flow structure and turbulence characteristics of the daytime atmosphere in a steep and narrow alpine valley aircraft measurements radio soundings and sonic data obtained during the map riviera field campaign in autumn 1999 in southern switzerland are used to investigate the flow structure temperature profiles and turbulence characteristics of the atmosphere in a steep and narrow alpine valley under convective conditions on all predominantly sunny days of the intensive observation periods a pronounced valley wind system develops in the southern half of the valley the daily up valley winds have a jet like structure and are shifted towards the eastern slope these up valley winds advect potentially colder air a process which appears to be balanced by vertical warm air advection from above the profiles of potential temperature show that with the onset of up valley winds the mixed layer consistently stops growing or on days with very strong up valley winds even stabilizes almost throughout the entire valley atmosphere this is probably due to a pronounced secondary circulation in the southern part of the valley which induces advection of warm air from above the secondary circulation appears to be a consequence of sharp curvature in the along valley topography turbulence variables are calculated from flight legs in the along valley direction turbulent kinetic energy tke scales surprisingly well i if a tke criterion tke 0 5 m2s 2 is employed as a definition of the boundary layer height and ii if the surface fluxes which exhibit a substantial spatial variability from the slope sites are used rather than those from directly beneath the profile considered significant site to site differences in incoming solar radiation seem to be the reason for this characteristic behaviour profiles of momentum flux scaled with a surface friction velocity reveal more scatter than the tke profiles but still show a consistent behaviour a surprisingly strong shear in the cross valley direction can be observed and is probably a result of the secondary circulation copyright 2004 royal meteorological society

discovery of miocene to early pleistocene deposits on mayaguana bahamas evidence for recent active tectonism on the north american margin we report here the discovery of miocene pliocene and early pleistocene shallow marine carbonates on mayaguana island southeastern bahamas that have so far not been observed on any other bahamian island spanning more than 17 m y but 12 m thick this stratigraphic succession only occurs along the northern coast of the island indicating that the mayaguana bank underwent minor subsidence throughout the late cenozoic and was tilted toward the south during the quaternary in addition to considerably extending the stratigraphic record of the bahamas islands our findings demonstrate that these carbonate banks were at different elevations and subsided at different rates during the neogene the young age of the tilting event detected on mayaguana further shows that parts of the southeastern margin of north america have recently undergone tectonic activity a long way from its actual boundary with the caribbean plate

the heat burst of 29 may 1976 abstract an unusual phenomenon occurred in central oklahoma in the late evening and early morning hours of 29 30 may 1976 surface temperatures suddenly rose as much as 6 c the sudden large temperature rise and humidity fall which sometimes accompanies nocturnal thunderstorms defines the heat burst the origin of a heat burst may be adiabatic subsidence near dissipating or rear edges or storms in addition to increasing temperature and falling relative humidity the hear burst is characterized by the erosion of clouds and radar echoes and gusty winds this paper documents the mesoscale events associated with this phenomenon

observations of polarimetric signatures in supercells by an x band mobile doppler radar abstractpolarimetric weather radars significantly enhance the capability to infer the properties of scatterers within a resolution volume previous studies have identified several consistently seen polarimetric signatures in supercells observed in the central united states nearly all of these studies used data collected by fixed site s and c band radars because there are few polarimetric mobile radars relatively little has been documented in high resolution polarimetric data from mobile radars compared to s and c bands there has been very limited examination of polarimetric signatures at x band the primary focus of this paper is on one signature that has not been documented previously and one that has had little documentation at x band the first signature seen in at least seven supercell datasets collected by a mobile x band polarimetric radar consists of a narrow band of locally reduced reflectivity factor zh and differential reflectivity typically near the location where the hook echo attac

observations of downslope winds and rotors in the falkland islands a field campaign aimed at observing the near surface flow field across and downwind of a mountain range on the falkland islands south atlantic is described the objective was to understand and eventually predict orographically generated turbulence the instrumentation was based primarily on an array of automatic weather stations awss which recorded 30 s mean surface pressure wind speed and direction at 2 m temperature and relative humidity for approximately one year these measurements were supported by twice daily radiosonde releases the densest part of the aws array was located to the south of the wickham mountain range across mount pleasant airfield mpa in northerly flow the array provides a detailed study of the flow downwind of the mountain range the dataset contains several episodes in which the flow downwind of the mountains is accelerated relative to the upwind flow during some of these episodes short lived typically 1 hour periods of unsteady flow separation are observed and these are associated with the formation of rotors aloft such events present a significant hazard to aviation at mpa examination of radiosonde profiles suggests that the presence of a strong temperature inversion at a height similar to the mountain height is a necessary condition for both downwind acceleration and the formation of rotors the data are used to show that the downwind fractional speed up is proportional to the non dimensional mountain height based on upstream near surface winds and a depth averaged brunt vaisala frequency diagnosed from radiosonde data similarly a relationship is established between a quantity that describes the spatial variability of the flow downwind of the mountains and the upstream wind and depth averaged brunt vaisala frequency the dependence of the flow behaviour on the froude number defined in the usual way for two layer shallow water flow and ratio of mountain height to inversion height is presented in terms of a flow regime diagram

observations of cross ridge flows across steep terrain a field experiment gaudex has been conducted to address the need for quantitative measurements of turbulence in the vicinity of steep terrain a dense network of automatic weather stations and turbulence towers was deployed along cross ridge transects over gaudergrat a steep triangular cross section ridge in eastern switzerland a new feature whereby ridge normal cross ridge flows develop at the crest even when the flow in each valley is oriented parallel to the ridge axis is identified this occurs independently of whether the flow is thermally or synoptically driven pressure measurements across the ridge show that this flow is driven by a cross ridge pressure gradient two mechanisms for generating cross ridge flows have been identified from measurements of pressure wind and temperature in most cases the pressure gradient arises from a difference in flow speeds between the two sides of the ridge caused by different valley geometries less commonly the cross ridge flow is explained by linear speed up of the ridge normal flow copyright 2008 royal meteorological society

properties and parameterization of the stable boundary layer over moderate topography numerical simulations are used to investigate the impact on the stable boundary layer of moderate topography with hill heights in some cases comparable to the undisturbed boundary layer depth area averaged properties of the resulting boundary layers which are often highly inhomogeneous are diagnosed the presence of the hills leads to enhanced turbulence and drag and a deepening of the area averaged boundary layers over and above that due to a simple displacement effect the ability of well established formulas for the depth of the boundary layer over homogeneous terrain to predict this deepening is investigated finally the implications of the results for the use in large scale weather and climate prediction models of effective roughness length parameterizations of the effects of hills are discussed while not capturing some of the more detailed effects the simplest approach of using a roughness length independent of stability is found to perform reasonably well in predicting the total surface drag

observations theory and modeling of the differential accumulation of antarctic megadunes antarctic megadunes are characterized by significant spatial differences in accumulation rate with higher accumulation on the windward side and near zero accumulation on the lee side this leads to spatial differences in physical properties of snow and surface roughness as well as to the upwind migration of the megadunes while previous studies agree that megadunes are a result of complex interactions between wind topography and snow it is not clear how they form or why they accumulate on the windward side here we use icesat observations dimensional analysis and atmospheric flow modeling to investigate what conditions are responsible for the accumulation patterns and upwind migration of the megadunes first we use icesat data to quantify the pattern of differential surface elevation change across the megadunes we then use dimensional analysis based on supercritical flow theory and atmospheric flow modeling to show that the megadunes topography and a stable atmosphere will always lead to upwind dune migration we show that a combination of persistent katabatic winds strong stability and spatial variability in surface roughness is responsible for the accumulation on the upwind slope and hence the upwind migration of the megadunes we further show that spatial differences in surface roughness are the primary control on accumulation magnitudes and hence dune migration velocity the dune migration velocity in turn influences the degree of snow metamorphism and the physical properties of snow that are relevant for paleoclimate records our findings pertain to the ongoing evolution of the megadunes but their genesis remains an open question

uplifted flank margin caves in telogenetic limestones in the gulf of orosei central east sardinia italy and their palaeogeographic significance abstract this work reports the results of geomorphological observations carried out in the coastal fico cave and surrounding areas baunei central east sardinia in the gulf of orosei a tidal notch generally believed to be of eemian mis 5e age is barely visible at 8 5 above present sea level asl some metres below the main entrance of the cave old cave passages now partially opened by cliff retreat and parallel to the coastline are clearly visible at around 14 m asl and correspond to the main level of fico cave two more notches are located higher at 22 and 50 m asl fico cave itself is composed of at least 6 clearly distinguished more or less horizontal levels 10 m below present sea level bsl and 14 22 40 50 and 63 m asl independent of the stratal dip arguing for a sea level and hence fresh water lens control cave passages develop along main fractures more or less parallel to the coastline and never extend landward for more than 150 m mostly ending blindly or diminishing in their dimensions progressively landward most passages only contain clay deposits lacking fluvial or marine sediments or typical fluvial erosion morphologies i e scallops it is suggested from this body of evidence that fico cave was formed in the coastal mixing zone along major discontinuities during several quaternary interglacial periods when sea level was high and relatively stable for enough time to develop large dissolutional voids the geomorphological observations indicate the main 14 m asl level of the cave to have formed during mis 9 and was heavily reworked during mis 5 while the higher levels are relative to older interglacial highstands that occurred between 1 ma and 325 ka the small active branch developed below present sea level has formed during mis 7 225 ka these observations shed new light on the position of the mis 5e highstand markers in this area of the coast much higher than previously thought

barchans of minqin sediment transport spatial changes in the rates of sand transport are a fundamental control of dune morphology a detailed field measurement of sand flux along the brink of a barchan was performed to explore the spanwise property of sand flux on the barchan surface setting the arc length of the brink at the tip of the longer horn to zero it was found that the value of sand flux increases with the arc length of the brink at first and then decreases at both low and high wind speeds the maximum occurs at the crest our result suggests that the spanwise distribution of sand flux cannot be neglected in the study of transverse dunes

slope effect on saltation over a climbing sand dune abstract results from a three year study are presented that integrate field work in israel physical modeling wind tunnel testing at uc davis and numerical solutions of grain trajectories to model and explain sand transport over a climbing dune field grain size analyses of surface and saltation trap materials taken along various positions of the slope suggest that only smaller particles u equal 30 cm s were able to climb a 20 degree slope in an escarpment normal to the prevailing strong wind direction numerical solutions of the particle trajectories are in good agreement with field measurements and confirm that particle motion is diminished at the base area of the slope and that the motion of larger sized particles is completely terminated which causes an accumulation of these particles the results suggest that the transport of the majority of the larger particles 230 m is by saltation the model is numerically extended to a general series of slopes particle sizes and friction speeds with similar tends exhibited

fine scale modeling of the boundary layer wind field over steep topography 1 this paper describes the adaptation of wind fields to steep and complex terrain using fine scale numerical modeling the work is motivated by the need of high resolution flow fields to predict snow transport and snow cover development for avalanche warning purposes applying the nonhydrostatic and compressible atmospheric prediction model advanced regional prediction system arps to steep alpine topography the boundary layer flow was simulated and evaluated against measurements the adaptation of the wind field to steep terrain for specific initial and boundary conditions was simulated the topography used in our study has a length scale of 500 m a typical height of 150 m and maximum slopes of 45 numerical experiments with idealized triangular ridges were conducted to find an adequate model configuration this analysis indicates that a high resolution grid with horizontal spacing of at least 25 m and vertical spacing of 3 m near the surface is necessary to reproduce small scale flow features such as speed up separation and recirculation the onset of flow separation is highly sensitive to initial and boundary conditions slope angle and surface roughness the results of the comparison between the model simulations and measurements on our experimental site show that typical wind field characteristics are well reproduced the simulated wind fields have been used to drive a numerical three dimensional snow drift model which is presented in a companion paper by lehning et al 2008

ground based measurements and dual doppler analysis of 3 d wind fields and atmospheric circulations induced by a meso γ scale inland lake 1 this paper presents a high resolution dual doppler analysis of lake breeze mesoscale circulation induced by an elongated reservoir with a mean width of 2 km and an area of 125 km2 compared to previous meso scale lake breeze studies based on point measurements or aircraft observations the present study provides both a unique quantification and a high resolution spatial and temporal 3 d visualization several hundred meters and 5 min respectively of the kinematic structure of the lake breeze initiation and evolution visible satellite images show a cloud free zone over the lake and adjacent land areas that was promoted by subsidence associated with the lake breeze circulation the background synoptic scale wind flow was almost parallel to the major axis of the lake and distinct lake breeze frontal zones formed along both shorelines spanning the length of the lake dual doppler analyses showed updrafts in the frontal zones perturbation horizontal velocities of 1 5 m s 1 on both sides of the lake and maximum downdrafts of 2 m s 1 centered over the lake vertical vorticity in the boundary layer was produced by differential friction between the smooth lake and adjacent land the circulations are robust and are maintained during the day against a minor change in background wind direction the study shows that the circulations produced by a small lake can generate significant mesoscale circulations that influence local climatology and identifies the importance of including such small mesoscale processes in global forecast models

orographic gravity waves close to the nonhydrostatic limit of vertical propagation abstract orographic gravity waves excited by a narrow mountain ridge are investigated with the aid of numerical simulations when the nondimensional mountain half width na u is around 1 n a and u being the brunt vaisala frequency the dimensional half width and the ambient wind speed respectively only part of the gravity wave spectrum excited by the mountain is able to propagate vertically in this case linear theory as well as numerical simulations with low mountains show two wind maxima one at the mountain crest and one in the lee of the mountain as na u is reduced below 1 the wind maximum in the lee weakens and moves farther downstream and the maximum at the crest intensifies rapidly with decreasing na u simulations in which a gap with a level axis is embedded in the mountain ridge demonstrate that the wind perturbations along the gap axis are qualitatively similar to those over the adjacent mountain ridge however their magnitude is substantially lower and the tendency to form a wind max

wind borne redistribution of snow across an antarctic ice rise redistribution of snow by the wind can drive spatial and temporal variations in snow accumulation that may affect the reconstruction of paleoclimate records from ice cores in this paper we investigate how spatial variations in snow accumulation along a 13 km transect across lyddan ice rise antarctica are related to wind borne snow redistribution lyddan ice rise is an approximately two dimensional ridge which rises about 130 m above the surrounding ice shelves local slopes on its flanks never exceed 0 04 despite this very smooth profile there is a pronounced gradient in snow accumulation across the feature accumulation is highest on the ice shelf to the east climatologically upwind of the ice rise and decreases moving westward with the lowest accumulation seen to the west climatologically downwind of the ice rise crest superimposed on this broad scale gradient are large 20 30 localized variations in accumulation on a scale of around 1 km that appear to be associated with local variations in surface slope of less than 0 01 the broad scale accumulation gradient is consistent with estimates of wind borne redistribution of snow made using wind speed observations from three automatic weather stations the small scale variability in accumulation is reproduced quite well using a snow transport model driven by surface winds obtained from an airflow model providing that both the wind shear and static stability of the upwind flow are taken into account we conclude that great care needs to be exercised in selecting ice core sites in order to avoid the possibility of blowing snow transport confounding climate reconstructions

a study of the tornadic region within a supercell thunderstorm abstract the transition of a supercell thunderstorm into its tornadic phase is investigated through high resolution numerical cloud model simulations initiated within the interior portion of a previously simulated mature supercell storm with the enhanced grid resolution the low level cyclonic vorticity increases dramatically and the gust front rapidly occludes as small scale downdrafts develop in the vicinity of the low level center of circulation as the occlusion progresses a ring of high vorticity air surrounds the circulation center and could be conducive to multiple vortex tornado formation numerous features of the simulated transition bear resemblance to those observed in tornadic storms in the model simulation the large low level vorticity is generated through the tilting and intense stretching of air from the inflow side of the storm this vertical vorticity is derived from the horizontal vorticity of the environmental shear and also from horizontal vorticity generated solenoidally as low l

scale selection in locally forced convective fields and the initiation of deep cumulus abstract deep cumulus dynamics has often been treated as an initial value problem where the long time effect of surface energy fluxes are neglected initiation is often assumed to follow from a strong localized deformation of the flow field which is elsewhere quiescent in nature however the atmosphere is rarely found in an undisturbed condition just prior to the inception of deep growth one likely cause of widespread motions is the natural modal response of the environment to surface energy fluxes which results in a field of disturbances evidence is presented in this paper for the possible existence of a class of solutions when deep convection is allowed to evolve in the context of a thermally forced field of shallow convection this class of solutions is neglected when one visualizes the growth of severe local storms in term of buoyant bubbles in an otherwise tranquil atmosphere considering deep cumulus initiation as a field problem severely limits the concept of an isolated cloud individual clou

experimental study of wind directional variability in the vicinity of a model valley this paper reports the results of a preliminary study examining the effects of valley presence on airflow direction and focuses on valleys situated in areas of low relief wind tunnel experiments are used to visualise near surface airflow over a series of models representing valleys oriented at different angles to mean airflow results indicate that the presence of a valley has no significant influence on airflow direction when the approach angle of the wind is perpendicular to the valley strike however any wind approach angle less than 90 is found to cause marked deflection of airflow to become more parallel to the valley analogies can be drawn between the surface streamlines recorded on the negative terrain of the valley models and those around positive terrain such as hills a discussion of air pressure perturbation over both positive and negative terrain concludes that valley structures can have a significant effect on overlying synoptic windflow the nature and magnitude of this effect is dependent upon a complex range of environmental parameters including valley morphometry wind speed and the thermal stability of the airflow the findings outlined have implications for the development of aeolian bedforms and processes of aeolian sedimentation in the vicinity of valleys

a three dimensional model of airflow and orographic rainfall enhancement a three dimensional model of airflow over hills has been used in conjunction with a two dimensional model of orographic rainfall enhancement this development has allowed the accurate production of rainfall contour maps in areas of complex terrain a comparison has been made using a variety of atmospheric stability profiles between the wind fields and rainfall distributions over a bell shaped hill and those over a two dimensional ridge of similar height the results show that in conditions of either stably stratified air or with an inversion layer aloft three dimensional airflow effects can lead to much reduced rainfall over a bell shaped hill it is shown that in such situations the use of a two dimensional approximation can introduce significant errors an example is presented of the rainfall distribution in complex hill terrain over south kintyre on the western coast of scotland

the structure of strongly stratified flow over hills dividing streamline concept in stably stratified flow over a three dimensional hill we can define a dividing streamline that separates those streamlines that pass around the hill from those that pass over the hill the height hs of this dividing streamline can be estimated by sheppard s simple energy argument fluid parcels originating far upstream of a hill at an elevation above hs have sufficient kinetic energy to rise over the top whereas those below hs must pass around the sides this prediction provides the basis for analysing an extensive range of laboratory observations and measurements of stably stratified flow over a variety of shapes and orientations of hills and with different upwind density and velocity profiles for symmetric hills and small upwind shear sheppard s expression provides a good estimate for hs for highly asymmetric flow and or in the presence of strong upwind shear the expression provides a lower limit for hs as the hills become more nearly two dimensional these experiments become less well defined because steady state conditions take progressively longer to be established the results of new studies are presented here of the development of the unsteady flow upwind of two dimensional hills in a finite length towing tank these measurements suggest that a very long tank would be required for steady state conditions to be established upstream of long ridges with or without small gaps and cast doubt upon the validity of previous laboratory studies

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

effects of realistic surface topography on seismic ground motion in the yangminshan region of taiwan based upon the spectral element method and lidar dtm we combine light detection and ranging lidar digital terrain model dtm data and an improved mesh implementation to investigate the effects of high resolution surface topography on seismic ground motion based upon the spectral element method in general topography increases the amplitude of shaking at mountain tops and ridges whereas valleys usually have reduced ground motion as has been observed in both records from past earthquakes and numerical simulations however the effects of realistic topography on ground motion have not often been clearly characterized in numerical simulations especially the seismic response of the true ground surface here we use lidar dtm data which provide two meter reso lution at the free surface and a spectral element method to simulate three dimensional 3d seismic wave propagation in the yangminshan region in taiwan incorporating the effects of realistic topography a smoothed topographic map is employed beneath the model surface in order to decrease mesh distortions due to steep ground surfaces numerical simulations show that seismic shaking in mountainous areas is strongly affected by topography and source frequency content the amplification of ground motion mainly occurs at the tops of hills and ridges whilst the valleys and flat topped hills experience lower levels of ground shaking interaction between small scale to pographic features and high frequency surface waves can produce unusually strong shaking we demonstrate that topographic variations can change peak ground accel eration pga values by 50 in mountainous areas and the relative change in pga between a valley and a ridge can be as high as a factor of 2 compared to a flat surface response this suggests that high resolution realistic topographic features should be taken into account in seismic hazard analysis especially for densely populated moun tainous areas

the influence of dem resolution on seismic landslide hazard assessment based upon the newmark displacement method a case study in the loess area of tianshui china the estimation uncertainties and spatial variability of input parameters are gaining more attention and have frequently been taken into account in seismic slope deformation predictions but the influence of dem resolution has rarely been investigated in this paper the impact of dem resolution on the seismic landslide hazard is investigated through the comparison between various seismic landslide hazard assessments evaluated from multi resolution 10 30 and 90 m dems in the loess area of tianshui china using the newmark displacement method the results show that the 90 m relatively coarse resolution dem underestimates the estimated newmark displacement the 30 and 10 m resolution dems basically give the similar predictions while the 10 m higher resolution gives higher resolution at the local convex topography such as scarps and ridge crests it suggests that the ability of newmark method to predict landslide occurrence accurately not only depends on the assigned shear strengths but also is controlled predominantly by the distribution of slope angles making accurate maps of seismic landslide hazards will require high resolution dem apart from the associated ground motion parameters and assigned shear strengths

measurements of the near surface flow over a hill the near surface flow over a hill with moderate slope and height comparable with the boundary layer depth is investigated through field measurements of the mean flow at 2 m surface pressure and turbulent momentum flux divergence between 8 and 15 m the measurements were made along an east west transect across the hill tighvein height 458 m approximate width 8 km on the isle of arran south west scotland during two separate periods each of around three weeks duration radiosonde ascents are used to determine the variation of a froude number fl u nl where u is the wind speed at the middle layer height hm n is the mean brunt vaisala frequency below this height and l is a hill length scale measurements show that for moderately stratified flows for which fl 0 25 a minimum in the hill induced surface pressure perturbation occurs across the summit and this is accompanied by a maximum in the near surface wind speed in the more strongly stratified case fl 0 25 the pressure field is more asymmetric and the lee slope flow is generally stronger than on the windward slope such a flow pattern is qualitatively consistent with that predicted by stratified linear boundary layer and gravity wave theories the near surface momentum budget is analysed by evaluating the dominant terms in a bernoulli equation suitable for turbulent flow measurements during periods of westerly flow are used to evaluate the dominant terms and the equation is shown to hold to a reasonable approximation on the upwind slope of the hill and also on the downwind slope away from the summit immediately downwind of the summit however the bernoulli equation does not hold possible reasons for this such as non separated sheltering and flow separation are discussed copyright 2002 royal meteorological society

sea level oscillations during the last interglacial highstand recorded by bahamas corals whether sea level was stable during the last interglacial remains a subject of debate an analysis of the u th ages of coral reefs in the bahamas corrected for open system behaviour confirms the presence of at least one oscillation within the sea level highstand

late quaternary sea level position evidence from bahamian carbonate deposition and dissolution cycles abstract the bahama islands offer a unique opportunity to examine late quaternary sea level position as the island group places significant constraints on the time and space boundary conditions for climatic events recorded there the bahamian archipelago extends as a series of large and small islands on shallow carbonate banks of various sizes for 1400 km across a climatic gradient wet in the northwest to dry in the southeast the entire island group is tectonically stable and consists solely of quaternary carbonate sediments with interspersed paleosols the islands reflect glacioeustatic sea level highstand positions in their eolian and subtidal suite of limestones a depositional record of platform flooding and carbonate sediment production a coeval record of phreatic cave development in the island s fresh water lenses also documents sea level highstand positions absolute dating of late pleistocene fossil corals and cave stalagmites by u th methods has produced an excellent record of the last interglacial marine isotope substage mis 5e holocene eolianites have been dated by 14 c to reveal platform flooding at 5000 ybp and sea level stabilization at 3000 ybp pleistocene eolianites have been dated by amino acid racemization analysis but subdivisons of the eolianites into separate mis 5a 5c and 5e deposits are controversial paleosols representing integrated aerosol dust deposition of 100 ka long platform exposure events during glaciations have been differentiated by paleomagnetic secular variation measurements previous interpretations of a beach unit to indicate a 20 m mis stage 11 sea level highstand and of large boulders to represent a mega tsunami appear to be incorrect phreatic caves in today s subaerial environment have been ascribed to mis 5e but some may have formed earlier carbonate deposition and dissolution cycles create a mass flux of co 2 sufficient to explain the atmospheric co 2 excursions of the quaternary

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

the application of predictive modeling techniques to landslides induced by earthquakes the case study of the 26 september 1997 umbria marche earthquake italy abstract during september and october 1997 an earthquake sequence of moderate magnitude struck the umbria and marche regions central italy as a consequence of the most severe shocks several landslides were triggered on bedrock calcareous debris and sandy clay deposits the landslide inventory collected in the field and by aerial photo interpretation provided an opportunity to test the accuracy of existing predictive relations for landslide hazard zoning and to formulate new ones shallow soil slides and debris slides were selected to verify the prediction performance of the methods which are based on a simplified model geotechnique 15 1965 139 that calculate landslide displacements during cyclic seismic loading rock falls were modeled using a different approach to produce an empirical predictive rule for determining the probability of detachment of blocks when landslides occur along pre existing or newly formed failure surfaces the arias intensity and destructiveness potential are the strong ground motion parameters that best relate to displacements the predictive relation proposed for rock falls evaluates the probability of occurrence as a function of the slope angle and the peak ground acceleration pga

atmospheric gravity waves and the rissaga phenomenon the atmospheric forcing of large sea level oscillations up to 1 5 m amplitude with about a 10 min period in some bays and inlets of the balearic islands is described using simultaneous measurements of pressure and sea level elevation in the port of ciutadella at the end of a large and narrow inlet during 5 7 july 1989 the influence of atmospheric pressure oscillations on these large sea level variations locally known as rissaga is investigated coherence and cross correlation functions reveal that the large oscillations in the inlet are associated with and probably forced by a 10 min gravity wave in the atmosphere the effect of longer period waves on the inlet is seen in the well known inverted barometric effect forcing small oscillations in the water level of just some centimetres these latter waves have a period of around 50 min and an unusually large amplitude of some 3 mb the phase spectrum between sea level and pressure suggests that the inlet may behave as a damped harmonic oscillator which during rissaga is externally forced by the atmospheric pressure oscillations

pressure and buoyancy fields derived from doppler radar data in a tornadic thunderstorm abstract a method for retrieval of pressure and buoyancy distributions in deep convection is applied to doppler radar data collected at two analysis times during the tornadic del city oklahoma thunderstorm of 20 may 1977 change of a previous version of the technique necessitated by application to real data include procedures for handling irregularly bounded volumes and missing data and new assumptions to include reflectivity data and turbulent effects in the equations internal consistency cheeks on the quality of retrieved pressure fields imply that the input data are generally of good quality and point out times and heights within the storm at which greater confidence can be placed in the derived fields in the pretornadic stage the pressure distribution includes at each level a high low couplet across the updraft with the maximum pressure gradient generally oriented along the environmental shear vector at that altitude these results are in agreement with predictions of linear theory locations of

regression models for estimating coseismic landslide displacement newmark s sliding block model is widely used to estimate coseismic slope performance early efforts to develop simple regression models to estimate newmark displacement were based on analysis of the small number of strong motion records then available the current availability of a much larger set of strong motion records dictates that these regression equations be updated regression equations were generated using data derived from a collection of 2270 strong motion records from 30 worldwide earthquakes the regression equations predict newmark displacement in terms of 1 critical acceleration ratio 2 critical acceleration ratio and earthquake magnitude 3 arias intensity and critical acceleration and 4 arias intensity and critical acceleration ratio these equations are well constrained and fit the data well 71 br 2 b88 but they have standard deviations of about 0 5 log units such that the range defined by the mean one standard deviation spans about an order of magnitude these regression models therefore are not recommended for use in site specific design but rather for regional scale seismic landslide hazard mapping or for rapid preliminary screening of sites 2007 elsevier b v all rights reserved

radar observations of mesoscale circulations induced by a small lake under varying synoptic scale flows 1 this paper examines doppler radar observations of springtime lake breeze lb circulations produced by a small reservoir mean width of 2 km wheeler lake on the tennessee river in northern alabama the analysis allows for the formation of a general understanding of the flow structures as a composite of many lb circulation events it is found that lb circulation once formed is robust and persistent over a range of background or synoptic scale wind flows despite the small size of wheeler lake and the relatively small differences between land and lake temperature often a few degrees celsius that drive the lb circulation the formation location strength and inland penetration of the wheeler lake breeze are highly sensitive to the background wind speed and direction with respect to the lakeshore resulting in complex spatial and temporal variations in the lb characteristics the lb front is most prominent as a radar fine line when the ambient flow is offshore opposing the lb background wind and perpendicular to the orientation 120 300 of the lake for wind speeds 4 5 m s 1 a radar detectable thin line delineating the lb front appears primarily on the upwind side of the lake either to the north or south while synoptic scale winds stronger than 5 m s 1 tend to destroy the breeze front entirely if the background wind is parallel to lake orientation and the wind is 4 m s 1 the lb circulations often develop on both sides of the lake the radar fine line often appears patchy and broad for low wind conditions near 2 m s 1 overall the findings of this study show that small lakes can generate persistent local circulations that follow similar patterns of behavior and respond to the synoptic flow as large lakes or sea breezes

vertical vorticity generation and mesocyclone sustenance in tornadic thunderstorms the observational evidence abstract doppler radar observations concerning the generation of vertical vorticity in tornadic thunderstorms are documented for two case studies and the role of downdrafts in intensifying vertical vorticity is examined the observations supporting recent numerical simulations show that production of vertical vorticity begins at the very roots of updraft as horizontal vorticity in low level inflow regions is tilted toward the vertical then as the flow passes through the updraft the tilted vorticity and preexisting vertical vorticity is amplified by convergence to create the tornado parental circulation or mesocyclone the low level mesocyclone intensification that heralds tornadogenesis seems to result from interaction between spreading rainy downdraft air and inflow air from the storm s right flank amplification of vertical vorticity by convergence surges in the region of interaction rear downdrafts which develop at approximately the time of tornadogenesis do not transport significant vorticity

underlying structures in orographic flow an analysis of measurements made on the isle of arran in a recent field experiment on the isle of arran scotland measurements of surface pressure and near surface wind fields were made along a roughly west east transect on the hill tighvein a principal components analysis of these measurements has been made to determine any significant atmospheric modes of variability and this objective method successfully identifies several physically meaningful flows copyright 2006 royal meteorological society

the role of midtropospheric winds in the evolution and maintenance of low level mesocyclones abstract using a three dimensional numerical model supercell simulations initialized in environments characterized by hodographs with large curvature in the lowest 3 km and a range of linear midlevel shears are investigated for low values of the midlevel shear 0 005 s 1 the storm develops a mesocyclone at the lowest model level within the first hour of the simulation the gust front starts to move ahead of the main updraft and cuts off the inflow to the storm by approximately 2 h resulting in decay of the initial storm and growth of a new rotating storm on the outflow as the midlevel shear increases to approximately 0 010 s 1 the initial development of the low level mesocyclone is delayed but the mesocyclone that develops is more persistent lasting for over 2 h further increases of the shear to 0 015 s 1 result in the suppression of any low level mesocyclone despite the presence of intense rotation at midlevels of the storm we hypothesize that differences in the distribution of precipitation

the cape canaveral sea and river breezes kinematic structure and convective initiation abstract this study examines complex flow patterns associated with the cape canaveral sea breeze and sea breeze front using dual doppler radar sounding and surface data collected on 26 july 1991 during the convection and precipitation electrification experiment this case focuses on a the structure of the sea breeze an associated trailing convergence line river induced convergence zones and thunderstorm outflow boundaries and b the development of convection where these features interacted variations in the direction of the sea breeze in the vicinity of irregular coastlines such as cape canaveral can lead to persistent zones of convergence within the sea breeze air the findings show that these zones of convergence in turn can locally increase the depth of the sea breeze air and create circulations at the top of the sea breeze which can support the development of convection the observational study is the first to document the development and evolution of the trailing convergence line over

a method for producing digital probabilistic seismic landslide hazard maps abstract the 1994 northridge california earthquake is the first earthquake for which we have all of the data sets needed to conduct a rigorous regional analysis of seismic slope instability these data sets include 1 a comprehensive inventory of triggered landslides 2 about 200 strong motion records of the mainshock 3 1 24 000 scale geologic mapping of the region 4 extensive data on engineering properties of geologic units and 5 high resolution digital elevation models of the topography all of these data sets have been digitized and rasterized at 10 m grid spacing using arc info gis software on a unix computer combining these data sets in a dynamic model based on newmark s permanent deformation sliding block analysis yields estimates of coseismic landslide displacement in each grid cell from the northridge earthquake the modeled displacements are then compared with the digital inventory of landslides triggered by the northridge earthquake to construct a probability curve relating predicted displacement to probability of failure this probability function can be applied to predict and map the spatial variability in failure probability in any ground shaking conditions of interest we anticipate that this mapping procedure will be used to construct seismic landslide hazard maps that will assist in emergency preparedness planning and in making rational decisions regarding development and construction in areas susceptible to seismic slope failure

observed near storm environment variations across the southern cumberland plateau system in northeastern alabama abstractthe sand mountain and lookout mountain plateaus in northeastern alabama have been established as a regional relative maximum in tornadogenesis reports within the southeastern united states

coriolis effects in mesoscale flows with sharp changes in surface conditions a general linearized shallow layer perturbation model where the approximately neutral lower layer of thickness h0 is situated below a stable upper layer i e an inversion with temperature change t is developed for steady mesoscale atmospheric flows over low lying topography whose height is less than h0 with the coriolis parameter f sharp changes in surface conditions surface roughness terrain elevation heat flux are modelled as a distributed body force through the lower layer the froude number of this layer is small typical cases of mesoscale discontinuities are examined the results are compared with those of a continuously stratified model and observations and with numerical mesoscale model results for a meteorological case study over the dover straits region of the english channel the main results are i if the wind direction is parallel to the edge line separating the change in surface roughness there are marked increases and decreases in these coastal winds whose maxima can occur over the sea within a distance of order h0 1 km of a coast the strength of these wind jets which do not occur in the absence of coriolis force decrease away from the edge line gradually over transverse length scales of the order of the rossby deformation radius changes to surface roughness lead to an increase in the wind speed perturbation in the downwind direction until limited by non linear effects when the wind is at an angle to a roughness change or coast the maxima occur at the coastline ii where there are sharp changes in the orientation of contours of constant roughness length e g at capes or bays on the coastline or wakes of high drag areas detached jets are formed in the downwind direction iii changes in surface elevation at a coast produce effects different from those of roughness a positive wind jet forms parallel to the coast in the direction of the wind when the coast is on the right looking downwind and a negative jet when the coast is on the left these jets do not increase in strength along the flow and do not persist downwind iv coriolis effects also determine how the inversion height varies near coastlines and surface roughness changes for example increasing decreasing inland over a distance lr when stable airflow approaches from the sea and the coast is on the right left of an observer looking downwind opposite in the southern hemisphere this mechanism is consistent with observed increasing decreasing cloudiness inland from a coast v other effects occur where the surface elevation changes gradually over a distance of order lr e g a wide shallow valley frictional effects are comparable with buoyancy and coriolis forces and flows perpendicular to the elevation change are deflected to the left in the northern hemisphere as observed in the rhine valley vi the shallow layer model simulates the major features of the low level flow field computed using the numerical mesoscale model with a horizontal resolution of 2 km i e of order h0 broad features were captured using a coarser resolution of 12 km vii the analysis provides a method of estimating errors associated with finite grid size in numerical mesoscale models copyright 2004 royal meteorological society

airflow over hills of moderate slope a three layer model is presented this describes the flow on an inversion capped boundary layer over hills of moderate size and slope the linearized vorticity equation is solved using non linear boundary conditions the pressure field developed in the boundary layer is used to calculate a modified inner region velocity field jackson and hunt 1975 a low level inversion with height i 2h is found to decrease the speed up near the ground when i 2h the flow of the inversion layer shows an increasing tendency to be subcritical this leads to a much increased speed up increasing the stability of air above the inversion increases the asymmetry of the flow this causes an upwind lull and a subsequent rapid increase in the flow speed with very high wind speeds at the summit and downwind comparison of the theory with simple observations made on great dun fell cumbria shows encouraging agreement

gravity wave drag produced by madeira the gravity wave drag exerted on the atmosphere by an isolated three dimensional mountain is here evaluated from observational data the representation of such drag in numerical weather prediction models is known to be of considerable importance and this study provides some rare field measurements for input and verification of parametrization schemes the results of a microbarograph experiment performed in the spring of 1993 on the island of madeira are presented the data obtained with thermostatically adjusted microbarographs located on the two sides of the island are analysed in terms of the gravity wave drag produced by the mountain the time series obtained show a high degree of coherency consistent with the idea that they represent a mesoscale signal not significantly affected by small scale perturbations the pressure signal at each station shows a superposition of different oscillations including a 5 7 day synoptic oscillation a 12 hour tide and an irregular oscillation with an amplitude of about 2 hpa which can be associated with gravity wave drag the pressure differences across the island essentially contain the gravity wave drag signal which somewhat surprisingly correlates rather well with linear estimates the estimated drag has an average value similar to those observed in the pyrex experiment despite the lower wind speeds typical of madeira

aeolus ii an interactive program for the simulation of aeolian sedimentation abstract a computer program has been developed to simulate two or three dimensional topographic change associated with aeolian sediment transport because predictions generated by available models of aeolian transport can vary by about an order of magnitude for a given set of environmental conditions selection of an appropriate model is problematic this program includes a number of models and provides for interactive selection of a desired model combination s to allow for comparison between model predictions topography represented by a set of coordinates in two or three dimensions is defined by bins of sediment differential rates of transport between adjacent bins resulting from variations in grain size slope and surface moisture content are used to determine mass flux and to adjust the topography in an iterative fashion sub routines allow the simulation of temporally varying levels of surface moisture resulting from evaporation and periodic restoration of upwind boundary conditions the wind field can be represented by a constant shear velocity by a spatial cross shore distribution of shear velocities or by a time series of values representing multiple wind events output is in the form of a graphic display or tabulated results written to disk example results are presented which qualitatively suggest that simulated topographic changes are reasonable areas where further refinement is needed to improve correspondence with reality are identified and discussed

modelling stably stratified boundary layer flow over low hills the mixed spectral finite difference model for neutrally stratified atmospheric boundary layer flow over complex terrain has been extended to include the effects of stable stratification with a simple turbulent kinetic energy and mixing length turbulence closure scheme to allow internal gravity wave propagation we have constructed a steady background flow such that wind velocity and buoyancy frequency are constants above the boundary layer with the assumption that there are momentum and heat sinks to balance the flux divergences in the governing equations model results are compared with inviscid theory special emphasis is placed on the pressure or form drag on topography

a background investigation of tornado activity across the southern cumberland plateau terrain system of northeastern alabama abstractthe effects of terrain on tornadoes are poorly understood efforts to understand terrain effects on tornadoes have been limited in scope typically examining a small number of cases with li

kinematic structure of mesovortices in the eyewall of hurricane ike 2008 derived from ground based dual doppler analysis abstractprevious work has shown that vorticity mixing in the tropical cyclone tc inner core can promote mesovortex mv formation and impact storm intensity observations of mvs have largely been serendipitous but are necessary to improve understanding of these features and their role in tc dynamics this study presents nearly 10 h of ground based dual doppler analysis of mvs in the eyewall of hurricane ike 2008 near and during landfall derived 3d winds vertical vorticity horizontal divergence and perturbation pressures are analyzed results indicate persistent kinematic field arrangements and evolving vertical structures perturbation pressure retrievals suggest local pressure minima associated with the mvs preferential updraft locations appear to transition cyclonically about the local vorticity maximum as the mvs progress around the eye based on published observational datasets the dual doppler updraft magnitudes in ike s mvs are within the top 5 10 of tc vertical velocities the mvs are m

hook echoes and rear flank downdrafts a review abstract nearly 50 years of observations of hook echoes and their associated rear flank downdrafts rfds are reviewed relevant theoretical and numerical simulation results also are discussed for over 20 years the hook echo and rfd have been hypothesized to be critical in the tornadogenesis process yet direct observations within hook echoes and rfds have been relatively scarce furthermore the role of the hook echo and rfd in tornadogenesis remains poorly understood despite many strong similarities between simulated and observed storms some possibly important observations within hook echoes and rfds have not been reproduced in three dimensional numerical models

direct surface thermodynamic observations within the rear flank downdrafts of nontornadic and tornadic supercells abstract despite the long surmised importance of the hook echo and rear flank downdraft rfd in tornadogenesis only a paucity of direct observations have been obtained at the surface within hook echoes and rfds in this paper in situ surface observations within hook echoes and rfds are analyzed these mobile mesonet data have unprecedented horizontal spatial resolution and were obtained from the verifications of the origins of rotation in tornadoes experiment vortex and additional field experiments conducted since the conclusion of vortex the surface thermodynamic characteristics of hook echoes and rfds associated with tornadic and nontornadic supercells are investigated to address whether certain types of hook echoes and rfds are favorable or unfavorable for tornadogenesis tornadogenesis is more likely and tornado intensity and longevity increase as the surface buoyancy potential buoyancy as measured by the convective available potential energy and equivalent potential temperature in the r

the influence of different simplified sliding block models and input parameters on regional predictions of seismic landslides triggered by the northridge earthquake abstract regional seismic landslide hazard maps are based on predictions of rigid sliding block displacement derived from estimates of earthquake ground shaking topography geology and shear strength the confidence in these predictions requires comparisons with field observations of landslide occurrence during previous well documented earthquakes this paper presents a comparison between observed landslides from the 1994 northridge california earthquake and predicted landslides based on sliding block displacement estimates seven empirical displacement models each of which uses a different combination of ground motion parameters are investigated to evaluate which models and associated ground motion parameters best predict seismic landslides using best estimates of ground shaking and shear strength properties from the northridge earthquake sliding displacements are calculated and compared with the locations of observed landslides only 20 40 of the observed landslides are captured and the total area of predicted landslides is much larger than observed the ability to predict landslide occurrence accurately depends less on the displacement model and associated ground motion parameters and more on the uncertainty in the model parameters particularly the assigned shear strengths because current approaches do not take into account the spatial variability of shear strength within individual geologic units the accuracy of the predictive models is controlled predominantly by the distribution of slope angles within a geologic unit assigning overly conservative low shear strength values results in a higher percentage of landslides accurately identified but also results in a large over estimation of the total landslide area making more accurate maps of seismic landslide hazards will require methods to define intra formational variations in shear strength

review the atmospheric boundary layer an overview is given of the atmospheric boundary layer abl over both continental and ocean surfaces mainly from observational and modelling perspectives much is known about abl structure over homogeneous land surfaces but relatively little so far as the following are concerned i the cloud topped abl over the sea predominantly ii the strongly nonhomogeneous and nonstationary abl iii the abl over complex terrain these three categories present exciting challenges so far as improved understanding of abl behaviour and improved representation of the abl in numerical models of the atmosphere are concerned

the accuracy of vertical air velocities from doppler radar data abstract eight methods of calculating vertical air velocity in a column are compared each method requires some or all of the following data horizontal divergence vertical precipitation velocity hydrometeor terminal fall speed and vertical air velocity boundary conditions some or all of these quantities are commonly deduced or specified by a researcher during the analysis of doppler radar data the responses of the methods to different magnitudes and behaviors of errors in the input data are examined with a monte carlo method the experiments are conducted with both random and systematic errors two idealized kinds of systematic errors are considered bias error a constant error through the column and trend error an error of constant magnitude that changes sign at the midpoint of the mass of the column the performances of the methods are mapped over error space a researcher knowing approximately the characteristics of the errors of a particular set of doppler radar data can use the results of

dynamic analysis of a slope failure from the 6 august 1979 coyote lake california earthquake abstract the coyote lake california earthquake of 6 august 1979 m l 5 7 provided a rare opportunity to perform a dynamic numerical analysis of a seismically induced slope failure using actual strong motion records the earthquake displaced a preexisting slump on the northeast shore of lake anderson and formed a fissure 20 m long offsets of 9 mm vertically and 18 mm horizontally were measured across the fissure the slump is 9 km northwest of the located epicenter but within 100 m of the mapped trace of the calaveras fault two strong motion records were written in the vicinity of the slump coyote creek 5 km to the southeast and gilroy 6 15 km to the southeast these records combined with field measurements of the slope estimates of the material properties and a dynamic numerical model based on the newmark analysis of seismic slope stability to calculate a predicted displacement for the landslide a displacement of 27 mm calculated using the n50 e component of the gilroy 6 record is in excellent agreement with the displacement measured in the field 21 mm however displacements of only 0 12 mm calculated using the 250 component of the coyote creek strong motion record reflect significant local variations in seismic shaking intensity because strong motion records and slope failures rarely coincide this landslide provides an important test case for our understanding of the dynamics of seismically induced landslides as well as a warning that local seismologic variations need to be considered in any design applications

the initiation and horizontal scale selection of convection over gently sloping terrain abstract two and three dimensional numerical simulations were performed to investigate the scale selection and initiation of both moist and dry convection over gentle western and gentle eastern slopes where the latter represents an idealization of the eastern colorado region of the great plains of north america this work extends earlier studies of thermally forced convection by considering a model framework that is large enough to resolve both the convective scale dynamics as well as the larger scale dynamics within which the convection is embedded as a result the scale interaction problem leading to the selection of the dominant deep modes of the troposphere and consequent convection initiation is more realistically treated the main physical mechanisms involved in the initiation of convection in these studies are the usual boundary layer instabilities leading to the development of eddies and or shear aligned rolls the excitation of gravity waves by the boundary layer motions interacting with the fr

a case study of lee waves over the lake district in northern england the structure and intensity of stationary orographically forced over the lake district and northern pennines on he afternoon of 26 november 1991 is determined through a combination of field observations and high resolution numerical modelling observations were provided by the meteorological office s c130 aircraft at four different levels and by five radisondes of differing ascent rates released in rapid succession from an observing station located on the cumbrian coast vertical velocity was inferred from both of these data sources and with the help of satellite imagery it was possible to build up a comprehensive picture of the lee wave structure in addition a non hydrostatic primitive equation model was run with a 2 km grid covering a 180 km square region of the northern pennines in an attempt to simulate the gravity wave motion observed the model was initialized with an upstream profile formed by merging a descent profile obtained from the aircraft with one from the sondes the model orography was defined using a terrain height data set with 500 m resolution and with some smoothing to the model grid after about four hours of integration the model achieves a quasi steady state with strong lower tropospheric lee waves verification on the model response was sought by comparing the vertical velocity in the model along the paths of the aircraft and sondes with that actually deduced from the observations the overall agreement of the simulated amplitude and phase of the lee waves with that observed is very encouraging as found in a different case study shutts 1992 the success of the model in predicting lee wave motion gives strong support for the use of these models for the development of gravity wave drag parametrization schemes the domain averaged surface frictional stress was found to be much larger than the wave drag and consistent with the high roughness lengths likely in the case of mountainous terrain

air flow over a two dimensional hill studies of velocity speed up roughness effects and turbulence wind tunnel measurements have been made of the streamwise mean and turbulent velocities over a rough bell shaped two dimensional hill with height h and maximum slope 0 26 placed in a neutrally stable boundary layer of thickness 10 h and roughness length zo 0 02 h close agreement is found between the mean velocity and predictions obtained from taylor s 1977 computational model and jackson and hunt s 1975 analytical linearized model for locations at or upwind of the hill top but not in the wake examination of the models shows that the shear stresses are only important in an inner region close to the hill surface so that as suggested by jackson and hunt 1975 the perturbation to the mean flow outside this region is essentially inviscid the theory shows that over very rough surfaces such as wooded or urban terrain the height of this inner region can be of the same order as the height of the roughness elements so that in our experiments no measurements could be made in this region in a second experiment flow over a smooth hill on a rough surface was studied the additional increase of wind speed over the hill top can be estimated by assuming a linear superposition of the velocity changes produced by the changes in elevation and in surface roughness in this case rough to smooth in the lee of a hill however the change in roughness significantly alters the flow with flow separation being suppressed and here a linear superposition is not appropriate finally we consider why observed changes in turbulence structure close to the surface differ from those well above the surface calculations of these changes based on the simple theoretical arguments of equilibrium shear layers and rapidly distorted turbulent flows agree well with turbulence measurements in wind tunnels and in the field

gis application for regional assessment of seismically induced slope failures in the sierra nevada range south spain along the padul fault complete rupture of the padul fault represents one of the largest plausible earthquakes in the sierra nevada range one of the most seismically active regions of spain we performed a regional assessment of earthquake triggered slope instabilities in the western part of the range to determine the most likely types of failures from such an earthquake in the region and suggest where such failures have a higher likelihood of occurring these results are broadly useful for management of regional life lines and future development first a slope instability inventory of the sierra nevada was produced to identify the most common instability types subsequently the newmark s sliding rigid block methodology implemented in a geographic information system was used to obtain the distribution of newmark displacements in the area considering a mw 6 6 earthquake on the padul fault the newmark displacements were then compared to the distribution of the inventoried slope instabilities to identify the areas where seismicity could reactivate old slope instabilities or generate new ones and to identify the involved landslide typology the most likely seismically induced slope instabilities in the sierra nevada are rock falls and rock slides these types of instabilities could be triggered by newmark displacements of 2 cm or less