laboratory experiments simulating the geomorphic response to tectonic uplift 1 we present the results of an experimental study of topography dynamics under conditions of constant precipitation and uplift rate the experiment is designed to develop a complete drainage network by the growth and propagation of erosion instabilities in response to tectonic perturbations the quantitative analysis of topographic evolution is made possible by using telemetric lasers that perform elevation measurements at an excellent level of precision we focus our study on the effect of initial surface organization and of uplift rate on both the transient dynamics and the steady state forms of topography we show that the transient phase is strongly dependent on the initial internally drained area which is found to decrease exponentially with time the topography always reaches a steady state whose mean elevation depends linearly on uplift rate with a strictly positive value when uplift is zero steady state surfaces are characterized by a well defined slope area power law with a constant exponent of 0 12 and an amplitude that depends linearly on uplift rate with a strictly positive value when uplift is zero these results are consistent with a stream power law erosion model that includes a nonnegligible threshold for particle detachment uncertainty regarding the sediment transport length is resolved by calibrating the transient dynamics with a surface process model reappraising published results on the linear dependency between mean elevation or relief and denudation rate we suggest that an erosion threshold is worth considering for large scale systems

australian east coast cyclones part i synoptic overview and case study abstract the meteorological conditions for the development of australian east coast cyclones are described the main synoptic precursor is a trough or dip in the easterly wind regime over eastern australia the cyclones are a mesoscale development which occurs on the coast in this synoptic environment they form preferentially at night in the vicinity of a marked low level baroclinic zone and just equatorward of a region of enhanced convection resulting from flow over the coastal ranges three different types of east coast cyclone have been identified types 1 and 3 are very small systems which can have lifetimes as short as 16 hours during which hurricane force winds have been observed to develop the other type 2 system is a meso synoptic scale cyclone that can bring sustained strong winds and flood rainfall over several days because of their intensity rapid development and occasional tiny size these systems are a major forecast problem

a seasonal climatology of rossby wave breaking in the 320 2000 k layer abstract differential advection in rossby waves can lead to potential vorticity pv p contours on isentropic surfaces folding over in latitude py 0 in a process called rossby wave breaking rwb exploring the properties of rwb may shed light on underlying dynamics and enable quantification of irreversible transport a seasonal climatology of py and rwb statistics is presented for the 320 850 k layer using ncep reanalysis data during 1979 2005 and for the 320 2000 k layer using the met office ukmo data during 1991 2003 a primary goal is to depict the spatial extent and seasonality of rwb maxima this analysis shows seven distinct rwb regimes poleward and equatorward of the subtropical westerly jets poleward and equatorward of the stratospheric polar night jets flanking the equator in the stratosphere and mesosphere equatorward of subtropical monsoon anticyclones and the summertime polar stratosphere a striking pv gradient maximum exists at the equator throughout the layer 360 2000 k flanke

a quasi geostrophic diagnosis of the zonal flow associated with cut off lows over south africa and surrounding oceans the zonal flow associated with cut off lows cols comprises two jet streaks of different spatial extents the smaller scale jet streak located north of the cols forms as a result of meridional divergence of vorticity advection and it is quasi stationary relative to the cols it dissipates as the cols do the same the larger scale jet streak gives rise to anticyclonic and equatorward rossby wave breaking rwb as it propagates southeasterly to the base of the ridge south of the col and then northeasterly beyond that point as the jet streak propagates it brings with it the anticyclonic barotropic shear that causes the rossby waves to break its propagation is caused by zonal momentum advection by the zonal flow from jet streak entrance to its exit as it propagates its northwesterly southeasterly orientation changes to one that is more zonal to become south westerly northeasterly at the end of the col life cycle this change in orientation is due to meridional advection of zonal momentum where the meridional flow advects momentum southward northward at the jet streak entrance exit the jet streaks form a split jet structure and the winds between the streaks is decelerated by vorticity advection convergence because the flow and col and rwb life cycle are coupled understanding the dynamics that underlie the changes in the col ambient flow contributes to resolving the outstanding rwb col causality problem

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

self organized criticality in layered lacustrine sediments formed by landsliding landsliding is the dominant mass wasting process in humid temperate uplands and an important regulator of sediment yield from steep land drainage basins information about the magnitude and frequency distribution of landslides has been derived from aerial photography but it has proved difficult to set limits on the long term scaling behavior of landsliding because the requirements of spatial and temporal coherence and the large number of observations necessary to undertake magnitude versus frequency analyses are not easy to fulfill we use a 2250 yr long record of hillslope erosion associated with extreme hydrologic events preserved in sediments from lake tutira new zealand to investigate scaling in landslide deposits both the magnitude versus frequency distribution of sediment layers attributed to landsliding and the distribution of time intervals between landsliding events take the form of power laws the former with an exponent b 2 06 and the latter with an exponent b 1 4 these results suggest that the erosional events originate from a self organized critical process and are in agreement with observations of scaling in turbidite deposits and grain flows in controlled laboratory experiments the implications are that the aggregate behavior of landsliding at the catchment scale is orderly and that the stratigraphic record preserves a unique long term perspective on a fundamental geomorphic process and the extreme hydrologic events that trigger it

intrusions into the tropical upper troposphere three dimensional structure and accompanying ozone and olr distributions abstract the evolution and structure of stratospheric intrusions into the upper troposphere ut over the northern tropical pacific is examined in terms of both potential vorticity pv and ozone o3 analysis of 20 years of ncep ncar reanalysis pv shows that the intrusion events have remarkably similar evolution and structure at 350 k with all events producing narrow tongues of high pv that have an almost north south orientation and last around 3 days nearly all events extend up into the lower stratosphere but only for a small percentage is there deep downward penetration the intrusions explain a large amount of the observed variability in upper tropospheric o3 above hilo hawaii with large values occurring when a tongue of high pv passes over hilo and low values when hilo is just upstream of a high pv tongue there is also an increase in total column ozone within the pv tongues but for most intrusions the increase is relatively small the relationship between deep convection as diagnosed by sate

fitting degradation of shoreline scarps by a nonlinear diffusion model the diffusion model of degradation of topographic features is a promising means by which vertical offsets on holocene faults might be dated in order to calibrate the method we have examined present day profiles of wave cut shoreline scarps of late pleistocene lakes bonneville and lahontan it may be assumed that these scarps were initially at least as steep as the angle of repose offsets range from 1 to 12 m and present slope angles range from 9 to 29 a parameter called apparent diffusion age defined as half the mean square horizontal extent of the slope function of each profile is plotted as a function of scarp offset the points show a clear trend of apparent age increasing nearly linearly with offset if linear diffusion held and scarps were initially vertical apparent diffusion age would be the same for all the shoreline profiles the increasing trend can only partly be explained by nonvertical initial scarp slope and therefore the rate of transport of material downslope must increase significantly faster than a linear law in the range of slopes spanned by the data the transport law must become linear at small slope to reduce scatter between profiles with varying ambient slopes the transport law adopted for the purpose of dating is k0 1 5s2 where s is local slope the transport coefficient k0 is correlated inversely with fan slope suggesting that there is a dependence on the particle size distribution a table is included that allows easy application of the model to scarps with simple initial shape

storm tracks in the southern hemisphere abstract from 1979 to 1989 global european centre for medium range weather forecasts ecmwf analyses of many meteorological variables important in baroclinic storms have been bandpass filtered to highlight fluctuations on 2 to 8 day time scales in order to illuminate the relationships among the variables in baroclinic storm track regions because of the greater zonal symmetry in the southern hemisphere sh versus the northern hemisphere nh it is possible to examine these relationships over a zonal sector without being dominated by local effects associated with jet stream entrance and exit regions of the storm tracks the bandpassed variance of geopotential height is used to define the storm track and its meridional profile has a pronounced midlatitude maximum in the sh the locations of the jet stream and the variance maxima of meridional and zonal velocity components vorticity vertical motion specific humidity and temperature all bear a distinctive relationship to the storm track but the lat

using hilltop curvature to derive the spatial distribution of erosion rates 1 erosion rates dictate the morphology of landscapes and therefore quantifying them is a critical part of many geomorphic studies methods to directly measure erosion rates are expensive and time consuming whereas topographic analysis facilitates prediction of erosion rates rapidly and over large spatial extents if hillslope sediment flux is nonlinearly dependent on slope then the curvature of hilltops will be linearly proportional to erosion rates in this contribution we develop new techniques to extract hilltop networks and sample their adjacent hillslopes in order to test the utility of hilltop curvature for estimating erosion rates using high resolution 1 m digital elevation data published and new cosmogenic radionuclide analyses in the feather river basin california suggest that erosion rates vary by over an order of magnitude 10 to 250 mm kyr 1 hilltop curvature increases with erosion rates allowing calibration of the hillslope sediment transport coefficient which controls the relationship between gradient and sediment flux having constraints on sediment transport efficiency allows estimation of erosion rates throughout the landscape by mapping the spatial distribution of hilltop curvature additionally we show that hilltop curvature continues to increase with rising erosion rates after gradient limited hillslopes have emerged hence hilltop curvature can potentially reflect higher erosion rates than can be predicted by hillslope gradient providing soil production on hilltops can keep pace with erosion finally hilltop curvature can be used to estimate erosion rates in landscapes undergoing a transient adjustment to changing boundary conditions if the response timescale of hillslopes is short relative to channels

climatology of the stratospheric polar vortex and planetary wave breaking abstract we use the distribution of ertel s potential vorticity pv on the 850 k isentropic surface to establish a climatology for the transient evolution of the planetary scale circulation in the northern hemisphere winter midstratosphere we compute pv distribution from gridded nmc daily temperature and height maps for the 10 and 30 mb levels and show that a very good approximation for 850 k pv can be derived from 10 mb heights and temperatures alone we assume that reversals of the latitudinal gradient of pv localized in longitude and latitude may be regarded as signatures of planetary wave breaking wave breaking identified by such signatures tends to occur mainly in the vicinity of the aleutian anticyclone with a secondary maximum over europe the area of the polar vortex defined as the area enclosed by pv contours greater than a certain critical value is strongly influenced by wave breaking erosion of the polar vortex due to transport and mixing of pv leads to a preconditioned state when def

connections between potential vorticity intrusions and convection in the eastern tropical pacific abstract the connections between intrusions of stratospheric air into the upper troposphere and deep convection in the tropical eastern pacific are examined using a combination of data analysis potential vorticity pv inversion and numerical simulations analysis of ncep ncar reanalyses and satellite measurements of outgoing longwave radiation during intrusion events shows increased cloudiness lower static stability upward motion and a buildup of convective available potential energy cape at the leading edge of the intruding tongue of high pv potential inversion inversion calculations show that the upper level pv makes the dominant contribution to the changes in the quantities that characterize convection this supports the hypothesis that upper level pv anomalies initiate and support convection by destabilizing the lower troposphere and causing upward motion ahead on the pv tongue the dominant role of the upper level pv is confirmed by simulations using the fifth generation pennsylvania state u

the spatial variation of weathering and soil depth across a triassic sandstone outcrop in this study we used an archive of borehole logs from the british geological survey to collect information on the spatial structure of weathering that extends from the surface to competent bedrock across the triassic sherwood sandstone group outcrop 750 km2 in the east midlands uk the borehole logs were used to estimate the thickness of the soil n 280 and soil and saprolite ss the overburden of ice may have increased sub glacial pore water pressure with the fractures and faults acting as a drainage system for the removal of dissolved weathering products

estimates of the rate of regolith production using and from an alpine hillslope abstract the production of regolith is a fundamental geomorphic process because most surface processes transport only unconsolidated material we use concentrations of the cosmogenic radionuclides crns 10 be and 26 al in regolith and bedrock to deduce the rate of production of regolith on an alpine hillslope in the wind river range wy these calculations are based on a theoretical model which we develop here this model shows that it is important to consider dissolution of regolith in regolith production and in basin averaged erosion rate studies rates of production of regolith are uniform along the hillslope and the mean rates for the entire hillslope deduced from 10 be and 26 al are 14 3 4 0 and 13 0 4 0 m ma 1 respectively rates of production of regolith deduced from 10 be concentrations in regolith mantled bedrock support the rates deduced from regolith concentrations in the alpine environment examined here the rate of production of regolith beneath 90 cm of regolith is nearly twice as fast as the average rate of production of regolith on bare rock surfaces which small et al small e e anderson r s repka j l finkel r 1997 erosion rates of alpine bedrock summit surfaces deduced from in situ 10 be and 26 al earth and planetary science letters 150 413 425 previously documented rock mantled with regolith probably weathers more rapidly than bare rock because the water required for frost weathering is limited on bare rock surfaces because the hillslope examined here is convex with constant curvature and regolith production and thickness are uniform down the slope the regolith volume flux must be proportional to the local slope of the hillside therefore our results are consistent with gilbert s gilbert g k 1909 the convexity of hilltops journal of geology 17 344 350 steady state hillslope hypothesis if tor height and the difference between rates of weathering on bare and regolith mantled rock provide a fair estimate of the age of summit flats steady state hillslope conditions have been attained in less than several million years

quantification of soil production and downslope creep rates from cosmogenic 10be accumulations on a hillslope profile average soil transport rates over a period of 3500 yr on a convex soil mantled hillslope have been quantified using a mass balance model that incorporates the soil concentration of the cosmogenic isotope 10 be the 10 be model results support the assumption used in most geomorphic models that the soil creep rate is proportional to surface gradient the predicted diffusion coefficient is 360 55 cm 3 yr 1 cm 1 contour length and the average rate of soil production is 0 026 0 007 cm yr within the uncertainty of this technique the data do not reject g k gilbert9s hypothesis that some hillslopes may exist in a condition of dynamic equilibrium with a uniform soil production rate however the model does not require an assumption of dynamic equilibrium and may be an approach that uniquely allows the quantification of a local soil production rate law

two paradigms of baroclinic wave life cycle behaviour two idealized baroclinic wave 6 life cycles examined here suggest a framework of opposite extremes a in which to view the behaviour of real synoptic scale disturbances in middle latitudes and b in which to interrelate the synoptic and wave theoretic viewpoints using the saturation propagation saturation sps picture of wave 6 life cycle behaviour the two life cycles dented by lc1 and lc2 are higher resolution versions of the simmons hoskins basic and anomalous cases showing strong and weak late decay of eddy kinetic energy eke they illustrate in varying degrees two extreme types of behaviour here disignated anticyclonic and cyclonic and epitomized by strongly contrasting upper air trough behaviour anticyclonic behaviour dominates the late stages of lc1 and is characterized by backward tilted thinning troughs being advected anticyclonically and equatorward as in the commoner cases of planetary scale mid stratospheric rossby wave breaking cyclonic behaviour dominates lc2 and is characterized by forward tilted broadening troughs wrapping themselves up cyclonically and poleward producing major cut off cyclones in high latitudes these morphologies are visualized by upper air maps of potential temperature on the nominal tropopause defined as a constant potential vorticity surface some atmospheric mid latitude disturbances examined here using the same visualization applied to operational analyses show the same two extreme types of trough behaviour together with intermediate cases the sps picture is re examined using eliassen palm and refractive index cross sections it is shown in particular by reference to a wave activity theorem of haynes that the late stages of lc2 can be looked upon as a remarkably clear and morphologically novel large amplitude counterpart of the nonlinear reflection scenario of rossby wave critical layer theory the late stages of lc1 by constrast look more akin to an nonlinear critical layer absorption scenario lc2 exhibits region of largely undular pv contours adjacent to a nonlinear of irreversiby deformen pv contous in the latter region pv rearrangement and hence absorption of rossby wave activity has largely ceased this accounts for the more persistent ekee in the lc2 case

climatological features of cutoff low systems in the northern hemisphere this study presents the first multidecadal climatology of cutoff low systems in the northern hemisphere the climatology was constructed by using 41 yr 1958 98 of ncep ncar reanalysis data and identifying cutoff lows by means of an objective method based on imposing the three main physical characteristics of the conceptual model of cutoff low the 200 hpa geopotential minimum cutoff circulation and the specific structure of both equivalent thickness and thermal front parameter fields several results were confirmed and climatologically validated 1 the existence of three preferred areas of cutoff low occurrence the first one extends through southern europe and the eastern atlantic coast the second one is the eastern north pacific and the third one is the northern china siberian region extending to the northwestern pacific coast the european area is the most favored region 2 the known seasonal cycle with cutoff lows forming much more frequently in summer than in winter 3 the short lifetime of cutoff lows most cutoff lows lasted 2 3 days and very few lasted more than 5 days and 4 the mobility of the system with few cutoff lows being stationary furthermore the long study period has made it possible i to find a bimodal distribution in the geographical density of cutoff lows for the european sector in all the seasons with the exception of winter a summer displacement to the ocean in the american region and a summer extension to the continent in the asian region and ii to detect northward and westward motion especially in the transitions from the second to third day of occurrence and from the third to fourth day of occurrence the long term cutoff low database built in this study is appropriate to study the interannual variability of cutoff low occurrence and the links between cutoff lows and jet stream systems blocking or major modes of climate variability as well as the global importance of cutoff low in the stratosphere troposphere exchange mechanism which will be the focus of a subsequent paper

fragmentation of stratospheric intrusions evidence is presented pointing to the existence of rich and coherent subsynoptic and mesoscale flow features at tropopause levels these features are related to and evolve from the classical v shaped intrusions of stratospheric air down to tropospheric elevations it is shown that intrusions can develop into elongated 2000 3000 km and slender 200 km streamers and that thereafter such a streamer can roll up to form a train of stalactite shaped vortex subentities with an accompanying substantial thinning of the intervening filament in addition there are indications that the vortices themselves can develop a spirallike interior structure of interleaved stratospheric and tropospheric air these inferences are based upon two independent but complementary sources analysis of the potential vorticity distribution on tropopause transcending isentropic surfaces derived from the analysis fields of the european centre for medium range weather forecasts either directly or indirectly using a contour advection technique and imagery from the water vapor channel of the european space agency meteosat 4 satellite streamers were observed to occur with a frequency of approximately one per week over central and southern europe during the winter of 1991 1992 the fragmentation is linked to the instability or self development of a filament of enhanced potential vorticity and it can modify or instigate surface weather systems moreover by inducing a substantial and rapid enlargement of the intrusion s surface area it greatly enhances the potential for local irreversible mixing of stratospheric and tropospheric air

a new perspective of the climatological features of upper level cut off lows in the southern hemisphere this study presents a detailed view of the seasonal variability of upper level cut off lows cols in the southern hemisphere the cols are identified and tracked using data from a 36 year period of the european centre for medium range weather forecast reanalysis era interim the objective identification of the cols uses a new approach which is based on 300 hpa relative vorticity minima and three restrictive criteria of the presence of a cold core stratospheric potential vorticity intrusion and cut off cyclonic circulation the highest col activity is in agreement with previous studies located near three main continental areas australia south america and africa with maximum frequencies usually observed in the austral autumn the col mean intensity values show a marked seasonal and spatial variation with maximum minimum values during the austral winter summer a unique feature that has not been observed previously in studies based on the geopotential the link between intensity and lysis is examined and finds that weaker systems are more susceptible to lysis in the vicinity of the andes cordillera associated with the topographic rossby wave lysis and genesis regions are close to each other confirming that cols are quasi stationary systems also cols tend to move eastward and are faster over the higher latitudes the mean growth decay rates coincide with the major genesis and lysis density regions such as the significant decay values across the andes all year as a consequence of using vorticity for the tracking method a longer lifetime of cols is detected than in other studies but this does not affect the total frequency of occurrence comparisons with other studies suggest that the differences in seasonality are due to uncertainties in the reanalyses and the methods used to identify cols

relationships between cut off lows and the semiannual and southern oscillations the characteristics of southern cut off lows cols are studied for the period 1979 2008 the systematic identification of cols is realized by applying an original automated scheme using mean daily geopotential height and air temperature at 500 hpa ncep doe ii reanalysis data from closed lows trajectories established from the equator to the polar jet stream extratropical lows are analyzed and the stage of cut off is defined as a secluded low presenting a cold core from 4 843 cases the general col features are presented and confirm several previous results such as the geographic distribution which shows that they are more frequent in the latitudinal band contained between 20 s and 45 s and in close proximity to the continents on a seasonal time scale cols are more numerous from late summer to autumn with a maximum of frequency in march april in winter june july august they are fewer but deeper than during the rest of the year in the median domain 32 5 s the annual cycle of the frequency is bimodal and present two peaks during transitional seasons in this zone the seasonal cycle varies in accordance with the semiannual oscillation thereby when the meridional gradient of temperature pressure is reinforced between mid and high latitudes cols are more frequent in the median domain over the period 1979 2008 the annual cols frequency exhibits a positive trend of about 25 this increase is associated with a widening of the latitudinal domain of occurrence equatorward as well as poleward the trend is linked with an abrupt positive shift in the number of cols generation between 1998 and 1999 the geographical distribution of cols frequency varies significantly in accordance with el nino southern oscillation with more col s at lower higher latitudes during la nina el nino events principally in the southern pacific

hillslope evolution by nonlinear creep and landsliding an experimental study landscape evolution models are widely used to explore links between tectonics climate and hillslope morphology yet mecha nisms of hillslope erosion remain poorly understood here we use a laboratory hillslope of granular material to experimentally test how creep and landsliding contribute to hillslope erosion in our experimental hillslope disturbance driven sediment transport rates increase nonlinearly with slope due to dilation driven gran ular creep and become increasingly episodic at steep slope angles as creep gives way to periodic landsliding we use spectral analysis to quantify the variability of sediment flux and estimate the slope dependent transition from creep to landsliding the power spec trum of sediment flux steepens with hillslope gradient exhibiting fractal 1 f scaling just below the creep landsliding transition by evolving the experimental hillslope under fixed base level boundary conditions we demonstrate how disturbance driven transport gen erates hillslope convexity the transient evolution is consistent with numerical predictions derived from a recently proposed nonlinear transport model as initially steep hillslopes are lowered rapidly by landsliding before slopes decay slowly by creep dominated transport

influence of barotropic shear on the poleward advection of upper tropospheric air abstract the characteristics of the poleward advection of upper tropospheric air are investigated using meteorological analyses and idealized numerical models isentropic deformations of the tropopause during northern hemisphere winter are examined using maps of ertel s potential vorticity together with contour advection calculations large poleward excursions of upper tropospheric air are observed during rossby wave breaking events these poleward breaking events occur in regions of diffluence over the eastern atlantic ocean europe region and over the eastern pacific ocean north america region and the evolution of the tropospheric air depends on the local meridional shear in anticyclonic or weak cyclonic shear the tropospheric air tilts downstream broadens and wraps up anticyclonically whereas in cyclonic shear the tropospheric air tilts upstream thins and is advected cyclonically the role of ambient barotropic flow is further examined by considering the flow in two numerical models a pl

approaches to dynamic equilibrium in theoretical simulations of slope development the model slop3d is used to identify characteristic aspects of slope development under different conditions a series of slopes along the kall valley in the northern eifel is reproduced by a developmental sequence of model slopes the spatial and temporal variations of the components of slope development systems relief slope form weathering rates denudation rates are discussed by means of mass movement and wash denudation models the negative feedbacks between system components create a tendency towards the establishment of a dynamic equilibrium which is reached however only if the endogenic and exogenic conditions remain constant for the required relaxation time the latter is shown to be a function of slope length of the rate of uplift of the denudational process type and of the intensity of exogenic inputs e g precipitation varying rock resistance leads to the development of shield inselbergs only if the rate of denudation becomes higher than the maximum possible weathering rate of the resistant bedrock

statistical description of slope dependent soil transport and the diffusion like coefficient 1 for hillslopes undergoing diffusive soil transport it is often assumed that the soil flux is proportional to the local land surface gradient where the coefficient of proportionality is like a diffusion coefficient inasmuch as transport involves quasi random soil particle motions related to biomechanical mixing and similar dilational processes a slope dependent relation arises from a balance between particle fluxes that tend to loft a soil and gravitational settling of particles into available pore space a specialized form of the fokker planck equation adapted to such particle motions clarifies how the particle flux involves advective and diffusive parts this in turn contributes to a kinematic description of the diffusion like coefficient ingredients of this coefficient include an active soil thickness a characteristic particle size the porosity in excess of a consolidated porosity and the rate of particle activation as a function of depth these last two ingredients vertical porosity structure and activation rate in effect characterize the magnitude and frequency of settling particle motions related to biological activity and thereby set the rate constant of the transport process the significance of land surface slope is that it is a measure of the downslope component of slope normal lofting that is balanced by settling because the diffusion like coefficient contains the soil thickness the analysis suggests that the soil flux is proportional to the depth slope product the analysis is consistent with published profiles of soil creep displacement and with published estimates of soil flux obtained by downslope integration of soil production rates for hillslopes in california and australia

gcm simulations of eastern australian cutoff lows abstract the ability of the csiro 9 general circulation model gcm to capture surface cutoff lows over eastern australia is investigated by comparing composites of ten gcm cases with ten observed lows the lows are also studied individually to compare their development and movement as well as synoptic features which may have been smoothed out in the compositing process finally the incidence of all such lows in the 1 co2 and 2 co2 simulations are examined to determine the possible effects a doubling of co2 will have on their occurrence the gcm surface lows were found to develop from an upper level cutoff low in a manner similar to the observed lows in both sets this development took place between the upper level subtropical and polar jets in all seasons except summer where only one jet was evident latent heat release appeared to play an important role in the intensification of the surface lows the main difference between the two sets of cutoff lows was that the gcm surface lows tended to dev

how well can hillslope evolution models explain topography simulating soil transport and production with high resolution topographic data the morphology of hillslopes is a direct refl ection of tectonic forcing and climatic and biologic processes that drive soil production mobilization and transport soil transport on hillslopes affects river incision by providing tools for channel abrasion and controls the distribution of sediment that infl uences aquatic habitat although numerous hillslope transport relationships have been proposed over the past 60 years a comprehensive analysis of model predictions for a real landscape has not been performed here we use high resolution topographic data obtained via airborne laser swath mapping alsm to simulate the long term evolution of oregon coast range hillslopes and test three published transport models and a new model that accounts for nonlinear depth and slopedependent transport analysis of one dimensional steady state solutions for these four models suggests that plots of gradient curvature may be diagnostic for distinguishing model predictions to evaluate two dimensional model predictions for our fi eld site we assumed local steady state erosion for a 72 000 m 2 sequence of hillslopes and valleys after calibrating each of the four models we imposed constant base level lowering for cells within the valley network simulated 500 000 yr of soil production and transport and determined which transport model best preserved morphologic patterns that describe the current landscape form models for which fl ux varies proportionally with hillslope gradient generated broadly convex hilltops inconsistent with the sharp crested steep sided slopes of our study site whereas the two nonlinear slope dependent models produced convex planar slopes consistent with current hillslope form our proposed nonlinear slope and depth dependent model accounts for how soil thickness controls the magnitude of biogenic disturbances that drive transport this model best preserved the current landscape form particularly the narrow sharply convex hilltops characteristic of the oregon coast range according to our formulation which provides an explicit linkage for relating the distribution of biota to hillslope processes the degree of hilltop convexity varies nonlinearly with the ratio of erosion rate to maximum soil production rate highlighting the profound infl uence of soil depth on hillslope evolution

drainage basin responses to climate change recent investigations have shown that the extent of the channel network in some drainage basins is controlled by a threshold for overland flow erosion the sensitivity of such basins to climate change is analyzed using a physically based model of drainage basin evolution the golem model simulates basin evolution under the action of weathering processes hillslope transport and fluvial bedrock erosion and sediment transport results from perturbation analyses reveal that the nature and timescale of basin response depends on the direction of change an increase in runoff intensity or a decrease in vegetation cover will lead to a rapid expansion of the channel network with the resulting increase in sediment supply initially generating aggradation along the main network followed by downcutting as the sediment supply tapers off by contrast a decrease in runoff intensity or an increase in the erosion threshold will lead to a retraction of the active channel network and a much more gradual geomorphic response cyclic changes in runoff intensity are shown to produce aggradational degradational cycles that resemble those observed in the field cyclic variations in runoff also lead to highly punctuated denudation rates with denudation concentrated during periods of increasing runoff intensity and or decreasing vegetation cover the sediment yield from threshold dominated basins may therefore exhibit significant variability in response to relatively subtle environmental changes a finding which underscores the need for caution in interpreting modern sediment yield data

geomorphic limits to climate induced increases in topographic relief recognition of the potential for strong dynamic coupling between atmospheric and tectonic processes has sparked intense cross disciplinary investigation and debate on the question of whether tectonics have driven long term climate change or vice versa it has been proposed that climate change might have driven the uplift of mountain summits through an isostatic response to valley incision because isostasy acts to compensate mean elevations the debate hinges on the question of whether climate change can significantly increase topographic relief or more precisely increase the volume of missing mass between summits and ridges here we show that in tectonically active mountain ranges geomorphic constraints allow only a relatively small increase in topographic relief in response to climate change thus although climate change may cause significant increases in denudation rates potentially establishing an important feedback between surficial and crustal processes neither fluvial nor glacial erosion is likely to induce significant isostatic peak uplift

bedrock incision rock uplift and threshold hillslopes in the northwestern himalayas the topography of tectonically active mountain ranges reflects a poorly understood competition between bedrock uplift and erosion dating of abandoned river cut surfaces in the northwestern himalayas reveals that the indus river incises through the bedrock at extremely high rates 2 12 mm yr 1 in the surrounding mountains the average angles of hillslopes are steep and essentially independent of erosion rate suggesting control by a common threshold process in this rapidly deforming region an equilibrium is maintained between bedrock uplift and river incision with landsliding allowing hillslopes to adjust efficiently to rapid river down cutting

micro relief development in polygonal patterned ground in the dry valleys of antarctica polygonal patterned ground in polar regions of both earth and mars has received considerable attention in comparison with the size shape and arrangement of the polygons the diverse micro relief and topography termed here simply relief of polygonal patterned ground have been understudied and yet the relief reflects important conditions and processes occurring directly below the ground surface and it can be observed readily in the field and through remote sensing herein we describe the relief characteristic of the simplest and relatively young form of patterned ground in the dry valleys of antarctic we also develop a numerical model to examine the generation of relief due to subsurface material being shouldered aside contraction cracks by incremental sand wedges growth and to down slope creep of loose granular material on the surface we model the longterm subsurface deformation of ice cemented permafrost as a non linear viscous material our modeling is guided and validated using decades of field measurements of surface displacements of the permafrost and relief this work has implications for assessing the activity of surfaces on earth and mars and much larger scale potential manifestations of incremental wedging in icy material namely the distinct paired ridges on europa

on the maintenance of potential vorticity in isentropic coordinates we present a diagnostic study of the maintenance of the potential vorticity pv on isentropic surfaces in the troposphere to the lower stratosphere using ten years of analyses produced by the european centre for medium range weather forecasts after a brief three dimensional description of the general circulation in isentropic coordinates we examine the budgets of the pv evolution equation by decomposing the flow into its mean high frequency transient and low frequency transient parts we assess the role of these various scales of motion in the maintenance of the mean pv distribution the contribution of vortical and thickness fluxes is also investigated one interesting result is the key role of the divergent part of the transient flow along the tropopause in the midlatitudes which creates a large pv sink region we give here a tentative explanation the pv maps are also used to generate a climatology of a wave activity called pseudomomentum that indicates four centres of wave activity over the atlantic and pacific the first two are located in the northern hemisphere storm tracks and the two others in the upper tropospheric subtropical areas between the 310 k and the 350 k levels

climatology of intrusions into the tropical upper troposphere regions of upper tropospheric equatorial westerly winds observed over the pacific and atlantic oceans during northern fall to spring are important for extratropical tropical interactions this paper focuses on one feature of these westerly ducts that has received relatively little attention to date the occurrence of rossby wave breaking events that transport tongues of extratropical air deep into the tropics mix tropical and subtropical air and can affect deep convection a climatology of these intrusion events formed from 20 years of meteorological analyses shows a strong dependence on the basic state flow notably intrusion events are found to occur almost exclusively within westerly ducts with more events in the presence of stronger equatorial westerlies it is also found that there is strong interannual variability in the frequency of pacific events with fewer events during the warm phases of enso consistent with the changes in the basic flow since these intrusion events laterally mix trace constituents and have been linked to tropical convection their spatial and temporal variability may cause related variability in the distribution of trace constituents and tropical convection

evaluating hillslope diffusion and terrace riser degradation in new zealand and idaho 1 the relationship of sediment flux to surface slope is a predominant control on the evolution of transport limited hillslopes although both linear and nonlinear sediment flux models have been proposed and widely debated this functional relationship remains one of the outstanding questions in geomorphology we examine degradation of fluvial terrace risers in new zealand and idaho in order to test the linear diffusion model and to better understand the relationship between sediment flux and slope we implement three techniques based on the linear diffusion model as well as a geometric scaling method that uses proportional relationships in riser geometry rather than a specific transport equation model to assess rates of degradation we show that techniques that utilize the riser midpoint slope as the primary metric of degradation as opposed to the full scarp profile offer the simplest and most reliable assessment of riser degradation our findings suggest that the linear diffusion model does not accurately describe terrace riser degradation except for low angle risers for which linear and nonlinear forms are indistinguishable results from the geometric scaling method show that degradation rates in both regions differ by a factor of two between equator and pole facing risers and that diffusion ages of idaho risers are approximately 2 times those of new zealand risers similar geometric trends in riser evolution from both regions reveal that terrace riser degradation is governed by a widely applicable relationship between sediment flux and slope

evolution of the santa cruz mountains california through tectonic growth and geomorphic decay i describe a strategy for modeling a specific large scale topographic feature that recognizes the discrepancy between tectonic and geomorphic scales and allows for important feedbacks between these processes in the geomorphic model the largest channel in each 4 4 km cell is explicitly treated the channel incision being driven by a stream power rule hillslopes internal to each cell respond rapidly to incision of the local channel prompting their treatment in the model as steady state forms i present analytic expressions for the local relief which is controlled by the local channel incision rate and rate constants associated with the dominant hillslope process either diffusive or landsliding initial conditions include any preexisting topography and a lightly etched a channel network the model is illustrated using the santa cruz mountains california i show that an earlier hypothesis that the santa cruz mountains are due to advection of topography past an uplift source related to a restraining bend in the san andreas fault remains viable when more specific geomorphic processes are considered the local tectonics are represented by crustal thickening necessitated by conservation of mass in the bend right lateral translation of crust with respect to the bend and flexural response to the distributed load the model produces reasonable geographic and statistical distributions of topography using rates of tectonic and geomorphic processes that are within the range of those measured locally this argues that this restraining bend is a long lived feature of the san andreas fault the slightly higher crest and shorter length of the southern santa cruz mountains may potentially be explained by slightly faster slip of the crust west of the fault with respect to the bend than of that to the east deflection is minimal beneath these relatively small mountains disallowing the interesting feedback of erosionally driven uplift the predicted pattern of exhumation could be used to guide the search for fission track sites that could aid in the testing of the model

the link between cut off lows and rossby wave breaking in the southern hemisphere the climatological link between cut off low col pressure systems that occur from 20 to 50 s and rossby wave breaking rwb in the southern hemisphere sh is examined for 1979 2008 it is shown that cols are associated with either rwb events 89 or with potential vorticity pv intrusions where there is north south advection of high pv air 11 in the vast majority of cols the rwb events occur upstream on or before the day of the col formation the evolution of the pv geopotential heights static stability absolute vorticity and temperature advection fields during the cols are consistent with the formation of high pv anomalies that induce cyclonic circulations as predicted by theory rwb plays a key role in producing the split flow associated with cols in the sh which in turn produces absolute vorticity anomalies by shear curvature vorticity conversion and creates static stability anomalies the cols associated with rwb at 330 k are deeper and more persistent than those associated with 350 k rwb and surface processes differ depending on the isentropic surface on which the associated rwb occurs the seasonality of the rwb and cols are similar and is linked to the seasonal march of the westerly jets copyright 2010 royal meteorological society

the influence of climate and microclimate aspect on soil creep efficiency cinder cone morphology and evolution along the eastern mediterranean golan heights although hillslope evolution has been subject to much investigation for more than a century the effect of climate on the morphology of soil mantled hillslopes remains poorly constrained in this study we perform numerical simulations of volcanic cinder cones in the golan heights eastern mediterranean to estimate soil transport efficiency across a significant north south gradient in mean annual precipitation 1100 to 500 mm we use the initial cinder cone morphology constrained by stratigraphy the modern hillslope form surveyed with sub meter accuracy and the eruption age based on 40ar 39ar chronology to predict the best fit value of the soil transport coefficient diffusivity based on a nonlinear transport model our results indicate that the best fit diffusivity k varies from 1 to 6 m2 ka 1 among the five cinder cones in our field area diffusivity k values vary systematically with precipitation and hillslope aspect specifically k is higher on south facing drier hillslopes and decreases with mean annual precipitation we interpret this climate dependency to reflect vegetation driven variations in apparent soil cohesion which increases with root network density and attenuation of rain splash and overland flow erosion which increases with vegetative ground cover to assess how vegetative root mass and ground cover vary with precipitation and aspect we quantified the spatial distribution of ndvi normalized difference vegetation index from aster satellite images and observed spatial variations that correlate with our calibrated values of k analysis of previously studied cinder cones in the usa can be used to extend our framework to arid domains this endeavor suggests a humped relationship between k and precipitation with maximum diffusivity at mean annual precipitation of 400 600 mm copyright 2017 john wiley sons ltd

evidence for nonlinear diffusive sediment transport on hillslopes and implications for landscape morphology steep soil mantled hillslopes evolve through the downslope movement of soil driven largely by slope dependent transport processes most landscape evolution models represent hillslope transport by linear diffusion in which rates of sediment transport are proportional to slope such that equilibrium hillslopes should have constant curvature between divides and channels on many soil mantled hillslopes however curvature appears to vary systematically such that slopes are typically convex near the divide and become increasingly planar downslope this suggests that linear diffusion is not an adequate model to describe the entire morphology of soil mantled hillslopes here we show that the interaction between local disturbances such as rainsplash and biogenic activity and frictional and gravitational forces results in a diffusive transport law that depends nonlinearly on hillslope gradient our proposed transport law 1 approximates linear diffusion at low gradients and 2 indicates that sediment flux increases rapidly as gradient approaches a critical value we calibrated and tested this transport law using high resolution topographic data from the oregon coast range these data obtained by airborne laser altimetry allow us to characterize hillslope morphology at 2 m scale at five small basins in our study area hillslope curvature approaches zero with increasing gradient consistent with our proposed nonlinear diffusive transport law hillslope gradients tend to cluster near values for which sediment flux increases rapidly with slope such that large changes in erosion rate will correspond to small changes in gradient therefore average hillslope gradient is unlikely to be a reliable indicator of rates of tectonic forcing or baselevel lowering where hillslope erosion is dominated by nonlinear diffusion rates of tectonic forcing will be more reliably reflected in hillslope curvature near the divide rather than average hillslope gradient

the wintertime southern hemisphere split jet structure variability and evolution a persistent feature of the southern hemisphere upper level time mean flow is the presence of a split jet across the south pacific east of australia during the austral winter the split jet is composed of the subtropical jet stj on its equatorward branch and the polar front jet pfj on its poleward branch the ncep ncar reanalysis is used to investigate the structure and evolution of the split jet results show that the presence absence of the pfj determines the degree of split flow given that the stj is a quasi steady feature a splitflow index sfi is developed to quantify the variability of the split jet in which negative values represent strong split flow and positive values nonsplit flow correlations with teleconnection indices are investigated with the sfi positively correlated to the southern oscillation index and negatively correlated to the antarctic oscillation the sfi is used to construct composites of heights temperature and wind for split flow and non split flow days the composites reveal that relatively cold conditions occur in the south pacific in association with nonsplit flow regimes and split flow regimes occur when relatively warm conditions prevail in the latter situation cold air bottled up over antarctica helps to augment the background tropospheric thickness gradient between antarctica and the lower latitudes with a resulting increase in the thermal wind and the pfj it is surmised that frequent cold surges out of antarctica moving into the south pacific are associated with non split flow regimes in this context the variability of the split jet responds to large scale baroclinic processes and is further modulated by synoptic scale disturbances

wildfire thermochronology and the fate and transport of apatite in hillslope and fluvial environments 1 wildfire heating of the outer few centimeters of exposed rock or soil generates shortduration high temperature thermal events that produce characteristic thermochronologic signatures in minerals contrasting activation energies of fission track annealing and he diffusion in apatite lead to a kinetic crossover whereby wildfire heating resets fission track ft ages much faster than u th he ages resulting in inverted ft he ages in single grains this can be used to trace wildfire affected detritus at the earth s surface we show that in exposed bedrock inverted apatite ft he ages vary systematically with depth to 3 cm and detrital clasts on hillslopes also show strong but heterogeneous wildfire resetting signatures in soils colluvium and low order channel sediments strongly wildfire reset apatite grains are abundant and in some cases dominate the population of detrital apatite to depths at least as great as 10 cm wildfire reset apatite is rare however in fluvial sediments sampled from larger basins indicating a strong fractionation of apatite populations from hillslopes to rivers characteristic dissolution features in hillslope apatite and slower relative dissolution rates of other common minerals suggest that wildfire reset apatite grains are rare or absent in rivers because they dissolve relatively rapidly in soil profiles apatite that does contribute to fluvial sediments is likely to be dominantly derived from bedrock landslides in steep regions or from large clasts containing grains protected from both wildfire heating and dissolution this means that apatite in fluvial sediment is spatially fractionated with respect to its sources in the catchment even if catchment erosion rates are spatially uniform

geomorphic significance of postglacial bedrock scarps on normal fault footwalls the existence of well preserved holocene bedrock fault scarps along active normal faults in the mediterranean region and elsewhere suggests a dramatic reduction in rates of rock weathering and erosion that correlates with the transition from glacial to interglacial climate we test and quantify this interpretation using a case study in the italian central apennines holocene rates are derived from measurements of weathering pit depth along the magnola scarp where previous cosmogenic cl 36 analyses constrain exposure history to estimate the average hillslope erosion rate over similar to 10 5 years we introduce a simple geometric model of normal fault footwall slope evolution the model predicts that the gradient of a weathering limited footwall hillslope is set by fault dip angle and the ratio of slip rate to erosion rate if either slip or erosion rate is known the other can be derived applying this model to the magnola fault yields an estimated average weathering rate on the order of 0 2 0 4 mm yr more than 10 times higher than either the holocene scarp weathering rate or modern regional limestone weathering rates a numerical model of footwall growth and erosion in which erosion rate tracks the oxygen isotope curve reproduces the main features of hillslope and scarp morphology and suggests that the hillslope erosion rate has varied by about a factor of 30 over the past one to two glacial cycles we conclude that preservation of carbonate fault scarps reflects strong climatic control on rock breakdown by frost cracking

vegetation and wildfire controls on sediment yield in bedrock landscapes steep rocky landscapes commonly exhibit high sediment yields and are especially sensitive to climate tectonics and wildfire predicting landscape response to these perturbations demands a quantitative understanding of erosion processes however existing models for hillslope sediment production and transport do not apply to landscapes with patchy soil and slopes that exceed the angle for sediment stability here we present field measurements in southern california usa which indicate that sediment storage on steep slopes is enabled by vegetation that traps sediment upslope we find that the storage capacity of unburned vegetation dams follows a geometric scaling model with a cubic dependence on effective plant width and an inverse dependence on local slope measured sediment volumes behind burned vegetation dams indicate a loss of at least 75 relative to unburned dams and when expanded to the catchment scale our measurements match records of postfire sediment yield from nearby retention basins contrary to existing models our observations indicate that wildfire induced sediment yield is driven by transient storage and release of sediment by vegetation dams rather than increased bedrock to soil conversion rates without a feedback between soil production and wildfire fire may play little role in long term landscape evolution and increasing fire frequency in response to climate change may not result in heightened sedimentation hazards due to supply limitations

anelastic earth structure from the coherency of the ambient seismic field 1 cross correlation of the ambient seismic field is now routinely used to measure seismic wave travel times however relatively little attention has been paid to other information that could be extracted from these signals in this paper we demonstrate the relationship between the spatial coherency of the ambient field and the elastodynamic green s function in both time and frequency domains through measurement of the frequency domain coherency as a function of distance we sequentially recover phase velocities and attenuation coefficients from these measurements we generate 1 d shear wave velocity and attenuation models for southern california the ambient field measurements of attenuation and the exceptional path coverage that results from the many possible interstation measurements allow us to extend q estimates over a range of frequencies that has previously been difficult to analyze using earthquake data measurements from paths that cross major sedimentary basins show both lower wave speeds and lower quality factors than other paths as expected our results indicate that there is a wealth of information available in the spatial coherency of the ambient seismic field

from mass wasting to slope stabilization putting constrains on a tectonically induced transition in slope erosion mode a case study in the judea hills israel calcrete coated remnants of landslide debris and alluvial deposits are exposed along the presently stable hillslopes of the soreq drainage judea hills israel these remnants indicate that a transition from landslide dominated terrain to dissolution controlled hillslope erosion had occurred this transition possibly occurred due to the significant decrease in tectonic uplift during the late cenozoic the study area is characterized by sub humid mediterranean climate the drainage hillslopes are typically mantled by thick calcrete crusts overlying upper cretaceous marine carbonate rocks using tt osl dating of aeolian quartz grains incorporated in the calcrete which cements an ancient landslide deposit we conclude that incision of 100 m occurred from 1056 262 to 688 86 ka due to 0 3 westward tilt of the region such incision invoked high frequency of landslide activity in the drainage the ages of a younger landslide remnant alluvial terrace and alluvial fan all situated only a few meters above the present level of the active streambed range between 688 86 ka and 244 25 ka and indicate that since 688 86 the soreq base level had stabilized and that landslide activity decreased significantly by the middle pleistocene copyright 2012 john wiley sons ltd

identification and era 15 climatology of potential vorticity streamers and cutoffs near the extratropical tropopause abstract a novel approach is introduced to identify potential vorticity pv streamers and cutoffs as indicators of rossby wave breaking near the extratropical tropopause and to compile climatologies of these features on different isentropic surfaces the method is based on a contour searching algorithm that identifies the dynamical tropopause 2 potential vorticity units pvu pvu 1 10 6 k kg 1 m2 s 1 isoline on isentropic surfaces the contour is then analyzed to search for cutoffs and filament like streamers whereas the identification of cutoffs is unambiguous the one for streamers requires the specification of two parameters that determine the width and length of the contour feature to be classified as a streamer this technique has been applied to the pv distribution in the northern hemisphere on isentropes from 295 to 360 k during the time period from 1979 to 1993 using the 15 yr european centre for medium range weather forecasts ecmwf re analysis era 15 the climatology reveals a pronou

macroscale dynamics of experimental landscapes abstract we review results from laboratory scale modelling of erosion and relief dynamics under variable uplift and rainfall rates under constant values of these forcing parameters an experimental landscape typically evolves towards a steady state between uplift and erosion and we show how the geometry of the steady state landscape adjusts to the rates of uplift and rainfall the comparison between these laboratory scale landscapes and the natural ones is not straightforward because contrary to analogue modelling in tectonics natural conditions of relief evolution cannot be downscaled to the laboratory without any scale distortions laboratory scale modelling in geomorphology is therefore only experimental not analogue despite these limitations experimental models may be used to provide physical tests for numerical models and they give insights into first order behaviours and directions for future research

growth and lateral propagation of fault related folds in the siwaliks of western nepal rates mechanisms and geomorphic signature 1 we study the controls on drainage development in tectonically active regions using a numerical tectonic surface processes model combining tectonic uplift caused by fault related folding with erosion by fluvial incision hillslope diffusion and landsliding our model shows the fundamental control exerted by the dip of the detachment underlying the folds on drainage evolution when the detachment is horizontal the relative rates of tectonic uplift and fluvial incision control the evolution for a nonzero dip in contrast the lateral displacement gradient associated with fold propagation sets up a lateral slope behind the active structure which deflects the stream network we also demonstrate the importance of landsliding for the attainment of realistic and steady state topography in contrast discontinuous tectonic movements do not appear to influence the system we apply our model to the dundwa fault related fold ridge siwalik nepal we estimate a remarkably low mean propagation rate for different segments of the structure this finding together with the structure and morphology of the ridge leads us to propose that the ridge developed by linkage of several component segments the drainage evolution predicted when modeling this scenario compares favorably with field observations our models provide insights into the dynamics of fault related fold propagation in particular as a result of fault segment linkage estimates of propagation rate of these structures may be strongly scale dependent and the observed morphology and drainage patterns on fault related fold ridges may be controlled by fault geometry rather than by the relative rates of tectonics and surface processes

a midlatitude climatology and interannual variability of 200 and 500 hpa cut off lows abstracta climatology of midlatitude 200 and 500 hpa cut off low systems in the northern and southern hemispheres is constructed from the ncep ncar reanalysis by detecting and tracking under one

pleistocene relief production in laramide mountain ranges western united states gently sloped summits and ridges collectively referred to as summit flats are abundant in many laramide ranges in the western united states the erosion rate of summit flats is 10 m m y on the basis of the concentrations of cosmogenic radionuclides because erosion rates in valleys between summit flats are an order of magnitude faster relief within these ranges is currently increasing by about 100 m m y if summit flat erosion is slower than rock uplift driven by the isostatic response to valley erosion then this relief production could result in increased summit elevations the mean depth of material eroded from a smooth surface fit to existing summit flats varies from 280 to 340 m in four laramide ranges based on geographic information system gis analyses of digital elevation models this erosion would result in a maximum of 250 300 m of rock uplift assuming airy isostasy however because the laramide ranges examined here are narrow relative to the flexural wavelength of the lithosphere erosionally driven rock uplift is limited to 50 100 m over the past several million years summit erosion would approximately offset this rock uplift therefore we conclude that summit elevations have remained essentially constant even though several hundred meters of relief has been produced on the basis of valley and summit erosion rates and the average depth of erosion we estimate that relief production in laramide ranges began at ca 3 ma we hypothesize that this relief production was climatically driven and was associated with the onset or enhancement of alpine glaciation in these ranges

trouble with diffusion reassessing hillslope erosion laws with a particle based model 1 many geomorphic systems involve a broad distribution of grain motion length scales ranging from a few particle diameters to the length of an entire hillslope or stream studies of analogous physical systems have revealed that such broad motion distributions can have a significant impact on macroscale dynamics and can violate the assumptions behind standard local gradient flux laws here a simple particle based model of sediment transport on a hillslope is used to study the relationship between grain motion statistics and macroscopic landform evolution surface grains are dislodged by random disturbance events with probabilities and distances that depend on local microtopography despite its simplicity the particle model reproduces a surprisingly broad range of slope forms including asymmetric degrading scarps and cinder cone profiles at low slope angles the dynamics are diffusion like with a short range thin tailed hop length distribution a parabolic convex upward equilibrium slope form and a linear relationship between transport rate and gradient as slope angle steepens the characteristic grain motion length scale begins to approach the length of the slope leading to planar equilibrium forms that show a strongly nonlinear correlation between transport rate and gradient these high probability long distance motions violate the locality assumption embedded in many common gradient based geomorphic transport laws the example of a degrading scarp illustrates the potential for grain motion dynamics to vary in space and time as topography evolves this characteristic renders models based on independent stationary statistics inapplicable an accompanying analytical framework based on treating grain motion as a survival process is briefly outlined

results from a new model of river basin evolution this paper briefly describes a model of the erosional development of catchments and their channel networks the model differentiates between the dominant transport processes in hillslope and channels the development of channels and hillslopes occurs in an integrated manner as a function of physically observable mechanisms the growth of a river basin is qualitatively described the model concepts are used to study the basin during periods of growth transient periods as well as during dynamic equilibrium this leads to hypotheses about the relationship between slopes relief tectonic uplift erodability runoff and catchment area it is shown that the model leads to very reasonable and desirable behaviour of hillslopes during retreat and degradation

rossby wave propagation and teleconnection patterns in the austral winter abstract observational evidence of and theoretical support for the northern and southern hemisphere teleconnection patterns in the austral southern hemisphere winter are examined through an upper troposphere streamfunction teleconnectivity map and time lag cross correlation analysis using ecmwf initialized analysis 2oo hpa winds for the 11 june august periods from 1979 to 1989 as was previously found for the northern hemisphere winter the regions of strong teleconnectivity particularly in the winter hemisphere tend to he oriented in the zonal direction and coincide with the location of the major jet streams although equatorward propagation from the northern and southern hemispheres is observed little evidence of cross equatorial propagation has been found for comparison the response of a barotropic model linearized about a climatological 300 hpa june august time mean flow to localized forcing is determined it is found that the activity tends to be trapped inside each of the southern hemisphere

global relationship between fronts and warm conveyor belts and the impact on extreme precipitation abstractextratropical cyclones are responsible for many extreme precipitation events in the midlatitudes warm conveyor belts wcbs and fronts are known to be related to the uplift and hence the precipitation within cyclones the authors have investigated the link between wcbs and fronts and how such a link impacts the occurrence of extreme precipitation events wcb trajectories have been calculated from the era interim dataset and low level below 790 hpa and midlevel 790 600 hpa wcbs have been considered these have been matched with objectively identified fronts i e characterized by an overlap of wcb and front somewhere along the front about 10 of cold fronts 8 of warm fronts identified using a thermal criterion and 15 of wind fronts identified using a wind shift method are matched with wcbs while up to 70 of wcbs are matched with fronts some wcbs especially in the southern hemisphere are not matched with either type of front up to 70 east of australia the relationship betwe

hillslope evolution by nonlinear creep and landsliding an experimental study comment and reply roering et al 2001 1 describe very careful and interesting experiments that beautifully illustrate the transition from steady downhill creep at low gradients to highly dynamic transport on steep slopes they interpret this behavior in terms of a single nonlinear diffusion coefficient

a climatology of rossby wave breaking on the southern hemisphere tropopause abstracta 30 yr climatology of rossby wave breaking rwb on the southern hemisphere sh tropopause is formed using 30 yr of reanalyses composite analysis of potential vorticity and meridional fluxes of wave activity show that rwb in the sh can be divided into two broad categories anticyclonic and cyclonic events while there is only weak asymmetry in the meridional direction and most events cannot be classified as equatorward or poleward in terms of the potential vorticity structure the position and structure of the fluxes associated with equatorward breaking differs from those of poleward breaking anticyclonic breaking is more common than cyclonic breaking except on the lower isentrope examined 320 k there are marked differences in the seasonal variations of rwb on the two surfaces with a winter minimum for rwb around 350 k but a summer minimum for rwb around 330 k these seasonal variations are due to changes in the location of the tropospheric jets and dynamical tropopause during winter the

rossby wave breaking in the southern hemisphere wintertime upper troposphere abstract the characteristics of rossby wave propagation and breaking in the southern hemisphere upper troposphere during winter are examined although the southern hemisphere subtropical jet is more zonally symmetric than that of the northern hemisphere there are still significant zonal variations in the upper tropospheric flow in particular the flow within a given sector 120 longitude can generally be characterized into one of four different configurations i a single jet ii a broken subtropical jet iii a polar jet at the upstream end of the subtropical jet or iv a polar jet at the downstream end of the subtropical jet using potential vorticity thinking and barotropic wind shear arguments it is argued that the characteristics of the rossby wave propagation and breaking will differ between each flow configuration consistent with these arguments examination of potential vorticity maps and contour advection calculations show differing wave breaking characteristics in particular t

burial and turbulent transport by bioturbation a 27 year experiment in southeast australia in order to assess the net effect and relative importance of geomorphic processes at two natural woodland sites in southeast australia 100 small tiles were placed on the soil surface in 1979 and their movement was monitored over the course of nearly three decades rates of tile burial and other tile displacement were considerable but also markedly random being largely inconsistent with expected patterns of displacement by orthodox creep and rainwash processes this included substantial upslope displacement and burial depths that ranged from zero to 5 cm we suggest that such turbulent transport in the topsoil has mostly been caused by the direct and indirect transfer of soil and clasts by animals and plants i e bioturbation in addition to direct evidence of biota interacting with tiles the effectiveness of bioturbation at our sites has been well established and the overall tile burial rate of 0 25 to 0 4 mm yr 1 is comparable to rates of surface mounding patterns of tile movement are generally consistent with soils geomorphic theory regarding the biomantle and bioturbation driven stonelayer formation and provide further evidence that soil transfer and slope movement in many situations are markedly random and complex processes copyright 2010 john wiley sons ltd

a climatology of rossby wave breaking along the subtropical tropopause ten years 1986 95 of global analyses from the european centre for medium range weather forecasts are used to investigate the temporal and spatial distributions of rossby wave breaking rwb at 350 k along the tropopause herein defined by the 61 5 potential vorticity pv unit 10 26 km 2 s21 kg21 contours though many studies acknowledge rwb as an important contributor to the complex of mixing processes in the atmosphere there exists no prior climatological study of its distribution near the tropopause as in previous studies rwb is identified in the global analyses by southward directed pv gradients at 350 k rwb along the tropopause occurs preferentially during summer over the midoceans in relative proximity to the planetary scale high pressure systems in the subtropics isentropic trajectories at 350 k show that outflow from the tops of these subtropical highs directly participates in rwb over the adjacent downstream oceanic regions two regions are highlighted in this study the north pacific during boreal summer and the south atlantic during austral summer synoptic maps of breaking rossby waves in these regions are provided to reveal the acute tropopause folding in the meridional plane which characteristically accompanies rwb the rich interaction between the tropical flow and the extratropical westerly current exhibited by these cases suggests that the subtropical highs serve as important agents in the coupling between the tropical troposphere and the extratropical stratosphere as expected from theoretical considerations the locations where rwb occurs most frequently known as surf zones are shown to coexist with regionally weak time mean wind speeds and horizontal gradients of pv at 350 k

baroclinic wave breaking and the internal variability of the tropospheric circulation abstract a simple model of the tropospheric circulation based on a 10 level primitive equation model is forced by linearly relaxing the potential temperature toward an idealized zonally symmetric equilibrium field the model equations are integrated in time until a statistically steady state is obtained the local relationship between the state of the background flow the direction of wave propagation and subsequent wave breaking at the tropopause level is then investigated maps of potential vorticity pv on isentropic surfaces are analyzed and all four different types of wave breaking described recently by peters and waugh are shown to occur it is found that cyclonic wave breaking events are usually initiated by poleward fluxes of wave activity and anticyclonic events by equatorward fluxes composites are then used to show that equatorward fluxes are associated with a jet that is locally broad and weak with relatively strong isentropic pv gradients to its equatorward flank by contrast poleward

blocking and rossby wave breaking on the dynamical tropopause in the southern hemisphere abstract rossby wave breaking on the dynamical tropopause in the southern hemisphere the 2 pvu surface is investigated using the era 40 dataset the indication of wave breaking is based on reversal in the meridional gradient of potential temperature and persistent large scale wave breaking is taken as a strong indication that blocking may be present blocking in the midlatitudes is found to occur predominantly during wintertime in the pacific and is most vigorous in the east pacific while during summertime the frequency of blocking weakens and its extent becomes confined to the west pacific the interannual variability of blocking is found to be high wave breaking occurs most frequently on the poleward side of the polar jet and has some but not all of the signatures of blocking so it is referred to as high latitude blocking in general cyclonic wave breaking occurs on the poleward side of the polar jet otherwise anticyclonic breaking occurs however at least in wintertime wave breaking in th

a review of the structure and dynamics of upper level frontal zones abstract this article presents a review of upper level fronts with the intent of synthesizing observational and modeling studies into a conceptual and dynamical description of these fronts and their evolution relative to the life cycle of midlatitude baroclinic waves the discussion begins by tracing present day concepts concerning the structure of upper level frontal systems which are based on composite analyses of radiosonde and aircraft data from their origins in the pioneering analyses of upper air data in the 1930s perspectives from scales both smaller and larger than upper level frontal systems are provided respectively by considering the effects of turbulent processes on frontal structure and dynamics and by relating variations in frontal structure to the evolution of the baroclinic waves that provide the dynamical environment for upper level frontogenesis the dynamics of upper level fronts are shown to comprise the interactions between the primary geostrophic and secondary ageostrophic cir