Experimental study of the sublimation of ice through an unconsolidated clay layer: Implications for the stability of ice on Mars and the possible diurnal variations in atmospheric water     

Vincent Chevrier  Daniel R. Ostrowski 《Icarus》2008,196(2):459-476

We have studied the sublimation of ice and water vapor transport through various thicknesses of clay (<63 μm grain size). We experimentally demonstrate that both adsorption and diffusion strongly affect the transport of water, and that the processes of diffusion and adsorption can be separately quantified once the system comes to a steady state. At shallow depths of clay, water vapor transport is determined by diffusion through both the atmosphere and the clay layer, whereas at greater depth the rate of sublimation of the ice is governed only by diffusion through the clay. Using two different models, we determine the diffusion coefficient for water vapor through unconsolidated clay layer to be 1.08±0.04×¹⁰⁻⁴ and . We also determined the adsorption isotherms for the clay layer, which follow the Langmuir theory at low water vapor pressure (<100 Pa, where a monolayer of water molecules forms on the surface of the clay) and the BET theory at higher pressure (where multiple water layers form). From our analysis of both types of isotherms we determined the adsorption constants to be and c=30±10, respectively, and specific surface areas of 1.10±0.2×¹⁰⁵ and , respectively. Finally, we report a theoretical kinetic model for the simultaneous diffusion and adsorption from which we determine adsorption kinetic constants according to the Langmuir theory of and . If the martian regolith possesses diffusive properties similar to those of the unconsolidated montmorillonite soil we investigated here, it would not represent a significant barrier to the sublimation of subsurface ice. However, at the low subsurface temperatures of high latitude (180 K on average), ice could survive from the last glaciation period (about 300 to 400,000 years ago). Higher subsurface temperatures in the equatorial regions would prevent long-timescale survival of ice in the shallow subsurface. In agreement with previous work, we show that adsorption of water by a clay regolith could provide a significant reservoir of subsurface water and it might account for the purported diurnal cycle in the water content of the atmosphere.  相似文献   

归一化水汽指数与地表温度的关系   总被引：7，自引：4，他引：3  

钱乐祥  崔海山 《地理研究》2008,27(6):1358-1367

城市热岛的遥感研究,传统上主要利用归一化植被指数作为指标来评估地表温度-植被之间的关系。本研究探讨了以归一化水汽指数作为评估其与地表温度关系的适应性,比较了归一化水汽指数和归一化植被指数在表达城市热岛效应方面的效力。利用"单窗算法"和3个不同时段的TM/ETM+数据获取了珠江三角洲核心区域的地表温度分布图,分析了两种指数与地表温度之间的关系。对局部区域逐像元和对区域总体分析的结果表明:不同时段的地表温度与归一化水汽指数之间均存在较强的线性关系,而地表温度与归一化植被指数之间的线性关系相对较弱。说明在城市化的环境下,与传统上常用归一化植被指数作为指标来定量分析地表温度相比,归一化水汽指数提供了一种互补的、甚至更加有效的衡量指标。  相似文献   

雨雪冰冻天气多普勒雷达产品特征   总被引：4，自引：2，他引：2  

沈永生  杨远航  章达华  游火龙  杨希 《气象科技》2010,38(2):189-192

2008年1月下旬至2月上旬福建省西部北部出现了历史罕见的雨雪冰冻灾害。利用多普勒雷达反射率、回波顶高、径向速度、垂直风廓线等产品对此次雨雪冰冻天气进行特征分析,通过分析发现:①冰晶和雪的回波强度通常比连续性降水回波弱,在反射率图上,回波表现为边缘毛松,丝缕状纹理结构明显,边缘模糊不清,没有确定的边界;②回波顶高和零度层较低,因为垂直方向大气相对较稳定,不利于对流发展,降水粒子没有发展到高空;③在径向速度图上存在牛眼,说明在低空有急流存在。在低层有环形的零速度线,中高层的零速度线为倒"S"形,表明低层有风切变存在,中高层有冷平流;④风廓线图上高层为西南风,中层为西北风,低层为西南风,近地层为东北风。说明从近地层到高层为"冷-暖-冷-暖"的层结结构,有利于冻雨天气形成。  相似文献   

Relationship Between the Number of Summer Typhoons Engendered over the Northwest Pacific and South China Sea and Main Climatic Conditions in the Preceding Winter and Spring          下载免费PDF全文

XIAO Ziniu  LIANG Hongli  LI Chongyin 《Acta Meteorologica Sinica》2010,24(4):441-451

Based on the monthly NCEP/NCAR reanalysis data, OLR (outgoing longwave radiation) data, and tropical cyclone data from the Typhoon Annual and Tropical Cyclone Annual edited by China Meteorological Administration, the relationship between the number of tropical cyclones (with the strongest wind ≥17 m s-1, including tropical storm, strong tropical storm, and typhoon, simply called typhoon in this paper)engendered over the Northwest Pacific and South China Sea in summer and the associated climate conditions is studied. First, the characteristics and di?erences of the climatic conditions between the years with more typhoons and those with fewer typhoons are compared. The results show that the summer typhoon has a close relationship with SST (sea surface temperature) and ITCZ (intertropical convergence zone) anomalies in the preceding winter and spring. With a La Niena like SST anomaly (SSTA) pattern in the preceding winter and spring, the ITCZ will move northwestward and be enhanced around 160°E in the equatorial central Pacific from the preceding winter to spring.The activity of the Pacific ITCZ is in general stronger and its location is more northward than usual, especially in the typhoon genesis region in West Pacific. This background is propitious to have more typhoons in summer. On the other hand, an El Nieno like SSTA pattern in the preceding winter will be companied with weaker ITCZ activities, and its location is more southward over the equatorial western Pacific from the preceding winter to spring; this background is propitious to have fewer typhoons in summer. In the year with more typhoons, the warm SST over West Pacific in the preceding winter provides a favorable condition for typhoon fromation in the following summer. It enhances the convergence in the troposphere and increases the water vapor supply to the warm SST region. In the following spring, the perturbation of the tropical ITCZ plays a more important role.When the ITCZ moves northward in spring, anomalous convergence will appear over the warm SST region and inspire the positive feedback between the large-scale moisture flux at low levels and the latent heat release in the atmosphere, which benefits the typhoon genesis in summer. Otherwise, if cold SST maintains over the northwestern Pacific during the preceding winter and spring, the convergence in the troposphere is disfavored and the water vapor supply to the cold SST region is reduced, which will bring about weaker ITCZ activities and the perturbation is lacking in the following spring. It then results in fewer summer typhoons.  相似文献   

基于TVDI的西藏地区旱情遥感监测   总被引：2，自引：0，他引：2  

扎西央宗  杨秀海  边巴次仁  胡豪然  卓玛 《气象科技》2010,38(4):495-499

西藏大部分地区属干旱或重干旱区,干旱发生较为频繁,是影响农牧业生产最严重的灾害之一。文章利用拉萨接收站的中分辨率成像光谱仪(MODIS)资料提取的归一化植被指数(NDVI)和地表温度(ST),构建ST-IND-VI特征空间,依据该特征空间设计的温度植被旱情指数作为旱情指标,找出适合该地区的旱情判别模式,以2005～2008年6～7月同时段西藏地区卫星资料、气象旱情监测结果以及土壤相对湿度观测数据为例,进行旱情对比分析。结果表明,利用温度植被旱情指数(TVDI)法对西藏地区进行夏季干旱动态监测是可行的。  相似文献   

我国地面气温参考站点遴选的依据、原则和方法   总被引：17，自引：0，他引：17  

任国玉  张爱英  初子莹  周江兴  任玉玉  周雅清 《气象科技》2010,38(1):78-85

由于城市化和观测环境变化的影响,我国现有国家级气象台站网观测的地面气温资料许多已不能满足气候变化检测研究的要求。利用我国全部气象观测站网的台站信息,对地面气温资料序列质量进行了系统评价,遴选出可用于气温变化研究的参考站点。这项工作建立了地面气温参考站点遴选的原则、方法和步骤,并据此确定了138个地面气温参考站。这些台站可代表背景地面气温场,其长期气温观测资料可用作城市台站或国家级台站城市化增温评价的参考,也可直接用于我国地面气温变化的检测分析。  相似文献   

基于MODIS的珠江三角洲地区区域热岛的分布特征   总被引：7，自引：2，他引：5  

饶胜  张惠远  金陶陶  窦浩洋 《地理研究》2010,29(1):127-136

通过MODIS地温数据,研究了珠三角地区由于快速的城市化过程造成的区域性大范围温度升高现象,即"区域"热岛现象。分析结果表明,MODIS数据能够较好地反映出区域城市化进程中区域地表热环境的变化。不同下垫面的温度差异是形成区域热岛的基础。在大规模连片的城市化过程中,城镇用地的周边区域受到温度升高的影响,地表温度也相应升高,从而造成了区域大面积的温度升高,形成了区域热岛。从空间形态看,区域热岛的空间格局与城镇用地的空间布局具有较高的相关性,大城市或城市连绵区往往是区域热岛的中心。城市连绵区及其周边区域的热岛现象十分明显,而位于研究区的西南和东北方位的城镇分布比较分散,对应的区域热岛现象并不显著。  相似文献   

汶川地震地表破裂面形貌特征   总被引：1，自引：0，他引：1  

魏占玉  石峰  高翔  徐长鹏  何宏林 《地学前缘》2010,17(5):53

准确描述破裂面形貌对于我们理解地震断层作用是非常重要的,破裂面的形貌特征包含许多关于地震和断层机制的有用信息。在Mw7.9 2008汶川地震中断层活动产生了两个新鲜的破裂面,八角庙破裂面和沙坝破裂面。我们使用3D便携式激光扫描仪(Tri mble GX)对两个破裂表面进行测量,在野外微观尺度上研究了破裂面形貌特征。通过能谱密度和均方值两个方法分析破裂面形貌,新鲜的破裂面表现为自相仿性,能谱密度和均方值均与剖面长度存在幂律关系。在能谱密度与空间频率的对数图中,能谱密度曲线存在明显的拐点,该拐点所对应的波长称为"特征波长",表明单一分形不能准确描述破裂面形貌。八角庙破裂面在平行滑动方向上的特征波长为7 mm,在垂直方向上特征波长略大一些(区域Ⅰ为10 mm,区域Ⅱ为9 mm);沙坝破裂面在平行滑动方向上的特征波长为8 mm,但垂直方向上特征波长略小(6 mm)。均方值曲线的最小二乘拟合直线的斜率为Hurst指数,该指数依赖于剖面线方向并描述破裂面形貌的各向异性,H指数的最小值和最大值分别与平行擦痕和垂直擦痕方向对应,这与野外断层面擦痕测量结果一致。沙坝破裂面的H指数极坐标图中存在次级H指数峰值(对应剖面线方向为85°和160°),这揭示破裂面上存在一组隐匿擦痕。该组隐匿擦痕为汶川地震之前断层活动中形成的,但这还不足以推测上一次断层活动的时间和规模。另外,通过比较新鲜节理面和破裂面表明H指数是否大于0.8反映了断层类型。在整个空间频率域上,能谱密度曲线斜率(-α)和均方值曲线斜率(H)的线性拟合关系为α=1.22+1.72H,并不严格满足两者之间理论关系式,α=1+2H。这个差异是由于测量信号噪音、破裂面的多分形性和分析方法的差异造成的。  相似文献   

青藏高原典型地区的地貌量化分析——兼对高原“夷平面”的讨论   总被引：17，自引：0，他引：17  

刘静  丁林  曾令森  Paul TAPPONNIER  Yves GAUDEMER 《地学前缘》2006,13(5):285-299

利用新近公布的SRTM数字高程模型(DEM),选取青藏高原北部及高原内、外流区域进行大尺度定量地貌分析。分析表明,青藏高原不同地区的地貌差异反映了它们在地貌演化上的阶段性。在高原北部的祁连山地区,局部地区绝对高程增加的同时,地势起伏反而变缓。这些地区水系的发育程度普遍较低,剥蚀物质往往只经过近距离的搬运仍滞留在逆冲褶皱带内,山间盆地和平地成为山间小河的侵蚀堆积基准,因此“削高填低”的过程有效地降低了局部地形起伏。高原平坦地势是伴随着造山过程及之后的高海拔侵蚀基准和内流型水系条件下“削高填低”剥蚀过程的结果。我们认为高原内部为现今仍在承受剥蚀的地势平坦面。它的形成具穿时性,是内流型水系河流下切侵蚀能力弱化的结果,不直接反映海拔的高低。如果平坦侵蚀面的形成与海拔高程无必然的关联,或侵蚀面可以在任何海拔高度形成,而不一定代表以海平面为基准的准平原,那么它就不能作为一个可靠的参照面用于直接示踪和约束高原的抬升量和抬升时间。  相似文献   

共反射面叠加在实际地震资料处理中的应用   总被引：1，自引：2，他引：1  

覃天  王拥军  高峰昌  张联盟 《物探与化探》2006,30(4):330-333

共反射面叠加方法运用3个地震波场参数来描述地下反射面元时距关系,不对地下反射界面形状做任何假设,并且是一种不依赖于宏观速度模型的反射波成像方法。共反射面叠加利用了邻近多个共反射点道集的相似性,提高了资料的覆盖次数,从而压制了随机噪声,增强反射波同相轴的连续性,大幅提高了地震资料的信噪比。通过在实际地震资料处理中的应用,证明了该方法的这些特性。  相似文献