Sublimation of the Martian CO₂ Seasonal South Polar Cap     

Frédéric Schmidt  Bernard Schmitt  Francois Forget  Patrick Martin  Jean-Pierre Bibring  the OMEGA Team 《Planetary and Space Science》2010,58(10):1129-1138

The polar condensation/sublimation of CO₂, that involve about one fourth of the atmosphere mass, is the major Martian climatic cycle. Early observations in visible and thermal infrared have shown that the sublimation of the Seasonal South Polar Cap (SSPC) is not symmetric around the geographic South Pole.Here we use observations by OMEGA/Mars Express in the near-infrared to detect unambiguously the presence of CO₂ at the surface, and to estimate albedo. Second, we estimate the sublimation of CO₂ released in the atmosphere and show that there is a two-step process. From Ls=180° to 220°, the sublimation is nearly symmetric with a slight advantage for the cryptic region. After Ls=220° the anti-cryptic region sublimation is stronger. Those two phases are not balanced such that there is 22% ± 9 more mass the anti-cryptic region, arguing for more snow precipitation. We compare those results with the MOLA height measurements. Finally we discuss implications for the Martian atmosphere about general circulation and gas tracers, e.g. Ar.  相似文献   

确定数值预报模式中扩散系数的一个客观方法     

朴景辰  邹晓蕾 《南京气象学院学报》2009,32(3):339-350

当数值预报模式的分辨率得到提高时,模式中扩散系数的数值大小必然随之改变。通常情况下,一方面,扩散系数的数值应足够大（即有下限值）,以便过滤掉模式中不想要的小尺度噪音;另一方面,扩散系数的数值应尽量小（即有上限值）,以免出现计算不稳定。本文提出一种确定高分辨率模式中扩散系数数值大小的客观方法,即＂双试验＂（twin experiment）同化方法（初始低分辨率模式的预报结果作为＂观测资料＂,新的高分辨率模式作为同化模式）,从而通过伴随变分同化方法来确定控制变量（即扩散系数）的数值大小。本文采用一维浅水模式测试和描述上述试验方案。通过低分辨率模式预报结果和高分辨率模式预报结果的比较（高、低分辨率模式预报结果的比较在低分辨率模式格点上进行）,采用最小二乘法可客观求得适用于高分辨率模式的扩散系数的＂最优＂值。数值试验结果表明,采用这种方法得到的高分辨率模式的扩散系数,不仅能过滤掉模式中不想要的小尺度噪音,而且能够避免出现计算不稳定。研究还指出,当扩散系数的大小略微超过其上限值时（这种情况在极小化迭代中有可能会出现）,计算不稳定的出现将使目标函数的数值迅速增加,并导致极小化程序收敛的失败;时间步长的减小（约20%）可以显著地改进目标函数的条件数,从而可避免极小化程序收敛的失败。  相似文献   

The Arctic Ocean—a Canadian perspective from IPY     

H. Melling  R. Francois  P. G. Myers  W. Perrie  A. Rochon  R. L. Taylor 《Climatic change》2012,115(1):89-113

Canada??s IPY program funded seven marine projects spanning the North American Arctic. Work embraced oceanography, air-sea interactions, storm response, paleo-climate and trace-element chemistry. Notable findings are emerging. Conditions in the Beaufort were unusual in 2007, with very high air pressure bringing strong winds, rapid ice drift, thin winter ice, enhanced shelf-break upwelling and a maximum in freshwater retention in the Beaufort Gyre. A mapping of trace chemicals suggests that Arctic mid-depth circulation may also have reversed. Study of Canadian Arctic through-flow revealed a net annual seawater export of 44,000 cubic kilometres from the Arctic to Baffin Bay. Observations of sea ice, sustained through the IPY, affirmed that ice cover is the key attribute of Arctic seas, with wind as a potent agent in its variation. Surveys have shown that the anthropogenic decline in seawater alkalinity is aggravated in the Arctic by low temperature and low salinity resulting from ice melt. Careful experiments have revealed that Arctic phytoplankton growth is constrained by scarcity of dissolved iron where light levels are low. A manganese fingerprint in sediments has tracked changing sea level during the Ice Age. Sediment-core analysis has revealed the Arctic Oscillation as a dominant cause of long-period climate variations during the Holocene. One project has demonstrated how multi-tasked vessels can maintain a watch on Canada??s Arctic within a reliable affordable logistic framework, while a wave forecast model developed by another for the Beaufort is suitable for operational use.  相似文献   

Differentiation and crystallization conditions of basalts from the Kerguelen large igneous province: an experimental study   总被引：2，自引：2，他引：0  

Marcus Freise  Francois Holtz  Marcus Nowak  James S. Scoates  Holger Strauss 《Contributions to Mineralogy and Petrology》2009,158(4):505-527

Phase relations of basalts from the Kerguelen large igneous province have been investigated experimentally to understand the effect of temperature, fO₂, and fugacity of volatiles (e.g., H₂O and CO₂) on the differentiation path of LIP basalts. The starting rock samples were a tholeiitic basalt from the Northern Kerguelen Plateau (ODP Leg 183 Site 1140) and mildly alkalic basalt evolved from the Kerguelen Archipelago (Mt. Crozier on the Courbet Peninsula), representing different differentiation stages of basalts related to the Kerguelen mantle plume. The influence of temperature, water and oxygen fugacity on phase stability and composition was investigated at 500 MPa and all experiments were fluid-saturated. Crystallization experiments were performed at temperatures between 900 and 1,160°C under oxidizing (log fO₂ ~ ΔQFM + 4) and reducing conditions (log fO₂ ~ QFM) in an internally heated gas-pressure vessel equipped with a rapid quench device and a Pt-Membrane for monitoring the fH₂. In all experiments, a significant influence of the fO₂ on the composition and stability of the Mg/Fe-bearing mineral phases could be observed. Under reducing conditions, the residual melts follow a tholeiitic differentiation trend. In contrast, melts have high Mg# [Mg²⁺/(Mg²⁺ + Fe²⁺)] and follow a calk-alkalic differentiation trend at oxidizing conditions. The comparison of the natural phenocryst assemblages with the experimental products allows us to constrain the differentiation and pre-eruptive conditions of these magmas. The pre-eruptive temperature of the alkalic basalt was about 950–1,050°C. The water content of the melt was below 2.5 wt% H₂O and strongly oxidizing conditions (log fO₂ ~ ΔQFM + 2) were prevailing in the magma chamber prior to eruption. The temperature of the tholeiitic melt was above 1,060°C, with a water content below 2 wt% H₂O and a log fO₂ ~ ΔQFM + 1. Early fractionation of clinopyroxene is a crucial step resulting in the generation of silica-poor and alkali-rich residual melts (e.g., alkali basalt). The enrichment of alkalis in residual melts is enhanced at high fO₂ and low aH₂O.  相似文献   

Diagenesis and fluid system evolution in the Northern Oman Mountains,United Arab Emirates     

Liesbeth Breesch  Rudy Swennen  Benoit Vincent  Francois Roure  Richard Ellison 《Journal of Geochemical Exploration》2009

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Mercury exosphere I. Global circulation model of its sodium component     

Francois Leblanc  R.E. Johnson 《Icarus》2010,209(2):280-300

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Detailed seismic stratigraphy of Lago Puyehue: implications for the mode and timing of glacier retreat in the Chilean Lake District     

Katrien Heirman  Marc De Batist  Francois Charlet  Jasper Moernaut  Emmanuel Chapron  Robert Brümmer  Mario Pino  Roberto Urrutia 《第四纪科学杂志》2011,26(7):665-674

Lago Puyehue is a glacigenic lake in the Chilean Lake District (40°S) with a complex deglaciation history. A detailed seismic–stratigraphic study of its sedimentary infill indicates a much earlier retreat of the glacier from the Lago Puyehue basin than the neighbouring glacier from the Lago Rupanco basin. Because of their close proximity, Rupanco meltwater streams played an important part in the depositional processes of Lago Puyehue. A timing discrepancy between the in‐lake ages of a sediment core and the outer‐lake ages of moraine deposits (re)opens the discussion on the timing of deglaciation in the Southern Hemisphere. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Late Holocene high precipitation events recorded in lake sediments and catchment geomorphology,Lake Vuoksjávrátje,NW Sweden          下载免费PDF全文

Annika Berntsson  Krister N. Jansson  Malin E. Kylander  Francois De Vleeschouwer  Sebastien Bertrand 《Boreas: An International Journal of Quaternary Research》2015,44(4):676-692

In this paper, we show the potential of combining multi‐proxy analysis of lake sediments with catchment geomorphology to better understand palaeoenvironmental changes. Previous studies have suggested that alpine lakes in N Sweden may be highly sensitive to variations in catchment erosion and precipitation, and that this sensitivity may influence ecologically based reconstructions of past temperature changes. We analysed lake sediments covering the last 5100 years from the alpine Lake Vuoksjávrátje in NW Sweden in order to identify different erosional regimes in the lake catchment, sediment sources and lake sedimentary processes, which ultimately affect the palaeoecological record. The measured proxies include elemental geochemistry from XRF core scanning, grain size, sediment accumulation rates, fraction of terrestrial organic carbon and geomorphological mapping, supported by previously published chironomid and total organic carbon data. From the integrated results we identified time intervals when increased intensity of precipitation altered sedimentation and lake catchment erosional processes. The most prominent event occurred c. 2900 cal. a BP and is interpreted to be the result of excessive precipitation, possibly related to the climatic shift towards cooler and wetter conditions referred to as the 2.8 ka event.  相似文献   

Viscosity of flux-rich pegmatitic melts     

Alexander Bartels  Francesco Vetere  Francois Holtz  Harald Behrens  Robert L. Linnen 《Contributions to Mineralogy and Petrology》2011,162(1):51-60

Viscosity experiments were conducted with two flux-rich pegmatitic melts PEG0 and PEG2. The Li₂O, F, B₂O₃ and P₂O₅ contents of these melts were 1.04, 4.06, 2.30 and 1.68 and 1.68, 5.46, 2.75 and 2.46 wt%, respectively. The water contents varied from dry to 9.04 wt% H₂O. The viscosity was determined in internally heated gas pressure vessels using the falling sphere method in the temperature range 873–1,373 K at 200 and 320 MPa pressure. At 1,073 K, the viscosity of water-rich (~9 wt% H₂O) melts is in the range of 3–60 Pa s, depending on the melt composition. Extrapolations to lower temperature assuming an Arrhenian behavior indicate that highly fluxed pegmatite melts may reach viscosities of ~30 Pa s at 773 K. However, this value is a minimum estimation considering the strongly non-Arrhenian behavior of hydrous silicate melts. The experimentally determined melt viscosities are lower than the prediction of current models taking compositional parameters into account. Thus, these models need to be improved to predict accurately the viscosity of flux-rich water bearing melts. The data also indicate that Li influences significantly the melt viscosity. Decreasing the molar Al/(Na + K + Li) ratio results in a strong viscosity decrease, and highly fluxed melts with low Al/(Na + K + Li) ratios (~0.8) have a rheological behavior which is very close to that of supercritical fluids.  相似文献   

An operational model to simulate post-accidental radionuclide transfers in Toulon marine area: preliminary development   总被引：2，自引：1，他引：1  

Celine Duffa  Francois Dufois  Sylvain Coudray 《Ocean Dynamics》2011,61(11):1811-1821

As part of its development of post-accident management tools, the French Institute for Radiological Protection and Nuclear Safety is setting up a model to simulate radionuclide dispersion in the Toulon marine area (one of France’s main military ports). The model is based on the MARS 3D code developed by IFREMER. It reproduces hydro-sedimentation phenomena in the Bay of Toulon with a horizontal spatial resolution of 100 m and 30 vertical sigma levels and also factors in radioactive decay and dissolved/particulate distribution of the radionuclides studied. With no tide, the major currents in this area are generated by the wind. The model effectively reproduces the resulting hydrodynamic phenomena, which were measured throughout the summer of 2009 in the channel that links the Little Bay to the Large Bay of Toulon. When the Mistral (wind from the West/Northwest) blows, a surface current quickly appears, which pushes water southwards from the Little Bay, and which is offset by a bottom current (upwellings). When the wind blows from the East, the currents move in the opposite direction, and southeasterly waves, dependent on wind strength and fetch, occur in the Large Bay. Here, we give an example of the simulated dispersion of radionuclides released directly into the surface waters near the Arsenal, demonstrating the constraint relative to dispersion generated by the half-closed configuration of the Little Bay. Sediment in the Little Bay also forms an area where the most highly reactive radionuclides would accumulate, and where the lack of waves has the effect of considerably limiting the phenomena of resuspension.  相似文献