authigenic spherules in k t boundary sediments at caravaca spain and raton basin colorado and new mexico may not be impact derived the k t boundary interval at barranco del gredero caravaca spain consists of three units a light gray cretaceous marl a 1 to 3 mm thick ferruginous clay called the k t boundary impact layer because of its content of shock metamorphosed quartz grains and an overlying greenish gray clay a conspicuous feature of the impact layer is its content of potassium feldspar particles called sanidine spherules by some authors the particles consist of a porous mesh work of prismatic potassium feldspar crystals clearly of authigenic origin their shape distribution and texture suggest that they are not altered basaltic melt droplets formed during impact of an extraterrestrial object as advocated by some proponents of the impact extinction theory of alvarez moreover authigenic spherules also occur in a thin kaolinitic claystone layer at the k t boundary in continental sedimentary rocks of the raton basin colorado and new mexico this layer is overlain by another claystone 5 8 mm thick that records the abrupt appearance of shock metamorphosed quartz grains in the local stratigraphic section four compositional types of spherules kaolinite goyazite layered goyazite kaolinite and jarosite occur in the lower of the two claystone layers because the spherules are 1 not in a bed containing shock metamorphosed minerals 2 common at some and rare at other localities and 3 hollow and form peculiarly shaped intergrown masses suggest that they are not altered microtektites or melt droplets

aerial crystallization of hematite in impact bombs from the araguainha astrobleme mato grosso central brazil optical and scanning electron microscope sem observations of hematite impact bombs from the araguainha astrobleme in central brazil reveal an aerodynamically stable microstructure which is interpreted to reflect the aerial crystallization of hypervelocity melt globules derived from fe rich sedimentary target rocks the bombs are composed of an aggregate of preferentially oriented conic units with different degrees of packing giving rise to porous and massive hematite varieties these varieties generally occupy the front and rear of the bombs respectively quartz fragments with planar deformation features are common in the porous domains and represent ejected solid particles captured by the bombs during cooling the absence of typical contorted shapes in these bombs reflects the lack of spin during their ballistic trajectory the bombs are enriched in rh 4 ru ir and pd 5 and pt 30 relative to the indigenous level of target sediments this suggests the presence of a projectile derived component in their constitution single composition oxidic bombs pure hematite and pure silica predominate in this occurrence indicating that a mechanism of segregation has operated in the ejected melt volumes

influence of the monsoon trough on westward propagating tropical waves over the western north pacific part i observations abstractthe present study investigates the possible linkage between the monsoon trough and the interannual variability of the activity of westward propagating tropical waves wtw over the western north pacific wnp during july november for the period 1979 2007 it is shown that the interannual variability of wtw activity is closely related to the location of the monsoon trough during the years when the enhanced weakened monsoon trough extends eastward retreats westward the lower tropospheric wtw activity is above below normal within the southeastern quadrant of the wnp furthermore this study evaluates different wave structures and dynamics of two types of wtws equatorial rossby er waves and mixed rossby gravity mrg tropical depression td type waves in strong monsoon trough s mt and weak monsoon trough w mt years over the wnp there is a significant change in the three dimensional structure as those waves propagate westward to the east of the monsoon trough for the td mrg waves an

asteroids and early precambrian crustal evolution abstract major enigmas arising from the archaean crustal record are capable of resolution in terms of the combined role of episodic mega impacts and of long term mantle processes the terrestrial impact record suggests that for very large impact structures the degree of preservation of proximal deformation effects decreases with the increase in the magnitude of the associated thermal effects a consequence of extensive recrystallization and melting this focuses attention on thermal igneous and metamorphic peaks as possible clues of impact events isotopic age studies define principal thermal events about 3 5 3 0 and 2 7 0 1 gyr and less well defined episodes succeeded by protracted thermal fluctuations in infracrustal high grade metamorphic zones the bulk of the igneous activity associated with these episodes took place over relatively short time spans of c 20 30 106 years interpretations of these episodes in terms of internal dynamics of the earth are inconsistent with the thermal behavior of silicate rheologies in a continuously convecting mantle regime a triggering of these episodes by the mantle rebound response to intermittent extra terrestrial asteroid impacts is considered on the basis of 1 identification of major impacts from distal ejecta horizons marked by iridium anomalies and impact earthquake triggered diamictite breccia and olistostromes 2 the relationships between microtektite horizons and volcanic activity 3 geochemical and experimental evidence for mantle upwelling from the transition zone and catastrophic adiabatic melting required to generate peridotitic komatiites episodic differentiation accretion growth of sial consequent on these events is capable of resolving the volume problem which arises from comparisons between modern continental crust and sial produced by continuous two stage mantle melting processes taking the temporal decline in heat flow into account impact shock effects on the archaean crust have been largely obscured by 1 outpouring of voluminous basic ultrabasic lavas inundating shock deformed crust and extending beyond the perimeters of impact excavated basins 2 gravity subsidence and downfaulting of terrestrial mare accounting for the anatexis of sub greenstones basement 3 extensive shearing and recrystallization of impact structures breccias and mineral deformation features beneath impact excavated basins relics of which may be retained in structural windows in high grade metamorphic terrains isostatic subsidence and anatexis of thick mare type piles and underlying impacted crust resulted in intracrustal comagmatic plutonic and volcanic suites within periods in the order of15 30 106 years as controlled by post impact mantle convection cooling subsequent isostatic updoming of remobilized basement gneiss terrains and the rise of their anatectic products along major normal shears bearing an analogy to metamorphic core complexes resulted in the multiple gneiss granite complexes amidst greenstone dominated terrains recurrent post tectonic thermal fluctuations and magmatic activity reflect a long term existence of anomalous mantle regions beneath original mega impact sites and thermal perturbations related to distal impacts a broad age zonation in some archaean shields suggests lateral migration and terrane accretion in a convection driven plate tectonic regime

a global view of equatorial waves and tropical cyclogenesis abstractthis study investigates the number of tropical cyclone formations that can be attributed to the enhanced convection from equatorial waves within each basin tropical depression td type disturbances i e easterly waves were the primary tropical cyclone precursors over the northern hemisphere basins particularly the eastern north pacific and the atlantic in the southern hemisphere however the number of storms attributed to td type disturbances and equatorial rossby waves were roughly equivalent equatorward of 20 n tropical cyclones formed without any equatorial wave precursor most often over the eastern north pacific and least often over the western north pacific the madden julian oscillation mjo was an important tropical cyclone precursor over the north indian south indian and western north pacific basins the mjo also affected tropical cyclogenesis by modulating the amplitudes of higher frequency waves each wave type reached the attribution threshold 1 5 times more often and tropi

factors for interannual variations of september october rainfall in hainan china the present study investigates the year to year variations of september october rainfall in hainan china for the period 1965 2010 the dominant circulation anomalies feature a cyclone an anticyclone over the indochina peninsula and northern south china sea an anticyclone a cyclone over subtropical western north pacific and lower level convergence divergence over the maritime continent in the wet dry years these circulation anomalies are responses to an east west sea surface temperature sst anomaly pattern withnegative positive sst anomaliesin theequatorialcentralpacificandpositive negative sstanomalies around the maritime continent in the wet dry years although the sst anomaly pattern is similar but with opposite anomaly the sst signal in the equatorial central pacific is more significant in the dry years than in the wet years this difference indicates a larger case to case variability in the wet years than in the dry years thelargevariabilityinthewetyearsisattributedtocontributionsoftropicalcyclones tcs andintraseasonal oscillations isos there are more tcs impinging on hainan and the tc tracks are closer to the island in the wet years than in the dry years the rainfall shows large intraseasonal variations with periods of 10 20 and 30 60 days during september october in the wet years the 10 20 day iso originates from the maritime continent whereas the 30 60 day iso develops over tropical indian ocean and propagates northeastward to northern south china sea in contrast the iso signal is much weaker in the dry years

interannual variability of the intraseasonal oscillation and its impact on the summertime wave patterns and tropical cyclones over the western north pacific abstractin this study intraseasonal oscillations isos and submonthly wave patterns were separated into maximal variance maxv and minimal variance minv years on the basis of iso variance from july to october the mean state 850 hpa streamfunction for submonthly cases indicated that in the minv years tropical cyclones tcs formed near areas southeast of those in the maxv years isos propagated northward in the maxv years whereas a weaker westward propagating tendency was observed in the minv years track analysis of the centers of the submonthly cyclonic anomalies suggested that the background flow dictated the propagation routes of the easterly cyclonic anomalies in the maxv years however the propagation routes of the westerly cyclonic anomalies were barely affected by the background flow further analysis of the iso mean flow patterns showed that in the maxv years the propagation routes of the westerly cyclonic anomalies were more likely controlled by the anomalous easterly flow generated by

northwestward propagation of the intraseasonal oscillation in the western north pacific during the boreal summer structure and mechanism abstract the convection of the intraseasonal timescale in the western north pacific during the boreal summer tends to propagate northwestward in the philippine sea to near 20 n and then continues propagating westward the formation of enhanced convection in the western north pacific is a result of the merging of a convective system moving eastward along the equator and a westward propagating low level convergence anomaly which is located to the east of a vortex in the subtropics a positive feedback between the anomalous circulation and convection leads to a rapid enhancement of the system the strengthened southwesterly associated with the vortex enhances evaporation over the oceans e g the eastern indian ocean the bay of bengal and the south china sea and transports moisture northeastward the moisture converges at the northwestern corner of the convection and results in a potentially unstable atmosphere the result is the northwestward propagation of the coupled circulation convection system in

relationship of boreal summer 10 20 day and 30 60 day intraseasonal oscillation intensity over the tropical western north pacific to tropical indo pacific sst the present study contrasts interannual variations in the intensity of boreal summer 10 20 day and 30 60 day intraseasonal oscillations isos over the tropical western north pacific and their factors a pronounced difference is found in the relationship of the two isos to el nino southern oscillation the 10 20 day iso intensity is enhanced during el nino developing summer whereas the 30 60 day iso intensity is enhanced during la nina decaying summer the above different relationship is interpreted as follows the equatorial central and eastern pacific sst anomalies modify vertical wind shear lower level moisture and vertical motion in a southeast northwest oriented band from the equatorial western pacific to the tropical western north pacific where the 10 20 day isos originate and propagate these background field changes modulate the amplitude of 10 20 day isos preceding equatorial central and eastern pacific sst anomalies induce sst anomalies in the north indian ocean in summer which in turn modify vertical wind shear and vertical motion over the tropical western north pacific the modified background fields influence the amplitude of the 30 60 day isos when they reach the tropical western north pacific from the equatorial region a feedback of iso intensity on local sst change is identified in the tropical western north pacific likely due to a net effect of isos on surface heat flux anomalies this feedback is more prominent from the 10 20 day than the 30 60 day iso intensity change

ejecta layer at the cretaceous tertiary boundary bass river new jersey ocean drilling program leg 174ax a continuously cored borehole drilled at bass river new jersey recovered a cretaceous tertiary k t succession with a 6 cm thick spherule layer immediately above the boundary below the spherule layer the cretaceous glauconitic clay is extensively burrowed and contains the uppermost maastrichtian micula prinsii calcareous nannofossil zone spherical impressions of spherules at the top of the cretaceous indicate nearly instantaneous deposition of ejecta from the chicxulub impact the thickest ejecta layer shows clearly that a single impact occurred precisely at k t boundary time above the spherule layer the glauconitic clay contains the planktonic foraminiferal p0 and p alpha zones indicating 1 a complete k t succession and 2 continuous deposition interrupted only by fallout of the ejecta layer clay clasts within a 6 cm interval above the spherule layer contain cretaceous microfossils and may be rip up clasts from a tsunami or possibly a megastorm event extinction of the cretaceous planktonic foraminifers and burrowing organisms occurs abruptly at the k t boundary thus the bass river k t succession unequivocally links the chicxulub bolide impact to the mass extinctions at the end of the mesozoic

relationship between summertime intraseasonal oscillations and submonthly wave patterns under meridional periodic fluctuations abstractin this study submonthly wave patterns under the periodically fluctuating japan south china sea jscs pattern were separated into intraseasonal oscillation iso westerly and easterly phases the composite results showed that the wave patterns in the westerly jscs high and low phases were more effectively organized and situated in a more intense monsoon trough than their counterparts in the easterly phase tropical cyclones tcs tended to occur over cyclonic systems of the wave patterns where minimal vertical shear axes were also located more tcs formed in the westerly jscs phases near areas where maximal moisture convergence was located taiwan experienced heavier rainfall during the westerly jscs phases because the iso enhanced the monsoon troughs for the cyclonic system of the wave pattern to develop near taiwan in the westerly jscs high phase additionally in the westerly jscs low phase a stronger southeasterly mean flow generated by the iso steered the wave pattern and tcs farther west

mixed rossby gravity waves and western pacific tropical cyclogenesis part i synoptic evolution abstract a large amplitude mixed rossby gravity wave packet is identified in the western pacific using 6 10 day bandpass filtered winds individual disturbances of 2300 3000 km wavelength propagated westward as the packet moved slowly eastward the packet first appeared and subsequently amplified within a region of active convection associated with the madden julian oscillation mjo which was isolated by low pass filtered outgoing longwave radiation the packet lasted about 5 weeks then rapidly dispersed as the active mjo moved away from it to the east west of 150 e individual disturbances within the packet turned northwestward away from the equator indicating an apparent transition from mixed rossby gravity waves to off equatorial tropical depression td type disturbances cyclones filled with cloud and anticyclones cleared during the transition nevertheless convective structure consistent with mixed rossby gravity waves remained outside the circulation centers and three tropical cyclones for

shock metamorphism of quartz in nature and experiment ii significance in geoscience the occurrence of shock metamorphosed quartz is the most common petrographic criterion for the identification of terrestrial impact structures and lithologies its utility is due to its almost ubiquitous occurrence in terrestrial rocks its overall stability and the fact that a variety of shock metamorphic effects occurring over a range of shock pressures have been well documented these shock effects have been generally duplicated in shock recovery experiments and thus serve as shock pressure barometers after reviewing the general character of shock effects in quartz the differences between experimental and natural shock events and their potential effects on the shock metamorphism of quartz are explored the short pulse lengths in experiments may account for the difficulty in synthesizing the high pressure polymorphs coesite and stishovite compared to natural occurrences in addition post shock thermal effects are possible in natural events which can affect shock altered physical properties such as refractive index and cause annealing of shock damage and recrystallization the orientations of planar microstructures however are unaffected by post impact thermal events except if quartz is recrystallized and provide the best natural shock barometer in terms of utility and occurrence the nature of planar microstructures particularly planar deformation features pdfs is discussed in some detail and a scheme of variations in orientations with shock pressure is provided the effect of post impact events on pdfs is generally limited to annealing of the original glass lamellae to produce decorated pdfs resulting from the exsolution of dissolved water during recrystallization basal 0001 pdfs differ from other pdf orientations in that they are multiple mechanical brazil twins which are difficult to detect if not partially annealed and decorated the occurrence and significance of shock metamorphosed quartz and its other phases namely coesite stishovite diaplectic glass and lechatelierite are discussed for terrestrial impact structures in both crystalline non porous and sedimentary porous targets the bulk of past studies have dealt with crystalline targets where variations in recorded shock pressure in quartz have been used to constrain aspects of the cratering process and to estimate crater dimensions at eroded structures in sedimentary targets the effect of pore space results in an inhomogeneous distribution in recorded shock pressure and temperature which requires a different classification scheme for the variation of recorded shock compared to that in crystalline targets this is discussed along with examples of variations in the relative abundances of planar microstructures and their orientations which are attributed to textural variations in sedimentary target rocks examples of the shock metamorphism of quartz in distal ejecta such as at the k t boundary and from nuclear explosions are illustrated and are equivalent to that of known impact structures except with respect to characteristics that are due to long term post shock thermal effects finally the differences between the deformation and phase transformation of quartz by shock and by endogenic tectonic and volcanic processes are discussed we confirm previous conclusions that they are completely dissimilar in character due to the vastly different physical conditions and time scales typical for shock events compared to tectonic and volcanic events well characterized and documented shock effects in quartz are unequivocal indicators of impact in the natural environment

the terrestrial impact cratering record approximately 130 terrestrial hypervelocity impact craters are currently known due to variations in preservation and in geologic knowledge this sample is biased towards young x 20 km craters on the cratons of australia europe including the former u s s r and north america the rate of discovery of new craters is 3 5 craters per year although modified by erosion terrestrial impact craters exhibit the range of morphologies observed for craters on other terrestrial planetary bodies such as the moon terrestrial craters provide essential ground truth data on the geologic effects of impact and the subsurface structure of impact craters which can be used to constrain interpretations of lunar samples and models of crater formation due to erosion and its effects on form terrestrial craters are recognized primarily by the occurrence of shock metamorphic effects these include shatter cones microscopic planar deformation features solid state and fusion glasses high pressure polymorphs and whole rock melting and vaporization shock recovery experiments indicate that these features occur over shock pressures of 5 gpa to x 100 gpa terrestrial craters have a set of geophysical characteristics which are largely the result of the passage of a shock wave and impact induced fracturing they include gravity and magnetic lows and reductions in seismic velocity the gravity anomalies are seldom greater than 30 mgal due to the limiting effects of lithostatic pressure on fracturing at large complex craters the gravity signature may include a central relative gravity high due to uplift and short wavelength central magnetic anomalies due to a variety of processes much current work is focused on the effects of impact on earth evolution previous work on shock metamorphism and the contamination of impact melt rocks by meteoritic siderophile elements provides a basis for the interpretation of the physical and chemical evidence from cretaceous tertiary boundary sites as resulting from a major impact suggestions that other biological boundaries in the stratigraphie record are due to periodic impacts are not supported by time series analysis of the terrestrial cratering record by analogy with the lunar record and modelling of the effects of very large impacts it has been proposed that biological and atmospheric evolution of the earth could not stabilize before the end of the late heavy bombardment 3 8 ga ago the present terrestrial cratering rate is 5 4 2 7 10 15 km 2a 1 for a diameter 20 km this represents a local threat on historic time scales on a global scale a major impact sufficient to cripple human civilization severely will occur on time scales of 106 a

quasi periodic behavior of the pacific japan pattern affecting propagation routes of summertime wave patterns and the associated tropical cyclone tracks over the western north pacific abstractthis study introduces a modified pacific japan pj index that exhibits a substantial periodicity of 5 16 days in the east asian summer monsoon region the quasi periodic fluctuations of the pj index can indicate changes in the large scale circulation systems in the pj high phase the wave pattern propagates northwestward from the western north pacific tropics to an area near northern luzon and is then forced to move westward because of a stationary anomalous high pressure system over southern japan the tropical cyclones tcs associated with the anomalous low pressure systems tend to follow a straight moving propagation route through the northern south china sea the anomalous cyclonic flow causes heavy rainfall in eastern taiwan however in the pj low phase the wave pattern and tcs follow a recurving propagation route toward higher latitudes the circulation pattern typically brings heavy rainfall to northern taiwan in the pj low phase therefore wave patterns under the influence of the qu

insights into the morphology geometry and post impact erosion of the araguainha peak ring structure central brazil the 40 km wide araguainha structure is the largest and best exposed complex impact crater in south america it was excavated in flat lying sediments of the intracratonic parana basin where target rocks are well exposed and have remained undeformed since the impact event ca 245 ma despite the excellent state of preservation and exposure information available on the target rock stratigraphy post impact erosion and morphology of the structure is limited our combined field observations and remote sensing analysis demonstrate that araguainha preserves all features of a shallowly eroded peak ring crater the interior of the structure exposes a central peak surrounded by a 5 km wide annular basin and two main ring features 10 12 and 14 18 km from the center analysis of the pre impact stratigraphy present morphology and crater dimensions indicates that excavation related to the transient cavity formation was extensive in the annular basin but minimal to nonexistent beyond the inner ring feature the formation of the inner ring feature can be reconciled with compressional stresses during outward collapse of the central uplift and inward slumping of the crater walls regional stratigraphic data combined with field observations indicate two periods of post impact erosion associated with exhumation of the parana basin we estimate that 250 350 m of fallback deposits and target rocks have been removed by erosion erosion also accounted for removal of the proximal ejecta immediately outside the rim of the structure in contrast to previous suggestions that the impact took place in a shallow marine environment our observations are more consistent with an extremely shallow brackish to freshwater lacustrine environment with little effect on the developing impact crater

origin of the summertime synoptic scale wave train in the western north pacific abstract the origin of the summertime synoptic wave train in the western north pacific is investigated with a multilevel nonlinear baroclinic model a realistic three dimensional summer mean state is specified and eigenvectors are calculated by introducing small perturbation initially to the model numerical experiments indicate that the origin of the synoptic wave train may arise from instability of the summer mean flow in the presence of a convection frictional convergence cfc feedback in the lack of the cfc feedback the summer mean flow supports only a least damped mode characterized by a northwest southeast oriented wave train pattern with a zonal wavelength of 2500 km in the presence of both the realistic summer mean flow and the cfc feedback the model reproduces a fast growing mode whose structure and propagation characters are similar to the observed sensitivity experiments with different initial perturbation patterns indicate that the model solution is not sensitive to initial conditions

linking shock textures revealed by bse cl and ebsd with u pb data la icp ms and sims from zircon from the araguainha impact structure brazil

impact of interannually varying background circulation on summertime wave patterns and tropical cyclone tracks in the western north pacific this study analyzed summertime wave patterns in the western north pacific by separating them into those during el nino en and la nina ln years for 1979 2015 the background flow revealed that in the en years the subtropical high was weaker and the east asian summer monsoon trough was deeper and extended farther southeastward the composite results indicated that in the en years tropical cyclone tc tracks were more solid and stably associated with wave pattern propagation routes because the circulation anomalies were significantly stronger however in the ln years when the wave patterns were weak under the shorter and less organized monsoon trough due to the enhanced subtropical high the tc tracks and cyclonic anomalies were irregular and sporadic further background flow analyses indicated that the en circulation favored the development of the monsoon trough and east west expansion and contraction of the subtropical ridge whereas the stronger subtropical ridge dominated most western north pacific areas in the ln years therefore the monsoon trough was weaker in the ln years and induced recurving tcs to take more scattered routes near taiwan and china s east coast therefore taiwan experienced more rainfall during recurving tc periods in the ln years than in the en years for the straight moving tcs passing through taiwan rainfall was concentrated over southern taiwan in the en years but more evenly distributed in the ln years thus background flow changes strongly affect wave patterns and tcs

possible linkage between the monsoon trough variability and the tropical cyclone activity over the western north pacific abstractthe present study investigates the influence of the monsoon trough mt on the interannual variability of tropical cyclone tc activity over the western north pacific during july november for the period 1979 2007 it is shown that the tc activity is closely related to the mt location during the years when the mt extends eastward retreats westward more less tcs form within the southeastern quadrant of the western north pacific such a relationship can be explained by the changes in large scale environmental factors associated with the movement of the mt an eastward extension of the mt coincides with warmed ocean surface enhanced convection increased relative humidity in the lower and midtroposphere reduced vertical shear of zonal wind intensified upper level divergence and low level anomalous cyclonic vorticity over the southeast quadrant of the western north pacific these conditions associated with the eastern extension of the mt are favorable for tc genesis while those associated w

enso phase dependent td and mrg wave activity in the western north pacific the three dimensional structure and evolution characteristics of tropical depression td and mixed rossby gravity wave mrg type disturbances in the tropical western north pacific during el nino and la nina summers are investigated based on observational and reanalysis data a clear mrg to td transition was observed during el nino summers while such a transition is unclear during la nina summers the vertical structure of the td mrg waves appears equivalent barotropic during el nino but becomes tilted eastward with height during la nina the diagnosis of barotropic energy conversion shows that both the rotational and divergent components of the background flow change associated with e1 nino southern oscillation enso are responsible for energy conversion from the mean flow to the td mrg perturbations a further examination of the pure mrg mode shows that its intensity does not vary between el nino and la nina while its phase speed does a faster slower westward propagation speed during la nina el nina is attributed to enhanced reduced mean easterlies in the western equatorial pacific the heating associated with the mrg wave appears more anti symmetric during la nina than during el nino in contrast to the mrg waves the amplitude of the td waves depends greatly on the enso phase the enhanced suppressed td disturbances during el nino la nina is attributed to greater less barotropic energy conversion associated with the background flow change the vertical structure of the td waves appears quasi barotropic in the geopotential height field but baroclinic in the divergence field

three dimensional evaluation of fabric evolution and metamorphic reaction progress in polycyclic and polymetamorphic terrains a case from the central italian alps

recognition of eroded astroblemes abstract the morphology of lunar craters degrades only slowly by the formation of new impacts and their ejecta it is not the same on earth because of weathering and tectonism generally the typical crater topography has disappeared and the term impact structure or astrobleme is applied on planetary surfaces as on the moon two classes of craters are recognized based on their depth to diameter ratio simple bowl shaped and complex readjusted flat bottomed craters with a sharp transition from simple to complex pike 1977 1980 on earth small simple craters retain some of their typical rimmed pit morphology because they are generally recent many are associated with meteorite fragments large impact structures or astroblemes in addition to their specific circular features are recognized as such only by the presence of shock metamorphism criteria such as dense minerals coesite stishovite diaplectic minerals and glass maskelynite planar deformation features in minerals principaly in quartz and feldspars and shattercones which are commonly used these criteria are abundant in allochthonous breccia particularly in fall back breccia among which there are glass fragments such as tectite or microtectite glass spherules shards droplets rods etc but on the floor of the astroblemes the criteria of shock metamorphism are restricted to the central part which is often covered or eroded using the measurements of nine astroblemes visited a scaling model is presented for two types of craters readjusted along listric slip surfaces a well readjusted model based on data from charlevoix and manicouagan canada and a partly readjusted model based on data from the ries germany both possess a central uplift and a ring graben there is also on the floor of the astrobleme a specific type of breccia mylolisthenite and pseudotachylite associated with the displacement along the autochthonous masses of rocks in very large impact structures the shock metamorphism is able to melt a part of the floor grieve and cintala 1992 the heat resulting from the superheated impact melt destroys a part of the shock metamorphism criteria

iso modulation on the submonthly wave pattern and recurving tropical cyclones in the tropical western north pacific abstract this study demonstrates the multiscale nature from synoptic to intraseasonal time scales of the atmospheric flow in the tropical western north pacific the multiscale features include intraseasonal oscillations iso northwestward propagating submonthly wave patterns and recurving tropical cyclones tcs in the iso westerly phase the wave pattern was better organized and the tcs were clustered near the cyclonic circulation of the wave pattern during the genesis development and propagation on the other hand the wave pattern and tcs were weak and poorly organized in the iso easterly phase the distinct characteristics between the westerly and easterly phases could be attributed to the iso modulation on the monsoon trough and the subtropical anticyclonic ridge the iso in the westerly phase provided a favorable background e g enhanced monsoon trough and moisture confluent zone for the wave tc pattern development while the iso in the easterly phase provided a less favorable environment

influence of the monsoon trough on westward propagating tropical waves over the western north pacific part ii energetics and numerical experiments abstractpart i of this study examined the modulation of the monsoon trough mt on tropical depression td type mixed rossby gravity mrg and equatorial rossby er waves over the western north pacific based on observations this part investigates the interaction of these waves with the mt through a diagnostics of energy conversion that separates the effect of the mt on td mrg and er waves it is found that the barotropic conversion associated with the mt is the most important mechanism for the growth of eddy energy in both td mrg and er waves the large rotational flows help to maintain the rapid growth and tilted horizontal structure of the lower tropospheric waves through a positive feedback between the wave growth and horizontal structure the baroclinic conversion process associated with the mt contributes a smaller part for td mrg waves but is of importance comparable to barotropic conversion for er waves as it can produce the tilted vertical structure the growth rates of the waves are much larg

contributions of tropical waves to tropical cyclone genesis over the western north pacific the present study investigates the relationship between the tropical waves and the tropical cyclone tc genesis over the western north pacific wnp for the period 1979 2011 five wave types are considered in this study it is shown that the tc genesis is strongly related to enhanced low level vorticity and convection of tropical waves and significant difference are detected in the tc modulation by dynamic and thermodynamic components of the waves more tcs tend to form in regions of waves with overlapping cyclonic vorticity and active convection about 83 2 of tcs form within active phase of tropical waves mainly in a single wave and two coexisting waves each wave type related genesis accounts for about 30 of all tc geneses except for the kelvin waves that account for only 25 2 of tc geneses the number of each wave type related tc genesis consistently varies seasonally with peak in the tc season july november which is attributed to a combined effect of active wave probability and intensity change the interannual variation in the tc genesis is well reproduced by the tropical wave related tc genesis especially in the region east of 150 e an eastward extension of the enhanced monsoon trough coincides with increased tropical wave activity by accelerated wave mean flow interaction

northwestward propagating wave patterns over the tropical western north pacific during summer abstract the possible relationship between northwestward propagating wave disturbances and tropical cyclones over the tropical western north pacific during summer is studied using data assimilated by the navy s global model during may september 1989 91 a multiple set canonical correlation mcc analysis is applied to the 850 hpa meridional v component over a core domain covering the western pacific the analysis seeks the maximal geometrically averaged correlation between 12 consecutive twice daily fields two mcc components with a 90 phase difference and comparable variances that combine to nearly one third of the total variance describe the northwestward propagating pattern with a period near 8 9 days upstream of this steady northwestward propagating pattern there is a weaker westward propagation along 5 n that may be traced back to 170 e the surface pressure cell advancing east of the philippines is consistent with low level winds for a circulation in gradient wind balance it has a zonal wave

asymmetric modulation of western north pacific cyclogenesis by the madden julian oscillation under enso conditions abstractthe present study investigates the modulation by the madden julian oscillation mjo and the impact of the el nino southern oscillation enso on tropical cyclone tc genesis in the western north pacific wnp during the period 1975 2010 results reveal a stronger modulation of cyclogenesis by the mjo during el nino years while the modulations in neutral and la nina years are comparable to each other the asymmetric background modification by enso is found to greatly affect the extent of mjo modulation under different enso conditions first mjo activity is intensified and extends farther eastward during el nino years instead of being confined west of 150 e as in neutral and la nina periods thus the influence of mjo is stronger and more zonally widespread in el nino years causing significant differences in cyclogenesis parameters in most parts of the wnp in el nino years cyclogenesis is further enhanced in the active phase due to synchronization of mjo signals with favorable background enso

use of platinum group elements for impactor identification terrestrial impact craters and cretaceous tertiary boundary abstract this study presents the abundances of ru ir pt pd rh and au platinum group elements pge in the ejecta layer at the cretaceous tertiary boundary and melt rocks from east clearwater lake brent new quebec and lake wanapitei impact craters all believed to have been formed by the impact of chondritic projectiles the objective was to evaluate the pure application of pge interelement ratios e g ru ir for impactor identification to compare the utility of both melt rocks and ejecta deposits for this purpose and to expand the pge database for these craters the similarity of pge interelement ratios within the chondrite and iron meteorite groups precludes their use in the fine classification of impactors of this composition introduction of indigenous pge from country rock may contaminate the original meteoritic signature in addition the extent of pge fractionation during impact and melt sheet cooling and of post sedimentary pge remobilization must be evaluated in each case for east clearwater the pge chondrite normalized plot is flat indicating a chondritic impactor based on ru ir and cr ir ratios a cl or l chondrite is most likely however variation of ratios with depth in the core makes any fine classification of the projectile tenuous for the brent and new quebec craters the flat chondrite normalized pge plot indicates a chondritic impactor but finer classification is precluded by possible post syn depositional pge fractionation at lake wanapitei ni cr and cr ir ratios indicate a ll chondrite impactor wolf et al 1980 but sparse pge data for this chondrite type does not allow further classification of the projectile a flat chondrite normalized pge plot indicates a chondritic rather than an iron impactor at lake wanapitei the global ejecta layer at the cretaceous tertiary boundary has a chondritic pge signature but only when the integrated flux of pge on a global scale is considered individual sites may not show chondritic ratios due to differential pge remobilization resulting from local differences in depositional environment continental vs marine and to vaporization and or condensation pge fractionation occurring during impact the results for melt rocks and the k t ejecta deposit indicate that pge can be used for impactor identification but primarily in combination with other siderophile chalcophile meteoritic elements and their ratios

the role of tropical waves in tropical cyclogenesis abstract this paper analyzes relationships between tropical wave activity and tropical cyclogenesis in all of the earth s major tropical cyclone basins twenty nine years of outgoing longwave radiation data and global reanalysis winds are filtered and analyzed to determine statistical relationships between wave activity in each basin and the corresponding cyclogenesis composite analyses relative to the storm genesis locations show the structures of the waves and their preferred phase relationships with genesis five wave types are examined in this study including mixed rossby gravity waves tropical depression type or easterly waves equatorial rossby waves kelvin waves and the madden julian oscillation the latter is not one of the classical tropical wave types but is a wavelike phenomenon known to have a strong impact on tropical cyclogenesis tropical cyclone formation is strongly related to enhanced activity in all of the wave filter bands except for the kelvin band in each basin the structure o