late holocene erosion in upland britain climatic deterioration or human influence the evidence for enhanced erosion in upland britain during the late holocene is evaluated though there is widespread evidence for recent soil erosion on high plateaux this has not been precisely dated radiocarbon dating confirms the occurrence of late holocene solifluction on high ground but at only one site has evidence been found for recent accelerated activity several areas however have yielded evidence of late holocene debris cone accumulation and parts of the scottish highlands experienced a drastic increase in debris flow activity over the past few centuries climatic deterioration and vegetation degradation resulting from overgrazing or burning are frequently cited as the causes of enhanced erosion but cause and effect are often related only by coincidence of timing in consequence only circumstantial evidence links erosion with climatic deterioration though anthropogenic influences have been more firmly established at a few sites the role of extreme events in initiating phases of uplan

holocene river development and environmental change in upper wharfedale yorkshire dales england this paper provides the first radiometrically dated evidence of holocene alluvial landform development in upper wharfedale yorkshire dales four river terraces are identified terraces 1 and 2 are closely linked to late devensian and early holocene environmental change with gravel reworked from local glacial and periglacial sources prior to cementation by carbonate rich waters u series dating of cement provides age estimates for cementation of between ca 5 1 7 4 kyr bp for terrace 1 and ca 3 6 8 0 kyr bp for terrace 2 u series dating of tufas overlying terraces 1 and 2 produced ages of ca 4 2 4 5 kyr bp and ca 2 1 2 2 kyr bp respectively and provide upper age limits for terrace formation terrace 3 marks a change in sediment calibre supply and sedimentation style and 14c dating suggests that the principal source of fine grained material may be agricultural expansion in the yorkshire dales from ca ad 600 1350 cal yr bp radiocarbon dates indicate that terrace 4 was deposited from the eleventh century with initiation of the contemporary floodplain between the fifteenth and seventeenth centuries ad both these lowest units contain sediments contaminated with heavy metals as a result of mining activities within the catchment the evidence presented in this study is comparable to that of research undertaken in upland environments elsewhere in northern and western britain thereby adding to the corpus of information currently available for evaluating the fluvial geomorphological response to climate and vegetation change during the holocene copyright 2000 john wiley sons ltd

microphysical characteristics of three anvils sampled during the central equatorial pacific experiment abstract in situ microphysical measurements of three anvils were made 17 march 1 april and 4 april 1993 during the central equatorial pacific experiment for several constant altitude penetrations in the same direction or opposite the ambient wind from 7 to 14 km ice water contents iwcs derived from an optical array probe increased downward in the anvil concentrations also increased but not as quickly median mass dimensions defined as the ice crystal maximum dimension below which half of the mass is contained increased from averages of less than 0 1 mm near the tops to averages of about 0 5 mm near the bases substantial variations in cloud parameters occurred in the horizontal direction as well with larger iwcs and concentrations closer to the convective core and its remnants small crystals were measured and categorized according to their shapes with the video ice particle sampler which detects particles with dimensions greater than 5 m for small iwcs especially prevalent at cloud tops

the mesoscale and microscale structure and organization of clouds and precipitation in midlatitude cyclones viii a model for the seeder feeder process in warm frontal rainbands abstract previous field studies have indicated that warm frontal rainbands form when ice particles from a seeder cloud grow as they fall through a lower level feeder cloud in this paper we present results from a parameterized numerical model of the growth processes that can lead to the enhancement of precipitation in a seeder feeder type situation the model is applied to two types of warm frontal rainbands in the first type 1 situation the vertical air motions are typical of those associated with slow widespread lifting in the vicinity of warm fronts in the second type 2 situation the vertical air motions are stronger and more characteristic of the mesoscale the model simulations show that in the type 1 situations the growth of the seed ice crystals within the feeder zone is due to vapor deposition the feeder zone in this case is slightly sub saturated with respect to water due to the presence of the seed crystals in regions where the feeder zone is not seeded from aloft snow cryst

the two dimensional dynamics of west african squall lines the two dimensional dynamics of multicell and unicell squall lines are examined using a numerical model both types feature a convective jump updraught with extensive deep rearward extending anvils the multicell case contains travelling convection cells and is unsteady but persistent whereas the unicell case is quasi steady in the multicell case an extensive density current is produced by the evaporation and drag of rain falling from a succession of convection cells which travel rearwards relative to the density current head the circulation within the density current is complex and consists of three mutually interactive branches a rotor a cold downdraught and a subsidence region in the unicell case a density current is not produced and the updraught is forced by a propagating wave of elevation generated as an interaction between the updraught water loading and evaporation in a very localized area the squall line structure is compared with other models and it is shown that certain propagating two dimensional tropical and mid latitude squall lines are dynamically similar their detailed structure being controlled by the inflow wind profile the multicell case is compared with a quasi two dimensional west african squall line which occurred on 22 june 1981 during the convection profonde tropicale copt 81 experiment performed in the northern part of the ivory coast good agreement is found between the model and the observations and hence the dynamics of the observed squall line is quantified the unicell case in which a density current and conventional downdraughts are absent has yet to be identified in atmospheric observations

the transition zone and secondary maximum of radar reflectivity behind a midlatitude squall line results retrieved from doppler radar data abstract thermodynamic and microphysical retrieval techniques are applied to dual doppler synthesized air motion fields for a midlatitude squall line which passed through the oklahoma kansas preliminary regional experiment for the stormscale operational and research meteorology program pre storm observational array in kansas and oklahoma on 10 11 june 1985 the retrieved pressure and potential temperature fields are consistent with surface network and sounding data while the retrieved microphysical fields show the characteristic secondary maximum of radar reflectivity in the stratiform region and the band of low reflectivity or transition zone lying between the leading convective line and the secondary maximum the retrieved fields indicate the processes producing the secondary maximum and transition zone minimum of radar reflectivity more quantitatively than has been possible in previous studies the primary processes accounting for these features of the radar reflectivity pattern were 1 the subst

a physical explanation of the relation between flank uplifts and the breakup unconformity at rifted continental margins rift flank uplifts and the breakup or postrift unconformity are characteristic features of many rifted passive or atlantic type continental margins but are not predicted as primary features of simple lithospheric stretching models the explanations that have been proposed for their origin remain controversial either because they call upon special circumstances or because they are difficult to test plane strain finite element models are used in this paper to explore the dynamics of lithospheric necking during rifting and rupture the results agree with the conceptual interpretation that uplift of the rift boundaries to form flank mountains and uplift of the basin responsible for the breakup unconformity are related consequences of regional isostatic compensation of mass that is redistributed during the necking and rupture phases although the amplitudes of these uplifts depend on the model parameter values the relations between and relative signs of these two effects appear to be fundamental the explanation we propose may have been missed in recent studies because there has been a tendency to concentrate on kinematic stretching models which assume local isostatic equilibrium through out the rifting process such an approach is predicated on the assumption that the lithosphere has an insignificant strength or flexural rigidity during extension which is not true if our explanation is correct

mesoscale air motions associated with a tropical squall line abstract composites of radar and wind observations in a coordinate system attached to a moving tropical squall line confirm that such a squall system is composed of two separate circulation features a convective squall line region and a stratiform anvil region the squall line region is characterized by mesoscale boundary layer convergence which feeds deep convective updrafts and mid to upper level divergence associated with outflow from the cells the anvil region is characterized by mid level convergence which feeds both a mesoscale downdraft below the anvil and a mesoscale updraft within the anvil cloud before this study the mesoscale updraft in the anvil cloud of the tropical squall system had been somewhat speculative and both the anvil updraft and downdraft had been inferred only qualitatively the occurrence of the anvil updraft is now proven and quantitative profiles of the mesoscale anvil updraft and downdraft have been obtained

a tropical squall line observed during the copt 81 experiment in west africa part 1 kinematic structure inferred from dual doppler radar data abstract this paper deals with the analysis of a tropical squall line observed on 22 june 1981 during the copt 81 convection profonde tropicale experiment the present part i is restricted to the study of the kinematic structure of the system which moved in a moderately unstable atmosphere faster than the environmental air at all levels at the observation time the squall line was in a mature stage the explicit description of the airflow within the system was inferred from dual and single doppler radar data the general characteristics of the squall line are found to be very similar to those of tropical squall lines observed during previous experiments such as vhimex or gate a large cloud system composed of an organized convective line ahead of an extensive trailing anvil cloud stratiform rain fast motion and long lasting structure and a well marked gust front signature at ground level the overall airflow presents a three dimensional structure at the leading edge convective scale updrafts a

the structure and decay of a rainband in hurricane irene 1981 abstract the mesoscale thermodynamic kinematic and reflectivity structure of a rainband observed in hurricane irene on 27 september 1981 is presented data are from 16 aircraft passes from 150 to 4700 m msl through the rainband which was located ssw of the circulation center of the northward moving hurricane cross sections of the rainband as a function of height and radial distance from the storm center reveal the following 1 little or no decrease of e in the subcloud layer associated with the weak convective cells in the rainband 2 large differences in static stability between the north and south sides of the band 3 a change of the radial wind component in the subcloud layer from flow toward the circulation center to flow away from it as the rainband weakens the decay of the rainband is believed to be related to mesoscale subsidence and the location of the rainband relative to the motion of the hurricane melting and evaporation of hydrometeors falling between the eyewall and the rainband are

a numerical study of the stratiform region of a fast moving squall line part ii relationship between mass pressure and momentum fields abstract in a companion paper a two dimensional simulation of a fast moving tropical squall line was successfully compared to observations performed during the copt81 experiment over west africa the full ice phase parameterization is shown to be crucial in the simulation of trailing anvil precipitation different diagnostic tools are applied to the simulated fields to further our understanding of the scale interactions within a squall line type mesoscale convective system the pressure organization is characterized by two marked features important for explaining the inner circulation first a front to rear midlevel pressure gradient and second the surface pressure mesohigh extending from the gust front to the rear of the most active part of the trailing stratiform region based on the hydrostatic approximation an original method of decomposition of the pressure field is proposed whereby dynamical and buoyant contributions depend only on the horizontal and vertical respectively the mean pressure i

the west african squall line observed on 23 june 1981 during copt 81 mesoscale structure and transports abstract durirg the night of 23 24 june 1981 new korhogo ivory coast a squall line passed over the instrumented area of the copt 81 experiment observations were obtained with a dual doppler radar system a sounding station and 22 automatic meteorological surface stations data from these instruments and from satellite pictures were analyzed to depict the kinematic and thermodynamic structure of the squall line composite analysis techniques were used to obtain a vertical cross section of the reflectivity structure and of the wind field relative to the line the redistributions of air moisture and thermodynamic energy by the convection wet calculated through averaged two dimensional wind fields from a dual doppler radar system the method also allowed the evaluation of the exchanges that were occurring between the convective and the stratiform regions this squall line had many similarities with tropical squall lines previously described by others the leading convective part composed of intense updr

microphysical observations in summer monex convective and stratiform clouds abstract two dimensional images of ice particles observed by a noaa wp 3d research aircraft during the summer monsoon experiment smonex are examined these images were obtained in the temperature interval from 25 to 0 c the particle structures and size distributions found in convective and stratiform clouds are compared branched crystals were located predominantly in stratiform clouds while column shaped crystals were located commonly in both stratiform and convective clouds stratiform clouds particularly those observed at temperature warmer than 7 c had a much greater percentage concentration of large ice particles 0 8 mm in diameter and many of these ice particles were aggregates or branched crystals the importance of aggregation and deposition above the melting level in the stratiform clouds is strongly suggested by these findings ice particle number concentrations measured with the cloud probe were often very high in convective clouds with a maximum value of approximately 800 l 1 the

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

microphysical characteristics of squall line stratiform precipitation and transition zones simulated using an ice particle property evolving model abstracta quasi idealized 3d squall line case is simulated using a novel bulk microphysics scheme called the ice spheroids habit model with aspect ratio evolution ishmael in ishmael the evolution of ice particle properties e g mass shape maximum diameter density and fall speed are predicted during vapor growth sublimation riming and melting allowing ice properties to evolve from various microphysical processes without needing separate unrimed and rimed ice categories ishmael produces both a transition zone and an enhanced stratiform precipitation region and ice particle properties are analyzed to determine the characteristics of ice that lead to the development of these squall line features rimed particles advected rearward from the convective region produce the enhanced stratiform precipitation region the transition zone results from hydrometeor sorting the evolution of ice particle properties in the convective region leads to fall speeds that favor ice advecting rearward of the tran

aircraft observations of ice crystal evolution in an altostratus cloud abstract observations from a lagrangian spiral descent within altostratus cloud associated with a cold front were used to study the evolution of ice particle spectra by following populations of ice crystals as they fell through the cloud the flight track was corrected for wind effects and was divided into distinct regions for spatial comparison of ice particle spectra analysis of size spectra for particles larger than 800 m revealed heterogeneity on horizontal scales of 5 km in average particle diameter and concentration in the temperature range 40 to 20 c the ice crystal evolution was dominated by diffusional growth although observations of the evolution of the bimodal size spectra suggested that aggregation was occurring between 20 and 10 c aggregation dominated evolution

archean crustal evolution of the aldan shield siberia geochemical and isotopic constraints abstract the relatively unknown aldan shield in eastern siberia is made up of archean granite greenstone and high grade gneiss terrains as commonly observed in many precambrian shield areas new results of geochemical and isotopic study on two terrains of contrasting metamorphic grades olekma granite greenstone and west aldan granulite gneiss terrains are present with the following principal conclusions being reached 1 the crustal evolution of the aldan shield started as early as 3 5 ga as suggested by the tdm model ages of a few high grade gneisses and a retrograded granulite enclave but the most important crust forming and tectonothermal event is firmly established at ca 3 0 ga 2 new shrimp and pb evaporation analyses on zircons have confirmed the presence of crustal rocks older than 3 ga however the zircon u pb systems appear to have been disturbed by later thermal effects and no components of 3 5 ga have been identified 3 komatiitic and basaltic amphibolites form important supracrustal sequences in the olekma terrain both group i and ii komatiites occur and garnet or majorite fractionation in mantle melting processes is likely to have taken place during the genesis of group ii komatiites overall depleted mantle sources were involved in the geneses of basic and ultrabasic magmas as evidenced from lree depletion and nd isotopic compositions nd t 2 crustal contamination was not significant as suggested by the low la nb ratios 1 in komatiites and metabasalts 4 as common to most archean tonalite trondhjemite granodiorite ttg rocks the aldan granitic gneisses also show highly fractionated rare earth element ree patterns with heavy ree depletions suggesting that separation of garnet and amphibole has occurred during melting of their mafic sources 5 although the olekma and west aldan terrains have undergone different metamorphic evolution there is no substantial difference in the time of major crust forming events at 3 0 ga and a strong proterozoic thermal disturbance at 2 ga furthermore from the geochemical comparison of the two terrains it is concluded that the nature of mantle sources for basic ultrabasic magmas and the process of ttg magma generation are similar in both terrains and that the granulite facies rocks cannot be considered as the restites of intracrustal melting

evidence for mediaeval soil erosion in the south hams region of devon uk a major theme of research into the causes of past and present soil erosion has been to determine the relative importance of climate and land use change in influencing holocene erosion rates previous work suggests that land use change especially the conversion of woodlands into agricultural land is the main factor influencing long term increases in soil erosion a study of an extensive minerogenic sediment deposit in a wetland at slapton ley in devon suggests that agricultural intensification occurred before the onset of sedimentation a silty clay layer c 40 cm thick in the valley bottom wetland of the slapton sewage works marsh the base of the silty clay layer lies at an altitude of between 2 2 and 2 6 m aod and has been radiocarbon dated at two locations conventional radiocarbon ages 2 were 910 160 yr and 960 140 yr bp successful radiocarbon dating of the upper surface of this minerogenic layer at one location yielded a conventional radiocarbon age of 730 120 yr bp within the errors

dating of post glacial landforms in the central howgills little is known of holocene landform development in upland britain this paper describes a site at middle langdale in the howgill fells of cumbria where large but now stabilized and inactive gullies cut through periglacial material at the base of the gullies large debris cones have buried earlier alluvial sediments on the valley floor on these sediments and buried by the debris cones is a well developed organic soil from which two 14c dates have been obtained in an attempt to estimate the age range of the soil these dates range from 2580 55 years bp for the fine particulate fraction from the base of the organic horizon to 940 95 years bp for fossil rootlets from the uppermost organic layer immediately below the overlying debris cones the pollen evidence suggests that the valley floor site was initially dominated by alder carr and later by a juncus marsh with birch alder and hazel nearby the pollen from the surrounding upland area suggests woodland on the valley sides dominated by oak and elm that was later replaced by a more open environment rich in heath species and in which disturbed ground species were present the magnetic evidence indicates a stable local environment during soil formation but shows a sudden inwash of unweathered debris at the top of the buried soil the evidence suggests that the valley floor was geomorphologically stable throughout the period of soil formation although there was a local change in valley floor vegetation and a reduction of woodland cover on the valley sides at sometime during the period the evidence then points to major geomorphological changes a wave of soil erosion gully development and debris cone deposition perhaps following the scandinavian introduction of sheep farming in the tenth century a d

microphysical properties of convectively generated fall streaks within the stratiform comma head region of continental winter cyclones abstractthis paper presents analyses of the microphysical structure of comma head stratiform precipitation in 14 continental cyclones focusing on fall streaks of hydrometeors produced by cloud top convective generating cells data were obtained at temperatures between 4 and 45 c using in situ instrumentation and the w band university of wyoming cloud radar all operated aboard the national science foundation national center for atmospheric research c 130 analyses are presented first for a case study of one cyclone followed by statistical analyses of the full dataset using radar based objective classifications the statistical percentile number concentrations averaged 1 9 times larger within the fall streaks compared to the regions between them and the corresponding ice water content and median mass diameter values averaged 2 2 and 1 1 times larger ice phase conditions were predominant within the stratiform precipitation with deposition and aggregation the primary ice growth mechanisms no distinc

the generation and propagation of a nocturnal squall line part i observations and implications for mesoscale predictability abstract the initiation and forcing of a squall line on 26 27 may 1985 near wichita kansas is examined the squall line is secondary convection in the sense that it is preceded in the diurnal cycle by other mesoscale convective systems the squall fine develops in synoptic conditions frequently associated with convective weather in the central united states this includes moderate shear moderate to high convective available potential energy a quasi stationary dryline a low level southerly jet and an 85 kpa moist tongue the initiation of free convection is specifically attributed to a gust front that propagates into a low level jet with attendant horizontal vorticity convergence and moisture the gust front initially propagates as a gravity current and subsequently as an internal undular bore observations of gravity currents gravity waves and the collision of radar echo boundaries provide valuable clues for short period forecasting they establish the presence of potential triggering mechanism

kinematic and precipitation structure of the 10 11 june 1985 squall line abstract high frequency 90 min rawinsonde data from a special mesoscale network 26 sites have been combined with wind profiler dense automated surface network data 80 stations spaced 50 km apart and a series of high resolution dual doppler radar analyses in a common framework attached to a moving squall line system to form a comprehensive dataset describing the mature phase of the 10 11 june 1985 squall line observed during pre storm the dual doppler radar analyses covered a 200 300 km2 area from the leading edge of the convective line to the back edge of the trailing stratiform precipitation region thus providing high resolution wind information over a very broad portion of the storm system the comprehensive analysis is used to resolve several aspects of the trailing stratiform region that had remained unclear from previous studies first a difference in the horizontal scale was found between the mesoscale updraft which at upper levels was on the scale of the trailing stratiform cloud a

a preliminary morphology of precipitation systems in tropical northern australia a preliminary morphology of convective systems observed in the vicinity of darwin australia is presented several types of tropical convection during monsoonal and break season flow are identified using specific examples and compared with a range of systems observed worldwide in the general context of the bulk richardson number a significant spectrum of convective activity ranging from low shear and low convective available potential energy cape to high shear and moderate to high cape typical of mid latitude severe storms is identified significant differences between monsoonal flow and break season systems are apparent the formation of convective lines perpendicular to the low level shear and the apparent balance between advancing shallow cold pools and the shear are ubiquitous features convective scale downdraughts and mesoscale descent appear to be responsible for redistribution of 700 mb momentum to the planetary boundary layer pel the motion of the break season squall lines appears to result from an equilibrium between the cold pool and the undisturbed environmental pel flow deviations from this balance are hypothesized to result in the observed propagating and non propagating or slow moving modes examples of these modes are given showing the classical continuous development of new cells in a balanced state along the leading edge of long lived squalls and in the propagating case the discontinuous development of new cells on the cold pool ahead of the squall

river response to rapid holocene environmental change evidence and explanation in british catchments macklin m g jones a f lewin j 2010 river response to rapid holocene environmental change evidence and explanation in british catchments quaternary science reviews 29 13 14 1555 1576 sponsorship welsh assembly government and the higher education funding council for wales for funding this study through its support of the centre for catchment and coastal research at aberystwyth university

hydrometeor evolution in rainbands over the california valley abstract hydrometeor distributions were measured in two rainbands that passed over the california valley the ground radar was used to vector the university of wyoming s instrumented king air aircraft to the top of the rainband at which time an onboard computer algorithm was used to make multiple penetrations of an ensemble of ice particles that were assumed to descend at 1 or 2 m s 1 while drifting downwind distribution parameters were calculated for each penetration and the changes in these parameters were used to infer the different modes of growth that the particles undergo it was found that there were five distinct regions of particle growth nucleation and depositional growth were the dominant processes near the top of the rainband the hydrometeors then fell through a region of aggregation from the 20 c level to the 10 c level ice crystal multiplication was the dominant process from the 10 c level to the 4 level from 4 to o c aggregation was again the dominant processes below the 0 c l

late holocene floodplain incision and alluvial fan formation in the central grampian highlands scotland chronology environment and implications a section cut across an alluvial fan and the underlying floodplain terrace in the central grampian highlands provides an unusually complete record of late holocene events at ca 2 7 2 4 cal kyr bp floodplain aggradation was replaced by net floodplain incision pollen evidence and charcoal counts provide no evidence for contemporaneous anthropogenic landscape change and the timing of the transition suggests that it reflects an increase in high magnitude erosive flood events following overall climatic deterioration the overlying fan was deposited by torrential hyperconcentrated flows during three brief storm generated depositional events at ca 2 2 2 1 1 9 1 8 and 0 9 0 7 cal kyr bp separated and succeeded by prolonged periods of stability and peat accumulation during these three events a cumulative total of ca 6750 m3 of sediment was deposited probably in no more than a few hours over a timescale of two millennia these findings imply that proposed links between human activity and the development of alluvial fans or debris cones require reassessment and that different elements of the holocene alluvial landscape have responded in different ways to the same climatic inputs aggregation of dating evidence relating to aggradation or incision of alluvial landforms at different scales therefore may produce misleading results copyright 1999 john wiley sons ltd

holocene alluvial fan and terrace formation in the bowland fells northwest england in the bowland fells lancashire northwest england in the headwater valleys of the hodder river system is a suite of holocene fluvial landforms debris cones and alluvial fans at tributary junctions and river terraces along the main valleys post date late pleistocene forms and pre date the modern valley floor alluvial forms eight 14c dates from wood samples incorporated within the terrace and fan deposits have allowed two main phases of holocene erosion to be identified with debris cone fan deposition taking place after c 5400 bp but before c 1900 bp and again at c 900 bp some of the fans and cones are complex with deposits attributable to both phases others are simple and attributable only to the later phase in the headwaters an upper terrace at c 5400 bp pre dates the cones and a lower terrace is contemporaneous with the first debris cone phase lower downvalley the youngest of three terraces date from c 5000 bp or earlier indicating that the sequence is less complex downstream

holocene alluvial fan development in the macgillycuddy s reeks southwest ireland holocene alluvial landforms in the macgillycuddy9s reeks southwest ireland were investigated to determine the controls and timing of postglacial geomorphic activity detailed geomorphologic analysis of three alluvial fan and debris cones within high level cirque basins demonstrates evidence of episodic phases of late holocene surface aggradation and incision radiocarbon dates from peat horizons above and below inorganic units show that phases of aggradation cluster into two distinct periods the first after 230 790 calibrated cal yr a d and the second from 1510 cal yr a d to the present an additional phase of fan aggradation at one site is dated after 1040 1280 cal yr a d all three phases coincide with episodes of enhanced late holocene valley floor alluviation and debris flow activity from upland britain alluvial fans and debris cones have developed primarily as a result of the resedimentation of late midlandian wisconsin drift and talus slopes and mobilization of materials involved flooding transitional flow and debris flow processes pollen analysis of peat horizons interbedded with alluvial fan and debris cone sediments indicates that land use changes were an important factor in lowering the threshold for local slope erosion phases of aggradation also coincide with well documented episodes of climate change and hence fan development is probably a function of both anthropogenic and climatic forcing a sequence of events may have involved initial slope destabilization due to overgrazing and removal of vegetation that was followed by debris mobilization and fan aggradation during intense rainstorms associated with climate change

zircon age constraints on sediment provenance in the caspian region sensitive high resolution ion microprobe shrimp u pb ages for detrital zircons from the caspian region reveal the age ranges of basement terrains that supplied the sediment one sample from the modern volga river has groupings at c 340 370 ma c 900 1300 ma and c 1450 1800 ma with a small number of older zircons this is consistent with derivation from the precambrian basement of the east european craton and palaeozoic arcs in the urals mid and late proterozoic components may be derived from beyond the present volga drainage basin such as the sveconorwegian orogen a bajocian sandstone from the greater caucasus has 73 zircons that post date 350 ma ages cluster at c 165 185 ma c 220 260 ma c 280 360 ma and c 440 460 ma this pattern suggests derivation from palaeozoic basement of the greater caucasus itself and or the scythian platform and igneous rocks generated at a jurassic arc in the lesser caucasus four samples from the lower pliocene productive series of the south caspian basin have common phanerozoic grains and groups between c 900 1300 ma and 1500 2000 ma each sample contains zircons dated to c 2700 ma the overall age patterns in the productive series samples suggest a combination of east european craton and greater caucasus source components

holocene debris cone evolution in glen etive western grampian highlands scotland stratigraphic investigations radiocarbon dating of buried soils and pollen analyses were employed to reconstruct the history of development of a fluvially reworked debris cone in glen etive paraglacial aggradation of debris flow deposits resulted in cone formation between c 10000 yr b p and c 4000 yr b p until supplies of sediment from upslope were effectively exhausted and debris flow activity ceased there ensued a prolonged period of stability and soil development on the cone surface this ended sometime after c 550 yr b p when human interference including burning resulted in destruction of the natural vegetation cover and triggered fluvial incision and the development of an alluvial fan of reworked sediment that buried the lower part of the debris cone the wider implications of these findings are discussed

the dependence of numerically simulated convective storms on vertical wind shear and buoyancy abstract the effects of vertical wind shear and buoyancy on convective storm structure and evolution are investigated with the use of a three dimensional numerical cloud model by varying the magnitude of buoyant energy and one directional vertical shear over a wide range of environmental conditions associated with severe storms the model is able to produce a spectrum of storm types qualitatively similar to those observed in nature these include short lived single cells certain types of multicells and rotating supercells the relationship between wind shear and buoyancy is expressed in terms of a nondimensional convective parameter which delineates various regimes of storm structure and in particular suggests optimal conditions for the development of supercell type storms applications of this parameter to well documented severe storm cases agree favorably with the model results suggesting both the value of the model in studying these modes of convection as well as the value of this representation i

the theoretical effect of metasomatism on sm nd isotopic systems abstract if sm and nd are mobilized during fluid rock interaction fractionation of the ratio between sm and nd in geological units may take place the fractionation can be characterized by a fractionation factor f which can attain any value between d sm d nd and 1 d sm d nd depending on the fluid rock ratio during ree transfer if such fractionations are not recognized this will induce errors in sm nd isotopic interpretations of age and provenance of the affected geological units the apparent ages and nd values are functions of the true values f and the time lapse between petrogenesis and secondary disturbance the functional relationships can be closely approximated by direct proportionalities

the sarmatian crustal segment precambrian correlation between the voronezh massif and the ukrainian shield across the dniepr donets aulacogen abstract sarmatia is the southernmost crustal segment of the east european precambrian craton the phanerozoic dniepr donets aulacogen dda subdivides it into unequal halves the ukrainian shield in the south and the voronezh massif in the north correlation between the ukrainian shield and the voronezh massif is reviewed the overall structure and age province subdivision of sarmatia are assessed and constraints are imposed on displacement along the dda it is shown that differences in the trends of the principal basement structures highlighted by magnetic anomalies outlining palaeoproterozoic banded iron formations are a consequence of the heterogeneous structure of the archaean palaeoproterozoic basement rather than the kinematics of the opening of the dda only minor right lateral displacement along the dda has occurred the main crustal units of the ukrainian shield i e the azov middle dniepr and ingul ingulets blocks correlate excellently with the oskol sumy and sevsk blocks of the voronezh massif which allows the definition of three coherent oskol azov sumy dniepr and sevsk ingulets crustal domains presently available radiometric datings show that these three domains all have archaean crustal ages of 3 65 3 0 3 2 3 1 and 3 1 2 8 ga respectively the inter domain boundaries appear largely to have existed already in the archaean but were subsequently masked by palaeoproterozoic deformation and overlain by proterozoic cover and nappe piles amongst the three crustal domains of central and eastern sarmatia the oskol azov and sevsk ingulets ones have been reworked substantially in the palaeoproterozoic while the sumy dniepr domain acted as a stable cratonic unit although apparently rotating anti clockwise between 2 3 and 2 1 ga ago the palaeoproterozoic banded iron belts of sarmatia can be subdivided into the cratonic margin krivoy rog type and the interior intra domain oskol type the former outline the cratonic sumy dniepr domain while the latter associate with nw se continental rifting that followed archaean zones of weakness inside the oskol azov domain the bryansk block in the northwestern part of the voronezh massif is a part of the large bryansk bragin granulite domain which was formed between ca 2 2 and 2 1 ga ago and extends into the northwestern ukrainian shield in the east the lipetsk losev volcanic belt and the east voronezh turbidite schist province follow the boundary between the sarmatian and volgo uralian crustal segments together these two crustal units appear to represent a palaeoproterozoic orogenic environment ca 2 1 2 0 ga in age

a numerical investigation of squall lines part ii the mechanics of evolution abstract the physical processes involved in the evolution of the model squall line presented in part i of this study are examined it is found that both the thermal and dynamic effects are important in the development of the midlevel meso scale low pressure zone located just to the rear of the convective core based on this observation a positive feedback mechanism is proposed to explain the abrupt transformation of the more or less upright convection line into a quasi steady meso scale convective system possessing an extensive trailing stratiform region in order to set the stage for this transformation to take place the convective updraft is required to possess an initial upshear tilt qualitative arguments are given to show that this initial tilt might be the result of a moderate wind shear at low levels and none or reverse shear in the middle to high levels results from model sensitivity experiments are presented to support the theory in addition to the dynamic effects of the low level wind sh

interpreting alluvial archives sedimentological factors in the british holocene fluvial record abstract a holocene alluvial archive of 506 dated units for great britain is analysed in terms of the sedimentation styles involved the database is classified by sedimentation unit channel sediments palaeochannel fills floodplain surface sediments floodbasins and colluvial deposits and alluvial ensemble fans and cones upland gullies and streams braided systems and active inactive meandering and anastomosing systems floodplain palaeochannel and floodbasin sediments dominate the record mostly from meandering anastomosing systems different sediment units show varied potential for recording environmental change some are relatively poorly dated with respect to the volumes of material involved whilst many dates float in periods of depositional activity which lasted for extended time periods much dated activity is autogenic and of relatively little value in interpreting external environmental influence ensembles and units are similar in age patterns in some respects commonly they exhibit sets of short term peaks in sedimentation activity but differ in others floodbasins and to an extent braided systems feature in the earlier holocene whilst dated fan deposition is more evident in the late holocene there is a general bias towards sediment units of late holocene age which probably reflects preservation factors previous british holocene alluviation models are reviewed it is suggested that the majority of earlier models reflect partial views imposed by limited regional coverage and available dating

development and forcing of the rear inflow jet in a rapidly developing and decaying squall line during bamex abstract this study examines the development structure and forcing of the rear inflow jet rij through the life cycle of a small short lived squall line over north central kansas on 29 june 2003 the analyses were developed from airborne quad doppler tail radar data from the noaa and nrl p 3 aircraft obtained over a 2 h period encompassing the formation development and decay of the squall line during the bow echo and mesoscale convective vortex experiment bamex the strengthening of the system relative rear inflow to 17 m s 1 was concurrent with the formation of a bow echo an increased dynamic pressure gradient beneath the rearward tilted updraft and two counterrotating vortices at either end of the bow the later weakening of the rij to 8 m s 1 was concurrent with the weakening of the bow a decreased dynamic pressure gradient at midlevels behind the bow and the weakening and spreading of the vortices in a modeling study weisman quantified the forcing mechanisms responsible for the developm

mesoscale and convective structure of a hurricane rainband abstract the mesoscale thermodynamic kinematic and radar structure of a hurricane floyd rainband observed on 7 september 1981 is presented data are from 26 aircraft passes through the rainband from 150 to 6400 m a composite technique which presents rainband structure as a function of distance from the storm circulation center reveals inflow from the outer edge of the band and a partial barrier to this flow below 3 km in the direction parallel to rainband orientation radar reveals cellular reflectivity structure on the upwind and central portions of the rainband the frequency of cellular precipitation decreases in favor of stratiform precipitation further downwind as the band spirals gradually towards the eyewall in the radial direction a decrease of 12 k in e is observed across the rainband in the subcloud layer convective scale up and downdrafts that are associated with cellular reflectivity structure are hypothesized to be responsible for the thermodynamic modification of the cloud and subc

the sensitivity of two dimensional simulations of tropical squall lines to environmental profiles abstract two dimensional experiments are carried out to determine the effect of various wind and thermodynamic structure on squall line characteristics two ideas concerning the effect of shear are found useful in explaining many of the outcomes of the numerical experiments first in two dimensions shear in the absence of vorticity sources and sinks is detrimental to convection kuo asai second there is a specific value of low level slim interacting with a cold pool which produces deep uplift and hence strong forcing of convection rotunno et al results suggest that moist midlevel air tends to be favorable for squall lines increasing the total buoyancy or altering the distribution of buoyancy with height such that it is increased at low levels produces stronger systems with updrafts more tilted from the vertical the formula by von karm n for the speed of a gravity current gives qualitative agreement with the speed of most of the simulated systems however at least two additional factors need

flood alluviation and entrenchment holocene valley floor development and transformation in the british uplands the morphology sedimentary properties and sequence of recent coarse grained flood deposits and earlier holocene alluvial fills were investigated in thinhope burn a small 12 km2 catchment in the northern pennine uplands northern england twenty one large flood events are recorded by distinctive cobble boulder bars sheets and splays and boulder berms and lobes lichenometric analysis showed that all but one of these floods dated from the mid eighteenth century the timing of large floods between 1766 and 1960 corresponds with major hydroclimatic trends evident in northern britain and northwest europe over this period discharge estimates suggest that flood magnitudes have decreased since the mid eighteenth century channel and flood plain metamorphosis in late roman times and in the eighteenth century following major valley floor entrenchment locally as much as 8 m would appear to have been caused by increased runoff and flood magnitude this was linked to a shift to a wetter climate with flow augmented by iron age and roman woodland clearance and drainage of the catchment in more recent times results from this study suggest that current models of longer term holocene and pleistocene valley floor development in the british uplands may need to be re evaluated

the age of alluvial fan deposition at a site in the southern uplands of scotland the age of a large alluvial fan debouching onto the valley floor of the river tweed in southern scotland and the sequence of events relating to this are investigated using geomorphological sedimentological palynological archaeological and radiocarbon dating evidence prior to fan deposition the tweed valley floor seems to have been covered by a wooded peat at a time of low fluvial activity the fan commenced deposition in the 11th century ad and appears to have been a local event the tweed showing no response to this accelerated sedimentation later perhaps 200 years later the tweed commenced overbank deposition of the only flandrian terrace preserved local proxy data are examined in order to define the causes of these events but difficulties in temporal correlation despite the good resolution of the radiocarbon chronology mean that the causes of these events remain unknown

catchment hydro geomorphological responses to environmental change in the southern uplands of scotland lake sediment and geomorphic evidence from the loch of the lowes st mary s loch basin in the central southern uplands of scotland provide a multiproxy reconstruction of changing sediment availability and transmission through the catchment interrogation of magnetic geochemical and grain size parameters for lake and catchment materials suggests it is possible to identify independent proxies that reflect both supply availability and discharge capacity controls on the sediment signal chronological control for the lake sediment record is proposed by linking a 210pb 137cs chronology for the last c 120 yr to an age depth profile based on proposed temporal correlations between cyclic hirm lf variability and the north atlantic oscillation geochronological studies on debris cones and alluvial fans yield evidence for episodic hillslope gullying 2000 0 bc with more extensive region wide slope instability ad 700 900 1100 1300 and after ad 1450 1550 and gully stabilization over the last 150 years the latter two episodes coincide with the lake sediment evidence for increased sediment supply from ad 1600 declining after ad 1870 the capacity related lake proxies appear to identify phases of increased flooding ad 1625 1650 1680 1700 1730 1760 1800 1815 1850 1880 1910 1930 1960 1970 and possibly the 1990s close correspondence between the sediment flood archive and historical records of flooding in scotland suggests that lake catchment systems of this type have the potential to yield valuable information on past hydrological response

a synoptic and photographic climatology of low precipitation severe thunderstorms in the southern plains abstract the occurrence of an unusual type of severe thunderstorm difficult to identify by radar has been documented in the southern plains all of the three storms previously studied occurred near the dryline although tornadoes and large hail were produced little rain was observed at the ground and there was no evidence of a strong surface downdraft two were described as bell shaped ten more cases of this rare type of storm have been recently documented visually and on radar a photographic and synoptic climatology of this class of storm the low precipitation severe storm is suggested on the basis of an analysis of the comparison among 11 of these cases it is found that these storms form in a supercell like environment which is drier in the moist layer and more weakly sheared than that of well documented supercells in oklahoma implications of our findings and additional storm characteristics are discussed in light of the larger sample size

a test of ice self collection kernels using aircraft data abstract aircraft observations from the cirrus regional study of tropical anvils and cirrus layers crystal florida area cirrus experiment face campaign obtained in the anvil of a large convective storm from 26 july 2002 are presented during this flight a lagrangian spiral descent was made allowing the evolution of the ice particle size distribution to be followed relative humidities during 1 km from 11 to 3 c of the descent were within 4 of ice saturation it was assumed that the ice particle size distribution was evolving through the process of aggregation alone three idealized ice ice collection kernels were used in a model of ice aggregation and compared to the observed ice particle size distribution evolution a geometric sweep out kernel a golovin sum of particle masses kernel and a modified golovin kernel sum of particle masses raised to a power the golovin kernel performed worst the sweep out kernel produced good agreement with the observations when a constant aggregation eff

terraced fills of pleistocene and holocene age in the rheidol valley wales the legacy of repeated pleistocene glaciations has endowed many welsh river valleys with locally thick successions of glacial and alluvial sediments investigations of a well preserved flight of terraced sediments with good exposures at capel bangor on the afon rheidol mid wales has allowed its quaternary valley fill stratigraphy to be examined in detail study has revealed five terraced fills consisting of seven distinct sedimentary units these range from late devensian ice contact and ice marginal deposits to holocene high sinuosity stream sediments with episodes of man induced accelerated deposition of fine grained alluvium and to aggradation and subsequent incision associated with historic metal mining examination of general sedimentary properties e g granulometry sedimentary structures terrace surface morphology show both differences in the pattern and controls of deposition and also progressive changes over late devensian and holocene times the sediments of the rheidol valley record the response and subsequent recovery of a drainage basin to glaciation and the increasing influence of man on sediment yields channel processes and sediment quality

a diagnostic modelling study of the trailing stratiform region of a midlatitude squall line abstract a kinematic model with continuity equations for sensible heat water vapor cloud water cloud ice rain snow and graupel is used to determine the steady state thermodynamic and microphysical processes associated with the observed mesoscale air motion fields in the trailing stratiform region of the 22 may 1976 oklahoma squall line two versions of the observed air motions are used a low resolution but areally extensive flow pattern derived from the composite sounding data of ogura and liou and a high resolution but less areally extensive flow field obtained from the dual doppler radar analysis of smull and houze model calculations based on the high resolution doppler derived mesoscale air motions show that the location and horizontal scale of the region of most intense stratiform precipitation are determined by the pattern of horizontal transport and fallout of snow and low density graupel particles advected into the stratiform region from the leading line of convective cells the stratiform

vertical variability of cloud hydrometeors in the stratiform region of mesoscale convective systems and bow echoes abstract during the bow echo and mesoscale convective vortex experiment the noaa p 3 research aircraft executed 17 spiral descents to the rear of convective lines to document the vertical variability of hydrometeors above within and below the stratiform melting layer ten spirals were behind lines that exhibited bowing at some stage in their evolution although quick descents on some spirals forced sampling of different particle zones clear trends with respect to temperature were seen for 16 spirals the ambient relative humidity with respect to ice was in the range of 100 4 at temperatures between 10 c and the melting layer but exhibited steady decreases below the melting layer to an average relative humidity with respect to water of 77 15 at 9 c in contrast one spiral conducted on 29 june 2003 directly behind a developing bow echo had a relative humidity with respect to ice averaging 85 at heights above the 0 c level and relative humidity with respect to ice further decreased below the

initiation of convective storms at radar observed boundary layer convergence lines abstract the origin of 653 convective storms occurring over a 5000 km2 area immediately east of the colorado rocky mountains from 18 may to 15 august 1984 was examined seventy nine percent of the 418 storms that initiated within the study area occurred in close proximity to radar observed boundary layer convergence lines this percentage increased to 95 when only the more intense storms 60 dbze were considered colliding convergence lines initiated new storms or intensified existing storms in 71 of the cases a new storm took a median time of 24 min to grow to 30 dbz following line collision the convergence lines ranged in length between ten and several hundred kilometers both radar and mesonet stations indicated that the primary convergence was concentrated in a zone 0 5 to 5 km in width these lines were characterized on doppler radar as thin lines of enhanced reflectivity between 0 and 20 dbze and as a line of strong radial or azimuthal gradient in doppler velocity these lines were observed ev

mesoscale motion fields associated with a slowly moving gate convective band abstract the structure of the convective band of 14 september in the dense gate observing array is determined using wind and thermodynamic data primarily from multiple aircraft penetrations which are well distributed in the vertical and in time the well defined mesoscale features in the line which are 10 40 km in scale quasi two dimensional and persist for several hours determine the distribution of the convective scale features which are 5 km or less in size three dimensional not generally detectable for more than one flight leg at the leading edge a 30 km zone of strong ascent is computed from two dimensional continuity here lifting of the ambient air creates a favorable environment not found elsewhere for deep cumulonimbus clouds to develop their updrafts are weak 2 4 m s 1 on the average behind the updraft zone below 3 4 km is a broad descent zone it corresponds to the stratiform rain area and has little convection and some drying at lower levels on the average the mass flux by

the linear dynamics of squall line mesohighs and wake lows two surface pressure features that commonly accompany squall lines the mesohigh and the wake low may be explained at least in part as a linear response to the low level cooling associated with stratiform precipitation this response is numerically simulated for two and three dimensional moving and stationary low level coolings characteristic of squall line stratiform regions when the cooling is defined to move and to have three dimensional structure both a mesohigh and a mesolow develop and their structures and evolutions resemble those of squall line mesohighs and wake lows when an upper boundary is introduced directly above the cooling the response approaches a steady state in which a mesohigh mesolow couplet is centered on the cooling the simulations and the steady state analysis presented here help to explain observed characteristics of squall line mesohighs and wake lows including their life cycles and positioning relative to precipitation structures

microphysical and thermodynamic structure and evolution of the trailing stratiform regions of mesoscale convective systems during bamex part i observations abstract this study used airborne and ground based radar and optical array probe data from the spiral descent flight patterns and horizontal flight legs of the noaa p 3 aircraft in the trailing stratiform regions tsrs of mesoscale convective systems mcss observed during the bow echo and mesoscale convective vortex experiment bamex to characterize microphysical and thermodynamic variations within the tsrs in the context of the following features the transition zone the notch region the enhanced stratiform rain region the rear anvil region the front to rear flow the rear to front flow and the rear inflow jet axis one spiral from the notch region nine from the enhanced stratiform rain region and two from the rear anvil region were analyzed along with numerous horizontal flight legs that traversed these zones the spiral performed in the notch region on 29 june occurred early in the mcs life cycle and exhibited subsaturated conditions throughout its depth the nine spirals performed within the

geochemistry of the krivoy rog banded iron formation ukraine and the impact of peak episodes of increased global magmatic activity on the trace element composition of precambrian seawater abstract pure superior type banded iron formation bif samples from the krivoy rog supergroup ukraine are excellent archives of ambient early precambrian seawater they show low concentrations of incompatible elements such as zr hf and th and shale normalized rare earths and yttrium rey sn patterns similar to those of modern seawater i e heavy rey sn enriched patterns with positive la sn gd sn and y sn anomalies lack of ce sn and presence of positive eu sn anomalies indicate rey contributions to anoxic ferruginous seawater from high temperature hydrothermal fluids the depositional age of the krivoy rog bif is ill defined but a late archean to paleoproterozoic age has been suggested based on u pb zircon ages for units stratigraphically above and below the bif we determined sm nd isotopic compositions of pure and impure samples from the krivoy rog bif which yield an errorchron with an apparent age of 2406 350 ma mswd 15 that falls within this broad age range all pure bif samples show chondrite normalized subscript cn rey patterns with strong positive eu cn anomalies that are typical for archean but rather rare and much less pronounced in proterozoic bifs associated schists also show archean rather than post archean style rey distributions the rey geochemistry of both chemical and epiclastic sediments therefore is more consistent with a late archean rather than a post archean depositional age of the krivoy rog supergroup initial nd values of impure bifs and of associated schist reveal variable contributions from ttgs less radiogenic in nd and a more radiogenic component possibly comprised of basement amphibolites or mafic volcanics of the stratigraphically underlying new krivoy rog group the purest krivoy rog bif representing local krivoy rog seawater displays an nd 2 60 ga value of 2 3 this value is less radiogenic than impure krivoy rog bifs or other near contemporaneous neoarchean pure chemical sediments to preserve this specific local isotopic fingerprint in anoxic archean seawater the krivoy rog bif must have been deposited in an isolated sea basin with limited exchange with ferruginous deep waters of the open ocean a compilation of rey data for high purity precambrian bifs reveals that eu cn eu cn ratios of precambrian seawater follow a general global evolution curve that shows specific peaks which reflect times of increased high temperature hydrothermal rey input into seawater following declining eu cn eu cn ratios from the eoarchean to the mesoarchean the ratios suddenly rise at 2 7 ga and reach a maximum at 2 6 ga indicating an increased flux of high temperature hydrothermal rey to neoarchean seawater which supports the hypothesis that times of widespread bif deposition coincided with periods of intense submarine hydrothermal activity probably triggered by major mantle plume events this association is supported by a strong increase of the nd t values of pure seawater archives at 2 7 2 6 ga which reflects an increased flux of mantle nd into seawater these results suggest that eu rey systematics and potentially nd systematics are robust tools to indentify episodes of enhanced mantle plume activity

riphean rifting and major palaeoproterozoic crustal boundaries in the basement of the east european craton geology and geophysics abstract the east european craton which occupies the northeastern half of the european continent is characterized by the presence of giant even transcratonic systems of riphean meso to neoproterozoic rifts aulacogens the largest of these riphean rift systems tend to follow the course of palaeoproterozoic sutures and junction zones that subdivide the craton into three crustal segments with autonomous development histories these segments named fennoscandia volgo uralia and sarmatia are marked by distinct t magsat anomalies genetically the intersegment junction zones represent different types of collisional and accretional interaction between the component crustal segments of the craton in accordance with this the riphean rift systems vary in width the presence or absence of moho uplifts and other properties like for instance heat flow values however all of them follow belts of weakly magnetized crust studded with local magnetic maxima due to the presence of mafic rocks associated with the rifting the rift system intersegment junction zone relationships in consequence similarly represent a range of variation and cannot be referred to one single model

holocene alluviation and land use change on callaly moor northumberland england archaeological survey and palaeoenvironmental investigations in coe burn callaly moor northumberland have examined the chronology and nature of prehistoric and historic land use change in a small upland river catchment these studies have revealed an intensively used landscape with evidence of late neolithic to bronze age medieval and post medieval land use and settlement two episodes of valley floor alluviation are identified and dated to the middle late bronze age and post medieval periods magnetic mineral and geochemical analyses of fine sediments from the older alluvial fill show it to contain a high proportion of topsoil which is believed to have been produced by soil erosion resulting from bronze age tree clearance and cultivation deposition of the younger alluvial fill post ad 1500 was associated with the inwash of relatively unweathered bedrock generated by coal mining in the catchment it is demonstrated that by integrating archaeological field survey with off site palaeoenvironmental investigations a much fuller picture of human activity and land use change has emerged than otherwise would have been the case studies of this type may be particularly useful in other upland river catchments where archaeological survival is limited or poor

tropical inversions near the 0 c level abstract soundings taken from the tropical western pacific warm pool region during toga coare reveal the common occurrence of temperature and moisture perturbations near the 0 c level the perturbations frequently are characterized by shallow layers of increased stability or occasionally temperature inversions and reversals or inflections in the vertical profile of specific humidity similar temperature and moisture inversions have been observed elsewhere in the tropics and midlatitudes but have not received much attention isothermal layers are known to exist just below the melting level in stratiform rain regions however not all stable layers observed over the warm pool are confined to precipitation systems the perturbation in the specific humidity profile accounts for the often observed double peak structure in the apparent moisture sink q2 in tie tropics stratification of the data based on relative humidity criteria indicates that the stable layers near the 0 c level generally fall into two main

modeling study of a tropical squall type convective line abstract a multidimensional and time dependent cloud scale model is used to investigate the dynamic and micro physical processes associated with convective and stratiform regions within a tropical squall type convective line the evolution of the total convective and stratiform portions of rainfall is also estimated by using model output a three dimensional version of the model covers a horizontal domain about 96 96 km2 frequently the horizontal extent of an observed stratiform region is over a few hundred kilometers therefore a two dimensional version of the model with a 512 km horizontal length is also used to incorporate a complete stratiform region two dimensional model result recapture many interesting features as observed in particular the fractional portion of stratiform rain as well as its fractional area coverage are in good agreement with observations a significant amount of ice particles melted to rain near the freezing level in the trailing part of the modeled squall system during i

mesoscale updraft magnitude and cloud ice content deduced from the ice budget of the stratiform region of a tropical cloud cluster abstract radar observations obtained during winter monex describe the three dimensional structure and development of the mesoscale stratiform region of a tropical cloud cluster the magnitudes of the mesoscale updraft and cloud ice mass content within an upper tropospheric stratiform cloud deck are deduced from a formulation of the ice budget of the stratiform region measurements of radar reflectivity at upper levels serve as the primary input data aircraft observations of ice particles are also used to guide the calculations the mesoscale updraft magnitude and cloud ice mass content are determined hourly over a period of 12 h the updraft velocities were 10 23 cm s 1 and the cloud ice contents were 0 1 0 3 g m 3 the vertical velocity estimates agree well with estimates obtained for the same cloud cluster by johnson 1982 using the kinematic method

hillslope gullying in the solway firth morecambe bay region great britain responses to human impact and or climatic deterioration abstract in the solway firth morecambe bay region of great britain there is evidence for heightened hillslope instability during the late holocene after 3000 cal bp little or no hillslope geomorphic activity has been identified occurring during the early holocene but there is abundant evidence for late holocene hillslope erosion gullying and associated alluvial fan and valley floor deposition interpretation of the regional radiocarbon chronology available from organic matter buried beneath alluvial fan units suggests much of this geomorphic activity can be attributed to four phases of more extensive gullying identified after 2500 2200 1300 1000 1000 800 and 500 cal bp both climate and human impact models can be evoked to explain the crossing of geomorphic thresholds and palaeoecological data on climatic change bog surface wetness and human impact pollen together with archaeological and documentary evidence of landscape history provide a context for addressing the causes of late holocene geomorphic instability high magnitude storm events are the primary agent responsible for gully incision but neither such events nor cooler wetter climatic episodes appear to have produced gully systems in the region before 3000 cal bp increased gullying after 2500 2200 cal bp coincides with population expansion during iron age and romano british times the widespread and extensive gullying after 1300 1000 cal bp and after 1000 800 cal bp coincides with periods of population expansion and a growing rural economy identified during norse times 9 10th centuries ad and during the medieval period 12 13th centuries ad these periods were separated by a downturn associated with the harrying of the north ad 1069 to 1070 the gullying episode after 500 cal bp also coincides with increased anthropogenic pressure on the uplands with population growth and agricultural expansion after ad 1500 following 150 years of malaise caused by livestock and human the black death plagues poor harvests and conflicts on the scottish english border the increased susceptibility to erosion of gullies is a response to increased anthropogenic pressure on upland hillslopes during the late holocene and the role of this pressure appears crucial in priming hillslopes before subsequent major storm events in particular the cycles of expansion and contraction in both population and agriculture appear to have affected the susceptibility of the upland landscape to erosion and the hillslope gullying record in the region therefore contributes to understanding of the timing and spatial pattern of human exploitation of the upland landscape

mesoscale organization and cloud microphysics in a bay of bengal depression abstract airborne radar and cloud microphysical data were obtained throughout a monsoon depression observed over the bay of bengal on 3 8 july 1979 during the summer monsoon experiment of the global atmospheric research programme the precipitation in the disturbance occurred in mesoscale rain areas 100 300 km in horizontal dimension with the largest areas tending to be elongated in the east west or northwest southeast direction these mesoscale precipitation features resembled the rain areas of equatorial cloud clusters each mesoscale precipitation feature contained intense convective cells but the area covered by rain was predominantly stratiform the convective cells in the mesoscale features were sometimes arranged in rapidly moving rather narrow arc shaped east west lines with the stratiform precipitation trailing the line in other cases the convective cells were more randomly embedded in the stratiform rain ice particle images obtained at flight level temperatures of 5 to 25 c indicated the

the chronology of late quaternary fluvial activity in part of the milfield basin northeast england the sediment stratigraphy of a 4 m thick intercalated holocene alluvial fill and valley floor peat at a site in the milfield basin northumberland has been dated by a series of eight 14c assays and related to a previously analysed pollen record the sequence extends from the earliest holocene until c 2800 cal bp prior to the onset of peat inception substantial amounts of channel trenching can be demonstrated to have occurred in the milfield basin during the loch lomond stadial there is no measurable early holocene accelerated fluvial activity but a major flooding event occurred at c 7500 cal bp much earlier than recorded elsewhere in the region the explanation for this is not clear however the cessation of mid holocene overbank sedimentation at c 4000 3500 cal bp is tentatively correlated with slope stability associated with woodland regeneration 1998 john wiley sons ltd

late quaternary river terrace development in the macgillycuddy s reeks southwest ireland abstract geomorphological sedimentological pedostratigraphical and palaeoecological analyses of fluvial and glacigenic deposits infilling the gaddagh valley macgillycuddy s reeks southwest ireland are used to elucidate the patterns and controls of late quaternary valley floor development in a 3 km reach of the catchment lying immediately downvalley of two mid basin lakes lough gouragh and lough callee a total of four holocene alluvial terraces terrace level tl 2 5 and a modern floodplain tl 6 have been identified and lie inset within a strath terrace comprising late quaternary midlandian till tl 1 the combination of mid basin lakes and flanking strath terraces acted to decouple the gaddagh channel from upper catchment and valley side debris sources shortly after regional deglaciation postglacial fluvial terrace development in the study reach has therefore occurred primarily in response to hydrological changes and reworking of local valley floor deposits rather than catchment wide debris supply changes pollen analyses of valley floor peat deposits interbedded with minerogenic alluvium indicate that anthropogenic disturbance of catchment tree cover had commenced by c a 1690 1450 cal bc and that the catchment was largely cleared of woodland by later prehistoric times major phases of incision and alluviation represented by terraces tl 3 5 however have been radiocarbon dated to the period after 250 530 cal ad and broadly correspond with holocene fluvial records elsewhere in the region upland britain and northwest europe although fluvial system responses to hydrological changes will have been promoted by anthropogenic disturbances of catchment vegetation cover the timing of late holocene incision and alluviation episodes are interpreted as reflecting enhanced flood frequencies and or magnitudes associated with late holocene climatic shifts in the gaddagh valley however we hypothesise that the headwater lakes lough gouragh and lough callee may also have exerted a critical control on the postglacial evolution of the valley floor in particular high magnitude flooding is likely to have been instrumental in valley floor entrenchment and formation of tl 3 tl 4 and tl 5 terraces

evolution of the archaean aulian gneiss complex middle dnieper gneiss greenstone terrain ukrainian shield shrimp upb zircon evidence abstract the aulian gneiss complex agc forms the main part of the middle dnieper gneiss greenstone terrain ukrainian shield as domal blocks between greenstone belts the complex consists of three main units the oldest consists of interlayered tonalitic gneisses amphibolites and ultramafic schists and are grouped into the supracrustal aulian series the second unit comprises coarse grained tonalitic and trondhjemitic gneisses which formed as small intrusive bodies within aulian series rocks the third unit contains diverse migmatites and gneissic granitoids collectively named the dniepropetrovsk granitoids and forming the main component of the agc shrimp u pb geochronology has been undertaken on these units of the agc weighted mean 207 pb 206 pb 2 ages for different zircon types in each sample are as follows 1 aulian series tonalitic gneisses 3196 13 and 3079 9 ma coarse grained amphibolite metagabbro of tholeiitic composition 3181 5 ma fine grained melanoamphibolite metavolcanic of basalt komatiitic composition 3078 17 ma 2 small intrusions into the aulian series trondhjemitic gneiss 3122 2 and 3081 5 ma 3 dniepropetrovsk granitoids tonalite 3074 7 ma trondhjemite 3070 ma these results allow the following synthesis for the agc 3200 3180 ma ago supracrustal dacite basalt komatiite sequence was formed and then 3120 ma ago it was intruded by trondhjemites and tonalites at 3080 ma metamorphism of amphibolite facies and perhaps local in situ partial melting caused growth of new zircon in the older lithologies and was accompanied by intrusion of younger of tonalites and trondhjemites these u pb zircon results have not substantiated a previous interpretation of sm nd whole rock isotopic data that very early archaean 3900 ma mafic components are present in the aulian series of agc

late devensian and holocene landscape change in the uplands of the isle of man abstract the late glacial and holocene geomorphology of the manx uplands has received scant attention in previous researches solifluction deposits and terraces provide the earliest evidence for geomorphic activity after deglaciation fluvial incision into drift choked valleys is correlated with the formation of the large mountain front alluvial fans that flank the manx uplands formation of these alluvial fans is constrained to 15 000 10 500 cal years bp by 14 c dates on organic deposits beneath and above the alluvial fan gravels alluvial fan and river terraces along four valleys postdate this incision optically stimulated luminescence osl and 14 c dating provide a tentative chronology for these landforms the higher terraces are late glacial fluvial surfaces that were probably occupied by rivers into the holocene incision during the late holocene led to the abandonment of the higher surfaces producing a suite of younger river terraces and alluvial fan surfaces independent dating constrains this fluvial activity to post bronze age 3500 2800 cal years bp increased human activity and climatic change during the late holocene are possible causes for this increased geomorphic activity

tornadoes and downbursts in the context of generalized planetary scales abstract in order to cover a wide range of horizontal dimensions of airflow the author proposes a series of five scales maso meso miso to be read as my so moso and muso arranged in the order of the vowels a e 1 o u the dimensions decrease by two orders of magnitude per scale beginning with the planet s equator length chosen to be the maximum dimension of masoscale for each planet mesoscale highs and lows were described on the basis of mesoanalyses while sub mesoscale disturbances were depicted by cataloging over 20 000 photographs of wind effects taken from low flying aircraft during the past 15 years various motion thus classified into these scales led to a conclusion that extreme winds induced by thunderstorms are associated with misoscale and mososcale airflow spawned by the parent mesoscale disturbances

two dimensional convection in non constant shear a model of mid latitude squall lines numerical simulations of two dimensional deep convection are analysed using analytical models extended to include shallow downdraughts and non constant shear the cumulonimbus are initiated by low level convergence created by a finite amplitude downdraught these experiments have constant low level shear and differ only in the profile of mid and upper level winds quasi steady convenction is produced if the mid and upper level flow has small shear and the low level shear is large the surface precipitation ismaximized for no intial relative relative flow aloft if stationary this storm p o can give prodigious locilized rainfall p o is the two dimentisonal equivalent of the supercell these results are placed in context with previous two dimensional simulations attention is drawn to the similiarity with previous two dimensional simulations attention is drawn to the similarity with squall lines in central and eastern u s a storm p o is analysed by construction of time averaged fields of streamfunction vorticity teperature and height deviation the smoothness of these fields suggests a conceptual model of the storm dynamics which involves cooperation between distinct charcteristic flows an overturning updraught a jump type updraught a shallow downdraught a low level rotor and a boundary layer an idealized analytical model is described by solution of the equations for steady convection these solutions for the remote flow are derived from energy conversation mass continuity and a momentum budget and they give relationships between the non dimensional parameteres of the problem it is apparent that the convection is a high froude or low richardson number flow demanding the existence of a cross storm pressure gradient inherent in this idealized model is a vortex sheet between updraught and down draught and it is considered that the dynamical instability of this sheet is related to complexities in the numerical simulation furthermore these results show that in two dimensions both non constant shear and a shallow downdraught are necessary to maintain steady convection

a comparison of the results of a two dimensional numerical simulation of a tropical squall line with observations abstract a comparison of the results of a two dimensional numerical simulation of a tropical squall line with observations shows good agreement in most respects the two dimensional model should provide a valuable research tool for understanding the physical processes that are taking place and for discovering the effects of different wind and thermodynamic environments on squall line characteristics in the simulation high pressure develops ahead of the system relative to that behind at most levels the momentum flux is mainly confined to below 6 km and in the region of strong convection the squall line is multicellular and significant perturbations are associated with convection embedded in the stratiform region considerable horizontal accelerations occur at large distances from the region of strong convection away from the system aloft and towards it at low levels the effect of excluding the ice phase in the simulation is shown to lead to cloud tops some 3 km lower than when it is incorporated alth

effect of vertical wind shear on numerically simulated multicell storm structure abstract a strictly two dimensional cloud model was used to gauge the effect of vertical wind shear on the mature phase behavior of model simulated multicellular storms extending the previous work of the authors we specifically examined the propagation speed quasi equilibrium behavior storm scale and updraft orientation of the model storms as a function of shear intensity we also considered the precipitation efficiencies of our model storms and applied density current and rotunno klemp weisman theories to our results our previous work revealed that model storms could achieve a mature phase consisting of repetitive multicellular development when certain numerical obstacles were overcome this was referred to as a quasi equilibrium state we found herein that this state was also reached by model storms even when subjected to a very wide range of low level wind shear intensities although the temporal behavior during this stage was clearly dependent on the shear we also found a very systematic rela

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

the mesoscale and microscale structure and organization of clouds and precipitation in midlatitude cyclones part v the substructure of narrow cold frontal rainbands abstract the organization and structure of a narrow cold frontal rainband ncfr on the small mesoscale and the microscale have been investigated through quantitative radar reflectivity doppler radar observations airborne observations and surface measurements the ncfr was composed of small mesoscale regions of heavy precipitation called precipitation cores pcs oriented at an angle to the synoptic scale cold front in horizontal cross section the pcs were roughly elliptical in shape areas of lighter precipitation called gap regions grs separated the pcs the pcs were so oriented that their loading edges were regions of strong low level convergence the weather associated with the passage of a pc resembled that of a squall line gust front with concurrent windshifts and pressure checks occurring 5 min before heavy precipitation and a fall in temperature the changes in surface weather that accompanied the passage of a gr were more variable but tended to be less marked than for pcs thus the se

thermodynamic properties of mesoscale convective systems observed during bamex dropsonde observations from the bow echo and mesoscale convective vortex experiment bamex are used to document the spatiotemporal variability of temperature moisture and wind within mesoscale convective systems mcss onion type sounding structures are found throughout the stratiform region of mcss but the temperature and moisture variability is large composite soundings were constructed and statistics of thermodynamic variability were generated within each subregion of the mcs the calculated air vertical velocity helped identify subsaturated downdrafts it was found that lapse rates within the cold pool varied markedly throughout the mcs layered wet bulb potential temperature profiles seem to indicate that air within the lowest several kilometers comes from a variety of source regions it was also found that lapse rate transitions across the 0 c level were more common than isothermal melting layers the authors discuss the implications these findings have and how they can be used to validate future high resolution numerical simulations of mcss

four zircon ages from one rock the history of a 3930 ma old granulite from mount sones enderby land antarctica ion microprobe u th pb analyses of zircons from a granulite grade orthogneiss from mount sones enderby land antarctica record the ages of four principal events in the history of the gneiss three of which already have been recognized through previous isotopic dating of other samples the structure of the zircons indicates at least four different stages of growth the several zircon ages were obtained by grouping the analyses according to the stage they represented in the observed stratigraphic succession of growth and thereby defining separate u pb discordance patterns for each stage the stratigraphically oldest zircon rare discrete cores is indistinguishable in age from the most common euhedrally zoned zircon both crystallized when the tonalitic precursor of the orthogneiss was emplaced into the crust 3927 10 ma ago making the orthogneiss currently the oldest known terrestrial rock the outer parts of most grains and some whole grains recrystallized at 2948 31 17 ma during or immediately after possibly 100 ma of high granulite grade metamorphism the recrystallized zircon was isotopically disturbed by tectonism associated with reactivation of the southern margin of the napier complex at 1000 ma in the intervening time at 2479 23 ma the cores and zoned zircon suffered a major isotopic disturbance involving movement of radiogenic pb which left most of the crystals with radiogenic pb deficiencies but produced local radiogenic pb excesses in others a new generation of zircon characterized by very high th u and low u grew at that time that event deformation and possibly a minor rise in temperature produced widespread perturbations of other isotopic systems throughout the napier complex

three dimensional week long simulations of toga coare convective systems using the mm5 mesoscale model abstract a three dimensional nonhydrostatic mesoscale model the pennsylvania state university national center for atmospheric research mesoscale model mm5 is used to simulate the evolution of convective systems over the intensive flux array ifa during the tropical ocean global atmosphere coupled ocean atmosphere response experiment during 19 26 december 1992 the model is driven by a time varying ifa mean forcing based on the average advective tendencies of temperature and moisture over the ifa the domain averaged horizontal wind is kept close to the observed ifa mean using newtonian relaxation periodic lateral boundary conditions are imposed simulations with three horizontal grid spacings 2 15 and 60 km are conducted with 15 and 60 km resolution subgrid scale cumulus convection is parameterized while mesoscale convective organization is explicitly resolved over a 600 km 2 domain with 2 km resolution convection is fully resolved over a 210 km 2 domain despite their different horizo

the influence of microphysics in the formation of intense wake lows a numerical modeling study abstract a two dimensional cloud model is used to investigate whether microphysical processes alone within the stratiform rain regions of mesoscale convection systems can induce strong descent and intense surface wake lows accompanying such systems idealized simulations are run with a domain that captures the back edge of the stratiform rain region a simplified microphysical field representing snow alone is prescribed within the stratiform cloud to produce radar reflectivities similar to observations when the prescribed snow field is assumed time independent strong subsidence develops but does not induce an intense wake low since microphysical cooling strongly opposes adiabatic warming simply increasing snow quantities although resulting in heavier rain rates and stronger subsidence does not produce significant pressure falls however when precipitation rates are prescribed to decrease with time as might occur with collapsing precipitation cores subsidence induces greater pressure falls and a