geomagnetic field intensity and reversals during the past four million years a long and continuous record of the geomagnetic field intensity shows that intensity variations are dominated by two modes major episodes of field regeneration prevail on timescales of a few thousand years immediately after most reversals whereas stable polarity states are characterized by a slow 0 5 myr relaxation process reversals can be seen as the consequence of a progressive degradation of the dipole field

variable density flow and solute transport simulation of regional aquifers containing a narrow freshwater saltwater transition zone variable density flow and solute transport simulation of aquifer systems containing narrow transition zones between freshwater and saltwater requires particular attention to certain aspects of the numerical method and its application to be successful typically only cases involving wide transition zones have been simulated with variable density transport models possibly because of inaccuracies in the modeling approaches used the major components of a successful approach are threefold first functionally consistent approximation of terms involved in fluid velocity calculations is necessary in the case of galerkin finite element methodology a significant modification is required to the standard approach in order to achieve consistency second the simulator must be verified in a particular series of tests the usual tests using henry s problem for verification of density dependent transport simulators are inadequate to check for consistency of the velocity approximations and for the accuracy of simulating flow driven by bouyancy forces third adequately fine spatial discretization is required when applying the simulator for spatial stability of the numerical transport solution and to allow accurate representation of narrow transition zones and the effects of low transverse dispersivity the effectiveness of this approach is demonstrated through simulation of the flow of fresh and saline groundwater in the layered basalt aquifer of southern oahu hawaii the transition zone in this regional flow system is narrow except near the discharge area where it is broadly dispersed simulation of this common situation with an inconsistent approximation gives grossly incorrect results while simulation with a consistent model provides a robust tool for analysis of system hydrology

satellite observations of circulation in the eastern bering sea satellite infrared observations of the eastern bering sea shelf and basin were analyzed from december 1979 to august 1981 a region of warm surface water which extends from the gulf of alaska through the aleutian passes into the bering sea was observed coincident with a band of warm surface water and with eddies along the shelf break the spatial and temporal relationships of these patterns imply a surface inflow through unimak and other western aleutian passes flow along the shelf break including eddies along the bering slope current and cyclonic flow in the basin the proposed generating mechanisms for eddies along the shelf break include topographic interactions baroclinic instabilities and rossby waves

tides in the strait of gibraltar the strait of gibraltar is where the transition occurs between two distinct tidal regimes the north atlantic where tidal ranges are in excess of 2 m and the western mediterranean where tidal ranges are less than 1 m within the strait the tide is principally semidiurnal observations indicate that on average 96 of the bottom pressure and 74 of the current variability are contained in the semidiurnal band 2 cpd the structure of the local cotidal chart of the m2 tidal constituent is complicated but can be explained in terms of the along and across strait momentum balances along the strait the pressure gradient is mainly balanced by the acceleration of the flow although friction can be of appreciable magnitude corresponding to a decay time scale of 3 16 hours across the strait the momentum balance appears mostly geostrophic but better observations would be required to explain residual terms available observations indicate that the m2 tide has no net energy flux through the strait at the sill the tidal transport in the upper layer exceeds that in the lower layer by nearly a factor of 2 at the eastern end of the strait between algeciras and ceuta the tidal transport is larger in the lower layer this apparent shift in the location of maximum tidal transport is explained in terms of the kinematics of the interface between atlantic and mediterranean waters a mean transport of 0 21 sv due to subinertial and tidal flows carries atlantic water through the strait compensated by an approximately equal return in the lower layer

on the bering sea ice edge front an oceanographic field program was carried out along the bering sea ice edge in winter 1982 83 to investigate the temperature salinity front associated with and paralleling the winter ice edge currents were measured using taut wire moorings that were in place over winter and an intensive ctd survey was carried out of the frontal structure in midwinter february march the midwinter front separated cold 0 c more saline 32 5 outer shelf water the front had northwestward baroclinic currents paralleling the front ice edge with near surface speeds of 5 6 cm s and an associated transport of about 0 3 106 m3 s these baroclinic currents were superimposed on a regional barotropic along isobath flow resulting in north westward midwinter upper layer flows with monthly mean speeds exceeding 10 cm s an upper layer flow component was directed beneath the ice and provided heat adequate to melt the ice and limit advance of the edge the resulting low salinity meltwater was mixed vertically to maintain the front by wind acting across a highly mobile hydrodynamically rough ice cover subtidal fluctuations were not significantly affected by the front or the ice cover and local winds accounted for less than one quarter of the observed current variability the remainder being probably due to regional variations in the barotropic flow

low frequency variations in currents near the shelf break northeast gulf of alaska abstract we present current observations from depths of 20 50 100 and 175 m obtained over a 3 year period near the northeast gulf of alaska shelf break and emphasize a 2 year continuous segment from 50 m depth these records indicate that a moderate 16 cm s 1 at 50 m mean flow was directed at all depths along shelf toward the northwest variance was high and had nearly normal distributions in along and across shelf components the mean alongshelf speed varied from 12 cm s 1 in summer to 20 cm s 1 in winter and a more distinct seasonal cycle was evident in monthly kinetic energies of wind and current very low frequency vlf 0 8 at 95 level fluctuating kinetic energy of the current contained in the vlf band was a significant fraction 34 of the total kinetic energy and displayed an increase over the two years with no seasonal trend trends in the wind ki

reply to comment by a fiori et al on comparison of fickian and temporally nonlocal transport theories over many scales in an exhaustively sampled sandstone slab

saw toothed pattern of relative paleointensity records and cumulative viscous remanence several studies of relative paleointensity data derived from marine sediments spanning the last 4 myr display an asymmetrical saw toothed pattern polarity reversals of the geomagnetic field are associated with low points in paleofield intensity preceded by a long term progressive decay of the field and followed by a rapid post transitional recovery 1 3 since similar behavior is observed in far flung sites whose rock magnetic records are different it is argued that the world wide saw toothing represents geomagnetic field behavior 3 we present an alternative explanation calling on the effect of hard viscous remanence

power law breakthrough curve tailing in a fracture the role of advection summary we offer an explanation of the strongly tailed solute breakthrough curve typically observed when a tracer test is conducted in fractured bedrock in this example we limit the model to a single planar fracture of varying aperture flow heterogeneity derives from variable fracture aperture which implies variable transmissivity t the analysis employs a physically based model well suited to strong heterogeneity and relies only upon advective transport the purely advective model is able to explain a power law trend of magnitude 2t o 3 in the breakthrough curve tail a range that has been found in field tracer experiments the principle cause of this trend is the comparatively slow transport in zones of small transmissivity tight aperture slow advection occurs when either heterogeneity variance of ln t i s strong or when the assumed heterogeneity distribution is non gaussian thus we link breakthrough tailing to the statistical parameters for the transmissivity field

on exchange of water between the gulf of alaska and the bering sea through unimak pass we present the first long term current and bottom pressure observations from unimak pass alaska and adjacent locations on the gulf of alaska and bering sea shelves vector mean current recorded between march and august 1980 was 12 cm s toward 284 t or onto the bering sea shelf however magnitude decreased from 20 cm s to 6 cm s between the first and second halves of the record at shorter periods 3 10 days current fluctuations in the pass were strongly coherent k2 0 7 with the pressure difference measured along the axis of the pass and this was coherent with geostrophic wind estimates the results indicated that wind induced sea level perturbation was the dominant forcing mechanism for fluctuations relations among current bottom pressure pressure difference and geostrophic wind time series also showed that dynamic variaton on the gulf of alaska shelf was primarily responsible for current fluctuations in the pass hydrographic data indicated that a baroclinic current existed along the gulf of alaska coast and this flow became the long term mean flow through the pass we suggest that this feature was the extension of the kenai current the historic supposition that water is transported from the gulf of alaska into the bering sea was verified however the waters are of coastal origin rather than from the alaskan stream

dynamics of the foehn mechanism in the mcmurdo dry valleys of antarctica from polar wrf foehn events over the mcmurdo dry valleys mdvs the largest ice free region of antarctica promote glacial melt that supports biological activity in the lakes streams rocks and soils although mdvs foehn events are known to depend upon the synoptic scale circulation the physical processes responsible for foehn events are unknown a polar optimized version of the weather research and forecasting model polar wrf is used for a case study of a representative summer foehn event from 29 december 2006 to 1 january 2007 in order to identify and explain the mdvs foehn mechanism pressure differences across an elevated mountain gap upstream of the mdvs provide forcing for southerly flow into the western upvalley entrance of the mdvs complex terrain over the elevated gap and the mdvs leads to mountain wave effects such as leeside acceleration hydraulic jumps wave breaking and critical layers these mountain wave effects depend on the ambient geostrophic wind direction pressure driven channelling then brings the warm dry foehn air downvalley to eastern mdv sites brief easterly intrusions of maritime air into the eastern mdvs during foehn events previously have been attributed to either a sea breeze effect in summer or local cold pooling effects in winter in this particular case the easterly intrusions result from blocking effects of nearby ross island and the adjacent antarctic coast temperature variability during the summer foehn event which is important for meltwater production and biological activity when it exceeds 0 c primarily depends on the source airmass rather than differences in foehn dynamics

formation and circulation of the cold intermediate layer in the gulf of saint lawrence 1 the local heat content and formation rate of the cold intermediate layer cil in the gulf of saint lawrence are examined using a combination of new in situ wintertime observations and a three dimensional numerical model the field observations consist of five moorings located throughout the gulf over the period of november 2002 to june 2003 the observations demonstrate a substantially deeper surface mixed layer in the central and northeast gulf than in regions downstream of the buoyant surface outflow from the saint lawrence estuary the mixed layer depth in the estuary remains shallow 60 m throughout winter with the arrival of a layer of near freezing waters between 40 and 100 m depth in april an eddy permitting ice ocean model with realistic forcing is used to hindcast the period of observation the model simulates well the seasonal evolution of mixed layer depth and cil heat content although the greatest heat losses occur in the northeast the most significant change in cil heat content over winter occurs in the anticosti trough the observed renewal of cil in the estuary in spring is captured by the model the simulation highlights the role of the northwest gulf and in particular the separation of the gaspe current in controlling the exchange of cil between the estuary and the gulf in order to isolate the effects of inflow through the strait of belle isle on the cil heat content we examine a sensitivity experiment in which the strait is closed this simulation shows that the inflow has a less important effect on the cil than was suggested by previous studies

padm2m a penalized maximum likelihood model of the 0 2 ma palaeomagnetic axial dipole moment summary we present a new time varying model for palaeomagnetic axial dipole moment padm for the past 2 myr and compare it with earlier virtual axial dipole moment vadm reconstructions which have been based on stacking and averaging scaled relative palaeointensity records the padm is derived from both absolute and relative palaeointensity data and constructed using a new penalized maximum likelihood pml approach to recover a cubic b spline representation of axial dipole field variations on million year timescales the pml method is explicitly intended to reduce bias in estimating the true axial dipole moment that arises in average vadm reconstructions we apply the pml method to a set of 96 032 published data 1800 palaeointensities from igneous rocks 3300 archaeointensities and 86 relative palaeointensity time series of variable lengths and resolutions two models are discussed padm2mp is a trial model based on a subset of the nine longest available sedimentary records padm2m uses a comprehensive data set 76 records 81 446 data 10 records were eliminated and is our preferred model padm2m has a lower mean than existing vadm reconstructions but shows similarities in long period variability some differences in timing amplitude and resolution of certain features can be attributed to variations in age assignments others result from our more comprehensive data set and a reduction in bias attributable to pml modelling padm2m has an average axial dipole moment over 0 2 ma of 5 3 1022 am2 with a standard deviation of 1 5 1022 am2 the brunhes chron average 6 2 1022 am2 is higher than for earlier epochs of matuyama 4 8 1022 am2 as seen in some previous studies the power spectrum for our model agrees with previous estimates of the global palaeomagnetic power spectrum for frequencies up to about 102 myr 1 we see no distinctive evidence in the power spectrum for orbital forcing of geodynamo behaviour

a theoretical study of mountain barrier jets over sloping valleys abstract a shallow water model is developed to examine the dynamics of mountain barrier jets over a mesoscale sloping valley between two mountain ridges in this model the cold air trapped in the valley is represented by a shallow water layer that is coupled with the upper layer flow through a free slip interface the pressure gradient exerted from the upper layer plus the pressure gradient generated by the sloping cold layer itself drive the cold air down the valley forming a jet against the surface friction in the cross valley direction the jet induced coriolis force is balanced by the pressure gradient force for a given cross valley terrain profile the solution is controlled by eight dimensional environmental parameters in the nondimensional space the solution is controlled only by three parameters the froude number modified by the ratio between the valley width and the rossby radius of deformation the surface drag coefficient normalized by the ratio between the valley depth and the inertial r

astronomical ages for miocene polarity chrons c4ar c5r 9 3 11 2 ma and for three excursion chrons within c5n 2n abstract ocean drilling program odp site 1092 from the sub antarctic south atlantic produced a clear magnetic stratigraphy for the late miocene evans h f channell j e t upper miocene magnetic stratigraphy from odp site 1092 sub antarctic south atlantic recognition of cryptochrons in c5n geophys jour int 153 2003 483 496 three short intervals of reverse polarity were identified within the long 1 myr normal polarity subchron c5n 2n these excursion chrons were tentatively correlated to the three cryptochrons identified within subchron c5n 2n from ne pacific marine magnetic anomaly data new oxygen isotope data from odp site 1092 have allowed astronomical calibration of eight polarity chron boundaries in the interval between c4ar 1n and c5r 1n 9 3 11 2 ma as well as calibration of the three excursion chrons identified within c5n 2n the new polarity chron ages in the c4ar 1n c5r 1n interval differ from a current 2004 timescale by up to 48 kyr the astrochronology yields durations in the 3 4 kyr range for the three excursion chrons in c5n 2n the relative paleointensity record from site 1092 and hence the three excursion chrons can be correlated to the deep tow magnetic anomaly record from 19 s on the east pacific rise epr based on published correlation of the epr deep tow record with the sea surface magnetic anomaly stack from the ne pacific the three excursion chrons do not correspond to the cryptochrons recognized in the ne pacific stack

dynamical aspects of the flow through the strait of belle isle abstract we present an analysis of 50 days of current meter and sea revel data collected in a long narrow strait connecting the gulf of st lawrence to the atlantic ocean the dynamical balances implied by a scale analysis of the equation of motion are compared with the data for semidiurnal and diurnal tides and for low frequency flows the main result being that the near surface currents along the strait are as expected in geostrophic balance with the sea level slope across the strait the flow appears to be driven by the sea level difference between opposite ends of the strait produced by large scale meteorological forcing and a regression model involving acceleration and friction suggests a spindown time of 1 1 days the near bottom currents are significantly less than those new the surface at both levels the currants are reasonably uniform across the channel apart from the possibility of nearshore intensification at the lower level the vertical and horizontal structure of the low frequency curre

the structure and evolution of gap outflow over the gulf of tehuantepec mexico abstract mesoscale model simulations are used to examine the structure and dynamics of a gap outflow event over the gulf of tehuantepec mexico that was associated with a surge of cold air along the eastern slopes of the sierra madre the simulated gap outflow winds emerged from chivela pass reached a maximum speed of 25 m s 1 and turned anticyclonically as they fanned out over the gulf northerly winds were also able to ascend the mountains east and to a lesser extent west of chivela pass indicating that the movement of cold air across the sierra madre was not confined to the pass a mesoscale pressure ridge was aligned along the axis of the gap outflow jet which was flanked to the west by an anticyclonic eddy and to the east by a weaker cyclonic eddy a model derived trajectory along the axis of the outflow jet traced an inertial path with anticyclonic curvature produced primarily by the coriolis acceleration the cross flow pressure gradient acceleration along this trajectory was negligible be

deciphering records of geomagnetic reversals polarity reversals of the geomagnetic field are a major feature of the earth s dynamo questions remain regarding the dynamical processes that give rise to reversals and the properties of the geomagnetic field during a polarity transition a large number of paleomagnetic reversal records have been acquired during the past 50 years in order to better constrain the structure and geometry of the transitional field in addition over the past two decades numerical dynamo simulations have also provided insights into the reversal mechanism yet despite the large paleomagnetic database controversial interpretations of records of the transitional field persist they result from two characteristics inherent to all reversals both of which are detrimental to an ambiguous analysis on the one hand the reversal process is rapid and requires adequate temporal resolution on the other hand weak field intensities during a reversal can affect the fidelity of magnetic recording in sedimentary records this paper is aimed at reviewing critically the main reversal features derived from paleomagnetic records and at analyzing some of these features in light of numerical simulations we discuss in detail the fidelity of the signal extracted from paleomagnetic records and pay special attention to their resolution with respect to the timing and mechanisms involved in the magnetization process records from marine sediments dominate the database they give rise to transitional field models that often lead to overinterpret the data consequently we attempt to separate robust results and their subsequent interpretations from those that do not stand on a strong observational footing finally we discuss new avenues that should favor progress to better characterize and understand transitional field behavior

freshening of the alaska coastal current recorded by coralline algal ba ca ratios arctic ocean freshening can exert a controlling influence on global climate triggering strong feedbacks on ocean atmospheric processes and affecting the global cycling of the world s oceans glacier fed ocean currents such as the alaska coastal current are important sources of freshwater for the bering sea shelf and may also influence the arctic ocean freshwater budget instrumental data indicate a multiyear freshening episode of the alaska coastal current in the early 21st century it is uncertain whether this freshening is part of natural multidecadal climate variability or a unique feature of anthropogenically induced warming in order to answer this a better understanding of past variations in the alaska coastal current is needed however continuous long term high resolution observations of the alaska coastal current have only been available for the last 2 decades in this study specimens of the long lived crustose coralline alga clathromorphum nereostratum were collected within the pathway of the alaska coastal current and utilized as archives of past temperature and salinity results indicate that coralline algal mg ca ratios provide a 60 year record of sea surface temperatures and track changes of the pacific decadal oscillation a pattern of decadal to multidecadal ocean atmosphere climate variability centered over the north pacific algal ba ca ratios used as indicators of coastal freshwater runoff are inversely correlated to instrumentally measured alaska coastal current salinity and record the period of freshening from 2001 to 2006 similar multiyear freshening events are not evident in the earlier portion of the 60 year ba ca record this suggests that the 21st century freshening of the alaska coastal current is a unique feature related to increasing glacial melt and precipitation on mainland alaska

evidence for gap flows in the birch creek valley idaho abstracta field study was conducted of flows in the birch creek valley in eastern idaho there is a distinct topographic constriction in the birch creek valley that creates two subbasins an upper and lower valley the data were classified into one of three groups based on synoptic influence weak absent high wind speeds and other evidence of synoptic influence gap flows commonly developed downwind of the constriction in association with the weak absent group but also occurred in association with the two synoptic groups suggesting the potential for more diverse origins in general the frequency and strength of gap flows appeared to be linked to the development of the requisite thermal regime and minimization of any synoptically driven southerly winds that would suppress outflows gap flows were characterized by high wind speeds with jetlike vertical profiles along the axis of the lower valley for all three groups the morning transition in the upper valley and western sidewall usually proceeded sligh

the 1993 superstorm cold surge frontal structure gap flow and tropical impact in the wake of the eastern united states cyclone of 12 14 march 1993 a cold surge originating over alaska and western canada brought northerlies exceeding 20 m s21 and temperature decreases up to 158c over 24 h into mexico and central america this paper addresses the multiscale aspects of the surge from the planetary scale to the mesoscale focusing on 1 the structure and evolution of the leading edge of the cold surge 2 the reasons for its extraordinary intensity and equatorward extent and 3 the impact of the surge on the tropics specifically on the strength of the trade winds and on the sea surface temperature in the eastern pacific the cold surge was initiated as a developing cyclone over the gulf of mexico and an upstream anticyclone east of the rockies caused an along barrier pressure gradient to form forcing topographically channeled northerlies along the rocky and sierra madre mountains to transport cold air equatorward on the mesoscale the leading edge of the cold surge possessed nonclassical frontal structure for example as the cold surge entered mexico the coldest air and the strongest wind arrived at about 900 hpa before affecting the surface suggestive of a tipped forward leading edge to the surge also satellite imagery and surface observations indicate that the leading edge appeared to be successively regenerated in the warm presurge air the cold surge had characteristics reminiscent of a kelvin wave a tipped forward cold front a pressure jump line a bore and a gravity current but none of these conceptual dynamical models was fully applicable associated with the cold surge gap winds up to 25 m s21 were observed in the gulfs of tehuantepec a tehuantepecer fonseca papagayo and panama owing to the strong cross mountain pressure gradient in the case of the tehuantepecer a rope cloud emanated from the isthmus of tehuantepec and turned anticyclonically consistent with an inertial oscillation on the synoptic and planetary scales the extraordinary equatorward extent of the cold surge was aided by topographic channeling similar to cold air damming by a low latitude upper tropospheric trough and by the lower branch of the secondary circulation associated with a confluent jet entrance region aloft the cold surge also impacted the tropical atmosphere and ocean by contributing to the strengthening of the northeast trade winds over the eastern pacific ocean and by inducing local cooling of the sea surface temperature in the gulfs of tehuantepec and papagayo by about 48 88c

satellite observations of the wind jets off the pacific coast of central america part ii regional relationships and dynamical considerations abstract satellite estimates of winds at 10 m above the sea surface by the nasa scatterometer nscat during the 9 month period october 1996 june 1997 are analyzed to investigate the correlations between the three major wind jets along the pacific coast of central america and their relationships to the wind and pressure fields in the inter american seas and eastern tropical pacific comparisons with sea level pressure confirm the conventional view that tehuantepec wind variations are driven by pressure variations in the gulf of mexico associated with north american cold air outbreaks the three jets sometimes developed sequentially from north to south statistically however the papagayo and panama jets were poorly correlated with variations of the tehuantepec jet over the nscat observational period the papagayo and panama jets were significantly correlated with each other and were coupled to coherent variations of the trade winds extending from the caribbean sea to the eastern tropical pacific the det

low frequency sea level variability in the vicinity of the east river tidal strait the east river is a narrow tidal strait connecting long island sound with the lower hudson estuary the sound and estuary both communicate with the new york bight subtidal fluctuations in sea level difference between the ends of the strait which are coherent with barotropic flow through the strait are produced mainly by direct setup in the sound and estuary and by sea level fluctuations primarily wind forced in the bight approximately 70 of the variance in subtidal sea level difference can be accounted for by the two components of wind stress the direction of dominant wind forcing wind stress direction producing maximum response varies considerably with frequency response functions relating sea level difference to wind stress components computed for 128 day series for sea level and winds allow us to interpret the direction of dominant forcing in terms of the relative contributions of direct setup and sea level fluctuations in the bight

a census of mesoscale eddies in shelikof strait alaska during 1989 over a 5 month period in the spring and summer of 1989 12 mesoscale eddies were identified crossing a section of moored current meters in the shelikof sea valley this represents the first census of mesoscale eddies on the northwestern gulf of alaska continental shelf the majority of eddies 7 were observed in may and june anticyclonic eddies outnumbered cyclonic eddies two to one but all had characteristics similar to eddies previously observed in the region analysis of the current meter time series revealed that the mean speeds volume transport and the structure of the flow at the present location were similar to current meter and hydrographic measurements during other years in the sea valley we suggest that 1989 was a typical year in terms of eddy formation as well the proliferation of mesoscale eddies in this region in spring has an impact on the larval dispersal and eventual recruitment of walleye pollock

frictional processes in straits friction and mixing can be dynamically significant in straits as in many oceanographic situations for weak time dependent homogeneous flows geostrophy friction and acceleration can all play roles in limiting the flow through a strait and the ratio of the geostrophic elevation difference across the strait to the frictional difference along the strait may be of importance in more general situations a specific question for quasi steady exchange flows through straits concerns the influences of friction and entrainment on hydraulic control within the context of layered models these effects tend to drive a flow towards hydraulic criticality in the downstream direction and to shift control points downstream however friction and entrainment also induce vertical gradients in velocity and density rendering layered models dubious in such situations the conditions for hydraulic control have been uncertain even for a homogeneous fluid there is an apparent contradiction between control conditions based on a similarity assumption for the velocity profile on the one hand and on the speed of long waves on the other the resolution of this contradiction is discussed it seems that if the frictional forces only involve local flow properties then inviscid long waves are arrested at the control section though this is shifted from its location for inviscid flow but that if flow derivatives along the channel are involved the condition changes for a homogeneous flow with shear internal friction and bottom friction the control section is shifted downstream partway to where it would be for a slab flow with bottom friction while the parameterization of bottom friction actually seems to be reasonably well established the nature and quantification of internal and lateral frictional processes are uncertain in a rotating system secondary cross strait flows are expected to be driven by the vertical gradient of the vertical reynolds stress and can provide estimates of the magnitude of bottom and internal friction

remote sensing of the correlation between breakpoint oscillations and infragravity waves in the surf and swash zone a novel remote sensing methodology to determine the dominant infragravity mechanism in the inner surf and swash zone in the field is presented video observations of the breakpoint motion are correlated with the shoreline motion and inner surf zone water levels to determine the relationship between the time varying breakpoint oscillations and the shoreline motion the results of 13 field data sets collected from three different beaches indicate that inside the surf zone the dominance of bound wave or breakpoint forcing is strongly dependent on the surf zone width and the type of short wave breaking infragravity generation by bound wave release was stronger for conditions with relatively narrow surf zones and plunging waves breakpoint forcing was dominant for wider surf zones and spilling breaker conditions

on a recent solute transport laboratory experiment involving sandstone and its modeling 1 we analyze and simulate laboratory data on flow and solute transport in a submeter scale sample of massillon sandstone and we re evaluate studies that have stated that these data indicate a failure of the advection dispersion and that nonlocal modeling approaches are necessary our examination reveals experimental issues including artificial edge effects in the data as well as inconsistency in the measured solute injection rates when the edge effects are removed the data no longer exhibit power law tailing our simulations show that failure of the advection dispersion equation has not been demonstrated and that nonlocal approaches are not necessary

transport through unimak pass alaska we examined inflow through unimak pass 200 m deep which is the only major connection between the shelves of the north pacific ocean and the eastern bering sea geostrophic transport was generally northward from the gulf of alaska into the bering sea the flow through the pass appeared to be modulated by the seasonal cycle of freshwater discharge on shorter time scales transport also was affected by semi daily variations in tidal mixing this effect was significant and not anticipated near bottom currents measured from moorings were maximum during winter and significantly correlated r 0 7 with the alongshore winds although the flow through unimak pass transported some nutrients from the north pacific ocean the gulf of alaska shelf is not the major source of nutrients to the bering sea shelf

foehn jets over the larsen c ice shelf antarctica previously unknown foehn jets have been identified to the east of the antarctic peninsula ap above the larsen c ice shelf these jets have major implications for the east coast of the ap a region of rapid climatic warming and where two large sections of ice shelf have collapsed in recent years during three foehn events across the ap leeside warming and drying is seen in new aircraft observations and simulated well by the met office unified model metum at 1 5 km grid spacing in case a weak southwesterly flow and an elevated upwind inversion characterise a highly nonlinear flow regime with upwind flow blocking in case c strong northwesterly winds characterise a relatively linear case with little upwind flow blocking case b resides somewhere between the two in flow regime linearity the foehn jets apparent in aircraft observations where available and metum simulations of all three cases are mesoscale features up to 60 km in width originating from the mouths of leeside inlets through back trajectory analysis they are identified as a type of gap flow in cases a and b the jets are distinct being strongly accelerated relative to the background flow and confined to low levels above the larsen c ice shelf they resemble the shallow foehn of the alps case c resembles a case of deep foehn with the jets less distinct the foehn jets are considerably cooler and moister relative to adjacent regions of calmer foehn air this is due to a dampened foehn effect in the jet regions in case a the jets have lower upwind source regions and in the more linear case c there is less diabatic warming and precipitation along jet trajectories due to the reduced orographic uplift across the mountain passes

high resolution 10be and paleomagnetic recording of the last polarity reversal in the chiba composite section age and dynamics of the matuyama brunhes transition we present new magnetic direction and relative paleointensity and beryllium isotope 10 be 9 be and 10 be 9 be ratio results covering the last geomagnetic reversal i e the matuyama brunhes transition mbt from the chiba composite section cbcs east central japan the very high sedimentation rates 90 cm ka of the studied site a candidate site for the global boundary stratotype section and point gssp of the lower middle pleistocene boundary allow the acquisition of a dataset of exceptional resolution coupled cosmogenic 10 be and magnetic results measured on the same samples demonstrate that the magnetization acquisition conserved the timing of rapid geomagnetic features allowing accurate paleomagnetic interpretations a polarity switch ps capturing most of the angular deviation occurring between 771 9 and 773 9 ka was followed by a directional instability rebound ic1 until 768 5 ka this sequence with 5 4 ka duration was characterized by a weak dipole field as low as 2 3 0 3 10 22 am 2 four rapid episodes of directional instabilities preceding and following the ps ic1 phase completed the reversal sequence the asymmetry observed between the long term dipole decay and sharp recovery and rapid oscillations 1 ka demonstrate the complex transitional field behavior during dipole moment low before reestablishment of the full polarity state our observations reinforce the fact that most reversal records do not integrate the full field behavior associated with the geodynamo action although this poses problems for understanding the underlying physical processes that produce reversals it does not hamper stratigraphic correlations among most geologic records

low level easterly winds blowing through the tsugaru strait japan part ii numerical simulation of the event on 5 10 june 2003 abstractthis paper investigates the structures of and diurnal variations in low level easterly winds blowing through the tsugaru strait and mutsu bay on 5 10 june 2003 using a numerical weather prediction model cool air that accompanies prevailing easterly winds owing to the persistence of the okhotsk high intrudes into the strait and the bay below 500 m during the nighttime and retreats during the daytime this cool air intrusion and retreat induce diurnal variations in the winds in the east inlet of the strait in mutsu bay and in the west exit of the strait in the east inlet a daytime increase in air temperature within the strait produces a large air temperature difference with the inflowing cool air and the resulting pressure gradient force accelerates the winds the cool air flowing into mutsu bay is heated over land before entering the bay during the daytime the resulting changes in cool air depth and in pressure gradient force strengthen the daytime winds in the west exit local pressure gra

variability in the gulf of alaska from geosat altimetry data satellite altimetry was used to examine annual and interannual variability in the gulf of alaska region crossover data from the geosat geodetic mission gm and collinear data from the exact repeat mission erm were processed separately to form sea surface height anomalies at grid points the time series from the gm and erm were then combined to produce a 3 75 year data set the time series from the erm data set agreed fairly well with hydrographic dynamic heights at several locations with an average correlation of 0 70 between the two data sets the combined and erm altimetric data sets were analyzed using empirical orthogonal functions eofs these revealed variability that occurs primarily on annual and interannual time scales a comparison with eof analysis of the atmospheric pressure field during the same time periods showed that the annual variation in pressure seemed to be reflected in both the combined and erm altimetric data sets the amplitude time series of the first mode in the combined data set was very similar to the north pacific pressure index during the 1985 1989 time frame the maximum correlation was at a lag of 250 days finally an interannual mode was present in all three data sets which was closely linked to the baroclinic variations measured by the hydrographic data

glacial meltwater input to the alaska coastal current evidence from oxygen isotope measurements results of a study of the oxygen isotopic composition of coastal pelagic and fresh waters from the northern gulf of alaska region are presented this study was undertaken to investigate whether isotopic tracers could be of use in determining the important freshwater inputs to the alaska coastal current acc and whether they could confirm the presence of the acc in coastal waters west of kodiak island the alaska coastal current the major coastal circulation feature of the northern gulf of alaska can be distinguished from oceanic waters on the basis of its lower salinity at least as far west as kodiak island this study adds significantly to the small amount of oxygen isotopic information available for the waters of this region the isotopic results suggest that in late summer glacial meltwater may provide a substantial portion of the total freshwater runoff into the acc and that the acc does extend as far to the west as unimak pass

idealized three dimensional modeling of seasonal variation in the alaska coastal current 1 seasonal variation of the buoyancy and downwelling wind forced alaska coastal current acc and the fate of freshwater contained in it is considered using idealized analytical and numerical models of the acc formed from a half line source of buoyant inflow the coastal current initially develops two dimensionally but becomes three dimensional from a balance between coastal influx of buoyancy and its downstream transport which leads to a coastal current depth limit hmax 1 2 where x is along shelf distance q is the line source strength for unit length f is the coriolis frequency and g is the reduced gravity of the buoyant inflow this limit is unchanged under downwelling wind stress and is reached on timescales of less than 1 month for the acc the coastal current width is roughly constant in x and increases in time at the same rate as the two dimensional solution imposition of a downwelling wind stress results in an approximate balance among wind stress and along and cross shelf momentum advection so that the current width is reduced to ywind ld 1 2 where ld is the rossby radius of deformation is the wind stress and 0 is a reference density waves eddying motions eventually grow in the half line source coastal current with wavelengths proportional to the coastal current width and with a downstream phase speed slower than the maximum current speed these features cause an offshore flux of buoyant water a broader coastal current and further accumulation of buoyancy on the shelf increasing downwelling wind stress reduces the effects of the instabilities continual accumulation of buoyancy on the shelf occurs during all model runs but is nearly absent under maximum winter downwelling wind stress it is suggested that freshwater accumulation on the shelf during spring summer and fall may be largely lost downstream during winter

sea level variations in relation to coastal flow around the gulf of alaska adjusted sea level deviations at six tide stations around the gulf of alaska were examined in light of our recent knowledge of the flow regime on the east side of the gulf a maximum in the deviations seems to be caused by winter barotropic flow on the shelf on the north side of the gulf the maximum in fall is apparently produced by a marked increase in flow of the baroclinic coastal current farther west the seasonal sea level signal is appreciably reduced

eruptions of pavlof volcano and their possible modulation by ocean load and tectonic stresses all nine magmatic eruptions at pavlof volcano in six of the years from 1973 to 1984 have occurred between september 9 and november 20 volumes of erupted material range from 0 1 to 15 9 106 m3 dense rock equivalent at an average rate of 3 106 m3 yr 1 the volumes are estimated from eyewitness reports for two eruptions the others are estimated from a relationship that we derive between eruption volume and harmonic tremor duration and amplitude the volume of lava erupted is approximately time predictable a significant correlation exists between the eruptions and yearly nontidal variations in sea level and may result from ocean loading calculated volume changes beneath the volcano due to ocean loading are from 0 02 to 2 times eruption volumes and we postulate that the volcano acts as a long period several month volume strain meter with lava being preferentially erupted when strain beneath the volcano is compressive the volcano did not erupt during the period 1978 1980 when tilt seismic data and sea level data indicate that deep aseismic slip may have occurred models of this event predict a volume increase beneath the volcano that might have compensated strain from magma injection these observations indicate that pavlof volcano may be responsive to small slow changes in ambient stresses or strains and that these changes may modify or trigger eruptions

numerical simulation of a low level jet over complex terrain in southern iran the lut desert of iran is an elongated valley oriented north northwest to south southeast the valley descends southward to the jaz murian dry lake through a pass the navy s coupled ocean atmosphere mesoscale prediction system is used to study a northerly low level jet in the valley and across the dry lake the dynamics of the jet are investigated with force balance and froude numbers to determine the contribution of various mechanisms to the jet formation and maintenance the jet is initiated as a channeled gap flow in the convergent topography of the lut valley by the valley parallel pressure gradients generated by the large scale processes and by the presence of cold air over the valley s sloping terrain the pressure gradient is mainly counteracted by the frictional force the imbalance between them controls the intensity and persistence of the jet in the valley farther south the jet evolves into a downslope flow resembling a hydraulic jump on the steep slope of the dry lake a transition of subcritical situation to supercritical faster flow is found at the mountain crest between the lut valley and dry lake the depth of stably stratified cold layer the static stability of upstream inversion and magnitude of upstream winds all determine the jet configuration over the dry lake the lee troughing over the gulf of oman and the persian gulf as the large scale inland flow crosses the coastal mountains supports this low level jet through the increased along jet pressure gradient the jet is also influenced by diurnal forcing being strong at night and weak during daytime

modeling effects of tidal and wave mixing on circulation and thermohaline structures in the bering sea process studies 1 ocean circulation and the tidal current in the bering sea are simulated simultaneously using a coupled ice ocean model ciom with tidal and parameterized wave mixing to investigate several important physical processes the simulated circulation pattern in the deep basin is relatively stable cyclonic and has little seasonal change the bering slope current is estimated at 5 sv and the kamchatka current at 20 sv the modeled volume transports through the aleutian passes compared reasonably well with observations it is confirmed that subtidal clockwise circulation around st george and st paul islands are driven by tidal rectification the simulation results show that wind wave mixing and tidal stirring are the main factors controlling the formation of the upper and the bottom mixed layers respectively the mechanism of thermocline and the cold pool summer minimum temperature water formation in the middle shelf are investigated in depth the ciom reproduces the cold winter convective water in the middle shelf that forms the bottom cold pool which persists throughout the summer until sea surface cooling and strong wind mixing in fall leading to an unstable vertical water column and eventually to vertically well mixed water in the winter sensitivity experiments show that tidal and wind wave mixing are two important factors in accurately estimating the volume of the cold pool which is the ideal marine habitat for cold water species

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

a multiwinter analysis of channeled flow through a prominent gap along the northern california coast during caljet and pacjet abstract experimental observations from coastal and island wind profilers aircraft and other sensors deployed during the california land falling jets experiment of 1997 98 and the pacific land falling jets experiment of 2000 01 2003 04 were combined with observations from operational networks to document the regular occurrence and characteristic structure of shallow 400 500 m deep cold airstreams flowing westward through california s petaluma gap from the central valley to the coast during the winter months the petaluma gap which is the only major air shed outlet from the central valley is 35 50 km wide and has walls extending at most a modest 600 900 m above the valley floor based on this geometry together with winter meteorological conditions typical of the region e g cold air pooled in the central valley and approaching extratropical cyclones this gap is predisposed to generating westward directed ageostrophic flows driven by along gap pressure differences two case studies and a fiv

geomagnetic dipole strength and reversal rate over the past two million years independent records of relative magnetic palaeointensity from sediment cores in different areas of the world can be stacked together to extract the evolution of the geomagnetic dipole moment1 2 and thus provide information regarding the processes governing the geodynamo so far this procedure has been limited to the past 800 000 years 800 kyr ref 3 which does not include any geomagnetic reversals here we present a composite curve that shows the evolution of the dipole moment during the past two million years this reconstruction is in good agreement with the absolute dipole moments derived from volcanic lavas which were used for calibration we show that at least during this period the time averaged field was higher during periods without reversals but the amplitude of the short term oscillations remained the same as a consequence few intervals of very low intensity and thus fewer instabilities are expected during periods with a strong average dipole moment whereas more excursions and reversals are expected during periods of weak field intensity we also observe that the axial dipole begins to decay 60 80 kyr before reversals but rebuilds itself in the opposite direction in only a few thousand years

the nutrient salinity and stable oxygen isotope composition of bering and chukchi seas waters in and near the bering strait seawater nutrient salinity and oxygen 18 data collected from 1990 to 1993 in the bering and chukchi seas were used to identify potential sources of nutrients and water masses that result in formation of the arctic ocean upper halocline and its associated nutrient maximum water matching the delta sup 18 o values of the arctic ocean upper halocline and containing sufficient or a nearly sufficient nutrient and salinity concentration was collected in subsurface waters in the summer in portions of the bering sea particularly the gulf of anadyr however nutrient concentrations significantly declined in this north flowing water over the shallow continental shelf before it reached the bering strait as a consequence of biological utilization and dilution with nutrient poor and oxygen 18 depleted fresh water therefore it does not appear likely that the flow of unaltered water through the bering strait in the summer plays a critical role in the formation of the arctic ocean upper halocline the role of other mechanisms for contributing pacific derived waters to the arctic ocean nutrient maximum is considered copyright 1997 american geophysical union

gap flows through idealized topography part ii effects of rotation and surface friction numerical simulations are conducted of geostrophically balanced flow over an isolated mountain cut by a horizontal gap the relative importance of the along gap synoptic scale pressure gradient and terraininduced mesoscale circulations for the generation of gap winds was examined by changing the direction of the synoptic scale wind relative to the topography in all cases the forcing associated with mesoscale circulations generated by the mountain was at least as significant as the synoptic scale pressure gradient in the cases where a component of the large scale flow was directed perpendicular to the ridge the dynamics were dominated by either the vertical momentum fluxes due to mountain lee waves or by mesoscale pressure gradients associated with upstream blocking or lee troughing mesoscale circulations were also important when the large scale flow was parallel to the ridge because surface friction turned the low level winds toward the high pressure side of the ridge partially blocking the flow and enhancing the along gap pressure gradient the flow in the interior of a very long uniform gap was also simulated for a case with the synoptic scale winds parallel to the ridge so that the synoptic scale pressure gradient was down the gap the flow in the interior of the long gap was not horizontal and not in a simple dynamical balance between acceleration the pressure gradient force and surface friction even the flow in the lowest 150 m was gradually subsiding subsidence and lateral momentum flux convergence at low levels near the center of the gap were important contributors to the mass and along gap momentum budgets

ultrahigh resolution marine magnetic anomaly profiles a record of continuous paleointensity variations a distinctive pattern of small scale marine magnetic anomalies 25 100 nt amplitude 8 25 km wavelength tiny wiggles is superimposed on the more generally recognized seafloor spreading pattern between anomalies 24 and 27 in the indian ocean by normalizing and stacking multiple profiles it is demonstrated that this pattern of tiny wiggles is a high resolution recording of paleodipole field behavior between chrons c24 and c27 the pattern of tiny wiggles between anomalies 26 and 27 is compared to an ultrafast spreading 82 mm yr half rate profile from the southeast pacific where a similar signal is observed confirming the paleodipole field origin of the anomalies two basic models are considered in which the tiny wiggles are attributed either to short polarity intervals or to paleointensity fluctuations we conclude that tiny wiggles are most likely caused by paleointensity fluctuations of the dipole field and are a ubiquitous background signal to most fast spreading magnetic profiles the implications of this study are that 1 tiny wiggles may provide information on the temporal evolution of the geomagnetic dynamo 2 the small scale anomalies observed in the jurassic quiet zones may be due to paleointensity fluctuations 3 tiny wiggles are potential time markers in large regions of uniform crustal polarity such as the cretaceous quiet zones and 4 much of the variance in anomaly profiles normally attributed to crustal eraplacement processes particularly at fast and ultrafast spreading rates is actually due to intensity variations in the paleomagnetic field

distribution and transport patterns of northern rock sole lepidopsetta polyxystra larvae in the southeastern bering sea abstract we report the size abundance and distribution horizontal vertical of northern rock sole lepidopsetta polyxystra larvae collected from ichthyoplankton surveys on the southeastern bering sea shelf near unimak island in unimak pass and in the gulf of alaska south of unimak island the greatest abundances of larvae occurred within unimak pass and in the bering sea northeast of unimak island larvae were smaller and more abundant in 2002 than in 2003 larval abundance and size varied with depth highest abundances were at depths of 10 30 m during the day and larger fish appeared to migrate from below 20 m to 0 10 m at night there was evidence of multiple spawning locales and larval dispersal pathways that were depth and area specific northern rock sole larvae spawned west of unimak pass along the aleutian islands may be transported northward by the bering slope current larvae spawned in the gulf of alaska and advected through unimak pass are differentially dispersed primarily to the middle and outer shelves along the 100 m and 200 m isobaths or along the alaska peninsula larvae spawned along the alaska peninsula east of unimak island appear to have the greatest chance of being transported to nursery areas in the coastal domain dispersal of near surface northern rock sole larvae in any of these locations is likely influenced by wind driven advection but below surface 10 m northern rock sole larval transport is probably more affected by factors that modulate geostrophic flow rather than wind driven surface currents

long term observations of north atlantic current transport at the gateway between western and eastern atlantic in the western north atlantic warm and saline water is brought by the north atlantic current nac from the subtropics into the subpolar gyre four inverted echo sounders with high precision pressure sensors pies were moored between 47 40 n and 52 30 n to study the main pathways of the nac from the western into the eastern basin the array configuration that forms three segments northern central and southern allows partitioning of the nac and some assessment of nac flow paths through the different mid atlantic ridge fracture zones we exploit the correlation between the nac transport measured between 2006 and 2010 and the geostrophic velocity from altimeter data to extend the time series of nac transports to the period from 1992 to 2013 the mean nac transport over the entire 21 years is 27 5 sv consisting of 60 warm water of subtropical origin and 40 subpolar water we did not find a significant trend in the total transport time series but individual segments had opposing trends leading to a more focused nac in the central subsection and decreasing transports in the southern and northern segments the spectral analysis exhibits several significant peaks the two most prominent are around 120 days identified as the time scale of meanders and eddies and at 4 9 years most likely related to the nao transport composites for the years of highest and lowest nao indices showed a significantly higher transport 2 9 sv during strong nao years mainly in the southern segment

comment on comparison of fickian and temporally nonlocal transport theories over many scales in an exhaustively sampled sandstone slab by e d major et al

diffuse spectral reflectance of surficial sediments indicates sedimentary environments on the shelves of the bering sea and western arctic abstract visible diffuse spectral reflectance dsr has been described by previous workers as an efficient tool for extracting lithological compositions clay minerals iron oxyhydroxides carbonates and diatoms in sedimentary material the spatial patterns of these components are essential to understanding the processes driving their distribution and accumulation in the marine environment some of these processes include sea ice variability nutrient supply current flow patterns current strength sediment supply provenance and bathymetry the dsr derivatives and varimax rotated principal component analysis vpca of the spectral data collected from 234 core samples identified five leading components that account for variations in sediment lithology of the surface samples from the bering sea and western arctic these spectral components were then matched to spectral standards to identify the mineral assemblages responsible for them the components responsible for the vpca trends are chlorite muscovite goethite phycoerythrin phycocyanin smectite calcite dolomite and illite chlorophyll a the spatial pattern of the inorganic components is indicative of provenance and processes controlling their transportation and depositional patterns while the organic components are indicative of areas of primary productivity and driving mechanisms the chlorite muscovite assemblage which is sourced dominantly from the yukon river has maximum values on the bering sea shelf this is the source of the chlorite muscovite transport to the chukchi sea the chlorite muscovite assemblage also has a main transport route to the aleutian basin in the northern bering sea shelf the chukchi sea on the western arctic ocean shelf is a region of highly reducing condition this is based on the lowest values for the goethite phycoerythrin phycocyanin assemblage supported by the high carbonate concentrations at this location the carbonate distribution pattern on the bering sea shelf also appears to be tidally influenced this is because their spatial pattern divides the bering shelf into three domains which are similar to the three hydrographic domains on the bering shelf a function of tidal influence the smectite assemblage reaches maximum values along the coast of the chukotka peninsula in the chukchi sea denoting the chukotka peninsula as a major source area of smectite and supporting the notion for volcanically derived sediment to the chukchi sea another likely source of smectite to the chukchi sea is via the bering strait the illite in the illite chlorophyll a assemblage shows maximum values and distribution on the western arctic ocean shelf indicating the western arctic ocean shelf to be a main province of illite all the high values of the illite chlorophyll a component on the bering sea shelf are chlorophyll a from diatoms our results support the usefulness of the dsr method as an effective and efficient tool for provenance analysis and understanding the processes controlling sediment and biologic distribution in this case in the marine environment

sea level variability due to meteorological forcing in the northeast gulf of st lawrence in an attempt to understand the causes of low frequency flow through the strait of belle isle we relate sea level data from four stations in the northeast gulf of st lawrence to meteorological forcing our main tool is a multiple regression at each frequency of sea level on local atmospheric pressure and two orthogonal large scale pressure gradients which represent geostrophic winds the results show an inverted barometer response to atmospheric pressure and a frequency dependent response to wind which can be tentatively interpreted in terms of coastal setup due to wind driven longshore currents or barotropic setup of semi enclosed regions such as the northeast gulf or the whole gulf a simple model for barotropic flow through the strait is developed in order to provide an estimate from data at the western end of the strait of sea level changes on the labrador shelf

gap winds in the strait of juan de fuca abstract gap winds can be defined as a flow of air in a sea level channel which accelerates under the influence of a pressure gradient parallel to the axis of the channel in february 1980 two distinct cases of gap winds were observed in the strait of juan de fuca between western washington state and british columbia during a study that measured spatial variation of low level marine winds and other parameters from the noaa p 3 research aircraft and a dense network of surface stations which included eight meteorological buoys these two cases were a high pressure region over central british columbia and a low pressure system propagating northward seaward of the washington coast both cases produced strong easterly winds of 13 15 m s 1 at the western end of the strait of juan de fuea the high pressure region provided a drainage air mass from the interior of british columbia which flowed through the straits of georgia and juan de fuca and eventually into the pacific ocean this air mass remained nearly hom

observations of the phase of tidal currents along a strait abstract the phase of the m2 surface elevation tide changes by 100 along a 40 km length of cook strait new zealand acoustic doppler current profiler measurements are presented that show a change of only 12 in the phase of depth averaged semidiurnal tidal currents along this same length this phase change supports the general result developed by vennell which states that the phase of the cross sectional average velocity is approximately constant along a short strait of variable cross sectional area vennell also developed a relationship between the constant phase of tidal currents along the strait and the amplitude and phase of the surface elevation tide at the ends of a short strait the velocity phase given by this relationship is shown to agree well with the observed tidal velocity phase in cook strait and one other strait

comment on comparison of fickian and temporally nonlocal transport theories over many scales in an exhaustively sampled sandstone slab by elizabeth major et al

numerical simulations and observations of airflow through the alenuihāhā channel hawaii abstractduring the summer sustained winds in the alenuih h channel hawaii may exceed 20 m s 1 with higher gusts the advanced research weather research and forecasting model is used to diagnose airflow in the hawaiian coastal waters high resolution 2 km runs are performed for july 2005 covering the alenuih h channel and nested in a 6 km state domain under normal trade wind conditions 7 8 m s 1 winds at the channel entrance are 1 2 m s 1 faster than upstream due to the convergence of the deflected airflows by the islands of maui and hawaii and accelerate through the channel due to along gap pressure gradients and lower pressure in the wakes of both islands the acceleration is accompanied by descending airflow 9 cm s 1 in the exit region with lowering of the trade wind inversion deceleration occurs downstream of the channel exit with a rapid change from sinking motion to rising motion 3 cm s 1 under normal or strong trade wind conditions the flow is subcritical froude number fr

geomagnetic intensity variations over the past 780 kyr obtained from near seafloor magnetic anomalies knowledge of past variations in the intensity of the earth s magnetic field provides an important constraint on models of the geodynamo a record of absolute palaeointensity for the past 50 kyr has been compiled from archaeomagnetic and volcanic materials and relative palaeointensities over the past 800 kyr have been obtained from sedimentary sequences but a long term record of geomagnetic intensity should also be carried by the thermoremanence of the oceanic crust here we show that near seafloor magnetic anomalies recorded over the southern east pacific rise are well correlated with independent estimates of geomagnetic intensity during the past 780 kyr moreover the pattern of absolute palaeointensity of seafloor glass samples from the same area agrees with the well documented dipole intensity pattern for the past 50 kyr a comparison of palaeointensities derived from seafloor glass samples with global intensity variations thus allows us to estimate the ages of surficial lava flows in this region the record of geomagnetic intensity preserved in the oceanic crust should provide a higher time resolution record of crustal accretion processes at mid ocean ridges than has previously been obtainable

magnetic paleointensity stratigraphy and high resolution quaternary geochronology successes and future challenges abstract magnetic paleointensity stratigraphy is used to detect variations in the strength of earth s ancient magnetic field paleointensity studies have demonstrated that a dominantly dipolar geomagnetic signal can be recorded in a globally coherent manner in different types of sediments and in non sedimentary archives including ice core records and marine magnetic anomaly profiles the dominantly dipolar nature of geomagnetic paleointensity variations provides a global geophysical signal that has come to be widely used to date quaternary sediments despite the many successful applications of paleointensity assisted chronology the mechanisms by which sediments become magnetized remain poorly understood and there is no satisfactory theoretical foundation for paleointensity estimation in this paper we outline past successes of sedimentary paleointensity analysis as well as remaining challenges that need to be addressed to place such work on a more secure theoretical and empirical foundation we illustrate how common concepts for explaining sedimentary remanence acquisition can give rise to centennial to millennial offsets between paleomagnetic and other signals which is a key limitation for using paleointensity signals for geochronology our approach is intended to help non specialists to better understand the legitimate uses and limitations of paleointensity stratigraphy while pointing to outstanding problems that require concerted specialist efforts to resolve

saw toothed pattern of sedimentary paleointensity records explained by cumulative viscous remanence abstract the relative paleointensity of the earth s magnetic field from odp site 851 has been characterized by progressive decay towards polarity reversals followed by sharp recovery of pre reversal values 1 we resampled the gilbert gau reversal boundary of this deep sea core and show that during demagnetization this saw toothed pattern disappears further the recently published cumulative viscous remanence model 2 using the herewith obtained paleointensity record and constraints from thermal treatment replicates the saw tooth of 1 implying that it is of non geomagnetic origin

recent current observations in the eastern yellow sea observations of current velocity pressure and temperature in the eastern yellow sea from january 10 through april 12 1986 together with geostrophic winds calculated from surface atmospheric pressure distributions are analyzed for a study of the synoptic band response of the yellow sea to the wintertime winds north wind pulses in the winter monsoon are found to give rise to northward flow bursts in the yellow sea trough which appear to peak just as the wind relaxes and to be driven by a synoptic band north to south rise in bottom pressure synchronous with the north wind pulses the existence of a similar rise in coastal sea level indicates that the observed southward pressure rise is but an offshore extension of a setup along the west coast of south korea forced by the north wind pulses the advection by northward flow bursts of warm water from the south apparently causes the measured temperature to be substantially higher in the trough than in coastal waters at the same latitude and the observed rate of cooling in the trough to be less than half of that in coastal waters to the east a winter to spring transition is also found in the bottom pressure records obtained in the trough in which the mean north to south gradient in winter reverses suddenly in early march a similar reversal also appears in sea level records along the west coast of south korea the reversal appears to be triggered by the weakening of the north winds at the arrival of spring

circulation on the central bering sea shelf july 2008 to july 2010 1 we examine the july 2008 to july 2010 circulation over the central bering sea shelf using measurements at eight instrumented moorings hindcast winds and numerical model results at sub tidal time scales the vertically integrated equations of motion show that the cross shelf balance is primarily geostrophic the along shelf balance is also mainly geostrophic but local accelerations wind stress and bottom friction account for 10 40 of the momentum balance depending on season and water depth the shelf exhibits highly variable flow with small water column average vector mean speeds 5 cm s 1 mean peak speeds in summer 3 6 cm s 1 10 30 cm s 1 are smaller than in winter and fall 6 12 cm s 1 30 70 cm s 1 low frequency flows 1 4 cpd are horizontally coherent over distances exceeding 200 km vertical coherence varies seasonally degrading with the onset of summer stratification because effects of heating and freezing are enhanced in shallow waters warm summers increase the cross shelf density gradient and thus enhance northward transport cold winters with increased ice production and brine rejection increase the now reversed cross shelf density gradient and enhance southward transport although the baroclinic velocity is large enough to influence seasonal transports wind forced ekman dynamics are primarily responsible for flow variations the system changes from strong northward flow with coastal convergence to strong southward flow with coastal divergence for northerly and easterly winds respectively under northerly and northwesterly winds nutrient rich waters flow toward the central shelf from the north and northwest replacing dilute coastal waters that are carried south and west

sar derived gap jet characteristics in the lee of the philippine archipelago abstract gap jet characteristics were analyzed in the lee of the philippine archipelago during the 2004 2009 winter monsoon seasons november march using wind fields derived from envisat synthetic aperture radar sar images jet characteristics were derived for the philippine island gap jets and compared to those from theoretical literature and experimental studies it was found that 18 of 31 jets characterized from 13 sar images followed the defined power laws or classic case and were similar to the defined scale equations the remaining 13 jets did not follow the classic case and resulted from jet interaction with islands adjacent jets and variable atmospheric conditions these non classic jets were grouped based upon similarities and referred to as decreasing increasing and reverse classic cases distinct deviations from the classic case included downstream increases in velocity and decreases in jet width it was found that the orientation of the wind field relative to topography significantly impacted jet classification and thereby made it difficult to characterize jets by region for all 31 jets the initial jet width dictated the distance at which a jet became self similar wherein a larger initial jet width required a greater distance for self similarity

high resolution observations and numerical simulations of easterly gap flow through the strait of juan de fuca on 9 10 december 1995 abstract this paper examines the three dimensional flow and dynamics of easterly gap flow through the strait of juan de fuca on 9 10 december 1995 using high resolution observations and model simulations the observations were obtained during the fourth intensive observing period during the second phase of the coastal observation and simulation with topography field experiment one of the most important data sources was the noaa p 3 aircraft which provided flight level data reflectivity and doppler winds as it flew down the strait of juan de fuca below 900 m the flow accelerated from 7 to 14 m s 1 at the entrance to the strait with a significant cross gap component and confluence over the eastern sections of the strait below 500 m the easterly flow approaching the western exit of the strait accelerated from 15 to 20 m s 1 as the 900 m deep easterly flow exited the gap it decreased in depth and accelerated to 25 m s 1 creating a shallow swath of diffluent winds below 300 m later in the event whe

marine magnetic anomalies evidence that tiny wiggles represent short period geomagnetic polarity intervals since the 1960 s the geomagnetic polarity time scale which is based on marine magnetic anomalies has become fundamentally important in geochronology despite the importance of marine magnetic anomaly records there has been longstanding uncertainty about the meaning of the smallest anomalies observed in these records small amplitude short wavelength anomalies are frequently observed in marine magnetic anomaly records across fast spreading oceanic crust s 50 mm yr the origin of these small scale anomalies referred to as tiny wiggles has remained controversial over the last 30 years tiny wiggles have been interpreted to represent either short period polarity intervals or largescale fluctuations in the ancient field intensity we present palaeomagnetic evidence from a sedimentary record from the north pacific ocean which demonstrates that two short but clearly resolvable polarity zones in addition to a probable geomagnetic excursion occur within chron c5n 2n 9 92 10 95 ma where three tiny wiggles have been reported on marine magnetic anomaly profiles relative palaeointensity data indicate that the field collapsed prior to and during the reversals and during the excursion but that it recovered to higher field intensities within the polarity intervals before collapsing to low values at the succeeding polarity transition this indicates that some tiny wiggles represent real short period geomagnetic polarity intervals while others may represent geomagnetic excursions the existence of such short polarity intervals confirms the predictions of statistical analyses of geomagnetic reversal frequency and indicates that tiny wiggles represent the maximum resolution of geomagnetic polarity intervals in marine magnetic anomaly records fl 2000 elsevier science b v all rights reserved

windstorms along the western side of the washington cascade mountains part i a high resolution observational and modeling study of the 12 february 1995 event abstract this paper describes the leeside wind event of 12 february 1995 in which a swath of strong low level easterly flow with gusts to 35 40 m s 1 extended downwind of a major gap in the cascade mountains over the puget sound lowlands low level easterly flow approaching the olympics was decelerated to less than 5 m s 1 resulting in enhanced over 30 cm snowfall along the windward side of the barrier in addition to conventional synoptic observations high resolution data sources were utilized profilers on both sides of the cascades a wsr 88d doppler radar located in northern puget sound and nonhydrostatic model simulations down to 1 km resolution with the exception of underpredicting heavy snowfall to the east of the olympics many of the mesoscale features of this event were realistically simulated including cold air damming over eastern washington strong winds downwind of the gaps a mountain wake downstream of mount rainier and flow splitting around the olympics a major objective of th

gap flow in an alpine valley during a shallow south fohn event observations numerical simulations and hydraulic analogue this paper examines the three dimensional structure and dynamics of southerly hybrid gap mountain flow through the wipp valley wipptal austria observed on 30 october 1999 using high resolution observations and model simulations the observations were obtained during a shallow south fohn event documented in the framework of the mesoscale alpine programme map three important data sources were used the airborne differential absorption lidar leandre 2 the ground based doppler lidar teaco2 and in situ measurements from the national oceanic and atmospheric administration p 3 aircraft this event was simulated down to 2 km horizontal resolution using the non hydrostatic mesoscale model meso nh the structure and dynamics of the flow were realistically simulated the combination of high resolution observations and numerical simulations provided a comprehensive three dimensional picture of the flow through the wipptal in the gap entrance region brenner pass austria the low level jet was not solely due to the channelling of the southerly synoptic flow through the elevated gap part of the wipptal flow originated as a mountain wave at the valley head wall of the brenner pass downstream of the pass the shallow fohn flow had the characteristics of a downslope windstorm as it rushed down towards the inn valley inntal and the city of innsbruck austria downhill of the brenner pass the strongest flow was observed over a small obstacle along the western side wall the nosslachjoch rather than channelled in the deeper part of the valley just to the east further north the low level jet was observed in the centre of the valley approximately halfway between brenner pass and innsbruck where the along axis direction of the valley changes from north to north north west the low level jet was observed to be deflected to the eastern side wall of the wipptal interaction between the stubaier alpen the largest and highest topographic feature to the west of the wipptal and the south westerly synoptic flow was found to be the primary mechanism responsible for the deflection the along and cross valley structure and dynamics of the flow were observed to be highly variable due to the influence of surrounding mountains localized steep slopes within the valley and outflows from tributaries the gschnitztal and the stubaital to the west of the wipptal for that shallow fohn case observations and simulations provided a large body of evidence that downslope flow created thinning thickening fluid and accelerations decelerations reminiscent of mountain wave hydraulic theory along the wipptal two hydraulic jump like transitions were observed and simulated i on the lee slope of the nosslachjoch and ii in the gschnitztal exit region a hydraulic solution of the flow was calculated in the framework of reduced gravity shallow water theory the down valley evolution of the froude number computed using leandre 2 p 3 flight level and teaco2 measurements confirmed that these transitions were associated with super to subcritical transitions copyright 2002 royal meteorological society

fluctuations of the paleomagnetic field during chron c5 as recorded in near bottom marine magnetic anomaly data near bottom magnetic data contain information on paleomagnetic field fluctuations during chron c5 as observed in both the north and south pacific the north pacific data include 12 survey lines collected with a spatial separation of up to 120 km and the south pacific data consist of a single long line collected on the west flank of the east pacific rise epr at 19 s the north pacific magnetic profiles reveal a pattern of linear short wavelength 2 to 5 km anomalies tiny wiggles that are highly correlated over the shortest 3 8 km to longest 120 km separations in the survey magnetic inversions incorporating basement topography show that these anomalies are not caused by the small topographic relief the character of the near bottom magnetic profile from anomaly 5 on the west flank of the epr formed at a spreading rate more than twice that of the north pacific displays a remarkable similarity to the individual and stacked lines from the north pacific survey area over distances corresponding to 1 m y 19 lows in the magnetic anomaly profile can be correlated between the north and south pacific lines modeling the lows as due to short polarity events suggests that they may be caused by rapid swings of the magnetic field between normal and reversed polarities with little or no time in the reversed state owing to the implausibly high number of reversals required to account for these anomalies and the lack of any time in the reversed state we conclude that the near bottom signal is primarily a record of paleointensity fluctuations during chron c5 spectral analysis of the north pacific near bottom lines shows that the signal is equivalent to a paleointensity curve with a temporal resolution of 40 to 60 kyr while measurements of the smallest separations of correctable dips in the field suggest a temporal resolution of 36 kyr

orographic influences on rainfall and track deflection associated with the passage of a tropical cyclone abstract in this study a nonhydrostatic mesoscale model coupled ocean atmosphere mesoscale prediction system coamps was adopted to simulate supertyphoon bilis 2000 and investigate the dynamics of orographic rain and track deflection accompanying the storm as it passes the central mountain range cmr of taiwan both the storm track and its associated orographic rainfall distribution are well predicted by the numerical model the intensity of the storm is underpredicted resulting in a discontinuous track due to the lack of specifying a bogus vortex at the time of model initialization cyclonic curvature of the storm track over the island topography track as well as major circulation features are similar to previous studies of landfalling typhoons affecting taiwan the model overpredicts the total amount of accumulated rainfall generalization of the flux model proposed in a 2001 study by lin and coauthors is used to help predict and understand the observed rainfall distribution by calculating bo

a new geomagnetic polarity time scale for the late cretaceous and cenozoic we have constructed a magnetic polarity time scale for the late cretaceous and cenozoic based on an analysis of marine magnetic profiles from the world s ocean basins this is the first time since heirtzler et al 1968 published their time scale that the relative widths of the magnetic polarity intervals for the entire late cretaceous and cenozoic have been systematically determined from magnetic profiles a composite geomagnetic polarity sequence was derived based primarily on data from the south atlantic anomaly spacings in the south atlantic were constrained by a combination of finite rotation poles and averages of stacked profiles fine scale information was derived from magnetic profiles on faster spreading ridges in the pacific and indian oceans and inserted into the south ariantic sequence based on the assumption that spreading rates in the south atlantic were smoothly varying but not necessarily constant a time scale was generated by using a spline function to fit a set of nine age calibration points

barrier jets during tamex abstract a barrier jet is frequently found along the northwestern coast of taiwan in the prefrontal southwesterly flow regime during the taiwan area mesoscale experiment tamex it has a maximum wind speed of 14 m s 1 at approximately 1 km above the surface with a vertical wind shear approximately 10 10 3 s 1 below and 4 10 3 s 1 above that altitude during tamex the southwesterly monsoon flow strengthens over taiwan when the low level pressure trough surface front moves toward the southeastern china coast the barrier jet is a result of the stably stratified airflow past an island obstacle under a small froude number o 1 flow regime during the occurrence of a barrier jet a windward pressure ridge is observed along the southwestern coast due to island blocking in low levels the incoming southwesterly flow decelerates off the southwestern coast and moves around the island along the western coast the deflected airflow accelerates northward with a large cross contour wind component down the p

asymmetry in growth and decay of the geomagnetic dipole revealed in seafloor magnetization abstract geomagnetic intensity fluctuations provide important constraints on time scales associated with dynamical processes in the outer core padm2m is a reconstructed time series of the 0 2 ma axial dipole moment adm after smoothing to reject high frequency variations padm2m s average growth rate is larger than its decay rate the observed asymmetry in rates of change is compatible with longer term diffusive decay of the adm balanced by advective growth on shorter time scales and provides a potentially useful diagnostic for evaluating numerical geodynamo simulations we re analyze the padm2m record using improved low pass filtering to identify asymmetry and quantify its uncertainty via bootstrap methods before applying the new methodology to other kinds of records asymmetry in distribution of axial dipole moment derivatives is quantified using the geomagnetic skewness coefficient s g a positive value indicates the distribution has a longer positive tail and the average growth rate is greater than the average decay rate the original asymmetry noted by ziegler and constable 2011 is significant and does not depend on the specifics of the analysis a long term record of geomagnetic intensity should also be preserved in the thermoremanent magnetization of oceanic crust recovered by inversion of stacked profiles of marine magnetic anomalies these provide an independent means of verifying the asymmetry seen in padm2m we examine three near bottom surveys a 0 to 780 ka record from the east pacific rise at 19 s a 0 to 5 2 ma record from the pacific antarctic ridge at 51 s and a chron c4ar c5r 9 3 11 2 ma record from the ne pacific all three records show an asymmetry similar in sense to padm2m with geomagnetic skewness coefficients s g 0 results from padm2m and c4ar c5r are most robust reflecting the higher quality of these geomagnetic records our results confirm that marine magnetic anomalies can carry a record of the asymmetric geomagnetic field behavior first found for 0 2 ma in padm2m and show that it was also present during the earlier time interval from 9 3 11 2 ma

a probabilistic assessment of the next geomagnetic reversal author s buffett b davis w abstract 2018 american geophysical union all rights reserved deterministic forecasts for the next geomagnetic reversal are not feasible due to large uncertainties in the present day state of the earth s core a more practical approach relies on probabilistic assessments using paleomagnetic observations to characterize the amplitude of fluctuations in the geomagnetic dipole we use paleomagnetic observations for the past 2 myr to construct a stochastic model for the axial dipole field and apply well established methods to evaluate the probability of the next geomagnetic reversal as a function of time for a present day axial dipole moment of 7 6 1022 a m2 the probability of the dipole entering a reversed state is less than 2 after 20 kyr this probability rises to 11 after 50 kyr an imminent geomagnetic reversal is not supported by paleomagnetic observations the current rate of decline in the dipole moment is unusual but within the natural variability predicted by the stochastic model

eruptions of pavlof volcano alaska and their possible modulation by ocean load and tectonic stresses re evaluation of the hypothesis based on new data from 1984 1998 thirteen of sixteen magmatic eruptions of pavlof volcano in nine of the years from 1973 to 1998 have occurred between september 9 and december 29 volumes of erupted material range from 0 3 to 16 10 6 m 3 dense rock equivalent a significant correlation exists between the eruptions and yearly nontidal variations in sea level and may result from ocean loading calculated volume changes beneath the volcano due to ocean loading are from 0 02 to 0 6 times eruption volumes and it is postulated that the volcano acts as a long period several months volume strainmeter with lava being preferentially erupted when strain beneath the volcano is compressive previous observations of a tilt reversal and new observations of tectonic activity and eruptions in the spring and summer of 1986 also suggest tectonic modulation of eruptions the volcano appears to be responsive to small slow changes in ambient stresses or strains and these changes may modify or trigger eruptions

contribution of volcanism and tectonism to axial and flank morphology of the southern east pacific rise 17 10 17 40 s from a study of layer 2a geometry multichannel seismic images from the east pacific rise 17 10 17 40 s are used to study the geometry of seismic layer 2a in the near axis region wave equation datuming is applied to stacked common midpoint data to remove the distorting effects of seafloor topography on the layer 2a event processed stacks are compared with seafloor morphology and tectonic fabric imaged in side scan sonar data assuming layer 2a corresponds with the extrusive crust these data are used to study the relationship between volcanism and tectonism in the accumulation of the extrusive layer and to assess the contribution of extrusives to ridge crest and ridge flank morphology we find variations in axial thickening of layer 2a which imply twofold variation in the width of the extrusive layer accumulation zone as well as systematic changes in the pattern of accumulation of this layer on the ridge flanks the layer 2a horizon mimics abyssal hill relief consistent with a horst and graben origin for this topography short wavelength variations in the thickness of layer 2a are superimposed on this relief which we attribute to volcanic modification of tectonic topography at the edge of the neovolcanic zone the integrated off axis thickness of layer 2a is correlated with ridge cross sectional area and indicates persistent 100 000 years spatial gradients in extrusive layer thickness systematic changes in the cross axis shape of the ridge observed over distances of 5 10 km cannot be attributed to the extrusive layer and it appears that axial structure beneath the volcanics governs the cross axis morphology of the ridge

the alaska coastal current continuity of transport and forcing current moorings were deployed on the continental shelf at 13 locations in the northwest gulf of alaska they measured the alaska coastal current at three positions along the coast during april october 1991 the strongest currents were in the confined region of shelikof strait mean daily transport was as large as 2 5 106 m3 s 1 mean transport over the 6 month period ranged from 0 85 106 m3 s 1 at the easternmost line off gore point to 0 64 106 m3 s1 at the westernmost section shelikof strait indicating significant transport to the south of kodiak island the transports were well correlated r 0 8 and in phase with each other and were also correlated with wind r 0 6 data suggest that in shelikof strait and off gore point baroclinic flow is 75 and 40 respectively of total transport

on the alaska coastal current in the western gulf of alaska analyses of wind adjusted sea level temperature salinity and current data show that the alaska coastal current acc flows generally westward from shelikof strait to the shumagin islands the seasonal nature of the acc in the western gulf of alaska is similar to that in the northern gulf but minimum salinity maximum current speeds and changes in baroclinic transport are less extreme to the west southwest of shelikof strait the acc apparently is bifurcated by the bathymetry one branch continues flowing along the alaska peninsula and the other flows south the southward flowing branch may rejoin the westward flowing one in the sea valley just east of the shumagin islands

mg ca ratios in coralline algae record northwest atlantic temperature variations and north atlantic oscillation relationships climate variability in the north atlantic has been linked in part to the north atlantic oscillation nao the nao influences marine ecosystems in the northwestern atlantic and transport variability of the cold labrador current understanding historic patterns of nao variability requires long term and high resolution climate records that are not available from instrumental data here we present the first century scale proxy record of sea surface temperature sst variability from the newfoundland shelf a region from which other annual resolution shallow marine proxies are unavailable the 116 year record was obtained from three sites along the eastern newfoundland shelf using laser ablation inductively coupled mass spectrometry determined mg ca ratios in the crustose coralline alga clathromorphum compactum the alga is characterized by a high mg calcite skeleton exhibiting annual growth increments and a century scale lifespan results indicate positive correlations between interannual variations in mg ca ratios and both station based and gridded instrumental sst in addition the record shows high spatial correlations to sst across the newfoundland shelf and the gulf of st lawrence before 1950 the mg ca proxy record reveals significant departures from gridded temperature records while the newfoundland shelf is generally considered a region of negative correlations to the nao the algal time series as well as a recent modeling study suggest a variable negative relationship with the nao which is strongest after 1960 and before the mid 1930s

tidal forcing of the water mass interface in the strait of messina the tidal currents of the strait of messina and their effect on the displacement of the water mass interface are discussed utilizing the historical velocity data of francesco vercelli taken from 100 anchor stations during 1922 and 1923 the data show a complex strongly tidal behavior in which speeds of 200 300 cm s are attained over the sill messina is an amphidromic point for the tides of the two main basins of the mediterranean sea and two distinct water masses flow through the strait at different stages of the tide the subsurface levantine intermediate water flowing north alternating with surface tyrrhenian water flowing south the time evolution of the interface between the two marine water layers at the semidiurnal periodicity is computed from the observed distribution of acceleration term for the baroclinic component this interface shows large vertical oscillations with amplitudes of 100 m intersecting both the surface and bottom the results are in reasonable agreement with recent satellite data and other recent field observations and numerical experiments an estimate of the mean position of the interface is made by assuming that the potential energy required to uplift the interface from the equilibrium depth of 150 m to the observed 30 m depth over the sill is derived from the time independent contribution of the nonlinear field acceleration term the results are in reasonable agreement with observations

a high resolution numerical simulation of the wind flow in the ross island region antarctica abstract a detailed description of the characteristics of the three dimensional wind flow for the ross island region of antarctica is presented this region of antarctica has complex topographic features and the wind flow is dependent on the topography and the local meteorological conditions high resolution nonhydrostatic numerical simulations are conducted over a high resolution domain in the ross island region two simulations are performed corresponding to the two dominant wind flow patterns in the ross island region the first simulation is a light wind case with a stable lower atmosphere and the second is a high wind speed event froude number calculations along with a study of the equation of motion are included for a more complete understanding of the dynamics of the wind flow the results of the simulations show a favorable correlation to past research results and observations and provide a more complete understanding of the three dimensional wind flow in the region in addition to a more tho

source of tiny wiggles in chron c5 a comparison of sedimentary relative intensity and marine magnetic anomalies 1 in addition to the well established pattern of polarity reversals short wavelength fluctuations are often present in both sea surface data tiny wiggles and near bottom anomaly data while a high degree of correlation between different geographical regions suggests a geomagnetic origin for some of these wiggles anomaly data alone cannot uniquely determine whether they represent short reversals or paleointensity variations independent evidence from another geomagnetic recording medium such as deep sea sediments is required to determine the true nature of the tiny wiggles we present such independent evidence in the form of sedimentary relative paleointensity from chron c5 we make the first comparison between a sedimentary relative paleointensity record odp site 887 at 54 n 148 w and deep tow marine magnetic anomaly data 43 n 131 w bowers et al 2001 for chron c5 the sediment cores are densely sampled at 2 5 kyr resolution the inclination record shows no evidence for reverse intervals within the 1 myr long normal chron c5n 2n rock magnetic measurements suggest that the primary magnetic carrier is pseudo single domain magnetite we choose a partial anhysteretic magnetization parm as our preferred normalizer and the resulting relative paleointensity record is used as input to a forward model of crustal magnetization we then compare the results of this model with the stacked deep tow anomaly records the two records show a significant degree of correlation suggesting that the tiny wiggles in the marine magnetic anomalies are likely produced by paleointensity variations an analysis of our sampling density suggests that if any reverse intervals exist at this site they are likely to be 5 kyr in duration furthermore we suggest that reverse intervals during chron c5n 2n documented in other locations are unlikely to be global

characteristics and variability of the inner front of the southeastern bering sea the inner front of the southeastern bering sea shows marked spatial variability in frontal characteristics created by regional differences in forcing mechanisms differences in forcing mechanisms sea ice advance retreat and storm strength and timing and early spring water properties result in strong interannual variability in biological chemical and physical features near the front we have developed a simple model based on surface heat flux and water column mixing to explain the existence of cold belts cont shelf res 19 14 1999 1833 associated with such fronts hydrography fluorescence and nutrient observations show that pumping of nutrients into the euphotic zone occurs and this can prolong primary production at the inner front the effectiveness of this process depends on two factors the existence of a reservoir of nutrients in the lower layer on the middle shelf and the occurrence of sufficient wind and tidal energy to mix the water column

orographic precipitation forcing along the coast of northern california during a landfalling winter storm abstractthis study documents orographic precipitation forcing along the coastal mountains of northern california during the landfall of a significant winter storm over the period 16 18 february 2004 the primary observing asset is a scanning x band doppler radar deployed on the coast at fort ross california which provides low level e g below 1 km msl horizontal and vertical scans of radial velocity and reflectivity to characterize airflow and precipitation structures further context is provided by a wind profiling radar a radio acoustic sounding system rass balloon soundings buoys a gps receiver and surface meteorological sensors the winter storm is divided into two episodes each having pre cold frontal low level jet llj structures and atmospheric river characteristics episode 1 has a corridor of terrain trapped airflow tta that forms an interface with the llj the interface extends 25 km offshore in a 0 5 km vertical layer and the western edge of this interface near the ocean surf