geoelectric field measurements on a planetary scale oceanographic and geophysical applications the characteristics of an initial year of electric field measurements obtained from a long 3900 krn unpowered submarine cable extending from point arena california to hanauma bay hawaii are reported the power spectrum estimated from the cable time series is similar to that from seafloor point electric field sensors at frequencies above 1 cpd but differs at lower frequencies by decreasing monotonically down to at least 0 02 cpd the multiple squared coherence between the cable data and three component geomagnetic fluctuations measured at fresno ca is high t2 0 9 from 1 0 0 09 cpd then declines slowly with decreasing frequency maps of the squared coherence between the cable voltage and the sur face air pressure wind stress and wind stress curl derived from the fleet numerical oceanography center product over the entire eastern north pacific show no significant relationships at frequencies above 0 05 cpd but strong nonlocal coherence with the wind stress curl forcing obtains at lower frequencies taken together these observations support a transition from high frequency dominance by external sources to low frequency dominance by oceanic motional sources at 0 05 0 1 cpd a considerably smaller value than has previously been observed with point electric field sensors on the ocean bottom the difference is caused by horizontal averaging of the short spatial scale motional component over the long submarine cable

large scale electric field measurements on the earth s surface a review there exist only a few reported measurements of quasi stationary near dc electric potentials over very large spatial scales hundreds of kilometers or more on the earth s surface such measurements have typically been made using unpowered submarine telecommunications cables the measurements pose unique experimental challenges and require careful procedures to avoid data contamination by electrode contact potentials and local ground currents in addition there are possible interpretational problems from pervasive poorly understood low frequency electric fields induced by ocean water motion through the earth s stationary magnetic field nevertheless estimates of the magnitude of the electric field computed from large scale potential difference measurements made principally to date in the pacific ocean can be used to place a limit on the size of the toroidal magnetic field at the core mantle boundary under certain conditions on the earth s electrical conductivity profile thus large scale electric potential measurements can serve as an adjunct probe of the earth s dynamo process in addition to measurements of the poloidal magnetic field and its secular changes made at and above the surface of the earth a review of all of these data suggests that the toroidal and poloidal magnetic fields at the top of the core are comparable in magnitude

observations and modeling of wind driven currents in the northeast pacific abstract velocity measurements from the interior of the alaskan gyre are presented from a current meter mooring deployed in 4000 m of water at 49 33 n 138 38 w in the vicinity of ocean weather station p the mooring held five current meters which spanned the depth of the water column the data reveal surface intensified motions with flow fluctuations in the upper layers of the water column characterized by long period o 100 d time scales of variability at abyssal depths the flow displays shorter o 20 d time scales of variability the data are compared with observations from one of the nepac moorings in the northeast pacific 42 n 152 w similar characteristics in kinetic energy levels in the vertical structure of the flow and in the vertical variation of eddy time scales are found at this location the current measurements are considered in terms of the linear theory of directly wind driven variability of muller and frankignoul a comparison with simulated currents from a quasigeostrophic num

the relationship between deep ocean currents and winds east of barbados abstract observations of currents collected at the polymode array iii cluster c 16 n 54 w are compared with radiosonde winds measured at barbados 13 n 62 w using a linear response analysis the winds and the currents are coherent throughout the water column 5400 m over the subinertial frequency range of 0 025 to 0 25 cpd the coherence is highest between the east west wind stress and north south currents over smooth topography the wind related ocean currents have a rms of 2 5 cm s 1 at 500 m and 1 1 cm s 1 at 4000 m and account for approximately one third of the total eddy kinetic energy the wind current phase is depth independent and does not vary significantly over the 200 km horizontal scale of the array the response amplitude is surface intensified and increases with decreasing frequency which is consistent with a deterministic theoretical model the coherence values and response estimates suggest an off resonant barotropic response to large scale wind forcing

observations of the boundary current system at 26 5 n in the subtropical north atlantic ocean abstract five current meter moorings and four horizontal electric field records spanning june 1990 february 1992 are used to describe the mean structure and variability of the vertically averaged velocity field and volume transport extending 425 km east of abaco the bahamas at 26 5 n examination of zonal and meridional velocity sections shows that while meandering may explain part of the variability there is substantial evidence for pulsation of the core dwbc velocity in the record intermittently strong northward flow is observed 225 km east of abaco that is significantly coherent and out of phase with the currents closer to the boundary at periods of 50 100 d and longer suggesting recirculation this is never observed 315 km offshore at 380 km offshore and extending east at least 60 km a strong dominantly southward flow is observed that is coherent with both that near abaco in phase and in the intervening recirculation zone out of phase at long periods the net mean transport over 17 month

tsunami signals from the 2006 and 2007 kuril earthquakes detected at a seafloor geomagnetic observatory 1 a seafloor geomagnetic observatory in the northwest pacific detected clear electromagnetic em variations associated with tsunami passage from two earthquakes that occurred along the kuril trench previous seismological analyses indicated that the m8 3 earthquake on 15 november 2006 was an underthrust type on the landward slope of the trench while the m8 1 earthquake on 13 january 2007 was a normal fault type on the seaward side the em measurements enabled precise monitoring of the tsunami propagation direction as well as particle motion of the seawater the estimated horizontal water velocity differs significantly for the 2006 and 2007 tsunamis in terms of initial motion and dispersive characters being consistent with the hydrodynamic simulation results of the tsunamis namely the tsunami induced horizontal geomagnetic components showed opposite signs for the rise and retreat waves as expected from the electric current wall hypothesis the dispersion effect is more remarkable in the 2007 event with a smaller source region of its tsunamigenic earthquake the 2007 tsunamis therefore tend to violate the long wave approximation the boussinesq approximation was required to reproduce the dispersive character of the 2007 event in our numerical simulation in terms of tsunami forecast an important advantage of em sensors over conventional tsunami sensors such as seafloor pressure gauges is their capability of vector measurements in addition to their ability to monitor particle motions the first peak of the downward magnetic component always precedes the tsunami peak suggesting a significant improvement in global tsunami warning systems if vector em sensors are integrated into the existing systems

the barotropic electromagnetic and pressure experiment 1 barotropic current response to atmospheric forcing during 1986 1987 an array of horizontal electrometers which measure the subinertial barotropic velocity was deployed for 11 months in the central north pacific to study atmospherically forced motions in a low eddy kinetic energy region significant coherence is found to be ubiquitous between the barotropic velocity and one or more surface atmospheric variables over the north pacific the maximum squared coherence between currents and wind stress curl at all periods greater than 3 days is typically 0 6 rarely below 0 4 and occasionally above 0 8 and is dominantly nonlocal although local coherence is seen at some sites especially at the shorter periods both the coherence and the intersite pattern similarity are strongest at the periods of relative maxima in the barotropic current autospectra e g at 6 8 10 14 and 20 50 days the locations at which the wind stress curl forces the motions at each site and for each period have been determined while there is substantial intersite variability some of the observed patterns of squared coherence over the north pacific are very similar to those predicted by simple linear smooth bottomed quasi geostrophic models of atmospherically forced barotropic currents the forcing location is occasionally found to be the same spot for all oceanic instruments especially at the autospectral maxima in barotropic current more commonly distinct forcing locations are found for each instrument even when closely spaced suggesting topographic influence in other cases multiple forcing locations are implicated for the motions at a single station all of this site and period dependent variability of the forcing location is incompatible with the simple models and is due either to the known spatial inhomogeneity of the curl forcing field or to topographic effects the importance of the former is emphasized using simple arguments based on analytic transfer functions between the atmospheric and oceanic variables and on observed wavenumber spectra for wind stress curl quantitative assessment of topographic effects must await suitable numerical models in addition maximum likelihood wavenumber spectra of the barotropic currents have been estimated in those bands with an adequate number of coherent sensors the wavenumbers at the spectral peaks are compatible with the dispersion relation for rossby waves modified by the observed large scale linearly sloping topography which shoals to the northeast the observed group velocities are in general quite consistent with the inferred forcing locations based on the ocean atmosphere coherences

variability of the wind stress curl over the north pacific implications for the oceanic response the subinertial frequency wavenumber structure and spatial coherence of wind stress curl and their spatial and temporal variability are described with the emphasis on characteristics which affect the ocean s response to the wind stress curl forcing function wind stress curl over the north pacific between 25 o and 60on was computed for 3 years 1985 1988 from the fleet numerical oceanography center wind product the range from winter peak to summer trough for the mean and variance are typically a factor of 3 4 and 10 respectively with superimposed interannual changes of up to a factor of 2 power spectra vary seasonally and interannually in an essentially frequency independent manner that is consistent with the curl variance however the spectrum over the period band 5 100 days often fails a statistical test for whiteness at the 95 level zonal and meridional wavenumber spectra were estimated for 13 sites distributed around the central eastern north pacific using the maximum likelihood method directional trends with frequency are comparable to those from earlier studies if 3 year long data segments are analyzed with approximate wavenumber symmetry except for the zonal term at mid latitudes for periods shorter than 10 days where eastward propagation is dominant however spectra for shorter data sections sometimes display eastward and westward excursions which are only weakly similar over distances of 1000 km and essentially dissimilar over longer separations the spatial correlation structure of wind stress curl is shown typically to have a main lobe of 1000 km and multiple intercorrelation lobes separated by 2000 km the strength and location of the intercorrelation peaks vary slowly with time these results suggest that curl behavior is more complex than was previously believed that the use of long term averages of or simple parameterizations for the frequency wavenumber spectrum of wind stress curl in model studies may be unrealistic and that more attention to actual curl characteristics at the time oceanic measurements are collected will be required to reconcile models with observations

geomagnetic induction on a transatlantic communications cable the phenomenon of geomagnetically induced currents in long conductors has been recognized since the mid nineteenth century when the use of the telegraph became prevalent in north america and europe1 powering systems of telegraph and telephone cables are now engineered to eliminate large current surges although the occasional significant geomagnetic disturbance such as those produced by the february 19582 august 19723 flare events can still be a problem however induced voltages can be used with complementary geophysical and geological data to deduce features of the earth s crust and upper mantle13 14 improved scientific understanding of mag netospheric phenomena means that the geomagnetic induction process in long conductors and thus in the earth are better understood for example the cable outage problem associated with the august 1972 geomagnetic storm interval was qualitatively attributed not to the line currents associated with normal auroral current systems but rather to the significant enhanced currents flowing on the magnetosphere boundary at the time of an extreme compression of this boundary in greatly enhanced solar wind conditions3 we have measured the geomagnetic induction phenomenon on modern day long cables to get better assessments of the induced currents in various types of geomagnetic variations our initial work was concerned with induction in the transatlantic telecommunications cable no 6 tat 6 which is laid between green hill rhode island 41 4 n 71 7 w geographic and st hilaire de riez france 46 7 n 1 9 w 4 we concentrate quantitatively here on induction by the solar induced quiet day currents sq in the ionosphere and find that calculated values agree well with observed values of sq

a local time dependent sverdrup balance in the eastern north pacific ocean direct observations of the dynamic balance between time dependent winds and deep ocean currents are described for the eastern north pacific ocean at 42 n 152 w currents from 150 to 4000 meters below the surface at frequencies from 0 01 to 0 1 cycle per day are significantly correlated with the wind stress curl derived from u s navy operational wind fields the horizontal currents are depth independent below 300 meters and they flow parallel to the potential vorticity gradient derived from the earth9s rotation and the large scale bottom topography these characteristics are expected for such periodic motions with horizontal scales larger than 500 kilometers and represent a generalized sverdrup balance between the atmospheric forcing and the oceanic response

stochastically forced current fluctuations in vertical shear and over topography the effects of constant vertical shear of zonal velocity uniform meridional bottom slope and a deep meridional wall representing the mid atlantic ridge on the response of a linear two layer quasi geostrophic ocean to stochastic wind stress curl forcing are investigated the model is motivated by discrepancies in energy levels and distributions between recent observations and a similar model without shear or topography that predicted remote coherences relatively well the results indicate that the presence of mean shear can significantly enhance the wind generation of surface intensified oceanic kinetic energy at frequencies above the zero shear cutoff for free baroclinic waves the primary effect of the sloping topography is enhanced barotropic response near the barotropic topographic sverdrup resonance where topographic and planetary potential vorticity gradients cancel the wall inhibits the barotropic response and increases coherences on the mooring side of the wall remote coherences for 49 day period fluctuations are due to long barotropic waves as in the previous model so the present model only partially reconciles the previous discrepancies

motional induction effect on the planetary scale geoelectric potential in the eastern north pacific geoelectric potentials induced by seawater motion on a planetary scale were studied using voltage differences measured on the hawaii 1 haw 1 submarine cable between hanauma bay oahu hawaii and point arena california the motionally induced field was extracted from a 3 6 year segment of the haw 1 voltage by cancelling the component that is coherent with the externally produced geomagnetic field at honolulu the corrected voltage shows significant coherence with atmospheric variables wind stress curl wind stress and surface pressure estimated from the european centre for medium range weather forecasts product at points throughout the pacific basin at periods from 5 to 133 days this suggests that the voltage reflects regional to basin wide depth averaged barotropic water currents that are directly wind driven contour maps of the squared coherence reveal that 1 peak coherence as large as 0 6 0 8 is seen at points both near the cable and nonlocally 2 higher coherence is seen at periods where the cable voltage power spectrum peaks and 3 spatial patterns of the coherence vary with period comparison of power spectra or coherence maps for individual years shows that the wind driven flow fluctuates temporally owing to long term variations of the wind field the main features of these observations are consistent with those from point electric field measurements suggesting that planetary scale voltages measured with cables can serve as a useful tool to monitor large scale water currents at long periods

a seasonal signal in ocean currents to abyssal depths long term 9 32 month current meter records from the eastern north atlantic 41 n 59 n suggest that remote from the influence of the western boundary current eddy kinetic energy ke at all depths is principally a function of wind stress and stratification generated during the winter and early spring propagating to abyssal depths and decaying to a minimum in late summer although this seasonal variation in ke has not previously been described from the midlatitude ocean some theoretical basis for it is presented

the barotropic response of the subpolar north pacific to stochastic wind forcing in a recent observational study koblinsky et al 1989 attempted to demonstrate that the topographic sverdrup balance can account for mesoscale current fluctuations with periods between 10 and 100 days in the abyssal north pacific however the topographic sverdrup balance proved difficult to verify systematically over the north pacific in this paper the conditions required to obtain the topographic sverdrup balance are investigated through numerical experiments with a stochastically forced barotropic quasi geostrophic numerical model of the subpolar north pacific in the numerical experiments the topographic sverdrup balance emerges from area averages of the terms in the vorticity equation but only for periods longer than about 40 days when the averages are taken over 4 4 region this period increases when averages are taken over progressively smaller regions an examination of vorticity balances at individual points along sections through the model domain indicates that the topographic sverdrup balance is not obtained at individual points even for very long period motions the possibility of verifying topographic sverdrup dynamics with oceanic data is considered it is argued that topographically generated small scales in the velocity field reduce the likelihood that the topographic sverdrup balance can be systematically observed in velocity measurements from individual current meter moorings the results suggest that the vorticity balance is complex and that topographic sverdrup dynamics cannot be expected to provide an adequate explanation for the seasonal modulation of the abyssal eddy kinetic energy that is observed with moored instrumentation in the north pacific

late paleozoic calc alkaline to shoshonitic magmatism and its geodynamic implications yuximolegai area western tianshan xinjiang article i nfo continuous late paleozoic magmatic activity in the western tianshan xinjiang china temporally overlapped the late carboniferous collision between the tarim and the kazakhstan yili plates isotopic dating whole rock geochemistry and isotopic characteristics of a suite of calc alkaline to shoshonitic rocks from yuximo legai area in the eastern end of the awulale mountains help define the tectonic evolution of this part of the tianshan zircon u pb ages of a quartz diorite and a quartz syenite porphyry are 310 8 2 1 ma and 284 4 3 6 ma respectively the geochemical and isotopic characteristics of late carboniferous igneous rocks including the quartz diorite as well as basaltic andesite and k rich trachyandesite indicate an evolu tion from calc alkaline towards shoshonitic series this was generated by the partial melting of the hydrated mantle wedge induced by changing subduction angles the younger quartz syenite porphyry however was more likely derived from the partial melting of a thickened crust in a post collisional setting or the partial melting of hot juvenile basalt in the lower crust during early permian delamination of the subcontinental lithospheric mantle therefore the generation of the calc alkaline to shoshonitic igneous rocks in yuximole gai area is genetically linked to the geodynamic evolution of the western tianshan from convergent subduc tion to collision during the late paleozoic

northeastern pacific mantle conductivity profile from long period magnetotelluric sounding using hawaii to california submarine cable data we present results of a long period magnetotelluric mt investigation of the electrical structure beneath the eastern north pacific the electric field data consist of 2 years of continuously recorded voltages across an unpowered 4000 km long submarine telephone cable haw 1 extending from point arena california to oahu hawaii the electric field measurements are coherent to some degree with magnetic field measurements from honolulu observatory at periods of 0 1 to 45 days this coherence is enhanced at long periods over that observed with point electric field sensors due to horizontal averaging of the motional electric fields of spatial scale smaller than the cable length significantly diminishing their effect robust controlled leverage mt response estimates and their jacknife confidence limits are computed for the haw 1 to honolulu data an equivalent scalar mt response obtained from honolulu magnetic variations data is used to correct the haw 1 mt response for static shift and to extend the mt response estimate to periods of 100 days the composite response function satisfies necessary and sufficient conditions for consistency with a one dimensional conductivity structure and is most sensitive to structure between 150 and 1000 km inversion of the mt response reveals a conductive zone 0 05 0 1 s m between 150 and 400 km depth and a positive gradient below 500 km these observations are consistent with previous mt studies in the north pacific this upper mantle conductivity is too high to be explained by solid state conduction in dry olivine using reasonable mantle geotherms calculations based on measurements of hydrogen solubility and diffusivity in olivine indicate that h dissolved in olivine possibly combined with a lattice preferred orientation consistent with measured seismic anisotropy provide sufficient conductivity enhancement to explain the inversion results the high conductivity may also be explained by the presence of gravitationally stable partial melt comparison of the haw 1 results with long period mt studies conducted on land reveals differences in upper mantle conductivity between different tectonic regimes in particular the upper mantle beneath the pacific ocean is considerably more conductive than that beneath the canadian shield and similar in conductivity to that beneath the basin and range

evidence for wind driven current fluctuations in the western north atlantic two subsurface current meter moorings were deployed for 20 months along 70 w in a low energy portion of the western north atlantic the resulting data were compared with estimates of the wind stress curl in an attempt to seek a relationship between currents below the mixed layer and meteorological forcing at subinertial frequencies currents and temperature tend to be significantly coherent with the curl and are most coherent with the curl at remote locations usually more than 500 km away from the mooring and generally to the east coherences generally decrease with increasing frequency the current response is surface intensified a linear stratified model for stochastically wind forced rossby waves in a flat bottomed ocean is presented as an attempt to rationalize the results the effort was not entirely successful so that it appears that a more realistic model perhaps including bottom topography and mean currents will be needed to rationalize these observations fully

the evolution of the asian plate in burma the post cretaceous evolution of the asian plate in burma is strongly influenced by the spreading of the eastern indian ocean and the movement of greater india northward the western part of burma apparently was an area which received clastic sediments during the early mesozoic times during the end of the mesozoic the eastern part of burma emerged from the ocean the western part formed the shelf area with a slowly westwards migrating geosyncline indoburman geosyncline to the west of it flysch sediments of upper cretaceous age have been found in this area the collision of the indian plate with the asian plate changed the sedimentary conditions in burma the emergence of the indoburman ranges happened during the miocene generating an outer island arc and forming the bay of bengal the subduction along the w coast of burma changed in the n with the approach of continental indian crust and led to thrusts in the n part of the indoburman ranges today subduction appears to be active only s of 18 n in the eastern bay of bengal the opening of the andaman sea fits into the dynamical development of the area

currents forced by stochastic winds with meridionally varying amplitude motivated by discrepancies between observations and previous theory we present a stochastically forced model of wind driven current fluctuations that includes the observed northward intensification of wind stress curl a feature absent from a previous model the model is linear barotropic and quasi geostrophic it is bounded by absorbing walls along lines of constant latitude in the north and south and is unbounded east and west the northward wind intensification causes a northward bias in the coherence of wind stress curl and currents that is similar to that observed art unanticipated secondary maximum occurs northeast of the mooring in the low frequency 37 day period meridional velocity coherence predictions