are the viking lander sites representative of the surface of mars abstract global remote sensing observations of mars are compared with remote sensing observations of the two viking lander site regions and with orbiter and lander imaging of the sites the lander sites do not fit most of the global trends of remote sensing data the presence of a duricrust in the top meter of the surface is inferred for most regions of high thermal inertia although the duricrust is thinner at the lander sites than elsewhere regions of low thermal inertia are covered by greater than several centimeters of unconsolidated dust a thin microns thick layer of bright dust appears at the surface at the lander sites and these locations may be regions of incipient formation of low thermal inertia the lander sites are intermediate in structure between classical bright and dark regions and are distinctive from most of the rest of the planet

an aerodynamic roughness length map derived from extended martian rock abundance data many boundary layer processes simulated within a mars general circulation model mgcm including the description of the processes controlling dust rising from the martian surface are highly sensitive to the aerodynamic roughness length z0 on the basis of rock size frequency distributions inferred from different martian landing sites and earth analog sites we have first established that lognormal modeled rock size frequency distributions are able to reproduce correctly the observed martian rock populations we have validated the hypothesis that the rock abundance of a given area could be estimated at a first order from its thermophysical properties namely its thermal inertia i and its albedo we have demonstrated the possibility of using rock abundance to estimate the roughness density on mars and to retrieve subsequently the aerodynamic roughness length by using semi empirical relationships based on terrestrial wind tunnel and field measurements by combining our methodology with remote sensing measurements of the thermal emission spectrometer aboard mars global surveyor we have derived a global map of the aeolian aerodynamic roughness length with a 1 8 1 8 resolution over the entire martian surface contrary to what is often assumed the martian aeolian aerodynamic roughness length is spatially highly heterogeneous at the fullest resolution the martian aerodynamic roughness length varies from 10 3 cm to 2 33 cm about 84 of the martian surface seems to be characterized by an aeolian aerodynamic roughness length value lower than 1 cm the spatially uniform value that most of the mgcms simulations have assumed recently since the aerodynamic roughness length z0 is a key parameter in deriving the erosion threshold wind velocities we anticipate a significant impact of our findings on the efficiencies for lifting dust in future mgcms

comparison of the vertical distributions of cloud properties from idealized extratropical deep convection simulations using various horizontal resolutions abstractthe authors coarse grained and analyzed the output from a large eddy simulation les of an idealized extratropical supercell storm using the weather research and forecasting wrf model with various horizontal resolutions 200 m 400 m 1 km and 3 km the coarse grained physical properties of the simulated convection were compared with explicit wrf simulations of the same storm at the same resolution of coarse graining the differences between the explicit simulations and the coarse grained les output increased as the horizontal grid spacing in the explicit simulation coarsened the vertical transport of the moist static energy and total hydrometeor mixing ratio in the explicit simulations converged to the les solution at the 200 m grid spacing based on the analysis of the coarse grained subgrid vertical flux of the moist static energy the authors confirmed that the nondimensional subgrid vertical flux of the moist static energy varied with the subgrid fractional cloudiness according to a fun

toward process based modeling of geochemical soil formation across diverse landforms a new mathematical framework we present a mathematical model that integrates geochemical and geomorphic processes responsible for soils elemental and mineralogical evolution on diverse landforms eroding to depositional to level grounds this new model combines a hillslope sediment mass balance and a soil geochemical mass balance we model soils as the sum of a physically disturbed zone pdz and the underlying physically undisturbed but chemically altered zone caz the model considers processes including the production of pdz weathering front propagation mineral specific dissolution colloidal translocation and colluvial transport thus this study serves to 1 review preexisting models of pedogenic processes and to 2 offer a framework to integrate the geochemical and geomorphic processes active in soils we further discuss the implications of our model in 1 scaling chemical weathering reactions from mineral grains to pedons to soil catenas 2 understanding the emergence of geochemical soil catenas and 3 coupling physical and chemical weathering processes

landsliding and the evolution of normal fault bounded mountains much of the tectonic and climatic history in high relief regions such as the mountains of the western u s basin and range province is contained in the morphology of hillslopes drainage networks and other landforms that range in scale from 10 1 to 101km to understand how these landforms evolve we have developed a numerical landscape evolution model that combines a detailed tectonic displacement field with a set of physically based geomorphic rules bedrock landsliding long recognized as a significant geomorphic process in mountainous topography is for the first time explicitly included in the rule set in a series of numerical experiments we generate synthetic landscapes that closely resemble mountainous topography observed in the basin and range the production of realistic landscapes depends critically on the presence of bedrock landslides and landsliding yields rates of long term erosion that are comparable in magnitude to those of fluvial erosion the erosive efficiency of bedrock landsliding implies that hillslopes may respond very quickly to changes in local base level and that fluvial erosion is the rate limiting process in steady state experimental landscapes our experiments generate power law distributions of landslide sizes somewhat similar to both field and laboratory observations thus even a simple model of bedrock landsliding is capable of quantitatively reproducing mountainous topography and landslide distributions and represents a significant step forward in our understanding of the evolution of normal fault bounded ranges

the atmospheric boundary layer and the gray zone of turbulence a critical review recent increases in computing power mean that atmospheric models for numerical weather prediction are now able to operate at grid spacings of the order of a few hundred meters comparable to the dominant turbulence length scales in the atmospheric boundary layer as a result models are starting to partially resolve the coherent overturning structures in the boundary layer in this resolution regime the so called boundary layer gray zone neither the techniques of high resolution atmospheric modeling a few tens of meters resolution nor those of traditional meteorological models a few kilometers resolution are appropriate because fundamental assumptions behind the parameterizations are violated nonetheless model simulations in this regime may remain highly useful in this paper a newly formed gray zone boundary layer community lays the basis for parameterizing gray zone turbulence identifies the challenges in high resolution atmospheric modeling and presents different gray zone boundary layer models we discuss both the successful applications and the limitations of current parameterization approaches and consider various issues in extending promising research approaches into use for numerical weather prediction the ultimate goal of the research is the development of unified boundary layer parameterizations valid across all scales

influence of chemical denudation on hillslope morphology 1 models of hillslope evolution involving diffusion like sediment transport are conventionally presented as an equation in which the changes in land surface elevation or soil thickness are balanced by the divergence of soil transport and tectonic uplift soil production or both these models typically do not include the loss or gain of mass in hillslope soils due to processes of chemical weathering and deposition we formulate a more general depth integrated equation for the conservation of soil mass on a hillslope that includes a term representing chemical deposition or denudation this general depth integrated equation is then simplified to determine the one dimensional form of a steady state hillslope which experiences both mechanical and chemical denudation the differences in morphology between hillslopes only experiencing diffusion like mechanical sediment transport and hillslopes experiencing both diffusion like mechanical sediment transport and chemical denudation are explored under the conditions of a downslope increase in local soil lowering rate due to chemical weathering the hillslope profile will depart from the parabolic shape predicted by models that incorporate only linear diffusion like mechanical sediment transport in addition hillslopes that experience both chemical and mechanical denudation may have a convex concave profile at steady state a necessary condition for such steady state profiles is that the chemical denudation rate must exceed the mechanical denudation rate we further suggest that combinations of other physical parameter values such as total denudation rate average soil depth sediment diffusivity and the increase in soil depth away from the divide that lead to steady state convex concave hillslope profiles may exist in a wide variety of natural settings

geomorphically driven late cenozoic rock uplift in the sierra nevada california geologists have long accepted that the sierra nevada california experienced significant late cenozoic tectonically induced uplift a flexural isostatic model presented here shows however that a large fraction of the primary evidence for uplift could be generated by the lithospheric response to coupled erosion of the sierra nevada and deposition in the adjacent central valley and therefore requires less tectonic forcing than previously believed the sum of range wide erosion and the resultant isostatic rock uplift would have lowered sierra mean elevation by 200 to 1000 meters since 10 million years ago and could also have increased summit elevations during the current period of relief production

explicit convection and scale aware cumulus parameterizations high resolution simulations over areas of different topography in germany abstractan increase in the spatial resolution of regional climate model simulations improves the representation of land surface characteristics and may allow the explicit calculation of important physical processes such as convection the present study investigates further potential benefits with respect to precipitation based on a small ensemble of high resolution simulations with wrf with grid spacings up to 1 km the skill of each experiment is evaluated regarding the temporal and spatial performance of the simulation of precipitation of one year over both a mountainous region in southwestern germany and a mainly flat region in northern germany this study allows us to differentiate between the impact of grid spacing topography and convection parameterization furthermore the performance of a state of the art convection parameterization scheme in the gray zone of convection is evaluated against an explicit calculation of convection only our evaluation demonstrates the following high resolution si

effects of bedrock landslides on cosmogenically determined erosion rates abstract the successful quantification of long term erosion rates underpins our understanding of landscape formation the topographic evolution of mountain ranges and the mass balance within active orogens the measurement of in situ produced cosmogenic radionuclides crns in fluvial and alluvial sediments is perhaps the method with the greatest ability to provide such long term erosion rates although deep seated bedrock landsliding is an important erosional process in active orogens its effect on crn derived erosion rates is largely unquantified we present a numerical simulation of cosmogenic nuclide production and distribution in landslide dominated catchments to address the effect of bedrock landsliding on erosion rates results of the simulation indicate that the temporal stability of erosion rates determined from crn concentrations in sediment decreases with increased ratios of landsliding to bedrock weathering rates within a given catchment area and that as the frequency of landsliding increases larger catchment areas must be sampled in order to accurately evaluate long term erosion rates in addition results of this simulation suggest that sediment sampling for crns is the appropriate method for determining long term erosion rates in regions dominated by mass wasting processes whereas bedrock surface sampling for crns may generally underestimate long term erosion rates response times of crn concentrations to changes in erosion rate indicate that climatically driven cycles of erosion may be detected but that complete equilibration of crn concentrations to new erosional conditions may take tens of thousands of years comparison of simulated crn derived erosion rates with a new data set of such rates from the nepalese himalaya underscore the conclusions drawn from the model results

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

rates and timing of earth surface processes from in situ produced cosmogenic be 10 beryllium 10 is the longest lived of the seven known unstable isotopes of be it results mostly from the interaction of cosmic radiation primarily neutrons with a variety of target atoms by spallation the splitting of nuclei lal 1988 it can also be produced at very low levels by radio disintegration of u and th sharma and middleton 1989 although all radioactive be isotopes are produced in the atmosphere via cosmic ray reactions arnold 1956 lal and peters 1967 morris et al chapter 5 this volume in this paper we are most interested in 10be produced in rock which we refer to as in situ produced such in situ produced 10be is a cosmic ray dosimeter functioning as a quantitative monitor of near surface residence time in some geologic situations 10be can be used as a chronometer allowing one to estimate the duration of surface exposure in other settings 10be can be used as a tracer allowing one to estimate the rate distribution and behavior of earth surface processes rates of 10be production are very low in rocks exposed at earth s surface 102 atoms g 1 y 1 resulting in typical in situ produced 10be concentrations termed activities of 103 to 107 atoms g 1 the development of accelerator mass spectrometry ams in the 1980s allowed routine measurement of 10be at levels typical of rocks exposed near earth s surface elmore and phillips 1987 analytical refinements in the 1990s lowered detection limits by an order of magnitude allowing dating of exposure periods 103 years in favorable geologic and geographic situations simple exposure histories at high altitude and latitude most in situ 10be is measured in quartz mineral separates where the primary spallation target is o lal and arnold 1985

explicit filtering and reconstruction to reduce grid dependence in convective boundary layer simulations using wrf les abstractas model grid resolutions move from the mesoscale to the microscale turbulent structures represented in atmospheric boundary layer simulations change dramatically at intermediate resoluti

slope distributions threshold hillslopes and steady state topography digital elevation models of two steady state mountain ranges the olympic mountains om and oregon coast range ocr are used to examine relationships between slope distributions the development of threshold hillslopes and steady state topography plots of drainage area versus slope for these mountain ranges exhibit substantial scatter that complicates comparison of range form to analytical theories and landscape evolution models contour plots of the density of such data reveal an attractor at the scale of the transition from hillslope processes to channel processes and log bin averaging reveals trends that parallel predictions of steady state erosion laws but with different rate laws for five distinct process domains hillslopes valley heads and colluvial bedrock and alluvial valley segments slope histograms computed for 100 km2 areas defined by a 10 10 km grid throughout the om exhibit approximately normal or exponential distributions in areas of active rock uplift and depositional topography respectively local slope distributions in the ocr also tend to be normally distributed but some are left skewed in areas with gentler slopes mean slopes determined both over the above referenced grid and a 10 km diam moving window are relatively invariant in the core of the om in spite of strong contrasts in bedrock erodibility and gradients in long term rock uplift rates in contrast the mean slopes in the ocr parallel latitudinal gradients in rock uplift rates and bedrock erodibility hence the slope distributions in the om and ocr reflect distinct relationships between development of threshold bedrock and soil mantled hillslopes and steady state topography

evolution of hillslope soils the geomorphic theater and the geochemical play abstract how and how fast do hillslope soils form as the landscape s morphology changes over time here results are shown from an ongoing study that simultaneously examines the morphologic and geochemical evolution of soil mantled hillslopes that have been exposed to distinctively different denudation history in northern sierra nevada california the authors are investigating a tributary basin to the middle fork feather river a major incision signal from the river is well marked in a knickpoint within the tributary basin which stretches from its mouth to the feather river at an elevation of 700 m to the plateau at an elevation of 1500 m hillslopes are significantly steeper below the knickpoint the area s total denudation rates are currently being constrained using cosmogenic radio nuclides but a previous study suggested an order of magnitude difference in total denudation rates below and above the knickpoint when compared with topographic attributes calculated from lidar data physical erosion rates can be modeled as a linear function of ridge top curvature surprisingly over the wide range of total denudation rates soil thicknesses do not vary significantly until a threshold point where soil mantled landscapes abruptly shift to bedrock dominated landscapes bioturbation by tree falls appear to buffer soil thickness over the wide range of physical soil erosion rates from three hillslopes with different physical erosion rates the concentrations of zr which were considered conserved during dissolution and leaching were determined and used as a proxy for the degree of mass losses via chemical denudation there is a general trend that colluvial soils along the hillslopes with lower physical erosion rates are enriched in fine size fractions zr and pedogenic crystalline fe oxides likewise the saprolites show greater degrees of chemical denudation at the sites above the knickpoint presumably because of the saprolites longer turnover time in the slowly eroding landscapes in the two steep hillslopes below the knickpoint no significant or systematic topgraphic trends were found for soil geochemistry however soils show increasing zr enrichment in the downslope direction in the hillslope above the knickpoint which suggests a critical denudation rate beyond which soils turnover time is too short to develop a geochemical catena as detailed crn based soil production rates and catchment scale denudation rates are acquired the data will be combined with a mass balance model to calculate the rates of chemical denudation and weathering in soils and saprolites along the denudation gradient

convergence behavior of idealized convection resolving simulations of summertime deep moist convection over land convection resolving models crms can explicitly simulate deep convection and resolve interactions between convective updrafts they are thus increasingly used in numerous weather and climate applications however the truncation of the continuous energy cascade at scales of mathcal o 1 km poses a serious challenge as in kilometer scale simulations the size and properties of the simulated convective cells are often determined by the horizontal grid spacing delta x in this study idealized simulations of deep moist convection over land are performed to assess the convergence behavior of a crm at delta x 8 4 2 1 km and 500 m two types of convergence estimates are investigated bulk convergence addressing domain averaged and integrated variables related to the water and energy budgets and structural convergence addressing the statistics and scales of individual clouds and updrafts results show that bulk convergence generally begins at delta x 4 km while structural convergence is not yet fully achieved at the kilometer scale despite some evidence that the resolution sensitivity of updraft velocities and convective mass fluxes decreases at finer resolution in particular at finer grid spacings the maximum updraft velocity generally increases and the size of the smallest clouds is mostly determined by delta x a number of different experiments are conducted and it is found that the presence of orography and environmental vertical wind shear yields more energetic structures at scales much larger than delta x sometimes reducing the resolution sensitivity overall the results lend support to the use of kilometer scale resolutions in crms despite the inability of these models to fully resolve the associated cloud field

shear flow instability in the stable nocturnal boundary layer as observed by doppler lidar during cases 99 abstract this study investigates a shear flow instability observed in the stably stratified nighttime boundary layer on 6 october 1999 during the cooperative atmosphere surface exchange study cases 99 in south central kansas a scanning doppler lidar captured the spatial structure and evolution of the instability and high rate in situ sensors mounted on a nearby 60 m tower provided stability and turbulence data with excellent vertical resolution data from these instruments are analyzed and linear stability analysis lsa is employed to carefully characterize the wave field its interaction with the mean flow and its role in turbulence generation the event persisted for about 30 min and was confined within the shear zone between the surface and a low level jet llj maximum eigenvalues corresponding to the fastest growing mode of the lsa showed good agreement with the basic wave parameters determined from the lidar data good qualitative agreement was also obtained between the eigenfunction of the f

modelling convectively induced secondary circulations in the terra incognita with terrsysmp advances in high performance computing have led to kilometre and even sub kilometre scale regional simulations with numerical weather prediction models this range of grid resolution also termed terra incognita approaches the length scale of the most energetic eddies of the convective atmospheric boundary layer abl which accordingly can only be inadequately resolved this dilemma becomes particularly obvious when simulating convectively induced secondary circulations ciscs in the terra incognita because the modelled cisc like circulations also termed m ciscs are poorly resolved and exhibit a grid resolution dependence previous studies have pointed out this problem using different modelling platforms and also suggested options for attenuating poorly resolved m ciscs with methods specific to the applied abl schemes this study examines m ciscs at horizontal grid resolutions of o 1km using the terrestrial systems modeling platform terrsysmp for idealised and real case studies the analysis of simulations using different surface heterogeneity and grid resolutions of o 1km shows that the presence of a super adiabatic layer near the surface and the increase of the horizontal grid resolution allow the critical rayleigh number to be exceeded generating poorly resolved m ciscs whose amplitudes are strongly dependent on the horizontal grid resolution we show that the asymptotic turbulent mixing length scale in the used abl scheme can be tuned in a way that m ciscs are attenuated while the non resolved turbulence dealt with by the abl scheme effectively propagates the surface fluxes into the abl and sustains reasonable abl profiles

landscape response to tectonic forcing digital elevation model analysis of stream profiles in the mendocino triple junction region northern california the topographic evolution of orogens is fundamentally dictated by rates and patterns of bedrock channel incision quantitative field assessments of process based laws are needed to accurately describe landscape uplift and denudation in response to tectonics and climate we evaluate and calibrate the shear stress or similar unit stream power bedrock incision model by studying stream profiles in a tectonically active mountain range previous work on emergent marine terraces in the mendocino triple junction region of northern california provides spatial and temporal control on rock uplift rates digital elevation models and field data are used to quantify differences in landscape morphology associated with along strike northwest to southeast changes in tectonic and climatic conditions analysis of longitudinal profiles supports the hypothesis that the study area channels are in equilibrium with current uplift and climatic conditions consistent with theoretical calculations of system response time based on the shear stress model within uncertainty the profile concavity of the trunk streams is constant throughout the study area 0 43 as predicted by the model channel steepness correlates with uplift rate these data help constrain the two key unknown model parameters the coefficient of erosion k and the exponent associated with channel gradient n this analysis shows that k cannot be treated as a constant throughout the study area despite generally homogeneous substrate properties for a reasonable range of slope exponent values n best fit values of k are positively correlated with uplift rate this correlation has important implications for landscape evolution models and likely reflects dynamic adjustment of k to tectonic changes due to variations in orographic precipitation and perhaps channel width sediment load and frequency of debris flows the apparent variation in k makes a unique value of n impossible to constrain with present data

evaluation of the impact of horizontal grid spacing in terra incognita on coupled mesoscale microscale simulations using the wrf framework abstractcoupled mesoscale microscale simulations are required to provide time varying weather dependent inflow and forcing for large eddy simulations under general flow conditions such coupling ne

investigating the scale adaptivity of a size filtered mass flux parameterization in the gray zone of shallow cumulus convection abstractin this study the scale adaptivity of a new parameterization scheme for shallow cumulus clouds in the gray zone is investigated the eddy diffusivity multiple mass flux ed mf n scheme is

changes in the saltation flux following a step change in macro roughness author s gillies john a etyemezian vicken nikolich george nickling william g kok jasper f

hanging valleys in fluvial systems controls on occurrence and implications for landscape evolution 1 we document and characterize hanging valleys in a fluvially eroded landscape in eastern taiwan our conceptual model for the initiation of hanging valleys builds on a recently proposed model of bedrock incision in which erosion actually becomes less efficient on very steep channel gradients if a pulse of incision in the main stem outpaces the tributary response the gradients at tributary mouths may therefore pass a threshold value beyond which erosional efficiency declines giving rise to a mismatch between trunk and tributary erosion rates this mismatch is expected at junctions with small tributaries where a step function decrease in drainage area also leads to sharp contrasts in water and sediment flux between trunk and tributary channels the occurrence of hanging valleys in actively uplifting fluvial landscapes such as the central range of taiwan suggests that the most common parameterizations of bedrock erosion which typically assume a monotonic positive correlation between channel gradient and incision rate may be violated in very steep channels in addition hanging valleys could greatly increase the response time of landscapes to tectonic perturbations since catchments above these tributary mouths will be insulated from these perturbations until a new suite of processes e g weathering and rock mass failure wear through the hanging valley lip the results of this study underscore the need for a more complete understanding of bedrock erosion processes and the incorporation of process transitions and threshold conditions into landscape evolution models

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

a scale adaptive turbulent kinetic energy closure for the dry convective boundary layer abstracta pragmatic scale adaptive turbulent kinetic energy tke closure is proposed to simulate the dry convective boundary layer for a variety of horizontal grid resolutions from 50 m typical of large eddy simulation models that use three dimensional turbulence parameterizations closures up to 100 km typical of climate models that use one dimensional turbulence and convection parameterizations closures since parameterizations closures using the tke approach have been frequently used in these two asymptotic limits a simple method is proposed to merge them with a mixing length scale formulation for intermediate resolutions this new scale adaptive mixing length naturally increases with increasing grid length until it saturates as the grid length reaches mesoscale model resolution the results obtained using this new approach for dry convective boundary layers are promising the mean vertical profiles of potential temperature and heat flux remain in good agreement for different resolutions a contin

responses of soil mantled hillslopes to transient channel incision rates 1 channel incision drives hillslope morphology in humid soil mantled landscapes when channel incision rates change numerous hillslope soil properties e g erosion rates soil thickness and soil production adjust in response to this change here we investigate the timescales of adjustment of hillslope soil properties when channel incision rates change in time an idealized soil mantled hillslope linear sediment flux law and soil density equal to bedrock density is investigated and the transient evolution of this hillslope is determined analytically this analysis reveals two dominant adjustment timescales the longer of these two timescales determines the rate at which the entire hillslope adjusts to a change in channel incision rates and is proportional to 4 2 2d where is the length of the hillslope and d is the sediment diffusivity numerical simulations are then used to examine responses of hillslopes that involve nonlinear behavior e g hillslopes that experience nonlinear sediment transport or have soil thicknesses that respond to the soil production function using these numerical models we show that the ratio between the soil density s and the density of the soil parent material can alter the long term response of the hillslope such that the characteristic timescale becomes 4 2 2d s in addition we show that the adjustments of the soil erosion rate the soil production rate and the soil thickness have different characteristic response timescales hillslopes that experience sediment flux that is proportional to the depth slope product respond on longer timescales than hillslopes that experience a linear sediment flux law when channel incision rates increase we illustrate how the spatial pattern of hillslope response to changes in channel incision rates can be used to constrain either channel incision histories or hillslope response timescales if the hillslope response timescale is known the pattern of hillslope disturbance can be used to constrain the celerity of a incision wave as it moves upstream through a channel if the channel incision history is known the hillslope response timescale may be evaluated on the basis of the spatial pattern of hillslope disturbance

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

the size frequency and areal distribution of rock clasts at the spirit landing site gusev crater mars 1 size frequency and nearest neighbor spacing measurements derived from the mars exploration rover spirit s panoramic camera images of the gusev landing site reveal that rock clasts on the intercrater plains are smaller better sorted and more evenly spaced than clasts found near the crater rims the even clast spacing is interpreted to be due to wind transport which acts to minimize surface roughness during periods of high velocity wind

a grid refinement based approach for modeling the convective boundary layer in the gray zone algorithm implementation and testing abstracta grid refinement based method is implemented in a community atmospheric model to improve the representation of convective boundary layer cbl turbulence on gray zone i e o 1 km grids at this resolution cbl convection is partially resolved and partially subgrid scale sgs such that neither traditional mesoscale planetary boundary layer pbl schemes nor sgs closures for large eddy simulations less are appropriate the proposed method utilizes two way interactive nesting to refine the horizontal resolution of the unstable surface layer of the daytime cbl sgs turbulent mixing in the fine nest and coarse parent grids are parameterized by an les turbulence closure and a pbl scheme respectively the method does not rely on predetermined empirical functions to introduce grid scale dependency and in theory works with any pbl scheme compared to the stand alone gray zone simulation the proposed approach shows improvements in terms of higher order statistics the timing of the onset of re

convectively induced secondary circulations in fine grid mesoscale numerical weather prediction models abstractmesoscale numerical weather prediction models using fine grid o 1 km meshes for weather forecasting environmental assessment and other applications capture aspects of larger than grid mesh size convectively induced secondary circulations ciscs such as cells and rolls that occur in the convective planetary boundary layer pbl however 1 km grid spacing is too large for the simulation of the interaction of ciscs with smaller scale turbulence the existence of ciscs also violates the neglect of horizontal gradients of turbulent quantities in current pbl schemes both aspects poorly resolved ciscs and a violation of the assumptions behind pbl schemes are examples of what occurs in wyngaard s terra incognita where horizontal grid spacing is comparable to the scale of the simulated motions thus model ciscs m ciscs cannot be simulated reliably this paper describes how the superadiabatic layer in the lower convective pbl together with increased horizontal resolution allow the critical ra

nighttime turbulent events in a steep valley a nested large eddy simulation study this numerical study investigates the nighttime flow dynamics in owens valley california nested highresolution large eddy simulation les is used to resolve stable boundary layer flows within the valley on 17 april during the 2006 terrain induced rotor experiment the valley atmosphere experiences weak synoptic forcings and is largely dominated by buoyancy driven downslope and down valley flows tower instruments on the valley floor record a continuous decrease in temperature after sunset except for a brief warming episode this transient warming event is modeled with good magnitude and temporal precision with les analysis of the les flow field confirms the event to be the result of a slope to valley flow transition as previously suggested by researchers based on field observations on the same night a northerly cold airflow from the great basin is channeled through a pass on the eastern valley sidewall the current plunges into the stable valley atmosphere overshooting the altitude of its neutral buoyancy and generating a large scale oscillatory motion the resulting cross valley flow creates strong vertical shear with the down valley flow in the lower layers of the atmosphere a portion of the cross valley flow is captured by a scanning lidar the nested les is in good agreement with the lidar recorded radial velocity furthermore the les is able to resolve kelvin helmholtz waves and ejection and sweep events at the two layer interface which lead to topdown vertical mixing

new constraints on sediment flux dependent river incision implications for extracting tectonic signals from river profiles we present new field data from rivers draining across active normal faults that incise across the same lithology at the fault have been subjected to similar climatic regimes and tectonic settings and were perturbed by a well documented increase in fault slip rate ca 1 ma in spite of these similarities the rivers exhibit markedly different long profiles and patterns of catchment incision we use channel slope and hydraulic geometry data for each river to calculate bed shear stresses b and show that there is no simple relationship between peak b and the relative uplift rates across the faults u which differ by a factor of four the long term average sediment supply to each channel q s estimated from time averaged catchment erosion rates can explain the b versus u data if bedload modulates bedrock incision rate e in a strongly nonlinear way together these field data allow us for the first time to evaluate theoretical predictions of the role of sediment on river profile evolution and to quantify the magnitude of the effect in natural systems

modeling aeolian sediment transport thresholds on physically rough martian surfaces a shear stress partitioning approach article i nfo this paper explores the effect that large roughness elements 0 30 m 0 26 m 0 36 m may have on entrainment of sediment by martian winds using a shear stress partitioning approach based on a model developed by raupach et al raupach m r gillette d a leys j f 1993 the effect of roughness elements on wind erosion threshold journal of geophysical research 98 d2 3023 3029 this model predicts the shear stress partitioning ratio defined as the percent reduction in shear stress on the intervening surface between the roughness elements as compared to the surface in the absence of those elements this ratio is based on knowledge of the geometric properties of the roughness elements the characteristic drag coefficients of the elements and the surface and the assumed effect these elements have on the spatial distribution of the mean and maximum shear stresses on mars unlike on earth the shear stress partitioning caused by roughness can be non linear in that the drag coefficients for the surface as well as for the roughness itself show reynolds number dependencies for the reported range of martian wind speeds the shear stress partitioning model of raupach et al is used to evaluate how conditions of the martian atmosphere will affect the threshold shear stress ratio for martian surfaces over a range of values of roughness density using as an example a 125 m diameter particle with an estimated threshold shear stress on mars of 0 06 n m 2

high frequency sediment transport responses on a vegetated foredune wind flow and sand transport intensity were measured on the seaward slope of a vegetated foredune during a 16 h storm using an array of sonic anemometers and wenglor laser particle counters the foredune had a compound seaward slope with a wave cut scarp about 0 5 m high separating the upper vegetated portion from the lower dune ramp which was bare of vegetation wind direction veered from obliquely offshore at the start of the event to obliquely onshore during the storm peak and finally to directly onshore during the final 2 h as wind speed dropped to below threshold sand transport was initially inhibited by a brief period of rain at the start of the event but as the surface dried and wind speed increased sand transport was initiated over the entire seaward slope transport intensity was quite variable both temporally and spatially on the upper slope as a result of fluctuating wind speed and direction but overall magnitudes were similar over the whole length ten minute average transport intensity correlates strongly with mean wind speed measured at the dune crest and there is also strong correlation between instantaneous wind speed and transport intensity measured at the same locations when the data are smoothed with a 10 s running mean transport on the beach for onshore winds is decoupled from that on the seaward slope above the small scarp when the wind angle is highly oblique but for wind angles 45 from shore perpendicular some sand is transported onto the lower slope copyright 2012 john wiley sons ltd

transient channel incision along bolinas ridge california evidence for differential rock uplift adjacent to the san andreas fault 1 the rates and spatial distribution of active deformation provide critical constraints on the geodynamics of deforming lithosphere yet such data are often difficult to acquire in eroding landscapes where poor preservation of geomorphic or stratigraphic markers hinders strain reconstruction recent advances in understanding of the relationship between bedrock channel profile form and erosion rate have led to their use as an index of rock uplift rate in steady state landscapes here we extend this analysis to landscapes experiencing a transient increase in erosion rate using an example from the marin county region of northern california we characterize channel and hillslope gradients in a series of small watersheds along a monolithologic portion of the franciscan terrane in marin county channel steepness indices vary strongly from north to south along the ridge and correspond with the progressive development of relief on threshold hillslopes along valley walls these patterns argue that recent channel incision has engendered a transient adjustment of hillslope gradient as incision outpaces soil production rates these differences in landscape form and inferred incision rate are explained by differential rock uplift within the region east of the san andreas fault relationships between channel gradient and incision rate suggest a threefold to fivefold difference in incision rate across the region and place a minimum bound on differential rock uplift rates our study highlights how landscape analysis can place bounds on the distribution of earth deformation in both space and time and thus lends insight into the processes driving that deformation

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

stream incision tectonics uplift and evolution of topography of the sierra nevada california abstract stream incision faulting thermochronologic and geobarometric data suggest that sierra nevada topography is a consequence of two periods of uplift stream incision of up to 1 km has occurred since 5 ma maximum eocene miocene incision was 150 m uplift of the sierra nevada westward tilting stream incision and east down normal and dextral faulting along the present eastern escarpment of the range began at 5 ma estimates of late cenozoic crestal rock uplift for different areas in the sierra nevada range from 1440 to 2150 m low summit erosion rates suggest that the rock uplift approximates the surface uplift of crestal summits tertiary stream gradients were lower than modern ones suggesting that the bottoms of the canyons have been uplifted in the late cenozoic and that the mean elevation of the sierra nevada has increased the elevation of pre cenozoic basement rocks above the base of tertiary paleochannels ranges from 1000 m in the south and

denudation rates determined from the accumulation of in situ produced 10be in the luquillo experimental forest puerto rico we present a simple method for estimation of long term mean denudation rates using in situ produced cosmogenic 10be in fluvial sediments procedures are discussed to account for the effects of soil bioturbation mass wasting and attenuation of cosmic rays by biomass and by local topography our analyses of 10be in quartz from bedrock outcrops soils mass wasting sites and riverine sediment from the icacos river basin in the luquillo experimental forest puerto rico are used to characterize denudation for major landform elements in that basin the 10be concentration of a discharge weighted average of size classes of river sediment corresponds to a long term average denudation of 43 m ma 1 consistent with mass balance results

formation of fluvial hanging valleys theory and simulation 1 although only recently recognized hanging tributary valleys in unglaciated tectonically active landscapes are surprisingly common stream power based river incision models do not provide a viable mechanism for the formation of fluvial hanging valleys thus these disequilibrium landforms present an opportunity to advance our understanding of river incision processes in this work we demonstrate that thresholds apparent in sediment flux dependent bedrock incision rules provide mechanisms for the formation of hanging valleys in response to transient pulses of river incision we simplify recently published river incision models in order to derive analytical solutions for the conditions required for hanging valley formation and use these results to guide numerical landscape evolution simulations analytical and numerical results demonstrate that during the response to base level fall sediment flux dependent incision rules may create either temporary or permanent hanging valleys these hanging valleys form as a consequence of 1 rapid main stem incision oversteepening tributary junctions beyond some threshold slope or 2 low tributary sediment flux response during the pulse of main stem incision thus limiting the tributary s capacity to keep pace with main stem incision the distribution of permanent and temporary hanging valleys results from four competing factors the magnitude of base level fall the upstream attenuation of the incision signal the lag time of the sediment flux response and the nonsystematic variation in tributary drainage areas within the stream network the development of hanging valleys in landscapes governed by sediment flux dependent incision rules limits the transmission of base level fall signals through the channel network ultimately increasing basin response time

bedrock landsliding river incision and transience of geomorphic hillslope channel coupling evidence from inner gorges in the swiss alps 1 the formation of inner gorges cut into bedrock has been explained as relief rejuvenation by fluvial incision in response to rapid base level drop repeated glaciations frequent pore pressure driven landsliding focused at hillslope toes or catastrophic outburst flows from natural dam failures prominent inner gorges occur in soft mesozoic bundner schist and lower tertiary flysch units of the formerly glaciated alpenrhein catchment eastern swiss alps their channel and hillslope morphologies differ from basins characterized by strong glacial or landslide imprints while formally resembling the theoretically predicted transient response of detachment limited bedrock rivers to rapid base level fall by headward knickpoint migration assuming a postglacial onset of fluvial bedrock incision into a last glacial maximum surface in response to base level drop induced by downwasting of trunk valley glaciers requires downcutting rates e 20 mm yr 1 and requires hillslopes to adjust by frequent landsliding toward development of a threshold state we test this scenario using data on surface uplift geomorphometry geomorphic hillslope coupling and probabilistic slope stability models we find that adjustment of inner gorge walls through landsliding is mainly strength limited and structurally controlled and threshold conditions are restricted to the lower 25 of local hillslope relief mass movement processes on upper hillslopes remain largely decoupled from channel incision despite inferred postglacial specific sediment yields of 104 m3 km 2 yr 1 from the studied basins conversely several constraints imposed by fluvial bedrock detachment postglacial sediment yields and bedrock landsliding argue for a pre holocene origin for at least some of the inner gorges in the area this implies partial protection of fluvial gorge topography by subglacial sediment fill during the last wurm extensive glaciation and implies that glaciers were insufficient to fully eradicate fluvially sculpted bedrock topography this leads us to conclude that lithology and major climate oscillations should be considered as further alternative controls on inner gorge formation

saltation threshold on earth mars and venus new formulations valid for wide ranges of particle diameter and density and gas density are presented for prediction of saltation threshold speed for small particles a low air density wind tunnel was used to extend the range of previous investigations and to separate the effects of reynolds number and interparticle forces of cohesion the new formulations are used to predict saltation threshold for atmospheric conditions on the surface of the earth mars and venus

martian dust storms 1999 mars orbiter camera observations the mars orbiter camera on board the mars global surveyor from march 9 1999 ls 107 where ls is the areocentric longitude of the sun measured in degrees from mars northern spring equinox to december 31 1999 ls 274 has obtained 7 5 km pixel 1 daily global maps of the martian surface in two wavelength bands blue 400 450 nm and red 575 625 nm visual inspection of these maps during the 1999 dust storm season has resulted in the detection of 783 dust storms ranging in size from local 102 km2 to regional 1 6 106 km2 no global storms were observed the difference in the numbers of dust storms occurring in the two hemispheres north 343 south 440 was not statistically significant fifty percent of the regional size dust storms formed as a result of the merger of two or more smaller local storms the regional storms from ls 207 to ls 223 were observed to move from the northern hemisphere into the southern hemisphere between 30 w and 50 w longitude this cross equatorial transport of dust suggests the location of the low lying southward flowing branch of the hadley circulation observations show that dust storms occur in several regions on mars at the two polar cap edges at the base of high elevation regions in the northern hemisphere near the polar hood during northern fall and at mid latitudes in both hemispheres specific regions such as solis planum and hesperia which were regions of significant dust activity in the past showed almost no dust storm activity in 1999 suggesting that regional dust sources are variable over a 20 year time frame one region of exceptional activity not noted previously was the arcadia amazonis border however other regions such as near elysium mons acidalia chryse hellas noachis argyre cimmeria and sirenum again were active dust storm regions relative dust opacities were modeled for 117 red wavelength events and ranged from 0 54 diffuse haze to 2 13 concentrated local events from the dust opacities we estimated the north polar sedimentation rate to be 6 0 10 10 4 g cm 2 yr 1 a factor of 40 smaller than previous estimates from the two 1977 global dust storms pollack et al 1979 along with the global dust mass loading 2 6 4 0 10 4 g cm 2 and cross equatorial dust mass loading 3 6 10 4 g cm 2 the 1999 cross equatorial mass dust loading suggests that the southern hemisphere subtropical latitudes require at least 2 3 martian years to replenish their dust sources before global storms can form

size frequency distributions of rocks on mars and earth analog sites implications for future landed missions the size frequency distribution of rocks at the viking landing sites and a variety of rocky locations on the earth that formed from a number of geologic processes all have the general shape of simple exponential curves which have been combined with remote sensing data and models on rock abundance to predict the frequency of boulders potentially hazardous to future mars landers and rovers rock data from the near field of the viking landers where dimensions can be measured accurately in stereo images and estimates from the far field of viking 1 have convex up curved shapes on log log graphs of cumulative frequency per square meter or cumulative fractional area versus diameter the rock data show a sharp drop off at large diameters and a progressive approach to a plateau with decreasing diameter approaching the total rock coverage which can be fit well with simple exponential functions similar shaped size frequency distributions of rocks are found at a wide variety of rocky surfaces on the earth and can be fit well with simple exponential functions this distribution is compatible with fracture and fragmentation theory which provides a physical basis for its wide application a combined fit to rock area data at both viking sites was made with a general exponential function in which the pre exponential is the total area covered by rocks simple linear height versus diameter relationships were also derived from height diameter ratios at the viking sites which suggest that rockier areas on mars have higher standing rocks than less rocky areas height was then substituted into the general exponential function derived for diameter yielding the cumulative fractional area of rocks versus height for any given total rock coverage on mars results indicate that most of mars is rather benign with regard to hazards from landing on large rocks for total rock coverage of 8 equivalent to modal rock coverage on mars and the viking 1 site without the outcrops about 1 of the surface is covered by 20 cm or higher rocks a lander designed to accommodate landing on 0 5 m high boulders such as the mars pathfinder airbag system could land on a surface covered by about 20 rocks similar to the viking 2 site which is rockier than 95 of the planet with 1 of the surface covered by rocks of 0 5 m or higher

soil production in heath and forest blue mountains australia influence of lithology and palaeoclimate an erratum has been published for this article in earth surfaces processes and landforms 25 13 2005 1683 1686 recent determinations of soil production from in situ cosmogenic nuclides indicate that production decreases exponentially with soil depth this contrasts with a long held assumption that maximum soil production occurs under a soil cover of finite depth sites in the blue mountains australia show a sharp decrease of soil depth where vegetation changes from forested plateau surfaces to heath covered spurs and bands of bare rock in the heath suggest that soil production depends on presence of a finite depth of soil the substrate varies from hard ferruginized sandstone to soft saprolite in situ 10be determinations indicate that apparent rates of erosion and soil production are greater under the relatively thin heath soil than under the thicker forest soil but in contrast to other studies these sites do not show significant depth dependence of apparent soil production the pattern reflects both hardness variation in the rock substrate and the effect of late quaternary climatic change optically stimulated luminescence osl dating indicates that soil 30 cm depth is of holocene age whereas the deeper soil is substantially older the age break coincides with a stone line interpreted as a former surface lag deposit assuming that pre holocene soil depths were 30 cm less than today recalculated soil production tends to decrease with increasing depth soil production at this site requires soil cover but bare rock patches and vegetation comprise a shifting mosaic in the long term average rates of erosion and soil production decrease with increasing soil depth copyright 2005 john wiley sons ltd

cosmogenic nuclide based investigation of spatial erosion and hillslope channel coupling in the transient foreland of the swiss alps abstract transient landscape disequilibrium is a common response to climatic fluctuations between glacial and interglacial conditions such landscapes are best suited to the investigation of catchment wide response to changes in incision the geomorphology of the trub and grosse fontanne adjacent stream systems in the napf region of the swiss molasse was analyzed using a 2 m lidar dem the two catchments were impacted by the last glacial maximum lgm even though the glaciers never overrode this region they did however cause base levels to drop by as much as 80 m despite their similar tectonic lithologic and climatic settings these two basins show very different responses to the changing boundary conditions stream profiles in the trub tend to be smooth while in the fontanne numerous knickzones are visible similarly cut and fill terraces are abundant in the trub watershed but absent in the fontanne where deep valleys have been incised the trub appears to be a coupled hillslope channel system because the morphometrics throughout the basin are uniform the morphology of hillslopes upstream of the knickzones in the fontanne is identical to that of the trub basin but different downstream of the knickzones suggesting that the lower reaches of the fontanne have been decoupled from the hillslopes however the rapid incision of the fontanne is having little effect on the adjacent upper hillslopes we tested this interpretation using cosmogenic 10 be derived basin averaged denudation rates and terrace dating the coupled nature of the trub basin is supported by the similarity of denudation rates 350 50 mm ky 1 at a variety of spatial scales upstream of the knickzones rates in the fontanne 380 50 mm ky 1 match those of the trub downstream of the knickzones denudation rates increase to 540 100 mm ky 1 the elevated rates in the downstream areas of the fontanne are due to rapid incision causing a decoupling of the hillslope from the channel basin response time and the magnitude of base level drop exert the principal control over the difference in geomorphic response between the two basins the timing of the filling of the trub valley 17 2 ka and the initial incision of the fontanne 16 3 ka were calculated verifying that these are responses to late glacial perturbations unique lithologic controls allow for one of the fastest regolith production rates yet to be reported 380 mm ky 1

the convective boundary layer in the terra incognita numerical simulations of a convective boundary layer cbl are performed to investigate model behavior in the terra incognita also known as the gray zone the terra incognita of the cbl refers to a range of model grid spacing that is comparable to the size of the most energetic convective eddies which are on the order of the boundary layer depth using the rayleigh benard thermal instability as reference a set of idealized simulationsisused toshow that grayzone modelingisnot onlya numericalchallenge but also poses dynamical difficulties when the grid spacing falls within the cbl gray zone grid dependent convection can occur the size of the initial instability structures is set by the grid spacing rather than the natural state of the flow this changes higher order flow statistics and poses fundamental difficulties for gray zone modeling applications

strong tectonic and weak climatic control of long term chemical weathering rates the relationships among climate physical erosion and chemical weathering have remained uncertain because long term chemical weathering rates have been difficult to measure here we show that long term chemical weathering rates can be measured by combining physical erosion rates inferred from cosmogenic nuclides with dissolution losses inferred from the rock to soil enrichment of insoluble elements we used this method to measure chemical weathering rates across 22 mountainous granitic catchments that span a wide range of erosion rates and climates chemical weathering rates correlate strongly with physical erosion rates but only weakly with climate implying that by regulating erosion rates tectonic uplift may significantly accelerate chemical weathering rates in granitic landscapes

the martian dust storm of sol 1742 after nearly five earth years on mars the mutch memorial station viking lander 1 finally witnessed a local dust storm that eroded trenches conical piles and other disturbed surfaces in the sample field and near the lander the event called the dust storm of sol 1742 occurred late in the third winter of lander observations between sols 1728 and 1757 analyses of tiny new wind tails and movement of materials indicate that the eroding winds were variable but more northeasterly than those that had previously shaped the surface pebbly residues and movement of 4 5 mm clods suggest drag velocities or friction speeds of the winds were about 2 2 4 0 m s wind speeds at the height of the meteorology boom 1 6 m were probably about 40 50 m s much of the observed erosion could have occurred in a few to several tens of seconds but somewhat longer times are suggested by analogy with the erosion of terrestrial soils most of the erosion occurred where preexisting equilibrium conditions of surface configurations and surface material properties had been altered by the lander during landing and during surface sampler activities but thin layers of bright fine grained dust were also removed and redistributed surfaces where preexisting equilibrium conditions were unaltered appeared to be uneroded

extraterrestrial dunes an introduction to the special issue on planetary dune systems abstract aeolian dune fields have been described on earth mars venus and titan the plethora of data returned from recent planetary missions has enabled a new era in planetary geomorphic studies much of our understanding of planetary dune systems comes from the application of earth analogs wind tunnel experiments and modeling studies despite the range of atmospheric pressures composition and gravity many of the dune forms on extraterrestrial surfaces are similar to those on earth although some have notable differences in bedform scale and composition as an introduction to the special issue on planetary dune systems this paper summarizes the current state of knowledge of planetary dune studies and highlights outstanding questions that require further investigation

gopher bioturbation field evidence for non linear hillslope diffusion it has generally been assumed that diffusive sediment transport on soil mantled hillslopes is linearly dependent on hillslope gradient fieldwork was done near santa barbara california to develop a sediment transport equation for bioturbation by the pocket gopher thomomys bottae and to determine whether it supports linear diffusion the route taken by the sediment is divided into two parts a subsurface path followed by a surface path the first is the transport of soil through the burrow to the burrow opening the second is the discharge of sediment from the burrow opening onto the hillslope surface the total volumetric sediment flux as a function of hillslope gradient is found to be qs cm3 cm 1 a 1 176 dz dx 3 189 dz dx 2 68 dz dx 34 dz dx 0 4 this result does not support the use of linear diffusion for hillslopes where gopher bioturbation is the dominant mode of sediment transport a one dimensional hillslope evolution program was used to evolve hillslope profiles according to non linear and linear diffusion and to compare them to a typical hillslope the non linear case more closely resembles the actual profile with a convex cap at the divide leading into a straight midslope section copyright 2000 john wiley sons ltd

sand transport by wind on complex surfaces field studies in the mcmurdo dry valleys antarctica 1 field experiments on boundary layer winds and sand transport in the victoria valley antarctica have provided information on the spatial and temporal variability of sand transport across coarse sand surfaces covered with isolated roughness elements rock clusters five sand transport events with a duration ranging between 9 6 and 22 h were studied sand transport threshold velocity was determined using the time faction equivalence method and varied between 0 30 and 0 35 m s 1 mean rates of sand transport ranged from 0 008 to 0 072 g cm s 1 sand transport was variably intermittent with continuous saltation intermittency 1 occurring from 11 to as much as 31 of the time for all events there is a close temporal correspondence between intermittency values shear velocity u m s 1 and the ratio u u t u t is threshold shear velocity sand flux and sand transport intensity as measured by piezoelectric saltation sensors although the roughness density of this site is low partitioning of shear stress between the rock clusters and the intervening sand surface is important to the spatial pattern of sand transport and acts to increase the mean threshold wind shear velocity or shear stress for sediment transport by approximately 1 2 times compared to a bare sand surface the effective local threshold wind shear velocity however varies by up to 6 times from the smoother sand areas to the most protected areas of the rock clusters as a result continuous and widespread sand transport will only occur at this site when the overall wind shear velocity exceeds 0 58 m s 1 1 6 u t minimum

lateral migration of hillcrests in response to channel incision in soil mantled landscapes 1 we investigate lateral migration of hillcrests in response to vertical offsets or transient incision rates of channels bordering these hillcrests in soil mantled landscapes for hillslopes undergoing sediment transport that is linearly proportional to the slope the hillcrest offset distance is one quarter of the ratio of the vertical offset between the channels to the relief of the symmetric hillslope if channels are downcutting at different rates the speed of hillcrest migration will depend on the ratio of the downcutting rates and the density ratio which is the ratio of the bulk density of the bedrock to the bulk density of the soil the density ratio plays a fundamental role in determining the transient response of the hillcrest lower density ratios lead to faster transient responses to changes in channel downcutting rates other parameters that affect the transient response of the hillcrest are the magnitude of transient differences in downcutting between the two channels the time averaged incision rate and a ratio of the elevation of the hillslope to a length that characterizes the decay in soil production with increasing soil thickness different parameters will be important for different sediment flux laws the profile of soil thickness reacts to transient changes in downcutting at a different rate than surface topography hillslopes experiencing transient channel downcutting may have surface topography that is symmetric about the hillcrest but will at the same time have a soil thickness profile that is asymmetric

a grid refinement based approach for modeling the convective boundary layer in the gray zone a pilot study abstractthe model gray zone refers to the range of grid spacings comparable to the dominant length scale of the flow in the gray zone the flow is partially resolved and partially subgrid scale sgs neither ensemble averaging based parameterizations nor turbulence closures are appropriate for parameterizing the effects of sgs motions on the resolved flow the gray zone of the convective boundary layer cbl is in the range of cbl depth typically o 1 km a new approach that seeks explicit resolution of the unstable surface layer through a nest layer of fine grid spacing is proposed to improve cbl parameterization in the gray zone to provide the theoretical basis for the approach a linear analytic model is presented and one way nested simulations are performed to investigate the dynamical coupling between the surface layer and the mixed layer the analytic model shows that at the onset of thermal instability the vertical and horizontal structures of the mixed layer are set by surface layer forcings

three mars years viking lander 1 imaging observations the mutch memorial station viking lander 1 on mars acquired imaging and meteorological data over a period of 2245 martian days 3 3 martian years this article discusses the deposition and erosion of thin deposits ten to hundreds of micrometers of bright red dust associated with global dust storms and the removal of centimeter amounts of material in selected areas during a dust storm late in the third winter atmospheric pressure data acquired during the period of intense erosion imply that baroclinic disturbances and strong diurnal solar tidal heating combined to produce strong winds erosion occurred principally in areas where soil cohesion was reduced by earlier surface sampler activities except for redistribution of thin layers of materials the surface appears to be remarkably stable perhaps because of cohesion of the undisturbed surface material

distribution of active rock uplift along the eastern margin of the tibetan plateau inferences from bedrock channel longitudinal profiles 1 current models of long term river incision into bedrock suggest that the local rate of differential rock uplift should exert a primary control on the gradient of channel longitudinal profiles however discrimination of this effect from the influence of variations in substrate erodibility sediment flux precipitation and transient changes in profile shape has proved difficult in practice here we investigate the controls on the spatial distribution of bedrock channel gradients adjacent to the sichuan basin in an effort to assess the degree and nature of active deformation along this margin of the tibetan plateau analysis of river longitudinal profiles utilizing a channel steepness index a measure of profile gradient normalized for drainage area reveals a zone of anomalously steep channels adjacent to the topographic front of the plateau margin channel profiles are systematically less steep in their headwater reaches on the plateau and in their lower reaches east of the plateau margin comparison of steepness indices to mapped lithologic variations reveals that lithology has only a limited influence on channel gradient in this field area we observe no systematic relationship between steepness indices and upstream drainage area channels of all size are steeper near the plateau margin we argue that these systematic changes are not readily explained as a consequence of increased sediment flux or of orographic precipitation we are led to conclude that steep channel profiles along the topographic front of the plateau reflect active differential rock uplift between this region and the foreland

quantitative analysis of land surface topography land surface topography significantly affects the processes of runoff and erosion a system which determines slope aspect and curvature in both the down slope and across slope directions is developed for an altitude matrix also the upslope drainage area and maximum drainage distance are determined for every point within the altitude matrix a fortran 66 program performs the analysis

hillslope response to tectonic forcing in threshold landscapes hillslopes are thought to poorly record tectonic signals in threshold landscapes numerous previous studies of steep landscapes suggest that large changes in long term erosion rate lead to little change in mean hillslope angle measured at coarse resolution new lidar derived topography data enables a finer examination of threshold hillslopes here we quantify hillslope response to tectonic forcing in a threshold landscape to do so we use an extensive cosmogenic beryllium 10 10 be based dataset of catchment averaged erosion rates combined with a 500 km 2 lidar derived 1 m digital elevation model to exploit a gradient of tectonic forcing and topographic relief in the san gabriel mountains california we also calibrate a new method of quantifying rock exposure from lidar derived slope measurements using high resolution panoramic photographs two distinct trends in hillslope behavior emerge below catchment mean slopes of 30 modal slopes increase with mean slopes slope distribution skewness decreases with increasing mean slope and bedrock exposure is limited above mean slopes of 30 our rock exposure index increases strongly with mean slope and the prevalence of angle of repose debris wedges keeps modal slopes near 37 resulting in a positive relationship between slope distribution skewness and mean slope we find that both mean slopes and rock exposure increase with erosion rate up to 1 mm a in contrast to previous work based on coarser topographic data we also find that as erosion rates increase the extent of the fluvial network decreases while colluvial channels extend downstream keeping the total drainage density similar across the range our results reveal important textural details lost in 10 or 30 m resolution digital elevation models of steep landscapes and highlight the need for process based studies of threshold hillslopes and colluvial channels

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