AchutaRao K., K. R. Sperber, 2006: ENSO simulation in coupled ocean-atmosphere models: Are the current models better? Climate Dyn., 27, 1- 15.10.1007/s00382-006-0119-7dc3ddee6e7535da5406f682772b9fd72http%3A%2F%2Fwww.springerlink.com%2Findex%2F61226027u2151774.pdfhttp://www.springerlink.com/index/61226027u2151774.pdfMaintaining a multi-model database over a generation or more of model development provides an important framework for assessing model improvement. Using control integrations, we compare the simulation of the El Niño/Southern Oscillation (ENSO), and its extratropical impact, in models developed for the 2007 Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report with models developed in the late 1990s [the so-called Coupled Model Intercomparison Project-2 (CMIP2) models]. The IPCC models tend to be more realistic in representing the frequency with which ENSO occurs, and they are better at locating enhanced temperature variability over the eastern Pacific Ocean. When compared with reanalyses, the IPCC models have larger pattern correlations of tropical surface air temperature than do the CMIP2 models during the boreal winter peak phase of El Niño. However, for sea-level pressure and precipitation rate anomalies, a clear separation in performance between the two vintages of models is not as apparent. The strongest improvement occurs for the modelling groups whose CMIP2 model tended to have the lowest pattern correlations with observations. This has been checked by subsampling the multi-century IPCC simulations in a manner to be consistent with the single 80-year time segment available from CMIP2. Our results suggest that multi-century integrations may be required to statistically assess model improvement of ENSO. The quality of the El Niño precipitation composite is directly related to the fidelity of the boreal winter precipitation climatology, highlighting the importance of reducing systematic model error. Over North America distinct improvement of El Niño forced boreal winter surface air temperature, sea-level pressure, and precipitation rate anomalies to occur in the IPCC models. This improvement is directly proportional to the skill of the tropical El Niño forced precipitation anomalies. |
Ando K., T. Hasegawa, 2009: Annual zonal displacement of Pacific warm pool in association with El Niño onset. SOLA, 5, 149- 152.10.2151/sola.2009-038e11a6a2c-4ba9-448c-81c0-e2ba70cee19685d219059404212f6b0f4fb79962c519http%3A%2F%2Fwww.researchgate.net%2Fpublication%2F240792085_Annual_Zonal_Displacement_of_Pacific_Warm_Pool_in_Association_with_El_Nio_Onsetrefpaperuri:(15fda4dc6adf31cdd098d04ea0084086)http://www.researchgate.net/publication/240792085_Annual_Zonal_Displacement_of_Pacific_Warm_Pool_in_Association_with_El_Nio_OnsetUsing satellite-derived surface current products, we examined annual current variations in the equatorial Pacific Ocean and associated zonal displacement of the Pacific warm pool. Annual current variations, generated mainly by annual equatorial Rossby waves, displaced the warm pool eastward (westward) during boreal spring-summer (winter), with accompanying increase (decrease) in the zonal heat advection at a rate of 0.2-0.4 °C mon-1 in the warm pool region in normal years when neither El Ni09o nor La Ni09a event take place; similar seasonal increases (decreases) have also been observed in El Ni09o years. Annual zonal currents variations attributable to oceanic Rossby waves provide more (less) favorable background sea surface conditions for the onset of El Ni09o during boreal summer (winter) by weakening (strengthening) the zonal sea surface temperature gradient through eastward (westward) heat transport near the equator in the warm pool region. Annual zonal currents variations might play a key role in seasonally locking the onset of El Ni09o events in the warm pool region. |
Bellenger H., E. Guilyardi, J. Leloup, M. Lengaigne, and J. Vialard, 2014: ENSO representation in climate models: from CMIP3 to CMIP5. Climate Dyn., 42, 1999- 2018.10.1007/s00382-013-1783-z0377e61785b7b51c6747de775f778856http%3A%2F%2Flink.springer.com%2Farticle%2F10.1007%2Fs00382-013-1783-zhttp://link.springer.com/article/10.1007/s00382-013-1783-zWe analyse the ability of CMIP3 and CMIP5 coupled oceantmosphere general circulation models (CGCMs) to simulate the tropical Pacific mean state and El Niño-Southern Oscillation (ENSO). The CMIP5 multi-model ensemble displays an encouraging 30% reduction of the pervasive cold bias in the western Pacific, but no quantum leap in ENSO performance compared to CMIP3. CMIP3 and CMIP5 can thus be considered as one large ensemble (CMIP3+CMIP5) for multi-model ENSO analysis. The too large diversity in CMIP3 ENSO amplitude is however reduced by a factor of two in CMIP5 and the ENSO life cycle (location of surface temperature anomalies, seasonal phase locking) is modestly improved. Other fundamental ENSO characteristics such as central Pacific precipitation anomalies however remain poorly represented. The sea surface temperature (SST)-latent heat flux feedback is slightly improved in the CMIP5 ensemble but the wind-SST feedback is still underestimated by 20-50% and the shortwave-SST feedbacks remain underestimated by a factor of two. The improvement in ENSO amplitudes might therefore result from error compensations. The ability of CMIP models to simulate the SST-shortwave feedback, a major source of erroneous ENSO in CGCMs, is further detailed. In observations, this feedback is strongly nonlinear because the real atmosphere switches from subsident (positive feedback) to convective (negative feedback) regimes under the effect of seasonal and interannual variations. Only one-third of CMIP3+CMIP5 models reproduce this regime shift, with the other models remaining locked in one of the two regimes. The modelled shortwave feedback nonlinearity increases with ENSO amplitude and the amplitude of this feedback in the spring strongly relates with the models ability to simulate ENSO phase locking. In a final stage, a subset of metrics is proposed in order to synthesize the ability of each CMIP3 and CMIP5 models to simulate ENSO main characteristics and key atmospheric feedbacks. |
Bosc C., T. Delcroix, and C. Maes, 2009: Barrier layer variability in the western Pacific warm pool from 2000 to 2007. J. Geophys. Res. (Oceans) , 114,C06023, doi:10.1029/2008JC 005187.10.1029/2008JC005187615e739cfc300b30a0037d4e005a8a76http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1029%2F2008JC005187%2Fcitedbyhttp://onlinelibrary.wiley.com/doi/10.1029/2008JC005187/citedby[1] Major features of the equatorial portion of the western Pacific warm pool (WP) were brought to light through the analysis of an unprecedented collection of temperature and salinity profiles derived from Argo floats from 2000 to 2007. A region of thick (>15–25 m) and quasi-permanent barrier layers (BLs) was found to occur in a band from 10° to 20° longitude to the west of the maximum zonal sea surface salinity gradient (68 S/ 68 x ), which occurs at the eastern edge of the WP. In this region, thick BLs and associated maxima (68 S/ 68 x ) were displaced eastward (westward) during El Ni09o (La Ni09a) over a distance of more than 6000 km. The thickness of the BL in this region is, to the first order, proportional to 68 S/ 68 x and quasi-permanently associated with the occurrence of sea surface temperatures warmer than 28–29°C, which are a good proxy for maximum atmospheric convection for the current Pacific climate. Statistics indicated that a thick BL forms preferentially under low wind conditions, heavy precipitation, eastward advection of low sea surface salinity, zonal current vertical shear, and/or in conjunction with equatorial downwelling Kelvin and Rossby waves (favoring the vertical stretching of the upper water column). None of these processes seemed to dominate the others, indicating that the formation of a thick BL results from a combination of different and complex mechanisms. The fact that a thick BL represents a quasi-permanent feature in the WP signifies that its specific stratification and likely impact on the sea surface temperature balance should be accounted for in coupled models. |
Brown J. N., C. Langlais, and C. Maes, 2014: Zonal structure and variability of the Western Pacific dynamic warm pool edge in CMIP5. Climate Dyn., 42( 11-12), 3061- 3076.10.1007/s00382-013-1931-58f0c6c1578a07d24ab1bb67f0468e0efhttp%3A%2F%2Flink.springer.com%2F10.1007%2Fs00382-013-1931-5http://link.springer.com/10.1007/s00382-013-1931-5The equatorial edge of the Western Pacific Warm Pool is operationally identified by one isotherm ranging between 28° and 2902°C, chosen to align with the interannual variability of strong zonal salinity gradients and the convergence of zonal ocean currents. The simulation of this edge is examined in 19 models from the World Climate Research Program Coupled Model Intercomparison Project Phase 5 (CMIP5), over the historical period from 1950 to 2000. The dynamic warm pool edge (DWPE), where the zonal currents converge, is difficult to determine from limited observations and biased models. A new analysis technique is introduced where a proxy for DWPE is determined by the isotherm that most closely correlates with the movements of the strong salinity gradient. It can therefore be a different isotherm in each model. The DWPE is simulated much closer to observations than if a direct temperature-only comparison is made. Aspects of the DWPE remain difficult for coupled models to simulate including the mean longitude, the interannual excursions, and the zonal convergence of ocean currents. Some models have only very weak salinity gradients trapped to the western side of the basin making it difficult to even identify a DWPE. The model’s DWPE are generally 1–202°C cooler than observed. In line with theory, the magnitude of the zonal migrations of the DWPE are strongly related to the amplitudes of the Nino3.4 SST index. Nevertheless, a better simulation of the mean location of the DWPE does not necessarily improve the amplitude of a model’s ENSO. It is also found that in a few models (CSIROMk3.6, inmcm and inmcm4-esm) the warm pool displacements result from a net heating or cooling rather than a zonal advection of warm water. The simulation of the DWPE has implications for ENSO dynamics when considering ENSO paradigms such as the delayed action oscillator mechanism, the Advective-Reflective oscillator, and the zonal-advective feedback. These are also discussed in the context of the CMIP5 simulations. |
de Boyer Montègut, C., G. Madec, A. S. Fischer, A. Lazar, D. Iudicone, 2004: Mixed layer depth over the global ocean: An examination of profile data and a profile-based climatology. J. Geophys. Res., 109,C12003, doi: 10.1029/2004JC002378.10.1029/2004JC0023788c02fa6f-97d7-44e7-92d0-f6805545b581549958876721e0d1668cf9a76d379a68http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1029%2F2004JC002378%2Ffullrefpaperuri:(b278d666ae5864c3adc7b3522464f007)http://onlinelibrary.wiley.com/doi/10.1029/2004JC002378/fullA new 2° resolution global climatology of the mixed layer depth (MLD) based on individual profiles is constructed. Previous global climatologies have been based on temperature or density-gridded climatologies. The criterion selected is a threshold value of temperature or density from a near-surface value at 10 m depth (ΔT = 0.2°C or Δσ = 0.03 kg m613). A validation of the temperature criterion on moored time series data shows that the method is successful at following the base of the mixed layer. In particular, the first spring restratification is better captured than with a more commonly used larger criteria. In addition, we show that for a given 0.2°C criterion, the MLD estimated from averaged profiles results in a shallow bias of 25% compared to the MLD estimated from individual profiles. A new global seasonal estimation of barrier layer thickness is also provided. An interesting result is the prevalence in mid- and high-latitude winter hemispheres of vertically density-compensated layers, creating an isopycnal but not mixed layer. Consequently, we propose an optimal estimate of MLD based on both temperature and density data. An independent validation of the maximum annual MLD with oxygen data shows that this oxygen estimate may be biased in regions of Ekman pumping or strong biological activity. Significant differences are shown compared to previous climatologies. The timing of the seasonal cycle of the mixed layer is shifted earlier in the year, and the maximum MLD captures finer structures and is shallower. These results are discussed in light of the different approaches and the choice of criterion. |
de Boyer Montègut, C.J. Mignot, A. Lazar, S. Cravatte, 2007: |
Delcroix T., J. Picaut, 1998: Zonal displacement of the western equatorial Pacific "fresh pool". J. Geophys. Res., 103, 1087- 1098.10.1029/97JC01912fd576955-fe26-4a49-8136-8b73ecc164ab0286d4ba9c9f757158501c1ea11f3376http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1029%2F97JC01912%2Ffullrefpaperuri:(3c8f3559b999907363215f48103cd986)http://onlinelibrary.wiley.com/doi/10.1029/97JC01912/fullABSTRACT |
Delcroix T., G. Alory, S. Cravatte, T. Corrège, and M. McPhaden, 2011: A gridded sea surface salinity data set for the tropical Pacific with sample applications (1950-2008). Deep-Sea Res.,Part I, 58, 38- 48.10.1016/j.dsr.2010.11.00216675dd533eeeb892690d8af9fd1df83http%3A%2F%2Fwww.sciencedirect.com%2Fscience%2Farticle%2Fpii%2FS0967063710002128http://www.sciencedirect.com/science/article/pii/S0967063710002128We present a gridded data set of Sea Surface Salinity (SSS) for the tropical Pacific (120°E–70°W; 30°N–30°S), with a grid resolution of 1° longitude, 1° latitude and 1 month, from 1950 to 2008. The product, together with its associated error field, is derived from an objective analysis of about 10 million validated SSS records, with most of the data originating from Voluntary Observing Ships, TAO/TRITON moorings and Argo profilers (during the most recent period). We expect this product to benefit studies in oceanography, meteorology and paleoceanography. As examples of applications, we analyse: (a) the seasonal and ENSO (El Ni09o Southern Oscillation) modes of observed SSS variability, (b) the ability of 23 coupled models used in the Intergovernmental Panel for Climate Change 4th Assessment Report (IPCC AR4) to simulate the mean SSS and these two time varying modes, and (c) the usefulness of the SSS product of its associated error field in calibrating and validating the paleo-salinity time series. We anticipate improvements and regular updates to our product, as more SSS data become available from in situ networks and from the ongoing and near-future satellite-derived observations by SMOS (Soil Moisture and Ocean Salinity) and Aquarius. |
Gill A. E., 1982: Atmosphere-Ocean Dynamics. Academic Press,662 pp. |
Godfrey, J. S., Coauthors, 1995: The role of the Indian Ocean in the global climate system: recommendations regarding the global ocean observing system. Report of the Ocean Observing System Development Panel,Report No. 6, Texas A&M University, College Station, Texas, 89 pp.964efef2dd85897be7f72ff9bf568ecbhttp%3A%2F%2Fioc-goos-oopc.org%2Fdocuments%2Foosdp%2Foosdp_br6.pdfhttp://ioc-goos-oopc.org/documents/oosdp/oosdp_br6.pdfon recent numerical model results, since models will have to play major roles in an Figure 2.Sverdrup stream function for annual mean depth-integrated flow, calculated from the winds of Ocean eddies can sometimes play an important role in the horizontal transport of heat and |
Guilyardi E., P. Braconnot, F. F. Jin, S. T. Kim, M. Kolasinski, T. Li, and I. Musat, 2009: Atmosphere feedbacks during ENSO in a coupled GCM with a modified atmospheric convection scheme. J.Climate, 22, 5698- 5718.10.1175/2009JCLI2815.1ffd437f787daaa133a0009f708eff4c6http%3A%2F%2Fwww.cabdirect.org%2Fabstracts%2F20093348417.htmlhttp://www.cabdirect.org/abstracts/20093348417.htmlThe too diverse representation of ENSO in a coupled GCM limits one's ability to describe future change of its properties. Several studies pointed to the key role of atmosphere feedbacks in contributing to this diversity. These feedbacks are analyzed here in two simulations of a coupled GCM that differ only by the parameterization of deep atmospheric convection and the associated clouds. Using t... |
IPCC, 2013: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change,T. F. Stocker et al., Eds., Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 1535 pp.5d57966d86fc9d2c74ddedc130ce11fbhttp%3A%2F%2Fwww.researchgate.net%2Fpublication%2F242691805_Intergovernmental_Panel_on_Climate_Change_Fifth_Assessment_Reporthttp://www.researchgate.net/publication/242691805_Intergovernmental_Panel_on_Climate_Change_Fifth_Assessment_ReportFifth Assessment ReportThe Intergovernmental Panel on Climate Change (IPCC) publishes Assessment Reports every six to seven years, with the IPCC First Assessment report published in 1990. The Fifth Assessment Report is being published in stages across 2013 and 2014.Each of the three Working Groups contributes to the development of Assessment Reports: |
Ji D., Coauthors, 2014: Description and basic evaluation of BNU-ESM version1. Geoscientific-Model Dev-Discuss, 7, 1601- 1647.10.5194/gmdd-7-1601-2014d99f76e8-53b8-4337-a324-da901578d12806781b75ef3910d10a4fcd9586f7e330http%3A%2F%2Fwww.researchgate.net%2Fpublication%2F262954172_Description_and_basic_evaluation_of_BNU-ESM_version_1refpaperuri:(ae74426ec249880110273c67f1aefee3)http://www.researchgate.net/publication/262954172_Description_and_basic_evaluation_of_BNU-ESM_version_1ABSTRACT An earth system model has been developed at Beijing Normal University (Beijing Normal University Earth System Model, BNU-ESM); the model is based on several widely evaluated climate model components and is used to study mechanisms of ocean-atmosphere interactions, natural climate variability and carbon-climate feedbacks at interannual to interdecadal time scales. In this paper, the model structure and individual components are described briefly. Further, results for the CMIP5 (Coupled Model Intercomparison Project phase 5) pre-industrial control and historical simulations are presented to demonstrate the model's performance in terms of the mean model state and the internal variability. It is illustrated that BNU-ESM can simulate many observed features of the earth climate system, such as the climatological annual cycle of surface air temperature and precipitation, annual cycle of tropical Pacific sea surface temperature (SST), the overall patterns and positions of cells in global ocean meridional overturning circulation. For example, the El Niño-Southern Oscillation (ENSO) simulated in BNU-ESM exhibits an irregular oscillation between 2 and 5 years with the seasonal phase locking feature of ENSO. Important biases with regard to observations are presented and discussed, including warm SST discrepancies in the major upwelling regions, an equatorward drift of midlatitude westerly wind bands, and tropical precipitation bias over the ocean that is related to the double Intertropical Convergence Zone (ITCZ). |
Levitus S., 1982: Climatological atlas of the world ocean. NOAA Prof. Pap. 13,173, U.S. Gov. Print. Off., Washington, D. C.10.1029/EO064i049p00962-022a22d895dc8e0375396f6174f150597chttp%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1029%2FEO064i049p00962-02%2Ffullhttp://onlinelibrary.wiley.com/doi/10.1029/EO064i049p00962-02/fullClimatological atlas of the world ocean LEVITUS S. NOAA Prof.Paper 13 173, 1982 |
Lindstrom E., R. Lukas, R. Fine, E. Firing, S. Godfrey, G. Meyers, and M. Tsuchiya, 1987: The western equatorial Pacific Ocean circulation study. Nature, 330, 533- 537.10.1038/330533a0ac4c0c1dcf73b34ea2374a64b53a0a82http%3A%2F%2Fwww.nature.com%2Fnature%2Fjournal%2Fv330%2Fn6148%2Fpdf%2F330533a0.pdfhttp://www.nature.com/nature/journal/v330/n6148/pdf/330533a0.pdfABSTRACT A recent set of oceanographic measurements in the western equatorial Pacific has revealed the existence of previously undescribed major ocean currents and upper-ocean mixed-layer structure. The measurements also confirm a 20-year-old hypothesis on the water-mass origins of the Equatorial Undercurrent in the Pacific Ocean. |
Lukas R., E. Lindstrom, 1991: The mixed layer of the western equatorial Pacific Ocean. J. Geophys. Res., 96, 3343- 3357.10.1029/90JC019519e3ba019-8491-405d-8bbf-2aa753e987c249bde5fc550d4b2bd790536f4ff111eehttp%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1029%2F90JC01951%2Fpdfrefpaperuri:(4c154191467cbebd541e5adee7240b17)http://onlinelibrary.wiley.com/doi/10.1029/90JC01951/pdfThe mixed layer of the western equatorial Pacific and its thermodynamics are poorly known because of a general lack of data. Conductivity-temperature-depth (CTD) profiles from the recent Western Equatorial Pacific Ocean Circulation Study (WEPOCS) cruises have been analyzed for various measures of the upper layer and mixed layer thickness, using criteria which depend on vertical gradients of temperature, salinity, and density. From 434 profiles, the average mixed layer depth in the western equatorial Pacific during the two WEPOCS cruises was 29 m, which is about a factor of 3 shallower than had previously been thought. The mean depth of the top of the thermocline was found to be 64 m, so there is a nearly isothermal layer that is deeper than the mixed layer. This discrepancy is attributable to salinity stratification. It is hypothesized that the waters in this -arrier- layer between the bottom of the mixed layer and the top of the thermocline are formed to the east of the WEPOCS region, and subducted below the shallow and lighter mixed layer waters found in the west. Under light wind conditions, there was a tendency for warm and thin layers to form at the sea surface as a result of diurnal heating; however, there did not appear to be any nighttime maximum to the mixed layer depth associated with convective overturn due to cooling. This contrast with the central Pacific may be caused by the influence of salinity on the thermodynamics of the mixed layer. A strong westerly wind burst was observed during WEPOCS II, and apparently the mixed layer nearly doubled in depth while cooling by more than 1C. Evidence of downwelling near the equator, and upwelling off the equator, was seen in the distribution of temperature, salinity, and density in the meridional section along 143E, which was occupied immediately following the wind event. This event was apparently strong enough to erode through the salinity-stratified layer and into the thermocline, resulting in the observed cooling. The results of this study suggest that except during strong wind events, entrainment cooling may not be an important component of the heat budget of the western Pacific warm pool. This has potentially important implications for the El Niño/Southern Oscillation (ENSO) phenomenon. |
Maes C., M. J. McPhaden, D. Behringer, 2002: Signatures of salinity variability in tropical Pacific Ocean dynamic height anomalies. J. Geophys. Res., 107(C12),8012, doi: 10.1029/ 2000JC000737.10.1029/2000JC000737555c8c7b6208cecc3f7bbb6ae5e75abfhttp%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1029%2F2000JC000737%2Ffullhttp://onlinelibrary.wiley.com/doi/10.1029/2000JC000737/fullAbstract Top of page Abstract 1.Introduction 2.Data Sets and Selection Procedure 3.Observed Features 4.Temperature and Salinity EOFs 5.Discussion and Conclusion Acknowledgments References Supporting Information [1] The vertical variability of the salinity field, with emphasis on interannual timescales, is examined within the tropical Pacific Ocean (10°N–10°S) using a compilation of the conductivity-temperature-depth (CTD) casts for the period 1975–1998. Compared to the vertical dependence of temperature that exhibits a systematic maximum variability at the depth of the main thermocline, the salinity typically shows a maximum variability in the surface layers. One notable region where this rule is violated is the southwestern and central Pacific Ocean. Below the surface, salinity variability is correlated with the strong gradients in mean salinity above and below the subsurface salinity maximum. It is shown that using conventional mean T - S curves to estimate salinity profiles from temperature observations leads to strong biases because of the large scatter around the T - S relationships. From the surface to the bottom of the thermocline, the dispersion of the T - S diagrams is large regardless of whether the conditions are representative of “El Ni09o” or “La Ni09a” conditions. Error introduced in computing the dynamic height anomaly (DHA) is larger than 2 dyn. cm (dynamic centimeters) throughout the tropical Pacific if salinity variability is neglected. This error represents 30% of the total variability of the sea surface height in the western Pacific, and more than 50% in the south central Pacific. In order to estimate salinity variability when direct measurements are not available, an empirical orthogonal function analysis of existing temperature and salinity profiles was conducted. It is shown that a relatively low number of dominant modes, typically less than 6, are sufficient to explain 80% or more of the total variance. The separate contributions of the temperature and salinity fields to the DHA are then examined. The salinity contribution is generally smaller than the temperature contribution, though in some instances the two oppose one another, resulting in lowered dynamic height anomalies. These results confirm that salinity variability should not be neglected in ocean analyses that attempt to infer vertical changes in density from sea level fluctuations within the tropical Pacific Ocean. |
Maes C., J. Picaut, and S. Belamari, 2005: Importance of the salinity barrier layer for the buildup of El Niño. J.Climate, 18( 1), 104- 118. |
Maes C., K. Ando, T. Delcroix, W. S. Kessler, M. J. McPhaden, and D. Roemmich, 2006: Observed correlation of surface salinity, temperature and barrier layer at the eastern edge of the western Pacific warm pool. Geophys. Res. Lett. , 33(6),L06601, doi:10.1029/2005GL024772.10.1029/2005GL0247721088f09eb8eac2ff2d0010816a0e1030http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1029%2F2005GL024772%2Fabstracthttp://onlinelibrary.wiley.com/doi/10.1029/2005GL024772/abstract[1] Recent theory suggests that ocean-atmosphere interactions in the western Pacific warm pool are of fundamental importance to interannual variations associated with El Niño and the Southern Oscillation (ENSO). The warm pool encompasses the highest mean sea surface temperatures (SSTs) in the world ocean, intense atmospheric deep convection and heavy rainfall, and the formation of thick salt-stratified barrier layers that help to sustain the high SSTs. This study shows that the eastern edge of the warm pool is characterized by a strong zonal salinity front throughout 2002-2004. The analysis also indicates a tighter empirical relationship than previously observed between the eastern edge of the warm pool, high SSTs, the presence of barrier layers, and the fetch of westerly wind bursts. These results suggest that such a frontal region is a critical in controlling ocean-atmosphere interactions in the western Pacific warm pool and highlight the importance of the upper ocean salinity in climate variability. |
Maes C., S. Belamari, 2011: On the impact of salinity barrier layer on the Pacific Ocean mean state and ENSO. SOLA, 7( 655), 97- 100.10.2151/sola.2011-0256e54191e75edab983fff8b4646598dadhttp%3A%2F%2Fwww.researchgate.net%2Fpublication%2F277395515_On_the_Impact_of_Salinity_Barrier_Layer_on_the_Pacific_Ocean_Mean_State_and_ENSOhttp://www.researchgate.net/publication/277395515_On_the_Impact_of_Salinity_Barrier_Layer_on_the_Pacific_Ocean_Mean_State_and_ENSOObservational studies of the western Pacific Ocean have suggested since the mid-1980s that the barrier layer resulting from the salinity stratification within the mixed layer could influence significantly the ocean-atmosphere interactions. Numerical experiments based on a CGCM are designed and analyzed in such a goal. The formation of the barrier layer is primarily identified as resulting from a tilting/shearing mechanism in which horizontal and vertical gradients of salinity, as well as the dynamical response of the ocean to westerly winds, are tightly coupled. When the contribution of salinity to the computation of the horizontal pressure gradient force in the ocean model is cancelled within the equatorial warm pool, both the mean climatology and the low frequency variability are affected as the result of a complete annihilation of the barrier layer. The decreased sensitivity of the coupling between the SST, winds and atmospheric deep convection is likely due to the deepening of the ocean mixed layer that cools the SST and weakens the amplitude of its variability. These local changes within the western Pacific warm pool also induce a basin scale response that weakens the amplitude of ENSO variability. These results suggest that the formation of the barrier layer is a key element of the whole Pacific ocean-atmosphere coupled system. |
Masson S., J.-P. Boulanger, C. Menkes, P. Delecluse, and T. Yamagata, 2004: Impact of salinity on the 1997 Indian Ocean dipole event in a numerical experiment. J. Geophys. Res., 109,C02002, doi: 10.1029/2003JC001807.10.1029/2003JC001807be4cbb61cc2a5421fc9949d0c5a67e15http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1029%2F2003JC001807%2Ffullhttp://onlinelibrary.wiley.com/doi/10.1029/2003JC001807/full[1] The role of salinity during the onset and growth of the 1997 Indian Ocean Dipole Mode event is explored with an ocean general circulation model thoroughly validated to observations. In fall 1997, anomalous easterlies drive an Indian Ocean equatorial circulation similar to that regularly observed in the Pacific Ocean: a South Equatorial Current (SEC) near the equator, an Equatorial Under Current (EUC) subsurface, and intense upwelling in the eastern part of the basin. The SEC transports westward the eastern Indian Ocean fresh pool creating, along the equator, a shallow salinity stratification favoring the creation of a barrier layer. In our experiment, the shallow top of the thermocline limits the barrier layer thickness to about 10 m; nevertheless, salinity has a significant impact on sea surface temperature (SST). Indeed, the shallow salinity stratification along the equator traps the wind forcing in a thin surface mixed-layer. The reduction of wind momentum penetration decreases the deceleration of the EUC, and the greater amplitude of wind momentum input in surface layers strengthens the SEC. This intensification of the equatorial zonal circulation increases the Sumatra upwelling and its associated meridional circulation. This strengthening of the whole equatorial circulation shifts upward the thermohaline structure and reinforces the cold SST anomaly off Sumatra by about 20%. Overall, the effect of salinity on the 1997 Indian Ocean Dipole is to reinforce the oceanic anomalies favoring a strengthening of the air-sea interactions. |
McPhaden M. J., J. Picaut, 1990: El Niño-Southern oscillation displacements of the western equatorial Pacific warm pool. Science, 250, 1385- 1388. |
McPhaden M. J., S. E. Zebiak, and M. H. Glantz, 2006: ENSO as an integrating |
Mignot J., C. de Boyer Montègut, and M. Tomczak, 2009: On the porosity of barrier layers. Ocean Science, 5, 379- 387.10.5194/os-5-379-2009fc639743bd5e1d259b288707ef8c45e2http%3A%2F%2Fwww.oalib.com%2Fpaper%2F2634498http://www.oalib.com/paper/2634498Barrier layers are defined as the layer between the pycnocline and the thermocline when the latter are different as a result of salinity stratification. We present a revisited 2-degree resolution global climatology of monthly mean oceanic Barrier Layer (BL) thickness first proposed by de Boyer Montgut et al. (2007). In addition to using an extended data set, we present a modified computation method that addresses the observed porosity of BLs. We name porosity the fact that barrier layers distribution can, in some areas, be very uneven regarding the space and time scales that are considered. This implies an intermittent alteration of air-sea exchanges by the BL. Therefore, it may have important consequences for the climatic impact of BLs. Differences between the two computation methods are small for robust BLs that are formed by large-scale processes. However, the former approach can significantly underestimate the thickness of short and/or localized barrier layers. This is especially the case for barrier layers formed by mesoscale mechanisms (under the intertropical convergence zone for example and along western boundary currents) and equatorward of the sea surface salinity subtropical maxima. Complete characterisation of regional BL dynamics therefore requires a description of the robustness of BL distribution to assess the overall impact of BLs on the process of heat exchange between the ocean interior and the atmosphere. |
Picaut J., M. Ioualalen, C. Menkes, T. Delcroix, and M. J.McPhaden, 1996: Mechanism of the zonal displacements of the Pacific warm pool: Implications for ENSO. Science,274, 1486-1489, doi: 10.1126/science.274.5292.1486.10.1126/science.274.5292.14868929400277b014dc49b1e1e5a978d5554ef46a9http%3A%2F%2Fwww.jstor.org%2Fstable%2F2892213http://www.jstor.org/stable/2892213The western equatorial Pacific warm pool is subject to strong east-west migrations on interannual time scales in phase with the Southern Oscillation Index. The dominance of surface zonal advection in this migration is demonstrated with four different current data sets and three oceans models. The eastward advection of warm and less saline water form the western Pacific together with the westward advection of cold and more saline water from the central-eastern Pacific induces a convergence of water masses at the eastern edge of the warm pool and a well-defined salinity front. The location of this convergence is zonally displaced in association with El Nino-La Nina wind-driven surface current variations. These advective processes and water-mass convergences have significant implications for understanding and simulating coupled ocean-atmosphere interactions associated with El Nino-Southern Oscillation (ENSO). |
Rao R. R., R. Sivakumar, 2003: Seasonal variability of sea surface salinity and salt budget of the mixed layer of the north Indian Ocean. J. Geophys. Res., 108(C1),3009, doi: 10.1029/2001JC000907.10.1029/2001JC0009072832b36ef2602578d9371fe7a80a9b66http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1029%2F2001JC000907%2Ffullhttp://onlinelibrary.wiley.com/doi/10.1029/2001JC000907/fullAbstract Top of page Abstract 1.Introduction 2.Data 3.Analysis and Discussion 4.Summary Acknowledgments References [1] A subset of the recently published salinity database of the global oceans is utilized to characterize and explain the observed seasonal variability of sea surface salinity of the north Indian Ocean, in greater detail than has been possible previously. The influence of salinity on the seasonal evolution of near-surface mixed layer depth is highlighted. The relative importance of freshwater flux (evaporation minus precipitation) and horizontal advection in accounting the observed seasonal variability of sea surface salinity is evaluated. The influence of massive river outflow in producing the observed sea surface salinity minima in the coastal northwestern Bay of Bengal during August-eptember is highlighted. The observed interannual variability of sea surface salinity along two major shipping lanes in the tropical Indian Ocean in relation to El Niño is examined. The annual average of sea surface salinity shows contrasting distributions in the Arabian Sea and the Bay of Bengal due to differences in hydrological forcing. The seasonal variability of sea surface salinity is most pronounced in the coastal region of the northern Bay of Bengal, northwestern Arabian Sea, and the southeastern Arabian Sea. The incorporation of salinity effect reduces the thickness of the near-surface mixed layer, and this reduction is most pronounced in the Bay of Bengal, where it builds up from June to July and becomes most prominent by February in the following year, when the freshening effects of hydrological forcing through local rainfall and river discharges are felt the most on the near-surface layers. The salt budget analysis of the mixed layer shows a broad agreement between the patterns of observed and diagnosed seasonal changes caused by freshwater flux and horizontal advection, despite limitations in the accuracy of these estimates. The freshwater input through rainfall and river discharges in the Bay of Bengal far exceeds evaporation, causing surplus freshwater for export. Horizontal advection of salinity is found to be important in the southeastern Arabian Sea during winter and in the western and eastern Arabian Sea during the summer monsoon season and in the Bay of Bengal throughout the year with the exception of premonsoon season. The pronounced dilution observed during the height of the summer monsoon season in the coastal northwestern Bay of Bengal is attributed to peak discharges from major rivers. Historic data along two major shipping lanes in the tropical Indian Ocean have clearly revealed the signature of El Niño in the interannual variability of sea surface salinity. |
Roemmich D., Coauthors, 2009: The Argo Program: Observing the global ocean with profiling floats. Oceanography, 22, 34- 43.10.5670/oceanog.2009.3648107fb61663ef3230835c711f2c103bhttp%3A%2F%2Fwww.researchgate.net%2Fpublication%2F33549908_The_Argo_Program__observing_the_global_ocean_with_profiling_floats%3Fev%3Dauth_pubhttp://www.researchgate.net/publication/33549908_The_Argo_Program__observing_the_global_ocean_with_profiling_floats?ev=auth_pubThe Argo Program has created the first global array for observing the subsurface ocean. Argo arose from a compelling scientific need for climate-relevant ocean data; it was made possible by technology development and implemented through international collaboration. The float program and its data management system began with regional arrays in 1999, scaled up to global deployments by 2004, and achieved its target of 3000 active instruments in 2007. US Argo, supported by the National Oceanic and Atmospheric Administration and the Navy through the National Oceanographic Partnership Program, provides half of the floats in the international array, plus leadership in float technology, data management, data quality control, international coordination, and outreach. All Argo data are freely available without restriction, in real time and in research-quality forms. Uses of Argo data range from oceanographic research, climate research, and education, to operational applications in ocean data assimilation and seasonal-to-decadal prediction. Argo's value grows as its data accumulate and their applications are better understood. Continuing advances in profiling float and sensor technologies open many exciting possibilities for Argo's future, including expanding sampling into high latitudes and the deep ocean, improving near-surface sampling, and adding biogeochemical parameters. |
Sato K., T. Suga, and K. Hanawa, 2006: Barrier layer in the subtropical gyres of the world's oceans. Geophys. Res. Lett., 33,L08603, doi: 10.1029/2005GL025631.10.1029/2005GL02563116a2d150-c13e-49b4-981b-51694dec2b42b1d19727cc6b9caa99d4b75e8a9e1d28http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1029%2F2005GL025631%2Fcitedbyrefpaperuri:(f8f594f57321c5a7c29e5478bf1fea3d)http://onlinelibrary.wiley.com/doi/10.1029/2005GL025631/citedby[1] Barrier layers (BLs) in the subtropical gyres of the world's oceans are detected using all temperature and salinity profiles obtained by Argo floats from Jan. 2000 to Jun. 2005. The synoptic BLs are distributed patchily in the area where climatological BLs are continuously distributed. They are thicker and occur more frequently during Jan.–Apr. (Jul.–Nov.) in the Northern (Southern) Hemisphere with some differences in thickness and occurrence rates among the oceans. We suggest that the same formation mechanism of BLs as that in the North Pacific, i.e., the subduction of high salinity water at sharp salinity fronts on a small scale of approximately 100 km is at work in the other subtropical gyres. Seasonal change of the mixed layer depth contributes to the seasonality of BL thickness and frequency in all subtropical gyres. |
Sprintall J., M. Tomczak, 1992: Evidence of the barrier layer in the surface layer of the tropics. J. Geophys. Res., 97, 7305- 7316.10.1029/92JC004070053ffd9e755b23edb9587ec7e4f9466http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1029%2F92JC00407%2Fabstracthttp://onlinelibrary.wiley.com/doi/10.1029/92JC00407/abstractComparisons between isothermal depth to the top of the thermocline, and the mixed layer depth based on a σ t criterion were undertaken for the tropical world oceans. In three equatorial regions, a shallower mixed layer than isothermal layer occurs, implying the presence of a strong halocline above the thermocline. This distance separating the top of the thermocline and the bottom of the mixed layer is referred to as the “barrier layer”, in relation to its impediment to vertical heat flux out of the base of the mixed layer. Different mechanisms are responsible for maintaining the barrier layer in each of the three regions. In the western equatorial Pacific Ocean a salinity budget confirmed that heavy local precipitation most likely results in the isothermal but salt-stratified layer. In the northwest equatorial Atlantic, it is hypothesized that high salinity waters are subducted at the subtropics during winter and advected westward as a salinity maximum in the upper layers of the tropics, resulting in the barrier layer. In the eastern equatorial Indian Ocean, monsoonal related rainfall and river runoff contribute significantly to the freshwater flux, producing salt stratification in the surface. These results suggest the need to include the effects of salinity stratification when determining mixed layer depth. |
Stoens, A., Coauthors, 1999: The coupled physical new production system in the equatorial Pacific during the 1992-1995 El Niño. J. Geophys. Res., 104, 3323- 3339. |
Su H., J. H. Jiang, 2012: Tropical clouds and circulation changes during the 2006/07 and 2009/10 El Niños. J. Climate,26, 399-413, doi: 10.1175/JCLI-D-12-00152.1. |
Taylor K. E., R. J. Stouffer, and G. A. Meehl, 2012: An overview of CMIP5 and the experiment design. Bull. Amer. Meteor. Soc., 93, 485- 498.10.1175/BAMS-D-11-00094.102496a28-fd74-494f-9dd0-772d832581a7d378bae55de68ca8b37ba4ba57a3c0b9http%3A%2F%2Fwww.researchgate.net%2Fpublication%2F235793806_An_Overview_of_CMIP5_and_the_Experiment_Design%3Fev%3Dauth_pubrefpaperuri:(102c64f576f0dc49ca552e6df691421b)http://www.researchgate.net/publication/235793806_An_Overview_of_CMIP5_and_the_Experiment_Design?ev=auth_pubThe fifth phase of the Coupled Model Intercomparison Project (CMIP5) will produce a state-of-the- art multimodel dataset designed to advance our knowledge of climate variability and climate change. Researchers worldwide are analyzing the model output and will produce results likely to underlie the forthcoming Fifth Assessment Report by the Intergovernmental Panel on Climate Change. Unprecedented in scale and attracting interest from all major climate modeling groups, CMIP5 includes “long term” simulations of twentieth-century climate and projections for the twenty-first century and beyond. Conventional atmosphere–ocean global climate models and Earth system models of intermediate complexity are for the first time being joined by more recently developed Earth system models under an experiment design that allows both types of models to be compared to observations on an equal footing. Besides the longterm experiments, CMIP5 calls for an entirely new suite of “near term” simulations focusing on recent decades and the future to year 2035. These “decadal predictions” are initialized based on observations and will be used to explore the predictability of climate and to assess the forecast system's predictive skill. The CMIP5 experiment design also allows for participation of stand-alone atmospheric models and includes a variety of idealized experiments that will improve understanding of the range of model responses found in the more complex and realistic simulations. An exceptionally comprehensive set of model output is being collected and made freely available to researchers through an integrated but distributed data archive. For researchers unfamiliar with climate models, the limitations of the models and experiment design are described. |
Vannière, B., E. Guilyardi, G. Madec, F. J. Doblas-Reyes, S. Woolnough, 2011: Using seasonal hindcasts to understand the origin of the equatorial cold tongue bias in CGCMs and its impact on ENSO. Climate Dyn., 40, 963- 981.10.1007/s00382-012-1429-67f0a8978cdfbd632fe750e979a2ef78ahttp%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fp256401w5h8621vr%2Fhttp://www.springerlink.com/content/p256401w5h8621vr/The cold equatorial SST bias in the tropical Pacific that is persistent in many coupled OAGCMs severely impacts the fidelity of the simulated climate and variability in this key region, such as the ENSO phenomenon. The classical bias analysis in these models usually concentrates on multi-decadal to centennial time series needed to obtain statistically robust features. Yet, this strategy cannot fully explain how the models errors were generated in the first place. Here, we use seasonal re-forecasts (hindcasts) to track back the origin of this cold bias. As such hindcasts are initialized close to observations, the transient drift leading to the cold bias can be analyzed to distinguish pre-existing errors from errors responding to initial ones. A time sequence of processes involved in the advent of the final mean state errors can then be proposed. We apply this strategy to the ENSEMBLES-FP6 project multi-model hindcasts of the last decades. Four of the five AOGCMs develop a persistent equatorial cold tongue bias within a few months. The associated systematic errors are first assessed separately for the warm and cold ENSO phases. We find that the models are able to reproduce either El Niño or La Nina close to observations, but not both. ENSO composites then show that the spurious equatorial cooling is maximum for El Niño years for the February and August start dates. For these events and at this time of the year, zonal wind errors in the equatorial Pacific are present from the beginning of the simulation and are hypothesized to be at the origin of the equatorial cold bias, generating too strong upwelling conditions. The systematic underestimation of the mixed layer depth in several models can also amplify the growth of the SST bias. The seminal role of these zonal wind errors is further demonstrated by carrying out ocean-only experiments forced by the AOCGCMs daily 10-meter wind. In a case study, we show that for several models, this forcing is sufficient to reproduce the main SST error patterns seen after 1month in the AOCGCM hindcasts. |
Vialard J., P. Delecluse, 1998: An OGCM study for the TOGA decade: II. Barrier-layer formation and variability. J. Phys. Oceanogr., 28, 1089- 1106.10.1175/1520-0485(1998)028<1089:AOSFTT>2.0.CO;2a0b2915a-57b2-4626-81ee-aee354ea51a583820fae20eaf2fdaebcc7e5cb251ccfhttp%3A%2F%2Fwww.researchgate.net%2Fpublication%2F236867194_An_OGCM_Study_for_the_TOGA_Decade._Part_II_Barrier-Layer_Formation_and_Variabilityrefpaperuri:(6e6f2b1048b354e64b5a3c5b89059ebd)http://www.researchgate.net/publication/236867194_An_OGCM_Study_for_the_TOGA_Decade._Part_II_Barrier-Layer_Formation_and_VariabilityAbstract A set of OGCM experiments is used to investigate the processes responsible for barrier layer (BL) formation in the Pacific Ocean. As in existing datasets, BL appears in the present experiments both in the western Pacific (WP) and under the intertropical convergence zone (ITCZ). In the WP, the BL displays a strong interannual variability linked to ENSO variability, in qualitative agreement with the observations of Ando and McPhaden. In both the equatorial and 3-8S bands, a subduction process is responsible for BL formation. In the equatorial region, it results from a strong downwelling near the salinity front created by convergence between central Pacific salty water and WP freshwater. In the southern region, the subduction of the South Equatorial Current salty water involves mainly mixed layer thinning due to the freshening of the surface layer by rain and equatorial divergence of water from the eastward fresh equatorial jets. The formation of BL under the ITCZ is found to be mostly related to local precipitation. The impact of the BL presence is then investigated. The BL interannual variability modifies the surface layer heat budget by switching on and off the entrainment cooling. The haline stratification traps most of the wind stress in the surface layer of the fresh and warm pool and induces strong eastward currents in response to westerly wind bursts (WWBs). The overall effect of salinity stratification is to retain heat and momentum in the upper layer of the WP by restraining the exchanges with the cooler waters from below and from the central Pacific. The combined effect of zonal advection and mixing after a WWB results in an eastward shift of the thick BL regions along the equator. These properties of the BL structure might favor the growth of unstable air-ea interactions in the central Pacific after a WWB. |
Yim B. Y., S.-W. Yeh, Y. Noh, B.-K. Moon, and Y.-G. Park, 2008: Sea surface salinity variability and its relation to El Niño in a CGCM. Asia-Pacific J. Atmos. Sci., 44( 2), 173- 189.b9afe325-294a-43e2-aeb4-d30ac5674ee9100bc5dbf2456ab4a4dfe14a89258105http%3A%2F%2Fwww.dbpia.co.kr%2FJournal%2FArticleDetail%2F834575refpaperuri:(e41ce65c05869167ed9e28c8cba17295)http://www.dbpia.co.kr/Journal/ArticleDetail/834575We explore the characteristics of sea surface salinity (SSS) variability along with its relation to the El Ni09o by analyzing results from a coupled general circulation model (CGCM). The CGCM simulates realistic El Ni09o as well as the mean and the variability of SSS. The SSS anomaly variability is dominated on interannual timescales with its maximum variance in the western tropical Pacific, and large positive SSS anomaly events occur prior to El Ni09o. The SSS variability and its associated barrier layer thickness are related to the El Ni09o in the CGCM. Between two subsequent El Ni09o events a buildup of warm water is evident as indicated by a large barrier layer thickness in the western equatorial Pacific. Weak stratification due to high SSS anomalies helps to discharge the heat stored in the thick barrier layer in the western equatorial Pacific, initiating El Ni09o development. Further analysis is conducted to support the role of SSS variability associated with El Ni09o in terms of the variability of heat content anomalies. |
Yu J. Y., S. T. Kim, 2011: Reversed spatial asymmetries between El Niño and La Niña and their linkage to decadal ENSO modulation in CMIP3 models. J.Climate, 24, 5423- 5434. |
Yu J. Y., S. T. Kim, 2010: Identification of central-Pacific and Eastern-Pacific types of ENSO in CMIP3 models. Geophys. Res. Lett., 37,L15705, doi: 10.1029/2010GL044082.10.1029/2010GL0440824d0d9929747e174c45a9bae079669504http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1029%2F2010GL044082%2Ffullhttp://onlinelibrary.wiley.com/doi/10.1029/2010GL044082/full[1] Much understanding of the El Niño-Southern Oscillation (ENSO) has been obtained from the analyses of the climate simulations produced for World Climate Research Programme's Coupled Model Intercomparison Project phase 3 (CMIP3). However, most of these analyses do not consider the existence of the Eastern-Pacific (EP) and Central-Pacific (CP) types of ENSO events, which have been increasingly recognized as two distinct types of interannual sea surface temperature (SST) variation in the tropical Pacific. This study uses a regression-Empirical Orthogonal Function method to identify how well these two ENSO types are captured in the pre-industrial simulations of nineteen CMIP3 models. It is concluded that most CMIP3 models (13 out of 19) can produce realistically strong CP ENSOs, but only a few of them (9 out of 19) can produce realistically strong EP ENSOs. Six models that realistically simulate both the EP and CP ENSOs and their intensity ratio are identified. By separating the SST variability into these two types, it is further revealed that the leading periodicity of the simulated EP ENSO is linearly related to the latitudinal width of SST variability and varies from 1 to 5 years. As for the simulated CP ENSO, its leading periodicity is either 2 or 4 years depending on whether its SST variability is located to the east of the dateline or in the western-Pacific warm pool, respectively. The identification produced in this study offers useful information to further understand the two types of ENSO using the CMIP3 models. |
Zhang R. H., A. J. Busalacchi, 2009: Freshwater flux (FWF)-induced oceanic feedback in a hybrid coupled model of the tropical Pacific. J.Climate, 22, 853- 879.10.1175/2008JCLI2543.1225d0f4ba2754545f070de44e940a770http%3A%2F%2Fwww.cabdirect.org%2Fabstracts%2F20093123132.htmlhttp://www.cabdirect.org/abstracts/20093123132.htmlThe impacts of freshwater flux (FWF) forcing on interannual variability in the tropical Pacific climate system are investigated using a hybrid coupled model (HCM), constructed from an oceanic general circulation model (OGCM) and a simplified atmospheric model, whose forcing fields to the ocean consist of three components. Interannual anomalies of wind stress and precipitation minus evaporation, (P 09 E), are calculated respectively by their statistical feedback models that are constructed from a singular value decomposition (SVD) analysis of their historical data. Heat flux is calculated using an advective atmospheric mixed layer (AML) model. The constructed HCM can well reproduce interannual variability associated with ENSO in the tropical Pacific. HCM experiments are performed with varying strengths of anomalous FWF forcing. It is demonstrated that FWF can have a significant modulating impact on interannual variability. The buoyancy flux (QB) field, an important parameter determining the mixing and entrainment in the equatorial Pacific, is analyzed to illustrate the compensating role played by its two contributing parts: one is related to heat flux (QT) and the other to freshwater flux (QS). A positive feedback is identified between FWF and SST as follows: SST anomalies, generated by El Ni01±o, nonlocally induce large anomalous FWF variability over the western and central regions, which directly influences sea surface salinity (SSS) and QB, leading to changes in the mixed layer depth (MLD), the upper-ocean stability, and the mixing and the entrainment of subsurface waters. These oceanic processes act to enhance the SST anomalies, which in turn feedback to the atmosphere in a coupled ocean09 tmosphere system. As a result, taking into account anomalous FWF forcing in the HCM leads to an enhanced interannual variability and ENSO cycles. It is further shown that FWF forcing is playing a different role from heat flux forcing, with the former acting to drive a change in SST while the latter represents a passive response to the SST change. This HCM-based modeling study presents clear evidence for the role of FWF forcing in modulating interannual variability in the tropical Pacific. The significance and implications of these results are further discussed for physical understanding and model improvements of interannual variability in the tropical Pacific ocean09 tmosphere system. |
Zhang R. H., G. H. Wang, D. K. Chen, A. J. Busalacchi, and E. C. Hackert, 2010: Interannual biases induced by freshwater flux and coupled feedback in the tropical Pacific. Mon. Wea. Rev., 138, 1715- 1737.10.1175/2009MWR3054.1dd2ee5d97426032e549fb7e6f96b1eb0http%3A%2F%2Fwww.researchgate.net%2Fpublication%2F249621950_Interannual_Biases_Induced_by_Freshwater_Flux_and_Coupled_Feedback_in_the_Tropical_Pacifichttp://www.researchgate.net/publication/249621950_Interannual_Biases_Induced_by_Freshwater_Flux_and_Coupled_Feedback_in_the_Tropical_PacificFreshwater flux (FWF) forcing induced feedback has not been represented adequately in many coupled ocean-atmosphere models of the tropical Pacific. Previously, various approximations have been made in representing the FWF forcing in climate modeling. In this article, using a hybrid coupled model (HCM), sensitivity experiments are performed to examine the extent to which this forcing and related feedback effects can contribute to tropical biases in interannual simulations of the tropical Pacific. The total FWF into the ocean, represented by precipitation (P) minus evaporation (E), (P - E), is separated into its climatological part and interannual anomaly part: FWF(Total) = (P - E)(clim) + FWF(inter). The former can be prescribed (seasonally varying); the latter can be captured using an empirical model linking with large-scale sea surface temperature (SST) variability. Four cases are considered with different FWF(inter) specifications: interannual (P - E) forcing [FWF(inter) = (P - E)(inter)], interannual P forcing (FWF(inter) = P(inter)), interannual E forcing (FWF(inter) = -E(inter)), and climatological (P - E) forcing (FWF(inter) = 0.0), respectively. The HCM-based experiments indicate that different FWF(inter) approximations can modulate interannual variability in a substantial way. The HCM with the interannual (P - E) forcing, in which a positive SST - (P - E)(inter) feedback is included explicitly, has a reasonably realistic simulation of interannual variability. When FWF(inter) is approximated approximated in some ways, the simulated interannual variability can be modulated significantly: it is weakened with the climatological (P - E) forcing and is even more damped with the interannual E forcing but is exaggerated with the interannual P forcing. Quantitatively, taking the interannual (P - E) forcing run as a reference, the Nino-3 SST variance can be reduced by about 12% and 26% in the climatological (P - E) forcing run and interannual E forcing run, respectively, but overestimated by 11% in the P(inter) forcing run. It is demonstrated that FWF can be a clear bias source for coupled model simulations in the tropical Pacific. |
Zhang R. H., S. E. Zebiak, R. Kleeman, and N. Keenlyside, 2005: Retrospective El Niño forecasts using an improved intermediate coupled model. Mon. Wea. Rev., 133, 2777- 2802.10.1175/MWR3000.1d7e01395-11cf-4052-9d08-8d6ef0786c74c56515f86939e580924fd4743b4cc8fchttp%3A%2F%2Fwww.researchgate.net%2Fpublication%2F242443365_Retrospective_El_Nio_Forecasts_Using_an_Improved_Intermediate_Coupled_Modelrefpaperuri:(d31ce0f823315f5ab6f96a7ab6efe803)http://www.researchgate.net/publication/242443365_Retrospective_El_Nio_Forecasts_Using_an_Improved_Intermediate_Coupled_ModelAbstract A new intermediate coupled model (ICM) is presented and employed to make retrospective predictions of tropical Pacific sea surface temperature (SST) anomalies. The ocean dynamics is an extension of the McCreary baroclinic modal model to include varying stratification and certain nonlinear effects. A standard configuration is chosen with 10 baroclinic modes plus two surface layers, which are governed by Ekman dynamics and simulate the combined effects of the higher baroclinic modes from 11 to 30. A nonlinear correction associated with vertical advection of zonal momentum is incorporated and applied (diagnostically) only within the two surface layers, forced by the linear part through nonlinear advection terms. As a result of these improvements, the model realistically simulates the mean equatorial circulation and its variability. The ocean thermodynamics include an SST anomaly model with an empirical parameterization for the temperature of subsurface water entrained into the mixed layer ( T e ), which is optimally calculated in terms of sea surface height (SSH) anomalies using an empirical orthogonal function (EOF) analysis technique from historical data. The ocean model is then coupled to a statistical atmospheric model that estimates wind stress ( ) anomalies based on a singular value decomposition (SVD) analysis between SST anomalies observed and anomalies simulated from ECHAM4.5 (24-member ensemble mean). The coupled system exhibits realistic interannual variability associated with El Niño, including a predominant standing pattern of SST anomalies along the equator and coherent phase relationships among different atmosphere-cean anomaly fields with a dominant 3-yr oscillation period. Twelve-month hindcasts/forecasts are made during the period 1963-2002, starting each month. Only observed SST anomalies are used to initialize the coupled predictions. As compared to other prediction systems, this coupled model has relatively small systematic errors in the predicted SST anomalies, and its SST prediction skill is apparently competitive with that of most advanced coupled systems incorporating sophisticated ocean data assimilation. One striking feature is that the model skill surpasses that of persistence at all lead times over the central equatorial Pacific. Prediction skill is strongly dependent on the season, with the correlations attaining a minimum in spring and a maximum in fall. Cross-validation experiments are performed to examine the sensitivity of the prediction skill to the data periods selected for training the empirical T e model. It is demonstrated that the artificial skill introduced by using a dependently constructed T e model is not significant. Independent forecasts are made for the period 1997-2002 when no dependent data are included in constructing the two empirical models ( T e and ). The coupled model has reasonable success in predicting transition to warm phase and to cold phase in the spring of 1997 and 1998, respectively. Potential problems and further improvements are discussed with the new intermediate prediction system. |
Zheng F., R. H. Zhang, 2012: Effects of interannual salinity variability and freshwater flux forcing on the development of the 2007/08 La Nina event diagnosed from Argo and satellite data. Dyn. Atmos.Oceans, 57, 45- 57.10.1016/j.dynatmoce.2012.06.002d3cc1d9d-f605-4098-bd57-df98b939f3bb656b2a4256d28f9f949e51953b9f2b56http%3A%2F%2Fwww.sciencedirect.com%2Fscience%2Farticle%2Fpii%2FS0377026512000255refpaperuri:(0aaf3da1adce24a55f25f133bfdbb6cc)http://www.sciencedirect.com/science/article/pii/S0377026512000255Oceanic salinity and its related freshwater flux (FWF) forcing in the tropical Pacific have been of increased interest recently due to their roles in the El Niño-Southern Oscillation (ENSO), the global climate and water cycle. A comprehensive data analysis is performed to illustrate the significant effects of interannual salinity variability and FWF forcing during the 2007/08 La Niña event using three-dimensional temperature and salinity fields from Argo profiles, and some related fields derived from the Argo and satellite-based data, including the mixed layer depth (MLD), heat flux, freshwater flux, and buoyancy flux ( Q B ). It is demonstrated that during the developing phase of 2007/08 La Niña, a negative FWF anomaly and its associated positive sea surface salinity (SSS) anomaly in the western-central basin act to increase oceanic density and de-stabilize the upper ocean. At the same time, the negative FWF anomaly tends to reduce a positive Q B anomaly and deepen the mixed layer (ML). These related oceanic processes act to strengthen the vertical mixing and entrainment of subsurface water at the base of ML, which further enhance cold sea surface temperature (SST) anomalies associated with the La Niña event, a demonstration of a positive feedback induced by FWF forcing. |
Zheng F., R. H. Zhang, 2015: Interannually varying salinity effects on ENSO in the tropical Pacific: A diagnostic analysis from Argo. Ocean Dynamics, 65( 5), 691- 705.10.1007/s10236-015-0829-7f64ced5ac1a888d314fa376088b22037http%3A%2F%2Flink.springer.com%2F10.1007%2Fs10236-015-0829-7http://link.springer.com/10.1007/s10236-015-0829-7In this paper, three-dimensional temperature and salinity fields from Argo profiles are used to diagnose the interannual variations of some related upper oceanic fields in the tropical Pacific, with a focus on interannually varying salinity effects on the El Ni09o-Southern Oscillation (ENSO) events. It is clearly demonstrated that the salinity field plays a significantly large role in modulating the density and mixed layer (ML) over the western-central tropical Pacific. In particular, the contribution of interannually varying salinity to the interannual variations in density, ML, and stratification is surprisingly larger than that of interannually varying temperature. Over the entire region west of the dateline, the salinity effects are not limited to the surface but are clearly seen below the ML as represented in density and stratification fields. Furthermore, the mechanism for how the anomalous salinity field is modulating the ENSO cycle is investigated and explained through the El Ni09o (2009–2010) and La Ni09a (2010–2011) cases. Evidently, salinity field is shown to exert a significant influence on interannual variability as it directly affects the vertical mixing and entrainment at the base of the ML, the processes important to sea surface temperature (SST) in the equatorial regions. |
Zheng F., R. H. Zhang, and J. Zhu, 2014: Effects of interannual salinity variability on the barrier layer in the western-central equatorial Pacific: A diagnostic analysis from Argo. Adv. Atmos. Sci.,31(3), 532-542, doi: 10.1007/s00376-013-3061-8.10.1007/s00376-013-3061-85fab2c995c6adf49f5c3ddae861178d3http%3A%2F%2Flink.springer.com%2F10.1007%2Fs00376-013-3061-8http://d.wanfangdata.com.cn/Periodical_dqkxjz-e201403004.aspx |
Zheng F., H. Wang, and L. Y. Wan, 2015: Effects of interannual salinity variability on the dynamic height in the western equatorial Pacific as diagnosed by Argo. Acta Oceanologica Sinica, 34( 5), 22- 28.10.1007/s13131-015-0663-2615a12217a5057d12b98be809c720a12http%3A%2F%2Flink.springer.com%2F10.1007%2Fs13131-015-0663-2http://d.wanfangdata.com.cn/Periodical_hyxb-e201505003.aspx |
Zhi H., R. H. Zhang, P. F. Lin, and L. N. Wang, 2015: Simulation of salinity variability and the related freshwater flux forcing in the tropical pacific: An evaluation using the Beijing Normal University Earth System Model (BNU-ESM). Adv. Atmos. Sci.,32, 1551-1564, doi: 10.1007/s00376-015-4240-6.10.1007/s00376-015-4240-62aa9323c-ca21-4a9d-961f-f590d6ab5712bda8b2729287999d56e99f05f9e2d965http%3A%2F%2Fwww.cnki.com.cn%2FArticle%2FCJFDTotal-DQJZ201511010.htmhttp://d.wanfangdata.com.cn/Periodical/dqkxjz-e201511010The climatology and interannual variability of sea surface salinity(SSS) and freshwater flux(FWF) in the equatorial Pacific are analyzed and evaluated using simulations from the Beijing Normal University Earth System Model(BNU-ESM).The simulated annual climatology and interannual variations of SSS, FWF, mixed layer depth(MLD), and buoyancy flux agree with those observed in the equatorial Pacific. The relationships among the interannual anomaly fields simulated by BNU-ESM are analyzed to illustrate the climate feedbacks induced by FWF in the tropical Pacific. The largest interannual variations of SSS and FWF are located in the western-central equatorial Pacific. A positive FWF feedback effect on sea surface temperature(SST) in the equatorial Pacific is identified. As a response to El Nino-outhern Oscillation(ENSO),the interannual variation of FWF induces ocean processes which, in turn, enhance ENSO. During El Ni ?no, a positive FWF anomaly in the western-central Pacific(an indication of increased precipitation rates) acts to enhance a negative salinity anomaly and a negative surface ocean density anomaly, leading to stable stratification in the upper ocean. Hence, the vertical mixing and entrainment of subsurface water into the mixed layer are reduced, and the associated El Ni ?no is enhanced. Related to this positive feedback, the simulated FWF bias is clearly reflected in SSS and SST simulations, with a positive FWF perturbation into the ocean corresponding to a low SSS and a small surface ocean density in the western-central equatorial Pacific warm pool. |
Zhu J. S., G. Q. Zhou, R. H. Zhang, and Z. B. Sun, 2013: Improving ENSO prediction in a hybrid coupled model with an embedded entrainment temperature parameterisation. Int. J. Climatol., 33( 2), 343- 355.10.1002/joc.3426a5f713f5117bed9e24af397ffd345568http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1002%2Fjoc.3426%2Fabstracthttp://onlinelibrary.wiley.com/doi/10.1002/joc.3426/abstractABSTRACT Improving El Niño/Southern Oscillation (ENSO) forecast remains a great challenge in the climate‐predicting community. Previously, an improved solution to sea surface temperature (SST) anomaly simulations in the tropical Pacific was obtained by explicitly embedding into an ocean general circulation model (OGCM) a separate SST anomaly submodel with an empirical parameterisation for the temperature of subsurface water entrained into the ocean mixed layer (T e ). In the present work, the benefit of the approach is explored and demonstrated in terms of ENSO prediction. A hybrid coupled ocean‐atmosphere model (HCM) is utilized to perform two retrospective ENSO forecasts, differing in the way SST anomaly fields are taken for their coupling to the atmosphere, one directly from the OGCM (referred to as a standard coupling, HCMstd), and another from the embedded SST anomaly submodel with optimized T e parameterisation (referred to as an embedded coupling, HCMembed). The results indicate that ENSO forecasts can be effectively improved using the embedded approach; the predicted Niño‐3.4 SST anomaly correlation is higher by 0.1–0.2 at a 12‐month lead time in the HCMembed than in the HCMstd, and the corresponding root‐mean‐square (RMS) error is lower by 0.1–0.2 °C. Further improvements and applications are discussed. Copyright 08 2012 Royal Meteorological Society |
Zhu J. S., B. H. Huang, R. H. Zhang, Z. Z. Hu, A. Kumar, M. A. Balmaseda, L. Marx, and J. L. Kinter III, 2014: Salinity anomaly as a trigger for ENSO events. Sci. Rep., 4,6821, doi: 10.1038/srep06821.10.1038/srep068212535228536cfb64042c90c435f825fb7a5449842http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fpubmed%2F25352285http://www.ncbi.nlm.nih.gov/pubmed/25352285According to the classical theories of ENSO, subsurface anomalies in ocean thermal structure are precursors for ENSO events and their initial specification is essential for skillful ENSO forecast. Although ocean salinity in the tropical Pacific (particularly in the western Pacific warm pool) can vary in response to El Niño events, its effect on ENSO evolution and forecasts of ENSO has been less explored. Here we present evidence that, in addition to the passive response, salinity variability may also play an active role in ENSO evolution, and thus important in forecasting El Niño events. By comparing two forecast experiments in which the interannually variability of salinity in the ocean initial states is either included or excluded, the salinity variability is shown to be essential to correctly forecast the 2007/08 La Niña starting from April 2007. With realistic salinity initial states, the tendency to decay of the subsurface cold condition during the spring and early summer 2007 was interrupted by positive salinity anomalies in the upper central Pacific, which working together with the Bjerknes positive feedback, contributed to the development of the La Niña event. Our study suggests that ENSO forecasts will benefit from more accurate salinity observations with large-scale spatial coverage. |