random variability explains apparent global clustering of large earthquakes 1 the occurrence of 5 mw 8 5 earthquakes since 2004 has created a debate over whether or not we are in a global cluster of large earthquakes temporarily raising risks above long term levels i use three classes of statistical tests to determine if the record of m 7 earthquakes since 1900 can reject a null hypothesis of independent random events with a constant rate plus localized aftershock sequences the data cannot reject this null hypothesis thus the temporal distribution of large global earthquakes is well described by a random process plus localized aftershocks and apparent clustering is due to random variability therefore the risk of future events has not increased except within ongoing aftershock sequences and should be estimated from the longest possible record of events

sting jets in simulations of a real cyclone by two mesoscale models the existence of sting jets as a potential source of damaging surface winds during the passage of extratropical cyclones has recently been recognized however there are still very few published studies on the subject furthermore although it is known that other models are capable of reproducing sting jets in the published literature only one numerical model the met office unified model metum has been used to numerically analyze these phenomena this article aims to improve our understanding of the processes that contribute to the development of sting jets and show that model differences affect the evolution of modeled sting jets a sting jet event during the passage of a cyclone over the united kingdom on 26 february 2002 has been simulated using two mesoscale models namely the metum and the consortium for small scale modeling cosmo model to compare their performance given the known critical importance of vertical resolution in the simulation of sting jets the vertical resolution of both models has been enhanced with respect to their operational versions both simulations have been verified against surface measurements of maximum gusts satellite imagery and met office operational synoptic analyses as well as operational analyses from the ecmwf it is shown that both models are capable of reproducing sting jets with similar though not identical features through the comparison of the results from these two models the relevance of physical mechanisms such as evaporative cooling and the release of conditional symmetric instability in the generation and evolution of sting jets is also discussed

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

attempted predation on early paleozoic cornulitids abstract cornulitids appeared in the middle ordovician and the earliest repairs to their shells are reported from the upper ordovician katian of baltica and north america hirnantian shell repair is common in the silurian sheinwoodian unattached cornulitid cornulites cellulosus from the baltica and is interpreted here as a result of failed predation scalloped divoted and embayed type of shell repairs occur in three species of cornulites the species with the most repairs c cellulosus yielded a shell repair frequency of 20 7 with 29 specimens there are probable antipredatory adaptations such as spines and extremely thick vesicular walls in the morphology of silurian cornulitids the morphological and ecological evolution of cornulitids could thus have been partially driven by predation

volatile emission during the eruption of baitoushan volcano china north korea ca 969 ad magma volume dre 24 5 km3 the main phase ca 95 vol is represented by comenditic tephra deposited dominantly as widespread fallout blankets and proximal ignimbrites the eruption column is estimated to have reached ca 25 km and thus entered the stratosphere a late phase 5 vol is represented by trachyte emplaced chiefly as moderately welded ignimbrites the comendites contain 3 and the trachytes 10 20 vol phenocrysts mainly anorthoclase hedenbergite and fayalite primary glassy melt inclusions with no signs of leakage were found only in phenocrysts in the comenditic tephra whereas those in phenocrysts in the trachytes are devitrified the comendite magma is interpreted to have been generated by fractional crystallization from a trachyte magma represented by melt inclusions in the phenocrysts in the comendite tephra the mass of volatiles emitted to the atmosphere during the eruption was estimated using the petrologic method the average h2o concentration of the comenditic matrix glass is 1 5 wt probably largely secondary and of the corresponding melt inclusions 5 2 wt melt inclusions in feldspar and quartz present the highest halogen concentrations with a calculated average for chlorine of 4762 ppm and for fluorine of 4294 ppm the comenditic matrix glasses are represented by a fluorine rich 3992 ppm f and fluorine poor group 2431 ppm f averaging 3853 ppm for chlorine only 20 of all sulfur analyses of the comenditic matrix glasses and melt inclusions are above the detection limit of 250 ppm s the difference between pre and post eruptive concentration of h2o is at least 3 7 0 6 wt h2o taking into consideration re hydration of the matrix glass and possible leakage of melt inclusions the difference between pre and post eruptive concentrations of the halogens amounts to 909 90 ppm cl and 1863 280 ppm and 302 40 ppm f the difference for s was estimated based on the average of the maximum s concentrations in the melt inclusions 455 ppm s and the detection limit resulting in 205 40 ppm s the calculated mass of volatiles injected into the atmosphere based on the erupted magma volume and volatile data is 1796 453 megatons for h2o 45 10 megatons for chlorine 42 11 megatons for fluorine and 2 0 6 megatons for sulfur the 969 20 ad eruption of baitoushan volcano one of the largest eruptions of the past 2000 years is thought to have had a substantial but possibly short lived effect on climate

ordovician trilobites from the tafilalt lagerstatte new data and reappraisal of the bou nemrou assemblage

wind profiler observations of a sting jet some of the most damaging surface winds experienced in midlatitude cyclonic storms have been attributed to a phenomenon known as a sting jet previous studies have deduced how sting jets develop from their midtropospheric origin but there have been no direct observations of these wind features in the midtroposphere during windstorm jeanette on 27 october 2002 the tip of the storm s cloud head passed over a vhf wind profiler at aberystwyth wales allowing the structure of a sting jet to be measured with high spatial and temporal resolution these observations showed a multiple slantwise structure to the sting jet region with two tails of increased winds that persisted after the passing of the cloud head aloft simulations by the met office unified model um showed that the slantwise structure followed w surfaces and that the sting jet descended along surfaces as it passed over the uk accelerating and drying during its descent the horizontal and vertical scales of the observed structures are compatible with slantwise convection releasing conditional symmetric instability within the cloud head further observations of the sting jet were obtained by a uhf wind profiler at cardington in eastern england where the sting jet had merged with the cold conveyor belt circulating around the storm an unstable temperature profile in the lowest kilometre over cardington enabled damaging gusts of strong winds to be brought to the surface in convective plumes however this strong vertical mixing was not represented correctly in the um copyright 2009 royal meteorological society

reconnection at the high latitude magnetopause during northward interplanetary magnetic field conditions the polar spacecraft had a prolonged encounter with the high latitude dayside magnetopause on may 29 1996 this encounter with the magnetopause occurred when the interplanetary magnetic field was directed northward from the three dimensional electron and ion distribution functions measured by the hydra instrument it has been possible to identify nearly all of the distinct boundary layer regions associated with high latitude reconnection the regions that have been identified are 1 the cusp 2 the magnetopause current layer 3 magnetosheath field lines that have interconnected in only the northern hemisphere 4 magnetosheath field lines that have interconnected in only the southern hemisphere 5 magnetosheath field lines that have interconnected in both the northern and southern hemispheres 6 magnetosheath that is disconnected from the terrestrial magnetic field and 7 high latitude plasma sheet field lines that are participating in magnetosheath reconnection reconnection over this time period was occurring at high latitudes over a broad local time extent interconnecting the magnetosheath and lobe and or plasma sheet field lines in both the northern and southern hemispheres newly closed boundary layer field lines were observed as reconnection occurred first at high latitudes in one hemisphere and then later in the other these observations establish the location of magnetopause reconnection during these northward interplanetary magnetic field conditions as being at high latitudes poleward of the cusp and further reinforce the general interpretation of electron and ion phase space density signatures as indicators of magnetic reconnection and boundary layer formation

acceleration of near surface strong winds in a dry idealised extratropical cyclone to understand near surface strong winds in extratropical cyclones a simulation of a dry idealised baroclinic wave is presented the forces that accelerate the winds are analysed using the terms in the horizontal momentum equation two regions of strong near surface winds developed within the simulation one to the east of the low centre and the other to the southwest the flow to the east resembling the cold conveyor belt accelerated as it passed through the strong pressure gradient associated with the warm frontal zone this acceleration was reduced by friction near the surface the winds to the southwest were characterised by three airstreams one airstream consisted of air parcels that started north of the warm front near the surface accelerated north of the warm front encircled the low and continued to accelerate to the southwest of the low the increases in wind speed in this airstream also part of the cold conveyor belt resulted from the along flow pressure gradient force being greater than friction the second airstream consisted of air parcels that descended west of the cold front and maintained their speed during descent until they were slowed either by friction in the boundary layer or as they moved southward against the local pressure gradient between these two airstreams a third airstream was characterised by air parcels that accelerated during descent from the mid to lower troposphere whilst moving around the bent back front this airstream bears some resemblance to the sting jet and was accelerated by the pressure gradient force on descent until it encountered increased friction or moved against the local pressure gradient

dynamical aspects of the october storm 1987 a study of a successful fine mesh simulation a diagnostic study of a successful numerical simulation of the october storm 1987 is described this good non operational forecast was obtained using the meteorological office s fine mesh model run from a revised analysis at 00 gmt on 15 october 1987 the meteorological office s mesoscale model was also run using initial conditions at 12 gmt 15 october obtained by interpolating the above fine mesh forecast fields to examine the benefits of very high horizontal resolution 15km grid length diagnostic maps and cross sections derived are used to address two scientific issues i the role of weak moist slantwise stability or alternatively positive slantwise convective potential energy ii the dynamical significance of the striking cloud structure the cloud head seen in the satellite imagery early in the storm s life it appears that the baroclinic zone in which the storm develops is highly receptive to forcing by an upper trough and the warm boundary layer air just ahead of the main surface front is characterized by substantial slantwise convective available energy the cloud head is identified with a region of intense slantwise ascent in the warm air just above the main frontal zone its great meridional extent is associated with the upper tropospheric outflow and horizontal spreading of air which has recently undergone rapid slantwise ascent the low level temperature field exhibits throughout the development period a remarkable shape preserving thermal ridge of considerable intensity the sensitivity of the forecast to the removal of surface energy fluxes and latent heat of condensation are investigated separately it is found that on the timescale of the simulation surface energy fluxes have negligible impact on the explosive development on the other hand the contribution of latent heat release to the development appears to dominate the dry baroclinic instability process

symbiotic interactions in the ordovician of baltica abstract eleven symbiotic associations between taxa occur in the ordovician of baltica most involving colonial animals bryozoans formed the most numerous associations including possible polychaete bioclaustrations possible polychaete borings conulariids and crinoids and had the highest number of symbiosis cases in baltica the late ordovician symbiotic associations differ from those in the middle ordovician by a remarkable increase in the numbers of recorded cases this is most likely explained by the great ordovician biodiversification event gobe the higher faunal diversity may have created more opportunities for symbiotic relationships these changes in the symbiotic interactions in the ordovician of baltica were probably not related to climate change but had an evolutionary cause

high altitude cusp flow dependence on imf orientation a 3 year cluster statistical study 1 we report on the statistical properties of the plasma flows measured by the cluster spacecraft in the high altitude cusp region of the northern hemisphere as a function of the interplanetary magnetic field imf orientation with selected clock angle intervals the technique uses a magnetic field model taking into account the actual solar wind conditions and level of geomagnetic activity in order to model the magnetopause and cusp displacements as a function of these conditions the distributions of the magnetic field vector show a clear consistency with the imf clock angle intervals chosen and demonstrate that the technique used here fixes the positions of the cusp boundaries adequately the antisunward convection observed in the exterior cusp suggests that this region is statistically quite convective under southward imf while for northward imf the region appears more stagnant the presence of large parallel downward flows at the equatorward edge of the cusp shows that plasma penetration occurs preferentially at the dayside low latitude magnetopause for southward imf conditions in contrast under northward imf the results are suggestive of plasma penetration from the poleward edge of the cusp combined with a substantial sunward convection but no flows are observed at all at the dayside boundary with the plasma sheet the comparison of the measured flow speed with the alfven speed suggests that the magnetosheath adjacent to the external boundary is more sub alfvenic even for high magnetic latitudes under northward imf than under southward imf this result is consistent with the preference for the plasma depletion layer to develop under such conditions the transverse plasma convection in the exterior cusp appears to be controlled by the imf by component as well for dawnward duskward imf orientations the convection is preferentially directed toward dusk dawn these results are interpreted as strong arguments in favor of the cusp being structured at large scales by the occurrence of magnetic reconnection at the high latitude magnetopause for northward imf and at the low latitude magnetopause for southward imf

the fezouata fossils of morocco an extraordinary record of marine life in the early ordovician the discovery of the fezouata biota in the latest tremadocian of southeastern morocco has significantly changed our understanding of the early phanerozoic radiation the shelly fossil record shows a well recognized pattern of macroevolutionary stasis between the cambrian explosion and the great ordovician biodiversification event but the rich soft bodied fezouata biota paints a different evolutionary picture the fezouata assemblage includes a considerable component of cambrian holdovers alongside a surprising number of crown group taxa previously unknown to have evolved by the early ordovician study of the fezouata biota is in its early stages and future discoveries will continue to enrich our view of the dynamics of the early phanerozoic radiation and of the nature of the fossil record supplementary material a complete faunal list is available at http www geolsoc org uk sup18843

the sting at the end of the tail damaging winds associated with extratropical cyclones strong surface winds often accompany the low level jets that occur along the cold fronts of extratropical cyclones but there is evidence that the strongest surface winds occur in a distinctly different part of a certain class of cyclone the most damaging extratropical cyclones go through an evolution that involves the formation of a bent back front and cloud head separated from the main polar front cloud band by a dry slot when the cyclone attains its minimum central pressure the trailing tip of the cloud head bounding the bent back front forms a hook which goes on to encircle a seclusion of warm air the most damaging winds occur near the tip of this hook the sting at the end of the tail observations of the great storm of october 1987 in south east england are re examined in some detail to study this phenomenon the cloud head is shown to have a banded structure consistent with the existence of multiple mesoscale slantwise circulations air within these circulations leaves the hooked tip of the cloud head and enters the dry slot much faster than the rate of travel of the cloud head tip implying rapid evaporation and diabatic cooling immediately upwind of the area of damaging surface winds the circumstantial evidence from the observational study leads one to hypothesize that the mesoscale circulations and the associated evaporative heat sinks may play an active role in strengthening the damaging winds regardless of how important this role may be the evolution of the cloud pattern seen in satellite imagery is a useful tool for nowcasting the occurrence and location of the worst winds copyright 2004 royal meteorological society

the role of mesoscale instabilities in the sting jet dynamics of windstorm tini sting jets sj occur as an additional region of low level strong winds in some shapiro keyser type extra tropical cyclones while sjs are widely accepted as being distinct from the warm and cold conveyor belts the mechanisms responsible for their occurrence are still not fully understood here we determine the relative importance of the release of mesoscale instabilities and synoptic scale cyclone dynamics so addressing an area of current debate numerical weather prediction simulations of a sj containing windstorm are analysed and lagrangian trajectories used to assess the evolution of and mesoscale atmospheric instabilities e g symmetric and inertial instabilities in the descending airstream the sj undergoes a two stage descent cooling via sublimation followed by a large acceleration accompanied by instability release combined tilting and stretching of vorticity play a major role in the local onset of instability on the airstream vorticity and frontogenesis fields have a narrow slantwise banded structure in the cloud head and around the sj the descending sj modifies the widespread frontolysis expected from the large scale dynamics alone in the frontal fracture region a coarser resolution simulation also generates strong winds in the frontal fracture region although these are significantly weaker than in the higher resolution simulation the sj airstream in the coarser resolution simulation undergoes a weaker descent without instability generation and descends in a widespread frontolytic region hence while the sj undergoes a process of destabilisation that enhances its descent and acceleration in the higher resolution simulation enhancing the strong winds already generated by the synoptic scale cyclone dynamics this destabilisation does not occur in the sj produced by a coarser resolution simulation resulting in weaker winds this analysis reveals the synergy between the paradigms of sj occurrence through the release of mesoscale instabilities and synoptic scale cyclone dynamics and demonstrates that the current debate may in part be a consequence of the model resolutions used by different studies

coordinated biotic and abiotic change during the great ordovician biodiversification event darriwilian assembly of early paleozoic building blocks abstract the ordovician period records an extraordinary biodiversity increase known as the great ordovician biodiversification event gobe which coincided with a series of environmental changes to the earth system notably a cooling global ocean increased oxygenation and increased nutrient supply from volcanism and continental weathering the co evolution of earth and its biota during this interval has been studied in various contexts on multiple paleocontinents emerging patterns depend on the lens of investigation here we summarize the current state of understanding by reviewing and synthesizing the fossil and sedimentary records recent paleontological studies mainly focused on rhynchonelliform articulated brachiopods bryozoa cephalopods trilobites graptolites echinoderms and reef organisms have documented details of diversification body size increase development of ecosystem complexity and intensification of inter continental dispersal from the late cambrian through late ordovician biomass increased markedly between the early and middle ordovician furthermore diversification rates increase statistically during the mid darriwilian age both globally and regionally coincident with these biotic changes geochemical proxies record significant changes to earth s physical system oceanic temperatures decreased and atmospheric oxygen levels increased to near modern levels in concert with the middle ordovician diversification of shelly fauna anoxic pulses ceased and evidence for deep ocean ventilation prevails in middle ordovician strata furthermore a major middle late ordovician change in oceanic strontium isotopic composition indicates increased weathering of juvenile volcanic rocks and delivery of nutrients to marine settings this multi proxy dataset records near simultaneous changes in fossil rich shallow marine environments during exactly the interval of greatest diversification by integrating biotic and geochemical datasets a clear picture of the co evolution of earth and its biota emerges indicating that the darriwilian was the critical interval facilitating increased capacity of ecosystems we therefore recommend restricting the term gobe to indicate this short interval of rapid diversification and ecosystem change and using ordovician radiation when referencing the sum of diversifications that occurred throughout the ordovician period

symbiotic endobiont biofacies in the silurian of baltica abstract the distribution of symbiotic endobionts in silurian stromatoporoids of estonia is correlated with the diverse sedimentary facies formed in this portion of the baltica palaeocontinent these depositional environments are characterized by different symbiotic endobiont associations there are two onshore shallow water and one offshore deeper water symbiotic endobiont associations water depth was not the only controlling factor for their distribution seawater nutrient levels hydrodynamics especially substrate stability sedimentation rates and distribution of stromatoporoid hosts may have also played important roles

near surface strong winds in a marine extratropical cyclone acceleration of the winds and the importance of surface fluxes a rapidly developing extratropical cyclone named tini brought strong winds to ireland and the united kingdom on 12 february 2014 a mesoscale model simulation is used to analyze the development of the strong winds through the terms in the horizontal momentum equation the maximum of near surface wind speed equatorward of the cyclone was composed of two different airstreams that underwent different paths to acceleration first horizontally moving air in the cold conveyor belt was accelerated by the along flow pressure gradient force but was decelerated by friction second descending air accelerated into the eastern end of the maximum of near surface wind speed and was associated in part with a sting jet caused by the increasing along flow horizontal pressure gradient force at lower levels when this descending air entered the boundary layer it too was decelerated by surface friction surface fluxes of heat and moisture were necessary to destabilize and deepen the boundary layer allowing mixing of the strongest winds from the free troposphere down to the surface a simulation with the surface fluxes turned off during cyclogenesis showed a more stable boundary layer around the bent back front which inhibited the strongest winds from reaching the surface the descent of the sting jet air was associated with a maximum in quasigeostrophic omega which consisted of both synoptic scale and mesoscale descent the latter associated with frontolysis occurring at the end of the bent back front thus the near surface wind maximum was created by the synoptic scale and mesoscale dynamics whereas localized moist processes were negligible

invertebrate epibionts on ordovician conulariids from the prague basin czech republic bohemia abstract approximately 4 of just over 5000 conulariids from ten ordovician formations in the prague basin czech republic exhibit invertebrate epibionts and or attachment scars the commonest epibionts are craniid brachiopods followed by bryozoans and edrioasteroids which are invariably articulated less abundant are monoplacophorans sphenothallus sp lichenocrinus sp and an indeterminate invertebrate epibionts occur on anaconularia anomala archaeoconularia conulariella sp and pseudoconularia grandissima though predominantly on a anomala and archaeoconularia from open shelf deposits in the upper ordovician letna and zaho any formations in which conulariids are substantially more abundant than in other formations epibionts on a particular conulariid belong to a single species or up to three species and major taxa except for monoplacophorans epibionts occur on the external surface of the conulariids in some cases with brachiopods bryozoans or edrioasteroids present on all four faces brachiopods and edrioasteroids present on all four faces show little variation between the faces in their size range also brachiopods show apparent random trending of the antero posterior axis while edrioasteroids on some specimens of a anomala and archaeoconularia are preferentially centered on or near the facial midline on schott bearing specimens of a anomala exhibiting brachiopods and or edrioasteroids these and other epibionts are absent on the schott bryozoans on some a anomala and archaeoconularia cover portions of all four faces and corners and on two specimens of a anomala the schott too is encrusted a similar case involving edrioasteroids on archaeoconularia sp from the upper ordovician upper tiouririne formation of morocco is documented these results highlight the importance of ordovician conulariids as biological substrates especially in perunica and south polar gondwana and indicate that encrustation occurred both on live individuals and on dead ones the corners and midlines influenced the settlement and subsequent growth of brachiopods and edrioasteroids and conulariids bearing these epibionts were buried catastrophically

symbiosis of conulariids with trepostome bryozoans in the upper ordovician of estonia baltica abstract the trepostome bryozoans diplotrypa abnormis d bicornis d petropolitana esthoniopora communis e subsphaerica mesotrypa excentrica m expressa m raritabulata and monotrypa jewensis have symbiotic associations with the conulariid climacoconus bottnicus in the upper ordovician of estonia all bryoimmured conulariids are very small and oriented perpendicular or nearly so to the growth surface of the host trepostome colony muddy seafloors may have promoted this symbiosis between conulariids and bryozoans because the former required a hard substrate for attachment it is possible that the numerous smaller specimens among endobiotic conulariids usually died as juveniles together with their bryozoan host or alternatively the smaller endobiotic conulariids may have been lilliput forms of free living conulariids that died at a mature age conulariid trepostome associations were likely not a result of accidental intergrowth of two organisms additional protection against predators provided by the calcitic bryozoan skeleton may have been among the benefits for the conulariid symbionts usually trepostomes with conulariid symbionts do not contain other invertebrates but in the katian in some cases they also hosted anoigmaichnus bioclaustrations the exact type of symbiosis between trepostomes and conulariids remains unresolved but most likely the associations were slightly parasitic or commensal the available data suggest that bryozoans preferred cnidarians over the other invertebrates as symbionts

pre hirnantian latest ordovician benthic community assemblages controls and replacements in a siliciclastic dominated platform of the eastern anti atlas morocco lower middle ashgill sedimentary strata from the mediterranean region have recorded a key episode of temperate to cold water carbonate productivity predating the onset of the hirnantian glaciation the latitudinal position of the moroccan margin of north gondwana during ashgill should have been adequate for the recorded development of carbonate factories however carbonate productivity was neither homogeneous nor laterally persistent as documented in the eastern anti atlas whereas in the erfoud area the bryozoan dominated limestones of the ashgill khabt el hajar formation indicate the intensive activity of carbonate factories these were dramatically reduced in the tiskaouine and gaiz jbels alnif area ca 100 km to the wsw of erfoud in alnif the caradoc ashgill transition lies within the ktaoua group which represents a siliciclastic dominated platform partly truncated by the hirnantian glaciogenic unconformity there three distinct carbonate factories are recognized across the caradoc ashgill transition and early mid ashgill times primarily controlled by accommodation space distance from source areas and subsequent siliciclastic input and benthic community replacements i quiescent episodes of prograding sandy shoals are indicated by a distinct assemblage of epibenthic to quasi endobenthic brachiopods heterorthids drabovids and rafinesquinids and non pelmatozoan echinoderms sphaeronitids and aristocystitids that colonized inclined foresets ii bryozoan thickets rich in robust and delicate branching and encrusting growth forms flourished on carbonate substrates of the distal offshore parts of the platform during major flooding episodes and iii stratigraphically condensed densely fossiliferous phosphatized coquinas display peaks in biodiversity patterns as they are rich in epibenthic rhynchonellid heterorthid and rafinesquinid brachiopods calymenid dalmanitid cheirurid and illaenid trilobites sinuitid eotomariid and holopeid gastropods and hyolithids other episodic and environmentally restricted carbonate factories developed on the alnif mixed platform but are incompletely constrained due to the allochthonous character of their benthic pelagic assemblages which are ecologically mixed due to the effects of continuous shallow water erosive reworking and taphonomically complex histories these shelly carbonate factories allow recognition of the dominant benthic community assemblages that predated the onset of the hirnantian glaciation on this part of the moroccan margin of north gondwana

global frequency of magnitude 9 earthquakes for decades seismologists have sought causal relationships between maximum earthquake sizes and other properties of subduction zones with the underlying notion that some subduction zones may never produce a magnitude 9 or larger event the 2004 andaman m w 9 2 earthquake called into question such ideas given multicentury return times of the greatest earthquakes ignorance of those return times and our very limited observation span i suggest that we cannot yet make such determinations present evidence cannot rule out that any subduction zone may produce a magnitude 9 or larger earthquake based on theoretical recurrence times i estimate that one to three m9 earthquakes should occur globally per century and the past half century with five m9 events reflects temporal clustering and not the long term average

the dynamic evolution of the palaeozoic geography of eastern asia abstract new palaeogeographical reconstructions are presented for eleven time intervals through the palaeozoic of the eastern asia region from the middle cambrian at 510 ma to the end of the permian at 250 ma they centre on the continental blocks of north china south china and annamia indochina and their relationships with northeastern gondwana which was united to form part of pangea from the late carboniferous onwards also shown is the continent of tarim during the lower palaeozoic as well as the hutag uul songliao and khanka jiamasu bureya terranes both of which straddle the russian mongolian and chinese borders today from silurian times onwards we conclude that annamia and south china were united as a single continent throughout the lower palaeozoic and early devonian and were translocated by major strike slip faulting along the northeastern gondwana margin during that period from off afghanistan to outboard of the sibumasu and australian sectors of the superterrane they left the gondwana marginal area together during the lower devonian opening of the palaeotethys ocean but very shortly afterwards they themselves divided into the two separate continental blocks that we recognise today not to reunite until the triassic the various cambrian to permian rocks found in japan largely represent active volcanic arcs which originally lay to the southeast of south china although the carboniferous was more quiescent there the neotethys ocean opened during the permian dividing sibumasu and the tibetan terranes from gondwana and the palaeotethys ocean started to close progressively in the upper palaeozoic as most of the east asian continents and smaller terranes moved towards siberia the positions of the various continents and terranes have been deduced from a mixture of palaeomagnetic and faunal data the positions of large igneous provinces and kimberlites and the need to provide kinematic continuity between maps of successive ages however many uncertainties remain

epibionts on shells in the sarka formation a sparsely occupied niche in the lower to middle darriwilian oretanian ordovician in the prague basin czech republic abstract epizoic invertebrates attached to shells are a rare component of the fauna of the sarka formation middle ordovician early to middle darriwilian of the prague basin barrandian area in the czech republic epibionts are known exclusively from siliceous nodules and consist of echinoderms edrioasteroids and possible crinoid holdfasts monoplacophorans and bryozoans all attached to a very small number of host taxa among them hyoliths are the strongly preferred substrate 60 of observed host shells with edrioasteroids possible crinoid holdfasts and the monoplacophoran pygmaeoconus attaching exclusively to these organisms epizoan holdfasts were also found on a unique ramose problematic fossil considered to be the first octocoral specimen from the sarka formation most of the host are interpreted have been colonized during life only a few shells were used for attachment post mortem all epibionts are attached to the outer surface of the shell with the exception of the monoplacophoran barrandicella which is attached to the internal surface of empty conulariid thecae some of the epibionts shed additional light on the mode of life of their hosts including the bivalve redonia which is shown to be semi infaunal rather than infaunal more generally epibionts in the sarka formation attest to a very low level of occupancy of this significant niche during the early stages of the great ordovician biodiversification event

the sting at the end of the tail model diagnostics of fine scale three dimensional structure of the cloud head this is the second in a series of papers on the sting at the end of the tail a mesoscale region of potentially damaging surface winds that can occur close to the evaporating tip of a cloud head wrapped around the bent back front of an extratropical cyclone in the first paper the sting phenomenon was identified from a purely observational study of the great storm of october 1987 in the present paper an observationally validated forecast run from a high resolution numerical weather prediction model is used to examine the evolving three dimensional structure of the sting phenomenon it is shown that the damaging surface winds in the october 1987 storm were due to a well defined mesoscale sting jet sj identifiable as a coherent ensemble of trajectories originating in cloudy air at about 650 hpa there is evidence of multiple mesoscale slantwise circulations and the sj appears to form within the descending part of these circulations air within the sj descends to the 900 hpa level over a period of about 4 h during which time it accelerates from less than 20 to above 45 m s 1 with extremes greater than 50 m s 1 although the wet bulb potential temperature of air in the sj remains constant during its descent to 900 hpa evaporation leads to a reduction of up to 5 k or more in dry bulb potential temperature in some parts of the jet the sj is situated behind the primary cold front and is distinct from the associated warm conveyor belt low level jet it is also distinct from the cold conveyor belt low level jet which remains below and behind it as the sj skirts the bent back front crown copyright 2005

origin of strong winds in an explosive mediterranean extratropical cyclone abstractduring 2 3 december 2012 the black sea and east coast of romania were affected by a rapidly deepening mediterranean cyclone the cyclone developed a bent back front along which short lived

investigating the imf cone angle control of pc3 4 pulsations observed on the ground many studies have shown that pc3 4 pulsations 0 014 0 1 hz observed in earth s magnetosphere during daytime hours originate in the ion foreshock region of the solar wind just upstream from earth s bow shock they occur when the interplanetary magnetic field imf is primarily radial when the imf cone angle xb 45 however our knowledge of ion foreshock conditions is often incomplete because of the very limited number of spacecraft providing upstream data in this study we compared 13 months of wave observations at two widely separated ground stations hornsund svalbard and halley antarctica to imf values in the omni database in order to test this relation values of xb and the empirically predicted wave frequency fcalc 0 06 bimf were compared to daily fourier spectrograms displaying pulsation power and frequency although there was often good temporal agreement between low xb and increased pc3 4 wave power numerous counterexamples were also evident a statistical study of wave activity in quarter hour increments showed that pc3 4 pulsations were associated with low xb values 81 of the time at hornsund and 83 at halley imf cone angle data from all available upstream monitors were compared to wave observations for a more limited number of days many of these showed inconsistent imf orientations this study indicates some of the limitations of the existing upstream monitors and provides a quantitative estimate 80 of the accuracy of the omni data set in characterizing conditions near the nose of earth s bow shock under predominantly radial imf conditions

integrated brachiopod based bioevents and sequence stratigraphic framework for a late ordovician subpolar platform eastern anti atlas morocco the upper ordovician katian hirnantian brachiopods of tafilalt eastern anti atlas are locally abundant diverse and well preserved providing a near continuous record of faunal change on a high latitude siliciclastic dominated platform a chronostratigraphic framework based on brachiopod distribution and preservation in shell accumulation events and integrated with sequence stratigraphy has been generated for the katian interval which has allowed correlation with the chitinozoan based chronostratigraphic and sequence stratigraphic framework erected for the central anti atlas in tafilalt two katian transgressive regressive composite depositional sequences c 60 and 170 m thick and related to third order fluctuations in sea level were unaffected by hirnantian glaciogenic erosion they were deposited on a mixed platform with a bryonoderm association dominated by brachiopods bryozoans and echinoderms brachiopods developed in high energy inner shelf areas whereas bryozoans mainly trepostomates and fenestrates and pelmatozoans cystoids and crinoids dominated in low energy outer shelf areas brachiopod accumulations mark distinct event surfaces such as lag and event concentrations hydraulic simple and composite concentrations related to transgressive surfaces and hiatal condensed concentrations marking maximum flooding surfaces the taphonomic condensation displayed by the hirnantian alnif member which onlaps the erosive base of glaciogenic tunnel channels is explained as reworking and resedimentation of allochthonous robust biogenic hard parts sourced from the underlying katian ktaoua group

skillful prediction of multidecadal variations in volcanic forcing stratospheric sulfate injections from explosive volcanic eruptions are a primary natural climate forcing improved statistical models can now capture and simulate dynamical relationships in temporal variations of binary data leveraging these new techniques the presented analysis clearly indicates that the number of large eruptions in the most recent records of explosive volcanism cannot be considered to be fully random including dynamical dependence in our models improves their ability to reproduce the historical record and thus forms a strong basis for skill in statistical prediction possible geophysical mechanisms behind the identified multi decadal variations are discussed including variations in the observed length of day

sequence stratigraphy and depositional facies of lower ordovician cyclic carbonate rocks southern missouri u s a abstract lower ordovician cyclic carbonate strata of southern missouri were deposited in a warm shallow epeiric sea on a fully aggraded carbonate platform sedimentological characteristics distinguish the jefferson city and cotter dolomites from the underlying gasconade and roubidoux formations mixed carbonate siliciclastic sedimentation characterizes the roubidoux formation with sandstones accounting for up to 60 of sedimentation the gasconade jefferson city and cotter dolomites exhibit an increased occurrence of chalcedonic chert nodules in very similar shape and texture to the gypsum and anhydrite nodules common on modern sabkha supratidal flats casts of halite and ghosts of gypsum laths also exist in the jefferson city and cotter strata but are rarely found in the underlying units facies analysis from drill cores and outcrop sections provides the basis for identifying two major meter scale cycle types type i cycles consist of algal stromatolites tidal flat laminites mechanical and algal ooid grainstones wavy peloidal wackestones and quartz sandstones interpreted as peritidal facies they are the dominant components of the roubidoux formation jefferson city dolomite and cotter dolomite type ii cycles consist mostly of subtidal facies such as strongly burrowed mudstone thrombolite boundstone and stromatolites type i cycles are thinner and represent highstand systems tracts whereas the thicker type ii cycles represent transgressive systems tracts and are dominant in the gasconade dolomite the cycle stacking patterns facies changes and the intrabasinal correlatability of fischer plots made from the widely spaced sections argue for a eustatic control on sea level fluctuation on the platform interbasinal correlation with other north american basins is possible using biostratigraphic information and comparison of fischer plots five missouri sequences correlate with those described for other regions the continent wide uniformity in cycle stacking patterns indicates a primarily eustatic control on lower ordovician meter scale cycle development regional tectonic and autocyclic controls probably account for general differences in sedimentation pattern among the correlated basins

conditional symmetric instability in sting jet storms sting jets are transient mesoscale jets of air that descend from the tip of the cloud head towards the top of the boundary layer in severe extratropical cyclones and can lead to damaging surface wind gusts this recently identified jet is distinct from the well documented jets associated with the cold and warm conveyor belts one mechanism proposed for their development is the release of conditional symmetric instability csi here the spatial distribution and temporal evolution of several csi diagnostics in four severe storms are analysed a sting jet has been identified in three of these storms for comparison we also analysed one storm that did not have a sting jet even though it had many of the apparent features of sting jet storms the sting jet storms are distinct from the non sting jet storms by having much greater and more extensive conditional instability ci and csi csi is released by ascending air parcels in the cloud head in two of the sting jet storms and by descending air parcels in the other sting jet storm by contrast only weak ci to ascending air parcels is present at the cloud head tip in the non sting jet storm csi released by descending air parcels as diagnosed by decaying downdraught slantwise convective available potential energy dscape is collocated with the sting jets in all three sting jet storms and has a localised maximum in two of them consistent evolutions of saturated moist potential vorticity are found we conclude that csi release has a role in the generation of the sting jet that the sting jet may be driven by the release of instability to both ascending and descending parcels and that dscape could be used as a discriminating diagnostic for the sting jet based on these four case studies copyright 2011 royal meteorological society and british crown copyright the met office

the linkage between the warm and the cold conveyor belts in an idealized extratropical cyclone abstractthis study continues the investigation of airstreams in idealized moist baroclinic waves and addresses the formation of the cold conveyor belt ccb its linkage to the warm conveyor belt wcb and their impact on the development of a midlatitude cyclone the ccb is identified as a coherent bundle of trajectories characterized by weak ascent and a strong increase of potential vorticity pv along the flow in contrast to the wcb defined as the trajectories with maximum ascent the authors illuminate the role of the two conveyor belts in the formation of two strong pv anomalies that form in the upper wcb negative pv anomaly and lower troposphere ccb positive pv anomaly respectively and thereby establish a link between these airstreams and relevant aspects of the dynamics of extratropical cyclones the ccb moves close to the surface along the colder side of the bent back front and experiences a pv increase as it passes below a region of maximum latent heat release at midtropospheric level

baltica a synopsis of vendian permian palaeomagnetic data and their palaeotectonic implications torsvlk t h smethurst m a van der voo r trench a abrahamsen n and halvorsen e 1992 baltlca a synopsis of vendlan permmn palaeomagnetic data and their palaeotectonlc implications earth sci rev 33 133 152 in light of recent additions to the palaeozoic palaeo magnetlc data base particularly for the ordovlclan era a revised apparent polar wander apw path for baltica has been constructed following a rigorous synthesis of all late precambrlan perm lan data the apw path is characterized by two prominent loops firstly a late precambrlan camb rlan loop probably relating to a rifting event and secondly a younger loop relating to a mid silurian scandlan colhsion event these features imply major change in plate tectonic reconfiguratlon baltlca probably represented an individual continental unit m early palaeozoic times and was positioned m high southerly latitudes in an inverted geographic orientation in such a reconstruction baltlca was separated from the northern margin of gondwana by the tornqulst sea and from laurentla by the iapetus ocean the tornqulst zone is thus interpreted as a passive or dextral transform margin during the early palaeozoic while undergoing counter clockwise rotations up to 1 6 ma baltica drifted northward through most ol the palaeozoic except for a short period of southerly movement in late silurian early devonian times after colhslon with laurentla rapid movements in latitude up to 9 cm yr are noted m late precambrlan earl y palaeozoic times and slgmficant decrease in velocities throughout palaeozoic time probably reflect the progressive amalgamation of a larger continent by early devonian euramerlca and permian pangea times the tornqulst sea had a principal component of palaeo east west orientation hence it is difficult to be precise in the timing of when micro continents such as eastern avalonla and the european masslfs ultimately collided along the southwestern margin of baltica these micro continents are considered to have been peripheral to gondwana m high southerly latitudes during the early ordovlclan eastern avalonla clearly had rifted off gondwana by llanvlrn llanded o times and may have collided with baltlca during late ordovlclan times although the present available sdunan palaeomagnetlc data from eastern avalonia may suggest colhslon in late silurian times across the lapetus facing margin of baltica laurentla was s tuated in equatorml to southerly latitudes during most of the lower palaeozoic these continents collided in mid silurian times l e a first collision between southwestern norway and greenland scotla nd which gave rise to the early scandlan orogeny 425 ma in southwestern norway possible followed by a later but less dramatic scandlan event in northern norway at around 410 ma since baltlca was geographically reverted m early palaeozoic times the colhsional margin could not have been a margin that once rifted off laurentm as assumed in a number of plate tectonic models

the role of evaporating showers in the transfer of sting jet momentum to the surface the most damaging winds in a severe extratropical cyclone often occur just ahead of the evaporating ends of cloud filaments emanating from the so called cloud head these winds are associated with low level jets lljs sometimes occurring just above the boundary layer the question then arises as to how the high momentum is transferred to the surface an opportunity to address this question arose when the severe st jude s day windstorm travelled across southern england on 28 october 2013 we have carried out a mesoanalysis of a network of 1 min resolution automatic weather stations and high resolution doppler radar scans from the sensitive s band chilbolton advanced meteorological radar camra along with satellite and radar network imagery and numerical weather prediction products we show that although the damaging winds occurred in a relatively dry region of the cyclone there was evidence within the llj of abundant precipitation residues from shallow convective clouds that were evaporating in a localized region of descent we find that pockets of high momentum were transported towards the surface by the few remaining actively precipitating convective clouds within the llj and also by precipitation free convection in the boundary layer that was able to entrain evaporatively cooled air from the llj the boundary layer convection was organized in along wind rolls separated by 500 to about 3000 m the spacing varying according to the vertical extent of the convection the spacing was greatest where the strongest winds penetrated to the surface a run with a medium resolution version of the weather research and forecasting wrf model was able to reproduce the properties of the observed llj it confirmed the llj to be a sting jet which descended over the leading edge of a weaker cold conveyor belt jet

attribution of strong winds to a cold conveyor belt and sting jet a high resolution version of the wrf weather research and forecasting model has been used to study the fine structure of a cloud head and its associated cold conveyor belt jet cj and sting jet sj in an intense extratropical cyclone that produced damaging surface winds in northern ireland and central scotland on 3 january 2012 the model was run with many different initialisation times and physical parametrisations and a run was selected that verified well against a variety of observations new methods have been devised to visualise the 3d structure of the cj and sj and to attribute strong surface winds to one or other of them and the validity of regarding the sj as a semi lagrangian feature has been assessed the model suggests that whereas the cj remained mainly below the 850hpa level as it circulated around the bent back front the sj consisted of a stream or streams of air within the bent back frontal zone that first ascended from close to the surface into the middle and upper level parts of the cloud head before descending from evaporating cloud filaments at the tip of the cloud head and reaching the top of the boundary layer slightly ahead of the cj the simulations did not support the idea that either the evaporation or conditional symmetric instability csi played a major role in the development of these jets the strong gusts up to 47ms 1 w hich were recorded on the north coast of ireland appear to have been due mainly to the cj which by then was undercutting the sj the sj was responsible for stronger surface winds than the cj several hours earlier during the initial stage of frontal fracture but only for a limited period

dynamics of sting jet storm egon over continental europe impact of surface properties and model resolution intense shapiro keyser cyclones are often accompanied by a sting jet sj an air stream that descends from the cloud head into the frontal fracture region and can cause extreme surface gusts previous case studies have concentrated on the north atlantic and the british isles here we present the first ever detailed analysis of an sj over continental europe and investigate the influence of topography on its dynamical evolution based on observations and high resolution simulations using the icosahedral nonhydrostatic model icon windstorm egon intensified over the english channel and then tracked from northern france to poland on 12 13 january 2017 causing gusts of almost 150 km h 1 and important damage icon reproduces the storm dynamics although it delays the explosive deepening shifts the track southward over belgium and germany and underestimates gusts over land storm characteristics show weak sensitivity to varying grid spacing between 1 6 and 6 5 km while switching off the convection parametrization at 3 3 km grid spacing improves correlations with surface observations but deteriorates the mean error trajectories reveal typical sj characteristics such as mid level descent strong acceleration and conditional symmetric and other mesoscale instabilities while evaporative cooling is stronger than in previous cases from the literature preventing drying during descent the sj identification and the occurrence of mesoscale instabilities depend considerably on model resolution convective parametrization output frequency and employed thresholds for trajectory selection sensitivity experiments with modified surface characteristics show that the combined effects of warm air blocking by the alps higher roughness over land and reduced surface fluxes cause egon to fill more quickly and to move on a faster more northern track across germany while the sj response is complex showing some compensating effects surface gusts strongly increase when roughness is reduced these results suggest that weather forecasters in continental europe should be more aware of the potential risks associated with sjs

stacked slantwise convective circulations it is well known that classical ana cold fronts tend to be characterized by mesoscale circulations in which upright line convection feeds a layer of concentrated rearward slantwise ascent occasionally however as in the case study presented in this paper two and sometimes more of these mesoscale circulations coexist within the same cold frontal zone the two slantwise circulations described were observed to be stacked one above the other with a vertical wavelength of less than 2 km although it is often suspected that the circulations at ana cold fronts are enhanced by mesoscale processes such as conditional symmetric instability csi or m adjustment it is notoriously difficult to discriminate between these circulations and the larger scale transverse circulation within which they are embedded the occurrence in this study of multiple circulations with small vertical scale helps to distinguish them from the large scale circulation and this has motivated the detailed examination of this case mesoscale circulations of the kind described are difficult to detect numerical weather prediction nwp models even high resolution models do not usually represent them and conventional observations do not show them clearly this study takes advantage of observations from a high resolution microwave doppler radar plus a high resolution analysis of ultra high frequency wind profiler radar data analysed in the context of output from an operational mesoscale nwp model the study defines the mesoscale structure of the event sufficiently carefully to provide a basis for future idealized modelling studies to investigate the possible roles of csi and m adjustment both of which appear to play a part in the maintenance of the circulations

ice core evidence for an explosive tropical volcanic eruption 6 years preceding tambora high resolution analyses of ice cores from antarctica and greenland reveal an explosive volcanic eruption in the tropics in a d 1809 which is not reflected in the historical record a comparison in the same ice cores of the sulfate flux from the a d 1809 eruption to that from the tambora eruption a d 1815 indicates a near equatorial location and a magnitude roughly half that of tambora thus this event should be considered comparable to other eruptions producing large volumes ofsulfur rich gases such as coseguina krakatau agung and el chichtn the increase in the atmospheric concentration of sulfuric acid may have contributed to the northern hemisphere cooling observed in the early nineteenth century and may account partially for the decline in surface temperatures which preceded the eruption of tamborn in a d 1815

biostratigraphy and palaeoecology of lower ordovician graptolites from the fezouata shale moroccan anti atlas abstract the fezouata shale fezouata formation has produced the most complete lower ordovician graptolite succession known from the african continent which was studied from 32 sections located along the western central and eastern moroccan anti atlas a composite biostratigraphic and chronostratigraphic scheme is presented for the entire formation that in ascending order comprises the anisograptus matanensis rhabdinopora flabelliformis anglica zones uppermost lower tremadocian adelograptus tenellus and aorograptus victoriae zones middle tremadocian araneograptus murrayi and hunnegraptus copiosus zones upper tremadocian cymatograptus protobalticus zone lower floian baltograptus jacksoni zone middle floian and the baltograptus minutus zone plus an azygograptus interval upper floian most of these zones or biozones are recorded for the first time in africa together with important graptolite species such as ancoragraptus bulmani spjeldnaes cym protobalticus monsen b jacksoni rushton clonograptus multiplex nicholson b minutus tornquist and azygograptus eivionicus elles a correlation with the graptolite sucession from the algerian sahara is also suggested reinforced by the common record of the minute anisograptid choristograptus louhai legrand providing its second world occurrence in the tremadocian of morocco the prior late tremadocian dating of the fezouata lagerstatte is here extended to the middle floian as revealed by the graptolite biochronology the repeated record along the lower and middle parts of the fezouata formation of deep water mesopelagic species of the genera araneograptus with mass occurrences of conical colonies together with large horizontal rhabdosomes of paratemnograptus paradelograptus clonograptus tetragraptus and holograptus schizograptus do not fit the sedimentological interpretation of deposition of these strata in much shallower inshore to mid shelf environments this inconsistency has implications when inferring the living conditions of the fezouata soft bodied assemblages

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

a rugose coral bryozoan association from the lower devonian of nw spain abstract a new rugose coral cystoporate bryozoan association is here described from the devonian of nw spain this is the first evidence of intergrowths between devonian rugose corals and bryozoans in this case bryozoans provided a suitable substrate for the settlement of corals which were subsequently encrusted by the bryozoans the hypothesis of intergrowth between living organisms is supported by the absence of encrustation of the rugose coral calices by the cystoporates we suggest that the association was specific and developed through chemical mediation this symbiosis was facultative for the bryozoans but likely not for the corals the association provided the bryozoan host with additional substrate for encrustation as well as protection from various predators and it allowed the rugose corals to grow in a muddy environment and benefit from the feeding currents of the bryozoans

convergent morphology in small spiral worm tubes spirorbis and its palaeoenvironmental implications calcareous tube worms generally identified as spirorbis range from ordovician to recent often profusely encrusting shells and other substrates whereas recent spirorbis is a polychaete annelid details of tube structure in pre cretaceous spirorbis suggest affinities with the microconchida an extinct order of possible lophophorates although characteristically palaeozoic microconchid tube worms survived the permian mass extinction before being replaced in late mesozoic ecosystems by true spirorbis recent spirorbis is stenohaline but spirorbiform microconchids also colonized freshwater brackish and hypersaline environments during the devonian triassic anomalies in the palaeoenvironmental distributions of fossil spirorbis are explained with the recognition of this striking convergence between microconchids and true spirorbis

distinguishing the cold conveyor belt and sting jet airstreams in an intense extratropical cyclone abstractstrong winds equatorward and rearward of a cyclone core have often been associated with two phenomena the cold conveyor belt ccb jet and sting jets here detailed observations of the mesoscale structure in this region of an intense cyclone are analyzed the in situ and dropsonde observations were obtained during two research flights through the cyclone during the diabatic influences on mesoscale structures in extratropical storms diamet field campaign a numerical weather prediction model is used to link the strong wind regions with three types of airstreams or coherent ensembles of trajectories two types are identified with the ccb hooking around the cyclone center while the third is identified with a sting jet descending from the cloud head to the west of the cyclone chemical tracer observations show for the first time that the ccb and sting jet airstreams are distinct air masses even when the associated low level wind maxima are not spatially distinct in the model the ccb experie

observations of the mesoscale sub structure in the cold air of a developing frontal cyclone observations from 58 dropwindsondes released in a mesoscale array during the fronts 92 experiment are interpreted in the context of satellite imagery to derive the mesoscale structure and evolution of parts of a frontal cyclone developing over the eastern north atlantic a conceptual model involving the intertwining of dry intrusion and cloud head flows is corroborated and is used to provide the framework for interpreting the detailed mesoscale behaviour in the cold air two distinct dry intrusions were responsible for two cold fronts trailing south westwards from the tip of the cloud head both were surface features at the beginning of our study but the leading one evolved into an upper front with mid level convection as the dry intrusion responsible for it overran the warm sector areas of both high and low potential vorticity were indicated within the dry intrusions upon encountering a critical level of zero system relative velocity at the top of the moist boundary layer the dry intrusions arrival was associated with the development of multiple dry and moist laminae near the top of the boundary layer the vertical wavelength of the laminae was about 1 km and they extended over 200 km in the front normal direction with a slope of typically 1 in 60 although most parts of the laminae were subsaturated their circulations combined with the double structure of the dry intrusions to produce multiple shallow cloud lines within the boundary layer these formed as an extension of the south western tip of the cloud head associated with the developing cyclone possible mechanisms for generating the observed structures are discussed

ordovician palaeogeography with new palaeomagnetic data from the montagne noire southern france a joint palaeomagnetic and ar 40 ar 39 study has been performed on two olistolithic blocks from the cabrieres wildflysch in the montagne noire region of the massif central in france there andesitic volcanic and volcaniclastic rocks of llanvirn early caradoc age ca 470 458 ma occur despite extensive secondary alteration destruction of the dominant magnetic mineral phase and ar 40 ar 39 whole rock experiments that demonstrate that the volcanic rocks suffered significant argon loss a positive fold test and the presence of dual polarities suggest that a primary ordovician magnetisation has mostly survived this is one of the few documented cases where the argon system was substantially reset whilst a subordinate set of small relatively unaltered magnetite grains probably hosted in silicates still carry the original in this case ordovician remanence the new data show that the montagne noire region was located at high southerly latitudes 68degrees 19 15 during the mid ordovician this latitude represents the location for nw gondwana of which the massif central was a part palaeomagnetic data from all the central european massifs and terranes demonstrate a close link to the gondwana margin during the lower and middle ordovician

the lower ordovician fezouata konservat lagerstatte from morocco age environment and evolutionary perspectives abstract the lower ordovician fezouata konservat lagerstatte from southern morocco has been one of the major palaeontological discoveries of the last decade it provides a unique insight into one of the most critical periods in the evolution of marine life the cambrian ordovician transition however its potential for deciphering key trends in animal diversification was hitherto largely limited by major uncertainties concerning its stratigraphic position age and environmental setting based on extensive fieldwork fossil evidence and facies recognition our study provides clarification on these three crucial issues exceptional preservation is limited to two intervals within the fezouata shale graptolites indicate a late tremadocian age for the fezouata konservat lagerstatte as a whole which is supported by biostratigraphical evidence provided by acritarchs sedimentological features and reconstructed patterns of relative sea level changes indicate relatively shallow water environmental conditions under distal storm influence in an offshore to lower shoreface siliciclastic ramp setting the fezouata biota represents a unique and exceptional window into the palaeobiodiversity in open marine conditions thus contrasting with the other ordovician konservat lagerstatten presently known in our analyses of this new set of data we pave the way for accurate temporal faunal and environmental comparisons with other lower palaeozoic konservat lagerstatten and unlock the full potential of the fezouata biota to better understand the processes and scenarios of early animal radiations

credible occurrence probabilities for extreme geophysical events earthquakes volcanic eruptions magnetic storms 1 statistical analysis is made of rare extreme geophysical events recorded in historical data counting the number of events k with sizes that exceed chosen thresholds during specific durations of time under transformations that stabilize data and model parameter variances the most likely poisson event occurrence rate k applies for frequentist inference and also for bayesian inference with a jeffreys prior that ensures posterior invariance under changes of variables frequentist confidence intervals and bayesian jeffreys credibility intervals are approximately the same and easy to calculate 1 k z 2 2 k z 2 2 where z is a parameter that specifies the width z 1 z 2 corresponding to 1 68 3 2 95 4 if only a few events have been observed as is usually the case for extreme events then these error bar intervals might be considered to be relatively wide from historical records we estimate most likely long term occurrence rates 10 yr occurrence probabilities and intervals of frequentist confidence and bayesian credibility for large earthquakes explosive volcanic eruptions and magnetic storms

reexamining the cold conveyor belt abstract despite the popularity of the conveyor belt model for portraying the airflow through midlatitude cyclones questions arise as to the path of the cold conveyor belt the lower tropospheric airflow poleward of and underneath the warm front some studies beginning with carlson s analysis of the eastern u s cyclone of 5 december 1977 depict the cold conveyor belt moving westward reaching the northwest quadrant of the storm turning abruptly anticyclonically rising to jet level and departing the cyclone downstream hereafter the anticyclonic path other studies depict the cold conveyor belt reaching the northwest quadrant turning cyclonically around the low center and remaining in the lower troposphere the cyclonic path to clarify the path of the cold conveyor belt the present study reexamines carlson s analysis of the cold conveyor belt using an observational and mesoscale numerical modeling study of the 5 december 1977 cyclone this reexamination raises several previously unappreciated

interhemispheric observations of dayside convection under northward imf 1 the reverse convection potential and electric field under northward interplanetary magnetic field imf has been shown to saturate at a larger value in the summer than in the winter previous studies of reverse convection under northward imf have suggested that in the winter hemisphere much of the reconnection involves internal reconnection with over draped field lines from the summer hemisphere we present a case study in which reverse convection was simultaneously visible in the northern and southern hemispheres near the northern winter solstice we use superdarn radar velocity measurements to demonstrate that the sunward reverse convection along the noon meridian is significantly faster in the summer hemisphere we also use dmsp energetic particle data to demonstrate that in the winter hemisphere some of the convection circulates on closed field lines which is a signature of internal reconnection these results suggest that internal reconnection is much less effective in transmitting the interplanetary electric field ief into the ionosphere

palaeobiogeography palaeoecology and evolution of lower ordovician conulariids and sphenothallus medusozoa cnidaria with emphasis on the fezouata shale of southeastern morocco abstract the fossil record of conulariids cnidaria scyphozoa extends downward into the topmost part of the ediacaran system but the first appearance of diverse widespread conulariids is in siliciclastic rock units of early ordovician age which collectively host at least six conulariid genera some of these same units also contain sphenothallus a probable medusozoan that frequently co occurs with conulariids in ordovician and younger deposits lower ordovician conulariid localities are distributed among five originally southern hemisphere terranes namely core gondwana archaeoconularia eoconularia and teresconularia armorica conularia azaisi avalonia archaeoconularia eoconularia and exoconularia perunica archaeoconularia conularia and conulariella and south china conulariella c azaisi currently known from the southern montagne noire france probably represents a new genus sphenothallus occurs in south china north china korea armorica southern montagne noire and core gondwana morocco in southeastern morocco burgess shale type konservat lagerstatten in the fezouata shale tremadocian floian yield archaeoconularia sp eoconularia sp and at least one species of sphenothallus this low diversity conulariid assemblage is most similar to the tremadocian assemblage of wales avalonia which likewise consists of a single species each of archaeoconularia and eoconularia in the fezouata shale archaeoconularia sp and eoconularia sp frequently occur in monospecific mass associations such associations probably represent an original clumped distribution on the seafloor additionally some eoconularia sp occur in v like pairs or radial clusters and also some specimens were attached at the apical end to a phosphatic brachiopod or to a corner sulcus of a larger specimen of eoconularia sp similar conulariid brachiopod associations consisting of conularia trentonensis and onniella sp occur in the upper ordovician katian collingwood shale of southern ontario canada

life in a living substrate modular endosymbionts of bryozoan hosts from the devonian of spain abstract a new bioclaustration structure is described from the emsian lower devonian aguion formation of asturias nw spain it is the result of intergrowth of two bryozoan species leioclema elegans and loxophragma cf leptum hosting an unknown soft bodied modular symbiont these structures point to the development of host specific symbiotic associations in which both partners grew simultaneously the association is tentatively assessed as commensalism no evidence suggesting parasitism or mutualism has been found a revision of the existing literature on devonian bryozoans reveals that tubular structures similar to those described herein have been observed in different regions of the world only a few trepostome genera developed this kind of association during the devonian and leioclema seems to have been a suitable partner in intergrowths with a range of soft bodied and skeletonized organisms it is suggested that the association described herein was relatively common during the devonian and that molecular factors such as chemical mediation may have played a role in conducting the development of these specific intergrowths

benthic carbonate factories of the phanerozoic marine carbonate precipitation occurs in three basic modes abiotic or quasi abiotic biotically induced and biotically controlled on a geologic scale these precipitation modes combine to form three carbonate production systems or factories in the benthic environment 1 tropical shallow water factory dominated by biotically controlled mainly photo autotrophic and abiotic precipitates 2 cool water factory dominated by biotically controlled mainly heterotrophic precipitates and 3 mud mound factory dominated by biotically induced mainly microbial and abiotic precipitates sediment accumulations of the factories differ in composition geometry and facies patterns and some of these differences appear prominently in seismic data thus facilitating subsurface prediction the characteristic accumulation of the tropical factory is the flat topped often reef rimmed platform in cool water systems reefs in high energy settings are scarce and hydrodynamic influence dominates producing seaward sloping shelves and deep water sediment drifts often armored by skeletal framework the typical accumulation of the mud mound factory is groups of mounds in deeper water where the mud mound factory expands into shallow water it forms rimmed platforms similar to the tropical factory the tropical factory is most productive the mud mound factory reaches 80 90 and the cool water factory 20 30 of the tropical growth rate the three factories represent end members connected by transitions in space transitions in time are linked to biotic evolution

the life cycle of an extratropical marine cyclone part ii mesoscale structure and diagnostics abstract this is the second of two articles describing the evolving structure and selected physical processes within an intense extratropical marine cyclone observed during the experiment on rapidly intensifying cyclones over the atlantic erica field program part i describes the 24 h frontal cyclone evolution through 6 h horizontal analyses of observations taken by specially deployed observing systems from air land and sea part ii presents frontal scale and precipitation structures and physical processes from analyses based primarily on research aircraft observations taken during three phases of the cyclone s life cycle horizontal analyses at 350 m above ground level describe the cyclone s mesoscale frontal baroclinic structure and associated flow patterns the vertical structure and evolution of the cyclone s cold front warm front and bent back front are illustrated in cross sectional analyses of potential temperature wind velocity potential vorticity pv front relative transverse flow vecto

diverse early endobiotic coral symbiont assemblage from the katian late ordovician of baltica abstract a diverse early endobiotic coral symbiont assemblage has been detected within heliolitid tabulate corals of katian age from northwestern estonia this assemblage indicates that the earliest endobiotic coral symbiont communities were not restricted to north america the symbiotic endobiont assemblage comprises abundant cornulites aff celatus and rare conchicolites hosholmensis and chaetosalpinx sp the cornulitids are the earliest known symbiotic endobionts of this group the symbiotic endobionts presumably occurred in certain hosts only and preferred protoheliolites dubius over propora speciosa this record indicates that early endobiotic cornulitids were more diverse than previously thought and appeared in large numbers in the katian it is possible that the appearance of abundant skeletal symbiotic coral endobionts may coincide with the global ordovician biodiversification event supporting the hypothesis of escape from increased predation

symbiotic endobionts in paleozoic stromatoporoids abstract stromatoporoids hosted a diverse fauna of symbiotic endobionts during the silurian and devonian assemblages of symbiotic endobionts from the ordovician silurian and devonian differ significantly the only symbiotic association in the ordovician is cornulitid stromatoporoid the diversity of silurian and devonian symbiotic associations is similar but the taxonomic compositions of the silurian i e rugosans syringoporids cornulitids lingulids chaetosalpinx and helicosalpinx and devonian i e syringoporids torquaysalpinx chaetosalpinx streptindytes and rugosans associations are different symbiotic corals dominated both silurian and devonian associations rugosans dominated the silurian associations and syringoporids dominated the devonian associations

sting jets in extratropical cyclones a review this paper reviews the current state of knowledge of sting jets in extratropical cyclones sting jets were formally identified in 2004 by the pioneering work of keith browning reviewing this and subsequent studies we define the sting jet as a coherent air flow that descends from mid levels inside the cloud head into the frontal fracture region of a shapiro keyser cyclone over a period of a few hours leading to a distinct region of near surface stronger winds it therefore lies above the cold conveyor belt during some stage its life but at least in some cases descends to reach the top of boundary layer ahead of the cold conveyor belt it is not attributed to a specific mechanism in this definition we conclude that it is likely that a continuum of sting jet descent and speed up mechanisms exists at one extreme is balanced descent partly associated with frontolysis in the frontal fracture region more horizontally small scale and stronger frontolytic descent may occur associated with weak stability to slantwise convective downdraughts instability to slantwise convective downdraughts may occur in some systems leading to multiple slantwise convective downdraughts associated with the release of conditional symmetric instability and even possibly symmetric instability the global climatology of sting jets and the interaction between the atmospheric boundary layer and sting jets are revealed as specific areas where more research is needed finally we describe eight myths and misunderstandings that exist in the current literature with the aim of guiding future research into the sting jet phenomenon

occurrence rate of extreme magnetic storms 1 we investigate the occurrence rate of magnetic storms at the earth during the first part of our study the standard and integral distribution functions of magnetic storm value minimal dst index for the period 1963 2012 are analyzed and results show that the standard and integral distribution functions have power law tails with indexes 4 4 and 3 4 respectively during the second part statistical analysis of occurrence rate of magnetic storms induced by different types of interplanetary drivers is made using omni data for the period 1976 2000 using our catalog of large scale types of solar wind streams we study storms induced by interplanetary coronal mass ejections icmes separately magnetic clouds mcs and ejecta and both types of compressed regions corotating interaction regions cirs and sheaths for these types of drivers we calculate the integral probabilities of storms with minimum dst 50 70 100 150 and 200 nt the highest probability in this interval of dst is observed for mcs with the probabilities for other drivers being 3 10 times lower extrapolation of these results to extreme storms shows that a magnetic storm as large as the carrington storm in 1859 with dst 1760 nt is observed on the earth with frequency not higher than one event during 500 years