ordovician faunas of burgess shale type the renowned soft bodied faunas of the cambrian period which include the burgess shale disappear from the fossil record in the late middle cambrian after which the palaeozoic fauna dominates the disappearance of faunas of burgess shale type curtails the stratigraphic record of a number of iconic cambrian taxa one possible explanation for this loss is a major extinction but more probably it reflects the absence of preservation of similar soft bodied faunas in later periods here we report the discovery of numerous diverse soft bodied assemblages in the lower and upper fezouata formations lower ordovician of morocco which include a range of remarkable stem group morphologies normally considered characteristic of the cambrian it is clear that biotas of burgess shale type persisted after the cambrian and are preserved where suitable facies occur the fezouata biota provides a link between the burgess shale communities and the early stages of the great ordovician biodiversification event

influence of dissolved oxygen on secular patterns of marine microbial carbonate abundance during the past 490 myr abstract shallow marine benthic microbial carbonate sediments declined episodically during the phanerozoic they were relatively abundant during the cambrian mid ordovician late devonian mississippian mid permian mid late triassic and to a lesser degree in the late jurassic early cretaceous they were least abundant when invertebrate especially reef diversity was relatively high in the mid ordovician late devonian early mid permian late triassic mid late jurassic and early cretaceous to present day these intervals of microbial carbonate abundance and invertebrate diversity generally alternate transitionally with one another but lows and periods of overlap also occur lows when benthic microbial carbonate abundance and invertebrate diversity both declined are apparent during the pennsylvanian and early mid jurassic overlaps when microbial carbonates and invertebrates were both relatively common occur in the early cambrian and late jurassic overall these patterns broadly support suggestions that microbial carbonate abundance declined as calcified invertebrates increased to further explore these relationships we compared microbial carbonate abundance and invertebrate diversity with estimates of changes in sea surface temperature and marine dissolved oxygen for the past 490 myr this analysis suggests that invertebrate diversity varied directly with oxygen availability invertebrate diversity was low when dissolved oxygen was low in the early ordovician late devonian early triassic and early mid jurassic it appears that by reducing invertebrate diversity low oxygen levels favored microbial carbonates at the same time low oxygen levels likely stimulated anaerobic metabolisms favoring carbonate precipitation this study suggests that dissolved oxygen was a major control on secular patterns of marine microbial carbonate abundance during the phanerozoic together with marine temperature and carbonate saturation state

mesovortices within the 8 may 2009 bow echo over the central united states analyses of the characteristics and evolution based on doppler radar observations and a high resolution model simulation abstracta derecho producing bow echo event over the central united states on 8 may 2009 is analyzed based on radar observations and a successful real data wrf simulation at 0 8 km grid spacing emphasis is placed on documenting the existence evolution and characteristics of low level mesovortices mvs that form along the leading edge of the bowing system the genesis of near surface high winds within the system is also investigated significant mvs are detected from the radar radial velocity using a linear least squares derivatives llsd method and from the model simulation based on calculated vorticity both the observed and simulated bow echo mvs predominantly form north of the bow apex mvs that develop on the southern bow tend to be weaker and shorter lived than their northern counterparts vortex mergers occur between mvs during their forward movement which causes redevelopment of some mvs in the decaying stage of the bow echo mvs located at or near the bow apex are found to persist for a not

re dating changyang cave in hubei province southern china abstract owing to the unearthed left maxillary fragment and left lower premolar fossil in 1950s changyang cave was regarded as an important hominin site where middle pleistocene hominins are first discovered in southern china however only two bovine tooth fossils have been dated to 194 24 20 ka and 196 20 17 ka by u series dating since 1980s in this work the stratigraphy of changyang cave was re investigated by applying u th dating method for eight new tooth fossils obtained from fossil layer and two carbonate crystal samples from clay cement on the wall of this cave new dating results showed that the ages of the two carbonate crystals are 256 and 233 ka respectively and those of the eight tooth fossils are concentrated from 193 ka to 143 ka considering the ages of the two previous fossils new carbonate crystals and new eight tooth fossils we suggested that the age range of changyang hominin is between 196 and 143 ka

early ordovician reef construction in anhui province south china a geobiological transition from microbial to metazoan dominant reefs the lower ordovician records a transition from microbial to metazoan dominant reefs immediately prior to the great ordovician biodiversification event the hunghuayuan formation late tremadocian early floian of the jianxin section in anhui province south china includes well preserved reefs which consist of a combination of microbial boundstones and microbial lithistid sponge receptaculitid boundstones the microbial boundstones are characteristically made up of nodular or columnar stromatolites produced by an irregular alternation of girvanella rich layers and thick micrite layers in which the filamentous calcimicrobe girvanella and bioclasts occur sporadically microbial biofilms including the filamentous microbes may have trapped and bound lime mud and or precipitated micrite during their growth and metabolic activities these activities contemporaneously contributed to substrate stabilisation encrustation and the construction of microbialite frameworks stromatolites in contrast the microbial lithistid sponge receptaculitid boundstones are characterised by more micritic constituents than skeletal reef building constituents thin and or domal crusts produced by peloid and dense micrite together with various proportions of girvanella occur upon bioclastic sediments and reef building skeletal organisms these micritic crusts with girvanella therefore played roles as binders and stabilisers and as consolidators by encrusting reef building skeletal organisms in the boundstones it is remarkable that the degradation of lithistid sponges due to microbial decay produced micrite in the sponge bodies as a result lithistid sponges played an apparently inconspicuous but potentially significant role as micrite producers as well as automicrite framework constructors these lower ordovician reefs in which microbialites e g stromatolites dominate but coexist with metazoans e g sponges were widespread at the time they provide excellent examples for understanding reefal palaeoecology during the transition from microbe dominant reefs to reefs enriched in metazoans

observations of a squall line and its near environment using high frequency rawinsonde launches during vortex2 abstract rawinsonde data were collected before and during passage of a squall line in oklahoma on 15 may 2009 during the second verification of the origins of rotation in tornadoes experiment vortex2 nine soundings were released within 3 h allowing for unprecedented analysis of the squall line s internal structure and nearby environment four soundings were released in the prestorm environment and they document the following features low level cooling associated with the reduction of solar isolation by a cirrus anvil abrupt warming 1 5 k in 30 min above the boundary layer which is probably attributable to a gravity wave increases in both low level and deep layer vertical wind shear within 100 km of the squall line and evidence of ascent extending at least 75 km ahead of the squall line the next sounding was released 5 km ahead of the squall line s gust front it documented a moist absolutely unstable layer within a 2 km deep layer of ascent with vertical air velocity of approximately 6 m s 1

structure of a midlatitude squall line formed in strong unidirectional shear abstract data from five doppler radars the surface mesonet aircraft and rawinsondes from the cooperative convective precipitation experiment ccope are used to document the structure and evolution of a squall line with unusually persistent cells and an anvil that spreads downwind in strong upper level westerlies the environmental sounding showed linear shear of 4 m s 1 km 1 through the troposphere a convective available potential energy of 600 m2 s 2 and a convective richardson number of 10 based on the wind in the lowest 6 km the orientation of the squall line comprised of high reflectivity centers spaced 20 40 km apart changed with time initially the squall line axis was normal to the environmental shear but with time it became parallel to the shear vector as the northeastern portion of the subcloud cold dome merged with cold air generated by individual storms that had formed ahead of the line the intensity of the cells within the squads line diminished as its axis became more parallel

temporal variation in calcification in marine cyanobacteria periods of widespread abundance of calcified cyanobacteria in marine environments are here termed cyanobacterial calcification episodes cces intense such episodes occurred in the cambrian early ordovician late devonian and mid late triassic mild episodes occurred during the early carboniferous and jurassic early cretaceous possible episodes during parts of the silurian and permian await confirmation cyanobacterial calcification is not obligate but is dependent upon environmental factors favouring carbonate precipitation cyanobacterial calcification episodes are therefore interpreted as reflecting periods of increased marine carbonate precipitation this is supported by the general abundance of marine carbonate cements and oolites during cyanobacterial calcification episodes cyanobacterial calcification episodes correspond with phanerozoic periods for which elevated global temperatures have been inferred they do not appear to correlate closely with inferred changes in aragonite calcite facilitation the sandberg curve and p co2 through time it is concluded that variations in the precipitation rates of abiotic and quasi abiotic marine carbonates through time have been controlled primarily by temperature the mineralogy of these precipitates appears instead to have been mainly influenced by p co2 and the mg ca ratio also linked to sea level through plate tectonic processes thus the controls on rate and mineralogy of precipitation were independent of one another

the response of simulated nocturnal convective systems to a developing low level jet some recent numerical experiments have examined the dynamics of initially surface based squall lines that encounter an increasingly stable boundary layer akin to what occurs with the onset of nocturnal cooling the present study builds on that work by investigating the added effect of a developing nocturnal low level jet llj on the convective scale dynamics of a simulated squall line the characteristics of the simulated llj atop a simulated stable boundary layer are based on past climatological studies of the llj in the central united states a variety of jet orientations are tested and sensitivities to jet height and the presence of lowlevel cooling are explored the primary impacts of adding the llj are that it alters the wind shear in the layers just above and below the jet and that it alters the magnitude of the storm relative inflow in the jet layer the changes to wind shear have an attendant impact on low level lifting in keeping with current theories for gust front lifting in squall lines the changes to the system relative inflow in turn impact total upward mass flux and precipitation output both are sensitive to the squall line relative orientation of the llj the variations in updraft intensity and system relative inflow are modulated by the progression of the lowlevel cooling which mimics the development of a nocturnal boundary layer while the system remains surfacebased the below jet shear has the largest impact on lifting whereas the above jet shear begins to play a larger role as the system becomes elevated similarly as the system becomes elevated larger changes to systemrelative inflow are observed because of the layer of potentially buoyant inflowing parcels becoming confined to the layer of the llj

a theory for strong long lived squall lines abstract we study herein the mechanics of long lived line oriented precipitating cumulus convection squall lines using two and three dimensional numerical models of moist convection these models used in juxtaposition enable us to address the important theoretical issue of whether a squall line is a system of special long lived cells or whether it is a long lived system of ordinary short lived cells our review of the observational literature indicates that the latter is the most consistent paradigm for the vast majority of cases but on occasion a squall line may be composed of essentially steady supercell thunderstorms the numerical experiments presented herein show that either type of squall line may develop from an initial line like disturbance depending on the magnitude and orientation of the environmental shear with respect to the line with shallow shear oriented perpendicular to the line a long lived line evolves containing individually short lived cells our analysis of this type o

effect of nutrient availability on marine origination rates throughout the phanerozoic eon the diversity of marine life has varied throughout the past 500 million years statistical analyses suggest that fluctuations in the availability of marine nutrients has been one important regulator of rates of origination during this time

u series dating of locality 15 at zhoukoudian china and implications for hominid evolution this paper reports u series dates on speleothem samples from locality 15 at zhoukoudian one of the richest paleolithic sites in northern china the age of the lower part of layer 2 is securely bracketed between 155 000 and 284 000 yr the underlying layer 3 dates back at least 284 000 yr layer 4 further below should be older still possibly by a cycle on the specmap time scale before 284 000 yr ago these ages much greater than the previous estimates of 110 000 140 000 yr from u series and electron spin resonance dating of fossil teeth suggest that locality 15 was broadly contemporaneous with locality 4 new cave and with the uppermost strata of locality 1 peking man site the physical evolution and cultural development evidenced by the timing of the zhoukoudian localities are in line with the opinion of chinese anthropologists for a regional transition from homo erectus to archaic homo sapiens c 2004 university of washington all rights reserved

a comparison of the vorticity dynamics governing the oceanic bomb cyclone of 4 5 january 1989 and the super derecho of 8 may 2009

mesoscale vertical motions near nocturnal convection initiation in pecan abstractradiosonde measurements from the plains elevated convection at night pecan 2015 field campaign are used to diagnose mesoscale vertical motions near nocturnal convection initiation ci these ci events occur in distinctly different environments including ones with 1 strong forcing for ascent associated with a synoptic cold front and midtropospheric short wave 2 nocturnal low level jets interacting with weaker quasi stationary fronts or 3 the absence of a surface front or boundary altogether radiosonde derived vertical motion profiles in each of these ci environments are characterized by low to midtropospheric ascent the representativeness of these vertical motion profiles is supported by distributions of corresponding mesoscale averages from model produced 0 6 h ensemble forecasts thermodynamic data from radiosondes are then analyzed along with selected model ensemble members to elucidate the role of the vertical motions on subsequent ci in a case with strong forcing for mesoscale asce

low tropospheric shear in the structure of squall lines impacts on latent heating under layer lifting ascent abstractthis study analyzes the dependence of the intensity of simulated midlatitude squall lines sls at maturity on the strength of the environmental low tropospheric shear focusing on the amplitude of the latent heating produced within the deep convective region the hypothesis motivating this investigation is that shear fundamentally affects system strength by modulating the mean convective instability of the storm relative inflowing air which is justified by the layer lifting nature of convection in sls the layer lifting model of convection llmc is proposed for measuring convective instability in the context of sls wherein latent heating is estimated by contemplating the storm relative inflow of cape this framework is used for defining llmc indices for the precipitation rate and the updraft s strength and verticality idealized sls at maturity simulated in a variety of kinematic and thermodynamic environments encompass wide ranging values of llmc indices and degrees of cold pool shear balanc

triple doppler analysis of a discretely propagating long lived high plains squall line abstract a nonsevere squall line that developed on 21 june 1993 along the northern foothills of the colorado rocky mountains is analyzed using a series of triple doppler analyses this squall line developed in a relatively dry environment characterized by weak low level but strong upper level vertical shear of the horizontal winds the drier thermodynamic profile as characterized by a higher lifting condensation level and weak low level shear resulted in convection forming not along but rather 7 10 km behind the leading edge of the shallow cold pool the strong upper level shear established a predominantly leading anvil this led to a suppression zone immediately ahead of the leading line which in turn resulted in a discrete mode of propagation of the squall line three different cycles were observed each cycle had a distinct line of convective cells that initiate intensify and then decay in each case the new cells developed 20 40 km out ahead of the decaying line of the previous cycle many studi

exceptional fossil record distribution of soft tissue preservation through the phanerozoic preservation of soft bodied fossil biotas konservat lagerstaten that preserve traces of volatile nonmineralized tissues readily degraded by bacteria are not evenly spaced through geologic time when compared to outcrop area exceptional faunas appear to be over represented in the cambrian and jurassic these concentrations in time correspond to particular environments indicating that controls on the distribution of exceptional faunas may have operated on a global scale the reduction in the number of exceptional faunas after the cambrian may reflect the evolution and diversification of deep bio turbators specific conditions favoring stagnation and episodic burial were required to ensure preservation in younger rocks

structure and evolution of numerically simulated squall lines abstract using a three dimensional numerical cloud model we investigate the effects of vertical wind shear on squall line structure and evolution over a wide range of shear magnitudes depths and orientations relative to the line we find that the simulated squall lines are most sensitive to the magnitude of the component of shear perpendicular to the line and that we may reproduce much of the range of observed structures by varying this single parameter for weak shear a line of initially upright to downshear tilted short lived cells quickly tilts upshear producing a wide band of weaker cells extending behind the surface outflow boundary for moderate to strong shear the circulation remains upright to downshear tilted for longer periods of time with vigorous short lived cells confined to a relatively narrow band along the system s leading edge at later times however these systems may also weaken as the circulation tilts upshear for strong deep shears oriented obliquely to the line the squal

ambient conditions associated with the maintenance and decay of quasi linear convective systems crossing the northeastern u s coast abstractquasi linear convective systems qlcss crossing the atlantic coastline over the northeastern united states were classified into three categories based on their evolution upon encountering the coast composite analyses show that convective lines that decay near the atlantic coast or slowly decay over the coastal waters are associated with 900 800 hpa frontogenesis with greater ambient 0 3 km vertical wind shear for the slowly decaying lines systems that maintain their intensity over the coastal ocean are associated with 900 hpa warm air advection but with little low level frontogenetical forcing neither sea surface temperature nor ambient instability was a clear delimiter between the three evolutions sustaining convective lines have the strongest environmental 0 3 km shear of the three types and this shear increases as these systems approach the coast in contrast the low level shear decreases as decaying and slowly decaying convective lines move toward the atlantic coastline there was als

mass spectrometric u series dating of new cave at zhoukoudian china abstract we report here mass spectrometric u series dates on calcite samples from new cave one of the zhoukoudian localities the lowermost sub layer of the capping flowstone dates to ca 120 ka implying the absence of late pleistocene cultural deposits within the cave the second flowstone layer was formed between 248 and 269 ka marking possibly the minimum age of the hominid fossil three samples taken from the lowest accessible strata date to ca 300 ka suggesting an even greater antiquity for the cultural horizon at the bottom of the depositional sequence the new age assignment from previously estimated early late pleistocene to late middle pleistocene makes new cave broadly contemporaneous with the uppermost strata of the peking man site this is in line not only with the observation that the previously established chronological sequence for chinese middle late pleistocene sites may have been underestimated as a whole but also with the hypothesis that human occupation of the zhoukoudian sites has been more or less continuous over hundreds of thousand years

did cooling oceans trigger ordovician biodiversification evidence from conodont thermometry the ordovician period long considered a supergreenhouse state saw one of the greatest radiations of life in earth9s history previous temperature estimates of up to 70 c have spawned controversial speculation that the oxygen isotopic composition of seawater must have evolved over geological time we present a very different global climate record determined by ion microprobe oxygen isotope analyses of early ordovician silurian conodonts this record shows a steady cooling trend through the early ordovician reaching modern equatorial temperatures that were sustained throughout the middle and late ordovician this favorable climate regime implies not only that the oxygen isotopic composition of ordovician seawater was similar to that of today but also that climate played an overarching role in promoting the unprecedented increases in biodiversity that characterized this period

mesoscale air transport at a midlatitude squall line in europe a numerical analysis this study examines a fast propagating squall line over western and central europe a high resolution regional weather prediction model is used to analyze the three dimensional wind field and the corresponding air mass transport induced by the mesoscale convective system the squall line can be divided into a bow shaped strong part with a continuous line of heavy convective precipitation and a weaker part exhibiting several isolated multi cell storms in the strong part a deep and intense rear inflow jet occurs with relative wind speeds of 12 18 m s 1 this part is also characterized by moderate to strong wind shear in contrast to the weaker part of the squall line where a shallow cold pool surges under the potentially unstable presquall air to investigate the air mass transport along the squall line in the model simulations passive fluid tracers are initialized in several vertical layers with different thermodynamic conditions at the strong part of the squall line a very efficient vertical tracer transport occurs potentially warm low level air is lifted from the lowermost 2 km to the upper troposphere where an organized horizontal outflow is observed the potentially coldest presquall air descends just in front of the updraught region and partly penetrates the convective precipitation area in the weaker part of the squall line the potential instability is not significantly reduced because the vertical air mass transport is less effective there additionally passive tracers are used to analyze the composition of the cold pool which turns out to be a very heterogeneous mixture of descending post frontal cold air and presquall air originating at different heights

tt osl and post ir irsl dating of the dali man site in central china abstract showing features associated with archaic homo sapiens and evolved homo erectus the dali skull is a key fossil for understanding human evolution in china various dating methods such as u series irsl tl esr esr u series and stratigraphical correlation with central loess plateau sequence were used to estimate the antiquity the dali man site with varying results in this study a total of 12 samples were taken in the sequence in the dali man site from the aeolian loess palaeosol sequence and underlying fluvial deposit layers including the palaeoanthropological level and dated by several optically stimulated luminescence osl methods coarse grained quartz sar osl thermally transferred osl tt osl and k feldspar post ir infrared ir stimulated luminescence post ir irsl pirir 290 methods results show that the tt osl and pirir 290 ages were consistent up to 100 ka for older samples the feldspar ages were significantly older these pirir 290 ages increased with the stratigraphy up to 310 ka the best age estimation of the dali man layer providing by the feldspar pirir 290 suggested that the dali man lived in late period of l3 mis 8 stage furthermore correlating the pirir 290 ages between 267 7 13 9 ka and 258 3 14 2 ka and new pollen analysis we proposed a new viewpoint that the dali man was likely to live during a transitional period from glacial to interglacial climate in the s2 l3 mis 7 8 stage

views on applying rkw theory an illustration using the 8 may 2009 derecho producing convective system abstractthis work presents an analysis of the vertical wind shear during the early stages of the remarkable 8 may 2009 central u s derecho producing convective system comments on applying rotunno klemp weisman rkw theory to mesoscale convective systems mcss of this type also are provided during the formative stages of the mcs the near surface based shear vectors ahead of the leading convective line varied with time location and depth but the line normal component of the shear in any layer below 3 km ahead of where the strong bow echo developed was relatively small 6 9 m s 1 concurrently the midlevel 3 6 km line normal shear component had magnitudes mostly 10 m s 1 throughout in a previous companion paper it was hypothesized that an unusually strong and expansive low level jet led to dramatic changes in instability shear and forced ascent over mesoscale areas these mesoscale effects may have overwhelmed the interactions between the cold pool and low level shear that modulate system st

significant contribution of authigenic carbonate to marine carbon burial carbon is removed from the earth s surface through the formation and burial of carbon bearing rocks and minerals an analysis of pore water profiles collected from marine sediments around the globe suggests that the precipitation of authigenic calcium carbonate accounts for around 10 of the carbonate that accumulates in marine sediments globally carbon is removed from the earth s surface through the formation and burial of carbon bearing rocks and minerals1 2 the formation of calcium carbonate and its burial in marine sediments accounts for around 80 of the total carbon removed from the earth s surface however the fraction of calcium carbonate that precipitates in the oceans versus that which precipitates authigenically in marine sediments is unclear here we compile measurements of the calcium concentration of pore fluids collected at 672 seafloor sites around the globe to calculate the global flux of calcium within marine sediments we use these data combined with alkalinity measurements of pore fluids to quantify authigenic calcium carbonate precipitation we estimate that the net calcium flux into marine sediments that can be ascribed to authigenic carbonate precipitation amounts to around 1 1012 mol yr 1 as such we estimate that authigenic carbonate precipitation accounts for at least 10 of global carbonate accumulation we show that much of the precipitation occurs along the eastern margins of ocean basins where organic matter delivery to the sea floor is likely to be high we suggest that authigenic calcium carbonate precipitation represents a non negligible component of the global carbon cycle

the great ordovician biodiversification event gobe the palaeoecological dimension abstract the great ordovician biodiversification event gobe saw a spectacular increase in marine biodiversity at all taxonomic levels largely within the phyla established much earlier during the so called cambrian explosion the diversification was probably the result of a combination of several geological and biological processes and the positive feedbacks resulting from them the present paper reviews the palaeoecological dimension of the gobe it involved major increases in s and biodiversity largely associated with the rise of the paleozoic evolutionary fauna dominated by suspension feeders and involving a greater occupation of ecospace and more complex ecological structures in the ecological evolutionary units p1 and p2 in the benthos these include more complex food webs than those of the cambrian greater tiering especially above the sediment water interface and the development of guild structures indicating increased competition between taxa for particular resources the ordovician is characterized by a profound change in reef composition with a switch from microbial dominated reefs in the early and middle ordovician to metazoan dominated reefs in the late ordovician increases in complexity of deep water trace fossil assemblages began in the early ordovician and mark the increasing exploitation in that environment and the development of hardgrounds permitted bioerosion and encrusting strategies together with the appearance of cryptic communities within the water column the gobe involved a significant increase in the diversity of the phytoplankton and the development of a diverse zooplankton including planktotrophic larvae from a range of invertebrate clades this revolution in the plankton enabled the establishment of a diverse fauna of pelagic vertebrates molluscs and arthropods and promoted the rise of suspension feeders in the benthos an escalation amongst predators and thus community evolution may also have been a major driver of biodiversification

u series dating of hominin fossil bearing panlong cave in guangdong province southern china two hominin teeth and an abundance of faunal remains were recovered from panlong cave in guangdong province southern china in 1987 the site has remained largely unknown to the prehistoric community mainly for the lack of reliable chronological constraints this paper reports high precision mass spectrometric u series dating of eight calcite samples from the extant cross section based on the dates on the overlying flowstone layers the hominin teeth should be definitely older than 292 10 ka furthermore as indicated by the u series ages on the secondary calcite formations the fossiliferous deposits should be older than 441 18 ka these dates support the paleontological inference that panlong cave may predate the nearby maba hominin site the hominin specimens from the site may thus represent an early member of the ailuropoda stegodon fauna and one of the oldest non erectus middle pleistocene hominin fossils in southern china

comments on a numerical investigation of the organization and interaction of the convective and stratiform regions of tropical squall lines ce commentaire de l article de lafore et montcreiff 1989 sur l organisation des lignes de grains tropicales est une comparaison avec l article de rottuno et al 1988 afin de mettre en evidence des resultats et des points de vue communs

effects of upper level shear on the structure and maintenance of strong quasi linear mesoscale convective systems recent observational studies have shown that strong midlatitude mesoscale convective systems mcss tend to decay as they move into environments with less instability and smaller deep layer vertical wind shear these observed shear profiles that contain significant upper level shear are often different from the shear profiles considered to be the most favorable for the maintenance of strong long lived convective systems in some past idealized simulations thus to explore the role of upper level shear in strong mcs environments a set of two dimensional 2d simulations of density currents within a dry statically neutral environment is used to quantify the dependence of lifting along an idealized cold pool on the upper level shear a set of three dimensional 3d simulations of mcss is produced to gauge the effects of the upper level shear in a more realistic framework results from the 2d experiments show that the addition of upper level shear to a wind profile with weak to moderate low level shear increases the vertical displacement of parcels despite a decrease in the vertical velocity along the cold pool interface parcels that are elevated above the surface 1 2 km overturn and are responsible for the deep lifting in the deep shear environments while the surface based parcels typically are lifted through the cold pool region in a rearward sloping path this deep overturning helps to maintain the leading convection and greatly increases the size and total precipitation output of the convective systems in more complex 3d simulations even in the presence of 3d structures these results show that the shear profile throughout the entire troposphere must be considered to gain a more complete understanding of the structure and maintenance of strong midlatitude mcss

relationship between system slope and updraft intensity in squall lines in recent years there has been debate about whether squall lines have an optimal state it has been repeatedly demonstrated that the slope of a squall line s convective region is related to the comparative magnitudes of the squall line s cold pool and the base state vertical wind shear the present work addresses a related assertion that squall line intensity ought to be maximized for an upright updraft zone a simple demonstration shows that upright systems realize more of their buoyancy because their attendant downwarddirected perturbation pressure gradient accelerations are weaker

palaeoecology and evolution of marine hard substrate communities abstract marine organisms have occupied hard substrates since the archaean shells rocks wood and sedimentary hardgrounds offer relatively stable habitats compared to unconsolidated sediments but the plants and animals which inhabit them must develop means to gain and defend this premium attachment space hard substrate communities are formed by organisms with a variety of strategies for adhering to and or excavating the substrates they inhabit while mobile grazers organically attached and even soft bodied organisms may leave evidence of their former presence in ancient hard substrate communities a superior fossil record is left by sessile encrusters with mineralised skeletons and by borers which leave trace fossils furthermore encrusters and borers are preserved in situ retaining their spatial relationships to one another and to the substrate spatial competition ecological succession oriented growth and differential utilisation of exposed vs hidden substrate surfaces can all be observed or inferred hard substrate communities are thus excellent systems with which to study community evolution over hundreds of millions of years here we review the research on modern and ancient hard substrate communities and point to some changes that have affected them over geological time scales such changes include a general increase in bioerosion of hard substrates particularly carbonate surfaces through the phanerozoic this is at least in part analogous to the infaunalisation trends seen in soft substrate communities encrusting forms show an increase in skeletalisation from the palaeozoic into the mesozoic and cenozoic which may be a response to increasing levels of predation hard substrate communities considering borers and encrusters together show a rough increase in tiering through the phanerozoic which again parallels trends seen in soft substrate communities this extensive review of the literature on living and fossil hard substrate organisms shows that many opportunities remain for large scale studies of trends through time at the community and clade levels palaeontologists will especially benefit by closer integration of their work with that of neontologists particularly in aspects of ecology such as larval recruitment competition and succession

environment and early evolution of the 8 may 2009 derecho producing convective system abstractthis study documents the complex environment and early evolution of the remarkable derecho that traversed portions of the central united states on 8 may 2009 central to this study is the comparison of the 8 may 2009 derecho environment to that of other mesoscale convective systems mcss that occurred in the central united states during a similar time of year synoptic scale forcing was weak and thermodynamic instability was limited during the development of the initial convection but several mesoscale features of the environment appeared to contribute to initiation and upscale growth including a mountain wave a midlevel jet streak a weak midlevel vorticity maximum a denver cyclone and a region of upper tropospheric inertial instability the subsequent mcs developed in an environment with an unusually strong and deep low level jet llj which transported exceptionally high amounts of low level moisture northward very rapidly destabilized the lower troposphere and enhanced frontogenetica

the role of convectively generated rear inflow jets in the evolution of long lived mesoconvective systems abstract in this study the structure of convectively generated rear inflow jets and their role in the evolution of long lived mesoconvective systems are investigated through an analysis of idealized three dimensional simulations using a nonhydrostatic cloud model rear inflow jets are generated within these systems in response to the upshear tilting of the convective circulation as the horizontal buoyancy gradients along the back edge of the expanding system create a circulation that draws midlevel air in from the rear within this framework a wide range of rear inflow strengths and structures are produced depending on the magnitude of the ambient convective available potential energy cape and the vertical wind shear in general for environments characterized by weak to moderate vertical wind shear and weak to moderate cape the rear inflow jet descends and spreads along the surface well behind the leading edge of the gust front and the subsequent convective activity becomes weaker however for e

mass spectrometric u series dating of the chaoxian hominin site at yinshan eastern china the fossils of chaoxian hominin widely accepted as representing archaic homo sapiens in eastern china were recovered from the middle or slightly higher levels of layer 2 deposits of a collapsed cave at yinshan anhui province results of mass spectrometric u series dating of intercalated speleothem calcites are presented based mainly on four broadly coeval calcite samples the hominin fossils should be bracketed in the range of 310 360 ka or somewhat older these ages are much older than the previous estimate at 160 200 ka based on the u series dating of fossil teeth and bones and may be cited as supporting evidence for an earlier h erecrus archaic h sapiens interface in china c 2009 elsevier ltd and inqua all rights reserved

large scale meteorological conditions associated with midlatitude mesoscale convective complexes abstract objective analyses of composited meteorological conditions attending ten mesoscale couvective complexes mcc reveal a number of distinctive characteristics and important interactions with the large scale environment the systems appear to be linked to eastward progression of a weak middle tropospheric short wave trough initial thunderstorms develop within a region of mesoscale convergence and lifting that is apparently forced primarily by low level warm advection the mcc system acquires mesoscale organization while it moves eastward ahead of the short wave trough diabatic heating eventually produces a system that is warm core in the middle troposphere and cold core in upper levels the mature mcc exhibits many similarities to tropical convective systems although it occurs within a considerably different large scale setting inflow within the lower half of the troposphere feeds convection within a region characterized by significant net upward mass flux and widespread precipitation thickne

simulation of a progressive derecho using composite initial conditions abstract this study focuses on the progressive derecho a widespread convectively induced windstorm produced by a mesoscale convective system that often occurs within a relatively benign synoptic scale environment sounding data from 12 progressive derechos which occurred in weakly forced large scale environments are composited in order to examine important large scale features in the preconvective environment this analysis captures many features that are common in warm season derecho environments such as an upper level wind maximum a relatively dry midtroposphere and low level warm advection initial and boundary conditions for the pennsylvania state university national center for atmospheric research fifth generation mesoscale model mm5 are created using this analysis a three dimensional horizontally nonhomogeneous explicitly resolved simulation of a progressive derecho is produced and compared to previous more idealized simulations of similar convective systems that have been used to expla

the temporal behavior of numerically simulated multicell type storms part i modes of behavior abstract the temporal behavior of mature multicellular model storms created in an experiment that varied the vertical wind shear layer depth is examined herein these storms form new cells at low levels on the storm s forward side in or near the forced lifting zone at the edge of the evaporationally chilled subcloud cold air pool each moves upward and rearward within the storm as it intensifies matures and decays and becomes replaced by a new cell development as a result the storms oscillate in time with respect to updraft intensity and the generation of condensation and surface rainfall a few model storms oscillate in a simply periodic fashion during maturity generating a series of nearly identical cells separated by a nearly constant period other storms are still periodic but in a more complex fashion manifesting repeat cycles consisting of two or more cells several simulations appear quite aperiodic spectral analyses of temporal statistics reveal the existence of a fundamental period of o

the influence of the shear induced pressure gradient on thunderstorm motion abstract in the present investigation we propose a simple theory to explain how a veering environmental wind shear vector can cause an initially symmetric updraft to grow preferentially to the right of the shear vector and acquire cyclonic rotation the explanation offered is based on linear theory which predicts that interaction of the mean shear with the updraft produces favorable vertical pressure gradients along its right flank to asses the validity of linear theory for large amplitude updrafts the three dimensional shallow anelastic equations are numerically integrated using a simple parameterization for latent heating within a cloud and the linear and nonlinear forcing terms are separately analyzed these results suggest that although the nonlinear effects strongly promote splitting of the updraft the linear forcing remains the dominant factor in preferentially enhancing updraft growth on the right flank we believe this differential forcing is a major contributor to the observed predominance o

development of an intense warm core mesoscale vortex associated with the 8 may 2009 super derecho convective event abstractin this study the dynamical processes contributing to warm core meso scale vortex formation associated with the 8 may 2009 super derecho are examined utilizing two complementary quasi lagrangian approaches a circulation budget and backward trajectory analyses applied to a fortuitous numerical simulation of the event warm core meso scale vortex formation occurs in a deeply moist potentially stable environment that is conducive to the development of near surface rotation and is somewhat atypical compared to known derecho supporting environments air parcels in the vicinity of the developing vortex primarily originate near the surface in the streamwise vorticity rich environment associated with the vertical wind shear of the low level jet immediately to the east of the eastward moving system cyclonic vertical vorticity is generated along inflowing air parcels primarily by the ascent induced tilting of streamwise vorticity and amplified primarily by ascent induced vortex tube stretching de

radar and damage analysis of severe bow echoes observed during bamex abstract this study examines damaging wind production by bow shaped convective systems commonly referred to as bow echoes recent idealized numerical simulations suggest that in addition to descending rear inflow at the bow echo apex low level mesovortices within bow echoes can induce damaging straight line surface winds in light of these findings detailed aerial and ground surveys of wind damage were conducted immediately following five bow echo events observed during the bow echo and mesoscale convective vortex mcv experiment bamex field phase these damage locations were overlaid directly onto weather surveillance radar 1988 doppler wsr 88d images to i elucidate where damaging surface winds occurred within the bow shaped convective system in proximity to the apex north of the apex etc and then ii explain the existence of these winds in the context of the possible damaging wind mechanisms the results of this study provide clear observational evidence that low level mesovortices wit

the structure evolution and dynamics of a nocturnal convective system simulated using the wrf arw model abstractprevious studies have documented a nocturnal maximum in thunderstorm frequency during the summer across the central united states forecast skill for these systems remains relatively low and the explanation for this nocturnal maximum is still an area of active debate this study utilized the wrf arw model to simulate a nocturnal mesoscale convective system that occurred over the southern great plains on 3 4 june 2013 a low level jet transported a narrow corridor of air above the nocturnal boundary layer with convective instability that exceeded what was observed in the daytime boundary layer the storm was elevated and associated with bores that assisted in the maintenance of the system three dimensional variations in the system s structure were found along the cold pool which were examined using convective system dynamics and wave theory shallow lifting occurred on the southern flank of the storm conversely the southeastern flank had deep lifting with favorable integrated vertical shear ov

a theory for strong long lived squall lines revisited based on the analysis of idealized two and three dimensional cloud model simulations rotunno et al hereafter rkw and weisman et al hereafter wkr put forth a theory that squall line strength and longevity was most sensitive to the strength of the component of low level 0 3 km agl ambient vertical wind shear perpendicular to squall line orientation an optimal state was proposed by rkw based on the relative strength of the circulation associated with the storm generated cold pool and the circulation associated with the ambient shear whereby the deepest leading edge lifting and most effective convective retriggering occurred when these circulations were in near balance since this work subsequent studies have brought into question the basic validity of the proposed optimal state based on concerns as to the appropriate distribution of shear relative to the cold pool for optimal lifting as well as the relevance of such concepts to fully complex squall lines especially considering the potential role of deeper layer shears in promoting system strength and longevity in the following the basic interpretations of the rkw theory are reconfirmed and clarified through both the analysis of a simplified two dimensional vorticity streamfunction model that allows for a more direct interpretation of the role of the shear in controlling the circulation around the cold pool and through an analysis of an extensive set of 3d squall line simulations run at higher resolution and covering a larger range of environmental shear conditions than presented by wkr

speleothem derived asian summer monsoon variations in central china 54 46 ka the oxygen isotope signature delta o 18 of stalagmite si3 collected from shizi cave in north east sichuan province provides an asian summer monsoon asm record in central china for the period 54 46 ka the si3 delta o 18 record clearly shows a negative delta o 18 excursion centred around 49 4 ka which was reported in hulu cave in east china but not identified in the speleothem records from south west china as a whole this record displays a higher coherence with the two hulu records from east china than with the speleothem delta o 18 records from south west china suggesting that at 54 46 ka central china was influenced more by the east asian summer monsoon than by the indian summer monsoon it also displays a significant negative delta o 18 excursion at 47 5 46 6 ka which is not clearly documented in two other speleothem delta o 18 records previously reported from south west china this suggests that details of the greenland interstadial 12 warrant further investigations in future in monsoonal china the si3 delta o 18 record displays more significant centennial scale variations than the other four speleothem delta o 18 records from east and south west china which may be due to the fact that the study site is closer to the north west boundary of the asm and more sensitive to variations of the asm than east and south west china copyright c 2011 john wiley sons ltd

rear inflow in squall lines with trailing stratiform precipitation abstract the relative airflow and accompanying precipitation structure of squall lines trailed by mesoscale regions of stratiform rain are examined with emphasis on the occurrence of rear inflow i e the intrusion of environmental air into these storms across the trailing precipitation boundary three cases from kansas and oklahoma provide examples of strong rear inflow which crosses the back edge of the stratiform precipitation area at relative speeds exceeding 10 m s 1 the vertical profiles of relative flow at the trailing precipitation boundary of these three systems were remarkably similar with the rear inflow confined to a jet like layer centered at about 550 mb doppler radar data for two of these cases showed that the rear inflow jet occupied a continuous channel extending from middle levels at the back edge of the stratiform region to lower levels of the leading convective region where it merged with outflow from convective downdrafts to bolster the leading gust front strong front to rea

mesoscale surface pressure and temperature features associated with bow echoes abstract this study examines observed mesoscale surface pressure temperature and wind features of bow echoes bow echo events in the area of the oklahoma mesonet are selected for study to take advantage of high resolution surface data thirty six cases are identified using 2 km resolution radar reflectivity data over a 4 yr period 2002 05 their surface features are interrogated using the mesonet data distinct surface features usually associated with squall lines the mesohigh and cold pool are found to also accompany bow echoes a common surface pattern preceding bowing is identified prior to new bowing development the mesohigh surges ahead of the convective line while the cold pool remains centered behind it surface winds shift to a ground relative outflow pattern upon arrival of the mesohigh surge approximately 30 min later a new bowing segment forms with its apex slightly to the left with respect to the direction of system motion of the mesohigh surge the cold pool follows the convective

structures and dynamics of quasi 2d mesoscale convective systems abstract recently three distinct archetypes for midlatitude linear mesoscale convective systems mcss have been identified this article focuses on the fundamentals of two of these archetypes convective lines with trailing stratiform ts precipitation and convective lines with leading stratiform ls precipitation both the ts and ls modes typically exhibit quasi 2d reflectivity patterns and quasi 2d environmental storm relative wind fields ongoing work has revealed that there are three common flow structures for these quasi 2d mcss front fed ts systems which are sustained by front to rear storm relative inflow as well as front fed ls and rear fed ls systems which are sustained by rear to front storm relative inflow this paper summarizes the observed structures of the front fed ts front fed ls and rear fed ls modes and then outlines an idealized numerical experiment in which these modes were simulated the authors analyze the basic simulated kinematic and microphysical structures and provid

co evolution of eukaryotes and ocean oxygenation in the neoproterozoic era the oxygenation of the earth s deep oceans is often thought to have triggered the evolution of simple animals a review article proposes that instead the evolution of animal life set off a series of biogeochemical feedbacks that promoted the oxygenation of the deep sea

thermal ionization mass spectrometry u series dating of a hominid site near nanjing china mass spectrometric u series dating of speleothems from tangshan cave combined with ecological and paleoclimatic evidence indicates that nanjing man a typical homo erectus morphologically correlated with peking man at zhoukoudian should be at least 580 k y old or more likely lived during the glacial oxygen isotope stage 16 similar to 620 ka such an age estimate which is similar to 270 ka older than previous electron spin resonance and alpha counting u series dates has significant implications for the evolution of asian h erectus dentine and enamel samples from the coexisting fossil layer yield significantly younger apparent ages that of the enamel sample being only less than one fourth of the minimum age of nanjing man this suggests that u uptake history is far more complex than existing models can handle as a result great care must be taken in the interpretation of electron spin resonance and u series dates of fossil teeth

responses of quaternary rainforest vertebrates to climate change in australia a new previous termmiddle pleistocenenext term vertebrate fossil record from eastern australia dated by u disequilibrium series records the first quaternary record of an australian tropical rainforest fauna this exceptionally rich fauna underwent extinction after a long period of relative faunal stability spanning several glacial cycles and persisted probably until 280 000 years ago some time between 280 000 and 205 000 years ago the rainforest fauna was replaced by a xeric adapted fauna since that time the xeric adapted fauna was replaced by a mesic adapted fauna which was established by the holocene this is the first vertebrate faunal evidence in australia of the previous termmiddle pleistocenenext term mid brunhes climatic event mbe a major climatic reorganisation that led to increased aridity in northern australia from around 300 000 years ago several independent palaeoclimate proxies suggest that the climatic shift to aridity was due to increased climatic variability and weakened northern monsoons which may be manifested in the extinction of the aseasonal rainforest fauna and its replacement by an arid adapted fauna we extend the temporal ranges of several taxa from the pliocene into the previous termmiddle pleistocene next term we also reveal a longer palaeobiogeographic connection of rainforest taxa and lineages shared between new guinea and australia than was previously thought and show that their extinction on mainland australia occurred sometime after 280 000 years ago

mechanisms supporting long lived episodes of propagating nocturnal convection within a 7 day wrf model simulation abstract a large domain explicit convection simulation is used to investigate the life cycle of nocturnal convection for a one week period of successive zonally propagating heavy precipitation episodes occurring over the central united states similar to climatological studies of phase coherent warm season convection the longest lived precipitation episodes initiate during the late afternoon over the western great plains 105 100 w reach their greatest intensity at night over the central great plains 100 95 w and typically weaken around or slightly after sunrise over the midwest 95 85 w the longest lived episodes exhibit average zonal phase speeds of 20 m s 1 consistent with radar observations during the period composite analysis of the life cycle of five long lived nocturnal precipitation episodes indicates that convection both develops and then propagates eastward along an east west oriented lower tropospheric frontal zone an elevated 2 km deep layer of high e air helps sustain convect

the role of momentum transport in the motion of a quasi idealized mesoscale convective system abstract momentum transport is examined in a simulated midlatitude mesoscale convective system mcs to investigate its contribution to mcs motion momentum budgets are computed using model output to quantify the role of specific processes in determining the low level wind field in the system s surface based cold pool results show that toward the leading convective line of the mcs and near the leading edge of the cold pool the momentum field is most strongly determined by the vertical advection of the storm induced perturbation wind across the middle rear of the system the wind field is largely a product of the pressure gradient acceleration and to a lesser extent the vertical advection of the background environmental i e base state wind the relative magnitudes of the vertical advection terms in an eulerian momentum budget suggest that for gust front driven systems downward momentum transport by the mcs is a significant driver of mcs motion and potentially severe surface winds results furthe

middle late ordovician darriwilian sandbian decoupling of global sulfur and carbon cycles isotopic evidence from eastern and southern laurentia abstract middle late ordovician sequences from the appalachian basin and arbuckle mountain regions of north america were analyzed for carbonate associated sulfate 34 s cas and pyrite 34 s pyr paired with carbonate 13 c carb and organic matter 13 c org chemostratigraphy two major negative drops in 34 s cas 12 excursions are recognized the older decline in 34 s cas occurs within the histiodella holodentata phragmodus polonicus conodont zones and the younger drop is within the cahabagnathus sweeti amorphognathus tvaerensis baltoniodus gerdae subzone zones these overall these negative shifts in 34 s cas have an antithetical relationship with positive shifts in 34 s pyr 10 and 13 c carb 2 recorded in the same successions the older negative 34 s cas shift is coincident with the widely documented mid darriwilian 13 c excursion mdice and the younger negative 34 s cas shift is coincident with another positive 13 c carb shift in the early sandbian geochemical modeling of these sulfur isotope shifts suggests that a decrease in the global rate of pyrite burial or isotope fractionation between seawater sulfate and sedimentary pyrite could account for these negative 34 s cas trends additionally a substantial increase in the weathering flux of pyrite to the global oceans could also explain these secular sulfur isotope trends while increased crustal weathering is broadly consistent with a sea level lowstand and the seawater 87 sr 86 sr isotope record of change in continental weathering in the late darriwilian stage of the ordovician geologic and geochemical proxy evidence do not support distinct pulses of continental weathering required to generate two separate negative shifts in 34 s cas these antithetical isotope trends may be best explained by changes in the marine redox state that significantly reduced microbially mediated pyrite burial and organic matter remineralization rates pulses of oceanic ventilation would have expanded habitable environments for marine organisms and thus is broadly consistent with major increases in biodiversification during this period of the ordovician

initial 26al 10be burial dating of the hominin site bailong cave in hubei province central china with the discovery of homo erectus teeth stone artifacts and a rich fauna bailong cave in northern hubei province is an important hominin archaeological site in china however due to the lack of suitable dating methods the previous age estimates all come from biostratigraphic correlations here we report the first application of a radio isotopic dating method to the site three 26al 10be measurements of two quartz samples give a weighted mean burial age of 0 76 0 06 million years ma 1 taking into account possible bias of the dating method stratigraphic order and evidence for rapid sedimentation the cultural deposits of the site should be somewhat younger than the above date this is consistent with previous biostratigraphic age estimates at around the early middle pleistocene transition and possibly indicates an earlier human coexistence with stegodon ailuropoda fauna than previously estimated

the genesis of severe long lived bow echoes abstract a series of idealized simulations using a nonhydrostatic cloud model is used to investigate the genesis of bow echoes a bow shaped system of convective cells that is especially noted for producing long swaths of damaging surface winds it is hypothesized that severe long lived bow echoes represent a dynamically unique form of mesoconvective organization being produced for a restricted range of environmental conditions including a convective available potential energy cape of at least 2000 m2 s2 and vertical wind shears of at least 20 m s 1 over the lowest 2 5 5 km agl the key structural features include a 40 100 km long bow shaped segment of convective cells with a strong rear inflow jet extending to the leading edge of the bow at 2 3 km agl and cyclonic and anticyclonic eddies referred to as bookend vortices on the northern and southern flanks of the bowed segment respectively this structure characteristically develops three to four hours into the lifetime of a convective system a