an examination of the breakup of marine stratus a three dimensional numerical investigation abstract cloud top entrainment instability as a mechanism for the breakup of marine stratus is examined with a three dimensional planetary boundary layer pbl model specifically we examine the criterion developed by randall and deardorff this criterion states that stratus will break up if the equivalent potential temperature gradient at cloud top becomes less than a critical value to examine this hypothesis we simulate a horizontally uniform stratus layer which is excited from above by small random temperature perturbations the buoyancy instability ratio bir defined as e e crit and computed at cloud top is calculated locally across the domain and also averaged to define a mean value six cases involving different wind speeds and above cloud soundings produce different initial birs and different breakup sequences in general we find that a mean bir greater that one is a necessary condition for stratus breakup however we also find that the timing of breakup following achievement of th

large scale responses of complex shaped coastlines to local shoreline stabilization and climate change 1 when modeling the large scale km evolution of coastline morphology the influence of natural forces is not the only consideration ongoing direct human manipulations can substantially drive geomorphic change in this paper we couple a human component to a numerical model of large scale coastline evolution incorporating beach nourishment periodically placing sand on the beach also called beach replenishment or beach fill beach nourishment is the most prevalent means humans employ to alter the natural shoreline system in our case study the carolina coastline beach nourishment can cause shorelines adjacent to those that are nourished to shift both seaward and landward when we further consider how changes to storm behaviors could change wave climates the magnitude of morphological change induced by beach nourishment can rival that expected from sea level rise and affect the coast as far as tens of kilometers away from the nourishment site in some instances nonlocal processes governing large scale cuspate cape coastline evolution may transmit the human morphological signal over surprisingly large hundreds of kilometer distances

convectively forced internal gravity waves results from two dimensional numerical experiments two dimensional numerical simulations were performed to investigate the nature of tropospheric internal gravity waves of the type which are observed to occur above active thermal convection over an unstable boundary layer these gravity waves are believed to be excited by a combination of pure thermal forcing and by the boundary layer eddies and cumulus clouds acting as obstacles to the flow in the presence of mean environmental wind shear large amplitude internal gravity waves were obtained in the simulations with amplitudes and horizontal scales similar to the 12 june 1984 aircraft observations over western nebraska this was a day with strong wind shear in the lowest 3 km above the ground and with scattered cumulus clouds topping the boundary layer the simulations show that there is significant difference between the early time solutions as might be predicted by linear theory and late time solutions for the boundary layer eddy structure a layer interaction occurs in which gravity waves of the stable layer are excited by the boundary layer convection there is evidence to suggest that this layer interaction occurs both with and without shear but that it is stronger in the presence of low level shear results indicate that shear or the obstacle effect is a more efficient generator of gravity waves than is the pure thermal forcing the simulations show that the gravity waves initially forced by the boundary layer eddies lead to a feedback mechanism that acts to organize the boundary layer eddies and the cumulus convection the solutions suggest that the character of fair weather convection moist or dry is a non local problem involving at times the full depth of the troposphere the clouds produced in the simulations have very little influence on the wave field or boundary layer eddy structure as they are relatively small cumuli on the other hand the clouds are strongly influenced by the interactions between the wave and eddy fields upshear growth of cumulus clouds similar to that which is frequently observed in nature is reproduced in the simulations the development of feeder feeder is used here in a dynamical sense only clouds on typically the upshear side of the cloud is found to be a result of the interaction between the gravity wave field and the dry and moist convection the relative phase velocity between the gravity waves and the cloud plays a crucial role in determining the character of the cumulus cloud growth in the present simulations these simulations suggest that the dynamics both internal and external to the boundary of a cumulus cloud is a complicated mix between wave dynamics and the usually considered convection dynamics a brief discussion of the implications of the present results to cloud boundary baroclinic instability dynamics is also presented

determining shoreline response to sea level rise abstract the bruun rule is the most widely used method for determining shoreline response to sea level rise it assumes that the active portion of an offshore profile rises with rising sea level and the sand required to raise the profile is transported from the shoreline it is difficult to evaluate the efficacy of the bruun rule because sea level rise often has a lesser effect on shoreline change than that produced by sand sources sinks and longshore transport gradients in addition some shorelines have advanced seaward with rising sea level dean 1987 showed that equilibrium profile theory predicts that rising sea levels produce landward sand movement forced by nonlinear waves this paper presents an equation with terms representing all phenomena affecting shoreline change including bruun rule recession onshore sand transport sand sources and sinks and longshore transport gradients as an example of its use rates of onshore transport are determined along the 275 km florida southwest coast usa and a 19 km portion of this coast using known values for sand sources sinks and longshore transport gradients then future shoreline changes are projected for both coasts from 2015 to 2065 and for the southwest coast from 2015 to 2100 using sea level rise projections from the intergovernmental panel on climate change beach nourishment is shown to be a very effective adaptation strategy for sea level rise with shoreline change projections useful to estimate required rates of beach nourishment to counter sea level rise

a model of marine boundary layer cloudiness for mesoscale applications abstract a one dimensional version of a multilevel mesoscale model is used to represent the cloud topped boundary layer ctbl turbulent exchanges are parameterized with a prognostic equation for the turbulent kinetic energy and an improved length scale formulation furthermore the scheme is extended to give a statistical description of the subgrid scale condensation with a one and a half order closure several observed reference cases are simulated in order to test the model against observational data and results obtained with a higher order turbulence model the latter one is used as a powerful approach for testing the closure of the second order moments involved in the partial cloudiness scheme two of the reference cases are extracted from stratocumulus sc observations off the coast of the united kingdom with a purely buoyancy driven and a purely shear driven ctbl respectively the third experiment tries to reproduce a case of californian sc clouds where both turbulent effects are important final

on the occurrence of cloud streets over northern germany cloud street observations over northern germany are analysed with respect to wind and temperature profiles obtained from routine radiosonde stations in the area in nearly all cases the wind profiles on cloudstreet days were characterized by an inflection point in the cross wind component with unstable stratification of the boundary layer the height of the inflection point was found to be related to the convection height on those days which may suggest the importance of both inflection point and convective instability for explanation of cloud street development

precipitation generated oscillations in open cellular cloud fields cloud simulation is one of the most challenging tasks in regional to global scale climate modelling in many cases the physical mechanisms responsible for observed cloud dynamics are unknown making it difficult to simulate their structure and behaviour realistically feingold et al use satellite imagery and numerical models to show how downdrafts induced by precipitating clouds produce an open cellular cloud pattern characterized by low reflectivity that oscillates between different metastable states the resulting cloud structure forms an oscillating and self organizing cloud field as new cloud patterns emerge to replace the old ones cloud simulation is one of the most challenging tasks in regional to global scale modelling in many cases the physical mechanisms responsible for observed cloud dynamics are unknown making it difficult to realistically simulate their structure and behaviour these authors show that open cellular clouds characterized by low albedo can be created by precipitation driven downdrafts and that the resulting cloud structure forms an oscillating self organizing cloud field cloud fields adopt many different patterns that can have a profound effect on the amount of sunlight reflected back to space with important implications for the earth s climate these cloud patterns can be observed in satellite images of the earth and often exhibit distinct cell like structures associated with organized convection at scales of tens of kilometres1 2 3 recent evidence has shown that atmospheric aerosol particles through their influence on precipitation formation help to determine whether cloud fields take on closed more reflective or open less reflective cellular patterns4 5 the physical mechanisms controlling the formation and evolution of these cells however are still poorly understood6 limiting our ability to simulate realistically the effects of clouds on global reflectance here we use satellite imagery and numerical models to show how precipitating clouds produce an open cellular cloud pattern that oscillates between different weakly stable states the oscillations are a result of precipitation causing downward motion and outflow from clouds that were previously positively buoyant the evaporating precipitation drives air down to the earth s surface where it diverges and collides with the outflows of neighbouring precipitating cells these colliding outflows form surface convergence zones and new cloud formation in turn the newly formed clouds produce precipitation and new colliding outflow patterns that are displaced from the previous ones as successive cycles of this kind unfold convergence zones alternate with divergence zones and new cloud patterns emerge to replace old ones the result is an oscillating self organized system with a characteristic cell size and precipitation frequency

accelerated relative sea level rise and rapid coastal erosion testing a causal relationship for the louisiana barrier islands abstract the role of relative sea level rise as a cause for the rapid erosion of louisiana s barrier island coast is investigated through a numerical implementation of a modified bruun rule that accounts for the low percentage of sand sized sediment in the eroding louisiana shoreface shore normal profiles from 150 km of coastline west of the mississippi delta are derived from bathymetric surveys conducted during the 1880s 1930s and 1980s an rms difference criterion is employed to test whether an equilibrium profile form is maintained between survey years only about half the studied profiles meet the equilibrium criterion this represents a significant limitation on the potential applicability of the bruun rule the profiles meeting the equilibrium criterion along with measured rates of relative sea level rise are used to hindcast shoreline retreat rates at 37 locations within the study area modeled and observed shoreline retreat rates show no significant correlation thus in terms of the bruun approach relative sea level rise has no power for hindcasting and presumably forecasting rates of coastal erosion for the louisiana barrier islands

mechanisms for the mesoscale organization of tropical cloud clusters in gate phase iii part i shallow cloud bands abstract mesoscale cloud clusters are a frequently observed feature of the tropical atmosphere and are primarily responsible for the observed large scale vertical mass flux given that the forcing for such convection comes from widely separated horizontal scales boundary layer motions on the scale of 1 km and weak ascent on a scale of over 1000 km the persistent organization of cloud clusters into the scale 10 50 km presents an important problem in this article part i two and three dimensional numerical simulations of convection under a capping inversion at 2 km are presented to demonstrate that the mechanism responsible for mesoscale organization of clouds requires neither deep convection nor large scale forcing the case study used as a basis for these simulations is one of several instances reported by lemone and meitin of mesoscale cloud bands during gate phase iii these observations are remarkable in that the cloud bands are shallow yet possess a rather large horizontal periodicity in the ra

three examples of fair weather mesoscale boundary layer convection in the tropics abstract evidence indicates that fair weather to towering cumulus clouds over the east atlantic ocean during gate were frequently organized into mesoscale structures three examples of such structures are examined using gust probe aircraft data collected in parallel straight and level flight tracks at 150 m and covering an area greater than 30 30 km the aircraft two cases or rawinsonde one case data provide vertical profiles of mean wind temperature and mixing ratio cloud patterns are revealed from an upward looking infrared sensor on the aircraft and radar and satellite pictures the data show that the cumulus were organized into bands with horizontal wavelengths of 15 25 km the circulations appear to extend through the subcloud layer with all the fields at 150 m well related to the cloudiness overhead since the circulations are aligned with the subcloud layer shear and travel in a direction parallel to the subcloud layer wind in the two cases for which band movement is documented it is be

an assessment of marine atmospheric boundary layer roll detection using sentinel 1 sar data abstract the ability of high resolution synthetic aperture radar sar to detect marine atmospheric boundary layer mabl roll induced roughness modulation of the sea surface wave field is well known this study presents sar measurements of mabl rolls using global coverage data collected by the european space agency s c band sentinel 1a satellite in 2016 2017 an automated classifier is used to identify likely roll events from more than 1 3 million images that were acquired at two incidence angles of 23 and 36 5 in either vv or hh polarization characteristics of the detected rolls are examined for different wind speeds polarizations incidence and relative azimuth angles roll detection counts are much higher at the higher incidence angle and nearly equivalent for vv and hh polarizations detection depends strongly on the relative azimuth with roll detection rates at crosswind being 3 10 times lower than for up or downwind all data show a low wind speed threshold near 2 m s 1 and that rolls are most commonly observed at wind speeds near 9 m s 1 for all viewing configurations we find that rolls induce a wide range of mean surface wind speed modulation with the most frequent value being 8 3 5 roll detection at crosswind is associated with stronger roll induced surface wind enhancement dependencies of roll detection on the incidence and relative azimuth angles are consistent with rapid short scale wind wave adjustments to the roll induced surface wind gusts these cm scale waves are highly directional and provide limited crosswind backscatter at shallower incidence angles the same roll induced surface forcing is thus not equally detectable at all viewing geometries or polarizaions stronger and possibly longer duration wind forcing is likely needed to produce detectable roll induced modulations at crosswind

embedded cellular convection in moist flow past topography abstract marginally unstable air masses impinging upon a mountain ridge may lead to the development of a nominally stratiform orographic cloud with shallow embedded convection rainfall amounts and distribution are then strongly influenced by the convective dynamics in this study the transition from purely stratiform orographic precipitation to flow regimes with embedded convection is systematically investigated to this end idealized cloud resolving numerical simulations of moist flow past a two dimensional mountain ridge are performed in a three dimensional domain a series of simulations with increasing upstream potential instability shows that the convective dynamics may significantly increase precipitation amounts intensity and efficiency to an extent that cannot be replicated by two dimensional simulations under conditions of uniform upstream flow the embedded convection is of the cellular type it is demonstrated that simple stability measures of the upstream profile are poor predictors for

numerical simulation of the stratus to cumulus transition in the subtropical marine boundary layer part i boundary layer structure abstract a stratus to cumulus transition sct that resembles observations occurred in lagrangian numerical simulations of the subtropical marine boundary layer over the northeastern pacific ocean southwest of california the lagrangian approach involves translating the domain along the climatological boundary layer trajectory at a rate equal to the observed surface wind speed the sst is increased at a corresponding rate the simulations did not include drizzle the diurnal cycle divergence changes or mesoscale circulations and thus demonstrate that these processes are not essential for an sct a 2d numerical cloud model that can explicitly represent large convective eddies is used turbulence at scales smaller than the large eddies is parameterized using a third moment turbulence closure this type of model requires no cloud regime specific input and is computationally economical for multiday simulations the results suggest that there are four stages in the transition from the stratus topped boundary

observations of longitudinal rolls in a near neutral atmosphere abstract aircraft and satellite data an used to study the structure of longitudinal roll vortices in a nearly neutral zi l 1 2 where zi is the inversion height and l is the monin obukhov length boundary layer over the ice covered bering sea during february steam fog formed over cracks and leads in the ice was used as a tracer to delineate the various scales of roll motion seen in satellite images the satellite information combined with aircraft data collected by the noaa p 3 indicated the presence of a hierarchy of roll vortex motions it is suggested that interactions of the various scales of motion resulted in certain scales dominating in one area and other scales dominating in another two kilometer wavelength variations an attributed to the inflection point instability mechanism while 12 15 km variations seen to have been reinforced by the upstream topography on the chukotka peninsula organization of the fog banks on scales of 30 km was also present and may be attributable to resonant subharm

a single doppler radar study of horizontal roll convection in a lake effect snow storm abstract the boundary layer structure and circulation over lake michigan were probed with a doppler radar and an aircraft during a lake effect snow storm on 9 december 1978 evidence is presented that observed wind parallel echo bands and satellite cloud bands resulted from horizontal roll convection in the boundary layer the organization of precipitation within the roll field is discussed and the roll geometry is compared with cases of dry horizontal roll convection reported in the literature

cloudiness and marine boundary layer dynamics in the astex lagrangian experiments part i synoptic setting and vertical structure abstract a goal of the atlantic stratocumulus transition experiment astex southeast of the azores islands in the east central atlantic ocean during june 1992 was to examine the coupled evolution of cloud dynamical and thermodynamical vertical structure in a marine boundary layer mbl air mass as it advected from cold to warm water in the trade winds in two lagrangian observation periods during astex an unprecedentedly complete view of mbl and cloud evolution was achieved by nearly continuous aircraft coverage of such an air mass for 36 48 hours using three boundary layer aircraft supplemented by satellite ship and balloon observations during the first lagrangian period an accelerated stratocumulus to trade cumulus transition occurred in a clean marine air mass in the second lagrangian period a 200 hpa deep decoupled modified continental mbl persisted with almost no change in structure cumulus rising into intermittent stratocumulus were observed throughout the period the two contrasting a

the application of stokes wave theory under changing sea levels in the irish sea abstract although recent models of wave dominated coastal systems have incorporated the stokes wave equations neither the flow predictions nor the shorewards limits of the theory have been adequately tested with field or laboratory experiments results are reported from 315 laboratory measurements of peak onshore and offshore flow speeds under a variety of wave conditions use of the complete data set indicates that predictions of nearbed flow velocity by stokes second order theory are not accurate over the entire range of depths tested and the importance of defining a shallow water limit is discussed the results suggest that the ratio of the first two harmonics of the nearbed flows is a useful criterion for constraining the depth range of the corrected wave theory the results also indicate that flow velocity attenuates more rapidly with depth than is predicted by theory and an empirical correction is derived these analyses are applied to the wave dominated seabed off the west coast of the isle of man in the central irish sea and show that the corrected theory is applicable to within 80 m of the shoreline at high water on a typical spring tidal cycle

sea level sediment supply and coastal changes examples from the coast of ireland abstract sediment supply and pre existing shoreline morphology are crucial factors in controlling coastal changes due to sea level rise using examples from both southeast and northeast ireland it can be shown that sea level change may trigger a sequence of events which leads to both static and dynamic shoreline equilibrium cliff erosion and longshore sediment movement in east co wexford has led to injection of sediment onto the shelf and the growth under both wave and tide regimes of linear offshore shoals these shoals now control the pattern of shoreline erosion and provide a template for possible stepwise evolution of the coast under any future sea level rise in contrast the nearby coast of south co wexford comprises a series of coarse clastic barriers moving monotonously onshore via overwash processes here the behavior of the barrier is conditioned by the antecedent morphology of both the beach face and stream outlet bedforms finally the rock platform coast of co antrim presents a far more resistant shoreline to incident marine processes yet even here there is strong evidence of present process control over so called raised platforms and embayments it is concluded that coastal sediment supply and dynamics together with coastal morphology and its interaction with waves present a far more complex variety of sea level indicators than is normally acknowledged

geochemical precursors to seismic activity studies of earthquake precursory phenomena during the last several decades have found that significant geophysical and geochemical changes can occur prior to intermediate and large earthquakes among the more intensely investigated geochemical phenomena have been 1 changes in the concentrations of dissolved ions and gases in groundwaters and 2 variations in the concentrations of crustal and mantle volatiles in ground gases the concentration changes have typically showed no conanomalies trend either increasing or decreasing and the spatial and temporal distribution of the observed anomalies have been highly variable as a result there is little agreement on the physical or chemical processes responsible for the observed anomalies mechanisms proposed to account for precursory groundwater anomalies include ultrasonic vibration pressure sensitive solubility pore volume collapse fracture induced increases in reactive surfaces and aquifer breaching fluid mixing precursory changes in soil gas composition have been suggested to result from pore volume collapse micro fracture induced exposure of fresh reactive silicate surfaces and breaching of buried gas rich horizons an analysis of the available field and laboratory data suggests that the aquifer breaching fluid mixing ab fm model can best account for many of the reported changes in temperature dissolved ion and dissolved gas concentrations in groundwater ultrasonic vibration and pressure sensitive solubility models cannot reasonably account for the geochemical variations observed and although the pore collapse model could explain some of the observed chemical changes in groundwater and ground gas uncertainties remain regarding its ability to generate anomalies of the magnitude observed other geochemical anomalies in particular those associated with hydrogen and radon seem best accounted for by increases in reactive surface areas irsa model that may accompany precursory deformation around the epicenter of an impending earthquake analysis of the probable response of these models to the earthquake preparation process as well as to other environmental factors suggests that geochemical monitoring programs can provide information that may be valuable in forecasting the probability of an earthquake however because of the complexity of the earthquake preparation process the absolute prediction of seismic events using geochemical methods alone does not presently appear to be feasible

aerosol and cloud microphysical characteristics of rifts and gradients in maritime stratocumulus clouds a cloud rift is characterized as a large scale persistent area of broken low reflectivity stratocumulus clouds usually surrounded by a solid deck of stratocumulus a rift observed off the coast of california was investigated using an instrumented aircraft to compare the aerosol cloud microphysical and thermodynamic properties in the rift with those of the surrounding solid stratocumulus deck the microphysical characteristics in the solid stratocumulus deck differ substantially from those of a broken cellular rift where cloud droplet concentrations are a factor of 2 lower than those in the solid cloud furthermore cloud condensation nuclei ccn concentrations were found to be about 3 times greater in the solid cloud area compared with those in the rift although drizzle was observed near cloud top in parts of the solid stratocumulus cloud the largest drizzle rates were associated with the broken clouds within the rift area and with extremely large effective droplet sizes retrieved from satellite data minimal thermodynamic differences between the rift and solid cloud deck were observed in addition to marked differences in particle concentrations evidence of a mesoscale circulation near the solid cloud rift boundary is presented this mesoscale circulation may provide a mechanism for maintaining a rift but further study is required to understand the initiation of a rift and the conditions that may cause it to fill a review of results from previous studies indicates similar microphysical characteristics in rift features sampled serendipitously these observations indicate that cloud rifts are depleted of aerosols through the cleansing associated with drizzle and are a manifestation of natural processes occurring in marine stratocumulus

horizontal roll and boundary layer interrelationships observed over lake michigan abstract on 7 9 and 10 january 1981 some 35 hours of organized horizontal roll convection in the boundary layer over lake michigan were probed with two airplanes and two radars from the university of chicago lake snow project during this time roll wavelength varied from 1 5 to 13 7 km roll depth from 0 9 to 2 1 km and roll aspect ratio from 1 0 to 9 1 the roll axes changed orientation to remain within 10 of the inversion level geostrophic wind direction and the maximum transverse wind speed varied from 1 to 2 m s 1 boundary layer parameters such as wind speed wind direction over water fetch surface layer instability and upstream stability also varied over the same period the roll orientations and the variations of roll wavelength and maximum roll transverse wind speed with rayleigh number and richardson number are examined with reference to theoretical models of roll convection the observations suggest that roll orientation roll wavelength and roll transverse wind speed depend primari

atmospheric boundary layer rolls observed by the synthetic aperture radar aboard the ers 1 satellite two synthetic aperture radar sar images acquired by the european remote sensing satellite ers 1 over the jade weser estuary in the german bight of the north sea on january 2 and 20 1992 are analyzed the images show sea surface manifestations of atmospheric boundary layer rolls this is inferred from the orientation of the quasi periodic sea surface patterns which are aligned approximately with the wind direction from the ratio of the wavelength of the patterns to the height of the boundary layer and from the conditions encountered in the atmospheric boundary layer as measured quasi simultaneously by radiosondes the atmospheric boundary layer rolls were generated by a dynamic instability on january 2 and by a thermal instability on january 20 for the first time quantitative estimates of variations of the wind velocity at the sea surface associated with the atmospheric rolls are extracted from a spaceborne radar sar image it is shown that wind velocities derived from sar image intensity variations are in agreement with theoretical estimates

late holocene coastal change in the southwestern cape south africa abstract radiocarbon dated elevated marine deposits and the record of anthropogenic and natural debris in archaeological deposits on the west coast of south africa indicate that significant coastal remodelling has taken place in the past 4300 years in response to sea level change geological and archaeological investigation of elevated deposits of sub fossil shell abandoned lagoons and washover bars has shown that many of these features relate to a mid holocene high stand of the sea of about 2 3 m above modern mean sea level the detailed course of local late holocene sea level change cannot be resolved from these elevated geological deposits but information from archaeological sites provides valuable indirect evidence of the effects of coastal change in response to minor fluctuations in relative sea level

seasonal changes in beach topography and beach volume in delaware abstract a beach study was conducted along a shore segment of the delaware coast from march 1982 through to april 1983 results indicate that beach topography and beach volume varied with changes in wave climatic regimes the regimes in turn were generally in phase with the winter and summer seasons because both the magnitude and frequency of storm waves were higher during winter than in summer the winter beach shape was concave upward following the winter storms of 1981 1982 swells rebuilt the beach in two stages from march through to august 1982 in the first stage the beach vertically accreted aggraded and in the second it laterally accreted prograded the aggrading stage involved the welding of a swash bar to the foreshore thereafter swash overtopping caused deposition on and landward of the bar in time the swash bar attained a berm and swale topography the prograding stage started when the swash could no longer overtop the berm crest which confined deposition to the foreshore this stage occurred following a minor or moderate storm event that shifted the berm crest upward and landward or during a neap tidal stage that occurred after the construction of a spring tide berm between march and the end of august 1982 60 m 3 of sediments per 1 m of beach were deposited on the shore of this value 67 was attributed to aggradational processes while the remaining 33 was attributed to progradational processes swells as well as storm waves caused vertical accretion storm waves contributed 20 of the total sediment volume deposited on the beach when the shore was at its maximum sediment volume for 1982 the beach topography was convex upward an inverse relationship existed between the mean monthly sediment volume and the mean monthly surge variability the surge level was used as an index of wave conditions high surge levels were associated with large waves while low surge levels were associated with small waves when surge variability was high during the winter sediment volume on the beach was low and conversely when surge variability was low in summer sediment volume was high correlation analysis showed that 80 of the variance of the mean monthly sediment volume was explained by the mean monthly surge variability

the structure of the unstable marine boundary layer viewed by lidar and aircraft observations abstract the combination of vertical lidar and in situ meteorological observations from two aircraft provide an unprecedented view of the marine atmospheric boundary layer mabl during a cold air outbreak to a first approximation the lidar reflectivity is associated with the concentration of sea salt aerosols across the capping inversion the lidar reflectivity contours approximate isentropes and streamlines thereby defining the inversion within the mixed layer high reflectivity cores are associated with updrafts carrying aerosol rich air upward and conversely these effects are enhanced by increasing humidity in updraft and decreasing humidity in downdrafts that operate to increase and decrease aerosol sizes narrow high reflectivity columns extend upward from the ocean indicating that organized flow exists all the way to the surface entrainment across the inversion is manifested by small scale perturbations 200 500 m superimposed upon the large scale sim 1 2 km undulations of the inversion

cold air outbreak during gale lidar observations and modeling of boundary layer dynamics abstract two cold air outbreaks were studied during the genesis of atlantic lows experiment a lidar system was operated to observe the boundary layer evolution and the development of clouds on the first day 30 january 1986 boundary layer rise was less than 50 of the value for the second day 2 march 1986 on the first day only a thin broken cloud cover formed while on the second day a thick solid cloud deck formed although the average moisture content was 60 of that on the first day a trajectory slab model was employed to simulate the evolution of the layer over the ocean near the cast atlantic shore the model allows for vertical gradients in conservative variables under neutrally buoyant conditions the primary effect of these assumptions which are based on observed thermodynamic profiles is to reduce cloudiness to be more in line with observations boundary layer depth was reasonably well predicted as was sensible and latent heat flux

gas geochemistry and seismotectonics a review abstract publications on soil and spring gases have been examined regarding their relationships with both tectonic and seismic activities the main sources behaviours and uses of species detected in soils and springs are displayed and their mode of sampling and analysing briefly described the main patterns of degassing in soils are described and we outline the wide range of geochemical signatures as the result of both permeability and mineralogical contrasts because thermomineral waters have been in contact with great volumes of crustal rocks at various depths spring gases might be more representative of the local environment than soil gases moreover gas signature comparisons show that spring gases are much more enriched with deep gases and slightly contaminated by atmospheric gases therefore they can be considered as better samples for identifying precursors of earthquakes environmental perturbations are examined and it is shown from divergent cases that pressure temperature soil moisture or earth tides may generate very high perturbations of the degassing process such effects demonstrate that no systematic correction law can be proposed and that removing external contributions from gas concentrations must be performed case by case this demonstrates therefore the need for the simultaneous measurement of external parameters during gas monitoring a qualitative examination of about 150 claimed precursors proposed in the literature has been reviewed as noted by previous authors anomalies appear at distances sometimes much greater than typical source dimensions and occur in the field of strain higher than 10 9 most of them being in the field of strain higher than 10 8 taking into account the very high heterogeneity of such a set of data we can suggest that amplitudes of gas anomalies are independent of both magnitudes and epicentral distances of related earthquakes suggesting local conditions to control amplitudes on the contrary precursory time and duration of anomalies seem to increase both with magnitudes and epicentral distances abundant evidence demonstrates the major role of crustal fluids in the earthquake cycle many works have outlined the fact that crustal instabilities can appear as the result of low stress strain perturbations during loading it has been suggested that motion of fluids may occur at various scales from microcrack fluid transfer up to changes of hydraulic levels of water tables the study of subsequent anomalies is expected to supply a tool for earthquake prediction following previous authors we outline the need for further methodological improvements including the setting up of multiparameter station networks and the simultaneous recording of the main external parameters atmospheric pressure water and air temperature soil moisture for signal processing

sedimentary balances land and sea with special reference to the icelandic south coast from torlakshofn to dyrholaey river nourishment of shores practical analogies on artificial nourishment abstract the sedimentary balances between land and sea are discussed with particular reference to the 140 km long pocket beach between two major headlands on the sandy icelandic south coast rivers supply large quantities of material to the coast comparing the known transport of material by the rivers to the area of the continental shelf and using the recorded sea level rise at the port of reykjavik a balance was found the development of equilibrium profiles in relation to profile geometry grain sizes and outer boundaries for material movement by wave action is discussed and practical suggestions on future nourishment procedures are presented profile nourishment will be more practical and economical than beach nourishment

radon content of groundwater as an earthquake precursor evaluation of worldwide data and physical basis the properties of a worldwide data set of 91 radon 222 rn anomalies the frequency of occurrence the precursor time interval and the distribution of peak amplitudes are correlated with earthquake data such as the respective magnitude and epicentral distance these anomalies were reported as precursors to earthquakes in the united states ussr china japan and iceland although the data set is incomplete and limited by experimental deficiencies several consistent patterns emerge radon anomalies from different tectonic regions show similar patterns the radon anomalies occur at greater epicentral distances for earthquakes of the larger magnitude anomalies preceding large earthquakes m 6 are frequently observed at a distance of 100 to 500 km these distances are larger than several times the rupture dimensions of the future earthquakes the time from the onset of an anomaly to the time of the earthquake the precursor time increases with magnitude but decreases with distance between epicenter and radon station in addition radon anomalies are observed more frequently prior to large earthquakes than prior to small ones indicating that the preparation zone increases in size as magnitude increases the peak amplitude does not scale with magnitude but forms a consistent pattern with epicentral distance in that the larger the earthquake magnitude the farther away the largest amplitudes tend to occur the preparation zone of the earthquake where the anomalies occur forms an almost continuous annulus that expands with time away from the future rupture zone the outer radius of this annulus scales with the earthquake magnitude model calculations indicate that strain fields of at most 10 6 to 10 8 strain caused the radon anomalies if these strains are divided by the appropriate precursor time minimum strain rates from 10 7 day 1 to 10 10 day 1 are obtained such small strains and strain rates suggest that in most cases neither mechanical crack growth induced by dilatancy nor mechanical coupling between pore pressure and the rock matrix caused the anomalies large changes in the orientation of the local strain field however could occur and affect the local stress intensity factor since changes in the stress intensity factor can result in stress corrosion the occurrence of radon anomalies is attributed to slow crack growth controlled by stress corrosion in a rock matrix saturated by groundwater

the effect of stress on radon emanation from rock a uranium bearing granitic rock of known radon emanation was deformed to failure under uniaxial stress radon emanation and microcrack activity were recorded continuously during the test radon concentration in the closed system was measured by an alpha detector a decrease in emanation was observed during the initial loading of the sample and is interpreted as associated with the closure of pre existing cracks within the rock at a uniaxial stress equal to approximately one half the ultimate strength a temporary increase 50 in the radon emanation was observed that correlated with an increase in microcracking within the sample when the stress was removed for several hours the original emanation was restored however once the specimen failed a temporary emanation increase of 120 was observed the emanation then decreased to a level nearly 5 greater than the prefailure specimen emanation

entrainment instability and vertical motion as causes of stratocumulus breakup entrainment instability is thought to be a cause of stratocumulus breakup at the interface between the cloud and the overlying air mixtures may form which are negatively buoyant because of cloud droplet evaporation quantities devised to predict breakup 2 x and m are obtained from aircraft observations and are tested against cloud observations from satellite often the parameters indicate that breakup should occur but the clouds remain sometimes for several days one possible explanation for breakup is vertical motion from passing synoptic cyclones several cases suggest that breakup is associated with the downward vertical motion from the cold air advected behind an eastward moving cyclone

rheology of the lithosphere selected topics we review recent results concerning the rheology of the lithosphere with special attention to the following topics 1 the flexure of the oceanic lithosphere 2 deformation of the continental lithosphere resulting from vertical surface loads and forces applied at plate margins 3 the rheological stratification of the continents 4 strain localization and shear zone development and 5 strain induced crystallographic preferred orientations and anisotropies in body wave velocities we conclude with a section citing the 1983 1986 rock mechanics literature by category

numerical simulations and a conceptual model of the stratocumulus to trade cumulus transition abstract a two dimensional eddy resolving model is used to study the transition from the stratocumulus topped boundary layer to the trade cumulus boundary layer the 10 day simulations use an idealized lagrangian trajectory representative of summertime climatological conditions in the subtropical northeastern pacific the sea surface temperature is increased steadily at 1 5 k day 1 reflecting the southwestward advection of the subtropical marine boundary layer by the trade winds while the free tropospheric temperature remains unchanged results from simulations with both a fixed diurnally averaged shortwave radiative forcing and a diurnally varying shortwave forcing are presented a two stage model for the boundary layer evolution consistent with these simulations is proposed in the first stage decoupling is induced by increased latent heat fluxes in the deepening boundary layer after decoupling cloud cover remains high but the cloudiness regime changes from a single stratocumulus layer to sporadic

the mesoscale stability of entrainment into cloud topped mixed layers abstract the lilly type models for stratocumulus capped mixed layers are shown to allow for a mesoscale instability in which mesoscale fluctuations of buoyancy and humidity are reinforced in phase by entrainment in a model of an amtex mixed layer this mesoscale instability has a maximum growth rate of about 2 10 5s 1 at wavelengths 30 times the depth of the mixed layer the instability is able to account for the existence and broad scale of the stratiform cloud patterns known as mesoscale cellular convection

observations of the interaction between cumulus clouds and warm stratocumulus clouds in the marine boundary layer during astex abstract decoupling of the marine boundary layer beneath stratocumulus clouds and the formation of cumulus clouds at the top of a surface based mixed layer sml have frequently been observed and modeled when such cumulus clouds penetrate the overlying stratocumulus layer the cloud microphysics and hence the radiative properties of the cloud are altered locally observations made during a series of lagrangian experiments in the azores as part of the atlantic stratocumulus transition experiment astex june 1992 have been analyzed to ascertain how the properties of a stratocumulus layer with which cumulus clouds are interacting differ from those of an unaffected cloud layer the results suggest that in regions where cumulus clouds penetrate the cloud layer the stratocumulus is thickened as the cumuli spread out into its base transport of air from the sml into the cloud by convective updrafts is observed and the increase in available moisture within the penetrating cumulus clouds results in increased

a simple dynamical model of a stratocumulus topped boundary layer abstract some latent heating effects on horizontal wavenumber selection and cell circulation patterns in stratocumulus topped boundary layers are investigated via a study of two dimensional shallow moist boussinesq convection no entrainment and zero moisture flux assumptions are used to develop a simple latent heating representation accordingly upward and downward motions below a uniform cloud base are assumed to be dry adiabatic and those above cloud base are moist adiabatic a nonlinear nine coefficient low order spectral model is developed in which representations of all nonlinear and linear terms of the original system of partial differential equations are retained in dry rayleigh benard convection the first convective steady solution branching from the conductive state is assumed to occur at the smallest value of the critical rayleigh number and the resulting flow field is dominated by one horizontal wavenumber in this case the circulation patterns are symmetric because the horizontal wavelen

mesoscale shallow convection in the atmosphere this paper is a review of the observational experimental theoretical and numerical studies of mesoscale shallow convection msc in the atmosphere typically msc is 1 to 2 km deep has a horizontal length scale of a few to a few tens of kilometers and takes distinctive planforms linear and hexagonal the former is called a cloud street roll or band while the latter is called mesoscale cellular convection mcc comprising three dimensional cells msc is characterized by its shape horizontal extent convective depth and aspect ratio the latter is the ratio of the horizontal extent to that in the vertical for cells the horizontal extent is their diameter whereas for rolls it is their spacing rolls usually align along or at angles of up to 10 from the mean horizontal wind of the convective layer with lengths from 20 to 200 km widths from 2 to 10 km and convective depths from 2 to 3 km the typical value of aspect ratio ranges from 2 to 20 rolls may occur over both water surface and land surfaces mesoscale convective cells may be divided into two types open and closed open cell circulation has downward motion and clear sky in the cell center surrounded by cloud associated with upward motion closed cells have the opposite circulation both types of cell have diameters ranging from 10 to 40 km and aspect ratios of 5 to 50 and both occur in a convective layer with a depth of about 1 to 3 km both the magnitude and direction of horizontal wind in the convective layer change little with height msc results from a complex and incompletely understood mix of processes these processes are outlined and their interplay is examined through a review of theoretical and laboratory analyses and numerical modeling of msc

problems in characterizing dynamics of mud shore profiles the relationship between profile shape and wave forcing at shores composed of soft mud is examined at a given still water level the modality of change in profile shape under wave action depends on the fluidization potential of mud which in turn is contingent on the wave characteristics and the dissipative properties of mud an important determinant of profile shape in areas where mud can be fluidized is the wave attenuation coefficient comparatively large values of this coefficient tend to correlate with erosional concave upward profiles and low values with accretionary convex upward shapes assuming that the rate of energy dissipation per unit area of nonbreaking normally incident waves is constant in the nearshore shallow zone an equation to simulate soft mud shore profiles has been developed this equation is shown to be applicable to profile data obtained from a variety of mud shore environments however it is noted that realistic simulations of the accretionary and erosional characteristics

a systematic compilation of earthquake precursors article a survey of published scientific literature was undertaken to identify and catalog observed earthquake pre cursors the earthquake precursors selected for analysis included electric and magnetic fields gas emissions groundwater level changes temperature changes surface deformations and seismicity for each of these precursors the published scientific literature was searched to document the statistics of each reported earth quake precursor spatial extent time duration amplitude signal noise ratio to analyze dependence of the observable for each precursor on earthquake magnitude and to explore proposed physical models to explain eachearthquakeprecursor somegeneralcharacteristics wereobservedfortheseprecursoryphenomena first the largest amplitude precursory anomalies tend to occur before the largest magnitude earthquakes also the number of precursory anomalies tends to increase the closer in time to the occurrence of the earthquake finally theprecursoryanomaliestendtooccurclosetotheeventualepicenterof theearthquake ingeneral the physical models indicate that all of the precursory phenomena are related to deformation that occurs near the fault prior to the main earthquake while the models provide plausible physical explanations for the pre cursors there are many free parameters in the models that are poorly resolved

wave climate coastal sediment budget and shoreline changes for the danube delta abstract since its formation approximately 12 000 years ago the coastal zone of the danube delta experienced alternating periods of accretion and erosion related to the natural process of lobe abandonment caused by river avulsion over the last 150 years the effects of human interventions modified these natural trends regulation of the danube river e g the iron gates barrages facilitating navigation and controlling river discharge construction and extension of the sulina entrance jetties and dredging of the sulina mouth bar for navigational purposes are examples of human interventions that influenced and still influence the actual state of the danube delta coastal zone most importantly these interventions diminished the quantity of sediments reaching the coast and consequently led to a severe retreat of the shoreline especially in the sulina sf gheorghe coastal sector to investigate and quantify the recent sediment budget and associated shoreline changes along the danube delta coastal zone we constructed a hindcast of the wave climate the alongshore transport capacity and the resulting sediment budget using a numerical coastline model on a local scale it was found that overwash plays an important role i e the observed evolution of sahalin spit island shows a cross shore landward migration that is much larger than could be explained by the calculated alongshore sediment transport gradients on a delta scale however the resulting alongshore sediment transport gradients and associated sediment budgets comply very well with the observations confirming the dominant role of wave induced alongshore transport and giving confidence in our predictions regarding the shoreline position for the next 25 and 50 years the results of this study indicate the potential for broader applicability of the model to other deltas especially those in wave dominated settings

properties of a simulated convective boundary layer in an idealized supercell thunderstorm environment abstractnearly all previous numerical simulations of supercell thunderstorms have neglected surface fluxes of heat moisture and momentum this choice precludes horizontal inhomogeneities associated with dry boundary layer convection in the near storm environment as part of a broader study on how mature supercell thunderstorms are affected by a convective boundary layer cbl with quasi two dimensional features i e boundary layer rolls this paper documents the methods used to develop a realistic cbl in an idealized environment supportive of supercells the evolution and characteristics of the modeled cbl including the horizontal variability of thermodynamic and kinematic quantities known to affect supercell evolution are presented the simulated rolls result in periodic bands of perturbations in temperature moisture convective available potential energy cape vertical wind shear and storm relative helicity srh vertical vorticity is shown to arise within the boundary layer through the tilt

gravity waves compensating subsidence and detrainment around cumulus clouds abstract gravity waves play an important role in the redistribution of heat and moisture in a deep convecting cloud field we explore this role in a two dimensional numerical experiment on a simple moist convecting system consisting of an isolated long lasting nonprecipitating cloud in a calm atmosphere with no surface forcing the cloud develops a horizontally averaged density variation with height which is neutrally buoyant with respect to a moist adiabatic the buoyancy difference between the cloud and the undisturbed sounding produces circulations that can be understood as spreading gravity waves which adjust the environmental buoyancy to be equal to the cloud buoyancy by compensating subsidence unlike the circulations inside clouds this adjustment takes place without turbulent mixing hence the buoyancy adjustment time t1 during which the environment comes into rough buoyant equilibrium with the clouds is much shorter than the mixing time t2 which it takes a tracer initially concentrated at s

surface based observations of mesoscale cumulus stratocumulus interaction during astex abstract data obtained from the island of santa maria in the azores during the atlantic stratocumulus transition experiment astex are used to describe cloud and boundary layer structure for a 24 h period on 15 june 1992 over the east central atlantic 37 n 25 10 w the evolution of the mesoscale cloud structure during a 24 h period in the vertical column above the surface site was characterized using a 94 ghz radar a laser ceilometer 3 h radiosonde ascents and surface micrometeorological instrumentation mesoscale circulations and drizzle were found to be key elements of the boundary layer clouds observed in this region during the late night and predawn hours of the study period a single layer of stratocumulus that averaged 200 m in thickness topped a well mixed marine boundary layer mesoscale cellular convection mcc which had ascending regions with horizontal dimensions of 7 km was observed during this period at sunrise decoupling was imposed on this mcc and extreme mesoscale variatio

separation of volatile components from rocks under mechanical loading as the source of hydrogeochemical anomalies preceding earthquakes one of the most important problems for the theory and practice of earthquake prediction is that of the source of substances in the formation of precursory hydrogeochemical anomalies volatile components that are separated from rocks at mechanical loading present one of the sources a large scale model experiment is conducte with a 50 000 ton press the results reveal the regularities of water radon mercury and helium separation from large basalt and granite samples that are subjected to a cyclically increasing uniaxial pressure to fracture at 75 and 180 mpa for basalt and granite respectively premonitory rock fracture is found to be accompanied by the separation of volatile components from rocks predictive properties of the components are associated with their chemical nature and the forms in which they exist in rocks water release during mechanical loading increases gradually with the increase in loading helium separation begins at the early stages of the cracking process comparison of the data on degassing with data on bulk strain and acoustic emission shows that the major part of radon is released at the stage of avalanche type crack interaction and at the dynamic stage of the formation of an earthquake source whereas mercury degasses mainly at the dynamic stage immediately before fracture of the sample

a new perspective on meso scale shoreline dynamics through data driven analysis abstract the twin ambits of climate change and coastal development have raised public awareness of shoreline management simultaneously they have highlighted a gap in our understanding of sediment transport and morphodynamic processes at time and space scales appropriate for shoreline management purposes here we analyse an exceptional set of beach surveys gathered over a period of twenty two years along the suffolk coast eastern uk that extends over approximately 80 km to investigate the meso scale shoreline variations the surveys have been made biannually along fixed transects spaced at approximately 1 km intervals as part of a strategic monitoring exercise undertaken by the coastal authorities to assist in shoreline management planning changes in beach volume foreshore slope and shoreline position have been computed to investigate both spatial and temporal changes the analysis reveals some distinct responses to the physical processes of tides and waves anthropogenic interventions and geological controls neither a clear relationship between the presence of sea defences and beach response nor an ordered regional scale shoreline movement are evident temporal variations in beach volumes and position provide a similarly complex picture with recessionary accretionary and stable behaviour all apparent within the study site there is evidence of quasi cyclic behaviour at some locations as well as a reduction in variability over time scales beyond approximately five years

near surface density currents observed in the southeast pacific stratocumulus topped marine boundary layer abstractdensity currents i e cold pools or outflows beneath marine stratocumulus clouds are characterized using 30 days of ship based observations obtained during the 2008 variability of american monsoon systems vamos ocean cloud atmosphere land study regional experiment vocals rex in the southeast pacific an air density increase criterion applied to the improved meteorological imet sensor data identified 71 density current front core peak density and tail dissipating zones the similarity in speeds of the mean density current propagation speed 1 8 m s 1 and the mean cloud level advection relative to the surface layer wind 1 9 m s 1 allowed drizzle cells to deposit elongated density currents in their wakes scanning doppler lidar captured prefrontal updrafts with a mean intensity of 0 91 m s 1 and an average vertical extent of 800 m updrafts were often surmounted by low lying shelf clouds not connected to the overlying stratocumulus cloud the observed density currents were 5 10 time

gas geochemistry applied to earthquake prediction an overview terrestrial gases in groundwater and soil air have been extensively studied in recent years in seismically active areas especially in ussr china japan and united states in search of premonitory changes that might be useful for earthquake prediction concentrations of radon helium hydrogen mercury carbon dioxide and several other volatiles have been found generally to be anomalously high along active faults suggesting that the faults may be paths of least resistance for the terrestrial gases generated or stored in the earth to escape to the atmosphere temporal gas concentration changes with durations of a few hours to many months have been observed before many large earthquakes at a relatively small number of favorably situated stations at epicentral distances of up to several hundreds of kilometers these sensitive stations are generally located along active faults especially at intersections or bends of faults or some other structurally weak zones possibly because of tectonic strain concentration at such places however gas concentrations especially those measured at or near the ground surface may also be significantly affected by meteorological hydrological and other nontectonic changes in the environment the nontectonically induced variations must be carefully eliminated or recognized in the search of true earthquake related anomalies

precipitation onset as the temporal reference in convective self organization in a dry convective boundary layer convective patterns of typical scales spontaneously develop qualitatively similar to those in a fluid which is placed between two horizontal plates and sufficiently heated from below as soon as precipitating cumulus clouds form this pattern is disturbed and a transition to a different state occurs here we use idealized large eddy simulations to explore how the horizontal scale of convection is modified during this transition in the course of a diurnal cycle before onset of precipitation cells with relatively constant diameter self organize with diameters roughly on the scale of the atmospheric boundary layer height we find that the onset of precipitation then signals an approximately linear increase in horizontal scale with time for our transient simulations this scale increase progresses at a speed which is relatively insensitive to modifications in mean surface temperature modifications in the rate at which surface temperature changes or the initial lapse rate when exploring the strength of the spatial correlations we find that precipitation onset causes a sudden disruption of order and a subsequent decline of organization until precipitation eventually ceases we discuss possible implications for the development of extreme precipitation events

exploring shoreface dynamics and a mechanistic explanation for a morphodynamic depth of closure using energetics based formulations for wave driven sediment transport we develop a robust methodology for estimating the morphodynamic evolution of a cross shore sandy coastal profile in our approach wave driven cross shore sediment flux depends on three components two onshore directed terms wave asymmetry and wave streaming and an offshore directed slope term in contrast with previous work which applies shallow water wave assumptions across the transitional zone of the lower shoreface we use linear airy wave theory the cross shore sediment transport formulation defines a dynamic equilibrium profile and by perturbing about this steady state profile we present an advection diffusion formula for profile evolution morphodynamic peclet analysis suggests that the shoreface is diffusionally dominated using this depth dependent characteristic diffusivity timescale we distinguish a morphodynamic depth of closure for a given time envelope even though wave driven sediment transport can and will occur at depths deeper than this morphodynamic closure depth the rate of morphologic bed changes in response to shoreline change becomes asymptotically slow linear wave theory suggests a shallower shoreface depth of closure and much sharper break in processes than shallow water wave assumptions analyzing hindcasted wave data using a weighted frequency magnitude approach we determine representative wave conditions for selected sites along the u s coastline computed equilibrium profiles and depths of closure demonstrate reasonable similarities except where inheritance is strong the methodology espoused in this paper can be used to better understand the morphodynamics at the lower shoreface transition with relative ease across a variety of sites and with varied sediment transport equations

an observational study of cloud topped mixed layers abstract the turbulence and mean structure of oceanic stratocumulus was studied using aircraft data collected during the summer of 1976 off the coast of california three cloud topped mixed layers were studied in detail they consisted of 1 a thin cloud capped by an inversion at a height of 1000 m 2 a relatively thick but broken cloud layer capped by a weak inversion at 600 m and 3 a solid cloud capped by a strong inversion at 600 m the mean temperature moisture liquid water and radiative characteristics obtained for these three cases were compared heat and moisture fluxes were also calculated and compared although there was considerable variation in the characteristics of the three cloud topped mixed layers studied all indicated the validity of the general approach used in simple mixed layer models of stratocumulus but for these models to be useful they should be generalized to allow clouds other than solid clouds to be modeled the measurements indicate that cloud microphysics may be impo

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

sea level rise and impacts on nearshore sedimentation an overview impacts on nearshore sedimentation arising from potential sea level change of the magnitude predicted in intergovernmental panel on climatic change scenarios associated with global warming are reviewed for sandy duned coasts the obvious sedimentation impacts include potential erosion of coastal dunes with implied deposition of the eroded material in the nearshore possible deepening of embayments and flooding of wetlands for the sandy coasts a number of two dimensional models are available for predicting shoreline change but there are significant difficulties in applying bruun type models for dune erosion and assessment of sediment redistribution over the inner shelf and for predicting the amount of shoreline retreat for a given rate of sea level rise if the beach profile contains excessive sand relative to its equilibrium profile sensu dean 1991 then shoreline retreat may not occur upon sea level rise from the evidence of kiel bay at least in these semi enclosed basin types it is during major transgressions that maximum deposition in adjacent basins occurs due to the sea eroding weakly consolidated and weathered surface regolith but at the same time climatic patterns were re adjusting and probably contributed to maximum deposition in adjacent shelf and basins below wave base

the relationship between radar reflectivities and clouds associated with horizontal roll convection on 8 august 1982 abstract horizontal convective rolls hcrs and cloudstreets that occurred in northeastern colorado are studied using doppler radar data cloud photography and vertical soundings examination of the environment in which the hcrs form indicates a boundary layer wind speed that is much lower than those measured in previous studies evidence shows that the hcrs form in a well defined boundary layer yet the cloudstreets that develop seem to exist within a stable layer above a relationship between the radar reflectivity echoes and the cloudstreets is firmly established the echoes are aligned directly under the cloudstreets the echoes at lower levels are shown to be caused by convergence of particulate matter into updraft portions of the hcr circulation yet evidence indicates the cloud level echoes are due to backscatter from refractive index inhomogeneities at the surfaces of rising thermals examination of the echoes show that the strongest and tallest echoes are associated with cloud formation and tha

annual and interannual changes on a reef fringed pocket beach kailua bay hawaii abstract historical aerial photographs and topographic survey sheets are used to establish a 70 year shoreline history 1926 1996 for kailua beach oahu hawaiian islands the shoreline has migrated seaward over this period at an average rate of 0 5 m yr with a maximum net accretion along the beach of 58 7 m and a maximum net erosion of 13 2 m net accretion has taken place even while sea levels have risen on the order of 0 1 m semi annual and monthly beach profile surveys 1995 1999 at seven transects reveal short term variations of shoreline position sand volume and beach shape a relationship between beach width and corresponding sand volume fluctuations established from the beach profile data is applied to the historical shoreline change data to establish a history of sand volume fluctuations results show that kailua has experienced a net accretion of 673 000 m3 of sand over the period 1926 1996 with average annual rates of volume change varying between 6 8 m3 m yr and 0 1 m3 m yr the most recent period 1989 1996 shows a net volume increase of 41 000 m3 given the lack of sand inputs at the ends of the beach exchange with offshore deposits is a likely mechanism for long term accretional trends seasonal fluctuations in kailua beach morphology dominate the variability with a response to seasonal wave state that varies along the length of the beach in magnitude and sign at least four alongshore zones are observed with the first and third zones exhibiting high low sand volumes during the summer winter and the second and fourth zones exhibiting opposite behavior with high low volumes during the winter summer although seasonal sand accumulation varies along the beach the overall beach profile is largely maintained moreover changes in sand volume occur in phase over the subaqueous and subaerial sections of the beach this behavior suggests that longshore rather than cross shore sand transport is important at annual time scales a simple seasonal transport pattern is proposed to account for these observed fluctuations which depends in part on the topography of the offshore reef

the influence of coastal shape on winter mesoscale air sea interaction abstract in the case of cold air outbreaks the combination of the coastal shape and the sea surface temperature sst pattern is shown to have a profound effect in establishing a low level mesoscale atmospheric circulation as a result of differential heating due to both variations in overwater path length and the sst a convergence or divergence line then forms along a line exactly downwind of the major bend in the coastline this is consistent with the structure of the cloud patterns seen in a high resolution landsat picture of the cloud streets the major features are also simulated well with a boundary layer model the dominant convergence line is marked by notably larger clouds to its cast the convective roll clouds grow downstream in accord with the deepening of the boundary layer to its west i e coastal side near the convergence line where the induced pressure field forces a strong westerly component in the boundary layer the wind shear across the inversion gives rise to kelvin helmholtz w

experimental studies of he and ar degassing during rock fracturing abstract we studied degassing of he and ar from granite basalt and volcanic tuff samples which were subjected to uniaxial compression from the samples which were fractured in the dilatant region he was always degassed while degassing of ar dependent not only on the dilatancy but also on the type of rock and the compressional conditions such as wet room dry or vacuum conditions it is concluded that degassing of rare gases from the compressed samples depends primarily on the generation of new surface area by dilatancy

large eddy simulation of the convective atmospheric boundary layer abstract large eddy simulations of a free convective atmospheric boundary layer with an overlying capping inversion are considered attention is given to the dependence of the results upon the various factors influencing the simulation the subgrid model the domain size and the mesh resolution by providing artificial constraints upon the convection the results also provide extra insight into the underlying dynamics the gross features of the boundary layer such as the overall energy budget are not sensitive to the details of the simulations but a number of important factors are revealed it has been found that near the surface the subgrid diffusivity must be larger than is usually supposed in order for the vertical velocity skewness to have the correct sign this region of the flow has a significant subgrid scale heat flux and it seems that the subgrid model requires improvement in such cases a revised model which under statically unstable conditions allows the mixing length of the subgrid scale tu

observations of diurnal variation in a cloud capped marine boundary layer abstract observations are presented of the turbulent structure of a cloud capped boundary layer during the 1987 fire marine stratocumulus project the measurements were made from san nicolas island off the coast of california using instruments attached to the cable of a tethered balloon a marked diurnal variation is demonstrated through a direct comparison of observations made around local noon and approximately 12 hours later emphasis is given to the decoupling of the boundary layer during the morning into a separate cloudy layer and surface mixed layer

on polarimetric characteristics in sar images of mesoscale cellular convection in the marine atmospheric boundary layer 1 convection is an important phenomenon in the marine atmospheric boundary layer mabl previous spaceborne radar studies of such have been limited to single polarization data and therefore their focus was on the variation in intensity of the radar return which was constrained by the existence of a single polarization image pattern representing different atmospheric and oceanic phenomena in this paper we study the polarimetric characteristics of mesoscale cellular convection mcc in the mabl using high resolution data from fully polarimetric hh vv hv and vh radarsat 2 rs 2 synthetic aperture radar sar images in conjunction with closely collocated mesoscale atmospheric model simulations to identify the mcc signatures to compare the polarimetric characteristics of mcc with those of the ocean surface our analysis also includes 641 open ocean surface quad polarization rs 2 sar images collocated with 52 national data buoy center buoys the open ocean surface sar images exhibit different polarimetric characteristics from those of mcc thus we differentiate mcc from other open ocean phenomena based on identifiable polarimetric sar characteristics