1,695 research outputs found
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Seven-year climatology of dust opacity on Mars
This paper describes the procedure we have used to produce multi-annual dust scenarios for Martian years 24 to 30 from a multi-instrument dataset of total dust opacity observations. This procedure includes gridding the observations on a pre-defined longitude-latitude grid with 1 sol resolution in time, and spatially interpolating the results to obtain complete daily maps of total dust opacity. We used weighted binning as gridding technique, and spatial kriging as method of interpolation. The new dust scenarios are available as NetCDF files, easy to interface to any model including global circulation and mesoscale models for the Martian atmosphere
Is Gliese 581d habitable? Some constraints from radiative-convective climate modeling
The recently discovered exoplanet Gl581d is extremely close to the outer edge
of its system's habitable zone, which has led to much speculation on its
possible climate. We have performed a range of simulations to assess whether,
given simple combinations of chemically stable greenhouse gases, the planet
could sustain liquid water on its surface. For best estimates of the surface
gravity, surface albedo and cloud coverage, we find that less than 10 bars of
CO2 is sufficient to maintain a global mean temperature above the melting point
of water. Furthermore, even with the most conservative choices of these
parameters, we calculate temperatures above the water melting point for CO2
partial pressures greater than about 40 bar. However, we note that as Gl581d is
probably in a tidally resonant orbit, further simulations in 3D are required to
test whether such atmospheric conditions are stable against the collapse of CO2
on the surface.Comment: 9 pages, 11 figures. Accepted for publication in Astronomy &
Astrophysic
Nernst effect and disorder in the normal state of high-T_{c} cuprates
We have studied the influence of disorder induced by electron irradiation on
the Nernst effect in optimally and underdoped YBa2Cu3O(7-d) single crystals.
The fluctuation regime above T_{c} expands significantly with disorder,
indicating that the T_{c} decrease is partly due to the induced loss of phase
coherence. In pure crystals the temperature extension of the Nernst signal is
found to be narrow whatever the hole doping, contrary to data reported in the
low-T_{c} cuprates families. Our results show that the presence of "intrinsic"
disorder can explain the enhanced range of Nernst signal found in the pseudogap
phase of the latter compounds.Comment: revised version. to be published in Physical Review Letter
3D climate modeling of close-in land planets: Circulation patterns, climate moist bistability and habitability
The inner edge of the classical habitable zone is often defined by the
critical flux needed to trigger the runaway greenhouse instability. This 1D
notion of a critical flux, however, may not be so relevant for inhomogeneously
irradiated planets, or when the water content is limited (land planets).
Here, based on results from our 3D global climate model, we find that the
circulation pattern can shift from super-rotation to stellar/anti stellar
circulation when the equatorial Rossby deformation radius significantly exceeds
the planetary radius. Using analytical and numerical arguments, we also
demonstrate the presence of systematic biases between mean surface temperatures
or temperature profiles predicted from either 1D or 3D simulations.
Including a complete modeling of the water cycle, we further demonstrate that
for land planets closer than the inner edge of the classical habitable zone,
two stable climate regimes can exist. One is the classical runaway state, and
the other is a collapsed state where water is captured in permanent cold traps.
We identify this "moist" bistability as the result of a competition between the
greenhouse effect of water vapor and its condensation. We also present
synthetic spectra showing the observable signature of these two states.
Taking the example of two prototype planets in this regime, namely Gl581c and
HD85512b, we argue that they could accumulate a significant amount of water ice
at their surface. If such a thick ice cap is present, gravity driven ice flows
and geothermal flux should come into play to produce long-lived liquid water at
the edge and/or bottom of the ice cap. Consequently, the habitability of
planets at smaller orbital distance than the inner edge of the classical
habitable zone cannot be ruled out. Transiting planets in this regime represent
promising targets for upcoming observatories like EChO and JWST.Comment: Accepted for publication in Astronomy and Astrophysics, complete
abstract in the pdf, 18 pages, 18 figure
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Martian meso/micro-scale winds and surface energy budget
Regional, diurnal and seasonal variations of surface
temperature are particularly large on Mars. This is mostly due to the Martian surface remaining close to radiative equilibrium. Contrary to most terrestrial locations, contributions of sensible heat flux (i.e. conduction/convection exchanges between atmosphere and surface) to the surface energy budget [hereinafter SEB] are negligible on Mars owing to lowatmospheric density and heat capacity (e.g. Figure 2 in Savijärvi and Kauhanen, 2008). This radiative control of surface temperature is a key characteristic of the Martian environment and has crucial consequences on the the Martian geology, meteorology, exobiology, etc.
In order to identify the impact of this Martian peculiarity to near-surface regional-to-local atmospheric circulations,
we employ our recently-built Martian limited-area meteorological model (Spiga and Forget, 2009). We use horizontal resolutions adapted to the dynamical phenomena we aim to resolve: from several tens of kilometers to compute regional winds (mesoscale simulations) to several tens of meters to compute atmospheric boundary-layer winds (microscale or turbulent-resolving simulations, also called Large-Eddy Simulations, LES)
A Fission-Fusion Hybrid Reactor in Steady-State L-Mode Tokamak Configuration with Natural Uranium
Opioid prescribing for acute postoperative pain : an overview of systematic reviews related to two consensus statements relevant at patient, prescriber, system and public health levels
Peer reviewedPublisher PD
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Data assimilation insights on selecting the most valuable atmospheric measurements
We discuss how objective guidance on selecting the most valuable atmospheric measurements on future Mars spacecraft missions can be provided through already developed Martian atmospheric data assimilation systems, and in particular through Observing System Simulation Experiments (OSSEs) which are widely used to design instruments for the Earth’s atmosphere
Spin Dynamics in Cuprates: Optical Conductivity of HgBa2CuO4
The electron-boson spectral density function I^2ChiOmega responsible for
carrier scattering of the high temperature superconductor HgBa2CuO4 (Tc = 90 K)
is calculated from new data on the optical scattering rate. A maximum entropy
technique is used. Published data on HgBa2Ca2Cu3O8 (Tc = 130 K) are also
inverted and these new results are put in the context of other known cases. All
spectra (with two notable exceptions) show a peak at an energy (Omega_r)
proportional to the superconducting transition temperature Omega_r ~= 6.3
kB.Tc. This charge channel relationship follows closely the magnetic resonance
seen by polarized neutron scattering, Omega_r^{neutron} ~= 5.4 kB.Tc. The
amplitudes of both peaks decrease strongly with increasing temperature. In some
cases, the peak at Omega_r is weak and the spectrum can have additional maxima
and a background extending up to several hundred meV
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