microseismicity and its time frequency characteristics of the left bank slope at the jinping first stage hydropower station during reservoir impoundment the instability risk associated with the left bank slope of the jinping first stage hydropower station in south western china may increase as a result of the initial impoundment of the reservoir and the raising and lowering of the reservoir level to improve our understanding of the rock slope stability and the real time behaviour of the composite system of rock slope and dam an existing microseismic ms monitoring system installed on may 2009 was improved in early 2014 this investigation represents the first time such a technique has been used to evaluate the stability of a high rock slope in china the safety and maintenance of the rock slope during the reservoir impoundment were investigated through the development of fast and accurate real time event location technique aimed at assessing the evolution and migration of the seismic activity and through the development of capabilities for forecasting the rock slope stability numerous ms events in the rock slope have been recorded using the ms monitoring system zones of damaged rock mass were identified based on a spatio temporal analysis of the seismic activity during the impoundment period moreover a waveform decomposition method based on the s transform was proposed for processing the seismic waveforms during the construction and impoundment periods of the left bank slope and the time frequency characteristics of seismic events during these two periods were thus compared the understanding of the relationships between the time frequency parameters variations in the seismic signals and the rock mass damage can provide a basis for evaluating the stability of similar rock slopes

mechanism of groundwater bursting in a deep rock salt mine region a case study of the anpeng trona and glauber mines china this paper investigated two incidents which occurred in anpeng trona and glauber mines in china to understand the mechanism of groundwater bursting there are two locations in the anpeng mines where groundwater bursting occurred since mid november 2008 and february 2009 respectively a systematic exploration of the geological conditions operation of the mines the hydrogeochemistry of groundwater bursting and groundwater conducted passageways was implemented the result reveals that the solution mining leakage was serious and the leaked water was the source for groundwater bursting the fractures cracks faults and mining wells formed connections with one another during solution mining such solution welled up and rose along the conducted passages and recharged shallow aquifers before finally reaching the ground surface as groundwater bursting the impacts of groundwater bursting on the environment are serious thus this study provides a basis for effective prevention of groundwater bursting and rational design of solution mining drainage plans

on the connection between benguela and equatorial atlantic ninos and the role of the south atlantic anticyclone for the eastern tropical atlantic two recurring el nino like phenomena with high interannual sst anomalies have been described one centered in the equatorial region as part of the atlantic zonal mode and one off angola referred to as benguela nino both events are supposed to be generated not locally but by a relaxation of the trade winds in the western equatorial atlantic here the connection between sst variations in the two regions is investigated with observational data sets as well as ocean model simulations they are correlated to such an extent that joint events should rather be viewed as one atlantic nino an intriguing feature counterintuitive in view of the remote forcing mechanism is that sst anomalies off angola precede those in the equatorial atlantic we show this behavior to be related to the difference in thermocline depths and a different seasonality of interannual sst variability in the two regions while benguela ninos peak in austral fall due to the angola benguela front being located furthest to the south and high interannual variability in coastal kelvin wave activity warm events at the equator are phase locked to austral winter when the thermocline is shallow perturbation experiments confirm the importance of remote forcing from the equator for sst variability off angola and demonstrate the leading role of wind stress in the generation of sst anomalies in the eastern tropical atlantic these wind stress variations are shown to be linked to fluctuations in the strength of the south atlantic anticyclone a connection that might be important with respect to the predictability of atlantic ninos

atmosphere ocean mechanisms of climate anomalies in the angola tropical atlantic sector abstract interannual variations in the large scale atmospheric and oceanic fields over the tropical atlantic are studied in relation to rainfall anomalies on the angola coast departure patterns are constructed by stratification with respect to extremely dry and wet years and by correlation with rainfall in angola which is concentrated in march april the analysis suggests a causality chain of atmospheric oceanic anomalies variations of westward wind stress on the western equatorial atlantic constitute an early link in this chain the annual cycle is characterized by a relaxation of the wind stress from september november to february march anomalous seasonal relaxation of easterly wind stress over the western equatorial atlantic remotely forces the sea surface temperature sst departures in the eastern south atlantic a large relaxation being followed by positive sst departures sea surface temperature modulates the rainfall over downstream angola by controlling the atmospheric moisture and stability

the source of benguela ninos in the south atlantic ocean 1 the intermittent occurrence of anomalous warm events in the upwelling regions of the pacific el ninos has been intensively studied pacific ninos have striking effects on the local ecosystem hence on the fisheries and on rainfall similar dramatic events have been observed in the south atlantic off the coasts of angola and namibia and named benguela ninos they tend not to occur in unison with their pacific counterpart and may thus have unrelated forcing mechanisms using an ocean general circulation model forced by real winds and verified with satellite data it is shown that benguela ninos are generated by specific wind stress events in the west central equatorial atlantic and progress from there as subsurface temperature anomalies that eventually outcropped only at the south west african coast these results suggest that it now may be possible to predict the occurrence of these disruptive events with a lead time of 2 months

relationship between the equatorial and meridional modes of climatic variability in the tropical atlantic the tropical atlantic ocean exhibits two primary modes of interannual climate variability an equatorial mode analogous to but weaker than the pacific el nino phenomenon and a meridional mode that does not have a pacific counterpart the equatorial mode is responsible for warm and cold sea surface temperature sst events mainly in the gulf of guinea and is identifiable by abnormal changes in the equatorial thermocline slope resulting from zonal wind anomalies in the western tropical atlantic the meridional mode is characterized by a north south interhemispheric gradient of sst anomalies here it is shown using observed surface and subsurface oceanic temperatures that the meridional mode is linked to the equatorial mode at both decadal and short interannual 1 2 years time scales both modes involve north south displacements of the itcz as in the annual response

dynamics of outgassing and plume transport revealed by proximal unmanned aerial system uas measurements at volcan villarrica chile volcanic gas emissions are intimately linked to the dynamics of magma ascent and outgassing and on geological timescales constitute an important source of volatiles to the earth s atmosphere measurements of gas composition and flux are therefore critical to both volcano monitoring and to determining the contribution of volcanoes to global geochemical cycles however significant gaps remain in our global inventories of volcanic emissions particularly for co2 which requires proximal sampling of a concentrated plume for those volcanoes where the near vent region is hazardous or inaccessible unmanned aerial systems uas provide a robust and effective solution to proximal sampling of dense volcanic plumes in extreme volcanic environments here we present gas compositional data acquired using a gas sensor payload aboard a uas flown at volcan villarrica chile we compare uas derived gas timeseries to simultaneous crater rim multi gas data and uv camera imagery to investigate early plume evolution so2 concentrations measured in the young proximal plume exhibit periodic variations that are well correlated with the concentrations of other species by combining molar gas ratios co2 so2 1 48 1 68 h2o so2 67 75 and h2o co2 45 51 with the so2 flux 142 17 t day from uv camera images we derive co2 and h2o fluxes of 150 t day and 2850 t day respectively we observe good agreement between time averaged molar gas ratios obtained from simultaneous uas and ground based multi gas acquisitions however the uas measurements made in the young less diluted plume reveal additional short term periodic structure that reflects active degassing through discrete audible gas exhalations

respective roles of remote and local wind stress forcings in the development of warm sst errors in the south eastern tropical atlantic in a coupled high resolution model processes involved in the development of the warm sea surface temperature sst bias in the tropical south eastern atlantic seta in a high resolution hr version of the cnrm cm model are evaluated based on full field initialized seasonal hindcasts starting at 1 february of each year for 2000 2009 whereas the initial sst growth is likely associated with local atmospheric forcing its further development is due to remote oceanic processes a mixed layer heat budget analysis in seta indicates a spurious warm horizontal advection observed as far as south of 25 s that appears at the beginning of march it is associated with an erroneous oceanic mean state at the equator resulting from the mean equatorial westerly wind bias a sensitivity experiment with corrected wind stress over the equatorial region suggests that the remote forcing explains about 57 of the seta sst bias in march may comparison with a lower resolution lr version of the model reveals that in general similar processes are responsible for the sst bias in both models a strong reduction of the bias in the hr model is observed only over the near coastal southern benguela region due to a better representation of atmospheric and oceanic processes controlling the coastal upwelling overall the results of the inter comparison of the seta sst bias evolution in different sensitivity experiments performed in this study can be interpreted in terms of the relative contributions of erroneous warm horizontal advection associated with equatorial forcing and cold horizontal advection associated with local offshore ekman transport

role of ocean mesoscale structures in shaping the angola low pressure system and the southern africa rainfall southern african climate is under the influence of both tropical and subtropical systems which result in a complex region where important interactions co exist over a large spectrum of spatiotemporal scales the angola low al situated on boundary between tropical and subtropical southern africa has been diagnosed as a key driver of moisture distribution in the region on daily to seasonal time scales it has been demonstrated that the al pressure system is sensitive to the dynamics of the neighbouring oceans but to date no study has considered the model resolution of air sea interactions required to simulate this sensitivity using sensitivity experiments with a regional atmospheric model which differ only in the mesoscale sea surface temperature sst forcing characteristics either the full spectrum of sst variability or only its large scale components are included we first quantify the importance of sst gradients on the al strength and variability the results suggest that the mesoscale sst variability of the angola benguela frontal zone abfz plays a key role in al activity particularly during the late summer synoptic scale tropical lows which form the al are automatically detected and the results suggest more extreme events occur when the model is forced by mesoscale ssts everywhere and in the abfz area only the rainfall resulting from those events suggests that tropical low episodes are associated with nearly 15 of the total rain in angola and namibia the link between al dynamics and wet spells is also discussed with the former showing a different spatial pattern as well as frequency when the ocean is fully resolved

deformation characteristics of rock salt with mudstone interbeds surrounding gas and oil storage cavern abstract this paper discusses the deformation differences that occur due to the presence of thin mudstone layers in underground storage caverns in rock salt both plasticity and viscosity are considered in the displacement calculations the results show that both creep deformation and deformation distinction i e the differences in the creep behavior between the salt rock and the mudstone are very large under the condition of high effective stresses when the inner diameters of salt caverns are 40 60 m the maximum radial convergence can reach 24 m and the deformation distinction can reach up to 6 m 30 years after the completion of cavern by solution mining the affected areas are however are restricted to the vicinity of the cavern the tightness of the cavern may not be violated if the distance between the caverns is greater than this amount the extension of plastic and dilatancy zones in rock salt is limited to three times the cavern diameter when elasto plastic mudstone interbeds are included tensile failure zones are present in the vicinity of the cavern and the plasticity zone stretches through the entire layer this could cause a loss of cavern tightness or stability if the mudstone interbeds creep although the creep rate is 2 orders lower than that of rock salt yielding is strongly de escalated but the deformation distinction is not affected

evolution of interannual warm and cold events in the southeast atlantic ocean extreme warm episodes in the southeast atlantic ocean known as benguela ninos have devastating envi ronmental impacts and have been shown to be remotely forced to place these extreme events into perspective the investigation is here extended to minor warm events as well as to cold episodes to this end different sets of observations have been combined with outputs from a numerical simulation of the tropical atlantic for the period 1982 99 it is shown that both warm and cold surface events develop regularly in the same specific region along the coast of angola and namibia some cold events compete in magnitude with major warm episodes local sea air heat flux exchanges do not seem to precondition the sea surface in the angola benguela region prior to the arrival of an event most warm and cold episodes are large scale events despite their limited surface signature they appear to be generated by wind anomalies in the western and central equatorial atlantic in the same way as benguela ninos seasonal fluctuations of the depth and shape of the tropical thermocline seem partly to control the way subsurface anomalies eventually impact the surface during austral summer surface anomalies create an identifiable pool centered near 158s whereas in winter they show an elongated pattern along the coast stretching toward the equator local upwelling or downwelling favorable wind regimes as well as local net heat fluxes may modulate the surface expression of events

the influence of environmental conditions on weathering of porous rocks by gypsum a non destructive study using acoustic emissions gypsum is one of the most universally distributed salts in weathered materials but little is known about the influence of environmental conditions on the damage generated by gypsum in stones to quantify the damage induced by gypsum crystallization acoustic emission techniques are employed to record the elastic energy released during salt crystallization cycles in a limestone different environmental conditions have been established during the cooling and drying periods in traditional salt crystallization cycles during drying two different temperatures 50 and 25 c and relative humidity low 25 at 50 c and 65 at 25 c and high 99 have been applied the acoustic emission signals are filtered by a frequency analysis in order to eliminate signals corresponding to external noise or artifacts our experimental results show that acoustic emission activity is higher under high relative humidity conditions than under low relative humidity conditions and also higher when drying at 50 c than at room temperature microscopic observations on the weathered samples indicated that under high relative humidity conditions and at room temperature gypsum crystallizes not on the sample surface like in the other samples but deeper in the inner part of the sample in good agreement with previously published data we show that using acoustic emissions as usually done in rock mechanics is also very useful in the study of stone decay and weathering processes in the laboratory

forcing of anomalous sea surface temperature evolution in the tropical atlantic during pacific warm events the seasonal evolution of anomalous interhemispheric sea surface temperature sst gradients in the tropical atlantic from january to april is studied by composites of the 10 warmest warm and 10 coldest cold januaries during 1948 1993 in the equatorial pacific using comprehensive ocean atmosphere data set ship observations in the warm as compared with the cold years an anomalous weakening of the northward sst gradient develops mainly due to anomalous warming in the tropical north atlantic this stems from the combination of three forcings all related to the weakened north atlantic trade winds during pacific warm events most important are the reduced latent heat flux in much of the tropical north atlantic and anomalous downwelling equatorward of 20 n with a further contribution from increased net radiation resulting from the reduced cloudiness due to the diminished convergence in the downstream portion of the north atlantic trades in response to the development of warm anomalies in the tropical north atlantic during january march the cross equatorial northward winds accelerate to april and this leads south of the equator not only to ekman downwelling enhanced divergence reduced cloudiness and increased net radiation but also to enhanced wind speed and evaporation the result is a modest anomalous warming in the western tropical south atlantic increased air temperature over the entire basin presumably due to atmospheric advection from the pacific has little effect on the atlantic sst pattern the anomalous interhemispheric sst gradient controlled primarily by the warm anomaly in the north atlantic has a pivotal role to play in steering the late boreal winter atmospheric circulation in the tropical atlantic sector and thus regional climate anomalies

atmospheric effects in the angola benguela frontal zone the angola benguela front is the generic border between on the one hand the benguela current and the coastal upwelling regime along the southwest african coastline and on the other hand the warm southward flowing angola current this frontal zone has a variable morphology geographic location and thermal characteristics it has been suggested that this variability may be related to changing wind patterns we have studied the thermal characteristics of the surface expression of the frontal zone for a 74 day period using daily thermal infrared images and compared these to wind patterns from synoptic weather maps there is little correlation between the location of the northern and the southern front that form the envelope for this frontal zone the location of the southern front largely determines the thermal gradient across the entire frontal zone large short term displacements in the geographic location of the frontal zone as well as short term variations in its thermal characteristics are shown to be strongly correlated to the atmospheric pressure gradient of the south atlantic anticyclone with a 1 day lag period this is true irrespective of the latitude changes of the center of the south atlantic anticyclone

the impacts of inter el nino variability on the tropical atlantic and northeast brazil climate abstractin this study observations and numerical simulations are used to investigate how different el nino events affect the development of sst anomalies in the atlantic and how this relates to the brazilian northeast ne precipitation the results show that different types of el nino have different impacts on the sst anomalies of the equatorial and tropical south atlantic but a similar sst response in the tropical north atlantic strong and long weak and short el ninos with the main heating source located in the eastern central pacific generate cold warm anomalies in the cold tongue and benguela upwelling regions during boreal winter and spring when the sst anomalies in the eastern equatorial and tropical south atlantic are cold warm the meridional sst gradient across the equator is positive negative and the itcz is not allowed allowed to move southward during the boreal spring as a consequence the precipitation is below above the average over the ne thus strong and long weak and s

el nino sea level and currents along the south american coast comparison of observations with theory abstract interannual sea level fluctuations along the south american coast and 7 3 year long current records at 30 s off central chile were examined with a low frequency linear numerical model the model includes stratification and shelf and slope bottom topography which varies alongshore the coastal flow is driven by interannual alongshore wind stress and an interannual alongshore pressure gradient resulting from el nino la nina pressure fluctuations at the equator calculations suggest that along the south american coast the coastal interannual variability is primarily due to the remote equatorial forcing rather than interannual coastal alongshore wind stress past work using this model has shown that due to the scattering of lower vertical modes to higher ones by bottom friction the model predicts a low frequency jet trapped near the bottom along the continental slope until now adequate interannual current time series were unavailable to check this prediction analysis of the observations shows th

rock salt dilatancy boundary from combined acoustic emission and triaxial compression tests abstract this paper presents an experimental investigation of rock salt dilatancy boundary based on combined acoustic emission and triaxial compression tests carried out on the rock salt samples from the asse salt mine germany the experimental results were evaluated to determine the dilatancy boundary under specified stress stress loading rate and pore pressure pore volume changes caused by deviatoric stresses were measured during triaxial compression tests the dilatancy boundary was then determined from the maximum compression on a stress strain curve which separates the compression and dilatancy regions variations in acoustic emissions that occur during microcrack development under triaxial compression were recorded with ten sensors mounted on the outer surface of the cylindrical samples a spontaneous increase observed in the cumulative number of acoustic events is consistent with the dilatancy boundary determined from the minimum pore volume it is confirmed that the dilatancy boundary depends on both stress loading rate and pore pressure the dilatancy boundary slightly decreases with increasing the loading rate but increases with increasing the minor normal stress high pore pressures accelerate the dilatancy a biot coefficient of 0 25 for asse rock salt was determined from the dilatancy boundary an analysis of two dimensional 2d fractal dimensions determined for several samples shows that the samples with smaller dimensions have slightly higher dilatancy boundaries the dilatancy boundary values of asse rock salt are lower than those reported for crystalline rocks although both rock types show similar dilatancy behaviour

does the south american monsoon influence african rainfall abstract teleconnections between the south american monsoon and southern african rainfall are investigated for years with benguela nino or nina events in the south atlantic during these events it is found that substantial rainfall anomalies also occur over south america in addition to those previously known for southern africa the appearance of large rainfall anomalies in the south american monsoon region prior to the onset of the benguela nino proper suggests that anomalous convection over south america may influence the evolution of both the sst anomalies and the african rainfall anomalies associated with benguela nino events this teleconnection between south america and southern african rainfall may occur directly via atmospheric circulation anomalies induced by convection over south america or indirectly via the effect of induced circulation anomalies on regional sst to investigate these teleconnections a vorticity equation model which is linearized about a realistic basic state and which in

structure of interannual to decadal climate variability in the tropical atlantic sector abstract a search for coupled modes of atmosphere ocean interaction in the tropical atlantic sector is presented previous studies have provided conflicting indications of the existence of coupled modes in this region the subject is revisited through a rotated principal component analysis performed on datasets spanning the 36 yr period 1958 93 the analysis includes four variables sea surface temperature oceanic heat content wind stress and atmospheric diabatic heating the authors find that the first rotated principal component is associated with fluctuations in the subtropical wind system and correlates with the north atlantic oscillation nao while the second and third modes which are the focus of interest are related to tropical variability the second mode is the atlantic nino mode with anomalous sea surface temperature and anomalous heat content in the eastern equatorial basin wind stress weakens to the west of anomalously warm water while convection is shifted south and eastward surface

differences in the acoustic emission characteristics of rock salt compared with granite and marble during the damage evolution process rock salt cavities for energy storage are important elements of energy supply management and sustainability the mechanical properties of other common rocks have already been adequately investigated but a systematic characterization of the differences in acoustic emission ae characteristics among rock salt and other common rocks is needed in this study the ae characteristics of the full regime uniaxial compression of rock salt and common rocks such as granite and marble were determined a damage variable based on ae parameters and a methodology for its determination were established including an analysis of the characteristics of the ae time space evolution the ae amplitude distribution and the damage evolution based on ae parameters clear differences were observed in the ae characteristics of rock salt compared with granite and marble during the damage evolution process the ae activity and energy release of rock salt with coarse grains and nonuniform structures decreased gradually with increasing stress level the ae activity of rock salt appeared in a continuous group occurring form the ae spatial distribution of rock salt was relatively uniform without a definite rupture surface the ae amplitude distribution varied slowly and the proportion of ae events with small amplitudes increased gradually during compression in rock salt moreover the damage in rock salt predominantly occured during the pre peak period resulting in a large damage variable of 0 9 at peak stress by contrast the damage variables of granite and marble are only 0 5 and 0 1 respectively at peak stress rock salt exhibited less damage when approaching failure resulting in a gentler and steadier process and the plastic characteristics of rock salt are relatively obvious these properties to some extent ensure the safety of underground storage engineering when rock salt is chosen as the medium

influences of filling abandoned salt caverns with alkali wastes on surface subsidence abandoned salt caverns particularly those that allow free draining of brine are serious potential causes of subsidence above salt mines filling such caverns with alkali wastes may eliminate these troubles based on the filling project in jingshen salt mine of china the influences of filling abandoned free draining salt caverns with alkali wastes on surface subsidence are discussed the deposition characteristics of alkali waste slurry were studied by laboratory simulation tests it is found that alkali waste slurry has good flowability during injection into a cavern based on the results of compression tests under drained conditions a distribution model of void ratio of sediment is established a method for determining the ultimate subsidence value is presented based on the distribution model the relationship of average effective stress and void ratio of the sediment is also established further a method for predicting development process of surface subsidence is presented finally the specific application procedure of the prediction methods is discussed according to the research results filling free draining salt caverns with alkali wastes can restrain surface subsidence successfully the reasons can be summed up as volume convergence of salt caverns slows down after the caverns are filled owing to the supporting effect of alkali wastes on the rock surrounding caverns and then subsidence slows down and decreases and finally subsidence stops when the fill material is compacted to its compressed limit

tropical atlantic sea surface temperature variability and its relation to el nino southern oscillation past analyses of tropical atlantic sea surface temperature variability have suggested a dipole behavior between the northern and southern tropics across the intertropical convergence zone itcz by analyzing an improved 43 year 1950 1992 record of sst smith et al 1996 and other data derived from the comprehensive ocean atmosphere data set coads it is shown that the regions north and south of the itcz are statistically independent of each other at the seasonal to interannual timescales dominating the data confirming the conclusions of houghton and tourre 1992 some dipole behavior does develop weakly during the boreal spring season when there is a tendency for sst anomaly west of angola to be opposite of that in the tropical north atlantic it is further shown that tropical atlantic sst variability is corre lated with pacific e1 nifio southern oscillation enso variability in several regions the ma jor region affected is the north atlantic area of ne trades west of 40ow along 10on 20on and extending into the caribbean there about 50 80 of the anomalous sst variability is associ ated with the pacific enso with atlantic warmings occurring 4 5 months after the mature phases of pacific warm events an analysis of local surface flux fields derived from coads data shows that the enso related atlantic warmings occur as a result of reductions in the surface ne trade wind speeds which in turn reduce latent and sensible heat losses over the region in ques tion as well as cooling due to entrainment this enso connection is best developed during the boreal spring following the most frequent season of maximum enso anomalies in the pacific a region of secondary covariability with enso occurs along the northern edge of the mean itcz position and appears to be associated with northward migrations of the itcz when the north at lantic warmings occur although easterly winds are intensified in the western equatorial atlantic in response to pacific warm events they do not produce strong local changes in sst contrary to expectations from studies based on equatorial dynamics these teleconnected wind anomalies do not give rise to significant correlations of sst in the gulf of guinea with the pacific enso as the teleconnection sequence matures strong se trades at low southern latitudes follow the de velopment of the north atlantic sst anomaly and precede by several months the appearance of weak negative sst anomalies off angola and stronger positive anomalies extending eastward from southern brazil along 15o 30os

an overlooked feature of tropical climate inter pacific atlantic variability 1 both the tropical pacific and atlantic host an equatorial mode of interannual variability called the pacific el nino and the atlantic nino respectively although the pacific el nino does not correlate with the atlantic nino anomalous warming or cooling of the two equatorial oceans can form an inter pacific atlantic sea surface temperature sst gradient variability that induces surface zonal wind anomalies over equatorial south america and over some regions of both ocean basins the zonal wind anomalies act to bridge the interaction of the two ocean basins reinforcing the inter pacific atlantic sst gradient through atmospheric walker circulations and oceanic dynamics thus a positive feedback seems to exist for climate variability of the tropical pacific atlantic oceans and atmosphere system in which the inter basin sst gradient is coupled to the overlying atmospheric wind rainfall responds to the inter pacific atlantic sst gradient by showing an anti symmetric configuration between the two equatorial oceans suggesting that rainfall is sensitive to the equatorial inter basin sst gradient regardless of which ocean is anomalously warm or cold

correlational fractal characterisation of stress and acoustic emission during coal and rock failure under multilevel dynamic loading abstract the fractal characterisation of stress and acoustic emission ae of coal and rock failure may provide quantitative guidance for analysing the stability of rock mass during excavation engineering the correlation between stress and ae data was calculated using fractal theory methods and grassberger procaccia g p algorithms to evaluate the damage and degree of flaw in coal and rock materials under multilevel dynamic loading mdl first the mechanical properties of the testing device were developed to obtain synchronous data regarding the stress and aes of coal and rock specimens under mdl second strength deterioration behaviour and the felicity effect during coal and rock failure are compared under different levels of dynamic loading the results show that cumulative dynamic loading are less than the uniaxial compression strength of coal and rock the felicity effect is notable and felicity ratios decrease to 1 with increased loading velocity finally stresses and ae signals are considered as the data mining specimens of correlation dimensions based on the g p algorithm fractal characteristics on stress and ae coupling properties become more notable as the correlated dimensions become larger however the felicity effect is less prominent reflecting a lesser degree of damage and flaws in coal and rock materials therefore this study suggests a data mining method for the correlation dimension to be applied in an in situ monitoring system for rock mass excavation engineering

modeling deformation and damage of rock salt using the discrete element method abstract rock salt is considered to be a suitable host rock formation for radioactive waste repositories however local stress changes caused by drift construction lead to the evolution of an excavation damaged zone edz such an edz can have a major impact on the safety of a radioactive waste repository because it can violate the integral sealing function due to the development of a permeable microcrack network the objective of this investigation is the development of a modeling strategy that can be used to simulate the damage behavior of rock salt at grain scale for this purpose discrete element modeling techniques were used in combination with polyhedral shaped elements voronoi polyhedra in order to duplicate the shape and arrangement of grains to calibrate the material parameters used in the constitutive models and to validate the relevant damage and fracture processes uniaxial compression tests were combined with acoustic emission measurements overall deformation behavior and crack evolution was reproduced by modeling and validated by lab experiments the new proposed modeling strategy based on dem and voronoi polyhedra shows new possibilities to simulate the mechanical behavior of rock salt in a realistic manner by explicitly considering the fracture processes at grain scale

atlantic sst gradient and the influence of enso 1 the relationship between the boreal winter el nino sst anomaly and boreal spring tropical atlantic sst gradient north atlantic minus south atlantic is investigated using a long detrended sst record for both el nino and la nina concordant cases same sign for nino3 index and atlantic sst gradient slightly dominate over discordant ones reflecting the fact that the nino3 index correlates more strongly with the north atlantic than the south atlantic sst anomaly the ratio of the numbers of concordant and discordant cases is 4 3 overall indicating strong non enso influences on the atlantic sst gradient the composite of the concordant cases shows an sst anomaly in the north atlantic with the same sign as nino3 and an opposite signed anomaly off the southwest coast of africa resembling benguela nino that of the discordant cases is dominated by a pre existing sst anomaly with the same sign as nino3 in the south central south atlantic

a model investigation of internal variability in the angola benguela frontal zone 1 in this study a regional ocean model is applied to the tropical southeast atlantic ocean with the aim of investigating internal variability of the angola benguela front the model is forced at the upper boundary with monthly climatologies of windstress heat and freshwater fluxes the model results suggest that anomalous northward southward positions of the angola benguela frontal zone are connected to anomalous intensities of the front anomalous northward shifts of the angola benguela frontal zone appear to be associated with an anticyclonic circulation pattern in the area that shifts the frontal system toward the north this anomalous circulation also forces changes in coastal upwelling that in turn alter upper ocean temperatures such as to enhance the meridional temperature gradient across the front this mechanism is seasonally dependent and most clearly established during austral spring and summer a comparison between model variability near the angola benguela frontal zone and other modes of variability suggests that variability resulting from the monthly climatological forcing could at times account for the same amount of variability as that induced by the el nino southern oscillation and for up to 20 of the variability apparent during major warm events in the southeast atlantic such as benguela ninos

fractal property of spatial distribution of acoustic emissions during the failure process of bedded rock salt abstract a rock mechanics test system and the acoustic emission ae test system were employed to perform experiments on bedded rock salt samples under uniaxial compression and indirect tension based on the basic theory of fractal geometry a column covering method is proposed to analyze the fractal property of the spatial distribution of acoustic emissions during the rock damage and failure process the experimental results indicate obvious differences in failure features for different parts of a sample due to the structural differences in bedded rock salt the consistency between the failure state and the ae spatial distribution is confirmed the relationships of the stress and energy release with the fractal dimension of the ae spatial distribution are established an increase in the fractal dimension corresponds to a decrease in the stress and an increase in the energy release which is consistent with the theoretical analysis when the fractal dimension obtained from uniaxial compression and indirect tensile tests is less than 2 20 and 2 57 respectively the stresses in the bedded rock salt sample are over 80 of the peak stress a great amount of accumulated damage occurs leading to the global failure of the bedded rock salt sample therefore it is possible to forecast the failure state of bedded rock salt by inspecting the variation between the stress or the energy release and the fractal dimension of the ae spatial distribution

stability evaluation of the underground gas storage in rock salts based on new partitions of the surrounding rock based on uniaxial and triaxial compression experiments the yield dilatancy and failure behaviors of the jianghan rock salts were investigated accurate description of the yield and failure behaviors is helpful to reduce the space between storage caverns and offer more storage in a salt mine of limited extent the experimental results showed that the yield function is a straight line and thus the tresca yield criterion can be used to describe the yield behavior of the tested rock salt the second invariant of the plastic strain was used as the hardening parameter to analyze the hardening behavior of the rock salt the result shows that the rock salt is an isotropic hardening material from the perspective of yielding the rock salt acts like metals while from the perspective of failure it acts like rocks the dilatancy boundary was estimated in each experiment by determining the volume turnover point from compression to dilatation it is found that the dilatancy boundary for the jianghan rock salt is different from the results in the previous studies especially under high stresses shear and splitting failures were observed in the compression tests splitting failure was analyzed based on the elastic theory for thick cylinders the results indicate that failure depends on confining pressure when the confining pressure is equal or greater than 5 mpa the rock salt never breaks even when the axial strain reaches 20 a no broken condition was imported into the mohr coulomb criterion based on the yield dilatancy failure model the rock surrounding an underground gas storage ugs is divided into four zones elastic plastic permeability and failure zone a new stability criterion based on the partitions is proposed the constitutive model was modified and the state parameters were self defined in flac3d a geologic model for the jianghan ugs was constructed to provide an example of the stability evaluation based on the partitions of the surrounding rock the minimum internal pressure in emergency was also discussed for the jianghan ugs

waves along the equator in the atlantic abstract spectra of two hundred days of data from five inverted echo sounders deployed along the equator in 1983 84 and a thousand days of 30 crossings of the equator by the topex poseidon altimeter in 1993 95 are both found to have enhanced variance of sea surface displacement in two frequency bands centered nominally about 50 1 and 25 1 cycles day complex empirical orthogonal function analysis of the two bands finds much of the variance being accounted for by eastward and westward propagating waves respectively that are coherent across the basin the eastward propagating wave is identifiable as a first mode kelvin wave with a period of 54 49 days in the sounder altimeter dataset a basinwide wavelength and a speed of 2 1 1 8 m s 1 it is suggested that the westward propagating wave is a surface expression of the meridional oscillation of the equatorial undercurrent about the equator presumably induced by a tropical instability wave with a period of 24 28 days a wavelength of 600 580 km

some overlooked features of tropical atlantic climate leading to a new nino like phenomenon abstract the atlantic nino an equatorial zonal mode akin to the pacific el nino southern oscillation enso is phase locked to boreal summer when the equatorial easterly winds intensify and the thermocline shoals in the gulf of guinea a suite of satellite and in situ observations reveals a new mode of tropical atlantic variability that displays many characteristics of the zonal mode but instead peaks in november december nd this new mode is found to be statistically independent from both the atlantic nino in the preceding summer and the pacific enso the origin of this nd zonal mode lies in an overlooked aspect of the seasonal cycle in the equatorial atlantic in november the equatorial easterly winds intensify for the second time increasing upwelling and lifting the thermocline in the gulf of guinea an analysis of high resolution climatological data shows that these dynamical changes induce a noticeable sst cooling in the central equatorial atlantic the shoaling thermocline and increased upwelli

influence of the atlantic zonal mode on monsoon depressions in the bay of bengal during boreal summer the influence of the atlantic zonal mode azm or the atlantic nia o on monsoon depressions in the bay of bengal during the boreal summer june august is studied our analysis shows that there is a statistically significant difference in the number of monsoon depressions in the bay of bengal between the warm and cold phases of the azm more fewer monsoon depressions form during the cold warm phase of azm it also shows that there are differences in spatial pattern of trajectories of monsoon depressions during the cold phase of azm the tracks are relatively long and seem to cluster along the axis of core monsoon region compared to the warm phase of azm the analysis indicates an increase a reduction in low level cyclonic vorticity and midtropospheric humidity but a reduction an increase in vertical wind shear due to anomalous circulation pattern all of these changes are favorable for the enhancement suppression of monsoon depressions during the cold warm phase of the azm our analysis further shows a teleconnection pathway by which the azm can influence the remote indian ocean this could have implications for enhancing monsoon prediction skill especially during non el nia o southern oscillation years key points influence of the azm on monsoon depressions during boreal summer cold warm azm increases decreases number of monsoon depressions the difference in large scale atmospheric conditions in the bob during azm

role of interannual kelvin wave propagations in the equatorial atlantic on the angola benguela current system the link between equatorial atlantic ocean variability and the coastal region of angola namibia is investigated at interannual time scales from 1998 to 2012 an index of equatorial kelvin wave activity is defined based on prediction and research moored array in the tropical atlantic pirata along the equator results show a significant correlation between interannual pirata monthly dynamic height anomalies altimetric monthly sea surface height anomalies ssha and ssha calculated with an ocean linear model this allows us to interpret pirata records in terms of equatorial kelvin waves estimated phase speed of eastward propagations from pirata equatorial mooring remains in agreement with the linear theory emphasizing the dominance of the second baroclinic mode systematic analysis of all strong interannual equatorial ssha shows that they precede by 1 2 months extreme interannual sea surface temperature anomalies along the african coast which confirms the hypothesis that major warm and cold events in the angola benguela current system are remotely forced by ocean atmosphere interactions in the equatorial atlantic equatorial wave dynamics is at the origin of their developments wind anomalies in the western equatorial atlantic force equatorial downwelling and upwelling kelvin waves that propagate eastward along the equator and then polewards along the african coast triggering extreme warm and cold events respectively a proxy index based on linear ocean dynamics appears to be significantly more correlated with coastal variability than an index based on wind variability results show a seasonal phasing with significantly higher correlations between our equatorial index and coastal ssta in october april season

enso related modulation of coastal upwelling in the eastern atlantic an index of enso in the pacific during early boreal winter is shown to account for a significant part of the variability of coastal sst anomalies measured a few months later within the wind driven west african coastal upwelling region from 10 n to 26 n this teleconnection is thought to result from an atmospheric bridge between the pacific and atlantic oceans leading to warm cold enso events being associated with a relaxation intensification of the atlantic trade winds and of the wind induced coastal upwelling this enso related modulation of the wind driven coastal upwelling appears to contribute to the connection observed at the basin scale between enso and sst in the north atlantic the ability to use this teleconnection to give warnings of large changes in the west african upwelling several months in advance is successfully tested using data from the 1998 and 1999 enso events

steps in the intensification of benguela upwelling over the walvis ridge during miocene and pliocene upwelling is a significant part of the ocean circulation controlling largely the transport of nutrient rich cold waters to the surface and therefore influencing ocean productivity and global climate the benguela upwelling system bus is one of the major upwelling areas in the world previous reconstructions of the bus mainly focused on the onset and intensification in southern and central parts but changes of the northern part have been rarely investigated in detail using the late miocene to pliocene organic walled dinoflagellate cyst record of odp site 1081 we reconstruct and discuss the early upwelling history over the walvis ridge with a special focus on the movement of the angola benguela front abf we suggest that during the late miocene the angola current flowed southwards over the walvis ridge more frequently than today because the abf was probably located further south as a result of a weaker meridional temperature gradient a possible strengthening of the meridional gradient during the latest miocene to early pliocene in combination with uplift of south western africa intensified the upwelling along the coast and increased the upwelling s filaments over the walvis ridge an intermediate period from 6 2 to 5 5 ma is shown by the dominance of habibacysta tectata cysts of a cool tolerant dinoflagellate known from the northern atlantic indicating changing oceanic conditions contemporaneous with the messinian salinity crisis from 4 3 ma on the upwelling signal got stronger again and waters were well mixed and nutrient rich our results indicate a northward migration of the abf as early as 7 ma and the initial stepwise intensification of the bus

on enso coastal currents and sea levels abstract sea level measurements along the western coast of the americas have shown that there is a strong signal at enso frequencies approximately 2 2 yr 1 to 2 5 yr 1 that propagates poleward at about 40 to 90 cm s 1 this enso sea level signal must be associated with enso coastal currents but because adequate interannual current time series are unavailable the structure and strength of these currents are not known coastal enso currents must be fundamentally affected by bottom topography and bottom friction but previous theory has not taken these effects into account a near boundary numerical model with realistic bottom friction stratification and shelf and slope topography was therefore constructed to study enso coastal flow i at enso frequencies previous results for models with no bottom topography and no bottom friction suggest that sea level should not propagate poleward with realistic bottom friction and bottom topography coastal sea level propagates poleward at speeds similar to tho

evolution of dilatancy and permeability in rock salt during hydrostatic compaction and triaxial deformation combined gas permeability and p and s wave velocity measurements were carried out on rock salt samples from the gorleben salt dome and the morsleben salt mine under hydrostatic and triaxial loading condions mostly at room temperature permeabilities in the as received samples vary between 10 16 and 2x10 20 m 2 the initial permeability is primarily due to decompaction induced by drilling core retrieval and sample preparation hydrostatic loading gives rise to a marked decrease of permeability and a coeval significant increase of p and s wave velocities due to progressive closure of grain boundary cracks tending to approach the in situ matrix permeability 18 mpa differential stress at 10 mpa confining pressure to similar to 30 mpa at confining pressures above similar to 70 mpa dilatancy is due to the opening of grain boundary and 100 cleavage cracks and depends on the applied confining pressure the orientation of the open cracks is primarily controlled by the loading geometry system compression extension as a consequence permeability increases dramatically with progressive dilatancy followed by a period of plus minus constant permeability during strain hardening up to 10 axial strain or even more this suggests that the evolution of permeability is not only a function of dilatancy but also of microcrack linkage importantly the anisotropic crack array within the samples causes a strong directional dependence of permeability

experimental investigation of mechanical properties of bedded salt rock abstract because of salt cavern utilization for liquid gas and solid waste storage salt rock mechanical properties are needed for assessments of facility stability and safety bedded salt deposits are widespread and used as much or more than diapiric salt bodies as storage facility hosts but experimental data on the mechanical properties of bedded salt rock with impurities are far less common than data available on relatively pure diapiric salt rocks through laboratory uniaxial and triaxial compression experiments on rock salt halite interlayers anhydrite and bedded composite specimens anhydrite halite and mudstone halite differences in mechanical properties of the various lithologies are explored in the composite specimens the weakest or the most deformable component governs the behavior also the properties of bedded composite lithology specimens tend to be in between the property ranges of the pure lithologies the elastic modulus of the bedded salt rock increases from 5 3 to 24 1 gpa with an increase in the confining stress from 0 to 15 mpa with some evidence of sample damage the ductile transition for halite at the strain rates used is at about 3 10 mpa with increasing 3 the anhydrite halite composite lithology deformation showed strain hardening and a strong trend to ductile behavior as the halite bands tended to dominate the behavior strain incompatibility effects exist along interfaces between creeping and non creeping phases in anhydrite halite composite lithologies mudstone halite rocks tended to be extremely weak compared with all other specimens

warm events in the tropical atlantic abstract sea surface temperature in the eastern equatorial atlantic ocean undergoes anomalous warming events of 1 2 c every few years the warm anomalies reach their maximum strength in northern hemisphere summer when equatorial upwelling normally brings cold thermocline water to the surface by compositing surface observations from a 28 year record we are able to identify consistent features in anomalies of sst and winds the composites show that the sst anomalies in northern summer are confined to the eastern equatorial region with reduced zonal winds to the west and reduced northward trade winds to the east accompanying these changes in winds are enhanced convection near the equator caused by a southward shift and intensification of the intertropical convergence zone later in the year sst south of the equator becomes elevated as a result by spring of the year following the equatorial anomaly convection in the western side of the basin is much higher than normal to understand the ocean dynami