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A climatology of the stratosphere is determined from a 20-year integration with the stratospheric version of the Atmospheric
General Circulation Model LMDz. The model has an upper boundary at near 65 km, uses a Doppler spread non-orographic gravity
waves drag parameterization and a subgrid-scale orography parameterization. It also has a Rayleigh damping layer for resolved
waves only (not the zonal mean flow) over the top 5 km. This paper describes the basic features of the model and some aspects
of its radiative-dynamical climatology. Standard first order diagnostics are presented but some emphasis is given to the model’s
ability to reproduce the low frequency variability of the stratosphere in the winter northern hemisphere. In this model, the
stratospheric variability is dominated at each altitudes by patterns which have some similarities with the arctic oscillation
(AO). For those patterns, the signal sometimes descends from the stratosphere to the troposphere. In an experiment where the
parameterized orographic gravity waves that reach the stratosphere are exaggerated, the model stratosphere in the NH presents
much less variability. Although the stratospheric variability is still dominated by patterns that resemble to the AO, the
downward influence of the stratosphere along these patterns is near entirely lost. In the same time, the persistence of the
surface AO decreases, which is consistent with the picture that this persistence is linked to the descent of the AO signal
from the stratosphere to the troposphere. A comparison between the stratospheric version of the model, and its routinely used
tropospheric version is also done. It shows that the introduction of the stratosphere in a model that already has a realistic
AO persistence can lead to overestimate the actual influence of the stratospheric dynamics onto the surface AO. Although this
result is certainly model dependent, it suggests that the introduction of the stratosphere in a GCM also call for a new adjustment
of the model parameters that affect the tropospheric variability. 相似文献
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The LMDZ4 general circulation model: climate performance and sensitivity to parametrized physics with emphasis on tropical convection 总被引：3，自引：11，他引：3
Frédéric Hourdin Ionela Musat Sandrine Bony Pascale Braconnot Francis Codron Jean-Louis Dufresne Laurent Fairhead Marie-Angèle Filiberti Pierre Friedlingstein Jean-Yves Grandpeix Gerhard Krinner Phu LeVan Zhao-Xin Li François Lott 《Climate Dynamics》2006,27(7-8):787-813
The LMDZ4 general circulation model is the atmospheric component of the IPSL–CM4 coupled model which has been used to perform climate change simulations for the 4th IPCC assessment report. The main aspects of the model climatology (forced by observed sea surface temperature) are documented here, as well as the major improvements with respect to the previous versions, which mainly come form the parametrization of tropical convection. A methodology is proposed to help analyse the sensitivity of the tropical Hadley–Walker circulation to the parametrization of cumulus convection and clouds. The tropical circulation is characterized using scalar potentials associated with the horizontal wind and horizontal transport of geopotential (the Laplacian of which is proportional to the total vertical momentum in the atmospheric column). The effect of parametrized physics is analysed in a regime sorted framework using the vertical velocity at 500 hPa as a proxy for large scale vertical motion. Compared to Tiedtke’s convection scheme, used in previous versions, the Emanuel’s scheme improves the representation of the Hadley–Walker circulation, with a relatively stronger and deeper large scale vertical ascent over tropical continents, and suppresses the marked patterns of concentrated rainfall over oceans. Thanks to the regime sorted analyses, these differences are attributed to intrinsic differences in the vertical distribution of convective heating, and to the lack of self-inhibition by precipitating downdraughts in Tiedtke’s parametrization. Both the convection and cloud schemes are shown to control the relative importance of large scale convection over land and ocean, an important point for the behaviour of the coupled model. 相似文献
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K. L. Page R. Willingale P. T. O'Brien N. R. Tanvir J. P. Osborne B. Zhang S. T. Holland A. J. Levan A. Melandri R. L. C. Starling D. Bersier D. N. Burrows J. E. Geach P. Maxted 《Monthly notices of the Royal Astronomical Society》2009,395(1):328-334
Swift -detected GRB 080307 showed an unusual smooth rise in its X-ray light curve around 100 s after the burst, at the start of which the emission briefly softened. This 'hump' has a longer duration than is normal for a flare at early times and does not demonstrate a typical flare profile. Using a two-component power-law-to-exponential model, the rising emission can be modelled as the onset of the afterglow, something which is very rarely seen in Swift -X-ray light curves. We cannot, however, rule out that the hump is a particularly slow early-time flare, or that it is caused by upscattered reverse shock electrons. 相似文献
5.
N. R. Tanvir A. J. Levan E. Rol R. L. C. Starling J. Gorosabel R. S. Priddey D. Malesani P. Jakobsson P. T. O'Brien A. O. Jaunsen J. Hjorth J. P. U. Fynbo A. Melandri A. Gomboc B. Milvang-Jensen A. S. Fruchter M. Jarvis C. A. C. Fernandes T. Wold 《Monthly notices of the Royal Astronomical Society》2008,388(4):1743-1750
Gamma-ray bursts (GRBs) are powerful probes of the early Universe, but locating and identifying very distant GRBs remain challenging. We report here the discovery of the K -band afterglow of Swift GRB 060923A, imaged within the first hour post-burst, and the faintest so far found. It was not detected in any bluer bands to deep limits, making it a candidate very high- z burst ( z ≳ 11) . However, our later-time optical imaging and spectroscopy reveal a faint galaxy coincident with the GRB position which, if it is the host, implies a more moderate redshift (most likely z ≲ 2.8 ) and therefore that dust is the likely cause of the very red-afterglow colour. This being the case, it is one of the few instances so far found of a GRB afterglow with high-dust extinction. 相似文献
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P. D. Dobbie M. R. Burleigh A. J. Levan M. A. Barstow R. Napiwotzki J. B. Holberg I. Hubeny S. B. Howell 《Monthly notices of the Royal Astronomical Society》2005,357(3):1049-1058
We have undertaken a detailed near-infrared spectroscopic analysis of eight notable white dwarfs, predominantly of southern declination. In each case the spectrum failed to reveal compelling evidence for the presence of a spatially unresolved, cool, late-type companion. Therefore, we have placed an approximate limit on the spectral type of a putative companion to each degenerate. From these limits we conclude that if GD659, GD50, GD71 or WD2359−434 possesses an unresolved companion then most probably it is substellar in nature ( M < 0.072 M⊙ ) . Furthermore, any spatially unresolved late-type companion to RE J0457−280, RE J0623−374, RE J0723−274 or RE J2214−491 most likely has M < 0.082 M⊙ . These results imply that if weak accretion from a nearby late-type companion is the cause of the unusual photospheric composition observed in a number of these degenerates then the companions are of very low mass, beyond the detection thresholds of this study. Furthermore, these results do not contradict a previously noted deficit of very-low-mass stellar and brown dwarf companions to main sequence F, G, K and early-M type primaries ( a ≲ 1000 au). 相似文献
7.
Phu Le Vo 《GeoJournal》2007,70(1):75-89
The management of water resources is an unfinished effort of the international community. Rapid urbanization has transcended
the management capacity of governments in developing countries. Since the renovation policy launched in 1986, Ho Chi Minh
City, Vietnam, has experienced the fastest urbanization and industrialization process. This has placed severe constraints
on the use of water resources and management capacity of the local government. The abstraction of groundwater has exceeded
the limiting volume (520,000 m3/day) and the annual drawdown of water table is 2–3 m. In addition, the quality of urban water bodies is increasingly exacerbated
by a huge volume of untreated industrial and domestic wastewater. These are hampering water demand, use and the capacity of
the municipal authority in managing water resources. The purpose of this paper is to analyze the impact of urbanization on
water resources. Current issues and challenges in the management practices of water resources are discussed. It will propose
a new paradigm of water management in Ho Chi Minh City. 相似文献
8.
Levan N. Tsintsadze 《Astrophysics and Space Science》2000,274(4):719-723
We consider the system of neutrino-antineutrino
– plasma taking into account theirweak Fermi interaction, when the density of neutrinos andthe plasma particles are rather high and their collective interactionplays a vital role. New fluid instabilities driven by strong neutrino flux in aplasma are observed. It is shown that a bunch of neutrinos, drifting witha constant velocity across a homogeneous plasma, can also induce emission oflower energy neutrinos due to scattering, i.e. the decay of a heavy neutrinoH into a heavy and a light neutrino L(HHL) in a plasma. Furthermore we find thatthe neutrino production in stars does not lead in general to energy lossesfrom the neutron stars. 相似文献
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Broad-bandpass flux measurements with effective wavelengths at 20, 27 and 85 μm are presented for four asteroids—2 Pallas, 7 Iris, 15 Eunomia, and 45 Eugenia. The observations were made during the Far Infrared Sky Survey Experiment (FIRSSE) with a super-fluid helium-cooled telescope flown to exospheric altitudes aboard a sounding rocket. The 20- and 27-μm fluxes are consistent with published 10- and 20-μm photometry. However, the 85-μm fluxes are a factor of 2 to 3 lower than a Planck law extrapolation of the shorter wavelength fluxes. If the thermal radiation from asteroids at these wavelenghts is adequately described by graybody emission, as is expected on the basis of models of asteroid radiation discussed in the literature, then the value of emissivity in the 85-μm bandpass is likely to be substantially lower than the 10- to 20-μm value. The decrease in emissivity between 20 and 85 μm suggested for these asteroids is in qualitative agreement with studies, both observational and theoretical, of emissivity of a lunar-type regolith. Fluxes measured at 20 and/or 27 μm are also reported for an additional 16 asteroids. 相似文献