dynamical response of equatorial indian ocean to intraseasonal winds zonal flow nonlinear and linear 4 layer ocean models are used to explore the dynamics of intraseasonal 20 90 day periods zonal flow in the equatorial indian ocean the model simulations suggest that the observed 40 60 day zonal surface current is forced primarily by wind associated with the madden julian oscillation mjo which peaks at 40 60 days the strongest spectral peak of zonal flow however occurs at 90 day period in the model and a corresponding 90 day peak appears in the observed sea level data the 90 day current results from the preferential excitation of kelvin and rossby waves by the lower frequency component of intraseasonal wind and from the enhancement by rossby waves reflected from the eastern ocean boundary

oceanic equatorial waves and the 1991 93 el nino abstract equatorial kelvin and rossby waves associated with the 1991 93 el nino warm event were detected in temperature observations made by the tropical atmosphere ocean tao buoy array intraseasonal kelvin waves were a prominent part of equatorial thermocline depth variability and were well represented by a simple model consisting only of first and second mode baroclinic kelvin waves the second mode was essential to properly represent the observed amplitude thermocline depth variability at 5 n and 5 s was dominated by annual and interannual rossby waves which were found to have been largely wind forced in midbasin with little if any signal associated with eastern boundary reflection an evaluation of the wyrtki buildup hypothesis and the delayed oscillator hypothesis in connection with the 1991 93 events showed that a long lag about two years occurred between the arrival of the downwelling signal in the west and the subsequent initiation of el nino this was considerably longer than suggested

seaglider observations of equatorial indian ocean rossby waves associated with the madden julian oscillation during the cindy dynamo field campaign of september 2011 january 2012 a seaglider was deployed at 80 e and completed 10 north south sections between 3 and 4 s measuring temperature salinity dissolved oxygen concentration and chlorophyll fluorescence these high resolution subsurface observations provide insight into equatorial ocean rossby wave activity forced by three madden julian oscillation mjo events during this time period these rossby waves generate variability in temperature o 1 c salinity o 0 2 g kg 1 density o 0 2 kg m 3 and oxygen concentration o 10 mol kg 1 associated with 10 m vertical displacements of the thermocline the variability extends down to 1000 m the greatest depth of the seaglider observations highlighting the importance of surface forcing for the deep equatorial ocean the temperature variability observed by the seaglider is greater than that simulated in the ecco jpl reanalysis especially at depth there is also marked variability in chlorophyll fluorescence at the surface and at the depth of the chlorophyll maximum upwelling from rossby waves and local wind stress curl leads to an enhanced shoaling of the chlorophyll maximum by 10 25 m in response to the increased availability of nutrients and light this influence of the mjo on primary production via equatorial ocean rossby waves has not previously been recognized

on sampling the ocean using underwater gliders surface to 1000 m and back took 5 6 h and covered 5 3 km resulting in a horizontal speed of 0 26 m s 1 seasoar undulated between the surface and 400 m completing a cycle in 11 min while covering 2 6 km for a speed of 3 9 m s 1 adjacent profiles of temperature and salinity are compared between the two platforms to prove that each is accurate spray and seasoar data are compared through sections isopycnal spatial series and wave number spectra the relative slowness of the glider results in the projection of high frequency oceanic variability such as internal waves onto spatial structure the projection is caused by doppler smearing because of finite speed and aliasing due to discrete sampling the projected variability is apparent in properties measured on depth surfaces or in isopycnal depth no projected variability is seen in observations of properties on constant density surfaces because internal waves are intrinsically filtered wave number spectra suggest that projected variability affects properties at constant depth at wavelengths shorter than 30 km these results imply that isobaric quantities like geostrophic shear are valid at wavelengths longer than 30 km while isopycnal quantities like spice may be analyzed for scales as small as a glider measures

influences of storm erosion and deposition on rhythmites of the upper wenchang formation upper ordovician around tonglu zhejiang province china abstract tonglu rhythmites upper ordovician in zhejiang province east central china display three orders of cyclicity in sandstone and mudstone layer thickness millimeter thick alternations of sandstone and mudstone laminae are ascribed to single tidal cycles centimeter thick alternations of sand dominated layers sdls and mud dominated layers mdls are interpreted to be related to alternation of storm and calm weather conditions with a periodicity longer than that forced by neap spring tidal cyclicity the sdls are interpreted as storm deposits on the basis of presence of scour structures abundant intraformational mud pebbles oscillation ripples and thinning upward trends in the sandstone laminae a third meter thick cycle of variations in sandstone lamina thickness is interpreted as a reflection of cross shore changes in coastal dynamics and water depth in the subtidal intertidal environment storm waves usually considered to be random destructive factors to normal cyclic deposits are here highlighted as effective agents of sediment transport and deposition of the sand dominated layers this study aims at improving our facies level understanding of the genesis and preservation of storm related tidal flat rhythmites on open coasts and highlights the fact that storm related facies can mimic the cyclicity that is commonly ascribed to neap spring tidal variation

ocean temperature and salinity components of the madden julian oscillation observed by argo floats new diagnostics of the madden julian oscillation mjo cycle in ocean temperature and for the first time salinity are presented the mjo composites are based on 4 years of gridded argo float data from 2003 to 2006 and extend from the surface to 1 400 m depth in the tropical indian and pacific oceans the mjo surface salinity anomalies are consistent with precipitation minus evaporation fluxes in the indian ocean and with anomalous zonal advection in the pacific the argo sea surface temperature and thermocline depth anomalies are consistent with previous studies using other data sets the near surface density changes due to salinity are comparable to and partially offset those due to temperature emphasising the importance of including salinity as well as temperature changes in mixed layer modelling of tropical intraseasonal processes the mjo forced equatorial kelvin wave that propagates along the thermocline in the pacific extends down into the deep ocean to at least 1 400 m coherent statistically significant mjo temperature and salinity anomalies are also present in the deep indian ocean

ocean rossby waves as a triggering mechanism for primary madden julian events the madden julian oscillation mjo is sporadic with episodes of cyclical activity interspersed with inactive periods however it remains unclear what may trigger a madden julian mj event which is not immediately preceded by any mjo activity a primary mj event a combination of case studies and composite analysis is used to examine the extent to which the triggering of primary mj events might occur in response to ocean dynamics the case studies show that such events can be triggered by the arrival of a downwelling oceanic equatorial rossby wave which is shown to be associated with a deepening of the mixed layer and positive sea surface temperature sst anomalies of the order of 0 5 1 c these sst anomalies are not attributable to forcing by surface fluxes which are weak for the case studies analysed furthermore composite analysis suggests that such forcing is consistently important for triggering primary events the relationship is much weaker for successive events due to the many other triggering mechanisms which operate during periods of cyclical mjo activity this oceanic feedback mechanism is a viable explanation for the sporadic and broadband nature of the mjo additionally it provides hope for forecasting mj events during periods of inactivity when mjo forecasts generally exhibit low skill copyright c 2011 royal meteorological society

tidal bedding and tidal cyclicities within the intertidal sediments of a microtidal estuary dyfi river estuary west wales u k abstract in the microtidal dyfi river estuary west wales the characteristic sedimentary structure within the intertidal sediments is tidal bedding this consists of sand mud couplets by means of thickness measurements and detailed observations the following conclusions can be drawn 1 the thicknesses of and structures in both mud layer and sand layer of each couplet vary systematically downward in the studied cores and trenching profiles variations are mainly due to differences in the current speed and tidal range between tides to difference of individual neap spring tides and to the possible effect of filtering of currents due to being in the intertidal zone 2 the patterns of sand mud couplet thickness variations reflect two main types of tidal cyclicities diurnal inequality and the neap spring neap tidal cycle which is in turn related to the lunar cycle 3 the mud layer of each couplet represents deposition from suspension at times of tidal slack no ebb slack water period during low tide in the intertidal zone thus no ebb mud deposition during low water whilst the sand layer is deposited by asymmetrical bidirectional tidal currents in either the ebb or flood half of a tidal cycle 4 the tidal regime derived from these variation patterns is characterized by a mixed predominantly semi diurnal form which is comparable with the present tidal regime 5 finally it can be concluded that tidal bedding patterns are the structural expressions of tidal cyclicity

dynamical ocean forcing of the madden julian oscillation at lead times of up to five months abstractthe authors show that a simple three dimensional ocean model linearized about a resting basic state can accurately simulate the dynamical ocean response to wind forcing by the madden julian oscillation mjo this includes the propagation of equatorial waves in the indian ocean from the generation of oceanic equatorial kelvin waves to the arrival of downwelling oceanic equatorial rossby waves in the western indian ocean where they have been shown to trigger mjo convective activity simulations with idealized wind forcing suggest that the latitudinal width of this forcing plays a crucial role in determining the potential for such feedbacks forcing the model with composite mjo winds accurately captures the global ocean response demonstrating that the observed ocean dynamical response to the mjo can be interpreted as a linear response to surface wind forcing the model is then applied to study primary madden julian events which are not immediately preceded by any mjo activity or by any apparen

geographical variability of the first baroclinic rossby radius of deformation global 1 83 18 climatologies of the first baroclinic gravity wave phase speed c1 and the rossby radius of deformation l1 are computed from climatological average temperature and salinity profiles these new atlases are compared with previously published 5 83 58 coarse resolution maps of l1 for the northern hemisphere and the south atlantic and with a 1 83 18 fine resolution map of c1 for the tropical pacific it is concluded that the methods used in these earlier estimates yield values that are biased systematically low by 5 15 owing to seemingly minor computational errors geographical variations in the new high resolution maps of c1 and l1 are discussed in terms of a wkb approximation that elucidates the effects of earth rotation stratification and water depth on these quantities it is shown that the effects of temporal variations of the stratification can be neglected in the estimation of c1 and l1 at any particular location in the world ocean this is rationalized from consideration of the wkb approximation

the dynamics of the southwest monsoon current in 2016 from high resolution in situ observations and models abstractthe strong stratification of the bay of bengal bob causes rapid variations in sea surface temperature sst that influence the development of monsoon rainfall systems this stratification

the lunar orbit in the late precambrian and the elatina sandstone laminae the discovery of layered sediments of the elatina formation of south australia has attracted intense speculation regarding their origin1 2 the formation 10 m layer of graded sandstone consists of a pattern of light bands of periodically varying thickness3 a sequence of dark bands separates on average 11 6 light bands the spacing of these dark bands exhibits a rich and complex spectrum previously the periodicity has been attributed to the sunspot cycle and unassigned but putative solar periods prompted by a letter from g e williams summarizing new field data from the adelaide region south australia which imply that the elatina varves may be tidal we re examined the dark band spectrum and propose a luni solar tidal interaction model as the source of the laminae

mimoc a global monthly isopycnal upper ocean climatology with mixed layers a monthly isopycnal mixed layer ocean climatology mimoc global from 0 to 1950 dbar is compared with other monthly ocean climatologies all available quality controlled profiles of temperature t and salinity s versus pressure p collected by conductivity temperature depth ctd instruments from the argo program ice tethered profilers and archived in the world ocean database are used mimoc provides maps of mixed layer properties conservative temperature absolute salinity sa and maximum p as well as maps of interior ocean properties sa and p to 1950 dbar on isopycnal surfaces a third product merges the two onto a pressure grid spanning the upper 1950 dbar adding more familiar potential temperature and practical salinity s maps all maps are at monthly 0 5 0 5 resolution spanning from 80 s to 90 n objective mapping routines used and described here incorporate an isobath following component using a fast marching algorithm as well as front sharpening components in both the mixed layer and on interior isopycnals recent data are emphasized in the mapping the goal is to compute a climatology that looks as much as possible like synoptic surveys sampled circa 2007 2011 during all phases of the seasonal cycle minimizing transient eddy and wave signatures mimoc preserves a surface mixed layer minimizes both diapycnal and isopycnal smoothing of s as well as preserves density structure in the vertical pycnoclines and pycnostads and the horizontal fronts and their associated currents it is statically stable and resolves water mass features fronts and currents with a high level of detail and fidelity

a dynamical ocean feedback mechanism for the madden julian oscillation composite analysis is applied to study the dynamical ocean response to madden julian mj events measured by anomalies in sea surface height from the merged topex poseidon european remote sensing satellite altimetry dataset in each of the tropical ocean basins significant equatorial waves are forced which are shown to modulate the sea surface temperature sst by 0 2 0 3 degc in the absence of strong surface heat fluxes in the indian ocean there is a clear dynamical response which may play a significant role in generating later mj events surface westerly winds associated with the active phase of the madden julian oscillation mjo force an eastward propagating oceanic downwelling equatorial kelvin wave which on reaching the eastern boundary at sumatra forces reflected downwelling equatorial rossby waves and coastal kelvin waves the coastal kelvin waves propagate southwards towards northern australia and northwards into the bay of bengal and will be important for local physical chemical and biological processes the equatorial rossby waves propagate westward across the indian ocean arriving in the western indian ocean approximately 80 100 days after the initial kelvin wave was generated the arrival of these waves generates positive sst anomalies which leads to convection and may trigger the next but one mj event or amplify the low frequency tail of the mjo this constitutes a coupled feedback mechanism from the ocean dynamics onto the mjo somewhat similar to the delayed oscillator mechanism for the el nino southern oscillation

deep ocean impact of a madden julian oscillation observed by argo floats using the new argo array of profiling floats that gives unprecedented space time coverage of the upper 2000 meters of the global ocean we present definitive evidence of a deep tropical ocean component of the madden julian oscillation mjo the surface wind stress anomalies associated with the mjo force eastward propagating oceanic equatorial kelvin waves that extend downward to 1500 meters the amplitude of the deep ocean anomalies is up to six times the amplitude of the observed annual cycle this deep ocean sink of energy input from the wind is potentially important for understanding phenomena such as el nino southern oscillation and for interpreting deep ocean measurements made from ships

oceanic impetus for convective onset of the madden julian oscillation in the western indian ocean abstracta theory for intraseasonal atmosphere ocean atmosphere feedback is supported whereby oceanic equatorial rossby waves are partly forced in the eastern indian ocean by the madden julian oscillation mjo reemerge in the western indian ocean 70 days later and force large scale convergence in the atmospheric boundary layer that precedes mjo deep convection downwelling equatorial rossby waves permit high sea surface temperature sst and enhance meridional and zonal sst gradients that generate convergent circulations in the atmospheric boundary layer the magnitude of the sst and sst gradient increases are 0 25 c and 1 5 c mm 1 1 megameter is equal to 1000 km respectively the atmospheric circulations driven by the sst gradient are estimated to be responsible for up to 45 of the intraseasonal boundary layer convergence observed in the western indian ocean the sst induced boundary layer convergence maximizes 3 4 days prior to the convective maximum and is hypothesized to serve as a trigger for

precambrian tidal and glacial clastic deposits implications for precambrian earth moon dynamics and palaeoclimate abstract over the past decade the study of precambrian clastic tidal rhythmites stacked laminae of sandstone siltstone and mudstone that display periodic variations in thickness reflecting a strong tidal influence on sedimentation has provided accurate palaeotidal and palaeorotational data palaeotidal records obtained from tidal rhythmites may be systematically abbreviated however and derived periods and frequencies can be misleading the validity of such values including past length of day can be assessed by testing for internal self consistency through application of the laws of celestial mechanics such a test supports the estimated length of day of 21 9 0 4 h derived from the late neoproterozoic 620 ma elatina reynella rhythmites in south australia and the indicated mean rate of lunar retreat of 2 16 0 31 cm year since 620 ma the validity of estimated lengths of day obtained from other precambrian tidal rhythmites remain unverified because the data sets contain only one primary value directly determined from the rhythmites the elatina reynella data militate against significant earth expansion at least since 620 ma and suggest that the free nutation or tipping of the earth s fluid core has undergone a resonance with the earth s annual forced nutation since the neoproterozoic glaciogenic deposits are readily distinguishable from ejecta resulting from impacts with earth crossing bodies palaeomagnetic data based on the geocentric axial dipole model for the geomagnetic field indicate that neoproterozoic and palaeoproterozoic glaciation and cold climate near sea level occurred in low palaeolatitudes this enigmatic finding may imply global glaciation or an increased obliquity of the ecliptic and is relevant to modelling the effect of ice sheet formation on the earth s obliquity history by obliquity oblateness feedback mechanisms through multidisciplinary studies clastic sedimentology and geophysics together can make substantial contributions to understanding precambrian earth moon dynamics and global palaeoenvironments

intraseasonal behavior of clouds temperature and motion in the tropics abstract the spectral character of tropical convection is investigated in an 11 yr record of outgoing longwave radiation from the advanced very high resolution radiometer to identify interaction with the tropical circulation along the equator in the eastern hemisphere the space time spectrum of convection possesses a broad peak at wave numbers 1 3 and eastward periods of 35 95 days significantly broader than the dynamical signal of the madden julian oscillation mjo this quasi discrete convective signal is associated with a large scale anomaly that propagates across and modulates time mean or climatological convection over the equatorial indian ocean and western pacific outside that region the convective signal is small even though under amplified conditions coherence can be found east of the date line and in the subtropics having a zonal scale of approximately wavenumber 2 anomalous convection propagates eastward at some 5 m s 1 and suppresses as well as reinforces climatological convection

internal lee waves and baroclinic bores over a tropical seamount shark hot spot abstract oceanographic observations were made with a subsurface oceanographic mooring over the summit and flanks of two neighbouring seamounts in the tropical indian ocean to identify processes that may be responsible for the aggregation of silvertip sharks carcharhinus albimarginatus in the deep water drop off surrounding the summits the seamounts which are in the chagos archipelago in the british indian ocean territories are narrow in horizontal extent 15 sides that rise from depths of 600 m and flat summits at a depth of 70 m they are subjected to forcing at subinertial basin scales and local scales that include a mixed tidal regime and storm generated near inertial waves at the drop off at a depth of between 70 and 100 m isotherms oscillate at both diurnal and semidiurnal frequencies with amplitudes of 20 30 m the waves of tidal origin are accompanied by short period 5 min internal waves with amplitudes o 10 m and frequencies close to the local buoyancy frequency n within the thermocline which is the maximum frequency possible for freely propagating internal waves the tidal oscillations result from internal lee waves with 30 m vertical wavelength generated by the prevailing currents over the supercritical seamount flanks whereby the bottom slope is greater than the internal tide wave slope the near n waves are due to enhanced shear associated with the hydraulic jumps that form from the lee waves due to the abrupt transition from steeply sloping sides to a relatively flat summit the jumps manifest themselves as bottom trapped bores that propagate up the slope towards the summit further observations over the summit reveal that the bores subsequently flush the summits with cold water with tidal periodicity the bores which have long wave phase speeds more than double that of the bore particle velocities are characterised by intense vertical velocities 0 1 m s 1 and inferred local resuspension but relatively little turbulence based on temperature overturns our results strongly implicate lee waves as the dynamic mechanism of leading order importance to the previously observed accumulation of biomass adjacent to the supercritical slopes that are commonplace throughout the archipelago we propose that further investigation should identify the spatiotemporal correlation between internal wave activity and fish schooling around the summit and whether such schooling attracts predators

oceanic rossby waves acting as a hay rake for ecosystem floating by products recent satellite observations of rossby waves and chlorophyll anomalies propagating in subtropical gyres have suggested that wave induced upwelling could stimulate photosynthesis instead we show that chlorophyll maxima are located in abnormally warm water in rossby wave induced convergences this excludes inputs of nutrients from deeper water we argue that the sea color anomalies are not caused by chlorophyll but by floating particles evolved from the ecosystem and accumulated by rossby waves acting as marine hay rakes in convergence zones such processes may be determinant for the distribution of living organisms in oligotrophic areas

tracing the source of ancient reworked organic matter delivered to the north atlantic ocean during heinrich events a major effort of the geochemical and paleoclimate community has been to identify the specific sources of the ice rafted debris ird in heinrich layers hls although the general consensus is that the majority of the ird originated from the hudson area of northern canada the specific sources are not well constrained here we compare the diagnostic organic geochemical signature of hls to that of a number of paleozoic outcrops across the former margin of the laurentide ice sheet we show that the biomarker signature of upper ordovician strata from southampton and baffin island is compatible with that found in hls in the labrador sea and north atlantic while the biomarker signature of other paleozoic formations from the former margin of the laurentide ice sheet is not in addition to the biomarker signature key inorganic characteristics 18o end and 87sr 86sr ratios of these formations from southampton and baffin island are consistent with those reported from hls the location of these formations in and around the hudson strait is compatible with palaeo ice flow regimes through the hudson strait allowing for easy entrainment and rapid transport to the ocean based on these results we propose that these specific upper ordovician formations form a main source of ird in hls and hence infer an active role of the hudson strait paleo ice flow in these events