1,695 research outputs found
On the equatorial Pacific response to the 1982/1983 EI Nino—Southern Oscillation event
The ocean\u27s response to the 1982/83 EI Nino—Southern Oscillation event was the largest ever documented. In this paper we explore the effects of certain details of the observed zonal wind stress anomaly field upon the ocean\u27s response using a linear, adiabatic, reduced gravity, analytical model. The increase in magnitude of the downwelling response over the composite of previous EI Nino events is attributed to the eastward translation of the observed westerly wind anomaly and the double peaked downwelling at the South American coast is attributed to the amplitude modulation of this anomaly. Effects of an easterly anomaly which appeared to the west of the dateline midway through the event are also considered
A Linear Analysis of Equatorial Atlantic Ocean Thermocline Variability
Observed variations in the Atlantic Ocean\u27s equatorial thermocline are compared at four locations with simultations using an analytical reduced-gravity model. The comparison shows the essential features of the seasonal wind-forced thermocline response to be accounted for by a linear superposition of equatorial long waves, evolving basinwide, tending to bring the zonal pressure gradient into balance with the wind stress. A frequency response function is derived whose properties provide a basis for discussing the large scale features of the equatorial Atlantic Ocean\u27s seasonal cycle-for example, its evolution along the equator, the maximum upwelling region observed in the Gulf of Guinea and the secondary upwelling season also observed there. Clarification is also given to the issue of remote versus local forcing for these features
Probing the size of extra dimension with gravitational wave astronomy
In Randall-Sundrum II (RS-II) braneworld model, it has been conjectured
according to the AdS/CFT correspondence that brane-localized black hole (BH)
larger than the bulk AdS curvature scale cannot be static, and it is
dual to a four dimensional BH emitting the Hawking radiation through some
quantum fields. In this scenario, the number of the quantum field species is so
large that this radiation changes the orbital evolution of a BH binary. We
derived the correction to the gravitational waveform phase due to this effect
and estimated the upper bounds on by performing Fisher analyses. We
found that DECIGO/BBO can put a stronger constraint than the current table-top
result by detecting gravitational waves from small mass BH/BH and BH/neutron
star (NS) binaries. Furthermore, DECIGO/BBO is expected to detect 10 BH/NS
binaries per year. Taking this advantage, we found that DECIGO/BBO can actually
measure down to m for 5 year observation if we know that
binaries are circular a priori. This is about 40 times smaller than the upper
bound obtained from the table-top experiment. On the other hand, when we take
eccentricities into binary parameters, the detection limit weakens to m due to strong degeneracies between and eccentricities. We also
derived the upper bound on from the expected detection number of extreme
mass ratio inspirals (EMRIs) with LISA and BH/NS binaries with DECIGO/BBO,
extending the discussion made recently by McWilliams. We found that these less
robust constraints are weaker than the ones from phase differences.Comment: 19 pages, 10 figures. Published in PRD, typos corrected, references
and footnotes adde
Comparison of the X-TRACK altimetry estimated currents with moored ADCP and HF radar observations on the West Florida Shelf
The performance of coastal altimetry over a wide continental shelf is
assessed using multiple-year ocean current observations by moored Acoustic
Doppler Current Profilers (ADCP) and high frequency (HF) radar on the West
Florida Shelf. Across track, surface geostrophic velocity anomalies, derived
from the XTRACK along-track sea level anomalies are compared with the near
surface current vector components from moored ADCP observations at mid shelf.
The altimeter derived velocity anomalies are also directly compared with the HF
radar surface current vector radial components that are aligned perpendicular
to the satellite track. Preliminary results indicate the potential usefulness
of the along-track altimetry data in contributing to descriptions of the
surface circulation on the West Florida Shelf and the challenges of such
applications. On subtidal time scales, the root mean square difference (rmsd)
between the estimated and the observed near surface velocity component
anomalies is 8 11 cms-1, which is about the same magnitude as the standard
deviations of the velocity components themselves. Adding a wind-driven Ekman
velocity component generally helps to reduce the rmsd values
Detecting very-high-frequency relic gravitational waves by electromagnetic wave polarizations in a waveguide
The polarization vector (PV) of an electromagnetic wave (EW) will experience
a rotation in a region of spacetime perturbed by gravitational waves (GWs).
Based on this idea, Cruise's group has built an annular waveguide to detect
GWs. We give detailed calculations of the rotations of the polarization vector
of an EW caused by incident GWs from various directions and in various
polarization states, and then analyze the accumulative effects on the
polarization vector when the EW passes n cycles along the annular waveguide. We
reexamine the feasibility and limitation of this method to detect GWs of high
frequency around 100 MHz, in particular, the relic gravitational waves (RGWs).
By comparing the spectrum of RGWs in the accelerating universe with the
detector sensitivity of the current waveguide, it is found that the amplitude
of the RGWs is too low to be detected by the waveguide detectors currently
running. Possible ways of improvements on detection are discussed also.Comment: 18pages, 10 figures, accepted by ChJA
Neutron star properties in a chiral SU(3) model
We investigate various properties of neutron star matter within an effective
chiral model. The predictions of this model are
compared with a Walecka-type model. It is demonstrated that the importance of
hyperon degrees are strongly depending on the interaction used, even if the
equation of state near saturation density is nearly the same in both models.
While the Walecka-type model predicts a strange star core with strangeness
fraction , the chiral model allows only for
and predicts that , and will not exist in star, in
contrast to the Walecka-type model.Comment: 13 pages, Revtex, 5 figs include
The Madison plasma dynamo experiment: a facility for studying laboratory plasma astrophysics
The Madison plasma dynamo experiment (MPDX) is a novel, versatile, basic
plasma research device designed to investigate flow driven magnetohydrodynamic
(MHD) instabilities and other high- phenomena with astrophysically
relevant parameters. A 3 m diameter vacuum vessel is lined with 36 rings of
alternately oriented 4000 G samarium cobalt magnets which create an
axisymmetric multicusp that contains 14 m of nearly magnetic field
free plasma that is well confined and highly ionized . At present, 8
lanthanum hexaboride (LaB) cathodes and 10 molybdenum anodes are inserted
into the vessel and biased up to 500 V, drawing 40 A each cathode, ionizing a
low pressure Ar or He fill gas and heating it. Up to 100 kW of electron
cyclotron heating (ECH) power is planned for additional electron heating. The
LaB cathodes are positioned in the magnetized edge to drive toroidal
rotation through torques that propagate into the
unmagnetized core plasma. Dynamo studies on MPDX require a high magnetic
Reynolds number , and an adjustable fluid Reynolds number , in the regime where the kinetic energy of the flow exceeds the magnetic
energy (vv). Initial results from MPDX are presented
along with a 0-dimensional power and particle balance model to predict the
viscosity and resistivity to achieve dynamo action.Comment: 14 pages, 13 figure
Northwest Africa (NWA) 8785, an EL3 Chondrite with FeO-Rich Matrix
The enstatite (E) chondrites are enigmatic but important for understanding the evolution of the terrestrial planets. They have highly reduced mineral assemblages in which enstatite (near pure in compostion) is the dominant silicate, metal is abundant and contains >2.5 wt. % Si in some EH3s, elements which are generally lithophile in most chondrites occur as sulfide and some E3s contain nitrides and carbides. Notably, stable isotope compositions are similar to the Earth-Moon. Aside from E chondrite clasts in the Kaidun breccia, the enstaite chondrites are dry, lacking evidence of ever having hydrous minerals, distinguishing them from most other chondrite groups and suggesting they formed relatively close to the sun, inside of the snow line. Compared to other chondrite groups, the E3s are also matrix-poor, with EH3s having ~4-12 vol. % and EL3s 5 vol % matrix. Here we present a study of NWA 8785, a remarkable new EL3 chondrite with an FeO-rich, fine-grained matrix. Our goals are to understand E chondrite matrix and the evolution and alteration history of the EL3 parent body
US IOOS coastal and ocean modeling testbed: Inter-model evaluation of tides, waves, and hurricane surge in the Gulf of Mexico
A Gulf of Mexico performance evaluation and comparison of coastal circulation and wave models was executed through harmonic analyses of tidal simulations, hindcasts of Hurricane Ike (2008) and Rita (2005), and a benchmarking study. Three unstructured coastal circulation models (ADCIRC, FVCOM, and SELFE) validated with similar skill on a new common Gulf scale mesh (ULLR) with identical frictional parameterization and forcing for the tidal validation and hurricane hindcasts. Coupled circulation and wave models, SWAN+ADCIRC and WWMII+SELFE, along with FVCOM loosely coupled with SWAN, also validated with similar skill. NOAA\u27s official operational forecast storm surge model (SLOSH) was implemented on local and Gulf scale meshes with the same wind stress and pressure forcing used by the unstructured models for hindcasts of Ike and Rita. SLOSH\u27s local meshes failed to capture regional processes such as Ike\u27s forerunner and the results from the Gulf scale mesh further suggest shortcomings may be due to a combination of poor mesh resolution, missing internal physics such as tides and nonlinear advection, and SLOSH\u27s internal frictional parameterization. In addition, these models were benchmarked to assess and compare execution speed and scalability for a prototypical operational simulation. It was apparent that a higher number of computational cores are needed for the unstructured models to meet similar operational implementation requirements to SLOSH, and that some of them could benefit from improved parallelization and faster execution speed
Semi-Analytic Stellar Structure in Scalar-Tensor Gravity
Precision tests of gravity can be used to constrain the properties of
hypothetical very light scalar fields, but these tests depend crucially on how
macroscopic astrophysical objects couple to the new scalar field. We develop
quasi-analytic methods for solving the equations of stellar structure using
scalar-tensor gravity, with the goal of seeing how stellar properties depend on
assumptions made about the scalar coupling at a microscopic level. We
illustrate these methods by applying them to Brans-Dicke scalars, and their
generalization in which the scalar-matter coupling is a weak function of the
scalar field. The four observable parameters that characterize the fields
external to a spherically symmetric star (the stellar radius, R, mass, M,
scalar `charge', Q, and the scalar's asymptotic value, phi_infty) are subject
to two relations because of the matching to the interior solution, generalizing
the usual mass-radius, M(R), relation of General Relativity. We identify how
these relations depend on the microscopic scalar couplings, agreeing with
earlier workers when comparisons are possible. Explicit analytical solutions
are obtained for the instructive toy model of constant-density stars, whose
properties we compare to more realistic equations of state for neutron star
models.Comment: 39 pages, 9 figure
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