origin of decadal el nino southern oscillation like variability in a coupled general circulation model 1 the origin of decadal el nino southern oscillation like variability hereinafter referred to as dev is analyzed in coupled general circulation model cgcm simulations the cgcm experiments test the null hypothesis for the existence of dev that is that dev is linear damped and stochastically forced by atmospheric internal dynamics in order to test this hypothesis we employ the interactive ensemble coupling strategy it is found that the spatially averaged variance of sea surface temperature anomaly ssta and heat content anomaly hca associated with the dev is linearly related to the amplitude of atmospheric internal dynamics this result suggests that the dev is primarily noise forced but that damped coupled feedbacks and or internal ocean dynamics enhance this variability the ssta variability associated with the dev appears to be of a basin type standing mode with a triangular shape however the decadal evolution of the hca associated with the dev shows a systematic westward propagation from the central north pacific and the eastern south pacific both a singular vector analysis and noise variance analysis based on the coupled simulation results support the argument that atmospheric noise in the subtropics leads to the excitation of the dev

modality of semiannual to multidecadal oscillations in global sea surface temperature variability 1 repeating the history of study on el nino southern oscillation enso in the 1980s interdecadal oscillation ido in climate variability is currently an area of active research and debate following the recognition of its emerging significance in nature and science in this work a two dimensional propagating modal extraction technique is applied to a reconstructed global monthly sea surface temperature sst data set spanning 1854 through 2007 to examine the spatiotemporal structure of sst variability with an emphasis on the fine modal pattern of idos in the time domain it is revealed that a canonical modal spectrum of decadal to centennial sst variability constitutes four most distinct oscillations with periodicities at 9 0 13 0 21 2 and 62 2 years which are naturally defined as primary modes and are respectively termed as the subdecadal mode the quasidecadal mode the interdecadal mode and the multidecadal mode modes s q i and m they join the energeticannual mode mode a and two major enso modes at 3 7 and 5 8 years modes b and c as well as a dozen of secondary modes ranging from semiannual to multidecadal in determining the key pattern of sst related climate variability in the space domain seven modally dynamic areas analogous to the nino regions for enso are clearly identified and are named as ido zones contrary to enso dominant ido zones are most visible in the extratropical oceans especially in the north atlantic north pacific sectors while secondary signatures are observed in the tropical oceans the array of four primary modes with respect to seven major zones yields a sophisticated yet canonical pattern of idos leading to a basic conclusion that multimodality for a given region and multiregionality for a given mode are fundamental features of the ido system

source of low frequency modulation of enso amplitude in a cgcm we study the relationship between changes in equatorial stratification and low frequency el nino southern oscillation enso amplitude modulation in a coupled general circulation model cgcm that uses an anomaly coupling strategy to prevent climate drifts in the mean state the stratification is intensified at upper levels in the western and central equatorial pacific during periods of high enso amplitude furthermore changes in equatorial stratification are connected with subsurface temperature anomalies originating from the central south tropical pacific the correlation analysis of ocean temperature anomalies against an index for the enso modulation supports the hypothesis of the existence of an oceanic tunnel that connects the south tropical pacific to the equatorial wave guide further analysis of the wind stress projection coefficient onto the oceanic baroclinic modes suggests that the low frequency modulation of enso amplitude is associated with a significant contribution of higher order modes in the western and central equatorial pacific in the light of these results we suggest that in the cgcm change in the baroclinic mode energy distribution associated with low frequency enso amplitude modulation have its source in the central south tropical pacific

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

rectification of enso variability by interdecadal changes in the equatorial background mean state in a cgcm simulation the link between the changes in equatorial background stratification and el nino southern oscillation enso modulation is investigated using a simulation from a 260 yr long coupled general circulation model cgcm the work focuses on the role of nonlinearities associated with equatorial wave dynamics as a first step the low frequency change in mean stratification is diagnosed and documented from the shallow water parameters derived from a vertical mode decomposition of the cgcm the parameters vary differently according to the baroclinic mode order which may explain why a flattening thermocline does not necessarily lead to reduced enso activity estimations of baroclinic mode contributions to zonal current anomalies indicate that the decadal variability projects differently for the baroclinic modes as compared to the interannual variability in particular the high order modes associated with decadal variability have a more pronounced signature in the western pacific whereas that associated with interannual variability i e enso shows more energy in the eastern pacific in the light of the results of the cgcm vertical mode decomposition an intermediate coupled model icm is used to test whether the nonlinearities associated with the changes in the baroclinic mode energy distribution can lead to coherent enso modulation the results indicate that rectification of the interannual variability enso time scales by the interdecadal variability associated with changes in the oceanic mean states takes place in the icm the rectified effect results mostly in an increased variability and skewness of the zonal advection which tends to produce a zonal seesaw of the sea surface temperature anomaly a tropical mechanism for producing enso modulation is then proposed that reconciles both the rectified effect resulting from nonlinearities associated with equatorial wave dynamics and the tropical decadal mode of thermocline depth arising from ekman pumping anomalies located in the central south pacific

long term el nino southern oscillation enso like variation with special emphasis on the south pacific mechanisms for el nino southern oscillation enso like decadal 7 35 years variability are analyzed using observational data when a decadal positive temperature anomaly occurs in the eastern tropical pacific the atmospheric response excites negative wind stress curl in the western tropical south pacific which causes the thermocline to shoal and induce a negative temperature anomaly there the cold anomaly moves northwestward to the western and central equatorial region and then turns eastward along the equator to reverse the original temperature anomaly in the east the eastward propagation of the oceanic signal along the equatorial thermocline correlates with a zonal wind anomaly the cold anomaly in the east grows through tropical air sea interaction and induces a positive wind stress curl in the western tropical south pacific associated with the atmospheric teleconnection in the southern hemisphere subsequent evolution of the negative phase is similar to that of the positive phase the complete scenario for this enso like decadal variability due to the air sea interaction processes within the tropics has a period of 14 years we also discuss enso like variation on the interdecadal 35 years timescale with possible relationship to the 1976 1977 climate regime shift

decadal variations of pacific north equatorial current bifurcation from multiple ocean products in this study we examine the decadal variations of the pacific north equatorial current nec bifurcation latitude nbl averaged over upper 100 m and underlying dynamics over the past six decades using 11 ocean products including seven kinds of ocean reanalyzes based on ocean data assimilation systems two kinds of numerical simulations without assimilating observations and two kinds of objective analyzes based on in situ observations only during the period of 1954 2007 the multiproduct mean of decadal nbl anomalies shows maxima around 1965 1966 1980 1981 1995 1996 and 2003 2004 and minima around 1958 1971 1972 1986 1987 and 2000 2001 respectively the nbl decadal variations are related to the first empirical orthogonal function mode of decadal anomalies of sea surface height ssh in the northwestern tropical pacific ocean which shows spatially coherent variation over the whole region and explains most of the total variance further regression and composite analyzes indicate that northerly southerly nbl corresponds to negative positive ssh anomalies and cyclonic anticyclonic gyre anomalies in the northwestern tropical pacific ocean these decadal circulation variations and thus the decadal nbl variations are governed mostly by the first two vertical modes and attribute the most to the first baroclinic mode the nbl decadal variation is highly positively correlated with the tropical pacific decadal variability tpdv around the zero time lag with a lead of about half the decadal cycle the nbl displays closer but negative relationship to tpdv in four ocean products possibly manifesting the dynamical role of the circulation in the northwestern tropical pacific in the phase shifting of tpdv

decadal variability of the pacific subtropical cells and its relevance to the sea surface height in the western tropical pacific during recent decades decadal variability of the pacific subtropical cells stcs and associated sea surface height ssh in the western tropical pacific during recent decades are examined by using an historical ogcm simulation the model represents decadal variations of the stcs concurrent with tropical pacific thermal anomalies the eastern tropical pacific is warmer when the stcs are weaker and cooler when they are stronger the spatial patterns of the ssh in the western tropical pacific show different features depending on events associated with decadal variability during the warm phase 1977 1987 the ssh anomalies exhibit deviations from a meridionally symmetric distribution with weakly positive strongly negative anomalies in the western tropical north south pacific analysis of the heat budget in the upper tropical pacific indicates that the termination of the warm phase around 1985 results from a poleward heat transport anomaly that is induced by a horizontal gyre associated with the ssh anomalies during the cold phase 1996 2006 in contrast the ssh anomalies are nearly meridionally symmetric with positive anomalies in both hemispheres enhanced easterly wind anomalies contribute to the development of the cold phase after the late 1990s

seismic signature of a permeable dual porosity layer of the key reservoir properties permeability seems to be the most elusive since the middle of the 90s various seismic attributes have been proposed to map permeability by using detailed analysis of the frequency content of reflected wavetrains some attributes are expected to show a relative increase of high frequency content with increased permeability other attributes assume the opposite actually both these trends were observed a possible explanation of these observations is here derived from an effective model of a permeable dual porosity layer enclosed by impermeable rocks for such a model the reflected wavetrain can be regarded as a sum of three components one of which is related to acoustic impedance contrasts another to extra compliance caused by p wave induced fluid flows between fractures and intergranular pores with a high aspect ratio and a third to the fluid flow induced inelastic attenuation in layered reservoirs all the components tend to be frequency dependent and the well k

interannual variability in a tropical atmosphere ocean model influence of the basic state ocean geometry and nonlinearity abstract the behavior of a tropical coupled atmosphere ocean model is analyzed for a range of different background states and ocean geometries the model is essentially that of cane and zebiak for the tropical pacific except only temporally constant background states are considered here for realistic background states and ocean geometry the model solutions feature oscillations of period of 3 5 yr by comparing the full model solution with a linearized version of the model it is shown that the basic mechanism of the oscillation is contained within linear theory a simple linear analog model is derived that describes the nature of the interannual variability in the coupled tropical atmosphere ocean system the analog model highlights the properties that produce coupled atmosphere ocean instability in the eastern ocean basin and the equatorial wave dynamics in the western ocean basin that are responsible for a delayed negative feedback into this instability growth the growth rate of the local instabil

interdecadal decadal climate variability from multicoral oxygen isotope records in the south pacific convergence zone region since 1650 a d 1 in the south pacific interdecadal decadal oceanic and atmospheric variability referred to as the interdecadal pacific oscillation ipo is most pronounced in the south pacific convergence zone spcz salinity front region here we have used annual average oxygen isotope 18o time series from five coral cores collected from fiji and tonga in this region to construct a fiji tonga interdecadal decadal pacific oscillation f t idpo index of low frequency 9 and 55 years climate variability back to 1650 a d we first demonstrate the consistency between this f t idpo index and a mean sea level msl pressure based spcz position index spi 1891 2000 thus verifying the ability of coral 18o to record past interdecadal decadal climatic variations in this region back to 1891 the f t idpo index is then shown to be synchronous with the ipo index 1856 2000 suggesting that this coral based index effectively represents the interdecadal decadal scale climate variance back to 1650 the regularity of the f t idpo index indicates that interdecadal decadal variability in the spcz region has been relatively constant over the past 350 years with a mean frequency of 20 years variance peaks near 11 and 35 years there is a consistent antiphase correlation of the f t idpo index and the interdecadal decadal components in equatorial pacific coral 18o series from maiana and palmyra this observation indicates that the eastward expansion westward contraction of the eastern salinity front of the western pacific warm pool wpwp occurs simultaneously 1 year with the westward eastward shift of the spcz salinity front during positive ipo negative ipo phases this is the same relationship observed during the phases of the el nino southern oscillation

variations in the pacific decadal oscillation since 1853 in a coral record from the northern south china sea 1 the pacific decadal oscillation pdo has been shown to have significant climatic and environmental impacts across the pan pacific basin however there are no records of pdo activity from the south china sea scs the largest marginal sea in the northwest pacific ocean this study suggests that a series of geochemical profiles obtained from a modern coral in the northern scs records annual pdo activity dating back to 1853 these geochemical data are significantly correlated with the pdo index and their patterns of variation closely match those of the pdo index over the last century the relationship between the pdo and coral geochemistry may be related to the influence of the pdo on rainfall on hainan island rainfall patterns influence the volume of terrestrial runoff which in turn is a primary determinant of 18o and 18o values in coral however coral 13c values are also influenced by the 13c suess effect the results indicate that sr ca ratios in coral are affected by a combination of sea surface temperature and terrestrial runoff

enso like and enso induced tropical pacific decadal variability in cgcms abstractoutputs from coupled general circulation models cgcms are used in examining tropical pacific decadal variability tpdv and their relationships with el nino southern oscillation enso herein tpdv is classified as either enso induced tpdv eit or enso like tpdv elt based on their correlations with a decadal modulation index of enso amplitude and spatial pattern eit is identified by the leading eof mode of the low pass filtered equatorial subsurface temperature anomalies and is highly correlated with the decadal enso modulation index this mode is characterized by an east west dipole structure along the equator elt is usually defined by the first eof mode of subsurface temperature of which the spatial structure is similar to enso generally this mode is insignificantly correlated with the decadal modulation of enso eit closely interacts with the residuals induced by enso asymmetries both of which show similar spatial structures on the other hand elt is controlled by slowly varying oc

observational evidence for propagation of decadal spiciness anomalies in the north pacific 1 the propagation of density compensated warm salty or cool fresh spiciness anomalies in the north pacific thermocline is investigated using argo profiles for the period 2001 2008 a cool fresh spiciness anomaly on 25 25 5 kg m 3 isopycnals appears in the eastern subtropical north pacific at 120 w 150 w in 2003 2004 with a salinity anomaly of about 0 15 pss 78 this spiciness anomaly migrates southwestward and arrives in the western tropical north pacific at 145 e 175 w in 2008 with the salinity anomaly decreasing to about 0 043 pss 78 two warm salty anomalies are observed to propagate along the same path from 2003 to 2005 and after 2005 the propagation path and speed of the anomalies are in good agreement with advection by the mean geostrophic current in the course of propagation the anomalies are diffused and are subject to high frequency injection of spiciness anomalies especially in the eastern subtropical north pacific

teleconnections in the geopotential height field during the northern hemisphere winter abstract contemporaneous correlations between geopotential heights on a given pressure surface at widely separated points on earth referred to as teleconnections in this paper are studied in an attempt to identify and document recurrent spatial patterns which might be indicative of standing oscillations in the planetary waves during the northern hemisphere winter with time scales on the order of a month or longer a review of existing literature on the subject reveals the existence of at least four such patterns the north atlantic and north pacific oscillations identified by walker and bliss 1932 a zonally symmetric seesaw between sea level pressures in polar and temperature latitudes first noted by lorenz 1951 and what we will refer to as the pacific north american pattern which has been known to operational long range forecasters in this country since the 1950 s a data set consisting of nmc monthly mean sea level pressure and 500 mb height analyses for a 15 year period is used as a basis fo

origin of upper ocean warming and el nino change on decadal scales in the tropical pacific ocean the cause of decadal scale variability in the tropical pacific ocean such as that marked by the 1976 77 shift in the el nino southern oscillation1 2 3 4 5 6 7 is poorly understood unravelling the mechanism of the recent decade long warming in the tropical upper ocean is a particularly important challenge given the link to el nino variability but establishing the hypothesized interannual decadal oceanic connections between middle latitudes and tropics has proved elusive8 here we present observational evidence that pacific upper ocean warming and decadal changes in the el nino southern oscillation after 1976 may originate from decadal mid latitude variability in the middle 1970s the north pacific ocean is observed to have undergone a clear phase transition a see saw subsurface temperature anomaly pattern that rotates clockwise around the subtropical gyre at middle latitudes a subsurface warm anomaly formed in the early 1970s from subducted surface waters and penetrated through the subtropics and into the tropics thus perturbing the tropical thermocline and driving the formation of a warm surface water anomaly that may have influenced el nino in the 1980s the identification of this teleconnection of extratropical thermal anomalies to the tropics through a subsurface ocean bridge may enable improved prediction of decadal scale climate variability

model assessment of decadal variability and trends in the tropical pacific ocean abstract in this report global coupled ocean atmosphere models are used to explore possible mechanisms for observed decadal variability and trends in pacific ocean ssts over the past century the leading mode of internally generated decadal 7 yr variability in the model resembles the observed decadal variability in terms of pattern and amplitude in the model the pattern and time evolution of tropical winds and oceanic heat content are similar for the decadal and enso timescales suggesting that the decadal variability has a similar delayed oscillator mechanism to that on the enso timescale the westward phase propagation of the heat content anomalies however is slower and centered slightly farther from the equator 12 vs 9 n for the decadal variability cool sst anomalies in the midlatitude north pacific during the warm tropical phase of the decadal variability are induced in the model largely by oceanic advection anomalies an index of observed sst over a broad triangular region of the tropi

south pacific origin of the decadal enso like variation as simulated by a coupled gcm 1 the hypothesis of the south pacific origin of the decadal 7 35 years enso like variation is investigated based on 200 year outputs of the echam4 opa oasis coupled gcm associated with the decadal warm cold sst anomalies in the tropical pacific an anomalous cyclonic anticyclonic circulation which is tilted in a southeast northwest direction appears in the south pacific this results in anomalous upward downward ekman pumping along the northeastern edge of the anomalous circulation and hence shallowing deepening the oceanic thermocline there such an external source of heat content tends to slowly discharge recharge the tropical ocean on the decadal timescale the above result is consistent with the observational study of luo and yamagata 2001 besides the model reproduces amazingly a high lagged correlation between the global land surface temperature and the decadal nino3 sst despite the model biases this suggests a potential prediction skill of the global warming based on the enso like decadal variation

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

dynamics and mechanisms of decadal variability of the pacific south america mode over the 20th century in this paper decadal variability of the pacific south america psa mode is examined from year 1871 to 2008 based on the newly developed ocean and atmosphere reanalysis products the psa mode mirroring the pacific north america mode in the northern hemisphere emerges as the second eof mode of 500 mb geopotential height anomalies the mode displays substantial interannual decadal variability with distinct timescales between 3 8 and 10 18 years respectively the decadal variability of the psa mode is found to be associated with the coupled ocean atmosphere interaction over the subtropical south and tropical pacific the subduction of the subtropical temperature anomalies in the south pacific in conjunction with the tropical subtropical atmospheric teleconnection plays important role in the decadal variability of the psa mode

transient electromagnetic finite difference time domain earth modeling over steel infrastructure including highly conductive steel infrastructure into electromagnetic em earth modeling is motivated by the fact that long metal cased boreholes have the potential to be used as boosting antennas that enable larger source dipole moments and greater signal penetration depths unfortunately geophysical algorithms designed to simulate em responses over rather regional scales are complicated by material property contrasts and structure geometries that are more typical for em engineering applications hence the great majority of earth modeling algorithms that consider em responses from steel cased boreholes use integral equation methods to be able to model complex casing scenarios we revisited the finite difference time domain fdtd method to advance the modeling of transient em field responses from steel cased boreholes a time dependent function that allows for larger fdtd time steps in the dufort frankel method was developed alleviating the generally large computational overhead we compared our method against three different kinds of benchmark solutions to demonstrate the reliability of the fdtd field solutions these test cases were carried out to check the feasibility of a final hydraulic fracturing study images of the electric current distribution in a sheetlike rock fracture were calculated for the cases with and without the presence of a connecting borehole casing demonstrating the casing s potential of illuminating deep target zones

exploring the mesoscale activity in the solomon sea a complementary approach with a numerical model and altimetric data the solomon sea is an area of high level of eddy kinetic energy eke and represents a transit area for the low latitude western boundary currents llwbcs connecting the subtropics to the equatorial pacific and playing a major role in enso dynamics this study aims at documenting the surface mesoscale activity in the solomon sea for the first time our analysis is based on the joint analysis of altimetric data and outputs from a 1 12 model simulation the highest surface eke is observed in the northern part of the basin and extends southward to the central basin an eddy tracking algorithm is used to document the characteristics and trajectories of coherent mesoscale vortices cyclonic eddies generated in the south basin are advected to the north by the llwbcs before merging with stationary mesoscale structures present in the mean circulation anticyclonic eddies are less numerous they are generated in the southeastern basin propagate westward reach the llwbcs and dissipate the seasonal and interannual modulations of the mesoscale activity are well marked at seasonal time scale maximum minimum activity is in may june september at interannual time scale the mesoscale activity is particularly enhanced during la nina conditions if instabilities of the regional circulations seem to explain the generation of mesoscale features the modulation of the mesoscale activity seems to be rather related with the intrusion at solomon strait of the surface south equatorial current rather than to the llwbcs by modulating the horizontal and vertical shears suitable for instabilities

mechanisms of tropical pacific interannual to decadal variability in the arpege orca global coupled model spatial and temporal structures of interannual to decadal variability in the tropical pacific ocean are investigated using results from a global atmosphere ocean coupled general circulation model the model produces quite realistic mean state characteristics despite a sea surface temperature cold bias and a thermocline that is shallower than observations in the western pacific the periodicity and spatial patterns of the modelled el nino southern oscillations enso compare well with those observed over the last 100 years although the quasi biennial timescale is dominant lag regression analysis between the mean zonal wind stress and the 20 c isotherm depth suggests that the recently proposed recharge oscillator paradigm is operating in the model decadal thermocline variability is characterized by enhanced variance over the western tropical south pacific 7 s the associated subsurface temperature variability is primarily due to adiabatic displacements of the thermocline as a whole arising from ekman pumping anomalies located in the central pacific south of the equator related wind anomalies appear to be caused by sst anomalies in the eastern equatorial pacific this quasi decadal variability has a timescale between 8 years and 20 years the relationship between this decadal tropical mode and the low frequency modulation of enso variance is also discussed results question the commonly accepted hypothesis that the low frequency modulation of enso is due to decadal changes of the mean state characteristics

a north pacific decadal variability in subduction rate 1 analysis of results from a global eddy resolving general circulation model has revealed the existence of a north pacific decadal variability in subduction rate this decadal variability corresponds well with the pacific decadal oscillation pdo the zero lag correlation between the two time series reaches 0 61 for the period of integration 1950 2003 and increases to as high as 0 80 after the climate shift in the mid 1970s much of the north pacific decadal variability in subduction rate is due to changes in winter mixed layer depth which in turn are closely related to changes in surface wind and heat flux

low frequency variability of temperature in the vicinity of the equatorial pacific thermocline in soda role of equatorial wave dynamics and enso asymmetry the simple ocean data assimilation soda reanalysis 1958 2001 is used to investigate the decadal variability in the equatorial thermocline in the pacific whereas the thermocline depth exhibits weak variation at decadal time scales the temperature change in the vicinity of the thermocline in the western pacific is significant and has a vertical scale of 150 m based on a modal decomposition of the model variability it is shown that such temperature change can be interpreted to a large extent as vertical displacements of the isotherms associated with the kelvin and first meridional rossby waves of the first three baroclinic modes this indicates that decadal change at the subsurface in the warm pool region may be forced by the winds consistent with the results of a multimode linear model simulation the decadal mode of vertical temperature can be described by the first two dominant statistical modes eofs the first mode is associated with changes in the slope of the thermocline swallowing in the western central pacific and deepening in the eastern pacific representative of the 1976 77 climate shift and ahead of the enso modulation and the second mode corresponds to a basinwide uplift of the thermocline and behind the enso modulation it is further shown that the subsurface temperature in the warm pool region is negatively skewed which results from the enso asymmetry the results are consistent with the hypothesis of change in mean state resulting from the residual effect of the asymmetric enso variability

low frequency variability of the south pacific subtropical gyre as seen from satellite altimetry and argo abstractlow frequency variability of the south pacific subtropical gyre is investigated using satellite altimeter and argo data in most of the region studied both sea surface height and steric height exhibit a linearly increasing trend with its largest amplitude in the western part of the basin analysis of the argo data reveals that the steric height increase north of 30 s is primarily caused by variations in the upper 500 m while the steric height increase south of 30 s is determined by variations in the whole depths from the sea surface to 1800 m with contributions from below 1000 m accounting for about 50 of the total variance most of the steric height increase is due to thermal expansion except below 1000 m where haline contraction is of comparable magnitude with thermal expansion correspondingly the south pacific subtropical gyre has strengthened in the past decade within the latitude range between 10 and 35 s transport of the gyre circulation increased by 20 30 in the upper 1000 m an

interdecadal sea surface temperature sea level pressure coupled variability in the south pacific ocean 1 the main coupled sea surface temperature sst sea level pressure slp variability at interdecadal timescale in the south pacific is studied by means of correlation and combined complex empirical orthogonal function cceof analyses the sst slp coupled variability presents a bidecadal cycle from mid 1950s to 1970s and a decadal cycle from 1980s to early 1990s reproducing the enso like interdecadal oscillation particularly the first sst slp cceof mode describes the bidecadal cycle characterized by westward progression of sst and slp anomalies along the tropical pacific while the second sst slp cceof mode shows the decadal cycle with eastward development during both bidecadal and decadal cycles the sst fluctuations in the eastern equatorial pacific and along the western coast of south america are primarily forced by equatorial zonal wind variability specially during the bidecadal cycle the alongshore sst variability south of 30 s is maintained and reinforced by meridional coastal wind fluctuations associated with a stationary slp pattern off southern chile this stationary slp pattern appears connected to sst fluctuations in the central tropical pacific

upper ocean thermal variations in the north pacific during 1970 1991 abstract a newly available extensive compilation of upper ocean temperature profiles was used to study the vertical structure of thermal anomalies between the surface and 400 m depth in the north pacific during 1970 1991 a prominent decade long perturbation in climate occurred during this time period surface waters cooled by 1 c in the central and western north pacific and warmed by about the same amount along the west coast of north america from late 1976 to 1988 comparison with data from coads suggests that the relatively sparse sampling of the subsurface data is adequate for describing the climate anomaly the vertical structure of seasonal thermal anomalies in the central north pacific shows a series of cold pulses beginning in the fall of 1976 and continuing until late 1988 that appear to originate at the surface and descend with time into the main thermocline to at least 400 m depth individual cold events descend rapidly 100 m yr 1 superimposed upon a slower cooling 15 m yr 1 the inter

subduction of decadal north pacific temperature anomalies observations and dynamics abstract observations of oceanic temperature in the upper 400 m reveal decadal signals that propagate in the thermocline along lines of constant potential vorticity from the ventilation region in the central north pacific to approximately 18 n in the western pacific the propagation path and speed are well described by the geostrophic mean circulation and by a model of the ventilated thermocline the approximate southward speed of the thermal signal of 7 mm s 1 yields a transit time of approximately eight years the thermal anomalies appear to be forced by perturbations of the mixed layer heat budget in the subduction region of the central north pacific east of the date line a warm pulse was generated in the central north pacific by a series of mild winters from 1973 to 1976 and reached 18 n around 1982 after 1978 a succession of colder winters initiated a cold anomaly in the central north pacific that propagated along a similar path and with a similar speed as the warm anomaly then arrived in the west

enso like interdecadal variability 1900 93 a number of recent studies have reported an enso like eof mode in the global sea surface temperature sst field whose time variability is marked by an abrupt change toward a warmer tropical eastern pacific and a colder extratropical central north pacific in 1976 77 the present study compares this pattern with the structure of the interannual variability associated with the enso cycle and documents its time history back to 1900 the analysis is primarily based on the leading eofs of the sst anomaly and anomaly deviation fields in various domains and the associated expansion coefficient or principal component time series which are used to construct global regression maps of sst sea level pressure slp and a number of related variables the use of anomaly deviations i e departures of local sst anomalies from the concurrent global mean sst anomaly reduces the influence of global mean sst trends upon the structure of the eofs and their expansion coefficient time series an important auxiliary time series used in this study is a southern oscillation index based on marine surface observations by means of several different analysis techniques the time variability of the leading eof of the global sst field is separated into two components one identified with the enso cycle related variability on the interannual timescale and the other a linearly independent residual comprising all the interdecadal variability in the record the two components exhibit rather similar spatial signatures in the global sst slp and wind stress fields the sst signature in the residual variability is less equatorially confined in the eastern pacific and it is relatively more prominent over the extratropical north pacific the corresponding slp signature is also stronger over the extratropical north pacific and its counterpart in the cold season 500 mb height field more closely resembles the pna pattern the amplitude time series of the enso like pattern in the residual variability reflects the above mentioned shift in 1976 77 as well as a number of other prominent features including a shift of opposite polarity during the 1940s

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

controlled source electromagnetic monitoring of reservoir oil saturation using a novel borehole to surface configuration to advance and optimize secondary and tertiary oil recovery techniques it is essential to know the areal propagation and distribution of the injected fluids in the subsurface we investigate the applicability of controlled source electromagnetic methods to monitor fluid movements in a german oilfield bockstedt onshore northwest germany as injected brines highly saline formation water have much lower electrical resistivity than the oil within the reservoir the main focus of this study is on controlled source electromagnetic simulations to test the sensitivity of various source receiver configurations the background model for the simulations is based on two dimensional inversion of magnetotelluric data gathered across the oil field and calibrated with resistivity logs three dimensional modelling results suggest that controlled source electromagnetic methods are sensitive to resistivity changes at reservoir depths but the effect is difficult to resolve with surface measurements only resolution increases significantly if sensors or transmitters can be placed in observation wells closer to the reservoir in particular observation of the vertical electric field component in shallow boreholes and or use of source configurations consisting of combinations of vertical and horizontal dipoles are promising preliminary results from a borehole to surface controlled source electromagnetic field survey carried out in spring 2014 are in good agreement with the modelling studies

the marine controlled source electromagnetic response of a steel borehole casing applications for the neptune canada gas hydrate observatory gas hydrates are a potential energy resource a possible factor in climate change and an exploration geohazard the university of toronto has deployed a permanent seafloor time domain controlled source electromagnetic csem system offshore vancouver island within the framework of the neptune canada underwater cabled observatory hydrates are known to be present in the area and due to their electrically resistive nature can be monitored by 5 permanent electric field receivers however two cased boreholes may be drilled near the csem site in the near future to understand any potential distortions of the electric fields due to the metal we model the marine electromagnetic response of a conductive steel borehole casing first we consider the commonly used canonical model consisting of a 100 m 100 m thick resistive hydrocarbon layer embedded at a depth of 1000 m in a 1 m conductive host medium with the addition of a typical steel production casing extending from the seafloor to the resistive zone results show that in both the frequency and time domains the distortion produced by the casing occurs at smaller transmitter receiver offsets than the offsets required to detect the resistive layer second we consider the experimentally determined model of the offshore vancouver island hydrate zone consisting of a 5 5 m 36 m thick hydrate layer overlying a 0 7 m sedimentary half space with the addition of two borehole casings extending 300 m into the seafloor in this case results show that the distortion produced by casings located within a 100 m safety zone of the csem system will be measured at 4 of the 5 receivers we conclude that the boreholes must be positioned at least 200 m away from the csem array so as to minimize the effects of the casings

observation of spiciness interannual variability in the pacific pycnocline monthly gridded fields predominantly based on global argo in situ temperature and salinity data are used to analyze the density compensated anomaly of salinity spiciness anomaly in the pycnocline of the subtropical and tropical pacific ocean between 2004 and 2011 interannual variability in the formation propagation and fate of spiciness anomalies are investigated the spiciness anomalies propagate on the isopycnal surface sq 25 5 along the subtropical tropical pycnocline advected by the mean currents they reach the pacific western tropics in about 5 6 years in the southern hemisphere and about 7 8 years in the northern hemisphere their amplitude strongly diminishes along the way and only very weak spiciness anomalies seem to reach the equator in the western tropics a complex eof analysis of interannual salinity anomalies on sq 25 5 highlights two dominant modes of variability at interannual scale i the former shows a variability of 5 7 years predominant in the northern hemisphere and ii the latter displays an interannual variability of 2 to 3 years more marked in the southern hemisphere the significant correlation of this second mode with enso index suggests that spiciness formation in the southeastern pacific sep is affected by enso tropical interannual variability a diagnosis of the mechanisms governing the interannual generation of spiciness in the sep region leads the authors to suggest that the spiciness interannual variability in the sub surface is linked to the equatorward migration of the isopycnal outcrop line sq 25 5 into the area of maximum salinity quantitative analysis based on turner angle reveals the dominance of the spiciness injection mechanism occurring through convective mixing at the base of mixed layer

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

a modeling study of the relative roles of tropical and extratropical sst anomalies in the variability of the global atmosphere ocean system abstract in three parallel experiments an atmospheric general circulation model has been subjected to observed monthly varying sea surface temperature ssi conditions in each of the following domains near global ocean goga run tropical pacific toga run and midlatitude north pacific moga run four independent realizations were obtained for the model response to the sequence of sst anomalies during the 1946 88 period in each of the above regions the principal modes of coupling between the imposed sst forcing and the simulated northern hemisphere wintertime 5 1 5 mb height field in various experiments have been identified using a singular value decomposition svd procedure the leading svd mode for the goga experiment is qualitatively similar to that based on observational data although the amplitudes of the simulated height anomalies are notably lower than the observed value the sst pattern of this mode resembles that associated with el nino events the accompanying 5 1 5 mb height anomaly i

pacific decadal oscillation tropical pacific forcing versus internal variability abstractthe pacific decadal oscillation pdo is the leading mode of sea surface temperature sst variability over the north pacific north of 20 n its south pacific counterpart south of 20 s

hydro frac monitoring using ground time domain electromagnetics as motivation for considering new electromagnetic techniques for hydraulic fracture monitoring we develop a simple financial model for the net present value offered by geophysical characterization to reduce the error in stimulated reservoir volume calculations this model shows that even a 5 improvement in stimulated reservoir volume for a 1 billion barrel bbl field results in over 1 billion u s dollars us in net present value over 24 years for us 100 bbl oil and us 0 5 billion for us 50 bbl oil the application of conductivity upscaling often used in electromagnetic modeling to reduce mesh size and thus simulation runtimes is shown to be inaccurate for the high electrical contrasts needed to represent steel cased wells in the earth finescale finite difference modeling with 12 22 mm cells to capture the steel casing and fractures shows that the steel casing provides a direct current pathway to a created fracture that significantly enhances the response compared with neglecting the steel casing we consider conductively enhanced proppant such as coke breeze coated sand and a highly saline brine solution to produce electrically conductive fractures for a relatively small frac job at a depth of 3 km involving 5 000 bbl of slurry and a source midpoint to receiver separation of 50m the models show that the conductively enhanced proppant produces a 15 increase in the electric field strength in line with the transmitter in a 10 m background in a 100 m background the response due to the proppant increases to 213 replacing the conductive proppant by brine with a concentration of 100 000 ppm nacl the field strength is increased by 23 in the 100 m background and by 2 3 in the 10 m background all but the 100 000 ppm nacl brine in a 10 m background produce calculated fracture induced electric field increases that are significantly above 2 a value that has been demonstrated to be observable in field measurements

quantifying surface to reservoir electromagnetics for waterflood monitoring in a saudi arabian carbonate reservoir abstractwe modeled surface to borehole controlled source electromagnetics to assess the sensitivity of electromagnetic fields to the detection and evolution of the waterfront position in a saudi arabian carbonate reservoir we studied a test well drilled for research purposes at the edge of the current waterfront the 3d reservoir saturations were obtained by using a black oil simulator and later converted to resistivity using archie s empirical relation the anisotropic overburden model was derived from the upscaling of triaxial resistivity logs acquired from the surface to reservoir depth in the well the modeling study was performed by the combination of 3d finite element time domain and 3d finite difference frequency domain methods using surface galvanic sources in radial and transverse polarization modes with borehole receivers results indicated that the electric field components have the largest sensitivity to static reservoir resistivity distributions and to the time lapse resistivity changes the

control of decadal and bidecadal climate variability in the tropical pacific by the off equatorial south pacific ocean abstractdelayed negative feedback processes determining intrinsic decadal and bidecadal time scales for the tropical variability in the pacific are investigated based on climate model experiments by comparing a control run driven by preindustrial forcing and partial blocking runs driven by the same forcing but with ocean temperature and salinity restored to climatology in selected regions subsurface oceanic signals of south pacific origin are shown to precede sst variability in the nino 3 4 region using a linear reduced gravity ocean model driven only by wind stress changes and an offline tracer model oceanic wave adjustment triggered by changes of wind stress curl in the south pacific extratropics is suggested to be essential for the decadal component of the equatorial sst while slower isopycnal advection of subsurface temperature anomalies from the formation region of south pacific eastern subtropical mode water controls the bidecadal component the intrinsic time scales of the tropical variability

quasi decadal and inter decadal climate fluctuations in the pacific ocean from a cgcm diagnostic analyses in the pacific have revealed distinct quasi decadal qd and inter decadal id climate fluctuations with coherent varying patterns of sea surface temperature sst and sea level pressure slp anomalies from a 200 year cgcm simulation distinct low frequency fluctuations are also obtained qd i e 8 12 years period band and id i e 18 25 years period band traced modeled qd evolution reveals equatorial sst anomalies resembling enso while tropical recharge discharge mechanisms seem to be operating the traced modeled id evolution reveals high latitudes spatially coherent patterns with maximum sst anomalies in the vicinity of the subarctic frontal zone safz and subtropical gyres through advection contrary to qd sst anomalies the modeled id sst anomalies peak away from the equator as observed qd fluctuations may then be viewed as low frequency enso phenomena while id fluctuations may set up thermal background modulating frequency and intensity of enso

formation mechanism for isopycnal temperature salinity anomalies propagating from the eastern south pacific to the equatorial region abstract equatorward propagation of temperature salinity or spiciness anomalies on an isopycnal surface emanating from the eastern subtropical south pacific and their formation mechanism are investigated based on a hindcast simulation with an eddy resolving quasi global ocean general circulation model because of density compensating meridional distributions of temperature and salinity the meridional density gradient is weak at the sea surface in the eastern subtropical south pacific with these mean fields cool sea surface temperature anomalies sstas can make the outcrop line of an isopycnal surface migrate equatorward more than 5 and induce warm and salty anomalies on the isopycnal surface subducted warm salty anomalies propagate to the equatorial region over approximately 5 yr and may influence equatorial isopycnal temperature salinity anomalies although the associated effects are unclear if these anomalies could further induce warm eastern equatorial sstas that are positively correlated wit