冬季东亚副热带急流和温带急流协同变化与我国冷空气活动的关系

利用NCEP/NCAR再分析资料和地面台站气温观测资料,分析了冬季东亚副热带急流（EASJ）和东亚温带急流（EAPJ）强度变化特征及其与我国境内冷空气活动的关系。以（45°N～60°N, 70°E～110°E）和（27.5°N～37.5°N,130°E～160°E）区域平均的300 hPa全风速分别表征冬季EAPJ和EASJ的强度,将两支急流的强度变化分为四种情况：EAPJ和EASJ同强（SS）、同弱（WW）、以及强弱（SW）、弱强（WS）。分析四种急流强度变化情形下中国境内冷空气活动强度、路径、持续时间以及源地的不同特征,发现当EAPJ和EASJ均强时,冷空气从内蒙古中东部入侵,主要影响华北、东北和东部沿海地区,强度较弱,持续时间短,冷空气源地位于新地岛以东的洋面及陆地上;当EAPJ和EASJ均弱时,冷空气从新疆北部入侵,影响我国大部分地区,强度强,持续时间长,冷空气源地位于巴尔喀什湖西部;当EAPJ强,EASJ弱时,冷空气从我国东北入侵,主要影响我国东北部,中国南部降温不明显,冷空气强度较强,持续时间短,冷空气源地位于中、西西伯利亚地带;当EAPJ弱,EASJ强时,冷空气从内蒙古中部入侵,进而影响华北和我国东部地区,但冷空气强度较弱,冷空气源地位于贝加尔湖的西侧。进一步分析急流强度四种变化情形下的环流特征发现,EAPJ、EASJ均弱时,西伯利亚高压偏强,阿留申低压偏弱,东亚大槽偏深,中国东部的偏北风强,而EAPJ弱、EASJ强时,尽管西伯利亚高压和阿留申低压偏强,东亚大槽偏深,但中国东部的偏北风并不是很强,而另两种情况时,西伯利亚高压较弱,东亚大槽也较弱,中国东部的偏北风偏弱。     

夏季南黄海跨锋断面的生态环境特征及锋区生态系的提出

基于2006年夏季综合调查资料,分析和研究了南黄海陆架锋的分布以及跨锋断面的生态环境特征,并结合锋区的生物学和生态学现象,提出了锋区生态系的观点.结果表明:在南黄海西部冷水团边界附近海域存在因潮混合而形成的浅水陆架锋(潮汐锋),其中以长江口东北部至江苏北部外海、山东石岛外海和海州湾外侧的陆架锋最明显,而且与表层冷水区相...     

Long wavelength gravity anomalies over India: Crustal and lithospheric structures and its flexure

Long wavelength gravity anomalies over India were obtained from terrestrial gravity data through two independent methods: (i) wavelength filtering and (ii) removing crustal effects. The gravity fields due to the lithospheric mantle obtained from two methods were quite comparable. The long wavelength gravity anomalies were interpreted in terms of variations in the depth of the lithosphere–asthenosphere boundary (LAB) and the Moho with appropriate densities, that are constrained from seismic results at certain points. Modeling of the long wavelength gravity anomaly along a N–S profile (77°E) suggest that the thickness of the lithosphere for a density contrast of 0.05 g/cm³ with the asthenosphere is maximum of ∼190 km along the Himalayan front that reduces to ∼155 km under the southern part of the Ganga and the Vindhyan basins increasing to ∼175 km south of the Satpura Mobile belt, reducing to ∼155–140 km under the Eastern Dharwar craton (EDC) and from there consistently decreasing south wards to ∼120 km under the southernmost part of India, known as Southern Granulite Terrain (SGT).The crustal model clearly shows three distinct terrains of different bulk densities, and thicknesses, north of the SMB under the Ganga and the Vindhyan basins, and south of it the Eastern Dharwar Craton (EDC) and the Southern Granulite Terrain (SGT) of bulk densities 2.87, 2.90 and 2.96 g/cm³, respectively. It is confirmed from the exposed rock types as the SGT is composed of high bulk density lower crustal rocks and mafic/ultramafic intrusives while the EDC represent typical granite/gneisses rocks and the basement under the Vindhyan and Ganga basins towards the north are composed of Bundelkhand granite massif of the lower density. The crustal thickness along this profile varies from ∼37–38 km under the EDC, increasing to ∼40–45 km under the SGT and ∼40–42 km under the northern part of the Ganga basin with a bulge up to ∼36 km under its southern part. Reduced lithospheric and crustal thicknesses under the Vindhyan and the Ganga basins are attributed to the lithospheric flexure of the Indian plate due to Himalaya. Crustal bulge due to lithospheric flexure is well reflected in isostatic Moho based on flexural model of average effective elastic thickness of ∼40 km. Lithospheric flexure causes high heat flow that is aided by large crustal scale fault system of mobile belts and their extensions northwards in this section, which may be responsible for lower crustal bulk density in the northern part. A low density and high thermal regime in north India north of the SMB compared to south India, however does not conform to the high S-wave velocity in the northern part and thus it is attributed to changes in composition between the northern and the southern parts indicating a reworked lithosphere. Some of the long wavelength gravity anomalies along the east and the west coasts of India are attributed to the intrusives that caused the breakup of India from Antarctica, and Africa, Madagascar and Seychelles along the east and the west coasts of India, respectively.     

雷达强度数据中的阵风锋特征统计和自动识别

利用江苏南京2009-2012年天气雷达数据结合地面自动站风场资料分析江苏沿江地区阵风锋变化特征、阵风锋弧长与移速关系,及其在雷达反射率因子图像中呈现的总体、局部特征,详细分析了三种窄带回波回波带反射率因子分布特征。通过设计反映回波带平坦性的计算方法实现定量分析窄带回波分布异同功能。根据回波带径向波形特征判断径向波形的波宽、波峰个数、波峰阈值和波形双边梯度等特性,实现阵风锋径向波段识别。在对反射率因子图像预处理基础上,结合回波平坦性测试方法和阵风锋径向波形识别算法达到自动识别阵风锋回波的目的。识别效果表明:回波带平均值5 d BZ的独立阵风锋回波识别准确率达87%以上,回波带平均值10 d BZ的混合型阵风锋回波识别准确率达89%以上。对弱阵风锋识别成功率仍较低。     

夏季南黄海浅海潮汐锋对小拟哲水蚤和叶绿素a分布的影响

为分析夏季南黄海潮汐锋及其对浮游动物和初级生产分布的影响,本文利用2011年夏季航次的水文数据、小拟哲水蚤(Paracalanus parvus)样品及叶绿素a资料,对南黄海潮汐锋区位置及小拟哲水蚤丰度和叶绿素a分布进行了研究,探讨了夏季南黄海潮汐锋对小拟哲水蚤丰度和初级生产分布的影响。结果表明,在调查水域存在明显的浅海潮汐锋;小拟哲水蚤丰度高值(18267ind/m3)出现在锋区,其低丰度值(1480ind/m3)出现于锋区附近混合区,两者之间相差1个数量级,其丰度由远岸层化区至锋区逐渐升高。叶绿素a表层浓度高值(4.7μg/L)出现在锋区附近层化区,锋区叶绿素a表层浓度较低(2.2μg/L)。锋区中出现小拟哲水蚤丰度高、表层叶绿素a浓度较低的现象,表明桡足类的摄食压力对初级生产具有明显影响。可见,潮汐锋是影响南黄海浮游生物分布的重要驱动因子。本研究可为深入探讨潮汐锋对跨锋区生物要素分布乃至海洋生态系统结构与功能的影响提供重要依据。     

长江口及其邻近海区环流和温、盐结构动力学研究IV 盐度结构

盐度的数值模拟结果表明: 一年四季长江口及其邻近海区的盐度分布均为近岸低, 外海高,近岸与外海盐差大。冬季近岸和外海的上层盐度呈垂直均匀分布, 陡坡及外海的底层出现层化; 近岸特别是长江口及其以南近岸盐度的水平变化显著, 外海变化缓慢。春季在长江口以北, 近岸至外海的表层至近底层盐度呈垂直均匀分布, 近岸至外海的底层存在一个向北延伸的盐舌; 长江口及其以南近岸和外海的表层至次表层盐度呈垂直均匀分布, 在近岸稍远的表层至次表层形成盐跃层, 其强度自近岸至外海和自表层至底层逐渐减弱; 在陡坡区的底层盐度几乎呈均匀分布, 并保持高盐特征。夏季除长江口及其以南近岸浅水区盐度呈垂直均匀分布外, 其它区域盐度均出现剧烈分层, 在长江冲淡水区形成强盐跃层, 其强度自表层至底层迅速减弱, 陡坡至外海的底层盐度大致呈均匀分布且保持高盐特征。秋季长江口以北近岸浅水区表层盐度低且出现层化, 表层以下盐度高且呈垂直均匀分布; 近岸以远自表层至底层呈垂直均匀分布, 在外海上层盐度低且呈垂直均匀分布, 而底层盐度高并出现分层;长江口及其以南近岸浅水区盐度呈垂直均匀分布, 陡坡区出现层化, 其盐度为表层低, 底层高; 层化自表层至底层逐渐增强, 并随陡坡至外海的减弱, 上层又逐渐变为垂直均匀分布。     

Cold seeps at the salt front in the Lower Congo Basin II: The impact of spatial and temporal evolution of salt-tectonics on hydrocarbon seepage

This study investigates the distribution and evolution of seafloor seepage in the vicinity of the salt front, i.e., the seaward boundary of salt-induced deformation in the Lower Congo Basin (LCB). Seafloor topography, backscatter data and TV-sled observations indicate active fluid seepage from the seafloor directly at the salt front, whereas suspected seepage sites appear to be inactive at a distance of >10 km landward of the deformation front. High resolution multichannel seismic data give detailed information on the structural development of the area and its influence on the activity of individual seeps during the geologic evolution of the salt front region. The unimpeded migration of gas from fan deposits along sedimentary strata towards the base of the gas hydrate stability zone within topographic ridges associated with relatively young salt-tectonic deformation facilitates seafloor seepage at the salt front. Bright and flat spots within sedimentary successions suggest geological trapping of gas on the flanks of mature salt structures in the eastern part of the study area. Onlap structures associated with fan deposits which were formed after the onset of salt-tectonic deformation represent potential traps for gas, which may hinder gas migration towards seafloor seeps. Faults related to the thrusting of salt bodies seawards also disrupt along-strata gas migration pathways. Additionally, the development of an effective gas hydrate seal after the cessation of active salt-induced uplift and the near-surface location of salt bodies may hamper or prohibit seafloor seepage in areas of advanced salt-tectonic deformation. This process of seaward shifting active seafloor seepage may propagate as seaward migrating deformation affects Congo Fan deposits on the abyssal plain. These observations of the influence of the geologic evolution of the salt front area on seafloor seepage allows for a characterization of the large variety of hydrocarbon seepage activity throughout this compressional tectonic setting.     

EC-thin资料在低槽冷锋类降水过程人工增雨潜力区识别中的应用

选取8次冀中南地区低槽冷锋类降水过程,基于实况资料、微波辐射计资料、毫米波测云仪资料,利用EC-thin模式资料,分析研究EC-thin资料在人工增雨潜力区识别中的应用。结果表明：低槽冷锋类降水过程的共同特征为中高层30°—50°N、100°—120°E低槽东移,地面冷锋以西北路径或偏西路径南下影响冀中南地区;无论平原还是山区,低云量、气柱总含水量、大气可降水量、850 hPa比湿总体上呈现随降雨量增大而增大的趋势;当冀中南地区受低槽冷锋类天气系统影响时,在平原地区,当低云量、气柱总含水量、大气可降水量、850 hPa比湿预报平均值分别为6成、31 kg·m^-2、37 kg·m^-2、6 g·kg^-1以上时可进行人工增雨作业;在山区,当低云量、气柱总含水量、大气可降水量、850 hPa比湿预报平均值分别为5成、21 kg·m^-2、29 kg·m^-2、4 g·kg^-1以上时可进行人工增雨作业;此外最佳人工增雨阶段为各物理量值达到最大并开始减小阶段。     

象山港盐度锋面及其动力成因

基于盐度观测资料,证实了象山港夏季存在双潮锋的锋面系统,而在冬季该锋面现象消失。本文借助潮锋理论分析了该盐度锋面系统形成的动力机制,并进一步讨论了象山港径流量变化对锋面形成和消退的控制作用。结果表明,丰水期浮力输入是象山港锋面形成的最主要因素。     

一次冷锋大暴雨过程的多普勒雷达观测分析

2003年6月22—23日受冷锋和低空急流影响, 湖北省东部地区出现了一次区域性大暴雨过程。用每6 min一次的武汉多普勒雷达资料, 详细分析了冷锋和低空急流天气系统在多普勒雷达径向速度PPI、速度垂直剖面VCS和速度谱宽产品上的主要特征和演变特点。结果表明:PPI上冷锋对应一条径向速度辐合线, 由于多普勒雷达所测的是径向速度, 辐合线在向雷达站移动过程中出现逐渐“变短”的现象。因在冷锋附近低层的风垂直切变相对较大, 多普勒雷达所测的速度谱宽很大, 这一特征对确定冷锋的位置很有帮助。中尺度低空急流在PPI速度图上表现为有较大径向速度切向梯度的大风核, 且距离雷达站越远这一特征越明显。在上述分析基础上, 还结合地面逐时雨量资料等分析讨论了产生暴雨中尺度对流系统的传播与冷锋和低空急流的关系。