atmospheric rotors and severe turbulence in a long deep valley abstractthe conceptual model of an atmospheric rotor is reexamined in the context of a valley using data from the terrain induced rotor experiment t rex conducted in 2006 in the southern sierra nevada and owens valley california all t rex cases with strong mountain wave activity have been investigated and four of them iops 1 4 6 and 13 are presented in detail their analysis reveals a rich variety of rotorlike turbulent flow structures that may form in the valley during periods of strong cross mountain winds typical flow scenarios in the valley include elevated turbulence zones downslope flow separation at a valley inversion turbulent interaction of in valley westerlies and along valley flows and highly transient mountain waves and rotors the scenarios can be related to different stages of the passage of midlatitude frontal systems across the region the observations from owens valley show that the elements of the classic rotor concept are modulated and at times almost completely offset

empirical relationships among seismic velocity effective pressure porosity and clay content in sandstone we use a multivariate analysis to investigate the influence of effective pressure pe porosity and clay content c on the compressional velocity vp and shear velocity vs of sandstones laboratory measurements on water saturated samples of 64 different sandstones provide a large data set that was analyzed statistically for each sample relationships between effective pressure and vp and vs have been determined all samples were well fit by relationships that have an exponential increase in velocity at low pe tapering to a linear increase with pe for pe greater than 0 2 kbar there are differences in the pressure dependences of velocity for different rocks particularly at very low pressures however the differences cannot be attributed to or c for the combined set of measurements from all samples the best fitting formulations are vp 5 77 6 94 1 73c 0 446 pe e 16 7pe and vs 3 70 4 94 1 57c 0 361 pe e 16 7pe while this is admittedly a very simplified parameterization it is remarkable how well

recent geothermal investigations in honduras an overview abstract since 1985 the los alamos national laboratory and the u s geological survey have worked with the empresa nacional de energia electrica of honduras to perform a geothermal assessment of six areas in honduras a combination of reconnaissance and detailed techniques was used to eliminate from consideration the sites of lower potential detailed geophysical investigations were performed at two high potential sites and three geothermal gradient coreholes were drilled at the highest potential site platanares high temperature fluids were encountered in two of these coreholes while one hole was non flowing evaluation of all the data collected suggests that there are two levels to the geothermal reservoir at platanares a shallow 1 2 km reservoir at a temperature of 225 is indicated by fluid geothermometers

elastic anisotropy of tambo gneiss from promontogno switzerland a comparison of crystal orientation and microstructure based modelling and experimental measurements author s vasin rn kern h lokajicek t svitek t lehmann e mannes dc chaouche m wenk hr abstract the authors 2017 felsic and mafic gneisses constitute large proportions of the upper and lower continental crust gneisses often display high anisotropy of elastic properties associated with preferred orientations of sheet silicates here we study the elastic anisotropy of a sample of tambo gneiss from promontogno in the central alps we apply optical microscopy time of flight neutron diffraction neutron and x ray tomography to quantify mineral composition and microstructures and use them to construct self consistent models of elastic properties they are compared to results of ultrasonic measurements on a cube sample in a multi anvil apparatus and on a spherical sample in an apparatus that can measure velocities in multiple directions both methods provide similar results it is shown that models of microstructure derived elastic properties provide a good match with ultrasonic experiment results at pressures above 100 mpa at a pressure of 0 1 mpa the correspondence between the model and the experiment is worse this may be caused by an oversimplification of the model with respect to microfractures or uncertainties in the experimental determination of s wave velocities and elastic tensor inversion the study provides a basis to determine anisotropic elastic properties of rocks either by ultrasonic experiments or quantitative models based on microstructures this information can then be used for interpretation of seismic data of the crust

aircraft measurements of mountain waves and their associated momentum flux over the british isles the hercules and canberra aircraft of the meteorological research flight have made a number of flights to investigate mountain waves over different mountainous areas of the british isles results from five flight days are presented in this study for each flight day the observed values of the dominant wavelength and the wave amplitude as a function of height were compared with the values predicted by two dimensional linear lee wave theory good agreement was obtained in four of the five cases measurements of the vertical flux of horizontal momentum show that the largest values were obtained when the wavelength was 20 9 km and the waves were only weakly trapped on this occasion the flux was observed to be constant with height in the range over which measurements were made supporting a theoretical result of eliassen and palm the value 0 35nm 2 is comparable with some aircraft measurements made over the rocky mountains

compressional and shear wave velocities as a function of confining stress in dry sandstones a laboratory study was carried out to investigate the influence of confining stress on compressional and shear wave velocities for a set of rock samples from gas producing sandstone reservoirs in the cooper basin south australia the suite of samples consists of 22 consolidated sublitharenites with helium porosity ranging from 2 6 to 16 6 we used a pulse echo technique to measure compressional and shear wave velocities on dry samples cylindrical 4 6 2 cm at room temperature and at elevated confining stress 60 mpa compressional and shear wave velocities in samples increase non linearly with confining stress a regression equation of the form v a be dp gives a good fit to the measured velocities with improved prediction of velocities at high confining stresses compared with equations suggested by other studies the predicted microcrack closure stresses of the samples show values ranging from 70 mpa to 95 mpa and insignificant correlation with porosity permeability or clay content there is a positive correlation between change in velocity with core porosity and permeability but this association is weak and diminishes with increasing confining stress experimental results show that pore geometry grain contact type and distribution and location of clay particles may be more significant than total porosity and clay content in describing the stress sensitivity of sandstones at in situ reservoir effective stress the stress dependence of cooper basin sandstones is very large compared with data from other studies the implication of our study for hydrocarbon exploration is that where the in situ reservoir effective stress is much less than the microcrack closure stress of the reservoir rocks the variation of reservoir effective stress could cause significant changes in velocity of the reservoir rocks the velocity changes induced by effective stress in highly stress sensitive rocks can be detected at sonic log and probably surface seismic frequencies

ultrasonic moduli for fluid saturated rocks mavko jizba relations rederived and generalized mavko and jizba propose a quantitative model for squirt dispersion of elastic wave velocities between seismic and ultrasonic frequencies in granular rocks their central results are the expressions for the so called unrelaxed frame bulk and shear moduli computed under an assumption that the stiff pores are drained or dry but the soft pores are filled with fluid mavko jizba expressions are limited to liquid saturated rocks but become inaccurate when the fluid bulk modulus is small e g for gas saturated rocks we have derived new expressions for unrelaxed moduli of fluid saturated porous rocks using sayers kachanov discontinuity formalism the derived expressions generalize the established mavko jizba relations to gas saturated rocks reduce to mavko jizba results when the pore fluid is liquid and yield dry moduli when fluid bulk modulus tends to zero we tested this by comparing our model and the model of mavko and jizba against laboratory measurements on a sample of westerly granite

mountain waves over mont blanc influence of a stagnant boundary layer abstract a stationary mountain wave embedded in southwesterly flow over mont blanc in the alps was observed simultaneously by three research aircraft and three types of remote sensing gps dropsondes airborne light detecting and ranging lidar and rapid scan satellite imagery these observations provide a basis for testing linear and nonlinear theories of how mountain waves over complex terrain are controlled by the ambient wind profile especially the effects of a low level stagnant layer and the jet stream aloft the layer of blocked flow near the ground reduced the amplitude of the wave generation the strong wind and weak stability in the upper troposphere forced the wave into a decaying evanescent state in spite of this evanescent condition no lee waves were observed the authors resolve this paradox by demonstrating that the stagnant layer below 3 km played an additional role it was able to absorb downward reflected waves preventing the formation of a resonant cavity linear theory inclu

the owles iop2b lake effect snowstorm dynamics of the secondary circulation abstractintense lake effect snowfall results from a long lake axis parallel llap precipitation band that often forms when the flow is parallel to the long axis of an elongated body of water such as lake ontario the intensity and persistence of the localized precipitation along the downwind shore and farther inland suggests the presence of a secondary circulation that helps organize such a band and maintain it for some time as the circulation is advected inland unique airborne vertical plane dual doppler radar data are used here to document this secondary circulation in a deep well organized llap band observed during intensive observing period iop 2b of the ontario winter lake effect systems owles field campaign the circulation centered on a convective updraft intensified toward the downwind shore and only gradually weakened inland the question arises as to what sustains such a circulation in the vertical plane across the llap band wrf model simulations indicate that the primary llap band a

secondary gravity wave generation over new zealand during the deepwave campaign multiple events during the deep propagating gravity wave experiment measurement program revealed mountain wave mw breaking at multiple altitudes over the southern island of new zealand these events were measured during several research flights from the national science foundation national center for atmospheric research gulfstream v aircraft utilizing a rayleigh lidar an na lidar and an advanced mesospheric temperature mapper simultaneously a flight on 29 june 2014 observed mws with horizontal wavelengths of 80 120 km breaking in the stratosphere from 10 to 50 km altitude a flight on 13 july 2014 observed a horizontal wavelength of 200 240 km mw extending from 20 to 90 km in altitude before breaking data from these flights show evidence for secondary gravity wave sgw generation near the breaking regions the horizontal wavelengths of these sgws are smaller than those of the breaking mws indicating a nonlinear generation mechanism these observations reveal some of the complexities associated with mw breaking and the implications this can have on momentum fluxes accompanying sgws over mw breaking regions

hydraulic aspects of fohn winds in an alpine valley this study examines the applicability of single layer hydraulic theory to alpine fohn winds in the example of the flow in the brenner pass region austria italy the south fohn is described as the gap flow over the pass and along the associated wipp valley numerical shallow water simulations for a wide range of initial conditions including shallow and deep fohn cases are discussed and compared with selected measurements collected within the mesoscale alpine programme map the observational analyses are based on doppler and aerosol backscatter lidar data for a specific fohn case and on surface observations and radiosoundings for all fohn cases observed within the 70 day map special observing period sop radiosoundings at a location upstream south and downstream north of the brenner pass reveal that the average map sop fohn case had subcritical flow south and nearly critical flow north of the brenner pass the hydraulic model indicates flow transition to a supercritical state near the pass a hydraulic jump 2 km further north mainly subcritical flow in the upper wipp valley except near the brenner and especially for shallow fohn a tendency to becoming supercritical in the lower wipp valley the model results suggest that the vertical topographic contraction exerts stronger control for the flow at the brenner gap than the lateral contraction in accordance with doppler lidar measurements the hydraulic model captures the decrease of the wind speed in the across valley direction from east to west in the northern part of the valley this asymmetric flow pattern is a result of the complex valley geometry rather than of the influence of upper level synoptic winds as suggested in a previous study for some observed cases the strength of the temperature inversion at the top of the fohn layer decreased across the brenner pass presumably due to entrainment processes consequently the reduced gravity decreased as well there are two major reasons for the only moderate agreement between the hydraulic parameters retrieved from soundings and those provided by the model the model assumes a constant value of reduced gravity and the calculation of hydraulic parameters for fohn cases without a strong and sharp temperature inversion is ambiguous essential flow patterns in the simulated fields such as the location of the pressure minimum and wind speed maxima compare well with the surface observations along a valley transect indications for a steeply amplified or breaking gravity wave resembling a hydraulic jump to the lee of the two mountain ridges are found in lidar observations as well as in the simulations copyright 2004 royal meteorological society

foehn cold pool interactions in the inn valley during piano iop2 a case study is presented of a south foehn emanating from the wipp valley austria which encountered a cold air pool cap in the inn valley near the city of innsbruck the analysis is based on data collected during the second intensive observation period of the penetration and interruption of alpine foehn piano field experiment foehn was initiated on 3 november 2017 by an eastward moving trough and terminated in the afternoon of 5 november 2017 by a cold front passage on two occasions reversed foehn flow deflected at the mountain ridge north of innsbruck penetrated to the bottom of the inn valley the first breakthrough occurred in the afternoon of 4 november 2017 it was transient and locally limited to the northwest of the city the second final breakthrough occurred in the morning of 5 november 2017 and was recorded by all surface stations in the vicinity of innsbruck it started with a foehn air intrusion to the northeast of innsbruck and continued with the westward propagation of the foehn cap boundary along the valley subsequently observed northerly winds above the city were caused by an atmospheric rotor a few hours later and prior to the cold front passage the cap pushed back and lifted the foehn air from the ground during both nights shear flow instabilities formed at the foehn cap interface which resulted in turbulent heating of the cap and cooling of the foehn however this turbulent heating cooling was partly compensated by other mechanisms especially in the presence of strong spatial cap heterogeneity during the second night heating in the cap was most likely overcompensated by negative horizontal temperature advection

a high resolution dual doppler technique for fixed multiantenna airborne radar a new technique is presented for the analysis of data collected by pairs of aircraft ac mounted fixed radar beams directed 30deg apart leading to two dimensional wind field syntheses in the horizontal and vertical planes the technique was applied to the 95 ghz wyoming cloud radar wcr configurations aboard the university of wyoming king air and the national center for atmospheric research c 130 research ac the construction of the data grid allows to closely follow the ac flight attitude and thus the beam scanned surfaces with a resolution between 30 and 45 m a weighted least squares method is employed to solve the velocity inverse decomposition problem for every valid grid cell the effect on the solution of the nonmeasured cross plane wind component is minimized by using an external estimate of the ambient wind the error sources are discussed and maximum expected values for the velocity field errors are provided with reference to the radar system the data collection process and specific aspects of the target under investigation these uncertainties 1 2 m s are quantified for two case studies that show the potential of the technique in retrieving the kinematic field in transects of cumulus and stratus clouds the technique produces smooth fine scale kinematic fields although each velocity point is the result of an independent calculation and no binding constraint is imposed among neighboring points as is done in other dual doppler techniques

numerical and observational case study of a deep adriatic bora a detailed analysis of bora winds is presented that were observed on 28 march 2002 in the north eastern part of the adriatic sea very high resolution numerical simulations are compared with airborne surface and balloon observations the key instrument for the verification of the numerical results is an aerosol backscatter lidar on board the dlr falcon research aircraft the high spatial resolution of the model and of the observational dataset allows several small scale aspects of the bora winds to be explored the study emphasises the great impact of boundary layer effects including convective mixing and surface friction on the structure of the bora flow the numerical model reveals that the diurnal cycle of the planetary boundary layer causes a diurnal variation of the gravity wave amplitude and consequently a variation in the bora strength the downslope flow is strongest during the night time when the impinging air mass is stably stratified and exhibits a low level jet the bora strength weakens during the daytime due to the evolution of a neutrally stratified convective boundary layer lidar observations and simulations both suggest that the observed bora winds are driven by the dynamics of orographic gravity waves in the deep north easterly cross mountain flow steeply amplified but non breaking gravity waves as well as trapped lee waves are found throughout the troposphere vertical separation of the boundary layer over the steep leeward terrain slope prevents the bora flow from reaching the coast as a result the flow is kept aloft in a series of at least three unsteady trapped lee waves before it reattaches to the surface over the sea downstream of the mountains no clear evidence is found for the existence of low level rotors underneath these lee waves the ability of the model to capture the trapped waves is found to depend on the horizontal model resolution bora winds are identified as jets emanating from several mountain gaps the physical mechanism for the gap flow formation is boundary layer separation controlled by surface friction flow separation is more effective over the highest terrain where a broad wake forms downstream with weak winds compared to the mountain gaps where the strong bora flow eventually reattaches to the surface the strongest gap jet belongs to the vratnik pass upstream of the town senj and forms the primary shear line in the northern adriatic with a corresponding potential vorticity pv banner the numerical model reveals several secondary orographic pv banners and embedded pv filaments the vertical pv distribution exhibits a two layer structure with pv anomalies at lower higher elevations originating from mountain gaps isolated mountain peaks surface friction has a minor direct effect on pv generation but has a major indirect effect in controlling the mechanism for the generation of pv in a simulation without surface friction the primary pv banner forms as a result of gravity wave breaking in the more realistic simulation however the primary mechanism for pv generation is flow separation controlled by surface friction copyright 2005 royal meteorological society

diurnal variation of downslope winds in owens valley during the sierra rotor experiment abstract the impact of diurnal forcing on a downslope wind event that occurred in owens valley in california during the sierra rotors project srp in the spring of 2004 has been examined based on observational analysis and diagnosis of numerical simulations the observations indicate that while the upstream flow was characterized by persistent westerlies at and above the mountaintop level the cross valley winds in owens valley exhibited strong diurnal variation the numerical simulations using the coupled ocean atmosphere mesoscale prediction system coamps capture many of the observed salient features and indicate that the in valley flow evolved among three states during a diurnal cycle before sunrise moderate downslope winds were confined to the western slope of owens valley shallow penetration state surface heating after sunrise weakened the downslope winds and mountain waves and eventually led to the decoupling of the well mixed valley air from the westerlies aloft around local noon decoupled

elastic piezosensitivity of porous and fractured rocks understanding the stress dependencies of seismic velocities is important for interpreting a variety of seismic data ranging from amplitude versus offset avo and velocity analysis to overpressure prediction and 4d seismic monitoring of reservoirs sometimes rather complex forms of these dependencies based on specific models of porous space geometry are used for example spherical contacts models duffy and mindlin 1957 merkel et al 2001 duffy merkel 2001 and crack contacts models gangi and carlson 1996 carcione and tinivella 2001 have been used in different studies gangi96 however usually the pore pressure velocity dependence along with the velocity dependence on the confining pressure are phenomenologically described by the following simple relationship zimmerman et al 1986 eberhart phillips et al 1989 freund 1992 jones 1992 prasad and manghnani 1997 khaksar et al 1999 carcione and tinivella 2001 kirstetter and macbeth 2001

deriving microstructure and fluid state within the icelandic crust from the inversion of tomography data the inversion of seismic data to infer rock microstructural properties and fluid flow patterns in the crust is a challenging issue in this paper we develop an effective medium model for estimating velocities in porous media including both pores and cracks and use it to derive the distribution of crack density beneath the reykjanes peninsula from accurate tomography data outside the active hydrothermal areas crack density is shown to decrease with depth there are two main reasons for this the closure of cracks because of the increasing overburden and the secondary filling of cracks because of hydrothermal flows however crack density may locally increase with depth beneath the southwestern part of the kleifarvatn lake this is consistent with the presence of a deep reservoir with supercritical fluids under pressure which may activate hydrofracturing processes we recognize that capturing the link between seismic data and the physical properties of crust is very difficult this study shows that a combination of mechanical concepts and effective medium theory contributes to improve our understanding of the phenomena occurring within the icelandic crust

airborne radar observations of lake effect snowbands over the new york finger lakes abstractthe vast majority of lake effect snow research throughout the years has focused on the north american great lakes since they are often associated with strong lake effect events that produce heavy downstream snowfall this study investigates a lake effect snow event that instead occurred over two smaller lakes the new york finger lakes which are just o 5 km wide and o 50 km long a pair of well defined snowbands that formed over seneca and cayuga lakes the two largest of the finger lakes were sampled from above by a vertically pointing doppler radar and lidar on board the university of wyoming king air uwka with typical widths matching the widths of the lakes and depths of less than 1000 m the long lake axis parallel bands were actually quite intense for their size for example updrafts of 2 3 m s 1 or greater within the band cores were common and reflectivity occasionally exceeded 5 dbz airborne dual doppler data show that both bands were sometimes accompanied by a well defined therm

numerical simulations of two layer flow past topography part i the leeside hydraulic jump abstractlaboratory observations of the leeside hydraulic jump indicate it consists of a statistically stationary turbulent motion in an overturning wave from the point of view of the shallow water equations swe the hydraulic jump is a discontinuity in fluid layer depth and velocity at which kinetic energy is dissipated to provide a deeper understanding of the leeside hydraulic jump three dimensional numerical solutions of the navier stokes equations nse are carried out alongside swe solutions for nearly identical physical initial value problems starting from a constant height layer flowing over a two dimensional obstacle at constant speed it is demonstrated that the swe solutions form a leeside discontinuity owing to the collision of upstream moving characteristic curves launched from the obstacle consistent with the swe solution the nse solution indicates the leeside hydraulic jump begins as a steepening of the initially horizontal density interface subsequently the nse solution indicates o

horizontal and temporal variability of mountain waves over mont blanc aircraft observations of mountain waves over mont blanc during the 2 november 1999 mesoscale alpine programme map case study are analysed the present paper focuses on the horizontal and temporal variability of the wave field and its momentum fluxes results from the first met office unified model new dynamics simulation of a real mountain wave case are presented the wave field and its fluxes are reproduced reasonably well considering the complexity of the problem the wave momentum fluxes are observed to be extremely variable which is surprising considering the stationarity of the wave field although some variation is observed in the vertical velocity magnitude the flux variability may result from the increasing midtropospheric wind shear with time the simulated wind fields are used to investigate the horizontal variability in the wave field the along track wave momentum flux is affected only slightly by a 2 km change in the position of the transect relative to mont blanc due to its displacement from the centre of the wave more important in this particular case is the effect of the averaging length on the flux profile due to the limited downstream extent of the wave field with large fluxes observed immediately over mont blanc however the position of the transect affects the apparent extent of the wave field and the magnitude of the variation in the cross wind component crown copyright 2003

the evolution of lee wave rotor activity in the lee of pike s peak under the influence of a cold frontal passage implications for aircraft safety abstract a lee wave rotor system interacting with an approaching cold front in the lee of pike s peak near colorado springs colorado on 1 april 1997 is studied observationally and numerically dynamical effects associated with the approaching cold front caused the amplification of the evolving lee wave and rotor creating increasingly more hazardous flight conditions for nearby airports the rapidly evolving winds measured by a doppler lidar and 915 mhz wind profilers and simulated by the regional atmospheric modeling system rams produced light to moderate turbulence for a research aircraft making missed approaches at the colorado springs airport during the wave amplification phase as the cold front approached the foothills the lee wave rotor system ended abruptly reducing hazardous flight conditions the doppler lidar s detailed measurements of the lee wave rotor system allowed for an evaluation of rams ability to capture these complex wind features qualitative and quantitative comparisons betw

blowing snow as a natural glaciogenic cloud seeding mechanism abstractwinter storms are often accompanied by strong winds especially over complex terrain under such conditions freshly fallen snow can be readily suspended most of that snow will be redistributed across the landscape e g behind obstacles but some may be lofted into the turbulent boundary layer and even into the free atmosphere in areas of boundary layer separation near terrain crests or in hydraulic jumps blowing snow ice crystals mostly small fractured particles thus may enhance snow growth in clouds this may explain why shallow orographic clouds with cloud top temperatures too high for significant ice initiation may produce usually light snowfall with remarkable persistence while drifting snow has been studied extensively the impact of blowing snow on precipitation on snowfall itself has not airborne radar and lidar data are presented to demonstrate the presence of blowing snow boundary layer separation and the glaciation of shallow supercooled orographic clouds further evidenc

observations simulations and analysis of nonstationary trapped lee waves abstract although considerable understanding of mountain waves has been gained with the aid of the steady state assumption it is clear that mountain waves evolve over time group velocity arguments indicate that this evolution can occur in less than 1 h this study uses observations of trapped lee waves to measure the rate at which their horizontal wavelengths change including a detailed analysis of two events in which such changes are clearly documented in one case doppler lidar observations show a steady increase in horizontal wavelength of 6 h 1 over 4 h and clearly illustrates the relationship between the wave clouds and wave motions in a second case visible satellite imagery reveals an increase in wavelength of 14 h 1 which is related to temporal changes in vertical air motions measured by wind profilers within the wave field hourly vertical profiles of wind and virtual temperature measured by radio acoustic sounding systems rass and wind profilers reveal important changes in the wave env

analysis of ducted motions in the stable nocturnal boundary layer during cases 99 abstract data obtained with multiple instruments at the main site of the 1999 cooperative atmosphere surface exchange study cases 99 are employed to examine the character and variability of wave motions occurring in the stable nocturnal boundary layer during the night of 14 october 1999 the predominant motions are surprisingly similar in character throughout the night exhibiting largely westward propagation horizontal wavelengths of 1 to 10 km phase speeds slightly greater than the mean wind in the direction of propagation and highly coherent vertical motions with no apparent phase progression with altitude additionally vertical and horizontal velocities are in approximate quadrature and the largest amplitudes occur at elevated altitudes of maximum stratification these motions are interpreted as ducted gravity waves that propagate along maxima of stratification and mean wind and that are evanescent above and occasionally below the altitudes at which they are ducted modal structures for ducte

stratospheric gravity wave fluxes and scales during deepwave abstractduring the deep propagating gravity wave experiment deepwave project in june and july 2014 the gulfstream v research aircraft flew 97 legs over the southern alps of new zealand and 150 legs over the tasman sea and southern ocean mostly in the low stratosphere at 12 1 km altitude improved instrument calibration redundant sensors longer flight legs energy flux estimation and scale analysis revealed several new gravity wave properties over the sea flight level wave fluxes mostly fell below the detection threshold over terrain disturbances had characteristic mountain wave attributes of positive vertical energy flux efz negative zonal momentum flux and upwind horizontal energy flux in some cases the fluxes changed rapidly within an 8 h flight even though environmental conditions were nearly unchanged the largest observed zonal momentum and vertical energy fluxes were mfx 550 mpa and efz 22 w m 2 respectively a wide variety of disturbance scales were found at flight level over

gap flows results from the mesoscale alpine programme an overview of advances in the observation modelling forecasting and understanding of flows through gaps achieved in the mesoscale alpine programme is given gaps are lateral constrictions of topography level gaps often combined with vertical terrain changes passes of the possible flow configurations only an asymmetric one relatively deep and slow upstream accelerating and thinning downstream which connects two different reservoirs on each side of the gap is examined the flow is strongly nonlinear making hydraulics reduced gravity shallow water theory rather than linear theory the simplest conceptual model to describe gap flow results from idealized topographical and flow conditions are presented together with gap flows through a pass in the central alpine wipp valley for a given depth of the upstream reservoir the gap controls the mass flux through it and marks the transition from a subcritical flow state upstream to a supercritical one downstream which eventually adjusts to the downstream reservoir in a hydraulic jump three gap flow prototypes were found a classical layer one with neutral stratification and a capping inversion and two with a continuous stratification for which a special analytical self similar hydraulic solution exists in all three cases a deepening wedge of nearly mixed and stagnant air forms on top of the gap flow plunging down from the pass the descent causes a warming and relative drying of the air making gap flows a special case of fohn topographical variations smaller than the gap scale cause additional hydraulic jumps flow separation vorticity banners gravity waves and interactions with cold pools turbulent friction cannot be neglected the climatological frequency of gap flows depends on the establishment of two different reservoirs and reaches 20 for the wipp valley copyright 2007 royal meteorological society

energy flux and wavelet diagnostics of secondary mountain waves abstract in recent years aircraft data from mountain waves have been primarily analyzed using velocity and temperature power spectrum and momentum flux estimation herein it is argued that energy flux wavelets i e pressure velocity wavelet cross spectra provide a more powerful tool for locating and classifying different types of mountain waves in the first part of the paper pressure velocity cross spectra using various linear mountain wave solutions are shown to be capable of disentangling collocated waves with different propagation directions and wavelength a field of group velocity vectors can also be determined in the second part the energy flux wavelet technique is applied to five cases of mountain waves entering the stratosphere from the terrain induced rotor experiment t rex in 2006 perturbation pressure along the flight track is determined using aircraft static pressure corrected hydrostatically with gps altitude in four of the cases collocated long up propagating and short down prop

the influence of inversions on rotors abstract rotors are small scale circulations about a horizontal or quasi horizontal axis that usually form in conjunction with high amplitude mountain waves the moderate to severe turbulence often found within rotors is a hazard to aviation observations and numerical model studies have revealed two types of mountain wave rotor systems the first type is associated with trapped waves whereas the second less common type resembles a hydraulic jump it has long been known that an upstream near mountaintop inversion plays an important role in mountain wave rotor formation in this study the role of the upstream inversion strength and height in an environment with sheared flow and over a barrier with a steep lee slope is investigated it is found that the second mountain wave rotor type is more likely to form when a strong near mountaintop inversion is present baroclinic generation of horizontal vorticity within the inversion along the lee slope leads to overturning in an upstream direction and spreadin

anisotropic effective medium modeling of the elastic properties of shales shales are complex porous materials normally consisting of percolating and interpenetrating fluid and solid phases the solid phase is generally comprised of several mineral components and forms an intricate and anisotropic microstructure the shape orientation and connection of the two phases control the anisotropic elastic properties of the composite solid we develop a theoretical framework that allows us to predict the effective elastic properties of shales its usefulness is demonstrated with numerical modeling and by comparison with established ultrasonic laboratory experiments the theory is based on a combination of anisotropic formulations of the self consistent sca and differential effective medium dem approximations this combination guarantees that both the fluid and solid phases percolate at all porosities our modeling of the elastic properties of shales proceeds in four steps first we consider the case of an aligned biconnected clay fluid composite composed of ellipsoidal inclusion

detailed dual doppler structure of kelvin helmholtz waves from an airborne profiling radar over complex terrain part i dynamic structure abstractkelvin helmholtz kh waves are remarkably common in deep stratiform precipitation systems associated with frontal disturbances at least in the vicinity of complex terrain as is evident f

on the pressure field in the slope wind layer abstract it has been suggested by some authors that the momentum equation for thermally driven slope flow should contain a horizontal pressure gradient term in addition to the buoyancy term it is shown that this suggestion is incorrect and leads to a spurious increase in along slope forcing unless the vertical component of the perturbation pressure gradient is included as well along slope accelerations due to the horizontal and vertical perturbation pressure gradients cancel each other exactly if the temperature perturbation is constant along the slope based on the concept of hydrostatic equilibrium perpendicular to the slope the error associated with neglecting the vertical component of the pressure gradient and the error due to the assumption of vertical hydrostatic equilibrium are evaluated a revised conceptual diagram of the relationship between buoyancy and pressure forces within the slope wind layer is presented

noble gases from honduras geothermal sites the elemental and isotopic composition of noble gases in hot springs and geothermal test wells were determined as part of a collaborative project to evaluate the potential for geothermal development in honduras central america the relative abundances of the noble gases in samples from the test wells indicate recharge temperatures for the geothermal systems equivalent to mean annual temperatures a common ratio of radiogenic 40ar to 4he of 0 35 corresponding to a k u ratio of 2 104 was found in samples from three of the studied areas platanares azacualpa and san ignacio a constant ratio may imply a common reservoir rock possibly the valle de angeles group of cretaceous to eocene age 3he 4he ratios are correlated in a positive sense with so4 concentration and in a negative sense with geothermal reservoir temperatures determined from chemical geothermometers these correlations are best explained by dilution of primary geothermal fluids with cooler sulfate rich waters the cooler waters inhibit deep boiling preserving high 3he 4he ratios in the surface springs in the el olivar region either the cool diluting fluid is sulfate poor or there is additional excess 3he provided by nearby quaternary trachytic to basaltic volcanism of the southern yojoa graben

elastic full waveform inversion of multicomponent ocean bottom cable seismic data application to alba field u k north sea elastic full waveform inversion of multichannel seismic data represents a data driven form of analysis leading to direct quantification of the subsurface elastic parameters in the depth domain previous studies have focused on marine streamer data using acoustic or elastic inversion schemes for the inversion of p wave data in this paper p and s wave velocities are inverted for using wide angle multicomponent ocean bottom cable obc seismic data inversion is undertaken using a two dimensional elastic algorithm operating in the time domain which allows accurate modeling and inversion of the full elastic wavefield including p and mode converted ps waves and their respective amplitude variation with offset avo responses results are presented from the application of this technique to an obc seismic data set from the alba field north sea after building an initial velocity model and extracting a seismic wavelet the data are inverted instages in the first stage the intermediate wavelength p wave v

geology of the platanares geothermal area departamento de copan honduras abstract the platanares geothermal area departamento de copan honduras is located within a graben that is complexly faulted the graben is bounded on the north by a highland composed of paleozoic metamorphic rocks in contact with cretaceous tertiary redbeds of unknown thickness these are unconformably overlain by tertiary andesitic lavas rhyolitic ignimbrites and associated sedimentary rocks the volcanic rocks are mostly older than 14 ma and thus are too old to represent the surface expression of an active crustal magma body thermal fluids that discharge in the area are heated during deep circulation of meteoric water along faults in a region of somewhat elevated heat flow geothermometry based upon the chemical composition of thermal fluids from hot springs and from geothermal gradient coreholes suggests that the reservoir equilibrated at temperatures as high as 225 to 240 c within the cretaceous redbed sequence three continuously cored geothermal gradient holes have been drilled fluids of about 165 c have been produced from two drilled along a nw trending fault zone from depths of 250 to 680 m a conductive thermal gradient of 139 c km at a depth of 400 m was determined from the third well drilled 0 6 km west of that fault zone these data indicate that the platanares geothermal area holds considerable promise for electrical generation by moderate to hightemperature geothermal fluids

a new velocity model for clay sand mixtu res1 none of the standard porosity velocity models e g the time average equation raymer s equations is satisfactory for interpreting well logging data over a broad depth range clays in the section are the usual source of the difficulty through the bias and scatter that they introduce into the relationship between porosity and p wave transit time because clays are composed of fine sheet like particles they normally form pores with much smaller aspect ratios than those associated with sand grains this difference in pore geometry provides the key to obtaining more consistent resistivity and sonic log interpretations a velocity model for clay sand mixtures has been developed in terms of the kuster and toksoz effective medium and gassmann theories in this model the total pore space is assumed to consist of two parts 1 pores associated with sand grains and 2 pores associated with clays including bound water the essential feature of the model is the assumption that the geometry of pores associated with sand grains is significantly different from that associated with clays because of this porosity in shales affects elastic compliance differently from porosity in sand stones the predictive power of the model is demonstrated by the agreement between its predictions and laboratory measurements and by its ability to predict sonic logs from other logs over large depth intervals where formations vary from unconsolidated to consolidated sandstones and shales

alpine gravity waves lessons from map regarding mountain wave generation and breaking the two month special observing period of the mesoscale alpine programme map in autumn 1999 included a variety of complex mountain wave events seven wave events were carefully analyzed compared with numerical models and described in published papers these detailed investigations revealed some common dynamical elements i e the importance of low level processes involving the slow moving boundary layer low level wind shear causing either wave absorption or decoupling spilling upstream blocking and latent heat release based on these studies it is clear that any quantitative prediction of mountain wave generation must take full account of these lower troposphere processes the newest numerical models show significant skill in simulating these effects using these models the climatology of waves over the alps can be studied copyright 2007 royal meteorological society

heat flow at the platanares honduras geothermal site meert j g and smith d l 1991 heat flow at the platanares honduras geothermal site in f goff editor honduras a geothermal investigation j volcanol geotherm res 45 91 99 three boreholes pltg 1 pltg 2 and pltg 3 were drilled in the platanares honduras geothermal system to evaluate the geothermal energy potential of the site the maximum reservoir temperature was previously estimated at 225 240 c using various types of chemical and isotopic geothermometry geothermal gradients of 139 239 c km calculated from two segments of the temperature depth profile for borehole pltg 2 were used to project a minimum depth to the geothermal reservoir of 1 2 1 7 km borehole pltg 1 exhibited an erratic temperature distribution attributed to fluid movement through a series of isolated horizontal and subhorizontal fractures the maximum measured temperature in borehole pltg 1 was 150 4 c and in pltg 2 the maximum measured temperature was 104 3 c pltg 3 was drilled after this study and the maximum recorded temperature of 165 c is similar to the temperature encountered in pltg 1 heat flow values of 392 mwm 2 and 266 mwm 2 represent the first directly measured heat flow values for honduras and northen central america radioactive heat generation based on gamma ray analyses of uranium thorium and potassium in five core samples is less than 2 0 wm 3 and does not appear to be a major source of the high heat flow several authors have proposed a variety of extensional tectonic environments for western honduras and these heat flow values along with published estimates of heat flow are supportive of this type of tectonic regime

determination of effective grain geometry for electrical modeling of sedimentary rocks accurate electrical modeling of sedimentary rocks is crucial for the interpretation of electrical survey data and must take into account the geometric information of the rock grains we have developed an incremental model for the multiphase electrical conductivity of sedimentary rocks on the theoretical basis of differential effective medium models the developed incremental model was first validated on clean and clay rich sandstones and then applied to simulate the conductivity offive digitally created rock samples with different spectra of grain aspect ratios the conductivity is calculated as a function of water conductivity at full water saturation and an effective grain aspect ratio for a two phase medium is determined to reproduce the electrical behavior of the digital rocks it was found that the effectivegrain aspect ratio can either be determined analytically or estimated from the aspect ratio spectrum a link between the obtained effective grain aspect ratio and the cementation coefficient widely used in petrophysics has been established the cementation coefficient increases with the decrease of the grain aspect ratio increasing the z axis depolarization factor and grain conductivity and the increase of sample porosity it showed that the cementation coefficient can be interpreted as a measure of the connectivity of pores as well as the conductivity of the grains our results gave us new insights into the physical meanings of the grain aspect ratio and cementation coefficient which could be used to facilitate the electrical modeling or interpretation of reservoir rocks

pressure effects on the joint elastic electrical properties of reservoir sandstones we conducted a laboratory study of the joint elastic electrical properties of sixty three brine saturated sandstone samples to assess the likely impact of differential pressure confining minus pore fluid pressures in the range 8 60 mpa on the joint interpretation of marine seismic and controlled source electromagnetic survey data the samples showed a wide range of petrophysical properties representative of most sandstone reservoirs we found that a regression equation comprising both a constant and an exponential part gave a good fit to the pressure dependence of all five measured geophysical parameters ultrasonic p and s wave velocity attenuation and electrical resistivity electrical resistivity was more pressure sensitive in clay rich sandstones with higher concentrations of low aspect ratio pores and micropores than in clean sandstones attenuation was more pressure sensitive in clean sandstones with large open pores macropores than in clay rich sandstones pore shape did not show any influence on the pressure sensitivity of elastic velocity as differential pressure increases the effect of the low aspect ratio pores and micropores on electrical resistivity becomes stronger than the effect of the macropores on attenuation further analysis of correlations among the five parameters as a function of pressure revealed potentially diagnostic relationships for geopressure prediction in reservoir sandstones

an effective medium algorithm for calculating water saturations at any salinity or frequency an algorithmic approach is used to mix the conductivities and geometric factors of the disperse components the rock and hydrocarbon particles with the host conductivity formation water the theoretical basis for the algorithm is the hanai bruggeman hb equation which itself incorporates only one disperse component the new approach the incremental model accommodates geometric factors such as sand and shale porosity exponents saturation exponent and also accommodates the associated grain conductivities its advantage over previous methods is that it works at any water salinity or tool frequency while allowing saturation and porosity exponents to have values other than 1 5 the algorithm is general and is written to accommodate simultaneous mixing of up to three disperse components and the formation water but it can be extended to accommodate any number of disperse components in its application to shaley sands hydrocarbon and sand elements are set to zero conductivity at low frequency but they can be nonzero for calculating saturations at higher frequencies the reason for this is that hydrocarbon and sand conductivities are real and very close to zero at low frequencies but at high frequencies the dielectric constants become significant making the complex conductivities nonzero the incremental model compared well with the waxman smits model on multiple water conductivity saturation data from two published experimental data sets the model is adaptable to other rock conductivity problems such as vuggy porosity vuggy water saturation and clay coated sand grains the potential exists for the algorithm to be part of a comprehensive computer program for calculating rock conductivities and saturations using many different combinations of rock fabrics and compositions

on the onset of bora and the formation of rotors and jumps near a mountain gap this study investigates the onset phase of a strong adriatic bora windstorm that occurred on 4 april 2002 the target area is a gap about 20 km wide embedded in the coastal mountain barrier of the dinaric alps that favours strong jet like winds airborne aerosol back scatter lidar measurements on board the dlr falcon research aircraft together with surface and upper air observations are used to verify high resolution numerical experiments conducted with the mesoscale atmospheric model rams and a single layer shallow water model swm especially during the breakthrough phase of the bora the flow at the gap exit exhibits a complex spatial structure and temporal evolution on a transect through the centre of the gap a hydraulic jump forms this is located close to the coast throughout the night and starts to propagate downstream in the early morning on a transect through the edge of the gap a lee wave induced rotor becomes established due to boundary layer separation it starts to propagate downstream about two hours after the jump this flow evolution implies that the onset of strong winds at the coast occurs several hours earlier downstream of the centre of the gap than downwind of the edge of the gap consequently the wind field in the vicinity of rijeka airport located downwind of the gap is strongly inhomogeneous and transient and represents a potential hazard to aviation measured bora winds at the surface exceed 20 ms 1 and the simulated wind speed in the gap wind layer exceeds 30 ms 1 the simulated turbulent kinetic energy exceeds 10 m2 s 2 rams indicates that wave breaking near a critical level is the dominant mechanism for the generation of the windstorm gap jets can be identified downstream of several mountain passes the simulated wave pattern above the dinaric alps the wave decay with height due to directional wind shear and the strong flow descent on the leeward side of the barrier are supported by measured back scatter intensities basic bora flow features including gap jets and jumps are remarkably well reproduced by swm simulations the rams reference run captures observed flow phenomena and the temporal flow evolution qualitatively well a cold low level bias an overestimated bora inversion strength and a slightly too early bora onset are probably related to insufficient turbulent mixing in the boundary layer the amplitude of trapped gravity waves the time of the bora breakthrough and the inversion strength are found to be quite sensitive to the turbulence parametrization copyright 2008 royal meteorological society

tectonic interpretation of the morphology of honduras the morphotectonics of honduras have been studied using existing geologic and topographic maps and imaging done from satellites and the following interpretations have been made during the late oligocene to early miocene a wide strike slip boundary existed in western honduras and eastern guatemala and produced east west trending basins containing the coarse clastic rocks of the subinal formation marine geophysical studies of the continental shelf of honduras show that during the rest of the miocene and the early pliocene the boundary was inactive but motion resumed in the late pliocene to pleistocene and produced horsts on the north coast of honduras in northwestern honduras the east northeast trending alignment of the jocotan copan and charnelecon river valleys may result from crustal flexuring rather than from faulting as previously proposed because the postulated fault the jocotan chamelecon fault cannot be reconciled with available geologic maps the northwest and northeast flowing rivers of central and eastern honduras define domains of strike slip faulting that have probably rotated 30 from an original set of conjugate fractures widespread deposition of conglomerates suggests that strike slip movements began in the mid cretaceous and reoccurred at intervals culminating in the development of pull apart basins in western honduras during the late pliocene at the present time no further strike slip movement is possible as the faults defining each domain lie parallel and perpendicular to the middle america trench new conjugate fractures however cut honduras along north south and east northeast trends and have also separated into domains in the domain of north south fractures easterly directed ductile extension of the lithosphere beneath western honduras and guatemala is opening up rifts but the domain of east northeast fractures is characterized by strike slip motion that has produced left lateral pull aparts in central honduras early workers identified no rift valley extending from the gulf of fonseca to the caribbean and there is no fresh evidence upon which to base the existence of one today the notion of the honduras depression which has persisted over the last half century stems from misinterpretation of the maps and writings of karl sapper

rock physics developments in seismic exploration a personal 50 year perspective i present an historical overview of the major developments in rock physics over the past half century key developments are described for both modeling and laboratory experiments and how they have been applied in seismic exploration reservoir characterization and monitoring in particular i chronicle the development of laboratory methods for determining the velocity and attenuation of elastic waves in rock samples at sonic and ultrasonic frequencies this is followed by a description of the validity of theories originally developed by gassmann and biot in the 1950s and employed for describing the propagation of elastic waves in fluid saturated porous media i outline problems and solutions in the use of ultrasonic measurements to predict velocities and attenuation at seismic frequencies field and laboratory studies are described in which a range of frequencies seismic through sonic and ultrasonic was covered and successfully modeled i describe procedures developed during the 1950s and 1960s for interpreting laboratory measurements in terms of pore structure and degree of saturation based on self consistent and scattering theories laboratory equipment used for determining the elastic properties of anisotropic materials is described along with a discussion of the results obtained including the correlation between both fluid permeability and prediction of in situ state of stress with the degree of shear wave splitting finally i discuss the application of rock physics developments to reservoir characterization and monitoring in particular to time lapse seismic monitoring

exploration drilling and reservoir model of the platanares geothermal system honduras central america abstract results of drilling logging and testing of three exploration core holes combined with results of geologic and hydrogeochemical investigations have been used to present a reservoir model of the platanares geothermal system honduras geothermal fluids circulate at depths 1 5 km in a region of active tectonism devoid of quaternary volcanism large artesian water entries of 160 to 165 c geothermal fluid in two core holes at 625 to 644 m and 460 to 635 m depth have maximum flow rates of roughly 355 and 560 l min respectively which are equivalent to power outputs of about 3 1 and 5 1 mw thermal dilute alkali chloride reservoir fluids tds 1200 mg kg are produced from fractured miocene andesite and cretaceous to eocene redbeds that are hydrothermally altered fracture permeabillity in producing horizons is locally greater than 1500 and bulk porosity is 6 a simple fracture dominated volume impedance model assuming turbulent flow indicates that the calculated reservoir storage capacity of each flowing hole is approximately 9 7 106 l kg cm 2 tritium data indicate a mean residence time of 450 yr for water in the reservoir multiplying the natural fluid discharge rate by the mean residence time gives an estimated water volume of the platanares system of 0 78 km3 downward continuation of a 139 c km conductive gradient at a depth of 400 m in a third core hole implies that the depth to a 225 c source reservoir predicted from chemical geothermometers is at least 1 5 km uranium thorium disequilibrium ages on calcite veins at the surface and in the core holes indicate that the present platanares hydrothermal system has been active for the last 0 25 m y

climatology of the sierra nevada mountain wave events abstract this note presents a satellite based climatology of the sierra nevada mountain wave events the data presented were obtained by detailed visual inspection of visible satellite imagery to detect mountain lee wave clouds based on their location shape and texture consequently this climatology includes only mountain wave events during which sufficient moisture was present in the incoming airstream and whose amplitude was large enough to lead to cloud formation atop mountain wave crests the climatology is based on data from two mountain wave seasons in the 1999 2001 period mountain wave events are classified in two types according to cloud type as lee wave trains and single wave clouds the frequency of occurrence of these two wave types is examined as a function of the month of occurrence october may and region of formation north middle south or the entire sierra nevada range results indicate that the maximum number of mountain wave events in the lee of the sierra nevada occurs in the m

momentum flux estimates for south georgia island mountain waves in the stratosphere observed via satellite abstract we show high resolution satellite observations of mountain wave events in the stratosphere above south georgia island in the remote southern atlantic ocean and compute the wave momentum fluxes for these events the fluxes are large and they imply important drag forces on the circulation small island orography is generally neglected in mountain wave parameterizations used in global climate models because limited model resolution treats the grid cell containing the island as ocean rather than land our results show that satellite observations can be used to quantitatively constrain mountain wave momentum fluxes and they suggest that mountain waves from island topography may be an important missing source of drag on the atmospheric circulation

effects of fluids and dual pore systems on pressure dependent velocities and attenuations in carbonates theeffectsoffluidsubstitutiononp ands wavevelocitiesin carbonates of complex texture are still not understood fully the often used gassmann equation gives ambiguous results when compared with ultrasonic velocity data we present theoretical modelingofvelocityandattenuationmeasurementsobtainedata frequency of 750 khz for six carbonate samples composed of calcite and saturated with air brine and kerosene although porosities 2 14 and permeabilities 0 74 md are relatively low velocity variations are large differences between the highest and lowest p and s wave velocities are about 18 and 27 for brine saturated samples at 60 and 10 mpa effective pressure respectively s wave velocities are measured for two orthogonal polarizations forfourofsixsamples anisotropyisrevealed the gassmann model underpredicts fluid substitution effects by 2 for three samples and by as much as 5 for the rest of the six samples moreover when dried they also show decreasing attenuationwithincreasingconfiningpressure tomodelthisbehavior we examine a pore model made of two pore systems one constitutesthemainanddrainableporosity andtheotherismade ofundrainedcracklikeporesthatcanbeassociatedwithgrain tograincontacts inaddition thesedriedrocksamplesaremodeled to contain a fluid filled pore system of grain to grain contacts potentiallycausinglocalfluidflowandattenuation forthetheoretical model we use an inclusion model based on the t matrix approach whichalsoconsiderseffectsofporetextureandgeometry and porefluid global and local fluidflow by using a dualpore system we establish a realistic physical model consistently describingthemeasureddata

turbulence characteristics in an elevated shear layer over owens valley abstract characteristics of turbulence in the lower and middle troposphere over owens valley have been examined using aircraft in situ measurements obtained from the terrain induced rotor experiment the two events analyzed in this study are characterized by a deep turbulent layer from the valley floor up to the midtroposphere associated with the interaction between trapped waves and an elevated shear layer kelvin helmholtz kh instability develops above the mountaintop level and often along the wave crests where the richardson number is reduced the turbulence induced by kh instability is characterized by a progressive downscale energy cascade a well defined inertial subrange up to 1 km and large eddies with vertical to horizontal aspect ratios less than unity the turbulence below the mountaintop level is largely shear induced associated with wave steepening and breaking and is more isotropic evaluation of structure functions indicates that while the turbulence energy cascade is predominately dow

fluid inclusions and preliminary studies of hydrothermal alteration in core hole pltg 1 platanares geothermal area honduras abstract the platanares geothermal area in western honduras consists of more than 100 hot springs that issue from numerous hot spring groups along the banks or within the streambed of the quebrada de agua caliente brook of hot water evaluation of this geothermal area included drilling a 650 m deep pltg 1 drill hole which penetrated a surface mantling of stream terrace deposits about 550 m of tertiary andesitic lava flows and cretaceous to lower tertiary sedimentary rocks in the lower 90 m of the drill core fractures and cavities in the drill core are partly to completely filled by hydrothermal minerals that include quartz kaolinite mixed layer illite smectite barite fluorite chlorite calcite laumontite biotite hematite marcasite pyrite arsenopyrite stibnite and sphalerite the most common open space fillings are calcite and quartz biotite from 138 9 m depth dated at 37 41 ma by replicate 40 ar 39 ar analyses using a continuous laser system is the earliest hydrothermal mineral deposited in the pltg 1 drill core this mid tertiary age indicates that at least some of the hydrothermal alteration encountered in the pltg 1 drill core occured in the distant past and is unrelated to the present geothermal system furthermore homogenization temperatures t h and melting point temperatures t m for fluid inclusions in two of the later formed hydrothermal minerals calcite and barite suggest that the temperatures and concentration of dissolved solids of the fluids present at the time these fluid inclusions formed were very different from the present temperatures and fluid chemistry measured in the drill hole liquid rich secondary fluid inclusions in barite and caicite from drill hole pltg 1 have t h values that range from about 20 c less than the present measured temperature curve at 590 1 m depth to as much as 90 c higher than the temperature curve at 46 75 m depth many of the barite t h measurements ranging between 114 and 265 c plot above the reference surface boiling point curve for pure water assuming hydrostatic conditions however the absence of evidence for boiling in the fluid inclusions indicates that at the time the minerals formed the ground surface must have been at least 80 m higher than at present and underwent stream erosion to the current elevation near surface mixed layer illite smectite is closely associated with barite and appears to have formed at about the same temperature range about 120 to 200 c as the fluid inclusion t h values for barite fluid inclusion t h values for calcite range between about 136 and 213 c several of the calcite t h values are significantly lower than the present measured temperature curve the melting point temperatures t m of fluid inclusion ice yield calculated salinities ranging from near zero to as much as 5 4 wt nacl equivalent which suggest that much of the barite and calcite precipitated from fluids of significantly greater salinity than the present low salinity platanares hot spring water or water produced from the drill hole

effects of porosity and clay content on wave velocities in sandstones the ultrasonic compressional vp and shear vs velocities and first arrival peak amplitude ap were measured as functions of differential pressure to 50 mpa and to a state of saturation on 75 different sandstone samples with porosities ranging from 2 to 30 percent and volume clay content c ranging from 0 to 50 percent respectively both vp and vs were found to correlate linearly with porosity and clay content in shaly sandstones at confining pressure of 40 mpa and pore pressure of 1 0 mpa the best least squares fits to the velocity data are vp km s 5 59 6 93 2 18c and vs km s 3 52 4 91 1 89c deviations from these equations are less than 3 percent and 5 percent for vp and vs respectively the velocities of clean sandstones are significantly higher than those predicted by the above linear fits about 7 percent for vp and 11 percent for vs which indicates that a very small amount of clay 1 or a few percent of volume fraction significantly reduces the elastic moduli of sandstones for shaly

short wave signatures of stratospheric mountain wave breaking abstract recent stratospheric mountain wave measurements over the sierra nevada indicate that downgoing secondary waves may be common or even ubiquitous in large wave events because of their short wavelengths they may dominate the vertical velocity field near the tropopause and they give a remote indicator of wave breaking farther aloft using a 2d numerical model the authors have simulated the secondary wave generation process with qualitative agreement in the wave location phase speed wavelength i e 10 20 km and amplitude a key to the analysis was the use of morlet wavelet cross spectra on both the observational and simulated fields several characteristics of the simulated secondary waves were unexpected first the secondary waves are generated with good efficiency approaching 20 of the primary upgoing wave momentum flux second whereas most of the secondary waves are downward the shorter components reflect upward from the tropopause giving a kind of lee wave trapping in the lower str

wave induced boundary layer separation in the lee of the medicine bow mountains part i observations abstracttwo cases of mountain waves rotors and the associated turbulence in the lee of the medicine bow mountains in southeastern wyoming are investigated in a two part study using aircraft observations and numerical simulations in part i observations from in situ instruments and high resolution cloud radar on board the university of wyoming king air aircraft are presented and analyzed measurements from the radar compose the first direct observations of wave induced boundary layer separation the data from these two events show some striking similarities but also significant differences in both cases rotors were observed yet one looks like a classical lee wave rotor while the other resembles an atmospheric hydraulic jump with midtropospheric gravity wave breaking aloft high resolution 30 30 m2 dual doppler syntheses of the two dimensional velocity fields in the vertical plane beneath the aircraft reveal the boundary layer separation the scale and structure of the attendant rotors and downsl

secondary generation of gravity waves associated with the breaking of mountain waves abstract the generation of small scale gravity waves associated with the breaking of mountain waves in the stratosphere has been simulated within a fully compressible nonhydrostatic two dimensional numerical model the model includes the mesosphere and offers sufficiently high spatial resolution to characterize the breaking and generation of gravity waves in the stratosphere the mean flow is initialized by cira86 at 40 n in february a bell shaped mountain with 30 km half width and 1 5 km height is located in the bottom of the modeled domain the primary wave forced by the mountain propagates into the stratosphere with amplitude increasing with height and subsequently breaks in the lower stratosphere after the primary wave breaking significant wave activity is simulated in the stratosphere these secondary waves are generated at both the upstream and the downstream edges of the breaking zone analysis is mostly focused on downstream small scale waves the horizontal and vertical wavelengths of the se

lee wave resonances over double bell shaped obstacles lee wave resonance over double bell shaped obstacles is investigated through a series of idealized highresolution numerical simulations with the nonhydrostatic coupled ocean atmosphere mesoscale prediction system coamps model using a free slip lower boundary condition the profiles of wind speed and stability as well as terrain derive from observations of lee wave events over the sierra nevada and inyo mountains from the recently completed terrain induced rotor experiment t rex numerical experiments show that double bell shaped obstacles promote trapped lee waves that are in general shorter than those excited by an isolated ridge while the permissible trapped lee wave modes are determined by the upstream atmospheric structure primarily vertical wind shear the selected lee wave wavelengths for two obstacles that are close or equal in height are dictated by the discrete terrain spectrum and correspond to higher harmonics of the primary orographic wavelength which is equal to the ridge separation distance the exception is the smallest ridge separation distance examined one that corresponds to the owens valley width and is closest to the wavelength determined by the given upstream atmospheric structure for which the primary lee wave and orographic wavelengths were found to nearly coincide the influence two mountains exert on the overall lee wave field is found to persist at very large ridge separation distances for the nonlinear nonhydrostatic waves examined the ridge separation distance is found to exert a much stronger control over the lee wave wavelengths than the mountain half width positive and negative interferences of lee waves which can be detected through their imprint on wave drag and wave amplitudes were found to produce appreciable differences in the flow structure mainly over the downstream peak with negative interference characterized by a highly symmetric flow pattern leading to a low drag state

a geochemical model of the platanares geothermal system honduras abstract results of exploration drilling combined with results of geologic geophysical and hydrogeochemical investigations have been used to construct a geochemical model of the platanares geothermal system honduras three coreholes were drilled two of which produced fluids from fractured miocene andesite and altered cretaceous to eocene conglomerate at 450 to 680 m depth large volume artesian flows of 160 165 c predominantly bicarbonate water are chemically similar to but slightly less saline than widespread boiling hot spring waters the chemistry of the produced fluid is dominated by equilibrium reactions in sedimentary rocks at greater depths and higher temperatures than those measured in the wells chemical isotope and gas geothermometers indicate a deep fluid temperature of 200 245 c and reflect a relatively short residence time in the fractures feeding the wells chloride enthalpy relations as well as isotopic and chemical compositions of well discharges thermal springs and local cold waters support a conceptual model of ascending high temperature minimum 225 c parent fluid that has cooled conductively to form the 160 165 c shallow to 680 m fluid encountered by the wells the hot spring waters are formed by boiling and steam loss from more or less conductively cooled parent fluid the more dilute boiling spring waters cl 32 mg kg have cooled from 225 c to about 160 c by conduction and from 160 c to 98 c by boiling the most concentrated boiling spring waters cl 37 mg kg have cooled from 225 c to about 200 c by conduction and from 200 c to 98 c by boiling intermediate concentrations reflect mixed cooling paths

a simple way to model the pressure dependency of rock velocity abstract modeling the pressure dependency of rock velocity is important for interpreting and comparing the seismic and earthquake data from different depths this study develops a multicomponent differential effective medium model for the elastic properties of porous rocks with two types of pores in the grain background without mixing order the developed model is applied to modeling the pressure dependent elastic velocity of porous rocks by incorporating the variation of stiff and compliant porosity as a function of pressure the pressure dependent stiff and compliant porosity were inverted from the measured total porosity under pressure using a dual porosity model and the unknown constant stiff and compliant pore aspect ratios were inverted by best fitting the modeled velocity to the measured data application of the approach to a low porosity granite and a medium porosity sandstone sample showed that the pressure dependency of rock velocity can be satisfactorily modeled by the developed model using the pressure dependent stiff and compliant porosity and carefully estimated stiff and compliant pore aspect ratio values

the intense lee wave rotor event of sierra rotors iop 8 abstract a large amplitude lee wave rotor event observationally documented during sierra rotors project intensive observing period iop 8 on 24 26 march 2004 in the lee of the southern sierra nevada is examined mountain waves and rotors occurred over owens valley in a pre cold frontal environment in this study the evolution and structure of the observed and numerically simulated mountain waves and rotors during the event on 25 march in which the horizontal circulation associated with the rotor was observed as an opposing easterly flow by the mesonetwork of surface stations in owens valley are analyzed the high resolution numerical simulations of this case performed with the coupled ocean atmosphere mesoscale prediction system coamps run with multiple nested grid domains the finest grid having 333 m horizontal spacing reproduced many of the observed features of this event these include small amplitude waves above the sierra ridge decoupled from thermally forced flow within the valley and a l

using satellite observations to constrain parameterizations of gravity wave effects for global models abstract small scale gravity waves are common features in atmospheric temperature observations in satellite observations these waves have been traditionally difficult to resolve because the footprint or resolution of the measurements precluded their detection or clear identification recent advances in satellite instrument resolution coupled to innovative analysis techniques have led in the last decade to some new global datasets describing the temperature variance associated with these waves such satellite observations have been considered the best hope for quantifying the global properties of gravity waves needed to constrain parameterizations of their effects for global models although global maps of averaged gravity wave temperature variance have now been published from a variety of different instruments on earth orbiting platforms these maps have not provided the needed constraints the present paper first summarizes what has been learned from traditional temporally and spatially averaged analyse

effective elasticity of fractured rocks a snapshot of the work in progress exploration and development of naturally fractured reservoirs rely on understanding and interpretation of certain signatures associated with seismic waves propagating through cracked rocks this understanding comes primarily from the effective media theories that predict an overall elastic behavior of a solid containing many inhomogeneities cracks in particular whose sizes are too small to be seen individually by the waves to model seismic responses of fractured formations a geophysicist typically has a choice between the effective media schemes of hudson and schoenberg while the two predictions usually deviate slightly for liquid filled cracks the differences are significant when the fractures are dry explaining the origin of these differences and selecting a more accurate scheme is the first goal of this tutorial our second more challenging task is to prove that simply adding the compliance contributions of cracks as if they were isolated and noninteracting remains sufficiently accurate even for fractures that grossly violate the basic theoretical assumption of penny shaped cracks real fractures have notoriously irregular shapes might be partially closed and often form interconnected networks yet these details of fracture microgeometry turn out to be unimportant for the effective elasticity given a typical noise level in seismic data no closed form theory exists for irregular fracture shapes however take into account finite element simulations on so called digital rocks demonstrate which features of the crack geometry have to be taken into account because they influence propagation of long compared to the size of fractures seismic waves and which features can be ignored

modeling elastic properties of siliciclastic rocks we have modeled the effective elastic moduli and hence the compression and shear wave velocities of dry sandstones the modeling is distinctly different in two ranges of porosity from zero to the consolidation limit con consolidated regime where the rock is treated as continuous material containing pores and cracks and from con to the critical porosity c where the rock is transitioning to a granular material unconsolidated regime in the consolidated regime the modeling is micromechanics based and yields the moduli in terms of porosity pore shape factor and crack density based on the noninteraction approximation with the mori tanaka correction for interactions by necessity it contains empirical parameters reflecting highly irregular shapes of pores and microcracks in the unconsolidated regime we propose empirical relations of the mori tanaka type where pore shape factors assume large values consistent with very soft concave pore shapes typical in this regime combined the two

mountain waves entering the stratosphere using the national science foundation nsf ncar gulfstream v and the nsf wyoming king air research aircraft during the terrain induced rotor experiment t rex in march april 2006 six cases of sierra nevada mountain waves were surveyed with 126 cross mountain legs the goal was to identify the influence of the tropopause on waves entering the stratosphere during each flight leg part of the variation in observed parameters was due to parameter layering heaving up and down in the waves diagnosis of the combined wave layering signal was aided with innovative use of new gps altitude measurements the ozone and water vapor layering correlated with layered bernoulli function and cross flow speed gps corrected static pressure was used to compute the vertical energy flux confirming for the first time

observations and numerical simulations of subrotor vortices during t rex high resolution observations from scanning doppler and aerosol lidars wind profiler radars as well as surface and aircraft measurements during the terrain induced rotor experiment t rex provide the first comprehensive documentation of small scale intense vortices associated with atmospheric rotors that form in the lee of mountainous terrain although rotors are already recognized as potential hazards for aircraft it is proposed that these small scale vortices or subrotors are the most dangerous features because of strong wind shear and the transient nature of the vortices a life cycle of a subrotor event is captured by scanning doppler and aerosol lidars over a 5 min period the lidars depict an amplifying vortex with a characteristic length scale of 500 1000 m that overturns and intensifies to a maximum spanwise vorticity greater than 0 2 s 1 radar wind profiler observations document a series of vortices characterized by updraft downdraft couplets and regions of enhanced reversed flow that are generated in a layer of strong vertical wind shear and subcritical richardson number the observations and numerical simulations reveal that turbulent subrotors occur most frequently along the leading edge of an elevated sheet of horizontal vorticity that is a manifestation of boundary layer shear and separation along the lee slopes as the subrotors break from the vortex sheet intensification occurs through vortex stretching and in some cases tilting processes related to three dimensional turbulent mixing the subrotors and ambient vortex sheet are shown to intensify through a modest increase in the upstream inversion strength which illustrates the predictability challenges for the turbulent characterization of rotors

the evolution of middle america and the gulf of mexico caribbean sea region during mesozoic time a plate tectonic model for the evolution of middle america and the gulf of mexico caribbean sea region is presented the model which is based upon the existence of the mojave sonora megashear incorporates into the triassic pangea reconstruction three microplates between north and south america thus avoiding the overlap of the bullard fit these plates are the yaqui bounded on the north by the mojave sonora megashear the east and west maya plates bounded on the north by the mexican volcanic zone and on the south by a predecessor of the motagua fault zone and the chortis plate parts of guatemala and honduras during late jurassic time as north america split away from europe africa and south america shear with left lateral sense of displacement occurred along the transform faults that bounded the micro plates if 800 km of left lateral displacement along the mojave sonora megashear 300 km along the mexican volcanic belt and 1 300 km along a proto motagua megashear are restored and if yucatan and cuba are rotated to fit against northern south america then 1 a curvilinear belt of late paleozoic rocks that show lithologic as well as paleontologic similarities extends across the reconstruction and links outcrops in texas eastern mexico nuclear central america and colombia 2 a mediterranean like sea is delineated that was a precursor of most of the present gulf of mexico 3 correlation is implied between the distinctive quartzose san cayetano formation of cuba and the caracas and juan griego groups of venezuela geometric constraints suggest that probably shear initially occurred along the mexican volcanic zone near the end of the middle jurassic subsequently probably about 160 m y ago displacements that total 800 km began along the mojave sonora megashear contemporaneously yucatan and fragments of pre cretaceous rocks that compose parts of central and western cuba migrated northward toward their present positions rotation of yucatan was facilitated by considerable displacement along the proto motagua zone and along a zone that is probably coincident with the modern salina cruz fault accumulation of widespread major salt units of late jurassic callovian to early oxfordian age in the gulf basin probably occurred contemporaneously with the arrival of these blocks at their present positions clastic units that interfinger with some of the youngest salt units and rim the gulf of mexico have not recorded major recognized translations since their accumulation clockwise rotation of south america and the chortis plate occurred during early cretaceous time this movement which was manifested by subduction of jurassic ocean floor against the previously rifted precursor of the island of cuba and under parts of hispaniola and puerto rico is recorded by circum caribbean orogeny abrupt changes in the relative motions between north and south america during late cretaceous time may have resulted in extension and outpourings of basalt upon the jurassic rocks of the ocean floor of the venezuelan basin west of beata ridge sea floor spreading formed the colombian basin related subduction occurred as the chortis plate including part of central america the nicaraguan rise and southeastern cuba was sutured against the maya east plate along the present motagua fault and cayman trench our model is constrained by published geologic data the relative positions of north and south america from atlantic sea floor magnetic anomalies and the requirement that the major transform faults be compatible with the poles of rotation for the appropriate relative motions between north and south america paleomagnetic data from middle america are sparse but do not conflict with the predicted motions of some of the microplates especially chortis

initial condition sensitivities and the predictability of downslope winds the sensitivity of downslope wind forecasts to small changes in initial conditions is explored by using 70 memberensemblesimulationsoftwoprototypicalwindstormsobservedduringtheterrain inducedrotor experiment t rex the10 weakestand 10 strongest ensemblemembersare compositedand compared for each event in the first case the 6 h ensemble mean forecast shows a large amplitude breaking mountain wave and severe downslope winds nevertheless the forecasts are very sensitive to the initial conditions because the difference in the downslope wind speeds predicted by the strong and weak member composites grows to larger than 28 m s 21 over the 6 h forecast the structure of the synoptic scale flow one hour prior to the windstorm and during the windstorm is very similar in both the weak and strong member composites wave breaking is not a significant factor in the second case in which the strong winds are generated by a layer of high static stability flowing beneath a layer of weaker mid and upper tropospheric stability in this case thesensitivitytoinitialconditionsisweakerbutstillsignificant thedifferenceindownslopewindspeeds between the weak and strong member composites grows to 22 m s 21 over 12 h during and one hour before the windstorm the synoptic scale flow exhibits appreciable differences between the strong and weakmember composites although this case appears to be more predictable than the wave breaking event neither case suggests that much confidence should be placed in the intensity of downslope winds forecast 12 or more hours in advance

climatology of high wind events in the owens valley california the climatology of high wind events in the owens valley california a deep valley located just east of the southern sierra nevada is described using data from six automated weather stations distributed along the valley axis in combination with the north american regional reanalysis dataset potential mechanisms for the development of strong winds in the valley are examined contrary to the common belief that strong winds in the owens valley are westerly downslope windstorms that develop on the eastern slope of the sierra nevada strong westerly winds are rare in the valley instead strong winds are highly bidirectional blowing either up northward or down southward the valley axis high wind events are most frequent in spring and early fall and they occur more often during daytime than during nighttime with a peak frequency in the afternoon unlike thermally driven valley winds that blow up valley during daytime and down valley during nighttime strong winds may blow in either direction regardless of the time of the day the southerly up valley winds appear most often in the afternoon a time when there is a weak minimum of northerly down valley winds indicating that strong wind events are modulated by local along valley thermal forcing several mechanisms including downward momentum transfer forced channeling and pressure driven channeling all play a role in the development of southerly high wind events these events are typically accompanied by strong south southwesterly synoptic winds ahead of an upper level trough off the california coast the northerly high wind events which typically occur when winds aloft are from the northwest ahead of an approaching upper level ridge are predominantly caused by the passage of a cold front when fast moving cold air behind the surface front undercuts and displaces the warmer air in the valley forced channeling by the sidewalls of the relatively narrow valley aligns the wind direction with the valley axis and enhances the wind speeds

using surface pressure variations to categorize diurnal valley circulations experiments in owens valley abstract harmonic analysis has been applied to data from nearly 1000 automatic surface observation system asos stations over the united states to extract diurnal pressure signals the largest diurnal pressure amplitudes 200 pa and the earliest phases 0600 lst for surface pressure maximum were found for stations located within deep mountain valleys in the western united states the origin of these unique characteristics of valley pressure signals is examined with a detailed study of owens valley california analysis of observational data from the terrain induced rotor experiment t rex project shows that the ratio of the valley surface pressure to temperature amplitude can be used to estimate the daily maximum mixed layer depth h on days with strong westerly winds above the valley the mixed layer is found to be shallower than on quiescent days because of a flushing effect in the upper parts of the valley idealized two dimensional weather research and forecasting model simulations were used to

preservation of contrasting geothermal gradients across the caribbean north america plate boundary motagua fault guatemala 1 strike slip plate boundaries juxtapose crustal blocks that may have different geodynamic origins and therefore different thermal structures thermo kinematic modeling of this type of strike slip plate boundary predicts an asymmetric signature in the low temperature thermochronologic record across the fault age elevation profiles of zircon u th he ages across the motagua fault a 500 km long segment of the transform boundary between the north american and caribbean plates document a sharp cooling age discontinuity across the fault this discontinuity could be interpreted as a difference in denudation history on each side of the fault however a low relief miocene erosional surface extends across the fault this surface has been uplifted and incised and provides a geomorphic argument against differential denudation across the fault by integrating magmatic volcanic and heat flow data age elevation profiles and thermo kinematic modeling we propose that large horizontal displacement along the motagua fault has offset a persistent geothermal asymmetry across the fault and explains both the age discontinuities and the age elevation patterns this study illustrates how thermochronology can be used to detect large strike slip displacements and more generally opens new perspectives in understanding the impact of nonuniform thermal structures on thermochronologic results

turbulence in breaking mountain waves and atmospheric rotors estimated from airborne in situ and doppler radar measurements atmospheric turbulence generated in flow over mountainous terrain is studied using airborne in situ and cloud radar measurements over the medicine bow mountains in southeast wyoming usa during the nasa orographic clouds experiment nasa06 in 2006 two complex mountain flow cases were documented by the university of wyoming king air research aircraft carrying the wyoming cloud radar the structure of turbulence and its intensity across the mountain range are described using the variance of vertical velocity w2 and the cube root of the energy dissipation rate 1 3 edr for a quantitative analysis of turbulence from the cloud radar the uncertainties in the doppler wind retrieval have to be taken into account such as the variance of hydrometeor fall speed and the contamination of vertical doppler velocity by the horizontal wind a thorough analysis of the uncertainties shows that 25 accuracy or better can be achieved in regions of moderate to severe turbulence in the lee of the mountains while only qualitative estimates of turbulence intensity can be obtained outside the most turbulent regions two nasa06 events exhibiting large amplitude mountain waves mid tropospheric wave breaking and rotor circulations are examined moderate turbulence is found in a wave breaking region with w2 and edr reaching 4 8 m2 s 2 and 0 25 m2 3 s 1 respectively severe turbulence is measured within the rotor circulations with w2 and edr respectively in the ranges of 7 8 16 4 m2 s 2 and 0 50 0 77 m2 3 s 1 a unique result of this study is the quantitative estimation of the intensity of turbulence and its spatial distribution in the interior of atmospheric rotors provided by the radar derived turbulence fields

three dimensional characteristics of stratospheric mountain waves during t rex abstract measurements from the national science foundation national center for atmospheric research nsf ncar gulfstream v g v obtained during the recent terrain induced rotor experiment t rex indicate marked differences in the character of the wave response between repeated flight tracks across the sierra nevada which were separated by a distance of approximately 50 km observations from several of the g v research flights indicate that the vertical velocities in the primary wave exhibited variations up to a factor of 2 between the southern and northern portions of the racetrack flight segments in the lower stratosphere with the largest amplitude waves most often occurring over the southern flight leg which has a terrain maximum that is 800 m lower than the northern leg multiple racetracks at 11 7 and 13 1 km altitudes indicate that these differences were repeatable which is suggestive that the deviations were likely due to vertically propagating mountain waves that varied systematically in am

spectral gap characteristics in a daytime valley boundary layer a correct estimation of turbulent variances and covariances in the atmospheric boundary layer relies on the determination of turbulent perturbations of wind speed components and scalar quantities which requires the presence of a so called spectral gap the goal of this work is to determine the range of gap scales necessary to define turbulent perturbations in a daytime valley boundary layer to accomplish this we analyze data from a large number of propeller vane and sonic anemometers using the fast fourier transformation and the multiresolution flux decomposition daytime gap scales are found to range from 17 to 29 min and show large spatial variability across the valley floor and the adjacent slopes synoptically driven conditions that favor the occurrence of mesoscale phenomena such as rotors and mountain waves shift daytime gap scales toward longer periods the low frequency end of the gap is also affected by the presence of slope winds that are characterized by a periodicity ranging from 80 to 200 min finally we present a conceptual model of the daytime valley spectral gap which summarizes the findings of this study

high resolution doppler lidar observations of transient downslope flows and rotors abstractthe authors present observations of the temporal evolution of downslope windstorms with rotors and internal hydraulic jumps of unprecedented detail and spatiotemporal coverage the observations were carried out by means of a coherent doppler lidar in the lee of the southern sierra nevada range during the sixth intensive observational period of the terrain induced rotor experiment t rex in 2006 two representative flow regimes are analyzed and juxtaposed in this paper the first case shows pulses of high momentum air that propagate eastward through the valley with an internal hydraulic jump on the leading edge the region downstream of the transient internal hydraulic jump is characterized by turbulence but no coherent rotor circulation was observed during the second case the strongest windstorm of the field campaign t rex occurred the observed features of this event resemble the classical notion of a rotor altogether the doppler lidar observations of both downslope flow events reveal a comp

regional gravity investigation of honduras central america abstract a regional gravity study of honduras was performed as part of a major study of the geothermal resource potential of honduras this study was conducted by los alamos national laboratory in cooperation with the honduras government regional offshore free air and onshore bouguer gravity maps and residual isostatic gravity maps of honduras and surrounding regions were produced from these data several regional crustal and upper mantle models were produced these models pass through two local geothermal sites platanares and san ignacio the regional geologic and tectonic implications of the models and their relevance to the geothermal potential of honduras and to six well known geothermal sites in particular are examined no obvious regional structures observed in the gravity data can explain the thermal enhancement in general or the specific geothermal sites more local tectonic or structural conditions must control the distribution of the thermally enhanced areas