Dissipation process of summer tropical easterly waves in Western North Pacific

Tropical easterly waves are common features in the trade wind zones and they are important sources of tropical cyclogenesis. Despite numerous studies have analyzed the genesis and maintenance of easterly waves in the Western North Pacific, few had examined their dissipation processes. Focusing on tropical easterly waves during May-September of 1979–2017, this study shows that most of the easterly waves (∼70 %) eventually dissipate when encountering the monsoon trough and associated westerlies, while 22 % were carried northward by the monsoonal southwesterly flows and became recurving disturbances. Less than 10 % of easterly waves propagate across the South China Sea against the prevailing monsoon westerlies and into the Indochina peninsula. The vorticity budget analysis illustrates that total vortex stretching in the lower troposphere is the key factor in propelling the small number of easterly waves westward, suggesting that stronger and more convectively active easterly waves tend to move further into the developed monsoon trough. This echoes the previous observation that tropical disturbances alone have a limited probability in developing into a typhoon, for those disturbances or easterly waves almost always need to interact with the monsoon trough or a monsoon gyre, as well as other intraseasonal features to sustain the organized convection and rotation.     

2017年辽东湾夏季潮汐锋位置变化的分析

近海潮汐锋的分布和变化，主要受表层风摩擦、底层潮混合、净热通量和浮力平流的影响。基于2017年7、8月份辽东湾东部海域的实测数据，并结合ROMS（Regional Ocean Model System）模拟结果，利用考虑浮力平流效应的Stigebrandt公式对夏季辽东湾潮汐锋的位置变化进行了诊断计算，计算结果与ROMS模拟的潮汐锋位置符合较好，进一步探讨了风、净热通量和浮力平流对锋面位置变化的影响。主要结论如下：（1）位于辽东湾北部和东、西沿岸浅水区的潮汐锋呈"几"字形分布；（2）2017年6-7月潮汐锋位置变动不大，7月份仅在辽东湾东、西两岸潮汐锋位置略微向深水区移动，这主要是净热通量整体略微减小和风场略微增大造成的，浮力平流作用效果不够显著；（3）2017年8月辽东湾潮汐锋位置较7月向深水区大幅移动，最大移动距离约为20km，辽东湾8月份净热通量的大幅减弱起到了重要作用，浮力平流使潮汐锋位置向浅水区偏移，其调节效果比较显著。     

热带气旋Haiyan(2013)快速增强过程内核涡度变化机制的数值模拟研究

选取西北太平洋热带气旋Haiyan(2013)为研究对象,利用中尺度数值模式WRF对其快速增强(RI)过程进行了高时空分辨率的数值模拟,推导出一个包含不同尺度系统相互作用的垂直涡度诊断方程来探究TC内核区域相对涡度的变化特征及其与RI的联系。诊断结果表明:涡旋尺度散度项(stre2)、倾斜项(tilt2)和垂直平流项(advv2)对涡度收支的影响最为重要。RI开始前,stre2在边界层内对涡度收支为正贡献,边界层之上则为负贡献;tilt2在低层促进涡度增加;advv2分布与stre2相反,在低层为负值,高层为正值。RI开始后,stre2在低层(高层)对涡度的正(负)贡献显著增强;tilt2在低层(高层)对涡度的促进(抑制)作用明显增强,但在中层出现正负贡献相互交替的情况;advv2在低层对涡度的正贡献也有所增强。     

Temporal Irregularities in the Macrobenthic Community and Deep-Water Advection in Wismar Bay (Western Baltic Sea)

Wismar Bay is a shallow coastal embayment in the Western Baltic Sea which is polluted by various industries. Macrobenthos data collected between 1986–91 are examined for qualitative and quantitative changes attributable to oxygen depletion and the subsequent time needed for recovery. Regular oceanographic surveys since 1976 indicate one episode of oxygen deficiency, caused by deep-water intrusion into the study area. However, principal component analyses show that the benthic community alternated between periods of relative stability and sudden change at both of the deeper sites examined. Deep-water intrusions from outside the bay are documented twice followed by sudden changes in the benthic community, but similar events may also have occurred in other years. The benthos showed little resilience when impacted, and the changes in the benthic community during July–August are proposed to monitor the future influence of the deep-water intrusions.     

The Spring Phytoplankton Bloom in the Coastal Temperate Ocean: Growth Criteria and Seeding from Shallow Embayments

A method based on time-series of conductivity, temperature and depth (CTD) profiles which successfully determines favourable phytoplankton growth conditions for the spring bloom in nearshore temperate coastal waters was developed. The potential for shallow embayments to influence phytoplankton species composition in larger adjacent waters was also investigated. At temperate latitudes, such embayments should have favourable phytoplankton growth conditions earlier in the spring than open waters as bathymetry limits vertical mixing and thus increases light availability. The study area was Nanoose Bay, which is connected to the Strait of Georgia, British Columbia. Data were collected 2–3 times per week during the winter-spring of 1992 and 1993. A mooring with 5 current meters was placed at the mouth of the bay in 1992. The conservation equation for a scalar was used to estimate the balance between advective transport and biological source and sink terms. Variability in physical conditions and biological response between years was tremendous. Results indicate that seeding from the bay was not possible in 1992 but could have been in 1993. However, to conclusively determine the importance of Nanoose Bay on the spring bloom species composition in the Strait of Georgia, more extensive work is required. This revised version was published online in August 2006 with corrections to the Cover Date.     

Strain analysis and vorticity of flow in the Northern Sardinian Variscan Belt: Recognition of a partitioned oblique deformation event

A field example of strain partitioning has been analysed along the Nurra–Asinara transect of the NW Sardinian Variscan chain (Italy). The section in the Nurra–Asinara area is in a continuous sequence of tectono-metamorphic complexes made of low- to high-grade metamorphic rocks affected by a polyphase tectonic history. The principal fabric of the area is controlled by a D2 progressive deformation phase in which the strain is partitioned into folds and shear zone domains. The D2 stretching lineation and shear sense show a clear change from south to north. The principal meso- and micro-structures, vorticity gauges and a quantitative kinematic analysis of local strain suggest that the D2 kinematic history could be envisaged as an oblique heterogeneous deformation similar to the transpressive systems described in ancient and modern settings elsewhere. Using a simple kinematic model we also propose that both a transpressive system followed by “thrusting” or a partitioned transpressive system could be responsible for the fabric distribution and strain accumulation described in the study transect.     

基于卫星和Argo观测的阿拉伯海中北部海表盐度季节和年际变化

基于美国国家航天局（NASA）发射的水瓶座（Aquarius/SAC-D）卫星和欧洲航天局（ERA）发射的土壤湿度与海洋盐度（SMOS）卫星的观测资料,以及Argo海表盐度资料,重点分析了阿拉伯海中北部海表盐度的季节和年际变化.年平均情况下,Argo、Aquarius和SMOS表现出相似的海表盐度分布形态,均表现了阿拉伯海中北部高达36.5 psu的高盐特征.阿拉伯海中北部海表盐度在2—3月出现最低值,在4月之后快速升高,并在夏季西南季风的成熟阶段达到最高.阿拉伯海中北部海表盐度显著的季节变化与季风风场引起的大量蒸发和平流输送相关.夏季风期间,Ras al Hadd急流将来自阿曼湾的高盐水向东向南输送到阿拉伯海中北部海域,使海表盐度升高并达到最高值;冬季风期间,冬季风环流系统在印度半岛西侧海域形成向北的低盐水输送,造成阿拉伯海中北部海表盐度降低.该低盐水平流在冬季风后期能够影响到阿曼海.阿拉伯海中北部海表盐度年际变化主要与季风驱动的季风环流系统的变化相关,尤其是冬季风期间向北流动的印度西侧沿岸流的强弱与该区域海表盐度年际变化关系密切.     

近百年中国两次年代际气候变暖中的冷、暖平流背景

近百年中国气候经历了两次明显的年代际变暖,分别发生在20世纪40年代之前和70年代之后。由大气环流变化引起的冷、暖平流异常可为理解两次变暖提供参考。首先基于最新研制的近百年32站气温观测和集合经验模分解（Ensemble Empirical Mode Decomposition,EEMD）方法揭示两次变暖过程中国的冷、暖分布格局,进而利用全球格点气温和海平面气压资料计算了同期地转风导致的温度平流。结果表明,20世纪40年代中国华北北部至东北大部分地区和华南沿海局部地区偏冷而中东部至西南内陆大部分地区偏暖的年代际气候异常,站点冷、暖异常与大尺度温度平流的空间关联系数达0.85;而对于近20年中国气候变暖而言,这一关联系数仅0.49。研究结果从一个新颖的角度说明:早期变暖过程中气候系统内部过程如大气环流异常的作用较大,而近几十年气候变暖则更多地受迫于外强迫。