我国近海热带气旋活动的气候特征及其与大尺度环境场的关系

利用1949~2004年共54 a的热带气旋资料,通过对历年影响我国近海(距海岸线300 n mile范围内)25°N以北及以南热带气旋的基本要素特征值的分析,发现我国近海25°N以北与以南热带气旋影响的频数和年代际变化不一致,尤其是20世纪80年代中期以来呈现反位相特征,近海25°N以北TC偏多,强度强;25°N以南TC偏少,强度弱.对热带气旋个数偏多年与偏少年对应的夏季海温场、高度场的合成分析,发现25°N以北偏多年比以南偏多年的东太平洋海温负距平强度大、范围广,高度距平场上反映出25°N以北偏多年西太平洋(包括南海)负高度距平区更为偏北、偏东;25°N以北TC偏少年时,中东太平洋海温为正距平区,高度场上太平洋低纬区域基本为正距平区,太平洋高纬区域是负距平区,而以南TC偏少年中东太平洋海温是负距平区,高度场上太平洋高纬区域是正距平区.文中还对当年前期各月海温场、高度场与当年以北、以南热带气旋个数分别作了相关分析,得出了一些实用有效的预报因子.     

北极涛动年代际变化对华北地区干旱化的影响

华北地区夏季降水在20世纪70年代中期以后进入年代际偏少阶段,表现出明显的干旱化趋势。华北干旱加剧具有特殊的大气环流背景,主要表现为在20世纪70年代中期以后亚洲大陆东部的热低压减弱,同时对流层低层到高层东亚夏季风环流减弱。这种异常的大气环流背景主要是由海陆热力差异和北极涛动的年代际变化造成的。近二十几年来,北极涛动维持在高指数位相是导致东亚地区大气环流异常的重要原因,并由此造成了华北干旱的加剧。     

中国平流层CH4的分布特征和季节变化

利用UARS卫星上HALOE试验的1992—2003年CH4资料,分析了中国平流层的CH4混合比分布特征,并对CH4混合比在不同纬度上的季节变化作了详细分析。结果表明,中国平流层CH4混合比随着高度逐渐减小,在经向上有较大差异,总是南边大于北边,而各个纬度带上的分布则较均匀。分析结果还表明,中国平流层CH4混合比在DJF的季节距平与MAM有相反的符号,而且中心位置基本吻合。此外,季节变率最大的是MAM—DJF,而不是JJA—DJF。并且在平流层低层的夏半年有明显的高值带,这可能与上升运动和辐散辐合作用有关。     

Vertical structure of tidal currents in the Xuliujing Section of Changjiang River Estuary

Three long-term fixed acoustic Doppler current profilers were first used for investigating the vertical structure of tidal currents in Xuliujing Section of Changjiang River Estuary. Moreover, three different periods(spring, summer and fall) were also considered for investigating seasonal variations. The semi-diurnal tides were the most energetic, with along-channel speed of up to 80 cm/s for M₂ constituent, which dominates at all stations with percent energy up to 65%–75% during seaso...     

Surface velocity estimations of ice shelves in the northern Antarctic Peninsula derived from MODIS data

The ice shelves in the northern Antarctic Peninsula are highly sensitive to variations of temperature and have therefore served as indicators of global warming. In this study, we estimate the velocities of the ice shelves in the northern Antarctic Peninsula using co-registration of optically sensed images and correlation module (COSI-Corr) in the Environment for Visualizing Images (ENVI) based on Moderate Resolution Imaging Spectroradiometer (MODIS) images during 2000-2012, from which we conclude that the ice ?ow directions generally match the peninsulas pattern and the crevasse, ice flows mainly eastward into the Weddell Sea. The spatial pattern of velocity field exhibits an increasing trend from the western grounding line to the maximum at the middle part of the ice shelf front on Larsen C with a velocity of approximately 700 ma^-1, and the velocity field shows relatively higher values in its southerly neighboring ice shelf (e.g. Smith Inlet). Additionally, ice ?ows are relatively quicker in the outer part of the ice shelf than in the inner parts. Temporal changes in surface velocities show a continuous increase from 2000 to 2012. It is worth noting that, the acceleration rate during 2000-2009 is relatively higher than that during 2009-2012, while the ice movement on the southern Larsen C and Smith Inlet shows a deceleration from 2009 to 2012.     

Alternate bars in a sandy gravel bed river: generation,migration and interactions with superimposed dunes

A field study was carried out to investigate the development of alternate bars in a secondary channel of the Loire River (France) as a function of discharge variations. We combined frequent bathymetric surveys, scour chains and stratigraphical analysis of deposits with measurements and modelling of flow dynamics. The channel exhibited migrating bars, non‐migrating bars and superimposed dunes. Possible mechanisms of bar initiation were found to be chutes associated with changes of bank direction and instability resulting from interactions between existing bars during the fall in water level after floods. We propose that the reworking of bar sediments during low flows (high width‐to‐depth ratio β), reinforced by high values of the Shields mobility parameter, can explain the formation or re‐generation of new alternate migrating bars during a subsequent flood. The migration pattern of the bars was found to be cyclic and to depend mainly on (i) channel layout and (ii) the dynamics of superimposed dunes with heights and lengths depending on location and discharge value. For instance, the hysteresis affecting the steepness of dunes influences the flow resistance of the dunes as well as the celerity of migrating bars during flood events. We compare the findings from the field with results from theoretical studies on alternate bars. This gives insight in the phenomena occurring in the complex setting of real rivers, but it also sheds light on the extent to which bar theories based on idealized cases can predict those phenomena. Copyright © 2014 John Wiley & Sons, Ltd.     

Spatial variations of tidal water level and their impact on the exposure patterns of tidal land on the central Jiangsu coast

The exposed area of intertidal zone varies with tidal water level changes. If intercomparisons of satellite images are adopted as a method to determine geomorphological changes of the intertidal zone in response to accretion or erosion processes, then the e?ect of water level variations must be evaluated. In this study, two Landsat TM images overpassing the central Jiangsu coastal waters on 2 January and 7 March 2002, respectively, were treated by the changing detection analysis using Image Di?erencing and Post-classiˉcation Comparison. The simultaneous tide level data from four tide gauge stations along the coast were used for displaying the spatial variations of water levels and determining the elevations of waterlines. The results show that the spatial variations of water levels are highly signiˉcant in the central Jiangsu coastal waters. The huge di?erences of tidal land exposure patterns between the two imaging times are related mainly to the spatial variations of tidal water levels, which are controlled by the di?erences in tidal phases for di?erent imaging times and the spatial variations of water level over the study area at each imaging time. Under complex tidal conditions, e.g., those of the central Jiangsu coastal waters, the tide-surge model should be used to eliminate e?ectively the e?ects of water level variations on remote sensing interpretation of geomorphological changes in the intertidal zone.     

Spatial and temporal variations of Synechococcus and picoeukaryotes in the Taiwan Strait,China

The size-fractionated phytoplankton biomass, and the spatial and temporal variations in abundance of Synechococcus (SYN) and picoeukaryotes (PEUK) were measured in the Taiwan Strait during three cruises (August 1997, February-March 1998, and August 1998). The results show that picophytoplankton and nanophytoplankton dominate the phytoplankton biomass, in average of 38% and 40%, respectively. SYN and PEUK varied over time in abundance and carbon biomass, greater in summer than in winter, in range of (7.70–20...     

Spatial and temporal variations of <Emphasis Type="Italic">Synechococcus</Emphasis> and picoeukaryotes in the Taiwan Strait,China

The size-fractionated phytoplankton biomass, and the spatial and temporal variations in abundance of Synechococcus (SYN) and picoeukaryotes (PEUK) were measured in the Taiwan Strait during three cruises (August 1997, February–March 1998, and August 1998). The results show that picophytoplankton and nanophytoplankton dominate the phytoplankton biomass, in average of 38% and 40%, respectively. SYN and PEUK varied over time in abundance and carbon biomass, greater in summer than in winter, in range of (7.70–209.2)×10⁶ and (0.75–15.4)×10⁶ cells/cm² in the abundance, and 1.93–52.3 and 1.57–32.4 μgC/cm² in the carbon biomass, for SYN and PEUK, respectively. The horizontal distributions of both groups were diurnal but heterogeneous in abundance, depending on the groups and layer of depths. Temperature is the key controlling factor for picophytoplankton distribution (especially in winter) in the Strait. Supported by Natural Science Foundation of China (No.40730846; 40521003)     

福建漳浦前湖湾沉溺古树林成因

根据2008年7月对从前湖湾古树林埋藏剖面和钻孔连续采集的142个样品进行粒度参数测量,分析了古树林成因和埋藏地的沉积环境变迁。用前湖湾周边已知沉积相:海滩、入海河流、河口浅滩、海岸沙丘以及滨海沼泽样本作为目标判据,将平均粒径Mz、标准偏差σ1和峰态Kg设为判别参数,与剖面和钻孔样品进行聚类判别,结果表明,42KaBP前湖湾古树林被海湾—河口相变过程埋藏,经历了6个阶段:河口浅滩阶段、浅滩—沙丘交替阶段、浅滩—河流演变阶段、淡水沼泽阶段、海滩沙丘阶段和现代风沙阶段,是气候—环境演变导致了前湖湾沉溺古树林的埋藏。