global sea level rise published values for the long term global mean sea level rise determined from tide gauge records exhibit considerable scatter from about 1 mm to 3 mm yr this disparity is not attributable to instrument error long term trends computed at adjacent sites often agree to within a few tenths of a millimeter per year instead the differing estimates of global sea level rise appear to be in large part due to authors using data from gauges located at convergent tectonic plate boundaries where changes of land elevation give fictitious sea level trends in addition virtually all gauges undergo subsidence or uplift due to postglacial rebound pgr from the last deglaciation at a rate comparable to or greater than the secular rise of sea level modeling pgr by the ice 3g model of tushingham and peltier 1991 and avoiding tide gauge records in areas of converging tectonic plates produces a highly consistent set of long sea level records the value for mean sea level rise obtained from a global set of 21 such stations in nine oceanic regions with an average record length of 76 years during the period 1880 1980 is 1 8 mm yr 0 1 this result provides confidence that carefully selected long tide gauge records measure the same underlying trend of sea level and that many old tide gauge records are of very high quality

localization of the gravity field and the signature of glacial rebound the negative free air gravity anomaly centred on hudson bay canada shows a remarkable correlation with the location of the laurentide ice sheet suggesting that this gravity anomaly is the result of incomplete post glacial rebound this region however is also underlain by higher than average mantle seismic velocities suggesting that the gravity low might result instead from dynamic topography associated with convective downwellings here we analyse the global gravity field as a simultaneous function of geographic location and spectral content we find that the hudson bay gravity low is unique with anomalously high amplitude in the spectral band where the power from the laurentide ice load is greatest and the relaxation times predicted for viable models of viscous relaxation are longest we estimate that about half of the hudson bay gravity anomaly is the result of incomplete post glacial rebound and derive a mantle viscosity model that explains both this gravity signature and the characteristic uplift rates for the central laurentide and fennoscandian regions this model has a jump in viscosity at 670 km depth comparable to that in dynamic models of the geoid highs over subducted slabs but lacks a low viscosity asthenosphere consistent with a higher viscosity in the upper mantle beneath shields than in oceanic regions

observation of glacial isostatic adjustment in stable north america with gps 1 motions of three hundred and sixty global positioning system gps sites in canada and the united states yield a detailed image of the vertical and horizontal velocity fields within the nominally stable interior of the north american plate by far the strongest signal is the effect of glacial isostatic adjustment gia due to ice mass unloading during deglaciation vertical velocities show present day uplift 10 mm yr near hudson bay the site of thickest ice at the last glacial maximum the uplift rates generally decrease with distance from hudson bay and change to subsidence 1 2 mm yr south of the great lakes the hinge line separating uplift from subsidence is consistent with data from water level gauges along the great lakes showing uplift along the northern shores and subsidence along the southern ones horizontal motions show outward motion from hudson bay with complex local variations especially in the far field although the vertical motions are generally consistent with the predictions of gia models the horizontal data illustrate the need and opportunity to improve the models via more accurate descriptions of the ice load and laterally variable mantle viscosity

observation of coexisting mesoscale lake effect vortices over the western great lakes mesoscale vortices are one of several types of wintertime lake effect structures that are observed over the great lakes region as cold arctic air is rapidly modified from below by warm lake waters these vortices are thought to occur less frequently than other lake effect structures such as wind parallel snowbands e g kristovich 1993 which are responsible for greater than half of the yearly snowfall downwind of the western great lakes kelly 1986 and more intense shore parallel snowbands which can produce localized heavy snowfalls e g braham 1983 through the examination of visible satellite imagery forbes and merritt 1984 found 14 cases of mesoscale vortex formation over the great lakes in the years 1978 82 this suggests that on average a mesoscale vortex will occur within the great lakes region less than four times a winter during an early winter lakeeffect event on 13 november 1995 intense land breeze circulations and four mesoscale vortices 50 km diameter developed over lakes superior huron and michigan simultaneously fig 1 this unique observation of coexisting lake effect vortices over the western great lakes has not previously been reported in the literature and suggests that atmospheric conditions favorable for vortex development were widespread throughout the region previous cases have typically observed a single vortex suggesting that favorable meteorological conditions were localized the author is aware of only two other reported observations of simultaneous mesoscale vortices within the great lakes region schoenberger 1986 pitts et al 1977 however the lake effect vortices that schoenberger 1986 and

present day 3d velocity field of eastern north america based on continuous gps observations the saint lawrence river valley in eastern canada was studied using observations of continuously operating gps cgps stations the area is one of the most seismically active regions in eastern north america characterized by many earthquakes which is also subject to an ongoing glacial isostatic adjustment we present the current three dimensional velocity field of eastern north america obtained from more than 14 years 9 years on average of data at 112 cgps stations bernese gnss and gitsa software were used for cgps data processing and position time series analysis respectively the results show the counterclockwise rotation of the north american plate in the no net rotation model with the average of 16 8 0 7 mm year constrained to itrf 2008 we also present an ongoing uplift model for the study region based on the present day cgps observations the model shows uplift all over eastern canada with the maximum rate of 13 7 1 2 mm year and subsidence to the south mainly over northern usa with a typical rate of 1 to 2 mm year and the minimum value of 2 7 1 4 mm year we compared our model with the rate of radial displacements from the ice 5g model both models agree within 0 02 mm year at the best stations however our model shows a systematic spatial tilt compared to ice 5g the misfits between two models amount to the maximum relative subsidence of 6 1 1 1 mm year to the east and maximum relative uplift of 5 9 2 7 mm year to the west the intraplate horizontal velocities are radially outward from the centers of maximum uplift and are inward to the centers of maximum subsidence with the typical velocity of 1 1 6 0 4 mm year that is in agreement with the ice 5g model to the first order

space geodetic constraints on glacial isostatic adjustment in fennoscandia analysis of global positioning system gps data demonstrates that ongoing three dimensional crustal deformation in fennoscandia is dominated by glacial isostatic adjustment our comparison of these gps observations with numerical predictions yields an earth model that satis es independent geologic constraints and bounds both the average viscosity in the upper mantle 5 x 10 20 to 1 x 10 21 pascal seconds and the elastic thickness of the lithosphere 90 to 170 kilometers we combined gps derived radial motions with fennoscandian tide gauge records to estimate a regional sea surface rise of 2 1 0 3 mm year furthermore ongoing horizontal tectonic motions greater than 1 mm year are ruled out on the basis of the gps derived three dimensional crustal velocity field

optimal locations for gps measurements in north america and northern europe for constraining glacial isostatic adjustment summary we determine the optimal location in north america and fennoscandia for uplift rate or tangential velocity data that will be useful for addressing ice sheet thickness lithospheric thickness lateral viscosity variation and background viscosity profile in the lower mantle an optimal location is defined by where sensitivity lies above the current accuracy of gps measurements the approach here is different from previous studies that compute sensitivity kernels for viscosity perturbations within a small volume of the mantle the advantage of the current approach is that the total effect of 3 d lateral heterogeneity in the mantle related to seismic tomography of the whole mantle can be studied the sensitivity of ice sheet models and lateral lithospheric thickness variations are also studied our results show that in north america more permanent gps stations are needed in northern canada especially in a region west of the hudson bay until the rocky mountains in fennoscandia the gps network is almost adequate but it should be extended to the last known gia affected areas in the russian part of east europe and to central europe in addition we show locations of prospective gps sites that are sensitive to all four parameters ice sheet thickness lithospheric thickness lateral viscosity variation and background viscosity profile in the lower mantle and locations that are sensitive to only one two or three parameters thus the results are useful for the inversion of one individual parameter or for the separation of the effects of two or more parameters in inversions

investigation of glacial isostatic adjustment in the northeast u s using gps measurements 1 we have been observing three dimensional site velocities at over 60 permanent gps stations in the northeastern u s for the purpose of inferring mantle viscosity and thus improving current models of glacial isostatic adjustment gia we estimate the upper and lower mantle viscosity by comparing radial site velocities from a subset of continuous gps measurements with numerical gia predictions our inferences are consistent with previous esti mates obtained using different methods and data sets

radial profile of mantle viscosity results from the joint inversion of convection and postglacial rebound observables we present new inferences of the radial profile of mantle viscosity that simultaneously fit long wavelength free air gravity harmonics associated with mantle convection and a large set of decay times estimated from the postglacial uplift of sites within previously glaciated regions hudson bay arctic canada and fennoscandia the relative sea level variation at these latter sites is constrained by age height pairs obtained by geological survey rather than the subjective trends which are commonly used in glacial isostatic adjustment gia studies our viscosity inferences are generated using two approaches first we adopt a relative viscosity profile which is known to provide a good fit to the free air gravity harmonics and determine an absolute scaling which yields a best fit to the gia decay time constraints second we perform an iterative nonlinear joint inversion of the two data sets in both cases our inferred profiles are characterized by a significant increase of viscosity 2 orders of magnitude with depth to values of 1022 pa s in the bottom half of the lower mantle the new viscosity profiles are shown to satisfy constraints based on the postglacial uplift of both fennoscandia the classic haskell 1935 number and hudson bay which have commonly been invoked to argue for an isoviscous mantle furthermore the models are used to predict a set of long wavelength signatures of the gia process these include predictions of gia induced variations in 1 the length of day over the late holocene period 2 the earth s precession constant and obliquity over the last 2 6 myr and 3 the present day zonal harmonics of the geopotential jl l 7 the predictions 1 and 3 bound the late holocene and ongoing mass flux between the large polar ice sheets greenland and antarctic and the global oceans to small values 0 4 mm yr equivalent eustatic sea level rise

lake effect mode and precipitation enhancement over the tug hill plateau during owles iop2b abstractimproved understanding of the influence of orography on lake effect storms is crucial for weather forecasting in many lake effect regions the tug hill plateau of northern new york hereafter tug hill rising 500 m above eastern lake ontario experiences some of the most intense snowstorms in the world herein the authors investigate the enhancement of lake effect snowfall over tug hill during iop2b of the ontario winter lake effect systems owles field campaign during the 24 h study period total liquid precipitation equivalent along the axis of maximum precipitation increased from 33 5 mm at a lowland 145 m msl site to 62 5 mm at an upland 385 m msl site the latter yielding 101 5 cm of snow however the ratio of upland to lowland precipitation or orographic ratio varied with the mode of lake effect precipitation strongly organized long lake axis parallel bands some of which formed in association with the approach or passage of upper level short wave troughs produced the highest pre

synthetic dual doppler analysis of a winter mesoscale vortex abstract this article presents a detailed examination of the kinematic structure and evolution of the 5 december 1997 winter mesoscale vortex in the vicinity of lake michigan using the synthetic dual doppler sdd technique when such a mesoscale event propagates a distance large enough that the viewing angle from a single doppler radar changes by about 30 and the circulation is sufficiently steady during this time period then the sdd method can reveal reliable details about the circulation one such detail of the observed vortex was a pattern of convergence and divergence associated with radial bands where heavier snowfall was located another was the steadiness and vertical coherence of the derived vorticity and convergence patterns within the cyclonic circulation on 5 december 1997 the observed reflectivity field remained remarkably steady for nearly 2 5 h as the vortex moved southeastward allowing for the application of the sdd technique the reflectivity field exhibited a pronounced asymmetric c

glacioisostatic influences on virginia s late pleistocene coastal plain deposits abstract the late pleistocene of virginia s outer coastal plain consists of sediments dated to marine isotope stages mis 5 and 3 two members from the tabb formation south of the chesapeake bay in southeastern virginia and two formations east of the bay on the southern delmarva peninsula were dated using optically stimulated luminescence osl the stratigraphically older butlers bluff member yielded osl ages of 70 ka 62 78 ka mis 5a and the younger poquoson member and wachapreague formation mis 3 ages of approximately 43 ka 33 50 ka and 42 ka 33 54 ka respectively these shoreface and near shore geologic units reached maximum altitudes ranging from 3 to 12 m above present sea level and were deposited when established glacial eustatic sea level curves suggest that sea levels were significantly lower than present by approximately 40 m if these new ages and the sea level curves are correct there must have been regional uplift of more than 40 m probably due to isostatic adjustments of forebulges peripheral to north american ice sheets when they were at their maxima during mis 6 and mis 2 if the late mis 6 forebulge collapse continued throughout mis 5 and mis 4 we propose that regional land elevations may have been low enough for deposition to occur during the lower eustatic sea levels of mis 3 during late mis 3 the units experienced renewed uplift followed by subsidence to present day elevations if this paraglacial region is not yet in isostatic equilibrium and still requires further forebulge subsidence this could explain the present day altitude and age discrepancies associated with these relict marine deposits

geodetic constraints on glacial isostatic adjustment in europe 1 direct measurements of surface deformation due to glacial isostatic adjustment gia in europe have been so far mostly limited to the present day uplift area here we use permanent gps networks results to investigate the significance of gia effects in europe south of fennoscandia we show that uplift in fennoscandia is surrounded by subsidence reaching as far south as the alps with a maximum vertical rate of 1 5 mm yr between 50 5 53 n horizontal velocity gradients show shortening between fennoscandia and north central europe with strain rates of 10 9 yr 1 and principal compressional strain axis pointing to the gulf of bothnia in a radial pattern we find a very good quantitative agreement with the 3d surface displacement predicted by milne et al 2001 although the increase of misfit in far field of fennoscandia suggests that geodetic data outside of the uplift area may bring additional constraints to the rheological parameters used in gia models

sea level change glacial rebound and mantle viscosity fornorthern europe northwestern europe remains a key region for testing models of glacial isostasy because of the good geological record of crustal response to the glacial unloading since the time of the last glacial maximum models for this rebound and associated sea level change require a detailed knowledge of the ice sheet geometry including the ice thickness through time existing ice sheet reconstructions are strongly model dependent and inversions of sea level data for the mantle response may be a function of the model assumptions thus inverse solutions for the sea level data are sought that include both ice and earth model parameters as unknowns sea level data from fennoscandia the north sea the british isles and the atlantic and english channel coasts have been evaluated and incorporated into the solutions the starting ice sheet for fennoscandia is based on a reconstruction of a model by denton hughes 1981 that is characterized by quasi parabolic cross sections and symmetry about the load centre both global northwestern europe as a whole and regional subsets of the data solutions have been made for earth model parameters and ice height scaling parameters the key results are as follows 1 the response of the upper mantle to the changing ice and water loads is spatially relatively homogenous across scandinavia the north sea and the british isles 2 this response can be adequately modelled by an effective elastic lithosphere of thickness 65 85 km and by an effective upper mantle viscosity from the base of the lithosphere to the 670 km depth seismic discontinuity of about 3 4 1020 pa s the effective lower mantle viscosity is at least an order of magnitude greater 3 the ice thickness over scandinavia at the time of maximum glaciation was only about 2000 m much less than the 3400 m assumed in the denton hughes model 4 the ice profiles are asymmetric about the centre of the ice sheet with those over the western part being consistent with quasi parabolic functions whereas the ice heights over the eastern and southern regions increase much more slowly with distance inwards from the ice margin

climatology of lake effect snowstorms of the great salt lake abstract characteristics of lake effect snowstorms associated with the great salt lake are described using wsr 88d radar imagery 16 well defined and 18 marginal lake effect events were identified from september 1994 through may 1998 excluding june august with the former used for more detailed analysis precipitation during the well defined events was frequently characterized by the irregular development of radar echoes over and downstream of the great salt lake the most commonly observed precipitation structures were solitary wind parallel bands that developed along or near the major axis of the gsl and broad area precipitation shields with embedded convective elements that formed near the southern shoreline regional scale composite analyses and rawinsonde derived statistics showed that the lake effect events occurred in post frontal westerly to northerly 700 hpa flow following the passage of an upper level trough and associated low level cold front the lake effect environment was characterized by

20th century sea level change along the eastern us unravelling the contributions from steric changes greenland ice sheet mass balance and late pleistocene glacial loading we have considered the influence of ocean temperature and salinity changes mass changes of the greenland ice sheet gis and the isostatic response of the solid earth to the most recent glacial cycle on 20th century sea level change along the us east coast with the intention of better understanding the observed signal as well as determining the potential of the tide gauge data for constraining the recent past 50 100 yr mass balance of the gis and earth viscosity structure our results show that the signal due to steric changes is large and displays a complex spatial variation which can account for a significant portion of the observed signal in contrast that due to changes in the gis is relatively small and insensitive to the specific geometry of the mass balance model adopted as a consequence the tide gauge data alone are not capable of providing useful constraints on either the magnitude or form of recent gis mass balance our inference of mantle viscosity structure based on the tide gauge data was affected dramatically when the steric effect was accounted for an earth model with an upper mantle viscosity of 8 1019 pa s and a lower mantle viscosity of 5 1022 pa s produced the best fit to the steric corrected data the optimal fit to the uncorrected data was obtained for upper and lower mantle viscosities of 5 1020 pa s and 1022 pa s respectively

continuous gps measurements of postglacial adjustment in fennoscandia 1 geodetic results 1 data collected under the auspices of the bifrost gps project yield a geographically dense suite of estimates of present day three dimensional 3 d crustal deformation rates in fennoscandia johansson et al 2002 a preliminary forward analysis of these estimates milne et al 2001 has indicated that models of ongoing glacial isostatic adjustment gia in response to the final deglaciation event of the current ice age are able to provide an excellent fit to the observed 3 d velocity field in this study we revisit our previous gia analysis by considering a more extensive suite of forward calculations and by performing the first formal joint inversion of the bifrost rate estimates to establish insight into the physics of the gia response in the region we begin by decomposing a forward prediction into the three contributions associated with the ice ocean and rotational forcings from this analysis we demonstrate that recent advances in postglacial sea level theory in particular the inclusion of rotational effects and improvements in the treatment of the ocean load in the vicinity of an evolving continental margin involve peak signals that are larger than the observational uncertainties in the bifrost network the forward analysis is completed by presenting predictions for a pair of fennoscandian ice histories and an extensive suite of viscoelastic earth models the former indicates that the bifrost data set provides a powerful discriminant of such histories the latter yields bounds on the assumed constant upper and lower mantle viscosity nu um nu lm specifically we derive a 95 confidence interval of 5 x 10 20 less than or equal to nu um less than or equal to 10 21 pa s and 5 x 10 21 less than or equal to nu lm less than or equal to 5 x 10 22 pa s with some preference for elastic lithospheric thickness in excess of 100 km the main goal of the bayesian inverse analysis is to estimate the radial resolving power of the bifrost gps data as a function of depth in the mantle assuming a reasonably accurate ice history we demonstrate that this resolving power varies from similar to 200 km near the base of the upper mantle to similar to 700 km in the top portion of the lower mantle we conclude that the bifrost data are able to resolve structure on radial length scale significantly smaller than a single upper mantle layer however these data provide little constraint on viscosity in the bottom half of the mantle finally elements of both the forward and inverse analyses indicate that radial and horizontal velocity estimates provide distinct constraints on mantle viscosity

gps crustal strain postglacial rebound and seismic hazard in eastern north america the saint lawrence valley example 1 we present global positioning system gps measurements that constrain the amplitude pattern and origin of crustal deformation in the saint lawrence valley quebec one of the most seismically active regions of eastern north america the gps network shows coherent southeastward motion of 0 6 0 2 mm yr 1 relative to north america and uplift of 2 6 0 4 mm yr 1 network average horizontal strain rates are mostly ese wnw shortening at 1 7 1 0 10 9 yr 1 the shortening rate across the charlevoix seismic zone is about twice as big as the regional average these measurements are consistent with both postglacial rebound pgr models and the deformation style indicated by earthquake focal mechanisms although the gps data do not discriminate between various models of crustal deformation they provide important constraints on large earthquake recurrence assuming that the gps strain estimates are representative of seismic moment release they constrain the maximum magnitude of truncated gutenberg richter recurrence statistics in the charlevoix seismic zone to mx 7 8 0 6 one m 7 earthquake per 400 1300 years the remarkable agreement between the gps strain rates seismic catalogue statistics and pgr predictions suggests that in charlevoix most of the pgr driven crustal strain may be released by large m 7 earthquakes in the rest of the saint lawrence valley pgr strain rates are significantly larger than seismic strain rates suggesting either that pgr deformation remains mostly elastic or that large events are more frequent than indicated by small earthquake statistics i e characteristic earthquakes

boudinage structure some new interpretations based on elastic plastic finite element simulations abstract an elastic plastic finite element method based on the prandtl reuss equations of plastic flow and involving equivalent stresses and strains is used to study boudinage structure our choice of data for the simulations was guided by published stress strain curves for marble matrix and quartzite boudin the essential parameters being yield stress and rock hardness defined by the slope of the stress strain curve all models assume an initial fracture and slight separation and therefore only simulate post fracture behaviour the simulations suggest that boudin shape is determined by boudin hardness maximum stresses are concentrated in the corners which therefore shows the most shape modification matrix hardness determines the amount of boudin separation direct comparison with natural examples is restricted to boudins suffering no significant pre fracture plastic deformation i e rectangular and barrel shaped boudins although other types are likely to have the characteristics of barrel and pinch and swell styles the simulations do not consider the nature and timing of boudin defining fractures but these are important in determining the style of boudinage which ultimately develops some mechanical problems associated with the infilling of inter boudin gaps by ductile rock matrix are discussed and two models proposed the first based on yielding fracture mechanics is used to explain boudins with wedge shaped or otherwise nonmatching ends the second a hydraulic model is proposed to account for gaps between rectangular boudins that are filled by ductile rock matrix

observations of misovortices within a long lake axis parallel lake effect snowband during the owles project abstractrecent lake effect snow field projects in the eastern great lakes region have revealed the presence of misovortices with diameters between 40 and 4000 m along cyclonic horizontal shear zones within long lake axis parallel bands one particular band in which an abundance of misovortices developed occurred on 7 january 2014 the leading hypothesis for lake effect misovortexgenesis is the release of horizontal shearing instability hsi an analysis of three dimensional dual doppler wind syntheses reveals that two criteria for hsi are satisfied along the horizontal shear zone strongly suggesting that hsi was the likely cause of the misovortices in this case furthermore the general lack of anticyclonic cyclonic vortex couplets throughout the event reveal that tilting of horizontal vorticity into the vertical is of less importance compared to the release of hsi and subsequent strengthening via vortex stretching a wrf simulation depicts misovortices along the horizontal shear zone within the simulat

gap filling mobile radar observations of a snow squall in the san luis valley abstracton 24 january 2017 a convective snow squall developed in the san luis valley of colorado this squall produced rapidly varying winds at san luis valley airport in alamosa with gusts up to 12 m s 1 and an associated visibility drop to 1 4 km from unlimited in less than 10 minutes this snow squall was largely undetected by the operational wsr 88d radar network due to the sangre de cristo range of the rocky mountains lying between the valley and the nearest wsr 88d radar in pueblo colorado this study presents observations of the snow squall from the x band noaa x pol radar which was deployed in the san luis valley during the event these observations document the squall developing from individual convective cells and growing upscale into a linear squall with peak radial velocities of 15 m s 1 the environment conducive to the development of this snow squall is examined using data from the high resolution rapid refresh model which shows an environment unstable to ascending surface based parcel

analysis of gps measurements in eastern canada using principal component analysis continuous global positioning system cgps position time series from eastern north america constrain the pattern and magnitude of regional crustal deformation initial analysis delineates consistent uplift patterns as expected from glacial isostatic adjustment gia predictions but the associated horizontal deformation is not definitive in part due to the short time periods for a significant number of the available stations we employ an eigenpattern decomposition in order to define a unique finite set of deformation patterns for this continuous gps data similar in nature to the empirical orthogonal functions historically employed in the analysis of atmospheric and oceanographic phenomena the method derives the eigenvalues and eigenstates from the diagonalization of the correlation matrix using a karhunen loeve expansion kle the kle technique is used to identify the important modes in both time and space for the cgps data modes that potentially include signals such as horizontal and vertical gia tectonic strain and seasonal effects here we filter both the vertical and horizontal velocity patterns on different spatiotemporal scales in order to study the potential geophysical sources after the removal of correlated and random noise the method is successful in disaggregating the linear vertical signal from more variable and less spatially correlated signals the vertical and horizontal results are compared to the predictions of the ice 3g gia loading model with a number of plausible mantle viscosity profiles the horizontal velocity analysis allows for qualitative differentiation between several potential gia models and suggests that with longer time series this technique can be employed to remove correlated noise and improve estimates of crustal strain patterns and their sources

a comparison of vlbi data with the ice 3g glacial rebound model crustal motion predicted by the ice 3g glacial rebound model exhibits a pattern of tangential horizontal divergence away from the centres of uplift which in north america and europe are located around hudson bay and the gulf of bothnia tangential velocities reach peak magnitudes of 1 2 mm yr and must be included when predicting very long baseline interferometry vlbi baseline length change rates due to post glacial rebound out of 18 observed vlbi baselines examined 3 are situated such that their predicted length rates are around their 2 uncertainties or greater it is encouraging that 2 of these baselines exhibit predicted length rates within 2 of the observed rates

climatological characteristics and orographic enhancement of lake effect precipitation east of lake ontario and over the tug hill plateau abstractlake effect snowstorms east of lake ontario are frequently intense and contribute to substantial seasonal accumulations especially over the tug hill plateau hereafter tug hill which rises at a gentle 1 25 slope to 500 m above lake level using a variety of datasets including radar imagery from the ktyx fort drum new york wsr 88d this paper examines the characteristics of lake effect precipitation east of lake ontario over 13 cool seasons 16 september 2001 15 may 2014 during this period days with at least 2 h of lake effect account for 61 76 of the mean cool season snowfall and 24 37 of the mean cool season liquid precipitation mean monthly lake effect frequency and snowfall peak in december and january the highest lake effect frequency and snowfall occur over the western and upper tug hill with an arm of relatively high lake effect frequency and snowfall extending to the southeast shore of lake ontario to the east lee lake effect frequency and snowfall decrease abruptly ov

mesoscale vortices over the great lakes in wintertime abstract the occasional occurrence of wintertime mesoscale lake vortices is documented the vortices are readily discernible in satellite imagery in which they take one of three forms a miniature comma cloud a swirl of cloud bands resembling a miniature tropical storm or a swirl of cloud streets despite their impressive appearance in satellite imagery these vortices are usually relatively mild in comparison with other lake effect storms and produce only gusty winds and brief snow squalls as they move onshore the vortices are accompanied by a slightly lowered surface pressure and a weak cyclonic low level wind circulation fourteen vortices were detected over the great lakes in the years 1978 82 they occurred under conditions of relatively weak surface pressure gradient with a ridge of high pressure usually found over or west of the region convergence was generally detected in the surface winds prior to vortex development apparently related to land breeze circulations comparisons are made betw

ice 3g a new global model of late pleistocene deglaciation based upon geophysical predictions of post glacial relative sea level change a new high resolution global model of late pleistocene deglaciation is inferred on the basis of geophysical predictions of postglacial relative sea level variations in which the ice ocean solid earth interaction is treated in a gravitationally self consistent fashion for the purpose of these analyses the radial viscoelastic structure of the planet is assumed known on the basis of previously published sensitivity tests on solutions of the forward problem only radiocarbon controlled relative sea level histories from sites that were actually ice covered with one or two additions are employed to constrain the model leaving relative sea level rsl data from sites that were not ice covered to be employed to confirm its consistency results for these confirmatory analyses are reported elsewhere here the new deglaciation model referred to as ice 3g is compared to previous models derived by several independent means and tested against a number of additional observations other than sea level histories including geologically controlled retreat isochrones oxygen isotope data from deep sea sedimentary cores and coral terrace elevations the latter two observations strongly constrain the net sea level rise that has occurred since the onset of deglaciation and therefore the mass of ice that melted during the last glacial interglacial transition

model simulations examining the relationship of lake effect morphology to lake shape wind direction and wind speed abstract idealized model simulations with an isolated elliptical lake and prescribed winter lake effect environmental conditions were used to examine the influences of lake shape wind speed and wind direction on the mesoscale morphology this study presents the first systematic examination of variations in lake shape and the interplay between these three parameters the array of 21 model simulations produced cases containing each of the three classic lake effect morphologies i e vortices shoreline bands and widespread coverage and in some instances the mesoscale circulations were composed of coexisting morphologies located over the lake near the downwind shoreline or inland from the downwind shore as with lake effect circulations simulated over circular lakes the ratio of wind speed u to maximum fetch distance l was found to be a valuable parameter for determining the morphology of a lake effect circulation when variations of lake shape wind speed and wind direction were introduced f

glacial isostatic adjustment and the anomalous tide gauge record of eastern north america sea level variations as recorded by the global network of tide gauges represent a rich data set for studying a wide range of natural and anthropogenic phenomena such as the sea level rise induced by possible global warming for this purpose long term sea level trends must be corrected for the contaminating effects of continuing glacial isostatic adjustment1 5 gia the numerical correction procedure has for sites on the east coast of north america yielded a set of highly anomalous sea level rates characterized by systematic geographical trends2 4 5 we demonstrate that these trends are a consequence of inadequacies in the previous standard numerical prediction for gia in particular we find that the well known trends in the gia corrected tide gauge rates are eliminated if the lower mantle viscosity of the earth model used in the gia prediction is increased this result obviates the need to explain the anomalous trend as a manifestation of gulf stream ocean circulation4 or neotectonic processes2

comparison of observations with idealized model results for a method to resolve winter lake effect mesoscale morphology abstract forecasters in the great lakes region have for several decades recognized a general relationship of wind speed and overlake fetch to lake effect snowstorm morphology a recent study using idealized mesoscale model simulations of lake effect conditions over circular and elliptical lakes showed the ratio of wind speed to maximum fetch distance u l may be used to effectively predict lake effect snowstorm morphology the current investigation provides an assessment of the u l criteria using observational datasets previously published great lakes lake effect snowstorm observational studies were used to identify events of known mesoscale morphology hindcasts of nearly 640 lake effect events were performed using historical observations with u l as the predictor results show that the quantity u l contains important information on the different mesoscale lake effect morphologies however it provides only a limited benefit when being used to predict mesoscale morphology in real lake effect situations

step wise growth of biotite porphyroblasts in pelitic schists of the western lys caillaouas massif pyrenees abstract detailed optical and electron microscope sem and tem examination of biotite blasts from pelitic schists of the western lys caillaouas massif in the pyrenees reveals a variety of microstructures suggesting growth of the blasts before and after a thermal peak during the d2 deformation in the early stages of growth the biotites had 001 at high angles to s1 and they appear to have existed as thin 001 parallel plates in many cases blastesis is suggested to have involved growth of the biotites into their own continuously dilating pressure shadows inclusions with dentate grain boundaries banded structures and radiator fin intergrowths suggest a mechanism analogous to the ramsay crack seal model for vein formation but here involving step wise dilation of a pressure shadow cavity into which the adjacent blast itself was growing

a spectral formalism for computing three dimensional deformations due to surface loads 2 present day glacial isostatic adjustment using a spherically symmetric self gravitating linear viscoelastic earth model we predict present day three dimensional surface deformation rates and baseline evolutions arising as a consequence of the late pleistocene glacial cycles in general we use realistic models for the space time geometry of the final late pleistocene deglaciation event and incorporate a gravitationally self consistent ocean meltwater redistribution the predictions of horizontal velocity presented herein differ significantly in both their amplitude and their spatial variation from those presented in an earlier analysis of others which adopted simplified models of both the late pleistocene ice history and the earth rheology an important characteristic of our predicted velocity fields is that the melting of the laurentide ice sheet over canada is capable of contributing appreciably to the adjustment in europe the sensitivity of the predictions to variations in mantle rheology is investigated by considering a number of different earth models and by computing appropriate frechet kernels these calculations suggest that the sensitivity of the deformations to the earth s rheology is significant and strongly dependent on the location of the site relative to the ancient ice sheet the effects on the predictions of three dimensional deformation rates of altering the ice history or adopting approximate models for the ocean meltwater redistribution have also been considered and found to be important the former especially so finally for a suite of earth models we provide predictions of the velocity of a number of baselines in north america and europe we find that in general both radial and tangential motions contribute significantly to baseline length changes and that these contributions are a strong function of the earth model we have furthermore found a set of earth models which together with the ice 3g deglaciation chronology produce predictions of baseline length changes that are consistent with very long baseline interferometry measurements of baselines within europe

subsidence along the atlantic coast of north america insights from gps and late holocene relative sea level data the atlantic coast of north america is increasingly affected by flooding associated with tropical and extratropical storms exacerbated by the combined effects of accelerated sea level rise and land subsidence the region includes the collapsing forebulge of the laurentide ice sheet high quality records of late holocene relative sea level rsl rise are now available allowing separation of long term glacial isostatic adjustment induced displacement from modern vertical displacement measured by gps we compare geological records of late holocene rsl to present day vertical rates from gps for many coastal areas there is no significant difference between these independent data exceptions occur in areas of recent excessive groundwater extraction between virginia 38 n and south carolina 32 5 n the present day subsidence rates in these areas are approximately double the long term geologic rates which has important implications for flood mitigation tide gauge records therefore should be used with caution for studying sea level rise in this region

the partitioning of deformation in flowing rock masses abstract most geological structures owe their development to heterogeneous and or non steady flow flow partitioning refers to the division of the instantaneous velocity field into components related to translation strain and rotation flow partitioning during the development of a geological structure usually changes with time and different histories of flow are involved at different points in the developing structure heterogeneity leads to the development of flow domains with different characteristics notably the degree of non coaxiality of deformation and different partitionings of the rotational component of flow into shear induced vorticity and spin during non steady flow there is often continual repartitioning of vorticity between the spin and shear induced components spin is an important aspect of flow leading to the development of structure this paper discusses the partitioning of deformation in a flowing rock mass coaxial flow tends to occur in isotropic materials in regions near weakly constrained boundaries non coaxial flow is favoured by suitably oriented material anisotropy and or the presence of well defined boundary constraints involving parallel relative displacements a developing anisotropy e g a crystallographic fabric in a shear zone can induce a change from coaxial to non coaxial flow other effects are related to the scale of approximation for example bulk shear induced vorticity can be locally converted to spin flow in the crust and mantle of the earth produces geological structures on all scales and involves many different types of rheological response the factors that affect flow partitioning e g spin versus non coaxial deformation are therefore of interest

convective evolution across lake michigan during a widespread lake effect snow event abstract lake effect snowstorms generally develop within convective boundary layers which are induced when cold air flows over relatively warm lakes in fall and winter mesoscale circulations within the boundary layers largely control which communities near the downwind shores of the lakes receive the most intense snow the lack of quantitative observations over the lakes during lake effect storms limits the ability to fully understand and predict these mesoscale circulations this study provides the first observations of the concurrent spatial and temporal evolution of the thermodynamic and microphysical boundary layer structure and mesoscale convective patterns across lake michigan during an intense lake effect event observations analyzed in this study were taken during the lake induced convection experiment lake ice aircraft and sounding observations indicate that the lake effect snows of 13 january 1998 developed within a convective boundary layer that grew rapidly across lake michigan boundary

near field hydro isostasy the implementation of a revised sea level equation summary we describe how the existing sea level equation incorrectly predicts the change in sea level and thus the ocean load in ice covered subgeoidal geographic regions during periods of deglaciation we go on to present a new sea level equation that overcomes this problem and we describe how this equation can be solved in a gravitationally self consistent manner by employing a well known spectral technique application of the new theory to predict relative sea level rsl histories and present day 3 d solid surface deformation rates in northeastern canada based on a single earth model characterized by a lithospheric thickness of 100 km and upper and lower mantle viscosities of 5 1020 and 5 1021 pa s respectively demonstrates that a significant error is introduced when the original theory is employed to predict the oceanic component of the surface load predictions of rsl curves show a discrepancy of 40 per cent at sites where data have been obtained and employed to constrain models of earth viscosity structure and ice sheet histories this error will significantly bias estimates of mantle viscosity structure and ice thicknesses that are based on the original theory in addition predictions of 3 d deformation rates differ by up to 25 per cent in some regions and so future applications that employ these data to constrain models of the glacial isostatic adjustment process should adopt the improved sea level theory in contrast estimates of inverse decay times from the predicted rsl curves are insensitive to within the observational error to the improvement in the surface load introduced by the new theory thus viscosity structure inferences based on this parametrization and the original sea level equation are unaffected by the error in the ocean load finally the new theory predicts a eustatic i e globally uniform rise in sea level over the postglacial period that is 11 m lower than that determined via the original theory therefore estimates of the global ice budget at the last glacial maximum based on far field rsl data and the original sea level theory will be too small by 10 per cent

crack seal fibre growth mechanisms and their significance in the development of oriented layer silicate microstructures abstract an analysis of crack seal fibre growth mechanisms has shown two important implications of the crack seal process for the interpretation of microstructures in low grade metamorphic rocks 1 1 the ability of fibre growth to track the incremental separation history of crack walls depends on details of the nucleation and growth mechanisms 2 2 fibrous crystals may develop cristallographic preferred orientations in certain crack seal situations the microstructures of layer silicates and associated phases developed in several examples of syntectonic intragranular microfracture sites and veins indicates that layer silicate 001 and grain shape preferred orientation can develop during crack seal deformation by oriented growth mechanisms during successive crack seal increments preferred orientation may develop in response to an interaction between anisotropic growth kinetics and the displacement history resulting in preferential rejoining by syntaxial overgrowth of pulled apart grains having fast growth directions parallel to the incremental displacement direction across a microcrack preferred orientation may also be developed and enhanced in crack seal growth sites by overgrowth of previously oriented layer silicates in the microcrack walls in this case the crystallographic preferred orientation need not be simply related to the displacement history during crack seal fibre growth since crack seal processes may operate on all scales down to the minimum size of a microfracture in a deforming rock such mechanisms of layer silicate preferred orientation development are expected to be very significant in developing and enhancing foliation during deformation involving microfracture and solution transfer processes

present day post glacial sea level change far from the late pleistocene ice sheets implications for recent analyses of tide gauge records we examine the sensitivity of predictions of the present day rate of sea level change due to glacial isostatic adjustment gia in two regions located within the far field of the late pleistocene ice sheets europe north africa and the western pacific caribbean to variations in the mantle viscosity profile the regions considered here encompass the location of 11 of 21 sites used in a recent determination based on gia corrected tide gauge records of the global rate of secular sea level change our analysis suggests that the mean gia correction at the 11 far field sites may vary by as much as 0 5 mm yr depending on the adopted earth model and we derive a bound on the residual secular sea level rise of 1 1 to 1 6 mm yr this bound is consistent with our analysis of the tide gauge record from the u s east coast and it suggests that previous estimates of the residual sea level rise represent an upper bound