enso simulated by intermediate coupled models and evaluated with observations over 1970 98 part ii role of the off equatorial ocean and meridional winds introducing new parameterizations of subsurface temperature and atmospheric convection in the cane and zebiak model allows the reproducing of oscillations with a period close to 4 yr equatorial wind anomalies that are located close to the date line and realistic amplitudes of sst wind and thermocline anomalies in the equatorial pacific both in warm and cold phases when the weight given to the atmospheric convection term is increased the simulated wind maximum along the equator is displaced farther west and the amplitude and duration of the warm events decrease compared to the simulations with the standard parameterization the enso like oscillations are not lost when the friction is increased with a decay time ranging from 30 to 12 months off equatorial baroclinic ocean and wind anomalies are much less strong but still necessary for the system to oscillate unrealistic easterlies are still present in the eastern pacific replacing the atmospheric model by a statistical relationship between sst and wind stress anomalies allows further reducing of these deficiencies the simulated enso like events are in good agreement with observed oceanic and atmospheric fields in terms of amplitude and spatial patterns within 158 of the equator sensitivity tests to the statistics prescribed in the atmospheric component show that the model simulates warm events with duration and amplitude that increase with the eastern penetration of the westerlies in the central pacific whereas cold events do not last longer and easterlies remain located at the date line whatever their strength after warm events the model simulates a gain of heat content on average in the north and similar features are found in

viscosity structure of the crust and upper mantle in western nevada from isostatic rebound patterns of the late pleistocene lake lahontan high shoreline received 13 july 2005 revised 26 october 2006 accepted 31 january 2007 published 8 june 2007 1 large lakes can both produce and record significant crustal deformation we present an analysis of the isostatic rebound pattern recorded in the shorelines of paleolake lahontan in western nevada using a layered maxwell viscoelastic model the inferred viscosity structure depends on loading history we use three variants of a well documented lake surface elevation model as input and recover corresponding estimates of viscosity and density structure a simple two layer model with an elastic plate over an inviscid half space fits the observed elevation pattern quite well with a residual variance of 32 of the data variance using multilayered finite viscosity models the residual variance is reduced to 20 of the data variance which is very near to the noise level in the higher resolution models the viscosity is below 10 18 pa s over the depth range from 80 to 160 km the minimum viscosity is very similar to the value that has been seen in the eastern great basin from similar analyses of lake bonneville shorelines but the lowviscosity zone is thinner beneath bonneville making small adjustments to a seismically derived density structure allows an improved fit to the shoreline observations additionally we find that small variations in proposed loading models can result in presumably spurious density inversions and suggest that this modeling approach provides a test for loading histories

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

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

predicted bounds on peak global mean sea level during marine isotope stages 5a and 5c abstract estimates of marine isotope stage mis 5c and 5a global mean sea level gmsl based on marine terraces and coastal indicators range from 15 37 m and 9 30 m below present respectively tectonic displacement and glacial isostatic adjustment gia complicate efforts to refine this range we revisit this issue using numerical predictions of post glacial sea level change and updated estimates of site specific tectonic signals based upon these predictions laurentide and cordilleran peripheral bulge dynamics and variations in the gravitational effect of these ice masses dominate the gia signal along the east and west coasts of north america published compilations suggest that mis 5 sea level indicators extending from virginia to the caribbean lie on the outer flank of the peripheral bulge while those along a transect from oregon to baja california sit on the inner flank of the bulge our gia modeling reconciles these data by adopting a significantly weaker i e lower viscosity upper mantle in analyzing data on the pacific coast relative to the atlantic an inference supported by seismic tomography we present a sensitivity analysis that compares the observed elevation of globally distributed high stand markers to a suite of gia simulations that vary the earth model and gmsl from the last interglaciation mis 5e 130 115 ka to 70 ka we conclude that gmsl peaked at 8 5 4 6 m 1 during mis 5a and 9 4 5 3 m during mis 5c a more restrictive analysis yields slightly wider bounds corresponding to 10 5 5 5 m and 11 1 6 6 m respectively

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

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

on the structure of the southern oscillation abstract a realistic oceanic general circulation model is forced with winds observed over the tropical pacific between1967 and 1979 the structure of the simulated southern oscillation is strikingly different in the western andeastern sides of the basin because the principal interannual zonal wind fluctuations are confined to the westand are in the form of an equatorial jet this causes thermocline displacements to have maxima offthe equatorin the west where the curl of the wind is large but on the equator in the east zonal phase propagation bothon and offthe equator is at different speeds in the west and east the phase pattern is complex and there is on interannual time scale no explicit evidence ofindividuai equatorial waves these results lead to a modificationof the delayed oscillator mechanism originally proposed by schopfand suarez to explain a continual southernoscillation the results also permit an evaluation of the various coupled ocean atmosphere models that simulatethe southern osci

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

diagenetic k feldspar textures a tem study and model for diagenetic feldspar growth abstract diagenetic k feldspar overgrowths from the permo triassic continental clastic sediments of the elgin area in scotland were examined using conventional petrographic techniques and transmission electron microscopy to investigate the mechanisms of feldspar authigenesis the detrital k feldspar in these rocks is tartan twinned whereas the diagenetic k feldspar is untwinned the overgrowths are optically homogeneous but are not in optical continuity with the detrital grains overgrowths are up to 50 m thick and comprise numerous rhombs indicating that nucleation was a relatively easy process most overgrowths consist of a mosaic of micron sized rhombs nucleation on different twin planes on the detrital grain surface resulted in different orientations of the diagenetic nuclei the different orientations were propagated into the overgrowth as new nuclei formed on the surface of pre existing diagenetic crystals the detrital k feldspar is triclinic maximum microcline diagenetic k feldspar deviates only slightly from monoclinic orthoclase even though the triclinic polymorph is the stable k feldspar under the low temperature conditions of growth disordered crystals involve a simpler nucleation growth mechanism than ordered crystals consequently disordered crystals grow faster than ordered crystals monoclinic feldspar has disordered al si and triclinic feldspar has ordered al si diagenetic feldspar has metastable low triclinicity because this crystal structure could grow faster than the stable feldspar nanometer scale growth zones occur within individual rhomb representing variations in al si disorder such variations probably result from subtle variations in the state of supersaturation of the pore fluids and therefore in the rate of growth the interface between the detrital grain and the overgrowth represents no profound break in the feldspar crystal lattice despite the change in crystallography but is marked by the termination of twin planes in the detrital grain and the presence of dislocations in the overgrowth the termination of twins resulted in strain in the overgrowth which was relieved by the formation of dislocations small pores representing fluid inclusions and rare clay grains also occur at the interface

diagnostic studies of pacific surface winds abstract analyses are performed using surface winds derived from the monthly mean fsu pacific pseudo stress fields vorticity budget calculations reveal the relative contributions of various terms and allow simplification of the full momentum equations based on the simplified equations a procedure is developed for estimating surface pressure and then adjusting the winds the wind field adjustments fall well within the uncertainty of the data while allowing generally large imbalances in the vorticity budget to be removed completely further validation of the procedure is provided by comparisons between estimated and observed pressure anomalies the adjusted winds and pressure are then used to infer boundary layer and upper level forcing within the context of particular model formulations these forcing fields an compared with sea surface temperature outgoing longwave radiation and highly reflective cloud data in order to infer the dominant mechanisms contributing to observed surface circulation anom

interactive feedback between enso and the indian ocean abstract a feedback process of the indian ocean sst on enso is investigated by using observed data and atmospheric gcm it is suggested that warming in the indian ocean produces an easterly wind stress anomaly over indonesia and the western edge of the pacific during the mature phase of el nino the anomalous easterly wind in the western pacific during el nino helps a rapid termination of el nino and a fast transition to la nina by generating upwelling kelvin waves thus warming in the indian ocean which is a part of the el nino signal operates as a negative feedback mechanism to enso this indian ocean feedback appears to operate mostly for relatively strong el ninos and results in a la nina one year after the mature phase of the el nino this 1 yr period of phase transition implies a possible role of indian ocean enso coupling in the biennial tendency of the enso atmospheric gcm experiments show that indian ocean sst forcing is mostly responsible for the easterly wind anomalies in the western pacific

dislocation damping and anisotropic seismic wave attenuation in earth s upper mantle crystal defects form during tectonic deformation and are reactivated by the shear stress associated with passing seismic waves although these defects known as dislocations potentially contribute to the attenuation of seismic waves in earth s upper mantle evidence for dislocation damping from laboratory studies has been circumstantial we experimentally determined the shear modulus and associated strain energy dissipation in pre deformed synthetic olivine aggregates under high pressures and temperatures enhanced high temperature background dissipation occurred in specimens pre deformed by dislocation creep in either compression or torsion the enhancement being greater for prior deformation in torsion these observations suggest the possibility of anisotropic attenuation in relatively coarse grained rocks where olivine is or was deformed at relatively high stress by dislocation creep in earth s upper mantle

interactive feedback between enso and the indian ocean in an interactive ensemble coupled model an interactive feedback between enso and the indian ocean is investigated using a center for ocean land atmosphere studies cola interactive ensemble coupled model from a long term simulation of the coupled gcm it is shown that el nino events terminate relatively rapidly when the indian ocean sst is anomalously warm the anomalous indian ocean warming induces the anomalous easterlies over the western pacific by modulating the walker circulation in turn the anomalous easterlies generate oceanicupwelling kelvin waves over the western pacific which propagate eastward and accelerate the decay of the warm sst in the eastern pacific as a result el nino terminates relatively quickly and the phase transition from el nino to la nina progresses rapidly these interactive processes are consistent with those derived from the previous observational analyses

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

implications of deformation following the 2002 denali alaska earthquake for postseismic relaxation processes and lithospheric rheology 1 during the first 2 years following the 2002 mw 7 9 denali alaska strike slip earthquake a large array of global positioning system gps receivers recorded rapid postseismic surface motions extending at least 300 km from the rupture and at rates of more than 100 mm yr in the near field here we use three dimensional 3 d viscoelastic finite element models to infer the mechanisms responsible for these postseismic observations we consider afterslip both from an inversion of gps displacements and from stress driven forward models poroelastic rebound and viscoelastic flow in the lower crust and upper mantle several conclusions can be drawn 1 no single mechanism can explain the postseismic observations 2 significant postseismic flow below a depth of 60 km is required to explain observed far field motions best explained by a weak upper mantle with a depth dependent effective viscosity that ranges from 1019 pa s at the moho 50 km depth to 3 4 1018 pa s at 100 km depth 3 shallow afterslip within the upper crust occurs adjacent to and beneath the regions of largest coseismic slip 4 there is a contribution from deformation in the middle and lower crust from either lower crustal flow or stress driven slip afterslip is preferred over broad viscoelastic flow owing to the existence of seismic velocity discontinuities across the fault at depth though our modeling does not favor either mechanism if the process is viscoelastic relaxation the viscosity is a factor of 3 greater than the inferred mantle viscosity 5 poroelastic rebound probably contributed to the observed postseismic deformation in the immediate vicinity of the denali totschunda junction these conclusions lead us to infer an alaskan mechanical lithosphere that is about 60 km thick overlying a weak asthenosphere and a denali fault that cuts through the entire lithosphere with shear accommodated by faulting in the top 20 km and time dependent aseismic shear below

using short term postseismic displacements to infer the ambient deformation conditions of the upper mantle 1 to interpret short term postseismic surface displacements in the context of key ambient conditions e g temperature pressure background strain rate water content creep mechanism we combined steady state and transient flow into a single constitutive relation that can explain the response of a viscoelastic material to a change in stress the flow law is then used to investigate mantle deformation beneath the eastern california shear zone following the 1999 m7 1 hector mine earthquake the flow law parameters are determined using finite element models of relaxation processes constrained by surface displacement time series recorded by 55 continuous gps stations for 7 years following the earthquake results suggest that postseismic flow following the hector mine earthquake occurs below a depth of 50 km and is controlled by dislocation creep of wet olivine diffusion creep models can also explain the data but require a grain size 3 5 mm that is smaller than the inferred grain size 10 20 mm based on the mantle conditions at these depths in addition laboratory flow laws predict dislocation creep would dominate at the stress grain size conditions that provide the best fit to diffusion creep models model results suggest a transient creep phase that lasts 1 year and has a viscosity 10 times lower than subsequent steady state flow in general agreement with laboratory observations the postseismic response is best explained as occurring within a relatively hot upper mantle e g 1200 1300 c at 50 km depth with a long term background mantle strain rate of 0 1 0 2 mstrain yr consistent with the observed surface strain rate long term background shear stresses at the top of the mantle are 4 mpa then decrease with depth to a minimum of 0 1 0 2 mpa at 70 km depth before increasing slowly with depth due to the pressure dependence of viscosity these conditions correspond to a background viscosity of 10 21 pa s within a thin mantle lid that decreases to 5 10 19 pa s within the underlying asthenosphere this study shows the utility of using short term postseismic observations to infer long term mantle conditions that are not readily observable by other means

quantifying the relationship between short wavelength dynamic topography and thermomechanical structure of the upper mantle using calibrated parameterization of anelasticity oceanic residual depth varies on 5000 km wavelengths with amplitudes of 1 km a component of this short wavelength signal is dynamic topography caused by convective flow in the upper 300 km of the mantle it exerts a significant influence on landscape evolution and sea level change but its contribution is often excluded in geodynamic models of whole mantle flow using seismic tomography to resolve buoyancy anomalies in the oceanic upper mantle is complicated by the dominant influence of lithospheric cooling on velocity structure here we remove this cooling signal from global surface wave tomographic models revealing a correlation between positive residual depth and slow residual velocity anomalies at depths 300 km to investigate whether these anomalies are of sufficient amplitude to account for short wavelength residual depth variations we calibrate an experimentally derived parameterization of anelastic deformation at seismic frequencies to convert shear wave velocity into temperature density and diffusion creep viscosity asthenospheric temperature anomalies reach 150 c in the vicinity of major magmatic hotspots and correlate with geochemical and geophysical proxies for potential temperature along mid ocean ridges locally we find evidence for a 150 km thick low viscosity asthenospheric channel incorporating our revised density structure into models of whole mantle flow yields reasonable agreement with residual depth observations and suggests that 30 km deviations in local lithospheric thickness account for a quarter of total amplitudes these predictions remain compatible with geoid constraints and substantially improve the fit between power spectra of observed and predicted dynamic topography this improvement should enable more accurate reconstruction of the spatio temporal evolution of cenozoic dynamic topography

a new inference of mantle viscosity based upon joint inversion of convection and glacial isostatic adjustment data we present new profiles of mantle viscosity derived on the basis of non linear occam style joint inversions of an extensive set of data associated with mantle convection and glacial isostatic adjustment gia the convection related observables include satellite derived free air gravity harmonics the geodetically inferred excess ellipticity of the cmb and tectonic plate motions the gia constraints involve two classes of observables previously shown to be relatively insensitive to errors in the late pleistocene ice history the so called fennoscandian relaxation spectrum frs and a set of site specific decay times determined from the postglacial sea level history in hudson bay and sweden the inverted viscosity profiles show a significant three orders of magnitude increase from the upper mantle mean value of f4 10 20 pa s to a high viscosity 10 23 pa s peak at

transient rheology of the uppermost mantle beneath the mojave desert california abstract geodetic data indicate that the m7 1 hector mine california earthquake was followed by a brief period a few weeks of rapid deformation preceding a prolonged phase of slower deformation we find that the signal contained in continuous and campaign global positioning system data for 2 5 years after the earthquake may be explained with a transient rheology quantitative modeling of these data with allowance for transient linear biviscous rheology in the lower crust and upper mantle demonstrates that transient rheology in the upper mantle is dominant its material properties being typified by two characteristic relaxation times 0 07 and 2 years the inferred mantle rheology is a jeffreys solid in which the transient and steady state shear moduli are equal consideration of a simpler viscoelastic model with a linear univiscous rheology 2 fewer parameters than a biviscous model shows that it consistently underpredicts the amplitude of the first 3 months signal and allowance for a biviscous rheology is significant at the 99 0 confidence level another alternative model deep postseismic afterslip beneath the coseismic rupture predicts a vertical velocity pattern opposite to the observed pattern at all time periods considered despite its plausibility the advocated biviscous rheology model is non unique and should be regarded as a viable alternative to the non linear mantle rheology model for governing postseismic flow beneath the mojave desert

upper mantle seismic wave velocity effects of realistic partial melt geometries we investigate seismic wave velocity reduction resulting from the presence of partial melt in the upper mantle the amount of shear and bulk modulus reduction produced by the presence of a connected network of realistically shaped and naturally organized melt inclusions is found using finite element calculations the geometries of the inclusions are taken directly from laboratory experiments of mantle melting with finite element meshes constructed to conform to these shapes the shear and bulk moduli of the composite material are found for both the unrelaxed isolated inclusions and relaxed pressure equalized inclusions cases by assigning appropriate material properties to the fluid modulus reduction from deformation simulations of a solid containing realistically shaped and ellipse shaped melt inclusions quantify the effect of melt pocket cuspateness and melt pocket organization on seismic velocity reduction the three dimensional response is estimated from two dimensional distributions of the melt phase by determining the mode ii and mode iii components of elastic modulus reduction separately and summing their effects in general cuspate and naturally organized melt inclusions cause greater velocity reduction it is shown that v and vs reduction per percent partial melt are at least 3 6 and 7 9 respectively even higher values for velocity reduction are possible above 1 melt fraction if melt exists only in tubules below 1 melt fraction the lower more conservative values of velocity reduction are 070 greater for vp and 84 greater for vs than the analytically determined values for ellipsoidal inclusions somewhat greater effects are possible if nonrandom organization of melt occurs on scales greater than our model

the antarctica component of postglacial rebound model ice 6g_c vm5a based on gps positioning exposure age dating of ice thicknesses and relative sea level histories

anomalous tropical ocean circulation associated with la nina modoki 1 el nino modoki is a variant of el nino characterized by warming around the dateline flanked by anomalous cooling in the east and west however the opposite phase la nina modoki has received little attention because the prominent cooling of sea surface temperature sst during major la nina events is observed in the central pacific and thus it is difficult to define the two different types of cold events from the sst anomaly pattern here we demonstrate that cold events in 2000 and 2008 can be clearly distinguished from traditional la nina events using surface currents derived from satellite observations during 2000 and 2008 anomalous zonal currents in the equatorial pacific demonstrate divergence with westward currents west of the dateline and eastward currents east of it these currents are opposite to the circulation pattern during the 2004 el nino modoki event an empirical orthogonal function eof analysis of surface currents for the period 1993 2009 shows a circulation anomaly pattern similar to that in 2000 2004 and 2008 in the second eof the first eof is consistent with traditional el nino la nina events and does not exhibit a current reversal along the equator our results also indicate that strong cyclonic anticyclonic circulation anomalies occur in the tropical western pacific around 5 n 15 n during the 2004 2000 and 2008 el nino la nina modoki events and during the strong traditional el nino la nina events of 1997 1998 these circulation anomalies are related to an sst gradient in the western and central pacific

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

combination mode dynamics of the anomalous northwest pacific anticyclone abstractnonlinear interactions between enso and the western pacific warm pool annual cycle generate an atmospheric combination mode c mode of wind variability the authors demonstrate that c mode dynamics are responsible for the development of an anomalous low level northwest pacific anticyclone nwp ac during el nino events the nwp ac is embedded in a large scale meridionally antisymmetric indo pacific atmospheric circulation response and has been shown to exhibit large impacts on precipitation in asia in contrast to previous studies the authors find the role of air sea coupling in the indian ocean and northwestern pacific only of secondary importance for the nwp ac genesis moreover the nwp ac is clearly marked in the frequency domain with near annual combination tones which have been overlooked in previous indo pacific climate studies furthermore the authors hypothesize a positive feedback loop involving the anomalous low level nwp ac through el nino and c mode interactions the development o

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

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

seismic wave attenuation energy dissipation in viscoelastic crystalline solids seismic imaging as a tool to understand the structure and perhaps the dynamics of the planet at depth involves the spatially resolved combined study of wave velocities and velocity dispersion wave birefringence and wave attenuation mechanical absorption when integrated with insights from petrology plus or minus input from magneto tellurics specific hypotheses concerning structure at depth can be formulated cf karato 1993 karato and karki 2001 the recent advances in tomography have allowed significant improvements in spatial resolution which also have allowed ever more exacting hypotheses of structure to be articulated nevertheless as is nicely illustrated by the relatively recent seismic analyses of an accreting plate margin the east pacific rise e g toomey et al 1998 webb and forsyth 1998 the structures inferred at depth can vary significantly clearly the interpretation of seismic data is limited specifically by a lack of understanding of the physical processes by which low frequency wave absorption occurs particularly in the cases a where melt is present and or b where the material is being actively plastically deformed this chapter emphasizes the mineral physics materials science of mechanical absorption specifically in dense materials at elevated temperature the interest then is in employing the physical study of mechanical absorption to understand natural phenomena such as those mentioned above beyond questions of the basic mineral physics of absorption the guiding interest the community of scholars pursuing the ideas is in isolating actual absorption mechanisms operative in the geological setting thereby allowing for a greater discrimination in the interpretation of seismic data at the outset i note that this contribution does not seek to be a comprehensive review of the ideas and work involved in the physics of mechanical absorption there are marvelous reviews in the literature that are both authoritative and current i refer to these frequently in contemplating my own

glacial isostatic adjustment and the radial viscosity profile from inverse modeling 1 a formal inverse procedure is used to infer radial mantle viscosity profiles from several observations related to the glacial isostatic adjustment process the data sets consist of late pleistocene and holocene sea level data from scandinavia the barents sea central europe canada and the far field as well as observations of changes in the earth s rotation and gravitational field and present day uplift and gravity changes in scandinavia inferences of mantle viscosity are robust against assumptions such as the a priori viscosity model and model discretization however the quality of ice sheet reconstruction remains crucial for the inverse inference the importance to discuss regional mantle viscosity models in view of the lateral variability in mantle properties has been evident our inference suggests a two order of magnitude increase of mantle viscosity with depth and volume averaged upper and lower mantle viscosities around 7 1020 and 2 1022 pa s respectively mantle viscosity does not need to increase sharply across the 660 km seismic discontinuity the viscosity profiles suggested are also able to reconcile the large scale geoid anomaly related to mantle convection

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

rheology of the lithosphere inferred from postseismic uplift following the 1959 hebgen lake earthquake 1 we have modeled the broad postseismic uplift measured by geodetic leveling in the epicentral area of the 1959 mw 7 3 hebgen lake montana earthquake a normal faulting event in the northern basin and range province to fit the observed uplift we calculate synthetic postseismic deformation using the relaxation response of a gravitational viscoelastic earth to the earthquake for a model with an elastic plate overlying a viscoelastic half space we find that the elastic thickness is 38 8 km which is close to the local crustal thickness the half space viscosity is estimated at 4 1018 0 5 pa s the leveling data do not require a viscous lower crust but permit a lower bound viscosity of 1020 pa s the observed broad uplift cannot be explained by physically plausible afterslip on and below the coseismic fault however local deformation across the coseismic surface rupture requires shallow afterslip reaching the surface the postseismic deformation induced by the estimated viscoelastic structure decays exponentially with a time constant of 15 years because of coupling between the elastic layer and the viscoelastic substrate this relaxation time is significantly longer than the 2 year maxwell relaxation time of the viscous half space itself our result suggests the importance of postseismic relaxation in interpreting high precision global positioning system velocities for example our model results suggest that postseismic transient velocities from both the 1959 hebgen lake and the 1983 mw 6 9 borah peak earthquakes are currently as large as 1 2 mm yr

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

slow instabilities in tropical ocean basin global atmosphere models abstract the effect of ocean boundaries on instability in coupled ocean natmosphere models is determined eigenvalues and eigenvectors are calculated for coupled systems featuring an ocean basin bounded zonally by a flat continent the atmosphere is periodic zonally about the globe the oceanic and atmospheric dynamics are both represented by linear shallow water equations on the equatorial plane the calculation involves latitudinal series expansion and longitudinal finite differencing certain of the modes i e eigenvectors have amplitudes that grow with time the growth being a direct result of the ocean atmosphere coupling comparison is made to modes previously determined for the theoretically simpler case where the ocean is zonally unbounded growing modes in the bounded ocean case correspond in aspects of behavior and structure to particular modes of appropriate wavelength in the unbounded ocean basin the basic mechanism of instability is the same in both cases growing modes in the bounded o

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

nonlinear interdecadal changes of the el nino southern oscillation nonlinear interdecadal changes in the el nino southern oscillation enso phenomenon are investigated using several tools a nonlinear canonical correlation analysis nlcca method based on neural networks a hybrid coupled model and the delayed oscillator theory the leading nlcca mode between the tropical pacific wind stress ws and sea surface temperature sst reveals notable interdecadal changes of enso behaviour before and after the mid 1970s climate regime shift with greater nonlinearity found during 1981 99 than during 1961 75 spatial asymmetry for both sst and ws anomalies between warm el nino and cool la nina events was significantly enhanced in the later period during 1981 99 the location of the equatorial easterly anomalies was unchanged from the earlier period but in the opposite enso phase the westerly anomalies were shifted eastward by up to 25 according to the delayed oscillator theory such an eastward shift would lengthen the duration of the warm events by up to 45 but leave the duration of the cool events unchanged supporting evidence was found from a hybrid coupled model built with the lamont dynamical ocean model coupled to a statistical atmospheric model consisting of either the leading nlcca or cca mode

defect microdynamics in minerals and solid state mechanisms of seismic wave attenuation and velocity dispersion in the mantle the propagation of seismic waves in the earth s mantle can be significantly affected by relaxation processes causing attenuation and velocity dispersion reduction this paper reviews the solid state mechanisms of relaxation processes based on the theory of defect microdynamics in solids together with some experimental observations on defects in minerals particularly in olivine for a given mechanism to have a significant effect on seismic wave propagation both the density and the mobility of the defects must be in an appropriate range the examination of the densities and geometry and mobilities of defects in olivine shows that dislocation and or grain boundary mechanisms can have a significant effect on seismic wave propagation although wide distributions of geometrical factors such as spacing of pinning points and of mobilities are required to explain all available data point defect mechanisms however are unlikely to be important because their densities are too small and or their mobilities are too large since the dislocation density and or grain size are determined in most cases by the long term tectonic stress seismic wave attenuation and velocity dispersion reduction involving these defects are likely to depend on the magnitude of the tectonic stress as well as the temperature theoretical considerations suggest a wide range of dependence of seismic wave attentuation and velocity dispersion on the long term tectonic stress this is particularly the case for dislocation mechanisms and warrants careful experimental investigation dislocations and or grain boundaries cause anelastic behavior relaxation peaks when they are pinned or blocked at some points pinning or blocking becomes ineffective at high temperatures and or low frequencies causing a transition to viscoelastic behavior both laboratory and seismological observations of internal friction are dominated by the high temperature background where internal friction increases monotonically with temperature which can be interpreted as a gradual transition to viscoelastic behavior or to a wide distribution of relaxation times however in most experimental studies to date the dislocation densities or the grain sizes were not well controlled making it difficult to identify the attenuation mechanisms and preventing any quantitative applications to earth the need for better characterization of defect microstructures in experimental specimens is emphasized

dissipation at tidal and seismic frequencies in a melt free anhydrous mars 1 the measured inward motion of phobos provides a constraint on the tidal dissipation factor q within mars we model viscoelastic dissipation inside a convective mars using a modified burgers model based on laboratory experiments on anhydrous melt free olivine the model tidal q is highly sensitive to the mantle potential temperature and grain size assumed but relatively insensitive to the bulk density and rigidity structure q thus provides a tight constraint on the martian interior temperature by fitting the observed tidal q and tidal love number k2 values and requiring present day melt generation we estimate that for a grain size of 1 cm the current mantle potential temperature is 1625 75 k similar to that of the earth this estimate is consistent with recent petrologically derived determinations of mantle potential temperature but lower than estimates in some thermal evolution models the presence of water in the martian mantle would reduce our estimated temperature our preferred mantle grain size of 1 cm is somewhat larger than that of the earth s upper mantle the predicted mantle seismic q is about 130 and is almost independent of depth the martian lithosphere represents a high seismic velocity lid which should be readily detectable with future seismological observations

inferences of mantle viscosity based on ice age data sets radial structure we perform joint nonlinear inversions of glacial isostatic adjustment gia data including the following postglacial decay times in canada and scandinavia the fennoscandian relaxation spectrum frs late holocene differential sea level dsl highstands based on recent compilations of australian sea level histories and the rate of change of the degree 2 zonal harmonic of the geopotential j2 resolving power analyses demonstrate the following 1 the frs constrains mean upper mantle viscosity to be 3 1020 pa s 2 postglacial decay time data require the average viscosity in the top 1500 km of the mantle to be 1021 pa s and 3 the j2 datum constrains mean lower mantle viscosity to be 5 1021 pa s to reconcile 2 and 3 viscosity must increase to 1022 1023 pa s in the deep mantle our analysis highlights the importance of accurately correcting the j2 observation for modern glacier melting in order to robustly infer deep mantle viscosity we also perform a large series of forward calculations to investigate the compatibility of the gia data sets with a viscosity jump within the lower mantle as suggested by geodynamic and seismic studies and conclude that the gia data may accommodate a sharp jump of 1 2 orders of magnitude in viscosity across a boundary placed in a depth range of 1000 1700 km but does not require such a feature finally we find that no 1 d viscosity profile appears capable of simultaneously reconciling the dsl highstand data and suggest that this discord is likely due to laterally heterogeneous mantle viscosity an issue we explore in a companion study

understanding key roles of two enso modes in spatiotemporal diversity of enso abstractel nino southern oscillation enso events exhibit a diversity of amplitudes spatial patterns and life cycles while the 3 7 yr low frequency lf and 2 3 yr quasi biennial qb bands co

inferred rheological structure and mantle conditions from postseismic deformation following the 2010 mw 7 2 el mayor cucapah earthquake author s dickinson lovell h huang mh freed am fielding e burgmann r andronicos c abstract the author s 2017 the 2010mw7 2elmayor cucapah earthquake provides a unique target of postseismic study as deformation extends across several distinct geological provinces including the coldmesozoic arc crust of the peninsular ranges and newly formed hot extending lithosphere within the salton trough we use five years of global positioning system measurements to invert for afterslip and constrain a 3 d finite element model that simulates viscoelastic relaxation we find that afterslip cannot readily explain far field displacements more than 50 km from the epicentre these displacements are best explained by viscoelastic relaxation of a horizontally and vertically heterogeneous lower crust and upper mantle lower viscosities beneath the salton trough compared to the peninsular ranges and other surrounding regions are consistent with inferred differences in the respective geotherms our inferred viscosity structure suggests that the depth of the lithosphere asthenosphere boundary lab is 65 km below the peninsular ranges and 32 km beneath the salton trough these depths are shallower than the corresponding seismic lab this suggests that the onset of partial melting in peridotite may control the depth to the base of the mechanical lithosphere in contrast the seismic lab may correspond to an increase in the partial melt percentage associated with the change from a conductive to an adiabatic geotherm

mobility of continental mantle evidence from postseismic geodetic observations following the 1992 landers earthquake the crust around the rupture zone of the 1992 landers earthquake has continued to deform in the years following the earthquake at rates 3 times greater than pre earthquake rates we use a combination of global positioning system gps and synthetic aperture radar insar data collected during a 3 year epoch following the earthquake in order to investigate postseismic mechanisms responsible for the high transient velocities in order to maximize the potential signal from viscoelastic relaxation we evaluate and model postseismic relaxation following the first few months of documented accelerated deformation the combination of gps and insar data allows us to establish viscoelastic relaxation of the lower crust and upper mantle as the dominant postseismic process and to discriminate among possible viscoelastic models the data particularly require the presence of a highly ductile uppermost mantle beneath the central mojave domain with temperature between the wet and dry basalt solidus this is consistent with independent seismic and geochemical inferences of a regionally warm uppermost mantle further consideration of seismic velocity variations in conjunction with faulting patterns within the mojave desert suggests that the primary faulting characteristics of the mojave desert namely the pervasive late cenozoic deformation within the eastern california shear zone versus the near absence of faults in the western mojave domain are controlled by the rheology of the uppermost mantle

polycrystal anelasticity at near solidus temperatures elasticity anelasticity and viscosity of polycrystalline aggregates were measured at the near solidus temperatures ranging from below to above the solidus temperature tm the result shows that the mechanical effects of the partial melting are twofold changes just below the solidus temperature in the absence of melt and changes at the solidus temperature due to the onset of partial melting as homologous temperature t tm increases from about 0 92 to 1 high frequency part of the attenuation spectrum significantly grows viscosity of the grain boundary diffusion creep is also reduced in this temperature range these changes are caused by a solid state mechanism and have a large amplitude even for the samples which can generate very small amounts of melt at the solidus temperature at the onset of melting further increases in the elastic anelastic and viscous compliances occur these changes are caused by the direct effects of the melt phase and are very small for the samples with very small melt fractions mechanical properties of a partially molten aggregate are determined by these twofold changes and when melt fraction is small the former changes are dominant we performed a parameterization of the present experimental results and applied the obtained empirical formula to the seismic tomographic data in the upper mantle the present model explains well the steep reduction of the seismic shear wave velocity in the oceanic lithosphere just below the solidus temperature

tropical pacific sea surface temperatures and preceding sea level pressure anomalies in the subtropical north pacific 1 the correspondence of sea surface temperature sst anomalies to changes in antecedent large scale sea level pressure anomalies is investigated using reanalysis data by statistically examining linearly coupled precursor sea level pressure fields and subsequent sst fields for different lag periods it is possible to isolate a precursor mode of sea level pressure slp variability in the central subtropical north pacific that precedes variations in the january march el nino southern oscillation enso by approximately 12 15 months a sea level pressure index which captures the important characteristics of this precursor mode of variability is developed and evaluated it is shown that both analyzed and observed versions of the index are significantly correlated with the january march enso one year later the slp index is then used to examine the evolution of the surface circulation and temperature structures leading up to mature enso events initially the january march subtropical north pacific slp anomalies are associated with changes in the intensity of the subtropical trade wind regime over the north pacific as well as with sst anomalies over the eastern equatorial pacific and subtropical central pacific in agreement with the correlation statistics associated with the slp and lagged nino3 4 indices both the sea level pressure field and the sst field subsequently develop enso like structures over the course of the following year significant discussion of these results and pertinent areas of future research are provided within the broader context of the enso system

enso simulated by intermediate coupled models and evaluated with observations over 1970 98 part i role of the off equatorial variability enso simulations are investigated in 30 yr integrations of various intermediate coupled models and compared with observed sst wind and thermocline depth anomalies over the tropical pacific the cane and zebiak model simulates warm events with a period close to the observations but with westerlies that are located 30 8 east of them and thermocline anomalies in the western pacific that are much shallower between two warm events the model simulates a series of three weak and short cold sst peaks and hardly ever simulates easterlies the sst in the eastern equatorial pacific is not sensitive to thermocline depth anomalies but to the anomalous downwelling of surface currents induced by ekman shear the model simulates a pair of very strong cyclonic wind stress curl anomalies on both sides of the equator in the eastern off equatorial domain between 78 and 158 lat these are necessary to maintain the oscillatory regime so are the ocean meridional rossby modes higher than 5 the thermocline zonal slopes required to balance the off equatorial curl anomalies are about three times steeper than the ones required to balance the zonal stress along the equator thus the off equator exerts an excess of zonal pressure which by continuity affects the equatorial ocean and plays a crucial role in reversing and triggering the growing events six months after the warm peaks the whole ocean between 158s and 158n is significantly upwelled the equatorial oceanic heat content is recharged from the south prior to a warm event contrary to simulations when the model is driven by observed wind anomalies increasing the friction in the baroclinic ocean does not decrease the off equatorial variability but significantly alters the low frequency oscillations that are no longer enso like introducing the parameterization of subsurface temperature derived from hydrographic profiles in the ocean component does not allow the coupled model to recover cold events as in a forced context introducing the parameterization of convection derived from high cloud temperature measurements is the most effective improvement but results still poorly agree with observations and are in contrast with the simulations driven by observed sst biased toward westerlies in the central pacific upwelled thermocline in the west and warm sst in the east thus modifying the ocean component only or the atmosphere only does not have the same impact on simulations as in a forced context the coupling allows new mechanisms to grow and govern the model behavior one of them is the slow meridional oceanic mass adjusment in quasi sverdrup balance with the winds

off equatorial westward propagating rossby waves in the tropical pacific during the 1982 83 and 1986 87 enso events abstract analysis of anomalous vertically averaged temperatures tav in the tropical pacific ocean for the eight year period 1979 86 finds the development during the onset phase one to two years before the mature phase of the two enso events of the period having dynamically significant similarities both north and south of the equator during the onset phase of both enso events each beginning in the off equatorial western tropical pacific about 10 latitude positive anomalies of tav occurred during northern autumn winter one year prior to the mature phase of each enso event in both northern and southern hemispheres this corroborates model results of pazan et al and supports the hindcasting forecasting capability of enso events obtained by white et al though the latter considered only the northern hemisphere it is also demonstrated that the development of positive tav anomalies in northern autumn winter along the tropical maritime western boundary of both hemispheres was associated with wind

anelasticity from seismic to tidal timescales theory and observations abstract we examine strain energy dissipation of earth s normal modes and body tides in order to compare these observations with predictions from an experimental model of intrinsic dissipation for this comparison we employ a recently developed self consistent treatment of modes and tides that includes the separation of dynamical processes self gravity and inertia from intrinsic attenuation we select a set of normal modes and tides with similar depth sampling centered on the lower mantle without contributions from the core this dataset ranges from 7 min to 18 6 yr or about 6 decades in frequency the results show that the attenuation of the higher frequency modes defines a broad plateau in dissipation inferred experimentally to occur at the transition from elastic to anelastic behavior whereas the attenuation of lower frequency tides falls on a frequency dependent absorption band this reconciles published seemingly contradictory models of dissipation for modes versus tides the absorption band for modes terminates at periods where tidal models infer its onset microphysically the experimental data can be explained by elastically accommodated grain boundary sliding producing a broad plateau at short periods transitioning to diffusionally assisted grain boundary sliding at longer periods corresponding to an absorption band extrapolation of the fit to the experimental data with parameters adopted for the lower mantle can reconcile the seismological and geodetic observations

on the atmospheric responses to tropical pacific heating during the mature phase of el nino the atmospheric heating and sea surface temperature sst anomalies during the mature phase of el nino are observed to show both eastern and western pacific anomaly patterns with positive anomalies in the equatorial eastern central pacific and negative anomalies in the off equatorial western pacific the detailed spatial patterns of the heating anomalies differ from the sst anomalies the heating anomalies are more equatorially confined than the sst anomalies and maxima of positive and negative heating anomalies are located farther to the west than the sst anomalies the gill zebiak atmospheric model assumes that the atmospheric initial heating has the same spatial patterns as the sst anomalies this assumption results in some unrealistic model simulations for el nino when the model heating anomaly forcing is modified to resemble the observed heating anomalies during the mature phase of el nino the model simulations have been improved to 1 successfully simulate equatorial easterly wind anomalies in the western pacific 2 correctly simulate the position of maximum westerly wind anomalies and 3 reduce unrealistic easterly wind anomalies in the off equatorial eastern pacific this paper shows that off equatorial western pacific negative atmospheric heating or cold sst anomalies are important in producing equatorial easterly wind anomalies in the western pacific these off equatorial cold sst anomalies in the western pacific also contribute to equatorial westerly wind anomalies observed in the central pacific during the mature phase of el nino although off equatorial cold sst anomalies in the western pacific are smaller than equatorial positive sst anomalies in the eastern pacific they are enough to produce atmospheric responses of comparable magnitude to the equatorial eastern pacific this is because the atmospheric mean state is convergent in the western pacific and divergent in the equatorial eastern pacific by either removing the atmospheric mean convergence or removing off equatorial cold sst anomalies in the western pacific the atmospheric responses show no equatorial easterly wind anomalies in the western pacific in the gill zebiak model the mean wind divergence field is an important background state whereas the mean sst is secondary

measures of dissipation in viscoelastic media extended toward continuous characterization across very broad geophysical time scales author s lau hcp holtzman bk abstract 2019 american geophysical union all rights reserved we develop a conceptual quantitative framework whereby measurements of earth s viscoelasticity may be assessed across the broad range of geophysical processes spanning seismic wave propagation postseismic relaxation glacial isostatic adjustment and mantle convection doing so requires overcoming three challenges a separating spatial variations from intrinsic frequency dependence in mechanical properties b reconciling different conceptual and constitutive viscoelastic models used to interpret observations at different frequencies and c improving understanding of linear and nonlinear transient deformation mechanisms and their extrapolation from laboratory to earth conditions we focus on b first demonstrating how different mechanical models lead to incompatible viscosity estimates from observations we propose the determination of the complex viscosity a frequency dependent parameter complementary to other measures of dissipation including frequency dependent moduli and attenuation from such observations to reveal a single underlying broadband mechanical model the complex viscosity illuminates transient creep in the vicinity of the maxwell time where most ambiguity lies

the global attenuation structure of the upper mantle 1 a large data set of fundamental mode rayleigh wave amplitudes is analyzed to derive a new global three dimensional model of shear wave attenuation in the upper mantle the amplitude observations span a range of periods between 50 and 250 s and are derived from earthquakes with mw 6 0 that occurred between 1993 and 2005 four separate factors may influence an amplitude anomaly intrinsic attenuation along the raypath elastic focusing effects along the raypath uncertainties in the strength of excitation and uncertainties in the response at the station in an earlier paper dalton and ekstrom 2006a dependence of the retrieved attenuation structure on these terms was shown to be significant and an approach was developed to invert the amplitudes simultaneously for each term the new three dimensional attenuation model qrfsi12 which is the subject of this paper is derived using this method the model contains large lateral variations in upper mantle attenuation 60 to 100 and exhibits strong agreement with surface tectonic features at depths shallower than 200 km at greater depth qrfsi12 is dominated by high attenuation in the southeastern pacific and eastern africa and low attenuation along many subduction zones in the western pacific resolution tests confirm that the change in pattern of attenuation above and below 200 km depth can be determined with confidence using the fundamental mode data set the new model is highly correlated with global models of shear wave velocity particularly in the uppermost mantle suggesting that the same factors may control both seismic attenuation and velocity in this depth range however forcing the lateral perturbations in attenuation to match those found in global velocity models decreases the data variance reduction which suggests that subtle differences between patterns of attenuation and velocity are robust

grain boundary sliding in san carlos olivine flow law parameters and crystallographic preferred orientation 1 we performed triaxial compressive creep experiments on aggregates of san carlos olivine to develop a flow law and to examine microstructural development in the dislocation accommodated grain boundary sliding regime gbs each experiment included load and temperature steps to determine both the stress exponent and the activation energy grain boundary maps created with electron backscatter diffraction data were used to quantify grain size distributions for each sample inversion of the resulting data produced the following flow law for gbs gbs 104 8 0 8 2 9 0 3 d0 7 0 1 exp 445 20 kj mol 1 rt with d and gbs in units of mpa m and s 1 respectively although relatively weak crystallographic preferred orientations cpos have 010 maxima parallel to the compression direction along with 100 and 001 girdles perpendicular to the compression direction cpos and subgrain boundary misorientation axes suggest that the 010 100 slip system contributes significantly to deformation we propose that these experimental results are best modeled by a deformation mechanism in which strain is accomplished primarily through grain boundary sliding accommodated by the motion of dislocations extrapolation of our flow laws to mantle conditions suggests that gbs is likely to be the dominant deformation mechanism in both lithospheric shear zones and asthenospheric flow and therefore strong upper mantle seismic anisotropy can not be attributed solely to the dominance of dislocation creep

north pacific premonitory sign of the enso event 1 the premonitory sign of the enso event shows up in the north pacific subtropical mode water stmw 18 months earlier and this should be useful in forecasting the occurrence of this important phenomenon the premonitory connection involves an air sea coupling between the longtime persistent mid latitude ssta induced by the remote re emergence of stmw and the following spring subtropical atmospheric circulation anomalies examination of the air sea interaction reveals that the following spring subtropical atmospheric circulation which responds to the longtime persistent ssta is dominated by the anomalous negative positive geopotential height downstream of the negative positive ssta in the strong weak stmw case then the tropics adjust to these anomalies through coupled dynamics producing enso like pattern of variability details of the connection and possible process are presented

global glacial isostasy and the surface of the ice age earth the ice 5g vm2 model and grace abstract the 100 kyr quasiperiodic variation of continental ice cover which has been a persistent feature of climate system evolution throughout the most recent 900 kyr of earth history has occurred as a consequence of changes in the seasonal insolation regime forced by the influence of gravitational n body effects in the solar system on the geometry of earth s orbit around the sun the impacts of the changing surface ice load upon both earth s shape and gravitational field as well as upon sea level history have come to be measurable using a variety of geological and geophysical techniques these observations are invertible to obtain useful information on both the internal viscoelastic structure of the solid earth and on the detailed spatiotemporal characteristics of glaciation history this review focuses upon the most recent advances that have been achieved in each of these areas advances that have proven to be central to the construction of the refined model of the global process of glacial isos

slow variability in the equatorial west central pacific in relation to enso abstract six years of upper ocean velocity temperature and surface wind data collected in the west central pacific at 0 170 w reveal a slow ocean dynamical mode associated with the el nino southern oscillation enso latent and sensible heat flux calculations using the basin wide tropical atmosphere ocean tao array data show a coincident slow ocean atmosphere thermodynamical mode beginning with the la nina conditions in 1988 through the peak el nino conditions in 1992 the equatorial undercurrent euc speed decreased along with the surface zonal wind stress and the zonal pressure gradient simultaneous with these were increasing trends in the richardson number above the euc core and in sea surface temperature sst after peak warming was achieved the variations in all of these quantities reversed in a movement toward their previous la nina conditions as this evolved within the ocean the sensible and latent heat fluxes increased with large values emanating eastward from the western pacific the

effects of partial melting on seismic velocity and attenuation a new insight from experiments the effects of partial melting on seismic velocity and attenuation have long been studied by focusing on the direct effects of melt such as the poroelastic effect the direct effects are generally very small for a very small melt fraction because geochemical studies have shown that the melt fraction during partial melting is very small 0 1 it is difficult to explain upper mantle low velocity regions by the direct effects of melt recent experimental studies by using a rock analog have captured a significant enhancement of polycrystal anelasticity just before partial melting in the absence of melt this newly recognized effect enables us to interpret seismological and geochemical observations consistently the new anelasticity model significantly changes the interpretation of upper mantle seismic structures this review summarizes the recent progress in the understanding of polycrystal anelasticity starting from a basic knowledge of linear anelasticity

viscosity estimates for the crust and upper mantle from patterns of lacustrine shoreline deformation in the eastern great basin the deformed shorelines of lake bonneville constitute a classic source of information on lithospheric elastic thickness and upper mantle viscosity we describe and apply a new model to a recently augmented data set new data better constrain both the complex spatio temporal pattern of the lake load and the crustal deformation response to that load the history of lake level fluctuations has been significantly refined and somewhat modified this is due to both more radiocarbon dates from within the bonneville basin and to an improved calibration of the radiocarbon timescale itself the data which constrain the crustal deformation pattern consist of ages and shoreline elevations from several hundred points which sample three major levels of lake bonneville and corresponding elevations from the high stands of three smaller lakes situated to the west of lake bonneville the data from the smaller lakes help elucidate the pattern of deflection which occurred beyond the edge of the big lake the geometry of the earth model incorporates an arbitrary number of layers overlying a half space and the rheology of each level can accommodate an arbitrary number of maxwell viscoelastic elements in parallel the inverse modeling comprises three complementary approaches for the simplest configurations we performed a direct search of the parameter space and delineated the irregular boundary of the subspace of acceptable models for more complex configurations we constrained the elastic parameters to their seismically determined values and then solved for viscosity versus depth profiles by either expressing the log viscosity versus log depth profile as a series of specially constructed orthogonal polynomials or by allowing each of 8 10 layers plus the half space to have an independently determined viscosity we found that the data do not strongly support nor can they conclusively exclude a more complex rheology than simple maxwell viscoelasticity the orthogonal polynomial solution exhibits an essentially monotonic decrease in viscosity with depth the most rapid change occurs at shallow depths decreasing from 1023 pa s at 3 km to 102o pa s at 30 km the decrease is much more gradual below with only another factor of 5 decrease between 30 and 300 km depth the unconstrained solution exhibits a rapid decrease in viscosity with depth from 2x 10 24 pa s in the top 10 km to 4x 1017 pa s at a depth of 40 km a nearly isoviscous asthenospheric region extends from 40 to 150 km and is underlain by a mantle lithospheric region with increased viscosity 2x 102o pa s extending from 150 to 300 km depth and by a uniform viscosity 1019 pa s half space below

rapid termination of the 2006 el nino and its relation to the indian ocean 1 we investigated the rapid termination of the 2006 el nino using observed data and a coupled ocean atmosphere general circulation model cgcm observed data showed development of an anomalous south indian ocean sio anticyclone associated with the concurrent indian ocean dipole during september november 2006 at the end of 2006 the eastward retreat of the sio anticyclone in response to the indian ocean warming generated an easterly anomaly over the western pacific and the resultant oceanic upwelling kelvin wave terminated the el nino cgcm experiments indicated that the formation of the sio anticyclone was influenced remotely by the pacific ocean sst anomalies and that the easterly anomaly over the western pacific at the end of 2006 was reinforced by the indian ocean sst anomalies these results suggest that interactive feedback between the indian and pacific oceans helped the rapid termination of the 2006 event

teleconnected influence of north atlantic sea surface temperature on the el nino onset influence of north atlantic sea surface temperature sst anomalies on tropical pacific sst anomalies is examined both summer and winter north atlantic sst anomalies are negatively related to central eastern tropical pacific sst anomalies in the subsequent months varying from 5 to 13 months in particular when the north atlantic is colder than normal in the summer an el nino event is likely to be initiated in the subsequent spring in the tropical pacific associated with summer cold north atlantic sst anomalies is an anomalous cyclonic circulation at low level over the north atlantic from subsequent october to april corresponded to this local response an sst induced heating over the north atlantic produces a teleconnected pattern similar to the east atlantic west russia teleconnection the pattern features two anticyclonic circulations near england and lake baikal and two cyclonic circulations over the north atlantic and near the caspian sea the anticyclonic circulation near lake baikal enhances the continent northerlies and strengthens the east asian winter monsoon these are also associated with an off equatorial cyclonic circulation in the western pacific during the subsequent winter and spring which produces equatorial westerly wind anomalies in the western pacific the equatorial westerly wind anomalies in the winter and spring can help initiate a pacific el nino event following a cold north atlantic in the summer

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