地—空界面天然中子辐射场的扰动及其环境意义

介绍了地—空界面天然中子流的来源和轻便型天然中子流测量仪器。论述了地—空界面天然中子辐射场的扰动。理论与长期观测表明,在地—空界面上天然中子流注量率随高程的增加而呈指数规律增加,而在近地表(20m内)却随距地面高度的增加而呈指数规律减少;天然中子流注量率与大气压力呈负相关关系,气压系数为(-0.060～-0.064)中子计数/30min/kPa;地—空界面天然中子流的纬度效应与高空中更显著;天然中子流注量率异常与气象的变化密切相关;地表介质的含水率增高,则地—空界面上升快中子流明显降低。通过对地一空界面天然中子流测量,可以揭示气象的瞬态变化、确定地表介质的含水率的关系,以及在地震预报与环境电离辐射评价方面具有重要的科学意义与实用价值。     

Transport over a narrow shelf: Exuma Cays, Bahamas

Current meter and temperature data were collected over a 402-day period from an outer shelf and a tidal channel study site in the Exuma Cays, Bahamas. The shelf width is less than 2 km, and floods and ebbs through a nearby tidal channel extend across the entire shelf and reduce coherence of wind forcing and along-shelf flow. The data are used in perturbation analyses to investigate the across-shelf turbulent transport of heat and momentum over seasonal time scales. Data show a net landward transport of both heat and momentum over the course of the study, but the perturbation products contain distinct seasonal cycles. In fall and winter months, across-shelf heat and momentum fluxes are landward, while during spring and summer months fluxes are seaward. Comparison of shelf-water temperature with the temperature of bank water leaving on the ebb suggests that seasonal cycles of across-shelf heat and momentum in shelf waters are influenced by the seasonal export of relatively warm and cool water from Great Bahama Bank.Responsible Editor: Iris Grabemann     

冻融试验对土中含水量分布的影响

The silty clay and silty loam are two typical soil types obtained from two test sites along the Qinghai-Tibet railway. The two types of soil have been designed various initial dry densities, water eontents, temperature conditions in repeated freezing and thawing tests with free access to water at the bottom. Afterfreeze-thaw cycles, the moisture content in the freeze-thaw zone increases more than that in the unfrozen zone to the peak approximately at the top of the samples. With comparison of the water contents in the frozen and thawed states, the moisture content in the upper freeze-thaw zone in the frozen state is greater than that in the thawed state, while that in unfrozen zone in the frozen state is smaller than that in the thawed state. Within the region of the frost front, the water content in frozen state is smaller than that in thawed state. These findings help to study the freeze-thaw mechanisms deeply and perfect the forecasting module of moisture transferring in freeze-thaw cycles.     

渍水麦田土壤水分动态模型研究

根据土壤水分平衡原理，建立了一个反映土壤渍水、可与小麦生长模型耦合的土壤水分动态模型，尤其考虑了因地下水位较浅而引起的毛管上升水量和土壤导水率的变化对土壤含水量的影响。采用盆栽小麦水分试验资料验证了日蒸散量的模拟值，利用湖北荆州农业气象试验站和江苏金坛农业气象试验站的土壤水分历史资料对建立的模型进行了综合测试和验证，结果表明:蒸散量、地下水位和0～50 cm土壤含水量的模拟值与实测值具有较好的一致性，模型能可靠地预测多雨和渍水地区麦田土壤水分的变化动态     

SSM/I资料反演大范围地表湿度试验

利用SSM/ I遥感数据, 结合2002年汛期“973”外场观测资料及T106资料, 借助微波辐射传输正演模型, 通过物理反演原理提取SSM/ I低频19 GHz通道像元平均地表微波比辐射率, 然后利用地表微波辐射模型, 估算SSM/ I像元的地表湿度信息。以2002年8月中旬发生在长江流域的暴雨天气过程为例, 将反演得到的地表湿度信息与地面观测到的降水信息进行对比分析, 并与地面的洪涝特征进行对比分析, 得到了与地面降水观测结果较为一致的对比结果。     

洪山泉流量动态系统分析

为查明洪山泉域的开采程度,在前人研究基础上,建立了现阶段泉流量-降雨量的线性模拟模型。通过对模型的系统辨识,对系统的"慢时变"现象作出了合理解释,并发现系统在1994年以后发生了"快时变",说明开采量从1995年开始迅猛增加。同时,由多年来泉流量序列的自相关分析,发现其宏观周期到2000年基本保持不变,说明虽然第二输入(即人为开采量)对该系统的作用已不可忽略,但尚未达到足以改变其宏观频率的程度。     

夏季红枫湖地区农田土壤-大气界面汞交换通量的初步研究

采用动力学通量箱法(Dynamic Flux Chamber)与高时间分辨率大气测汞仪联用技术对贵州红枫湖地区土壤-大气界面间汞交换通量进行了初步研究.结果显示,红枫湖地区土壤-大气界面间汞交换通量变化范围为-8.6 ng～215.3 ng@m-2@h-1,平均27.4士40.1 ng/m2@h(n=255);且土壤与大气界面间的汞交换是双向的既有土壤汞的释放,又有大气汞的沉降,主要以土壤汞的释放为主(n释放=253,n沉降=2n).土壤汞的释放通量与土壤温度、气温、光照强度有强相关关系,相关系数分别为0.80、0.83、0.74.     

四川雅安地质灾害时空预警试验区初步研究

借鉴美国旧金山湾和香港地区的经验,提出了地质灾害监测预警试验区建设和研究思路。经过近两年的工作,初步建成了四川雅安地质灾害监测预警试验区。取得的阶段性成果主要有:(1)根据现场考察和试验区地质灾害数据库,统计研究了降雨型滑坡的几何特征;(2)建成了由20台遥测雨量计构成的降雨观测网,取得了2002年4月～2003年8月的降雨观测数据;(3)结合历史降雨资料分析,初步研究了雅安试验区的年、日、小时和十分钟最大降雨特征;(4)研制了斜坡岩土体含水量野外监测仪,取得了桑树坡试验点2003年4月～8月的实时监测数据;(5)自上而下分4层研究了斜坡岩土层含水量变化,发现了岩土层含水量变化对降雨过程的滞后性;(6)基于区域地质灾害评价预警的递进分析理论与方法(AMFP),利用地质灾害因子分析结果,分别计算了雅安试验区地质灾害"发育度"和"潜势度";(7)利用2003年8月23～25日的过程降雨观测资料,对雅安试验区在该降雨过程中发生的地质灾害事件进行了时空预警反演模拟研究,计算出的地质灾害"危险度"分布比较符合实际,"危险度"可以作为预警指数使用。     

Hydro-thermal performance of multilayer capillary barriers in arid lands

In this study, a capillary barrier system was designed and tested for an arid land environment. To simulate arid land conditions of high temperature and sub-irrigation systems, the barrier was subjected to thermal and hydraulic gradients in opposite directions; to test the barrier system under these severe conditions, an experimental apparatus was designed and fabricated. The multilayer capillary barrier consisted of three layers made of silica sand, a mixture of sand and bentonite in equal portions, and a mixture of clay (25%) and aggregate (75%). Several one dimensional coupled heat and moisture tests were performed. Temperature variations along the thickness of the barrier were recorded as a function of time, and at the end of each test, the barrier was sliced into small sections, for the determination of volumetric water content as a function of distance from the heat source. The experimental results were discussed in view of the barrier's intended purpose of its ability to store moisture for long time durations. Coupled heat and moisture flow equations were developed and solved numerically via a finite difference method. Diffusivity parameters were calculated by using experimental results, a numerical model, and Powell's conjugate directions method of nonlinear optimization. The model was calibrated and the results were discussed. Good agreement between calculated and experimental results was obtained. This revised version was published online in July 2006 with corrections to the Cover Date.     

Soil moisture potential and water content in the unsaturated zone within the arid Ejina Oasis in Northwest China

Three soil profiles were selected in the Ejina Oasis, northwest China, to determine water content profiles and evolution of soil moisture potentials in the unsaturated zone within the arid area. The total soil moisture potentials have been monitored for about 3 months in 2001 at different depths in the soil profiles. The occurrence and movement of water in the unsaturated zone was analyzed using the zero flux plane (ZFP) method. It is shown that convergent ZFPs and divergent ZFPs may occur at depths between 0.5 and 3.0 m, and that the depth of the ZFPs was controlled by the root zone of plants growing on the land surface. Profiles of the total soil moisture potentials were observed to be coincident with those of the water contents at the three experimental sites. The total soil moisture potential showed a slight increasing trend and the ZFPs tend to vanish from summer to winter as the water extraction by roots decreased. Evapotranspiration through vegetation has an important bearing on the water content and the total potential in the unsaturated zone.