Onset of Convection,Heat Flow and Thickness of the Europa‘s ice Shell     

Ruiz  Javier 《Earth, Moon, and Planets》1997,77(2):99-104

The observational evidence given by Galileo spacecraft about Europa supports an icy rigid layer of several kilometers over another ductile layer of ice in convection, which floats over an internal ocean of liquid water. Before the onset of convection, heat is transmitted into the crust by conduction. The heat flow analysis in the potentially convective layer gives values higher than those obtained previously by tidal dissipation models, and suggests that the ice may be limited to a thin layer of ∼4 km total thickness. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Near Infrared Spectra of two Asteroids with low Tisserand Invariant     

Julie Ziffer  Humberto Campins  Javier Licandro  Noemi Pinilla-Alonso  Yanga Fernandez  Schelte J. Bus 《Earth, Moon, and Planets》2005,97(3-4):203-212

We present near infrared reflectance spectra from 0.8 to 2.5 μm of two asteroids with low Tisserand invariant, 1373 Cincinnati and 2906 Caltech. We compare our spectra with cometary nuclei and other asteroids in their class. Asteroids Cincinnati and Caltech have Tisserand invariant values of 2.72 and 2.97, respectively, values less than 3 are considered suggestive of cometary origin. The observed spectral slopes in the near-infrared are consistent with both the spectra of cometary nuclei and of primitive asteroids. However, both asteroids have features in the near-infrared that are not seen in cometary nuclei, but are present in other X-type asteroids. 1373 Cincinnati has a sharp slope change between 0.75 and 1.0 μm and 2906 Caltech has a broad and shallow absorption between 1.35 and 2.2 μm. Our attempts to model the visible and near-infrared spectrum of these two objects, with the components successfully used by Emery and Brown (2004, Icarus 164, 104–121) to fit Trojan asteroids, did not yield acceptable fits.Visiting Astronomer at the Infrared Telescope Facility, which is operated by the University of Hawaii under contract to the National Aeronautics and Space Administration.  相似文献   

Using SHRIMP zircon dating to unravel tectonothermal events in arc environments. The early Palaeozoic arc of NW Iberia revisited     

Jacobo Abati  Pedro Castieiras  Ricardo Arenas  Javier Fernndez‐Surez  Juan Gmez Barreiro  Joseph L. Wooden 《地学学报》2007,19(6):432-439

Abstract Dating of zircon cores and rims from granulites developed in a shear zone provides insights into the complex relationship between magmatism and metamorphism in the deep roots of arc environments. The granulites belong to the uppermost allochthonous terrane of the NW Iberian Massif, which forms part of a Cambro‐Ordovician magmatic arc developed in the peri‐Gondwanan realm. The obtained zircon ages confirm that voluminous calc‐alkaline magmatism peaked around 500 Ma and was shortly followed by granulite facies metamorphism accompanied by deformation at c. 480 Ma, giving a time framework for crustal heating, regional metamorphism, deformation and partial melting, the main processes that control the tectonothermal evolution of arc systems. Traces of this arc can be discontinuously followed in different massifs throughout the European Variscan Belt, and we propose that the uppermost allochthonous units of the NW Iberian Massif, together with the related terranes in Europe, constitute an independent and coherent terrane that drifted away from northern Gondwana prior to the Variscan collisional orogenesis.  相似文献   

Pyrolisis of phosphorylated molecules and survivability limits during the atmospheric passage in earth-like planets     

Vicente Marcano  Javier Campins  Cesyen Cedeño  Ernesto Palacios-Prü 《Planetary and Space Science》2004,52(7):613-621

There is evidence that space energy sources could give place to the appearance of phosphorylated nucleosides outside of Earth. These compounds may have been delivered mainly by interplanetary dust particles due to the lower temperatures experienced during atmospheric deceleration and impacts to the terrestrial surface. In this report, we communicate the results of pyrolytic studies to simulate atmospheric survivability of adenosine-5′-diphosphates (ADP) (and adenosine-5′-monophosphate, adenosine and adenine as degradation products) at temperatures <500°C and at various time intervals. Our results revealed that phosphorylated and non-phosphorylated nucleosides transported by IDPs having sizes of 10⁻⁶- could resist temperatures up to 500°C generated during atmospheric entry. However, atmospheric passage should not exceed a time due to the thermal lability of these molecules. Because of the high half-life showed by ADP in the presence of meteoritic powder, it is thought that extraterrestrial delivery of very complex biomolecules is more suitable under such protected conditions. These data indicate that the formation of a Fe²⁺- and/or Ca²⁺-complex could increase the stability of the molecules in the presence of meteoritic matter. Therefore, if the synthesis of nucleosides, nucleotides or oligonucleotides could take place in icy bodies, then micron-sized dust could have contributed significantly to the availability of phosphorylated nucleosides in the early Earth or in extrasolar early Earth-like planets, and thereby could have allowed the arising of an early biological activity.  相似文献   

Modeling of smectite illitization in burial diagenesis environments     

Javier Cuadros 《Geochimica et cosmochimica acta》2006,70(16):4181-4195

The kinetics of smectite illitization in shale samples from eight wells have been modeled using the equation −dS/dt = kK^0.25S⁵ [Cuadros, J., Linares J., 1996. Experimental kinetic study of the smectite-to-illite transformation. Geochim. Cosmochim. Acta60, 439-453], where S is the proportion of smectite layers in illite-smectite (I-S), t is time, k is the rate constant and K is the concentration of potassium. The I-S compositions and the physical parameters were obtained from the literature. Potassium concentration is the only unknown parameter and it was chosen to fit the experimental data. I propose that this variable is termed “effective K concentration,” as it is affected not by the actual K concentration alone but also by those of other cations that compete with K for the smectite interlayer sites, especially Ca, by ion mobility in the sediments and possibly by other variables. The kinetic equation allows an accurate fit to the experimental data in all the wells, reproducing both the illitization onset and the patterns of the plots of % smectite vs. depth. The relative changes of the values of “effective K concentration” compare well with K/Ca equivalent ratios in the whole rock. Three of the modeled wells, located in near proximity, produced similar “effective K concentration” patterns. These results support the validity of the equation used in the models. They also suggest that this equation can be used to assess K concentrations in sediments and K mobility within basins.  相似文献   

利用遥感技术建立墨西哥热带地上生物量模型(英文)     

AGUIRRE-SALADO Carlos Arturo  TREVIO-GARZA Eduardo Javier  AGUIRRE-CALDERóN Oscar Alberto  JIMéNEZ-PéREZ Javier  GONZáLEZ-TAGLE Marco Aurelio  VALDEZ-LAZALDE José René  MIRANDA-ARAGóN Liliana  AGUIRRE-SALADO Alejandro Iván 《地理学报(英文版)》2012,22(4):669-680

Spatially-explicit estimation of aboveground biomass(AGB) plays an important role to generate action policies focused in climate change mitigation,since carbon(C) retained in the biomass is vital for regulating Earth’s temperature.This work estimates AGB using both chlorophyll(red,near infrared) and moisture(middle infrared) based normalized vegetation indices constructed with MCD43A4 MODerate-resolution Imaging Spectroradiometer(MODIS) and MOD44B vegetation continuous fields(VCF) data.The study area is located in San Luis Potosí,Mexico,a region that comprises a part of the upper limit of the intertropical zone.AGB estimations were made using both individual tree data from the National Forest Inventory of Mexico and allometric equations reported in scientific literature.Linear and nonlinear(expo-nential) models were fitted to find their predictive potential when using satellite spectral data as explanatory variables.Highly-significant correlations(p = 0.01) were found between all the explaining variables tested.NDVI62,linked to chlorophyll content and moisture stress,showed the highest correlation.The best model(nonlinear) showed an index of fit(Pseudo-r2) equal to 0.77 and a root mean square error equal to 26.00 Mg/ha using NDVI62 and VCF as explanatory variables.Validation correlation coefficients were similar for both models:lin-ear(r = 0.87**) and nonlinear(r = 0.86**).  相似文献   

Extreme climatic events in the Amazon basin   总被引：1，自引：0，他引：1  

Jose Antonio Marengo  Javier Tomasella  Wagner R. Soares  Lincoln M. Alves  Carlos A. Nobre 《Theoretical and Applied Climatology》2012,107(1-2):73-85

During 2009 the Amazon basin was hit by a heavy flooding with a magnitude and duration few times observed in several decades. Torrential rain in northern and eastern Amazonia during the austral summer of 2008–2009 swelled the Amazon River and its tributaries. By July 2009, water levels of the Rio Negro, a major Amazon tributary, reached at Manaus harbor a new record, the highest mark of the last 107?years. During the 2008–2009 hydrological year, the rainy season on northern and northwestern Amazonia started prematurely, and was followed by a longer-than-normal rainy season. An anomalously southward migration of the ITCZ during May–June 2009, due to the warmer than normal surface waters in the tropical South Atlantic, was responsible for abundant rainfall in large regions of eastern Amazonia and Northeast Brazil from May to July 2009. We also compared the flood of 2009 with other major events recorded in 1989 and 1999. The hydrological consequences of this pattern were earlier than normal floods in Amazon northern tributaries, which peak discharges at their confluences with the main stem almost coincided with the peaks of southern tributaries. Since the time displacement of the contribution to the main stem of northern and southern Amazon tributaries is fundamental for damping flood waves in the main stem, the simultaneous combinations of peak discharges of tributaries resulted in an extreme flood.  相似文献   

From brightening to dimming in sunshine duration over the eastern and central Tibetan Plateau (1961–2005)     

Qinglong You  Shichang Kang  Wolfgang-Albert Flügel  Arturo Sanchez-Lorenzo  Yuping Yan  Jie Huang  Javier Martin-Vide 《Theoretical and Applied Climatology》2010,101(3-4):445-457

The Tibetan Plateau (TP) with an average elevation of over 4,000 m asl is the highest and most extensive highland in the world. We used monthly mean sunshine duration from the Chinese Meteorological Administration to examine the spatial and temporal variability of sunshine duration at 71 stations with elevations above 2,000 m asl in the eastern and central TP during the 1961–2005 period. The temporal evolution of the mean annual sunshine duration series shows a significant increase from 1961 to 1982 at a rate of 49.8 h/decade, followed by a decrease from 1983 to 2005 at a rate of ?65.1 h/decade, with an overall significant decrease at a rate of ?20.6 h/decade during the whole 1961–2005 period, which is mainly due to the summer and spring seasons. This confirms the evidence that sunshine duration in the TP ranges from brightening to dimming in accordance with sunshine duration trends in the rest of China. The surface solar radiation downwards from ERA-40 reanalysis data in the same region confirms the brightening/dimming phenomenon shown by the sunshine duration before/after the 1980s. Otherwise, additional climatic variables such as low cloud amount, total cloud amount, precipitation, relative humidity and water vapor pressure, in most cases, exhibit significant negative correlation with sunshine duration in the TP on an annual and seasonal basis before and after 1982, respectively. The trends of these variables suggest that changes in some of them might be related to the brightening and dimming detected with the use of sunshine duration measurements over the TP. We also hypothesize that the impact of anthropogenic aerosols upon the climatic variables analyzed cannot be rejected, especially in the significant increase in low cloud cover since approximately 1980.  相似文献   

Impacts of warm and cold situations in the Mediterranean basins on the West African monsoon: observed connection patterns (1979–2006) and climate simulations     

Bernard Fontaine  Javier Garcia-Serrano  Pascal Roucou  Belen Rodriguez-Fonseca  Teresa Losada  Fabrice Chauvin  Sébastien Gervois  Sivarajan Sijikumar  Paolo Ruti  Serge Janicot 《Climate Dynamics》2010,35(1):95-114

Using both empirical and numerical ensemble approaches this study focuses on the Mediterranean/West African relationship in northern summer. Statistical analyses utilize skin temperature, sea surface temperature, in situ and satellite rainfall, outgoing longwave radiation (OLR) observations and reanalyzed data winds and specific humidity on isobaric surfaces. Numerical investigations are based on a large set of sensitivity experiments performed on four atmospheric general circulation models (AGCM): ARPEGE-Climat3, ECHAM4, LMDZ4 and UCLA7.3. Model outputs are compared to observations, discussed model by model and with an ensemble (multi-model) approach. As in previous studies the anomalous Mediterranean warm events are associated with specific impacts over the African monsoon region, i.e., a more intense monsoon, enhanced flux convergence and ascendances around the ITCZ, a strengthening of low level moisture advection and a more northward location of ascending motion in West Africa. The results show also new features (1) thermal variability observed in the two Mediterranean basins has unalike impacts, i.e. the western Mediterranean covaries with convection in Gulf of Guinea, while the eastern Mediterranean can be interpreted as Sahelian thermal-forcing; (2) although observations show symmetry between warming and cooling, modelling evidences only support the eastern warming influence; (3) anomalous East warm situations are associated with a more northward migration of the monsoon system accompanied by enhanced southwertely flow and weakened northeasterly climatological wind; (4) the multi-model response shows that anomalous East warm surface temperatures generate an enhancement of the overturning circulation in low and high levels, an increase in TEJ (Tropical Eeasterly Jet) and a decrease in AEJ (African Eeasterly Jet).  相似文献   

Gas kinematics in the halo of the warm ULIRG PKS1345+12     

Javier Rodríguez Zaurín  Joanna Holt  Clive N. Tadhunter  Rosa M. González Delgado 《Astrophysics and Space Science》2009,324(2-4):225-229

We use long-slit spectra taken with the William Herschel Telescope on La Palma and high-resolution Hubble Space Telescope imaging to study the gas kinematic in the halo of the ultraluminous infrared/radio galaxy PKS1345+12 (z=0.122). Our long-slit spectra show line splitting at the locations of massive star clusters ( $10^{6}<M_{\mathrm{SSC}}^{\mathrm{YSP}}<10^{7}$ M_⊙), indicating that they are moving at up to 450 km?s^?1 with respect to the local ambient gas. Given their kinematics, it is plausible that these super star clusters have been formed either in fast-moving gas streams or tidal tails that are falling back into the nuclear regions as part of the merger process, or as a consequence of jet-induced star formation linked to the extended, diffuse radio emission detected in the halo of the galaxy.  相似文献