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Conditional nonlinear optimal perturbation: Applications to stability, sensitivity, and predictability

Science China Earth Sciences 2009年第7期52卷 883-906页

作者： DUAN WanSuo MU Mu State Key laboratory of Numerical Modeling for Atmospheric Sciences and geophysical fluid dynamics Institute of Atmospheric PhysicsChinese Academy of SciencesBeijing 100029China

Conditional nonlinear optimal perturbation (CNOP) is a nonlinear generalization of linear singular vector (LSV) and features the largest nonlinear evolution at prediction time for the initial perturbations in a given constraint. It was proposed initially for predicting the limitation of predictability of weather or climate. Then CNOP has been applied to the studies of the problems related to predictability for weather and climate. In this paper, we focus on reviewing the recent advances of CNOP's applications, which involves the ones of CNOP in problems of ENSO amplitude asymmetry, block onset, and the sensitivity analysis of ecosystem and ocean's circulations, etc. Especially, CNOP has been primarily used to construct the initial perturbation fields of ensemble forecasting, and to determine the sensitive area of target observation for precipitations. These works extend CNOP's applications to investigating the nonlinear dynamical behaviors of atmospheric or oceanic systems, even a coupled system, and studying the problem of the transition between the equilibrium states. These contributions not only attack the particular physical problems, but also show the superiority of CNOP to LSV in revealing the effect of nonlinear physical processes. Consequently, CNOP represents the optimal precursors for a weather or climate event; in predictability studies, CNOP stands for the initial error that has the largest negative effect on prediction; and in sensitivity analysis, CNOP is the most unstable (sensitive) mode. In multi-equilibrium state regime, CNOP is the initial perturbation that induces the transition between equilibriums most probably. Furthermore, CNOP has been used to construct ensemble perturbation fields in ensemble forecast studies and to identify sensitive area of target observation. CNOP theory has become more and more substantial. It is expected that CNOP also serves to improve the predictability of the realistic predictions for weather and climate events play

关键词： optimal perturbation predictability stability sensitivity

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Improving the hydraulic performance of a high-speed submersible axial flow pump based on CFD technology

International Journal of Fluid Engineering

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International Journal of fluid Engineering 2024年第1期 91-108页

作者： Lu Rong Martin B?hle Gu Yandong Institute of fluid Mechanics and fluid Machinery Rhineland-Palatinate Technical University Research Center of fluid Machinery Engineering and Technology Jiangsu University College of Hydraulic Science and Engineering Yangzhou University

The hydraulic performance of a high-speed submersible axial flow pump is investigated to reduce its energy consumption. A more efficient and stable optimization method that combines parametric design, computational fluid dynamics, and a computer algorithm is proposed. The main aim is to broaden the high-efficiency operating zone, so the average efficiency under multiple conditions is optimized while considering rotor–stator matching. The design-of-experiments method and a radial-basis-function neural network are combined to form the optimization platform, and automatic optimization of the pump design is realized through repeated execution of design and simulation. The flow loss mechanism inside the pump is studied in depth via the entropy generation rate, and regression analysis shows that the pump efficiency is influenced mainly by the blade angles. After optimization, the target efficiency is increased by 8.34%, and the flow field distribution shows that the channel vortex and hydraulic loss are controlled effectively. Finally, the results are validated by experiment. The proposed optimization approach has advantages in saving manpower and obtaining globally optimal solutions.

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Temporal Variations of the Spring Persistent Rains and South China Sea Sub-high and Their Correlations to the Circulation and Precipitation of the East Asian Summer Monsoon

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Acta meteorologica Sinica 2008年第4期22卷 530-537页

作者：万日金王同美吴国雄 Shanghai Typhoon Institute of the China Meteoroloyical Administration Department of Atmospheric Sciences Zhongshan University laboratory of Atmospheric Sciences and geophysical fluid dynamics

National Meteorological Information Center （NMIC） rainfall data and NCEP/NCAR daily circulation reanalysis data are employed to establish the onset-pentad time index of the spring persistent rains （SPR） and the decay-pentad time index of the South China Sea （SCS） sub-high. These indexes are used to study the relationship between the factors in SPR period and their relations to the circulation and precipitation of the East Asian summer monsoon （EASM）. Results show that, the summer rainfall over southeastern China decreases when SPR onset is late. For then EASM strengthens and the cyclonic circulation around the Tibetan Plateau （TP） strengthens, which makes abnormal anti-cyclonic circulation （cyclonic convergent circulation weakens） appear over southeastern China. When the decay of SCS sub-high delays, abnormal flood prevails over the middle and lower reaches of the Yangtze River （MLYR） and to the south. That is mainly caused by EASM weakening while SCS sub-high strengthening, then the abnormal southwesterly over South China and the abnormal northerlies of anti-cyclonic circulation around the TP converge over the Yangtze Valley. The two indexes have high correlations with multivariate ENSO index （MEI） in March, indicating that the climate abnormity in East Asia is related to global climate abnormity tightly. The two time indexes are independent of each other, which is favorable for the prediction of the anomalies of the circulation and precipitation of EASM. From this point of view, we must take the global climate background into account when we analyze and predict the East Asian summer circulation and precipitation.

关键词： spring persistent rains (SPR) East Asian summer monsoon (EASM) the South China Sea (SCS) sub-high correlation analysis time indices

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Uncertainty in the 2℃ Warming Threshold Related to Climate Sensitivity and Climate Feedback

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Journal of Meteorological Research 2015年第6期29卷 884-895页

作者：周天军陈晓龙 State Key laboratory of Numerical Modeling for Atmospheric Sciences and geophysical fluid dynamics Institute of Atmospheric PhysicsChinese Academy of Sciences University of the Chinese Academy of Sciences

Climate sensitivity is an important index that measures the relationship between the increase in greenhouse gases and the magnitude of global *** in climate change projection and climate modeling are mostly related to the climate *** climate sensitivities of coupled climate models determine the magnitudes of the projected global *** this paper,the authors thoroughly review the literature on climate sensitivity,and discuss issues related to climate feedback processes and the methods used in estimating the equilibrium climate sensitivity and transient climate response（TCR）,including the TCR to cumulative CO2 *** presenting a summary of the sources that affect the uncertainty of climate sensitivity,the impact of climate sensitivity on climate change projection is discussed by addressing the uncertainties in 2℃ *** that call for further investigation in the research community,in particular the Chinese community,are discussed.

关键词： climate sensitivity radiative forcing climate feedback 2℃ threshold greenhouse gases climate model

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Effects of Crop Growth and Development on Land Surface Fluxes

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Advances in Atmospheric Sciences 2011年第4期28卷 927-944页

作者：陈锋谢正辉 State Key laboratory of Numerical Modeling for Atmospheric Sciences and geophysical fluid dynamics Institute of Atmospheric PhysicsChinese Academy of Sciences Zhejiang Institute of Meteorological Sciences

In this study, the Crop Estimation through Resource and Environment Synthesis model （CERES3.0） was coupled into the Biosphere-Atmosphere Transfer Scheme （BATS）, which is called BATS CERES, to represent interactions between the land surface and crop growth processes. The effects of crop growth and development on land surface processes were then studied based on numerical simulations using the land surface models. Six sensitivity experiments by BATS show that the land surface fluxes underwent substantial changes when the leaf area index was changed from 0 to 6 m2 m-2. Numerical experiments for Yucheng and Taoyuan stations reveal that the coupled model could capture not only the responses of crop growth and development to environmental conditions, but also the feedbacks to land surface processes. For quantitative evaluation of the effects of crop growth and development on surface fluxes in China, two numerical experiments were conducted over continental China： one by BATS CERES and one by the original BATS. Comparison of the two runs shows decreases of leaf area index and fractional vegetation cover when incorporating dynamic crops in land surface simulation, which lead to less canopy interception, vegetation transpiration, total evapotranspiration, top soil moisture, and more soil evaporation, surface runoff, and root zone soil moisture. These changes are accompanied by decreasing latent heat flux and increasing sensible heat flux in the cropland region. In addition, the comparison between the simulations and observations proved that incorporating the crop growth and development process into the land surface model could reduce the systematic biases of the simulated leaf area index and top soil moisture, hence improve the simulation of land surface fluxes.

关键词： crop growth and development leaf area index land surface model land surface fluxes

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Understanding the Surface Temperature Cold Bias in CMIP5 AGCMs over the Tibetan Plateau

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Advances in Atmospheric Sciences 2017年第12期34卷 1447-1460页

作者： Xiaolei CHEN Yimin LIU Guoxiong WU State Key laboratory of Numerical Modeling for Atmospheric Sciences and geophysical fluid dynamics Institute of Atmospheric Physics Chinese Academy of Sciences University of Chinese Academy of Sciences

The temperature biases of 28 CMIP5 AGCMs are evaluated over the Tibetan Plateau(TP) for the period 1979–2005. The results demonstrate that the majority of CMIP5 models underestimate annual and seasonal mean surface 2-m air temperatures(Tas) over the TP. In addition, the ensemble of the 28 AGCMs and half of the individual models underestimate annual mean skin temperatures(Ts) over the TP. The cold biases are larger in Tasthan in Ts, and are larger over the western TP. By decomposing the Tsbias using the surface energy budget equation, we investigate the contributions to the cold surface temperature bias on the TP from various factors, including the surface albedo-induced bias, surface cloud radiative forcing, clear-sky shortwave radiation, clear-sky downward longwave radiation, surface sensible heat flux, latent heat flux,and heat storage. The results show a suite of physically interlinked processes contributing to the cold surface temperature *** negative surface albedo-induced bias associated with excessive snow cover and the surface heat fluxes are highly anticorrelated, and the cancelling out of these two terms leads to a relatively weak contribution to the cold bias. Smaller surface turbulent fluxes lead to colder lower-tropospheric temperature and lower water vapor content, which in turn cause negative clear-sky downward longwave radiation and cold bias. The results suggest that improvements in the parameterization of the area of snow cover, as well as the boundary layer, and hence surface turbulent fluxes, may help to reduce the cold bias over the TP in the models.

关键词： surface temperature cold bias CMIP5 AMIP Tibetan Plateau surface energy budget

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An Evaluation of RegCM3_CERES for Regional Climate Modeling in China

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Advances in Atmospheric Sciences 2013年第4期30卷 1187-1200页

作者：陈锋谢正辉 Zhejiang Institute of Meteorological Sciences State Key laboratory of Numerical Modeling for Atmospheric Sciences and geophysical fluid dynamics Institute of Atmospheric Physics Chinese Academy of Sciences

A 20-year simulation of regional climate over East Asia by the regional climate model RegCM3_CERES （Regional Climate Model version 3 coupled with the Crop Estimation through Resource and Environment Synthesis） was carried out and compared with observations and the original RegCM3 model to compre- hensively evaluate its performance in simulating the regional climate over continental China. The results showed that RegCM3_CERES reproduced the regional climate at a resolution of 60 km over China by using ERA40 data as the boundary conditions, albeit with some limitations. The model captured the basic char- acteristics of the East Asian circulation, the spatial distribution of mean precipitation and temperature, and the daily characteristics of precipitation and temperature. However, it underestimated both the intensity of the monsoon in the monsoonal area and precipitation in southern China, overestimated precipitation in northern China, and produced a systematic cold temperature bias over most of continental China. Despite these limitations, it was concluded that the RegCM3_CERES model is able to simulate the regional climate over continental China reasonably well.

关键词： regional climate model model validation

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Diurnal and Seasonal Variations of CO2Fluxes and Their Climate Controlling Factors for a Subtropical Forest in Ningxiang

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Advances in Atmospheric Sciences 2015年第4期32卷 553-564页

作者： JIA Binghao XIE Zhenghui ZENG Yujin WANG Linying WANG Yuanyuan XIE Jinbo XIE Zhipeng State Key laboratory of Numerical Modeling for Atmospheric Sciences and geophysical fluid dynamics Institute of Atmospheric Physics Chinese Academy of Sciences University of Chinese Academy of Sciences

In this study, the diurnal and seasonal variations of CO2 fluxes in a subtropical mixed evergreen forest in Ningxiang of Hunan Province, part of the East Asian monsoon region, were quantified for the first time. The fluxes were based on eddy covariance measurements from a newly initiated flux tower. The relationship between the CO2 fluxes and climate factors was also analyzed. The results showed that the target ecosystem appeared to be a clear carbon sink in 2013, with integrated net ecosystem CO2exchange（NEE）, ecosystem respiration（RE）, and gross ecosystem productivity（GEP） of-428.8, 1534.8 and1963.6 g C m^-2yr^-1, respectively. The net carbon uptake（i.e. the-NEE）, RE and GEP showed obvious seasonal variability,and were lower in winter and under drought conditions and higher in the growing season. The minimum NEE occurred on12 June（-7.4 g C m^-2d^-1）, due mainly to strong radiation, adequate moisture, and moderate temperature; while a very low net CO2 uptake occurred in August（9 g C m^-2month^-1）, attributable to extreme summer drought. In addition, the NEE and GEP showed obvious diurnal variability that changed with the seasons. In winter, solar radiation and temperature were the main controlling factors for GEP, while the soil water content and vapor pressure deficit were the controlling factors in summer. Furthermore, the daytime NEE was mainly limited by the water-stress effect under dry and warm atmospheric conditions, rather than by the direct temperature-stress effect.

关键词： net ecosystem exchange diurnal and seasonal variations climate controlling factors subtropical mixed forest East Asian monsoon r

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ENSO Amplitude Change in Observation and Coupled Models

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Advances in Atmospheric Sciences 2008年第3期25卷 361-366页

作者：张琼关月杨海军 State Key laboratory of Numerical Modeling for Atmospheric Sciences and geophysical fluid dynamics(LASG) Institute of Atmospheric PhysicsChinese Academy of SciencesBeijing 100029 State Key laboratory of Numerical Modeling for Atmospheric Sciences and geophysical fluid dynamics(LASG)Institute of Atmospheric Physics Chinese Academy of Sciences Department of Atmospheric Science School of PhysicsPeking UniversityBeijing 100871

Observations show that the tropical E1 Nifio-Southern Oscillation （ENSO） variability, after removing both the long term trend and decadal change of the background climate, has been enhanced by as much as 60% during the past 50 years. This shift in ENSO amplitude can be related to mean state changes in global climate. Past global warming has caused a weakening of the Walker circulation over the equatorial Indo-Pacific oceans, as well as a weakening of the trade winds and a reduction in the equatorial upwelling. These changes in tropical climatology play as stabilizing factors of the tropical coupling system. However, the shallower and strengthening thermocline in the equatorial Pacific increases the SST sensitivity to thermocline and wind stress variabilities and tend to destabilize the tropical coupling system. Observations suggest that the destabilizing factors, such as the strengthening thermocline, may have overwhelmed the stabilizing effects of the atmosphere, and played a deterministic role in the enhanced ENSO variability, at least during the past half century. This is different from the recent assessment of IPCC-AR4 coupled models.

关键词： ENSO variability global warming thermocline Equatorial Pacific

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Simulated Change in the Interannual Variability of South Asian Summer Monsoon in the 21st Century

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Advances in Atmospheric Sciences 2010年第5期27卷 992-1002页

作者：富元海陆日宇 State Key laboratory of Numerical Modeling for Atmospheric Sciences and geophysical fluid dynamics/Center for Monsoon System Research Institute of Atmospheric Physics Chinese Academy of Sciences

This study investigates the projected changes in interannual variability of South Asian summer monsoon and changes of ENSO–monsoon relationships in the 21st century under the Intergovernmental Panel on Climate Change （IPCC） scenarios A1B and A2, respectively, by analyzing the simulated results of twelve Coupled Model Intercomparison Project Phase 3 （CMIP3） coupled models. The dynamical monsoon index （DMI） was adopted to describe the interannual variability of South Asian summer monsoon, and the standard deviation （SD） was used to illustrate the intensity of interannual variability. It was found that most models could project enhanced interannual variability of monsoon in the 21st century. The multi-model ensemble （MME） results showed increases in the interannual variability of DMI： 14.3% and 20.0% under scenarios A1B and A2, respectively. The MME result also showed increases in the rainfall variability are of about 10.2% and 22.0% under scenarios A1B and A2. The intensification of interannual variability tended to occur over the regions that have larger variability currently; that is, ＂the strong get stronger＂. Another finding was that ENSO–monsoon relationships are likely to be enhanced in the 21st century. The dynamical component of the monsoon will be more closely correlated to ENSO in the future under global warming, although the ENSO–summer rainfall relationship cannot be reasonably projected by current models. This suggests that the South Asian summer monsoon is more predictable in the future, at least dynamically.

关键词： climate change interannual variability South Asian summer monsoon ENSO–monsoon rela- tionship

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