近20年中国地区云量变化趋势

利用国际卫星云气候学计划（ISCCP）最新的D2云气候资料集,给出总云量、高云量及中云量在我国地区的分布特征;分别对季节平均和年平均的时间序列进行线性趋势分析,并进行效果检验。结果表明：近20年来中国大部分地区总云量没有显著的变化趋势,但是,在华南地区和西北部分地区的总云量有增加的趋势,青藏高原中部的总云量有所减少;在不同季节,各地总云量、高云量和中云量的变化趋势是不同的。     

Paddy soil — A suitable target for monitoring heavy metal pollution by magnetic proxies

A preliminary magnetic study around Meishan steel mill in Nanjing (SE China) was carried out combining geochemical analysis with scanning electron microscopy (SEM) to prove that paddy soil can be a suitable target for environmental study on heavy metal pollution. Magnetic background investigation showed a strong variation in this area due to different land uses and soil types. Magnetic susceptibilities (MS) measured on forest soils are much higher than in paddy fields, and values below 20 cm of the soil surface in forest with parent material of Xiashu loess are several times higher than in paddy soil with parent material of fluvisol. Measurements on vertical profiles show that paddy soil has a very low and stable magnetic background with mass-specific MS around 15 × 10^{− 8} m³ kg^{− 1}. A strong enhancement of MS values is found in the upper ~ 20 cm of paddy soil predominated by multidomain and pseudo single domain magnetite. However, relatively low S-ratios (0.57 to 0.85) reveal a significant contribution of imperfect anti-ferromagnetic minerals. Detailed research on a paddy soil core at site C719 near the steel mill indicates strong correlation between magnetic mineral concentration-related parameters (χ, ARM, SIRM) and heavy metal concentrations of Cu, Pb and Zn. In addition, typical anthropogenic Fe-spherules are detected in top paddy soil by means of SEM, which indicates that the increase of susceptibility in upper soil is mainly caused by steel mill emission. Mapping of MS in paddy fields across the steel mill area shows a decrease of MS with the distance to the major emission zone. Positive correlation between χ and Zn is found by measuring surface soil samples around the steel mill. Because of low background and high homogeneity of the ~ 20 cm uppermost mixing layer paddy fields are especially suitable for magnetic surface mapping of heavy metal pollution.     

A fractal model for the starting pressure gradient for Bingham fluids in porous media embedded with randomly distributed fractal-like tree networks

An analytical expression is derived for the starting pressure gradient for Bingham fluids in porous media embedded with randomly distributed fractal-like tree networks based on fractal theory and technique. The proposed model relates the flow rate and the starting pressure gradient to the structural parameters of porous media and microstructural parameters of fractal-like tree networks, the yield stress and fractal dimensions of porous media and maximum mother diameter of randomly distributed fractal-like tree networks. The results show that the starting pressure gradient decreases with the increase of porosity of matrix material, fractal dimension for mother diameters, diameter ratio and permeability, and the starting pressure gradient increases with the increase of the length ratio and the yield stress. The model predictions from the present model for the starting pressure gradient are in good agreement with the available expression.     

科尔沁沙地1826年以来榆树树轮宽度年表的建立及降水重建

利用10个采样点230个树木年轮样本,通过树轮分析程序,建立了科尔沁沙地区域1826～2008年共计183年长度的榆树树轮宽度年表.通过分析发现,水热条件与科尔沁沙地榆树生长关系密切.以标准年表及年表t+1年和t+2年序列重建了区域1826～2006年年降水.从过去181年来看,年降水重建序列具有2年、12年、18年和...     

江西省“中国天然氧吧”气候资源与创建条件分析

利用江西省1974—2016年气象资料和2016年空气负氧离子、环境空气质量、断面出境水质等监测资料,重点分析了全省旅游气候要素、大气质量、水质状况的时空分布特征,采用天然氧吧评价指标(T/CMSA0002—2017),对江西省"中国天然氧吧"创建条件进行了评估。结果表明,江西北部、中部、东部和南部区域空气负(氧)离子浓度等级均在6—7级,环境空气质量达标率在92%以上,空气质量、出境水质均达到国家Ⅱ类以上标准,旅游资源丰富,交通便利、设施配套完善,综合指标评分高,符合天然氧吧的评价标准。     

青藏高原冬春积雪影响亚洲夏季风的研究进展

青藏高原积雪作为亚洲夏季降水异常的一个预测因子已有很长历史。统计分析表明,青藏高原冬春积雪与印度夏季降水反相关,与我国长江中下游夏季降水多为正相关,不同作者对此现象给出了一些可能的解释,如地表反照率效应和积雪一水文效应。但积雪的这种跨季节滞后影响的具体物理过程仍有争议。另一方面,青藏高原冬春积雪资料存在不确定性,这对相关物理机制的理解造成了很大困难。通过回顾和梳理前人在该领域的研究成果,提出了高原积雪影响亚洲季风的未来研究方向。     

江西及其临近区域同化系统中不同季节背景误差协方差特征及其对降水预报影响

在不同季节背景下,对比分析多元变量相关的背景误差协方差特征,了解其在天气过程中的作用,可以改进同化系统性能,提高降水数值预报水平。对比分析汛期和非汛期江西及其临近区域多元变量相关的背景误差协方差特征,分别选取2019年汛期和非汛期的2次降水过程,设计2组循环同化试验,探讨多元变量相关的背景误差协方差对江西降水预报效果的影响。结果表明,相较于非汛期,汛期分析变量对风场、温度场和水汽场的贡献值整体上要更大,且汛期各个控制变量的背景场误差更为显著。多元变量试验的降水预报评估效果整体上更好,其汛期预报效果改善更显著。汛期与非汛期的多元变量试验降水预报结果更接近实况,且相对非汛期降水而言,汛期多元变量试验模拟效果更好,模拟的降水分布及强度与实况更为接近。     

2012年12月20-23日巴州寒潮降雪天气的特征分析

利用常规观测资料、自动站、T639客观分析资料,结合天气学原理和天气动力学诊断分析方法,对2012年12月20-23日巴音郭楞蒙古自治州（以下简称巴州）的寒潮天气过程的成因和降雪天气特征进行分析,并给出巴州降雪天气概念模型。结果表明：这次寒潮降雪过程是北欧阻塞高压向东南衰退,导致脊前横槽转成竖槽东南移,高空冷空气南压至40°N附近,造成巴州强降温、强降雪等寒潮天气,降雪阶段关键影响系统是700 hPa上的冷暖切变和风场辐合,水汽主要源自中低层西北方的经向和低层东南方的纬向输送;后续的冷凝降雪和阴雪阶段天气局地特征明显,水汽源自850 hPa至近地层局地的垂直输送。     

Ontogenetic development in the morphology and behavior of loach （Misgurnus anguillicaudatus） during early life stages

Loach （Misgurnus anguillicaudatus） is a commercially important fish in China and an ideal aquaculture species. However, culturists experience high larval and juvenile mortality during mass production. To provide insight into ways to improve larviculture techniques, we describe the morphological characteristics and behavior of loach during the larval and early juvenile stages. Yolksae larvae ranged from 2.8 to 4.0 mm body length （BL） between days 0 to 4; preflexion larvae ranged from 3.6 to 5.5 mm BL between days 4 to 6; flexion larvae ranged from 4.8 to 8.1 mm BL between days 5 and 14; and post-flexion larvae ranged from 7. l to 15.7 mm BL between days 11 to 27; the minimum length and age of juveniles was 14.1 mm BL and 23 d, respectively. Loach are demersal from hatch through to the early juvenile stages. A suite of morphological characteristics （e.g., external gill filament and ventral mouth opening） and behavioral traits have developed to adapt to demersal living. We observed positive allometric growth in eye diameter, head length, head height, and pectoral fin length during the early larval stages, reflecting the priorities in the development of the organs essential for survival. Our results provide a basis for developing techniques to improve the survival of larval and juvenile loach during mass production.     

Green functions with pulsating sources in a two-layer fluid of finite depth

The derivation of Green function in a two-layer fluid model has been treated in different ways.In a two-layer fluid with the upper layer having a free surface,there exist two modes of waves propagating due to the free surface and the interface.This paper is concerned with the derivation of Green functions in the three dimensional case of a stationary source oscillating.The source point is located either in the upper or lower part of a two-layer fluid of finite depth.The derivation is carried out by the method of singularities.This method has an advantage in that it involves representing the potential as a sum of singularities or multipoles placed within any structures being present.Furthermore,experience shows that the systems of equations resulted from using a singularity method possess excellent convergence characteristics and only a few equations are needed to obtain accurate numerical results.Validation is done by showing that the derived two-layer Green function can be reduced to that of a single layer of finite depth or that the upper Green function coincides with that of the lower,for each case.The effect of the density on the internal waves is demonstrated.Also,it is shown how the surface and internal wave amplitudes are compared for both the wave modes.The fluid in this case is considered to be inviscid and incompressible and the flow is irrotational.