北极高分辨率海冰冰间水道模拟评估分析

冰间水道只占北极冰区的1%~10%,但在海洋和大气之间的能量和水汽交换中起着重要作用。目前对冰间水道数值模拟结果的分析主要集中在水道出现频率的空间分布和水道面积占比的时空变化,而有关水道形态特征(长、宽和走向)模拟结果的分析较少。本文基于采用黏塑性流变学的高分辨率(2 km)冰海耦合模式模拟的海冰厚度来提取冰间水道,并利用3种MODIS冰间水道遥感产品进行形态特征的对比分析。分析结果显示,在波弗特海,模拟水道出现频率的空间分布与WH2015和H2019两种遥感产品基本一致;模拟结果中宽度大于6 km的水道数量概率密度和总长度符合遥感产品呈现的幂律分布规律,对2~4 km窄水道的分布受模式可解析能力限制本研究模式分辨率尚无法正确估计,存在低估;模拟水道总长度与遥感反演的结果在1月和3月相关性较好,但无法再现遥感产品中2月和4月的明显变化趋势;模拟水道和遥感产品总体走向一致,二者都显示,加拿大群岛以北和波弗特海东南部沿岸区域水道走向几乎与海岸线和冰速方向平行,模拟水道受陆地阻隔的影响更大,在波弗特海中部冰间水道和冰速发生转向的位置不一致。本研究揭示了当前高分辨率海冰模式对不同冰间水道形态特征的模拟能力的符合程度及不足之处,将有助于进一步的模式改进。

利用海冰密集度数据分析北极冰间湖变化

冰间湖内存在强烈的海-气相互作用和结冰析盐过程,在极区以及全球气候系统中起着重要作用。本文基于数字图像处理技术,从AMSR-E高分辨卫星遥感海冰密集度数据中提取了长时间序列的冰间湖变化信息,研究北极冰间湖内的净水面积、净水表面的净热通量(向上为正)、产冰量和产盐量的季节和年际变化,比较不同冰间湖区域之间的差异。研究结果表明:总净水面积分别在结冰初期和末期存在极大值,而由于总净水面积季节变化幅度不是很大,总产冰量和产盐量的季节变化主要受净热通量影响,在1月份存在极大值;在不同冰间湖区域内净水面积的季节变化中,进入结冰期越早的冰间湖内净水面积越快达到首次极大值;净热通量的年际变化趋势总体上是减小的,总净水面积是增加大的,其中靠近太平洋和大西洋入流口的冰间湖内净热通量减小的速率要比其他区域快,靠近亚欧大陆的冰间湖内净水面积增长速率要比其他区域大;总产冰量的年际变化同总净水面积基本一致,也是呈增加趋势。最后通过研究冰间湖的年际变化信息同海冰范围变化的相关性,发现如果连续多年冰间湖内年平均净热通量为负的异常,那么海冰范围将出现一次极小值。

基于卫星图像的北极冰间水道形态学特征分析

随着全球气候变暖,北极海冰面积逐渐减小,冰厚逐渐变薄,海冰在海浪的影响下会变得很脆弱,容易断裂形成裂缝,更易形成冰间水道,有助于北极航道的通航。同时,冰间水道是极地地区海洋与大气之间热量与动量交换的重要通道之一,因此在全球气候变暖的背景下,分析冰间水道的形态学特征,对于研究北极海区的动量和热量收支以及预测航道通航具有重要意义。文中利用Hilditch的冰间水道骨架技术,基于Landsat8的图像数据,分析了9月楚科奇海和波弗特海附近冰间水道倾角、长度和冰间水道距离等冰间水道的分布特征。结果表明,此时冰间水道倾角的分布集中在74°～114°之间,冰间水道长度和距离变化范围较大,分别在2～3 km和50～220 m之间。

基于被动微波遥感数据的冰间水道提取及验证

采用Aqua卫星搭载的微波扫描辐射计AMSR2以及FY-3D卫星搭载的微波成像仪MWRI 89 GHz单通道被动微波亮温数据,利用空间滤波增强冰间水道的线状特征,结合系点线性插值的方法提取波弗特海和弗拉姆海峡的冰间水道,最后对提取结果形态学特征进行研究,并分析海冰密集度和冰间水道的关系,结果表明被动微波对尺度较大的冰间水道具有较好的提取效果。在形态学特征上,被动微波亮温数据具有提取宽度大于1/3像元分辨率的冰间水道的可能性,但提取水道总面积略小于热红外遥感提取结果。通过LSD算法得到的冰间水道长度被动微波数据源整体上是MODIS数据的2倍。利用最小外接矩形统计从AMSR2、MWRI提取出来的冰间水道其宽度分布均服从幂律分布的规律。冰间水道面积占比与海冰密集度呈现负相关的关系。

利用多源遥感数据识别波弗特海冰间水道

采用MODIS可见光反射率、热红外亮温和RadarSat-2双极化后向散射等多源数据,通过建立决策树综合判断来识别波弗特海域冬季的冰间水道及其内部冰型,并进行精度评价。研究发现,MODIS热红外只能粗略提取冰间水道轮廓;而高分辨率的RadarSat-2影像可以提供更多海冰类型信息,但是不同冰型的后向散射信号有重叠,影响水道提取的精度。研究结合多源数据建立决策树,综合极化后向散射和表面温度等参数来判断海冰类型,从而识别不同发育阶段的冰间水道。该方法的识别精度优于单变量方法。高分辨率Sentinel-2光学影像验证了不同阶段冰间水道的顺序分布。多源数据的应用有助于更准确地计算水道区域的海-气热通量和产冰量,同时为船只导航提供更详细的冰情信息。

北极冰间水道区域的物理过程和遥感观测研究进展

冰间水道是海冰区在风力和洋流作用下形成的线状断裂带。总结了冰间水道区域海洋—海冰—大气相互作用的物理机制和水道遥感的研究现状。冰间水道是极区海洋与大气间水热交换的重要窗口,是冬季产冰析盐和夏季融冰产生淡水的重要场所,也是极区动物赖以生存的栖息地和迁徙通道。利用水道与浮冰之间在反照率、表面温度、发射率和粗糙度等性质上的差异,可通过光学、红外和微波等多种遥感手段来识别和提取水道。随着北极海冰厚度的减小和季节性衰退的提前,波弗特海的水道宽度、面积和出现频率均呈现增加的态势。在北极海冰不断减少的态势下,未来需要结合现场和遥感观测重新评估水道表面能量收支及其对区域能量平衡的贡献,更准确地认识其在北极气候变暖放大效应中的作用。

北冰洋次表层暖水形成机制的研究

分析了北冰洋加拿大海盆上层海水温度结构特征,针对在海冰覆盖区域普遍发生的次表层暖水现象,建立了冰海耦合的一维柱形模式,成功模拟了次表层暖水的垂向结构和形成机制,证明了太阳辐射加热和表层冷却是次表层暖水的成因。通过数值实验定量分析了形成次表层暖水各因子的作用,表明太阳辐射是形成次表层暖水的能量来源;长波辐射、气温和比湿等其他大气因子对次表层暖水强度有较大影响;在厚冰区不能形成次表层暖水,海冰越薄,水道面积越大,则冰下次表层海水温度升高得就越快,薄冰和冰间水道是形成次表层暖水的主要能量通道;通过模式的拟合给出湍扩散系数垂向变化的估值,冰下表层海水垂向湍扩散系数为5.0×10-3m2/s左右,而次表层垂向湍扩散系数却快速降低到1.0×10-6m2/s,表明跃层导致的稳定性增大是形成次表层暖水尖峰的关键因素。

北极航运与“一带一路”战略

2015年1 2月1 5日,由美国政府赞助的一项年度国际评估报告指出,北极正在继续变暖,2015年的陆地气温创下过去115年来的新高。2015年冬季北极海冰在2月25日达到最大面积,比往常提早了15天,并创下自1979年有卫星记录以来冬季北极海冰的最小面积记录。

空间遥感技术在自然灾害预报、监测及救灾工作中的应用

本文综合分析了空间遥感技术在自然灾害预报、监测及救灾工作中的应用,并着重分析了,它在台风、洪水、海冰、森林火灾等自然灾害中的应用,并提出了进一步研究的对策。

卫星助力南极科考航线海冰监测

好莱坞大片《全民公敌》中最令人印象深刻的,莫过于全天候无死角的卫星侦察技术了随着技术的进步,遥感枝术在空间分辨率已突破亚米级,可以辨别停靠在路边的车辆型号但是想要做到电影中随时随地想看哪就看哪的程度尚很难实现从原理上很容易理解：分辨率越高,图像幅宽越窄,也意味着卫星需要绕更多的圈数才可能再对同一地点进行监测因此在很多卫星遥感应用中,时间分辨率比空间分辨率更为关键以发生在2014年的我国＂雪龙号＂极地科考船脱困与救援事件为例.

南极大陆沿岸地面臭氧损耗事件的研究

利用南极大陆沿岸中山站2008—2013年的地面臭氧连续观测数据和相关资料,对地面臭氧损耗事件(ODE)进行研究。结果显示,春季南极中山站常发生臭氧损耗事件。在该事件发生期间,气象要素有明显的突变过程,包括气温明显下降,风向由偏东风转变为偏北风,风速随之下降。来自海冰区的偏北风增多,风速很小,使臭氧浓度维持在较低水平。地面臭氧损耗事件主要与南极沿岸海冰区的活性溴(BrO)浓度有关。春季南极大陆沿岸海冰冻融过程中形成的冰间水道和冰间湖,在低温的作用下会再次冻结,形成薄冰和霜花。卫星资料能够观测到薄冰区释放的活化海盐溴高浓度区,活性溴与臭氧发生化学反应形成地面臭氧损耗事件。臭氧损耗现象是在未受到人为影响的自然状态下发生的,与中高纬度地区光化学反应导致臭氧消耗有所不同。

冰与水的完美结合

冰间湖对于很多人而言是个陌生的名词。有人会顾名思义,以为冰间湖就是冰里面的湖,所以会出现这样的问题：冰间湖有底吗？从海面上看,冰间湖确实像是被白色海冰包围的一泓湖水,但是在海面以下,冰间湖下的海洋和周边海冰下的海洋是没有边界、完全贯通的。所以,冰间湖的＂底＂,可以说是广阔无际的海洋。

Effects of the Ice Bath Time after Heat Shock and the Incubation Time on the Efficiency of Chemical Transformation Method

[Objective] The aim of the research was to study the effect of the ice bath time after heat shock and the incubation time on the transformation efficacy,and to establish a simple and quick transformation method.[Method]Competent cells were prepared with two buffer solutions;with the ice bath time after heat shock and the recovery time as the variables,the relationship between these two factors and transformation efficacy was studied.[Result]The transformation efficacy was the best when the ice bath time was 2 min and the recovery time was 30 or 40 min;when the ice bath time and the recovery time was 0 min,a certain amount of transformants still could be obtained.[Conclusion]The ice bath time after heat shock and the recovery time had certain impact on transformation efficacy,but they were not the decisive factors.Therefore,in the general transformation experiment,these two steps could be omitted.

Effects of Freezing Disaster on Green-up Date of Vegetation Using MODIS/EVI Time Series Data

In the field of global changes, the relationship between plant phenology and climate, which reflects the response of terrestrial ecosystem to global climate change, has become a key subject that is highly concerned. Using the moderate-resolution imaging spectroradiometer (MODIS)/enhanced vegetation index(EVI) collected every eight days during January- July from 2005 to 2008 and the corresponding remote sensing data as experimental materials, we constructed cloud-free images via the Harmonic analysis of time series (HANTS). The cloud-free images were then treated by dynamic threshold method for obtaining the vegetation phenology in green up period and its distribution pattern. And the distribution pattern between freezing disaster year and normal year were comparatively analyzed for revealing the effect of freezing disaster on vegetation phenology in experimental plot. The result showed that the treated EVI data performed well in monitoring the effect of freezing disaster on vegetation phenology, accurately reflecting the regions suffered from freezing disaster. This result suggests that processing of remote sensing data using HANTS method could well monitor the ecological characteristics of vegetation.

Average iron isotopic compositions of the upper continental crust：constrained by loess from the Chinese Loess Plateau

Iron isotopic composition of the upper continental crust(UCC) is critical for understanding Fe mobilization and migration through the Earth. Because rocks exposed at Earth's surface have heterogeneous δ^(56)Fe, finegrained clastic sediments can be used to estimate the average composition of UCC. In this study, we report δ^(56)Fe of loess-paleosol sequences from Yimaguan, Chinese Loess Plateau(CLP), to constrain the average Fe isotopic composition of UCC. The loess-paleosol sequences in this area formed in glacial-interglacial cycles and are characterized by varying degrees of weathering. Our data show that the loess-paleosol layers have extremely homogeneous Fe isotopic compositions with δ^(56)Fe ranging from 0.06‰ to 0.12‰, regardless of variations in the major element composition and weathering intensity. Our study indicates that since Fe isotopes are not significantly fractionated during loess deposition, the loess can be regarded as representative of UCC. It follows that the average δ^(56)Fe of UCC is 0.09‰± 0.03‰(2SD), consistent with previous estimates based on igneous rock data.

Integrated reliability of travel time and capacity of urban road network under ice and snowfall conditions

In order to evaluate and integrate travel time reliability and capacity reliability of a road network subjected to ice and snowfall conditions,the conceptions of travel time reliability and capacity reliability were defined under special conditions.The link travel time model(ice and snowfall based-bureau public road,ISB-BPR) and the path choice decision model(elastic demand user equilibrium,EDUE) were proposed.The integrated reliability was defined and the model was set up.Monte Carlo simulation was used to calculate the model and a numerical example was provided to demonstrate the application of the model and efficiency of the solution algorithm.The results show that the intensity of ice and snowfall,the traffic demand and supply,and the requirements for level of service(LOS) have great influence on the reliability of a road network.For example,the reliability drops from 65% to 5% when the traffic demand increases by 30%.The comprehensive performance index may be used for network planning,design and maintenance.

Spatial distribution of Ice Shelf Water in front of the Amery Ice Shelf,Antarctica in summer

As a unique low-temperature water mass in Antarctic coastal region, the Ice Shelf Water (ISW) is an important component for the formation of the Antarctic Bottom Water (AABW). In this paper, we present a criterion for ISW identification based on freezing point at the sea surface, and we study spatial distribution of ISW in front of the Amery Ice Shelf (AIS) and its flow path in Prydz Bay by analyzing hydrographic data from Australian cruises in 2001 and 2002, as well as Chinese cruises in 2003, 2005, 2006, and 2008, all being made in the austral summer. The relatively cold and fresh ISW occurred as several discrete water blocks with cold cores in front of the AIS, within the depth range of 100?600 m, under the seasonal thermocline. ISW had obvious temporal and spatial variations and the spatial distribution pattern changed greatly after 2005. Most of ISW was concentrated west of 73°E during 2001 to 2003 and 2006, but it was widespread to east in 2005 and 2008. In all observation years, a small amount of cold ISW always occurs at the west end of the AIS front section, where the coldest ISW in the whole section also occurred in 2001, 2003 and 2006. Considering general cyclonic circulation pattern under the AIS, the ISW flowing out from west end of the AIS front might have experienced the longest cooling period under ice shelf, so it would have the lowest temperature. Analysis of data from meridian sections in Prydz Bay in 2003 implied that ISW in the west could spread north to the continental break along the east flank of the Fram Bank near 70.5°E, mix with the upwelling Circumpolar Deep Water and possibly contribute to the formation of AABW.

Sea surface temperature and salinity reconstruction based on stable isotopes and Mg/Ca of planktonic foraminifera in the western Pacific Warm Pool during the last 155 ka

Changes in sea surface temperature （SST）, seawater oxygen isotope （δ18Osw）, and local salinity proxy （δ18Osw-ss ） in the past 155 ka were studied using a sediment core （MD06-3052） from the northern edge of the western Pacific Warm Pool （WPWP）, within the flow path of the bifurcation of the North Equatorial Current. Our records reveal a lead-lag relationship between paired Mg/Ca-SST and δ18O during Termination II and the last interglacial period. Similarity in SST between our site and the Antarctic temperature proxy and in CO2 profile showed a close connection between the WPWP and the Antarctic. Values of 818Osw exhibited very similar variations to those of mean ocean δ18Osw, owing to the past sea-level changes on glacial-interglacial timescale. Calculated values of δ18O reflect a more saline condition during high local summer insolation （SI） periods. Such correspondence between δ18O and local SI in the WPWP may reflect complex interaction between ENSO and monsoon, which was stimulated by changes in solar irradiance and their influence on the local hydrologic cycle. This then caused a striking reorganization of atmospheric circulation over the WPWP.

Paleomagnetic Excursions Recorded in the Yanchi Playa in Middle Hexi Corridor, NW China Since the Last Interglacial

Paleomagnetic determinations on lithological profiles of two paralleled[( )-275(long )]drilling cores covering the past 130 kyr B.P., GT40 and GT60, from the Yanchi Playa in the arid Northwestern China, indicate that a series of pronounced paleomagnetic excursions have been documented. By correlating our results with published regional and worldwide reports, 4 excursion events out of 10 apparent reversal signals (labeled from GT-1 to GT-10) were identified as excursion events coeval with the Mono Lake Event ([(28.4)( )]kyr~[(25.8)( )]kyr), Laschamp Event ([(43.3)( )]kyr^40.5 kyr), Gaotai Event (82.8 kyr~[(72.4)25( )]kyr) and the Blake Event (127.4 kyr^113.3 kyr), respectively. GT-9 correlates with the above-mentioned Gaotai Event, GT-7 and GT-6 correspond to two stages of the Laschamp Event and GT-5 to the Mono Lake Event. It is noteworthy that the so-called Gaotai Event has not been reported as a pronounced paleomagnetic excursion in the Northwestern China. Every magnetic excursion event corresponds to paleointensity minima, anteceding those established abrupt paleoclimatic change events, such as the Younger Drays and the Heinrich Events (H1-H6)[(. )-250( )]Here,[( )-250( )]we tentatively[( )-250( )]propose that these geomagnetic excursions/reversals can be viewed as precursors to climate abruptness. During the transitional stages when the earths magnetic field shifted between a temporal normal and a negative period, the earths magnetic paleointensity fell correspondingly to a pair of minima. Although more precise chronology and more convincing rock magnetic parameter determinations are essentially required for further interpretation of their intricate coupling mechanism, these results may have revealed, to some extent, that the earths incessantly changing magnetic field exerts an strong influence on the onset of saw-tooth shaped abrupt climate oscillations through certain feedback chains in arid Central Asia or even North Hemispheric high latitude regions.

Correspondence between the ENSO-like state and glacial- interglacial condition during the past 360 kyr

In the warming world, tropical Pacific sea surface temperature （SST） variation has received considerable attention because of its enormous influence on global climate change, particularly the El Nino-Southern Oscillation process. Here, we provide new high-resolution proxy records of the magnesium/ calcium ratio and the oxygen isotope in foraminifera from a core on the Ontong-Java Plateau to reconstruct the SST and hydrological variation in the center of the Western Pacific Warm Pool （WPWP） over the last 360 000 years. In comparison with other Mg/Ca-derived SST and δ18O records, the results suggested that in a relatively stable condition, e.g., the last glacial maximum （LGM） and other glacial periods, the tropical Pacific would adopt a La Nifia-like state, and the Walker and Hadley cycles would be synchronously enhanced. Conversely, El Nino-like conditions could have occurred in the tropical Pacific during fast- changing periods, e.g., the termination and rapidly cooling stages of interglacial periods. In the light of the sensitivity of the Eastern Pacific Cold Tongue （EPCT） and the inertia of the WPWP, we hypothesize an inter-restricted relationship between the WPWP and EPCT, which could control the zonal gradient variation of SST and affect climate change.