mechanisms limiting the northward extent of the northern summer monsoons over north america asia and africa abstract mechanisms determining the poleward extent of summer monsoon convergence zones for north america asia and africa are examined in an intermediate atmospheric model coupled with a simple land model and a mixed layer ocean observations show that thermodynamical factors associated with the net heat flux into the atmospheric column provide favorable conditions for the monsoon convergence zone to extend farther poleward than actually occurs to understand the discrepancy a series of experiments are designed to test the importance of mechanisms previously examined in the south american case by the authors namely soil moisture ventilation and the interactive rodwell hoskins mechanism the latter refers to the interaction between baroclinic rossby wave dynamics and convective heating in north america experiments suggest that ventilation by both temperature and moisture advection is a leading effect the interactive rodwell hoskins mechanism tends to favor east coast rainfall and west coast dryne

simulated effect of a forest road on near surface hydrologic response and slope stability forest management practices often result in significant changes to hydrologic and geomorphic responses at or near the earth s surface a well known but not fully tested hypothesis in hillslope hydrology geomorphology is that a near surface permeability contrast caused by the surface compaction associated with forest roads can result in diverted subsurface flow paths that produce increased up slope pore pressures and slope failure the forest road focused on in this study is located in a steep forested zero order catchment within the h j andrews experimental forest oregon a three phase modelling effort was employed to test the aforementioned hypothesis i two dimensional vertical slice steady state heterogeneous saturated subsurface flow simulations at the watershed scale for establishing the boundary conditions for the catchment scale boundary value problem in ii ii two dimensional vertical slice transient heterogeneous variably saturated subsurface flow simulations at the catchment scale for estimating near surface hydrologic response and pore pressure distributions and iii slope stability analyses using the infinite slope approach driven by the pore pressure distributions simulated in ii for assessing the impact of the forest road both observed and hypothetical rainfall events are used to drive the catchment scale simulations the results reported here support the hypothesis that a forest road can have an effect on slope stability the permeability contrast associated with the forest road in this study led to a simulated altering of slope parallel subsurface flow with increased pore pressures up slope of the road and for a large rainfall event a slope failure prediction copyright 2005 john wiley sons ltd

deriving mechanisms and thresholds for cliff retreat in soft rock cliffs under changing climates rapidly retreating cliffs of the suffolk coast uk abstract understanding changing thresholds and mechanisms for retreat in soft rock cliffs is important under changing climates this can be achieved through combining detailed field observation long term process and morphological monitoring and numerical modelling the cliffs of the suffolk coast southern north sea have exhibited long term 1883 2010 recession rates of 3 5 m a 1 rising to 4 7 m a 1 in the period 1993 2010 annual to biannual ground survey data and the application of gis techniques to digitised records of changing shoreline position from historic maps and aerial photography reveal considerable decadal scale variations in cliff recession within which are nested inter annual fluctuations in rates of retreat archival datasets on significant periods of onshore winds and their interaction with high water levels including the incidence of storm surges and rainstorm events are used to determine thresholds for cliff base erosion and its propagation upwards through the cliff profile in addition the geo slope dynamic coupled hydrology stability model is used to establish thresholds for cliff face failures driven by variations in rainfall inputs retreat mechanisms are complex governed by cliff geology both as a primary control on suction loss and through its interaction with basal marine conditions the study allows a general model of cliff retreat for soft rock cliffs to be put forward whereby a resistant basal platform is overlain by more erodible weakly and moderately cemented sands and gravels in this model the varying balance between marine and terrestrial forcing factors are reflected in low 7 m a 1 modes of cliff retreat

transient seepage model for saturated unsaturated soil systems a geotechnical engineering approach a two dimensional finite element model is proposed to simulate transient seepage for complex groundwater flow systems the complete soil system is treated as a continuum encompassing flow in both saturated and unsaturated zones in the unsaturated zone the air phase is assumed to be continuous and open to atmospheric pressure the coefficient of permeability of the unsaturated soil is assumed to be a function of pore water pressure the governing differential equation is derived within a framework familiar to geotechnical engineers the stress state variables and the constitutive relationships for an unsaturated soil are used in the derivation the finite element solution to the governing differential equation is based on the galerkin weighted residual method the nonlinearity of the equation is solved by iterative procedures the finite element formulation is implemented into a computer model named trasee the model can be applied to a wide variety of problems involving complex boundary conditions and geo

orographic effects of the tibetan plateau on the east asian summer monsoon an energetic perspective this paper investigates the dynamical processes through which the tibetan plateau tp influences the east asian summer monsoon easm within the framework of the moist static energy mse budget using both observations and atmospheric general circulation model agcm simulations the focus is on the most prominent feature of the easm the so called meiyu baiu mb which is characterized by a well defined southwest northeast elongated quasi stationary rainfall band spanning from eastern china to japan and into the northwestern pacific ocean between mid june and mid july observational analyses of the mse budget of the mb front indicate that horizontal advection of moist enthalpy and primarily of dry enthalpy sustains the front in a region of otherwise negative net energy input into the atmospheric column a decomposition of the horizontal dry enthalpy advection into mean transient and stationary eddy fluxes identifies the longitudinal thermal gradient due to zonal asymmetries and the meridional stationary eddy velocity as the most influential factors determining the pattern of horizontal moist enthalpy advection numerical simulations in which the tp is either retained or removed show that the tp influences the stationary enthalpy flux and hence the mb front primarily by changing the meridional stationary eddy velocity with reinforced southerly wind over the mb region and northerly wind to its north changes in the longitudinal thermal gradient are mainly confined to the near downstream of the tp with the resulting changes in zonal warm air advection having a lesser impact on the rainfall in the extended mb region

subtropical anticyclones and summer monsoons the summer subtropical circulation in the lower troposphere is characterized by continental monsoon rains and anticyclones over the oceans in winter the subtropical circulation is more strongly dominated by the zonally averaged flow and its interactions with orography here the mechanics of the summer and winter lowertropospheric subtropical circulation are explored through the use of a primitive equation model and comparison with observations by prescribing in the model the heatings associated with several of the world s monsoons it is confirmed that the equatorward portion of each subtropical anticyclone may be viewed as the kelvin wave response to the monsoon heating over the continent to the west a poleward flowing low level jet into a monsoon such as the great plains jet is required for sverdrup vorticity balance this jet effectively closes off the subtropical anticyclone to the east and also transports moisture into the monsoon region the low level jet into north america induced by its monsoon heating is augmented by a remote response to the asian monsoon heating the rossby wave response to the west of subtropical monsoon heating interacting with the midlatitude westerlies produces a region of adiabatic descent it is demonstrated here that a local diabatic enhancement can lead to a strengthening of the descent longitudinal mountain chains act to block the westerly flow and also tend to produce descent in this region below the descent sverdrup vorticity balance implies equatorward flow that closes off the subtropical anticyclone to the west and induces cool upwelling in the ocean through ekman transport feedbacks involving for example sea surface temperatures may further enhance the descent in these regions the conclusion is that the mediterranean type climates of regions such as california and chile may be induced remotely by the monsoon to the east hence it can be argued that the subtropical circulation in summer comprises a set of weakly interacting monsoon systems each involving monsoon rains a low level poleward jet a subtropical anticyclone to the east and descent and equatorward flow to the west in winter it is demonstrated how the nonlinear interaction between the strong zonal mean circulation associated with the winter hadley cell and the mountains can define many of the large scale features of the subtropical circulation the blocking effect of the longitudinal mountain chains is shown to be very important subsequent diabatic effects such as a local diabatic enhancement would appear to be essential for producing the observed amplitude of these features

role of seasonal transitions and the westerlies in the interannual variability of the east asian summer monsoon precipitation a recent hypothesis holds that changes to the east asian summer rainfall are characterized by changes in the timing and duration of its intraseasonal stages controlled by the meridional position of the westerlies relative to the tibetan plateau this hypothesis is examined in the context of the leading mode of east asian summer july aug rainfall one phase of this tripole mode characterized by less rainfall over central eastern china and increased rainfall over northeastern and southeastern china is tied to an earlier termination of meiyu that results in a significantly shorter meiyu and longer midsummer stage this phase also exhibits an earlier northward transition of the westerlies to the north of the plateau essentially mirroring the changes to precipitation seasonality the reverse does not hold true for the opposite phase our results show direct observational evidence for the meridional position of the westerlies to control east asian summer monsoon seasonality

interaction of the westerlies with the tibetan plateau in determining the mei yu termination abstractthis study explores how the termination of the mei yu is dynamically linked to the westerlies impinging on the tibetan plateau it is found that the mei yu stage terminates when the maximum

nonlinear intraseasonal phases of the east asian summer monsoon extraction and analysis using self organizing maps abstractthe hypothesis that regional characteristics of the east asian summer monsoon easm result from the presence of nonlinear coupled features that modulate the seasonal circulation and rainfall at the intraseasonal time scale is advanced in this study to examine this hypothesis the authors undertake the analysis of daily easm variability using a nonlinear multivariate data classifying algorithm known as self organizing mapping som on the basis of various som node analyses four major intraseasonal phases of the easm are identified the first node describes a circulation state corresponding to weak tropical and subtropical pressure systems strong upper level jets weakened monsoonal winds and cyclonic upper level vorticity this mode related to large rainfall anomalies in southeast china and southern japan is identified as the mei yu baiu phase the second node represents a distinct circulation state corresponding to a strengthened subtropical high monsoonal winds and anticyclonic upper lev

the mechanical impact of the tibetan plateau on the seasonal evolution of the south asian monsoon the impact of the tibetan plateau on the south asian monsoon is examined using a hierarchy of atmospheric general circulation models during the premonsoon season and monsoon onset april june when westerly winds over the southern tibetan plateau are still strong the tibetan plateau triggers early monsoon rainfalldownstream particularlyoverthebay ofbengalandsouth china the downstreammoist convection is accompanied by strong monsoonal low level winds in experiments where the tibetan plateau is removed monsoon onset occurs about a month later but the monsoon circulation becomes progressively stronger and reaches comparable strength during the mature phase during the mature and decaying phase of monsoon july september when westerly winds over the southern tibetan plateau almost disappear monsoon circulation strength is not much affected by the presence of the tibetan plateau a dry dynamical core with east west oriented narrow mountains in the subtropics consistently simulates downstream convergence with background zonal westerlies over the mountain in a moist atmosphere the mechanically driven downstream convergence is expected to be associated with significant moisture convergence the authors speculate that the mechanically driven downstream convergence in the presence of the

role of seasonal transitions and westerly jets in east asian paleoclimate abstract the summer rainfall climate of east asia underwent large and abrupt changes during past climates in response to precessional forcing glacial interglacial cycles as well as abrupt changes to the north atlantic during the last glacial however current interpretations of said changes are typically formulated in terms of modulation of summer monsoon intensity and do not account for the known complexity in the seasonal evolution of east asian rainfall which exhibits sharp transition from the spring regime to the meiyu and then again from the meiyu to the summer regime we explore the interpretation that east asian rainfall climate undergoes a modulation of its seasonality during said paleoclimate changes following previous suggestions we focus on role of the westerly jet over asia namely that its latitude relative to tibet is critical in determining the stepwise transitions in east asian rainfall seasons in support of this linkage we show from observational data that the interannual co variation of june july august rainfall and upper tropospheric zonal winds show properties consistent with an altered timing of the transition to the meiyu summer and with more northward shifted westerlies for earlier transitions we similarly suggest that east asian paleoclimate changes resulted from an altered timing in the northward evolution of the jet and hence the seasonal transitions in particular the transition of the jet from south of the plateau to the north that determines the seasonal transition from spring rains to the meiyu in an extreme scenario which we speculate the climate system tended towards during stadial cold phases of d o stadials and periods of low northern hemisphere summer insolation the jet does not jump north of the plateau essentially keeping east asia in prolonged spring conditions we argue that this hypothesis provides a viable explanation for a key paleoproxy signature of d o stadials over east asia namely the heavier mean 18o of precipitation as recorded in speleothem records the southward jet position prevents the low level monsoonal flow which is isotopically light from penetrating into the interior of east asia as such precipitation there will be heavier consistent with speleothem records this hypothesis can also explain other key evidences of east asian paleoclimate changes in particular the occurrence of dusty conditions during north atlantic stadials and the southward migration of the holocene optimal rainfall

the effects of orography on midlatitude northern hemisphere dry climates abstract the role of mountains in maintaining extensive midlatitude arid regions in the northern hemisphere was investigated using simulations from the gfdl global climate model with and without orography in the integration with mountains dry climates were simulated over central asia and the interior of north america in good agreement with the observed climate in contrast moist climates were simulated in the same regions in the integration without mountains during all season but summer large amplitude stationary waves occur in response to the tibetan plateau and rocky mountains the midlatitude dry regions are located upstream of the troughs of these waves where general subsidence and relatively infrequent storm development occur and precipitation is thus inhibited in summer this mechanism contributes to the dryness of interior north america as a stationary wave trough remains east of the rockies but is not effective in eurasia due to seasonal changes in the atmospheric circulation the dryness

seasonal transitions and the westerly jet in the holocene east asian summer monsoon abstractthe holocene east asian summer monsoon easm was previously characterized as a trend toward weaker monsoon intensity paced by orbital insolation it is demonstrated here that this evolution is more accurately characterized as changes in the transition timing and duration of the easm seasonal stages spring pre mei yu mei yu midsummer and tied to the north south displacement of the westerlies relative to tibet to this end time slice simulations across the holocene are employed using an atmospheric general circulation model self organizing maps are used to objectively identify the transition timing and duration of the easm seasonal stages compared to the late holocene an earlier onset of mei yu and an earlier transition from mei yu to midsummer in the early to mid holocene are found resulting in a shortened mei yu and prolonged midsummer stage these changes are accompanied by an earlier northward positioning of the westerlies relative to tibet invoking changes to seasonal transitions al

the contribution of landslides to landscape evolution in europe abstract after a review of some analytical and conceptual models of slope evolution with the intervention of mass movements a proposal is made of a series of indicators for the quantitative description of landscape evolution in relation to mass movements the ratio between landslide mobilisation rate and downwearing rate is proposed as a quantitative measure of the significance of mass movements in landscape evolution a subdivision of european regions with respect to their susceptibility to landsliding as a process of landscape evolution is proposed the role of landsliding for the evolution of landscape in some regions is described the data presented show that landsliding may in some cases be the main contributor to landscape change

groundwater modelling of a weathered gneissic cover knowledge of the groundwater regime which is generally necessary in studying the stability of slopes is of fundamental importance in the analysis of landslides involving intensely weathered rocks as in the case of a landslide in the western sila massif southern italy reactivated by heavy and prolonged rainfall for this landslide the total absence of displacements during the actual quiescence period and the long return period of the critical rainfall events did not allow measurement of the critical pore pressures capable of reactivating the landslide to solve such a problem a saturated unsaturated flow model was calibrated taking into account in situ pore pressure measurements acquired over a long period of time the analyses permitted determination of the role played by the hydraulic heterogeneity of the involved soils and the hydraulic boundary conditions for simulation of the response of in situ pore pressures to rainfall such conditions were therefore used to predict the critical unknown valu

the different configurations of the east asian polar front jet and subtropical jet and the associated rainfall anomalies over eastern china in summer abstractto investigate the concurrent impacts of the east asian polar front jet eapj and subtropical jet easj on the summer rainfall over eastern china positive strengthened eapj with weakened easj and negative weakened eapj with strengthened easj configurations are identified in the positive configuration rainfall decreases in the northern part of eastern china and increases in the southern part vice versa in the negative configuration the possible mechanisms maintaining the two jet configurations are further proposed from the perspectives of sea surface temperature sst and synoptic scale transient eddy activities stea in the positive configuration meridional distributed cold warm sst anomalies over the eastern north pacific may induce regional circulation and meridional temperature gradient anomalies which can strengthen the eapj and weaken the easj the central pacific la nina like sst anomalies are related with the arctic vortexlike anomalies in the stratosphere which may strength

the formation mechanism of the bonin high in august the bonin high is a subtropical anticyclone that is predominant near japan in the summer this anticyclone is associated with an equivalent barotropic structure often extending throughout the entire troposphere although the equivalent barotropic structure of the bonin high has been known for years among synopticians because of its importance to the summer climate in east asia there are few dynamical explanations for such a structure the present paper attempts to provide a formation mechanism for the deep ridge near japan we propose a new hypothesis that this equivalent barotropic ridge near japan is formed as a result of the propagation of stationary rossby waves along the asian jet in the upper troposphere the silk road pattern first the monthly mean climatology is examined in order to demonstrate this hypothesis it is shown that the enhanced asian jet in august is favourable for the propagation of stationary rossby waves and that the regions of descent over the eastern mediterranean sea and the aral sea act as two major wave sources second a primitive equation model is used to simulate the climatology of august the model successfully simulates the bonin high with an equivalent barotropic structure the upper tropospheric ridge is found to be enhanced by a height anomaly of more than 80 m at 200 hpa when a wave packet arrives sensitivity experiments are conducted to show that the removal of the diabatic cooling over the asian jet suppresses the silk road pattern and formation of an equivalent barotropic ridge near japan while the removal of the diabatic heating in the western pacific does not copyright 2003 royal meteorological society

effect of the east asian westerly jet s intensity on summer rainfall in the yangtze river valley and its mechanism abstractmany studies have shown that the northward southward displacement of the east asian westerly jet eawj drastically reduces increases summer rainfall in the yangtze river valley yrv however the effect of the jet s intensity on interannual variation in summer rainfall has not been systematically studied the present study investigates the effect of the eawj s intensity on this interannual variation and analyzes the mechanism by which this process occurs in early summer the eawj consists of two branches one located over northern continental east asia western branch eawjwb and one extending from southern china to the northern pacific eastern branch eawjeb the former merges into the latter over the yellow sea a stronger eawjeb leads to increased rainfall in the yrv while the eawjwb does not significantly affect rainfall in the yrv the faster eawjeb directly strengthens midtropospheric warm advection over the yrv because the corresponding changes in the meridional wind and horizo

monsoons itczs and the concept of the global monsoon earth s tropical and subtropical rainbands such as intertropical convergence zones itczs and monsoons are complex systems governed by both large scale constraints on the atmospheric general circulation and regional interactions with continents and orography and coupled to the ocean monsoons have historically been considered as regional large scale sea breeze circulations driven by land sea contrast more recently a perspective has emerged of a global monsoon a global scale solstitial mode that dominates the annual variation of tropical and subtropical precipitation this results from the seasonal variation of the global tropical atmospheric overturning and migration of the associated convergence zone regional subsystems are embedded in this global monsoon localized by surface boundary conditions parallel with this much theoretical progress has been made on the fundamental dynamics of the seasonal hadley cells and convergence zones via the use of hierarchical modeling approaches including aquaplanets here we review the theoretical progress made and explore the extent to which these advances can help synthesize theory with observations to better understand differing characteristics of regional monsoons and their responses to certain forcings after summarizing the dynamical and energetic balances that distinguish an itcz from a monsoon we show that this theoretical framework provides strong support for the migrating convergence zone picture and allows constraints on the circulation to be identified via the momentum and energy budgets limitations of current theories are discussed including the need for a better understanding of the influence of zonal asymmetries and transients on the large scale tropical circulation

petroleum geochemistry of oil and gas from barbados implications for distribution of cretaceous source rocks and regional petroleum prospectivity petroleum produced from the barbados accretionary prism at woodbourne field on barbados is interpreted as generated from cretaceous marine shale deposited under normal salinity and dysoxic conditions rather than from a tertiary source rock as previously proposed barbados oils correlate with some oils from eastern venezuela and trinidad that are positively correlated to extracts from upper cretaceous la luna like source rocks three distinct groups of barbados oils are recognized based on thermal maturity suggesting petroleum generation occurred at multiple levels within the barbados accretionary prism biodegradation is the most significant process affecting barbados oils resulting in increased sulfur content and decreased api gravity barbados gases are interpreted as thermogenic having been co generated with oil and show mixing with biogenic gas is limited gas biodegradation occurred in two samples collected from shallow reservoirs at the woodbourne field the presence of cretaceous source rocks within the barbados accretionary prism suggests that greater petroleum potential exists regionally and perhaps further southeast along the passive margin of south america likewise confirmation of a cretaceous source rock indicates petroleum potential exists within the barbados accretionary prism in reservoirs that are deeper than those from woodbourne field

effects of soil moisture dynamics on slope failure at hyrum reservior utah field observations of shoreline conditions at hyrum reservoir utah were conducted during the summers of 1991 to 1993 a process of bluff retreat is described for a multiple layered bluff environment of sand and clay layers failure is initiated by wetting and drying of clay sediments which produces horizontal cracks within bluff material these cracks appear to penetrate to a depth of approximately 100 150 mm before initiating vertical cracking in the sediments the vertical cracks are propagated by continued drying of the surface sediment ultimately leading to failure of the bluff material the physical dimensions of sediment blocks succumbing to this mechanism range from a few hundred millimetres up to 3 m on a side with a depth of approximately 100 150 mm the mechanism described here appears to operate optimally when the supply of subsurface moisture is abundant and nearly continuous throughout the spring and early summer reservoir draw down large capillary fringe effects in the bluff and periodic wetting from upslope undrained hollows are the dominant moisture controls at this site moisture delivery to the face is strongly influenced by anisotropy of saturated hydraulic conductivity in the alternating clay and sand layers and related differences in sediment texture

on the three dimensional propagation of stationary waves abstract a locally applicable nonzonally averaged conservation relation is derived for quasi geostrophic stationary waves on a zonal flow a generalization of the eliassen palm relation the flux which appears in this relation constitutes it is argued a useful diagnostic of the three dimensional propagation of stationary wave activity this is illustrated by application to a simple theoretical model of a forced rossby wave train and to a northern hemisphere winter climatology results of the latter procedure suggest that the major forcing of the stationary wave field derives from the orographic effects of the tibetan plateau and from nonorographic effects diabatic heating and or interaction with transient eddies in the western north atlantic and north pacific oceans and siberia no evidence is found in the data for wave trains of tropical origin forcing by the orographic effects of the rocky mountains seems to be of secondary importance

the continuum of northern hemisphere teleconnection patterns and a description of the nao shift with the use of self organizing maps abstract in this study the method of self organizing maps soms is used with ncep ncar reanalysis data to advance the continuum perspective of northern hemisphere teleconnection patterns and to shed light on the secular eastward shift of the north atlantic oscillation nao that began in the late 1970s a 20 pattern som analysis of daily wintertime northern hemisphere sea level pressure reveals a continuum of patterns that correspond closely with well known teleconnection patterns this analysis also reveals that interdecadal variability of the hemispheric sea level pressure field may be understood in terms of changes in the frequency distribution within the continuum of sea level pressure patterns described by the som based on the continuum perspective illustrated with the som the above secular shift of the nao may be understood as a change in dominance from westward displaced negative nao like patterns to eastward displaced positive nao like patterns though westward and eastward displaced nao

changing character of rainfall in eastern china 1951 2007 the topography and continental configuration of east asia favor the year round existence of storm tracks that extend thousands of kilometers from china into the northwestern pacific ocean producing zonally elongated patterns of rainfall that we call frontal rain events in spring and early summer known as meiyu season frontal rainfall intensifies and shifts northward during a series of stages collectively known as the east asian summer monsoon using a technique called the frontal rain event detection algorithm we create a daily catalog of all frontal rain events in east china during 1951 2007 quantify their attributes and classify all rainfall on each day as either frontal resulting from large scale convergence or nonfrontal produced by local buoyancy topography or typhoons our climatology shows that the east asian summer monsoon consists of a series of coupled changes in frontal rain event frequency latitude and daily accumulation furthermore decadal changes in the amount and distribution of rainfall in east china are overwhelmingly due to changes in frontal rainfall we attribute the south flood north drought pattern observed beginning in the 1980s to changes in the frequency of frontal rain events while the years 1994 2007 witnessed an uptick in event daily accumulation relative to the rest of the study years this particular signature may reflect the relative impacts of global warming aerosol loading and natural variability on regional rainfall potentially via shifting the east asian jet stream

multiple seepage faces on layered slopes and their implications for slope stability analysis this study provides an analysis of the water table configuration and pore pressure distribution in layered hillsides a finite element model was used to simulate two dimensional saturated unsaturated steady state flow through layered slopes a laboratory sand tank experiment was used to verify the physical foundation of the mathematical model it is shown that layered slopes feature multiple seepage faces perched water tables and wedge shaped unsaturated zones the pore pressure distribution and the distribution of multiple seepage faces are strongly dependent on the position of the impeding layers and their hydraulic properties predictions of pore pressure fields based on homogeneous saturated analyses may be significantly in error when applied to problems on layered slopes slope stability analyses on layered slopes that do not take into account the presence of unsaturated wedges beneath the impeding layers can lead to overdesign of the stable slope angle key words groundwater conditions unsatu

formation and distribution of heavy oil and tar sands in china on the basis of geological and geochemical data mainly from china combined with data from other countries it is found that formation and distribution of global heavy oil and tar sands is controlled by alpine tectonic movements they form two accumulation belts the alpine and the circum pacific heavy oils and tar sands in western and eastern china belong to alpine himalayan belt and circum pacific belt respectively the geochemical data shows that the progressive sequence of resistance of polycyclic aromatic hydrocarbons to biodegradation is triaromatic steroid hydrocarbons chrysene series phenanthrene series and naphthalene series a certain amount of heavy oil in china originates from immature or low maturity oil which is much higher in viscosity and in the hetero compound fraction content than mature oil heavy oil and tar sands in china are widely distributed and abundant it is estimated that the undiscovered heavy oil resources are 25 billion tons meanwhile the potential of tar sands resources is also great

remote sensing detection of heavy oil through spectral enhancement techniques in the western slope zone of songliao basin china landsat 7 enhanced thematic mapper plus etm imagery was used to identify anomalous areas caused by hydrocarbon leakage in fula erji in the western slope of songliao basin china three image enhancement techniques including principal component analysis pca band ratioing and false color composition fcc were used based on the spectral characteristics of hydrocarbon induced minerals and the eigenvectors of pca the best four principal components pcs 1345 pc3 the third component of the pca on bands 1 3 4 and 5 1357 pc3 3457 pc4 and 123457 pc4 were selected for fcc combined with band ratios of 3 1 4 3 and 7 5 according to the tonal characteristics of the surface near wells and their visual expression four fcc images were acquired for hydrocarbon induced area delineation the result indicates that anomalies are expressed as a faint tone blob and are mostly located in the holocene sediments an analysis of two cross sections traversing the identified anomalies suggests that they are closely related to the anomalous area interpreted from the four fcc images field data of magnetic susceptibility and delta carbonate are consistent with the distribution of the tonal anomalies and suggest a positive spatial association between the identified anomalous area and the hydrocarbon leakage environment

processes of coastal bluff erosion in weakly lithified sands pacifica california usa abstract coastal bluff erosion and landsliding are currently the major geomorphic processes sculpting much of the marine terrace dominated coastline of northern california in this study we identify the spatial and temporal processes responsible for erosion and landsliding in an area of weakly lithified sand coastal bluffs located south of san francisco california using the results of a five year observational study consisting of site visits terrestrial lidar scanning and development of empirical failure indices we identify the lithologic and process controls that determine the failure mechanism and mode for coastal bluff retreat in this region and present concise descriptions of each process bluffs composed of weakly cemented sands unconfined compressive strength ucs between 5 and 30 kpa fail principally due to oversteepening by wave action with maximum slope inclinations on the order of 65 at incipient failure periods of significant wave action were identified on the basis of an empirical wave run up equation predicting failure when wave run up exceeds the seasonal average value and the bluff toe elevation the empirical relationship was verified through recorded observations of failures bluffs composed of moderately cemented sands ucs up to 400 kpa fail due to precipitation induced groundwater seepage which leads to tensile strength reduction and fracture an empirical rainfall threshold was also developed to predict failure on the basis of a 48 hour cumulative precipitation index but was found to be dependent on a time delay in groundwater seepage in some cases

seasonality and interannual variability of the westerly jet in the tibetan plateau region abstract in this study 40 yr ecmwf re analysis era 40 data are used for the description of the seasonal cycle and the interannual variability of the westerly jet in the tibetan plateau region to complement results based on the analysis of monthly mean horizontal wind speeds an occurrence based jet climatology is constructed by identifying the locations of the jet axes at 6 hourly intervals throughout 1958 2001 thus a dataset describing the highly transient and localized features of jet variability is obtained during winter and summer the westerly jet is located respectively to the south and north of the tibetan plateau during the spring and autumn seasons there are jet transitions from south to north and vice versa the median dates for these transitions are 28 april and 12 october the spring transition is associated with large interannual variations while the fall transition occurs more reliably within a 3 week period the strength of the jet exhibits a peculiar seasonal cycle during northw

the response of an idealized atmosphere to orographic forcing zonal versus meridional propagation abstracta dry atmospheric general circulation model is forced with large scale gaussian orography in an attempt to isolate a regime in which the model responds linearly to orographic forcing and then to study the departures from linearity as the orography is increased in amplitude in contrast to previous results which emphasized the meridional propagation of orographically forced stationary waves using the standard held suarez h s control climate it is found that the linear regime is characterized by a meridionally trapped zonally propagating wave meridionally trapped waves of this kind have been seen in other contexts where they have been termed circumglobal waves as the height of the orography is increased the circumglobal wave coexists with a meridionally propagating wave and for large enough heights the meridionally propagating wave dominates the response a barotropic model on a sphere reproduces this trapped wave in the linear regime and also reproduces the transition to meridional pro

processes controlling the mean tropical pacific precipitation pattern part i the andes and the eastern pacific itcz abstract the question of why the intertropical convergence zone itcz is generally north of the equator in the tropical pacific is addressed experiments with an atmospheric general circulation model coupled to idealized representations of the ocean show that the presence of the andes is enough to lower sea surface temperature sst off the west coast of south america through evaporation thus promoting a north south asymmetry with the itcz north of the equator which is amplified by interactions between the ocean and the atmosphere the evaporative cooling results mainly from the subsidence of low specific humidity air which is due in turn to the mechanical effect of the andes on the zonal mean flow the positive feedback from low level clouds on sst is an important factor for the efficiency of the mechanism described west of 120 w the presence of the rockies and himalayas produces a comparable forcing to that of the andes but this is not enough to reverse or neutralize the north south asymmetry se

zonal extension and retraction of the subtropical westerly jet stream and evolution of precipitation over east asia and the western pacific abstractthe relationship between the zonal extension and retraction of the east asian subtropical westerly jet stream easwj and the seasonal evolution of precipitation is investigated the easwj exhibits significant zonal variations associated with its seasonal evolution which affects both large scale atmospheric circulation and precipitation over east asia and the north pacific the midlatitude rain belts and the intertropical convergence zone are located more eastward and southward during jet extensions compared to jet retractions the seasonal cycle of the zonal variations of easwj can be divided into four periods december february march may june july and september november particularly in the mei yu period of june july jet retraction events are associated with a northward shift of rain belts over eastern china which may play an important role in the northward movement of the mei yu rain belt to the huaihe river valley of eastern china after 1999 the zonal extension and retraction of the jet

baiu rainband termination in atmospheric and coupled atmosphere ocean models abstractthe baiu rainband is a summer rainband stretching from eastern china through japan toward the northwestern pacific the climatological termination of the baiu rainband is investigated using the japanese 25 yr reanalysis jra 25 a stand alone atmospheric general circulation model gcm forced with observed sea surface temperature sst and an atmosphere ocean gcm aogcm the baiu rainband over the north pacific abruptly shifts northward and weakens substantially in early july in the atmospheric gcm agcm too early compared to observations late july the midtroposphere westerly jet and its thermal advection explain this meridional shift of the baiu rainband but the ocean surface evaporation modulates the precipitation intensity in agcm deep convection in the subtropical northwestern pacific sets in prematurely displacing the westerly jet northward over the cold ocean surface earlier than in observations the suppressed surface evaporation over the cold ocean suppresses precipitation even

asynchronous responses of east asian and indian summer monsoons to mountain uplift shown by regional climate modelling experiments it has been demonstrated in climate models that both the indian and east asian summer monsoons ism and easm are strengthened by the uplift of the entire asian orography or tibetan plateau tp i e bulk mountain uplift such an effect is widely perceived as the major mechanism contributing to the evolution of asian summer monsoons in the neogene however geological evidence suggests more diachronous growth of the asian orography i e regional mountain uplift than bulk mountain uplift this demands a re evaluation of the relation between mountain uplift and the asian monsoon in the geological periods in this study sensitivity experiments considering the diachronous growth of different parts of the asian orography are performed using the regional climate model cosmo clm to investigate their effects on the asian summer monsoons the results show that different from the bulk mountain uplift the regional mountain uplift can lead to an asynchronous development of the ism and easm while the ism is primarily intensified by the thermal insulation mechanical blocking effect of the southern tp zagros mountains the easm is mainly enhanced by the surface sensible heating of the central northern and eastern tp such elevated surface heating can induce a low level cyclonic anomaly around the tp that reduces the ism by suppressing the lower tropospheric monsoon vorticity but promotes the easm by strengthening the warm advection from the south of the tp that sustains the monsoon convection our findings provide new insights to the evolution of the asian summer monsoons and their interaction with the tectonic changes in the neogene

the development of multiple seepage faces on layered slopes this study provides an analysis of the water table configuration and hydraulic head distribution in layered hillsides a finite element model was used to simulate two dimensional saturated unsaturated steady state flow through layered slopes a laboratory sand tank experiment was used to verify the physical foundation of the mathematical model it is shown that layered slopes feature multiple seepage faces perched water tables and wedge shaped unsaturated zones the hydraulic head distribution and water table configuration are strongly dependent on the position of the impending layers and the ratio of the hydraulic conductivity between adjacent layers this work has geotechnical implications with regard to slope stability and the control of groundwater inflows into excavations it has hydrogeological implications with regard to flow path analysis in contamination studies it has geomorphological implications with respect to landform development by mass movements and surface water erosions and to drainage network development through piping

instability caused by a seepage impediment in layered fill slopes the underlying cause of loose fill slope failures in hong kong has been attributed to static liquefaction during heavy rainfall a series of centrifuge model tests and numerical analyses were condu

large scale dynamics of the meiyu baiu rainband environmental forcing by the westerly jet abstract meiyu baiu is the major rainy season from central china to japan brought by a zonally elongated rainband from june to mid july large scale characteristics and environmental forcing of this important phenomenon are investigated based on a reanalysis dataset the meiyu baiu rainband is accompanied by a trough of sea level pressure horizontal shears and sharp moisture gradients near the surface a westerly jet tilted northward with height and large northeastward moisture transport from the south the analysis here reveals the westerly jet as an important culprit for meiyu baiu along the rainband mean ascending motion corresponds well with a band of warm horizontal temperature advection in the midtroposphere throughout summer this adiabatic induction of upward motion originates from the advection of warm air by the westerlies from the eastern flank of the tibetan plateau the ascending motion both induces convection and is enhanced by the resultant condensational heating the westerly jet anch

examination of the seepage face boundary condition in subsurface and coupled surface subsurface hydrological models a seepage face is a nonlinear dynamic boundary that strongly affects pressure head distributions water table fluctuations and flow patterns its handling in hydrological models especially under complex conditions such as heterogeneity and coupled surface subsurface flow has not been extensively studied in this paper we compare the treatment of the seepage face as a static dirichlet versus dynamic boundary condition we assess its resolution under conditions of layered heterogeneity we examine its interaction with a catchment outlet boundary and we investigate the effects of surface subsurface exchanges on seepage faces forming at the land surface the analyses are carried out with an integrated catchment hydrological model numerical simulations are performed for a synthetic rectangular sloping aquifer and for an experimental hillslope from the landscape evolution observatory the results show that the static boundary condition is not always an adequate stand in for a dynamic seepage face boundary condition especially under conditions of high rainfall steep slope or heterogeneity that hillslopes with layered heterogeneity give rise to multiple seepage faces that can be highly dynamic that seepage face and outlet boundaries can coexist in an integrated hydrological model and both play an important role and that seepage faces at the land surface are not always controlled by subsurface flow the paper also presents a generalized algorithm for resolving seepage face outflow that handles heterogeneity in a simple way is applicable to unstructured grids and is shown experimentally to be equivalent to the treatment of atmospheric boundary conditions in subsurface flow models

southward shift of westerlies intensifies the east asian early summer rainband following el nino author s kong w chiang jch abstract 2020 american geophysical union all rights reserved an intensification of east asian rainfall usually occurs in summers following el nino we propose that this teleconnection is mediated via the westerlies impinging on the tibetan plateau through el nino s control on tropical tropospheric temperature this is distinct from previous studies that attribute the el nino s influence to changes in the western pacific subtropical anticyclone the warming in the eastern equatorial pacific leads to uniform warming of the entire tropical troposphere which sharpens the temperature gradient between the tropics and the subtropics and shifts the westerlies southward the westerlies impinge over the tibetan plateau for longer and through interaction with the topography induce intense and persistent extratropical northerlies downstream of the plateau that in turn intensifies the east asian rainband the rainband has previously been shown to intensify in a similar manner in a warming climate suggesting that the el nino response provides an analog for future changes

effects of mountain uplift on east asian summer climate investigated by a coupled atmosphere ocean gcm abstract to study the effects of progressive mountain uplift on east asian summer climate a series of coupled general circulation model cgcm experiments were performed eight different mountain heights were used 0 no mountain 20 40 60 80 100 control run 120 and 140 the land sea distribution is the same for all experiments and mountain heights are varied uniformly over the entire globe systematic changes in precipitation pattern and circulation fields as well as sea surface temperature sst appeared with progressive mountain uplift in summertime precipitation area moves inland on the asian continent with mountain uplift while the pacific subtropical anticyclone and associated trade winds become stronger the mountain uplift resulted in an sst increase over the western tropical pacific and the maritime continent and an sst decrease over the western indian ocean and the central subtropical pacific there is a drastic change in the east asian circulations with the threshold value

on slope instability induced by seepage erosion this paper is focused on seepage erosion causing liquefaction processes and rapid slope failures one case history which occurred along an old fluvial terrace in the po plain northern italy is

the meridional displacement of the summer asian jet silk road pattern and tropical sst anomalies abstractthe silk road pattern srp which depicts the teleconnection pattern along the asian jet has been extensively investigated and commonly described as the leading mode of upper tropospheric meridional wind anomalies in summer in this study the srp is identified as having a significant relationship with the meridional displacement of the asian jet jmd which manifests as the leading mode of upper tropospheric zonal wind anomalies this significant relationship is confirmed by the correlation coefficient between the indices for jmd and srp which is 0 39 and reaches statistical significance at the 0 01 level when the asian jet is in a northward southward displacement the phase of srp tends to be shown as anticyclonic cyclonic anomalies over western asia and east asia and cyclonic anticyclonic anomalies over europe and central asia the authors propose an internal atmospheric mechanism for this relationship in addition it is found that the jmd is significantly affected by the tropical s