environmental perturbations caused by the impacts of asteroids and comets we review the major impact associated mechanisms proposed to cause extinctions at the cretaceous tertiary geological boundary we then discuss how the proposed extinction mechanisms may relate to the environmental consequences of asteroid and comet impacts in general our chief goal is to provide relatively simple prescriptions for evaluating the importance of impacting objects over a range of energies and compositions but we also stress that there are many uncertainties we conclude that impacts with energies less than about 10 mt are a negligible hazard for impacts with energies above 10 mt and below about 104 mt i e impact frequencies less than one in 6 104 years corresponding to comets and asteroids with diameters smaller than about 400 m and 650 m respectively blast damage earthquakes and fires should be important on a scale of 104 or 105 km which corresponds to the area damaged in many natural disasters of recent history however tsunami excited by marine impacts could be more damaging flooding a kilometer of coastal plain over entire ocean basins in the energy range of 104 105 mt intervals up to 3 105 years corresponding to comets and asteroids with diameters up to 850 m and 1 4 km respectively water vapor injections and ozone loss become significant on the global scale in our nominal model such an impact does not inject enough submicrometer dust into the stratosphere to produce major adverse effects but if a higher fraction of pulverized rock than we think likely reaches the stratosphere stratospheric dust causing global cooling would also be important in this energy range thus 105 mt is a lower limit where damage might occur beyond the experience of human history the energy range from 105 to 106 mt intervals up to 2 106 years corresponding to comets and asteroids up to 1 8 and 3 km diameter is transitional between regional and global effects stratospheric dust sulfates released from within impacting asteroids and soot from extensive wild fires sparked by thermal radiation from the impact can produce climatologically significant global optical depths of the order of 10 moreover the ejecta plumes of these impacts may produce enough no from shock heated air to destroy the ozone shield between 106 and 107 mt intervals up to 1 5 107 years corresponding to comets and asteroids up to 4 and 6 5 km diameter dust and sulfate levels would be high enough to reduce light levels below those necessary for photosynthesis ballistic ejecta reentering the atmosphere as shooting stars would set fires over regions exceeding 107 km and the resulting smoke would reduce light levels even further at energies above 107 mt blast and earthquake damage reach the regional scale 106 km tsunami cresting to 100 m and flooding 20 km inland could sweep the coastal zones of one of the world s ocean basins fires would be set globally light levels may drop so low from the smoke dust and sulfate as to make vision impossible at energies approaching 109 mt 108 years the ocean surface waters may be acidified globally by sulfur from the interiors of comets and asteroids the cretaceous tertiary impact in particular struck evaporate substrates that very likely generated a dense widespread sulfate aerosol layer with consequent climatic effects the combination of all of these physical effects would surely represent a devastating stress on the global biosphere

fireball passes and nothing burns the role of thermal radiation in the cretaceous tertiary event evidence from the charcoal record of north america high soot contents have been reported in cretaceous tertiary k t sedimentary rocks leading to the suggestion that the amount of thermal power delivered from the chicxulub impact was sufficient to have ignited wildfires soot cannot be used to indicate fire location however as soot from one large fire could spread globally sources other than biomass burning could also yield soot charcoal in nonmarine sedimentary rocks here quantified in situ in polished blocks provides a unique tool to record the distribution of wildfires and therefore assess the extent of any thermal radiation associated with the impact at chicxulub the k t and lowermost tertiary sedimentary rocks of six nonmarine sequences colorado to saskatchewan contain no charcoal or below background levels of charcoal and a significant quantity of noncharred organic materials revealing that there was no distinctive wildfire across the north american continent related to the k t event this finding indicates that the k t impact cannot have delivered a peak irradiance of 95 kw m 2 of thermal power to the atmosphere and 19 kw m 2 to the ground therefore the thermal power delivered from the impact to north america did not have the destructive potential previously predicted high amounts of thermal radiation were not responsible for the environmental perturbations or extinctions associated with the k t event

the global stratigraphy of the cretaceous tertiary boundary impact ejecta the chicxulub crater ejecta stratigraphy is reviewed in the context of the stratigraphy of underlying and overlying rock sequences the ejecta sequence is regionally grouped in a thick polymict and monomict breccia sequences inside the crater and within 300 km from the rim of the crater known from drill holes in and close to the breater and exposures near the border of yucatan and belize b gulf of mexico region 2500 m from the crater with up to 9 m thick complex tsunami wave influenced tektite bearing sequences in shallow marine 500 m deep environments and tektite bearing decimeter thick gravity flow deposits in deep water sites c an intermediate region between 2500 and 4000 km from the crater where centimeter thick tektite bearing layers occur and d a global distal region with a millimeter thin ejecta layer the distal ejecta layer is characterized by sub millimeter sized microkrystites often rich in ni rich spinels and altered clinopyroxene wherever present the ejecta layers mark exactly the sudden mass mortality horizon of the k t boundary what exactly caused the mass mortality is still uncertain but it appears the main event leading to the k t mass extinctions

constraints on the thermal energy released from the chicxulub impactor new evidence from multi method charcoal analysis it has been suggested by various workers that an extraterrestrial impact at the k t boundary delivered sufficient thermal power to ignite globally extensive wildfires numerous models have sought to predict the amount of thermal power released by the impact but none have considered the distribution of wildfire indicators in k t rocks probably the most distinctive product from combustion of biomass is charcoal the abundance of charcoal across the k t boundary at eight non marine sites in north america stretching from colorado in the south to saskatchewan in the north is recorded using three separate methods that allow quantitative analyses of microscopic to macroscopic charcoal particles this study not only provides the first extensive study of charcoals across the k t boundary but also uses the presence or absence of charred material to predict the extent and severity of the thermal pulse released by the k t impact across the area predicted to have suffered the most extreme environmental effects the k t rocks contain on average between four and eight times according to the method used less charcoal than the cretaceous rock record and non charred plant remains are abundant in the k t rocks the below background charcoal abundance and the high proportion of noncharred material in the k t and lowermost tertiary rocks across the western interior of north america suggest that there were no significant wildfires in this area associated with the k t event although soot and polyaromatic hydrocarbons pahs have been reported in the k t rocks we suggest that the soot morphology and pah types are more consistent with a source from the vaporization of hydrocarbons rather than biomass for spontaneous ignition of vegetation temperatures 545 c are necessary whereas smouldering will begin at 325 c the below background levels of charcoal in the k t rocks allow the ground temperatures following the k t impact to be constrained to between no more than 545 c at any point and not above 325 c for any significant period this implies a maximum irradiance of 2 at the ground surface and that no more than 6 kw m 2 of thermal power was delivered to the ground for more than a few hours therefore our results show that the fossil record indicates that the impact at chixculub did not generate sufficient thermal power to ignite extensive wildfires

winter monsoon convection in the vicinity of north borneo part i structure and time variation of the clouds and precipitation abstract radar and satellite observations in the vicinity of northern borneo obtained during the international winter monsoon experiment wmonex showed that the convection in that region underwent an extremely regular diurnal cycle over the sea to the north of borneo the general level of convective activity was increased during monsoon surges and during the passages of westward propagating near equatorial disturbances convective activity was decreased during monsoon lulls the diurnal cycle was well defined regardless of whether the general level of convective activity was enhanced or suppressed by synoptic scale events the cycle of convection over the sea was especially well documented it was typically initiated at about midnight when an offshore low level wind began where this wind met the monsoonal northeasterly flow usually just off the coast convective cells formed after midnight the convection continued to develop and by 0800 lst it had evolved into an organized mesoscale system with a

a hybrid 3 d electromagnetic method for induction detection of hydraulic fractures through a tilted cased borehole in planar stratified media as one of the most important nondestructive characterization techniques electromagnetic em methods can be used in the subsurface fracture detection especially for hydraulic fracture evaluation in unconventional petroleum exploration and development the multiscale nature of long but extremely thin 3 d fractures is difficult for conventional em modeling methods such as the finite element method fem in numerical simulation the problem becomes even more challenging when the effects of tilted borehole casing and planar stratified media need to be considered so far modeling a tilted borehole in layered media is still a major challenge for conventional methods in this paper we present the hybrid numerical mode matching method with the stabilized biconjugate gradient fast fourier transform method as the forward modeling algorithm that can efficiently model 3 d fractures in planar stratified media with a cased borehole environment numerical results validate the accuracy of the hybrid forward method and show orders of magnitude higher efficiency of this forward solver than the fem

the direct current response of electrically conducting fractures excited by a grounded current source abstracthydraulic fracture stimulation of low permeability reservoir rocks is an established and cross cutting technology for enhancing hydrocarbon production in sedimentary formations and increasing heat exchange in crystalline geothermal systems whereas the primary measure of success is the ability to keep the newly generated fractures sufficiently open long term reservoir management requires a knowledge of the spatial extent morphology and distribution of the fractures knowledge primarily informed by microseismic and ground deformation monitoring to minimize the uncertainty associated with interpreting such data we investigate through numerical simulation the usefulness of direct current dc resistivity data for characterizing subsurface fractures with elevated electrical conductivity by considering a geophysical experiment consisting of a grounded current source deployed in a steel cased borehole in doing so the casing efficiently energizes the fractures with steady current finite element

how hydrofractures become arrested fluids in the earth s crust are commonly transported by hydrofractures such as dykes and mineral veins many of which become arrested at various crustal depths hydrofractures are commonly arrested some showing blunt tips at contacts between soft low young s modulus and stiff high young s modulus layers for example many dyke tips are arrested at contacts between soft pyroclastic rocks and stiff basaltic lava flows and vein tips at contacts between soft marl and stiff limestone theoretical models indicate that overpressured buoyant hydrofractures in homogeneous isotropic host rocks should normally reach the surface in layered host rocks however abrupt changes in young s moduli horizontal discontinuities and layers with unusually high fracture perpendicular stresses encourage hydrofracture arrest it is proposed that for layer parallel loading stiff layers favour hydrofracture arrest during active compression but soft layers during extension it is concluded that for hydrofracture propagation to occur the stress field along its potential pathway must be essentially homogenous

winds in the strait of gibraltar summary automated meteorological observations were made from october 1985 to september 1986 in the narrows of the strait of gibraltar additional surface and upper air measurements were made in the strait from may to july 1986 the main wind events in summer were mostly mesoscale levanters winds from the east through the strait and a lesser number of synoptic scale levanters and westerlies during mesoscale levanters the wind speed increased and the pressure decreased from gibraltar downstream through the narrows as far as tangier a mesoscale low and the highest winds were found over the axis of the strait north of tangier high velocity 20 m s winds occurred only under 1 km height the air temperature profile became progressively warmer moving from gibraltar towards tangier a weak air temperature inversion decreased in height to the west of the narrows venturi flow as an explanation for the downstream increase of the low level winds during a levanter is inconsistent with observations a new model is proposed to explain the wind field associated with levanter winds in the strait that includes some orographic blocking and low level convergence into the narrows some west side divergence due to drag over water and leeside heating that generates a leeside mesoscale low pressure the surface low accelerates the surface winds to their maximum strength well downstream of the narrows a similar flow regime has been observed recently in the sea level channel between hawaii and maui

interaction of potential vorticity anomalies in extratropical cyclogenesis part ii sensitivity to initial perturbations in part i of this series of papers the static potential vorticity pv inversion diagnostics are performed to examine the lateral and vertical interactions between two upper level northern and southern troughs and their possible influences on the development of the march 1993 superstorm this study continues the investigation of the relative importance of two pv anomalies associated with the short wave troughs and their interaction in the surface cyclogenesis by considering their individual roles as an initial value problem the piecewise pv inversion technique is first used to isolate the upper level disturbances with a balanced vortex for each the vortex is then either removed or its intensity doubled by subtracting the balanced vortex from or adding to the control initial conditions with the modified initial conditions a mesoscale model is integrated for 36 h to examine how each of the upper level disturbances contributes to the surface development it is found that the northern and southern troughs play different roles in the surface cyclogenesis without the northern trough the eastward propagation of the southern trough slows down and the surface development is severely impeded more rapid cyclogenesis occurs when the northern trough s intensity is doubled on the other hand the deepening rate increases considerably when the southern trough is removed doubling the southern trough intensity slows the eastward progression of the northern trough and leads to a reduced deepening rate in conclusion the northern trough is crucial for the rapid development of the superstorm whereas the southern trough is important only during the incipient stage of the cyclone in particular a much stronger surface cyclone could be spawned in the absence of the southern trough this finding appears to contradict the previous work on the roles of trough mergers in extratropical cyclogenesis

k pg extinction reevaluation of the heat fire hypothesis 1 the global debris layer created by the end cretaceous impact at chicxulub contained enough soot to indicate that the entire terrestrial biosphere had burned preliminary modeling showed that the reentry of ejecta would have caused a global infrared ir pulse sufficient to ignite global fires within a few hours of the chicxulub impact this heat pulse and subsequent fires explain the terrestrial survival patterns in the earliest paleocene because all the surviving species were plausibly able to take shelter from heat and fire underground or in water however new models of the global ir heat pulse as well as the absence of charcoal and the presence of noncharred organic matter have been said to be inconsistent with the idea of global fires that could have caused the extinctions it was suggested that the soot in the debris layer originated from the impact site itself because the morphology of the soot the chain length of polycyclic aromatic hydrocarbons and the presence of carbon cenospheres were said to be inconsistent with burning the terrestrial biosphere these assertions either are incorrect or have alternate explanations that are consistent with global firestorms we show that the apparent charcoal depletion in the cretaceous paleogene layer has been misinterpreted due to the failure to correct properly for sediment deposition rates we also show that the mass of soot potentially released from the impact site is far too low to supply the observed soot however global firestorms are consistent with both data and physical modeling

a windstorm in the lee of a gap in a coastal mountain barrier abstract this paper describes a localized windstorm that struck some areas of northwest washington state on 28 december 1990 with winds exceeding 45 m s 1 resulting in extensive property damage treefalls and power outages arctic air originating within the interior of british columbia descended into a mesoscale gap in the coast cascade mountains and then accelerated ageostrophically to the west this gap acceleration is explained quantitatively by a three way balance among the pressure gradient force friction and inertia the flow maintained its integrity as a narrow current of high speed air as it exited the gap and subsequently accelerated over water troughing in the lee of the cascade mountains enhanced the horizontal pressure gradient over northwest washington this pressure gradient approximately balanced frictional drag resulting in only minimal acceleration farther south the flow decelerated as the current spread out horizontally

an improved method for hydrofracture induced microseismic event detection and phase picking the ability to detect small microearthquakes and identify their p and s phase arrivals is a key issue in hydrofracture downhole monitoring because of the low signal to noise ratios s n an array based waveform correlation approach matched filter is applied to improve the detectability of smallmagnitudeeventswithmechanismsandlocationssimilar to a nearby master event after detecting the weak events a transformed spectrogram method is used to identify the phase arrivals the technique has been tested on a downhole monitoring data set of the microseismic events induced by hydraulic fracturing it is shown that for this case one event with a s n around 6 db which is barely detectable using an array stacked short time average long time average sta lta detector under a reasonable false alarm rate is readily detected on the array stacked correlation traces the transformedspectrogramanalysisofthedetectedeventsimproves p ands phasepicking

an application of potential vorticity inversion to improving the numerical prediction of the march 1993 superstorm in this study a methodology is proposed to improve the model initial conditions based on available surface temperature observations from ships buoys and drifters it is tested with the numerical prediction of the 12 14 march 1993 superstorm that is initialized at its incipient stage over the gulf of mexico in this methodology the authors make use of the piecewise potential vorticity pv inversion technique and treat the temperature errors at the lowest level as a surrogate pv anomaly after inverting the wind and mass perturbations from the surface thermal anomaly and its pertinent interior pv anomaly a three dimensional dynamically consistent set of errors are obtained and added to the model initial conditions to improve the representation of the lower troposphere over the data sparse ocean it is found that the numerical model prediction initialized with the modified initial conditions exhibits significant improvements in the early rapid deepening and the track of the superstorm over ocean the development of a prefrontal squall line and the central sea level pressure traces during the life cycle of the cyclone as verified against observations these results show that the methodology proposed is promising in improving the representation of lower tropospheric meteorological variables in the model initial conditions based on available surface observations over data sparse regions

fire across the k t boundary initial results from the sugarite coal new mexico usa abstract it has been hypothesized that major global fires occurred following a bolide impact at the cretaceous tertiary boundary evidence for this has been mainly from soot or black carbon at a number of marine boundary sites as well as the occurrence of inertinites fusinite in coals above the boundary in addition the occurrence of fossil charcoal inertinites in potential tsunami deposits has been used to strengthen this idea however fire is known to have been widespread throughout the cretaceous based on the distribution of fossil charcoal and it is necessary to evaluate the claims for a global fire at the k t boundary within the context of this more extensive record of ancient fires the occurrence of the k t boundary within the sugarite coal sequence in the raton basin new mexico offers the opportunity to assess the incidence of fire in local peat forming vegetation in the latest cretaceous across the cretaceous tertiary boundary interval and in the earliest tertiary the distribution of fire products i e fossil charcoal is assessed using a combination of inertinite group macerals in polished blocks of coal and plant particles released by chemical maceration of coal inertinite group macerals fusinite semifusinite inertodetrinite which represent fossil charcoal and particles of charcoal in maceration residues are abundant throughout the sugarite coal sequence both before during and after the k t boundary event samples from below the boundary yield inertinites that constitute more than 20 of the coal three horizons are inertinite rich 50 fire was obviously an important element of the terrestrial environment during the latest cretaceous high inertinite values and abundant charcoal particles characterize the latest cretaceous part of the coal the carbonaceous shale just below the boundary the boundary interval itself and tertiary coals and carbonaceous shales above the boundary charcoal in mineral rich units of the latest cretaceous immediately below the boundary in the boundary interval and in the tertiary is dominated by small inertodetrinite particles these might have been wind blown from regional fires or they may reflect reworking during erosion which led to sediment input into the mire in either case the charcoal signature in these units is the same irrespective of their position in the sequence our data combined with that from two other sites in terrestrial sequences in north america show that fires were an integral part of mire ecosystems through the latest cretaceous and into the early tertiary therefore evidence for distinctive global wildfires at the cretaceous tertiary boundary would have to be sought from careful consideration of other aspects of charcoal deposition including flux rates for charcoal and soot

a diagnostic analysis of the superstorm of march 1993 abstract in this study the synoptic evolution of the march 1993 superstorm is documented using conventional observations and the predictability and deepening mechanisms of the storm are investigated using a newly implemented mesoscale version of the canadian regional finite element rfe mode it is found that although the rfe model can predict well the large scale background flow associated with the storm it fails to predict various important mesoscale elements when it is initialized with fields that contain weak signals of the low level circulations however when the storm is located close to the data rich region the model has considerable skill in predicting those mesoscale elements such as a prefrontal squall line upper and low level jets as well as the quantitative aspects of their associated precipitation observational analysis reveals that the storm developed in a convectively unstable prestorm environment with ample moisture content it first experienced an antecedent surface vorticity g

simulation of dc dual laterolog measurements in complex formations a fourier series approach with nonorthogonal coordinates and self adapting finite elements dual laterolog dll makes use of a galvanic conduction principle to focus electrical currents into rock formations therebyminimizingshoulderandboreholeeffectsinthemeasurement of formation resistivity the tool includes two separate focusing systems deep sensing lld and shallow sensing modes lls laterolog current focusing systems were designed for operation primarily in vertical boreholes penetrating horizontal layers only recently their design has been revised for operation in deviated wells in the presence of electrical anisotropy we simulated three dimensional3ddllmeasurementsindipping invaded and electrically anisotropic formations and appraised the corresponding effects on apparent resistivity logs simulations were performedbycombiningtheuseofafourier seriesexpansionin anonorthogonalsystemofcoordinateswithanexisting2dgoaloriented higher order and self adaptive finite element method this numerical algorithm yields accurate solutions in limited cputimebecauseonlyafewfouriermodesareneededtosimulate practical applications for the calculation of focused currents we introduced an embedded postprocessing method that incorporates a synthetic focusing principle to compute current intensitiesateachiterativestepofoptimalmeshrefinements our numerical method accurately simulates 3d dll measurements in rock formations that exhibit extreme contrasts of electrical resistivity simulations indicate that lls resistivity logs are more sensitive to both invaded and anisotropic layers than lld resistivity logs in deviated wells shoulder bed effects on apparent resistivitylogsincreasewithanincreaseofdipangle andareemphasized across thin conductive layers electrical anisotropy effects on apparent resistivity logs increase substantially with dip angle

a goal oriented framework for rapid integral equation based simulation of borehole resistivity measurements of 3d hydraulic fractures abstractwe have developed a goal oriented framework for fast integral equation based simulation of low frequency borehole resistivity measurements of 3d arbitrarily shaped hydraulic fractures the framework explores the possibility of applying various approximate integral equation methods to simulate borehole electromagnetic em measurements acquired in the vicinity of 3d hydraulic fractures generated with electrically conductive proppant it includes four approximate methods that are progressively more accurate costly and rigorous each method is used to approximate the method of moments solution of the integral equation and to evaluate extract quantities of interest e g bucked signals detected at receivers when compared with rigorous fast fourier transform fft accelerated method of moments solutions the numerical results obtained with the four methods indicate the following 1 all of the approximate methods capture the main features of the quantities of interest e g the shape of detected s

survival in the first hours of the cenozoic for several hours following the chicxulub impact the entire earth was bathed with intense infrared radiation from ballistically reentering ejecta the global heat pulse would have killed unsheltered organisms directly and ignited fires at places where adequate fuel was available sheltering underground within natural cavities or in water would have been a necessary but not always sufficient condition for survival survival through sheltering from an initial thermal pulse is not adequately considered in literature about cretaceous tertiary nonmarine extinctions we compare predicted intense short term thermal effects with what is known about the fossil record of nonmarine vertebrates and suggest that paleontological evidence of survival is compatible with theoretical results from bolide physics

doppler radar observation of a land breeze cold front abstract during the early morning hours of ii january 1981 a very narrow intense band of snow which had formed along the leading edge of a land breeze cold front was viewed by cp 4 radar near muskegon michigan the front formed well inland and moved through the area from the northeast shortly after dawn the driving force for the land breeze was the large temperature contrast that existed between radiationally cooled air over the northern highlands of lower michigan and the relatively warm lake modified air near the shore of lake michigan the possibility that the observed snowband was associated with a mesoscale feature other than the land breeze is investigated an analysis of minimum temperatures in the great lakes region for 11 january 1981 shows that a strong temperature gradient existed over western lower michigan this gradient reached a maximum value well inland rather than at the lake shore radar observations show the band to be over 80 km long and only 4 km wide oriented roughly parallel t

sensitivity analysis for the appraisal of hydrofractures in horizontal wells with borehole resistivity measurements abstractwe numerically evaluate the possibility of using borehole electromagnetic measurements to diagnose and quantify hydraulic fractures that have been artificially generated in a horizontal well hydrofractures are modeled as thin disks perpendicular to the well and filled with either sand based or electrically conductive proppant the study focuses on the effect of thickness and length radius of hydrofractures to assess their effects on specific configurations of borehole resistivity instruments numerical results indicate that several measurements e g those obtained with low and high frequency solenoids could be used to assess the thickness of a fracture however only low frequency measurements performed with electrodes and large spacing between transmitter and receivers 18 m exhibit the necessary sensitivity to reliably and accurately estimate the length of long hydrofractures up to 150 m in open hole wells in the case of steel cased wells the casing acts as a long electrode whereby

observations and modeling of a mesoscale cold surge during wispit a transient feature marked primarily by a sudden increase in wind speed and brief period of heavy snow was observed over northeastern colorado on 11 12 march 1993 little if any abrupt changes in surface pressure or temperature were noted such as might accompany a gravity current gradual temperature falls and pressure rises were observed behind the velocity surge however there was no cyclonic wind shift nor did the feature last for more than a few hours suggesting that it was not likely a classical front data indicate that the surge originated near the peak of the cheyenne ridge a 400 m east west elongated hill near the border between colorado and wyoming simulations using an idealized two dimensional isentropic model show that a transient resembling observed surge results from impulsively started flow over heated terrain heating creates convergence that is in phase with the velocity surge at the leading edge of the topographic wave the result is a coherent disturbance in velocity which moves downstream at nearly the mean flow speed simulations with the pennsylvania state university national center for atmospheric research nonhydrostatic model mm5 using a horizontal resolution of 6 7 km capture the evolution of the observed surge these simulations support the identification of the surge as a topographic wave modified by heating but they also indicate an important role played by latent heating in the updraft at the leading edge of the surge because the latent heating occurs mainly downstream from the cheyenne ridge the formation of the topographic wave is unaltered by it however the updraft at the leading edge of the surge it greatly intensified leading to a narrow propagating band of heavy snow

a family of frontal cyclones over the western atlantic ocean part i a 60 h simulation despite marked improvements in the predictability of rapidly deepening extratropical cyclones many operational models still have great difficulties in predicting frontal cyclogenesis that often begins as a mesoscale vortex embedded in a large scale parent cyclone system in this paper a 60 h simulation and analysis of a family of frontal cyclones that were generated over the western atlantic ocean during 13 15 march 1992 are performed using the pennsylvania state university national center for atmospheric research mesoscale model with a fine mesh grid size of 30 km although it is initialized with conventional observations the model reproduces well the genesis track and intensity of the frontal cyclones their associated thermal structure and precipitation pattern as well as their surface circulations as verified against the canadian meteorological centre analysis and other available observations it is shown that each frontal cyclone is initiated successively to the southwest of its predecessor in the cold sector first appearing as a pressure trough superposed on a baroclinically unstable basic state in the lowest 150 300 hpa then it derives kinetic energy from the low level available potential energy as it moves over an underlying warm ocean surface with weak static stability toward a leading large scale frontal zone and deepens rapidly by release of latent heat occurring in its own circulations one of the frontal cyclones originating in the cold air mass deepens 44 hpa in 42 h and overwhelms the parent cyclone after passing over the warm gulf stream water into the leading frontal zone these cyclones have diameters ranging from 500 to 1100 km as denoted by the last closed isobar and are spaced 1000 1400 km apart between their circulation centers during the mature stage they begin to establish their own cold warm frontal circulations once their first closed isobars appear thus distorting the leading large scale frontal structures and altering the distribution and type convective versus stratiform of precipitation it is found that the frontal cyclones accelerate and experience their central pressure drops as they move from high to low pressure regions toward the parent cyclone center and then they decelerate and fill as they travel away from the parent cyclone their spatial and temporal scales vertical structures as well as deepening mechanisms are shown to differ significantly from those typical extratropical cyclones as previously studied

detection and quantification of 3d hydraulic fractures with vertical borehole induction resistivity measurements abstract we have investigated the ability of low frequency induction resistivity measurements to detect and appraise hydraulic fractures induced near vertical boreholes integral equation based simulations indicate that coplanar measurements can detect fractures when they are injected with electrically conductive proppant to increase their conductivity contrast with the shale background specifically when a logging tool consisting of one transmitter and two receivers that are 1 2 and 1 5 m away is used to detect fractures with the effective electrical conductivity of 100 s m in a homogeneous shale formation of 1 3 s m conductivity the measurements 1 can indicate the boundary of fractures intersecting with vertical boreholes by the signal spikes generated only when the tool enters exits fractures 2 can detect fractures as small as approximately 0 15 m and differentiate fractures up to approximately 10 m in width 3 can detect fractures with height as small as 0 3 m 4 can differentiate ellipti

modeling low frequency electrode type resistivity tools in invaded thin beds the authors formulate and implement a numerical mode matching nmm method to model electrode type resistivity tools in invaded thin beds the authors derive the low frequency approximation of the maxwell s equations to obtain the partial differential equation for the potential field the new nmm program is validated by comparing the numerical results with those obtained from other dc programs it is found that this new program is much faster than the program using the finite element method fem and hence is useful for routine interpretation of resistivity logs and for inversion

sequential palynological changes across the composite cretaceous tertiary k t boundary claystone and contiguous strata western canada and montana u s a the boundary claystone in the western canada basin is composed of three intimately associated layers with a regional distribution a basal brownish grey hackly claystone a middle brownish black sa

gap winds in the strait of juan de fuca abstract gap winds can be defined as a flow of air in a sea level channel which accelerates under the influence of a pressure gradient parallel to the axis of the channel in february 1980 two distinct cases of gap winds were observed in the strait of juan de fuca between western washington state and british columbia during a study that measured spatial variation of low level marine winds and other parameters from the noaa p 3 research aircraft and a dense network of surface stations which included eight meteorological buoys these two cases were a high pressure region over central british columbia and a low pressure system propagating northward seaward of the washington coast both cases produced strong easterly winds of 13 15 m s 1 at the western end of the strait of juan de fuea the high pressure region provided a drainage air mass from the interior of british columbia which flowed through the straits of georgia and juan de fuca and eventually into the pacific ocean this air mass remained nearly hom

the influence of mesoscale features of the sea surface temperature distribution on marine boundary layer winds off the scotian shelf during the superstorm of march 1993 abstract this paper studies the mesoscale wind field during the blizzard of march 1993 off the east coast of north america and examines the influence of the sea surface temperature distribution on surface winds can the gulf stream and its meanders by its strong influence on the marine boundary layer generate mesoscale features in the wind field numerical simulations of the storm are carried out using the mc2 a fully elastic nonhydrostatic model simulations are conducted at different resolutions 50 25 10 5 and 2 km with both detailed and smoothed sst fields so as to examine the influence of these parameters on the marine boundary layer winds results from these numerical simulations are compared with surface observations from buoys the study reveals some mesoscale features in the wind field caused by the gulf stream s meanders and the warm eddies of the sst field in a stable boundary layer the meanders shaped a 50 55 kt 26 28 m s 1 band of winds in a general 40 45 kt 21 23 m s 1 wind fi

the ohio valley wave merger cyclogenesis event of 25 26 january 1978 part i multiscale case study abstract the long standing observational view of cyclogenesis involves an interaction between tropopause and surface based finite amplitude disturbances there are however instances where more than one upper level disturbance contributes to low level development a subset of these events involves wave or trough merger which has been defined as the amalgamation of two or more distinct 500 hpa vorticity maxima an example of this phenomenon involving a case of very intense continental cyclogenesis 25 26 january 1978 over the eastern united states is selected to elucidate the origin and evolution of precursor disturbances from the planetary scale to the mesoscale the analysis of this event reveals that the two well defined tropopause based disturbances that contribute to cyclogenesis have distinctly different origins and are brought together by confluent planetary scale flow one of these disturbances originates over the western north pacific ocean 10 days prior to cyclogenesis and tracks eastward

trajectories and distribution of material ejected from the chicxulub impact crater implications for postimpact wildfires 1 the trajectories of low and high energy ejecta from the chicxulub impact crater have been computed using a numerical code and compared with analyses of debris deposited in k t boundary sections these calculations indicate that low energy ejecta produces centimeter to meter thick deposits within 4000 km of the point of impact although its azimuthal distribution depends on the incident angle of the projectile with the surface of the earth the high energy ejecta or vapor plume rises through the atmosphere and isotropically expands at the top of the atmosphere the velocity of this ejecta increases as it rises approximately 12 of the high energy ejecta is lost because it reaches escape velocities while 25 of the material reaccretes within 2 hours 55 reaccretes within 8 hours and 85 reaccretes within 72 hours this ejecta is distributed globally but it is concentrated around the chicxulub impact site and at the antipode corresponding to india and the indian ocean 65 million years ago it is also slightly smeared in a longitudinal direction because of earth s rotation because this debris does not reaccrete all at once the collisional shock heating of the atmosphere will be drawn out over a period of a few days and will occur in pulses this could be an important factor when calculating postimpact chemical reactions in the stratosphere the calculations also indicate the ejecta would have ignited wildfires on several continents around the world although the distribution of those fires depends partly on the trajectory of the projectile

a technique for diagnosing three dimensional ageostrophic circulations in baroclinic disturbances on limited area domains abstract the methodology developed by keyser et al for representing and diagnosing three dimensional vertical circulations in baroclinic disturbances using a two dimensional vector streamfunction referred to as the psi vector is restricted to f plane channel model geometry the vertical circulation described by the psi vector consists of the irrotational or divergent part of the ageostrophic wind and the vertical velocity a key property of the psi vector is that its projections onto arbitrarily oriented orthogonal vertical planes yield independent vertical circulations allowing separation of a three dimensional vertical circulation into two two dimensional components and thus objective assessment of the extent to which a three dimensional vertical circulation is oriented in a preferred direction here the methodology for determining the psi vector is modified to be suitable for real data applications the modifications consists of reformulating the diagnostic equations to apply to conformal map pr

the electrical field in a borehole with a casing the electric field on the borehole axis in the presence of a casing can be divided into three zones the near intermediate and far zones within the intermediate zone determination of the second derivative of the potential allows me to define the formation resistivity outside the casing the electric field at large distances from the borehole has a radial direction that provides a sufficient depth of investigation in this direction the measurement requires knowledge of the casing conductance application of transmission line theory is based on the fact that the electric field in the formation is radial within the intermediate zone resulting in the conclusion that the vertical resolution of such a measurement would depend only upon the spacing of the electrodes required to estimate the second derivative of the potential

hst imaging of atmospheric phenomena created by the impact of comet shoemaker levy 9 hubble space telescope hst images reveal major atmospheric changes created by the collision of comet shoemaker levy 9 with jupiter plumes rose to 3000 kilometers with ejection velocities on the order of 10 kilometers second 1 some plumes were visible in the shadow of jupiter before rising into sunlight during some impacts the incoming bolide may have been detected impact times were on average about 8 minutes later than predicted atmospheric waves were seen with a wave front speed of 454 20 meters second 1 the hst images reveal impact site evolution and record the overall change in jupiter s appearance as a result of the bombardment

interaction of potential vorticity anomalies in extratropical cyclogenesis part i static piecewise inversion the relative importance of various potential vorticity pv perturbations and their mutual interactions associated with the superstorm of 12 14 march 1993 are investigated by applying a piecewise pv inversion diagnostic system to a 36 h simulation of the storm it is shown that the contributions from all pv anomalies to the surface development increase with time although their relative significance varies during the rapid deepening stage in general the upper level dry pv anomalies contribute the most to the rapid deepening of the storm followed in order by the lower level thermal anomaly and latent heat release comparing the pv anomalies and their inverted circulations reveals that there exists a favorable phase tilt between the upper and lower level anomalies that allows lower and upper level mutual interactions in which the circulations associated with the upper level pv anomalies enhance the lower level anomalies and vice versa in addition to the vertical interactions lateral interactions are also present among the upper level pv anomalies and the background flow it is also found that the background flow advection dominates the vortex vortex and vortex background flow interactions in the deepening of the storm the vortex vortex interactions of the two upper level positive pv anomalies cause the negative tilt of the main upper level trough during the rapid deepening period

the structure and evolution of gap outflow over the gulf of tehuantepec mexico abstract mesoscale model simulations are used to examine the structure and dynamics of a gap outflow event over the gulf of tehuantepec mexico that was associated with a surge of cold air along the eastern slopes of the sierra madre the simulated gap outflow winds emerged from chivela pass reached a maximum speed of 25 m s 1 and turned anticyclonically as they fanned out over the gulf northerly winds were also able to ascend the mountains east and to a lesser extent west of chivela pass indicating that the movement of cold air across the sierra madre was not confined to the pass a mesoscale pressure ridge was aligned along the axis of the gap outflow jet which was flanked to the west by an anticyclonic eddy and to the east by a weaker cyclonic eddy a model derived trajectory along the axis of the outflow jet traced an inertial path with anticyclonic curvature produced primarily by the coriolis acceleration the cross flow pressure gradient acceleration along this trajectory was negligible be

meteorological tower measurements of a surface cold front abstract measurements from the boulder atmospheric observatory meteorological research tower are used to describe the structure and physical processes of a strong surface cold front analysis reveals that the horizontal gradients in temperature and wind velocity at the front are concentrated within a 200 m distance and measured vertical velocities exceed 5 m s 1 at the leading edge of the front calculations with the miller frontogenesis equation show the magnitude and relative importance of cross frontal confluence versus differential vertical motion tilting in forcing frontogenesis

moment tensor inversion of microseisms from the b sand propped hydrofracture m site colorado abstract we apply a moment tensor inversion algorithm to microseismic events generated by hydrofracturing our dataset consists of microseismic events associated with a hydraulic fracturing experiment conducted at the gri doe m site near rifle colorado the event recordings were from a vertical string of 3 component accelerometer pods that are cemented in a borehole the accelerograms clearly show p and s waves which can be rotated into the sh and sv components to invert the p and s amplitudes for moment tensors we use just the first two peaks after the first arrival using this amplitude information and the average pulse width we formed a symmetric stylized pulse for integration and we inverted for the moment tensor resolution tests revealed that with the source microseism to receiver geometry we have at the m site where all receivers are in one borehole and at the same azimuth from the source we can extract the five deviatoric components of the moment tensor using combinations of p sh and sv amplitudes for example a minimum data set of 3 p wave 2 sv wave and 1 sh wave amplitudes to obtain the sixth component which is the isotropic component requires amplitude information from receivers at another azimuth we studied seven high quality events in detail and tested their results against two alternative source geometries these microseismic events tend to have a major double couple nodal plane aligned parallel to the main hydrofracture plane rather than have their tension t axes aligned parallel to the regional minimum principal compressive stress direction the events have seismic moments m0 on the order of 10 5 nm and moment magnitudes mw of about 2 5

simulation of multifrequency borehole resistivity measurements through metal casing using a goal oriented hp finite element method the authors simulate multifrequency through casing resistivity tool measurements operating at different frequencies in a borehole environment for the assessment of rock formation properties rock formations are assumed to exhibit axial symmetry around the axis of a vertical borehole the simulations are performed with a goal oriented hp adaptive finite element method that delivers exponential convergence rates in terms of the quantity of interest for example the second vertical difference of the electric potential against the cpu time numerical results confirm the efficiency and accuracy of the method allowing for high accuracy and reliable simulations of borehole logging measurements in the presence of highly conductive steel casing the study of different tool configurations shows the advantages of using calibrated instruments with toroid antennas located on the borehole wall the agreement between the numerical and analytical results when the latter is available is quantified errors on the simulations are consistently below 0 1

feasibility study for 2d frequency dependent electromagnetic sensing through casing we perform a numerical sensitivity study of various physical phenomena of interest for borehole resistivity logging applications in steel cased wells specifically we analyze the sensitivity of through casing measurements for detecting water invasion shale laminated sands and electrical anisotropy in the formation in addition we study the influence of the frequency of operation on through casing resistivity measurements the sensitivity analysis is performed using a highly accurate and reliable numerical method based on a 2d self adaptive goal oriented high order finite element method fem this method can be applied to simulate all types of resistivity logging measurements including normal laterolog induction and through casing resistivity measurements results quantify the effects of several physical phenomena that can be sensed through casing and that can be measured with accurate sensors we find that water invasion and shale laminated sands behind casing can be detected and accurately qua

analysis of electromagnetic induction for hydraulic fracture diagnostics in open and cased boreholes in this paper the sensitivity and detectability of an electromagnetic induction tool for hydraulic fracture detection are analyzed by calculating the electromagnetic response from an orthogonal transverse fracture otf in an open or cased borehole using the improved numerical mode matching method the otf is modeled as a slim circular disk which is axially symmetric with respect to the borehole axis and filled with a conductive or magnetic proppant the feasibility of the induction tool for fracture diagnostics was validated via scaled down experimental measurements we then quantitatively analyze the induction response sensitivity to different proppant parameters such as conductivity and permeability to evaluate the effectiveness of the induction logging tool for fracture detection the analysis reveals that the short spaced receiver can accurately locate the fracture position and distinguish small sized fractures while the long spaced receiver can differentiate fractures with large dimension casings with different thicknesses conductivities and permeabilities are modeled together with the fracture to investigate their effects in fracture detection finally the application of the induction tool to a fracture network is evaluated

hydro frac monitoring using ground time domain electromagnetics as motivation for considering new electromagnetic techniques for hydraulic fracture monitoring we develop a simple financial model for the net present value offered by geophysical characterization to reduce the error in stimulated reservoir volume calculations this model shows that even a 5 improvement in stimulated reservoir volume for a 1 billion barrel bbl field results in over 1 billion u s dollars us in net present value over 24 years for us 100 bbl oil and us 0 5 billion for us 50 bbl oil the application of conductivity upscaling often used in electromagnetic modeling to reduce mesh size and thus simulation runtimes is shown to be inaccurate for the high electrical contrasts needed to represent steel cased wells in the earth finescale finite difference modeling with 12 22 mm cells to capture the steel casing and fractures shows that the steel casing provides a direct current pathway to a created fracture that significantly enhances the response compared with neglecting the steel casing we consider conductively enhanced proppant such as coke breeze coated sand and a highly saline brine solution to produce electrically conductive fractures for a relatively small frac job at a depth of 3 km involving 5 000 bbl of slurry and a source midpoint to receiver separation of 50m the models show that the conductively enhanced proppant produces a 15 increase in the electric field strength in line with the transmitter in a 10 m background in a 100 m background the response due to the proppant increases to 213 replacing the conductive proppant by brine with a concentration of 100 000 ppm nacl the field strength is increased by 23 in the 100 m background and by 2 3 in the 10 m background all but the 100 000 ppm nacl brine in a 10 m background produce calculated fracture induced electric field increases that are significantly above 2 a value that has been demonstrated to be observable in field measurements

detection and quantification of three dimensional hydraulic fractures with horizontal borehole resistivity measurements this paper investigates the suitability of low frequency borehole resistivity measurements for detecting and appraising hydraulic fractures the effects of the borehole logging tool s transmitter receiver spacing orientation and operating frequency as well as the fracture s shape cross sectional area dip and electrical conductivity contrast with the embedding formation are quantified using an fast fourier transform fft accelerated integral equation solver simulation results for a logging tool that consists of one transmitter and two receivers in a homogeneous shale formation of 1 3 s m conductivity show the following 1 longer transmitter receiver spacings can differentiate larger fractures while shorter transmitter receiver spacings can detect smaller fractures specifically the tool can differentiate fractures up to 1000 m 2 in area if the receivers are 18 and 19 2 m away from the transmitter but this long spacing configuration cannot detect fractures smaller than 10 m 2 in area and requires the effective electrical conductivity of the fracture to be larger than 100 s m in comparison the tool can detect fractures as small as 1 m 2 in area if the receivers are 1 2 and 1 5 m away from the transmitter even if the effective electrical conductivity of the fracture is only 10 s m but this short spacing configuration cannot distinguish fractures larger than 10 m 2 in area 2 coaxial measurements are sensitive to the fracture cross sectional area but cannot differentiate fractures of the same area with different cross sectional shapes or dips transverse copolarized measurements can discern axially symmetric fractures from asymmetric ones for example in long spacing configuration they can differentiate elliptical fractures with an aspect ratio of 8 from circular or square fractures if their areas are within 1 m 2 to 1000 m 2 cross polarized measurements can quantify fracture dip and become more sensitive as the dip angle increases for example in long spacing configuration they can detect 15 dipping fractures that are larger than 100 m 2 in area but cannot distinguish them while they can detect and distinguish 60 dipping fractures if their areas are in the range of 100 1000 m 2 3 the measurements are mostly insensitive to the operating frequency in the 10 hz 1 khz range in the short spacing configuration and depend moderately on the operating frequency in the long spacing configuration 4 the relative strength of the measured signals is proportional to the fracture effective electrical conductivity when the fracture is more than ten times conductive compared to the embedding rock formation 5 short spacing measurements exhibit higher resolution the tool can differentiate two fractures as long as they are more than 1 m 4 m away from each other in the short spacing long spacing configuration 6 in complex fracture networks not only major branches but intermediate and small branches contribute to the shape and magnitude of measured signals the contributions depend mainly on the area and position of the branches

two severe freezes in brazil precursors and synoptic evolution abstract two freezes with repercussions on world coffee markets struck brazil in recent years one during fgge in 1979 the other in 1981 data from multiple sources including satellites and drifting buoys were analyzed for early warning signs and synoptic evolution of the freeze events two important precursors were found 1 a slowly moving long wave pattern in the central south pacific ocean amplified greatly one to two days before frontogenesis in south america and four to five days before the freezes in brazil 2 the long wave ridge when at maximum amplitude was located near the southern andes and the next long wave trough downstream was located in the south atlantic at the longitude of brazil this configuration channeled subantarctic air northward entirely over land into subtropical latitudes frontogenesis in low latitudes in the mid pacific was the first sign of wave amplification in the 1979 case subsequent frontogenesis in northern argentina was accelerated by the opportune approach of a s

multiscale hydraulic fracture modeling with discontinuous galerkin frequency domain method and impedance transition boundary condition to facilitate the detection of hydraulic fractures by electromagnetic survey a discontinuous galerkin frequency domain dgfd method is introduced in this paper to efficiently model the fracture responses under complicated geophysical environments in the proposed dgfd method the computational domain can be split into multiple subdomains with nonconformal meshes the riemann solver upwind flux is introduced to evaluate the numerical flux the impedance transition boundary condition itbc is employed to facilitate fracture modeling by approximating fractures as surfaces numerical results show that the itbc works well for different fracture conductivities dipping angles operation frequencies as well as different sources for both small and large scale fractures it also shows good agreement with the references the responses of fractures increase as their conductivities become larger large dipping angles can cause spikes on the responses in a borehole for a magnetic source higher operation frequencies can enhance the signal level while for an electric source the sensitivity to frequency is small when no borehole is considered the responses due to an electric source are in general larger than those due to a magnetic one however when a borehole with conductive mud is included the responses can be reversed for the electric and magnetic sources for multiple fractures outside a cased borehole the signal level of an electric source is significantly reduced while that of a magnetic source remains at a similar level compared with the scenario without a casing with the proposed technique multiscale modeling of hydraulic fractures in complicated geophysical environments becomes possible

the 1993 superstorm cold surge frontal structure gap flow and tropical impact in the wake of the eastern united states cyclone of 12 14 march 1993 a cold surge originating over alaska and western canada brought northerlies exceeding 20 m s21 and temperature decreases up to 158c over 24 h into mexico and central america this paper addresses the multiscale aspects of the surge from the planetary scale to the mesoscale focusing on 1 the structure and evolution of the leading edge of the cold surge 2 the reasons for its extraordinary intensity and equatorward extent and 3 the impact of the surge on the tropics specifically on the strength of the trade winds and on the sea surface temperature in the eastern pacific the cold surge was initiated as a developing cyclone over the gulf of mexico and an upstream anticyclone east of the rockies caused an along barrier pressure gradient to form forcing topographically channeled northerlies along the rocky and sierra madre mountains to transport cold air equatorward on the mesoscale the leading edge of the cold surge possessed nonclassical frontal structure for example as the cold surge entered mexico the coldest air and the strongest wind arrived at about 900 hpa before affecting the surface suggestive of a tipped forward leading edge to the surge also satellite imagery and surface observations indicate that the leading edge appeared to be successively regenerated in the warm presurge air the cold surge had characteristics reminiscent of a kelvin wave a tipped forward cold front a pressure jump line a bore and a gravity current but none of these conceptual dynamical models was fully applicable associated with the cold surge gap winds up to 25 m s21 were observed in the gulfs of tehuantepec a tehuantepecer fonseca papagayo and panama owing to the strong cross mountain pressure gradient in the case of the tehuantepecer a rope cloud emanated from the isthmus of tehuantepec and turned anticyclonically consistent with an inertial oscillation on the synoptic and planetary scales the extraordinary equatorward extent of the cold surge was aided by topographic channeling similar to cold air damming by a low latitude upper tropospheric trough and by the lower branch of the secondary circulation associated with a confluent jet entrance region aloft the cold surge also impacted the tropical atmosphere and ocean by contributing to the strengthening of the northeast trade winds over the eastern pacific ocean and by inducing local cooling of the sea surface temperature in the gulfs of tehuantepec and papagayo by about 48 88c

fireball passes and nothing burns the role of thermal radiation in the cretaceous tertiary event evidence from the charcoal record of north america comment and reply comment belcher et al 2003 1 reported that at six locations across north america quantities of charcoal in the cretaceous tertiary k t boundary clay are about an order of magnitude below background levels they interpreted this absence of charcoal as evidence for the absence of a global

atmospheric structure and momentum balance during a gap wind event in shelikof strait alaska abstract gap winds occur in topographically restricted channels when a component of the pressure gradient is parallel to the channel axis aircraft flight level data are used to examine atmospheric structure and momentum balance during an early spring gap wind event in shelikof strait alaska alongshore sea level pressure ridging was observed vertical cross sections show that across strait gradients of boundary layer temperature and depth accounted for the pressure distribution geostrophic adjustment of the mass field to the along strait wind component contributed to development of the observed pressure pattern boundary layer structure and force balance during this event was similar to that often observed along isolated barriers however the rossby radius was lager than the strait width and atmospheric structure in the strait exit region indicates transition of the flow to open coastline conditions two across strait momentum budgets show that the coriolis force and across strait pressure gradient w