instability waves in the equatorial atlantic ocean abstract evidence is presented for the generation of planetary waves by barotropic instability within the cyclonic shear region of the atlantic ocean s south equatorial current sec immediately following the springtime intensification of the southeast trade wind which accelerates the sec westward a packet of waves with central periodicity of around 25 days is observed lasting for about three cycles independent wavenumber analyses on 1983 and 1984 data give newly identical zonal wavelengths and phase speed estimates of around 1100 km and 50 cm s 1 the waves are anisotropic and spatially inhomogeneous with generation confined primarily to the mixed layer an energetics analysis using 1983 data centered upon the equator at 28 w shows a rapid increase in total perturbation energy tpe reaching values of 2000 erg cm 3 within two weeks the subsequent decrease in tpe at this location is due primarily to meridional pressure work divergence baroclinic instability is negligible because both the meridional

average seasonal variation of the atlantic equatorial currents from historical ship drifts abstract surface currents in the tropical atlantic were studied using historical ship drift data these are the only available data capable of resolving the long term seasonal fluctuations of currents over a broad geographical region the north equatorial countercurrent was found to extend as a continuous eastward flowing current across the atlantic in the band 5 8 n from july to december the maximum average eastward velocity was 30 cm s 1 during july september east of 20 w the countercurrent continued throughout the year west of 20 w and from january to june the countercurrent disappeared and westward currents were observed average westward velocity reached 20 cm 1 in april and may centered near 40 w the annual cycle in surface velocity 20 cm s 1 amplitude agrees closely with that of geostrophic velocity inferred from variations in thermocline depth across the counter current jets centered near 2 n and 4 s separated by a minimum near 1 s the northern jet has a large 14 cm s 1 semiannual v

a further study of the tropical western hemisphere warm pool abstract variability of the tropical western hemisphere warm pool whwp of water warmer than 28 5 c which extends seasonally over parts of the eastern north pacific the gulf of mexico the caribbean and the western tropical north atlantic tna was previously studied by wang and enfield using the da silva data from 1945 93 using additional datasets of the ncep ncar reanalysis field and the ncep sst from 1950 99 and the levitus climatological subsurface temperature the present paper confirms and extends the previous study of wang and enfield the whwp alternates with northern south america as the seasonal heating source for the walker and hadley circulations in the western hemisphere during the boreal winter a strong hadley cell emanates northward from the amazon heat source with subsidence over the subtropical north atlantic north of 20 n sustaining a strong north atlantic anticyclone and associated northeast ne trade winds over its southern limb in the tna this circulation including the ne

investigation of the north brazil current retroflection and north equatorial countercurrent variability 1 eight years of topex poseidon altimeter derived sea height anomaly and climatological hydrographic data are used to investigate the temporal and spatial variability of the north brazil current nbc retroflection and the north equatorial countercurrent necc the nbc retroflection exhibits a mean position of 6 6 n 2 0 with a strong annual signal and year to year variability the annual cycle of its location follows the meridional migration of the itcz and the strength of the wind stress curl over the equatorial atlantic a marked shift in the annual mean location of the nbc retroflection is observed in 1998 1999 that appears to be linked to an increase in wind stress curl during this period the mean latitude of the necc is estimated to be 6 0 n 1 3 with a semiannual cycle showing maximum northerly locations in february and august the baroclinic transport of the necc varies predominantly on an annual cycle with maximum transport of 12 sv occurring in november

seasonal modes of surface cooling in the gulf of guinea a numerical simulation of the tropical atlantic ocean indicates that surface cooling in upwelling zones of the gulf of guinea is mostly due to vertical mixing at the seasonal scale the spatial structure and the time variability of the northern and southern branches of the south equatorial current sec and of the guinea current are correlated with the timing and distribution of turbulent heat fluxes in the gulf of guinea through modulation of the velocity shear at the subsurface these surface currents control the vertical turbulent exchanges bringing cold and nutrient rich waters to the surface this mechanism explains the seasonality and spatial distribution of surface chlorophyll concentrations better than the generally accepted hypothesis that thermocline movements control the nutrient flux the position of the southern sec explains why the cold tongue and high chlorophyll concentrations extend from the equator to 4 s in the southeastern part of the basin

critical taper model of fold and thrust belts and accretionary wedges the fold and thrust belts and submarine accretionary wedges that lie along compressive plate boundaries are one of the best understood deformational features of the earth s upper crust although there is considerable natural variation among the many fold and thrust belts and accretionary wedges that have been recognized and explored several features appear to be universal in cross section fold and thrust belts and accretionary wedges occupy a wedge shaped deformed region overlying a basal detachment or decollement fault the rocks or sediments beneath this fault show very little deformation the decollement fault characteristically dips toward the interior of the mountain belt or in the case of a submarine wedge toward the island arc the topography in contrast slopes toward the toe or deformation front of the wedge deformation within the wedge is generally dominated by imbricate thrust faults verging toward the toe and related fault bend folding two north american fold and thrust belts that exhibit these features are shown in figure 1 neither of these two examples is tectonically active today the southern canadian fold and thrust belt was active during the late jurassic and cretaceous 150 100 ma whereas the southern appa lachians were deformed during the late carboniferous to permian alle ghenian orogeny 300 250 ma figure 2 shows two examples that are currently active the taiwan fold and thrust belt produced by the sub duction of the eurasian plate beneath the philippine sea plate suppe 1981 1987 and the barbados accretionary wedge produced by the sub

diagnostic model of the three dimensional circulation in the upper equatorial pacific ocean abstract to investigate the processes that maintain the large scale annual average thermal structure of the equatorial pacific the three dimensional ocean circulation for a large area is determined from a diagnostic model applied to repeated meridional hydrographic sections along 150 w and 11o w from 5 n to 5 s geostrophic balances are used to determine velocity profiles from 0 to 500 db across the boundaries of the region zonal velocities across 150 w and 110 w at approximately 1 lattitude intervals from 5 n to 5 s and meridional velocities across 5 n and 5 s averaged over the zonal distance between 150 w and 110 w poleward wind driven flows across 5 n and 5 s based on climatological zonal wind stress are added to the geostrophic velocities in the mixed layers to achieve overall mass conservation the reference dynamic height field at 500 db is adjusted at four of the 21 stations by about 1 dyn cm horizontal nondivergence is used to determine meridional velocities between 0 75 and 5 latitudes

a description of coads surface meteorological fields and the implied sverdrup transports for the atlantic ocean from 30 s to 60 n abstract using coads data spanning 1947 1988 we describe the regional nature of the atlantic ocean wind driven circulation between 30 8 and 60 n and its annual and interannual variability the sverdrup streamfunction defines the circulation gyres our focus is on three central gyres the northern hemisphere anticyclonic subtropical gyre the cyclonic tropical gyre just north of the equator and the clockwise equatorial gyre straddling the equator this rendition of the sverdrup streamfunction computed with constant drag coefficient and air density compares favorably with that from other climatologies in the straits of florida analyses suggest that differences between the annual cycle in sverdrup transport and observations may be due to regional winds farther north in the tropical gyre the sverdrup circulation argues against a continuous western boundary current transporting water from the equatorial region into the caribbean in boreal winter bringing to question the mechanisms for the known interh

decadal and interannual sst variability in the tropical atlantic ocean abstract the mechanisms regulating interannual and decadal variations of sea surface temperature sst in the tropical atlantic are examined observed variations of sea surface temperature are typically in the range of 0 3 0 5 c and are linked to fluctuations in rainfall on both the african and south american continents the authors use a numerical model to simulate the observed time series of sea surface temperature for the period 1960 1989 based on the results experiments are conducted to determine the relative importance of heat flux and momentum forcing two dominant timescales for variability of sst are identified a decadal timescale that is controlled by latent heat flux anomalies and is primarily responsible for sst anomalies off the equator and an equatorial mode with a timescale of 2 5 years that is dominated by dynamical processes the interhemispheric gradient of anomalous sst the sst dipole is primarily linked to the former process and thus results from the gradual strengthening and weak

a linear analysis of equatorial atlantic ocean thermocline variability abstract observed variations in the atlantic ocean s equatorial thermocline are compared at four locations with simulations using an analytical reduced gravity model the comparison shows the essential features of the seasonal wind forced thermocline response to be accounted for by a linear superposition of equatorial long waves evolving basinwide tending to bring the zonal pressure gradient into balance with the wind stress a frequency response function is derived whose properties provide a basis for discussing the large scale features of the equatorial atlantic ocean s seasonal cycle for example its evolution along the equator the maximum upwelling region observed in the gulf of guinea and the secondary upwelling season also observed there clarification is also given to the issue of remote versus local forcing for these features

the zonal momentum balance of the equatorial undercurrent in the central pacific abstract current velocity data from an array of subsurface moorings deployed during the tropical instability wave experiment from may 1990 to june 1991 are used to diagnose the upper ocean zonal momentum balance at 0 140 w the flow field and associated zonal momentum flux divergence are fully three dimensional over the upper 250 m consistent with the earliest descriptions and theoretical ideas of the equatorial undercurrent euc estimates of the vertical stress divergence show dynamical flow regimes that change between the surface and the base of the euc being essentially linear modified by nonlinearity near the surface weakly nonlinear at the euc core and fully nonlinear below the core the vertical stress divergence is much larger over the lower portion of the euc than previously reported but this is consistent with the observed downstream deceleration of the euc and the idea that vertical mixing is important in maintaining the thermostad nonlinearity becomes increasingly important with dec

on the annual cycle of equatorial upwelling in the central atlantic ocean abstract the annual cycle of the upper ocean s vertical velocity component w on the equator at 28 w is examined by integrating the continuity equation using current meter data from the seasonal response of the equatorial atlantic experiment the annual cycle consists in part of an intense but brief 1 month upwelling season beginning with the onset of strong easterly wind stress in boreal spring this upwelling is followed by weaker downwelling during the summer despite the persistence of strong easterly wind stress the record length averaged w profile shows that maximum upwelling 0 6 10 3 cm s 1 is located slightly above the core of the equatorial undercurrent and downwelling is located below the base of the thermocline the standard deviations are about tenfold the magnitude of the means independent evidence supporting these results are that 1 sea surface temperature sst is related to w during the springtime changes in easterly wind stress with the observed and computed isotherm displacem

on the baroclinic response of the zonal pressure gradient in the equatorial atlantic ocean temperature time series obtained from surface moorings deployed along the equator in the atlantic ocean during the seasonal response of the equatorial atlantic experiment and the programme francais ocean et climat dans l atlantique equatorial were used to investigate the baroclinic response of the zonal pressure gradient due to the sloping isopycnals the zonal pressure gradient evolved as a complicated function of time depth and zonal position the most rapid and spatially inhomogeneous variations corresponded to periods of rapidly changing easterly wind stress following these periods the baroclinic response due to the sloping isopycnals was observed to overshoot its intended equilibrium before relaxing to it in so doing it tended to buffer pressure gradient variations at the depth of the equatorial undercurrent euc over much of the year the isopycnal slopes opposed the surface slope after the winds relaxed in winter however the isopycnal slopes reversed and acted in concert with the surface slope thereby enhancing the pressure gradient at the depth of the euc relative to that at the surface this reversal might be important in maintaining the euc during times of weak easterly wind stress the vertical structure of the zonal pressure gradient varied with the depth of the thermocline when the winds were weak and the thermocline was shallow the baroclinic response of the zonal pressure gradient due to the sloping isopycnals was primarily effected in the upper 50 m after the winds intensified and the thermocline deepened the baroclinic response extended down to at least 150 m

surface drifter pathways originating in the equatorial atlantic cold tongue 1 subtropical cells stcs connect subduction zones of the eastern subtropics of both hemispheres to the equatorial current systems via equatorward flow in the thermocline some of this thermocline water is converted back into warm near surface water in the eastern equatorial cold tongue from whence it is exported poleward here we examine the export pathways from the cold tongue in the atlantic based on recently available near surface drifter data we find that similar to its pacific counterpart water upwelled in the atlantic cold tongue follows multiple pathways back into the subtropics but not directly to the subduction zones thus the subtropical cells are open to extensive influence from and exchange with the subtropical and midlatitude ocean

variability of the mixed layer heat budget in the eastern equatorial atlantic during 2005 2007 as inferred using argo floats we examine the variability of the sea surface temperatures in the eastern equatorial atlantic during 2005 2007 by using argo profiling floats prediction and research moored array in the atlantic buoys and satellite in situ and atmospheric data sets the eastern equatorial atlantic characterized by shallow mixed layers all yearlong is divided into nine boxes of nearly equal surface area with respect to the dynamics and thermodynamics in this region monthly mixed layer heat budgets are computed in each box from 10 day argo profiles in all the boxes the net surface heat flux is one of the main causes of the seasonal evolution of sea surface temperatures for the 3 studied years the amount of short wave radiation penetrating through the base of the mixed layer and horizontal heat advection may locally contribute to the temperature variability while entrainment has a weaker contribution to balance the heat budget a residual term exists which includes all processes that cannot be calculated with observations as well as the possible errors in the other terms this residual is more intense in the cold tongue and the northern region and exhibits a clear seasonal cycle with minimum negative values in boreal summer and maximum values in winter this residual compares well with available observations of vertical turbulent mixing collected during etude de la circulation oceanique et des echanges ocean atmosphere dans le golfe de guinee campaigns 2005 2007 in the eastern equatorial atlantic when assuming that the residual is mostly associated with vertical turbulent mixing it can be conjectured that turbulent mixing is a significant cooling source in the cold tongue and north of the equator

some overlooked features of tropical atlantic climate leading to a new nino like phenomenon abstract the atlantic nino an equatorial zonal mode akin to the pacific el nino southern oscillation enso is phase locked to boreal summer when the equatorial easterly winds intensify and the thermocline shoals in the gulf of guinea a suite of satellite and in situ observations reveals a new mode of tropical atlantic variability that displays many characteristics of the zonal mode but instead peaks in november december nd this new mode is found to be statistically independent from both the atlantic nino in the preceding summer and the pacific enso the origin of this nd zonal mode lies in an overlooked aspect of the seasonal cycle in the equatorial atlantic in november the equatorial easterly winds intensify for the second time increasing upwelling and lifting the thermocline in the gulf of guinea an analysis of high resolution climatological data shows that these dynamical changes induce a noticeable sst cooling in the central equatorial atlantic the shoaling thermocline and increased upwelli

improved phase corrections for transoceanic tsunami data in spatial and temporal source estimation application to the 2011 tohoku earthquake systemic travel time delays of up to 15 min relative to the linear long waves for transoceanic tsunamis have been reported a phase correction method which converts the linear long waves into dispersive waves was previously proposed to consider seawater compressibility the elasticity of the earth and gravitational potential change associated with tsunami motion in the present study we improved this method by incorporating the effects of ocean density stratification actual tsunami raypath and actual bathymetry the previously considered effects amounted to approximately 74 for correction of the travel time delay while the ocean density stratification actual raypath and actual bathymetry contributed to approximately 13 4 and 9 on average respectively the improved phase correction method accounted for almost all the travel time delay at far field stations we performed single and multiple time window inversions for the 2011 tohoku tsunami using the far field data 3 h travel time to investigate the initial sea surface displacement the inversion result from only far field data was similar to but smoother than that from near field data and all stations including a large sea surface rise increasing toward the trench followed by a migration northward along the trench for the forward simulation our results showed good agreement between the observed and computed waveforms at both near field and far field tsunami gauges as well as with satellite altimeter data the present study demonstrates that the improved method provides a more accurate estimate for the waveform inversion and forward prediction of far field data

a description of the annual cycle in sea surface temperature and upper ocean heat in the equatorial atlantic abstract temperature and velocity time series obtained by surface moorings during the seasonal response of the equatorial atlantic experiment are used to investigate the role of ocean dynamics upon the annual cycle of equatorial sea surface temperature sst and upper ocean heat the annual cycle in sst is explained by different mechanisms each operant at different phases of the cycle the boreal springtime decrease in sst results from upwelling in response to the seasonal intensification of easterly wind stress this upwelling causes the seasonal formation of the cold tongue along the equator in the central and eastern portions of the basin an early summer increase in sst is attributed to the meridional convergence of reynolds heat flux associated with surface current instability generated waves after the instability waves abate sst and mixed layer depth remain relatively steady from late summer through fall when the advective terms are small and cancelling suggesting that surface heating is then

further studies on the response of the equatorial thermocline in the atlantic ocean to the seasonally varying trade winds upper ocean temperature data obtained during the seasonal response of the equatorial atlantic experiment and the francais ocean et climat dans l atlantique equatorial program are used to describe the variations of the thermocline observed along the equator from february 1983 to september 1984 in response to rapid seasonal changes in zonal wind stress the thermocline underwent sequences of upwelling followed by downwelling or conversely depending upon whether the winds were intensifying or relaxing these sequences increased systematically in magnitude and duration to the east both the sequential behavior and its zonal inhomogeneity represent departures from the slowly varying and in phase climatological description of the annual thermocline response an analytical reduced gravity equatorial long wave model forced by zonal wind stress distributions representative of the variations observed along the equator was employed to reconcile the differences between the 1983 1984 synoptic measurements and the climatologically averaged description qualitative agreements between the model results and the data were found for many salient features of the annual cycle including the zonal pressure gradient calculated by finite difference the features in the model arise as interference patterns between directly forced and reflected kelvin and long rossby waves that are generated with each change in the wind stress the manner in which the wind stress changes from year to year is therefore crucial to the equatorial ocean s response

satellite derived surface current divergence in relation to tropical atlantic sst and wind the relationships between tropical atlantic ocean surface currents and horizontal mass divergence sea surface temperature sst and winds on monthly to annual time scales are described for the time period from 1993 through 2003 surface horizontal mass divergence upwelling is calculated using surface currents estimated from satellite sea surface height surface vector wind and sst data with a quasi linear steadystate model geostrophic and ekman dynamical contributions are considered the satellite derived surface currents match climatological drifter and ship drift currents well and divergence patterns are consistent with the annual north south movement of the intertropical convergence zone itcz and equatorial cold tongue evolution while the zonal velocity component is strongest the meridional velocity component controls divergence along the equator and to the north beneath the itcz zonal velocity divergence is weaker but nonnegligible along the equator a strong divergence upwelling season in the central eastern equatorial atlantic peaks in may while equatorial sst is cooling within the cold tongue in addition a secondary weaker and shorter equatorial divergence occurs in november also coincident with a slight sst cooling the vertical transport at 30 m depth averaged across the equatorial atlantic ocean between 2 s and 2 n for the record length is 15 6 10 6 m 3 s 1 results are consistent with what is known about equatorial upwelling and cold tongue evolution and establish a new method for observing the tropical upper ocean relative to geostrophic and ekman dynamics at spatial and temporal coverage characteristic of satellite based observations

mixed layer shear generated by wind stress in the central equatorial pacific abstract sixteen months of wind and current profile observations in the central equatorial pacific show the response of the upper ocean shear to local wind forcing the shear at the ocean surface is significantly correlated with the wind stress in direction but not in magnitude implying that the vertical eddy viscosity coefficient is proportional to the square of the wind speed or to the stress using this variable eddy viscosity coefficient in stommel s model of the equatorial undercurrent we calculate shears in the mixed layer that compare well with the observations the flow is downwind on the equator and tends toward and ekman spiral off the equator