承德初霜冻预报指标分析及其预报方法

应用常规观测资料与ncep1°×1°再分析资料,对承德市各县区初霜的时空分布特征及南北县区初霜出现时间的稳定性进行了分析,在对117个初霜环流形势分析的基础上,建立了初霜预报的天气概念模型;筛选因子,分县区确立了预报指标;采用概率、指标、数值预报产品相结合的方法及概率区间取值法建立了分县区初霜预报模型;检验表明,该模型对于中重度初霜冻预报准确率可达95%以上,对轻度初霜的预报准确率可达68%以上,无漏报出现。     

博州农区近50年终霜冻的变化趋势

利用博州农区3个气象站1958-2007年的终霜冻观测资料,分析了其变化趋势。结果表明：博州不同地区终霜冻出现时间差异较大,温泉地区较博乐、精河地区分别偏早15d、20d;在博州自东向西随着海拔高度的增加,终霜冻的变幅增加,不稳定性增加;博州农区终霜冻的变化均呈提前趋势,博乐、精河、温泉三地又以博乐最为明显,提前速率为0.17d／a;博州农区终霜冻的变化具有明显的阶段性;博州三地终霜冻年际变化均具有4-5a、15a的振荡周期,而温泉还具有不同于其他两地的35a振荡周期。     

HYDROLOGICAL FUNCTION OF A MOUNTAIN FEN AT LOW ELEVATION UNDER DRY CONDITIONS

Mountain fens are limited in their spatial extent but are vital ecosystems for biodiversity, habitat, and carbon and water cycling. Studies of fen hydrological function in northern regions indicate the timing and magnitude of runoff is variable, with atmospheric and environmental conditions playing key roles in runoff production. How the complex ecohydrological processes of mountain fens that govern water storage and release as well as peat accumulation will respond to a warmer and less snowy future climate is unclear. To provide insight, we studied the hydrological processes and function of Sibbald fen, located at the low end of the known elevation range in the Canadian Rocky Mountains, over a dry period. We added an evapotranspiration function to the Spence hydrological function method to better account for storage loss. When frozen in spring and early summer, the fen primarily transmits water. When thawed, the fen's hydrological function switches from water transmission to water release, leading to a summertime water table decline of nearly 1 m. Rainfall events larger than 5 mm can transiently switch fen hydrological function to storage, followed by contribution, depending on antecedent conditions. The evapotranspiration function was dominant only for a brief period in late June and early July when rainfall was low and the ground was still partially frozen, even though evapotranspiration accounted for the largest loss of storage from the system. This research highlights the mechanisms by which mountain peatlands supply baseflow during drought conditions, and the importance of frozen ground and rainfall in regulating their hydrological function. The study has important implications for the sustainability of low elevation mountain fens under climate change.     

冬小麦拔节期灌溉防霜冻效果研究

以矮抗58为研究对象,在冬小麦拔节期设置灌溉与未灌溉两种水分处理,通过对无霜冻年份(2012年)和晚霜冻年份(2013年)的对比试验,分析晚霜冻害对冬小麦群体密度、干物质积累、产量及其构成要素的影响,探讨拔节期灌溉的防霜效果。研究结果表明:1)孕穗-抽穗期发生晚霜冻害可使冬小麦群体密度下降、产量显著降低。2012年的产量整体高于2013年的,且2012年未灌溉处理的产量显著高于2013年灌溉处理的(P0.05);受霜冻影响,2013年灌溉与未灌溉的成熟期密度分别比抽穗期下降11.8%和14.8%,地上部分总干物质重先显著下降而后逐渐恢复,和抽穗期相比其下降幅度分别为18.5%(灌溉)和33.7%(未灌溉)。2013年成熟期叶片干重占地上部分总干物质重比例为43.5%(灌溉)和41.0%(未灌溉),显著高于2012年的16.3%(灌溉)和4.1%(未灌溉)。2)无论是否有霜冻害发生,拔节期灌溉均可显著提高产量,灌溉处理产量分别比未灌溉处理的偏高16.3%(2012年)和24.5%(2013年)。霜冻年份拔节期灌溉处理可显著降低穗粒数损失和抽穗期以后叶面积指数的衰减速度。3)2013年灌溉处理较2012年灌溉处理减产23.6%,未灌溉处理较2012年未灌溉处理减产32.9%。拔节期灌溉能够有效减少霜冻造成的产量损失,但这主要是由水分增加所引起,抽穗期的冬小麦抗霜能力并没有提高。     

Frost-heave properties of saturated compacted silty clay under one-side freezing condition

In seasonally frozen regions, the frost-heave properties of soil play a significant role in its upper-structure performance and durability. To investigate the frost-heave behaviors of saturated, compacted silty clay soil widely used as subgrade material, a series of one-side freezing tests was carried out; and the freezing depth and frozen front effected by the compactness, temperature, overburden pressure, and water-supply condition were analyzed and discussed. The results show that the moving speed of the frozen front and growth rate of the frozen depth are positively correlated. The frost heave is maximum in the frost-heave stability condition. The frost ratio of saturated soil is proportional to the water supply and cooling temperature under a one-side freezing condition. The frost ratio of saturated soil is inversely proportional to the initial compactness of the soil specimen and the overburden pressure.     

安徽省茶叶春霜冻发生规律及风险分布

基于2010—2014年安徽省78个市县茶园面积资料,把安徽省茶叶种植基地县划分为3个茶区。利用1980—2014年早春日最低气温观测资料,计算了茶区各基地县春霜终日、春霜日数和不同等级霜冻害发生频率,并对其分布特征进行了分析。结果表明:近35a安徽省茶区平均终霜期南部早于北部;春霜日数皖西大别山茶区出现最多,皖南黄山茶区最少。特晚终霜日和偏晚终霜日的指标日皖南宣城茶区均明显迟于皖西和皖南黄山茶区。特晚终霜日主要发生在20世纪80年代,偏晚终霜日主要发生在80年代和90年代。近35年轻度春霜冻皖西大别山茶区(六安)发生频率最高,中度和重度春霜冻皖南宣城茶区(绩溪)发生频率最高,轻度、中度和重度春霜冻发生频率均随年代呈下降趋势。依据风险分析理论对安徽茶区基地县进行了春霜冻风险分析,得出其风险的空间分布特点,结论可为指导春茶生产提供气象保障。     

福建霜冻时空分布特征及环流背景分析

利用福建省内68个地面测站1981—2011年1—4月、10—12月逐日观测资料,结合最低地表温度、天气现象、最低气温作为福建霜冻判别指标,探讨福建霜冻气候特征及环流背景形势。研究发现:1)福建年平均霜冻天数、初(终)霜冻日、无霜冻期具有明显地域差异,等值线基本呈东北—西南走向,与台站海拔高度具有良好相关性。区域平均初霜冻日、终霜冻日、无霜冻期总体分别呈推迟、提前、延长的变化趋势。2)全省大范围霜冻天气呈现发生频率低、过程持续时间短、总体逐渐减少的特征。3)霜冻越强,发生越晚,结束越早,且出现天数越少。4)随着形势场特征线略有南压,霜冻逐渐增强,反之减弱。     

Changes in growing season in the Northeastern United States

ABSTRACT

Changes in growing season length (GSL) are of concern for agricultural, phenological, economic, epidemiological, and bioclimatological reasons. This research identifies spatial and temporal changes over the last several decades in GSL, along with the day-of-year of the last spring freeze and first autumn freeze, for the northeastern United States – a region particularly susceptible to such changes due to the large population and intense economic activities. Results suggest that growing season has significantly increased in length since 1980 as compared to prior to 1980, and both spatial and temporal variation in GSL has decreased for the region over time. Changes to GSL for this region are driven more by a shift in the first autumn freeze date than the last spring freeze date. The areas of greatest increase in GSL in the pre- vs. post-1980 period tend to be in the high elevations, near large water bodies, and near the largest cities. Results will assist environmental planners as they prepare mitigation and adaptation strategies amid a changing environment.     

A three‐phase thermo‐hydro‐mechanical finite element model for freezing soils

Artificial ground freezing (AGF) is a commonly used technique in geotechnical engineering for ground improvement such as ground water control and temporary excavation support during tunnel construction in soft soils. The main potential problem connected with this technique is that it may produce heave and settlement at the ground surface, which may cause damage to the surface infrastructure. Additionally, the freezing process and the energy needed to obtain a stable frozen ground may be significantly influenced by seepage flow. Evidently, safe design and execution of AGF require a reliable prediction of the coupled thermo‐hydro‐mechanical behavior of freezing soils. With the theory of poromechanics, a three‐phase finite element soil model is proposed, considering solid particles, liquid water, and crystal ice as separate phases and mixture temperature, liquid pressure, and solid displacement as the primary field variables. In addition to the volume expansion of water transforming into ice, the contribution of the micro‐cryo‐suction mechanism to the frost heave phenomenon is described in the model using the theory of premelting dynamics. Through fundamental physical laws and corresponding state relations, the model captures various couplings among the phase transition, the liquid transport within the pore space, and the accompanying mechanical deformation. The verification and validation of the model are accomplished by means of selected analyses. An application example is related to AGF during tunnel excavation, investigating the influence of seepage flow on the freezing process and the time required to establish a closed supporting frozen arch. Copyright © 2013 John Wiley & Sons, Ltd.