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

boundary layer friction in midlatitude cyclones results from an idealized three dimensional baroclinic life cycle model are interpreted in a potential vorticity pv framework to identify the physical mechanisms by which frictional processes acting in the atmospheric boundary layer modify and reduce the baroclinic development of a midlatitude storm considering a life cycle where the only non conservative process acting is boundary layer friction the rate of change of depth averaged pv within the boundary layer is governed by frictional generation of pv and the flux of pv into the free troposphere frictional generation of pv has two contributions ekman generation which is directly analogous to the well known ekman pumping mechanism for barotropic vortices and baroclinic generation which depends on the turning of the wind in the boundary layer and low level horizontal temperature gradients it is usually assumed at least implicitly that an ekman process of negative pv generation is the mechanism whereby friction reduces the strength and growth rates of baroclinic systems although there is evidence for this mechanism it is shown that baroclinic generation of pv dominates producing positive pv anomalies downstream of the low centre close to developing warm and cold fronts these pv anomalies are advected by the large scale warm conveyor belt flow upwards and polewards fluxed into the troposphere near the warm front and then advected westwards relative to the system the result is a thin band of positive pv in the lower troposphere above the surface low centre this pv is shown to be associated with a positive static stability anomaly which rossby edge wave theory suggests reduces the strength of the coupling between the upper and lower level pv anomalies thereby reducing the rate of baroclinic development this mechanism which is a result of the baroclinic dynamics in the frontal regions is in marked contrast with simple barotropic spin down ideas finally we note the implications of these frictionally generated pv anomalies for cyclone forecasting

life cycle simulations of shallow frontal waves and the impact of deformation strain the life cycle of shallow frontal waves and the impact of deformation strain on their development is investigated using the idealized version of the met office non hydrostatic unified model which includes the same physics and dynamics as the operational forecast model frontal wave development occurs in two stages first a deformation strain is applied to a front and a positive potential vorticity pv strip forms generated by latent heat release in the frontal updraught second as the deformation strain is reduced the pv strip breaks up into individual anomalies the circulations associated with the pv anomalies cause shallow frontal waves to form the structure of the simulated frontal waves is consistent with the conceptual model of a frontal cyclone deeper frontal waves are simulated if the stability of the atmosphere is reduced deformation strain rates of different strengths are applied to the pv strip to determine whether a deformation strain threshold exists above which frontal wave development is suppressed an objective method of frontal wave activity is defined and frontal wave development was found to be suppressed by deformation strain rates 0 4 10 5 s 1 this value compares well with observed deformation strain rate thresholds and the analytical solution for the minimum deformation strain rate needed to suppress barotropic frontal wave development the deformation strain rate threshold is dependent on the strength of the pv strip with strong pv strips able to overcome stronger deformation strain rates leading to frontal wave development than weaker pv strips copyright 2006 royal meteorological society

new psittacosaur occurrences in inner mongolia psittacosaur materials were collected from seven localities in the course of dinosaur project fieldwork in inner mongolia two new species of psittacosaurus are recognized bringing the number of well defined species to six one based on a nearly complete skeleton resembles psittacosaurus mongoliensis but is a smaller animal with a relatively larger head and longer tail the other species possesses jugal horns but exhibits a different combination of characters than psittacosaurus sinensis and psittacosaurus xinjiangensis a larger matrix of taxa and characters than is presently available will be necessary to resolve adequately phylogenetic relationships within the genus psittacosaurs were small dinosaurs the skeletons of which are preserved in unusual completeness in proximity to aeolian environments of deposition their small brain size relative to that of modern mammals of similar body size implies a relatively restricted behavioral repertoire

a simple model for the synoptic analysis of cold fronts a split cold front model with an over running upper front or humidity front ahead of a surface front or humidity front is shown to provide a useful representation of the principal characteristics of many katafronts the use of such a model leads to more consistent analyses especially of cloud and rain than are achieved using unmodified classical concepts

the structure and evolution of a simulated midlatitude cyclone over land abstract using output from a mesoscale model simulation this paper describes the evolution of the three dimensional temperature and humidity structures of an intense cyclone that developed over the eastern half of the united states during 14 16 december 1987 some specific findings include the following the occlusion process at the surface appeared similar to the classical paradigm with the cold front catching up with the warm front aloft a warm type occlusion structure formed as an upper baroclinic zone merged with the surface based occluded front the frontogenesis associated with the cold and warm fronts was initially continuous but as the system evolved a break in the frontogenesis along the northern section of the cold front developed a single frontogenesis feature appeared to support both the warm and occluded fronts a quasi linear region of convective activity was observed in advance of the surface cold front this convective line was associated with an upper level humidity front wh

high resolution analysis of frontal fracture abstract a mesoscale array of dropwindsondes released in a small rapidly deepening frontal wave cyclone in the eastern north atlantic during the fronts 92 experiment has been assimilated into a 17 km grid mesoscale model nested within the meteorological office s operational limited area model the mesoscale model reproduced the evolving cloud pattern with cloud head and dry slot seen in satellite imagery it also revealed a well defined evolution in the three dimensional thermodynamic structure associated with the process known as frontal fracture the frontal fracture was revealed most clearly in the pattern of wet bulb potential temperature w which was distorted by an effective differential rotation the rotation increasing with height this led to backward tilted w surfaces and ana cold frontal characteristics in the cloud head to the north of the center of rotation and to forward tilted w surfaces and kata cold frontal characteristics in the dry slot to the south of the center of rota

structure of a frontal system over the northeast pacific ocean abstract a frontal system passed over the storm transfer and response experiment project area on 17 november 1980 as revealed by ship born rawinsonde surface and radar information this northeast pacific storm exhibited three components it linked surface and 500 mb troughs with marked surface windshift and associated confluence and horizontal wind shear but exhibiting no surface temperature change a midtropospheric cold katafront and an upper moisture front that was moving ahead more rapidly than the other components the upper moisture front was marked by a moisture gradient across the trailing edge of a large cloud region that moved with the winds at 500 mb or higher due to the horizontal thermal homogeneity of the marine boundary layer the confluence associated with the surface trough did not cause low level cold frontogenesis high w values of the upper portion of the frontal system indicate that air was advected from much farther south important characteristics of frontal system evolution

response of rapidly developing extratropical cyclones to sea surface temperature variations over the western kuroshio oyashio confluence region the dynamical response of rapidly developing extratropical cyclones to sea surface temperature sst variations over the western kuroshio oyashio confluence wkoc region was examined by using regional cloud resolving simulations this study specifically highlights an explosive cyclone that occurred in early february 2014 and includes a real sst experiment cntl run and two sensitivity experiments with warm and cool sst anomalies over the wkoc region warm and cool runs the results derived from the cntl run indicated that moisture supply from the ocean was enhanced when the dry air associated with the cold conveyor belt ccb overlapped with warm currents further the evaporated moisture contributed substantially to latent heat release over the bent back front with the aid of the ccb leading to cyclone intensification and strengthening of the asymmetric structure around the cyclone s center such successive processes were more active in the warm run than in the cool run the dominance of the zonally asymmetric structure resulted in a difference in sea level pressure around the bent back front between the two runs the wkoc sst variations have the potential to affect strong wind distributions along the ccb through modification of the cyclone s inner system additional experiments with two other cyclones showed that the cyclone response to the wkoc sst variations became evident when the ccb north of the cyclone s center overlapped with that region confirming that the dry nature of the ccb plays an important role in latent heat release by allowing for larger moisture supply from the ocean

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

a family of frontal cyclones over the western atlantic ocean part i a 60 h simulation despite marked improvements in the predictability of rapidly deepening extratropical cyclones many operational models still have great difficulties in predicting frontal cyclogenesis that often begins as a mesoscale vortex embedded in a large scale parent cyclone system in this paper a 60 h simulation and analysis of a family of frontal cyclones that were generated over the western atlantic ocean during 13 15 march 1992 are performed using the pennsylvania state university national center for atmospheric research mesoscale model with a fine mesh grid size of 30 km although it is initialized with conventional observations the model reproduces well the genesis track and intensity of the frontal cyclones their associated thermal structure and precipitation pattern as well as their surface circulations as verified against the canadian meteorological centre analysis and other available observations it is shown that each frontal cyclone is initiated successively to the southwest of its predecessor in the cold sector first appearing as a pressure trough superposed on a baroclinically unstable basic state in the lowest 150 300 hpa then it derives kinetic energy from the low level available potential energy as it moves over an underlying warm ocean surface with weak static stability toward a leading large scale frontal zone and deepens rapidly by release of latent heat occurring in its own circulations one of the frontal cyclones originating in the cold air mass deepens 44 hpa in 42 h and overwhelms the parent cyclone after passing over the warm gulf stream water into the leading frontal zone these cyclones have diameters ranging from 500 to 1100 km as denoted by the last closed isobar and are spaced 1000 1400 km apart between their circulation centers during the mature stage they begin to establish their own cold warm frontal circulations once their first closed isobars appear thus distorting the leading large scale frontal structures and altering the distribution and type convective versus stratiform of precipitation it is found that the frontal cyclones accelerate and experience their central pressure drops as they move from high to low pressure regions toward the parent cyclone center and then they decelerate and fill as they travel away from the parent cyclone their spatial and temporal scales vertical structures as well as deepening mechanisms are shown to differ significantly from those typical extratropical cyclones as previously studied

morphodynamics of a bedrock alluvial meander bend that incises as it migrates outward approximate solution of permanent form in meandering rivers cut into bedrock erosion across a channel cross section can be strongly asymmetric at a meander apex deep undercutting of the outer bank can result in the formation of a hanging cliff which may drive hillslope failure whereas the inner bank adjoins a slip off slope that connects to the hillslope itself here we propose a physically based model for predicting channel planform migration and incision point bar and slip off slope formation bedrock abrasion the spatial distribution of alluvial cover and adaptation of channel width in a mixed bedrock alluvial channel we simplify the analysis by considering a numerical model of steady uniform bend flow satisfying cyclic boundary conditions thus in our analysis sediment supply i e the total volume of alluvium in the system is conserved in our numerical simulations the migration rate of the outer bank is a specified parameter our simulations demonstrate the existence of an approximate state of dynamic equilibrium corresponding to a near solution of permanent form in which a bend of constant curvature width cross sectional shape and alluvial cover distribution migrates diagonally downward at constant speed leaving a bedrock equivalent of a point bar on the inside of the bend channel width is set internally by the processes of migration and incision we find that equilibrium width increases with increasing sediment supply but is insensitive to outer bank migration rate the slope of the bedrock point bar varies inversely with both outer bank migration rate and sediment supply although the migration rate of the outer bank is externally imposed here we discuss a model modification that would allow lateral side wall abrasion to be treated in a manner similar to the process of bedrock incision this article is protected by copyright all rights reserved

variation of frontal and precipitation structure along a cold front a diagnostic study is presented to illustrate the sequence of events in which a warm conveyor belt wcb flow is drawn into the circulation of a developing extratropical cyclone and interacts with dry air aloft to produce distinctive precipitation structures the poleward boundary of the upstream end of the wcb was associated with a classical ana cold frontal structure the other end of the wcb flow closer to the cyclone centre was overrun by a dry intrusion of low wet bulb potential temperature air to give a split kata cold front the orientation of the surface cold front i e the wcb boundary changed significantly between these two parts but the orientation of the surface geostrophic flow within the wcb changed relatively little between the two parts the surface cold front was characterized in most places by a narrow cold frontal rainband composed of shallow line convection elements precipitation cores aligned nearly parallel to the surface geostrophic flow in the wcb the changing relationship between the frontal orientation and the direction of the surface flow accounts for the fact that the line convection elements occurred end to end to give almost two dimensional line convection along the classical ana part of the cold front but were non aligned and widely spaced along the split cold front part

systematic model forecast error in rossby wave structure diabatic processes can alter rossby wave structure consequently errors arising from model processes propagate downstream however the chaotic spread of forecasts from initial condition uncertainty renders it difficult to trace back from root mean square forecast errors to model errors here diagnostics unaffected by phase errors are used enabling investigation of systematic errors in rossby waves in winter season forecasts from three operational centers tropopause sharpness adjacent to ridges decreases with forecast lead time it depends strongly on model resolution even though models are examined on a common grid rossby wave amplitude reduces with lead 5 days consistent with underrepresentation of diabatic modification and transport of air from the lower troposphere into upper tropospheric ridges and with too weak humidity gradients across the tropopause however amplitude also decreases when resolution is decreased further work is necessary to isolate the contribution from errors in the representation of diabatic processes

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

fastex iop17 cyclone introductory synoptic study with field data this paper introduces the study of the early development phase of the iop17 frontal cyclone of the fastex field experiment fronts and atlantic storm track experiment with the support of observations from fastex observing platforms a synoptic description highlights the development of mesoscale features of interest in the operational meteo france arpege action de recherche petite echelle grand echelle analysis cycle i e cloud head dry wedge and upper level jet outflow a discussion attempts to isolate two significant differences of the present cyclone life cycle compared with previous well known conceptual models of maritime cyclone life cycles i the indirect role of an upper level precursor in triggering the surface low ii the existence of a diabatic regime taking over from the baroclinic development to sustain the deepening rate of the cyclone these two mechanisms are the subject of two companion papers

the occlusion process in a midlatitude cyclone over land abstract a historical review highlights the lack of consensus regarding the structure and evolution of occluded fronts and cyclones in order to better understand the occlusion process this paper and its companion examine a model simulation of the 14 16 december 1987 cyclone over the eastern united states the structure of an occluded front was observed at low levels as the cold front caught up with the warm front while aloft an upperlevel frontal zone appeared to play a role in the occlusion process although the thermal structure of this storm suggested that a cold type occlusion should have formed the model simulation produced a warm type occlusion structure an extensive review of the literature on occluded fronts suggested that cold type occlusions are rare if they exist at al1 finally the occluded front simulated in this case is compared critically to the norwegian t bone and other conceptual models of cyclone evolution

the poleward motion of extratropical cyclones from a potential vorticity tendency analysis abstractthe poleward propagation of midlatitude storms is studied using a potential vorticity pv tendency analysis of cyclone tracking composites in an idealized zonally symmetric moist gcm a detailed pv budget reveals the important role of the upper level pv and diabatic heating associated with latent heat release during the growth stage the classic picture of baroclinic instability emerges with an upper level pv to the west of a low level pv associated with the cyclone this configuration not only promotes intensification but also a poleward tendency that results from the nonlinear advection of the low level anomaly by the upper level pv the separate contributions of the upper and lower level pv as well as the surface temperature anomaly are analyzed using a piecewise pv inversion which shows the importance of the upper level pv anomaly in advecting the cyclone poleward the pv analysis also emphasizes the crucial role played by latent heat release in the poleward motion of the cyclone the l

structure of a frontal cyclone a diagnostic study of a mid latitude cyclone has been carried out using routinely available numerical weather prediction model products and imagery the cyclone was intense but not exceptionally so and the results are believed to have some generality the detailed description of the cyclone structure just before it began to deepen rapidly integrates concepts from a number of researchers into a common framework a dominant feature of the cyclone close to its centre was the cloud head a region of cloud with a sharp convex outer edge which formed poleward of the main polar front cloud band the cloud head was caused by two flows that entered it from the east ascending and fanning out within it one flow the cold conveyor belt brought low wet bulb potential temperature w air back into the cloud head from low levels ahead of the warm front the other flow was due to high w air that peeled off from the base of the main warm sector airflow i e part of the warm conveyor belt and travelled in the boundary layer back towards the cyclone centre first undercutting dry air that had earlier descended from the upper troposphere called a dry intrusion and then ascending at the upper boundary of the cloud head above the cold conveyor belt the transverse circulation that gave the ascent within the cloud head also led to the cold front fracturing along its length into two separate sharp surface cold fronts with a more diffuse frontal region in between frontal fracture the two sharp surface cold fronts were associated with narrow cold frontal rainbands line convection one of the line convection segments forming the southern edge of the cloud head the overrunning of the dry intrusion in the region of the frontal fracture led to a structure known as a split front in which an upper level humidity front began to run ahead of the position of the surface cold front a feature of the cyclone at this intermediate stage in its evolution was that a large proportion of the precipitation was being generated by ascent of relatively cold air the cold conveyor belt in the cloud head as part of the thermally indirect circulation at the left exit of a developing secondary upper level jet

coarse grained debris flow dynamics on erodible beds a systematic set of flume experiments is used to investigate the features of velocity profiles within the body of coarse grained debris flows and the dependence of the transport sediment concentration on the relevant parameters runoff discharge bed slope grain size and form the flows are generated in a 10 m long laboratory flume initially filled with a layer consisting of loose debris after saturation a prescribed water discharge is suddenly supplied over the granular bed and the runoff triggers a debris flow wave that reaches nearly steady conditions three types of material have been used in the tests gravel with mean grain size of 3 and 5 mm and 3 mm glass spheres measured parameters included triggering water discharge volumetric sediment discharge sediment concentration flow depth and velocity profiles the dynamic similarity with full sized debris flows is discussed on the basis of the relevant dimensionless parameters concentration data highlight the dependence on the slope angle and the importance of the quasi static friction angle the effects of flow rheology on the shape of velocity profiles are analyzed with attention to the role of different stress generating mechanisms a remarkable collapse of the dimensionless profiles is obtained by scaling the debris flow velocity with the runoff velocity and a power law characterization is proposed following a heuristic approach the shape of the profiles suggests a smooth transition between the different rheological regimes collisional and frictional that establish in the upper and lower regions of the flow and is compatible with the presence of multiple length scales dictated by the type of contacts instantaneous or long lasting between grains

comments on the evolution and dynamical role of reduced upper tropospheric potential vorticity in intensive observing period one of fastex abstract the existence and production of reduced upper tropospheric potential vorticity rupv by heating is considered an objective technique is used that identifies anomalies of pv arising from a particular physical process here latent heat release the evolution of two rupv anomalies and a related diabatically increased lower tropospheric pv ilpv anomaly occurring during intensive observing period one of the cyclones from the fronts and atlantic storm track experiment fastex is examined using model analyses sounding data and trajectory calculations three distinct airflows are identified emanating from the ilpv anomaly each with a different evolution results show that rupv anomalies exist in the atmosphere and in a weaker form in numerical models the dynamical role of rupv anomalies is examined using a nonlinear balance pv inversion and reruns of the u k meteorological office limited area model this shows that instantaneously the flow and temperature perturbations associated with rupv an

mechanisms controlling the downstream poleward deflection of midlatitude storm tracks abstractthe atlantic and pacific storm tracks in the northern hemisphere are characterized by a downstream poleward deflection which has important consequences for the distribution of heat wind and precipitation in the midlatitudes in this study the spatial structure of the storm tracks is examined by tracking transient cyclones in an idealized gcm with a localized ocean heat flux the localized atmospheric response is decomposed in terms of a time and zonal mean background flow a stationary wave and a transient eddy field the lagrangian tracks are used to construct cyclone composites and perform a spatially varying pv budget three distinct mechanisms that contribute to the poleward tilt emerge transient nonlinear advection latent heat release and stationary advection the downstream evolution of the pv composites shows the different role played by the stationary wave in each region in the region where the tilt is maximized all three mechanisms contribute to the poleward propagation of the

high precision 40ar 39ar age for the jehol biota abstract abundant fossils of the terrestrial jehol biota including plants insects dinosaurs birds mammals and freshwater invertebrates were discovered from the yixian formation and the overlying jiufotang formation in inner mongolia hebei province and liaoning province northeastern china because of the exceptional preservation of fossils the jehol biota is one of the most important mesozoic lagerstatten and is referred to as a mesozoic pompeii the jehol biota has provided a rare opportunity to address questions about the origin of birds the evolution of feathers and flight the early diversification of angiosperms and the timing of placental mammal radiation six tuff samples and two basalt samples collected from the tuchengzi the yixian and the jiufotang formations near the classic outcrops in western liaoning ne china yielded high precision 40 ar 39 ar ages we obtain an age of 129 7 0 5 ma for a basaltic lava from the bottom of the yixian formation and an age of 122 1 0 3 ma for a tuff from the lowermost part of the overlying jiufotang formation our age results provide an age calibration of the whole yixian formation and show that the whole formation was deposited entirely within early cretaceous time over an interval of 7 ma

break up of a stratospheric streamer observed by mst radar the break up of a stratospheric streamer over the british isles is described using satellite mesosphere stratosphere troposphere mst radar and in situ observations together with european centre for medium range weather forecasts analyses the streamer started as a thin ribbon of high potential vorticity to the west of the british isles as this was strained by the background flow it broke up into a series of mesoscale vortices mst radar and ozonesonde observations delineated a tropopause fold to the west of the initial streamer taking the form of a thin layer of stratospheric air embedded in a deep layer of descending upper tropospheric air the fold appears to have been mixed out by small scale turbulence as the streamer broke up this break up also generated strong inertia gravity waves which broke just above the tropopause introducing extensive mixing to the lowermost stratosphere one of the mesoscale vortices returned over the mst radar showing a very indistinct tropopause typical of a synoptic scale cut off low this vortex was also responsible for the development of a rain band on its eastern flank which brought significant rainfall to the british isles at a time when the synoptic flow pattern was strongly anticyclonic

diagnosing the influence of diabatic processes on the explosive deepening of extratropical cyclones a novel version of the classical surface pressure tendency equation pte is applied to era interim reanalysis data to quantitatively assess the contribution of diabatic processes to the deepening of extratropical cyclones relative to effects of temperature advection and vertical motions the five cyclone cases selected lothar and martin in december 1999 kyrill in january 2007 klaus in january 2009 and xynthia in february 2010 all showed explosive deepening and brought considerable damage to parts of europe for xynthia klaus and lothar diabatic processes contribute more to the observed surface pressure fall than horizontal temperature advection during their respective explosive deepening phases while kyrill and martin appear to be more baroclinically driven storms the powerful new diagnostic tool presented here can easily be applied to large numbers of cyclones and will help to better understand the role of diabatic processes in future changes in extratropical storminess

early cretaceous dinosaur faunas in china an introduction preliminary evidence suggests that during the early cretaceous there were separate dinosaur faunas in northern and southern asia the northern fauna the psittacosaurus fauna is well known and based upon collections from numerous localities and formations throughout northern china and southern mongolia although the southern fauna is still poorly known and based upon collections from only a small number of sites it appears to be distinguished by the absence of psittacosaurs the discovery of psittacosaurus in thailand suggests that the division is probably ecological in nature

the spatial distribution and evolution characteristics of north atlantic cyclones a climatology of extratropical cyclones is produced using an objective method of identifying cyclones based on gradients of 1 km height wet bulb potential temperature cyclone track and genesis density statistics are analyzed and this method is found to compare well with other cyclone identification methods the north atlantic storm track is reproduced along with the major regions of genesis cyclones are grouped according to their genesis location and the corresponding lysis regions are identified most of the cyclones that cross western europe originate in the east atlantic where the baroclinicity and the sea surface temperature gradients are weak compared to the west atlantic east atlantic cyclones also have higher 1 km height relative vorticity and lower mean sea level pressure at their genesis point than west atlantic cyclones this is consistent with the hypothesis that they are secondary cyclones developing on the trailing fronts of preexisting parent cyclones the evolution characteristics of composite west and east atlantic cyclones have been compared the ratio of their upper to lower level forcing indicates that type b cyclones are predominant in both the west and east atlantic with strong upper and lower level features among the remaining cyclones there is a higher proportion of type c cyclones in the east atlantic whereas types a and c are equally frequent in the west atlantic

intraseasonal variability of wintertime frontal activity and its relationship with precipitation anomalies in the vicinity of south america the intraseasonal variability of the frontal activity and its connection with the variability of the atmospheric circulation and precipitation in the southern hemisphere is studied the frontal activity is defined as the relative vorticity times the local temperature gradient a band pass filter was applied to retain the intraseasonal timescales an empirical orthogonal function analysis was applied to the filtered frontal activity anomalies the two main modes show positive and negative centers located mainly over the southern pacific ocean and south american sector and are in quadrature with each other a similar pattern was found when the main modes of intraseasonal variability of the 500 hpa geopotential height were projected on the frontal activity suggesting that the variability of fronts are influenced by the variability of the large scale atmospheric circulation moreover the precipitation anomalies projected on the main modes of both frontal activity and 500 hpa geopotential height show similar structures especially over the southern pacific ocean and south america which may indicate that the variability of fronts controls the variability of precipitation the lagged regression of the time series of the frontal activity areally averaged over one of the centers of action against the frontal activity anomaly field shows at lags 8 and 8 a similar pattern suggesting a period of around 17 days for each mode moreover lagged regression between times series of frontal activity and precipitation anomalies reveals an opposite pattern between southeastern south america and southern chile being precipitation anomalies over these two regions anti correlated due to the frontal activity

the age of the dinosaur bearing sediments at tebch inner mongolia people s republic of china the coarsening upward clastic sequence at tebch inner mongolia china containing the dinosaur psittacosaurus mongoliensis comprises the remains of a fluviolacustrine system deposited in an extensional tectonic setting the presence of asteropollis sp cf asteropollis trichotomosulcatus singh singh 1983 in conjunction with the absence of tricolpate pollen indicates a barremian or possibly early aptian age the overlying tebch basalt dated by the 40ar 39ar laser step heating method yields a mid aptian age of 110 0 52 ma this chronology supports the argument that the juifotang formation of the jehe group in western liaoning is early cretaceous with the jurassic cretaceous boundary very low within or below the base of the jehe group our data also suggest that the berriasian hauterivian neocomian age suggested for the one known russian locality that has yielded p mongoliensis shestakovskaya svita at gorno altayaskaya avtonomnaya oblast may be excessively old

a lagrangian based analysis of extratropical cyclones ii a detailed case study a detailed case study analysis is undertaken of the occurrence of significant coherent ensembles of trajectories cets that accompany atlantic cyclogenesis the approach is based upon the lagrangian based analysis scheme introduced in part i the analysis reveals the existence of several distinct moist ascending and dry descending cets two types of moist ascending cets associated with strong condensational processes ascend from the boundary layer of the warm sector either in the close vicinity of the cyclone centre or in the trailing cold frontal region the latter is the main contributor to the precipitation along the cold front during the early phase of the development another type of moist cets distinguished by maximum water vapour flux travels at low levels through the warm sector and ascends to mid tropospheric levels in the warm frontal region where it produces strong precipitation around the time of maximum storm intensity cets with an upper level origin are linked to the classical dry intrusion different cets correspond to strong descent of upper level tropospheric air that penetrated to the lower troposphere the movement of stratospheric air toward the centre of the maturing cyclone and an event of stratosphere to troposphere exchange upstream of the upper level trough two different visualizations of time sequences of the moist ascending cets indicate that they represent well defined flexible tubes or airstreams that exist over a time period comparable with the duration of the main cyclone intensification they provide a translating flexible but coherent river bed for the quasi continuous ascent of moist boundary layer air to the upper troposphere these tubes are akin to the concept of warm conveyor belts and the present analysis method objectively diagnoses their geometrical and physical characteristics and potential vorticity pattern some consideration is also given to the relationship of cets and tropospheric rivers and to possible shortcomings of the approach

dye tracer technique for rill flows by velocity profile measurements abstract water flow on hillslope soil surface supplies energy which is required to detach soil particles to transport and deposit sediments therefore flow velocity is a key variable related to hillslope hydrodinamics of soil erosion processes among the different methods available for measuring velocity of shallow interrill and rill flow the trace technique is widely used trace technique is applied by adding a material salt magnetic material water isotope floating object and then measuring the speed of the material to travel a known distance from the injection point when flow velocity is measured using a dye tracing method the mean velocity is calculated by multiplying the measured surface velocity of the leading edge of the tracer plume by a correction factor which was generally empirically deduced the main uncertainty of the dye tracing technique stands in the estimate of this correction factor which is the ratio between the mean flow velocity and the surface velocity the main goal of this paper is establishing a theoretical relationship for calculating the correction factor by using a power velocity profile at first the developed analysis demonstrated that the correction factor only depends on the exponent of the power velocity distribution eq 5 then this theoretical expression of the correction factor was applied using the velocity profiles measured by baiamonte and ferro for the condition of sediment free flow in motion on a rough bed and by coleman for a sediment laden flow moving on a smooth flume using the correction factor values calculated by the velocity measurements carried out for the sediment free flow in motion on a rough bed the relationship between the correction factor and roughness height was established in agreement with a previous study by ali et al for a sediment free flow the correction factor increases with roughness height finally the velocity profile measurements carried out for a sediment laden flow in motion on a smooth bed were used to state the effect of sediment load on the correction factor this last analysis allowed to conclude in agreement with li and abrahams and zhang et al that the correction factor decreases when the sediment load increases

the three dimensional distribution of clouds around southern hemisphere extratropical cyclones 1 the organization and for the first time the three dimensional structure of clouds associated with the southern hemisphere cyclones are studied using active observations from the cloudsat and calipso satellites first a composite cyclone is constructed from more than 800 individual cases in the years 2007 and 2008 using the cyclone centre as the composite reference point it is shown that the three dimensional cloud distribution around the composite cyclone agrees well with conceptual models of extratropical cyclones composite mean fields of sea level pressure vertical motion potential temperature and relative humidity are superposed on the three dimensional cloud structure to better define the relationship between the clouds and dynamical properties of extratropical cyclones the methodology used here reveals the relationship between dynamical and cloud processes in three dimensions around cyclones and provides the foundation for in depth evaluations of the ability of climate models to simulate the cloud and dynamical structures of southern hemisphere extratropical cyclones

pacific and atlantic bomb like deepenings in mature phase a comparative study the mesoscale dynamics of a secondary cyclone sampled during the field phase of the fronts and atlantic storm track experiment fastex are documented using airborne doppler radar data the high quality of the mesoscale airborne doppler dataset collected within this secondary cyclone is highlighted this study demonstrates however the need to combine in the near future airborne doppler radar and dropsonde measurements in order to access multiscale processes involved in the mature stage of this fastex cyclone both in clear air and in precipitating regions the studied secondary cyclone developed on the trailing cold front of a parent low situated over greenland and underwent the most explosive deepening roughly 54 mb in 24 hours sampled in the multiscale sampling area during fastex the main flows responsible for the mesoscale organization of the cyclone are a warm airflow emerging from the base of the synoptic warm conveyor belt that generates the most active part of the cloud head a dry intrusion approaching in the dry slot the cyclone centre a cold conveyor belt that contributes to the upward mass transport towards the upper part of the polar front cloud band and a cold northerly flow in the western part of the cloud head which tends to wrap around the low centre and is likely to release convective instability through air sea interactions this study also documents a slight shift in position between the high vertical vorticity core associated with the active part of the cloud head and the location of the pressure minimum the detailed three dimensional structure of this atlantic secondary cyclone is also compared with that gathered within another bomb like deepening defined as more than a 24 mb surface pressure drop in 24 hours observed over the pacific ocean during the coastal observation and simulation with topography coast experiment some similarities are found the main differences appear to be linked to the warm seclusion that is exclusive to the studied pacific cyclone more pronounced ascending motions are found within the cloud head of the pacific reference case and the deepening results from a more constructive effect of geostrophic and non geostrophic processes than for the atlantic reference case

interactions of tropopause depressions with an ex tropical cyclone and sensitivity of forecasts to analysis errors abstract this paper focuses on the coupling between an ex tropical cyclone and two preexisting mesoscale tropopause depressions tds the tds approached the cyclone from widely separated sources after becoming cut off from different upper level troughs upstream the first part of the paper combines meteosat imagery with products from the limited area version of the operational u k meteorological office unified model to reveal the 3d structure and evolution of the mesoscale features each td was a potential vorticity pv maximum characterized by dry intrusion air descending slantwise beneath an upper level jet streak each td generated its own cloud head and each is believed to have contributed to the deepening of the surface cyclone later parts of the paper identify errors in model forecasts and attribute them to analysis errors in the position of one of the tds two methods are used to locate the analysis errors both are capable of being used in real time the first is the identification via satelli

pathways of river water to the surface layers of stratified reservoirs this study uses tracer experiments to characterize the fate of a cold plunging river into a mediterranean reservoir under different stratification conditions three tracer experiments in lake beznar spain demonstrate that a significant fraction of the inflow may be quickly entrained into the surface mixed layer sml rather than flowing to lower depths we observe that a fraction and possibly all of river inflow entrains into the sml when the density current forms intrusions at the top of the metalimnetic layer intrusions near the base of the sml form due to lighter interfacial fluid at the top of the density current with intermediate properties between river reservior water when there is sufficient dilution of the cold inflow and abrupt density changes at the base of the sml consequently a layer of fluid splits from the denser part of the current and intrudes just below the sml while any remaining fluid flows to lower depths we parameterize this splitting behavior in terms of the transition richardson number ri12 2 1 0 1 where 0 1 and 2 are densities of the inflow the sml and the metalimnetic layer underneath respectively and is the total dilution through the plunge zone and subsequent entrainment splitting occurs when ri12 1 consistent with previous laboratory experiments we use this theory to predict the seasonal fate of river water during the stratification of lake beznar and identify the conditions that favor the formation of intrusions near the base of the sml

upper and lower troposphere coupling processes involved in the fastex iop16 frontal cyclone this paper investigates processes involved in the development of the secondary low sampled on 17 february 1997 during the field phase of the fronts and atlantic storm track experiment fastex this low is a fast moving frontal wave that emerged from the trailing cold front of a parent low situated over greenland the dynamics of this cyclone and its environment are described using the european centre for medium range weather forecasts analysis corresponding to intensive observing period 16 of fastex the ageostrophic circulation is retrieved and analysed in the upper and in the lower levels in the upper levels it is found that the curvature of the upper level jet plays a crucial role in suppressing or amplifying the vertical motions in the lower levels in the region where the cloud head emerges the vertical motion is scrutinized in the light of forcings which are acting it is found that the vertical motions are the response to a geostrophic forcing reinforced by diabatic processes the conjunction of vertical motions in the lower levels associated with vertical motions in the upper levels leads in the developing period to a coupling process that seems to be following theoretical calculations at the origin of the subsequent development of the cyclone the instability processes involved in the development of the studied secondary cyclone are also investigated the atmosphere appears neutral for upright convection while the region of the coupling corresponds to a region which is potentially unstable with respect to slantwise convection the tendency of the atmosphere is to relax this instability the vertical motions of the coupling processes are then reinforced by the relaxation of slantwise instability copyright 2002 royal meteorological society

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

dynamics of a bomb like deepening secondary cyclone from airborne doppler radar during the second field phase of the coast coastal observations and simulations with topography experiment an extremely deep secondary cyclone was sampled over the open pacific ocean by an airborne doppler radar this secondary low led a few hours later to strong damage from central california to washington as it moved northward along the western us coast the present paper gives mesoscale dynamical insight into this deep secondary low it reveals a warm seclusion situation with the colder airflow that cyclonically encircles the low centre in quasi gradient wind balance state a conceptual representation of the mesoscale airflow circulation in the low centre area is given this study also validates new analysis methods developed to access three dimensional dynamical fields at mesoscale from airborne doppler radar measurements within secondary cyclones these methods will be used intensively to process airborne radar data gathered during the field phase of the fastex fronts and atlantic storm track experiment project so as to scrutinize multiscale processes involved in secondary cyclogenesis over the atlantic

dry intrusions lagrangian climatology and dynamical impact on the planetary boundary layer abstractdry air intrusions dis are dry deeply descending airstreams from the upper troposphere toward the planetary boundary layer pbl the significance of dis spans a variety of aspects including the interaction with convection extratropical cyclones and fronts the pbl and extreme surface weather here a lagrangian definition for di trajectories is used and applied to ecmwf interim reanalysis era interim data based on the criterion of a minimum descent of 400 hpa during 48 h a first global lagrangian climatology of di trajectories is compiled for the years 1979 2014 allowing quantitative understanding of the occurrence and variability of dis as well as the dynamical and thermodynamical interactions that determine their impact dis occur mainly in winter while traveling equatorward from 40 50 latitude dis typically reach the lower troposphere with maximum frequencies of 10 in winter in the storm track regions as well as over the mediterranean sea arabian sea and eastern north pa

an analytical solution for groundwater flow to a vertical well in a triangle shaped aquifer the problem of drawdown and determination of velocity field near a fully penetrating pumping well which is located in a confined aquifer is investigated an isosceles triangular domain defining the geometry of the aquifer is considered in this paper the combination of streams with without impervious layer forms the boundaries of the domain of interest the concept of image well is employed to formulate the problem the method of green s function together with two dimensional fourier series expansion is used to obtain the closed form solution for the problem the isopotential lines and corresponding velocity field are presented for a particular position of pumping well also the water depletion from interfacing streams is analytically calculated for different positions of pumping well and the results are plotted the plots can be effectively used in water resources management and environmental engineering

frontogenesis in the presence of small stability to slantwise convection abstract it is often observed that despite the existence of near neutrality to slantwise convection rainbands and snowbands can persist for long periods with narrow intense updrafts producing large quantities of precipitation in many cases this is probably due to the presence of active frontogenesis which as shown here maintains such structures in order to investigate this process we use two dimensional semigeostrophic theory to solve the deformation forced frontogenesis problem for a circumstance in which the stability to moist slantwise convection is small but positive in this case numerical simulation is necessary to determine the evolution of the front several previous studies have described the role of diabatic forcing in modifying the cross frontal circulation by use of the sawyer eliassen equation in particular analytic solutions of that equation for the case of small moist symmetric stability show that a narrow updraft should occur ahead of the maximum geostrophic frontogenesis numeri

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

the properties and genesis environments of south atlantic cyclones a new climatology of south atlantic cyclones is produced to provide new insights into the conditions leading to genesis in different regions of the domain cyclones are identified and tracked based on the relative vorticity at 850 hpa computed from the ncep cfsr winds the characteristics of the cyclones are obtained by diagnostic variables sampled within a radial distance from the cyclone centers to produce the spatial distribution of cyclone properties at the time of genesis also cyclone centered composites are used to analyze the cyclone structure and evolution during their genesis there are four main cyclogenesis regions in the south atlantic ocean the southern brazilian coast se br 30 circ text s over the continent near the la plata river discharge region la plata 35 circ text s the southeastern coast of argentina arg 40 circ text s 55 circ text s and the southeastern atlantic se sao centered at 45 circ text s and 10 circ text w we found that cyclogenesis northward of 35 circ text s occurs mainly due to low level forcing associated with moisture transport in the summer and is associated with upper level forcing in the winter due to a strong baroclinic environment southward of 35 circ text s cyclones develop in a high baroclinic environment throughout the year with only a small influence from moist processes the cyclone composites reveal that se br and se sao cyclones are associated with secondary development the la plata cyclones development is influenced by an orographic low in their early stages and arg cyclones are influenced by thermal advection as an essential mechanism in the reduction of static stability

single crystal 40ar 39ar dating of the olorgesailie formation southern kenya rift single crystal laser fusion sup 40 ar sup 39 ar analyses and several conventional bulk fusion sup 40 k sup 40 ar dates have been used to determine the age of volcaniclastic strata within the olorgesailie formation and of associated volcanic and sedimentary units of the southern kenya rift in the principal exposures along the southern edge of the legemunge plain the formation spans the interval from approximately 500 to 1 000 ka deposition continued to the east along the ol keju nyiro river where a tuff near the top of the formation has been dated at 215 ka in these exposures the formation is unconformably overlain by sediments dated at 49 ka a possible source for the olorgesailie tephra the ol doinyo nyokie volcanic complex contains as ash flow dated at approximately 1 ma extending the known age range of this complex to encompass that of virtually the entire olorgesailie formation in the legemunge plain these geologic examples illustrate the importance of the single crystal sup 40 ar sup 39 ar dating technique whereby contaminant altered or otherwise aberrant grains can be identified and eliminated from the determination of eruptive ages for reworked or altered pyroclastic deposits the authors have presented a computer modeling procedure based on an inverse isochron analysis thatmore promotes a more objective approach to trimming sup 40 ar sup 39 ar isotope data sets of this type less

mesoscale analysis of the activation of a cold front during cyclogenesis summary the archetypal mesoscale structure of an ana cold front comprises a narrow cold frontal rainband ncfr associated with line convection embedded within a wide cold frontal rainband wcfr due to the slantwise ascent associated with a strong transverse front mesoscale circulation whereas most mesoscale observational studies have concentrated on this mature stage the present paper explores by means of a detailed case study how such a mature frontal system develops from pre existing features the study is based upon the synthesis of data spanning many scales in the form of satellite imagery observations from conventional and multi parameter doppler radar and surface reports together with diagnostics from an operational mesoscale forecast model the cold frontal zone in this case is characterized by multiple cold fronts the dominant second cold front is studied in detail from the point of view of its evolution and its relationship to neighbouring fronts especially the leading front associated with the initial polar front cloud band the dominant cold front started as a shallow rope cloud in the cold sector and at a fairly early stage it produced a ncfr due to line convection then over a period of only a few hours a dry intrusion and an associated strong direct transverse front circulation led to the formation of a canopy of mid level cloud and a wcfr the wcfr was attributable not only to the rearward ascending outflow from the line convection but also to the re invigoration of ascent within the initial polar front cloud band that the line convection was undercutting although the transverse circulation was probably intensified by precipitation processes it is inferred that it was mainly a manifestation of the larger scale environmental flow that existed independently of the major precipitation features

mesoscale aspects of a dry intrusion within a vigorous cyclone the results of a diagnostic study using radar and satellite imagery together with surface reports and output from regional and mesoscale models are presented for an occasion of a rapidly deepening cyclone that crossed the british isles the study shows how air descended from near tropopause level in the form of mesoscale dry intrusions which appeared to overrun parts of the warm conveyor belt ahead of a surface cold front one of the dry intrusions is analysed in detail because it is thought to have led to the large changes that were observed in the character of the wide frontal rain band in some places the precipitation was entirely suppressed whilst in other places the precipitation became convective with a tornadic squall line developing although the effect of the dry intrusion was seen most clearly in the precipitation distribution as determined by radar the approach of the dry intrusion was also clearly detected in the satellite water vapour imagery and foreshadowed in the model forecasts the mesoscale model despite some limitations reproduced many of the observed mesoscale features it also provided insight into the detailed behaviour of the dry intrusion associated with the tornadic squall line it showed that the dry intrusion was characterized by a mesoscale filament of high potential vorticity pv which was extruded from the lower part of a large region of high pv near a low tropopause the extruded pv anomaly plunged to within a kilometre of the surface where it overran part of the warm conveyor belt the dry intrusion was also characterized by relatively low wet bulb potential temperature w and it led to potential instability where it overran the warm air the warm conveyor belt itself was characterized not only by a high w but also by a separate strip of high pv generated locally mainly by condensation the quality of the mesoscale model simulation gives grounds for optimism that such models are capable in principle of predicting severe mesoscale weather events when as in this case they are orchestrated by resolved larger scale dynamics

storm track dynamics this paper reviews the current state of observational theoretical and modeling knowledge of the midlatitude storm tracks of the northern hemisphere cool season observed storm track structures and variations form the first part of the review the climatological storm track structure is described and the seasonal interannual and interdecadal storm track variations are discussed in particular the observation that the pacific storm track exhibits a marked minimum during midwinter when the background baroclinicity is strongest and a new finding that storm tracks exhibit notable variations in their intensity on decadal timescales are highlighted as challenges that any comprehensive storm track theory or model has to be able to address physical processes important to storm track dynamics make up the second part of the review the roles played by baroclinic processes linear instability downstream development barotropic modulation and diabatic heating are discussed understanding of these processes forms the core of our current theoretical knowledge of storm track dynamics and provides a context within which both observational and modeling results can be interpreted the eddy energy budget is presented to show that all of these processes are important in the maintenance of the storm tracks the final part of the review deals with the ability to model storm tracks the success as well as remaining problems in idealized storm track modeling which is based on a linearized dynamical system are discussed perhaps on a more pragmatic side it is pointed out that while the current generation of atmospheric general circulation models faithfully reproduce the climatological storm track structure and to a certain extent the seasonal and enso related interannual variations of storm tracks in depth comparisons between observed and modeled storm track variations are still lacking

climatology and dynamics of the link between dry intrusions and cold fronts during winter part ii front centred perspective the conceptual picture of an extratropical cyclone typically includes a cold front and a dry intrusion di behind it by objectively identifying fronts and dis in ecmwf era interim data for 1979 2014 part i quantified the climatological relationship between cold fronts and dis driven by the finding that front intensity and frontal precipitation are enhanced in the presence of dis here we employ a front centred perspective to focus on the dynamical and thermodynamical environment of cold fronts with and without dis in the northern hemisphere winter distinguishing between trailing fronts that connect to a parent cyclone and isolated fronts examples of dis behind each type illustrate the baroclinic environment of the trailing front and the lack of strong temperature gradients across the isolated front composite analyses of north atlantic and north pacific fronts outline the major differences in the presence of dis compared to similar fronts but without dis in their vicinity the magnitude and spatial structure of the modification by dis depends on the front intensity yet generally with dis trailing fronts occur with stronger slp dipole deeper upper tropospheric trough stronger 10 m wind gusts enhanced ocean sensible and latent heat fluxes in the cyclone cold sector and heavier precipitation isolated weak fronts exhibit similar behaviour with different spatial structure this study highlights the central role of dis for shaping the variability of fronts and their associated environment and impact

mesoscale dynamics of a deepening secondary cyclone in fastex iop16 three dimensional structure retrieved from dropsonde data the mesoscale dynamics of a secondary cyclone sampled during the field phase of the fronts and atlantic storm track experiment fastex intensive observation period iop 16 are documented using airborne dropsonde data the method proposed to recover the mesoscale analytical three dimensional 3 d dynamic fields from the dropsonde measurements is evaluated using simulated fields airborne in situ measurements and airborne doppler radar measurements these simulations and comparisons indicate that the method is able to resolve the mesoscale structures within the studied secondary cyclone both in the regions of clear air and precipitation it appears however that the most accurate description of the 3 d dynamic fields in both these regions would be obtained by combining doppler and dropsonde measurements the studied secondary cyclone is a fast moving frontal wave that developed on the trailing cold front of a parent low situated over greenland using the dropsonde derived 3 d fields the mesoscale flows involved in the organization of the secondary cyclone are described the potential vorticity and equivalent potential vorticity fields deduced from the basic analytical fields indicate that the atmosphere is roughly neutral to moist slantwise instability this configuration is known to significantly promote frontogenesis the vertical configuration of the jets and circulations within this secondary cyclone are compared with the coupling uncoupling scheme of shapiro a slight coupling is found between the thermally indirect circulation and the ageostrophic circulation the obtained coupling is however not as developed as in the ideal case described by shapiro which may explain the small upward velocities in our case airborne doppler radar and dropsonde measurements are combined so as to infer the multi scale processes involved in the mesoscale and convective scale organization of the atlantic secondary cyclones and to evaluate the new emerging theoretical interpretations of secondary cyclogenesis

ice lollies an ice particle generated in supercooled conveyor belts on 21 january 2009 a maturing low pressure weather system approached the uk along with several associated frontal systems as a part of the aerosol properties processes and influences on the earth s climate clouds project an observational research flight took place in southern england sampling the leading warm front of this system during the flight a distinctive hydrometeor type was repeatedly observed which has not been widely reported in previous studies we refer to the hydrometeors as drizzle rimed columnar ice or ice lollies for short due to their characteristic shape we discuss the processes that led to their formation using in situ and remote sensing data

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

chemical air mass differences near fronts two case studies are presented of aircraft measurements ozone noy co and meteorological parameters in the vicinity of fronts located over the eastern side of the north atlantic ocean during spring 1994 the aim of these studies was twofold 1 to investigate whether frontal circulations can transport ozone from the boundary layer to the free troposphere in well defined layer and 2 to ascertain whether or not conveyor belts associated with extratropical cyclones exhibit well defined chemical signatures the first case study march 2 1994 sampled a well defined ozone enhanced layer within the free troposphere it is demonstrated that this air was transferred from the boundary layer to the free troposphere during the development of a baroclinic wave two warm conveyor belts sampled within this flight one associated with the developing baroclinic wave and the other with a mature low pressure system displayed clear and contrasting chemical signatures a consequence of their geographically different origins during the second case study april 25 1994 both the dry intrusion and the warm conveyor belt of a mature occluded low pressure system were sampled their chemical signatures in particular that of the dry intrusion showed that interleaving of the two airstreams had occurred probably in the vicinity of the occluded front it is thus demonstrated that chemical measurements within conveyor belts provide valuable information on the nature history and extent of these coherent flows

evolution and mesoscale structure of a polar low outbreak an observational study of an unusual polar low outbreak is described in which four lows formed in succession near south east iceland because all the lows tracked south east close to scotland an unusually dense network of surface observations was available for analysis including radar this complemented the geostationary and polar orbiting satellite data that are more commonly used in polar low studies each of the four polar lows displayed a different structure and evolution the first was a circular convective low the second a relatively weak surface signature of an upper level feature while the final two cyclones appeared as a wave train with one cyclone decaying and the other developing into an intense disturbance because of the high resolution of the surface data it was possible to identify unambiguously mesoscale frontal features within the polar lows these are described in detail a close examination was made of the final intense low which showed that its evolution and frontal structure closely matched those found in standard conceptual models of rapidly developing maritime cyclones this polar low also showed evidence of a warm core and symmetric instability within an extensive cloud head

high resolution observations of the trowal warm frontal region of two continental winter cyclones abstract this paper compares the structure of the trough of warm air aloft trowal warm frontal region of two continental wintertime cyclones the cyclones were observed over the central great lakes region during the lake induced convection experiment snowband dynamics project field campaign the cyclones had different origins with the first forming east of the colorado rockies and the second forming over the gulf of mexico they were associated with different upper level flow regimes one located just north of a nearly zonal jet and the other located just west of a nearly meridional jet both storms produced heavy swaths of snow across the states of illinois wisconsin and michigan high resolution observations of frontal structure were made during flights of the national center for atmospheric research electra aircraft using dropsondes and the electra doppler radar tail radar system the high resolution observations suggest a different arrangement of air masses in the trowal region compared with the

the dichotomous structure of the warm conveyor belt the warm conveyor belt wcb of an extratropical cyclone generally splits into two branches one branch wcb1 turns anticyclonically into the downstream upper level tropospheric ridge while the second branch wcb2 wraps cyclonically around the cyclone centre here the wcb split in a typical north atlantic cold season cyclone is analysed using two numerical models the met office unified model and the cosmo model the wcb flow is defined using off line trajectory analysis the two models represent the wcb split consistently the split occurs early in the evolution of the wcb with wcb1 experiencing maximum ascent at lower latitudes and with higher moisture content than wcb2 wcb1 ascends abruptly along the cold front where the resolved ascent rates are greatest and there is also line convection in contrast wcb2 remains at lower levels for longer before undergoing saturated large scale ascent over the system s warm front the greater moisture in wcb1 inflow results in greater net potential temperature change from latent heat release which determines the final isentropic level of each branch wcb1 also exhibits lower outflow potential vorticity values than wcb2 complementary diagnostics in the two models are utilised to study the influence of individual diabatic processes on the wcb total diabatic heating rates along the wcb branches are comparable in the two models with microphysical processes in the large scale cloud schemes being the major contributor to this heating however the different convective parametrization schemes used by the models cause significantly different contributions to the total heating these results have implications for studies on the influence of the wcb outflow in rossby wave evolution and breaking key aspects are the net potential temperature change and the isentropic level of the outflow which together will influence the relative mass going into each wcb branch and the associated negative pv anomalies at the tropopause level flow

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

the relation of moist symmetric instability and upper level potential vorticity anomalies to the observed evolution of cloud heads the cloud head phenomenon has been known for some time as a precursor of rapid cyclogenesis based upon satellite imagery two stages of cloud head development are identified in this study that can be related to early and late stages of the associated cyclone weakly convex cloud heads emerge from the baroclinic zone at an early stage in cyclogenesis and strongly convex cloud heads develop in association with the rapid deepening of the cyclone trajectories are used to highlight the role of an upper level potential vorticity pv anomaly in the growth of the strongly convex cloud head and the main flow associated with the growth of the strongly convex cloud head is viewed using isentropic analysis the possible role of moist symmetric instability in the development of both weakly and strongly convex cloud heads is discussed and a new diagnostic for measuring the vertically integrated extent of realizable symmetric vrs instability based on the moist geostrophic pv is introduced royal meteorological society 2002 g j shutt s contribution is crown copyright

timing of the jiufotang formation jehol group in liaoning northeastern china and its implications the timing of the jiufotang formation remains speculative despite recent progress in the study of the jehol biota in this paper we contribute to this topic with ar 40 ar 39 dating on k feldspar sanidine and orthoclase from tuffs interbedded within the fossil bearing shales of the jiufotang formation from the upper part of the jehol group in chaoyang liaoning northeastern china ar 40 39 ar step heating analyses of k feldspar and the shrimp u pb zircon data indicate that tuffs at the shangheshou section erupted at 120 3 0 7 million years ago this result confirms an aptian age for the jiufotang formation that was mainly based on biostratigraphic evidence it also places stringent controls on the age of the fossils from the formation providing a minimum age 120 ma for the four winged dinosaur microraptor and the seed eating bird jeholornis

north atlantic storm driving of extreme wave heights in the north sea the relationship between storms and extreme ocean waves in the north sea is assessed using a long period wave dataset and storms identified in the interim ecmwf re analysis era interim an ensemble sensitivity analysis is used to provide information on the spatial and temporal forcing from mean sea level pressure and surface wind associated with extreme ocean wave height responses extreme ocean waves in the central north sea arise due to intense extratropical cyclone winds from either the cold conveyor belt northerly wind events or the warm conveyor belt southerly wind events the largest wave heights are associated with northerly wind events which tend to have stronger wind speeds and occur as the cold conveyor belt wraps rearwards round the cyclone to the cold side of the warm front the northerly wind events provide a larger fetch to the central north sea to aid wave growth southerly wind events are associated with the warm conveyor belts of intense extratropical cyclones that develop in the left upper tropospheric jet exit region ensemble sensitivity analysis can provide early warning of extreme wave events by demonstrating a relationship between wave height and high pressure to the west of the british isles for northerly wind events 48 hours prior southerly wind extreme events demonstrate sensitivity to low pressure to the west of the british isles 36 hours prior

thermal structure and airflow in a model simulation of an occluded marine cyclone abstract a very fine mesh model simulation of the ocean ranger storm of february 1982 is used to study the thermal structure and airflow in an intense marine cyclone in particular the study investigates the structures of the occluded front and the secluded pool of warm air in the simulated cyclone and examines the formation of these structures with the help of a large number of air trajectories it was found that in the model simulation the largest thermal gradient occurred along the occluded front not along the warm or cold fronts and that the intense gradient was a product of strong warm and occludofrontogenesis in the inflowing air the occluded front was embedded within air that was earlier located within the baroclinic zone ahead of the low center not air that was in proximity to the historical warm and cold fronts the warm air in the seclusion likewise originated in the baroclinic zone ahead of the low the seclusion at low levels resulted from a tongue of slower moving relatively warm air be

field flume reveals aquatic vegetation s role in sediment and particulate phosphorus transport in a shallow aquatic ecosystem abstract flow interactions with aquatic vegetation and effects on sediment transport and nutrient redistribution are uncertain in shallow aquatic ecosystems here we quantified sediment transport in the everglades by progressively increasing flow velocity in a field flume constructed around undisturbed bed sediment and emergent macrophytes suspended sediment 100 m became dominant at higher velocity steps after a threshold shear stress for bed floc entrainment was exceeded shedding of vortices that had formed downstream of plant stems also occurred on that velocity step which promoted additional sediment detachment from epiphyton modeling determined that the potentially entrainable sediment reservoir 46 g m 2 was similar to the reservoir of epiphyton 66 g m 2 but smaller than the reservoir of flocculent bed sediment 330 g m 2 all suspended sediment was enriched in phosphorus by approximately twenty times compared with bulk sediment on the bed surface and on plant stems indicating that the most easily entrainable sediment is also the most nutrient rich and likely the most biologically active

on the dependence of boundary layer ventilation on frontal type 1 case study simulations with idealized tracers have been used to determine the relationship between the dynamics and conceptual representations of different midlatitude frontal systems and the amount distribution and time scale of boundary layer ventilation by these systems the key features of ventilation by a kata and ana cold frontal system are found to be quantitatively and also often qualitatively similar to the main ventilation pathways which are the conveyor belts cloud head and other convection the conveyor belts and cloud head occur within cloud implying that they can be identified using satellite imagery differences in the transport by the two systems can be related to their conceptual representations and include a sensitive dependence on the diurnal cycle for the kata but not the ana cold frontal case

multiple controls on rift basin sedimentation in volcanic settings insights from the anatomy of a small early cretaceous basin in the yanshan belt northern north china this paper deals with a small continental rift basin in a volcanic setting and tries to decipher potential controls on its synrift sedimentation the luanping basin which is a well exposed early cretaceous rift basin in the yanshan belt on the northern periphery of the north china block was chosen as a case study we show that extensive and vigorous volcanism took place just prior to the onset of basin formation and continued into a synrift period basin fills consist predominantly of lacustrine fan delta braid delta and volcaniclastic deposits lacustrine facies are composed mostly of deep lake deposits that appear to have been established soon after basin initiation fan delta systems developed along two high angle border faults the master northern hongqi fault and the secondary western xiaobaiqi fault fan delta fronts were built up primarily by gravelly and sandy debrites and turbidites braid delta deposits are restricted to the eastern corner of the basin and are characterized by an aggregation of braid plain conglomeratic deposits underwater extrusions of magma and pyroclastic flows are inferred from the presence of volcanic breccias ignimbrites andesitic pillows and peperites which are enclosed by host lacustrine deposits deep lake and fan delta systems persisted throughout the synrift period indicating a rapid subsidence rate with both adequate sediment and water supply the high angle border faults are thought to have played a critical role in creating large accommodation space and simultaneous displacements of the hongqi and xiaobaiqi faults led to the localization of a major depocenter in the western part of the basin one dimensional backstripping analysis of three stratigraphic sections shows that the luanping basin experienced marked synrift tectonic subsidence up to 2 km at a subsidence rate close to 0 2 mm yr 1 we propose that the high rate of basin subsidence might have been caused mainly by left lateral transtensional faulting and was enhanced by the superposition of basement downsag induced by underlying magma withdrawal a predominance of volcanic particles in both debrites and sandstones suggests that source areas were erodible volcanic edifices a humid paleoclimate is inferred which not only provided enough water supply but also promoted weathering of volcanic rocks in source areas thus maintaining both the deep lake environment and sediment influx we conclude that relatively small and isolated rift basins in volcanic settings can experience both rapid subsidence and receive thick lacustrine deposits if they are under the combined control of favorable structure climate and magmatism the model proposed here is believed to be applicable to other rift basins in similar volcano tectonic settings

high frequency turbulence and suspended sediment concentration measurements in the garonne river tidal bore the study details new sediment concentration measurements associated with some turbulence characterisation conducted at high frequency in the undular tidal bore of the garonne river france acoustic doppler velocimetry was used and the suspended sediment concentration was deduced from the acoustic backscatter intensity the field data set demonstrated some unique flow features of the tidal bore including some large and rapid turbulent velocity fluctuations during and after the bore passage some unusually high suspended sediment concentration was observed about 100 s after the tidal bore front lasting for more than 10 min it is thought that the tidal bore passage scoured the bed and convected upwards the bed material reaching the free surface after the bore passage behind the tidal bore the net sediment flux magnitude was 30 times larger than the ebb tide net flux and directed upstream a striking feature of the data set was the intense mixing and suspended sediment motion during the tidal bore and following flood tide this feature has been rarely documented

interpretation of satellite imagery of a rapidly deepening cyclone model output and observational data are used to interpret in detail satellite images of a distinctive cloud system several hundred kilometres long which was observed before and during rapid cyclonic development that occurred over england conceptual models are forwarded which account for the structure of the major cloud areas and upper level moisture fields as observed by water vapour imagery immediately prior to and following the onset of vigorous cyclogenesis the cloud system corresponded to what r b weldon refers to as a baroclinic leaf cloud and was characterized by ana cold frontal ascent the baroclinic leaf lay within an area of enhanced ascent ahead of a major upper level trough a jet streak which originated upstream propagated rapidly around the base of the upper trough a tongue of dry air centred on the left flank of this jet streak lay immediately upstream of the leaf cloud and had a major influence on its subsequent development this intrusion of dry air was well represented by the meteorological office fine mesh model which showed it as a pronounced tongue of recently descended air with high potential vorticity which originated in the upper troposphere and lower stratosphere rapid cyclogenesis occurred as the dry intrusion overran low level air of high w within a warm conveyor belt at the southern tip of the leaf cloud interaction of the dry intrusion and baroclinic leaf cloud is shown to be particularly important in accounting for the detailed distribution of weather it also suggests a way of pinpointing the location and timing of vigorous cyclogenesis

effects of cloud diabatic heating on the early development of the fastex iop17 cyclone a set of numerical simulations is used to study the first development phase of the fastex cyclone a particularly well sampled frontal cyclone system that developed on the trailing front of a primary large scale baroclinic wave during intensive observation period 17 iop17 of fastex the fronts and atlantic storm track experiment the role of diabatically induced vertical circulations is investigated with a combination of diagnostic tools including a generalized omega equation and keyser s psi vector technique applied to the model outputs the full physics simulation shows a good agreement with observed data particularly the splitting of the upper level flow into a pair of jet streaks analysis of the contributions to the vertical ageostrophic transverse circulations near the jet streak pair structure shows that a positive feedback exists between the storm s dynamical configuration and the diabatic processes in the second part of the paper this interpretation is confirmed by a sensitivity analysis excluding cloud processes results suggest that after initial baroclinic growth the storm evolves towards a purely diabatic deepening regime leading to a diabatic rossby wave mechanism as proposed by recent wave cisk conditional instability of the second kind theoretical studies

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

djadokhta formation correlative strata in chinese inner mongolia an overview of the stratigraphy sedimentary geology and paleontology and comparisons with the type locality in the pre altai gobi because the bayan mandahu redbeds of inner mongolia share similar sedimentary facies and fossil assemblages with the djadokhta formation of pre altai gobi the two units are interpreted as stratigr

the role of the environmental flow in the development of secondary frontal cyclones the impact of the environmental flow on the development of secondary frontal cyclones is investigated several case studies are examined as examples of secondary frontal cyclone events observed in the north atlantic western europe sector a simple measure of growth is defined to chart their development the vorticity attribution technique of bishop is utilized to calculate the action of the large scale environmental flow on the fronts in particular the environmental along front stretching shown to be important in theoretical models of frontal instabilities is calculated the role of the environmental deformation appears to be crucial as part of a baroclinic life cycle stretching deformation acts to build up a front but suppress along front waves if the stretching rate diminishes barotropic instabilities may then break out diagnostics are examined to try to ascertain the growth mechanisms at work in each frontal cyclone case a range of values for the commonly prescribed deformation frontogenesis and shearing frontogenesis parameters are calculated

secondary cyclogenesis the initiation phase of a frontal wave observed over the eastern atlantic the initiation phase of a secondary frontal wave in the wake of a primary cyclogenesis event over the atlantic is documented north of the trailing surface cold front and south west of the primary cyclone an intense upper level jet generates a direct and transverse ageostrophic circulation in its entrance region evidence is shown for two conflicting roles of this circulation first stabilization of the front through frontogenetic cross frontal low level convergence and second an increase of the potential for instability of the front through diabatic e g latent heat release potential vorticity pv redistribution in the upward branch of the circulation following saturation of the primary cyclogenesis and the associated along front north eastwards shift of the upper level jet the low level branch of the ageostrophic circulation behaves like a zipper closing on the front while in the upward branch an anomalous strip of pv builds along the cold front isentropic pv maps show that parcles of stratospheric origin embedded in the downward branch of the ageostrophic circulation a tropopause fold may have ended in the vicinity of the strip of anomalous low level pv perhaps contributing to an increase in the potential for instability of the surface front using the domain independent attribution method of bishop it is shown that the frontal wave forms on a part of the cold front where first the along front stretching rate due to the environmental flow decays below the critical threshold value 0 6 10 5 s 1 prescribed by theoretical studies and second the across front frontogenetic component due to the ageostrophic circulation decays this is consistent with semi geostrophic theory where the cross frontal convergence and the stretching deformation are linked through the sawyer eliassen equation results add to other recent observational findings that the potential for instability the evolving environmental flow and the induced ageostrophic convergence each have a crucial role in differentiating between frontal waves that will grow and those that will be suppressed

secondary frontal waves in the north atlantic region a dynamical perspective of current ideas the current understanding of the dynamics of secondary cyclogenesis on frontal systems in the north atlantic region is reviewed these secondary cyclones are often poorly forecast and in extreme cases can have damaging consequences but because of their small scales and potential for rapid growth detailed observations and analyses are limited in this paper recent work is described and compared it is argued that on the synoptic scale the development of primary baroclinic waves is well understood but on the subscales of these systems where the secondaries develop there is a wider variety of mechanisms which may cause or modify cyclone growth this variety may be reflected in a wider range of resulting systems various dynamical models have been postulated secondary frontal waves are seen as the instability of a low level potential vorticity strip or warm band at a front with possible finite amplitude triggering by upper level features latent heating is thought to provide a suitable unstable potential vorticity strip but the degree to which the latent heating contributes to the instability itself is a matter of dissent secondary systems are often shallow so boundary layer processes are important but the influence of these is not well understood laboratory experiments have suggested that the boundary layer will act to suppress instability in general frontogenetic strain flow while acting to intensify the basic state front suppresses wave development in contrast recent work suggests that a frontolytic strain flow may be important in enhancing the development of one class of waves the fastex experiment an international field study of north atlantic secondary cyclogensis has recently attempted to observe these systems in detail it is hoped that the data which have been obtained will help to resolve some of the outstanding issues in this field

parcel theory in three dimensions and the calculation of scape slantwise convective available potential energy scape is a measure of the degree to which the atmosphere is unstable to conditional symmetric instability csi it has until now been defined by parcel theory in which the atmosphere is assumed to be nonevolving and balanced that is two dimensional when applying this two dimensional theory to three dimensional evolving flows these assumptions can be interpreted as an implicit assumption that a timescale separation exists between a relatively rapid timescale for slantwise ascent and a slower timescale for the development of the system an approximate extension of parcel theory to three dimensions is derived and it is shown that calculations of scape based on the assumption of relatively rapid slantwise ascent can be qualitatively in error for a case study example of a developing extratropical cyclone scape calculated along trajectories determined without assuming the existence of the timescale separation show large scape values for parcels ascending from the warm sector and along the warm front these parcels ascend into the cloud head within which there is some evidence consistent with the release of csi from observational and model cross sections this region of high scape was not found for calculations along the relatively rapidly ascending trajectories determined by assuming the existence of the timescale separation

introduction to the special issue commemorating the 30th anniversary of the royal tyrrell museum of palaeontology with a summary of the museum s early history and its research contributions located just west of drumheller in southern alberta canada the royal tyrrell museum of palaeontology rtmp is nestled among outcrops of the upper cretaceous horseshoe canyon formation exposed along the red deer river valley fig 1 since it officially opened on 25 september 19851 the museum has become one of alberta s must see tourist attractions a significant contributor to the local economy and earned an international reputation for the quality of its palaeontological collections and the research conducted by its scientists the rtmp is unique within canada in being the only government supported museum dedicated to palaeontology and it is one of the few such institutions in the world fig 1 the royal tyrrell museum of palaeontology a front of museum and main entrance circa 2010 looking westwards and with horizontal beds of the upper cretaceous horseshoe canyon formation exposed in the walls of the red deer river valley in the distance b aerial photograph oblique angle and looking to the north northeast the museum sits on top of the number 7 coal seam sensu gibson 1977 and at the base of the horsethief member of the horseshoe canyon formation d a eberth pers comm 2015 that stratigraphic position correlates with an age of about 71 5 ma i e late campanian and lies within the upper part of the edmontosaurus regalis pachyrhinosaurus canadensis dinosaur assemblage zone see eberth et al 2013 fig 6 c the iconic running theropod logo that until recently graced the exterior of the museum below a life sized tyrannosaurid sculpture by brian cooley one of many such sculptures by cooley that have been featured at the museum since its opening in 1985 and with the education wing opened in 2003 as the atco tyrrell learning centre in the background d the cretaceous alberta life sized diorama opened in 2007 an example of a rtmp exhibit that relies heavily on discoveries and interpretations by museum researchers in this case work done in the albertosaurus bonebed and at other localities throughout the horseshoe canyon formation all photographs courtesy of the royal tyrrell museum of palaeontology this special issue of the canadian journal of earth sciences presents a collection of papers commemorating the rtmp s 30th or pearl anniversary our rationale for doing a 30th anniversary volume was two fold first it is an opportunity to showcase the breadth of research conducted by current and former museum scientists as well as by some colleagues having a history of collaboration with the rtmp the 13 invited papers included in this volume are a mix of review and original research papers all thematically focused on the geology and palaeontology of alberta to varying degrees each contribution is the result of work supported by the rtmp and relies on specimens housed in the museum s collections second the 30th anniversary is an opportunity to reflect on the rtmp s history and its research program as is typical for most institutions the rtmp has done little to formally document its own history this year likely will be the last major milestone for which the original generation of museum staff are still working and available to share their recollections about the museum fieldwork and research already deaths and departures have winnowed away part of the original

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

timing of the late jehol biota new geochronometric constraints from the jixi basin ne china abstract the jehol biota is a world famous early cretaceous terrestrial ecosystem in east asia and has revealed exceptionally well preserved fossils which provide significant insights into the origin and evolution of birds and feathers and the early diversifications of mammals and angiosperms after the long lived controversies over the timing of the biota varying from late jurassic to early cretaceous in last century the lifespan of the early middle jehol biota has been precisely dated from barremian to early aptian ca 131 120 ma by a series of recent radiometric analyses however few well constrained ages are available for the late jehol biota hindering our complete understanding of the evolutionary history of the terrestrial ecosystem alternating marine and non marine deposits of the chengzihe formation in eastern heilongjiang have yielded a non marine bivalve assemblage of the jehol biota basal angiosperms and cretaceous marine index bivalves which collectively offer crucial and indisputable clues against the prevailing jurassic time of the biota since 1990s here we present the first discovery of tephra layers from the chengzihe formation dated by zircon u pb geochronology as ca 116 111 ma providing the first quantitative age calibration for the early angiosperms and the jehol bivalve assemblage therefore we demonstrate that the duration of the jehol biota extends to late aptian early albian approximately 4 9 myr younger than the currently accepted age limits

oyu tolgoi mongolia siluro devonian porphyry cu au mo and high sulfidation cu mineralization with a cretaceous chalcocite blanket the oyu tolgoi porphyry cu au mo deposit is located in the gobi desert of southern mongolia the deposit consists of three main mineralized zones north central and south oyu interpreted to constitute at least two separate porphyry copper centers oyu tolgoi is associated with a series of small structurally controlled stocks and dikes of monzonitic and dioritic composition which intrude a sequence of siluro devonian volcanic and sedimentary rocks country rocks consist of pillow basalt and basaltic andesite interbedded with fine grained clastic sedimentary horizons the sequence is interpreted to have formed in a subaqueous island arc volcanic environment which formed part of the extensive paleozoic tuva mongol arc these island arc rocks are covered by carboniferous terrigenous sequences and are intruded by carboniferous syenite and granite and permian alkaline granite much of the area is covered by poorly consolidated cretaceous sedimentary sequences central oyu consists of a multiple phase hydrothermal breccia crosscutting an altered fine grained feldspar porphyry containing porphyry type alteration and mineralization the breccia underwent texture destructive advanced argillic alteration characterized by several associations of quartz alunite dickite pyrophyllite sericite and zunyite plus lesser svanbergite and fluorite these associations overprint earlier formed k silicate and quartz sericite illite assemblages copper mineralization at central oyu is present in a supergene chalcocite blanket that formed at the expense of a pyrite rich hypogene chalcocite covellite tennantite arsenosul vanite sulvanite chalcopyrite bornite sulfide suite that accompanied the advanced argillic alteration event at south oyu a feldspar hornblende porphyry of monzonitic composition intrudes a sequence of fine grained andesite and basaltic andesite hypogene copper gold mineralization occurs as early magnetite rich pyrite poor quartz chalcopyrite bornite stockworks and sheeted veinlets hydrothermal alteration is composed of biotite and k feldspar with apatite and minor albite magnetite averages 7 to 10 vol percent and copper and gold grades vary sympathetically these early assemblages are overprinted by a sericite chlorite event with ore grade copper and erratic gold and molybdenum values and also by structurally controlled pyrite rich advanced argillic alteration k ar ages show that the hypogene copper gold mineralization at south oyu is latest silurian earliest devonian 411 3 ma and that the entire district was intruded by postmineralization syenite during the carboniferous 307 4 ma the supergene chalcocite blanket at central oyu formed in the early cretaceous earliest late cretaceous based on ages for supergene alunite of 117 1 and 93 1 ma which makes central oyu one of the oldest preserved chalcocite blankets in the world chalcocite blanket preservation was favored by climatic desiccation into the late cretaceous and the tertiary it is inferred that significant regional uplift took place at the silurian devonian boundary this synmineral ization uplift and erosion may have been in part responsible for the telescoping of the hydrothermal systems at oyu tolgoi including the superposition of epithermal style associations over higher temperature deeper seated assemblages typical of the porphyry environment

cyclone surface pressure fields and frontogenesis from nasa scatterometer nscat winds two extratropical marine cyclones and their associated frontal features are examined by computing surface pressure fields from nasa scatterometer nscat winds a variational method solves for a new surface pressure field by blending high resolution 25 km relative vorticity computed along the satellite track with an initial geostrophic vorticity field employing this method with each successive pass of the satellite over the study area allows this surface pressure field to evolve as dictated by the relative vorticity patterns computed from nscat winds the result is a high resolution surface pressure field that captures features such as fronts and low pressure centers in more detail than national centers for environmental prediction ncep reanalyses while using the actual relative vorticity to adjust the geostrophic vorticity ignores the ageostrophy of surface winds which can be significant in the vicinity of fronts and jet streaks it is a necessary approximation given that the technique uses only surface data the nscat surface pressure fields prove to be nearly as accurate as ncep reanalyses when compared to ship and buoy observations which is an encouraging result given that ncep reanalyses incorporate a myriad of data sources and the nscat fields rely primarily on one source in addition the high resolution relative vorticity fields computed from nscat winds reveal the location of surface fronts in great detail these fronts are verified using ncep analyses in situ data and satellite imagery

turbulent and advective momentum fluxes in streams 1 the scope of the present paper is the evaluation of the exchange of momentum in natural streams to explore the contribution that turbulence and secondary currents have on the shear stress distributions within the flow and hence evaluate the overall hydraulic resistance existing methods for the evaluation of shear stresses in rivers are examined with respect to their applicability to complex flow fields and a new mathematical formulation for analyzing the shear stresses affecting the longitudinal velocity distribution is presented this new method enables one to estimate the time averaged principal shear stress and its particular components due to turbulence and secondary currents directly from three dimensional velocity data an acoustic doppler velocimeter adv was used to measure the currents and turbulence at five cross sections of two field sites over a wide range of discharges the results of the cross sectional measurements reflect the nonuniformity of the river bed roughness cross sectional form and planform limited applicability was found for methods based on the theory of two dimensional boundary layer flows shear stresses estimated using the new method emphasize the dominance of secondary currents on the total momentum flux momentum fluxes caused by secondary currents were an order of magnitude larger than momentum fluxes due to turbulence