interaction of a tropical cyclone with a high amplitude midlatitude wave pattern waviness analysis trough deformation and track bifurcation an idealized scenario of extratropical transition et is investigated in which a tropical cyclone interacts with a high amplitude upper level wave pattern and well developed surface cyclones early during the interaction the external forcing of the upper level wave by the et system is quantified based on a metric for the waviness of the midlatitude flow local amplification of the wave pattern is diagnosed associated prominently with the trough downstream of et this amplified trough however exhibits pronounced anticyclonic breaking and thus in contrast to many previous et studies it is not clear that the amplification of the upper level wave propagates into the farther downstream region subsequently the et system merges with the upstream cyclone the upstream trough undergoes strong deformation and cyclonic breaking associated with straining due to the cyclonic circulation of the et system with the decay of this trough the et system weakens considerably and the upper level wave pattern changes locally to a zonal flow orientation this zonal flow pattern then extends into the downstream region and promotes the decay of the downstream baroclinic systems as in previous studies the evolution of et exhibits large sensitivity to the initial location of the tropical cyclone examining the steering flow s topology i e identifying the stagnation points and the streamlines emanating from these points helps to identify three different regimes a no et regime and two et regimes reminiscent of the northwest and northeast patterns respectively introduced previously by harr et al a stagnation point located on the axis of the upstream trough governs the bifurcation into no et and et regimes a stagnation point located on the axis of the downstream ridge governs the bifurcation into northwest and northeast patterns

the flank margin model for dissolution cave development in carbonate platforms the bahama islands contain many abandoned dissolution caves at elevations between two and seven metres above current sea level the development of dissolution caves in tropical carbonate islands is dependent on the position and nature of the freshwater lens lens position is controlled by sea level which in stable carbonate platforms like the bahamas is a function of glacioeustatic sea level still stands caves in the bahamas that are currently subaerial must have developed during past higher sea levels during the late quaternary sea levels higher than present have been relatively short lived and that limits the amount of time that a freshwater lens could be situated at the elevation required for the cave formation the bahama islands are low lying landforms where only aeolian ridges extend to elevations higher than six metres above current sea level past high sea level events greatly reduced the exposed land area of the bahama islands thus also limiting both the catchment for and size of freshwater lenses caves must be younger than the rock in which they are developed most subaerial bahamian caves are found in limestones that are less than 150000 years old development of large dissolution caves under these limitations of time and lens size requires a powerful dissolutional mechanism the mixing of discharging freshwater with tide pulsed incoming marine water under the flanks of emergent dune ridges may have produced the conditions necessary bahamian caves formed by this process are phreatic chambers with complex interconnections and blind tubes their presence demonstrates that significant dissolution can occur rapidly as a result of the mixing of fresh and marine waters beneath small carbonate islands

palaeo mixing zone karst features from palaeocene carbonates of north spain criteria for recognizing a potentially widespread but rarely documented diagenetic system abstract marine meteoric mixing zone dissolution effects are a major feature of present day karst systems in carbonate platforms yet are rarely reported in the geological record an example is described from the upper danian platform limestones of the alava province in the western pyrenees north spain this consists of several narrow zones with sponge like porosity analogous to the swiss cheese features found in present day mixing zones these zones are stained by fe oxides and overlie limestones which are irregularly dolomitized and contain disseminated pyrite these high porosity zones are interpreted as having developed in marine mixing zones where mixing corrosion and microbially mediated processes increased dissolution if collapsed ancient mixing zones could be misinterpreted as terra rossa palaeosols the main criteria to identify them as mixing zone products are their occurrence below a palaeo meteoric phreatic zone their association with stratified oxic and anoxic redox zones and petrographic evidence for highly variable calcite saturation states

cloud resolving ensemble simulations of the august 2005 alpine flood in this study we explore the potential benefits of applying a cloud resolving ensemble prediction system eps 2 2 km grid spacing over its driving synoptic scale limited area eps cosmo leps 10 km grid spacing driven by the ecmwf eps for a case of heavy precipitation over the alpine region the selected event is the devastating august 2005 flood that affected the northern alpine slopes the cloud resolving eps includes an explicit treatment of deep convection and dynamically downscales the cosmo leps information results are compared against rain gauge and radar data furthermore the sensitivity of the results to initial versus lateral boundary uncertainties are analyzed using a series of additional simulations comparison of the cloud resolving and its driving limited area eps pinpoints the high skill of both ensembles in simulating the major phase of heavy precipitation the high resolution eps yields more realistic rain amounts in particular in areas of active convection but in general the resolution induced differences tend to be smaller than typical member to member variability the differences between the two ensembles can be tied to the synoptic situation stratiform or convective precipitation location of the cyclone to the mesoscale interaction of the flow with the topography flow over the alpine ridge and to the experimental set up lead time and computational domain for the considered event and set up the growth of initial perturbations dominates over lateral boundary uncertainties during the first 12 integration hours afterwards the ensemble spread is controlled by large scale error growth advected from the lateral boundaries into the domain copyright 2008 royal meteorological society

integrated pan arctic melt onset detection from satellite active and passive microwave measurements 2000 2009 1 an integrated pan arctic melt onset data set is generated for the first time by combining estimates derived from active and passive microwave satellite data using algorithms developed for the northern high latitude land surface ice caps large lakes and sea ice the data set yields new insights into the spatial and temporal patterns of mean melt onset date mmod and the associated geographic and topographic controls for example in the terrestrial arctic tree fraction and latitude explain more than 60 of the variance in mmod with the former exerting a stronger influence on mmod than the latter elevation is also found to be an important factor controlling mmod with most of the arctic exhibiting significant positive relationships between mmod and elevation with a mean value of 24 5 m d 1 melt onset progresses fastest over land areas of uniform cover or elevation 40 80 km d 1 or both and slows down in mountainous areas on ice caps and in the forest tundra ecotones over sea ice melt onset advances very slowly in the marginal seas while in the central arctic the rate of advance can exceed 100 km d 1 comparison of the observed mmod with simulated values from the third version of the canadian coupled global climate model showed good agreement over land areas but weaker agreement over sea ice particularly in the central arctic where simulated mmod is about 2 3 weeks later than observed because of a cold bias in simulated surface air temperatures over sea ice

dynamics of orographically triggered banded convection in sheared moist orographic flows abstract shallow orographic convection embedded in an unstable cap cloud can organize into convective bands previous research has highlighted the important role of small amplitude topographic variations in triggering and organizing banded convection here the underlying dynamical mechanisms are systematically investigated by conducting three dimensional simulations of moist flows past a two dimensional mountain ridge using a cloud resolving numerical model most simulations address a sheared environment to account for the observed wind profiles results confirm that small amplitude topographic variations can enhance the development of embedded convection and anchor quasi stationary convective bands to a fixed location in space the resulting precipitation patterns exhibit tremendous spatial variability since regions receiving heavy rainfall can be only kilometers away from regions receiving little or no rain in addition the presence of banded convection has important repercussions on the area mean pr

far upstream precursors of heavy precipitation events on the alpine south side this study examines the upper level flow pattern that foreshadows the comparatively frequent co occurrence of heavy precipitation events on the alpine south side together with potential vorticity pv streamers aloft over western europe it is hypothesized that each streamer is itself preceded by a dynamically distinctive and a thermodynamically active flow associated with the space time development and the ultimate breaking over europe of synoptic scale rossby waves the ecmwf european centre for medium range weather forecasts era 40 dataset is used to examine the nature of a streamer s coherent precursor pattern by deriving seasonal composites of refined hovmoller diagrams the upper level pattern of the pv and its gradient and mid tropospheric diabatic heating for the autumn and winter seasons the composites reveal a significant and coherent wave packet precursor signal in the pv field that can be traced back 1 week to the central and eastern pacific contemporaneously the coherent signatures in the composite pv gradient field and diabatic heating fields are conducive to triggering and or supporting the wave signal and also contribute to subsequent downstream wave breaking in spring the composite precursor pv signal appears over and propagates eastward from the atlantic basin and its limited zonal extent is attributed to the lack of a coherent pv waveguide in summer the signal appears essentially in situ in the hovmoller analysis but extends across the atlantic basin in the pv composite results an indication is also provided of the extent to which the composite characteristics are evident in two individual events and note is made of the study s implications for medium range forecasting copyright 2008 royal meteorological society

the impact of extratropical transition on the downstream flow an idealized modelling study with a straight jet the interaction of a tropical cyclone undergoing extratropical transition et with the midlatitude synoptic scale flow is investigated using full physics numerical experiments with idealized initial conditions the emphasis is on the impact on the midlatitude flow downstream of the et event the midlatitude flow is represented by a balanced straight jet stream as the tropical cyclone approaches the jet a ridge trough couplet and a distinct jet streak form in the upper level flow a midlatitude cyclone develops rapidly downstream of the et system and the further evolution is characterized by downstream baroclinic development based on hovmoller diagrams the upper level development is interpreted as the excitation and subsequent dispersion of a rossby wave train on the potential vorticity gradient associated with the jet the characteristics of this wave train are sensitive to the structure of the jet and to moist processes in the midlatitudes the tropical cyclone undergoing et acts as a sustained forcing for the wave train and the structure of the et system impacts the development most significantly one to two wavelengths downstream of et piecewise inversion of potential vorticity complemented by the partitioning of the flow into its rotational and divergent parts is applied to assess the impact of the et system quantitatively both the cyclonic circulation and the outflow of the tropical cyclone are important contributors to the formation and amplification of the ridge trough couplet the outflow anomaly reduces the eastward motion of the ridge trough couplet significantly and thus promotes phase locking between the tropical cyclone and the upper level pattern copyright 2008 royal meteorological society

dynamics of rossby wave packets in a quantitative potential vorticity potential temperature framework abstractrossby wave packets rwps have been associated with increased atmospheric predictability but also with the growth and propagation of forecast uncertainty to address the important question of under which conditions rwps imply high and low predictability a potential vorticity potential temperature pv framework is introduced to diagnose rwp dynamics finite amplitude rwps along the midlatitude waveguide are considered and are represented by the synoptic scale wavelike undulations of the tropopause the evolution of rwps is examined by the amplitude evolution of the individual troughs and ridges troughs and ridges are identified as pv anomalies on levels intersecting the midlatitude tropopause by partitioning the pv tendency equation individual contributions to the amplitude evolution are identified a novel aspect is that the important role of the divergent flow and the diabatic pv modification is quantified explicitly arguably prominent upper tropospheric divergent flow is associated

sea level curve for the middle to early late ordovician in the armorican massif western france icehouse third order glacio eustatic cycles abstract this contribution deals with the middle to early late ordovician of the armorican massif western france the aim is to reconstruct a multi order eustatic curve from the stratigraphic record the studied section crozon peninsula area shows sediments deposited in tidal to storm dominated shelf environments a sequence analysis facies and stacking pattern analyses combined with a gamma ray record and a backstripping procedure was carried out chitinozoan assemblages provide the biostratigraphic framework including time calibration the stratigraphic succession is dominated by the stacking of sequences representing different orders of sea level change i e very high formosa and pissotensis biozones of the darriwilian the reconstructed sea level curve reveals that most of the third order cycles comprise three fourth order cycles of assumed 400 kyr duration this 1 2 myr duration of the ordovician third ordersequences suggests that they may be related to long period obliquity cycles an orbital forcing characteristic of icehousesequences in the late cenozoic and the quaternary these results imply that the major part of the middle and early late ordovician was characterized by icehouse conditions and third orderglacio eustatic cycles a time calibration of the chitinozoan biozones was developed from the sequential analysis it suggests that the early darriwilian biozones from henryi to calix biozones have short durations of several 10 to several 100 kyr whereas the pissotensis biozone has a temporal extent of several myr extending into the early sandbian

log derived thickness and porosity of the barnett shale fort worth basin texas implications for assessment of gas shale resources this study estimates reservoir quality and free gas storage capacity of the barnett shale in the main natural gas producing area of the fort worth basin by mapping log derived thickness porosity and porosity feet in the barnett shale the density porosity dphi log curve is a very useful tool to quantitatively assess shale gas resources and gamma ray gr and neutron porosity log curves are important factors in identifying the shale gas reservoir the key data were digital logs from 146 wells selected based on the availability of gr and density log curves log quality and good spatial distribution the barnett shale pay zone was determined on the basis of 1 dphi 5 2 high gr values commonly 90 api units 3 no significant intercalated carbonate rich beds and 4 individual pay zones being thick enough to be commercially successful for the current design of horizontal wells in the study area the barnett shale pay zone varies from about 165 ft 50 m to 420 ft 128 m in thickness h average dphi values of individual wells for the pay zone vary from 8 5 to 14 0 porosity feet maps of the pay zone show that areas of high dphi h values coincide with areas of high natural gas production indicating that log derived porosity feet maps are a good method for evaluating reservoir quality and assessing natural gas resource in the barnett shale play a limitation to this method is shown in the northwestern corner of the study area which is located in the liquids rich window with lower thermal maturity

anomalous blocking over greenland preceded the 2013 extreme early melt of local sea ice the arctic marine environment is undergoing a transition from thick multi year to first year sea ice cover with coincident lengthening of the melt season such changes are evident in the baffin bay davis strait labrador sea bdl region where melt onset has occurred 8 days decade 1 earlier from 1979 2015 a series of anomalously early events has occurred since the mid 1990s overlapping a period of increased upper air ridging across greenland and the northwestern north atlantic we investigate an extreme early melt event observed in spring 2013 below the 1981 2010 melt climatology with respect to preceding sub seasonal mid tropospheric circulation conditions as described by a daily greenland blocking index gbi the 40 days prior to the 2013 bdl melt onset are characterized by a persistent strong 500 hpa anticyclone over the region gbi 1 on 75 of days this circulation pattern advected warm air from northeastern canada and the northwestern atlantic poleward onto the thin first year sea ice and caused melt about 50 days earlier than normal the episodic increase in the ridging atmospheric pattern near western greenland as in 2013 exemplified by large positive gbi values is an important recent process impacting the atmospheric circulation over a north atlantic cryosphere undergoing accelerated regional climate change

interaction between dynamics and cloud microphysics in orographic precipitation enhancement a high resolution modeling study of two north alpine heavy precipitation events abstract interactions of atmospheric dynamics and cloud microphysics with the alpine orography are investigated for two north alpine heavy precipitation cases 20 22 may 1999 and 22 23 august 2005 both cases were related to a deep cyclone propagating slowly eastward along the alps advecting moist air of mediterranean origin toward the northern side of the alps a validation against high resolution rain gauge data reveals that the average model bias is below 15 in the region of interest but there is a tendency to systematically underestimate very heavy precipitation a scale decomposition of the discrepancies between model and observations reveals that errors on the meso scale contribute at least as much to the total model error as discrepancies on the meso scale on the scale of single mountain ridges and valleys the formation of precipitation maxima at valley locations is investigated with particular emphasis on a region in which a valley receives systematically more precipitation than the adj

features and effects of basement faults on deposition in the tarim basin the tarim basin as the largest inland oil producing basin in china is a large scale composite basin which formed from a palaeozoic craton basin that was overprinted by a mesozoic cenozoic foreland basin based on comprehensive analyses of gravitational data aeromagnetic data and seismic data from the basin 38 basement faults can be identified demonstrating that the tarim basin has undergone several tectonic cycles according to their distributional locations in the basin basement faults can be divided into marginal and internal basin basement faults moreover on the basis of the distribution characteristics in the plane and controlling effects on the basin the basement faults can be divided into 20 primary basement faults and 18 secondary basement faults combined with the interpretations of seismic profiles we can determine the relationship between the basement faults and sedimentary cover faults considering the section balance of seismic profiles we find that some basement faults are syn depositional with continuous long term activity during the basin s evolution and control the deposition in the basin by counting fault growth indexes of the main sections it is obvious that different parts of the same fault have different growth indexes but show similar activity within the same geological period the faults stress states remain consistent with their geological history although the growth indexes of different faults are inconsistent

spatial and temporal variability in snowmelt onset over arctic sea ice climate models suggest surface warming in the arctic will be rapid and pronounced implying substantial changes in snowmelt onset are likely this research therefore examines spatial and temporal variability in passive microwave derived snowmelt onset dates over arctic sea ice the objectives are to understand better the regional characteristics of snowmelt and to document whether the snowmelt onset record shows signs of climate change snowmelt onset dates are derived with scanning multichannel microwave radiometer and special sensor microwave imager brightness temperature data and they are subsequently stratified into 13 regions to analyze spatial and temporal variability results illustrate significant spatial variability in snowmelt onset with the median annual snowmelt onset date in one region of the arctic typically being statistically different from most other regions the examination of temporal variability also shows large interannual differences in the median snowmelt onset date in most regions additionally trends towards earlier snowmelt onset are documented in the vvest central arctic lincoln sea beaufort sea and canadian arctic archipelago regions

a global climatology of tropical moisture exports in a recent paper a climatology of tropical moisture exports tmes to the northern hemisphere nh was constructed on the basis of 7 day forward trajectories started daily from the tropical lower troposphere which were required to reach a water vaporflux of at least 100 g kg 21 ms 21 somewhere north of 358n it was shownthattmescontributesignificantlytoregionalprecipitation here theauthorscomplement andextend this work by i using 6 hourly european centre for medium range weather forecasts ecmwf interim re analysis era interim data from 1979 to 2010 instead of the earlier 40 yr ecmwf re analysis era40 ii extending the climatology to the southern hemisphere sh and iii relating tme events to atmospheric rivers ars previously discussed in the literature the main conclusions are as follows first the tme climatology is not sensitive to the reanalysis dataset second sh tme shows four activity centers the central and eastern pacific ocean 1708 908w near the south pacific convergence zone eastern south america and the adjacent atlantic ocean 608w 08 near the south atlantic convergence zone the western indian ocean 308 808e and western australia 1108 1408e third tme activity in the sh peaks in austral summer because of highermoisture contents and possiblybecause of increased rossby wave activityfrom the

the impact of typhoon jangmi 2008 on the midlatitude flow part ii downstream evolution extratropical transition et of a tropical cyclone tc can modify the midlatitude flow and thus have implications for the weather and predictability in downstream regions such as north america or europe albeit recurving and undergoing et the downstream impact of typhoon jangmi in september 2008 during the thorpex pacific asian regional campaign t parc was weak in this study we explore the physical processes inhibiting the reintensification of jangmi and governing the forecast uncertainty during et the focus is on the relative contribution of the tc and the midlatitude flow quasi geostrophic diagnostics reveal that jangmi is located south of and in phase with a midlatitude trough jangmi does not couple with the region favourable for reintensification ahead of the trough and subsequently decays instead a weak frontal wave like cyclone develops the role of the phasing of typhoon jangmi and the midlatitude rossby wave pattern is tested in sensitivity experiments with the cosmo model in which jangmi has been relocated the simulations reveal two contrasting groups of scenarios the first group reflects the weak actual et and subsequent decay accompanied by a broad ridge over the pacific the second group is characterized by a strong et with extratropical reintensification the triggering of a pronounced rossby wave train and downstream cyclogenesis the displacement of jangmi s initial position in the two contrasting groups is less than 1 25 130 km in the frame moving with the environmental background flow a critical bifurcation point for the track of jangmi exists the relative position to this bifurcation point determines whether jangmi decays or reintensifies and triggers a rossby wave train a simple discrimination parameter is derived that allows for classifying the scenarios the observed behaviour gives a simple explanation for the reduced predictability of the track and of the midlatitude flow in downstream regions during et

mesogenetic dissolution of the middle ordovician limestone in the tahe oilfield of tarim basin nw china abstract the mesogenetic dissolution is well developed in the middle ordovician yijianfang formation o2yj limestone and the dissolution pores are very important for petroleum accumulation in the south slope area of the tahe oilfield which lies in the north of the tarim basin northwestern china mottled dotted or laminar dissolution can be observed in the o2yj limestone under microscope the grains lime matrix and all stages of calcite cements including oil inclusion bearing blocky calcite cements can all be found dissolved ubiquitously the stylolites in the limestone were enlarged and rounded because of dissolution some dolomite rhombs precipitated along stylolites in burial environment were found dissolved as well the dissolution of the blocky calcite cements and dolomite rhombs and the enlarging of stylolites demonstrate that the dissolution took place in the mesogenetic environment concentration of trace elements including rees of the eroded part of the o2yj limestone is intermediate between that of the uneroded part and that of the underlying lower ordovician limestone hydrocarbon source rocks both 13cpdb and 18opdb values of the eroded part are less than those of the uneroded part respectively the geochemical characteristics indicate that the eroding fluids are hydrocarbon bearing fluids coming from the underlying hydrocarbon source rocks

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

characterization and discrimination of paleokarst breccias and pseudobreccias in carbonate rocks insight from ordovician strata in the northern tarim basin china abstract ordovician carbonates in the central and southern halahatang area of the tarim basin host highly productive hydrocarbon reservoirs previous studies suggest that the yingshan and yijianfang formations the primary producing intervals have been extensively karstified however the current author has not observed significant karst features in the formations based on the detailed study of 380 m long cores from 16 wells in the current study true breccias are only identified in two wells in the lianglitage formation including crackle and mosaic breccias as well as chaotic clast supported breccias the breccias are interpreted as karst related breccias that formed in near surface environments during pre silurian subaerial exposure and timing of karstification probably coincided with eustatic sea level fall caused by the middle katian glaciation widespread karst features of the yijianfang and yingshan formations identified as breccias or sediment filled cavities in many previous studies are actually only a mottled fabric pseudobreccia caused by selective diagenetic alteration and infiltration of bitumen in the deeper subsurface the color difference between pseudoclasts and pseudomatrix does not reflect a mixture of clasts and cave sediments but instead is characterized by distinct nevertheless commonly subtle variations in the limestone texture and whether bitumen is present one the basis of core and thin section observations sem scanning electron microscope and xrd x ray diffraction analyses the author presents criteria to distinguish karst breccias and pseudobreccias that can be applied to other similar carbonate deposits discrimination between karst breccias and nodular limestones is also presented differentiation of karst and pseudokarst features serves not only an academic interest but also has important applications for the exploration and development of carbonate reservoirs

melt onset over arctic sea ice controlled by atmospheric moisture transport the timing of melt onset affects the surface energy uptake throughout the melt season yet the processes triggering melt and causing its large interannual variability are not well understood here we show that melt onset over arctic sea ice is initiated by positive anomalies of water vapor clouds and air temperatures that increase the downwelling longwave radiation lwd to the surface the earlier melt onset occurs the stronger are these anomalies downwelling shortwave radiation swd is smaller than usual at melt onset indicating that melt is not triggered by swd when melt occurs early an anomalously opaque atmosphere with positive lwd anomalies preconditions the surface for weeks preceding melt in contrast when melt begins late clearer than usual conditions are evident prior to melt hence atmospheric processes are imperative for melt onset it is also found that spring lwd increased during recent decades consistent with trends toward an earlier melt onset

the role of high and low frequency dynamics in blocking formation time evolutions of prominent blocking flow configurations over the north pacific and europe are compared based upon composites for the 30 strongest events observed during 27 recent winter seasons fluctuations associated with synoptic scale migratory eddies have been filtered out before the compositing a quasi stationary wave train across the atlantic is evident during the blocking amplification over europe while no counterpart is found to the west of the amplifying blocking over the north pacific correlation between the tropopause level potential vorticity pv and meridional wind velocity associated with the amplifying blocking is found to be negative over europe in association with the anticyclonic evolution of the low pv center but it is almost zero over the north pacific feedback from the synoptic scale eddies as evaluated in the form of 250 mb geopotential height tendency due to the eddy vorticity flux convergence accounts for more than 75 of the observed amplification for the pacific blocking and less than 45 for the european blocking this difference is highlighted in two types of contour advection with surgery experiments in one of them pv contours observed four days before the peak blocking time were advected by composite time series of the low pass filtered observational wind and in the other experiment they were advected by the low pass filtered wind from which the transient eddy feedback evaluated as above had been removed at every time step hence the latter data should be dominated by low frequency dynamics for the european blocking both experiments can reproduce the anticyclonic evolution of low pv air within a blocking ridge as observed for the pacific blocking in contrast the observed intrusion of low pv air into the higher latitudes cannot be reproduced without the transient feedback furthermore in a barotropic model initialized with the composite 250 mb flow observed three days before the peak time a simulated blocking development over the north pacific is more sensitive to the insertion of the observed transient feedback than that over europe these results suggest that the incoming wave activity flux associated with a quasi stationary rossby wave train is of primary importance in the blocking formation over europe whereas the forcing by the synoptic scale transients is indispensable to that over the north pacific

synoptic behavior of baroclinic eddies during the blocking onset abstract synoptic behavior of individual baroclinic eddies in the course of their interactions with amplifying blocking anticyclones is examined based upon a 30 year record of the tropospheric circulation in the northern hemisphere winter high pass filtered as well as unfiltered fields of geopotential height and potential vorticity were composited relative to the onset of the five different types of blocking patterns before the compositing the entire sequence of the fields was slightly shifted in time and space in such a way that the strongest baroclinic eddy during the onset of each blocking event occupies a prescribed position in the upstream storm track when it reaches its maximum intensity since this shifting considerably reduces the cancellation between the individual high frequency migratory eddies this type of compositing can present a more synoptically oriented view of those interactions than conventional compositing in our composite results one or two pairs of cyclonic and anticyclonic

the role of upper level dynamics and surface processes for the pakistan flood of july 2010 in july and august 2010 floods of unprecedented impact afflicted pakistan the floods resulted from a series of intense multi day precipitation events in july and early august at the same time a series of blocking anticyclones dominated the upper level flow over western russia and breaking waves i e equatorward extrusions of stratospheric high potential vorticity pv air formed along the downstream flank of the blocks previous studies suggested that these extratropical upper level breaking waves were crucial for instigating the precipitation events in pakistan here a detailed analysis is provided of the extratropical forcing of the precipitation piecewise pv inversion is used to quantify the extratropical upper level forcing associated with the wave breaking and trajectories are calculated to study the pathways and source regions of the moisture that precipitated over pakistan limited area model simulations are carried out to complement the lagrangian analysis the precipitation events over pakistan resulted from a combination of favourable boundary conditions with strong extratropical and monsoonal forcing factors above normal sea surface temperatures in the indian ocean led to an elevated lower tropospheric moisture content surface monsoonal depressions ensured the transport of moist air from the ocean towards northeastern pakistan along this pathway the air parcel humidity increased substantially 60 90 of precipitated moisture via evapotranspiration from the land surface extratropical breaking waves influenced the surface wind field substantially by enhancing the wind component directed towards the mountains which reinforced the precipitation

the downstream impact of tropical cyclones on a developing baroclinic wave in idealized scenarios of extratropical transition the interaction of a tropical cyclone with a developing baroclinic wave is investigated in an idealized scenario of extratropical transition et the impact of et is examined by comparing and analyzing two numerical baroclinic wave experiments a traditional experiment in which baroclinic development is excited by a localized upper level perturbation on a realistic jet profile and an experiment in which additionally a model tropical cyclone is inserted south of the jet at the initial time et occurs in a wavy upper level flow while baroclinic surface systems are still weak the characteristic direct impact of et on the midlatitude flow is the formation of a distinct jet streak and the amplification of a ridge trough couplet in the adjacent downstream region the subsequent rapid cyclogenesis downstream is a direct consequence of these upper level flow modifications this faster and stronger development constitutes the amplification of the leading edge of downstream development both the upper level wave pattern and the surface development are subsequently amplified in the region further downstream the formation of the ridge adjacent to the intensified downstream cyclone is analyzed in detail to elucidate the next stage in the downstream dispersion of the et impact ridge building in the et scenario exhibits characteristics distinct from those in the life cycle experiment wave breaking feedback from the modified low level frontal structure and diabatic processes all contribute to the high amplitude wave pattern downstream of et the downstream impact of et is highly sensitive to the initial storm location and intensity the considerable amplification of the leading edge found in the reference experiment is the most widespread and rapidly propagating impact we thus speculate that this leading edge represents an optimal location of the midlatitude circulation where et can lead to the most significant impact on the downstream flow copyright 2010 royal meteorological society

the extratropical transition and precipitation distribution of hurricane floyd 1999 abstract several recent landfalling tropical cyclones e g dennis floyd and irene 1999 have highlighted a need for a refinement in the forecasting paradigms and techniques in the area of quantitative precipitation forecasting floyd proved to be a particularly challenging forecast problem as it was accompanied by catastrophic flooding over large regions of the east coast in spite of its relatively quick northward movement the extent and intensity of the precipitation distribution was strongly modulated by the storm s interaction with a midlatitude trough in an attempt to better understand and quantify the relevant dynamics during this interaction potential vorticity pv and quasigeostrophic perspectives are utilized as floyd approached the east coast precipitation shifted to the left of the storm track due to the presence of a deep midlatitude trough in the ohio valley the juxtaposition of a cold core pv anomaly associated with the midlatitude trough and a warm core pv anomaly associated with

a chronology of paleozoic sea level changes sea levels have been determined for most of the paleozoic era 542 to 251 million years ago but an integrated history of sea levels has remained unrealized we reconstructed a history of sea level fluctuations for the entire paleozoic by using stratigraphic sections from pericratonic and cratonic basins evaluation of the timing and amplitude of individual sea level events reveals that the magnitude of change is the most problematic to estimate accurately the long term sea level shows a gradual rise through the cambrian reaching a zenith in the late ordovician then a short lived but prominent withdrawal in response to hirnantian glaciation subsequent but decreasingly substantial eustatic highs occurred in the mid silurian near the middle late devonian boundary and in the latest carboniferous eustatic lows are recorded in the early devonian near the mississippian pennsylvanian boundary and in the late permian one hundred and seventy two eustatic events are documented for the paleozoic varying in magnitude from a few tens of meters to 125 meters

palaeokarst evidence for widespread regression and subaerial exposure in the middle katian upper ordovician of baltoscandia significance for global climate we report on widespread and contemporary palaeokarst in the middle katian upper ordovician of sweden estonia and latvia the first major palaeokarst horizon to be reported from the ordovician of baltoscandia the solution features occurwithin a fewmetres of thick zone of limestone immediately belowthe widespread fjacka shale and are related to an unconformity with preserved palaeorelief in the slandrom limestone in sweden and the time equivalent saunja formation in estonia and latvia facies evidence for a karst origin comes fromseveral outcrops and core sections and includes 1 frequent karren likemorphologies interpreted as swiss cheese karst sensu baceta et al 2001 2 local occurrences of solution collapse breccia 3 presence of bladed pseudospar crystals in solution cavities and 4 carbon isotope values indicating meteoric influence to the succession these findings are herein put in context with previously reported large scale erosional channels that may cut down several tens of metres below the fjacka shale in the subsurface baltic sea area and with regional anomalous thickness variations in the slandrom limestone and saunja formation all together forming strong support for regional exposure of the baltoscandian continent in the middle katian high resolution stable isotopic data show that the regression and lowstand of sea level overlap with thewaynesville carbon isotope excursion it resulted in basin wide cessation of carbonate production near the amorphognathus superbus and a ordovicicus conodont zonal boundary the contemporary development of palaeokarst in different confacies belts of the basin suggests that this was an extraordinary sea level lowstand herein interpreted as reflecting a middle katian glaciation less

the balanced dynamical nature of a rapidly intensifying oceanic cyclone abstract aided with a numerical simulation the authors diagnose the synoptic scale evolution of an intense extratropical cyclone over the western atlantic ocean from the perspective of balanced dynamics using potential vorticity inversion techniques the authors show that even during the period of largest growth rate early in the life cycle the balance equations capture much of the nondivergent wind irrotational wind and height tendency fields the structure of the cyclone evolves from a maximum amplitude at the tropopause to a maximum amplitude at the surface as the system moves offshore the vertical phase structure remains slightly upshear tilted throughout less than one quarter wavelength cyclogenesis is interpreted in terms of a baroclinic wave propagating through a varying basic state in which surface development is rapid because of the sudden response of the wave structure to a changing environment the mature cyclone structure strongly resembles cases of continental cyclones except that t

heavy precipitation on the alpine southside an upper level precursor analyses of four separate autumnal events of very heavy precipitation on the southern slopes of the european alps indicate that each was accompanied by a strikingly similar anomaly at upper tropospheric levels it took the form of a narrow 500km deep 4km and elongated 2000 km streamer of intruded stratospheric air sic high potential vorticity air extending north south from the british isles to the western mediterranean in each case the streamer translated comparatively slowly eastward and the storm event ensued as its forward flank approached the alpine ridge empirical indicators and theoretical considerations support the thesis that the streamer is an ubiquitous dynamically significant and distinctive precursor of storms on the alpine southside

influence of upstream diabatic heating upon an alpine event of heavy precipitation abstract narrow extended troughs associated with elongated streamers of potential vorticity pv are a frequent feature of upper tropospheric flow and they can instigate or modify surface weather systems in this study consideration is given to the generation of one particular pv streamer that was itself a dynamical precursor of a heavy precipitation event in the alpine region it is shown that the streamer s parturition over the eastern north atlantic is linked to a prior event of cyclo and frontogenesis upstream over the western north atlantic diagnostic trajectory analysis and heuristic simulations with a limited area nwp model suggest that the streamer s origin is influenced crucially by the following chain of physical processes cloud diabatic heating associated with the upstream cyclogenesis enhances a downstream negative pv anomaly in the upper troposphere and the flow associated with this anomaly subsequently helps transform a farther downstream preexisting broad positive pv anomaly into an elo

dynamics of a local alpine flooding event in october 2011 moisture source and large scale circulation alpine heavy precipitation events often affect small catchments although the circulation pattern leading to the event extends over the entire north atlantic the various scale interactions involved are particularly challenging for the numerical weather prediction of such events unlike previous studies focusing on the southern alps here a comprehensive study of a heavy precipitation event in the northern alps in october 2011 is presented with particular focus on the role of the large scale circulation in the north atlantic european region during the event exceptionally high amounts of total precipitable water occurred in and north of the alps this moisture was initially transported along the flanks of a blocking ridge over the north atlantic subsequently strong and persistent northerly flow established at the upstream flank of a trough over europe and steered the moisture towards the northern alps lagrangian diagnostics reveal that a large fraction of the moisture emerged from the west african coast where a subtropical upper level cut off low served as an important moisture collector wave activity flux diagnostics show that the ridge was initiated as part of a low frequency large scale rossby wave train while convergence of fast transients helped to amplify it locally in the north atlantic a novel diagnostic for advective potential vorticity tendencies sheds more light on this amplification and further emphasizes the role of the ridge in amplifying the trough over europe operational forecasts misrepresented the amplitude and orientation of this trough for the first time this study documents an important pathway for northern alpine flooding in which the interaction of synoptic scale to large scale weather systems and of long range moisture transport from the tropics are dominant moreover the trapping of moisture in a subtropical cut off near the west african coast is found to be a crucial precursor to the observed european high impact weather

carbonate dissolution in a modern mixing zone the potential for dissolution of calcite and aragonite and precipitation of dolomite by the mixing of fresh and saline ground waters has been demonstrated theoretically1 3 although geologists have used these processes in the explanation of the diagenesis of recent4 7 and ancient8 12 carbonates there has been only limited investigation of the geochemical processes of modern mixing zones13 14 here we report the results of chemical and rock profiling through a modern mixing zone on andros island in the bahamas our results demonstrate undersaturation of the waters in the mixing zone with respect to aragonite and calcite and corresponding pervasive dissolution of the carbonate rocks at this level undersaturation is significantly enhanced by bacterial processes which are also responsible for precipitation of an iron rich crust despite chemical supersaturation precipitation of dolomite was not observed thereby casting some doubt on the mixing zone model of dolomitization

origin and architecture of fractured cavernous carbonate reservoirs and their influences on seismic amplitudes ordovician carbonate is important for petroleum exploration and production in the tarim basin the matrix porosity of the carbonate reservoirs is usually less than 2 because of their age old sedimentary history and depth deeper than 5500 m the storage spaces are secondary dissolution pores and fractures which are dominated by visible dissolution caves holes and fractures zhou et al 2006 the reservoirs are therefore called fractured cavernous reservoirs good quality reservoir usually appears as a strong reflection called bead like reflection or br on poststack seismic sections and the corresponding reservoir is called a fracture cave body fcb which is the main drilling target of current e p in tarim basin the fcbs are unevenly distributed in carbonate strata and the storage spaces inside an fcb are also unevenly distributed therefore the reservoirs have both macroscopic and microscopic heterogeneities which bring great challenges to petroleum exploration

ordovician stable carbon isotope stratigraphy in the tarim basin nw china abstract the tarim basin located in nw china represents one of china s major palaeoplates its palaeogeographic position in the ordovician however is debated in this study we present biostratigraphically controlled stable carbon isotope data from some 600 samples spanning almost the entire ordovician in order to provide a tool that can be used for future chemostratigraphic correlations the data correlate well with results from south china and several major global 13c excursions such as the mdice dw2 3 saice sa2 gice ka1 and whitewater excursion ka4 are documented for the first time from the tarim basin major sedimentary gaps are detected in the lower floian between the penglaiba and yinshan formations in the upper darriwilian to lower sandbian between the dawangou and saergan or kanling formations and in the latest sandbian between the kanling and qilang formations as well as between the tumuxiuke and lianglitag formations three scenarios for the depositional history of the late darriwilian to early sandbian saergan formation which represents an important hydrocarbon source rock in the tarim basin are discussed with respect to their bio and chemostratigraphic implications the mid upper ordovician rocks recording high 13c values have been deposited during transgressive or highstand intervals whereas the regressive intervals are mostly missing this results in a stacking of several positive excursions and thus chemostratigraphic correlation without biostratigraphic control might produce misleading results especially for shallow water carbonates

disentangling the forcing mechanisms of a heavy precipitation event along the alpine south side using potential vorticity inversion extreme precipitation events along the alpine south side as are often forced by upper level positive potential vorticity pv anomalies over western europe these so called pv streamers go along with a dynamical forcing for upward motion a reduction of the static stability in the troposphere hence facilitating convection and are associated with low level winds that transport moisture toward the alps a case of heavy precipitation is examined using the 40 yr ecmwf re analysis data piecewise pv inversion ppvi and the limited area climate high resolution model chrm are used to assess the influences of mesoscale parts of the streamer on the precipitation event the impacts on the vertical stability are quantified by the convective available potential energy cape and an index of static stability very sensitive areas in terms of the stability are located beneath the southern tip of the streamer smaller changes in the stability are observed in the alpine region the moisture transport toward the alps is sensitive to the amplitude of the streamer which influences the amount of water that can be transported along its eastern flank the impacts of the topography on the flow are assessed by calculating an average inverse froude number whether or not the air parcels are blocked by or lifted over the barrier going along with suppressed and enhanced precipitation respectively depends on the vertical stability and the impinging wind velocity two parameters that are inherently linked to the pv streamer and its substructure

response of late ordovician paleoceanography to changes in sea level continental drift and atmospheric pco2 potential causes for long term cooling and glaciation abstract we performed sensitivity experiments using an ocean general circulation model at two stages of the late ordovician caradoc 454 ma ashgill 446 ma under a range of atmospheric pco2 values 8 18 pal pre industrial atmospheric level at high and low sea level the model results indicate that the long term cooling trend during the late ordovician can be explained by progressive cooling of the global ocean in response to falling levels of atmospheric pco2 sea level change and paleogeographic change these results also explain the occurrence of low latitude cool water carbonates in north america in all simulations a drop in sea level led to a reduction in poleward ocean heat transport this indicates a possible positive feedback that could have enhanced global cooling in response to sea level drop during the late ordovician alterations in poleward ocean heat transport linked to changes of atmospheric pco2 also indicate that there is a threshold of 10 pal above which ocean current change cannot be responsible for glaciation in the late ordovician continental drift could explain the observed global cooling trend in the late ordovician through a combined poleward ocean heat transport feedback and increased ice albedo effect if atmospheric pco2 was low during the entire late ordovician the model results further indicate that the response of meridional overturning to changes in paleogeography atmospheric pco2 and sea level is stronger than the response of surface circulation to these perturbations because the overturning circulation is so strong meridional overturning was the dominant mechanism for described changes in heat transport in the late ordovician