应用AMSR-E 89 GHz遥感数据反演北极多年冰密集度

被动微波辐射计AMSR-E在89GHz频段的空间分辨率几乎是其它低频段的2倍。到目前为止,已经有成熟的算法采用AMSR-E 89GHz频段的数据来反演整体海冰的密集度,而本文根据89GHz频段亮温数据针对一年冰、多年冰以及无冰水面的不同特性,提出了一种反演多年冰密集度的方法(AC)。计算了2007年北极的整体海冰和多年冰密集度,并与NASA TEAM算法(NT)的结果作了比较。对于整体海冰密集度,两种算法反演的结果基本一致。从日平均上来看,AC算法得到的整体海冰覆盖面积只比NT算法多25万km2。但是对于多年冰的反演结果,AC算法得到的结果比NT的结果要多出146万km2,冬季差别尤其大。造成这种差别的原因可能是AC算法对于北极表面气温的变化比较敏感。另外,AC算法计算得到2007年最大海冰覆盖面积为1400万km2,最小海冰覆盖面积为400万km2,这与其它研究结果一致。     

评价我国鄱阳湖流域森林生态系统碳动态对植树造林与未来气候变化的响应

20世纪80年代我国鄱阳湖流域实施造林再造林工程,该区域森林面积大幅增加。大规模植物造林可能极大地影响该区域森林碳库与碳收支的变化。因此,气候变化背景下鄱阳湖流域碳平衡对中国碳循环有重要的作用。但是我们对于该地区长时间尺度的碳平衡,特别是在未来气候变化和CO2浓度上升的条件下森林生态系统碳源／汇趋势的了解不多。本研究利用过程模型InTEC模型结合区域气候模式（RIEMS2．0）模拟的未来气候资料估算了鄱阳湖流域1981—2050年碳收支情况。1981—2000年,年NPP的快速增加主要归因于大规模的植树造林;森林土壤有机碳（0-30cm）在植树造林初期每年降低1％。同时该地区森林在过去20年期间从碳源转化为碳汇。2040—2050年森林总碳库相比较2001—2010年增加0．78PgC。基于气候变化和CO2浓度增加（A1B）背景下,鄱阳湖流域NEP趋向于稳定（20—30Tgcy^-1）,除了少数年份因为干旱引发了大的碳汇损失。模拟结果同样表明水分是控制该地区NEP年际变化的主要因子而NPP的年际波动主要受到温度的影响。     

Late Pleistocene glaciations at Lake Donggi Cona,eastern Kunlun Shan (NE Tibet): early maxima and a diminishing trend of glaciation during the last glacial cycle

The Burhan Budai Shan in NE Tibet represents a key location for examining the variable influence of the mid‐latitude westerly and monsoonal circulations on late Quaternary glaciations in this sector of the Tibetan Plateau. Our study investigates the glacial history of mountains near Lake Donggi Cona (35°17′N, 98°33′E) using field mapping in combination with ¹⁰Be surface exposure dating and numerical reconstructions of former glacial equilibrium line altitudes (palaeo‐ELA). A set of 23 new exposure ages, collected from moraines in four glacial valleys, ranges from 45 to 190 ka, indicating ice expansion during the early and middle part of the last glacial cycle, and during the penultimate and possibly an earlier Mid‐Pleistocene glaciation. Ice advances reaching 12–15 km in length occurred at around 190–180 ka (≥MIS 6), between 140–100 ka (late MIS 6/MIS 5), and 90–65 ka (late MIS 5/early MIS 4), with a maximum ELA depression of 400–500 m below the estimated modern snowline. Exposure ages from the valley headwaters further indicate a small glaciation between c. 60–50 ka (late MIS 4/early MIS 3), which was essentially restricted to the cirque areas. Significantly, we find no evidence for any subsequent glaciation in the area during MIS 2 or the Holocene period. These results indicate a diminishing trend of glaciation in the region since at least MIS 4, and corroborate the case of a ‘missing LGM’ in the more interior parts of the northeastern Tibetan Plateau. The emerging pattern suggests that the most favourable conditions for glaciation during the Late Pleistocene correspond to periods of relatively moderate cooling combined with an intermediate or rising East Asian monsoon strength.     

Analysis of Wellbore Skin Samples—Typology,Composition, and Hydraulic Properties

The presence of a wellbore skin layer, formed during the drilling process, is a major impediment for the energy‐efficient use of water wells. Many models exist that predict its potential impacts on well hydraulics, but so far its relevant hydraulic parameters were only estimates or, at best, model results. Here, we present data on the typology, thickness, composition, and hydraulic properties obtained from the sampling of excavated dewatering wells in lignite surface mines and from inclined core drilling into the annulus of an abandoned water well. Despite the limited number of samples, several types of skin were identified. Both surface cake filtration and particle straining in the aquifer occur. The presence of microcracks may be a determining feature for the hydraulic conductivity of skin layers. In the case of the well‐developed water supply well, no skin layer was detected. The observed types and properties of wellbore skin samples can be used to test the many mathematical skin models.     

Zoned CaAl-rich chondrule in Bali: New evidence against the primordial condensation model

One large (8.5 mm) chondrule in the Bali carbonaceous chondrite is strongly enriched in refractory elements similarily to the white objects in Allende which are widely believed to be “primitive” condensates. However, detailed investigations show the Bali chondrule to have an element distribution opposite to that predicted by the “primitive condensation” models. Refractory elements like Ti and Al are enriched at or near the surface of the chondrule. The contents of some volatile elements, e.g. Na, Si, and Cr, are higher in the central portion. It is suggested that this chondrule - and similar objects in other C-chondrites - originated in one, or more likely several, impact events and that the element distribution is the result of volatilization-condensation.     

Acoustic Emissions Monitoring during Inelastic Deformation of Porous Sandstone: Comparison of Three Modes of Deformation

In some reservoirs, large deformations can occur during oil or gas production because of the effective stress change. For very porous rocks, these production operations can be sufficient to cause inelastic deformation and irreversible damage. Rock formations can undergo deformation by different mechanisms, including dilatancy or pore collapse. In the laboratory, it has been shown that the inelastic deformation and failure mode of porous rocks are pressure sensitive. Indeed, when subjected to an overall compressive loading, a porous rock may fail by shear localization, compaction localization, or by cataclastic compaction. Acoustic emission (AE) records provide important information to understand the failure mode of rocks: the spatial evolution of damage as well as the source mechanisms can be followed using this technique. In this paper, we present three different laboratory axisymmetric compression experiments, performed on Bleurswiller sandstone, which enable us to compare the acoustic emission signature of these three modes of deformation. Our data show that compaction localization and cataclastic compaction are characterized by similar acoustic signatures (in terms of AE sources characteristics and evolution of AE number), in comparison to the acoustic signature from shear localization. This implies similar micromechanisms involved during compaction bands formation and cataclastic compaction.     

Existence and stability of strong potential double layers

An elementary integral equation technique is used to construct strong and weak stationary shock solutions from the one-dimensional Vlasov equation. It is shown that the plasma is Penrose stable in all points in space under certain conditions.This work was supported in part by the Atomic Energy Commission Grant No. AT(11-1)-2059, and NSF Grant GA-31676.supported by a CSIR bursary.     

Beobachtungen in der libyschen Sahara

Zusammenfassung Vom Westrand der Großen Syrte zieht sich eine grabenartige tektonische Senke in SSO-Richtung bis zu den Djofra-Oasen, die in einer Ausweitung dieses Systems liegen. Begleitender Vulkanismus liefert neben Einzelvulkanen auf tektonischen Linien vom Eozän bis ins Alluvium ausgedehnte Deckenergüsse. Diese gehören genetisch zum Graben und liegen südlich der Senke der Djofra-Oasen. Noch weiter südlich verläuft die Störungszone parallel zum Graben des Roten Meeres bis zu dem vulkanbesetzten Tibestigebirge. Auf halbem Wege liegen alluviale Einzelvulkane. Die klimatische Entwicklung zeigt seit dem Tertiär mindestens fünf deutliche Pluvialzeiten, deren jüngste wahrscheinlich dem Capsien, die zweitjüngste vielleicht etwa dem Acheul entspricht. Die Grundwässer liegen in zwei Stockwerken und stammen teils aus dem Tibestigebirge, teils aus örtlichen Niederschlägen (des letzten Pluvials). Das heutige Grundwasser ist ein Rest.Die Beobachtungen stammen aus Wüstenfahrten in den Jahren 1941 und 1942. Da durch die Zeitumstände ein großer Teil der Bilder, Gesteine und Fossilien sowie viele Aufzeichnungen verloren gegangen sind, bleibt die Darstellung etwas skizzenhaft.