192 research outputs found
The circulation pattern and day-night heat transport in the atmosphere of a synchronously rotating aquaplanet: Dependence on planetary rotation rate
In order to investigate a possible variety of atmospheric states realized on a synchronously rotating aquaplanet, an experiment studying the impact of planetary rotation rate is performed using an atmospheric general circulation model (GCM) with simplified hydrological and radiative processes. The entire planetary surface is covered with a swamp ocean. The value of planetary rotation rate is varied from zero to the Earth’s, while other parameters such as planetary radius, mean molecular weight and total mass of atmospheric dry components, and solar constant are set to the present Earth’s values. The integration results show that the atmosphere reaches statistically equilibrium states for all runs; none of the calculated cases exemplifies the runaway greenhouse state. The circulation patterns obtained are classified into four types: Type-I characterized by the dominance of a day-night thermally direct circulation, Type-II characterized by a zonal wave number one resonant Rossby wave over a meridionally broad westerly jet on the equator, Type-III characterized by a long time scale north-south asymmetric variation, and Type-IV characterized by a pair of mid-latitude westerly jets. With the increase of planetary rotation rate, the circulation evolves from Type-I to Type-II and then to Type-III gradually and smoothly, whereas the change from Type-III to Type-IV is abrupt and discontinuous. Over a finite range of planetary rotation rate, both Types-III and -IV emerge as statistically steady states, constituting multiple equilibria. In spite of the substantial changes in circulation, the net energy transport from the day side to the night side remains almost insensitive to planetary rotation rate, although the partition into dry static energy and latent heat energy transports changes. The reason for this notable insensitivity is that the outgoing longwave radiation over the broad area of the day side is constrained by the radiation limit of a moist atmosphere, so that the transport to the night side, which is determined as the difference between the incoming solar radiation and the radiation limit, cannot change greatly
"Gtool5": a Fortran90 library of input/output interfaces for self-descriptive multi-dimensional numerical data
A Fortran90 input/output library, "gtool5", is developed for use with numerical simulation models in the fields of Earth and planetary sciences. The use of this library will simplify implementation of input/output operations into program code in a consolidated form independent of the size and complexity of the software and data. The library also enables simple specification of the metadata needed for post-processing and visualization of the data. These aspects improve the readability of simulation code, which facilitates the simultaneous performance of multiple numerical experiments with different software and efficiency in examining and comparing the numerical results. The library is expected to provide a common software platform to reinforce research on, for instance, the atmosphere and ocean, where a close combination of multiple simulation models with a wide variety of complexity of physics implementations from massive climate models to simple geophysical fluid dynamics models is required
correlations from the stopped reaction on He
We have investigated correlations of coincident pairs from the
stopped reaction on He, and clearly observed and
branches of the two-nucleon absorption process in the
invariant mass spectra. In addition, non-mesonic reaction channels, which
indicate possible exotic signals for the formation of strange multibaryon
states, have been identified.Comment: 5 pages, 3 figures, submitted to Physical Review Letter
Structure near ++ threshold in the in-flight He reaction
To search for an S= -1 di-baryonic state which decays to , the reaction was studied at 1.0 GeV/.
Unobserved neutrons were kinematically identified from the missing mass
of the reaction in order to have a large
acceptance for the final state. The observed events,
distributed widely over the kinematically allowed region of the Dalitz plot,
establish that the major component comes from a three nucleon absorption
process. A concentration of events at a specific neutron kinetic energy was
observed in a region of low momentum transfer to the . To account
for the observed peak structure, the simplest S-wave pole was assumed to exist
in the reaction channel, having Breit-Wigner form in energy and with a Gaussian
form-factor. A minimum method was applied to deduce its mass
2355 (stat.) (syst.) MeV/c, and decay-width
110 (stat.) (syst.) MeV/c,
respectively. The form factor parameter 400 MeV/ implies that the
range of interaction is about 0.5Comment: 12pages, 8 figure
Measurement of the strong interaction induced shift and width of the 1s state of kaonic deuterium at J-PARC
The antikaon-nucleon interaction close to threshold provides crucial
information on the interplay between spontaneous and explicit chiral symmetry
breaking in low-energy QCD. In this context the importance of kaonic deuterium
X-ray spectroscopy has been well recognized, but no experimental results have
yet been obtained due to the difficulty of the measurement. We propose to
measure the shift and width of the kaonic deuterium 1s state with an accuracy
of 60 eV and 140 eV respectively at J-PARC. These results together with the
kaonic hydrogen data (KpX at KEK, DEAR and SIDDHARTA at DAFNE) will then permit
the determination of values of both the isospin I=0 and I=1 antikaon-nucleon
scattering lengths and will provide the most stringent constraints on the
antikaon-nucleon interaction, promising a breakthrough. Refined Monte Carlo
studies were performed, including the investigation of background suppression
factors for the described setup. These studies have demonstrated the
feasibility of determining the shift and width of the kaonic deuterium atom 1s
state with the desired accuracy of 60 eV and 140 eV.Comment: 12 pages, 9 figure
Increased insolation threshold for runaway greenhouse processes on Earth like planets
Because the solar luminosity increases over geological timescales, Earth
climate is expected to warm, increasing water evaporation which, in turn,
enhances the atmospheric greenhouse effect. Above a certain critical
insolation, this destabilizing greenhouse feedback can "runaway" until all the
oceans are evaporated. Through increases in stratospheric humidity, warming may
also cause oceans to escape to space before the runaway greenhouse occurs. The
critical insolation thresholds for these processes, however, remain uncertain
because they have so far been evaluated with unidimensional models that cannot
account for the dynamical and cloud feedback effects that are key stabilizing
features of Earth's climate. Here we use a 3D global climate model to show that
the threshold for the runaway greenhouse is about 375 W/m, significantly
higher than previously thought. Our model is specifically developed to quantify
the climate response of Earth-like planets to increased insolation in hot and
extremely moist atmospheres. In contrast with previous studies, we find that
clouds have a destabilizing feedback on the long term warming. However,
subsident, unsaturated regions created by the Hadley circulation have a
stabilizing effect that is strong enough to defer the runaway greenhouse limit
to higher insolation than inferred from 1D models. Furthermore, because of
wavelength-dependent radiative effects, the stratosphere remains cold and dry
enough to hamper atmospheric water escape, even at large fluxes. This has
strong implications for Venus early water history and extends the size of the
habitable zone around other stars.Comment: Published in Nature. Online publication date: December 12, 2013.
Accepted version before journal editing and with Supplementary Informatio
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