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

density porosity and magnetic susceptibility of carbonaceous chondrites abstract we report physical properties bulk and grain density magnetic susceptibility and porosity measured using nondestructive and noncontaminating methods for 195 stones from 63 carbonaceous chondrites grain densities over the whole population average 3 44 g cm 3 ranging from 2 42 g cm 3 ci1 orgueil to 5 66 g cm 3 cb bencubbin magnetic susceptibilities in log units of 10 9 m3 kg 1 averaged log 4 22 ranging from 3 23 cv3 axtell to 5 79 cb bencubbin porosities averaged 17 ranging from 0 for a number of meteorites to 41 for one stone of the co ornans notably we found significant differences in porosity between the oxidized and reduced cv subgroups with the porosities of cvo averaging approximately 20 and cvr porosities approximately 4 overall porosities of carbonaceous chondrite falls trend with petrographic type from type 1 ci near 35 type 2 cm cr averaging 23 type 3 cv co 21 to type 4 ck and some co averaging 15 there is also a significant decrease in porosity between meteorites of shock stage s1 and those of s2 indicative of shock compression

the porosities of ordinary chondrites models and interpretation densities and porosities for 285 ordinary chondrites have been assembled and analyzed measured chondrite porosities are bimodal finds have an average porosity of 30 we conclude that mild degrees of weathering fill pore spaces lowering grain densities and porosities without significantly changing the bulk size or mass of the sample by assuming an original pristine grain density as a function of the meteorite s mineralogy determined by its class we can derive model pristine porosities these model porosities cluster around an average value of 10 for all classes of ordinary chondrites ordinary chondrites do not show any correlation of porosity model or measured with petrographic grade or sample size over a range from 0 2 g to 2 kg however we do see a correlation between shock state and porosity shock blackened meteorites are less porous than other meteorites furthermore less severely shocked meteorites show a much broader range of porosities with the maximum porosity seen among meteorites of a given shock class falling linearly as a function of that shock class this is consistent with the idea that shock compresses and closes pore space analysis of meteorite porosity provides a lower bound to the fine scale porosity of asteroids our densities even with 10 primordial porosity are significantly higher than inferred densities of possible asteroid parent bodies these asteroids are probably loose piles of rubble

on the yearly phase delay of winter intraseasonal mode in the western united states in the western united states persistent and recurrent flow patterns not only modulate precipitation events but also result in prolonged surface inversion episodes in this region the frequency of persistent ridge trough events ranges between 20 and 40 days well within the intraseasonal timescale based on ncep reanalysis data starting at 1949 with a focus on the interior west we observed that episodes of prolonged ridge trough events appear to occur about a week later every year and resets every 5 7 years a previously undocumented phenomenon examined herein diagnostic analyses indicate that the interplay between regional intraseasonal flow patterns and the north atlantic oscillation nao alternates the preferred timeframe for the persistent ridge trough events to occur this may result from different phases of the nao shifting the winter mean ridge and such shifts modulate the occurrence and timing of persistent ridge trough events when the timing changes evolve around the quasi 6 years cycle of the nao the resultant evolution forms what appears to be a steady phase delay in the ridge trough events year after year these results are a further step in disclosing the multiple scale interaction between intraseasonal and interannual modes and its regional climate weather impact

collisional facilitation of aqueous alteration of cm and cv carbonaceous chondrites abstract cm chondrites exhibit a strong correlation between the degree of alteration and the extent of particle alignment i e the strength of the petrofabric it seems likely that the s1 shock stage of essentially every cm and the high matrix abundance 70 vol of these samples ensured that the shock waves that produced cm petrofabrics by collapsing matrix pores and squeezing chondrules into pore spaces were significantly attenuated and were too weak to damage olivine crystal lattices random collisions on the cm body produced petrofabrics and created fractures in the target rocks subsequent impact mobilization of water caused hydrated phases to form preferentially in the more fractured regions those with the strongest petrofabrics the less deformed less fractured cm regions experienced lower degrees of aqueous alteration many cv3 chondrites also have petrofabrics roughly half are from the oxidized bali like subgroup cv3 oxb roughly half are from the reduced subgroup cv3 r and none is from the oxidized allende like subgroup cv3 oxa which is less altered than cv3 oxb nearly all cvs with petrofabrics are s3 s4 and nearly all cvs that lack petrofabrics are s1 oxidized cvs have much higher porosities typically 20 28 than reduced cvs 0 6 8 facilitating more extensive aqueous alteration the cv3 r chondrites formed from low porosity material that inhibited oxidation during alteration the oxidized cv subgroups formed from higher porosity materials the cv3 oxb samples were shocked became extensively fractured and developed petrofabrics the cv3 oxa samples were not shocked and never developed petrofabrics when water was mobilized both sets of porous cv chondrites became oxidized the more fractured cv3 oxb subgroup was more severely altered

circumglobal teleconnections the jet stream waveguide and the north atlantic oscillation abstract monthly and seasonally averaged upper tropospheric northern hemisphere winter fields are examined to determine whether the waveguiding effect of the time averaged tropospheric jets on low frequency disturbances that is predicted by theory does affect the behavior of these disturbances it is found that indeed disturbances in the vicinity of the mean jets particularly the jet that stretches across south asia are fundamentally different from those that reside in regions where the mean winds have weaker meridional gradients like the mid pacific patterns of variability in the jets tend to be smaller scale and to consist of zonally oriented chains of anomalies while variability in the mid pacific is composed of patterns with distinct meridional orientation because they are meridionally trapped and zonally elongated patterns associated with the jet stream waveguide connect activity at points that are much farther apart than do patterns in other regions of the globe within the south asian waveg

quantified whole section trace element mapping of carbonaceous chondrites by synchrotron x ray fluorescence microscopy 1 cv meteorites abstract we present the application of a new synchrotron based technique for rapid mapping of trace element distributions across large areas of the cv3 meteorites allende and vigarano this technique utilizes the australian synchrotron x ray fluorescence microscopy xfm beam line with its custom designed and built x ray detector array called maia xfm with maia allows data to be collected using a 2 m spot size at very low dwell times 0 1 0 5 ms resulting in maps of entire thin sections in 5 h maia is an energy dispersive detector system with a large collection solid angle which allows full spectral acquisition and high sensitivity hence there is no need to constrain the elements of interest a priori we collected whole section maps 2 cm 1 cm from 3 thick sections of allende and a single map 2 cm 1 5 cm from a thick section of vigarano our experimental conditions provide data for elements with 20 z 40 k shell ca through zr and the l emissions of os ir pt au and pb we illustrate the unique capabilities of this technique by presenting observations across myriad length scales from the centimeter scale down to the detection of sub micrometer particles within these objects our initial results show the potential of this technique to help decipher spatial and textural variations in trace element chemistry between cais chondrules matrix and other chondritic components we also illustrate how these datasets can be applied to understanding both nebular and parent body processes within meteorites

observed and simulated intraseasonal variability of the wintertime planetary circulation abstract the persistence of the planetary scale simulation over the north pacific ocean is investigated during 18 northern hemisphere winters from 1965 66 to 1982 83 quasi stationary flow patterns dominate 20 periods during the 6 el nino winters in contrast 29 such periods are observed during the remaining 12 winters nearly all of the quasi stationary episodes during el nino winters exhibit negative 500 mb geopotential height anomalies in the gulf of alaska aleutian island region during the other 12 winters episodes characterized by positive height anomalies in that region occur as frequently as those exhibiting negative height anomalies the observed persistence of the planetary circulation is contrasted to that simulated by the ucla general circulation model ten winters of model output are analyzed during five winters sea surface temperatures ssts are prescribed to evolve through their climatological seasonal cycle while during the other five winters sst anomalies corresponding to idealized

the fall and recovery of the tagish lake meteorite the tagish lake c2 ungrouped carbonaceous chondrite fall of january 18 2000 delivered 10 kg of one of the most primitive and physically weak meteorites yet studied in this paper we report the detailed circumstances of the fall and the recovery of all documented tagish lake fragments from a strewnfield at least 16 km long and 3 to 4 km wide nearly 1 kg of pristine meteorites were collected one week after the fall before new snow covered the strewnfield the majority of the recovered mass was collected during the spring melt ground eyewitnesses and a variety of instrument recorded observations of the tagish lake fireball provide a refined estimate of the fireball trajectory from its calculated orbit and its similarity to the remotely sensed properties of the d and p class asteroids the tagish lake carbonaceous chondrite apparently represents these outer belt asteroids the cosmogenic nuclide results and modeled production indicate a prefall radius of 2 1 2 4 m corresponding to 60 90 tons consistent with the observed fireball energy release the bulk oxygen isotope compositions plot just below the terrestrial fractionation line tfl following a trend similar to the cm meteorite mixing line the bulk density of the tagish lake material 1 64 0 02 g cm 3 is the same within uncertainty as the total bulk densities of several c class and especially d and p class asteroids the high microporosity of tagish lake samples 40 provides an obvious candidate material for the composition of low bulk density primitive asteroids

recent tectonic activity on pluto driven by phase changes in the ice shell the new horizons spacecraft has found evidence for geologic activity on the surface of pluto including extensional tectonic deformation of its water ice bedrock see moore et al 2016 one mechanism that could drive extensional tectonic activity is global surface expansion due to the partial freezing of an ocean we use updated physical properties for pluto and simulate its thermal evolution to understand the survival of a possible subsurface ocean for thermal conductivities of rock less than 3 w m 1 k 1 an ocean forms and at least partially freezes leading to recent extensional stresses in the ice shell in scenarios where the ocean freezes and the ice shell is thicker than 260 km ice ii forms and causes global volume contraction since there is no evidence for recent compressional tectonic features we argue that ice ii has not formed and that pluto s ocean has likely survived to present day

seasonal and diurnal variations in ampere observations of the birkeland currents compared to modeled results we reduce measurements made by the active magnetosphere and planetary electrodynamics response experiment ampere to give the total birkeland field aligned current flowing in both hemispheres in monthly and hourly bins we analyze these totals using 6 years of data 2010 2015 to examine solar zenith angle driven variations in the total birkeland current flowing in both hemispheres simultaneously for the first time a diurnal variation is identified in the total birkeland current flowing consistent with variations in the solar zenith angle a seasonal variation is also identified with more current flowing in the northern southern hemisphere during bartels rotations in northern southern summer for months close to equinox more current is found to flow in the northern hemisphere contrary to our expectations we also conduct the first test of the milan 2013 model for estimating birkeland current magnitudes with modifications made to account for solar contributions to ionospheric conductance based on the observed variation of the birkeland currents with season and time of day the modified model using the value of d averaged by bartels rotation scaled by 1 7 is found to agree with the observed ampere currents with a correlation of 0 87 in the northern hemisphere and 0 86 in the southern hemisphere the improvement over the correlation with dayside reconnection rate is demonstrated to be a significant improvement to the model the correlation of the residuals is found to be consistent with more current flowing in the northern hemisphere this new observation of systematically larger current flowing in the northern hemisphere is discussed in the context of previous results which suggest that the northern hemisphere may react more strongly to dayside reconnection than the southern hemisphere

the cr chondrite clan implications for early solar system processes in this paper we review the mineralogy and chemistry of calcium aluminum rich inclusions cais chondrules feni metal and fine grained materials of the cr chondrite clan including cr ch and the metal rich cb chondrites queen alexandra range 94411 hammadah al hamra 237 bencubbin gujba and weatherford the members of the cr chondrite clan are among the most pristine early solar system materials which largely escaped thermal processing in an asteroidal setting bencubbin weatherford and gujba may be exceptions and provide important constraints on the solar nebula models these constraints include 1 multiplicity of cai formation 2 formation of cals and chondrules in spatially separated nebular regions 3 formation of cais in gaseous reservoir s having o 16 rich isotopic compositions chondrules appear to have formed in the presence of o 16 poor nebular gas 4 isolation of cais and chondrules from nebular gas at various ambient temperatures 5 heterogeneous distribution of al 26 in the solar nebula and 6 absence of matrix material in the regions of cai and chondrule formation

inhomogeneity of asteroid 2008 tc3 almahata sitta meteorites revealed through magnetic susceptibility measurements abstract magnetic susceptibility measurements were performed on freshly fallen almahata sitta meteorites most recovered samples are polymict ureilites those found in the first 4 months since impact before the meteorites were exposed to rain have a magnetic susceptibility in the narrow range of 4 92 0 08 log 10 9 am2 kg 1 close to the range of other ureilite falls 4 95 0 14 log 10 9 am2 kg 1 reported by rochette et al 2009 the almahata sitta samples collected 1 yr after the fall have similar values 4 90 0 06 log 10 9 am2 kg 1 revealing that the effect of 1 yr of terrestrial weathering was not severe however our reported values are higher than derived from polymict brecciated ureilites 4 38 0 47 log 10 9 am2 kg 1 rochette et al 2009 containing both falls and finds confirming that these are significantly weathered additionally other fresh looking meteorites of nonureilitic compositions were collected in the almahata sitta strewn field magnetic susceptibility measurements proved to be a convenient nondestructive method for identifying nonureilitic meteorites among those collected in the almahata sitta strewn field even among fully crusted three such meteorites no 16 25 and 41 were analyzed and their composition determined as eh6 h5 and el6 respectively zolensky et al 2010 a high scatter of magnetic susceptibility values among small 5 g samples revealed high inhomogeneity within the 2008 tc3 material at scales below 1 2 cm

almahata sitta fragment ms ch characterization of a new chondrite type abstract among the several hundred mostly small meteorite fragments recovered within the almahata sitta strewn field one fragment ms ch weighing 5 68 g was detected that represents a new type of chondritic meteorite the detection of short lived cosmogenic radionuclides clearly indicates that this chondrite fragment results from a fresh meteorite fall consistent with the almahata sitta event in october 2008 the fundamental mineralogical characteristics of the almahata sitta fragment ms ch can be summarized as follows 1 the almost equilibrated olivine has high fa contents of about 36 mole the fragment is of petrologic type 3 8 0 1 2 the metal abundance of the rock is on the order of 2 5 vol 3 the mean chondrule size has been determined to be roughly 450 m 4 point counting and imaging indicate that the matrix abundance is approximately 45 vol 5 cr spinels have much lower tio2 concentrations than typical spinels within r chondrites 6 calcium aluminum rich inclusions are spinel rich and severely altered having abundant na and or cl rich alteration products spinel also contains significant concentrations of fe and zn 7 magnetites and platinum group element rich phases sulfides tellurides and arsenides characteristic of both r and ck chondrites were not found in fragment ms ch and 8 the mean oxygen isotope composition of three small fragments of almahata sitta ms ch is 17o 4 35 18o 4 94 and 17o 1 76 the oxygen isotopes relate ms ch to r chondrites no established chondrite group having all these characteristics exists

the porosity and permeability of chondritic meteorites and interplanetary dust particles abstract we have investigated the porosity of a large number of chondritic interplanetary dust particles idps and meteorites by three techniques standard liquid gas flow techniques a new noninvasive ultrasonic technique and image processing of backscattered images the latter technique is obviously best suited to sub kilogram sized samples we have also measured the gas and liquid permeabilities of some chondrites by two techniques standard liquid gas flow techniques and a new nondestructive pressure release technique we find that chondritic idps have a somewhat bimodal porosity distribution peaks are present at 0 and 4 porosity a tail then extends to 53 type 1 3 chondrite matrix porosities range up to 30 with a peak at 2 the bulk porosities for type 1 3 chondrites have the same approximate range as exhibited by the matrix which indicates that other components of the bulk meteorites including chondrules and aggregates have the same average porosity as the matrix these results reveal that the porosities of primitive materials at scales ranging from nanogram to kilogram are similar which implies that similar accretion dynamics operated through 12 orders of size magnitude permeabilities of the investigated chondrites vary by several orders of magnitude and there appears to be no simple dependence of permeability with degree of aqueous alteration chondrite type or porosity

the contamination of the surface of vesta by impacts and the delivery of the dark material abstract the dawn spacecraft recently observed the presence of dark material which in turn proved to be associated with the presence of oh and h rich material on the surface of vesta the source of this dark material has been almost unanimously identified with the low albedo asteroids likely analogous to the carbonaceous chondrites found on earth that impacted on vesta over its lifetime however it is still a matter of debate whether the delivery of the dark material is associated with a few large impact events to micrometeorites or to the continuous secular flux of impactors on vesta the continuous flux scenario in particular predicts that a significant fraction of the exogenous material accreted by vesta should be due to non dark impactors likely analogous to ordinary chondrites which instead represent only a minor contaminant in the howardite eucrite diogenite meteorites in this work we explored the continuous flux scenario and its implications for the composition of the vestan regolith taking advantage of the data from the dawn mission and the howardite eucrite diogenite meteorites to constrain the contamination history of vesta we developed a model for the delivery of the exogenous material to vesta and verified how the results it supplies are sensitive to the different parameters we consider we calibrated the flux of impactors predicted by our model with the number of dark craters observed inside the rheasilvia basin and we tested the assumptions on the impact conditions by studying the formation of cornelia crater and of its dark deposits with a hydrocode simulation we used our calibrated model to show that the stochastic events scenario and the micrometeoritic flux scenario are just natural consequences of the continuous flux scenario we then used the model to estimate the amounts of dark and hydroxylate materials that were delivered on vesta since the late heavy bombardment and we showed how our results match well with the values estimated by the dawn mission we finally used our model to assess the amount of fe and siderophile elements that the continuous flux of impactors would mix in the vestan regolith concerning the siderophile elements we focused our attention on the role of ni the results we obtained are in agreement with the data available on the fe and ni content of the howardite eucrite diogenite meteorites and can be used as a reference frame in future studies of the data from the dawn mission and of the howardite eucrite diogenite meteorites our model cannot yet provide an answer to the conundrum of the fate of the missing non carbonaceous contaminants but we discuss some possible reasons for this discrepancy with the otherwise coherent picture described by our results

the density and porosity of meteorites from the vatican collection abstract we have developed a nondestructive technique to measure the densities and porosities of large 50 g to several kilogram meteorite samples and have begun a systematic measurement program starting with meteorites from the vatican observatory collection our technique utilizes a modified archimedean method 40 m glass spheres substituting for the fluid to determine bulk density and an unusually large he pycnometer to determine grain density from these the porosity is calculated we report here our first results for 89 samples nearly doubling the published database on porosities of meteorite hand samples including porosities of 35 different meteorites these include several types not previously reported eight iron meteorites six stony iron meteorites an enstatite chondrite the ci carbonaceous chondrite orgueil and the shergottite nakhlatite chassignite snc meteorite nakhla

asteroid 2008 tc 3 almahata sitta a spectacular breccia containing many different ureilitic and chondritic lithologies abstract asteroid 2008 tc3 impacted earth in northern sudan on october 7 2008 the meteorite named almahata sitta was classified as a polymict ureilite in this study 40 small pieces from different fragments collected in the almahata sitta strewn field were investigated and a large number of different lithologies were found some of these fragments are ureilitic in origin whereas others are clearly chondritic as all are relatively fresh w0 w0 1 and as short lived cosmogenic radioisotopes were detected within two of the chondritic fragments there is strong evidence that most if not all belong to the almahata sitta meteorite fall the fragments can roughly be subdivided into achondritic ureilitic 23 samples and chondritic lithologies 17 samples among the ureilitic rocks are at least 10 different lithologies a similar number of different chondritic lithologies also exist most chondritic fragments belong to at least seven different e chondrite rock types eh3 el3 4 el6 el breccias several different types of el and eh impact melt rocks and impact melt breccias some of the latter are shock darkened in addition two h group ordinary chondrite lithologies were identified and one sample of a chondrite type that is so far unique the latter has some affinities to r chondrites oxygen isotope compositions of 14 fragments provide further fundamental information on the lithological heterogeneity of the almahata sitta meteorite based on the findings presented in this study the reflectance spectrum of asteroid 2008 tc3 has to be evaluated in a new light

a new metal rich chondrite grouplet abstract a new grouplet of primitive metal rich chondrites here called the cb c carbonaceous b bencubbinite chondrites has been recognized it includes bencubbin weatherford hammadah a1 hamra hh 237 and queen alexandra range que 94411 paired with que 94627 their mineral compositions as well as their oxygen and nitrogen isotopic compositions indicate that they are closely related to the cr and ch chondrites all of which are members of the more inclusive cr clan cb chondrites have much greater metal silicate ratios than any other chondrite group widely increasing the range of metal silicate fractionation recorded in solar nebular processes they also have the greatest moderately volatile lithophile element depletions of any chondritic materials metal has compositional trends and zoning patterns that suggest a primitive condensation origin in contrast with metal from other chondrite groups cb chondrites as well as other cr clan chondrites have much heavier nitrogen higher 15n 14n than that in other chondrite groups the primitive characteristics of the cb chondrites suggest that they contain one of the best records of early nebular processes another chondrite grosvenor mountains 9555 1 is petrographically similar to the cb chondrites but its mineral and oxygen and nitrogen isotope compositions indicate that it formed from a different nebular reservoir

evidence for impact induced pressure gradients on the allende cv3 parent body consequences for fluid and volatile transport carbonaceous chondrites such as those associated with the vigarano cv parent body exhibit a diverse range of oxidative reduced alteration mineralogy mcsween 1977 although fluids are often cited as the medium by which this occurs rubin 2012 a mechanism to explain how this fluid migrates and why some meteorite subtypes from the same planetary body are more oxidized than others remains elusive in our study we examined a slab of the well known allende cv3oxa meteorite using several petrological techniques e g fry s and flinn and computerized tomography ct we discover it exhibits a strong penetrative planar fabric resulting from strain partitioning among its major components calcium aluminum rich inclusions cais 64 5 ct matrix 21 5 fry chondrules 17 6 ct in addition to the planar fabric we found a strong lineation defined by the alignment of the maximum elongation of flattened particles interpreted to have developed by an impact event the existence of a lineation could either be non coaxial deformation or the result of a mechanically heterogeneous target material in the later case it could have formed due to discontinuous patches of sub surface ice and or fabrics developed through prior impact compaction macpherson and krot 2014 which would have encouraged preferential flow within the target material immediately following the impact compacting pore spaces we suggest that structurally controlled movement of alteration fluids in the asteroid parent body along pressure gradients contributed to the formation of secondary minerals which may have ultimately lead to the different oxidized subtypes

a striking example of the atmosphere s leading traveling pattern abstract conventional and complex empirical orthogonal function eof techniques show that for at least four months during the fall and winter of 1979 80 a large amplitude large scale traveling flow anomaly existed in the troposphere and stratosphere this feature evolved in a cyclic manner exhibiting an average period of about 23 days its phase propagation was toward the west while its amplitude was concentrated in a broad envelope centered over canada the phenomenon was equivalent barotropic in the troposphere and increased in amplitude with altitude it represented about 25 of the variance of geopotential heights in the troposphere and stratosphere for the months of november through march the meridional and zonal structure of the zonal wavenumber one component of the traveling anomaly is similar to that of the theoretical 16 day wave however it is distinct from that theoretical mode in that its period is longer and in the troposphere zonal wave two makes a large contribution to its structur

atmospheric blocking space time links to the nao and pna in the northern hemisphere regions characterized by an enhanced frequency of atmospheric blocking overlap significantly with those associated with the major extra tropical patterns of large scale climate variability namely the north atlantic oscillation nao and the pacific north american pna pattern there is likewise an overlap in the temporal band width of blocks and these climate patterns here the nature of the linkage between blocks and the climate patterns is explored by using the era 40 re analysis data set to examine 1 their temporal and spatial correlation and 2 the interrelationship between blocks and the nao pna it is shown that a strong anti correlation exists between blocking occurrence and the phase of the nao pna in the north atlantic western north pacific and that there are distinctive inter basin differences with a clear geographical over north atlantic and quantitative over north pacific separation of typical blocking genesis lysis regions during the opposing phases of the climate patterns an empirical orthogonal function eof analysis points to a significant influence of blocking upon the nao pattern identifiable as the leading eof in the euro atlantic and a temporal analysis indicates that long lasting blocks are associated with the development of negative nao pna index values throughout their life time in addition an indication of a cause and effect relationship is set out for the north atlantic linkage

density magnetic susceptibility and the characterization of ordinary chondrite falls and showers bulk and grain densities of 132 ordinary chondrites from the vatican observatory collection were measured and compared with their magnetic susceptibility for the most part using previously measured values ten new susceptibility measures were taken for this study grain density and magnetic susceptibility combined provide a reliable method of classifying un weathered ordinary chondrites unlike traditional chemical tests this method is fast nondestructive and characterizes the whole rock making it especially appropriate for surveying large collections the system is less viable for finds extensive weathering of metallic iron in an h chondrite can cause it to plot among l chondrites while heavily weathered l chondrites plot among the ll group this system has revealed outlier stones that may be misclassified meteorites or mislabeled samples in every case where the magnetic susceptibility of a meteorite does not fit its putative classification the grain density is also found to be in disagreement in a manner consistent with either severe weathering or misidentification an analysis of stones from five showers shows that excluding outliers these samples tend to cluster tightly within their appropriate groups in a plot of grain versus magnetic susceptibility

shock metamorphism of carbonaceous chondrites abstract we have studied shock effects in carbonaceous chondrites using optical microscopy of thin sections and find that our petrographic classification of progressive shock metamorphism in ordinary chondrites can also be applied to carbonaceous chondrites we find that sixty nine carbonaceous chondrites can be assigned to four shock stages si to s4 largely on the basis of shock effects in olivine the least shocked chondrite groups are cm2 and co3 thirty six out of thirty eight members are classified as shock stage s1 differences between the mean shock levels of certain groups of chondrites e g co3 and cv3 are probably due to stochastic differences in the sampling of their parent bodies however there is an overall tendency for the mean shock level of carbonaceous chondrites and ordinary chondrites to increase with increasing petrologic type that may reflect real differences in the shock level of near surface materials on their parent bodies caused by intrinsic variations in the chemical and physical properties of these materials petrologic type 2 and 3 chondrites are more porous and richer in volatiles than types 4 to 6 the greater porosity of types 2 3 causes higher post shock temperatures and melting at lower pressures and the higher volatile contents ensure that strongly shocked material is more readily dispersed on release from high pressure we suggest that type 2 3 material shocked above 20 30 gpa normally escapes from the parent asteroids and forms particles that are too small to survive as meteorites in the cv3 group there is a correlation between the degree of chondrule flattening and the intensity of shock metamorphism analogous to that discovered in ordinary chondrites by sneyd et al 1988 suggesting that shock rather than static overburden pressure is responsible for chondrule flattening we infer that the correlations are due to collapse of pores under shock pressures of at least 5 10 gpa and that shock is an important process affecting many physical properties of type 2 4 chondrites

an observed connection between the north atlantic oscillation and the madden julian oscillation abstract based on the bivariate madden julian oscillation mjo index defined by wheeler and hendon and 25 yr 1979 2004 of pentad data the association between the north atlantic oscillation nao and the mjo on the intraseasonal time scale during the northern hemisphere winter season is analyzed time lagged composites and probability analysis of the nao index for different phases of the mjo reveal a statistically significant two way connection between the nao and the tropical convection of the mjo a significant increase of the nao amplitude happens about 5 15 days after the mjo related convection anomaly reaches the tropical indian ocean and western pacific region the development of the nao is associated with a rossby wave train in the upstream pacific and north american region in the atlantic and african sector there is an extratropical influence on the tropical intraseasonal variability certain phases of the mjo are preceded by the occurrence of strong naos a significant change of upper zonal

petrology of alh85085 a chondrite with unique characteristics abstract alh85085 has several characteristics which set it apart from any known chondritic group its chondrules are smaller 25 75 m the majority are cryptocrystalline and all are volatile na k s depleted feni metal is more abundant 40 9 wt than in any other chondrite and sulfide abundance is low 1 1 matrix material does not surround the chondrules and fragments but occurs as lithic clasts lumps up to 300 m across the bulk composition of alh85085 is lower in na si and s si and higher in ni si fe si and mg si than in other chondritic groups the ca si al si and mg si ratios are closest to those of the renazzo chondrite grouplet cr matrix lumps are most similar to cr and murchison group cm chondrite matrices survival of this fragile matrix material as lithic clasts indicates that they were added just prior to the agglomeration of the chondrite all components chondrules fragments matrix lumps fall within a narrow size range which may be the result of aerodynamic sorting if so the sorting must have occurred after chondrule solidification and following a period of chondrule breakage since fragments from larger chondrules are present the ni vs co trend in the feni metal overlaps that of metal in cr chondrites and bencubbin these trends are similar to those of calculated nebular condensation paths indicating a nebular origin the cryptocrystalline texture and volatile depletion of the chondrules indicate that most chondrules were heated to temperatures above the liquidus although alh85085 cannot now be assigned to any known chondrite group it shares many similarities with cr chondrites and the bencubbin metal silicate chondritic assemblage and may be part of a chondritic group closely related to these meteorites

origin of the pluto charon system constraints from the new horizons flyby abstract new horizon s accurate determination of the sizes and densities of pluto and charon now permit precise internal models of both bodies to be constructed assuming differentiated rock ice structures we find that pluto is close to 2 3 solar composition anhydrous rock by mass and charon 3 5 solar composition anhydrous rock by mass pluto and charon are closer to each other in density than to other large 1000 km diameter kuiper belt bodies despite this we show that neither the possible presence of an ocean under pluto s water ice shell and no ocean within charon nor enhanced porosity at depth in charon s icy crust compared with that of pluto are sufficient to make pluto and charon s rock mass fractions match all four small satellites styx nix kerberos hydra appear much icier in comparison with either pluto or charon in terms of a giant impact origin both these inferences are most consistent with the relatively slow collision of partly differentiated precursor bodies canup astrophys j 141 35 2011 this is in turn consistent with dynamical conditions in the ancestral kuiper belt but implies that the impact precursors themselves accreted relatively late and slowly to limit 26 al and accretional heating the iciness of the small satellites is not consistent with direct formation of the pluto charon system from a streaming instability in the solar nebula followed by prompt collapse of gravitationally bound pebble piles a proposed formation mechanism for kuiper belt binaries nesvorn et al astron j 140 785 793 2010 growth of pluto scale bodies by accretion of pebbles in the ancestral kuiper belt is not ruled out however and may be needed to prevent the precursor bodies from fully differentiating due to buried accretional heat prior to the charon forming impact

magnetic classification of stony meteorites 2 non ordinary chondrites a database of magnetic susceptibility measurements on different non ordinary chondrites c e r and ungrouped populations is presented and compared to our previous similar work on ordinary chondrites it provides an exhaustive study of the amount of iron nickel magnetic phases essentially metal and magnetite in these meteorites in contrast with all the other classes cm and cv show a wide range of magnetic mineral content with a two orders of magnitude variation of whether this is due to primary parent body differences metamorphism or alteration remains unclear c34 and c2 yield similar values to the ones shown by ck and cm respectively by order of increasing the classes with well grouped are r co ck ci kak cr e ch cb based on magnetism eh and el classes have indistinguishable metal content outliers that we suggest may need to have their classifications reconsidered are acfer 202 co elephant moraine eet 96026 c45 meteorite hills met 01149 and northwest africa nwa 521 ck asuka a 88198 lapaz icefield lap 031156 and sahara 98248 r values can also be used to define affinities of ungrouped chondrites and propose pairing particularly in the case of cm and cv meteorites

el nino modoki and its possible teleconnection 1 using observed data sets mainly for the period 1979 2005 we find that anomalous warming events different from conventional el nino events occur in the central equatorial pacific this unique warming in the central equatorial pacific associated with a horseshoe pattern is flanked by a colder sea surface temperature anomaly ssta on both sides along the equator empirical orthogonal function eof analysis of monthly tropical pacific ssta shows that these events are represented by the second mode that explains 12 of the variance since a majority of such events are not part of el nino evolution the phenomenon is named as el nino modoki pseudo el nino modoki is a classical japanese word which means a similar but different thing the el nino modoki involves ocean atmosphere coupled processes which include a unique tripolar sea level pressure pattern during the evolution analogous to the southern oscillation in the case of el nino hence the total entity is named as el nino southern oscillation enso modoki the enso modoki events significantly influence the temperature and precipitation over many parts of the globe depending on the season the impacts over regions such as the far east including japan new zealand western coast of united states etc are opposite to those of the conventional enso the difference maps between the two periods of 1979 2004 and 1958 1978 for various oceanic atmospheric variables suggest that the recent weakening of equatorial easterlies related to weakened zonal sea surface temperature gradient led to more flattening of the thermocline this appears to be a cause of more frequent and persistent occurrence of the enso modoki event during recent decades

lime silicates in amoeboid olivine aggregates in carbonaceous chondrites indicator of nebular and asteroidal processes mno feo ratios in olivine from amoeboid olivine aggregates aoas reflect conditions of nebular condensation and can be used in concert with matrix textures to compare metamorphic conditions in carbonaceous chondrites lime low iron mn enriched olivine was identified in aoas from y 81020 co3 05 kaba cv 3 1 and in y 86009 cv3 y 86751 cv3 nwa 1152 cr cv3 but was not identified in aoas from efremovka cv3 1 3 4 or allende cv 3 6 according to thermodynamic models of nebular condensation lime olivine is stable at lower temperatures than mn poor olivine and at low oxygen fugacities dust enrichment 95 in our study whereas efremovka aoas are slightly fe rich fo 92 aoa olivines from kaba are mostly forsteritic but rare fe rich olivine precipitated from an aqueous fluid a combination of precipitation of fe rich olivine and diffusion of fe into primary olivine grains resulted in iron rich compositions fo97 59 in allende aoas variations from fine grained nonporous matrix toward higher porosity and coarser lath like matrix olivine can be divided into six stages represented by 1 y 81020 efremovka nwa 1152 2 y 86751 lithology b 3 y 86009 4 kaba 5 y 86751 lithology a 6 allende these stages are inferred to represent general degree of metamorphism although the specific roles of thermally driven grain growth and diffusion versus aqueous dissolution and precipitation remain uncertain

climate and rock weathering a study of terrestrial age dated ordinary chondritic meteorites from hot desert regions abstract ordinary chondrites oc recovered from the desert areas of roosevelt county new mexico the nullarbor region of western australia and the algerian and libyan sahara for which 14c terrestrial ages have been determined were examined by 57fe mossbauer spectroscopy oc were chosen as a standard sample to investigate weathering processes as their well constrained trace and bulk element chemistry normative mineralogy and isotopic composition define a known pre weathering starting composition given that terrestrial ages are known it is possible to compare initially very similar samples that have been subsequently weathered in a range of climatic regimes from the present day to 44 ka bp in addition recently fallen equilibrated oc contain iron only as fe0 and fe2 thus the abundance of ferric iron is directly related to the level of terrestrial weathering mossbauer spectroscopy identifies two broad types of ferric alteration paramagnetic phases akaganeite lepidocrocite and goethite and magnetically ordered principally magnetite and maghemite oc finds show a range in the percentage of total fe existing as fe3 from zero to over 80 however oxidation is comparable between fragments of the same oc separated since their time of fall i e paired meteorites our results indicate several features of meteorite weathering that may result from climatic or geomorphologic conditions at the accumulation site 1 saharan samples are overall less weathered than non saharan samples which may be related to the relatively recent age ca 20 ka of the saharan accumulation surface 2 broad differences between sites in the rate of weathering arising from regional differences in climate 3 consistent differences in the weathering products between samples that fell during humid periods and those that fell during more arid periods those falling during humid periods contain a higher proportion of magnetically ordered ferric oxides 4 one region the nullarbor that shows a variation in the total amount of ferric species that closely matches the climatic record for this area of australia for the last 30 ka points 3 and 4 may be related to the identification of a rapid initial weathering phase the majority of weathering occurs in the first few hundred years after fall followed by passivation of weathering by porosity reduction porosity reduction and the associated restriction in the ability of water to penetrate the sample appears to be the mechanism whereby a weathering assemblage formed during the brief initial period of oxidation is preserved through subsequent climatic cycles over the terrestrial lifetime of the sample

the meteoritical bulletin no 86 2002 july abstract meteoritical bulletin no 86 lists information for 1154 newly classified meteorites comprising 661 from antarctica 218 from africa 207 from asia 203 of which are from oman 62 from north america 3 from south america and 3 from europe information is provided for 5 falls el idrissia undulung dashoguz el tigre and yafa noteworthy specimens include 7 martian meteorites dhofar 378 grove mountains 99027 northwest africa 856 1068 and 1110 and sayh al uhaymir 060 and 090 4 lunar meteorites dhofar 301 302 303 and 489 9 new iron meteorites a mesosiderite northwest africa 1242 an ungrouped stony iron meteorite dar al gani 962 and a wide variety of other interesting stony meteorites including ch ck cm cr cv r enstatite unequilibrated ordinary and ungrouped chondrites primitive achondrites howardite eucrite diogenite hed achondrites and ureilites

constraining the pressure threshold of impact induced calcite twinning implications for the deformation history of aqueously altered carbonaceous chondrite parent bodies calcite twinning in carbonaceous chondrite meteorites can be used to reconstruct the deformation history and the parent body environment during and or after aqueous alteration but the shock pressure threshold at which the twins develop is unknown accordingly the aim of this study is to determine the magnitude of shock pressure that is needed to generate calcite twins this was done by measuring the depths of twinning beneath the resulting craters from experimental impacts in six calcite targets combined with hydrocode modelling of the peak pressures at the corresponding depths within the targets brecciation fracturing and calcite e twinning occur below the floors of all the craters and results from the hydrocode modelling show that the twins start to form at shock pressures of 110 to 480 mpa which is at least a factor of ten higher than the 10 mpa that is considered to be required to produce calcite twins in low strain rate terrestrial settings these pressures are equivalent to shock stage s1 as determined by olivine microstructures and consistent with calcite twinning in carbonaceous chondrites being a result of impact gardening in shallow levels of their asteroidal parent bodies

density porosity and magnetic susceptibility of achondritic meteorites as part of a large scale survey of meteorite bulk and grain densities porosities and magnetic susceptibilities we measured these properties for 174 stones from 106 achondritic meteorites these include four lunar meteorites 15 stones from 10 shergottites nakhlites and chassignites sncs 96 stones from 56 howardites eucrites and diogenites heds 17 stones from nine aubrites two angrites and 16 stones from 10 ureilites four stones of three acapulcoites as well as four stones of three lodranites and 15 stones from eight primitive achondrites those meteorites derived from basalts and crustal material of differentiated parent bodies have lower densities and magnetic susceptibilities on an average than the more primitive achondrites which have a higher percentage metal a notable exception is the one chassignite in the study chassigny which has a high grain density of 3 73 0 04 g cm 3 ureilites have magnetic susceptibilities consistent with primitive achondrites but lower grain densities porosities do not vary considerably between most of the groups with most stones 5 14 porous although on an average ureilites and brachinites have lower porosities with most stones less than 7 porous for primitive achondrites the higher metal content causes finds to exhibit weathering effects similar to what is observed in ordinary chondrites with a reduction in grain density magnetic susceptibility and porosity as compared with unweathered falls for lunites sncs and heds no such effect is observed we also observe that grain density and magnetic susceptibility used in conjunction distinguish shergottites nakhlites and chassignites from each other shergottites and nakhlites have low grain densities averaging 3 31 and 3 41 g cm 3 respectively whereas chassigny is 3 7 g cm 3 in magnetic susceptibility shergottities and chassignites are similar averaging 2 85 and 2 98 in log units of 10 9 m3 kg 1 respectively with nakhlites averaging higher at 3 42

enso regulation of mjo teleconnection the extratropical teleconnections associated with madden julian oscillation mjo are shown to have an action center in the north pacific where the pressure anomalies have opposite polarities between the phase 3 convective indian ocean and phase 7 convective western pacific of the mjo the teleconnection in the same phase of mjo may induce opposite anomalies over east asia and north america between el nino and la nina years during mjo phase 3 a gigantic north pacific anticyclonic anomaly occurs during la nina making coastal northeast asia warmer wetter than normal but the west us colder drier whereas during el nino the anticyclonic anomaly is confined to the central north pacific hence the northwest us experiences warmer than normal weather under influence of a downstream cyclonic anomaly during phase 7 an extratropical cyclonic anomaly forms over the northwest pacific during la nina due to convective enhancement over the philippine sea causing bitter winter monsoon over japan whereas during el nino the corresponding cyclonic anomaly shifts to the northeast pacific due to enhanced convection over the equatorial central pacific which causes warm and wet conditions along the west coast of us and canada further the presence of enso induced seasonal anomalies can significantly modify mjo teleconnection but the aforementioned mjo teleconnection can still be well identified during phase 3 the mjo teleconnection pattern over north pacific will be counterbalanced enhanced by el nino la nina induced seasonal mean anomalies during phase 7 on the other hand the mjo teleconnection anomalies in the northeastern pacific will be enhanced during el nino but reduced during la nina thereby the impacts of mjo teleconnection on the north america is expected to be stronger during el nino than during la nina

chondrites as samples of differentiated planetesimals abstract chondritic meteorites are unmelted and variably metamorphosed aggregates of the earliest solids of the solar system the variety of metamorphic textures in chondrites motivated the onion shell model in which chondrites originated at varying depths within a parent body heated primarily by the short lived radioisotope 26 al with the highest metamorphic grade originating nearest the center allende and a few other chondrites possess a unidirectional magnetization that can be best explained by a core dynamo on their parent body indicating internal melting and differentiation here we show that a parent body that accreted to 200 km in radius by 1 5 ma after the formation of calcium aluminum rich inclusions cais would have a differentiated interior and ongoing accretion would add a solid undifferentiated crust overlying a differentiated interior consistent with formational and evolutionary constraints inferred for the cv parent body this body could have produced a magnetic field lasting more than 10 ma this hypothesis represents a new model for the origin of some chondrites presenting them as the unprocessed crusts of internally differentiated early planetesimals such bodies may exist in the asteroid belt today the shapes and masses of the two largest asteroids 1 ceres and 2 pallas can be consistent with differentiated interiors conceivably with small iron cores with hydrated silicate or ice silicate mantles covered with undifferentiated crusts

stony meteorite porosities and densities a review of the data through 2001 in this review we summarize the data published up to december 2001 on the porosity and density of stony meteorites these data were taken from 925 samples of 454 different meteorites by a variety of techniques most meteorites have densities on the order of 3 to 4 g cm 3 with lower densities only for some volatile rich carbonaceous meteorites and higher densities for stony irons for the vast majority of stones porosity data alone cannot distinguish between different meteorite compositions average porosities for most meteorite classes are around 10 though individual samples can range as high as 30 porosity unbrecciated basaltic achondrites appear to be systematically less porous unless vesicles are present the measured density of ordinary chondrites is strongly controlled by the amount of terrestrial weathering the sample has undergone with porosities steadily dropping with exposure to the terrestrial environment a theoretical grain density based on composition can model pre weathered porosities the average model porosity for h and ll chondrites is 10 while l chondrite model porosities average only 6 a statistically significant difference

the late fall extratropical response to enso sensitivity to coupling and convection in the tropical west pacific abstract the extratropical response to el nino in late fall departs considerably from the canonical el nino signal observational analysis suggests that this response is modulated by anomalous forcing in the tropical west pacific twp so that a strong fall el nino teleconnection is more likely when warm sst conditions and or enhanced convection prevail in the twp while these twp sst anomalies may arise from noise and or long term variability they may also be generated by differences between el nino events through variations in the tropical atmospheric bridge this bridge typically drives subsidence west of the date line and enhanced trade winds over the far twp which cool the ocean in late fall however some relatively weaker and or more eastward shifted el nino events produce a correspondingly weakened and displaced tropical bridge which results in no surface cooling and enhanced convection in the twp because the north pacific circulation is very sensitive to forcing from the twp at this time

a new rossby wave breaking interpretation of the north atlantic oscillation this paper proposes the hypothesis that the low frequency variability of the north atlantic oscillation nao arises as a result of variations in the occurrence of upper level rossby wave breaking events over the north atlantic these events lead to synoptic situations similar to midlatitude blocking that are referred to as high latitude blocking episodes a positive nao is envisaged as being a description of periods in which these episodes are infrequent and can be considered as a basic unblocked situation a negative nao is a description of periods in which episodes occur frequently a similar but weaker relationship exists between wave breaking over the pacific and the west pacific pattern evidence is given to support this hypothesis by using a two dimensional potential vorticity based index to identify wave breaking at various latitudes this is applied to northern hemisphere winter data from the 40 yr ecmwf re analysis era 40 and the events identified are then related to the nao certain dynamical precursors are identified that appear to increase the likelihood of wave breaking these suggest mechanisms by which variability in the tropical pacific and in the stratosphere could affect the nao