viscosity and finite strength of the mantle as determined from water and ice loads summary some recent examples of transient earth loads lake bonneville utah glacier bay alaska northeast greenland indicate that both the viscosity and finite strength of the mantle are lower than is commonly presumed a time constant 1 e of 4000 years is estimated for lake bonneville and of 1000 years for northeast greenland a strain rate of 10 14 is typical these figures imply viscosities in a homogeneous half space ranging from 1020 to 1021 poises an upper limit of finite strength is set by lake bonneville at a few times 106 dyn cm2 if mountain ranges like the sierra nevada or himalaya are regarded as dynamically supported rather than static systems this low value is not incompatible with other geologic observations

intraplate extensional tectonics of the eastern basin range inferences on structural style from seismic reflection data regional tectonics and thermal mechanical models of brittle ductile deformation the general lack of a correlation between earthquakes and surface faulting in the interior of the western u s cordillera has motivated our efforts to evaluate the geometry structural style and mechanism of normal faulting characteristic of this region of intraplate extension to address the problem we have interpreted over 1500 km of seismic reflection data and constructed detailed cross sections of the upper crust rheological models of the continental crust were calculated to examine the possibility of shallow quasi plastic flow and its influence on faulting in the eastern basin range the western colorado plateau and the middle rocky mountains our data and interpretations have revealed the following styles of cenozoic deformation 1 steep to low angle dip normal faulting along the wasatch fault 2 low angle dip and listric normal faulting possibly associated with movement on preexisting thrusts 3 the occurrence of asymmetric mostly eastward tilted tertiary basins that are bounded by low to moderate dipping planar and listric faults and 4 at least three vertically stacked en echelon low angle reflections in the mid to upper crust that dip gently westward from 3 km beneath the wasatch plateau to over 15 km at the utah nevada border these reflections are interpreted as normal detachment faults the structural style of the pervasive low to moderate angle dipping faults cannot be easily reconciled with classic brittle failure theory but the interpreted termination of normal faults at or above the deeper low angle reflections suggests the presence of shallow zones of ductile deformation that may have accommodated slip an important observation based on interpretations of seismic reflection profiles is that normal fault zones dip more gently in the subsurface than their associated scarps in unconsolidated surficial deposits segment boundaries of the wasatch fault zone apparently coincide with the positions of east trending displacement transfer structures in thrust sheets and the position of the precambrian uinta aulacogen suggesting that preexisting crustal structure partly controls the geometry of extension to examine the influence of ductile deformation quasi plastic flow was modeled for appropriate geotherms of the basin range and colorado plateau crusts these models provide constraints on the depth to the frictional quasi plastic transition that occurs as shallow as 8 km in the eastern basin range this depth also corresponds to the approximate depth above which most accurately determined earthquake foci for small earthquakes m 5 5 appear to nucleate at 10 15 km in or near the brittle ductile transition the rheological modeling suggests that a thermally deforming continental lithosphere plays an important role in the evolution of this extending intraplate region large scale low angle reflections may represent decollements and normal faults at the top of upper crustal zones of reduced shearing strength and higher ductility

seal evaluation and confinement screening criteria for beneficial carbon dioxide storage with enhanced coal bed methane recovery in the pocahontas basin virginia abstract the geological storage of carbon dioxide in appalachian basin coal seams is one possible sink for sequestration of greenhouse gases with the added benefit of enhanced coal bed methane ecbm recovery the pocahontas basin part of the central appalachian basin of southwestern virginia is a major coal bed methane cbm province with production mostly from coal beds in the lower pennsylvanian pocahontas and new river formations as part of the southeast regional carbon sequestration partnership s phase ii research program a co 2 injection demonstration well was installed into lower pennsylvanian coal bed methane producing strata in southwest virginia samples of siliciclastic lithologies above coal beds in this oakwood field well and from several other cores in the nora field were taken to establish a baseline of the basic confinement properties of overlying strata to test seal competency at local and regional scales strata above cbm producing coal beds in the pocahontas and new river formations consist of dark gray shales silty gray shales heterolithic siltstones sandstones and shales lithic sandstones and quartzose sandstones standard measurements of porosity permeability and petrography were used to evaluate potential leakage hazards and any possible secondary storage potential for typical lithologies both lithic and quartz rich sandstones exhibit only minor porosity with generally low permeability 2 ecbm traps one of the most promising confining intervals above the major coal bed methane producing interval is the hensley shale member analyses of 1500 geophysical logs in southwest virginia indicate that this unit is moderately thick 50 ft 15 m laterally continuous 3000 km 2 and a homogenous shale which coarsens upward into siltstone and sandstone or is truncated by sandstone calculations from two mercury injection capillary porosimetry tests of the shale indicate that a displacement entry pressure of 207 psi 1427 kpa would generate an estimated seal capacity of 1365 ft 416 m of co 2 before buoyant leakage scanning electron microscopy indicates a microfabric of narrow pore throats between quartz grains floating in a clay matrix modeled median pore throat size between micro fabric matrix grains for the shale is estimated at 0 26 m these characteristics indicate that the shale where fractures and joints are limited would be an adequate regional confining interval for deeper co 2 storage with ecbm

morphological analysis of the lake lahontan shoreline and beachfront fault scarps pershing county nevada abstract with the diffusion equation representation of landform evolution providing reference calculations quantitative comparisons between profiles of the high stand of lake lahontan presented here and profiles of the lake bonneville shoreline scarps analyzed elsewhere reveal that the two sets of scarps are nearly identical morphologically when care is exercised in the selection of profiles the lahontan high stand scarps are remarkably reproducible from one profile to the next highly suggestive evidence that the processes that have shaped and changed the shape of these landforms are correspondingly regular slope angle differences of only 2 are both discernible and interpretable features of these late quaternary landforms cut in weakly consolidated alluvium at a level of uncertainty of no more than 50 per cent the mass diffusivity of the lahontan high stand is the same as the lake bonneville shoreline 1 1 gkg 1 gkg 1 m 2 ka this result suggests that much can be learned about the ages of late quaternary fault scarps cut in weakly consolidated alluvium throughout the basin and range province from their morphology alone the beachfront fault scarps themselves truncated by lake lahontan in our study area are morphologically only slightly older 15 to 18 ka bp than the lahontan high stand 12 ka bp

a theory for strong long lived squall lines abstract we study herein the mechanics of long lived line oriented precipitating cumulus convection squall lines using two and three dimensional numerical models of moist convection these models used in juxtaposition enable us to address the important theoretical issue of whether a squall line is a system of special long lived cells or whether it is a long lived system of ordinary short lived cells our review of the observational literature indicates that the latter is the most consistent paradigm for the vast majority of cases but on occasion a squall line may be composed of essentially steady supercell thunderstorms the numerical experiments presented herein show that either type of squall line may develop from an initial line like disturbance depending on the magnitude and orientation of the environmental shear with respect to the line with shallow shear oriented perpendicular to the line a long lived line evolves containing individually short lived cells our analysis of this type o

horizontal strain across the wasatch front near salt lake city utah two adjacent geodetic networks span a 105 km extent of the wasatch fault zone in north central utah one of the networks located in the vicinity of salt lake city was observed by the national ocean service national geodetic survey nos ngs in 1962 1963 triangulation mode and again in 1973 1974 combined triangulation trilateration mode to the north in the vicinity of ogden the u s geological survey usgs performed five separate trilateration surveys of the second network during the 1972 1981 interval when fit to a model assuming both temporal and spatial homogeneity for the strain rate the two independent data sets yield mutually consistent strain rate tensors subsets of the nos ngs data however suggest spatial variation in the strain field and a subset of the usgs data indicates a possible temporal variation in the strain rate the quality of the data is such that we are uncertain whether or not these apparent variations represent actual tectonic signals the strain rate tensors for the two complete data sets suggest an underlying deformational pattern characterized by east west e w maximum principal strain extension positive this pattern may also be inferred from regional seismicity and quaternary geology the suspected variations would imply that the area to the north of salt lake city experienced significant e w compression preceding 1978 in contradiction to the underlying strain pattern this compression may be caused by the mountainous block eastward adjacent to the fault zone displacing westward along a shallow angle west dipping detachment surface we speculate on the existence of an e w trending zone of weakness for example secondary faults located north of salt lake city to explain how the stress field to the north may be decoupled from that to the south where e w compression has not been detected while seismic and geologic information contribute some plausibility to our speculations the evidence for the existence of the suspected variations is inconclusive

geometry of flexural uplift by continental rifting in corinth greece understanding early rifting of continental lithosphere requires accurate descriptions of up bended rift margins and footwalls that correlate in space and time with the elastic flexural uplift that produces them here we characterize the geometry of elastic flexural uplift produced by continental rifting at its spatiotemporal scale in nature 10s km 10 4 10 6 yr using geomorphic evidence from the uplifting margin of the corinth rift greece our geomorphic analyses of space borne topography novelly outline the coherent elastic flexure of continental lithosphere along and across the rift margin and throughout faulting 10 6 yr as defined by the distribution of footwall uplift south of the active bounding fault topography and river drainages outline an elastic flexure signal that increases exponentially towards the bounding fault across the footwall for 50 km and changes in amplitude along the footwall following a parabola that decays from the rift center and has a 60 km wavelength such continental lithosphere up bend correlates with the scale of the rift and appears maximum in the center of the rift where drainage reversal of large catchments suggests rapid slip rates at the bounding fault this is consistent with the growth of a new rift scale high angle normal fault the coherency of elastic flexure in space and time implies highly localized strain in the rift bounding fault and suggests that the fault transects continental lithosphere with long term strength the unparalleled record of flexural uplift and highly localized strain in the landscape of corinth suggest these processes are intrinsic to early continental rifting elsewhere

lithospheric flexure and the evolution of sedimentary basins the sediments that have accumulated in sedimentary basins during geological time represent a load on the lithosphere that should respond by flexure simple elastic and viscoelastic maxwell plate models have been used to examine quantitatively the contribution of flexure to basin formation the models have been used to predict the stratigraphy and gravity anomalies associated with basins for different thermal and loading histories the predictions of the models have been compared with observed stratigraphy and free air gravity anomalies from interior and cratonic basins the best overall fit to the observations is for an elastic plate model in which the flexural strength of the lithosphere increases with age a similar model has recently been used successfully to explain observations from continental margin basins oceanic islands and seamounts and deep sea trench outer rise systems this model explains the increase in the overall width of basins during their evolution as well as the stratigraphy of the basin edges the apparent decrease in the widths of some basins through time can be explained by the model if sediment deposition is followed by erosion of the basin and its edges the models results suggest that the flexural properties of continental and oceanic lithosphere are generally similar and that flexure is an important factor to consider in backstripping studies in which the tectonic subsidence of a basin is isolated and stratigraphic studies in which relative changes of sea level are estimated

multi scale description of a sahelian synoptic weather system representative of the west african monsoon a reference case of a sahelian weather system observed during the hydrological atmospheric pilot experiment hapex sahel in august 1992 is described from a seasonal viewpoint as well as from synoptic and convective system viewpoints it is shown that the case study is representative of the climatology at all these scales and presents many interacting scales and physical processes at intraseasonal scale the monsoon onset is characterized by an abrupt shift of precipitation together with a latitudinal migration of the african easterly jet aej and convection at the month and day scales the convective activity occurs in an apparent zonal break of the tropical easterly jet the month of august 1992 exhibits intense synoptic activity the vorticity field is characterized by northerly dry and southerly wet components located at 850 hpa on each side of the aej their intraseasonal modulation on a period of 20 to 40 days leads to active and break phases of the synoptic activity around 21 august the 700 hpa vorticity field features the propagation of a typical easterly wave with a westward propagation of a cyclonic circulation followed by an anticyclonic circulation convective activity occurs mainly ahead of the 700 hpa vorticity maximum with the formation of a squall line on air mountains propagating south westward at 15 m s 1 the convective system propagates about twice as fast as the vortex core in contrast with the convection in the european centre for medium range weather forecasts re analysis which stays in phase with the vorticity the squall line corresponds to the largest contributor to the systems passing in august 1992 over the hapex sahel region its environmental conditions and its effects on the atmosphere including the surface parameters are presented copyright 2002 royal meteorological society

test of a convective wake parameterization in the single column version of ccm3 abstract a convective wake parameterization incorporated into the single column scm version of the ncar community climate model ccm3 is tested using observational data from 12 squall line cases to determine whether it can successfully reproduce convectively driven wakes in a global climate model the key spatial thermodynamic and kinematic properties of the modeled versus the observed wakes are examined as these features determine the effects of the wakes on surface fluxes and the initiation of convection effects that should be simulated correctly in general circulation models if deep convection and the resulting earth atmosphere energy exchanges are to be adequately represented results from these simulations indicate that while the scm convective wake scheme combination generally produced long lasting squall wake systems the wakes were often too shallow too warm and too moist these differences occurred despite the ability of ccm3 s standard cumulus parameterization to provide the wake scheme

production characteristics and reservoir analysis of coalbed methane reservoirs abstract six appalachian coalbed methane cbm projects are reviewed and evaluated in terms of reservoir engineering techniques and cbm recoverability these include three non mine related projects in the northern appalachian basin one non mine related and two mine related projects in the central appalachian basin of southwestern virginia generally low production rates and low cbm reserves are characteristic of the central and northern appalachian basin therefore minimizing production costs is fundamental to the economic success of a cbm project in these regions well deliverability is determined through permeability testing and through production data analysis using a reservoir simulator to history match historic production data all of the non mine related projects utilize vertical wells with well spacings of 60 to 100 acre 0 23 0 40 km 2 that produce from multiple coalbeds at depths as much as 762 m the targets are coalbeds of the pocahontas and new river formations and correlative lee formation in the nora field of virginia equitable resources developer well spacing is 60 acre 0 23 m 2 and recoverability is high 30 60 of initial gas in place well stimulation is by foam or water as the fracture medium the average gas in place is 675 mmscf well 1 and the expected lifetime of the wells is 30 years cost of water disposal is a major economic factor in cbm development in the appalachian basin water disposal is accomplished by using water disposal holes injection wells rather than surface water discharged which is generally not permitted water disposal in the central appalachian basin involves relatively low volumes of water 30 stb day 1 declining to 1 to 2 stb day 1 in the northern appalachian basin in indiana county pa belden and blake developer vertical cbm holes penetrate six to eight allegheny formation coalbeds water and a sand proppant are used for stimulation production levels are low 1 well 1 the life of a vertical cbm hole drilled in advance of mining is 3 to 5 years this type of hole may be converted to a gob hole after mining is completed gob gas is recovered mainly from coalbeds above the mined coalbed and has high recoverability of as much as 10 mmscf day 1 well 1 horizontal cbm holes produce almost pure methane and typically have 1 year of production

reinterpretation of the exposed record of the last two cycles of lake bonneville western united states a substantially modified history of the last two cycles of lake bonneville is proposed the bonneville lake cycle began prior to 26 000 yr b p the lake reached the bonneville shoreline about 16 000 yr b p poor dating control limits our knowledge of the timing of subsequent events lake level was maintained at the bonneville shoreline until about 15 000 yr b p or somewhat later when catastrophic downcutting of the outlet caused a rapid drop of 100 m the provo shoreline was formed as rates of isostatic uplift due to this unloading slowed by 13 000 yr b p the lake had fallen below the provo level and reached one close to that of great salt lake by 11 000 yr b p deposits of the little valley lake cycle are identified by their position below a marked unconformity and by amino acid ratios of their fossil gastropods the maximum level of the little valley lake was well below the bonneville shoreline based on degree of soil development and other evidence the little valley lake cycle may be equivalent in age to marine oxygenisotope stage 6 the proposed lake history has climatic implications for the region first because the fluctuations of lake bonneville and lake lahontan during the last cycle of each were apparently out of phase there may have been significant local differences in the timing and character of late pleistocene climate changes in the great basin second although the bonneville and little valley lake cycles were broadly synchronous with maximum episodes of glaciation environmental conditions necessary to generate large lakes did not exist during early wisconsin time

modification of wave cut and faulting controlled landforms from a casual observation that the form of degraded fault scarps resembles the error function this investigation proceeds through an elementary diffusion equation representation of landform evolution to the application of the resulting equations to the modern topography of scarplike landforms the morphologic observations can be analyzed either in the form of one or more cross strike elevation profiles or in the form of the slope offset plot a point plot of maximum scarp slope versus scarp offset working with either or both of these data representations for nine geologic structures which range in age from 3 to 400 ka b p and in offset from 1 to 50 m we apply analytical solutions for the vertical initial value scarp the vertical continuous offset scarp and the finite slope initial value scarp the model calculations are intrinsically ambiguous yielding as the final answer only the product t in the case of the initial value problem or the product a 1 in the case of the repeated faulting problem here t is the age of a single scarp forming event 2a is the vertical slip rate and is the mass diffusivity a single profile across three sea cliffs along the santa cruz california coast is analyzed as three separate initial value problems a reasonably constrained age for the sea cliff standing above the highway 1 platform returns 11 gkg 1 gkg 1 m2 ka with this we can date the two older sea cliffs in fact we do the converse age estimates for these two older sea cliffs based on a uniform rate of uplift both yield the same as for the lower sea cliff we treat a single profile of the raymond fault in pasadena san marino in terms of the repeated faulting problem for it the uplift rate of r crook and others yields 16 gkg the very substantial preexisting offset across the raymond fault must have been buried leveled some 230 ka b p when the modern topography began to form our analysis of the lake bonneville shoreline scarps reveals a dependence of t on 2a suggestive of nonlinear modification processes this appearance is treated with the finite slope initial value scarp model to determine 1 1 gkg for the lake bonneville shoreline scarps the suggestion of m n machette that approximately 100 000 year old meter high scarps are unobservable in weakly consolidated alluvial terranes of the basin and range and rio grande rift valley provinces can be formulated as 1 gkg the coincidence between this inequality and the lake bonneville shoreline is striking and it suggests that the value of 1 gkg may be generally applicable as a good first approximation to the modification of alluvial terranes within the semiarid regions of the western united states the lake bonneville shoreline is the basis for dating four sets of fault scarps in west central utah the drum mountains fault scarps can be modeled in several different circumstances but the most likely interpretation is that these fault scarps formed as the result of a single episode of normal faulting 3 6 to 5 7 ka b p the younger age is associated with quite low initial slope angles 25 the other three sets of fault scarps show no evidence for finite initial value slopes fault scarps along the eastern base of the fish springs range are very young 3 ka b p we estimate the age of fault scarps along the western flank of the oquirrh mountains to be 32 ka b p which meets the weak geologic constraint that they be older than the lake bonneville shoreline fault scarps along the northeastern margin of the sheeprock mountains are even older 53 ka b p an intriguing consequence of our single event analysis of these scarps is that an 11 5 m offset occurred in a single earthquake

deglaciation induced vertical motion of the north american continent and transient lower mantle rheology the last deglaciation event of the current ice age which began approximately 18 000 years ago and ended about 7000 years ago continues to exert a profound influence on the vertical motion of the solid earth in and surrounding the regions which were once ice covered observations of such vertical motions may be employed to constrain the radial viscoelastic structure of the planet and therefore to contribute in an important way to the understanding of geodynamic processes in general in this paper both present day rates of vertical motion as recorded on tide gauges and long time scale records of vertical motion as recorded in 14c controlled relative sea level histories are employed to refine previously constructed models of the radial viscoelastic structure an interesting sidelight to this analysis is the demonstration that the lower mantle viscosity inferred from the vertical motion data could represent a transient rather than the steady state value a fact which would help considerably to reconcile the small viscosity stratification required by the glacial rebound data with the large stratification which seems to be required by some recent analyses of the geoid height anomalies associated with internal density heterogeneity of the mantle which has been revealed by application of seismic tomographic techniques a further product of these new analyses is obtained by the application of the glacial isostatic adjustment model to filter this signal from the secular trends of relative sea level observed on tide gauges from both the east and west coasts of the north american continent these results may be important in the context of recently proposed scenarios of climatic change

pleistocene deglaciation and the earth s rotation implications for mantle viscosity summary recent results from the analysis of postglacial rebound data suggest that the viscosity of the earth s mantle increases through the transition region models which fit both relative sea level and free air gravity data have viscosities which increase from a value near 1022 poise in the upper mantle beneath the lithosphere to a value of about 1023 poise in the lower mantle in this paper we analyse the effect of deglaciation upon the earth s rotation and thereby show that the observed secular trend polar wander evident in the ils ipms pole path and measurements of the non tidal acceleration of the length of day are both consistent with the viscosity profile deduced from postglacial rebound the two analyses are therefore mutually reinforcing

comparison between a three dimensional simulation and doppler radar data of a tropical squall line transports of mass momentum heat and moisture abstract results from a detailed three dimensional cloud model are extensively compared with doppler radar data in the case of a fast moving tropical squall line observed during the copt81 experiment the comparisons use a two dimensional statistical analysis in which we consider each four dimensional field as the sum of a two dimensional averaged vertical field and a four dimensional residual field representative of along line and temporal fluctuations these fluctuations are analyzed by computing the time average of spatial variances and the temporal variance of spatial averages the results indicate good agreement in both quality and quantity particularly for the vertical velocity and line normal wind the consequences of this agreement are two fold first a physical and comprehensive model of the convective part of a tropical squall line emerges that is coherent with both observations and simulations this conceptual model emphasizes the importance of along line fluctuations second it is possib

a numerical investigation of the organization and interaction of the convective and stratiform regions of tropical squall lines abstract a set of 13 two dimensional numerical simulations based on the 22 and 23 june soundings from the convectionprofonde tropicale in 1981 copt81 experiment in west africa is used to study the organization and interactionof the convective and stratiform regions of squall line type convective systems the initial wind profiles arecharacterized by the african easterly jet aej and the tropical easterly jet tej located at about 3 5 km and14 km respectively the physical processes that generate and maintain the mesoscale inflow at the rear of squall line type mesoscaleconvective systems are thereby examined horizontal potential temperature gradients generated by a combinationof latent heat release in the convective region and unsaturated mesoscale descent both modulated by evaporation cause a horizontal pressure gradient and generate horizontal line parallel vorticity the rear inflow is a consequenceof these processes the convective activity induces a significant upscale influence ahead of the

complex exposure histories of chert clasts in the late pleistocene shorelines of lake lisan southern israel activities of 26 al and 10 be in five chert clasts sampled from two beach ridges of late pleistocene lake lisan precursor of the dead sea in southern israel indicate low rates of chert bedrock erosion and complex exposure burial and by inference transport histories the chert clasts were derived from the senonian mishash formation a chert bearing chalk which is widely exposed in the nahal zin drainage basin the drainage system that supplied most of the material to the beach ridges simple exposure ages assuming only exposure at the beach ridge sampling sites range from 35 to 354 ky using the ratio 26 al 10 be total clast histories range from 0 46 to 4 3 my unrelated to the clasts current position and exposure period on the late pleistocene beach ridges 160 177 m below sea level optically stimulated luminescence dating of fine sediments from the same and nearby beach ridges yielded ages of 20 0 s 1 4 ka and 36 1 s 3 3 ka these ages are supported by the degree of soil development on the beach ridges and correspond well with previously determined ages of lake lisan which suggest that the lake reached its highest stand around 27 000 cal years bp if the clasts were exposed only once and than buried beyond the range of significant cosmogenic nuclide production then the minimum initial exposure and the total burial times before delivery to the beach ridge are in the ranges 50 1300 ky and 390 3130 ky respectively alternatively the initial cosmogenic dosing could have occurred during steady erosion of the source bedrock back calculating such rates of rock erosion suggests values between 0 4 and 12 m my 1 t he relatively long burial periods indicate extended sediment storage as colluvium on slopes and or as alluvial deposits in river terraces some clasts may have been stored for long periods in abandoned pliocene and early pleistocene routes of nahal zin to the mediterranean before being transported again back into the nahal zin drainage system and washed on to the shores of lake lisan during the late pleistocene copyright 2003 john wiley sons ltd

numerical study of a sahelian synoptic weather system initiation and mature stages of convection and its interactions with the large scale dynamics summary a 24 h multi scale simulation of the life cycle of a sahelian squall line is presented the initial and coupling e elds have been taken from the european centre for medium range weather forecasts re analysis era 15 after humidity corrections to avoid spurious absolute and conditional convective instabilities comparisons of modelsynthetic and meteosat infra red radiances indicate that the simulated scenario of convection development and structure are realistic though differences are found concerning the size of the squall line with a delay of 2 3 h the simulated arc shaped structure and surface signature e t well with radar and ground station observations respectively the mature stage of the simulated squall line presents a cross line structure similar to conceptual models an intense rear to front e ow is generated below the trailing stratiform part an acceleration of the african easterly jet aej is simulated behind the system occurring across its full width this leads to the generation of a dipole of counter rotating vortices the resulting potential vorticity signature leads to local reinforcement of the barotropic instability on the north e ank of the aej this simulation is used to analyse the impact of the convection at synoptic scales and to compare it with era 15 it suggests that the convection contributes to reinforce the monsoon at least up to 500 km the monsoon ine ow moves eastward and westward with time scales shorter and longer than 24 h respectively the tropical easterly jet intensie es to the south west of the convection area up to 700 km away the aej is strongly intensie ed ahead of the trough where active convection occurs organized convection developing in the vicinity of the aej core induces weakening of the aej ahead of the squall line and strengthening behind it a common result in the simulation and in era 15 is that the aej core moves westward faster due to the convective activity

control of deep convection by sub cloud lifting processes the alp closure in the lmdz5b general circulation model recently a new conceptual framework for deep convection scheme triggering and closure has been developed and implemented in the lmdz5b general circulation model based on the idea that deep convection is controlled by sub cloud lifting processes such processes include boundary layer thermals and evaporatively driven cold pools wakes which provide an available lifting energy that is compared to the convective inhibition to trigger deep convection and an available lifting power alp at cloud base which is used to compute the convective mass flux assuming the updraft vertical velocity at the level of free convection while the alp closure was shown to delay the local hour of maximum precipitation over land in better agreement with observations it results in an underestimation of the convection intensity over the tropical ocean both in the 1d and 3d configurations of the model the specification of the updraft vertical velocity at the level of free convection appears to be a key aspect of the closure formulation as it is weaker over tropical ocean than over land and weaker in moist mid latitudes than semi arid regions we propose a formulation making this velocity increase with the level of free convection so that the alp closure is adapted to various environments cloud resolving model simulations of observed oceanic and continental case studies are used to evaluate the representation of lifting processes and test the assumptions at the basis of the alp closure formulation results favor closures based on the lifting power of sub grid sub cloud processes rather than those involving quasi equilibrium with the large scale environment the new version of the model including boundary layer thermals and cold pools coupled together with the deep convection scheme via the alp closure significantly improves the representation of various observed case studies in 1d mode it also substantially modifies precipitation patterns in the full 3d version of the model including seasonal means diurnal cycle and intraseasonal variability

upper mantle viscosity derived from the difference in rebound of the provo and bonneville shorelines lake bonneville basin utah twenty four new field measurements of elevation of provo level and bonneville level shoreline terraces provide data for reanalysis of isostatic rebound in the lake bonneville basin analysis of the differential rebound between the provo shoreline maximum rebound of 43 m and the bonneville shoreline maximum rebound of 69 m requires that the latter be an equilibrium shoreline within the possible measurement errors the provo shoreline formed after the elastic lithosphere had attained at least 91 equilibration to the removal of the water load between the bonneville and provo shorelines within the errors the provo may also represent an equilibrium shoreline from the new data presented in this paper the best estimate of the upper limit of effective viscosity of the uppermost mantle assuming a half space model and a 2000 year time interval between the bonneville and provo shorelines is 2 1019 n s m 2 2 1020 p in addition comparison of shoreline rebound profiles for both shorelines with theoretical plate flexure models indicates that the mean flexural rigidity of the basin and range lithosphere in this region is 1 1023 n m or slightly less

the dependence of numerically simulated convective storms on vertical wind shear and buoyancy abstract the effects of vertical wind shear and buoyancy on convective storm structure and evolution are investigated with the use of a three dimensional numerical cloud model by varying the magnitude of buoyant energy and one directional vertical shear over a wide range of environmental conditions associated with severe storms the model is able to produce a spectrum of storm types qualitatively similar to those observed in nature these include short lived single cells certain types of multicells and rotating supercells the relationship between wind shear and buoyancy is expressed in terms of a nondimensional convective parameter which delineates various regimes of storm structure and in particular suggests optimal conditions for the development of supercell type storms applications of this parameter to well documented severe storm cases agree favorably with the model results suggesting both the value of the model in studying these modes of convection as well as the value of this representation i

numerical archetypal parameterization for mesoscale convective systems abstractvertical shear commonly organizes atmospheric convection into coherent multiscale structures the associated countergradient vertical transport of horizontal momentum by organized convection can enhance the wind shear and transport kinetic energy upscale however organized convection and its upscale effects are not represented by traditional mass flux based parameterizations the present paper sets the archetypal dynamical models originally formulated by the second author into a parameterization context by utilizing a nonhydrostatic anelastic model with segmentally constant approximation nam sca using a two dimensional framework as a starting point nam sca spontaneously generates propagating tropical squall lines in a sheared environment high numerical efficiency is achieved through a novel compression methodology the numerically generated archetypes produce vertical profiles of convective momentum transport that are consistent with the analytic archetype

flexural uplift of rift flanks due to mechanical unloading of the lithosphere during extension we suggest that the uplift of rift flanks results from mechanical unloading of the lithosphere during extension and consequent isostatic rebound this mechanism is presented as an alternative to explanations for rift flank uplift involving thermal or dynamic processes and magmatic thickening of the crust our hypothesis is based on two critical concepts first the lithosphere retains finite mechanical strength or flexural rigidity during extension second isostatic rebound uplift of the lithosphere follows when the kinematics of extension produces a surface topographic depression that is deeper than the level to which the surface of the extended lithosphere would subside assuming local isostatic compensation we develop and analyze two kinematic models for instantaneous extension of the lithosphere to show that flexural rebound is a viable explanation for the uplift of rift flanks we first investigate the isostatic consequences of finite simple slip on an initially planar dipping normal fault cutting the entire lithosphere when the lithosphere retains flexural rigidity during extension the topography resulting from this model resembles a half graben and the footwall rift flank is flexurally uplifted this simple normal faulting model explains free air gravity anomalies and topography observed at rift flanks in oceanic lithosphere such as broken ridge in the eastern indian ocean the caroline ridges sorol trough in the western equatorial pacific and the coriolis trough behind the new hebrides island arc we then investigate a general kinematic model for lithospheric extension where simple slip on a surface of arbitrary shape is accompanied by pure shear extension in the upper and lower plates when the simple slip component is not zero or the distribution of pure shear in the upper and lower plates is not identical the surface of slip can be regarded as a detachment by simplification our general model accounts for pure shear extension of the lithosphere that is uniform with depth in this case detachments have no meaning in the geologic sense however the kinematics of depth independent pure shear may nevertheless be described in terms of a surface which we term a kinematic reference surface at some depth in the lithosphere we speculate that the depth of this surface may be rheologically controlled the magnitude of rift flank uplift by flexure depends critically on the depth of this reference surface in contrast if local isostasy is assumed when the lithosphere undergoes a given amount of depth independent pure shear the resulting topography will be the same regardless of how the kinematics of that extension are formulated the basin and rift flank topography and free air gravity anomaly over young continental rifts such as the rhine graben can be satisfied using our general extensional model with a small amount 5 km of extension along a listric shaped detachment soling into the crust mantle boundary because the flexural rebound mechanism explains the observed topography and gravity anomaly over both oceanic and continental extensional domains we suggest that rheological differences between the two lithospheric types may not be important in their overall response to extension

shifting the diurnal cycle of parameterized deep convection over land 1 in most atmospheric circulation models used for climate projections cloud and convective processes are not explicitly resolved but parameterized such models are known to produce a diurnal cycle of continental thunderstorms in phase with insolation while observed precipitation peaks in late afternoon we propose a new approach which corrects this long standing bias of parameterized convection in this approach deep convection triggering and intensity are controlled by sub cloud processes here boundary layer thermals and gust fronts and potentially orography or surface heterogeneities the representation of the diurnal cycle of deep convection is greatly improved in 1d mode with rainfall maximum delayed from midday to late afternoon provided parameterizations account for the key role played by shallow cumulus in preconditioning deep convection and by gust fronts in the self sustaining of thunderstorms in the afternoon

life cycle of a mesoscale circular gust front observed by a c band doppler radar in west africa abstracton 10 july 2006 during the special observation period sop of the african monsoon multidisciplinary analysis amma campaign a small convective system initiated over niamey and propagated westward in the vicinity of several instruments activated in the area including the massachusetts institute of technology mit c band doppler radar and the atmospheric radiation measurement arm mobile facility the system started after a typical convective development of the planetary boundary layer it grew and propagated within the scope of the radar range so that its entire life cycle is documented from the precluding shallow convection to its traveling gust front the analysis of the observations during the transitions from organized dry convection to shallow convection and from shallow convection to deep convection lends support to the significant role played by surface temperature heterogeneities and boundary layer processes in the initiation of deep convection in semiarid conditions the analysis

two phase rate transient analysis of a hydraulically fractured coal seam gas well a case study from the ordos basin china abstract apart from implications related to coal seam gas csg reservoir engineering such as stress and desorption dependent permeability 2 phase flow of gas and water adds further complications to rate transient analysis rta techniques in csg reservoirs this paper introduces the concept of area of influence ai to calculate water saturation in transient formation linear flow for 2 phase rta in hydraulically fractured csg wells the relevant equations are derived and discussed and the application of the ai is demonstrated using reservoir simulation the area of influence allows a superior estimation of water saturation compared to the dynamic drainage area dda in under saturated csg reservoirs and hence improves the estimation of fracture half length a practical workflow is also developed and presented to estimate reservoir and hydraulic fracture properties using 2 phase rta for hydraulically fractured vertical wells the presented workflow works in a reverse order by first analysing boundary dominated flow regime and then proceeds to other existing flow regimes developed at earlier production history of the well although analysis of each flow regime provides a standalone method to calculate some of reservoir properties the full development of all flow regimes allows crosschecking and brings more confidence into calculation in this workflow the reservoir properties derived from later flow regimes feeds earlier flow regimes to extract other reservoir variables such as fracture half length a hydraulically fractured csg well from the ordos basin china is analysed using ai and the proposed workflow to demonstrate the field application of this study

a reevaluation of the isostatic rebound of lake bonneville recent data pertaining to the uplift of the provo and bonneville shorelines of the late pleistocene lake bonneville are evaluated in a reanalysis using a rigorous model of deformation of a plane earth comprising an elastic layer overlying a viscoelastic channel the new observations constrain the wavelength and amplitude of the uplift of two shorelines formed at two different epochs and they partly resolve the ambiguities in the plausible mechanical parameters found in previous solutions the results indicate that the effective thickness of the elastic lithosphere is 28 to 30 km equal to the seismically determined crustal thickness in the region the estimate of the upper mantle viscosity in the region varies from 1 5 3 4 lo19 pa s to 2 1 5 8 l018 pa s depending on whether the upper mantle is assumed to be of uniform viscosity or the flow is confined to a narrow channel in the asthenosphere the predicted rate of present uplift at the center of the desiccated lake is 0 06 mm yr and 0 03 mm yr for the shallow channel and uniform mantle models respectively these values are beyond the first order leveling accuracies and the question of the existence of a narrow channel in the region cannot be resolved with the available observations

erosion isostatic rebound models for uplift an application to south eastern australia summary a mountain s history includes two distinctive phases one of active tectonism and construction followed by one of erosion and passive isostatic rebound in the first phase uplift is driven by tectonic mechanisms while in the second phase base levels of the terrain are regionally uplifted it is this latter phase that is modelled here the starting model is a mountain range initially in isostatic equilibrium on a viscoelastic plate defined by the effective flexural rigidity d and relaxation time 7 the rate of erosion at any time t is assumed to be proportional to the elevation at that time with an erosional time constant 7 for a given present day topography the uplift erosion gravity and stress can be computed through time as functions of d 7 7 and the time to at which the erosional rebound mechanism became the dominant landscaping process the model has been applied to the highlands of south eastern australia which we assume to be an erosional residue of the palaeozoic lachlan fold belt observations of rivers cutting through cainozoic basalts and other geomorphological indicators of uplift can then be interpreted in terms of the isostatic rebound and there is no need to invoke active tectonic uplift mechanisms the model parameters that fit the observations are t 150 3 50myr dt 2 5 x ioz4nmmyr and to 180 200myr the predicted late palaeozoic fold belt topography is about 75 per cent greater than the present day values topographic depressions are predicted to have occurred along the margins of the formerly elevated areas and the model is relevant to understanding the evolution of basins flanking the highlands within the highland area erosion generally exceeds uplift but in some regions the two are approximately equal in keeping with recent geomorphological observations the flexural stresses associated with the erosion initially increase with time and maximum values in south eastern australia are predicted to occur in late cainozoic time with the stress state near the surface being mainly tensional

reservoir simulation based modeling for characterizing longwall methane emissions and gob gas venthole production abstract longwall mining alters the fluid flow related reservoir properties of the rocks overlying and underlying an extracted panel due to fracturing and relaxation of the strata these mining related disturbances create new pressure depletion zones and new flow paths for gas migration and may cause unexpected or uncontrolled migration of gas into the underground workplace one common technique to control methane emissions in longwall mines is to drill vertical gob gas ventholes into each longwall panel to capture the methane within the overlying fractured strata before it enters the work environment thus it is important to optimize the well parameters e g the borehole diameter and the length and position of the slotted casing interval relative to the fractured gas bearing zones this paper presents the development and results of a comprehensive dynamic three dimensional reservoir model of a typical multi panel pittsburgh coalbed longwall mine the alteration of permeability fields in and above the panels as a result of the mining induced disturbances has been estimated from mechanical modeling of the overlying rock mass model calibration was performed through history matching the gas production from gob gas ventholes in the study area results presented in this paper include a simulation of gas flow patterns from the gas bearing zones in the overlying strata to the mine environment as well as the influence of completion practices on optimizing gas production from gob gas ventholes

the lageos constraint on deep mantle viscosity results from a new normal mode method for the inversion of viscoelastic relaxation spectra the recently observed acceleration in the node of the orbit of the lageos satellite has previously been shown to provide a good constraint on the viscosity of the earth s mantle beneath the 670 km seismic discontinuity this paper explores the extent to which the previously inferred lower mantle viscosity may be traded off against variations of other properties of the radial viscoelastic structure we show explicitly that the nontidal acceleration of rotation inferred from the lageos data and predicted as a consequence of the earth s response to the last deglaciation event of the current ice age is relatively insensitive both to variations of lithospheric thickness and to the presence or absence of plausible chemical heterogeneity across the 670 km interface it therefore provides a high quality constraint on the viscosity of the deep mantle with the upper mantle viscosity fixed at the nominal value of 1021 pa s the bounds on lower mantle viscosity lm are such that 2 1021 pa s lm 6 1021 pa s even when allowance is made for the presence of a viscous boundary layer at the base of the upper mantle such as would exist if the mantle convective circulation were layered

rheology of the lithosphere selected topics we review recent results concerning the rheology of the lithosphere with special attention to the following topics 1 the flexure of the oceanic lithosphere 2 deformation of the continental lithosphere resulting from vertical surface loads and forces applied at plate margins 3 the rheological stratification of the continents 4 strain localization and shear zone development and 5 strain induced crystallographic preferred orientations and anisotropies in body wave velocities we conclude with a section citing the 1983 1986 rock mechanics literature by category

current status and geological conditions for the applicability of cbm drilling technologies in china a review abstract coalbed methane cbm drilling technology is critical in achieving efficient cbm development the geological conditions for cbm development in china are complex including special terrain high rank coal areas deep coal seams multiple superposed coal seams and coal measure gas symbiosis areas steeply inclined coal seam areas and tectonic coal seam areas therefore it is critical to apply the optimum drilling technology in each different area this paper first reviews the current cbm drilling technologies and gas production behaviors in china it is found that although vertical wells and cluster well groups are common well types for cbm development in china u v and l shaped horizontal wells and multilateral horizontal wells have been favored for cbm development in recent years the paper then discusses the applicability of different well types to geological conditions and proposes a modification method for well design in various geologic conditions this method uses the coal structure ro in situ stress and ratio of critical desorption pressure to the reservoir pressure as the main inputs

investigation of longwall goaf gas flows and borehole drainage performance by cfd simulation abstract to reduce methane emissions into the workings of a longwall panel the mechanisms of gas emissions and migration within the longwall goaf must first be understood additionally high performance drainage boreholes must be designed many variables affect the goaf gas flow and borehole drainage efficiency namely the gas release characteristics of gas sources the heights of caved and fractured zones of the goaf the location of the drainage borehole and the position of the effective drainage section the portion of the perforated case and the uncased open hole this paper illustrates how these variables influence the goaf gas flow patterns and borehole performances through cfd simulations a permeability model and a gas release curve which reflect observations from experiments geomechanical modellings mine site monitoring and borehole drainage data were constructed for the mining disturbed strata and incorporated into the cfd model the cfd model was calibrated with the actual drainage data from the surface boreholes at a coal mine simulation results show that the gas drainage velocities around the perimeter of the panel goaf are higher than in the central goaf which is consistent with the overlying annular fracture zone model established from csiro previous research boreholes located within the annular area drew methane at a higher flow rate than those located in the central area leading to a significant reduction of methane emissions to the ventilation system goaf geometry with higher caved and fractured zones has lower pressure and methane concentration but higher gas flow velocity the location of the effective drainage section of the borehole has significant influence on drainage performance boreholes with the bottom end located in the lower region of the fractured zone 20 m above the roof can draw more methane than those located in the upper region of the fractured zone 70 m above the roof and those located in the caved zone 2 m above the roof

great salt lake and precursors utah the last 30 000 years sediment cores up to 6 5 m in length from the south arm of great salt lake utah have been correlated radiocarbon ages and volcanic tephra layers indicate a record of greater than 30 000 years a variety of approaches have been employed to collect data used in stratigraphic correlation and lake elevation interpretation these include acoustic stratigraphy sedimentologic analyses mineralogy geochemistry major element c o and s isotopes and organics paleontology and pollen the results indicate that prior to 32 000 year b p an ephemeral saline lake playa system was present in the basin the perennial lake which has occupied the basin since this time rose in a series of three major steps the freshest water conditions and presumably highest altitude was reached at about 17 000 year b p the lake remained fresh for a brief period followed by a rapid increase in salinity and sharp lowering in elevation to levels below that of the present great salt lake the lake remained at low elevations and divided at times into a north and south basin until about 8 000 year b p since that time with the exception of two short rises to about 1290 m the lake level has remained near the present elevation of 1280 m

the global population of mesoscale convective complexes a global set of 714 mesoscale convective complexes is compiled and some of the common properties of the convective systems are identified and examined from a global perspective the data set includes date of occurrence time of first storms initiation maximum extent termination duration cold cloud shield areas and tracks from initiation to termination it is found that the typical convective complex is nocturnal generates a cold cloud shield area of approximately 350 000 km2 and persists for about 10 h the largest systems and most persistent systems tend to occur near the summer solstices for the globe about 400 systems occur each year primarily over land areas most systems develop in favoured zones although some activity occurs over every continent except antarctica and all major oceans the concentration of activity into favoured zones indicates that there must be special dynamic and or thermodynamic conditions necessary for convection to organize into convective complexes activity is strongly tied to the solar day and shifts from 35 s in early january to about 50 n during the boreal summer and back to 35 s by december within the northern hemisphere there is a pronounced poleward migration as the jet stream shifts northward relatively little migration occurs in the ocean dominated southern hemisphere where the subtropical jet remains quasi stationary over the convective complex regions the nocturnal life cycles copious rainfall large cloud shields and great frequency of mesoscale convective complexes suggest that they may be significant contributors to the global hydrologic cycle and earth system energy budget

a tropical squall line observed during toga coare extended comparisons between simulations and doppler radar data and the role of midlevel wind shear abstract results from a three dimensional cloud model are extensively compared with airborne doppler radar data in the case of a tropical oceanic squall line observed during the tropical ocean global atmosphere coupled ocean atmosphere response experiment the comparison is based on the precipitation patterns the dynamical and thermodynamical distributions and the vertical transport of horizontal momentum the model simulates the evolution of the mesoscale convective system mcs frontal convective line from a quasi linear to a broken pattern the area located south of the break which designates the region where the mcs leading edge reorientates from the n s to the e w direction is composed of a pronounced bow shaped structure with two vortices located on both sides of a strong rear inflow the vertical circulation is characterized by a jump updraft and an overturning downdraft both structures exhibit a vertical intense updraft in the break zone whereas the jump updraft is more sloped and less in

lake bonneville constraints on lithospheric thickness and upper mantle viscosity from isostatic warping of bonneville provo and gilbert stage shorelines the deformed shorelines of the late pleistocene lake bonneville provide an excellent opportunity to analyze the response of the earth to surface loads of relatively short wavelengths 400 km and short duration 30 kyr recently revised estimates of the lake loading history and an expanded compilation of shoreline elevations for the bonneville 1550 m provo 1440 m and gilbert 1300 m shorelines have prompted us to reexamine the deflection the earth model we use is identical with that employed by nakiboglu and lambeck and consists of an elastic plate overlying a maxwell viscoelastic channel and a rigid base our calculation differs from that of nakiboglu and lambeck in two respects we used a significantly more detailed load model and we compared our results with observations from three distinct shorelines the lake elevation history spans 32 kyr in 18 piecewise linear segments the water load is computed at each time step from a digital terrain model 4 4 km cell size and a specified lake elevation we find that the use of three separate shorelines significantly reduces the acceptable region of parameter space the effective elastic lithospheric thickness is 23 2 km the mantle viscosity is 1 2 0 2 1020 pa s and the depth to a significant viscosity increase is no less than 300 km though it might be much more examination of the residual deflections differences between observed and computed shoreline elevations reveals a regional tilt down to the ne of 6 10 5 which we attribute to collapse of the peripheral bulge produced by the laurentide ice sheet

possible controls of hydrogeological and stress regimes on the producibility of coalbed methane in upper cretaceous tertiary strata of the alberta basin canada the coalbed methane potential and producibility of any coal bearing strata are strongly affected by the hydrogeological regime of formation waters and by coal permeability which in turn depends on the effective stress regime of the coals peat that accumulated in the alberta basin during the late cretaceous and early tertiary led to the formation of coal deposits that may contain significant coalbed methane resources the flow of formation waters plays an important role in the maintenance and producibility of this resource the present day flow is driven by gravity topography and erosional rebound and is controlled by rock permeability and the presence of gas saturated sandstones the estimated gas in place in the tertiary upper cretaceous coals decreases significantly with stratigraphic age ranging between less than 2 bcf mi2 in the lower coal zones and 12 bcf mi2 in the uppermost coals the gas content especially of the deeper coals is lower than would be expected for the corresponding coal rank and burial depth most likely because the underpressuring has caused the release of gas from the coals and accumulation in adjacent sands the shallow coals although of low rank may contain important amounts of late stage biogenic methane the salinity of formation water in shallow coal seams where the flow is driven by topography is low generally less than 1500 mg l although in places it reaches 3000 5000 mg l the salinity of formation water in the deeper underpressured strata in the west central part of the basin is significantly higher reaching 18 000 mg l this affects treatment and or disposal strategies with regard to the water produced concurrent to coalbed methane the producibility of this resource depends on coal permeability which decreases west southwestward with increasing burial depth from the order of several darcys in the shallow zones to millidarcys in the deep zones the minimum effective stress which affects coal permeability by closing fractures increases west southwestward from zero at the erosional edge of these strata to approximately 20 mpa near the rocky mountain deformation front fractures including those in coal seams will generally be vertical and will propagate on a southwest northeast axis along the direction of the maximum horizontal stress in a direction generally perpendicular to the rocky mountain deformation front considering the hydrogeological and stress regimes in conjunction with estimations of the gas content in coals the region with probably good coalbed methane potential and producibility are the ardley coal zone in the scollard formation and maybe to a lesser extent the coal zones of the stratigraphically deeper edmonton and belly river groups along their respective subcrop in central and southern alberta the deep edmonton and belly river strata in western and central alberta have most likely a reduced coalbed methane potential as a result of lower gas content and of low permeability these regional considerations need to be applied against local studies of coal thickness rank permeability and gas content to identify the best targets for coalbed methane exploration and production

fault behavior and characteristic earthquakes examples from the wasatch and san andreas fault zones paleoseismological data for the wasatch and san andreas fault zones have led to the formulation of the characteristic earthquake model which postulates that individual faults and fault segments tend to generate essentially same size or characteristic earthquakes having a relatively narrow range of magnitudes near the maximum analysis of scarp derived colluvium in trench exposures across the wasatch fault provides estimates of the timing and displacement associated with individual surface faulting earthquakes at all of the sites studied the displacement per event has been consistently large measured values range from 1 6 to 2 6 m and the average is about 2 m on the basis of variability in the timing of individual events as well as changes in scarp morphology and fault geometry six major segments are recognized along the wasatch fault on the basis of the most likely number of surface faulting events 18 that have occurred on segments of the wasatch fault zone during the past 8000 years an average recurrence interval of 400 666 years with a preferred average of 444 years is calculated for the entire zone geologic data on the distribution of slip associated with prehistoric earthquakes and slip rates along the south central segment of the san andreas fault suggest that the m 8 1857 earthquake is a characteristic earthquake for this segment comparisons of earthquake recurrence relationships on both the wasatch and san andreas faults based on historical seismicity data and geologic data show that a linear constant b value extrapolation of the cumulative recurrence curve from the smaller magnitudes leads to gross underestimates of the frequency of occurrence of the large or characteristic earthquakes only by assuming a low b value in the moderate magnitude range can the seismicity data on small earthquakes be reconciled with geologic data on large earthquakes the characteristic earthquake appears to be a fundamental aspect of the behavior of the wasatch and san andreas faults and may apply to many other faults as well

two dimensional convection in non constant shear a model of mid latitude squall lines numerical simulations of two dimensional deep convection are analysed using analytical models extended to include shallow downdraughts and non constant shear the cumulonimbus are initiated by low level convergence created by a finite amplitude downdraught these experiments have constant low level shear and differ only in the profile of mid and upper level winds quasi steady convenction is produced if the mid and upper level flow has small shear and the low level shear is large the surface precipitation ismaximized for no intial relative relative flow aloft if stationary this storm p o can give prodigious locilized rainfall p o is the two dimentisonal equivalent of the supercell these results are placed in context with previous two dimensional simulations attention is drawn to the similiarity with previous two dimensional simulations attention is drawn to the similarity with squall lines in central and eastern u s a storm p o is analysed by construction of time averaged fields of streamfunction vorticity teperature and height deviation the smoothness of these fields suggests a conceptual model of the storm dynamics which involves cooperation between distinct charcteristic flows an overturning updraught a jump type updraught a shallow downdraught a low level rotor and a boundary layer an idealized analytical model is described by solution of the equations for steady convection these solutions for the remote flow are derived from energy conversation mass continuity and a momentum budget and they give relationships between the non dimensional parameteres of the problem it is apparent that the convection is a high froude or low richardson number flow demanding the existence of a cross storm pressure gradient inherent in this idealized model is a vortex sheet between updraught and down draught and it is considered that the dynamical instability of this sheet is related to complexities in the numerical simulation furthermore these results show that in two dimensions both non constant shear and a shallow downdraught are necessary to maintain steady convection

dual doppler radar analysis of a midlatitude squall line with a trailing region of stratiform rain abstract the mesoscale structure of a squall line system that passed over oklahoma on 22 may 1976 is investigated by dual doppler radar analysis the mature storm consisted of a leading line of deep convection which exhibited organized multicellular structure trailed by an extensive region of stratiform precipitation marked by a radar bright band at the melting level these contrasting radar echo regimes were separated by a narrow band of weak reflectivity at lower levels which has been termed the transition zone while conventional and single doppler radar analyses documented the persistence of this precipitation structure and revealed the corresponding kinematic structure in one part of the mature storm the dual doppler analysis demonstrates the pervasiveness of these features over much of the squall line s length the structure of a midtropospheric maximum of rearward system relative flow crossing the system is particularly well described by the dual doppler data this mesoscale current originat

a unified convection scheme unicon part i formulation abstractthe author develops a unified convection scheme unicon that parameterizes relative i e with respect to the grid mean vertical flow subgrid vertical transport by nonlocal asymmetric turbulent eddies unicon is a process based model of subgrid convective plumes and mesoscale organized flow without relying on any quasi equilibrium assumptions such as convective available potential energy cape or convective inhibition cin closures in combination with a relative subgrid vertical transport scheme by local symmetric turbulent eddies and a grid scale advection scheme unicon simulates vertical transport of water species and conservative scalars without double counting at any horizontal resolution unicon simulates all dry moist forced free and shallow deep convection within a single framework in a seamless consistent and unified way it diagnoses the vertical profiles of the macrophysics fractional area plume radius and number density as well as the microphysics production and evaporati

rear inflow in squall lines with trailing stratiform precipitation abstract the relative airflow and accompanying precipitation structure of squall lines trailed by mesoscale regions of stratiform rain are examined with emphasis on the occurrence of rear inflow i e the intrusion of environmental air into these storms across the trailing precipitation boundary three cases from kansas and oklahoma provide examples of strong rear inflow which crosses the back edge of the stratiform precipitation area at relative speeds exceeding 10 m s 1 the vertical profiles of relative flow at the trailing precipitation boundary of these three systems were remarkably similar with the rear inflow confined to a jet like layer centered at about 550 mb doppler radar data for two of these cases showed that the rear inflow jet occupied a continuous channel extending from middle levels at the back edge of the stratiform region to lower levels of the leading convective region where it merged with outflow from convective downdrafts to bolster the leading gust front strong front to rea

pleistocene deglaciation and the earth s rotation a new analysis summary this paper is concerned with an analysis of the effect of the pleistocene glacial cycle upon the earth s rotation we demonstrate that two important geophysical observables may be explained as aspects of the rotational response to surface mass loading by ice sheets these are the astronomically observed non tidal component of the acceleration of planetary rotation and the secular drift of the rotation pole relative to the surface geography which is evident in the ils pole path the former observation is shown to provide an unambiguous constraint upon the viscosity of the planetary mantle and requires a depth dependence of this parameter which is the same as that which has previously been inferred in studies of the relative sea level variations and free air gravity anomalies associated with post glacial rebound the observed secular drift of the pole cannot provide an independent estimate of the viscosity of the mantle because it depends jointly upon mantle viscosity and lithospheric thickness with the viscosity profile fixed by the rebound data the observed speed of polar wander suggests a continental lithospheric thickness which is in excess of that appropriate for old ocean basins but nevertheless in accord with independent constraints

normal faulting and flexure in an elastic perfectly plastic plate abstract an elastic perfectly plastic plate model has been developed to analyze the flexure associated with normal faulting the model consists of a thin layer which is completely cut by a normal fault overlying a fluid substratum for a given applied bending moment at the fault the relationship between the amount of displacement on the fault and the extent of the failure zone can be calculated the model is applied to the wasatch front region in the eastern basin and range province usa to determine the correlation of its parameters with geological and geophysical data in the vicinity of a major normal fault the wasatch fault along which there has been 3 4 km of late cenozoic uplift in this region most seismic activity occurs away from the wasatch fault in a zone 30 km wide roughly centered 30 km east of the fault this activity occurs at depths of 15 km or less in order to match the observations the lithospheric layer must have a flexural rigidity of 0 5 to 1 1 1022 n m and a yield stress of 1 2 kb and must have zero applied bending moment at the fault the effective mechanical thickness of the lithosphere in this region is 20 25 km these results indicate that the lithosphere in long term mechanical studies in the eastern basin and range is thin and weak evaluating these results as compared to the seismic lithospheric thickness and temperature regime of the region produces some interesting correlations with studies in oceanic regions

convection driven tectonics on venus an analysis is presented for convective stress coupling to an elastic lithosphere as it applies to tectonic deformation on venus theoretical solutions are introduced for the response of a mathematically thick elastic plate overlying a newtonian viscous medium with an exponential depth dependence of viscosity a green s function solution is obtained for the viscous flow driven by a harmonic density distribution at a specified depth it is shown that during the transient phase of the solution the field quantities stress velocity displacement in both media depend upon the rheology of both media whereas in steady state the solutions become uncoupled due to this uncoupling stresses obtained from a purely viscous solution can be applied as boundary conditions at the base of an isolated elastic plate i show for such a plate that 1 shear stress imparted at the base of the lower boundary can induce large in plane stretching mode forces and 2 these forces can be estimated directly from free air gravity anomalies without detailed knowledge of the density distribution in the underlying flow free air gravity anomalies for venus imply in plane forces of about 2 3 1012 n m in plane forces of this magnitude are capable of extensive disruption of the venusian lithosphere to demonstrate this an elastic plastic analysis is carried out for the deformation of a model venus lithosphere the calculation is based on a lithospheric strength envelope and uses gravity and topography as a guide to the magnitude of stresses imparted by convective flow the results predict that dynamic uplift of venusian topography must be accompanied by extensive brittle failure and viscous flow in the lithosphere geoid anomalies and geoid to topography ratios for venusian topographic features are large compared to values for thermal swells in earth s ocean basins this suggests that dynamic support of topography must be an important process on venus further a low viscosity zone is probably not present beneath the venusian lithosphere a comparative analysis suggests that tectonic deformation of the lithosphere associated with dynamically supported topography on earth is unimportant

patterns of tropical pacific convection anomalies and associated extratropical wave trains in amip5 in this paper the performance of 18 coupled model intercomparison project phase 5 cmip5 models forced by observational ssts in simulating the tropical pacific convective variation and the atmospheric responses in the extratropics are assessed the multi model ensemble mean results of 18 cmip5 models show that five major patterns of tropical pacific convection anomaly in winter can indeed be well reproduced however the simulation of the corresponding extratropical responses for each pattern exists some deficiency except for the la nina pattern compared with observations we defined an optimized subset of well performing models access1 0 canam4 ccsm4 cmcc cm hadgem2 a mpi esm mr in tropical pacific deep convection according to the ranking of model skill score these models exhibit approximately identical convection anomaly patterns in both amplitude and spatial structure to the observation which potentially might improve the representation of extratropical teleconnections with the tropical pacific especially for the cp el nino cpen ep el nino epen and western cp w cp patterns both evident atmospheric anomalies of cpen and epen patterns over the na e sector and the northeastward propagating wave trains of w cp pattern can be quite well simulated in the high skilled models

a density current parameterization coupled with emanuel s convection scheme part i the models abstract the aim of the present series of papers is to develop a density current parameterization for global circulation models this first paper is devoted to the presentation of this new wake parameterization coupled with emanuel s convective scheme the model represents a population of identical circular cold pools the wakes with vertical frontiers the wakes are cooled by the precipitating downdrafts while the outside area is warmed by the subsidence induced by the saturated drafts the budget equations for mass energy and water yield evolution equations for the prognostic variables the vertical profiles of the temperature and humidity differences between the wakes and their exterior they also provide additional terms for the equations of the mean variables the driving terms of the wake equations are the differential heating and drying due to convective drafts the action of the convection on the wakes is implemented by splitting the convective tendency and attributing the effect of the precip

departures from convective equilibrium with a rapidly varying surface forcing convective equilibrium is a long standing and useful concept for understanding many aspects of the behaviour of deep moist convection for example it is often invoked in developing parametrizations for large scale models however the equilibrium assumption may begin to break down as models are increasingly used with shorter time steps and finer resolutions here we perform idealized cloud system resolving model simulations of deep convection with imposed time variations in the surface forcing a range of rapid forcing time scales from 1 to 36 h are used in order to induce systematic departures from equilibrium for the longer forcing time scales the equilibrium assumption remains valid in at least the limited sense that cycle integrated measures of convective activity are very similar from cycle to cycle for shorter forcing time scales cycle integrated convection becomes more variable with enhanced activity on one cycle being correlated with reduced activity on the next suggesting a role for convective memory further investigation shows that the memory does not appear to be carried by the domain mean thermodynamic fields but rather by structures on horizontal scales of 5 20 km such structures are produced by the convective clouds and can persist beyond the lifetime of the cloud even through to the next forcing cycle

a parameterization of mesoscale enhancement of surface fluxes for large scale models abstract the paper investigates the enhancement of surface fluxes by atmospheric mesoscale motions the authors show that horizontal wind variabilities induced by these motions i e gustiness need to be considered in the parameterization of surface fluxes used in general circulation models gcms as they always occur at subgrid scale it is argued that there are two different sources of gustiness deep convection and boundary layer free convection the respective scales time and length and the convective patterns are very different for each of these sources a general parameterization of the gustiness distinguishing these two effects is proposed for boundary layer free convection the gustiness is related to the free convection velocity to establish this relationship both observations and numerical simulations are used revisiting the coupled ocean atmosphere response experiment data the authors propose a new value of the proportionality coefficient that links the free convection velocity and th

slip rate variations on faults in the basin and range province caused by regression of late pleistocene lake bonneville and lake lahontan late pleistocene regression of two large pluvial lakes lake bonneville and lake lahontan caused considerable lithospheric rebound in the basin and range province usa here we use finite element models to show how lake growth and regression affect the temporal and spatial slip evolution on faults near the former lakes our results show that fluctuations in the volume of lake bonneville caused along strike slip variations on the wasatch normal fault with a pronounced slip rate increase on its northern and central parts during lake regression the response of normal and strike slip faults near the ring shaped lake lahontan depends on their location within the rebound area faults located in the centre of rebound show a slip rate increase during lake regression whereas strike slip faults at the periphery decelerate all slip rate variations are caused by differential stress changes owing to changing lake levels regardless of the individual fault response

an analysis of reservoir conditions and responses in longwall panel overburden during mining and its effect on gob gas well performance abstract niosh conducted a cooperative research study to provide direct measurements of changing reservoir conditions in longwall panel overburden the field measurements documented changes in permeabilities methane concentrations fluid pressures and the effects of adjacent gob gas ventholes ggvs on niosh boreholes drilled in the study panel three different stratigraphic horizons were monitored by the niosh boreholes results indicated that the gob gas venthole fracture network formed 24 to 46 m 80 to 150 ft ahead of the mining face overburden permeabilities within the same overburden test zones were 1 md prior to undermining increasing to hundreds or thousands of md during undermining permeabilities measured seven months after undermining showed additional increases the relationship between changing reservoir conditions longwall face position and surface movement is discussed recommendations are made to optimize ggv performance by evaluating changes in subsidence produced by mining resulting in rock stresses that substantially influence induced fracture permeability mechanisms to account for the observed changes in reservoir conditions are reported

a study of the earth s response to surface loading with application to lake bonneville summary analytical solutions are presented for the deformation of a three layered plane earth with elastic viscoelastic rheology and subject to time dependent vertical surface loads the models investigated are 1 elastic or viscoelastic layers overlying an inviscid fluid 2 viscoelastic half space 3 elastic layer over a viscoelastic layer with different boundary conditions at the base of the second layer emphasis is given to the interdependence between the dominant parameters of thickness of the elastic layer the effective viscosity of the viscoelastic layer the change in viscosity with depth and the wavelength and duration of loading the models have been applied to the loading and unloading of the late pleistocene pluvial lake bonneville using the load histories given by crittenden the studies differ from earlier analyses of the bonneville uplift in several important aspects including a rigorous treatment of the horizontal and vertical coupling between the elastic and viscoelastic media the mantle is treated as viscoelastic rather than as a viscous medium the wavelength information has been introduced by using a more realistic model for the load geometry and the effect of the wasatch fault has been considered the models indicate that the two principal parameters defining the rebound are the effective viscosity of the upper mantle and the effective thickness of the elastic layer and that those two parameters can be separated only if both wavelength and amplitude information of the deformation is available at more than one epoch observations of uplift at one epoch are not sufficient to resolve the thickness of the elastic layer and the effective viscosity of the upper mantle but upper bounds for these quantities are well established as 30km and 1 2 10 poise respectively the uplift results do not confirm or deny the possibility of a low viscosity channel in the upper mantle but this can be resolved only if the uplift data are supplemented with observations of the present uplift rate the published rates are controversial but if valid they point to a thin 15 km elastic layer and a relatively narrow 200km low viscosity channel while the models predict uplift near the centre of the former lake they also predict that the peripheral regions should be subsiding appreciably if flow is confined into a shallow channel of low viscosity observations reported by anderson bucknam suggests such behaviour likewise the present rate of uplift changes sign at some distance from the centre of the lake and detailed observations of warping of the shorelines and repeated levelling in the area may yield further constraints on the rebound model copyright