mesoscale convective systems in weakly forced large scale environments part ii generation of a mesoscale initial condition abstract a series of five mesoscale convective systems mcss developed within a weakly forced large scale environment on 11 and 12 may 1982 two of these systems had a large component of motion against the midtroposphoric flow and propagated in a direction nearly opposite to that of the traveling upper level disturbances this description of the evolution of convection is very different from traditional ones in which convection develops and moves more or less in phase with traveling upper level disturbances observations indicate that the initiation and evolution of convection are tied to mesoscale features that are not well observed by the conventional observing network making the structure of the model initial condition a potentially crucial factor in the success or failure of any subsequent numerical simulation it is found that the initial conditions created using the conventional initialization procedure of the pennsylvania state university national center for atmospheric research mesoscale model d

numerical simulation of the meso β scale structure and evolution of the 1977 johnstown flood part i model description and verification abstract the pennsylvania state university ncar mesoscale model originally developed by anthes and warner is modified to simulate the meso scale structure and evolution of convectively driven weather systems the modifications include i two way interactive nested grid procedures ii the fritsch chappell convective parameterization scheme and iii the blackadar boundary layer package an 18 h simulation of the johnstown flood of july 1977 is conducted compared to the documentation of hoxit et al and bosart and sanders the simulation reproduced many of the different aspect of the mesoscale convective complex and squall line that were responsible for the heavy rain over western pennsylvania in particular the model predicts the size propagation rate and orientation of the mesoscale convective components that were observed in the mid atlantic states the simulated evolution of the planetary boundary layer cool outflow boundaries and surface pressure perturbations such as meso scale lows h

displacement of salt by the laurentide ice sheet abstract in central new york deformation of salt of the salina formation by the laurentide ice sheet is shown by a thinning of the salt stratum in and near the outcrop zone where it was overridden by the ice sheet and by a thickening down dip near the glacial limit less definitive suggestions of deformation by glacial overriding of the salina outcrop zone in northeastern ohio are seen in salt cored anticlines in the vicinity of the glacial limit in the lower peninsula of michigan isopachs of salt curve around saginaw bay which suggests that the salt was displaced southwestward away from the bay by pressure of the saginaw lobe of the ice sheet all but one of the major paleozoic salt deposits of north america lie in a zone that girdles two thirds of the canadian shield from where glacial erosion removed all but occasional outliers of phanerozoic strata

observations and fine grid simulations of a convective outbreak in northeastern spain importance of diurnal forcing and convective cold pools the life cycle and interactions of a series of convective systems that developed in northeastern spain during the afternoon of 7 august 1996 are examined based on remote sensing products surface observations and numerical simulations most of the convection was organized in two mesoscale convective systems mcss and a line of storms attached to the pyrenees mountains one of these storms produced rainfalls in excess of 200 mm in 3 h and severe flash floods in the biescas area the end of the convection in the biescas area occurred after merger of the storm with one of the mcss that approached from the southwest a high resolution 4 km grid length simulation of the event reproduces the observed timing and interactions of the convective systems as well as the general rainfall pattern the highly localized rainfall core at biescas is well located although the peak rainfall amount is underestimated the success of the model at triggering the convection at the proper locations and time results from a reasonably accurate prediction of mesoscale features of the low level flow pattern such as a thermal mesolow in the ebro valley deformation zone upslope wind systems and the pushing of a cold front in the upper portion of the valley after the onset of the initial convection the role of the convectively induced cold pools and outflows for the propagation of the convective systems is shown to be very important in particular the mcs interacting with the biescas convection was driven by strong mesoscale ascent established between the convectively induced outflows the upvalley southeasterly winds sustained by the mesolow and the downvalley northwesterly winds associated with the cold front after the interaction the convection in biescas ceased because of the interruption of the southerly upslope flow caused by the convective cold pools finally the explosive character of convection after noon and its initial focusing in uplands and slopes suggest that diurnal forcing could have played a decisive role this idea is validated by means of simulations

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

investigation of microphysical processes occurring in isolated convection during name abstracta major objective of the north american monsoon experiment name was to quantify microphysical processes within convection occurring near the steep topography of northwestern mexico a previous study compared examples of isolated convection using polarimetric radar data and noted a dependence on mixed phase processes via drop freezing and subsequent riming growth along the coastal plain and western slopes with an even greater role of melting ice in rainfall production over the highest terrain despite the higher frequency of these isolated cells compared to organized convective systems the latter were responsible for 75 of rainfall therefore this study seeks to evaluate the role of mesoscale organization on microphysical processes and describes the evolution of these systems as a function of topography similar to isolated convection both warm rain and ice based processes played important roles in producing intense rainfall in organized convection although similarities existed between cell

new evidence for vegetation development and timing of upper middle pleistocene interglacials in northern germany and tentative correlations abstract this paper discusses palynological investigations and new 230th u ages of two upper middle pleistocene sequences of the formerly glaciated northern german lowlands the reinsdorf sequence at the open mine of schoningen lower saxony and the north friesian site of leck new 230th u ages of late interglacial organic layers of the archaeological lake margin site of the reinsdorf sequence ranging from 280 to 343 ka give evidence for a correlation of those deposits with marine isotope stage mis 9 near and long distance correlation by means of palynological investigations of holsteinian and related interglacial continental deposits and their correlation with the mis is discussed isotopic investigations of uranium and thorium from organic rich mud deposits at core leck 8 point to an open system and age estimation by 230th u dating remains therefore unclear compared to other upper middle pleistocene warm periods in north germany correlations of the leck interglacial with the holsteinian and the reinsdorf interglacial can be excluded in comparison with sediment successions from the nachtigall section at hoxter and the section ottostrase at gottingen the leck interglacial is discussed as a correlative of a warm temperate phase of mis 7

the role of catastrophic geomorphic events in central appalachian landscape evolution abstract catastrophic geomorphic events are taken as those that are large sudden and rare on human timescales in the nonglaciated low seismicity central appalachians these are dominantly floods and landslides evaluation of the role of catastrophic events in landscape evolution includes assessment of their contributions to denudation and formation of prominent landscape features and how they vary through space and time tropical storm paths and topographic barriers at the blue ridge and allegheny front create significant climatic variability across the appalachians for moderate floods the influence of basin geology is apparent in modifying severity of flooding but for the most extreme events flood discharges relate mainly to rainfall characteristics such as intensity duration storm size and location landslide susceptibility relates more directly to geologic controls that determine what intensity and duration of rainfall will trigger slope instability large floods and landslides are not necessarily effective in producing prominent geomorphic features large historic floods in the piedmont have been minimally effective in producing prominent and persistent geomorphic features in contrast smaller floods in the valley and ridge produced erosional and depositional features that probably will require thousands of years to efface scars and deposits of debris slide avalanches triggered on sandstone ridges recover slowly and persist much longer than scars and deposits of smaller landslides triggered on finer grained regolith even though the smaller landslides may have eroded greater aggregate volume the surficial stratigraphic record can be used to extend the spatial and temporal limits of our knowledge of catastrophic events many prominent alluvial and colluvial landforms in the central appalachians are composed of sediments that were deposited by processes similar to those observed in historic catastrophic events available stratigraphic evidence shows two scales of temporal variation one related to quaternary climate changes and a more recent higher frequency variation due to rare events during the holocene in much of the central appalachians landforms related to quaternary climate changes persist as the most prominent features despite the modifying effects of late holocene catastrophic events

physical interpretations of regional variations in the scaling exponents of flood quantiles the concepts of simple scaling and multiscaling provide a new theoretical framework for the study of spatial or regional flood frequency relations and their underlying physical generating mechanisms in particular the scaling exponents in the power law relationship between flood quantiles and drainage areas contain a basic signature of invariance regarding the spatial variability of floods and therefore suggest different hypotheses regarding their physical generating mechanisms if regional floods obey simple scaling then the slopes do not vary with return periods on the other hand if regional floods obey multiscaling then the slopes vary with return periods in a systematic manner this premise is expanded here by investigating the empirical variations in the scaling exponents in three states of the usa new york new mexico and utah distinct variations are observed in the exponents among several regions within each state these variations provide clear empirical evidence for the presence of both simple scaling and multiscaling in regional floods they suggest that snowmelt generated floods exhibit simple scaling whereas rainfall generated floods exhibit multiscaling results from a simple rainfall runoff experiment along with the current research on the spatial scaling structure of mesoscale rainfall are used to give additional support to these physical hypotheses underlying two different scaling structures observed in floods in addition the rainfall runoff experiment suggests that the behaviour of the flood exponents in small basins is determined by basin response rather than precipitation input this finding supports the existence of a critical drainage area as has been reported for the appalachia flood data in the usa such that the spatial variability in floods in basins larger than the critical size is determined by the precipitation input and in basins smaller than the critical size is determined by the basin response

positive feedbacks associated with erosion of glacial cirques and overdeepenings the principal points of water input to a glacier are the bergschrund in cirques and crevasse fields lower on the glacier crevasse fields commonly occur over convexities at the heads of overdeepenings in glacier beds the amplitude of subglacial water pressure fluctuations is large just down glacier from these points of water input erosion by quarrying is likely in such areas erosion is thus inferred to be localized on the headwalls of cirques and overdeepenings in the case of overdeepenings this leads to a positive feedback process in which a perturbation in the bed causes crevassing at the surface resulting in erosional forces that accentuate the perturbation when subglacial water flows up an adverse bed slope leading out of a cirque or overdeepening much of the viscous energy dissipated is used to warm the water to keep it at the pressure melting temperature as the ice thins and the pressure decreases in such situations subglacial conduits are maintained by high water pressures rather than by melting of conduit walls in the limit water pressures apparently become so high that water is forced out along the ice bed interface and the conduits collapse the products of erosion are then no longer flushed out and a protective till layer accumulates by limiting erosion on such adverse bed slopes this till layer controls the geometry of these overdeepened basins

structure and evolution of numerically simulated squall lines abstract using a three dimensional numerical cloud model we investigate the effects of vertical wind shear on squall line structure and evolution over a wide range of shear magnitudes depths and orientations relative to the line we find that the simulated squall lines are most sensitive to the magnitude of the component of shear perpendicular to the line and that we may reproduce much of the range of observed structures by varying this single parameter for weak shear a line of initially upright to downshear tilted short lived cells quickly tilts upshear producing a wide band of weaker cells extending behind the surface outflow boundary for moderate to strong shear the circulation remains upright to downshear tilted for longer periods of time with vigorous short lived cells confined to a relatively narrow band along the system s leading edge at later times however these systems may also weaken as the circulation tilts upshear for strong deep shears oriented obliquely to the line the squal

an observational and modeling study of the interaction of low level southwesterly flow with the olympic mountains during coast iop 4 abstract this paper presents an observational and modeling study of the three dimensional flow and precipitation around the olympic mountains of northwest washington state for a case of relatively steady south southwesterly flow this study utilized data from coast iop 4 the fourth intensive observing period during the coastal observation and simulation with topography field experiment that took place during 9 10 december 1993 one of the most important data sources was the noaa p 3 aircraft which provided flight level data reflectivity and doppler winds as it flew around the olympics features that were mapped successfully with the noaa p 3 included flow splitting around the windward pressure ridge strong southeasterlies to approximately 25 m s 1 northeast of the olympics caused by downgradient acceleration into the lee trough the rapid transition from strong southeasterlies to lighter easterlies 5 10 m s 1 in the strait of juan de fuca strong downslope flow and a hydraulic jump like transiti

pre weichselian quaternary glaciations of the british isles the netherlands norway and adjacent marine areas south of 68 n implications for long term ice sheet development in northern europe within this paper we review the pre weichselian glacial history of northern europe focussing on evidence from the british isles netherlands norway and adjacent marine areas that record the activity of the british bis and scandinavian sis ice sheets the objective of the paper is to examine the long term evolution of the two ice sheets in order to determine their level of synchronicity and their relationship to the plio pleistocene record of northern hemisphere glaciation geological evidence demonstrates striking long term similarities between the behaviour of the bis and sis with a step wise intensification in the glacial signal 1 first ice rafted debris ird input onto the continental margin at ca 2 7 2 6 ma and restricted glaciation prior to ca 1 1 ma 2 initiation of more lowland style glaciation from 1 1 ma 3 repeated shelf edge glaciations from 0 45 ma these steps coincide with a major intensification of the northern hemisphere climate signal at the beginning of the quaternary and the mid pleistocene transition temporal and spatial variabilities in the behaviour of different sectors of the bis and sis appear to reflect regional scale geographic latitude elevation climatic moisture temperature and glaciological deformable beds controls that modulate the build up of ice volume in the main ice accumulation areas relative to global climate forcing and its subsequent lateral expansion 2010 nerc

palaeohydrological characteristics and palaeogeographic reconstructions of incised valley fill systems insights from the namurian successions of the united kingdom and ireland namurian carboniferous eustatic fluctuations drove the incision and backfill of shelf crossing valley systems located in humid subequatorial regions which are now preserved in successions of the united kingdom and ireland the infills of these valleys archive the record of palaeoriver systems whose environmental hydrological and palaeogeographic characteristics remain unclear a synthesis of sedimentological data from fluvial strata of 18 namurian incised valley fills in the united kingdom and ireland is undertaken to elucidate the nature of their formative river systems and to refine regional palaeogeographic reconstructions quantitative analyses are performed of facies proportions of geometries of incised valley fills and related architectural elements and of the thickness of dune scale sets of cross strata reconstruction of the size of the drainage areas that fed these valleys is attempted based on two integrative approaches flow depth estimations from dune scale cross set thickness statistics and scaling relationships of incised valley fill dimensions derived from late quaternary examples the facies organization of these incised valley fills suggests that their formative palaeorivers were perennial and experienced generally low discharge variability consistent with their climatic context however observations of characteristically low variability in cross set thickness might reflect rapid flood recession perhaps in relation to sub catchments experiencing seasonal rainfall variations in facies characteristics including inferences of flow regime and cross set thickness distributions might reflect the control of catchment size on river hydrology the degree to which is considered in light of data from modern rivers palaeohydrological reconstructions indicate that depth estimations from cross set thickness contrast with observations of barform and channel fill thickness and projected thalweg depths exceed the depth of some valley fills limitations in data and interpretations and high bedform preservation are recognized as possible causes with consideration of uncertainties in the inference of catchment size the palaeogeography of the valley systems has been tentatively reconstructed by integrating existing provenance and sedimentological data the approaches illustrated in this work can be replicated to the study of palaeohydrological characteristics and palaeogeographic reconstructions of incised valley fills globally and through geological time

a statistical model of extreme storm rainfall a model of storm rainfall is developed for the central appalachian region of the united states the model represents the temporal occurrence of major storms and for a given storm the spatial distribution of storm rainfall spatial inhomogeneities of storm rainfall and temporal inhomogeneities of the storm occurrence process are explicitly represented the model is used for estimating recurrence intervals of extreme storms the parameter estimation procedure developed for the model is based on the substitution principle method of moments and requires data from a network of rain gages the model is applied to a 5000 mi2 12 950 km2 region in the valley and ridge province of virginia and west virginia

poisson s ratio values for rocks abstract compared to other basic mechanical properties of rocks poisson s ratio is an elastic constant of which the significance is generally underrated yet in rock mechanics there is a considerable number of diverse areas which require a prior knowledge or estimation of the value of poisson s ratio this paper examines the values and applications of poisson s ratio in rock mechanics following an historical account of the initial controversy whether it was a material constant or not the effects of poisson s ratio in the elastic deformation of materials intact rocks and rock masses are briefly reviewed also the reported values of poisson s ratio for some elements materials and minerals are compiled while typical ranges of values are presented for some rocks and granular soils finally poisson s ratio classifications are recommended for isotropic intact rocks

salt as a 3d element in structural modeling example from the central european basin system abstract based on a well constrained 3d structural model of the central european basin system 3d modeling has been carried out to understand the regional scale regularities between movements of the upper permian zechstein salt and the major post permian tectonic events the 3d reconstruction of the paleo thickness of upper permian salt at the end of the permian period demonstrates that areas of thickened upper permian salt correlate with the present day distribution of the largest salt structures within the central european basin system this spatial correlation implies that the distribution of salt thickness at the end of deposition partially controlled the structural style of the basin during post permian phases of salt tectonics moreover the results of 3d salt redistribution for post permian times indicate that the initiation of salt movements took place in the triassic the triassic extensional events triggered several phases of salt movements within the coeval depocenters of the central european basin system such as the glueckstadt graben the horn graben the norwegian danish basin the fjerritslev trough and the himmerland graben and the polish basin during the late jurassic early cretaceous extensional transtensional tectonic event the strongest salt movement occurred within the central graben the lower saxony basin and the pompeckj block the intensity of the late jurassic early cretaceous phase of salt tectonics is essentially declining from the marginal areas of the central european basin system towards the horn graben the glueckstadt graben and adjacent areas the late early cretaceous early late cretaceous is characterized by tectonic quiescence without strong salt movements over the entire study area the next regional phase of salt movements was triggered by late cretaceous early cenozoic inversion involving almost the entire central european basin system in terms of renewed salt movements inversion related thick skinned salt tectonics is observed along the nw se trending elbe fault system and the teisseyre tornquist zone where strongest compressional deformations were localized on the contrary a thin skinned character of salt movements was prevailing within the largest part of the north german basin post inversion cenozoic subsidence was also accompanied by salt activity related either to diapiric rise due to regional shortening and or to local roughly e w directed extension the cenozoic phase of salt movements was especially prominent within the marginal troughs of the glueckstadt graben

radar studies of heavy convective rainfall in mountainous terrain heavy rainfall topography storm motion and storm evolution are closely linked for four storms that produced catastrophic flooding along the front range of the rocky mountains and the east slope of the blue ridge mountains storms selected for detailed study in this paper are the rapidan storm of june 27 1995 the fort collins storm of july 28 1997 the buffalo creek storm of july 12 1996 and the monocacy storm of june 18 1996 the buffalo creek storm and the fort collins storm occurred in the front range of the rocky mountains in colorado the rapidan and monocacy storms occurred along the east slopes of the blue ridge of virginia and southern pennsylvania the four storms caused catastrophic flooding at drainage basin scales between 1 and 1000 km 2 the scale of flood response for these events imposes a need to characterize rainfall variability at very fine space scales and timescales of the order of 1 km spatial scale and 1 5 min timescale a fundamental issue for the hydrometeorology of extreme rainfall in mountainous terrain is whether anomalously large rainfall accumulations in orographic convection result from anomalously slow net storm motion anomalously large rainfall rates or both anomalous storm motion and processes resulting in catastrophic rainfall rates are examined for each of the four storms of particular importance for anomalous storm motion in orographic convection are interactions between the low level wind field and terrain features

mesoscale numerical study of two cases of long lived quasi stationary convective systems over eastern spain a set of mesoscale numerical simulations using the pennsylvania state university national center for atmospheric research model is used to investigate two cases of extreme precipitation over eastern spain both cases 3 4 november 1987 and 20 october 1982 were characterized by quasi stationary mesoscale convective systems that developed over the valencia region and lasted more than 30 and 12 h respectively rainfall totals in 24 h exceeded 800 mm on 3 4 november and 400 mm on 20 october at some localities of that region the first event occurred within a weak and very stagnant synoptic pattern under a persistent easterly northeasterly low level jet stream impinging on the valencian orography in contrast the second case involved a westwardmoving surface low driven by an upper level jet streak which evolved along the northern edge of an upperlevel cutoff low over north africa in both cases the mesoscale model forecast spatial details of the precipitation field reasonably accurately as well as capturing its long duration but underestimated the storm total precipitation model output fields suggest that the development of a surface mesolow by latent heat release as well as lee cyclogenesis induced by the atlas mountains could have played an important role in both events by providing low level convergence and enhanced upslope winds thus a factor separation technique is used to explore this issue for the event of 3 4 november 1987 latent heat is decisive for explaining the precipitation maximum over central valencia and the atlas orography induces rainfall enhancement over the same zone for the event of 20 october 1982 the latent heat release is again shown to be important whereas the atlas mountains orography factor appears to inhibit rainfall this is the first time that it has been documented that the atlas induced modulation of the surface pressure field is not a positive factor for heavy precipitations over eastern spain this exceptional case may be due to a negative interaction between the atlas mountains and the upper level dynamics and frontal forcing for this event

glacio seismotectonics ice sheets crustal deformation and seismicity abstract the last decade has witnessed a significant growth in our understanding of the past and continuing effects of ice sheets and glaciers on contemporary crustal deformation and seismicity this growth has been driven largely by the emergence of postglacial rebound models pgm constrained by new field observations that incorporate increasingly realistic rheological mechanical and glacial parameters in this paper we highlight some of these recent field based investigations and new pgms and examine their implications for understanding crustal deformation and seismicity during glaciation and following deglaciation the emerging glacial rebound models outlined in the paper support the view that both tectonic stresses and glacial rebound stresses are needed to explain the distribution and style of contemporary earthquake activity in former glaciated shields of eastern canada and fennoscandia however many of these models neglect important parameters such as topography lateral variations in lithospheric strength and tectonic strain built up during glaciation in glaciated mountainous terrains glacial erosion may directly modulate tectonic deformation by resetting the orogenic topography and thereby providing an additional compensatory uplift mechanism such effects are likely to be important both in tectonically active orogens and in the mountainous regions of glaciated shields in general the short term response to ice fluctuations is similar to the earth s response to fluctuations in water reservoirs with the subsequent increase or decrease in seismicity which depends on the pre existing stress state when the ice fluctuations occur on the spatial scale and magnitude of the late pleistocene glaciation and deglaciation however the viscoelastic response of the earth especially the mantle causes significant changes in crustal deformation and earthquake activity that is spatially extensive and temporally complex the regions of greatest ice thickness and the regions marginal to the late pleistocene ice sheets indicate the most dramatic evidence of earthquake faulting the mantle response to these large ice mass fluctuations and the change in mass between the oceans and land caused and continues to cause measureable crustal deformation at hundreds of kilometres from the ice margins for both tectonically active and cratonic regions palaeoseismic investigations of late pleistocene and holocene faults are an important tool in evaluating earthquake hazard the predicted response of the earth over this time however is very dependent on the model assumed for most regions far more carefully designed field observations are needed to constrain the existing rheological and ice models

three dimensional numerical modeling of slip rate variations on normal and thrust fault arrays during ice cap growth and melting 1 changes in the volumes of ice caps considerably alter the stress state of the lithosphere by generating a transient signal that is added to the tectonic background stress field these stress field changes in turn affect crustal deformation and in particular the slip behavior of existing faults here we use three dimensional finite element models to investigate how arrays of normal and thrust faults near a growing and subsequently melting ice cap are influenced in their slip evolution the results show that regardless of fault dip both types of faults experience a decrease in their slip rate during ice cap advance and an increase in their slip rate during ice cap retreat if they are located beneath the ice cap in contrast faults outside the ice cap that are loaded on their footwall or hanging wall only show the opposite pattern their slip rate increases during glacial loading and decreases during subsequent unloading if the load is located along strike of the fault that is at one of its tips the slip behavior of normal and thrust faults is different the normal fault shows a slip rate increase during unloading the thrust fault during loading our results explain the location and timing of deglaciation induced paleoearthquakes in scandinavia and the contrasting slip histories reported from normal faults in the basin and range province which are located at different positions relative to the former yellowstone ice cap more generally our findings imply that a uniform slip behavior of faults in formerly glaciated regions should not be expected

tunnel valleys concepts and controversies a review abstract although erosion of valleys by subglacial meltwater was first proposed more than 100 years ago the processes that produced these valleys under past ice sheets have remained a topic of vigorous debate the most commonly hypothesized mechanisms have included gradual formation by sediment deformation into the incipient valleys under steady state conditions and subsequent transport by meltwater to the ice margin time transgressive formation along a retreating ice margin by drainage of surface meltwater to the bed or release of impounded meltwater behind a marginal permafrost wedge probably catastrophically and rapid erosion during widespread catastrophic basal sheetflood events recent application of new and enhanced imaging techniques has led to the identification of many new tunnel valleys both on land and offshore throughout the regions glaciated during former ice ages in addition new advances in understanding of subglacial hydrology both from modelling and field instrumentation have helped to constrain the drainage of meltwater from past ice sheet beds this work elucidates the role of subglacial groundwater flow systems in evacuating meltwater from the bed but also shows that groundwater flow alone was not enough to maintain ice bed meltwater pore pressures below the level of ice flotation both modelling and field observations indicate that subglacial conduits oriented parallel to glacial flow lines reorganize groundwater flow systems into basins containing lateral flow toward conduits cut upward into the ice or downward into the bed because of the inability of groundwater flow to account for all the meltwater produced by basal melting other drainage mechanisms involving both non channelized and channelized meltwater flow have been proposed the notion of catastrophic drainage of impounded basal meltwater is still favored by many and the discovery of hundreds of subglacial lakes beneath the antarctic ice sheet and the likelihood of similar lakes beneath pleistocene ice sheets provides a source of water for those advocating catastrophic formation for tunnel valleys proponents of catastrophic drainage consider the valleys to be channels reflecting the width and perhaps depths of flows that formed them tunnel valleys produced by the scandinavian ice sheet have been described and mapped on land as well as on the sea bed valleys and networks of valleys some of which are totally buried have been linked to 3 or more glaciations tunnel valley networks from the last weichselian glaciation in denmark can be related to specific ice margins developed during ice retreat in north america most research has focused on tunnel valleys associated with ice margins formed by the last wisconsin glaciation along the southern margin of the laurentide ice sheet

response of salt structures to ice sheet loading implications for ice marginal and subglacial processes abstract during the past decades the effect of glacioisostatic adjustment has received much attention however the response of salt structures to ice sheet loading and unloading is poorly understood our study aims to test conceptual models of the interaction between ice sheet loading and salt structures by finite element modelling the results are discussed with regard to their implications for ice marginal and subglacial processes our models consist of 2d plane strain cross sections which represent simplified geological cross sections from the central european basin system the model layers represent i sedimentary rocks of elastoplastic rheology ii a viscoelastic diapir and layer of salt and iii an elastoplastic basement on top of the model a temporarily variable pressure simulates the advance and retreat of an ice sheet the durations of the individual loading phases were defined to resemble the durations of the pleistocene ice advances in northern central europe the geometry and rheology of the model layers and the magnitude spatial distribution and timing of ice sheet loading were systematically varied to detect the controlling factors all simulations indicate that salt structures respond to ice sheet loading an ice advance towards the diapir causes salt flow from the source layer below the ice sheet towards the diapir resulting in an uplift of up to 4 m the diapir continues to rise as long as the load is applied to the source layer but not to the crest of the diapir when the diapir is transgressed by the ice sheet the diapir is pushed down up to 36 m as long as load is applied to the crest of the diapir during and after ice unloading large parts of the displacement are compensated by a reversal of the salt flow plastic deformation of the overburden is restricted to the area immediately above the salt diapir the displacements after unloading range between 3 1 and 2 7 m larger displacements are observed in models with deep rooted diapirs thicker ice sheets longer duration of the loading phase thicker salt source layers and lower viscosity of the salt the rise or fall of diapirs triggered or amplified by ice sheet loading are likely to affect glacigenic deformation erosion and deposition above the diapir and within the rim synclines ice load induced uplift in front of an ice sheet will provide favourable conditions for the formation of push moraines for example by creating a topographic obstacle and inclining potential detachments subglacial subsidence of salt structures will enhance erosion by providing a preferential drainage pathway and fracturing of the overburden of the salt structure and thereby contribute to the incision of tunnel valleys however the resulting displacements are probably too low to have a marked effect on the advance or retreat pattern of the ice sheets

regional flood frequency analysis using extreme order statistics of the annual peak record a regional flood frequency model is developed for estimating recurrence intervals of extreme floods the regionalization procedure developed in this paper differs notably from the u s geological survey index flood method dalrymple 1960 in that a large quantile rather than the mean annual flood is used as the index flood based on a result from extreme value theory exceedances of the specified quantile are modeled by a generalized pareto distribution the generalized pareto distribution has two parameters a scale parameter and a shape parameter it is assumed that the shape parameter does not vary from basin to basin implying that annual peak distributions for all basins have the same upper tail thickness the scale parameter on the other hand not only varies from basin to basin but may also depend on covariate information such as drainage area or indicator functions for basin geology likelihood based inference procedures are developed for the regional flood frequency model the model is applied to extreme floods of the central appalachian region of the united states

representation of basin scale in flood peak distributions a lognormal cascade model is developed for representing basin scale in flood peak distributions the model is developed from the multiplicative cascade modeling framework developed by gupta and waymire 1990 for spatial hydrologic processes the lognormal cascade model has a simple parameterization of basin scale that can represent either simple scaling or multiscaling processes likelihood based statistical inference procedures are developed for parameter estimation and hypothesis testing for the lognormal cascade model the lognormal cascade model is used to examine scale properties of annual flood peaks from 104 stations in the central appalachian region of maryland and virginia drainage area for the basins ranges from 0 3 square miles 0 78 km2 to nearly 10 000 square miles 26 100 km2 the empirical results suggest two hypotheses concerning scaling properties of central appalachian flood peaks 1 the multiscaling hypothesis holds over the entire range of scales for this hypothesis some anomalous properties of flood peaks in small basins must be dealt with and 2 scaling properties of rainfall and the channel floodplain system impose a peak in variability of flood magnitudes for basins with drainage area between 10 and 100 square miles between 26 and 260 km2

slope of alluvial fans in humid regions of japan taiwan and the philippines abstract this study constructed a database for 690 alluvial fans in humid regions of japan taiwan and the philippines and analyzed their slopes and other morphometric parameters such as the area and relief ratio of the source area this type of comprehensive geomorphological research on alluvial fans in humid regions has been limited although numerous studies have dealt with fans in arid and semi arid regions semi conical depositional landforms larger than 2 km2 and steeper than 0 11 0 002 m m were selected as alluvial fans about 60 of the fans formed during the holocene and the rest 40 formed during the pleistocene mean fan slopes for both all the quaternary fans and holocene fans follow a lognormal frequency distribution the distribution also fits slopes of fans belonging to a certain areal range the area and relief ratio of the source area which correlate well with the fan slope also follow a lognormal distribution indicating the dimensions of fan basin systems vary gradually rather than abruptly these findings contrast with a previous notion that depositional landforms rarely have slopes of 0 5 0 009 to 1 5 0 026 and hence only semi conical landforms steeper than 1 5 should be called alluvial fans

palaeoglaciology of an ice sheet through a glacial cycle the european ice sheet through the weichselian abstract satellite images provide unique means of identifying large scale flow generated lineations produced by former ice sheets they can be interpreted to reconstruct the major elements which make up the integrated large scale structure of ice sheets ice divides ice streams interstream ridges ice shelves calving bays the evolving palaeoglaciological structure of the european ice sheet during its decay from the last glacial maximum lgm is reconstructed by reference to these components and in the context of a new map showing isochrons of retreat during the retreat phase in particular the time dependent dynamic evolution of the ice sheet and the pattern of ice stream development are reconstructed crossing lineations are widespread the older ones are suggested to have formed during molten bed phases of ice sheet growth and preserved by frozen bed conditions during the glacial maximum particularly in areas which lay during deglaciation beneath ice divides and inter ice stream ridges both areas of slow flow and possibly frozen bed conditions four phases of growth a1 to a4 and five phases of decay r1 to r5 are used to describe the major climatically and dynamically determined stages in the evolution of the ice sheet through the last glacial cycle the growth and decay patterns are quite different and associated with major shifts in the ice divide reflecting growth from the fennoscandian mountains and decay away from marine influenced margins these patterns were determined by the locations of nucleation areas spatial patterns of climate and calving at marine margins the prevalence of streaming within the retreating ice sheet suggests that the mean elevation of the ice sheet was lower than predicted from glaciological models which do not include streaming and that this might reconcile glaciological models and earth rheology models which infer paleao ice sheet thickness by inverting sea level data

scaling properties of canadian flood flows this study investigated the spatial scaling properties of canadian flood flows namely annual maximum mean 1 5 and 7 day flows using both the product moments pms and probability weighted moments pwms both approaches demonstrate that flood flows in climatic regions 1 pacific 2 south british columbia mountains 3 yukon and northern british columbia 6 northeastern forest 7 great lakes and st lawrence rivers 8 atlantic and 10 arctic tundra exhibit simple scaling with scaling exponent h close to 0 90 while flood flows in regions 4 prairie provinces 5 northwestern forest and 9 mackenzie does not with scaling exponent h close to 0 50 the plots of coefficient of variations of flood flows versus drainage area indicate that cv remains almost constant in regions 1 2 3 6 7 8 and 10 while it decreases as drainage area increases in regions 4 5 and 9 these results demonstrate that the index flood method is applicable in climatic regions 1 2 3 6 7 8 and 10 while it is not in climatic regions 4 5 and 9 the physical backgroud of the simple scaling of flood flows in most canadian climatic regions is that snowmelt or rain on snow runoff is a dominant flood generating mechanism across the country copyright 2008 john wiley sons ltd

scaling and physiographic controls on streamflow behaviour on the precambrian shield south central ontario summary relationships explaining streamflow behaviour in terms of drainage basin physiography greatly assist efforts to extrapolate streamflow metrics from gauged to ungauged basins in the same landscape the dorset environmental science centre desc has monitored streamflow from 22 small basins 3 4 190 5 ha on the precambrian shield in south central ontario in some cases since 1976 the basins exhibit regional coherence in their interannual response to precipitation however there is often a poor correlation between streamflow metrics from basins separated by as little as 1 km this study assesses whether inter basin variations in such metrics can be explained in terms of basin scale and physiography several characteristics annual maximum minimum and average flow exhibited simple scaling with basin area while magnitude range and timing of annual maximum daily runoff showed scaling behaviour consistent with the representative elementary area rea concept this rea behaviour is partly attributed to convergence of fractional coverage of the two dominant and hydrologically contrasting land cover types in the desc region with increasing basin size three principal components pcs explained 82 4 of the variation among basin physiographic properties and several runoff metrics magnitude and timing of annual minimum daily runoff mean number of days per year with 0 streamflow exhibited significant relationships with one or more pc significant relationships were obtained between basin quickflow qf production and the pcs on a seasonal and annual basis almost all of which were superior to simple area based relationships basin physiography influenced qf generation via its control on slope runoff water storage and hydrologic connectivity however this role was minimized during spring when qf production in response to large rain on snow events was relatively uniform across the desc basins the pc based relationships and inter seasonal changes in their form were consistent with previous research conducted at point slope and basin scales in the desc region and perceptions of key hydrological processes in these small basins may not have been as readily obtained from scaling studies using streamflow from larger basins this process understanding provides insights into scaling behaviour beyond those derived from simple scaling and rea analyses the physiography of the study area is representative of large portions of the precambrian shield such that basin streamflow behaviour could potentially be extended across much of south central ontario this would assist predictions of streamflow conditions at ungauged locations development and testing of hydrological models for this landscape and interpretation of inter basin and intra annual differences in hydrochemical behaviour on the southern precambrian shield

suppression of earthquakes by large continental ice sheets the interior regions of antarctica and greenland are aseismic no earthquake larger than body wave magnitude 4 5 5 0 is known for either except along coastal zones or continental shelves here i advance an explanation for this lack of seismic activity in terms of pressure effects produced by the continental ice sheets that mantle both continents

the sedimentary record and rates of quaternary vertical tectonic movements in nw poland abstract analysis based on drilling lithostratigraphic geophysical and geodetic data showed that the spatial differentiation pattern of the pleistocene cover displays a direct connection with the structural pattern of the permo mesozoic complex the main features of the pleistocene cover such as the thickness stratigraphic section facies variability and the shape of the sub quaternary surface are adapted to the distribution of local permo mesozoic tectonic elements salt tectonic folds grabens and singular blocks this is expressed by a reduction in the thickness and stratigraphic section of pleistocene sediments overlying uplifted tectonic elements in relation to those which were lowered facies variability within the pleistocene complex is in many places connected with the location of salt tectonic folds and this connection is manifested by the gradual disappearance of water laid series over salt anticlines the most intensive isostatically driven vertical displacements occurred during the cromerian holsteinian and eemian interglacial periods transformation of repeated levelling data allowed the velocity of recent vertical displacements between examined tectonic elements to be estimated at 0 3 2 0 mm yr and this is comparable to the velocity of pleistocene movements the pleistocene displacements between tectonic elements exerted a decisive influence on the development of their glaciogenic sedimentary cover

mesoscale convective systems in weakly forced large scale environments part i observations abstract during a 24 h period beginning 1200 utc 11 may 1982 a series of five mesoscale convective systems mcss developed within a weakly forced large scale environment analyses indicate that the large scale flow created a broad region of potential buoyant energy but owing to a restraining inversion and weak large scale upward motion convection was initiated only where lifting associated with mesoscale features was able to eliminate the inversion the series of mcss developed sequentially and moved eastward across the moist axis two of these systems had a large component of motion against the mean tropospheric flow and propagated in a direction nearly opposite to that of the traveling upper level disturbances each system produced an outflow of cold downdraft air that spread progressively farther south than that from the preceding system this description of the development and evolution of convection is very different from traditional ones wherein convection develops and moves more or less in pha

the surprising role of orography in the initiation of an isolated thunderstorm in southern england abstract many factors both mesoscale and larger scale often come together in order for a particular convective initiation to take place the authors describe a modeling study of a case from the convective storms initiation project csip in which a single thunderstorm formed behind a front in the southern united kingdom the key features of the case were a tongue of low level high w air associated with a forward sloping split front overrunning lower w air above a convergence line and a lid of high static stability air which the shower was initially constrained below but later broke through in this paper the authors analyze the initiation of the storm which can be traced back to a region of high ground dartmoor at around 0700 utc in more detail using model sensitivity studies with the met office unified model metum it is established that the convergence line was initially caused by roughness effects but had a significant thermal component later dartmoor had a key role in the developmen

numerical simulation of an intense squall line during 10 11 june 1985 pre storm part i model verification abstract a 24 h nested grid simulation of an intense squall line during the 1985 pre storm experiment is presented using an improved version of the pennsylvania state university national center for atmospheric research three dimensional mesoscale model although the model is initialized at 1200 utc 10 june 1985 with conventional meteorological observations it reproduces remarkably well many observed meso scale features that are analyzed from the high resolution network data these include 1 the generation of two areas of deep convection at the model initial time 2 the timing of the initiation of the squall line along a surface front 9 h into the model integration 3 the development of several convective bands at 2100 utc 4 the rapid intensification and rapid dissipation processes of the squall line as it entered and moved out of the network respectively 5 the generation of a presquall mesolow a squall induced mesohigh and a wake low as well as corresponding multiple surface convergence diverg

salt flow by aggrading and prograding overburdens the mechanisms responsible for segmentation of salt sheets and their emplacement into higher stratigraphic levels are not separable and act simultaneously three sets of centrifuge models with strongly planar anisotropic anisotropy the ratio between the effective viscosities in pure and simple shear ranging between 4 8 and 16 4 microlaminate overburdens are used to study the effect of aggradation and progradation on segmentation and emplacement of allochthonous salt sheets in the first set of models a tabular buoyant source layer was overlain by tabular anisotropic overburden simulating aggradation during centrifuging the underlying ductile source layer was segmented into individual wall like diapirs by the subsiding blocks formed due to extension and faulting of the overburden the extensional zone in these models started at the spreading edge free face of the model and migrated backwards in the second set of models a tabular buoyant source layer was overlain successively by wedges of anisotropic overburdens simulating progradation during centrifuging the buoyant layer was displaced from the back of the model where loading was higher towards the free face in the front of the model where overburden units were thinner overburden units extended at the back and the middle of the model while contractional structures dominated at the front where asymmetric diapirs formed overhangs that spread basinward to form salt sheets in the third set of models a wedge shaped buoyant source layer was overlain successively by wedges of anisotropic overburden simulating progradation the overburden wedge created a lateral pressure gradient ranging from 144 pa at the back of the model to 80 pa at the front when deformed in the centrifuge in these models as in the second set of models the underlying buoyant mass was displaced basinward by the subsiding thicker overburden units at the back of the model contractional structures dominated the deformation at the leading edge of the wedge comparison of model results suggests that progradation as in the second and third sets of models loads underlying salt differentially displaces it downdip and segments it as it segments at the back the salt flows laterally to areas of lower loading by intruding through the thinner overburden units and forming secondary salt sheets at the front on the other hand aggradation of uniform overburden segments a buoyant sheet into two dimensional salt walls or stocks as in the first set of models

numerical study of convection observed during the winter monsoon experiment using a mesoscale two dimensional model abstract a two dimensional version of the pennsylvania state university mesoscale model has been applied to winter monsoon experiment data in order to simulate the diurnally occurring convection observed over the south china sea the domain includes a representation of part of borneo as well as the sea so that the model can simulate the initiation of convection also included in the model are parameterizations of mesoscale ice phase and moisture processes and longwave and shortwave radiation with a diurnal cycle this allows use of the model to test the relative importance of various heating mechanisms to the stratiform cloud deck which typically occupies several hundred kilometers of the domain frank and cohen s cumulus parameterization scheme is employed to represent vital unresolved vertical transports in the convective area the major conclusions are ice phase processes are important in determining the level of maximum large scale heating and vertical motion because there is a strong anvil componen

wavelet analysis of the interannual variability in southern quebec streamflow the objectives of this study are to describe the local interannual variability in southern quebec canada streamflow based on wavelet analysis and to identify plausible climatic teleconnections that could explain these local variations scale averaged wavelet power spectra are used to simultaneously assess the interannual and spatial variability in 18 contiguous annual streamflow time series the span of available observations 1938 2000 allows depicting the variance for periods up to about 12 yr the most striking feature in the 2 3 yr band and in the 3 6 yr band the 6 12 yr band is dominated by white noise and is not considered further is a net distinction between the timing of the interannual variability in local western and eastern streamflows which may be linked to the local climatology this opens up the opportunity to construct two regional time series using principal component pc analysis then for each band linear relationships are sought between the regional streamflow and five selected climatic indices the pacific north america pna the north atlantic oscillation nao the northern hemisphere annular mode nam the baffin island west atlantic bwa and the sea surface temperature anomalies over the nino 3 region enso3 the correlation analysis revealed the presence of a change point in the streamflow time series as reported by others occurring around 1970 for example the west and east 2 3 yr bands are positively correlated to pna since 1970 which was not the case prior to that change point the proposed regional east west divide is particularly evident prior to 1970 with a negative nam correlation for the west and a positive nam and negative enso3 for the east the picture for the less energetic 3 6 yr band is mixed with alternating dominance of teleconnection patterns but the 1970 change point holds