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1.
The spatial–temporal variation of dry and wet periods in Iran based on comparing SPI and RDI indices
Drought is a natural hazard which can cause harmful effects on water resources. To monitor drought, the use of an indicator and determination of wet and dry period trend seem to have an important role in quantifying the drought analysis. In this paper, in addition to the comparison of Reconnaissance Drought Index (RDI) and Standardized Precipitation Index (SPI), based on the most appropriate probability distribution function, it was tried to examine the trends of dry and wet periods based on the mentioned indices. Accordingly, the meteorological data of 30 synoptic stations in Iran (1960–2014) was used and the trend was analyzed using the Mann–Kendall test by eliminating the effect of any significant autocorrelation coefficients at 95% confidence level (modified Mann–Kendall). Comparing results between the time series of RDI and SPI drought indices based on statistical indicators (RMSE?<?0.434, R2?>?0.819 and T-statistic?<?0.419) in all studied stations revealed that the behavior of the two indices was roughly the same and the difference between them was not significant. The trend analysis results of RDI and SPI indices based on modified Mann–Kendall test showed that the variation of dry and wet periods was decreasing in most of the studied stations (five cases were significant). In addition, the results of the trend line slope of dry and wet periods related to the drought indices in the studied area indicated that the slope was negative for SPI and RDI indices in 70% and 50% of stations, respectively. 相似文献
2.
Relationship and its instability of ENSO--Chinese variations in droughts and wet spells 总被引：1，自引：0，他引：1
SU MingFeng & WANG HuiJun Nansen-Zhu International Research Center Institute of Atmospheric Physics Chinese Academy of Sciences Beijing China Graduate University of Chinese Academy of Sciences Beijing China 《中国科学D辑(英文版)》2007,(1)
Monthly data of Self-Calibrated Palmer Drought Severity Index (PDSI) from 1951 to 2000 are calculated using historical precipitation and temperature data for Chinese 160 stations. Temporal and spatial pat-terns of the first empirical orthogonal function (EOF) of the PDSI reveals a fairly linear trend resulting from trends in precipitation and surface temperature, which is similar to the linear PDSI trend during 1951―2000 calculated using all monthly data. The EOF analysis also reveals that the leading mode correlates significantly with ENSO events in time and space. The ENSO EOF shows that during the typical warm phase of ENSO, surface conditions are drier in most regions of China, especially North China, but wetter than normal in the southern regions of Changjiang River, and Northwest China. During the typical cold phase of ENSO, these anomalies reverse sign. From 1951 to 2000, there are large multi-year to decadal variations in droughts and wet spells over China, which are all closely related to strong El Nio events. In other words, when one strong El Nio event happens, there is a possible big variability in droughts and wet spells over China on the multi-year or decadal scale. Studies also sug-gest that during the last 2―3 decades climate changes over China, especially North China's drying and northwest China's wetting, are closely related to the shift in ENSO towards warmer events and global warming since the late 1970s. The instability of the relationship is also studied. It is revealed that there is a good correlation between ENSO and Chinese variations in droughts and wet spells in the 3―8-year band, but the correlation between ENSO and Chinese variations in droughts and wet spells is instable. Studies suggest that there are decadal changes in the correlation: the wavelet coherency between ENSO and Chinese variations in droughts and wet spells is high during 1951―1962 and 1976―1991, but low during 1963―1975 and 1992―2000. 相似文献
3.
White Island is an active andesitic-dacitic composite volcano surrounded by sea, yet isolated from sea water by chemically sealed zones that confine a long-lived acidic hydrothermal system, within a thick sequence of fine-grained volcaniclastic sediment and ash. The rise of at least 106 m3 of basic andesite magma to shallow levels and its interaction with the hydrothermal system resulted in the longest historical eruption sequence at White Island in 1976–1982. About 107 m3 of mixed lithic and juvenile ejecta was erupted, accompanied by collapse to form two coalescing maar-like craters. Vent position within the craters changed 5 times during the eruption, but the vents were repeatedly re-established along a line linking pre-1976 vents. The eruption sequence consisted of seven alternating phases of phreatomagmatic and Strombolian volcanism. Strombolian eruptions were preceded and followed by mildly explosive degassing and production of incandescent, blocky juvenile ash from the margins of the magma body. Phreatomagmatic phases contained two styles of activity: (a) near-continuous emission of gas and ash and (b) discrete explosions followed by prolonged quiescence. The near-continuous activity reculted from streaming of magmatic volatiles and phreatic steam through open conduits, frittering juvennile shards from the margins of the magma and eroding loose lithic particles from the unconsolidated wall rock. The larger discrete explosions produced ballistic block aprons, downwind lobes of fall tephra, and cohesive wet surge deposits confined to the main crater. The key features of the larger explosions were their shallow focus, random occurrence and lack of precursors, and the thermal heterogeneity of the ejecta. This White Island eruption was unusual because of the low discharge rate of magma over an extended time period and because of the influence of a unique physical and hydrological setting. The low rate of magma rise led to very effective separation of magmatic volatiles and high fluxes of magmatic gas even during phreatic phases of the eruption. While true Strombolian phases did occur, more frequently the decoupled magmatic gas rose to interact with the conduit walls and hydrothermal system, producing phreatomagmatic eruptions. The form of these wet explosions was governed by a delicate balance between erosion and collapse of the weak conduit walls. If the walls were relatively stable, fine ash was slowly eroded and erupted in weak, near-continous phreatomagmatic events. When the walls were unstable, wall collapse triggered larger discrete phreatomagmatic explosions. 相似文献
4.
The concept of structure–soil–structure dynamic interaction was introduced, and the research methods were discussed. Based on several documents, a systematic summary of the history and status of the structure–soil–structure dynamic interaction research that considers adjacent structures was proposed as a reference for researchers. This study is in the initial stage, given its complexity and excessive simplification of the model for soil and structures, and should be carried forward for its significance. An attempt was made to summarize the common major computer programs in this area of study. Furthermore, the advantages, disadvantages, and applicability of such programs were discussed. The existing problems and the future research trend in this field were also examined. 相似文献
5.
Ofra Klein-BenDavid D. Graham Pearson Geoff M. Nowell Chris Ottley John C.R. McNeill Pierre Cartigny 《Earth and Planetary Science Letters》2010,289(1-2):123-133
Sub-micrometer inclusions in diamonds carry high-density fluids (HDF) from which the host diamonds have precipitated. The chemistry of these fluids is our best opportunity of characterizing the diamond-forming environment. The trace element patterns of diamond fluids vary within a limited range and are similar to those of carbonatitic/kimberlitic melts that originate from beneath the lithospheric mantle. A convecting mantle origin for the fluid is also implied by C isotopic compositions and by a preliminary Sr isotopic study (Akagi, T., Masuda, A., 1988. Isotopic and elemental evidence for a relationship between kimberlite and Zaire cubic diamonds. Nature 336, 665–667.). Nevertheless, the major element chemistry of HDFs is very different from that of kimberlites and carbonatites, varying widely and being characterized by extreme K enrichment (up to ～ 39 wt.% on a water and carbonate free basis) and high volatile contents. The broad spectrum of major element compositions in diamond-forming fluids has been related to fluid–rock interaction and to immiscibility processes.Elemental signatures can be easily modified by a variety of mantle processes whereas radiogenic isotopes give a clear fingerprint of the time-integrated evolution of the fluid source region. Here we present the results of the first multi radiogenic-isotope (Sr, Nd, Pb) and trace element study on fluid-rich diamonds, implemented using a newly developed off-line laser sampling technique. The data are combined with N and C isotope analysis of the diamond matrix to better understand the possible sources of fluid involved in the formation of these diamonds. Sr isotope ratios vary significantly within single diamonds. The highly varied but unsupported Sr isotope ratios cannot be explained by immiscibility processes or fluid-mineral elemental fractionations occurring at the time of diamond growth. Our results demonstrate the clear involvement of a mixed fluid, with one component originating from ancient incompatible element-enriched parts of the lithospheric mantle while the trigger for releasing this fluid source was probably carbonatitic/kimberlitic melts derived from greater depths. We suggest that phlogopite mica was an integral part of the enriched lithospheric fluid source and that breakdown of this mica releases K and radiogenic Sr into a fluid phase. The resulting fluids operate as a major metasomatic agent in the sub-continental lithospheric mantle as reflected by the isotopic composition and trace element patterns of G10 garnets. 相似文献
6.
Could alluvial knickpoint retreat rather than fire drive the loss of alluvial wet monsoon forest,tropical northern Australia? 
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下载免费PDF全文 Drainage rejuvenation through headward migration of alluvial knickpoints is common in ephemeral semi‐arid streams, but has not yet been described for tropical rivers. In the Australian monsoon tropics (AMT), wet monsoon forests have an important ecological function, and are present along many alluvial valleys and springs within a eucalypt‐savanna dominated landscape. Using a combination of LiDAR, remote sensing and field evidence, we observe the ongoing destruction of wet monsoon forest through hydro‐geomorphic feedbacks, along with the headward retreat of an alluvial knickpoint at Wangi Creek in Litchfield National Park, Northern Territory. Due to the highly transmissive shallow aquifer along the lower Wangi Creek, this knickpoint retreat leads to a downstream drop in in‐channel water level, which in turn drives a decrease in the local groundwater table. The lowered groundwater level causes the shallow anabranches and formerly water saturated peaty floodplain soil to desiccate, which results in a reduction of vegetation density. The resulting dry surface conditions allow annual to bi‐annual high frequency low‐intensity fires to affect the monsoon forest, while wet rainforest upstream of the knickpoint remains intact. In this paper, we argue that such hydro‐geomorphic feedbacks may cause the initial destabilization of the forest, which then provides the necessary conditions for the impact of fire. This scenario thus challenges the prevalent view that fire is a first‐order control on the spatial extent of wet monsoonal rainforest in the study area, and provides a new and testable hypothesis for further studies in the AMT. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
7.
Concerns about the water–energy–food (WEF) nexus have motivated many discussions regarding new approaches for managing water, energy and food resources. Despite the progress in recent years, there remain many challenges in scientific research on the WEF nexus, while implementation as a management tool is just beginning. The scientific challenges are primarily related to data, information and knowledge gaps in our understanding of the WEF inter-linkages. Our ability to untangle the WEF nexus is also limited by the lack of systematic tools that could address all the trade-offs involved in the nexus. Future research needs to strengthen the pool of information. It is also important to develop integrated software platforms and tools for systematic analysis of the WEF nexus. The experience made in integrated water resources management in the hydrological community, especially in the framework of Panta Rhei, is particularly well suited to take a lead in these advances. 相似文献
8.
Full waveform inversion algorithms are widely used in the construction of subsurface velocity models. In the following study, we propose a Laplace–Fourier-domain waveform inversion algorithm that uses both Laplace-domain and Fourier-domain wavefields to achieve the reconstruction of subsurface velocity models. Although research on the Laplace–Fourier-domain waveform inversion has been published recently that study is limited to fluid media. Because the geophysical targets of marine seismic exploration are usually located within solid media, waveform inversion that is approximated to acoustic media is limited to the treatment of properly identified submarine geophysical features. In this study, we propose a full waveform inversion algorithm for isotropic fluid–solid media with irregular submarine topography comparable to a real marine environment. From the fluid–solid system, we obtained P and S wave velocity models from the pressure data alone. We also suggested strategies for choosing complex frequency bands constructed of frequencies and Laplace coefficients to improve the resolution of the restored velocity structures. For verification, we applied our Laplace–Fourier-domain waveform inversion for fluid–solid media to synthetic data that were reconstructed for fluid–solid media. Through this inversion test, we successfully restored reasonable velocity structures. Furthermore, we successfully extended our algorithm to a field data set. 相似文献
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10.
Aurélie Muller Jean-Noël Bacro Michel Lang 《Stochastic Environmental Research and Risk Assessment (SERRA)》2008,22(1):33-46
Depth–duration–frequency curves estimate the rainfall intensity patterns for various return periods and rainfall durations.
An empirical model based on the generalized extreme value distribution is presented for hourly maximum rainfall, and improved
by the inclusion of daily maximum rainfall, through the extremal indexes of 24 hourly and daily rainfall data. The model is
then divided into two sub-models for the short and long rainfall durations. Three likelihood formulations are proposed to
model and compare independence or dependence hypotheses between the different durations. Dependence is modelled using the
bivariate extreme logistic distribution. The results are calculated in a Bayesian framework with a Markov Chain Monte Carlo
algorithm. The application to a data series from Marseille shows an improvement of the hourly estimations thanks to the combination
between hourly and daily data in the model. Moreover, results are significantly different with or without dependence hypotheses:
the dependence between 24 and 72 h durations is significant, and the quantile estimates are more severe in the dependence
case. 相似文献
11.
A statistical study of magnetosphere–ionosphere coupling in the Lyon–Fedder–Mobarry global MHD model
B. Zhang W. Lotko M.J. Wiltberger O.J. Brambles P.A. Damiano 《Journal of Atmospheric and Solar》2011,73(5-6):686-702
The statistics of magnetosphere–ionosphere (MI) coupling derived from a two-month long run of the Lyon–Fedder–Mobarry (LFM) global simulation model are investigated. MI coupling characteristics such as polar cap potential and field-aligned current (FAC), downward Poynting flux and vorticity of ionospheric convection are compared with observed statistical averages and with results from the Weimer 05 empirical model. The comparisons for eight different IMF clock-angle orientations show that the LFM model produces reasonably accurate average distributions of the Region I and Region II currents. Both current systems have average amplitudes similar to those observed by the Iridium satellite constellation; however, the average LFM amplitudes are smaller by a factor of two compared with the values from the Weimer 05 model. The comparisons of polar cap potential show that the LFM model produces reasonable patterns of ionospheric convection, but the average cross polar cap potential (CPCP) is greater than the observed results by a factor of approximately 2 and greater than Weimer 05 by a factor of 1.5. The differences in convection in LFM results relative to the Weimer 05 model accounts for much of the difference in the Poynting flux patterns and integrated power produced by the two models. The comparisons of average ionospheric field-aligned vorticity show good agreement on the dayside; however, the LFM model gives higher nightside vorticity which may imply that the ionospheric conductance on the nightside is too small in the simulation. 相似文献
12.
David Love Stefan Uhlenbrook Gerald Corzo-Perez Steve Twomlow Pieter van der Zaag 《水文科学杂志》2013,58(5):687-703
Abstract Two types of monthly water balance models at basin scale are used: PE models use precipitation and potential evapotranspiration (PET) as their observed input data, whereas P models need only precipitation. Calibration proceeds by comparing model runoff and observed runoff. Calibration is entirely automatic with the exclusion of subjective elements. All models differ only by their actual evapotranspiration equations. PE models from previous papers are generalized essentially by replacing the constant evapotranspiration parameter by a periodic one, thus increasing the number of parameters by two (a “parameter” is an unknown constant to be estimated, and which is a characteristic of the river basin to be described). P models use a periodic “driving force”, which is intended to represent periodicity of hydrological phenomena, normally originating in the (unavailable) PET time series. These eight PE models and three P models are then applied to 55 river basins in 10 countries with widely diverging climates and soil conditions. A marked improvement of model performance in about one third of the basins is due to the introduction of the above mentioned periodic functions. Even when PET data are available it is sometimes useful to consider P models. P models scarcely perform less well than PE models. An engineer, wanting to try out as few models as possible on a given river basin, can restrict his attention to the optimization of two or three models. The paper is an extension of a long effort towards monthly water balance models, and is believed to give a solution in most circumstances. 相似文献
13.
Multivariate time series modeling approaches are known as useful tools for describing, simulating, and forecasting hydrologic variables as well as their changes over the time. These approaches also have temporal and cross-sectional spatial dependence in multiple measurements. Although the application of multivariate linear and nonlinear time series approaches such as vector autoregressive with eXogenous variables (VARX) and multivariate generalized autoregressive conditional heteroscedasticity (MGARCH) models are commonly used in financial and economic sciences, these approaches have not been extensively used in hydrology and water resources engineering. This study employed VARX and VARX–MGARCH approaches in modeling mean and conditional heteroscedasticity of daily rainfall and runoff records in the basin of Zarrineh Rood Dam, Iran. Bivariate diagonal VECH (DVECH) model, as a main type of MGARCH, shows how the conditional variance–covariance and conditional correlation structure vary over the time between residuals series of the fitted VARX. For this purpose, five model fits, which consider different combinations of twofold rainfall and runoff, including both upstream and downstream stations, have been investigated in the present study. The VARX model, with different orders, was applied to the daily rainfall–runoff process of the study area in each of these model fits. The Portmanteau test revealed the existence of conditional heteroscedasticity in the twofold residuals of fitted VARX models. Therefore, the VARX–DVECH model is proposed to capture the heteroscedasticity existing in the daily rainfall–runoff process. The bivariate DVECH model indicated both short-run and long-run persistency in the conditional variance–covariance matrix related to the twofold innovations of rainfall–runoff processes. Furthermore, the evaluation criteria for the VARX–DVECH model revealed the improvement of VARX model performance. 相似文献
14.
ABSTRACTRecords of precipitation extremes are essential for hydrological design. In urban hydrology, intensity–duration–frequency curves are typically estimated from observation records. However, conventional approaches seldom consider the areal extent of events. If they do, duration-dependent area reduction factors are used, but precipitation is measured at only a few locations. Due to the high spatial variability of precipitation, it is relatively unlikely that a gauged observation network will capture the extremes that occur during a precipitation event. Therefore, the area reduction approach cannot be regarded as the reduction of an observed maximum. To investigate precipitation extremes, spatial aspects need to be considered using different approaches. Here, we both address the conventional practice of area reduction and consider a within-area chance of increased precipitation, defined as the maximum precipitation intensity observed in a cluster within a selected domain. The results show that (1) the risk of urban flooding is routinely underestimated in current design practice, and (2) traditional calculations underestimate extremes by as much as 30–50%. We show how they can be revised sensibly. 相似文献
15.
The dynamic through–soil interaction between nearby pile supported structures in a viscoelastic half-space, under incident S and Rayleigh waves, is numerically studied. To this end, a three-dimensional viscoelastic BEM–FEM formulation for the dynamic analysis of piles and pile groups in the frequency domain is used, where soil is modelled by BEM and piles are simulated by one-dimensional finite elements as Bernoulli beams. This formulation has been enhanced to include the presence of linear superstructures founded on pile groups, so that structure–soil–structure interaction (SSSI) can be investigated making use of a direct methodology with an affordable number of degrees of freedom. The influence of SSSI on lateral spectral deformation, vertical and rotational response, and shear forces at pile heads, for several configurations of shear one-storey buildings, is addressed. Maximum response spectra are also presented. SSSI effects on groups of structures with similar dynamic characteristics have been found to be important. The system response can be either amplified or attenuated according to the distance between adjacent buildings, which has been related to dynamic properties of the overall system. 相似文献
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Ocean Dynamics - Channel–shoal patterns are often observed in the back–barrier basins of inlet systems and are important from both an economical and ecological point of view. Focussing... 相似文献
18.
The coupled ocean–atmosphere–wave–sediment transport (COAWST) model is used to hindcast Hurricane Ivan (2004), an extremely intense tropical cyclone (TC) translating through the Gulf of Mexico. Sensitivity experiments with increasing complexity in ocean–atmosphere–wave coupled exchange processes are performed to assess the impacts of coupling on the predictions of the atmosphere, ocean, and wave environments during the occurrence of a TC. Modest improvement in track but significant improvement in intensity are found when using the fully atmosphere–ocean-wave coupled configuration versus uncoupled (e.g., standalone atmosphere, ocean, or wave) model simulations. Surface wave fields generated in the fully coupled configuration also demonstrates good agreement with in situ buoy measurements. Coupled and uncoupled model-simulated sea surface temperature (SST) fields are compared with both in situ and remote observations. Detailed heat budget analysis reveals that the mixed layer temperature cooling in the deep ocean (on the shelf) is caused primarily by advection (equally by advection and diffusion). 相似文献
19.
《Journal of Applied Geophysics》2010,72(4):157-161
An intimate mathematical relation between Hartley and Hilbert transforms is given here in contrast with the well known Fourier and Hilbert transform relations. It is interesting to note that the Fourier–Hilbert and Hartley–Hilbert transforms while possessing the same magnitude differ in phase by 270°. The inverse Hartley–Hilbert transform returns the original function unlike the Fourier–Hilbert transform which results the negative of the original function. Further, it may be realized that the envelope defined here of the analytic signal in both Fourier–Hilbert and Hartley–Hilbert domains numerically remain the same while differing in polarity. The feasibility of Hartley–Hilbert transform for a straight forward interpretation, total magnetic anomaly due to a thin plate from Tejpur, India and self potential data of the Sulleymonkey anomaly in the Ergani Copper district, Turkey are illustrated in contrast with the Fourier–Hilbert transform. This pair of transforms have innumerable geophysical applications. 相似文献