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Mesoscale SST perturbation-induced impacts on climatological precipitation in the Kuroshio-Oyashio extension region,as revealed by the WRF simulations

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Journal of Oceanology and Limnology 2019年第2期37卷 385-397页

作者： GAO Jiaxiang zhang rong-hua WANG Hongna CAS Key Laboratory of Ocean Circulation and Waves Institute of Oceanology Chinese Academy of Sciences Qingdao 266071China University of Chinese Academy of Sciences Beijing 100049 China Laboratory for Ocean Dynamics and Climate Qingdao National Laboratory for Marine Science and Technology Qingdao 266237 China

Mesoscale coupling between perturbations of mesoscale sea surface temperature (SST) and lowlevel winds has been extensively studied using available high-resolution satellite observations. However, the climatological impacts of mesoscale SST perturbations (SST meso ) on the free atmosphere have not been fully understood. In this study, the rectified eff ect of SSTmeso on local climatological precipitation in the Kuroshio- Oyashio Extension (KOE) region is investigated using the Weather Research and Forecasting (WRF) Model;two runs are performed, one forced by low-resolution SST fields (almost no mesoscale signals) and another by additional high-resolution SSTmeso fields extracted from satellite observations. Climatological precipitation response to SST meso is characterized mainly by enhanced precipitation on the warmer flank of three oceanic SST fronts in this region. The results show that the positive correlation between the 10-m wind speed perturbations and SSTmeso is well captured by the WRF model with a reasonable spatial pattern but relatively weak strength. The addition of SSTmeso improves the climatological precipitation simulated by WRF with a better representation of fine-scale structures compared with satellite observations. A closer examination on the underlying mechanism suggests that while the pressure adjustment mechanism can explain the climatological precipitation enhancement along the fronts and the relatively high contribution of the convective precipitation, other factors such as synoptic events should also be taken into consideration to account for the seasonality of the precipitation response.

关键词： mesoscale SST perturbations and eff ects WRF model Kuroshio-Oyashio Extension climatological precipitation

Effects of Interannual Salinity Variability on the Barrier Layer in the Western-Central Equatorial Pacific:A Diagnostic Analysis from Argo

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Advances in Atmospheric Sciences 2014年第3期31卷 532-542页

作者： ZHENG Fei zhang rong-hua ZHU Jiang International Center for Climate and Environment Science Institute of Atmospheric Physics Chinese Academy of Sciences Key Laboratory of Ocean Circulation and Waves Institute of Oceanology Chinese Academy of Sciences Earth System Science Interdisciplinary Center University of MarylandCollege ParkMaryland 20740USA

ABSTRACT In this paper, interannual variations in the barrier layer thickness （BLT） are analyzed using Argo three-dimensional temperature and salinity data, with a locus on the effects of interannually varying salinity on the evolution of the El Nifio Southern Oscillation （ENSO）. The interannually varying BLT exhibits a zonal seesaw pattern across the equatorial Pacific during ENSO cycles. This phenomenon has been attributed to two different physical processes. During E1 Nifio （La Nifia）, the barrier layer （BL） is anomalously thin （thick） west of about 160°E, and thick （thin） to the east. In the western equatorial Pacific （the western part： 130°-160°E）, interannual variations of the BLT indicate a lead of one year relative to those of the ENSO onset. The interannual variations of the BLT can be largely attributed to the interannual temperature variability, through its dominant effect on the isothermal layer depth （ILD）. However, in the central equatorial Pacific （the eastern part： 160~E- 170~W）, interannual variations of the BL almost synchronously vary with ENSO, with a lead of about two months relative to those of the local SST. In this region, the interannual variations of the BL are significantly affected by the interannually varying salinity, mainly through its modulation effect on the mixed layer depth （MLD）. As evaluated by a onedimensional boundary layer ocean model, the BL around the dateline induced by interannual salinity anomalies can significantly affect the temperature fields in the upper ocean, indicating a positive feedback that acts to enhance ENSO.

关键词： barrier layer salinity effect ENSO Argo

Seasonal variability of the Kuroshio Current at the PN Section in the East China Sea based on in-situ observation from 1987 to 2010

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Acta Oceanologica Sinica 2015年第5期34卷 12-21页

作者： WEI Yanzhou PEI Yuhua zhang rong-hua Key Laboratory of Ocean Circulation and Wave Institute of OceanologyChinese Academy of Sciences University of the Chinese Academy of Sciences State Key Laboratory of Satellite Ocean Environment Dynamics Second Institute of OceanographyState Oceanic Administration College of Physical and Environmental Oceanography Ocean University of China

As the spatio-temporal variability of the Kuroshio is highly influenced by mesoscale eddies, representing its seasonal variability characteristics requires sufficiently long term observations to reduce the uncertainties. Geostrophic velocity data estimated from hydrographic observation from 1987 to 2010 and the shipboard ADCP velocity data from 1993 to 2008 at the PN Section in the central East China Sea are collected to view the seasonal variability objectively. From both types of observation, it is found that the seasonal climatology mean of the Kuroshio Current exhibits significant difference in three areas, which are located at the Kuroshio Current core and its two flanks in a shallow layer less than 300 m, with the weakest northeast current at the core in autumn, the strongest counter current on the right flank in spring, and the strongest northeast current on the left flank in autumn, respectively. The seasonal variance of the Kuroshio Current also exhibits significant difference on the off- shore side of the Kuroshio, with larger variance in spring and summer while smaller variance in autumn and winter. For the current parallel to the PN Section, the ratio of the seasonal variability component to the intraseasonal variability component is relatively smaller than that for the current perpendicular to the PN Section. Further analyses indicate that the seasonal variability at the PN Section is tightly linked to the upstream and downstream current variability.

关键词： Kuroshio Current seasonal variability East China Sea significance test

Representing surface wind stress response to mesoscale SST perturbations in western coast of South America using Tikhonov regularization method

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Journal of Oceanology and Limnology 2020年第3期38卷 679-694页

作者： CUI Chaoran zhang rong-hua WANG Hongna WEI Yanzhou Key Laboratory of Ocean Circulation and Waves Institute of OceanologyChinese Academy of SciencesQingdao 266071China Center for Ocean Mega-Science Chinese Academy of SciencesQingdao 266071China University of Chinese Academy of Sciences Beijing 100049China Qingdao National Laboratory for Marine Science and Technology Qingdao 266000China State Key Laboratory of Satellite Ocean Environment Dynamics Second Institute of OceanographyMinistry of Natural ResourcesHangzhou 310012China

Interaction between mesoscale perturbations of sea surface temperature(SSTmeso)and wind stress(WSmeso)has great influences on the ocean upwelling system and turbulent mixing in the atmospheric boundary *** daily Quik-SCAT wind speed data and AMSR-E SST data,SSTmeso and WSmeso fields in the western coast of South America are extracted by using a locally weighted regression method(LOESS).The spatial patterns of SSTmeso and WSmeso indicate strong mesoscale SST-wind stress coupling in the *** coupling coefficient between SSTmeso and WSmeso is about 0.0095 N/(m^2·℃)in winter and 0.0082 N/(m^2·℃)in *** on mesoscale coupling relationships,the mesoscale perturbations of wind stress divergence(Div(WSmeso))and curl(Curl(WSmeso))can be obtained from the SST gradient perturbations,which can be further used to derive wind stress vector perturbations using the Tikhonov regularization *** computational examples are presented in the western coast of South America and the patterns of the reconstructed WS meso are highly consistent with SSTmeso,but the amplitude can be underestimated *** matching the spatially averaged maximum standard deviations of reconstructed WSmeso magnitude and observations,a reasonable magnitude of WSmeso can be obtained when a rescaling factor of 2.2 is *** current ocean models forced by prescribed wind cannot adequately capture the mesoscale wind stress response,the empirical wind stress perturbation model developed in this study can be used to take into account the feedback effects of the mesoscale wind stress-SST coupling in ocean *** applications are discussed for taking into account the feedback effects of the mesoscale coupling in largescale climate models and the uncoupled ocean models.

关键词： mesoscale air-sea coupling Tikhonov’s regularization method western coast of South America

Processes Leading to Second-Year Cooling of the 2010–12 La Ni?a Event,Diagnosed Using GODAS

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Advances in Atmospheric Sciences 2015年第3期32卷 424-438页

作者： FENG Licheng zhang rong-hua WANG zhanggui CHEN Xingrong National Marine Environmental Forecasting Center State Oceanic Administration Key Laboratory of Ocean Circulation and Waves Institute of OceanologyChinese Academy of Sciences Earth System Science Interdisciplinary Center (ESSIC) University of MarylandCollege ParkMaryland USA 20740

Isopycnal analyses were performed on the Global Ocean Data Assimilation System （GODAS） to determine the oceanic processes leading to so-called second-year cooling of the La Nina *** 2010-12,a horseshoe-like pattern was seen,connecting negative temperature anomalies off and on the Equator,with a dominant influence from the South *** the 2010 La Nina event,warm waters piled up at subsurface depths in the western tropical *** in early 2011,these warm subsurface anomalies propagated along the Equator toward the eastern basin,acting to reverse the sign of sea surface temperature （SST） anomalies （SSTAs） there and initiate a warm ***,throughout early 2011,pronounced negative anomalies persisted off the Equator in the subsurface depths of the South *** isopycnal surfaces outcropped in the central equatorial Pacific,negative anomalies from the subsurface spread upward along with mean circulation pathways,naturally initializing a cold *** the summer,a cold SSTA reappeared in the central basin,which subsequently strengthened due to the off-equatorial effects mostly in the South *** SSTAs acted to initiate local coupled air-sea interactions,generating atmospheric-oceanic anomalies that developed and evolved with the second-year cooling in the fall of ***,the cooling tendency in mid-2012 did not develop into another La Nina event,since the cold anomalies in the South Pacific were not strong *** analysis of the 2007-09 La Nina event revealed similar processes to the 2010-12 La Nina event.

关键词： La Ni(n)a second-year cooling off-equatorial effects isopycnal analyses circulation pathways GODAS

Variability of sea surface height in the South China Sea and its relationship to Pacific oscillations

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Acta Oceanologica Sinica 2015年第12期34卷 80-92页

作者： PEI Yuhua zhang rong-hua zhang Xiangming JIANG Lianghong WEI Yanzhou College of Oceanic and Atmospheric Sciences Ocean University of China State Key Laboratory of Satellite Ocean Environment Dynamics Second Institute of Oceanography State Oceanic Administration Key Laboratory of Ocean Circulation and Waves Institute of Oceanology Chinese Academy of Sciences

The spatio-temporal variability modes of the sea surface height in the South China Sea（SCS-SSH） are obtained using the Cyclostationary Empirical Orthogonal Function（CSEOF） method, and their relationships to the Pacific basin scale oscillations are examined. The first CSEOF mode of the SCS-SSH is a strongly phase-locked annual cycle that is modulated by a slowly varying principal component（PC）; the strength of this annual cycle becomes reduced during El Ni？o events（at largest by 30% off in 1997/98） and enhanced during La Ni？a events. The second mode is a low frequency oscillation nearly on decadal time scale, with its spatial structure exhibiting an obscure month-dependence; the corresponding PC is highly correlated with the Pacific Decadal Oscillation（PDO） *** independent oscillations in the Pacific are isolated by using the independent component（IC） analysis（ICA）method, and their effects on the SCS-SSH are examined. It is revealed that the pure ENSO mode（which resembles the east Pacific ENSO） has little effect on the low frequency variability of the SCS-SSH while the ENSO reddening mode（which resembles the central Pacific ENSO） has clear effect. As the ENSO reddening mode is an important constituent of the PDO, this explains why the PDO is more important than ENSO in modulating the low frequency variability of SCS-SSH. Meridional saddle like oscillation mode, the Kuroshio extension warming mode, and the equatorial cooling mode are also successfully detected by the ICA, but they have little effect on the low frequency variability of the SCS-SSH. Further analyses suggest the Pacific oscillations are probably influencing the variability of the SCS-SSH in ways that are different from that of the sea surface temperature（SST） in the SCS.

关键词： South China Sea sea surface height ENSO PDO

Sensitivity of ENSO Variability to Pacific Freshwater Flux Adjustment in the Community Earth System Model

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Advances in Atmospheric Sciences 2014年第5期31卷 1009-1021页

作者： KANG Xianbiao huaNG ronghui WANG zhanggui zhang rong-hua Center for Monsoon System Research Institute of Atmospheric Physics Chinese Academy of Sciences University of the Chinese Academy of Sciences National Marine Environmental Forecasting Center State Oceanic Administration National Marine Environmental Forecasting Center State Oceanic Administration Key Laboratory of Ocean Circulation and Waves Institute of Oceanology Chinese Academy of Sciences

The effects of freshwater flux （FWF） on modulating ENSO have been of great interest in recent years. Large FWF bias is evident in Coupled General Circulation Models （CGCMs）, especially over the tropical Pacific where large precipitation bias exists due to the so-called ＂double ITCZ＂ problem. By applying an empirical correction to FWF over the tropical Pacific, the sensitivity of ENSO variability is investigated using the new version （version 1.0） of the NCAR＇s Community Earth System Model （CESM1.0）, which tends to overestimate the interannual variability of ENSO accompanied by large FWF into the ocean. In response to a small adjustment of FWF, interannual variability in CESM1.0 is reduced significantly, with the amplitude of FWF being reduced due to the applied adjustment part whose sign is always opposite to that of the original FWF field. Furthermore, it is illustrated that the interannual variability of precipitation weakens as a response to the reduced interannual variability of SST. Process analysis indicates that the interannual variability of SST is damped through a reduced FWF-salt-density-mixing-SST feedback, and also through a reduced SST-wind-thermocline feedback. These results highlight the importance of FWF in modulating ENSO, and thus should be adequately taken into account to improve the simulation of FWF in order to reduce the bias of ENSO simulations by CESM.

关键词： ENSO freshwater flux CESM

Quantitative Analysis of the Feedback Induced by the Freshwater Flux in the Tropical Pacific Using CMIP5

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Advances in Atmospheric Sciences 2015年第10期32卷 1341-1353页

作者： ZHI Hai zhang rong-hua LIN Pengfei WANG Lanning The Earth System Modeling Center and College of Atmospheric Sciences Nanjing University of Information Science and Technology Key Laboratory of Ocean Circulation and Waves Institute of OceanologyChinese Academy of Sciences State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics Institute of Atmospheric PhysicsChinese Academy of Sciences College of Global Change and Earth System Science Beijing Normal University

Freshwater flux （FWF） directly affects sea surface salinity （SSS） and hence modulates sea surface temperature （SST） in the tropical Pacific. This paper quantifies a positive correlation between FWF and SST using observations and simulations of the fifth phase of the Coupled Model Intercomparison Project （CMIP5） to analyze the interannual variability in the tropical Pacific. Comparisons among the displacements of FWF, SSS and SST interannual variabilities illustrate that a large FWF variability is located in the west-central equatorial Pacific, covarying with a large SSS variability, whereas a large SST variability is located in the eastern equatorial Pacific. Most CMIP5 models can reproduce the fact that FWF leads to positive feedback to SST through an SSS anomaly as observed. However, the difference in each model＇s performance results from different simulation capabilities of the CMIP5 models in the magnitudes and positions of the interannual variabilities, including the mixed layer depth and the buoyancy flux in the equatorial Pacific. SSS anomalies simulated from the CMIP5 multi-model are sensitive to FWF interannual anomalies, which can lead to differences in feedback to interannual SST variabilities. The relationships among the FWF, SSS and SST interannual variabilities can be derived using linear quantitative measures from observations and the CMIP5 multi-model simulations. A 1 mm d-1 FWF anomaly corresponds to an SSS anomaly of nearly 0.12 psu in the western tropical Pacific and a 0.11℃ SST anomaly in the eastern tropical Pacific.

关键词： feedback freshwater flux CMIP5 correlation

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)

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Advances in Atmospheric Sciences 2015年第11期32卷 1551-1564页

The 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-Southern Oscillation （ENSO）, the interannual variation of FWF induces ocean processes which, in turn, enhance ENSO. During El Nino, 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 E1 Nino 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.

关键词： freshwater flux salinity feedback tropical Pacific BNU-ESM