Spatial characteristics of surface and atmospheric properties during HartX     

S. Ernst  M. Wüthrich 《Theoretical and Applied Climatology》1996,53(1-3):59-67

Summary Remote sensing and ground measurements were used to evaluate the homogeneity of the Scots pine plantation of Hartheim and the interactions between the forest and its surroundings during HartX.Remote sensing data contribute to characterization of the Scots pine plantation of Hartheim in terms of surface properties and thermal and biological characteristics of the forest. The surroundings of the main experiment site in the forest has homogenous normalized difference vegetation index, microwave specle and brightness temperatures to all directions for at least 500 m. Local sensible heat flux estimates using satellite measured brightness temperatures andin situ measured wind and air temperatures showed good agreement.On some days during HartX the test area was influenced by advection of dry air from the northern Upper Rhine Valley. Agricultural surroundings close to the forest are influenced by breezes flowing out of the forest during radiative nights with weak large-scale motion.With 7 Figures  相似文献   

Estimating the crust permeability from fluid-injection-induced seismic emission at the KTB site   总被引：8，自引：0，他引：8  

Sergei A. Shapiro    Ernst Huenges  Günter Borm 《Geophysical Journal International》1997,131(2):F15-F18

During the hydraulic-fracturing experiment in the German Continental Deep Drilling Borehole (KTB) in December 1994, microseismic activity was induced. Here we develop a technique for estimating permeability using the spatio-temporal distribution of the fluid-injection-induced seismic emission. The values we have obtained for the KTB experiment (0.25times10^-16 to 1.0times10^-16 1.0times10^-16 m²) are in a very good agreement with the previous hydraulic-type permeability estimates from KTB deep-observatory studies. In addition, our estimates of the hydraulic diffusivity support the previously calculated value for the upper crust, which is of the order of 1 m² s^-1. However, this estimate now relates to the depth range 7.5-9 km.  相似文献   

Glacial morphology and post-glacial contourites in northern Prince Gustav Channel (NW Weddell Sea,Antarctica)     

Camerlenghi  Angelo  Domack  Eugene  Rebesco  Michele  Gilbert  Robert  Ishman  Scott  Leventer  Amy  Brachfeld  Stefanie  Drake  Allison 《Marine Geophysical Researches》2001,22(5-6):417-443

We present the results of a marine geophysical investigation of the northern Prince Gustav Channel. By comparative analysis of multibeam bathymetric data, single channel seismic reflection profiles, underway chirp sonar data, ADCP current data and sediment coring, we define the main morphological elements of the area. In particular we define the glacial morphogenesis in relation to the excavation of inner shelf basins and troughs along structural discontinuities and lithologic boundaries. We identify streamlined surfaces that testify to the grounding of ice and past ice flow directions. These glacial forms are found only on glacial tills preserved in the deepest part of the basins, while net erosion to bedrock has occurred elsewhere. Since the Last Glacial Maximum (LGM), the relict glacial morphology has been draped by hemipelagic and diatomaceous mud, and bottom currents have played a major role in focusing sedimentation within small depocentres, that we define as contouritic drifts. Based on shallow sediment architecture and supported by direct measurements, we propose that the direction of bottom water flow is from the outer shelf into the Prince Gustav channel as a result of a combination of tidal currents and ice shelf-related thermohaline circulation.  相似文献   

The glacimarine sedimentary environment of Expedition Fiord, Canadian High Arctic     

Robert Gilbert  Alec E. Aitken  Donald S. Lemmen 《Marine Geology》1993,110(3-4):257-273

Expedition Fiord is a small, shallow inlet on the west coast of Axel Heiberg Island near 80°N latitude. It receives runoff and sediment at its head from a 1079 km² drainage basin, 72% of which is glacier-covered. Subbottom acoustic survey and cores from the fiord floor were used to assess the sedimentary environment. Most of the sediment is deposited within 3 km of the inflow from suspension in the overflowing cap and by gravity flows on the foreset beds of the delta. Occasionally, weak turbidity currents reach the mid fiord where they deposit fine-grained sediments. Icebergs from a large calving glacier in an adjacent fiord raft additional sediment, especially to the outer part of the fiord. They also scour the seafloor, although the persistent ice cover and slow currents in the fiord restrict this process. Except near the inflow, the total sediment accumulation since deglaciation is less than 20 m, and the rates of 0.5–1 mm/yr have not varied significantly to the present. A thicker deposit in the outer fiord is probably related to an early Holocene glacier margin near that location.  相似文献   

Visual determination of sex in live Pacific halibut     

St-Pierre  Gilbert 《ICES Journal of Marine Science》1992,49(3):373-376

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The aerodynamic behaviour of volcanic aggregates   总被引：1，自引：1，他引：0  

S J Lane  J S Gilbert  M Hilton 《Bulletin of Volcanology》1993,55(7):481-488

A large proportion of solid material transported within the atmosphere during volcanic eruptions consists of particles less than 500 m in diameter. The majority of these particles become incorporated into a wide range of aggregate types, the aerodynamic behaviour of which has not been determined by either direct observation or in the laboratory. In the absence of such data, theoretical models of fallout from volcanic plumes make necessarily crude assumptions about aggregate densities and fall velocities. Larger volcanic ejecta often consists of pumice of lower than bulk density. Experimental data are presented for the fall velocities of porous aggregates and single particles, determined in systems analogous to that of ejecta falling from a volcanic plume. It is demonstrated that the fall of aggregates may be modelled in identical fashion to single particles by using a reduced aggregate density dependent on the porosity, and a size corresponding to an enclosing sphere. Particles incorporated into aggregates attain a substantially higher fall velocity than single particles. This is due to the larger physical dimensions of the aggregate, which overcomes the effect of lower aggregate density. Additionally, the internal porosity of the aggregate allows some flow of fluid through the aggregate and this results in a small increase in fall velocity. The increase in fall velocity of particles incorporated into aggregates, rather than falling individually, results in the enhanced removal of fine material from volcanic plumes.  相似文献   

Sedimentation of tephra by volcanic plumes: I. Theory and its comparison with a study of the Fogo A plinian deposit,Sao Miguel (Azores)   总被引：1，自引：1，他引：0  

M I Bursik  R S J Sparks  J S Gilbert  S N Carey 《Bulletin of Volcanology》1992,54(4):329-344

Sedimentation of ejecta from volcanic plumes has been studied as a function of distance from the source in the Fogo A plinian deposit, Sao Miguel, Azores. The Fogo A trachytic pumice deposit is reversely graded and can be divided into two parts on the basis of pumice colour, abundance of syenite accessory lithic clasts and distribution. The lower syenite-poor part was dispersed to the south and was clearly influenced by wind. The upper syenite-rich part is coarsegrained and has a nearly symmetrical distribution around the vent. Elongation of isopachs to the east indicate a weak wind influence. The grain-size variations of lithic and crystal components in the upper coarse part were studied. Total accumulation and accumulation per unit area (expressed in kg/m²) show good fits to a gaussian function at distances greater than 7 km for grain diameters less than 2 cm. These results agree with a theoretical model for a radially spreading turbulent current moving over a quiescent fluid. The gaussian coefficient is shown to be a function of grain size and the flow rate of material into the umbrella region of the eruption column. The coefficient is therefore also a function of column height. The column height deduced from these data is 21 km, which is in broad agrrement with the column height of 27 km deduced from maximum clast dispersal using the method of Carey and Sparks (1986). The accumulation of clasts larger than 2 cm agrees with a theory for the fallout of clasts from the margins of the ascending eruption column, which treats the plume as a succession of large eddies that decrease their mass of particles as an exponential function of time. Calculations are also presented for the influence of the radial inflow of surrounding air into the column on the deposition of clasts. These calculations constrain the wind speed during the later part of the Fogo A eruption to be at most a few metres per second. The study has allowed four different dynamic categories of clast behaviour to be recognised in eruption columns.  相似文献   

Global momentum loss in a non-expanding Universe     

Ernst Fischer 《Astrophysics and Space Science》1992,190(1):149-153

Applying the basic concepts of general relativity to the global motion of a particle in a mass-filled universe leads to a loss of momentum relative to the rest frame of the Universe. This loss is caused by the different running times of the gravitational interaction quanta exchanged with masses in front and behind the moving particle, if the signal velocity is limited to the speed of light. Due to this gravitational viscosity of space, the energy of photons will be reduced with the time, and thus with the distance of the emitting source. This red shift is superimposed on the Doppler shift in an expanding universe. A discussion of the limiting case of vanishing expansion leads to predictions about mass and radius of the Universe. The value of the mass density in such a steady-state universe must be about three times the closing density discussed in Big-Bang theories. The existence of the gravitational viscosity casts severe doubts on all estimations of the age of the Universe derived from the red-shift data.  相似文献   

Volcanic particle aggregation in explosive eruption columns. Part I: Parameterization of the microphysics of hydrometeors and ash   总被引：1，自引：3，他引：1  

C. Textor  H.F. Graf  M. Herzog  J.M. Oberhuber  William I. Rose  G.G.J. Ernst   《Journal of Volcanology and Geothermal Research》2006,150(4):359-377

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Mars: simply red?     

Ernst Hauber  Gerhard Neukum 《Astronomy& Geophysics》2006,47(2):2.16-2.24

Ernst Hauber and Gerhard Neukum present a new perspective on the martian surface on the basis of two years of observations by the High resolution Stereo Camera, part of ESA's Mars Express mission.
All HRSC images shown are copyright ESA/DLR/FU Berlin (G Neukum).  相似文献