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The impact of mid‐latitude oceanic frontal zones with sharp meridional sea‐surface temperature (SST) gradients on the middle atmosphere circulation during austral winter is investigated by comparing two idealized experiments with a high‐top gravity wave (GW) permitting general circulation model. Control run is performed with realistic frontal SST gradients, which are artificially smoothed in no‐front run. The control run simulates active baroclinic waves and GW generation around the mid‐latitude SST front, with GWs propagating into the stratosphere and mesosphere. In the no‐front run, by contrast, baroclinic‐wave activity is significantly suppressed, and GWs with smaller amplitude are excited and then dissipated at higher altitudes in the mesosphere. Westward wave forcing in the winter hemisphere was more pronounced in the control run up to ∼0.03 hPa, resulting in a more realistic reproduction of the middle atmospheric polar vortex. The results demonstrate the importance of realistic mid‐latitude ocean conditions for simulating the middle atmosphere circulation. Plain Language Summary The impact of the mid‐latitude oceanic fronts characterized by sharp sea‐surface temperature (SST) gradients is investigated using a global gravity‐wave permitting atmospheric model that represents the troposphere, stratosphere and mesosphere. Two idealized experiments were conducted with different SST profiles. Control run features a realistic SST profile characterized by frontal SST gradients in mid‐latitudes, while they are smoothed out artificially in the “no‐front” run. In winter the no‐front run simulates significantly suppressed generation of synoptic‐scale cyclones and anticyclones, which results in reduced upward propagation of higher‐frequency gravity waves into the stratosphere, exerting marked impact on the large‐scale circulation extending as high as the mesopause. Notably higher gravity wave activity in the control run leads to a weaker, and more realistic wintertime polar vortex in the stratosphere and mesosphere. This study emphasizes the potential influence of mid‐latitude oceanic conditions on the atmospheric circulation, not only in the troposphere but also throughout the stratosphere and mesosphere. Key Points High‐top global model simulations are conducted to examine the impact of a mid‐latitude oceanic front on the atmospheric circulation The oceanic front enhances tropospheric baroclinic‐wave activity and generation of gravity waves propagating into the middle atmosphere The enhanced gravity waves act to reduce cold bias of the wintertime polar vortex in the Southern Hemisphere middle atmosphere

Air‐sea exchanges across oceanic fronts are critical in powering cloud formation, precipitation, and atmospheric storms. Oceanic submesoscale fronts of scales 1–10 km are characterized by strong sea surface temperature (SST) gradients. However, it remains elusive how submesoscale fronts affect the overlying atmosphere due to a lack of high‐resolution observations or models. Based on rare high‐resolution in situ observations in the Kuroshio Extension region, we quantify the air‐sea exchanges across an oceanic submesoscale front. The cross‐front SST and turbulent heat flux gradients reaches 2.4°C/km and 47 W/m2/km, respectively, far stronger than that typically found in mesoscale‐resolving products. The stronger SST gradient drives substantially stronger air‐sea fluxes and vertical mixing than mesoscale fronts, enhancing cloud formations. The intense air‐sea exchanges across submesoscale fronts are confirmed in idealized model simulations, but not resolved in mesoscale‐resolving climate models. Our finding provides essential knowledge for improving simulations of cloud formation, precipitation, and storms in climate models. Plain Language Summary Oceanic fronts, characterized by large sea surface temperature (SST) gradients, are ubiquitous in the global ocean. Through intense heat and moisture release, these oceanic fronts induce large horizontal gradient of sea level pressure or increasing vertical mixing intensity in the lower atmosphere, are critical in powering cloud formation, precipitation, and atmospheric storms, but are sensitive to SST gradients. Oceanic submesoscale fronts of spatial scales 1–10 km are characterized by strong SST gradients. However, our knowledge of how the submesoscale fronts affect the overlying atmosphere is by and large void, due to a lack of high‐resolution observations or models. Here, based on high‐resolution in situ observations and model simulations, we show that submesoscale fronts drive much stronger air‐sea exchanges and vertical mixing as compared to mesoscale fronts, with significant implications for marine atmosphere boundary layer changes and cloud formations. Limited by the coarse resolution, the intense air‐sea exchanges across submesoscale fronts are not resolved in mesoscale‐resolving climate models. These results highlight the importance of submesoscale air‐sea interactions and call for a proper representation of submesoscale air‐sea exchanges in the next generation of climate models. Key Points Observations show strong gradient in sea surface temperature and turbulent heat flux across a submesoscale oceanic front Submesoscale fronts drive substantially stronger air‐sea fluxes and vertical mixing than mesoscale fronts The intense air‐sea exchanges across submesoscale fronts are not resolved in mesoscale‐resolving climate models

In response to the demand for high-precision acoustic support under the condition of limited data, this study utilized high-resolution reanalysis data and in situ observation data to extract the Kuroshio Extension Front (KEF) section through front-line identification methods. By combining the parameterized oceanic front model and the statistical features of big data, the parameterized oceanic front was reconstructed. A proxy dataset was generated using the Latin hypercube sampling method, and the sound speed reconstruction model based on the PIX2PIX model was trained and validated using single sound speed profiles at different positions of the oceanic front, combined with the parameterized oceanic front model. The experimental results show that the proposed sound speed reconstruction model can significantly improve the reconstruction accuracy by introducing the parameterized front model as an additional input, especially in the shallow-water area. The mean absolute error (MAE) of the full-depth sound speed reconstruction for this model is 0.63~0.95 m·s−1, and the structural similarity index (SSIM) is 0.76~0.78. The MAE of the sound speed section within a 1000 m depth is reduced by 6.50~37.62%, reaching 1.95~3.31 m·s−1. In addition, the acoustic support capabilities and generalization of the model were verified through ray tracing models and in situ data. This study contributes to advancing high-precision acoustic support in data-limited oceanic environments, laying a solid groundwork for future innovations in marine acoustics.

Oceanic fronts delineate the boundaries between distinct water masses within the ocean, typically marked by shifts in weather patterns and the generation of oceanic circulation. These fronts are identified in research on intelligent oceanic front detection primarily by their significant temperature gradients. The refined identification of oceanic fronts is of great significance to maritime material transportation and ecological environment protection. In view of the weak edge nature of oceanic fronts and the misdetection or missed detection of oceanic fronts by some deep learning methods, this paper proposes an oceanic front detection method based on the U-Net model that integrates Edge-Attention-Module and the Feature Pyramid Network Module (FPN-Module). We conduct detailed statistical analysis and change rate calculation of the oceanic front, and batch process to obtain preliminary high-quality annotation data, which improves efficiency and saves time. Then, we perform manual corrections to correct missed detections or false detections to ensure the accuracy of annotations. Approximately 4800 days of daily average sea temperature fusion data from CMEMS (Copernicus Marine Environment Monitoring Service) are used for analysis, and an Encoder-Edge-FPN-Decoder Network (EEFD-Net) structure is established to enhance the model’s accuracy in detecting the edges of oceanic fronts. Experimental results demonstrate that the improved model’s front identification capability is in strong agreement with fronts segmented and annotated using the threshold method, with IoU and weighted Dice scores reaching 98.81% and 95.56%, respectively. The model can accurately locate the position of oceanic fronts, with superior detection of weak fronts compared to other network models, capturing smaller fronts more precisely and exhibiting stronger connectivity.

Schematic diagram of two typical modes in the variabilities of wintertime North Pacific basin‐scale oceanic fronts and associated atmospheric eddy‐driven jet: (a) the enhanced westerly jet mode corresponding to an enhanced STFZ and an southward shifted SAFZ, caused by the PDO‐like SST anomaly, and (b) the northward shifted westerly jet mode corresponding to an enhanced SAFZ and an northward shifted STFZ, caused by the NPGO‐like SST anomaly. Note that the climatological westerly jet is shaded. The role of oceanic fronts in the midlatitude air–sea interaction remains unclear. This study defines new indexes to quantify the intensity and location of two basin‐scale oceanic frontal zones in the wintertime North Pacific, i.e. the subtropical and subarctic frontal zones (STFZ, SAFZ). With these indexes, two typical modes, which are closely related to two large‐scale sea surface temperature (SST) anomaly patterns resembling Pacific Decadal Oscillation (PDO) and North Pacific Gyre Oscillation (NPGO), respectively, are found in the oceanic front variabilities as well as in their associations with the midlatitude atmospheric eddy‐driven jet. Corresponding to an PDO‐like SST anomaly pattern, an enhanced STFZ occurs with a southward shifted SAFZ, which is associated with enhanced overlying atmospheric front, baroclinicity and transient eddy vorticity forcing, thus with an intensification of the westerly jet; and vice versa. On the other hand, corresponding to an NPGO‐like SST pattern, an enhanced SAFZ occurs with a northward shifted STFZ, which is associated with a northward shift of the atmospheric front, baroclinicity, transient eddy vorticity forcing, and westerly jet; and vice versa. These results suggest that the basin‐scale oceanic frontal zone is a key region for the midlatitude air–sea interaction in which the atmospheric transient eddy's dynamical forcing is a key player in such an interaction.

Oceanic fronts involved by ocean currents led to strong gradients of temperature, density and salinity, which have significant effects on underwater sound propagation. This paper focuses on the impact of the oceanic front on three-dimensional underwater sound propagation. A joint experiment of ocean acoustic and physical oceanography at the western North Pacific fronts is introduced. The measurement data for sound waves passed through the oceanic front is processed. The results are analysed and compared with the numerical simulation. It was found that transmission loss presented some difference when the source was located in the front centre and sound waves propagated towards water mass on opposite sides of the front centre. And when the sound field is excited by the underwater explosion at a depth of 200 m, the effects of the horizontal refraction cannot be neglected. On the other hand, the transmission loss for sound pressure fell sharply and rose rapidly at the side of cold water masses.

At present, some shortcomings of the research on coupling modeling of the oceanic front–sound field may need attention: (1) Most of the acoustic propagation simulation is based on ideal front models, but the application of investigated marine data is lacking. (2) Most studies focus on the acoustic field characteristics, with the influence of fronts on acoustic propagation, but few studies aim at the direct quantitative analysis of the performance of underwater acoustic detection in oceanic fronts. To deal with the above problems, based on the measured data in the northwest Pacific Ocean, here, we first design different sound source layout schemes and calculate sound field characteristics in the sub-Arctic front using the ray theory. Then, the cumulative detection probability model is built based on the active sonar equation to evaluate the efficiency of underwater detection. Finally, the detection probability is calculated and expressed by regionalization, and the influence of the sub-Arctic front on underwater detection is quantitatively analyzed. The results show that the sub-Arctic front can significantly affect the underwater acoustic detection. The sound source located in the front in the cold-water mass has a better detection performance, especially detecting towards cold water (horizontal detection range > 60 km). In contrast, the sound source located in the warm-water mass has a poor detection performance (horizontal detection range in shallow sea < 10 km).

Using the Community Earth System Model framework, the authors build a very-high-resolution quasi-global coupled model by coupling an eddy-resolving quasi-global ocean model with a high-resolution atmospheric model. The model is successfully run for six years under present climate conditions, and the simulations are evaluated against observational and reanalysis data. The model is capable of simulating large-scale oceanic and atmospheric circulation patterns, sea surface temperature (SST) fronts, oceanic eddy kinetic energy, and fine-scale structures of surface winds. The ocean mesoscale structure-induced air-sea interaction characteristics are explored in detail. The model can effectively reproduce positive correlations between SST and surface wind stress induced by mesoscale structures through comparison with observations. The positive correlation is particularly significant over regions with strong oceanic fronts and eddies. However, the responses of wind stress to eddy-induced SST are weaker in the simulation than in the observations, although different magnitudes exist in different areas. Associated with weak wind responses, surface sensible heat flux responses to eddy-induced SST are underestimated slightly, while surface latent heat flux responses are overestimated because of the drier atmospheric boundary layers in the model. Both momentum mixing and pressure adjustment mechanisms play important roles in surface wind changes over oceanic fronts and eddies in the high-resolution model.

Two decades of high-resolution satellite observations and climate modeling studies have indicated strong ocean–atmosphere coupled feedback mediated by ocean mesoscale processes, including semipermanent and meandrous SST fronts, mesoscale eddies, and filaments. The air–sea exchanges in latent heat, sensible heat, momentum, and carbon dioxide associated with this so-called mesoscale air–sea interaction are robust near the major western boundary currents, Southern Ocean fronts, and equatorial and coastal upwelling zones, but they are also ubiquitous over the global oceans wherever ocean mesoscale processes are active. Current theories, informed by rapidly advancing observational and modeling capabilities, have established the importance of mesoscale and frontal-scale air–sea interaction processes for understanding large-scale ocean circulation, biogeochemistry, and weather and climate variability. However, numerous challenges remain to accurately diagnose, observe, and simulate mesoscale air–sea interaction to quantify its impacts on large-scale processes. This article provides a comprehensive review of key aspects pertinent to mesoscale air–sea interaction, synthesizes current understanding with remaining gaps and uncertainties, and provides recommendations on theoretical, observational, and modeling strategies for future air–sea interaction research.

Large-scale oceanic fronts, such as in western boundary currents, have been shown to play an important role in the dynamics of atmospheric storm tracks. Little is known about the influence of mesoscale oceanic eddies on the free troposphere, although their imprint on the atmospheric boundary layer is well documented. The present study investigates the response of the tropospheric storm track to the presence of sea surface temperature (SST) anomalies associated with an eddying ocean. Idealized experiments are carried out in a configuration of a zonally reentrant channel representing the midlatitudes. The SST field is composed of a large-scale zonally symmetric front to which are added mesoscale eddies localized close to the front. Numerical simulations show a robust signal of a poleward shift of the storm track and of the tropospheric eddy-driven jet when oceanic eddies are taken into account. This is accompanied by more intense air–sea fluxes and convective heating above oceanic eddies. Also, a mean heating of the troposphere occurs poleward of the oceanic eddying region, within the storm track. A heat budget analysis shows that it is caused by a stronger diabatic heating within storms associated with more water advected poleward. This additional heating affects the baroclinicity of the flow, which pushes the jet and the storm track poleward.