the dynamics of southern ocean storm tracks abstractthe mechanisms that initiate and maintain oceanic storm tracks regions of anomalously high eddy kinetic energy are studied in a wind driven isopycnal primitive equation model with idealized bottom topography storm tracks are found downstream of the topography in regions strongly influenced by a large scale stationary meander that is generated by the interaction between the background mean flow and the topography in oceanic storm tracks the length scale of the stationary meander differs from that of the transient eddies a point of distinction from the atmospheric storm tracks when the zonal length and height of the topography are varied the storm track intensity is largely unchanged and the downstream storm track length varies only weakly the dynamics of the storm track in this idealized configuration are investigated using a wave activity flux related to the eliassen palm flux and eddy energy budgets it is found that vertical fluxes of wave activity which correspond to eddy growth

residual mean solutions for the antarctic circumpolar current and its associated overturning circulation abstract residual mean theory is applied to the streamwise averaged antarctic circumpolar current to arrive at a concise description of the processes that set up its stratification and meridional overturning circulation on an f plane simple solutions are found in which transfer by geostrophic eddies colludes with applied winds and buoyancy fluxes to determine the depth and stratification of the thermocline and the pattern of associated residual meridional overturning circulation

stationary rossby wave propagation in a baroclinic atmosphere observational studies of teleconnections in both soisticial seasons have suggested various patterns of behaviour linked mainly to westerly jets and equatorial westerlies these have been interpreted using barotropic rossby wave theory and simulated using stationary forcing in barotropic models linearized about 300 hpa flows in this paper the relevant propagation behaviour is investigated using a baroclinic model with three dimensional climatological basic states time integrations are performed using localized thermal forcing as a wavemaker the propagation results are qualitatively very similar to those obtained with the barotropic model though there are quantitative differences the westerly jets still act as strong waveguides the shorter wavelengths and smaller wave activity speeds found with the baroclinic model are generally in better agreement with observation propagation into and from the upper tropospheric equatorial westerlies in the east pacific propagation across north america and propagation from europe across the arabian gulf are all found the extent to which upper tropospheric westerlies reach towards the equator influences the propagation into those regions barotropic models can only represent such behaviour if the basic state reflects the near equatorial upper tropospheric zonal wind structure

downward coupling between the stratosphere and troposphere the relative roles of wave and zonal mean processes abstract wave and zonal mean features of the downward dynamic coupling between the stratosphere and troposphere are compared by applying a time lagged singular value decomposition analysis to northern hemisphere height fields decomposed into zonal mean and its deviations it is found that both zonal and wave components contribute to the downward interaction with zonal wave 1 due to reflection dominating on the short time scale up to 12 days and the zonal mean due to wave mean flow interaction dominating on the longer time scale it is further shown that the two processes dominate during different years depending on the state of the stratosphere winters characterized by a basic state that is reflective for wave 1 show a strong relationship between stratospheric and tropospheric wave 1 fields when the stratosphere is leading and show no significant correlations in the zonal mean fields on the other hand winters characterized by a stratospheric state that does not reflect waves show a strong relat

parameterizing ocean eddy transports from surface to bottom 1 we consider new parameterization schemes for the extra transport velocity by eddies in a stratified fluid with particular emphasis on baroclinic instability these come in the form of elliptic equations previously unmentioned which we derive for the eddy induced overturning stream function they guarantee decrease of the mean field potential energy our principal example gives a relationship between the vertical shear of the overturning velocity and the buoyancy torque of the main geostrophic current the parameterized velocity is nonsingular at the bottom and the sea surface contrasting with previous constant coefficient theories based on depth diffusion idealized two dimensional numerical experiments successfully reproduce meridional overturning circulation even when the background density gradient is uniform everywhere the eady problem or when the bottom is steeply sloped we further demonstrate that adding an eddy form drag wave stress term in the trm momentum equations yields overturning of the velocity field

influence of the quasi biennial oscillation on the north pacific and el nino teleconnections 1 reanalysis and model data are used to study el nino southern oscillation enso teleconnections in the north pacific during boreal winter el nino events appear to have a significantly stronger teleconnection when the equatorial stratospheric quasi biennial oscillation qbo is in its westerly phase relative to its easterly phase at 70 hpa in both the reanalysis record and in the whole atmosphere community climate model the difference is much larger in the reanalysis however composites of easterly qbo at 70 hpa show an anomalous ridge over the north pacific which explains part of the weakening of el nino teleconnections associated with this ridge are easterly anomalies at the climatological subtropical jet position and westerly anomalies in the deep tropics a shallow water model linearized about such zonal wind anomalies gives a weaker extratropical response to a deep tropical vorticity anomaly suggesting a dynamical explanation of how the qbo can influence the extratropical response to anomalous enso convection these results suggest that modification of wave propagation is likely an important cause of the observed differences in el nino teleconnections between easterly and westerly qbo phases but sampling variability and differences in underlying tropical convection are also likely contributors

seismic imaging of the aftershock zone of the 2001 mw 7 7 bhuj earthquake india 1 detailed seismic tomography reveals that the 2001 mw 7 7 bhuj earthquake was associated with a 10 14 increase in vp and vs and a 10 decrease in vp vs in the 10 to 35 km depth range covering a 2750 km2 area beneath the aftershock zone this anomaly could be attributed to the existence of a lithological heterogeneity or a pluton of mafic composition that might have intruded during the rifting in early jurassic 160 ma the banni basin and the wagad uplift are found to be associated with high velocity intrusive bodies extending from 5 to 35 km depth a few patches of low vp and vs and high vp vs between 10 to 30 km depth have also been detected on the causative 45 south dipping north wagad fault nwf for the 2001 mainshock which may be attributed to a fluid filled fractured rock matrix

source rupture process of the 2004 chuetsu mid niigata prefecture japan earthquake inferred from waveform inversion with dense strong motion data abstract the kinematic source rupture process of the 2004 chuetsu mid niigata prefecture japan earthquake is estimated from strong motion data by the linear waveform inversion method in order to develop appropriate green s functions one dimensional velocity structure models for each station are constructed by modeling the aftershock waveforms the estimated top of the bedrock is deeper at the western side of the fault and relatively shallow at the eastern side this tendency coincides with other investigations of seismic tomography and microtremor array observations the obtained source model shows large slips in the vicinity of the hypocenter the reverse slipping rupture originated from the deeper part of the fault and propagated toward the up dip and southwest directions the near surface slip is small two tests are demonstrated to check the stability of the obtained source model the first test examines the effects of the number of available stations on the solution and the second test examines how the difference in the target waveform type affects the solution the number of stations affects the variation of slip amount and more than 12 stations appear to be sufficient to obtain a stable solution in this case the difference in the target wave type in the data set does not significantly affect the solution if the number of stations is sufficient and the green s functions are well calibrated the model obtained using calibrated velocity structure models shows clear image of high slip area compared to the model obtained using a single velocity structure model

eddy advective and diffusive transports of heat and salt in the southern ocean there are two distinct mechanisms by which eddies provide systematic transport of tracer on isopycnals the advective transport associated with the slumping of isopycnals and the diffusive transport associated with down gradient diffusion depending on the large scale tracer distribution eddy advective transport has either the same direction as or opposite direction to eddy diffusive transport as a consequence eddy advection and eddy diffusion can reinforce each other for some tracers but oppose each other for other tracers using scaling analysis it is argued that the relative directions of eddy advective and diffusive transports can be determined simply from the relative slopes of tracers and isopycnals an eddy resolving 1 12 global ocean model is used to illustrate the two eddy transport mechanisms for temperature and salinity in the southern ocean applications to other tracers such as oxygen are discussed the diagnosed eddy diffusivity for temperature and salinity is found to be considerably different from the eddy diffusivity for eddy advective transport velocity

a model of the zonally averaged stratification and overturning in the southern ocean the ocean area south of the antarctic circumpolar current acc frontal system is a region of major watermass modification influx of north atlantic deep water nadw small scale mixing eddy transport and diffusion as well as the fluxes of momentum and buoyancy at the sea surface combine in a complex array of processes to generate the unique stratification of the southern ocean with its southward uprising isopycnals and northward flux of antarctic intermediate water aaiw and antarctic bottom water comprehensive analytical models of this scenario are rare the authors develop and apply a model based on zonally and temporally averaged theory to explain the conversion of nadw into aaiw with all of the aforementioned processes contained in an extremely simplified way eddies appear via a transformed eulerian mean tem approach with a conventional downgradient parameterization of the meridional density flux the structure of the eddy coefficient is estimated from hydrographic and wind stress data by a simple inverse approach mixing is limited to a near surface layer and is treated in a most simple entrainment form the model determines the zonal mean density stratification in the southern ocean and the baroclinic transport of the acc from the applied wind stress and the surface density flux and unravels the role and importance of the different processes responsible for shaping the stratification ekman and eddy induced advection and pumping mixing surface buoyancy flux and eddy induced diffusion all of these processes must be present to yield an agreement between the simulated stratification and the observed one but details of their parameterization might not be too critical the acc transport is shown to have a contribution forced by the local wind stress as well as another contribution relating to the nonlocal forcing by wind stress and density flux over the entire antarctic zone

direct enso impact on east asian summer precipitation in the developing summer in the developing stage of enso the east asia summer precipitation easp shows a large variability that is significantly different from that in the decaying summer in this study we will focus on understanding the direct el nino impact on the precipitation over east asia in the developing summer in the observation it is found that in its developing summer the el nino sea surface temperature anomaly affects the easp directly from the eastern central tropical pacific with little interference from the rest of the global ocean the corresponding precipitation anomaly exhibits a tri pole pattern with two positive nodes in northeast and southeast china sandwiched by a negative node in northern central china the tri pole precipitation response is mainly attributed to the el nino induced cyclonic anomaly in northeast asia and the anticyclonic anomaly in the western north pacific which are part of the circulation anomalies of a circumglobal wave teleconnection in the subtropical jet in the northern hemisphere and a low level meridional wave train along east asia coast these circulation anomalies are generated by the summer el nino in three pathways 1 the vertical motion induced perturbation over the central eastern tropical pacific entering into the subtropical jet excites a circumglobal wave train propagation eastward along the jet 2 the el nino induced dipole heating across the equatorial maritime continent is mainly responsible for the meridional wave propagation along east asia coast 3 the el nino induced indirect heating over northwest india triggers another perturbation in the jet waveguide all contributing to the precipitation variation in east asia further demonstration indicates the atmospheric response to the el nino direct heating and perturbation over the tropical pacific has the major contribution to the el nino induced circulation anomaly as to the el nino indirect heating over northwset india a zonal wave train response in the upper midlatitude which is mainly confined in the eurasia sector makes a competing contribution to the circulation anomaly over east asia

transient response of an atmospheric gcm to north atlantic sst anomalies abstract a high resolution atmospheric general circulation model gcm is used to evaluate the atmospheric response to north atlantic sea surface temperature sst anomalies the transient evolution of the response is studied in detail the linear and nonlinear effects can thus be contrasted and separated by their different time scales baroclinic patterns related directly to the surface anomalies quickly reach their maximum manifestation however barotropic patterns related to the mid and upper troposphere eddy vorticity fluxes have longer time scales with much more important amplitude able to gradually replace the initial baroclinic response this study thus provides an evolutional picture of the two types of response in a gcm

an analysis of tropical instability waves in a numerical model of the pacific ocean 2 generation and energetics of the waves this work was supported by the department of com merce noaa under grant na56gp0026 one of the au thors sm was partially supported by a nasa global change fellowship ngt 30288 another author ab was supported by a ucar postdoctoral fellowship

circumglobal teleconnections the jet stream waveguide and the north atlantic oscillation abstract monthly and seasonally averaged upper tropospheric northern hemisphere winter fields are examined to determine whether the waveguiding effect of the time averaged tropospheric jets on low frequency disturbances that is predicted by theory does affect the behavior of these disturbances it is found that indeed disturbances in the vicinity of the mean jets particularly the jet that stretches across south asia are fundamentally different from those that reside in regions where the mean winds have weaker meridional gradients like the mid pacific patterns of variability in the jets tend to be smaller scale and to consist of zonally oriented chains of anomalies while variability in the mid pacific is composed of patterns with distinct meridional orientation because they are meridionally trapped and zonally elongated patterns associated with the jet stream waveguide connect activity at points that are much farther apart than do patterns in other regions of the globe within the south asian waveg

ground motion scaling in the kachchh basin india deduced from aftershocks of the 2001 mw 7 6 bhuj earthquake we studied the excitation propagation and site effects in the kachchh basin of india by using ground motion recordings from a temporary seismograph network deployed to study aftershocks of the m w 7 6 bhuj earthquake of 26 january 2001 the kachchh basin has been proposed as a useful analog region for studying hazard in other earthquake prone but slowly deforming regions such as the central united states the earthquakes we studied ranged in size from about m 2 to m 5 2 and travel paths ranged from a few kilometers to about a hundred kilometers there was a broad range of focal depths among the aftershocks so the data were divided into two overlapping subsets to test the sensitivity of the derived propagation and source parameters to focal depth parameters we constrained include the source excitation terms related to stress drop a frequency dependent attenuation operator a geometric spreading function and an operator to account for site effects our results indicate that seismic wave attenuation in kachchh crust is very low similar to other continental intraplate areas such as central and eastern north america we also estimated seismic moments and stress drops for the earthquakes by fitting single corner frequency source model spectra to the observed spectra corrected for propagation by using our derived parameters stress drops were found to scale with seismic moment and to be rather high overall by using a stochastic point source model to estimate mainshock ground motions we found that the distance decay of expected peak ground motions assuming a stress drop of 15 20 mpa compare well with the scant observations for the bhuj earthquake ground motion predictions for kachchh based on bhuj aftershock data support the idea that the region may have similar hazard to proposed analog areas in north america

direct impacts of different types of el nino in developing summer on east asian precipitation this study revisits the impacts of different types of el nino on east asian summer precipitation easp with observed and re analyzed data from 1958 to 2015 it focuses on the boreal summer preceding peaks of el nino when prominent sst anomalies are mainly situated in the tropical pacific distinct responses of easp are obtained for the three identified types of sst anomalies noted as summer ep eastern pacific el nino summer mp mixed type pacific el nino and summer cp central pacific el nino in the case of summer ep el nino there is a robust south north rainfall dipole with anomalous dry conditions in north china and wet conditions in southeast china such a rainfall pattern is mainly attributed to a low pressure anomaly over northeast asia for summer mp el nino it presents a tripolar pattern of precipitation anomalies with wetness along the yangtze huaihe river valley and dryness in both south and north china this is due to the presence of low pressure anomalies over northeast china and a westward shift of the western pacific subtropical high summer cp el nino shows a triangle pattern of precipitation anomalies with wet conditions in both southern and northern china but dry conditions in the jianghuai region north of the yangtze river in east china caused by low pressure anomalies over central north china further study investigates how different types of summer el nino induce different changes of the walker circulation and associated large scale convergence divergence outside the tropics and ultimately provoke different responses of atmospheric circulation for summer ep el nino tropical perturbations over the east central tropical pacific and over north india can enter into the subtropical jet and make a mid latitude low pressure belt response at upper levels of the atmosphere for summer mp el nino the perturbation over the east central tropical pacific seems ineffective in transmitting atmospheric anomalies to mid latitudes as a result they are mainly confined to the tropics and lead to a general rise of the upper level geopotential height over the entire tropics however the perturbation over northwest africa can excite northeastward propagating rossby waves in mid high latitudes for summer cp el nino the induced fluctuant wave train within the subtropical jet is likely the competing effect of perturbations over the east central tropical pacific north india and north africa furthermore for all the three types of summer el nino perturbations can trigger a similar low level meridional wave train along the east asian coast through the monsoon trough however a slight westward shift of the wave train makes a sensitive impact on easp

three dimensional ground motion modelling in the kachchh rift zone gujarat india abstract the strong motion dataset of the 6 april 2006 bhuj aftershock of mw5 5 from 16 three component accelerograph stations are used here to perform a detailed ground motion modelling in the kachchh rift basin first we estimate the 1 d velocity structure model down to the bedrock at 16 accelerograph sites through the genetic algorithm inversion of strong motion waveforms then a 3 d velocity structure model of the basin is constructed using the modelled 1 d velocity structure and constraints from earlier seismological vs30 estimation by ps logging and masw and seismic exploration studies in the region we modelled low frequency 0 1 1 hz ground motions excited by the 6 april 2006 event using the finite difference method fdm assuming a point source to access the robustness of the constructed velocity structure model at most of the stations the observed and simulated velocity waveforms are found to be in good agreement in terms of both amplitude and ground motion duration we also computed synthetic ground velocities at numerous locations within the basin for both the 2001 bhuj mainshock finite fault source and the 2006 aftershock point source cases using the 3 d velocity structure model for both the cases we notice significant amplifications of amplitudes and elongation of shaking at stations lying within the basin while smaller amplifications are noticed at stations away from the basin our fdm modelling for the 2001 bhuj mainshock at lower frequency

on the pressure gradient force over steep topography in sigma coordinate ocean models abstract the error in computing the pressure gradient force near steep topography using terms following coordinates is investigated in an ocean model using the family of vertical differencing schemes proposed by arakawa and suarez the truncation error is estimated by substituting known buoyancy profiles into the finite difference hydrostatic and pressure gradient terms the error due to hydrostatic inconsistency which is not simply a space truncation error is also documented the results show that the pressure gradient error is spread throughout the water column and it is sensitive to the vertical resolution and to the placement of the grid points relative to the vertical structure of the buoyancy field being modeled removing a reference state as suggested for the atmosphere by gary reduces the truncation error associated with the two lowest vertical modes by a factor of 2 to 3 as an example the error in computing the pressure gradient using a standard 10 level primitive equation model appl

recipe for predicting strong ground motion from crustal earthquake scenarios we developed a recipe for predicting strong ground motions based on a characterization of the source model for future crustal earthquakes from recent developments of waveform inversion of strong motion data used to estimate the rupture process we have inferred that strong ground motion is primarily related to the slip heterogeneity inside the source rather than average slip in the entire rupture area asperities are characterized as regions that have large slip relative to the average slip on the rupture area the asperity areas as well as the total rupture area scale with seismic moment we determined that the areas of strong motion generation approximately coincide with the asperity areas based on the scaling relationships the deductive source model for the prediction of strong ground motions is characterized by three kinds of parameters outer inner and extra fault parameters the outer fault parameters are defined as entire rupture area and total seismic moment the inner fault parameters are defined as slip heterogeneity inside the source area of asperities and stress drop on each asperity based on the multiple asperity model the pattern of rupture nucleation and termination are the extra fault parameters that are related to geomorphology of active faults we have examined the validity of the earthquake sources constructed by our recipe by comparing simulated and observed ground motions from recent inland crustal earthquakes such as the 1995 kobe and 2005 fukuoka earthquakes

low frequency variability of southern ocean jets both observations and high resolution numerical models show that the southern ocean circumpolar flow is concentrated in a large number approximately 8 to 12 of narrow filamentary jets it is shown here that coherent jets exhibit a range of low frequency variability on timescales of months to years that can lead to displacement and to intermittent formation and dissipation of jets using output from an eddy resolving ocean general circulation model in local regions near topographic features the impact of energy exchange between eddy and mean flow components on jet persistence and variability is examined a novel approach that uses a time dependent definition of the mean flow provides a clearer picture of eddy mean flow interactions in regions with spatially and temporally varying flow structure the dynamics are largely consistent with those in idealized quasi geostrophic models including topographically organized and surface enhanced reynolds stress forcing of the mean flow jets form during periods of enhanced eddy activity but may persist long after the eddy activity has decayed similarly jets may evolve in a downstream sense with jet formation localized near topography and undergoing modification in response to changing bathymetry the evolution of both temperature and potential vorticity is used to show that the low frequency variability of the jets impacts water mass structure and tracer transport this study highlights various examples of southern ocean dynamics that will prove difficult to capture through parameterizations in coarser climate models

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

the wind driven ocean circulation with an isopycnal thickness mixing parameterization abstract numerical solutions are examined for the nearly adiabatic large scale ocean circulation in a midlatitude rectangular domain with steady wind driving the model used is the balance equations and its various subsets hence dynamical effects at finite rossby number are included the solutions are steady ones and the necessary transports by the missing mesoscale eddies are parameterized in part using the authors previous proposal for isopycnally oriented mixing of tracers and isopycnal thickness or static stability this yields qualitatively credible quasi adiabatic solutions for realistic magnitudes for the subgrid scale transport coefficients among these solutions are ones with nearly homogeneous fields of potential vorticity on upper thermocline isopycnal surfaces even though the parameterized eddy mixing does not act directly to this end

toward real time regional earthquake simulation ii real time online earthquake simulation ros of taiwan earthquakes abstract we developed a real time online earthquake simulation system ros to simulate regional earthquakes in taiwan the ros uses a centroid moment tensor solution of seismic events from a real time moment tensor monitoring system rmt which provides all the point source parameters including the event origin time hypocentral location moment magnitude and focal mechanism within 2 min after the occurrence of an earthquake then all of the source parameters are automatically forwarded to the ros to perform an earthquake simulation which is based on a spectral element method sem a new island wide high resolution sem mesh model is developed for the whole taiwan in this study we have improved sem mesh quality by introducing a thin high resolution mesh layer near the surface to accommodate steep and rapidly varying topography the mesh for the shallow sedimentary basin is adjusted to reflect its complex geometry and sharp lateral velocity contrasts the grid resolution at the surface is about 545 m which is sufficient to resolve topography and tomography data for simulations accurate up to 1 0 hz the ros is also an infrastructural service making online earthquake simulation feasible users can conduct their own earthquake simulation by providing a set of source parameters through the ros webpage for visualization a shakemovie and shakemap are produced during the simulation the time needed for one event is roughly 3 min for a 70 s ground motion simulation the ros is operated online at the institute of earth sciences academia sinica http ros earth sinica edu tw our long term goal for the ros system is to contribute to public earth science outreach and to realize seismic ground motion prediction in real time

the statistical connection between tropospheric and stratospheric circulation of the northern hemisphere in winter abstract the associated anomaly patterns of the stratospheric geopotential height field and the tropospheric geopetential and temperature height fields of the northern hemisphere are determined applying the canonical correlation analysis with this linear multivariate technique the coupled modes of variability of lime series of two fields are isolated in the space of empirical orthogonal functions the one dataset is the 50 hpa geopotential height field the other set consists of different height fields of the tropospheric pressure levels 200 500 700 and 850 hpa and the temperature of the 850 hpa pressure level for the winter months december january february two natural coupled modes a barotropic and a baroclinic one of linear relationship between stratospheric and tropospheric circulation are found the baroclinic mode describes a connection between the strength of the stratospheric cyclonic winter vortex and the tropospheric circulation over the north atlantic the corresponding temperature

do tropical cells ventilate the indo pacific equatorial thermocline source waters of the indo pacific equatorial thermocline are studied with a high resolution ocean model in the annual mean fields tropical and subtropical overturning cells are found that upwell at the equator and downwell at 5 degrees and 20 degrees poleward of the equator respectively tropical cells are common in ocean models but their role in ventilating the equatorial thermocline is obscure because the downwelled water is too warm to match the subsurface equatorial waters the tropical cells are much weaker when the overturning is considered in density coordinates when high frequency mass fluxes are included tropical cells are compensated by an eddy induced overturning seasonal variations and tropical instability waves are responsible for the compensation it follows that only subtropical cells transfer surface water to the equatorial thermocline strong tropical cells are shown to be an artefact

2001 bhuj india earthquake engineering seismoscope recordings and eastern north america ground motion attenuation relations engineering seismoscope data collected at distances less than 300 km for the m 7 7 bhuj india mainshock are compatible with ground motion attenuation in eastern north america ena the mainshock ground motion data have been corrected to a common geological site condition using the factors of joyner and boore 2000 and a classification scheme of quaternary or tertiary sediments or rock we then compare these data to ena ground motion attenuation relations despite uncertainties in recording method geological site corrections common tectonic setting and the amount of regional seismic attenuation the corrected bhuj dataset agrees with the collective predictions by ena ground motion attenuation relations within a factor of 2 this level of agreement is within the dataset uncertainties and the normal variance for recorded earthquake ground motions

the dynamics of the antarctic circumpolar current abstract the dynamics of the antarctic circumpolar current acc in a near eddy resolving model of the southern ocean fram are investigated a streamwise coordinate system is used rather than a more conventional approach of considering zonally averaged quantities the motivation for this approach is the large deviation from a purely zonal flow made by the current comparisons are made with a zonal mean analysis of the same model it is found that the topographic form drag is the main sink of the momentum that is input by the wind however in contrast to a zonal mean analysis other terms namely horizontal mixing bottom friction and advection of momentum are no longer negligible the total effect of transient eddies is to produce a drag on the mean flow again in contrast to the zonally averaged case the vertical penetration of stress is considered a generalized formula is derived for the interfacial form stress averaged along a convoluted path and that includes nonquasigeostrophic effects the i

a numerical study on the successive formation of meddy like lenses 1 we present a process study on the sustaining mechanism of lens formation using a series of numerical experiments of a density current over a sloping bottom with a cape along the coastline water parcels in the bottom density current are shed into the offshore region leading to periodic formation of anticyclonic lenses as part of baroclinic dipolar vortices the cyclonic partner is more prominent at the surface and the coupled vortices are carried by the mean current established in the offshore region parameter dependence of dipole generation is examined which suggests that the background current is necessary for the detached eddies to be coherent in the downstream direction and for shedding events to repeat nof and pichevin 1996 it is also shown that the density mixing of the bottom current provides criteria for cyclogenesis at the sea surface a detailed analysis is given by a five layer model forced by a water mass source sink which reproduces the baroclinic dipolar vortices similar to those observed in the preceding z coordinate model we find that the dipole generation is due to the finite amplitude divergence convergence of the baroclinic current passing the cape stern and chassignet 2000 the overall analyses suggest three necessary conditions for successive eddy formation 1 a localized variation in the coastline causing the finite amplitude disturbance 2 mixing of mediterranean water with the surrounding fluids leading to anticyclonic rotation of meddies as well as cyclogenesis at the surface and 3 background currents that advect the detached vortices out of the source region index terms 4255 oceanography general numerical modeling 4219 oceanography general continental shelf processes 4520 oceanography physical eddies and mesoscale processes 4528 oceanography physical fronts and jets keywords eddy shedding dense water plume numerical simulation

eddy dynamics in a primitive equation model sensitivity to horizontal resolution and friction a primitive equation model of an idealized ocean basin driven by simple study wind and buoyancy forcing at the surface is used to study the dynamics of mesoscale eddies model statistics of a six year integration using a fine grid 1 6 0 2 with reduced coefficients of horizontal friction are compared to those using a coarser grid 1 3 0 4 but otherwise identical configuration eddy generation in both model cases is primarily due to the release of mean potential energy by baroclinic instability horizontal reynolds stresses become significant near the midlatitude jet of the fine grid case with a tendency for preferred energy transfers from the eddies to the mean flow using the finer resolution eddy kinetic energy nearly doubles at the surface of the subtropical gyre and increases by factors of 3 4 over the jet region and in higher latitudes the spatial characteristics of the mesoscale fluctuations are examined by calculating zonal wavenumber spectra and velocity autocorrelation functions with the higher resolution the dominant eddy scale remains approximately the same in the subtropical gyre but decreases by a factor of 2 in the subpolar areas the wavenumber spectra indicate a strong influence of the model friction in the coarse grid case especially in higher latitudes using the coarse grid there is almost no separation between the energetic eddy scale and the scale where friction begins to dominate leading to steep spectra beyond the cutoff wavenumber using the finer resolution an inertial subrange with a k 3 power law begins to emerge in all model regions outside the equatorial belt despite the large increase of eddy intensity in the fine grid model effects on the mean northward transport of heat are negligible strong eddy fluxes of heat across the midlatitude jet are almost exactly compensated by changes of the heat transport due to the mean flow

on the changing nature of the regional connection between the north atlantic oscillation and sea surface temperature 1 evidence is presented that the correlation between the north atlantic oscillation nao in terms of the nao index and the north atlantic sea surface temperature sst is not stationary this is inferred from both reanalysis data from the u s national centers for environmental prediction national center for atmospheric research ncep ncar and the kaplan sea surface temperature data set two phases of winterly north atlantic atmosphere ocean covariability are identified by means of linear regression and correlation analysis during the recent decades since the late 1960s early 1970s and during the first 3 decades of the twentieth century the north atlantic sst is strongly correlated to the regional atmospheric circulation in the north atlantic sector i e the north atlantic oscillation during these periods the nao index defined as the difference of normalized sea level pressures on the azores and iceland is characterized by pronounced decadal variability and by mainly positive values in contrast the nao index is only weakly correlated to the north atlantic sst from the 1930s to the early 1960s when the nao index is characterized by weak decadal variability remote influences in particular from the tropical pacific region become important especially for the sst in the western tropical north atlantic

direct impact of el nino on east asian summer precipitation in the observation this study investigates the direct impact of el nino in the tropical pacific on the east asian summer precipitation generalized equilibrium feedback assessment is used to isolate this direct impact from interrelated ocean forcings in the observations results indicate that the el nino can directly influence the summer precipitation in east china significantly the precipitation response presents a tri pole pattern with anomalous wet in the southeast and the northeast china and anomalous dry in the northern china amplitude of the precipitation response is around 20 of the total precipitation for 1 c el nino forcing in most area of the east china with maximal response up to 30 c the tri pole precipitation response is attributed to an el nino induced cyclonic anomaly in the northeast asia and an anticyclonic anomaly in the western north pacific wnp the anomalous cyclone deepens the east asian trough southwestward favoring an air ascending in front of the trough in the southeast and the northeast china and an air descending at the rear of the trough in the northern china the anomalous anticyclone in the wnp strengthens the wnp subtropical high northeastward providing adequate water vapor to the southeast china the anomalous cyclone and anomalous anticyclone work together to generate the tri pole precipitation response pattern in the east china further investigation suggests that these two key anomalous circulations are part of a northwestward propagating rossby wave which is excited by the el nino warming induced convection over the subtropical west central pacific this study can serve as a reference for the prediction of the east asian precipitation in both the developing and decaying summer of el nino

north pacific north atlantic relationships under stratospheric control 1 based on a linear regression correlation analysis of monthly mean atmospheric sea level pressure slp data from the national centers for environmental prediction ncep reanalysis 1948 2000 we find a significant anticorrelation between pressure in the northern north atlantic and north pacific only if the stratospheric circulation is in the strong polar vortex regime but not when the vortex is weak since some general circulation models gcms e g european center hamburg echam4 are biased toward the strong vortex regime svr they tend to reproduce this anticorrelation already in the mean the pattern of the arctic oscillation ao is shown to be consistent with the mean surface pressure differences between the two stratospheric regimes the typical sw ne tilt of the node line of the north atlantic oscillation nao found with linear analyses i e with such that do not take the regime character of the stratospheric circulation into account in northern hemisphere winter is due to a superposition of correlation patterns based on physical processes working in the troposphere a strictly meridional dipole and the pattern resulting from planetary wave refraction in the strong vortex regime and those produced by the rapid transition from one stratospheric regime to the other with subsequent downward propagation of the signal this result underlines the necessity of the application of nonlinear statistics or the restriction of linear statistics to variations in the stable quasi linear environment of natural regimes

bulk sediment qp and qs in the mississippi embayment central united states we have estimated p wave ands wave anelastic attenuation coefficients for the thick unconsolidated sediments of the mississippi embayment central united states using the spectral distance decay of explosion p and rayleigh waves the sediment trapped p wave psed is observed to ranges of 80 km at 10 hz and 1 hz rayleigh waves are observed out to 130 km from a 5000 lb borehole explosion in the northern part of the embayment rayleigh waves of 4 hz are seen to distances of 3 km from a smaller 50 lb explosion analysis of the group velocity and amplitude distance decay of both waves yields an average qs of 100 and qp of 200 for embay ment sediments that are independent of frequency scatter in the q estimates comes from interference of multiple p wave reverberations and rayleigh wave modes the attenuation model is self consistent in that it is the same as obtained by the analysis of synthetic seismograms using the inferred q values inferred qp and qs values are more than three times higher than previous estimates and imply that unconsolidated sediments of the embayment do not significantly attenuate small strain earthquake ground motions these estimates represent a lower bound to q of the sediments since significant scattering is observed in the waveform data that contributes to the distance decay of wave amplitude higher q values also imply that the unconsolidated sedi ments of the embayment will form an efficient wave guide for surface waves radiated from shallow earthquakes or large earthquakes that rupture into the sediments pro ducing high amplitude long duration wave trains that should be considered in earth quake hazard assessments

the central pacific as the export region of the el nino southern oscillation sea surface temperature anomaly to antarctic sea ice 1 in the mature season of el nino rossby waves do not easily propagate into the polar region and the seasonal climatology of sea ice is minimal austral summer is a barrier to the persistent antarctic dipole pattern adp in sea ice the sea surface temperature sst anomaly of central pacific type el nino cp el nino in the central pacific contributes to a strong rossby wave response and weakening of the polar front jet that yields strong adp in austral spring just before the adp barrier the strong adp produces intensive sea ice air feedback which allows the adp anomaly to breach the barrier in the conventional el nino ep el nino events the upper level structure cannot contribute to the strong anomalous high pressure in ep el nino events the anomalous high in the bellingshausen sea is replaced by an anomalous low after the austral autumn following the mature season whereas the anomalous high pressure persists up to the austral winter in the cp el nino in the cp el nino the adp persists until austral winter after the mature season of el nino whereas in the ep el nino it does not persist after austral summer the central pacific cold sst anomaly of la nina together with the seasonal sst climatology prolongs the opposite phase of the adp anomaly up to the austral winter consequently the tropical climate anomaly is exported to extratropics at the central pacific in the southern hemisphere

characteristics of deformation and past seismicity associated with the 1819 kutch earthquake northwestern india the 1819 earthquake in kutch northwestern india is one of the most significant events to have occurred in a plate interior setting despite being the second largest among the stable continental region scr earthquakes this event has not been analyzed within the context of present day understanding of earthquake seismology coseismic changes related to this earthquake include massive ground deformation in a wide low lying tidal flat area although detailed historic accounts of this earthquake exist many questions regarding the mode of deformation and the seismic history of the region remain unresolved we explored the region nearly 180 years after the earthquake and the information gathered adds to our understanding of this event and provides a fresh perspective on this unique intraplate seismogenic zone a 90 km long tract of elevated land with a peak height of 4 3 m is the most visible surface expression of this earthquake we surveyed and analyzed the morphological features of this scarp and also carried out exploratory trenching in this region the scarp morphology is suggestive of a growing fold related to a buried north dipping thrust rather than a discrete fault that could have resulted from a surface rupture the extensive liquefaction field associated with the earthquake offered an ideal setting to explore the paleoearthquake history age data of liquefaction features suggest that a previous event of comparable size must have occurred 800 1000 years ago seismic activity appears to be related to the reactivation of an ancient rift in a stress regime that is dominated by nearly north south compression

estimation of sedimentary thickness in kachchh basin gujarat using sp converted phase an inexpensive method using natural earthquake data is utilized for determining the sedimentary thickness in kachchh the institute of seismological research isr is operating a network of broadband seismographs and strong motion accelerographs in gujarat we used data from 13 broadband seismographs and two strong motion accelerographs in the study the stations are within 5 to 80 km from the epicenters in this study the s to p converted phase sp is used this phase is generated due to large impedance contrast between sediments and basement this phase is clear in the vertical component the difference in the travel times of s and sp phases and velocities of p and s waves is used for determining the sedimentary layer thickness the thickness of sediments beneath each of these 15 stations was determined covering an area of 23 500 sq km

observational constraints on the tropospheric and near surface winter signature of the northern hemisphere stratospheric polar vortex a composite analysis of northern hemisphere s mid winter tropospheric anomalies under the conditions of strong and weak stratospheric polar vortex was performed on ncep ncar reanalysis data from 1948 to 2013 considering as additional grouping criteria the coincidental states of major seasonally relevant climate phenomena such as el nino southern oscillation enso quasi biennial oscillation and strong volcanic eruptions the analysis reveals that samples of strong polar vortex nearly exclusively occur during cold enso states while a weak polar vortex is observed for both cold and warm enso the strongest tropospheric and near surface anomalies are found for warm enso and weak polar vortex conditions suggesting that internal tropospheric circulation anomalies related to warm enso constructively superpose on dynamical effects from the stratosphere additionally substantial differences are found between the continental winter warming patterns under strong polar vortex conditions in volcanically disturbed and volcanically undisturbed winters however the small size samples obtained from the multi compositing prevent conclusive statements about typical patterns dominating effects and mechanisms of stratosphere troposphere interaction on the seasonal time scale based on observational reanalysis data alone hence our analysis demonstrates that patterns derived from observational reanalysis time series need to be taken with caution as they not always provide sufficiently robust constraints to the inferred mechanisms implicated with stratospheric polar vortex variability and its tropospheric and near surface signature notwithstanding this argument we propose a limited set of mechanisms that together may explain a relevant part of observed climate variability these may serve to define future numerical model experiments minimizing the sample biases and thus improving process understanding

roles of mesoscale eddies in the kuroshio paths a high resolution ocean general circulation model is developed to simulate connections between the kuroshio path variations and mesoscale eddy activities as realistically as possible the climatological mean of the modeled kuroshio takes a nearshore nonlarge meander path it is found that the model is capable of simulating two types of nonlarge meander state and a possible version of the large meander state the offshore nonlarge meander is generated through interaction between the kuroshio and an anticyclonic eddy the large meander occurs just after significant intensification of the anticyclonic kuroshio recirculation successive intrusion of anticyclonic eddies from the upstream region is responsible for this process those anticyclonic eddies are advected by the kuroshio from the region northeast of luzon island and increase the upstream kuroshio volume transport on an interannual time scale the cyclonic eddies propagating from the kuroshio extension region on the other hand weaken the kuroshio meander after the merger the kuroshio path variations south of japan thus seem to be closely related to eddy activities in the subtropical gyre system

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

sediment thicknesses and qs vs qp relations in the kachchh rift basin gujarat india using sp converted phases delineation of the top sedimentary structure and its qs vs qp relationship using the travel time difference of direct s and converted sp phase is key to understanding the seismic hazard of any sedimentary basin area we constructed filtered displacement waveforms from local etna episensor acceleration recordings as well as local velocity recordings of aftershocks of the 2001 bhuj earthquake recorded by the kachchh seismological network of the national geophysical research institute ngri hyderabad india during 2001 2004 stations are within 15 70km of epicenters and the resulting displacement waveforms are generally simple displaying prominent p sp and s wave pulses particle motion of p and s waves suggest near vertical raypaths consistent with preliminary depth estimates the direct s wave on the horizontal component is characterized by lower frequency content than the converted sp phase on the vertical component this difference in frequency content between s and sp phases can be explained in terms of different attenuation effects for p and s waves in the unconsolidated sediments the sp phase is generated by s to p phase conversion at the base of mesozoic sediments of the kachchh basin travel time inversion velest of 2565 p and 2380 s arrivals from 658 well located aftershocks recorded at 8 14 three component local seismic stations led to 1 d velocity models indicated very slow sediments in the upper 0 2 km depth range vp 2 92 km s and vs 0 90 km s and an increasing trend of velocities with depth at 2 40 km depth the estimated sediment thicknesses beneath 12 accelerograph and 6 seismograph sites from the estimated velocity model and the travel time difference between s and converted sp phases reaches a maximum of 1 534 0 117 km beneath bandri near the location of 2001 bhuj mainshock and attains a minimum sediment thickness of 0 858 0 104 km beneath ramvav and burudia the spectral ratios between sp and s from 159 three component accelerograms have been used to study seismic wave attenuation in the kachchh rift basin the estimated qs vs qp relations for 12 accelerograph sites vary from qs 0 184 qp at chobari to qs 0 505 qp at dudhai for stations chobari chopdwa jahawarnagar vondh and tapar the spectral ratio slopes and hence the calculated qs vs qp relations are effectively the same and the correlation coefficients are quite high 0 91 0 93 stations adhoi manfara new dudhai dudhai and sikara have similar qs vs qp relationships to each other and also have high correlation coefficients 0 78 0 87 the spectral ratios for stations anjar and ramvav are small and poorly constrained resulting in less reliable qs vs qp relations this could be due to noisy data fewer available waveforms or scattering due to velocity heterogeneities and or interface irregularities

a possible origin of intraplate earthquakes in the kachchh rift zone india since the 2001 mw7 7 bhuj earthquake abstract we herein use the joint inversion of p receiver functions and fundamental mode group velocity dispersion data 9 70 s of rayleigh and love waves to estimate crustal and lithospheric thicknesses at twenty three component mobile broadband stations in kachchh gujarat modeled moho depths range from 35 to 43 km while lithospheric thicknesses vary from 64 to 106 km the main result of our modelling is the delineation of a marked crustal 2 4 km as well as lithospheric 10 20 km thinning and a 2 6 drop in vs across the lithosphere asthenosphere boundary lab within the samkhiali graben associated with gravity high underlying the central kachchh rift zone krz where 95 of the continued aftershock activity took place since 2001 such a large drop in vs could be attributed to the presence of carbonatite melts in the upper mantle our modeling reveals a 4 km crustal thinning below the central krz and a 4 km crustal thickening below the surrounding riftless regions this kind of crustal structure is inferred to induce large flexural deviatoric stresses 50 100 mpa in the upper crust thereby these stresses in the presence of regional plate tectonic stresses can bring the samkhiali graben below the central krz near to the critical stress level while stress transfer meteoric water in the upper crust and metamorphic fluid as well volatile co2 flows in the lower crust provide the required triggering effect to the critically stressed graben structure down to 35 km depth for generating continued aftershock activity in the kachchh rift zone since 2001 we also propose that the deeper circulation of volatile co2 through the inferred conduit related to the 65 ma deccan plume activity extending from lower crust down to asthenosphere plays a key role in the generation of uninterrupted occurrence of earthquakes in the kachchh rift zone gujarat india

the 26 january 2001 m 7 6 bhuj india earthquake observed and predicted ground motions although local and regional instrumental recordings of the devastating 26 january 2001 bhuj earthquake are sparse the distribution of macroseismic effects can provide important constraints on the mainshock ground motions we compiled available news accounts describing damage and other effects and interpreted them to obtain modified mercalli intensities mmis at 200 locations throughout the indian subcontinent these values are then used to map the intensity distribution throughout the subcontinent using a simple mathematical interpolation method although preliminary the maps reveal several interesting features within the kachchh region the most heavily damaged villages are concentrated toward the western edge of the inferred fault consistent with western directivity significant sediment induced amplification is also suggested at a number of locations around the gulf of kachchh to the south of the epicenter away from the kachchh region intensities were clearly amplified significantly in areas that are along rivers within deltas or on coastal alluvium such as mudflats and salt pans in addition we use fault rupture parameters inferred from teleseismic data to predict shaking intensity at distances of 0 1000 km we then convert the predicted hard rock ground motion parameters to mmi by using a relationship derived from internet based intensity surveys that assigns mmi based on the average effects in a region the predicted mmis are typically lower by 1 3 units than those estimated from news accounts although they do predict near field ground motions of approximately 80 g and potentially damaging ground motions on hard rock sites to distances of approximately 300 km for the most part this discrepancy is consistent with the expected effect of sediment response but it could also reflect other factors such as unusually high building vulnerability in the bhuj region and a tendency for media accounts to focus on the most dramatic damage rather than the average effects the discrepancy may also be partly attributable to the inadequacy of the empirical relationship between mmi and peak ground acceleration pga when applied to india the mmi pga relationship was developed using data from california earthquakes which might have a systematically different stress drop and therefore a different frequency content than intraplate events when a relationship between response spectra and mmi is used we obtain larger predicted mmi values in better agreement with the observations

isopycnal mixing in ocean circulation models abstract a subgrid scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non eddy resolving ocean circulation models the mixing is applied in isopycnal coordinates to isopycnal layer thickness or inverse density gradient as well as to passive scalars temperature and salinity the transformation of these mixing forms to physical coordinates is also presented

westward motion of mesoscale eddies abstract since the pioneering work of nof the determination of the westward drift of mesoscale eddies under the planetary beta effect has been a recurrent theme in mesoscale oceanography and several different formulae have been proposed in the literature here recpatiulation is sought and within the confines of a single layer model a generalized formula is derived although it is similar to nof s the present formula is established from a modified definition and with fewer assumptions it also recaptiulates all other formulae for the one layer model and applies to a wide variety of situations including cases when the vortex develops a wake of rossby waves or undergoes axismmetrization following the derivation of the formula a physical interpretation clarifies the migration mechanism which can be divided between a self induced propulsion and a reaction from the displaced ambient fluid numerical simulations with primitive and geostrophic equations validate the formula for a variety of length sc

characterization of the causative fault system for the 2001 bhuj earthquake of mw 7 7 abstract precise hypocenters erh m w 2 0 5 3 delineate a east west trending blind thrust dipping 45 towards south named as north wagad fault nwf about 25 km north of kachchh main land fault kmf as the causative fault for the 2001 bhuj earthquake of m w 7 7 the aftershock zone involves a crustal volume of 60 40 35 km 3 lying between kmf and nwf the waveform inversion of 45 aftershocks of m 3 0 5 3 suggest that the e w trending south dipping reverse faulting mainly characterizes the aftershock zone however some reverse faulting along nw se as well as ne sw planes and some strike slip faulting along nw se trending vertical plane are also noticed the estimated p axes point on an average towards n s while t axes orient in e w agreeing well with the prevailing regional plate tectonic stress directions the estimated velocity model from one dimensional inversion of 8000 p and 5000 s travel times from 600 aftershocks deciphers a detailed crustal structure of the region upper 0 6 km on an average suggests a low velocity zone characterizing the jurassic and younger sediments the depth range 6 42 km is characterized on an average by larger values of v p 6 31 to 6 98 km s with an average of 6 71 km s v s 3 64 to 4 05 km s with an average of 3 85 km s and v p v s 1 69 to 1 81 with an average of 1 75 the high crustal velocities can be attributed to the existence of a high velocity mafic intrusive rift pillow structure beneath the region probably emplaced during the rifting time this brittle competent high velocity zone beneath the epicentral area in response to the compression due to the northward movement of the indian plate could induce sufficient local stress perturbation for generating large intraplate earthquakes of m w 7 5 in the lower crust further within the overall higher velocity depth range a layer characterized by large values of v p 6 98 km s v s 3 854 km s and v p v s 1 81 is found in the depth range of 20 5 30 km which is inferred to be fractured and saturated high crack density and probably fluid filled presence of numerous fractures in this layer is confirmed by a high b value 0 75 1 1 in this layer this layer might have facilitated the nucleation process of the 2001 bhuj earthquake the major rupture and 47 of the aftershocks have occurred within this layer

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

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

energetics of eddy mean flow interactions in the gulf stream region a detailed energetics analysis of the gulf stream gs and associated eddies is performed using a highresolution multidecadal regional ocean model simulation the energy equations for the time mean and timevaryingflowsarederivedasatheoreticalframeworkfortheanalysis theeddy meanflowenergycomponents and their conversions show complex spatial distributions in the along coast region the cross stream and cross bump variations are seen in the eddy mean flow energy conversions whereas in the off coast region a mixed positive negative conversion pattern is observed the local variations of the eddy mean flow interaction are influenced by the varying bottom topography when considering the domain averaged energetics theeddy meanflowinteractionshowssignificantalong streamvariability upstreamofcapehatteras the energy is mainly transferred from the mean flow to the eddy field through barotropic and baroclinic instabilities upon separating from the coast the gs becomes highly unstable and both energy conversions intensify when the gs flows into the off coast region an inverse conversion from the eddy field to the mean flow dominates the power transfer for the entire gs region the mean current is intrinsically unstable and transfers 28 26gw of kinetic energy and 26 80gw of available potential energy to the eddy field the mesoscaleeddykineticenergyisgeneratedbymixedbarotropicandbaroclinicinstabilities contributing28 26 and 9 15gw respectively beyond directly supplying the barotropic pathway mean kinetic energy also provides 11 55gw of power to mean available potential energy and subsequently facilitates the baroclinic instability pathway

dependence of the structure of the northern hemisphere annular mode on the polarity of enso 1 the structure of the northern hemisphere annular mode nam is shown to be significantly different during warm and cold winters of the enso cycle during warm winters the arctic center of action of the annular mode is more prominent and extends deeper into siberia its related surface air temperature signal is stronger and the compensating outer ring in the sea level pressure field is much broader encompassing the entire tropics during cold winters the nam signature is much more pronounced over the pacific sector the sea level pressure pattern exhibits a north pacific center of action positively correlated with the atlantic center and pronounced deflections of the storm track are also evident it is suggested that the former features are associated with the equatorward displacement of the jet stream and the storm tracks during warm winters of the enso cycle and the latter is related to the the more pronounced break in the subtropical jet stream over the pacific sector during cold winters

energetics of the global ocean the role of layer thickness form drag abstract understanding the role of mesoscale eddies in the global ocean is fundamental to gaining insight into the factors that control the strength of the circulation this paper presents results of an analysis of a high resolution numerical simulation in particular the authors perform an analysis of energetics in density space such an approach clearly demonstrates the role of layer thickness form drag residual effects of hydrostatic pressure perturbations which is hidden in the classical analysis of the energetics of flows for the first time in oceanic studies the global distribution of layer thickness form drag is determined this study provides direct evidence to verify some basic characteristics of layer thickness form drag that have often been assumed or speculated about in previous theoretical studies the results justify most of the previous assumptions and speculations including those associated with i the presence of an oceanic energy cycle explaining the relationship between layer th

the surface branch of the zonally averaged mass transport circulation in the troposphere the near surface branch of the overturning mass transport circulation in the troposphere containing the equatorward flow is examined in isentropic and geometric coordinates a discussion of the zonal momentum balance within isentropic layers shows that the equatorward flow at a given latitude is confined to isentropic layers that typically intersect the surface at that latitude as a consequence of mass transport within the surface mixed layer much of the equatorward flow occurs in layers with potential temperatures below the mean surface potential temperature in the conventional transformed eulerian mean formulation for geometric coordinates the surface branch of the overturning circulation is represented in an unrealistic manner streamlines of the residual circulation do not close above the surface a modified residual circulation is introduced that is free from this defect and has the additional advantage that its computation unlike that of the conventional residual circulation does not require division by the static stability which may approach zero in the planetary boundary layer it is then argued that cold air advection by the residual circulation is responsible for the formation of surface inversions at all latitudes in idealized gcms with weak thermal damping also included is a discussion of how a general circulation theory for the troposphere must be built upon a theory for the near surface meridional mass fluxes

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

characterizing surface geology liquefaction potential and maximum intensity in the kachchh seismic zone western india through microtremor analysis abstract this study presents results of microtremor analysis carried out over diverse geological formations and liquefaction sites in the kachchh seismic zone of western india which is host to the deadliest intraplate earthquake m w 7 7 microtremors were recorded at 36 sites with single stations and 7 sites with an array the microtremor array measurements were made using triangular arrays with sensors kept at 30 90 m radii the rayleigh wave velocities are estimated from the array data using high resolution frequency wavenumber f k analysis and the 1d shear wave velocity structure is determined by inversion we found a good correlation between surface geology resonant frequency and amplitude of the horizontal to vertical spectral ratio hvsr curve and shear wave velocity the ground vulnerability index k g values in the liquefied areas are found to be higher than those in the adjacent areas devoid of liquefaction broad or multiple peaks in the hvsr curves and large variations in the shear velocity models could be attributable to the structural and tectonic complexity in the maximum intensity area further our results show that the average fundamental frequencies are around 0 32 hz for the quaternary 0 80 hz for tertiary 1 8 hz for cretaceous 1 8 hz for jurassic and 2 3 hz for the deccan trap formations the inverted s wave velocity varies from 190 to 1350 m s down to a depth of 200 m for the quaternary 220 to 680 m s down to 100 m for tertiary 236 to 1160 m s for cretaceous 670 to 1780 m s for jurassic and 260 to 2440 m s for the deccan trap sites the results of microtremor analysis corroborate the observations from the available geophysical geological and borehole data

on the driving processes of the atlantic meridional overturning circulation because of its relevance for the global climate the atlantic meridional overturning circulation amoc has been a major research focus for many years yet the question of which physical mechanisms ultimately drive the amoc in the sense of providing its energy supply remains a matter of controversy here we review both observational data and model results concerning the two main candidates vertical mixing processes in the ocean s interior and wind induced ekman upwelling in the southern ocean in distinction to the energy source we also discuss the role of surface heat and freshwater fluxes which influence the volume transport of the meridional overturning circulation and shape its spatial circulation pattern without actually supplying energy to the overturning itself in steady state we conclude that both wind driven upwelling and vertical mixing are likely contributing to driving the observed circulation to quantify their respective contributions future research needs to address some open questions which we outline

isopycnal averaging at constant height part i the formulation and a case study simple eulerian averaging of velocities density and tracers at constant position is the most natural way of averaging however eulerian averaging gives incorrect watermass distributions and properties as well as spurious diabatic circulations such as the deacon cell instead of averaging at constant height averaging along isopycnals removes such fictitious mixing and diabatic circulations such isopycnal averaging is normally performed at constant latitude that is averaging along isopynals as they heave up and down as a result height information is lost and the sea surface becomes much warmer or lighter than with simple eulerian averaging in fact averaging can be performed along arbitrarily aligned surfaces this study considers a particular case in which isopycnal averaging is performed at constant height thus this new isopycnal averaging follows isopycnals as they meander horizontally at constant z height information is now retained at the cost of losing latitudinal information the advantage of this averaging is that it avoids the problem of giving a surface that is too warm associated with this new isopycnal averaging a vertical transport streamfunction in r z space can be defined in analogy to the conventional meridional overturning streamfunction in y r space here in part i this constant height isopycnal averaging is explained and illustrated in an idealized zonal channel model in part ii the relationship between the two different isopycnal averagings and the eulerian mean eddy flux divergence is explored

rupture process of the 26 january 2001 mw 7 6 bhuj india earthquake from teleseismic broadband data we investigate the rupture process of the 26 january 2001 bhuj india m w 7 6 earthquake through inversion of teleseismic broadband body waves this earthquake ranks as one of the most important recent events due to its occurrence within a stable continental interior where such events are rare the bhuj earthquake occurred on a moderately dipping blind thrust fault within an ancient failed rift about 70 of the seismic moment released in the earthquake was confined to a very small area 375 km2 surrounding the hypocenter and at depths below 12 km the static stress drop of the bhuj earthquake is anomalously high 20 mpa the source time history of the event indicates very rapid onset to the moment release and most likely high slip velocities within the deep asperity this suggests that some of the damage near the epicenter may have been caused by anomalously high frequency ground motions the teleseismic data also indicate the presence of a second area of large slip in the shallow part of the bhuj fault although the depth extent of this shallow large slip area is not resolved comparisons of the predicted ground motions with observed intensities suggest that substantial slip occurred in the upper 10 km of the fault in order to explain the distribution of high intensities to the west and northwest of the fault the upper surface layers near the bhuj fault consist of unconsolidated low rigidity sediments and alluvium the upper 10 km of the bhuj fault may therefore be in a conditionally stable region that normally deforms through aseismic creep and can sustain seismic rupture only when dynamically stressed by rupture of the high strength deep asperity we suggest that this deep asperity may be related to a lithologic anomaly of ultramafic composition

source parameters of the anjar earthquake of july 21 1956 india and its seismotectonic implications for the kutch rift basin abstract the kutch rift basin is a major seismic region in india characterized by a low earthquake occurrence rate but a very high maximum intensity the largest event in the region is the great kutch earthquake of 1819 estimated m w 7 8 however lacking instrumental data its exact source parameters are not well known the anjar or rann of kutch earthquake of july 21 1956 m w 6 0 took place very close to the 1819 kutch event and caused considerable damage and casualties our modeled waveforms of teleseismic p and sh waves and p wave first motions determine a reverse faulting mechanism strike 235 dip 46 5 and rake 85 as well as source parameters for the anjar earthquake a previous strike slip mechanism for this event has been eliminated on the basis of waveform constraints the two nodal planes of our solution both strike northeast sub parallel to the trend of the kutch rift very close to the trend of the isoseismals the seismic moment is 1 19 10 25 dyne cm the focal depth and the stress drop are 15 km and 162 bar respectively the anjar reverse fault may represent a reactivated normal fault undergoing tectonic inversion in the kutch rift zone under present day compressional stress two larger earthquakes adjacent to anjar but outside of the kutch rift are also found to be mainly reverse faulting with a minor strike slip component judging from available information the great kutch event of 1819 is most likely a reverse faulting event

the deadliest intraplate earthquake the recent earthquake in the bhuj region took a toll of at least 30 000 lives in their perspective gupta et al 1 discuss what may be the cause of the large but infrequent earthquakes in this region which is not near any tectonic plate boundary the earthquake hazard in the region was well recognized before the disaster however and adherence to the building codes for high risk areas may have prevented much human tragedy 1 http www sciencemag org cgi content full 291 5511 2101

isopycnal momentum budget of the antarctic circumpolar current in the fine resolution antarctic model abstract the momentum budget of the antarctic circumpolar current acc is analyzed using data from the fine resolution antarctic model fram using density as a vertical coordinate since density is approximately conserved on streamlines this steady budget is balanced volume heat and salt budgets are also computed within density layers although these remain time dependent the leading order momentum balance is of approximate equality of the form drag on the top and bottom surfaces of each undulating density layer but because density layers outcrop at the surface this does not imply that the surface wind stress is simply transferred downward by form drag without change of amplitude restricting attention to the net form drag on a layer this is found to be balanced by coriolis force and if the layer outcrops the amount of wind stress put into the layer where it outcrops between 40 and 60 of the density layers at any latitude outcrop somewhere at the surface so that wind stress can be moved d

bi decadal variability excited in the coupled ocean atmosphere system by strong tropical volcanic eruptions decadal and bi decadal climate responses to tropical strong volcanic eruptions sves are inspected in an ensemble simulation covering the last millennium based on the max planck institute earth system model an unprecedentedly large collection of pre industrial sves up to 45 producing a peak annual average top of atmosphere radiative perturbation larger than 1 5 wm 2 is investigated by composite analysis post eruption oceanic and atmospheric anomalies coherently describe a fluctuation in the coupled ocean atmosphere system with an average length of 20 25 years the study provides a new physically consistent theoretical framework to interpret decadal northern hemisphere nh regional winter climates variability during the last millennium the fluctuation particularly involves interactions between the atlantic meridional overturning circulation and the north atlantic gyre circulation closely linked to the state of the winter north atlantic oscillation it is characterized by major distinctive details among them the most prominent are a a strong signal amplification in the arctic region which allows for a sustained strengthened teleconnection between the north pacific and the north atlantic during the first post eruption decade and which entails important implications from oceanic heat transport and from post eruption sea ice dynamics and b an anomalous surface winter warming emerging over the scandinavian western russian region around 10 12 years after a major eruption the simulated long term climate response to sves depends to some extent on background conditions consequently ensemble simulations spanning different phases of background multidecadal and longer climate variability are necessary to constrain the range of possible post eruption decadal evolution of nh regional winter climates

baroclinic rossby wave forcing and barotropic rossby wave response to stratospheric vortex variability abstract an analysis is performed on the dynamical coupling between the variability of the extratropical stratospheric and tropospheric circulations during the northern hemisphere winter obtained results provide evidence that in addition to the well known charney and drazin mechanism by which vertical propagation of baroclinic rossby waves is nonlinearly influenced by the zonal mean zonal wind topographic forcing constitutes another important mechanism by which nonlinearity is introduced in the troposphere stratosphere wave driven coupled variability on the one hand vortex variability is forced by baroclinic rossby wave bursts with positive negative peaks of baroclinic rossby wave energy occurring during rapid vortex decelerations accelerations on the other hand barotropic rossby waves of zonal wavenumbers s 1 and 3 respond to the vortex state and strong evidence is presented that such a response is mediated by changes of the topographic forcing due to zonal mean zonal wind anomalies progres