On the warm/cold regime shift in the South China Sea: Observation and modeling study     

P. Swapna  Jianping Gan  Alexis Lau  Jimmy Fung 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(7):1039-1056

Remote sensing data sets and a high-resolution three-dimensional regional ocean model were utilized to investigate the shifting of warm/cold regime and the associated sea level variation in the South China Sea (SCS) during 2000–2003. Both the altimetry data and the model results showed an increase in the sea level (warm phase) followed by an abrupt decrease (cold phase) in the SCS during 2000–2003. Heat budget calculations performed with the model revealed excess heat advection from the western Pacific warm pool into the SCS during the warm phase than the cold phase. The warm phase, which occurred during La Niña episodes, resulted from the intrusion of abnormally warmer western Pacific water that increased the heat content and thus sea level in the SCS. The cold phase, which occurred during El Niño episodes, was triggered by a reduction in the net atmospheric heat flux followed by cold water advection into the SCS. Decrease in the rate of precipitation minus evaporation (P?E) also accounted for the falling of sea level during cold phase. The present study integrated the available remote sensing data and advanced numerical model to identify the time-dependent three-dimensional dynamic and thermodynamic forcing that are important in governing the warm/cold regime shift in the SCS.  相似文献   

Comment on ‘Kişi Ö. 2009. Daily pan evaporation modelling using multi‐layer perceptrons and radial basis neural networks. Hydrological Processes 23: 213–223’     

Jimmy Moreno  Shalamu Abudu  A. Salim Bawazir  J. Phillip King 《水文研究》2010,24(21):3115-3118

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Measurement of debris mass changes and assessment of the dam-break flood potential of earthquake-triggered Hattian landslide dam   总被引：1，自引：1，他引：0  

Ahsan Sattar  Kazuo Konagai  Takashi Kiyota  Takaaki Ikeda  Jorgen Johansson 《Landslides》2011,8(2):171-182

The Hattian landslide, which was triggered by the 2005 Kashmir earthquake, formed one of largest landslide dams in the world and it has posed a serious threat of flooding to people living in the lower reach of the Jhelum River. In order to understand deformation occurring in the body of the dam, physical measurements using a Differential Global Positioning System (DGPS) were conducted. Gradual deformation and slowly developing backward erosion initially were observed, leading eventually to a sudden creation of a deep hollow on the downstream slope of the landslide dam. The dimensions of this eroded gully were determined by laser scanning, and the results showed a significant loss of soil volume and a large change in the body of the dam. A breach formation model was used to predict the outflow hydrograph generated by constant downcutting of dam during a breaching event. A run-off analysis of the outflow hydrograph was conducted to evaluate inundation levels of flood waves in case the dam is breached. Hazardous downstream locations were identified near the junction of the Karli and Jhelum Rivers, suggesting a need for early warning system in order to avoid loss of lives.  相似文献   

Analysis of spatial temperature variations in regions of massive star formation     

S. Yu. Malafeev  I. I. Zinchenko  L. E. Pirogov  L. E. B. Johansson 《Astronomy Letters》2005,31(4):239-244

Using the 20-m Onsala Observatory telescope (Sweden), we performed observations of the CH₃C₂H(6-5) line toward several regions of massive star formation to estimate the kinetic temperature of the gas and study its variations over the sources. Intense lines were detected in five objects. For these, we estimated the kinetic temperature of the gas near the CS and N₂H⁺ molecular emission peaks by the method of population diagrams. A significant temperature difference between these peaks is noticeable only in W3 and, to a lesser degree, in DR 21. In the remaining cases, it is insignificant. This indicates that the chemical differentiation of the molecules in these regions cannot be associated with temperature variations. The kinetic temperature determined from methyl acetylene observations is usually slightly higher than the temperature estimated from ammonia observations. This is probably because the methyl acetylene emission originates in denser, i.e., deeper and hotter layers of the cloud.  相似文献   

Grenvillian and Caledonian evolution of eastern Svalbard – a tale of two orogenies     

Åke Johansson  David G. Gee  Alexander N. Larionov  Yoshihide Ohta  Alexander M. Tebenkov 《地学学报》2005,17(4):317-325

Svalbard is located in the north-west corner of the Barents Sea shelf and the Eurasian Plate, in a key area for interpreting Caledonian and older orogens in the Arctic region. Recent U–Pb dating in the Nordaustlandet Terrane of eastern Svalbard shows this terrane to consist of a Grenville-age basement, overlain by Neoproterozoic to early Palaeozoic platformal sediments, and intruded by Caledonian anatectic granites. Deformation, metamorphism and crustal anatectic magmatism occurred both during the Grenvillian (960–940 Ma) and Caledonian (450–410 Ma) orogenies. This evolution shows great similarities with that of eastern Greenland. In the classical model, eastern Svalbard is placed outboard of central east Greenland in pre-Caledonian time. Alternatively, it may have been located north-east of Greenland and transferred west and rotated anticlockwise during Caledonian continent–continent collision. In the Neoproterozoic, easternmost Svalbard may have been part of a wider area of Grenville-age crust, now fragmented and dispersed around the Arctic.  相似文献   

Analysis of soil consolidation by vertical drains with double porosity model     

Xu‐Sheng Wang  Jiu Jimmy Jiao 《国际地质力学数值与分析法杂志》2004,28(14):1385-1400

The soil around a drain well is traditionally divided into smeared zone and undisturbed zone with constant hydraulic conductivity. In reality, hydraulic conductivity of the soil changes continuously and it may not be always appropriate to approximate its distribution with two zones. In this study, the horizontal hydraulic conductivity of the soil is described by an arbitrary function of radial distance. The horizontal flow under equal strain condition is analysed for a soil–drain system with a circular or regular polygonal boundary. It is found that the horizontal flow can be generally characterized with a linear equation in which the flow rate of water through soil–drain interface is proportional to the difference between the average excess pore pressure in the soil and the excess pore pressure in the drain well. The water exchange between the drain and the soil is analogous to that between fractures and matrix in a double porosity system, a popular conceptual model of fracture rocks. On the basis of this characterization, a simplified approach to analyse soil–drain systems is developed with one‐dimensional double porosity model (DPM). Analytical solutions for both fully and partially penetrating drains are derived. The solution for partially penetrating drains is compared with both numerical and approximate analytical results in literature. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

Observations of martian gullies and constraints on potential formation mechanisms: II. The northern hemisphere     

Jennifer L. Heldmann  Ella Carlsson  Henrik Johansson  Owen B. Toon 《Icarus》2007,188(2):324-344

The formation process(es) responsible for creating the observed geologically recent gully features on Mars has remained the subject of intense debate since their discovery. We present new data and analysis of northern hemisphere gullies from Mars Global Surveyor data which is used to test the various proposed mechanisms of gully formation. We located 137 Mars Orbiter Camera (MOC) images in the northern hemisphere that contain clear evidence of gully landforms and analyzed these images in combination with Mars Orbiter Laser Altimeter (MOLA) and Thermal Emission Spectrometer (TES) data to provide quantitative measurements of numerous gully characteristics. Parameters we measured include apparent source depth and distribution, vertical and horizontal dimensions, slopes, orientations, and present-day characteristics that affect local ground temperatures. Northern hemisphere gullies are clustered in Arcadia Planitia, Tempe Terra, Acidalia Planitia, and Utopia Planitia. These gullies form in craters (84%), knobby terrain (4%), valleys (3%), other/unknown terrains (9%) and are found on all slope orientations although the majority of gullies are equator-facing. Most gullies (63%) are associated with competent rock strata, 26% are not associated with strata, and 11% are ambiguous. Assuming thermal conductivities derived from TES measurements as well as modeled surface temperatures, we find that 95% of the gully alcove bases with adequate data coverage lie at depths where subsurface temperatures are greater than 273 K and 5% of the alcove bases lie within the solid water regime. The average alcove length is 470 m and the average channel length is 690 m. Based on a comparison of measured gully features with predictions from the various models of gully formation, we find that models involving carbon dioxide, melting ground ice in the upper few meters of the soil, dry landslide, and surface snowmelt are the least likely to describe the formation of the martian gullies. Although some discrepancies still exist between prediction and observation, the shallow and deep aquifer models remain as the most plausible theories. Interior processes involving subsurface fluid sources are generally favored over exogenic processes such as wind and snowfall for explaining the origin of the martian gullies. These findings gleaned from the northern hemisphere data are in general agreement with analyses of gullies in the southern hemisphere [Heldmann, J.L., Mellon, M.T., 2004. Icarus 168, 285-304].  相似文献   

    

S. Johansson  V. S. Letokhov 《Astronomy Letters》2004,30(6):433

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Mesoproterozoic to Palaeozoic Evolution of Eastern Svalbard and Barentsia     

ke Johansson  Alexander Larionov  Yoshihide Ohta  Alexander Tebenkov 《Gondwana Research》2001,4(4):645-646

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Future vegetation changes in thawing subarctic mires and implications for greenhouse gas exchange—a regional assessment   总被引：1，自引：1，他引：0  

Julia Bosi?  Margareta Johansson  Terry V. Callaghan  Bernt Johansen  Torben R. Christensen 《Climatic change》2012,115(2):379-398

One of the major concerns regarding climate change in high latitudes is the potential feedback from greenhouse gases (GHG) being released from thawing peat soils. In this paper we show how vegetational patterns and associated GHG fluxes in subarctic palsa (peat mounds with a permanently frozen core) mires can be linked to climate, based on field observations from fifteen palsa sites distributed in northern Fennoscandia. Fine resolution (100?m) land cover data are combined with projections of future climate for the 21st century in order to model the potential future distribution of palsa vegetation in northern Fennoscandia. Site scale climate-vegetational relationships for two vegetation types are described by a climate suitability index computed from the field observations. Our results indicate drastic changes in the palsa vegetational patterns over the coming decades with a 97?% reduction in dry hummock areas by 2041?C2060 compared to the 1961?C1990 areal coverage. The impact of these changes on the carbon balance is a decrease in the efflux of CO₂ from 130 kilotonnes C y^?1 to a net uptake of 11 kilotonnes C y^?1 and a threefold increase in the efflux of CH₄ from 6 to 18 kilotonnes C y^?1 over the same period and over the 5,520?km² area of palsa mires. The combined effect is equivalent to a slight decrease in CO₂-C emissions, from 182 to 152 kilotonnes C y^?1. Main uncertainties involve the ability of the vegetation community to adapt to new conditions, and long-term changes in hydrology due to absence of ice and frost heaving.  相似文献