Flood events and their effects in a Himalayan mountain river: Geomorphological examples from the Buri Gandaki Valley,Nepal     

Gerrit Tombrink 《山地科学学报》2017,14(7):1303-1316

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Ocean-atmosphere dynamics changes associated with prominent ocean surface turbulent heat fluxes trends during 1958–2013     

Hu Yang  Jiping Liu  Gerrit Lohmann  Xiaoxu Shi  Yongyun Hu  Xueen Chen 《Ocean Dynamics》2016,66(3):353-365

Three prominent features of ocean surface turbulent heat fluxes (THF) trends during 1958–2013 are identified based on the Objectively Analyzed air-sea Fluxes (OAFlux) data set. The associated ocean-atmosphere dynamics changes are further investigated based on the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis. First, the THF are enhanced over the mid-latitude expansions of the subtropical western boundary currents (WBCs). An intensified oceanic heat transport, forced by stronger near-surface zonal wind, is likely to be the cause of such THF tendency. Second, the THF are reduced over the tropical eastern Pacific Ocean, which is primarily caused by the decreasing near-surface wind speed and sea surface temperature (SST), associated with a local coupled ocean-atmosphere cooling mode. Finally, the THF are reduced over the northern tropical Atlantic Ocean, which is attributed to the decreasing air-sea humidity and temperature differences as a result of the convergence of near-surface air and the divergence of ocean currents (upwelling).  相似文献   

Solar Eclipses and the Surface Properties of Water     

Fuchs  Elmar C.  Oudakker  Gerrit  Justinek  Martin  Dyer  Nigel  Woisetschläger  Jakob  Godines  Kevin  Mäder  Matthias  Freund  Friedemann T. 《Earth, Moon, and Planets》2019,123(1-2):15-43

Earth, Moon, and Planets - During four solar eclipse events (two annular, one total and one partial) a correlation was observed between a change in water surface tension and the magnitude of the...  相似文献   

Modeling urban expansion by using variable weights logistic cellular automata: a case study of Nanjing,China     

Bangrong Shu  Martha M. Bakker  Honghui Zhang  Yongle Li  Wei Qin  Gerrit J. Carsjens 《International journal of geographical information science》2017,31(7):1314-1333

Simulation models based on cellular automata (CA) are widely used for understanding and simulating complex urban expansion process. Among these models, logistic CA (LCA) is commonly adopted. However, the performance of LCA models is often limited because the fixed coefficients obtained from binary logistic regression do not reflect the spatiotemporal heterogeneity of transition rules. Therefore, we propose a variable weights LCA (VW-LCA) model with dynamic transition rules. The regression coefficients in this VW-LCA model are based on VW by incorporating a genetic algorithm in a conventional LCA. The VW-LCA model and the conventional LCA model were both used to simulate urban expansion in Nanjing, China. The models were calibrated with data for the period 2000–2007 and validated for the period 2007–2013. The results showed that the VW-LCA model performed better than the LCA model in terms of both visual inspection and key indicators. For example, kappa, accuracy of urban land and figure of merit for the simulation results of 2013 increased by 3.26%, 2.96% and 4.44%, respectively. The VW-LCA model performs relatively better compared with other improved LCA models that are suggested in literature.  相似文献   

MERIS and the red-edge position   总被引：1，自引：0，他引：1  

Jan G. P. W. Clevers  Steven M de Jong  Gerrit F Epema  Freek van der Meer  Wim H Bakker  Andrew K Skidmore  Elisabeth A Addink 《International Journal of Applied Earth Observation and Geoinformation》2001,3(4):313

The Medium Resolution Imaging Spectrometer (MERIS) is a payload component of Envisat-1. MERIS will be operated over land with a standard 15 band setting acquiring images with a 300 m spatial resolution. The red-edge position (REP) is a promising variable for deriving foliar chlorophyll concentration, which plays an important role in ecosystem processes. The objectives of this paper are: (1) to study which factors effect the REP of vegetation, (2) to study whether this REP can be derived from the MERIS standard band setting and (3) to show what REP represents at the scale of MERIS data. Two different data sets were explored for simulating the REP using MERIS bands: (1) simulated data using reflectance models and (2) airborne reflectance spectra of an agricultural area obtained by the airborne visible-infrared imaging spectrometer (AVIRIS). A “linear method”, assuming a straight slope of the reflectance spectrum around the midpoint of the slope, was a robust method for determining the REP and the MERIS bands at 665, 708.75, 753.75 and 778.75 nm could be used for applying the “linear method” for REP estimation. Results of the translation to the scale of MERIS data were very promising for applying MERIS at, for instance, the ecosystem level.  相似文献   

A 1-D atmospheric energy balance model developed for ocean modelling     

D. Chen  R. Gerdes  G. Lohmann 《Theoretical and Applied Climatology》1995,51(1-2):25-38

Summary We present a simple, deterministic energy balance model. The model is designed to represent the atmospheric component of the coupled atmosphere-ocean system. It is a one dimensional, global model with time and space resolutions of one year and 10° of latitude respectively. The model predicts the surface air temperature and estimates the surface freshwater flux diagnostically. The coupling between the atmospheric model and an ocean model is accomplished by heat and freshwater fluxes at their interface. The heat flux is calculated according to the difference in the surface air temperature and ocean surface temperature, while the freshwater flux is estimated from the latent heat transport in the atmosphere by a diagnostic equation. Two parameterizations for the latent heat transport are proposed, which distinguishes the two versions of the model.Before proceeding with interactive runs, we study the behaviour of the model in a decoupled mode. Some experiments with initial conditions altered and external forcings changed ar carried out to investigate the sensitivity and stability of the model. In particular, the influence of the ice-albedo feedback on model solutions is examined. The results of these experiments may be helpful both in understanding the characteristics of the model and in interpreting results when the model is coupled to an OGCM.With 9 Figures  相似文献   

Die Mittleren Geschwindigkeiten Der Sterne In 58 Kugelförmigen Sternhaufen     

Werner Lohmann 《Astrophysics and Space Science》1975,32(1):153-163

The mean velocities of the stars in 58 globular clusters are derived from the photometric measurements of Kron and Mayall (1960). The mass-visual brightness ratio is used. The velocities are falling in the interval 2.9v11.6 km s^–1, their mean value is 6.75 km s^–1.

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Mitteilungen Serie A.  相似文献   

Late Quaternary carbonate sedimentation at the Sierra Leone Rise (eastern equatorial Atlantic Ocean)     

W.B. Curry  G.P. Lohmann 《Marine Geology》1986,70(3-4):223-250

In the eastern equatorial Atlantic Ocean, changes in the concentration of carbonate in Late Quaternary sediments resulted from reduced production of carbonate in surface waters and increased dilution with non-carbonate sediments during glacial maxima. During glacial stages, production of carbonate in surface water (measured as its accumulation rate in shallow, undissolved cores) decreased by one half. The glacial accumulation rate of non-carbonate components increased 1.5 to 4 times over Holocene values; the greatest increases occurred in the deepest cores.

Carbonate dissolution during stages 2, 3 and 4 increased the proportion of foraminiferal fragments and decreased the accumulation rate of susceptible species in the deep sites. In shallow sites, slightly increased dissolution can be detected during stage 3 while greatly increased dissolution occurred during stage 4. Bathymetric profiles of foraminiferal fragmentation and accumulation document a shoaling of the foraminiferal lysocline by 1000 m during glacial isotopic stages. We present a mass balance model of sediment accumulation for carbonate and insoluble components and from this model we estimate the rate of downslope transport and dissolution of carbonate at the Sierra Leone Rise. Our results show that during stage 4 the rate of carbonate loss to dissolution was greater than the rate observed today or during other interglacial stages. The calculated rates of dissolution for stages 2 and 3 are not significantly different from those calculated for stage 1.  相似文献   

A twentieth-century reanalysis forced ocean model to reconstruct the North Atlantic climate variation during the 1920s     

W. A. Müller  D. Matei  M. Bersch  J. H. Jungclaus  H. Haak  K. Lohmann  G. P. Compo  P. D. Sardeshmukh  J. Marotzke 《Climate Dynamics》2015,44(7-8):1935-1955

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Factors influencing the removal of fine non-cohesive sediment by vortex settling basin at small river abstraction works     

Kuria Kiringu  Gerrit Basson 《国际泥沙研究》2021,36(4):501-511

Diverted sediment causes a wide range of problems at small diversion works.The difference in water levels between low flows and floods,low investment capital and presence of cohesive sediment and fine non-cohesive sediment coupled with a requirement for a high level of supply assurance makes the design of such hydraulic structures complex.Vortex settling basins(VSBs)offer a promising alternative to conventional settling structures or hydro-cyclones.In the current study,parameters affecting the trapping of particles>75 mm were numerically investigated using ANSYS Fluent and were validated by physical modeling.It was established that the inlet velocity needs to be maintained at 0.26 m/s,the underflow to inflow ratio should be between 0.05 and 0.10,the cylinder height to cylinder diameter ratio should be greater than 0.5,and the positioning of the inlet pipe to cylinder height ratio should be greater than 0.7,with a cone of slope ratio of 2:1(V:H)and the cylinder diameter to inlet diameter ratio should be 8.2.These parameters form the basic design guidelines for VSB use at small diversion works(<100 L/s duty capacity).  相似文献