1,895 research outputs found
Baroclinic Vorticity Production in Protoplanetary Disks; Part I: Vortex Formation
The formation of vortices in protoplanetary disks is explored via
pseudo-spectral numerical simulations of an anelastic-gas model. This model is
a coupled set of equations for vorticity and temperature in two dimensions
which includes baroclinic vorticity production and radiative cooling. Vortex
formation is unambiguously shown to be caused by baroclinicity because (1)
these simulations have zero initial perturbation vorticity and a nonzero
initial temperature distribution; and (2) turning off the baroclinic term halts
vortex formation, as shown by an immediate drop in kinetic energy and
vorticity. Vortex strength increases with: larger background temperature
gradients; warmer background temperatures; larger initial temperature
perturbations; higher Reynolds number; and higher resolution. In the
simulations presented here vortices form when the background temperatures are
and vary radially as , the initial vorticity
perturbations are zero, the initial temperature perturbations are 5% of the
background, and the Reynolds number is . A sensitivity study consisting
of 74 simulations showed that as resolution and Reynolds number increase,
vortices can form with smaller initial temperature perturbations, lower
background temperatures, and smaller background temperature gradients. For the
parameter ranges of these simulations, the disk is shown to be convectively
stable by the Solberg-H{\o}iland criteria.Comment: Originally submitted to The Astrophysical Journal April 3, 2006;
resubmitted November 3, 2006; accepted Dec 5, 200
Drilling of shallow marine sulfide-sulfate mineralisation in south-eastern Tyrrhenian Sea, Italy; Seafloor sulfides, Tyrrhenian Sea, highsulfidation; hydrothermal systems, Palinuro
Semi-massive to massive sulfides with abundant late native sulfur were drilled in a shallowwater hydrothermal system in an island arc volcanic setting at the Palinuro volcanic complex in the Tyrrhenian Sea, Italy. Overall, 12.7 m of sulfide mineralisation were drilled in a sediment-filled
depression at a water depth of 630 - 650 m using the
lander-type Rockdrill I drill rig of the British Geological
Survey. Polymetallic (Zn, Pb, Sb, As, Ag) sulfides
overlie massive pyrite. The massive sulfide mineralisation contains a number of atypical minerals, including enargite-famatinite, tennantite-tetrahedrite, stibnite, bismuthinite, and Pb-,Sb-, and Ag-sulfosalts, that do not commonly occur in mid-ocean ridge massive sulfides. Analogous to subaerial epithermal deposits, the occurrence of these minerals and the presence of abundant native sulfur suggest an intermediate to high sulfidation and/or high oxididation state of the hydrothermal fluids in contrast to the near-neutral and reducing fluids from which base metal-rich massive sulfides along mid-ocean ridges typically form. Oxidised conditions during sulfide deposition are likely related to the presence of magmatic volatiles in the mineralising fluids that were derived from a degassing magma chamber below the Palinuro volcanic complex
An unstructured CD-grid variational formulation for sea ice dynamics
For the numerical simulation of earth system models, Arakawa grids are
largely employed. A quadrilateral mesh is assumed for their classical
definition, and different types of grids are identified depending on the
location of the discretized quantities. The B-grid has both velocity components
at the center of a cell, the C-grid places the velocity components on the edges
in a staggered fashion, and the D-grid is a ninety-degree rotation of a C-grid.
Historically, B-grid formulations of sea ice dynamics have been dominant
because they have matched the grid type used by ocean models. In recent years,
as ocean models have increasingly progressed to C-grids, sea ice models have
followed suit on quadrilateral meshes, but few if any implementations of
unstructured C-grid sea ice models have been developed. In this work, we
present an unstructured CD-grid type formulation of the elastic-viscous-plastic
rheology, where the velocity unknowns are located at the edges, rather than at
the vertices, as in the B-grid. The notion of a CD-grid has been recently
introduced and assumes that the velocity components are co-located at the
edges. The mesh cells in our analysis have sides, with greater than or
equal to four. Numerical results are included to investigate the features of
the proposed method. Our framework of choice is the Model for Prediction Across
Scales (MPAS) within E3SM, the climate model of the U.S. Department of Energy,
although our approach is general and could be applied to other models as well.
While MPAS-Seaice is currently defined on a B-grid, MPAS-Ocean runs on a
C-grid, hence interpolation operators are heavily used when coupled simulations
are performed. The discretization introduced here aims at transitioning the
dynamics of MPAS-Seaice to a CD-grid, to ultimately facilitate improved
coupling with MPAS-Ocean and reduce numerical errors associated with this
communication
On the Role of Global Warming on the Statistics of Record-Breaking Temperatures
We theoretically study long-term trends in the statistics of record-breaking
daily temperatures and validate these predictions using Monte Carlo simulations
and data from the city of Philadelphia, for which 126 years of daily
temperature data is available. Using extreme statistics, we derive the number
and the magnitude of record temperature events, based on the observed Gaussian
daily temperatures distribution in Philadelphia, as a function of the number of
elapsed years from the start of the data. We further consider the case of
global warming, where the mean temperature systematically increases with time.
We argue that the current warming rate is insufficient to measurably influence
the frequency of record temperature events over the time range of the
observations, a conclusion that is supported by numerical simulations and the
Philadelphia temperature data.Comment: 11 pages, 6 figures, 2-column revtex4 format. For submission to
Journal of Climate. Revised version has some new results and some errors
corrected. Reformatted for Journal of Climate. Second revision has an added
reference. In the third revision one sentence that explains the simulations
is reworded for clarity. New revision 10/3/06 has considerable additions and
new results. Revision on 11/8/06 contains a number of minor corrections and
is the version that will appear in Phys. Rev.
The Relationship of Left Ventricular Trabeculation to Ventricular Function and Structure Over a 9.5-Year Follow-Up The MESA Study
Left ventricular (LV) trabeculation is highly variable among individuals and is increased in some diseases (e.g., congenital heart disease or cardiomyopathies), but its significance in population-representative individuals is unknown
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