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Influence of Late Springtime Surface Sensible Heat Flux Anomalies over the Tibetan and Iranian Plateaus on the Location of the South Asian High in Early Summer

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Advances in Atmospheric Sciences 2019年第1期36卷 93-103页

作者： Haoxin ZHANG Weiping li weijing li Laboratory for Climate Studies China Meteorological Administration University of Chinese Academy of Sciences Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters Nanjing University of Information Science and Technology

Variation in the location of the South Asian High （SAH） in early boreal summer is strongly influenced by elevated surface heating from the Tibetan Plateau （TP） and the Iranian Plateau （IP）. Based on observational and ERA-Interim data, diagnostic analyses reveal that the interannual northwestward-southeastwaxd （NW-SE） shift of the SAH in June is more closely correlated with the synergistic effect of concurrent surface thermal anomalies over the TP and IP than with each single surface thermal anomaly over either plateau from the preceding May. Concurrent surface thermal anomalies over these two plateaus in May are characterized by a negative correlation between sensible heat flux over most parts of the TP （TPSH） and IP （IPSH）. This anomaly pattern can persist till June and influences the NW-SE shift of the SAH in June through the release of latent heat （LH） over northeastern India. When the IPSH is stronger （weaker） and the TPSH is weaker （stronger） than normal in May, an anomalous cyclone （anticyclone） appears over northern India at 850 hPa, which is accompanied by the ascent （descent） of air and anomalous convergence （divergence） of moisture flux in May and June. Therefore, the LH release over northeastern India is strengthened （weakened） and the vertical gradient of apparent heat source is decreased （increased） in the upper troposphere, which is responsible for the northwestward （southeastward） shift of the SAH in June.

关键词： Tibetan Plateau Iranian Plateau surface sensible heat flux latent heat of condensation South Asian High

Interdecadal Variability of the Afro-Asian Summer Monsoon System

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Advances in Atmospheric Sciences 2017年第7期34卷 833-846页

作者： Yi li Yihui DING weijing li Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters Nanjing University of Information Science and TechnologyNanjing 210044China Chinese Academy of Meteorological Sciences Beijing 100081China National Climate Center Beijing 100081China

The Afro-Asian summer monsoon is a zonally planetary-scale system, with a large-scale rainbelt covering Africa, South Asia and East Asia on interdecadal timescales both in the past century（1901-2014） and during the last three decades（1979-2014）. A recent abrupt change of precipitation occurred in the late 1990 s. Since then, the entire rainbelt of the Afro-Asia monsoon system has advanced northwards in a coordinated way. Consistent increases in precipitation over the Huanghe-Huaihe River valley and the Sahel are associated with the teleconnection pattern excited by the warm phase of the Atlantic Multidecadal Oscillation（AMO）. A teleconnection wave train, with alternating cyclones/anticyclones, is detected in the upper troposphere. Along the teleconnection path, the configuration of circulation anomalies in North Africa is characterized by coupling of the upper-level anticyclone（divergence） with low-level thermal low pressure（convergence）, facilitating the initiation and development of ascending motions in the Sahel. Similarly, in East Asia, a coupled circulation pattern also excites ascending motion in the Huanghe-Huaihe River valley. The synchronous increase in precipitation over the Sahel and Huanghe-Huaihe River valley can be attributed to the co-occurrences and in-phase changes of ascending motion. On the other hand, the warm phase of the AMO results in significant warming in the upper troposphere in North Africa and the northern part of East Asia. Such warming contributes to intensification of the tropical easterly jet through increasing the meridional pressure gradient both at the entrance region（East Asia） and the exit region（Africa）. Accordingly, precipitation over the Sahel and Huanghe-Huaihe River valley intensifies, owing to ageostrophic secondary cells. The results of this study provide evidence for a consistent and holistic interdecadal change in the Afro-Asian summer monsoon.

关键词： monsoon troposphere warming Africa valley ascending meridional divergence tropical northward

Why Is the East Asian Summer Monsoon Extremely Strong in 2018?——Collaborative Effects of SST and Snow Cover Anomalies

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Journal of Meteorological Research 2019年第4期33卷 593-608页

作者： lijuan CHEN Wei GU weijing li Laboratory for Climate Studies National Climate CenterChina Meteorological AdministrationBeijing 100081 Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters Nanjing University of Information Science&TechnologyNanjing 210044

In 2018,summer precipitation was above normal in North and Northwest China and below normal around the Yangtze River valley,due to an extremely strong East Asian summer monsoon(EASM).The atmospheric circulation anomalies in East Asia and key external forcing factors that influence the EASM in 2018 are explored in this *** results show that there existed an anomalous cyclonic circulation near the Philippines,while the western Pacific subtropical high was located more northward than its normal *** the mid–high latitudes,a negative geopotential height anomaly center was found near the Ural Mountains,suppressing the blocking *** such a circulation pattern,precipitation near the Yangtze River valley decreased because local divergence and subsidence intensified,whereas precipitation in northern China increased due to large amounts of water vapor transport by anomalously strong southerly *** analyses reveal that the strong EASM circulation in 2018 might result from the joint influences of several external forcing *** weak La Ni?a event that started from October 2017,the positive North Atlantic Tripolar mode(NAT)in spring 2018,and the reduced snow cover over the Tibetan Plateau in winter 2017/18 all collaboratively contributed to formation of the cyclonic circulation anomaly near the Philippines,leading to the extremely strong ***,the positive NAT and the reduced Tibetan snow cover may have caused the negative geopotential height anomaly near the Ural Mountains,in favor of a strong *** above external factors and their reinforcing impacts on the EASM are further verified by two groups of similar historical cases.

关键词： East Asian summer monsoon external forcing factors La Nina North Atlantic Tripolar mode Indian Ocean basin mode snow cover of the Tibetan Plateau

BRAKE TEST OF SiCp/A356 BRAKE DISK AND INTERPRETATION OF EXPERIMENTAL RESULTS

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Chinese Journal of Mechanical Engineering 2007年第5期20卷 74-79页

作者： YANG Zhiyong HAN Jianmin li weijing WANG Jinhua School of Mechanical Electronic and Control Engineering Beijing Jiaotong University Beijing 100044 China

Material properties are obvious different between aluminum matrix composites and iron and steel materials. After the brake disk braked at the same speed, the average temperature of the aluminum brake disk is 1.5 times as high as one of iron and steel brake disk, the thermal expansion value of the aluminum brake disk is 2 times as big as one of iron and steel brake disk. Mechanical property of the material decreases with the temperature increasing generally during braking, on the other hand, the big thermal stress in the brake disk happens because the material expansion is constrained. Firstly, the reasons of the thermal stress generation and the fracture failure of brake disks during braking are analyzed qualitatively by virtue of three-bar stress frame and sandwich deformation principles in physic, and then the five constraints which cause the thermal stress are summarized. On the base of the experimental results on the 1：1 emergency brake test, the thermal stress and temperature fields are simulated; The behavior of the fracture failure is interpreted semi-quantitatively by finite element analysis, There is the coincident forecast for the fraction position in term of the two methods. In the end, in the light of the analysis and calculation results, it is the general principles observed by the structure design and assembly of the brake disk that are summarized.

关键词： Brake disk Brake test Thermal stress Heat flux Finite element analysis

Effect of Silicon on the casting properties of Al-5.0%Cu alloy

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Rare Metals 2006年第z2期25卷 133-135页

作者： li weijing CUI Shihai HAN Jianmin XU Chao School of Mechanical Electronic and Control Engineering Beijing Jiaotong University Beijing 100044 China College of Mechanical Engineering Tianjin University of Science and Technology Tianjin 300222 China School of Mechanical Electronic and Control Engineering Beijing Jiaotong University Beijing 100044 China School of Mechanical Electronic and Control Engineering Beijing Jiaotong University Beijing 100044 China

Poor casting properties restrict the application of high strength casting Al-5.0%Cu alloy. The addition of element can improve the casting properties of this alloy. Effect of Si on the casting properties of Al-5.0%Cu alloy was studied. It has been found that the addition of Si can improve the casting properties of Al-5.0%Cu alloy obviously. With the increase of Si content, the hot cracking tendency of the alloy decreases significantly, and the fluidity of the alloy increases firstly and then decreases slowly. When the content of Si element is higher than 2wt.%, the fluidity of the alloy increases greatly with the increasing of Si content.

关键词： Al-Cu casting aluminum alloy casting properties hot cracking tendency fluidity

Influence of Si on Interfacial Combination of SiCp/Al-Mg-Si Composite

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Journal of Rare Earths 2004年第z2期22卷 69-72页

作者： Han Jianmin li Ronghua li Mingwei Cui Shihai li weijing Wang Jinhua School of Mechanical Electronic and Control EngineeringBeijing Jiaotong UniversityBeijing 100044China

The scanning electron microscopy (SEM) analysis results of Si distribution in the interface between SiC reinforcements and aluminum matrix of a stir casting SiCp/Al-Mg-Si composite were presented. Results show that there is Si precipitation deposit on the interface of the composite and Si connects with SiC reinforcements in one side and connects with aluminum matrix in the other side. Si phase plays as a connecting bridge, which contributes to the interfacial combination of SiCp/Al composite.

关键词： interfacial combination Si SiCp/Al-Mg-Si composite

Extremely Active Tropical Cyclone Activities over the Western North Pacific and South China Sea in Summer 2018: Joint Effects of Decaying La Nina and Intraseasonal Oscillation

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Journal of Meteorological Research 2019年第4期33卷 609-626页

作者： lijuan CHEN Zhensong GONG Jie WU weijing li Laboratory for Climate Studies National Climate CenterChina Meteorological AdministrationBeijing 100081 Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters Nanjing University of Information Science&TechnologyNanjing 210044

In summer 2018,a total of 18 tropical cyclones(TCs)formed in the western North Pacific(WNP)and South China Sea(SCS),among which 8 TCs landed in China,ranking respectively the second and the first highest since *** of these TCs travelled northwest to northward,bringing in heavy rainfall and strong winds in eastern China and *** present study investigates the impacts of decaying La Nina and intraseasonal oscillation(ISO)on the extremely active TCs over the WNP and SCS in summer 2018 by use of correlation and composite *** is found that the La Nina episode from October 2017 to March 2018 led to above-normal sea surface temperature(SST)over central–western Pacific,lower sea level pressure and 500-hPa geopotential height over WNP,and abnormally strong convective activities over the western Pacific in summer *** preceding oceanic thermal conditions and their effects on circulation anomalies are favorable to TC genesis in *** examination reveals that the monsoon trough was located further north and east,inducing more TCs in northern and eastern WNP;and the more eastward WNP subtropical high as well as the significant wave train with a"-+-+"height anomaly pattern over the midlatitude Eurasia–North Pacific region facilitated the northwest to northward TC *** analyses reveal that two successively active periods of Madden–Julian Oscillation(MJO)occurred in summer 2018 and the boreal summer intraseasonal oscillation(BSISO)was also active over WNP,propagating northward significantly,corresponding to the more northward TC *** MJO was stagnant over the Maritime Continent to western Pacific,leading to notably enhanced convection in the lower troposphere and divergence in the upper troposphere,conducive to TC *** a word,the extremely active TC activities over the WNP and SCS in summer 2018 are closely linked with the decaying La Nina,and the MJO and BSISO;their joint effects result in increased TC occurrences and th

关键词： western North Pacific(WNP) tropical cyclone(TC) La Nina event Madden-Julian Oscillation(MJO) boreal summer intraseasonal oscillation(BSISO)

An observational study of snow aging and the seasonal variation of snow albedo by using data from Col de Porte, France

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Chinese Science Bulletin 2014年第34期59卷 4881-4889页

作者： Ajiao Chen Weiping li weijing li Xin liu Chinese Academy of Meteorological Sciences National Climate Center China Meteorological Administration Laboratory for Climate Studies China Meteorological Administration Laboratory of Tibetan Environment Changes and Land Surface Processes Institute of Tibetan Plateau Research Chinese Academy of Sciences

An 18-year long(1993–2011) comprehensive dataset of snow and meteorological variables from Col de Porte, France is used to analyze the variation of shortwave broadband albedo with elapsed time after snowfalls(snow aging) during each snow season. The effects of air temperature, snow surface temperature and snow depth on snow albedo are investigated. An index based on the accumulation of air temperature over several consecutive days with daily mean higher than 2.5 °C is proposed to divide each snow-covered period into a dry and the following wet snow season when this index reaches 18 °*** results indicate that snow surface albedo decreases exponentially with time in both dry and wet snow *** albedo reduction with snow aging is small at low surface temperature and the reduction rate increases with the rise of surface temperature. However, the reduction rate is widely scattered within the observed range of temperature, implying a loose relationship between snow albedo and snow surface temperature. Snow albedo in wet snowseason is generally smaller and decreases faster than in dry snow season. For Col de Porte site, snow depths to effectively mask the underlying surface are 21 and 33 cm in dry and wet snow season respectively.

关键词：季节变化反照率口门老化法国空气温度表面温度积雪深度

Thermodynamic modeling of the La-Mg-Y system and Mg-based alloys database

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Rare Metals 2006年第5期25卷 492-500页

作者： DU Zhenmin GUO Cuiping li Changrong ZHANG weijing Department of Materials Science and Engineering University of Science and Technology Beijing Beijing 100083 China

As an example of the La-Mg-Y system, the method how to set up the themaodynamic model of individual phases was introduced in the process of thermodynamic optimization. The solution phases （liquid, body-centered cubic, face-centered cubic, hexagonal close-packed and double hexagonal close-packed） were modeled with the Redlich-Kister equation. The compound energy model has been used to describe the thermodynamic functions of the intermetallic compounds in the La-Mg-Y systems. The compounds Mg2Y, Mg24Y5, Mg12La, Mg17La2, Mg41Las, Mg3La and Mg2La in the La-Mg-Y system were treated as the formulae （Mg,Y）2（La,Mg,Y）, Mg24（La,Mg,Y）4Y, Mg12（La, Y）, Mg17（La,Y）2, Mg41（La,Y）5, Mg3（La,Mg,Y） and Mg2（La, Y）, respectively. A model （La, Mg,Y）0.5（La,Mg,Y）0.5 was applied to describe the compound MgM formed by MgLa and MgY in order to cope with the order-disorder transition between body-centered cubic solution （A2） and MgM with CsCl-type structure （B2） in the La-Mg-Y system. The Gibbs energies of individual phases were optimized in the La-Mg, La-Y and La-Mg-Y systems by CALPHAD technique. The projection of the liquidus surfaces for the La-Mg-Y system was predicted. The Mg-based alloys database including 36 binary and 15 ternary systems formed by Mg, Al, Cu, Ni, Mn, Zn and rare earth elements was set up in SGTE standard.

关键词： La-Mg-Y system thermodynamic modeling CALPHAD technique order-disorder transition Mg-based alloys database