a limited area model of the gulf stream design initial experiments and model data intercomparison abstract a primitive equation n layer eddy resolving creation model has been applied to the gulf stream system from cape hatteras to cast of the grand banks 78 45 w 30 48 n within the limitations of the model realistic coastlines bottom topography and forcing functions have been used a two layer version of the model was driven by observed mean climatological wind forcing and mass transport prescribed at inflow outflow was determined by a radiation boundary condition and an integral constraint on the mass field in each layer specification of a deep western boundary current dwbc was included in some model runs six numerical experiments from a series of over fifty integrated to statistical equilibrium were selected for detailed description and intercomparison with observations the basic case consisted of a flat bottom regime driven by wind forcing only realistic inflow transport in the upper layer was then prescribed and two different outflow specifications at the eastern boundary were s

about the role of westerly wind events in the possible development of an el nino in 2014 similarities between early 1997 and 2014 has prompted climate scientists to wonder if an el nino matching the 1997 el nino of the century could develop in 2014 until april 2014 the equatorial pacific exhibited positive heat content anomalies along with an eastward warm pool displacement similar to those found during the onset of strong el nino events yet in july 2014 the warm pool had retreated back to its climatological positions and equatorial temperature anomalies were much weaker than in mid 1997 dedicated oceanic simulations reveal that these weak interannual anomalies can be attributed to differences in westerly wind event wwe sequences in contrast with 1997 the lack of wwes from april to june significantly limited the growth of eastern pacific anomalies and the eastward warm pool displacement in 2014 with the absence of additional wwe activity prospects for a mature el nino in late 2014 are fading

seasonal fluctuations of the surface north equatorial countercurrent necc across the pacific basin 1 based on multisatellite derived sea surface current sea surface height anomaly and geostrophic current data the annual variability of the surface necc across the pacific basin is investigated inferred from the surface current data the necc axis east and west of the dateline moves northward along its pathway in the latter half of a year and the first half of a year respectively the sea surface height anomaly in the necc region and the meridional movement of necc are well reproduced by a linear wind driven first mode baroclinic rossby wave model model experiments by setting the phase speed of baroclinic rossby wave or the ekman pumping to zero in different regions are carried out to clarify the influence of rossby wave and local ekman pumping on the movement of necc east of the dateline both ekman pumping and rossby wave are important in determining the northward movement of the necc axis however the necc axis west of the dateline moves northward primarily due to the westward transmission of positive sea surface height anomalies or downwelling rossby waves that originate in the east of the dateline the local ekman pumping plays a minor role in controlling the migration of the necc axis west of the dateline

equatorial subthermocline currents across the pacific recent sections crossing the equator at nine longitudes from 146 e to 86 w show zonal currents below 400 m similar to those found in a 16 month mean section on 159 w from the pacific equatorial ocean dynamics pequod program in 1982 1983 most of the new measurements were made with a lowered acoustic doppler current profiler eastward current extrema north and south intermediate countercurrents are found in all sections about 2 from the equator in the depth range 500 1500 m with the possible exceptions of 146 e where topography complicates the picture south of the equator and 150 e where the sections extend only from 1 s to 2 n poleward of the intermediate countercurrents westward flow is found near 3 from the equator in most of the sections on the equator from 250 500 m depth a westward equatorial intermediate current is found in many but not all of the sections similarly it is present in the pequod mean but not in all synoptic sections below the intermediate currents and countercurrents an eastward current near 3000 m was found at and south of the equator in the pequod mean and in the new sections from 150 e to 110 w near 4000 m there is westward flow south of the equator in the pequod mean and near the equator in the new sections from 179 e to 135 w geostrophic currents calculated from an 8 year mean hydrographic section at 165 e also resemble the pequod mean although not conclusive the evidence presented here indicates that these currents are basin scale components of the general circulation perhaps involving vigorous horizontal recirculation in a set of basin wide elongated gyres within a few degrees of the equator

the problem of gulf stream separation a barotropic approach inertial separation of a western boundary current from an idealized continent is studied in a homogeneous ocean circulation model a number of processes are identified that either encourage or prevent separation at a coastal promontory in this model for a single gyre wind forcing a free slip boundary condition forces the stream to follow the coastline whereas the no slip condition allows separation at a sharp corner a prescribed countergyre to the north of the stream is not necessary to achieve separation if the no slip condition is used premature separation occurs for wind fields that do not extend beyond the latitude of the cape for a more realistic wind field and coastline two distinct states of the stream are found at small reynolds numbers the current fails to separate and develops a stationary anticyclonic meander north of the cape stronger currents separate and drive a recirculation in the lee of the continent

geostrophic circulation in the tropical north pacific ocean based on argo profiles absolute geostrophic currents in the north pacific ocean are calculated from the newly gridded argo profiling float data using the p vector method for the period of 2004 11 the zonal geostrophic currents based on the argo profile data are found to be stronger than those based on the traditional world ocean atlas 2009 woa09 data a westward mean geostrophic flow underneath the north equatorial countercurrent is identified using the argo data which is evidenced by sporadic direct current measurements and geostrophic calculations in history this current originates east of the date line and transports more than 4 x 10 6 m 3 s 1 of water westward in the subsurface northwestern tropical pacific ocean the authors name this current the north equatorial subsurface current the transport in the geostrophic currents is compared with the sverdrup theory and found to differ significantly in several locations analyses have shown that errors of wind stress estimation cannot account for all of the differences the largest differences are found in the area immediately north and south of the bifurcation latitude of the north equatorial current west of the date line and in the recirculation area of the kuroshio and its extension where nonlinear activities are vigorous it is therefore suggested that the linear dynamics of the sverdrup theory is deficient in explaining the geostrophic transport of the tropical northwestern pacific ocean

separation of a density current from the bottom of a continental slope abstract separation from the continental slope of stratified jets like the gulf stream involves the sliding of successive isopycnal layers from a nearly horizontal bottom to the adjacent offshore isopycnal in the deep ocean one mechanism for producing such an effect is due to a downstream convergence of slope isobaths as shown herein for a 1 layer density model upstream of the convergence a geostrophically balanced jet is assumed with an inshore region of cyclonic vorticity resting on the continental slope and an offshore anticyclonic region resting on the isopycnal interface above heavier water for o 1 rossby number and cross stream topographic variation the steady transverse current displacements forced by slowly varying downstream topography are computed for supercritical upstream flow i e fast compared to free topographic waves offslope displacements are produced by converging isobaths extrapolation of the small amplitude result suggests that the mechanism is quantitatively important fo

seasonal eddy kinetic energy modulations along the north equatorial countercurrent in the western pacific seasonal eddy kinetic energy eke variability and its associated eddy energy conversion processes in the western tropical pacific are investigated using satellite altimeter observations and a global eddy resolving ocean general circulation model ogcm both the altimeter observed sea surface height anomalies and the ogcm simulation show an area with enhanced eke east of the mindanao island centered around 133 e and 5 n this enhanced eke area corresponds to the location of the quasi stationary meander of the north equatorial countercurrent necc and is bordered to the south by the halmahera eddy the mesoscale eke in this area exhibits a clear seasonality strong in summer july august and weak in winter november january and much of this seasonality is confined to the upper 200 m layer an investigation into the upper ocean eddy energetics based on the ogcm simulation reveals that the areal barotropic eddy energy conversion rate has an annual cycle similar to the eke variations while the areal baroclinic eddy energy conversion is found to be much smaller that the barotropic conversion rate and exhibits no clear seasonal changes this indicates that the eke variations are largely controlled by barotropic conversion of the seasonally varying regional circulation by examining the seasonal background circulation changes we find that the amplification of the barotropic eddy energy conversion rate in july august is related to the seasonal evolution of the mindanao current and the new guinea coastal current that amplifies the curvature and amplitude of the quasi stationary meander of the necc and results in an elevated eke level through increased regional barotropic conversion

interaction of the gulf stream and deep western boundary current where they cross the long timescale variability of the deep western boundary current dwbc where it crosses under the gulf stream is analyzed using a 3 year array of bottom current meters and inverted echo sounders the relationship of this variability to fluctuations in the upper layer gulf stream is specifically addressed at periods shorter than a year the dwbc variability shows no relationship to the local gulf stream 100 day fluctuations show a pulsing of the dwbc transport whereas longer period fluctuations are indicative of a meandering type variability by contrast on timescales greater than a year variations in the orientation and transport of the dwbc are directly related to such fluctuations in the local gulf stream the coupling reveals that the dwbc is forced by changes in the gulf stream rather than causing such variations which is in contrast to earlier modeling results

formation of high pressure minerals in shocked l6 chondrite yamato 791384 constraints on shock conditions and parent body size we have studied the high pressure phases observed in yamato 791384 l6 chondrite host meteorite mainly consists of olivine pyroxenes and plagioclase glass mineral fragments observed in the veins and the vein margin region of the host meteorite were partially or totally transformed into high pressure phases ringwoodite majorite akimotoite naalsi3o8 hollandite and jadeite matrix of the shock vein contains majorite pyrope solid solution the spatial distribution indicates that high pressure phases are present in the shock veins and host rocks adjacent to the shock veins investigation of the high pressure phases revealed that in y791384 fragments and adjacent matrix were subjected to pressures around of 18 23 gpa and the vein experienced temperatures around 2300 c during the shock event ringwoodite lamellae were observed in the host olivine adjacent to the vein kinetic investigation for ringwoodite lamellar growth in olivine indicates that the shocked meteorite experienced the pressure for at least 4 s such long duration of the pressure pulse indicates that the size of the parent body was greater than 10 km

mooring observations of equatorial currents in the upper 1000 m of the western pacific ocean during 2014 time depth variations of the equatorial currents over the upper 1000 m depth in the western pacific ocean were directly measured by acoustic doppler current profiler moorings at 2 degrees n 140 degrees e and 4 7 degrees n 140 degrees e during january august 2014 intraseasonal variations of the equatorial currents with periods of 37 73 days were observed encompassing the north equatorial countercurrent necc northern branch of the south equatorial current sec equatorial undercurrent euc equatorial intermediate current eic north intermediate countercurrent nicc and north equatorial subsurface current nesc compared with previous studies based mainly on shipboard synoptic surveys the 8 month time series of velocity profiles provided direct evidence for the existence of nesc captured reversals of the eic in may and the nesc in june from westward to eastward direction and revealed larger vertical extensions of the sec and nesc and greater depths of the eic and nicc than previously thought according to a global analysis product of ocean surface current during january april 2014 the necc was located around its southernmost position and with its the weakest intensity over the past 20 years some of the anomalous characteristics of these flows may be related to the fickle el nino of 2014

pressure induced amorphization of albitic plagioclase in an externally heated diamond anvil cell 1 high pressure and high temperature experiments of albitic plagioclase up to 41 gpa and 270 c were carried out using an externally heated diamond anvil cell raman spectroscopy and transmission electron microscopy of the recovered samples revealed that the amorphization of albite was complete at 37 gpa and room temperature the amorphization pressure at 170 c was nearly the same as that at room temperature in contrast the pressure largely decreased to 31 gpa at 270 c in comparison with the amorphization pressure of albite in laboratory shock experiments that in the present static compression experiments is significantly lower 10 gpa even at room temperature this suggests that shorter pressure duration results in a lower degree of amorphization of plagioclase the formation of maskelynite in shocked meteorites does not necessarily require the very high shock pressure 30 90 gpa that was previously estimated on the basis of shock recovery experiments

north atlantic barotropic vorticity balances in numerical models abstractnumerical simulations are conducted across model platforms and resolutions with a focus on the north atlantic barotropic vorticity diagnostics confirm that the subtropical gyre is characterized by an inviscid balance primarily between the applied wind stress curl and bottom pressure torque in an area integrated budget over the gulf stream the northward return flow is balanced by bottom pressure torque these integrated budgets are shown to be consistent across model platforms and resolution suggesting that these balances are robust two of the simulations at 100 and 10 km resolutions produce a more northerly separating gulf stream but obtain the correct integrated vorticity balances in these simulations viscous torque is nonnegligible on smaller scales indicating that the separation is linked to the details of the local dynamics these results are shown to be consistent with a scale analysis argument that suggests that the biharmonic viscous torque in particular is upsetting the inviscid

how does the deep western boundary current cross the gulf stream abstract the manner in which the deep western boundary current dwbc crosses the gulf stream is investigated using data from a hydrographic survey conducted in 1990 absolute geostrophic velocity vectors are computed using in situ float data to obtain the reference level three density layers are considered in detail two mid depth layers which together make up the shallowest water mass component of the dwbc 500 1200 m and a deep layer consisting of the norwegian greenland overflow water 2500 3500 m the shallowest layer does not make it through the crossover and is completely entrained by the gulf stream however the resulting drop in equatorward transport is almost completely replenished by offshore entrainment just south of the crossover in the intermediate layer which is denser than the gulf stream coming off the shelf part of the dwbc recirculates to the northeast while the onshoremost portion continues equatorward in the deep layer only a small amount of recirculation occurs the lateral

intermediate zonal jets in the tropical pacific ocean observed by argo floats abstractargo float data in the tropical pacific ocean during january 2003 august 2011 are analyzed to obtain lagrangian subsurface velocities at their parking depths maps of mean zonal velocities at 1000 and 1500 m are presented at both depths a series of alternating westward and eastward zonal jets with a meridional scale of 1 5 is seen at the basin scale from 10 s to 10 n these alternating jets with mean speeds about 5 cm s 1 are clearly present in the western and central parts of the basin but weaken and disappear approaching the eastern coast they are stronger in the southern hemisphere along the equator at both 1000 and 1500 m a westward jet is seen the jets closer to the equator are remarkably zonally coherent across the basin but the jets farther poleward appear broken in several segments in the western half of the basin the 1000 m zonal jets appear to slant slightly poleward from east to west at the western boundary in the south east of solomon islands and papua new guinea the al

dynamics of the gulf stream deep western boundary current crossover part i entrainment and recirculation abstract a regional primitive equation model is applied to the study of the interaction between the gulf stream and the deep western boundary current dwbc where they cross at cape hatteras it is found that for a wide range of forcing parameters the upper core of the dwbc is split into two mean paths at the crossover one flowing toward the south along the western boundary and the other flowing toward the cast under the gulf stream the eastward branch is entrained into the southern recirculation gyre and after being diverted into the interior for up to 1500 km eventually returns to the western boundary current and continues to flow southward this recirculation and mixing is shown to have a significant impact on the separation point and mean path of the gulf stream the basin scale stratification and the properties of the dwbc south of the crossover for most configurations the lower dwbc remains largely on the western boundary and interacts only weakly with the interior the entrainment of the upp

intermediate intraseasonal variability in the western tropical pacific ocean meridional distribution of equatorial rossby waves influenced by a tilted boundary abstractintermediate depth intraseasonal variability isv at a 20 90 day period as detected in velocity measurements from seven subsurface moorings in the tropical western pacific is interpreted

enhanced warming of the northwest atlantic ocean under climate change the intergovernmental panel on climate change ipcc fifth assessment of projected global and regional ocean temperature change is based on global climate models that have coarse 100 km ocean and atmosphere resolutions in the northwest atlantic the ensemble of global climate models has a warm bias in sea surface temperature due to a misrepresentation of the gulf stream position thus existing climate change projections are based on unrealistic regional ocean circulation here we compare simulations and an atmospheric co2 doubling response from four global climate models of varying ocean and atmosphere resolution we find that the highest resolution climate model 10 km ocean 50 km atmosphere resolves northwest atlantic circulation and water mass distribution most accurately the co2 doubling response from this model shows that upper ocean 0 300 m temperature in the northwest atlantic shelf warms at a rate nearly twice as fast as the coarser models and nearly three times faster than the global average this enhanced warming is accompanied by an increase in salinity due to a change in water mass distribution that is related to a retreat of the labrador current and a northerly shift of the gulf stream both observations and the climate model demonstrate a robust relationship between a weakening atlantic meridional overturning circulation amoc and an increase in the proportion of warm temperate slope water entering the northwest atlantic shelf therefore prior climate change projections for the northwest atlantic may be far too conservative these results point to the need to improve simulations of basin and regional scale ocean circulation

direct measurements of upper ocean currents and water properties across the tropical pacific during the 1990s abstract meridional sections of upper ocean zonal currents potential temperature and salinity are estimated at ten longitudes from 143 e to 95 w using conductivity temperature depth and acoustic doppler current profiler data from 172 synoptic sections taken in the tropical pacific between 138 e and 86 w mostly in the 1990s data reduction is carried out in a potential isopycnal and mixed layer framework to preserve a sharp pycnocline a mixed layer water property extrema and velocity extrema mean zonal currents potential temperatures and salinities are produced at each longitude the seasonal cycles of these fields are also estimated as well as a simple el nino southern oscillation enso cycle zonal sections along the equator are also presented properties of the near equatorial zonal currents including transports temperatures and salinities are estimated separately from the synoptic sections the seasonal cycles of these quantities and their correlations with the southern oscillation index are investigated the work is distinguished from most existing literature in that direct estimates of zonal velocity are combined with contemporaneous temperature and salinity data allowing trans pacific estimates of near equatorial current transports and properties including those of the northern branch of the south equatorial current the new guinea coastal undercurrent and the equatorial undercurrent

host rock solid state transformation in a shock induced melt vein of tenham l6 chondrite abstract the host rock fragments entrained in a 580 m wide melt vein of the tenham l6 chondrite were investigated using field emission scanning electron microscopy fesem and transmission electron microscopy tem to better understand the solid state transformation mechanisms and the shock conditions the melt vein consists of a matrix of silicate plus metal sulfide that crystallized from immiscible melts and sub rounded host rock fragments that have been entrained in the melt and transformed to polycrystalline high pressure silicates by solid state transformation mechanisms these high pressure phases include ringwoodite low ca majorite clinoenstatite hollandite structured plagioclase and ca rich majorite the ca rich majorite occurs as a symplectitic intergrowth with a ca poor amorphous silicate phase in a 200 m diameter chondrule in the vein this intergrowth seems to be the result of a disproportionate breakdown of a ca rich clinopyroxene precursor into ca rich majorite and femg sio 3 perovskite which subsequently vitrified upon pressure release the tem observations suggest that most solid state transformations in the tenham are reconstructive the transformation of olivine to polycrystalline ringwoodite appears to involve incoherent intracrystalline nucleation and interface controlled growth lamellae in partially transformed olivine are not continuous coherent lamellae but rather lamellae of polycrystalline ringwoodite which is inconsistent with a coherent lamellar transformation mechanism growth rate calculations based on published kinetic data suggest that the time required to grow 1 m ringwoodite crystal is 100 ms at 1600 k suggesting that the minimum shock pulse of approximately 100 ms

intraseasonal variability of the surface zonal currents in the western tropical pacific ocean characteristics and mechanisms abstractthe surface circulation of the tropical pacific ocean is characterized by alternating zonal currents such as the north equatorial current nec north equatorial countercurrent necc south equatorial current sec and south equatorial countercurrent secc in situ measurements of subsurface moorings and satellite observations reveal pronounced intraseasonal variability isv 20 90 days of these zonal currents in the western tropical pacific ocean wtpo the amplitude of isv is the largest within the equatorial band exceeding 20 cm s 1 and decreases to 10 cm s 1 in the necc band and further to 4 8 cm s 1 in the nec and secc the isv power generally increases from high frequencies to low frequencies and exhibits a peak at 50 60 days in the necc sec and secc these variations are faithfully reproduced by an ocean general circulation model ogcm forced by satellite winds and parallel model experiments are performed to gain insights into the underlying mechanisms it is found that large sca

annual reversal of the equatorial intermediate current in the pacific observations and model diagnostics abstract a large reversal of zonal transport below the thermocline was observed over a period of 6 months in the western pacific ocean between 2 s and the equator from 26 2 sv 1 sv 106 m3 s 1 eastward in october 1999 to 28 6 sv westward in april 2000 to document this reversal and assess its origin an unprecedented collection of adcp observations of zonal currents 2004 06 together with a realistic ogcm simulation of the tropical pacific was analyzed the results of this study indicate that this reversal is the signature of intense annual variability in the subsurface zonal circulation at the equator at the level of the equatorial intermediate current eic and the lower equatorial intermediate current l eic in this study the eic and the l eic are both shown to reverse seasonally to eastward currents in boreal spring and winter for the l eic over a large depth range extending from 300 m to at least 1200 m the peak to peak amplitude of the annual cycle of subthermocline zonal currents at

gulf stream s induced sea level rise and variability along the u s mid atlantic coast 1 recent studies indicate that the rates of sea level rise slr along the u s mid atlantic coast have accelerated in recent decades possibly due to a slowdown of the atlantic meridional overturning circulation amoc and its upper branch the gulf stream gs we analyzed the gs elevation gradient obtained from altimeter data the florida current transport obtained from cable measurements the north atlantic oscillation nao index and coastal sea level obtained from 10 tide gauge stations in the chesapeake bay and the mid atlantic coast an empirical mode decomposition hilbert huang transformation emd hht method was used to separate long term trends from oscillating modes the coastal sea level variations were found to be strongly influenced by variations in the gs on timescales ranging from a few months to decades it appears that the gs has shifted from a 6 8 year oscillation cycle to a continuous weakening trend since about 2004 and that this trend may be responsible for recent acceleration in local slr the correlation between long term changes in the coastal sea level and changes in the gs strength was extremely high r 0 85 with more than 99 99 confidence that the correlation is not zero the impact of the gs on slr rates over the past decade seems to be larger in the southern portion of the mid atlantic bight near cape hatteras and is reduced northward along the coast the study suggests that regional coastal sea level rise projections due to climate change must take into account the impact of spatial changes in ocean dynamics

sverdrup and nonlinear dynamics of the pacific equatorial currents abstract the sverdrup circulation in the tropical pacific is constructed from satellite scatterometer winds compared with measured ocean currents and diagnosed in an ocean gcm previous depictions of the sverdrup circulation near the equator have shown only weak vertically integrated flows here it is shown that the actual transports are not weak this discrepancy could be due either to inaccuracies in the wind forcing or to sverdrup dynamics being too simple in this region scatterometer winds show a strip of positive curl along the sst front north of the equator in the eastern pacific that is due to wind speed changes induced by the front including that additional element of curl forcing greatly improves the realism of the sverdrup representation but the magnitudes of the equatorial transport are still too small by a factor of about 2 although the nonlinear advective and friction terms are small in the model momentum balance they are o 1 in the vorticity balance especially because their meridi

local sensitivities of the gulf stream separation abstractrobust and accurate gulf stream separation remains an unsolved problem in general circulation modeling whose resolution will positively impact the ocean and climate modeling communities oceanographic literature does not face a shortage of plausible hypotheses that attempt to explain the dynamics of the gulf stream separation yet a single theory that the community agrees on is missing in this paper the authors investigate the impact of the deep western boundary current dwbc coastline curvature and continental shelf steepening on the gulf stream separation within regional configurations of the massachusetts institute of technology general circulation model artificial modifications to the regional bathymetry are introduced to investigate the sensitivity of the separation to each of these factors metrics for subsurface separation detection confirm the direct link between flow separation and the surface expression of the gulf stream in the mid atlantic bight it is shown that the gulf stream

boundary current separation in a quasigeostrophic eddy resolving ocean circulation model abstract the response of a rectangular flat bottom eddy resolving quasigeostrophic ocean to a steady double gyre wind stress is studied to assess the sensitivity of the solutions to a partial slip lateral boundary condition in which tangential stress is proportional to tangential velocity the constant of proportionality has limiting values of zero and infinity corresponding to free slip no stress and no slip conditions respectively seven numerical solutions corresponding to the values 0 0 2 0 3 5 5 0 6 5 8 0 and 100 0 are obtained which span the free slip and no slip limits significant qualitative changes in the time mean behavior of the solutions are observed to occur with increasing these changes include a gradual retreat of the separation points of the western boundary currents in the subtropical and subpolar gyres a dramatic reduction in the basin integrated reservoirs of mean and eddy kinetic energy a weakening of bottom dissipation and its replacement by lateral dissipat

gulf stream dynamics along the southeastern u s seaboard abstractthe gulf stream strongly interacts with the topography along the southeastern u s seaboard between the straits of florida and cape hatteras the dynamics of the gulf stream in this region is investigated with a set of realistic very high resolution simulations using the regional ocean modeling system roms the mean path is strongly influenced by the topography and in particular the charleston bump there are significant local pressure anomalies and topographic form stresses exerted by the bump that retard the mean flow and steer the mean current pathway seaward the topography provides through bottom pressure torque the positive input of barotropic vorticity necessary to balance the meridional transport of fluid and close the gyre scale vorticity balance the effect of the topography on the development of meanders and eddies is studied by computing energy budgets of the eddies and the mean flow the baroclinic instability is stabilized by the slope everywhere except past the bump the flow

contrasting intraseasonal variations of the equatorial pacific ocean between the 1997 1998 and 2015 2016 el nino events oceanic intraseasonal variability isv plays a vital role in the initiation and development of el nino events mooring observations reveal contrasting characteristics of upper ocean zonal current isv during different el nino events compared to the 1997 1998 event isv of the 2015 2016 event was significantly weaker by around 30 50 over the equatorial pacific basin and the variability maximum was shifted to the east similar to 160 degrees e these differences can be largely explained by wind forcing features isv of surface winds in 2015 is overall weaker than in 1997 intraseasonal westerly wind bursts in 1997 occurred near the western boundary and originated from the indian ocean whereas in 2015 perturbations were mainly propagated from the northeast pacific and achieved the peak power at similar to 160 degrees e of the equator these changes are likely associated with the decadal warming of the northeast subtropical pacific and weakening of the indian ocean intraseasonal oscillation plain language summary sea surface warmings of strong el nino events are usually triggered by intraseasonal oscillations prior to the events particularly intraseasonal eastward ocean currents generated by westerly wind bursts carry the warm water of the western pacific warm pool to the central pacific and contribute to the surface warming in this paper we compare the intraseasonal zonal current variations during two strong el nino events namely the 1997 1998 and 2015 2016 events although the two el nino events were of comparable strengths intraseasonal variations in 1997 were stronger than those in 2015 by 3050 these differences can be largely explained by the contrasting features of wind forcing intraseasonal oscillations were originated from the indian ocean in 1997 whereas those in 2015 were mainly from the northeast subtropical pacific the varying origin is likely associated with the warming of the northeast subtropical pacific and weakened indian ocean intraseasonal oscillation during recent years

five year climatological survey of the gulf stream system and its associated rings a 5 year climatological survey of the gulf stream system s landward surface edge defines the mean standard deviation extreme limits annual and interannual variabilities and frequency distributions along 0 5 longitudinal transects from 91 to 44 w the climatology covers the loop current in the gulf of mexico and the gulf stream in the northwest atlantic ocean autocorrelations and power spectra are derived for longitudinal transects between 79 5 and 57 5 w the study also investigates the observed warm core ring and cold core ring movements and their areal extent the observed data are compiled from the oceanographic analysis charts produced by the national oceanic and atmospheric administration which utilize infrared satellite imagery and in situ observations east of cape hatteras the gulf stream system landward surface edge exhibits both interannual and annual signals the interannual variability is equal to the annual variability the mean monthly gulf stream position for the longitudinal band 70 44 w shifts from farthest north in september to farthest south in february the magnitude of the annual shift is largest near the grand banks frequency distributions of the gulf stream system position are quasi normal nearly everywhere autocorrelation plots from the 5 year time series of gulf stream positions at longitudinal transects 79 5 57 5 w exhibit three well defined e folding time regimes with a maximum time of 10 weeks at 72 w power spectrums from 79 5 to 57 5 w are red spectrums having dominant peaks of 1 year period or greater the largest total spectra energies are found at 61 w the loop current sheds rings at two apparent spatial scales which are labeled major 307 km mean and minor 185 km mean warm core rings annually the loop current sheds about one major warm core ring which translates into the western basin of the gulf of mexico and one minor warm core ring which is usually reabsorbed by the loop current the major loop current warm core ring sheddings have no seasonal preference loop current warm core rings have a mean velocity of 2 4 km d west southwest an average of 22 gulf stream warm core rings are formed and absorbed annually between 75 and 44 w the largest frequency of warm core ring formations is seen near the new england seamounts while the largest frequency of warm core ring absorptions is found near cape hatteras gulf stream warm core rings can absorb each other as occurred in 14 of the absorption cases with the highest frequency just upstream of the new england seamounts the gulf stream warm core rings have a surface diameter decay rate of 0 026 per week loop current warm core rings are similar the gulf stream warm core rings have a mean velocity of 2 4 km d west southwest cold core rings have a mean cool core surface diameter of 105 km and a mean velocity of 1 km d southwest more definitive conclusions on cold core rings are not possible as ring identification and tracking by satellite infrared imagery is tentative

gulf stream generated topographic rossby waves abstract an inverse ray tracing model is applied to observations of 40 day topographic rossby waves on the continental slope off of cape hatteras north carolina to determine their origin the rays are traced seaward and extend into the deep gulf stream where the bottom slope remains strong enough that topographic dominates planetary this enable coupling to occur between eastward propagating gulf stream meanders and topographic waves with eastward phase speed and matching zonal wavelength previous satellite observations indicate that the most frequently occurring gulf stream meanders have a period of 40 days and the model reveals that as these meanders pass a topographic bend near 71 72 w they are able to couple to the observed topographic waves traced back from cape hatteras the 40 day gulf stream meanders occur in bursts which leads to associated bursts of the topographic waves

revisiting the circulation of the east australian current its path separation and eddy field abstract the traditional view of the east australian current eac as depicted in many schematics is of a continuous boundary current that flows along the shelf off eastern australia between approximately 18 s and about 32 5 s where it separates from the coast and continues either towards new zealand along the tasman front or towards tasmania as the eac extension additionally it is widely recognised that eddies are prevalent in the eac region particularly south of the eac separation we revisit this long standing paradigm and suggest that the eac is perhaps better viewed as a continuous meandering stream flowing adjacent to the coast that feeds a field of mesoscale eddies observations show that eac eddies are prevalent over a broad region of the western tasman sea as far north as 25 s typically with maximum intensity between 30 and 35 s at any instant in time the eac jet is usually evident as a poleward stream adjacent to the continental shelf edge other commonly accepted components of the eac system including the tasman front and eac extension are rarely seen as distinct identifiable features rather these features are evident only in time mean fields when the eddy variability is filtered out it is also common for the eac to be spatially discontinuous due to the presence of eddies often with multiple short streams that sometimes separate and re attach to the coast recognition of the eac as an eddy dominated current system has seen many recent studies focus on various aspects of eddies in the eac system providing new insights into mesoscale ocean dynamics recent studies of individual eddies have shown that the circulation within eddies including tilting and vertical motion is more complex than previously understood a summary of these studies along with a review of the eac system particularly its path separation and eddy field is presented here