Influence of Coriolis Parameter Variation on Langmuir Turbulence in the Ocean Upper Mixed Layer with Large Eddy Simulation

Langmuir turbulence is a complex turbulent process in the ocean upper mixed layer. The Coriolis parameter has an important effect on Langmuir turbulence through the Coriolis–Stokes force and Ekman effect, however, this effect on Langmuir turbulence has not been systematically investigated. Here, the impact of the Coriolis parameter on Langmuir turbulence with a change of latitude (LAT) from 20°N to 80°N is studied using a non-hydrostatic large eddy simulation model under an ideal condition. The results show that the ratio of the upper mixed layer depth to Ekman depth scale (RME) RME = 0.266 (LAT = 50°N) is a key value (latitude) for the modulation effect of the Coriolis parameter on the mean and turbulent statistics of Langmuir turbulence. It is found that the rate of change of the sea surface temperature, upper mixed layer depth, entrainment flux, crosswind velocity, downwind vertical momentum flux, and turbulent kinetic energy budget terms associated with Langmuir turbulence are more evident at RME ≤ 0.266 (LAT ≤ 50°N) than at RME ≥ 0.266 (LAT ≥ 50°N). However, the rate of change of the depth-averaged crosswind vertical momentum flux does not have a clear variation between RME ≤ 0.266 and RME ≥ 0.266. The complex changes of both Langmuir turbulence characteristics and influence of Langmuir turbulence on the upper mixed layer with latitude presented here may provide more information for further improving Langmuir turbulence parameterization.     

青藏高原北部湖泊沉积物中基于不同碳源可培养细菌多样性

前人研究显示微生物群落对有机碳源的利用具有选择性,但是纯菌株对碳源利用的选择性却不甚明了。此外,在盐湖环境中微生物出于能量的考虑可能选择性利用有机碳源以抵抗盐度渗透压。因此,盐度可能间接地影响微生物对有机碳源的利用。然而,目前类似的相关研究较少。采用单碳源纯培养技术、16S rRNA基因序列分析和相关统计方法,研究了青藏高原北部6个湖泊(洱海、青海湖、托素湖、尕海1、尕海2、小柴旦湖)沉积物中基于不同碳源可培养细菌多样性及其与盐度的响应关系。采用7种不同类型的单碳源(甲酸钠、乙酸钠、丙酮酸钠、乳酸钠、葡萄糖、纤维素、混合氨基酸)进行培养筛选。共获得10个细菌分类属的75株纯培养菌株,它们分属于γ-变形菌纲的气单胞菌属(Aeromonas)、盐单胞菌属(Halomonas)、希瓦氏菌属(Shewanella)、假单胞菌属(Pseudomonas)、假交替单胞菌属(Pseudoalteromonas)、弧菌属(Vibrio),β-变形菌纲的脱氯单胞菌属(Dechloromonas)以及芽孢杆菌纲的芽孢杆菌属(Bacillus)、微小杆菌属(Exiguobacterium)和游动球菌属(Planococcus)。其中,盐单胞菌属菌株可利用研究中使用的所有碳源类型,说明这类细菌具有广泛碳代谢途径,可能潜在参与了青藏高原北部湖泊碳循环过程。研究发现所得纯菌株对不同碳链长度碳源的利用具有选择性,即随着盐度增高,某些菌株偏向利用结构更加复杂的碳源。总之,盐度不仅影响着纯培养细菌群落多样性,而且还影响着细菌对碳源类型的选择。     

Different response of vegetation to permafrost change in semi-arid and semi-humid regions in Qinghai–Tibetan Plateau

The effects of the depth of the active layer of permafrost on aboveground vegetation in semi-arid and semi-humid regions of the Qinghai–Tibetan Plateau were studied. The depth of active permafrost was measured and aboveground vegetation recorded. Differences in correspondence between permafrost depth and aboveground vegetation in semi-arid and semi-humid regions were analyzed. Vegetation cover and biomass were well correlated with permafrost depth in both semi-arid and semi-humid regions, but the correlation coefficient in the semi-arid region was larger than in the semi-humid region. With the increase in permafrost depth, vegetation cover and biomass decreased in both regions. Species richness and diversity decreased with increasing depth of permafrost in the semi-arid region. In the semi-humid region, these at first increased and then decreased as permafrost depth increased. It seems likely that vegetation on the Qinghai–Tibetan Plateau will degenerate to different degrees due to permafrost depth increasing as a result of climatic warming. The influence would be especially remarkable in the semi-arid region.     

上混合中剪切湍流和朗缪尔环流动力特征差异

Large eddy simulation(LES) is used to investigate contrasting dynamic characteristics of shear turbulence(ST)and Langmuir circulation(LC) in the surface mixed layer(SML). ST is usually induced by wind forcing in SML. LC can be driven by wave-current interaction that includes the roles of wind, wave and vortex forcing. The LES results show that LC suppresses the horizontal velocity and greatly modifies the downwind velocity profile, but increases the vertical velocity. The strong downwelling jets of LC accelerate and increase the downward transport of energy as compared to ST. The vertical eddy viscosity Km of LC is much larger than that of ST. Strong mixing induced by LC has two locations. They are located in the 2ds–3ds(Stokes depth scale) and the lower layer of the SML,respectively. Its value and position change periodically with time. In contrast, maximum Km induced by ST is located in the middle depth of the SML. The turbulent kinetic energy(TKE) generated by LC is larger than that by ST. The differences in vertical distributions of TKE and Km are evident. Therefore, the parameterization of LC cannot be solely based on TKE. For deep SML, the convection of large-scale eddies in LC plays a main role in downward transport of energy and LC can induce stronger velocity shear(S2) near the SML base. In addition, the large-scale eddies and S2 induced by LC is changing all the time, which needs to be fully considered in the parameterization of LC.     

Quantitative Analysis of Natural and Human Factors of Oasis Change in the Tail of Shiyang River over the Past 60 Years

The human and natural factors complicit in the driving forces of oasis change have always received considerable interest from the international research community. In this study, we used principal component analysis of natural and socio-economic statistical factors to quantitatively analyze the causal relationships and their contributions to the observed periodic expansion or shrinkage of the Minqin Oasis over almost 60 years. Our results show that human factors were the dominant factors governing expansion or shrinkage, with average contributions of 69.38% and 76.16%, respectively. Moreover, policy decisions have been the pivotal human factors. Under the influence of various policies, we have found that water resource utilization, land reclamation, population explosion, ecological protection and economic development have each played leading roles in different periods. This study provides a scientific basis for modelling the dynamics of an oasis for sustainable management.     

Remote Sensing for Watershed Hydrology: Issues and Challenges

With significant development since the beginning of the 21st century, hydrologic remote sensing becomes one of the most active disciplines in earth sciences, offering numerous opportunities and advances for watershed hydrology and other disciplines of geography. This commentary highlights the specialty and restriction of remote sensing for watershed hydrology on three aspects: watershed closure in water budget, watershed-scale effectiveness of hydrologic parameter retrievals, and watershed model inputs for data assimilation. The current challenges include rational watershed-scale validation, uncertainty control in retrievals, and error sources in data assimilation.     

河南第四纪泥灰岩岩溶发育特征及其供水意义

通过泥灰岩形成环境的分析,认为它属第四纪下更新世山前坡麓面状弱水流作用环境下形成。其岩溶地下水运移模式,根据其地质构造环境的差异及人类活动的影响,可划分为三种,其中第Ⅲ种模式水源地的水资源量较大。      

提升气象卫星高速数据解调性能的研究与试验

随着风云气象卫星事业的飞速发展,卫星观测通道数量不断增加、时间和空间分辨率不断提高,原始数据码速率已经由每秒几十兆比特上升为几百兆比特,不久将达到千兆以上.卫星的主要任务是获取遥感数据,从某种角度而言,卫星的价值等价于遥感数据的质量和大小.原始数据通过无线电载波传输至地面站,从载波中准确无误地解调出原始数据,是风云卫星...     

气候变化对媒介传播性疾病传播影响的评估模型

旨在综述评估各类模型在媒介传播性疾病中的应用前景。首先对媒介传播性疾病的流行及其与气候特征间的相关关系进行了分析,在此基础上综述了评估模型的种类与评估方法,包括气候因子决定性模型和数理统计学模型两大类,并分别以疟疾、血吸虫病和登革热等3种媒介传播性疾病为例,列举了两类模型在这些疾病中的应用与评估方法。最后提出了气候变化对媒介传播性疾病传播影响的未来研究方向和重点, 今后研究要评估气候变化对疾病传播造成的已有影响,预测未来影响范围与强度及预见未来变局,并提出科学的适应对策。     

气侯变化对人体健康影响的研究进展

从高温热浪、极端气候事件、空气污染、海平面上升等角度综述了气候变化对人类健康的影响,就气候变化对媒介传播性、水源性、食源性、呼吸道传染病以及部分慢性非传染病的影响进行了阐述,并提出了该领域亟待解决的科学问题和研究重点,包括法律体系的建立、机理的研究、疾病负担的测量以及成本效益分析等.