中国天山西部山区森林积雪消融过程观测分析——以巩乃斯河谷为例

通过对2013年春季中国科学院天山积雪与雪崩研究站区内阳坡无林地和阴坡不同开阔度森林内积雪深度、融雪速率以及常规气象的观测,分析了融雪期不同开阔度森林积雪的消融过程以及积雪表面能量平衡特征。结果表明:不同开阔度林冠下积雪深度具有相同的变化趋势,森林的林冠开阔度越大,林下积雪深度越大,林下积雪开始消融和完全消融的时间越晚,消融期也越长。森林积雪融雪开始和结束时间比阳坡无林地区晚20~30 d左右。融雪前期林冠开阔度越大,其林下融雪速率越小。融雪后期则森林开阔度越大,森林积雪的融雪速率越大。不同时期由于不同开阔度林冠下雪面能量收支以及雪层深度等物理特性的差异,从而使不同开阔度林冠下森林积雪融雪速率的相对大小,融雪速率最大值出现时间和日变化特征均不相同。晴天森林积雪的消融速率和日变化特征取决于净短波辐射和长波辐射变化特征。降水期间,其融雪速率的变化则主要受降水形式、降水量以及积雪深度等雪层特性的影响。     

融雪期天山西部森林积雪表面能量平衡特征

通过对2013年春季中国科学院天山积雪与雪崩研究站站区内阳坡开阔地和阴坡雪岭云杉80%和20%开阔度林冠下气温、大气湿度、风速以及雪面短波和长波辐射的观测研究,分析了融雪期不同开阔度林冠下积雪表面能量平衡特征。结果表明:由于植被影响,阴坡雪岭云杉林冠下积雪表面净短波辐射和显热明显小于阳坡开阔地,但净长波辐射损失小于阳坡开阔地。阴坡林冠下积雪表面总能量明显小于阳坡开阔地,因此阴坡森林积雪融雪开始消融和结束时间明显晚于阳坡开阔地。在阴坡,林冠开阔度越大,雪面获得的净短波辐射和显热越大,但损失的净长波辐射和潜热也越大。不同开阔度林冠下和阳坡开阔地积雪表面的净短波辐射、显热和潜热有相同的日变化特征,但是森林积雪表面夜晚的显热和潜热多为0 W/m2;阴坡森林积雪表面长波辐射日变化特征明显不同于阳坡开阔地雪面。     

中国天山西部季节性森林积雪物理特性

积雪特殊的物理特性对冰雪水文过程、积雪生态系统、不同尺度的气候系统有重要影响。目前对林下积雪物理特性缺乏系统性研究,因此对天山雪岭云杉林下季节性积雪深度、沉降速率、密度和含水率进行观测分析。结果表明：林下积雪深度小于开阔地;林下积雪沉降速率和新雪密实化率小于开阔地,且稳定期沉降速率小于融雪期。稳定期林下积雪密度小于开阔地,林下雪层密度最大值位于中粒雪层,开阔地则位于粗粒雪层;融雪期则全层密度趋于一致。稳定期林下雪层含水率随深度递减,开阔地雪层最大值出现粗粒雪层;融雪期雪层汗水峰值出现在细粒雪层,新雪层最小,林下雪层由细粒雪层到深霜层始终呈减小趋势,开阔地雪层由细粒雪层至中粒雪层逐渐减小,粗粒雪层至深霜层逐渐增大;稳定期雪层含水率日变化随深度的递减逐渐减小,开阔地大于林下;开阔地的新雪层和细粒雪层含水率的日变化大于林下,粗粒雪层到深霜层则小于林下。     

中国西北地区季节性积雪的性质与结构

中国内陆地区积雪分布十分广泛。根据西北地区大陆性气候条件下形成的“干寒型”积雪的特征 ,对中国天山和阿尔泰山山区的季节性积雪进行了观测与分析。结果表明 ,该区最大积雪深度达 15 2cm(1997) ,积雪层一般由新雪 (或表层凝结霜 )、细粒雪、中粒雪、粗粒雪、松散深霜、聚合深霜层和薄融冻冰层组成。与“湿暖型”积雪相比 ,“干寒型”积雪的性质具有密度小 (新雪的最小密度为 0 .0 4 g/cm3 )、含水率少 (隆冬期 <1% )、温度梯度大(最大可达 - 0 .5 2℃ /cm)、深霜发育层厚等特点 ,并且变质作用以热量交换和雪层压力变质作用为主。据中国科学院天山积雪与雪崩研究站 (43°2 0N ,84°2 9E ,海拔 1776m)的观测资料 ,中国内陆干旱区冬季积雪期雪面太阳辐射通量以负平衡为主 ,新雪雪面反射率达 96 % ,短波辐射在干寒型积雪中的穿透厚度达 2 8cm。春季积雪消融期 ,深霜层厚度可占整个积雪层厚度的 80 %。随着气温的升高 ,雪粒间的键链首先融化 ,使积雪变得松散 ,内聚力、抗压、抗拉和抗剪强度降低 ,积雪含水率也随之增大 ,整个积雪层趋于接近 0℃的等温现象 ,因此 ,春季天山、阿尔泰山等山地全层性湿雪崩频繁发生     

天山巩乃斯河谷融雪期积雪物质平衡初步研究

本文利用１９９４年３月中，下旬在中间科学院天山积雪雪崩研究站（以下简称积雪站）野外观测到的部分资料，对融雪期季节性积雪的物质平衡进行初步分析，同时利用物质平衡方程对积雪日融出量进行计算。     

季节性森林积雪融雪期雪层含水率垂直廓线与时间变化特征

利用snow fork雪特性分析仪测量天山积雪与雪崩研究站融雪期开阔地(站区内气象观测场)与雪岭云杉林下雪层含水率,分析季节性森林积雪融雪期雪层含水率垂直廓线和时间变化特征以及与气温的关系。结果表明:由于开阔地和林下积雪接受的太阳辐射、雪层密度和雪层污化程度等的不同,开阔地、树冠边缘及距树干1m处的雪层含水率垂直廓线特征、雪层含水率的日变化特征以及融雪期雪层含水率随时间的变化特征各异;雪层含水率受气温因子影响最大,融雪期雪层含水率随气温变化呈指数增加,由于开阔地和林下微气象条件的不同,三点雪层含水率对日均温、最高温、最低温、日较差以及逐时气温的响应也不同,且雪层含水率对气温的滞后效应也各异。     

中国天山西部山地积雪辐射平衡研究

本文给出了1986-1987年冬春两季积雪辐射平衡的数据以及积雪辐射平衡与短波辐射平衡、长波辐射平衡的同步变化关系;指出了短波辐射平衡对融雪的积极作用,强调了积雪反射率对融雪过程的负反馈机制;并将积雪辐射平衡与融土辐射平衡进行了类比;从能量平衡的观点对不同容重的积雪融化速率进行了分析.该文的结果对研究积雪融化具有重要意义。     

季节性积雪区不同遮挡条件下深霜发育比较

以中国科学院天山积雪雪崩研究站为研究区,在2009～2010年冬季观测期利用体视显微镜(XTZ-E)及拍照设备和雪特性分析仪(Snow Fork),对3种遮挡条件的开阔地(0遮挡)、树缘(50%遮挡)和树下(90%遮挡)的积雪深霜进行连续观测,比较和分析西北季节性积雪区不同遮挡条件下的深霜发育特征。研究表明:1)深霜发育主要受温度制约,其次是温度梯度。由不同遮挡条件引起积雪累积和太阳辐射差异而导致雪深不同,从而形成的温度环境差异,是深霜发育差异的根本原因。2)深霜发育厚度与雪深呈正相关关系,有开阔地(0遮挡)>树缘(50%遮挡)>树下(90%遮挡),融雪期深霜的消减速率为树下>开阔地>树缘。3)深霜冰晶粒径呈先减小(稳定累积期-过渡期)再增大(-融雪期)的变化,积雪稳定累积期后,深霜粒径开阔地>树缘>树下。4)2009～2010年冬季雪深大,因而圆角深霜(DHxr)和圆角刻面冰晶(FCxr)在深霜中发育最多,二者共占70%～80%。开阔地易发育杯型深霜(DHcp),树缘和树下则易发育柱状条纹深霜(DHla)、棱柱状深霜(DHpr)和刻面冰晶(FCso)。深霜中胶结态冰晶约占10%～30%,其比例在开阔地深霜中递减,而在树缘和树下处递增。     

基于EOS/MODIS遥感数据改进式融雪模型

在中国西部的中纬度干旱和半干旱山区,融雪水是极其重要的水资源,融雪径流对河流的补给量在春季甚至可达75%以上,但是急剧的融雪也容易引发洪水,所以从水资源的有效利用和洪水预警方面看,有必要了解大范围的积雪消融状况。基于积雪层能量平衡原理建立融雪模型,利用正午过境的EOS/MODIS的Terra卫星遥感数据反演模型中的参数,结合气象数据获得瞬时的能量平衡信息,然后根据B.Sequin、B.ltier和谢贤群的研究推算日融雪量,改善了融雪模型的算法。另外采用遥感数据对雪盖进行实时监测,避免在进行融雪量估算时候对无雪区的错误估算。     

季节性冻土水热对融雪及气温的响应

近年来,随着气候变化,伊犁河谷积雪消融加快,极端水文事件的频度和强度也在加大。通过利用中国科学院天山积雪站附近小流域的土壤水热和积雪融雪观测数据,对研究区积雪消融规律、冻土水热变化特征及其对气温和融雪量的响应进行了分析。结果表明:在冻土融解阶段,土壤温度的变化依赖大气温度的变化,而土壤水分受融雪量和气温的影响较大,高度相关。表层土壤含水率的变幅最大,而深层土壤水分值较稳定,土壤水热的季节性变化自秋-冬-春大致呈现"下降-平稳-上升"的趋势。在冻土层上边界,土壤含水率随着累积融雪量的增加而增加并达到饱和值,而冻土层下边界(40 cm深度)土壤水分保持非饱和稳定状态。在山区,降雪量是水资源形成的主要来源。融雪量与大气温度的相关性显著(系数为0.785),融雪量对水资源形成的贡献率为40%左右。研究冻土水热对融雪和气温的响应过程,对于新疆水资源形成机理、转化利用以及洪水预报具有重要的参考价值。     

The influence of subtropical cold fronts on the surface energy balance of a semi-arid site

The passage of subtropical cold fronts through central Australia produces the only significant mesoscale meteorological features in the region. The interaction of these cold fronts with the surface energy balance strongly affects the local weather and climate. The surface energy balance was measured at a semi-arid site in Alice Springs, central Australia, to determine how it was influenced by the passage of subtropical cold fronts. Both Bowen ratio and eddy correlation methods were used. The daytime energy balance of the site showed high net radiation that was partitioned into 75% sensible heat flux and 25% soil heat flux with little or no latent heat flux. At night there was a large net radiative loss that was balanced primarily by a loss of heat from the soil. The cold fronts predominately passed through Alice Springs at night and showed a strong surface signature. The fronts brought moister air resulting in higher water vapour pressures during their passage. The nocturnal boundary layer was often disturbed as the front passed, resulting in warm, moist air being mixed down toward the land surface. Mixing decreased the soil heat flux and increased latent heat fluxes toward the surface. Moisture that accumulated at the surface at these times was often evaporated after a return to drier conditions. During the daytime, surface signatures in soil and sensible heat fluxes were less distinct due to the strong convective mixing. Latent heat fluxes followed a similar trend to the nocturnal case.     

THE STUDY ON LATENT AND SENSIBLE HEAT FLUX OVER MIRE IN THE SANJIANG PLAIN

Energy exchange is one of the most importantprocesses in wetland ecosystems,because it has agreat influence on temperature,water transport,plantgrowth,productivityetc.(Dennison and Berry,1989).On small scales,understanding of surface en-ergy exchange is n…     

三江平原季节性积水沼泽湿地能量平衡要素研究

2005年6月1日到8月30日,在中国科学院三江平原沼泽湿地生态试验站沼泽综合试验场季节性积水沼泽湿地,观测了净辐射和土壤热通量;利用Penman-Monteith公式和地表能量平衡方程式计算了潜热通量和感热通量;同时用SHAW模型对以上4个能量平衡要素进行了模拟研究,并用观测值以及模型效率、标准差和平均方差检验和评价了其模拟效果。结果表明,三江平原季节性积水沼泽湿地净辐射在6月末至7月初较大;潜热通量主要受净辐射的影响,与土壤水分关系不密切;沼泽湿地地表在6月初至8月中旬以吸收能量为主,8月末以后则开始释放能量;感热通量在植物生长季的初期和末期较大,在中期则比较小。SHAW模型能较好的模拟出沼泽湿地的净辐射、潜热通量和土壤热通量;该模型虽对感热通量的模拟结果并不理想,但能较好的模拟其变化趋势。这说明SHAW模型基本适用于对季节性浅积水沼泽湿地（水深小于10cm）能量平衡各要素的模拟。     

INFLUENCE OF SUBARCTIC VEGETATION COVER ON SNOWMELT

An examination of the three major components of the energy balance has shown that subarctic vegetation cover markedly alters the relative importance of these components for the snowmelt. It has been found that the contribution of net radiation decreases as forest cover decreases while sensible and latent heat contributions to the snowmelt increase with decreasing forest cover. The decrease in the importance of net radiation with decreasing forest cover is due to the effect of the forest cover on albedo and the effects of the forest cover on the long-wave radiation component of the radiation balance. This situation seems to be typical for open canopy forests. The increase in importance of sensible and latent heat in the open is due to the increase in wind speed from the forest to open sites.     

天山北坡低山丘陵干草原生长季蒸散特征

基于HL20波文比系统获得了天山北坡低山丘陵干草原2013-2015年的能量、气象观测数据,采用波文比-能量平衡法对其生长季（4～10月）蒸散特征进行了分析。结果表明：（1）生长季蒸散日内变化总体呈现中午最高、早晚变小和夜间蒸散微弱的特征,阴雨天蒸散日内变化相对复杂,蒸散强度通常弱于晴天;2013-2015年生长季蒸散量平均值为353.2 mm,生长季蒸散量在不同年份、不同季节和不同月份差异较大;2013-2015年生长季凝结水占降水量的比例分别为9.7%,18.8%和16.8%,日均凝结水量分别为0.177 mm,0.179 mm和0.316 mm。（2）生长季潜热和感热占据了净辐射能的主体且总体上潜热小于感热,白天潜热最大值出现之前,潜热会出现短暂小幅降低的情况。生长季感热和潜热逐日对比变化与植被长势密切相关。（3）波文比在夜间波动较大,变化复杂,白天上午波文比从负值增大到<1的正值,再到>1的正值,中午波文比为>1的正值,20：00左右波文比值开始回落。     

土地覆被变化过程中叶面积指数与降水量对地表能量平衡的贡献——基于SiB2的模拟结果

土地覆被变化过程中,叶面积指数（LAI）是地表能量平衡重要的影响因素,且与降水等多种因素存在交互作用。以2003 年中国东北地区农田、森林和草地三种覆被类型和三种LAI月变化过程为研究对象,着重分离出土地覆被变化过程中LAI对地表能量平衡的作用,认清覆被和LAI 变化对地表能量平衡的相对作用。利用SiB2 模型研究不同降水条件下土地覆被和LAI 变化对地表能量平衡的影响。结果表明：① 覆被变化对净辐射的影响最大,年均14.5W·m^-2左右。② LAI 主要改变净辐射对潜热和显热的分配,对农田和草地而言,LAI 增加明显提高（减小）潜热（显热）分配比例;对森林而言,LAI对潜热和显热分配的影响较弱。③ 降水对净辐射的分配起重要作用,降水增加,潜热增加。④ 表层土壤水分受降水和LAI 调控,与潜热有相反的变化趋势。     

石河子垦区沙漠和绿洲下垫面生态条件下能量交换特征

 在古尔班通古特沙漠南部流动沙区及其以南100 km的滴灌棉田为绿洲下垫面的生态条件下,分析研究了能量输送的不同模式和日变化进程。在沙漠生态条件下, 大部分净辐射用于感热通量的散失,另一部分用于向地下传输,少部分则用于潜热输送;与沙漠相比,在滴灌棉田生态条件下的绿洲能量输送的基本模式为: 农田蒸散的潜热能量占绝大部分,少部分用于感热通量和土壤热通量的消耗,另一个与沙漠不同的特征是绿洲存在地表能量平衡差额。     

Surface energy balance of Keqicar Glacier,Tianshan Mountains,China, during ablation period

The meteorological data of ablation season in 2005 were recorded by two automatic weather stations on Keqicar Glacier, in the southwest Tianshan Mountains of China. One is operated on the glacier near the equilibrium line with an altitude of 4,265 m (Site A) and another is operated on the glacier ablation area with an altitude of 3,700 m (Site B). These data were used to analyze the meteorological conditions and the surface energy balance (SEB) of Keqicar Glacier. Net radiation was directly measured, and turbulent heat fluxes were calculated using the bulk aerodynamic approach, including stability correction. The ablation value of 0.68 m w.e. derived from four ablation stakes is in close correspondence to the modeled value of 0.71 m w.e. During the observation period, net radiation accounts for 81.4% of the total energy with its value of 63.3 W/m². The rest energy source is provided by the sensible heat flux with a value of 14.4 W/m². Energy is consumed mainly by melting and evaporation, accounting for 69.5% and 29.7% of the total energy with their values of 54.0 and 23.0 W/m², respectively. Radiative energy dominates energy exchanges at the glacier-atmosphere interface, governed by the variation in net shortwave radiation. Net short-wave radiation varies significantly due to the effects of cloudiness and the high albedo caused by solid precipitation. Wind speed influences the turbulent heat fluxes distinctively and sensible heat flux and latent heat flux are much larger in July with high wind speed.     

FACTORS INFLUENCING THE VARIABILITY OF MIDWINTER SNOW-DEPTH DECREASE IN THE NORTHERN GREAT PLAINS OF THE UNITED STATES

Meltwater from snow provides an important source of fresh water for agriculture, domestic use, and hydroelectric power in many regions of the world. In the winter and early spring, however, rapid ablation of the snowpack can lead to environmental hazards such as flooding.

Most snowmelt research has relied on measured data, which have limited the spatial and temporal resolution of the studies. Generally, these studies have been conducted at single locations over periods of a few days to a few weeks. This project investigates snowdepth changes on a more expansive scale by using a one-dimensional mass- and energy-balance model (SNTHERM) to compute the convective and radiative fluxes associated with large snow-depth change events. Midwinter snow-depth changes and the variability in snow-depth changes are evaluated for a 25-year time period over the northern Great Plains region of the United States during February.

Statistical analyses indicate that variations in sensible heat flux have the greatest influence on midwinter variability of snow-depth changes. This is shown by the consistently strong relationship between modeled sensible heat-flux values and changes in snow depth over the entire study period and at nearly every station. Mean daily temperature followed by mean daily dew-point temperature show the next strongest statistical relationships with snow-cover ablation. Radiative fluxes and net solar radiation in particular, have low correlations with changes in snow depth and are therefore found to have little impact on snow-depth change variability during the month of February. Although net solar radiation is not highly correlated with the variability of decreases in depth, its energy input is nevertheless an important source of energy for ablation processes. [Key words: snow melt, modeling, Great Plains.]