projections of the tropical atlantic vertical wind shear and its relationship with enso in sp ccsm4 abstractthe vertical wind shear over the tropical atlantic ocean and its relationship with enso are analyzed in the superparameterized community climate system model version 4 sp ccsm4 and in the conventional ccsm4 the climatology of vertical wind shear over the tropical atlantic and the enso shear relationship are well simulated in the control runs of sp ccsm4 and ccsm4 however because of different representations of cloud processes in a warmer climate such as the representative concentration pathway 8 5 rcp8 5 scenario sp ccsm4 projects increased mean westerlies at 200 hpa during july through october jaso whereas ccsm4 projects decreased mean westerlies at 200 hpa over the equatorial atlantic the different changes in the upper level wind further contribute to different projection of jaso mean vertical wind shear over the equatorial atlantic in the rcp8 5 scenario when excluding the linear trend projection of the enso shear relationships by sp ccsm4 retains similar features as in the obs

simulations of the west african monsoon with a superparameterized climate model part ii african easterly waves abstractthe relationship between african easterly waves and convection is examined in two coupled general circulation models the community climate system model ccsm and the superparameterized ccsm sp ccsm in the ccsm the easterly waves are much weaker than observed in the sp ccsm a two dimensional cloud resolving model replaces the conventional cloud parameterizations of ccsm results show that this allows for the simulation of easterly waves with realistic horizontal and vertical structures although the model exaggerates the intensity of easterly wave activity over west africa the simulated waves of sp ccsm are generated in east africa and propagate westward at similar although slightly slower phase speeds to observations the vertical structure of the waves resembles the first baroclinic mode the coupling of the waves with convection is realistic evidence is provided herein that the diabatic heating associated with deep convection provides energy to the waves simulated in sp ccsm in co

instability of the axisymmetric monsoon flow and intraseasonal oscillation 1 a linear model of intermediate complexity based on quasi equilibrium theory is used in a zonally symmetric aquaplanet configuration to investigate the stability of the mean summer monsoon flow in the south asian region in the control case the mean state has one linearly unstable mode that corresponds in period and structure to the variability in the nonlinear model described by bellon and sobel 2008 and to the observed 30 to 60 d mode of intraseasonal variability this mode features propagation of the precipitation anomalies from the equator to the monsoon trough around 20 n both the period of this mode and its direction of propagation are determined by the direction and magnitude of the mean meridional baroclinic flow the wind induced surface heat fluxes associated with the surface westerlies in the northern tropics are an important contributor to the instability of the mode the mechanisms of propagation and reinitiation of convection are further described 1 meridional advection of vorticity by the mean flow is responsible for the creation of free tropospheric vorticity north of the convection center this vorticity in turn creates boundary layer convergence via coriolis acceleration and subsequent northward movement of the convection 2 meridional advection of zonal momentum creates equatorial free tropospheric easterlies on the equator these easterlies in turn generate low level convergence via the term of the coriolis acceleration and cause the reemergence of convection at the equator

the distribution of geothermal fields on the juan de fuca ridge near bottom water temperatures were mapped along 400 km of the strike of the juan de fuca ridge as part of a combined sea marc seabeam experiment to image the variability of morphology and structure along a spreading center segment the water temperature data collected by a continuously towed thermistor chain in addition to salinity data indicate that there are four geothermal areas spaced at distances of 100 km from each other south of the cobb propagator and one field just to the north of the propagator on the endeavor ridge segment each thermal region is located above a morphological dome on the spreading center these domes are an average of 100 200 m shallower than the rest of the axis the structure of bottom water suggests that the geothermal regions are on average 20 km long and that the heat from these fields raises the temperature in the water column by a minimum of 0 06 sup 0 c up to 300 m above the bottom two simple models are used to estimate the heat flux associated with these features

effects of intraseasonal oscillation on south china sea summer monsoon onset understanding of south china sea scs summer monsoon scssm onset response to tropical intraseasonal oscillation iso is critical for extended range prediction of scssm onset in this study we investigate the effect of iso on scssm onset for the period of 1980 2013 the 34 onset cases are classified into three groups early onsets around may 6th normal onsets around may 21st and late onsets around june 8th and the late onsets are even later than the indian monsoon onsets before each onset the scs experiences a dry iso phase to precondition the convective energy due to the easterly wind anomalies of the wet iso phase over the tropical indian ocean for the group of early onsets over the southern bay of bengal monsoon region for the group of normal onsets and over the southern indian monsoon region for the group of late onsets after each onset the scssm is supported by the westerly wind anomalies of the dry iso phase over these associated regions each early scssm onset is triggered by the northwestward propagating rossby wave of the wet iso in the western pacific which comes from the indian ocean for each normal late onset the scssm is triggered by synoptic scale low level westerlies in conjunction with seasonal low level westerlies when the wet iso moves to the northern bay of bengal region indian monsoon region since this convection to the north of 10 n cannot excite the easterly wind anomalies associated with kelvin wave responses over the scs to suppress the convection the mechanisms explaining the mean state controlled iso scssm onset relationship are also discussed

distributions of hydrothermal activity along the mid atlantic ridge interplay of magmatic and tectonic controls abstract hydrothermal activity has been investigated along three different sections of the slow spreading mid atlantic ridge mar 11 20 30 n 36 38 n and the reykjanes ridge 57 45 63 06 n when considered in total the incidence of venting along these three sections of the mar compares well with the predictions of a model in which frequency of venting is linearly related to ridge crest spreading rate at the scale of individual study areas however departure from the model is observed by up to an order of magnitude venting is anomalously rare along the reykjanes ridge but anomalously abundant along the mar 36 38 n whilst such variability may be within the error of the linear spreading rate model we note that the interplay between magmatic and tectonic processes also differs between the three study areas in the case of the reykjanes ridge we propose that the low incidence of venting reported may reflect a limitation of the sampling investigative strategy because the style of venting which predominates may not give rise to conventional black smoker hydrothermal plumes along the oblique and broadly segmented mar 36 38 n we propose that vigorous hydrothermal venting in broad segment end non transform discontinuities may be focussed along deeply penetrating active faults with the requisite heat supply being supported through some combination of along axis magmatic intrusions and thermal release associated with the serpentinisation of crustal peridotites

recent volcanic events and the distribution of hydrothermal venting at the lucky strike hydrothermal field mid atlantic ridge 1 we present new high resolution bathymetry and backscatter data acquired in 2006 with the rov victor 6000 over the lucky strike hydrothermal field mid atlantic ridge as long term monitoring of the lucky strike area momar project is being implemented these new high resolution data offer an unprecedented view of the distribution of hydrothermal edifices eruptive facies and small scale tectonic features in the lucky strike vent field we show that vents located in the nw and ne correspond with wide expanses of lumpy seafloor which we interpret as primarily made of broken chimneys and sulfide edifices they are found above scarps with relief 50 m or on associated mass wasting deposits by contrast the se and sw vents correspond with small expanses of lumpy seafloor and are located near smaller scarps which we interpret as more recent faults hydrothermal edifices in the sw venting area appear very recent postdating the emplacement and faulting of the most recent lava we propose that this difference in the age of hydrothermal edifices does not mean that hydrothermal venting itself is more recent in the southern part of the lucky strike field because preexisting sulfide deposits there may have been buried by recent volcanic deposits instead the older edifices in the northern part of the hydrothermal field may have been allowed more time to grow because they are set above the level of recent lava flows the formation of a lava lake is the most recent eruptive event detected at lucky strike lava drainback is evidenced by benches and lava pillars suggesting a close connection with an underlying magma reservoir which probably corresponds to the melt body imaged by singh et al 2006 we have found no evidence that this lake was active for months to decades as lava lakes at terrestrial volcanoes it may instead have formed as a lava pond with successive lava flows covering the eruptive vents as proposed for similar features at the epr the horizontal surface of the lake is deformed only near its southwestern shore along a nne trending set of faults and fissures which appear to control the distribution of hydrothermal chimneys

role of the boundary layer moisture asymmetry in causing the eastward propagation of the madden julian oscillation the moisture budget associated with the eastward propagating madden julian oscillation mjo was diagnosed using 1979 2001 40 yr ecmwf re analysis era 40 data a marked zonal asymmetry of the moisture relative to the mjo convection appears in the planetary boundary layer pbl below 700 hpa creatingapotentiallymoreunstablestratificationtotheeastofthemjoconvectionandfavoringtheeastward propagation of mjo the pbl integrated moisture budget diagnosis indicates that the vertical advection of moisture dominates the low level moistening ahead of the convection a further diagnosis indicates that the leading term in the vertical moisture advection is the advection of the background moisture by the mjo ascending flow associated with pbl convergence the cause of the zonally asymmetric pbl convergence is further examined it is found that heating induced free atmospheric wave dynamics account for 75 90 of the total pbl convergence while the warm sst anomaly induced by air sea interaction contributes 10 25 of the total pbl convergence the horizontal moisture advection also plays a role in contributing to the pbl moistening ahead of the mjo convection the leadingterm in the moistureadvectionis the advectionacross the backgroundmoisture gradient by the mjo flow in the western indian ocean maritime continent and western pacific the meridional moisture advection by the mjo northerly flow dominates while in the eastern indian ocean the zonal moisture advection is greater the contribution of the moisture advection by synoptic eddies is in generalsmall ithas a negativeeffect overthetropicalindianoceanand westernpacificandbecomespositive in the maritime continent region

water column anomalies associated with hydrothermal activity in the guaymas basin gulf of california abstract sea floor hydrothermal activity in the guaymas basin gulf of california is quite different from that associated with ridge crest spreading centers injection of hydrothermal fluids occurs in the bottom of a semi enclosed basin and water column anomalies produced by this activity increase to much higher values than in the open ocean in the guaymas basin the hydrothermal venting generates large clouds of fine suspended particulate matter spm 100 300 m above active mounds and chimneys these hydrothermal clouds have potential temperature anomalies of about 0 010 0 020 c are enriched in dissolved silica particulate manganese and depleted in dissolved oxygen relative to areas away from the vents the particulate manganese values increase from about 3 nmol kg at 1000 m well above the enclosing topography of the subsill basin to 100 150 nmol kg in the clouds of spm and in the bottom nepheloid layer the particulate mn in the hydrothermal clouds appears to originate from both direct precipitation of dissolved mn2 injected by the vents and entrainment of mn rich spm in the rising hydrothermal plumes injection of silica rich vent fluids into the basin bottom waters produces a silica anomaly of 10 15 mol relative to the other deep basins of the gulf of california spillover of guaymas basin deep water produces a silica plume just above the basin sill depth which is detectable to the mouth of the gulf a simple two endmember mixing model indicates that the deep waters of the guaymas basin contain approximately 0 1 hydrothermal fluid oxygen anomalies associated with the hydrothermal clouds are on the order of 5 mol relative to regions away from active vents the basin as a whole shows a depletion in oxygen of about 13 mol relative to the other deep basins of the gulf the mixing model shows that this oxygen consumption can be explained by the oxidation of dissolved sulfide and methane injected by the hydrothermal vents box models of the deep basins of the southern gulf of california indicate that the guaymas basin has a significantly higher source term for dissolved silica and sink term for dissolved oxygen than the other basins the calculated flux of hydrothermal fluids into the guaymas basin is 10 12 m3 s

mechanisms of poleward propagating intraseasonal convective anomalies in cloud system resolving models abstract an envelope of convection that propagates both poleward and eastward accounts for the largest fraction of intraseasonal variance of the tropical atmosphere during boreal summer here the mechanisms of poleward propagating convective anomalies are examined in a nonhydrostatic model with zonally symmetric boundary conditions integrated on a beta plane at resolutions high enough to explicitly represent moist convection when the domain has a narrow zonal dimension of 100 km or less the model produces a quasisteady intertropical convergence zone itcz meridionally propagating transients are produced for some prescribed sea surface temperature distributions but these transients are shallow vanish at finer resolutions and have a structure that bears little resemblance to that of observed poleward propagating anomalies this is in sharp contrast to previous studies that obtained robust poleward propagating anomalies in axisymmetric models using parameterized moist convection and it suggests that

mechanisms of northward propagating intraseasonal oscillation over the south china sea during the pre monsoon period abstractin the present study the spatiotemporal structures of the northward propagating intraseasonal oscillation iso over the south china sea scs in the premonsoon period are analyzed by usin

on the relationship between sst gradients boundary layer winds and convergence over the tropical oceans a linear mixed layer model that skillfully reproduces observed surface winds and convergence over the tropicaloceans is used to examine the relative influenceof boundarylayer and free tropospheric processes on the distribution of climatological surface winds and convergence the semiempirical model assumes a subcloud layer momentum force balance between pressure gradients coriolis acceleration linearized friction and downward momentum mixing and it utilizes boundary conditions from the 40 yr ecmwf re analysis era 40 observed pressure gradients are linearly decomposed into boundary layer defined as the region below 850 hpa and free tropospheric components and the surface winds and convergence associated with these components are computed results show that surface zonal winds are predominantly associated with a combination of free tropospheric pressure gradients and downward momentum mixing whereas the distribution of convergence is primarily due to boundary layer temperature gradients which are closely related to sst gradients the authors conclude that the climatological distribution of boundary layer convergence is primarily a function of the pattern of sst gradients and is better regarded as a cause rather than a consequence of deep convection

coupling between northward propagating intraseasonal oscillations and sea surface temperature in the indian ocean using a hybrid atmosphere ocean coupled model it is shown that during the boreal summer northwardpropagating intraseasonal oscillations npisos are strongly coupled to the underlying sea surface temperature sst in the indian ocean sector on the one hand the intraseasonal atmospheric convection changes the sst through solar radiation latent heat flux and mixed layer entrainment on the other the induced sst fluctuations feed back to affect the intraseasonal convection the preferential northward rather than southward propagation of boreal summer isos in the indian ocean is partially explained by an interaction among the summer mean climate state the atmospheric disturbances and the ocean surface temperature a solution to an atmosphere only model forced with daily sst produces much stronger npisos than a similar solution forced with monthly mean sst amip type run the atmosphere only model however even when it is forced by daily sst from the coupled model with a small amount of noise in the initial and or boundary conditions is unable to reproduce the npisos in the coupled case in the coupled system intraseasonal sst anomalies are forced by intraseasonal atmospheric convection and hence are in quadrature with the convection in the stand alone atmospheric model however sst acts only as a boundary forcing and the resultant atmospheric convection has almost the same phase with the underlying sst one consequence is that the intensity of the sst forced intraseasonal convection in the stand alone atmospheric model is considerably weaker than in the coupled model finally solutions indicate that the northward movement of the off equatorial convection in the northern indian ocean is more closely related to local intraseasonal sst anomalies than to the equatorial eastward moving madden julian oscillation positive negative sst anomalies in the northern indian ocean lead the active break phases of the intraseasonal convection by about 2 pentads 10 days therefore intraseasonal sst anomalies in the northern indian ocean are potentially a useful index to forecast active break spells of the south asian summer monsoon

active and relict sea floor hydrothermal mineralization at the tag hydrothermal field mid atlantic ridge the tag hydrothermal field is a site of major active and inactive volcanic hosted hydrothermal mineralization in the rift valley of the slow spreading mid atlantic ridge at 26 degree n the axial high is the principal locus of present magmatic intrusions the tag field contains three main areas of present and past hydrothermal activity 1 an actively venting high temperature sulfide mound 2 two former high temperature vent areas 3 a zone of low temperature venting and precipitation of fe and mn oxide deposits the volcanic centers occur at the intersections between ridge axis parallel normal faults and projected axis transverse transfer faults the intersections of these active fault systems may act as conduits both for magmatic intrusions from sources beneath the axial high that build the volcanic centers and for hydrothermal upwelling that taps the heat sources radiometric dating of sulfide samples and manganese crusts in the hydrothermal zones and dating of sediments intercalated with pillow lava flows in the volcanic center adjacent to the active sulfide mound indicate multiple episodes of hydrothermal activity throughout the field driven by heat supplied by episodic intrusions over a period of at least 140 times 10 sup 3 yr the sulfide deposits are built by juxtaposition and superposition during relatively long residence times near episodic axial heat sources counterbalanced by mass wasting in the tectonically active rift valley of the slow spreading oceanic ridge hydrothermal reworking of a relict hydrothermal zone by high temperature hydrothermal episodes has recrystallized sulfides and concentrated the first visible primary gold reported in a deposit at an oceanic ridge

metabasalts axial hot springs and the structure of hydrothermal systems at mid ocean ridges knowledge of the chemical transfer and mineralogical transformations that occur when sea water reacts with basalt at elevated temperatures and pressures can be used along with geological and geophysical data to deduce the typical structure and evolutionary sequence for hydrothermal systems within the oceanic crust along the axis of a mid ocean ridge studies of metabasalt and metadiabase dredged from fault scarps along the axial valley of the mid atlantic ridge reveal consistent relationships among the bulk chemistry of the altered rocks and their secondary mineralogy mineral abundances and mineral compositions especially for chlorite these relationships can be interpreted in terms of the distribution of alteration with respect to time temperature and water rock ratio in young crust assemblages of chl ab ep act chl ab ep act qtz chl ab qtz and chl qtz are produced at successively higher effective sea water to rock ratios within the temperature range of the greenschist facies 250 to 450 c toward higher ratios chlorites tend to become more mg rich pillow basalts of layer 2 are commonly altered under these conditions by sea water on the descending rather than the ascending limb of a convection system this type of alteration which reflects moderately high water rock ratios may characteristically occur above a still partially molten magma chamber as the magma chamber solidifies and is then penetrated more pervasive alteration of the deeper part of layer 2 and of layer 3 occurs at lower water rock ratios producing solutions such as those recovered from springs on the galapagos rift and the east pacific rise at 21 n localized upwelling limbs of the convection system can produce veins filled with quartz sulfides and fe rich chlorite

mechanisms of northward propagating intraseasonal oscillation a comparison between the indian ocean and the western north pacific abstract mechanisms of northward propagating intraseasonal oscillations isos over the indian ocean io and the western north pacific wnp are examined for the possibility of their existence in observations they include the following 1 the vorticity advection effect which is associated with the advection of anomalous baroclinic vorticity by mean baroclinic meridional winds 2 the vertical wind shear effect which is the vertical advection associated with the meridional gradient of baroclinic divergence and mean easterly vertical wind shear 3 the moisture advection effect induced by mean flow and 4 the air sea interaction via surface latent heat flux because of differences in mean state the influence of each mechanism on the northward propagating isos is different between the io and the wnp the vorticity advection effect is consistently found over both the io and the wnp while the air sea interaction has different impacts on the northward propagating isos over the io and the wnp the vertic

hydrography above the mid atlantic ridge 33 40 n and within the lucky strike segment as part of the french american ridge atlantic program the french american zero angle photon spectrometer and rocks fazar cruise conducted water column studies between 33 and 40 n along the mid atlantic ridge mar to detect hydrothermal activity and map its influence this paper describes the large scale hydrography within the axial valley with particular emphasis on the hydrothermally active lucky strike segment 37 17 n the fazar study area is affected by the presence of the azores current and mediterranean water mw although the mw core has been mapped as far north as 50 n off the ridge the northern boundary of the mw within the mar in the fazar study area exists as a strong front south of the azores platform this front is most likely caused by the shallower ridge crest becoming a physical barrier to the mw the lucky strike segment lies within this front and as a result has complicated hydrography which can obscure hydrothermal temperature and salinity anomalies

flow rates in the axial hot springs of the east pacific rise 21 n implications for the heat budget and the formation of massive sulfide deposits abstract the first in situ measurements of flow rates in submarine hot springs temperatures between 275 and 350 c were made in the hot springs of the east pacific rise at 21 n during november 1981 the flow rates ranged between 0 7 and 2 4 m s we estimate that the total rates at which heat and mass are transported from the three hot spring areas obs national geographic and southwest vents are ca 2 2 108 w and 150 kg of fluid s respectively the very high rate of heat loss precludes the existence of hot springs as steady state features of the east pacific rise at 21 n we estimate that hot springs are active for a maximum of ca 40 000 years chemical and or mechanical clogging of the vents can drastically reduce the lifetime of the hot springs using a simple model of plume development 1 we calculated that less than 3 of the sulfide particles that are entrained in the hydrothermal plumes at 21 n settle from the plumes before dispersal by a lateral submarine current at a height of ca 250 m above the seafloor 2 the time that is required to form the sulfide mounds that surround the hot springs by the accumulation of sulfide particles that settle from the plumes is ca 70 85 years the current rate at which sulfide particles settle from the hydrothermal plumes and accumulate near the hot springs appears to be too small to lead to the formation of large massive sulfide deposits such as the mavrouni deposit on cyprus 3 within the time limits that are suggested by our thermal energy balance calculations

seasonality of the structure and propagation characteristics of the mjo the seasonality of the madden julian oscillation mjo is documented in observational data and a nonlinear shallow water model is used to help interpret some of the contrasts in mjo structure between the boreal winter season november march ndjfm and the asian summer monsoon period june september jjas at upper tropospheric levels the flanking rossby waves remain centered around 28 degrees n s year round but they tend to be stronger in the winter hemisphere where the climatological mean jet stream is stronger rendering the subtropical circulation more sensitive to forcing by a near equatorial heat source amplitudes of the mjo related deep convection and lower tropospheric zonal wind are stronger in the summer hemisphere where the column integrated water vapor is larger during ndjfm the equatorial asymmetry is subtle as in the annual mean moisture convergence into swallowtail shaped regions of enhanced deep convection is an integral part of the equatorial rossby wave signature and the eastward propagation is due to moistening of the air to the east of the enhanced convection by poleward moisture advection during the asian summer monsoon in jjas the convection assumes the form of northward propagating west northwest east southeast oriented rainbands embedded within cyclonic shear lines these features are maintained by frictional convergence of moisture and their northward propagation is mainly due to the presence of features in the climatological mean fields that is the west east moisture gradient over india and the arabian sea and the southwesterly low level monsoon flow over the northwest pacific

an atlantic hydrothermal plume trans atlantic geotraverse tag area mid atlantic ridge crest near 26 n the physical characteristics of an atlantic hydrothermal plume and its seafloor sources are described from the first data set of water column properties associated with a high temperature source area at a slow spreading oceanic ridge the observations comprise five near bottom tows of a camera color video and still temperature sensor array through the buoyant portion and 23 conductivity temperature depth ctd profiles through the neutrally buoyant portion of the plume made at the trans atlantic geotraverse hydrothermal field in the rift valley of the mid atlantic ridge at 26 08 n 44 49 w in july 1985 the source area is a mound up to 250 m wide and 50 m high constructed primarily of massive sulfides between depths of 3620 and 3670 m at the base of the east wall flow and discharge regimes systematically changed from the center to the edge of the mound high temperature black smokers vented at fast rates 1 m s from discrete sulfide chimneys and at slow rates from fractures and clear solutions vented at slow rates from diffuse sources in the inner zone of the mound intermediate temperature blue white and white smokers vented at slow rates from discrete sulfide sulfate chimneys and clear solutions vented from diffuse sources in the middle zone patchy diffuse discharge of clear solutions through sulfide talus occurred in the outer zone the diffuse discharge of clear solutions and the discrete discharge from the white smokers were observed to turbulently rise up to several meters above the seafloor where the discharge was laterally advected in prevailing laminar flow at several centimeters per second a convective heat flux of 8 8 106 w for only the black smokers that vented from fractures was estimated by applying a buoyant plume model to temperature anomalies measured with the towed array this value is intermediate between values estimated for entire vent fields at the fast spreading east pacific rise discharge from the black smokers rose to form the neutrally buoyant portion of the plume that was cold and fresh relative to surrounding seawater where it attained density equilibrium between 190 and 350 m above the mound in contrast hydrothermal plumes observed in the pacific were warm and salty relative to surrounding seawater the difference is attributed to the effect on plume density of entrainment during rise through opposite salinity profiles that decrease downward in the atlantic and increase downward in the pacific resulting in different temperature salinity compensations at neutral buoyancy the temperature difference between the neutrally buoyant portion of the plume and surrounding seawater negative for the atlantic positive for the pacific is not a unique function of convective heat flux from a source area as a consequence of both the effect of the entrainment of salinity on plume density and the separation of diffuse and discrete components of discharge the hydrothermal plume and the hydrothermal mound are inferred to have grown in size and complexity in response to the development of hydrothermal flow and discharge regimes for at least the past 104 years

origin of low frequency intraseasonal oscillations in the tropical atmosphere iii monsoon dynamics abstract this is the third in a series of papers to study the origin of intraseasonal oscillations in this paper we address the issue of the interaction of the monsoon large scale circulation and intraseasonal oscillations we show that as a result of the interaction of the large scale monsoon flow with the near equatorial intraseasonal oscillation unstable baroclinic disturbances are generated over the monsoon region these disturbances have spatial scales of approximately 3000 4000 km and periods of 5 6 days with the vertical wave axis tilting eastward with height the rapid development of these cyclonic disturbances along 15 20 n and the concomitant weakening of the equatorial disturbances are accompanied by the rapid northward shift of the rising branch of the local hadley circulation they may also be identified with the observed sudden jump of the mei yu rainband over east asia and the inverse relationship between the monsoon itcz and the equatorial itcz over india and east asia from a linear s

hydrothermal anomalies in the lucky strike segment on the mid atlantic ridge 37 17 n abstract as part of the fara french american ridge atlantic project the northern mid atlantic ridge mar was surveyed for hydrothermal activity between 33 and 40 n during the fazar cruise in august october 1992 after detection of hydrothermal activity in the lucky strike segment 37 17 n a detailed water column survey was undertaken in this region during a follow up cruise with the dsrv alvin several active high temperature vents were found on the summit of an central seamount here we focus on the results of the water column survey undertaken during the fazar cruise the influence of mediterranean water and the site s shallow depth complicates the hydrography at lucky strike background temperature and salinity gradients are usually too complex to indicate hydrothermal anomalies clearly light transmission anomalies within the lucky strike region were small but were detected throughout the segment from mid depth 1500 m all the way to the valley seafloor 2300 m depth the large depth range covered by these anomalies probably results from vertical mixing as well as the presence of multiple vent sources at various depths methane anomalies and a temperature anomaly observed deeper than the vents documented by alvin further support the idea of additional deeper vents within this segment particle samples of the deep particle layer are enriched in fe and trace metals

mechanisms of meridional propagating high frequency intraseasonal oscillation associated with a persistent rainfall over south china abstractthe present study divides the intraseasonal variations into high frequency intraseasonal oscillation hf iso with a 5 20 day period and low frequency iso lf iso with a 30 60 day period here defined hf iso is heavily different from some previous work because over south china persistent rainfall pr is not only related to the quasi biweekly oscillation 10 20 day period but also connected with the quasi weekly oscillation 5 10 day period associated with a pr over south china during the first half of june 2016 pr1606 the propagating components of the convections are largely attributed to the hf isos moreover both southward and northward propagating hf isos are found in this case over southern china the moisture advection dominated by anomalous flow and mean water vapor plays an important role in the southward propagation of the hf iso and the cloud radiation effect may be also at least partially responsible for the southward shift of the associated convective zone neverthele

hydrothermal scavenging at the mid atlantic ridge modification of trace element dissolved fluxes abstract we have carried out an icp ms study of the distributions of trace elements fe ca mg al mn cu zn v as cr co pb y mo ag sn cd and be in particulate material collected from the tag hydrothermal plume 26 n mid atlantic ridge to examine the extent to which fluxes of dissolved trace elements emitted from hydrothermal vent fluids are balanced by the precipitation of associated particulate phases comparison of particulate trace element distributions with particulate fe concentrations within the neutrally buoyant plume reveals that the distribution of trace elements within the plume is controlled by the following processes i co precipitation from vent fluids ii scavenging from seawater and iii preferential settling from the plume and oxidative dissolution within the water column for y and be continuous scavenging from seawater appears to be important whereas for v as and cr it appears that conditions suitable for uptake into particles may be restricted to the buoyant portion of the hydrothermal plume from a comparison of trace element fe ratios in the particles and associated mid atlantic ridge vent fluids it appears that for many elements e g cu co ag pb al cd be and zn the flux of dissolved material from vent fluids is matched closely by the precipitation of hydrothermal particulate phases of the various elements studied here hydrothermal activity only appears to act as a significant source for dissolved ca and dissolved mn

roles of barotropic convective momentum transport in the intraseasonal oscillation both observational data analysis and model simulations suggest that convective momentum transport cmt by cumulus convection may play a significant role in the intraseasonal oscillations iso by redistributing atmospheric momentum vertically through fast convective mixing process the authors present a simple theoretical model for the iso by parameterizing the cumulus momentum transport process in which the cmt tends to produce barotropic wind anomalies that will affect the frictional planetary boundary layer pbl in the model with equatorial easterly vertical wind shear vws it is found that the barotropic cmt tends to select most unstable planetary scale waves because cmt suppresses the equatorial ekman pumping of short waves which reduces the shortwave instability from the pbl moisture convergence and accelerates the shortwave propagation the model with subtropical easterly vws has behavior that can be qualitatively different from the model with equatorial easterly vws and has robust northward propagation the basic mechanism of this northward propagation is that the cmt accelerates the barotropic cyclonic wind to the north of iso which will enhance the precipitation by pbl ekman pumping and favor the northward propagation the simulated northward propagation is sensitive to the strength and location of the seasonal mean easterly vws these results suggest that accurate simulation of the climatological mean state is critical for reproducing the realistic iso in general circulation models

low frequency equatorial waves in vertically sheared zonal flow part i stable waves abstract the mechanism by which a vertically sheared zonal flow affects large scale low frequency equatorial waves is investigated with two level equatorial plane and spherical coordinates models vertical shears couple barolinic and barotropic components of equatorial wave motion affecting significantly the rossby wave and westward propagating yanai wave but not the kelvin wave this difference results from the fact that the barotropic component is a modified rossby mode and can be resonantly excited only by westward propagating internal waves the barotropic components emanate poleward into the extratropics with a pronounced amplitude while the baroclinic components remain equatorially trapped a westerly vertical shear favors the trapping of rossby and yanai waves in the upper troposphere whereas an easterly shear tends to confine them in the lower troposphere as such their westward propagation is slowed down by both westerly and easterly shears when the strength of the vertical shear varies w

active break cycles diagnosis of the intraseasonal variability of the asian summer monsoon in this study various diagnostics have been applied to daily observed outgoing longwave radiation olr and ecmwf reanalysis era products to provide a comprehensive description of the active break cycles associated with the asian summer monsoon and to address the differing behaviour of the two dominant time scales of intraseasonal variability 10 20 days and 30 60 days composite analysis of olr based on filtered daily all india rainfall air for the 40 day 30 60 days intraseasonal mode indicates that during active phases convection is significantly enhanced over the indian continent extending over the bay of bengal maritime continent and equatorial west pacific while convection is suppressed over the equatorial indian ocean and northwest tropical pacific resulting in a quadrapole structure over the asian monsoon domain in response to this heating pattern the large scale hadley lateral and the two east west transverse tropical circulations are enhanced there is also a significant impact on the extra tropical circulation through excitation and propagation of rossby waves in contrast the 15 day mode is more regional to the monsoon domain and has a prominent east west orientation in convection only the local hadley circulation over the monsoon region is modulated by this mode the evolution of these two modes as revealed by pop principal oscillation pattern analysis shows that the 40 day mode originates over the equatorial indian ocean once formed it has poleward propagation on either side of the equator and eastward propagation into the equatorial west pacific from the equatorial west pacific northward propagation over the west pacific and westward propagation into the indian longitudes are prominent the propagative features are complex and interactive and are responsible for the quadrapole structure in convection seen from the composites the interannual variability assessed from the pop coefficient time series indicates that the 40 day mode is strong during the onset phase of the monsoon in all the years but systematic propagation over the entire season depends crucially on the activity of the oceanic tcz tropical convergence zone the pop analysis of the 15 day mode indicates that this event originates over the equatorial west pacific associated with westward propagating rossby waves amplifies over the northwest tropical pacific and modulates both the continental and oceanic tczs over indian longitudes simultaneously this mode is pronounced during the established phase of the monsoon due to the complexity in the propagational features of both the intraseasonal modes it is concluded that understanding the subseasonal variability of one regional component of the asian summer monsoon asm requires understanding the entire asm system

coupled model simulations of boreal summer intraseasonal 30 50 day variability part 1 systematic errors and caution on use of metrics boreal summer intraseasonal 30 50 day variability bsisv over the asian monsoon region is more complex than its boreal winter counterpart the madden julian oscillation mjo since it also exhibits northward and northwestward propagating convective components near india and over the west pacific here we analyze the bsisv in the cmip3 and two cmip2 coupled ocean atmosphere models though most models exhibit eastward propagation of convective anomalies over the indian ocean difficulty remains in simulating the life cycle of the bsisv as few represent its eastward extension into the western central pacific as such few models produce statistically significant anomalies that comprise the northwest to southeast tilted convection which results from the forced rossby waves that are excited by the near equatorial convective anomalies our results indicate that it is a necessary but not sufficient condition that the locations the time mean monsoon heat sources and the easterly wind shear be simulated correctly in order for the life cycle of the bsisv to be represented realistically extreme caution is needed when using metrics such as the pattern correlation for assessing the fidelity of model performance as models with the most physically realistic bsisv do not necessarily exhibit the highest pattern correlations with observations furthermore diagnostic latitude time plots to evaluate the northward propagation of convection from the equator to india and the bay of bengal also need to be used with caution here incorrectly representing extratropical tropical interactions can give rise to apparent northward propagation when none exists in association with the eastward propagating equatorial convection despite these cautions the use of multiple cross checking diagnostics enables the fidelity of the simulation of the bsisv to be meaningfully assessed

diagnosing the column integrated moist static energy budget associated with the northward propagating boreal summer intraseasonal oscillation column integrated moist static energy mse budgets associated with the northward propagating boreal summer intraseasonal oscillation bsiso are diagnosed for the bay of bangel bob and western north pacific wnp regions while an active bsiso convection is in phase with a positive column integrated mse perturbation the mse tendency exhibits a marked north south asymmetry about the convection with positive negative anomaly to its north south an mse budget diagnosis reveals that the advection of anomalous mse by the background southwesterly plays a dominant role in causing such an asymmetry and thus promotes the northward propagation as the anomalous rainband associated with the bsiso has a northwest southeast tilted structure the anomalous bsiso wind plays a negative role because the low level easterly anomaly to the north of the bsiso convection tends to suppress the surface evaporation through reduced near surface wind speed inhibiting the north south asymmetry in addition as maximum background mse appears over the asian land region the advection by the low level easterly anomaly contributes negatively over the wnp while it has little impact over the bob when the bsiso convection is near the equator a much stronger subsidence anomaly appears to the north than the south due to the equatorial asymmetry of the summer mean state this leads to a greater mse tendency north of the equator due to greater anomalous vertical mse advection supporting the initiation of the northward propagation

quantifying diffuse and discrete venting at the tour eiffel vent site lucky strike hydrothermal field 1 the relative heat carried by diffuse versus discrete venting of hydrothermal fluids at mid ocean ridges is poorly constrained and likely varies among vent sites estimates of the proportion of heat carried by diffuse flow range from 0 to 100 of the total axial heat flux here we present an approach that integrates imagery video and temperature measurements to accurately estimate this partitioning at a single vent site tour eiffel in the lucky strike hydrothermal field along the mid atlantic ridge fluid temperatures photographic mosaics of the vent site and video sequences of fluid flow were acquired during the bathyluck 09 cruise fall 2009 and the momarsat 10 cruise summer 2010 to the lucky strike hydrothermal field by the rov victor6000 aboard the french research vessel the pourquoi pas ifremer france we use two optical methods to calculate the velocities of imaged hydrothermal fluids 1 for diffuse venting diffuse flow velocimetry tracks the displacement of refractive index anomalies through time and 2 for discrete jets particle image velocimetry tracks eddies by cross correlation of pixel intensities between subsequent images to circumvent video blurring associated with rapid velocities at vent orifices exit velocities at discrete vents are calculated from the best fit of the observed velocity field to a model of a steady state turbulent plume where we vary the model vent radius and fluid exit velocity our results yield vertical velocities of diffuse effluent between 0 9 cm s 1 and 11 1 cm s 1 for fluid temperatures between 3 c and 33 5 c above that of ambient seawater and exit velocities of discrete jets between 22 cm s 1 and 119 cm s 1 for fluid temperatures between 200 c and 301 c above ambient seawater using the calculated fluid velocities temperature measurements and photo mosaics of the actively venting areas we calculate a heat flux due to diffuse venting from thin fractures of 3 15 2 22 mw discrete venting of 1 07 0 66 mw and by incorporating previous estimates of diffuse heat flux density from tour eiffel diffuse flux from the main sulfide mound of 15 6 mw we estimate that the total integrated heat flux from the tour eiffel site is 19 82 2 88 mw and that the ratio of diffuse to discrete heat flux is 18 we discuss the implication of these results for the characterization of different vent sites within lucky strike and in the context of a compilation of all available measurements of the ratio of diffuse to discrete heat flux

sea level rise depth dependent carbonate sedimentation and the paradox of drowned platforms a mathematical model of carbonate platform evolution is presented in which depth dependent carbonate growth rates determine platform top accumulation patterns in response to rising relative sea level this model predicts that carbonate platform evolution is controlled primarily by the water depth and sediment accumulation rate conditions at the onset of relative sea level rise the long standing paradox of a drowned platform arose from the observation that maximum growth rate potentials of healthy platforms are faster than those of relative sea level rise the model presented here demonstrates that a carbonate platform could be drowned during a constant relative sea level rise whose rate remains less than the maximum carbonate production potential this scenario does not require environmental changes such as increases in nutrient supply or siliciclastic sedimentation to have taken place a rate of relative sea level rise that is higher than the carbonate accumulation rate at the initial water depth is the only necessary condition to cause continuous negative feedbacks to the sediment accumulation rates under these conditions the top of the carbonate platform gradually deepens until it is below the active photic zone and drowns despite the strong maximum growth potential of the carbonate production factory this result effectively resolves the paradox of a drowned carbonate platform test modelling runs conducted with 2 5 m and 15 m initial sea water depths at bracketed rates of relative sea level rise have determined how fast the system catches up and maintains the keep up phase this is the measure of time necessary for the basin to respond fully to external forcing mechanisms the duration of the catch up phase of platform response termed carbonate response time scales with the initial sea water depth and the platform top aggradation rate the catch up duration can be significantly elongated with an increase in the rate of relative sea level rise the transition from the catch up to the keep up phases can also be delayed by a time interval associated with ecological re establishment after platform flooding the carbonate model here employs a logistical equation to model the colonization of carbonate producing marine organisms and captures the initial time interval for full ecological re establishment this mechanism prevents the full extent of carbonate production to be achieved at the incipient stage of relative sea level rise the increase in delay time due to the carbonate response time and self organized processes associated with biological colonization increase the chances for platform drowning due to deepening of water depth ca 10 m furthermore this implies a greater likelihood for an autogenic origin for high frequency cyclic strata than has been estimated previously

seasonal persistence and propagation of intraseasonal patterns over the indian monsoon region the space time evolution of convection over the monsoon region containing the indian subcontinent the indian ocean and the west pacific has been studied a multi channel singular spectrum analysis of the daily outgoing longwave radiation has yielded two intraseasonal oscillatory patterns and two large scale standing patterns as the most dominant modes of intraseasonal variability the oscillatory modes vary on time scales of about 45 and 28 days and their average cycles of variability are shown to correspond to the life cycles of active and break periods of monsoon rainfall over india during an active break cycle a convection dry anomaly zone first appears in the equatorial indian ocean subsequently expands to cover the indian subcontinent and finally contracts to disappear in the northern part of india some eastward and northward movements are found to be associated with both oscillatory modes while westward movement may also be associated with the 28 day mode the oscillatory modes are shown to have a large spatial scale extending to the west pacific one of the standing modes has anomalies of uniform sign covering the entire region and is related to el nino and southern oscillation enso pattern the other standing mode has a dipole structure in the equatorial indian ocean associated with large scale anomalies over india with the same sign as those over the western part of the dipole these two standing modes persist throughout the monsoon season each maintaining its respective pattern the seasonal mean monsoon is mainly determined by the two standing patterns without much contribution from the oscillatory modes the relative role of the standing patterns enso mode and dipole mode seems to be important in determining the seasonal mean during certain years

tracking the dispersal of hydrothermal plumes from the juan de fuca ridge using suspended matter compositions in 1988 and 1989 particles from on and off axis neutrally buoyant plumes over the juan de fuca ridge were sampled to study their changing composition with distance from the ridge crest plume depth and particle composition in off axis hydrothermal plumes were used to identify plume sources and trajectories iron and phosphorus concentrations and in particular p fe molar ratios were found to be sensitive indicators of hydrothermal phases in the suspended matter phosphorus vanadium and arsenic are scavenged from solution where dissolved iron from hydrothermal vents oxidizes in seawater and forms submicrometer sized particles of fe oxyhydroxide the p fe molar ratio 0 23 is essentially the same for vent fields along cleft and endeavour segments indicating that the scavenging processes are the same for both regions high p fe ratios are observed over the south and north cleft segment vent fields and to the west along the vance seamount chain the seamounts evidently function as a barrier bathymetrically steering the hydrothermal plumes to the west away from the ridge crest since particles from the endeavour vent field are greatly enriched in copper relative to hydrothermal plumes from other vent fields along the juan de fuca ridge copper concentrations in the plumes can be used to distinguish plume sources based on water column depth and elemental composition hydrothermal plume particles from specific vent fields on the juan de fuca ridge may be tracked as much as several tens of kilometers from their source using particle compositions

hydrothermal vents near a mantle hot spot the lucky strike vent field at 37 n on the mid atlantic ridge the lucky strike hydrothermal field occurs in the summit basin of a large seamount that forms the shallow center of a 65 km long ridge segment near 37 n on the mid atlantic ridge the depth and chemistry of the ridge segment are influenced by the azores hot spot and this hydrothermal field is the first atlantic site found on crust that is dominated by a hot spot signature multiple hydrothermal vents occur over an area of at least 300 m by 700 m vent morphologies range from flanges and chimneys with temperatures of 200 212 c to black smoker chimneys with temperatures up to 333 c cooler fluids from northern vents have higher chlorinities and lower gas volumes while hotter southern fluids have chlorinities 20 below seawater with higher gas volumes suggesting phase separation has influenced their compositions all gas volumes in fluids are higher than those at tag and snake pit hydrothermal fields black smokers exhibit their typical mineralogy except that barite is a major mineral particularly at lower temperature sites which contrasts with previously investigated atlantic sites the fluid chemistry distribution of the relict sulfide deposits on the seamount summit in the areas investigated using dsv alvin and contact relationships between active vent sites and surrounding basaltic and sulfide substrate suggest that the hydrothermal system has a long history and may have recently been rejuvenated fauna at the lucky strike vent sites are dominated by a new species of mussel and include the first reported sea urchins the lucky strike biological community differs considerably from other vent fauna at the species level and appears to be a new biogeographic province the lucky strike field helps to constrain how variations in the basaltic substrate influence the composition of hydrothermal fluids and solids because basalt compositions at lucky strike are 10 30 times enriched in incompatible elements compared to other atlantic hydrothermal sites such as tag snake pit and broken spur the incompatible element

on the role of sea surface temperature gradients in forcing low level winds and convergence in the tropics abstract we examine the importance of pressure gradients due to surface temperature gradients to low level p 700 mb flow and convergence in the tropics over time scales 1 month the latter plays a crucial role in determining the distribution of cumulonimbus convection and rainfall our approach is to consider a simple one layer model of the trade cumulus boundary layer wherein surface temperature gradients are mixed vertically consistent with ecmwf analyzed data the top of the layer is taken at 700 mb the influence from higher levels is intentionally suppressed by setting horizontal pressure gradients and frictional stresses to zero at the top of the layer horizontal convergence within the layer is taken up by cumulonimbus mass flux however the development of the cumulonimbus mass flux is associated with a short relaxation time o hr roughly the development time for such convection during this short time horizontal convergence acts to redistribute mass so as to reduce horizontal pressur

structures and mechanisms of the northward propagating boreal summer intraseasonal oscillation abstract the spatial and temporal structures of the northward propagating boreal summer intraseasonal oscillation bsiso are revealed based on the analysis of both the echam4 model simulation and the ncep ncar reanalysis the bsiso structure and evolution characteristics simulated by the model bear many similarities to those derived from the ncep ncar reanalysis the most notable features are the remarkable meridional asymmetries relative to the bsiso convection in the vorticity and specific humidity fields a positive vorticity perturbation with an equivalent barotropic structure appears a few latitude degrees north of the convection center the maximum specific humidity also shows a clear northward shift in the lower troposphere two internal atmospheric dynamics mechanisms are proposed to understand the cause of the northward propagation of the bsiso the first is the vertical shear mechanism the key process associated with this mechanism is the generation of barotropic vorticity due to the couplin

helium and methane measurements in hydrothermal fluids from the mid atlantic ridge the snake pit site at 23 n methane and helium isotopes concentrations have been measured in hydrothermal fluids of black smoker vents at the snake pit area mar 23 n as part of the hydrosnake cruise with the submersible nautile the samples contain large quantities of helium and methane with endmember values of 4 6 10 5 cm3 stp g for helium and 1 38 10 3 cm3 stp g for methane the helium isotopic ratio 3he 4he is 8 4 times the atmospheric ratio these values are strikingly similar to those already obtained on the east pacific rise the ch4 3he ratio is also quite similar ch4 3he 2 6 106 suggesting a non biogenic origin of this gas in the fluids assuming that the range of variation of the 3he concentration data obtained so far from various tectonic settings is close to the genuine range of values encountered on mid ocean ridges the global mass flow involved in the hydrothermal circulation at the ridge s axis is estimated between 1000 and 3000 m3 of water sec leading to a residence time of the global ocean with respect to the hydrothermal circulation between 15 and 45 million years this estimate implies that in addition to the individual vents smokers there is an extensive diffuse circulation of hydrothermal fluids along the ridges in agreement with recent observations concerning heat budgets at hydrothermal sites in the eastern pacific

convectively coupled equatorial waves 1 convectively coupled equatorial waves ccews control a substantial fraction of tropical rainfall variability their horizontal structures and dispersion characteristics correspond to matsuno s 1966 solutions of the shallow water equations on an equatorial beta plane namely kelvin equatorial rossby mixed rossby gravity and inertio gravity waves because of moist processes the tilted vertical structures of ccews are complex and their scales do not correspond to that expected from the linear theory of dry waves the dynamical structures and cloud morphology of ccews display a large degree of self similarity over a surprisingly wide range of scales with shallow convection at their leading edge followed by deep convection and then stratiform precipitation mirroring that of individual mesoscale convective complexes ccews have broad impacts within the tropics and their simulation in general circulation models is still problematic although progress has been made using simpler models a complete understanding of ccews remains a challenge in tropical meteorology

hydrothermal venting from the summit of a ridge axis seamount axial volcano juan de fuca ridge we have mapped the distribution and intensity of submarine hydrothermal emissions from the summit caldera of axial volcano by means of hydrographic and chemical sampling of the water column during annual cruises in four consecutive years 1985 1988 these investigations were undertaken to ascertain the strength of hydrothermal venting relative to other vent fields on the juan de fuca ridge and to gauge the importance of axial volcano as a source of hydrothermal emissions to the northeast pacific ocean measurable temperature anomalies are mostly restricted to a 200 m thick water column within the caldera where they range from a background level of 0 01 c to local maxima of 0 02 0 1 c above known high temperature vent fields the temperature anomaly plume is significantly smaller in both extent and intensity than plumes emitted by vent fields on other segments of the juan de fuca ridge a maximum estimate of the total heat flux from the summit based on the total excess heat and advective velocity of the plume is 8 108 w hydrothermal venting seems surprisingly small for an edifice that testifies to a long term oversupply of magma at a single axial location we speculate that additional heat may be lost from axial volcano by diffuse percolation of sea water over broad areas of its flanks and by magma eruption and venting along flank rift zones

black smokers massive sulphides and vent biota at the mid atlantic ridge the discovery of black smokers massive sulphides and vent biota in the rift valley of the mid atlantic ridge demonstrates that this assemblage of hydrothermal phenomena is not limited to intermediate to fast spreading oceanic ridges hydrothermal exchange processes may thus be important at the ridges which extend through the atlantic ocean and western indian ocean comprising more than half of the 55 000 km global length of seafloor spreading centres

subseasonal intensity variation of the south asian high in relationship to diabatic heating observation and cmip5 models this study investigates the subseasonal intensity variation of south asian high sah and the dynamic linkage with precipitation induced diabatic heating during the summer of 1979 2005 based on the observation and 18 models from the coupled model intercomparison project cmip5 the sah s intensity variation with a period of approximately 10 36 days is identified both in the observation and 18 models by performing an empirical orthogonal function eof analysis on the standardized subseasonal anomalies in geopotential height at 100 hpa over the sah s main body region with the observed strengthening of the sah an enhanced rainfall belt between 70 120 e migrates northward from the equatorial region the northward propagating rainfall belt occupies almost the whole indian subcontinent indochina peninsula and subtropical east asian regions between 20 40 n when the sah reaches the strongest the relative vorticity diagnosis reveals the dynamical linkage between the subseasonal sah s intensity variation and the precipitation anomalies over the asian monsoon region 1 the observed northward propagating rainfall band forms a horizontal gradient of diabatic heating favoring an enhancement of the sah over its southern part 2 when the rainfall band approaches the regions of south and east asia between 20 40 n the increased vertical gradient of diabatic heating in the upper level contributes significantly to the intensification of the sah 3 the horizontal advection process favors the westward expansion of the sah the observation to model comparisons indicate that the model s capacity to reproduce the sah s intensity variation is highly associated with simulations of the anomalous rainfall band and its northward propagation a realistic reproduction of precipitation anomalies is fundamental to simulating the dynamical processes related to diabatic heating and thus the simulation of the sah s subseasonal intensity variation

structure temporal evolution and heat flux estimates from the lucky strike deep sea hydrothermal field derived from seafloor image mosaics 1 here we demonstrate with a study of the lucky strike hydrothermal field that image mosaicing over large seafloor areas is feasible with new image processing techniques and that repeated surveys allow temporal studies of active processes lucky strike mosaics generated from 56 000 images acquired in 1996 2006 2008 and 2009 reveal the distribution and types of diffuse outflow throughout the field and their association with high temperature vents in detail the zones of outflow are largely controlled by faults and we suggest that the spatial clustering of active zones likely reflects the geometry of the underlying plumbing system imagery also provides constraints on temporal variability at two time scales first based upon changes in individual outflow features identified in mosaics acquired in different years we document a general decline of diffuse outflow throughout the vent field over time scales up to 13 years second the image mosaics reveal broad patches of seafloor that we interpret as fossil outflow zones owing to their association with extinct chimneys and hydrothermal deposits these areas encompass the entire region of present day hydrothermal activity suggesting that the plumbing system has persisted over long periods of time loosely constrained to hundreds to thousands of years the coupling of mosaic interpretation and available field measurements allow us to independently estimate the heat flux of the lucky strike system at 200 to 1000 mw with 75 to 90 of this flux taken up by diffuse hydrothermal outflow based on these heat flux estimates we propose that the temporal decline of the system at short and long time scales may be explained by the progressive cooling of the amc without replenishment the results at lucky strike demonstrate that repeated image surveys can be routinely performed to characterize and study the temporal variability of a broad range of vent sites hosting active processes e g cold seeps hydrothermal fields gas outflows etc allowing a better understanding of fluid flow dynamics from the sub seafloor and a quantification of fluxes

northward propagation mechanisms of the boreal summer intraseasonal oscillation in the era interim and sp ccsm abstractmechanisms for the northward propagation np of the boreal summer intraseasonal oscillation bsiso and associated asian summer monsoon asm are investigated using data from the interim ecmwf re analysis era interim herein called erai and the superparameterized community climate system model sp ccsm analyzed mechanisms are 1 destabilization of the lower troposphere by sea surface temperature anomalies 2 boundary layer moisture advection and boundary layer convergence associated with 3 sst gradients and 4 barotropic vorticity anomalies mechanism indices are regressed onto filtered olr anomaly time series to study their relationships to the intraseasonal oscillation iso and to equatorial rossby er waves northward propagation in erai and sp ccsm is promoted by several mechanisms but is dominated by boundary layer moisture advection and the barotropic vorticity effect sst linked mechanisms are of secondary importance but are nonnegligible the magnitudes of np mechanisms vary from

detection of hydrothermal plumes on the northern mid atlantic ridge results from optical measurements abstract several water column surveys conducted on the northern mid atlantic ridge have been instrumental in the discovery of three new hydrothermal venting sites and seven other active segments hydrothermal sources have yet to be pinpointed in six of these segments in this study the observed frequency of high temperature venting from 23 n to 41 n on the mid atlantic ridge mar a distance of approximately 1900 km is one venting system per 150 km of ridge combining these data with those of other investigators for the region from 12 n to 41 n leads to an approximate venting frequency of one site per 90 km of ridge although venting frequencies on sections of the mar within this region are as high as one site per 25 km to support this frequency of venting and considering the larger dimensions of the mar rift valley the ratio of axial to off axis heat loss must be higher on the mar than on faster spreading ridges

the boreal summer intraseasonal oscillation relationship between northward and eastward movement of convection the summertime intraseasonal oscillation iso is an important component of the south asian monsoon lagged regressions of intraseasonally filtered 25 80 days outgoing longwave radiation olr reveal that centers of convection move both northward and eastward from the central equatorial indian ocean subsequent to the initiation of an iso eastward movement of convection is also seen at indian subcontinent latitudes 10 8 208n based on the regression results the summertime iso convection signal appears as a band tilting northwestward with latitude and stretching from the equator to about 208n viewed along any meridian convection appears to propagate northward while equatorial convection propagates to the east to examine the robustness of the connection between eastward and northward movement individual isos are categorized and composited relative to the strength of the large scale eastward component of convection in the central equatorial indian ocean it is found that the majority of isos that exhibit northward movement onto the indian subcontinent 42 out of 54 isos or 78 also exhibit eastward movement into the western pacific ocean it is also found that when convection in the central indian ocean is not followed within 10 20 days by convection in the western pacific ocean 12 out of 54 isos or 22 the independent northward movement of convection in the indian ocean region is somewhat stunted the link between the eastward and northward movement of convection is consistent with an interpretation of the summertime iso in terms of propagating equatorial modes the northward moving portion of convection is forced by surface frictional convergence into the low pressure center of the rossby cell that is excited by equatorial iso convection a similar convergence pattern is seen for the northern winter iso but it does not generate poleward movement due to relatively cool ssts underlying the surface convergence

geomorphological evidence of carbonate build up demise on equatorial margins a case study from offshore northwest australia abstract the demise of miocene carbonate build ups in the browse basin northwest australia has been explained as relating to geological and oceanographic processes these include accelerated tectonic subsidence driven by subduction ocean cooling following the mid miocene climate optimum nutrient excess poisoning by sediment drifts and local erosion driven by current winnowing occurring discretely or simultaneously here we critically assess the evidence for these different mechanisms using a combination of high resolution 3 d seismic data regional 2 d seismic profiles and numerical stratigraphic forward modelling seismic interpretation and numerical modelling found that the proposed uniform subsidence rate of 125 m ma between 16 5 ma and 5 33 ma for the northern browse basin belde et al 2017 when combined with the published estimate of eustatic sea level in miller et al 2005 was insufficient to drown the miocene carbonate sequence and generate the geomorphological changes barrier reef to isolated carbonate build ups observed on seismic data instead a subsidence profile comprising pulses of rapid and slow subsidence is required significantly our results suggest that subsidence rates exceeded 400 m ma in the northern browse basin and that parts of the basin record the accumulation of sediment drifts these sediment drifts are interpreted to have buried some carbonate build ups while suspended sediment reduced light transmissivity inhibiting carbonate production thus we postulate that current activity and excess nutrient supply are key but often overlooked oceanographic processes that lead to the demise of carbonate build ups

diffuse hydrothermal fluids from lucky strike hydrothermal vent field evidence for a shallow conductively heated system chemical analysis of 18 diffuse hydrothermal fluids collected from the lucky strike hydrothermal vent site reveals the presence of less than 7 high temperature hydrothermal end member temperature li and temperature mg relationships for the diffuse fluids indicated two sample groups one group of three samples had temperatures which fell on or below the temperatures expected for conservative mixing between seawater and high temperature vent fluids consistent with mixing and cooling the second grouping had diffuse fluid temperatures greater than expected from conservative mixing of high temperature end member fluids and seawater this indicates that the diffuse hydrothermal effluent was heated conductively during its formation the lucky strike site is characterized by a hydrothermal slab of basaltic fragments indurated by silica and barite it is proposed that the diffuse fluids circulate within the cracks of the slab forming a shallow short pass hydrothermal convection system the source of heat is likely to be high temperature hydrothermal fluids circulating beneath the hydrothermal slab the chemistry of the diffuse fluids shows no evidence for silica precipitation suggesting that the slab is not actively forming from the diffuse fluids at the present

mechanisms of monsoon low frequency variability surface hydrological effects abstract observations indicate that monsoon systems are characterized by orderly large scale and low frequency variations with a time scale of two weeks and sometimes longer regions of ascending motion are observed to form to the north of the equator and propagate slowly northward across southeast asia the propagation appears to be associated with the active break sequence of the summer monsoon which acts as a modulator on the activity of the synoptic scale disturbances a zonally symmetric non linear two layer model containing an interactive ocean and a continent poleward of 18 n is used to investigate the mechanisms which produce the observed low frequency variability only when a full hydrology cycle is considered does the model product variations which resemble the observed structures mechanisms are traced to include the interaction of the components of the total heating function the sensible heat input in the boundary layer although considerably smaller than the other heating components de

hydrothermal activity along the slow spreading lucky strike ridge segment mid atlantic ridge distribution heatflux and geological controls we have reviewed available visual information from the seafloor and recently acquired microbathymetry for several traverses across the lucky strike segment to evaluate the distribution of hydrothermal activity we have identified a new on axis site with diffuse flow ewan and an active vent structure similar to 1 2 km from the axis capelinhos these sites are minor relative to the main field and our total heatflux estimate for all active sites 200 1200 mw is only slightly higher than previously published estimates we also identify fossil sites w of the main lucky strike field a circular feature similar to 200 m in diameter located on the flanks of a rifted off axis central volcano is likely a large and inactive hydrothermal edifice named grunnus we find no indicator of focused hydrothermal activity elsewhere along the segment suggesting that the enhanced melt supply and the associated melt lenses required to form central volcanoes also sustain hydrothermal circulation to form and maintain large and long lived hydrothermal fields hydrothermal discharge to the seafloor occurs along fault traces suggesting focusing of hydrothermal circulation in the shallow crust along permeable fault zones

mechanism for northward propagation of boreal summer intraseasonal oscillation convective momentum transport 1 this study demonstrates that the momentum transport by cumulus convection plays a significant role in the organization and northward propagation of intraseasonal iso convection anomalies over the indian and western pacific regions during boreal summer a version of seoul national university s atmosphere ocean coupled general circulation model simulates northward propagation when convective momentum transport cmt is implemented the northward propagation disappears when cmt is disabled an axially symmetric shallowwatermodel withaparameterized cmtis used to understand the role of cmt in the northward propagation of iso the basic mechanism of northward propagation is the lower level convergence to the north of convection which is induced by the secondary meridional circulation associated with large momentum mixing by convection in the region of large mean vertical shear a large meanverticalshearexistsinsouthasianregionduringboreal summer citation kang i s d kim and j s kug 2010 mechanism for northward propagation of boreal summer intraseasonal oscillation convective momentum transport geophys res lett 37 l24804 doi 10 1029 2010gl045072

how to measure the strength of the east asian summer monsoon defining the intensity of the east asian summer monsoon easm has been extremely controversial this paper elaborates on the meanings of 25 existing easm indices in terms of two observed major modes of interannual variation in the precipitation and circulation anomalies for the 1979 2006 period the existing indices can be classified into five categories the east west thermal contrast north south thermal contrast shear vorticity of zonal winds southwesterly monsoon and south china sea monsoon the last four types of indices reflect various aspects of the leading mode of interannual variability of the easm rainfall and circulations which correspond to the decaying el nino while the first category reflects the second mode that corresponds to the developing el nino the authors recommend that the easm strength can be represented by the principal component of the leading mode of the interannual variability which provides a unified index for the majority of the existing indices this new index is extremely robust captures a large portion 50 of the total variance of the precipitation and three dimensional circulation and has unique advantages over all the existing indices the authors also recommend a simple index the reversed wang and fan index which is nearly identical to the leading principal component of the easm and greatly facilitates real time monitoring the proposed index highlights the significance of the mei yu baiu changma rainfall in gauging the strength of the easm the mei yu which is produced in the primary rain bearing system the east asian ea subtropical front better represents the variability of the easm circulation system this new index reverses the traditional chinese meaning of a strong easm which corresponds to a deficient mei yu that is associated with an abnormal northward extension of southerly over northern china the new definition is consistent with the meaning used in other monsoon regions worldwide where abundant rainfall within the major local rain bearing monsoon system is considered to be a strong monsoon

global analysis of the pressure adjustment mechanism over sea surface temperature fronts using airs aqua data 1 we investigate the signatures of atmospheric pressure adjustment mechanism for surface wind convergence divergence over major sea surface temperature sst frontal regions using global observations of satellite sounding and scatterometer lower tropospheric air thickness which includes a sea level pressure component modified by air temperature in the marine atmospheric boundary layer is analyzed and the relation between the laplacian of the thickness and wind convergence are examined among four sst frontal regions in mid latitudes correlation between the thickness laplacian and wind convergence is the largest over the gulf stream followed by those for the agulhas return current and for the brazil malvinas current and relatively small but still significant over the kuroshio oyashio extension these correlations strongly suggest that the pressure adjustment mechanism ubiquitously plays an important role in air sea interaction over the global sst frontal regions furthermore air temperatures in the first two regions exhibit sst relating signatures even in the mid troposphere

mechanism of the northward propagating intraseasonal oscillation insights from a zonally symmetric model abstract the propagation and initiation mechanisms of the boreal summer intraseasonal oscillation bsiso in the south asian summer monsoon are examined with a zonally symmetric atmospheric model in the axially symmetric model the effects of zonally propagating atmospheric waves are intentionally excluded the model specifies mean flows and depicts the lowest baroclinic mode and a barotropic mode in the free troposphere the two vertical modes are coupled by the time mean vertical wind shear the model atmosphere produces a 15 20 day oscillation which is characterized by northward propagation of convection from south of the equator to the indian monsoon trough region and a reinitiation of convection in the region between 10 s and the equator the northward propagation in the model is produced by the free troposphere barotropic divergence which leads convection by about a quarter of a cycle the vertical advection of summer mean easterly vertical wind shear by perturbation vertical motion inside the con

a model for the boreal summer intraseasonal oscillation abstract the tropical intraseasonal oscillation iso exhibits pronounced seasonality the boreal summer iso is more complex than its winter counterpart due to the coexistence of equatorial eastward off equatorial westward and northward propagating low frequency modes and their interactions based on observational evidence and results obtained from numerical experiments a mechanism is proposed for the boreal summer iso in which the northern hemisphere summer monsoon nhsm circulation and moist static energy distribution play essential roles with a climatological july mean basic state the life cycle of model low frequency waves consists of four processes an equatorial eastward propagation of a coupled kelvin rossby wave packet an emanation of moist rossby waves in the western pacific a westward propagation and amplification of the rossby waves in south asian monsoon regions and a reinitiation of the equatorial disturbances over the central indian ocean the life cycle spans about one month and p

hydrothermal methane venting between 12 n and 26 n along the mid atlantic ridge hydrographic surveys along the mid atlantic ridge mar between 12 n and 26 n carried out from 1984 to 1990 show a variable pattern of ch4 rich water column plumes the vertical distribution of ch4 at stations located every 20 40 km is presented along this 1200 km long section of the mar ch4 venting is clearly demonstrated ch4 enriched fluids rise from vents as plumes spreading is confined to the axial valley due to the topography of the mar ch4 contents from 45 nmol to 675 nmol kg are measured in the buoyant plumes above the two active hydrothermal sites mark 23 n tag 26 n known at present whereas ch4 anomalies up to 3 6 nmol kg are typically observed in plumes emitted either on the inner floor on the walls and or at the top of the rift mountains along the studied ridge section ch4 concentrations 45 mol to 144 mol kg in mark and tag vent fluids are of the same order of magnitude as those found in the east pacific rise fluids even though ch4 is known to be unstable with respect to oxidation by dissolved oxygen and in spite of its microbial oxidation in plumes these results confirm ch4 to be a good indicator to track hydrothermal plumes and to map the variation of hydrothermal activity along mid oceanic ridges moreover between 12 and 26 n along the mar ch4 results show that while hydrothermal activity is present everywhere along the ridge it is predominant near fracture zones fz kane fz 15 20 n fz comparison of ch4 tracer with total dissolvable manganese tdm tracer in plumes allows us to differentiate subseafloor hydrothermal processes the high tdm ch4 found above tag and mark areas is indicative of basalt seawater interaction while at 15 n the low tdm ch4 provides evidence of fluid circulation in ultrabasic rocks ch4 data confirm the association between mantle degassing hydrothermal activity and serpentinization along this 12 26 n section of the mid atlantic ridge

coral reefs and sea level change abstract coral reefs provide significant evidence for former sea level positions because of their geological preservation and suitability for dating interpretation of this evidence presumes an understanding of reef geomorphology modern reef organism distributions and environmental factors influencing them fossil reef terraces formed during the last interglacial marine oxygen isotope mis substage 5e 128 116 ka are prevalent on many tropical shorelines and there has been ongoing debate as to the height reached by sea level during that highstand observations from numerous last interglacial sites suggest that sea level was at least 3 m above present sea level implying less extensive icesheets than at present an elevation of 6 m has commonly been adopted when correcting tectonically active sites for uplift recent compilations suggest elevations up to 8 9 m but incorporate few observations from reefs where the last interglacial is found below sea level oscillation of sea level during mis 5e has been interpreted from several sites with recent studies inferring rapid rise of several metres at the end of the interglacial these interpretations are at the limits to the precision with which corals can currently be dated and their palaeo water depths inferred it is not surprising that constraining last interglacial sea level changes within uncertainties of less than 1 2 m remains controversial considering sea level variations recognised between reef sites in the holocene and observed geographical variation in isostatic or flexural adjustments fossil coral reefs on uplifting margins also provide clear evidence for mis substages 5c and 5a and those on huon peninsula indicate fluctuations related to heinrich events mis 3 interpretations show considerable variability between sites with still greater uncertainties about sea level timing and elevation during previous interglacials future study of extensive sequences of fossil reefs preserved on rapidly subsiding margins could address these uncertainties submerged reefs have already yielded important information about sea level rise during the last deglaciation coring around barbados and tahiti as well as on the huon peninsula has produced a broadly consistent picture of ice melt reflecting eustatic change since the last glacial maximum these studies have shown the sensitivity of reefs to rapid sea level rise associated with meltwater pulses with some reefs drowning while others back stepped integrated ocean drilling program iodp expeditions to tahiti and recently the great barrier reef extended these records but details of timing nature and impact of deglacial meltwater pulses remain elusive studies of holocene reefs have indicated different growth strategies some kept up with sea level while others caught up when sea level decelerated holocene sea level appears to have experienced a gradual rise up to present across the caribbean providing accommodation space for reefs to accrete vertically whereas in the indo pacific sea level has been near its present level since 7 ka with many reef flats emergent following a slight fall of sea level caused by ocean siphoning microatolls on reef flats provide perhaps the clearest evidence of past sea level position but in their absence novel biological or other sea level indicators are required to better constrain palaeo water depths there is an urgent need for further research from additional key reef locations not only to decipher processes driving past sea level change and its geographical variability but also to better understand how coral reefs will respond in the context of future sea level rise

real time observation of dispersed hydrothermal plumes using nephelometry examples from the mid atlantic ridge abstract as part of the 1984 1985 noaa vents program on the mid atlantic ridge nephelometry was used to provide real time detection and tracking of dispersed hydrothermal plumes at all nine 1984 study sites hydrothermal activity was detected by in situ real time nephelometer measurements and later confirmed by dissolved mn and particulate fe measurements these same techniques were employed in a site specific survey of the trans atlantic geotraverse tag area in 1985 where large water column anomalies in turbidity and in dissolved mn helped lead to the discovery of high temperature black smokers the optical response of the nephelometer was to hydrothermally derived particulate matter thus strong correlations existed between the nephelometer readings and total suspended matter r 0 98 n 34 and particulate fe r 0 88 n 32 in addition digital nephelometer data correlated well with dissolved mn r 0 88 n 78 throughout a large concentration range 0 2 31 0 nmol kg these data provide good evidence for the utility of in situ nephelometer measurements for locating and surveying plumes from hydrothermal vents it also appears possible within limits to predict concentrations of in situ total suspended matter of particulate fe and of dissolved mn

role of north indian ocean air sea interaction in summer monsoon intraseasonal oscillation abstractair sea coupling processes over the north indian ocean associated with the indian summer monsoon intraseasonal oscillation miso are investigated observations show that miso convection an

theory applied to the mid atlantic ridge hydrothermal plumes the finite difference approach a system of differential equations describing the entrainment of ambient seawater during the rise of a buoyant hydrothermal plume has been solved by an explicit finite difference method chosen for its ease of application an equation for tracer concentration has been added so that concentrations in the neutrally buoyant plume can be calculated for those elements whose background profiles vary over the depth range of the buoyant plume the height of plume rise can be related directly to the thermal and hydrothermal vent flux for the tag vent field 26 n mar five plume layers have been identified the calculated heat flux is 500 940 mw and the fluid flux is 0 210 0 392 m3 s 1 the fluid flux to the neutrally buoyant plume is 1460 2740 m3 s 1 calculated plume concentrations of mn compared with measurements made at tag in 1988 indicate that there is either 50 removal of manganese in the buoyant plume or that low temperature vent fluids contribute about 50 of the total thermal output of the tag vent field