NUMERICAL EXPERIMENT OF IMPACT OF SEA SURFACE TEMPERATURE IN SOUTH CHINA SEA AND WARM POOL/WEST PACIFIC ON EAST ASIAN SUMMER MONSOON

By using the NCAR CCM1 model, we have designed six sensitive experiments, which areincreased and decreased SST (sea surface temperature) by 1℃ each in the SCS (South China Sea)and in the West Pacific warm pool, increased and decreased SST by 1℃ in the warm pool withincreased SST by 1℃ in the SCS. All experiments are integrated from April to July. Comparingwith the control experiment, we have analyzed the anomalies of the wind field at the upper andlower layers, the anomalies of the seasonal variability of the monsoon and precipitation for eachexperiment. In the result, we have found that the SST anomaly (SSTA) in the SCS greatly affectsthe seasonal variability of the SCS monsoon and precipitation in China, especially during the coldperiod of SST in the SCS. The impact of SSTA in the warm pool on SCS monsoon is also found.but is weak as compared to the effect of SST anomaly in the SCS. Besides, its impact on rainfall inChina is uncertain.     

A Forest Commons Revival in Slovenia

Forest commons in Slovenia are a poorly known indigenous institution for common resource management. They are a functional entity linked to a specific community that establishes interpersonal and intergenerational ties, as well as a link to the resource. We refer to shared ownership of resource, once made of pastures; today forests prevail. Collective property management remained despite community changes and legislation development. Today registered forest commons represent approximately one-third of those that existed before 1945. We highlight seven developmental turns to explain their revival. Six indicators are used in the analysis of current conditions. Forest commons are a potentially effective response to forest management challenges in Slovenia but also a potential model of social cohesion, rational resource use, and a balance between forest use and conservation. However, they are plagued by state ignorance, which hinders statistically sound analyses.     

储层毛细管压力曲线在东海油气储量计算中的应用

本文阐述了利用储层毛细管压力曲线计算含油炮和度的方法,该方法在东海油气储量计算中取得良好的结果。     

对流移入杭州湾后飑线发展机制分析

利用多源观测资料,对2021年4月30日发生在黄淮地区的一次强对流过程中由不同类型风暴系统造成的极端对流大风进行了探讨。研究表明,此次强对流过程发生在东北冷涡背景下的强风垂直切变和层结不稳定环境中,地面气旋及锋面触发了初始对流,在之后近10 h的传播过程中经历了组织化发展、孤立风暴新生、发展、合并与重组等不同阶段。期间,由两种不同类型风暴产生了特征相异的对流性大风：第一阶段,以江苏淮安站为代表,苏中极端对流性大风（36.2 m/s）是由发展强烈的超级单体风暴引发下击暴流所致。对流风暴低层呈现出明显的钩状回波特征,对应深厚的具有显著气旋性旋转的中气旋,在地面极端大风临近时刻,中气旋存在同时向上和向下拉伸、水平尺度快速收缩过程。贯穿整个风暴的下沉气流位于风暴钩状回波后侧,这支强下沉气流至地面附近迅速向外辐散,伴随风暴内强反射率核快速下降,导致淮安产生时、空尺度小且空间分布显著不连续的极端大风。第二阶段,以江苏南通地区为代表,苏东南地区极端大风的发展过程涉及多尺度天气系统的相互作用。线状对流系统前部存在明显的阵风锋,造成较大范围10级以上的地面大风;南通通州湾极端大风（47.9 m/s）发生在阵风锋后侧,其形成一方面是由于线形对流风暴造成的强冷池与地面冷锋相叠加,形成更强的气压梯度,另一方面与地面中尺度气旋入海过程中的快速发展以及风暴后侧倾斜向前的下沉气流导致的高空风动量下传有关。     

Response characteristics of plunge pool slabs of Xiaxiluodu Hydropower Station to flood discharge pulsating-pressure under valley deformation conditions

The key problem of the energy dissipation scheme of the arch dam body flood discharge and plunge pool below the dam is the stability problem of the plunge pool slab. As the protection structure of the underwater bed, the plunge pool slab bears the continuous impact of high-speed water flow. The hourly average dynamic water pressure on the slab is one of the main loads directly affecting the stability of the slab and is the main factor causing its erosion destruction. After the impoundment of the Xiluodu Hydropower Station, the measuring line of valley width in the plunge pool area has been continuously shrinking. By 2020, the cumulative shrinking value is about 80 ​mm. In light of the general background condition of valley shrinkage, daily inspection, annual detailed inspection, underwater inspection and drainage inspection of the plunge pool found that the plunge pool has experienced different degrees of damage, which greatly influences the long-term safety stability of the plunge pool. In this paper, the prototype observation data of flood discharge is used as the input load of pulsating-pressure, and the stress and displacement distribution of the plunge pool structure under the vibration load of flood discharge is analyzed under the condition that the stress and strain state of the plunge pool is changed under the influence of valley displacement. The results show that the stress, strain, and displacement distribution of the plunge pool are mainly caused by valley deformation, the vibration caused by flood discharge is little in influence, and the impact effect of deep hole flood discharge tongue on the plunge pool slab is weak.     

复杂地形下北京一次局地雷暴新生和增强机制初探

利用变分多普勒雷达分析系统, 结合多普勒雷达观测、 地面自动站、 风廓线仪、 加密探空等非常规观测资料, 对北京地区2011年8月9日局地雷暴的新生和增强机制进行了较精细的分析。结果表明: 该过程是一次发生在弱垂直风切变环境下的局地强对流雷暴大风过程, 环境场有较强的不稳定能量(CAPE达2 798 J·㎏^-1), 地面高比湿带(＞20 g·kg^-1)在山前聚集, 城区西部山前存在一较强γ中尺度热辐合中心, 前期大气环境条件十分有利于对流发生发展; 上游移进北京的强雷暴受地形强迫作用影响, 其产生的冷池出流被抬高, 冷空气叠加在地面γ中尺度热辐合中心之上, 使山前局地大气层结更不稳定, 另一方面, 强冷池出流产生的边界层高层偏北风与近地面弱的偏南风构成有利于对流新生的垂直风切变, 地面热辐合中心、 边界层热力和动力不稳定的增强共同作用是局地雷暴新生的主要机制; 上游冷池出流边界(阵风锋)伴有的强温度梯度和边界层辐合上升运动是原有局地新生雷暴显著增强的主要原因; 多单体雷暴相互碰撞合并产生的辐合上升运动是局地雷暴得以持续的关键因素。     

大洋硅藻席沉积与冰期旋回中的碳-氮循环

成席硅藻勃发与沉积埋藏过程链接了海洋有机碳生成-输出-埋藏以及大洋深部溶解无机碳的生成与储存的全过程,该过程及其对大洋碳-氮循环的潜在重大影响正引起学术界的关注。通过搜集整理一系列文献及数据,对成席硅藻在细胞层面的特殊功能、勃发机制以及硅藻席沉积物的时空分布特征进行了总结,尝试讨论硅藻席沉积对轨道时间尺度上全球碳-氮循环的潜在影响。由于成席硅藻具有一系列特点,包括在弱光条件下生存、利用大液泡来存储营养盐和调控浮力、与固氮蓝细菌共生、尿素循环等,导致成席硅藻在寡营养的层化水体中或者大洋锋面处容易获得生存竞争优势并发生勃发。根据沉积记录,在第四纪冰期,热带-亚热带大西洋以及热带西太平洋-东印度洋出现大规模的Ethmodiscus rex硅藻席勃发并向海洋内部输出大量有机碳。有机碳中的绝大部分都在水柱中发生降解,只有少部分保存到海底沉积物中。推测硅藻席勃发贡献了冰期深海内部“呼吸碳库”的增长以及大气二氧化碳浓度的降低。由于E. rex勃发加快了海洋上层营养盐的周转速率,因此也可能促进了冰期海洋氮储库的扩张。此外,氧同位素14/12期和4/2期间同时出现大洋无机碳碳同位素重值事件和热带-亚热带硅藻席勃发事件,二者之间可能存在机制上的关联。因此,成席硅藻是耦合大洋碳-氮循环的重要组成部分,进一步厘清地质历史时期硅藻席勃发规模及其在海洋元素循环中的作用,有助于解开冰期旋回尺度上的全球碳-氮循环之谜。     

Effects of initial step height on the headcut erosion of bank gullies: a case study using a 3D photo-reconstruction method in the dry-hot valley region of southwest China

Abstract

Headcut erosion has been recognized as one of the main processes involved in gully development in the dry-hot valley region of southwest China. To examine the effect of initial step height on headcut erosion processes, three headcuts were constructed ranging in height from 0.75 to 1.25 m on an active bank gully head, and a series of scouring experiments were conducted under a flow discharge of 120 L min^?1. The morphological evolutions of the plunge pools and soil loss volume were estimated by three-dimensional photo-reconstruction methods (3D-PR). As the step height increased, the experimental results showed that: (1) the transformed potential energy and shear stress would increase by approximately 4.89 J s^?1 and 26.4 Pa on average when the step height increased 0.25 m; (2) the mean depth and width of the plunge pool exhibited obvious growth, and the morphology of the cross-section developed from approximately V-shaped to U-shaped; and (3) soil loss volume increased logarithmically, with total soil loss volumes of 0.076, 0.105 and 0.116 m³, respectively. Although the significant effects of the initial step height on headcut erosion were verified, further quantitative studies are required to quantify the mechanism of headcut erosion, especially for plunge pool erosion.     

Geochemistry of coral from Papua New Guinea as a proxy for ENSO ocean–atmosphere interactions in the Pacific Warm Pool

A Porites sp. coral growing offshore from the Sepik and Ramu Rivers in equatorial northern Papua New Guinea has yielded an accurate 20-year history (1977–1996) of sea surface temperature (SST), river discharge, and wind-induced mixing of the upper water column. Depressions in average SSTs of about 0.5–1.0 °C (indicated by coral Sr/Ca) and markedly diminished freshwater runoff to the coastal ocean (indicated by coral δ¹⁸O, δ¹³C and UV fluorescence) are evident during the El Niño – Southern Oscillation (ENSO) events of 1982–1983, 1987 and 1991-1993. The perturbations recorded by the coral are in good agreement with changes in instrumental SST and river discharge/precipitation records, which are known to be diagnostic of the response of the Pacific Warm Pool ocean–atmosphere system to El Niño. Consideration of coastal ocean dynamics indicates that the establishment of northwest monsoon winds promotes mixing of near-surface waters to greater depths in the first quarter of most years, making the coral record sensitive to changes in the Asian–Australian monsoon cycle. Sudden cooling of SSTs by 1°C following westerly wind episodes, as indicated by the coral Sr/Ca, is consistent with greater mixing in the upper water column at these times. Furthermore, the coral UV fluorescence and oxygen isotope data indicate minimal contribution of river runoff to surface ocean waters at the beginning of most years, during the time of maximum discharge. This abrupt shift in flood-plume behaviour appears to reflect the duration and magnitude of northwest monsoon winds, which tend to disperse flood plume waters to a greater extent in the water column when wind-mixing is enhanced. Our results suggest that a multi-proxy geochemical approach to the production of long coral records should provide comprehensive reconstructions of tropical paleoclimate processes operating on interannual timescales.     

南川市三泉镇岩溶区农田生态系统植被碳库的动态变化

通过农田样方观测与实验分析获得南川市三泉镇农田生态系统主要农作物的含碳率、经济系数、果实水分系数,结合该区近26年来( 1980- 2005)主要农作物产量与耕地面积的相关数据,用农作物产量与碳储量转换模型计算法估算和分析该区农田生态系统植被碳库的总量及构成的动态变化。结果发现: 近26年来该镇农田植被碳库和碳密度略有提高,具有微弱的碳汇效应。与邻近的四川盆地非岩溶区相比,该区农田植被碳密度较低。针对农田生态系统植被碳库的构成特点和动态特征,该镇今后应进行作物结构调整,适度增加水稻等大春作物的种植和马铃薯、油菜和饲料等小春作物的种植面积,稳定小麦等作物的播种面积; 加强农田基本建设,发展生态农业,以进一步提高农田生态系统植被碳库的碳储量和碳密度。