automated analysis of the temporal behavior of the double intertropical convergence zone over the east pacific this paper presents new methods for an automated analysis of the double intertropical convergence zone ditcz phenomena on a daily time scale over the east pacific long term geostationary operational environmental satellite goes visible and infrared data are used to spatially identify and segment the convection zones over the east pacific basin on both sides of the equator and to track the temporal variability of the itcz specifically to identify cases of ditczs northern or southern itcz or non presence events for the segmentation approach image processing techniques are developed to extract information about the spatial features of the itcz in both hemispheres for each satellite image these features serve as input to a temporal classification algorithm that is based on a combination of hidden semi markov model hsmm and support vector machine svm methods the performance of the proposed method is competitive with human experts and the methodology can thus be used to conduct an in depth analysis of the ditcz such an analysis could provide precise information for refining existing weather and climate models over the sparsely observed east pacific where the ditcz is greatly over represented in most models

the 36cl 36ar 40k 41k records and cosmic ray production rates in iron meteorites this is the first contribution towards a reevaluation of exposure histories of iron meteorites and of the constancy of the cosmic ray flux over the last billion years as recorded in these fossil detectors we have performed new 36cl 26al 10be and noble gas measurements including determination of the shielding parameter s 4he 21ne in samples with published k data the k isotopic data coupled to 36ar and 36cl concentrations permit selection of meteorites which have only experienced simple constant geometry irradiation histories these objects can be used for the calibration of shielding dependent production rates within these metallic detectors in order to carry out production rate calibrations based on 40k 41k data we assume constancy of the cosmic flux during the interval 150 to 700 my ago we note that meteorites with very old potassium ages cannot be included in this calibration as these meteorites require distinct parameter sets a calibration data set representing a total of 13 meteorites was used to compute long term 0 5 gy average production rates these average production rates of 36cl from this particular calibration set are significantly 28 lower than those determined for the recent 10 my cosmic ray flux we also document here the quality of the resulting potassium production rate parameter m0 s with a calculated isochron for irons of group iva

assessment of seasonal prediction of south pacific convergence zone using apcc multi model ensembles we have quantified and examined the south pacific convergence zone spcz characteristics for the purpose of its seasonal prediction by defining two orientation indices strength and area the multi model ensemble mme tends to simulate the enso associated shift of spcz orientation especially for the 1 month forecast lead the migration of the spcz orientation indices associated with enso phases is clear in the observation and the mme the variation of the spcz strength and area associated with enso phases is not as clear as in the spcz orientation in spite of marginal changes in the spcz strength and area related to enso phases the spcz strength becomes a bit stronger during el nino and weaker during la nina which is represented in individual models and mme the performance of the mme in simulating the variability of the spcz orientation strength and area is also examined we found that the mme reasonably predicts the observed interannual variability of the western portion of the spcz with systematic and marginal shift southward compared to the western part of the spcz the mme seems to have a limitation in predicting the variability of the eastern part in comparison to the spcz orientation the mme is not capable of predicting the strength and area of the spcz the interannual variability of the spcz strength in the mme is systematically weaker compared to that in the analysis by comparison with spcz orientation and strength the spcz area is not resolved in the mme the spcz is a main source of precipitation in the south pacific and the spcz predictability also influences high impact weather prediction such as tropical cyclones therefore skillful predictions of seasonal variability of the spcz could benefit users who utilize the seasonal forecasting information for their decision making in many applicable sectors

theory of melt segregation a review abstract the processes by which melt is extracted from partially molten source regions at depth are collectively known as melt segregation during the past three years a dynamical theory has been developed which provides a unified description of the mechanical thermodynamical and chemical aspects of melt segregation in this theory a partially molten region is regarded as a deformable porous medium or matrix saturated with melt migration of melt relative to the matrix can be driven either by the buoyancy of the melt or by nonhydrostatic pressure gradients associated with the deformation of the matrix this paper reviews the basic governing equations of the theory and the solutions which have been obtained during the past three years

the cosmic ray exposure history of the twannberg iron meteorite iig the twannberg iron meteorite is one out of only six members of the group iig the combined noble gas and radionuclide data obtained in this new systematic study indicate that twannberg with its 570 recently recovered specimens was a large object with a preatmospheric radius in the range of 2 m which corresponds to 250 9 10 kg the cosmic ray exposure age for twannberg is 182 45 ma the most surprising result is the long terrestrial age of tterr 202 33 34 ka which is unexpected considering the humid conditions in switzerland however this age is in accord with glaciation events indicating that the less shielded samples from mt sujet were found close to the position of the original strewn field whereas the samples from gruebmatt and twannbach which are from more shielded positions were glacially transported to the east northeast during the second last ice age 185 130 ka ago from an original position west of mt sujet

connectivity of molten fe alloy in peridotite based on in situ electrical conductivity measurements implications for core formation in terrestrial planets abstract the connectivity of molten fe s in peridotite has been experimentally investigated by means of in situ electrical conductivity measurements at high temperatures and 1 gpa starting materials were powdered mixtures of peridotite klb 1 with various amounts 0 3 6 13 19 24 vol of the 1 gpa eutectic composition in the fe fes binary system at temperatures above the eutectic point in the fe fes system 980 c and below the solidus of klb1 1200 c molten fe s in a solid silicate matrix interconnects when the volume fraction is over 5 conductivity temperature paths indicate that in the presence of partial silicate melting the connectivity of molten fe s in a peridotite matrix is inhibited based on observations of retrieved samples the percolation threshold of fe s melts in the presence of low to moderate degrees of silicate melt is estimated at 13 2 vol these results indicate that if the volume fraction of fe alloy in a planetesimal was initially greater than 5 and if early heating by decay of radionuclides raised the temperature of the interior above the fe alloy melting point initial metal segregation was controlled by permeable flow of molten iron alloy in a solid silicate matrix these conditions were likely met by many terrestrial objects in the early solar nebula efficient removal of residual fe alloy 5 vol from silicate requires high degree melting of silicate so that metal can segregate as droplets giant impacts during the final stage of accretion of large planetary objects could supply the energy required for high degrees of melting alternatively if initial metal segregation were delayed until a planetary object grew to large size 1000 km in diameter release of gravitational potential energy due to metal segregation could contribute enough heat to form a magma ocean

processes controlling the mean tropical pacific precipitation pattern part ii the spcz and the southeast pacific dry zone the nature of the south pacific convergence zone spcz is addressed by focusing on the dry and cool zone bounded by it and the coast of south america through numerical experiments as shown in a companion paper this dry zone is due to a large extent to orographically forced subsidence here it is shown that the northwestward expansion of this dry zone can be explained by advection of low moist static energy by the trade winds these results provide an explanation of the geometry of the western edge of the dry zone and therefore of the eastern edge of the adjacent spcz sea surface temperature underneath the spcz is enhanced by relatively high near surface humidity through evaporative processes which feeds back into its organization however in this model this feedback is not critical for the existence of the spcz the subsidence associated with the itcz in the north hemisphere negatively affects the precipitation rate in the spcz it was also found that the sensitivity of the forced response is largest for peak orographic heights below 3000 m which indicates that the exact representation of the andes in numerical models might not be as critical as that of lower orography such as that in southern africa

interannual variability of the south pacific convergence zone and implications for tropical cyclone genesis the interannual variability of the south pacific convergence zone spcz and its influence on tropical cyclone tc genesis in the south pacific are investigated using observations and era40 reanalysis over the 1979 2002 period in austral summer the spcz displays four typical structures at interannual timescales the first three are characterized by a diagonal orientation of the spcz and account for 85 of the summer seasons one is close to climatology and the other two exhibit a 3 northward or southward departure from the spcz climatological position in contrast the fourth one that only encompasses three austral summer seasons the extreme 1982 1983 and 1997 1998 el nino events and the moderate 1991 1992 el nino event displays very peculiar behaviour where the spcz largely departs from its climatological position and is zonally oriented variability of the western central pacific equatorial sea surface temperature sst is shown to modulate moisture transport south of the equator thereby strongly constraining the location of the spcz the spcz location is also shown to strongly modulate the atmospheric circulation variability in the south pacific with specific patterns for each class however independently of its wide year to year excursions the spcz is always collocated with the zero relative vorticity at low levels while the maximum vorticity axis lies 6 to the south of the spcz position this coherent atmospheric organisation in the spcz region is shown to constrain tropical cyclogenesis to occur preferentially within 10 south of the spcz location as this region combines all the large scale atmospheric conditions that favour the breeding of tcs this analysis also reveals that cyclogenesis in the central pacific in the vicinity of french polynesia only occurs when the spcz displays a zonal orientation while this observation was previously attributed to el nino years in general different characteristics of el nino southern oscillation enso related pacific equatorial warming are shown to impact differently on the spcz position suggesting that for regional scales such as the south pacific the spcz classification is more appropriate than a simple enso index to characterize tc interannual variability these findings suggest that forecasting the strength of el nino through sst variations in the eastern pacific may not be sufficient to accurately predict cyclogenesis in the south pacific especially east of the dateline

detecting the itcz in instantaneous satellite data using spatiotemporal statistical modeling itcz climatology in the east pacific abstract a markov random field mrf statistical model is introduced developed and validated for detecting the east pacific intertropical convergence zone in instantaneous satellite data from may through october the mrf statistical model uses satellite data at a given location as well as information from its neighboring points in time and space to decide whether the given point is classified as itcz or non itcz two different labels of itcz occurrence are produced ir only labels result from running the model with 3 hourly infrared data available for a 30 yr period 1980 2009 all data labels result from running the model with additional satellite data visible and total precipitable water available from 1995 to 2008 ir only labels detect less area of itcz than all data labels especially where the itcz is shallower yet qualitatively the results for the two sets of labels are similar the seasonal distribution of the itcz through the summer half year is presented showing typical location and e

daily states of the march april east pacific itcz in three decades of high resolution satellite data abstractzonally elongated areas of cloudiness that make up the east pacific intertropical convergence zone itcz can take on several configurations in instantaneous observations a novel statistical model is used to automatically assess the daily state of the east pacific itcz using infrared satellite images from 1980 to 2012 four itcz states are defined based on itcz location relative to the equator north nitcz and south sitcz of the equator simultaneously north and south of the equator ditcz for double itcz and over the equator eitcz a fifth itcz state is used to classify days when no zonally elongated area of cloudiness is present aitcz for absent itcz the itcz states can occur throughout the year except for the eitcz which is not present during june october with the nitcz state dominating in terms of frequency of occurrence interannual variability of the state distribution is large the most striking variability in itcz states is observed in spring during march april the ditcz

molybdenum isotope anomalies in meteorites constraints on solar nebula evolution and origin of the earth the early evolution of the solar nebula involved substantial transport of mass resulting in mixing and homogenization of isotopically diverse materials that were contributed to the solar system from multiple stellar nucleosynthetic sources the efficiency of this mixing as well as its timescale can be quantified by determining nucleosynthetic isotope variations among meteorites and terrestrial planets here we present mo isotopic data for a wide range of samples including ca al rich inclusions chondrites and differentiated meteorites as well as martian and terrestrial samples most meteorites are depleted in s process mo relative to the earth and only the iab iiicd irons angrites and martian meteorites have terrestrial mo isotopic compositions in contrast most ca al rich inclusions are enriched in r process mo but one inclusion is characterized by a large s process deficit molybdenum isotopic anomalies in the bulk meteorites correlate with those in ru exactly as predicted from nucleosynthetic theory but no obvious correlation is apparent between mo and ni anomalies therefore s process mo and ru seem to be hosted in the same carrier which must be distinct from the carrier responsible for isotopic anomalies in the fe group elements ni cr ti furthermore the isotopic heterogeneity in mo and other elements contrasts with the isotopic homogeneity for hf and os indicating that different s process carriers once existed in the early solar nebula and that only some of these were heterogeneously distributed the mo isotopic anomalies of meteorites and their components decrease over time and with increasing size of the parent bodies providing evidence for a progressive homogenization of the solar nebula however the carbonaceous chondrites exhibit larger mo anomalies than expected for their age indicating that they received a greater portion of material from the outer solar system where homogenization was slow than other meteorite parent bodies and terrestrial planets compared to the meteorites earth is enriched in s process mo and must have accreted from material distinct from the meteorites combined mo and o isotopic data show that the composition of the earth cannot be reconstructed by any known combination of meteorites implying that meteorites may be inappropriate proxies for the isotopic composition of the bulk earth this is exemplified by the covariation of 92mo and 142nd anomalies in chondrites showing that the 142nd deficit of chondrites compared to the accessible earth may not unequivocally be interpreted as a signature of an early differentiation of the earth however further high precision isotopic data are needed to evaluate the role of chondrites in defining the isotopic composition of the earth

relative influences of the interdecadal pacific oscillation and enso on the south pacific convergence zone 1 the south pacific convergence zone spcz one of the most extensive features of the global atmospheric circulation is shown to vary its location according to both the polarity of the el nino southern oscillation enso and of the interdecadal pacific oscillation ipo we first demonstrate that the ipo can be regarded as the quasi symmetric pacific wide manifestation of the pacific decadal oscillation that has been described for the north pacific shifts in the position of the spcz related to enso on interannual time scales and to the ipo on decadal time scales appear to be of similar magnitude and are largely linearly independent a station pressure based index of variations in spcz latitude is shown to be significantly related to the polarity of the ipo when enso influences are accounted for movements of this sensitive section of the spcz have occurred in phase with those of the ipo since the 1890s

reply to comment by peters et al 2015 on cosmogenic 180w variations in meteorites and re assessment of a possible 184os 180w decay system

development of convection along the spcz within a madden julian oscillation a subtropical rossby wave propagation mechanism is proposed to account for the poleward and eastward progression of intraseasonal convective anomalies along the south pacific convergence zone spcz that is observed in a significant proportion of madden julian oscillations mjos large scale convection associated with an mjo is assumed to be already established over the indonesian region the latent heating associated with this convection forces an equatorial rossby wave response with an upper tropospheric anticyclone centred over or slightly to the west of the convection large potential vorticity pv gradients associated with the subtropical jet and the tropopause lie just poleward of the anticyclone and large magnitude pv air is advected equatorwards on the eastern side of the anticyclone this high pv air or upper tropospheric trough is far enough off the equator that it has associated strong horizontal temperature gradients and it induces deep ascent on its eastern side at a latitude of about 15 30 if this deep ascent is over a region susceptible to deep convection such as the spcz then convection may be forced or triggered hence convection develops along the spcz as a forced response to convection over indonesia the response mechanism is essentially one of subtropical rossby wave propagation this hypothesis is based on a case study of a particularly strong mjo in early 1988 and is tested by idealized modelling studies the mechanism may also be relevant to the existence of the mean spcz as a forced response to mean indonesian convection

diurnal cycle of the south pacific convergence zone in 30 years of satellite images 2015 american geophysical union a data set of three hourly south pacific convergence zone spcz location and extent from which ir temperature within the spcz may be obtained for 1980 2012 november april is used to examine the diurnal cycle of the spcz maximum spcz area occurs at 15 00 18 00 local standard time lst two minima in mean ir temperature are evident one at 13 00 16 00 lst nearly coinciding with the maximum in area and the second in the early morning hours at 05 00 07 00 lst when area is at a minimum the morning minimum in mean ir temperature is associated with a peak in deep convection while the afternoon minimum is associated with a peak in midlevel clouds on average the morning minimum in ir temperature dominates in the tropical regions of the spcz while the afternoon ir temperature minimum dominates in the subtropical regions of the spcz the relative strength of the two ir temperature minima is affected by the seasonal cycle intraseasonal variability associated with active madden julian oscillation events and interannual variability due to the el nino southern oscillation the morning ir temperature minimum becomes more dominant when the spcz is more frequently present or when the spcz is shifted toward the equator in terms of cloud height midlevel clouds dominate at all times in all regions of the spcz and peak in abundance between 15 00 18 00 lst low level clouds peak near midnight and then transition to high level clouds which peak between 03 00 06 00 lst just before sunrise

application of clustering algorithms to trmm precipitation over the tropical and south pacific ocean abstractunderstanding multiscale rainfall variability in the south pacific convergence zone spcz a southeastward oriented band of precipitating deep convection in the south pacific is critical

horizontal and vertical structure of observed tropospheric equatorial rossby waves equatorial rossby er waves are identified in an 8 year data set of national meteorological center operational analyses the westward moving waves have symmetric circulations about the equator and eastward energy dispersion with maximum zonal wind perturbations along the equator and meridional wind maxima roughly 10 15 off the equator they have maximum amplitude in the lower troposphere and are associated with convective signals at roughly the mean latitude of the tropical convergence zones the circulations thus possess many of the features of the equatorially trapped n 1 rossby modes derived by matsuno 1966 they are generally around zonal planetary wavenumber 6 scale and have a deep nearly equivalent barotropic structure up to 100 mbar this is in contrast with the madden julian oscillation and mixed rossby gravity waves which generally have a first baroclinic mode vertical structure during the intensive observing period iop of the tropical ocean global atmosphere toga coupled ocean atmosphere response experiment coare and in other years westward propagating er disturbances along the equator are observed by using 6 to 30 day filtered circulation data at 850 mbar zonal wind anomalies at 850 mbar are preferentially associated with like signed anomalies in a deep layer at this frequency as was observed during coare the er waves are most common during northern winter in the central pacific although they can be detected sporadically over the other ocean basins and in other seasons as well one source for the equatorial rossby waves appears to be upper level extratropical rossby wave activity propagating into the eastern pacific although the equatorial waves are sometimes present during the northern summer when the extratropical source is absent we cite evidence that propagation of er wave activity from the central into the western pacific is related to occurrences of westerly wind bursts

reconstructing the south pacific convergence zone position during the presatellite era a la nina case study abstractsixty four southwest pacific island meteorological stations were used to develop enso related austral warm season november april rainfall climatologies for 1961 90 historical data for the same station set were then examined for 1955 56 one of the strongest la ninas of the twentieth century the pattern for that event was typical of a well coupled protracted la nina with above normal rainfall 150 observed for 17 stations in the case study tropical cyclone tracks were also used to illustrate the proximal effects of historical storms on station rainfall several stations that were located along the northern edge of the tropical cyclone swarm but south of a region of anomalously low rainfall were selected as possible candidates having been close to the mean south pacific convergence zone spcz location linear interpolations between those stations highlighted a likely spcz position for the 1955 56 event the reconstructed spcz location indicated a position southwest of normal consistent wi

contribution of neutron capture reactions to observed tungsten isotopic ratios to study whether tungsten isotopic ratios observed in terrestrial samples relative to w ratios in an iron meteorite could be made by neutron capture reactions in the iron meteorite the fluxes of thermal and epithermal neutrons in a large iron meteoroid toluca were calculated using monte carlo particle production and transport codes peak neutron capture rates on w isotopes were calculated to occur at depths of 30 34 cm the calculated changes in the 182w 183w due to neutrons are much less than those observed in terrestrial samples relative to iron meteorites indicating a non cosmogenic origin of the observed w isotopic ratios

a global climatology of tropical moisture exports in a recent paper a climatology of tropical moisture exports tmes to the northern hemisphere nh was constructed on the basis of 7 day forward trajectories started daily from the tropical lower troposphere which were required to reach a water vaporflux of at least 100 g kg 21 ms 21 somewhere north of 358n it was shownthattmescontributesignificantlytoregionalprecipitation here theauthorscomplement andextend this work by i using 6 hourly european centre for medium range weather forecasts ecmwf interim re analysis era interim data from 1979 to 2010 instead of the earlier 40 yr ecmwf re analysis era40 ii extending the climatology to the southern hemisphere sh and iii relating tme events to atmospheric rivers ars previously discussed in the literature the main conclusions are as follows first the tme climatology is not sensitive to the reanalysis dataset second sh tme shows four activity centers the central and eastern pacific ocean 1708 908w near the south pacific convergence zone eastern south america and the adjacent atlantic ocean 608w 08 near the south atlantic convergence zone the western indian ocean 308 808e and western australia 1108 1408e third tme activity in the sh peaks in austral summer because of highermoisture contents and possiblybecause of increased rossby wave activityfrom the

el nino southern oscillation time scale covariation of sea surface salinity and freshwater flux in the western tropical and northern subtropical pacific we examined the covariation of sea surface salinity sss and freshwater flux in the western tropical and northern subtropical pacific on the el nino southern oscillation timescale using a canonical correlation analysis of monthly data between 2001 and 2013 the dominant covariation i e the first canonical mode has large positive and negative amplitudes in regions east of the philippines and new guinea respectively and reaches peaks in autumn to winter of el nino years the positive sss anomaly east of the philippines is advected to the kuroshio extension region we found that the second canonical mode is another coupled variation with localized amplitudes of sss under the atmospheric convergence zones in winter to spring of la nina years however the negative sss anomaly is annihilated possibly by the evaporation in the subtropical region

a 173 year stable isotope record from a tropical south pacific coral 0 we have generated a 173 year long time series a d 1806 to 1979 of changes in the 18 o and 13 c composition of a coral head platygyra lamellina to investigate environmental change in the climatologically sensitive region of the tropical south pacific little is known about decadal and centennial scale climate change at sea level in this region our coral is from near the south coast of espiritu santo island 15 s 167 e republic of vanuatu the stable isotope record from this coral is consistent with meteorological and oceanographic records during the period of overlap in the records 1964 1978 18 o values positively correlate with sst r 0 77 and 13 c values are highly coherent with rainfall r 0 82 at the annual cycle these relations suggest that the 18 o signal in this coral is a function of variations in sst and rainfall induced changes in sss whereas the 13 c signal may be related to rainfall and cloud cover modulation of photosynthesis in the coral 18 o and 13 c values are positively correlated over the entire length of the record r 0 65 a relation that is even stronger between 1806 and 1866 r 0 81 i e prior to the time of possible anthropogenic influence on the 13 c record because of the positive correlation between temperature and rainfall in this region we interpret the long term record of 18 o in terms of joint variations of these two variables the most significant cool dry excursion in the santo record occurs during the nineteenth century 1832 1866 and ends abruptly in 1866 with a change to modern values superimposed on this pattern is a slight 0 2 cooling drying toward the end of the twentieth century cross spectral analysis of the 18 o and 13 c records indicates a strong concentration of variance at the quasi biennial 2 years and el nino southern oscillation enso 4 5 years frequency bands in addition to a 15 year peak found also in global temperature records cross spectral analysis of coral isotope records from santo and the philippine sea indicate a concentration of variance at enso 4 5 years frequency bands however comparison of the santo coral isotope record with high latitude northern hemisphere temperature records indicates that the major cool dry excursion in the santo record 1832 1866 is not seen in the northern hemisphere record if verified in other tropical south pacific coral records the results have implications concerning the global scale of cooling for little ice age events

eastern margin variability of the south pacific convergence zone 1 the influence of low level inflow wind and its high frequency variability on the spatial characteristics of the eastern margin of the south pacific convergence zone spcz is examined compositing daily and 5 day mean low level wind precipitation and tropospheric moisture data reveals a clear relationship between high frequency zonal inflow variations and the eastern spcz margin with relaxation of trade wind intensity associated with increased moisture near the mean eastern spcz margin and an eastward displacement of the convection an idealized 2 dimensional model demonstrates that variations in dry air inflow cause tropospheric moisture and precipitation variations akin to those observed in this prototype factors affecting the extent of spcz variability are also important to the mean margin position spcz margin shifts under natural variability thus offer an observational target against which to evaluate simulated interactions of inflow air mass characteristics with convection

interannual variability of the southern hemisphere 500 mb flow regional characteristics abstract studies of the interannual variability of the 500 mb flow in the southern hemisphere for 1972 78 have revealed 1 a quasi biennial fluctuation in the zonal mean geopotential height and westerly wind fields where there is a systematic poleward progression of anomalies and 2 a longer period fluctuation primarily in wave 1 which has been identified with the southern oscillation these phenomena are further studied regionally by considering four 90 sectors results show the dominant contributions to the fluctuations in the zonal mean fields come from the australasian and south pacific sectors only in the australasian region is the quasi biennial poleward progression of anomalies strongly evident the south pacific is dominated by lower frequency fluctuations associated with the southern oscillation however the sequences in all four sectors are correlated with those in the zonal mean fields when the flow is stronger than normal in mid latitudes it tends to be weaker than normal in low and hig

alpha decay of 184os revealed by radiogenic 180w in meteorites half life determination and viability as geochronometer abstract the decay of the rare nuclide 184os by alpha emission to 180w has been theoretically predicted but was previously never observed in experiments variable excesses of 180w were recently observed for iron meteorites but the contribution to these excesses by 184os decay was regarded as insignificant here we present combined 180w and os w concentration data for meteorites and terrestrial rocks now indicating that the 180w heterogeneities can be explained by decay of 184os a combined 184os 180w isochron for iron meteorites and chondrites yields a decay constant value of 184 os of 6 49 1 34 10 14 a 1 half life 1 12 0 23 10 13 yr in good agreement with theoretical estimates the 184os 180w decay system may constitute a viable tracer and chronometer for important geological processes like core formation silicate differentiation or late accretion processes this is illustrated by a measured 180w deficit in terrestrial basalts relative to chondrites by 1 16 0 69 parts in 10 000 consistent with core formation 4 5 ga ago

evidence for homogeneous distribution of osmium in the protosolar nebula separate s r and possibly p process enriched and depleted components have been shown to host os in low metamorphic grade chondrites although no measureable os isotopic anomalies have yet been discovered for bulk chondrites here iron meteorites from groups iab iiab iiiab iva and ivb as well as the main group pallasites are examined many of these meteorites show well resolved anomalies in e190os e189os and e186osi the anomalies however differ from those observed in chemically extracted components from chondrites and are interpreted to reflect long term exposure of the meteorites to cosmic rays rather than nucleosynthetic effects a neutron capture model is presented that can well account for observed isotopic variations in 190os and 189os the same model predicts greater enrichment in 186osi than is observed for at least one iron suggesting as yet unaccounted for effects or failings of the model despite the variable anomalies resulting from cosmic ray exposure each of the major meteorite groups examined contains at one member with normal os isotopic compositions that are unresolved from chondritic compositions this indicates that some domains within these meteorites were little affected by cosmic rays these domains are excellent candidates for application of the 182hf 182w system for dating metal silicate segregation on their parent bodies the normal os also implies that os was homogeneously distributed throughout the protosolar nebula on the scale of planetesimal accretion within the current level of analytical resolution the homogeneity in os contrasts with isotopic heterogeneity present for other siderophile elements including mo ru and w the contrast in the scale of anomalies may reflect a late stage injection of s and p process rich material into the coalescing nebula alternately nebular thermal processing and destruction of some presolar host phases of mo ru and w may also be responsible

investigating solid mantle upwelling beneath mid ocean ridges using u series disequilibria ii a local study at 33 s mid atlantic ridge abstract uranium series disequilibria have been used to study the physical melting regime along a section of the southern mid atlantic ridge where the largest mantle bouguer anomaly yet observed on ridges exists zero age excesses for 230th 238u and 231pa 235u are age constrained by the presence of measured 226ra 230th disequilibria by this criterion 7 out of 15 samples are younger than 8000 years zero age 230th 238u range between 1 06 and 1 25 while zero age 231pa 235u range between 1 77 and 3 57 concentrations of th range from 100 to 866 ppb and strongly correlate with k ti the u series data differentiate the segment with the large gravity anomaly from the surrounding segments specifically this segment shows combined 231pa and 230th systematics unlike any observed in morb thus far having exceptionally low zero age 231pa excesses the u series data can be modeled using upwelling rates similar to the half spreading rate of this area of ridge the disequilibria systematics for the anomalous segment 4 possibly suggest a solid upwelling rate that is a factor of two higher than the adjacent segments the similarity between melting at segment 4 and at ocean islands is noted

the influence of diabatic heating in the south pacific convergence zone on rossby wave propagation and the mean flow the south pacific convergence zone spcz is a northwest southeast oriented precipitation band over the south pacific ocean latent heat release from condensation leads to substantial diabatic heating which has potentially large impacts on local and global climate the influence of this diabatic heating within the spcz is investigated using the intermediate general circulation model igcm4 precipitation in the spcz has been shown to be triggered by transient rossby waves that originate in the australian subtropical jet and are refracted towards the equatorial eastern pacific a rossby wave triggers a spcz convective event with associated diabatic heat release and vortex stretching consequently the rossby wave is dissipated in the spcz region these features are simulated well in a control integration of igcm4 in an experiment convective heating is prescribed to its climatological value in the spcz region during the rossby wave events and dynamic forcing from rossby waves is decoupled from the usual thermodynamic response in this experiment rossby waves over the spcz region are not dissipated confirming the vortex stretching mechanism from previous studies furthermore the change in rossby wave propagation has an impact on momentum transport overall the effect of the rossby wave induced convection in the spcz is to decrease the strength of the pacific subtropical jet and the equatorial eastern pacific upper tropospheric westerlies by about 2 6 m s 1 following these changes to the basic state two potential feedbacks in the spcz and larger pacific climate system are suggested increased spcz convection due to the enhancement of negative zonal stretching deformation in the spcz region and decreased equatorward refraction of rossby waves into the westerly duct leading to less spcz events as the convective events in the spcz have a significant impact on pacific mean climate it is crucial that the spcz is represented correctly in climate models

a multiscale framework for the origin and variability of the south pacific convergence zone the diagonal south pacific convergence zone spcz is the major climatological precipitation feature over the pacific region during the northern hemisphere winter however the basic mechanisms that control its structure and variability are only partly understood here an analysis of the spcz is carried out in a multiscale framework this identifies two modes that dominate a westward shifted spcz and an enhanced spcz which occur independently of each other within both modes the primary mechanism for the initiation of precipitation is a transient synoptic wave propagating along the subtropical jet which is then refracted by the basic state toward the westerly duct over the central equatorial pacific individual vorticity centres in the wave become elongated with a diagonal northwest southeast tilt convection then occurs in a diagonal band in the poleward flow ahead of the cyclonic vorticity anomaly in the wave however latent heat release in the convection leads to upper tropospheric divergence and anticyclonic vorticity forcing which dissipates the wave shutting off the convective forcing and stopping the precipitation hence each individual wave or event only lasts a few days and contributes a discrete pulse of diagonally oriented precipitation to the region the sum of these events leads to the diagonal climatological spcz event occurrence is a stochastic process the probability of which is modified by lower frequency variability of the basic state including the madden julian oscillation mjo and el nino southern oscillation enso for example during periods of enhanced convection over the eastern indian ocean to western pacific mjo phases 3 6 and la nina the westerly duct expands westwards allowing synoptic waves to refract equatorwards earlier and increasing the probability of westward shifted spcz events hence both the existence and variability of the spcz depend fundamentally on scale interactions between dynamical processes on time scales ranging from daily to interannual copyright 2011 royal meteorological society

early mid holocene sst variability and surface ocean water balance in the southwest pacific 1 we present early mid holocene records of sr ca 18o and 18osw from marine archives collected in vanuatu two porites sp corals 6 7 6 5 ka bp and a tridacna maxima giant clam 6 2 6 0 ka bp sr ca 18o and 18osw were used as proxies for sea surface temperature sst and sea surface salinity sss the fossil geochemical records were compared to modern porites sp and t maxima records reconstructed mean ssts from the two fossil porites sp and from the modern coral are similar implying that the western pacific warm pool wpwp southern edge had reached its modern location by 6 7 6 5 ka bp the post glacial sst rise in the southwest pacific was thus completed by the early mid holocene the two early mid holocene corals and the giant clam recorded saltier conditions than modern related to 1 a decoupling between the precipitation regime and the spcz due to a northerly position of this climatic feature and 2 an increase of the moisture transport to the extra tropics driven by a strengthened or extended hadley cell the longest 18o coral profile displays an el nino southern oscillation enso signal reduced by 20 30 compared to the period 1928 1992 in concordance with the reduced enso variability observed in the pacific area during the first half of the holocene however the decoupling between the spcz and the precipitation regime may have also contributed to the weak enso signal recorded in the early mid holocene coral 18o profile

pt re os systematics of group iiab and iiiab iron meteorites the pt re os isotopic and elemental systematics of 13 group iiab and 23 group iiiab iron meteorites are examined as has been noted previously for iron meteorite groups and experimental systems solid metal liquid metal bulk distribution coefficients d values for both iiab and iiiab systems show dos dre dpt 1 during the initial stages of core crystallization assuming closed system crystallization the latter stages of crystallization for each core are generally characterized by dpt dre dos the processes governing the concentrations of these elements are much more complex in the iiiab core relative to the iiab core several crystallization models utilizing different starting parameters and bulk distribution coefficients are considered for the re os pair each model has flaws but in general the results suggest that the concentrations of these elements were dominated by equilibrium crystallization and subsequent interactions between solid metal and both equilibrium and evolved melts late additions of primitive metal to either core were likely minor or nonexistent the 187re 187os systematics of the iiab and iiiab groups are consistent with generally closed system behavior for both elements since the first several tens of ma of the formation of the solar system consistent with short lived chronometers the re os isochron ages for the complete suites of iiab and iiiab irons are 4530 50 ma and 4517 32 ma respectively and are similar to previously reported re os ages for the lower ni endmembers of these two groups both isochrons are consistent with but do not require crystallization of the entire groups within 10 30 ma of the initiation of crystallization the first high precision 190pt 186os isochrons for iiab and iiiab irons are presented the pt os isochron ages for the iiab and iiiab irons calculated using the current best estimate of the for 190pt are 4323 80 ma and 4325 26 ma respectively the re os and pt os ages do not overlap within the uncertainties the younger apparent ages recorded by the pt os system likely reflect error in the 190pt decay constant the slope from the pt os isochron is combined with the age from the re os isochron for the iiiab irons to calculate a revised of 1 415 10 12 a 1 for 190pt although additional study of this decay constant is still needed

rb sr chronology of volatile depletion in differentiated protoplanets babi ador and all revisited abstract a strong depletion in moderately volatile elements is a characteristic feature of many planetary bodies in the inner solar system and either reflects the rapid accretion of planetesimals from an incompletely condensed solar nebula or is the result of energetic collisions during planetary accretion to better constrain the origin and timescales of this volatile depletion we have precisely measured sr isotope compositions in angrites eucrites and ca al rich inclusions cai angrites have an initial 87sr 86sr ador 0 698978 0 000004 which is indistinguishable from 87sr 86sr babi 0 698970 0 000028 obtained for eucrites in agreement with earlier studies we find that angrites and eucrites have higher initial 87sr 86sr ratios than cai at face value corresponding to model timescales for volatile loss of several millions of years however all the investigated cai are characterized by elevated 84sr 86sr ratios compared to angrites and eucrites which we interpret to reflect an excess of r process sr in the cai if this is correct then the nucleosynthetic sr isotope anomalies in the cai require an upward correction of their measured 87sr 86sr after this correction cai have an initial 87sr 86sr cai 0 698975 0 000008 which is indistinguishable from ador and babi this implies volatile loss from the angrite and eucrite parent bodies within less than 1 ma after formation of cai the volatile depleted nature of these differentiated protoplanets thus most likely reflects their rapid accretion from volatile poor dust in an incompletely condensed solar nebula

dynamics of titan s high pressure ice layer abstract the presence of 40ar in titan s atmosphere and the replenishment of methane argue for the exchange between the interior and the atmosphere these observations triggered the present study that aims to determine the conditions under which the high pressure hp ice layer likely present between the deep ocean and the silicate core poses a barrier for the exchange of volatiles we model heat and water transport through this convecting hp ice layer using a two phase numerical model of solid ice liquid water mixture we observe that for a large range of heat fluxes from the silicate core and hp ice layer thicknesses a few percent of liquid water forms at the interface with the silicates liquid water being less dense than the hp ice it creates additional buoyancy thus facilitating the transport of volatiles towards the ocean our results also show that convection is characterized by the presence of hot and the absence of cold plumes we derive a scaling law that describes the dependence of a critical heat flux for the onset of melting at the silicates interface on the thickness of the hp ice layer and the ice viscosity we also study the processes at the interface with the base of the ocean where a few tens of kilometers thick layer of temperate partially molten ice is present we find a scaling law for its thickness that depends mainly on the ice viscosity and the density difference between the ice and water water from this partially molten temperate layer flows into the ocean thus completing the connection with the silicate core the water flux depends primarily on the amount of heat supplied from the silicates future evolution models that will use the scaling laws derived in this study will place bounds on the timing of these exchange processes using cassini data and reasonable values of hp ice viscosity and silicate heat flux we predict melting at the silicates hp ice interface at present time

interannual signature in daily itcz states in the east pacific in boreal spring abstractthe intertropical convergence zone itcz in the east pacific is located north of the equator during most of the year in daily data it is most variable in march april when it may be located north of the equator nitcz on both sides of the equator ditcz or south of the equator sitcz or it may be absent when convection does not take on a zonally elongated form additionally in strong el nino years it is located on the equator during the boreal winter half year here the focus is on conditions when the itcz has a presence south of the equator ditcz sitcz and composites of various fields are compared to normal conditions i e when the itcz is north of the equator nitcz composites of sea surface temperature sst precipitation outgoing longwave radiation and the upper level circulation show very similar patterns for ditcz and sitcz days where the latter cases have almost double the amplitude of the former the sitcz state is viewed as an extreme case of the ditcz state both

isotopic records from archeological giant clams reveal a variable climate during the southwestern pacific colonization ca 3 0ka bp abstract the lapita colonization which occurred in the late holocene is one of the most remarkable prehistorical human colonizations to explore the possible influence of el nino southern oscillation enso on this event bulk oxygen 18 o shell and carbon 13 c shell stable isotope records were obtained from eight fossil tridacna sp and hippopus hippopus giant clams unearthed from lapita archeological sites of new caledonia and vanuatu these giant clams were dated ca 3 8 2 3 ka bp these 18 o shell and 13 c shell records were used as proxies for combined sea surface temperature and salinity and precipitation in addition geochemical records were obtained from modern conspecifics from new caledonia to create a baseline against which fossil giant clam records could be compared the isotopic records revealed the occurrence of two distinct climate states in new caledonia ca 3 2 2 3 ka bp one climate state was characterized by climatic conditions similar to those observed today and the second was comparable to warmer and wetter conditions similar to vanuatu s modern climate considering that previous paleo climate reconstructions in the west pacific did not show a shift of the mean climatic state and that they revealed a weak centennial climate variability our results suggest that the climatic mean state has been alternating between these two states at a decadal or an inter annual frequency this strong climate variability recorded in the giant clam shells may reflect an increase in the enso variability supporting the hypothesis of an enso forced lapita colonization as suggested by anderson et al 2006

the south pacific convergence zone spcz a review abstract the circulation features associated with the south pacific convergence zone spcz and its accompanying cloud band are reviewed and discussed the paper focuses on the following topics location structure and characteristics of the spcz theories and observations concerning its existence the significance and scope of the spcz in global scale circulation patterns quasi periodic changes in its location and strength and synoptic scale features within its regional influence e g cyclones subtropical jets it concludes with some challenging problems for the future

the electrical structure of the slave craton the slave craton in northwestern canada a relatively small archean craton 600400 km is ideal as a natural laboratory for investigating the formation and evolution of mesoarchean and neoarchean sub continental lithospheric mantle sclm excellent outcrop and the discovery of economic diamondiferous kimberlite pipes in the centre of the craton during the early 1990s have led to an unparalleled amount of geoscientific information becoming available over the last 5 years deep probing electromagnetic surveys were conducted on the slave using the natural source magnetotelluric mt technique as part of a variety of programs to study the craton and determine its regional scale electrical structure two of the four types of surveys involved novel mt data acquisition one through frozen lakes along ice roads during winter and the second using ocean bottom mt instrumentation deployed from float planes the primary initial objective of the mt surveys was to determine the geometry of the topography of the lithosphere asthenosphere boundary lab across the slave craton however the mt responses revealed completely serendipitously a remarkable anomaly in electrical conductivity in the sclm of the central slave craton this central slave mantle conductor csmc anomaly is modelled as a localized region of low resistivity 10 15 v m beginning at depths of f80 120 km and striking ne sw where precisely located it is spatially coincident with the eocene aged kimberlite field in the central part of the craton the so called corridor of hope and also with a geochemically defined ultra depleted harzburgitic layer interpreted as oceanic or arc related lithosphere emplaced during early tectonism the csmc lies wholly within the ne sw

subseasonal to interannual variability of rainfall over new caledonia sw pacific daily rainfall occurrence and amount at 55 stations over new caledonia nc 20 s 166 e are examined throughout the calendar year during 1980 2010 using a hidden markov model hmm daily rainfall variability is described in terms of six discrete rainfall states identified by the hmm three states are interpreted as trade wind regimes associated with persistent low level anticyclonic conditions and weak to strong easterlies the most prevalent state state 1 36 of days is dry everywhere and is characterized by an elongated anticyclone centered around australia nc is located on the eastern edge of this anticyclone this state is predominant from mid may to mid december and peaks in september the second most prevalent state state 2 27 of days and the last trade regime state 4 12 of days are most frequent in austral summer states 2 and 4 are associated with the subtropical anticyclone centered south of nc close to its climatological location in austral summer and light state 2 to moderate state 4 rainfall mostly along the windward coast a distinct state state 3 11 of days is mostly associated with wintertime extratropical eastward traveling troughs between new caledonia and new zealand inducing light rainfall over the sw of the main island of new caledonia the two last states 5 and 6 are infrequent 15 of days but account for almost 70 of total rainfall across the archipelago they occur mostly in austral summer with their frequency of occurrence peaking in late february early march these states are associated with synoptic wave traveling eastward from eastern australia leading to a strong influx of moisture from the equatorial latitudes when the associated cyclonic centre is located west of new caledonia the wettest state is also strongly modulated by intra seasonal 15 80 days variability these events contribute to intermittent southwestward shifts of the south pacific convergence zone from its mean location northeast of new caledonia on interannual timescales the occurrence of the rainfall states is modulated by el nino southern oscillation enso events the enso impact is strongest from mid august to march with more less frequent trade regimes 1 2 and less more frequent unstable trade regime 4 and states 5 6 during central pacific warm cold enso events stochastic simulations of daily rainfall occurrence and amount at the 55 stations are generated by using predictors based on nino 4 sea surface temperature index and a local intra seasonal 15 80 days olr index superimposed on a climatological annual cycle the cross validated skill peaks in september november

the south pacific convergence zone in cmip5 simulations of historical and future climate the south pacific convergence zone spcz is evaluated in historical simulations from 26 coupled model intercomparison project phase 5 cmip5 models and compared with previous generation cmip3 models a subset of 24 cmip5 models are able to simulate a distinct spcz in the december to february djf austral summer although the position of the spcz in these models is too zonal compared with observations the spatial pattern of spcz precipitation is improved in cmip5 models relative to cmip3 models although the spurious double itcz precipitation band in the eastern pacific is intensified in many cmip5 models all cmip5 models examined capture some interannual variability of spcz latitude and 19 models simulate a realistic correlation with el nino southern oscillation in simulations of the twenty first century under the rcp8 5 emission scenario no consistent shift in the mean position of the djf spcz is identified several models simulate significant shifts northward and a similar number of models simulate significant southward shifts the majority of cmip5 models simulate an increase in mean djf spcz precipitation and there is an intensification of the eastern pacific double itcz precipitation band in many models most models simulate regions of increased precipitation in the western part of the spcz and near the equator and regions of decreased precipitation at the eastern edge of the spcz decomposition of spcz precipitation changes into dynamic and thermodynamic components reveals predominantly increased precipitation due to thermodynamic changes while dynamic changes lead to regions of both positive and negative precipitation anomalies

noble gases in the xinjiang armanty iron meteorite a big object with a short cosmic ray exposure age abstract we measured the concentrations and isotopic ratios of the cosmogenic noble gases he ne and ar in the very large iron meteorite xinjiang iiie the 3he and 4he data indicate that a significant portion of the cosmogenic produced helium has been lost via diffusion or in a recent impact event high 22ne 21ne ratios indicate that contributions to the cosmogenic 21ne from sulfur and or phosphorous are significant by combining the measured nuclide concentrations with model calculations for iron meteorites we were able to determine the preatmospheric diameter of xinjiang to 260 320 cm which corresponds to a total mass of about 70 135 tons the cosmic ray exposure age of xinjiang is 62 16 ma i e relatively short compared to most of the other iron meteorites with the current database we cannot firmly determine whether xinjiang experienced a complex irradiation history the finding of 3he and 4he losses might argue for a recent impact event and therefore for a complex exposure

coral oxygen isotope records of interdecadal climate variations in the south pacific convergence zone region 1 the south pacific convergence zone spcz a region of high rainfall is a major feature of subtropical southern hemisphere climate and contributes to and interacts with circulation features across the pacific yet its past temporal variability and forcing remain only partially understood here we compare coral oxygen isotopic 18o series spanning a d 1997 1780 and a d 2001 1776 from two genera of hermatypic corals in fiji located within the spcz to examine the fidelity of these corals in recording climate change and spcz interdecadal dynamics one of these coral records is a new 225 year subannually resolved 18o series from the massive coral diploastreaheliopora diploastrea s use in climate reconstructions is still relatively new but this coral has shown encouragingly similar interannual variability to porites the coral genus most commonly used in pacific paleoclimate studies in fiji we observe that interdecadal 18o variance is also similar in these two coral genera and diploastrea contains a larger amplitude interdecadal signal that more closely tracks instrumental based indices of pacific interdecadal climate change and the spcz than porites both coral 18o series record greater interdecadal variability from 1880 to 1950 which is consistent with the observations of folland et al 2002 who reported higher variability in spcz position before 1945 these observations indicate that diploastrea will likely provide a significant new source of long term climate information from the spcz region

the south pacific convergence zone in three decades of satellite images interannual variability seasonal evolution and intraseasonal variability of the south pacific convergence zone spcz are quantified using a new data set of 3 hourly spcz labels available from 1980 to 2012 nov apr the spcz label is a binary field indicating presence 1 or absence 0 of the spcz at each grid point 1 2 longitude by 1 2 latitude as a function of time and is the output of a bayesian spatiotemporal statistical model that takes in instantaneous data from geostationary satellites the statistical model is designed to emulate the way human observers identify the spcz results show two distinct parts to the spcz the western tropical part and the eastern subtropical part at times the two parts do not connect when they do connect they are oriented quite differently such that the subtropical part has a steeper meridional slope the spcz is present 50 70 of the time in the tropics from jan to mar and is usually anchored to the warm sea surface temperature sst distribution of the equatorial west pacific the subtropical part does not have the same sensitivity to the underlying sst distribution and is present more often in nov dec and apr than in jan mar when the sst is highest interannual variability in spcz location is strongly associated with el nino southern oscillation enso however no change in overall spcz area is detected in association with enso on the intraseasonal time scale composite analysis shows the distinct spatial patterns in spcz presence associated with each phase of the madden julian oscillation key points developed a 30 year 3 hourly data set of spcz location and extent presents interannual and intraseasonal variability of spcz location presents seasonal evolution of spcz location and extent 2013 american geophysical union all rights reserved

chemical classification of iron meteorites xi multi element studies of 38 new irons and the high abundance of ungrouped irons from antarctica abstract we report concentrations of 14 elements in the metal of 38 iron meteorites and a pallasite the meteorites are classified based on these data and on structural observations three samples are paired with previously classified irons thus these additional 35 irons raise the number of well classified independent iron meteorites to 598 one yamato iron contains 342 mg g ni the second highest ni content in an iab iron after oktibbeha county two small irons from western australia appear to be metal nodules from mesosiderites several of the new irons are from antarctica of 24 independent irons from antarctica 8 are ungrouped the fraction 0 333 is much higher than the fraction 0 161 among all 598 classified irons statistical tests show that it is highly improbable 2 9 probability that the antarctic population is a random sample of the larger population the difference is probably related to the fact that the median mass of antarctic irons is about two orders of magnitude smaller than that of non antarctic irons it is doubtful that the difference results from fragmentation patterns yielding different size distributions favoring smaller masses among ungrouped irons more likely is the possibility that smaller meteoroids tend to sample a larger number of asteroidal source regions perhaps because small meteoroids tend to have higher ejection velocities or because small meteoroids have random walked a greater increment of orbital semimajor axis away from that of the parent body

a dynamical framework for the origin of the diagonal south pacific and south atlantic convergence zones the south pacific convergence zone spcz and south atlantic convergence zone sacz are diagonal bands of precipitation that extend from the equator southeastward into the southern hemisphere over the western pacific and atlantic oceans respectively with mean precipitation rates over 5 mm day 1 they are a major component of the tropical and global climate in austral summer however their basic formation mechanism is not fully understood here a conceptual framework for the diagonal convergence zones is developed based on calculations of the vorticity budget from reanalysis and rossby wave theory wave trains propagate eastward along the southern hemisphere subtropical jet with initially quasi circular vorticity centres in the zonally sheared environment on the equatorward flank of the jet these vorticity centres become elongated and develop a northwest southeast tilt ray tracing diagnostics in a non divergent barotropic rossby wave framework then explain the observed equatorward propagation of these diagonal vorticity structures toward the westerly ducts over the equatorial pacific and atlantic the baroclinic component of these circulations leads to destabilisation and ascent ahead of the cyclonic vorticity anomaly in the wave triggering deep convection because of the high sea surface temperatures in this region latent heat release then forces additional ascent and strong upper tropospheric divergence with an associated anticyclonic vorticity tendency a vorticity budget shows that this cancels out the advective cyclonic vorticity tendency in the wave train over the spcz and dissipates the wave within a day the mean spcz is consequently comprised of the sum of these pulses of diagonal bands of precipitation similar mechanisms also operate in the sacz however the vorticity anomalies in the wave trains are stronger and the precipitation and negative feedback from the divergence and anticyclonic vorticity tendency are weaker resulting in continued propagation of the wave and a more diffuse diagonal convergence zone

p process 180w anomalies in iron meteorites nucleosynthetic versus non nucleosynthetic origins abstract heavy proton rich stable isotopes belong to the least abundant isotopes in the solar system their formation mechanisms and their stellar sources are most likely different from those of neutron capture generated r and s process nuclei that comprise the majority of nuclides heavier than iron heavy p nuclide abundances in meteorites are therefore potentially useful in deciphering distinct stellar contributions to the nascent solar system we therefore conducted the first high precision measurements of the heavy p process isotope 180 w achieving a typical precision of 0 7 e units for ca 300 ng w measured samples comprise metals from magmatic and non magmatic iron meteorites as well as metal from one h4 chondrite nwa 926 and two reduced terrestrial basalts from disko island greenland and the dzheltul ski massif from eastern siberia russia the analyzed iron meteorites show clearly resolvable 180 w anomalies of up to 6 e units conversely the chondritic metal and both terrestrial samples exhibit 180 w abundances indistinguishable from the standard value as cosmogenic effects during space exposure of the meteoroids may have affected the 180 w budget cosmic ray exposure of the meteorites has to be critically evaluated we therefore propose a method to approximate cosmogenic contributions to the 180 w signatures in order to unravel nucleosynthetic 180 w abundance anomalies our study reveals significant cosmogenic effects only for the longest exposed meteorites shifting 180 w anomalies always to lower values average cosmic ray correction factors can be estimated to lie between 0 01 and 0 30 e 180 w units per 100 myr of exposure cosmogenic effects for most of the analyzed meteorites therefore appear to be negligible with respect to the analytical precision achieved for iron meteorites in addition to cosmic ray exposure radiogenic effects can be caused by putative decay of 184 os or by decay of 180 ta in its ground state whereas potential alpha decay of 184 os could shift 180 w anomalies to higher values but only up to levels that are within the analytical error of 0 5 e units for most samples no significant production of 180 w could have occurred from 180 ta decay notably we identified significant and systematic abundance variations in 180 w between different iron meteorite groups indicating that these isotope anomalies are characteristic for their entire parent asteroids our finding of decreasing excesses in 180 w from early formed magmatic iron meteorites 3 8 1 2 units towards later formed non magmatic iron meteorites 0 6 0 5 units the analyzed chondrite and both terrestrial rocks 0 3 0 7 e units may thus mirror progressive homogenization of 180 w in the early solar nebula this overall trend is also supported by a co variation between 180 w and metal segregation ages for the different iron meteorite groups as well as by a co variation between 180 w deviations and the respective asteroidal accretion ages such an interpretation would suggest progressive homogenization of the solar nebula within about 2 5 to 6 myr

microstructure evolution of aqueous fluid bearing wehrlites implications for the fluid distribution in polymineralic rocks 1 the microstructure of aqueous fluid bearing wehrlites was experimentally studied in order to investigate the fluid distribution in polymineralic rocks wehrlites of various forsterite diopside ratios were synthesized with 1 0 1 5 wt water at 1200 c and 1 2 gpa for 1 5 668 hours conspicuous grain growth drag and coagulation of pore fluids were observed in the time series experiments the pore fluids were classified into two types those surrounded only by a single phase g type and those surrounded by both forsterite and diopside i type in the short time runs the relative volume fraction of i type pores in all the pores fi agrees well with the value calculated from an ideal pore distribution model in which all the grains are randomly distributed the fi of wehrlites with various forsterite diopside ratios increased with average grain size and reached a steady state value at 80 90 in about 160 163 hours the increase of fi is explained by interphase boundary trapping g type pore fluids move faster than i type and the number of g type becoming i type by being trapped into the interphase boundary per unit time is larger than that of i type pores transforming to g type the experimental results suggest that large fractions of pore fluids might be distributed at the grain junctions surrounded by more than two mineral phases in natural rocks as a result of grain growth the connectivity of the fluid network in polymineralic rocks may be strongly influenced by modal composition of the rocks as well as by the dihedral angles among the fluid and two mineral phases

origin of the south pacific convergence zone abstract the importance of the presence of south america and australia to the existence and orientation of the south pacific convergence zone spcz during january is explored using the ecmwf t21 model each of the continents is removed from the model and replaced with an ocean surface and the resulting precipitation and circulation associated with the spcz are then compared to a perpetual january control run results show that the presence of south america and the equatorial pacific upwelling zone does not appear to be crucial to the spcz but that the removal of australia destroys the southern monsoon and substantially weakens the western part of the spcz this suggests that the northwest southeast orientation of the spcz during southern summer is more dependent on interactions with the midlatitude westerlies over the south pacific than on the distribution of sea surface temperature and land over the southern hemisphere

lightning activity analyses with respect to the spcz location 1 the south pacific convergence zone spcz stretches over the west pacific warm pool southeastward to french polynesia the island climate update monthly publishes the mean location deduced from the total rainfall on the other hand the world wide lightning location network monthly provides data from which the lightning activity distribution in the 0 30 south latitude and 150 240 west longitude area can be drawn scanning this rectangle from west to east allows the spots of maximum lightning activity to be located versus the longitude fitting the location of these maxima with a polynomial function leads to a curve comparable with the monthly mean position of the spcz showing that this band of cloudiness is one of the main sources of lightning in this whole area

tropical midlatitude interactions in the indian and pacific sectors of the southern hemisphere abstract observations and three general circulation model gcw simulations are analyzed to study interannual processes and interactions involved in the tropical indian and pacific sectors and higher southern latitudes major features involving the observed eastward progression of the tropical convective maximum from the indian monsoon in northern summer to the australian monsoon and pacific in southern summer are represented in all three model simulations this suggests that the distribution of land and sea accounts for the observed seasonal position of the convective maximum in these regions however the south pacific convergence zone spcz is not present at any time of year in the slab ocean models due to the anomalously warm sea surface temperatures simulated in the equatorial pacific analyses of observed zonal mean 500 mb temperatures and sea level pressure from 10 to 80 s for warm event composites minus cold event composites representing two extremes of interannual variation show the period of

el nino la nina and the nonlinearity of their teleconnections the paradigm of an atmospheric system varying linearly with respect to extreme phases of the el nino southern oscillation is questioned it is argued that the global response to tropical pacific sea surface temperature forcing will be inherently nonlinear a physical basis for this intrinsic nonlinearity is the thermodynamic control on deep convection climate statistics for warm and cold events of the tropical pacific are analyzed separately for the northern winter periods during 1950 96 composite analysis of 500 mb heights reveal planetary scale teleconnection patterns as noted in earlier studies a new result is the evidence for an appreciable 358 longitude phase shift between the warm and cold event circulation composites and the two wave trains appear to have different tropical origins a large nonlinear component in north american surface climate anomalies is also found which is consistent with such a phase shift in teleconnections in the tropics rainfall anomalies also show evidence of nonlinear behavior the maximum rain anomalies along the equator are located east of the date line during warm events but west of the date line during cold events the interpretation of this behavior is complicated however by the fact that composite warm event sst anomalies are not the exact inverse of their cold event counterparts idealized atmospheric general circulation model agcm experiments are performed in order to test the question of whether the observed nonlinearity is an intrinsic property of the atmospheric system the model is forced with a composite sst anomaly that undergoes a realistic seasonally varying enso life cycle as described by e rasmusson and t carpenter both positive and negative phases of the sst anomaly are used and a 40 member ensemble of warm and cold event model simulations is conducted a nonlinear climate response in the agcm is found that closely resembles the observed composites including a shift in the equatorial positions of the maxmium rain responses and a phase shift of teleconnection patterns in the upper troposphere barotropic model experiments indicate that the inherent nonlinearity in the tropical rain response may itself be responsible for the phase shift in the extratropical teleconnection patterns

group iva irons new constraints on the crystallization and cooling history of an asteroidal core with a complex history we report analyses of 14 group iva iron meteorites and the ungrouped but possibly related elephant moraine eet 83230 for siderophile elements by laser ablation icp ms and isotope dilution eet was also analyzed for oxygen isotopic composition and metallographic structure and fuzzy creek currently the iva with the highest ni concentration was analyzed for metallographic structure highly siderophile elements hse re os and ir concentrations vary by nearly three orders of magnitude over the entire range of iva irons while ru pt and pd vary by less than factors of five chondrite normalized abundances of hse form nested patterns consistent with progressive crystal liquid fractionation attempts to collectively model the hse abundances resulting from fractional crystallization achieved best results for 3 wt s compared to 0 5 or 9 wt s consistent with prior studies concentrations of hse and other refractory siderophile elements estimated for the bulk iva core and its parent body are in generally chondritic proportions projected abundances of pd and au relative to more refractory hse are slightly elevated and modestly differ from l ll chondrites which some have linked with group iva based on oxygen isotope similarities abundance trends for the moderately volatile and siderophile element ga cannot be adequately modeled for any s concentration the cause of which remains enigmatic further concentrations of some moderately volatile and siderophile elements indicate marked progressive depletions in the iva system however if the iva core began crystallization with 3 wt s depletions of more volatile elements cannot be explained as a result of prior volatilization condensation processes the initial iva core had an approximately chondritic ni co ratio but a fractionated fe ni ratio of 10 indicates an fedepleted core this composition is most easily accounted for by assuming that the surrounding silicate shell was enriched in iron consistent with an oxidized parent body the depletions in ga may reflect decreased siderophilic behavior in a relatively oxidized body and more favorable partitioning into the silicate portion of the parent body phosphate inclusions in eet show d 17 o values within the range measured for silicates in iva iron meteorites eet has a typical ataxitic microstructure with precipitates of kamacite within a matrix of plessite chemical and isotopic evidence for a genetic relation between eet and group iva is strong but the high ni content and the newly determined rapid cooling rate of this meteorite show that it should continue to be classified as ungrouped previously reported metallographic cooling rates for iva iron meteorites have been interpreted to indicate an inwardly crystallizing 150 km radius metallic body with little

experimental constraints on permeable gas transport in crystalline silicic magmas the gas and fluid transport in magmas via permeable flow through interconnected bubble networks controls the rate of outgassing from magmas ascending in volcanic conduits and the fluid transport in the mushy boundary layer of magma reservoirs hence clarifying its mechanism and rate is crucial to understanding the explosivity of volcanic eruptions and the evolution and dynamics of a magma reservoir recent experimental studies have determined the gas permeabilities in crystal free rhyolite and basalt however no experimental study has investigated the effect of the crystal contents on the permeable gas transport in magmas in this study we performed decompression experiments for hydrous rhyolitic melts having crystallinities of 30 and 50 vol to examine the effect of crystals on the bubble microstructure and gas permeability during magma vesiculation size controlled 100 meshed corundum crystals were used as an analog of the phenocrysts in silicic magmas microstructural analyses using x ray ct showed that bubbles coalesce and their connectivity increases with a decrease in the final pressure after the decompression that is an increase in the vesicularity as long as the vesicularities of melt part in the crystal free basis melt vesicularity were similar no clear effect of the crystallinity on the degree of bubble coalescence and connectivity was observed at melt vesicularities 68 vol this result indicates that the permeable fluid transport through a deep volcanic conduit which has been proposed on the basis of the observations of volcanic gases and natural products is so slow that other processes like shear deformation or magma convection may be needed to explain the observations

why the south pacific convergence zone is diagonal during austral summer the majority of precipitation over the pacific ocean is concentrated in the south pacific convergence zone spcz the surface boundary conditions required to support the diagonally northwest southeast oriented spcz are determined through a series of experiments with an atmospheric general circulation model continental configuration and orography do not have a significant influence on spcz orientation and strength the key necessary boundary condition is the zonally asymmetric component of the sea surface temperature sst distribution this leads to a strong subtropical anticyclone over the southeast pacific that on its western flank transports warm moist air from the equator into the spcz region this moisture then intensifies diagonal bands of convection that are initiated by regions of ascent and reduced static stability ahead of the cyclonic vorticity in rossby waves that are refracted toward the westerly duct over the equatorial pacific the climatological spcz is comprised of the superposition of these diagonal bands of convection when the zonally asymmetric sst component is reduced or removed the subtropical anticyclone and its associated moisture source is weakened despite the presence of rossby waves significant moist convection is no longer triggered the spcz disappears the diagonal spcz is robust to large changes up to 6 c in absolute sst i e where the sst asymmetry is preserved extreme cooling change 6 c results in a weaker and more zonal spcz due to decreasing atmospheric temperature moisture content and convective available potential energy

the multiphase grain control percolation its implication for a partially molten rock a model of percolation process named the multiphase grain control percolation mgcp is proposed in order to estimate the connectivity of the melt phase in a partially molten rock in which spatial melt distribution is determined by the combination of surrounding grain species according to the stability of the melt phase at the grain boundaries three types of percolation model are introduced the corner percolation the edge percolation and the corner edge ce percolation the ce percolation can be reduced to the corner or edge percolation the connectivity of the melt phase is determined as a function of modal composition in a multiphase grain system for various combinations of grain species surrounding the corner or edge occupied by the melt phase we obtain the critical grain fraction at which the connectivity changes abruptly from 0 to 1 the critical grain fraction estimated from the mgcp does not coincide with that from the ordinary percolation model in which random distribution of the melt phase is assumed as a geophysical application of the mgcp we construct the connectivity diagrams modal composition diagram of the connectivity of the melt phase for two partially molten peridotites by using the experimental results of dihedral angle measurements from these diagrams we predict that the melt phase is connected extensively if fraction of olivine exceeds 63 vol for a natural peridotite composed of olivine orthopyroxene and clinopyroxene and 38 vol for a synthetic peridotite composed of olivine and orthopyroxene for the former peridotite we further estimate critical melt fraction it is shown that the melt phase can be connected extensively when the melt fraction exceeds 0 8 vol in the peridotite composed of more than 63 vol olivine

excess 180w in iiab iron meteorites identification of cosmogenic radiogenic and nucleosynthetic components abstract the origin of 180 w excesses in iron meteorites has been a recently debated topic here a suite of iiab iron meteorites was studied in order to accurately determine the contribution from galactic cosmic rays gcr and from potential decay of 184 os to measured excesses in the minor isotope 180 w in addition to w isotopes trace element concentrations re os ir pt w were determined on the same samples as well as their cosmic ray exposure ages using 36 cl 36 ar systematics these data were used in combination with an improved model of gcr effects on w isotopes to correct effects resulting from neutron capture and spallation reactions after these corrections the residual 180 w excesses correlate with os w ratios and indicate a clear contribution from 184 os decay a newly derived decay constant is equivalent to a half life for 184 os of 3 38 2 13 10 13 a furthermore when the data are plotted on an os w isochron diagram the intercept e 180 w i 0 63 0 35 reveals that the iiab parent body was characterized by a small initial nucleosynthetic excess in 180 w upon which radiogenic and gcr effects were superimposed this is the first cogent evidence for p process variability in w isotopes in early solar system material