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71.
Marc A. Vallée Larry Newitt Ian R. Mann Mouhamed Moussaoui Régis Dumont Pierre Keating 《Pure and Applied Geophysics》2007,164(1):161-176
Geomagnetic activity affects aeromagnetic surveys. Geomagnetic variations are quite complex and can be quantified in different
ways. A measure of geomagnetic activity that is useful for planning aeromagnetic surveys is the Pc3 pulsation index developed
by the Australian Space Weather Agency. Purposeful to developing guidelines for planning aeromagnetic surveys in Canada, we
study the variations in Pc3 index amplitude over Canada in 2000. This study shows distinct patterns associated with the sub-auroral
zone, the auroral zone, and the polar cap. Average Pc3 index activity is higher during the months of February, July, September,
and November in the auroral and sub-auroral zones. The station in the polar cap exhibits maximum activity near midday during
the summer months. Detailed analysis of a magnetic storm shows that Pc3 index amplitude during the beginning of the solar
storm is least important at the polar cap. The mean Pc3 index also relates to solar wind parameters such as the solar wind
velocity and the vertical polarity of the interplanetary magnetic field. Analysis of the morning maximum of the Pc3 index
observed in the auroral zone can be used to develop guidelines for planning aeromagnetic surveys in Canada and other areas
of the world affected by auroral zones. 相似文献
72.
Wusi Yue Marc B. Parlange Charles Meneveau Weihong Zhu René van Hout Joseph Katz 《Boundary-Layer Meteorology》2007,124(2):183-203
Turbulent flow in a corn canopy is simulated using large-eddy simulation (LES) with a Lagrangian dynamic Smagorinsky model.
A new numerical representation of plant canopies is presented that resolves approximately the local structure of plants and
takes into account their spatial arrangement. As a validation, computational results are compared with experimental data from
recent field particle image velocimetry (PIV) measurements and two previous experimental campaigns. Numerical simulation using
the traditional modelling method to represent the canopy (field-scale approach) is also conducted as a comparison to the plant-scale
approach. The combination of temporal PIV data, LES and spatial PIV data allows us to couple a wide range of relevant turbulence
scales. There is good agreement between experimental data and numerical predictions using the plant-scale approach in terms
of various turbulence statistics. Within the canopy, the plant-scale approach also allows the capture of more details than
the field-scale approach, including instantaneous gusts that penetrate deep inside the canopy. 相似文献
73.
Marcelo Chamecki René van Hout Charles Meneveau Marc B. Parlange 《Boundary-Layer Meteorology》2007,125(1):25-38
An expression for the vertical equilibrium concentration profile of heavy particles, including the effects of canopy on the
eddy diffusivity as well as corrections for atmospheric stability, is proposed. This expression is validated against measurements
of vertical concentration profiles of corn pollen above a corn field. The fitted theoretical profiles show that particle settling
is correctly accounted for. The sensitivity to variations in the turbulent Schmidt number, settling velocity and stability
corrections are explicitly characterized. The importance of independent measurements of the surface flux of pollen in future
experiments is noted. 相似文献
74.
Marc G. Genton 《Mathematical Geology》1998,30(7):853-871
In the context of robust statistics, the breakdown point of an estimator is an important feature of reliability. It measures the highest fraction of contamination in the data that an estimator can support before being destroyed. In geostatistics, variogram estimators are based on measurements taken at various spatial locations. The classical notion of breakdown point needs to be extended to a spatial one, depending on the construction of most unfavorable configurations of perturbation. Explicit upper and lower bounds are available for the spatial breakdown point in the regular unidimensional case. The difficulties arising in the multidimensional case are presented on an easy example in IR2
, as well as some simulations on irregular grids. In order to study the global effects of perturbations on variogram estimators, further simulations are carried out on data located on a regular or irregular bidimensional grid. Results show that if variogram estimation is performed with a 50% classical breakdown point scale estimator, the number of initial data likely to be contaminated before destruction of the estimator is roughly 30% on average. Theoretical results confirm the previous statement on data in IRd
, d 1. 相似文献
75.
Michael O. Garcia Ken H. Rubin Marc D. Norman J. Michael Rhodes David W. Graham David W. Muenow Khalil Spencer 《Bulletin of Volcanology》1998,59(8):577-592
Samples of basalt were collected during the Rapid Response cruise to Loihi seamount from a breccia that was probably created
by the July to August 1996 Loihi earthquake swarm, the largest swarm ever recorded from a Hawaiian volcano. 210Po–210Pb dating of two fresh lava blocks from this breccia indicates that they were erupted during the first half of 1996, making
this the first documented historical eruption of Loihi. Sonobuoys deployed during the August 1996 cruise recorded popping
noises north of the breccia site, indicating that the eruption may have been continuing during the swarm. All of the breccia
lava fragments are tholeiitic, like the vast majority of Loihi's most recent lavas. Reverse zoning at the rim of clinopyroxene
phenocrysts, and the presence of two chemically distinct olivine phenocryst populations, indicate that the magma for the lavas
was mixed just prior to eruption. The trace element geochemistry of these lavas indicates there has been a reversal in Loihi's
temporal geochemical trend. Although the new Loihi lavas are similar isotopically and geochemically to recent Kilauea lavas
and the mantle conduits for these two volcanoes appear to converge at depth, distinct trace element ratios for their recent
lavas preclude common parental magmas for these two active volcanoes. The mineralogy of Loihi's recent tholeiitic lavas signify
that they crystallized at moderate depths (∼8–9 km) within the volcano, which is approximately 1 km below the hypocenters
for earthquakes from the 1996 swarm. Taken together, the petrological and seismic evidence indicates that Loihi's current
magma chamber is considerably deeper than the shallow magma chamber (∼3–4 km) in the adjoining active shield volcanoes.
Received: 21 August 1997 / Accepted: 15 February 1998 相似文献
76.
Marc Elmouttie Bärbel Koribalski Scott Gordon Keith Taylor Sally Houghton Tracy Lavezzi Raymond Haynes & Keith Jones 《Monthly notices of the Royal Astronomical Society》1998,297(1):49-68
The TAURUS-2 Fabry–Perot interferometer, mounted on the 3.9-m Anglo-Australian Telescope, has been used to observe the Circinus galaxy. We have mapped the intensity and velocity distribution of the ionized hydrogen in the galaxy using the Balmer series Hα spectral line.
The semiresolved core (observed with a seeing disc of 30 pc) appears amorphous in shape, which is commonly observed in Seyfert 2 galaxies. Its peak coincides with the core position measured in the radio continuum, suggesting that ionized gas surrounds a non-thermal source.
A circumnuclear ring or spiral of radius 220 pc and a rotational velocity of 350 km s−1 (assuming circular motions) surrounds the core. The inclination angle of this feature, i =40°±10°, is less than that of the previously observed radio continuum disc. The velocity channel maps obtained for the Hα ring show that the kinematics resemble those of a rotating ring and the intensity displays a complex structure indicative of several, unresolved, H II regions. We believe the ring to represent a circumnuclear starburst.
Our Hα data also show the presence of the previously detected [O III ] ionization cone to the north-west of the core, measuring more than 400 pc in length. We suggest that the ionization cone lies in a different plane from that of the starburst ring and is directed away from us. Several kinematic components of the core are derived and we calculate an outflow velocity in excess of 150–200 km s−1 for gas above the core of Circinus. We also present evidence for inflowing ionized gas at the centre of Circinus.
The correlation of the Hα and radio continuum features is discussed, as well as the possible presence of a starburst-driven superwind in the Circinus galaxy. 相似文献
The semiresolved core (observed with a seeing disc of 30 pc) appears amorphous in shape, which is commonly observed in Seyfert 2 galaxies. Its peak coincides with the core position measured in the radio continuum, suggesting that ionized gas surrounds a non-thermal source.
A circumnuclear ring or spiral of radius 220 pc and a rotational velocity of 350 km s
Our Hα data also show the presence of the previously detected [O III ] ionization cone to the north-west of the core, measuring more than 400 pc in length. We suggest that the ionization cone lies in a different plane from that of the starburst ring and is directed away from us. Several kinematic components of the core are derived and we calculate an outflow velocity in excess of 150–200 km s
The correlation of the Hα and radio continuum features is discussed, as well as the possible presence of a starburst-driven superwind in the Circinus galaxy. 相似文献
77.
R.O. Fournier M.L. Sorey R.H. Mariner A.H. Truesdell 《Journal of Volcanology and Geothermal Research》1979,5(1-2)
Temperatures of aquifers feeding thermal springs and wells in Long Valley, California, estimated using silica and Na-K-Ca geothermometers and warm spring mixing models, range from 160/dg to about 220°C. This information was used to construct a diagram showing enthalpy-chloride relations for the various thermal waters in the Long Valley region. The enthalpy-chloride information suggests that a 282 ± 10°C aquifer with water containing about 375 mg chloride per kilogram of water is present somewhere deep in the system. That deep water would be related to 220°C Casa Diablo water by mixing with cold water, and to Hot Creek water by first boiling with steam loss and then mixing with cold water. Oxygen and deuterium isotopic data are consistent with that interpretation. An aquifer at 282°C with 375 mg/kg chloride implies a convective heat flow in Long Valley of 6.6 × 107 cal/s. 相似文献
78.
Dr. Richard F. Wright Prof. Albert Matter Marc Schweingruber Ulrich Siegenthaler 《Aquatic Sciences - Research Across Boundaries》1980,42(2):101-126
A 2-year study of sedimentation in Lake Biel reveals that three major factors can account for the spatial and temporal patterns
of tripton sedimentation. Allochthonous inputs of particulate matter mostly derived from the Aare river during spring snowmelt
and other high-water periods, provide about 50% of the carbonate and 50% of the siliceous matter collected in sediment traps.
Phytoplankton activity in this eutrophic, hard-water lake accounts for the rest of the carbonate and siliceous matter, the
latter being mostly diatom frustules. Sedimentation rates are thus highest during periods of maximum river flooding, maximum
phytoplankton activity and following the breakdown of the thermocline, at which time trapped particles settle out. Resuspension
of sediment is important in at least one basin. Resolution of carbonate appears to be minor. 相似文献
79.
Marc Schoeller 《Journal of Hydrology》1976,28(1):45-52
The relationship line between two chemical constituents dissolved in groundwater does not always begin at the graph origin, but at a fixed coordinates point. This allows the separation between rain water, infiltrating water and groundwater. Besides, this relationship line is not always linear. Equations are given for the curvilinear case. 相似文献
80.
The distribution of individual values of the apparent resistivities given by two M-T soundings made over two different kinds of subsurface geology is described and computed. This distribution is Gaussian only if the logarithm of the resistivity values are used. Consequently, a statistical stability is obtained when the mean and standard deviation are calculated in log-space. Log-space is a mathematical space that may have one or more logarithmical dimensions; in this case two. 相似文献