spatiotemporal evolution of paludification associated with autogenic and allogenic factors in the black spruce moss boreal forest of quebec canada paludification is the most common process of peatland formation in boreal regions in this study we investigated the autogenic e g topography and allogenic fire and climate factors triggering paludification in different geomorphological contexts glaciolacustrine silty clayey and fluvioglacial deposits within the quebec black spruce picea mariana moss boreal forest paleoecological analyses were conducted along three toposequences varying from a forest on mineral soil to forested and semi open peatlands plant macrofossil and charcoal analyses were performed on basal peat sections 50 cm and thick forest humus sphagnum in microdepressions paludification resulted in the decline of some coniferous species such as abies balsamea and pinus banksiana the paleoecological approach along toposequences allowed us to understand the spatiotemporal dynamics of paludification and its impacts on the vegetation dynamics over the holocene

holocene carbon accumulation rates from three ombrotrophic peatlands in boreal quebec canada impact of climate driven ecohydrological change understanding the processes controlling peatland carbon c sequestration is critical to anticipate potential changes in the global c cycle in response to climate change although identification of these factors may be relatively straightforward on seasonal timescales at centennial to millennial timescales complexities arise because of interactions between climate vegetation hydrology and long term ecological processes to better understand the factors controlling long term c accumulation holocene rates of c sequestration were quantified from three pristine ombrotrophic peatlands in boreal quebec northeastern canada 52 n 75 76 w bulk density and loss on ignition analyses combined with radiocarbon dating and age depth modelling were used to estimate long term apparent rates of carbon accumulation past changes in vegetation and water table depth were obtained from plant macrofossil and testate amoeba analysis earliest regional peat accumulation started 7520 cal bp with long term rates of c s

a composite life cycle of nonsquall mesoscale convective systems over the tropical ocean part i kinematic fields abstract the wind fields associated with cloud clusters observed during the global atmospheric research program s atlantic tropical experiment gate are investigated a compositing procedure is devised to isolate the cluster circulations satellite observed cloud cover estimates by cox and griffith form the basis for the identification and classification of clusters and for the determination of their life cycles the compositing criteria focus on the upper tropospheric portions of anvil clouds that are a prominent feature of cloud clusters the compositing procedure is applied to a set of objectively analyzed upper air winds for phase 3 of gate prepared by k v ooyama and j h chu the results show that slow moving cloud clusters tend to form in regions of relatively small vertical wind shear and that the shear at the cluster center decreases during the cluster life cycle squall clusters on the other hand have significantly larger lower tropospheric shear changes in the total horizontal wind field

influence of mesoscale topography on tropical cyclone tracks further examination of the channeling effect abstractobservations have documented typhoons experiencing pronounced track deflection before making landfall in taiwan in this study idealized full physics model experiments are conducted to assess the orographic influence on tropical cyclone tc track an intense and westward moving tc is simulated to approach the bell shaped terrain imitating the taiwan topography sensitivity numerical experiments are carried out to evaluate the topographic effect under different flow regimes and parameters such as tc intensity terrain height and incident angle of the tc movement toward the topography all the presented simulated storms experience southward track deflection prior to landfall different from the mechanism related to the channeling effect induced low level northerly jet as suggested in previous studies this study indicates the leading role of the northerly asymmetric flow in the midtroposphere in causing the southward deflection of the simulated tc tracks the midtropospheric northerly asymmetric

a numerical study of the effect of island terrain on tropical cyclones abstract a triply nested movable mesh model was used to study the behavior of tropical cyclones encountering island mountain ranges the integration domain consisted of a 37 wide and 45 long channel with an innermost mesh resolution of 1 6 the storms used for this study were embedded in easterly flows of 5 and 10 m s 1 initially realistic distributions of island topography at 1 6 resolution were inserted into the model domain for the region of the caribbean including the islands of cuba hispaniola and puerto rico the island of taiwan and the region of luzon in the northern philippines it was found that the islands affected the basic flow as well as the wind field directly associated with the storm system the combination of these effects caused changes in the track and translational speed of the storm in particular in the case of the 5 m s 1 easterly flow the storm accelerated and veered to the north well before reaching taiwan for the other island distributions the northward deflecti

holocene changes in seasonal precipitation highlighted by fire incidence in eastern canada postglacial fire history has been reconstructed for eastern canada from charcoal influx anomalies from 30 sites taken from a lacustrine charcoal database the reconstruction exhibits coherent patterns of fire occurrence in space and time the early holocene is characterised by high fire incidence there is a major change to much lower occurrence slightly after 8 ka bp a return to more fire appears after 3 ka bp this sequence does not fit with the hydro climatic reconstruction deduced from lake level reconstructions for northeastern north america which indicates a dry early and mid holocene and a wet late holocene fire occurrence however closely matches summer relative humidity inferred from 18o the differences between fire frequency and lake level history are due to changes in the seasonality of precipitation and drought frequency lake levels are essentially controlled by winter precipitation while summer precipitation controls fire occurrence the early holocene before 8 7 5 ka bp experienced dry summers due to higher solar radiation and dry adiabatic winds from the residual laurentide ice sheet the middle holocene was dominated by wet summers due to stability of the atlantic air mass over eastern canada after 2 5 ka bp summers became drier albeit not as fire conducive as during the early holocene late holocene summers conducive to fire are explained by more frequent incursions of dry cool pacific or cold arctic air masses over eastern canada

expanded response surfaces a new method to reconstruct paleoclimates from fossil pollen assemblages that lack modern analogues pollen based paleoclimatic interpretations of late glacial to early holocene climates 17 9 ka in midwestern north america are hampered by samples that lack modern analogues unresolved questions include the magnitude and direction of temperature seasonality i e were these climates more or less seasonal than present and the temporal changes in precipitation central to the no analogue problem is the truncation of modern pollen climate relationships for abundant late glacial taxa such as fraxinus here we present a new method called the expanded response surface ers method developed to reconstruct climates from no analogue pollen assemblages and applied to a high resolution late glacial pollen record from crystal lake illinois to test hypotheses about late glacial climates the key assumptions central to the ers method are 1 plant species and pollen abundances follow symmetrical unimodal distributions along climatic gradients 2 taxa with truncated distributions in modern climate space occupy a subset of their fundamental niche and 3 expansion of truncated distributions by mirroring around the distributional mode recovers the portion of the fundamental niche not realized in the modern climate space with the ers method we expanded modern pollen climate relationships by mirroring pollen abundances for each taxon around a mode defined with respect to four climate axes mean winter temperature mean summer temperature mean winter precipitation and mean summer precipitation the ers method reconstructed past temperatures and precipitation during the height of no analogue conditions 14 160 12 370 cal yr bp for 37 of the crystal lake samples where techniques that employed only modern observational data found matches for only 13 of the fossil samples the total climate space of the expanded taxa set allowed analogue matches under more seasonal than present climates with higher than present precipitation the ers climate reconstructions for the height of no analogue conditions indicated cooler than present summer and winter temperatures similar to present seasonal range in temperatures higher than present winter precipitation and similar to present summer precipitation these results thus suggest that high moisture availability helped drive the formation of the midwestern no analogue communities with high fraxinus nigra abundances but do not show higher than present temperature seasonality notwithstanding the higher than present insolation seasonality at this time during the no analogue late glacial interval picea mariana f nigra and larix stands probably grew on low lying poorly drained soils in the crystal lake region whereas abies picea glauca quercus and ostrya carpinus grew on upland positions with better soil drainage

the influence of island topography on typhoon track deflection abstracthigh resolution simulations for typhoon krosa 2007 and a set of idealized experiments are conducted using a full physics model to investigate the eminent deflection of typhoon track prior to its landfall over mountainous island topography the terrain height of taiwan plays the most important role in typhoon krosa s looping motion at its landfall while the surface properties details in the topographic shape of taiwan and the cloud microphysics are shown to be secondary to the track deflection a simulation with 3 km resolution and realistic model settings reproduces the observed krosa s track while that with 9 km resolution fails suggesting that high resolution to better resolve the typhoon terrain interactions is important for the prediction and simulation of typhoon track deflection prior to landfall results from idealized experiments with model configurations mimicking those of supertyphoon krosa show that vortices approaching the northern and central topography are significantly deflec

the effect of hawai i s big island on track and structure of tropical cyclones passing to the south and west abstractthe effect of the big island of hawai i on tropical cyclone tc track and structure is investigated using the weather research and forecasting wrf model the high 4000 m mountains of the big island modulate lower tropospheric flow in such a way that it can influence tcs hundreds of kilometers away from the island when a tc approaches from the east the blocking of lower tropospheric flow leads to a slowing of the tc s movement as a tc passes close to the south side of the big island it deviates southward the tc core convection and winds can become axisymmetric because of the blocking of the stronger northeasterly flow to the north of the storm the authors hypothesize that this axisymmetrization led to the unexpected eye formation of hurricane flossie 2007 just southeast of the big island as a tc moves into the lee southwest side of the big island the flow associated with the island wake leads to a track deviated to the right the hurricane dot 1959 simulations suggest that this

relationships between charcoal particles in air and sediments in west central siberia production and size of charred particles determine transport and deposition in lakes lack of such data is a principal obstacle to interpretation of past fire from charcoal profiles our two part a

effects of landfall location and the approach angle of a cyclone vortex encountering a mesoscale mountain range abstractthe orographic effects of landfall location approach angle and their combination on track deflection during the passage of a cyclone vortex over a mesoscale mountain range are investigated using idealized model simulations for an elongated mesoscale mountain range the local vorticity generation driving the cyclone vortex track deflection is more dominated by vorticity advection upstream of the mountain range by vorticity stretching over the lee side and its immediate downstream area and by vorticity advection again far downstream of the mountain as it steers the vortex back to its original direction of movement the vorticity advection upstream of the mountain range is caused by the flow splitting associated with orographic blocking it is found that the ideally simulated cyclone vortex tracks compare reasonably well with observed tracks of typhoons over taiwan s central mountain range cmr in analyzing the relative vorticity budget the authors found that jumps in the vortex path are lar

a numerical study of the track deflection of supertyphoon haitang 2005 prior to its landfall in taiwan abstract a series of numerical simulations are conducted using the advanced research version of the weather research and forecasting model with a 4 km fine mesh to examine the physical processes responsible for the significant track deflection and looping motion before the landfall of supertyphoon haitang 2005 in taiwan which poses a unique scientific and forecasting issue in the control experiment a low level northerly jet induced by the channeling effect forms in the western quadrant of the approaching storm where the inner core circulation is constrained by the presence of taiwan s terrain because of the channeling effect the strongest winds of the storm are shifted to the western portion of the eyewall the northerly advection flow averaged asymmetric winds within 100 km radius results in a sharp southward turn of the westward moving storm the time series of the advection flow shows that the advection wind vectors rotate cyclonically in time and well match the motion of the simulated vortex

on the geographic asymmetry of typhoon translation speed across the mountainous island of taiwan abstractthis paper examines the effect of topographically phase locked convection on the motion of typhoons across the island of taiwan data for 84 typhoons that reached taiwan s eastern coast from 1960 to 2010 are analyzed with motions compared to the long term average overland translation speed for 61 continuous track typhoons among all cases 77 of the slow moving tropical cyclones tcs made landfall on the northern end of taiwan s eastern coast while 60 of the fast storms had southeastern coastal landfalls this geographic asymmetry with respect to typhoon translation speeds widened after landfall as the slow movers typically decelerated during the overland period whereas the faster tcs sped up in particular the average overland duration was 16 h for the slow class compared to only 3 h for the fast moving typhoons the combination of slower translation with longer duration for the northern class of tcs led to large rainfall on the southwestern slope of the island s central mountain range we

interaction of typhoons with the taiwan orography part i upstream track deflections abstract a combined observational and numerical modeling approach is used to study the upstream track deflections of westward moving tropical cyclones approaching the mountainous terrain of taiwan although the standard deviations are large the mean track deflections are larger and have a different orientation for storms approaching the southern end of the island from those approaching the northern end the deflections tend to be larger for weaker and slower moving storms two distinct regions of upstream track deflections that are detected in the observations are explored in a sensitivity study with a 45 km horizontal resolution and 16 layer numerical model as the outer circulation of the tropical cyclone begins to interact with the mountain barrier the zonal decelerations and southward track deflections are explained by an enhanced blocking and deflection of the environmental flow advecting the cyclone the larger effect for southern approaching storms compared to northern storms is because the stron

reconstruction of the long term fire history of an old growth deciduous forest in southern quebec canada from charred wood in mineral soils charcoal particles are widespread in terrestrial and lake environments of the northern temperate and boreal biomes where they are used to reconstruct past fire events and regimes in this study we used botanically identified and radiocarbon dated charcoal macrofossils in mineral soils as a paleoecological tool to reconstruct past fire activity at the stand scale charcoal macrofossils buried in podzolic soils by tree uprooting were analyzed to reconstruct the long term fire history of an old growth deciduous forest in southern quebec charcoal fragments were sampled from the uppermost mineral soil horizons and identified based on anatomical characters spruce picea spp fragments dominated the charcoal assemblage along with relatively abundant wood fragments of sugar maple acer saccharum and birch betula spp and rare fragments of pine pinus cf strobus and white cedar thuja canadensis ams radiocarbon dates from 16 charcoal fragments indicated that forest fires were widespread during the early holocene whereas no fires were recorded from the mid holocene to present the paucity of charcoal data during this period however does not preclude that a fire event of lower severity may have occurred at least eight forest fires occurred at the study site between 10 400 and 6300 cal yr b p with a dominance of burned conifer trees between 10 400 and 9000 cal yr b p and burned conifer and deciduous trees between 9000 and 6300 cal yr b p based on the charcoal record the climate at the study site was relatively dry during the early holocene and more humid from 6300 cal yr b p to present however it is also possible that the predominance of conifer trees in the charcoal record between 10 400 and 6300 cal yr b p created propitious conditions for fire spreading the charcoal record supports inferences based on pollen influx data labelle c richard p j h 1981 vegetation tardiglaciaire et postglaciaire au sud est du parc des laurentides quebec geographie physique et quaternaire 35 345 359 of the early arrival of spruce and sugar maple in the study area shortly after deglaciation we conclude that macroscopic charcoal analysis of mineral soils subjected to disturbance by tree uprooting may be a useful paleoecological tool to reconstruct long term forest fire history at the stand scale d 2005 university of washington all rights reserved

orographic influence on a drifting cyclone abstract in this study a primitive equation numerical model is adopted to investigate the orographic influence on a drifting cyclone over an idealized topography similar to that of taiwan for a cyclone propagating from the east and impinging on the central portion of the mountain a northerly surface jet tends to form upstream of the mountain between the primary cyclone and the mountain due to blocking and channeling effects two pressure ridges and one trough are also produced when the cyclone approaches the mountain the low level vorticity and low pressure centers decelerate and turn southward upstream of the mountain due to orographic blocking at the same time the upstream low level vorticity is blocked by the mountain the abrupt increase of surface vorticity and the contraction of cyclone scale on the lee side are explained by the generation of new potential vorticity pv due to wave breaking associated with the severe downslope wind and hydraulic jump the generation of this new pv is evidenc

a multiscale numerical study of hurricane andrew 1992 part vi small scale inner core structures and wind streaks abstract the objectives of part vi of this series of papers are to a simulate the finescale features of hurricane andrew 1992 using a cloud resolving grid length of 2 km b diagnose the formation of small scale wind streaks and c perform sensitivity experiments of varying surface fluxes on changes in storm inner core structures and intensity as compared to observations and a previous 6 km model run the results show that a higher resolution explicit simulation could produce significant improvements in the structures and evolution of the inner core eyewall and spiral rainbands and in the organization of convection the eyewall becomes much more compact and symmetric with its width decreased by half and the radius of maximum wind is reduced by 10 to 20 km a zone of deep and intense potential vorticity pv is formed at the edge of the eye a ring of maximum pv is collocated in regions of maximum upward motion in the eyewall and interacts strongly with the eyewall convection the convective cor

the late holocene record of aeolian and fire activity in northern quebec canada a set of 196 14c dates was used to reconstruct late holocene aeolian activity in the hudson bay area along a south north transect crossing the northern boreal forest the forest tundra and the shru

changes in fire regime explain the holocene rise and fall of abies balsamea in the coniferous forests of western quebec canada the coniferous boreal forest of northeastern north america is characterized by large and severe fire events and dominated by black spruce picea mariana with scattered patches of balsam fir abies balsamea a species otherwise predominant in the more southern mixedwood boreal forests characterized by smaller and less severe fire events because balsam fir is a late successional species ill adapted to fire this study aimed at determining if the scattered balsam fir patches found in the coniferous forest were relics of a former fire regime characterized by less frequent and or severe conflagrations fire and vegetation history were assessed for a coniferous forest site through analyses of charcoal pollen and plant macroremains preserved in lake sediments peat and hydromorphic forest soil pollen and macroremains analyses show that black spruce dominated the local vegetation since deglaciation c 8000 cal yr bp balsam fir was abundant around the site during the warm and humid summers of the hypsithermal between c 7000 and 3500 cal yr bp before gradually declin ing during the cool and dry neoglacial which was characterized by increased fire frequency and severity scattered balsam fir patches in the coniferous forest result from the fragmentation of formerly larger popula tions and are presently in disequilibrium with climate

control parameters for the influence of a mesoscale mountain range on cyclone track continuity and deflection abstract in this study prospective control parameters are identified for diagnosing the continuity and deflection of cyclone tracks across a mesoscale mountain range based on idealized simulations of a westward moving cyclone it was found that the cyclone track becomes a discontinuous continuous track and the cyclone experiences more less deflection with a combination of small large values of vmax nh u nh r ly u flx and vmax fr and large small value of h lx the symbols are defined as follows vmax the maximum tangential wind n the brunt vaisala frequency h the mountain height u the basic wind speed r the radius of vmax f the coriolis parameter and lx and ly the horizontal scales of the mountain in x and y directions respectively a conceptual model is proposed to explain track deflection and continuity for a westward moving cyclone encountering idealized topography representative of the central mountain range of taiwan with weak orographic blocking a cyclone crosses over the mount

increased atmospheric dust deposition during the neoglacial in a boreal peat bog from north eastern canada abstract dust deposition in north eastern canada was estimated from the geochemical signature of a boreal peat bog from the james bay lowlands the rare earth elements and other lithogenic elements as well as nd isotopes were measured by q icp ms icp oes and mc icp ms respectively along a 4 20 m peat core covering the last 7000 years a principal component analysis performed on the geochemical dataset shows that rees display the same chemical behavior as other lithogenic elements such as al and ti which suggests that they are immobile in the peat column and can be used as tracers of dust deposition after 4000 cal yr bp peaks in dust deposition associated with greater variability in testate amoebae assemblages and plant macrofossil composition as well as a change in nd values are observed between 7000 and 4100 cal yr bp the nd values varied from 36 to 29 while they gradually increased from 4100 cal yr bp until 1500 cal yr bp suggesting proportionally less dust from local source s is deposited in favor of more regional source s from 1500 cal yr bp nd values remained relatively stable around 15 and 12 most of the dust peaks correspond to documented cold and dry periods likely linked to intrusion of arctic air masses a migration of the polar front might explain the more frequent intrusion of arctic air masses in the region and the greater variability in the lg2 record over the last 4000 years

revisiting the relationship between eyewall contraction and intensification abstractin the widely accepted convective ring model of tropical cyclone intensification the intensification of the maximum winds and the contraction of the radius of maximum winds rmw occur simultaneously this study shows that in idealized numerical simulations contraction and intensification commence at the same time but that contraction ceases long before peak intensity is achieved the rate of contraction decreases with increasing initial size while the rate of intensification does not vary systematically with initial size utilizing a diagnostic expression for the rate of contraction it is shown that contraction is halted in association with a rapid increase in the sharpness of the tangential wind profile near the rmw and is not due to changes in the radial gradient of the tangential wind tendency it is shown that a number of real storms exhibit a relationship between contraction and intensification that is similar to what is seen in the idealized simulations in particular the statistical

soil charcoal stability over the holocene across boreal northeastern north america abstract the analysis of macroscopic wood charcoal fragments extracted from soils is frequently used as a palaeoecological tool for reconstructing stand scale forest composition and fire history here we explored the putative loss of palaeoecological information due to charcoal degradation through time and in different biogeographical settings we compared the relationship between charcoal mass and abundance for soil samples from five biogeographical regions of boreal northeastern north america spanning most of the holocene period we verified whether charcoal o 2 mm conservation differed as a consequence of different taphonomical processes between organic and mineral soil types we also assessed the mass abundance relationship as a function of charcoal residence time in soil overall the slope of the regression between charcoal particles mass g and abundance number of particles was 0 0042 the slope was not significantly different in samples from organic and mineral soil and all biogeographical regions had similar slope values except one higher charcoal fragmentation probably due to high colluvial activity charcoal conservation also did not vary according to residence time in soil this study shows that macroscopic soil charcoal particles resist fragmentation over millennia in different biogeographical settings and under the influence of various taphonomical processes