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Interpreting the sea surface temperature warming trend in the Yellow Sea and East China Sea

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Science China Earth Sciences 2017年第8期60卷 1558-1568页

作者： pei yuhua LIU XiaoHui HE HaiLun State Key Laboratory of Satellite Ocean Environment Dynamics Second Institute of OceanographyState Oceanic Administration

Previous studies have demonstrated that the low-frequency sea surface temperature(SST) variability in the Yellow Sea and East China Sea(YECS) is linked to large-scale climate variability, but explanations on the mechanisms vary. This study examines the low-frequency variability and trends of some atmospheric and oceanic variables to discuss their different effects on the YECS warming. The increasing temperature trend is also observed at a hydrographic section transecting the *** increasing rate of ocean temperature decreases with depth, which might result in an increase in vertical stratification and a decrease in vertical mixing, and thus plays a positive role on the YECS warming. The surface net heat flux(downward positive)displays a decreasing trend, which is possibly a result of the YECS warming, and, in turn, inhibits it. Wind speeds show different trends in different datasets, such that its role in the YECS warming is uncertain. The trends in wind stress divergence and curl have large uncertainties, so their effects on SST warming are still unclear. The Kuroshio heat transport calculated in this study,displays no significantly increasing trend, so is an unlikely explanation for the SST warming. Limited by sparse ocean observations,sophisticated assimilative climate models are still needed to unravel the mechanisms behind the YECS warming.

关键词： Sea surface temperature East China Sea Yellow Sea Regional climate change Surface heat flux

Roles of different physical processes in upper ocean responses to Typhoon Rammasun(2008)-induced wind forcing

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Science China Earth Sciences 2019年第4期62卷 684-692页

作者： yuhua pei Rong-Hua ZHANG Dake CHEN State Key Laboratory of Satellite Ocean Environment Dynamics Second Institute of OceanographyMinistry of Natural Resources CAS Key Laboratory of Ocean Circulation and Waves Institute of Oceanology Chinese Academy of Sciences Qingdao National Laboratory for Marine Science and Technology University of Chinese Academy of Sciences

This study investigates the roles of different physical processes in the oceanic response to tropical cyclones(TCs) in the Pacific, using an ocean general circulation model with several numerical experiments. A case study is focused on Typhoon Rammasun, which passed through the northwestern tropical Pacific in May 2008. TC-induced wind stress fields are extracted using a locally-weighted regression(Loess) method from a six-hourly Cross-Calibrated Multi-Platform satellite scatterometer wind product. By comparing model experiments with TC wind forcing being explicitly included or not, the effects of TC on the ocean are isolated in a clean way. The local oceanic response is characterized by a cooling in the surface layer that persists along the typhoon track as a cold wake, and a deepening of the mixed layer(ML). The TC-induced wind can affect the ocean through the momentum effects, the ML processes(the stirring effect on the ML depth), and heat flux(via wind speed), *** of numerical experiments with these different underlying processes explicitly represented or not indicate that vertical mixing and upwelling are dominant processes responsible for surface cooling, while the surface heat flux also plays a nonnegligible role. Specifically, vertical mixing, upwelling and surface heat flux account for respectively ～53%, ～31% and ～16% of the sea surface temperature cooling. However, for the ML response, the vertical mixing and surface heat flux are dominant processes for the ML deepening, while the contribution from upwelling process is negligible. This study provides new insights into how TC-indcued wind forcing affects the ocean by isolating each different individual process in a clear way, which differs from previous direct heat budget analyses.

关键词： Ocean response to typhoon Ocean modeling Vertical mixing The tropical Pacific

A case study of the consistency problem in the inverse estimation

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Acta Oceanologica Sinica 2017年第9期36卷 45-51页

作者： WEI Yanzhou KANG Xianbiao pei yuhua State Key Laboratory of Satellite Ocean Environment Dynamics Second Institute of Oceanography State Oceanic Administration Hangzhou 310012 China Key Laboratory of Ocean Circulation and Waves Institute of Oceanology Chinese Academy of Sciences Qingdao 266071 China University of Chinese Academy of Sciences Beijing 100049 China College of Air Traffic Management Civil Aviation Flight University of China Guanghan 618307 China

Inverse technique is a widely used method in oceanography, but it has a problem that the retrieved solutions often violate model prior assumptions. To tune the model has consistent solutions, an iteration approach, which successively utilizes the posterior statistics for next round inverse estimation, is introduced and tested from a real case study. It is found that the consistency may become elusive as the determinants of solution and noise covariance matrices become zero in the iteration process. However, after several steps of such operation, the difference between posterior statistics and the model prior ones can be gradually reduced.

关键词： regularization consistency inverse problems box inverse model L-curve method

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

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

A New Probability Distribution Function of Wave Steepness

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Journal of Ocean University of China 2008年第3期7卷 246-250页

作者： JIANG Xiulan ZHENG Guizhen pei yuhua College of Physical and Environmental Oceanography Ocean University of China Qingdao 266003 P. R. China School of Science Qingdao Technological University Qingdao 266033 P. R. China

Wave steepness is an important characteristic describing the severity of sea state in ocean engineering. In the existing theoretical and experimental studies,wave steepness is often substituted by some related quantities. In this paper,a new probability density function(pdf) of steepness,which is a pdf of the steepness in its original definition,is obtained for narrowband Gaussian processes. The drawback inherent in the previous theoretical pdfs of steepness,that is,the probability density at zero steepness is nonzero,has been eliminated. Laboratory experiments were conducted in a wind-wave flume to measure the wave steepness distribution. Comparisons among laboratory measurements and some theoretical pdfs of steepness show that the new pdf generally fits the data better than the one proposed by Zheng et al.(1999) .

关键词： wave wave steepness statistical distribution