Remote Wind Forcing Research Articles

Seasonal and Interannual Variability Between Upper Ocean Processes and the Slope Current in the Region Around the Cosmonauts Sea Off East Antarctica

AbstractThe impacts of large‐scale climate variability on the current system and meridional transport in the Cosmonauts Sea off East Antarctica are studied by employing the satellite‐observed absolute dynamic topography (ADT) data and reanalysis hydrographic data. Three currents converge in the Cosmonauts Sea: the Antarctic Circumpolar Current (ACC), the Weddell Gyre Eastern Branch (WGeb) and the Antarctic Slope Current (ASC) containing the Antarctic Slope Front (ASF) topographically locked in the slope region. Strong seasonal and interannual variations are associated with these currents. The ACC and ASC are both stronger in autumn and weaker in spring and summer, while the WGeb extends eastward in winter and retreats in summer. On the interannual timescale, the Southern Annular Mode (SAM) reinforces the westerlies during its positive phase, pushing the ACC southward and suppressing westward ASC, and vice versa. The results on related mechanisms suggest the significant barotropic modulations induced by the winds on ocean dynamics from both the sea surface and interior ocean. The westerlies could affect the meridional sea level gradient through Ekman transport convergence, inducing the geostrophic adjustment of currents. Moreover, the vorticity input from the wind field produces meridional water transport under the topographic and planetary β‐effects, potentially influencing the structure of the ASF and associated ASC. This frontal adjustment is superimposed on the background barotropic variations and causes strong local responses of the currents to the remote wind forcing, which indicates a propagation of variability signals from large‐scale barotropic circulations to frontal‐scale baroclinic currents in the ocean interior.

The weakening AMOC under extreme climate change

Changes in the Atlantic Meridional Overturning Circulation (AMOC) in the quadrupled CO2 experiments conducted under the sixth Coupled Model Intercomparison Project (CMIP6) are examined. Increased CO2 triggers extensive Arctic warming, causing widespread melting of sea ice. The resulting freshwater spreads southward, first from the Labrador Sea and then the Nordic Seas, and proceeds along the eastern coast of North America. The freshwater enters the subpolar gyre north of the separated Gulf Stream, the North Atlantic Current. This decreases the density gradient across the current and the current weakens in response, reducing the inflow to the deepwater production regions. The AMOC cell weakens in tandem, first near the North Atlantic Current and then spreading to higher and lower latitudes. This contrasts with the common perception that freshwater caps the convection regions, stifling deepwater production; rather, it is the inflow to the subpolar gyre that is suppressed. Changes in surface temperature have a much weaker effect, and there are no consistent changes in local or remote wind forcing among the models. Thus an increase in freshwater discharge, primarily from the Labrador Sea, is the precursor to AMOC weakening in these simulations.

Surface circulation in the Gulf of Thailand from remotely sensed observations: seasonal and interannual timescales

Abstract. The Gulf of Thailand (GoT), a shallow semi-enclosed basin located in the western equatorial Pacific, undergoes much wind variabilities on both seasonal and interannual timescales that produce complex surface circulation. The local Ekman pumping modifies sea level in the northern GoT, while remote wind forcing influences sea level variability at the GoT western boundary, potentially through the coastal trapped Kelvin waves. The importance of the Ekman current on ageostrophic current is also important; the stronger influence of the Ekman current is found toward the southern part of the GoT. The GoT circulation reverses its direction seasonally following the monsoon wind reversal which is well-captured by the most dominant complex empirical orthogonal function explaining 28 % of the total circulation variance. During the monsoon transition, a strong meridional current along the western boundary that connects to the flow at the GoT southeastern entrance is observed. This implies high exchange between the GoT and the South China Sea and thus modification of the GoT water. On the interannual timescale, the GoT circulation is directly impacted by both the El Niño–Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD). Interestingly, the two climate modes have different spatial influences on the GoT circulation. The IOD dominates the interannual current along the GoT western boundary and the southern boundary of the observing domain (8∘ N), while the ENSO correlates with that in the interior. The results highlight the complex circulation pattern as being contributed by different dynamics over each region of the GoT.

Water Exchange Between the Gulf of Ob and the Kara Sea During Ice-Free Seasons: The Roles of River Discharge and Wind Forcing

The Gulf of Ob is among the largest estuaries in the World Ocean in terms of area, watershed basin, and freshwater discharge. In this work, we describe the roles of river discharge and wind forcing on the water exchange between the Gulf of Ob and the Kara Sea during ice-free seasons. This work is based on the extensive in situ measurements performed during 10 oceanographic surveys in 2007–2019. Due to large river runoff (∼530 km3 annually) and low tidal forcing (<0.5 m/s), the estuarine processes in the Gulf of Ob during the ice-free season are generally governed by gravitational circulation. Local wind forcing significantly affects general estuarine circulation and mixing only in rare cases of strong winds (∼10 m/s). On the other hand, remote wind forcing over the central part of the Kara Sea regularly intensifies estuarine—sea water exchange. Eastern winds in the central part of the Kara Sea induce upwelling in the area adjacent to the Gulf of Ob, which increases the barotropic pressure gradient between the gulf and the open sea. As a result, intense and distant (120–170 km) inflows of saline water to the gulf occur as compared to the average conditions (50–70 km). Remote wind forcing has a far stronger impact on saltwater intrusion into the Gulf of Ob than the highly variable river discharge rate. In particular, saltwater reaches the shallow central part of the gulf only during upwelling-induced intense inflows. In the other periods (even under low discharge conditions), fresh river water occupies this area from surface to bottom. The upwelling-induced intense inflows occur on average during a quarter of days (July to October) when the gulf is free of ice. They substantially increase the productivity of phytoplankton communities in the gulf and modify the taxa ratio toward the increase of brackish water species and the decrease of freshwater species.

Interannual Variability in Sea Surface Height at Southern Midlatitudes of the Indian Ocean

AbstractThis study examines interannual variability in sea surface height (SSH) at southern midlatitudes of the Indian Ocean (10°–35°S). Our focus is on the relative role of local wind forcing and remote forcing from the equatorial Pacific Ocean. We use satellite altimetry measurements, an atmospheric reanalysis, and a one-dimensional wave model tuned to simulate observed SSH anomalies. The model solution is decomposed into the part driven by local winds and that driven by SSH variability radiated from the western coast of Australia. Results show that variability radiated from the Australian coast is larger in amplitude than variability driven by local winds in the central and eastern parts of the south Indian Ocean at midlatitudes (between 19° and 33°S), whereas the influence from eastern boundary forcing is confined to the eastern basin at lower latitudes (10° and 17°S). The relative importance of eastern boundary forcing at midlatitudes is due to the weakness of wind stress curl anomalies in the interior of the south Indian Ocean. Our analysis further suggests that SSH variability along the west coast of Australia originates from remote wind forcing in the tropical Pacific, as is pointed out by previous studies. The zonal gradient of SSH between the western and eastern parts of the south Indian Ocean is also mostly controlled by variability radiated from the Australian coast, indicating that interannual variability in meridional geostrophic transport is driven principally by Pacific winds.

Mean Conditions and Seasonality of the West Greenland Boundary Current System near Cape Farewell

AbstractThe structure, transport, and seasonal variability of the West Greenland boundary current system near Cape Farewell are investigated using a high-resolution mooring array deployed from 2014 to 2018. The boundary current system is comprised of three components: the West Greenland Coastal Current, which advects cold and fresh Upper Polar Water (UPW); the West Greenland Current, which transports warm and salty Irminger Water (IW) along the upper slope and UPW at the surface; and the Deep Western Boundary Current, which advects dense overflow waters. Labrador Sea Water (LSW) is prevalent at the seaward side of the array within an offshore recirculation gyre and at the base of the West Greenland Current. The 4-yr mean transport of the full boundary current system is 31.1 ± 7.4 Sv (1 Sv ≡ 106m3s−1), with no clear seasonal signal. However, the individual water mass components exhibit seasonal cycles in hydrographic properties and transport. LSW penetrates the boundary current locally, through entrainment/mixing from the adjacent recirculation gyre, and also enters the current upstream in the Irminger Sea. IW is modified through air–sea interaction during winter along the length of its trajectory around the Irminger Sea, which converts some of the water to LSW. This, together with the seasonal increase in LSW entering the current, results in an anticorrelation in transport between these two water masses. The seasonality in UPW transport can be explained by remote wind forcing and subsequent adjustment via coastal trapped waves. Our results provide the first quantitatively robust observational description of the boundary current in the eastern Labrador Sea.

Variations of the North Equatorial Current Bifurcation and the SSH in the Western Pacific Associated With El Niño Flavors

AbstractThis study presents different variations of the North Equatorial Current Bifurcation (NECB) in the development of the canonical El Niño, the Central Pacific El Niño I (CP‐I El Niño), and the Central Pacific El Niño II (CP‐II El Niño) in autumn and investigates the dynamic mechanism by analyzing Simple Ocean Data Assimilation data sets. It is suggested that the meridional shifts of the NECB are negatively related to the sea surface height (SSH) near the coast of the Philippines. The NECB shifts northward in autumn of the development phase of both canonical and CP‐II El Niño events, whereas it moves insignificantly for CP‐I El Niño events. During the development phase of canonical and CP‐II El Niños, the remote positive wind stress curl anomalies in the central and western tropical Pacific between 12°N and 15°N are responsible for the variations of the NECB, which can induce the westward Rossby waves of negative SSH anomalies and thus result in the northward shift of the NECB several months later. However, the local wind stress curl anomalies near the Philippine coast are significantly negative and result in locally positive SSH anomalies for CP‐I El Niños. Such anomalous positive SSHs are offset by the negative counterparts that result from the remote wind forcing in the western tropical Pacific. Therefore, the meridional shifts of the NECB are not significant in autumn for CP‐I El Niños. A one and a half layer‐reduced gravity model is used to conduct experiments to further confirm the above results.

Interannual Variability of the Natal Pulse

AbstractSatellite altimetry data and high‐resolution model output are used to investigate the mechanism of interannual variations of the solitary meander in the Agulhas Current, called the Natal Pulse. It is shown that most of the Natal Pulses are triggered by anticyclonic eddies originating from the Southeast Madagascar Current (SEMC) and anticyclonic eddies of the Mozambique Channel are the secondary source. In addition to the barotropic conversion suggested by previous studies, the advection of eddy kinetic energy (EKE) plays a statistically significant role in the growth of the Natal Pulse. The number of anticyclonic eddies arriving at the Natal Bight largely explains the interannual variations in the Natal Pulse. The barotropic conversion from the SEMC, whose interannual variations are likely related to the remote wind forcing, is the main EKE source and corresponds well with the interannual variations of anticyclonic eddies generated off the southern coast of Madagascar. It is also shown that the interannual variations of the Natal Pulse are linked to large‐scale wind variability in the southern Indian Ocean.

Interannual variation of the South China Sea circulation during winter: intensified in the southern basin

Surface geostrophic current derived from altimetry remote sensing data, and current profiles observed from in-situ Acoustic Doppler Current Profilers (ADCP) mooring in the northern South China Sea (NSCS) and southern South China Sea (SSCS) are utilized to study the kinetic and energetic interannual variability of the circulation in the South China Sea (SCS) during winter. Results reveal a more significant interannual variation of the circulation and water mass properties in the SSCS than that in the NSCS. Composite ananlysis shows a significantly reduced western boundary current (WBC) and a closed cyclonic eddy in the SSCS at the mature phase of El Nino event, but a strong WBC and an unclosed cyclonic circulation in winter at normal or La Nina years. The SST is warmer while the subsurface water is colder and fresher in the mature phase of El Nino event than that in the normal or La Nina years in the SSCS. Numerical experiments and energy analysis suggest that both local and remote wind stress change are important for the interannual variation in the SSCS, remote wind forcing and Kuroshio intrusion affect the circulation and water mass properties in the SSCS through WBC advection.

The role of remote wind forcing in the subinertial current variability in the central and northern parts of the South Brazil Bight

Data analysis of continental shelf currents and coastal sea level, together with the application of a semi-analytical model, are used to estimate the importance of remote wind forcing on the subinertial variability of the current in the central and northern areas of the South Brazil Bight. Results from both the data analysis and from the semi-analytical model are robust in showing subinertial variability that propagates along-shelf leaving the coast to the left in accordance with theoretical studies of Continental Shelf Waves (CSW). Both the subinertial variability observed in along-shelf currents and sea level oscillations present different propagation speeds for the narrow northern part of the SBB (~ 6–7 m/s) and the wide central SBB region (~ 11 m/s), those estimates being in agreement with the modeled CSW propagation speed. On the inner and middle shelf, observed along-shelf subinertial currents show higher correlation coefficients with the winds located southward and earlier in time than with the local wind at the current meter mooring position and at the time of measurement. The inclusion of the remote (located southwestward) wind forcing improves the prediction of the subinertial currents when compared to the currents forced only by the local wind, since the along-shelf-modeled currents present correlation coefficients with observed along-shelf currents up to 20% higher on the inner and middle shelf when the remote wind is included. For most of the outer shelf, on the other hand, this is not observed since usually, the correlation between the currents and the synoptic winds is not statistically significant.

Origins of Eddy Kinetic Energy in the Bay of Bengal

AbstractBy analyzing satellite observational data and ocean general circulation model experiments, this study investigates the key processes that determine the spatial distribution and seasonality of intraseasonal eddy kinetic energy (EKE) within the Bay of Bengal (BOB). It is revealed that a complicated mechanism involving both local and remote wind forcing and ocean internal instability is responsible for the generation and modulation of EKE in this region. High‐level EKE mainly resides in four regions: east of Sri Lanka (Region 1), the western BOB (Region 2), northwest of Sumatra (Region 3), and the coastal rim of the BOB (Region 4). The high EKE levels in Regions 1 and 2 are predominantly produced by ocean internal instability, which contributes 90% and 79%, respectively. Prominent seasonality is also observed in these two regions, with higher EKE levels in boreal spring and fall due to enhanced instability of the East Indian Coast Current and the Southwest Monsoon Current, respectively. In contrast, ocean internal instability contributes 49% and 52% of the total EKE in Regions 3 and 4, respectively, whereas the atmospheric forcing of intraseasonal oscillations (ISOs) also plays an important role. ISOs produce EKE mainly through wind stress, involving both the remote effect of equatorial winds and the local effect of monsoonal winds. Equatorial‐origin wave signals significantly enhance the EKE levels in Regions 3 and 4, in the form of reflected Rossby waves and coastal Kelvin waves, respectively. The local wind forcing effect through Ekman pumping also has a significant contribution in Regions 3 and 4 (24% and 22%, respectively).

Response of the Internal Wave Field to Remote Wind Forcing by Tropical Cyclones

AbstractIn the tropical North Atlantic, mean winds introduce relatively little energy into the internal wave field, but hurricanes act as very energetic sources for near-inertial waves. In addition to the eventlike passage of such tropical cyclones, changes in the wind speed north of the trade wind system induce a seasonal cycle in surface swell, with potential implications for the high-frequency part of the internal wave field. Using a 5-yr mooring time series in the interior of the tropical North Atlantic at 16°N, the temporal variability of internal wave energy south of the main hurricane track in different frequency bands is studied, and the magnitude of its variability, along with possible energy transfer mechanisms, is analyzed. The results show that changes in near-inertial energy are dominated by the passage of internal waves generated by hurricanes centered several hundred kilometers north of the mooring. The major role of hurricanes in the generation of near-inertial waves is also seen in an extended slab model that takes the horizontal divergence of the near-inertial current field at the mixed layer base into account. A seasonal cycle is observed in the energy at the high-frequency end (frequencies above 6 cpd) of the internal wave spectrum. It is not in phase with the near-inertial energy variability but covaries with changes in the local surface waves. These high-frequency internal waves are most energetic at times when large-amplitude surface swell with long periods and correspondingly long wavelengths is observed.

Reverse Estuarine Circulation Due to Local and Remote Wind Forcing, Enhanced by the Presence of Along‐Coast Estuaries

AbstractEstuarine exchange flow governs the interaction between oceans and estuaries and thus plays a large role in their biogeochemical processes. This study investigates the variability in estuarine exchange flow due to offshore oceanic conditions including upwelling/downwelling, and the presence of a river plume offshore (from a neighboring estuary). We address these processes via numerical simulations at the mouth of the Salish Sea, a large estuarine system in the Northeast Pacific. An analysis of the Total Exchange Flow indicates that during the upwelling season, the exchange flow is fairly consistent in magnitude and oriented in a positive (into the estuary at depth and out at the surface) direction. However, during periods of downwelling favorable winds, the exchange flow shows significantly more variability including multiple reversals, consistent with observations, and surface intrusions of the Columbia River plume which originates 250 km to the south. Numerical along‐strait momentum budgets show that the exchange flow is forced dominantly by the pressure gradients, particularly the baroclinic. The pressure gradient is modified by Coriolis and sometimes advection, highlighting the importance of geostrophy and local adjustments. In experiments conducted without the offshore river plume, reversals still occur but are weaker, and the baroclinic pressure gradient plays a reduced role. These results suggest that estuaries along strong upwelling coastlines should experience significant modulation in the exchange flow during upwelling versus downwelling conditions. Additionally, they highlight the importance of nearby estuaries impacting one‐another, not only in terms of connectivity, but also altering the exchange flow.

Multi-decadal variations of the South Indian Ocean subsurface temperature influenced by Pacific Decadal Oscillation

Over recent decades, a strong subsurface cooling trend in the South Indian Ocean (SIO) occurred, despite a continuous sea surface warming. Previous studies suggest this long-term (around 1960–2000) cooling trend is mainly driven by remote Pacific atmospheric forcing or local Indian Ocean (IO) forcing. This study reveals that the dominant driver of the SIO subsurface cooling trend in different periods is closely related to the phase of Pacific Decadal Oscillation (PDO). Our results suggest that the local IO wind forcing is responsible for the majority of the subsurface cooling trend and overwhelms a weak warming trend induced by the remote tropical Pacific wind forcing during the negative-phase period of PDO during 1960–76. However, this situation reverses during the PDO positive-phase period during 1977–98. Our analysis suggests that the PDO strengthens/weakens the tropical Pacific trade winds during negative/positive phase periods. Furthermore, the multi-decadal variations in the western Pacific induced by PDO impact the SIO subsurface temperature via baroclinic Rossby waves.

On the Drivers and Predictability of Seasonal-to-Interannual Variations in Regional Sea Level

Abstract Observations and eddy-permitting ocean model simulations are used to evaluate the drivers of sea level variability associated with 15 modes of climate variability covering the Atlantic, Pacific, Indian, and Southern Oceans. Sea level signals are decomposed into barotropic, steric, and inverted barometer contributions. Forcings are decomposed into surface winds, buoyancy fluxes, and Ekman pumping. Seasonal-to-interannual sea level variability in the low latitudes is governed almost entirely by the thermosteric response to wind forcing associated with tropical modes of climate variability. In the extratropics, changes to dynamic sea level associated with atmospheric modes of variability include a substantial barotropic response to wind forcing, particularly over the continental shelf seas. However, wind-driven steric changes are also important in some locations. On interannual time scales, wind-forced steric changes dominate, although heat and freshwater fluxes are important in the northwest Atlantic, where low-frequency sea level variations are associated with changes in the Atlantic meridional overturning circulation. Using the version 3 of the Met Office Decadal Prediction System (DePreSys3), the predictability of large-scale dynamic sea level anomalies on seasonal-to-interannual time scales is evaluated. For the first year of the hindcast simulations, DePreSys3 exhibits skill exceeding persistence over large regions of the Pacific, Atlantic, and Indian Oceans. Skill is particularly high in the tropical Indo-Pacific because of the accurate initialization and propagation of thermocline depth anomalies associated with baroclinic adjustments to remote wind forcing. Skill in the extratropics is hindered by the limited predictability of wind anomalies associated with modes of atmospheric variability that dominate local and/or barotropic responses.

Remote forcing of subsurface currents and temperatures near the northern limit of the California Current System

AbstractLocal and remote wind forcing of upwelling along continental shelves of coastal upwelling regions play key roles in driving biogeochemical fluxes, including vertical net fluxes of carbon and nutrients. These fluxes are responsible for high primary productivity, which in turn supports a lucrative fishery in these regions. However, the relative contributions of local versus remote wind forcing are not well quantified or understood. We present results of coherence analyses between currents at a single mooring site (48.5°N, 126°W) in the northern portion of the California Current System (CalCS) from 1989 to 2008 and coincident time series of North America Regional Reanalysis (NARR) 10 m wind stress within the CalCS (36–54°N, 120–132°W). The two‐decade‐long current records from the three shallowest depths (35, 100, and 175 m) show a remote response to winds from south as far as 36°N. In contrast, only temperatures at the deepest depth (400 m) show strong coherences with remote winds. Weaker local wind influence is observed in both the currents and 400 m temperatures but is mostly due to the large spatial coherence within the wind field itself. Lack of coherence between distal winds and the 400 m currents suggests that the temperature variations at that depth are driven by vertical motion resulting from poleward travelling coastal trapped waves (CTWs). Understanding the effects of remote forcing in coastal upwelling regions is necessary for determining the occurrence and timing of extreme conditions in coastal oceans, and their subsequent impact on marine ecosystems.

Spatial and temporal variability of the velocity and hydrographic structure in a weakly stratified system, Broad Sound, Casco Bay, Maine

AbstractThe velocity and hydrographic structure across Broad Sound, a north‐south orientated subsystem of Casco Bay, ME that lacks continuous coastal boundaries, were characterized using velocity observations from two moorings in late summer/fall of 2013 and velocity and density observations from a repeat‐transect ship survey conducted over a tidal cycle during the same period. At tidal time scales, the system is dominated by a barotropic semidiurnal standing wave with a west to east decrease in tidal amplitude and relatively minimal phase change across the majority of the transect. The stratification (vertical differences of 0.5–1.0 kg m−3) was generally laterally uniform and stronger during the flood phase which is hypothesized to result from stronger offshore stratification. The mean circulation had strong lateral shear with inflow over the deepest point in the bathymetric cross section and eastern slope and outflow over the western slope. There was also vertical shearing of the horizontal velocities with stronger northward (or northward trending) velocities at depth. The depth‐averaged subtidal fluctuations were relatively small (∼2–3 cm s−1) and uncorrelated between mooring sites suggesting the vertically uniform current response associated with remote wind forcing is of limited importance. On the other hand, the depth‐dependent velocity fluctuations at the subtidal time scale were, in large part (∼36–72%), driven by wind forcing. The net flux ratio, a means of quantifying the relative importance of the vertical and lateral shear in the flow field, was typically ∼0.44 indicating the structure of the local wind response favored vertically sheared flow.

Vertical structure and variation of currents observed in autumn in the Korea Strait

To observe vertical structure and temporal variations of currents in the Tsushima Warm Current region of the Korea Strait, a moored buoy system was deployed in autumn 2009. The moored buoy system measured vertical profiles of current, temperature, and salinity for 24 days and a background hydrographic survey was performed. Along-strait northeastward currents were dominant in the upper layer (8–35 m). The mean current veers counterclockwise from 48 m to 74 m as much as 50°, and its speed is reduced with depth. There were distinct northward onshore currents near the bottom (65–80 m). It was demonstrated that thermal wind relation holds in the inclined pycnocline layer, which generates the counterclockwise veering current structure. Density gradient along the strait is a main factor producing the cross-strait onshore current component below the upper-layer and the cross-strait density gradient reduces the along-strait current component with depth. Previous studies have never focused on the effect of the along-strait density structure on current structure. The first Empirical Orthogonal Function mode (CM1) of current variability explains 70% of local current variations and its vertical structure is close to the mean current structure. The correlation analysis among variations of CM1 current, slope of sea level anomaly (SSLA) and local wind anomaly revealed that the variation of CM1 current is mainly related to the variation of SSLA across the strait (c-SSLA), which is known to be controlled by remote and local wind forcing. Similarity between vertical structures of mean and CM1 current suggests that thermal wind relation is the main dynamics maintaining the counterclockwise turning of CM1 current below the upper layer although the upperlayer CM1 current is controlled by c-SSLA through barotropic geostrophic relation. Time series of temperature and salinity indicate that the thermohaline front between Korean Coastal Water and Tsushima Warm Current Water meanders in time and migrates over the mooring station back and forth. The front meandering and migration also affect the local SSLA and CM1 current variations in autumn in the Korea Strait.

Spatial patterns of warming off Western Australia during the 2011 Ningaloo Niño: Quantifying impacts of remote and local forcing

In austral summer 2011, an unprecedented Ningaloo Niño event occurred off the west coast of Australia, with sea surface temperature anomalies reaching 5°C and significant impacts on marine ecosystems. In this study, a high resolution (~2km) hydrodynamic model (Regional Ocean Modeling System) is used to simulate the variations in the near-surface temperature in the region from 2009 through mid-2011. Model results indicate that the peak temperatures in the broad mid-west coast of Australia during the event are predominantly due to poleward advection of warmer, tropical water (≈2/3 contribution). In addition, positive air–sea heat flux into the ocean also contributes (≈1/3 contribution) to the rise in temperature. The anomalous advection of warm water is caused by changes in the poleward flowing Leeuwin Current due to both local and remote wind forcing. In early 2011, the Leeuwin Current intensified owing to remote forcing by the equatorial easterly wind anomalies in the Pacific Ocean associated with the 2010–2011 La Niña. In addition, the southerly winds off the west coast of Australia weakened, allowing the Leeuwin Current to further intensify in speed at the peak of the event. Concurrently, the inshore, equatorward Capes Current was suppressed and reversed direction. The poleward flow over the shelf contributed to near-shore warming in contrast to cooling by upwelling and equatorward advection from the Capes Current in previous years.

DESIGN AND IMPLEMENTATION OF THE OCEANOGRAPHIC MODELING AND OBSERVATION NETWORK (REMO) FOR PHYSICAL OCEANOGRAPHY STUDIES AND OCEAN FORECASTING

This paper is concerned with the planning, implementation and some results of the Oceanographic Modeling and Observation Network, named REMO, for Brazilian regional waters. Ocean forecasting has been an important scientific issue over the last decade due to studies related to climate change as well as applications related to short-range oceanic forecasts. The South Atlantic Ocean has a deficit of oceanographic measurements when compared to other ocean basins such as the North Atlantic Ocean and the North Pacific Ocean. It is a challenge to design an ocean forecasting system for a region with poor observational coverage of in-situ data. Fortunately, most ocean forecasting systems heavily rely on the assimilation of surface fields such as sea surface height anomaly (SSHA) or sea surface temperature (SST), acquired by environmental satellites, that can accurately provide information that constrain major surface current systems and their mesoscale activity. An integrated approach is proposed here in which the large scale circulation in the Atlantic Ocean is modeled in a first step, and gradually nested into higher resolution regional models that are able to resolve important processes such as the Brazil Current and associated mesoscale variability, continental shelf waves, local and remote wind forcing, and others. This article presents the overall strategy to develop the models using a network of Brazilian institutions and their related expertise along with international collaboration. This work has some similarity with goals of the international project Global Ocean Data Assimilation Experiment OceanView (GODAE OceanView).