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

cretaceous demise of the moa plate and strike slip motion at the gondwana margin radiolaria and paleomagnetic data from deep sea drilling project sites 595 and 596 indicate that early cretaceous seafloor was formed at moderate to high latitudes in the pacific this inference requires a cretaceous spreading ridge south of the pacific phoenix ridge and substantial dextral strike slip motion at the gondwana margin the previously unrecognized southern oceanic plate called here the moa plate was obliquely subducted beneath the gondwana margin and material accreted from it is now part of the eastern province of new zealand

some aspects of the effect of surface friction on flows over mountains the effect of surface friction on flow over mountains in stratified fluids is investigated using a two dimensional version of the naval research laboratory s non hydrostatic coupled ocean atmosphere mesoscale prediction system coamps without surface friction flow over a mountain attains a maximum speed at the surface on the lee slope with surface friction the flow speed vanishes at the surface and reaches a maximum near the top of the boundary layer bl corresponding to this wind distribution is a shallow layer of very large vertical wind shear beneath the jet maximum and a weaker but deeper sheared layer elsewhere this strong shear generates maximum turbulent kinetic energy tke at the jet maximum region meanwhile the buoyancy effect associated with the mountain gravity wave inhibits the production of the tke above the jet maximum region the combined effects of shear and buoyancy lead to a very shallow bl on the lee slope in general surface friction reduces the amplitude of mountain gravity waves comparison of the flow fields with the outline of the bl height indicates that flow characteristics correspond closely to the distribution of the bl height it is hypothesized that the reduction in mountain wave amplitude in the presence of surface friction is due to the reduction in the slope of the bl height as compared to the terrain height for narrower and or higher mountains the bl height exhibits a secondary peak on the lee side that further modifies the wave simulations using the bl height as a solid mountain without surface friction confirm that characteristics of flow over the mountain are associated with the distribution of bl height rather than the terrain height field as the non dimensional mountain height increases the magnitude of the effect of surface friction decreases due to decreasing bl depth on the lee side with the result that the bl height profile becomes closer to the terrain height field the effect of surface friction on asymmetric mountains is also investigated without surface friction the pressure drag shows distinctive reduction with a secondary peak on the downstream side but the effect is less when the secondary peak is on the upstream side with surface friction all three mountains have similar pressure drag corresponding to their similar bl height profiles copyright 2003 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

cretaceous oblique extensional deformation and magma accumulation in the fosdick mountains migmatite cored gneiss dome west antarctica 1 the fosdick mountains west antarctica expose a 15 x 80 km migmatite cored gneiss dome consisting of migmatitic gneisses diatexite migmatite and subhorizontal leucogranite sheets the fosdick dome was emplaced and exhumed in the mid cretaceous due to oblique extension associated with the west antarctic rift system along the west antarctic new zealand segment of east gondwana the dome is bounded to the south by a dextral oblique detachment structure and to the north by an inferred dextral strike slip fault within the fosdick dome and in the detachment zone granite occupies leucosomes dikes sills and dilatant and shear structures the pattern of kilometer scale domains of migmatite and granite suggest that lithologic variations and heterogeneous deformation boudinage resulted in pressure gradients that enhanced melt flow and magma accumulation in the fosdick dome steep foliations are overprinted folded and transposed by subhorizontal fabrics the crosscutting relationship is interpreted as a transition from wrench deformation to oblique divergence steep structures in the dome host concordant subvertical leucosome and granite sheets yielding shrimp u pb zircon ages between ca 117 and 114 ma prevalent subhorizontal domains host large volumes of subhorizontal diatexite migmatite and granite sheets that yield u pb zircon ages between ca 109 and 102 ma these ages indicate a timescale for melt influx of approximately 15 ma and that the transition from wrench to oblique divergence may have occurred in as little as 5 ma granites with crystallization ages between ca 109 and 102 ma were also emplaced in the south fosdick detachment zone indicating that the detachment was active during oblique divergence shrimp u pb titanite ages between ca 102 and 97 ma for late to post tectonic diorite dikes are interpreted as emplacement ages and give a minimum age for gneissic foliation development during detachment faulting the fosdick mountains preserve a record of the middle to lower crustal response to a transition from wrench to oblique extensional deformation overprinting structural relationships show that a change in the angle of oblique extension can induce accumulation of subhorizontal magma sheets and lead to initiation of a detachment zone

a new theory for downslope windstorms and trapped mountain waves abstractlinear mountain gravity waves forced by a nonlinear surface boundary condition are derived for a background wind that is null at the surface and increases smoothly to reach a constant value aloft and for a constant buoyancy frequency in this configuration the mountain waves have a critical level just below the surface that is dynamically controlled by the surface and minimum richardson number j when the flow is very stable and when the depth over which dissipations act is smaller than the mountain height this critical level dynamics easily produces large downslope winds and foehns the downslope winds are more intense when the stability increases and much less pronounced when it decreases when j goes below 1 in contrast the trapped lee waves are very small when the flow is very stable start to appear when and can become pure trapped waves e g not decaying downstream when the flow is unstable for for the trapped waves these results are explained by the fact that the critical l

two stage rifting of zealandia australia antarctica evidence from 40ar 39ar thermochronometry of the sisters shear zone stewart island new zealand the sisters shear zone is a newly discovered late cretaceous detachment fault system exposed for 40 km along the southeast coast of stewart island southernmost new zealand footwall rocks consist of variably deformed ca 310 and 105 ma granites that range from undeformed to protomylonite mylonite and ultramylonite the hanging wall includes non marine conglomerate and brittley deformed granite k feldspar thermochronometry of the footwall indicates moderately rapid cooling 20 30 c m y due to tectonic denudation over the interval ca 89 82 ma return to slow cooling at 82 ma coincides with the age of the oldest seafloor adjacent to the campbell plateau and reflects the mechanical transition from continental extension to lithospheric rupture and formation of the pacific antarctic ridge our findings support a two stage rift model for continental breakup of this part of the gondwana margin stage one ca 101 88 ma is the northward propagation of continental extension and the tasman ridge as recorded in mylonite dredged from the ross sea and the paparoa core complex stage two ca 89 82 ma is extension between the campbell plateau and west antarctica leading to formation of the pacific antarctic ridge

blocking descent and gravity waves observations and modelling of a map northerly fohn event a northerly fohn event observed during the special observational period of the mesoscale alpine programme is investigated based on observational analysis and numerical modelling the focus of this study includes three dynamical processes associated with mountain perturbations and their interactions namely windward flow blocking descent and warming on the lee side and mountain waves observations indicate the presence of a deep weak flow layer underneath a stable layer associated with alpine scale blocking satellite imagery reveals a fohninduced cloud free area to the south of the alps which is consistent with flow descent diagnosed from radiosondes and constant volume balloons moderate amplitude stationary waves were observed by research aircraft over the major alpine peaks satellite images and balloon data indicate the presence of stationary trapped wave patterns located to the north of the alpine massif satisfactory agreement is found between observations and a real data coamps simulation nested to 1 km resolution coamps indicates the presence of trapped waves associated with a sharp decrease of scorer parameter above a stable layer in the mid troposphere underneath the stable layer moist low level flow is blocked to the north of the alps the warm air in the stable layer descends in the lee and recovers its altitude over a relatively short horizontal distance through a hydraulic jump blocking reduces the effective mountain and hence significantly reduces mountain drag a simple empirical formula for estimation of the effective mountain height he is derived based on numerical simulations the formula states he hc h hc where h is the real mountain height and hc is the critical mountain height to have flow stagnation copyright 2005 royal meteorological society

on the diurnal variation of mountain waves abstract the diurnal variation of mountain waves and wave drag associated with flow past mesoscale ridges has been examined using the coupled ocean atmosphere mesoscale prediction system coamps and an analytical boundary layer bl model the wave drag exhibits substantial diurnal variation in response to the change in the atmospheric bl characteristics such as the bl depth shape factor and stability during daytime a convective bl develops characterized by a shallow shear layer near the surface and a deep well mixed layer aloft both of which tend to decrease the wave drag as a result the convective bl could significantly weaken mountain waves and reduce the momentum flux by up to 90 near the surface the flow pattern resembles a potential flow with a surface wind maximum located near the ridge crest during nighttime a shallow stable bl develops and the modulation of wave drag by the stable nocturnal bl is governed by the bl froude number fr if the bl flow is supercritical the drag incr

dynamics of the foehn mechanism in the mcmurdo dry valleys of antarctica from polar wrf foehn events over the mcmurdo dry valleys mdvs the largest ice free region of antarctica promote glacial melt that supports biological activity in the lakes streams rocks and soils although mdvs foehn events are known to depend upon the synoptic scale circulation the physical processes responsible for foehn events are unknown a polar optimized version of the weather research and forecasting model polar wrf is used for a case study of a representative summer foehn event from 29 december 2006 to 1 january 2007 in order to identify and explain the mdvs foehn mechanism pressure differences across an elevated mountain gap upstream of the mdvs provide forcing for southerly flow into the western upvalley entrance of the mdvs complex terrain over the elevated gap and the mdvs leads to mountain wave effects such as leeside acceleration hydraulic jumps wave breaking and critical layers these mountain wave effects depend on the ambient geostrophic wind direction pressure driven channelling then brings the warm dry foehn air downvalley to eastern mdv sites brief easterly intrusions of maritime air into the eastern mdvs during foehn events previously have been attributed to either a sea breeze effect in summer or local cold pooling effects in winter in this particular case the easterly intrusions result from blocking effects of nearby ross island and the adjacent antarctic coast temperature variability during the summer foehn event which is important for meltwater production and biological activity when it exceeds 0 c primarily depends on the source airmass rather than differences in foehn dynamics

kinematic finite strain and vorticity analysis of the sisters shear zone stewart island new zealand abstract the sisters shear zone ssz on stewart island new zealand is a greenschist facies extensional shear zone active prior to and possibly during the development of the pacific antarctica spreading ridge at 76 ma we report quantitative kinematic and rotation data as well as apatite fission track aft ages from the ssz early kinematic indicators associated with the nne trending stretching lineation formed under upper greenschist facies metamorphism and show alternating top to the nnw and top to the sse senses of shear during progressive exhumation lowermost greenschist facies and brittle ductile kinematic indicators depict a more uniform top to the sse sense of shear in the topmost ssz just below the detachment plane deformed metagranites in the ssz allow the reconstruction of deformation and flow parameters the mean kinematic vorticity number w m ranges from 0 10 to 0 89 smaller numbers prevail in the deeper parts of the shear zone with a higher degree of simple shear deformation in the upper parts of the shear zone deeper and upper parts relate to present geometry high finite strain intensity correlates with low w m and high w m numbers near the detachment correlate with relatively weak strain intensity finite strain shows oblate geometries overall our data indicate vertical and possibly temporal variations in deformation of the ssz most aft ages cluster around 85 75 ma we interpret the aft ages to reflect the final stages of continental break up just before and possibly during the initiation of sea floor spreading between new zealand and antarctica

stably stratified shear flow over low hills summary an analysis is presented for the mean flow over hills with low slopes for various kinds of stable stratification in the approach flow the froude number f based on the height is always greater than unity the analysis is based on dividing up the flow into different regions with different dynamics we concentrate on the flow in the inviscid outer region of the flow it is shown that in the lower part of the outer region the middle layer where the shear is large the upwind velocity profile and the shape of the hill rather than the upwind density profile largely determine the vertical perturbation velocity in the upper layer the structure of the flow depends largely on the form of the upwind density profile for example this largely determines the location of maximum surface wind new solutions for stable conditions are obtained when there is a constant density gradient when n ub 0 z2 and when there is an elevated inversion layer in the first and third of these cases we compare the results with the hydrostatic approximation and also obtain new general formulae for the near surface winds an approximate formula is developed for surface winds at arbitrary values of f 1 for uniform stable stratification

terrane boundary reactivation barriers to lateral fault propagation and reactivated fabrics rifting across the median batholith zone great south basin new zealand prominent pre existing structural heterogeneities within the lithosphere may localise or partition deformation during tectonic events the ne trending great south basin offshore new zealand formed perpendicular to a series of underlying crustal terranes including the dominantly granitic median batholith zone which along with the boundaries between individual terranes exert a strong control on rift physiography and kinematics we find that the crustal to lithospheric scale southern terrane boundary of the median batholith zone is associated with a crustal scale shear zone that was reactivated during late cretaceous extension between zealandia and australia this reactivated terrane boundary is oriented at a high angle to the faults defining the great south basin we identify a large granitic laccolith along the southern margin of the median batholith expressed as sub horizontal packages of reflectivity and acoustically transparent areas on seismic reflection data the presence of this strong granitic body inhibits the lateral south westward propagation of ne trending faults which segment into a series of splays that rotate to align along the margin as they approach further we also identify two e w and ne sw oriented basement fabrics likely corresponding to prominent foliations which are exploited by small scale faults across the basin we show that different mechanisms of structural inheritance are able to operate simultaneously and somewhat independently within rift systems at different scales of observation the presence of structural heterogeneities across all scales need to be incorporated into our understanding of the structural evolution of complex rift systems

the interplay and effects of deformation and crystallized melt on the rheology of the lower continental crust fiordland new zealand abstract microstructural electron backscatter diffraction ebsd and misorientation analyses of a migmatitic granulite facies orthogneiss from the exhumed lower crust of a cretaceous continental arc in fiordland new zealand show how deformation was accommodated during and after episodes of melt infiltration and high grade metamorphism microstructures in garnet omphacite plagioclase and k feldspar suggest that an early stage of deformation was achieved by dislocation creep of omphacite and plagioclase with subsequent deformation becoming partitioned into plagioclase continued deformation after melt infiltration resulted in strain localization in the leucosome of the migmatite where a change of plagioclase deformation mechanism promoted the onset of grain boundary sliding most likely accommodated by diffusion creep in fine recrystallized plagioclase grains our results suggest three distinctive transitions in the rheology of the lower crust of this continental arc where initial weakening was primarily achieved by deformation of both omphacite and plagioclase subsequent strain localization in plagioclase of the leucosome indicates that the zones of former melt are weaker than the restite and that changes in deformation mechanisms within plagioclase and an evolution of its strength primarily control the rheology of the lower crust during and after episodes of melting and magma addition

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

impact of surface characteristics on flow over a mesoscale mountain dynamical downscaling of atmospheric flow over iceland has revealed that prominent downslope accelerated flows are not merely extreme events but rather constitute a strong climatological signal over the larger ice caps ice caps are characterised by smooth and cold surfaces and both of these properties have previously been found to enhance downslope flows in this article we investigate the response of downslope accelerated flow over hofsjokull in central iceland to an increase in surface roughness and a change in surface temperature corresponding to the effect of melting hofsjokull s ice cap we do so by exploring the flow over hofsjokull for a summertime case by means of several numerical sensitivity experiments in the experiments we find a stronger downslope flow acceleration with than without the ice cap while an increased surface roughness distinctly dampens the downslope flow the effect of changing the surface temperature is minimal this study is both of general relevance through its exploration of factors affecting downslope acceleration of stably stratified flow and also of interest because glaciers diminish rapidly in a changing climate

mineral fish their morphological classification usefulness as shear sense indicators and genesis mineral fish are sheared and commonly asymmetric mineral grains or clusters of grains this work reports 11 sub types of mineral fish showing a top to se sense of ductile shearing in the karakoram metamorphic complex kmc the mineral fish are of three broad geometries sigmoid lenticular and parallelogram reliable senses of shear are indicated by the overall asymmetry and inclination of mineral fish on the other hand the true shear sense is not always indicated by either the orientations of their cleavage planes or those of the individual grains in composite mineral fish the ranges of local orientations of single sigmoid mineral fish that include the lower values 23 in the kmc indicate their extensive ductile shearing the studied mineral fish were products of a range of deformation mechanisms including homogeneous deformation simple shear intra granular slip crystal plastic deformation fracturing and synthetic shearing additionally some examples might have undergone duplex slips and a few nucleated and grew either prior to or during the top to se shearing

detachment faulting and the evolution of passive continental margins major detachment faults play a key role in the lithospheric extension process in the basin and range province and may also be important in other continental extension terranes such detachment faulting leads to an inherent asymmetry of extensional structure and of uplift subsidence patterns detachment models developed for the formation of metamorphic core complexes can also be applied to the formation of passive continental margins we therefore suggest the existence of upper plate and lower plate passive margins these give rise to a complementary asymmetry of opposing margins after continental breakup transfer faults offset marginal features and allow margins to switch from upper plate to lower plate characteristics along strike

post mid cretaceous tectonic and topographic evolution of western marie byrd land westantarctica insights from apatite fissiontrack and u th sm he data

paleoclimate and polar wander abstract fossil faunas floras and 18 o temperatures indicate that weak or no meridional temperature gradients existed over the continents from triassic to eocene for much of this time tropical pacific 18 o temperatures were some ten degrees colder than at present while arctic and antarctic regions apparently enjoyed warm temperate to semitropical climates polar wander involving displacement of the poles to what are now tropical marine latitudes is offered to explain this uniformly warm paleoclimate this hypothesis is supported by a theoretical model which is discussed

tracking the influence of a continental margin on growth of a magmatic arc fiordland new zealand using thermobarometry thermochronology and zircon u pb and hf isotopes 1 geothermobarometric radiogenic isotopic and thermochronologic data are used to track the influence of an ancient continental margin western province on development of an adjacent carboniferous cretaceous magmatic arc outboard median batholith in fiordland new zealand the data show a record of complicated mesozoic gondwana margin growth paragneiss within the outboard median batholith is of carboniferous to jurassic age and records burial to middle crustal depths in late jurassic early cretaceous during subduction related plutonism and arc thickening in contrast western province metasedimentary rocks in the area of study immediately west of the outboard median batholith are late cambrian early ordovician in age recrystallized at the amphibolite facies in the late devonian early carboniferous and exhibit no evidence for mesozoic textural or isotopic reequilibration a phase of deformation between 128 and 116 ma deformed exhumed and cooled the outboard median batholith to greenschist facies temperatures while large parts of the western province underwent 9 kbar metamorphic conditions zircon grains from mesozoic inboard plutons are isotopically more evolved hf t 2 3 to 4 0 than those in the outboard median batholith hf t 9 4 to 11 1 the contrasting zircon hf isotope ratios absence of s type plutons or proterozoic early paleozoic inherited zircon and the apparent absence of early paleozoic metasedimentary rocks indicates that the outboard median batholith is unlikely to be underlain by the western province continental lithosphere the new data are consistent with the outboard median batholith representing an allochthonous although not necessarily exotic arc that was juxtaposed onto the gondwana continental margin along the intervening grebe mylonite zone

cretaceous termination of subduction at the zealandia margin of gondwana the view from the paleo trench abstract during the permian to cretaceous zealandia occupied a position on the proto pacific facing convergent margin of gondwana subduction on this margin ceased somewhere between 105 ma and perhaps 70 ma but the timing of this tectonic transition remains controversial resolution of this uncertainty is important for tectonic reconstructions of the southwest pacific and for global plate tectonic models here we revisit the problem by reference to new stratigraphic and geochemical data from the east coast basin of new zealand which occupied a position adjacent to and possibly superimposed on the relict cretaceous subduction trench at the time subduction ceased this basin is expected to preserve direct structural and stratigraphic evidence for or against late cretaceous subduction in western parts of the east coast basin the western sub belt a conspicuous unconformity separates undoubted accretionary prism rocks of the torlesse composite terrane from younger cretaceous cover units strata beneath and overlying this unconformity vary in age from place to place but abundant paleontological data and published ages of detrital zircons some reinterpreted herein indicate that exposed torlesse rocks are nowhere younger than 100 ma overlying zealandia megasequence cover strata are mostly younger than 110 ma between 110 and 85 ma the entire length of the western sub belt reveals complex stratigraphic architecture of relatively small scale depocentres subjected to alternating episodes of subsidence and local uplift and erosion there is widespread evidence for compression on the western sub belt over this period although the overall amount of shortening is likely to be relatively modest in contrast the eastern sub belt preserves a record of near continuous and apparently simple deposition over the same interval of time we see little and somewhat equivocal evidence for extension in either sub belt through the late cretaceous superimposed on this general pattern we observe discrete widespread or basin wide tectonic events at 95 ma and within the intervals 86 83 ma and 83 81 ma indicated by the presence of unconformities and sedimentary facies changes importantly all these events can be correlated with coeval events recorded elsewhere in zealandia suggesting that the east coast basin was subject to the same tectonic regime as the rest of zealandia and shared a common history during the mid to late cretaceous integrating these findings with data from elsewhere in zealandia we argue that there is diverse evidence to indicate that subduction finished along the new zealand segment of the gondwana margin by 100 ma that said the causes of on going late cretaceous compression in the east coast basin and in other parts of zealandia are not well constrained although several possible explanations are plausible there are few analogue abandoned subduction margins described in the literature however the situation in the south shetland trench shows strong similarities with patterns and complexities observed in the east coast basin

ross sea mylonites and the timing of intracontinental extension within the west antarctic rift system there are few direct constraints on the timing and style of faulting in the ross sea sector of the west antarctic rift system although cretaceous plate reconstructions indicate that ross sea extension between east and west antarctica occurred prior to breakup of the gondwana margin ca 80 ma mylonitic gneisses dredged from the eastern ross sea indicate shear zone deformation considerably earlier at 98 95 ma strain analysis of fab rics indicates 85 100 extension overprinting brittle structures record translation of shear zone gneisses into the upper crust samples yield sensitive high resolution ion microprobe u pb zircon ages of 102 97 ma correlated to byrd coast granite onshore and concordant 40 ar 39 ar biotite and k feldspar ages of 98 95 ma indicating that granites were mylonitized soon after emplacement and cooled rapidly apatite fission track data corroborate this rapid cooling event and reveal a second rapid cooling event ca 80 ma evidence for contemporaneous deformation and a similar thermal evolution at deep sea drilling project site 270 on the ross sea central high and for a migmatite dome on land attests to the regional extent of intracontinental extension extension occurred at a time of complex microplate interactions along the cretaceous active gondwana margin sug gesting that distributed deformation in the overriding antarctic plate may be related to plate boundary dynamics

large amplitude mountain wave breaking over greenland abstract a large amplitude mountain wave generated by strong southwesterly flow over southern greenland was observed during the fronts and atlantic storm track experiment fastex on 29 january 1997 by the noaa g iv research aircraft dropwindsondes deployed every 50 km and flight level data depict a vertically propagating large amplitude wave with deep convectively unstable layers potential temperature perturbations of 25 k that deformed the tropopause and lower stratosphere and a vertical velocity maximum of nearly 10 m s 1 in the stratosphere the wave breaking was associated with a large vertical flux of horizontal momentum and dominated by quasi isotropic turbulence the coupled ocean atmosphere mesoscale prediction system coamps nonhydrostatic model with four nested grid meshes with a minimum resolution of 1 7 km accurately simulates the amplitude location and timing of the mountain wave and turbulent breakdown finescale low velocity plumes that resemble wakelike structures emanate from highl

dislocation creep regimes in quartz aggregates abstract using optical and tem microscopy we have determined that three regimes of dislocation creep occur in experimentally deformed quartz aggregates depending on the relative rates of grain boundary migration dislocation climb and dislocation production within each regime a distinctive microstructure is produced due primarily to the operation of different mechanisms of dynamic recrystallization at lower temperatures and faster strain rates the rate of dislocation production is too great for diffusion controlled dislocation climb to be an effective recovery mechanism in this regime recovery is accommodated by strain induced grain boundary migration recrystallization with an increase in temperature or decrease in strain rate the rate of dislocation climb becomes sufficiently rapid to accommodate recovery in this regime dynamic recrystallization occurs by progressive subgrain rotation with a further increase in temperature or decrease in strain rate dislocation climb remains sufficiently rapid to accommodate recovery however in this regime grain boundary migration is rapid thus recrystallization occurs by both grain boundary migration and progressive subgrain rotation the identification of the three regimes of dislocation creep may have important implications for the determination of flow law parameters and the calibration of recrystallized grain size piezometers in addition the identification of a particular dislocation creep regime could be useful in helping to constrain the conditions at which a given natural deformation has occurred

focusing of relative plate motion at a continental transform fault cenozoic dextral displacement 700 km on new zealand s alpine fault reversing 225 km of late cretaceous sinistral motion the widely accepted 450 km cenozoic dextral strike slip displacement on new zealand s alpine fault is large for continental strike slip faults but it is still less than 60 of the cenozoic relative plate motion between the australian and pacific plates through zealandia with the remaining motion assumed to be taken up by rotation and displacement on other faults in a zone up to 300 km wide we show here that the 450 km total displacement across the alpine fault is an artifact of assumptions about the geometry of new zealand s basement terranes in the eocene and the actual cenozoic dextral displacement across the active trace is greater than 665 km with more than 700 km and 94 of the relative plate motion in the last 25 ma at an average rate in excess of 28 mm yr it reverses more than 225 km and 300 km of sinistral shear through zealandia in the late cretaceous when zealandia lay on the margin of gondwana providing a direct constraint on the kinematics of extension between east and west antarctica at this time