Seasonal upwelling on the Western and Southern Shelves of the Gulf of Mexico

An 8-year database of sea surface temperature (SST), 7 years of Sea-viewing Wide Field-of-view Sensor (SeaWiFS) ocean color images, wind fields, and numerical model results are analyzed to identify regions and periods of coastal upwelling on the western and southern shelves of the Gulf of Mexico. On the seasonal scale, it is found that on the Tamaulipas, Veracruz, and southwestern Texas–Louisiana shelves there are upwelling favorable winds from April to August, when southeasterly winds are dominant and cold SST anomalies associated with upwelling are observed along their coasts. However, during summer, values of chlorophyll-a concentration are lower than those in autumn and winter, which are high due to advection of old bloom biological material from upstream. During winter, there is a cold front on the Tamaulipas shelf produced by advection of cold water from the Texas–Louisiana shelf and not due to upwelling. On the eastern Campeche Bank, persistent upwelling is observed due to favorable winds throughout the year with cold SST and large chlorophyll-a content along the inner shelf from May to September. On the Tamaulipas shelf, the summer upwelling delays the annual SST peak until September, while in most of the Gulf SST peaks in August. This difference is due to the end of the upwelling favorable wind conditions and the September seasonal current reversal.     

SST observations of upwelling induced by tidal straining in the Rhine ROFI

In this paper SST imagery and a three-dimensional numerical model of a river plume were employed to detect upwelling induced by tidal straining in the Rhine ROFI (region of fresh water influence). Previous studies have shown that the Rhine ROFI in the North Sea exhibits strong cross-shore density gradients that compete with tidal and wind mixing to establish stratification. During neap periods with low mixing energy an area measuring 30 km offshore by 100 km alongshore becomes stratified. When the ROFI is stratified strong cross-shore currents are observed, with surface currents rotating anti-cyclonically and bottom currents rotating cyclonically. The cross-shore currents interact with the cross-shore density gradients to produce a semi-diurnal cycle of stratification. Due to continuity requirements imposed by the proximity of the coast, the offshore-directed surface currents and onshore-directed bottom currents should lead to coastal upwelling.     

Numerical study on the summer upwelling system in the northern continental shelf of the South China Sea

A three-dimensional baroclinic nonlinear numerical model is employed to investigate the summer upwelling in the northern continental shelf of the South China Sea (NCSCS) and the mechanisms of the local winds inducing the coastal upwelling, associated with the QuikSCAT wind data. First, the persistent signals of the summer upwelling are illustrated by the climatological the Advanced Very High-Resolution Radiometer (AVHRR) Sea Surface Temperature (SST) image over 1985–2006 and field observations in 2006 summer. Then, after the successful simulation of the summer upwelling in the NCSCS, four numerical experiments are conducted to explore the different effects of local winds, including the wind stress and wind stress curl, on the coastal upwelling in two typical strong summer upwelling regions of the NCSCS. The modeled results indicate that the summer upwelling is a seasonal common phenomenon during June–September in the NCSCS with the spatial extent of a basin-scale. Typical continental shelf upwelling characteristics are clearly shown in the coastal surface and subsurface water, such as low temperature, high salinity and high potential density in the east of the Hainan Island, the east of the Leizhou Peninsula and the southeast of the Zhanjiang Bay (noted as the Qiongdong-QD), and the inshore areas from the Shantou Coast to the Nanri Islands of the Fujian Coast (noted as the Yuedong-YD). The analysis of the QuikSCAT wind data and modeled upwelling index suggests that the local winds play significant roles in causing the coastal upwelling, but the alongshore wind stress and wind stress curl have different contributions to the upwelling in the Qiongdong (QDU) and the coastal upwelling in the Yuedong (YDU), respectively. Furthermore, model results from the numerical experiments show that in the YD the stable alongshore wind stress is a very important dynamic factor to induce the coastal upwelling but the wind stress curl has little contribution and even unfavorable to the YDU. However, in the QD the coastal upwelling is strongly linked to the local wind stress curl. It is also found that not only the offshore Ekman transport driven by the alongshore wind stress, the wind stress curl-induced Ekman pumping also plays a crucial effect on the QDU. Generally, the wind stress curl even has more contributions to the QDU than the alongshore wind stress.     

A numerical study of the effect of the marginal sea on coastal upwelling in a non-linear inertial model

Inertia theory and the finite element method are used to investigate the effect of marginal seas on coastal upwelling. In contrast to much previous research on wind-driven upwelling, this paper does not consider localized wind effects, but focuses instead on temperature stratification, the slope of the continental shelf, and the background flow field. Finite element method, which is both faster and more robust than finite difference method in solving problems with complex boundary conditions, was developed to solve the partial differential equations that govern coastal upwelling. Our results demonstrate that the environment of the marginal sea plays an important role in coastal upwelling. First, the background flow at the outer boundary is the main driving force of upwelling. As the background flow strengthens, the overall velocity of cross-shelf flow increases and the horizontal scale of the upwelling front widens, and this is accompanied by the movement of the upwelling front further offshore. Second, temperature stratification determines the direction of cross-shelf flows, with strong stratification favoring a narrow and intense upwelling zone. Third, the slope of the continental shelf plays an important role in controlling the intensity of upwelling and the height that upwelling may reach: the steeper the slope, the lower height of the upwelling. An additional phenomenon that should be noted is upwelling separation, which occurs even without a local wind force in the nonlinear model.     

Climatological distribution of lightning density observed by satellites in China and its circumjacent regions

The 0.5°×0.5°grid resolution distribution of lightning density in China and its circumjacent regions have been analyzed by using the satellite-borne OTD (Apr 1995-Mar 2000) and LIS (Dec 1997-Mar 2003) databases. It is shown that: (i) Firstly, the variability of the lightning density (LD) is particularly pronounced over the different subareas, 9 times greater over the south than the north side of Himalayas Mountains, 2.5 times greater over the eastern than the western area of China. While the maximum and minimum LD are respectively 31.4fl/km2/a (in Guangzhou region) and less than 0.2fl/km2/a (in the desert of western China). Secondly, the LD of China's continent regularly varies with latitude and distance off coast, which is consistent with annual mean precipitation in varying trend. In conclusion, the Qinghai-Tibet Plateau, the China's three-step staircase topography and the latitude are three important factors affecting macro-scale characteristics of the LD distribution, (ii) The regional differences     

由ERS-1波形重构确定我国近海平均海平面

近海岸区域平均海面高在大地测量学、物理海洋学以及地球物理学研究中具有非常重要的意义.受各种条件的制约和限制,目前卫星测高技术主要应用于深海区域,在近海区域尤其是海岸线附近区域的应用几乎为空白.本文根据ERS-1测高卫星回波波形特征,采用五参数线性模型,由最小二乘拟合方法,对近海区域尤其是靠近海岸线附近的ERS-1测高波形数据进行波形重构.比较波形重构前、后解算平均海面高,表明波形重构技术不仅明显改善了解算近海海面高的精度,而且增加了近海测高海平面的分辨率,并使卫星测高有效观测延伸至海岸线附近.随后,本文利用波形重构后海面高数据构造了近海多年平均海平面,并对我国近海海平面特征进行了初步分析.     

Intracratonic asthenosphere upwelling and lithosphere rejuvenation beneath the Hoggar swell (Algeria): Evidence from HIMU metasomatised lherzolite mantle xenoliths

The mantle xenoliths included in Quaternary alkaline volcanics from the Manzaz-district (Central Hoggar) are proto-granular, anhydrous spinel lherzolites. Major and trace element analyses on bulk rocks and constituent mineral phases show that the primary compositions are widely overprinted by metasomatic processes. Trace element modelling of the metasomatised clinopyroxenes allows the inference that the metasomatic agents that enriched the lithospheric mantle were highly alkaline carbonate-rich melts such as nephelinites/melilitites (or as extreme silico-carbonatites). These metasomatic agents were characterized by a clear HIMU Sr–Nd–Pb isotopic signature, whereas there is no evidence of EM1 components recorded by the Hoggar Oligocene tholeiitic basalts. This can be interpreted as being due to replacement of the older cratonic lithospheric mantle, from which tholeiites generated, by asthenospheric upwelling dominated by the presence of an HIMU signature. Accordingly, this rejuvenated lithosphere (accreted asthenosphere without any EM influence), may represent an appropriate mantle section from which deep alkaline basic melts could have been generated and shallower mantle xenoliths sampled, respectively. The available data on lherzolite xenoliths and alkaline lavas (including He isotopes, Ra < 9) indicate that there is no requirement for a deep plume anchored in the lower mantle, and that sources in the upper mantle may satisfactorily account for all the geochemical/petrological/geophysical evidence that characterizes the Hoggar swell. Therefore the Hoggar volcanism, as well as other volcanic occurrences in the Saharan belt, are likely to be related to passive asthenospheric mantle uprising and decompression melting linked to tensional stresses in the lithosphere during Cenozoic reactivation and rifting of the Pan–African basement. This can be considered a far-field foreland reaction of the Africa–Europe collisional system since the Eocene.     

中国地磁台观测的2014年地磁急变

地磁急变（jerk）是起源于地球外核并在导电地幔过滤效应后在地球表面观测到的一种地磁现象,其反映了地核内部某些动力学过程.Jerks在空间范围上既可以是区域性的,也可以是全球性的.中国地区地磁台能否检测到2014年jerk？针对这一问题,利用中国大陆10个地磁台的磁静日月均值和CHAOS-6全球磁场模型,分析了X、Y和Z分量2008—2018年期间的长期变化,估算了2014年前、后的长期加速度值,确定了2014年地磁jerk的时间和强度.研究表明中国地磁台Y分量的长期变化为"Λ"型,Z分量存在明显的"V"型,具有典型的jerk特点.Y分量jerk出现的时间大约在2014年6月,比非洲大陆的Algeria TAM台和南美洲French Guiana KOU台时间滞后大约4个月.这暗示着产生jerks的地核流体波动的时序特点.中国西部和东北部地磁台的长期变化形态有明显的差别,主要由非偶极磁场引起.CHAOS-6模型与地面台站的长期变化形态并非始终一致.本文结果有助于更好地理解和解释长期变化的时间演变和地理分布,并为深入探讨jerks的地核起源和驱动机制提供新的观测约束.     

中国地磁台观测的2014年地磁急变

地磁急变（jerk）是起源于地球外核并在导电地幔过滤效应后在地球表面观测到的一种地磁现象,其反映了地核内部某些动力学过程.Jerks在空间范围上既可以是区域性的,也可以是全球性的.中国地区地磁台能否检测到2014年jerk？针对这一问题,利用中国大陆10个地磁台的磁静日月均值和CHAOS-6全球磁场模型,分析了X、Y和Z分量2008—2018年期间的长期变化,估算了2014年前、后的长期加速度值,确定了2014年地磁jerk的时间和强度.研究表明中国地磁台Y分量的长期变化为"Λ"型,Z分量存在明显的"V"型,具有典型的jerk特点.Y分量jerk出现的时间大约在2014年6月,比非洲大陆的Algeria TAM台和南美洲French Guiana KOU台时间滞后大约4个月.这暗示着产生jerks的地核流体波动的时序特点.中国西部和东北部地磁台的长期变化形态有明显的差别,主要由非偶极磁场引起.CHAOS-6模型与地面台站的长期变化形态并非始终一致.本文结果有助于更好地理解和解释长期变化的时间演变和地理分布,并为深入探讨jerks的地核起源和驱动机制提供新的观测约束.     

Long term variations in the mesospheric mean flow observed at Grahamstown (South Africa) and Adelaide (Australia)

The seasonal and interannual behaviour of monthly mean winds at a height of 90 km recorded at Grahamstown (33.3°S, 26.5°E) and Adelaide (34.5°S, 138.5°E) between 1987 and 1994 are compared. The zonal wind is found to be consistently stronger at Grahamstown and is always eastward, whereas at Adelaide it sometimes reverses. Maxima tend to occur near the solstices, the primary maximum during summer at Grahamstown, in agreement with satellite results, and during winter at Adelaide. The meridional wind also tends to be stronger at Grahamstown, but at both stations is predominantly northward with a maximum in summer and generally not as strong as the zonal component. This seasonal behaviour is reasonably well understood in terms of the interaction of the mean flow with gravity waves propagating up from below, with coriolis forces also playing an important role in the case of the meridional wind. Satellite observations do not generally support the idea that longitudinal differences between the stations could be attributed to the presence of a tropospheric/stratospheric stationary wave. It is suggested that these differences are more probably associated with local effects. Interannual zonal wind patterns at the two sites are similar over the summer months but are less well correlated during the rest of the year. The underlying causes of this variability are not well understood but are most probably global in nature, at least during the summer.     

Alkaline Phosphatase Activity and Utilization of Dissolved Organic Phosphorus by Algae in Subtropical Coastal Waters

Alkaline phosphatase activity (APA) and the availability of dissolved organic phosphorus (DOP) to marine algae were determined in Xiamen Bay and in algal batch culture systems. Results showed that APA changed with seasons, increasing to the highest value in summer and decreasing to the lowest in autumn and spring in Xiamen Bay. Tests on natural populations of planktonic algae and bacteria community showed that algae were mostly responsible for DOP utilization, while bacteria could not take up DOP compounds. Results from algal batch cultures also supported the above conclusion. Relationships between APA and environmental factors indicated that APA was negatively correlated with phosphorus level such as phosphate and small molecular DOP, and APA played an important role in utilization of DOP by algae. All the results emphasized the ecological significance of DOP in subtropical coastal waters.     

Coastal currents caused by superposition of coastal-trapped waves and near-inertial oscillations observed near the Noto Peninsula, Japan

Current observations were made from 14 July 2006 to 31 March 2007, using an acoustic Doppler current profiler mounted on the seafloor near the eastern coast of the Noto Peninsula, Japan, to investigate strong coastal currents induced by large-amplitude coastal-trapped waves (CTWs) and near-inertial fluctuations (NIFs). The CTWs were generated by the winter monsoon and the passage of a typhoon during the observation period. Two types of strong currents with velocities higher than 50 cm s^-1 were observed. One type, the strong current in winter (SCW), had the coast on the left to its direction of flow. This current was observed after a strengthening of the winter monsoon in January 2007. The other type, the strong current in fall (SCF), had the coast on the right to its direction of flow and was observed after the passage of a typhoon in September 2006. The SCW was inferred to be formed mainly by low-mode CTWs without NIFs. Compared to the SCW, the SCF had a more complicated vertical structure and time variations. The SCF was inferred to be generated by low-mode CTWs strengthened by NIFs. The contributions of NIFs to the strong coastal currents became important when the wind stress direction was rotating clockwise.     

近地磁尾重联中哨声波和Hall磁场的Cluster观测

在2001～2003年Cluster飞船通过近地磁尾期间,共探测到14次重联事件,在这些事件中同时还观测到等离子体波活动.本文把14次事件分为三大类,其中：第I类包含了8次事件,它们是在等离子体片内先于重联事件观测到波活动,并且还同时观测到Hall磁场.经过分析判断,这类事件中观测到的波是右旋偏振的哨声波.第II类包含了2次事件,这类事件也观测到了Hall磁场和右旋偏振的哨声波.第Ⅲ类也包含了2次事件,这类事件只是普通的重联事件,没有观测到Hall磁场,但是波活动明显先于重联事件.在我们观测的14次事件中,比较强烈的哨声波和Hall 磁场是一一对应的,因此哨声波可能主要是在Hall磁场的四极结构区激发的.     

大尺度场向电流及其与单色极光电子的联系——Swarm卫星观测

Swarm卫星A/C在480 km左右高度伴飞,通过二者磁场观测数据,可在不需假设无限大垂直电流片的情况下更加真实地计算出场向电流（FAC）.本文利用最新的Swarm观测数据,研究了大尺度场向电流的时空分布特征,及其对行星际条件的依赖;结合极光沉降粒子时空分布信息,探究了场向电流可能载流子及其源区.分析发现：（1）IMF B_z分量主要控制FAC的强度大小,B_y分量主要改变FAC的结构与分布,最为明显的是0区FAC;（2）昏侧1区上行FAC与单色极光电子的高发区域具有较高的重合度,且在不同行星际条件下均表现出相类似的纬度分布;（3）在上述区域内,FAC密度与单色极光电子能通量表现出较好的相关性.这表明单色极光电子对昏侧1区上行电流起着重要贡献.

     

Coastal pollution hazards in southern California observed by SAR imagery: stormwater plumes, wastewater plumes, and natural hydrocarbon seeps

Stormwater runoff plumes, municipal wastewater plumes, and natural hydrocarbon seeps are important pollution hazards for the heavily populated Southern California Bight (SCB). Due to their small size, dynamic and episodic nature, these hazards are difficult to sample adequately using traditional in situ oceanographic methods. Complex coastal circulation and persistent cloud cover can further complicate detection and monitoring of these hazards. We use imagery from space-borne synthetic aperture radar (SAR), complemented by field measurements, to examine these hazards in the SCB. The hazards are detectable in SAR imagery because they deposit surfactants on the sea surface, smoothing capillary and small gravity waves to produce areas of reduced backscatter compared with the surrounding ocean. We suggest that high-resolution SAR, which obtains useful data regardless of darkness or cloud cover, could be an important observational tool for assessment and monitoring of coastal marine pollution hazards in the SCB and other urbanized coastal regions.     

Preferential percolation quantified by large water content sensors with artifactual macroporous envelopes

For many scientific and practical tasks, it is important to estimate the soil–water percolation fluxes. This paper builds on measurements with large horizontal time‐domain reflectometry water content sensors in a loamy Mollisol. The sensors were installed into pre‐drilled holes and the gaps between them, and the soil was filled with a slurry of local soil with water. This gave rise to envelopes around them that contained artificial macropores. The sensors reacted to intensive rains by a rapid increase of their readings, often above the native soil's porosity, followed by an almost equally rapid decrease. The paper explores the feasibility of quantifying the rapid percolation, based on these anomalous water content peaks, and demonstrates that this is possible in principle, if the processes are simulated by a suitable model. A two‐dimensional dual porosity non‐equilibrium (mobile‐immobile) model was tried. The envelope around the sensor was modelled as an annulus with higher porosity and hydraulic conductivity, which attracts preferential flow and amplifies the percolation signal. With the model at hand, the flux hydrographs can be derived from model simulations and measured precipitation. For contrast, the Durner equilibrium dual porosity model was tried but was found little suitable. However, even the mobile‐immobile model did not perform perfectly. Simulated water contents were similar to the measured ones at some depths but not in the others, and the percolation fluxes were overestimated, compared to cumulative soil–water balance. Efforts to improve model performance were not successful. Hence, the model structure needs to be improved. Copyright © 2015 John Wiley & Sons, Ltd.     

DEMETER卫星观测的LF/MF电场频谱特征初步研究

利用法国DEMETER卫星观测的电场数据,研究了中国及邻区（0deg;——60deg;N,60deg;E——140deg;E）,频段为10KHz——3MHz,时间段为2008年1月1日——2008年９月12日期间的平均功率谱密度特征．文中选择了犓狆指数的日平均值小于或等于4的数据,获得LF频段（10——20 MHz）和MF频段（20 KHz——3 MHz）以16天为周期的昼侧和夜侧的平均功率谱密度空间分布图,得到了以下初步结果．LF频段：① 昼侧,不同频率的谱在对应时段上形态相似度不高,主要呈现纬度分带特征．夜侧,不同频率的谱在对应时段上形态相似度较高,主要差异在于谱的幅度,同一频率不同时段的谱分带特征不明显;② 昼侧谱的幅度值跨度要比夜侧的小很多,前者一般为1——1．5个数量级,而后者一般在2个以上,甚至达到4个数量级;③ 在汶川地震前后,平均功率谱密度在成都——兰州一线存在明显的变化．MF 频段：① 昼侧,不同频率对应时段的谱形态没有明显的相似性,同一频率不同时段的谱形态可能具有较好、弱或不具有相似性,具有明显、弱或不具纬度分带特征．夜侧,某些频段对应时段的谱形态具有明显的相似性,同一频率不同时段或者分时期的不同时段的谱形态具有较好的相似性,不具有明显的纬度分带特征,具有弱分区或者弱经度分带特征;② 昼侧和夜侧的谱幅度变化都不大,基本都在0.5个数量级之内;③ 在汶川地震前后没有发现明显的平均功率谱密度变化．     

暴时等离子体层顶密度不规则结构对SAR弧的调制

SAR弧的磁层源区对应环电流与等离子体层顶重叠区域, 而等离子体层顶常常观测到密度不规则结构.之前还没有暴时等离子体层顶密度不规则结构对SAR弧调制的观测报道.本文报道了地基成像和磁层、电离层卫星对2013年10月9日磁暴恢复相期间发生的SAR弧的联合观测事件.在SAR弧的磁层源区, Van Allen Probe B卫星观测到了密度不规则结构, 其中存在EMIC波、环电流离子分布和非线性电场结构.联合观测表明: 该区域中的环电流离子分布通过库伦碰撞产生的热流通量足以驱动SAR弧, 热流通量受到密度不规则结构的调制, 形成空间上的小尺度分布, 环电流离子中几keV的质子和几十keV的氧离子对这个过程起主导作用; 此外, 位于等离子体层顶密度不规则结构的低密度区的非线性结构电场引起的低能电子沉降可能是造成这次SAR弧非常明亮的原因.

     

“引江济星”工程及风场环境影响广东肇庆星湖水龄分布特征

目前大量景观类湖泊在人工布局下呈现形状不规整的特点,容易造成湖湾水体滞留形成死水区,水质恶化问题日益突出,本文以星湖为研究区域,建立基于环境流体生态动力学(EFDC)模型的星湖水动力—风场耦合模型,以水龄作为衡量水体交换速率的指标,设计12种工况模拟计算不同出入湖通道布局及流量配比、"引江济星"工程和风场对星湖水龄时空分布的影响.结果表明:星湖水龄存在季节性和空间性分布差异,春季主导风向与湖体流动主方向互斥,抑制了波海湖水体交换,导致水龄在春季较长,而秋季南西南季风促进中心湖等水体交换,致使水龄偏短,也反映出风向的影响存在湖区空间异质性,风向为南东南时星湖整体水龄最小;入湖口通道布局及流量配比对湖区水体交换速率存在影响,以外坑为波海湖入湖口且波海湖、中心湖、仙女湖入流比为4∶3∶3时,星湖整体水龄最小,拟建的青莲湖出水口和仙女湖出水口能有效加快青莲湖东北部和仙女湖东南部的水体交换速率;综合考虑调水引流效益、经济投资、生态开发和占地的成本,方案二为最优调水引流方案.本研究强调入湖口布局、流量大小和比例、及风场等因素对城市内湖水体置换的影响,为人为干扰下的景观湖泊的治理和管控提供科学支撑.