models of coastally trapped disturbances during the spring and summer the climatological northerly flow along the u s west coast is occasionally interrupted by transitions to southerly flow that have a limited offshore scale and appear to be manifestations of marine layer flow that is rotationally trapped by the coastal mountains existing climatological and observational studies suggest that a synoptic scale offshore flow initiates these coastally trapped disturbances ctds using idealized simulations produced with a 3d nonhydrostatic model the authors find that an imposed offshore flow will produce ctds in idealized coastal environments the imposed flow first weakens the prevailing northerly flow in the marine layer and lowers the pressure at the coast the marine layer flow around this low pressure evolves toward geostrophic balance but is retarded as it encounters the coastal mountains to the south of the low and subsequently deepens the marine layer in this region the elevated marine layer then begins progressing northward as a kelvin wave and later may steepen into a bore or gravity current this progression being the ctd many observed features accompanying ctds are found in the numerical simulations including the formation of a mesoscale pressure trough offshore and deep southerlies in the ctd at the coast stability in the atmosphere above the marine layer can give rise to topographically trapped rossby waves and stronger ctd winds in these stable conditions propagation of wave energy away from the disturbance does not preclude strong quasi steady propagating ctds

recent ventifact development on the central oregon coast western usa the unusual location of ventifacts on a boulder built jetty at the mouth of the siuslaw river oregon coast western usa allows ventifact age and wind abrasion rates to be estimated with some precision the jetty was built mainly between 1892 1901 and extended throughout the twentieth century consideration of historical shoreline position and the history of jetty construction and repair suggests the ventifacts have formed since about 1930 morphologically the ventifacts are aligned south to north reflecting winter winds and sediment transport from the adjacent beach wind parallel grooves and ridges with sharp sinuous crests are developed on inclined boulder surfaces on top of the jetty and reflect suspended sand transport in wind vortices deeply pitted surfaces on steep boulder surfaces nearest the beach reflect impact by saltating sand grains based on present wind regimes 1992 2000 from three regional weather stations southerly winds above the sand transport threshold occur for 21 9 29 6 per cent of the time based on estimated depth of loss from boulder surfaces wind abrasion rates are calculated to be on the order of 0 24 1 63 mm a 1 this is the first well constrained field estimate of ventifact age and ventifaction rate from a modern coastal environment copyright c 2003 john wiley sons ltd

observed dynamics of coastal flow at cape mendocino during coastal waves 1996 abstract airborne in situ and remote meteorological measurements from around cape mendocino california sampled during the coastal waves 1996 field program are analyzed for three different days 7 12 and 26 june 1996 two days conformed to typical summertime conditions with a strong northerly downcoast flow while the wind on the third day was weaker on the first 2 days the flow was supercritical in the sense that the froude number was larger than unity and these 2 days feature expansion fans in the lee of the cape on the third day no such phenomenon was observed all 3 days had a strong thermal wind caused by the marine inversion sloping down toward the coast on the first 2 days the flow aloft was westerly or northerly so that the thermal wind added to the background flow results in a strong jet on the third day the flow aloft was southerly and consequently even with the added thermal wind the northerly flow in the marine layer was too weak to be supercritical the main difference between t

coastally trapped wind reversals along the united states west coast during the warm season part i climatology and temporal evolution abstract the northerly winds that predominate along the u s west coast during april september are interrupted periodically by abrupt reversals to southerly flow the climatology and composite temporal evolution of these reversals from point conception to the canadian border are documented using hourly data from moored coastal buoys and coastal marine automated network stations for the period 1981 91 the reversals are divided into two categories coastally trapped reversals in which the southerly flow is highly ageostrophic and restricted to the coastal zone and synoptic reversals which are associated with landfalling troughs or fronts coastally trapped events occur on average about 1 5 times per month along the central and northern california coast about twice a month near the california oregon border and about once a month near the oregon washington border the ratio of coastally trapped reversals to synoptic reversals is higher during july september and lower during april june particularly in t

catalina eddies and coastally trapped disturbances abstract observations show that coastally trapped disturbances ctds often accompany catalina eddies that appear in the southern california bight in a previous modeling study of ctds using simple environments and forcings simulations of ctds also evolved a mesoscale eddy that played a critical role in ctd formation and evolution in this study the simple environments and forcings are extended to model the southern california bight and simulations produce both catalina eddies and ctds the simulated catalina eddies and the mesoscale eddies in the previous ctd studies are dynamically equivalent the primary mechanism for eddy formation in the simulations is lee troughing and eddies and ctds are produced provided that 1 there is sufficient stratification in the environment 2 the offshore flow is of sufficient strength breadth and duration and 3 there is sufficient terrain to produce significant lee troughing the simulations show that ctds can propagate out of the bight region when synoptic winds

numerical modeling of a coastal trapped disturbance part i comparison with observations abstract the coastal trapped disturbance ctd of 15 17 may 1985 represents an example of a strong mesoscale trapped event along the west coast of north america with abrupt transitions in many basic meteorological parameters in this study a comparison between observations and a numerical simulation of this event using the regional atmospheric modeling system rams is presented the model is shown to realistically reproduce ctd characteristics such as the coastal transition from northerly to southerly flow as a mesoscale coastal ridge of higher pressure with associated drops in marine layer temperature propagates northward along the west coast of north america simulated sea level pressure and temperature fields near the surface match well with observations especially at the synoptic scale the model realistically simulates mesoscale sea level pressure and 6 h pressure changes during the event the modeled hourly time evolution of sea level pressure and the southerly transitions at a series of coastal

sensitivity of coastally trapped disturbance dynamics to barrier height and topographic variability in a numerical model abstract the sensitivity of a coastally trapped disturbance ctd to topographic height is examined using simulations of the 15 18 may 1985 ctd these simulations include three with uniform topography in which the north american west coast mountains are represented by a three piece uniform ramp at the coast leading to a constant plateau inland and three with realistic topography in each trio of uniform and realistic topography simulations there is a control case in which the terrain height closely approximates reality and two variations in which the topography is multiplied everywhere by a topographic multiplication factor tmf of 1 5 and 0 5 to assess the sensitivity of the simulation to the barrier height average propagation speeds increased decreased by 15 20 with the increased decreased tmf it was found that the position of the ctd leading edge generally followed close behind a leading pressure trough minimum which propagated northward along the coast in a manner similar to a topographi

on the origin of atmospheric frontal lines off the east coast of taiwan observed on spaceborne synthetic aperture radar images abstract frontal lines having offshore distances typically between 40 and 80 km are often visible on synthetic aperture radar sar images acquired over the east coast of taiwan by the european remote sensing satellites 1 and 2 ers 1 and ers 2 and envisat in a previous paper the authors showed that they are of atmospheric and not of oceanic origin however in that paper they did not give a definite answer to the question of which physical mechanism causes them in this paper the authors present simulations carried out with the fifth generation pennsylvania state university national center for atmospheric research mesoscale model which shows that the frontal lines are associated with a quasi stationary low level convergence zone generated by the dynamic interaction of onshore airflow of the synoptic scale wind with the coastal mountain range of the island of taiwan reversed airflow collides with the onshore flowing air leading to an uplift of air which is often accompanied by the formation of bands

transcritical flows in the coastal marine atmospheric boundary layer abstract numerical solutions of shallow water flow in a variable width channel are computed to model the summertime marine atmospheric boundary layer off the u s west coast using an idealization of the coastline in the vicinity of point arena california as an example several steady state base flows are presented that are hydraulically transcritical these flows are strongly nonlinear weakly rotational and are forced by constant pressure gradients and damped by nonlinear bottom drag at the sea surface the transcritical base flows are supercritical in the vicinity of bends in the coastline but are subcritical to the north upstream and to the south downstream where the coastline is straight within the supercritical region orographic bends in the coastline produce expansion fans and compression jumps the same structures found in globally supercritical flows when the imposed pressure gradient forcing is increased the resulting base flow has a supercritical to subcritical transitional jump that

small amplitude coastally trapped disturbances and the reduced gravity shallow water approximation solutions are obtained for linear hydrostatic disturbances propagating parallel to the face of an uninterrupted topographic step in an infinitely deep stably stratified fluid on an plane these waves are vertically trapped because their frequencies are smaller than the coriolis parameter and the height of the topographic step is finite these waves are referred to as step trapped kelvin waves because they are dynamically similar to internal kelvin waves throughout the layer of fluid below the top of the topographic step these waves appear to provide an idealized semi analytic model for the coastally trapped disturbances observed to propagate parallel to mountainous coastlines in several parts of the world computations are performed for a basic state with uniform static stability and for a three layer basic state in which the two lowest layers represent the marine boundary layer and a strong capping inversion one might suppose that the linear dynamics of hydrostatic disturbances in the three layer basic state could be well approximated by a reduced gravity shallow water model but this is not the case in particular the reduced gravity shallow water model does not provide reliable estimates for the phase speed of linear step trapped kelvin waves this defect suggests that detailed quantitative comparisons between marine boundary layer flows and the reduced gravity shallow water system may not have any intrinsic physical significance nevertheless these results do not preclude the possibility of constructing useful qualitative analogies between marine boundary layer flows and the reduced gravity shallow water model

evolution geochimique superficielle naissante des anorthosites cas du profil de château richer quebec canada the initial stages of the superficial geochemical weathering of anorthosites have been investigated in a deposit at ch teau richer quebec the parent rock consists almost exclusively of andesine and is weathered to a thickness of about 120 cm a till overburden indicates that the profile was truncated by the wisconsinian ice the rock is not extensively disintegrated but the chemical weathering is rather intense the parker diagram shows a strong decrease of the weathering index from the parent rock to the weathering zone while this is not the case for other crystalline rocks in the area it may be accounted for by the fragility of the plagioclase the 2 m fraction which amounts to 2 of the soil presents an evolution that is influenced by the site especially the drainage conditions at the base of the profile drainage is poor and 2 1 minerals smectite and vermiculite are present in addition to 40 kaolinite the 1 1 mineral increases to 60 near the contact with the till while the amount of 2

aircraft observations of a coastally trapped wind reversal off the california coast abstract the summertime marine atmospheric boundary layer off the california coast is normally characterized by northerly winds associated with the pacific high this pattern is occasionally disturbed by episodes of southerly winds and a finger of fog or low stratus adjacent to the coastline extending approximately 100 km offshore these events propagate northward along the coast with speeds between 5 and 12 m s 1 and have a life span of several days these occurrences have been referred to as coastally trapped wind reversals ctwrs coastally trapped disturbances or southerly surges the ctwr event of 22 25 june 2006 was explored by the university of wyoming king air research aircraft to document the physical characteristics of the wind reversal in an attempt to infer the forcing mechanisms responsible for the propagation two flights from 23 june are presented that are representative of the ctwr during its mature stage sawtooth maneuvers depict the ctwr vertical structure and isobaric legs directly

a nonhydrostatic mesoscale simulation of the 10 11 june 1994 coastally trapped wind reversal abstract during the summer months the california coast is under the influence of persistent northwesterly flow several times each summer this regime is disrupted by coastally trapped wind reversals ctwr in which the northwesterly flow is replaced by southerlies in a narrow zone along the coast controversy exists as to the physical mechanisms responsible for initiation and maintenance of ctwrs while it is clear that coastal terrain is important in creating the trapped response the precise role played by terrain is unclear in the present study these issues are investigated using a nonhydrostatic mesoscale model to simulate the 10 11 june 1994 ctwr event the results show that the model successfully reproduces many of the observed features of this event including anomalous vertical structure involving the relatively shallow boundary layer with a warm nearly neutral layer above the northward propagation of southerly flow in advance of a tongue of coastal stratus fog and a substantial reduction i

synoptic scale structure and the character of coastally trapped wind reversals abstract coastally trapped wind reversals that occur along the u s west coast have been described in numerous other studies the synoptic scale environment and the forcing of a coastally trapped kelvin wave are highly linked in the development of these wind reversals however not all wind reversals appear to behave like propagating kelvin waves and the analysis of coastal buoy observations for three years indicates that different types of disturbances occur both propagating disturbances and nonpropagating disturbances occur with similar frequencies while the synoptic scale characteristics associated with propagating and nonpropagating wind reversals are sometimes rather subtle several distinct differences occur that suggest a direct link between the coastal dynamics and the synoptic scale forcing synoptic forcing characterized by persistent low level offshore flow favors the development of propagating disturbances while weak nonsustained offshore flow characterizes nonpropagating disturbances the

statistically significant relation between radon flux and weak earthquakes in the dead sea rift valley detailed monitoring of radon rn flux in gravel was carried out for a period of eight years near the active dead sea rift fault the temporal relationship between hundreds of weak earthquakes 4 6 ml 0 and rn flux signals was tested for time intervals related to the start time of 110 rn flux signals earthquakes located within three pull apart grabens of the dead sea rift valley were found to occur preferentially within the time interval of the first 3 days after the start time of 110 rn anomalies and the excess of earthquakes 82 relative to the expected value is highly significant p 003 however a similar relationship is not found in the two weeks preceding or following the start time of the rn anomalies for earthquakes occurring within the dead sea rift in structurally higher segments or out of the dead sea rift

kelvin waves and internal bores in the marine boundary layer inversion and their relationship to coastally trapped wind reversals abstract detailed observations of a coastally trapped disturbance or wind reversal on 10 11 june 1994 along the california coast provide comprehensive documentation of its structure based on aircraft wind profiler radio acoustic sounding system and buoy measurements unlike the expectations from earlier studies based on limited data which concluded that the deepening of the marine boundary layer mbl was a key factor the 1994 data show that the perturbation was better characterized as an upward thickening of the inversion capping the mbl as the event propagated over a site the reversal in the alongshore wind direction occurred first within the inversion and then 3 4 h later at the surface a node in the vertical structure defined here as the altitude of zero vertical displacement is found just above the inversion base with up to 200 m upward displacements of isentropic surfaces above the node and 70 m downward displacements below although this is a single event it is shown that the vertic

large scale structure in wind forcing over the california current system in summer abstractthe wind that drives oceanic eastern boundary upwelling systems is highly variable in many locations the standard deviation of wind velocity on time scales of days to weeks is larger than the mean in the 1600 km long california current system ccs the spatial decorrelation scale of the wind fluctuations is 400 800 km suggesting wind fluctuations in the north and south ends of the system are not related yet there is also the suggestion in the literature of a larger scale structure in the fluctuations here empirical orthogonal function eof analysis of buoy and satellite wind velocities confirms the existence of that structure this analysis covers a larger spatial domain than previous eof studies in the ccs and to allow for propagation of the wind fluctuations includes an approach for calculating hilbert eofs from time series with gaps the large scale structure in the wind fluctuations is a quasi dipole pattern spanning the coastline from washington through california it accounts f

aircraft observations and numerical simulations of the developing stage of a southerly surge near southern california abstractsummertime low level winds in the marine boundary layer off the california coast are predominantly from the north this pattern is interrupted periodically by southerly winds and low stratus that can propagate for hundreds of kilometers northward along the coast these events have been termed coastally trapped disturbances coastally trapped wind reversals and southerly surges their forcing has been the subject of extensive study and debate southerly surges remain difficult to forecast yet have a significant impact on coastal activities the beginning stage of a southerly surge on 16 june 2012 was explored during the precision atmospheric marine boundary layer experiment measurements of the horizontal wind and pressure field in the marine layer offshore from cape arguello hours prior to the onset of the surge were made using the university of wyoming king air research aircraft airborne measurements show that a horizontal pressure field is established with higher pressure to the south just pri

thermal mesoscale circulations on the baltic coast 1 numerical case study a three dimensional mesoscale numerical model is utilized to investigate a well documented seabreeze event taken from experimental data the simulations are not set up as a model validation instea

a model investigation of the dynamics of a coastally trapped disturbance abstract numerical simulations of the 15 17 may 1985 coastally trapped disturbance ctd event along the west coast of north america are compared with the schematic model of ctd evolution developed by skamarock rotonno and klemp srk which was based upon more idealized simulations it is shown that the general evolution of the simulated may 1985 ctd is consistent with the srk schematic model it is further shown that secondary effects not contained in the srk simulations such as diurnal radiation variations and mesoscale topographic variations can account for the variable ctd initiation and propagation observed both in nature and in the present numerical simulations diurnal radiation variations coupled with differential heating of land and ocean appear to play an important role in setting up the alongshore temperature gradient necessary for ctd formation and evolution the modeled ctd is found to change dynamical characteristics from an initial kelvin wave bore similar to that discussed by ralph

high resolution real time modeling of the marine atmospheric boundary layer in support of the aosn ii field campaign abstract the navy s coamps atmospheric model has been used to provide twice daily real time forecasts of 72 h duration in support of the aosn ii field campaign during august 2003 the model was configured with four grid meshes with a minimum horizontal grid increment of 3 km a statistical analysis of the model forecasts using available buoy observations demonstrates the skill of the atmospheric model predictions with characteristic wind speed rms and bias errors of 1 3 m s 1 and less than 0 5 1 0 m s 1 respectively and temperature rms errors of 1 2 c and biases typically less than 1 0 c the highest resolution mesh provides more accurate wind speed variances during the upwelling periods in the nearshore region where the wind speed gradients and diurnal variations are the largest persistent and strong low level winds from a northwesterly direction were associated with a mid tropospheric trough and jet stream that was substantially stronger than the overall mean monthly conditions during the relaxation periods which were relatively infrequent during august 2003 the trough was weaker than the mean conditions with a closed low west of the coast that resulted in southerlies near the coast during upwelling favorable conditions the mean marine inversion was substantially stronger than during the relaxation periods with the surface stress field exhibiting maxima in the lee of prominent coastal capes and topography particularly during the periods of strong larger scale low level flow the persistent mean stress pattern that is topographically locked yields maxima in the stress curl pattern that induce favorable regions of coastal upwelling near and downwind of the coastal promontories and headlands