Vanishing Horizontal Sea Surface Temperature Gradients at Low Wind Speeds

Sea surface temperature (SST) is a result of multiple interactions in air-sea processes. During days with strong insolation and low wind speed, there may be uneven net heating of the water layer near the surface of the ocean, when there are horizontal temperature gradients at the sea surface. Cooling of the water caused by evaporation, sensible, or longwave radiative, heat loss would be greater from warm water compared to that from relatively cold water. As a result, under low wind speed conditions and clear skies, the horizontal SST discontinuities, occurring at fronts, eddies, or in storm wakes, may diminish or even vanish. This phenomenon is illustrated here with some field and modelling results. The dependence on latitude and mean environmental conditions of the difference in warming on the cold and warm side of SST discontinuities is explored. The time dependence is important for the impact on remote sensing of SST, and it is found to be short enough that substantial masking of SST gradients can occur during the first six hours of the diurnal heating cycle, but the effect would continue to grow if calm and solar heating persist for several subsequent days. An integrated effect of this uneven net heating is seen in the seasonal masking of subsurface temperature gradients in the Gulf of Mexico and Florida Straits.     

预处理共轭梯度法在VVP三维风场反演中的应用

本文从VVP(Volume Velocity Processing)方法的原始方程出发，进行三维风场反演的实验，在分析体积中心点反演十个变量，对病态矩阵的求解采用了预处理共轭梯度方法。通过对实测资料的分析，结果表明：预处理共轭梯度方法能较好的处理矩阵的病态问题，反演的水平二维风场、散度项和变形项结果比较合理，散度项和形变项量级都在10^-6～10^-3之间，水平速度和垂直速度量级在10^-1～10^1之间。     

1961-2013年东北与华北气温变化速度空间差异

全球气候的不断变化使得生物生境受到极大影响。气温作为最基本的气候要素,其变化迁移会胁迫生物对此做出响应,造成生物群落的迁徙。气温变化速度将气温看作物质的运动,能够直观地表示气温时空变化特征,对研究生物分布地理界限变化具有重要的指导意义。本文利用1961-2013年的全国每月平均温度数据集,分析了过去50多年中国东北与华北地区之间气温变化速度的区域差异。结果表明：东北与华北两地区整体气温变化速度均值为5.60 km/year,速度范围主要集中于0~9 km/year之间,约占总数的90%。东北地区气温变化速度均值大于华北地区。其中,东北速度均值为5.85 km/year,华北为5.41 km/year。从区域内部来看,东北地区气温变化速度整体较高,三省中黑龙江与吉林速度较高,辽宁省速度变化相对较小。华北气温变化速度高值区域主要分布在内蒙古高原与河北、天津的小部分地区,其他地区的气温变化速度则相对较小。     

厦门同安湾红树林及临近光滩沉积物孔隙水中溶解活性磷和亚铁分布特征的对比分析

为了解红树林与光滩磷、铁地球化学行为的差异,借助薄膜扩散梯度技术(ZrO-Chelex DGT),对厦门同安湾红树林及临近光滩孔隙水中溶解活性磷(DRP)、Fe~(2+)浓度进行了原位测量,并采集了相应沉积物柱状样进行测定分析。结果表明:(1)Fe~(2+)与DRP呈现较好的线性正相关,说明磷的吸附/解吸与铁氧化还原循环有关;(2)在不同深度,光滩孔隙水中DRP浓度均高于对应深度红树林。在浅层,由于溪水的补给造成光滩的磷富集;在深层,红树植物根部吸收导致磷浓度下降,光滩有机质含量较多,矿化释放DRP使其浓度较高;(3)孔隙水中的Fe~(2+)浓度分布表明,红树林区域随着深度的增加,逐渐由好氧环境进入厌氧环境;而光滩沉积物氧化还原环境可能受到红树林的影响,孔隙水Fe~(2+)在垂向上波动分布。     

全球升温对中国区域温度纬向梯度的影响

利用中国气象中心160站点的实际观察资料,对中国半个世纪的气温变化分时间段进行了计算分析。用各个站点52年的气温序列斜率与纬度和海拔分别做了相关分析,发现气温变化幅度和纬度有着很好的相关性,特别是在冬季;但气温变化和海拔没有相关性。另外,通过对不同季节的温度变化情况进行计算和纬向分析,发现随着全球气温的持续上升,气温的纬向梯度在变小,变化的幅度是冬季大、夏季小,高纬度地区大、低纬度地区小。最后指出造成气温纬度梯度减小的主要原因是大陆度随纬度的不同分布。     

高精度曲面建模的一种快速算法

 高精度曲面建模(HASM)是一种全新的曲面建模方法,其整个过程可分为偏微分方程的离散、采样方程建立和代数方程组求解3个阶段。目前所采用的求解对称正定方程组的方法主要是共轭梯度法。为了解决HASM的计算速度问题,本文给出了2种新的预处理共轭梯度算法,分别为不完全Cholesky分解共轭梯度法和对称逐步超松弛预处理共轭梯度法。实验表明,不完全Cholesky分解共轭梯度法收敛速度最快,且这2种预处理方法均比其他方法具有更快的收敛速度。     

Natural variation of macrophyte vegetation of lowland streams at the regional level

In the present study, we present a synopsis of two macrophyte surveys of physiographic units in northwest Germany carried out over one decade. Data were used to test a set of hypotheses on macrophyte distribution at the regional level. Rank–frequency curves resembled the broken stick model. Twenty-one species of the 59 most frequent species occurred at high frequencies above 15%. Helophytes made up a high percentage (12 of 21) of the frequent species. Phalaris arundinacea was the most frequent species in both sampling periods. Most species showed no considerable change in frequency over time, among them the core hydrophytes. Spatial variation of species frequencies among physiographical units showed a unimodal distribution in relation to frequency. Spatial variation of frequencies of functional groups was significantly lower. Most uneven distribution among physiographical units was found in cryptogams. DCA ordinations of physiographical units showed a spatial gradient from alluvial plains to higher grounds units, which remained constant over time. CCA ordination of physiographical units in relation to environmental parameters identified two main axes, an altitudinal gradient and an alkalinity gradient. Species composition of units corresponded to the main landscape pattern of alluvial plains, glacial lowlands, and higher grounds on Mesozoic rock. Species diversity showed a complex behavior. Diverse units were found both in alluvial plains and glacial lowlands of intermediate elevation. The study may help defining regionally differentiated reference states for stream management, benchmarking indicator scores of species and avoiding application of assessment methods outside their range of applicability.     

The response of Clitellata (Annelida) to environmental gradients in spring fens

Patterns in aquatic Clitellata assemblage composition are known to be driven by several environmental gradients, with water chemistry and substratum characteristics being particularly important. In this study we explored 54 isolated spring fens across the eastern Czech Republic and Slovakia. These fens varied in calcium and magnesium concentrations, forming a sharp and well defined environmental gradient running from calcium-poor acidic fens to extremely calcium-rich tufa-forming fens. We found that the main changes in clitellate species composition were controlled by this gradient, and/or total organic carbon content, over a wide area, including fen sites differing in other environmental conditions and historical development. However, this pattern was weakened in sites with a high organic matter content, which represented a second driver of change in assemblage composition along with water temperature. Three main types of fens were determined using cluster analysis based on clitellate assemblage composition. However, only the first type, which included tufa-forming fens, was found to fit with the previously established spring fen types based on vegetation (i.e. extremely mineral-rich fens with a tufa, brown-moss mineral-rich fens, mineral-rich Sphagnum fens and mineral-poor Sphagnum fens). The second clitellate type included sites with low temperatures and occasional desiccation, while the third type was characterised by high temperatures and trophy. Using eight environmental predictors, we were able to significantly explain changes in the population abundances of all 12 common species (i.e. recorded at 15-plus sites). The results from individual species modelling also suggests that an increase in organic matter content can trigger compositional shifts towards assemblages of common eurytopic tubificid species. Thus, human-induced eutrophication and negative changes in spring fen hydrology, mainly drying up, can represent a serious threat for species-specific assemblages of aquatic clitellates, especially at alkaline sites due to their isolated and spatially limited nature.     

安徽省阜阳盆地及周边大地热流分布特征

阜阳盆地位于周口坳陷的东部,地热资源丰富,但基础地热地质研究相对较少,尤其对区内大地热流研究尚属空白。为深入研究本区地热资源,为地热资源潜力评价提供数据支持和科学依据,本文基于收集的6口钻孔测温资料、实测的4口稳态测温数据以及61块岩心样品热导率测试数据,计算出了4个大地热流值。研究结果表明：研究区0~2 281 m内现今地温梯度为23.4℃/km~35.5℃/km,平均值为27.9℃/km;热导率介于0.968~4.932 W/（m·K）之间,平均值为1.959 W/（m·K）;对应的大地热流值介于44.7~63.8 mW/m²之间,平均值为53.4 mW/m²,与周口坳陷已发布的各大地热流平均值53.4 mW/m²一致,但却较明显低于中国大陆地区（平均值60.4 mW/m²）、中国东部（平均值61.9 mW/m²）、研究区东部两淮煤田（平均值58.3 mW/m²）以及南部秦岭造山带（平均值61.4 mW/m²）,并发现与四川盆地、柴达木盆地等国内主要的克拉通型盆地较接近,同时远远低于汾渭地堑、渤海湾盆地等新生代构造活跃的裂谷型盆地,反映出区域构造处于稳定状态;同时,区内热流之间有一定的差异,主要是受区域地质构造背景、基底起伏、沉积盖层、断裂活动等影响。

     

共和盆地恰卜恰地热区现今地热特征

恰卜恰地热区位于青海共和盆地的东北部,是我国重要的具有干热岩地热资源勘探开发潜力的地区之一.自2013年起,不同的研究者针对该区开展了大量地球物理探测工作,然而现今地热场的研究相对较少.本文基于4口干热岩钻孔的稳态测温资料和81块岩芯样品的热导率测试数据,计算了研究区4个大地热流值.研究结果表明：研究区基底花岗岩层现今地温梯度为39.0~45.2℃·km^-1,平均值为41.3℃·km^-1,大地热流值介于93.3~111.0 mW·m^-2之间,平均值为102.2 mW·m^-2,与我国主要的克拉通型盆地（如柴达木盆地、四川盆地和鄂尔多斯盆地）和新生代裂谷型盆地（如渤海湾盆地）相比,该区属于青藏高原高热流背景下的局部异常高地温梯度和高大地热流区.分析认为,研究区高地热异常可能暗示共和盆地浅部（20 km以浅）存在局部异常热源体（岩浆囊）.