Pacific tropical–extratropical thermocline water mass exchanges in the NCAR Coupled Climate System Model v.3

In this study we document how model biases in extratropical surface wind and precipitation, due to ocean–atmosphere coupling, are communicated to the equatorial Pacific thermocline through Pacific Subtropical Cell (STC) pathways. We compare the simulation of climate mean Pacific Subtropical Cells (STCs) in the NCAR Community Climate System Model version 3 (CCSM3) to observations and to an uncoupled ocean simulation (the ocean component of the CCSM3 forced by observed wind stress and surface fluxes). We use two versions of the CCSM3 with atmospheric resolution of 2.8° (T42) and 1.4° (T85) to investigate whether the climate mean STCs are sensitive to the resolution of the atmospheric model.Since STCs provide water that maintains the equatorial thermocline, we first document biases in equatorial temperature and salinity fields. We then investigate to what extent these biases are due to the simulation of extratropical–tropical water mass exchanges in the coupled models. We demonstrate that the coupled models’ cold and fresh bias in the equatorial thermocline is due to the subduction of significantly fresher and colder water in the South Pacific. This freshening is due to too much precipitation in the South Pacific Convergence Zone. Lagrangian trajectories of water that flows to the equatorial thermocline are calculated to demonstrate that the anomalously large potential vorticity barriers in the coupled simulations in both the North and South Pacific prevent water in the lower thermocline from reaching the equator. The equatorial thermocline is shown to be primarily maintained by water that subducts in the subtropical South Pacific in both the coupled and uncoupled simulations. It is shown that the zonally integrated transport convergence at the equator in the subsurface branch of the climate mean STCs is well simulated in the uncoupled ocean model. However, coupling reduces the net equatorward pycnocline transport by 4 Sv at 9°S and 1 Sv at 9°N. An increase in the atmospheric resolution from T42 to T85 results in more realistic equatorial trades and off-equatorial convergence zones.     

ENSO循环相关的海洋异常信号传播特征及其机制

通过分析最新的海洋模式同化资料(EstimatingtheCirculationandClimateoftheOcean,EC CO),研究了ENSO循环相关的海洋异常信号在太平洋中的传播过程。研究发现,导致ENSO位相变化的温跃层异常信号主要从北太平洋西传而来,该区与赤道东太平洋相反的温跃层异常信号到达西太暖池区,再从西太暖池沿赤道传到东太平洋,可使ENSO向反位相发展。该异常信号沿赤道东传过程中热带西南太平洋也会出现类似的温跃层异常变化,但是随着异常信号东移和从南太平洋东边界10°S左右传来的反异常信号入侵,热带西南太平洋的异常信号逐渐减弱并消失。稳定性分析表明,北太平洋较大面积区域存在斜压不稳定性或正压不稳定性,有利于ENSO相关的温跃层异常信号以Rossby波形式有效地西传;而在南太平洋,不稳定区的面积较小,且主要局限于海盆东侧,因而传播较弱,这样就造成了ENSO信号在太平洋南、北半球的非对称传播。一般来说,ENSO信号主要在以赤道波导区、东边界、北太平洋纬向区域和西边界组成的回路中循环,在南半球的传播不明显。     

The 1997–1998 oceanic El Niño signal along the southeast and northeast Pacific boundaries—an altimetric view

Changes in the sea surface heights (SSH) and geostrophic currents along the eastern boundaries of the Pacific (North, Central and South America) are examined during the 1997–1998 El Niño using altimeter data and proxy winds. These show that ‘symmetric’ SSH signals left the equator and propagated into both Hemispheres in two episodes, with primary periods of high equatorial SSH during May–July and October–December 1997. These are the ‘distant signals’ from the mid-latitude perspective. As the signals spread poleward in each Hemisphere, their loss of symmetry demonstrates the degree to which they were altered by topographic features, local winds, and/or local currents. The first four EOFs are calculated for 2-D SSH fields in 10° wide strips along the eastern margins (60°N–60°S) and extending out along the equator from the coast to 110°W. These account for approximately 40% of the overall variability and represent the main features of the seasonal cycles and El Niño interannual variability. Snapshots of the 2-D SSH fields depict the structure of the El Niño signal at different phases of its evolution.     

南北向压强梯度力与太平洋赤道潜流的关系

赤道潜流（the Equatorial Undercurrent： EUC）对于大洋环流和全球气候变化有着重要的作用。赤道海区,随着科氏力逐渐趋向于0,地转平衡无法维持,赤道流系无法用地转理论描述。在很多研究中,ENSO、温跃层、海表高度、赤道风应力分布以及其他相关海气要素成为潜流研究的重点要素;压强可以视为温、盐、密、深的复杂关系映射,然而较少有研究将关注重点放在南北向压强梯度力上（the Northward Pressure Gradient： NGT）。在此,本文揭示了南北向压强梯度力的特定函数形式（the Function of Northward Pressure gradient： FNP）与赤道潜流的一个诊断关系。基于原始方程和尺度分析方法,我们得出了该关系的表达形式。结果表明：贝塔效应可能是造成FNP与赤道潜流密切相关的重要影响因子;赤道潜流的垂向结构部分受限于FNP的结构分布;对于赤道潜流来说,南北向压强梯度力相较于东西向压强梯度力更为重要。     

The circulation of the eastern tropical Pacific: A review

During the 1950s and 1960s, an extensive field study and interpretive effort was made by researchers, primarily at the Scripps Institution of Oceanography, to sample and understand the physical oceanography of the eastern tropical Pacific. That work was inspired by the valuable fisheries of the region, the recent discovery of the equatorial undercurrent, and the growing realization of the importance of the El Niño phenomenon. Here we review what was learned in that effort, and integrate those findings with work published since then as well as additional diagnoses based on modern data sets.Unlike the central Pacific, where the winds are nearly zonal and the ocean properties and circulation are nearly independent of longitude, the eastern tropical Pacific is distinguished by wind forcing that is strongly influenced by the topography of the American continent. Its circulation is characterized by short zonal scales, permanent eddies and significant off-equatorial upwelling. Notably, the Costa Rica Dome and a thermocline bowl to its northwest are due to winds blowing through gaps in the Central American cordillera, which imprint their signatures on the ocean through linear Sverdrup dynamics. Strong annual modulation of the gap winds and the meridional oscillation of the Intertropical Convergence Zone generates a Rossby wave, superimposed on the direct forcing, that results in a southwestward-propagating annual thermocline signal accounting for major features of observed thermocline depth variations, including that of the Costa Rica Dome, the Tehuantepec bowl, and the ridge–trough system of the North Equatorial Countercurrent (NECC). Interannual variability of sea surface temperature (SST) and altimetric sea surface height signals suggests that the strengthening of the NECC observed in the central Pacific during El Niño events continues all the way to the coast, warming SST (by zonal advection) in a wider meridional band than the equatorially trapped thermocline anomalies, and pumping equatorial water poleward along the coast.The South Equatorial Current originates as a combination of equatorial upwelling, mixing and advection from the NECC, and Peru coastal upwelling, but its sources and their variability remain unresolved. Similarly, while much of the Equatorial Undercurrent flows southeast into the Peru Undercurrent and supplies the coastal upwelling, a quantitative assessment is lacking. We are still unable to put together the eastern interconnections among the long zonal currents of the central Pacific.     

Altimeter-derived surface circulation in the large-scale NE Pacific Gyres. : Part 2: 1997–1998 El Niño anomalies

Changes in the sea surface heights (SSH) and geostrophic transports in the NE Pacific are examined during the 1997–1998 El Niño using altimeter data, sea level pressure (SLP) fields, proxy winds and satellite sea surface temperature (SST). Most of the signal occurs along the boundaries of the basin from Panama to the Alaska Peninsula. Changes in the SSH and alongshore transports along the boundaries are caused both by propagation of signals from the south (stronger between the equator and the Gulf of California) and by local and basin-scale winds (stronger between the Pacific Northwest and the Alaska Peninsula). Two periods of high SSH occur at the equator, May–July 1997 and October 1997–January 1998. The first coastal SSH signal moved quickly polewards to approximately 24°N in early June, then stalled and moved farther north during transient events in July–September. Large-scale wind forcing combined with the equatorial signals during the second period of high equatorial SSH (Fall 1997) to move the high SSH and poleward transports quickly around the Alaska Gyre. A connection between the boundary currents and the interior North Pacific developed as part of the large-scale response to the basin-scale winds, after changes in the boundaries. Decreases in anomalies of SSH and poleward transports began in January 1998 south of 40°N and in February 1998 farther north.     

Seasonal cooling and blooming in tropical oceans

The relative importance of tropical pelagic algal blooms in not yet fully appreciated and the way they are induced not well understood. The tropical Atlantic supports pelagic blooms together equivalent to the North Atlantic spring bloom. These blooms are driven by thermocline tilting, curl of wind stress and eddy upwelling as the ocean responds to intensified basin-scale winds in boreal summer. The dimensions of the Pacific Ocean are such that seasonal thermocline tilting does not occur, and nutrient conditions are such that tilting might not induce bloom, in any case. Divergence at the equator is a separate process that strengthens the Atlantic bloom, is more prominent in the eastern Pacific, and in the Indian Ocean induces a bloom only in the western part of the ocean. Where western jet currents are retroflected from the coast off Somalia and Brazil, eddy upwelling induces prominent blooms. In the eastward flow of the northern equatorial countercurrents, positive wind curl stress induces Ekman pumping and the induction of algal blooms aligned with the currents. Some apparent algal bloom, such as that seen frequently in CZCS images westwards from Senegal, must be due to interference from airborne dust.     

赤道中印度洋上层环流结构与季节变化特征分析

本文通过分析RAMA印度洋观测浮标系统锚系ADCP实测资料,对赤道中印度洋上层海流季节变化进行了研究。研究结果表明,0°,80.5°E纬向流垂向剖面呈现上150m层一致的东向流,而经向流在100m以浅呈现表层向北次表层向南的翻转流结构。赤道中印度洋上层纬向流季节信号被半年周期的东向射流Wyrtki Jets(WJs)所控制。WJs发生于季风方向转换的季节,4—5月份较弱,10—11月份较强。赤道中印度洋上层经向流年周期信号显著。北半球夏季与冬季分别出现风应力旋度驱动的Sverdrup南向流与北向流。本文结论为赤道中印度洋上层环流季节变化特征的研究提供了观测角度的支持。     

The Rossby wave as a key mechanism of Indian Ocean climate variability

We analyze the time-longitude structure of composite cases from model-assimilated ocean data in the period 1958–1998, following on from earlier work by Huang and Kinter (J. Geophys. Res. 107(C11) (2002) 3199) that studied east–west thermocline variability in the Indian Ocean. Our analysis focuses on the Rossby wave signal along the thermocline ridge in the tropical SW Indian Ocean (10°S, 60–80°E), where wind stress curl is important. Anomalous winds in the equatorial east Indian Ocean force successive Rossby waves westward at speeds of 0.1 m s⁻¹±30%. With a wavelength of 7000 km, the period of oscillation is in the range 1.9–5.2 years. The Indian Ocean Rossby wave is partially resonant with the global influence of the El Nino–Southern Oscillation, except during quasi-biennial rhythm. The presence of the Rossby wave offers potential predictability for east–west atmospheric circulation systems and climate that affect resources in countries surrounding the Indian Ocean.     

Thermostads and circulation in the upper layer of the Atlantic Ocean

There are three major permanent thermostads with roughly the same potential densities in the upper layer of the Atlantic Ocean. One is the thermostad of the 13°C Water in the equatorial Atlantic. The original type of the 13°C Water is formed in the thermocline in the eastern sector of the South Atlantic subtropical gyre by vertical mixing of dense, low-salinity water from the winter outcrop farther south and overlying less dense, high-salinity water. There might also be a lateral contribution of relatively high-salinity water from the Indian Ocean. The original 13°C Water thus formed is transported northwestward along the northern edge of the subtropical gyre and fed into the North Brazilian Current, which flows equatorward along the coast of Brazil. In the region of the equator, the Equatorial Undercurrent and the subsurface North and South Equatorial countercurrents branch off from the North Brazilian Current and carry the 13°C Water eastward to the thermostad region. Vertical mixing does not explain the development of the thermostad, but is found to be essential in determining the ultimate characteristics of the 13°C Water. The other two thermostads are those of the 18°C Water in the Sargasso Sea and the Subantarctic Mode Water in the western South Atlantic. Unlike the 13°C Water, both of these mode waters are formed as thermostads in the surface layer by winter convection, but vertical mixing in the subtropical gyres may play a role in determining their characteristics. All the three thermostads appear to be required to balance the system of flows in opposing directions.     

Spatial and temporal structure of Tropical Pacific interannual variability in 20th century coupled simulations

Tropical Pacific interannual variability is examined in nine state-of-the-art coupled climate models, and compared with observations and ocean analyses data sets, the primary focus being on the spatial structure and spectral characteristics of El Niño-Southern Oscillation (ENSO). The spatial patterns of interannual sea surface temperature (SST) anomalies from the coupled models are characterized by maximum variations displaced from the coast of South America, and generally extending too far west with respect to observations. Thermocline variability is characterized by dominant modes that are qualitatively similar in all the models, and consistent with the “recharge oscillator” paradigm for ENSO. The meridional scale of the thermocline depth anomalies is generally narrower than observed, a result that can be related to the pattern of zonal wind stress perturbations in the central-western equatorial Pacific. The wind stress response to eastern equatorial Pacific SST anomalies in the models is narrower and displaced further west than observed. The meridional scale of the wind stress can affect the amount of warm water involved in the recharge/discharge of the equatorial thermocline, while the longitudinal location of the wind stress anomalies can influence the advection of the mean zonal temperature gradient by the anomalous zonal currents, a process that may favor the growth and longer duration of ENSO events when the wind stress perturbations are displaced eastwards. Thus, both discrepancies of the wind stress anomaly patterns in the coupled models with respect to observations (narrow meridional extent, and westward displacement along the equator) may be responsible for the ENSO timescale being shorter in the models than in observations. The examination of the leading advective processes in the SST tendency equation indicates that vertical advection of temperature anomalies tends to favor ENSO growth in all the CGCMs, but at a smaller rate than in observations. In some models it can also promote a phase transition. Longer periods tend to be associated with thermocline and advective feedbacks that are in phase with the SST anomalies, while advective tendencies that lead the SST anomalies by a quarter cycle favor ENSO transitions, thus leading to a shorter period.     

A review of the shelf-slope circulation along Australia’s southern shelves: Cape Leeuwin to Portland

A review is presented of the ocean circulation along Australia’s southern shelves and slope. Uniquely, the long, zonal shelf is subject to an equatorward Sverdrup transport that gives rise to the Flinders Current - a small sister to the world’s major Western Boundary Currents. The Flinders Current is strongest near the 600 m isobath where the current speeds can reach 20 cm/s and the bottom boundary layer is upwelling favourable. It is larger in the west but likely intermittent in both space and time due to possibly opposing winds, thermohaline circulation and mesoscale eddies. The Flinders Current may be important to deep upwelling within the ubiquitous canyons of the region.During winter, the Leeuwin Current and local winds act to drive eastward currents that average up to 20-30 cm/s. The currents associated with the intense coastal-trapped wave-field (6-12 day band) are of order 25-30 cm/s and can peak at 80-90 cm/s. Wintertime winds and cooling also lead to downwelling to depths of 200 m or more and the formation of dense coastal water within the Great Australian Bight and the South Australian Sea. Within the Great Australian Bight, the thermohaline circulation associated with this dense water is unknown, but may enhance the eastward shelf-edge, South Australian Current. The dense salty water formed within Spencer Gulf is known to cascade as a gravity current to depths of 200 m off Kangaroo Island. This dense water outflow and meanders in the shelf circulation also fix the locations of a sequence of quasi-permanent mesoscale eddies between the Eyre Peninsula and Portland.During summer, the average coastal winds reverse and surface heating leads to the formation of warm water in the western Great Australian Bight and the South Australian Sea. No significant exchange of shelf water and gulf water appears to occur due to the presence of a dense, nutrient-rich (sub-surface) pool that is upwelled off Kangaroo Island. The winds lead to weak average coastal currents (<10 cm/s) that flow to the north-west. In the Great Australian Bight, the wind stress curl can lead to an anticyclonic circulation gyre that can result in shelf-break downwelling in the western Great Australian Bight and the formation of the eastward, South Australian Current. In the east, upwelling favourable winds and coastal-trapped waves can lead to deep upwelling events off Kangaroo Island and the Bonney Coast that occur over 3-10 days and some 2-4 times a season. The alongshore currents here can be large (∼40 cm/s) and the vertical scales of upwelling are of order 150 m (off Kangaroo Island) and 250 m (off the Bonney Coast).Increasing evidence suggests that El Nino events (4-7 year period) can have a major impact on the winter and summer circulation. These events propagate from the Pacific Ocean and around the shelf-slope wave-guide of West Australia and into the Great Australian Bight. During winter El Nino events, the average shelf currents may be largely shut-down. During summer, the thermocline may be raised by up to 150 m. The nature and role of tides and surface waves is also discussed along with uncertainties in the general circulation and future research.     

Direct measurements of deep current at 162°E south of the equator in the Melanesian Basin: a trial to detect a cross-equatorial deep western boundary current

We conducted 1-year-long mooring observations four times below 2000?m, slightly south of the equator (2°39?? to 4°35??S) at 162°E in the Melanesian Basin in order to detect the southward deep western boundary return current crossing the equator. Contrary to our initial expectation of the deep flow scheme in the equatorial western boundary region, the observed results indicated a fairly complicated flow configuration. We analyzed the results with the help of a high-resolution model simulation. The ensemble average of the horizontal flow at each level near the deep western boundary indicates a significant westward flow at 2000 and 2250?m, with an insignificant southward component at 2500 and 2750?m. The annual mean meridional transports are very small (>1?Sv) and insignificant, with an ensemble-averaged value of 0.3?Sv (southward) ±0.4?Sv at most. Combining this with high-resolution model results, it is deduced that the southward transport of the deep western boundary current (DWBC) leaving the equator may be smaller than those obtained by low-resolution models, because of trapping of its fairly large fraction in the equatorial zone. Annual-scale flow patterns are classified into several categories, mainly based on the meridional-flow dominating or the zonal-flow dominating pattern. A case of the meridional-flow dominating patterns may possibly capture an annual-scale variability of DWBC, because its meridional transport variation, though somewhat weak, is consistent with that simulated. The zonal-flow dominating regime includes two types: long-lasting, almost steady westward flows and long-term zonal flow oscillations. The former seems to comprise well-known zonally elongated and meridionally narrow structures of the zonal flow beneath the thermocline in the equatorial region. The ensemble-averaged flow mentioned above is dominated by this type at the upper two levels 2000 and 2250?m, with total westward transport of 1.6?±?0.7?Sv. The latter type seems to be a manifestation of the vertically propagating equatorial annual Rossby waves.     

Why was the 2008 Indian Ocean Dipole a short-lived event?

In this paper, the role of equatorial oceanic waves in affecting the evolution of the 2008 positive Indian Ocean Dipole (IOD) event was evaluated using available observations and output from a quasi-analytical linear wave model. It was found that the 2008 positive IOD was an early matured and abruptly terminated event: developed in April, matured in July, and diminished in September. During the development and the maturation of the 2008 positive IOD event, the wind-forced Rossby waves played a dominant role in generating zonal current anomalies in the western equatorial Indian Ocean, while a complex interplay between the wind-forced upwelling Kelvin waves and the eastern-boundary-generated Rossby waves accounted for most of the variability in the eastern basin. The latter induced eastward zonal current anomalies near the eastern boundary during the peak phase of the event. The 2008 positive IOD event was abruptly terminated in mid-July. We found that there were strong eastward zonal currents in mid-July, though the surface wind anomalies in the eastern basin continued to be westward (upwelling favorable). Our analysis shows that these eastward zonal currents mainly resulted from the easternboundary-generated upwelling Rossby waves, although the contribution from the wind-forced downwelling Kelvin waves was not negligible. These eastward zonal currents terminated the zonal heat advection and provided a favorable condition for surface heat flux to warm the eastern basin.     

Effects of horizontal mixing on the upper ocean temperature in the equatorial Pacific Ocean

The influence of horizontal mixing on the thermal structure of the equatorial Pacific Ocean is examined based on a sigma coordinate model.In general,the distributions of the temperature and currents si...     

Wind and current patterns in an arctic coast Lagoon

The response of wind-drift currents to the prevailing summer wind regime is reported for Simpson Lagoon on the Beaufort Sea (Arctic Ocean) coast of Alaska. Wind and current measurements were taken over the period July 17 to October 20 and August 11 to September 18, 1972, respectively, at a site eastward of the Colville River delta. Mean wind speeds and the frequency of occurrence of westerly storms tend to increase from July to October. Prevailing currents within the lagoon are towards the W to NW driven by the prevailing northeasterly winds. Relatively rapid reversals of current direction occur in response to alternating easterly and westerly winds. Cross correlations of power spectra of the filtered E-W components of the lagoon current record with the concurrent wind data gave a periodicity of 4–5 days at a 70% level of coherence. A linear correlation of −0·83 was obtained between the E-W components of the filtered current record and the wind record, and net water transport (from a progressive current vector analysis) over this period was determined to be towards the WNW with a mean vector velocity of 10·6 cm/sec.     

Unusual large-scale phytoplankton blooms in the equatorial Pacific

Unusual large-scale accumulations of phytoplankton occurred across 10,000 km of the equatorial Pacific during the 1998 transition from El Niño to La Niña. The forcing and dynamics of these phytoplankton blooms were studied using satellite-based observations of sea surface height, temperature and chlorophyll, and mooring-based observations of winds, hydrography and ocean currents. During the bloom period, the thermocline (nutricline) was anomalously shallow across the equatorial Pacific. The relative importance of processes that enhanced nutrient flux into the euphotic zone differed between the western and eastern regions of the blooms. In the western bloom region, the important vertical processes were turbulent vertical mixing and wind-driven upwelling. In contrast, the important processes in the eastern bloom region were wave-forced shoaling of nutrient source waters directly into the euphotic zone, along-isopycnal upwelling, and wind-driven upwelling. Advection by the Equatorial Undercurrent spread the largest bloom 4500 km east of where it began, and advection by meridional currents of tropical instability waves transported the bloom hundreds of kilometers north and south of the equator. Many processes influenced the intricate development of these massive biological events. Diverse observations and novel analysis methods of this work advance the conceptual framework for understanding the complex dynamics and ecology of the equatorial Pacific.     

Interdecadal Variations of ENSO Signals and Annual Cycles Revealed by Wavelet Analysis

Interdecadal variations of El Niño/Southern Oscillation (ENSO) signals and annual cycles appearing in the sea surface temperature (SST) and zonal wind in the equatorial Pacific during 1950–1997 are studied by wavelet, empirical orthogonal function (EOF) and singular value decomposition (SVD) analyses. The typical timescale of ENSO is estimated to be about 40 months before the late 1970s and 48–52 months after that; the timescale increased by about 10 months. The spatial pattern of the ENSO signal appearing in SST also changed in the 1970s; before that, the area of strong signal spread over the extratropical regions, while it is confined near the equator after that. The center of the strongest signal shifted from the central and eastern equatorial Pacific to the South American coast at that time. These SST fluctuations near the equator are associated with fluctuations of zonal wiond, whose spatial pattern also shifted considerably eastward at that time. In the eastern equatorial Pacific, amplitudes of annual cycles of SST are weak in El Niño years and strong in La Niña years. This relation is not clear, however, in the 1980s and 1990s.     

有界赤道大洋波包解及其年际年代际变率

Linearized shallow water perturbation equations with approximation in an equatorial β plane are used to obtain the analytical solution of wave packet anomalies in the upper bounded equatorial ocean. The main results are as follows. The wave packet is a superposition of eastward travelling Kelvin waves and westward travelling Rossby waves with the slowest speed, and satisfies the boundary conditions of eastern and western coasts, respectively.The decay coefficient of this solution to the north and south sides of the equator is inversely proportional only to the phase velocity of Kelvin waves in the upper water. The oscillation frequency of the wave packet, which is also the natural frequency of the ocean, is proportional to its mode number and the phase velocity of Kelvin waves and is inversely proportional to the length of the equatorial ocean in the east-west direction. The flow anomalies of the wave packet of Mode 1 most of the time appear as zonal flows with the same direction. They reach the maximum at the center of the equatorial ocean and decay rapidly away from the equator, manifested as equatorially trapped waves. The flow anomalies of the wave packet of Mode 2 appear as the zonal flows with the same direction most of the time in half of the ocean, and are always 0 at the center of the entire ocean which indicates stagnation, while decaying away from the equator with the same speed as that of Mode 1. The spatial structure and oscillation period of the wave packet solution of Mode 1 and Mode 2 are consistent with the changing periods of the surface spatial field and time coefficient of the first and second modes of complex empirical orthogonal function(EOF)analysis of flow anomalies in the actual equatorial ocean. This indicates that the solution does exist in the real ocean, and that El Ni?o-Southern Oscillation(ENSO) and Indian Ocean dipole(IOD) are both related to Mode 2.After considering the Indonesian throughflow, we can obtain the length of bounded equatorial ocean by taking the sum of that of the tropical Indian Ocean and the tropical Pacific Ocean, thus this wave packet can also explain the decadal variability(about 20 a) of the equatorial Pacific and Indian Oceans.     

The 20°C isotherm depth and sea level in the western equatorial pacific

A high correlation exists between the 20°C isotherm depth at the north equatorial countercurrent trough of dynamic topography and the monthly mean sea level at Truk Island. The meridional topography of the main thermocline depth can be used to monitor the strength of the equatorial currents, in the same manner as dynamic heights and sea levels at oceanic islands are used.