Estimate the influence of snow grain size and black carbon on albedo

Estimation of the influence of snow grain size and black carbon on albedo is essential in obtaining the accurate albedo. In this paper, field measurement data, including snow grain size, snow depth and...     

Radiometric investigation of different snow covers in Svalbard

This paper examines the relationship between reflectance and physical characteristics of the snow cover in the Arctic. Field data were acquired for different snow and ice surfaces during a survey carried out at Ny-Ålesund, Svalbard, in spring 1998. In each measurement reflectance in the spectral range 350 - 2500 nm, snow data (including temperature, grain size and shape, density and water content), surface layer morphology, and vertical profile of the snow pack were recorded detailed analysis of reflectance based on the physical was performed. Field reflectance data were also re-sampled at the spectral intervals of Landsat TM to compare the ability of identifying different snow targets at discrete wavelength intervals. This analysis shows that reliable data on snow structure and thickness are necessary to understand albedo changes of the snow surfaces.     

2013-2014年夏季南极普里兹湾海面反照率走航观测研究

在 2013—2014年南半球夏季时对南极普里兹湾海区的反照率进行了走航观测。利用安装于破冰船船头的高光谱辐照度计测量入射和反射的350—920 nm的太阳短波辐射, 基于此观测数据, 经计算得到了反照率。分析比较不同下垫面的反照率, 通过比较不同航段的观测结果, 得到了反照率的空间变化以及从海冰融化期至冻结初期的变化。不同下垫面的反照率差异较大, 有积雪覆盖的固定冰反照率最大, 有积雪覆盖的浮冰其次, 而积雪融化的浮冰则反照率有所降低。新冰的反照率较低, 有积雪覆盖的新冰反照率迅速增加。比较不同波段的反照率, 发现融化期由于积雪含水量较大, 增加了对近红外辐射的吸收, 降低了该波段的反照率。结合卫星遥感(AMSR-2)和人工观测的海冰密集度, 发现区域平均的反照率主要取决于海冰密集度, 然而也受下垫面物理特征影响, 例如2月底至3月初形成的新冰, 反照率只有老冰的1/3— 1/2。新冰形成, 会直接增加海冰密集度, 但由于其反照率较低, 对空间平均反照率的贡献较小。因此, 若要建立合理的冰水混合区的反照率参数化方案, 必须充分考虑海冰类型和冰面积雪的物理状态, 并考虑反照率的波长依赖性。     

沙尘源区LST/Albedo时序变化与TSP的对比分析——以2001年春季中国北方强沙尘过程为例

20 0 1年春季 ,中国北方多次受到沙尘天气的影响 ,给人们的生产、生活带来严重的威胁 ,引起了亚洲国家的广泛重视。利用卫星监测数据采集沙尘云图变化、运移路径、地表覆盖和沙尘过程中的地面反照率、温度、湿度、粗糙度等物理参数反演实验结果 ,可以弥补地面观测站点稀少、数据不连续的缺陷。本文以 2 0 0 1年 3月到 5月的几次沙尘天气为例 ,介绍基于地表覆盖的AVHRR的LST/Albedo反演结果与TSP (沙尘干量 )对比分析 ,发现它们具有较好的相关性。从而反映了沙尘暴发生前后地表能量的变化状况 ,能为预测预警沙尘天气的危害提供及时客观的空间信息。     

新疆天山及北疆地区积雪反照率差异

新疆天山和北疆地区是我国三大稳定积雪区之一,积雪反照率的变化显著地影响其地表吸收的太阳辐射能量。2018年1~3月,在新疆天山和北疆地区进行了积雪反照率观测,发现研究区的积雪反照率存在明显的时空差异。时间上,由于受到气温变化的影响,研究区的积雪反照率整体呈现下降的趋势,而且不同时期的下降幅度有差异,1月末~3月初反照率的降低相比1月初~1月末反照率降低更加明显。空间上,由于受到污化物的影响,各区域（阿勒泰地区、塔城地区、天山北坡和伊犁河谷）的积雪反照率之间存在差异,其中天山地区（天山北坡和伊犁河谷）的积雪反照率低于北疆地区（阿勒泰地区和塔城地区）,天山北坡的反照率最低;在积雪稳定期及消融期,污化物对积雪反照率的影响最为明显。     

Evaluation of the SNOWPACK model’s metamorphism and microstructure in Canada: a case study

The snow thermodynamic multi-layer model SNOWPACK was developed to address the risk of avalanches by simulating the vertical properties of snow. Risk and stability assessments are based on the simulation of the vertical variability of snow microstructure, as well as on snow cohesion parameters. Previous research has shown systematic error in grain size simulations (equivalent optical grain size) over several areas in northern Canada. To quantify the simulated errors in snow grain size and uncertainties in stability, the snow specific surface area (SSA) was measured with a laser-based instrument. Optical grain size was retrieved to validate the optical equivalent grain radius from SNOWPACK. The two study plots are located in Glacier National Park, BC, and Jasper National Park, AB, Canada. Profiles for density and stratigraphic analysis were obtained as well as grain size profiles, combined with snow micropenetrometer (SMP) measurements. Density analysis showed good agreement with the simulated values (R² = 0.76). Optical grain size analysis showed systematic overestimation of the modeled values, in agreement with the current literature. The error in SSA evolution for a rounding environment was mostly constant, whereas error for conditions driven by a temperature gradient was linked to the size of the facetted grains.     

Snow and sea ice thermodynamics in the Arctic:Model validation and sensitivity study against SHEBA data

Evolution of the Arctic sea ice and its snow cover during the SHEBA year were simulated by applying a high-resolution thermodynamic snow/ice model (HIGHTSI).Attention was paid to the impact of albedo on snow and sea ice mass balance,effect of snow on total ice mass balance,and the model vertical resolution. The SHEBA annual simulation was made applying the best possible external forcing data set created by the Sea Ice Model Intercomparison Project.The HIGHTSI control run reasonably reproduced the observed snow and ice thickness.A number of albedo schemes were incorporated into HIGHTSI to study the feedback processes between the albedo and snow and ice thickness.The snow thickness turned out to be an essential variable in the albedo parameterization.Albedo schemes dependent on the surface temperature were liable to excessive positive feedback effects generated by errors in the modelled surface temperature.The superimposed ice formation should be taken into account for the annual Arctic sea ice mass balance.     

Synoptic conditions of heavy snowfalls in Europe

Synoptic conditions of heavy snowfalls at four stations in Europe (Oslo, Bremen, Smolensk and Budapest) were analyzed using daily data of snow cover depth from 50 winter seasons (1960/1961–2009/2010). Composite maps of the sea level pressure and 500 hPa geopotential height means and anomalies were presented for the days with an increase in snow depth by ≥10 cm, for each station separately. In the same way, maps were presented for the 850 hPa temperature and the precipitable water content. Additionally, 48 h back trajectories of air masses for the chosen days with the highest amount of snowfall were constructed, using the NOAA HYSPLIT model. Negative anomalies of sea level pressure and 500 hPa heights, which correspond to low‐pressure systems spreading over Europe, are prerequisites for the occurrence of heavy snowfalls at each analyzed location. In Budapest, heavy snowfalls appear as a result of cyclonic cold fronts from the Mediterranean Sea. Another typical location of snow‐bringing low‐pressure systems is the Baltic Sea region. Negative pressure anomalies over the North Atlantic with a low‐pressure centre over the Norwegian Sea cause snowfalls in Oslo. There are two main sources of air masses bringing abundant snowfalls in Europe: the Atlantic region and Mediterranean. According to back trajectories, the humid air masses are transported over long distances and on the way they are shifted from the low troposphere in the source regions to the upper layers.     

青藏高原腹地多年冻土区地表反照率的季节变化及主要影响因子

准确获取青藏高原地表反照率的季节变化特征对高原地表能水循环研究具有重要意义。本文利用青藏高原多年冻土区西大滩和唐古拉2007年的气象及辐射数据,运用相关分析方法研究了太阳高度角、积雪及活动层冻融过程对地表反照率变化的影响。结果显示:冷暖季降雪过程中地表反照率的变化差异较明显;地表无积雪覆盖期间,地表反照率与气温和表层土壤含水量呈反相关关系。利用多元回归分析法构建了以积雪日数和气温为影响因子的月均地表反照率计算回归方程,经检验与观测值对比平均相对误差为7.1%,可用于青藏高原北部地表反照率的估算。     

Densification and grain coarsening of melting snow

A field work was conducted at Moshiri in Japan. The work included intensive snow pit work, taking snow grain photos, recording snow and air temperatures, as well as measuring snow water content. By treating the snow as a viscous fluid, it is found that the snow compactive viscosity decreases as the density increases, which is opposite to the relation for dry snow. Based on the measurements of snow grain size, it is shown that, similar to the watersaturated snow, the frequency distributions of grain size at different times almost have the same shape. This reveals that the waterunsaturated melting snow holds the same graincoarsening behavior as the watersaturated snow does. It is also shown that the waterunsaturated melting snow coarsens much more slowly than the watersaturated snow. The C value, which is the viscosity when the snow density is zero, is related to the mean grain size and found to decrease with increasing grain size. The decreasing rate of C value increases with decreasing graincoarsening rate.     

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。     

末次间冰期以来渭河上游气候演化的黄土记录研究

对渭河上游樊家台剖面末次间冰期以来黄土地层的粒度与CaCO3进行综合分析表明,末次间冰期时,受夏季风影响较大,粒度较细,CaCO3有较强的淋溶与淀积,气候呈现较为暖湿的特点;末次冰期时,受冬季风影响较强,粒度较粗,CaCO3淋溶淀积微弱,气候较为干冷。间冰期早期（相当于深海氧同位5e阶段）由于夏季风较强,粉尘堆积较少,古土壤向下发育,并与下部土壤融合,导致粒度较5a、5c阶段粗;2阶段的早期,由于粉尘源区出现了高湖面,环境湿度大,造成此时段早期黄土粒度较晚期细;表现出区域气候的特点。     

北极新奥尔松(Ny-lesund)地区环境中有机碳组成来源的初步分析

对2010年8月从北极新奥尔松地区(Ny-lesund)中国黄河站附近所采集的土壤、沉积物和苔藓进行整体指标[OC%,TN%,δ13C(‰)]和木质素(lignin-derived phenols)分析;并对土壤和沉积物进行粒度分析。结果显示OC%与TN%具有相同的来源;但是粒度并不是控制有机物分布的主要因素。数据显示当地木质素主要来自当地的维管植物和苔藓,但是可能会受到当地动物或者微生物的影响。木质素的降解参数(Ad/Al)v值的大小顺序为沉积物土壤苔藓,可能是由于苔藓的表面吸附了细颗粒的煤炭,但是缺少14C数据,无法定量计算煤炭对环境中有机碳的贡献;另外一个降解参数肉桂基酚类两种单体(CAD/FAD)比值由苔藓、土壤、沉积物依次降低,反映出成岩作用增强,木质素降解程度增加。综合OC%、TN%、δ13C(‰)和木质素数据,中国北极黄河站周围环境中的有机碳来源主要为当地的苔藓和维管植物,也有可能吸附了一些煤颗粒,但是由于技术手段的限制,煤炭的贡献在当前的数据解析下无法定量评估。     

基于HJ-1数据的木孜塔格峰地区雪深时空变化

以木孜塔格峰地区为研究区,从不同坡度、坡向的样方内测量雪深和采集光谱,通过分析归一化差分雪盖指数（Normalized Difference Snow Index,NDSI）、反照率、HJ-1卫星的红外波段反射率与雪深的相关关系,建立了适用于HJ-1星的积雪深度反演模型,估算出2012年4月14日-25日木孜塔格峰地区的雪深时空变化,并结合实测数据进行验证。结果表明:反照率反演模型的复相关系数为0.992;通过NDSI阈值区分混合雪盖像元和积雪像元,雪深估测精度可达92.78%。冰川区的反照率、NDSI与海拔的相关系数分别为0.626和0.733,且高海拔带反照率值明显高于低海拔带的反照率值。受西风带降雪的影响,非冰川区的北坡雪深值较大;西坡、南坡次之;东坡最小,且雪深最大值出现在坡度约等于10°处。雪深估测的相对误差随着样地的坡度增大而增加,坡度为15°时相对误差较大。     

广州市人行天桥叶面滞尘粒度特征及其来源

对2009 年广州城区36 座人行天桥上采集的植被叶面滞尘样品进行粒度分析,粒度结果显示：叶面滞尘多为沙质粉沙,粉沙、沙和黏土体积分数的平均值分别为53.99%、41.34%和4.67%;粒度频率分布呈三峰型,主峰态在10~200 μm 之间。4 个市辖区叶面滞尘的粒度特征都较为相似,说明整个广州城区的叶面滞尘在成因和来源上都较为一致。叶面滞尘中的总悬浮颗粒物（TSP≤100 μm）体积分数极高,PM2.5 和PM10 体积分数略低;PM2.5/PM10 的平均值为0.36,推测其更多来自道路扬尘与建筑扬尘等局地污染源。风沙动力研究指示：其物源主要是由城区30km范围内短距离悬浮搬运而来,属内源性颗粒物。     

Intra-annual variability of satellite observed surface albedo associated with typical land cover types in China

Surface albedo is a primary causative variable associated with the process of surface energy exchange. Numerous studies have examined diurnal variation of surface albedo at a regional scale; however, few studies have analyzed the intra-annual variations of surface albedo in concurrence with different land cover types. In this study, we amalgamated surface albedo product data (MCD43) from 2001 to 2008, land-use data (in 2000 and 2008) and land cover data (in 2000); quantitative analyses of surface albedo variation pertaining to diverse land cover types and the effect of the presence/absence of ground snow were undertaken. Results indicate that intra-annual surface albedo values exhibit flat Gaussian or triangular distributions depending upon land cover types. During snow-free periods, satellite observed surface albedo associated with the non-growing season was lower than that associated with the growing season. Satellite observed surface albedo during the presence of ground snow period was 2-4 times higher than that observed during snow-free periods. Surface albedo reference values in typical land cover types have been calculated; notably, grassland, cropland and built-up land were associated with higher surface albedo reference values than barren while ground snow was present. Irrespective of land cover types, the lowest surface albedo reference values were associated with forested areas. Proposed reference values may prove extremely useful in diverse research areas, including ecological modeling, land surface process modeling and radiation energy balance applications.     

中国北方不同区域典型站点降尘特性的对比

2001年4月—2002年3月,选择位于中国北方沙尘源区的沙坡头和奈曼及位于黄土高原的古县进行了一年的大气降尘监测,并对不同季节降尘量、降尘粒度分布和元素组成进行了系统分析。不同站点大气降尘的这些特性的相同点可能反映了中国北方大气降尘的共性,不同点则反映了沙尘源区与沉降区大气降尘的差异。相同点主要表现为:降尘均主要源于地表沙尘释放,且以地方性颗粒物为主;季节分布均为春季最大、夏季次之、秋季最小;冬半年降尘中远源粉尘含量均大于夏半年,且降尘均主要表现为常态存在的非尘暴降尘。差异性主要表现为:奈曼和古县降尘中人为影响较大;古县降尘受远源影响最大,奈曼次之,沙坡头最小;降尘中粗颗粒物含量以沙坡头最高,古县略低于奈曼;粒度特征的季节变化受风力、源区距离、搬运方式和源区物质组成等因素的共同影响,且具有明显的区域差异。此外,降尘粒度大小与风力并不一定呈正相关,因此,利用黄土粒度来指示冬季风强度时必须结合其他代用指标才能做出较正确的判断。     

Meltwater production in Antarctic blue-ice areas: sensitivity to changes in atmospheric forcing

In the near coastal regions of Dronning Maud Land, Antarctica, below-surface ice-melt in blue-ice areas has been observed. The low scattering coefficients of the large-grained blue-ice allow penetration of solar radiation, thus providing an energy source below the ice surface. The sub-surface meltwater is significant enough to show up on remote-sensing imagery in the form of ice-covered lakes. Adjacent snow-accumulation areas have much higher scattering coefficients and consequently limit solar radiation penetration in these regions. These snow and ice surfaces are generally below freezing, and little surface melting occurs. To assess the response of these melt features to changes in atmospheric forcings such as cloudiness, air temperature, and snow accumulation, a physically-based model of the coupled atmosphere, radiation, snow, and blue-ice system has been developed. The model consists of a heat transfer equation with a spectrally-dependent solar-radiation source term. The penetration of radiation into the snow and blue-ice depends on the surface albedo, and the snow and blue-ice grain size and density. Model simulations show that ice melt occurring in this area is sensitive to potential variations in atmospheric forcing. Under certain conditions more traditional surface melting occurs and, under other conditions, the existing melt processes can be shut down completely. In light of the sensitivity of this system to variations in atmospheric forcing, and the ability to view melt-related features using remote sensing, a tool exists to efficiently monitor variations in Antarctic coastal climate.     

陕西省榆林市秋冬季黑碳观测研究

利用2011年秋冬季榆林大气成分站黑碳浓度、颗粒物质量浓度、大气能见度、地面气象资料,计算边界层高度、气溶胶吸收系数、大气消光系数,导出单次散射反照率,并对其进行分析讨论。结果表明：（1） 榆林秋冬季平均黑碳浓度为2.6 μg·m^-3。（2）黑碳占颗粒物质量浓度PM_1.0比值为10.6%,黑碳与颗粒物质量浓度PM_1.0、PM_2.5、PM₁₀相关系数分别为0.91、0.91、0.72。（3）黑碳浓度受边界层高度影响,沙漠风场对黑碳的堆积输送起主导作用。（4） 榆林地区气溶胶吸收系数与大气消光系数比值为16.8%。（5）单次散射反照率平均值为0.72。     

中亚沙尘气溶胶时空分布特征及潜在扩散特性分析

中亚地处干旱和半干旱气候区,是全球沙尘气溶胶贡献度较大的区域。利用中分辨率成像光谱仪（Moderate-resolution Imaging Spectrometer, MODIS）和云—气溶胶偏振雷达（Cloud-Aerosol Lidar with Orthogonal Polarization, CALIOP）遥感数据,从宏观角度对2002-2015年中亚地区气溶胶光学厚度（Aerosol Optical Depth, AOD）时空分布特征及沙尘气溶胶光学特性垂直分布特征进行分析,利用拉格朗日混合型的扩散模型（Hybrid Single Particle Lagrangian Integrated Trajectory, HYSPLIT）讨论沙尘运输的季节性变化。结果表明：① 中亚AOD空间分布呈现显著的季节性差异,四季均值春（0.412）>夏（0.258）>冬（0.167）>秋（0.159）,14年间呈现增加趋势;② 中亚AOD高值区域主要集中于咸海地区和新疆的塔里木盆地,其中,咸海地区AOD年均值为0.278,年均增幅为3.175%,主要受咸海退化所导致的干涸湖底裸露面积加大的影响;塔克拉玛干沙漠地区AOD年均值为0.421,年均增幅0.062%,主要受温度和风速两方面的影响,不同季节下主导因素略有差异;③ 尘源区气溶胶主要集中在近地面0~2 km范围内,沙漠上空气溶胶退偏比范围（10%~45%）略大于咸海上空（15%~30%）;咸海地区色比值（0.3~0.8）小于沙漠地区（0.5~0.9）,且在0~2 km和4~6 km有两个高频色比值分别为0.5和0.3,说明相比沙尘气溶胶,咸海地区的盐尘气溶胶球形程度较高,颗粒更小,飘散高度更高;④ 咸海地区盐尘潜在扩散方向主要以东北,西南和南为主,向东北方向的扩散距离最远,影响范围可达俄罗斯中部地区,西南方向扩散路径高度和距离较近,主要影响乌兹别克斯坦和土库曼斯坦,但发生比例相对较高,塔克拉玛干沙漠地区起尘后大部分沙尘颗粒仍沉降在尘源区附近,向东部地区扩散的沙尘气溶胶,主要影响中国青海、甘肃、宁夏、陕西等地区。