Distinguishing between vapor- and liquid-formed ground ice in the northern martian regolith and potential for biosignatures preserved in ice bodies     

Denis Lacelle  David Fisher 《Icarus》2008,197(2):458-469

In this study, various approaches that can potentially distinguish between vapor- and liquid-derived ground ice in the martian regolith (petrography, geochemistry, stable OH isotopes, CO₂O₂N₂Ar gas composition) are examined using terrestrial ground ice examples. Although the stable OH isotope composition ratios can distinguish between vapor- and liquid-derived terrestrial ground ice, there might be to much mixing between the various water reservoirs on Mars to effectively use it, and, like on Earth, petrographic and geochemical approaches need to be complemented with additional supporting evidences. Of the different approaches currently being employed to determine the origin of terrestrial massive ground ice and icy sediments, it is the concentration of CO₂ and the O₂/Ar, N₂/Ar and N₂/O₂ ratios of air entrapped in the ice that has proven to be the less ambiguous and most discriminatory. This is because the molar ratios of atmospheric gases change during their dissolution in water due to differences in their relative solubilities, thus providing distinctive ratios for the dissolved gases. The gas composition of air entrapped in the ice not only distinguishes between vapor- and liquid-derived ground ice, but any deviation from the theoretical dissolved values can provide insights into potential physical and biological processes operating in the subsurface, a key component for astrobiology.  相似文献   

Albedo models for the residual south polar cap on Mars: Implications for the stability of the cap under near-perihelion global dust storm conditions     

Boncho P. Bonev  Gary B. Hansen  Philip B. James 《Planetary and Space Science》2008,56(2):181-193

It is uncertain whether the residual (perennial) south polar cap on Mars is a transitory or a permanent feature in the current Martian climate. While there is no firm evidence for complete disappearance of the cap in the past, clearly observable changes have been documented. Observations suggest that the perennial cap lost more CO₂ material in the spring/summer season prior to the Mariner 9 mission than in those same seasons monitored by Viking and Mars Global Surveyor. In this paper we examine one process that may contribute to these changes—the radiative effects of a planet encircling dust storm that starts during late Martian southern spring on the stability of the perennial south polar cap. To approach this, we model the radiative transfer through a dusty planetary atmosphere bounded by a sublimating CO₂ surface.A critical parameter for this modeling is the surface albedo spectrum from the near-UV to the thermal-IR, which was determined from both space-craft and Earth-based observations covering multiple wavelength regimes. Such a multi-wavelength approach is highly desirable since one spectral band by itself cannot tightly constrain the three-parameter space for polar surface albedo models, namely photon “scattering length” in the CO₂ ice and the amounts of intermixed water and dust.Our results suggest that a planet-encircling dust storm with onset near solstice can affect the perennial cap's stability, leading to advanced sublimation in a “dusty” year. Since the total amount of solid CO₂ removed by a single storm may be less than the total CO₂ thickness, a series of dust storms would be required to remove the entire residual CO₂ ice layer from the south perennial cap.  相似文献   

极地海冰浮标的现状与应用综述          下载免费PDF全文

郭井学孙波  李群雷瑞波  李丙瑞李娜 《极地研究》2011,23(2):149-157

海冰是气候系统的一个重要组成要素,原位观测是获取海冰特征参数以及开展海冰变化研究的重要手段.本文主要对以海冰为目标和平台的极地浮标的发展与应用进行综合阐述,简述了国际北极浮标计划和国际南极浮标计划的发展情况,以七种常用的浮标对极区海冰、大气和上层海洋等物理参数的监测为例归纳总结了海冰浮标的系统特性和技术特点,最后结合近...  相似文献   

我国西北和内蒙古地区春季沙尘暴的年代际变化及原因探析   总被引：6，自引：4，他引：2  

曾淑玲  程一帆  王式功  巩崇水  尚可政 《中国沙漠》2010,30(5):1200-1206

利用1961—2005年西北及内蒙古地区208个地面气象站春季沙尘暴日数的观测资料,对沙尘暴发生的年代际变化进行了分析。结果显示,20世纪60年代和70年代沙尘暴偏多,80年代沙尘暴开始减少,90年代最少,21世纪的前5 a沙尘暴呈现出先增多后减少的趋势。基于1961—2005年的NCEP资料进行了原因探析,结果表明：①在沙尘暴多发年代,我国北方大部分区域风速出现了正距平,而在沙尘暴少发的年代,风速呈现出负距平;②在沙尘暴多发的年代,我国中高纬地区出现明显的气旋性流场距平,其南侧西风增强了我国西北及内蒙古地区偏西风风速,而在沙尘暴少发的年代,则与之相反;③极锋锋区在60—70年代强度偏强,从80年代开始强度呈现出明显的减弱趋势,21世纪初期锋区强度继续减弱,但其中心位置有小幅的自北向南移动。  相似文献   

西北太平洋: 21世纪的地理--政治枢纽   总被引：2，自引：1，他引：1  

王国梁 《世界地理研究》2002,11(2):13-19

20世纪初,英国著名地理学家麦金德在其名著《历史的地理枢纽》一书中,通过对地理大发现以后世界政治地图,尤其是欧洲政治地图变化的分析,提出了“大陆腹地”的概念,并把中、东欧地区称为国际政治的“枢纽”地区。二战以后,美、英等西方国家正是基于麦金德的这一思路,把围堵“枢纽”地区作为其全球战略的重中之重,拉开了长达半个世纪的“冷战”帷幕。冷战结束以后,世界政治地理格局发生了重大变化,西北太平洋地区以其重要的地理位置、蓬勃发展的经济和急剧增长的军备,成为国际地缘政治中新的“枢纽”地区。本文从政治军事地理角度对这一问题进行了初步研究,供关心西北太平洋地区局势的同仁参考。  相似文献   

Results of Optical Monitoring of Cataclysmic Variable GK Per in 2004     

Irina Voloshina  Valerian Sementsov 《Astrophysics and Space Science》2006,304(1-4):287-289

The preliminary results of ground-based UBV photometric and CCD observations of cataclysmic variable GK Per during the outburst in autumn of 2004 are presented.  相似文献   

Quantitative analysis of the relationship between polar ionospheric currents and auroral electrojet indices   总被引：1，自引：0，他引：1  

XU Wenyao & CHEN Gengxiong Institute of Geology  Geophysics  Chinese Academy of Sciences  Beijing  China 《中国科学D辑(英文版)》2005,48(3):376-383

Magnetic storms and substorms are principalprocesses of energy transition from the solar wind intothe magnetosphere-ionosphere system and dissipationin the system. They are also important events whichthe space physics study and space weather predictionhave been focused on. Magnetic storms are describedby means of the magnetic index Dst, which is calcu-lated using the magnetic disturbances of horizontalcomponent recorded at 5 low-latitudinal stations, rep-resenting approximately the symmetric r…  相似文献   

On the existence of an optimal control of ship automatic steering instruments     

GAOCunchen GUOJifeng 《中国海洋大学学报(英文版)》2005,4(2):185-188

The existence of linear quadratic optimal control of ship automatic steering instruments is studied. Firstly, the sufficient conditions for the quadratic integrability of the solutions of linear second order time-variant differential equations are developed. Secondly, the optimal control form of the ship automatic steering instrument is obtained by using the dynamic programming method, which guarantees a minimal ship sway range, during long-distance navigation, by using as little energy as possible. Finally, based on the above mentioned sufficient conditions, the conditions for the realization of optimal control are obtained, which provides a foundation for choosing the weighted coefficients for optimal control in engineering.  相似文献   

Central polar cap convection response to short duration southward Interplanetary Magnetic Field     

P. T. Jayachandran  J. W. MacDougall 《Annales Geophysicae》2000,18(8):887-896

Central polar cap convection changes associated with southward turnings of the Interplanetary Magnetic Field (IMF) are studied using a chain of Canadian Advanced Digital Ionosondes (CADI) in the northern polar cap. A study of 32 short duration (1 h) southward IMF transition events found a three stage response: (1) initial response to a southward transition is near simultaneous for the entire polar cap; (2) the peak of the convection speed (attributed to the maximum merging electric field) propagates poleward from the ionospheric footprint of the merging region; and (3) if the change in IMF is rapid enough, then a step in convection appears to start at the cusp and then propagates antisunward over the polar cap with the velocity of the maximum convection. On the nightside, a substorm onset is observed at about the time when the step increase in convection (associated with the rapid transition of IMF) arrives at the polar cap boundary.  相似文献   

小型船用油水分离器     

杨传祖  揣华建 《广东海洋大学学报》1992,(1)

介绍了小型船用油水分离器的工作原理,主要参数计算,影响性能的因素及装船要求。  相似文献