enhanced turbulence and energy dissipation at ocean fronts the ocean surface boundary layer mediates air sea exchange in the classical paradigm and in current climate models its turbulence is driven by atmospheric forcing observations at a 1 kilometer wide front within the kuroshio current indicate that the rate of energy dissipation within the boundary layer is enhanced by one to two orders of magnitude suggesting that the front rather than the atmospheric forcing supplied the energy for the turbulence the data quantitatively support the hypothesis that winds aligned with the frontal velocity catalyzed a release of energy from the front to the turbulence the resulting boundary layer is stratified in contrast to the classically well mixed layer these effects will be strongest at the intense fronts found in the kuroshio current the gulf stream and the antarctic circumpolar current all of which are key players in the climate system

a probabilistic model of debris flow delivery to stream channels demonstrated for the coast range of oregon usa debris flows are important geomorphic agents in mountainous terrains that shape channel environments and add a dynamic element to sediment supply and channel disturbance identification of channels susceptible to debris flow inputs of sediment and organic debris and quantification of the likelihood and magnitude of those inputs are key tasks for characterizing spatial and temporal patterns found in channel conditions and associated habitats in a river network widely available digital elevation and land cover data 10 m dems and 25 m satellite imagery offer the potential to assess debris flow runout paths over regional extents this paper presents a model for using these data to calculate empirical probabilities for debris flow runout over dem determined flow paths and shows how these probabilities can be combined over all sources to estimate the potential for debris flow delivery to stream reaches throughout entire channel networks the model is calibrated and model predictions are compared to field mapped debris flow travel paths from study sites in the coast range of oregon usa this model predicts debris flow probability over channel reach scales that can be aggregated to basin scale measures of debris flow potential it offers unprecedented ability to characterize debris flow effects over channel networks providing a tool for risk assessment and for generating hypotheses that relate topographic and forest cover controls on debris flow runout to the types and abundance of channel habitats in a river basin

detailed debris flow hazard assessment in andorra a multidisciplinary approach abstract in many mountainous areas the rapid development of urbanisation and the limited space in the valley floors have created a need to construct buildings in zones potentially exposed to debris flow hazard in these zones a detailed and coherent hazard assessment is necessary to provide an adequate urban planning this article presents a multidisciplinary procedure to evaluate the debris flow hazard at a local scale our four step approach was successfully applied to five torrent catchments in the principality of andorra located in the pyrenees the first step consisted of a comprehensive geomorphologic and geologic analysis providing an inventory map of the past debris flows a magnitude frequency relationship and a geomorphologic geologic map these data were necessary to determine the potential initiation zones and volumes of future debris flows for each catchment a susceptibility map and different scenarios were the principal outcome of the first step as well as essential input data for the second step the runout analysis a one dimensional numerical code was applied to analyse the scenarios previously defined first the critical channel sections in the fan area were evaluated then the maximum runout of the debris flows on the fan was studied and finally simplified intensity maps for each defined scenario were established the third step of our hazard assessment was the hazard zonation and the compilation of all the results from the two previous steps in a final hazard map the base of this hazard map was the hazard matrix which combined the intensity of the debris flow with its probability of occurrence and determined a certain hazard degree the fourth step referred to the hazard mitigation and included some recommendations for hazard reduction in andorra this four step approach is actually being applied to assess the debris flow hazard the final hazard maps at 1 2000 scale provide an obligatory tool for local land use planning experience achieved during the study showed that the collaboration between geologists geomorphologists engineers and decision makers is essential and that only a multidisciplinary approach allows for solving all the problems of such a complex process as debris flows finally we propose that our approach may be applied to other mountainous areas adapting the hazard matrix to new local conditions

alaska landfast sea ice links with bathymetry and atmospheric circulation 1 using radarsat synthetic aperture radar sar imagery of northern alaska and northwestern canada we calculated a mean climatology of the annual landfast ice cycle for the period 1996 2004 we also present the monthly minimum mean and maximum landfast ice extents throughout the study area these data reveal where and when the landfast is most stable and which sections of the coast are susceptible to midseason breakout events stabilization of landfast ice is strongly related to the advance of the seaward landfast ice edge slie into waters around 18 m deep isobaths near this depth are a good approximation for midseason landfast ice extent comparison with work from the 1970s suggests a reduced presence of landfast ice in this region of the arctic due to later formation and earlier breakup this will likely lead to an increase in coastal erosion and may also have profound effects upon subsistence activities which are intimately linked to the timing of marine mammal migration patterns interannually landfast ice formation correlates with the incursion of pack ice into coastal waters suggesting that the later mean date of formation in recent years may be related to the increasingly northward location of the perennial sea ice edge the timing of breakup correlates well with onset of thawing air temperatures analysis of regional data shows a multidecadal trend toward earlier thaw onset which suggests that the observed change in breakup dates may be part of a longer term trend

climatology of barrier jets along the alaskan coast part i spatial and temporal distributions abstract this paper investigates the temporal and spatial climatology of coastal barrier jets in the gulf of alaska the jets are divided into two categories based upon the origin of the air involved classic barrier jets fed primarily by onshore flow and hybrid jets fed primarily by gap flow from the continental interior the analyses are compiled from five years 1998 2003 of synthetic aperture radar images from the radarsat 1 satellite totaling 3000 images thermodynamic and kinematic data from the ncep reanalysis is used in the interpretation of the results the majority of coastal barrier jets occur during the cool season with the coastline near mount fairweather and the valdez cordova mountains experiencing the greatest number of barrier jets hybrid jets are even more strongly restricted to the cool season and are commonly found to the west of cross sound yakutat bay and icy bay some interannual variability in the total number of jets is observed coastal barrier jet formation is associate

flow of winter transformed pacific water into the western arctic abstract the dynamics of the flow of dense water through barrow canyon is investigated using data from a hydrographic survey in summer 2002 the focus is on the winter transformed bering water the highest volumetric mode of winter water in the chukchi sea which drains northward through the canyon in spring and summer the transport of this water mass during the time of the survey was 0 2 0 3 sv as the layer flowed from the head of the canyon to the mouth it sank decelerated and stretched strong cyclonic relative vorticity was generated on the seaward side of the jet which compensated for the stretching this adjustment was incomplete however in that it did not extend across the entire current possibly because of internal mixing due to shear instabilities the resulting vorticity structure of the flow at the canyon mouth was conducive for baroclinic instability and eddy formation multiple eddies of winter transformed bering water were observed along the chukchi beaufort shelfbreak those to the west of barrow canyon were in the process of being spawned by the eastward flowing shelfbreak current emanating from herald canyon while the single eddy observed to the east originated from the barrow canyon outflow it is argued that such an eddy formation is a major source of the ubiquitous cold core anti cyclones observed historically throughout the canada basin implications for the ventilation of the upper halocline of the western arctic are discussed

dendrogeomorphic evidence of debris flow frequency and magnitude at mount shasta california debris flow deposits and woody vegetation adjacent to and growing within the channels of whitney bolam mud ash and panthe creeks provide a 300 year record of debris flow frequency at mount shasta dendrochronologic tree ring dating methods for the debris flows proved consistent with available documented records of debris flows nine debris flows not reported in the historic record were documented and dated dendrochronologically the oldest tree ring date for a mudflow was about 1670

an empirical method for estimating travel times for wet volcanic mass flows travel times for wet volcanic mass flows debris avalanches and lahars can be forecast as a function of distance from source when the approximate flow rate peak discharge near the source can be estimated beforehand the near source flow rate is primarily a function of initial flow volume which should be possible to estimate to an order of magnitude on the basis of geologic geomorphic and hydrologic factors at a particular volcano least squares best fits to plots of flow front travel time as a function of distance from source provide predictive second degree polynomial equations with high coefficients of determination for four broad size classes of flow based on near source flow rate extremely large flows 1 000 000 m3 s very large flows 10 000 1 000 000 m3 s large flows 1000 10 000 m3 s and moderate flows 100 1000 m3 s a strong nonlinear correlation that exists between initial total flow volume and flow rate for instantaneously generated debris flows can be used to estimate near source flow rates in advance differences in geomorphic controlling factors among different flows in the data sets have relatively little effect on the strong nonlinear correlations between travel time and distance from source differences in flow type may be important especially for extremely large flows but this could not be evaluated here at a given distance away from a volcano travel times can vary by approximately an order of magnitude depending on flow rate the method can provide emergency management officials a means for estimating time windows for evacuation of communities located in hazard zones downstream from potentially hazardous volcanoes

lateral dispersion over the continental shelf analysis of dye release experiments lateral dispersion over the continental shelf was examined using dye studies performed as a part of the coastal mixing and optics experiment four experiments performed at intermediate depths each lasting 2 5 5 days were examined in some cases the dye patches remained fairly homogeneous both vertically and horizontally throughout an experiment in other cases significant patchiness was observed on scales ranging from 2 to 10 m vertically and a few hundred meters to a few kilometers horizontally the observations showed that the dye distributions were significantly influenced by shearing and straining on scales of 5 10 m in the vertical and 1 10 km in the horizontal superimposed on these larger scale distortions were simultaneous increases in the horizontal second moments of the dye patches with corresponding horizontal diffusivities based on a fickian diffusion model of 0 3 4 9 m 2 s 1 analysis of the dye data in concert with shear estimates from shipboard acoustic doppler current profiler observations showed that the existing paradigms of shear dispersion and dispersion by interleaving water masses cannot account for the observed diffusive spreading of the dye patches this result suggests that some other mechanisms provided an additional diffusivity of order 0 2 4 6 m 2 s 1 an alternative mechanism dispersion by vortical motions caused by the relaxation of diapycnal mixing events may explain the observed dispersion in some cases

submesoscale streamers exchange water on the north wall of the gulf stream the gulf stream is a major conduit of warm surface water from the tropics to the subpolar north atlantic here we observe and simulate a submesoscale 20 km mechanism by which the gulf stream exchanges water with subpolar water to the north along isopycnals the front has a sharp compensated temperature salinity contrast with distinct mixed water between the two water masses 2 and 4 km wide this mixed water does not increase downstream despite substantial energy available for mixing a series of streamers detrain this water at the crest of meanders subpolar water replaces the mixed water and resharpens the front the water mass exchange accounts for a northward flux of salt of 0 5 2 5 psu m2 s 1 large scale diffusivity o 100 m2 s 1 this is similar to bulk scale flux estimates of 1 2 psu m2 s 1 and supplies fresher water to the gulf stream required for the production of 18 subtropical mode water

enhanced mixing across the gyre boundary at the gulf stream front the gulf stream front separates the north atlantic subtropical and subpolar ocean gyres water masses with distinct physical and biogeochemical properties exchange across the front is believed to be necessary to balance the freshwater budget of the subtropical gyre and to support the biological productivity of the region however the physical mechanisms responsible have been the subject of long standing debate here the evolution of a passive dye released within the north wall of the gulf stream provides direct observational evidence of enhanced mixing across the gulf stream front numerical simulations indicate that the observed rapid cross frontal mixing occurs via shear dispersion generated by frontal instabilities and episodic vertical mixing this provides unique direct evidence for the role of submesoscale fronts in generating lateral mixing a mechanism which has been hypothesized to be of general importance for setting the horizontal structure of the ocean mixed layer along the gulf stream front in the north atlantic these observations further suggest that shear dispersion at sharp fronts may provide a source of freshwater flux large enough to explain much of the freshwater deficit in the subtropical mode water budget and a flux of nutrients comparable to other mechanisms believed to control primary productivity in the subtropical gyre

effects of wood on debris flow runout in small mountain watersheds 1 debris flows have typically been viewed as two phase mixtures of sediment and water but in forested mountain landscapes wood can represent a sizable fraction of total flow volume the effects of this third phase on flow behavior are poorly understood to evaluate whether wood can have a significant effect on debris flow runout in small mountainous watersheds we used a landscape scale model combining empirical stochastic and physical submodels of storms fires forest growth tree fall wood decay soil production and diffusion landslide initiation debris flow runout and fluvial sediment transport we examined changes in the cumulative distribution function of debris flow runout lengths in a small 2 km2 watershed in the oregon coast range due to presence or absence of two hypothesized effects of wood 1 velocity reduction due to entrainment of wood in the runout path and 2 velocity reduction due to changes in flow direction angle the model was calibrated such that the distribution for simulations including both effects was similar to that measured in the study basin and amounts of wood in the simulation and the field both fallen in small valleys and incorporated by debris flows were comparable removal of either effect or both significantly shifted runout length distributions to longer lengths simulations and field observations indicate that with wood fluvial transport is a significant source of sediment output few debris flows reach the outlet and debris flow deposits are widely distributed throughout the network simulations indicate that without wood basin sediment yield greatly increases that yield is dominated by longer runout debris flows and that debris flow deposits are concentrated in the low gradient reach near the outlet

estimation of debris flow magnitude in the eastern italian alps the estimation of debris ow magnitude is an essential step in the assessment of debris ow hazard although different methods have been developed for the assessment of debris ow magnitude this is still a dif cult task because of the complexity of ow processes and the lack of data to test estimation procedures in many mountainous regions data on debris ow magnitude from 127 basins in the eastern italian alps have been collected from scienti c and technical journals technical reports historical documents gathered from local archives and eld surveys these data were used to develop and test different predictive approaches encompassing regression equations geomorphological surveys and probabilistic analysis of time series regression techniques were used to correlate debris ow magnitude to morphometric parameters and geological characteristics of the basins values of the channel debris yield rate contribution per unit length of channel proposed in the literature were compared with data from the study area for identifying reference values for channel stretches of different morphological characteristics although limited to the few basins in which suf cient data were available the probabilistic analysis of time series of debris ow magnitude provides indications about the relations between magnitude and frequency of debris ows some observations about the capability and drawbacks of considered methods are presented and the combined use of different approaches for the estimation of debris ow magnitude is suggested copyright 2004 john wiley sons ltd

upwelling on the continental slope of the alaskan beaufort sea storms ice and oceanographic response 1 the characteristics of pacific born storms that cause upwelling along the beaufort sea continental slope the oceanographic response and the modulation of the response due to sea ice are investigated in fall 2002 a mooring array located near 152w measured 11 significant upwelling events that brought warm and salty atlantic water to shallow depths when comparing the storms that caused these events to other aleutian lows that did not induce upwelling interesting trends emerged upwelling occurred most frequently when storms were located in a region near the eastern end of the aleutian island arc and alaskan peninsula not only were these storms deep but they generally had northward tending trajectories while the steering flow aloft aided this northward progression the occurrence of lee cyclogenesis due to the orography of alaska seems to play a role as well in expanding the meridional influence of the storms in late fall and early winter both the intensity and frequency of the upwelling diminished significantly at the array site it is argued that the reduction in amplitude was due to the onset of heavy pack ice while the decreased frequency was due to two different upper level atmospheric blocking patterns inhibiting the far field influence of the storms

parameterization of mixed layer eddies part i theory and diagnosis ageostrophic baroclinic instabilities develop within the surface mixed layer of the ocean at horizontal fronts and efficiently restratify the upper ocean in this paper a parameterization for the restratification driven by finite amplitude baroclinic instabilities of the mixed layer is proposed in terms of an overturning streamfunction that tilts isopycnals from the vertical to the horizontal the streamfunction is proportional to the product of the horizontal density gradient the mixed layer depth squared and the inertial period hence restratification proceeds faster at strong fronts in deep mixed layers with a weak latitude dependence in this paper the parameterization is theoretically motivated confirmed to perform well for a wide range of mixed layer depths rotation rates and vertical and horizontal stratifications it is shown to be superior to alternative extant parameterizations of baroclinic instability for the problem of mixed layer restratification two companion papers discuss the numerical implementation and the climate impacts of this parameterization

the evolution of a front in turbulent thermal wind balance part 1 theory here we examine the influence of small scale turbulence on the evolution of fronts in the ocean and atmosphere specifically we consider the evolution of an initially balanced density front subject to an imposed viscosity and diffusivity as a simple analogue for small scale turbulence at late times the dominant balance is found to be the quasisteady turbulent thermal wind balance with time evolution due to an advection diffusion balance in the buoyancy equation we use the leading order balance to determine analytical similarity solutions for the spreading of a front and find that the spreading rate is maximum for an intermediate value of the ekman number with the spreading resulting from shear dispersion associated with the cross front flow and vertical diffusion of density in response to shear dispersion the front evolves towards a density profile that is nearly linear in the cross front coordinate at the edges of the frontal zone the density field develops large curvature and these regions are associated with narrow bands of intense vertical velocity

linking debris flow hazard assessments with geomorphology debris flow hazard assessment schemes are commonly based on empirical physical or numerical methods and techniques inherent in all methods is generally the assumption of unlimited sediment supply this study compares model inputs of sediment requirements for debris flows with estimated sediment reproduction from both solifluction and rockwall retreat the analysis is carried out in bildudalur a community in the westfjords of iceland geomorphic techniques are applied to determine the set of natural processes acting in this landscape to estimate spatial distribution of relevant processes to approximate level of processes activity and to provide information for scenario modeling debris flow volumes are determined by coupling rainfall magnitudes and catchment sizes with average sediment contents rockwall retreat and solifluction rates are based on literature reviews for a rainstorm with a 10 year return period debris flow volumes are calculated for 12 different creeks rates are assumed for solifluction with a velocity of 0 25 m yr at an average depth of 0 5 m and for rockwall retreat with 2 mm yr comparing sediment requirements with estimated sediment reproduction leads to a factor of deficit ranging between 6 2 and 8 5 thus the sediment storage is not refilled as fast as the next potential triggering rainfall occurs consequently if a debris flow has occurred in the past all sediment is removed and the following rainstorm event is djustt causing a flood which is by far less destructive than a debris flow event the challenge of future debris flow hazard assessment schemes is to include geomorphic analysis to be able to obtain more sustainable results d 2004 elsevier b v all rights reserved

geomorphic evidence for present day snow avalanche and debris flow impact in the icelandic westfjords the geomorphic impact of present day processes on slopes with emphasis on the impact of snow avalanches and debris flows is investigated in north western iceland data are obtained from topographical maps aerial photographs and field survey as well as from measurements of talus characteristics and estimates of the volumes of recent deposits the impact of various kinds of snow avalanches dry and wet slab avalanches and slush flows that have occurred recently in the area is shown the effects of avalanches including material transport and avalanche boulder tongue development and the resulting landforms are identified and analysed the geomorphic significance of debris flows is also examined their deposits described and erosional and depositional landforms channels levees and lobes measured the geomorphological impact in the icelandic westfjords area is discussed in relation to research in other environments observations indicate that snow avalanches are locally significant but their impact on talus slopes and talus cones where there are also debris flow deposits is moderate in contrary debris flow deposits are a strong geomorphic agent on slopes

open ocean submesoscale motions a full seasonal cycle of mixed layer instabilities from gliders abstractthe importance of submesoscale instabilities particularly mixed layer baroclinic instability and symmetric instability on upper ocean mixing and energetics is well documented in regions of strong persistent fronts such as the kuroshio and the gulf stream less attention has been devoted to studying submesoscale flows in the open ocean far from long term mean geostrophic fronts characteristic of a large proportion of the global ocean this study presents a year long submesoscale resolving time series of near surface buoyancy gradients potential vorticity and instability characteristics collected by ocean gliders that provides insight into open ocean submesoscale dynamics over a full annual cycle the gliders continuously sampled a 225 km2 region in the subtropical northeast atlantic measuring temperature salinity and pressure along 292 short 20 km hydrographic sections glider observations show a seasonal cycle in near surface stratification throughout the fall september november

practical research on quantitative calculation of debris flow magnitude and disaster intensity wind scale or earthquake magnitude is easier to remember and to be understood by the community although many systems of classifying debris flows are presently available it is necessary to propose an index as simple as wind scale or earthquake magnitude for measuring debris flows based on the principles used in wind scale and earthquake magnitude calculation this paper presents the concepts of debris flow magnitude and disaster intensity as well as a new numerical calculation method debris flow magnitude is a quantitative index describing the scale of a debris flow the disaster intensity of a debris flow is a quantitative index describing the severity of the damage to society caused by a debris flow with their explicit definitions and simple concepts both indices are considered to be important both practically and theoretically

surface drifter pair spreading in the north atlantic 1 this study examines spreading of surface drifter pairs deployed as part of the clivar mode water dynamic experiment climode project in the gulf stream region the spreading is resolved at hourly resolution and quantified by relative dispersion and finite scale lyapunov exponents at scales from 1 3 km to 300 500 km the dispersion follows richardson s law indicating stirring by eddies comparable in scale to the pair separation distance at larger scales the spreading becomes a random walk described by a constant diffusivity the behavior from 1 3 km to the local deformation radius is inconsistent with the enstrophy cascade of 2 d quasigeostrophic turbulence to test various hypotheses for this result drifter pair spreading is examined for pairs that were not launched together pairs deployed in the eastern subtropical north atlantic and climode pairs subsampled to daily temporal resolution our results indicate the presence of significant energy at the submesoscale in the gulf stream region which flattens the wave number spectrum and dominates surface stirring at this scale range results in the less energetic subtropical eastern atlantic are more equivocal

shear flow dispersion internal waves and horizontal mixing in the ocean abstract two models of advection diffusion in the oscillatory sheared velocity field of an internal wave are discussed our goal is to develop intuition about the role of such currents in horizontal ocean mixing through the mechanism of shear dispersion the analysis suggests simple parameterizations of this process i e those in eqs 7 36 and 42 the enhanced horizontal diffusion due to the interaction of the vertical diffusion and vertical shear of the wave field can be described by an effective horizontal diffusivity which is equal to the actual horizontal diffusivity plus a term equal to the mean square vertical shear of horizontal displacement times the vertical diffusivity provided the vertical length scale of the horizontal velocity field is not too small in the limit of small vertical length scale the expression reduces to taylor s 1953 result in which the effective horizontal diffusivity is inversely proportional to the actual vertical diffusivity the solutions also incidentally

magnitude frequency relations in debris flow debris flow occurs frequently in mountainous regions in china because of the difficulties involved in predicting and catching live debris flows an assessment of the potential for debris flow is crucial in hazard mitigation magnitude frequency mf relations are of special significance in such assessments in previous studies mf relations have been inferred by analyzing environmental factors and historical records and using empirical relations this paper is concerned with the derivation of mf relations at regional and valley scales using a large database of statistics at the regional scale it is represented by the distribution of the valley area because the area is often taken to indicate the potential magnitude of debris flow statistics from over 5 000 debris flow valleys in various provinces in china show that a power law holds for the distribution i e p a a n where p a is the percentage of valleys with area a and n varies with region and thus describes regional differences at the valley scale a case study focusing on jiangjia gully jjg was conducted and the mf relations derived from it were expressed by the distributions of discharge and runoff i e the total volume of living debris flows observed over the last 40 years the distributions can be expressed as exponential functions where the exponents vary with the events these mf relations provide not only a potential quantitative reference for practical purposes but also hint at the intrinsic properties of the debris flow

evolution and dynamics of the flow through herald canyon in the western chukchi sea abstract the flow of summer and winter pacific water masses through herald canyon is investigated using data from a high resolution hydrographic velocity survey conducted in summer 2004 the survey was part of the russian american long term census of the arctic rusalca program and consisted of four cross canyon transects occupied over a 2 day period at the time of the survey dense winter water was entering the western side of the canyon from the chukchi sea flowing alongside a poleward jet of summer water on the canyon s eastern flank as the dense water progressed northward it switched sides of the canyon and underwent a sudden increase in layer thickness this coincided with vertical mixing near the interface of the winter and summer water producing a new water mass mode exiting the canyon all of these features are consistent with the notion of hydraulic activity occurring in the canyon a three layer hydraulic theory is applied to the flow which suggests that it is supercritical and that hydraulic control is likely a lock exchange formulation accurately predicts the northward transport of the winter water the origin of the winter water and the manner in which it drains into the canyon is investigated using satellite ice concentration data atmospheric re analysis fields historical in situ data and a simple circulation model finally the fate of the pacific water exiting the canyon and its connection to the chukchi shelfbreak current is discussed

topographically generated gravity waves in the brooks range alaska amplified wind events are identified over the brooks range in alaska with observed wind speed increasing from calm to 5 ms 1 over 24 to 36 hours in simulations using an limited area climate system model the wind events are captured consistently although generally display greater strength than observed cooling associated with the wind events lead to an identification of the ne region of the north slope of alaska below the inversion as the source region for the air flow analysis of the wind event of 7th january 1992 supports the nonlinear hydraulic model of gravity waves

the alaskan arctic frontal zone forcing by orography coastal contrast and the boreal forest abstract experiments have been conducted with a regional climate model to indicate the conditions required to generate preferred regions of frontal activity in the alaskan region several objective methods of frontal identification were first investigated it was found that the vertical component of relative vorticity a thermal front parameter t850 n where t850 is the 850 hpa temperature and n is a unit vector in the direction of the 850 hpa temperature gradient and a parameter derived from the q vector as a measure of vertical motionwere useful in combination to determine the occurrence of fronts the preferred locations for frontal activity were located to the southern side of the eastern brooks range and over the alaska range these diagnostics were then used to characterize frontal frequency in a series of experiments removing topographic and vegetation contrasts it was found that the removal of the treeline contrast and its associated heating gradient had a small effect on frontal frequ

zooplankton inside an arctic ocean cold core eddy probable origin and fate abstract in september 2004 an extensive survey of a cold core eddy in the canada basin western arctic was carried out with high horizontal resolution physical and chemical sampling and lower horizontal resolution biological sampling the eddy was located over the continental slope north of the chukchi shelf and had a radius of 8 km its core was centered at a depth of 160 m water mass characteristics and the presence of copepods from the north pacific ocean neocalanus flemingeri and metridia pacifica demonstrated that the core contained water of pacific origin vertical distributions of zooplankton were associated with the physical structure of the water column for most taxa concentrations in the eddy core were elevated compared with those in similar density water in the surrounding basin based on tracer age estimates and previous observations of eddy formation the eddy is believed to have been formed during the previous spring summer from the chukchi shelfbreak jet surprisingly the eddy also contained elevated abundances of arctic origin copepods metridia longa and calanus glacialis analysis of a shelf basin transect occupied in the region in august 2004 showed that these species were present in high abundances in relatively shallow water 50 m inshore of the shelfbreak due to upwelling of deeper basin water and copepods onto the shelf in response to easterly winds if the formation of the observed eddy occurred during or shortly after a period of such winds upwelled arctic origin copepods on the shelf might have been entrained into the feature our observations suggest that formation and subsequent migration of such eddies may provide a mechanism for transporting zooplankton from the chukchi shelf into the interior canada basin the periodic input of high abundances of zooplankton from productive shelf areas could affect food webs in the less productive basin

nutrient budgets in the subtropical ocean gyres dominated by lateral transport upward fluxes have been thought to dominate nutrient replenishment at the ocean surface a numerical model reveals that lateral transfer is an important source of phosphorus and nitrogen for all five subtropical gyres

eddy induced particle dispersion in the near surface north atlantic abstractthis study investigates the anisotropic properties of the eddy induced material transport in the near surface north atlantic from two independent datasets one simulated from the sea surface height altimetry and one derived from real ocean surface drifters and systematically examines the interactions between the mean and eddy induced material transport in the region the lagrangian particle dispersion which is widely used to characterize the eddy induced tracer fluxes is quantified by constructing the spreading ellipses the analysis consistently demonstrates that this dispersion is spatially inhomogeneous and strongly anisotropic the spreading is larger and more anisotropic in the subtropical than in the subpolar gyre and the largest ellipses occur in the gulf stream vicinity even at times longer than half a year the spreading exhibits significant nondiffusive behavior in some parts of the domain the eddies in this study are defined as deviations from the long term time mean the contr

wind waves and fronts frictional effects in a generalized ekman model abstractocean currents in the surface boundary layer are sensitive to a variety of parameters not included in classic ekman theory including the vertical structure of eddy viscosity finite boundary layer depth baroclinic pressure gradients and surface waves these parameters can modify the horizontal and vertical flow in the near surface ocean making them of first order significance to a wide range of phenomena of broad practical and scientific import in this work an approximate green s function solution is found for a model of the frictional ocean surface boundary layer termed the generalized ekman or turbulent thermal wind balance the solution admits consideration of general more physically realistic forms of parameters than previously possible offering improved physical insight into the underlying dynamics closed form solutions are given for the wind driven flow in the presence of coriolis stokes shear a result of the surface wave field and thermal wind shear arising from a baroclinic

alpine debris flows triggered by a 28 july 1999 thunderstorm in the central front range colorado on 28 july 1999 about 480 alpine debris flows were triggered by an afternoon thunderstorm along the continental divide in clear creek and summit counties in the central front range of colorado the thunderstorm produced about 43 mm of rain in 4 h 35 mm of which fell in the first 2 h several debris flows triggered by the storm impacted interstate highway 70 u s highway 6 and the arapahoe basin ski area we mapped the debris flows from color aerial photography and inspected many of them in the field three processes initiated debris flows the first process initiated 11 of the debris flows and involved the mobilization of shallow landslides in thick often well vegetated colluvium the second process which was responsible for 79 of the flows was the transport of material eroded from steep unvegetated hillslopes via a system of coalescing rills the third which has been termed the firehose effect initiated 10 of the debris flows and occurred where overland flow became concentrated in steep bedrock channels and scoured debris from talus deposits and the heads of debris fans these three processes initiated high on steep hillsides 30 in catchments with small contributing areas 8000 m2 however shallow landslides occurred on slopes that were significantly less steep than either overland flow process based on field observations and examination of soils mapping of the northern part of the study area we identified a relation between the degree of soil development and the process type that generated debris flows in general areas with greater soil development were less likely to generate runoff and therefore less likely to generate debris flows by the firehose effect or by rilling the character of the surficial cover and the spatially variable hydrologic response to intense rainfall rather than a threshold of contributing area and topographic slope appears to control the initiation process in the high alpine of the front range because debris flows initiated by rilling and the firehose effect tend to increase in volume as they travel downslope these debris flows are potentially more hazardous than those initiated by shallow landslides which tend to deposit material along their paths

density compensated thermohaline gradients and diapycnal fluxes in the mixed layer abstract density compensated temperature and salinity gradients are often observed in mixed layer fronts a possible explanation of this observation is that there is a systematic relation between the strength of a front defined as the buoyancy jump across the front and the thickness of a front if stronger fronts tend to be thicker then in an ensemble of random fronts in which the temperature and salinity jumps am independent random variables the temperature and salinity gradients will he correlated this correlation between the thermohaline gradients is such that heat and salt make antagonistic contributions to the buoyancy gradient that is them is buoyancy compensation the statistics of heat and salt fluxes across nearly compensated fronts are counterintuitive strong heat fluxes can occur across a front with weak thermal gradients and strong salinity gradients and vice versa as a specific model that relates the width of a front to the strength of a front a pair of coupled nonlinear diffusi

buoyancy and wind driven convection at mixed layer density fronts in this study the influence of a geostrophically balanced horizontal density gradient on turbulent convection in the ocean is examined using numerical simulations and a theoretical scaling analysis starting with uniform horizontal and vertical buoyancy gradients convection is driven by imposing a heat loss or a destabilizing wind stress at the upper boundary and a turbulent layer soon develops for weak lateral fronts turbulent convection results in a nearly homogeneous mixed layer ml whose depth grows in time for strong fronts a turbulent layer develops but this layer is not an ml in the traditional sense because it is characterized by persistent horizontal and vertical gradients in density the turbulent layer is however nearly homogeneous in potential vorticity pv with a value near zero using the pv budget a scaling for the depth of the turbulent low pv layer and its time dependence is derived that compares well with numerical simulations two dynamical regimes are identified in a convective layer near the surface turbulence is generated by the buoyancy loss at the surface below this layer turbulence is generated by a symmetric instability of the lateral density gradient this work extends classical scalings for the depth of turbulent boundary layers to account for the ubiquitous presence of lateral density gradients in the ocean the new results indicate that a lateral density gradient in addition to the surface forcing can affect the stratification and the rate of growth of the surface boundary layer