SW物候模型在北京樱花始花期预测中的应用

基于海淀气象站1981—2012年逐日平均气温资料和2014年3月逐日平均气温滚动预报资料,应用SW物候模型,进行了2014年北京玉渊潭公园杭州早樱始花期的预测试验,取得了较好的效果。试验结果表明:应用SW模型预测2014年杭州早樱的始花期,提前10天预测的结果(始花期为3月27日)和自然条件下的实况值偏差为3~4天,提前一周左右预测的结果(始花期为3月25日)和自然条件下的实况值,偏差为1~2天。研究结果进一步验证了SW物候模型用于观赏植物观赏期预测的适用性较高,可进行更广泛的业务试用。     

水位上升与荷载耦合作用下土坡稳定极限分析方法研究

边坡失稳产生的灾害不仅会给工农业生产带来巨大损失,也会对人民的生命财产安全造成巨大威胁。目前,滑坡灾害已与地震、火山并列成为全球3大地质灾害之一,其中由水库水位变化诱发的滑坡近来得到重视。因此,建立合理的边坡稳定性分析方法对预测以及防控滑坡灾害十分重要。实际中的边坡失稳过程往往在多种荷载因素的耦合作用下发生,但现有边坡极限分析等稳定性解析方法偏重于考虑单一荷载因素,难以合理考虑多类荷载耦合作用条件,缺乏对边坡稳定性依赖加载过程这一现象的合理解释。本文在极限分析原理的基础上,将水库区边坡所受荷载凝练为水位上升与坡顶加载的耦合作用。将水位荷载简化为水位线以下土体受到浮力以及黏聚力的减小,建立了一个土坡稳定性分析方法,编写了相应的数值计算程序,通过与离心模型试验结果进行对比验证了方法的有效性。该方法计算结果表明,边坡稳定性随坡顶荷载增加单调下降,而随水位上升表现出先降低后增加的非单调变化。因此,坡顶荷载与水位上升耦合加载过程中,边坡稳定性对于加载过程具有显著的依赖性。     

First-order analytic propagation of satellites in the exponential atmosphere of an oblate planet

The paper offers the fully analytic solution to the motion of a satellite orbiting under the influence of the two major perturbations, due to the oblateness and the atmospheric drag. The solution is presented in a time-explicit form, and takes into account an exponential distribution of the atmospheric density, an assumption that is reasonably close to reality. The approach involves two essential steps. The first one concerns a new approximate mathematical model that admits a closed-form solution with respect to a set of new variables. The second step is the determination of an infinitesimal contact transformation that allows to navigate between the new and the original variables. This contact transformation is obtained in exact form, and afterwards a Taylor series approximation is proposed in order to make all the computations explicit. The aforementioned transformation accommodates both perturbations, improving the accuracy of the orbit predictions by one order of magnitude with respect to the case when the atmospheric drag is absent from the transformation. Numerical simulations are performed for a low Earth orbit starting at an altitude of 350 km, and they show that the incorporation of drag terms into the contact transformation generates an error reduction by a factor of 7 in the position vector. The proposed method aims at improving the accuracy of analytic orbit propagation and transforming it into a viable alternative to the computationally intensive numerical methods.     

边坡破坏过程离心模型试验的应力位移场研究

提出了一种确定离心模型试验过程中边坡的应力和位移场及其变化过程的方法。基于物理测量与数值模拟相结合的思路,首先采用离心场非接触位移测量技术测量出边坡的位移场;然后通过数值模拟和反演分析等途径算出边坡的应力场。该方法已成功用于多个边坡离心模型试验中的应力位移场的确定,表明了该方法可以较好地得出离心模型试验过程中边坡的应力和位移场。边坡离心模型试验结果表明,边坡的破坏过程与应变局部化和应力集中的过程有着密切联系。     

SMOS reveals the signature of Indian Ocean Dipole events

The tropical Indian Ocean experiences an interannual mode of climatic variability, known as the Indian Ocean Dipole (IOD). The signature of this variability in ocean salinity is hypothesized based on modeling and assimilation studies, on account of scanty observations. Soil Moisture and Ocean Salinity (SMOS) satellite has been designed to take up the challenge of sea surface salinity remote sensing. We show that SMOS data can be used to infer the pattern of salinity variability linked with the IOD events. The core of maximum variability is located in the central tropical basin, south of the equator. This region is anomalously salty during the 2010 negative IOD event, and anomalously fresh during the 2011 positive IOD event. The peak-to-peak anomaly exceeds one salinity unit, between late 2010 and late 2011. In conjunction with other observational datasets, SMOS data allow us to draw the salt budget of the area. It turns out that the horizontal advection is the main driver of salinity anomalies. This finding is confirmed by the analysis of the outputs of a numerical model. This study shows that the advent of SMOS makes it feasible the quantitative assessment of the mechanisms of ocean surface salinity variability in the tropical basins, at interannual timescales.     

DISECA – A Matlab code for dispersive waveform calculations

The propagation velocity of certain elastic waves (so-called surface waves) in vertically inhomogeneous materials is dispersive. The dispersion determination is however frequently ambiguous. To verify the signal analysis reliability and to estimate the dispersive character of the waves an algorithm for dispersive waveform calculation was designed. It is based on the summation of frequency components, with shifts corresponding to the velocity dispersion and distance. The knowledge of physical parameters of the medium is not required. The resulting waveform only contains an individual dispersive wave of the selected mode, thus being particularly suitable for testing of methodologies for dispersive wave analysis.     

Processes controlling very low sedimentation rates on the continental slope of the Gonone-Orosei canyon system,NE Sardinia—terrestrial and oceanic significance

The narrow shelf and upper slope immediately above the Gonone canyon head off NE Sardinia represent areas of very low sedimentation rates. Along the sides of the canyon head (1,600 m water depth), the sediment deposits are homogeneous but show alternating light-grey intervals rich in carbonate and dark-grey ones rich in organic matter, possibly related to distal turbidite processes. Deposits older than 50,000 years are already encountered at core depths of 2.50 m, the sedimentation rates varying from 6–21 cm/10³ years in the lower parts of two cores and from 1.5–3 cm/10³ years in the upper parts. At about 35,000 years BP, both cores show a simultaneous drop in sedimentation rate by a factor of 3, probably in response to local mechanisms of channel avulsion. Lithological, mineralogical and geochemical properties reveal the environmental factors which are responsible for the extremely slow sediment accumulation. The southernmost sector of the coast, and partly also of the shelf, consists of Jurassic limestones which supply only small amounts of fine-grained material transported in suspension. During the last sea-level highstand, the accumulation of the Cedrino River pro-delta remained restricted to the coast, the low siliciclastic sediment yields resulting in poor shelf sediment trapping. The present morphology of the canyon head prevented the occurrence of gravity processes in the deeper part of the canyon system, including the coring sites. Accordingly, deposition was mainly fed by hemipelagic material of planktonic origin, together with only moderate terrigenous inputs. On a wider late Pleistocene timescale, seismic data indicate the occurrence of a coarse-grained, layered turbidite facies, implying a very different architecture of the canyon drainage system probably prior to 60,000 years BP.     

Study on daily surface evapotranspiration with SEBS in Tibet Autonomous Region简

The estimation of surface evapotranspiration （ET） with satellite dataset is one of the main subjects in the understanding of climate change, disaster monitoring and the circulation of water vapor and energy in Tibet Autonomous Region （TAR）. This research selects satellite images on January 11, April 6, July 31 and October 19 in 2010 as the representative of winter, spring, summer and autumn respectively, estimates the distribution of daily surface ET based on the surface energy balance system （SEBS） along with potential evapotranspiration （PET） and ET derived from Penman-Monteith （P-M） method. The results are obtained as follows. （1） The seasonal distribution of ET and PET basically decreases from the southeast part to the northwest part of TAR. Although ET and PET have similar spatial distributions, there are still some differences to estimate the extreme values especially the maximum value in the middle and southeastern parts of TAR. No matter what kind of methods we adopted, the maximum value of ET and PET always appears in summer, followed by autumn or spring while that in winter is the smallest. （2） In order to better understand the accuracy of SEBS model in the estimation of ET, we compared the ET from SEBS and the ET obtained from P-M method. Results show that the ET from SEBS could estimates the variation trend of actual ET, but it slightly underestimates or overestimates the value of ET as a whole, especially for those areas with thick forest. （3） The spatial distribution of Normalized Difference Vegetation Index （NDVI） exhibits a decreasing trend from the southeast part to the northwest part of TAR which displays remarkable consistency of distributions between ET and vegetation index. ET is well positively related to NDVI, minimum, mean, maximum air temperature and sunshine duration in different seasons while negatively related to precipitation, relative humidity and wind speed in summer.     

Tidally-induced melting events as the origin of south-pole activity on Enceladus

The intense activity at the south pole of Enceladus hints at an internal water reservoir. However, there is no direct evidence of liquid water at present and its long-term stability in the interior remains problematic. By modeling heat production and transfer in the ice shell in a spherical geometry, we show that tidal heating naturally leads to a concentration of convective hot upwellings in the south polar region, favoring the preservation of liquid water at depth. We show that large volumes of water are produced within the ice shell at the south pole during periods of elevated orbital eccentricity (3–5 times the present-day value). Strong lateral variations in the melt production and crystallization rates result in stress concentration in the south polar region, thus providing an explanation for the tectonic activity observed today. We predict that an internal ocean may be sustained over the long term as the consequence of repeated periods with elevated orbital eccentricity, leading to episodic melting and resurfacing events.