Effects Of Thermocline Research Articles

Impacts of the Thermocline Feedback Uncertainty on El Niño Simulations in the Tropical Pacific

AbstractAs a key dynamic element of the Bjerknes feedback mechanism, the thermocline effect (TE) is critically important to El Niño modeling. In this study, the potential influence of TE‐related parametric uncertainties on El Niño is investigated using the conditional nonlinear optimal parametric perturbation (CNOP) method based on an intermediate coupled model (ICM). The optimal perturbation of the TE‐related parameter (OTEP), which substantially affects El Niño simulations, is estimated through the CNOP approach. Results reveal that the El Niño simulation is highly sensitive to the TE uncertainty in the eastern equatorial Pacific, with OTEP‐induced simulation errors demonstrating an El Niño‐like growth trend. On one hand, as indicated by the simulated El Niño intensity, the uncertainty in the TE in the eastern region can easily affect the strength of the Bjerknes feedback‐related thermocline effect and atmospheric circulation. On the other hand, the enhanced TE is highly favored to accelerate the growth of the SST error due to the air–sea interaction, thus severely affecting the El Niño simulations. Therefore, adequately representing the TE in the equatorial eastern Pacific is emphasized for effectively improving El Niño simulations.

Innovative cryogenic Phase Change Material (PCM) based cold thermal energy storage for Liquid Air Energy Storage (LAES) – Numerical dynamic modelling and experimental study of a packed bed unit

Electrical energy storage represents a necessary link between sustainability goals and the enhancement of intermittent renewable energy sources penetration in electricity grids. Liquid air energy storage (LAES) is a promising large scale thermo-mechanical energy storage system whose round trip efficiency is largely affected by the performance of the sub-thermal energy storages. The high grade cold storage (HGCS) is by far the most important due to the crucial thermodynamic recovery of the waste cold stream released by the liquid air regasification process. LAES pilot plant and pre-commercial demonstrator, as well as the vast majority of the theoretical and experimental analysis found in literature studies, currently design to store that exergetically valuable cold source in sensible heat (SH) thermal energy storage, economically efficient but low energy density solution. Conversely, phase change material (PCM) has the potential to store a larger amount of energy using the same amount of storage volume. The objective of the present work is to numerically and experimentally investigate the thermal behaviour of a novel cryogenic HGCS packed bed filled by PCM and determine how the novelty introduced affects the LAES thermodynamic and economic performance compared to the SH configuration. To this end, a simplified transient one-dimensional numerical model to simulate the charging and discharging phase of the HGCS system has been developed and successfully validated against experimental results provided by literature for SH medium and an experimental campaign carried out on a novel lab scale HGCS at TESLAB@NTU for PCM, representing a unicum in literature for both PCM and LAES applications. The numerical results have shown that the introduction of a PCM in the HGCS mitigates the thermocline effect shown in SH configuration ensuring: a) longer discharge phase by means of the thermal buffer phenomena triggered by the phase change process and b) lower specific consumption compared to SH configuration (0.272 vs 0.330 kWhe/kgLA) due to a lower time average outlet temperature of the heat transfer fluid during the HGCS discharge, corresponding to LAES charge phase. From an economic perspective, the decrease of the time average specific consumptions results in a notable payback period inferior to 3 years, making the economic investment considerably attractive.

Model parameter-related optimal perturbations and their contributions to El Niño prediction errors

Errors in initial conditions and model parameters (MPs) are the main sources that limit the accuracy of ENSO predictions. In addition to exploring the initial error-induced prediction errors, model errors are equally important in determining prediction performance. In this paper, the MP-related optimal errors that can cause prominent error growth in ENSO predictions are investigated using an intermediate coupled model (ICM) and a conditional nonlinear optimal perturbation (CNOP) approach. Two MPs related to the Bjerknes feedback are considered in the CNOP analysis: one involves the SST-surface wind coupling ( $${\alpha _\tau }$$ ), and the other involves the thermocline effect on the SST ( $${\alpha _{Te}}$$ ). The MP-related optimal perturbations (denoted as CNOP-P) are found uniformly positive and restrained in a small region: the $${\alpha _\tau }$$ component is mainly concentrated in the central equatorial Pacific, and the $${\alpha _{Te}}$$ component is mainly located in the eastern cold tongue region. This kind of CNOP-P enhances the strength of the Bjerknes feedback and induces an El Nino- or La Nina-like error evolution, resulting in an El Nino-like systematic bias in this model. The CNOP-P is also found to play a role in the spring predictability barrier (SPB) for ENSO predictions. Evidently, such error growth is primarily attributed to MP errors in small areas based on the localized distribution of CNOP-P. Further sensitivity experiments firmly indicate that ENSO simulations are sensitive to the representation of SST-surface wind coupling in the central Pacific and to the thermocline effect in the eastern Pacific in the ICM. These results provide guidance and theoretical support for the future improvement in numerical models to reduce the systematic bias and SPB phenomenon in ENSO predictions.

Idealized Experiments for Optimizing Model Parameters Using a 4D-Variational Method in an Intermediate Coupled Model of ENSO

Large biases exist in real-time ENSO prediction, which can be attributed to uncertainties in initial conditions and model parameters. Previously, a 4D variational (4D-Var) data assimilation system was developed for an intermediate coupled model (ICM) and used to improve ENSO modeling through optimized initial conditions. In this paper, this system is further applied to optimize model parameters. In the ICM used, one important process for ENSO is related to the anomalous temperature of subsurface water entrained into the mixed layer (Te), which is empirically and explicitly related to sea level (SL) variation. The strength of the thermocline effect on SST (referred to simply as “the thermocline effect”) is represented by an introduced parameter, αTe. A numerical procedure is developed to optimize this model parameter through the 4D-Var assimilation of SST data in a twin experiment context with an idealized setting. Experiments having their initial condition optimized only, and having their initial condition plus this additional model parameter optimized, are compared. It is shown that ENSO evolution can be more effectively recovered by including the additional optimization of this parameter in ENSO modeling. The demonstrated feasibility of optimizing model parameters and initial conditions together through the 4D-Var method provides a modeling platform for ENSO studies. Further applications of the 4D-Var data assimilation system implemented in the ICM are also discussed.

An improved simulation of the 2015 El Ni\xf1o event by optimally correcting the initial conditions and model parameters in an intermediate coupled model

Large uncertainties exist in real-time predictions of the 2015 El Niño event, which have systematic intensity biases that are strongly model-dependent. It is critically important to characterize those model biases so they can be reduced appropriately. In this study, the conditional nonlinear optimal perturbation (CNOP)-based approach was applied to an intermediate coupled model (ICM) equipped with a four-dimensional variational data assimilation technique. The CNOP-based approach was used to quantify prediction errors that can be attributed to initial conditions (ICs) and model parameters (MPs). Two key MPs were considered in the ICM: one represents the intensity of the thermocline effect, and the other represents the relative coupling intensity between the ocean and atmosphere. Two experiments were performed to illustrate the effects of error corrections, one with a standard simulation and another with an optimized simulation in which errors in the ICs and MPs derived from the CNOP-based approach were optimally corrected. The results indicate that simulations of the 2015 El Niño event can be effectively improved by using CNOP-derived error correcting. In particular, the El Niño intensity in late 2015 was adequately captured when simulations were started from early 2015. Quantitatively, the Niño3.4 SST index simulated in Dec. 2015 increased to 2.8 °C in the optimized simulation, compared with only 1.5 °C in the standard simulation. The feasibility and effectiveness of using the CNOP-based technique to improve ENSO simulations are demonstrated in the context of the 2015 El Niño event. The limitations and further applications are also discussed.

Effects of artificial thermocline deepening on sedimentation rates and microbial processes in the sediment

Global warming affects the thermal stratification of freshwater lakes, and thus can lead to thermocline deepening. To follow the direct and indirect effects of thermocline shifts on processes at the sediment–water interface, the thermoclines in six of twelve lake enclosures were deepened by pumping warm surface water below the thermocline. Hypolimnetic temperatures increased and oxygen concentrations decreased due to the treatment. Path modeling suggests a correlation of the treatment to epilimnetic chlorophytes and hypolimnetic diatoms, while the dominant cryptophytes and cyanobacteria remained unaffected by the treatment. Sedimentation rates, ranging between 0.1 and 1.9 g m−2 day−1 per enclosure, correlated strongly with the selected phytoplankton groups, but were not affected by the treatment. Concentrations of elements (Ba, Mn, S, Sr), nutrients (NH4 +, PO4 3−, Si), and greenhouse gases (CO2, CH4, N2O) in the upper centimeter of the sediment were not affected by the hypolimnetic changes. Methane and carbon dioxide emission from the enclosures to the atmosphere were negligible. Bacterial and viral abundance in sediments were not affected by the treatment. Results suggest that the benthic ecosystem remains unaffected by slight changes in the pelagial. Further, we conclude that short-term warming does not increase greenhouse gas emissions from temperate, deep, oligo-mesotrophic lakes.

The roles of atmospheric wind and entrained water temperature (Te) in the second-year cooling of the 2010\u201312 La Ni\xf1a event

An intermediate coupled model (ICM) yields a successful real-time prediction of the sea surface temperature (SST) evolution in the tropical Pacific during the 2010–12 La Niña event, whereas many other coupled models fail. It was previously identified that the thermocline effect on the SST (including vertical advection and mixing), as represented by water temperature entrained into the mixed layer (Te) and its relationship with the thermocline fluctuation, is an important factor that affects the second-year cooling in mid-late 2011. Because atmospheric wind forcing is also important to ENSO processes, its role is investigated in this study within the context of real-time prediction of the 2010–12 La Niña event using the ICM in which wind stress anomalies are calculated using an empirical model as a response to SST anomalies. An easterly wind anomaly is observed to persist over the western-central Pacific during 2010–11, which acts to sustain a horse shoe-like Te pattern connecting large negative subsurface thermal anomalies in the central-eastern regions off and on the equator. Sensitivity experiments are conducted using the ICM to demonstrate how its SST predictions are directly affected by the intensity of wind forcing. The second-year cooling in 2011 is not predicted to occur in the ICM if the easterly wind anomaly intensity is weakly represented below certain levels; instead, a surface warming can emerge in 2011, with weak SST variability. The results of the current study indicate that the intensity of interannual wind forcing is equally important to SST evolution during 2010–11 compared with that of the thermocline effect. To correctly predict the observed La Niña conditions in the fall of 2011, the ICM needs to adequately represent the intensity of both the wind forcing and the thermocline effects.

Effects of Experimental Thermocline and Oxycline Deepening on Methylmercury Bioaccumulation in a Canadian Shield Lake

Environmental disturbances like deforestation or climate change may influence lake thermal and oxic stratification, thereby modifying cycles of contaminants such as mercury (Hg). In a lake naturally separated into three basins, the thermocline and oxycline of an experimental basin were deepened by 4 and 3 m, respectively, to study the effect on the methylmercury (MeHg) accumulation. This treatment decreased hypolimnetic MeHg concentration by approximately 90%, zooplankton concentrations by 30 to 50%, and in some fish by 45%. A multiple linear regression indicated that oxycline depth significantly influenced hypolimnetic MeHg concentrations, with no significant effect of thermocline depth, anoxic water volume, interface area of oxic-anoxic water, and sediment area in contact with anoxic water. Fish MeHg decline varied, with a greater response by low oxygen-tolerant bullhead. Increased pelagic primary and secondary production likely caused zooplankton and fish MeHg decreases via algal and growth dilution. Environmental changes leading to oxycline deepening are therefore predicted to cause a decrease in MeHg bioaccumulation in similar Canadian Shield lakes. If associated ecosystem impacts related to the deepening treatment are deemed acceptable, then this experiment provides a potential remediation method for small lakes confronted with MeHg accumulation.

Thermocline deepening and mixing alter zooplankton phenology, biomass and body size in a whole‐lake experiment

Summary Summer thermal stratification is thought to be one of the key structuring physical factors for north temperate lake zooplankton. Shifts associated with climate change may lead to altered thermocline depths in stratified lakes through changes to (i) wind stress and associated water column mixing or (ii) air temperature and precipitation. The effects of thermocline deepening through these two scenarios were simulated in a whole‐lake experiment to assess the effects on the phenology, biomass and mean body size of the zooplankton. The thermocline of a three‐basin dimictic lake was deepened to 7–8 m in one basin using a lake mixer. Through heat transfer, the thermocline of the adjacent basin was deepened to 6–7 m, while the third basin served as an unmanipulated control (4–5 m deep thermocline). Zooplankton community dynamics were followed weekly in a control year and in two experimental years. A before‐after‐control‐impact (BACI) statistical protocol was used to assess the effects of two treatments: Deepening and Deepening+Mixing. Thermocline depth was the main factor influencing zooplankton changes. The biomass and late‐season dominance by smaller‐bodied and more fish‐evasive species were favoured by deepening, leading to a decline in mean community body size, but an increase in total biomass. While many effects could be attributed to thermocline deepening, additional or exacerbated responses were observed when mixing was also present. This resulted mostly from a loss of the hypolimnetic refuge for zooplankton, which accentuated predation effects by warm‐water fish on larger cladocerans. Overall, our treatments promoted top‐down (predation) effects that increased over the 2 years of the experiment.

Effects of thermocline deepening on lake plankton communities

Theory predicts, and some evidence demonstrates that in lakes, the depth of the thermocline can have a large structural influence on the spatial distribution, and strongly influences the composition of plankton communities. However, experimental assessments of responses of the planktonic food web to thermocline depth have not yet been done at the whole-basin scale. We conducted an experiment wherein we artificially lowered the thermocline in an isolated basin of a three-basin lake, maintaining another isolated basin as a control. The vertical distribution and taxonomic composition of both phytoplankton and zooplankton were monitored throughout the summer months. Greater phytoplankton production, especially in the epilimnion, attributable mainly to increases in the chlorophytes was observed with thermocline deepening, but at the deepest thermoclines, production was limited. Total zooplankton biomass was unaffected by thermocline depth, suggesting top-down control by predators. Zooplankton biomass peaks were less pronounced in the manipulated basin, but tended to follow the thermocline whether at its normal position or as it was deepened. Zooplankton composition was significantly altered by large increases in densities of predatory cyclopoid copepods and rotifers; taxa commonly found in turbulent environments. Overall, both phytoplankton and zooplankton communities demonstrated important shifts in structure and composition in response to thermocline deepening.

Distribution of suspended particulate matter in the northern Bohai Bay in summer and its relation with thermocline

Field observations of suspended particulate matter (SPM) in the Bohai Bay, China have not been widely reported. The aim of this paper is to describe the horizontal and vertical distribution of mass and volume concentrations of SPM, respectively, based on observed data at 312 stations in the northern Bohai Bay during summer of 2006. A numerical model ECOMSED coupled with a sediment transport module was also established to further discuss the mechanism of the thermocline effect on the vertical distribution of SPM. The mass concentrations of SPM exhibited high inshore values and low offshore values in the horizontal distribution; while in the vertical direction, characteristics of the volume concentration of SPM can be divided into two types: one with a sharp peak at depth of 10–15 m and another without. The peak value at the depth of the thermocline was resulted from concentrated phytoplankton. A numerical experiment further displayed that the thermocline can also prevent particles from being resuspended upward.

East‐west asymmetry in nonlinear internal waves from Luzon Strait

The nonhydrostatic Regional Ocean Modeling System is applied to study the effects of thermocline shoaling/deepening, bathymetry, and asymmetric modulated tides on the soliton growth to the west and east of Luzon Strait in the South China Sea and western Pacific Ocean. Luzon Strait comprises a shallow east ridge and a deep west ridge, and its interaction with barotropic tidal currents yields strong westward internal tides that disperse into solitons. Satellite imagery indicates that the westward solitons are more numerous and better defined than the eastward solitons. The model results show that the eastward solitons are 45%, 39%, 28%, and 23% smaller than the westward solitons due to asymmetric modulated barotropic tides at the east ridge, a deeper Pacific Ocean, westward thermocline shoaling related to the Kuroshio current, and internal tide resonance in a double ridge configuration, respectively. Due to the westward location of the Kuroshio, little thermocline deepening occurs east of the east ridge. Hence, the influence of thermocline deepening on counteracting eastward soliton growth is small. The Kuroshio mainly enhances westward soliton growth. The dispersion of internal tides into solitons is governed by the balance between the nonlinearity parameter on the one hand and the nonhydrostatic and Coriolis dispersions on the other. It is shown that this balance favors soliton growth for thermocline shoaling, while it counters it for a deeper ocean. A series of double ridge experiments is performed, in which the distance between the ridges and the height of the west ridge are varied. For a semidiurnal tidal forcing and two Gaussian ridges separated by 100 km, barotropic to baroclinic energy conversion is enhanced at both ridges, causing larger westward internal tides and solitons. The combination of Coriolis forcing, thermocline shoaling, and a double ridge configuration enhances the distinctiveness of the so‐called type a and b solitons when a modulated tide occurs.

Is model parameter error related to a significant spring predictability barrier for El Niño events? Results from a theoretical model

Within a theoretical ENSO model, the authors investigated whether or not the errors superimposed on model parameters could cause a significant “spring predictability barrier” (SPB) for El Nino events. First, sensitivity experiments were respectively performed to the air-sea coupling parameter, α and the thermocline effect coefficient µ. The results showed that the uncertainties superimposed on each of the two parameters did not exhibit an obvious season-dependent evolution; furthermore, the uncertainties caused a very small prediction error and consequently failed to yield a significant SPB. Subsequently, the conditional nonlinear optimal perturbation (CNOP) approach was used to study the effect of the optimal mode (CNOP-P) of the uncertainties of the two parameters on the SPB and to demonstrate that the CNOP-P errors neither presented a unified season-dependent evolution for different El Nino events nor caused a large prediction error, and therefore did not cause a significant SPB. The parameter errors played only a trivial role in yielding a significant SPB. To further validate this conclusion, the authors investigated the effect of the optimal combined mode (i.e. CNOP error) of initial and model errors on SPB. The results illustrated that the CNOP errors tended to have a significant season-dependent evolution, with the largest error growth rate in the spring, and yielded a large prediction error, inducing a significant SPB. The inference, therefore, is that initial errors, rather than model parameter errors, may be the dominant source of uncertainties that cause a significant SPB for El Nino events. These results indicate that the ability to forecast ENSO could be greatly increased by improving the initialization of the forecast model.

Effects of thermocline on performance of underwater glider’s power system propelled by ocean thermal energy

The thermal glider’s changeable volume produces propelling force to power the glider’s descending and ascending through the thermocline. The different depth, thickness, and intensity of the thermocline at different seasons and locations affect the working processes of the glider’s power system. Based on the enthalpy method, a mathematical model of the underwater glider’s power system was established and the time efficiency of operation was introduced, so that the effects of different thermoclines on the underwater glider’s power system were analyzed theoretically. The simulation result shows that the thermocline affects the transition time of the phase change processes of working fluids within the thermal engine tubes. There exist the threshold values of the thermocline’s depth and upper thickness for the power system’s operation. A depth or upper thickness of the thermocline less than the corresponding threshold leads the power system to work abnormally. To keep the power system working efficiently, a glider must be kept in warm surface water for a certain period before it moves through cold water, so that the time efficiency of operation is reduced. A less time efficiency of operation is unfavorable to the thermal glider to penetrate through the ocean currents.

Effect of the internal tide on midfrequency transmission loss in the Shallow Water 2006 Experiment.

Nonlinear internal waves depress the high‐gradient region of the thermocline. After the waves have passed, it may take several hours for the thermocline to rise to its prewave level. To examine consequent acoustic effects, two acoustic data sets collected 18–19 August in SW06 were analyzed with one at a fixed range of 550 m and the other along a tow track out to 8.1 km. Both data sets allow the effects of the rising thermocline on acoustic propagation to be examined over a range of temporal and spatial scales. Signals transmitted are in the midfrequency band 1.5–10.5 kHz. The gradual rising of the thermocline is shown to change acoustic intensity by 5 and 2 dB for the fixed and towed source data, respectively. Using nearby oceanographic moorings, a simple plane wave ocean model is developed to provide time‐dependent environmental input to broadband acoustic modeling assuming range‐independency. Modeling results are shown to produce mean transmission loss results consistent with experimental observations at both the short and the long ranges. The results suggest that the rising thermocline effect of nonlinear internal waves on mean transmission loss is observable, significant, and predictable. The result has implications on geoacoustic inversion. [Work supported by ONR.]

On the heat budget of the Arabian Sea

This study analyzes the heat budget of the Arabian Sea using satellite-derived sea-surface temperature (SST) from 1985 to 1995 along with other data sets. For a better understanding of air–sea interaction, canonical average monthly fields representing the spatial and temporal structure of the various components of the heat balance of the Arabian Sea are constructed from up to 30 years of monthly atmospheric and oceanic data. The SST over the Arabian Sea is not uniform and continually evolves with time. Cooling occurs over most of the basin during November through January and May through July, with the greatest cooling in June and July. Warming occurs over most of the basin during the remainder of the year, with the greatest warming occurring in March and September. Results indicate that the sign of the net heat flux is strongly dependent on the location and month. The effects of net heat flux and penetrative solar radiation strongly influence the change in SST during February and are less important during August and September. Horizontal advection acts to cool the sea surface during the northeast monsoon months. During the southwest monsoon horizontal advection of surface waters warms the SST over approximately the southern half of the basin, while the advection of upwelled water from the Somalia and Oman coasts substantially cools the northern basin. The central Arabian Sea during the southwest monsoon is the only area where the change in SST is balanced by the entrainment and turbulent diffusion at the base of the mixed layer. Agreement between the temporal change in the satellite-derived SST and the change calculated from the conservation of heat equation is surprisingly good given the errors in the measured variables and the bulk formula parameters. Throughout the year, monthly results over half of the basin agree within 3°. Considering that the SST changes between 8° and 12° over the year, this means that our results explain from 62% to 75% of the change in SST over 56% of the Arabian Sea. Two major processes contribute to the discrepancy in the change in SST calculated according to the heat budget equation and the change in SST derived from satellite observations. The first is the effect of the horizontal advection term. The position of the major eddies and currents during the southwest monsoon greatly affects the change in SST due to the large gradient in temperature between the cold upwelled waters along the Somali coast to the warm waters in the interior of the basin. The second major process is the thermocline effect. In areas of shallow mixed-layer depth, high insolation and wind speeds of either less than 3 m/s or greater than 15 m/s, the bulk formulae parameterization of the surface heat fluxes is inappropriate.

Statistical and dynamical analyses of generation mechanisms of solitary internal waves in the northern South China Sea

This study analyzes the effects of thermocline shoaling on the ocean internal wave (IW) generation in the north South China Sea (NSCS). Seven years of satellite synthetic aperture radar (SAR) images from 1995 to 2001 are used for the statistical analysis of IW occurrence, and field measurements of sea surface wind, sea state, and vertical temperature profiles are used for analyzing IW generation and SAR imaging conditions. Latitudinal distribution of IW packets shows that 22% of IW packets distributed in the east of 118°E obviously originate from the Luzon Strait, and 78% of IW packets west of 118°E may propagate from the east or evolve into the solitons originating from the east boundary owing to the fission effect of shoaling thermocline. The yearly distribution of IW occurrence frequencies reveals an interannual variability, implying that there are long‐term and large‐scale processes modifying the SAR‐observed IW occurrence. The monthly SAR‐observed IW occurrence frequencies show that the high frequencies are distributed from April to July and reach a peak in June with a maximum frequency of 20%. The low occurrence frequencies are distributed in winter from December to February of next year with a minimum frequency of 1.5% in February. This study proposes that the IW generation needs the necessary and sufficient conditions: initial disturbance formation and wave amplitude growth. Owing to the dissipation effect on the initial disturbance, only fully grown waves have a chance to radiate out of the source region. A physical model and PKdV equation are adopted for analyzing the sufficient conditions for solitary IW amplitude growth. The results indicate that the thermocline shoaling provides the forcing to soliton amplitude growth, so that the soliton amplitude growth ratio (SAGR) serves as a decisive factor for the IW occurrence frequency. Theoretical analysis predicts a linear relation between the two. Application of theoretical models to field measurements in the Luzon Strait gives a correlation coefficient as high as 0.845 with a confidence level of 99% for months from March to November. The linear regression gives a correlation coefficient (R2) of 0.6519 and a SAGR threshold (minimum) value of 0.90 for IW occurrence. According to the theoretical solutions, the eastward propagating disturbances have no chance to grow up, so that they hardly appear on the east side of the submarine ridges in the eastern Luzon Strait.

A new approach to improved SST anomaly simulations using altimeter data: Parameterizing entrainment temperature from sea level

Observed Topex/Poseidon/Jason‐1 (T/P/J) altimeter sea level (SL) data are used to improve an empirical parameterization of the temperature of subsurface water entrained into the mixed layer (Te). An inverse modeling method is first adopted to estimate Te from a SST anomaly (SSTA) equation using observed SST and simulated upper ocean currents from an intermediate ocean model (IOM). An empirical relationship between anomalies of Te (estimated) and SL (observed) from T/P/J altimeter is then constructed by utilizing a singular value decomposition (SVD) of their covariance. As compared with SSTA simulations using modeled SL data, the use of T/P/J SL data allows observed information about dynamic ocean adjustments to be built directly into the empirical Te model being used to parameterize the thermocline effect on SSTAs. The improved Te model leads to better SSTA simulations in the tropical Pacific. Cross validation is made to examine the sensitivity of the SSTA simulations to the period chosen for training the Te model. The proposed approach provides a new way to more effectively use T/P/J altimeter data in climate studies.

Embedding a SST anomaly model in to a z‐coordinate oceanic GCM for producing El Niño oscillation in the tropical Pacific climate system

The sensitivity of simulated interannual variability to thermocline impacts on sea surface temperature (SST) is examined in a hybrid coupled model (HCM) of the tropical Pacific climate system, consisting of the latest version of the GFDL/NOAA Modular Ocean Model (MOM 3) and the atmospheric component of the Cane‐Zebiak (CZ) coupled model. Standard coupling of the two components has difficulty producing El Niño‐like oscillations, apparently due in part to the ocean general circulation model's (OGCM) problems in the far eastern equatorial Pacific, where the modeled subsurface influence on the SST is very weak. Analogous to the CZ model, a separate diagnostic SST anomaly model is explicitly embedded into the z‐coordinate OGCM, serving as an interface between the ocean and atmosphere in the HCM. The three components exchange anomaly information only. This embedding strategy has a significant effect on the coupled variability in the model system. Incorporating the embedded SST anomaly equation, in which the thermocline effect on SST is enhanced in the eastern equatorial Pacific, the HCM simulations exhibit oscillations on interannual time scales for a range of parameters. It is shown that the most realistic coupled behavior (e.g., 3–4 year oscillation) results from the appropriate depiction of entrainment temperature (Te) in association with the thermocline depth anomalies. The results support the hypothesis that current mixing parameterization in the OGCM is problematic in depicting vertical turbulent processes.

Variability in thermocline depth and strength, and relationships with vertical distributions of fish larvae and mesozooplankton in dynamic coastal waters

In this paper the dynamic nature of thermoclines is documented, and their influences on the vertical distributions of larval fishes and mesozooplankton in coastal waters off Sydney, southeastern Australia are tested. Significant small-scale spatial and temporal variability in thermocline depth and strength was observed, and even though there were strong depth-related differences in abundances of fish larvae and mesozooplankton, there were no predictable effects of thermoclines on their vertical distributions. Peak concentrations of some fish larvae were observed in thermoclines, but these patterns were not consistent among sampling locations and time periods. Fish larvae and mesozooplankton were most concentrated in the upper 30 m of the water column, regardless of thermocline position, and therefore trophic interactions among fish larvae and zooplankton would be strongest in this depth strata. Consequently, thermoclines were not considered the most important interface for trophic interactions in this dynamic coastal zone. We argue that thermoclines are probably not critical to the survival of fish larvae in relatively shallow coastal waters characterised by dynamic oceanographies where perturbations in the position and intensity of thermoclines are frequent.