impacts of convectively coupled kelvin waves on environmental conditions for atlantic tropical cyclogenesis abstracthigh amplitude convectively coupled equatorial atmospheric kelvin waves cckws are explored over the tropical atlantic during the boreal summer 1989 2009 focus is given to the atmospheric environmental conditions that are important for tropical cyclogenesis cckws are characterized by deep westerly vertical wind shear to the east of its convectively active phase and easterly vertical wind shear to the west of it this dynamical signature increases vertical wind shear over the western tropical atlantic ahead of the convectively active phase and reduces vertical wind shear after its passage the opposite is true over the eastern tropical atlantic where the climatological vertical wind shear is easterly positive total column water vapor tcwv anomalies progress eastward with the convectively active phase of the cckw whereas negative tcwv anomalies progress eastward with the convectively suppressed phase during the passage of the convectively active phase of the cckw a zonally oriented strip o

projections of the tropical atlantic vertical wind shear and its relationship with enso in sp ccsm4 abstractthe vertical wind shear over the tropical atlantic ocean and its relationship with enso are analyzed in the superparameterized community climate system model version 4 sp ccsm4 and in the conventional ccsm4 the climatology of vertical wind shear over the tropical atlantic and the enso shear relationship are well simulated in the control runs of sp ccsm4 and ccsm4 however because of different representations of cloud processes in a warmer climate such as the representative concentration pathway 8 5 rcp8 5 scenario sp ccsm4 projects increased mean westerlies at 200 hpa during july through october jaso whereas ccsm4 projects decreased mean westerlies at 200 hpa over the equatorial atlantic the different changes in the upper level wind further contribute to different projection of jaso mean vertical wind shear over the equatorial atlantic in the rcp8 5 scenario when excluding the linear trend projection of the enso shear relationships by sp ccsm4 retains similar features as in the obs

parametric representation of the primary hurricane vortex part i observations and evaluation of the holland 1980 model although numerical models are essential to hurricane forecasting many other applications require only statistical depiction of the wind distribution in holland s 1980 parametric profile radius of maximum wind maximum wind and a measure of the profile width describe the radial variation of the axisymmetric wind variants of the holland profile are used to predict insurance underwriting risk ocean response and storm surge inundation since these calculations guide high stakes financial and emergency managment decisions it is logical to test them against observations the hurricane research division s flight level database archives observations were obtained by noaa and u s air force reserve aircraft the data considered here are winds and geopotential heights observed during 606 lower and midtropospheric flights into atlantic and eastern pacific tropical cyclones during 1977 2000 the 493 profiles that meet quality control criteria are seasonally geographically representative least squares fits of the holland model to these data provide evaluation of the parameters distributions and critical examination of the profile s realism individual fitted profiles differ from the observations in a consistent pattern the areas of strong winds in the eyewall and of nearly calm winds at the vortex center are too wide beyond 2 or 3 times the eye radius the wind decreases too rapidly with distance from the center although the average bias in fitted profiles is 1ms 21 the root mean square error is 4 2 m s 21 5 2 m s21 for independent data maximum winds estimated from the fitted holland profile height wind relation average 2 5 m s 21 too strong with an rms error of 6 5 m s 21 the pattern of too strong wind spread over too much real estate exaggerates the occurrence of winds stronger than 50 m s 21 by 50

the bi decadal rainfall cycle southern annular mode and tropical cyclones over the limpopo river basin southern africa the association between bi decadal rainfall variability over southern africa and the rainfall contributed by tropical cyclonic systems from the southwest indian ocean swio provides a potential means towards understanding decadal scale variability over parts of the region a multi decadal period is considered focusing on the anomalous tropospheric patterns that induced a particularly wet 8 year long sub period over the limpopo river basin the wet sub period was also characterized by a larger contribution to rainfall by tropical cyclones and depressions the findings suggest that a broadening of the hadley circulation underpinned by an anomalous anticyclonic pattern to the east of southern africa altered tropospheric steering flow relative vorticity and moisture contents spatially during the sub period of 8 years these circulation modulations induced enhanced potential for tropical systems from the swio to cause precipitation over the limpopo river basin the same patterns are also conducive to increasing rainfall over the larger subcontinent therefore explaining the positive association in the bi decadal rainfall cycle and rainfall contributed by tropical cyclonic systems from the swio an overview of regional circulation anomlies during alternating near decadal wet and dry epochs is given the regional circulation anomalies are also explained in hemispheric context specifically in relation to the southern annular mode towards understanding variation over other parts of the southern hemisphere at this time scale

responses of tropical deep convection to the qbo cloud resolving simulations abstractobservational studies suggest that the stratospheric quasi biennial oscillation qbo can modulate tropical deep convection the authors use a cloud resolving model with a limited domain representing a convective column in the tropics to study the mechanisms of this modulation the large scale circulation is parameterized using the weak temperature gradient wtg approximation under which the parameterized large scale vertical motion acts to relax the horizontal mean temperature toward a specified reference profile temperature variations typically seen in easterly and westerly phases are imposed in the upper troposphere and lower stratosphere of this reference profile the responses of convection are studied over different sea surface temperatures holding the reference temperature profile fixed this can be thought of as studying the response of convection to the qbo over different relative ssts and also corresponds to different equilibrium precipitation rates in the control simulation the

changes and trends in debris flow frequency since ad 1850 results from the swiss alps although studies have repeatedly focused on feedbacks and impacts of climate change on mass movements in the past the inter relations between climatic variables and debris flow occurrence remain widely unclear and ambiguous to date most studies on past debris flow occurrence remained rather isolated reconstructions for single torrents or they were restricted to short time periods it is therefore the aim of this study to provide a regional chronology of past debris flow events for the zermatt valley swiss alps and to go beyond the simple dating of events based on tree ring reconstructed debris flow histories of eight torrents we shed light on changes and trends in debris flow occurrence climatic conditions prevailing during events and on potential evolutions in a future climate based on the analysis of tree ring records of 2467 conifers mainly larix decidua and picea abies 417 events between ad 1600 and 2009 were assessed decadal frequencies suggest peaks in debris flow activity after the end

climatology of vertical wind shear over the tropical atlantic abstract the spatiotemporal variability of the 200 850 hpa vertical wind shear over the tropical atlantic is examined for a period of 46 yr this work extends and updates past studies by considering a longer data record as well as a tropospheric deep measure of vertical wind shear composite fields are constructed to illustrate the spatial pattern of the large scale circulation associated with the mean and extreme cases of vertical shear within the tropical atlantic the contemporaneous relationship of vertical shear with el nino southern oscillation enso and sahel precipitation are also examined while the enso shear correlation appears to have slightly strengthened during the past decade the sahel shear correlation has become significantly degraded a combined empirical orthogonal function eof analysis of the zonal and meridional components of the vertical shear reveals interannual and multidecadal modes the leading eof exhibits mainly interannual variability and is highly correlated with enso th

postglacial topographic evolution of glaciated valleys a stochastic landscape evolution model the retreat of valley glaciers has a dramatic effect on the stability of glaciated valleys and exerts a prolonged influence on the subsequent fluvial sediment transport regime we have studied the evolution of an idealized glaciated valley during the period following retreat of ice using a numerical model the model incorporates a stochastic process to represent deepseated landsliding non linear diffusion to represent shallow landsliding and an approximation of the bagnold relation to represent fluvial sediment transport it was calibrated using field data from several recent surveys within british columbia canada we present ensemble model results and compare them with results from a deterministic linear diffusion model to show that explicit representation of large landslides is necessary to reproduce the morphology and channel network structure of a typical postglacial valley our model predicts a rapid rate of fluvial sediment transport following deglaciation with a subsequent gradual decline similar to that inferred for holocene time we also describe how changes in the model parameters affect the estimated magnitude and duration of the paraglacial sediment pulse

avulsions and the spatio temporal evolution of debris flow fans debris flows are water laden masses of sediment that move rapidly through channel networks and over alluvial fans where they can devastate people and property episodic shifts in the position of a debris flow channel termed avulsions are critical for debris flow fan evolution and for understanding flow hazards because avulsions distribute debris flow deposits through space and time however both the mechanisms of flow avulsion and their effects on the long term evolution of debris flow fans are poorly understood here we document and analyze the spatial and temporal patterns of debris flow activity obtained by repeat topographic analyses dendrogeomorphic and lichenometric reconstructions and cosmogenic radionuclide dating on 16 fans from japan usa switzerland france and kyrgyzstan where possible we analyze the observed spatio temporal patterns of debris flow activity in conjunction with high resolution topographic data to identify the main controls on avulsion we identify two main processes that control avulsions on debris flow fans operating over distinct time scales first during individual flows or flow surges deposition of sediment plugs locally blocks channels and forces subsequent flows to avulse into alternative flow paths plug deposition is a stochastic process but appears to depend in part on the sequence of flow volumes the geometry of the channel and the composition of the flows second over time scales of tens of events the average locus of debris flow deposition gradually shifts toward the topographically lower parts of a fan highlighting the importance of topographic compensation for fan evolution our documented debris flow avulsions often but not always follow a pattern of channel plugging backstepping of deposition toward the fan apex over one or more flows avulsion and establishment of a new active channel large flows can have contrasting impacts depending on whether or not they follow smaller flows that have deposited channel plugs these results suggest that avulsions and spatio temporal patterns of debris flow fan formation strongly depend on both the magnitude frequency distribution and the sequence of the flows feeding a fan while individual avulsions are generally abrupt and difficult to predict the presence of debris flow plugs and patterns of backstepping may be useful as indicators of impending avulsions over longer time scales the compensational tendency of flows to avulse into topographic depressions on the fan may also be used to identify sectors of the fan that are at risk of future inundation

nonlocality of atlantic tropical cyclone intensities 1 the assumption that tropical cyclones respond primarily to sea surface temperatures ssts local to their main development regions underlies much of the concern regarding the possible impacts of anthropogenic greenhouse warming on tropical cyclone statistics here the observed relationship between changes in sea surface temperature and tropical cyclone intensities in the atlantic basin is explored atlantic tropical cyclone intensity fluctuations and storm numbers are shown to depend not only upon sst anomalies local to the atlantic main development region but also in a negative sense upon the tropical mean sst this behavior is shown in part to be consistent with changes in the tropical cyclone potential intensity that provides an upper bound on storm intensity however atlantic tropical cyclone intensity fluctuations are more nonlocal than the potential intensity itself and specifically vary along with atlantic main development region sst anomalies relative to the tropical mean sst this suggests that there is no straightforward link between warmer ssts in the main development region and more intense tropical cyclones

mid to late holocene coastal environmental changes in southwest florida usa during the holocene florida experienced major changes in precipitation and runoff to better understand these processes shallow marine sediment cores from charlotte harbor southwest florida were studied covering approximately the past 9000 years whole core xrf scanning was applied to correlate different sediment cores on a river to sea transect biomarkers were used to identify periods with increased runoff and primary productivity the mid holocene sediments are characterized by a relatively large input of terrestrially derived organic matter with a maximum in precipitation and runoff around 5 kyr bp this maximum can be linked to large scale changes in the hydrological cycle involving shifts of the itcz bermuda azores high and polar front around 3 5 kyr bp charlotte harbor changed from a runoff dominated environment to a more oligotrophic and marine setting although other studies suggest that around this time precipitation in florida increased this is not reflected by the charlotte harbor

tropical gradient influences on caribbean rainfall 1 interbasin and intrabasin gradients play an important role as a part of a regional system of caribbean climate drivers which include the atlantic warm pool awp and the caribbean low level jet cllj when the caribbean is conditioned to be wet between may and november near surface geopotentials in the caribbean are lower than in the nearby eastern tropical pacific and east tropical atlantic as a result there is vertical ascent in the caribbean through to the middle troposphere which connects to zonal circulations with both the eastern tropical pacific and the eastern tropical atlantic the caribbean sea is also warm and there is a moderate easterly flow regime indicating a weakening of the trade winds deviations from this state caused by changes in one or both sides of the pacific caribbean and caribbean atlantic circulations and diagnosed by changes in their geopotential gradients reasonably track the transition of the caribbean from wet to dry and vice versa on intraseasonal and interannual time scales the study also uses changes to the gradients to offer insight into why the caribbean region is projected to be drier during its traditional rainy season in the face of warmer surface temperatures under global warming the caribbean seemingly enters into a july mode which persists for the duration of the boreal summer the mode is characterized by higher lower geopotentials in the caribbean pacific and atlantic a stronger cllj and anomalous descent in the caribbean in spite of the warmer surface temperatures

interannual variations in mixed rossby gravity waves and their impacts on tropical cyclogenesis over the western north pacific abstract the present study investigates the transition from mixed rossby gravity mrg waves to tropical depression td type disturbances and its interannual variations over the western north pacific wnp using ecmwf high resolution data for the years of 1980 2001 as the equatorially trapped mrg waves propagate westward into the wnp the mrg waves transit to td type disturbances because of background flow change interannual variations in the transition of mrg waves are related to monsoon circulation change in response to tropical convective heating over the warm pool wp region when the wp is in a warm state convective heating is enhanced in the western part of the wnp and the monsoon trough retreats westward which induces a westward shift of the wave transition zone in contrast when the wp is in a relatively cold state the eastward penetration of convection and monsoon trough shifts the wave transition to the eastern part of the wnp the zonal wind convergence and shear in the monsoon trough

assessing sedimentary records of paleohurricane activity using modeled hurricane climatology patterns of overwash deposition observed within back barrier sediment archives can indicate past changes in tropical cyclone activity however it is necessary to evaluate the significance of observed trends in the context of the full range of variability under modern climate conditions here we present a method for assessing the statistical significance of patterns observed within a sedimentary hurricane overwash reconstruction to alleviate restrictions associated with the limited number of historical hurricanes affecting a specific site we apply a recently published technique for generating a large number of synthetic storms using a coupled ocean atmosphere hurricane model set to simulate modern climatology thousands of overwash records are generated for a site using a random draw of these synthetic hurricanes a prescribed threshold for overwash and a specified temporal resolution based on sedimentation rates observed at a particular site as a test case we apply this monte carlo technique to a hurricane induced overwash reconstruction developed from laguna playa grande lpg a coastal lagoon located on the island of vieques puerto rico in the northeastern caribbean apparent overwash rates in the lpg overwash record are observed to be four times lower between 2500 and 1000 years b p when compared to apparent overwash rates during the last 300 years however probability distributions based on monte carlo simulations indicate that as much as 65 of this drop can be explained by a reduction in the temporal resolution for older sediments due to a decrease in sedimentation rates periods of no apparent overwash activity at lpg between 2500 and 3600 years b p and 500 1000 years b p are exceptionally long and are unlikely to occur above 99 confidence under the current climate conditions in addition breaks in activity are difficult to produce even when the hurricane model is forced to a constant el nino state results from this study continue to support the interpretation that the western north atlantic has exhibited significant changes in hurricane climatology over the last 5500 years

a model for the analysis of rapid landslide motion across three dimensional terrain a new numerical model for the dynamic analysis of rapid flow slides debris flows and avalanches has been developed the model is an extension of an earlier algorithm and is implemented using a nu

planetary and synoptic scale signatures associated with central american cold surges abstract motivated by outstanding issues from a previous case study of a midlatitude cold surge that affected mexico and central america the climatology of central american cold surges is examined in this paper an independently derived listing of 177 cold surge events is employed for which the following properties are tabulated onset date duration time between cold surge events latitude of maximum equatorward penetration min and 48 h maximum surface temperature change at merida mexico t these data show that 75 of the cold surges have durations of 2 6 days the same timescale as mobile disturbances in the westerlies also there does not appear to be any relationship between t and the duration of the event although cold surges that penetrate to low latitudes min 7 10 n have a weak tendency to persist longer than those that do not penetrate to low latitudes min 15 20 n in addition the reding data indicate that the cold surges tend to reach their most equatorward extent where

atlantic seasonal hurricane frequency part i el nino and 30 mb quasi biennial oscillation influences abstract this is the first of two papers on atlantic seasonal hurricane frequency in this paper seasonal hurricane frequency as related to e1 nino events during 1900 82 and to the equatorial quasi biennial oscillation qbo of stratospheric zonal wind from 1950 to 1982 is discussed it is shown that a substantial negative correlation is typically present between the seasonal number of hurricanes hurricane days and tropical storms and moderate or strong 15 cases el nin off the south american west coast a similar negative anomaly in hurricane activity occurs when equatorial winds at 30 mb are from an easterly direction and or are becoming more easterly with time during the hurricane season this association of atlantic hurricane activity with el nino can also be made with the southern oscillation index by contrast seasonal hurricane frequency is slightly above normal in non el nino years and substantially above normal when equatorial stratospheric winds blow from a westerly direction and or are bec

exploring typhoon variability over the mid to late holocene evidence of extreme coastal flooding from kamikoshiki japan sediment cores from two coastal lakes located on the island of kamikoshiki in southwestern japan lake namakoike and lake kaiike provide evidence for the response of a backbarrier beach system to episodic coastal inundation over the last 6400 years sub bottom seismic surveys exhibit acoustically laminated parallel to subparallel seismic reflectors intermittently truncated by erosional unconformities sediment cores collected from targeted depocenters in both lakes contain finely laminated organic mud interbedded with coarse grained units with depths of coarse deposits concurrent with prominent seismic reflectors the timing of the youngest deposit at kamikoshiki correlates to the most recently documented breach in the barrier during a typhoon in 1951 ad assuming that this modern deposit provides an analog for identifying past events paleo typhoons may be reconstructed from layers exhibiting an increase in grain size a break in fine scale stratigraphy and elevated sr concentrations

impact of a quaternary volcano on holocene sedimentation in lillooet river valley british columbia lillooet river drains 3850 km 2 of the rugged coast mountains in southwestern british columbia including the slopes of a dormant quaternary volcano at mount meager a drilling program was conducted 32 65 km downstream from the volcano to search for evidence of anomalous sedimentation caused by volcanism or large landslides at mount meager drilling revealed an alluvial sequence consisting of river channel bar and overbank sediments interlayered with volcaniclastic units deposited by debris flows and hyperconcentrated flows the sediments constitute the upper part of a prograded delta that filled a late pleistocene lake calibrated radiocarbon ages obtained from drill core at 13 sites show that the average long term floodplain aggradation rate is 4 4 mm a 1 and the average delta progradation rate is 6 0 m a 1 aggradation and progradation rates however varied markedly over time large volumes of sediment were deposited in the valley following edifice collapse events and the eruption of mount meager volcano about 2360 years ago causing pulses in delta progradation with estimated rates to 150 m a 1 over 50 yr intervals two of the volcaniclastic units identified in drill core correlate with previously documented strong acoustic reflectors in lillooet lake at the downstream end of the basin the mount meager massif constitutes only 2 of the lillooet river drainage but lithology counts of lillooet river channel gravels indicate that a disproportionate percentage of the sediment is derived from the volcano the data indicate that deposits of large debris flows are important elements of the sedimentary sequence and that mount meager dominates the sediment supply to lillooet river d 2005 elsevier b v all rights reserved

mid to late holocene changes in tropical atlantic temperature seasonality and interannual to multidecadal variability documented in southern caribbean corals proxy reconstructions of tropical atlantic sea surface temperature sst that extend beyond the period of instrumental observations have primarily focused on centennial to millennial variability rather than on seasonal to multidecadal variability here we present monthly resolved records of sr ca a proxy of sst from fossil annually banded diploria strigosa corals from bonaire southern caribbean sea the individual corals provide time windows of up to 68 years length and the total number of 295 years of record allows for assessing the natural range of seasonal to multidecadal sst variability in the western tropical atlantic during snapshots of the mid to late holocene comparable to modern climate the coral sr ca records reveal that mid to late holocene sst was characterised by clear seasonal cycles persistent quasi biennial and prominent interannual as well as inter to multidecadal scale variability however the magnitude of sst variations on these timescales has varied over the last 6 2 ka the coral records show increased seasonality during the mid holocene consistent with climatemodel simulations indicating that southern caribbean sst seasonality is induced by insolation changes on orbital timescales whereas internal dynamics of the climate system play an important role on shorter timescales interannual sst variability is linked to ocean atmosphere interactions of atlantic and pacific origin pronounced interannual variability in the western tropical atlantic is indicated by a 2 35 ka coral possibly related to a strengthening of the variability of the el nino southern oscillation throughout the holocene prominent inter to multidecadal sst variability is evident in the coral records and slightly more pronounced in the mid holocene we finally argue that our coral data provide a target for studying holocene climate variability on seasonal and interannual to multidecadal timescales when using further numerical models and high resolution proxy data

dynamic controls on erosion and deposition on debris flow fans debris flows are among the most hazardous and unpredictable of surface processes in mountainous areas this is partly because debris flow erosion and deposition are poorly understood resulting in major uncertainties in flow behavior channel stability and sequential effects of multiple flows here we apply terrestrial laser scanning and flow hydrograph analysis to quantify erosion and deposition in a series of debris flows at illgraben switzerland we identify flow depth as an important control on the pattern and magnitude of erosion whereas deposition is governed more by the geometry of flow margins the relationship between flow depth and erosion is visible both at the reach scale and at the scale of the entire fan maximum flow depth is a function of debris flow front discharge and pre flow channel cross section geometry and this dual control gives rise to complex interactions with implications for long term channel stability the use of fan stratigraphy for reconstruction of past debris flow regimes and the predictability of debris flow hazards

multiple scale hydrothermal circulation in 135 ma oceanic crust of the japan trench outer rise numerical models constrained with heat flow observations anomalous high heat flow is observed within 150 km seaward of the trench axis at the japan trench offshore of sanriku where the old pacific plate 135 ma is subducting individual heat flow values range between 42 and 114 mw m 2 with an average of 70 mw m 2 these values are higher than those expected from the seafloor age based on thermal models of the oceanic plate i e 50 mw m 2 the heat flow exhibits spatial variations at multiple scales regional high average heat flow 100 km and smaller scale heat flow peaks 1 km we found that hydrothermal mining of heat from depth due to gradual thickening of an aquifer in the oceanic crust toward the trench axis can yield elevated heat flow of the spatial scale of 100 km topographic effects combined with hydrothermal circulation may account for the observed smaller scale heat flow variations hydrothermal circulation in high permeability faults may result in heat flow peaks of a subkilometer spatial scale volcanic intrusions are unlikely to be a major source of heat flow variations at any scale because of limited occurrence of young volcanoes in the study area hydrothermal heat transport may work at various scales on outer rises of other subduction zones as well since fractures and faults have been well developed due to bending of the incoming plate

rapid 20th century warming in the caribbean and impact of remote forcing on climate in the northern tropical atlantic as recorded in a guadeloupe coral we have generated 104 year long 1895 1999 monthly 18o and sr ca time series from a fast growing diploria strigosa coral core drilled off guadeloupe island lesser antilles coral sr ca reliably records interannual to decadal surface air temperature sat variations in the region and shows a pronounced warming of approximately 1 5 c since 1950 with the strongest warming 1 2 c occurring since 1975 this warming is also evident in sat measured at guadeloupe which ends in 1951 thus our sr ca series extends the air temperature record by 56 years we find that the past few decades are the warmest years over the entire period of record the accelerated warming since 1950 is accompanied by a pronounced decrease in regional precipitation this dampens the warming signal indicated by coral 18o which is too low only 0 7 0 8 c since 1951 consistently 18osw estimated from the coral proxies also shows a strong decrease since 1950 our data suggest an inverse relationship between sat and precipitation i e warmer and drier for the latter half of the 20th century with the strongest trends since the mid 1970s this is consistent with recent observational and model data which report that while over the tropical oceans rainfall has increased due to an increase in sea surface temperatures precipitation over land regions is reduced a continuation of this warming and drying trend over caribbean land regions would have severe societal consequences especially in the context of anthropogenic warming the el nino southern oscillation enso and the north atlantic oscillation nao are the two major climate modes affecting large scale sst variability in the northern tropical atlantic both sr ca and 18o show a close relationship to enso and the nao a quantitative comparison between extremes in mean march may coral 18o and the nino3 and nao indices imply that climate variability in the northern tropical atlantic is mainly forced by tropical pacific and north atlantic variability spectral analysis suggests that the relative importance of enso and the nao is frequency dependent with enso dominating at interannual and the nao dominating at interdecadal time scales

frequency magnitude distribution of debris flows compiled from global data and comparison with post fire debris flows in the western u s abstract forecasting debris flow hazard is challenging due to the episodic occurrence of debris flows in response to stochastic precipitation and in some areas wildfires in order to facilitate hazard assessment we have gathered available records of debris flow volumes into the first comprehensive global catalog of debris flows n 988 we also present results of field collection of recent debris flows n 77 in the northern rocky mountains where debris flow frequency increases following wildfire as a first step in parameterizing hazard models we use frequency magnitude distributions and empirical cumulative distribution functions ecdfs to compare volumes of post fire debris flows to non fire related debris flows the ecdf of post fire debris flow volumes is significantly different at 95 confidence from that of non fire related debris flows suggesting that the post fire distribution is composed of a higher proportion of small events than that of non fire related debris flows the slope of the frequency magnitude distribution of post fire debris flows is steeper than that of non fire related debris flows corroborating evidence that small post fire debris flows occur with a higher relative frequency than non fire related debris flows taken together the statistical analyses suggest that post fire debris flows come from a different population than non fire related debris flows and their hazard must be modeled separately we propose two possible non exclusive explanations for the fact that the post fire environment produces a higher proportion of small debris flows 1 following fires smaller storms or effective drainage areas can trigger debris flows due to increased runoff and or decreases in root strength resulting in smaller volumes and increased probability of failure and 2 fire increases the probability and frequency of debris flows causing their distribution to shift toward smaller events due to limitations in sediment supply

climate change effects on landslides along the southwest coast of british columbia abstract antecedent rainfall and short term intense rainfall both contribute to the temporal occurrence of landslides in british columbia these two quantities can be extracted from the precipitation regimes simulated by climate models this makes such models an attractive tool for use in the investigation of the effect of global warming on landslide frequencies in order to provide some measure of the reliability of models used to address the landslide question the present day simulation of the antecedent precipitation and short term rainfall using the daily data from the canadian centre for climate modelling and analysis model cgcm is compared to observations along the south coast of british columbia this evaluation showed that the model was reasonably successful in simulating statistics of the antecedent rainfall but was less successful in simulating the short term rainfall the monthly mean precipitation data from an ensemble of 19 of the world s global climate models were available to study potential changes in landslide frequencies with global warming most of the models were used to produce simulations with three scenarios with different levels of prescribed greenhouse gas concentrations during the twenty first century the changes in the antecedent precipitation were computed from the resulting monthly and seasonal means in order to deal with models suspected difficulties in simulating the short term precipitation and lack of daily data a statistical procedure was used to relate the short term precipitation to the monthly means the qualitative model results agree reasonably well and when averaged over all models and the three scenarios the change in the antecedent precipitation is predicted to be about 10 and the change in the short term precipitation about 6 because the antecedent precipitation and the short term precipitation contribute to the occurrence of landslides the results of this study support the prediction of increased landslide frequency along the british columbia south coast during the twenty first century

impacts of a pinatubo size volcanic eruption on enso observations and model simulations of the climate responses to strong explosive low latitude volcanic eruptions suggest a significant increase in the likelihood of el nino during the eruption and post eruption years though model results have been inconclusive and have varied in magnitude and even sign in this study we test how this spread of responses depends on the initial phase of el nino southern oscillation enso in the eruption year and on the eruption s seasonal timing we employ the gfdl cm2 1 global coupled general circulation model to investigate the impact of the pinatubo 1991 eruption assuming that in 1991 enso would otherwise be in central or eastern pacific el nino la nina or neutral phases we obtain statistically significant el nino responses in a year after the eruption for all cases except la nina which shows no response in the eastern equatorial pacific the eruption has a weaker impact on eastern pacific el ninos than on central pacific el ninos we find that the ocean dynamical thermostat and to a lesser extent wind changes due to land ocean temperature gradients are the main feedbacks affecting el nino development after the eruption the el nino responses to eruptions occurring in summer are more pronounced than for winter and spring eruptions that the climate response depends on eruption season and initial enso phase may help to reconcile apparent inconsistencies among previous studies

debris flow volume quantile prediction from catchment morphometry estimation of the volumes of potential future debris flows is a key factor in hazard assessment and mitigation worldwide however there are few catchments for which detailed volume frequency information is available we 1 reconstructed volume frequency curves for 10 debris flow catchments in saline valley california usa from a large number of well preserved unmodified surficial flow deposits and 2 assessed the correlations between lobe volume quantiles and a set of morphometric catchment characteristics we found statistically significant correlations between lobe volume quantiles including median and maximum and catchment relief length planimetric distance from the fan apex to the most distant point along the watershed boundary perimeter and melton ratio relief divided by the square root of catchment area these findings show that it may be possible to roughly estimate debris flow lobe volume quantiles from basic catchment characteristics that can be obtained from globally available elevation data this may assist in design volume estimation for debris flow catchments where past flow volumes are otherwise unknown

dendrogeomorphic assessment and sediment transfer of natural vs mining induced debris flow activity in călimani mountains eastern carpathians romania abstract during the second half of the twentieth century in the central part of the c limani mountains the mining activities for sulfur rich ore extraction and processing produced significant landscape changes sediment transfers across the affected catchments started during the mining period and are still ongoing today more than two decades after the cessation of the mining activities in 1997 subsequently neither rehabilitation works nor erosion control measures were undertaken to stabilize the spoil heap deposits and natural reforestation also material consolidation was impeded by the highly unstable talus slopes moreover little is known about the frequency of the hydrogeomorphic processes responsible for sediment transfers and their consequences dendrogeomorphic investigations grain size analyses and topographic surveys were carried out to document the history of hydrogeomorphic activity the volume of material stored behind the retention dams and the rate of sediment accumulation tree ring analysis allowed us to reconstruct ten debris flow events in the natural environment as well as in mining disturbed environment for the period 1931 2017 and 1970 2017 respectively triggering of debris flows appears related to spring and summer precipitation originating from short duration convective systems or long lasting rainfalls in these remote mining areas the reconstructed frequency of debris flows return intervals of 8 1 and 4 7 years might be explained by the rainwater accumulation on the spoil heap platform and the availability of sediments which flow down the talus and then follow the stream channels to reach one of the sediment retention reservoirs 7 4 8 4 cm y 1

the role of debris supply conditions in predicting debris flow activity debris flow frequency and magnitude were determined for 33 basins in southwest british columbia basins were first classifiedaseitherweathering limitedortransport limitedusingadiscriminantfunctionbasedondebris contributingarea an area weighted terrain stability number and drainage density multiple regression was used to predict magnitude peak discharge frequency and activity frequency times magnitude within each group of basins model performance was improved by stratifying the total sample of debris flow basins into weathering and transport limited groups explained varianceincreasedbyanaverageof15percentinthetransport limitedsample indicatingthatsedimentsupplyconditionsin themoreactivebasinsarefundamentalinpredictingdebrisflowactivity anindependenttestoftheregressionmodelswith 11basinsyieldedgenerallygoodresultsfordebrisflowmagnitudeandpeakdischarge predictionofdebrisflowfrequency provedproblematicalinweathering limitedbasins themethodsdevelopedhereprovideestimatesofdebrisflowattributes in basins for which few data on past events are available copyright 1999 john wiley sons ltd

influence of mean flow on the enso vertical wind shear relationship over the northern tropical atlantic abstractvertical wind shear over the tropical atlantic ocean plays an important role in mediating hurricane activity the vertical shear variability over the main development region for atlantic hurricanes is affected by local factors as well as by the remote influence of the el nino southern oscillation enso phenomenon as indicated by observational and climate modeling analyses climate model simulations of the enso shear relationship are compared with observations it is shown that there is a strong influence of background mean flow on the enso shear relationship because of the inherently nonlinear nature of vertical wind shear in particular the simulation of zonal flow over the tropical atlantic is shown to play a critical role in how the remote influence of enso modulates the shear even with realistic simulations of the enso induced westerly anomaly in the upper troposphere overestimated easterly background flow in the model simulations can alter the relationship between enso and vertical wind

impact of the atlantic warm pool on the summer climate of the western hemisphere abstract the atlantic warm pool awp is a large body of warm water that comprises the gulf of mexico the caribbean sea and the western tropical north atlantic located to its northeastern side is the north atlantic subtropical high nash which produces the tropical easterly trade winds the easterly trade winds carry moisture from the tropical north atlantic into the caribbean sea where the flow intensifies forming the caribbean low level jet cllj the cllj then splits into two branches one turning northward and connecting with the great plains low level jet gpllj and the other continuing westward across central america into the eastern north pacific the easterly cllj and its westward moisture transport are maximized in the summer and winter whereas they are minimized in the fall and spring this semiannual feature results from the semiannual variation of sea level pressure in the caribbean region owing to the westward extension and eastward retreat of the nash the ncar community atmospher

leading tropical modes associated with interannual and multidecadal fluctuations in north atlantic hurricane activity abstract interannual and multidecadal extremes in atlantic hurricane activity are shown to result from a coherent and interrelated set of atmospheric and oceanic conditions associated with three leading modes of climate variability in the tropics all three modes are related to fluctuations in tropical convection with two representing the leading multidecadal modes of convective rainfall variability and one representing the leading interannual mode enso the tropical multidecadal modes are shown to link known fluctuations in atlantic hurricane activity west african monsoon rainfall and atlantic sea surface temperatures to the tropics wide climate variability these modes also capture an east west seesaw in anomalous convection between the west african monsoon region and the amazon basin which helps to account for the interhemispheric symmetry of the 200 hpa streamfunction anomalies across the atlantic ocean and africa the 200 hpa divergent wind anomalies and both the structure and spatial scale

reconstructing 7000 years of north atlantic hurricane variability using deep sea sediment cores from the western great bahama bank q1 enso show abrupt changes around 6000 yrs b p but most coastal sedimentary records do not span this time period establishing longer records is essential for understanding mid holocene patterns of storminess and their climatic drivers which will lead to better forecasting of how climate change over the next century may affect tropical cyclone frequency and intensity storms are thought to be an important mechanism for transporting coarse sediment from shallow carbonate platforms to the deep sea and bank edge sediments may offer an unexplored archive of long term hurricane activity here we develop this new approach reconstructing more than 7000 years of north atlantic hurricane variability using coarse grained deposits in sediment cores from the leeward margin of the great bahama bank high energy event layers within the resulting archive are 1 broadly correlated throughout an offbank transect of multi cores 2 closely matched with historic hurricane events and 3 synchronous with previous intervals of heightened north atlantic hurricane activity in overwash reconstructions from puerto rico and elsewhere in the bahamas lower storm frequency prior to 4400 yrs b p in our records suggests that precession and increased nh summer insolation may have greatly limited hurricane potential intensity outweighing weakened enso and a stronger west african monsoon factors thought to be favorable for hurricane development

last interglacial temperature seasonality reconstructed from tropical atlantic corals abstract reconstructions of last interglacial lig mis 5e 127 117 ka climate offer insights into the natural response and variability of the climate system during a period partially analogous to future climate change scenarios we present well preserved fossil corals diploria strigosa recovered from the southern caribbean island of bonaire caribbean netherlands these have been precisely dated by the 230 th u method to between 130 and 120 ka ago annual banding of the coral skeleton enabled construction of time windows of monthly resolved strontium calcium sr ca temperature proxy records in conjunction with a previously published 118 ka coral record our eight records of up to 37 years in length cover a total of 105 years within the lig period from these sea surface temperature sst seasonality and variability in the tropical north atlantic ocean is reconstructed we detect similar to modern sst seasonality of 2 9 c during the early 130 ka and the late lig 120 118 ka however within the mid lig a significantly higher than modern sst seasonality of 4 9 c at 126 ka and 4 1 c at 124 ka is observed these findings are supported by climate model simulations and are consistent with the evolving amplitude of orbitally induced changes in seasonality of insolation throughout the lig irrespective of wider climatic instabilities that characterised this period the climate model simulations suggest that the sst seasonality changes documented in our lig coral sr ca records are representative of larger regions within the tropical north atlantic these simulations also suggest that the reconstructed sst seasonality increase during the mid lig is caused primarily by summer warming a 124 ka old coral documents for the first time evidence of decadal sst variability in the tropical north atlantic during the lig akin to that observed in modern instrumental records

evolution of cheekye fan squamish british columbia holocene sedimentation and implications for hazard assessment cheekye fan a large 25 km 2 fan located at the head of howe sound southwestern british columbia has its origins in the collapse of the western flank of mount garibaldi onto a waning late pleistocene glacier followed by post glacial redistribution of colluvial glacial sediments reconstruction of internal fan architecture allowed characterization of the rapid decline in sediment delivery to the lower fan through the paraglacial period a result holding important implications for hazard assessment a ground penetrating radar profile on lower cheekye fan has reflectors with a steep 25 westerly dip lying between 48 and 26 m above sea level which are interpreted as foreset beds radiocarbon ages from marine deltaic deposits at the head of howe sound indicate that the sea stood at about 45 m above sea level at 10 200 bp together the data indicate that the head of howe sound was deglaciated by 10 200 bp that the fan had prograded 2 5 km into the fjord by this time and continued to prograde as relative sea level fell reflectors at 10 m above sea level with a steep southerly dip along the southern edge of the lower fan and radiocarbon ages in this vicinity indicate it had reached close to its modern extent by 8000 9000 bp calculation of the volume of sediment stored in the lower fan indicates that at least 90 of the material was deposited before 6000 bp this indicates that the cheekye fan is largely a relict feature putting its large size into context for future hazard assessments

the relationship between the southern oscillation index and tropical cyclone tracks in the eastern north pacific points of origin and downgradation of tropical cyclones in the eastern north pacific enp east of 160 w are related to the southern oscillation index soi during the hurricane season all enp tropical storms and hurricanes from 1966 through 1997 were grouped into three soi based categories those occurring during strong el nino events mean soi 0 6 or near zero periods 0 6 mean soi 0 6 during el nino storm seasons enp tropical cyclones originated approximately 5 7 617 km west and downgraded 7 5 780 km west of the long term mean longitudes for the positive soi group near zero group storms also followed more northerly tracks than the negative soi group storms however no significant differences in storm track are evident between the positive soi and near zero groups and the track length is not significantly different for any storm group

positive feedback and momentum growth during debris flow entrainment of wet bed sediment debris flows typically occur when intense rainfall or snowmelt triggers landslides or extensive erosion on steep debris mantled slopes the flows can then grow dramatically in size and speed as they entrain material from their beds and banks but the mechanism of this growth is unclear indeed momentum conservation implies that entrainment of static material should retard the motion of the flows if friction remains unchanged here we use data from large scale experiments to assess the entrainment of bed material by debris flows we find that entrainment is accompanied by increased flow momentum and speed only if large positive pore pressures develop in wet bed sediments as the sediments are overridden by debris flows the increased pore pressure facilitates progressive scour of the bed reduces basal friction and instigates positive feedback that causes flow speed mass and momentum to increase if dryer bed sediment is entrained however the feedback becomes negative and flow momentum declines we infer that analogous feedbacks could operate in other types of gravity driven mass flow that interact with erodible beds the mechanisms by which debris flows acquire mass and momentum as they entrain material are unclear large scale experiments suggest that the pore pressure of wet bed sediment increases as the flow moves over the bed leading to reduced friction and progressive scouring of the base

cool season sea level anomalies and storm surges along the u s east coast climatology and comparison with the 2009 10 el nino abstractclimatologies of sea level anomalies 0 05 m and daily mean storm surges 0 3 m are presented for the 1960 2010 cool seasons october april along the east coast of the united states at boston massachusetts atlantic city new jersey sewells point norfolk virginia and charleston south carolina the high sea level anomaly and the number of storm surges among the highest in the last half century during the 2009 10 cool season are comparable during strong el nino cool seasons high numbers of daily storm surges occur in response to numerous east coast extratropical cool season storms and have a positive correlation with the el nino phase of the el nino southern oscillation enso patterns of anomalously high sea levels are attributed to el nino related changes to atmospheric pressure over the gulf of mexico and eastern canada and to the wind field over the northeast u s continental shelf

geologic records of holocene typhoon strikes on the gulf of thailand coast abstract washover sedimentation resulting from modern typhoon strikes on the gulf of thailand coast forms anomalous sand layers in low energy coastal environments including marshes ponds and swales the primary diagnostic for recognizing prehistoric typhoon deposited sand layers in the geologic record are sharp upper and lower contacts between coarser grained transported sand layers and finer grained in situ sediments in this first paleotempestology study in thailand cores from two low energy settings on the gulf of thailand coast a coastal marsh near cha am and beach ridge plain swales near kui buri reveal geologic evidence of up to 19 typhoon strikes within the last 8000 years the sand layers have sharp upper and lower contacts with enclosing finer sediments some sand layers also contain other evidence of a sudden powerful landward directed surge of ocean water including gravel sized clasts offshore foraminifera abundant shell fragments plant debris and mud rip up clasts sand layers record eleven typhoon strikes at cha am ranging in age from ad 1952 to 7575 cal yr bp and eight typhoon strikes at kui buri ranging in age from 4075 to 7740 cal yr bp bayesian age depth models derived from eight ams radiocarbon dates suggest that the frequency of typhoon strikes was 2 5 times greater from 3900 to 7800 cal yr bp compared to 0 3900 cal yr bp possible explanations for this variability in the typhoon record are that typhoons were more frequent and or more intense in southeast asia in the mid holocene because of climatic changes associated with the mid holocene warm period or that the record reflects site sensitivity changes resulting from a mid holocene sea level highstand the preliminary finding of a possible link between warmer conditions and a greater frequency of intense typhoon strikes could have important societal implications given possible consequences of ongoing global warming

middle late holocene caribbean aridity inferred from foraminifera and elemental data in sediment cores from two cuban lagoons abstract coastal lagoons are rarely used as paleoclimate archives because of their complex geomorphic histories which can be affected by both climate and sea level change combined foraminiferal and xrf element analysis of sediment cores from punta de cartas and playa bailen cuba isolated the effects of climate change wet vs dry on the lagoon environments foraminiferal assemblages from both punta de cartas and playa bailen show increasing diversity over the past 4000 yr bp with a prominent increase at 1400 1100 yr bp assemblages were initially dominated by ammonia spp e g ammonia tepida and elphidium spp e g elphidium excavatum indicating brackish conditions but increased miliolid species e g triloculina spp quinqueloculina spp indicate a shift to more marine conditions up core correspondingly terrigenous input to the lagoon fe ti ti ca and k declined over the past 4000 yr bp with a flexion at 1200 1100 yr bp that is likely a consequence of decreasing precipitation fe ti and k have been used as proxies for detrital erosion and transport rates in tropical and sub tropical basins with greater input during wet periods but have rarely been applied to shallow lagoon systems coincident changes in the xrf and foraminiferal data indicate decreased freshwater input to the lagoon and support an inference for the onset of drier climate conditions similar temporal patterns in the foraminifera and xrf records from the two lagoons which are 10 km apart suggest a regional climate influence with increasingly arid conditions developing since the middle holocene 4 kyr bp a pronounced drying over the last 1200 years agrees with other climate records from the caribbean

contribution of dendrochronology to the determination of magnitude frequency relationships for landslides abstract the determination of magnitude frequency m f relationships is necessary for landslide hazard assessment ideally this is achieved by using inventories of past landslide events recorded by technical units or aerial photo interpretation however direct sources of landslide data are often unavailable dendrogeomorphological techniques allow us to determine the frequency of events but few attempts have been made to estimate landslide magnitude by analysing the spatial distribution of disturbed trees this paper addresses m f determination for rockfalls debris flows and complex slides obtained by dendrogeomorphology the cases presented require the appropriate understanding of both the geomorphological context and the disturbance caused by landslide motion on trees both small and large rockfalls can be identified and dated by reconstructing the trajectories in the forest stand the larger the rockfall size the longer the path the higher the number of affected trees and the greater the area of deposition of rock fragments the area of damaged trees is proposed as an indicator of the rockfall magnitude the frequency and extent of a series of debris flows were reconstructed by mapping their deposits using relative dating criteria and by dating damaged trees local and global mudslide reactivations were deduced by sampling various tree generations and by analysing the location of the disturbed trees in the landslide units magnitude cumulative frequency curves were determined for the three cases

frequency and magnitude of debris flows on cheekye river british columbia abstract natural hazard and risk assessments are predicated on a detailed understanding of the relationship between frequency and magnitude of the hazardous process under investigation when information is sought from the deep past i e several thousand years continuous event records do not exist and the researcher has to rely on proxy data to develop the frequency magnitude f m model such work is often prohibitively expensive and few well researched examples for mass movement are available worldwide the cheekye fan is a desirable location for land development and has a depth and breadth of previous research unprecedented on any debris flow fan in canada we pursued two principal strains of research to formulate a reliable f m relationship the first focuses on stratigraphic analyses combined with radiometric dating and dendrochronology to reconstruct a comprehensive picture of holocene debris flow activity the second approach examines hydrological limitations of rock avalanche evolution into debris flows through either entrainment of saturated sediments or by failure of a landslide generated dam and upstream impoundment we thus hypothesize that debris flows from cheekye river can be separated into two quasi homogenous populations those that are typically triggered by relatively small debris avalanches slumps or rock falls or simply by progressive bulking of in stream erodible sediments and those that are thought to result from transformation of rock avalanches our work suggests that debris flows exceeding some 3 million m3 in volume are unlikely to reach the cheekye fan as a result of limited water available to fully fluidize a rock avalanche this analysis has also demonstrated that in order to arrive at reasonable estimates for the frequency and magnitude of debris flows on a complex alluvial fan significant multidisciplinary efforts are required without the significant precursor investigations and the additional efforts of this study life and property may be jeopardized or the design of debris flow mitigation may be subject to considerable and unquantifiable error

climate modulation of north atlantic hurricane tracks the variability of north atlantic tropical storm and hurricane tracks and its relationship to climate variability is explored tracks from the north atlantic hurricane database for the period 1950 2007 are objectively separated into four groups using a cluster technique that has been previously applied to tropical cyclones in other ocean basins the four clusters form zonal and meridional separations of the tracks the meridional separation largely captures the separation between tropical and more baroclinic systems while the zonal separation segregates gulf of mexico and cape verde storms general climatologies of the seasonality intensity landfall probability and historical destructiveness of each cluster are documented and relationships between cluster membership and climate variability across a broad spectrum of time scales are identified composites with respect to cluster membership of sea surface temperature and other environmental fields show that regional and remote modes of climate variability modulate the cluster members in substantially

bracketing ages for the formation of the ring creek lava flow mount garibaldi volcanic field southwestern british columbia the ring creek lava flow extending from opal cone generally is considered to be the youngest volcanic feature in the southern section of the mount garibaldi volcanic field southwestern british columbia an in situ stump dated 10 650 70 bp beta 43865 obtained from a raised delta partially overridden by the lava flow indicates that the lava was extruded after ca 10 7 ka at the skookum creek and mamquam river confluence sediments eroded from the ring creek lava flow form an alluvial fan that contains charcoal dated 9360 160 bp beta 38914 which indicates that the extrusion probably occurred before ca 9 3 ka thus these radiocarbon ages bracket the age of the ring creek lava flow and indicate that volcanic activity in the southern section of the mount garibaldi volcanic field has been dormant since at least ca 9 3 ka

intensified impact of east indian ocean sst anomaly on tropical cyclone genesis frequency over the western north pacific abstracta recent finding is the significant impact of the sea surface temperature anomaly ssta over the east indian ocean eio on the genesis frequency of tropical cyclones tcs over the western north pacific wnp in this study it is shown that such an impact is significant only after the late 1970s the results based on both data analysis and numerical model experiments demonstrate that prior to the late 1970s the eio ssta is positively correlated with the equatorial central pacific ssta and the latter produces an opposite atmospheric circulation response over the wnp to the former as a result the impact of the eio ssta on the tc genesis over the wnp is largely suppressed by the latter after the late 1970s the area coverage of the eio ssta is expanding this considerably enhances the large scale circulation response over the wnp to the eio ssta and significantly intensifies the impact of the eio ssta on tc genesis frequency over the wnp the results from this study have great implications for s

dendrogeomorphic approaches for identifying the probable occurrence of debris flows and related torrential processes in steep headwater catchments the hrubý jesenik mountains czech republic abstract culminating parts of mid mountain ranges in central europe are interwoven by a network of high gradient streams these parts together with the surrounding slopes form a coupling system in which hazardous geomorphic processes such as landslides debris flows or flash floods can occur in the case of the hrub jesenik mountains eastern sudetes czech republic we present an evaluation of the debris flows and related torrential processes in the high gradient streams of the selected catchment based on dendrogeomorphic methods in addition to the classical dendrogeomorphic approaches we refined the procedure of identifying certain and probable events using new weighted indexes for event reconstruction additionally because of the steep narrow channels without a characteristic accumulation cone a new spatial approach is defined based on the spacing of disturbed trees for each event random distribution or clustering and location of disturbed trees in an individual section of the valley floor using kernel density analysis for each event and calculating the particular grids in arcgis software we are able to describe the spatial reach and probable nature of an event debris flow or hyperconcentrated flow dendrogeomorphic analysis of 397 sampled trees predominantly coniferous trees revealed 24 torrential events 15 certain nine probable since 1928 with peaks in 1991 1997 and 2010 according to index values in addition the spatial distribution of disturbed trees grouped in clusters in these years indicates debris flow events in the upper parts of the catchment it seems that new dendrogeomorphic approaches should be valuable in remote steep headwater catchments where several types of processes affect the valley floors

coupled response of the trade wind sst gradient and sst in the caribbean sea and the potential impact on loop current s interannual variability abstractair sea coupling in the intraamerican seas ias caribbean sea and gulf of mexico is studied through analyses of observational data from satellite reanalysis products and in situ measurements a strong coupling is found between the easterly trade wind u and meridional sst gradient t y across a localized region of the southern central caribbean sea from seasonal and interannual to decadal time scales the t y anomaly is caused by a variation in the strength of coastal upwelling off the venezuelan coast by the wind which in turn strengthens weakens for stronger weaker t y wind speeds and seasonal fluctuations in ias have increased in the past two decades with a transition near 1994 coinciding approximately with when the atlantic multidecadal oscillation amo turned from cold to warm phases in particular the seasonal swing from summer s strong to fall s weak trade wind has become larger the ocean s upper layer depth has also deepened by as much as 50 on average in the eastern gu

variations in global tropical cyclone activity and the madden julian oscillation since the midtwentieth century the madden julian oscillation mjo has been documented in previous studies to significantly impact tropical cyclone activity in all ocean basins most of these studies have utilized the wheeler hendon index this index is only available since 1974 the period over which remotely sensed outgoing longwave radiation data has been available our study utilizes a long reconstructed mjo index based on surface pressures which extends back to 1905 we document consistent modulation of tropical cyclone activity by the mjo in all basins over this time period these modulations are shown to be remarkably stable over the entire analysis period we also examine the combined impacts of el nino southern oscillation and the mjo on tropical cyclone activity in each basin over multidecadal time scales

atlantic multidecadal variability and associated climate impacts initiated by ocean thermohaline dynamics abstractthe sea surface temperature sst signature of atlantic multidecadal variability amv is a key driver of climate variability in surrounding regions low frequency atlantic meridional overt

effects of debris flow composition on runout depositional mechanisms and deposit morphology in laboratory experiments predicting debris flow runout is of major importance for hazard mitigation apart from topography and volume runout distance and area depends on debris flow composition and rheology but how is poorly understood we experimentally investigated effects of composition on debris flow runout depositional mechanisms and deposit geometry the small scale experimental debris flows were largely similar to natural debris flows in terms of flow behavior deposit morphology grain size sorting channel width depth ratio and runout deposit geometry lobe thickness and width in our experimental debris flows is largely determined by composition while the effects of initial conditions of topography i e outflow plain slope and channel slope and width and volume are negligible we find a clear optimum in the relations of runout with coarse material fraction and clay fraction increasing coarse material concentration leads to larger runout however excess coarse material results in a large accumulation of coarse debris at the flow front and enhances diffusivity increasing frontal friction and decreasing runout increasing clay content initially enhances runout but too much clay leads to very viscous flows reducing runout runout increases with channel slope and width outflow plain slope debris flow volume and water fraction these results imply that debris flow runout depends at least as much on composition as on topography this study improves understanding of the effects of debris flow composition on runout and may aid future debris flow hazard assessments

application of partial least squares regression to the diagnosis of year to year variations in pacific northwest snowpack and atlantic hurricanes 1 application of the method of partial least squares pls regression to geophysical data is illustrated with two cases 1 finding sea level pressure patterns over the north pacific associated with dynamically induced winter to winter variations in snowpack in the cascade mountains of western washington state and 2 finding patterns of sea surface temperature over the tropical oceans that modulate atlantic hurricane activity on a year to year basis in both examples two robust patterns in the predictor field are identified that in combination account for over half the variance in the target time series

spatial variations in major u s hurricane activity statistics and a physical mechanism abstract the authors provide a statistical and physical basis for understanding regional variations in major hurricane activity along the u s coastline on long timescales current statistical models of hurricane activity are focused on the frequency of events over the entire north atlantic basin the exception is the lead author s previous work which models the occurrence of hurricanes over the caribbean sea gulf of mexico and the southeast u s coast separately here the authors use statistics to analyze data from historical and paleoclimatic records to expand this work in particular an inverse correlation in major hurricane activity across latitudes at various timescales is articulated when activity is above normal at high latitudes it tends to be below normal at low latitudes and vice versa past research paleoclimatic records and historical data hint at the potential of using the north atlantic oscillation nao as an indicator of where storms will likely track over long timescales an excite

tropical storms representation and diagnosis in climate models and the impacts of climate change tropical storms are located and tracked in an experiment in which a high resolution atmosphere only model is forced with observed sea surface temperatures ssts and sea ice the structure geographic distribution and seasonal variability of the model tropical storms show some similarities with observations the simulation of tropical storms is better in this high resolution experiment than in a parallel standard resolution experiment in an anomaly experiment sea ice ssts and greenhouse gas forcing are changed to mimic the changes that occur in a coupled model as greenhouse gases are increased there are more tropical storms in this experiment than in the control experiment in the northeast pacific and indian ocean basins and fewer in the north atlantic northwest pacific and southwest pacific region the changes in the north atlantic and northwest pacific can be linked to el nino like behaviour a comparison of the tracking results with two empirically derived tropical storm genesis parameters is carried out the tracking technique and a convective genesis parameter give similar results both in the global distribution and in the changes in the individual basins the convective genesis parameter is also applied to parallel coupled model experiments that have a lower horizontal resolution the changes in the global distribution of tropical storms in the coupled model experiments are consistent with the changes seen at higher resolution this indicates that the convective genesis parameter may still provide useful information about tropical storm changes in experiments carried out with models that cannot resolve tropical storms

downward influence of qbo like oscillation on moist convection in a two dimensional minimal model framework abstractthe influence of the quasi biennial oscillation qbo like oscillation on moist convection is examined using the two dimensional minimal model framework of yoden et al with two series of parameter sweep experiments model top experiments with varying model height and low level nudging experiments with reduced zonal mean zonal wind toward zero from the surface to a certain level the qbo like oscillation in the mean zonal wind is a robust feature obtained in all the experiments including low top cases in which only the tropospheric portion is retained the zonal mean precipitation is modulated with a half period of the mean zonal wind oscillation in the model top experiments and a positive correlation exists between the precipitation intensity and the vertical shear of the mean zonal wind near the surface the precipitation modulation is weakened with a nudging of the low level mean zonal wind but appears again in the cases with the low level nudging in the middle and lower troposphere there is

significance of extreme hydro geomorphological events in the transformation of mountain valleys northern slopes of the western tatra range carpathian mountains poland abstract extreme events disturb the development paths of geomorphological systems the effect of such events on relief tends to persist for long periods of time and affects the future development of such systems this paper focuses on changes in middle mountain valleys associated with an extreme hydro geomorphological event that occurred in the western tatra mountains polish carpathian mountains in june of 2007 the geomorphological effects were mapped and an analysis of valley bottom deposits and dendro geomorphological data on tree roots and stems was used to identify patterns in the geomorphological transformation taking place during such events in addition the organic material obtained from fans was dated by means of carbon 14 dating the effects of previous extreme events in the study area and their geomorphological outcomes were compared four main valley section types were identified in the valley longitudinal profile unevenly aged from 14c 390 30 years ybp 1441 1631 cal ad to 14c 3760 70 ybp 4318 3962 cal bp organic material was revealed at different depths of each studied fan a complex structure with alternating layers of fine and coarse material from the analysed fans was identified the colluvial alluvial structure of fans suggests that extreme high energy events did occur more than once per century during the holocene this type of fan structure can be referred to as a patchwork in the study area rainfall with high energy potential occurs once in every 6 9 years and extreme hydro geomorphological events occur every 15 years this type of extreme event may not be exceptional in the history of middle mountain areas

the 1995 and 1996 north atlantic hurricane seasons a return of the tropical only hurricane hurricane activity over the north atlantic basin during 1995 and 1996 is compared to the combined hurricane activity over the previous four years 1991 94 the earlier period produced a total of 15 hurricanes compared to a total of 20 hurricanes over the latter period despite this similarity in numbers the hurricanes of 1995 and 1996 were generally of the tropical only variety which marks a substantial departure from activity during the early 1990s the return of tropical only hurricanes to the atlantic basin is likely the result of several global and local factors including cool sst conditions in the equatorial central and eastern pacific and warm ssts in the tropical atlantic the hurricane activity of 1995 and 1996 is more reminiscent of activity of some seasons during the early and mid 1950s

variation of tropical cyclone activity in the south indian ocean el nino southern oscillation and madden julian oscillation effects 1 the present study examines variation of tropical cyclone tc activity in the south indian ocean sio during tc seasons december march for the period 1979 2004 the impact of the el nino southern oscillation and the madden julian oscillation mjo on the variation is revealed through a composite analysis during el nino periods tc genesis was shifted westward enhancing the formation west of 75 e and reducing it east of 75 e these changes in the genesis correspond to a westward shift of convection it may be explained by a remote effect on the sio that is the increase in sea surface temperature in the central eastern pacific alters the walker circulation and forms an anomalous anticyclonic circulation in the east sio during el nino the spatial difference in tc passages between el nino and la nina shows a significant decrease to the southeast of madagascar but a moderate increase in the central midlatitude sio indicating that tcs move farther east during el nino this change is possibly due to the anomalous southwesterlies east of madagascar variation of tc activity also depends on various mjo phases frequent tc passages for phases 2 4 strong convective activity straddles along the equatorial indian ocean versus infrequent tc passages for other phases tc tracks tend to be more south oriented in phase 3 compared with those in phases 2 and 4 this is possibly caused by the increased steering northerlies which are a part of the anticyclonic rossby wave of gill type in response to the suppressed mjo related convection in the maritime continent

clustering of eastern north pacific tropical cyclone tracks enso and mjo effects 1 a probabilistic clustering technique is used to describe tropical cyclone tracks in the eastern north pacific on the basis of their shape and location the best track data set is decomposed in terms of three clusters these clusters are analyzed in terms of genesis location trajectory landfall intensity seasonality and their relationships with the el nino southern oscillation enso and madden julian oscillation mjo longitudinal track location plays a strong discriminating role in the regression mixture model s solution with the average track orientation becoming more zonal toward the west this progression encapsulates well the relationship between tropical cyclones over the eastern tropical pacific and the mjo or enso two of the clusters describe tropical cyclones tcs with tracks that lie near the coast of mexico and central america the most frequent cluster contains tracks that trend west northwestward while the second most frequent one has genesis locations that lie slightly to the southeast of those in the most frequent cluster and tracks that run typically parallel to the central american coast this second cluster is shown to be significantly associated with the westerly phase of the mjo the third least frequent cluster contains tcs with westward trajectories over the central and eastern equatorial pacific some of these tcs have an impact on hawaii and other islands as far as the central and western north pacific regions the least frequent cluster is strongly related to enso while the others are not it occurs significantly more frequently during el nino conditions examination of the large scale patterns of atmospheric circulation and sea surface temperature associated with each of our three clusters are consistent with previous studies anomalous low level westerly zonal winds from the monsoon trough and mjo meet anomalous easterlies near the region of genesis in each cluster

younger dryas readvance in squamish river valley southern coast mountains british columbia abstract stratigraphy and landforms in the brohm creek basin and lowermost mamquam river valley provide evidence for a readvance of a valley glacier in the southern coast mountains of british columbia during the younger dryas interval at brohm creek till containing wood 10 500 and 10 700 14 c yr old ca 12 500 12 900 cal yr old overlies an ice contact terrace that is correlative with similar terraces at the mouth of mamquam river 11 km to the south and 900 m lower in elevation a line linking the two sites has a slope of 5 which is similar to slopes of termini of present day valley glaciers in the southern coast mountains we used these observations to reconstruct the younger dryas glacier in squamish valley at the head of howe sound the glacier deflected landslide debris derived from steep slopes at the head of cheekye river basin on the west flank of mt garibaldi southward to an ice marginal lake at the mouth of mamquam river foreset bedded sediments in the core of a large fan at the mouth of cheekye river indicate the glacier terminus had retreated up squamish valley beyond cheekye and mamquam rivers by 10 200 14 c yr bp 11 900 cal yr old radiocarbon ages on the oldest postglacial sediments in a kettle on the landslide debris show that stagnant ice in the study area had melted before 10 000 14 c yr bp 11 500 cal yr bp the readvance of the squamish valley glacier during the younger dryas chronozone was probably driven by a regional climate reversal

tropical and subtropical north atlantic vertical wind shear and seasonal tropical cyclone activity abstractgiven recent insights into the role of anticyclonic rossby wave breaking awb in driving subseasonal and seasonal north atlantic tropical cyclone tc activity this study further examines

quantitative analysis of debris torrent hazards for design of remedial measures debris torrents which are rapid flows of soil and organic debris down steep mountain channels are a major natural hazard in many parts of british columbia a series of recent occurrences along the

impact of the cross tropopause wind shear on tropical cyclone genesis over the western north pacific in may the role of the 50 to 200 hpa zonal wind shear in modulating tropical cyclone tc genesis over the western north pacific wnp in may is investigated in this study concurrent with the strong cross tropopause shear over the key region 0 5 n 160 180 e suppressed convection was observed over the tropical wnp especially over the south china sea and the philippines the monsoon trough mt was confined westward however enhanced convection occurred in the weak shear years and the mt extended eastward this cross tropopause wind shear is negatively correlated with tc genesis in may with a decreased increased number of tcs corresponding to strong weak cross tropopause wind shear this cross tropopause wind shear can be treated as the combined impacts of the el nino southern oscillation enso events and the stratospheric quasi biennial oscillation qbo when decaying el nino events coupled with the easterly phase of the qbo were noted the cross tropopause wind shear was stronger with weakened convection and an enhanced western pacific subtropical high was observed tcs are rarely generated during these years in contrast the modulation of the qbo westerly phase on decaying la nina events is limited affected by the qbo westerly phase tc genesis in the may following la nina events is only slightly enhanced the energy analysis indicates that the combined impacts of the decaying el nino events and the qbo easterly phase might suppress the barotropic eddy kinetic energy conversion in may whereas the decaying la nina events and the qbo west phase act in an opposite manner

the dynamics of the enso atlantic hurricane teleconnection enso related changes to the north african asian jet affect atlantic basin tropical cyclogenesis abstract the nature of the teleconnection linking enso variability with atlantic basin tropical storm formation is investigated solutions of the linearized barotropic vorticity equation forced with august october el nino event divergence produce upper tropospheric vorticity anomalies over the sahel and at the mouth of the north african asian naa jet over the tropical atlantic these responses are similar in magnitude and orientation to observed enso vorticity variability for this region further investigation reveals that the vorticity anomalies over the subtropical atlantic develop primarily in response to very low wavenumber westward propagating stationary rossby waves excited by el nino related convective activity over the equatorial pacific ocean however the dynamics of this teleconnection change as the atlantic basin hurricane season progresses in august and september the response is dominated by the westward propagating stationary rossby waves that alter vorticity within the naa jet and to it

a probabilistic approach for landslide hazard analysis abstract we present a general framework for probabilistic landslide hazard analysis with respect to other quantitative hazard assessment approaches this probabilistic landslide hazard analysis has the advantage to provide hazard curves and maps and to be applicable to all typologies of landslides if necessary accounting for both their onset and transit probability the method quantifies for a given slope location the exceedance probability of being affected by a landslide with a specific local intensity within a reference time interval i e the hazard curve under the common assumption that landslides behave as a poisson process hazard maps are calculated reducing the hazard curve to single values by choosing a fixed probability of exceedance following standards or regulation requirements the method is based on the assessment of a landslide onset frequency a runout frequency for long runout landslides and the local definition of landslide intensity which can be expressed through different parameters according to landslide typology for long runout landslides the runout and spatially varying intensity and uncertainty are considered hazard curves and maps play a fundamental role in the design and dimensioning of mitigation structures in land planning and in the definition of risk and hazard management policies starting from the general framework we apply the methodology for rockfall hazard analysis and we test it in an area affected by the christchurch 2011 earthquake new zealand which triggered a large number of rockfalls killing five people

readvance of glaciers in the british columbia coast mountains at the end of the last glaciation abstract late quaternary sediments and landforms at the head of howe sound a fjord in the british columbia coast mountains provide a detailed record of final decay of the southwestern sector of the cordilleran ice sheet at the end of the pleistocene the upper reaches of mamquam river valley a mountain valley at the head of the fjord east of the town of squamish were ice free and locally treed as early as 14 000 years ago 11 900 14 c yr bp folding and faulting of late glacial lacustrine sediments in mamquam valley may record a glacier readvance correlative with the sumas event in the fraser lowland to the southeast by 12 900 years ago 10 690 14 c yr bp the trunk glacier in howe sound had retreated from a sumas age moraine at porteau cove 15 km south of squamish by 12 800 years ago 10 650 14 c yr bp the glacier terminus stood near the present fjord head with the sea at an elevation of about 40 50 m a s l shortly after 12 800 years ago during the younger dryas chronozone the trunk glacier in squamish valley readvanced a short distance and then retreated for a final time tributary valleys were probably completely deglaciated by 11 300 years ago 9920 14 c yr bp and certainly by 10 600 years ago 9360 14 c yr bp relative sea level fell as deglaciation progressed however it did not fall below its present datum in the squamish area until after 11 200 years ago at least 1300 years later than in the fraser lowland

a quantitative inference model for conductivity using non marine ostracode assemblages on san salvador island bahamas paleosalinity records from two lakes abstract quantitative records of past environments are needed to understand natural variability in ecosystems and their responses to climate change changes in ostracode assemblages through time can provide such records as ostracode species are sensitive to changes in their local environments before they can be used to indicate past environments however is it necessary to understand how distributions of assemblages change across environmental gradients to that end thirty two lakes on san salvador island bahamas were sampled for both ostracodes and nineteen limnological variables multivariate fuzzy set ordination indicates that change in ostracode assemblages is significantly and independently correlated with three environmental variables electrical conductivity salinity dissolved oxygen and alkalinity a transfer function was created to reconstruct past conductivity since changing conductivity of lakes on san salvador is influenced by changes in climate and sea level a 2 component weighted averaging partial least squares model performed best as a transfer function for conductivity with an apparent r 2 of 0 76 and an r 2 of 0 69 between observed and predicted conductivity as assessed by leave one out cross validation the resulting transfer function was then applied to two mid to late holocene sediment cores from which ostracode assemblages were sampled the late holocene conductivity records show that changes in conductivity of lakes on san salvador are broadly synchronous with times of enhanced enso activity corresponding to elevated conductivity in response to lower atlantic hurricane occurrence these results demonstrate that changing ostracode assemblages through time provide a reliable means to reconstruct past salinity and demonstrates the strong effect of enso on bahamian aridity

consistent decrease in north atlantic tropical cyclone frequency following major volcanic eruptions in the last three centuries injection of sulphate aerosols into the stratosphere following major volcanic eruptions alters global climate through the absorption and scattering of solar radiation one proposed consequence is a decrease in north atlantic tropical cyclone tc activity as was observed following the el chichon 1982 and mount pinatubo 1991 eruptions we test this relationship using documentary and proxy reconstructions of major volcanic eruptions and tc frequency in the north atlantic basin over the last three centuries we find a consistent reduction in the number of tcs formed during the 3 years following major eruptions compared to the preceding 3 years including after eruptions located at northern high latitudes our findings suggest that low latitude eruptions reduce atlantic tc frequency by decreasing local sea surface temperatures whereas the mechanisms for the decrease in tc frequency following high latitude eruptions are less clear and attribution is hampered by poor identification of these events

tree age control on reconstructed debris flow frequencies examples from a regional dendrogeomorphic reconstruction in the crimean mountains the crimean mountains ukraine are renowned for the highest occurrence of debris flows along the northern coast of the black sea but information on their origin frequency and triggers is widely lacking this study reconstructs a regional time series of debris flows in eight catchments located on the slopes above yalta dendrogeomorphic analyses were performed on 1122 increment cores selected from 566 black pines pinus nigra ssp pallasiana with clear signs of external damage induced by past debris flow activity the trees sampled were divided into old and young trees the sample contains 361 young trees with post 1930 innermost rings and 205 old trees with pre 1930 germination dates the two groups of trees were analyzed separately to identify possible age effects in the reconstructed debris flow series and to assess the ability of p nigra to record geomorphic disturbances over time we date a total of 215 debris flows back to ad 1701 and observe a mean decadal frequency of 6 9 events with a peak in activity during the 1940s 20 events the young trees record an increase in debris flow activity over the last 70 years whereas the frequency of events remained fairly constant in the old trees for the same period by contrast the formation of reaction wood became increasingly scarce with increasing tree age whereas the occurrence of abrupt growth suppression increased copyright 2014 john wiley sons ltd

debris flow velocities and superelevation in a curved laboratory channel the vortex equation is often used to estimate the front velocity of debris flows using the lateral slope of the flow surface through a channel bend of a given radius here we report on laboratory e

atlantic hurricane activity following two major volcanic eruptions 1 in 1982 and 1991 two major volcanic eruptions loaded the stratosphere with long lived sulfate aerosols altering the global climate by redistributing longwave and shortwave radiation at the surface and throughout the atmosphere cooling the surface and subsurface waters of the tropical oceans theory and observations demonstrate through direct and indirect mechanisms a causal relationship between tropical north atlantic sea surface temperatures and seasonal atlantic hurricane frequency duration and intensity therefore it is plausible that hurricane activity in the seasons immediately following these eruptions is diminished however to date such a theory remains untested here i use observations reanalysis data and output from a numerical model to suggest that the number duration and intensity of hurricanes in the years following the eruptions of el chichon 1982 and mount pinatubo 1991 decreased via the aerosol direct effect determining the effects of each eruption on seasonal cyclone activity is complicated by simultaneous positive enso events thus further study of the relationship between atlantic tropical cyclones and major volcanic eruptions is warranted