Easy Path Wavelet Transform on Triangulations of the Sphere

The computation of sparse representations of data on the sphere (e.g. topographical data) is a crucial step for further processing such as multiple separation, migration, imaging and sparsity promoting data-recovery. The Easy Path Wavelet Transform (EPWT) is a new tool for sparse data representation that has recently been introduced for image compression. In this paper we consider the EPWT on spherical triangulations. It is a locally adaptive transform that works along pathways through the array of function values and exploits the local correlations of the data in a simple appropriate manner. In our approach the usual discrete one-dimensional orthogonal or biorthogonal wavelet transform can be applied. The EPWT can be used for defining a multiresolution analysis on the sphere in which the scaling spaces and the wavelet spaces depend adaptively on the data. Issues of implementation of the EPWT are also considered.     

新疆东部雪岭云杉与胡杨树轮记录的干湿变化对比分析

利用采自新疆东部的雪岭云杉和胡杨树轮样本研制出区域树轮宽度年表。相关分析发现雪岭云杉区域树轮宽度年表与上年8月至当年月标准化蒸发指数(SPEI)变化有较好相关性,相关系数为0.67 (P<0.001, n=54),同时胡杨区域树轮宽度年表也表现出较强的干湿变化信号(r=0.48, P<0.001, n=54)。利用线性回归模型重建了新疆东部1725–2013年上年8月至当年月SPEI变化,方差解释量为45.3%。利用雪岭云杉区域树轮宽度年表能够较好地重建新疆东部自1725年以来的上年8月至当年7月的SPEI变化,方差解释量达45.3%。重建结果揭示新疆东部1725-1728年,1737-1758年,1765-1804年,1829-1834年,1845-1852年,1888-1904年, 1915-1923年,1932-1961年,1969-1973年,1986-2001年偏湿;1729-1736年,1759-1764年,1805-1828年,1835-1844年,1853-1887年,1905-1914年,1924-1931年,1962-1968年,1974-1985年,2002-2013年偏干。新疆东部干湿变化与天山中西部干湿变化在年际变化上存在很强一致性,但在年代际变化上存在显著差异,并与甘肃河西走廊干湿变化存在紧密。胡杨树轮宽度年表与雪岭云杉树轮宽度年表所指示的干湿变化在年代际上存在一致性,但是胡杨对干湿变化响应往往滞后于雪岭云杉。     

帕米尔东北部昆仑圆柏850年树轮宽度年表的建立及其气候意义

利用帕米尔高原东北缘的昆仑圆柏树轮资料建立了850 a的树轮宽度年表(1165—2014年),是目前新疆最长的树轮年表。树轮宽度指数与乌恰站的气象资料相关分析表明:树轮宽度主要受水分条件限制,与降水量、降水日数和水汽压呈一致的正相关,其中树轮宽度标准年表与乌恰上年10月—当年7月的降水量的相关系数达到0.671。宽度年表与最高气温和最低气温呈反相关:当年生长季及其前期的最高气温与轮宽指数负相关,而最低气温(当年5月以外)与树木的生长正相关,表明生长季的较高的最高气温和冬季的较低的最低气温不利于树木的生长。树轮宽度指数与CRU格点降水资料的空间相关分析表明其能较好地反映帕米尔高原东部的降水变化,其次与新疆天山山区中部和南疆平原区的降水也具有较好的相关性。     

太原市灰霾期间黑碳气溶胶形貌与成分分析

为掌握太原市冬季灰霾发生期间黑碳气溶胶形貌特征和化学成分变化特点,分别于2011-12-30T08:00至2012-01-01 T 04:00和2018-11-25 T 08:00至2018-11-27 T 04:00灰霾发生期间在山西大学环境与资源学院楼顶使用MAY七级冲击式颗粒采样器每隔4h采集空气动力学直径分别为0.25～0.5μm、0.5～1.0μm以及1～2μm的大气单颗粒分析样品,运用带超薄窗口能谱仪的扫描电镜(JEOL JSM-6390)测定了样品中4330个颗粒的二次电子像及X射线能谱,通过基于蒙特卡罗模拟程序的定量电子探针微区分析技术对每个颗粒的元素原子浓度进行了计算,并对颗粒进行了分类与计数。共检测到6类颗粒,分别是矿物尘、碳质颗粒、钠盐颗粒、二次颗粒、富铁颗粒和其他,其中黑碳气溶胶数量相对丰度在2011和2018年样品中平均为26.8%和34.2%。按照伸长率(E)、纵横比(R)、是否与其他物质结合等将其分为伸展型、支链型、嵌入或粘附型和团聚型4种,反映了黑碳颗粒不同的老化过程。2011年样品中团聚型和支链型数量较多,而2018年样品中伸展型和嵌入型多于团聚型和支...     

赛里木湖流域雪岭云杉(Picea schrenkiana)树木径向生长对气候变化的响应

选用赛里木湖流域海西沟雪岭云杉(Picea schrenkiana)树轮宽度标准化年表与温泉气象站历年逐月降水(月降水量,降水量≥0.1mm、≥1mm、≥2mm、≥5mm日数)、温度(月平均气温、月平均最高气温、月平均最低气温、平均地温)、积雪(积雪日数,积雪深度≥1cm、≥5cm、≥10cm日数)、月平均相对湿度、日照百分率及日照时数等主要气候因子,以相关函数法分析赛里木湖流域树轮宽度对气候变化的响应。结果表明:海西沟树轮宽度标准化年表与气候要素相关较好的月份集中在上年7月、上年8月、当年1月及当年7月,与降水、积雪、相对湿度正相关,而与温度、日照百分率、日照时数负相关。对器测资料上年1月到当年12月所有不同时段的顺序组合与海西沟树轮宽度标准化年表的年轮指数序列进行相关普查分析表明,在所有组合中上年8月至当年7月的降水量及降水≥5mm日数与树轮年表的相关性最好,相关系数分别为0.630和0.708,上年8月至当年7月的降水可能是该地区树轮径向生长的主要限制因子,海西沟树轮标准化宽度年表与周围的降水和PDSI均具有较好的相关性,该年表对天山北坡和中亚部分地区的降水及PDSI有较好的代表性。     

Reconstructing the spatial distribution of large vegetation formations during the mid-Holocene in Romania: a predictive modeling approach

The present study tests the usefulness of SoLIM software and GIS techniques for the reconstruction of large vegetation formations from the mid-Holocene period in Romania. We used current reference climate data (temperature, precipitation) and the current extent of ecological regions in Romania to derive climate optimality functions for each vegetation formation. The optimality functions were used to simulate current and past distributions of vegetation. The results showed that the current and mid-Holocene simulated spatial distributions of vegetation are quite similar. Changes were found for about 14% of the Romanian territory (33 946 km²), the most important being the retreat of coniferous forests in favor of mixed forests and of mixed forests in favor of forest steppe. The former is validated by previous pollen-based studies showing the transition from coniferous forests to mixed forests that occurred in several areas of the country after the mid-Holocene. The study demonstrates the potential of this methodological approach to reconstruct past vegetation formations, and at the same time that it is a straightforward and expert knowledge-based method. Although our application uses only climate factors, the results can be further refined by incorporating additional drivers (soil and landform information, site-specific pollen and fossil data, wildfire data) for a more accurate inference of paleovegetation.     

天山山区与南北疆夏季温度变化对比分析

利用新疆1959～2000年夏季温度资料,采用滑动平均、最大熵谱、经验正交、线性回归方法,分析天山山区近42年来夏季温度变化的基本特征,并与南疆、北疆进行比较。结果表明：①天山山区在夏季温度的冷暖变化阶段以及最炎热、最凉爽年出现的年份与南疆和北疆不同;②夏季温度空间分布的同向性变化北疆最大,天山山区居中,南疆最小;夏季温度空间反向变化南疆和天山山区较大,北疆较小;③夏季温度的年代际变化趋势不同,天山山区持续增温,北疆波动增温,南疆变化稳定;④三种夏季增温的覆盖范围以最低温度为最广,其增温率天山山区最大,南疆最小,北疆居中。     

Microtremor study of site effects and soil-structure resonance in the city of Ljubljana (central Slovenia)

The city of Ljubljana is located in one of the three areas with the highest seismic hazard in Slovenia, and it is also the most densely populated. Site effects due to Quaternary sediments, which fill the up to 200 m-deep basin, are characteristic of the whole city area, but they can be especially strong in the southern part of Ljubljana, which is built on very soft lacustrine deposits. Existing microzonation studies of the city are inadequate, since there is a lack of borehole, geophysical and earthquake data. The microtremor horizontal-to-vertical spectral ratio (HVSR) method was therefore applied to a 200 m dense grid of free-field measurements over an area of 45 km² (1,223 measuring points) in order to assess the fundamental frequency of the sediments. The main difficulties in microtremor measurement arose from high levels of traffic and industrial noise, and from underground structures. Experimental conditions which can influence data quality, such as strong wind and water saturation of soil, were analysed. Very clear HVSR peaks were obtained in the entire southern part of the city, whereas in the northern part the site response is in general lower due to lower impedance contrast of gravel with the bedrock. The iso-frequency map of sediments shows a distribution in the range of 0.9–10 Hz. In the southern part of Ljubljana, sediment frequency correlates well with the thickness of soft sediments known from geophysical investigations and sparse drilling. Average amplitude of the HVSR peaks is considerably higher in the southern part (6.7 ± 2.4) than in the northern part (4.0 ± 2.0) of the city, indicating a high impedance contrast of lacustrine sediments with the bedrock. Microtremor measurements were also performed inside 122 buildings of various heights. We focused on important public buildings and selected blocks of flats and houses. To assess the longitudinal and transverse fundamental frequencies of each building, amplitude spectra and the spectral ratio between the upper floor and the basement were analysed for both directions. When one of these frequencies is close to a nearby free-field fundamental frequency, a potential soil-structure resonance is present. This was found in 12 of the measured buildings. Three of them are tall residential buildings (from 10 to 15 floors) with a fundamental frequency of 2–3 Hz, and nine of them are low-rise buildings (from 3 to 5 floors) with a fundamental frequency ranging from 3 to 4.5 Hz. Using the relationship between fundamental frequency and height, the typical height of buildings that might cause soil-structure resonance can be estimated at a given sediment frequency obtained from free-field measurements.     

Relative Kinematics of the Leading Edge and the Prominence in Coronal Mass Ejections

We present a statistical analysis of the relationship between the kinematics of the leading edge and the eruptive prominence in coronal mass ejections (CMEs). We study the acceleration phase of 18 CMEs in which kinematics was measured from the pre-eruption stage up to the post-acceleration phase. In all CMEs, the three part structure (the leading edge, the cavity, and the prominence) was clearly recognizable from early stages of the eruption. The data show a distinct correlation between the duration of the leading edge (LE) acceleration and eruptive prominence (EP) acceleration. In the majority of events (78%) the acceleration phase onset of the LE is very closely synchronized (within ± 20 min) with the acceleration of EP. However, in two events the LE acceleration started significantly earlier than the EP acceleration (> 50 min), and in two events the EP acceleration started earlier than the LE acceleration (> 40 min). The average peak acceleration of LEs (281 m s⁻²) is about two times larger than the average peak acceleration of EPs (136 m s⁻²). For the first time, our results quantitatively demonstrate the level of synchronization of the acceleration phase of LE and EP in a rather large sample of events, i.e., we quantify how often the eruption develops in a “self-similar” manner.