impact of tropical pacific precipitation anomaly on the east asian upper tropospheric westerly jet during the boreal winter abstractthe leading mode of boreal winter precipitation variability over the tropical pacific for the period 1980 2010 shows a west east dipole pattern with one center over the western north pacific wnp and maritime continent and the other center over the equatorial central pacific cp observational evidence shows that the variability of the east asian upper tropospheric subtropical westerly jet eaj has a significant correlation with precipitation anomalies over the wnp and cp and that tropical precipitation anomalies over wnp and cp have a distinct influence on the variation of the eaj a series of numerical experiments based on a linear baroclinic model are performed to confirm the influence of the heating anomalies associated with precipitation perturbations over the wnp and cp on the eaj the results of numerical experiments indicate that a heat source over the wnp can excite a northward propagating rossby wave train in the upper troposphere over east asia and facilitate a poleward eddy momentum

controls on back arc basin formation the relationship between subduction and back arc spreading has been well known since the early days of plate tectonics however the reasons why back arc basins are associated with some subduction systems but not all has remained elusive we examine the kinematic controls on subduction and back arc basins for both the present day and cenozoic to differentiate between the major competing hypotheses for back arc basin formation and to explain their temporal and spatial distribution our new data set of subduction and back arc basin parameters uses a new set of paleo oceanic age grids muller et al 2005 associated with a moving atlantic indian ocean hot spot reference frame o neill et al 2005 the plate model includes detailed reconstructed spreading histories of back arc basins based on marine geophysical and satellite gravity data our combined rotation and oceanic paleo age model provides the age distribution of subducting lithosphere through space and time convergence rates and the absolute motion of the downgoing and overriding plates we find that back arc basins develop when the age of subducting normal oceanic lithosphere is greater than 55 million years additionally we establish an age dip relationship showing that the intermediate dip angle of the subducting slab is always greater than 30 with back arc spreading our results suggest that back arc basin formation is always preceded by an absolute motion of the overriding plate away from the subduction hinge thereby creating accommodation space between the overriding and subducting plates once back arc extension is established it continues regardless of overriding plate motion indicating back arc spreading is not a simple consequence of overriding plate behaviour the landward migration of the overriding plate as a precursor to back arc extension may indicate that extension on the overriding plate is influenced by the oceanward lateral flow of the mantle however once back arc extension is established rollback of the subduction hinge appears to be the primary force responsible for the continued creation of accommodation space our analysis indicates the driving mechanism for back arc extension is a combination of surface kinematics properties of the downgoing slab the effect of lateral mantle flow on the slab and mantle wedge dynamics

information content of slug tests for estimating hydraulic properties in realistic high conductivity aquifer scenarios summary a recently developed unified model for partially penetrating slug tests in unconfined aquifers malama et al in press provides a semi analytical solution for aquifer response at the wellbore in the presence of inertial effects and wellbore skin and is able to model the full range of responses from overdamped monotonic to underdamped oscillatory while the model provides a unifying framework for realistically analyzing slug tests in aquifers with the ultimate goal of determining aquifer properties such as hydraulic conductivity k and specific storage s s it is currently unclear whether parameters of this model can be well identified without significant prior information and thus what degree of information content can be expected from such slug tests in this paper we examine the information content of slug tests in realistic field scenarios with respect to estimating aquifer properties through analysis of both numerical experiments and field datasets first through numerical experiments using markov chain monte carlo methods for gauging parameter uncertainty and identifiability we find that 1 as noted by previous researchers estimation of aquifer storage parameters using slug test data is highly unreliable and subject to significant uncertainty 2 joint estimation of aquifer and skin parameters contributes to significant uncertainty in both unless prior knowledge is available and 3 similarly without prior information joint estimation of both aquifer radial and vertical conductivity may be unreliable these results have significant implications for the types of information that must be collected prior to slug test analysis in order to obtain reliable aquifer parameter estimates for example plausible estimates of aquifer anisotropy ratios and bounds on wellbore skin k should be obtained if possible a priori secondly through analysis of field data consisting of over 2500 records from partially penetrating slug tests in a heterogeneous highly conductive aquifer we present some general findings that have applicability to slug testing in particular we find that aquifer hydraulic conductivity estimates obtained from larger slug heights tend to be lower on average presumably due to non linear wellbore losses and tend to be less variable presumably due to averaging over larger support volumes supporting the notion that using the smallest slug heights possible to produce measurable water level changes is an important strategy when mapping aquifer heterogeneity finally we present results specific to characterization of the aquifer at the boise hydrogeophysical research site specifically we note that 1 k estimates obtained using a range of different slug heights give similar results generally within 20 2 correlations between estimated k profiles with depth at closely spaced wells suggest that k values obtained from slug tests are representative of actual aquifer heterogeneity and not overly affected by near well media disturbance i e skin 3 geostatistical analysis of k values obtained indicates reasonable correlation lengths for sediments of this type and 4 overall k values obtained do not appear to correlate well with porosity data from previous studies

evaluation of tsunami risk from regional earthquakes at pisco peru we evaluate tsunami risk for the port city of pisco peru where major liquefied natural gas facilities are planned we use a compilation of instrumental and historical seismicity data to quantify the sources of six earthquakes that generated tsunamis resulting in minor inundation 1974 to catastrophic destruction 1687 1746 1868 in pisco for each of these case scenarios the seismic models are validated through hydrodynamic simulations using the most code which compute both flow depth on virtual offshore gauges located in pisco harbor and the distribution of runup in the port and along the nearby beach space time histories of major earthquakes along central and southern peru are used to estimate recurrence times of tsunamigenic earthquakes we conclude that pisco can expect a metric tsunami capable of inflicting substantial damage every 53 years and a dekametric tsunami resulting in catastrophic destruction of infrastructures every 140 years the last such event occurred 138 years ago an important result of our study is that total destruction of the city of pisco during the famous 1868 arica tsunami requires an earthquake rupture straddling the nazca ridge which thus constitutes at best an imperfect barrier for the propagation of rupture during megathrust events this gives a truly gigantic size to the 1868 arica earthquake with a probable seismic moment reaching 1030 dyne cm

interdecadal change in the principal mode of winter spring precipitation anomaly over tropical pacific around the late 1990s evidence show that the dominant mode of winter spring precipitation anomaly over the tropical pacific experienced a pronounced interdecadal change around 1998 based on the extended empirical orthogonal function eeof technique a zonal dipole pattern of precipitation anomaly is dominant during the pre 1998 period corresponding to a positive principle component pc1 positive precipitation anomaly over the equatorial eastern pacific ep decays eastward from winter to spring which is identified as an eastward decaying ep mode during the post 1999 period there is a zonal triple pattern with enhanced precipitation over the equatorial central pacific cp and reduced precipitation over the western north pacific and equatorial southeastern pacific with a positive pc1 this triple pattern of precipitation anomaly maintains with decreasing amplitude from winter to spring which is called the fixedly decaying cp mode for short such interdecadal shift is controlled by differing sea surface temperature sst anomaly pattern the interdecadal differences of winter spring wind stress and thermocline over tropical pacific might result in the interdecadal change in the sst anomaly and then precipitation mode via modulating physical oceanic feedback processes in addition the effect of two distinct precipitation modes on the north pacific teleconnection and north american surface temperature anomaly was strikingly different before 1998 the eastward decaying ep mode might induce a significant tropical northern hemisphere tnh like teleconnection only in winter leading to a north to south pattern of north american temperature anomaly which is greatly limited in spring after 1999 a northwest to southeast response of north american temperature sustains from winter to spring resulting from the maintenance of the pacific north america pna like pattern simulated by the fixedly decaying cp mode

statistical evidence for the natural variation of the central pacific el nino 1 extensive studies claimed that the central equatorial pacific cp el nino has occurred more frequently and strongly than the eastern equatorial pacific el nino in recent years to explain this phenomenon spatial patterns and principal component time series from several sea surface temperature sst data sets in the tropical pacific are analyzed for the period of 1951 2010 cyclostationary empirical orthogonal function analysis separates two modes of sst variability which explain about 50 and 10 of the total sst variability respectively their spatial and temporal patterns are similar among the different sst data sets the first mode captures the typical el nino pattern while the second mode is a dipole pattern in the tropical pacific the two modes are by definition uncorrelated over the analysis period but are in phase since the late 1990s superposition of the two modes results in a significant warming in the cp region which is a potential explanation for a more frequent occurrence of the cp el nino in the recent decades similar analysis is conducted based on the 500 year data from the geophysical fluid dynamics laboratory climate model version 2 1 under the preindustrial condition the result is generally consistent with the observations yielding occasional in phase relationship between the two modes thus it cannot be ruled out that a more frequent occurrence of the cp el nino in recent years is a natural feature of the equatorial climate system

warm pool and cold tongue el nino events as simulated by the gfdl 2 1 coupled gcm recent studies report that two types of el nino events have been observed one is the cold tongue ct el nino which is characterized by relatively large sea surface temperature sst anomalies in the eastern pacific and the other is the warm pool wp el nino in which sst anomalies are confined to the central pacific here both types of el nino events are analyzed in a long term coupled gcm simulation the present model simulates the major observed features of both types of el nino incorporating the distinctive patterns of each oceanic and atmospheric variable it is also demonstrated that each type of el nino has quite distinct dynamic processes which control their evolutions the ct el nino exhibits strong equatorial heat discharge poleward and thus the dynamical feedbacks control the phase transition from a warm event to a cold event on the other hand the discharge process in the wp el nino is weak because of its spatial distribution of ocean dynamic field the positive sst anomaly of wp el nino is thermally damped through the intensified evap orative cooling

a pressure packer system for conducting rising head tests in water table wells abstract the pressure system developed for fully saturated well screens has been modified for conducting rising head tests in water table wells installed in highly permeable aquifers the pressure system consists of a compressed air source and 1 inch diameter pvc piping with a packer attached at the end the pressure system was evaluated in a series of rising head tests conducted in a well at a superfund site in new england the well was tested with slugs and with the pressure system within each technique estimates of hydraulic conductivity showed no difference comparison of hydraulic conductivity estimates between techniques slug test vs pressure test showed differences due to stratigraphy the interval tested using slug tests crossed two stratigraphic units the pressure system tested only one of these units we conclude that the pressure system may be used to characterize the vertical hydraulic conductivity distribution in a series of successive tests by changing the packer position and the screened interval tested

different impacts of various el nino events on the indian ocean dipole our early work wang and wang in j clim 26 1322 1338 2013 separates el nino modoki events into el nino modoki i and ii because they show different impacts on rainfall in southern china and typhoon landfall activity the warm sst anomalies originate in the equatorial central pacific and subtropical northeastern pacific for el nino modoki i and ii respectively el nino modoki i features a symmetric sst anomaly distribution about the equator with the maximum warming in the equatorial central pacific whereas el nino modoki ii shows an asymmetric distribution with the warm sst anomalies extending from the northeastern pacific to the equatorial central pacific the present paper investigates the influence of the various groups of el nino events on the indian ocean dipole iod similar to canonical el nino el nino modoki i is associated with a weakening of the walker circulation in the indo pacific region which decreases precipitation in the eastern tropical indian ocean and maritime continent and thus results in the surface easterly wind anomalies off java sumatra under the bjerknes feedback the easterly wind anomalies induce cold sst anomalies off java sumatra and thus a positive iod tends to occur in the indian ocean during canonical el nino and el nino modoki i however el nino modoki ii has an opposite impact on the walker circulation resulting in more precipitation and surface westerly wind anomalies off java sumatra thus el nino modoki ii is favorable for the onset and development of a negative iod on the frame of the bjerknes feedback

contrasting impacts of two types of enso on the boreal spring hadley circulation the possible influences of two types of enso i e the canonical enso and enso modoki em on hadley circulation hc during the boreal spring are investigated during 1979 2010 el ni no events are featured with a symmetric pattern in equatorial zonal mean sea surface temperature anomalies ssta with a maximum around the equator in contrast the zonal mean ssta associated with el ni modoki events shows an asymmetric structure with a maximum around 108n the contrasting underlying thermal structures corresponding with enso and em have opposite impacts on the simultaneous hc in el ni years a symmetric anomalous meridional circulation is seen with enhanced rising around the equator and anomalousdescentatabout158nand208s incontrast anasymmetricequatorialmeridionalcirculationisobserved for el ni modoki years with anomalous ascent around 108n and descent at about 108s and 208n the contrasting meridional circulation anomalies within enso and em are caused by their different meridional ssta structure this result is theoretically explained indicating that anomalous meridional circulation is subject to the meridional ssta gradient moreover the observed results are reproduced in numerical experiments driven by anomalous warming in the eastern and central pacific ocean thus the authors conclude that the anomalous hc linked to enso and em is induced by the accompanying meridional gradient in zonal mean ssta

recharge oscillator mechanisms in two types of enso the el ni oscillation enso tends to behave arguably as two different types or flavors in recent decades one is the canonical cold tongue type enso with major sea surface temperature anomalies ssta positionedoverthe easternpacific theotheris awarm pool typeensowith sstacenteredin the central pacific near the edge of the warm pool in this study the basic features and main feedback processes of these two types of enso are examined it is shown that the interannual variability of upper ocean heat content exhibits recharge discharge processes throughout the life cycles of both the cold tongue ct and warm pool wp enso types through a heat budget analysis with focus on the interannual frequency band the authors further demonstrate that the thermocline feedback plays a dominant role in contributing to the growth and phase transitions of both enso types whereas the zonal advective feedback contributes mainly to their phase transitions the westward shift of the ssta center of the wp enso and the presence of significant surface easterly wind anomalies over the far eastern equatorial pacific during its mature warm phase are the two main factors that lead to a reduced positive feedback for the eastern pacific ssta nevertheless both the wp and ct enso can be understood to a large extent by the recharge oscillator mechanism

a new paradigm for the predominance of standing central pacific warming after the late 1990s canonical el nino has a warming center in the eastern pacific ep but in recent decades el nino warming center tends to occur more frequently in the central pacific cp the definitions and names of this new type of el nino however have been notoriously diverse which makes it difficult to understand why the warming center shifts here we show that the new type of el nino events is characterized by 1 the maximum warming standing and persisting in the cp and 2 the warming extending to the ep only briefly during its peak phase for this reason we refer to it as standing cp warming cpw global warming has been blamed for the westward shift of maximum warming as well as more frequent occurrence of cpw however we find that since the late 1990s the standing cpw becomes a dominant mode in the pacific meanwhile the epochal mean trade winds have strengthened and the equatorial thermocline slope has increased contrary to the global warming induced weakening trades and flattening thermocline we propose that the recent predominance of standing cpw arises from a dramatic decadal change characterized by a grand la nina like background pattern and strong divergence in the cp atmospheric boundary layer after the late 1990s the anomalous mean cp wind divergence tends to weaken the anomalous convection and shift it westward from the underlying sst warming due to the suppressed low level convergence feedback this leads to a westward shift of anomalous westerly response and thus a zonally in phase sst tendency preventing eastward propagation of the sst anomaly we anticipate more cpw events will occur in the coming decade provided the grand la nina like background state persists

multi level slug tests in highly permeable formations 2 hydraulic conductivity identification method verification and field applications abstract using the developed theory and modified springer gelhar sg model an identification method is proposed for estimating hydraulic conductivity from multi level slug tests the computerized algorithm calculates hydraulic conductivity from both monotonic and oscillatory well responses obtained using a double packer system field verification of the method was performed at a specially designed fully penetrating well of 0 1 m diameter with a 10 m screen in a sand and gravel alluvial aquifer msea site shelton nebraska during well installation disturbed core samples were collected every 0 6 m using a split spoon sampler vertical profiles of hydraulic conductivity were produced on the basis of grain size analysis of the disturbed core samples these results closely correlate with the vertical profile of horizontal hydraulic conductivity obtained by interpreting multi level slug test responses using the modified sg model the identification method was applied to interpret the response from 474 slug tests in 156 locations at the msea site more than 60 of responses were oscillatory the method produced a good match to experimental data for both oscillatory and monotonic responses using an automated curve matching procedure the proposed method allowed us to drastically increase the efficiency of each well used for aquifer characterization and to process massive arrays of field data recommendations generalizing this experience to massive application of the proposed method are developed

tectonic control on sediment accretion and subduction off south central chile implications for coseismic rupture processes of the 1960 and 2010 megathrust earthquakes based on a compilation of published and new seismic refraction and multichannel seismic reflection data along the south central chile margin 33 46 s we study the processes of sediment accretion and subduction and their implications on megathrust seismicity in terms of the frontal accretionary prism fap size the marine south central chile fore arc can be divided in two main segments 1 the maule segment south of the juan fernandez ridge and north of the mocha block characterized by a relative large fap 20 40 km wide and 2 the chiloe segment south of the mocha block and north of the nazca antarctic south america plates junction characterized by a small fap 10 km wide in addition the maule and chiloe segments correlate with a thin 1 km thick and thick 1 5 km thick subduction channel respectively the mocha block lies between 37 5 and 40 s and is configured by the chile trench mocha and valdivia fracture zones this region separates young 0 25 ma oceanic lithosphere in the south from old 30 35 ma oceanic lithosphere in the north and it represents a fundamental tectonic boundary separating two different styles of sediment accretion and subduction respectively a process responsible for this segmentation could be related to differences in initial angles of subduction which in turn depend on the amplitude of the down deflected oceanic lithosphere under trench sediment loading on the other hand a small fap along the chiloe segment is coincident with the rupture area of the trans pacific tsunamigenic 1960 earthquake mw 9 5 while a relatively large fap along the maule segment is coincident with the rupture area of the 2010 earthquake mw 8 8 differences in earthquake and tsunami magnitudes between these events can be explained in terms of the fap size along the chiloe and maule segments that control the location of the updip limit of the seismogenic zone the rupture area of the 1960 event also correlates with a thick subduction channel chiloe segment that may provide enough smoothness at the subduction interface allowing long lateral earthquake rupture propagation

regional pore fluid pressures in the active western taiwan thrust belt a test of the classic hubbert rubey fault weakening hypothesis abstract we document regional pore fluid pressures in the active taiwan thrust belt using 55 deep boreholes to test the classic hubbert rubey hypothesis that high static fluid pressures depth normalized as pf rgz account for the extreme weakness of thrust faults since effective friction f f 1 taiwan fluid pressures are dominated by disequilibrium compaction showing fully compacted sediments with hydrostatic fluid pressures at shallow depths until the fluid retention depth zfrd 3 km below which sediments are increasingly undercompacted and overpressured the hubbert rubey fault weakening coefficient is a simple function of depth 1 0 6zfrd z we map present day and pre erosion fluid pressures and weakening 1 regionally and show that active thrusts are too shallow relative to zfrd for the classic hubbert rubey mechanism to be important which requires z 4zfrd 12 km to have the required order of magnitude hubbert rubey fault weakening of 1 0 15 the best characterized thrust is the chelungpu fault that slipped in the 1999 mw 7 6 chi chi earthquake which has a low effective friction f 0 08 0 12 yet lies near the base of the hydrostatic zone at depths of 1 5 km with a modest hubbert rubey weakening of 1 0 4 0 6 overpressured miocene and oligocene detachments at 5 7 km depth have 1 0 3 therefore other mechanisms of fault weakening are required such as the dynamical mechanisms documented for the chi chi earthquake

contrasting eastern pacific and central pacific types of enso abstract surface observations and subsurface ocean assimilation datasets are examined to contrast two distinct types of el nino southern oscillation enso in the tropical pacific an eastern pacific ep type and a central pacific cp type an analysis method combining empirical orthogonal function eof analysis and linear regression is used to separate these two types correlation and composite analyses based on the principal components of the eof were performed to examine the structure evolution and teleconnection of these two enso types the ep type of enso is found to have its sst anomaly center located in the eastern equatorial pacific attached to the coast of south america this type of enso is associated with basinwide thermocline and surface wind variations and shows a strong teleconnection with the tropical indian ocean in contrast the cp type of enso has most of its surface wind sst and subsurface anomalies confined in the central pacific and tends to onset develop and decay in situ

phase transition of the el nino southern oscillation a stationary sst mode a stationary sst mode is proposed to understand the physical mechanisms responsible for the phase transition of the el nino southern oscillation this stationary sst mode differs from the original delayed oscillator mode and the slow sst mode in the sense that it considers both balanced and unbalanced thermocline depth variations and does not take into account the zonal propagation of sst within this mode the walker circulation acts as a positive feedback mechanism to amplify and maintain an existing interannual sst anomaly whereas the hadley circulation acts as a negative feedback mechanism that dismisses the original anomaly and causes the phase shift from a warm cold to a cold warm episode the key to the cause of interannual oscillations in the stationary sst mode lies in the zonal mean thermocline depth variation that is not in equilibrium with the winds because of the nonequilibrium this part of the thermocline depth anomaly tends to have a phase lag with the wind or sst anomaly and therefore holds a key for the interannual oscillation the zonally asymmetric part of the thermocline depth anomaly on the other hand is always in sverdrup balance with the winds such a phase relationship agrees well with observations and with gcm simulations the stationary sst mode strongly depends on the basin width on the air sea coupling strength and on the seasonal cycle basic state for a reasonable parameter regime it depicts an interannual oscillation with a period of 2 7 years this stationary sst mode is also season dependent it has a maximum growth rate during the later part of the year and a negative growth rate during the northern spring which may explain the occurrence of the mature phases of the el nino in the northern winter and a rapid drop of the lagged correlation of the southern oscillation index in the boreal spring

two distinct modes of tropical indian ocean precipitation in boreal winter and their impacts on equatorial western pacific abstractthe observational analysis reveals two distinct precipitation modes the zonal dipole dp mode and the monopole mp mode in the tropical indian ocean tio during the el nino mature winter even though sea surface temperature anomalies sstas have a similar basinwide warming pattern referred to as the indian ocean basin mode iobm the formation of the two precipitation modes depends on the distinct evolutions of the ssta in the tropical pacific and indian ocean both of the precipitation modes are preceded by an indian ocean dipole iod the iod associated with the dp mode developed in late summer and was triggered by pacific el nino through a sumatra philippine pattern the iod associated with the mp mode developed in early summer when the pacific sstas were still normal the different iod onset time leads to salient differences in subsequent evolution including the transfer of a dipole sst pattern to a basinwide pattern as a result in the boreal winter the zonal ssta gradient assoc

plausible causes of the interdecadal change of the north pacific teleconnection pattern in boreal spring around the late 1990s an interdecadal change of the north pacific teleconnection pattern in the upper troposphere in boreal spring was noted around the late 1990s during the period of 1979 1998 a meridional dipole pattern with alternative cyclone and anticyclone to the south and the north of 45 n over north pacific was identified as the leading mode by applying the empirical orthogonal function eof technique onto the 300 hpa geopotential height anomaly after removing its zonal average this pattern is similar to the upper tropospheric structure of north pacific oscillation npo western pacific wp pattern during the period of 1999 2018 the meridional dipole is replaced by a northeast southwest orientated teleconnection with centers of activity over the subtropical central pacific and northeastern north pacific resembling a pacific north america pna teleconnection that is the upper level atmospheric teleconnection shifted from a npo wp like pattern to a pna like pattern in 1998 1999 for the plausible causes of this interdecadal change the effect of synoptic high frequency hf 2 8 day eddy and tropical convection over the central pacific are emphasized before 1998 1999 the npo wp like teleconnection could be ascribed to the vorticity forcing of the hf transient eddy activity over north pacific between 40 and 60 n with the role of tropical heating ignorable after 1998 1999 the spatial distribution of hf transient eddy activity shifted significantly from a north south pattern to a northeast southwest pattern sustaining a pna like teleconnection through the transportation of the eddy vorticity fluxes while the vorticity forcing of the subseasonal low frequency lf 10 90 day transient eddy activity plays a role in the maintenance of the teleconnection lobe over the subtropical central pacific in addition the tropical convection anomaly centers shifted towards the equatorial central pacific and maritime continent which can induce a poleward propagating rossby wave train and amplify the pna like teleconnection pattern

determination of the pore fluid pressure ratio at seismogenic megathrusts in subduction zones implications for strength of asperities and andean type mountain building 1 we construct the differential stress profile across the fore arc in a subduction zone from the force balance between the shear stress at seismogenic megathrust and the lithostatic pressure we assume that is written by 1 n where is the pore fluid pressure ratio is the coefficient of static friction and n is the normal stress given a density structure of the fore arc wedge we determine by comparing calculated fore arc stresses with observed ones as 0 95 0 98 in shikoku miyagi peru north chile and south chile and 0 90 0 93 in south vancouver island and washington the parameter averaged over the seismogenic megathrust is of the order of 10 mpa stress drops of great earthquakes in these zones occupy 14 87 and not a constant fraction of they on the other hand increase linearly with 1 we propose a simple fault model in which the area of asperities as a fraction of the total fault area is proportional to 1 variation of fractional area of asperities thus may explain the observed correlation and the regional variation of assuming that the differential stress at summit of the andean mountains is zero not at the coast as observed at present we determine to be 0 84 in north chile in the mountain building stage such a smaller value of along with 0 9 in subduction zones would suggest that variation of controls the tectonic style of the earth

changes in tropical pacific thermocline depth and their relationship to enso after 1999 abstractthe characteristics of el nino southern oscillation enso variability have experienced notable changes since the late 1990s including a breakdown of the zonal mean upper ocean heat content as a precursor for enso these changes also initiated a debate on the role of thermocline variations on the development of enso events since the beginning of the twenty first century in this study the connection between thermocline variations and el nino and la nina events is examined separately for the 1980 98 and 1999 2012 periods the analysis highlights the important role of thermocline variations in modulating enso evolutions in both periods it is found that thermocline variation averaged in the central tropical pacific including both equatorial and off equatorial regions is a good precursor for enso evolutions before and after 1999 while the traditional basinwide mean of equatorial thermocline variation is a good precursor only before 1999 the new precursor including both high frequency variabili

relation between subduction megathrust earthquakes trench sediment thickness and upper plate strain 1 giant earthquake moment magnitude mw 8 5 forecasts for subduction zones have been empirically related to both tectonic stresses and geometrical irregularities along the subduction interface both of these controls have been suggested as able to tune the ability of rupture to propagate laterally and in turn exert an important control on giant earthquake generation here we test these hypotheses and their combined influence by compiling a dataset of trench fill thickness a proxy for smoothing of subducting plate relief by sediment input into the subduction channel and upper plate strain a proxy for the tectonic stresses applied to the subduction interface for 44 segments of the global subduction network we statistically compare relationships between upper plate strain trench sediment thickness and maximal earthquake magnitude we find that the combination of both large trench fill 1 km and neutral upper plate strain explains spatial patterns of giant earthquake occurrence to a statistically significant degree in fact the concert of these two factors is more highly correlated with giant earthquake occurrence than either factor on its own less frequent giant earthquakes of lower magnitude are also possible at subduction zones with thinner trench fill and compressive upper plate strain extensional upper plate strain and trench fill 0 5 km appear to be unfavorable conditions as giant earthquakes have not been observed in these geodynamical environments during the last 111 years

the great sumatra andaman earthquakes imaging the boundary between the ruptures of the great 2004 and 2005 earthquakes segmentation along convergent margins controls earthquake magnitude and location but the physical causes of segment boundaries and their impact on earthquake rupture dynamics are still poorly understood one aspect of the 2004 and 2005 great sumatra andaman earthquakes is their abrupt termination along a common boundary this has led to speculation on the nature of the boundary its origin and why it was not breached for the first time the boundary has been imaged and with newly acquired marine geophysical data we demonstrate that a ridge on the subducting indo australian oceanic crust may exert a control on margin segmentation this suggests a lower plate influence on margin structure particularly its segmentation the ridge is masked by the sedimentary cover in the trench its most likely trend is nne ssw it is interpreted as a fracture zone on the subducting oceanic plate a ramp or tear along the eastern flank of the subducting fracture zone beneath simeulue island may be considered as an intensification factor in terms of rupture propagation barrier

interdecadal variation of the west african summer monsoon during 1979 2010 and associated variability this paper addresses the interdecadal variation of the west african summer monsoon wasm along with its background of atmospheric circulation and possible physical mechanism over the past 32 years 1979 2010 it is indicated that the wasm starts to strengthen from 1998 as the rainfall begins to increase over western west africa on the whole which shows a new interdecadal variation in this interdecadal variation the strengthened ascending motion corresponding to enhanced divergence convergence movement on the upper lower troposphere is prone to develop the local circulation of the monsoon moreover the strengthened southwestern eastern wind on the lower upper level leads to more moisture from the atlantic and the gulf of guinea transported to the west african continent in addition the summer subtropical high over the north atlantic and western west africa is strong and northward and the tropical east wind is also strong statistically the weaker stronger the spring north atlantic oscillation nao is the stronger weaker the tropical easterly is and then the wasm is also stronger but the effect of the nao on the decadal variation of the wasm is not so significant from the north atlantic anomaly sensitivity simulation with a single model this is also an indication that the relationship between the wasm and nao is complicated in an interdecadal time scale and is needed further study in terms of sea surface temperature sst variation the tendency is toward warming in the subtropical north pacific the south pacific and north atlantic numerical simulation experiments and data analysis show that the sst variation in the north pacific plays an important role in the latest interdecadal strengthening of the wasm during the past 32 years while the influences of the south pacific and the north atlantic sst anomalies are not so significant to the associated atmospheric circulation changes

causes of the el nino and la nina amplitude asymmetry in the equatorial eastern pacific abstract the amplitude asymmetry between el nino and la nina is investigated by diagnosing the mixed layer heat budget during the enso developing phase by using the three ocean assimilation products simple ocean data assimilation soda 2 0 2 soda 1 4 2 and the global ocean data assimilation system godas it is found that the nonlinear zonal and meridional ocean temperature advections are essential to cause the asymmetry in the far eastern pacific whereas the vertical nonlinear advection has the opposite effect the zonal current anomaly is dominated by the geostrophic current in association with the thermocline depth variation the meridional current anomaly is primarily attributed to the ekman current driven by wind stress forcing the resulting induced anomalous horizontal currents lead to warm nonlinear advection during both el nino and la nina episodes and thus strengthen weaken the el nino la nina amplitude the convergence divergence of the anomalous geostrophic mixed layer currents dur

an interdecadal change in southern china summer rainfall around 1992 93 the present study documents a pronounced interdecadal change in summer rainfall over southern china around 1992 93 and explores the plausible reasons for this change the summer rainfall is persistently below normal during 1980 92 and above normal during 1993 2002 coherent changes in atmospheric circulation are identified over east asia and the south china sea scs western north pacific wnp the increase in rainfall is accompanied by an increase in lower level convergence midtropospheric ascent and upperlevel divergence over southern china the changes in lower level winds feature two anomalous anticyclones one over the scs subtropical wnp and the other over north china mongolia the outflows from the two anomalous anticyclones converge over southern china leading to anomalous moisture convergence enhanced ascent and increased rainfall the development of the northern anticyclone is related to an increase in the tibetan plateau snow cover in the preceding winter spring that leads to a contrast in temperature change between the plateau and the surrounding regions the relatively small temperature change over the plateau coupled with increases in temperature to the west and the east leads to an increase in surface pressure extending northward from the plateau the development of the southern anticyclone is related to an increase in sea surface temperature in the equatorial indian ocean that enhances lower level convergence and ascent the accompanying upper level divergent flows from the tropical indian ocean to the scs wnp lead to the development of anomalous descent and lower level anomalous anticyclone over the scs wnp

two types of el nino events cold tongue el nino and warm pool el nino abstract in this study two types of el nino events are classified based on spatial patterns of the sea surface temperature sst anomaly one is the cold tongue ct el nino which can be regarded as the conventional el nino and the other the warm pool wp el nino the ct el nino is characterized by relatively large sst anomalies in the nino 3 region 5 s 5 n 150 90 w while the wp el nino is associated with sst anomalies mostly confined to the nino 4 region 5 s 5 n 160 e 150 w in addition spatial patterns of many atmospheric and oceanic variables are also distinctively different for the two types of el nino events furthermore the difference in the transition mechanism between the two types of el nino is clearly identified that is the discharge process of the equatorial heat content associated with the wp el nino is not efficient owing to the spatial structure of sst anomaly as a result it cannot trigger a cold event it is also demonstrated that zonal advective feedback i e zonal adve

interdecadal change in the tropical pacific precipitation anomaly pattern around the late 1990s during boreal spring abstractthe leading mode of boreal spring precipitation variability over the tropical pacific experienced a pronounced interdecadal change around the late 1990s the pattern before 1998 features positive precipitation anomalies over the equatorial eastern pacific ep with positive principle component years the counterpart after 1998 exhibits a westward shift of the positive center to the equatorial central pacific cp observational evidence shows that this interdecadal change in the leading mode of precipitation variability is closely associated with a distinctive sea surface temperature sst anomaly pattern the westward shift of the anomalous precipitation center after 1998 is in tandem with a similar shift of maximum warming from the ep to cp diagnostic analyses based on a linear equation of the mixed layer temperature anomaly exhibit that an interdecadal enhancement of zonal advection za feedback process plays a vital role in the shift in the leading mode of both the tropical pacific sst and t

zonal extension and retraction of the subtropical westerly jet stream and evolution of precipitation over east asia and the western pacific abstractthe relationship between the zonal extension and retraction of the east asian subtropical westerly jet stream easwj and the seasonal evolution of precipitation is investigated the easwj exhibits significant zonal variations associated with its seasonal evolution which affects both large scale atmospheric circulation and precipitation over east asia and the north pacific the midlatitude rain belts and the intertropical convergence zone are located more eastward and southward during jet extensions compared to jet retractions the seasonal cycle of the zonal variations of easwj can be divided into four periods december february march may june july and september november particularly in the mei yu period of june july jet retraction events are associated with a northward shift of rain belts over eastern china which may play an important role in the northward movement of the mei yu rain belt to the huaihe river valley of eastern china after 1999 the zonal extension and retraction of the jet

impact of shifting patterns of pacific ocean warming on north atlantic tropical cyclones two distinctly different forms of tropical pacific ocean warming are shown to have substantially different impacts on the frequency and tracks of north atlantic tropical cyclones the eastern pacific warming epw is identical to that of the conventional el nino whereas the central pacific warming cpw has maximum temperature anomalies located near the dateline in contrast to epw events cpw episodes are associated with a greater than average frequency and increasing landfall potential along the gulf of mexico coast and central america differences are shown to be associated with the modulation of vertical wind shear in the main development region forced by differential teleconnection patterns emanating from the pacific the cpw is more predictable than the epw potentially increasing the predictability of cyclones on seasonal time scales

influence of el nino modoki on spring rainfall over south china 1 using observed data sets from 1979 to 2006 the relationship between el nino modoki and spring rainfall over south china sc is investigated of particular interest is the difference in the influence on spring rainfall of typical el nino events and the recently recognized el nino modoki events which are characterized by distinct warm sea surface temperature anomalies ssta in the central pacific and weaker cold anomalies in the western and eastern parts of the basin associated with the ssta anomalous ascent occurs over the central pacific and downward flow is observed over the eastern and western pacific the anomalous flow is associated with anomalous convergence in the upper troposphere over the western pacific sc is influenced by an anomalous anticyclonic circulation with prevailing northeasterly anomalies the convective activity in sc becomes weaker resulting in reduced rainfall however the situation is different in the case of el nino in terms of the influence on rainfall over sc while el nino modoki events are accompanied by a significant reduction in rainfall over sc there is enhanced rainfall associated with el nino events moreover there exists a strong asymmetry in the relationship between sc spring rainfall typical el nino southern oscillation enso and enso modoki events it appears that these relationships are only statistically significant for positive events the asymmetric influence of positive and negative in two enso phenomena may explain the difference in their respective relationships with spring rainfall over sc

el nino modoki and its possible teleconnection 1 using observed data sets mainly for the period 1979 2005 we find that anomalous warming events different from conventional el nino events occur in the central equatorial pacific this unique warming in the central equatorial pacific associated with a horseshoe pattern is flanked by a colder sea surface temperature anomaly ssta on both sides along the equator empirical orthogonal function eof analysis of monthly tropical pacific ssta shows that these events are represented by the second mode that explains 12 of the variance since a majority of such events are not part of el nino evolution the phenomenon is named as el nino modoki pseudo el nino modoki is a classical japanese word which means a similar but different thing the el nino modoki involves ocean atmosphere coupled processes which include a unique tripolar sea level pressure pattern during the evolution analogous to the southern oscillation in the case of el nino hence the total entity is named as el nino southern oscillation enso modoki the enso modoki events significantly influence the temperature and precipitation over many parts of the globe depending on the season the impacts over regions such as the far east including japan new zealand western coast of united states etc are opposite to those of the conventional enso the difference maps between the two periods of 1979 2004 and 1958 1978 for various oceanic atmospheric variables suggest that the recent weakening of equatorial easterlies related to weakened zonal sea surface temperature gradient led to more flattening of the thermocline this appears to be a cause of more frequent and persistent occurrence of the enso modoki event during recent decades

effect of boreal spring precipitation anomaly pattern change in the late 1990s over tropical pacific on the atmospheric teleconnection observational evidence showed that the leading mode of precipitation variability over the tropical pacific during boreal spring experienced a pronounced interdecadal change around the late 1990s characterized by a precipitation pattern shift from an eastern pacific ep type to a central pacific cp type the distinct impacts of such a precipitation pattern shift on the extratropical atmospheric teleconnection were examined an apparent poleward teleconnection extending from the tropics to the north atlantic region was observed after 1998 while there was no significant teleconnection before 1998 to understand why only the cp type precipitation mode is associated with a striking atmospheric teleconnection after 1998 diagnostic analyses with the eliassen palm flux and rossby wave source rws based on the barotropic vorticity equation were performed the results show that for the ep type precipitation mode no significant rws anomalies appeared over the subtropical pacific due to the opposite effect of the vortex stretching and absolute vorticity advection processes for the cp type precipitation mode however there are both significant vorticity forcing source over the subtropical cp and clear poleward propagation of rossby wave the spatial distribution of the cp type precipitation pattern tends to excite a conspicuous anomalous southerly and a well organized negative vorticity center over the subtropical cp where both the mean absolute vorticity gradient and mean divergence flow are large hence the interaction between the heating induced anomalous circulation and the basic state made the generation of rossby waves conceivable and effective such corresponding teleconnection responses to the prescribed heating were also examined by using a linear baroclinic model lbm it turned out that significant poleward teleconnection pattern is only caused by the cp type precipitation mode rather than by the ep type precipitation mode further sensitive experiments demonstrated that the change in spring basic state before and after 1998 played a relatively minor role in exciting such a teleconnection pattern when compared with the tropical precipitation anomaly pattern change

anomalous winter climate conditions in the pacific rim during recent el nino modoki and el nino events present work compares impacts of el nino modoki and el nino on anomalous climate in the pacific rim during boreal winters of 1979 2005 el nino modoki el nino is associated with tripole dipole patterns in anomalies of sea surface temperature precipitation and upper level divergent wind in the tropical pacific which are related to multiple boomerangs of ocean atmosphere conditions in the pacific zonal and meridional extents of those boomerangs reflect their independent influences which are seen from lower latitudes in the west to higher latitudes in the east in the central pacific more moisture is transported from the tropics to higher latitudes during el nino modoki owing to displacement of the wet boomerang arms more poleward toward east discontinuities at outer boomerang arms manifest intense interactions between tropical and subtropical extratropical systems the pacific north american pattern and related climate anomalies in north america found in earlier studies are modified in very different ways by the two phenomena the seesaw with the dry north and the wet south in the western usa is more likely to occur during el nino modoki while much of the western usa is wet during el nino the moisture to the southwestern usa is transported from the northward shifted itcz during el nino modoki while it is carried by the storms traveling along the southerly shifted polar front jet during el nino the east asian winter monsoon related anticyclone is over the south china sea during el nino modoki as compared to its position over the philippine sea during el nino causing opposite precipitation anomalies in the southern east asia between the two phenomena

subtropics related interannual sea surface temperature variability in the central equatorial pacific abstract interannual sea surface temperature sst variability in the central equatorial pacific consists of a component related to eastern pacific sst variations called type 1 sst variability and a component not related to them called type 2 sst variability lead lagged regression and ocean surface layer temperature balance analyses were performed to contrast their control mechanisms type 1 variability is part of the canonical which is characterized by sst anomalies extending from the south american coast to the central pacific is coupled with the southern oscillation and is associated with basinwide subsurface ocean variations this type of variability is dominated by a major 4 5 yr periodicity and a minor biennial 2 2 5 yr periodicity in contrast type 2 variability is dominated by a biennial periodicity is associated with local air sea interactions and lacks a basinwide anomaly structure in addition type 2 sst variability exhibits a strong connection to the subtropics of both hemisphere

classifying el nino modoki i and ii by different impacts on rainfall in southern china and typhoon tracks based on their opposite influences on rainfall in southern china during boreal fall this paper classifies el nino modoki into two groups el nino modoki i and ii which show different origins and patterns of sst anomalies the warm sst anomalies originate in the equatorial central pacific and subtropical northeastern pacific for el nino modoki i and ii respectively thus el nino modoki i shows a symmetric sst anomaly distribution about the equator with the maximum warming in the equatorial central pacific whereas el nino modokiii displays an asymmetric distribution with the warmsstanomaliesextending fromthe northeastern pacifictotheequatorialcentralpacific additionally thewarmsstanomaliesintheequatorialcentralpacific extend farther westward for el nino modoki ii than for el nino modoki i similar to the canonical el nino el nino modoki i is associated with an anomalous anticyclone in the philippine sea that induces south westerly wind anomalies along the south coast of china and carries the moisture for increasing rainfall in southern china for el nino modoki ii an anomalous cyclone resides east of the philippines associated with northerly wind anomalies and a decrease in rainfall in southern china the canonical el nino and el nino modoki i are associated with a westward extension of the western north pacific subtropical high wnpsh whereas el nino modoki ii shifts the wnpsh eastward differing from canonical el nino and el nino modoki i el nino modoki ii corresponds to northwesterly anomalies of the typhoon steeringflow which are unfavorable for typhoons to make landfall in china

large scale natural gradient tracer test in sand and gravel cape cod massachusetts 3 hydraulic conductivity variability and calculated macrodispersivities hydraulic conductivity k variability in a sand and gravel aquifer on cape cod massachusetts was measured and subsequently used in stochastic transport theories to estimate macrodispersivities nearly 1500 k measurements were obtained by borehole flowmeter tests and permeameter analyses of cores the geometric mean for the flowmeter tests 0 11 cm s is similar to that estimated from other field tests the mean for the permeameter tests 0 035 cm s is significantly lower possibly because of compaction of the cores the variance for the flowmeter 0 24 is also greater than that for the permeameter 0 14 geostatistical analyses applying negative exponential models with and without nuggets reveal similar spatial correlation structures for the two data sets estimated correlation scales range from 2 9 to 8 m in the horizontal and from 0 18 to 0 38 m in the vertical estimates of asymptotic longitudinal dispersivity b 35 0 78 m are similar in magnitude to that observed in the natural gradient tracer test 0 96 m previously conducted at this site

the use of electrical resistivity tomograms as a parameterization for the hydraulic characterization of a contaminated aquifer abstract hydraulic characterization of a contaminated aquifer is an important step in depollution processes because its hydraulic parameters control the choice and efficiency of the depollution protocol to be adopted the characterization presented in this article uses a 3d electrical resistivity imagery to identify the spatial heterogeneities of a contaminated aquifer under tidal influence indeed we use a 3d resistivity model as a source of information to parameterize the reconstruction of the hydraulic conductivity in 3d by inverting a set of hydraulic data acquired on the 13 monitored wells in response to two pumping tests this parameterization relies on the identification of the main electro facies in the resistivity model in the saturated zone which will then be exploited in the hydraulic characterization to find their corresponding hydraulic conductivity values this strategy of parameterization permits to reduce the number of the hydraulic conductivity parameters to be identified to eight hydro facies with a stochastic algorithm called the adaptive metropolis algorithm the hydraulic responses associated with the pumping tests are obtained once the natural effect of the tide is removed the hydraulic conductivity model has permitted to highlight the main heterogeneities in the aquifer in which the hydraulic conductivity is ranging between 10 4 6 10 2 8 m s this range of variability reveals the permeable and smooth character of the aquifer in which the presence of coarse sand and flint blocks enhances its transmissivity these permeable zones are electrically identified by resistive anomalies in the 3d electrical resistivity imaging

an asymmetric mode of tropical indian ocean rainfall variability in boreal spring 1 an analysis of observational estimates has revealed an asymmetric mode of boreal spring rainfall and wind variability over the tropical indian ocean the asymmetric mode is characterized by opposite rainfall and surface wind anomalies north and south of the equator this mode is associated with a cross equatorial gradient in sea surface temperature anomalies the evolution of this mode is related to air sea interactions in the tropical indian ocean in particular surface heat fluxes play an important role in the initiation development and decay of this mode the occurrence of this mode in observations is closely linked to both el nino southern oscillation enso and the indian ocean dipole mode coupled general circulation model experiments indicate that this mode can occur in the absence of enso the variability associated with this mode enhances enso s teleconnection to the indian ocean and affects the seasonal transition in the tropical indian ocean

physical characteristics of subduction interface type seismogenic zones revisited 1 based on global earthquake catalogs the hypocenters nodal planes and seismic moments of worldwide subduction plate interface earthquakes were extracted for the period between 1900 and 2007 assuming that the seismogenic zone coincides with the distribution of 5 5 m 7 earthquakes the subduction interface seismogenic zones were mapped for 80 of the trench systems and characterized with geometrical and mechanical parameters using this database correlations were isolated between significant parameters to identify cause effect relationships empirical laws obtained in previous studies were revisited in light of this more complete accurate and uniform description of the subduction interface seismogenic zone the seismogenic zone was usually found to end in a fore arc mantle rather than at a moho depth the subduction velocity was the first order controlling parameter for variations in the physical characteristics of plate interfaces determining both the geometry and mechanical behavior as such the fast subduction zones and cold slabs were associated with large and steep plate interfaces which in turn had large seismic rates the subduction velocity could not account for the potential earthquake magnitude diversity that was observed along the trenches events with mw 8 5 preferentially occurred in the vicinity of slab edges where the upper plate was continental and the back arc strain was neutral this observation was interpreted in terms of compressive normal stresses along the plate interface large lateral ruptures should be promoted in neutral subduction zones due to moderate compressive stresses along the plate interface that allow the rupture to propagate laterally

subducted sediment thickness and mw 9 earthquakes i measure the thickness of subducted sediment ss beneath the decollement in the fore arc wedge and show that the average value of ss over a subduction zone segment ss is greater than 1 3 km in segments where mw 9 earthquakes have occurred and less than 1 2 km in segments without such large earthquakes in a previous study i showed that the stress drop of large earthquakes mw 7 averaged over a subduction zone segment is larger in segments where mw 9 earthquakes have occurred than in segments without such an event it has also been shown that is linearly related to 1 the pore fluid pressure ratio in the interplate megathrust in this study i revise the previous estimates of and and show that there is a positive correlation between ss and 1 i present a model that relates ss to 1 based on the porous flow of h2o in the subducted sediments which gives a theoretical basis for the correlation between ss and the combination of these parameters thus provides a better indicator for identifying segments where mw 9 earthquakes may occur based on this i propose that the tectonic environments where such huge events are likely to occur are 1 near collision zones 2 near subduction of spreading centers and 3 erosive margins with compressional fore arcs near the japanese islands se hokkaido is prone to such an event but the nankai trough is not