differences in atmospheric circulation between the development of weak and strong warm events in the southern oscillation abstract in this study temporal and spatial aspects of el nino warm event development are explored by comparing composite sequences of sea level pressure slp surface wind and sea surface temperature sst anomalies leading into strong and weak events el nino strength is found to be related to the magnitude and spatial extent of large scale slp anomalies that move in a low frequency mode in association with this it is also intricately linked to the amplitude and wavelength of the rossby waves in the southern midlatitudes the primary signature of the southern oscillation is a more pronounced standing wave of pressure anomalies between southeastern australia and the central south pacific leading into stronger events a strong reversal in the strength of the annual cycle between these two regions causes a stronger weaker slp gradient that drives southwesterly northwesterly wind stress forcing toward away from the western equatorial pacific in austral winter spring of year 0 1 thus pressur

an empirical model of tropical ocean dynamics to extend the linear stochastically forced paradigm of tropical sea surface temperature sst variability to the subsurface ocean a linear inverse model lim is constructed from the simultaneous and 3 month lag covariances of observed 3 month running mean anomalies of sst thermocline depth and zonal wind stress this lim is then used to identify the empirically determined linear dynamics with physical processes to gauge their relative importance to enso evolution optimal growth of sst anomalies over several months is triggered by both an initial sst anomaly and a central equatorial pacific thermocline anomaly that propagates slowly eastward while leading the amplifying sst anomaly the initial sst and thermocline anomalies each produce roughly half the sst amplification if interactions between the sea surface and the thermocline are removed in the linear dynamical operator the sst anomaly undergoes less optimal growth but is also more persistent and its location shifts from the eastern to central pacific optimal growth is also found to be essentially the result of two stable eigenmodes with similar structure but differing 2 and 4 year periods evolving from initial destructive to constructive interference variations among enso events could then be a consequence not of changing stability characteristics but of random excitation of these two eigenmodes which represent different balances between surface and subsurface coupled dynamics as found in previous studies the impact of the additional variables on lim sst forecasts is relatively small for short time scales over time intervals greater than about 9 months however the additional variables both significantly enhance forecast skill and predict lag covariances and associated power spectra whose closer agreement with observations enhances the validation of the linear model moreover a secondary type of optimal growth exists that is not present in a lim constructed from sst alone in which initial sst anomalies in the southwest tropical pacific and indian ocean play a larger role than on shorter time scales apparently driving sustained off equatorial wind stress anomalies in the eastern pacific that result in a more persistent equatorial thermocline anomaly and a more protracted and predictable enso event

algebraic reconstruction of a two dimensional velocity inhomogeneity in the high hazles seam of thoresby colliery a high proportion of faces started in mechanized coal mines run into underground faults the faults take many forms from the splitting of a seam through a hidden stress pattern caused by subsidence or folding to a washout or a vertical throw all faults reduce face output a throw of only 1 5 m can lead to a face being abandoned faults of this order cannot be mapped reliably from the surface they may be mapped in an underground seismic survey roadways of a mine may give access to fast refracting horizons above and below a coal seam waveguiding in the plane of the seam if it occurs simplifies migration of wave trains reflected from discrete faults the reduction problem involved in a fault mapping is only two dimensional given guiding whether leaky or not it is possible to map distributed faults of low reflectivity by shooting in transmission across a panel of coal algebraic reconstruction techniques are used here to reduce first break times of flight through a 425 x 950 m rectangular block of coal into the profile of a velocity inhomogeneity input data are derived by static correction from hand picked arrival times the reduction itself is effected using an algorithm which accommodates underground site access restrictions in back projecting first break velocities a truncated cosine is used to weight the relative contributions of rays passing at different distances from any given mapping point the reconstructed velocity field suggests that the coal panel is bisected by a ridge of higher velocity the suspicion of a ridge is reinforced by results of an aberration test based on a standard huygens kirchhoff migration the ridge is found to follow the general line of a system of pillars left in place during the mining of a lower horizon it is concluded that channel waves may be used to map subsidence into old workings underground coal seams apparently share with other sedimentary rocks the property of a pressure sensitive seismic velocity

relationship between optimal precursory disturbances and optimally growing initial errors associated with enso events implications to target observations for enso prediction by superimposing initial sea temperature disturbances in neutral years we determine the precursory disturbances that are most likely to evolve into el nino and la nina events using an earth system model these precursory disturbances for el nino and la nina events are deemed optimal precursory disturbances because they are more likely to trigger strong enso events specifically the optimal precursory disturbance for el nino exhibits negative sea surface temperature anomalies sstas in the central eastern equatorial pacific additionally the subsurface temperature component exhibits negative anomalies in the upper layers of the eastern equatorial pacific and positive anomalies in the lower layers of the western equatorial pacific the optimal precursory disturbance for la nina is almost opposite to that of el nino the optimal precursory disturbances show that both el nino and la nina originate from precursory signals in the subsurface layers of the western equatorial pacific and in the surface layers of the eastern equatorial pacific we find that the optimal precursory disturbances for el nino and la nina are particularly similar to the optimally growing initial errors associated with el nino prediction that have been presented in previous studies the optimally growing initial errors show that the optimal precursor source areas represent the sensitive areas for target observations associated with enso prediction combining the optimal precursory disturbances and the optimally growing initial errors for enso we infer that additional observations in these sensitive areas can reduce initial errors and be used to detect precursory signals thereby improving enso predictions

mechanisms of the 1997 1998 el nino la nina as inferred from space based observations 1 the intensity of the 1997 el nino and the 8 c sudden drop in sea surface temperature sst around 0 130 w during the turn into la nina in 1998 were a surprise to the scientific community this succession of warm and cold events was observed from start to finish with a comprehensive set of remotely sensed and in situ observations in this study we employ space based observations to demonstrate for the first time their maturity in capturing the preconditioning onset evolution and decay of the 1997 el nino and its transition into the 1998 la nina an accumulation of warm water in the west and equatorial wave reflection on the western ocean boundary appeared favorable for the development of el nino however the action of a series of westerly wind bursts from december 1996 to june 1997 notably in march 1997 was instrumental in setting up this huge el nino the westerly wind bursts excited equatorial downwelling kelvin waves and advected the eastern edge of the warm pool eastward which triggered a distinct warming over the central and eastern parts of the equatorial basin once these warmed regions joined the coupling between the sst and surface winds was fully effective and el nino reached its mature phase by that time much of the warm waters of the western equatorial pacific was transferred toward the east by surface eastward currents the demise of el nino and its turn into la nina in spring 1998 were due to the arrival in the east of various interrelated phenomena upwelling was brought from the west by favorable off equatorial wind stress curl and equatorial kelvin waves generated by easterly winds and wave reflection on the western ocean boundary additional upwelling was brought from the east by equatorial rossby waves generated by westerly winds these various upwelling signals were added to the general uplifting of the thermocline because of the slow discharge of the upper layer of the equatorial basin by diverging surface currents a series of equatorial kelvin and rossby waves characterized by upwelling and opposite surface currents led to the breakup of the warm waters the surfacing of the thermocline and the drastic drop in sst in may 1998 around 0 130 w with the arrival of cold water in the east the easterly winds expanded from the west and la nina turned into a growing mode this view of the 1997 1998 el nino la nina afforded from space enables the testing of various el nino theories

the south pacific meridional mode and its role in tropical pacific climate variability abstractthe pacific meridional mode a thermodynamically coupled mode of variability links extratropical pacific oceanic and atmospheric anomalies to the tropical pacific and may give rise to el n

an asymptotic expansion for the recharge discharge model of enso abstractthe dynamics of el nino southern oscillation enso in the equatorial pacific ocean are largely associated with the slow thermocline adjustment at interannual and basin scales this adjustment involves among other things the fast propagation and reflection of equatorial waves by wind stress forcing a simple and straightforward asymptotic expansion of the long wave equations is proposed using the low frequency approximation the asymptotic expansion is performed in fourier space retaining only the gravest equatorial long waves and baroclinic modes with the largest scale and considering small dissipation by friction and boundary reflections this leads to an asymptotic model for the thermocline response to wind stress forcing which is in essence the ocean component of the recharge discharge model of enso the asymptotic model is nonheuristic and in broad agreement with some essential results scattered in previous studies thermocline variability is divided into a sloping tilt mode that adjus

two different features of discharge of equatorial upper ocean heat content related to el nino events 1 oceanic and atmospheric anomaly fields in the tropical pacific are investigated to extract some characteristics from twelve el nino events in the past 49 years the results show that entire equatorial upper ocean heat content teq is discharged after the mature phase of seven el nino events a type events while teq is not well discharged in other five events b type events furthermore a type events generally have larger amplitudes of tropical oceanic and atmospheric anomalies than b type events in addition the durations of a type events are longer than those of b type events it is also found that a type events accompany large positive wind stress curl anomaly and resultant poleward sverdrup transport in the tropical south pacific after the mature phase of el nino events while b type events do not this appearance of large positive wind stress anomaly should be one of the reasons why teq is well discharged in a type events citation hasegawa t t horii and k hanawa 2006 two different features of discharge of equatorial upper ocean heat content related to el nino events geophys res lett 33 l02609 doi 10 1029 2005gl024832

the influence of an asymmetry in the sequence rock coal rock on the propagation of rayleigh seam waves small offsets in hard coal seams can be detected with the aid of seam channel waves transmission and reflection of seam waves depend among other parameters upon the symmetry properties of the sequence rock coal rock two typical unsymmetrical sequences are found in european coal deposits i coal seams with roof and floor of differing acoustic impedance and ii coal seams interlayered with rock and soil two dimensional analog models with appropriate impedance contrasts are used to study the effect of the unsymmetrical layers upon the propagation of rayleigh seam waves data analysis is based upon amplitude measurements both parallel and perpendicular to the layers and dispersion curves the effect of unsymmetrical roof rock 1 and floor rock 2 was studied with models containing homogeneous coal seams leaky mode wave groups with phase velocities cr in the range between the sv wave velocities r1 2 of the two rock materials i e r1 cr r2 form a characteristic part of the rayleigh seam wave signal using knott s energy coefficient calculations it is shown that in that range energy leakage into the surrounding rock by refracted sv waves is restricted to only one of the two interfaces namely coal rock 2 at the other interface coal rock 1 all waves are totally reflected thus the high amplitudes of these leaky mode wave groups are explained by quasi normal mode features the influence of a dirt bed on wave propagation was studied in models where the roof and the floor have the same elastic properties the maximum thickness of the dirt bed did not exceed 20 of the total seam thickness the effect of the bed s location within the seam was also investigated for all recorded normal mode wave groups either the total seam or the coal layers could be regarded as wave guides this was shown by the fact that the phases could be associated with the phase velocity dispersion curves calculated for the symmetrical sequence rock coal rock these curves are relevant under the condition that the thickness of the coal layer assumed under the calculation coincides with the thickness of the effective wave guide of the respective wave groups wave groups guided in the total seam are not influenced by either the thickness or the position of the dirt bed on the other hand for wave groups guided in the coal layers the quotient of signal amplitudes in the coal layers is influenced by the position of the dirt bed

interannual temperature variability in the tropical pacific and lagrangian heat transport pathways 1 in a previous study we found that volume variability during an el nino southern oscillation enso event is well described by variations in and redistribution of the heat content for any given region within the tropical pacific in this study we use numerical model temperature and velocity fields in a lagrangian analysis of heat content variability these three dimensional fields are used to examine specific warm and cool anomaly regions by computing trajectories back through time to the origins of the anomalously warm or cool water in particular we find that three distinct pathways are important in creating and maintaining the warm eastern equatorial anomaly including pathways in the basin interior in both hemispheres after this warm anomaly at peak enso off equatorial anomalies form both in the eastern pacific and in the far western pacific the west pacific off equatorial cool anomalies are attributed to enso variations in the ekman pumping in those regions

why do we have el nino quantifying a diabatic and nonlinear perspective using observations el nino due to its global impact on weather patterns ecosystems agriculture and public health has become as commonly known to the public as the recent global warming but why we have el nino is not yet as well answered as it may have been assumed linear theories have been successful in explaining the transition from the warm phase to the cold phase of the eastern tropical pacific that results from the rise and fall of el nino but failed to explain the asymmetry between the two phases a nonlinear theory for el nino has suggested that there exist two equilibrium states for the tropical pacific one is zonally symmetric or nearly so with the warm pool extending all the way to the eastern pacific and the other is strongly zonally asymmetric with the warm pool confined to the western half of the tropical pacific under this hypothesis enso results from the fact that under the current radiative heating both states are unstable resulting in the apparent wandering behavior in between these two states as seen in the observations to test this hypothesis the authors have obtained the best approximations for the two equilibrium states empirically using updated ocean assimilation data and quantified the stability of these two empirically obtained equilibrium states using two stability analysis methods the results suggest that the two states are unstable offering support for the nonlinear view of why we have el nino

investigation of a large scale mode of ocean atmosphere variability and its relation to tropical pacific sea surface temperature anomalies abstract by examining the linearly coupled atmospheric and oceanic signals related to interannual variability in sea surface temperatures and upper air wind fields a hemispheric scale ocean atmosphere teleconnection mode is isolated that is significantly correlated with equatorial pacific ssts 12 months later the interannual component of this teleconnection mode is related to a basin scale dipole in the upper air wind fields stretching across the extratropical pacific with additional anomalies extending from the eastern tropical pacific over north america and into the atlantic basin in addition it is related to variability in the sst field with warm anomalies found over the tropical subtropical western pacific as well as the equatorial eastern pacific also there are related cold anomalies over the extratropical central north pacific that extend down into the central subtropical tropical pacific diagnostic studies investigating the ocean atmosphere structure for this mode of variability indicate th

an evaluation of enso asymmetry in the community climate system models a view from the subsurface abstract the asymmetry between el nino and la nina is a key aspect of enso that needs to be simulated well by models in order to fully capture the role of enso in the climate system here the asymmetry between the two phases of enso in five successive versions of the community climate system model ccsm1 ccsm2 ccsm3 at t42 resolution ccsm3 at t85 resolution and the latest ccsm3 nr with the neale and richter convection scheme is evaluated different from the previous studies not only is the surface signature of enso asymmetry examined but so too is its subsurface signature by comparing the differences among these models as well as the differences between the models and the observations an understanding of the causes of the enso asymmetry is sought an underestimate of the enso asymmetry is noted in all of the models but the latest version with the neale and richter scheme ccsm3 nr is getting closer to the observations than the earlier versions the net surface heat flux is found to damp th

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

eastern equatorial pacific ocean t s variations with el nino 1 temperature salinity t s relationship variability in the pycnocline of the eastern equatorial pacific ocean nino3 region 5 s 5 n 150 w 90 w over the last two decades is investigated using observational data and model simulation a numerical model simulation using the mitgcm massachusetts institute of technology general circulation model suggests that during el nino years the water in the eastern equatorial pacific ocean becomes saltier by 0 1 to 0 2 and warmer by 0 5 to 1 c on density surfaces within the pycnocline this simulation is consistent with conductivity temperature depth ctd data collected mostly during tropical atmosphere ocean tao mooring maintenance cruises

eof analysis of upper ocean heat content 1956 2003 step like shift during the late 1970s from generally negative to generally positive values this shift coincided with the change in polarity of the pacific decadal oscillation pdo stephens et al 2001 observed a similar shift for 0 125 m heat content fields another area exhibiting substantial change is the gulf stream region which exhibits warming associated with this eof the second and third eofs are also associated with gyre and basin scale patterns of variability of the pacific ocean the second eof is characterized by a region of negative polarity extending westward from the eastern boundary of the tropical pacific ocean and by a region of positive polarity extending northeastward from the western boundary of the tropical pacific ocean the time variability of this pattern is characterized by a positive linear trend throughout the period the third eof is characterized by a transpacific region of negative polarity south of 5n in the pacific by positive polarity in the 5 15n latitude band and along 30n in the western pacific and by a region of negative polarity extending eastward along the kuroshio and then curving south and west the change in polarity along 5n is striking meinen and mcphaden 2000 found a similar feature in an eof analysis of the depth of the 20c isotherm for 1980 1999 they associated this feature

spatial distribution and the interdecadal change of leading modes of heat budget of the mixed layer in the tropical pacific and the association with enso using heat budget diagnosis of ocean mixed layer from the global ocean data assimilation system the spatial distribution of the leading modes of the heat budget was examined the analysis was for the tropical pacific in 1979 2013 and was based on combined empirical orthogonal function ceof analysis the interdecadal changes of the leading modes and their associations with el nino southern oscillation enso were also analyzed the first leading ceof mode ceof1 corresponds to the enso mature phase the contribution from the zonal advection was relatively small along the equator except the region near the pacific coast of central america the vertical entrainment and diffusion surface heat flux had pronounced maxima with positive negative values along the equatorial central and eastern pacific the meridional advection displayed a different spatial pattern with large positive values on both sides of the equator and smaller values along the equator the total meridional advection anomaly was mainly determined by advection of anomalous temperature by climatological current responsible for broadening of the enso ssta pattern meridionally the zonal advection varied almost simultaneously with the tendency of ocean temperature anomaly in the mixed layer the second leading ceof mode ceof2 included contribution to ssta tendency during the enso developing phase the distribution pattern and amplitude of the zonal advection in the eastern pacific in ceof2 was similar to but with opposite sign to that in ceof1 the amplitudes of the other dynamical and thermodynamical terms were smaller than that in ceof1 and spatial distributions displayed an opposite variation between the pacific coast of central america and central and eastern tropical pacific in ceof2 a comparison of two periods 1979 1999 and 2000 2013 suggested that coupling in the tropical pacific weakened at enso time scales and shifted to a relatively higher frequency regime from 2 to 4 years averaged in 1979 1999 to 1 5 3 years after 2000

analysis of the southward wind shift of enso in cmip5 models abstractduring the mature phase of el nino southern oscillation enso events there is a southward shift of anomalous zonal winds sws which has been suggested to play a role in the seasonal phase locking of enso motivated by the fact that coupled climate models tend to underestimate this feature this study examines the representation of the sws in phase 5 of the coupled model intercomparison project cmip5 it is found that most models successfully reproduce the observed sws although the magnitude of the zonal wind stress anomaly is underestimated several significant differences between the models with and without the sws are identified including biases in the magnitude and spatial distribution of precipitation and sea surface temperature sst anomalies during enso multiple linear regression analysis suggests that the climatological meridional sst gradient as well as anomalous enso driven convective activity over the northwest pacific both might play a role in controlling the sws while the mode

is enso a cycle or a series of events 1 after early ideas that saw el ninos as isolated events the advent of coupled models brought the conception of enso as a cycle in which each phase led to the next in a self sustained oscillation twenty two years of observations that represent the el nino and la nina peaks east pacific sst and the memory of the system zonal mean warm water volume suggest a distinct break in the cycle in which the coupled system is able to remain in a weak la nina state for up to two years so that memory of previous influences would be lost similarly while the amplitude of anomalies persists from the onset of a warm event through its termination there is no such persistence across the la nina break these observations suggest that el ninos are in fact event like disturbances to a stable basic state requiring an initiating impulse not contained in the dynamics of the cycle itself

quantifying the role of oceanic feedbacks on enso asymmetry the role of oceanic feedbacks in determining the asymmetry of el nino southern oscillation enso magnitude spatial structure and duration is quantified on the basis of a novel temperature variance budget results confirm previous studies that in the eastern pacific el nino warm temperature anomalies are larger in magnitude than la nina cold temperature anomalies mainly due to stronger positive oceanic feedbacks for el nino we find that la nina cold anomalies are typically stronger than el nino warm anomalies in the central pacific with a faster growth rate for cold anomalies due to a stronger positive thermocline feedback and weaker nonlinear damping the thermocline feedback related to recharge oscillator dynamics plays a dominate role and leads to asymmetry in the duration of el nino and la nina events in particular the thermocline feedback becomes significantly negative during the late decaying phase of el nino and speeds up its demise

north south asymmetry of warm water volume transport related with el nino variability 1 a better understanding of variability in the volume of warm water in the equatorial pacific pycnocline warm water volume or wwv is critical to understanding el nino southern oscillation enso variability we have investigated the meridional wwv transport in the northern nh and southern hemispheres sh using a high resolution general circulation model the transport in the western boundary region compensates the interior transport in the sh where sverdrup balance holds approximately in contrast such compensation does not hold in the nh because the boundary transport lags interior transport by about 7 months hence the wwv exchange in the nh has more impact on the recharge discharge of the equatorial wwv the north south asymmetry of the wwv transport which is interpreted based on the linear rossby theory is related with the southward migration of westerly wind and the negative wind curl over the northwestern off equatorial region after the mature stage of enso

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

the impact of convection on enso from a delayed oscillator to a series of events abstract the ncar community climate system model version 3 ccsm3 exhibits persistent errors in its simulation of the el nino southern oscillation enso mode of coupled variability the amplitude of the oscillation is too strong the dominant 2 yr period too regular and the width of the sea surface temperature response in the pacific too narrow with positive anomalies extending too far into the western pacific two changes in the parameterization of deep convection result in a significant improvement to many aspects of the enso simulation the inclusion of convective momentum transport cmt and a dilution approximation for the calculation of convective available potential energy cape are used in development integrations and a striking improvement in enso characteristics is seen an increase in the periodicity of enso is achieved by a reduction in the strength of the existing short circuited delayed oscillator mode the off equatorial response is weaker and less tropically confined largely as a

attenuation and anisotropy of channel waves in coal seams in recent years channel wave seismology has shown itself to be a useful aid to coal mining small geologic faults which interrupt a coal seam can seriously disrupt mining by modern longwall methods such features have been accurately predicted at distances of several hundred meters by underground seismic surveys the useful range of the method in a particular seam depends critically on the rate at which channel waves in the frequency range of interest 50 to 500 hz are attenuated during passage through the coal when no faulting is located by a given survey it is always important to know at what range a fault would have been detected had it been present to this end the attenuation characteristics must be studied frequently coal seams are highly anisotropic wave guides perpendicular to the bedding plane one or two cleat or cleavage planes exist along which the coal is extensively cracked and jointed recent work by crampin 1978 1981 and by hudson 1981 has shown that such systems of parallel

modelling of rayleigh type seam waves in disturbed coal seams and around a coal mine roadway summary wave propagation in coal seams is numerically modelled in order to identify approaches towards the reconnaissance beyond the heading face of an advancing coal mine roadway complete synthetic wavefields including p sv body waves and rayleigh type seam waves are calculated using a green s function approach for simple laterally homogeneous models and a parallel elastic 2 d 3 d finite difference modelling code for more realistic geometries for a simple three layer model the wavefield within the seam is dominated by a fundamental rayleigh seam mode symmetrical with respect to the centre of the seam on the vertical component and antisymmetrical on the horizontal component if the seam contains an interleaved dirt band with higher velocities and density higher modes dominate the wave propagation depending on the thickness of the dirt band wave propagation in laterally inhomogeneous coal seam models with disturbances like seam ends faults thinning washouts and seam splitting is strongly influenced by the type of disturbance amplitudes of seam waves reflected from these disturbances strongly depend on the fault throw and the degree of thinning or washout in some cases conversion to higher modes can occur in all investigated models those rayleigh seam wave phases are preferably reflected which have frequencies above the fundamental mode airy phase lower frequency phases are preferably transmitted however seam waves are not reflected from a seam splitting disturbance thus a detection of seam splitting with reflected seam waves appears to be impossible fd computations for 3 d models containing an ending tunnel parallel to the seam and a source beyond the heading face of the tunnel show that seam waves are converted into rayleigh waves at the tunnel face they propagate along the surface of the tunnel and interfere with the seam waves propagating beside the tunnel this effect has to be taken into account for subsequent treatment of experimental data where the locations of sources and receivers are restricted to a small seismic layout in the vicinity of the tunnel as tunnel surface waves have slightly lower frequencies than seam waves it may be feasible to separate tunnel waves from the seam wave reflections particularly because higher frequency phases of the seam wave are preferably reflected at seam disturbances polarization analysis showed that the elliptically polarized rayleigh type seam waves in the vertical radial plane can be distinguished from rayleigh tunnel waves propagating on the sidewall of the tunnel adjoining the coal layer with elliptical polarization in the radial transversal plane

modelling channel waves with synthetic seismograms in an anisotropic in seam seismic survey1 in seam seismic surveys with channel waves have been widely used in the united kingdom and elsewhere to map coal seams and to detect anomalous features such as dirt bands seam thinning and thickening and particularly in seam faulting although the presence of cleat induced anisotropy has been recognized in the past almost all previous analyses have assumed homogeneous isotropic or transversely isotropic coal seams channel waves however exhibit properties which cannot be fully explained without introducing anisotropy into the coal seam in this paper the authors model the observed in seam seismic channel waves with synthetic seismograms to gain an understanding of the effects of cleat induced anisotropy on the behavior of channel waves the results show a reasonable good match with the observations in traveltime relative amplitudes dispersion characteristics and particle motions the authors demonstrate that anisotropy in the surrounding country rocks contributes significantly to the coupling of channel wave particle motion although its effect is not as strong as the anisotropy in the coal seam the authors conclude that the effects of cleat and stress induced anisotropy are observed and can be modelled with synthetic seismograms and that anisotropy must be taken into account for the detailed interpretation of channel waves

radiocarbon as a thermocline proxy for the eastern equatorial pacific an ocean model is used to test the idea that sea surface delta 14 c behaves as a thermocline proxy in the eastern equatorial pacific the orca2 model which includes delta 14 c as a passive tracer has been forced with reanalysis fluxes over 1948 1999 and the output is compared with a previously reported galapagos delta 14 c record the model reproduces the abrupt increase in the seasonally minimum delta 14 c in 1976 77 found in the data this increase is associated with neither a shift of thermocline depth over the nino3 region nor a change in the relative proportion of northern southern source waters rather it is due to a decrease in the sub antarctic mode water samw component of the upwelling water thereby representing a decrease in entrainment of water from below the base of the directly ventilated thermocline

observations of warm water volume changes in the equatorial pacific and their relationship to el nino and la nina abstract this paper describes observed changes in surface winds sea surface temperature sst and the volume of water warmer than 20 c wwv in the equatorial pacific ocean for the period 1980 99 the purpose is to test recent hypotheses about the relationship between variations in wwv and the el nino southern oscillation enso cycle the results confirm inferences based on theory models and previous empirical analyses using proxy data namely sea level that enso involves a recharge and discharge of wwv along the equator and that the cyclic nature of enso results from a disequilibrium between zonal winds and zonal mean thermocline depth the authors also find that the magnitude of enso sst anomalies is directly related to the magnitude of zonal mean wwv anomalies furthermore for a given change in equatorial wwv the corresponding warm el nino sst anomalies are larger than the corresponding cold la nina anomalies this asymmetry between the warm and cold phases of the enso cycle implies differences

strong influence of westerly wind bursts on el nino diversity el nino diversity and its genesis are debated an overview of existing work along with a fuzzy clustering analysis and simulations suggest that the asymmetry irregularity and extremes of el nino result from westerly wind bursts

charging el nino with off equatorial westerly wind events the buildup of the warm water in the equatorial pacific prior to an el nino event is considered a necessary precondition for event development while the event initiation is thought to be triggered by bursts of westerly wind however in contrast to the view that warm water slowly builds up years before an el nino event the volume of warm water in the equatorial pacific doubled in the first few months of 2014 reaching values that were consistent with the warm water buildup prior to the extreme 1997 1998 el nino it is notable that this dramatic warm water buildup coincided with a series of westerly wind bursts in the western tropical pacific this study uses linear wave theory to determine the effect of equatorial and off equatorial westerly wind events on the warm water volume wwv of the pacific it is found that westerly wind events have a significant impact on equatorial wwv with all events initially acting to increase wwv which highlights why wwes are so effective at exciting enso in fact our results suggest that the single westerly wind burst which peaked in the first few days of march in 2014 was largely responsible for the coincident dramatic observed increase in wwv how long the equatorial region remains charged however depends on the latitude of the westerly wind event for instance a single equatorially symmetric westerly wind event ultimately acts to discharge wwv via the reflection of upwelling rossby waves which makes it difficult to more gradually build wwv given multiple wwes in contrast when the wind events occur off the equator the subsequent discharge is significantly damped and in some cases the equatorial region can hold the heat charge for the duration of the simulations 6 months as such off equatorial wwes can not only charge equatorial region wwv in the short term but are also a mechanism to more gradually build equatorial region wwv in the longer term given that these off equatorial wwes have a relatively small projection onto the equatorial kelvin wave we argue these events can be considered as a mechanism to modulate the background state in which enso operates

influence of the state of the indian ocean dipole on the following year s el nino el nino southern oscillation enso consists of irregular episodes of warm el nino and cold la nina conditions in the tropical pacific ocean 1 with significant global socio economic and environmental impacts 1 nevertheless forecasting enso at lead times longer than a few months remains a challenge 2 3 like the pacific ocean the indian ocean also shows interannual climate fluctuations which are known as the indian ocean dipole 4 5 positive phases of the indian ocean dipole tend to co occur with el nino and negative phases with la nina 6 9 here we show using a simple forecast model that in addition to this link a negative phase of the indian ocean dipole anomaly is an efficient predictor of el nino 14 months before its peak and similarly a positive phase in the indian ocean dipole often precedes la nina observations and model analyses suggest that the indian ocean dipole modulates the strength of the walker circulation in autumn the quick demise of the indian ocean dipole anomaly in november december then induces a sudden collapse of anomalous zonal winds over the pacific ocean which leads to the development of el nino la nina our study suggests that improvements in the observing system in the indian ocean region and better simulations of its interannual climate variability will benefit enso forecasts

generation mechanism of quasidecadal variability of upper ocean heat content in the equatorial pacific ocean 1 we investigate the relationship between oceanic and atmospheric anomaly fields in the tropical pacific on the quasidecadal qd 10 to 18 years scale is explored it is suggested that the anomalous wind stress curl in the tropical south pacific can generate the equatorial upper ocean heat content ohc anomalies on the qd scale via the sverdrup transport resembling that of the recharge discharge oscillator model for the dynamics of el nino southern oscillation enso the results also show that the wind stress curl anomalies in the tropical south pacific are accompanied by enso like qd scale anomaly patterns of the sea level pressure and sea surface temperature furthermore the results indicate that the equatorial qd scale ohc anomalies can also be generated by the enso like propagations of the ohc anomalies in the tropical north and south pacific this study presents a systematic linkage between the enso like qd scale ohc propagation in the tropical north and south pacific the sverdrup transport variation in the tropical south pacific and the enso like qd scale sst and slp anomalies in the tropical pacific

indian ocean dipolelike variability in the csiro mark 3 coupled climate model abstract coupled ocean atmosphere variability in the tropical indian ocean is explored with a multicentury integration of the commonwealth scientific and industrial research organisation csiro mark 3 climate model which runs without flux adjustment despite the presence of some common deficiencies in this type of coupled model zonal dipolelike variability is produced during july through november the dominant mode of variability of sea surface temperature resembles the observed zonal dipole and has out of phase rainfall variations across the indian ocean basin which are as large as those associated with the model el nino southern oscillation enso in the positive dipole phase cold sst anomaly and suppressed rainfall south of the equator on the sumatra java coast drives an anticyclonic circulation anomaly that is consistent with the steady response gill model to a heat sink displaced south of the equator the northwest southeast tilting sumatra java coast results in cold sea surface temperature

a proposed mechanism for the asymmetric duration of el nino and la nina el nino and la nina exhibit significant asymmetry not only in their spatial structure but also in their duration most el ninos terminate rapidly after maturing near the end of the calendar year whereas many la ninas persist into the following year and often reintensify in boreal winter through atmospheric general circulation model experiments it is shown that the nonlinear response of atmospheric deep convection to the polarity of equatorial pacific sea surface temperature anomalies causes an asymmetric evolution of surface wind anomalies over the far western pacific around the mature phase of el nino and la nina because of the eastward displacement of precipitation anomalies in the equatorial pacific during el nino compared to la nina surface winds in the western pacific are more affected by sst forcing outside the equatorial pacific which acts to terminate the pacific event

characteristics of stochastic variability associated with enso and the role of the mjo abstract to shed light onto the possible role of stochastic forcing of the el nino southern oscillation enso the characteristics of observed tropical atmospheric variability that is statistically uncoupled from slowly evolving sea surface temperature sst are diagnosed the madden julian oscillation mjo is shown to be the dominant mode of variability within these uncoupled or stochastic components the dominance of the mjo is important because the mjo generates oceanic kelvin waves and perturbs sst in the equatorial pacific that may feed back onto the el nino southern oscillation the seasonality present in the uncoupled zonal stress maximum in austral summer which reflects the seasonality of mjo activity is also transmitted to the eastern pacific thermocline variability by these kelvin waves hence the mjo component of the uncoupled stress could plausibly contribute to the observed phase locking of enso to the seasonal cycle during an el nino event maximum uncoupled zonal stress variance s

heat content variability related to enso events in the pacific abstract anomaly fields of upper ocean heat content ohc in the pacific basin from 30 s to 60 n over a 45 yr period are analyzed with special reference to their relationship with el nino southern oscillation enso events in the present study for convenience the ohc is defined as vertically averaged temperature from the sea surface to 300 m depth based on a cluster analysis it is found that interannual variability with a period of 3 6 yr is dominant in the eastern and western tropical pacific while multidecadal variability with a period of approximately 20 yr is dominant in mid to high latitudes in order to focus attention on the relationship between ohc anomalies and enso events 3 6 yr variations are extracted by a bandpassed filtering with half power points at 3 and 6 yr periods the result clearly shows the cyclic and anticlockwise propagation of ohc anomalies on the circuit in the northern tropical pacific that is an eastward propagation along the equator a northward propagation at the e

vertical structure variability and equatorial waves during central pacific and eastern pacific el ninos in a coupled general circulation model recent studies report that two types of el nino events have been observed one is the cold tongue el nino or eastern pacific el nino ep el nino which is characterized by relatively large sea surface temperature sst anomalies in the eastern pacific and the other is the warm pool el nino a k a central pacific el nino cp el nino or el nino modoki in which sst anomalies are confined to the central pacific here the vertical structure variability of the periods during ep and cp is investigated based on the gfdl cm2 1 model in order to explain the difference in equatorial wave dynamics and associated negative feedback mechanisms it is shown that the mean stratification in the vicinity of the thermocline of the central pacific is reduced during cp el nino which favours the contribution of the gravest baroclinic mode relatively to the higher order slower baroclinic mode energetic kelvin and first meridional rossby wave are evidenced during the cp el nino with distinctive amplitude and propagating characteristics according to their vertical structure mostly first and second baroclinic modes in particular the first baroclinic mode during cp el nino is associated to the ocean basin mode and participates to the recharge process during the whole el nino cycle whereas the second baroclinic mode is mostly driving the discharge process through the delayed oscillator mechanism this may explain that the phase transition from warm to neutral cold conditions during the cp el nino is delayed and or disrupted compared to the ep el nino our results have implications for the interpretation of the variability during periods of high cp el nino occurrence like the last decade

the role of reversed equatorial zonal transport in terminating an enso event abstractthis study shows the sudden basinwide reversal of anomalous equatorial zonal transport above the thermocline at the peaking phase of enso triggers rapid termination of enso events the anomalous equatorial zonal transport is controlled by the concavity of anomalous thermocline meridional structure across the equator during the developing phase of enso opposite zonal transport anomalies form in the western central and central eastern equatorial pacific respectively both are driven by the equatorial thermocline anomalies in response to zonal wind anomalies over the western central equatorial ocean at this stage the anomalous zonal transport in the east enhances enso growth through zonal sst advection in the mature phase of enso off equatorial thermocline depth anomalies become more dominant in the eastern pacific because of the reflection of equatorial signals at the eastern boundary as a result the meridional concavity of the thermocline anomalies is reversed in the east this change reve

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

the annual cycle modulation of meridional asymmetry in enso s atmospheric response and its dependence on enso zonal structure previous studies documented that a distinct southward shift of central pacific low level wind anomalies occurringduringtheensodecayingphaseiscausedbyaninteractionbetweenthewesternpacificannualcycleand el nino southern oscillation enso variability the present study finds that the meridional movement of the central pacificwindanomalies appears only duringtraditional eastern pacific el nino ep el nino eventsrather than in central pacific el nino cp el nino events in which sea surface temperature sst anomalies are confined to the central pacific the zonal structure of enso related sst anomalies therefore has an important effectonmeridionalasymmetryintheassociatedatmosphericresponseanditsmodulationbytheannualcycle in contrasttoepelninoevents thesstanomaliesofcpelninoeventsextendfartherwesttowardthewarmpool regionwithitsclimatological warmssts inthewarmpool region relativelysmallsstanomaliesarethusable to excite convection anomalies on both sides of the equator even with a meridionally asymmetric sst background state therefore almost meridionally symmetric precipitation and wind anomalies are observed over the central pacific during the decaying phase of cp el nino events the sst anomaly pattern of la nina events is similar to cp el nino events with a reversed sign accordingly no distinct southward displacement of the atmospheric response occurs over the central pacific during the la nina decaying phase these results have important implications for enso climate impacts over east asia since the anomalous low level anticyclone over the western north pacific is an integral part of the annual cycle modulated enso response

influence of westerly wind events stochasticity on el nino amplitude the case of 2014 vs 2015 the weak el nino of 2014 was preceded by anomalously high equatorial pacific warm water volume wwv and strong westerly wind events wwes which typically lead to record breaking el nino like in 1997 and 2015 here we use the cnrm cm5 coupled model to investigate the causes for the stalled el nino in 2014 and the necessary conditions for extreme el ninos this model is ideally suited to study this problem because it simulates all the processes thought to be critical for the onset and development of el nino it captures el nino preconditioning by wwv the wwes characteristics and their deterministic behaviour in response to warm pool displacements our main finding is that despite their deterministic control wwes display a sufficiently strong stochastic component to explain the distinct evolutions of el nino in 2014 and 2015 a 100 member ensemble simulation initialized with early spring equatorial conditions analogous to those observed in 2014 and 2015 demonstrates that early year elevated wwv and strong wwes preclude the occurrence of a la nina but lead to el ninos that span the weak with few wwes to extreme with many wwes range sensitivity experiments confirm that numerous strong wwes shift the el nino distribution toward larger amplitudes with a particular emphasis on summer fall wwes occurrence which result in a five fold increase of the odds for an extreme el nino a long simulation further demonstrates that sustained wwes throughout the year and anomalously high wwv are necessary conditions for extreme el nino to develop in contrast we find no systematic influence of easterly wind events ewes on the el nino amplitude in our model our results demonstrate that the weak amplitude of el nino in 2014 can be explained by wwes stochastic variations without invoking ewes or remote influences from outside the tropical pacific and therefore its peak amplitude was inherently unpredictable at long lead time

timing of subsurface heat magnitude for the growth of el nino events the subsurface heat buildup in the western tropical pacific and the recharge phase in equatorial heat content are intrinsic elements of el nino southern oscillation leading to changes in zonal wind stress sea surface temperature and thermocline tilt that characterize the growing and mature phases of el nino en events here we use numerical simulations to study the impact on subsequent en episodes of a sudden increase or decrease in ocean heat content during the recharge phase and compare results with previous studies in which this perturbation is prescribed earlier during the tilting mode we found that while not substantially affected by the phase at which a sudden rise in heat content is prescribed the timing and magnitude of the events are very sensitive to the phase at which a major decrease is imposed the different response to the phase of increases and decreases substantiates the importance of nonlinear subsurface ocean dynamics to the onset and growth of en episodes and provides insight into the irreversibility of the events at different stages of the oscillation

observations and mechanisms of a simple stochastic dynamical model capturing el nino diversity abstractel nino southern oscillation enso has significant impact on global climate and relevance for seasonal forecasts recently a simple modeling framework was developed that captures the enso diversity where state dependent stochastic wind bursts and nonlinear advection of sea surface temperature are coupled to a simple ocean atmosphere model that is otherwise deterministic linear and stable in this article the coupled model is compared with observations using reanalysis data over the last 34 yr where the observed non gaussian statistics and the overall mechanisms of enso are both captured by the model then the formation mechanisms of both the central pacific cp and the traditional el nino in the model are systematically studied first ocean rossby waves induced by easterly trade wind anomalies facilitate the heat content buildup then the reflected ocean kelvin waves and the nonlinear advection lead to positive sst anomalies in the cp region and create a cp el nino second two formation

robust enso across a wide range of climates abstractel nino southern oscillation enso is a pronounced mode of climate variability that originates in the tropical pacific and affects weather patterns worldwide growing evidence suggests that despite extensive changes in tropical climate enso was active over vast geological epochs stretching millions of years from the late cretaceous to the holocene in particular enso persisted during the pliocene when a dramatic reduction occurred in the mean east west temperature gradient in the equatorial pacific the mechanisms for sustained enso in such climates are poorly understood here a comprehensive climate model is used to simulate enso for a broad range of tropical pacific mean climates characterized by different climatological sst gradients it is found that the simulated enso remains surprisingly robust when the east west gradient is reduced from 6 to 1 c the amplitude of enso decreases only by 30 40 its dominant period remains close to 3 4 yr and the spectral peak stays above red noise t

the simplest enso recharge oscillator 1 eastern pacific sea surface temperature sst and mean equatorial pacific thermocline depth are key variables in el nino southern oscillation enso a linear fit to observations leads to a remarkably simple picture enso can be represented by a classical damped oscillator with sst and thermocline depth playing the roles of momentum and position respectively an independent fit of observed relationships between western and eastern thermocline depth central wind stress and eastern pacific sst yields the same picture and supports a recharge oscillator interpretation the oscillation arises from the interaction between the recharge time of the warm pool and the time delay between east and west pacific both finite kelvin wave speed and sst dynamics contribute to the time delay including seasonality in the description we find two periods of relative instability boreal spring with a large phase progression and autumn with nearly stationary phase

effects of ocean initial perturbation on developing phase of enso in a coupled seasonal prediction model coupled prediction systems for seasonal and inter annual variability in the tropical pacific are initialized from ocean analyses in ocean initial states small scale perturbations are inevitably smoothed or distorted by the observational limits and data assimilation procedures which tends to induce potential ocean initial errors for the el nino southern oscillation enso prediction here the evolution and effects of ocean initial errors from the small scale perturbation on the developing phase of enso are investigated by an ensemble of coupled model predictions results show that the ocean initial errors at the thermocline in the western tropical pacific grow rapidly to project on the first mode of equatorial kelvin wave and propagate to the east along the thermocline in boreal spring when the surface buoyancy flux weakens in the eastern tropical pacific the subsurface errors influence sea surface temperature variability and would account for the seasonal dependence of prediction skill in the nino3 region it is concluded that the enso prediction in the eastern tropical pacific after boreal spring can be improved by increasing the observational accuracy of subsurface ocean initial states in the western tropical pacific

meridional movement of wind anomalies during enso events and their role in event termination 1 observational analysis has shown that when el nino southern oscillation enso events typically reach their peak amplitude in boreal winter the associated zonal wind anomalies abruptly shift southward so that the maximum anomalous zonal wind is located around 5 7 s here an analysis utilizing multiple wind products identifies a clear enso phase nonlinearity in the extent of this meridional wind movement and its dynamically linked changes in equatorial heat content it is shown that the meridional wind movement and its discharging effect increase with increasing el nino amplitude while both remain relatively small regardless of la nina amplitude this result implies that asymmetries in the extent of the meridional wind shift may contribute to the observed asymmetry in the duration of el nino and la nina events we also evaluate the result sensitivities to wind product selection and discuss eastern pacific ep and central pacific cp el nino event differences

stress in the earth s crust the link between crustal fluids and extensive dilatancy anisotropy observations of seismic shear wave splitting birefringence along almost all raypaths in the earth9s crust have led to the recognition that the fluid filled cracks microcracks and pores known to pervade most rocks in the crust have been preferentially aligned by the prevailing stress field this phenomenon is known as extensive dilatancy anisotropy or eda and the fluid filled microstructures as eda cracks because the seismic effects can be modelled by distributions of parallel cracks the effects of these stress aligned eda cracks have been observed in many different areas and they appear ubiquitous in the upper 10 to 20 km of the crust many details of the crack geometry and the current stress field can be readily determined from records of the shear waves which have propagated through these aligned cracks in separate studies geochemists have confirmed the presence of microscopic fluid filled cavities in almost all geological material these are referred to as fluid inclusions and provide unequivocal evidence of crustal fluid circulation often along stress controlled fractures different stress episodes can be recognized in many rock samples and studies of fluid inclusions can be used to interpret the palaeo stress history of a rock where the in situ morphology of these inclusions is related to the current regional stress field this paper discusses the relationship between the fluid inclusions of the geochemical literature and eda cracks and concludes that the former may be regarded as one of the constituent inclusion types of extensive dilatancy anisotropy

on the relationship between indian ocean sea surface temperature and the transition from el nino to la nina the relationship between indian ocean sea surface temperature and the transition of el nino events into either la nina or el nino southern oscillation neutral conditions is examined in both observations and the retrospective ensemble hindcasts of the national center for environmental prediction climate forecast system the southern indian ocean is shown to demonstrate a particularly robust and consistent relationship with the evolution of these transitions these associations are described and a physical mechanism involving air sea interaction in the indian and western pacific oceans is proposed observations suggest that easterly surface wind anomalies in the western pacific ocean are associated with the emergence of la nina during boreal summer and fall here it is shown that these winds are significantly correlated to southern indian ocean sea surface temperature in the preceding spring that is characterized by a large scale zonal dipole of cool and warm anomalies in the southwestern and southeastern indian oceans respectively these associations are particularly pronounced for strong el nino conditions during the dissipation of which a pronounced wavetrain like atmospheric pattern accompanies sea surface temperature anomalies in the southern indian ocean together the circulation and sea surface temperature anomalies increase the meridional cross equatorial temperature gradient in the western indian ocean and mute intraseasonal variability while strengthening surface equatorial easterly winds in the indo pacific warm pool collectively these anomalies favor subsequent la nina development on the basis of these observed associations a predictive model that demonstrates skill in anticipating the nature of el nino transitions involving the southern indian ocean asian monsoon and el nino southern oscillation is proposed in the national center for environmental prediction climate forecast system the relationships described above are simulated both consistently and realistically despite model weaknesses further bolstering a key role of southern indian ocean and predictive relationship comparison of fully coupled and sea surface temperature forced simulations suggests a key role for air sea interaction in the observed associations moreover it is demonstrated that coupled simulations of el nino southern oscillation may benefit substantially from improved representation of indian ocean variability and indo pacific interaction

a cross hole and face to borehole in seam seismic experiment at invincible colliery australia an experimental cross hole and face to borehole in seam seismic survey was carried out at invincible colliery in the western coalfield of new south wales objectives were to determine propagation characteristics of the lithgow seam and to establish the infrastructure for seismic mapping hole to hole in australia the seam supports leaky p s and p sv modes these modes propagate with group velocities at 60 hz of 3 1 1 5 and 1 2 km s respectively particle motion polarization is well developed as is dispersion of the sh mode attenuation rates are high the seam is lossy q of approximately 20 two prominent structures were mapped by mode conversion one is believed to be a fracture zone the other a zone of intense roof thrusting the old workings and a minor strike slip fault which intersected raypaths were found to be relatively transparent to p and s waves at 60 hz telemetry delay and shot break timing errors of the exploder box are significant the resulting traveltime scatter is reduced by means of a least squares statics procedure the group velocity estimation algorithm based on fourier transform yields dispersion characteristics which can be matched with theoretical results for a simple model of a coal seam waveguide the experiment demonstrates the capability to retrieve in seam seismic data of diagnostic quality over an appreciable distance 2 km the experience gained in both survey layout and data processing will be beneficial to future seam wave surveying of australian coal mines

decadal scale variability of upper ocean heat content in the tropical pacific 1 decadal scale variability of upper ocean heat content ohc in the tropical pacific is investigated and is compared with that of enso scale the decadal scale ohc anomaly with a period of about 13 years shows anticlockwise propagations in the tropical north pacific like as that of enso scale it is also shown that the entire equatorial ohc anomaly leads nino 3 index anomaly by about a quarter about 3 years of the period of the decadal variability in the tropical pacific this time lag of a quarter of the period is consistent with the idea of the recharge oscillator model for enso dynamics further it is shown that the magnitude of leading ohc anomalies in the entire equatorial pacific is linearly related to the subsequent magnitudes of nino 3 and nino 3 4 indices this relationship is also similar with that of enso scale but there are several different points between them particularly in contrast with the enso scale the amplitude is larger in central equatorial pacific nino 3 4 region than in the eastern region nino 3 region

covariations between the indian ocean dipole and enso a modeling study the coevolution of the indian ocean dipole iod and el nino southern oscillation enso is examined using both observational data and coupled global climate model simulations the covariability of iod and enso is analyzed by applying the extended empirical orthogonal function eeof method to the surface and subsurface ocean temperatures in the tropical indian ocean and western pacific the first eeof mode shows the evolution of iod that lags enso whereas the second mode exhibits the transition from a dipole mode to a basin wide mode in the tropical indian ocean that leads enso the lead lag relationships between iod and enso are consistent with two way interactions between them a comparison between two 500 year model simulations with and without enso shows that enso can enhance the variability of iod at interannual time scale the influence of enso on the iod intensity is larger for the eastern pole than for the western pole and further is stronger in the negative iod phase than in the positive phase the influence of iod on enso is demonstrated by the improvement of enso prediction using sea surface temperature sst in the tropical indian ocean as an enso precursor the improvement of the enso forecast skill is found at both a short lead time 0 month and long leads 10 15 months the sst in the western pole has more predictive value than in the eastern pole the eastward propagation of surface and subsurface temperature signals from the western indian ocean that precedes the development of heat content anomaly in the tropical western pacific is the key for extending the lead time for enso prediction our results are consistent with previously reported findings but highlight the spatial temporal evolution of the enso iod system it is also illustrated that iod would have been more helpful in predicting the 1997 98 el nino than the 2015 16 el nino

optimal precursors of different types of enso events not all el nino southern oscillation enso events are the same their global impacts can differ substantially depending on whether the associated sea surface temperature sst anomalies are stronger in the central pacific cp or the eastern pacific ep the predictability of such differences is therefore of interest in this study the optimal two season precursors of different enso types are investigated in a linear inverse modeling framework using observational sst and thermocline depth data for 1958 2007 it is shown that different sst precursor types alone do not favor the generation of different enso types however initial subsurface conditions characterized by a deeper thermocline in the eastern pacific and a shallower thermocline in the central pacific favor the generation of ep type events while a shallower thermocline in the east and a deeper thermocline in the central western pacific are conducive to cp type events the predictability of different enso types thus depends importantly on initial subsurface conditions

wind stress variations and interannual sea surface temperature anomalies in the eastern equatorial pacific abstract vertical advection of temperature is the primary mechanism by which el nino southern oscillation enso time scale sea surface temperature sst anomalies are generated in the eastern equatorial pacific variations in vertical advection are mediated primarily by remote wind forced thermocline displacements which control the temperature of water upwelled to the surface however during some enso events large wind stress variations occur in the eastern pacific that in principle should affect local upwelling rates the depth of the thermocline and sst in this study the impact of these wind stress variations on the eastern equatorial pacific is addressed using multiple linear regression analysis and a linear equatorial wave model the regression analysis indicates that a zonal wind stress anomaly of 0 01 n m 2 leads to approximately a 1 c sst anomaly over the nino 3 region 5 n 5 s 90 150 w due to changes in local upwelling rates wind stress variations of this magnitude occurred in the easte

the influence of atmospheric convection on the interaction between the indian ocean and enso abstractin recent years it has been proposed that a negative positive indian ocean dipole iod in boreal autumn favors an el nino la nina at a lead time of 15 months observational analysis suggests that a negative iod might be accompanied by easterly anomalies over the western pacific such easterlies can enhance the western pacific warm water volume thus favoring el nino development from the following boreal spring onward however a gill model response to a negative iod forcing would lead to nearly zero winds over the western pacific the authors hypothesize that a negative iod or even a cool western indian ocean alone leads to low level air convergence and hence enhanced convectional heating over the maritime continent which in turn amplifies the wind convergence so as to cause easterly winds over the western pacific this hypothesis is tested by coupling an idealized indian ocean model and a convective feedback model over the maritime continent to the zebiak cane model it is found that for a

on the joint role of subtropical atmospheric variability and equatorial subsurface heat content anomalies in initiating the onset of enso events abstract previous research has shown that seasonal mean variations in both the subtropical extratropical sea level pressures over the central north pacific and the subsurface heat content anomalies in the western equatorial pacific are significantly related to the state of the el nino southern oscillation enso 12 18 months later here we find that positive negative subsurface temperature anomalies in the western equatorial pacific during boreal summer fall followed by negative positive anomalies in the sea level pressure fields over the subtropical central north pacific during boreal winter tend to result in positive negative mature enso events 12 15 months later i e during the following boreal winter when the intervening sea level pressure anomalies are of the same sign as the preceding heat content anomalies the correlation between the heat content anomalies and the following boreal winter enso state disappears there is still some relation between the boreal winter sea level pressure an

interannual and interdecadal variability of ocean temperature along the equatorial pacific in conjunction with enso in this paper the leading modes of ocean temperature anomalies ota along the equatorial pacific ocean are analyzed and their connection with el nino southern oscillation enso and interdecadal variation is investigated the first two leading modes of ota are connected with the different phases of the canonical enso and display asymmetric features of enso evolution the third leading mode depicts a tripole pattern with opposite variation of ota above the thermocline in the central pacific to that along the thermocline in the eastern and western pacific this mode is found to be associated with so called enso modoki insignificant correlations of this mode with the first two leading modes suggest that enso modoki may be a mode that is independent to the canonical enso and also has longer time scales compared with the canonical enso the fourth mode reflects a warming cooling tendency above below the thermocline since 2000 both the first and second modes have a large contribution to the interdecadal change in thermocline during 1979 2012 also the analysis also documents that both enso and ota shifted into higher frequency since 2000 compared with that during 1979 1999 interestingly the enso modoki related ota mode does not have any trend or significant interdecadal shift during 1979 2012 in addition it is shown that first four eof modes seem robust before and after 1999 2000 suggesting that the interdecadal shift of the climate system in the tropical pacific is mainly a frequency shift and the changes in spatial pattern are relatively small although the mean states over two periods experienced some significant changes

wind stress curl and enso discharge recharge in the equatorial pacific discharge and recharge of the warm water volume wwv above the 20 c isotherm in an equatorial pacific ocean box extending across the pacific from 156 e to the eastern ocean boundary between latitudes 5 s and 5 n are key variables in enso dynamics a formula linking wwv anomalies zonally integrated wind stress curl anomalies along the northern and southern edges of the box and flow into the western end of the box is derived and tested using monthly data since 1993 consistent with previous work a wwv balance can only be achieved if the 20 c isotherm surface is not a material surface that is warm water can pass through it for example during el nino part of the wwv anomaly entering the box is cooled so that it is less than 20 c and therefore passes out of the bottom of the box the 20 c isotherm surface the observations suggest that the anomalous volume passing through the 20 c isotherm is approximately the same as t the anomalous wwv entering the western end of the box therefore the observed wwv anomaly can be regarded as being driven by the anomalous wind stress curl along the northern and southern edges of the box the curl anomaly changes the wwv both by divergent meridional flow at the edges of the box and vortex stretching that is the sverdrup balance does not hold in the upper ocean a typical amplitude for the rate of change of wwv for the 5 s 5 n box is 9 6 sv sv 10 6 m 3 s 1 the wind stress curl anomaly and the transport anomaly into the western end of the box are highly correlated with the el nino index nino 3 4 the average sea surface temperature anomaly ssta over the region 5 s 5 n 170 120 w and nino 3 4 leads minus the wwv anomaly by one quarter of a cycle based on the preceding results a simple discharge recharge coupled enso model is derived only water warmer than about 27 5 28 c can give rise to deep atmospheric convection so unlike past discharge recharge oscillator models the west central rather than eastern equatorial sstas are emphasized the model consists of two variables t the ssta averaged over the region of strong enso air sea interaction in the west central pacific equatorial strip 5 s 5 n 156 e 140 w and d the 20 c isotherm depth anomaly averaged over the

a nonlinear analysis of the enso cycle and its interdecadal changes abstract the nonlinear principal component analysis nlpca via a neural network approach was applied to thermocline anomalies in the tropical pacific while the tropical sea surface temperature sst anomalies had been nonlinearly mapped by the nlpca mode 1 onto an open curve in the data space the thermocline anomalies were mapped to a closed curve suggesting that enso is a cyclic phenomenon the nlpca mode 1 of the thermocline anomalies reveals the nonlinear evolution of the enso cycle with much asymmetry for the different phases the weak heat accumulation in the whole equatorial pacific is followed by the strong el nino and the subsequent strong drain of equatorial heat content toward the off equatorial region precedes a weak la nina this asymmetric enso evolution implies that the nonlinear instability enhances the growth of el nino but dwarfs the growth of la nina the nonlinear enso cycle was found to have changed since the late 1970s for the pre 1980s the enso cycle associated with the ther

the global ocean imprint of enso 1 the enso related spatial patterns and global averages of ocean temperature salinity and steric height are estimated from over 7 years of argo data 2004 2011 substantial extratropical variability is seen in all variables in addition to familiar tropical enso signals surface layer 0 100 dbar and subsurface 100 500 dbar temperature variations are both important in determining steric height and sea surface height patterns for the two years prior to the 2009 el nino the upper 100 dbar of the ocean gained 3 3 1022 j yr 1 of heat while the 100 500 dbar layer lost a similar amount the enso related vertical redistribution of globally averaged heat content between surface and subsurface layers occurring throughout the record is due primarily to changes in the east west tilting of the equatorial pacific thermocline the large temperature changes in the individual layers mask the smaller vertically averaged temperature change in which the ocean loses heat when the surface layer is anomalously warm and gains heat when the surface layer is cool

an interhemispheric tropical sea level seesaw due to el nino taimasa abstractduring strong el nino events sea level drops around some tropical western pacific islands by up to 20 30 cm such events referred to as taimasa in samoa expose shallow reefs thereby causing severe damage to associated coral ecosystems and contributing to the formation of microatolls during the termination of strong el nino events a southward movement of weak trade winds and the development of an anomalous anticyclone in the philippine sea are shown to force an interhemispheric sea level seesaw in the tropical pacific that enhances and prolongs extreme low sea levels in the southwestern pacific spectral features in addition to wind forced linear shallow water ocean model experiments identify a nonlinear interaction between el nino and the annual cycle as the main cause of these sea level anomalies

thermoelastic stress in oceanic lithosphere due to hotspot reheating we investigate the effect of hotspot reheating on the intraplate stress field by modeling the three dimensional thermal stress field produced by nonuniform temperature changes in an elastic plate temperature perturbations are calculated assuming that the lithosphere is heated by a source in the lower part of the thermal lithosphere a thermal stress model for the elastic lithosphere is calculated by superposing the stress fields resulting from temperature changes in small individual elements the stress in an elastic plate resulting from a temperature change in each small element is expressed as an infinite series wherein each term is a source or an image modified from a closed form half space solution we apply the thermal stress solution to midplate swells in oceanic lithosphere with various thermal structures and plate velocities our results predict a stress field with a maximum deviatoric stress on the order of 100 mpa 1 kbar covering a broad area around the hotspot plume the predicted principal stress orientations show a complicated geographical pattern with horizontal extension perpendicular to the hotspot track at shallow depths and compression along the track near the bottom of the elastic lithosphere although stress data near oceanic swells are limited the source parameters of intraplate earthquakes near several hotspots are consistent with the thermal stress model these results indicate that thermal stress due to reheating may be an important contributor to stress fields near hotspots in old oceanic lithosphere

equatorial pacific thermostad response to el nino el ninos are characterized by a shift of warm surface water from the western to eastern equatorial pacific due to weakening of easterly trade winds this shift is associated with the pycnocline or thermocline the large vertical density gradient beneath the surface mixed layer shoaling in the west and deepening in the east inducing a redistribution of ocean heat with global impacts here the response of the pacific equatorial thermostad a layer of low vertical stratification below the pycnocline to el nino is investigated using a monthly argo float climatology and argo float deep velocity data a mean seasonal cycle trend and time lagged linear response to the nino3 4 index are fit by least squares to temperature and salinity at each gridpoint as well as to deep float velocities omitting the trend the results of these fits are used to characterize the response of physical properties in the thermostad including layer thickness and velocity to el nino by comparing the mean properties following neutral conditions nino3 4 0 c versus those following a moderate el nino nino3 4 1 c following an el nino a strengthening of the westward flowing equatorial intermediate current of about 2 7 106 m3 s 1 shifts about 97 1012 m3 of thermostad water from the east to the west allowing conservation of volume within the thermostad as the pycnocline above deepens in the east and shoals in the west this transport and volume change imply a 14 month time scale consistent with el nino this article is protected by copyright all rights reserved

leading modes of the upper ocean temperature interannual variability along the equatorial atlantic ocean in ncep godas abstractin this work the authors analyze the physical mechanisms of interannual variability of the upper ocean temperature anomaly ota in the equatorial atlantic ocean using ocean reanalysis from the national centers for environmental prediction ncep global ocean data assimilation system the variability of equatorial atlantic ota is dominated by two leading modes the first mode is characterized by same sign variation along the thermocline with pronounced amplitude in the central and eastern equatorial atlantic this mode represents the modulation of the overall thermocline depth at the equator generated by net heat convergence in the equatorial ocean with heat content first accumulated mainly in the off equatorial northwestern atlantic in response to anomalous wind curl associated with atlantic meridional mode the second leading mode shows an opposite variation between the western and eastern atlantic this mode is mainly driven by the zonal wind stress fluctuation confined in the southwestern tr

the role of the southward wind shift in both the seasonal synchronization and duration of enso events near the end of the calendar year when el nino events typically reach their peak amplitude there is a southward shift of the zonal wind anomalies which were centred around the equator prior to the event peak previous studies have shown that enso s anomalous wind stresses including this southward shift can be reconstructed with the two leading eofs of wind stresses over the tropical pacific here a hybrid coupled model is developed featuring a statistical atmosphere that utilises these first two eofs along with a linear shallow water model ocean and a stochastic westerly wind burst model this hybrid coupled model is then used to assess the role of this meridional wind movement on both the seasonal synchronization as well as the duration of the events it is found that the addition of the southward wind shift in the model leads to a christmas peak in variance similar to the observed timing although with weaker amplitude we also find that the added meridional wind movement enhances the termination of el nino events making the events shorter while this movement does not appear to play an important role on the duration of la nina events thus our results strongly suggest that the meridional movement of enso zonal wind anomalies is at least partly responsible for seasonal synchronization of enso events and the duration asymmetry between the warm el nino and cool la nina phases

equatorial atlantic interannual variability role of heat content 1 the dynamics of the equatorial atlantic zonal mode are studied using observed sea surface height ssh sea surface temperature sst and heat flux and reanalysis wind stress and upper ocean temperature principal oscillation pattern pop analysis shows that the zonal mode is an oscillatory normal mode of the observed coupled system obeying the delayed action recharge oscillator paradigm for el nino southern oscillation variations in equatorial averaged ssh a proxy for upper ocean heat content precede sst anomalies in the cold tongue by 4 5 months about a quarter of the pop period positive subsurface temperature anomalies appear in the west as a delayed response to the preceding cold event these propagate eastward where due to the shallow thermocline they can influence sst leading to the next warm event although sst variations exhibit weak westward propagation during some zonal mode events pop analysis indicates that to first order there is no zonal propagation in sst net surface heat flux anomalies generally act to damp sst anomalies the zonal mode explains a large amount 70 of sst variability in the east and a significant fraction 19 of equatorial variability thus the predictability potential in the equatorial atlantic on seasonal time scales may be considerably higher than currently thought

coherent tropical indo pacific interannual climate variability abstracta multichannel singular spectrum analysis mssa applied simultaneously to tropical sea surface temperature sst zonal wind and burstiness zonal wind variability reveals three significant oscillatory modes they all show a strong enso signal in the eastern pacific ocean po but also a substantial sst signal in the western indian ocean io a correlation based analysis shows that the western io signal contains linearly independent information on enso of the three indo pacific enso modes of the mssa one resembles a central pacific cp el nino while the others represent eastern pacific ep el ninos which either start in the central pacific and grow eastward epe or start near peru and grow westward epw a composite analysis shows that epw el ninos are preceded by cooling in the western io about 15 months earlier two mechanisms are discussed by which the western io might influence enso in the atmospheric bridge mechanism subsidence over the cool western io in autumn year 0 leads t

vertical seismic profiling in coal the intellection understanding of seismic wave propagation in coal measures demands direct observation of the wavefield progression two vertical seismic profiles with high spatial and temporal sampling were recently recorded in the sydney basin coalfields as part of an experimental coal seismic program static corrections and interval velocities were obtained by an automated system to determine first kicks and pulse rise times upgoing and downgoing waves were separated in the f k plane using a novel technique of contour slice filtering the isolated upgoing waves clearly display reflections from the major coal seams within the stratigraphic sequence the downgoing wave spectra were subjected to attenuation analysis the deduced specific quality factor q for permian coal measure rocks lies in the range 20 70 similar estimates were obtained in the time domain from measurements of pulse broadening synthetic vsp seismograms computed using an exact recursive formulation are an indispensable aid to interpretation they illustrate the filtering effects of coal seams and sequences and the effects of the contribution of internal and free surface multiple reflections in the recorded wavetrains

importance of background seasonality over the eastern equatorial pacific in a coupled atmosphere ocean response to westerly wind events coupled atmosphere ocean response to westerly wind events wwes which sometimes trigger el ninos was investigated using a coupled general circulation model to clarify its dependence on the timing and location of wwes twelve sets of 20 member ensembles were made with an idealized single wwe imposed in different months from january to july and at different longitudes from 160 circ e to 160 circ w the initial ocean states are set to be near neutral to el nino la nina so that the lagged response to wwes can be isolated the results show that sea surface temperature sst in the nino3 4 region increases largely and persistently favorable for el nino growth when a wwe is imposed in may whereas a wwe in march increases sst only in the easternmost pacific in both cases an oceanic kelvin wave propagates eastward to warm the eastern pacific when forced by the wwe in may a positive nino3 4 sst anomaly appears in boreal summer according to the seasonal outcrop of the equatorial thermocline and it can strongly interact with seasonally active tropical rain belt to amplify the sst response further a favorable combination of timing and location that maximize the impact of wwes on el ninos in the subsequent winter is suggested albeit its relevance to nature should severely be tested another experiment with initial ocean states in el nino la nina years showed that the wwes in may are efficient to amplify el nino similar to the neutral case but are not efficient to suppress la nina

meridional extent and interannual variability of the pacific ocean tropical subtropical warm water exchange altimetric observations of sea surface height anomaly ssha from the topex poseidon and ers satellites hydrography and the ecmwf and florida state university wind products are used to track warm water 20 c as it is exchanged between the equatorial pacific ocean and the higher latitudes during 1993 2003 the large el nino event of 1997 98 resulted in a significant discharge of warm water toward the higher latitudes within the interior of the pacific ocean the exchange of anomalous warm water volume with the northern hemisphere appears to be blocked under the intertropical convergence zone consistent with most current ideas on the time mean tropical subtropical exchange little of the warm water discharged northward across 5 and 8 n during the 1997 98 el nino event could be traced as far as 10 n to the south however these anomalous volumes of warm water were visible at least as far as 20 s primarily in the longitudes around 130 160 w in both hemispheres most of the warm water appeared to flow westward before returning to the tropics during the recharge phase of the el nino la nina cycle the buildup of warm water in the tropics before the 1997 98 el nino is shown to be fed primarily by warm water drawn from the region in the western pacific within 5 s 15 n the exchange cycle between the equatorial band and the higher latitudes north of the equator leads the cycle in the south by 6 8 months these results are found in all three datasets used herein hydrography altimetric observations of ssha and sverdrup transports calculated from multiple wind products which demonstrates the robustness of the results

ocean response to wind variations warm water volume and simple models of enso in the low frequency approximation abstract physical processes that control enso are relatively fast for instance it takes only several months for a kelvin wave to cross the pacific basin tk 2 months while rossby waves travel the same distance in about half a year compared to such short time scales the typical periodicity of el nino is much longer t 2 7 yr thus enso is fundamentally a low frequency phenomenon in the context of these faster processes here the author takes advantage of this fact and uses the smallness of the ratio ek tk t to expand solutions of the ocean shallow water equations into power series the actual parameter of expansion also includes the oceanic damping rate using such an expansion referred to here as the low frequency approximation the author relates thermocline depth anomalies to temperature variations in the eastern equatorial pacific via an explicit integral operator this allows a simplified formulation of enso dynamics based on an integro differential equation within this formulation

surface layer temperature balance in the equatorial pacific during the 1997 98 el nino and 1998 99 la nina abstract the surface layer temperature balance in the equatorial pacific has been examined for the period of 1996 99 by using data obtained from tropical atmosphere ocean buoy array at four locations along the equator namely 165 e 170 w 140 w and 110 w time rate change of sst horizontal temperature advection and heat fluxes at the sea surface are estimated directly from the data vertical fluxes of heat out of the base of the mixed layer related to changes in vertical mixing and upwelling are calculated as a residual results indicate that all terms in the temperature balance contributed to sst variations during different stages of the 1997 98 el nino and the 1998 99 la nina zonal advection was particularly important during the onset of the el nino in the central pacific the inferred vertical heat flux out of the base of the mixed layer was important most of the time and was especially pronounced in the eastern pacific during the termination phase of the el nino meridional advection due to e

heaving modes in the world oceans part of climate changes on decadal time scales can be interpreted as the result of adiabatic motions associated with the adjustment of wind driven circulation i e the heaving of the isopycnal surfaces heat content changes in the ocean including hiatus of global surface temperature and other phenomena can be interpreted in terms of heaving associated with adjustment of wind driven circulation induced by decadal variability of wind a simple reduced gravity model is used to examine the consequence of adiabatic adjustment of the wind driven circulation decadal changes in wind stress forcing can induce three dimensional redistribution of warm water in the upper ocean in particular wind stress change can generate baroclinic modes of heat content anomaly in the vertical direction in fact changes in stratification observed in the ocean may be induced by wind stress change at local or in the remote parts of the world oceans intensification of the equatorial easterly can induce cooling in the upper layer and warming in the subsurface layer the combination of this kind of heat content anomaly with the general trend of warming of the whole water column under the increasing greenhouse effect may offer an explanation for the hiatus of global surface temperature and the accelerating subsurface warming over the past 10 15 years furthermore the meridional transport of warm water in the upper ocean can lead to sizeable transient meridional overturning circulation poleward heat flux and vertical heat flux thus heaving plays a key role in the oceanic circulation and climate

pausing of the enso cycle a case study from 1998 to 2002 abstract the heat balance of the surface mixed layer is analyzed at the eastern equatorial pacific ocean 0 140 w in order to examine the transition from the 1998 la nina to the 2002 el nino the data used are observations from the tropical atmosphere ocean triangle trans ocean buoy network tao triton results show that interannual variation of eddy heat flux due to tropical instability waves slows the transition from la nina to el nino previous studies have described this slow transition as a pausing period of the enso cycle that is la nina lingers and el nino does not immediately appear despite a deepened thermocline heat balance analysis shows that the vertical heat advection anomaly and surface heat flux anomaly warm the mixed layer from 1999 to 2002 these warming anomalies cause the rise of the mixed layer temperature anomaly in the transition from la nina to el nino in contrast a cooling anomaly of the horizontal heat advection reduces the warming anomaly and slows down the transition fr