numerical modeling of asteroid survivability and possible scenarios for the morokweng crater forming impact the fate of the impactor is an important aspect of the impact cratering process defining impactor material as surviving if it remains solid i e does not melt or vaporize during crater formation previous numerical modeling and experiments have shown that survivability decreases with increasing impact velocity impact angle with respect to the horizontal and target density here we show that in addition to these impactor survivability depends on the porosity and shape of the impactor increasing impactor porosity decreases impactor survivability while prolate shaped polar axis equatorial axis impactors survive impact more so than spherical and oblate shaped polar axis equatorial axis impactors these results are used to produce a relatively simple equation which can be used to estimate the impactor fraction shocked to a given pressure as a function of these parameters by applying our findings to the morokweng crater forming impact we suggest impact scenarios that explain the high meteoritic content and presence of unmolten fossil meteorites within the morokweng crater in addition to previous suggestions of a low velocity and or high angled impact this work suggests that an elongated and or low porosity impactor may also help explain the anomalously high survivability of the morokweng impactor

model derived estimates of groundwater mean ages recharge rates effective porosities and storage in a limestone aquifer the edwards aquifer of south central texas u s a a highly fractured and faulted group of limestone formations is the major water supply for the san antonio area a discrete state compartment dsc model or mixing cell model based upon the conservation of environmental tritium within the aquifer was used to obtain estimates of groundwater mean ages recharge effective porosities and storage in the edwards aquifer in the vicinity of san antonio texas the model was calibrated and validated with the spatial and temporal 1953 1971 distributions of environmental 3h tritium in the groundwater the final model consisted of 34 cells eight of these cells represented the unconfined portion of the edwards aquifer in the vicinity of the balcones fault zone an area where recharge occurs via streamflow infiltration and direct infiltration of precipitation the model confirmed previous analyses of flow in the edwards system generally parallel to the balcones fault zone with restricted flow perpendicular to this zone groundwater mean ages ranged from 16 to over 130 yr the storage volume of the confined portion of the edwards aquifer is 30 9 km3 which corresponds to an average effective porosity of 4 8 range 1 9 8 the average annual recharge to the edwards aquifer during the period 1953 1971 was 0 614 km3 the study demonstrated that discrete state compartment models calibrated and validated with environmental tritium distributions can yield valuable hydrogeologic information that is difficult or expensive to obtain using traditional techniques the approach used in the study is particularly suited to limestone aquifers which are normally extremely difficult to analyze with traditional methods

ageostrophic geopotential fluxes in downstream and upstream development of baroclinic waves abstract with the use of a simple primitive equation model it is demonstrated that the convergence divergence of ageostrophic geopotential fluxes can be a major source sink of kinetic energy for both downstream and upstream development of baroclinic waves and can play a dominant role during the early stages of wave development it is also shown that both surface friction and effects lead to an asymmetry in the upstream versus downstream development with downstream development much stronger a total group velocity is defined based on ageostrophic fluxes and its relationship to the rate of wave packet spreading and to convective and absolute instability is discussed

high noble metal concentrations in a late pliocene sediment a 2 3 myr old layer in a sediment from the antarctic ocean contains ir and au at levels comparable with those at the cretaceous tertiary boundary a sizable fraction of the noble metals is contained in vesicular millimetre sized poly mineralic grains that closely resemble ablation debris from chondritic meteorites and there is little doubt that the noble metals resulted from the accretion of a large extraterrestrial object no massive extinctions or other evidence of environmental stress seem to be associated with this accretionary event

sedimentary signatures and processes during marine bolide impacts a review abstract studies of submarine impact craters resulting from impacts of comets or asteroids demonstrate that the presence of water and the physical properties of target rocks have a major influence on sedimentary processes associated with meteorite impacts this results in difference in sedimentary signature of bolide impacts in marine environments compared to subaerial impact craters in subaerial impacts the targets are commonly hard rocks frequently of igneous and or metamorphic origin whereas in submarine impacts the targets are mostly unconsolidated or poorly lithified sediments or sedimentary rocks with high volumes of pore water such differences result in variability in crater morphology and in sedimentary processes inside and outside the impact area impacts in shallow water marine neritic environments produced craters with low or absent rims and wide and shallow brims as characterize by both the montagnais on the scotian shelf the mjolnir in the barents sea 45 and 40 km in diameter respectively and the chesapeake bay 90 km in diameter lack of elevated rims is thought to be the result of current reworking and resurge of the water back into the excavated cavity as the water in the crater is vaporized during this process resurge gullies can be cut across the rim while mass and debris flows turbidites and other gravity deposits are produced as results of tsunami and crater wall and central high collapse during and after the crater excavation stage such deposits are found both within and outside the crater structure the only difference between gravity deposits triggered by an impact or other rare events such as earthquakes is the admixture of various melt particles and possible enrichments in iridium in the former impacts near the shelf edge may cause partial collapse of the continental margin as shown by the montagnais and chicxulub impacts some of the gravity and debris flows generated by margin collapse may be channelized with final deposits up to several hundred meters thick extending for hundreds of kilometers from the impact site other impact features such as shatter cones tektites spherules and ni spinels shocked quartz isotropication and partial melts are common to both submarine and subaerial impacts theoretical calculations of the destructive forces of mega tsunami waves triggered by meteorite impact in the ocean greatly exceed those based on geologic evidence a dearth of gigantic tsunami evidence for the chicxulub impact outside of the gulf of mexico where from theoretical modelling the maximum near bottom orbital velocity of water flow crossing the deep north atlantic basin should have been 1 m s could be the result of the mitigating effect of the bathymetry of surrounding area causing wave diffraction and interference calculated maximum horizontal orbital velocity near the seafloor at the shelf for the montagnais impact is 22 m s for a 200 m high wave 5 5 m s for a 50 m high wave at 500 km decreasing to 0 5 m s at 1000 km strong enough to scour the deep ocean bottom and produce distinct erosion surfaces and disconformities in marine sedimentary record however lack of cores across impact horizon prevents confirmation of occurrence of such bottom water flows

observational evidence for the mechanism of the poleward propagation of zonal wind anomalies over the north atlantic this study examines the physical mechanisms that drive the poleward propagation of zonal mean flow anomalies over the north atlantic during the boreal winter with ecmwf era40 reanalysis data that spans the years 1958 2001 an empirical orthogonal function eof analysis is performed on the zonal wind anomalies for the north atlantic domain based on time lag correlations between the first two eofs 14 poleward propagation events are identified a series of lagged composite calculations of the poleward propagation events reveals the following processes midlatitude synoptic scale rossby waves propagate equatorward and break when they encounter their critical latitudes in the tropics and subtropics a new critical latitude is generated slightly poleward of the previous critical latitude and the subsequent wave breaking occurs at this new critical latitude this interaction between the wave breaking and the critical latitude drives the poleward propagation of zonal mean zonal wind anomaly a comparison between the poleward propagation events and zonal index events indicates that the poleward propagation is associated with a relatively weak potential vorticity gradient over the subtropics these north atlantic poleward propagation events are found to be preceded by anomalously strong transient eddy activity over the subtropical north pacific and by anomalously weak tropical convection over the tropical atlantic ocean and the amazon copyright c 2012 royal meteorological society

a trajectory based investigation of physical and dynamical processes that govern the temporal evolution of the subtropical jet streams over africa abstracttropical subtropical and extratropical dynamical processes govern the synoptic scale evolution of the subtropical jet stream s over africa however the relative importance of the respective effects is still under debate and is the focus of this study interim ecmwf re analysis era interim data are used to calculate backward trajectories from the subtropical jet over africa during winter 2005 06 the trajectories allow for studying the jet dynamics from both a potential vorticity pv and an angular momentum point of view and for linking the two theoretical frameworks three cases of synoptic scale rossby wave breaking in the extratropics and subtropics are presented in detail they illustrate basic flow configurations where i the subtropical jet is mainly forced by tropical dynamics ii extratropical forcing contributes substantially to the jet acceleration and iii strong diabatic processes in the subtropics impact the jet the case study results are then generalized for the entire wint

laboratory investigations of marine impact events factors influencing crater formation and projectile survivability given that the earths surface is covered in around two thirds water the majority of impact events should have occurred in marine environments however with the presence of a water layer crater formation may be prohibited indeed formation is greatly controlled by the water depth to projectile diameter ratio as discussed in this paper previous work has shown that the underlying target material also influences crater formation e g gault and sonett 1982 baldwin et al 2007 in addition to the above parameters we also show the influence of impact angle impact velocity and projectile density for a variety of water depths on crater formation and projectile survivability the limiting ratio of water depth to projectile diameter on cratering represents the point at which the projectile is significantly slowed by transit through the water layer to reduce the impact energy to that which prohibits cratering we therefore study the velocity decay produced by a water layer using laboratory analytical and numerical modelling techniques and determine the peak pressures endured by the projectile for an impact into a water depth five times the projectile diameter the velocity of the projectile is found to be reduced to 26 32 its original value for deep water impacts we find that up to 60 of the original mass of the projectile survives in an oblique impact where survivability is defined as the solid or melted mass fraction of the projectile that could be collected after impact

circumglobal teleconnections and wave packets associated with israeli winter precipitation this investigation performs diagnostic analyses with ncep ncar reanalysis data and israeli precipitation data to examine the dynamical processes that drive the teleconnection pattern associated with israeli winter precipitation anomalies a dipole teleconnection pattern with one centre of action over western europe and another centre of action over the eastern mediterranean em is found to be associated with the winter precipitation anomalies in israel this pattern is referred to as the southern levant sl pattern the positive negative phase of the sl pattern is found to be closely associated with enhanced reduced precipitation in israel composites of the 300 hpa stream function field show that both phases of the sl pattern are associated with eastward propagating wave packets that traverse about three quarters of the distance across the globe these wave packets which have a phase speed that is close to zero originate over the northeast pacific the east coast of north america for the positive negative sl phase and propagate eastward across the north atlantic western europe the em and southern asia until they eventually decay over the northwest pacific as these wave packets pass over western europe and the em the sl pattern is triggered and anomalies in israeli winter precipitation occur the sl pattern is found to have an e folding time scale of 4 days which is determined by the group velocity of the wave packet the time averaged spatial structure of the circumglobal wave packet closely resembles the first empirical orthogonal function of the hemispheric 300 hpa meridional wind field this suggests that the circumglobal wave packet may be a fundamental pattern of variability which is relevant for the entire northern hemisphere copyright 2008 royal meteorological society

numerical modeling for target water depth estimation of marine target impact craters 1 marine impacts can develop a crater in the seafloor if the target water depth is shallow in relation to the size of the impactor the geology of this marine target crater is influenced by the layer of water in the upper part of the target the influence increases with increased water depth the target water depth is essential when calculating the magnitude of the impact event as the seafloor crater merely expresses some of the expended energy the target water depth for a marine target crater is often estimated by facies analysis of sediments related to the impact crater unfortunately often with ambiguous results we propose to combine the conventional methods with numerical modeling of the target water depth based on the special target water related features of the crater we used geological data from the lockne crater as constraints in a simulation with the sova hydrocode the simulations were done for three different target water depths 200 m 500 m and 1000 m within the likely depth range for the middle ordovician sea in which the impact occurred in order to obtain the minimum estimated size of the lockne crater by an asteroid impact at 20 km s the water depth must have been slightly less than 1 km and the impactor radius must have been about 400 m it was not possible to generate a crater with the geological features of lockne for target water depths of less than about 500 m however the ratio may be further constrained by factors such as impactor density impact angle and impact velocity

numerical modeling of impact induced modifications of the deep sea floor abstract the mechanics of oceanic impact events differ in several respects from the process that accompanies the strike of an asteroid on land in order to explore the cratering process on a water covered target a series of 2d hydrocode simulations for impact velocities of 10 15 20 and 30 km s and water depth diameter ratios between 5 and 7 have been carried out in particular these simulations were aimed to examine the effects of the asteroid on the deep sea floor the interaction of the impacting body and the water column causes loss of the body s kinetic energy both through oceanic drag and through mass loss due to hydrodynamic heating prior to hitting the ocean bottom regardless of whether the impactor actually hits the ocean floor the shock wave generated in the water column by the impact of the body on the water surface will leave behind unique traces in the marine sediments for example an asteroid of 1 km in diameter arriving at the ocean surface with a velocity of 20 km s induces a shock pressure of 6 gpa in the oceanic crust at a water depth of 5 km the passage of the shock wave along the water ocean bottom interface causes significant disturbance in the sediment layer moreover the collapse of the transient cavity that results from the passage of the projectile through the water column causes a strong surge of water that generates a displacement and redeposition of sediments on the ocean floor in order to examine sediment transport processes we introduce computationally a large amount of massless particles within the projectile and the target material and follow the movement of each individual particle tracer particles represent only forced material movement and do not account for any frictional forces thus comparisions with real sediment disturbances may be qualitative only for an impact velocity of 20 km s and a water depth diameter ratio of 5 this procedure reveals significant particle movements within a distance of 15 km from the center of the impact the only known deep sea impact structure so far the eltanin impact in the bellingshausen sea antarctica is characterized by a zone of chaotically mixed sediments that most probably originated from impact induced turbulent water currents based on the present observations which do not allow the identification of an impact structure at the ocean bottom our model yields estimates of a projectile diameter of 1 km and an impact velocity of 20 km s

persistence of the 500 mb height field during northern hemisphere winter abstract the persistence of the planetary scale circulation during the northern hemisphere winters from 1965 66 to 1981 82 is documented national meteorological center analyses of 500 mb geopotential height for the northern hemisphere poleward of 20 n are used instead of constructing auto correlation maps based on lime series at grid points time series are constructed that show the pattern correlations between daily hemispheric maps these time series provide information on the day to day changes in persistence of the winter circulation and allow comparisons of the intraseasonal and interannual variability of persistence the hemispheric circulation is usually quite persistent from day to day correlations between successive maps usually fall within the range 0 7 to 0 9 as the time between the maps is increased the correlations between these maps decreases at a rate faster than that expected of an autoregressive red noise process the hemispheric circulation rarely resembles closely the circulation

the positive north atlantic oscillation with downstream blocking and middle east snowstorms the large scale environment abstractin this study the atmospheric conditions for the december 2013 middle east snowstorm are examined from a case study perspective and by performing a composite analysis of extreme winter events from 1950 to 2013 using reanalysis data it is revealed that this snowstorm arises from the occurrence of an omega type european blocking eb with a strong downstream trough that is associated with a southward displaced positive phase north atlantic oscillation nao event in the anomaly field the eb exhibits a northeast southwest ne sw tilted dipole structure the type eb transports cold air into the middle east and produces snowfall within the trough over the middle east the composite analysis shows that the location of cold temperatures depends strongly on the tilting direction and strength of the eb dipole anomaly the ne sw northwest southeast nw se tilted eb dipole occurs with a southward northward displaced nao event the ne sw tilted eb dipole anomaly is associated with an arching

role of the east asian trough on the eastern mediterranean temperature variability in early spring and the extreme case of 2004 warm spell this study investigates the potential influence of the east asian trough eat on the eastern mediterranean temperature variability in early spring in connection with this it also examines the extreme case of the year 2004 when anomalous warming of the eastern anatolia resulted in unprecedented snowmelt runoff amounts in the euphrates and tigris basins in early march in the analyses we used reanalysis data gridded products of surface temperature and snow cover river discharge data and satellite imagery we employed an intensity index for the eat and a trough displacement index for the mediterranean trough medt to explore the relationship between the strength of the eat and the displacement of the medt at pentad resolution our analysis shows that there are statistically significant correlations at 99 confidence level between the strength of the eat and the zonal shift of the medt on some pentads e g 3rd 13th 37th and 59th but that the highest correlation occurs on the 13th pentad of the year corresponding to the early days of march it seems that on this pentad when the eat is strong the medt tends to be located in the west of its climatological position about 30 hbox 35 circ hbox e which causes warmer conditions over the eastern mediterranean in 2004 which appears to be an extreme year for this phenomenon the medt is positioned and deepened in the central mediterranean about 10 hbox 15 circ hbox e and extended towards central africa during the early days of march this synoptic pattern provided favorable conditions for the development of a tropical plume atmospheric river with a southwest northeast orientation carrying warm tropical african air towards the eastern mediterranean and anatolian highlands resulting in rapid melting of the snowpack as well as severe precipitation and thus flooding events in the eastern anatolia a key finding in our analysis is that the strengthening of the eat was instrumental to the increased amplitude of the ridge trough system over the euro mediterranean region in the early days of 2004 spring we highlight that the response of surface and upper level meteorological conditions to the amplitude of the ridge trough system enhanced by the strength of the eat might be crucial in the understanding of some of the extreme hydrometeorological events in the eastern mediterranean region

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

modulation of south asian jet wave train on the extreme winter precipitation over southeast china comparison between 2015 16 and 2018 19 abstracttwo extremely wet winters in 2015 16 and 2018 19 over southeast china are compared in this study south to north discrepancies appear in the spatial distribution of precipitation with anom

a high resolution record of holocene climate change in speleothem calcite from cold water cave northeast iowa high precision uranium thorium mass spectrometric chronology and 18o 13c isotopic analysis of speleothem calcite from cold water cave in northeast iowa have been used to chart mid holocene climate change significant shifts in 18o and 13c isotopic values coincide with well documented holocene vegetation changes temperature estimates based on 18o 16o ratios suggest that the climate warmed rapidly by about 3 c at 5900 years before present and then cooled by 4 c at 3600 years before present initiation of a gradual increase in 13c at 5900 years before present suggests that turnover of the forest soil biomass was slow and that equilibrium with prairie vegetation was not attained by 3600 years before present

on the dynamics of a storm track abstract an idealized primitive equation model is used to determine the factors controlling the dynamics and maintenance of eddy activity in a storm track the results show that localized regions of enhanced baroclinicity do not necessarily lead to localization of eddy activity by studying the energetics of the storm track it is shown that while baroclinic conversion does indeed correlate with the region of maximum baroclinicity it is the downstream radiation of energy through the ageostrophic geopotential fluxes which acts as a trigger for the development and maintenance of eddy activity over less baroclinic regions extending the region of eddy activity much further downstream from the region of high baroclinicity examples of eddy life cycles are given that show that convergence and divergence of ageostrophic fluxes can dominate baroclinic and barotropic conversion especially in regions with weak baroclinicity factors that may limit the zonal extent of a storm track are discussed evidence of down

classification seasonality and persistence of low frequency atmospheric circulation patterns abstract orthogonally rotated principle component analysis rpca of northern hemisphere 1 month mean 700 mb heights is used to identify and describe the seasonality and persistence of the major modes of interannual variability the analysis is detailed and comprehensive in that 1 a high resolution approximately equal area 358 point grid is used for the virtually maximum possible 35 year period of record 2 a positive bias in the nmc data base in the early 1950s in the subtropics is largely eliminated for the first time and 3 homogeneous separate analyses of each month of the year are carried out detailing the mouth to month changes in the dominant circulation patterns winter results are similar to those of other recent rpca and teleconnection studies except that some less obvious patterns are identified and further detail of the better known patterns is provided two north south dipole patterns are found over the pacific ocean west pacific oscillation and east pacific pattern and over the atla

asian jet waveguide and a downstream extension of the north atlantic oscillation abstract anomalous atmospheric fields associated with the north atlantic oscillation nao are analyzed on interannual and intraseasonal time scales in order to examine the extent to which the nao is a regional phenomenon analyses on the interannual time scale reveal that the nao signal is relatively confined to the euro atlantic sector in december while it extends toward east asia and the north pacific in february the difference is most clearly seen in the meridional wind anomaly which shows a wave train along the asian jet collocated with an anomalous vorticity source near the jet entrance diagnoses using a linear barotropic model indicate that this wave train is interpreted as quasi stationary rossby waves trapped on the asian jet waveguide and effectively excited by the anomalous upper level convergence over the mediterranean sea it is found that when the nao accompanies the mediterranean convergence mc anomaly most frequently seen in february the nao indeed has a much wider horizontal str

an energetic view of the relation between the mediterranean storm track and the north atlantic oscillation the time tendency equation of eddy kinetic energy eke includes some important forcing terms such as baroclinic conversion bcc barotropic conversion btc and energy flux this article compares the ensemble mean distribution of these forcing terms as well as the baroclinic generation bcg term in critical positive and critical negative months of the north atlantic oscillation nao focusing on the mediterranean and middle east regions results show that all the computed terms attain larger values and all the extrema are stronger in the positive phase the energy flux vectors point to energy transfer from the west of the atlantic and north of europe to the mediterranean region with the transfer being weaker in the positive phase there is energy flux divergence over the central region of the mediterranean sea which is more extensive in the positive phase relative to the negative phase the energy flux divergence leads to a radiation source in this region the direction of the energy flux vectors then indicates that the energy radiated from the central mediterranean region is transferred southeastward leading to an energy flux convergence over the red sea and the northeast of africa this convergence is stronger and more extensive in the positive phase which may be responsible for the observed larger value of the upper level eddy kinetic energy in the positive phase the patterns of the bcg and bcc together with the energy flux convergence suggest that while the mediterranean storm track is affected by the north atlantic storm track more strongly in the negative phase it acts as an independent centre of action by radiating energy southeastward in the positive phase copyright 2011 royal meteorological society

controls on trace element sr mg compositions of carbonate cave waters implications for speleothem climatic records abstract at two caves clamouse s france and ernesto ne italy cave drip and pool waters were collected and sampled at intervals over a 2 3 year period mg ca and sr ca concentration ratios corrected for marine aerosols are compared with those of bedrocks and in some cases aqueous leachates of soils and weathered bedrocks cave waters do not lie along mixing lines between calcite and dolomite of bedrock carbonate but typically show enhanced and covarying mg ca and sr ca four factors are considered as controlling processes 1 the much faster dissolution rate of calcite than dolomite allows for the possibility of increase of mg ca if water rock contact times are increased during drier conditions a theoretical model is shown to be comparable to experimental leachates 2 prior calcite precipitation along a flow path is a powerful mechanism for generating enhanced and covarying mg ca and sr ca ratios this mechanism requires the solution to lose co 2 into pores or caverns 3 incongruent dolomite dissolution has only limited potential and is best regarded as two separate processes of dolomite dissolution and calcite precipitation 4 selective leaching of mg and sr with respect to ca is shown to be important in leachates from ernesto where it appears to be a phenomenon of calcite dissolution in general selective leaching can occur whenever ca is sequestered into precipitates due to freezing or drying of soils or if there is derivation of excess sr and mg from non carbonate species the ernesto cave has abundant water supply which in the main chamber is derived from a reservoir with year round constant p co 2 of around 10 2 4 and no evidence of calcite precipitation in the karst above the cave two distinct but overlying trends of enhanced and covarying mg ca and sr ca away from the locus of bedrock compositions are due to calcite precipitation within the cave and at a variable drip site due to enhanced selective leaching at slow drip rates mg enhancement in the first chamber is due to a more dolomitic bedrock and longer residence times the clamouse site has a less abundant water supply and presents geochemical evidence of prior calcite precipitation both in the cave and in overlying porous dolomite dedolomitized limestone bedrock initial p co 2 values as high as 10 1 are inferred experimental incubations of clamouse soils which generated enhanced p co 2 and precipitated caco 3 had compositions similar to the karst waters calcite precipitation is inferred to be enhanced in drier conditions hydrological controls on cave water chemistry imply that the trace element chemistry of speleothems may be interpretable in palaeohydrological terms drier conditions tends to promote not only longer mean residence times enhancing dolomite dissolution and hence mg ca but also enhances degassing and calcite precipitation leading to increased mg ca and sr ca

preferred modes of variability and their relationship with climate change spatial structure of annular modes shows a remarkable resemblance to that of the recent trend in the observed circulation thompson et al this study performs a series of multilevel primitive equation model simulations to examine the extent to which the annular mode is capable of predicting changes in the zonal mean flow response to external heat perturbations each of these simulations represents a statistically steady state and differs from each other in the values of the imposed tropical heating h and high latitude cooling c defining the annular mode as the first empirical orthogonal function eof1 of zonal mean tropospheric zonal wind it is found that the climate predictability is generally high in the small c large h region of the parameter space but is markedly low in the large c small h region in the former region eof1 represents meridional meandering of the midlatitude jet while in the latter region eof1 and eof2 combine to represent coherent poleward propagation of zonal mean flow anomalies it is also found that the climate predictability tends to be higher with respect to changes in c than to changes in h the implications of these findings for the southern hemisphere climate predictability are also presented

is the north atlantic oscillation a breaking wave abstract given the recent observational evidence that the positive negative phase of the north atlantic oscillation nao is the remnant of anticyclonic cyclonic wave breaking this study uses a multilevel primitive equation model to investigate important dynamical attributes of the above wave breaking behavior for this purpose a hierarchy of different basic states two and three dimensional and initial perturbations are used with the three dimensional climatological flow as the basic state it is found that initial perturbations located equatorward poleward and upstream of the climatological atlantic jet lead to wave breaking similar to that of the positive negative nao phase consistently analysis of observational data indeed shows that the pacific storm track is displaced equatorward poleward prior the onset of the positive negative nao phase this result suggests that the latitudinal position of the pacific storm track plays an important role for determining the phase of the nao sen

laboratory impacts into dry and wet sandstone with and without an overlying water layer implications for scaling laws and projectile survivability scaling laws describing crater dimensions are defined in terms of projectile velocity and mass densities of the materials involved strength of the target and the local gravity here the additional importance of target porosity and saturation and an overlying water layer are considered through 15 laboratory impacts of 1 mm diameter stainless steel projectiles at 5 km s 1 into a an initially uncharacterized sandstone porosity 17 and b coconino sandstone porosity 23 the higher porosity dry sandstone allows a crater to form with a larger diameter but smaller depth than in the lower porosity dry sandstone furthermore for both porosities a greater volume of material is excavated from a wet target than a dry target by 27 30 comparison of our results with pi scaling dimensionless ratios of key parameters characterizing cratering data over a range of scales suggests that porosity is important for scaling laws given that the new data lie significantly beneath the current fit for ice and rock targets on a v versus 3 plot v gives cratering efficiency and 3 the influence of target strength an overlying water layer results in a reduction of crater dimensions with larger craters produced in the saturated targets compared to unsaturated targets a water depth of approximately 12 times the projectile diameter is required before craters are no longer observed in the targets previous experimental studies have shown that this ratio varies between 10 and 20 gault and sonett 1982 in our experiments 25 of the original projectile mass survives the impact

rossby wave packets on the midlatitude waveguide a review abstractrossby wave packets rwps are rossby waves for which the amplitude has a local maximum and decays to smaller values at larger distances this review focuses on upper tropospheric transient rwps along the midlatitude jet stream their central characteristic is the propagation in the zonal direction as well as the transfer of wave energy from one individual trough or ridge to its downstream neighbor a process called downstream development these rwps sometimes act as long range precursors to extreme weather and presumably have an influence on the predictability of midlatitude weather systems the paper reviews research progress in this area with an emphasis on developments during the last 15 years the current state of knowledge is summarized including a discussion of the rwp life cycle as well as rossby waveguides recent progress in the dynamical understanding of rwps has been based in part on the development of diagnostic methods these methods include algorithms to identify and track rwps

circumglobal teleconnection in the northern hemisphere summer analysis of the 56 yr ncep ncar reanalysis data reveals a recurrent circumglobal teleconnection cgt pattern in the summertime midlatitude circulation of the northern hemisphere this pattern represents the second leading empirical orthogonal function of interannual variability of the uppertropospheric circulation the cgt having a zonal wavenumber 5 structure is primarily positioned within a waveguide that is associated with the westerly jet stream the spatial phases of cgt tend to lock to preferred longitudes the geographically phase locked patterns bear close similarity during june august and september but the pattern in july shows shorter wavelengths in the north pacific north america sector the cgt is accompanied by significant rainfall and surface air temperature anomalies in the continental regions of western europe european russia india east asia and north america this implies that the cgt may be a source of climate variability and predictability in the above mentioned midlatitude regions the cgt has significant correlations with the indian summer monsoon ism and el nino southern oscillation enso however in normal ism years the cgt enso correlation disappears on the other hand in the absence of el nino or la nina the cgt ism correlation remains significant it is suggested that the ism acts as a conductor connecting the cgt and enso when the interaction between the ism and enso is active enso may influence northern china via the ism and the cgt additionally the variability of the cgt has no significant association with the arctic oscillation and the variability of the western north pacific summer monsoon the circulation of the wave train shows a barotropic structure everywhere except the cell located to the northwest of india where a baroclinic circulation structure dominates two possible scenarios are proposed the abnormal ism may excite an anomalous west central asian high and downstream rossby wave train extending to the north pacific and north america on the other hand a wave train that is excited in the jet exit region of the north atlantic may affect the westcentral asian high and thus the intensity of the ism it is hypothesized that the interaction between the global wave train and the ism heat source may be instrumental in maintaining the boreal summer cgt

the relationship between the north atlantic jet and tropical convection over the indian and western pacific oceans abstractboreal winter jet variability over the north atlantic is investigated using 40 yr european centre for medium range weather forecasts re analysis era 40 data where the variability is defined by the first eof of the zonal wind on seven vertical levels the principal component time series of this eof is referred to as the jet index a pattern correlation analysis indicates that the jet index more accurately describes intraseasonal north atlantic zonal wind variability than does the north atlantic oscillation nao a series of composite calculations of the jet index based on events of intraseasonal convective precipitation over the tropical indian and western pacific oceans reveals the following statistically significant relationships 1 negative jet events lead enhanced indian ocean precipitation 2 positive jet events lag enhanced indian ocean precipitation 3 positive jet events lead enhanced western pacific ocean precipitation and 4 negative jet events lag enhanced western pacific ocean p

application of the trace element and isotope geochemistry of strontium to studies of carbonate diagenesis carbonate rocks and natural waters exhibit a wide range in the concentration and isotopic composition of strontium this wide range and the quantifiable covariation of these parameters can provide diagnostic tools for understanding processes of fluid rock interaction careful consideration of the uncertainties associated with trace element partitioning sample heterogeneity and fluid rock interaction mechanisms is required to advance the application of the trace element and isotope geochemistry of strontium to studies of diagenesis goundwater evolution ancient seawater chemistry and isotope stratigraphy a principal uncertainty involved in the application of sr concentration variations to carbonate systems is the large range of experimental and empirical results for trace element partitioning of sr between mineral and solution this variation may be a function of precipitation rate mineral stoichiometry crystal growth mechanism fluid composition and temperature calcite and dolomite in ancient limestones commonly have significantly lower sr concentrations 20 70 p p m than would be expected from published trace element distribution coefficient values and sr ca ratios of most modern sedimentary pore waters this discrepancy probably reflects the uncertainties associated with determining distribution coefficient values as techniques improve for the analytical measurement and theoretical modelling of sr concentration and isotopic variations the petrological analysis of carbonate samples becomes increasingly important the presence of even small percentages of non carbonate phases with high rb concentrations and high 87 sr86 sr values such as clay minerals can have significant effects on the measured 87 sr 86 sr values of carbonate rocks due to the decay of 87rb to 87 sr for example a permian marine limestone with 50 p p m sr and 1 p p m rb will have a present day 87 sr 86 sr value that is 2 10 4 higher than its original value this difference is an order of magnitude greater than the analytical uncertainty and illustrates the importance of assessing the need for and accuracy of such corrections a quantitative evaluation of the effects of water rock interaction on sr concentrations and isotope compositions in carbonates strengthens the application of these geochemical tracers geochemical modelling that combines the use of trace elements and isotopes can be used to distinguish between different mechanisms of water rock interaction including diffusive and advective transport of diagenetic constituents in meteoric pore fluids during the recrystallization of carbonate minerals quantitative modelling may also be used to construct diagnostic fluid rock interaction trends that are independent of distribution coefficient values and to distinguish between mixing of mineral end members and fluid rock interaction

controls on the spatial and temporal variability of vadose dripwater geochemistry edwards aquifer central texas abstract a 4 yr study of spatial and temporal variability in the geochemistry of vadose groundwaters from caves within the edwards aquifer region of central texas offers new insights into controls on vadose groundwater evolution the relationship between vadose and phreatic groundwaters and the fundamental influence of soil composition on groundwater geochemistry variations in sr isotopes and trace elements mg ca and sr ca ratios of dripwaters and soils from different caves as well as phreatic groundwaters provide the potential to distinguish between local variability and regional processes controlling fluid geochemistry and a framework for understanding the links between climatic and hydrologic processes the sr isotope compositions of vadose cave dripwaters mean 87sr 86sr 0 7087 and phreatic groundwaters mean 87sr 86sr 0 7079 generally fall between values for host carbonates mean 87sr 86sr 0 7076 and exchangeable sr in overlying soils mean 87sr 86sr 0 7088 dripwaters have lower mg ca and sr ca ratios and higher 87sr 86sr values than phreatic groundwaters dripwater 87sr 86sr values also inversely correlate with both mg ca and sr ca ratios mass balance modeling combined with these geochemical relationships suggest that variations in fluid compositions are predominantly controlled by groundwater residence times and water rock interaction with overlying soils and host aquifer carbonate rocks consistent differences in dripwater geochemistry i e 87sr 86sr mg ca and sr ca between individual caves are similar to compositional differences in soils above the caves while these differences appear to exert significant control on local fluid evolution geochemical and isotopic variations suggest that the controlling processes are regionally extensive temporal variations in 87sr 86sr values and mg ca ratios of dripwaters from some sites over the 4 yr interval correspond with changes in both aquifer and climatic parameters these results have important implications for the interpretation of trace element and isotopic variations in speleothems as paleoclimate records as well as the understanding of controls on water chemistry for both present day and ancient carbonate aquifers

intraseasonal variations of the british baikal corridor pattern abstractthe british baikal corridor bbc pattern is the dominant waveguide mode trapped along the summertime polar front jet over northern eurasia it consists of four geographically fixed centers

oceanic impacts a growing field of fundamental geoscience the importance of oceanic impacts of collisional events and resulting energy release are briefly described data collection methods from the eltanin a mesosiderite projectile deep water impact are presented

the dynamics of nao teleconnection pattern growth and decay this investigation performs both diagnostic analyses with ncep ncar re analysis data and forced barotropic model calculations to examine the dynamical mechanisms associated with the growth and decay of the north atlantic oscillation nao teleconnection pattern the diagnostic calculations include projection and composite analyses of each term in the stream function tendency equation the results of the analyses reveal a complete life cycle of growth and decay within approximately two weeks the positive nao phase is found to develop after anomalous wavetrain propagation across the north pacific to the east coast of north america this contrasts with the negative nao phase which appeared to develop in situ both high frequency period 10 days transient eddy fluxes drive the nao growth after the nao anomaly attains its maximum amplitude the high frequency transient eddy fluxes continue to drive the nao anomaly in a manner that is consistent with a positive feedback process the decay of the nao occurs through both the divergence term and the low frequency transient eddy fluxes the temporal and spatial properties of the divergence term are found to be consistent with ekman pumping these results illustrate many important differences between the nao and pacific north american pna teleconnection patterns perhaps most striking being that the nao life cycle is dominated by nonlinear processes whereas the pna evolution is primarily linear in addition the relation between the nao and the zonal index is discussed copyright 2003 royal meteorological society

life cycles of north atlantic teleconnections under strong and weak polar vortex conditions this paper investigates the role of the strength of the polar stratospheric winter vortex in the dynamics of the life cycles of north atlantic teleconnections a new set of teleconnection patterns was produced from low pass filtered daily 300 hpa height data of ncep national centers for environmental prediction reanalysis data 1958 1998 all teleconnections are meridional dipoles which to a certain degree resemble the north atlantic oscillation based on surface pressure data there are two distinct teleconnections one over the eastern and one over the western north atlantic during episodes of weak polar vortex and only one over the central north atlantic during strong polar vortex episodes the teleconnections have periods of about two weeks stream function tendency analysis of the life cycles shows that the relatively simple resulting teleconnections evolve from very complex structures during the growth phase of the teleconnection indices there are strong and systematic differences between the two polar vortex regimes while in the weak vortex regime the anomaly growth is mainly driven by transient eddy vorticity fluxes from the low frequency domain in the strong vortex regime there is also low frequency advection of relative vorticity resulting from the interaction of low frequency eddies with stationary eddies copyright 2006 royal meteorological society

impact induced phyllosilicate formation from olivine and water abstract shock recovery experiments on mixtures of olivine and water with gas air were performed in a previous study to demonstrate water mineral interactions during impact events furukawa et al 2007 the products of these former experiments were investigated in the present study using transmission electron microscopy scanning electron microscopy and x ray powder diffraction with the aim of finding evidence of aqueous alteration serpentine formed on the surface of shocked olivine with well developed mosaicism the yield of serpentine depended on the water olivine ratio in the starting material indicating progressive serpentinization under water rich conditions comminution and mosaicism were developed in shocked olivine grains the temperature and pressure changes of the samples during the experiments were estimated by constructing hugoniots for mixtures of olivine and water combined with the results of an additional fracturing experiment on a shocked container pressures and temperatures reached 4 6 7 2 gpa and at least 230 390 c respectively for 0 7 s during in shock compression post shock temperatures reached a maximum of 1300 c when the shock wave reached the gas in the sample cavity the serpentine formed after the post shock temperature maximum most likely when temperatures dropped to between 200 and 400 c this is the first experiment to demonstrate the formation of phyllosilicates using heat supplied by an impact the present results and estimations suggest that phyllosilicates could form as a result of impacts into oceans as well as by impacts on terrestrial and martian crustal rocks and on some asteroidal surfaces where liquid or solid h 2 o is available a significant amount of phyllosilicates would have formed during the late heavy bombardment of meteorites on the hadean earth and such phyllosilicates might have affected the prebiotic carbon cycle

the circumglobal north american wave pattern and its relation to cold events in eastern north america extreme large scale north american cold events are associated with strong undulations in the tropospheric jet stream which bring cold polar air southward over the continent here we propose that th

shock metamorphism on the ocean floor numerical simulations abstract impact craters are unknown in deep ocean basins important reasons for this are that the ocean crust is younger than continents and the impacts are weakened by the water column laboratory experiments can show specific features of water impacts however impact velocities are too small

horizontal energy propagation in a barotropic atmosphere with meridional and zonal structure abstract to investigate how the propagation of energy away from steady sources may be influenced by the horizontal structure of the time averaged flow in the troposphere solutions to a barotropic model are displayed and interpreted the model is steady and linearized about a basic state which varies in latitude and longitude emphasis is placed on cases where the longitudinal variations are gradual many of the results can be analyzed by locally applying tools developed for zonally symmetric basic states e g ray tracing and refractive indices simple background flows are constructed which have longitudinally confined critical lines reflective surfaces wave guides and regions conducive to propagation an example is given in which longitudinal derivatives of the basic state are significant the theory of ray tracing in a two dimensional wind must be employed as an interpretive tool in this case it is concluded that zonal variations tend to enhance poleward equatorward propagation in large scale tr

evolution of eurasian teleconnection pattern and its relationship to climate anomalies in china the eurasian teleconnection pattern eu is a major mode of low frequency variability in the northern hemisphere winter with notable impacts on the temperature and precipitation anomalies in eurasia region to investigate the structure life cycle and dynamical mechanisms of eu pattern diagnostic analyses are conducted to clarify eu pattern evolution with an emphasis on eu development and decay in the developing stage a geopotential height anomaly over north atlantic emerges 6 days before eu peak phase and other three geopotential height anomalies appear one by one in the following days during this period all geopotential height anomalies experience considerable growth and the four center structure of eu pattern forms 2 days before peak phase the obvious wave train structure appears at 300 hpa the eu pattern growth is driven by both relative vorticity advection and transient eddy fluxes after the peak phase the geopotential height anomaly over north atlantic becomes weak as it decays earlier than other anomaly centers which leads to the classic three center structure of eu teleconnection pattern the complete life cycle of eu pattern experience considerable growth and decay within 10 days during the decaying stage the horizontal divergence and the transient eddy fluxes play important roles additionally the relationship of eu pattern to winter climate anomalies in china is also analyzed focusing on the decaying stage the impact of eu pattern on temperature and precipitation in china are significant in 2 4 days after eu peak phase and the distribution of temperature and precipitation anomaly has obvious regional differences

synoptic view of the north atlantic oscillation abstract this article investigates the synoptic characteristics of individual north atlantic oscillation nao events by examining the daily evolution of the potential temperature field on the nominal tropopause the 2 pvu surface this quantity is obtained from the national centers for environmental prediction national center for atmospheric research ncep ncar reanalysis dataset for the winter season for both phases the nao is found to originate from synoptic scale waves as these waves evolve into the low frequency nao pattern they break anticyclonically for the positive phase and cyclonically for the negative phase the results of this analysis suggest that it is the remnants of these breaking waves that form the physical entity of the nao throughout the nao events for both phases the nao is maintained by the successive breaking of upstream synoptic scale waves when synoptic scale disturbances are no longer present mixing processes play an important role in the nao decay as in other recent

unmelted meteoritic debris collected from eltanin ejecta in polarstern cores from expedition ant xii 4 abstract a total of 1 7 g of unmelted meteorite particles have been recovered from fs polarstern piston cores collected on expedition ant xii 4 that contain ejecta from the eltanin impact event most of the mass 1 2 g is a large single specimen that is a polymict breccia similar in mineralogy and chemistry to howardites or the silicate fraction of mesosiderites most of the remaining mass is in several large individual pieces 20 75 mg each that are polymict breccias fragments dominated by pyroxene and an igneous rock fragment the latter has highly fractionated ree similar to those reported in mafic clasts from mesosiderites other types of specimens identified include fragments dominated by maskelynite or olivine these pieces of the projectile probably survived impact by being blown off the back surface of the eltanin asteroid during its impact into the bellingshausen sea

the possible impact of the circumglobal wave train on the wet season dust storm activity over the northern arabian peninsula this study examines the influence of mid latitude circulation on the wet season october may dust storm activity dsa over the northern arabian peninsula for the period of 1983 2013 using observational and reanalysis gridded datasets dusty and clear days composites of the 200 hpa geopotential height anomalies reveal a pattern in the upper levels which is strongly correlated with the mid latitude circumglobal wave train cgt and exists 3 days prior to the outbreak of dust storms the regional surface conditions such as the mean sea level pressure low level temperature and winds etc that favor the dsa over the northern arabian peninsula display significant correlations with the cgt on intraseasonal time scale a time lagged analysis reveals that the eastward propagating cgt influences the surface pressure over the northern arabian peninsula and adjacent areas hence the dsa the dsa over the northern arabian peninsula is found to be more frequent during the positive phase of the north atlantic oscillation nao and the cold phase of the el nino southern oscillation la nina and less frequent during the negative phase of nao and the warm phase of the el nino southern oscillation el nino

mechanisms of eastern mediterranean rainfall variability abstract this paper presents a simple theory for the association between observed eastern mediterranean em rainfall anomalies and north atlantic na climate variability large scale na atmospheric mass rearrangements primarily a modulation of the icelandic low and the subtropical high pressure systems tend to extend beyond the na a particularly strong such teleconnection exists between the northern na and southern europe and the mediterranean basin pressure anomalies over greenland iceland are thus associated with reversed polarity anomalies centered over the northern adriatic affecting the entire mediterranean basin elevated greenland pressure is accompanied by an anomalous cyclone over the mediterranean and a mediterranean high pressure system is present when pressure over greenland is reduced in the em these anomalies result in anomalous southerlies during greenland highs and northerlies during greenland lows eastern mediterranean southerlies warm the em while northerlies cool locally b

thermodynamics of eastern mediterranean rainfall variability abstract this note focuses on thermodynamic changes caused by eastern mediterranean em subsidence anomalies subsidence anomalies are shown to modulate em wide stability with respect to moist ascent additionally convective available potential energy cape generation rates as well as mean cape change coherently during extreme em rainfall anomalies it is suggested that the resulting modulation of convective rain generation is the process directly responsible for the observed rainfall anomalies

breaking waves at the tropopause in the wintertime northern hemisphere climatological analyses of the orientation and the theoretical lc1 2 classification abstract breaking waves on the tropopause are viewed as potential vorticity pv streamers on middle world isentropic levels a northern hemisphere winter climatology of the streamers spatial distribution and meridional orientation is derived from the 40 yr ecmwf re analysis era 40 dataset and used to assess the nature and frequency of occurrence of breaking synoptic scale waves the streamers are grouped into two classes related to the so called cyclonic lc2 and anticyclonic lc1 patterns and the ambient wind strength and wind shear is also noted it is shown that the occurrence of cyclonic and anticyclonic pv streamers exhibits a distinct spatial variability in the horizontal and the vertical the majority of cyclonic pv streamers are found on lower isentropic levels that intersect the tropopause at more poleward latitudes whereas anticyclonic streamers predominate at higher elevations in the subtropics an analysis of the streamer patterns for the two phases of the north atlantic oscillation

high resolution temporal record of holocene ground water chemistry tracing links between climate and hydrology strontium isotope analysis of precisely dated calcite growth layers in holocene speleothems from barbados west indies reveals high resolution temporal variations in ground water composition and may provide a new approach to documenting the links between climate variability andfluctuations in the hydrologic cycle such as recharge rates andflow paths the speleothems grew in a cave that developed in a fresh water aquifer in upliftedpleistocenereeflimestones threeperiodsofground watersrisotopeevolutionare observed 87 sr 86 srvaluesdecreasedfrom6to4ka increasedfrom4to1ka anddecreased again after 1 ka the sr isotope oscillations appear to record periodic variations in the relative sr fluxes to ground water from exchangeable soil sites vs carbonate mineral reactions asreflectedin 87 sr 86 srvaluesofmodernbarbadosgroundwaters ahydrologic model that explains changes in ground waterflow routes in karst aquifers as a function of amountofrainfallrechargecanaccountforthespeleothemsrisotoperecord independent holoceneclimaterecordsthatindicateamajorperiodofaridityataround1 3 1 1kainthe american tropics correspond with periodic variations in rainfall on barbados that are predicted by this hydrologic model

smart 1 end of life shallow regolith impact simulations the smart 1 end of life impact with the lunar surface was simulated with impacts in a two stage light gas gun onto inclined basalt targets with a shallow surface layer of sand this simulated the probable impact site where a loose regolith will have overlaid a well consolidated basaltic layer of rock the impact angles used were at 5 and 10 from the horizontal the impact speed was 2 km s 1 and the projectiles were 2 03 mm diameter aluminum spheres the sand depth was between approximately 0 8 and 1 8 times the projectile diameter implying a loose lunar surface regolith of similar dimensions to the smart 1 spacecraft a crater in the basement rock itself was only observed in the impact at 10 incidence and where the depth of loose surface material was less than the projectile diameter in which case the basement rock also contained a small pit like crater in all cases the projectile ricocheted away from the impact site at a shallow angle this implies that at the smart 1 impact site the crater will have a complicated structure with exposed basement rock and some excavated rock displaced nearby and the main spacecraft body itself will not be present at the main crater

quasi stationary states in the southern hemisphere abstract pattern correlations between daily anomalies have been used to study the persistence of the southern hemisphere circulations the dataset consists of daily australian analyses of 500 mb heights and sea level pressure for the period from 1972 to 1983 compared to the northern hemisphere the pattern correlations are much lower and more variable in the southern hemisphere the mean one day lag autocorrelation is only 0 57 compared to 0 81 in the northern hemisphere the correlations increase significantly for the filtered anomalies which consist of the planetary wavenumbers from 0 to 4 subjective criteria based on the pattern correlations are used to select quasi stationary events a series of 5 or more daily maps is defined to be quasi stationary if the pattern correlations between all pairs of five consecutive maps in this time series are larger than or equal to 0 5 in winter quasi stationary events can be classified in terms of wavenumbers waves 3 and 4 are by far the dominant waves more

geological record and reconstruction of the late pliocene impact of the eltanin asteroid in the southern ocean in 1995 an expedition on board the research vessel fs polarstern explored the impact site of the eltanin asteroid in the southern ocean the only known asteroidimpact into a deep ocean basin analyses of the geological record of the impact region place the event in the late pliocene 2 15 myr and constrain thesize of the asteroid to be 1 km the explosive force inferred for this event places it at the threshold of impacts believed to have global consequences and its studyshould therefore provide a baseline for the reconstruction and modelling of similar events which are common on geological timescales

discovery of a 25 cm asteroid clast in the giant morokweng impact crater south africa meteorites provide a sample of solar system bodies and so constrain the types of objects that have collided with earth over time meteorites analysed to date however are unlikely to be representative of the entire population and it is also possible that changes in their nature have occurred with time large objects are widely believed to be completely melted or vaporized during high angle impact with the earth consequently identification of large impactors relies on indirect chemical tracers notably the platinum group elements here we report the discovery of a large 25 cm unaltered fossil meteorite and several smaller fragments within the impact melt of the giant 70 km diameter 145 myr old morokweng crater south africa the large fragment clast resembles an ll6 chondrite breccia but contains anomalously iron rich silicates fe ni sulphides and no troilite or metal it has chondritic chromium isotope ratios and identical platinum group element ratios to the bulk impact melt these features allow the unambiguous characterization of an impactor at a large crater furthermore the unusual composition of the meteorite suggests that the morokweng asteroid incorporated part of the ll chondrite parent body not represented by objects at present reaching the earth

velocity scaling of impact craters in water ice over the range 1 to 7 3 km s 1 the impact cratering behavior of polycrystalline ice at a temperature of 259 3 k has been investigated by 16 impacts with 1 mm aluminum 2017 alloy spheres density 2790 kg m 3 over the velocity range 1 to 7 3 km s 1 using a two stage light gas gun crater cross sectional profiles and diameter depth and volume data are presented it is found that there is no significant difference in power law energy exponents for scaling of crater diameter and volume between these data and previous low velocity 1 km s 1 ice impact data dimensionless pi group scaling was also found to scale the data in a way which can be readily combined with earlier lower velocity data and data at a lower ice temperature

influence of the background state on rossby wave propagation into the great lakes region based on observations and model simulations abstractthe authors investigate the relationship between hydrology in the great lakes basin namely overlake precipitation and transient rossby waves using the national centers for environmental prediction national center for atmospheric research ncep ncar reanalysis data and historical output from phase 3 of the coupled model intercomparison project cmip3 the preferred path of observed rossby wave trains associated with overlake precipitation on lake superior depends strongly on season and appears to be related to the time mean upper level flow during summer and fall the northern hemisphere extratropical jet is relatively narrow and acts as a waveguide such that rossby wave trains traversing the great lakes region travel along the extratropical pacific and atlantic jets during other months the pacific jet is relatively broad which allows more wave activity originating in the tropics to penetrate into the midlatitudes and influence lake superior precipitation analysis is extended to cmip3 mod

the continuum and dynamics of northern hemisphere teleconnection patterns this study presents an alternative interpretation for northern hemisphere teleconnection patterns rather than comprising several different recurrent regimes this study suggests that there is a continuum of teleconnection patterns this interpretation indicates either that 1 all members of the continuum can be expressed in terms of a linear combination of a small number of real physical modes that correspond to basis functions or 2 that most low frequency patterns within the continuum are real physical patterns each having its own spatial structure and frequency of occurrence daily ncep ncar reanalysis data are used that cover the boreal winters of 1958 97 a set of nonorthogonal basis functions that span the continuum is derived the leading basis functions correspond to well known patterns such as the pacific north american teleconnection and north atlantic oscillation evidence for the continuum perspective is based on the finding that 1 most members of the continuum tend to have similar variance and autocorrelation time scales and 2 that members of the continuum show dynamical characteristics that are intermediate between those of the surrounding basis functions the latter finding is obtained by examining the streamfunction tendency equation both for the basis functions and some members of the continuum the streamfunction tendency equation analysis suggests that north pacific patterns basis functions and continuum are primarily driven by their interaction with the climatological stationary eddies and that north atlantic patterns are primarily driven by transient eddy vorticity fluxes the decay mechanism for all patterns is similar being due to the impact of low frequency period greater than 10 days transient eddies and horizontal divergence analysis with outgoing longwave radiation shows that tropical convection is found to play a much greater role in exciting north pacific patterns a plausible explanation for these differences between the north atlantic and north pacific patterns is presented

the shape propagation and mean flow interaction of large scale weather systems abstract for a zonal average operator the eliassen palm flux provides a diagnostic of both eddy behavior and the feedback of the eddies onto the mean flow this paper addresses the diagnosis problem for other averaging operators and in particular for time averaging which has proved in recent years such a powerful means of viewing the three dimensional tropospheric flow the horizontal velocity correlation tensor gives a measure of the characteristic horizontal eddy shape at a point it also implies the direction of the group velocity relative to the mean flow in cases where such a concept is valid however the major emphasis here is on the mean flow feedback of eddies in this respect the eddy vorticity flux is determined by derivatives of the components of the anisotropic part of the tensor making a reasonable approximation allows the eddy vorticity flux convergence to be written in terms of e v 2 u 2 u v a simple interpretation of the mean flow feedback of eddies is then possible a sligh

the clay mineralogy of sediments related to the marine mjolnir impact crater the 40 km diameter mjolnir crater is located on the central barents sea shelf north of norway it was formed about 142 2 6 myr ago by the impact of a 12 km asteroid into the shallow shelf clays of the hekkingen formation and the underlying triassic to jurassic sedimentary strata a core recovered from the central high within the crater contains slump and avalanche deposits from the collapse of the transient crater and central high these beds are overlain by gravity flow conglomerates with laminated shales and marls on top here impact and post impact deposits in this core are studied with focus on clay mineralogy obtained from xrd decomposition and simulation analysis methods the clay sized fractions are dominated by kaolinite illite mixed layered clay minerals and quartz detailed analyses showed rather similar composition throughout the core but some noticeable differences were detected including varying crystal size of kaolinite and different types of illites and illite smectite these minerals may have been formed by diagenetic changes in the more porous fractured beds in the crater compared to time equivalent beds outside the crater rim long term post impact changes in clay mineralogy are assumed to have been minor due to the shallow burial depth and minor thermal influence from impact heated target rocks instead the clay mineral assemblages especially the abundance of chlorite reflect the impact and post impact reworking of older material previously an ejecta layer the sindre bed was recognized in a nearby well outside the crater represented by an increase in smectite rich clay minerals genetically equivalent to the smectite occurring in proximal ejecta deposits of the chicxulub crater such alteration products from impact glasses were not detected in this study indicating that little if any impact glass was deposited within the upper part of the crater fill crater fill deposits inherited their mineral composition from triassic and jurassic sediments underlying the impact site

the positive north atlantic oscillation with downstream blocking and middle east snowstorms impacts of the north atlantic jet abstracta recent study revealed that cold winter outbreaks over the middle east and southeastern europe are caused mainly by the northeast southwest ne sw tilting of european blocking eb associated with the positive phase north atlantic oscillation nao here the north atlantic conditions are examined that determine the eb tilting direction defined as being perpendicular to the dipole anomaly orientation using daily reanalysis data the nao events are classified into strong sjn and weak wjn north atlantic jet types a composite analysis shows that the eb is generally stronger and located more westward and southward during sjn events than during wjn events during sjn events the nao and eb dipoles exhibit ne sw tilting which leads to strong cold advection and large negative temperature anomalies over the middle east and southeastern europe in contrast northwest southeast nw se tilting without strong negative temperature anomalies over the middle east is seen during wjn events a nonline

catastrophic disruption of icy bodies with sub surface oceans abstract several icy bodies in the outer solar system have extensive internal oceans in several bodies the oceans are believed to be so extensive they decouple the interior core from the icy surface a major evolutionary driver in the solar system is high speed impacts which lead to cratering or even disruption of the target body here we consider how the presence of an internal ocean modifies the energy density needed to disrupt an icy body with an internal ocean we find that in laboratory experiments on decimetre scale bodies the energy density to cause disruption is 16 25 1 35 j kg 1 compared to 18 0 0 7 j kg 1 for solid ice bodies this suggests that for the purposes of impacts the bodies behave as if a solid with the same density predictions of the lifetimes of such icy bodies against impact disruption thus need not take the interior ocean into account

interaction of north atlantic baroclinic wave packets and the mediterranean storm track observational studies show that the main energy source for developing cyclones is due to downstream radiation from existing upstream disturbances this process is involved in the propagation of coherent wave packets linking the north atlantic and mediterranean storm tracks in winter to understand the link the rossby wave packets have been analyzed for the winter season 2004 05 by means of wave envelope energetic and wave activity diagnostics two specifically selected cases are presented one with clear propagation of the wave packet to the mediterranean region from the north atlantic storm track and the other with zonal propagation of the wave packets along the central latitude of the north atlantic storm track the dynamical effects leading to the distinct propagation characteristics of the two cases are discussed it is shown that the two cases make clear impacts on the horizontal flux of wave activity across a domain surrounding the mediterranean storm track