diffusion closure temperature and age of a mineral with arbitrary extent of diffusion theoretical formulation and applications the commonly used expression of the closure temperature tc of a diffusing species in a mineral as derived by m h dodson contrib mineral petrol 40 1973 259 264 is applicable only to systems which have undergone sufficient diffusion so that even the composition at the center of individual grains is significantly removed from that established at the onset of cooling we have extended dodson s formulation to include cases with arbitrarily small amount of diffusion and applied it to calculate tc and age profiles which would develop in single crystals of different geometries these results permit evaluation of the extent of resetting of mineral age and of ion exchange geothermometers during cooling the measured age profile of a mineral can also be used to constrain its cooling rate these applications have been illustrated for the cases of garnet biotite fe mg exchange geothermometer and the cooling age and closure temperatures of the sm nd and lu hf decay systems in garnet

relative array analysis of upper mantle lateral velocity variations in southern california spatial averaging of short period teleseismic p wave arrivals across scarlet constrains upper mantle lateral velocity variations beneath southern california we compare dt d back azimuth and averaged arrival time estimates determined from the entire network for 154 events to the same parameters derived from small subsets of scarlet the resulting relative array diagrams and plots of net subarray delays computed for 171 overlapping subarrays exhibit large anomalies that vary smoothly as a function of subarray position implying substantial lateral heterogeneity under the network patterns of mislocation vectors for more than 100 subarrays permit identification of an east west striking high velocity antiform beneath the transverse ranges further constraints on both the lateral configuration and depth of the anomaly are obtained through thin lens analysis of the net delay data where all the time perturbations are assumed to originate at a single depth projection of 2798 net delays requires a lens deeper than 100 km a representative lens at 150 km depth features low velocities beneath the salton trough as well as a concentrated high velocity zone between 116 3 118 3 w and 33 7 34 8 n consistent with the relative array diagrams and the pkp delay contours of hadley and kanamori 1977 therefore the bulk of the high velocity material observed by hadley and kanamori may in fact lie at or deeper than 150 km rather than 40 100 km this possibility prompts renewed speculation regarding the relationship of this body to the plate tectonic history of the region

live iron 60 in the early solar system isotopic analyses of nickel in samples from the differentiated meteorite chervony kut revealed the presence of relative excesses of 60ni ranging from 2 4 up to 50 parts per 104 these isotopic excesses are from the decay of the now extinct short lived nuclide 60fe and provide clear evidence for the existence of 60fe over large scales in the early solar system not only was 60fe present at the time of melting and differentiation that is fe ni fractionation of the parent body of chervony kut but also later at the time when basaltic magma solidified at or near the surface of the planetesimal the inferred abundance of 60fe suggests that its decay alone could have provided sufficient heat to melt small diameters of several hundred kilometers planetary bodies shortly after their accretion

potassium diffusion in melilite experimental studies and constraints on the thermal history and size of planetesimals hosting cais among the calcium aluminum rich inclusions cais excess 41 k 41 k which was produced by the decay of the short lived radionuclide 41 ca t1 2 0 1 myr has so far been detected in fassaite and in two grains of melilites these observations could be used to provide important constraints on the thermal history and size of the planetesimals into which the cais were incorporated provided the diffusion kinetic properties of k in these minerals are known thus we have experimentally determined k diffusion kinetics in the melilite end members akermanite and gehlenite as a function of temperature 900 1200 c and crystallographic orientation at 1 bar pressure the closure temperature of k diffusion in melilite tc k mel for the observed grain size of melilite in the cais and cooling rate of 10 100 c myr as calculated from our diffusion data is much higher than that of mg in anorthite the latter was calculated from the available mg diffusion data in anorthite assuming that the planetesimals were heated by the decay of 26 al and 60 fe we have calculated the size of a planetesimal as a function of the accretion time tf such that the peak temperature at a specified radial distance rc equals tc k mel the ratio rc r 3 defines the planetesimal volume fraction within which 41 k in melilite grains would be at least partly disturbed if these were randomly distributed within a planetesimal a similar calculation was also carried out to define r versus tf relation such that 26 mg was lost from 50 of randomly distributed anorthite grains as seems to be suggested by the observational data these calculations suggest that 60 of melilite grains should retain 41 k if 50 of anorthite grains had retained 26 mg assuming that tf was not smaller than the time of chondrule formation our calculations yield minimum planetesimal radius of 20 30 km depending on the choice of planetesimal surface temperature and initial abundance of the heat producing isotope 60 fe

a short duration of chondrule formation in the solar nebula evidence from 26al in semarkona ferromagnesian chondrules abstract the 26 al 26 mg systems of five ferromagnesian chondrules from the least metamorphosed ordinary chondrite semarkona ll3 0 were studied using a secondary ion mass spectrometer their glass or plagioclase portions contain excesses of 26 mg and in two chondrules the 26 mg excesses are well correlated with 27 al 24 mg which demonstrates the in situ decay of 26 al the initial 26 al 27 al ratios in these chondrules obtained from the slope of isochrons show a narrow range of between 6 10 6 and 9 10 6 indicating their short formation duration of less than 1 my if the solar nebula was initially homogeneous in al isotopes the chondrule formation ages are 2 my younger than those of cais our results based on the study of the least metamorphosed uoc are consistent with the previous studies on al rich chondrules that the chondrule formation started at least 2 my after cais alternatively the older records before 2 my were erased by chondrule recycling process it further suggests that the young apparent ages 3 to 5 my after cais for chondrules in type 3 4 uocs are due to the disturbance of the 26 al 26 mg system possibly during parent body metamorphism the result is not consistent with the extended nebular time scale of 5 my and the chondrule formation by planetary processes the ni isotopic analysis of the feo rich olivines in a type ii chondrule in semarkona did not show any detectable excess 60 ni in spite of their high fe ni ratios the upper limit of the initial 60 fe 56 fe ratio of the solar system was estimated to be 3 4 10 7 which is consistent with the previous estimate 0 2 1 9 10 7 from eucrites this result confirms that the 60 ni excess previously observed from cais was not due to the decay of the short lived nuclide 60 fe but a ni isotopic anomaly of nucleosynthetic origin

polarization tomography for p wave velocity structure in southern california we develop a tomographic inversion method that uses teleseismic p wave polarization data to obtain velocity structure polarization inversion has some intrinsic advantages over travel time inversion it is not influenced by source location and origin time errors it is not sensitive to deep mantle velocity structure and can be used iteratively to improve the tomographic result polarization inversion is more sensitive to near station velocity structure and to velocity gradient and is complementary to travel time inversion in this sense the method is applied to california institute of technology u s geological servey southern california array data the result is generally consistent with previous work and also reveals that the high velocity feature beneath the transverse ranges is bounded between 40 and 200 km depths and possibly has a second small piece at about 300 km depth the slow velocity anomaly under the salt on trough is limited to shallow depths less than about 60 km

revised model calculations for the thermal histories of ordinary chondrite parent bodies recent measurements of ordinary chondrite physical and thermal properties along with new geothermometry studies have provided the necessary parameters for updating a previously proposed model miyamoto et al 1981 for the thermal evolution and internal structure of ordinary chondrite parent bodies model calculations assumed a heat source term derived from the decay of 26al justification is provided differences from the previous model include varying the thermal diffusivity parameter with increasing temperature and decreasing porosity using variable physical and thermal parameters to provide end member models and incorporating a shortened thermal history of 60 ma obtained from new pb pb chronology of phosphates rather than 100 ma times of isotopic closure in chondrite phosphates overlap the thermal model estimates and postmetamorphic cooling rates from the model approximately coincide in both trend and magnitude with metallographic and fission track cooling rate data model calculations attempt to match peak metamorphic conditions in the central portions of these bodies and yield accretion ages between 1 4 to 3 1 ma after calcium aluminum inclusion cai formation model calculations also predict that both the h and the l chondrite parent asteroids consisted of 80 equilibrated and 20 unequilibrated chondritic material and that their original radii ranged from 80 to 95 km

thermal metamorphic history of a ca al rich inclusion constrained by high spatial resolution mg isotopic measurements with nanosims 50l abstract mg isotope data were collected by nanosims with high precision and high spatial resolution from a coarse grained type b ca al rich inclusion cai ek1 6 3 in the allende cv3 chondrite to evaluate the time scale of parent body thermal metamorphism the cai melilite and fassaite contain excesses of 26mg 26mg from the in situ decay of 26al the inferred initial ratio 26al 27al 0 5 8 2 4 10 5 is consistent with many previously reported coarse grained cais from cv chondrites e g macpherson et al 1995 however the anorthite has heterogeneous 26al 27al 0 ranging from 1 8 10 5 to 3 3 10 6 the 26al 26mg systematics within the anorthite is consistent with thermal diffusion of mg isotopes during metamorphism we also show that the heterogeneous distribution of 26mg in anorthite could have resulted from thermal diffusion of 26mg over a 0 6 0 8 ma time span mg diffusion thus may be responsible for the 26al 27al 0 heterogeneity within anorthite in cais

a study of mg and k isotopes in allende cais implications to the time scale for the multiple heating processes the measurements of magnesium and potassium isotopic compositions of refractory minerals in allende calcium aluminum rich inclusions cais 7r 19 1 hn3 1 and egg3 were taken by secondary ion mass spectrometry sims the 7r 19 1 contains 16 o rich and 16 o poor melilite grains and define a single isochron corresponding to an initial 26 al 27 al ratio of 6 6 1 3 10 5 the al mg isochron o isotope measurements and petrography of melilite in 7r 19 1 indicate that 16 o poor melilite crystallized within 0 4 myr after crystallization of 16 o rich melilite suggesting that oxygen isotopic composition of the cai forming region changed from 16 o rich to 16 o poor within this time interval the 16 o poor melilite is highly depleted in k compared to the adjacent 16 o rich melilite indicating evaporation during remelting of 7r 19 1 we determined the isochron for 41 ca 41 k isotopic systematics in egg3 pyroxene with 4 1 2 0 10 9 2 as an initial ratio of 41 ca 40 ca which is at least two times smaller than the previous result sahijipal et al 2000 the ratio of 41 ca 40 ca in the egg3 pyroxene grain agrees within error with the value obtained by hutcheon et al 1984 no evidence for the presence of 41 k excess decay product of a short lived radionuclide 41 ca was found in 7r 19 1 and hn3 1 we infer that the cai had at least an order of magnitude lower than canonical 41 ca 40 ca ratio at the time of the cai formation

the structure of gradually transforming marine stratocumulus during the astex first lagrangian experiment summary an analysis of the mean and turbulent structure of the planetary boundary layer is presented using aircraft data obtained during the atlantic stratocumulus transition experiment e rst lagrangian experiment the analysis of the mean vertical structure relies mostly on slant proe le data however part of the analysis also uses socalled porpoise runs in the vicinity of the cloud top the analysis of the turbulence structure utilizes all of the data horizontal eight legs as well as slant proe les and presents both scaled turbulence statistics and a spectral analysis the purpose is to investigate details in the temporal development of the e rst lagrangian experiment and to study the turbulent structure in order to e nd scale relations that can be utilized in improved modelling of the stratocumulus capped boundary layer the hypothesis is that so called cloud decoupling has a signie cant impact on the turbulence scaling the measured cloud water is corrected to become consistent between the two participating aircraft the corrected maximum cloud water is more constant in time than in previous studies of the erst lagrangian it is suggested that previously analysed temporal variability may be an artefact of using two different instruments to measure cloud water the cloud top jump in equivalent potential temperature is positive in the erst three eights sufe ciently large for a stable cloud top but decreases and becomes negative for the last two eights in line with the breaking up of the cloud eeld the upper part of the boundary layer warms and dries more rapidly than the lower suggesting entrainment to be a dominant factor in the development of the cloud the analysis of the porpoise e ight legs illustrates how sharp features at the cloud top inversion are smoothed out while analysing several proe les eight legs or even entire eights rather than normalizing each proe le with the height to the local cloud top scaling of the turbulent e uxes and the velocity variances shows that the cloud layer is decoupled throughout almost the entire erst lagrangian it is also shown that while surface layer scaling is appropriate for the marine atmospheric boundary layer mabl the cloud layer turbulence scales with convective scaling the lowfrequency spectrum has no spectral gap with the exception of the vertical velocity and continues to increase with decreasing frequency with only a change in slope this indicates the presence of mesoscale motions the cospectra of the turbulent euxes are very noisy throughout when averaging several spectra into height intervals the scales of the turbulence as indicated by the peak in the averaged spectra appear to vary with height above the surface in the mabl but to be height independent in the cloud layer an attempt to calculate a dissipation length scale shows scatter but is consistent with a dissipation length scale increasing linearly with height in the mabl but being roughly constant or possibly parabolic with height in the cloud layer

non traditional and emerging methods for characterizing diffusion in minerals and mineral aggregates the data summarized in this rimg volume reflect the growing interest among geoscientists in the characterization of atomic transport in natural materials interest in diffusion dates back to the early 20th century e g bowen 1921 but the need for constraints on mobility of atoms became especially important in the 1950s and 60s with our increasing reliance upon radioactive decay for determination of mineral and rock ages the question of decay product retention in relevant phases became vitally important with a few notable exceptions however experimental geoscientists did not take up the cause of diffusion in solids until the 1970s and 80s by that time the motivation for acquiring diffusion data had spread to many areas of petrology mineralogy and geochemistry and experimental techniques began to blossom the result is very much in evidence in this volume all experiments aimed at measuring a diffusion coefficient have two things in common a technique to introduce the diffusant of interest to the sample and a method to determine the extent of diffusion traditionally diffusion experiments are designed to take advantage of an existing solution to the non steady state diffusion equation and experiments are conducted in such a way as to reproduce as well as possible the boundary conditions specified for the solution for ease of analysis and interpretation most experiments are set up to limit diffusion to just one dimension most researchers have further settled on one of three general experiment designs 1 the interdiffusion couple 2 the thin film geometry or 3 the constant surface concentration design fig 1 noble gas geochemists including those interested in k ar ar ar and u th he dating methods have exploited 3 d variants of this last approach by conducting bulk degassing studies of minerals in which radiogenic noble gases have accumulated over time in the natural environment baxter 2010

cr diffusion in orthopyroxene experimental determination 53mn 53cr thermochronology and planetary applications we have determined cr diffusion coefficients d in orthopyroxene parallel to the a b and c axial directions as a function temperature at f o2 corresponding to those of the wustite iron wi buffer diffusion is found to be significantly anisotropic with d c d b d a conforming to an earlier theoretical prediction increase of f o2 from wi buffer conditions to 4 5 log unit above the buffer at 950 and 1050 c leads to decrease of d cr by a factor of two to three possibly suggesting significant contribution from an interstitial diffusion mechanism we have used the diffusion data to calculate the closure tem peratures tc of the mn cr decay system in orthopyroxene as a function of initial temperature t0 grain size a and cooling rate for spherical and plane sheet geometries we also present graphical relations that permit retrieval of cooling rates from knowledge of the resetting of mn cr ages in orthopyroxene during cooling t0 and a application of these relations to the mn cr age data of the cumulate eucrite serra de mageyields a tc of 830 980 c and cooling rates of 2 27 c myr at tc and 1 13 c myr at 500 c it is shown that the cooling of serra de mageto the closure temperature of the mn cr system took place at its original site in the parent body and thus implies a thickness for the eucrite crust in the commonly accepted hed parent body vesta of greater than 30 km this thickness of the eucrite crust is compatible only with a model of relatively olivine poor bulk mineralogy in which olivine constitutes 19 7 of the total asteroidal mass

control of deep convection by sub cloud lifting processes the alp closure in the lmdz5b general circulation model recently a new conceptual framework for deep convection scheme triggering and closure has been developed and implemented in the lmdz5b general circulation model based on the idea that deep convection is controlled by sub cloud lifting processes such processes include boundary layer thermals and evaporatively driven cold pools wakes which provide an available lifting energy that is compared to the convective inhibition to trigger deep convection and an available lifting power alp at cloud base which is used to compute the convective mass flux assuming the updraft vertical velocity at the level of free convection while the alp closure was shown to delay the local hour of maximum precipitation over land in better agreement with observations it results in an underestimation of the convection intensity over the tropical ocean both in the 1d and 3d configurations of the model the specification of the updraft vertical velocity at the level of free convection appears to be a key aspect of the closure formulation as it is weaker over tropical ocean than over land and weaker in moist mid latitudes than semi arid regions we propose a formulation making this velocity increase with the level of free convection so that the alp closure is adapted to various environments cloud resolving model simulations of observed oceanic and continental case studies are used to evaluate the representation of lifting processes and test the assumptions at the basis of the alp closure formulation results favor closures based on the lifting power of sub grid sub cloud processes rather than those involving quasi equilibrium with the large scale environment the new version of the model including boundary layer thermals and cold pools coupled together with the deep convection scheme via the alp closure significantly improves the representation of various observed case studies in 1d mode it also substantially modifies precipitation patterns in the full 3d version of the model including seasonal means diurnal cycle and intraseasonal variability

antarctic boundary layer parametrization in a general circulation model 1 d simulations facing summer observations at dome c the parametrization of the atmospheric boundary layer abl is critical over the antarctic plateau for climate modelling since it affects the large scale temperature inversion and the katabatic winds this study challenges state of the art parametrizations used in general circulation models to represent the clear sky summertime diurnal cycle of the abl at dome c antarctic plateau the laboratoire de meteorologie dynamique zoom model is run in a 1d configuration on the fourth gewex atmospheric boundary layers study case simulations are analysed and compared to observations giving insights into the sensitivity of one model that participates to the intercomparison exercise snow albedo and thermal inertia are calibrated leading to better surface temperatures using the so called thermal plume model improves the momentum mixing in the diurnal abl in stable conditions four turbulence schemes are tested best simulations are those in which the turbulence cuts off above 35m in the middle of the night highlighting the contribution of the longwave radiation in the abl heat budget however the nocturnal surface layer is not stable enough to distinguish between surface fluxes computed with different stability functions the absence of subsidence in the forcings and an underestimation of downward longwave radiation are identified to be likely responsible for a cold bias in the nocturnal abl apart from model specific improvements the paper clarifies on which are the critical aspects to improve in general circulation models to correctly represent the summertime abl over the antarctic plateau

tomographic image of the southern california mantle p wave teleseismic travel time delays recorded by the southern california array are inverted by the method of backprojection tomography to obtain images of variations in the p wave velocity structure to a depth of 750 km two major upper mantle features arc resolved one beneath the transverse ranges region and another beneath the salton trough region the transverse ranges feature appears as a curtainlike east trending high velocity anomaly this feature is 60 km thick extends most deeply on its eastern end to 250 km and attains a maximum velocity 3 greater than average southern california mantle of the same depth the salton trough feature which is not as well resolved as the transverse ranges feature is composed of low velocities in the upper 70 100 km these p wave velocities arc depressed 3 4 compared to average southern california mantle tests of the inversion indicate the major aspects of the imaged structure are authentic

shifting the diurnal cycle of parameterized deep convection over land 1 in most atmospheric circulation models used for climate projections cloud and convective processes are not explicitly resolved but parameterized such models are known to produce a diurnal cycle of continental thunderstorms in phase with insolation while observed precipitation peaks in late afternoon we propose a new approach which corrects this long standing bias of parameterized convection in this approach deep convection triggering and intensity are controlled by sub cloud processes here boundary layer thermals and gust fronts and potentially orography or surface heterogeneities the representation of the diurnal cycle of deep convection is greatly improved in 1d mode with rainfall maximum delayed from midday to late afternoon provided parameterizations account for the key role played by shallow cumulus in preconditioning deep convection and by gust fronts in the self sustaining of thunderstorms in the afternoon

initial 26al 27al in carbonaceous chondrite chondrules too little 26al to melt asteroids we report 26mg excesses correlated with al mg ratios in five chondrules from the primitive co3 0 chondrite yamato 81020 that yield a mean initial 26al 27al ratio of only 3 8 0 7 10 6 about half that of ordinary chondrite oc chondrules even if asteroids formed immediately after chondrule formation this ratio and the mean al content of co chondrites is only capable of raising the temperature of a well insulated co asteroid to 940 k which is more than 560 k too low to produce differentiation the same ratio combined with the higher al content of cv chondrites results in a cv asteroid temperature of 1100 k we calculate that the mean initial 26al 27al ratio of about 7 4 10 6 found in ll chondrules is only able to produce small amounts of melting too little to produce differentiation these results cast serious doubt on the viability of 26al as the heat source responsible for asteroid differentiation inclusion of 60fe raises temperatures about 160 k but this increment is not enough to cause differentiation even of an ll chondrite asteroid

relative array analysis of the southern california lithosphere lateral velocity structure in the lithosphere beneath southern california is investigated using relative array analysis in this form of analysis p wave polarization values measured by a subset of receivers subarray are compared to values measured by the entire set of receivers array the effects of lateral velocity structure beneath the subarray can be distinguished from the effects of average velocity structure beneath the entire array lateral velocity gradients can be mapped as the subarray window is moved across the network the method is insensitive to effects of near source and lower mantle heterogeneity does not lose resolution near the periphery of the array and utilizes a locally derived ray geometry lateral velocity variations beneath the california institute of technology united states geological survey network detected by relative array analysis can be compared directly to velocity anomalies found by inversion of travel time residuals two regions near the edge of the tomographic image developed by humphreys and clayton are investigated both regions are experiencing active tectonics relative array analysis suggests that relatively high velocity may be present beneath the westernmost transverse ranges this feature extends to a depth of roughly 80 km and may be related to the high velocity upper mantle anomaly imaged beneath the central and western transverse ranges relatively low velocity is associated with the crust and uppermost mantle south of the salton sea this feature is probably related to hot ascending mantle but is located east of the surface expression of the spreading axis in the imperial valley

diffusion kinetics of cr in olivine and 53mn 53cr thermochronology of early solar system objects we have determined the diffusion coefficient of cr in olivine as function of temperature oxygen fugacity fo2 and crystallographic orientation and used these data to develop a quantitative understanding of the resetting of the short lived 53 mn 53 cr decay system in olivine during cooling within meteorite parent body the diffusion of cr in olivine was found to be anisotropic and effectively indepen dent of fo2 between wustite iron buffer and two orders of magnitude above this buffer the diffusion data were used to calculate the spatially averaged mean closure temperature of the 53 mn 53 cr decay system in olivine as function of the initial temperature cooling rate and grain size and also the closure age profile of this system in olivine single crystal as function of radial distance and a dimensionless parameter that incorporates the effects of various parameters that affect the closure age we also present a thermochronolgic formulation that permits retrieval of cooling rates from the extent of resetting of the bulk 53 mn 53 cr closure age of olivine during cooling this method was applied to determine the cooling rate of the pallasite omolon which showed 53 mn 53 cr bulk age of olivine that is 10 myr younger than the age of the solar system the calculated cooling rate which is 20 40 c myr at 985 1000 c is in good agreement with the metallographic cooling rate at 500 c when the two results are considered in terms of a cooling model in which the reciprocal temperature increases linearly with time the inferred cooling rate of omolon which seems to be a sample from the core mantle boun dary yields a burial depth of 30 km in a parent body of at least 100 km radius

review of wave turbulence interactions in the stable atmospheric boundary layer flow in a stably stratified environment is characterized by anisotropic and intermittent turbulence and wavelike motions of varying amplitudes and periods understanding turbulence intermittency and wave turbulence interactions in a stably stratified flow remains a challenging issue in geosciences including planetary atmospheres and oceans the stable atmospheric boundary layer sabl commonly occurs when the ground surface is cooled by longwave radiation emission such as at night over land surfaces or even daytime over snow and ice surfaces and when warm air is advected over cold surfaces intermittent turbulence intensification in the sabl impacts human activities and weather variability yet it cannot be generated in state of the art numerical forecast models this failure is mainly due to a lack of understanding of the physical mechanisms for seemingly random turbulence generation in a stably stratified flow in which wave turbulence interaction is a potential mechanism for turbulence intermittency a workshop on wave turbulence interactions in the sabl addressed the current understanding and challenges of wave turbulence interactions and the role of wavelike motions in contributing to anisotropic and intermittent turbulence from the perspectives of theory observations and numerical parameterization there have been a number of reviews on waves and a few on turbulence in stably stratified flows but not much on wave turbulence interactions this review focuses on the nocturnal sabl however the discussions here on intermittent turbulence and wave turbulence interactions in stably stratified flows underscore important issues in stably stratified geophysical dynamics in general

k mg ti and ca isotopic compositions and refractory trace element abundances in hibonites from cm and cv meteorites implications for early solar system processes potassium and magnesium isotopic compositions of hibonites from the murchison cm and allende cv meteorites are determined by an ion microprobe to look for possible presence of the short lived nuclides 41ca and 26al at the time of their formation abundance anomalies in the neutron rich isotopes 50ti and 48ca as well as ree and additional refractory trace element abundances have also been determined to infer a plausible formation environment of the hibonites in the early solar system the results obtained in this study suggest a widespread distribution of the short lived nuclide 41ca in the early solar system observation of correlated presence of the two short lived nuclides 41ca and 26al on a microscopic scale in refractory hibonites and silicates from cm and cv meteorites suggests these nuclides to be cogenetic and support a stellar source for these and several other short lived nuclides in the early solar system moderate to high enrichments in the neutron rich isotopes 50ti and 48ca are seen in some of the analyzed hibonites our data for radiogenic and stable isotopic anomalies as well as refractory trace element abundance patterns in isolated cm hibonites with platelet morphology show trends similar to those reported earlier they are devoid of 41ca and 26al show large enrichment in 50ti and 48ca and have typical group iii ree patterns however hibonites present within hibonite spinel inclusions show variations in their ree patterns one of them shows the normally expected group ii ree pattern while another has an ultrarefractory ree pattern and a third has affinities towards platelet hibonites that appear to suggest a link between these two groups of hibonites with distinct morphological characteristics we propose a new model to explain the absence of the short lived nuclides 41ca and 26al in some of the hibonites whose ree abundance patterns and stable isotopic anomalies suggest that they are some of the first solar system solids assuming a stellar origin for these nuclides we attribute this absence to the very early formation of these hibonites near the central region of the collapsing protosolar cloud prior to the arrival of the short lived nuclides injected into the cloud from a stellar source

simulations of nocturnal drainage flows by a q2l turbulence closure model abstract nocturnal drainage flows observed over a nearly two dimensional ridge called rattlesnake hills near richland washington are simulated by using a simplified turbulence closure model in which only turbulence kinetic energy and turbulence length scale equations are solved prognostically the present model is slightly simpler than a level 2 5 model which has been extensively used in previous simulations of various atmospheric boundary layer phenomena wind and temperature profiles computed by the present model are generally in excellent agreement with observations made by towers erected on the slope of rattlesnake hills strong coupling between the mean and turbulence variables is also demonstrated

air sea fluxes and surface layer turbulence around a sea surface temperature front the observed effects of sharp changes in sea surface temperature sst on the air sea fluxes surface roughness and the turbulence structure in the surface layer and the marine atmospheric boundary layer are discussed in situ flux and turbulence observations were carried out from three aircraft and two ships within the fasinex framework three other aircraft used remote sensors to measure waves microwave backscatter and lidar signatures of cloud tops descriptions of the techniques intercomparison of aircraft and ship flux data and use of different methods for analyzing the fluxes from the aircraft data are described changing synoptic weather on three successive days yielded cases of wind direction both approximately parallel and perpendicular to a surface temperature front for the wind perpendicular to the front wind over both cold to warm and warm to cold surface temperatures occurred model results consistent with the observations suggest that an internal boundary layer forms at the sst

crystallization sequences of ca al rich inclusions from allende an experimental study the equilibrium crystallization sequence at 1 atmosphere in air of a melt corresponding in composition to the average composition of type b ca al rich inclusions from the allende meteorite is spinel 1550 c melilite 1400 c ak22 anorthite 1260 c ti al rich clinopyroxene 1230 c ti fassaite the melilite becomes increasingly akermanitic with decreasing temperature the pyroxene is similar in composition to fassaites from type b inclusions preliminary results suggest that the crystallization sequence is similar at oxygen fugacities near the iron wustite buffer the results of these experiments have been integrated with available phase equilibrium data in the system cao mgo al 2o 3 sio 2tio 2 and a phase diagram for predicting the crystallization sequences of liquids with compositions of coarse grained ca al rich inclusions has been developed available bulk compositions of coarse grained inclusions form a well defined trend in terms of major elements extending from type a and bl inclusions near the spinel melilite join to more pyroxene rich type b2 inclusions the trend deviates from the expected sequence of solid condensates from a nebular gas at p 10 3 atm if pure diopside is assumed to be the clinopyroxene that condenses the type a b1 end of the trend is similar in composition to calculated equilibrium condensates at 1202 1227 c and the trend as a whole parallels the sequence of condensates expected from diopside condensation at 1170 c the trend is consistent to first order with the condensation of solid ti rich fassaite in place of pure diopside at higher temperatures than those at which pure diopside is predicted to condense partially molten condensates may be likely in this case or if the nebular pressure is higher than 10 3 atm

momentum balance of katabatic flow on steep slopes covered with short vegetation katabatic flows over alpine mountainous terrain differ from their forested or bare slope counterparts due to the presence of well ventilated short vegetation the impact of a grass canopy and larger scale pressure perturbations on the one dimensional mean momentum balance is explored via theory and field measurements the model presented here reproduces the measured velocity jet shape and turbulent flux gradients these two features imply that even when monin obuhkov similarity theory breaks down its use for a stability adjusted mixing length remains effective to first order results reveal that outer layer pressure effects can be significant under low speed wind conditions at the top of the thin katabatic layer when larger variations in the wind direction are observed an analytical expression to estimate the jet height which can be utilized in large scale weather prediction models shows the importance of including canopy effects for the thin katabatic flow region above the vegetation

aseismic crustal deformation in the transverse ranges of southern california abstract geodetic data at a plate boundary can reveal the pattern of subsurface displacements that accompany plate motion we model these displacements as the sum of rigid block motion and the elastic effects of frictional drag between blocks the frictional interactions are represented by uniform dislocation on each of several rectangular fault patches we then estimate the block velocities and fault parameters from geodetic data our bayesian inversion procedure employs prior estimates based on geological and seismological data we apply the method to the transverse ranges using prior data from bird and rosenstock 1984 and geodetic data from the usgs trilateration networks and nasa vlbi measurements our model consists of 12 blocks and 27 rectangular fault patches the block motion inferred from the geodetic data has the same order of magnitude as the geologic estimates and for many faults the agreement is excellent however the geodetic data imply a displacement rate of about 20 mm yr 1 across the san andreas fault while the geologic estimates exceed 30 mm yr 1 the final model implies about 6 mm yr 1 of crustal shortening normal to the trend of the san andreas fault this is about half the rate implied by the prior model most of this shortening occurs on the sierra madre cucamonga and the white wolf fault systems aseismic fault motion is a major contributor to plate motion and the thickness of the frictional surface varies considerably from one fault to another the geodetic data can help to identify faults that are suffering rapid stress accumulation in the transverse ranges those faults are the san andreas san gabriel sierra madre pleito and white wolf faults

relationship between cooling rate and cooling age of a mineral theory and applications to meteorites we reviewed here the recent development on the mathematical formulation of closure temperature of a cooling geochronological system which permits direct retrieval of cooling rate from cooling age when the diffusion parameters grain size and initial temperature are known this formulation is used to show how the cooling rate can be retrieved by comparing the core and bulk age of a mineral determined by a single decay system the cooling rates of seven h chondrites of the metamorphic types h4 h5 and h6 were retrieved from the available data on the pb pb model ages of the phosphates and the diffusion kinetic data of pb in apatite the results are in excellent agreement with the metallographic cooling rates and show an inverse relation with the metamorphic grade of these chondrites we also addressed the problem of 90 ma younger sm nd mineral isochron age defined by orthopyroxene phosphate and plagioclase of the morristown mesosiderite compared to the pb pb age of the estherville mesosiderite it is shown that this younger age could have been a consequence of resetting during cooling instead of an impulsive heating event as suggested earlier

a thermal model for the differentiation of asteroid 4 vesta based on radiogenic heating a finite element code has been developed to model the thermal history of asteroid 4 vesta this is the first attempt to model the thermal history of a differentiated asteroid through core and crust formation and subsequent cooling until geochemical closure is attained the results of the simulation are consistent with chronological measurements and other constraints provided by cumulate and noncumulate eucrites believed to have been derived from vesta the work solves two major problems with the hypothesis of heating by decay of26al an extinct radionuclide postulated to be a plausible heat source in the early solar system first the model demonstrates that it is possible to keep the mantle of vesta hot for 100 ma thereby explaining the observed difference in ages between cumulate and noncumulate eucrites second the simulation offers a possible explanation of why detectable excesses of26mg the decay product of26al are not observed in noncumulate eucrites the simulation draws a model chronology of vesta and predicts times relative to cai formation for accretion at 2 85 myr core formation at 4 58 myr crust formation at 6 58 myr and geochemical closure at 100 myr for a h chondrite asteroidal bulk composition decay of60fe is found to cause no perceptible difference in the thermal history of vesta even when sequestered into a central core although chondritic xenoliths have not been described in hed igneous lithologies the thermal model suggests the possibility that a veneer of unmelted near surface material should remain

on the interaction of the bottom boundary layer and deep rings abstract the interaction of rings extending down to the ocean bottom and the bottom boundary layer bbl is studied numerically with a primitive equation model in which the bbl is resolved using the mellor yamada level 2 5 closure scheme the lower portions below the thermocline of rings with radii of 50 100 and 200 km are considered for rings of comparable strength the larger ones are found to have the stronger velocity footprint on the bottom the bbl is found to spin down this portion of rings by 60 in times 0 6 months with most of the energy transfer lost irretrievably to bottom friction for the larger rings and to potential energy for the smaller rings the classical constant eddy viscosity bbl formulation is found to yield similar spindown results as the model provided the eddy viscosity is chosen to give realistic bottom stress rather than bbl thickness the numerical model indicates that ekman pumping out of the bbl affects the bottom mixed layer thickness more so than the ekman pumping into the bbl and that maximum bottom mixed layer thicknesses are found not in regions of maximum flows but in upwelling regions of relatively strong flows because of the presence of the cold filament the hebble site is found to be unsuitable for testing the model conclusions about bottom layers

a thermal plume model for the convective boundary layer representation of cumulus clouds abstract the thermal plume model a mass flux scheme combined with a classical diffusive approach originally developed to represent turbulent transport in the dry convective boundary layer is extended here to the representation of cloud processes the modified parameterization is validated in a 1d configuration against results of large eddy simulations les as well as in a 3d configuration against in situ measurements for a series of cases of dry and cloudy convective boundary layers accounting for coherent structures of the mixed layer with the mass flux scheme improves the representation of the diurnal cycle of the boundary layer particularly its progressive deepening during the day and the associated near surface drying results also underline the role of the prescription of the mixing of air between the plume and its environment and of submean plume fluctuations

nickel and chromium isotopes in allende inclusions high precision nickel and chromium isotopic measurements have been carried out on nine allende inclusions 62ni 64ni excesses are present in at least three of the samples the magnitudes of the excesses are about 3 e units 1 e unit 1 part in 10 000 for64ni and about 1 e unit for62ni chromium isotopes measured for some of the same samples show general excesses on54cr of about 7 e units while small deficits are observed for53cr considering these isotope anomalies except those for53cr together with the excesses present in the samples of other neutron rich isotopes of the iron group elements the most likely mechanism responsible for these anomalies is a neutron rich statistical equilibrium process in addition there is an indication of elevated60ni in almost every inclusion measured however for alk 111 this excess was clearly resolved by our experimental technique this effect may be related to the decay of now extinct60fe but the present data are not sufficient to clearly demonstrate its existence in the early solar system an upper limit of 1 6 10 6 can be calculated for60fe 56fe at the time these allende inclusions crystallized

mg diffusion in anorthite implications for the formation of early solar system planetesimals we have measured the self diffusion coefficients of mg ca and sr in anorthitic plagioclase in order to assess the potential of mg isotopic heterogeneities in early solar system planetesimals to survive thermal metamorphism diffusion couples were constructed from polished single crystals of natural anorthite and synthetic isotopically enriched anorthite glass couples were annealed at atmospheric pressure and 1200 1400 c and isotopic concentration profiles were measured with an ion microprobe the results show that mg diffusion in anorthite is surprisingly fast with d mg being over 2 orders of magnitude greater than d sr this indicates that the diffusion coefficient of mg in anorthite cannot be approximated with that for sr mg diffusion in the c direction is also slightly faster than in the b direction while ca and sr diffusion appear to be isotropic the results provide important constraints on the thermochronological history of anorthite bearing mineral assemblages that preserve radiogenic 26 mg excesses in a planetesimal heated by the decay of 26 al the temperature at any point depends on the planetesimal size time of formation thermal conductivity and depth within the planetesimal given sufficient heating 26 mg heterogeneities produced by the in situ decay of 26 al in ca al rich inclusions cais and chondrules will be erased by diffusive equilibration using the self diffusion coefficient for mg in anorthite measured in this study we show that the common occurrence of 26 mg excesses in these inclusions requires that they must be stored in small 15 km bodies or the outermost rims of larger bodies for the first 1 2 million years of the solar system s history for early formed bodies larger than 15 km most of the mass will have been heated sufficiently for any radiogenic 26 mg to have been diffusively homogenized in the mg rich planetary environment