the cr renazzo type carbonaceous chondrite group and its implications abstract a petrologic geochemical and oxygen isotopic study of eight meteorites identified as cr renazzo type chondrites reveals that they have a set of similar properties that distinguishes them from other chondrite groups and confirms cr as a carbonaceous chondrite group characteristics of the cr group include 1 1 abundant large multilayered fe ni metal rich type i chondrules 2 2 abundant matrix and dark inclusions di that contain microchondrules microfragments and magnetite framboids and platelets 3 3 unique assemblages of serpentine and chlorite rich phyllosilicates and ca carbonates 4 4 ca carbonate rims on chondrules 5 5 abundant fe ni metal with a positive ni vs co trend and a solar ni co ratio 6 6 low abundance of refractory rich inclusions 7 7 amoeboid olivine aggregates aoa with mn rich and mn poor forsterite and 8 8 oxygen isotopic compositions that form a unique mixing line the cr chondrites are breccias consisting of two major components the large layered chondrules and the matrix dark inclusions al rais is an anomalous member in having a higher abundance of the dark inclusion component 70 vol and this accounts for its having a higher volatile content than other members of the group the conditions that prevailed during aqueous alteration of the cr chondrites differed from those of other hydrated chondrite groups and may be the result of a higher temperature environment than that for the ci and cm chondrites the cr chondrite components chondrules matrix dark inclusions etc experienced aqueous alteration to differing degrees prior to assembly of the host chondrites and dark inclusions represent a lithology that was altered by water to a greater degree than the rest of the meteorite the overall degree of hydration in cr chondrites varies among meteorites with al rais being the most hydrated the oxygen isotopic variation of the whole rocks chondrules and matrices may be related to degree of hydration indicating that cr chondrites interacted with a water rich component having heavy oxygen and that was the same as ci and cm water

microchondrules in three unequilibrated ordinary chondrites we report on a suite of microchondrules from three unequilibrated ordinary chondrites uocs microchondrules a subset of chondrules that are ubiquitous components of uocs commonly occur in fine grained chondrule rims although may also occur within matrix microchondrules have a variety of textures cryptocrystalline microporphyritic radial glassy in some cases their textures and in many cases their compositions are similar to their larger host chondrules bulk compositions for both chondrule populations frequently overlap the primary material that composes many of the microchondrules has compositions that are pyroxene normative and is similar to low ca pyroxene phenocrysts from host chondrules primary material rarely resembles olivine or plagioclase some microchondrules are composed of feo rich material that has compositions similar to the bulk submicron fine grained rim material these microchondrules however are not a common compositional type and probably represent secondary feo enrichment microchondrules may also be porous suggestive of degasing to form vesicles our work shows that the occurrence of microchondrules in chondrule rims is an important constraint that needs to be considered when evaluating chondrule forming mechanisms we propose that microchondrules represent melted portions of the chondrule surfaces and or the melt products of coagulated dust in the immediate vicinity of the larger chondrules we suggest that through recycling events the outer surfaces of chondrules were heated enough to allow microchondrules to bud off as protuberances and become entrained in the surrounding dusty environment as chondrules were accreting fine grained rims microchondrules are thus byproducts of cyclic processing of chondrules in localized environments their occurrence in fine grained rims represents a snapshot of the chondrule forming environment we evaluate mechanisms for microchondrule formation and hypothesize a potential link between the emergence of type ii chondrules in the early solar system and the microchondrule bearing fine grained rims surrounding type i chondrules

peak metamorphic temperatures in type 6 ordinary chondrites an evaluation of pyroxene and plagioclase geothermometry quantifying the peak temperatures achieved during metamorphism is critical for understanding the thermal histories of ordinary chondrite parent bodies various geothermometers have been used to estimate equilibration temperatures for chondrites of the highest metamorphic grade type 6 but results are inconsistent and span hundreds of degrees because different geothermometers and calibration models were used with different meteorites it is unclear whether variations in peak temperatures represent actual ranges of metamorphic conditions within type 6 chondrites or differences in model calibrations we addressed this problem by performing twopyroxene geothermometry using quilf95 on the same type 6 chondrites for which peak temperatures were estimated using the plagioclase geothermometer nakamuta and motomura 1999 we also calculated temperatures for published pyroxene analyses from other type 6 h l and ll chondrites to determine the most representative peak metamorphic temperatures for ordinary chondrites pyroxenes record a narrow overlapping range of temperatures in h6 865 926 c l6 812 934 c and ll6 874 945 c chondrites plagioclase temperature estimates are 96 179 c lower than pyroxenes in the same type 6 meteorites plagioclase estimates may not reflect peak metamorphic temperatures because chondrule glass probably recrystallized to plagioclase prior to reaching the metamorphic peak the average temperature for h l and ll chondrites 900 c which agrees with previously published oxygen isotope geothermometry is at least 50 c lower than the peak temperatures used in current asteroid thermal evolution models this difference may require minor adjustments to thermal model calculations

barotropic rossby waves radiating from tropical instability waves in the pacific ocean abstracttropical instability waves are triggered by instabilities of the equatorial current systems and their sea level signal with peak amplitude near 5 n is one of the most prominent features of the dynamic topography of the tropics cross spectral analysis of satellite altimetry observations shows that there is sea level variability in the pacific ocean as far north as hawaii i e 20 n that is coherent with the sea level variability near 5 n associated with tropical instability waves within the uncertainty of the analysis this off equatorial variability obeys the dispersion relation for nondivergent barotropic rossby waves over a fairly broad range of periods 26 38 days and zonal wavelengths 9 23 of longitude that are associated with tropical instability waves the dispersion relation and observed wave properties further suggest that the waves are carrying energy away from the instabilities toward the north pacific subtropical gyre which together with the observed coherence of the sea

observations of coupling between surface wind stress and sea surface temperature in the eastern tropical pacific satellite measurements of surface wind stress from the quikscat scatterometer and sea surface temperature sst from the tropical rainfall measuring mission microwave imager are analyzed for the three month period 21 july 20 october 1999 to investigate ocean atmosphere coupling in the eastern tropical pacific oceanic tropical instability waves tiws with periods of 20 40 days and wavelengths of 1000 2000 km perturb the sst fronts that bracket both sides of the equatorial cold tongue which is centered near 1 8s to the east of 1308w these perturbations are characterized by cusp shaped features that propagate systematically westward on both sides of the equator the space time structures of these sst perturbations are reproduced with remarkable detail in the surface wind stress field the wind stress divergence is shown to be linearly related to the downwind component of the sst gradient with a response on the south side of the cold tongue that is about twice that on the north side the wind stress curl is linearly related to the crosswind component of the sst gradient with a response that is approximately half that of the wind stress divergence response to the downwind sst gradient the perturbed sst and wind stress fields propagate synchronously westward with the tiws this close coupling between sst and wind stress supports the wallace et al hypothesis that surface winds vary in response to sst modification of atmospheric boundary layer stability

tropical instability wave energetics observations from the tropical instability wave experiment ocean velocity data from an array of subsurface moorings deployed from may 1990 to june 1991 during the tropical instability wave experiment are used to study the energetics of planetary waves in the vicinity of the equator at 1408w such waves observed from august to december 1990 were initiated by barotropic instability arising primarily from the cyclonic shear region of the south equatorial current and equatorial undercurrent just north of the equator subsequently local barotropic production continued to maintain and modulate these tropical instability waves through a combination of cyclonic shear and meridional velocity component divergence just north of the equator the end of the wave season coincided with the propagation past the array of a large intraseasonal kelvin wave

why the itcz is mostly north of the equator abstract although the distribution of sunshine is symmetrical about the equator the earth s climate is not climatic asymmetries are prominent in the eastern tropical pacific and atlantic oceans where the regions of maximum sea surface temperature convective cloud cover and rainfall are north of the equator this is the result of two sets of factors interactions between the ocean and atmosphere that are capable of converting symmetry into asymmetry and the geometries of the continents that determine in which longitudes the interactions are effective and in which hemisphere the warmest waters and the intertropical convergence zone are located the ocean atmosphere interactions are most effective where the thermocline is shallow because the winds can readily affect sea surface temperatures in such regions the thermocline happens to shoal in the eastern equatorial pacific and atlantic but not in the eastern indian ocean because easterly trade winds prevail over the tropical atlantic and pacific wher

mechanism of seasonal eddy kinetic energy variability in the eastern equatorial pacific ocean enhanced mesoscale eddy activities or tropical instability waves tiws exist along the northern front of the cold tongue in the eastern equatorial pacific ocean in this study we investigate seasonal variability of eddy kinetic energy eke over this region and its associated dynamic mechanism using a global eddy resolving ocean general circulation model ogcm simulation the equatorial mooring data and satellite altimeter observations the seasonal varying enhanced eke signals are found to expand westward from 100 w in june to 180 w in december between 0 6 n this westward expansion in eke is closely connected to the barotropically baroclinically unstable zonal flows that are in thermal wind balance with the seasonal varying thermocline trough along 4 n by adopting an 1 layer reduced gravity model we confirm that the seasonal perturbation of the thermocline trough is dominated by the anti cyclonic wind stress curl forcing which develops due to southerly winds along 4 n from june to december

an analysis of tropical instability waves in a numerical model of the pacific ocean 2 generation and energetics of the waves this work was supported by the department of com merce noaa under grant na56gp0026 one of the au thors sm was partially supported by a nasa global change fellowship ngt 30288 another author ab was supported by a ucar postdoctoral fellowship

the influence of sea surface temperature on surface wind in the eastern equatorial pacific weekly to monthly variability abstract temporal correlations between near equatorial surface wind and sea surface temperatures sst at 11 w in the eastern pacific ocean are investigated using data from an array of moored sensors between 5 n and 5 s the signature of tropical instability waves with periods of 20 30 days is apparent in time series of sst and both the meridional and zonal wind components results indicate the existence of a band of pronounced horizontal divergence in the surface wind field associated with the large meridional sst gradient equatorial front normally located just north of the equator perturbations of the equatorial front by the instability waves induce fluctuations in the overlying winds evidence of the air sea coupling is stronger in time series of the meridional gradients of wind and sst than between time series of the variables themselves the meridional differencing serves as a high pass filter in the space domain which removes planetary scale wind fluctuations that are unrelated to the local sst

alh85085 a unique volatile poor carbonaceous chondrite with possible implications for nebular fractionation processes abstract allan hills 85085 is a unique chondrite with affinities to the al rais renazzo clan of carbonaceous chondrites its constituents are less than 50 m in mean size chondrules and microchondrules of all textures are present nonporphyritic chondrules are unusually abundant the mean compositions of porphyritic nonporphyritic and barred olivine chondrules resemble those in ordinary chondrites except that they are depleted in volatile elements ca al rich inclusions are abundant and largely free of nebular alteration they comprise types similar to those in cm and co chondrites as well as unique types calcium dialuminate occurs in several inclusions metal silicate and sulfide compositions are close to those in cm co chondrites and al rais and renazzo c1 chondrite clasts and metal rich reduced clasts are present but opaque matrix is absent siderophile abundances in alh85085 are extremely high e g fe si 1 7 solar and volatiles are depleted e g na si 0 25 solar s si 0 03 solar nonvolatile lithophile abundances are similar to those in al rais renazzo and cm and co chondrites alh85085 agglomerated when temperatures in the nebula were near 1000 k in the same region where renazzo al rais and the ci chondrites formed agglomeration of high temperature material may thus be a mechanism by which the fractionation of refractory lithophiles occurred in the nebula chondrule formation must have occurred at high temperatures when clumps of precursors were small after agglomeration alh85085 was annealed and lightly shocked c1 and other clasts were subsequently incorporated during late stage brecciation

opaque phases in type ii chondrules from cr2 chondrites implications for cr parent body formation abstract we report the results of a detailed study of sulfide bearing opaque assemblages from the mac 87320 eet 92011 and renazzo cr carbonaceous chondrites the objectives of this study are to 1 characterize sulfide and associated phases within cr2 chondrites 2 determine the petrographic relationship between sulfides metals and chondrules 3 constrain the history of type ii chondrules 4 ascertain the environments in which type ii chondrules formed and were altered and 5 unravel the formation and alteration history of the cr parent body as recorded in sulfide bearing assemblages sulfide bearing opaque assemblages occur primarily within type ii feo rich chondrules the sulfide assemblages are concentrated near the chondrule edges assemblages in mac 87320 are composed of troilite phosphate and ni rich metal eet 92011 contains assemblages composed of pentlandite troilite and ni rich metal the assemblages in renazzo contain tochilinite magnetite troilite pentlandite and phosphate in all of the assemblages in renazzo the tochilinite is fine grained and intimately mixed with troilite pentlandite or magnetite opaque assemblages in cr chondrites record a complex history that includes both high and low temperature processes the morphology and composition of sulfides in cr2 chondrites suggests that the sulfide bearing assemblages originally formed in gas solid reactions in the nebula at temperatures above the fe fes eutectic 988 c many of the assemblages were subsequently aqueously altered on the cr chondrite parent body to various degrees at temperatures from 50 to 200 c we combine these observations and interpretations to provide a detailed model of the history of the cr parent body

dynamics on seasonal variability of eke associated with tiws in the eastern equatorial pacific ocean abstractenergetic mesoscale eddies vortices associated with tropical instability waves tiws exist in the eastern equatorial pacific ocean between 0 and 8 n this study examines the seasonal va

a linear relationship between enso intensity and tropical instability wave activity in the eastern pacific ocean the interannual variations of tropical instability waves tiws in the eastern pacific ocean and their relationships with enso intensity are studied using a 28 year long coupled atmosphere ocean general circulation model cgcm simulation the activity of tiws is measured by the root mean square value of the 50 day high pass filtered sea surface temperature sst perturbations produced in the simulation the cgcm realistically produces two branches of large tiw activity near the equator one at 2 n and the other at 2 s it is found that along both branches there are linear relationships between the year to year variations of tiw activity and those of enso intensity tiw activity is enhanced or reduced in proportion to the nino3 sst anomalies with larger activity in la nina years and smaller activity in el nino years it is found that enso modulates tiw activity in both branches primarily by changing the latitudinal sst gradient associated with the sst front immediately north of the equator weaker correlations are found between the year to year variations of tiw activity and those of the ocean current shears between the south equatorial current and the equatorial undercurrent or the north equatorial countercurrent this cgcm study suggests that the baroclinic instability associated with the northern sst front is a major generation mechanism for both the northern and southern tiw branches in the eastern pacific ocean

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

structure of intraseasonal kelvin waves in the equatorial pacific ocean abstract previous studies have shown that intraseasonal kelvin waves are a prominent mode of variability in the eastern and central equatorial pacific these waves appear to be remotely forced by wind variations in the western pacific and propagate eastward at approximately first baroclinic mode phase speeds in this study moored temperature and velocity time series data from 1984 to 1987 between 110 and 140 w are studied to isolate the kelvin wave structures and to document their wave mean flow interactions with the south equatorial current equatorial undercurrent ruc system observed structures at periods of 59 125 days have rms amplitudes of about 10 cm s 1 for zonal velocity and about 1 c for temperature in the thermocline these structures exhibit significant departures from linear no mean flow theory zonal velocity is intensified below the euc core and temperature variability in the thermocline is weaker on the equator than 1 5 off the equator additionally the wave temperature signal at the

burial of terrestrial organic matter in marine sediments a re assessment 1 calculations based on recent observations indicate that approximately one third of the organic matter presently being buried in marine sediments may be of terrestrial origin with the majority of this terrestrial organic matter tom burial occurring in muddy deltaic sediments these calculations further suggest that the remineralization of terrestrial organic matter in the oceans is also much less efficient than that of marine organic matter these two underappreciated observations have important implications in terms of our understanding of the controls on the global carbon cycle from a paleoceanographic perspective the results presented here also suggest that changes in tom burial on glacial interglacial timescales have the potential to impact the global carbon cycle i e atmospheric co2 levels

coupled ocean atmospheric waves on the equatorial front striking 20 30 day sea surface temperature waves observed along the equatorial front in the later half of the year are generally believed to be of an oceanic origin here we report the detection of atmospheric waves that are unambiguously tied to these oceanic waves using new satellite measurements of surface winds a general circulation model simulation reveals that these atmospheric waves have a shallow vertical structure trapped in the planetary boundary layer pbl unlike el nino southern oscillation where changes in deep convection are the cause of anomalous winds vertical wave motion penetrates well above the pbl and is likely to impact the distribution and transport of climatically important gas species such as ozone and dimethyl sulfide

physical properties of chondrules in different chondrite groups implications for multiple melting events in dusty environments chondrite groups cv ck cr with large average chondrule sizes have low proportions of rp plus c chondrules high proportions of enveloping compound chondrules high proportions of chondrules with thick igneous rims and relatively low proportions of type i chondrules containing sulfide in contrast chondrite groups cm co oc r eh el with smaller average chondrule sizes have the opposite properties equilibrated ck chondrites have plagioclase with relatively low na equilibrated oc r eh and el chondrites have more sodic plagioclase enveloping compound chondrules and chondrules with igneous rims formed during a remelting event after the primary chondrule was incorporated into a dustball repeated episodes of remelting after chondrules were surrounded by dust would tend to produce large chondrules rp and c chondrules formed by complete melting of their precursor assemblages remelting of rp and c chondrules surrounded by dust would tend to produce porphyritic chondrules as small dust particles mixed with the melt providing nuclei for crystallizing phenocrysts this process would tend to diminish the numbers of rp and c chondrules correlations among these chondrule physical properties suggest that chondrite groups with large chondrules were typically surrounded by thick dust rich mantles that formed in locally dusty nebular environments chondrules that were surrounded by thick dust mantles tended to cool more slowly because heat could not quickly radiate away slow cooling led to enhanced migration of sulfide to chondrule surfaces and more extensive sulfide evaporation these chondrules also lost na the plagioclase that formed from equilibrated ck chondrites was thus depleted in na

microchondrule bearing clast in the piancaldoli ll3 meteorite a new kind of type 3 chondrite and its relevance to the history of chondrules in the piancaldoli ll3 chondrite we found a mm sized clast containing 100 chondrules 0 2 64 m in apparent diameter much smaller than any previously reported that are all of the same textural type radial pyroxene fs1 17 this clast like other type 3 chondrites has a fine grained ferich opaque silicate matrix sharply defined chondrules abundant low ca clinopyroxene and minor troilite and si and cr bearing metallic fe ni however the very high modal matrix abundance 63 8 vol unique characteristics of the chondrules and absence of microscopically observable olivine indicate that the clast is a new kind of type 3 chondrite most chondrules have feo rich edges and chondrule size is inversely correlated with chondrule core feo concentration the first reported correlation of chondrule size and composition chondrules acquired fe by diffusion from fe rich matrix material during mild metamorphism possibly before final consolidation of the rock microchondrules those chondrules 100 m in diameter are also abundant in another new kind of type 3 chondrite clast in the rio negro l chondrite regolith breccia in other type 3 chondrite groups microchondrule abundance appears to be anticorrelated with mean chondrule size viz 0 02 0 04 vol in h and co chondrites and 0 006 vol in l ll and cv chondrites microchondrules probably formed by the same process that formed normal sized droplet chondrules melting of pre existing dustballs because most compound chondrules in the clast and other type 3 chondrites formed by collisions between chondrules of the same textural type we suggest that dust grains were mineralogically sorted in the nebula before aggregating into dustballs the sizes of compound chondrules and chondrule craters which resulted from collisions of similarly sized chondrules while they were plastic indicate that size sorting of dustballs occurred before chondrule formation probably by aerodynamic processes in the nebula we predict that other kinds of type 3 chondrites exist which contain chondrule abundances size ranges and proportions of textural types different from known chondrite groups

accretionary dust mantles in cm chondrites evidence for solar nebula processes abstract the texture and modal composition of fourteen carbonaceous chondrites of the cm group were studied in detail to unravel the origin of their various components and the evolution of their parent body ies the analysis and mapping of complete thin sections by scanning electron and optical microscopy revealed textural units in most samples in which all coarse grained primordial chondritic components chondrules chondrule fragments refractory inclusions particles rich in hydrous silicates pcp and various mineral fragments are coated by fine grained serpentine and tochilinite rich dust the dust mantled particles have spheroidal shapes and form a special lithology in which they are densely aggregated and compacted without any interstitial clastic material the dust mantles termed accretionary dust mantles and their host lithology called primary accretionary rock are interpreted as products of accretion processes in the solar nebula an origin by processes on the parent body is excluded for textural and mineralogical reasons most cm chondrites are affected by secondary impact induced brecciation of variable intensity except for yamato 791198 which is composed entirely of a primary accretionary rock obviously unaltered by secondary parent body processes such as aqueous alteration or brecciation the cm chondrites y74662 haripura cold bokkeveld kivesvaara mighei pollen nogoya y793321 alh 83100 murray and murchison consist of clasts of primary accretionary rock embedded in a fine grained clastic matrix derived from primary rock material the volume percentage of the clastic matrix ranges from 5 y74662 to 76 murchison bells and essebi are brecciated and affected by aqueous alteration to an extent that fragments of primary rock are not preserved the evaluation of literature data indicates that solar wind implanted noble gases are absent in the primary accretionary rock component of cm chondrites they are only present in brecciated samples it must be concluded from the relation between the content of trapped solar wind and degree of brecciation that 1 the solar noble gases are residing exclusively in the clastic matrix and 2 some cm chondrites are regolith breccias and others are fragmental or monomict breccias both types were formed on the parent body although the latter were never exposed to the solar wind based on the results of textural chemical and mineralogical investigations we conclude that a major portion of the water bearing phases in cm chondrites were produced by the hydration of refractory phases prior to the formation of dust mantles and prior to the formation of the recent cm parent body this process requires special physicochemical conditions which allow the crystallization of oh bearing silicates e g higher density of the nebula gas or special precursor planetesimals of the cm chondrite parent body

the origin of chondrules and chondrites debris from low velocity impacts between molten planetesimals we investigate the hypothesis that many chondrules are frozen droplets of spray from impact plumes launched when thin shelled largely molten planetesimals collided at low speed during accretion this scenario here dubbed splashing stems from evidence that such planetesimals intensely heated by 26al were abundant in the protoplanetary disk when chondrules were being formed approximately 2 myr after calcium aluminum rich inclusions cais and that chondrites far from sampling the earliest planetesimals are made from material that accreted later when 26al could no longer induce melting we show how splashing is reconcilable with many features of chondrules including their ages chemistry peak temperatures abundances sizes cooling rates indented shapes relict grains igneous rims and metal blebs and is also reconcilable with features that challenge the conventional view that chondrules are flash melted dust clumps particularly the high concentrations of na and feo in chondrules but also including chondrule diversity large phenocrysts macrochondrules scarcity of dust clumps and heating we speculate that type i feo poor chondrules come from planetesimals that accreted early in the reduced partially condensed hot inner nebula and that type ii feo rich chondrules come from planetesimals that accreted in a later or more distal cool nebular setting where incorporation of water ice with high 17o aided oxidation during heating we propose that multiple collisions and repeated re accretion of chondrules and other debris within restricted annular zones gave each chondrite group its distinctive properties and led to so called complementarity and metal depletion in chondrites we suggest that differentiated meteorites are numerically rare compared with chondrites because their initially plentiful molten parent bodies were mostly destroyed during chondrule formation

the three dimensional structure of an upper ocean vortex in the tropical pacific ocean in the equatorial pacific ocean easterly trade winds and the earth s rotation combine to drive surface currents away from the equator thereby causing cold nutrient rich subsurface water to upwell the front1 that forms between this upwelled water and warmer waters north of the equator is sometimes visible as a spectacular line in the sea 2 between 2 and 6 n westward propagating cusp shaped disturbances observed along this front3 have been attributed to the effect of dynamical instabilities in the system of zonal equatorial currents4 11but the connection between these phenomena remains unclear here we report extensive measurements from shipboard sensors satellite and drifting buoys which reveal the three dimensional structure of an anticyclonic eddy or vortex 500 km in diameter and centred at 4 n we suggest that cusp shaped disturbances of the front are caused by trains of large amplitude vortices which are driven by instability of the mean zonal shear we show that these vortices not only play an important role in the meridional transport of heat salt and momentum but are also associated with regions of intense horizontal convergence along the front where dramatic concentrations of marine life are observed

comparing wild 2 particles to chondrites and idps we compare the observed composition ranges of olivine pyroxene and fe ni sulfides in wild 2 grains with those from chondritic interplanetary dust particles idps and chondrite classes to explore whether these data suggest affinities to known hydrous materials in particular wild 2 olivine has an extremely wide composition range from fa096 with a pronounced frequency peak at fa1 the composition range displayed by the low calcium pyroxene is also very extensive from fs48 to fs0 with a significant frequency peak centered at fs5 these ranges are as broad or broader than those reported for any other extraterrestrial material wild 2 fe ni sulfides mainly have compositions close to that of fes with less than 2 atom ni to date only two pentlandite grains have been found among the wild grains suggesting that this mineral is not abundant the complete lack of compositions between fes and pentlandite with intermediate solid solution compositions suggests but does not require that fes and pentlandite condensed as crystalline species i e did not form as amorphous phases which later became annealed while we have not yet observed any direct evidence of water bearing minerals the presence of ni bearing sulfides and magnesium dominated olivine and low ca pyroxene does not rule out their presence at low abundance we do conclude that new investigations of major and minorelement compositions of chondrite matrix and idps are required

observed horizontal temperature advection by tropical instability waves 1 velocity data from moored current meters is combined with satellite sea surface temperature sst to compute oceanic mixed layer temperature advection by tropical instability waves tiws for the years 2002 to 2005 it is found that this process heats the equatorial mixed layer at an annual mean rate of 0 8 c month at 0 n 140 w and 2 8 c month at 0 n 110 w at 0 n 110 w approximately 25 of the heating is contributed by zonal temperature advection a process that has often been assumed to be negligible from a nine month segment of data may 2004 february 2005 the zonal temperature advection at 2 n 140 w has been estimated to be approximately 0 7 c month much larger than the equatorial value for the same time period thus the data supports a recent hypothesis that tropical instability waves contribute a significant mean zonal temperature advection with off equatorial maxima to the equatorial mixed layer heat budget comparisons with numerical model results suggest that current ocean general circulation models can realistically simulate important aspects of tropical eddy mixed layer interactions

wind generated equatorial kelvin waves observed across the pacific ocean abstract sea level fluctuations during 1978 80 at equatorial pacific islands separated by as much as one quarter of the earth s circumference are coherent at periods of 1 6 weeks with phases implying eastward propagation eastward speeds are 16 7 5 higher than expected for a linear first baroclinic mode kelvin wave based upon hydrography zonal winds in the western pacific exhibit variation on meridional scales comparable to those of equatorial ocean baroclinic motions roughly one quarter of sea level variance in the 1 6 week period range can be explained by local zonal wind alone the observed admittance magnitude o 0 1 cm sea level per m s 1 2 zonal wind pseudo stress and phase lag a few days sea level lagging wind can be accounted for in a linear model of baroclinic equatorial kelvin waves generated by a crudely idealized wind patch of 1000 km zonal scale zonal winds at the equator excite among other things low mode kelvin waves which are recognizable o 10000 km to the east of the for

eddy energetics in the upper equatorial pacific during the hawaii to tahiti shuttle experiment abstract eddy energetics in the central equatorial pacific ocean is examined using acoustic doppler current profiler velocities and ctd densities collected during the hawaii to tahiti shuttle experiment in 1979 80 three distinct sources of eddy energy are identified with varying degrees of statistical reliability and are interpreted as evidence for three separate instabilities of the mean flow field an instability at and just north of the equator occurs primarily in boreal summer and fall it arises from the cyclonic shear between the equatorial undercurrent and the south equatorial current sec north of the equator the instability is present only when and where both currents are well developed and there is little involvement of the shear between the sec and the north equatorial countercurrent necc the instability is characterized by local maxima in zonal and meridional eddy velocity variance strong u v reynolds stress and large mean flow to eddy kinetic energy conversion despite seasonal va

chondrules as products of dust collisions with totally molten droplets within a dust rich nebular environment an experimental investigation abstract chondrules are usually interpreted as the products of incomplete melting of mineral aggregates in the solar nebula and have textures controlled by the number of residual nuclei present after melting if barred olivine bo chondrules formed by nearly total melting at their respective liquidi i e over a wide temperature range it is surprising that there are so few totally glassy chondrules the occurrence of fine grained accretionary rims on chondrules suggests mineral dust in the chondrule forming environment which might have collided with totally molten droplets to produce chondrule textures we have therefore conducted experiments in which mineral dusts encounter molten droplets during their cooling at 500 c h and cause nucleation our experiments reproduce the majority of common chondrule textures the production of textures in our experiments is a function of the temperature at which dust is encountered the number of dust grains encountered and to a lesser extent the mineralogy of the encountered mineral grains crystal growth rates increase with lower dust encounter temperatures giving a textural range with increasingly skeletal or elongated crystals for lower temperature encounters we have produced some less commonly discussed types of chondrule textures e g barred olivine porphyritic olivine pyroxene bo pop by dust seeding that have not been reproduced by the incomplete melting of starting materials the reproduction of bo pop and excentroradial textures by dust collisions and the scarcity of natural totally glassy chondrules suggest that formation by seeding of total melts was common for chondrules with the lowest liquidus temperatures e g feo rich chondrules from these seeding experiments we suggest that the maximum melting temperature chondrules experienced is limited only to the temperature at which evaporation of chondrule liquid occurs however we have reproduced the very fine grained microporphyritic textures characteristic of type ia chondrules only by incomplete melting such chondrules could not have reached average internal temperatures above their liquidus temperatures the conclusion that at least some chondrules formed from total melts that collided with mineral dust during cooling indicates that chondrule formation occurred within a region of the nebula rich in mineral dust

the microstructure of semarkona and bishunpur abstract the ordinary chondrites semarkona and bishunpur appear to have experienced in situ hydrous alteration here we report the results of the first detailed tem examination of them which supports this conclusion in semarkona all but the most magnesian mafic minerals have been destroyed and primary sulphides most likely troilite have been partially altered to phyllosilicates and ni rich pyrrhotite in bishunpur alteration is confined to the production of smectite from an amorphous feldspathic material in the chondrule rims and interchondrule matrix during hydrous alteration of both meteorites the temperature probably did not exceed 260 c the equilibrium composition of the gas present during the alteration of semarkona was not solar but was dominated by h2o the formation of smectite does not require the presence of liquid water however evidence for the redistribution of elements such as ca zn and si over tens of microns or more implies that there was at least some transient grain boundary fluid present the alteration in semarkona and bishunpur is far from complete thermodynamic modelling suggests that more altered ordinary chondrites would be mineralogically similar to the cm and ci carbonaceous chondrites superficially the mineralogy mineral chemistry and bulk chemistry of semarkona matrix rims resemble those of some chondritic interplanetary dust particles cidps the ordinary chondrite parent bodies may therefore be a source of some cidps

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

trace element geochemistry of ordinary chondrite chondrules the type i type ii chondrule dichotomy we report trace element concentrations of silicate phases in chondrules from ll3 ordinary chondrites bishunpur and semarkona results are similar to previously reported data for carbonaceous chondrites with rare earth element ree concentrations increasing in the sequence olivine 10 k h than type i chondrules appreciable na concentrations 3 221 ppm are measured in olivine from both chondrule types type ii chondrules seem to have behaved as closed systems which may require chondrule formation in the vicinity of protoplanets or planetesimals at any rate higher solid concentrations in type ii chondrule forming regions may explain the higher oxygen fugacities they record compared to type i chondrules type i and type ii chondrules formed in different environments and the correlation between high solid concentrations and or oxygen fugacities with rapid cooling rates is a key constraint that chondrule formation models must account for

distinct 17 and 33 day tropical instability waves in subsurface observations abstract tropical instability waves tiws within a half degree of the equator in the pacific ocean have been consistently observed in meridional velocity with periods of around 20 days on the other hand near 5 n tiws have been observed in sea surface height ssh thermocline depth and velocity to have periods near 30 days tropical atmosphere ocean tao project moored equatorial velocity and temperature time series are used to investigate the spatial and temporal structure of tiws during 3 years of la nina conditions from 1998 through 2001 along 140 w where the tiw temperature and velocity variabilities are at their maxima these variabilities include two distinct tiws with periods of 17 and 33 days rather than one broadbanded process as predicted by modeling studies the 17 day tiw variability is shown to occur not only in meridional velocity at the equator but also in subsurface temperature at 2 n and 2 s while the 33 day tiw variability is observed primarily in subsurface temperature at 5

the influence of sea surface temperature on surface wind in the eastern equatorial pacific seasonal and interannual variability abstract the climate of the eastern pacific exhibits a pronounced equatorial asymmetry boundary layer air originating in the southern hemisphere trades crosses the equator and flows into the intertropical convergence zone itcz whose southern limit is nearly always located at least 4 to the north of the equator the sea surface temperature sst distribution is characterized by a prominent cold tongue centered 1 s a strong frontal zone centered 2 n and a warm eastward current centered near 5 n the surface wind field exhibits a pronounced horizontal divergence as the air flows northward across the oceanic frontal zone these features vary in strength in response to the annual cycle and the el nino southern oscillation phenomenon the northward cross equatorial surface winds the cold tongue and the frontal zone all tend to be strongest during the cold season july through november during the cold season of the coldest years when the cold tongue is most prominent the cross equatorial flow t

the importance of experiments constraints on chondrule formation models abstract we review a number of constraints that have been placed on the formation of chondrules and show how these can be used to test chondrule formation models four models in particular are examined the x wind model sudden exposure to sunlight 0 1 au from the proto sun with subsequent launching in a magnetocentrifugal outflow solar nebula lightning nebular shocks driven by eccentric planetesimals and nebular shocks driven by diskwide gravitational instabilities we show that constraints on the thermal histories of chondrules during their melting and crystallization are the most powerful constraints and provide the least ambiguous tests of the chondrule formation models such constraints strongly favor melting of chondrules in nebular shocks shocks driven by gravitational instabilities are somewhat favored over planetesimal bow shocks

matrices of type 3 ordinary chondrites primitive nebular records petrologic studies were made on the fine grained matrices of type 3 ordinary chondrites of the lowest petrologic subtype the matrix minerals in order of abundance are olivine fo99 to fo9 enstatite or bronzite augite or subcalcic augite albite fe ni metal troilite magnetite spinel mgal2o4 chromite and calcite fe and mg rich fluffy particles and albite like particles are also major constituents the chemical compositions of olivine and pyroxenes vary within and among the chondrites and are in gross disequilibrium showing that the matrix materials were hardly heated after their formation textural relationships indicate that magnesian olivine was formed after ca pyroxene followed by intermediate to iron rich olivine intermediate olivine was formed from enstatite and metallic iron under relatively oxidizing conditions the observations indicate that matrices of chondrites are neither the fragments of chondrules nor the precursors of chondrules they were mostly the products of condensation and reaction among solids and or between solids and the ambient gas mostly at low temperatures and thus they contain records of primitive processes in the nebula in order to explain the presence of olivines more iron rich than fo50 the presence of free sio2 or a high activity of sio2 in the gas is necessary which was not shown in previous thermochemical calculations mineral assemblages of matrix minerals of chondrites of different chemical groups differ systematically according to oxidation state of the parental meteorites indicating that they were formed at different oxygen fugacities the rims of chondrules and surrounding matrix materials must have accreted onto chondrules during turbulent movements of the nebula

downward lee wave radiation from tropical instability waves in the central equatorial pacific ocean a possible energy pathway to turbulent mixing turbulent mixing in the equatorial pacific ocean is an important process that controls diapycnal heat transport and hence affects the air sea interactions and global climate it is recently shown that in the eastern equatorial pacific strong mixing is induced in the thermocline by enhanced vertical shear associated with tropical instability waves tiws which propagate westward along the equator at a speed of 0 5 m s 1 with a wavelength of 1000 km in this study using a high resolution ocean general circulation model we show that the tiws can play an important role in inducing turbulent mixing in the thermocline also in the central equatorial pacific although the thermocline is too deep to be directly affected by the vertical shear of the tiws the front of the tiw is clearly manifested as a narrow strip of strong convergence of horizontal surface flow from which area downward and westward propagating internal waves are intermittently emanated these internal waves can be interpreted as lee waves generated by the surface flow convergence zone which acts like an inverted obstacle moving along the stratified ocean surface by inducing downward flow the associated downward energy flux below the surface mixed layer increases as the tiw structure becomes deeper toward the central equatorial pacific so that the energy pathway to turbulent mixing in the thermocline can be created the downward energy flux integrated over the entire equatorial pacific and averaged during january 2011 amounts to 8 1 gw occupying a significant fraction of the energy input to the tiws

monitoring the 1979 1985 equatorial pacific current transports with expendable bathythermograph data geostrophic transports of the major equatorial currents including the equatorial undercurrent and the south equatorial current have been estimated on a bimonthly basis in the central and western pacific over the 1979 1985 period this was made possible by a collection of carefully checked expendable bathythermograph xbt data and a few hydrocast and conductivity temperature depth data this collection considerably improved the number and quality of temperature profiles of the original institut francais de recherche scientifique pour le developpement en cooperation orstom scripps institute of oceanography tropical pacific xbt ship of opportunity program the temperature profiles were first grouped independently of longitude in regions around mean xbt tracks dynamic heights were then calculated relative to 400 db through a t s relationship deduced from the climatological levitus file geostrophic currents were calculated along the roughly south north oriented fiji hawaii and new caledonia japan mean xbt tracks using a specific technique this technique which combines fourier filtering in the meridional direction and in time also ensures the continuity across the equator between geostrophic currents deduced from the first and second derivatives of the meridional pressure field the filter coefficients in the meridional direction were determined through an adjustment of geostrophic currents to directly measured currents using the mean of data collected along 165 e during six tropical ocean and global atmosphere toga orstom cruises finally transports of the main equatorial currents were computed in a subjective way between 20 n and 20 s 0 400 m using monthly charts of geostrophic currents along the two mean xbt tracks the transports in the central pacific were compared to the transports derived from the semicontinuous direct current measurements taken during the hawaii tahiti shuttle experiment in 1979 1980 and during the line island profiling project pacific equatorial ocean dynamics experiment in 1982 1983 reasonable agreement demonstrates that it is possible to use xbt data for transport indexes of the major equatorial currents in the central and western pacific

tropical instability wave kinematics observations from the tropical instability wave experiment the kinematics of planetary waves originating from instability of the nearsurface equatorial currents are reported on using velocity measurements from an array of acoustic doppler current profilers deployed in the equatorial pacific during the tropical instability wave experiment a distinctive wave season was observed from august to december 1990 with wave energy confined primarily above the core of the equatorial undercurrent particle motions in the horizontal plane are described by eccentric ellipses oriented toward the north but tilting into the cyclonic shear of the south equatorial current the tilt is maximum near the surface just north of the equator and decreases to the south and with depth the distribution of wave variance is narrowband in both frequency and zonal wavenumber with central period zonal wavelength and westward directed phase propagation estimated to be 500 hours 1060 km and 59 cm s 1 respectively neither the meridional nor the vertical wavenumber component is statistically different from zero these results generally agree with previous findings on tropical instability waves from the atlantic and pacific oceans and in the undersampled arena of geophysical measurements they provide an example where statistical inference is supported by an ensemble of independent measurements

fine nickel poor fe ni grains in the olivine of unequilibrated ordinary chondrites abstract fine 2 m ni poor 10 mg g fe ni grains are common inclusions in the olivine in porphyritic chondrules in unequilibrated ordinary chondrites the olivine grains appear to be relicts that survived chondrule formation without melting the most common occurrence of this dusty metal is in the core of olivine grains having clear fe poor rims and surrounded either by small euhedral clear olivine grains zoned with feo increasing toward the border of the grains or by large elongated fe poor orthopyroxenes oriented parallel to the chondrule surface and enclosing small round olivine grains various amounts of ca al rich glass are always present the dusty metal is occasionally found in the rims of olivine grains either isolated in the matrix or included in chondrules a rare occurrence is as bands in highly deformed olivines this dusty metal appears to be the product of in situ reduction of feo from the host olivine among the possible reductants h2 or carbonaceous matter ch2 n seem the most likely hydrogen may have been implanted by solar wind or solar flare irradiation but this requires that dissipation of nebular gas occurred before the end of the chondrule formation process carbonaceous matter may have been implanted by shock less likely reductants are nebular co or c dissolved in the olivine lattice the large relict olivine grains may be nebular condensates or more likely fragments broken off earlier generations of chondrules

on the genesis of the equatorial annual cycle abstract a linear theory is proposed that can explain both the period and the westward propagation of the equatorial annual cycles in the sst and zonal wind a coupled model linearized about a mean state of the air sea system is used this model allows the surface winds to directly change the sst through surface evaporation and vertical mixing in contrast to the formulation of the conventional air sea coupling models that emphasize the effects of winds on ocean dynamics it is demonstrated that the characteristics of the equatorial seasonal cycle including its period phase and amplitude are determined to a large extent by the mean state of the air sea coupling system the meridional wind which is specified here is the most important forcing for the annual cycle in sst suggesting that the equatorial annual cycle is the response to an annual solar forcing in the off equatorial regions

oscillations of dynamic topography in the eastern equatorial pacific abstract for 14 months in 1980 81 surface dynamic height was monitored with inverted echo sounders at five sites from 0 to 9 n along 110 w these records show that the sec necc equatorial current system was well developed during the boreal summer and fall but weak and irregular during winter and spring when westward flow associated with the nec extended as far south as 6 n superimposed on the mean dynamic topography of this region are energetic 20 to 80 day oscillations longer periods being associated with higher latitudes near the equatorial ridge 5 n these oscillations have predominantly monthly periods and amplitude of 10 dyn cm comparable to the mean dynamic height difference across the necc the broad in phase meridional extent of these monthly oscillations implies that the principal mode of ridge variation is vertical undulation rather than meridional meandering producing large in phase monthly modulations in transport of the sec and necc oscillations or the equatorial ridge are correla

spatial and seasonal variations of submesoscale eddies in the eastern tropical pacific ocean abstractthe spatial and seasonal variations of submesoscale eddy activities in the eastern tropical pacific ocean 2 12 n 95 165 w are investigated based on a 1 10 ocean general circulation model ogcm in the studied region it is found that motions shorter than 500 km are subject to submesoscale dynamics with an o 1 rossby number and richardson number and a 2 spectral slope for kinetic energy suggesting that submesoscale eddies there can be well resolved by the model enhanced submesoscale eddy kinetic energy smke is found in the surface mixed layer centered at 5 n a complete smke budget analysis suggests that the submesoscale eddies in the surface mixed layer are generated mainly by the barotropic instability and secondarily by the baroclinic instability the nonlinear interactions lead to a significant forward energy cascade in the submesoscale range and play an important role in balancing the energy budget as a response to the change of energy input through barotropic instability the sm

western boundary currents regulated by interaction between ocean eddies and the atmosphere current climate models systematically underestimate the strength of oceanic fronts associated with strong western boundary currents such as the kuroshio and gulf stream extensions and have difficulty simulating their positions at the mid latitude ocean s western boundaries1 even with an enhanced grid resolution to resolve ocean mesoscale eddies energetic circulations with horizontal scales of about a hundred kilometres that strongly interact with the fronts and currents the bias problem can still persist2 to improve climate models we need a better understanding of the dynamics governing these oceanic frontal regimes yet prevailing theories about the western boundary fronts are based on ocean internal dynamics without taking into consideration the intense air sea feedbacks in these oceanic frontal regions here by focusing on the kuroshio extension jet east of japan as the direct continuation of the kuroshio we show that feedback between ocean mesoscale eddies and the atmosphere ome a is fundamental to the dynamics and control of these energetic currents suppressing ome a feedback in eddy resolving coupled climate model simulations results in a 20 40 per cent weakening in the kuroshio extension jet this is because ome a feedback dominates eddy potential energy destruction which dissipates more than 70 per cent of the eddy potential energy extracted from the kuroshio extension jet the absence of ome a feedback inevitably leads to a reduction in eddy potential energy production in order to balance the energy budget which results in a weakened mean current the finding has important implications for improving climate models representation of major oceanic fronts which are essential components in the simulation and prediction of extratropical storms and other extreme events3 4 5 6 as well as in the projection of the effect on these events of climate change

annual and interannual variability of the tropical instability vortices in the equatorial eastern pacific observed from lagrangian surface drifters abstractthis study documents the spatial distributions and temporal variations of anticyclonic eddies with identified radii 100 km in the equatorial eastern tropical pacific ocean viz tropical instability vortices tivs using lagrangian surface drifters the tivs identified from lagrangian surface drifters are distributed in a band along 5 n and are closely associated with latitudinal barotropically unstable shear between the westward south equatorial current sec and the eastward north equatorial countercurrent necc fewer tivs are identified from february to june when the shear between the sec and necc is weak whereas more tivs are found from july to january when the shear is enhanced the number of identified tivs also exhibits substantial interannual variability with fewer tivs identified during el nino events and more tivs found during la nina events this relationship is likely associated with the interannual variations of the zonal circulation in the equatorial pacific modulated by el ni