An examination of snow redistribution over smooth land‐fast sea ice     

J. Iacozza  D. G. Barber 《水文研究》2010,24(7):850-865

An understanding of temporal evolution of snow on sea ice at different spatial scales is essential for improvement of snow parameterization in sea ice models. One of the problems we face, however, is that long‐term climate data are routinely available for land and not for sea ice. In this paper, we examine the temporal evolution of snow over smooth land‐fast first‐year sea ice using observational and modelled data. Changes in probability density functions indicate that depositional and drifting events control the evolution of snow distribution. Geostatistical analysis suggests that snowdrifts increased over the study period, and the orientation was related to the meteorological conditions. At the microscale, the temporal evolution of the snowdrifts was a product of infilling in the valleys between drifts. Results using two shore‐based climate reporting stations (Paulatuk and Tuktoyuktuk, NWT) suggest that on‐ice air temperature and relative humidity can be estimated using air temperature recorded at either station. Wind speed, direction and precipitation on ice cannot be accurately estimated using meteorological data from either station. The temporal evolution of snow distribution over smooth land‐fast sea ice was modelled using SnowModel and four different forcing regimes. The results from these model runs indicate a lack of agreement between observed distribution and model outputs. The reasons for these results are lack of meteorological measurements prior to the end of January, lack of spatially adequate surface topography and discrepancies between meteorological variables on land and ice. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

西太平洋暖池热盐结构盐度场变异的主模态          下载免费PDF全文

秦思思  张启龙  尹宝树 《应用海洋学学报》2016,35(3):303-310

基于1950~2011年间的月平均温、盐度资料,以28℃等温线作为西太平洋暖池的定义标准,并取ΔT=-0.4℃,分别计算了暖池区(20°N~15°S,120°E~140°W)各格点混合层、障碍层和深层的平均盐度,构成了暖池热盐结构的盐度场.据此,运用EOF分解法分析了暖池热盐结构盐度距平场主要模态的变化特征及其与ENSO间的关系,并探讨了主要模态的年际变异机理.结果表明,暖池热盐结构盐度场第一模态揭示了盐度场变异的关键区位于暖池中部;该模态具有2~4a的年际变化和准10a的年代际变化,并在1977年前后经历了一次气候跃变(此外,深层盐度场第一模态还在1999年前后发生了一次气候跃变),且在跃变前后与不同类型的ENSO事件有较密切的联系.暖池中部混合层和障碍层盐度的变化比较一致,即在跃变前盐度为偏高期,而在跃变后则变为偏低期.暖池中部深层盐度在1977年以前和1999年之后皆处于偏高期,而在1978~1999年间则处于偏低期.而且,从混合层至深层,盐度的变化幅度逐渐变小.进一步分析表明,暖池中部混合层和障碍层盐度的年际变化主要是由纬向风、南赤道流(SEC)和降水共同引起的,即当东风增强(减弱)时,强(弱)SEC将携带更多(少)的高盐水进入混合层或潜沉至障碍层,同时局地降水的减少(增多),也使得混合层和障碍层的盐度增加(减少);深层盐度的年际变化主要是由SEC和赤道潜流(EUC)导致的,即当SEC增强(减弱)时,将有更多(少)的高盐水进入暖池,而当EUC增强(减弱)时则有更多(少)的低盐水流出暖池,从而使得暖池的深层盐度升高(降低).  相似文献   

温盐环流与全球增暖的数值模拟 (一)纬向平均温盐环流的模拟     

金向泽  张学洪 《大气科学》1994,18(Z1):769-779

本文是用简单海一气耦合模型模拟温盐环流在全球增暖事件中作用的研究工作的第一部分。为了建立一个简单海一气耦合模型，我们首先根据Ｗｒｉｇｈｔ和Ｓｔｏｋｅｒ等人的设计复制出一个包括大西洋、太平洋和南大洋在内的二维温盐环流模式，从等温、等盐和无运动的初始状态出发，在给定的年平均海表强迫下将模式积分了４０００年，模拟出了和原作相似的温盐环流。对模拟结果的分析表明，相对于北太平洋而言，北大西洋北部的高盐、低温特点（后者是由两大洋在地理上的差别决定的）是形成当代温盐环流的主要原因；从与温盐环流相联系的海表热通量来看，北大西洋北部是向大气提供热量的主要源地；模式温盐环流对于海表盐度通量的敏感性试验的结果表明，对于纬圈平均的二维模式而言，要想模拟出合理的温盐环流就必须人为地提高北大西洋北部的海表盐度，文章分析了这种作法的物理根据；模式中的对流过程对于温盐环流的维持是至关重要的，对比有无季节循环的试验结果可以看出，虽然温度场的明显的季节变化只出现在模式的最上面两层，但由于引进季节循环后冬季高纬海洋的对流活动加强，后者直接影响到温盐环流，使更多的深海热量上传并向大气释放。这是使海洋温跃层得以保持合理．厚度的一个重要原因。  相似文献   

温室气体浓度增加情景下大西洋温盐环流的演变   总被引：2，自引：0，他引：2  

牟林  吴德星  周刚  陈学恩  马超 《地球科学》2007,32(1):141-146

温室气体浓度增加(以CO2为主)引起的温盐环流演变在未来气候系统中扮演非常重要的角色.在最新的温室气体排放情景下,利用基于德国马普气象研究所为IPCC第四次评估报告而最新发展的气候模式(ECHAM5/MPIOM),对3种不同的温室气体排放假设(B1,A1B,A2)进行了可靠的数值模拟.在此基础上,就大西洋温盐环流和北大西洋深层水形成的变化,以及北大西洋不同海区的温盐环流对温室气体浓度增加的响应,对模拟结果进行了分析.研究揭示,到21世纪末,在3种CO2排放情景下,温盐环流强度分别减弱了4Sv(1Sv=106m3/s)、5.1Sv、5.2Sv,大体相当于减弱了20%、25%、25.1%.由于全球变暖引起副极地海区表层海水变暖变淡,拉不拉多海(LabradorSea)和丹麦海峡(DenmarkStrait)以南区域的深层对流有所减弱.而在格陵兰-冰岛-挪威海(GINSea)的情况相反,由于北大西洋暖流的增强,通过法鲁海峡(Faro-BankChannel)进入GIN海域的高盐水增加,导致GIN海域上层盐度(密度)增加,进而深层对流加强.在A1B情景下,由于全球变暖北大西洋的深层水生成率从16.2Sv降到了12.9Sv.  相似文献   

Analysis of A New Model for Unsaturated Flow in Porous Media Including Hysteresis and Dynamic Effects     

A.Y. Beliaev  R.J. Schotting 《Computational Geosciences》2002,5(4):345-368

A new model for unsaturated flow in porous media, including capillary hysteresis and dynamic capillary effects, is analyzed. Existence and uniqueness of solutions are established and qualitative and quantitative properties of (particular) solutions are analyzed. Some results of numerical computations are given. The model under consideration incorporates simple play-type hysteresis and a dynamic term (time-derivative with respect to water content) in the capillary relation. Given an initial water content distribution, the model determines which parts of the flow domain are in drainage and which parts are in imbibition. The governing equations can be recast into an elliptic problem for fluid pressure and an evolution equation for water content. Standard methods are used to obtain numerical results. A comparison is given between J.R. Philip's semi-explicit similarity solution for horizontal redistribution in an infinite one-dimensional domain and solutions of the new model.  相似文献   

三峡引水工程秦巴段输水隧洞稳定性分析     

李东林吴树仁  韩金良刘景儒 《地质通报》2007,26(3):321-326

三峡引水工程秦巴段隧洞总长占线路总长的80%。为了分析隧洞施工及运营中可能发生的工程地质问题,在地质调查、地应力测量和岩石力学参数测试的基础上,利用Ansys有限元软件对引水工程北部不同深度、不同截面形态的隧洞围岩的应力重分布情况进行了模拟计算,得到了圆形隧洞、城门形隧洞和马蹄形隧洞围岩的应力分布结果。利用Hoek-Brown强度准则,得到了隧洞围岩的强度/应力比值,进而对不同深度、不同截面形态的隧洞围岩的稳定性进行了分析。初步认为:隧洞埋深小于1000m时,应优先考虑圆形隧洞和马蹄形隧洞;埋深大于1000m时,应优先考虑城门形隧洞。这项研究成果为引水工程深埋隧洞的设计提供了参考依据。  相似文献   

Current and Thermohaline Characteristics of the Arabian Sea During January 1998     

CHEN Meixiang)  ZUO Juncheng)  LI Peiliang)  DU Ling)  and LI Lei)) Oceanography Department  Ocean University of China  Qingdao  P. R. China ) Key Laboratory of Coastal Disaster  Defence  Ministry of Education  Hohai University  Nanjing  P. R. China 《中国海洋大学学报(英文版)》2007,6(2):117-124

Based on a ship survey during January 1998, the characteristics of the flow, the thermohaline properties and the volume transport of the Arabian Sea are discussed. A strong westward flow exists between 10.5?N and 11?N, part of which turns to the south as the Somali current near the coast at about 10?N and the rest turns north. At the passage between the African continent and the So- cotra Island, the northern branch separates into two flows: the left one enters the passage and the right one flows eastward along the southern slope of the island. Off the island the flow separates once more, most of it meandering northeast and a small fraction flow- ing southeast. Volume transport calculation suggests that the tidal transport is one or two orders of magnitude smaller than the total transport in this region and it becomes more important near the coast. The average velocity of the flow in the upper layer (0-150 m) is about 20 cm s-1, with a maximum of 53 cm s-1 appearing east of the Socotra Island, and the subsurface layer (200-800 m) has an aver- age velocity of 8.6 cm s-1; the velocity becomes smaller at greater depths. The depth of the seasonal thermocline is about 100 m, above which there is a layer with well mixed temperature and dissolved oxygen. High-salinity and oxygen-rich water appears near the surface of the northern Arabian Sea; a salinity maximum and oxygen minimum at 100 m depth along 8?N testifies the subduction of surface water from the northern Arabian Sea. Waters from the Red Sea and the Persian Gulf also influence the salinity of the area.  相似文献   

The influence of thermohaline fronts on chlorophyll a concentrations during spring and summer in the southeastern Yellow Sea     

JANG Pung-Guk  LEE Tong Sup  KANG Jung-Hoon  SHIN Kyoungsoon 《海洋学报(英文版)》2013,32(9):82-90

A spatial and temporal variation in physiochemical parameters in the southeastern Yellow Sea(YS) is investigated in the spring and summer of 2009 to 2011.Nutrient show a strong negative relationship with chlorophyll a(Chl a) concentration in spring,and the subsurface chlorophyll a maxima(SCM) layer was associated with the nitracline in summer.In summer,the SCM was usually found within or above the pycnocline and at the depths of shoals from the open sea to the coastal sea due to tidal and/or topographical fronts in the southernmost study area.High Chl a concentrations were found in the central southern YS,where the YS cold water layer expanded under the pycnocline and encountered water masses during spring and summer.After a typhoon in the summer of 2011,Chl a concentration increased,especially in the central southern YS,where cold waters occurred below the pycnocline.The results suggest that the development of thermohaline fronts may play an important role in the growth and accumulation of phytoplankton biomass in the upper layer of the southeastern YS during spring and summer.  相似文献   

The watermass variability and southward shift of the Southern Hemispheremid-depth supergyre     

DUAN Yongliang  HOU Yijun  LIU Hongwei  LIU Yahao 《海洋学报(英文版)》2013,32(11):74-81

The Southern Hemisphere subtropical supergyre at intermediate depths connects all three ocean basins and plays a significant role in responding and conveying the climate-change-related variations in the glob- al ocean. On the basis of the Simple Ocean Data Assimilation/SODA） ocean reanalysis, the thermohaline variability and southward shift of the mid-depth supergyre are demonstrated. The steric height of the sub- surface relative to 1 500 m （400-1 500 m） from the SODA depicts exactly the flow patterns and variability of the oceanic supergyre. During 1958-2007 the water masses in the gyre interiors become cooler/fresher, with the significant exceptions of the Agulhas Current system and Agulhas leakage. The results also exhibit a pronounced strengthening of the inter-basin connection of the supergyre, and the strongest southward shift, by about 2.5° over the whole period, occurs in the central-south Pacific, which is associated with the changes in the basin-scale wind forcing.  相似文献   

不同辐射背景下大西洋热盐环流下沉区混合层深度变化     

李菁楠  陈学恩 《海洋与湖沼》2014,45(4):676-684

基于政府间气候变化专门委员会(Intergovernmental Panel on Climate Change,IPCC)4种最新辐射强迫情景,利用ECHAM5/MPI-OM(European Centre Hamburg Model 5/Max Planck Institute Ocean Model)气候模式输出的1850—2300年逐月混合层深度、海表面温度、海表面盐度数据,分析大西洋热盐环流下沉区混合层深度的变化情况。结果表明:随辐射强迫增加,热盐环流下沉区混合层深度下降,混合层深度振荡周期在格陵兰-冰岛-挪威海(Greenland Sea–Iceland Sea–Norwegian Sea,GIN)海域减小,在拉布拉多海(Labrador Sea,LAB)海域变化不大;与GIN海域相比,LAB海域混合层深度对辐射强迫变化更敏感;两海区温度对混合层深度的影响时间较长,混合层深度对盐度的变化反应迅速;混合层深度变化的主导因素在LAB海域中为盐度,而在GIN海域,低辐射强迫下温度主导混合层深度变化,中高辐射强迫下温度与盐度共同起主导作用。  相似文献