德雷克海峡上层海洋温度的年代际变化

采用经验模分解方法分析了德雷克海峡上层海洋温度的年代际变化特征.结果表明德雷克海峡上层海洋平均温度在1976-1986年以平均每年0.124 ℃的速度下降,而在1987-1998年以每年0.144 ℃的速度上升.与南方涛动指数的年代际时间尺度分量的相关性分析结果表明,热带太平洋海面气压场的变化对德雷克海峡上层海洋温度的年代际变化有一定影响.     

The use of selected pseudo-invariant targets for the application of atmospheric correction in multi-temporal studies using satellite remotely sensed imagery

Because atmospheric effects can have a significant impact on the data obtained from multi-spectral satellite remote sensing, it is frequently necessary to make corrections before any other image processing can be started. This paper describes a robust and relatively simple atmospheric correction method that uses pseudo-invariant targets (PITs) in conjunction with the empirical line method. The method is based on the selection of a number of suitable generic PITs, on the basis that they are large, distinctive in shape, and occur in many geographical areas. Whereas the multi-temporal normalization method corrects all images to a selected reference image, in this method images are simultaneously corrected using targets with a range of estimated surface reflectance values. The paper describes some applications of the method for a range of environmental studies involving water quality and air pollution monitoring, and mapping land-cover changes.     

1964-2019年辽宁省平均风速时空演变特征及其影响因素

风的变化程度和强弱会引起其他气象要素变化,探究风场时空分布及其历史变化规律,可为气候预报预测和风能科学利用提供重要参考.基于1964-2019年辽宁省23个气象站点风速及其他气象因子的逐日监测数据,利用小波分析及经验正交分解法对近56 a辽宁省风场、风速时空变化特征进行分析,并结合主成分分析法揭示其影响因素.结果表明:...     

Highland Boundary Fault Zone: Tectonic implications of the Aberfoyle earthquake sequence of 2003

The Highland Boundary Fault Zone (HBFZ) is one of the major faulted tectonic boundaries in Great Britain. Historically, seismicity has occurred in this zone around the town of Comrie. But an earthquake sequence that occurred in 2003 near the village of Aberfoyle (M_L 1.3–3.2) was the first significant activity to be recorded in the HBFZ since the installation of modern seismograph networks in the 1970s. This study describes detailed analysis of these data. The waveform signals of the events were almost identical and by applying a cross-correlation technique combined with multiple event location, the alignment of the events was found to be WSW–ENE. This alignment matches one of the nodal planes determined by joint focal mechanism analysis. The fault plane dips to the northwest, and shows oblique sinistral strike–slip with normal movement. The orientation of the event alignment matches the direction and orientation of observed features in the HBFZ. Hence, it is concluded that the WSW–ENE striking nodal plane was the causative fault that is associated with the HBFZ. The orientation of maximum compressional stress is rotated from the regional average expected due to the Mid-Atlantic ridge-push force. This rotation is possibly explained by stresses due to postglacial rebound. Smaller events in the sequence were used as empirical Green's functions and deconvolved from the larger events to determine source time functions. The corresponding corner frequencies matched results from spectral fitting, showing that the events were of relatively low stress drop.     

Spatial patterns from EOF analysis of soil moisture at a large scale and their dependence on soil,land-use,and topographic properties

We hypothesize that the spatial and temporal variation in large-scale soil moisture patterns can be described by a small number of spatial structures that are related to soil texture, land use, and topography. To test this hypothesis, an empirical orthogonal function (EOF) analysis is conducted using data from the 1997 Southern Great Plains field campaign. When considering the spatial soil moisture anomalies, one spatial structure (EOF) is identified that explains 61% of the variance, and three such structures explain 87% of the variance. The primary EOF is most highly correlated with the percent sand in the soil among the regional characteristics considered, but the correlation with percent clay is largest if only dry days are analyzed. When considering the temporal anomalies, one EOF explains 50% of the variance. This EOF is still most closely related to the percent sand, but the percent clay is unimportant. Characteristics related to land use and topography are less correlated with the spatial and temporal variation of soil moisture in the range of scales considered.     

The Role of Changes in the Annual Cycle in Earlier Onset of Climatic Spring in Northern China

Climatic changes in the onset of spring in northern China associated with changes in the annual cycle and with a recent warming trend were quantified using a recently developed adaptive data analysis tool, the Ensemble Empirical Mode Decomposition. The study was based on a homogenized daily surface air temperature (SAT) dataset for the period 1955–2003. The annual cycle here is referred to as a refined modulated annual cycle (MAC). The results show that spring at Beijing has arrived significantly earlier by about 2.98 d (10 yr)-1, of which about 1.85 d (10 yr)-1 is due to changes in the annual cycle and 1.13 d (10 yr)-1 due to the long-term warming trend. Variations in the MAC component explain about 92.5% of the total variance in the Beijing daily SAT series and could cause as much as a 20-day shift in the onset of spring from one year to another. The onset of spring has been advancing all over northern China, but more significant in the east than in the west part of the region. These differences are somehow unexplainable by the zonal pattern of the warming trend over the whole region, but can be explained by opposite changes in the spring phase of the MAC, i.e. advancing in the east while delaying in the west. In the east of northern China, the change in the spring phase of MAC explains 40%–60% of the spring onset trend and is attributable to a weakening Asian winter monsoon. The average sea level pressure in Siberia (55°–80°N, 50°–110°E), an index of the strength of the winter monsoon, could serve as a potential short-term predictor for the onset of spring in the east of northern China.     

某水电站库区滑坡滑速涌浪计算

对雅砻江流域某拟建电站库区边坡失稳后的滑速和涌浪高度进行计算。计算滑速采用潘家铮条分法,涌浪高度计算同时采用水科院经验公式法和潘家铮法两种方法。综合两种方法的计算结果获得库坝处滑坡产生的涌浪高度为0.41~0.88m,对拟建工程影响较小。此计算分析方法对类似工程具有借鉴意义。     

A new predictive formula for inception of regular wave breaking

Efforts are made to enhance the predictive formula for the inception of wave breaking. To achieve success, the existing formulas are extensively reviewed. They are categorized into four types, i.e., the McCowan type, the Miche type, the Goda type and the Munk type. The inherent relations among the different types are then exploited. The differences among each formula within a group are also discussed. Four representative formulas from the different types are chosen to compare with the measured data for a total number of 1193 cases reported in literatures. It is shown that Goda's and Ostendorf and Madsen's formulas are advantageous in general among the selected ones. Goda's formula, however, is found to be inaccurate as the beach slope becomes steeper than 1/10. Ostendorf and Madsen's formula is fairly good even for cases of very steep slopes, but its accuracy for the cases of ordinary slopes is not as good as Goda's. A new predictive formula for the inception of wave breaking is proposed. The unique index, defined by ψ′_b = (1.21 − 3.30λ_b)(1.48 − 0.54γ_b)ψ_b, where ψ_b = gH_b/C_b², H_b is the breaking wave height, C_b is the breaking wave celerity, λ_b is the breaking wave steepness, γ_b is the relative breaking wave height, and g is the gravity acceleration, is introduced. The incipient condition of wave breaking is then given by ψ′_b = 0.69. This formula is a significant improvement to the existing ones in terms of the accuracy. In addition, it is a local relation. Further verification shows that the proposed formula performs similarly well when applied to the field and to the waves over permeable bed.     

基于经验正交分析法的暴时热层大气密度时空分布规律

本文选取2002-2006年期间的36个强磁暴为研究对象,对CHAMP卫星加速度仪反演的实测大气密度进行经验正交分解,研究暴时热层大气密度的纬度分布特征,以及大气密度与ap指数、Dst指数的关系.结果表明,大气密度的纬度分布与季节相关,夏季半球的密度大于冬季半球,春秋季节南北半球的大气密度几乎对称分布;春秋季节白天大气密度在低纬地区呈现出赤道密度异常结构,在中高纬地区密度随纬度增加而减小,夜间则呈现抛物线的形状,赤道附近密度值最小.大气密度的纬度分布特征在若干天内具有良好的稳定性,发生时间相近的磁暴事件,纬度分布曲线非常相似,并且暴前与暴时的纬度分布变化不大.相关性分析表明,大气密度滞后ap指数2~6 h,相对Dst指数平均提前0~1 h,对磁暴的响应速度在日照区比在阴影区快,大气密度与ap指数、Dst指数具有较好的相关性.     

钦州湾人工海滩剖面变化过程

波浪和潮汐作用下的海滩剖面动态变化过程是海岸演变及沿海防护工程设计与旅游资源规划的核心内容。本文以广西钦州湾沙井半岛人工海滩为研究区, 基于GPS-RTK采集的2018年1月—2019年12月的逐月剖面高程实测数据, 通过分析剖面冲淤和单宽体积变化, 利用EOF(Empirical Orthogonal Function)函数揭示剖面的高程变化模式, 进而探讨海滩剖面的动态演变过程。研究的主要结果表明: 1) 在观测期间, 人工海滩剖面的冲淤情况整体展现出冬春季淤积、夏秋季侵蚀的变化特征; 2) 人工海滩剖面因泥沙横向输移而导致不同横向分带的单宽体积变化趋势呈差异性, 不同横向分带具有侵蚀与淤积交替出现的情况; 3) 人工海滩剖面的变化模式可划分为由强降雨及台风导致剖面高程明显降低的主要模式、波潮影响下的剖面高程经历强降雨及台风后逐渐淤积和恢复的次要模式、波浪破碎形成卷流引起滩面冲淤变化的其他模式。