Air-sea Interaction Research Articles

Assessing the importance of mesoscale sea‐surface temperature variations for surface turbulent cooling of the Kuroshio Extension in wintertime

Western boundary currents are well known to exhibit a strong eddy field and meandering on subseasonal timescales and wavelengths of a few hundreds of kilometers. However, the extent to which the ocean mesoscale activity associated with these motions can enhance the turbulent air–sea heat flux averaged over a large spatial domain has not been fully characterized. This study aims to do so during the cold season using reanalysis data and simplified air–sea interaction models. The correlation between sea-surface height anomaly and the wintertime mean heat fluxes does not indicate any significant relations between eddy activity and large-scale surface heat flux in the Kuroshio Extension during winter over the 2003–2018 period. The results from simple models designed to isolate the contributions from the eddies suggest that the eddy enhancement of the heat flux via a rectified effect (a bit more anomalous cooling over a warm mesoscale feature than anomalous heating over a cold one) is small compared with the long-time, large-spatial scale mean in the reanalysis data, especially along the Kuroshio Extension. It is found larger north of it, where it can reach 5 W · $$ \cdotp $$ m − 2 $$ {}^{-2} $$ . Although different datasets might disagree about the level of energy of the sea-surface temperature field at the mesoscale, a simple scaling analysis gives confidence in the relatively small values of the rectified effect found here.

Spatial and temporal characteristics of the precipitation response to the 4.2 ka event in the Asian summer monsoon region

The 4.2 ka event was the most abrupt climatic event during the transition between the middle and late Holocene. It had a profound influence on the regional ecological environment and human cultural development and was characterized by the rapid onset of aridification in the mid- and low-latitudes regions of the Northern Hemisphere. However, the nature, structure and spatial expression of the 4.2 ka event in the Asian summer monsoon (ASM) region are controversial. We produced a detailed record of regional vegetation change during the interval of 5000–3500 cal yr BP, based on a high-resolution (~10 yr) pollen record from Yazihai Lake, on the margin of the region influenced by the ASM. The results indicate that an interval of climatic aridification, correlative with the 4.2 ka event, occurred during 4340–3880 cal yr BP, with the duration of 460 yr. However, the structure of the event is relatively complex, with arid conditions during 4340–4280 cal yr BP, wetter conditions during 4280–4150 cal yr BP, and arid conditions during 4150–3880 cal yr BP. A comprehensive comparison of the results from Yazihai Lake with existing high-resolution and well-dated paleoclimate records from the ASM region show that the precipitation response to the 4.2 ka event was spatially and temporally synchronous, with a consistent of timing, duration, and structural characteristics in the northern and southwestern parts of the ASM region; whereas the opposite response occurred in the southeastern part, where the precipitation increased. We suggest that the driving mechanism of the 4.2 ka event was related to sea-air interactions in the low-latitude region. Sea surface temperature (SST) anomalies and the variation of the El Niño-Southern Oscillation (ENSO) in the tropical Pacific region was the main cause, which led to a weaker ASM circulation and a southward shift of the monsoon rainbelt. These changes resulted in decreased monsoonal precipitation and a dry climate in the northern and southwestern parts of the ASM region, but to increased precipitation in the southeastern part.

Local ocean–atmosphere interaction in Indian summer monsoon multi-decadal variability

The significant multi-decadal mode (MDM) of the Indian summer monsoon rainfall (ISMR) during the past two millennia provides a basis for decadal predictability of the ISMR and has a strong association with the North-Atlantic (NA) variability with the Atlantic Multi-decadal Oscillation (AMO) as a potential external driver. It is also known that the annual cycles and interannual variability of ISMR and sea surface temperatures (SST) over the tropical Indian Ocean (IO) are strongly coupled. However, the role of local air–sea interactions in maintaining or modifying the ISMR MDM remains unknown. A related puzzle we identify is that the IO SST has an increasing trend during two opposite phases of the ISMR MDM, namely during an increasing phase of ISMR (1901–1957) as well as a decreasing phase of ISMR (1958–2007). Here, using a twentieth-century reanalysis (20CR), we examine the role of air-sea interactions in maintaining two opposite phases of the ISMR MDM and unravel that the Bjerknes feedback is at the heart of maintaining the ISMR MDM but cannot explain the increasing trend of SST in the tropical IO during the opposite phases. Large-scale low-level vorticity influence on SST and net heat flux changes through circulation and cloudiness changes associated with the two phases of the ISMR MDM together contribute to the SST trends. The decreasing trend of low-level wind convergence during the period between 1958 and 2007 is a determining factor for the decreasing trend of ISMR in the backdrop of an increasing trend of atmospheric moisture content. Consistent with the lead of the AMO with respect to ISMR by about a decade, the AMO drives the transition from one phase of ISMR MDM to another by changing its phase first and setting up low-level equatorial zonal winds conducive for the transition.

The role of air–sea coupling on November–April intraseasonal rainfall variability over the South Pacific

We investigate the impact of resolving air-sea interaction on the simulation of the intraseasonal rainfall variability over the South Pacific using the ECHAM5 atmospheric general circulation model coupled with the Snow-Ice-Thermocline (SIT) ocean model. We compare the fully coupled simulation with two uncoupled ECHAM5 simulations, one forced with sea surface temperature (SST) climatology and one forced with daily SST from the coupled model. The intraseasonal rainfall variability over the South Pacific is reduced by 17% in the uncoupled model forced with SST climatology and increased by 8% in the uncoupled simulation forced with daily SST, suggesting the role of air–sea coupling and SST variability. The coupled model best simulates the key characteristics of the two dominant patterns (modes) of intraseasonal rainfall variability over the South Pacific with reasonable propagation and correct periodicity. The spatial structure of the two rainfall modes in all three simulations is very similar, suggesting the dynamics of the atmosphere primarily generate these modes. The southeastward propagation of rainfall anomalies associated with two leading rainfall modes in the South Pacific depends upon the eastward propagating Madden–Julian Oscillation (MJO) signals from the Indian Ocean and western Pacific. Air-sea interaction improves such propagation as both eastward and southeastward propagations are substantially reduced in the uncoupled model forced with SST climatology. The simulation of both eastward and southeastward propagations considerably improved in the uncoupled model forced with daily SST; however, the periodicity differs from the coupled model. Such discrepancy in the periodicity is attributed to the changes in the SST-rainfall relationship with weaker correlations and the nearly in-phase relationship, attributed to enhanced positive latent heat flux feedbacks.

The global monsoon system representation in BAM‐v1.2 and HadGEM3 climate simulations

AbstractThe features of monsoon systems in the Northern and Southern Hemispheres are analysed in climate simulations of two atmospheric models: the Brazilian Global Atmospheric Model version 1.2 (BAM‐v1.2) and the UK Met Office Hadley Centre Global Environment Model version 3 (HadGEM3). The results are compared to GPCP precipitation and ERA5 datasets. Although they have different configurations and parameterizations, the purpose is to evaluate their ability in representing key features of the global monsoon system. The spatial extent of the monsoon domains is well simulated by the models, as well as the main characteristics of the monsoons, although precipitation biases are noticed in the regions affected by the systems, consistent with vertical motion and moisture flux biases. The largest precipitation biases are found in the West Pacific Monsoon Region, extended to the east, and in the Australia Monsoon Region extended to the Maritime continent. Deficiencies in precipitation can be related to inaccuracy of vertical motion and humidity flux, as well as to the lack of air–sea interaction. However, the atmospheric circulation features at low and high levels are well represented in all monsoon regions, as well as the annual cycle of precipitation in those regions by both models. The divergence at high levels and convergence at low levels associated with ascending air movement and precipitation in monsoon regions are well represented by the models. An analysis of two monsoon indices at eight monsoon regions showed the models are generally able to simulate the relationship between precipitation and circulation features. In the majority of years, the signs of indices from the models agree with observations. Correlations of precipitation and circulation indices between models and observations show statistically significant values for some monsoon regions. The results obtained contribute to improving knowledge about global monsoon features and their representation in the two models.

Tropical volcanism enhanced the East Asian summer monsoon during the last millennium

Extreme East Asian summer monsoon (EASM) rainfall frequently induces floods that threaten millions of people, and has been generally attributed to internal climate variability. In contrast to the hydrological weakening theory of volcanic eruptions, here we present convergent empirical and modeling evidence for significant intensification of EASM rainfall in response to strong tropical volcanic eruptions. Our multi-proxy analyses show a significantly increased EASM in the first summer after tropical eruptions from 1470 AD to the present, and the more frequent occurrence of El Niños in the first boreal winter after eruptions is necessary for the enhanced EASM. Model simulation ensembles show that a volcano-induced El Niño and the associated stronger than non-volcanic El Niño warm pool air-sea interaction intensify EASM precipitation, overwhelming volcanic-induced moisture deficiency. This work sheds light on the intertwined relationship between external forcing and internal climate variability and potential flood disasters resulting from tropical volcanic eruptions.

Impact of Riverine Fresh Water on Indian Summer Monsoon: Coupling a Runoff Routing Model to a Global Seasonal Forecast Model

Rivers form an essential component of the earth system, with ~36,000 km3 of riverine freshwater being dumped into the global oceans every year. The role of rivers in controlling the sea-surface salinity and ensuing air-sea interactions in the Bay of Bengal (BoB) is well-known from observational studies; however, attempts to include rivers in coupled models used for seasonal prediction have been limited. This study reports the benefits of river routing in coupled models over prescribing observational river discharge and the impact on the Indian Summer Monsoon (ISM) simulation. Seasonal hindcasts are carried out using a state-of-the-art global coupled ocean-atmosphere-land-sea ice model, Climate Forecast System version 2, coupled to a runoff routing model. It is demonstrated that such a coupling leads to a better representation of the upper ocean stratification in northern BoB, causes mixed layer warming during July-August, and imparts a significant inter-annual variability to the mixed layer heat budget. The rainfall-runoff coupled feedback associated with ISM is captured better, and remote teleconnections with the equatorial Pacific are enhanced. Improved seasonal mean temperature and salinity profiles in the northern BoB lead to the formation of a thicker barrier layer, which is closely tied to the freshwater from rivers. These processes result in an overall enhancement of the ISM rainfall simulation skill, which stems from scale interactions between the sub-seasonal and seasonal variability of ISM. A significant community effort is required to reduce biases in land-surface processes to improve streamflow simulations, along with better parameterization of mixing of river water with the ocean.

Simulated microphysical properties of winter storms from bulk-type microphysics schemes and their evaluation in the Weather Research and Forecasting (v4.1.3) model during the ICE-POP 2018 field campaign

Abstract. This study evaluates the performance of four bulk-type microphysics schemes, Weather Research and Forecasting (WRF) double-moment 6-class (WDM6), WRF double-moment 7-class (WDM7), Thompson, and Morrison, focusing on hydrometeors and microphysics budgets in the WRF model version 4.1.3. Eight snowstorm cases, which can be sub-categorized as cold-low, warm-low, and air–sea interaction cases are selected, depending on the synoptic environment during the International Collaborative Experiment for Pyeongchang Olympics and Paralympics (ICE-POP 2018) field campaign. All simulations present a positive bias in the simulated surface precipitation for cold-low and warm-low cases. Furthermore, the simulations for the warm-low cases show a higher probability of detection score than simulations for the cold-low and air–sea interaction cases even though the simulations fail to capture the accurate transition layer for wind direction. WDM6 and WDM7 simulate abundant cloud ice for the cold-low and warm-low cases, and thus snow is mainly generated by aggregation. Meanwhile, Thompson and Morrison schemes simulate insignificant cloud ice amounts, especially over the lower atmosphere, where cloud water is simulated instead. Snow in the Thompson and Morrison schemes is mainly formed by the accretion between snow and cloud water and deposition. The melting process is analyzed as a key process to generate rain in all schemes. The discovered positive precipitation bias for the warm-low and cold-low cases can be mitigated by reducing the melting efficiency in all schemes. The contribution of melting to rain production is reduced for the air–sea interaction case with decreased solid-phase hydrometeors and increased cloud water in all simulations.

Monsoon depressions and air-sea interactions during different phases of monsoon intraseasonal oscillation

Monsoon depressions and air-sea interactions during different phases of monsoon intraseasonal oscillation

PAHs in the North Atlantic Ocean and the Arctic Ocean: Spatial Distribution and Water Mass Transport

AbstractIn the Arctic Ocean, it is still unclear what role oceanic transport plays in the fate of semivolatile organic compounds. The strong‐stratified Arctic Ocean undergoes complex inputs and outputs of polycyclic aromatic hydrocarbons (PAHs) from the neighboring oceans and continents. To better understand PAHs’ transport processes and their contribution to high‐latitude oceans, surface seawater, and water column, samples were collected from the North Atlantic Ocean and the Arctic Ocean in 2012. The spatial distribution of dissolved PAHs (∑9PAH) in surface seawater showed an “Arctic Shelf > Atlantic Ocean > Arctic Basin” pattern, with a range of 0.3–10.2 ng L−1. Positive matrix factorization modeling results suggested that vehicle emissions and biomass combustion were the major PAHs sources in the surface seawater. According to principal component analysis, PAHs in different water masses showed unique profiles indicating their different origins. Carried by the Norwegian Atlantic Current (0–800 m) and East Greenland Current (0–300 m), PAH individuals’ net transport mass fluxes ranged from −4.4 ± 1.7 to 53 ± 39 tons year−1 to the Arctic Ocean. We suggested the limited contribution of ocean currents on PAHs’ delivery to the Arctic Ocean, but their role in modulating PAHs’ air–sea interactions and other biogeochemical processes needs further studies.

Turbulence, Atmosphere and Climate Dynamics

The conference "Turbulence, Atmosphere and Climate Dynamics" dedicated to the memory of the Alexander M. Obukhov was held in Moscow from November 10 to 12, 2020. The topics of the conference covered the following scientific areas: turbulence; geophysical hydrodynamics; atmospheric and climate system dynamics; physics and composition of the atmosphere; air-sea interaction; wave propagation. The conference showed a high scientific level of almost all the presentations. Studies of turbulent, climatic and atmospheric processes are traditionally conducted in our country at the highest level, as evidenced by the publication in high-ranking scientific journals and the active participation of Russian scientists in international programs.List of Program committee, Organizing committee are avilable in this pdf.

Global trends in oceanic wind speed, wind-sea, swell, and mixed wave heights

The climatic trends of Wind Speed (WS) and wave height play a key role in wind and wave energy assessments, climate change analyses, and air-sea interactions, among many others. Using ERA5 reanalysis, this study reveals the climatic trends of global oceanic WS and wave height for 1979–2018, including the overall trends, regional and seasonal differences of the trends, with a special focus on the differences and similarities between the trends in wind-sea wave height (Hwind) and swell wave height (Hswell), as well as the contributions of climate indices to WS, Hwind, Hswell and Significant Wave Height (Hs) respectively, by employing linear regression and correlation analysis. The results show an overall global oceanic increase for 1979–2018 in WS (+0.47 cm/s/yr), with increases of +0.13, +0.28 and +0.32 cm/yr in Hwind, Hswell and Hs respectively, and a stronger increasing trend in the Southern Hemisphere than in the Northern Hemisphere. There is good agreement between the spatial distribution of annual and seasonal trends in WS and those of Hwind, as well as between Hswell and Hs. Areas with strong increasing trends of WS and Hwind are mainly located in the tropical South Indian Ocean and tropical Pacific Ocean. Hswell and Hs exhibit significant increases in most global oceans. The months with the broadest and strongest increase in Hswell and Hs are June-July-August (JJA). There is a close relationship among the WS, wave height climatology and the modes of climate variability. The wind has the strongest response to climate indices, followed by the wind-sea, with swell having a minimal response.

Climatic Change of Summer Rainstorms and the Water Vapor Budget in the Sichuan Basin

AbstractThis study aims to examine the variation of the characteristics of summer rainstorms and water vapor budget in the Sichuan Basin by using daily precipitation observation data and monthly mean ERA-Interim reanalysis data during 1979–2016. The results show that the spatial and temporal distribution of rainstorms in the Sichuan Basin is the result of the interaction between the special topography of the Sichuan Basin and different water vapor transports at low latitudes. The precipitation amount and frequency of rainstorms are mainly affected by the water vapor transports and budgets in different regions, and the intensity of rainstorms is mainly affected by the dynamic effects of regional and local topography, especially in the western and northern basin. The main reasons for the change of summer rainstorms in the Sichuan Basin include the atmospheric circulation over the key area of air–sea interaction in the tropical region, the anomalies of regional circulation, and water vapor transports in eastern China and the Sichuan Basin. A conceptual model for the summer rainstorm anomaly in the Sichuan Basin is proposed. With the establishment of consistent easterly airflow in the low-latitude tropical area (130°E–180°, 0°–10°N) and the anticyclone on its north, an anomalous southeasterly airflow and water vapor divergence maintain over eastern and southern China while an anomalous southeasterly airflow and water vapor convergence appear over the Sichuan Basin. So, more summer rainstorms occur in this region. Conversely, with the establishment of consistent westerly airflow in that same tropical area and the cyclone on its north, an anomalous easterly airflow and water vapor convergence maintain over eastern and southern China while an anomalous northeasterly airflow and water vapor divergence appear over the Sichuan Basin. So, fewer summer rainstorms occur in this region.Significance StatementRainstorm change in the Sichuan Basin has significant regional characteristics. This study aims to reveal the influence of regional variation of water vapor budget on summer rainstorms in the Sichuan Basin, which provides the important basis for the forecast of rainstorm in the Sichuan Basin, as well as new comprehension for the research and application of regional response to climate change. The amount and frequency of rainstorms are mainly affected by water vapor transports and budgets in different regions, and the intensity of rainstorms is mainly affected by the dynamic action of different regional and local topography. It reveals the new mechanism of multiscale interaction between the special topography of the Sichuan Basin and different water vapor transport in low latitudes.

Numerical Study on the Influence of Tropical Cyclone Characteristics on the Sea State and Sea Surface Roughness inside the Tropical Cyclones

The development of wind wave (i.e., sea state) inside an intense tropical cyclone (TC) is the dominant contributor to the sea surface roughness and thus significantly impacts the air–sea interaction. The sea state is known to vary with TC characteristics (intensity, size, and translation speed); however, comprehensive knowledge of the influence of TC characteristics on the sea state and sea surface roughness is quite limited, largely because of the lack of observations. In this study, numerical experiments are performed to investigate the influence of TC characteristics on the sea state and the sea surface roughness under a range of idealized TCs. The numerical results indicate that the sea states are systematically younger for a more intense or smaller TC, and their azimuthal variation is predominantly determined by the TC translation. The dependence of the sea surface roughness on wind speed shows systematic variations with the TC characteristics, which are most significant for a moderately moving TC.

A Ka-Band Wind Geophysical Model Function Using Doppler Scatterometer Measurements from the Air-Sea Interaction Tower Experiment

Physical understanding and modeling of Ka-band ocean surface backscatter is challenging due to a lack of measurements. In the framework of the NASA Earth Ventures Suborbital-3 Submesoscale Ocean Dynamics Experiment (S-MODE) mission, a Ka-Band Ocean continuous wave Doppler Scatterometer (KaBODS) built by the University of Massachusetts, Amherst (UMass) was installed on the Woods Hole Oceanographic Institution (WHOI) Air-Sea Interaction Tower. Together with ASIT anemometers, a new data set of Ka-band ocean surface backscatter measurements along with surface wind/wave and weather parameters was collected. In this work, we present the KaBODS instrument and an empirical Ka-band wind Geophysical Model Function (GMF), the so-called ASIT GMF, based on the KaBODS data collected over a period of three months, from October 2019 to January 2020, for incidence angles ranging between 40° and 68°. The ASIT GMF results are compared with an existing Ka-band wind GMF developed from data collected during a tower experiment conducted over the Black Sea. The two GMFs show differences in terms of wind speed and wind direction sensitivity. However, they are consistent in the values of the standard deviation of the model residuals. This suggests an intrinsic geophysical variability characterizing the Ka-band surface backscatter. The observed variability does not significantly change when filtering out swell-dominated data, indicating that the long-wave induced backscatter modulation is not the primary source of the KaBODS backscatter variability. We observe evidence of wave breaking events, which increase the skewness of the backscatter distribution in linear space, consistent with previous studies. Interestingly, a better agreement is seen between the GMFs and the actual data at an incidence angle of 60° for both GMFs, and the statistical analysis of the model residuals shows a reduced backscatter variability at this incidence angle. This study shows that the ASIT data set is a valuable reference for studies of Ka-band backscatter. Further investigations are on-going to fully characterize the observed variability and its implication in the wind GMF development.

Sea ice\u2013air interactions amplify multidecadal variability in the North Atlantic and Arctic region

Winter surface air temperature (Tas) over the Barents–Kara Seas (BKS) and other Arctic regions has experienced rapid warming since the late 1990s that has been linked to the concurring cooling over Eurasia, and these multidecadal trends are attributed partly to internal variability. However, how such variability is generated is unclear. Through analyses of observations and model simulations, we show that sea ice–air two-way interactions amplify multidecadal variability in sea-ice cover, sea surface temperatures (SST) and Tas from the North Atlantic to BKS, and the Atlantic Meridional Overturning Circulation (AMOC) mainly through variations in surface fluxes. When sea ice is fixed in flux calculations, multidecadal variations are reduced substantially (by 20–50%) not only in Arctic Tas, but also in North Atlantic SST and AMOC. The results suggest that sea ice–air interactions are crucial for multidecadal climate variability in both the Arctic and North Atlantic, similar to air-sea interactions for tropical climate.

Seasonal and Interannual Variability of Tidal Mixing Signatures in Indonesian Seas from High-Resolution Sea Surface Temperature

With their complex narrow passages and vigorous mixing, the Indonesian seas provide the only low-latitude pathway between the Pacific and Indian Oceans and thus play an essential role in regulating Pacific-Indian Ocean exchange, regional air-sea interaction, and ultimately, global climate phenomena. While previous investigations using remote sensing and numerical simulations strongly suggest that this mixing is tidally driven, the impacts of monsoon and El Niño Southern Oscillation (ENSO) on tidal mixing in the Indonesian seas must play an important role. Here we use high-resolution sea surface temperature from June 2002 to June 2021 to reveal monsoon and ENSO modulations of mixing. The largest spring-neap (fortnightly) signals are found to be localized in the narrow passages/straits and sills, with more vigorous tidal mixing during the southeast (boreal summer) monsoon and El Niño than that during the northwest (boreal winter monsoon) and La Niña. Therefore, tidal mixing, which necessarily responds to seasonal and interannual changes in stratification, must also play a feedback role in regulating seasonal and interannual variability of water mass transformations and Indonesian throughflow. The findings have implications for longer-term variations and changes of Pacific–Indian ocean water mass transformation, circulation, and climate.

The downward spiralling nature of the North Atlantic Subtropical Gyre

The Atlantic Meridional Overturning Circulation (AMOC) regulates the heat distribution and climate of Earth. Here we identify a new feature of the circulation within the North Atlantic Subtropical Gyre that is associated with the northward flowing component of the AMOC. We find that 70% of the water that flows northwards as part of the AMOC circulates the Gyre at least once before it can continue northwards. These circuits are needed to achieve an increase of density and depth through a combination of air-sea interaction and interior mixing processes, before water can escape the latitudes of the Gyre and join the northern upper branch of the AMOC. This points towards an important role of the Gyre circulation in determining the strength and variability of the AMOC and the northward heat transport. Understanding this newly identified role of the North Atlantic Subtropical Gyre is needed to properly represent future changes of the AMOC.

Viability of the mixed layer duct with observed dynamics

While the upper ocean of the north Pacific is largely mixed due to air-sea interaction, a 1000 km sea-soar transect shows the existence of stratification in the mixed layer that persists over many tens of kilometers. The effects of this stratification on mixed layer acoustic propagation depends on the sound speed differences across the different density layers, and observations show the sound speed varies rapidly both between and along the isopycnals. Acoustic models are used to separately quantify the importance of the mixed layer stratification and the density compensated sound speed variability on propagation in the mixed layer duct. The observed sound speed field is modeled as the superposition of three fields: a smooth background, the stratification field with slow isopycnal sound speed variability, and the remnant unstratified sound speed variation. The sound speed variation in the stratified mixed layer is attributed to internal waves and eddy filaments and in the unstratified field to ocean spice. Both types of observed sound speed variation significantly change, or completely block, mixed layer propagation. Examples are presented of blocking features in the tilt or spice fields separately, and where they exist only in the superposition of the two fields.

Sporadic Low Salinity Signals in the Oceanic Mixed Layer Observed by the Kuroshio Extension Observatory Buoy

The hourly measurements of air-sea interaction parameters made at the Kuroshio Extension Observatory (KEO) buoy since 2004 have produced an extensive dataset that can be used to understand the dynamics of the oceanic mixed-layer under extreme weather conditions. Our analysis of the KEO-buoy measurements reveals the presence of sporadic low-salinity signals (SLSSs) with duration of 1–2 days in the mixed-layer when, for example, tropical cyclones (TCs) approach. Here SLSS events are identified within the buoy data by using a flag which is set to unity when the value of normalized salinity falls below −1 (minus one). Application of this definition to the hourly time series of salinity measured at 10 m depth by the KEO buoy has allowed us to identify 244 SLSS events over the 11-year analysis period. Both winter (January-March) and spring (April-June) seasons show a peak in the composite time series of wind velocity subdiurnal variation (WVDV) near the start time of SLSS events. SLSS events can be terminated by the entrainment of saltier subsurface water parcels to the mixed-layer in response to storms. The discovery of the WVDV peaks following SLSS commencement is the reason the present study has adopted a time scale of 1-day wind velocity analysis. This temporal resolution has enabled us to identify a TC-related delay in the development of the WVDV peaks, which may represent a fundamental characteristic of the influence of TCs on these events.