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Assimilating the along-track sea level anomaly into the regional ocean modeling system using the ensemble optimal interpolation

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Acta Oceanologica Sinica 2014年第7期33卷 72-82页

作者： lyu guokun WANG Hui ZHU Jiang WANG Dakui XIE Jiping LIU Guimei Physical Oceanography Laboratory Ocean University of China Key Laboratory of Research on Marine Hazards Forecasting National Marine Environmental Forecasting CenterState Oceanic Administration College of Environmental Science and Engineering Ocean University of China State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry Institute of Atmospheric Physics Chinese Academy of Sciences International Center for Climate and Environmental Sciences Institute of Atmospheric Physics Chinese Academy of Sciences

The ensemble optimal interpolation （EnOI） is applied to the regional ocean modeling system （ROMS） with the ability to assimilate the along-track sea level anomaly （TSLA）. This system is tested with an eddy-resolving system of the South China Sea （SCS）. Background errors are derived from a running seasonal ensemble to account for the seasonal variability within the SCS. A fifth-order localization function with a 250 km localization radius is chosen to reduce the negative effects of sampling errors. The data assimilation system is tested from January 2004 to December 2006. The results show that the root mean square deviation （RMSD） of the sea level anomaly decreased from 10.57 to 6.70 cm, which represents a 36.6% reduction of error. The data assimilation reduces error for temperature within the upper 800 m and for salinity within the upper 200 m, although error degrades slightly at deeper depths. Surface currents are in better agreement with trajectories of surface drifters after data assimilation. The variance of sea level improves significantly in terms of both the amplitude and position of the strong and weak variance regions after assimilating TSLA. Results with AGE error （AGE） perform better than no AGE error （NoAGE） when considering the improvements of the temperature and the salinity. Furthermore, reasons for the extremely strong variability in the northern SCS in high resolution models are investigated. The results demonstrate that the strong variability of sea level in the high resolution model is caused by an extremely strong Kuroshio intrusion. Therefore, it is demonstrated that it is necessary to assimilate the TSLA in order to better simulate the SCS with high resolution models.

关键词： ensemble optimal interpolation regional ocean modeling system along-track sea level anomaly South China Sea variability

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基于变振动参数的驱动桥桥壳焊接应力消除研究

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热加工工艺 2014年第23期43卷 171-174页

作者：郭微吕国坤郑泉安徽水利水电职业技术学院机械工程系安徽合肥231603 江西昌河汽车有限公司江西景德镇333002 安徽农业大学工学院安徽合肥230036

针对传统振动强度方法消除焊接残余应力时容易导致残余应力消除效果不明显的问题,本文提出变振动强度进行焊接残余应力的消除方法。以汽车驱动桥桥壳焊接件为研究对象,针对实验中出现的焊接断裂问题,采用有限元方法与实验测量方法相结合... 详细信息

针对传统振动强度方法消除焊接残余应力时容易导致残余应力消除效果不明显的问题,本文提出变振动强度进行焊接残余应力的消除方法。以汽车驱动桥桥壳焊接件为研究对象,针对实验中出现的焊接断裂问题,采用有限元方法与实验测量方法相结合,得出了焊接残余应力数值约180 MPa,且验证了有限元模型的准确性;通过驱动桥模态分析和谐响应分析结果,确定了变振动强度方法的振动参数;在此基础上进行了传统振动强度和变振动强度两种方法的振动时效分析,分析结果显示采用变振动强度方法振动后的焊接残余应力仅为39.4 MPa,比传统振动强度方法更能有效的释放残余应力。

关键词：残余应力振动时效驱动桥壳

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盲孔法测量残余应力试验中塑性修正的插值方法

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热加工工艺 2014年第9期43卷 185-187,190页

作者：吕国坤陈黎卿陈永新张念生安徽农业大学工学院安徽合肥230036

使用盲孔法测量高残余应力时会引入塑性变形的影响。对塑性变形的影响进行修正的根本方法是对应变释放系数的修正。文中对有高残余应力的部件使用盲孔法测量残余应力,并用基于应变释放系数的新方法———插值方法进行修正。通过与A、B... 详细信息

使用盲孔法测量高残余应力时会引入塑性变形的影响。对塑性变形的影响进行修正的根本方法是对应变释放系数的修正。文中对有高残余应力的部件使用盲孔法测量残余应力,并用基于应变释放系数的新方法———插值方法进行修正。通过与A、B系数高残余应力状态修正对比发现:插值法对高残余应力的测量修正效果良好,相对误差较低,对实际测量有理论指导作用。

关键词：盲孔法残余应力塑性修正插值方法

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Influence of the Arctic on the Predictability of Eurasian Winter Extreme Weather Events

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Advances in Atmospheric Sciences 2020年第4期37卷 307-317页

作者： guokun DAI Mu MU Department of Atmospheric and Oceanic Sciences and Institute of Atmospheric Sciences Fudan UniversityShanghai 200438China

The linkage between the Arctic and midlatitudes has received much attention recently due to the rapidly changing *** investigations have been conducted to reveal the relationship between the Arctic and Eurasian extreme events from the perspective of climatological *** a prediction source for extreme events in Eurasia,Arctic conditions are crucial for extreme event ***,it is urgent to explore the Arctic influence on the predictability of Eurasian extreme events due to the large uncertainties in Arctic *** the sensitivity and nonlinearity of the atmospheric circulations in midlatitude to Arctic conditions,it is necessary to investigate the Arctic influences on Eurasian extreme weather events in case studies at weather time *** studies indicate that only perturbations in specific patterns have fast ***,the conditional nonlinear optimal perturbation approach is recommended for exploring the uncertainties in Arctic initial and boundary conditions and their synergistic effect on Eurasian extreme ***,the mechanism for extreme event formation may differ in different ***,more extreme cases should be investigated to reach robust conclusions.

关键词： Arctic uncertainties Eurasian extreme weather events synergistic effect optimization algorithms

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Targeted Observations for Improving Prediction of the NAO Onset

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Journal of Meteorological Research 2019年第6期33卷 1044-1059页

作者： guokun DAI Mu MU Zhina JIANG Department of Atmospheric and Oceanic Sciences&Institute of Atmospheric Sciences Fudan UniversityShanghai 200438 State Key Laboratory of Severe Weather Chinese Academy of Meteorological SciencesChina Meteorological AdministrationBeijing 100081

Based on the viewpoint that the North Atlantic Oscillation(NAO)has an intrinsic timescale of approximate two weeks and can be treated as an initial value problem,targeted observations for improving the prediction of the onset of NAO events are investigated by using the conditional nonlinear optimal perturbation(CNOP)method with a quasigeostrophic *** results show that flow-dependent sensitive areas for the prediction of NAO onset are mainly located over North Atlantic and its upstream *** observations over the main sensitive areas could improve NAO onset prediction in most cases(approximately 75%)due to reduced errors in anomalous eddy vorticity forcing(EVF)projection in the typical NAO ***,a flow-independent sensitive area is determined based on the winter climatological flow,which is located over North America and its adjacent *** NAO onset prediction can also be improved by targeted observations over the flow-independent sensitive area,but the skill improvement is somewhat lower than that derived from observations over the flow-dependent sensitive *** above results indicate that targeted observations over sensitive areas identified by the CNOP method can help to improve the onset prediction of NAO events.

关键词： North Atlantic Oscillation(NAO) targeted observations eddy vorticity forcing(EVF) conditional nonlinear optimal perturbation(CNOP)

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Evaluation of the Forecast Performance for North Atlantic Oscillation Onset

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Advances in Atmospheric Sciences 2019年第7期36卷 753-765页

作者： guokun DAI Mu MU Zhina JIANG Department of Atmospheric and Oceanic Sciences&Institute of Atmospheric Sciences Fudan UniversityShanghai200438China State Key Laboratory of Severe Weather Chinese Academy of Meteorological SciencesBeijing100081China

By utilizing operational forecast products from TIGGE(The International Grand Global Ensemble) during 2006 to 2015,the forecasting performances of the European Centre for Medium-Range Weather Forecasts(ECMWF), National Centers for Environmental Prediction(NCEP), Japan Meteorology Agency(JMA) and China Meteorological Administration(CMA) for the onset of North Atlantic Oscillation(NAO) events are assessed against daily NCEP–NCAR reanalysis data. Twenty-two positive NAO(NAO+) and nine negative NAO(NAO-) events are identified during this time period. For these NAO events,control forecasts, one member of the ensemble that utilizes the currently most proper estimate of the analysis field and the best description of the model physics, are able to predict their onsets three to five days in advance. Moreover, the failure proportion for the prediction of NAO-onset is higher than that for NAO+ onset, which indicates that NAO-onset is harder to forecast. Among these four operational centers, ECMWF has performs best in predicting NAO onset, followed by NCEP,JMA, and then *** forecasting performance of the ensemble mean is also investigated. It is found that, compared with the control forecast, the ensemble mean does not improve the forecasting skill with respect to the onset time of NAO events. Therefore,a confident forecast of NAO onset can only be achieved three to five days in advance.

关键词： NAO onset operational forecast TIGGE dataset

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Single-Molecule Kinetics of Nanoparticle Catalysis

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Nano Research 2009年第12期2卷 911-922页

作者： Weilin Xu Hao Shen guokun Liu Peng Chen Department of Chemistry and Chemical Biology Cornell UniversityIthacaNY 14853USA Department of Chemical Engineering University of CaliforniaBerkeleyCA 94720USA

Owing to their structural dispersion,the catalytic properties of nanoparticles are challenging to characterize in ensemble-averaged *** single-molecule approach enables studying the catalysis of nanoparticles at the single-particle level with real-time single-turnover *** article reviews our single-molecule fluorescence studies of single Au-nanoparticle catalysis,focusing on the theoretical formulations for extracting quantitative reaction kinetics from the single-turnover resolution catalysis *** discuss the single-molecule kinetic formulism of the Langmuir-Hinshelwood mechanism for heterogeneous catalysis,as well as of the two-pathway model for product dissociation *** formulism enables the quantitative evaluation of the heterogeneous reactivity and the differential selectivity of individual nanoparticles that are usually hidden in ensemble *** of this formulism to single-molecule catalytic kinetics of oligomeric enzymes is also discussed.

关键词： Single-nanoparticle catalysis single-molecule fluorescence detection Langmuir Hinshelwood mechanism reactivity heterogeneity parallel reaction pathways differential selectivity

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The Nature and Predictability of the East Asian Extreme Cold Events of 2020/21

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Advances in Atmospheric Sciences 2022年第4期39卷 566-575页

作者： guokun DAI Chunxiang LI Zhe HAN Dehai LUO Yao YAO Department of Atmospheric and Oceanic Sciences and Institute of Atmospheric Sciences Fudan UniversityShanghai 200438China CAS Key Laboratory of Regional Climate-Environment for Temperate East Asia Institute of Atmospheric PhysicsChinese Academy of SciencesBeijing 100029China

Three extreme cold events invaded China during the early winter period between December 2020 to mid-January 2021 and caused drastic temperature drops,setting new low-temperature records at many stations during 6−8 January *** cold events occurred under background conditions of low Arctic sea ice extent and a La Niña *** is somewhat expected since the coupled effect of large Arctic sea ice loss in autumn and sea surface temperature cooling in the tropical Pacific usually favors cold event occurrences in *** diagnosis reveals that the first cold event is related to the southward movement of the polar vortex and the second one is related to a continent-wide ridge,while both the southward polar vortex and the Asian blocking are crucial for the third ***,we evaluate the forecast skill for these three events utilizing the operational forecasts from the ECMWF *** find that the third event had the highest predictability since it achieves the best skill in forecasting the East Asian cooling among the three ***,the predictability of these cold events,as well as their relationships with the atmospheric initial conditions,Arctic sea ice,and La Niña deserve further investigation.

关键词： extreme cold event predictability Arctic atmospheric initial conditions Arctic sea ice La Niña

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A Nonlinear Representation of Model Uncertainty in a Convective-Scale Ensemble Prediction System

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Advances in Atmospheric Sciences 2022年第9期39卷 1432-1450页

作者： Zhizhen XU Jing CHEN Mu MU guokun DAI Yanan MA Department of Atmospheric and Oceanic Sciences&Institute of Atmospheric Sciences Fudan UniversityShanghai 200438China Numerical Weather Prediction Center China Meteorological AdministrationBeijing 100081China Chinese Academy of Meteorological Sciences China Meteorological AdministrationBeijing 100081China

How to accurately address model uncertainties with consideration of the rapid nonlinear error growth characteristics in a convection-allowing system is a crucial issue for performing convection-scale ensemble *** this study,a new nonlinear model perturbation technique for convective-scale ensemble forecasts is developed to consider a nonlinear representation of model errors in the Global and Regional Assimilation and Prediction Enhanced System(GRAPES)Convection-Allowing Ensemble Prediction System(CAEPS).The nonlinear forcing singular vector(NFSV)approach,that is,conditional nonlinear optimal perturbation-forcing(CNOP-F),is applied in this study,to construct a nonlinear model perturbation method for *** experiments are performed:One of them is the CTL experiment,without adding any model perturbation;the other two are NFSV-perturbed experiments,which are perturbed by NFSV with two different groups of constraint radii to test the sensitivity of the perturbation magnitude *** results show that the NFSV-perturbed experiments achieve an overall improvement and produce more skillful forecasts compared to the CTL experiment,which indicates that the nonlinear NFSV-perturbed method can be used as an effective model perturbation method for convection-scale ensemble ***,the NFSV-L experiment with large perturbation constraints generally performs better than the NFSV-S experiment with small perturbation constraints in the verification for upper-air and surface weather *** for precipitation verification,the NFSV-S experiment performs better in forecasts for light precipitation,and the NFSV-L experiment performs better in forecasts for heavier precipitation,indicating that for different precipitation events,the perturbation magnitude constraint must be carefully *** the findings above lay a foundation for the design of nonlinear model perturbation methods for future CAEPSs.

关键词： Convection-Allowing Ensemble Prediction System model uncertainty nonlinear forcing singular vector

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The Influence of Arctic Sea Ice Concentration Perturbations on Subseasonal Predictions of North Atlantic Oscillation Events

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Advances in Atmospheric Sciences 2023年第12期40卷 2242-2261,I0009-I0015页

作者： guokun DAI Mu MU Zhe HAN Chunxiang LI Zhina JIANG Mengbin ZHU Xueying MA Department of Atmospheric and Oceanic Sciences and Institute of Atmospheric Sciences Fudan UniversityShanghai 200438China CMA-FDU Joint Laboratory of Marine Meteorology Shanghai 200438China Shanghai Frontiers Science Center of Atmosphere-Ocean Interaction Shanghai 200438China Innovation Center of Ocean and Atmosphere System Zhuhai Fudan Innovation Research InstituteZhuhai 509031China CAS Key Laboratory of Regional Climate-Environment for Temperate East Asia Institute of Atmospheric PhysicsChinese Academy of SciencesBeijing 100029China State Key Laboratory of Severe Weather(LaSW) Chinese Academy of Meteorological SciencesBeijing 100081China Beijing Institute of Applied Meteorology Beijing 100029China Yantai Vocational College Yantai 264670China

The influence of Arctic sea ice concentration (SIC) on the subseasonal prediction of the North Atlantic Oscillation (NAO) event is investigated by utilizing the Community Atmospheric Model version 4. The optimal Arctic SIC perturbations which exert the greatest influence on the onset of an NAO event from a lead of three pentads (15 days) are obtained with a conditional nonlinear optimal perturbation approach. Numerical results show that there are two types of optimal Arctic SIC perturbations for each NAO event, with one weakening event (marked as type-1) and another strengthening event (marked as type-2). For positive NAO events, type-1 optimal SIC perturbations mainly show positive SIC anomalies in the Greenland, Barents, and Okhotsk Seas, while type-2 perturbations mainly feature negative SIC anomalies in these regions. For negative NAO events, the optimal SIC perturbations have almost opposite patterns to those in positive events, although there are some differences among these SIC perturbations due to different atmospheric initial conditions. Further diagnosis reveals that the optimal Arctic SIC perturbations first modify the surface turbulent heat flux and the temperature in the lower troposphere via diabatic processes. Afterward, the temperature in the low troposphere is mainly affected by dynamic advection. Finally, potential vorticity advection plays a crucial role in the 500-hPa geopotential height prediction in the northern North Atlantic sector during pentad 4, which influences NAO event prediction. These results highlight the importance of Arctic SIC on NAO event prediction and the spatial characteristics of the SIC perturbations may provide scientific support for target observations of SIC in improving NAO subseasonal predictions.

关键词： optimal Arctic SIC perturbation NAO event subseasonal prediction CNOP approach

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