosphere, particularly near the surface, remains poorly constrained. Using the LMD Venus Planetary Climate Model, we investigate the near‐surface thermal tides and their governing timescales. The simulations show that these tides are generated by heat transfer from the surface to the planetary boundary layer and produce a diurnal pressure response with a phase lag of about 30° $30{}^{\circ}$ corresponding to a radiative adjustment timescale of about 10 Earth days. In addition, a 35‐day oscillation appears within the stably stratified 10–20 km layer, consistent with a planetary‐scale internal gravity wave. These results suggest that coherent oscillations beyond the diurnal tide can develop in the deep atmosphere, with the surface pressure variability dominated by a superposition of three modes: the diurnal and semidiurnal tides and the 35‐day oscillation. Together, these components account for about 70 % $\%$ of the total surface pressure variance, with potential implications for gravity measurements by forthcoming missions such as VERITAS and EnVision.
Rachel Navon, E. Galanti, S. Lebonnois et al.· Journal of Geophysical Resea...· 0 citations
High-resolution numerical simulations and field efforts have revealed ubiquitous lateral buoyancy gradients around surface-intensified mesoscale eddies and emphasized the role of submesoscale turbulence in the energy cascade of geostrophic flows and vertical communication of tracers. However, active fronts and submesoscale turbulence, along with associated geostrophic energy dissipation, remain poorly understood in subsurface eddy fields, partly due to high-resolution observational limitations in the ocean interior. In this study, a field campaign observed a mesoscale intrathermocline eddy (ITE) with lens-shaped isopycnals and enhanced energy dissipation in the thermocline. The turbulent kinetic energy (TKE) dissipation rates measured by vertical microstructure profiler are significantly elevated to 10
−7
–10
−8
W kg
−1
in the ITE periphery, which are one to two orders of magnitude higher than surrounding subsurface areas (∼10
−9
W kg
−1
), and even comparable to mixed-layer values. Diagnostic results from the Gregg-Henyey-Polzin finescale parameterization do not support internal wave activity as the primary source of observed high dissipation rates, although contributions from high-frequency nonlinear internal waves cannot be resolved here. Meanwhile, 600-m-resolution Triaxus observations across the ITE reveal submesoscale-enhanced lateral buoyancy gradients, increased geostrophic shear, and decreased potential vorticity (PV) in regions of elevated TKE dissipation, indicating conditions favorable for frontal submesoscale instability. The consistency of density fronts, negative PVs, and symmetric instability implies that elevated dissipation in the ITE periphery are highly associated with submesoscale instabilities. These direct observations emphasize active fronts and submesoscale turbulence around the ITE and highlight their key role in the forward energy cascade and dissipation of subsurface geostrophic eddies.
Yuyi Liu, Zhiyou Jing, Haijin Cao et al.· Journal of Physical Oceanogr...· 0 citations