the dynamics of the extratropical response to madden julian oscillation convection the rossby wave source rws and the corresponding extratropical wave response to tropical convection associated with different phases of the madden julian oscillation mjo is investigated with the dynamical core of a climate model the initial flow is specified to correspond to the boreal winter climatological flow and an imposed tropical heating that is derived from the observed precipitation for all eight mjo phases one key question addressed here is why does the extratropical rossby wave train depart the subtropics at a longitude well to the east of the rws for all eight mjo phases it is found that the extratropical response over the north pacific and north america is almost entirely due to the mjo convection over the western tropical pacific the rws is excited within the first 24 h after the model heating is turned on for mjo phases 1 3 and 8 the rws leads to the development of a cyclonic anomaly over southeast asia via advection of the climatological absolute vorticity by the anomalous divergent wind in the subtropics and by horizontal convergence in the tropics mjo phases 4 7 show opposite features the resulting anomaly is then advected eastward by the climatological zonal wind toward the central pacific after which dispersion into the extratropics and the excitation of a pacific north american teleconnection pattern takes place

annular modes in the extratropical circulation part i month to month variability the leading modes of variability of the extratropical circulation in both hemispheres are characterized by deep zonally symmetric or annular structures with geopotential height perturbations of opposing signs in the polar cap region and in the surrounding zonal ring centered near 458 latitude the structure and dynamics of the southern hemisphere sh annular mode have been extensively documented whereas the existence of a northern hemisphere nh mode herein referred to as the arctic oscillation ao has only recently been recognized like the sh mode the ao can be defined as the leading empirical orthogonal function of the sea level pressure field or of the zonally symmetric geopotential height or zonal wind fields in this paper the structure and seasonality of the nh and sh modes are compared based on data from the national centers for environmental prediction national center for atmospheric research reanalysis and supplementary datasets the structures of the nh and sh annular modes are shown to be remarkably similar not only in the zonally averaged geopotential height and zonal wind fields but in the mean meridional circulations as well both exist year round in the troposphere but they amplify with height upward into the stratosphere during those seasons in which the strength of the zonal flow is conducive to strong planetary wave mean flow interaction midwinter in the nh and late spring in the sh during these active seasons the annular modes modulate the strength of the lagrangian mean circulation in the lower stratosphere total column ozone and tropopause height over mid and high latitudes and the strength of the trade winds of their respective hemispheres the nh mode also contains an embedded planetary wave signature with expressions in surface air temperature precipitation total column ozone and tropopause height it is argued that the horizontal temperature advection by the perturbed zonal mean zonal wind field in the lower troposphere is instrumental in forcing this pattern a companion paper documents the striking resemblance between the structure of the annular modes and observed climate trends over the past few decades

a physically based model for the topographic control on shallow landsliding a model for the topographic influence on shallow landslide initiation is developed by coupling digital terrain data with near surface through flow and slope stability models the hydrologic model topog o loughlin 1986 predicts the degree of soil saturation in response to a steady state rainfall for topographic elements defined by the intersection of contours and flow tube boundaries the slope stability component uses this relative soil saturation to analyze the stability of each topographic element for the case of cohesionless soils of spatially constant thickness and saturated conductivity the steady state rainfall predicted to cause instability in each topographic element provides a measure of the relative potential for shallow landsliding the spatial distribution of critical rainfall values is compared with landslide locations mapped from aerial photographs and in the field for three study basins where high resolution digital elevation data are available tennessee valley in marin county california mettman ridge in the oregon coast range and split creek on the olympic peninsula washington model predictions in each of these areas are consistent with spatial patterns of observed landslide scars although hydrologic complexities not accounted for in the model e g spatial variability of soil properties and bedrock flow control specific sites and timing of debris flow initiation within areas of similar topographic control

wave driven zonal flow vacillation in the southern hemisphere the variability of the zonal mean flow in the southern hemisphere during the period 1985 94 is studied using european centre for medium range forecasts analyses the dominant mode of variability has approximately equivalent barotropic variations of opposite signs centered at 40 8 and 608s this structure is dominant in all seasons and has similar variance in all seasons the temporal variance of the amplitude of this mode is well modeled as gaussian red noise with a correlation e folding time of about 10 days zonal wind anomalies are maintained against frictional drag by variations in the zonal flow accelerations driven by transient eddies and associated mean meridional circulations the eddy structures suggest that equatorward propagation is favored when the jet is displaced poleward and zonal propagation is favored when the jet is displaced equatorward

overturn and evolution of a crystallized magma ocean a numerical parameter study for mars 1 early in the history of terrestrial planets the fractional crystallization of a magma ocean can lead to a mantle stratification characterized by a progressive enrichment in heavy elements from the core mantle boundary to the surface such configuration is gravitationally unstable it causes mantle overturn and the formation of a stable chemical layering using simulations of thermo chemical convection we analyzed the consequences of overturn and subsequent layering on mantle dynamics assuming mars scaling parameters we found that the time needed to achieve chemical homogenization via convective mixing scales exponentially with the buoyancy ratio inline image which measures the relative importance of chemical to thermal buoyancy in addition when using a strongly temperature dependent viscosity the formation of a stagnant lid prevents the uppermost crystallized layers from sinking into the mantle in order to obtain their subduction an yielding mechanism must be invoked 2 in the context of mars evolution our results suggest that complete chemical mixing is unlikely to take place within time scales comparable with the planet s age magma ocean freezing could be thus responsible for the long term preservation of compositional heterogeneities as required by meteoritic evidence the lack of a surface highly enriched in incompatible elements and of a high density lid is difficult to reconcile with a stagnant lid regime operating throughout mars history an episode of surface mobilization induced by compositional overturn can resolve this difficulty provided that inline image is large enough too large buoyancy ratios however tend to suppress convective heat transport rendering it problematic to explain the late volcanic history of mars

landslide hazard evaluation a review of current techniques and their application in a multi scale study central italy in recent years growing population and expansion of settlements and life lines over hazardous areas have largely increased the impact of natural disasters both in industrialized and developing countries third world countries have difficulty meeting the high costs of controlling natural hazards through major engineering works and rational land use planning industrialized societies are increasingly reluctant to invest money in structural measures that can reduce natural risks hence the new issue is to implement warning systems and land utilization regulations aimed at minimizing the loss of lives and property without investing in long term costly projects of ground stabilization government and research institutions worldwide have long attempted to assess landslide hazard and risks and to portray its spatial distribution in maps several different methods for assessing landslide hazard were proposed or implemented the reliability of these maps and the criteria behind these hazard evaluations are ill formalized or poorly documented geomorphological information remains largely descriptive and subjective it is hence somewhat unsuitable to engineers policy makers or developers when planning land resources and mitigating the effects of geological hazards in the umbria and marche regions of central italy attempts at testing the proficiency and limitations of multivariate statistical techniques and of different methodologies for dividing the territory into suitable areas for landslide hazard assessment have been completed or are in progress at various scales these experiments showed that despite the operational and conceptual limitations landslide hazard assessment may indeed constitute a suitable cost effective aid to land use planning within this framework engineering geomorphology may play a renewed role in assessing areas at high landslide hazard and helping mitigate the associated risk

boreal winter links between the madden julian oscillation and the arctic oscillation abstract there is increasing evidence that the madden julian oscillation mjo modifies the mid to high latitude circulation and in particular appears to have a relationship to the leading mode of extratropical variability the arctic oscillation ao in this study new insights into the observed similarities between the mjo and the ao are explored it is shown that the eastward progression of the convectively active phase of the mjo is associated with a corresponding shift in the tendency and sign of the ao index moreover the ao and the mjo share several analogous features not only in the global circulation but also in surface temperature fields also the ao is linked to a pattern of eastward propagating mjo like variability in the tropics that is partially reproduced in free runs of the ncep climate forecast system cfs model finally it is shown that the structure of the ao as defined by the leading mode in the 1000 hpa geopotential height field is significantly altered based on the phase o

influence of the madden julian oscillation on wintertime surface air temperature and cold surges in east asia 1 the variations of wintertime surface air temperature sat and the occurrences of cold surges over east asia in association with the madden and julian oscillation mjo are examined the mjo is defined as a combination of the two leading empirical orthogonal function modes of 850 and 200 hpa zonal winds and outgoing longwave radiation in the tropics the spatial pattern and magnitude of sat anomalies over east asia significantly change with respect to mjo phases composite analysis reveals that the mjo sat relationship is mainly affected by strong temperature advection in the lower troposphere in addition occurrences of cold surges are identified using objectively determined synoptic criteria and their relation to the mjo is analyzed most extreme cold surges occur when the mjo convection center is located over the indian ocean and it is suggested that mjo induced circulation anomalies may reinforce the amplification of normal cold surges to extreme cold surges

northern hemisphere mid winter vortex displacement and vortex split stratospheric sudden warmings influence of the madden julian oscillation and quasi biennial oscillation we investigate the connection between the equatorial madden julian oscillation mjo and different types of the northern hemisphere mid winter major stratospheric sudden warmings ssws i e vortex displacement and vortex split ssws the mjo ssw relationship for vortex split ssws is stronger than that for vortex displacement ssws as a result of the stronger and more coherent eastward propagating mjos before vortex split ssws than those before vortex displacement ssws composite analysis indicates that both the intensity and propagation features of mjo may influence the mjo related circulation pattern at high latitudes and the type of ssws a pronounced quasi biennial oscillation qbo dependence is found for vortex displacement and vortex split ssws with vortex displacement split ssws occurring preferentially in easterly westerly qbo phases the lagged composites suggest that the mjo related anomalies in the arctic are very likely initiated when the mjo related convection is active over the equatorial indian ocean around the mjo phase 3 further analysis suggests that the qbo may modulate the mjo related wave disturbances via its influence on the upper tropospheric subtropical jet as a result the mjo related circulation pattern in the arctic tends to be wave number one wave number two 25 30 days following phase 3 i e approximately phases 7 8 when the mjo related convection is active over the western pacific during easterly westerly qbo phases which resembles the circulation pattern associated with vortex displacement vortex split ssws

landslides on coastal sage scrub and grassland hillslopes in a severe el nino winter the effects of vegetation conversion on sediment delivery during the 1997 1998 el nino record rainfall triggered 150 shallow landslides within a 9 5 km2 area near santa barbara cal ifornia they were studied to analyze the sediment delivery to val ley floors from landslides in coastal sage scrub and converted grasslands the conversion of coastal sage to grasslands primarily to provide pasturage for cattle is common in the region and the landscape s response may affect water quality reservoir infilling and debris flow hazards we explore the relationship between lateral root reinforcement and landslide volume by developing a slope stability analysis that incorporates root cohesion along the sides of the failure the stability analysis correctly predicts an inverse re lationship between landslide volume and hillslope angle in the sage the volumes of failures in the grasslands do not vary systemati cally with slope and are generally smaller than those in the sage from aerial photograph analysis and field mapping we find that there are 22 9 failures per square kilometer in the grasslands com pared to 13 2 failures per square kilometer in the sage despite the lower failure density in the coastal sage greater failure volumes and longer transport distances delivered more sediment to valley floors with a specific volumetric flux of 2 8 3 10 2 m 3 m 1 for this el nino compared to 1 73 10 2 m 3 m 1 in the grasslands we con clude that the conversion from vegetation with stronger and deeper roots coastal sage to vegetation with weaker and shallower roots grass has caused a pulse of increased landsliding in the grasslands because the soils are currently too thick for the prevailing root reinforcement we suggest that over time soils in the grassland hollows will become thinner as the evacuation by landslides is re peated until the landsliding rate declines to balance the soil sup plied from local colluvium production and diffusive processes upslope

global view of the intraseasonal oscillation during northern winter abstract in this study svd analysis is applied to a normalized 200 mb streamfunction olr covariance matrix to extract the most recurrent coupled pattern in the northern winter after the removal of the climatological seasonal cycle and seasonal means for each winter the first two singular vectors are on an intraseasonal timescale and the combination of the two forms an oscillation it is characterized by eastward propagation in the indian ocean and the western pacific standing oscillations in both the tropics and the extratropics and the poleward propagation of a zonally symmetric structure although there exists an eastwardly propagating pattern the phase relationship between geopotential wind and streamfunction fields is inconsistent with that of equatorial kelvin waves eastward propagation is most evident in the tropics of the southern hemisphere while the signals in the northern hemisphere are characterized by standing oscillations the distinct characteristics of the northern and southern he

disturbance regimes at the interface of geomorphology and ecology geomorphological processes are an integral part of ecosystem functioning and ecosystem functioning affects geomor phological processes increasingly widespread acknowledgement of this simple idea is manifest in a vigorous research community engaged with questions that address the two way interaction between biota and geomorphology at a range of scales and in a variety of terrestrial and aquatic environments geomorphological disturbances are a core element of biogeomorphological interest and although the disciplines of geomorphology and ecology have each developed languages and theories that help to explore model and understand disturbance events little attempt has been made to draw together these approaches following a brief review of these issues we introduce thirteen papers that investigate the interactions and feedbacks between geomorphological disturbance regimes and ecosystem functions these papers reveal the singularity of wildfire impacts the importance of landsliding for carbon budgeting and of vegetation accumulation for landsliding the zoogeomorphic role of iconic and cinderella animals in fluvial geomorphology biophysical interactions in aeolian fluvial and torrential environments and the utility of living ecosystems as archives of geomorphic events most of these papers were first presented in a conference session at the european geoscience union general assembly in 2010 and several others are from recent volumes of earth surface processes and landforms copyright 2012 john wiley sons ltd

a distributed slope stability model for steep forested basins a distributed physically based slope stability model dslam based on an infinite slope model a kinematic wave groundwater model and a continuous change vegetation root strength model is presented it is integrated with a contour line based topographic analysis and a geographic information system gis for spatial data extraction and display the model can be run with either individual rainfall events or long term sequences of storms these inputs can be either actual storm records or synthesized random events based on monte carlo simulation the model is designed to analyze rapid shallow landslides and the spatial distribution of safety factor fs in steep forested areas it can investigate the slope stability problem in both temporal and spatial dimensions for example the impact of timber harvesting on slope stability either at a given time or through an extended management period the probability of landslide occurrence for a given year and the delivery of landslide sediments to headwater streams the dslam model was applied in a steep forested drainage of cedar creek in the oregon coast ranges using actual spatial patterns of timber harvesting and measured rainfall during a major storm which triggered widespread landslides in that area in 1975 simulated volume and number of failures were 733 m3 and 4 respectively these values agreed closely with field measurements following the 1975 storm however the effect of parameter uncertainty may complicate this comparison for example when soil cohesion values of 2 0 and 3 0 kpa were used the failure volume changed by factors of 2 04 and 0 41 respectively compared with the average condition of 2 5 kpa used in the simulation for soil depths 30 higher and lower than the standard condition the failure volume changed by factors of 2 0 and 0 27 respectively when maximum root cohesion changed from 12 5 kpa average condition to 10 kpa the failure volume increased 1 73 fold for the case of 15 kpa the failure volume changed by a factor of 0 55 the simulated failures caused by the storm were mostly in hollows the simulations show that the spatial distribution of fs is controlled mainly by topography and timber harvesting patterns and is greatly affected by groundwater flow patterns during major rainstorms most areas with fs 3 0 corresponded with the distribution of blocks clear cut in 1968 and all elements with fs 2 0 were in areas clear cut in 1968 areas with low fs 1 0 1 6 expanded dramatically during the rainstorm and decreased at a slow rate after the storm factors of safety in hollows declined sharply during the storm

modulation of eastern north pacific hurricanes by the madden julian oscillation abstract hurricane and tropical storm statistics verify the modulation of eastern pacific tropical systems by the madden julian oscillation mjo as hypothesized by maloney and hartmann over twice as many named tropical systems hurricanes and tropical storms accompany equatorial 850 mb westerly anomalies than accompany equatorial easterly anomalies and the systems that do exist are stronger hurricanes are over four times more numerous during westerly phases of the mjo than during easterly phases the current study constructs a composite life cycle of the mjo during may november 1979 95 using an index based on the 850 mb equatorial zonal wind equatorial kelvin waves propagating eastward from convective regions of the western pacific ocean alter dynamical conditions over the eastern pacific ocean westerly easterly equatorial 850 mb wind anomalies are accompanied by enhanced suppressed convection over the eastern pacific hurricane region convection locally amplifies the wind anomalies over the ea

variability of antarctic circumpolar transport and the southern annular mode associated with the madden julian oscillation 1 the variability of oceanic antarctic circumpolar transport and the atmospheric southern annular mode sam on intraseasonal 30 70 day timescales is shown to be related to the tropical atmospheric madden julian oscillation mjo during southern winter approximately 7 days after anomalous mjo convection in the equatorial indian ocean peaks an atmospheric extratropical response is set up with anomalous surface westerlies around almost the entire latitude circle at 60 s this pattern projects strongly onto the sam and leads to an acceleration of the eastward circumpolar transport around antarctica as measured by tide gauges and bottom pressure recorders this ocean response is confirmed by a global ocean model which shows a maximum in the transport through drake passage 3 days after the atmospheric extratropical response

the relationship between the north atlantic jet and tropical convection over the indian and western pacific oceans abstractboreal winter jet variability over the north atlantic is investigated using 40 yr european centre for medium range weather forecasts re analysis era 40 data where the variability is defined by the first eof of the zonal wind on seven vertical levels the principal component time series of this eof is referred to as the jet index a pattern correlation analysis indicates that the jet index more accurately describes intraseasonal north atlantic zonal wind variability than does the north atlantic oscillation nao a series of composite calculations of the jet index based on events of intraseasonal convective precipitation over the tropical indian and western pacific oceans reveals the following statistically significant relationships 1 negative jet events lead enhanced indian ocean precipitation 2 positive jet events lag enhanced indian ocean precipitation 3 positive jet events lead enhanced western pacific ocean precipitation and 4 negative jet events lag enhanced western pacific ocean p

a statistical analysis of relationships between western north pacific tropical cyclones and extratropical circulation patterns accompanying the madden julian oscillation abstractrelationships between the madden julian oscillation mjo and the extratropical circulation have been studied extensively and applied in operational settings to improve subseasonal predicti

persistent north pacific circulation anomalies and the tropical intraseasonal oscillation abstract a composite analysis of multiyear 1985 93 global reanalyses produced by the ncep ncar and the nasa dao is used to show that the development of persistent north pacific pnp circulation anomalies during nh winter is linked to tropical intraseasonal oscillations the development is initiated over the tropical west pacific by anomalous convection characterized by an east west dipole structure one to two weeks prior to the extratropical onset time in both reanalyses as tropical heating moves eastward toward the central pacific anomalous divergent outflow associated with the local hadley circulation generates an anomalous rossby wave sink source in the subtropics consistent with the retraction extension of the pacific jet prior to onset the signature of the forced anomalies is a pair of cyclonic anticyclonic circulation anomalies centered near the node of the tropical heating dipole wave trains extending from the region of anomalous convection into the extratropics set the stage for th

on relationships between nonrecurving western north pacific tropical cyclones the madden julian oscillation and the east asian subtropical jet abstracta 200 hpa zonal momentum budget is performed to examine the role that western north pacific tropical cyclones tcs play in helping to organize intraseasonal extratropical circulation anoma

the latitude height structure of 40 50 day variations in atmospheric angular momentum abstract quasi periodic variations in the relative angular momentum of the atmosphere on time scales of around 40 50 days have been observed by langley et al 1981 a description of the two dimensional latitude height structure of the winds responsible for these changes is constructed here from five years of nmc twice daily global analyses using cross spectral and amplitude phase eigenvector techniques we find these variations are associated with wavelike motions in the tropical upper troposphere that propagate and downward in phase within the tropics a coherently connected midlatitude northern hemisphere component is also present whose phase is essentially independent of height we believe the tropical component to be the zonally averaged part of the motions described by madden and julian 1971 1972 the northern hemisphere midlatitude component may be a direct response to the tropical motions or both motions may be the common response to an as yet unidentified tropical forcing

the interaction of the madden julian oscillation and the arctic oscillation abstract tropical and extratropical interactions on the intraseasonal time scale are studied in the context of the arctic oscillation ao and the madden julian oscillation mjo to simplify the discussion a high low mjo phase is defined as strong suppressed convective activity over the indian ocean in the northern hemisphere nh winter season a high low ao phase is found more likely coupled with a high low mjo phase based on the regressed patterns and composites of various dynamical fields and quantities possible mechanisms linking the ao and the mjo are examined the analysis indicates that the mjo influence on extratropical circulations seems more evident than the ao influence on tropical circulations the mjo interacts with the ao through meridional dispersion of rossby waves in the pacific sector the geopotential height anomaly center over the north pacific associated with the mjo can either reinforce or offset the ao pacific action center as a result the ao pattern can be greatly a

the 1985 86 intraseasonal oscillation and the role of the extratropics abstract an intraseasonal oscillation that occurred in the 1985 86 northern winter is documented in this study the tropical convection of this event is dominated by the mixture of a standing oscillation over the maritime continent and an eastward moving feature from the indian ocean into the central pacific the time evolution of the upper tropospheric circulation patterns instead of propagating eastward along the equator as suggested in the existing composites of the intraseasonal oscillation is characterized by a series of wave patterns in the northern hemisphere and does not complete the cycle around the globe the familiar moist kelvin wave explanation for the intraseasonal oscillation receives little support from diagnosis of this event using zonal wind height field streamfunction and potential vorticity only in the lower troposphere near the date line is the convincing evidence for its existence found a scenario for the intraseasonal oscillation which is suggested by the analysis includes

development characteristics and dynamic structure of tropical intraseasonal convection anomalies abstract the development and dynamical structure of intraseasonal low frequency convection anomalies in the equatorial region are investigated using 10 years 1975 85 of outgoing longwave radiation olr and 7 years 1979 85 of 200 and 850 mb wind data the composite olr anomalies for 36 cases show a four stage development process initiation over equatorial africa rapid intensification when passing through the indian ocean mature evolution characterized by a weakening in the maritime continent and redevelopment over the western pacific and dissipation near the date line in moderate events or emanation from the equator toward north america and southeastern pacific in strong events a noticeable feature in vertical structure is that the 850 mb convergence leads convection and midtropospheric upward motion by about 30 degrees longitude in both developing and mature phases equatorial upper lower level easterly westerly anomalies and associated twin anomalous anticyclonic cyclonic circulation an

coupled ocean atmosphere response to indian ocean warmth 1 the coupled ocean atmosphere response to indian ocean warmth is studied it is shown with atmospheric models that indian ocean warmth forces a positive polarity phase of the north atlantic oscillation nao confirming results of previous studies coupled model experiments show that this nao response forces a local air sea feedback over the north atlantic ocean which intensifies the nao response this enhancement is realized through a positive feedback between the nao atmospheric circulation anomaly and a tripolar north atlantic sst pattern consistent with other studies on north atlantic air sea interactions it is concluded that the north atlantic and european climate response to indian ocean warming may be considerably greater than hitherto judged from the analyses of atmospheric model experiments alone

geomorphic process rates of landslides along a humidity gradient in the tropical andes areas with high landslide activity and diversity were encountered in the tropical andes of southern ecuador under contrasting semi arid to perhumid climatic conditions the objective of this study was to determine and compare geomorphic process rates of shallow landslides along this remarkable humidity gradient and subject to different types of human made and natural environmental changes geomorphic work geomorphic power and landslide mobilization rate lmr were therefore calculated for shallow landslides in two study areas with two separate geological or land use related subareas each while landslide ages were known in the perhumid reserva biologica san francisco rbsf area only an approximation of the frequency of critical landslide triggering rainfall events was available for the semi arid masamanaca area landslide volumes were estimated by volume area scaling generalized additive models gams were used as landslide susceptibility models in order to analyze the relative importance of topography and to downscale lmr values to a fine spatial resolution lmr in the perhumid rbsf area ranged from 2 mm yr 1 in the natural part of this area with tropical mountain rainforests to 5 mm yr 1 in the human influenced part the semi arid masamanaca area though subject to greater estimation uncertainties displayed lmr on the order of 0 4 to 4 mm yr 1 for shallow landslides the results provide a basis for the spatially differentiated assessment of landscape evolution and degradation in an area with a close relation between landslide activity natural vegetation succession and human land use

dependence of the structure of the northern hemisphere annular mode on the polarity of enso 1 the structure of the northern hemisphere annular mode nam is shown to be significantly different during warm and cold winters of the enso cycle during warm winters the arctic center of action of the annular mode is more prominent and extends deeper into siberia its related surface air temperature signal is stronger and the compensating outer ring in the sea level pressure field is much broader encompassing the entire tropics during cold winters the nam signature is much more pronounced over the pacific sector the sea level pressure pattern exhibits a north pacific center of action positively correlated with the atlantic center and pronounced deflections of the storm track are also evident it is suggested that the former features are associated with the equatorward displacement of the jet stream and the storm tracks during warm winters of the enso cycle and the latter is related to the the more pronounced break in the subtropical jet stream over the pacific sector during cold winters

biotic controls on shallow translational landslides in undisturbed tropical montane rainforests massive organic layers accommodate the majority of roots and only a small fraction of roots penetrate the mineral soil we investigated the contribution of vegetation to slope stability in such environments by modifying a standard model for slope stability to include an organic layer with distinct mechanical properties the importance of individual model parameters was evaluated using detailed measurements of soil and vegetation properties to reproduce the observed depth of 11 shallow landslides in the andes of southern ecuador by distinguishing mineral soil organic layer and above ground biomass it is shown that in this environment vegetation provides a destabilizing effect mainly due to its contribution to the mass of the organic layer up to 973 t ha 1 under wet conditions sensitivity analysis shows that the destabilizing effect of the mass of soil and vegetation can only be effective on slopes steeper than 37 9 this situation applies to 36 of the study area thus on the steep slopes of this megadiverse ecosystem the mass of the growing forest promotes landsliding which in turn promotes a new cycle of succession this feedback mechanism is worth consideration in further investigations of the impact of landslides on plant diversity in similar environments copyright 2012 john wiley sons ltd

the variability of root cohesion as an influence on shallow landslide susceptibility in the oregon coast range decades of quantitative measurement indicate that roots can mechanically reinforce shallow soils in forested landscapes forests however have variations in vegetation species and age which can dominate the local stability of landslide initiation sites to assess the influence of this variability on root cohesion we examined scarps of landslides triggered during large storms in february and november of 1996 in the oregon coast range and hand dug soil pits on stable ground at 41 sites we estimated the cohesive reinforcement to soil due to roots by determining the tensile strength species depth orientation relative health and the density of roots 1 mm in diameter within a measured soil area we found that median lateral root cohesion ranges from 6 8 23 2 kpa in industrial forests with significant understory and deciduous vegetation to 25 6 94 3 kpa in natural forests dominated by coniferous vegetation lateral root cohesion in clearcuts is uniformly 10 kpa some 100 year old industrial forests have s

factors controlling debris avalanche initiation heavy rainfall during a january 1983 storm triggered numerous debris avalanches and associated debris torrents in the smith creek basin western whatcom county washington united states four classes of debris avalanches are recognized wedges drainage depressions logging roads and discontinuity surfaces nine different debris avalanche headscarps that are representative of these four classes are studied in detail the geometric configuration of each headscarp the properties of soils comprising the headscarps and water tables based on numerical models of hillslope hydrology are used in limit equilibrium slope stability analyses to back calculate root cohesion cr values at failure the calculated values are consistent with those reported by others four groups of cr values are proposed and correlated with forest vegetation group i understory cr range from 1 6 to 2 1 kpa group ii scrub forest cr range from 2 1 to 2 5 kpa group iii mixed forest cr range from 2 5 to 3 0 kpa and group iv old

domination of hillslope denudation by tree uprooting in an old growth forest abstract razula forest preserve in the carpathian mountains of the czech republic is an unmanaged forest that has not been logged or otherwise anthropically disturbed for at least 83 years preceded by only infrequent selective logging we examined this 25 ha area to determine the dominant geomorphological processes on the hillslope tree uprooting displaces about 2 9 m 3 of soil and regolith per year representing about 1 5 uprooted trees ha 1 yr 1 based on forest inventory records dating back to 1972 and contemporary measurements of displaced soil and pit mound topography resulting from uprooting pits and mounds occupy 14 of the ground surface despite typical slope gradients of 0 05 mm 1 and up to 0 41 little evidence of mass wasting e g slump or flow scars or deposits colluvial deposits was noted in the field except in association with pit mound pairs small avalanche and ravel features are common on the upslope side of uproot pits surface runoff features were rare and poorly connected but do include stemwash erosion associated with stemflow no rills or channels were found above the valley bottom area and only small localized areas of erosion and forest litter debris indicating overland flow where these features occurred they either disappeared a short distance downslope indicating infiltration or indicate flow into tree throw pits surface erosion is also inhibited by surface armoring of coarse rock fragments associated with uprooting as well as by the nearly complete vegetation and litter cover these results show that the combination of direct and indirect impacts of tree uprooting can dominate slope processes in old growth unmanaged forests the greater observed expression of different hillslope processes in adjacent managed forests where tree uprooting dynamics are blocked by management activities suggests that human interventions can change the slope process regime in forest ecosystems

contrasting mountain and piedmont dynamics of sediment discharge associated with groundwater storage variation in the biobio river supply and transport of sediment in catchments involve processes with fundamental consequences for river management land use and the prediction of climate driven sediment fluxes in the present study we addressed spatial variability in the water routes through the surface and subsurface of a catchment and the suspended sediment discharge qs over a mountain piedmont system we analyzed daily suspended sediment concentration cs and water discharge q measurements at stations located in different topographic settings mountain and piedmont in the biobio river basin southern central andes 37 39 s in steep catchments the q versus qs relationship has a marked seasonal hysteresis in the piedmont qs is proportional to q with no seasonal hysteresis the contrast in the hysteresis pattern between catchments with different topographies is explained by differences in the routing of rainfall derived water in the piedmont most of the rainfall is converted into surface runoff because the water table is near the surface in the mountains groundwater storage results in large seasonal variations in the proportion of q that flows at the surface and transports sediment from the hillslopes producing hysteresis by separating the total q into two components direct discharge qd and base flow qb we observed the response of qs to the fraction of water that quickly leaves the catchment after a rainfall event qd similar results between the mountain and piedmont and the absence of hysteresis simplify the behavior of qs into a linear relationship with qd over the entire catchment and lead us to propose that sediment mobilization to the river along the biobio catchment is primarily controlled by overland flow our findings highlight the importance of an adequate hydrological model for understanding the erosion and transport processes of a catchment and which can be applied to other natural and modeled mountain piedmont systems

the shift of convection from the indian ocean to the western pacific ocean during a 30 60 day oscillation abstract a strong 30 60 day oscillation during november december 1981 is studied using analyzed winds from the national meteorological center outgoing longwave radiation and satellite low level moisture data the outgoing longwave radiation and 150 mb velocity potential for five adjacent events are also examined consistent features include the slow 5 m s 1 propagation of convective energy over the indian ocean western pacific ocean and the fast 15 m s 1 propagation of 150 mb tropical velocity potential in regions remote from the oceanic warm pool the individual events have characteristics of the seasonal and anomalous base state within which they are embedded for the november december 1981 event we concentrate on the details of the shift of convection from the eastern indian ocean to the western pacific ocean an intense cold surge and accompanying convective increase near 110 e precede the shift cast by about 12 days the regional 150 mb circulation responds to the enhanced convection with an i

eddy zonal flow feedback in the northern hemisphere winter abstract the variability of the zonal mean zonal wind in the northern hemisphere winter december march is studied using eof analysis and momentum budget diagnostics of ncep ncar reanalysis data 1976 2001 the leading eof of the zonal mean zonal wind is well separated from the remaining eofs and represents the north south movement of the midlatitude westerlies analysis of the momentum budget shows that a positive feedback between the zonal mean wind anomalies and the eddy momentum fluxes selects the leading eof of midlatitude variability like the southern hemisphere the baroclinic eddies reinforce the zonal wind anomalies while external rossby waves damp the wind anomalies in the northern hemisphere the quasi stationary eddies also reinforce the zonal wind anomalies but the baroclinic eddies are most important for the positive eddy zonal flow feedback the observations support the following feedback mechanisms 1 above normal baroclinic wave activity is generated in the region of enhanced wester