What causes the spread of model projections of ocean dynamic sea-level change in response to greenhouse gas forcing?     

Couldrey  Matthew P.  Gregory  Jonathan M.  Boeira Dias  Fabio  Dobrohotoff  Peter  Domingues  Catia M.  Garuba  Oluwayemi  Griffies  Stephen M.  Haak  Helmuth  Hu  Aixue  Ishii  Masayoshi  Jungclaus  Johann  Köhl  Armin  Marsland  Simon J.  Ojha  Sayantani  Saenko  Oleg A.  Savita  Abhishek  Shao  Andrew  Stammer  Detlef  Suzuki  Tatsuo  Todd  Alexander  Zanna  Laure 《Climate Dynamics》2021,56(1-2):155-187

Sea levels of different atmosphere–ocean general circulation models (AOGCMs) respond to climate change forcing in different ways, representing a crucial uncertainty in climate change research. We isolate the role of the ocean dynamics in setting the spatial pattern of dynamic sea-level (ζ) change by forcing several AOGCMs with prescribed identical heat, momentum (wind) and freshwater flux perturbations. This method produces a ζ projection spread comparable in magnitude to the spread that results from greenhouse gas forcing, indicating that the differences in ocean model formulation are the cause, rather than diversity in surface flux change. The heat flux change drives most of the global pattern of ζ change, while the momentum and water flux changes cause locally confined features. North Atlantic heat uptake causes large temperature and salinity driven density changes, altering local ocean transport and ζ. The spread between AOGCMs here is caused largely by differences in their regional transport adjustment, which redistributes heat that was already in the ocean prior to perturbation. The geographic details of the ζ change in the North Atlantic are diverse across models, but the underlying dynamic change is similar. In contrast, the heat absorbed by the Southern Ocean does not strongly alter the vertically coherent circulation. The Arctic ζ change is dissimilar across models, owing to differences in passive heat uptake and circulation change. Only the Arctic is strongly affected by nonlinear interactions between the three air-sea flux changes, and these are model specific.

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Structure and Evolution of Supergranulation from Local Helioseismology     

Johann Hirzberger  Laurent Gizon  Sami K. Solanki  Thomas L. Duvall Jr. 《Solar physics》2008,251(1-2):417-437

Supergranulation is visible at the solar surface as a cellular pattern of horizontal outflows. Although it does not show a distinct intensity pattern, it manifests itself indirectly in, for example, the chromospheric network. Previous studies have reported significant differences in the inferred basic parameters of the supergranulation phenomenon. Here we study the structure and temporal evolution of a large sample of supergranules, measured by using local helioseismology and SOHO/MDI data from the year 2000 at solar activity minimum. Local helioseismology with f modes provides maps of the horizontal divergence of the flow velocity at a depth of about 1 Mm. From these divergence maps supergranular cells were identified by using Fourier segmentation procedures in two dimensions and in three dimensions (two spatial dimensions plus time). The maps that we analyzed contain more than 10⁵ supergranular cells and more than 10³ lifetime histories, which makes possible a detailed analysis with high statistical significance. We find that the supergranular cells have a mean diameter of 27.1 Mm. The mean lifetime is estimated to be 1.6 days from the measured distribution of lifetimes (three-dimensional segmentation), with a clear tendency for larger cells to live longer than smaller ones. The pair and mark correlation functions do not show pronounced features on scales larger than the typical cell size, which suggests purely random cell positions. The temporal histories of supergranular cells indicate a smooth evolution from their emergence and growth in the first half of their lives to their decay in the second half of their lives (unlike exploding granules, which reach their maximum size just before they fragment).  相似文献   

Civil society and sanitation hydropolitics: A case study of South Africa’s Vaal River Barrage     

Johann W.N. Tempelhoff 《Physics and Chemistry of the Earth》2009,34(3):164-175

The Vaal River Barrage, situated on the south-eastern border of the Gauteng Province, has been part of the hydrological landscape of South Africa’s most populous and economically active region for more than eight decades. After its completion in 1923 the Barrage was compromised by the construction, upstream, of the Vaal Dam (1930-1933). Today the Vaal River Barrage is primarily a storage facility of sewage and industrial waste water. South Africa’s transition to a multi-racial democracy in 1994 saw a number of socio-economic and political transformations that affected the water infrastructure. In the field of sanitation infrastructure in particular, conditions have deteriorated to the extent that the health of people in many parts of the country is being compromised.Using the Vaal River Barrage as a case study, this article outlines the efforts by civil society to make the relevant government sectors aware of this hazardous state of affairs. particular attention is given to save our Vaal environment (SAVE), a non-governmental organisation, at the helm of an active campaign to reduce pollution in the Vaal River Barrage.  相似文献   

Water surface mapping from airborne laser scanning using signal intensity and elevation data     

Bernhard Höfle  Michael Vetter  Norbert Pfeifer  Gottfried Mandlburger  Johann Stötter 《地球表面变化过程与地形》2009,34(12):1635-1649

In recent years airborne laser scanning (ALS) evolved into a state‐of‐the‐art technology for topographic data acquisition. We present a novel, automatic method for water surface classification and delineation by combining the geometrical and signal intensity information provided by ALS. The reflection characteristics of water surfaces in the near‐infrared wavelength (1064 nm) of the ALS system along with the surface roughness information provide the basis for the differentiation between water and land areas. Water areas are characterized by a high number of laser shot dropouts and predominant low backscatter energy. In a preprocessing step, the recorded intensities are corrected for spherical loss and atmospheric attenuation, and the locations of laser shot dropouts are modeled. A seeded region growing segmentation, applied to the point cloud and the modeled dropouts, is used to detect potential water regions. Object‐based classification of the resulting segments determines the final separation of water and non‐water points. The water‐land‐boundary is defined by the central contour line of the transition zone between water and land points. We demonstrate that the proposed workflow succeeds for a regulated river (Inn, Austria) with smooth water surface as well as for a pro‐glacial braided river (Hintereisfernerbach, Austria). A multi‐temporal analysis over five years of the pro‐glacial river channel emphasizes the applicability of the developed method for different ALS systems and acquisition settings (e.g. point density). The validation, based on real time kinematic (RTK) global positioning system (GPS) field survey and a terrestrial orthophoto, indicate point cloud classification accuracy above 97% with 0·45 m planimetric accuracy (root mean square error) of the water–land boundary. This article shows the capability of ALS data for water surface mapping with a high degree of automation and accuracy. This provides valuable datasets for a number of applications in geomorphology, hydrology and hydraulics, such as monitoring of braided rivers, flood modeling and mapping. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Bedload transport measurements with impact plate geophones: comparison of sensor calibration in different gravel‐bed streams          下载免费PDF全文

Dieter Rickenmann  Jens M. Turowski  Bruno Fritschi  Carlos Wyss  Jonathan Laronne  Ronel Barzilai  Ian Reid  Andrea Kreisler  Johann Aigner  Hugo Seitz  Helmut Habersack 《地球表面变化过程与地形》2014,39(7):928-942

Indirect bedload transport measurements have been made with the Swiss plate geophone system in five gravel‐bed mountain streams. These geophone sensors record the motion of bedload particles transported over a steel plate mounted flush with the channel bed. To calibrate the geophone system, direct bedload transport measurements were undertaken simultaneously. At the Erlenbach in Switzerland, a moving‐basket sampler was used. At the Fischbach and Ruetz streams in Austria, a Helley–Smith type bedload sampler provided the calibration measurements. A Bunte‐type bedload trap was used at the Rofenache stream in Austria. At the Nahal Eshtemoa in Israel, Reid‐type slot bedload samplers were used. To characterize the response of the geophone signal to bedload particles impacting on the plate, geophone summary values were calculated from the raw signal and stored at one second intervals. The number of impulses, i.e. the number of peaks above a pre‐defined threshold value of the geophone output signal, correlated well with field measured gravel transport loads and was found to be a robust parameter. The relations of impulses to gravel transport loads were generally near‐linear, but the steepness of the calibration relations differed from site to site. By comparing the calibration measurements from the different field sites and utilizing insights gained during preliminary flume experiments, it has been possible to identify the main factors that are responsible for site specific differences in the calibration coefficient. The analysis of these calibration measurements indicates that the geophone signal also contains some information about the grain size distribution of bedload. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Polyphase scheelite and stanniferous silicates in a W-(Sn) skarn close to Felbertal tungsten mine,Eastern Alps     

Ordosch  Alexander  Raith  Johann G.  Schmidt  Steffen  Aupers  Karsten 《Mineralogy and Petrology》2019,113(5):703-725

Mineralogy and Petrology - The scheelite exploration target Messelingscharte (Eastern Tyrol, Austria) is located in vicinity of the world-class Felbertal tungsten deposit. W-(Sn) mineralisation...  相似文献   

柴达木盆地北缘晚中生代—新生代构造应力场——来自构造节理分析的证据   总被引：2，自引：1，他引：1  

任收麦  葛肖虹  刘永江  乔德武  尹成明  Franz NEUBAUER  Johann GENSER 《地质通报》2009,28(7):877-887

柴达木盆地的构造演化,尤其是中、新生代的构造演化历史及其影响程度一直存在争议。在冷湖0号、冷湖4号、鄂博梁、结绿素等剖面开展了野外构造节理测量,应用地层恢复技术,分析了柴北缘晚中生代—新生代构造应力场的演化过程。结果表明：晚侏罗世之后,柴北缘主要受东西方向的挤压,这与区域上的研究结果一致;早白垩世北西—南东向的挤压应力可能再次影响了侏罗系;晚白垩世受南北挤压应力的影响,地层隆升遭受剥蚀;始新世下干柴沟期至上新世狮子沟期,柴北缘处于弱活动时期,接受稳定沉积;上新统狮子沟组沉积之后,由于阿尔金山的隆升,盆地北缘主体受北西—南东向应力的影响,涉及地层包括上干柴沟组、下油砂山组和上油砂山组;早、中更新世七个泉期之后,受南北向构造应力场的强烈影响,在狮子沟组、上油砂山组和下油砂山组中都有其分量,较老地层的地表露头中也有记录,这期构造运动对柴北缘油气运聚具有破坏和二次成藏的作用。因此,围绕柴北缘其他地质剖面开展更进一步的构造节理测量和分析工作,对油气资源勘探具有指导意义。  相似文献   

Estimating trends of Atlantic meridional overturning circulation from long-term hydrographic data and model simulations     

Gerrit Lohmann  Helmuth Haak  Johann H. Jungclaus 《Ocean Dynamics》2008,58(2):127-138

The ocean meridional overturning circulation (MOC) plays a central role for the climate in the Atlantic realm. Since scenarios for future climate change indicate a significant reduction of the MOC under global warming, an assessment of variations and trends of the real MOC is important. Using observations at ocean weather ship (OWS) stations and along oceanic sections, we examine the hydrographic information that can be used to determine MOC trends via its signature in water mass properties obtained from model simulations with the climate model ECHAM5/MPI-OM. We show that temperature trends at mid-latitudes provide useful indirect measure of large-scale changes of deep circulation: A mid-depth warming is related to MOC weakening and a cooling to MOC strengthening. Based on our model experiments, we argue that a continuation of measurements at key OWS sites may contribute to a timely detection of a possible future MOC slowdown and to separate the signal from interannual-to-multidecadal MOC variability. The simulations suggest that the subsurface hydrographic information related to MOC has a lower variability than the MOC trend measured directly. Based on our model and the available long-term hydrographic data, we estimate non-significant MOC trends for the last 80 years. For the twenty-first century, however, the model simulations predict a significant MOC decline and accompanied mid-depth warming trend.  相似文献   

G. RYDER (Hrsg.): Proceedings of the Eighteenth Lunar rad Planetary Science Conference. Press Syndicate of the University of Cambridge,Cambridge, England,und Lunar and Planetary Institute,Houston, Texas, 1988. Preis: £ 60.-. ISBN 0-521-35090-5     

Johann Dorschner 《Astronomische Nachrichten》1990,311(4):262-262

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Simulation of Mt. Pinatubo Volcanic Aerosol with the Hamburg Climate Model ECHAM4     

C. Timmreck  H.-F. Graf  J. Feichter 《Theoretical and Applied Climatology》1999,62(3-4):85-108

Summary  We study the three-dimensional transport of Mt. Pinatubo volcanic cloud with the climate model ECHAM4. In order to obtain model results comparable with observations a Newtonian relaxation technique was applied, which forces prognostic model variables towards the observations. A comparison of the simulated aerosol distribution with satellite data reveals good agreement for the first months after the eruption. The model, however, is unable to simulate the tropical aerosol maximum in 1992 and also overestimates the vertical downward and northward transport of aerosols. Substantial improvement was achieved with the introduction of reduced advective vertical transport through the 380 K isentropic layer. Heating rates and top of the atmosphere fluxes, which were calculated online for the first half year after the eruption, are in the observed range. A comparison of Pinatubo simulations between three different vertical ECHAM4 versions (ECHAM4 L19, ECHAM4 L39, MA/ECHAM4) indicates that a vertical resolution of ≈ 700 m in the tropopause region is sufficient to realistically reduce the vertical transport through the tropopause. Consideration of the upper branch of the Brewer Dobson circulation in the MA/ECHAM4 model improves the geographical distribution of the volcanic cloud. The application of a relaxation technique can further reduce major shortcomings of stratospheric simulations with the standard climate model. There remain, however some critical points in the global transport characteristics in all three models which are not fully understood. Received December 19, 1997 Revised July 22, 1998  相似文献