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991.
This paper investigates the sensitivity of the numerical simulations of a near equatorial Typhoon Vamei (2001) to various
planetary boundary layer (PBL) parameterization schemes in the Pennsylvania State University (PSU)/National Centre for Atmospheric
Research (NCAR) non-hydrostatic mesoscale model (MM5). The numerical simulations are conducted on two domains at 45 and 15 km
grids nested in a one-way fashion. Four different PBL parameterization schemes including the Blackadar (BLK) scheme, the Burk–Thompson
(BURKT) scheme, the NCEP Eta model scheme and the NCEP medium range forecast (MRF) model scheme are investigated. Results
indicate that the intensity and propagation track of the simulated near equatorial typhoon system is not very sensitive to
the different PBL treatments. The simulated minimum central pressures and the maximum surface wind speeds differ by only 5–6 hPa
and 6–8 ms−1, respectively. Larger variations between the simulations occur during the weakening phase of the typhoon system. While all
schemes simulated the typhoon with reasonable accuracy, the ETA scheme produces the strongest storm intensity with the largest
heat exchanges over the marine environment and the highest warm moisture air content in the PBL around the core of the storm. 相似文献
992.
Guillaume Martinat Ying Xu Chester E. Grosch Andrés E. Tejada-Martínez 《Ocean Dynamics》2011,61(9):1369-1390
Turbulent shear flows on shallow continental shelves (here shallow means that the interaction with the solid, no-slip bottom
is important) are of great importance because tide- and wind-driven flows on the shelf are drivers of the transfer of momentum,
heat, and mass (gas) across the air–sea interface. These turbulent flows play an important role because vertical mixing and
current are vectors for the transport of sediment and bioactive material on continental shelves. Understanding the dynamics
of this class of flows presents complications because of the presence of a free surface and also because the flow can be driven
by a pressure gradient (a tidal current), a stress at the free surface (a wind-driven current), or a combination of both.
In addition, the flow can be modified by the presence of a wave field that can induce Langmuir circulation (Langmuir, Science
87:119–123, 1938). Large eddy simulation is used to quantify the effects of pressure gradient and wind shear on the distinctive structures
of the turbulent flow. From these computations, an understanding of the physics governing the turbulence of pressure-driven
and wind-driven flows, how they can interact in a normal or a tangential direction, and the effect of wave forcing on these
flows is obtained. 相似文献
993.
FerryBox - Application of continuous water quality observations along transects in the North Sea 总被引:1,自引:2,他引:1
In 2002, the Helmholtz-Zentrum Geesthacht, Germany, started to use FerryBox-automated monitoring systems on Ships of Opportunity
to continuously record standard oceanographic, biological and chemical in situ data in the North Sea. The present study summarises
the operational experience gathered since the beginning of this deployment and reflects on the potential and limits of FerryBox
systems as a monitoring tool. One part relates to the instrumental performance, constancy of shipping services, and the availability
and quality of the recorded in situ data. The other considers integration of the FerryBox observations in scientific applications
and routine monitoring campaigns. Examples are presented that highlight the added value of the recorded data for the study
of both long- and short-term variability in water mass stability, plankton communities and surface water productivity in the
North Sea. Through the assessment of technical and scientific performance, it is evident that FerryBoxes have become a valuable
tool in marine research that helps to fill gaps in coastal and open ocean operational observation networks. 相似文献
994.
William W. ChadwickJr Sigurjon Jónsson Dennis J. Geist Michael Poland Daniel J. Johnson Spencer Batt Karen S. Harpp Andres Ruiz 《Bulletin of Volcanology》2011,73(6):679-697
The May 2005 eruption of Fernandina volcano, Galápagos, occurred along circumferential fissures parallel to the caldera rim
and fed lava flows down the steep southwestern slope of the volcano for several weeks. This was the first circumferential
dike intrusion ever observed by both InSAR and GPS measurements and thus provides an opportunity to determine the subsurface
geometry of these enigmatic structures that are common on Galápagos volcanoes but are rare elsewhere. Pre- and post- eruption
ground deformation between 2002 and 2006 can be modeled by the inflation of two separate magma reservoirs beneath the caldera:
a shallow sill at ~1 km depth and a deeper point-source at ~5 km depth, and we infer that this system also existed at the
time of the 2005 eruption. The co-eruption deformation is dominated by uplift near the 2005 eruptive fissures, superimposed
on a broad subsidence centered on the caldera. Modeling of the co-eruption deformation was performed by including various
combinations of planar dislocations to simulate the 2005 circumferential dike intrusion. We found that a single planar dike
could not match both the InSAR and GPS data. Our best-fit model includes three planar dikes connected along hinge lines to
simulate a curved concave shell that is steeply dipping (~45–60°) toward the caldera at the surface and more gently dipping
(~12–14°) at depth where it connects to the horizontal sub-caldera sill. The shallow sill is underlain by the deep point source.
The geometry of this modeled magmatic system is consistent with the petrology of Fernandina lavas, which suggest that circumferential
eruptions tap the shallowest parts of the system, whereas radial eruptions are fed from deeper levels. The recent history
of eruptions at Fernandina is also consistent with the idea that circumferential and radial intrusions are sometimes in a
stress-feedback relationship and alternate in time with one another. 相似文献
995.
Matthew Patrick David Wilson David Fee Tim Orr Don Swanson 《Bulletin of Volcanology》2011,73(9):1179-1186
The first eruptive activity at Kīlauea Volcano’s summit in 25 years began in March 2008 with the opening of a 35-m-wide vent
in Halema‘uma‘u crater. The new activity has produced prominent very-long-period (VLP) signals corresponding with two new
behaviors: episodic tremor bursts and small explosive events, both of which represent degassing events from the top of the
lava column. Previous work has shown that VLP seismicity has long been present at Kīlauea’s summit, and is sourced approximately
1 km below Halema‘uma‘u. By integrating video observations, infrasound and seismic data, we show that the onset of the large
VLP signals occurs within several seconds of the onset of the degassing events. This timing indicates that the VLP is caused
by forces—sourced at or very near the lava free surface due to degassing—transmitted down the magma column and coupling to
the surrounding rock at 1 km depth. 相似文献
996.
Andrey Pleskachevsky Susanne Lehner Thomas Heege Claudius Mott 《Ocean Dynamics》2011,61(12):2099-2120
A method to obtain underwater topography for coastal areas using state-of-the-art remote sensing data and techniques worldwide
is presented. The data from the new Synthetic Aperture Radar (SAR) satellite TerraSAR-X with high resolution up to 1 m are
used to render the ocean waves. As bathymetry is reflected by long swell wave refraction governed by underwater structures
in shallow areas, it can be derived using the dispersion relation from observed swell properties. To complete the bathymetric
maps, optical satellite data of the QuickBird satellite are fused to map extreme shallow waters, e.g., in near-coast areas.
The algorithms for bathymetry estimation from optical and SAR data are combined and integrated in order to cover different
depth domains. Both techniques make use of different physical phenomena and mathematical treatment. The optical methods based
on sunlight reflection analysis provide depths in shallow water up to 20 m in preferably calm weather conditions. The depth
estimation from SAR is based on the observation of long waves and covers the areas between about 70- and 10-m water depths
depending on sea state and acquisition quality. The depths in the range of 20 m up to 10 m represent the domain where the
synergy of data from both sources arises. Thus, the results derived from SAR and optical sensors complement each other. In
this study, a bathymetry map near Rottnest Island, Australia, is derived. QuickBird satellite optical data and radar data
from TerraSAR-X have been used. The depths estimated are aligned on two different grids. The first one is a uniform rectangular
mesh with a horizontal resolution of 150 m, which corresponds to an average swell wavelength observed in the 10 × 10-km SAR
image acquired. The second mesh has a resolution of 150 m for depths up to 20 m (deeper domain covered by SAR-based technique)
and 2.4 m resolution for the shallow domain imaged by an optical sensor. This new technique provides a platform for mapping
of coastal bathymetry over a broad area on a scale that is relevant to marine planners, managers, and offshore industry. 相似文献
997.
Adrian Costea Quoc T. Le Gia Ernst P. Stephan Thanh Tran 《Studia Geophysica et Geodaetica》2011,55(3):465-477
We consider the exterior Neumann problem of the Laplacian with boundary condition on spheroids. We propose to use spherical
radial basis functions in the solution of the boundary integral equation arising from the Dirichlet-to-Neumann map. Our meshless
approach with radial basis functions is particularly suitable for handling scattered satellite data. We also propose a preconditioning
technique based on an overlapping domain decomposition method to deal with ill-conditioned matrices arising from the approximation
problem. 相似文献
998.
The hourly data of nine geomagnetic observatories situated in Central Europe have been analyzed using the generalized magnetovariation
(GMV) method designed recently for induction soundings of inhomogeneous media. In this method, impedance is one of transfer
functions in the differential relation between spectra of the magnetic components and their derivatives. The peculiarity of
this impedance is its correspondence to the magnetotelluric one estimated from the linear relations. Three transfer functions
have been estimated simultaneously for data of geomagnetic observatories, using three different routines working in the period
range from three hours up to two days. Noises in the source field components have been compared with noise in the estimated
plane field divergence. The multivariate errors-in-variables method was used to extract spatially and temporally coherent
geomagnetic field structure from the partially incoherent geomagnetic variations. This method allows estimating reliably impedances
and gradient tippers for each observatory, taking into consideration the Earth’s sphericity. The obtained responses have been
used for induction soundings and for detecting a deep inhomogeneity in the region. 相似文献
999.
Large parts of the tidal estuary of river Elbe (Germany) are characterized by regular patterns of sand dunes. They evolve
due to complex sand transport mechanisms and show multi-faceted migration patterns, which are influenced by hydrodynamic boundary
conditions such as runoff and tidal forces. This study aims at increasing the understanding of the way hydrodynamic boundary
conditions influence dune behavior. This is the basis of an effective sediment management as well as an important requirement
for planning offshore structures. From a unique data set of up to six annual bathymetrical multibeam soundings between 1995
and 2010, bedform characteristics and migration rates were processed and analyzed with a set of automated methods. The influence
of river runoff, water levels, current velocities, tidal range, and river depth on characteristics and migration were tested
statistically. The results show that migration is mainly dominated by the incoming flood tide while rates and directions depend
on the amount of runoff originating from the inland catchment. 相似文献
1000.
Physical parameters of explosive eruptions are typically derived from tephra deposits. However, the characterization of a
given eruption relies strongly on the quality of the dataset used, the strategy chosen to obtain and process field data and
the particular model considered to derive eruptive parameters. As a result, eruptive parameters are typically affected by
a certain level of uncertainty and should not be considered as absolute values. Unfortunately, such uncertainty is difficult
to assess because it depends on several factors and propagates from field sampling to the application and interpretation of
dispersal models. Characterization of explosive eruptions is made even more difficult when tephra deposits are poorly exposed
and only medial data are available. In this paper, we present a quantitative assessment of the uncertainty associated with
the characterization of tephra deposits generated by the two largest eruptions of the last 2,000 years of Cotopaxi volcano,
Ecuador. In particular, we have investigated the effects of the determination of the maximum clast on the compilation of isopleth
maps, and, therefore, on the characterization of plume height. We have also compared the results obtained from the application
of different models for the determination of both plume height and erupted volume and for the eruption classification. Finally,
we have investigated the uncertainty propagation into the calculation of mass eruption rate and eruption duration. We have
found that for our case study, the determination of plume height from isopleth maps is more sensitive to the averaging techniques
used to define the maximum clast than to the choice of dispersal models used (i.e. models of Carey and Sparks 1986; Pyle 1989) and that even the application of the same dispersal model can result in plume height discrepancies if different isopleth
lines are used (i.e. model of Carey and Sparks 1986). However, the uncertainties associated with the determination of erupted mass, and, as a result, of the eruption duration,
are larger than the uncertainties associated with the determination of plume height. Mass eruption rate is also associated
with larger uncertainties than the determination of plume height because it is related to the fourth power of plume height.
Eruption classification is also affected by data processing. In particular, uncertainties associated with the compilation
of isopleth maps affect the eruption classification proposed by Pyle (1989), whereas the VEI classification is affected by the uncertainties resulting from the determination of erupted mass. Finally,
we have found that analytical and empirical models should be used together for a more reliable characterization of explosive
eruptions. In fact, explosive eruptions would be characterized better by a range of parameters instead of absolute values
for erupted mass, plume height, mass eruption rate and eruption duration. A standardization of field sampling would also reduce
the uncertainties associated with eruption characterization. 相似文献