Wind Stress Curl Pattern Research Articles

An idealized modeling study of the mid-latitude variability of the wind-driven meridional overturning circulation

AbstractThe frequency and latitudinal dependence of the mid-latitude wind-driven meridional overturning circulation (MOC) is studied using theory and linear and nonlinear applications of a quasi-geostrophic numerical model. Wind-forcing is varied by either changing the strength of the wind or by shifting the meridional location of the wind stress curl pattern. At forcing periods less than the first mode baroclinic Rossby wave basin crossing time scale the linear response in the mid-depth and deep ocean is in phase and opposite to the Ekman transport. For forcing periods close to the Rossby wave basin crossing time scale, the upper and deep MOC are enhanced, and the mid-depth MOC becomes phase shifted, relative to the Ekman transport. At longer forcing periods the deep MOC weakens and the mid-depth MOC increases, but eventually for long enough forcing periods (decadal) the entire wind-driven MOC spins down. Nonlinearities and mesoscale eddies are found to be important in two ways. First, baroclinic instability causes the mid-depth MOC to weaken, lose correlation with the Ekman transport, and lose correlation with the MOC in the opposite gyre. Second, eddy thickness fluxes extend the MOC beyond the latitudes of direct wind forcing. These results are consistent with several recent studies describing the four-dimensional structure of the MOC in the North Atlantic.

Generation and propagation of 21-day bottom pressure variability driven by wind stress curl in the East China Sea

Between June 2015 and June 2017, two pressure-recording inverted echo sounders (PIESs) and five current and pressure-recording inverted echo sounders (CPIESs) deployed along a section across the Kerama Gap acquired a dataset of ocean bottom pressure records in which there was significant 21-day variability (Pbot21). The Pbot21, which was particularly strong from July-December 2016, was coherent with wind stress curl (WSC) on the continental shelf of the East China Sea (ECS) with a squared coherence of 0.65 for a 3-day time lag. A barotropic ocean model demonstrated the generation, propagation, and dissipation of Pbot21. The modeled results show that the Pbot21 driven by coastal ocean WSC in the ECS propagated toward the Ryukyu Island Chain (RIC), while deep ocean WSC could not induce such variability. On the continental shelf, the Pbot21 was generated nearly synchronously with the WSC from the coastline to the southeast but dissipated within a few days due to the effect of bottom friction. The detection of Pbot21 by the moored array was dependent on the 21-day WSC patterns on the continental shelf. The Pbot21 driven southeast of the Changjiang Estuary by the WSC was detected while the Pbot21 generated northeast of the Changjiang Estuary was not.

Short-Term Response of Chlorophyll-a Concentration to Change in Sea Surface Wind Field over Mesoscale Eddy

Short-term biological responses to sea surface wind field over mesoscale eddies were investigated using hourly ocean color chlorophyll-a (chl-a) concentration data from the Geostationary Ocean Color Imager (GOCI), scatterometer wind data, and satellite sea surface temperature (SST) data. Four warm eddies were identified from SST fronts, by subjectively fitting ellipses to selected points, and anticyclonically rotating current vectors were estimated from sequential chl-a images. Scatterometer data confirmed wind speed strengthening by approximately 30% over anticyclonic eddies, regardless of wind direction, caused by stability changes in the marine atmospheric boundary layer. The modified wind speed field produced a characteristic pattern of wind stress curl and Ekman pumping (EKP) over the eddies, showing positive and negative values on the left and right sides of the upwind direction, respectively. The EKP field was divided into three components: eddy current-induced, relative vorticity gradient-induced, and crosswind SST-induced terms. Short-term changes in the chl-a concentration showed a positive relation with EKP variations over most eddies. SST-induced EKP played a significant role in the eddies for 76% of the total variations, which is much higher than that in other oceans. This study emphasizes the significant effect of SST distribution and the biological responses to changes in an EKP field in relation to air–sea interactions and feedback processes in the East Sea (Sea of Japan).

The Modeling of the North Equatorial Countercurrent in the Community Earth System Model and its Oceanic Component

AbstractThe North Equatorial Countercurrent (NECC) simulated by a coupled ocean‐atmosphere model and its oceanic component have been investigated and compared against oceanographic observations. Coupled model simulations using the Community Earth System Model version 2 are compared against ocean‐ice simulations forced by the second phase of the Coordinated Ocean‐ice Reference Experiments (CORE) data set. The modeled circulation biases behave differently to the west of and to the east of 120°W: the CORE‐forced ocean model largely underestimates the NECC transport to the west and the coupled model underestimates it to the east. Further analysis suggests that the surface wind stress and its curl is the most important forcing term for correctly simulating the NECC in both models. West of 120°W, the NECC biases in the ocean model are attributed to the southward movement of the maximum easterly trade winds in the Northern Hemisphere and the associated wind stress curl (WSC) pattern; east of 120°W, the NECC biases in the coupled model are attributed to the weak northward cross‐equatorial winds and southwestward gap winds, which lead to a weak WSC gradient at the latitude of NECC. Further analysis confirms that the WSC biases comes mainly from the zonal wind bias, which may in turn relate to the protocol of CORE‐II of adjusting reanalysis winds toward satellite data, which include the relative wind effect.

Westward mountain-gap wind jets of the northern Red Sea as seen by QuikSCAT

We analyse ten years of QuikSCAT satellite surface winds to statistically characterize the spatio-temporal variability of the westward mountain-gap wind jets over the northern Red Sea. These wind jets bring relatively cold and dry air from the Arabian Desert, increasing heat loss and evaporation over the region similar to cold-air outbreaks from mid and subpolar latitudes. QuikSCAT captures the spatial structure of the wind jets and agrees well with in situ observations from a heavily instrumented mooring in the northern Red Sea. The local linear correlations between QuikSCAT and in situ winds are 0.96 (speed) and 0.85 (direction). QuikSCAT also reveals that cross-axis winds such as the mountain-gap wind jets are a major component of the regional wind variability. The cross-axis wind pattern appears as the second (or third) mode in the four vector Empirical Orthogonal Function analyses we performed, explaining between 6% to 11% of the wind variance. Westward wind jets are typical in winter, especially in December and January, but with strong interannual variability. Several jets can occur simultaneously and cover a large latitudinal range of the northern Red Sea, which we call large-scale westward events. QuikSCAT recorded 18 large-scale events over ten years, with duration between 3 to 8 days and strengths varying from 3–4 to 9–10 m/s. These events cause large changes in the wind stress curl pattern, imposing a remarkable sequence of positive and negative curl along the Red Sea main axis, which might be a wind forcing mechanism for the oceanic mesoscale circulation.

Variability and wind forcing of ocean temperature and thermal fronts in the Slope Water region of the Northwest Atlantic

AbstractSubsurface temperatures in the Slope Water region of the Northwest Atlantic from Argo profiling floats and on the adjacent continental shelf from ship‐based measurements are compared with the latitudinal position of the Shelf‐Slope Front (SSF) and the Gulf Stream North Wall (GSNW). The Slope Water and shelf temperature anomalies at 200 m depth are in agreement for the period, 2002–2015. For the period 1978–2015, shelf temperatures are significantly correlated with the SSF position, and to a lesser extent with the GSNW position. Annual SSF position anomalies near the Grand Banks at 50°W–55°W lead anomalies to the west at 65°W–75°W by 1–2 years. Wind stress curl is compared with the annual change in the SSF and GSNW latitudinal positions, rather than with the positions directly. Changes in the mean position of the SSF are related to the wind stress curl pattern in the mid‐Atlantic, with an 8 month lag. It is suggested that a wind pattern favoring a southward shift of the SSF is associated with a southward shift of the zero‐curl line near 40°W, resulting in an expanded subpolar gyre and enhanced flow of Labrador Current Water westward from the Tail of the Grand Banks. However, changes in the GSNW position are related to an NAO‐like wind stress curl pattern in the eastern Atlantic in the winter‐spring period, in agreement with other studies. High sea surface temperatures in the Gulf of Maine and on the Scotian Shelf in recent years can be largely attributed to positive local onshore wind anomalies.

From monsoon to marine productivity in the Arabian Sea: insights from glacial and interglacial climates

Abstract. The current-climate Indian monsoon is known to boost biological productivity in the Arabian Sea. This paradigm has been extensively used to reconstruct past monsoon variability from palaeo-proxies indicative of changes in surface productivity. Here, we test this paradigm by simulating changes in marine primary productivity for eight contrasted climates from the last glacial–interglacial cycle. We show that there is no straightforward correlation between boreal summer productivity of the Arabian Sea and summer monsoon strength across the different simulated climates. Locally, productivity is fuelled by nutrient supply driven by Ekman dynamics. Upward transport of nutrients is modulated by a combination of alongshore wind stress intensity, which drives coastal upwelling, and by a positive wind stress curl to the west of the jet axis resulting in upward Ekman pumping. To the east of the jet axis there is however a strong downward Ekman pumping due to a negative wind stress curl. Consequently, changes in coastal alongshore stress and/or curl depend on both the jet intensity and position. The jet position is constrained by the Indian summer monsoon pattern, which in turn is influenced by the astronomical parameters and the ice sheet cover. The astronomical parameters are indeed shown to impact wind stress intensity in the Arabian Sea through large-scale changes in the meridional gradient of upper-tropospheric temperature. However, both the astronomical parameters and the ice sheets affect the pattern of wind stress curl through the position of the sea level depression barycentre over the monsoon region (20–150° W, 30° S–60° N). The combined changes in monsoon intensity and pattern lead to some higher glacial productivity during the summer season, in agreement with some palaeo-productivity reconstructions.

Observed Basin-Scale Response of the North Atlantic Meridional Overturning Circulation to Wind Stress Forcing

Abstract The response of the North Atlantic meridional overturning circulation (MOC) to wind stress forcing is investigated from an observational standpoint, using four time series of overturning transports below and relative to 1000 m, overlapping by 3.6 yr. These time series are derived from four mooring arrays located on the western boundary of the North Atlantic: the RAPID Western Atlantic Variability Experiment (WAVE) array (42.5°N), the Woods Hole Oceanographic Institution Line W array (39°N), RAPID–MOC/MOCHA (26.5°N), and the Meridional Overturning Variability Experiment (MOVE) array (16°N). Using modal decompositions of the analytic cross-correlation between transports and wind stress, the basin-scale wind stress is shown to significantly drive the MOC coherently at four latitudes, on the time scales available for this study. The dominant mode of covariance is interpreted as rapid barotropic oceanic adjustments to wind stress forcing, eventually forming two counterrotating Ekman overturning cells centered on the tropics and subtropical gyre. A second mode of covariance appears related to patterns of wind stress and wind stress curl associated with the North Atlantic Oscillation, spinning anomalous horizontal circulations that likely interact with topography to form overturning cells.

Response of the Southern Benguela upwelling system to fine-scale modifications of the coastal wind

We analyze the results of a regional model of the Southern Benguela upwelling system forced by wind stress fields derived from QuikSCAT observations. Two different horizontal resolutions are considered for the wind stress: QS25 and QS50, corresponding to native 25 and 50km grids, respectively. The differences between both products highlight the primary importance of fine-scale momentum fluxes for both the structure and intensity of the wind- and wind-curl-driven upwelling. Using QS25, we show that the coastal Ekman transport is reduced, leading to a warmer SST and a reduced oceanic coastal jet. QS25 finer wind stress curl patterns also favor the development of a stronger and shallower poleward undercurrent. The addition of a coastal wind correction to QS25 lets us investigate the possible implications of an imbalance between Ekman transport and Ekman pumping: a wind reduction in the coastal band often reduces the SST cooling, but the two mechanisms compensate each other when the characteristic length scales of the coastal upwelling and the orography-induced wind drop-off are similar.

Wind-induced upwelling in the Kerguelen Plateau region

Abstract. In contrast to most of the Southern Ocean, the Kerguelen Plateau supports an unusually strong spring chlorophyll (Chl a) bloom, likely because the euphotic zone in the region is supplied with higher iron concentrations. This study uses satellite wind, sea surface temperature (SST), and ocean color data to explore the impact of wind-driven processes on upwelling of cold (presumably iron-rich) water to the euphotic zone. Results show that, in the Kerguelen region, cold SSTs correlate with high wind speeds, implying that wind-mixing leads to enhanced vertical mixing. Cold SSTs also correlate with negative wind-stress curl, implying that Ekman pumping can further enhance upwelling. In the moderate to high eddy kinetic energy (EKE) regions surrounding Kerguelen, we find evidence of coupling between winds and SST gradients associated with mesoscale eddies, which can locally modulate the wind-stress curl. This coupling introduces persistent wind-stress curl patterns and Ekman pumping around these long-lived eddies, which may modulate the evolution of Chl a in the downstream plume far offshore. Close to the plateau, this eddy coupling breaks down. Kerguelen has a significant wind shadow on its downwind side, which changes position depending on the prevailing wind and which generates a wind-stress curl dipole that shifts location depending on wind direction. This leads to locally enhanced Ekman pumping for a few hundred kilometers downstream from the Kerguelen Plateau; Chl a values tend to be more elevated in places where wind-stress curl induces Ekman upwelling than in locations of downwelling, although the estimated upwelling rates are too small for this relationship to derive from direct effects on upward iron supply, and thus other processes, which remain to be determined, must also be involved in the establishment of these correlations. During the October and November (2011) KErguelen Ocean and Plateau compared Study (KEOPS-2) field program, wind conditions were fairly typical for the region, with enhanced Ekman upwelling expected to the north of the Kerguelen Islands.

A Coupled Decadal Prediction of the Dynamic State of the Kuroshio Extension System

Abstract Being the extension of a wind-driven western boundary current, the Kuroshio Extension (KE) has long been recognized as a turbulent current system rich in large-amplitude meanders and energetic pinched-off eddies. An important feature emerging from recent satellite altimeter measurements and eddy-resolving ocean model simulations is that the KE system exhibits well-defined decadal modulations between a stable and an unstable dynamic state. Here the authors show that the decadally modulating KE dynamic state can be effectively defined by the sea surface height (SSH) anomalies in the 31°–36°N, 140°–165°E region. By utilizing the SSH-based KE index from 1977 to 2012, they demonstrate that the time-varying KE dynamic state can be predicted at lead times of up to ~6 yr. This long-term predictability rests on two dynamic processes: 1) the oceanic adjustment is via baroclinic Rossby waves that carry interior wind-forced anomalies westward into the KE region and 2) the low-frequency KE variability influences the extratropical storm tracks and surface wind stress curl field across the North Pacific basin. By shifting poleward (equatorward) the storm tracks and the large-scale wind stress curl pattern during its stable (unstable) dynamic state, the KE variability induces a delayed negative feedback that can enhance the predictable SSH variance on the decadal time scales.

Contrasting the evolution between two types of El Niño in a data assimilation model

Simulation outputs were used to contrast the distinct evolution patterns between two types of El Nino. The modeled isotherm depth anomalies closely matched satellite sea surface height anomalies. Results for the El Nino Modoki (central Pacific El Nino) corresponded well with previous studies which suggested that thermocline variations in the equatorial Pacific contain an east–west oscillation. The eastern Pacific El Nino experienced an additional north–south seesaw oscillation between approximately 15° N and 15° S. The wind stress curl pattern over the west-central Pacific was responsible for the unusual manifestation of the eastern Pacific El Nino. The reason why the 1982/1983 El Nino was followed by a normal state whereas a La Nina phase developed from the 1997/1998 El Nino is also discussed. In 1997/1998, the Intertropical Convergence Zone (ITCZ) retreated faster and easterly trade winds appeared immediately after the mature El Nino, cooling the sea surface temperature in the equatorial Pacific and generating the La Nina event. The slow retreat of the ITCZ in 1982/1983 terminated the warm event at a much slower rate and ultimately resulted in a normal phase.

Regional coupled ocean–atmosphere downscaling in the Southeast Pacific: impacts on upwelling, mesoscale air–sea fluxes, and ocean eddies

Ocean–atmosphere coupling in the Humboldt Current System (HCS) of the Southeast Pacific is studied using the Scripps Coupled Ocean–atmosphere Regional (SCOAR) model, which is used to downscale the National Center for Environmental Prediction (NCEP) Reanalysis-2 (RA2) product for the period 2000–2007 at 20-km resolution. An interactive 2-D spatial smoother within the sea-surface temperature (SST)–flux coupler is invoked in a separate run to isolate the impact of the mesoscale (∼50–200 km, in the oceanic sense) SST field felt by the atmosphere in the fully coupled run. For the HCS, SCOAR produces seasonal wind stress and wind stress curl patterns that agree better with QuikSCAT winds than those from RA2. The SCOAR downscaled wind stress distribution has substantially different impacts on the magnitude and structure of wind-driven upwelling processes along the coast compared to RA2. Along coastal locations such as Arica and Taltal, SCOAR and RA2 produce seasonally opposite signs in the total wind-driven upwelling transport. At San Juan, SCOAR shows that upwelling is mainly due to coastal Ekman upwelling transport, while in RA2 upwelling is mostly attributed to Ekman pumping. Fully coupled SCOAR shows significant SST–wind stress coupling during fall and winter, while smoothed SCOAR shows insignificant coupling throughout, indicating the important role of ocean mesoscale eddies on air–sea coupling in HCS. Coupling between SST, wind speed, and latent heat flux is incoherent in large-scale coupling and full coupling mode. In contrast, coupling between these three variables is clearly identified for oceanic mesoscales, which suggests that mesoscale SST affects latent heat directly through the bulk formulation, as well as indirectly through stability changes on the overlying atmosphere, which affects surface wind speeds. The SST–wind stress and SST–heat-flux couplings, however, fail to produce a strong change in the ocean eddy statistics. No rectified effects of ocean–atmosphere coupling were identified for either the atmospheric or oceanic mean conditions, suggesting that mesoscale coupling is too weak in this region to strongly alter the basic climate state.

Different effects of tropical cyclones generated in the South China Sea and the northwest Pacific on the summer South China Sea circulation

Tropical cyclones (TCs) that affect the South China Sea (SCS) can be generated in either the SCS or the northwestern Pacific (NWP). Using satellite measurements, the Sverdrup theory and a 1.5-layer nonlinear reduced gravity model, the present paper investigates the effects of SCS and NWP TCs on the summer SCS upper layer ocean circulation. Both SCS and NWP TCs enhance the summer mean circulation pattern of the cyclonic gyre in the northern SCS and the anti-cyclonic gyre in the southern SCS. However, the effect of SCS TCs is much larger than that of NWP TCs, although the number of SCS TCs is smaller than NWP TCs. This is because the SCS TCs-induced wind stress curl pattern is favorable for enhancing the summer SCS mean circulation.

Warm and saline events embedded in the meridional circulation of the northern North Atlantic

Ocean state estimates from 1958 to 2005 from the Simple Ocean Assimilation System (SODA) system are analyzed to understand circulation between subtropical and subpolar Atlantic and their connection with atmospheric forcing. This analysis shows three periods (1960s, around 1980, and 2000s) with enhanced warm, saline waters reaching high latitudes, alternating with freshwater events originating at high latitudes. It complements surface drifter and altimetry data showing the subtropical -subpolar exchange leading to a significant temperature and salinity increase in the northeast Atlantic after 2001. The warm water limb of the Atlantic meridional overturning cell represented by SODA expanded in density/salinity space during these warm events. Tracer simulations using SODA velocities also show decadal variation of the Gulf Stream waters reaching the subpolar gyre and Nordic seas. The negative phase of the North Atlantic Oscillation index, usually invoked in such variability, fails to predict the warming and salinization in the early 2000s, with salinities not seen since the 1960s. Wind stress curl variability provided a linkage to this subtropical/subpolar gyre exchange as illustrated using an idealized two ]layer circulation model. The ocean response to the modulation of the climatological wind stress curl pattern was found to be such that the northward penetration of subtropical tracers is enhanced when amplitude of the wind stress curl is weaker than normal. In this case both the subtropical and subpolar gyres weaken and the subpolar density surfaces relax; hence, the polar front moves westward, opening an enhanced northward access of the subtropical waters in the eastern boundary current.

Impact of nearshore wind stress curl on coastal circulation and primary productivity in the Peru upwelling system

Coastal upwelling dynamics are strongly affected by alongshore wind stress and nearshore wind stress curl. A coupled physical‐biogeochemical regional model and lagrangian diagnostics are used in the Peru current system to determine how the upwelling of nutrients and the primary productivity are impacted by the spatial structure of the nearshore wind stress. Three wind stress products derived from the ERS and QuikSCAT scatterometers and a smoothed QuikSCAT field, mainly differing in nearshore wind stress curl patterns, were used. Simulations are found to produce significantly different mean surface chlorophyll distributions and show that strong upwelling‐favorable nearshore wind stress curl may locally induce a wide coastal productive zone through upwelling of nutrient‐replete waters brought by a shoaling coastal undercurrent. Using wind stress products with realistic nearshore patterns is therefore crucial for the modeling of coupled physical‐biogeochemical coastal processes.

Interdecadal Variability of the Eastward Current in the South China Sea Associated with the Summer Asian Monsoon

Abstract Based on the Simple Ocean Data Assimilation (SODA) dataset and three types of Sverdrup streamfunction, an interdecadal variability of the eastward current in the middle South China Sea (SCS) during summer is identified. Both the pattern and strength of the summer Asian monsoon wind stress curl over the SCS contribute to the interdecadal variability of this current. From 1960 to 1979, the monsoon intensified and the zero wind stress curl line shifted southward. Both the core of positive wind stress curl in the northern SCS and the negative curl in the southern SCS moved southward and thus induced a southward shift of both the southern anticyclonic and northern cyclonic gyres, resulting in a southward displacement of the eastward current associated with these two gyres. In the meantime, the southern (northern) SCS anticyclonic (cyclonic) ocean gyre weakened (strengthened) and therefore also induced the southward shift of the eastward current near the intergyre boundary. In contrast, the eastward current shifted northward from 1980 to 1998 because the monsoon relaxed and the zero wind stress curl line shifted northward. After 1998, the eastward jet moved southward again as the zero wind stress curl line shifted southward and the SCS monsoon strengthened. The eastward current identified from the baroclinic streamfunction moved about 1.7° more southward than that from the barotropic streamfunction, indicating that the meridional position of the eastward current is depth dependent.

Seasonal Evolution of Aleutian Low Pressure Systems: Implications for the North Pacific Subpolar Circulation*

Abstract The seasonal change in the development of Aleutian low pressure systems from early fall to early winter is analyzed using a combination of meteorological reanalysis fields, satellite sea surface temperature (SST) data, and satellite wind data. The time period of the study is September–December 2002, although results are shown to be representative of the long-term climatology. Characteristics of the storms were documented as they progressed across the North Pacific, including their path, central pressure, deepening rate, and speed of translation. Clear patterns emerged. Storms tended to deepen in two distinct geographical locations—the Gulf of Alaska in early fall and the western North Pacific in late fall. In the Gulf of Alaska, a quasi-permanent “notch” in the SST distribution is argued to be of significance. The signature of the notch is imprinted in the atmosphere, resulting in a region of enhanced cyclonic potential vorticity in the lower troposphere that is conducive for storm development. Later in the season, as winter approaches and the Sea of Okhotsk becomes partially ice covered and cold, the air emanating from the Asian continent leads to enhanced baroclinicity in the region south of Kamchatka. This corresponds to enhanced storm cyclogenesis in that region. Consequently, there is a seasonal westward migration of the dominant lobe of the Aleutian low. The impact of the wind stress curl pattern resulting from these two regions of storm development on the oceanic circulation is investigated using historical hydrography. It is argued that the seasonal bimodal input of cyclonic vorticity from the wind may be partly responsible for the two distinct North Pacific subarctic gyres.

Recent progress in studies of the South China Sea circulation

The South China Sea (SCS) is a semi-enclosed marginal sea with deep a basin. The SCS is located at low latitudes, where the ocean circulations are driven principally by the Asia-Australia monsoon. Ocean circulation in the SCS is very complex and plays an important role in both the marine environment and climate variability. Due to the monsoon-mountain interactions the seasonal spatial pattern of the sea surface wind stress curl is very specific. These distinct patterns induce different basin-scale circulation and gyre in summer and winter, respectively. The intensified western boundary currents associated with the cyclonic and anticyclonic gyres in the SCS play important roles in the sea surface temperature variability of the basin. The mesoscale eddies in the SCS are rather active and their formation mechanisms have been described in recent studies. The water exchange through the Luzon Strait and other straits could give rise to the relation between the Pacific and the SCS. This paper reviews the research results mentioned above.

Decadal phase change in large‐scale sea level and winds in the Indo‐Pacific region at the end of the 20th century

Satellite observations of sea surface height (SSH) and wind stress for the period of 1993–2006 reveal a near‐coherent large‐scale decadal variability in much of the Indo‐Pacific region with a phase change at the turn of the 20th century. Trade wind variations in the tropical Pacific and South Indian Ocean are anti‐correlated with each other as are SSH differences across these two basins, implying anti‐correlated variation of the subtropical cells in the two oceans. Decadal changes in large‐scale SSH in the extra‐tropics are mostly associated with well‐defined patterns of wind stress curl indicating a near‐coherent decadal variation in the strength of subtropical and subpolar gyres. Together, these variations reflect a linkage in the circulation of the Pacific and Indian Oceans via atmospheric and oceanic bridges. The phase change in the tropical Pacific tends to occur earlier than elsewhere, suggesting a potential role of the tropical Pacific in regulating decadal variability of the entire region.