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1.
通过对河冰椎多年系统观测，对比分析其形成和发育，大致经过冰椎形成、发育、稳定、融化－冻结和消亡５年阶段。冰椎与稳定负温期的积温Σ－ｔ℃、土石冻（融）、空气相对湿度及水源补给形式有较高的相关性，为人工调蓄利用冰椎提供了科学依据。 相似文献
2.
Simulation of currents, ice melting, and vertical mixing in the Barents Sea using a 3-D baroclinic model 总被引：2，自引：0，他引：2
A baroclinic. 3-D model is described. It is adapted to the Barents Sea and includes thermodynamics and atmospheric input. The freezing and melting of ice is allowed for in the model. The main task of the study is to look at the development of the ice cover, the vertical mixing, and the vertical and horizontal density gradients.
Despite simple approximations in the air temperature input, realistic ice-cover is produced in the model area during simulation of a "freezing period" (winter). This intermediate result is briefly discussed and also forms the start of a "melting period" simulation (spring/summer). Atmospheric input data (wind, air pressure, and heat flux) from the spring and summer 1983 is used, and details about vertical mixing, temperature, and salinity are discussed. The simulation results demonstrate the temporal variation of the thermocline depth, the variation of the ice cover, and the horizontal changes of density. The conclusion is that despite often simplified input, the model seems to produce a physical picture characteristic of the Barents Sea. 相似文献
Despite simple approximations in the air temperature input, realistic ice-cover is produced in the model area during simulation of a "freezing period" (winter). This intermediate result is briefly discussed and also forms the start of a "melting period" simulation (spring/summer). Atmospheric input data (wind, air pressure, and heat flux) from the spring and summer 1983 is used, and details about vertical mixing, temperature, and salinity are discussed. The simulation results demonstrate the temporal variation of the thermocline depth, the variation of the ice cover, and the horizontal changes of density. The conclusion is that despite often simplified input, the model seems to produce a physical picture characteristic of the Barents Sea. 相似文献
3.
使用加拿大环北极冰间开放水道研究计划从2007年11月至2008年1月底整个极夜期间对北极阿蒙森湾的考察数据,研究了没有太阳加热条件下冰下海水的对流混合。结果表明,冬季冰下海水结构以对流混合为主要形式,混合层的深度达到数米至数十米。发生对流混合时并没有出现静力不稳定性现象,对流混合层密度小于下层水体密度,此处的对流混合不同于前人的发现,它是由于卤汁的不连续排放造成的。混合层的温度与海水的冰点非常接近,由结冰导致的密度对流所形成。跃层以下海水的温度也在持续下降,文中认为是通过跃层与上混合层交换热量导致的。在冬季的前期,混合层的厚度与混合层的盐度有很好的对应性,但晚冬两者有明显差别,混合层厚度趋于减小。通过对三个位置接近站位的观测结果表现对流混合层的演化规律,体现了对流混合层在整个冬季温度持续降低、盐度持续升高的特征。 相似文献
4.
SIMON J. COOK PETER G. KNIGHT DEBORAH A. KNIGHT RICHARD I. WALLER 《Geografiska Annaler: Series A, Physical Geography》2012,94(3):351-362
Debris in basal ice produced by glaciohydraulic supercooling is typically characterized by high proportions of silt. A prominent hypothesis for this silt‐dominance is that frazil ice growing in supercooled water preferentially traps silt from sediment‐laden water percolating through it. It has therefore been suggested that silt‐dominance may be diagnostic of glaciohydraulic supercooling. The aim of our work is to test this hypothesis that freezing sediment‐laden supercooled water necessarily produces ice dominated by silt. We do this by simulating two freezing processes under laboratory conditions: (1) percolation of sediment‐laden water through frazil ice; (2) turbulent supercooling and subsequent freezing of sediment‐laden water. In experiments repeated using different particle sizes (sand, silt and clay in individual experiments) both processes entrained sand most effectively and silt least effectively. In experiments using a sediment mixture dominated by medium to coarse silt, both processes produced ice facies dominated by particle sizes between fine sand and coarse silt. These results suggest that silt‐dominance should therefore not be expected for supercooled freeze‐on, and is not a reliable diagnostic signature for supercooling. The silt‐dominated character of basal ice types associated with supercooling may result from other controls such as a silt‐dominated sediment supply or subglacial water flow rates, rather than the freezing process. 相似文献
5.
冻融条件下土壤中水盐运移规律模拟研究 总被引：16，自引：0，他引：16
冻融作用是土壤盐碱化独特的形成机制,冻融条件下土壤中盐分迁移是水分对流、浓度梯度、温度梯度、不同溶质、土壤结构及质地等因素作用下的综合结果,温度是导致土壤中水分与盐分迁移的驱动力。在土壤冻融过程中,水分和盐分的两次迁移过程构成了特殊的水盐运动规律。在冻融过程中,土壤剖面结构发生变异,形成冻结层、似冻结层和非冻结层。冻结带土水势降低导致水分不断向冻层迁移,冻结缘以下的盐分同步向上运移,整个冻层的土壤含盐量明显增加;在融化过程中,随着地表蒸发逐渐强烈,使冻结过程中累积于冻结层中的盐分,转而向地表强烈聚集,使表层的盐分含量急剧上升。当冻结层未融通之前,尚未融化的冻层起到隔水的作用,不但阻止顶部融水向下层渗透,而且隔断了与下层水的联系。模拟实验结果充分证明了中国北方冻融区域土壤盐碱化的发生过程,为有效防治土壤盐碱化提供了理论依据。 相似文献
6.
Unidirectional freezing experiments under overburden pressure were carried out, in order to study the driving force of mois-ture migration of remodeled clay during freezing, through improving the indoo... 相似文献
7.
南极冰盖内部等时层记录了不同时期冰盖表面的特征及其演变,蕴含了丰富的冰下环境信息。目前,已成为研究大空间尺度与长时间尺度上南极冰盖演化及其底部环境的重要媒介。地球物理观测和数值模拟技术的综合使用,实现了南极冰盖内部等时层在大陆尺度上的可视化。通过这些内部等时层,冰川学研究将南极冰盖内部的古冰流与千年至百万年时间尺度的地貌及冰下环境的变化细节联系起来,得到了一系列数量化的结果。针对南极冰盖,综述产生内部等时层的冰盖动力学物理机理及其在冰川学上的应用,评估在五个方面的运用:(1)深冰芯断代与选址;(2)冰盖动力学过程;(3)冰盖物质平衡;(4)冰盖稳定性;(5)冰下环境。另外,基于对内部等时层的已有认识,对未来在内部等时层研究中可能需要强化的领域进行了归纳:(1)发展更精细描述并测试内部等时层结构时空变化的数值模拟技术框架面临的挑战;(2)如何从内部等时层蕴含的信息推断鉴别以目前南极冰盖作为初始条件的冰盖质量变化;(3)为获得更高分辨率的内部等时层结构图像,得到关于冰盖内部冰体形变与演化的更多数量化信息,如何强化冰盖冰下环境的重复观测。 相似文献
8.
Lake Kinneret (the Sea of Galilee) is a small freshwater lake (148 km2 and a mean depth of 20 m) situated in northern Israel. Throughout recent history there have been no known records of a total
ice formation on its top. Furthermore, given that convection requires an initial cooling of the entire lake down to 4 °C,
it is difficult to imagine how such a low-latitude lake, presently subject to two-digit temperatures during the winter, could
ever freeze. Lake Kinneret is, however, unique in the sense that there are dense (warm and salty) springs along its western
shore. The dynamics of the regions adjacent to these springs are investigated using a one-dimensional nonlinear analytical
ice model, a paleoceanographic record of the sea surface temperature of the Mediterranean Sea, and a statistical model. We
show that, because the water directly above the plume created by the salty springs does not convect when it is cooled down
to 4 °C, freezing of the region directly above the salty springs was possible during periods when the climate in the region
was somewhat cooler than it is today. We refer to this localized freezing situation as ‘springs ice’.
The analytical ice-model involves a slowly varying approach where the ice is part of a thin fresh and cold layer floating
on top of the salty and warm spring water below. During the ice formation process, the ice is cooled by the atmosphere above
and warmed by the spring water below. The plumes created by the springs have a length scale of 30 m, and it is argued that,
during the Younger Dryas when the air temperature in the region was probably 7 °C or more cooler than today, ‘springs ice’
(thick enough to support human weight) was formed once every 27 years or less. During the cold events 1500 and 2500 years
ago (when the atmospheric temperature was 3 °C or more lower than today) springs ice occurred about once in 160 years or less.
Since the duration of these cold events is of the same order as the springs ice recurrence time, there is a substantial chance
that at least one springs ice occurred during these cooler periods. With today's climate, the likelihood of a springs ice
is virtually zero (i.e., once in more than 10,000 years).
One set of those springs associated with the freezing is situated in Tabgha, an area where many archeological features associated
with Jesus Christ have been found. On this basis, it is proposed that the unusual local freezing process might have provided
an origin to the story that Christ walked on water. Since the springs ice is relatively small, a person standing or walking
on it may appear to an observer situated some distance away to be ‘walking on water’. This is particularly true if it rained
after the ice was formed (because rain smoothes out the ice’s surface). Whether this happened or not is an issue for religion
scholars, archeologists, anthropologists, and believers to decide on. As natural scientists, we merely point out that unique
freezing processes probably happened in that region several times during the last 12,000 years. 相似文献
9.
A coupled water and heat transport mode is established based on the Richards equation to study water flow and heat
transport in soil during freezing process. Both the finite difference and finite element method are used in the discretization,
respectively. Two different computer programs are written and used to simulate an indoor unidirectional frozen test. The
freezing depth, freezing rate and temperature variation are compared among lab tests, finite difference calculation simulation
and finite element calculation simulation. Result shows that: the finite difference method has a better performance in
freezing depth simulation while the finite element method has a better performance in numerical stability in
one-dimensional freezing simulation. 相似文献
10.
冰冻圈是气候系统重要的圈层,对气候系统有强烈的反馈作用,在全球变暖的背景下,冰冻圈的变化和预测研究愈来愈受到科学界的重视。近年来,冰冻圈的预测研究已经取得重要进展,主要表现在:海冰、积雪冻土等子系统模式发展迅速,开展了不少模式比较计划,这些模式能重现大尺度的季节变化和年际变化特征,模拟能力较以前有了大幅度提高。但模式模拟的不确定性仍普遍存在,主要表现在:冰盖等子系统的模式对于其内部的热力过程、其底部与海洋的相互作用过程缺乏有效的观测手段,认识不够清楚,湖冰河冰模式主要还依赖统计相关模型。随着遥感技术以及资料同化技术的不断应用,各个子系统物理过程认识的不断深入,冰冻圈模式预测将日趋完善,逐渐缩小不确定性。 相似文献
11.
Freezing of sediment in situ at the lake bottom using a freeze corer has become an important method for taking samples of
soft sediments aimed for detailed stratigraphic analyses. Over the past decades a variety of freeze corers have been designed,
from very simple metal tubes filled with dry ice that are dropped into the sediment to high-tech samplers using electric pumps,
hydraulics and liquid nitrogen. The freeze corer described here is a compromise of getting good samples without a too complicated
technique. It is designed for coring from lake ice, using a steel wire with a stopper on the ice to keep the corer in fixed
position during freezing. It consists of a thermos connected to a thin freeze wedge (width 15 cm, length 100 cm, max thickness
6 cm). The dry ice is kept in the thermos until the freeze wedge has been lowered into the sediment to avoid water freezing
on the wedge during descent through the water column; a wet steel-wedge surface disturbs the sediment stratigraphy less than
a wedge on which rapid freezing occurs. The dry ice is kept in the thermos by a trapdoor that is opened by a messenger. When
the trapdoor is opened the dry ice begins to drop into the wedge, which is filled with ethanol. This process continues concurrently
with the consumption of ice in the wedge until the thermos is empty. Using 6–8 kg of dry ice and 4 l of ethanol (95%), a 3-cm-thick
and up to 80-cm-long crust of frozen sediment is obtained in 20–25 min on each side of the wedge. The crust is easily detached
intact from the wedge using a small volume of hot water, poured inside the wedge. 相似文献
12.
Yoshinori Iizuka 《极地研究》2003,14(1):57-64
This paper presents a model of isotopic fractionation by freezing under near equilibrium conditions in an open system and uses the model to predict the fractionation curve and slope gradient of δ 18 O versus δD. The simulation results show that 1) the fractionation curve and slope gradient are determined by the ratio of freezing rate to input rate, 2) the isotopic value in the initial stage of freezing is determined by the isotopic value of initial water; 3) in the latter half of freezing in an open system, the isotopic value converges to a certain value determined by that of input water. These results suggest that the shape of the fractionation curve is the method to distinguish whether freezing occurred in a closed or open system. This analysis is applied to an isotopic curve observed in basal ice of Hamna Glacier, Sya drainage, East Antarctica. The isotopic curve indicates formation by regelation in an open system with a ratio of freezing/input rates of about 10/4. 相似文献
13.
湖冰物候事件是气候变化的敏感指示器。本文以西藏纳木错湖为研究对象,基于MODIS多光谱反射率产品数据监测了2000-2013年纳木错湖冰冻融日期,并结合多个气象站点的气象数据和实测湖面温度、湖面辐射亮温分析验证了湖冰变化的原因。纳木错湖冰变化较好地响应了区域气候变暖：开始冻结日期延迟和完全消融日期提前使湖冰存在期显著缩短(2.8 d/a)、湖冰冻结期增长、湖冰消融期缩短,其中消融期变化最为明显,平均每年缩短3.1 d。湖冰冻融日期的变化表明：2000年后纳木错湖冰冻结困难,消融加速,稳定性减弱。纳木错湖冰变化主要受湖面温度、湖面辐射亮温和气温变化的影响,它们可以作为气象因子来解释区域气候变化。 相似文献
14.
冬季结冰灌溉对苏打盐碱土水盐变化的影响 总被引：3，自引：0，他引：3
在苏打盐碱土区进行结冰灌溉试验,研究灌溉后盐碱土土壤水分和盐分的分布状况。试验分为淡水结冰灌溉(E)、微咸水结冰灌溉(D)、微咸水结冰灌溉+100%GR(石膏需求量)磷石膏(A),微咸水结冰灌溉+50%GR磷石膏(B),以及对照(CK),5个处理。灌溉水量为180 mm。试验结果表明灌溉融水增加了土壤耕层的含水量,为春播抗旱起到了重要作用。同时灌溉融水使土壤耕层主要离子Na+、Cl-、CO32-、HCO3-明显降低,使土壤耕层的盐碱化程度得到改善。不同处理方式之间比较,微咸水结冰灌溉洗盐效果和盐碱化改良效果明显好于淡水结冰灌溉,微咸水+磷石膏淋洗和改良效果好于微咸水结冰灌溉,且随着磷石膏施用量的增多,洗盐和改良效果更好。 相似文献
15.
16.
The existence of a large subglacial lake beneath the antarctic Ice Sheet at Terre Adélie indicates the presence of basal ice at its pressure-melting temperature. A numerical model of the ice-sheet thermal regime is employed using the balance velocity of the ice sheet as an initial model input in order to calculate ice-sheet basal temperatures. However, the results from this model show the Terre Adélie area to be characterised by basal freezing. Heat in addition to that accounted for in the model is thus required at the ice-sheet base in order for pressure melting temperatures to be attained. The sources for such heat are (1) an enhanced geothermal heat flux and (2) an increase in frictional heating caused by the flow of ice. In this paper the latter possibility is expanded by hypothesising that subglacial topography induces convergent ice flow around Terre Adélie, causing enhanced basal ice velocities. Model experiments indicate that an increase in ice velocity (from 7 to at least 42 m yr−1 ) is required to raise the temperature of the basal ice to the pressure melting value. Increased ice velocity, and consequent frictional heat production due to convergent ice flow, may therefore be important in explaining the location of the subglacial lake in this region. These results allow the process of convergent ice flow within a contemporary ice sheet to be quantified. A verification (or otherwise) of the model results may be possible if ice surface velocity measurements from modem GPS methods are made. 相似文献
17.
湖冰冰情物候特征是气候变化的敏感指示器之一。论文以呼伦湖为研究对象,基于MODIS、Landsat、GF-1、HJ-1等多源遥感影像及气象数据,利用RS和GIS技术综合分析了1986—2017年呼伦湖冰情物候特征及其对区域气候的响应。结果表明：① 呼伦湖年均开始冻结时间在10月下旬至11月上旬,从结冰开始到完全封冻的时间平均只有6.4 d;开始融冰时间在次年的4月上旬,消融期平均为32 d左右,到5月初或5月上旬湖冰完全融化。② 1986—2017年,在整个研究期呼伦湖完全封冻期呈现显著缩短趋势,平均缩短18.5 d;完全结冰时间有一定延迟现象,平均延后8.4 d;冰全部融化时间呈现提前趋势,平均提前了11.2 d。③ 湖冰冻结消融空间特征表现不同,冻结时先从湖岸形态较复杂地区结冰,然后由东岸向西岸迅速封冻,消融时先从湖泊西北岸开始,逐渐向东岸融化。④ 在影响因素方面,呼伦湖冰情特征主要受到区域气温、风速、风向等因素的影响。 相似文献
18.
Information about the spatial variations of snow properties and of annual accumulation on ice sheets is important if we are to understand the results obtained from ice cores, satellite remote sensing data and changes in climate patterns. The layer structure and spatial variations of physical properties of surface snow in western Dronning Maud Land were analysed during the austral summers 1999/2000, 2000/01 and 2003/04 in five different snow zones. The measurements were performed in shallow (1–2 m) snow pits along a transect extending 350 km from the seaward edge of the ice shelf to the polar plateau. These pits covered at least the last annual accumulation and ranged in elevation from near sea level to 2500 m a.s.l. The Ø18 O values and accumulation rates had a good linear correlation with the distance from the coast. The mean accumulation on the ice shelf was 312±28 mm water equivalent (w.e.); in the coastal region it was 215±43 mm w.e. and on the polar plateau it was 92±25 mm w.e. The mean annual conductivity and grain size values decreased exponentially with increasing distance from the ice edge, by 48%/100 km and 18%/100 km respectively. The mean grain size varied between 1.5 and 1.8 mm. Depth hoar layers were a common phenomenon, especially under thin ice crusts, and were associated with low dielectric constant values. 相似文献
19.
我国在1999年和2003年进行了两次北极考察,这两年海冰的冰情差别很大,分别对应冰情较重和较轻的年份。本文利用卫星遥感资料对1999年和2003年的海冰分布状况及其差异进行了全面的分析,并利用气温和风场资料深入研究形成这种差异的动力学原因。结果表明, 2003年的海冰冰情与1999年相比要轻很多,海冰面积在春季融冰季节和秋季冻结季节显著减小。2003年春季,来自白令海的海水提早半个月进入楚科奇海,导致海冰大范围融化。但是,到了夏季,海冰的面积减少过程停滞下来。而秋季楚科奇海封冻过程比1999年晚半个月。以上这些特征形成了2003年与1999年海冰的显著差异。研究结果表明, 2003年春季和秋季的气温比1999年要明显增高,最大月平均温差接近18°C,显著的高温为海冰融化的加剧和冻结的推迟提供了热量。直接影响海冰分布的是海面风场,两年风场的差异产生了来自白令海的太平洋入流的差异,对春季海冰融化的提前、夏季入流的减弱和秋季冻结过程的推迟起到关键的作用。季节性气象要素的年际差异可以归因于整个北极的AO系统变化, 2003年AO指数是正值, 1999年为负值,成为楚科奇海局地海冰变化的气候背景。 相似文献
20.
The origin of the large positive anomaly of the Fram Strait sea ice export which occurred in winter 1994/95 is analysed on the basis of a model simulation of the Arctic sea ice cover over the period 1993-98. The overall intra-annual and interannual variability in the model is in good agreement with observational estimates and the 1994/95 anomaly is well reproduced with an amplitude amounting to half of the mean winter value. Model results suggest that, concomitant to anomalous export velocities, larger than usual ice thickness in the strait contributes to the outstanding amplitude of the anomaly. Analysis on the ice thickness evolution in the strait indicates that the thick ice advected in Fram Strait at the end of the fall of 1994 originates in the anomalous cyclonic wind stress which prevailed during the preceding summer. This anomalous wind stress resulted in persistent convergence of the ice flow against the northern coasts of Canada and Greenland and in the formation of a large thickness anomaly north of Greenland. The anomaly then feeds the Fram Strait ice flow during those following winter months when the local wind forcing in the strait favours ice drift from the north-west. Our results suggest that short-term wind stress variations resulting in local thickness changes to the north of Fram Strait can lead to substantial variability of the Fram Strait ice export. 相似文献