中国与中西南亚国家贸易效率、潜力测算及其影响因素分析——基于随机前沿引力模型

选取2008年~2015年中国与中亚、西亚和南亚22个国家的贸易面板数据,运用随机前沿引力模型估计总贸易效率和潜力以及出口贸易效率和潜力,分析影响贸易效率和潜力的主要因素。研究表明,中国与中西南亚国家的非效率因素呈递减趋势,总贸易效率和出口贸易效率呈递增的变化趋势;中国与中亚、西亚和南亚三个区域的贸易发展较不均衡:最具有进出口潜力和提升空间的是中亚地区,最具有出口潜力和提升空间的则是南亚地区;经济规模和人口总量与贸易水平呈正相关关系,与贸易伙伴国首都之间的直线距离和共同边界对贸易水平呈现显著的负影响;根据区域性差异,提出对策建议:对于中亚地区而言,要建立便捷的通关制度,提高双边的贸易便利化水平;对于南亚地区而言,要有效发挥上海合作组织的机制作用,带动和扩大区域之间的贸易规模;对于西亚地区而言,要加大对重大物流基础设施的投资和建设,积极改善物流网络、构建运输国际通道。

Strengthened influence of the East Asian trough on spring extreme precipitation variability over eastern Southwest China after the late 1980s

The relationship between variations in the East Asian trough(EAT)intensity and spring extreme precipitation over Southwest China(SWC)during 1961-2020 is investigated.The results indicate that there is an interdecadal increase in the relationship between the EAT and spring extreme precipitation over eastern SWC around the late1980 s.During the latter period,the weak(strong)EAT corresponds to a strong and large-scale anomalous anticyclone(cyclone)over the East Asia-Northwest Pacific region.The EAT-related anomalous southerlies(northerlies)dominate eastern SWC,leading to significant upward(downward)motion and moisture convergence(divergence)over the region,providing favorable(unfavorable)dynamic and moisture conditions for extreme precipitation over eastern SWC.In contrast,during the former period,the EAT-related circulation anomalies are weak and cover a relatively smaller region,which cannot significantly affect the moisture and dynamic conditions over eastern SWC;therefore,the response in extreme precipitation over eastern SWC to EAT is weak over the period.The interdecadal change in the relationship between eastern SWC spring extreme precipitation and the EAT could be related to the interdecadal change in the EAT variability.The large(small)variability of the EAT is associated with significant(insignificant)changes in spring extreme precipitation over eastern SWC during the latter(former)period.

Modeling of the Second Indirect Effect of Anthropogenic Aerosols in East Asia

This study investigated the second indirect climatic effect of anthropogenic aerosols,including sulfate,organic carbon(OC) ,and black carbon(BC) ,over East Asia.The seasonal variation of the climatic response to the second indirect effect was also characterized.The simulation period for this study was 2006.Due to a decrease in autoconversion rate from cloud water to rain as a result of aerosols,the cloud liquid water path(LWP) ,and radiative flux(RF) at the top of the atmosphere(TOA) changed dramatically,increasing by 14.3 g m-2 and decreasing by-4.1 W m-2 in terms of domain and annual average.Both LWP and RF changed most in autumn. There were strong decreases in ground temperature in Southwest China,the middle reaches of the Yangtze River in spring and autumn,while maximum cooling of up to-1.5 K occurred in the Chongqing district.The regional and annual mean change in ground temperature reached-0.2 K over eastern China.In all seasons except summer,precipitation generally decreased in most areas north of the Yangtze River,whereas precipitation changed little in South China.Precipitation changed most in summer,with alternating bands of increasing(～40 mm) and decreasing(～40 mm) precipitation appearing in eastern China.Precipitation decreased by 1.5-40 mm over large areas of Northeast China and the Huabei Plain.The domain and annual mean change in precipitation was approximately-0.3 mm over eastern China.The maximum reduction in precipitation occurred in summer,with mean absolute and relative changes of-1.2 mm and-3.8%over eastern China.This study revealed considerable climate responses to the second indirect effect of aerosols over specific regions of China.

Model Analysis of the Anthropogenic Aerosol Effect on Clouds over East Asia

A coupled meteorology and aerosol/chemistry model WRF-Chem （Weather Research and Forecast model coupled with Chemistry） was used to conduct a pair of simulations with present-day （PD） and preindustrial （P1） emissions over East Asia to examine the aerosol indirect effect on clouds. As a result of an increase in aerosols in January, the cloud droplet number increased by 650 cm-3 over the ocean and East China, 400 cm-3 over Central and Southwest China, and less than 200 cm-3 over North China. The cloud liquid water path （LWP） increased by 40-60 g m-2 over the ocean and Southeast China and 30 g m-2 over Central China; the LWP in- creased less than 5 g m-2 or decreased by 5 g m2 over North China. The effective radius （Re） decreased by more than 4 pm over Southwest, Central, and Southeast China and 2 pm over North China. In July, variations in cloud properties were more uniform; the cloud droplet number increased by approximately 250400 cm-3, the LWP increased by approximately 30-50 g m 2, and Re decreased by approximately 3 μm over most regions of China. In response to cloud property changes from PI to PD, shortwave （SW） cloud radiative m-2 over the ocean and 10 forcing strengthened by 30 W W m-2 over Southeast China, and it weakened slightly by approximately 2-10 W m-2 over Central and Southwest China in January. In July, SW cloud radiative forcing strengthened by 15 W m-2 over Southeast and North China and weakened by l0 W m-2 over Central China. The different responses of SW cloud radiative forcing in different regions was related to cloud feedbacks and natural variability.

Grain Size and Metallic Trace Element Contents in Sediments of Kemaman Coast, Terengganu, Malaysia, South China Sea

A total of 43 sediment samples were collected at Kemaman coast, Terengganu, by using Smith Mclntyre grab. These sediments were analyzed to determine the grain size, sediment texture and metallic trace elements. Lazer diffraction method using PSA （particle size analyzer） was used to determine the grain size and sediment texture. Teflon bomb was used to digest the sediments for metallic trace elements concentration. Results showed that the study area was dominated with sand particles （60.5%） followed by loamy sand （20.9%）, sandy clay （16.3%） and silt loam （2.3%）. On the other hand, the average concentrations of each metallic trace elements were 0.12 pg/g for Cd; 36.6 lag/g for Cr; 9.51 pg/g for Cu; 11.6 ~tg/g for N： 41.5 ~tg/g for Zn and 29.3/ag/g for Pb. Based on the results, it was found out that coarse sediments showed lower levels of metallic trace elements and higher levels in fine sediments. In addition, enrichment factor was calculated to assess the pollution status of the study area. Based on the calculation, the enrichment of metallic trace elements ranked in the following order： Pb 〉 Cd 〉 Zn 〉 Cu 〉 Ni 〉 Cr. The significant enrichment of Pb and moderate enrichment of Cd and Zn indicated that there are anthropogenic inputs while the rest of the metals can be considered from natural sources although there are effects of anthropogenic inputs in some sampling location.

Litterfall,Litter Decomposition,and Nutrient Dynamics in Two Subtropical Bamboo Plantations of China

Bamboos are one of the fast-growing and multiple use species in the world, and thus bamboo forests/plantations play an important role in C sequestration at regional and global levels. We studied aboveground litterfall, litter decomposition and nutrient dynamics for two years in two subtropical bamboo ecosystems in Southwest China so as to test the hypothesis that litter quality determine the rate and nutrient dynamics during decomposition of different litter fractions. Mean annual total aboveground litter production ranged from 494 to 434 g m-2 in two bamboo stands （P stand, dominated by Pleioblastus amarus and H stand, hybrid bamboo dominated by Bambusa pervariabilis x Dendrocalamopsis daii）. Bulk （-80%） of litter production was contributed by leaf litter in two stands followed by twigs and sheathes. Different litter fractions represented considerable variations in the rates of mass loss and nutrient release. Variation of the mass remaining after 2 years of decomposition was significantly explained by initial C/N ratio and initial P concentration. Initial concentrations of N, P, Ca, and Mg explained 57.9%, 95.0%, 99.8% and 98.1%, respectively, of the variations of these elements mass remaining after 2 years of decomposition. The patterns of nutrient dynamics and the final amount remaining were mainly determined by their initial litter substrate quality in tl^ese two subtropical bamboo plantations.

Effects of Seasonal and Perennial Grazing on Soil Fauna Community and Microbial Biomass Carbon in the Subalpine Meadows of Yunnan, Southwest China

Grazing and over-grazing may drive changes in the diversity and functioning of below-ground meadow ecosystems. A field soil survey was conducted to compare microbial biomass carbon （Cmin） and soil fauna communities in the two main grassland management systems in subalpine regions of Yunnan Province, China： perennial grazing currently practiced due to increasing herd sizes and traditional seasonal grazing. A three-year exclosure experiment was then conducted to further compare the effects of different grazing practices, including treatments of no mowing, perennial grazing （NM ＋ G）, mowing followed by seasonal grazing （M ＋ G）, mowing and no grazing （M ＋ NG）, and no mowing or grazing （NM ＋ NG）. The comparative survey result revealed that Cmin and total density of soil fauna were significantly lower at a perennially grazed site than at a seasonally grazed site. The experiment results showed that in comparison to non-grazing treatments （M ＋ NG and NM ＋ NG）, grazing （NM ＋ G and M ＋ G） reduced total fauna density （by 150 individuals m-2） and the number of taxonomic groups present （by 0.32 taxa m-2）. Mowing decreased Cmin （by 0.31 mg g-l）. Furthermore, the NM ＋ G treatment （perennial grazing） had the lowest density of Collembola （16.24 individuals m-2）, one of the two most common taxonomic groups, although other taxonomic groups responded differently to the treatments. Treatment effects on soil fauna were consistent with those on above-ground grasses, in which C：N ratios were greatly reduced by grazing, with this effect being the greatest for the NM ＋ G treatment. In contrast, different grazing treatments had little effect on C：N ratio of soil. Furthermore, the traditional grazing method （mowing followed by seasonal grazing） may have less severe effects on some taxonomic groups than perennial grazing. Therefore, an appropriate management should aim to protect soil fauna and microbes in this area from over-grazing and against further degradation.