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

shallow marine carbon and oxygen isotope and elemental records indicate icehouse greenhouse cycles during the early jurassic 1 for much of the mesozoic record there has been an inconclusive debate on the possible global significance of isotopic proxies for environmental change and of sequence stratigraphic depositional sequences we present a carbon and oxygen isotope and elemental record for part of the early jurassic based on marine benthic and nektobenthic molluscs and brachiopods from the shallow marine succession of the cleveland basin uk the invertebrate isotope record is supplemented with carbon isotope data from fossil wood which samples atmospheric carbon new data elucidate two major global carbon isotope events a negative excursion of 2 at the sinemurian pliensbachian boundary and a positive excursion of 2 in the late pliensbachian the sinemurian pliensbachian boundary event is similar to the slightly younger toarcian oceanic anoxic event and is characterized by deposition of relatively deepwater organic rich shale the late pliensbachian strata by contrast are characterized by shallow marine deposition oxygen isotope data imply cooling locally for both events however because deeper water conditions characterize the sinemurian pliensbachian boundary in the cleveland basin the temperature drop is likely of local significance in contrast a cool late pliensbachian shallow seafloor agrees with previous inference of partial icehouse conditions both the large scale long term and small scale short duration isotopic cycles occurred in concert with relative sea level changes documented previously from sequence stratigraphy isotope events and the sea level cycles are concluded to reflect processes of global significance supporting the idea of an early jurassic in which cyclic swings from icehouse to greenhouse and super greenhouse conditions occurred at timescales from 1 to 10 ma

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

reconstructing past seawater mg ca and sr ca from mid ocean ridge flank calcium carbonate veins proxies for past seawater chemistry such as mg ca and sr ca ratios provide a record of the dynamic exchanges of elements between the solid earth the atmosphere and the hydrosphere and the evolving influence of life we estimated past oceanic mg ca and sr ca ratios from suites of 1 6 to 170 million year old calcium carbonate veins that had precipitated from seawater derived fluids in ocean ridge flank basalts our data indicate that before the neogene oceanic mg ca and sr ca ratios were lower than in the modern ocean decreased ocean spreading since the cretaceous and the resulting slow reduction in ocean crustal hydrothermal exchange throughout the early tertiary may explain the recent rise in these ratios

rheological evolution of the ocean crust a microstructural view rheological studies of the oceanic lithosphere have used direct observations of rocks and inferences based on thermal mechanical and experimental models modeling studies help to constrain an average crust and mantle rheology and the deep seated processes that control regional scale strength and stress field variations the smoothing of fine scale variations in such models can obscure many of the geological processes that influence strain localization and deformation partitioning in the ocean crust examination of deformation mechanisms and histories in ocean crust rocks provides a complementary approach to modeling examples of structures and deformation histories in diabases from deep sea drilling project ocean drilling program site 504b the hayes and atlantis fracture zones mid atlantic ridge and the troodos ophiolite cyprus are presented in conjunction with a synthesis of microstructural studies of the ocean crust over the last 25 years a survey of brittle quasi plastic and synmagmatic viscous deformation is used to demonstrate the influence of primary compositional and textural characteristics and variable magmatic and hydrothermal histories on deformation mechanisms and strain localization in the ocean crust geological evidence indicates that hydrothermal fluids strongly influence the nature of deformation and that effective stresses may be low due to fluid overpressures melt distribution will strongly influence strain localization at the base of the crust and synkinematic hydration during crystal plastic deformation plays a key role in the relative strengths of polyphase oceanic lithologies a schematic distribution of failure mechanisms in the ocean crust is used to discuss the controls on variations in lateral and vertical strength profiles and their possible relation to spreading rates although microstructural studies of ocean crust are still in their infancy they provide valuable constraints for rheological models and further insights to explain the distribution of seismicity at spreading centers and acoustic signatures

aircraft observations of the 12 15 july 2004 moisture surge event during the north american monsoon experiment abstract this paper describes aspects of a strong moisture surge over the gulf of california that was observed during the 2004 north american monsoon experiment although a variety of special observation platforms aid the analyses the authors focus on observations collected during two noaa research aircraft flights made on 12 and 13 july these flights sampled the initial and mature phases of a strong surge associated with tropical storm blas the first flight is identified by both a convective outflow and another feature both deeper and with larger spatial scale ahead of the outflow in association with the surge s leading edge the surge speed 18 m s 1 was identified from anomaly analysis of surface station pressure data observations show interesting multiscale features associated with the surge during its initial stages but do not allow for unambiguous identification of the surge s forcing mechanism or dynamical properties data from the second flight were used to describe the along and cross gu

large scale forcing of summertime monsoon surges over the gulf of california and the southwestern united states synoptic forcing of the gulf of california summertime low level wind field is described using a nested regional modeling system under appropriate synoptic conditions strong surge events develop that are characterized by persistent vertically extensive 1 2 km southerly flow extending along the entire gulf of california and into arizona california and even southern nevada these surge periods are initiated either by tropical cyclone activity to the south of baja california or by the westward propagation of lower tropospheric troughs from over the sierra madre occidental to the eastern pacific the flow over the gulf is primarily geostrophic and is associated with the presence of these low pressure centers to the south and west of baja california

observational analysis of a gust front to bore to solitary wave transition within an evolving nocturnal boundary layer abstract the evolution of a gust front to bore to solitary wave transition and comprehensive information on the evolving nocturnal boundary layer nbl associated with this change are described with analysis of radar and profiler measurements the observations were obtained on 21 june 2002 in the oklahoma panhandle during the international h2o project the evolution of this system from a strong bore initiated by a vigorous gust front to a solitary wave was observed over a 4 h period with doppler radar and surface measurements detailed information on the mature bore structure was obtained by a cluster of profiling instruments including two boundary layer wind profilers a lidar ceilometer and a microwave profiling radiometer a strong bore was initiated by an extensive gust front that perturbed an incipient nbl whose development prior to sunset was enhanced by shading from the parent mesoscale convective system at the time of bore formation the nbl was about 300 m deep and exhibited a surface t

simulation of a north american monsoon gulf surge event and comparison to observations abstractgulf surges are transient disturbances that propagate along the gulf of california goc from south to north transporting cool moist air toward the deserts of northwest mexico and the southwest united states during the north american monsoon they have been shown to modulate precipitation and have been linked to severe weather and flooding in northern mexico and the southwest united states the general features and progression of surge events are well studied but their detailed evolution is still unclear to address this several convection permitting simulations are performed over the core monsoon region for the 12 14 july 2004 gulf surge event this surge event occurred during the north american monsoon experiment which allows for extensive comparison to field observations a 60 h reference simulation is able to reproduce the surge event capturing its main characteristics speed and direction of motion thermodynamic changes during its passage and strong northward moisture flux while the ti

principal component analysis of the summertime winds over the gulf of california a gulf surge index a principal component analysis of the summertime near surface quick scatterometer quikscat winds is used to identify the leading mode of synoptic scale variability of the low level flow along the gulf of california during the north american monsoon season a gulf surge mode emerges from this analysis as the leading eof with the corresponding principal component time series interpretable as an objective index for gulf surge occurrence this index is used as a reference time series for regression analysis and compositing meteorological fields of interest to explore the relationship between gulf surges and precipitation over the core and marginal regions of the monsoon as well as the manifestation of these transient events in the large scale circulation it is found that although seemingly mesoscale features confined over the gulf of california gulf surges are intimately linked to patterns of large scale variability of the eastern pacific itcz and greatly contribute to the definition of the northward extent of the monsoonal rains

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

dynamics of a simulated north american monsoon gulf surge event abstractgulf surges are transient disturbances that propagate along the gulf of california goc from south to north transporting cool moist air toward the deserts of northwest mexico and the southwest united states during the north american monsoon they have been shown to modulate precipitation and have been linked to severe weather and flooding in northern mexico and the southwest united states the general features and progression of surge events are well documented but their detailed dynamical evolution is still unclear in this study a convection permitting simulation is performed over the core monsoon region for the 12 14 july 2004 gulf surge event and the dynamics of the simulated surge are examined initially convection associated with the tropical easterly wave precursor to tropical cyclone blas creates a disturbance in the southern goc on early 12 july this disturbance is a precursor to the gulf surge on 13 july and is a kelvin shock internal bore under the influence of rotation that diss

ducted coastal ridging over s e australia the intense and rapidly established coastal ridging which is a regular occurrence over south eastern australia during the warm seasons is investigated using a detailed case study and mesoscale numerical model simulations we suggest that the ridge is initiated by a forced kelvin type edge wave which forms on the south western edge of the great dividing range and is ducted in an anticlockwise sense around the coast the ridge is then stabilized by inertial modification and decays over a synoptic time scale of a few days our results apply to similar phenomena in other parts of the world notably southern africa and south america

the relationship between tropical easterly waves and surges over the gulf of california during the north american monsoon abstract coastally trapped disturbances which occur over the gulf of california and are commonly referred to as gulf surges are an important mechanism in the transport of low level moisture into the southwestern united states to determine whether or not gulf surges develop in association with the passage of tropical easterly waves as hypothesized in previous studies standard surface observations and european centre for medium range weather forecasts reanalysis data during the months of july and august over a 14 yr period are examined results indicate that tropical easterly wave troughs often cross western mexico 1 3 days prior to surge onset at yuma arizona indicating a strong correlation between these two events this analysis documents yet another mechanism by which the tropics influences convection in the midlatitudes

sr ca variations in cretaceous carbonates relation to productivity and sea level changes abstract we present high resolution sr ca measurements on coccolith dominated pelagic carbonates of berriasian valanginian albian santonian and campanian maastrichtian age from dsdp sites and tethyan land sections carbonate sr ca varies by up to 80 over both long and short timescales and may reflect either temporal variations in seawater sr ca or variable sr partitioning in biogenic carbonates numerical models of seawater sr and ca budgets indicate that while sea level changes can cause comparably large variations in the seawater sr ca ratio the timing and pattern of predicted sr ca variations agrees poorly with the carbonate record reef crises unrelated to sea level changes may also elevate seawater sr ca and in some cases the record of reef crises corresponds to increasing carbonate sr ca changes in sr partitioning likely due to changes in calcareous nannoplankton productivity also appear to control carbonate sr ca in these records cretaceous carbonate sr ca broadly covaries with indicators of productivity derived from microfossil ecology recent studies in sediment core tops and cultures have shown that sr partitioning in coccolith carbonate is strongly influenced by changes in coccolithophorid growth and calcification rate where the effects of changing seawater sr ca can be constrained by independent geological data carbonate sr ca measurements could provide a valuable perspective on changes in the productivity of calcareous nannoplankton and variations in the carbonate and carbon cycle in the cretaceous

characterizing the north american monsoon in the community atmosphere model sensitivity to resolution and topography abstractthis work examines the effect of horizontal resolution and topography on the north american monsoon nam in experiments with an atmospheric general circulation model observations are used

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

regional simulation of the low level monsoon winds over the gulf of california and southwestern united states using a fine scale 10 20 km nested regional modeling system synoptic variations in climatological summertime low level wind fields over the gulf of california and the southwestern united states are described under appropriate synoptic conditions strong surge events can develop these are characterized by low level southerly flow over the entire gulf of california with southerly winds extending into arizona california and southern nevada vertically these southerly winds are present through the bottom 1 2 km of the atmosphere southerly flow is persistent throughout the day with some local diurnal cycling over the foothills of the sierra madre occidental and northwestern mexico under nonsurge conditions the simulated low level winds have a significantly different geographic structure nighttime southerly flow is limited to the northeastern gulf and small portions of southwestern arizona flow over the central and southern gulf is northerly with weak variable winds over the foothills of the sierra madre occidental during the day southerly winds are present over the central and northern gulf of california extending into southwestern arizona however this southerly wind pattern does not support continuous flow from the mouth of the gulf into northwestern mexico instead there is a westerly component associated with predominantly upslope flow over the foothills of the sierra madre occidental and the sonora desert

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

some simple simulations of thunderstorm outflows three idealized simulations of thunderstorm outflows are presented each outflow is a response to an instantaneous low level cooling the vertical structures of the coolings differ as do the environments in which the outflows form and consequently the dynamics of the outflows differ one outflow is a gravity current another is a gravity wave and the third comprises both a gravity current and a gravity wave the horizontal transport of mass is important for the advance of the gravity current outflow but not for the gravity wave outflow and it is suggested that this is the defining dynamical distinction between the two outflows the simulations are compared to observations and it is suggested that some outflows previously characterized as gravity currents may better fit the gravity wave or gravity current wave archetypes it is also noted that the gravity wave component of an outflow may be generated directly by low level cooling in addition to the commonly suggested mechanism of the interaction of a gravity current with a stable layer

dynamic mechanisms of the gulf surge 1 the gulf surge is a summertime phenomenon associated with the north american monsoon that transports moisture from the gulf of california into western portions of the united states this phenomenon has been acknowledged operationally and by researchers for over 30 years the surge is typically linked to the presence of some sort of low pressure system such as an easterly wave mesoscale convective system or hurricane located near the southern end of the gulf of california proposed mechanisms for the gulf surge are gravity currents ageostrophic flows kelvin or rossby edge waves the purpose of this paper is to describe the fundamental dynamics of each of these mechanisms and assess their plausibility through scale analyses and idealized numerical simulations and to suggest signatures that may appear in data and output of more sophisticated numerical models

controls on carbonate skeletal mineralogy global co2 evolution and mass extinctions a quantitative compilation of carbonate skeletal mineralogy through the phanerozoic shows a progressive replacement of low mg calcite by aragonite this general trend overrides the subsidiary trend of greenhouse intervals favoring biogenic low mg calcite mineralogies calcite seas and icehouse intervals facilitating aragonite high mg calcite mineralogies aragonite seas the replacement of low mg calcite by aragonite was however achieved episodically at mass extinction intervals in particular the end permian extinction both preferentially removed species bearing unfavorable low mg calcite and allowed the selective radiation of biota with favorable aragonite this demonstrates the importance of incumbency in the evolution of skeletal mineralogy we suggest that the broad increase of aragonitic biota has been controlled by changes in atmospheric carbon dioxide partial pressure p co2 via carbonate mineral kinetics through the phanerozoic broadly decreasing p co2 levels led to decreasing total alkalinity and dissolved inorganic carbon and increasing oceanic ph superimposed upon this general trend there are cyclic episodes of relatively high p co2 and saturation state combined with a lower ratio of magnesium to calcium ions in seawater driven by the relatively slow changes in mid ocean ridge expansion rates mass extinction events many of which may have been caused by rapid global changes in temperature and or p co2 represent major intervals of turnover

possible role of gravity currents in northern california s coastal summer wind reversals north winds along the northern california coast in the summer of 1982 were interrupted by six events with southerly winds four of these events occurred under similar circumstances one of these four events is presented in detail at the start of this event the marine layer is thickened in the southern california bight a couple of days later the marine layer thickens from point conception to monterey then the marine layer thickness increase surges to the north along the coast to point arena where progression stopped and an eddy formed in this surging stage winds switched to southerlies as the leading edge of the event passed a day later the leading edge surged further to the north inshore winds were southerly and the lifted marine layer extended to cape blanco in oregon this event is interpreted as a gravity current surging up the coast the basic reservoir is the thickened marine layer in the southern california bight northerly progression is interrupted by a blocking wave near point arena where an eddy forms it is hypothesized that most of the major wind reversals along the northern california coast during the summer are gravity currents or kelvin waves in the marine layer that are formed to the south

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

surges over the gulf of california during the mexican monsoon abstract northward surges of relatively cool moist maritime air from the tropical pacific into the southwestern united states occur via the gulf of california every summer during the mexican monsoon season these surges advect large amounts of moisture northward and promote increased convective activity in arizona mesoscale model output from 32 successive 24 h simulations are used to examine both the large scale and mesoscale features associated with surge events model data are compared to high resolution aircraft measurements on two days showing clearly that the model is capable of reproducing many of the detailed structures found in the observations results from a large scale analysis indicate that strong surges are produced in the model when a midlatitude trough is in the proper phase relationship with a tropical easterly wave weak surges occur when this relationship is missing

modulation of eastern north pacific hurricanes by the madden julian oscillation abstract hurricane and tropical storm statistics verify the modulation of eastern pacific tropical systems by the madden julian oscillation mjo as hypothesized by maloney and hartmann over twice as many named tropical systems hurricanes and tropical storms accompany equatorial 850 mb westerly anomalies than accompany equatorial easterly anomalies and the systems that do exist are stronger hurricanes are over four times more numerous during westerly phases of the mjo than during easterly phases the current study constructs a composite life cycle of the mjo during may november 1979 95 using an index based on the 850 mb equatorial zonal wind equatorial kelvin waves propagating eastward from convective regions of the western pacific ocean alter dynamical conditions over the eastern pacific ocean westerly easterly equatorial 850 mb wind anomalies are accompanied by enhanced suppressed convection over the eastern pacific hurricane region convection locally amplifies the wind anomalies over the ea

analysis of 2002 and 2003 warm season precipitation from the north american monsoon experiment event rain gauge network analyses of rainfall characteristics and their linkage to physiographic features are made from the north american monsoon experiment name event rain gauge network nern in northwest mexico the findings are based on the network configuration for the 2002 and 2003 warm seasons despite the relatively short record used a clearer structure of core region monsoon rainfall is beginning to emerge in agreement with earlier coarser scale studies the seasonal precipitation maximum overlies the western slope of the sierra madre occidental but does not strictly parallel a particular elevation band it is shown that the distance to the gulf of california and potentially the configuration of the terrain profile may also play an important role in determining where the axis of maximum precipitation lies the diurnal cycles of precipitation frequency and intensity are shown to have distinct relationships to terrain elevation that are qualitatively similar to those observed over the front range of the rocky mountains in the central western united states the relationship between precipitation and gulf surge events occurring during the summer of 2003 is also explored

analysis of the 13 14 july gulf surge event during the 2004 north american monsoon experiment abstract gulf surges are disturbances that move northward along the gulf of california goc frequently advecting cool moist air from the goc or eastern tropical pacific ocean into the deserts of the southwest united states and northwest mexico during the north american monsoon nam little attention has been given to the dynamics of these disturbances because of the lack of reliable high resolution data across the nam region high temporal and spatial observations collected during the 2004 north american monsoon experiment are used to investigate the structure and dynamical mechanisms of a significant gulf surge on 13 14 july 2004 integrated sounding systems deployed along the east coast of the goc and an enhanced network of rawinsonde sites across the nam region are used in this study observations show that the 13 14 july gulf surge occurred in two primary stages the first stage was preceded by anomalous low level warming along the northern goc on 13 july sharp cooling moistening and increased

an observational and modeling study of an atmospheric internal bore during name 2004 abstract observations from the 2004 north american monsoon experiment name have been used to identify an atmospheric internal bore that occurred over the gulf of california goc on 31 july 2004 this bore disturbance was identified at bahia kino along the northwest coast of mexico during the late evening of 31 july it was hypothesized to have originated from the interaction of a gravity current from a large mesoscale convective system mcs which formed along the western slopes of the sierra madre occidental during the afternoon and a surface stable layer that developed from a sea breeze circulation it is suggested that the bore s energy was trapped at low levels by an elevated stable layer the vertical structure and undular nature of the bore was initially identified from 915 mhz wind profiler data at bahia kino results show a series of waves along the bore s leading edge and turbulent mixing of air from above the stable layer to the surface on the downstream face of the leading undulation the

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

constraining the marine strontium budget with natural strontium isotope fractionations 87sr 86sr δ88 86sr of carbonates hydrothermal solutions and river waters we present strontium sr isotope ratios that unlike traditional 87sr 86sr data are not normalized to a fixed 88sr 86sr ratio of 8 375209 defined as 88 86sr 0 relative to nist srm 987 instead we correct for isotope fractionation during mass spectrometry with a 87sr 84sr double spike this technique yields two independent ratios for 87sr 86sr and 88sr 86sr that are reported as 87sr 86sr and 88 86sr respectively the difference between the traditional radiogenic 87sr 86sr normalized to 88sr 86sr 8 375209 and the new 87sr 86sr values reflect natural mass dependent isotope fractionation in order to constrain glacial interglacial changes in the marine sr budget we compare the isotope composition of modern seawater 87sr 86sr 88 86sr seawater and modern marine biogenic carbonates 87sr 86sr 88 86sr carbonates with the corresponding values of river waters 87sr 86sr 88 86sr river and hydrothermal solutions 87sr 86sr 88 86sr hydend in a triple isotope plot the measured 87sr 86sr 88 86sr river values of selected rivers that together account for not vert similar18 of the global sr discharge yield a sr flux weighted mean of 0 7114 8 0 315 8 the average 87sr 86sr 88 86sr hydend values for hydrothermal solutions from the atlantic ocean are 0 7045 5 0 27 3 in contrast the 87sr 86sr 88 86sr carbonates values representing the marine sr output are 0 70926 2 0 21 2 we estimate the modern sr isotope composition of the sources at 0 7106 8 0 310 8 the difference between the estimated 87sr 86sr 88 86sr input and 87sr 86sr 88 86sr output values reflects isotope disequilibrium with respect to sr inputs and outputs in contrast to the modern ocean isotope equilibrium between inputs and outputs during the last glacial maximum 10 30 ka before present can be explained by invoking three times higher sr inputs from a uniquely glacial source weathering of shelf carbonates exposed at low sea levels our data are also consistent with the weathering peak hypothesis that invokes enhanced sr inputs resulting from weathering of post glacial exposure of abundant fine grained material

a cenozoic seawater sr ca record from benthic foraminiferal calcite and its application in determining global weathering fluxes a cenozoic multi species record of benthic foraminiferal calcite sr ca has been produced and is corrected for inter specific offsets typically less than 0 3 mmol mol and for the linear relationship between decreasing benthic foraminiferal sr ca and increasing water depth the water depth correction determined from holocene late glacial maximum and eocene paleowater depth transects is not vert similar0 1 mmol mol km the corrected cenozoic benthic foraminiferal sr ca record ranges from 1 2 to 2 0 mmol mol and has been interpreted in terms of long term changes in seawater sr ca enabling issues related to higher resolution variability in sr ca to be ignored we estimate that seawater sr ca was not vert similar1 5 times modern values in the late cretaceous but declined rapidly into the paleogene following a minimum in the eocene seawater sr ca increased gradually through to the present day with a minimum superimposed on this trend centered in the late miocene by assuming scenarios for changing seawater calcium concentration and using published carbonate accumulation rate data combined with suitable values for sr partition coefficients into carbonates the seawater sr ca record is used to estimate global average river sr fluxes these fluxes are used in conjunction with the seawater strontium isotope curve and estimates of hydrothermal activity tectonic outgassing to calculate changes in global average river 87sr 86sr through the cenozoic the absolute magnitude of sr fluxes and isotopic compositions calculated in this way are subject to relatively large uncertainties nevertheless our results suggest that river sr flux increased from 35 ma to the present day roughly two fold accompanied by an overall increase in 87sr 86sr by not vert similar0 to 0 001 between 75 and 35 ma river 87sr 86sr also increased by not vert similar0 001 to 0 002 but was accompanied by a decrease two to three fold in river sr flux

tectonic forcing of early to middle jurassic seawater sr ca the jurassic period ca 201 145 ma is marked by fundamental reorganizations of paleogeography paleoceanography ecosystems and the progressive shift from aragonite to calcite as the favored marine biogenic carbonate polymorph sr ca ratios of well preserved jurassic oysters and belemnites from sections in the uk and poland demonstrate that the sr ca ratio of seawater varied systematically throughout the early and middle jurassic in parallel with already documented seawater 87 sr 86 sr the sr flux from increased mid ocean ridge activity in the early jurassic outbalanced the input of riverine sr leading to gradually lower seawater 87 sr 86 sr associated with the parallel and strong decrease in seawater sr ca ratios this downward trend was reversed by enhanced continental input in the toarcian and aalenian but resumed in the bajocian and continued to the callovian parallel changes of seawater 87 sr 86 sr and sr ca suggest a common cause for these long term variations and are best explained by changes in the balance of continental weathering and hydrothermal fluxes these findings underline the strong control of global tectonic processes on the evolution of biomineralization and downplay the role of biomineral evolution in influencing strontium chemistry of seawater in the mid mesozoic

the formation of internal bores in the atmosphere a laboratory model summary recently several atmospheric observations have been interpreted as internal undular bores or internal solitary waves evolving from internal bores that propagate along low level temperature inversions it has been speculated that such disturbances are generated by some type of gravity current such as cold fronts sea breeze fronts and thunderstorm outflows interacting with an existing temperature inversion in this paper we describe a systematic laboratory study in a water channel of internal bores and their generation by the movement of gravity currents through a two layer model of the atmosphere we compare the results of our laboratory experiments with previous theories and numerical simulations and with several detailed atmospheric observations of internal bores at different stages of development