the representation of convection in mesoscale models part i scheme fabrication and calibration abstract currently there is no adequate cumulus parameterization suitable for use in mesoscale models having horizontal resolutions between 5 and 50 kilometers based on the similarity of the temporal and spatial evolution of the vertical variances between a ccope supercell and a generic tropical squall line as explicitly simulated by the regional atmospheric modeling system developed at colorado state university a convective parameterization scheme is developed that represents microscale turbulence with a modified second order closure scheme and cumulus draft scale eddies with a convective adjustment scheme the microscale turbulence scheme is based upon the mellor and yamada 2 5 level closure modified to predict solely on w w and includes zeman and lumley s formulation for the buoyancy driven mixed layer to close the pressure term and the eddy transport term if deep convection is indicated the microscale turbulence scheme includes contributions from cumulus draft scale fluxes determined from a clo

an outline of the plate tectonics of china china is principally a part of the eurasian plate but the margins of the indian and philippine sea plates are involved in the himalayas and in the coastal range of taiwan respectively within the eurasian plate the cathaysian paleoplate is separated from the angaraian paleoplate by the junggar hegen suture which contains paleozoic ophiolites and rare blueschists the three microplates of the cathaysian paleoplate consist of precambrian cratons and or phanerozoic accretionary fold belts these coalesced precambrian cratons record at least six stages of intense orogeny before cratonization the paleozoic to cenozoic accretionary fold belts of china can be correlated with similar events now found in west pacific andean and atlantic type active continental margins ophiolites occupying many of these tectonic zones provide evidence for the age and igneous history of oceanic crust formed during the paleozoic to cenozoic the presence of blueschist in some of these chinese sutures reveals evidence of large scale subduction and tectonic exhumation during consolidation of the eurasian plate cenozoic collision of the eurasian and indian plates produced deformation and uplift of the himalayas strongly influencing the tectonics of western china in contrast mesozoic tertiary evolution of eastern china is typical basin range geology similar to that of the western united states which included development of deep sedimentary basins along with calc alkaline plutonic and volcanic activity associated with crustal thinning and high heat flow the complicated tectonic evolution of china is greatly illuminated by the presence of ophiolites and blueschists in proterozoic to tertiary convergent boundaries these petrotectonic assemblages provide evidence of an extremely mobile history of plate movement in china

lower permian paleomagnetism of the tarim block northwestern china we collected 262 samples at 39 sites in three thick lower permian sections along the northwestern margin of the tarim block the lower permian sections are basalts interbedded with limestones or sandstones or shallow marine limestones and sandstones alone all with biostratigraphic age control alternating field af and thermal demagnetization experiments remove small secondary components and reveal characteristic magnetizations reversed directions consistent with the kiaman reversed interval similar directions between basalts sandstones and limestones a positive fold test and apparent polar wander and polarity changes recorded in underlying devonian sediments all attest to the primary nature of the remanence two paleomagnetic poles one from the limestone section 65 1 n 162 5 e k 128 a95 4 1 n 11 sites and the other from the two basalt sections 54 5 n 172 3 e k 66 a95 4 0 n 21 sites differ primarily in colatitude 8 1 6 5 suggesting a difference in magnetization age permian paleomagnetic poles from tarim siberia north china and south china all differ significantly suggesting substantial post permian relative motions

plate tectonic history basin development and petroleum source rock deposition onshore china abstract china comprises a mosaic of distinct continental fragments separated by fold belts these fold belts are suture zones resulting from the accretion of various fragments formerly separated by intervening areas of oceanic crust the major sedimentary basins onshore china can be classified into four groups those in western china are flexural developing as a result of north south compression in contrast those in the east are extensional and related to development of the pacific oceanic margin in central china basins have a more problematic origin those of north central china ordos sichuan are flexural basins controlled by eastward directed thrusting along their western margin in contrast basins further south chuxiong shiwandashan are predominantly extensional and related to major strike slip movements by synthesizing basin stratigraphies across china in tectonostratigraphic terms and in particular comparing the nature and timing of unconformities it is possible to formulate a coherent model for the palaeoreconstruction of china we identify five major tectonostratigraphic breaks which equate with the collision of the following continental fragments tarim north china carboniferous permian south china block permian triassic qiantang late triassic early jurassic lhasa block late jurassic early cretaceous and india early tertiary prior to permian times the southern margin of eurasia ran approximately along the northern border of modern china the late carboniferous collision of tarim north china with eurasia resulted in the development of a flexural basin junggar and deposition of non marine clastics to the south of the suture shallow marine deposition continued in the late permian early triassic the progressive collision from east to west of the south china block with the north china block resulted in a change to fluvial lacutrine sedimentation across the entire north china tarim block open marine carbonate deposition in the north of the south china block passed southward into a deeper marine clastic sequence deposited in a backarc basin further south a subduction zone existed along the southeastern margin of the south china block in western china northward subduction throughout the triassic resulted in the development of the songban ganzi accretionary prism with retroarc thrusting resulting in flexure and the first development of the tarim basin oblique collision of the qiantang block in the late triassic along the east of the south china block resulted in east west directed thrusting which initiated the suchuan and ordos basins continued strike slip deformation along the south western margin of the south china block resulted in the development of basins with a significant extensional component such as chuxiong the collision of the qiantang block with the southern edge of the tarim basin early jurassic resulted in a renewed clastic influx in both the tarim and junggar basins along the eastern pacific margin a compressional arc and retroarc basin in the south passed northwards into an extensional arc system subduction rollback of the extensional arc initiated rifting in the late jurassic in the eren and songliao basins the late jurassic early cretaceous collision of the lhasa block in the west rejuvenated the thrust systems bordering the western basin and resulted in a renewed clastic influx in the southeast the compressional arc phase culminated in widespread thrusting and folding of early cretaceous age in the northeast extension continued with the progressive migration of the rift system southward with time the arrival of the indian block in the early tertiary rejuvenated the bounding thrust belts of all the western basins in the east the change in convergence of the pacific plate to a more westerly direction is marked by extension and widespread rifting along the entire length of eastern china throughout most of china mesozoic and cenozoic deposition occurred in predominantly non marine environments source rocks in such settings comprise principally mudstones deposited in lakes organic rich mudstones these can accumulate in both deep and shallow lakes in order to accumulate substantial volumes the lake must be significant in space and time in china lacustrine orms occur in both rift and flexural basins lacustrine orms deposited under humid climatic conditions are restricted to the period of maximum tectonic subsidence in the flexural basins of western china source rock deposition follows basin initiation by 20 30 ma in the extensional basins of eastern china source rock deposition takes place 5 15 ma after basin initiation by contrast semi arid and arid climate lacustrine orms whilst being best developed during the period of maximum tectonic subsidence occur at all stages in the basin history

palaeomagnetic constraints on the collision and rotation of north and south china the eastern half of china is dominated by the north china block ncb and south china block scb separated by a complex fold system that trends roughly east west interpretation of the geology of this fold belt has led to a variety of estimates of the age of amalgamation of these two blocks1 7 palaeomagnetic results are few and have also been subject to conflicting interpretations8 11 here we present our own palaeomagnetic results for late permian rocks for both the scb and ncb and summarize other relevant palaeomagnetic data by reinterpreting the polarity given in some previous studies we are able to synthesize the results for the widespread emeishan basalts of the scb and to suggest a new model for the collision and relative rotation of the two blocks

postglacial emergence of amund and ellef ringnes islands nunavut implications for the northwest sector of the innuitian ice sheet this paper presents relative sea level curves from amund and ellef ringnes islands northwest queen elizabeth islands these curves are of exponential form and record continuous ongoing holocene emergence although northwest ellef ringnes island is experiencing a late holocene transgression isobases drawn on postglacial shorelines rise south eastward towards an uplift centre in norwegian bay these suggest the ringnes islands occupied the northwest radius of the innuitian uplift which is congruent with glacial geological evidence suggesting parts of the ringnes islands were covered by the late wisconsinan innuitian ice sheet the isobases provide a provisional reconstruction of glacioisostatic recovery within the northwest innuitian uplift their pattern supports earlier reconstructions that maximum late wisconsinan ice thickness occurred across norwegian bay marking the position of an ice divide which is consistent with ice flow features on amund ringnes island they record the diminishing thickness of the innuitian ice sheet from norwegian bay to the arctic ocean the absence of an isobase embayment across the ringnes islands suggests a relatively uniform ice load across both islands and hassel and massey sounds parallel isobases across peary channel indicate this ice load extended beyond massey sound although their northward deflection suggests an increasing influence of the former

holocene delevelling of devon island arctic canada implications for ice sheet geometry and crustal response the raised beaches and deltas of devon island contain an abundance of dateable materials a large set of radiocarbon dates 228 154 of which are new are used to construct relative sea level curves and isobase maps for the island the best materials for this purpose are driftwood logs 61 dates and bowhead whale bones 74 dates from raised beaches and mollusc shells from marine limit deltas 20 dates or from altitudes close to marine limit 14 dates during the last glacial maximum the island is thought to have lain beneath the southeastern flank of the innuitian ice sheet the relative sea level history is congruent with that inferred ice configuration the island spans half the ice sheet width relative sea level curves are of simple exponential form except near the glacial limit where an early holocene emergence proceeded to a middle holocene lowstand below present sea level which was followed by submergence attending the passage of the crustal forebulge the response times of relative sea lev

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

last glacial maximum and deglaciation of devon island arctic canada support for an innuitian ice sheet abstract the extent and origin of quarternary glaciers in the queen elizabeth islands of arctic canada especially during the last glacial maximum lgm has been debated for well over a century no consensus has yet emerged and the spectrum of interpretations within the last decade is the broadest ever the glacial geology of devon island strongly supports the late wisconsinan innuitian ice sheet hypothesis during lgm the southeastern part of the queen elizabeth islands was covered by an ice sheet flowing from a centre or a divide centrally located in the archipelago another ice divide extended from the centre across devon island flow from the innuitian centre and convergent flow from devon island and probably also from cornwallis and bathurst islands sustained an ice stream in wellington channel ice was locally advancing to its lgm limit about 23 ka bp recession in the vicinity of the present coastline was underway by 10 ka bp and final ice remnants west of the present devon ice cap vanished about 8 ka bp the island bears the same two part landscape zonation as do other islands and peninsulas in the region these reflect a cold based core and warm based periphery at lgm

warm core vortex amplification over land abstract a convectively generated mesoscale vortex that was instrumental in initiating and organizing five successive mesoscale convective systems over a period of three days is documented two of these convective systems were especially intense and resulted in widespread heavy rain with localized flooding based upon radar and satellite data the detectable size of the vortex became much larger following the strong convective developments nearly tripling its initial diameter over its three day life cycle during nighttime when convection typically intensified within the vortex movement of the system tended to slow following dissipation of the convection in the morning the daytime movement accelerated cross sections of potential vorticity taken through the vortex center clearly show a maximum at midlevels and a well defined minimum directly above the vortex and the potential vorticity maximum were essentially colocated and the system was nearly axisymmetric in the vertical over the three day life

deciphering patterns of postglacial sea level at the junction of the laurentide and innuitian ice sheets western canadian high arctic abstract recent sampling of deglacial and postglacial raised marine sediments across melville and eglinton islands in the western canadian high arctic yielded over 200 new radiocarbon dates on molluscs driftwood and other organic materials from this database eight relative sea level curves and an isobase map for the 9 5 cal ka bp shoreline were constructed the forms chronology and pattern of the relative sea level curves across the study area reflect the complex glacial history of this region including the asynchronous retreat of the formerly coalescent laurentide and innuitian ice sheets zone i relative sea level curves which show continuous emergence to present were observed in areas closer to greater last glacial maximum ice sheet loading at more distal sites transitional zone i ii curves display emergence followed by submergence in the mid to late holocene still ongoing related to forebulge migration and collapse an independent record of late holocene submergence is provided by radiocarbon dated driftwood which is accumulating at modern sea level due to re deposition during transgression geomorphic evidence of submergence at the modern coastline is widespread but does not distinguish areas that experienced a late holocene lowstand and subsequent transgression from those that are currently at their lowstand of special interest are the relative sea level histories of two areas that experienced earlier deglaciation by the laurentide ice sheet while remaining in the peripheral depression of the more stable and adjacent innuitian ice sheet the flat topped relative sea level curves from these sites appear to record unusually slow rates of glacioisostatic emergence for 1500 years immediately following deglaciation the relative sea level data presented in this paper provide important comparisons for sea level models which have been shown to fit poorly with previously published data from this region

ice age paleotopography a gravitationally self consistent theory of postglacial relative sea level change is used to infer the variation of surface ice and water cover since the last glacial maximum lgm the results show that lgm ice volume was approximately 35 percent lower than suggested by the climap reconstruction and the maximum heights of the main laurentian and fennoscandian ice complexes are inferred to have been commensurately lower with respect to sea level use of these ice age boundary conditions in atmospheric general circulation models will yield climates that differ significantly from those previously inferred on the basis of the climap data set

the relationship of surface pressure features to the precipitation and airflow structure of an intense midlatitude squall line abstract observations from the oklahoma kansas preliminary regional experiment for storm central ok pre storm have been used to document the surface pressure features accompanying an intense midlatitude squall line with trailing stratiform precipitation three well known features are observed a pre squall mesolow a squall mesohigh and a wake low particular attention is given to the wake low its life cycle and association with the trailing stratiform portion of the squall line during the formative stage the pressure field to the rear of the squall line mesohigh is relatively flat with only weak stratiform precipitation present as the squall line enters the developing to mature stages a pronounced wake low appears at the back edge of the surface stratiform precipitation area the squall line at this time is characterized by a strong rear inflow jet descending from the upper troposphere as far as 500 km behind the leading convective line to the lower troposphere just behind the line the trailin

late paleozoic polar wander path for the tarim platform and its tectonic significance abstract stepwise thermal and a f demagnetizations have been carried out on 518 samples 47 sites from the sishichang section across the akesu area in the tarim basin the results lead to a discussion on some problems concerning the tectonic history of the tarim platform and adjacent blocks during the late paleozoic from the late carboniferous until the early permian the tarim platform collided with the kazakhstan block siberian platform and russian platform no large displacements have occurred between these blocks since the mesozoic however the permian pole position of the tarim platform obviously differs from that for the sino korea platform the difference in paleolatitude between the tarim and sino korea platforms in the permian was about 10 their orientations were also different the paleomagnetic result is in contrast to the geologically accepted idea that the two platforms in question occur as a whole in the late paleozoic

upscale effects of deep convection during the north american monsoon abstractthe ability of deep monsoon convection to influence the larger scale circulation over north america is investigated for a 6 day long case study during the 2006 north american monsoon results from rossby wave ray tracing and numerical simulations using the advanced research weather research and forecasting model indicate that north american monsoon convection provides a source region for stationary rossby waves two wave trains are seen in the numerical model simulations with behaviors that agree well with expectations from theory and ray tracing the shorter and faster moving wave train moves eastward from the source region in mexico and reaches the western atlantic within 4 days the longer and slower moving wave train travels northeastward and reaches the coastal new england region within 6 days an upstream tail of anticyclonic vorticity extends westward from the source region into the central pacific ocean the monsoon convection appears to help cut off the low level anticyclonic flow by deve

continental growth of northwest china the northwest corner of china is the most interior part of central asia and includes parts of the siberian tarim and kazakhstan plates where the junggar and tarim basins are separated by the east west trending tianshan range a preliminary terrane map divides the area into thirteen separate areas which are classified into four types l continental 2 oceanic crust 3 island arc 4 composite the boundaries for these terranes are faults that have been previously defined either by geologic mapping or holocene activity passive consolidation of the southern margin of paleo asia is marked by accretion and subduction of the paleo tethys oceanic basins and by development of volcanic arcs paleomagnetic data indicate that the major plates and associated smaller terranes did not reach final consolidation until the permian or later the stratigraphic record reveals development of intracontinental basins in the late carboniferous followed by the pan asian thermal event that gave rise to widespread intrusion of a type granites of late paleozoic age the frontal collision of india along the southern border of asia in the paleocene reactivated nearly all of the older major strike slip and thrust faults formed during the late paleozoic consolidation of paleo asia the complex nature of the continental growth of central asia has produced and destroyed many varieties of sutures and reconstruction of the original plate and terrane configurations therefore is enigmatic

a numerical study of the genesis of extratropical convective mesovortices part i evolution and dynamics abstract the purpose of this study is to understand the genesis of extratropical convective mesovortices and the large scale environmental features that influence the vortex formation a hypothesis is proposed that mesovortices form in the stratiform rain regions of mesoscale convective systems mcss due to the reduction of static stability that reduces the effective local rossby radius in such regions a conceptual model of the mesoscale convective cyclogenesis is introduced which describes the three stages of the mesovortex formation a modified version of the pennsylvania state university national center for atmospheric research three dimensional hydrostatic mesoscale model is used to simulate mesovortex genesis in analytically generated pre mcs large scale environments the model simultaneously incorporates parameterized convection and a grid resolvable convective scheme containing the effects of hydrostatic water loading condensation evaporation freezing melting and sublimation a control si

the use of cloud resolving simulations of mesoscale convective systems to build a mesoscale parameterization scheme abstract a method is described for parameterizing thermodynamic forcing by the mesoscale updrafts and downdrafts of mesoscale convective systems mcss in models with resolution too coarse to resolve these drafts the parameterization contains improvements over previous schemes including a more sophisticated convective driver and inclusion of the vertical distribution of various physical processes obtained through conditional sampling of two cloud resolving mcs simulations the mesoscale parameterization is tied to a version of the arakawa schubert convective parameterization scheme that is modified to employ a prognostic closure the parameterized arakawa schubert cumulus convection provides condensed water ice and water vapor which drives the parameterization for the large scale effects of mesoscale circulations associated with the convection in the mesoscale parameterization determining thermodynamic forcing of the large scale depends on knowing the vertically integrated values and the vertical d

absolute reconstructions of the paleozoic oceans abstract the orientation of three intraplate magmatic belts the mongolian from 130 to 280 m y south siberian from 320 to 400 m y and baltic from 365 to 400 m y belts which can be considered as hot spot tracks are used together with apparent paleomagnetic pole wander paths to reconstruct true motions of continents during paleozoic times the reconstructions obtained show that the old late precambrian pangea continued to exist in the early paleozoic with an inner arrangement of constituent continents strongly different from that of the late paleozoic pangea the continents were constantly located in the eastern hemisphere only the western hemisphere was occupied by the paleo pacific oceans four oceans existed in paleozoic times between the continents in the eastern hemisphere 1 the iapetus which originated in the late precambrian and closed before devonian times 400 m y 2 the asiatic paleo ocean which originated in the late precambrian and closed 450 m y ago 3 the uralian paleo ocean which opened around 500 m y ago and closed in the latest permian 240 230 m y 4 the paleo tethys which opened in the ordovician 480 450 m y and became the mesozoic tethys life duration of the oceans was 200 400 m y the main trend in the earth s evolution during the paleozoic was a break up of the old precambrian supercontinent and construction of the new late paleozoic pangea

the postglacial relative sea level lowstand in newfoundland relative sea level in coastal regions of newfoundland fell from late glacial maximum levels to postglacial minima in several phases i an early period of high relative sea level when late wisconsinan ice was at the coast and discharging meltwater plumes into the ocean ii a period of rapidly falling relative sea level during which glaciers retreated inland and iii a period without glacier ice during which relative sea level continued to fall but at decreasing rates falling relative sea level caused fluvial incision of glacial deposits in some coastal embayments and culminated with the construction of lowstand marine deltas these deltas were submerged during the subsequent holocene transgression seismic reflection data from selected deltas show that they comprise wedges of sediment with prograded seaward dipping foreset style internal reflections the depth of the relative sea level lowstand varies spatially and it was diachronous it occurred relatively early and deep in peripheral regio

revision of the nw laurentide ice sheet implications for paleoclimate the northeast extremity of beringia and arctic ocean sedimentation abstract for the past half century reconstructions of north american ice cover during the last glacial maximum have shown ice free land distal to the laurentide ice sheet primarily on melville and banks islands in the western canadian arctic archipelago both islands reputedly preserve at the surface multiple laurentide till sheets together with associated marine and lacustrine deposits recording as many as three pre late wisconsinan glaciations the northwest corner of banks island was purportedly never glaciated and is trimmed by the oldest and most extensive glaciation banks glaciation considered to be of matuyama age 780 ka bp inside the limit of banks glaciation younger till sheets are ascribed to the thomsen glaciation pre sangamonian and the amundsen glaciation early wisconsinan stade the view that the western canadian arctic archipelago remained largely ice free during the late wisconsinan is reinforced by a recent report of two woolly mammoth fragments collected on banks and melville islands both dated to 22 ka bp these dates imply that these islands constitute the northeast extremity of beringia a fundamental revision of this model is now warranted based on widespread fieldwork across the adjacent coastlines of banks and melville islands including new dating of glacial and marine landforms and sediments on dundas peninsula southern melville island ams 14 c dates on ice transported marine molluscs within the most extensive laurentide till yield ages of 25 49 ka bp these dates require that late wisconsinan ice advanced northwestward from visount melville sound excavating fauna spanning marine isotope stage 3 laurentide ice that crossed dundas peninsula 300 m asl coalesced with melville island ice occupying liddon gulf coalescent laurentide and melville ice continued to advance westward through m clure strait depositing granite erratics at 235 m asl that require grounded ice in m clure strait as do streamlined bedforms on the channel floor deglaciation is recorded by widespread meltwater channels that show both the initial separation of laurentide and melvile ice and the successive retreat of laurentide ice southward across dundas peninsula into viscount melville sound sedimentation from these channels deposited deltas marking deglacial marine limit forty dates on shells collected from associated glaciomarine rhythmites record near synchronous ice retreat from m clure strait and dundas peninsula to north central victoria island 11 5 ka bp along the adjacent coast of banks island deglacial shorelines also record the retreat of laurentide ice both eastward through m clure strait and southward into the island s interior the elevation and age 11 5 ka bp of deglacial marine limit there is fully compatible with the record of ice retreat on melville island the last retreat of ice from mercy bay northern banks island previously assigned to northward retreat into m clure strait during the early wisconsinan is contradicted by geomorphic evidence for southward retreat into the island s interior during the late wisconsinan this revision of the pattern and age of ice retreat across northern banks island results in a significant simplification of the previous quaternary model our observations support the amalgamation of multiple till sheets previously assigned to at least three pre late wisconsinan glaciations into the late wisconsinan this revision also removes their formally named marine transgressions and proglacial lakes for which evidence is lacking erratics were also widely observed armouring meltwater channels originating on the previously proposed never glaciated landscape an extensive late wisconsinan laurentide ice sheet across the western canadian arctic is compatible with similar evidence for extensive laurentide ice entering the richardson mountains yukon farther south and with the innuitian ice sheet to the north widespread late wisconsinan ice in a region previously thought to be too arid to sustain it has important implications for paleoclimate ice sheet modelling arctic ocean ice and sediment delivery and clarifying the northeast limit of beringia

the laurentide and innuitian ice sheets during the last glacial maximum the late wisconsinan advance of the laurentide ice sheet started from a middle wisconsinan interstadial minimum 27 30 14 c ka bp when the ice margin approximately followed the boundary of the canadian shield ice extent in the cordillera and in the high arctic at that time was probably similar to present ice advanced to its late wisconsinan stage 2 limit in the northwest south and northeast about 23 24 14 c ka bp and in the southwest and far north about 20 21 14 c ka bp in comparison to some previous reconstructions of ice extent our current reconstruction has substantially more late wisconsinan ice in the high arctic where an innuitian ice sheet is generally acknowledged to have existed in the atlantic provinces where ice is now thought to have extended to the continental shelf edge in most places and on eastern baffin island where ice probably extended to the fiord mouths rather than to the fiord heads around most of the ice margin the late wisconsinan maximum ice extent either exceeded the extent of earlier wisconsinan advances or it was similar to the early wisconsinan advance ice marginal recession prior to 14 14 ck a bp occurred mainly in deep water and along the southern terrestrial fringe however heinrich event 1 probably drew down the entire central ice surface at 14 5 14 c ka bp sufficiently to displace the labrador sector outflow centre 900 km eastward from the coast of hudson bay the onset of substantial ice marginal recession occurred about 14 14 c ka bp in the northwest southwest and south but not until about 10 11 14 c ka bp in the northeast and in the high arctic thus the period of maximum ice extent in north america generally encompasses the interval from b24 21 to 14 14 c ka bp or considerably longer than the duration of the lgm defined as occurring during a period of low global sea level as well as during a time of relative climate stability b18 14 c ka bp the interval of advance of much of the laurentide ice sheet to its maximum extent between b27 14 c ka bp and b24 14 c ka bp coincides with a suggested interval of rapid fall in global sea level to near lgmlevels r 2001 elsevier science ltd all rights reserved

out of the woods driftwood insights into holocene pan arctic sea ice dynamics the collation of 913 driftwood samples from across the western arctic with spatiotemporal distribution and available provenance data enabled the production of a high resolution proxy based reconstruction of holocene arctic ocean surface current and sea ice dynamics regionally bounded driftwood based sea ice reconstructions studies suggest spatiotemporally complex past arctic sea ice extent and movement however a large scale compilation of holocene arctic driftwood has not previously been developed sparse driftwood in the early holocene 8 2 cal ka b p deglacial period was followed by increased driftwood deposition in the warmer mid holocene 8 2 4 2 cal ka b p characterized by an enhanced transpolar drift tpd 7 cal ka b p leading to sea ice loss through the fram strait driftwood incursion peaks show spatial e w progression from the eurasian archipelagos to greenland and the canadian arctic archipelago suggesting a progressive shift in the orientation of the tpd on centennial millennial time scales and intermediate phases in the arctic oscillation late holocene cooling 4 2 cal ka b p is indicated by increased influx of probably north american picea via a strengthened beaufort gyre bg which enhanced sea ice recirculation starting in the western arctic and progressing eastward in recent millennia 2 cal ka b p a more variable driftwood record alternates between bg and tpd dominance on centennial time scales to further constrain a spatiotemporal reconstruction of variations in holocene ocean current and sea ice dynamics a more definitive determination of driftwood provenance is recommended to build upon the current framework such as through radiogenic isotope tracing and adna analysis

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

the innuitian ice sheet configuration dynamics and chronology abstract portrayal of north american ice cover during the last glacial maximum is dominated by the laurentide ice sheet leaving little detail for the adjacent innuitian ice sheet iis four decades of geological fieldwork across the queen elizabeth islands now warrant specific treatment of the iis including its chronology configuration dynamics and retreat this reconstruction is relevant to the sedimentary history of the arctic ocean and to high latitude climate forcing the iis was composed of both an alpine and lowland sector the advance of the alpine sector occurred as recently as 19 14 c ka bp geological evidence configures outflow from alpine and lowland divides that produced several palaeo ice streams one extending northwestward across the canadian arctic archipelago to the polar continental shelf retreat of the iis commenced along its southwest margin 11 6 14 c ka bp however most of the ice sheet remained on the continental shelf during the younger dryas by 10 14 c ka bp marine based ice experienced widespread calving through the western and central archipelago in response to holocene warming and ongoing eustatic sea level rise the sea penetrated the eastern archipelago by 8 5 14 c ka bp gutting the alpine sector of the iis regional isobases record the glacioisostatic signature of the ice sheet and are congruent with the primary geological evidence the delayed buildup of the iis was out of phase with the growth of the laurentide ice sheet that occasioned climatic and glacio eustatic forcing in the innuitian region recent modelling experiments reinforce the hypothesis that growth of the laurentide ice sheet culminated in a split jet stream that temporarily favoured augmented precipitation and growth of the iis

structure and tectonic evolution of the tongbai dabie range in the east qinling collisional belt china recent work demonstrates that the tongbai dabie range which is considered to be the eastern segment of the important qinling belt in central china shows ample evidence of the collisional nature of this orogenic zone it is characterised by large thrust decollement structures with at least 140 km of horizontal displacement and it includes a melange nappe overthrust continental crust underthrust continental crust a marine nonmarine molasse formation and a foreland fold thrust belt its interpreted tectonic evolution can be subdivided into four main periods 1 ocean continent north dipping subduction during the silurian early devonian 2 continental collision in the late devonian 3 intracontinental subduction and large scale shallow crustal deformation beginning in the middle carboniferous and 4 upwarping and slicing by huge e w left lateral strike slip faults after the late jurassic and before the cenozoic right lateral movements on the faults which bound this belt

remagnetization and tectonic rotation of upper precambrian and lower paleozoic strata from the desert range southern nevada in the desert range of southern nevada miogeoclinal sedimentary rocks mostly shallow water limestones of latest precambrian through early ordovician age yield three components of magnetization having different blocking temperature spectra 1 a low blocking temperature component near the direction of the present axial dipole field 2 an intermediate blocking temperature component with northerly declination and inclination 60 and 3 a characteristic component with southeasterly declination and inclination 20 combinations of alternating field and thermal demagnetization indicate that the intermediate and characteristic components reside in magnetite the intermediate magnetization probably reflects a viscous partial thermoremanent magnetization vptrm imposed between the late cretaceous and mid cenozoic it was probably acquired when the strata were dipping slightly eastward the characteristic magnetization is probably a vptrm imposed during regional uplift in the late permian the degree of heating required to have destroyed any primary magnetization is consistent with the conodont color alteration index observed in the ordovician rocks additionally the characteristic magnetization in those rocks is younger than bedding disruption caused by major late stylolitization red purple mudstones from the middle member of the wood canyon formation in which a directionally similar characteristic magnetization resides in fine grained hematite also appear to have been remagnetized in these rocks the remagnetization probably reflects partial recrystallization as the blocking temperatures are too high to have been reset by burial heating the sampled sections have undergone relative tectonic rotation about a vertical axis consistent with late tertiary oroflexural bending that had been proposed on independent geologic evidence the characteristic magnetization probably provides a reliable estimate of the magnitudes of the vertical axis rotations as the regional geology suggests the desert range strata were essentially horizontal throughout the paleozoic the total observed relative rotation is 44 5 representing absolute counterclockwise rotation 27 4 of the northern part of the desert range and absolute clockwise rotation 17 5 of the southern part the only unit in the desert range sequence that may retain a primary magnetization is the late precambrian rainstorm member of the johnnie formation the characteristic magnetization of this unit exhibits two polarities and probably resides in specular hematite after correction for 18 of counterclockwise rotation the resulting pole 5 n 151 e is near other late hadrynian poles from north america

postglacial induced surface motion and gravity in laurentia for uniform mantle with power law rheology and ambient tectonic stress abstract previous investigations of postglacial sea levels around laurentia in a non linear earth without ambient stress found that non linear uniform mantle models cannot explain the relative sea level data around the ice margin in this study a 3d finite element model of postglacial readjustment is used to calculate the earth s response due to realistic ice and eustatic water loads on stratified mantle with non linear rheology and ambient tectonic shear stress by varying the creep parameter a and the ambient stress level in a uniform mantle it is found that the combination a around 3 10 35 pa 3 s 1 and ambient stress level around 10 mpa is able to explain the sea level data both outside and inside the laurentian ice margin although for certain sites inside a slightly thicker ice is required to improve the fit to the data other geophysical and geodetic observables namely uplift rate horizontal velocity free air gravity and the rate of change of gravity have also been calculated for this model

palaeomagnetism and palaeogeography of mongolia in the cretaceous permian and carboniferous preliminary data abstract the paper reports on the results of palaeomagnetic stability tests of oriented samples of lithologically different types of cretaceous permian and carboniferous rocks from northern and southern mongolia the permian andesites and tuffites from three localities barun buren tel tin gol and chulut tsagan del have yielded interesting results groups of normally and reversely polarized andesite tuffs were found even within a single outcrop by means of thermal field demagnetization and multicomponent analysis of the magnetization with a view to the number of samples 177 suitable for analysis and the number of localities 9 the reported palaeomagnetic data should be considered as preliminary the interpreted results indicate a different palaeogeographic evolution of northern and southern mongolia relative to the siberian platform and north china in the permian and carboniferous on the other hand similar apparent polar wander paths for north china lin et al 1985 and the studied regions of northern and southern mongolia indicate similar palaeogeographic evolution in the permian to carboniferous

late quaternary relative sea level change in the western gulf of maine evidence for a migrating glacial forebulge new radiocarbon dated cores obtained by vibracorers in the western gulf of maine confirm that a short lived relative sea level lowstand of 55 m occurred at 11 10 5 ka these cores and younger salt marsh data also reveal that rates of transgression varied throughout the holocene probably due to local variations in glacial isostasy the isostatic component is resolved by subtracting published approximations of eustatic sea level from our well determined observations of local relative sea level a large peak in the isostatic curve coincides with the lowstand and is interpreted as a forebulge 20 25 m in amplitude forebulge migration is estimated at 7 11 km 100 yr based on the timing of lowstands across the region

numerical simulation of the meso β scale structure and evolution of the 1977 johnstown flood part ii inertially stable warm core vortex and the mesoscale convective complex abstract a mesoscale warm core vortex associated with the mesoscale convective complex mcc that produced the 1977 johnstown flood is examined using a three dimensional nested grid model simulation of the flood episode in the simulation the vortex plays a key role in determining the evolution of the mcc a squall line and the distribution of heavy precipitation the vortex has a space scale of 100 200 km in diameter and a time scale of more than 18 hours its low pressure center extends from the midtroposphere down to the surface and its maximum vorticity occurs between 850 and 700 mb a pool of cool moist downdraft air develops in the surface to the 850 mb layer beneath the warm core while a cold dome forms in the vicinity of the tropopause above the warm core following forcing from repeated deep convection prior to model initial time the vortex is initiated by mesoscale ascent associated with a traveling meso scale wave genesis takes place in a nearly saturated slightly conditionally unstabl

isotopic studies bearing on the tectonics of the west junggar region xinjiang china isotopic investigations from the hercynian age fold belt between the kazakhstan and siberian cratons in the west junggar region determine the timing of tectonic evolution and the petrogenesis of the granitic rocks of the region sphene from the leucogabbro phase of the tangbale ophiolite melange the oldest member of the ophiolite sequences in the fold belt yields an isotopic pb pb age of 523 2 7 2 ma zircon from a postcollision alkali granite yields slightly discordant isotopic u pb ages that indicate magma crystallization at 321 4 6 7 ma dating it in the lower carboniferous period radiometric dating thus documents a time span of circa 200 ma for igneous activity in the area petrogenetic studies were made to test whether precambrian crustal rocks might underlie the junggar sedimentary basin initial lead isotope ratios determined from potassium feldspars from five alkali granites show clear affinity with ratios from mid ocean ridge basalts in pb isotope correlation diagrams sm nd data from sphene and apatite from one of the granites yield an initial end t 6 1 the granite sources are depleted mantle rocks of oceanic affinity that show no involvement of recycled aged granitic crustal rocks

the late quaternary history of greely fiord and its tributaries west central ellesmere island moraines and meltwater channels mark the limit of the last glaciation that interfingered with the sea around the perimeter of greely fiord and its tributaries the extent of this ice advance was dictated predominantly by its proximity to the sea consequently the large tidewater glaciers at the fiord heads today were so constrained by calving that they advanced only 5 10 km similarly grounding line deposits from widespread plateau ice caps also terminate just below marine limit the most extensive outlet glaciers which advanced 20 35 km beyond present margins are simply those that had access to the most extensive terrain above marine limit i e the northwest margin of the agassiz ice cap forty one new 14c dates are presented the onset of the last ice advance must predate marine shells collected from sediments overlying a former grounding line when sea level was 122 m higher than present at this site the lowermost shells collected from glaciomarine silts dated 38 070 410 bp whereas a surface s

a subtropical oceanic mesoscale convective vortex observed during sowmex timrex abstractthis study examines a subtropical oceanic mesoscale convective vortex mcv that occurred from 1800 utc 4 june to 1200 utc 6 june 2008 during intensive observing period iop 6 of the southwest monsoon experiment sowmex and the terrain influenced monsoon rainfall experiment timrex a dissipating mesoscale convective system reorganized within a nearly barotropic vorticity strip which formed as a southwesterly low level jet developed to the south of subsiding easterly flow over the southern taiwan strait a cyclonic circulation was revealed on the northern edge of the mesoscale rainband with a horizontal scale of 200 km an inner subvortex on a scale of 25 30 km with maximum shear vorticity of 3 10 3 s 1 was embedded in the stronger convection the vortex relative southerly flow helped create local potential instability favorable for downshear convection enhancement strong low level convergence suggests that stretching occurred within the mcv higher e air associated with significant pot

a numerical investigation of a convectively generated inertially stable extratropical warm core mesovortex over land part i structure and evolution abstract a 36 h nested grid numerical simulation of the life cycle of a convectively generated inertially stable warm core mesovortex is presented the vortex evolved from a mesoscale convective complex that developed from a squall line over oklahoma during 7 8 july 1982 a modified version of the pennsylvania state university national center for atmospheric research mesoscale hydrostatic model with a fine mesh grid resolution of 25 km is utilized for this study the model simultaneously incorporates parameterized convection and a grid resolved convective scheme containing the effects of hydrostatic water loading condensation evaporation freezing melting and sublimation genesis intensification and maintenance of a low to midtropospheric closed meso scale cyclone as well as the associated surface pressure perturbations the evolution of moist convection and the distribution and magnitude of total rainfall are simulated by the model similarly the observed amplification of a 700 mb meso sc

new paleomagnetic results from northern china collision and suturing with siberia and kazakhstan abstract we report new results from our paleomagnetic studies of the inner mongolia autonomous region in northeastern china and the xinjiang autonomous region in northwestern china primary magnetizations are isolated in tertiary cretaceous late jurassic and late permian rocks and secondary components of magnetization of late jurassic and recent ages are seen in strata of inner mongolia western junggar basin and part of the tarim block suffered widespread complete tectono thermal remagnetization at about 280 ma permian the paleomagnetic evidence suggests that the sampled areas in inner mongolia have been part of the north china block at least since late permian time and the junggar block collided with the tarim block by late permian time our own paleomagnetic results together with available data from other parts of eastern eurasia suggest a tectonic model in which kazakhstan europe and siberia collided with each other and formed the europe siberia kazakhstan plate eur sib kaz in late permian time to the east mongolia outer mongolia inner mongolia and the north china block were also wedged together forming the mongolia north china plate mon nc by this time these two composite continental plates were not a stable unit in the late permian the geometrical relationship of the paleomagnetic poles for these two plates suggests that collision initially occurred in the late permian near the western end 50 n 75 e of the southern siberian fold belt and progressed eastward as the mon nc plate rotated and clockwise about 117 relative to the eur sib kaz plate during the early mesozoic suturing and rotation were probably complete by the late jurassic significant relative motion between the tarim and siberia blocks continued from early triassic to late jurassic as tarim moved northeastward 1400 km relative to siberia

the chemical development of a hypersaline coastal basin in the high arctic we investigated a hypersaline seasonally isolated marine basin simb in the canadian high arctic to elucidate the role of brine rejection tidal forcing and groundwater input over the formation of hypersalinity analyses of physical parameters and seasonal sampling of ionic and isotopic composition were carried out on a coastal basin near shellabear point melville island northwest territories 75 n 113 w observations reveal daily and seasonal variability in the water column due to a seasonal tidal connection during the ice free season which lasts substantially longer than the period of freshwater inflow from the catchment an ice formation model of the volume of brine rejected from surface ice formed from marine water indicates that rapid saline enrichment of the basin due to ice formation is possible from tidally replenished marine water and that the current hypersalinity may have formed in less than a decade modeled isotopic composition of brines are consistent with observations and provide an alternative to freshwater isotopic dilution suggested by other workers a tidal connection is a critical consideration in lake evolution and many hypersaline polar lakes could have developed their current chemical composition before full marine isolation by contrast in some coastal lakes marine stratification caused by ice shelves before isolation provides a setting for minimal brine formation and subsequent meromictic conditions to develop hence the marine setting at the time of isolation represents a key factor in explaining divergent lake chemical evolution in the high arctic

a climatology of mesoscale model simulated low level wind jets over cook inlet and shelikof strait alaska abstract weather in the north gulf of alaska is characterized by a high frequency of deep synoptic scale low pressure systems especially during the cold season the strong pressure gradients of these storms interact with the extremely rugged terrain of the coastal mountains to produce a variety of channeled flows these surface wind regimes are not well documented in the scientific community due to the paucity of observations modeling of these phenomena in regions of complex terrain is of great interest to those working with hydrodynamic wave and pollutant transport models in coastal and shelf areas such models when coupled with ocean and coastal ecology counterparts give a broad view of the role surface winds play in shaping local coastal marine ecosystem in this region this paper presents a climatology of simulated low level wind jets over the domain of cook inlet and shelikof strait along alaska s south central coast daily simulations using the rams model were conducted in a 36 h forecast mode for the cold season period 10 1 03 to 3 31 04 systematic analysis of the resulting simulated low level wind field makes it possible to characterize these jets and gap flows in spatial and temporal detail the comparison between the rams winds and the synthetic aperture radar sar derived winds when available verifies the existence of these wind jets and the capability of the model to simulate these cases clearly the results of a study in this region depend on the fidelity of the model at these scales o 5 km the sar comparisons attempt to help establish this from the 6 months of simulations over cook inlet and shelikof strait the low level wind jets are classified into 10 different regimes by location and orientation these regimes are categorized into four more general groups cross channel westerly easterly and up and down inlet flows the nature of a particular regime is largely a function of pressure gradient orientation and local topography jets in the same group have a similar occurrence distribution with time some form of jet occurred in the study region almost daily each month of the period with december 2003 having the highest frequency of wind jets

doppler radar study of the trailing anvil region associated with a squall line abstract the kinematic structure and reflectivity distribution within a region of widespread precipitation associated with a summertime midlatitude illinois squall line as revealed by an analysis of doppler radar data are presented and discussed the squall line moved in a southeasterly direction while active convection forming on its leading edge moved in a northeasterly direction decaying thunderstorms and their anvils merged to form the extensive region of stratiform precipitation which trailed the squall line an extension of the vad velocity azimuth display method or the evad extended vad method has been developed for the analysis of single doppler radar data in contrast to the vad method which requires knowledge of the particle fall velocities or assumptions regarding it to calculate the divergence of the horizontal wind the evad method yields the vertical distributions of both the particle fall speed and the divergence also presented are results from a multiple doppler mdop analy

field observations of recent transgression on northern and eastern melville island western canadian arctic archipelago abstract after 11 000 years of glacio isostatically induced forced regression geomorphological evidence indicates that the coastline of eastern melville island western canadian arctic archipelago is now being transgressed recently developed coastal features associated with this transgression include drowned gullies and small estuaries barriers and lagoons barrier islands erosional notches backstepping beaches and drowned tundra vegetation and vehicle tracks dating from the 1970s we mainly attribute this relative sea level rise to the eastward migration of a peripheral crustal forebulge furthermore the reported transgression also includes a component from recent eustatic sea level rise during the 20th century recent earthquakes recorded in the gustav lougheed arch seismic zone located in byam martin channel 70 km east of melville island suggest that neotectonics could also be involved in local relative sea level adjustments other factors associated with global warming especially the formation of an earlier shore ice lead coupled with increased storm activity might also be responsible for some of the coastal changes our study indicates that the current zero isobase separating areas of net transgression from those of net regression is now located off the east coast of the island our field observations support recent glacio isostatic modelling that shows the island is presently undergoing a transgression

the role of convectively generated rear inflow jets in the evolution of long lived mesoconvective systems abstract in this study the structure of convectively generated rear inflow jets and their role in the evolution of long lived mesoconvective systems are investigated through an analysis of idealized three dimensional simulations using a nonhydrostatic cloud model rear inflow jets are generated within these systems in response to the upshear tilting of the convective circulation as the horizontal buoyancy gradients along the back edge of the expanding system create a circulation that draws midlevel air in from the rear within this framework a wide range of rear inflow strengths and structures are produced depending on the magnitude of the ambient convective available potential energy cape and the vertical wind shear in general for environments characterized by weak to moderate vertical wind shear and weak to moderate cape the rear inflow jet descends and spreads along the surface well behind the leading edge of the gust front and the subsequent convective activity becomes weaker however for e

sea level changes since the last glacial maximum an appraisal of the ipcc fourth assessment report the ipcc fourth assessment report ar4 stated that global sea level rose by about 120 m between the last glacial maximum lgm and 3 2 ka and did not rise again until the late 19th century a review of relevant literature demonstrates that the rise may have been larger by 10 15 m that the timing of stabilisation is poorly constrained within the last 7 ka bp and that the onset of modern rates of sea level rise is not synchronous and uniform across the globe the lgm lowstand as defined in the ar4 is based on the classic barbados sea level history but the sea level curve from this island may not be an accurate eustatic approximation if glacial isostatic adjustment gia processes were significant as suggested by various authors the barbados sea level curve revealed the existence of meltwater pulse mwp 1a at around 14 000 cal a bp questions about the source and causal mechanism of mwp 1a are still being explored by field scientists and gia modellers these problems have direct relevance for contemporary measurements of ice mass changes because space geodetic measurements rely on information provided by gia models to separate land motion from ice mass changes global patterns of holocene sea level change are controlled by regional sea level variability not only through isostatic and tectonic processes but also through steric effects longer wavelength gravitational changes produced by changing ice ocean mass flux and hemispheric scale perturbations in the earth s rotation eustasy is therefore merely a concept not a measurable quantity constraining the late holocene ice melt contribution to global sea level rise and determining regional sea level rise patterns in the 18th and 19th centuries are important future tasks for sea level scientists these will establish the baseline contributions to 20th and 21st century sea level rise and will help to determine the causes of modern rates of sea level rise constraining historical sea level accelerations and short term ice mass flux will aid models of ice sheet dynamics and help to reduce current uncertainties in future sea level predictions the ar4 shows that regional sea level variability is clearly present in sea level change patterns for the past 50 a and an important challenge for the next ipcc assessment is to incorporate this variability into regional future sea level rise scenarios copyright 2009 john wiley sons ltd

a high plains squall line associated with severe surface winds abstract the characteristics of a severe squall line are examined using data acquired from the 1981 cooperative convective precipitation experiment ccope the case is unusual in that the squall line was decoupled from an immediate surface based inflow source due to a meso scale 20 200 km outflow pool produced by a separate mesoscale convective system both systems participated in the development of a mesoscale convective complex which subsequently produced sustained severe surface winds throughout its entire life cycle despite the absolutely stable presquall atmospheric boundary layer the squall line produced radar reflectivity values of 70 dbz and storm induced outflow of 30 m s 1 aircraft soundings in the presquall environment suggest the storm was sustained by an elevated layer of high valued c air overriding the cold dome produced by the developing mcc the strongest surface winds were located upshear from the convective line and consisted of a northerly alongline component because the

large scale meteorological conditions associated with midlatitude mesoscale convective complexes abstract objective analyses of composited meteorological conditions attending ten mesoscale couvective complexes mcc reveal a number of distinctive characteristics and important interactions with the large scale environment the systems appear to be linked to eastward progression of a weak middle tropospheric short wave trough initial thunderstorms develop within a region of mesoscale convergence and lifting that is apparently forced primarily by low level warm advection the mcc system acquires mesoscale organization while it moves eastward ahead of the short wave trough diabatic heating eventually produces a system that is warm core in the middle troposphere and cold core in upper levels the mature mcc exhibits many similarities to tropical convective systems although it occurs within a considerably different large scale setting inflow within the lower half of the troposphere feeds convection within a region characterized by significant net upward mass flux and widespread precipitation thickne

circulations associated with a mature to decaying midlatitude mesoscale convective system part ii upper level features abstract the vertical structure of a midtropospheric mesovortex that developed during the decay of a midlatitude mesoscale convective system over kansas and oklahoma on 23 24 june 1985 is documented surface rawinsonde wind profiler and dual doppler data are used to define its structure as has been observed in other midlatitude and tropical cases the mesovortex occurred within the trailing stratiform precipitation region of a squall line system it was associated with a preexisting synoptic scale short wave trough and as the circulation developed it deformed the back edge of the stratiform precipitation region into a hooklike pattern the 100 200 km mesovortex was confined to the midtroposphere 3 8 km with a maximum amplitude just above the 0 c level the vortex axis sloped toward the northeast but its orientation changed hour by hour over the 2 h period of dual doppler coverage overall the mesovortex was warm core although its thermal structure was complex and apparently significantly infl

midlevel cyclonic vortices generated by mesoseale convective systems abstract despite the large number of convective systems that occur over the central united states every year there are typically only a few well defined midlevel vortices apparent in satellite imagery after the overlying anvil debris from some convective complexes has dissipated or advected away a climatology of mesoscale convectively generated vortex mcv events for 1981 1988 is presented and the synoptic setting in which the circulation becomes apparent is discussed proximity sounding data from numerous cases are used to examine features of the kinematic and thermodynamic setting of mcvs at various lifelycle stages defined by satellite imagery features ofthe large scale environment that appear conducive to the formation and longevity of mcvs include weak flow weak vertical shear weak background relative vorticity and intense horizontal and vertical moisture gradients the rapid mesovortex generation observed can be explained by the stretching term of the vorticity equation most mcvs emerge fro

the last glaciation of east central ellesmere island nunavut ice dynamics deglacial chronology and sea level change during the last glacial maximum of east central ellesmere island trunk glaciers inundated the landscape entering the smith sound ice stream accelerator mass spectrometry ams dates on individual shell fragments in till indicate that the ice advanced after 19 ka bp the geomorphic and sedimentary signatures left by the trunk glaciers indicate that the glaciers were polythermal the configuration and chronology of this ice is relevant to the reconstruction of ice core records from northwestern greenland the history of iceberg rafting of clastic sediments to northern baffin bay the reopening of the seaway between the arctic ocean and baffin bay and the regional variability of arctic paleoenvironments deglaciation began with the separation of ellesmere island and greenland ice at fiord mouths 8 8 5 ka bp ice reached fiord heads between 6 5 and 4 4 ka bp trunk glacier retreat from the fiords of east central ellesmere island occurred up to 3000 years later than in west coast fiords this later retrea

high resolution sequence stratigraphy of clastic shelves iv high latitude settings abstract high frequency clastic shelf sequences deposited in high latitude settings display marked differences in term of facies and stratigraphic architecture with respect to their lower latitude counterparts this is due to the presence of ice which 1 leads to the accumulation of glacigenic and glacimarine deposits 2 provides an additional control on accommodation and 3 determines the position of the shoreline transgressions and regressions in glaciated settings are controlled respectively by the retreat and advance of the ice shoreline i e the water ice contact irrespective of relative sea level changes once the ice retreats across the land the traditional land shoreline is exposed and the control on sequence architecture is exerted by the interplay between relative sea level changes and sediment supply as in low and middle latitude settings a general model that includes both glacial and non glacial climatic regimes is provided by this paper in this frame the classic sequence stratigraphic model represents one ice free end member which is opposed to an ice permanent end member between these end members sequences may accumulate in part under ice free conditions and in part under conditions dominated by ice on the shelf the main implication of this is that the classic sequence stratigraphic model may be viewed as only a possible scenario in the stratigraphic record rather than the rule

a midlatitude squall line with a trailing region of stratiform rain radar and satellite observations abstract a squall line exhibiting an extensive trailing region of stratiform precipitation passed over the observational network of the national severe storms laboratory on 22 may 1976 satellite imagery and conventional radar observations document its evolution from a broken line of thunderstorms to a system of mesoscale proportions and single doppler radar observations describe aspects of its mature structure satellite measurements of cloud top temperature showed the system to be a mesoscale convective complex mcc the life cycle of the system exhibited the stages of development seen in tropical cloud clusters at maturity two prominent mesoscale flow regimes were identified at midlevels one marked by inflow into the system s front and continuing toward its rear and another associated with inflow entering the extreme rear of the system the rear inflow was associated with a cyclonic midlevel vortex in the stratiform precipitation region it produced a concavity or notch in the back edge of th

gravel barrier migration and overstepping abstract despite the widespread occurrence of gravel barriers on mid to high latitude coasts understanding of their stability and relationship to gravel deposits on the inner continental shelf remains rudimentary on sand dominated coasts subject to rising relative sea level barrier overstepping has been postulated as a mechanism for preservation of beach deposits on the shelf but direct observation of overstepping events has been lacking observations at a site on the atlantic coast of canada reveal migration of a gravel barrier at 8 m a 1 landward over back barrier mud following abandonment of part of the barrier volume on the shoreface this provides clear evidence for overstepping and suggests that it may play a role in the formation of inner shelf gravel deposits integrity of the migrating stretching barrier depends on continued sediment supply from the headland source to a connecting ridge which must become progressively longer as the landward displacement of the barrier increases

a composite model of mesoscale convective complexes abstract a composite analysis technique is used to investigate the evolution of mesoscale features of mesoscale convective complexes mccs the early stage of the mcc lifecycle is characterized by convergence vertical motion and heating being centered in the lower troposphere as the mcc matures the level of peak upward motion and heating shifts to the upper troposphere the system achieves and maintains its maximum divergence upward motion and anticyclonic vorticity in the upper troposphere during the latter half of the life cycle this is in contrast to gate tropical clusters where the maximum divergence upward motion and anticyclonic vorticity occurred at the mature stage of the cluster and then weakened this difference might be explained by an mcc being an inertially stable form of mesoscale convective system whose radius exceeds the rossby radius of deformation the mcc is shown to be an efficient rain producer exhibiting a precipitation efficiency exceeding 100 at the mature stage due to th

tectonics of the qinling belt build up and evolution of eastern asia the structure and history of the qinling range which separates the north and south china cratons are a key to the tectonic evolution of eastern asia the mountain range is composed of a northern palaeozoic belt and a southern mesozoic belt the palaeozoic orogeny probably involved the closure of an oceanic basin along a north dipping subduction zone followed by south vergent obduction of ophiolites and intracontinental thrusting during the devonian the mesozoic belt appears to be the product of purely intracontinental shallow crustal deformation over a large decollement with at least 100 km of horizontal transport since the devonian both belts have been sliced by huge east west sinistral strike slip faults

dual doppler radar analysis of a midlatitude squall line with a trailing region of stratiform rain abstract the mesoscale structure of a squall line system that passed over oklahoma on 22 may 1976 is investigated by dual doppler radar analysis the mature storm consisted of a leading line of deep convection which exhibited organized multicellular structure trailed by an extensive region of stratiform precipitation marked by a radar bright band at the melting level these contrasting radar echo regimes were separated by a narrow band of weak reflectivity at lower levels which has been termed the transition zone while conventional and single doppler radar analyses documented the persistence of this precipitation structure and revealed the corresponding kinematic structure in one part of the mature storm the dual doppler analysis demonstrates the pervasiveness of these features over much of the squall line s length the structure of a midtropospheric maximum of rearward system relative flow crossing the system is particularly well described by the dual doppler data this mesoscale current originat

prediction and diagnosis of tropical cyclone formation in an nwp system part ii a diagnosis of tropical cyclone chris formation this is the second of a three part investigation into tropical cyclone tc genesis in the australian bureau of meteorology s tropical cyclone limited area prediction system tc laps the primary tc laps vortex enhancement mechanism convergence stretching and vertical advection of absolute vorticity in convective updraft regions was presented in part i in this paper part ii results from a numerical simulation of tc chris western australia february 2002 are used to illustrate the primary and two secondary vortex enhancement mechanisms that led to tc genesis in part iii a number of simulations are presented exploring the sensitivity and variability of genesis forecasts in tc laps during the first 18 h of the simulation a mature vortex of tc intensity developed in a monsoon low from a relatively benign initial state deep upright vortex cores developed from convergence stretching and vertical advection of absolute vorticity within the updrafts of intense bursts of cumulus convection individual convective bursts lasted for 6 12 h with a new burst developing as the previous one weakened the modeled bursts appear as single updrafts and represent the mean vertical motion in convective regions because the 0 15 grid spacing imposes a minimum updraft scale of about 60 km this relatively large scale may be unrealistic in the earlier genesis period when multiple smaller scale shorter lived convective regions are often observed but observational evidence suggests that such scales can be expected later in the process the large scale may limit the convection to only one or two active bursts at a time and may have contributed to a more rapid model intensification than that observed the monsoon low was tilted to the northwest with convection initiating about 100 200 km west of the low level center the convective bursts and associated upright potential vorticity pv anomalies were advected cyclonically around the low weakening as they passed to the north of the circulation center leaving remnant cyclonic pv anomalies strong convergence into the updrafts led to rapid ingestion of nearby cyclonic pv anomalies including remnant pv cores from decaying convective bursts thus convective intensity rather than the initial vortex size and intensity determined dominance in vortex interactions this scavenging of pv by the active convective region termed diabatic upscale vortex cascade ensured that pv cores grew successively and contributed to the construction of an upright central monolithic pv core the system scale intensification ssi process active on the broader scale 300 500 km radius also contributed latent heating slightly dominated adiabatic cooling within the bursts which enhanced the system scale secondary circulation convergence of low to midlevel tropospheric absolute vorticity by this enhanced circulation intensified the system scale vortex the diabatic upscale vortex cascade and ssi are secondary processes dependent on the locally enhanced vorticity and heat respectively generated by the primary mechanism

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

paleogeographic maps of the continents bordering the indian ocean since the early jurassic paleomagnetic data from the african plate from the early jurassic onward are critically re evaluated and updated resulting in a set of 30 paleopoles from which an apparent polar wander path is derived using 20 ma intervals this path is then used in conjunction with kinematic models of the indian and atlantic oceans to place other continents bordering the indian ocean eurasia india islands and plateaus madagascar seychelles mascarene and blocks involved in the collision of india with eurasia south tibet indochina in an absolute paleogeographic frame fixed with respect to africa paleogeographic maps are presented for the early jurassic pre breakup the jurassic cretaceous boundary anomaly ml5 the early cretaceous m2 the late cretaceous a 34 the cretaceous tertiary boundary a 29 the early eocene a 24 the middle eocene a 21 and the oligocene miocene boundary a 6 observed and predicted paleomagnetic directions for landmasses other than africa i e for western europe china korea india and australia which are not used in deriving the maps are found to be in very satisfactory agreement the quality of reconstructions as measured by rms discrepancies between observed and predicted paleolatitudes is of the order of 5 the main features of the paleogeographic maps are discussed with the aim of relating oceanic and on land geodynamic events the constraints provided by tibetan data on the india asia collision and the 20 ma reorganization of geology and plate boundaries in a band extending from the south china sea through tibet to the red sea system are discussed in more detail we emphasize the episodic nature of the breakup of gondwanaland and formation of the indian ocean and subsequent interaction with eurasia in which six major discrete events are identified separated by 30 ma phases of rather uniform plate motion

meso β scale characteristics of an episode of meso α scale convective complexes abstract a variety of meso scale 20 200 km 6 h convective complex mcc are described the analysis is based on a typical episode of mccs in the central united states thunderstorms in the mcc are generally well organized into meso scale convective features the larger mccs are typically preceded by several of these meso convective clusters or bands which tend to be aligned along linear meso scale features such as the eastern slope of the rockies or thermodynamic discontinuities evident in hourly surface or satellite data the intense development of these larger systems involves the growth merger and interaction of those meso convective feature located nearest the intersection of the meso axes along which they are aligned throughout the mature phase of the mcc multiple meso convective components may persist within the more uniform meso cloud shield as expanding regions of str

mesoscale organization of springtime rainstorms in oklahoma abstract radar reflectivity and raingage data obtained during six springtimes indicate the types of mesoscale organization that occur in association with major rain events in oklahoma at least 25 mm of rain in 24 h over an area exceeding 12 500 km2 in these storms the primary rain area is found to be a contiguous region of precipitation 10s to 100s of km in scale that consists partly of deep convection and partly of stratiform rain the patterns of rain formed by the convective and stratiform areas comprise a continuous spectrum of mesoscale structures about two thirds of the cases examined exhibited variations on the type of organization in which convective cells arranged in a moving line are followed by a region of stratiform rain storm organization was graded according to the degree to which it matched an idealized model of this leading line trailing stratiform structure the precipitation pattern was further graded according to whether its structure was relatively symmetric with respect to an a

a 10 000 yr b p extensive ice shelf over viscount melville sound arctic canada abstract late wisconsinan age glacial landforms and deposits indicate that an ice shelf of at least 60 000 km 2 flowed northwestward into viscount melville sound probably from the m clintock dome of the laurentide ice sheet the ice shelf overlapped coastal areas and laid winter harbour till up to 125 m above present sea level on the southern coast of melville island to 135 m on byam martin island to possibly 90 m on the northeast tip of banks island and to 150 m on the north coast of victoria island the contemporary sea level was 50 to 100 m higher than present it now rises eastward a maximum age of 10 340 150 yr b p for the till and thus the ice shelf advance is provided by shells in marine sediments which underlie it whereas a minimum age of 9880 150 yr b p is provided by overlying shells that postdate the ice advance the major advance of shelf ice into viscount melville sound may be the result of the rapid disintegration of the m clintock dome while the climate ameliorated in the western arctic

faulting associated with large earthquakes and the average rate of deformation in central and eastern asia we determine approximate average rates of deformation in portions of eastern and central asia for the last 80 years these rates are based on estimates of source dimensions average displacements seismic moments and orientations of faults of all large earthquakes m 7 5 and as many other major earthquakes m 7 0 as possible in asia since 1900 a major part of this study is the compilation of these data for separate parts of asia we combine seismic moment tensors to estimate the average rotational strain or deformation tensors for these regions for the last 80 years we estimate that shortening across the tien shan has occurred at 11 mm yr between 5 and 19 mm yr left lateral shear on easterly trending planes in mongolia in northwestern tibet gansu and ningxia and on the xianshuihe fault in western sichuan has been very rapid more than 10 mm yr in each region and apparently as rapid as 40 mm yr in northwestern tibet gansu and ningxia slower rates of a few to 10 mm yr appear to characterize east west extension and conjugate north south shortening of tibet the earthquake history of the himalaya is consistent with rates of underthrusting of more than 10 mm yr but is probably less than the convergence rate of india with eurasia of about 50 mm yr the overall strain field is consistent with a large part of india s penetration into eurasia being absorbed by the extrusion of material out of india s way as a result southeast china moved at about 21 mm yr east southeast with respect to eurasia in the last 80 years with an uncertainty of about a factor of 2 in this estimated rate

major changes in ice stream dynamics during deglaciation of the north western margin of the laurentide ice sheet abstract victoria island lies at the north western limit of the former north american laurentide ice sheet in the canadian arctic archipelago and displays numerous cross cutting glacial lineations previous work suggests that several ice streams operated in this region during the last wisconsinan glaciation and played a major role in ice sheet dynamics and the delivery of icebergs into the arctic ocean this paper produces the first detailed synthesis of their behaviour from the last glacial maximum through to deglaciation 21 9 5 cal ka bp based on new mapping and a previously published radiocarbon constrained ice sheet margin chronology over 70 discrete ice flow events flow sets are fitted to the ice margin configuration to allow identification of several ice streams ranging in size from large and long lived thousands of years to much smaller and short lived hundreds of years the reconstruction depicts major ice streams in m clure strait and amundsen gulf which underwent relatively rapid retreat from the continental shelf edge at some time between 15 2 and 14 1 cal ka bp a period which encompasses climatic warming and rapid sea level rise meltwater pulse 1a following this overall retreat was slower and the ice streams exhibited asynchronous behaviour the amundsen gulf ice stream continued to operate during ice margin retreat whereas the m clure strait ice stream ceased operating and was replaced by an ice divide within 1000 years this ice divide was subsequently obliterated by another short lived phase of ice streaming in m clintock channel 13 cal ka bp the timing of this large ice discharge event coincides with the onset of the younger dryas subsequently a minor ice divide developed once again in m clintock channel before final deglaciation of the island shortly after 9 5 cal ka bp it is concluded that large ice streams at the nw margin of the laurentide ice sheet equivalent in size to the hudson strait ice stream underwent major changes during deglaciation resulting in punctuated delivery of icebergs into the arctic ocean published radiocarbon dates constrain this punctuated delivery as far as is possible within the limits imposed by their precision and we note their coincidence with pulses of meltwater delivery inferred from numerical modelling and ocean sediment cores

confidence intervals for age estimates and deposition times in late quaternary sediment sequences distribution sampling from sequences of radiocarbon ages is used to obtain confidence intervals for intermediate age estimates sediment deposition times and thence pollen deposition rates three

forms response times and variability of relative sea level curves glaciated north america abstract relative sea level curves from glaciated north america reveal coherent spatial patterns of response times in the laurentide ice sheet area curve half lives range from 1 2 1 4 ka at the uplift centre to 1 7 2 ka in a ridge of high values inboard of the glacial limit half lives decline from this ridge to less than 1 ka along the margin in the innuitian ice sheet area half lives are about 2 ka at the uplift centre and decline to less than 1 ka at the margin the central laurentide response times are about half those of central fennoscandia this accords with the theoretical expectation that central response times are inversely proportional to ice sheet radius for ice loads large enough that rebound at the centre is insensitive to lithospheric thickness the innuitian central response time indicates that rebound at the centre of this ice sheet which is much smaller than the fennoscandian ice sheet remains sensitive to lithospheric thickness radial gradients in response times reflect the increasing influence of the lithosphere at sites increasingly closer to the margin along this gradient rebound progresses as though at the centres of smaller and smaller ice sheets that is the effective spatial scale of the ice load decreases toward the margin near the glacial limit postglacial isostatic adjustment is complicated by forebulge migration and collapse this is seen most strongly in the relative sea level record of atlantic canada which has subsided during the holocene more than 20 m more than the adjacent american seaboard the relative sea level history of some areas notably the st lawrence estuary is complicated by tectonic processes

unusual rates and patterns of holocene emergence ellesmere island arctic canada substantial postglacial emergence up to 150 m characterizes the canadian high arctic following the last glacial maximum across northern ellesmere island rapid emergence is not observed during the early stages of deglaciation as it is in other parts of arctic canada rather the curves show an interval of slow emergence c 1 m per century during initial ice retreat this is attributed to a slow rate of glacial rebound that was countered by a similar rate of eustatic sea level rise normally isobases drawn on postglacial shorelines define broad cells of uplift that mimic centres of former maximum ice thickness however isobases on the 8 ka bp shoreline surveyed throughout northern ellesmere island indicate more complex patterns of crustal uplift that seem in congruent with reported ice thicknesses on west central ellesmere island the isobases 110 150 m asl trace a plunging ridge aligned with geological structure across an area considered to have had minimal ice cover during the last glacial maximum the ridge may record an important structural influence associated with the geologically youthful sverdrup basin collectively this evidence cautions against the view that postglacial emergence has a universally predictable signature solely portraying former ice loads

balanced and unbalanced circulations in a primitive equation simulation of a midlatitude mcc part i the numerical simulation abstract a midlatitude mesoscale convective complex mcc which occurred over the central united states on 23 24 june 1985 was simulated using the regional atmospheric modeling system rams the multiply nested grid simulation agreed reasonably well with surface upper air and satellite observations and ground based radar plots the simulated mcc had a typical structure consisting of a leading line of vigorous convection and a trailing region of less intense stratiform rainfall several other characteristic mcc circulations were also simulated a divergent cold pool in the lower troposphere midlevel convergence coupled with a relatively cool descending rear inflow jet and relatively warm updraft structure and a cold divergent anticyclone in the tropopause region early in the mcc simulation a mesoscale convectively induced vortex mcv formed on the eastern edge of the convective line while frequently associated with mccs and other mesoscale convective systems mcss mcvs are more typically repo

three dimensional evolution of simulated long lived squall lines abstract simulations of squall lines using nonhydrostatic convection resolving models have been limited to two dimensions or three dimensions with the assumption of along line periodicity the authors present 3d nonhydrostatic convection resolving simulations produced using an adaptive grid model where the lines are finite in length and the restriction to along line periodicity is removed the base state for the simulations is characterized by weak shallow shear and high convective available potential energy cape an environment in which longlived midlatitude mesoscale convective systems mcss are observed the simulated systems bear strong resemblance to many observed systems suggesting that large scale forcing absent in the horizontally homogeneous environment is not needed to produce many of the distinguishing features of midlatitude mcss in simulations without coriolis forcing the presence of line ends leads to mature symmetric systems characterized by a central region of strong convectio

evolution and structure of the 6 7 may 1985 mesoscale convective system and associated vortex abstract observations collected during the oklahoma kansas pre storm experiment are used to document the evolution and structure of the mesoscale convective system mcs that occurred on 6 7 may 1985 the storm began when a short squall line developed in an area of preexisting thunderstorm activity thunderstorm updrafts along the squall line lifted warm moist air with its southerly momentum to the upper troposphere a broad region of convective outflow and a meso scale updraft region with a mean vertical velocity in excess of 15 10 3 mb s 1 were created a stratiform rain area with an embedded mesovortex formed behind the squall line the vortex resided beneath the deepest upper level outflow the mesovortex altered the wind field and consequently became the principal organizational feature within the mcs a descending current from the storm s rear that depending on location extended from 1 km to the upper troposphere was intensified and focused by the vortex the descending rear inflow had a peak

the sea level conundrum case studies from palaeo archives uncertainties in sea level projections for the 21st century have focused ice sheet modelling efforts to include the processes that are thought to be contributing to the recently observed rapid changes at ice sheet margins this effort is still in its infancy however leaving us unable to make reliable predictions of ice sheet responses to a warming climate if such glacier accelerations were to increase in size and frequency the geological record however has long identified examples of nonlinear ice sheet response to climate forcing shackleton nj opdyke nd 1973 oxygen isotope and paleomagnetic stratigraphy of equatorial pacific core v28 239 late pliocene to latest pleistocene geological society of america memoirs145 449 464 fairbanks rg 1989 a 17 000 year glacio eustatic sea level record influence of glacial melting rates on the younger dryas event and deep ocean circulation nature342 637 642 bard e hamelin b arnold m montaggioni l cabioch g faure g rougerie f 1996 sea level record from tahiti corals and the timing of deglacial meltwater discharge nature382 241 244 thus suggesting an alternative strategy for constraining the rate and magnitude of sea level change that we might expect by the end of this century copyright 2009 john wiley sons ltd

global glacial isostasy and the surface of the ice age earth the ice 5g vm2 model and grace abstract the 100 kyr quasiperiodic variation of continental ice cover which has been a persistent feature of climate system evolution throughout the most recent 900 kyr of earth history has occurred as a consequence of changes in the seasonal insolation regime forced by the influence of gravitational n body effects in the solar system on the geometry of earth s orbit around the sun the impacts of the changing surface ice load upon both earth s shape and gravitational field as well as upon sea level history have come to be measurable using a variety of geological and geophysical techniques these observations are invertible to obtain useful information on both the internal viscoelastic structure of the solid earth and on the detailed spatiotemporal characteristics of glaciation history this review focuses upon the most recent advances that have been achieved in each of these areas advances that have proven to be central to the construction of the refined model of the global process of glacial isos

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

isostatic adjustments in a full glacial sea during the last glaciation an ice free corridor existed between the northeast ellesmere island and northwest greenland ice sheets this corridor constituted a peripheral depression in which the marine limit marks the uppermost extent of a full glacial sea the full glacial sea is characterized by 1 14c dates on in situ marine shells that predate initial emergence unloading followed by 2 synchronous emergence from the marine limit throughout the peripheral depression relative sea level curves from the full glacial sea confirm previous morphostratigraphic and glacioisostatic evidence for limited ice extent during the last glaciation these curves also document the history of glacial unloading and the form of the relative sea level curve that one would theoretically expect in the peripheral depression the form of the curves presented here is unlike any other published emergence curves from arctic canada or from fennoscandia the relative sea level curves for northeast ellesmere island show three segme

mesoscale convective vortex formation in a weakly sheared moist neutral environment abstract idealized simulations of a diabatic rossby vortex drv in an initially moist neutral baroclinic environment are performed using the fifth generation national center for atmospheric research pennsylvania state university ncar psu mesoscale model mm5 the primary objective is to test the hypothesis that the formation and maintenance of midlatitude warm season mesoscale convective vortices mcvs are largely influenced by balanced flow dynamics associated with a vortex that interacts with weak vertical shear as a part of this objective the simulated drv is placed within the context of the bow echo and mesoscale convective vortex experiment bamex field campaign by comparing its tangential velocity radius of maximum winds cape and shear with the mcvs observed in bamex the simulations reveal two distinct scales of development at the larger scale the most rapidly growing moist baroclinic mode is excited and exponential growth of this mode occurs during the simulation embedded within the