statistical occurrence and mechanisms of the 2014 2016 delayed super el nino captured by a simple dynamical model the recent 2014 2016 period was marked by a failed el nino favoring a subsequent extreme el nino with dramatic worldwide impacts here this new type of major event so called the delayed super el nino is realistically captured by a simple dynamical model for the equatorial pacific with emphasis on the role of state dependent stochastic wind bursts we analyze qualitative analogues for this event compared and contrasted with the 1997 1998 super el nino in ensemble experiments based on the simple model in agreement with recent studies the timing and intensity of such an event is strongly controlled by atmospheric wind bursts both easterly and westerly in particular the early stalling by easterly wind bursts and subsequent development by westerly wind bursts as observed during 2014 2016 is consistently retrieved we show in addition that individual wind bursts may control the main characteristics of the event only during its early development while sequences of consecutive wind bursts have more important cumulative effects another important result from the present analysis is the significant statistical occurence of the delayed super el nino around 20 30 compared with the one of directly formed super events as that of 1997 1998 such a high occurence is directly linked to the random evolution of wind bursts and is retrieved here for all phases of the el nino southern oscillation used for the initiation of the ensemble experiments these results suggest that the delayed super el nino is not an unusual type of super event and could reoccur in the future

westerly wind events in the tropical pacific 1986 95 abstract based on examination of 10 yr of 10 m winds and wind anomalies from european centre for medium range weather forecasts ecwmf analysis definitions for westerly wind events wwes of eight different types are proposed the authors construct a composite for each type of event show that a simple propagating gaussian model satisfactorily describes the evolution of zonal wind anomaly for each type of event and determine the scales of each composite event by fitting the model to each composite the authors discuss the wwes that occurred during the tropical oceans global atmosphere coupled ocean atmosphere response experiment toga coare intensive observing period iop and show the extent to which these composite events are able to reproduce the major westerly wind features of the iop the frequency of occurrence of each type of wwe for each year of this record and by calendar month are described the authors find several types of events are negatively correlated with the annual mean troup souther

observational evidences of walker circulation change over the last 30 years contrasting with gcm results in order to examine the changes in walker circulation over the recent decades we analyzed the sea surface temperature sst deep convective activities upper tropospheric moistening sea level pressure slp and effective wind in the boundary layer over the 30 year period of 1979 2008 the analysis showed that the eastern tropical pacific has undergone cooling while the western pacific has undergone warming over the past three decades causing an increase in the east west sst gradient it is indicated that the tropical atmosphere should have responded to these sst changes increased deep convective activities and associated upper tropospheric moistening over the western pacific ascending region increased slp over the eastern pacific descending region in contrast to decreased slp over the western pacific ascending region and enhanced easterly wind in the boundary layer in response to the slp change these variations recognized from different data sets occur in tandem with each other strongly supporting the intensified walker circulation over the tropical pacific ocean since the sst trend was attributed to more frequent occurrences of central pacific type el nino in recent decades it is suggested that the decadal variation of el nino caused the intensified walker circulation over the past 30 years an analysis of current climate models shows that model results deviate greatly from the observed intensified walker circulation the uncertainties in the current climate models may be due to the natural variability dominating the forced signal over the tropical pacific during the last three decades in the twentieth century climate scenario runs by cmip3 cgcms

a nonlinear theory for el nino bursting abstract a new mechanism is proposed that explains two key features of the observed el nino southern oscillation enso phenomenon its irregularity and decadal amplitude changes using a low order enso model the authors show that the nonlinearities in the tropical heat budget can lead to bursting behavior characterized by decadal occurrences of strong el nino events la nina events are not affected a feature that is also seen in enso observations one key result of this analysis is that decadal variability in the tropics can be generated without invoking extratropical processes or stochastic forcing the el nino bursting behavior simulated by the low order enso model can be understood in terms of the concept of homoclinic and heteroclinic connections it is shown that this new model for enso amplitude modulations and irregularity although difficult to prove might explain some features of enso dynamics seen in more complex climate models and the observations

the normality of el nino the amplitude of the el nino southern oscillation enso would be normally distributed if the coupled pacific ocean atmosphere were a linear system forced by gaussian weather noise moment estimates of skewness and kurtosis demonstrate that this is not the case for monthly mean anomalies in pacific sea surface temperatures during 1950 97 the noted predominance of el nino events compared to la nina events is related to the high skewness in the eastern pacific skewness and kurtosis both exhibit an intriguing geographical variation from positive in the eastern to negative in the western pacific we have also examined nino 3 indices generated by three climate models having widely different complexity these exhibit a wide range of skewness and kurtosis values rather different from those found for the observations skewness and kurtosis can be used to diagnose non linear processes and provide powerful tools for validating models and for testing observed sea surface temperatures for the presence of possible climate change

formation of columbite and microlite after alteration of nb and ta bearing biotite from the lizaizhai pegmatite guangning ore district guangdong south china identification of a new potential nb ta mineralization type abstract the lizaizhai pegmatite is located in guangning guangdong province south china unlike common rare element li sn nb ta pegmatites in guangning which contain muscovite as the dominant mica the lizaizhai pegmatite represents a different type of rare element mineralization with biotite as the dominant mica our detailed study shows that the lizaizhai pegmatite can be divided into a border zone and a core zone biotite in the border zone contains lower contents of ta mean 121 ppm and higher contents of ti mean tio2 0 31 wt and nb mean 409 ppm compared with biotite in the core zone which contains slightly more ta mean 381 ppm than nb mean 375 ppm and ti mean tio2

how well do current climate models simulate two types of el nino in this study we evaluate the fidelity of current climate models in simulating the two types of el nino events using the pre industrial output in cmip3 archives it is shown that a few climate models simulate the two types of el nino events to some extent while most of the models have serious systematic problems in simulating distinctive patterns of sea surface temperature sst and precipitation anomaly associated with the two types of el nino that is they tend to simulate a single type of el nino it is shown that the ability of climate models in simulating the two types of el nino is related to the sensitivity of the atmospheric responses to the sst anomaly patterns models whose convective location is shifted to the east west as the sst anomaly center moves to the east west tends to simulate the two types of el nino events successfully on the other hand models whose location of convective anomaly is confined over the western or central pacific tends to simulate only the single type of el nino event it is also shown that the confinement of the convective anomaly over the western or central pacific is closely linked to the dry bias and the associated cold bias over the eastern pacific that is because positive el nino sst anomalies over the eastern pacific cannot increase local convection effectively when the total ssts are still too cold due to a cold bias this implies that the realistic simulation of climatology especially over the equatorial eastern pacific is essential to the successful simulation of the two types of el nino

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

a tropical stochastic skeleton model for the mjo el nino and dynamic walker circulation a simplified gcm abstracta simple dynamical stochastic model for the tropical ocean atmosphere is proposed that captures qualitatively major intraseasonal to interannual processes altogether including el nino south

equatorial pacific easterly wind surges and the onset of la nina events abstractthe processes responsible for the onset of la nina events have not received the same attention as those responsible for the onset of el nino events for which westerly wind events wwes in the tropical pacific have been identified as important contributors results here show that synoptic scale surface easterly wind surges ewss play an important role in the onset of la nina events akin to the role of wwes in the onset of el nino events it is found that ewss are a substantial component of zonal wind stress variance along the equatorial pacific using reanalysis wind stress fields validated against buoy measurements 340 ews events are identified between 1986 and 2012 their distributions in space time and el nino southern oscillation enso state are described about 150 ewss occur during enso neutral conditions during the months associated with la nina initiation and growth april december composites of changes in sea surface temperature anomaly ssta following these 150 events show s

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

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

geochronology geochemical and sr nd hf pb isotopic compositions of the granitoids in the yemaquan orefield east kunlun orogenic belt northern qinghai tibet plateau implications for magmatic fractional crystallization and sub solidus hydrothermal alteration abstract a general consensus has emerged that high field strength elements hfse can mobile to some extent in a hydrothermal fluid however there are hot debates on whether sub solidus hydrothermal alteration can lower the nb ta ratio in evolved melts in this study we present petrography geochronology and geochemistry of the barren and mineralized rocks in the yemaquan skarn iron deposit northern qinghai tibet plateau to probe magmatic hydrothermal transition the barren rocks consist of diorites granodiorites granites and syenogranites whereas the porphyritic granodiorites are associated with mineralization for an excellent consistency between the magmatic zircon u pb age 225 2 ma and the hydrothermal phlogopite 40 ar 39 ar age 225 1 5 ma the sr nd hf pb isotopic data demonstrate that the yemaquan granitoids are originated from a relatively homogenous enriched mantle with different degrees of crust contamination assimilation fractional crystallization afc trace elements signatures indicate that the porphyritic granodiorites related to mineralization display amphibole crystallization for high water contents whereas the barren granites have gone through biotite crystallization due to potassium enrichment by continuous upper crust contamination both of which are responsible for their nb ta ratios respectively modeling results suggest that a basaltic melt with nb ta ratio of 15 3 can reach a minimum nb ta ratio of 12 in the producing granodioritic melt by amphibole fractional crystallization based on partition coefficients of nb and ta between amphibole and melts from previous experiments this may explain the average nb ta ratio 13 7 of the barren granodiorites while it cannot account for the average nb ta ratio 8 4 of the mineralized porphyritic granodiorites and it is even lower than that of the granites 10 3 with biotite fractional crystallization exsolution of a magmatic hydrothermal fluid is inevitable when a water saturated magma emplaced in shallow crust leading to a transportation of certain chemical components from the magmatic melts to exsolved fluids because nb seems more mobile than ta in fluorine bearing fluids we contend that a preferentially transport nb over ta by sub solidus hydrothermal alteration can further lower the nb ta ratios of the mineralized porphyritic granodiorites which may also result in a broad range of hfse contents and their ratios in the altered porphyritic granodiorites formed in a post magmatic process

seasonality of tropical pacific decadal trends associated with the 21st century global warming hiatus equatorial pacific changes during the transition from a nonhiatus period pre 1999 to the present global warming hiatus period post 1999 are identified using a combination of reanalysis and observed data sets results show increased surface wind forcing has excited significant changes in wind driven circulation over the last two decades the core of the equatorial undercurrent intensified at a rate of 6 9 cm s 1 decade 1 similarly equatorial upwelling associated with the shallow meridional overturning circulation increased at a rate of 2 0 10 4 cm s 1 decade 1 in the central pacific further a seasonal dependence is identified in the sea surface temperature trends and in subsurface dynamics seasonal variations are evident in reversals of equatorial surface flow trends changes in subsurface circulation and seasonal deepening shoaling of the thermocline anomalous westward surface flow drives cold water zonal advection from november to february leading to surface cooling from december through may conversely eastward surface current anomalies in june july drive warm water zonal advection producing surface warming from july to november an improved dynamical understanding of how the tropical pacific ocean responds during transitions into hiatus events including its seasonal structure may help to improve future predictability of decadal climate variations

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

an advective reflective conceptual model for the oscillatory nature of the enso recent findings about zonal displacements of the pacific warm pool required a notable modification of the delayed action oscillator theory the current leading theory for the el nino southern oscillation enso simulations with a linearized coupled ocean atmosphere model resulted in 3 to 6 year enso like oscillations with many of the variable model parameters found to be very close to their observed values this simple model suggests that ocean processes that are ignored or underestimated in the delayed action oscillator theory such as zonal current convergence zonal advection of sea surface temperature and equatorial wave reflection from the eastern ocean boundary are fundamental to the development of the enso in particular to its manifestations in the central equatorial pacific

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

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

tropical pacific sea surface temperature anomalies el nino and equatorial westerly wind events abstract the authors examine global statistical relationships between westerly wind events wwes and sea surface temperature anomaly ssta variability using a compositing technique for the period 1986 98 the authors describe the extent to which equatorial wwes are associated with central and eastern equatorial pacific waveguide warming and with local ssta changes under the wwe their goal is to quantify the extent to which equatorial wwes are fundamental to the onset and maintenance of warm el nino southern oscillation conditions in order to understand the effect of wwes on ssta evolution they begin by examining how ssta changes in the absence of equatorial wwes they find that ssta tends toward mean climate values in the absence of equatorial wwes whether the eastern equatorial pacific has close to normal ssta or warmer than normal ssta the two equatorial wwe types whose main surface wind anomalies are west of the date line are associated with weak local surface cooling the equatorial wwe type t

modulation of equatorial pacific westerly easterly wind events by the madden julian oscillation and convectively coupled rossby waves synoptic wind events in the equatorial pacific strongly influence the el nino southern oscillation enso evolution this paper characterizes the spatio temporal distribution of easterly ewes and westerly wind events wwes and quantifies their relationship with intraseasonal and interannual large scale climate variability we unambiguously demonstrate that the madden julian oscillation mjo and convectively coupled rossby waves crw modulate both wwes and ewes occurrence probability 86 of wwes occur within convective mjo and or crw phases and 83 of ewes occur within the suppressed phase of mjo and or crw 41 of wwes and 26 of ewes are in particular associated with the combined occurrence of a crw mjo far more than what would be expected from a random distribution 3 wind events embedded within mjo phases also have a stronger impact on the ocean due to a tendency to have a larger amplitude zonal extent and longer duration these findings are robust irrespective of the wind events and mjo crw detection methods while wwes and ewes behave rather symmetrically with respect to mjo crw activity the impact of enso on wind events is asymmetrical the wwes occurrence probability indeed increases when the warm pool is displaced eastward during el nino events an increase that can partly be related to interannual modulation of the mjo crw activity in the western pacific on the other hand the ewes modulation by enso is less robust and strongly depends on the wind event detection method the consequences of these results for enso predictability are discussed

the initiation and developing mechanisms of central pacific el ninos abstractthe initiation and developing mechanisms of four major central pacific cp el nino events in 1994 2002 2004 and 2009 were investigated by analyzing oceanic and atmospheric reanalysis data a mixed layer heat budget analysis was conducted and the result shows that the initiation mechanism of the 1994 cp el nino is very different from other cp el ninos in 2000s while the developing mechanisms are similar among these events the initial sea surface temperature sst warming of the 1994 el nino was caused by enhanced solar radiation which was related to atmospheric meridional overturning circulation in association with positive sst anomaly forcing in the subtropical pacific the subtropical sst anomalies also induced anticyclonic surface wind stress curl anomalies which caused the formation of subsurface warmer waters in the off equatorial regions the off equatorial subsurface warmer waters were transported farther equatorward by the mean subsurface ocean currents leading to the subsurface wa

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

absolute or convective instability in the equatorial pacific and implications for enso the el nino southern oscillation enso is driven by ocean atmosphere inter actions in the equatorial pacific and this variability is often attributed to coupled modes that are evidenced by the temporal stability analysis of anomaly models here the further diagnostic of absolute convective instability is considered which assesses whether small perturbations localized in space and time e g random wind disturbances lead to instabilities that develop in place or propagate away from the perturbed region it is shown that boundary conditions play a secondary role for this approach and that the development of large scale wave packets in the equato rial pacific basin is possible as in the case of an infinite domain as an illustration two simple coupled models are diagnosed that rely either on thermocline processes or zonal advective processes the model with thermocline processes is absolutely unstable and therefore develops intrinsic oscillations while the model with zonal advective processes is convectively unstable and therefore acts as a noise amplifier the identification of the two instability regimes may characterize different enso formation mechanisms as a response to random wind disturbances for the abso lutely unstable regime a standing enso like oscillation can develop in the equato rial pacific without involving boundary reflections while for the convectively unsta ble regime boundary reflections are essential copyright c

seasonal dependence of the mjo enso relationship abstract observations of the development of recent el nino events suggest a pivotal role for the madden julian oscillation mjo previous attempts to uncover a systematic relationship between mjo activity and the el nino southern oscillation enso however have yielded conflicting results in this study the mjo enso relationship is stratified by season and the focus is on mjo activity in the equatorial western pacific the results demonstrate that mjo activity in late boreal spring leads el nino in the subsequent autumn winter for the period 1979 2005 spring is the season when mjo activity is least asymmetric with respect to the equator and displays the most sensitivity to sst variations at the eastern edge of the warm pool enhanced mjo activity in the western pacific in spring is associated with an eastward expanded warm pool and low frequency westerly surface zonal wind anomalies these sustained westerly anomalies in the western pacific are hypothesized to project favorably onto a developing el n

decadal changes of enso persistence barrier in sst and ocean heat content indices 1958 2001 decadal changes of el nino southern oscillation enso persistence barriers in various indices of sea surface temperature sst and ocean heat content ohc are examined in this study using observations and ocean data assimilation products for the period 1958 2001 it is found that the sst indices in the eastern and central equatorial pacific exhibit very different decadal barrier variability the variability is large for the eastern pacific sst indices nino1 2 and nino3 whose persistence barriers shifted abruptly in 1976 1977 and 1989 1990 in contrast the central pacific sst indices nino3 4 and nino4 experienced little decadal barrier variability and have had their persistence barriers fixed in spring in the past four decades the zonal mean ohc index averaged over the equatorial pacific shows decadal barrier changes similar to those in the eastern pacific sst indices and always leads the nino3 sst barrier by about one season it is noticed that the sst persistence barrier appeared first in the eastern pacific before 1976 1977 first in the central pacific between 1976 1977 and 1989 1990 and almost simultaneous in both the eastern and central pacific after 1989 1990 these timings coincide with the westward propagating eastward propagating and standing pattern of enso sst anomalies observed in these three periods these results suggest that enso sst anomalies in the equatorial pacific can be considered to consist of two different processes a central pacific process whose phase transition such as onset and barrier always happen in spring and an eastern pacific process whose phase transition and barrier change from decade to decade and are influenced by changes in the mean thermocline depth along the equatorial pacific

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

a western pacific oscillator paradigm for the el nino southern oscillation a data based hypothesis is presented on the mechanism of the el nino southern oscillation enso a major determinant of interannual global climate variability the hypothesis emphasizes the importance of off equator sea surface temperature and sea level pressure variations west of the dateline for initiating equatorial easterly winds over the far western pacific these winds compete with westerly winds over the equatorial central pacific enabling the coupled ocean atmosphere system to oscillate consistent with this hypothesis an analogical oscillator model is constructed that produces enso like oscillations the proposed mechanism differs from the delayed oscillator paradigm in that wave reflection at the western boundary is not a necessary condition for the coupled ocean atmosphere system to oscillate

nb ta fractionation in peraluminous granites a marker of the magmatic hydrothermal transition comment on the basis of geochemical and mineralogical features ballouard et al 2016 argue that magmatic fractionation alone cannot explain the formation of leucogranites with low nb ta ratios instead they propose that low ratios are better explained by post magmatic interaction with f bearing fluids although fluids may certainly play an important role in the formation of rare metal leucogranites the model proposed by ballouard et al lacks key details we contend that the principal features they attribute to magmatic hydrothermal processes are better explained by the magmatic fractionation model

deformation time series generation in areas characterized by large displacement dynamics the sar amplitude pixel offset sbas technique we exploit the amplitude information of a sequence of synthetic aperture radar sar images acquired at different times in order to generate displacement time series in areas characterized by large and or rapid deformation the size of which is on the order of the image s pixel dimensions we follow the same rationale of the small baseline subset sbas differential sar interferometry dinsar approach by coupling the available sar images into pairs characterized by a small separation between the acquisition orbits we exploit the amplitudes of the selected image pairs in order to calculate the relative across track range and along track azimuth pixel offsets po finally we apply the sbas inversion strategy to retrieve the range and azimuth displacement time series this approach referred to as pixel offset po sbas technique has been applied to a set of 25 envisat sar observations of the sierra negra caldera galapagos islands spanning the 2003 2007 time interval the retrieved deformation time series show the capability of the technique to detect and measure the large displacements affecting the inner part of the caldera that in correspondence to the october 2005 eruption reached several meters moreover by comparing the po sbas results to continuous gps measurements we estimate that the accuracy of the po sbas time series is on the order of 1 30th of a pixel for both range and azimuth directions

assessment of the ore forming process of the gejiu tin district south china abstract the gejiu tin district of southern china is the largest tin polymetallic ore district in the world even though the mining operation has lasted more than 2000 years in this area the metallogenic mechanism of this gigantic tin mineralization is still controversial based on petrographic geochemical and zirconological information from this study we present a particular model of the magma evolution and tin mineralization for the gejiu tin district the ore forming processes involved both a batholithic biotite monzogranite bmg emplaced at 94 ma and a satellitic muscovite alkali feldspar granite mag emplaced at 72 ma the bmg and the mag were produced from a long lived magma chamber by two stages of magmatic activity during intracontinental orogeny in the youjiang block the hiatus between the two magmatic stages indicates that the deep seated magma chamber persisted during the dominant phase of the orogeny progressive fractional crystallization of the magma caused the extreme enrichment of incompatible elements which include ore forming components such as tin aqueous fluids and other volatiles in the residual magma when the regional tectonic environment evolved into the extensional regime at 72 ma the highly fractionated residual magma ascended and once emplaced it formed the highly evolved mag with a mean zircon crystallization age of 71 8 1 2 ma the mag is temporally and spatially associated with cassiterite bearing quartz vein cqv with a mean zircon crystallization age of 72 6 1 6 ma this metallogenic model of the bmg mag cqv association is generally applicable to other granite related metallic deposits in south china southeast asia and elsewhere australia bolivia brazil usa etc the recognition of this bmg mag cqv association in regional geological survey may facilitate the future exploration for this type of deposit

identifying the skeleton of the madden julian oscillation in observational data the madden julian oscillation mjo skeleton model offers a theoretical prediction of the mjo s structure here a method is described for identifying this structure in observational data the method utilizes projections onto equatorial wave structures and a main question is can this method isolate the mjo without using temporal filtering or empirical orthogonal functions for the data projection a wide range of data is incorporated multiple variables wind geopotential height water vapor and as a proxy for convective activity outgoing longwave radiation multiple pressure levels 850 and 200hpa and multiple latitudes both equatorial and off equatorial such a data variety is combined using a systematic method and it allows for a distinction between the kelvin and rossby components of the mjo s structure results are illustrated for some well known cases and statistical measures are presented to quantify the variability of the mjo skeleton signal mjos x t and its amplitude mjosa t the robustness of the methods is demonstrated through a suite of sensitivity studies including tests with two projection methods when the projection is based on the skeleton model s energy as opposed to the standard l 2 energy water vapor is seen to be of primary importance finally a simple interpretation is given for the mjo skeleton structure it is related to the wave responseto amovingheatsource from eitherperspective themethods hereidentifysignalsthatproject onto coupled convection circulation patterns and the results suggest that a large portion of the mjo s structure is consistent with such a coupled pattern

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

indices of el nino evolution abstract to characterize the nature of el nino southern oscillation enso sea surface temperature sst anomalies in different regions of the pacific have been used an optimal characterization of both the distinct character and the evolution of each el nino or la nina event is suggested that requires at least two indices i sst anomalies in the nino 3 4 region referred to as n3 4 and ii a new index termed here the trans nino index tni which is given by the difference in normalized anomalies of sst between nino 1 2 and nino 4 regions the first index can be thought of as the mean sst throughout the equatorial pacific east of the date line and the second index is the gradient in sst across the same region consequently they are approximately orthogonal tni leads n3 4 by 3 to 12 months prior to the climate shift in 1976 77 and also follows n3 4 but with opposite sign 3 to 12 months later however after 1976 77 the sign of the tni leads and lags are reversed

magmatic hydrothermal evolution of rare metal pegmatites from the mesoproterozoic orange river pegmatite belt namaqualand south africa abstract the 450 km long orange river pegmatite belt intruded the namaqua sector of the mesoproterozoic namaqua natal province southern africa at ca 1 ga the western part of the belt is characterized by the occurrence of lct pegmatites locally mineralized in li ta nb be and bi most of these mineralized pegmatites display zonation with a quartz feldspar muscovite garnet beryl bearing aplite border and wall zone a quartz feldspar spodumene lepidolite bearing intermediate zone and a quartz k feldspar core the pegmatites and their granodioritic country rocks commonly show evidence of albitization and greisenization i e secondary muscovitization in this study detailed petrographic observations and the compositions of mica feldspar spodumene and nb ta oxide minerals are reported this information is combined with bulk country rock compositions and new u pb zircon and monazite ages plus sm nd isotope compositions of monazite to constrain the origin and magmatic hydrothermal evolution of weakly and strongly mineralized lct pegmatites the li ta be kokerboomrand i pegmatite emplaced at ca 985 ma during the main stage of pegmatite emplacement in the orange river belt and regional strike slip deformation it has end t monazite 14 3 and potentially formed by partial melting of paleoproterozoic rocks from the richtersveld magmatic arc alternatively mesoproterozoic sediments of the bushmanland subprovince may also provide a suitable magma source for the kokerboomrand i pegmatite the rare metal contents of muscovite and columbite group minerals cgm increase from the weakly mineralized to strongly mineralized pegmatites suggesting early stage fractional crystallization or variable partial melting conditions mica nb ta values of rare metal bearing minerals crystallized throughout the magmatic hydrothermal evolution of mineralized pegmatites during the magmatic dominated stage i constitutional zone refining likely induced a decrease of spodumene fe contents and increase of cgm ta contents toward the pegmatite core stage ii marks the pervasive circulation of an immiscible hydrosaline melt this stage is characterized by the replacement of the primary mineral assemblage by lamellar albite cleavelandite fluor calciomicrolite and cs ta rich li muscovite and zinnwaldite stage iii represents the progressive transition from a magmatic hydrothermal system dominated by a li cs ta rich hydrosaline melt toward a system mainly involving li cs ta bi rich aqueous fluids this stage is characterized by the crystallization of lepidolite and zero valence dominant pyrochlore as well as strong localized greisenization and bi mineralization magmatic hydrothermal alteration of the immediate country rock of the mineralized pegmatites is marked by the crystallization of albite li ta cs rich mica various nb ta oxide minerals and led to a strong decrease of the whole rock nb ta ratio plus significant rare metal enrichment our findings from the orange river belt demonstrate that an important role can be ascribed to melt melt and melt fluid immiscibility and metasomatism in the formation of pegmatite related rare metal deposits greisens and albitites associated with pegmatites and their immediate country rocks can be considered as favorable targets for li ta mineral exploration strong and pervasive metasomatism across the mineralized pegmatites and their country rocks suggests involvement of a parental medium that was highly enriched in water

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

systematic multiscale models for the tropics systematic multi scale perturbation theory is utilized to develop self consistent simplified model equations for the interaction across multiple spatial and or temporal scales in the tropics one of these models involves simplified equations for intraseasonal planetary equatorial synoptic scale dynamics ipesd this model includes the self consistent quasi linear interaction of synoptic scale generalized steady matsuno webster gill models with planetary scale dynamics of equatorial long waves these new models have the potential for providing self consistent prognostic and diagnostic models for the intraseasonal tropical oscillation other applications of the systematic approach reveal three different balanced weak temperature gradient wtg approximations for the tropics with different regimes of validity in space and time a synoptic equatorial scale wtg sewtg a mesoscale equatorial wtg mewtg which reduces to the classical models treated by others and a new seasonal planetary equatorial wtg spewtg both the spewtg and mewtg model equations have solutions with general vertical structure yet have the linearized dispersion relation of barotropic rossby waves thus these models can play an important role in theories for midlatitude connections with the tropics the models are derived both from the equatorial shallow water equations in a simplified context and also as distinguished limits from the compressible primitive equations in general

reinterpreting the thermocline feedback in the western central equatorial pacific and its relationship with the enso modulation vertical stratification changes at low frequency over the last decades are the largest in the western central pacific and have the potential to modify the balance between enso feedback processes here we show evidence of an increase in thermocline feedback in the western central equatorial pacific over the last 50 years and in particular after the climate shift of 1976 it is demonstrated that the thermocline feedback becomes more effective due to the increased stratification in the vicinity of the mean thermocline this leads to an increase in vertical advection variability twice as large as the increase resulting from the stronger enso amplitude positive asymmetry in the eastern pacific that connects to the thermocline in the western central pacific through the basin scale tilt mode although the zonal advective feedback is dominant over the western central equatorial pacific the more effective thermocline feedback allows for counteracting its warming cooling effect during warm cold events leading to the reduced covariability between sst and thermocline depth anomalies in the nino4 160 e 150 w 5 s 5 n region after the 1976 climate shift this counter intuitive relationship between thermocline feedback strength as derived from the linear relationship between sst and thermocline fluctuations and stratification changes is also investigated in a long term general circulation coupled model simulation it is suggested that an increase in enso amplitude may lead to the decoupling between eastern and central equatorial pacific sea surface temperature anomalies through its effect on stratification and thermocline feedback in the central western pacific

characterizing decadal to centennial variability in the equatorial pacific during the last millennium 1 the magnitude of sea surface temperature variability in the nino3 4 region of the equatorial pacific on decadal and longer timescales is assessed in observational data state of the art coupled model intercomparison project 5 climate model simulations and a new ensemble of paleoclimate reconstructions on decadal to multidecadal timescales variability in these records is consistent with the null hypothesis that it arises from multivariate red noise a multivariate ornstein uhlenbeck process generated from a linear inverse model of tropical ocean atmosphere dynamics on centennial and longer timescales both a last millennium simulation performed using the community climate system model 4 ccsm4 and the paleoclimate reconstructions have variability that is significantly stronger than the null hypothesis however the time series of the model and the reconstruction do not agree with each other in the model variability primarily reflects a thermodynamic response to reconstructed solar and volcanic activity whereas in the reconstruction variability arises from either internal climate processes forced responses that differ from those in ccsm4 or nonclimatic proxy processes that are not yet understood these findings imply that the response of the tropical pacific to future forcings may be even more uncertain than portrayed by state of the art models because there are potentially important sources of century scale variability that these models do not simulate