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The Indo‐Pacific warm pool (IPWP), enclosed by a 28°C isotherm, is vital in controlling atmospheric circulations affecting monsoonal flow. The warming trend of sea surface temperatures (SSTs) over the IPWP has expanded the IPWP region. This study examines the impact of the IPWP warming on the Indian summer monsoon rainfall (ISMR) patterns using ERA5 reanalysis and India Meteorological Department rainfall records based on station data from 1959 to 2021. Analyses based on correlation, regression and composite anomalies show the complex relationship between recent decades of IPWP expansion/warming and monsoon circulation. However, the effects of regional IPWP SST warming changes on the ISMR pattern remain unexplored. Here, we explore the changes in the monsoonal circulation owing to the warming and expansion of IPWP, by comparing two equal periods (1959–1989 and 1990–2021). The responses of monsoons to IPWP warming in these two periods revealed some interesting facts, but the complexity remained. Further, we examined the composite impacts of IPWP SST warming in three categories, that is, very cool, usual and extremely warm, on the dynamics of monsoon circulations. The very cool IPWP is associated with the dry monsoon, while the extremely warm IPWP produces copious rainfall over southern India and dryness over eastern north India. The study confirms the non‐linear relationship between IPWP warming and ISMR, which has been investigated in detail. [ABSTRACT FROM AUTHOR]

Over the subtropical Northeast Pacific (NEP), highly reflective low clouds interact with underlying sea surface temperature (SST) to constitute a local positive feedback. Recent modeling studies showed that, together with wind–evaporation–SST (WES) feedback, the summertime low cloud–SST feedback promotes nonlocal trade wind variations, modulating subsequent evolution of El Niño–Southern Oscillation (ENSO). This study aims to identify drivers of summertime low-cloud variations, using satellite observations and global atmosphere model simulations forced with observed SST. A transbasin teleconnection is identified, where the north tropical Atlantic (NTA) warming induced by the North Atlantic Oscillation (NAO) increases precipitation, exciting warm Rossby waves that extend into the NEP. The resultant enhancement of static stability promotes summertime low cloud–SST variability. By regressing out the effects of the preceding ENSO and NTA SST, atmospheric internal variability over the extratropical North Pacific, including the North Pacific Oscillation (NPO), is found to drive the NEP cooling by latent heat loss and subsequent summer low cloud–SST variability. With the help of the background trade winds and WES feedback, the SST anomalies extend southwestward from the low-cloud region, accompanied by ENSO in the following winter. This suggests the nonlocal effects of low clouds identified by recent studies. Analysis of a 500-yr climate model simulation corroborates the NTA and NPO forcing of NEP low cloud–SST variability and subsequent ENSO. [ABSTRACT FROM AUTHOR]

The evolution of double warm‐cores (DWC) during the secondary eyewall formation (SEF) and the subsequent eyewall replacement cycle (ERC) in Typhoon Trami (2018) was investigated in this study. Using a coupled atmosphere‐ocean model, the impacts of the typhoon‐induced sea surface cooling (SSC) on the DWC structure were also examined. In both the coupled and uncoupled simulations, the middle‐level warm‐core (MWC) decayed as the tangential wind expanded outward during the SEF, even in the absence of SSC. Under the thermal wind balance, the cooling of the MWC was an inherent result to ensure the dynamic consistency during the SEF. In contrast to the uncoupled simulation, the upper‐level warm‐core (UWC) decayed under the influence of SSC, significantly contributing to the rapid weakening of Trami. The negative effects of the SSC on the UWC were more detrimental to the intensity of Trami. Results from the potential temperature (PT) budget of improved accuracy indicated that the decrease in the warming due to the radial eddy advection was mainly responsible for the decay of the MWC. The flattened radial gradient of PT during the SEF accounted for the reduction in the dynamical eye warming associated with the asymmetric mixing. In addition to the convectively induced subsidence, the upper‐level asymmetric structures could also be affected by the SSC. Consequently, the increase in the cooling due to the enhanced asymmetry collaborated with the decrease in the adiabatic warming, leading to the decay of the UWC in the coupled simulation. Plain Language Summary: A warm‐core, characterized by higher temperature than the environment, is a typical feature at the center of typhoons. It is encircled by an eyewall where strong winds and heavy rain prevail that constitutes the most destructive region of typhoons. In intense typhoons, an outer eyewall may develop and gradually replace the original eyewall, a phenomenon commonly called the eyewall replacement cycle (ERC). In addition, a second warm‐core can also frequently form at a different altitude in intense typhoons, generally known as the double warm‐core (DWC) structure. When a double‐eyewall typhoon possesses the DWC structure, the relationship between these two unique structures still remains unknown. Using an atmosphere‐ocean coupled simulation, this study examines how the two warm‐cores evolve during the ERC of Typhoon Trami. The results show that the midlevel warm‐core naturally cools as the wind field expanded outward during the ERC. Additionally, the typhoon‐induced sea surface cooling (SSC) can weaken the upper‐level warm core, corresponding to the rapid weakening of Trami. Understanding these internal changes is crucial for better predicting typhoon's intensity and its hazards. Key Points: The decrease in the dynamic eye warming dominates the decay of the midlevel warm‐core during the eyewall replacement cycleThe typhoon‐induced sea surface cooling results in the decay of the upper‐level warm‐core, contributing to the rapid weakeningThe asymmetry within the eye region is modulated by the eyewall replacement cycle and air‐sea interaction, affecting how the warm cores evolve [ABSTRACT FROM AUTHOR]

The predictability of the El Niño‐Southern Oscillation (ENSO) is significantly limited by the spring predictability barrier (SPB). Our observational analysis suggests that considering high‐frequency wind components during the spring season may mitigate the SPB impact on ENSO predictability. The intraseasonal zonal wind in March over the equatorial western Pacific initially perturbs the sea surface temperature (SST). It contributes nearly 40% of the east‐west SST gradient after 2–3 months, ranking first among other calendar months. This significant contribution causes March to become the earliest month to effectively indicate the following ENSO direction due to the active eastward‐propagating Madden‐Julian oscillation (MJO) activity. Through the obvious variation of the eastward‐propagating MJO speed, it also shows the possible close relationship between the mean SST state and the interdecadal variability in intraseasonal zonal wind. Additionally, the current strong variability of intraseasonal zonal wind suggests the important role of atmospheric information in recent ENSO development. Plain Language Summary: The El Niño‐Southern Oscillation (ENSO) is known to have a far‐reaching impact on global climate. Our present climate models, however, remain large challenges in predicting ENSO events when the predictions made cross the boreal spring. In this study, we find that utilizing the atmospheric information in spring could weaken the challenges mentioned above. The intraseasonal zonal wind with a main period of 30–90 days over the equatorial western Pacific in March provides strong support for the ENSO developments after 2–3 months, with a contribution as high as nearly 40%, ranking first among other calendar months. This significant contribution establishes a strong connection between the ENSO peak states and the high‐frequency winds, and it causes March to become the earliest month to effectively indicate the following ENSO developments. Changes in long‐term mean sea surface temperature modulate the eastward propagation speed of convective activity, and it possibly establishes significant relationship with the intraseasonal zonal wind in March. Recently, the strong intraseasonal zonal wind has alerted us to focus on the high‐frequency winds in spring and their controlled processes, which could improve our prediction skills across the spring season. This study highlights the potential impact of intraseasonal zonal winds in March on ENSO's predictability as a critical predictor. Key Points: The intraseasonal zonal wind over the equatorial western Pacific in March has a uniquely connection with the subsequent ENSO evolutionThe background SST zonal gradient modulates the contribution of intraseasonal zonal wind through the eastward propagation of MJO activityRecent spring's high‐frequency wind components possibly enhance ENSO predictability by exciting subsequent significant oceanic response [ABSTRACT FROM AUTHOR]

High latitudes, including the Bering Sea, are experiencing unprecedented rates of change. Long-term Bering Sea warming trends have been identified, and marine heatwaves (MHWs), event-scale elevated sea surface temperature (SST) extremes, have also increased in frequency and longevity in recent years. Recent work has shown that variability in air–sea coupling plays a dominant role in driving Bering Sea upper-ocean thermal variability and that surface forcing has driven an increase in the occurrence of positive ocean temperature anomalies since 2010. In this work, we characterize the drivers of the anomalous surface air–sea heat fluxes in the Bering Sea over the period 2010–22 using ERA5 fields. We show that the surface turbulent heat flux dominates the net surface heat flux variability from September to April and is primarily a result of near-surface air temperature and specific humidity anomalies. The airmass anomalies that account for the majority of the turbulent heat flux variability are a function of wind direction, with southerly (northerly) wind advecting anomalously warm (cool), moist (dry) air over the Bering Sea, resulting in positive (negative) surface turbulent flux anomalies. During the remaining months of the year, anomalies in the surface radiative fluxes account for the majority of the net surface heat flux variability and are a result of anomalous cloud coverage, anomalous lower-tropospheric virtual temperature, and sea ice coverage variability. Our results indicate that atmospheric variability drives much of the Bering Sea upper-ocean temperature variability through the mediation of the surface heat fluxes during the analysis period. Significance Statement: A long-term ocean warming trend and a recent increase in marine heatwaves in the Bering Sea have been identified. Previous work showed that anomalies in the exchange of heat between the ocean and the atmosphere were the primary driver of Bering Sea temperature variability, but the processes responsible for the heat exchange anomalies were unknown. In this work, we show that the atmosphere is the primary driver of anomalies in the Bering Sea air–sea heat exchange and therefore plays an important role in altering the thermal state of the Bering Sea. Our results highlight the importance of understanding more about how the ocean and the atmosphere interact at high latitudes and how this relationship will be affected by future climate change. [ABSTRACT FROM AUTHOR]

Coastal upwelling, marked by cool sea surface temperatures, modulates the wind stress and heat fluxes at the air-sea interface. However, the impact of upwelling on offshore wind power has been scarcely studied. This study uses satellite sea surface temperature data and a numerical model to examine how coastal upwelling shapes the diurnal evolution of the marine boundary layer, focusing on implications for offshore wind energy. The study region is the U.S. Mid Atlantic Bight, specifically the coast of New Jersey, known for its persistent summertime upwelling events. We run numerical experiments with upwelling, and upwelling artificially removed, to assess differences in the atmospheric response. For the wind event considered, results agree with theory where a stable, upwelling-cooled atmospheric boundary layer leads to reduced air-sea drag and turbulence intensity, higher wind speeds at hub height, and greater vertical shear relative to the scenario with upwelling removed. This response is likely caused by a sea breeze superimposed on onshore background winds. Experiments with parameterized turbines show that an 18-hour power generation at a lease area close to the shore was 6.5% higher with upwelling (4.86 GWh and 4.56 GWh, respectively). While upwelling can modulate offshore wind, the nature of the modulation is strongly dependent on the boundary layer regimes, background wind direction, and synoptic or mesoscale weather patterns. [ABSTRACT FROM AUTHOR]

The Madden–Julian oscillation (MJO) is believed to play a significant role in triggering El Niño–Southern Oscillation (ENSO) events and affect the dynamics of ENSO. In this study, the dynamic forcing effects of MJO on the equatorial oceanic dynamic fields and the onsets of different types of ENSO events are investigated through sensitive experiments using spatiotemporally filtered forcing based on an anomalous shallow water model. The comparisons between observations and model responses provide meaningful insights into the extent of MJO's impacts on sea surface dynamics relative to other atmospheric variabilities. The following conclusions are made. First, the MJO-forced perturbations on zonal currents are stronger and more significant than those on sea surface heights. Second, MJO is essential for improving zonal current simulation in the western-central Pacific and generating activity centers of zonal currents in the eastern Pacific in the model. Third, MJO tends to contribute to the onset of El Niño events rather than La Niña events. Strong intraseasonal oceanic Kelvin waves forced by MJO are confirmed in simulations during the onset stages of the 1997/98 and 2004/05 events. The 120-day running standard deviations of zonal current and sea surface height anomaly series forced by MJO exhibit positive skewness similar to those of the 20–100-day band-passed observational series. Yet, not all the onsets of historical ENSO events are in company with strong MJO-related perturbations. Additionally, the wind stress formula can amplify the responses of zonal current and sea surface height anomalies to synoptic forcings with periods shorter than 20 days through entraining lower-frequency variabilities. Significance Statement: The Madden–Julian oscillation (MJO) is believed to be able to trigger El Niño–Southern Oscillation (ENSO) events and influence our understanding of the fundamental nature of ENSO. In this study, spatiotemporally filtered forcing experiments are implemented on an anomalous shallow water model. The results show that MJO is more important for improving the simulation of surface zonal currents rather than the sea surface heights and tends to contribute to the onset of El Niño events rather than La Niña events through triggering strong intraseasonal oceanic Kelvin waves. [ABSTRACT FROM AUTHOR]

The tropical Pacific convergence zone plays a crucial role in the global climate system. Previous research studies emphasized the cross-seasonal influence of the South Pacific quadrupole (SPQ) mode on the tropical Pacific climate. This study assesses the relationship between austral summer SPQ and austral winter tropical precipitation in phase 6 of the Coupled Model Intercomparison Project (CMIP6) models. The analysis emphasizes the historical experiments conducted within this time frame, spanning from 1979 to 2014. Our findings reveal that the SPQ is accurately represented in all CMIP6 models, but the connection between SPQ and precipitation is inadequately simulated in most models. To investigate the reasons behind these intermodel differences in reproducing SPQ-related processes, we categorize models into two groups. The comparisons demonstrate that the fidelity of model simulations in replicating the SPQ–tropical precipitation relationship hinges significantly on their capacity to reproduce the positive wind–evaporation–sea surface temperature (WES; SST) feedback over both the southwestern Pacific (25°–10°S; 150°E–160°W) and the southeastern Pacific (30°–10°S; 140°–80°W). This positive WES feedback propagates the SPQ signal into the tropics, intensifying the meridional gradient of SST anomaly in the tropical western-central Pacific, which consequently amplifies convection and rainfall in that area. In the group of models that failed to simulate this relationship accurately, the weakened WES feedback can be traced back to biases in wind speed and its variation. Furthermore, this WES feedback establishes a connection between SPQ and El Niño–Southern Oscillation (ENSO). A better rendition of the SPQ–tropical rainfall connection tends to result in a better simulation of the onset of SPQ-related ENSO events. As a result, this study advances our comprehension of extratropical impacts on the tropics, with the potential to enhance the accuracy of tropical climate simulation and prediction. Significance Statement: Tropical rainfall plays an important role in the global climate system. Beyond the well-known influence of El Niño–Southern Oscillation (ENSO) on the tropical rainfall, the sea surface temperature (SST) anomaly in the South Pacific has a cross-seasonal impact on the precipitation over the tropical Pacific via air–sea coupled processes. Such SST anomaly pattern shows a quadrupole structure in the extratropical South Pacific, known as the South Pacific quadrupole (SPQ) mode. However, the relationship between SPQ and tropical precipitation remains poorly simulated in most state-of-the-art climate models. One primary reason for this gap between observed and simulated relationships is the underestimation of wind speed and its variation over the south tropical Pacific in these models. This limitation undermines their ability to accurately represent the air–sea interactions that drive tropical precipitation patterns, leading to inaccuracies in simulations. Our study aims to bridge this knowledge gap by enhancing our understanding of the extratropical effects on the tropical Pacific. By exploring the mechanisms underlying the SPQ–precipitation connection, we expect to improve the simulation and prediction capabilities of tropical climate models, thereby enhancing our ability to forecast and adapt to future climatic changes. [ABSTRACT FROM AUTHOR]

Sea surface temperature anomaly (SSTA) of ocean eddies induces an anomalous air‐sea turbulent heat flux that acts to dampen SSTA. A two‐dimensional SSTA model explores the effect of air‐sea turbulent heat flux, parameterized as SSTA damping, in shaping eddy SSTA patterns. Increased SSTA damping transitions the SSTA pattern from a monopole to dipole, indicating the balance between eddy stirring of the background SST gradient and SSTA damping. The SSTA dipole pattern increases the correlation of eddy velocity and SSTA, but SSTA damping weakens the SSTA, resulting in an optimal damping rate maximizing lateral eddy surface heat transport. Globally, the SSTA damping rate increases toward the equator. In mid‐latitude and high‐latitude regions (e.g., the Kuroshio, the Gulf Stream, and the Southern Ocean), eddy SSTAs are monopoles, while the tropics and subtropics exhibit dipole SSTA patterns due to higher damping rates, facilitating greater lateral eddy heat transport when the SSTA is large. Plain Language Summary: Mesoscale ocean eddies, ranging from tens to hundreds of kilometers, exhibit distinct sea surface temperature anomaly (SSTA) patterns. In regions like the Kuroshio, the Gulf Stream, and the Southern Ocean, eddy SSTA exhibits a monopole pattern, with a single warm or cold core within the eddy. At lower latitudes, a dipole‐like pattern emerges, characterized by a pair of opposite‐sign SSTA surrounding the eddy. Previous studies attribute these SSTA patterns to the lateral stirring of background SST gradients by eddies. We develop a simplified SSTA model to highlight the role of eddy‐induced air‐sea turbulent heat flux in shaping eddy SSTA patterns. Eddy stirring of the background SST gradient generates SSTA, which induces anomalous sensible and latent heat flux that dampens SSTA. In the tropics and subtropics, effective SSTA damping balances the positive and negative SSTA generated by eddy stirring, resulting in a dipole‐like pattern. Conversely, at high latitudes, where SSTA damping is weaker, SSTA maintains its signature, yielding a monopole pattern. The transition from a monopole to a dipole pattern is facilitated by air‐sea heat flux, enhancing the correlation of eddy SSTA and velocity, while reducing SSTA variance, leading to an optimal damping rate that maximizes eddy heat transport. Key Points: Ocean eddies generate a dipole sea surface temperature anomaly (SSTA) pattern when air‐sea turbulent heat flux dampens SSTA counteracting eddy stirring of the background SSTThe dipole pattern enhances lateral eddy heat transport due to increased correlation between the eddies' horizontal velocity and SSTAThe SSTA damping rate due to air‐sea heat flux decreases toward the poles, maximizing lateral eddy heat transport in the subtropics [ABSTRACT FROM AUTHOR]

This study reveals a remarkable interdecadal intensification in the interannual variability of summer synoptic-scale disturbances (SSDs) over the western North Pacific (WNP) since the late 1980s. This intensification can be explained by the remarkable difference in circulation anomalies associated with the SSD intensity variability during 1959–1987 (P1) and 1988–2022 (P2). That is, the lower-tropospheric cyclonic circulation anomalies are more significant during P2 than P1. Accordingly, the meridional shear of zonal winds over the WNP is significantly stronger in P2, and thus favors the enhancement of SSD intensity through the kinetic energy conversion from the mean flow to SSDs. Further analysis suggests that the SSD intensity variation is significantly related to the sea surface temperature (SST) anomalies in the equatorial central Pacific and maritime continent in P2, which can induce the cyclonic or anticyclonic circulation anomalies over the WNP, but the SST anomalies are vague in P1. Finally, the more pronounced influence of tropical SST anomalies on circulations and SSDs over the WNP is attributed to the much warmer SSTs over the maritime continent in P2, which intensifies the responses of atmospheric circulations to SST anomalies. [ABSTRACT FROM AUTHOR]

We study two sea surface temperature (SST) warming events and upper ocean stratification changes in the northern South China Sea in 2022 using data from an EM‐APEX float and satellite observations. The diurnal warm layers (DWLs) and the increasing buoyancy frequency N2 above the top of the thermocline can restrict the penetration depth of nighttime convection and wind‐driven mixing, which prevents cooler water from mixing upward, allowing solar heating to increase the SST by more than 1°C in a few days. The stratification budget approach is used to reproduce observations below 40 m despite some uncertainties in estimating variables such as horizontal gradient. After the first SST warming event, the stratification changes in the subsurface layers constituted by an increase in N2 above 70 m and a decrease below this depth can be attributed to the combined effects of turbulent diffusion and vertical advection rather than to horizontal advection or penetrative solar radiation. This ocean interior mixing is likely caused by the shear of near‐inertial waves at ∼50 m, when the nighttime convection could not penetrate through the DWL's base around 20 m. The stratification budget approach fails to simulate the changes above 40 m after the second SST warming event partly due to the presence of a near‐surface freshwater layer. Our observations offer insights into the effect of inertial wave‐induced mixing in the ocean interior when near‐surface stratified layers are present, which can lead to changes in upper ocean stratification and SST. Plain Language Summary: The formation of near‐surface stratified layers, such as a diurnal warm layer (DWL), can restrict the penetration depth of the turbulent mixing caused by atmospheric forcing and prevent cooler subsurface water from mixing upward; as a result, the sea surface temperature (SST) remains warm. Strong shear from oceanic dynamics, such as inertial waves, can induce mixing in the ocean interior. Our observations show that when the nighttime convection cannot penetrate through the base of a DWL under low wind conditions, inertial wave‐induced mixing may influence the stratification near the top of the thermocline. The resulting restratification within the ocean surface boundary layer can then counteract the destratification forces from wind and nighttime convection. Solar heating can thus rapidly increase the SST by more than 1°C within a few days. Studying the effects of the DWL and inertial wave shear could improve climate and weather model forecasts in the future. Key Points: The presence of diurnal warm layers and stratification changes near the top of the thermocline can suppress nighttime convectionStrong shear of inertial waves enhances the vertical turbulent diffusion in the thermoclineThe increase of stratification in the ocean surface boundary layer warms the sea surface temperature by 1° within 5 days [ABSTRACT FROM AUTHOR]

Abstract Energetic cyclonic mesoscale eddies, which are called cold-core rings and are shed southward from the Kuroshio Extension jet and form closed streamlines, affect the atmosphere through the heat exchange across the sea surface. To investigate the effect of rings on the atmosphere, we performed atmosphere and ocean observations across a cold-core ring centered around 34.5° N, 150.0° E using a research vessel from November 2021 to January 2022 and a shallow-water profiling float from November 23 to 28, 2021. As heat is released from the sea surface, no significant spatial contrast in the sea surface and mixed layer temperatures was detected across the ring. Meanwhile, the sea surface wind was occasionally observed to be weak around the ring, possibly through the air–sea interactions. The wind drop-off maintained a turbulent heat flux small around the ring. The wind field associated with the wind drop-off was examined by the rotary empirical orthogonal function analysis of the satellite sea surface wind data. The minimum of the sea surface wind is found to shift northward relative to the ring center and to be more than approximately 5 m s $$^{-1}$$ - 1 lower than the surrounding region. The shallow-water profiling float deployed around the ring center observed a rapid freshening event in the mixed layer, which can be attributed to the water intrusion from the north of the Kuroshio Extension jet through the interaction with the jet. This suggests that the cold water from the north continually affects the atmosphere without leaving traces in the shipboard sea surface temperature observations.

The faster warming for Arctic Ocean surface air temperature (SAT) relative to that at lower latitude is connected with various processes, including local radiation feedback, poleward oceanic and atmospheric heat transport. It is unclear how combinations of different low‐frequency internal climate modes influence Arctic amplification on the decadal timescale. Here, the decadal Arctic SAT variation, its connection with the Atlantic meridional overturning circulation (AMOC) and possible underlying mechanisms, are investigated based on several independent observational proxies, pre‐industrial experiments, and historical large ensembles of two CMIP6 models. Our study suggests that AMOC and Arctic SAT vary in phase on the decadal timescale, whereas this relationship is insignificant at the interannual timescale. Further analysis shows that the AMOC accompanied with cross‐basin oceanic water/heat transport between Atlantic and Arctic would alter air–sea interface exchange over the melting ice regions, and then amplified poleward atmospheric heat and moisture transports. The resulting enhanced downward longwave radiation ultimately warms the Arctic SAT. Additionally, the decadal‐scale North Pacific Oscillation (NPO) can modulate the relationship between AMOC and Arctic SAT by influencing poleward moisture transport and cross‐basin circulation. Specifically, the phase shift of combined NPO and AMOC can contribute 14%–41% covariance relationship between AMOC and Arctic SAT. Our study provides potential sources for predicting the Arctic climate and constraining its uncertainty in future projections. Plain Language Summary: The Arctic has warmed faster than lower latitudes and is capable of influencing weather and climate. Previous studies suggest that Atlantic meridional overturning circulation (AMOC) can induce warming over the Arctic region, however, the underlying mechanism for AMOC influencing Arctic SAT and whether their relationship is stable are still unclear. In this study, we have identified the relationship between the AMOC and Arctic SAT during 1950–2014 on the decadal scale. Our results demonstrate that AMOC changes in phase with the Arctic SAT, which is dominated by surface downward longwave radiation resulting from poleward moisture and heat transport, and air‐ice‐sea interaction associated with AMOC. Additionally, the North Pacific Oscillation (NPO) can modulate the correlation between AMOC and Arctic SAT by influencing the meridional eddy advection of water vapor and cross‐basin processes. Specifically, the phase shift of combined NPO and AMOC can contribute 14%–41% covariance relationship between AMOC and Arctic SAT. Key Points: The Atlantic meridional overturning circulation (AMOC) change in phase with the Arctic surface air temperature (SAT) during 1950–2014 on a decadal timescale in multiple observationsDecadal Arctic SAT change associated with AMOC is dominated by surface downward longwave radiation, evaporation and poleward moisture transportThe North Pacific Oscillation accompanied with the cross‐basin processes modulates the relationship between AMOC and Arctic SAT [ABSTRACT FROM AUTHOR]

Bubble plumes play a significant role in the air–sea interface by influencing processes such as air–sea gas exchange, aerosol production, modulation of oceanic carbon and nutrient cycles, and the vertical structure of the upper ocean. Using acoustic Doppler current profiler (ADCP) data collected off the west coast of Ireland, we investigate the dynamics of bubble plumes and their relationship with sea state variables. In particular, we describe the patterns of bubble plume vertical extension, duration, and periodicity. We establish a power-law relationship between the average bubble penetration depth and wind speed, consistent with previous findings. Additionally, the study reveals a significant association between whitecapping coverage and observed acoustic volume backscatter intensity, underscoring the role of wave breaking in bubble plume generation. The shape of the probability distribution of bubble plume depths reveals a transition toward stronger and more organized bubble entrainment events during higher wind speeds. Furthermore, we show that deeper bubble plumes are associated with turbulent Langmuir number Lat ∼ 0.3, highlighting the potential role of Langmuir circulation on the transport and deepening of bubble plumes. These results contribute to a better understanding of the complex interactions between ocean waves, wind, and bubble plumes, providing valuable insights for improving predictive models and enhancing our understanding of air–sea interactions. Significance Statement: This research contributes to understanding bubble plume dynamics in the upper ocean and their relationship with sea state variables. The establishment of a power-law relationship between the bubble penetration depth and wind speed, along with the association between whitecapping coverage and acoustic backscatter intensity, contributes to improved predictive capabilities for air–sea interactions and carbon dioxide exchange. The identification of the potential influence of Langmuir circulation on bubble plume dynamics expands our understanding of the role of coherent circulations in transporting bubble plumes. Additionally, this study presents a clear methodology using commercial sensors such as an ADCP, which can be easily replicated by researchers worldwide, leading to potential advancements in our comprehension of bubble plume dynamics. [ABSTRACT FROM AUTHOR]

While decadal changes in Madden–Julian oscillation (MJO) have received considerable attention, the corresponding changes in Boreal Summer Intraseasonal Oscillation (BSISO) have yet to be well understood. In this study, we show the enhanced northward propagation of BSISO in the Western North Pacific (WNP) during the 2000s compared to the 1980s–1990s. Observational analyses and model experiments suggest this enhancement is partially attributed to the tropical Indian Ocean (TIO) warming. The TIO warming tends to increase the air-sea interaction, enhancing moisture anomalies in the free atmosphere. Consequently, this increase in moisture anomalies strengthens BSISO-scale convection through increased convective anomalies at the north of the BSISO center, thereby enhancing the northward propagation of BSISO. Additionally, vorticity changes resulting from mean-state zonal vertical shear also contribute to the BSISO decadal change. Our findings underscore the importance of considering the interaction between BSISO and changes in the ocean mean state in future assessments. [ABSTRACT FROM AUTHOR]

Numerical prediction of the interactions between wind and ocean waves is essential for climate modeling and a wide range of offshore operations. Large Eddy Simulation (LES) of the marine atmospheric boundary layer is a practical numerical predictive tool but requires parameterization of surface fluxes at the air–water interface. Current momentum flux parameterizations primarily use wave-phase adapting computational grids, incurring high computational costs, or use an equilibrium model based on Monin–Obukhov similarity theory for rough surfaces that cannot resolve wave phase information. To include wave phase-resolving physics at a cost similar to the equilibrium model, the MOving Surface Drag (MOSD) model is introduced. It assumes ideal airflow over locally piece-wise planar representations of moving water wave surfaces. Horizontally unresolved interactions are still modeled using the equilibrium model. Validation against experimental and numerical datasets with known monochromatic waves demonstrates the robustness and accuracy of the model in representing wave-induced impacts on mean velocity and Reynolds stress profiles. The model is formulated to be applicable to a broad range of wave fields and its ability to represent cross-swell and multiple wavelength cases is illustrated. Additionally, the model is applied to LES of a laboratory-scale fixed-bottom offshore wind turbine model, and the results are compared with wind tunnel experimental data. The LES with the MOSD model shows good agreement in wind–wave–wake interactions and phase-dependent physics at a low computational cost. The model's simplicity and minimal computational needs make it valuable for studying turbulent atmospheric-scale flows over the sea, particularly in offshore wind energy research. [ABSTRACT FROM AUTHOR]

Precipitation in eastern China exhibits large interannual variability during July with the northward movement of the monsoon rain belt. Thus, eastern China usually experiences severe droughts and floods in July. However, the influences of underlying surface thermal drivers, particularly the land factors, remain poorly understood. This study investigates the leading modes of July precipitation in eastern China and their potential influencing factors. The first and second empirical orthogonal function (EOF) modes show meridional dipole and tripolar precipitation anomalies in eastern China, respectively. The EOF1 mode is found to be closely associated with sea surface temperature (SST) anomalies in the tropical Pacific and North Atlantic Oceans in June, while the EOF2 mode is mainly linked to anomalous Indian Ocean SST and Indochina Peninsula soil moisture in June. During years with a strong El Niño–South Oscillation (ENSO) signal, the EOF1 mode is mainly related to the enhanced Walker and Hadley circulations associated with the cold tropical Pacific SST anomalies. In contrast, during years with a weak ENSO signal, the Eurasian midlatitude wave train and the westward zonal overturning circulation associated with tripole-like North Atlantic SST anomalies play a leading role. The EOF2 mode is mainly influenced by Indian Ocean SST anomalies that alter the Walker circulation and by soil moisture anomalies in the Indochina Peninsula that induce an anomalous regional cyclonic circulation. Numerical experiments further demonstrated that the combined effects of soil moisture and SST exert a more substantial impact than their individual effects. These results emphasize the importance of surface thermal factors in understanding regional climate dynamics. [ABSTRACT FROM AUTHOR]

As a key dynamic element of the Bjerknes feedback mechanism, the thermocline effect (TE) is critically important to El Niño modeling. In this study, the potential influence of TE‐related parametric uncertainties on El Niño is investigated using the conditional nonlinear optimal parametric perturbation (CNOP) method based on an intermediate coupled model (ICM). The optimal perturbation of the TE‐related parameter (OTEP), which substantially affects El Niño simulations, is estimated through the CNOP approach. Results reveal that the El Niño simulation is highly sensitive to the TE uncertainty in the eastern equatorial Pacific, with OTEP‐induced simulation errors demonstrating an El Niño‐like growth trend. On one hand, as indicated by the simulated El Niño intensity, the uncertainty in the TE in the eastern region can easily affect the strength of the Bjerknes feedback‐related thermocline effect and atmospheric circulation. On the other hand, the enhanced TE is highly favored to accelerate the growth of the SST error due to the air–sea interaction, thus severely affecting the El Niño simulations. Therefore, adequately representing the TE in the equatorial eastern Pacific is emphasized for effectively improving El Niño simulations. Plain Language Summary: Thermocline effect (TE) uncertainty seriously challenges numerous climate models. Focusing on the TE‐related parameter in an intermediate coupled model, this study quantitatively examines the impact of the TE on El Niño simulations. The spatial structure of the TE‐related parameters that cause the largest simulation errors is determined by employing an optimization algorithm (conditional nonlinear optimal parametric perturbation). Subsequently, a systematic analysis of the error scenarios resulting from these optimal TE‐related parameters is conducted with their underlying mechanisms being explored. Results indicate that the uncertainties in the TE in the eastern tropical Pacific tend to alter the intensity of the positive Bjerknes feedback, leading to considerable errors in El Niño simulations. Furthermore, these simulation errors are intensified by air–sea interactions. This study provides vital theoretical insights for augmenting the precision of ENSO predictions. Key Points: El Niño simulation is sensitive to the model uncertainty in the thermocline effect (TE) in the eastern equatorial PacificThe TE uncertainty‐related effects on vertical advection and Kelvin wave act to amplify El Niño warming, thus causing large simulation errorsThe simulation error in El Niño due to TE uncertainty is further increased by air–sea interaction (more than 30%) [ABSTRACT FROM AUTHOR]

Coupling a three-dimensional ocean circulation model to an atmospheric model can significantly improve forecasting of tropical cyclones (TCs). This is particularly true of forecasts for TC intensity (maximum sustained surface wind and minimum central pressure), but also for structure (e.g., surface wind-field sizes). This study seeks to explore the physical mechanisms by which a dynamic ocean influences TC evolution, using an operational TC model. The authors evaluated impacts of ocean-coupling on TC intensity and structure forecasts from NOAA's Hurricane Analysis and Forecast System v1.0 B (HFSB), which became operational at the NOAA National Weather Service in 2023. The study compared existing HFSB coupled simulations with simulations using an identical model configuration in which the dynamic ocean coupling was replaced by a simple diurnally varying sea surface temperature model. The authors analyzed TCs of interest from the 2020-2022 Atlantic hurricane seasons, selecting forecast cycles with small coupled track-forecast errors for detailed analysis. The results show the link between the dynamic, coupled ocean response to TCs and coincident TC structural changes directly related to changing intensity and surface wind-field size. These results show the importance of coupling in forecasting slower-moving TCs and those with larger surface wind fields. However, there are unexpected instances where coupling impacts the nearTC atmospheric environment (e.g., mid-level moisture intrusion), ultimately affecting intensity forecasts. These results suggest that, even for more rapidly moving and smaller TCs, the influence of the ocean response to the wind field in the near-TC atmospheric environment is important for TC forecasting. The authors also examined cases where coupling degrades forecast performance. Statistical comparisons of coupled versus uncoupled HFSB further show an interesting tendency: high biases in peak surface winds for the uncoupled forecasts contrast with corresponding low biases, contrary to expectations, in coupled forecasts; the coupled forecasts also show a significant negative bias in the radii of 34 kt winds relative to National Hurricane Center best track estimates. By contrast, coupled forecasts show very small bias in minimum central pressure compared with a strong negative bias in uncoupled. Possible explanations for these discrepancies are discussed. The ultimate goal of this work will be to enable better evaluation and forecast improvement of TC models in future work. [ABSTRACT FROM AUTHOR]

Using in situ observations collected by a drifting air-sea interface buoy (DrIB) in the northern South China Sea from August 30 to September 13, 2018, the extreme air-sea turbulent fluxes that occurred from September 8 to 13 during tropical cyclone (TC) Barijat were investigated. The most striking features were substantial increases in momentum and heat fluxes, with maximum increases of 10.8 m s-1 in the wind speed (WS), 0.73 N m-2 in the wind stress, 68.1 W m-2 in the sensible heat fluxes (SH) and 258.8 W m-2 in the latent heat fluxes (LH). The maximum WS, wind stress, SH and LH values amounted to 15.3 m s-1, 0.8 N m-2, 70.9 W m-2 and 329.9 W m-2, respectively. Using these new DrIB observations, the performance of two state-of-the-art, high-resolution reanalysis products, ERA5 and MERRA2, was assessed. The consistency of the observed values with ERA5 was slightly better than with MERRA2, reflected in higher correlations but both products underestimated the WS during TC conditions. In calm weather conditions, the turbulent heat fluxes were overestimated, because they simulated a too dry and cold atmospheric state, enhancing the air-sea differences in temperature and humidity. Considering that an accurate representation of the air-sea turbulent and momentum fluxes is essential for understanding and predicting ocean and atmospheric variability, our findings indicate that more high-quality temperature and relative humidity observations are required to evaluate and improve existing reanalysis products. [ABSTRACT FROM AUTHOR]

Energetic cyclonic mesoscale eddies, which are called cold-core rings and are shed southward from the Kuroshio Extension jet and form closed streamlines, affect the atmosphere through the heat exchange across the sea surface. To investigate the effect of rings on the atmosphere, we performed atmosphere and ocean observations across a cold-core ring centered around 34.5° N, 150.0° E using a research vessel from November 2021 to January 2022 and a shallow-water profiling float from November 23 to 28, 2021. As heat is released from the sea surface, no significant spatial contrast in the sea surface and mixed layer temperatures was detected across the ring. Meanwhile, the sea surface wind was occasionally observed to be weak around the ring, possibly through the air–sea interactions. The wind drop-off maintained a turbulent heat flux small around the ring. The wind field associated with the wind drop-off was examined by the rotary empirical orthogonal function analysis of the satellite sea surface wind data. The minimum of the sea surface wind is found to shift northward relative to the ring center and to be more than approximately 5 m s - 1 lower than the surrounding region. The shallow-water profiling float deployed around the ring center observed a rapid freshening event in the mixed layer, which can be attributed to the water intrusion from the north of the Kuroshio Extension jet through the interaction with the jet. This suggests that the cold water from the north continually affects the atmosphere without leaving traces in the shipboard sea surface temperature observations. [ABSTRACT FROM AUTHOR]

Enhanced warm pool eastward extension (WPEE) over the western‐central Pacific prior to the onset of El Niño has been observed following Madden‐Julian Oscillation (MJO) precipitation events. However, the mechanism driving the WPEE after the MJO precipitation remains unclear. This study investigates how MJO precipitation affects WPEE by analyzing the zonal momentum budget of two coupled atmosphere‐ocean model simulations with and without freshwater from Kerns and Chen (2021, https://doi.org/10.1016/j.ocemod.2021.101892). It is found that the zonal pressure gradient (ZPG) force created by decreasing salinity and density from MJO precipitation is a key driving force of the WPEE during the onset of El Niño in 2018. The ZPG forces eastward density currents, transporting warmer and fresher waters against persistent easterly winds. Eastward density currents can persist for up to 30 days post‐MJO precipitation. This new mechanism works in concert with two other well‐known MJO‐induced processes in the upper ocean: (a) deepening of thermocline by oceanic Kelvin waves excited by the MJO's westerly winds, and (b) increased SST due to the barrier layer formation. The cumulative effects of these interactive processes during consecutive MJO events reduce the Pacific basin‐scale east‐west temperature gradient, enhancing the WPEE. These processes can contribute to flattening the east‐west thermocline, decreasing in upwelling in the central Pacific, and warming in the eastern equatorial Pacific. Plain Language Summary: It is well known that the Madden‐Julian Oscillation (MJO) and El Niño‐Southern Oscillation (ENSO) affect global high‐impact weather and climate extreme events. In this study, we found that the MJO contributes to the start of El Niño by increasing sea surface temperature in the western Pacific and moving its warm water eastward in favor of developing El Niño. We use a high‐resolution coupled atmosphere‐ocean model representing the MJO precipitation realistically and its effects on the upper ocean. We show that rainfall from the MJO injects a large amount of freshwater into the ocean. It helps maintain surface warm water by forming a barrier layer that prevents the upwelling of cooler water from the deeper ocean. Furthermore, the warmer surface water propagates eastward for weeks after the MJO rainfall. This happens because freshwater increases the zonal density gradient and pressure difference, which forces eastward surface currents to carry warm water farther east than the MJO. Key Points: Madden‐Julian Oscillation (MJO) precipitation and freshwater forcing induce ocean density currents that persist for weeks after the MJO rainfallOcean density currents are mainly driven by zonal pressure gradients due to decreased salinity and increased east‐west density differencesThe long‐lasting eastward density currents contribute to the warm pool eastward extension prior to the onset of El Niño [ABSTRACT FROM AUTHOR]

Typhoons, fueled by warm sea surface waters, heighten concern as they increasingly interact with frequent Marine Heatwaves (MHWs) in a changing climate. Typhoon Hinnamnor (2022) weakened and re‐intensified as it approached the Korean Strait, interacting with an underlying MHW in the northern East China Sea (nECS). In‐situ observations and reanalysis products revealed a significant increase in latent heat loss from the nECS during the MHW period, contributing to the typhoon re‐intensification. Strong sea surface wind forcing with the typhoon enhanced vertical mixing and upwelling, resulting in a pronounced (0.90°C) sea surface cooling after the typhoon passage, facilitating MHW disappearance with reduced thermal stratification. During MHWs, increased background stratification increases temperature oscillations associated with semidiurnal internal tides. Furthermore, post‐typhoon changes in stratification weakened semidiurnal internal tides due to unfavorable conditions for generation from a nearby source. These findings highlight the importance of continuous time‐series observations to monitor interactions among climatic extremes. Plain Language Summary: Typhoons, powered by warm ocean waters, are causing more concern as they increasingly interact with frequent episodes of extremely warm sea conditions known as Marine Heatwaves (MHWs) in a changing climate. This study focuses on Typhoon Hinnamnor in 2022, which went through a weakening and then strengthened as it moved to the Korean Strait and encountered an MHW in the northern East China Sea (nECS). By using in‐situ data collected in the nECS and additional data analysis, we discovered a significant increase in heat loss from the nECS during the MHW, contributing to the intensification of typhoon. The powerful winds from the typhoon caused enhanced mixing and cooling of the sea surface after it passed, helping to cause the disappearance of the MHW and reduce the layering of temperatures in the ocean. During MHW, strong layering strengthens the temperature oscillation linked with the semidiurnal internal tides in the ocean. After typhoon passage there is a decrease in the layering in the ocean, thus weakening the internal tide. The study emphasizes the importance of continuous observations to understand and monitor these interactions in our changing climate. Key Points: Typhoon Hinnamnor (2022) re‐intensified after interacting with the underlying Marine Heatwave (MHW) in the East China SeaTyphoon wind‐driven mixing caused the disappearance of the underlying MHWStratification change accompanied by MHW, and typhoon reduced the local activities of semidiurnal internal tides [ABSTRACT FROM AUTHOR]

The North Atlantic Oscillation (NAO) and North Atlantic tripole sea surface temperature (SST_tri) are important modes in the atmosphere and ocean over the North Atlantic, respectively. The link between the two is well‐known. However, this link weakened during 1980–2001, which is particularly pronounced in late winter and was not detected in early winter. This phenomenon has not been well revealed. The role of NAO in the above correlation changes was discussed. In late winter, a significant eastward shift (up to 20° longitude) of NAO south center during 1980–2001 was observed in both observation and CMIP6, accompanied by the eastward expansion of NAO north center. Spatial shift of the NAO forced the region of strong air‐sea interactions to shift and resulting in the collapse of NAO‐related SST_tri. These findings deepen our understanding of the NAO on the subseasonal scale. Plain Language Summary: A significant correlation between the North Atlantic Oscillation (NAO) and the North Atlantic tripole sea surface temperature (SST_tri) is widely recognized. However, this study found that the correlation between the two was significantly weakened in late winter during 1980–2001 while no such change was detected in early winter. Therefore, this paper will focus on the late winter and discuss the role of NAO spatial structure in the above correlation changes. When the NAO south center is located over the North Atlantic, both observations and the climate models indicate that the corresponding North Atlantic SST shows a significant tripole pattern. However, during 1980–2001, the NAO south center shift significantly eastward from the North Atlantic toward Western Europe (up to 20° longitude). At the same time, the NAO north center expanded eastward significantly. The eastward shift of the NAO results in the significant eastward shift of the turbulent heat flux and wind stress anomalies. Shift in the region of strong air‐sea interaction led to the collapse of NAO‐related SST_tri. These findings deepen our understanding of the NAO on the subseasonal scale and also provide implications for subseasonal‐seasonal predictions of Eurasian climate extremes. Key Points: The link between NAO and North Atlantic tripole SST weakened obviously during 1980–2001 late winter, which was not detected in early winterThe eastward shift of ∼20° longitude in NAO south center forced the strong air‐sea interactions region to shift in observations and CMIP6NAO's spatial shift in late winter caused the changes in the link between NAO and North Atlantic tripole SST [ABSTRACT FROM AUTHOR]

Despite global warming, the sea surface temperature (SST) in the subpolar North Atlantic has decreased since the 1900s. This local cooling, known as the North Atlantic cold blob, signifies a unique role of the subpolar North Atlantic in uptaking heat and hence impacts downstream weather and climate. However, a lack of observational records and their constraints on climate models leave the North Atlantic cold blob formation mechanism inconclusive. Using simulations from phase 6 of Coupled Model Intercomparison Project, we assess the primary processes driving the North Atlantic cold blob within individual models and whether the mechanisms are consistent across models. We show that 11 out of 32 models, which we call "Cold Blob" models, simulate the subpolar North Atlantic cooling over 1900–2014. Further analyzing the heat budget of the subpolar North Atlantic SST shows that models have distinct mechanisms of cold blob formation. While 4 of the 11 Cold Blob models indicate decreased oceanic heat transport convergence (OHTC) as the key mechanism, another four models suggest changes in radiative processes making predominant contributions. The contribution of OHTC and radiative processes is comparable in the remaining three models. Such a model disagreement on the mechanism of cold blob formation may be associated with simulated base-state Atlantic meridional overturning circulation (AMOC) strength, which explains 39% of the intermodel spread in the contribution of OHTC to the simulated cold blob. Models with a stronger base-state AMOC suggest a greater role of OHTC, whereas those with a weaker base-state AMOC indicate that radiative processes are more responsible. This model discrepancy suggests that the cold blob formation mechanism diagnosed from single model should be interpreted with caution. Significance Statement: The mechanisms driving sea surface temperatures over the subpolar North Atlantic to cool since the 1900s remain uncertain due to the lack of direct observations. Here, we use a temperature change decomposition framework to dissect the historical trend of surface temperature simulated in multiple global climate models. The models diverge on whether the subpolar North Atlantic cooling is induced by reduced ocean heat transport convergence or altered radiative processes. Notably, the importance of ocean heat transport convergence is influenced by the simulated base-state strength of Atlantic meridional overturning circulation and the Irminger Sea's mixed layer depth. This finding cautions against concluding the cooling mechanism from a single model and highlights a need for ongoing observations to constrain AMOC-related climate projection in the subpolar North Atlantic. [ABSTRACT FROM AUTHOR]

Knowledge of spring warm pool in the Bay of Bengal (BoBWP) is key for further understanding the climate variability in this region and beyond, but little is known about the BoBWP climatological state and the related mechanisms. In this study, we investigate the spatial structure and evolution of the BoBWP using daily Optimum Interpolation SST data from 1982-2022 in combination with multi-source data. Our analysis shows that the BoBWP is located in the central bay (6°-13°N) with a thickness around 20m~ 40 m. Composite analysis indicates that the BoBWP emerges in early April, peaks in early May and dissipates in early June. During the developing period, the net heat flux dominates the formation of spring warm pool through significant air-sea coupling processes, and induces the warming rate of 0.27°C/10d in the mixed layer, which is far larger than the contribution of oceanic dynamical processes (0.01°C/10d). During the decaying period, the net heat flux also plays a dominant role, with a cooling rate of -0.21°C/10d, meanwhile ocean dynamical processes contribute to the cooling of the warm pool with a rate of -0.01°C/10d. Additionally, the SST and the area of the BoBWP are significantly correlated with ENSO (r=0.66 and 0.73, p=0.05). During El Niño decaying year, the BoBWP primarily expands in a southward direction, with a 75% increase in area. Conversely, during La Niña decaying year, the BoBWP almost disappears, with a 52% decrease. [ABSTRACT FROM AUTHOR]

Knowledge of the directional distribution of a wave field is crucial for a better understanding of complex air–sea interactions. However, the dynamic and unpredictable nature of ocean waves, combined with the limitations of existing measurement technologies and analysis techniques, makes it difficult to obtain precise directional information, leading to a poor understanding of this important quantity. This study investigates the potential use of a wavelet-based method applied to GPS buoy observations as an alternative approach to the conventional methods for estimating the directional distribution of ocean waves. The results indicate that the wavelet-based estimations are consistently good when compared to the framework of widely used parameterizations for the directional distribution. The wavelet-based method presents advantages in comparison with the conventional methods, including being purely data-driven and not requiring any assumptions about the shape of the distribution. In addition, it was found that the wave directional distribution is narrower at the spectral peak and broadens asymmetrically at higher and lower scales, particularly sharply for frequencies below the peak. The directional spreading appears to be independent of the wave age across the entire range of frequencies, implying that the angular width of the directional spectrum is primarily controlled by nonlinear wave–wave interactions rather than by wind forcing. These results support the use of the wavelet-based method as a practical alternative for the estimation of the wave directional distribution. In addition, this study highlights the need for continued innovation in the field of ocean wave measuring technologies and analysis techniques to improve our understanding of air–sea interactions. Significance Statement: This study presents a wavelet-based technique for obtaining the directional distribution of ocean waves applied to GPS buoy. This method serves as an alternative to conventional methods and is relatively easy to implement, making it a practical option for researchers and engineers. The study was conducted in a highly energetic environment characterized by high wind speeds and large waves, providing a valuable dataset for understanding the dynamics of marine environment in extreme conditions. This research has implications for improving our understanding of directional characteristics of ocean waves, which is crucial for navigation, offshore engineering, weather forecasting, and coastal hazard mitigation. This study also highlights the challenges associated with understanding wave directionality and emphasizes a need for further observations. [ABSTRACT FROM AUTHOR]

This work serves as an observation‐based exploration into the role of wave‐driven turbulence at the air‐sea interface by measuring Turbulent Kinetic Energy (TKE) dissipation rates above and below the sea surface. Subsurface ocean measurements confirm a TKE dissipation rate enhancement relative to the predicted law‐of‐the‐wall (εobs > εp), which appears to be fully supported by wave breaking highlighting the role of the transport terms in balancing the subsurface TKE budget. Simultaneous measurements of TKE dissipation rates on the atmospheric side capture a deficit relative to the law‐of‐the‐wall (εobs < εp). This deficit is explained in terms of wave‐induced perturbations, with observed convergence to the law‐of‐the‐wall at 14 m above mean sea level. The deficit on the atmospheric side provides an estimate of the energy flux divergence in the wave boundary layer. An exponential function is used to integrate in the vertical and provide novel estimates of the amount of energy going into the wave field. These estimates correlate well with classic spectral input parameterizations and can be used to derive an effective wave‐scale, capturing wind‐wave coupling purely from atmospheric observations intimately tied to wave‐induced perturbations of the air‐flow. These atmospheric and oceanic observations corroborate the commonly assumed input‐dissipation balance for waves at wind speeds in the 8‐14 ms−1 range in the presence of developed to young seas. At wind speeds above 14 ms−1 under young seas (U10cp>1.2 $\sfrac{{U}_{10}}{{c}_{p}} > 1.2$)observations suggest a deviation from the TKE input‐dissipation balance in the wave field. Plain Language Summary: A long‐term field campaign on the Western North Atlantic shelf provided observations of Turbulent Kinetic Energy (TKE) dissipation rates on both sides of the sea surface. These observations were used to track the energy exchange between the atmosphere and ocean that is mediated by surface waves. Deviations from the expected law‐of‐the‐wall scaling in our TKE dissipation rate estimates were linked to wind energy input leading to wave growth, wave breaking and the subsequent TKE injection into the water column. Observations confirm the subsurface enhancement of TKE relative to the classic law‐of‐the‐wall and showcase a TKE deficit on the atmospheric side. Atmospheric and oceanic TKE dissipation rates converge to the expected law‐of‐the‐wall profiles away from the surface but clearly show the importance of waves in atmosphere‐ocean interaction closer to the sea surface. Deviations from the law‐of‐the‐wall are presented as signature of wave‐induced turbulence close to the ocean surface. Key Points: Turbulent Kinetic Energy (TKE) dissipation rates across the interface show a deficit and enhancement supported by the wave fieldA depth integrated subsurface TKE budget highlights the relevance of the transport terms and their connection to wave breakingThe atmospheric TKE dissipation rate deficit can be explained in terms of wave‐induced perturbations mediating energy input to the waves [ABSTRACT FROM AUTHOR]

We perform quadrupled CO2 climate simulations with the Community Earth System Model version 1 (CESM1) to study how air-sea coupling affects the response of tropical rainfall under global warming. We use a hierarchy of ocean models to separate the effects of seasonal mixed-layer entrainment, wind-driven Ekman flows directed perpendicular to the wind, and the near-equator frictional flows directed in the same direction as the wind. We show that the Pacific Ocean's enhanced equatorial warming pattern (EEW) and equatorward ITCZ contraction observed in previous climate simulations emerge when the ocean model includes wind-driven Ekman and frictional flows. Furthermore, the near-equator frictional flow contributes more than half of the heat convergence in the equatorial Pacific Ocean. Finally, we show that although Ekman flow and near-equator frictional flow can both result in EEW, their coupled interactions with the Hadley circulation lead to opposite feedbacks on EEW's strength.

Abstract The predictability of the El Niño‐Southern Oscillation (ENSO) is significantly limited by the spring predictability barrier (SPB). Our observational analysis suggests that considering high‐frequency wind components during the spring season may mitigate the SPB impact on ENSO predictability. The intraseasonal zonal wind in March over the equatorial western Pacific initially perturbs the sea surface temperature (SST). It contributes nearly 40% of the east‐west SST gradient after 2–3 months, ranking first among other calendar months. This significant contribution causes March to become the earliest month to effectively indicate the following ENSO direction due to the active eastward‐propagating Madden‐Julian oscillation (MJO) activity. Through the obvious variation of the eastward‐propagating MJO speed, it also shows the possible close relationship between the mean SST state and the interdecadal variability in intraseasonal zonal wind. Additionally, the current strong variability of intraseasonal zonal wind suggests the important role of atmospheric information in recent ENSO development.

Coastal upwelling, marked by cool sea surface temperatures, modulates the wind stress and heat fluxes at the air-sea interface. However, the impact of upwelling on offshore wind power has been scarcely studied. This study uses satellite sea surface temperature data and a numerical model to examine how coastal upwelling shapes the diurnal evolution of the marine boundary layer, focusing on implications for offshore wind energy. The study region is the U.S. Mid Atlantic Bight, specifically the coast of New Jersey, known for its persistent summertime upwelling events. We run numerical experiments with upwelling, and upwelling artificially removed, to assess differences in the atmospheric response. For the wind event considered, results agree with theory where a stable, upwelling-cooled atmospheric boundary layer leads to reduced air-sea drag and turbulence intensity, higher wind speeds at hub height, and greater vertical shear relative to the scenario with upwelling removed. This response is likely caused by a sea breeze superimposed on onshore background winds. Experiments with parameterized turbines show that an 18-hour power generation at a lease area close to the shore was 6.5% higher with upwelling (4.86 GWh and 4.56 GWh, respectively). While upwelling can modulate offshore wind, the nature of the modulation is strongly dependent on the boundary layer regimes, background wind direction, and synoptic or mesoscale weather patterns.

Abstract Sea surface temperature anomaly (SSTA) of ocean eddies induces an anomalous air‐sea turbulent heat flux that acts to dampen SSTA. A two‐dimensional SSTA model explores the effect of air‐sea turbulent heat flux, parameterized as SSTA damping, in shaping eddy SSTA patterns. Increased SSTA damping transitions the SSTA pattern from a monopole to dipole, indicating the balance between eddy stirring of the background SST gradient and SSTA damping. The SSTA dipole pattern increases the correlation of eddy velocity and SSTA, but SSTA damping weakens the SSTA, resulting in an optimal damping rate maximizing lateral eddy surface heat transport. Globally, the SSTA damping rate increases toward the equator. In mid‐latitude and high‐latitude regions (e.g., the Kuroshio, the Gulf Stream, and the Southern Ocean), eddy SSTAs are monopoles, while the tropics and subtropics exhibit dipole SSTA patterns due to higher damping rates, facilitating greater lateral eddy heat transport when the SSTA is large.

The editorial in "Frontiers in Marine Science" discusses the importance of air-sea interaction in controlling energy exchange between the atmosphere and ocean, impacting the development of oceanic extreme events like tropical cyclones, extreme waves, and marine heatwaves. The research topic covers various aspects of air-sea interactions, including studies on tropical cyclones, extreme waves, marine heatwaves, mesoscale and large-scale air-sea interactions, and numerical simulations. The authors emphasize the need to improve understanding of these interactions to enhance climate and ocean prediction and mitigate potential damages, highlighting the significance of incorporating air-sea processes into weather and Earth System Models. [Extracted from the article]

The Pacific/North American (PNA) pattern is a major low‐frequency variability in boreal winter. A recent modeling study suggested that PNA variability increases through extratropical atmosphere‐ocean coupling, but the effect was not fully extracted due to a particular experimental design. By comparing coupled and two sets of uncoupled large‐ensemble global model simulations, here we show that the PNA‐induced horseshoe‐shaped sea‐surface temperature (SST) anomaly in the North Pacific returns a non‐negligible influence on the PNA itself. Its magnitude depends on the presence or absence of atmosphere‐ocean coupling. The coupling accounts for ∼16% of the PNA variance, while the horseshoe‐shaped SST anomaly explains only 5% under the uncoupled condition. The coupling reduces the damping of available potential energy by modulating turbulent heat fluxes and precipitation, magnifying the PNA variance. Precipitation processes in the extratropics as well as tropics are therefore important for realistically representing PNA variability and thereby regional weather and climate. Plain Language Summary: Atmospheric flow is not entirely random; patterns of circulation variability appear recurrently in the same regions, known as teleconnection patterns. A major wintertime teleconnection pattern over the North Pacific‐North American sector is called the Pacific/North American (PNA) pattern. It causes strong fluctuations in precipitation, air temperature, and pressure over North America through persistent strengthening or meandering of the jet stream. While the influence of tropical ocean variability, such as El Niño/La Niña, on the formation and persistence of the PNA has been known, the role of the extratropical ocean remains unclear. Here we perform a vast number of numerical model simulations to detect the influence of the extratropical ocean on PNA. We show that the atmosphere‐ocean coupling (two‐way interaction between the ocean and atmosphere) enhances the PNA variability (i.e., the magnitude of meandering and strengthening of the westerlies) compared to the uncoupled condition. Furthermore, we propose possible mechanisms behind this enhancement. The findings of this study are expected to contribute to improving the accuracy of long‐term forecasts, such as one‐month predictions, and reducing uncertainty in future climate change projections through the improvement of numerical models. Key Points: Extratropical air‐sea coupling enhances the variance of the Pacific/North American (PNA) pattern, which explains 16% of the total varianceThe enhancement is due to the reduced damping of available potential energy through modulations of turbulent heat fluxes and precipitationAtmosphere‐only simulation is likely to underestimate the impact of extratropical sea surface temperature anomalies on the PNA variability [ABSTRACT FROM AUTHOR]

The coupled nature of the ocean–atmosphere system frequently makes understanding the direction of causality difficult in ocean–atmosphere interactions. This study presents a method to decompose turbulent surface heat fluxes into a component which is directly forced by atmospheric circulation and a residual which is assumed to be primarily "ocean-forced." This method is applied to the North Atlantic in a 500-yr preindustrial control run using the Met Office's HadGEM3-GC3.1-MM model. The method shows that atmospheric circulation dominates interannual to decadal heat flux variability in the Labrador Sea, in contrast to the Gulf Stream where the ocean primarily drives the variability. An empirical orthogonal function analysis identifies several residual heat flux modes associated with variations in ocean circulation. The first of these modes is characterized by the ocean warming the atmosphere along the Gulf Stream and North Atlantic Current and the second by a dipole of cooling in the western subtropical North Atlantic and warming in the subpolar North Atlantic. Lead–lag regression analysis suggests that atmospheric circulation anomalies in prior years partly drive the ocean heat flux modes; however, there is no significant atmospheric circulation response in years following the peaks of the modes. Overall, the heat flux dynamical decomposition method provides a useful way to separate the effects of the ocean and atmosphere on heat flux and could be applied to other ocean basins and to either models or reanalysis datasets. Significance Statement: Variability of the ocean affects atmospheric circulation and provides a source of long-term predictability for surface weather. However, the atmosphere also affects the ocean. This makes the separation of cause and effect in such atmosphere–ocean interactions difficult. This paper introduces a method to separate "turbulent heat fluxes," the primary means by which the atmosphere and ocean influence one another, into a component driven by atmospheric variability and a component which is primarily related to ocean variability. The method is tested by applying it to a climate model simulation and is able to identify regions in which the exchange of heat between the ocean and atmosphere is dominated by atmospheric variability and regions which are dominated by the ocean. [ABSTRACT FROM AUTHOR]

As the strongest year-to-year fluctuation of the global climate system, El Niño–Southern Oscillation (ENSO) exhibits spatial–temporal diversity, which challenges the classical ENSO theories that mainly focus on the canonical eastern Pacific (EP) type. Besides, the complicated interplay between the interannual anomaly fields and the decadally varying mean state is another difficulty in current ENSO theory. To better account for these issues, the nonlinear two-region recharge paradigm model is extended to a three-region full-field conceptual model to capture the physics in the western Pacific (WP), central Pacific (CP), and EP regions. The results show that the extended conceptual model displays a rich dynamical behavior as parameters setting the efficiencies of upwelling and zonal advection are varied. The model can not only generate El Niño bursting behavior but also simulate the statistical asymmetries between the two types of El Niños and the warm and cold phases of ENSO. Finally, since both the anomaly fields and mean states are simulated by the model, it provides a simple tool to investigate their interactions. The strengthening of the upwelling efficiency, which can be seen as an analogy to a cooling thermocline associated with the oceanic tunnel to the midlatitudes, will increase the zonal gradient of the mean state temperature between the WP and EP, i.e., resembling a negative Pacific decadal oscillation (PDO) pattern along the equatorial Pacific. The influence of the zonal advection efficiency is quite the opposite, i.e., its strengthening will reduce the zonal gradient of the mean state temperature along the equatorial Pacific. [ABSTRACT FROM AUTHOR]

Accurate detection and attribution of past climate change are crucial for projecting future climate change and formulating proper policies. In this study, we show that the warming of the tropical Indian Ocean contributes to the observed wetting trend in the Tibetan plateau. The warming tropical Indian Ocean can lead to more precipitation around the Arabian Sea. The associated diabatic heating triggers the cyclonic atmospheric response in the lower troposphere over the Arabian Sea and eastern Africa. It also causes the enhancement and westward extension of the western North Pacific subtropical high. The in‐between airflow transports more moisture northward to the plateau, leading to the increased precipitation over the plateau. These large‐scale circulation patterns can be detected from the long‐term trends based on the observations and the large‐ensemble historical simulations. They can also be simulated by an atmospheric general circulation model forced by the observed warming merely in the tropical Indian Ocean. Plain Language Summary: The Tibetan plateau, often referred to the "Asian water tower," is the source region of many major rivers in Asia. It has experienced an increasing precipitation trend over the past few decades. In this study, we show that the warming tropical Indian Ocean contributes to this wetting trend. The warming tropical Indian Ocean can cause more precipitation around the Arabian Sea. The associated diabatic heating not only triggers an anomalous cyclone in the lower troposphere around the Arabian Sea and eastern Africa, but also causes the enhancement and westward extension of western North Pacific subtropical high. Consequently, the northward airflow between them transports more moisture to the plateau and causes more precipitation there. Our findings underscore the significant role of the warming tropical Indian Ocean in shaping the changing climate under global warming. Further research efforts are warranted to deepen our understanding of this phenomenon. Key Points: The warming tropical Indian Ocean increases the precipitation over the Arabian SeaThe associated large‐scale circulation anomalies transport more moisture northward to the plateauConsequently, more moisture converges over the plateau, leading to the increased precipitation [ABSTRACT FROM AUTHOR]

The connection between atmospheric blocking over the North Atlantic and the diabatic influence of the Gulf Stream is investigated using potential vorticity and moist potential vorticity diagnostics in the ERA5 reanalysis data set during wintertime (1979 - 2020). In line with previous research, the reliance atmospheric blocking has on turbulent heat fluxes over the Gulf Stream and its extension, for induction and maintenance, is shown to be significant. The air-sea heat flux generates negative potential vorticity air masses in the atmospheric boundary layer. These air masses subsequently contribute to the block's negative potential vorticity anomaly at upper levels through ascending motion in the warm conveyor belt. It is shown that the block's size and frequency partially depends on oceanic preconditioning via anomalous oceanic heat transport and heat content, prior to the blocking event, both of which allow for stronger turbulent heat fluxes. It is further hypothesized that the block feeds back positively on itself through the advection of cold dry air over the Gulf Stream, sustaining this air-sea interaction. This in turn decreases ocean heat content, eventually halting this air-sea interaction and severing the atmospheric block from its maintenance pathway. [ABSTRACT FROM AUTHOR]

The paper aims to demonstrate how to enhance the accuracy of offshore wind resource estimation, specifically by incorporating near-surface satellite-derived wind observations into mesoscale models. We utilized the Weather Research and Forecasting (WRF) Model and applied observational nudging by integrating ASCAT data over offshore areas to achieve this. We then evaluated the accuracy of the nudged WRF Model simulations by comparing them with data from ocean oil platforms, tall masts, and a wind lidar mounted on a commercial ferry crossing the southern Baltic Sea. Our findings indicate that including satellite-derived ASCAT wind speeds through nudging enhances the correlation and reduces the error of the mesoscale simulations across all validation platforms. Moreover, it consistently outperforms the control and previously published WRF-based wind atlases. Using satellite-derived winds directly in the model simulations also solves the issue of lifting near-surface winds to wind turbine heights, which has been challenging in estimating wind resources at such heights. The comparison of the 1-yr-long simulations with and without nudging reveals intriguing differences in the sign and magnitude between the Baltic and North Seas, which vary seasonally. The pattern highlights a distinct regional pattern attributed to regional dynamics, sea surface temperature, atmospheric stability, and the number of available ASCAT samples. Significance Statement: We aim to showcase a method for improving the precision of hub-height estimation of wind resources offshore. This involves integrating wind observations obtained from near-surface satellites into the model simulations. To assess the accuracy of the simulations, we compare the simulated winds to data gathered from multiple offshore sources, including oil platforms, tall masts, and a wind lidar installed on a commercial ferry. [ABSTRACT FROM AUTHOR]

Sea spray, originating from wave breaking under high wind conditions, can significantly affect turbulent heat fluxes at the air–sea interface. Even though polar lows (PLs) can become extreme weather features with gale‐force wind, the impact of sea spray on their development has rarely been investigated and is not considered in operational forecast models. In this study, the impact of sea spray on the development of two PLs over the Barents Sea is studied based on sensitivity experiments with an atmosphere–wave coupled model, where the spray‐mediated heat fluxes are parameterized. The results show that the impact of sea‐spray‐mediated heat fluxes on PL development is sensitive to the surface wind speed. In the case of the stronger PL, the higher surface wind speed results in significantly higher spray‐mediated heat fluxes. Consequently, these spray‐mediated heat fluxes intensify the convection and diabatic heating of the PL, resulting in its intensification. In comparison, the case with a weaker PL experiences less sea spray production and lower spray‐mediated heat fluxes due to its weaker surface wind speeds. Overall, we find that spray‐mediated sensible heat fluxes play an important role in the development of PLs, while the latent heat fluxes induced by sea spray have a relatively minor impact. [ABSTRACT FROM AUTHOR]

This study focuses on the influence of the sea spray polydispersity on the vertical transport of momentum in a turbulent marine atmospheric boundary layer in high-wind conditions of a hurricane. The Eulerian multifluid model treating air and spray droplets of different sizes as interacting interpenetrating continua is developed and its numerical solutions are analyzed. Several droplet size distribution spectra and correlation laws relating wind speed and spray production intensity are considered. Polydisperse model solutions have confirmed the difference between the roles small and large spray droplets play in modifying the turbulent momentum transport that have been previously identified by monodisperse spray models. The obtained results have also provided a physical explanation for the previously unreported phenomenon of the formation of thin low-eddy-viscosity "sliding" layers in strongly turbulent boundary layer flows laden with predominantly fine spray. Significance Statement: Achieving better accuracy in hurricane forecasts requires an in-depth understanding and accurate modeling of the ocean spray effect on the vertical fluxes of momentum and heat in a hurricane boundary layer. It has been shown that this effect depends on the size distribution of spray droplets, also known as spray polydispersity. This study aims to investigate the influence of a polydisperse spray on the vertical momentum transport within hurricane boundary layers by employing a modern theory of turbulent disperse multiphase flows. [ABSTRACT FROM AUTHOR]

This study investigated the dynamic and thermal responses of cyclonic eddies (CEs) to Typhoon Surigae in the western North Pacific Ocean using satellite data and a coupled ocean–atmosphere model. Observations and simulations revealed that the typhoon enhanced the two preexisting CEs (C1 and C2). After the typhoon passed the two eddies, the sea surface height (SSH) lowered and the eddy velocity increased above 200 m. C1 was stretched with elliptical deformation accompanied by an SSH trough and jets on the sides of the typhoon track at the eddy edge. The comparative experiments indicated that the typhoon caused the SSH of C1 and C2 to lower by 53.52% and 25.14% compared to conditions without the typhoon, respectively, and the kinetic energy of C1 and C2 to increase by 12 times and 65.76%, respectively. The positive vorticity anomaly input from the typhoon to the CEs was the main mechanism for the enhancement of the CEs. The enhanced CEs modulated the typhoon-induced sea surface temperature (SST) cooling, causing the temperature within the eddies to decrease by upwelling and mixing, and the SST cooling became significant at the center of the CEs and propagated westward with the eddies. This study also revealed that typhoons can significantly perturb eddy dynamic structures by enhancing or generating cyclonic cold eddies and eradicating anticyclonic eddies, thereby weakening the Kuroshio Current transport via eddy–Kuroshio interactions. [ABSTRACT FROM AUTHOR]

Standing meanders along the Antarctic Circumpolar Current (ACC) have been shown to be regions of elevated eddy variability, meridional heat transport, and vertical exchange. In this study, we investigate the influence of a standing meander south of Australia on air‐sea heat fluxes, upper ocean structure, and subduction in the 1/10° ACCESS‐OM2 ocean‐sea ice model forced by the JRA55 atmospheric reanalysis. We track the model's Subantarctic and Polar Fronts based on their jet and water mass structure, and produce composites of thermodynamical and dynamical properties of the meander in relaxed and flexed states. The standing meander induces trough‐to‐crest variations in surface heat flux, mixed layer depth (MLD), wind stress curl, vertical velocity, and subduction. At the crests, the ocean loses heat and the mixed layer is deeper; at the troughs, the ocean gains heat and the mixed layer is shallower. Wind stress curl, vertical velocity, and subduction change sign on entering and exiting crests and troughs. Vertical velocity due to the curvature of the meander is an order of magnitude larger than Ekman vertical velocity. The poleward excursion of Polar Front meander crests extends subduction to Antarctic Intermediate Water density classes. Finally, flexing of the meander enhances both air‐sea exchange and vertical velocity. The results show that standing meanders of the ACC influence the distribution and magnitude of air‐sea fluxes of heat and momentum and exchange between the surface and interior ocean. Plain Language Summary: Meanders along the Antarctic Circumpolar Current (ACC) funnel heat toward Antarctica. The research clarifies how meandering of ocean currents shapes air‐sea interaction and the transfer of surface ocean properties into the ocean interior in the ACC south of Australia. Meanders refer to curved patterns in the ACC's flow. We track specific ACC features and look at what is different inside and outside the meander in a computer model. We find that ocean meanders shape where the Southern Ocean gains and loses heat. These changes in heat exchange shape the mixed layer depth (MLD) in the ocean. The MLD is important for climate, biology productivity, and absorption of heat and carbon by the ocean. Meandering produces stronger vertical motion and increases sinking of water from the surface into the ocean interior, compared to regions where meanders are not present. When the meander flexes and becomes more curved, the vertical motion and atmosphere‐ocean exchange become even stronger. The results show that small‐scale patterns in ocean flow can have a strong influence on the atmosphere, with implications for climate and ocean circulation. These patterns are not well represented in climate models and our study is a step toward accounting for their absence. Key Points: Meanders in the Antarctic Circumpolar Current are locations of enhanced vertical velocity and air‐sea exchange of momentum and heatFlexing of the meander further enhances air‐sea exchange and vertical velocities due to increased curvaturePoleward excursion of meander crests extends subduction to Antarctic Intermediate Water densities along the Polar Front [ABSTRACT FROM AUTHOR]

Interannual sea surface temperature (SST) variations in the subtropical‐midlatitude Southern Hemisphere are often associated with a circumpolar wavenumber‐4 (W4) pattern. This study is the first attempt to successfully simulate the SST‐W4 pattern using a state‐of‐the‐art coupled model called SINTEX‐F2 and clarify the underlying physical processes. It is found that the SST variability in the southwestern subtropical Pacific (SWSP) plays a key role in triggering atmospheric variability and generating the SST‐W4 pattern during austral summer (December‐February). In contrast, the tropical SST variability has a very limited effect. The anomalous convection and associated divergence over the SWSP induce atmospheric Rossby waves confined in the westerly jet. Then, the synoptic disturbances circumnavigate the subtropical Southern Hemisphere, establishing an atmospheric W4 pattern. The atmospheric W4 pattern has an equivalent barotropic structure in the troposphere, and it interacts with the upper ocean, causing variations in mixed layer depth due to latent heat flux (LHF) anomalies. As incoming climatological solar radiation goes into a thinner (thicker) mixed layer, the shallower (deeper) mixed layer promotes surface warming (cooling). This leads to positive (negative) SST anomalies, developing the SST‐W4 pattern during austral summer. Subsequently, anomalous entrainment due to the temperature difference between the mixed layer and the water below the mixed layer, anomalous LHF, and disappearance of the overlying atmospheric W4 pattern cause the decay of the SST‐W4 pattern during austral autumn. These results indicate that accurate simulation of the atmospheric forcing and the associated atmosphere‐ocean interaction is essential to capture the SST‐W4 pattern in coupled models. Plain Language Summary: In the subtropical‐midlatitude Southern Hemisphere, we often observe year‐to‐year fluctuations in sea surface temperature (SST) linked to a specific pattern known as wavenumber‐4 (W4). This study represents the first successful attempt to simulate this temperature pattern using a climate emulator called SINTEX‐F2, allowing us to uncover its physical processes. Our research reveals that SST variations in the southwestern subtropical Pacific (SWSP) play a pivotal role in generating the W4 pattern in the atmosphere, subsequently influencing SST during austral summer. Interestingly, this pattern is almost independent of tropical SST variability. The process starts with heating in the SWSP, causing atmospheric disturbances. This leads to an undulation in mid‐latitude atmospheric flow, evolving into a well‐established global Rossby wave with four positive (negative) loading centers, forming a W4 pattern. This atmospheric wave interacts with the ocean's surface, leading to heat exchange between the atmosphere and the upper ocean. In turn, it influences the depth of the mixed layer in the upper ocean, which receives solar energy. When solar energy penetrates into a shallower (deeper) mixed layer, it warms (cools) the mixed layer effectively, resulting in higher (lower) SSTs. Afterwards, the energy exchange between the mixed layer and the deep ocean contributes to the decay of the SST pattern. Key Points: First attempt to successfully simulate the wavenumber‐4 (W4) pattern of Southern Ocean sea surface temperature (SST) using a coupled model, uncovering the underlying physical processesSouthwestern subtropical Pacific SST plays a crucial role in generating SST W4 pattern via circumpolar atmospheric variabilityThe ocean mixed layer and upper ocean processes are found to be important for the growth and decay of the SST pattern [ABSTRACT FROM AUTHOR]

Strong surface winds induced by polar lows (PLs) may affect the upper ocean. However, understanding of the oceanic responses and feedback processes associated with PLs remains insufficient, especially for observations. Using a combined analysis of satellite‐based sea surface temperature (SST) and PL tracking data, we investigated the oceanic response to 380 PL passages over the Nordic Sea occurring between 1999 and 2018. Consequently, two types of oceanic responses—warming and cooling—occurred in 32% and 40% of the total occurrences, respectively. The average magnitude of SST response was approximately ±0.2 K. Significant differences in upward surface turbulent heat flux (THF) between warming and cooling response cases were found, causing a significant difference in the decay rate after maximum PL development. By analyzing changes in the state variables of the THF, we identified two different feedback processes depending on the oceanic warming/cooling response. During a warming (cooling) response, the atmosphere near the surface becomes more unstable (stable), and the turbulence of the marine atmospheric boundary layer increases (decreases), which strengthens (weakens) the ocean surface wind and decreases (increases) temperature and specific humidity. These changes contribute to increasing (decreasing) the upward THF that influences PL development. The differences between these two responses may be caused by the state of the upper ocean layer, including temperature inversion. The analysis of the in situ observations of the upper ocean supports the hypothesis that a warming response occurs when inversion is strong. This study emphasizes the importance of feedback through oceanic responses for understanding and predicting PL. Plain Language Summary: Small but strong storms that occur at high latitudes often cause significant damage to society. When such a storm occurs, there is great interest in whether it develops or dissipates. In this study, we investigated the records of past storms in the Nordic Sea, focusing on changes in ocean surface temperatures measured by satellites. In certain cases, the water temperature decreased as the storm passed, whereas in others, the water temperature increased. We found that when the water temperature increased, more thermal energy was supplied to the storm from the ocean, and storm attenuation was smaller than when the water temperature decreased. Although the change in water temperature caused by the passage of a storm is small, at approximately 0.2°C, it has been revealed that, simultaneously, changes in near‐surface wind and air temperature occur, which cause thermal energy to be transferred to the storm. These results show that storms and the ocean are not unrelated and that ocean structure is crucial for predicting storms. Key Points: Satellite‐based data revealed two types of oceanic responses—surface warming and cooling—to the passage of polar lows (PLs) over the Nordic SeasOcean observation data suggest that the difference between the two responses is related to the vertical structure in the upper oceanResponses and feedback result in differences in the upward surface turbulent heat flux, which changes the characteristics of PLs [ABSTRACT FROM AUTHOR]

Among nine La Niña events since 1980, there are seven double-peaked La Niña events that typically persist for 2 years and peak twice in the two consecutive boreal winters. In the study, the individual impacts of the first and second peak episodes of such La Niña on the Antarctic sea ice in austral spring (September–November) were compared. The results suggest a difference. The first episode induces a tripolar distribution of sea ice concentration (SIC) with a negative anomaly in the Bellingshausen Sea sandwiched with positive anomalies in the Ross Sea and the northeastern Weddell Sea. The second causes an SIC reduction in most parts of the Southern Ocean except for the eastern Ross–western Amundsen Seas where an increase is observed. Mechanistically, the first episode forces one single Rossby wave train to propagate southeastward, causing a strong cyclone anomaly over the eastern Ross–Amundsen–Bellingshausen Seas along with a weak anticyclone over the Weddell Sea. In comparison, the second La Niña excites two branches of Rossby wave trains emanating from the southeastern tropical Indian Ocean and the central equatorial Pacific, respectively, which induce three anomalous anticyclones and two anomalous cyclones over the Southern Ocean. These different atmospheric circulation anomalies shape their different sea ice distributions between the two La Niña episodes through both dynamic and thermodynamic processes. The modeling results from CAM5 verify these differences. Significance Statement: Under global warming, the double-peaked La Niña occurs more frequently. The first and second La Niña episodes in such double-peaked La Niña are distinct from each other not only in their onset and developing mechanisms but also in their climate impacts. Based on observational analyses and model experiments, the study investigated the distinctive impacts of the first and second episodes on the austral spring Antarctic sea ice. The results reveal that the first episode excites one single southeastward-propagated Rossby wave train, while the second episode forces two branches of Rossby wave trains. These different atmospheric responses in the Southern Hemisphere shape the distinct sea ice distributions both dynamically and thermodynamically. The study also indicates the diversity of tropical–Antarctic teleconnections. [ABSTRACT FROM AUTHOR]

In this study, a diagnostic model for evaporation ducts was established based on the Coupled Ocean–Atmosphere–Wave–Sediment Transport (COAWST) and the Naval Postgraduate School (NPS) models. Utilizing this model, four sensitivity tests were conducted over the South China Sea from 21 September to 5 October 2008, when four tropical cyclones affected the study domain. These tests were designed with different roughness schemes to investigate the impact mechanisms of wave processes on evaporation duct simulation under extreme weather conditions. The results indicated that wave processes primarily influenced the evaporation duct heights by altering sea surface roughness and dynamical factors. The indirect impacts of waves without dynamical factors were rather weak. Generally, a decrease in local roughness led to increased wind speed, decreased humidity, and a reduced air–sea temperature difference, resulting in the formation of evaporation ducts at higher altitudes. However, this affecting mechanism between roughness and evaporation ducts was also greatly influenced by changes in regional circulation. In the eastern open sea areas of the South China Sea, changes in evaporative ducts were more closely aligned with local impact mechanisms, whereas the changes in the central and western areas demonstrated greater complexity and fewer local impacts due to variations in regional circulation. [ABSTRACT FROM AUTHOR]

A meridional dipolar atmospheric teleconnection between the Tasman Sea and the Southern Ocean, which describes a hybrid between the El Niño–Southern Oscillation, Indian Ocean Dipole and Southern Annular Mode, was referred to as the Hybrid Teleconnection (HT) pattern previously. We investigate its connection with East Asian summer rainfall and find the preceding May–June HT can be the precursor of the following July–August East Asian rainfall. The mechanism is examined based on analyses of observational datasets and historical runs of coupled models from phase 6 of the Coupled Model Intercomparison Project (CMIP6). The results suggest that a positive HT with positive 500 hPa geopotential height anomalies over the Tasman Sea but negative over the Southern Ocean in the preceding boreal early summer contributes to generating negative sea surface temperature (SST) anomalies in the western tropical Pacific (WP) by influencing surface heat exchange. The SST anomalies over WP persist into the mid-summer via the thermal memory of seawater, inducing interhemispheric meridional circulation and then exciting a Pacific-Japan-Pattern-like atmospheric circulation anomaly, which manifests as an anticyclone over the subtropical northwestern Pacific along with a cyclone near the Sea of Japan. This pattern induces intensified convergence and vertical ascend motion, and subsequently intensifies rainfall in the Yangtze River Basin. [ABSTRACT FROM AUTHOR]