ENSO variability and atmospheric response in a global coupled atmosphere-ocean GCM

The interannual variability associated with the El Ni?o/Southern Oscillation (ENSO) cycle is investigated using a relatively high-resolution (T42) coupled general circulation model (CGCM) of the atmosphere and ocean. Although the flux correction is restricted to annual means of heat and freshwater, the annual as well as the seasonal climate of the CGCM is in good agreement with that of the atmospheric model component forced with observed sea surface temperatures (SSTs). During a 100-year simulation of the present-day climate, the model is able to capture many features of the observed interannual SST variability in the tropical Pacific. This includes amplitude, lifetime and frequency of occurrence of El Ni?o events and also the phase locking of the SST anomalies to the annual cycle. Although the SST warming during the evolution of El Ni?os is too confined spatially, and the warming along the Peruvian coast is much too weak, the patterns and magnitudes of key atmospheric anomalies such as westerly wind stress and precipitation, and also their eastward migration from the western to the central equatorial Pacific is in accord with observations. There is also a qualitative agreement with the results obtained from the atmospheric model forced with observed SSTs from 1979 through 1994. The large-scale dynamic response during the mature phase of ENSO (December through February) is characterized by an eastward displacement and weakening of the Walker cell in the Pacific while the Hadley cell intensifies and moves equatorward. Similar to the observations, there is a positive correlation between tropical Pacific SST and the winter circulation in the North Pacific. The deepening of the Aleutian low during the ENSO winters is well captured by the model as well as the cooling in the central North Pacific and the warming over Canada and Alaska. However, there are indications that the anomalies of both SST and atmospheric circulation are overemphasized in the North Pacific. Finally, there is evidence of a coherent downstream effect over the North Atlantic as indicated by negative correlations between the PNA index and the NAO index, for example. The weakening of the westerlies across the North Atlantic in ENSO winters which is related to a weakening and southwestward displacement of the Icelandic low, is in broad agreement with the observations, as well as the weak tendency for colder than normal winters in Europe. Received: 31 October 1995 / Accepted: 29 May 1996     

建筑群邻近关系相似性计算

以建筑群的邻近关系为研究对象,在相似性理论的基础上,利用Delaunay三角网和Voronoi图,建立了基于相同特征量的邻近关系相似性模型和基于等距离关系曲线的邻近关系相似性模型,用于邻近关系相似性的定量化计算和判断。     

The origin of garnet and clinopyroxene in “depleted” Kaapvaal peridotites

A detailed petrographic, major and trace element and isotope (Re–Os) study is presented on 18 xenoliths from Northern Lesotho kimberlites. The samples represent typical coarse, low-temperature garnet and spinel peridotites and span a P–T range from 60 to 150 km depth. With the exception of one sample (that belongs to the ilmenite–rutile–phlogopite–sulphide suite (IRPS) suite first described by [B. Harte, P.A. Winterburn, J.J. Gurney, Metasomatic and enrichment phenomena in garnet peridotite facies mantle xenoliths from the Matsoku kimberlite pipe, Lesotho. In: Menzies, M. (Ed.), Mantle metsasomatism. Academic Press, London 1987, 145–220.]), all samples considered here have high Mg# and show strong depletion in CaO and Al₂O₃. They have bulk rock Re depletion ages (T_RD) >2.5 Ga and are therefore interpreted as residua from large volume melting in the Archaean. A characteristic of Kaapvaal xenoliths, however, is their high SiO₂ concentrations, and hence, modal orthopyroxene contents that are inconsistent with a simple residual origin of these samples. Moreover, trace element signatures show strong overall incompatible element enrichment and REE disequilibrium between garnet and clinopyroxene. Textural and subtle major element disequilibria were also observed. We therefore conclude that garnet and clinopyroxene are not co-genetic and suggest that (most) clinopyroxene in the Archaean Kaapvaal peridotite xenoliths is of metasomatic origin and crystallized relatively recently, possibly from a melt precursory to the kimberlite.

Possible explanations for the origin of garnet are exsolution from a high-temperature, Al- and Ca-rich orthopyroxene (indicating primary melt extraction at shallow levels) or a majorite phase (primary melting at >6 GPa). Mass balance calculations, however, show that not all garnet observed in the samples today is of a simple exsolution origin. The extreme LREE enrichment (sigmoidal REE pattern in all garnet cores) is also inconsistent with exsolution from a residual orthopyroxene. Therefore, extensive metasomatism and probably re-crystallization of the lithosphere after melt-depletion and garnet exsolution is required to obtain the present textural and compositional features of the xenoliths. The metasomatic agent that modified or perhaps even precipitated garnet was a highly fractionated melt or fluid that might have been derived from the asthenosphere or from recycled oceanic crust. Since, to date, partitioning of trace elements between orthopyroxene and garnet/clinopyroxene is poorly constrained, it was impossible to assess if orthopyroxene is in chemical equilibrium with garnet or clinopyroxene. Therefore, further trace element and isotopic studies are required to constrain the timing of garnet introduction/modification and its possible link with the SiO₂ enrichment of the Kaapvaal lithosphere.     

On the Issues of Scale,Resolution, and Fractal Analysis in the Mapping Sciences*

Scale and resolution have long been key issues in geography. The rapid development of analytical cartography, GIS, and remote sensing (the mapping sciences) in the last decade has forced the issues of scale and resolution to be treated formally and better defined. This paper addresses the problem of scale and resolution in geographical studies, with special reference to the mapping sciences. The fractal concept is introduced, and its use in identifying the scale and resolution problem is discussed. The implications of the scale and resolution problem on studies of global change and modeling are also explored.     

Oxygen depletion and phosphorus release following flooding of a cultivated wetland area in Denmark

Geografisk Tidsskrift, Danish Journal of Geography 108(2):17–25, 2008

The rewetting of altered wetlands is becoming increasingly widespread. When flooding cultivated soils, the oxygen (O₂) availability is reduced, subsequently, ferric hydroxides can dissolve and associated inorganic phosphorus (P) will be mobilized. This study shows the temporal and spatial dynamics of O₂ depletion following flooding using planar optodes and the subsequent release of Fe and P in two depth intervals in an experimental column set-up. The column was kept flooded for 48 days and thereafter partly drained and flooded again. Results document that large amounts of P (0.2 t P ha-¹) have accumulated in the present plough-layer (Ap) during the last 22 years, which represent roughly 15% of the present inorganic P stock in the Ap. As a result of flooding, fully anoxic conditions were observed within 3 days (within 10 h in Ap) and concentrations of dissolved Fe and P in the soil solution increased simultaneously after 7 days of flooding. Thus, P reaction kinetics was markedly delayed as compared to O₂ availability. P concentrations in soil water afterflooding (up to 0.15 mg L^?1) accounted for only 0.034% of the inorganic P stock in the Ap which is a significantly smaller fraction of the potential P-release as compared to previous investigations.

This is considered a result of only a minor fraction of the total inorganic P being directly associated with ferric hydroxides and thereby sensitive to short-term anoxic conditions as well as differences in the methodology used in this study (soil/water ratio). Finally, reactions releasing Fe and P were noted to be partly reversible upon draining.     

西南某巨型水电站坝区推覆断层研究

马家河坝断层发育于金沙江某巨型水电站库区,距坝址最近仅3km,且沿江两岸出露,主断面不同部分和次级断层结构样式和变形特征复杂。所以对断层的认识一直是大坝稳定性评价的重点也是争论的焦点。通过大比例尺野外填图、开挖平硐和室内构造解析获得了大量新资料,认为该断层是一个发育在地台内部的小型推覆构造。首次厘定了断层几何学和运动学特征和影响范围,分析了断层的动力学机制。这对大坝的施工和蓄水后的安全运行有重大意义。     

Isotopic offsets in throughfall and stemflow may have small effects on estimates of winter precipitation fractions

Forest canopies alter the amount and isotopic composition of precipitation reaching the forest floor. Thus retention, evaporation and transport processes in forest canopies, and their effects on water isotopes, are key to understanding forest water cycling. Using a two-year isotope dataset from a mixed beech/spruce forest in Zurich, Switzerland, we assessed the isotopic offsets between precipitation, throughfall and stemflow. We also analysed how these offsets affect estimates of the fraction of soil water that is derived from winter precipitation. Throughfall was typically enriched in heavy isotopes compared to precipitation, but isotopically lighter than stemflow, with average δ²H of −64.3 ‰, −59.9 ‰ and − 56.3 ‰ in precipitation, throughfall and stemflow, respectively. The differences between beech and spruce were rather small compared to the seasonal differences in precipitation isotopes. Isotopic offsets between precipitation and throughfall/stemflow were smaller during the spring and summer months (March through August) than during fall and winter (September through February). Bulk and mobile soil waters at 10 and 40 cm showed smaller seasonal variations than those in precipitation, throughfall and stemflow, and were isotopically lighter than recent precipitation, with the largest offsets occurring during the summer months (June through August) for bulk soil waters. Thus, bulk soil waters at both depths contain a mixture of precipitation from previous events and seasons, with over-representation of isotopically lighter winter precipitation. Mobile soil waters were more similar to recent precipitation than bulk soil waters were. Throughfall isotopes were slightly heavier than precipitation isotopes, resulting in different sinusoidal fits for seasonal isotopic cycles in precipitation and throughfall. These differences lead to small underestimates in the fraction of soil water originating from winter precipitation, when open-field precipitation rather than throughfall is used as the input data. Together our results highlight the importance of isotope measurements in throughfall and stemflow for the assessment of precipitation seasonality and water cycling across forested landscapes.     

地理信息图库一体更新方法

地图与DLG数据的更新方式之间既有区别又有联系,在研究DLG数据增量更新及地图与DLG数据一体化管理的基础上,提出一种地理信息图库一体更新方法,以地理实体为单位进行几何、属性和地图表达信息组织管理,获取DLG数据的增量信息并对增量信息进行地图表达得到符号图形增量信息。最后通过试验数据验证了该方法的有效性,且其具有易于计算机实现、效率高、可扩展性强、适于地图与DLG数据一体化更新等优点。