coastal southerlies and alongshore surges of the west coast of north america evidence of mesoscale topographically trapped response to synoptic forcing abstract one of the most important warm season weather phenomena of the west coast of north america is the temporal transition from northerly to southerly flow within a few hundred kilometers offshore from the coastal mountains such wind shifts are often accompanied by cooler temperatures higher pressure and a change from nearly cloud free to low overcast conditions the more vigorous coastal transitions termed alongshore surges are characterized by an abrupt change in wind direction a sudden increase in wind speed to 15 m s 1 or more a precipitous temperature drop exceeding 10 c and a sharp rise in sea level pressure this paper presents two detailed case studies of topographically trapped coastal southerlies the strong surge event of 15 17 may 1985 and the far weaker case of 3 7 may 1982 it is shown that coastal southerlies and alongshore surges are controlled by the alongshore pressure gradients created by the synoptic scale flow at low levels and within approximately one rossby radius of th

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

the structure and evolution of cold surges east of the rocky mountains abstract northerly surges of cold air often move southward along the eastern side of the rockies from southern canada into mexico the strongest surges which generally develop in midwinter are associated with temperature decreases and pressure rises of 20 30 c and 15 30 mb respectively within 24 h surges are usually accompanied by a meridionally elongated pressure ridge and strong low level ageostrophic winds that parallel the terrain the width of the pressure ridging is approximately 1000 km over the southern plains but decreases to only a few hundred kilometers when the surge enters mexico this paper provides a detailed description of a northerly surge to the east of the rocky mountains that occurred on 12 14 november 1986 using both observational and model data the structural evolution of the surge is analyzed in addition the dynamics of the event is explored by diagnosing the momentum thermodynamic energy and vorticity equations to determine the typical synoptic scale evolution of these

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

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

upstream effects of mesoscale mountains abstract the alpine experiment alpex has revealed that low level air is typically diverted around the alps without reaching the mountaintop in pursuit of an understanding of the physical basis of this phenomenon and of its generality we have explored the characteristics of orographic blocking of a rotating continuously stratified quid as revealed in a simple model problem retaining full nonlinear and transient effects hydrostatic dynamics is assumed and the obstacle is taken to be an infinitely long ridge with height h x the key questions treated are the strength of the upstream deceleration of cross mountain flow and the length scale over which the decelerated region extends by means of scale analysis the controlling parameters are found to be the rossby number ro u fl and the froude number fr nhm u where u is the speed of the oncoming flow f is the coriolis parameter l the mountain half width n the brunt vaisala frequency and hm is the maximum mountain height the scale analysis also

frictional properties of exhumed fault gouges in dfdp 1 cores alpine fault new zealand principal slip zone gouges recovered during the deep fault drilling project dfdp 1 alpine fault new zealand were deformed in triaxial friction experiments at temperatures t of up to 350 c effective normal stresses n of up to 156 mpa and velocities between 0 01 and 3 m s chlorite white mica bearing dfdp 1a blue gouge 90 62 m sample depth is frictionally strong friction coefficient 0 61 0 76 across all experimental conditions tested t 70 350 c n 31 2 156 mpa it undergoes a transition from positive to negative rate dependence as t increases past 210 c the friction coefficient of smectite bearing dfdp 1b brown gouge 128 42 m sample depth increases from 0 49 to 0 74 with increasing temperature and pressure t 70 210 c n 31 2 93 6 mpa the positive to negative rate dependence transition occurs as t increases past 140 c these measurements indicate that in the absence of elevated pore fluid pressures dfdp 1 gouges are frictionally strong under conditions representative of the seismogenic crust

observations and scale analysis of coastal wind jets abstract blocking of onshore flow by coastal mountains was observed south of vancouver island british columbia by the noaa p 3 aircraft on 1 december 1993 winds increased from 10 m s 1 offshore to 15 m s 1 nearshore and became more parallel to shore in the blocked region which had a vertical scale of 500 m and an offshore scale of 40 50 km these length scale and velocity increases are comparable to theory the flow was semigeostrophic with the coast being hydrodynamically steep that is the coast acts like a wall and the alongshore momentum balance is ageostrophic this is shown by the nondimensional slope parameter the burger number b hmn flm being greater than 1 where hm and lm are the height and half width of the mountain n is the stability frequency and f is the coriolis parameter the height scale is given by setting the local froude number equal to 1 that is hl u n 500 m where u is the onshore component of velocity this scale is appropriate when hl is less than the mountain height

coastal lows along the subtropical west coast of south america numerical simulation of a typical case abstract subsynoptic warm core low pressure areas are frequently observed along the west coast of subtropical south america during austral winter these so called coastal lows cls tend to develop as an upper air midlatitude ridge is approaching the subtropical andes and therefore while pressure is increasing aloft and farther to the south these cls have a profound impact in the coastal weather associated with a rapid transition from clear skies and stronger than average equatorward low level flow to overcast conditions and relaxed equatorward or even poleward flow weather conditions inland mostly reflect the associated changes in the strength and height of the base of the subsidence inversion in this work a mesoscale simulation of a typical cl episode is performed using a numerical weather prediction model the fifth generation pennsylvania state university ncar mesoscale model mm5 comparison with observations reveals that the model simulation properly captures the large scale pattern as we

synoptic forcing of coastal trapped disturbances in the marine atmospheric boundary layer abstract motivated by recent observations along the west coast of the united states the authors investigate the generation and propagation of coastal trapped disturbances in the marine atmospheric boundary layer analytic solutions are obtained in a linear shallow water reduced gravity model of the flow subject to forcing by upper level pressure disturbances and dissipation in the form of wind stress at the sea surface it is found that unless the mean alongshore flow is to the south with speeds larger than the gravity wave phase speed a northward propagating coastal trapped response develops the superposition of cross shore propagating forcing and the northward propagating response in marine layer thickness can give rise to surface pressure ridges at the coast with both narrow and broad cross shore extent wind reversals associated with the disturbance lead the change in surface pressure at the coast the magnitude of the response increases for weaker inversion strength greater undisturbed marine l

the dynamics of coastally trapped mesoscale ridges in the lower atmosphere abstract the dynamics of coastally trapped ridges that propagate in the marine layers of western north america and southeastern australia is examined a nonlinear semigeostrophic theory shows that the coastal ridges develop initially as an alongshore intrusion of denser marine air that is driven by the synoptic scale pressure gradient nonlinear kelvin waves evolve with the intruding flow on a slower time scale governed by the dynamic parameters if dispersive effects balance the nonlinearities then these waves evolve into solitary form otherwise the nonlinear waves steepen so that the leading edge of the ridge eventually propagates as a shock the theory is applied to two ridging events in california and one in southeastern australia in each case good agreement is found between theory and observations of the evolution times and propagation speeds of the coastal ridges the theory also explains the observed behavior of the events at prominent convex bends and gaps in the coastal topography

marine boundary layer clouds associated with coastally trapped disturbances observations and model simulations abstractmodeling marine low clouds and fog in coastal environments remains an outstanding challenge due to the inherently complex ocean land atmosphere system this is especially important in the c

evidence of kelvin waves in california s marine layer and related eddy generation abstract evidence suggests that an internal solitary kelvin wave exists in the marine layer along california the marine layer is lifted over the central coast by a weak cyclonic circulation this bump initially 850 m high moves to the north along the coast at 6 m s 1 the undisturbed layer depth is 100 200 m thick the crest height of the wave decreases to 500 m farther north winds under the raised marine layer are southerly the leading edge of the wave is easily followed by satellite as the thickened marine layer is marked by overcast stratus a greatly curved offshore leading edge indicates that nonlinear effects are important offshore scale in the overcast is about 300 km in the south and 50 km in the north surface pressure gradient alongshore is closely related to the marine layer depth the surface wind shifts when the leading and trailing edge of the wave passes northerly wave progression ceases at the sharp bend formed by cape mendocino at this time a vortex is formed in the marine laye

slip localization on the southern alpine fault new zealand 1 results of a detailed field study of the southern onshore portion of new zealand s alpine fault reveal that for 75 km along strike dextral normal slip on this long lived structure is highly localized in phyllosilicate rich fault core gouges and along their contact with more competent rocks at three localities martyr river mckenzie creek and hokuri creek we document complete cross sections through the fault new 40ar 39ar dates on mylonites combined with microstructural and mechanical data on phyllosilicate rich fault core gouges show that modern slip is localized onto a single steeply dipping 1 to 12 m thick fault core composed of impermeable k 10 20 to 10 22 m2 frictionally weak s 0 12 0 37 velocity strengthening illite chlorite and saponite chlorite lizardite fault gouges fault core materials are 1 comparable to those of other major weak cored faults e g san andreas fault and 2 most compatible with fault creep despite paleoseismic evidence of quasiperiodic large magnitude earthquakes mw 7 on this portion of the alpine fault we conclude that frictional properties of gouges at the surface do not characterize the overall seismogenic behavior of the southern alpine fault

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

simulation and prediction of the catalina eddy abstract observational studies generally suggest that the formation of the catalina eddy in the bight of southern california results from interaction between the synoptic scale northerly flow and the topographic barrier along the southern california coast in an attempt to better understand the eddy generation mechanisms a high resolution mesoscale model is initialized and forced on the lateral boundaries by nmc s large scale objective analysis and a detailed numerical study of the 26 30 june 1988 catalina eddy event is presented the model results compare favorably with the observations and generally support the aforementioned mechanism of the eddy formation it appears that a warm air mass over the bight resulting from adiabatic heating of low level downslope flow deflected by the mountain barrier significantly helps create the alongshore and offshore pressure gradients favorable for the generation of a cyclonic vorticity although current operational forecast models are capable of often accurately pr

influence of subduction zone conditions and gouge composition on frictional slip stability of megathrust faults to understand the temperature depth distribution of destructive earthquakes in subduction megathrusts and the mechanisms of nucleation of these events data on the frictional behaviour of phyllosilicate quartz rich megathrust fault gouges under in situ conditions are needed we performed rotary shear friction experiments at effective normal stresses of 25 200 mpa pore fluid pressures of 50 200 mpa at 140 600 c and sliding velocities of 1 100 m s using gouge mixtures with an illite quartz ratio between 65 35 and zero experiments on 65 35 mixtures deformed at an effective normal stress neff of 170 mpa a pore fluid pressure pf of 100 mpa and 150 500 c provided a reference dataset this showed three temperature dependent slip stability regimes with potentially unstable velocity weakening behaviour at 250 400 c and velocity strengthening at lower and higher temperatures the velocity weakening regime was found to shift towards higher temperatures with decreasing neff being located at 350 600 c at 50 mpa increasing quartz content and decreasing sliding velocity also displaced the velocity weakening regime towards lower temperatures increasing pf increased a b at all temperatures narrowing the temperature extent of the velocity weakening regime we explain our results qualitatively in terms of a microphysical model in which changes in friction coefficient and a b with velocity and temperature are brought about by changes in the relative importance of deformation of the clast phase by thermally activated stress corrosion cracking and pressure solution versus athermal granular flow of the mixture accompanied by dilatation our results imply that the depth extent of the seismogenic zone on subduction megathrusts depends not only on temperature and that to predict its location it is essential to have well constrained depth profiles for pore fluid pressure and effective normal stress

observations and analysis of the 10 11 june 1994 coastally trapped disturbance abstract a coastally trapped disturbance ctd characterized by southerly flow at the surface on 10 11 june 1994 was observed from the california bight to bodega bay during a field experiment along the california coast north south approximates the coast parallel direction data from a special observational network of wind profilers radio acoustic sounding systems special surface data balloon ascents and a research aircraft were used with satellite and synoptic data to explore both the ctd structure and the regional scale changes before the event the disruption of the climatological northerly flow along the central california coast which preconditioned the area for the development of a ctd began with the eastward movement of a surface high into washington and oregon and the amplification of a thermal low in northern california as with most ctds in the region this occurred over the 2 3 days preceding the ctd s initiation these large scale changes caused westward advection of warm continental

the large scale atmospheric structure accompanying new england coastal frontogenesis and associated north american east coast cyclogenesis an eleven case composite is constructed of the large scale flow configuration accompanying wintertime new england coastal frontogenesis events which are associated with atlantic coast cyclogenesis in the united states the pre coastal front environment is dominated by anticyclonic activity in the lower troposphere over the eastern great lakes the cold anticyclone moves eastward north of new england while slowly strengthening and is eventually responsible for the cold south easterly flow that participates in the developing coastal front circulation coastal frontogenesis commences in an increasingly favourable synoptic scale environment for ascending motion and pressure falls with both the passage of the 500 mb ridge axis and the onset of strong 850 mb warm air advection beneath the entrance region of a broad confluence zone at 500 mb the synoptic scale forcing for ascent over the developing coastal front is maximized from the cyclonic shear side of the jet in the base of the 500 mb trough to the anticyclonic shear side of the jet entrance region in the downstream confluence zone clearly identifiable departures in both the global scale wavenumbers 0 3 and large synoptic scale wavenumbers 4 8 waves from the long term climatological mean 1000 500 mb thickness field are observed during the evolution of the atlantic coast cyclogenesis event the major deviations from climatology in the wavenumbers 0 3 thickness deviation fields are negative anomalies in eastern asia the northern soviet union and the united states and positive anomalies over alaska and greenland the global scale thickness waves show substantial evolution in their transience and amplitude characteristics following the onset of the cyclogenesis event the wavenumbers 4 8 thickness anomaly analyses reveal initially quasi stationary amplification during the onset of cyclogenesis as atlantic coast cyclone development proceeds however a pronounced positive thickness anomaly is generated in the western atlantic and extends into new england similarly wavenumbers 4 8 thickness anomalies from eastern north america to western europe amplify and become more progressive

discrete proterozoic structural terranes associated with low p high t metamorphism anmatjira range arunta inlier central australia tectonic implications structural overprinting relationships indicate that two discrete terranes mt stafford and weldon occur in the anmatjira range northern arunta inlier central australia in the mt stafford terrane early recumbent structures associated with d1a 1b deformation are restricted to areas of granulite facies metamorphism and are overprinted by upright km scale folds f1c which extend into areas of lower metamorphic grade structural relationships are simple in the low grade rocks but complex and variable in higher grade equivalents the three deformation events in the mt stafford terrane constitute the first tectonic cycle d1 d2 deformation in the weldon terrane comprises the second tectonic cycle the earliest foliation s2a was largely obliterated by the dominant reclined to recumbent mylonitic foliation s2b produced during progressive non coaxial deformation with local sheath folds and w to sw directed thrusts locally d2d tectonites have been rotated by n s trending upright f2c folds but the regional upright fold event f2d also evident in the adjacent reynolds range rotated earlier surfaces into shallow plunging nw se trending folds that dominate the regional outcrop pattern the terranes can be separated on structural metamorphic and isotopic criteria a high strain d2 mylonite zone produced during w to sw directed thrusting separates the weldon and mt stafford terranes 1820 ma megacrystic granites in the mt stafford terrane intruded high grade metamorphic rocks that had undergone d1a and d1b deformation but in turn were deformed by s1c which provides a minimum age limit for the first structural metamorphic event 1760 ma charnockites in the weldon terrane were emplaced post d2a and metamorphosed under granulite facies conditions during d2b constraining the second tectonic cycle to this period each terrane is associated with low p high t metamorphism characterized by anticlockwise p t t paths with the thermal peaks occurring before or very early in the tectonic cycle these relations are not compatible with continental style collision nor with extensional tectonics as the deformation was compressional the preferred model involves thickening of previously thinned lithosphere at a stage significantly after 50 ma the early extensional event compression was driven by external forces such as plate convergence but deformation was largely confined to and around composite granitoid sheets in the mid crust the sheets comprise up to 80 of the terranes and induced low p high t metamorphism including migmatization thereby markedly reducing the yield strength and accelerating deformation of the country rocks mid crustal ductile shearing and reclined to recumbent folding resulted followed by upright folding that extended beyond the thermal anomaly thus thermal softening induced by heat focusing is capable of generating discrete structural terranes characterized by subhorizontal ductile shear in the mid crust localized around large granitoid intrusions

an observational and numerical study of an orographically trapped wind reversal along the west coast of the united states abstract observational analyses and a high resolution simulation using the pennsylvania state university ncar mesoscale model version 5 mm5 were used to describe the coastally trapped wind reversal of 19 21 july 1994 major findings include the following the event was initiated and controlled by changes in the synoptic scale flow and particularly by the development of offshore flow over the coastal terrain of oregon although synoptic control was dominant blocking of the inversion capped marine layer and mesoscale coastal pressure ridging were important components of the event the synoptic evolution associated with the trapped reversal was characterized by a shift from climatological near zonal 500 mb flow to high amplitude upper level ridging over the eastern pacific as this upper ridge moved northeastward the 850 mb flow over oregon became northeasterly and then southeasterly and 850 mb heights fell over western oregon the combination of falling heights aloft and increasing low level offshore

a theoretical study of cold air damming with upstream cold air inflow abstract the previously developed two layer model of cold air damming is extended to include upstream cold air inflow the upper layer is an isentropic cross mountain flow the lower layer is a cold boundary layer flow partially blocked by a two dimensional mountain with a cold dome formed on the windward side of the mountain the interface represents a sloping inversion layer coupling the two layers the shape of the interface can be approximated by a cubic polynomial and the interfacial coupling condition yields a set of algebraic equations that quantify the scale and intensity of the dammed flow as functions of the external parameters characterizing the environmental conditions it is found that the cold dome shrinks as the froude number increases or to a minor degree as the ekman number decreases or and the upstream inflow veers from northeasterly to southeasterly with respect to a longitudinal mountain to the west the mountain parallel jet speed increases as the ekman number decreases or and th

the west coast thermal trough mesoscale evolution and sensitivity to terrain and surface fluxes abstractdespite the significant impacts of the west coast thermal trough wctt on west coast weather and climate questions remain regarding its mesoscale structure origin and dynamics of particular interest is the relative importance of terrain forcing advection and surface heating on wctt formation and evolution to explore such questions the 13 16 may 2007 wctt event was examined using observations and simulations from the weather research and forecasting wrf model an analysis of the thermodynamic energy equation for these simulations was completed as well as sensitivity experiments in which terrain or surface fluxes were removed or modified for the may 2007 event vertical advection of potential temperature is the primary driver of local warming and wctt formation west of the cascades the downslope flow that drives this warming is forced by easterly flow associated with high pressure over british columbia canada when the terrain is removed from the model the wctt does not form and high

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

micromechanisms of creep in clay rich gouge from the central deforming zone of the san andreas fault we report the strength and constitutive behavior of gouge sampled from the central deforming zone cdz of the san andreas fault layers of flaked cdz gouge were sheared in the triaxial saw cut configuration using the stress relaxation technique to measure the gouge strength over 4 orders of magnitude in shear strain rate and at rates as low as 5 10 10s 1 and within an order of magnitude of in situ rates deformation conditions correspond to the in situ effective normal stress 100 mpa and temperature 65 to 120 c at the sampling depth of 2 7 km gouge was sheared dry and with brine pore fluid at 25 mpa pore pressure dry gouge is stronger and more rate strengthening than brine saturated gouge brine saturated cdz gouge strengthens with increasing strain rate and decreasing temperature and the dependencies of strength on strain rate and temperature increase at rates below 5 10 9s 1 at strain rates greater than 5 10 9s 1 the rate dependence is consistent with previous studies on the cdz gouge conducted at even higher rates the increase in rate dependence below 5 10 9s 1 indicates a change in the rate controlling deformation mechanism the magnitude of the friction rate dependence parameter a and the temperature sensitivity of a are consistent with crystal plasticity of the phyllosilicates we hypothesize a micromechanical model for the cdz gouge whereby a transition from fracture and delamination accommodated frictional flow to crystal plasticity accommodated frictional flow occurs with decreasing strain rate

the kinematic structure of a wasatch mountain winter storm during ipex iop3 the influence of orographic circulations on the precipitation structure of a wasatch mountain winter storm is examined using observations collected during the third intensive observing period iop3 of the intermountain precipitation experiment ipex the event featured the passage of a midlevel 700 550 hpa trough followed 3 h later by a surface trough prior to and during the midlevel trough passage large scale southwesterly flow impinged on the wasatch mountains low level confluence was observed between this southwesterly flow and along barrier southerly flow within 20 40 km of the wasatch mountains this confluence zone which moved toward the wasatch mountains during and following the passage of the midlevel trough was accompanied by low level convergence and precipitation enhancement over the upstream lowlands dual doppler analysis revealed the presence of a shallow along barrier jet near the base of the wasatch mountains that was surmounted by southwesterly cross barrier flow at mid and uppermountain levels this cross barrier flow produced strong 1 2 m s 1 ascent as it interacted with the steep windward slopes of the wasatch mountains where precipitation was roughly double that observed in the lowlands upstream flow deflection and splitting were also observed near the highest terrain features a narrow region of strong subsidence which at times exceede d2ms 1 was found to the lee of the wasatch and based on radar imagery appeared to modulate hydrometeor spillover aloft processes contributing to the evolution of the near barrier flow field including topographic blocking diabatic effects and surface friction contrasts are discussed

comparison of frictional strength and velocity dependence between fault zones in the nankai accretionary complex accretionary complexes host a variety of fault zones that accommodate plate convergence and internal prism deformation including the decollement imbricate thrusts and out of sequence thrusts or splays these faults especially the decollement and major splay faults are considered to be candidates for hosting slow slip events and large magnitude earthquakes but it is not clear what modes of slip should be expected at shallow levels or how they are related to fault rock frictional properties we conducted laboratory experiments to measure the frictional properties of fault and wall rock from three distinct fault zone systems sampled during integrated ocean drilling program expedition 316 and ocean drilling program leg 190 to the nankai trough offshore japan these are 1 a major out of sequence thrust fault termed the megasplay site c0004 2 the frontal thrust zone a region of diffuse thrust faulting near the trench site c0007 and 3 the decollement zone sampled 2 km from the trench site 1174 at 25 mpa effective normal stress at slip rates of 0 03 100 m s and in the presence of brine as a pore fluid we observe low friction 0 46 for all of the materials we tested however the weakest samples 0 30 are from the decollement zone material from the megasplay fault is significantly weaker than the surrounding wall rocks a pattern not observed in the frontal thrust and decollement all samples exhibit primarily velocity strengthening frictional behavior suggesting that earthquakes should not nucleate at these depths a consistent minimum in the friction rate parameter a b at sliding velocities of 1 3 m s 0 1 0 3 m d is observed at all three sites suggesting that these shallow fault zones may be likely to host slow slip events

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

coastally trapped wind reversals along the united states west coast during the warm season part ii synoptic evolution abstract this paper describes the synoptic evolution associated with coastally trapped wind reversals along the west coast of the united states from april through september gridded national centers for environmental prediction formerly national meteorological center synoptic analyses are composited relative to the initiation of both weak and strong coastal southerlies at four coastal buoys offshore of oregon and california a similar composite synoptic evolution accompanies the transition from northerlies to southerlies at each site at 500 mb there is anomalous ridging over the eastern pacific while at 850 mb and the surface the east pacific high extends into southwestern canada and the pacific northwest the result is offshore flow and subsidence along the mountainous west coast that produces a strengthening and coastal extension of the trough normally resident over the interior of southern and central california this anomalous coastal troughing weakens the offshore gradient and establishes an alon

numerical study of convection observed during the winter monsoon experiment using a mesoscale two dimensional model abstract a two dimensional version of the pennsylvania state university mesoscale model has been applied to winter monsoon experiment data in order to simulate the diurnally occurring convection observed over the south china sea the domain includes a representation of part of borneo as well as the sea so that the model can simulate the initiation of convection also included in the model are parameterizations of mesoscale ice phase and moisture processes and longwave and shortwave radiation with a diurnal cycle this allows use of the model to test the relative importance of various heating mechanisms to the stratiform cloud deck which typically occupies several hundred kilometers of the domain frank and cohen s cumulus parameterization scheme is employed to represent vital unresolved vertical transports in the convective area the major conclusions are ice phase processes are important in determining the level of maximum large scale heating and vertical motion because there is a strong anvil componen

effects of temperature on the frictional behavior of material from the alpine fault zone new zealand abstract temperature is widely believed to act as a primary control on fault rheology and therefore on the distribution of seismicity along plate boundary faults however there are few detailed measurements of the frictional strength and stability of natural fault gouges at elevated temperatures here we report on a suite of shearing experiments designed to investigate the frictional behavior of fault rocks sampled from depths of 111 5 142 9 m along the alpine fault in new zealand obtained by the international continental scientific drilling program icdp deep fault drilling project dfdp we tested five samples from the dfdp 1b pilot hole two hanging wall chloritic cataclasites two footwall granitic cataclasites and a fault gouge from the principal slip zone psz 1 each sample was sheared at a range of temperatures from 23 to 500 c and at an effective normal stress of 80 mpa the wall rock cataclasites exhibit an increase in the friction coefficient with temperature from 0 45 0 64 at 23 c to 0 87 at 500 c the psz 1 gouge exhibits lower friction coefficient values than the wall rock at temperatures 180 c 0 35 0 46 vs 0 45 0 65 but comparable values 0 87 0 90 at 500 c the variation in frictional strength is accompanied by a transition from velocity strengthening to velocity weakening behavior at temperatures 180 c for all materials extrapolation of the experimentally defined rheological critical stiffness of the fault material and the estimated in situ stiffness of the surrounding crust suggests upper and lower stability boundaries at 1 8 2 5 km and 8 5 8 8 km depth respectively the upper stability boundary is also consistent with the observed depth frequency distribution of earthquakes

a study of the forcing of the 22 25 june 2006 coastally trapped wind reversal based on numerical simulations and aircraft observations abstract coastally trapped wind reversals ctwrs occur periodically in the lowest several hundred meters of the marine boundary layer west of california and disrupt the northerly flow that typically occurs during summer south winds and coastal fog or low stratus accompany the ctwr which propagates northward along the coast a ctwr was observed off the california coast during late june 2006 that originated in the california bight and propagated northward to cape mendocino during the subsequent 2 day period this ctwr event was explored by the university of wyoming king air research aircraft to document the primary characteristics of the wind reversal numerical simulations of the ctwr event using the weather research and forecast modeling system were conducted to compare with observations and to provide a broader picture of the ctwr structure and evolution an analysis of the forcing mechanisms responsible for the june 2006 ctwr event is presented it is demonstrated that the mature ctwr for this case i

the west coast thermal trough climatology and synoptic evolution abstractalthough the west coast thermal trough wctt is the most important mesoscale feature over the u s west coast during the warm season its initiation evolution and structure are not well understood originating in the southwest united states this inverted trough can extend northward into oregon washington and british columbia with large impacts on temperature wind humidity and air quality using ncep s north american regional reanalysis narr annual and diurnal climatologies of wctts reaching the northwest united states were constructed for the entire year wctts are most frequent along the coast near the california oregon border with weaker maxima west of the cascade and coastal mountains over the coastal region they occur most often during autumn while east of the cascade mountains the highest frequency is during summer there is strong diurnal variability in wctt frequency during the summer with little diurnal variation in winter though compositing revealed important seasonal d

dynamics of a catalina eddy revealed by numerical simulation abstract through numerical simulations with the pennsylvania state university ncar mesoscale model the dynamics of a catalina eddy event that formed during the period 26 30 june 1988 off the coast of southern california is examined a strengthening and veering of the low level synoptic scale winds from climatological northwesterlies to northerlies results in a more pronounced effect of the coastal orography around the california bight region in particular relative vorticity formed by flow over the coastal terrain remains offshore prior to the formation of a quasi steady eddy within the bight the northerlies are strong enough to advect anomalously high vorticity out of the region the formation of a mature catalina eddy relies on a rapid deceleration of the synoptic scale northerlies on 30 june such that vorticity once formed remains in the bight the eddy is also strongly modulated by the diurnal cycle northwesterly flow around 500 m above mean sea level impinging on the mountains north of the b