charcoal records from thermokarst deposits in central yakutia eastern siberia implications for forest fire history and thermokarst development abstract macroscopic charcoal records from a thermokarst lake deposit in central yakutia eastern siberia were used to reconstruct the history of forest fires and investigate its relationship to thermokarst initiation high accumulation rates of charcoal and pollen were coincident in the basal deposits of the thermokarst lake which suggests that both were initially deposited on the forest floor and subsequently reworked and accumulated in the thermokarst depression high charcoal and pollen accumulation rates in the basal deposits dating to 11 000 9000 cal yr bp also indicate that the thermokarst topography developed during the early holocene a lower charcoal accumulation rate after ca 9000 cal yr bp suggests that thermokarst development has been inhibited since this time it also indicates that a surface fire regime has been predominant at least since ca 9000 cal yr bp in central yakutia

sequence stratigraphy of source rocks applied to the study of the kim meridgian tithonian in the north west european shelf dorset uk yorkshire uk and boulonnais france abstract in dorset and yorkshire england the sedimentation of kimmeridgianfrithonian age mutabilis to pallasioides zones shows ordered organic sequences the distribution of the organic matter content per cent total organic carbon petroleum potential hydrogen indices is not random but occurs as widespread primary organic rich cycles nested within each other these organic rich cycles with thicknesses of about 0 5 m show regular variations in organic carbon contents reaching a maximum value midway through the cycle they formed in response to widespread phenomena and can be correlated over long distances the cycles were deposited in marine environments mainly below the storm wave base they show little sedimentological evidence of sea level fluctuation either transgression or regression in the boulonnais france a more proximal setting the comparable strata show a greater lithological contrast and depositional environments corresponding to bathymetric changes are more easily determined a comparison of the distribution of organic matter through the sequence dated by ammonites in the three areas studied shows a good correlation between the distal dorset and yorkshire and the proximal boulonnais areas the main result of the biostratigraphic revision in the boulonnais france concerns the argiles de ch tillon which can be subdivided into two members these belong to the autissiodorensis zone autissiodorensis subzone and the gigas elegans zone respectively thus the kim meridgian tithonian boundary is located within this formation transgression does not appear to be the main factor determining the accumulation of autochthonous organic matter type ii not every major transgressive facies change seen in the kimmeridgian tithonian of the boulonnais is characterized by an enrichment in organic matter in the basinal area good source rocks with high petroleum potentials result from a conjunction between the physiography the transgression and the climate this last causes the variations in primary productivity which produce the organic rich cycles transgressions act mostly to reveal the climatic variations they are a necessary condition for the accumulation of the autochthonous organic matter but they are not sufficient by themselves as demonstrated by the transgressions in the autissiodorensis and elegans zones in the first instance the strata are depleted in organic matter in both the distal and proximal areas in the second instance type ii organic matter accumulated in both distal and proximal environments the vertical fluctuations in the total organic carbon contents the types of organic matter and the petroleum potentials of the organic rich cycles determine the oil potentials of transgressive sequences in sedimentary basins

rapid destruction of a stratospheric potential vorticity anomaly by convectively induced inertial instability during the southern wisconsin extreme flooding event of 20 august 2018

field and seismic images of sharp based shoreface deposits implications for sequence stratigraphic analysis abstract sharp based shoreface sandstones are of considerable interest because of their potential as hydrocarbon reservoirs and because they play an important role in the stratigraphic analysis of basin fills the sharp based shoreface sandstones studied herein are upper jurassic kimmeridgian tithonian and exposed along the coastal cliffs of the dover strait in northwestern france these series consist of tens of meter thick alternations of sandstones bodies and organic rich shales that can be correlated for over 30 km along coastal cliff exposures and tied to high resolution ca 1 m of sediment marine seismic profiles obtained several hundred meters offshore the units described here comprise two sharp based sandstone bodies each is composed of a basal progradational set of shoreface parasequences overlain by a progradational aggradational shoreface succession each sharp based sand body lies on a marine regressive surface of erosion and is truncated by a marine transgressive surface of erosion which in turn is overlain by a thin retrogradational ravinement lag or coarse grained planar laminated bedset the two progradational packages are separated by a third surface a subaerial exposure surface that is interpreted as a sequence boundary two distinct types of seismic units referred to as type a and type b have been identified in the study area seismic unit a has conformable upper and lower boundaries and parallel aggradational configurations seismic unit b is characterized by downlap and toplap boundaries and simple or compound sigmoid and oblique tangential progradational configurations a single sharp based shoreface sandstone body makes up the type b unit and typically consists of two compound superimposed progradational sets b1 b2 the lowermost set b1 corresponds in the field to the progradational set sensu stricto whereas b2 corresponds to a progradational aggradational set b1 and b2 are separated in outcrop by a sequence boundary these observations led us to reevaluate the sequence stratigraphic interpretation of sharp based shoreface sandstones it is proposed here that complete single sharp based shoreface sandstones bodies can be separated into two different systems tracts 1 a progradational set b1 seismic body at the base which corresponds to the forced regressive wedge systems tracts frwst of hunt and tucker 1992 and 2 a progradational aggradational set b2 at the top above the sequence boundary which corresponds to the lowstand systems tract lst of posamentier et al 1992 a complete sharp based shoreface sandstone body is bounded below the frwst by a regressive surface of marine erosion caused by the downward shift of wave base and by a transgressive surface of marine erosion or ravinement surface at the top of the lst

early evolution of vertical vorticity in a numerically simulated idealized convective line the generation and organization of mesoscale convective vortices mcvs is a recurring theme in midlatitude and tropical meteorology during the warm season in this work a simulation of a finite length idealized convective line in a westerly shear environment is investigated in the absence of ambient vertical vorticity an asymmetry in average vertical vorticity forms rapidly at early times in the present simulation this study focuses on the formation and organization of vertical vorticity at these early simulation times previous simulations suggest that tilting of either ambient or storm generated horizontal vorticity is the primary mechanism responsible for the formation organization and maintenance of mcvs this study confirms recent work regarding the generation of vertical vorticity at early times in the simulation a lagrangian budget analysis of the vertical vorticity equation however shows that vorticity convergence becomes a comparable and at times dominant mechanism for the enhancement and long term organization of vertical vorticity early in the simulation despite differences in the initial ambient horizontal vorticity hodograph and convective available potential energy the lagrangian budget analysis in the present midlatitude case is consistent with the lagrangian budget results of a previous tropical squall line simulation the study of idealized convective lines in midlatitude environmental conditions therefore provide valuable insight into understanding vertical vorticity production in tropical squall lines and their potential relevance to tropical cyclogenesis

a climatology of midlatitude mesoscale convective vortices in the rapid update cycle abstract climatological characteristics of mesoscale convective vortices mcvs occurring in the state of oklahoma during the late spring and summer of four years are investigated the mcv cases are selected based on vortex detection by an objective algorithm operating on analyses from the rapid update cycle ruc model consistent with a previous study true mcvs represent only about 20 of the mesoscale relative vorticity maxima detected by the algorithm the mcvs have a broad range of radii and intensities and their longevities range between 1 and 54 h their median radius is about 200 km and their median midlevel relative vorticity is 1 2 10 4 s 1 there appears to be no significant relationship between mcv longevity and intensity similar to past estimates approximately 40 of the mcvs generate secondary convection within their circulations the mean synoptic scale mcv environment is determined by the use of a ruc based composite analysis at four different stages in the mcv life cycle defined b

genesis of tropical storm eugene 2005 from merging vortices associated with itcz breakdowns part i observational and modeling analyses abstract although tropical cyclogenesis occurs over all tropical warm ocean basins the eastern pacific appears to have the highest frequency of tropical cyclogenesis events per unit area in this study tropical cyclogenesis from merging mesoscale convective vortices mcvs associated with breakdowns of the intertropical convergence zone itcz is examined this is achieved through a case study of the processes leading to the genesis of tropical storm eugene 2005 over the eastern pacific using the national centers for environmental prediction reanalysis satellite data and 4 day multinested cloud resolving simulations with the weather research and forecast wrf model at the finest grid size of 1 33 km observational analyses reveal the initiations of two mcvs on the eastern ends of the itcz breakdowns that occurred more than 2 days and 1000 km apart the wrf model reproduces their different movements intensity and size changes and vortex vortex interaction at nearly the right timing and location at

extreme rainfall and flooding from orographic thunderstorms in the central appalachians 1 the central appalachian region has experienced some of the largest rainfall accumulations in the world at time intervals less than 6 h including the 18 july 1942 smethport pennsylvania storm that produced 780 mm in less than 5 h the envelope curve of central appalachian flood peaks at small drainage areas less than 1000 km2 is dominated by orographic thunderstorm systems like the smethport storm orographic thunderstorm systems that have produced catastrophic flooding in the central appalachians are examined through observational and numerical model analyses using the weather research and forecasting wrf model analyses suggest that the frequency of catastrophic flooding varies over the central appalachian region and that small scale variation may be linked to the role of complex terrain in altering thunderstorm dynamics catastrophic flooding along the western margin of the central appalachians is dominated by four storms that occurred on 18 19 july 1889 1942 1977 and 1996 which were associated with warm season extratropical systems and were characterized by rapidly moving storm elements in complex terrain along the eastern margin and interior of the central appalachians catastrophic flooding is linked to four terrain locked orographic convective systems that occurred 17 18 june 1949 18 19 august 1969 27 june 1995 and 11 august 2003 wrf model simulations of the little river storm june 1949 rapidan storm june 1995 smethport storm 18 july 1942 and redbank storm 18 19 july 1996 are used to characterize ingredients of catastrophic rainstorms in the central appalachians

patterns of precipitation and mesolow evolution in midlatitude mesoscale convective vortices abstract surface pressure manifestations of mesoscale convective vortices mcvs that traversed oklahoma during the periods may august 2002 05 are studied using the weather surveillance radar 1988 doppler wsr 88d the oklahoma mesonet and the noaa profiler network data forty five mcvs that developed from mesoscale convective systems mcss have been investigated 28 62 of which exhibit mesolows detectable at the surface within this group three distinct patterns of precipitation organization and associated mesolow evolution have been identified the remaining 17 38 of the cases do not contain a surface mesolow two repeating patterns of precipitation organization are identified for the latter group the three categories of mcvs possessing a surface mesolow are as follows nineteen are classified as rear inflow jet mcvs and tend to form within large and intense asymmetric mcss rear inflow into the mcs enhanced by the development of an mcv on the left hand side relative to system motion pro

post saalian transformation of dry valleys in eastern europe an example from ne poland the studies were conducted in a dry valley in ne poland they were aimed at determining the origin of this structure and tracing the processes that have shaped the dry valley in a time span of about 130 ka the research included detailed geological mapping including piercing of a number of boreholes and electrical resistivity tomography ert surveys the obtained material was pollen analysed osl dated and the grain size distribution and the morphoscopy of sand quartz grains were investigated additionally the organic matter om content was determined based on the obtained results it was concluded that the structure currently occupied by sediments of the dry valley was formed during the warta stadial of the odranian glaciation saalian mis 6 as a glacial tunnel valley small probably isolated depressions functioned in the dry valley bottom after the ice sheet retreat the sediments record a full succession of climate oscillations from the eemian interglacial mis 5e pollen zones e1 to e7 through the early vistulian mis 5a 5d to mis 4 in the early vistulian the depressions functioned as lakes or got shallower and were replaced by peat bogs depending on the climate conditions during mis 4 the bottom of the dry valley was subjected to erosion as a result of concentrated water flow this caused draining of the existing depressions and their incorporation within the flow probably during mis 3 solifluction was activated on the slopes of the dry valley during lgm permafrost aggradation occurred in the study area recorded by two generations of epigenetic sand wedges and development of aeolian processes in contrast to analogous processes within the european sand belt the latter processes acted for a short time and only locally the final record are holocene soils it seems that the analysed valley is a good example of palaeoenvironmental conditions in eastern europe

comparison between high resolution seismic and sequence stratigraphic approaches applied to the upper jurassic deposits of the dover strait area northern france abstract this study is an attempt to interpret very high resolution seismic data usually devoted to shallow marine surveys in terms of very high resolution seismic and sequence stratigraphy at the scale of the reservoir seismic data are compared with outcrop based observations in order to discuss the geometrical relationships between rock bodies and the nature of the seismic reflections in terms of seismic facies related to type lithologies two high resolution seismic surveys using a sparker were performed in the dover strait area some 100s of metres away from the boulonnais coastal cliffs the aim was to look to the 130 m thick mixed siliciclastic carbonate deposits of upper jurassic age kimmeridgian tithonian cropping out at the sea floor and to compare them to the coastal cliffs exposures the 100 m apart seismic profiles exhibit a 100 m deep penetration and 1 m in vertical resolution upper 30 ms part of the profiles four seismic facies are recognised on the seismic profiles they comprise ten seismic units which can be grouped into three broad families group 1 has a parallel aggradational reflection configuration and conformable boundaries which may correspond to the transgressive and highstand systems tracts the seismic facies exhibit either a high continuity high amplitude corresponding to clayey mudstone lithologies of the mid ramp environment or a high continuity low amplitude corresponding to shaly lithologies of the outer ramp environment group 2 has a sigmoid progradational reflection configuration bounded at the base by a downlap surface and at the top by a toplap surface these boundaries correspond respectively in the field to a marine regressive surface of erosion and a marine transgressive surface of erosion the seismic facies is cross layered and exhibits a moderate continuity low to moderate amplitude and moderate frequency group 2 corresponds to the bioclastic sand prone facies of the inner ramp environment it is interpreted as lowstand sharp based shorefaces group 3 exhibits a progradational complex to chaotic configuration it lies on an erosional unconformity with paleogullies the seismic facies shows discontinuous reflections with moderate amplitude and high to moderate frequency it corresponds in the field to cross bedded sandstones in channel fill arrangements of fluvial origin wealdian deposits marking the top of the section the different systems tracts sequence boundaries and depositional sequences identified onshore can be recognised as well on the seismic profiles but the comparison demonstrates that seismic data complement the onshore sequence stratigraphic analysis by providing the geometrical relationships between systems tracts onlap downlap toplap that cannot be observed onshore the maximum flooding surfaces however present no specific seismic signature on such a low angle ramp profile it can only be identified precisely in the field which also help to relate lithologies to seismic facies this study represents one of the first attempts to interpret very high resolution seismic data at the outcrop scale it will be improved again in the future by the collection of impedance logs and synthetic seismic traces from cored sections on the coastal cliffs for comparison with the seismic data

an alternative to exotic spore or pollen addition in quantitative microfossil studies uncertainties in availability and formulation of exotic microfossils e g lycopodium spp eucalyptus spp to be added to microfossil preparations may be resolved by the use of plastic microspheres 25 0 1 0 m which are unaffected by standard pollen preparative treatments koh hcl hf acetolysis and organic solvents the microspheres are sensitive to strongly oxidizing treatments e g schulze s reagent h2o2 h2so4 reflux for diatom preparation but can be added following digestion of organic material preparation of microsphere suspensions in a suitable electrolyte e g nacl formic acid water permits calibration by coulter counter of suitable dilutions e g 5000 100 ml 1 for delivery by tipet volumetric flasks the uniformity and distinctive appearance of the microspheres not only facilitate recognition but also provide a constant reference for both size 25 m and volume 8180 m3 as well as a reference standard for computerized microfossil scanning the microspheres are inert

diurnal evolution and structure of long lived mesoscale convective vortices along the mei yu front over the east china plains abstractthe structure and diurnal evolution of long lived eastward propagating mesoscale convective vortices mcvs along typical summertime mei yu fronts over the east china plains are investigat

environmental cycles in the late jurassic northwest european epeiric basin interaction with atmospheric and hydrospheric circulations abstract despite the large size and the heterogeneity of the northwest european late jurassic kimmeridgian lower tithonian epeiric basin the sedimentary environment was rather uniform in general deposition of mudstones and the microlaminated organic rich sediments took place under low oxic to anoxic conditions detailed environmental analysis clearly points to a seasonal alternation of aerobic with anaerobic conditions in substrate and bottom water resulting in one year life cycles in the benthic environment the widespread uniformity of facies and the seasonal alternation in the oxygen budget of the benthic environments are best explained by a summer to winter change in the atmospheric circulation of the northern hemisphere this change strongly influenced the oceanographic situation in the northwestern european epeiric basin superposed on this one year cyclicity three more hierarchical levels of cycles are stratigraphically recorded they reflect a complex history of orbital forced and non orbital forced climatic changes and or eustatic sea level fluctuations in the late jurassic

processes controlling the structure and longevity of two quasi linear convective systems crossing the southern new england coast abstractthis paper explores the structural evolution and physical processes that explain the modification of two quasi linear convective systems qlcss that encountered the densely populated new york city atlantic coastal region one qlcs on 31 may 2002 traversed the atlantic coastal boundary with little change in its intensity producing widespread severe wind damage across new york city and long island during this event warm air advection at 925 hpa helped destabilize the layer above this level over the coastal zone while the marine boundary layer deepened below this level the 0 3 km line perpendicular vertical wind shear was relatively strong which supported ascent along the leading edge of the diabatically generated cold pool the surface based convective system became slightly elevated as it moved over the marine waters in contrast the 23 july 2002 qlcs decayed upon encountering the atlantic coastline despite its coincidence with a surface cold front the most unstable cape values during thi

the vertical structure of mesoscale convective vortices abstract simulations of two cases of developing mesoscale convective vortices mcvs are examined to determine the dynamics governing the origin and vertical structure of these features although one case evolves in strong vertical wind shear and the other evolves in modest shear the evolutions are remarkably similar in addition to the well known mesoscale convergence that spins up vorticity in the midtroposphere the generation of vorticity in the lower troposphere occurs along the convergent outflow boundary of the parent mesoscale convective system mcs lateral transport of this vorticity from the convective region back beneath the midtropospheric vorticity center is important for obtaining a deep column of cyclonic vorticity however this behavior would be only transient without a secondary phase of vorticity growth in the lower troposphere that results from a radical change in the divergence profile favoring lower tropospheric convergence following the decay of the nocturnal mcs subsequent con

the evolution of the 10 11 june 1985 pre storm squall line initiation development of rear inflow and dissipation abstract mesoscale analysis of surface observations and mesoscale modeling results show that the 10 11 june squall line contrary to prior studies did not form entirely ahead of a cold front the primary environmental features leading to the initiation and organization of the squall line were a low level trough in the lee of the rocky mountains and a midlevel short wave trough three additional mechanisms were active a southeastward moving cold front formed the northern part of the line convection along the edge of cold air from prior convection over oklahoma and kansas formed the central part of the line and convection forced by convective outflow near the lee trough axis formed the southern portion of the line mesoscale model results show that the large scale environment significantly influenced the mesoscale circulations associated with the squall line the qualitative distribution of along line velocities within the squall line is attributed to the larger scale circulations associated with the le

the johnstown flood of july 1977 a long lived convective system abstract the heavy rains responsible for the disastrous flash floods new johnstown pennsylvania on the night of 19 20 july 1977 are shown to be part of a large quasi circular mesoscale convective complex this complex can be traced back to an origin in south dakota nearly 96 h earlier the complex tends to become more compact and intense during the night with a radius of 150 km and to expand in response to new and peripheral convection during the day on the small synoptic scale the system is characterized by a pool of cool air at the surface and throughout the lower troposphere just north of the centroid of the rainstorm by a cyclonic circulation of substantial intensity in the lower and middle troposphere and by anticyclonic circulation in the upper troposphere airflow relative to the moving storm is southeasterly at the surface veering rapidly to southwesterly in the boundary layer and then to westerly in the upper troposphere substantial convective instability is present throughout the env

epigenetic salt accumulation and water movement in the active layer of central yakutia in eastern siberia observations of soil moisture and salt content were conducted from may to august at neleger station in eastern siberia seasonal changes of salt and soil moisture distribution in the active layer of larch forest undisturbed and a thermokarst depression known as an alas disturbed were studied electric conductivity ece of the intact forest revealed higher concentrations that increased with depth from the soil surface into the active layer and the underlying permafrost 1 ms cm 1 at 1 1 m to 2 6 ms cm 1 at 160 cm depth in the permafrost however a maximum value of 5 4 ms cm 1 at 0 6 m depth was found in the dry area of the alas the concentration of ions especially na mg2 ca2 so42 and hco3 in the upper layers of this long term disturbed site indicates the upward movement of ions together with water a higher concentration of solutes was found in profiles with deeper seasonal thawing the accumulation of salts in the alas occurs from spring through into the growing season the low concentration of salt in the surface soil layers appears to be linked to leaching of salts by rainfall there are substantial differences between water content and electric conductivity of soil in the forest and alas modern salinization of the active layer in the alas is epigenetic and it happens in summer as a result of spring water collection and high summer evaporation the gradual salt accumulation in the alas in comparison with the forest is controlled by the annual balance of water and salts in the active layer present climatic trends point to continuous permafrost degradation in eastern siberia increasing the risk of surface salinization which has already contributed to changing the landscape by hindering the growth of forest copyright 2006 john wiley sons ltd

the coupled moisture heat process of permafrost around a thermokarst pond in qinghai tibet plateau under global warming due to environmental disturbances such as local human activity and global warming melting of massive ground ice has resulted in thermokarst ponds which are extensively distributed in the qinghai tibet plateau qtp besides the global warming the thermokarst pond as a major heat source speeds up the moisture change and degradation of its surrounding permafrost to analyze the long term coupled moisture heat process near a representative nonpenetrative thermokarst pond in a permafrost region abundant temperature data over multiple years at different depths and horizontal distances from the center of the thermokarst pond have been collected at a field experimental station in qtp a numerical model is built to analyze this thermokarst pond the temperature and moisture processes of surrounding permafrost are simulated by this model and compared with measured temperature data our results show that if the rate of air temperature rise is 0 048 degrees c yr which refers to a 2 4 degrees c temperature rise over 50years the thawing fronts underneath the thermokarst pond move downward at a linear rate of 0 18m yr and the permafrost beneath the pond center would disappear after the year of 2281 beyond that time the impact range of the pond on the natural ground increases to about 50m in horizontal direction so a dish shape thawing zone occurs around the thermokarst pond simultaneously the moisture state is greatly changed in 2281 and becomes completely different from that in 2013 all of these would inevitably deteriorate the ecological and environmental system in qtp

geological and geomorphological evolution of a sedimentary periglacial landscape in northeast siberia during the late quaternary a wide variety of environmental records is necessary for analysing and understanding the complex late quaternary dynamics of permafrost dominated arctic landscapes a ne siberian periglacial key region was studied in detail using sediment records remote sensing data and terrain modelling all incorporated in a geographical information system gis the study area consists of the bykovsky peninsula and the adjacent khorogor valley in the kharaulakh ridge situated a few kilometres southeast of the lena delta in this study a comprehensive cryolithological database containing information from 176 sites was compiled the information from these sites is based on the review of previously published borehole data outcrop profiles surface samples and our own field data these archives cover depositional records of three periods from pliocene to early pleistocene the late pleistocene and the holocene the main sediment sequences on the bykovsky peninsula consist of up to 50 m thick ice rich permafrost deposits ice complex that were accumulated during the late pleistocene they were formed as a result of nival processes around extensive snowfields in the kharaulakh ridge slope processes in these mountains such as in the khorogor valley and alluvial proluvial sedimentation in a flat accumulation plain dominated by polygonal tundra in the mountain foreland bykovsky peninsula during the early to middle holocene warming a general landscape transformation occurred from an extensive late pleistocene accumulation plain to a strongly thermokarst dominated relief dissected by numerous depressions thermokarst subsidence had an enormous influence on the periglacial hydrological patterns the sediment deposition and on the composition and distribution of habitats climate deterioration lake drainage and talik refreezing occurred during the middle to late holocene the investigated region was reached by the post glacial sea level rise during the middle holocene triggering thermo abrasion of ice rich coasts and the marine inundation of thermokarst depressions

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

sequence analytical approach to the upper kimmeridgian lower tithonian storm dominated ramp deposits of the boulonnais northern france a landward time equivalent to offshore marine source rocks an interdisciplinary approach based on high resolution physical stratigraphy biostratigraphy organic matter analysis and clay mineralogy has been applied to the mixed siliciclastic carbonate kimmeridgian tithonian deposits of the boulonnais north western france these rocks are the age equivalents of some of the offshore marine source rocks of the north sea and were deposited in an overall storm dominated homoclinal ramp setting which may represent one of the most shore proximal sediments of this age cropping out in north western europe comparison with data from the yorkshire dorset lorraine and aquitaine areas allows the discrimination of three major transgressive regressive sediment packages with disconformities of interregional extent 1 from the baylei zone to top eudoxus zone 2 from the autissiodorensis zone to base scitulus zone 3 from the upper scitulus zone to the pectinatus zone the lower two regionally correlative disconformities correspond to the sequence boundaries at the top of the eudoxus zone and the top of the autissiodorensis zone formed by high frequency relative sea level variations during the periods of maximum transgression of the platform the latter disconformity the p1 nodule bed reflects a major tectonically induced reorganization of the north west european intrashelf sedimentary basin characterized by a shift in both the location of the main depocentre and the sources of sediment production

environmental variability in northeastern siberia during the last 13 300 yr inferred from lake diatoms and sediment geochemical parameters abstract in northeastern siberia russia a 1 2 m sediment core was retrieved and radiocarbon dated from a small and shallow lake located at the western side of the lower lena river n 69 24 e 123 50 81 m a s l the objective of this paper is to reconstruct the palaeoenvironmental variability and to infer major palaeoclimate trends that have occurred since 13 3 cal kyr bp we analysed the diatom assemblages sedimentology grain size total organic carbon toc total nitrogen tn and the elemental and mineralogical composition using x ray fluorescence xrf and x ray diffractometry xrd of the sediment core our results show parallel changes in the diatom species composition and sediment characteristics enhanced minerogenic sediment input and the occurrence of pyrite is indicative of a cold period between 12 7 and 11 6 cal kyr bp the diatom data enable a qualitative inference about the local ecological conditions to be made and reveal an oligotrophic lake system with alkaline and cold conditions during the earliest holocene moderately warmer climates are inferred for the period from 9 1 to 5 7 cal kyr bp the major shift in the diatom assemblage from dominance of small benthic fragilarioid taxa to a more complex diatom flora with an influx of several achnanthoid and naviculoid diatom species occurred after a transitional period of about 1400 yr 7 1 to 5 7 cal kyr bp at 5 7 cal kyr bp indicating a circumneutral and warmer hydrological regime during the holocene thermal maximum htm diatom valve concentrations declined starting 2 8 cal kyr bp but have been rising again since 600 cal yr bp this has occurred in parallel to the increased presence of acidophilous diatom taxa e g eunotia spp and decreased presence of small benthic fragilarioid species in the most recent sediments which is interpreted as the result of neoglacial cooling and subsequent recent climate warming our findings are compared to other lake inferred climate reconstructions along the lena river we conclude that the timing and spatial variability of the htm in the lower lena river area reveal a temporal delay from north to south

stratral architectures of late quaternary regressive transgressive cycles in the roussillon shelf sw gulf of lions france abstract a seismic and sequence stratigraphy scheme of the southwestern area of the gulf of lions shelf nw mediterranean basin is presented through the analysis of high resolution seismic profiles obtained with a minisparker system and calibrated with published seismic and core data of the adjacent languedoc area the observed stratigraphic architecture records the repetition of four regressive transgressive cycles which constitute high frequency depositional sequences dss regressive intervals dominate the generation of shelf sedimentary architecture within regressive intervals the identification of progressively shallower clinoforms from proximal to distal in a downdip direction constitutes a strong indicator of the occurrence of forced regressions this stratigraphic pattern documents the preservation of potential sand prone reservoirs encased within widespread regressive wedges and directly connected with organic matter rich muds as distally there is no sharp basal contact between the two the unusual preservation of pre last glacial maximum transgressive deposits is attributed to the combined influence of previous shelf topography and dominant wave regime the most significant transgressions were recorded by shallow water deposits in distal middle and proximal locations distal and proximal deposits develop over relatively steep surfaces which caused slower transgressions and favoured the generation of wave dominated coastal deposits in contrast middle deposits show moderate development over a smooth shelf profile as a consequence of rapid shoreline translation the analysis of spatial changes of regressive transgressive cycles provided important information about the nature of shelf processes and about the relative significance of regressive versus transgressive intervals within each individual ds whose development was led by recent high frequency sea level cycles dominance of 120 ka cycles would imply that transgressive deposits represent a partial record of glacial interglacial transgressions dominance of 20 ka cycles is not favoured by the fact that the preservation of quaternary deposits is apparently limited on the shelf

climate and vegetation dynamics in the tundra and forest zone during the late glacial and holocene abstract analysis of palynological successions has enabled reconstruction of climate variations throughout the late glacial and holocene in the tundra and forest zones of northern eurasia statistical analysis allows estimation of mean annual precipitation and mean annual and july temperatures based on palynological assemblages thus the dynamic relationships between climate and vegetation changes can be established throughout the late glacial and holocene climate fluctuations were more dramatic in eastern europe than in siberia primarily as a result of the influence of westerly air masses in contrast the autochthonous climate of siberia dominated by local air masses was less prone to influence from climate changes elsewhere in the northern hemisphere and shows only an attenuated younger dryas signal mid holocene warming characterizes all of northern eurasia although the regions of siberia most influenced by continental climates show less pronounced cooling during the later holocene sharp changes between summer monsoonal and winter anti cyclonic regimes characterize the pacific maritime region

rapid thermokarst evolution during the mid holocene in central yakutia russia the reconstruction of holocene thermokarst landform evolution is important to understand the potential impact of current global climate change on permafrost regions a multi proxy approach was applied to analyse the sedimentological and biogeochemical characteristics as well as pollen and lacustrine microfossils of a core profile drilled in a small pingo within a large central yakutian thermokarst basin alas age depth modelling with macrofossil 14c ages reveals high thermokarst deposit sedimentation rates and a complete thermokarst sequence spanning about 900 years during the mid holocene between 6750 and 5870 cal yr bp in total three stages of thermokarst landscape evolution have been identified thermokarst processes were initiated at 6750 to 6500 cal yr bp terrestrial conditions changed quickly to lacustrine conditions and a thermokarst lake rapidly emerged and grew to an estimated size of 120 600 m diameter and 7 5 15 m depth during only 150 years between 6500 and 6350 cal yr bp the dec

analysis of a small vigorous mesoscale convective system in a low shear environment part ii evolution of the stratiform precipitation and mesoscale flows abstract the evolution of the mesoscale flow and precipitation distribution are investigated for a small mesoscale convective system mcs that evolved in a nearly barotropic environment exhibiting moderate instability and weak wind shear observations primarily from a single doppler radar detail the growth of the mcs from the merger of several clusters and lines of vigorous convective cells into a mature state consisting of a weaker convective line trailed by an expanding stratiform precipitation region analysis of radar reflectivity reveals that this stratiform region formed in situ in the presence of weak mesoscale updraft as decaying convective cores coalesced rather than through rearward advection of ice particles directly from the convective region in the absence of sufficient low level shear the mcs collapsed rapidly as it assumed the structure of the archetypal convective line and trailing stratiform precipitation region velocity azimuth displays reveal mesoscale updrafts of about 70 cm s 1 d

forced regressions in a sequence stratigraphic framework concepts examples and exploration significance sequence stratigraphic concepts suggest that stratal geometries develop and are largely controlled by changes in relative sea level on the shelf lowstand deposits which form during falls and subsequent stillstands of relative sea level can be recognized by the presence of an unconformity at the base the isolated and basinward position relative to the previous shoreline and the abrupt seaward translation of shallow water and shoreline facies into the basin across an unconformity surface this seaward translation of facies and shoreline regression in response to relative sea level lowering is termed a forced regression a forced regression is independent of variations of sediment flux and is in contrast with normal regressions that occur in response to excess sediment flux relative to space available on the shelf i e accommodation forced regressions commonly are associated with a zone of sedimentary bypass subaerial exposure and possible fluvial erosion between the newly formed and preceding shorelines certain shelf sands previously interpreted as offshore or mid shelf sand bodies thus can be reinterpreted as stranded lowstand shorelines associated with forced regressions this alternative interpretation has economic significance insofar as it suggests different subsurface correlations and reservoir geometries with the potential for development of new play types and enhanced recovery in o der fields examples of forced regression can be observed at a variety of scales and ages several such examples include the modern east coulee fan delta and the lower cretaceous viking formation in alberta canada the quaternary rhone delta and the quaternary hudson valley system

the role of synoptic scale flow during tropical cyclogenesis over the north atlantic ocean abstract the synoptic scale flow during tropical cyclogenesis and cyclolysis over the north atlantic ocean is investigated using compositing methods genesis and lysis are defined using the national hurricane center nhc now known as the tropical prediction center best track data genesis lysis occurs when nhc first last identifies and tracks a tropical depression in the final best track dataset storm centered composites are created with the analysis of the tropical oceanic lower level atoll 900 hpa and 200 hpa winds for june november produced by nhc for the years 1975 93 results show that significant regional differences exist in 200 hpa flow during genesis across the atlantic basin composites of genesis in the western part of the basin show a 200 hpa trough ridge located to the west east of the atoll disturbance in the eastern half of the basin composites of genesis show a sprawling 200 hpa ridge centered northeast of the atoll disturbance the major axis of this elliptically shaped 20

a 10 year radar based climatology of mesoscale convective system archetypes and derechos in poland abstractin this study a 10 year 2008 2017 radar based mesoscale convective system mcs and derecho climatology for poland is presented this is one of the first attempt for a european country to

temporal significance of sequence boundaries abstract this paper analyses the temporal significance of stratigraphic surfaces bounding the marine portions of the depositional sequence genetic stratigraphic sequence and transgressive regressive sequence these bounding surfaces known as the correlative conformity c c maximum flooding surface mfs and conformable transgressive surface cts respectively may either be defined on the basis of stratal stacking patterns which we call type a surfaces or on the basis of water depth changes and relative sea level changes which we call type b surfaces the type a mfs and cts are time lines in a depositional dip section corresponding to the turnaround points from shoreline transgression to regression and vice versa they separate prograding coarsening upward from retrograding fining upward geometries with a timing determined by the interplay between the rates of sedimentation and relative sea level rise in the shoreline area the timing of type a mfs and cts is not affected by the offshore variations in sedimentation and subsidence rates but it is only controlled by the shoreline movements and the associated facies shifts the type a c c separates rapidly prograding and offlapping forced regressive strata from the overlying lower rate prograding and aggrading normal regressive strata this surface is diachronous younger basinward with the rate of offshore sediment transport the timing of the type a c c in the shoreline area corresponds to the end of relative sea level fall but it develops under relative sea level rise conditions offshore the timing of the type b mfs and cts depends on the offshore variations in the sedimentation and subsidence rates these surfaces defined on the basis of bathymetric changes become younger and older seaward respectively tending to merge together offshore the type b c c marks the end of relative sea level fall in any point along a depositional dip section it is diachronous older basinward as its timing depends on the offshore variations in subsidence rates the diachroneity of type b surfaces reaches a quarter of the period of the highest frequency variable whichever that is among the eustasy tectonics or sedimentation controls types a and b surfaces merge together in the shoreline area but they become temporally divergent offshore deepening upward and shallowing upward facies should not be confused with transgressive and regressive systems tracts the latter are strictly controlled by the shoreline movements which determine the direction of facies shifts and the stratal stacking patterns

warm core formation in tropical storm humberto 2001 at 0600 utc 22 september 2001 humberto was a tropical depression with a minimum central pressure of 1010 hpa twelve hours later when the first global positioning system dropwindsondes gps sondes were jettisoned humberto s minimum central pressure was 1000 hpa and it had attained tropical storm strength thirty gps sondes radar from the wp 3d and in situ aircraft measurements are utilized to observe thermodynamic structures in humberto and their relationship to stratiform and convective elements during the early stage of the formation of an eye the analysis of tropical storm humberto offers a new view of the pre wind induced surface heat exchange pre wishe stageoftropicalcycloneevolution humbertocontainedamesoscaleconvectivevortex mcv similar to observations of other developing tropical systems the mcv advects the exhaust from deep convection in the form of an anvil cyclonically over the low level circulation center on the trailing edge of the anvilanareaofmesoscaledescentinducesdryadiabaticwarmingin thelowertroposphere thenascentwarm core at low levels causes the initial drop in pressure at the surface and acts to cap the boundary layer bl as bl air flows into the nascent eye the energy content increases until the energy is released from under the cap on the down shear side of the warm core in the form of vigorous cumulonimbi which become the nascent eyewall this series of events show one possible path in which a mesoscale convective system may evolve into a warm cored structure and intensify into a hurricane

the integral role of a diabatic rossby vortex in a heavy snowfall event abstract on 24 25 february 2005 a significant east coast cyclone deposited from 4 to nearly 12 in 10 30 cm of snow on parts of the northeastern united states the heaviest snowfall and most rapid deepening of the cyclone coincided with the favorable positioning of an upper level short wave trough immediately upstream of a preexisting surface cyclone the surface cyclone in question formed approximately 15 h before the heaviest snowfall along a coastal front in a region of frontogenesis and heavy precipitation the incipient surface cyclone subsequently intensified as it moved to the northeast consistently generating the strongest convection to the east northeast of the low level circulation center the use of potential vorticity pv inversion techniques and a suite of mesoscale model simulations illustrates that the early intensification of the incipient surface cyclone was primarily driven by diabatic effects and was not critically dependent on the upper level wave these facts taken in conjunct

forced regressive wedge in the mesoproterozoic koldaha shale vindhyan basin son valley central india abstract the present paper highlights the sequence development within the mesoproterozoic koldaha shale member of the kheinjua formation vindhyan supergroup which records the occurrence of a forced regressive wedge and associated discontinuity surfaces at the base of the wedge nine lithofacies have been identified within the study area that are grouped into three lithofacies associations varying in depositional setting from outer shelf through shoreface foreshore beach to continental braidplain the outer shelf sediments are aggradational to slightly progradational representing highstand systems tract the rapidly progradational wedge shaped shoreface to foreshore beach succession occurs sharply or erosively above the outer shelf sediments and is bounded by a regressive surface of marine erosion rsme at the base and by a subaerial unconformity at the top this along with its downstepping trajectory supports deposition of this sedimentary wedge during falling sea level a laterally extensive soft sediment deformation zone occurs at the base of the wedge the forced regressive wedge is incised by fluvial braidplain deposits that rest on an erosive surface representing a sequence boundary the thin braidplain deposits are the product of aggradation during a subsequent early rise in relative sea level and thus they are inferred to represent a lowstand systems tract the constituent architectural elements that characterize the braidplain deposits are downstream accretion elements and small channel elements further landward the base and top of the shoreface wedge merge to form an unconformity across deposits that rest directly on the outer shelf sediments the identification of forced regressive wedges has significant economic importance in view of the potential occurrence of hydrocarbons within the proterozoic formations

estimating the mass flux of charcoal from sedimentary records effects of particle size morphology and orientation reconstructing past fire requires ways to compare concentration estimates obtained by different charcoal analysis methods these methods estimate concentrations from area measurements or particle counts on pollen slides on sieves and on thin sections and they do so at different magnifications depending on particle properties each method might give substantially different results image analysis of charred particles in thin sections of lake sediments is used to parameterize relationships among different concentration estimators we determined distributions of particle size shape and orientation in undisturbed sediments and assessed how those distributions affect concentration estimates particle diameter distributions were conservative across different magnifications particle shape was also conservative with major minor axis ratios near 2 5 our derived relationships among estimators could be used to improve comparability for all but the smallest particle classes which tended to be unpredictable

climatology of summer midtropospheric perturbations in the u s northern plains part i influence on northwest flow severe weather outbreaks northwest flow severe weather outbreaks nwf outbreaks describe a type of summer convective storm that occurs in areas of mid level nwf in the central united states convective storms associated with nwf outbreaks often travel a long distance systematically along a northwest southeast oriented track across the northern plains previous studies have observed that these migrating convective storms are frequently coupled with subsynoptic scale midtropospheric perturbations mps initiated over the rocky mountains this study traces mps for the decade of 1997 2006 using the north american regional reanalysis to examine their climatology and possible influence on nwf outbreaks mps are characterized by a well organized divergent circulation with persistent ascending motion at the leading edge promoting convection the divergent circulation is further enhanced by low level convergence along the northern terminus of the great plains low level jet the downstream propagation of mps assists in forming the progressive feature of the associated convective storms mps have a maximum frequency in july consistent with nwf outbreaks in july and august the fully developed north american anticyclone produces prevailing nwf over the northern plains where up to 60 of rainfall and storm reports are linked to mps the movement timing and rainfall distribution of mps remarkably resemble those of nwf outbreaks when encountering strong low level jets ascending motion and convergence of water vapor flux associated with mps intensify considerably and precipitation is greatly enhanced it is likely that nwf outbreaks are generated whenever mps occur in association with strong low level jets

subkilometer simulation of a torrential rain producing mesoscale convective system in east china part i model verification and convective organization abstracta nocturnal torrential rain producing mesoscale convective system mcs occurring during the mei yu season of july 2003 in east china is studied using conventional observations surface mesoanalysis satellite and radar data and a 24 h multinested model simulation with the finest grid spacing of 444 m observational analyses reveal the presence of several larger scale conditions that were favorable for the development of the mcs including mei yu frontal lifting moderate cold advection aloft and a moist monsoonal flow below and an elongated old cold dome left behind by a previously dissipated mcs results show that the model could reproduce the evolution of the dissipating mcs and its associated cold outflows the triggering of three separate convective storms over the remnant cold dome and the subsequent organization into a large mcs and the convective generation of an intense surface meso high and meso scale radar reflectivity morphologies in particular the model reproduces the passage of

surface cyclogenesis from convectively driven amplification of midlevel mesoscale convective vortices mesoscale convective vortices mcvs are midtropospheric warm core cyclonic circulations that often develop in the stratiform region of mesoscale convective systems typically divergent anticyclonically circulating mesoscale cold anomalies appear both above and below the mcv the upper level cold anomaly is usually found near the tropopause while the low level anomaly is surface based and exhibits locally higher pressure one aspect of mcvs that has received much attention recently is the role that they may play in tropical cyclogenesis of special interest is how an mcv amplifies when deep convection redevelops within the borders of its midlevel cyclonic circulation and how the amplified mcv transforms the divergent surface based cold pool with anomalously high surface pressure into a convergent cyclonic circulation with anomalously low pressure the pennsylvania state university national center for atmospheric research fifth generation mesoscale model is used to simulate an mcv that was instrumental in initiating within the borders of the midlevel vortex s circulation several successive cycles of convective development and decay over a 2 day period after each cycle of convection both the horizontal size of the cyclonic circulation and the magnitude of the potential vorticity associated with the vortex were observed to increase the simulation reproduces the development and evolution of the mcv and associated convective cycles mesoscale features responsible for the initiation of convection within the circulation of the vortex and the impact of this convection on the structure and evolution of the vortex are investigated a conceptual model is presented to explain how convective redevelopment within the mcv causes low level heights to fall and cyclonic vorticity to grow downward to the surface applying this conceptual model to a tropical marine environment is also considered

the vertical vorticity structure within a squall line observed during bamex banded vorticity features and the evolution of a bowing segment abstracta quasi linear convective line with a trailing stratiform region developed during the bow echo and mesoscale convective vortex experiment bamex while being sampled by two airborne doppler radars the finescale reflectivity and doppler velocities recorded by the radars documented the evolution of the convective line bands of positive and negative vertical vorticity oriented parallel to the convective line were resolved in the analysis this type of structure has rarely been reported in the literature and appears to be a result of the tilting and subsequent stretching of ambient horizontal vorticity produced by the low level wind shear vector with a significant along line component the radar analysis also documented the evolution of an embedded bow echo within the convective line embedded bow echoes have been documented for a number of years however a detailed analysis of their kinematic structure has not been previously reported in the literature the counterrotating circulation patterns tha

back to basics of sequence stratigraphy early miocene and mid cretaceous examples from the new jersey paleoshelf abstract many sequence stratigraphic approaches have used relative sea level curves that are dependent on models or preconceived notions to recognize depositional sequences key stratal surfaces and systems tracts leading to contradictory interpretations here we urge following basic sequence stratigraphic principles independent of sea level curves using seismic terminations facies successions and stacking patterns from well logs and sections and chronostratigraphic data to recognize sequence boundaries other stratal surfaces parasequences and systems tracts we provide examples from the new jersey siliciclastic paleoshelf from the 1 early miocene using academic based chronostratigraphic seismic core downhole and core log data and 2 mid cretaceous using commercial well log seismic and biostratigraphic data we use classic criteria to identify sequence boundaries on seismic profiles by reflection terminations onlap downlap erosional truncation and toplap in cores by surfaces of erosion associated with hiatuses detected using biostratigraphy and sr isotope stratigraphy and changes in stacking patterns and in logs by changes in stacking patterns maximum flooding surfaces mfss are major seismic downlap surfaces associated with changes from retrogradational to progradational parasequence stacking patterns systems tracts are identified by their bounding surfaces and fining generally deepening and coarsening generally shallowing upward trends in cores and well log stacking patterns our miocene examples of sequences m5 4 17 7 16 1 ma and m5 8 20 1 19 2 ma illustrate how basic sequence stratigraphic techniques reveal higher order sequences within myr scale composite sequences our mid cretaceous examples from the new jersey shelf provide a paleoshelf transect spanning the great stone dome to the outer continental shelf to identify parasequences sequences and systems tracts this sequence stratigraphic framework provides insights into myr scale coeval depositional environments across the paleoshelf and reservoir continuity and highlights the application of basic sequence stratigraphic criteria to reservoir scale evaluation not only for oil and gas resources but also for carbon storage

mesoscale convective vortices observed during bamex part ii influences on secondary deep convection abstract observations from the bow echo and mesoscale convective vortex mcv experiment are used to examine the role of the five mesoscale convective vortices described in part i on heavy precipitation during the daytime heating cycle persistent widespread stratiform rain without deep convection occurs for two strong mcvs in conditionally stable environments with strong vertical shear two other mcvs in moderate to strong vertical shear have localized redevelopment of deep convection termed secondary convection on their downshear side where conditional instability exists the strongest of the five mcvs occurs in weak vertical shear and has widespread secondary convection which is most intense on its conditionally unstable southeast periphery the two mcvs with only localized secondary convection have well defined mesoscale vertical motion couplets with downshear ascent and upshear descent above the planetary boundary layer pbl although the amplitude is significantly greater the kinematically der

holocene thermokarst dynamics in central yakutia a multi core and robust grain size endmember modeling approach abstract differentiating thermokarst basin sediments with respect to the involved processes and environmental conditions is an important tool to understand permafrost landscape dynamics and scenarios and future trajectories in a warming arctic and subarctic thermokarst basin deposits have complex sedimentary structures due to the variability of yedoma source sediments reworking during the late glacial to holocene climate changes and different stages of thermokarst history here we reconstruct the dynamic growth of thermokarst lakes and basins and related changes of depositional conditions preserved in sediment sequences using a combination of biogeochemical data and robust grain size endmember analysis remma this multi proxy approach is used on 10 sediment cores each 300 400 cm deep from two key thermokarst sites to distinguish four time slices that describe the holocene thermokarst lake basin evolution in central yakutia cy biogeochemical proxies and remma reveal fine grained sedimentation with rather high lake levels and or reducing conditions and coarse grained sedimentation with rather shallow lake levels and or oxidizing i e terrestrial conditions in relation to distal and proximal depositional and post sedimentary conditions statistical analysis suggests that the biogeochemical parameters are almost independent of thermokarst deposit sedimentology thus the biogeochemical parameters are considered as signals of secondary post sedimentary reworking the remma results are clearly reflecting grain size variations and depositional conditions this indicates small scale varying depositional environments frequently changing lake levels and predominantly lateral expansion at the edges of rapidly growing small thermokarst lakes and basins these small bodies finally coalesced forming the large thermokarst basins we see today in cy considering previous paleoenvironmental reconstructions in siberia we show the initiation of thaw and subsidence during the late glacial to holocene transition between about 11 and 9 cal kyrs bp intensive and extensive thermokarst activity for the holocene thermal maximum htm at about 7 to 5 cal kyrs bp severely fluctuating water levels and further lateral basin growth between 3 5 cal kyrs bp and 1 5 cal kyrs bp and the cessation of thermokarst activity and extensive frost induced processes i e permafrost aggradation after about 1 5 cal kyrs bp however gradual permafrost warming over recent decades in addition to human impacts has led to renewed high rates of subsidence and abrupt rapid cy thermokarst processes

thermokarst dynamics in western siberia insights from dendrochronological research abstract thermokarst dynamics and their underlying causes are investigated and reconstructed on the basis of muzhy weather station records western siberia of air temperature precipitation and snow cover and a tree ring chronology analysis of siberian stone pine pinus sibirica du tour the results indicate that the development of thermokarst over the last 50 years has depended primarily on increasing precipitation rather than increasing air temperature reconstruction of past thermokarst borderlines shows that the rate of thermokarst expansion in the second half of the 20th century increased to 7 4 cm year as compared to past rates ranging from 4 to 8 1 cm year

interactions between a developing mesoscale convective system and its environment part ii numerical simulation the 19 july 1993 mesoscale convective system mcs discussed in part i was simulated using the regional atmospheric modeling system rams the model was initialized with variable physiographic and atmospheric data with the goal of reproducing the convective system and its four dimensional environment four telescopically nested moving grids allowed for horizontal grid spacings down to 1 67 km on the cloud resolving grid comparisons with the analysis show that the propagation evolution and structure of this mcs were well simulated the simulation is used to further investigate the interactions between this mcs and its surrounding environment in part i the doppler derived winds indicated that upshear westward propagating gravity waves left uppertropospheric front to rear and midtropospheric rear to front flow perturbations in their wake a similar flow structure developed in the simulated mcs and unlike the doppler results the low frequency waves that produced it were resolved in the data in the simulation much of the convectively generated temperature and momentum perturbations propagated westward with the waves leaving a warm wake in the clear air trailing the system although the gravity waves traveled rearward the perturbation flow in their wake was not strong enough to reverse the upper tropospheric storm relative winds thus most of the anvil condensate advected ahead of the convective line as the mcs encountered the low level jet the midtropospheric upward mass flux increased but gravity wave motions became less detectable the upper tropospheric anvil pushed westward into the strong flow as the system expanded into a characteristically oval shape temperature and momentum perturbations propagated rearward along with the anvil in a disturbance that resembled an advective outflow unlike the gravity waves this disturbance became almost stationary with respect to the ground and it retained its continuity through the rest of the simulation vertical cross sections indicate that a large slab of convectively processed air had detrained into the upper troposphere prior to this event much of the warm temperature anomalies generated within the convective towers either remained in the updrafts or propagated outward with the gravity waves early on individual updrafts were relatively erect and although condensate did detrain eastward in the forward anvil the temperature anomalies did not propagate with it in contrast convective updrafts associated with the expanding oval anvil disturbance were more continuous and they tilted strongly westward with height

mesoscale convective systems 1 mesoscale convective systems mcss have regions of both convective and stratiform precipitation and they develop mesoscale circulations as they mature the upward motion takes the form of a deep layer ascent drawn into the mcs in response to the latent heating and cooling in the convective region the ascending layer overturns as it rises but overall retains a coherent layer structure a middle level layer of inflow enters the stratiform region of the mcs from a direction determined by the large scale flow and descends in response to diabatic cooling at middle to low levels a middle level mesoscale convective vortex mcv develops in the stratiform region prolongs the mcs and may contribute to tropical cyclone development the propagation of an mcs may have a discrete component but may further be influenced by waves and disturbances generated both in response to the mcs and external to the mcs waves of a larger scale may affect the propagation velocity by phase locking with the mcs in a cooperative mode the horizontal scale of an mcs may be limited either by a balance between the formation rate of convective precipitation and dissipation of stratiform precipitation or by the rossby radius of the mcv the vertical redistribution of momentum by an mcs depends on the size of the stratiform region while the net vertical profile of heating of the large scale environment depends on the amount of stratiform rain regional variability of the stratiform rain from mcss affects the large scale circulation s response to mcs heating

the genesis of hurricane guillermo texmex analyses and a modeling study abstract the transformation of a mesoscale convective system into hurricane guillermo was captured by aircraft and doppler wind data during the tropical experiment in mexico the early phase of the system evolves in a way very similar to previously documented mesoscale convective systems with a midlevel mesocyclone developing in the stratiform precipitation region more unusually the cyclone extends to low altitudes a weak cyclone is discernable even in the 300 m altitude wind field after another day of evolution a small surface based warm core cyclone is observed to develop within the relatively cold air associated with the mesocyclone aloft this mesocyclone develops into a hurricane over the subsequent day a nonhydrostatic axisymmetric numerical model is used to explore the evolution of the initially cold core midlevel vortex into a tropical cyclone a mesoscale midlevel showerhead is switched on in an initially quiescent tropical atmosphere overlying a warm ocean surface evaporation of t

the kinematics of a midlatitude continental mesoscale convective system and its mesoscale vortex the authors present a unique scale discriminating study of the environment relative circulations within a mesoscale convective system mcs and mesoscale convective vortex mcv the mcs a leading convective line and trailing stratiform region that became asymmetric passed through the national oceanic and atmospheric administration noaa profiler network npn in kansas and oklahoma on 1 august 1996 the mcv appeared in the mcs s stratiform region just prior to the system s mature stage and grew to a depth of over 12 km as the mcs dissipated the mcv did not apparently survive to the next day a spatial bandpass filter was used to divide observed wind into a component that was predominantly synoptic background wind and a component that was predominantly a mesoscale perturbation on that background wind a mesoscale updraft mesoscale downdraft and divergent outflows in the lower and upper troposphere were evident after the synoptic background wind was removed so these four circulations were internal and fundamental to the mcs the mesoscale perturbation in wind in the middle troposphere extended farther behind the mcs than ahead of it consistent with analytic studies and numerical simulations of gravity waves generated by heat sources characteristic of mcss with leading convective lines and trailing stratiform regions deepening of the mcv appeared to be reflected in the vertical wind shear at the vortex s center as the mcv strengthened the mesoscale shear through its lower part decreased perhaps as wind became more vortical at increasing altitudes mesoscale and synoptic vertical shears were of similar magnitude so an average of environmental soundings outside an mcs probably does not accurately represent the shear that affects an mcv this suggests the need to reevaluate how the kinematical settings of mcvs are diagnosed

the reconstruction of boreal forest fire history from lake sediments a comparison of charcoal pollen sedimentological and geochemical indices abstract fossil charcoal fossil pollen sedimentological and geochemical analyses of lake sediments have been used previously to reconstruct a history of local fires and resulting vegetation change the rationale behind these approaches is described and the usefulness of each technique for reconstructing fire history in the boreal forest is assessed empirically historical and dendrochronological records provide regional and local fire histories for a site in wood buffalo national park alberta canada the local and regional history of fires is compared with the microscopic charcoal content macroscopic charcoal content elemental carbon content fossil pollen content sedimentology and geochemistry of annually laminated sediments from a small lake there is no significant correlation between the abundance of microscopic charcoal macroscopic charcoal and total elemental carbon content of the sediments automated measures of microscopic charcoal abundance made with an image analysis system are correlated significantly with optical counts of microscopic charcoal none of the charcoal measures provide unequivocal records of local fire activity and the abundance of microscopic charcoal appears to be influenced by variations in regional fire activity however the highest depositional rate of macrofossil charcoal occurred during the time of a fire that burned within the drainage basin variations in sedimentological measures and geochemistry do not correlate with local fire activity fossil pollen percentages and accumulation rates display a pattern of variation that is consistent with observed vegetation responses to fire in the boreal forest what is likely apparent in the pollen record are the results of a series of burns of sufficient extent and intensity to kill most of the above ground biomass of the vegetation in an area at least as great as the drainage basin the inability of evidence from lake sediments to provide detailed histories of past fire activity is not surprising given the wide range of variation in the spatial extent proximity intensity and impact of individual fires

present day variability and holocene dynamics of permafrost affected lakes in central yakutia eastern siberia inferred from diatom records thermokarst lakes are assumed to develop cyclically driven by processes that are triggered by climate and maintained by internal feedbacks that may trigger lake drainage however the duration of these cycles remains uncertain as well as whether or not they affect the stabilization of lake ecosystems in permafrost regions over millennial time scales our research has combined investigations into modern lake to lake variability with a study of the long term development of individual lakes we have investigated the physico chemical and diatom compositions of a set of 101 lakes with a variety of different origins in central yakutia eastern siberia including thermokarst lakes fluvial erosion thermokarst lakes fluvial erosion lakes and dune lakes we found a significant relationship between lake genesis and the present day variability in environmental and diatom characteristics as revealed by multi response permutation procedures indicator species analyses and redundancy analyses environmental parameters also exhibit a significant correlation with variations in the diatom data for which they may have been to a substantial extent responsible mg and so4 concentrations together with ph and water depth were identified as the most important parameters influencing the variations in the diatom data almost as much as the entire environmental parameter set we were therefore able to establish a robust mg diatom transfer function which was then applied to three holocene lake records from these reconstructions together with a general interpretation of the diatom record including e g the ratio between benthic epiphytic and planktonic taxa we have been able to infer that all three of these lakes show 1 a continuous record with no desiccation events 2 high lake water levels during the early holocene 3 centennial to millennial scale variability and 4 high levels of variability during the early holocene but rather stable conditions during the late holocene a feature that is also known from other sites around the world we therefore concluded that the development of these three lakes was mainly driven directly by the climate rather than by thaw lake cycling

baroclinic transition of a long lived mesoscale convective vortex abstract the period 5 15 june 2003 during the field phase of the bow echo and mesoscale convective vortex mcv experiment bamex was noteworthy for the wide variety of mesoscale convective systems mcss that occurred of particular interest was a long lived mcv that formed in the trailing stratiform region of an mcs over west texas at 0600 utc 10 june this mcv was noteworthy for its i longevity as it can be tracked from 0600 utc 10 june to 1200 utc 14 june ii development of a surface cyclonic circulation and attendant 2 to 4 hpa sea level pressure perturbation iii ability to retrigger convection and produce widespread rains over several diurnal heating cycles and iv transition into a baroclinic surface cyclone with distinct frontal features baroclinic transition defined here as the acquisition of surface fronts occurred as the mcv interacted with a remnant cold front left behind by a predecessor extratropical cyclone over the great lakes region although the mcv developed well def

influence of balanced motions on heavy precipitation within a long lived convectively generated vortex abstract the forcing of heavy precipitation within a long lived convectively generated mesoscale vortex mcv is investigated with the aid of diagnoses from rapid update cycle gridded analyses organized convection within the mcv followed a distinct diurnal cycle which featured organized mesoscale convective systems mcss that matured overnight near the mcv center on successive days the mcv was typically most intense in the middle troposphere but intensified within the lower troposphere during the episodes of organized nocturnal convection the lower tropospheric vertical shear was an important organizing factor in mcs development and sustenance in the sense that its interaction with the cold temperature anomaly beneath the mcv center determined where balanced lower tropospheric ascent occurred from trajectory analyses we estimate that balanced ascent accounted for approximately half of the total vertical displacement of the thermodynamically unstable air that eventually composed elevated saturated

cretaceous evolution of the central asian proto paratethys sea tectonic eustatic and climatic controls the timing and mechanisms of the cretaceous sea incursions into central asia are still poorly constrained we provide a new chronostratigraphic framework based on biostratigraphy and magnetostratigraphy together with detailed paleoenvironmental analyses of cretaceous records of the proto paratethys sea fluctuations in the tajik and tarim basins the early cretaceous marine incursion in the western tajik basin was followed by major marine incursions during the cenomanian ca 100 ma and santonian ca 86 ma that reached far into the eastern tajik and tarim basins these marine incursions were separated by a turonian coniacian ca 92 86 ma regression basin wide tectonic subsidence analyses imply that the early cretaceous sea incursion into the tajik basin was related to increased pamir tectonism we find that thrusting along the northern edge of the pamir at ca 130 90 ma resulted in increased subsidence in a retro arc basin setting this tectonic event and coeval eustatic highstand resulted in the maximum observed geographic extent of the sea during the cenomanian ca 100 ma the following turonian coniacian ca 92 86 ma major regression driven by eustasy coincides with a sharp slowdown in tectonic subsidence during the late orogenic unloading period with limited thrusting the santonian ca 86 ma major sea incursion was likely controlled by eustasy as evidenced by the coeval fluctuations in the west siberian basin an early maastrichtian cooling ca 71 70 ma potentially connected to global late cretaceous trends is inferred from the replacement of mollusk rich limestones by bryozoan and echinoderm rich limestones

the variable nature of convection in the tropics and subtropics a legacy of 16 years of the tropical rainfall measuring mission satellite for over 16 years the precipitation radar of the tropical rainfall measuring mission trmm satellite detected the three dimensional structure of significantly precipitating clouds in the tropics and subtropics this paper reviews and synthesizes studies using the trmm radar data to present a global picture of the variation of convection throughout low latitudes the multiyear data set shows convection varying not only in amount but also in its very nature across the oceans continents islands and mountain ranges of the tropics and subtropics shallow isolated raining clouds are overwhelmingly an oceanic phenomenon extremely deep and intense convective elements occur almost exclusively over land upscale growth of convection into mesoscale systems takes a variety of forms oceanic cloud systems generally have less intense embedded convection but can form very wide stratiform regions continental mesoscale systems often have more intense embedded convection some of the most intense convective cells and mesoscale systems occur near the great mountain ranges of low latitudes the maritime continent and amazonia exhibit convective clouds with maritime characteristics although they are partially or wholly land convective systems containing broad stratiform areas manifest most strongly over oceans the stratiform precipitation occurs in various forms often it occurs as quasi uniform precipitation with strong melting layers connected with intense convection in monsoons and the intertropical convergence zone it takes the form of closely packed weak convective elements where fronts extend into the subtropics broad stratiform regions are larger and have lower and sloping melting layers related to the baroclinic origin of the precipitation

climatology of summer midtropospheric perturbations in the us northern plains part ii large scale effects of the rocky mountains on genesis propagating convective storms across the us northern plains are often coupled with preexisting midtropospheric perturbations mps initiated over the rocky mountains a companion study part i notes that such mps occur most commonly at 12 utc early morning and 00 utc late afternoon using a regional reanalysis and a general circulation model gcm this study investigates how such a bimodal distribution of the mp frequency is formed the results point to two possible mechanisms working together while each has a different timing in terms of maximum effect the diurnal evolutions between the midtropospheric flows over the rockies and over the great plains are nearly out of phase due to inertial oscillation during the nighttime the westerly flows at 700 500 mb over the rockies intensify while flows at the same level over the great plains turn easterly these two flows converge over the eastern rockies and induce cyclonic vorticity through vortex stretching after sunrise the convergence dissipates and the cyclonic vorticity is redistributed by horizontal vorticity advection moving it downstream this process creates a climatological zonally propagating vorticity signal which in turn facilitates the early morning mp genesis at 12 utc the analysis also reveals marked dynamic instability conducive to subsynoptic scale disturbances in the midtroposphere over the rockies strong meridional temperature gradients appear over the north facing slopes of the rockies due to terrain heating to the south and the presence of cooler air to the north this feature along with persistent vertical shear creates a charney stern type of instability i e sign changes of the meridional potential vorticity gradient meanwhile the development of terrain boundary layer reduces the rossby deformation radius which subsequently enhances the likelihood for baroclinic short waves such effects are most pronounced in the late afternoon and therefore are supportive to the mp genesis around 00 utc examination of gcm experiments with and without orography further supports the critical role of the rocky mountains and its associated boundary layer impacts on the formation of mps

genesis of typhoon nari 2001 from a mesoscale convective system 1 in this study the origin and genesis of typhoon nari 2001 as well as its erratic looping track are examined using large scale analysis satellite observations and a 4 day nested cloud resolving simulation with the finest grid size of 1 33 km observational analysis reveals that nari could be traced 5 days back to a diurnally varying mesoscale convective system with growing cyclonic vorticity and relative humidity in the lower troposphere and that it evolved from a mesoscale convective vortex mcv as moving over a warm ocean under the influence of a subtropical high a weak westerly baroclinic disturbance an approaching and departing typhoon danas to the east and the kuroshio current results show that the model reproduces the genesis final intensity looping track and the general convective activity of nari during the 4 day period it also captures two deep subvortices at the eye eyewall interface that are similar to those previously observed a few spiral rainbands and a midget storm size associated with nari s relatively dry and stable environment we find that 1 continuous convective overturning within the mcv stretches the low level vorticity and moistens a deep mesoscale column that are both favorable for genesis 2 nari s genesis does not occur until after the passage of the baroclinic disturbance 3 convective asymmetry induces a smaller sized vortex circulation from the preexisting mcv 4 the vortex vortex interaction with danas leads to nari s looping track and temporal weakening and 5 midlevel convergence associated with the subtropical high and danas accounts for the generation of a nearly upright eyewall

controls on acoustic properties of upper jurassic siliciclastic rocks boulonnais northern france more than 200 plugs from outcrop and a nearby borehole in a carbonaceous siliciclastic interval of late jurassic kimmeridgian to tithonian age were quantitatively analyzed for texture mineralogy and acoustic properties our primary goal was to study the effect of clay fraction smaller than 8 m silt sand fraction larger than 8 m and carbonate on the acoustic properties the quantitative nature and volume of the data made it possible to observe four dimensional relationships in contoured ternary diagrams primary control on the acoustic properties is exerted by porosity but the trend of this relationship significantly deviates from popular velocity transforms the contribution of clay silt sand and carbonate particular material and cement explains the remaining variation in acoustic properties although no clear linear thresholds are defined a general trend is that clay and carbonate content have opposite and overlapping effects on acoustic properties the influence of clay content progressively increases with decreasing carbonate content and visa versa with increasing carbonate content the variation of acoustic velocity at a given porosity value increases to nearly twice of that in the clay dominated sediment traditional classification boundaries are present but strongly overprinted by this interplay between clay and carbonate this study may have important implications for porosity and lithofacies prediction from wireline logs in similar mixtures of sediment in addition the quantitative character of the textural and mineralogical data may provide a direct link from acoustic properties to the primary depositional system and sequence stratigraphy

unusual shoreface sedimentology in the upper jurassic of the boulonnais northern france abstract two upper jurassic sandstone formations the gres de chatillon and gres de la creche of the boulonnais of northern france record shoreline conditions on the eastern margin of a large epicontinental sea the wessex basin the interpreted range of bedforms is more diverse than has been recorded from other shorelines either ancient or modern the lower shoreface to transition zone was characterized by small lunate dunes oscillatory ripples mudstone drapes and discrete burrowed beds indicating the alternation of moderate currents oscillatory flow and prolonged quiescent intervals the shoreface itself was dominated by dunes that ranged in height from a few decimeters to more than a meter the larger sizes are twice the height of any shoreface bedforms previously described paleocu rent indicators within the shoreface deposits are highly variable from bed to bed and within individual cosets a feature that may indicate deposition on a barred shoreface evidence for tides is care occasional herringbone cross stratification in contrast to many other ancient shoreface sandstone units storms left little sedimentary record rare large shell gravel bars in the upper offshore zone although they generated numerous erosion surfaces in the lower shoreface the unusual aspects of the boulonnais sandstone units may relate in part to the particular paleogeographic location of the region an open embayment regardless this is a rare example of a fair weather wave dominated medium sand shoreline from the geological record

a radar based climatology of mesoscale convective systems in the united states abstractthis research applies an automated mesoscale convective system mcs segmentation classification and tracking approach to composite radar reflectivity mosaic images that cover the contigu

the evolution of a thermokarst lake landscape late quaternary permafrost degradation and stabilization in interior alaska thermokarst processes characterize a variety of ice rich permafrost terrains and often lead to lake formation the long term evolution of thermokarst landscapes and the stability and longevity of lakes depend upon climate vegetation and ground conditions including the volume of excess ground ice and its distribution the current lake status of thermokarst lake landscapes and their future trajectories under climatewarming are better understood in the light of their long term development we studied the lake rich southern marginal upland of the yukon flats northern interior alaska using dated lake sediment cores observations of river cut exposures and remotely sensed data the region features thick up to 40 m quaternary deposits mainly loess that contain massive ground ice two of three studied lakes formed 11 000 12 000 cal yr bp through inferred thermokarst processes and fire may have played a role in initiating thermokarst development from 9000 cal yr bp all lakes exhibited steady sedimentation and pollen stratigraphies are consistentwith regional patterns the current lake expansion rates are low 0 to b7 cmyr 1 shoreline retreat compared with other regions 30 cm yr 1 or more this thermokarst lake rich region does not showevidence of extensive landscape lowering by lake drainage nor of multiple lake generations within a basin however lidar images reveal linear corrugations n5 m amplitude deep thermo erosional gullies and features resembling lake drainage channels suggesting that highly dynamic surface processes have previously shaped the landscape evidently widespread early holocene permafrost degradation and thermokarst lake initiation were followed by lake longevity and landscape stabilization the latter possibly related to establishment of dense forest cover partial or complete drainage of three lakes in 2013 reveals that there is some contemporary landscape dynamism holocene landscape evolution in the study area differs from that described from other thermokarst affected regions regional responses to future environmental change may be equally individualistic