Radiative properties of stellar plasmas and open challenges     

S. Turck-Chi??ze  G. Loisel  D. Gilles  L. Piau  C. Blancard  T. Blenski  M. Busquet  T. Caillaud  P. Coss??  F. Delahaye  G. Faussurier  J. Fariaut  F. Gilleron  J. A. Guzik  J. Harris  D. P. Kilcrease  N. H. Magee  J. C. Pain  Q. Porcherot  M. Poirier  G. Soullier  C. J. Zeippen  S. Bastiani-Ceccotti  C. Reverdin  V. Silvert  F. Thais  B. Villette 《Astrophysics and Space Science》2011,336(1):103-109

The lifetime of solar-like stars, the envelope structure of more massive stars, and stellar acoustic frequencies largely depend on the radiative properties of the stellar plasma. Up to now, these complex quantities have been estimated only theoretically. The development of the powerful tools of helio- and astero- seismology has made it possible to gain insights on the interiors of stars. Consequently, increased emphasis is now placed on knowledge of the monochromatic opacity coefficients. Here we review how these radiative properties play a role, and where they are most important. We then concentrate specifically on the envelopes of ?? Cephei variable stars. We discuss the dispersion of eight different theoretical estimates of the monochromatic opacity spectrum and the challenges we need to face to check these calculations experimentally.  相似文献   

Bioavailability of sediment-borne lead for ragworms (Hediste diversicolor) investigated by lead isotopes     

Sylvie Philippe  Céline Leterme  Sandric Lesourd  Lucie Courcot  Udo Haack  Jacinthe Caillaud 《Applied Geochemistry》2008

The Seine estuary possesses a heavily industrialised catchment area that contrasts significantly with that possessed by the smaller Authie estuary. For both of these northern French estuaries, Pb isotopic compositions and concentrations have been determined on specimens of Hediste diversicolor (ragworms) and on HCl leachates performed on related mudflat sediment. Three sampling campaigns were completed in 2003. As expected, the reactive Pb obtained by 1 M HCl leaching, shows higher concentrations and a more anthropogenic signature in samples from the Seine estuary than in samples from the Authie. However, neither of the two sites is free from the influence of anthropogenic Pb. Possible contaminant sources are discussed through comparisons with previously published data. For the more highly contaminated Seine estuary, most of the ragworm Pb signatures are similar to those of the sediments. In contrast, ragworms from the Authie site exhibit a higher proportion of anthropogenic Pb than the corresponding sediments. Various hypotheses are discussed to explain this significant discrepancy: (1) analytical artifacts, (2) migration of ragworm populations, (3) diet and feeding behaviour, and as the most likely explanation (4) an unsuitable leaching method for the extraction of bioavailable Pb.  相似文献   

The first multi-model ensemble of regional climate simulations at kilometer-scale resolution part 2: historical and future simulations of precipitation     

Pichelli  Emanuela  Coppola  Erika  Sobolowski  Stefan  Ban  Nikolina  Giorgi  Filippo  Stocchi  Paolo  Alias  Antoinette  Belu&#;i&#;  Danijel  Berthou  Segolene  Caillaud  Cecile  Cardoso  Rita M.  Chan  Steven  Christensen  Ole B&#;ssing  Dobler  Andreas  de Vries  Hylke  Goergen  Klaus  Kendon  Elizabeth J.  Keuler  Klaus  Lenderink  Geert  Lorenz  Torge  Mishra  Aditya N.  Panitz  Hans-Juergen  Sch&#;r  Christoph  Soares  Pedro M. M.  Truhetz  Heimo  Vergara-Temprado  Jesus 《Climate Dynamics》2021,56(11):3581-3602

This paper presents the first multi-model ensemble of 10-year, “convection-permitting” kilometer-scale regional climate model (RCM) scenario simulations downscaled from selected CMIP5 GCM projections for historical and end of century time slices. The technique is to first downscale the CMIP5 GCM projections to an intermediate 12–15 km resolution grid using RCMs, and then use these fields to downscale further to the kilometer scale. The aim of the paper is to provide an overview of the representation of the precipitation characteristics and their projected changes over the greater Alpine domain within a Coordinated Regional Climate Downscaling Experiment Flagship Pilot Study and the European Climate Prediction system project, tasked with investigating convective processes at the kilometer scale. An ensemble of 12 simulations performed by different research groups around Europe is analyzed. The simulations are evaluated through comparison with high resolution observations while the complementary ensemble of 12 km resolution driving models is used as a benchmark to evaluate the added value of the convection-permitting ensemble. The results show that the kilometer-scale ensemble is able to improve the representation of fine scale details of mean daily, wet-day/hour frequency, wet-day/hour intensity and heavy precipitation on a seasonal scale, reducing uncertainty over some regions. It also improves the representation of the summer diurnal cycle, showing more realistic onset and peak of convection. The kilometer-scale ensemble refines and enhances the projected patterns of change from the coarser resolution simulations and even modifies the sign of the precipitation intensity change and heavy precipitation over some regions. The convection permitting simulations also show larger changes for all indices over the diurnal cycle, also suggesting a change in the duration of convection over some regions. A larger positive change of frequency of heavy to severe precipitation is found. The results are encouraging towards the use of convection-permitting model ensembles to produce robust assessments of the local impacts of future climate change.

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Modelling the impact of a La Niña event on a South West Pacific Lagoon     

Fuchs R  Dupouy C  Douillet P  Caillaud M  Mangin A  Pinazo C 《Marine pollution bulletin》2012,64(8):1596-1613

In view of increasing environmental awareness and biodiversity conservation, understanding the main forcing mechanism driving biogeochemical cycles in coral reefs and lagoon coastal areas is a priority. La Ni?a events cause unbalanced situations in the Equatorial Pacific and result in enhanced precipitation in South West Pacific coastal areas. We investigated the impact of heavy rainfalls during the 2008 La Ni?a event on the New Caledonia lagoon using a 3D coupled on-line hydrodynamic-biogeochemical model. Simulations and data showed that the whole lagoon was impacted by river inputs and stronger hydrodynamics, enhancing chlorophyll-a concentration by a factor between 1.7 and 1.9. The coupled model provided new insights into plume transport, highlighting that eastern plumes can be advected northwards or can reach the South West Lagoon, depending on the balance between regional, tide-induced, and wind-induced surface currents. It also provided a synoptic view of lagoon biogeochemical-hydrodynamic response, when remote sensing data are not available due to cloud coverage.  相似文献