theoretical studies of convectively forced mesoscale flows in three dimensions part ii shear flow with a critical level convectively forced mesoscale flows in a shear flow with a critical level are theoretically investigated by obtaining analytic solutions for a hydrostatic nonrotating inviscid boussinesq airflow system the response to surface pulse heating shows that near the center of the moving mode the magnitude of the vertical velocity becomes constant after some time whereas the magnitudes of the vertical displacement and perturbation horizontal velocity increase linearly with time it is confirmed from the solutions obtained in present and previous studies that this result is valid regardless of the basic state wind profile and dimension the response to 3d finite depth steady heating representing latent heating due to cumulus convection shows that unlike in two dimensions a low level updraft that is necessary to sustain deep convection always occurs at the heating center regardless of the intensity of vertical wind shear and the heating depth for deep heating across a critical level little change occurs in the perturbation field below the critical level although the heating top height increases this is because downward propagating gravity waves induced by the heating above but not near the critical level can hardly affect the flow response field below the critical level when the basic state wind backs with height the vertex of v shaped perturbations above the heating top points to a direction rotated a little clockwise from the basic state wind direction this is because the v shaped perturbations above the heating top is induced by upward propagating gravity waves that have passed through the layer below where the basic state wind direction is clockwise relative to that above

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

geology of part of a long lived dynamic plate margin the coastal cordillera of north central chile latitude 30 51 31 s a complex composed of ultrabasic and basaltic lavas chert arkose and conglomerate was assembled in the coast of north central chile lat 30 30 31 s prior to 200 ma the character of and relationships between the rock formations exposed here are consistent with an autochthonous evolution of this part of chile in the last 200 ma three major episodes of deformation and metamorphism have been observed in this area the first episode f1 produced a compositional layering s1 and amphibolite facies metamorphism coeval with the intrusion of an extensive igneous complex between 220 and 200 ma a second episode of deformation f2 locally formed reverse faults and tight recumbent folds in s1 units in which f2 folds are well developed yield k ar and rb sr ages between 163 and 140 ma at between 140 and 126 ma upright open to tight folds f3 formed with sharp hinges and axial planes that strike north and dip steeply east structures of similar age style and orientation have been reported as far sou

a gravity wave drag matrix for complex terrain abstractwe propose a simplified scheme to predict mountain wave drag over complex terrain using only the regional average low level wind components u and v the scheme is tuned and tested on data f

phyllosilicate poor palagonitic dust from mauna kea volcano hawaii a mineralogical analogue for magnetic martian dust the mineralogical and elemental composition of dust size fractions 2 and 5 m of eight samples of phyllosilicate poor palagonitic tephra from the upper slopes of mauna kea volcano hawaii were studied by x ray diffraction xrd x ray fluorescence xrf visible and near ir reflectance spectroscopy mossbauer spectroscopy magnetic properties methods and transmission electron microscopy tem the palagonitic dust samples are spectral analogues of martian bright regions at visible and near ir wavelengths the crystalline phases in the palagonitic dust are in variable proportions plagioclase feldspar ti containing magnetite minor pyroxene and trace hematite no basal reflections resulting from crystalline phyllosilicates were detected in xrd data weak broad xrd peaks corresponding to x ray amorphous phases allophane nanophase ferric oxide possibly ferrihydrite and for two samples hisingerite were detected as oxidative alteration products of the glass residual unaltered glass was also present mossbauer spectroscopy showed that the iron bearing phases are nanophase ferric oxide magnetite titanomagnetite hematite and minor glass and ferrous silicates direct observation by tem showed that the crystalline and x ray amorphous phases observed by xrd and mossbauer are normally present together in composite particles and not normally present as discrete single phase particles ti bearing magnetite occurs predominantly as 5 150 nm particles embedded in noncrystalline matrix material and most likely formed by crystallization from silicate liquids under conditions of rapid cooling during eruption and deposition of glassy tephra and prior to palagonitization of glass rare spheroidal halloysite was observed in the two samples that also had xrd evidence for hisingerite the saturation magnetization js and low field magnetic susceptibility for bulk dust range from 0 19 to 0 68 am2 kg and 3 4 10 6 to 15 5 10 6 m3 kg at 293 k respectively simulation of the mars pathfinder magnet array ma experiment was performed on mauna kea volcano in areas with phyllosilicate poor palagonitic dust and with copies of the pathfinder ma on the basis of the magnetic properties of dust collected by all five ma magnets and the observation that the pathfinder mas collected dust on the four strongest magnets the value for the saturation magnetization of martian dust collected in the ma experiments is revised downward from 4 2 am2 kg to 2 5 1 5 am2 kg the revised value corresponds to 2 7 1 6 wt magnetite if the magnetic mineral is magnetite using js 92 am2 kg for pure magnetite fe3o4 or to 5 0 3 0 to 3 4 2 0 wt maghemite if the magnetic mineral is pure maghemite using js 50 to 74 am2 kg for pure maghemite fe2o3 comparison of the magnetic properties of bulk mauna kea palagonitic dust to those for dust collected by ma magnets shows that the ma magnets extracted culled a subset 25 34 wt of composite magnetic particles from bulk dust the extent of culling of martian dust is not well constrained because the mauna kea palagonitic dust satisfies the essential constraints of the pathfinder magnetic properties experiment composite and magnetic particles capable of being collected by five ma magnets a working hypothesis for the strongly magnetic mineral present in martian dust and soil is magnetite possibly ti bearing formed by rapid crystallization from silicate liquids having volcanic and or impact origins subsequent palagonitization of the glass produces the nanophase ferric oxide phases that dominate the spectral properties of martian bright regions at visible and near ir wavelengths magnetic and phyllosilicate poor palagonitic dust from mauna kea volcano is thus a spectral and magnetic analogue for magnetic martian dust

late paleozoic to triassic evolution of the gondwana margin evidence from chilean frontal cordilleran batholiths 28 s to 31 s upper paleozoic to triassic chilean granitoids in the andean frontal cordillera between 28 s and 31 s record crustal and mantle conditions at the gondwana margin during the final assembly and initial breakup of the pangea supercontinent this period overlaps the end of paleozoic terrane accretion and precedes andean subduction integration of new trace element and isotopic data with other information on the granitoids and the regional geology leads to a tectonic model that has implications for other parts of the gondwana margin in the model the carboniferous to early permian is a period of oblique convergence associated elqui complex granitoids are diverse those in the guanta and montosa units are predominantly related to subduction processes whereas those in the cochiguas and el volcan units are dominated by melting of the subduction complex and older crust progressive oblique collision of the last pre pangea terrane equis along the margin resulted in crustal thickening associated with shortening deformation of foreland basinal sedimentary rocks and uplift of the elqui complex subsequent gravitational collapse of the inactive slab and lithospheric delamination resulted in the production of large amounts of basalt which intruded and melted the crust producing the post collisional ingaguas complex the los carricitos granitoids formed in thickened crust whereas the chollay el colorado and el leon units formed in thinner crust the ingaguas complex is part of the choiyoi granite rhyolite province whose formation similar to that of other gondwana silicic provinces was probably accentuated by anomalously hot upper mantle associated with the pangea supercontinent

water ice nucleation characteristics of jsc mars 1 regolith simulant under simulated martian atmospheric conditions 1 water ice clouds in the martian atmosphere are governed by parameters such as number density and particle size distribution that in turn affect how they influence the climate with some of the underlying properties of cloud formation well known only for earth extrapolations to mars are potentially misleading we report here continued laboratory experiments to identify critical onset conditions for water ice formation under martian cloud forming temperatures and water partial pressures 155 182 k 7 6 10 5 to 7 7 10 3 pa h2o by observing the 3 m infrared band to monitor nucleation and growth we observe significant temperature dependence in the nucleation of ice on jsc mars 1 regolith simulant with critical saturation ratios scrit as high as 3 8 at 155 k at temperatures below 180 k ice nucleation on jsc mars 1 requires significant supersaturation potentially impacting the martian hydrological cycle

a three dimensional mountain wave imaged in satellite radiance throughout the stratosphere evidence of the effects of directional wind shear swath scanned thermal radiances from the advanced microwave sounding units amsu a on the noaa and aqua satellites are used to image the horizontal temperature structure of a long wavelength mountain wave that formed over southern scandinavia on 14 january 2003 data from all six stratospheric channels show this wave propagating through the full depth of the stratosphere in channels 9 11 altitudes 20 90 hpa the imaged wave has a phase structure broadly consistent with a stationary wave radiated by the southeastward flow over and above the quasi elliptical terrain of southern norway channel 12 radiances at 10 hpa however show a remarkable abrupt change in imaged wave structure the horizontal wavelength contracts phase lines rotate anticlockwise by 30 40 and peak activity migrates to the south to lie over denmark and northern germany similar structure persists in channels 13 and 14 at 2 5 hpa with progessively increasing radiance amplitudes these features are stable over the 10 hours of amsu a measurements from five separate overpasses and are validated against independent radiances acquired by the atmospheric infrared sounder airs and retrieved airs amsu a temperature profiles from the aqua overpass this change at the channel 11 12 interface coincides with an onset of anticlockwise rotation backing and intensification of background stratospheric winds with height fourier ray and spatial ray modelling incorporating these directionally sheared winds and simplified orographic forcing reproduce the salient features of the observations but only after wave induced temperature perturbations have been converted to channel radiances using a forward model the differential visibility of various components of this three dimensional mountain wave to the amsu a channel weighting functions has a first order impact on the observations at heights above 10 hpa once that is factored in the combined observations and modelling provide direct experimental support for the shutts model s predictions of how backing wind vectors affect the vertical evolution of three dimensional mountain waves implications of these observations for orographic gravity wave drag parametrization are briefly discussed copyright 2007 royal meteorological society

cloud formation under mars pathfinder conditions temperature data taken during the mars pathfinder entry are applied to a time dependent microphysical model of cloud formation our goal is to reproduce the characteristics of clouds observed at the pathfinder site we assume that the total water column abundance is 11 percipitable microns we also assume that the atmospheric dust initially has a lognormal size distribution with a modal radius of 0 6 m r eff 1 5 m and an optical depth of 0 5 three temperature profiles are used in the model calculations the first is the pathfinder entry observation the second is this same profile but with the inversion at 10 km removed the third simulation uses the temperature profiles calculated by the ames mars general circulation model for mars pathfinder conditions in all cases clouds form at altitudes of 35 45 km in addition lower thicker clouds form within the 10 km inversion of the unaltered profile while peak cloud formation occurred near local noon at 20 km for the gcm calculated profiles given a combination of all three temperature scenarios cloud optical depths particle sizes and colors are consistent with imp observations

evidence in cerro pampa volcanic rocks for slab melting prior to ridge trench collision in southern south america late miocene approx 12 ma hornblende bearing andesitic to dacitic documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage wasysym pagestyle empty declaremathsizes 10 9 7 6 begin document mathrm 63 to 68 sio 2 1 2 to 1 9 k 2 o end document adakite flows at the small cerro pampa center in patagonia 47 55 s 71 25 have some of the clearest slab melt geochemical signatures yet seen in a phanerozoic center on continental crust these magmas formed in response to melting of the hot thin slab that was subducting beneath south america prior to the collision of the chile rise at approx 6 ma or at approx 10 ma their n morb like 87 sr 86 sr 0 70285 0 70309 and low 206 pb 204 pb 18 44 18 59 ratios show that they could have been generated by

numerical simulations of the formation and evolution of water ice clouds in the martian atmosphere abstract a one dimensional aerosol model was used to study the microphysics of water ice cloud formation and evolution on mars the time dependent nature of the model permits realistic simulations of diurnal cycles the results are sensitive to the choice of the temperature profile the eddy diffusion coefficient the efficiency of nucleation of the condensation nuclei and the condensation history of the cloud simulations having a large diurnal temperature variation yield condensed water total optical depths of a few tenths in good agreement with the viking lander opacity data ice clouds are typically simulated at 25 30 km altitude with mean particle radii of 0 2 5 0 m we also obtain good agreement with the particle extinction observed in the viking orbiter limb data for a temperature profile constrained by the infrared thermal mapper data in order for repeated cloud formation to occur each day we need to include a vertical and or horizontal resupply of water and dust to the higher altitudes where the condensation occurs because of loss by sedimentation this can take the form of a micrometeoritic influx of particles at the top of the atmosphere or a latitudinal transport of material the efficiency of the nucleation process is determined by the contact angle changing this angle from 0 945 to 0 999 can have the effect of doubling the total ice optical depth of the cloud the time evolution of the cloud is important for comparison with the observations if a diurnal temperature change exists under these conditions the optical thickness of the cloud is dependent on the number of condensation cycles having previously occurred and the time of day this time dependence and the need for a resupply of material into the condensing region show that the cloud formation process cannot be considered a steady state phenomenon we have shown that the eddy diffusion coefficient and particle radii cannot be constrained by the available data even if a detailed model is used for the interpretation of the observations in our simulations there is an extensive vertical redistribution of water by clouds however water is only lost to the surface when the temperature is at the frost point near the ground precipitation across subsaturated layers is not significant

jurassic and early cretaceous island arc volcanism extension and subsidence in the coast range of central chile more than 2000 km 3 of acid and 9000 km 3 of basic volcanic rocks formed during the jurassic and early cretaceous in the coast range of central chile between 32 30 s and 34 s these rocks which constitute the major part of an 15 km thick pile of alternately marine and continental deposits issued from volcanic arcs situated between a land area with paleozoic basement in the west and a marginal sea in the east asthenospheric upwelling led to extension and bimodal volcanism the volcanic products were deposited in intra arc basins subsiding at high rates 100 300 m m y the source of the magmas became more depleted with time due to an increase in degree of partial melting and their compositions were modified by subduction related fluids and contamination with a progressively thinner and younger crust the basic lavas are of high k calc alkaline to shoshonitic affinity chemically resembling the lavas found in some mature island arcs in the western pacific the extension and subsidence resulted in a low relief topography close to sea level in contrast with the present day convergent type of andean volcanism at the same latitude where calc alkaline intermediate lavas erupt from volcanoes at great height above a thick crust

stationary gravity wave structure in flows with directional wind shear most theoretical studies of flow over mountains assume that the wind direction is constant for two dimensional orographic ridges this is not an issue since only the component of the wind across the ridge forces internal gravity waves a special case of rectilinear flow is when the wind component changes sign i e the wind direction changes discontinuously through 180 degrees such a point is a critical level for all stationary gravity waves for isolated three dimensional mountains the gravity wave response comprises waves of all azimuthal orientations and each of these may have a different critical level height depending on whether the wind backs or veers with height using a combination of ray tracing methods and stationary phase solutions the structure of the stationary hydrostatic gravity wave field generated by an isolated mountain is studied for a simple wind field which backs with height in contrast to the behaviour for unidirectional flow wave action does not accumulate indefinitely beneath the critical level but is continuously advected downwind by the component of the wind parallel to the phase lines instead of the wave energy becoming unbounded following a ray as in the 2d case the wave energy decays to zero along a trailing wake zone downwind of the mountain along phase lines this is just an extension of the asymptotic wake found in the linear solutions of smith for constant flow over an isolated mountain the work described here underlines the desirability of including the effects of selective critical level absorption in the gravity wave drag parametrization schemes of numerical weather prediction models

laboratory measurements of heterogeneous co2 ice nucleation on nanoparticles under conditions relevant to the martian mesosphere clouds of co2 ice particles have been observed in the martian mesosphere these clouds are believed to be formed through heterogeneous nucleation of co2 on nanometer sized meteoric smoke particles msps or upward propagated martian dust particles mdps large uncertainties still exist in parameterizing the microphysical formation process of these clouds as key physicochemical parameters are not well known we present measurements on the nucleation and growth of co2 ice on sub 4 nm radius iron oxide and silica particles representing msps at conditions close to the mesosphere of mars for both particle materials we determine the desorption energy of co2 to be fdes 18 5 0 2 kj mol 1 corresponding to fdes 0 192 0 002 ev and obtain m 0 78 0 02 for the contact parameter that governs heterogeneous nucleation by analyzing the measurements using classical heterogeneous nucleation theory we did not find any temperature dependence for the contact parameter in the temperature range examined 64 k to 73 k by applying these values for msps in the martian mesosphere we derive characteristic temperatures for the onset of co2 ice nucleation which are 8 18 k below the co2 frost point temperature depending on particle size this is in line with the occurrence of highly supersaturated conditions extending to 20 k below frost point temperature without the observation of clouds moreover the sticking coefficient of co2 on solid co2 was determined to be near unity we further argue that the same parameters can be applied to co2 nucleation on upward propagated mdps

terrain induced turbulence over lantau island 7 june 1994 tropical storm russ case study numerical simulations of terrain induced turbulence associated with airflow over lantau island of hong kong are presented lantau is a relatively small island with three narrow peaks rising to between 700 and 950 m above mean sea level this research was undertaken as part of a project to better understand and predict the nature of turbulence and shear at the new airport site on the island of chek lap kok which is located to the lee of lantau intensive ground and aerial observations were taken from may through june 1994 during the lantau experiment lantex this paper focuses on flow associated with the passage of tropical storm russ on 7 june 1994 during which severe turbulence was observed the nature of the environmental and topographic forcing on 7 june 1994 resulted in the turbulence and shear being dominated by the combination of topographic effects and surface friction high resolution numerical simulations initialized using local sounding data were performed using the clark model the simulation results indicate that gravity wave dynamics played a very minor role in the flow distortion and generation of turbulence as a result of this flow regime relatively high vertical and horizontal resolution was required to simulate the mechanically generated turbulence associated with tropical storm russ results are presented using a vertical resolution of 10 m near the surface and with horizontal resolutions of both 125 and 62 5 m over local nested domains of about 13 24 km on a side the 125 m model resolution simulated highly distorted flow in the lee of lantau with streaks emanating downstream from regions of sharp orographic gradients at this resolution the streaks were nearly steady in time at the higher horizontal resolution of 62 5 m the streaks became unstable resulting in eddies advecting downstream within a distorted streaky mean flow similar to the 125 m resolution simulation the temporally averaged fields changed little with the increase in resolution however there was a three to fourfold increase in the temporal variability of the flow as indicated by the standard deviation of the wind from a 10 min temporal average overall the higher resolution simulations compared quite well with the observations whereas the lower resolution cases did not the high resolution experiments also showed a much broader horizontal and vertical extent for the transient eddies the depth of orographic influence increased from about 200 m to over 600 m with the increase in resolution a physical explanation using simple linear arguments based on the blocking effects of the eddies is presented the nature of the flow separation is analyzed using bernoulli s energy form to display the geometry of the separation bubbles the height of the 80 m2 s22 energy surface shows eddies forming in regions of large orographic gradients and advecting downstream tests using both buoyancy excitation and stochastic backscatter to parameterize the underresolved dynamics at the 125 m resolution are presented as well as one experiment testing the influence of static stability suppressing turbulence development all these tests showed no significant effect implications of these results to the parameterization of mechanically induced turbulence in complex terrain are discussed

a new gravity wave drag scheme incorporating anisotropic orography and low level wave breaking impact upon the climate of the uk meteorological office unified model a new anisotropic gravity wave drag parametrization scheme which represents high drag states modelled on hydraulic jump flow blocking and internal wave reflection theory including trapped lee waves is presented the scheme is shown to represent the breaking of waves over mountains better than previous schemes by comparison with mesoscale simulations of pyrex case studies extended simulations of the meteorological office unified model at climate resolution are presented showing the impact of the new scheme and a combination of the scheme with a new orographic roughness parametrization results show a changed distribution of surface gravity wave surface stress mostly due to mountain anisotropy and a greater tendency for lower troposphere wavc drag inclusion of the orographic roughness parametrization halves the gravity wave stress the combined effect of these schemes for climate integrations being a slight improvement to the tropospheric flow

observations and numerical simulations of mountain waves in the presence of directional wind shear three research aircraft observed small amplitude gravity waves over the south western french alps on 13 november 1999 during the mesoscale alpine programme map radiosonde ascents and global positioning system dropsondes deployed by map research aircraft indicate that the upstream flow was characterized by topographic blocking below 2 km and low level directional wind shear associated with a synoptic scale depression that extended above the alpine crest the in situ vertical velocity data from the three research aircraft and backscatter from lidar onboard the low level and upper level aircraft exhibit gravity wave signatures in the lower troposphere that are characterized by relatively short horizontal wavelengths on a scale of 5 km or less the in situ flight level and backscatter data also suggest a rapid decrease in the wave amplitude with height due to a directional critical layer that partially absorbs wave energy in the lower to middle troposphere in concert with a decrease in the scorer parameter with height that traps the wave energy numerical simulation results obtained from the non hydrostatic coupled ocean atmosphere mesoscale prediction system model using a horizontal resolution of 556 m indicate the presence of low level wave breaking above the highest peaks and confirm the presence of trapped waves and a directional critical level results based on linear theory and nonlinear model simulations suggest that the absorption of wave energy associated with the directional critical layer has an important impact on the wave characteristics including the momentum flux copyright 2006 royal meteorological society

hoods mists frosts and ice caps at the poles of mars the sequence of seasonal events that occurs each martian year around the two poles of mars is more precisely described due to the input of new telescopic surveys and polarimetric measurements combined with available orbital photographs viking lander images and atmospheric pressure recordings the interplays between vaporization and condensation of both carbon dioxide and water products seasonally at work around both poles produce clouds and mists in the atmosphere and frosts and ices at the surface the succession of occurrences of prepolar hood frost depositions polar hood formations and evolutions and surface cap depositions and vaporizations is described for both poles as a function of the seasonal evolution parameter ls planetocentric longitude of the sun

ice nucleation by surrogates of martian mineral dust what can we learn about mars without leaving earth 1 water and carbon dioxide ice clouds have been observed in the martian atmosphere where they are dynamic parts of that planet s water and carbon cycles many martian atmospheric models struggle to correctly predict clouds and with insufficient data some use untested simplifications that cloud formation occurs exactly at the saturation point of the condensed phase or at the same conditions as terrestrial cirrus clouds to address the lack of data we have utilized an 84 m3 cloud chamber built for studies of high altitude cirrus and polar stratospheric ice clouds in the earth s atmosphere and adapted to martian conditions using this chamber we have been able to produce water ice clouds from aerosol in an inert and low pressure atmosphere mimicking that of mars at temperatures between 189 and 215 k we investigated cloud formation by mineral dust particulates of a similar composition and size to those found on mars we show that these surrogate materials nucleate effectively at the higher temperatures with minor temperature dependence at saturations ratios with respect to the ice phase of 1 1 similar to what has been found for terrestrial cirrus at the lower end of the temperature range this saturation rises to 1 9 a result consistent with previous studies

non hydrostatic effects on mountain wave breaking in directional shear flows mountain waves excited by narrow 3d orography are investigated using idealized numerical simulations of atmospheric flows with directional wind shear the stability of these waves is compared with the stability of hydrostatic mountain waves the focus is on understanding how wave breaking is modified via gravity wave critical level interaction when non hydrostatic dispersive effects arise the influence of non hydrostatic effects on wave breaking appears to be a function of the intensity of the background shear increasing the stability of the flow inhibiting wave breaking for weak wind shear but decreasing it instead enhancing wave breaking for stronger wind shear

mineralogy of martian atmospheric dust inferred from thermal infrared spectra of aerosols 1 we have utilized optical constants derived from thermal infrared spectra acquired by the mariner 9 infrared interferometer spectrometer m9 iris and mars global surveyor thermal emission spectrometer mgs tes during periods of relatively high dust low water ice opacity to generate synthetic transmission and emission spectra of the atmospheric dust using libraries of transmission and emission spectra of common rock forming minerals and their alteration products we applied a linear deconvolution algorithm to the spectra to model the dust mineralogy models of the m9 iris transmission data generally are of poor quality and the mineralogical results of these fits are unlikely to be valid fits to the tes transmission spectrum and tes and iris emission spectra are of better quality and suggest that the dust mineralogy is dominated by framework silicates feldspar and or zeolite with carbonate sulfate pyroxene and olivine identified near but below generalized detection limits evidence for phyllosilicates is not robust our results combined with those from in situ measurements and other visible to infrared spectral studies suggest that framework silicates probably feldspar dominate the dust mineralogy with lesser amounts of olivine pyroxene amorphous material hematite and magnetite and that the dust largely is the product of mechanical weathering of basaltic rocks with minor chemical alteration

wave breaking and critical levels for propagating inertio gravity waves in the lower stratosphere this paper analyses and interprets the formation of mixed layers due to propagating inertio gravity waves observed during the fronts and atlantic storm track experiment the data used are high vertical resolution soundings launched from different sites located in the north atlantic sector in agreement with other studies attributing the origin of the inertio gravity waves to the adjustment of the jet stream near fronts the largest waves observed are often located in the vicinity of and above frontal bands the amplitude of these waves is large enough that they give rise to narrow mixed layers by a detailed analysis of the waves characteristics we can distinguish whether such a mixing is favoured by the presence of an inertia critical level where f or results from wave induced convective instability occurring far from critical levels here is the wave intrinsic frequency and f is the coriolis parameter these observations highlight the importance of inertio gravity waves in the vertical exchanges that occur in the stratosphere copyright 2002 royal meteorological society

are crustal thickness variations in old mountain belts like the appalachians a consequence of lithospheric delamination comparison of moho geometry and reflection character of active collision zones like the alps with those of fossil collision zones like the appalachians lends support for the view that lithospheric delamination is both a common and fundamentally important component of collisional orogeny in particular the relative crustal thinning commonly observed beneath the internides of old collisional orogens is an expected consequence of delamination neither precollisional crustal thickness variations nor an unrelated postcollision extensional event is required to produce this feature acceptance of the delamination hypothesis in turn fundamentally alters one s view of the tectonic evolution of old collisional orogens in the case of the appalachians delamination has direct implications for the interpretation of alleghanian granites the direction of subduction leading to final closure between laurentia and gondwana and the thermal state of the lithosphere at the onset of atlantic rifting a corollary of the delamination hypothesis is that lateral reflectivity variations cannot be used to define paleogeographic terranes in the deep crust of old orogens conversely the observation that delamination leaves a distinctive geophysical imprint on the crust itself provides an important additional clue for deciphering the tectonic evolution of such regions

the seasonal behavior of water ice clouds in the tharsis and valles marineris regions of mars mars orbiter camera observations abstract the mars global surveyor mars orbiter camera was used to obtain global maps of the martian surface with equatorial resolution of 7 5 km pixel in two wavelength ranges blue 400 450 nm and red 575 625 nm the maps used were acquired between march 15 1999 ls 110 and july 31 2001 ls 205 corresponding to approximately one and a quarter martian years using the global maps cloud area in km2 has been measured daily for water ice clouds topographically corresponding to olympus mons ascraeus mons pavonis mons arsia mons alba patera the western valles marineris canyon system and for other small surface features in the region seasonal trends in cloud activity have been established for the three tharsis volcanoes olympus mons and alba patera olympus ascraeus and pavonis mons show cloud activity from about ls 0 220 with a peak in cloud area near ls 100 one of our most interesting observational results is that alba patera shows a double peaked feature in the cloud area with peaks at ls 60 and 140 and a minimum near ls 100 arsia mons shows nearly continuous cloud activity the altitudes of several of these clouds have been determined from the locations of the visual cloud tops and optical depths were measured for a number of them using the disort code of stamnes et al 1988 appl opt 27 2502 2509 several aspects of the observations e g cloud heights effects of increased dust on cloud activity are similar to simulations in richardson et al 2002 j geophys res 107 5064 a search for short period variations in the cloud areas revealed only indirect evidence for the diurnal cloud variability in the afternoon hours unambiguous evidence for other periodicities was not found

interactions between topographic airflow and cloud precipitation development during the passage of a winter storm in arizona abstract a case study showing comparisons between observations and numerical simulations of the passage of a winter storm over complex terrain is presented the interactions between the mesoscale and cloud environments and the microphysical and dynamical processes are addressed using both observations and numerical simulations a three dimensional time dependent nested grid model was used to conduct numerical simulations of the three dimensional airflow and cloud evolution over the mogollon rim and adjacent terrain in arizona the modeling results indicated that the flow patterns and cloud liquid water clw were closely linked to the topography to a large extent gravity waves excited by the flow over the mountains determine the distribution of clouds and precipitation the waves extend through deep layers of the atmosphere with substantial updrafts and downdrafts at times exceeding 5 m s 1 the simulated vertical velocities and horizontal wavelengths of about 20 km were in good agreement with the air

observations of martian ice clouds by the mars global surveyor thermal emission spectrometer the first martian year successful operation of the mars global surveyor spacecraft beginning in september 1997 ls 184 has permitted extensive observations over more than a martian year initially thin normal optical depth 0 06 at 825 cm 1 ice clouds and hazes were widespread showing a distinct latitudinal gradient with the onset of a regional dust storm at ls 224 ice clouds vanished in the southern hemisphere to reappear gradually after the decay of the storm the zonally averaged cloud opacities show little difference between the beginning and end of the first martian year a broad low latitude cloud belt with considerable longitudinal structure was present in early northern summer apparently characteristic of the northern summer season it vanished between ls 140 and 150 the latitudinal extent of this feature is apparently controlled by the ascending branch of the hadley circulation the most opaque clouds optical depth 0 6 were found above the summits of major volcanic features these showed spatial structure possibly associated with wave activity variety among low lying late morning clouds suggests localized differences in circulation and microclimates limb observations showed extensive optically thin optical depth 0 04 stratiform clouds at altitudes up to 55 km considerable latitude and altitude variations were evident in ice clouds in early northern spring ls 25 near 30 km thin clouds extended from just north of the equator to 45 n nearly to the north polar vortex a water ice haze was present in the north polar night ls 30 at altitudes up to 40 km because little dust was present this probably provided heterogeneous nucleation sites for the formation of co2 clouds and snowfall at altitudes below 20 km where atmospheric temperatures dropped to the co2 condensation point the relatively invariant spectral shape of the water ice cloud feature over space and time indicates that ice particle radii are generally between 1 and 4 m

delamination in collisional orogens during continental collision the weight of the downgoing slab may lead to extensional shearing in the descending plate permitting separation of the downdip dense oceanic lithosphere from the adjacent lighter continental lithospher separation may occur by means of a lithosphere penetrating normal sense shear zone by means of pure shear necking of the lithosphere or by some combination of these mechanisms during separation the continental crust attached to the lower plate may undergo an episode of extensional tectonics the proximity of asthenosphere to crust may result in syntectonic regional metamorphism and plutonism if the continents continue to converge following delamination a compressive tectonic regime will be reestablished in the crust the subsequent cooling of asthenosphere at the base of the crust may lead to the establishment of a continuous flat moho the likely imbrication of crustal and mantle lithologies during delamination and during the subsequent compressive tectonic regime as well as underplating associated with syntectonic plutonism may account for the seismic complexities observed at moho depths beneath some mountain belts

three dimensional numerical model simulations of airflow over mountainous terrain a comparison with observations abstract numerical simulations of airflow over two different choices of mountainous terrain and the comparisons of results with aircraft observations are presented two wintertime casts for flow over elk mountain wyoming where surface heating is assumed to be zero and one case for airflow over mt withington new mexico where surface heating is strong are considered in the elk mountain simulations the flow becomes approximately steady state since the upstream conditions are assumed to be constant and the surface heating is assumed to be zero the response is significantly different in the two cases in one case dynamic elk strong lee waves formed with a horizontal separation of 10 km whereas in the second case microphysical elk mainly weak untrapped waves formed with a vertical wavelength of 2 5 km because of the presence of the lee waves in the first case it is shown that the ridges south of elk mountain affect the flow near elk mountain in the second case where there were no strong lee waves

synoptic responses to mountain gravity waves encountering directional critical levels abstract a heuristic model is used to study the synoptic response to mountain gravity waves gws absorbed at directional critical levels the model is a semigeostrophic version of the eady model for baroclinic instability adapted by smith to study lee cyclogenesis the gws exert a force on the large scale flow where they encounter directional critical levels this force is taken into account in the model herein and produces potential vorticity pv anomalies in the midtroposphere first the authors consider the case of an idealized mountain range such that the orographic variance is well separated between small and large scale contributions in the absence of tropopause the pv produced by the gw force has a surface impact that is significant compared to the surface response due to the large scales for a cold front the gw force produces a trough over the mountain and a larger amplitude ridge immediately downstream it opposes somehow to the response due to the large scales of the mountain range whic

severe downslope windstorm calculations in two and three spatial dimensions using anelastic interactive grid nesting a possible mechanism for gustiness abstract the clark nonhydrostatic anelastic code is extended to allow for interactive grid nesting in both two and three spatial dimensions tests are presented which investigate the accuracy of three different quadratic interpolation formulae which are used to derive boundary conditions for the fine mesh model application of the conservation condition of kurihara and others is shown to result in significant improvements in the treatment of interactive nesting a significant improvement in the solutions for interactive versus parasitic nesting is also shown in the context of forced gravity wave flow this result for the anelastic system is in agreement with the earlier results of phillips and shukla who considered the hydrostatic shallow water system of equations the interactive nesting model is applied to the simulation of the severe downslope windstorm of 11 january 1972 in boulder using both two and three spatial dimensions the three dimensional simulation results in a gustiness signature in the

mountain wave turbulence in the presence of directional wind shear over the rocky mountains abstractmountain wave turbulence in the presence of directional wind shear over the rocky mountains in colorado is investigated pilot reports pireps are used to select cases in which moderate or severe turbulence encounters were reported in combination with significant directional wind shear in the upstream sounding from grand junction colorado gjt for a selected case semi idealized numerical simulations are carried out using the wrf arw atmospheric model initialized with the gjt atmospheric sounding and a realistic but truncated orography profile to isolate the role of directional wind shear in causing wave breaking sensitivity tests are performed to exclude the variation of the atmospheric stability with height the speed shear and the mountain amplitude as dominant wave breaking mechanisms significant downwind transport of instabilities is detected in horizontal flow cross sections resulting in mountain wave induced turbulence occurring at large horizontal distances from the first wave br

numerical simulations of orographic gravity waves in flows which back with height numerical simulations are carried out to determine the steady state gravity wave structure above a circularly symmetric bell shaped hill when the wind backs with height two types of idealized basic state flow are considered one representing the advection of a uniform baroclinic shear flow and the other being a flow of constant speed but with a wind vector that rotates uniformly in height of particular interest is the nature of the critical level processes that must appear at all heights due to the three dimensionality of the wave field and the rotation of the wind vector as suggested by linear theory a critical level or asymptotic wake is found downwind of the hill at any height where downwind refers to the wind at that level only for small hills where the nondimensional mountain height unity the simulated vertical momentum flux profiles are in very good agreement with linear hydrostatic wave theory if it is assumed that wave component critical level absorption is total i e no wave transmission or reflections are permitted the vertical momentum fluxes generated by a 1 km high hill show nonlinear enhancement by a factor of about 1 5 an interesting feature of the gravity wave field generated by this 1 km mountain is an asymptotic wake that is dominated by a single intense shear layer in which the richardson number is order unity

mineralogic and compositional properties of martian soil and dust results from mars pathfinder mars pathfinder obtained multispectral elemental magnetic and physical measurements of soil and dust at the sagan memorial station during the course of its 83 sol mission we describe initial results from these measurements concentrating on multispectral and elemental data and use these data along with previous viking snc meteorite and telescopic results to help constrain the origin and evolution of martian soil and dust we find that soils and dust can be divided into at least eight distinct spectral units based on parameterization of imager for mars pathfinder imp 400 to 1000 nm multispectral images the most distinctive spectral parameters for soils and dust are the reflectivity in the red the red blue reflectivity ratio the near ir spectral slope and the strength of the 800 to 1000 nm absorption feature most of the pathfinder spectra are consistent with the presence of poorly crystalline or nanophase ferric oxide s sometimes mixed with small but varying degrees of well crystalline ferric and ferrous phases darker soil units appear to be coarser grained compacted and or mixed with a larger amount of dark ferrous materials relative to bright soils nanophase goethite akaganeite schwertmannite and maghemite are leading candidates for the origin of the absorption centered near 900 nm in imp spectra the ferrous component in the soil cannot be well constrained based on imp data alpha proton x ray spectrometer apxs measurements of six soil units show little variability within the landing site and show remarkable overall similarity to the average viking derived soil elemental composition differences exist between viking and pathfinder soils however including significantly higher s and cl abundances and lower si abundances in viking soils and the lack of a correlation between ti and fe in pathfinder soils no significant linear correlations were observed between imp spectral properties and apxs elemental chemistry attempts at constraining the mineralogy of soils and dust using normative calculations involving mixtures of smectites and silicate and oxide minerals did not yield physically acceptable solutions we attempted to use the pathfinder results to constrain a number of putative soil and dust formation scenarios including palagonitization and acid fog weathering while the pathfinder soils cannot be chemically linked to the pathfinder rocks by palagonitization this study and mcsween et al 1999 suggest that palagonitic alteration of a martian basaltic rock plus mixture with a minor component of locally derived andesitic rock fragments could be consistent with the observed soil apxs and imp properties

the geochemical characteristics of granitoids in contrasting arcs and comments on magma sources geochemical variations in modern subduction related igneous suites with respect to arc maturity in time and space are illustrated using data for both volcanic suites basalt andesite and dacite and intrusive granitoid suites diorite tonalite granodiorite and granite from circum pacific arcs using trace element data we suggest that two groups of processes control the natural variation in the parental magmas of both suites a subduction zone enrichment of lithospheric mantle locally coupled with crustal assimilation allied with fractional crystallization afc in zones of thickened crust all of which yield magmas with enhanced concentrations of the large ion lithophile lil elements k rb th u lrees etc b with increasing distance from the active trench contributions from within plate sub continental lithosphere producing mantle derived magmas with enhanced levels of high field strength hfs elements among which nb ta hf and y are particularly distinctive thus even for the evolved granitoids of intrusive arc series ratios of hfs lil elements not significantly affected by crystal fractionation such as ta nb k rb la may throw some light on the origin of mafic intermediate precursor magmas in terms of these elements we suggest the following groupings for interpreting the tectonic associations of granitoid suites 1 primitive calcic arc granitoids with low lil and hfs element abundances 2 normal calc alkaline continental arc granitoids with enhanced lil element abundances and low hfs lil ratios 3 mature alkali calcic arc granitoids with high levels of lil and hfs elements and higher hfs lil ratios 4 back arc anorogenic alkaline granitoids with the highest levels of hfs elements

pressure drag and momentum fluxes due to the alps ii representation in large scale atmospheric models a three dimensional numerical model with interactive grid nesting is used to study the pressure drag and associated momentum fluxes due to the alpine complex for a specified upstream wind and static stability profile four basic questions are addressed which are relevant to the problems of flow description in the vicinity of mountains and the impact of orography in the context of mesoscale numerical weather prediction and general circulation models i what is the dependence of basic quantities such as the pressure drag on the model s horizontal resolution ii is there a need for non hydrostatic dynamics to account properly for the flow characteristics near steep mountains iii is there an effective role for enhanced orography such as an envelope formulation iv might a gravity wave drag parametrization scheme be able to represent adequately the highest resolution fluxes and surface drag in a much coarser resolution model a series of experiments with both hydrostatic and non hydrostatic models at resolutions of 80 40 20 10 and 5 km is analysed and two of these experiments are repeated with an envelope orography it is concluded that hydrostatic simulations are sufficient to describe the basic dynamics even at 5 km resolution however there is a strong dependence of the drag and momentum fluxes on resolution with the drag at 80 km resolution being almost half that at the highest resolution it is also shown that the use of an envelope orography at coarser resolutions can compensate significantly for the drag under estimation but is less effective in representing the vertical stress profiles or the direction of the stress vectors which are systematically in error at the coarsest resolution the potential role of gravity wave drag is confirmed and possible improvements considered it is suggested that both envelope orography and gravity wave drag may make a significant contribution until resolutions are as high as 10 to 20 km

multiple sources for the coastal batholith of central chile 31 34 s geochemical and sr nd isotopic evidence and tectonic implications abstract the coastal batholith of central chile between 31 and 34 s represents a locus of long lived c 200 ma plutonic activity it is composed of four plutonic complexes santo domingo limari papudo quintero and illapel these complexes which occur as north trending discontinuous belts that decrease in age eastward were emplaced during four major episodes of arc magmatism the santo domingo complex carboniferous comprises hornblende biotite bearing tonalites and granodiorites with abundant mafic enclaves and enclave free granites the association of enclave bearing granitoids and enclave free granites resulted from different degrees of mixing of crustal and mantle derived magmas the limari complex lower jurassic is a bimodal association of crustal leucogranites and mantle derived gabbros the lithology of the papudo quintero complex middle jurassic varies from hornblende pyroxene diorite to biotite granite the main rock types namely tonalites and granodiorites commonly contain mafic enclaves the granitoids and the enclaves have remarkably similar ree patterns and are similar in sr nd isotope composition which suggest that they represent a cogenetic suite of mantle origin the illapel complex cretaceous consists of hornblende bearing tonalites trondhjemites and granodiorites that resemble the rocks of ttg suites the end values and initial 87 sr 86 sr ratios sri for the mafic rocks of the carboniferous complex end 2 0 and 3 5 sri c 0 7057 differ markedly from those of the mesozoic mafic rocks end 1 9 to 5 4 sri 0 7033 to 0 7039 the cretaceous rocks being the most depleted with regard to sr nd a change from carboniferous lithosphere dominated sources to mesozoic asthenosphere dominated sources of the magmas that started in the early jurassic is recognized slab components can be recognized in the source of the cretaceous rocks the crustal source of the lower jurassic leucogranites was more isotopically depleted and refractory than that of the carboniferous granites on the other hand no crustal participation in the origin of the middle jurassic and cretaceous felsic granitoids is recognized they are differentiated from mantle derived magmas progressive removal of old lithospheric mantle during the mesozoic due to a process of lithospheric delamination would explain the profound change in the subcrustal source as well as the melting and modification towards a more refractory nature of the continental crust

the role of the mantle during crustal extension constraints from geochemistry of volcanic rocks in the lake mead area nevada and arizona one of the fundamental questions in areas of large magnitude extension and magmatism is the role of the mantle in the extension process the lake mead area is ideally suited for developing models that link crustal and mantle processes because it contains both mantle and crustal boundaries and it was the site of large magnitude crustal extension and magmatism during miocene time in the lake mead area the boundary between the amagmatic zone and the northern colorado river extensional corridor parallels the lake mead fault system and is situated just to the north of lake mead this boundary formed between 11 and 6 ma during and just following the peak of extension and corresponds to a contact between two mantle domains during thinning and replacement of the lithospheric mantle in the northern colorado river extensional corridor the lithospheric mantle in the amagmatic zone remained intact contrasting behavior to the north and south of this boundary may have produced the mantle domain boundary the domain to the north of the boundary is characterized by mafic lavas with a lithospheric mantle isotopic and geochemical signature nd 3 to 9 87 sr 86 sr 0 706 0 707 to the south of the boundary in the northern colorado river extensional corridor lavas have an ocean island basalt oib mantle signature and appear to have only a minor lithospheric mantle component in their source nd 0 to 4 87 sr 86 sr 0 703 0 705 mafic lavas of the northern colorado river extensional corridor represent the melting of a complex and variable mixture of asthenospheric mantle lithospheric mantle and crust pliocene alkali basalt magmas of the fortification hill field represent the melting of a source composed of a mixture of asthenospheric mantle high u pb himu like mantle and lithospheric mantle depth of melting of alkali basalt magmas remained relatively constant from 12 to 6 ma during and just after the peak of extension but probably increased between 6 and 4 3 ma following extension miocene and pliocene low nd and high 87 sr 86 sr magmas and tholeiites at malpais flattop were derived from a lithospheric mantle source and were contaminated as they passed through the crust the shift in isotopic values due to crustal interaction is no more than 4 units in nd and 0 002 in 87 sr 86 sr and does not mask the character of the mantle source the change in source of basalts from lithospheric mantle to asthenospheric mantle with time the oib character of the mafic lavas and the himu like mantle component in the source are compatible with the presence of rising asthenosphere as an upwelling convective cell or plume beneath the northern colorado river extensional corridor during extension the lake mead fault system a major crustal shear zone parallels the mantle domain boundary the lake mead fault system may locally represent the crustal manifestation of differential thinning of the lithospheric mantle