rates and processes of bedrock incision by the upper ukak river since the 1912 novarupta ash flow in the valley of ten thousand smokes alaska the rates and patterns of bedrock channel incision significantly influence landscape evolution and long term interactions among climate tectonics and erosion unfortunately only sparse field data are available to quantify the controls on river incision rates we exploit the diversion of the upper ukak river by an ash flow in 1912 to measure rates of incision along a newly formed bedrock channel minimum estimates of the rate of incision into intact rock vary from 0 01 to 0 10 m yr 1 this variation reflects differences in channel slope channel width lithologic facies and intensity of jointing as well as the effects of upstream knickpoint migration a streampower type incision model adequately explains the incision rate data provided 1 variations in channel width are prescribed on the basis of field measurements 2 the slope exponent is significantly less than unity n 0 4 0 2 and 3 observed downstream changes in lithologic facies and the intensity of jointing account for the apparent twofold downstream decrease in the coefficient of erosion despite the very rapid rate of incision calibrated stream power erosion coefficients for the ukak river k 2 4 10 4 m 0 2 yr 1 to 9 0 10 4 m 0 2 yr 1 are within the range of previously published estimates two plausible explanations for the low values of the slope exponent n are that incision rate is limited by either 1 a combination of physical weathering and hydrodynamic joint block extraction or 2 block fracture due to bedload impacts modulated on steeper channel segments by suspension of a significant fraction of the sediment load

western pacific interannual variability associated with the el nino southern oscillation observations of sea surface temperature sst sea level pressure slp surface wind and outgoing longwave radiation olr show that the el nino southern oscillation enso displays western pacific anomaly patterns in addition to eastern pacific anomaly patterns during the warm phase of enso warm sst and low slp anomalies in the equatorial eastern pacific and low olr anomalies in the equatorial central pacific are accompanied by cold sst and high slp anomalies in the off equatorial western pacific and high olr anomalies in the off equatorial far western pacific also while the zonal wind anomalies over the equatorial central pacific are westerly those over the equatorial far western pacific are easterly the nearly out of phase behavior between the eastern and western tropical pacific is also observed during the cold phase of enso but with anomalies of opposite sign these western pacific interannual anomaly patterns are robust features of enso independent of data sets it is argued that equatorial easterly westerly wind anomalies over the far western pacific during the warm cold phase of enso are initiated by off equatorial western pacific cold warm sst anomalies and that these winds are important for the evolution of enso an atmosphere model is employed to demonstrate that small off equatorial western pacific cold warm sst anomalies compared to those in the east are sufficient to produce equatorial easterly westerly wind anomalies as observed over the far western pacific the coupled ocean atmosphere model of zebiak and cane is then modified to investigate the evolution of the western pacific interannual anomaly patterns in a coupled ocean atmosphere system by including a meridional structure to the subsurface temperature parameterization in the western pacific the modified model produces both western and eastern pacific interannual anomaly patterns

arcades products of stress controlled and discontinuity related weathering abstract weathering patterns on sandstone cliff faces and sloping surfaces were studied from the viewpoint of gravity induced stress combined with the presence of planar discontinuities in the rock critical evaluation of hundreds of photos taken in various regions around the world numerical modelling using finite element method including automatic stress controlled element removal technique of erosion modelling and physical in situ modelling of friable sandstone revealed the formation of a specific sub group of weathering forms related to planar discontinuities due to their striking similarity with elements known from architecture these pits are introduced as arcades or arcade like forms these pits and cavities vary in size but they are similar in shape coalesced into trains along the discontinuities and separated from each other by hourglass shaped pillars in their origin and geometry these forms differ from widely known cavernous weathering forms such as honeycombs and tafoni we have shown that arcade shape and size are controlled by the redistribution of gravity induced stress along planar discontinuities and the resulting stress shadows the stress shadow zones along the discontinuities are characterized by material loss owing to various weathering and erosional mechanisms although overlooked as yet stress controlled weathering along discontinuities has a strong effect on rock surface morphology and arcades can be taken as its principal example

double and single itczs with and without clouds abstracta major bias in tropical precipitation over the pacific in climate simulations stems from the models tendency to produce two strong distinct intertropical convergence zones itczs too often several mechanisms have been proposed that may contribute to the emergence of two itczs but current theories cannot fully explain the bias this problem is tackled by investigating how the interaction between atmospheric cloud radiative effects acres and the large scale circulation influences the itcz position in an atmospheric general circulation model simulations are performed in an idealized aqua planet setup and the longwave and the shortwave acres are turned off individually or jointly the low level moist static energy mse is shown to be a good predictor of the itcz position therefore a mechanism is proposed that explains the changes in mse and thus itcz position due to acres consistently across simulations the mechanism implies that the itcz moves equatorward if the hadley circulation strengt

fluvial erosion of inscriptions and petroglyphs at siega verde spain low grade metamorphics such as slates and schists tend to be subjected to relatively rapid surface deterioration by both weathering and fluvial wear if the rate at which such processes are effective on these relatively soft rocks could be calibrated through their effects on surfaces of known ages this would provide a possibility of estimating the age of petroglyphs on similar facies and in similar environments an attempt of quantifying these processes is presented using the petroglyph site of siega verde in western spain as an example a series of dated inscriptions occurring at a site of zoomorphic petroglyphs provide the data to plot rock surface deterioration against time the involvement of numerous variables prevents this method from providing much precision but it is adequate to offer indications of order of magnitude of age the zoomorphs at siega verde have been attributed to the upper palaeolithic but this method suggests that most of the site s anthropic markings are under 200 years old this finding is supported by several other factors such as the degree of repatination of the supposedly pleistocene petroglyphs and the presence of a recent terrace predating these

importance of a stochastic distribution of floods and erosion thresholds in the bedrock river incision problem 1 fluvial erosion of bedrock occurs during occasional flood events when boundary shear stress exceeds a critical threshold to initiate incision therefore efforts to model the evolution of topography over long timescales should include an erosion threshold and should be driven by a stochastic distribution of erosive events however most bedrock incision models ignore the threshold as a second order detail in addition climate is poorly represented in most landscape evolution models so the quantitative relationship between erosion rate and measurable climatic variables has been elusive here we show that the presence of an erosion threshold when combined with a well constrained probabilistic model of storm and flood occurrence has first order implications for the dynamics of river incision in tectonically active areas first we make a direct calculation of the critical shear stress required to pluck bedrock blocks for a field site in new york second we apply a recently proposed stochastic threshold bedrock incision model to a series of streams in california with known tectonic and climatic forcing previous work in the area has identified a weak relationship between channel gradient or relief and rock uplift rate that is not easily explained by simpler detachment limited models the results with the stochastic threshold model show that even low erosion thresholds which are exceeded in steep channels during high frequency flood events fundamentally affect the predicted relationship between gradient and uplift rate in steady state rivers in a manner consistent with the observed topography this correspondence between theory and data is however nonunique models in which a thin alluvial cover may act to inhibit channel incision in the low uplift rate zone also provide plausible explanations for the observed topography third we explore the broader implications of the stochastic threshold model to the development of fluvial topography in active tectonic settings we suggest that continued field applications of geomorphic models including physically meaningful thresholds and stochastic climate distributions are required to advance our knowledge of interactions among surficial climatic and crustal processes

synoptic settings of westerly wind bursts the morphology of westerly wind bursts wwbs during the 1980s is investigated using 1000 mbar winds analyzed by the european center for medium range weather forecasts ecmwf the variety of synoptic situations in which wwbs occur are explored so that the dynamics of wwb generation and maintenance can be studied and so that those interested in short and long term forecasts of conditions over the equatorial pacific will have an increased knowledge of those elements associated with wwbs wwbs are identified by searching for episodes in which the zonal wind was at least 5 m s 1 over at least 10 longitude for two or more days this definition based on surface winds rather than elevated winds or wind anomalies reflects the impact wwbs have on air sea interaction processes the spatial and temporal criteria provide a synoptic scale envelope for such interactions and mitigate against erroneous analyses according to these criteria 131 distinct wwbs occurred during the 1980s a new two dimensional classification scheme has been developed the nine patterns in it describe the near surface flow during 90 of these wwbs a single cyclone or a series of cyclones in one or both hemispheres and several different types of cross equatorial flow are the major components of the patterns only 8 of the bursts were associated with concurrent cyclones in both the northern and southern hemispheres four bursts involving cross equatorial flow are subjected to further study the flow is decomposed into barotropic and baroclinic parts and into rotational and divergent baroclinic components one of the bursts was predominantly barotropic and another predominantly baroclinic the cross equatorial flow in all four cases was predominantly divergent in nature the information from these cases coupled with the typical vertical structures and small meridional length scales associated with the various synoptic patterns suggests that simple baroclinic models of circulations driven by near equatorial heating are not adequate to describe the dynamics during wwbs

simulating the growth of tafoni throughout the world large caves in rocks tafoni are found which originate from salt weathering the mechanisms that control their development are poorly understood the growth of tafoni has been studied with a model that describes how a rock surface containing a small pit disintegrates by salt crystallization during wetting drying cycles in the model the rock is mapped on a grid the migration and crystallization of salts are simulated explicitly in the drying phase of a cycle at the end of each wetting drying cycle the amount of salt deposited at the grid nodes is evaluated and the shape of the rock surface is adjusted by removing nodes the length of the drying period in a single cycle proved to be the key parameter for short drying periods the amount of crystallized salt at the surface is proportional to the drying rate therefore for short drying periods most salts are deposited at the more exterior parts of the rock surface as a result most damage will develop at these parts of the surface which results in smooth surfaces due to the characteristics of the drying process for long drying periods most salts accumulate at regions with low evaporation rates which are the sheltered parts of the rock surface these parts are not exposed to the wind or the sun as a result the pit grows and a tafone develops copyright 2004 john wiley sons ltd

impacts of vertical structure of large scale vertical motion in tropical climate moist static energy framework abstractinteractions between cumulus convection and its large scale environment have been recognized as crucial to the understanding of tropical climate and its variability in this study the moist static energy mse budget is employed to investigate the potential impact of the vertical structure of large scale vertical motion in tropical climate based on results from both reanalysis data and model simulation two domains are selected over the western and eastern pacific with vertical motion profiles that are dominated by top heavy and bottom heavy structures respectively the bottom heavy structure is climatologically associated with more shallow convection while the top heavy structure is related to more deep convection the column integrated vertical mse advection of top heavy vertical motion is positive while that of bottom heavy vertical motion tends to be negative controlling factors responsible for the above vertical mse advection contrast are discussed based on a simple decomposition of the

mjo signals in latent heating results from trmm retrievals abstract four tropical rainfall measuring mission trmm datasets of latent heating were diagnosed for signals in the madden julian oscillation mjo in all four datasets vertical structures of latent heating are dominated by two components one deep with its peak above the melting level and one shallow with its peak below profiles of the two components are nearly ubiquitous in longitude allowing a separation of the vertical and zonal temporal variations when the latitudinal dependence is not considered all four datasets exhibit robust mjo spectral signals in the deep component as eastward propagating spectral peaks centered at a period of 50 days and zonal wavenumber 1 well distinguished from lower and higher frequency power and much stronger than the corresponding westward power the shallow component shows similar but slightly less robust mjo spectral peaks mjo signals were further extracted from a combination of bandpass 30 90 day filtered deep and shallow components largest amplitudes of bo

origin of honeycombs testing the hydraulic and case hardening hypotheses abstract cavernous weathering cavernous rock decay is a global phenomenon which occurs in porous rocks around the world although honeycombs and tafoni are considered to be the most common products of this complex process their origin and evolution are as yet not fully understood the two commonly assumed formation hypotheses hydraulic and case hardening were tested to elucidate the origin of honeycombs on sandstone outcrops in a humid climate mechanical and hydraulic properties of the lips walls between adjacent pits and backwalls bottoms of pits of the honeycombs were determined via a set of established and novel approaches while the case hardening hypothesis was not supported by the determinations of either tensile strength drilling resistance or porosity the hydraulic hypothesis was clearly supported by field measurements and laboratory tests fluorescein dye visualization of capillary zone vapor zone and evaporation front upon their contact demonstrated that the evaporation front reaches the honeycomb backwalls under low water flow rate while the honeycomb lips remain dry during occasional excessive water flow events however the evaporation front may shift to the lips while the backwalls become moist as a part of the capillary zone as the zone of evaporation corresponds to the zone of potential salt weathering it is the spatial distribution of the capillary and vapor zones which dictates whether honeycombs are created or the rock surface is smoothed a hierarchical model of factors related to the hydraulic field was introduced to obtain better insights into the process of cavernous weathering

the indian monsoon and its variability for over 300 years the monsoon has been viewed as a gigantic land sea breeze it is shown in this paper that satellite and conventional observations support an alternative hypothesis which considers the monsoon as a manifestation of seasonal migration of the intertropical convergence zone itcz with the focus on the indian monsoon the mean seasonal pattern is described and why it is difficult to simulate it is discussed some facets of the intraseasonal variation such as active weak cycles break monsoon and a special feature of intraseasonal variation over the region namely poleward propagations of the itcz at intervals of 2 6 weeks are considered vertical moist stability is shown to be a key parameter in the variation of monthly convection over ocean and land as well as poleward propagations special features of the bay of bengal and the monsoon brought out by observations during a national observational experiment in 1999 are briefly described

el nino southern oscillation related ocean atmosphere coupling in the western equatorial pacific using 43 years of comprehensive ocean atmosphere data set and related data for the period 1950 1992 an examination is made into the regional dependence of ocean atmosphere coupling in relation to the el nino southern oscillation enso the cross correlation between sea surface temperature sst and sea level pressure slp anomalies over the global tropics shows two patterns of significant negative correlation consistent with a local hydrostatic response of slp to sst 1 the eastern pacific where the correlation is symmetric about and largest on the equator and 2 the western pacific where symmetric regions of negative correlation are found off the equator separated by a region of positive correlation on the equator anomalies within these two patterns vary out of phase with each other while the slp anomalies on both sides of the basin are of similar magnitude the sst anomalies in the east are much larger than those in the west despite this disparity in the sst anomaly magnitudes between the eastern and western pacific we argue that the ocean atmosphere couplings in the western and west central pacific are important for enso the off equator sst anomalies in the west enhance the slp anomalies there and they appear to initiate easterly wind anomalies over the far western pacific during the peak el nino phase of enso as these easterlies evolve their effect upon the ocean tends to oppose that of the westerly wind anomalies found over the west central pacific these competing effects suggest a mechanism that may contribute to coupled ocean atmosphere system oscillations the west central equatorial pacific the region separating the eastern and western patterns while exhibiting large momentum and heat flux exchanges shows minimum correlation between sst and slp thus neither the sst and slp anomaly magnitudes nor the correlation between them is alone indicative of ocean atmosphere coupling and the regional dependence for such coupling in relation to enso appears to be more complicated than mechanistic interpretations of enso would suggest

structure of large scale convective anomalies over tropical oceans abstract geographical variations in the variance and cross correlation of monthly mean sea surface temperature sst outgoing longwave radiation olr a proxy for deep convection and vertical motion and convergence of winds at the surface and at 850 mb across the tropical indian and pacific oceans are examined within about 10 of the equator at most longitudes the variance of these quantities associated with the seasonal cycle is less than the variance associated with anomalies from the seasonal cycle largest variances in the sst and surface convergence data occur across the eastern near equatorial pacific whereas olr and 850 mb convergence variances are largest across the western pacific olr anomalies are significantly correlated with collocated sst and surface convergence anomalies from the date line eastward to the south american coast but are uncorrelated west of the date line the olr and 850 mb convergence anomalies are significantly correlated from about 120 w westward but are uncorrelated

atmospheric convergence feedback in a simple model for el nino abstract a parameterization is developed for the feedback between dynamics and heating associated with moisture convergence in the tropical atmospheric boundary layer the feedback improves the ability of a simple model to simulate observed anomalies of the tropical atmosphere during el nino events in particular two features of the observations are reproduced by including the feedback process the smaller scale of atmospheric anomalies as compared to sst anomalies and the focusing of the anomalies in the vicinity of the mean convergence zones the principal remaining shortcomings of the model are discussed

cloud components of the intertropical convergence zone 1 this study explores the roles of different synoptic scale cloud systems in the making of the intertropical convergence zone itcz outgoing longwave radiation olr data are used to represent both the mean itcz and cloud systems an olr threshold of 205 w m 2 is used to distinguish daily mean deep convective clouds from nondeep clouds zonally moving synoptic scale cloud systems are identified through a cloud tracking method mean olr of the itcz is decomposed into five components westward and eastward moving synoptic scale deep convective clouds random nonpropagating deep convective clouds nondeep clouds and clear sky backgrounds hypothetical itczs each composed of one of the cloud components and the clear sky background are constructed and compared the largest synoptic scale cloud constituents of the itcz are nondeep clouds and deep clouds with no persistent tendency of zonal propagation each of the two comprises about 40 45 of total cloud signals in the itcz a weak itcz could exist solely because of westward propagating synoptic scale deep convective clouds in reality these westward propagating clouds contribute 25 40 of deep convective clouds and 10 20 of total clouds in the itcz contributions from eastward propagating synoptic scale clouds are much smaller 8 of the deep convective clouds and less than 5 of total clouds in the itcz an itcz without any zonally propagating synoptic scale deep convective clouds would be diffused in latitude the cloud compositions in the itcz and other tropical convective zones are compared their discrepancies indicate fundamental characteristics in large scale environments for the cloud components in different regions

geoelectric investigations into sandstone moisture regimes implications for rock weathering and the deterioration of san rock art in the golden gate reserve south africa the clarens sandstone in the golden gate reserve south africa is the canvas for a collection of san bushmen rock art dating from neolithic times until as recently as 150 years ago this rock art is under threat from human interference but also to a greater degree from weathering processes on the rock surface the dominant weathering processes occurring in the rock shelters which host the rock art are flaking and honeycombing two rock shelter sites in the reserve have been investigated using electric resistivity tomography ert and supportive methods for measuring surface moisture protimeter and surface hardness equotip these non destructive techniques can be used in situ to assess the extent of weathering within a rock outcrop and are especially suited for investigations in sensitive areas such as rock art sites moisture movement has been mapped and related to the weathering processes observed on the surface the aim of the study is to aid rock art conservation in the golden gate reserve through a better understanding of the driving processes of surface weathering the evidence shows that the extensive flaking and honeycombing found in the rock shelters is most likely caused by water pockets in the near surface zone which are replenished through internal moisture transport driving the superficial weathering processes these weathering processes pose a significant problem rock art in the golden gate reserve shows severe deterioration due to flaking conservation strategies should therefore take internal processes into account as much as their superficial expression

scale issues in weathering studies a review of the major scale issues in weathering studies reveals concerns over the fundamental spatio temporal distributions of weathering phenomena as well as issues of upscaling microscope based observations and linking different scales of observations in explanations of landform development various strategies are proposed which can be used to tackle these issues many rooted in non linear dynamical systems ideas as an initial step spatio temporal scale distributions are estimated here for weathering processes landforms and controls based on a range of empirical data two case studies of phytokarst in grand cayman and blistering and scaling of building stones are presented to illustrate the types of data that might be used to establish more convincing scale linkages in weathering investigations

the enso related west pacific sea surface temperature gradient abstractel nino southern oscillation enso events are accompanied by an anomalous zonal sea surface temperature sst gradient over the west pacific ocean defined here as the west pacific sst gradient wpg the wpg is defined as the standardized difference between area averaged sst over the central pacific ocean nino 4 region and west pacific ocean 0 10 n 130 150 e while the direction of the wpg follows enso cycles the magnitude of the gradient varies considerably between individual el nino and la nina events in this study el nino and la nina events are grouped according to the magnitude of the wpg and tropical sst circulations and precipitation are examined for the period 1948 2011 until the 1980s the wpg showed little trend as the west and central pacific warmed at similar rates however the west pacific has recently warmed faster than the central pacific which has resulted in an increased wpg during la nina events the temporal evolution and distribution of tropical pacific sst as we

fast evolving conduits in clay bonded sandstone characterization erosion processes and significance for the origin of sandstone landforms abstract in strelec quarry the czech republic an underground conduit network 300 m long with a volume of 10 4 m 3 and a catchment of 7 km 2 developed over 5 years by groundwater flow in cretaceous marine quartz sandstone similar landforms at natural exposures conduits slot canyons undercuts are stabilized by case hardening and have stopped evolving the quarry offers a unique opportunity to study conduit evolution in sandstone at local to regional scales from the initial stage to maturity and to characterize the erosion processes which may form natural landforms prior to stabilization a new technique was developed to distinguish erodible and non erodible sandstone surfaces based on measurements of relative erodibility drilling resistance ambient and water saturated tensile strength ts at natural and quarry exposures three distinct kinds of surfaces were found 1 erodible sandstone exposed at 60 of surfaces in quarry this sandstone loses as much as 99 of ts when saturated 2 sub vertical fracture surfaces that are non erodible already prior to exposure at ground surface and which keep considerable ts if saturated 3 case hardened surfaces that start to form after exposure in favorable conditions they became non erodible and reach the full ts in just 6 years an increase in the hydraulic gradient from 0 005 to 0 02 triggered conduit evolution based on long term monitoring of water table in 18 wells and inflows to the quarry rapidly evolving major conduits are characterized by a channel gradient of 0 01 a flow velocity 40 cm s and sediment concentration 10 g l flow in openings with a discharge 1 ml s and hydraulic gradient 0 05 exceeds the erosion threshold and initiates piping in the first phase of conduit evolution fast concentrated flow mobilizes erodible sandstone between sets of parallel fractures in the shallow phreatic zone in the second phase the conduit opening mainly expands vertically upward into the vadose zone by mass wasting of undercut sandstone slabs mass wasting is responsible for 90 of mobilized sandstone sides of the mature conduits are protected by non erodible fracture surfaces natural landforms were probably formed very rapidly by overland flow piping and possibly fluidization during or at the end of the glacial periods when sandstone was not yet protected by case hardening

river incision into bedrock mechanics and relative efficacy of plucking abrasion and cavitation improved formulation of bedrock erosion laws requires knowledge of the actual processes operative at the bed we present qualitative field evidence from a wide range of settings that the relative efficacy of the various processes of fluvial erosion e g plucking abrasion cavitation solution is a strong function of substrate lithology and that joint spacing fractures and bedding planes exert the most direct control the relative importance of the various processes and the nature of the interplay between them are inferred from detailed observations of the morphology of erosional forms on channel bed and banks and their spatial distributions we find that plucking dominates wherever rocks are well jointed on a submeter scale hydraulic wedging of small clasts into cracks bashing and abrasion by bedload and chemical and physical weathering all contribute to the loosening and removal of joint blocks in more massive rocks abrasion by suspended sand appears to be rate limiting in the systems studied here concentration of erosion on downstream sides of obstacles and tight coupling between fluid flow patterns and fine scale morphology of erosion forms testify to the importance of abrasion by suspended load rather than bedload particles mechanical analyses indicate that erosion by suspended load abrasion is considerably more nonlinear in shear stress than erosion by plucking in addition a new analysis indicates that cavitation is more likely to occur in natural systems than previously argued cavitation must be considered a viable process in many actively incising bedrock channels and may contribute to the fluting and potholing of massive unjointed rocks that is otherwise attributed to suspended load abrasion direct field evidence of cavitation erosion is however lacking in terms of the well known shear stress or stream power erosion law erosion by plucking is consistent with a slope exponent n of 2 3 to 1 whereas erosion by suspended load abrasion is more consistent with a slope exponent of 5 3 given that substrate lithology appears to dictate the dominant erosion process this finding has important implications for long term landscape evolution and the models used to study it

diagnostic studies of pacific surface winds abstract analyses are performed using surface winds derived from the monthly mean fsu pacific pseudo stress fields vorticity budget calculations reveal the relative contributions of various terms and allow simplification of the full momentum equations based on the simplified equations a procedure is developed for estimating surface pressure and then adjusting the winds the wind field adjustments fall well within the uncertainty of the data while allowing generally large imbalances in the vorticity budget to be removed completely further validation of the procedure is provided by comparisons between estimated and observed pressure anomalies the adjusted winds and pressure are then used to infer boundary layer and upper level forcing within the context of particular model formulations these forcing fields an compared with sea surface temperature outgoing longwave radiation and highly reflective cloud data in order to infer the dominant mechanisms contributing to observed surface circulation anom

rapid honeycomb weathering tafoni formation in greywacke s e australia the development of honeycomb weathering on seawalls of non marine lower cretaceous greywacke built in 1943 and 1949 shows that under certain conditions this type of tafoni is a significant factor in the retrogradation of rocky coasts

relationships between monthly precipitation and sst variations in the tropical pacific region abstract the relationships between the patterns of monthly sea surface temperature sst variations and those of precipitation in the tropical pacific ocean region are examined the rainfall data utilized are derived from satellite observations of outgoing longwave radiation a composite empirical orthogonal function eof analysis of the sst and precipitation indicates a dominant mode of variation linking sst variations in the eastern equatorial region with those of mnwi about 30 westward one point correlation analyses show that this general relationship is present for all points in the eastern and central ocean but that no significant sst rainfall correlations are evident for sst points wen of about the dateline the one point correlation analyses also suggest that during time periods outside of el nin s the rainfall response to sst changes is largely confined to the areas of climatological precipitation maxima suggesting only a minor alteration in the large scale circulation on the other hand du

escarpment retreat in sedimentary tablelands and cuesta landscapes landforms mechanisms and patterns abstract although the general concept that escarpments in layered rocks retreat through time was offered more than 150 years ago recognizing the exact mechanisms patterns and rates of retreat remains a challenge in this paper we provide the state of the art of the theme of escarpment retreat reviewing both the classic contributions often forgotten but important case studies and the latest research in separate parts of the paper we discuss 1 terminology applied to the geomorphology of escarpments 2 the main assumptions and pathways of long term evolution of escarpments including conceptual models presented so far 3 processes involved in cliff retreat mainly weathering mass movements and erosion 4 the role of spring erosion and fluvial processes leading to fluvial dissection and development of canyons present in many tablelands 5 the possible role of climate change in escarpment evolution 6 rates of escarpment retreat in conclusions we summarize the major advances in our understanding of escarpment evolution of the last two three decades such as the recognition of the key role of emerging groundwater in non uniform escarpment retreat of an important role of silica dissolution and underground removal of dissolved solids increasing appreciation of rock properties in governing the patterns of escarpment retreat the proposal that cliffs do not necessarily retreat via catastrophic rock slope failures but may disintegrate in situ and the first attempts to date escarpment retreat using cosmogenic isotopes finally the remaining gaps and possible research priorities for the future are identified

the 1997 98 el nino evolution relative to previous el nino events abstract the evolution of the 1997 98 el nino is described using ncep sst and olr data ncep ncar reanalysis sea level pressure slp fields and the florida state university surface wind data from november 1996 to january 1997 the eastern pacific is characterized by equatorial cold sst and high slp anomalies while the western pacific is marked by off equatorial warm sst anomalies and off equatorial anomalous cyclones corresponding to this distribution are high olr anomalies in the equatorial central pacific and low olr anomalies in the off equatorial far western pacific the off equatorial anomalous cyclones in the western pacific are associated with a switch in the equatorial wind anomalies over the western pacific from easterly to westerly these equatorial westerly anomalies then appear to initiate early sst warmings around the date line in january february 1997 and around the far eastern pacific in march 1997 subsequently both the westerly wind and warm sst anomalies along with the low olr ano

structural evolution in heating profiles of the mjo in global reanalyses and trmm retrievals abstract diabatic and latent heating profiles from four global reanalyses and three tropical rainfall measuring mission trmm algorithms were compared first generally for the tropics and then in the context of the madden julian oscillation mjo most of them exhibit three heating maxima corresponding to known convection centers over south america africa and the indian western pacific warm pool but they still differ substantially in many ways most noticeably a double peak vertical structure with one peak in the upper and the other in the lower troposphere and relative weak heating over the maritime continent in comparison to heating over the indian and western pacific oceans are clearly seen in some heating data but absent in others heating profiles associated with the mjo were diagnosed through composites and case studies the composites were constructed as functions of mjo phases at three longitudes representing the indian ocean maritime continent and western pacific respectively four mjo ev

moisture expansion as a deterioration factor for sandstone used in buildings the expansion processes that develop in building stones upon changes of moisture content may be an important contributing factor for their deteriorations until recently few data could be found in the literature concerning this parameter and weathering processes moreover the processes that may be responsible for the moisture related expansion of natural building stones are not yet completely understood to further elucidate this process extensive mineralogical petrophysical and fabric investigations were performed on eight german sandstones in order to obtain more information regarding the weathering process and its dependence on the rock fabric the analysed sandstones show a wide range of pore size distributions and porosities a positive correlation with the fabric and the pore space can be found for all studied petrophysical parameters the intensity of the expansion and related swelling pressure cannot be attributed only to the swelling of clay minerals the investigations suggest that the micropores and the resulting disjoining pressure during wet dry cycles also play an important role the results obtained suggest that the mechanism is related to the presence of liquid water within the porous material

chronology of latest pleistocene lake level fluctuations in the pluvial lake chewaucan basin oregon usa new accelerator mass spectrometer radiocarbon ages from gastropods in shore deposits within the pluvial lake chewaucan basin combined with stratigraphical and geomorpho logical evidence identify an abrupt rise and fall of lake level at ca 12 14 c ka the lake level high is coeval with lake level lows in the well dated records of palaeolakes bonneville and lahontan and with a period of relatively wet conditions in the more southerly owens lake basin this spatial pattern of pluvial lake levels in the western usa at 12 14 c ka indicates a variable synoptic response to climate forcing at this time copyright 2001 john wiley sons ltd

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

salt and ice crystallisation in porous sandstones salt and ice crystallisation in the pore spaces causes major physical damage to natural building stones the damaging effect of these processes can be traced back to physically induced stress inside of the rock while crystallizing the increasing scientific research done during the past century has shown that there are numerous parameters that have an influence on the weathering resulting from these processes however the working mechanisms of the stress development within the rock and its material dependency are still subject to discussion this article gives an overview of salt and ice weathering additionally laboratory results of various sandstones examined are presented salt crystallisation tests and freeze thaw tests were done to obtain information about how crystallisation weathering depends on material characteristics such as pore space water transportation and mechanical features simultaneous measuring of the length alternating during the salt and ice crystallisation has revealed detailed information on the development of crystal in the pore spaces as well as the development of stress these findings can help to understand the damaging mechanisms

parallel retreat of rock slopes underlain by alternation of strata abstract characteristic landscapes e g cuesta cliff and overhang of caprock or stepped terrain formed by differential erosion can be found in areas composed of variable geology exhibiting different resistances to weathering parallel retreat of slopes defined as recession of slopes without changes in their topography is sometimes observed on slopes composed of multiple strata however the conditions needed for such parallel retreat have not yet been sufficiently clarified in this study we elucidated the conditions for parallel retreat of rock slopes composed of alternating layers using a geometric method in addition to evaluate whether various rock slopes fulfilled the conditions for parallel retreat we analyzed topographic data obtained from periodic measurement of rock slopes in the aka kuzure landslide central japan our geometric analysis of the two dimensional slopes indicates that dip angle slope gradient and erosion rate are the factors that determine parallel retreat conditions however dip angle does not significantly affect parallel retreat conditions in the case of steep back slopes slope gradient 40 in contrast dip angle is an important factor when we consider the parallel retreat conditions in dip slopes and gentler back slopes slope gradient

gypsum a review of its role in the deterioration of building materials the deterioration of buildings and monuments by gypsum is the result of crystallization cycles of this salt although gypsum can dehydrate to a hemihydrate the mineral bassanite and to an anhydrate the mineral anhydrite this reaction occurs in nature on a geological time scale and therefore it is unlikely to occur when gypsum is found on and in building materials the caso4 h2o system appears deceptively simple however there are still discrepancies between the experimental and thermodynamically calculated data the reason for the latter can be attributed to the slow crystallization kinetics of anhydrite apart from this the large numbers of studies carried out on this system have focused on industrially important metastable phases such as the hemihydrate and soluble anhydrite the paper presents a review of the studies dealing with the phase equilibria of the caso4 h2o system as well as the influence of other salts on the solubility of gypsum it tries to glean out the relevant information that will serve to explain the deterioration observed on building materials by the crystallization of gypsum and thus allows developing improved conservation methods

the role of rock surface hardness and internal moisture in tafoni development in sandstone the development of cavernous weathering features such as tafoni remains poorly understood in particular the roles played by internal moisture and case hardening remain unclear in this study electric resistivity tomography ert has been used to map moisture distribution within inner walls of tafoni developed in sandstone and an equotip device used to measure rock surface hardness as a proxy measure of the degree of weathering and case hardening seven large tafoni in the golden gate highlands national park south africa varying in size and degree of development have been monitored a dynamic relationship between surface hardness degree of weathering and internal moisture regimes has been found we propose a new conceptual model which illustrates the complex interaction between case hardening and internal moisture and suggests a new direction for cavernous weathering research copyright 2011 john wiley sons ltd

tropical oceanic rainfall and sea surface temperature structure parsing causation from correlation in the mjo abstractbased upon on the findings of y li and r e carbone the association of tropical rainfall with sst structure is further explored with emphasis on the mjo passband analyses include the tropical indian ocean maritime continent and tropical western pacific regions the authors examine the anomalies of and correlations between sst structure the frequency of rainfall events and rainfall amount based on detailed examination of a 49 month time series all findings are statistical inferences and interpretations consistent with established theory the statistical inferences are broadly consistent with a pivotal role played by the convergent laplacian of sst together with an expected but somewhat indirect role of sst itself the main role of sst in the mjo passband appears limited to production of moist static energy which is highly correlated with cumulative precipitation yet bears a decidedly conditional relationship to the occurrence of rainfall if rain occurs then more rain is likely over

diagnosis of weathering damage on rock cut monuments in petra jordan studies of many years combining in situ investigation and laboratory analysis have provided comprehensive information on weathering damage on the rock cut monuments in the ancient city of petra in jordan these rock cut monuments represent outstanding world heritage many hundred monuments were carved by the nabataeans from bedrock about 2000 years ago the awareness of increasing weathering damage on the monuments has resulted in international efforts towards their preservation the damage diagnosis has addressed the complex mutual relationships between stone types stone properties monument exposure regimes environmental influences weathering phenomena development and extent of weathering damage and weathering progression the rocks were classified lithostratigraphically and petrographically results on weathering forms weathering profiles and weathering products obtained from monument mapping in situ measurements and laboratory studies revealed a complex diversity of weathering phemomena with respect to type and intensity damage categories and damage indices were used to create a reproducible quantitative rating of weathering damage detailed results on weathering forms allowed the characterization and quantification of weathering progression including weathering prognoses stone properties and states of weathering damage were jointly considered for the rating of the rocks susceptibility to weathering the systematic evaluation of weathering damage and monument exposure regimes can enhance the assessment of weathering factors and processes

modeling tropical convergence based on the moist static energy budget abstract the vertically integrated moist static energy equation provides a convenient starting point for the construction of simple models of the time mean low level convergence in the tropics a vertically integrated measure of the moist static stability the gross moist stability proves to be of central importance minima in this quantity mark the positions of the tropical convergence zones we argue that the positions of these minima are determined by the time mean moisture field which is in turn closely tied to the time mean surface temperature

weaker links between zonal convective clustering and itcz width in climate models than in observations strong links are seen in observations between convective clustering and several properties of the intertropical convergence zone itcz these links suggest that biases in how climate models simulate the itcz may be related to model biases in convective clustering or that there may be biases in how models represent the relationship between clustering and the itcz we investigate these issues by analyzing convective clustering and the link between clustering and itcz properties in 18 climate models we find that the links between variability in convective clustering and variability of itcz properties are generally weaker and less robust in models than in observations by contrast model biases in the climatological convective clustering explain a substantial fraction of the climatological double itcz bias though they do not explain biases in the climatological itcz width

convective initiation near the andes in subtropical south america abstractsatellite radar and radiometer data indicate that subtropical south america has some of the deepest and most extreme convective storms on earth this study uses the full 15 yr trmm precipitation radar dataset in conjunction with high resolution simulations from the weather research and forecasting model to better understand the physical factors that control the climatology of high impact weather in subtropical south america the occurrence of intense storms with an extreme horizontal dimension is generally associated with lee cyclogenesis and a strengthening south american low level jet sallj in the la plata basin the orography of the andes is critical and model sensitivity calculations removing and or reducing various topographic features indicate the orographic control on the initiation of convection and its upscale growth into mesoscale convective systems mcss reduced andes experiments show more widespread convective initiation weaker average storm intensity and more rapid propagation

quantitative study of a rapidly weathering overhang developed in an artificially wetted sandstone cliff those factors controlling the weathering and erosion of sandstone on the field scale are still not well understood in this study a specific sandstone overhang and its surroundings with artificially induced and extremely high erosion rates was subjected to a complex investigation contrast between the erosion rate of the wet and dry portions of the same cliff enabled isolation of the factors responsible for rapid sandstone retreat erosion rates moisture and salt content as well as suction were monitored in the field mineral phases and water chemistry were analyzed the measurement of tensile strength laboratory frost weathering tests and numerical modeling of stress were performed the acquired data show that an increase of moisture content in pores in the area of the studied overhang decreased tensile strength of the sandstone to 14 of its dry value and increases the sandstone weathering and erosion rate by nearly 4 orders of magnitude compared to the same sandstone under natural moisture condition outside on the cliff area consequently frost weathering in combination with wetting weakening was found to play a major role in weathering erosion of the sandstone cliff and overhang frost weathering rate in both the laboratory and field increases up to 15 times with decreasing gravity induced stress the results also indicate that sandstone landforms in temperate climates may potentially develop very rapidly if the pore space is nearly saturated with water and will later remain relatively stable when the moisture content decreases as a general implication it is suggested that overhangs in central europe and elsewhere might be the result of rapid frost weathering of nearly saturated sandstone during the last glacial this article is protected by copyright all rights reserved

the relationship of low level winds and moisture to convection in the tropical pacific abstract strong convection in the tropical pacific is found to be enhanced when low level winds are westerly and poleward directed this means that winds which blow opposite to the normal easterly equatorward trade wind flow are associated with strong convection linear regression demonstrates that about 30 40 of the variance in conviction across the pacific during the 1982 83 el nino can be explained by low level precipitable water plus the low level winds

field measurements of incision rates following bedrock exposure implications for process controls on the long profiles of valleys cut by rivers and debris flows until recently published rates of incision of bedrock valleys came from indirect dating of incised surfaces a small but growing literature based on direct measurement reports short term bedrock lowering at geologically unsustainable rates we report observations of bedrock lowering from erosion pins monitored over 1 7 yr in 10 valleys that cut indurated volcanic and sedimentary rocks in washington oregon california and taiwan most of these channels have historically been stripped of sediment their bedrock is exposed to bed load abrasion plucking and seasonal wetting and drying that comminutes hard intact rock into plates or equant fragments that are removed by higher fl ows consequent incision rates are proportional to the square of rock tensile strength in agreement with experimental results of others measured rates up to centimeters per year far exceed regional long term erosionrate estimates even for apparently minor sediment transport rates cultural artifacts on adjoining strath terraces in washington and taiwan indicate at least several decades of lowering at these extreme rates lacking sediment cover lithologies at these sites lower at rates that far exceed long term rock uplift rates this rate disparity makes it unlikely that the long profi les of these rivers are directly adjusted to either bedrock hardness or rock uplift rate in the manner predicted by the stream power law despite the observation that their profi les are well fi t by power law plots of drainage area vs slope we hypothesize that the threshold of motion of a thin sediment mantle rather than bedrock hardness or rock uplift rate controls channel slope in weak bedrock lithologies with tensile strengths below 3 5 mpa to illustrate this hypothesis and to provide an alternative interpretation for power law plots of area vs slope we combine shields threshold transport concept with measured hydraulic relationships and downstream fi ning rates in contrast to fl uvial reaches none of the hundreds of erosion pins we installed in steep valleys recently scoured to bedrock by debris fl ows indicate any postevent fl uvial lowering these results are consistent with episodic debris fl ows as the primary agent of bedrock lowering in the steepest parts of the channel network above 0 03 0 10 slope

observations on the role of lithology in strath terrace formation and bedrock channel width field observations from western washington and eastern tibet indicate a strong lithologic influence on strath terrace formation and highlight the response of bedrock channel width to spatial gradients in bedrock erodibility and or rock uplift rates measurements of local bedrock bed and bank erosion rates together with observations of the role of weathering processes on erosion of siltstones and sandstones illustrate a mechanism that underlies a conceptual model that predicts a strong lithological control on strath terrace formation direct measurements of bedrock erosion rates in lithologies susceptible to accelerated erosion upon sub aerial exposure show that lateral rates of bedrock bank erosion can substantially exceed vertical incision below the perennial flow level due to an asymmetry in erodibility between perennially submerged rock and rock exposed to cyclic wetting and drying on bedrock channel walls under such conditions the rapid weathering mediated lowering of bedrock exposed above baseflow promotes development of a beveled bedrock platform that could become a strath terrace upon abandonment in contrast to previous studies channel widths measured across a substantial gradient in lithology slope and long term erosion rates in eastern tibet do not follow conventional relations where channel width scales as a power law function of drainage area instead as they flow across a zone of rapid uplift these channels systematically narrow relative to the predicted width extrapolated from traditional power law relations field studies from a wide range of geological settings and lithologies support the interpretation that in general strath terraces tend to be more extensive in rivers flowing over weak sedimentary rock and tend to be poorly developed and or preserved where rivers flow over hard erosion resistant rock

the dynamics of idealized convection schemes and their effect on the zonally averaged tropical circulation in this paper the effect of a simple convection scheme on the zonally averaged tropical general circulation is examined within an idealized moist gcm to obtain broad classifications of the influence of convection on the tropics this is accomplished with a simplified convection scheme in the style of betts and miller the scheme is utilized in a moist gcm with simplified physical parameterizations gray radiation with zonally symmetric slab mixed layer ocean boundary conditions comparisons are made with simulations without a convection scheme i e with large scale condensation lsc only with the moist convective adjustment mca parameterization and with various formulations and parameter sets with a simplified betts miller sbm scheme with the control run using the sbm scheme the tropics become quieter and less dependent on horizontal resolution as compared with the lsc or mca simulations the hadley circulation mass transport is significantly reduced with the sbm scheme as is the itcz precipitation an important factor determining this behavior is the parameterization of shallow convection without shallow convection the convection scheme is largely ineffective at preventing convection from occurring at the grid scale the sensitivities to convection scheme parameters are also examined the simulations are remarkably insensitive to the convective relaxation time and only mildly sensitive to the relative humidity of the reference profile provided significant large scale condensation is not allowed to occur the changes in the zonally averaged tropical circulation that occur in all the simulations are understood based on the convective criteria of the schemes and the gross moist stability of the atmosphere

a unified oscillator model for the el nino southern oscillation the delayed oscillator the western pacific oscillator the recharge discharge oscillator and the advective reflective oscillator have been proposed to interpret the oscillatory nature of the el nino southern oscillation enso all of these oscillator models assume a positive ocean atmosphere feedback in the equatorial eastern and central pacific the delayed oscillator assumes that the western pacific is an inactive region and wave reflection at the western boundary provides a negative feedback for the coupled system to oscillate the western pacific oscillator emphasizes an active role of the western pacific in enso the recharge discharge oscillator argues that discharge and recharge of equatorial heat content cause the coupled system to oscillate the advective reflective oscillator emphasizes the importance of zonal advection associated with wave reflection at both the western and eastern boundaries motivated by the existence of these different oscillator models a unified oscillator model is formulated and derived from the dynamics and thermodynamics of the coupled ocean atmosphere system consistent with enso anomaly patterns observed in the tropical pacific this oscillator model considers sea surface temperature anomalies in the equatorial eastern pacific zonal wind stress anomalies in both the equatorial central pacific and the equatorial western pacific and thermocline depth anomalies in the off equatorial western pacific if the western pacific wind forced response is neglected thermocline and zonal wind stress anomalies in the western pacific are decoupled from the coupled system and the unified oscillator reduces to the delayed oscillator if wave reflection at the western boundary is neglected the unified oscillator reduces to the western pacific oscillator the mathematical form of the recharge discharge oscillator can also be derived from this unified oscillator most of the physics of the advective reflective oscillator are implicitly included in the unified oscillator and the negative feedback of wave reflection at the eastern boundary is added to the unified oscillator with appropriate model parameters chosen to be consistent with those of previous oscillator models the unified oscillator model oscillates on interannual timescales

variability of monthly averaged surface and 850 mb winds at tropical pacific islands abstract we examine the variability of monthly mean winds at 850 mb and the surface from five island stations in the tropical western pacific ocean climatological winds and 850 mb surface wind shear are evaluated and used to construct time series of monthly mean wind and shear anomalies wind variance at 850 mb tends to be substantially greater than at the surface and large temporal variations in shear are found prominent anomalies are associated with el nino southern oscillation periods composite el nino event anomalies are examined it is found that the westerly wind anomalies associated with warm central pacific sea surface temperatures are stronger at 850 mb than at the surface and that the anomalous 850 mb surface shears are as large as the surface wind anomalies themselves several simple techniques are described to investigate the feasibility of estimating surface wind anomalies from 850 mb wind anomalies because strong correlations exist between the zonal winds at these levels zonal est

linking weathering and rock slope instability non linear perspectives weathering is linked complexly to the erosion and evolution of rock slopes weathering influences both the strength of rock slopes and the stresses that act upon them while weathering has often been portrayed in an over simplified way by those studying rock slope instability in reality it consists of multiple processes acting over different spatial and temporal scales with many complex inter linkages through a demonstration of the sources of non linearities in rock slope weathering systems and their implications for rock slope instability this paper proposes five key linkages worthy of further study copyright 2012 john wiley sons ltd

climate driven bedrock incision in an active mountain belt measurements of fluvial bedrock incision were made with submillimeter precision in the east central range of taiwan where long term exhumation rates and precipitation driven river discharge are independently known they indicate that valley lowering is driven by relatively frequent flows of moderate intensity abrasion by suspended sediment is an important fluvial wear process and channel bed geometry and the presence of widely spaced planes of weakness in the rock mass influence erosion rate and style

low level inversions over the tropical pacific thermodynamic structure of the boundary layer and the above inversion moisture structure abstract the structure of the boundary layer over a broad region of the equatorial pacific is studied using dropwinsonde measurements made in january february may and june of 1979 low level inversions of sufficient strength to inhibit deep convection are found to be present in more than 50 of the soundings these inversions appear to play a critical role in regulating convective activity over the central and eastern pacific the tops of the inversions have an average pressure level of approximately 300 mb and show little latitudinal or longitudinal variation the majority of the inversion soundings approximately 70 have a reversal in the mixing ratio profile qreversal above the inversion that appears as a dry layer at the top of the inversion layer capped by a relatively moist layer this moist layer is on the average 2 g kg 1 more moist than the corresponding soundings that have no qreversal no systematic regional or temporal variations in the frequency of occurrence of the qreversal or the str

sandstone landforms shaped by negative feedback between stress and erosion the formation and preservation of sandstone landforms such as pillars and arches is enigmatic experiments and numerical modelling show that load bearing material weathers more slowly and thus the internal stress field can shape and stabilize sandstone landforms

behavior of deep convective clouds in the tropical pacific deduced from isccp radiances abstract we analyze the properties of deep convection over the equatorial pacific and its relationship to sea surface temperature sst and surface wind divergence using isccp radiance data for july 1983 and january 1984 deep convective clouds dcc are diagnosed with both a combined visible infrared threshold method and an infrared only threshold method the visible channel is important in diagnosing deep convection in different regions with different surface and atmospheric properties because of the existence of large scale variations of dcc top altitudes the itcz and spcz exhibit changes in these two months that are characteristic of both the el nino and seasonal cycles deep convection is latitudinally confined to a much smaller spatial scale than that suggested by maps of outgoing longwave radiation diurnal variations of dcc cover and associated mesoscale cirrus anvil cloud cac cover are out of phase with deep convection peaking in the early morning throughout the equatorial pacific the diurna

calculating tropical winds from time mean sea level pressure fields abstract the time mean tropical surface momentum balance is investigated with a simple model that calculates tropical surface winds from time mean sea level pressure fields the model domain is the global tropical strip centered on the equator with lateral boundaries at 30 latitude steady state surface winds are numerically calculated from the nonlinear horizontal momentum equations with forcing from observed climatological monthly mean sea level pressures and prescribed lateral boundary winds dissipation is parameterized by linear damping and diffusion comparisons of model winds with observed climatological monthly mean winds show realistic simulations in most regions and in all months the poorest simulations occur in the meridional component of the wind in near equatorial areas of strongly convergent or weak winds in these areas and in the near equatorial region generally diffusion processes make a significant positive contribution to the realism of the model winds horizontal nonlinear advect

wetting weakening of tertiary sandstones microscopic mechanism the micromechanism accounting for wetting weakening of tertiary sandstones was studied it was found that intragranular fracture prevails for all dry sandstones however when the sandstone is wet intergranular fracture occurs for type b sandstones therefore one sandstone from type a sandstones ms1 and another from type b tk were selected to further investigate the nature of the matrix it was found that 1 for both sandstones the major mineral components of the matrix are illite and kaolinite except that the ms1 sandstone has more chlorite 2 leaching of matrix induced an increase of porosity and consequently results in leaching softening and 3 among the mineral composition chlorite is easiest to be dissolved and leached out and induces a more significant increase of porosity which in turn results in a more significant leaching softening

a western pacific oscillator paradigm for the el nino southern oscillation a data based hypothesis is presented on the mechanism of the el nino southern oscillation enso a major determinant of interannual global climate variability the hypothesis emphasizes the importance of off equator sea surface temperature and sea level pressure variations west of the dateline for initiating equatorial easterly winds over the far western pacific these winds compete with westerly winds over the equatorial central pacific enabling the coupled ocean atmosphere system to oscillate consistent with this hypothesis an analogical oscillator model is constructed that produces enso like oscillations the proposed mechanism differs from the delayed oscillator paradigm in that wave reflection at the western boundary is not a necessary condition for the coupled ocean atmosphere system to oscillate

experimental weathering of sandstone by combinations of salts laboratory experiments are described that examined the effectiveness of certain naturally occurring combinations of salts as weathering agents cubes of a highly quartzose sandstone were repeatedly soaked in one of a series of salt solutions and then oven dried to simulate natural weathering the weathering effect of both potassium alum and ammonium alum is enhanced by the presence of alunogen or gypsum whereas sodium chloride depresses the effect of the alums sodium chloride combined with gypsum is confirmed as appreciably more destructive than either of the salts alone the results indicate that it is difficult to predict the weathering behaviour of combinations of salts from the weathering behaviour of the salts individually possible causes of enhanced weathering by some combined salt solutions are discussed

rapid salt weathering in the coastal namib desert implications for landscape development data on the rate and style of breakdown on naturally occurring rock types are important to improving geomorphological understanding of landscape development in arid environments two years exposure of rock blocks cut from an english limestone bath stone as well as locally relevant namibian rocks karibib marble and damara granite within four distinctive microenvironments in and around a coastal salt pan environment reveals high rates of breakdown in the bath stone blocks observable breakdown in the marble blocks and weight gains and strength increases in the granite blocks breakdown is associated with high conductivities and large amounts of halite and gypsum within the surface sediments frequency of wetting and drying appears to be a major control on the resultant breakdown rates these findings can be compared with recent data from further inland in the namib desert which suggest very slow rates of breakdown of similar blocks of damara granite and karibib marble even where salts are readily available high rates of rock breakdown within coastal salt pans appear to contribute to dust production and the effective flattening of relief along the coastal strip

a physical model for the rate of coastal tafoni development to explain the temporal change in growth rates of tafoni on homogeneous insoluble rocks modeling is carried out based on a formulated relationship for weathering induced reduction of rock strength the model is expressed by z z c 1 sqrt t ast t where z is the depth of tafoni z c is the ultimate depth t is the time and t is the time lag application of the model to the pacific coast of japan reveals that 1 the model accurately describes tafoni development 2 average growth rates presented by most previous studies are underestimated and 3 an exponential decrease in growth rates stems from strength reduction by inherent rock weathering

zonal momentum balance in the tropical atmospheric circulation during the global monsoon mature months abstractin this paper zonal momentum balances of the tropical atmospheric circulation during the global monsoon mature months january and july are analyzed in three dimensions based on the ecmwf interim re analysis era interim it is found that the dominant terms in the balance of the atmospheric boundary layer abl in both months are the pressure gradient force the coriolis force and friction the nonlinear advection term plays a significant role only in the asian summer monsoon regions within the abl in the upper troposphere the pressure gradient force the coriolis force and the nonlinear advection are the dominant terms the transient eddy force and the residual force which can be explained as convective momentum transfer over open oceans are secondary yet cannot be neglected near the equator zonal mean equatorial upper troposphere easterlies are maintained by the absolute angular momentum advection associated with the cross equatorial hadley circulation equatorial upper troposphere ea

investigations into the relationship between changes in internal moisture regimes and rock surface deterioration in cavernous sandstone features cavernous features commonly develop in sandstone but their development over time remains enigmatic it has been suggested that moisture movements within the rock mass play a key role in the location development and dynamics of cavernous features in this research the role of internal moisture movement is tested through monitoring moisture and surface deterioration dynamics in april 2008 and april 2009 within two large cavernous features mega tafoni in the golden gate highlands national park south africa gghnp data are presented from surveys of internal moisture using electrical resistivity tomography ert surface moisture using a protimeter and deterioration using surface hardness as recorded with an equotip as a proxy for surface deterioration across five 2 45 m long transects in addition a high resolution temperature record is presented to assess the influence of micro climates within the caverns the results indicate consistency in the gross spatial pattern of moisture flow within the rock mass over a one year period but significant changes in mean moisture contents and in the fine detail of moisture patterning some noticeably weakened areas had developed within the central parts of the cavernous features often linked to wetter subsurface conditions supporting the theory that core softening is a main driver of cavernous feature formation however in some areas surface hardening is also found to be associated with wetter subsurface conditions supporting the theory that case hardening is a main driver of cavernous feature formation in addition the presence of well established biofilms suggests an even more complex interaction between moisture surface development and biological activity a model is presented therefore which integrates this paradox by proposing a non linear relationship between moisture dynamics facilitation of biofilm formation and deterioration within cavernous features

some atmospheric processes governing the large scale tropical circulation in idealized aquaplanet simulations abstract the large scale tropical atmospheric circulation is analyzed in idealized aquaplanet simulations using an atmospheric general circulation model idealized sea surface temperatures ssts are used as lower boundary conditions to provoke modifications of the atmospheric general circulation results show that 1 an increase in the meridional sst gradients of the tropical region drastically strengthens the hadley circulation intensity 2 the presence of equatorial zonal sst anomalies weakens the hadley cells and reinforces the walker circulation and 3 a uniform sst warming causes small and nonsystematic changes of the hadley and walker circulations in all simulations the jet streams strengthen and move equatorward as the hadley cells strengthen and become narrower some relevant mechanisms are then proposed to interpret the large range of behaviors obtained from the simulations first the zonal momentum transport by transient and stationary eddies is shown to modulate the eddy driven jets whic

variable weathering response in sandstone factors controlling decay sequences differences in weathering response characteristics of fine and coarse grained stanton moor sandstone samples were assessed in a laboratory weathering simulation experiment using a variable combination of salt weathering and freeze thaw cycles preliminary analysis of permeability characteristics identified similar mean values for each type of stanton sandstone but significant differences in the range of values between the two sample sets with coarse grained samples of stanton moor sandstone displaying a restricted range of values in comparison to fine grained samples which showed much greater within block variation data indicated that the greater the range in initial permeability values the greater the potential for salt and moisture ingress and retention and hence eventual disruption of the fabric of the stone experimental data also identified different stages in decay sequences with significant structural change occurring during the initial preparatory stage before material breakdown and loss became apparent evidence suggests that relatively minor structural and mineralogical differences between samples of the same stone type can have a significant influence on weathering behaviour resulting in distinct rates and patterns of breakdown copyright 2005 john wiley sons ltd

numerical modeling of the evolution of arcades and rock pillars abstract arcades i e lenticular and other specifically shaped hollows controlled by discontinuities have recently been recognized as a weathering form typical for sandstones weathered quartzites granites or tuffs they are produced by accelerated weathering and erosion in stress shadows related to the redistribution of gravity induced stress along planar discontinuities in the rock these forms occur worldwide in various settings inland humid arid and coastal the origin of arcades has been demonstrated via physical experiments and supported by a relatively simplistic numerical modeling however details on their shaping and the evolution of related forms have not been explained we performed an advanced numerical modeling to produce various shapes of arcades and rock pillars during the erosion of rock masses dissected by discontinuities we demonstrate that the erosion model in which erosion takes place when the maximum principal stress is below a certain critical value can adequately describe the formation of arcades in the modeling we set higher critical values for stresses at discontinuities than in a homogeneous material representing a rock mass to represent the higher tendency for disintegration of the discontinuity material which was weakened by the discontinuity formation processes by applying various discontinuity geometries and values of critical stresses we were able to reproduce the formation of various arcade shapes and complex three dimensional clusters of arcade cavities with rock pillars discontinuities and stress controlled erosion weathering are the only necessary conditions for arcade formation

modeling tropical pacific sea surface temperature 1970 87 abstract an attempt is made to model the sea surface temperature sst of the tropical pacific ocean between january 1970 and august 1987 the sst is computed using the model and heat flux parameterization discribed in the climatological study of seager et al the model is forced with the observed winds as given by the florida state university analysis the results indicate that while short period variability in the model and observations is largely uncorrelated variability with periods greater than about one year is well represented in the model each el nino that occurred in this time period is captured by the model the main discrepancies in the evolution of the 1982 83 and 1986 87 model el nino events are the inability of the model equatorial sst anomaly to cool in early 1983 and the disappearance of the 1986 87 anomaly during 1987 the results suggest a number of conclusions in the east pacific equatorial kelvin waves excited by variations in the trade wind strength in the central and west pacific

an episode of rapid bedrock channel incision during the last glacial cycle measured with 10be we use 10 be to infer when how fast and why the susquehanna river incised through bedrock along the u s atlantic seaboard one of the world s most prominent and ancient passive margins although the rate at which large rivers incise rock is a fundamental control on the development of landscapes relatively few studies have directly measured how quickly such incision occurs either in tectonically active environments or along passive margins exposure ages of fluvially carved bedrock strath terraces preserved along the lower susquehanna river demonstrate that even along a passive margin large rivers are capable of incising through rock for short periods of time at rates approaching those recorded in tectonically active regions such as the himalayas over eighty samples collected along and between three prominent levels of strath terraces within holtwood gorge indicate that the susquehanna river incised more than 10 meters into the appalachian piedmont during the last glacial cycle beginning 36 ka incision rates increased dramatically and remained elevated until 14 ka the northern half of the susquehanna basin was glaciated during the late wisconsinan however similar rates and timing of incision occurred in the unglaciated potomac river basin immedi ately to the south the concurrence of incision periods on both rivers suggests that glaciation and associated meltwater were not the primary drivers of incision instead it appears that changing climatic conditions during the late pleistocene promoted an increase in the frequency and magnitude of flood events capable of exceeding thresholds for rock detachment and bedrock erosion thus enabling a short lived episode of rapid incision into rock although this study has constrained the timing and rate of bedrock incision along the largest river draining the atlantic passive margin the dates alone cannot explain fully why or by what processes this incision occurred however cosmogenic dating offers compelling evidence that episodes of rapid incision into bedrock are tied to glacial cycles and changes in global climate these results and the methods we employ provide valuable insights into the nature of bedrock channel incision not only along the susquehanna river and passive margins but also across a wide range of settings around the globe because river incision into bedrock transmits the effects of changing climate and tectonics through fluvial networks to hillslopes comprehending when where and why rivers incise has important implications for the evolution of land scapes

sandstone weathering a century of research and innovation abstract a review of sandstone weathering research particularly in the past 100 years reveals a trajectory of enquiry from early description and classification of features to development of process based explanations to decreasing scales of investigation and a disparity between understanding of process es and explanations of the genesis of sandstone weathering features developments in expositions on mesoscale weathering features on sandstone surfaces are discussed demonstrating a range of approaches to weathering phenomena field based and laboratory based that must be linked to provide an explanation of observed features on a landform scale throughout the twentieth century a thematic chronology highlights certain trends in research description of forms often in arid and semi arid environments single process form models an emphasis on experimentation difficulties in measuring weathering rates and a persistent emphasis on physical causes of breakdown a new research agenda is promoted in which biodeterioration and chemical processes gain parity a holistic approach based on conceptual modeling of weathering systems gains prominence and scale issues are addressed more rigorously

el nino southern oscillation and madden julian 30 60 day oscillations during 1981 1982 an important issue in understanding the low frequency oscillations of the atmosphere and the ocean atmosphere system concerns the role of transients during individual events this question is examined from an observational point of view for the period from september 1981 to april 1982 which includes the transitional phase of the 1982 1983 el nino southern oscillation enso cycle as well as six madden julian 30 60 day oscillations mjo for the developing enso it is shown that interannual transitions in the anomalous atmospheric circulation and in the sea surface temperatures in the western central pacific coincide with the passage of strong mjos from the indian to pacific oceans for a mjo during december 1981 evidence is provided that the shift of convection from the eastern indian ocean to the western pacific ocean involves transients having periods around 10 days the role of transients is discussed from the perspective of these interannual and intraseasonal modes

experimental frost weathering of sandstone by various combinations of salts weathering experiments are reported combining frost and a range of salts that occur naturally on rock faces in western and central europe potassium and ammonium alums enhanced frost weathering quite considerably both singly and in combination though they were less potent than halite the destructiveness of which at sub zero temperatures was again confirmed by contrast alunogen and gypsum had little or no effect on rates of frost weathering either singly or in combination combining halite and gypsum produced breakdown that was intermediate between that of the two salts individually as did the combination of gypsum and potassium alum breakdown in solutions of ammonium alum and gypsum and in a combination of potassium and ammonium alum with gypsum caused greater breakdown over 25 cycles of freeze thaw than was recorded with the salts singly the results extend the range of salts known to enhance frost weathering and show that it is difficult to predict the aggressiveness of combinations of salts by experimenting with each salt separately copyright 2001 john wiley sons ltd

vertical mode decompositions of 2 day waves and the madden julian oscillation abstract vertical structures of 2 day waves and the madden julian oscillation mjo are projected onto vertical normal modes for a quiescent tropical troposphere three modes capture the gross tropospheric structure of 2 day waves while only two modes are needed to represent most of the baroclinic structure of the mjo deep circulations that project onto the first baroclinic mode are associated with deep cumulonimbus and stratiform rainfall shallow circulations that project onto higher wavenumber modes are associated with precipitating shallow cumulus and congestus and stratiform rainfall for both disturbances the horizontal divergence contributed by shallow modes is an important factor in the column integrated moist enthalpy budget these modes converge moist static energy for a time prior to when deep circulations export moist static energy these results highlight the importance of properly representing the effects of shallow cumulus congestus and stratiform precipitation in theories of convective

the influence of cross equatorial pressure gradients on the location of near equatorial convection tomas and webster note that in regions where there is a substantial cross equator surface pressure gradient there is locally anticyclonic absolute vorticity on the low pressure side of the equator and thus the flow in this region meets the parcel criterion for inertial instability they hypothesize that the atmospheric response to this absolute vorticity distribution is a convergence divergence doublet in the boundary layer the convergence centre results in strong convection and thus is very important in determining the strength and location of convection i e the intertropical convergence zones whereas the divergence centre results in suppressed convection in this work a zonally symmetric model of the boundary layer is developed to investigate this hypothesis further an analysis of a linearized version of the model indicates that although the observed flow in these regions meets the parcel criterion for instability it does not satisfy the linear stability criteria because of the stabilizing influence of dissipation and the finite vertical scale much greater shear than that observed is required for linear instability it is noted however that when the parcel criterion is met one of the nonlinear terms which was neglected in the linear analysis may have an important influence on the flow several experiments are performed integrating the full nonlinear model relaxing back to a pressure distribution having a cross equatorial gradient to test whether the observed vorticity wind and convergence distributions can be well simulated it is found that the simulations reach a steady state in which there is a region of locally anticyclonic absolute vorticity on the low pressure side of the equator this absolute vorticity distribution results in an anomalous acceleration of the meridional wind and a convergence divergence doublet similar to that observed by tomas and webster this response is explained as resulting from accelerations that act to bring the zonal flow out of geostrophic balance as it passes through the region of locally anticyclonic absolute vorticity the response of the meridional wind to the strength of the pressure gradient is quasi linear for small and somewhat larger values of forcing but between these values there is a range where the response is highly nonlinear i e large increases in the strength of the meridional wind result from small changes in the pressure gradient it is suggested that this nonlinear response may play a role in the observed sudden onset of the monsoon circulations the nonlinear model is also forced using pressure distributions taken from observations the resulting steady state simulated vorticity wind and convergence distributions closely match the observations for the cases of pressure distributions taken from the east pacific and east atlantic during july when forced using the pressure distribution from the indian ocean region during july the model produces an unrealistically strong meridional wind response some improvement is obtained by including the latitudinally dependent zonal pressure gradient force which is moderately strong in this region finally the model is forced using a pressure distribution taken from observations in the central pacific ocean during july in this case the cross equator pressure gradient is near zero

slow variability in the equatorial west central pacific in relation to enso abstract six years of upper ocean velocity temperature and surface wind data collected in the west central pacific at 0 170 w reveal a slow ocean dynamical mode associated with the el nino southern oscillation enso latent and sensible heat flux calculations using the basin wide tropical atmosphere ocean tao array data show a coincident slow ocean atmosphere thermodynamical mode beginning with the la nina conditions in 1988 through the peak el nino conditions in 1992 the equatorial undercurrent euc speed decreased along with the surface zonal wind stress and the zonal pressure gradient simultaneous with these were increasing trends in the richardson number above the euc core and in sea surface temperature sst after peak warming was achieved the variations in all of these quantities reversed in a movement toward their previous la nina conditions as this evolved within the ocean the sensible and latent heat fluxes increased with large values emanating eastward from the western pacific the

extended wind stress analyses for enso abstract surface wind stresses are fundamental to understanding el nino yet most observational stress products are too short to permit multidecadal enso studies two exceptions are the florida state university subjective analysis fsu1 and the ncep ncar reanalysis ncep1 which are widely used in climate research here the focus is on the aspects of the stress most relevant to enso namely the climatological background anomaly spectrum response to sst changes subannual noise forcing and seasonal phase locking and how these differ between fsu1 and ncep1 over the tropical pacific for 1961 99 the ncep1 stress climatology is distinguished from fsu1 by weaker equatorial easterlies stronger off equatorial cyclonic curl stronger southerlies along the peruvian coast and weaker convergence zones with weaker seasonality compared to fsu1 the ncep1 zonal stress anomalies x are weaker less noisy and show less persistent westerly peaks during el nino events ncep1 also shows a more stationary spec

estimates of large scale divergence in the lower troposphere over the western equatorial pacific a network of 915 mhz wind profilers measured half hourly lower tropospheric winds over the western equatorial pacific with vertical resolutions as high as 100 m during november 1992 through february 1993 the intensive observing period iop of the tropical ocean global atmosphere coupled ocean atmosphere response experiment toga coare these wind data are used in conjunction with collocated surface wind measurements to examine the near surface divergent flow over the western pacific warm pool during austral summer as well as the synoptic scale variability of divergence in both time and space the synoptic scale wind field estimated from profiler data exhibits stronger near surf ace divergence than sonde based estimates from the same time period temporal variations of the lower tropospheric divergence profiles are described by three vertical structure functions derived from varimax rotated eigenvector analysis one vertical mode appears to be associated with deep convection one with near surface processes and one with shallower convection these structure functions vary zonally across the coare region with the convective modes having convergence maxima at lower elevations to the west of the intensive flux array ifa than over and east of it