Temporal and spatial variability of cation and silica export in an alpine watershed,Emerald Lake,California

A reaction set of possible mineral weathering reactions is proposed to explain observed cation and silica export for the Emerald Lake watershed, a small Sierra Nevada, California catchment. The reaction set was calculated through a stoichiometric mole‐balance method, using a multiyear record of stream flow and snowpack chemical analyses and site‐specific mineral compositions. Reaction‐set calculations were intended to explore how the processes controlling stream cation and silica export depend on differing bedrock mineralogy across the catchment as snowmelt and runoff patterns change over the year. Different regions within the watershed can be differentiated by lake inflow subdrainages, each exhibiting different stream‐flow chemistry and calculated weathering stoichiometry, indicating that different silica and cation generation processes are dominant in wet steep portions of the catchment. Short‐term differences in stream concentrations were assumed to reflect ion exchange equilibria and rapid biological processes, whereas long‐term persistent stream concentration differences in different areas of the catchment were assumed to reflect spatial variability in mineral weathering stoichiometry. Mineralogical analyses of rock samples from the watershed provided site‐specific chemical compositions of major mineral species for reaction calculations. Reaction sets were evaluated by linear regression of calculated versus observed differences between snowmelt and stream‐flow chemistry and by a combined measure. Initially, single weathering reactions were balanced and evaluated to determine the reactions that best explained observed stream chemical export. Next, reactions were combined, using mineral compositions from different rock types to estimate the dependence of ion fluxes on lithology. The seasonal variability of major solute calculated fluxes is low, approximately one order of magnitude, relative to the observed three orders of magnitude variability in basin discharge. Reaction sets using basin‐averaged lithology and Aplite lithologies gave superior explanations of stream chemical composition. Copyright © 2004 John Wiley & Sons, Ltd.     

南极纳尔逊冰帽的雪层及其成冰作用研究

纳尔逊冰帽雪—粒雪的演化依赖于融水渗浸冻结作用下的暖变质过程。积雪的密实化过程的快慢,取决于温度条件和融水的参与程度,以及自身的物理状况。粒雪的密实化过程表现为均匀且变幅小。纳尔逊冰帽成冰深度在23～25m,成冰历时17～19年。成冰带分为暖渗浸—重结晶带,渗浸—冻结带,消融带。     

Snow water equivalent over Eurasia in the next 50 years projected by aggregated CMIP3 models

Based on remote sensing snow water equivalent (SWE) data, the simulated SWE in 20C3M experiments from 14 models attending the third phase of the Coupled Models for Inter-comparison Project (CMIP3) was first evaluated by computing the different percentage, spatial correlation coefficient, and standard deviation of biases during 1979–2000. Then, the diagnosed ten models that performed better simulation in Eurasian SWE were aggregated by arithmetic mean to project the changes of Eurasian SWE in 2002–2060. Results show that SWE will decrease significantly for Eurasia as a whole in the next 50 years. Spatially, significant decreasing trends dominate Eurasia except for significant increase in the northeastern part. Seasonally, decreasing proportion will be greatest in summer indicating that snow cover in warmer seasons is more sensitive to climate warming. However, absolute decreasing trends are not the greatest in winter, but in spring. This is caused by the greater magnitude of negative trends, but smaller positive trends in spring than in winter. The changing characteristics of increasing in eastern Eurasia and decreasing in western Eurasia and over the Qinghai-Tibetan Plateau favor the viewpoint that there will be more rainfall in North China and less in the middle and lower reaches of the Yangtze River in summer. Additionally, the decreasing rate and extent with significant decreasing trends under SRES A2 are greater than those under SRES B1, indicating that the emission of greenhouse gases (GHG) will speed up the decreasing rate of snow cover both temporally and spatially. It is crucial to control the discharge of GHG emissions for mitigating the disappearance of snow cover over Eurasia.     

Methods for extraction of microorganism DNA from glacier surface snow

In order to thoroughly investigate the diversity of glacier microorganisms, four DNA extraction methods with different lysis patterns were tested and two screened methods (the Bosshard-Bano method and the Zhou method) were optimized for the most effective form of the filter membrane (cut vs. uncut), the DNA extraction method, and the precipitation method. The two optimized methods were then compared with the commercial Mo-Bio DNA extraction kit, and the results showed that the kit was generally suitable for extraction of microorganism DNA from glacier surface snow. Procedurally, it was found that a modified Bosshard- Bano method (i.e., cutting the filter membrane into pieces, using a specific lysis pattern [lysozyme (5 mg/mL)-protease K (1 mg/mL)-CTAB (1%)-SDS (1%)], performing the extraction only once by chloroform-isoamyl alcohol (24:1), and conducting DNA precipitation by pure ethanol) was also an effective and less expensive method for extraction of microorganism DNA from glacier surface snow.     

中国降雪气候学特征

利用逐日地面降雪观测资料,分析中国25oN以北范围内降雪量、降雪日数、雪带分布和各强度降雪的气候学特征,得到以下结论:①雪季长度与年降雪日数在东部呈纬向分布,大兴安岭北部最长(>210 d),长江以南最短(常年无雪或偶尔降雪);在西部青海省南部和西藏自治区北部最长(>300 d),滇、川、藏交界处及新疆自治区北部较长,南疆较短(<60 d)。年降雪量东南部最少,东北和西北北部较多(>30 mm),青海和西藏降雪量最多(>60 mm)。平均降雪强度江淮一带最大。②根据雪季降雪频次划分中国的雪带,东北大部、内蒙自治区东部、新疆北部、青藏高原大部、秦岭等地区为常年多雪带;长江以南的滇南、四川盆地、江浙沿海等地区为永久无雪带;其余地区为常年降雪带和偶尔降雪带。③不同区域各级降雪日数占总降雪日数的比例都是暴雪日数最少,大雪日数其次,小雪日数最多;但中雪降雪量占总降雪量的比例在东北北部、华北、西北、新疆、东南、青藏高原东部等区域仅高于小雪降雪量,而在黄-淮地区仅次于暴雪降雪量。④降雪年内分配在东北北部、西北、新疆、青藏高原东部等地区都呈双峰型,最多雪时节在早冬和晚冬、早春,隆冬时节并不是降雪最多时间,黄-淮和东南地区呈单峰型,东南地区峰值更陡。⑤总降雪日数和除暴雪外的各等级降雪日数与地理位置关系较明显,在中国东部主要随着纬度升高增加,在中国西部随海拔高度增加而增加;随着纬度升高,东部和西部的总降雪强度都减小,西部的小雪强度也减小。     

2011年全球重大天气气候事件及其成因

2011年,全球气温偏高,为有观测记录以来的第十个暖年,是近60年来出现拉尼娜事件的年份中全球气温最高的一年。2011年,全球热带气旋活动较常年偏少。4月,一次拉尼娜事件结束,9月又一次拉尼娜事件生成。年初,低温、寒流席卷亚洲大部,暴风雪频繁袭击北美地区。西欧和中国东部出现严重春旱。夏季,非洲东部经历了20世纪80年代以来最严重的干旱,而东南亚、巴基斯坦和中南美洲洪涝灾害严重。全球极端偏暖事件主要出现在欧洲西部和西北部、南亚南部、东亚中西部、北美东南部等地;极端偏冷事件主要出现在东亚、澳大利亚、非洲南部和美国东北部和西部等地。而南美中东部、东南亚及中国东南部、日本、澳大利亚北部、非洲西部等地出现了极端强降水事件。研究发现,2010／2011年拉尼娜事件和台风活动是导致东南亚洪涝出现的重要原因,而巴基斯坦洪涝主要与印度洋正位相偶极型海温分布有关。     

基于不同雪深的地面温度、雪（草）面温度与气温的关系

以新疆塔城基准站自动气象站2006年11月—2010年3月积雪深度≥0cm的451天为样本,对0cm地面温度、雪面（草面）温度、气温及云量、日照时数、雪深进行统计分析,找出不同积雪深度下地面温度、雪（草）面温度与气温的关系,结果显示：雪（草）面温度在积雪期,变化趋势与气温一致,受云量及日照时数影响明显,平均雪温低于平均气温;地温随雪深变化有20cm和50cm两个分界点,雪深≤20cm时,地温受雪深、气温影响较大,变化趋势与气温基本一致,地温高于气温,雪层较薄时,受云量和日照影响较明显。雪深超过20cm时,地温变幅趋向定值,地温变化仅受长时间温度变化影响,且不低于-5℃;雪深超过50cm时,地温趋于定值（-1℃）。     

乌鲁木齐逐月气温资料均一化检验和订正

选用1951-2008年乌鲁木齐市气象站逐月最高、最低及平均气温资料,用标准正态检验（SNHT）方法对逐月气温资料序列进行均一化检验,并选用差值法对因迁站引起的断点资料进行订正,检验结果显示,月气温序列断点所在的年份与年序列中检验出的断点基本相对应,即气温资料均在迁站距离较远的1975年产生了断点;各月的检验结果存在一定的差异,5-9月气温较高的月份资料受迁站的影响较大,而且产生了断点,并通过了0.05的显著性水平。用不同的权重比例对月序列进行订正,并选择累积距平方法对5-9月气温序列订正前后的变化趋势作了比较分析,发现订正前后趋势确有较显著的变化。     

黄土高原一次β中尺度大暴雨特征及成因分析

利用NCEP／NCAR逐日6h分析资料和常规观测资料,分析了2011年2月25日一28日山西连续降雪天气过程（以下简称2．25降雪）。①2．25降雪过程经历了三个阶段：2月25日为回流降雪阶段,26日一27日为倒槽冷锋与回流降雪共同影响降雪阶段,28日为低空切变线影响降雪阶段。②2．25降雪过程涵盖了华北地区大到暴雪的三个类型：回流类降雪、倒槽冷锋类降雪、低空切变线类降雪。③通过温湿场分析得出,对于低空切变线类降雪,对流层中层的湿核对降雪的开始有一定的指示意义。降雪未开始之前对流层中层有湿核,随着时间的推移,湿核向低层扩展,整个对流层中低层变为高湿区,降雪开始。当对流层中层变为干区,并向低层扩展,降雪过程结束。对于回流类降雪,低层回流对回流降雪起到冷垫的作用。④通过涡度场分析得出,对流层低层的负绝对涡度中心对其东侧的降水有指示意义,如果其东侧对流层低层配合有正涡度核,降雪强度较大,维持时间较长。⑤地面层出现的负绝对涡度中心说明近地面层有小高压系统的存在,这是因为低层回流冷垫作用形成的孤立小高压体。⑥28日降雪维持机制是条件性对称不稳定。     

基于实际灾情的青海高原雪灾等级（评估）指标研究

利用1951—2008年青海高原雪灾实际灾情资料,通过统计计算各年份雪灾造成的牲畜死亡率,并进行排序,参照了计算SPI(标准化降水指数)不同等级干旱在全部干旱中所占比例的过程,确定了不同雪灾等级的阈值,制订了基于实际灾情的雪灾指标。并对几次典型雪灾过程进行评估检验,结果表明:本研究确定的雪灾等级与DB63雪灾标准基本一致。在青海高原牧区,用雪灾造成的实际牲畜死亡率来确定雪灾等级指标,评估雪灾受灾程度,是一种较为科学和具有很好的现实指导意义的新方法。