age distribution and stratigraphy of glacier peak tephra in eastern washington and western montana united states tephra layers from williams lake fen wildcat lake and east wenatchee washington and kearns basin lost trail pass sheep mountain bog and marys frog pond montana were analyzed by electron mi

numerical simulation of the transient response of the kuroshio leading to the large meander formation south of japan using a three dimensional primitive equation numerical model that takes realistic topography into account we successfully reproduce the observed transient response of the kuroshio south of japan during the transition from the nonlarge meander path to the large meander path the transient response is triggered by the generation of what is called the trigger meander off the southeastern coast of kyushu resulting from the supply of cyclonic vorticity through vertical stretching caused by the interaction between the kuroshio and the anticyclonic mesoscale eddy approaching the tokara strait the trigger meander thus generated propagates eastward south of shikoku while inducing an anticyclone cyclone pair in the lower ocean after the trigger meander passes cape shiono misaki it slows down and rapidly amplifies so that the kuroshio loops back west of the izu ogasawara ridge then the sharpness of the meander trough gradually relaxes and the large meander path is attained during the rapid amplification of the trigger meander off cape shiono misaki the abyssal anticyclone develops while being trapped by the local topographic feature koshu seamount located 200 km to the south of cape shiono misaki this abyssal anticyclone plays a crucial role in intensifying the trigger meander trough in the upper ocean via cross frontal advection the intensified trigger meander trough then further amplifies the abyssal anticyclone over koshu seamount this joint evolution of the upper ocean meander trough and the abyssal anticyclone suggests that baroclinic instability enhanced by koshu seamount is the dominant mechanism for the rapid amplification of the trigger meander leading to the large meander formation south of japan

interannual variability of the kuroshio transport in response to the wind stress field over the north pacific its relation to the path variation south of japan we have investigated the interannual variability in the kuroshio transport focusing on the baroclinic response of the upper ocean to the long term variation of the wind stress field over the north pacific from 1961 to 1987 first temporal change of the kuroshio transport at the western boundary from 17 to 31 n has been estimated on the assumptions that the kuroshio is a baroclinic flow confined in the upper layer and that the effect of interior wind stress curl on the volume transport at the western boundary is transferred by nondispersive baroclinic rossby wave peak values in the estimated transport appear in its beginning region 17 21 n when or just before the kuroshio settles into a meandering state south of japan in 1975 1981 and 1986 these peaks are due to negative wind stress curl anomalies which are induced by the intensified trade winds in the central and eastern tropical north pacific on and just after an el nino event and in the western tropical north pacific months to years before the next el nino event such peaks are not found in the barotropic sverdrup transport in downstream regions i e in the east china sea and south of japan north of 23 n on the contrary the estimated transports through baroclinic and barotropic responses do not have such good correlation to the path variation temporal change in thermocline depths estimated from bathythermograph data clearly shows the westward propagations of positive anomalies by nondispersive baroclinic rossby waves at latitudes of the beginning of the kuroshio south of 21 n which is in phase with peaks of the kuroshio baroclinic transport at the western boundary on the other hand there are only the local propagations of the anomalies in the downstream regions as previous studies reported however it is emphasized that temporal change of the geostrophic transport in the east china sea 28 n is coincident with that of the baroclinic transport at the beginning of the kuroshio not with that at the same latitude a numerical experiment with a nonlinear reduced gravity model confirms that temporal changes of the transport in the east china sea and south of japan are due to the advective nonlinear effect of the kuroshio itself while the linear baroclinic response to the wind stress field is dominant in its beginning region

effects of stretching on maintaining the kuroshio meander 1 using a two way nested grid ocean general circulation model driven by a repeat annual cycle forcing the kuroshio path variation is examined by varying the strength of wind forcing for climatological or 10 weaker wind forcing both large meander lm and non large meander nlm paths alternately appear with each type of path continuing for a few years to a decade this timescale and path transition processes are generally consistent with observations for the lm path the main balance in the depth integrated vorticity equation for the upper ocean is shown to be between the beta advection and stretching terms the stretching term is comparable to and has the same sign as the beta term at the western side of the meandering part indicating that the stretching term has the effects of shortening the wavelength and stabilizing the lm path the stretching term is mainly determined by downwelling caused by crossing of the upper and deep flows contrary to the above two cases only the nlm path appears for 10 stronger wind forcing it is suggested that the strength of climatological wind forcing is near the upper limit that allows the lm path to occur in this study the control experiment is carried out by choosing parameterizations and parameter values to reproduce the kuroshio path variation as realistic as possible therefore the results from the two sensitivity experiments are expected to represent a realistic response of the kuroshio path variation

a glacier peak and mount saint helens j volcanic ash couplet and the timing of deglaciation in the colville valley area washington a late pleistocene volcanic ash couplet consisting of a glacier peak ash layer and an underlying mount saint helens j ash layer has been identified at three sites in the colville valley area of nor

tephrochronology of late wisconsin deglaciation and holocene glacier fluctuations near glacier peak north cascade range washington abstract tephra layers near glacier peak in the north cascade range provide limiting dates for four periods of alpine glacier advance field relations suggest that late wisconsin alpine glaciers last advanced prior to the eruption of tephra layers from glacier peak about 11 250 yr b p late wisconsin deglaciation in the central north cascades was complete prior to the glacier peak tephra eruptions glaciers again expanded in the early holocene about 8400 8300 yr b p soil formed in alpine meadows during an episode of mild climate in the middle holocene prior to at least two intervals of glacier expansion an older episode between 5100 and 3400 yr b p and a younger episode within the last 1000 yr

geometry forced coherent structures as a model of the kuroshio large meander abstract the bimodality of the kuroshio path south of japan is presented from a new viewpoint of direct interaction of current with local coastal geometry by solving the barotropic quasi geostrophic equation in a channel with steplike coastal geometry we demonstrate that the model kuroshio can actually show the localized bimodal behavior for a reasonable range of inlet current speed the amplitude of the large meander is approximately given by 2umax in contrast to all nonlocal model results our local coherent structures have nothing to do with the basin size geometry such as kyushu and the izu ogasawara ridge in general the present study suggests that even a small feature of coastline geometry may trigger a big change in a nearshore current

formation process of the kuroshio large meander in 2004 1 formation process of the 2004 kuroshio large meander has been examined using a data assimilation and prediction system the small meander southeast of kyushu that occurred in december 2003 remains stationary until the next spring the vorticity analysis indicates that this small meander is maintained by a balance between the advection and the bottom pressure torque on the continental slope this balance is achieved as a result of reducing the advection by a westward propagating negative temperature anomaly originating in the wind stress field the small meander starts moving eastward around may 2004 when an anticyclonic eddy east of the tokara strait is intensified by coalescing of two anticyclonic eddies at that time a deep anticyclonic eddy is generated below the kuroshio by a cross frontal flow the deep anticyclonic eddy grows up during its eastward propagation then a southward flow in the eastern part of the eddy carries the kuroshio path offshore bringing about the large meander the eddy energetic analysis indicates that baroclinic instability is essentially responsible for this large meander formation the sensitivity analysis reveals that the small meander and the intensified anticyclonic eddy significantly affect the phase speed and the amplitude of the meander respectively it is also revealed that a slow phase speed and a large amplitude of the meander are regarded as conditions for the stationary large meander which is also applicable to the past large meanders in the 2004 large meander these conditions coexist by the stationary small meander staying until the intensified anticyclonic eddy triggers baroclinic instability

geomorphic and climatic change over the past 12 900 yr at swiftcurrent lake glacier national park montana usa abstract glaciated alpine landscapes are sensitive to changes in climate shifts in temperature and precipitation can cause significant changes to glacier size and terminus position the production and delivery of organic mass and in the hydrologic energy related to the transport of water and sediment through proglacial environments a sediment core representing a 12 900 yr record collected from swiftcurrent lake located on the eastern side of glacier national park montana was analyzed to assess variability in holocene and latest pleistocene environment the spectral signature of total organic carbon content toc since 7 6 ka matches that of solar forcing over 70 500 yr timescales periodic inputs of dolomite to the lake reflect an increased footprint of grinnell glacier and occur during periods when sediment sinks are reduced glacial erosion is increased and hydrologic energy is increased grain size carbon nitrogen c n ratios and toc broadly define the termination of the younger dryas chronozone at swiftcurrent lake as well as major holocene climate transitions variability in core parameters is linked to other records of temperature and aridity in the northern rocky mountains over the late pleistocene and holocene

late pleistocene and holocene seasonal temperatures reconstructed from fossil beetle assemblages in the rocky mountains abstract mutual climatic range mcr analysis was applied to 20 fossil beetle assemblages from 11 sites dating from 14 500 to 400 yr b p the fossil sites represent a transect of the rocky mountain region from northern montana to central colorado the analyses yielded estimates of mean july and mean january temperatures the oldest assemblage 14 500 yr b p yielded mean july values of 10 11 c colder than present and mean january values 26 30 c colder than present postglacial summer warming was rapid as indicated by an assemblage dating 13 200 yr b p with mean july values only 3 4 c cooler than modern by 10 000 yr b p several assemblages indicate warmer than modern mean summer and winter values by 9000 yr b p mcr reconstructions indicate that both summer and winter temperatures were already declining from an early holocene peak mean july values remained above modern levels and mean january values remained below modern levels until 3000 yr b p a series of small scale oscillations followed

the northern hemisphere tropospheric response to changes in the gravity wave drag scheme in a perpetual january gcm the sensitivity of a general circulation model climatology to changes in the gravity wave drag scheme is investigated with particular emphasis being placed upon the northern hemisphere wintertime tropospheric circulation it is found that by weakening the upper level drag the ferrel cell circulation intensifies to the north resulting in a greater than 10 k cooling in the region of the arctic tropopause the poleward side of the northern hemisphere sub tropical jet intensifies in the region of 60 70 n and a poleward shift is observed in the eddy meridional momentum flux a large part of the response is zonally asymmetric with the aleutian and icelandic lows becoming shallower with weakened upper level gravity wave drag by comparing the results of a gravity wave drag scheme having a wave breaking vertical profile with those of a simple uniform drag profile scheme it appears that the tropospheric response to weakened upper level drag depends very little upon the choice of vertical drag profile in the troposphere

major and trace element characterization expanded distribution and a new chronology for the latest pleistocene glacier peak tephras in western north america keuhn s c froese d g carrara p e foit jr f f pearce n j g rotheisler p 2009 major and trace element characterization expanded distribution and a new chronology for the latest pleistocene glacier peak tephras in western north america quaternary research 71 2 201 216 sponsorship nserc discovery grant alberta ingenuity new faculty award to duane froese

stable paths of the kuroshio south of japan determined by the wind stress field 1 to investigate the role of the wind stress field in determining stable paths of the kuroshio south of japan we have executed numerical experiments with a two layer wind driven ocean model changing zonal and meridional wind stress distributions four types of path two straight and two meandering paths have been found and their appearance has been classified into three categories in category i straight and meandering paths coexist multiple equilibrium only a meandering straight path appears in category ii iii a meandering path tends to appear when the sverdrup transport along the southern coast of japan decreases downstream strongly and the wind stress curl is anomalously negative in the western region near japan whereas a straight path is apt to occur with the positive anomaly detailed examination of the results has revealed the following mechanism determining stable paths of the kuroshio the wind stress field first determines the pressure difference p between the two ends of the southern coast of japan when p is smaller than a certain threshold only a meandering path can exist since the along coast pressure decrease in a straight path state is much larger than p category ii conversely when p is larger than another threshold only a straight path is consistent with the larger p category iii both paths can appear when p is between the two thresholds category i the climatological wind stress field in the north pacific subtropical region has been suggested to be in category i

homogenization of potential vorticity in planetary gyres the mean circulation of planetary fluids tends to develop uniform potential vorticity q in regions where closed time mean streamlines or closed isolines of mean potential vorticity exist this state is established in statistically steady flows by geostrophic turbulence or by wave induced potential vorticity flux at the outer edge of the closed contours the expelled gradients of q are concentrated beyond this transition lies motionless fluid or a different flow regime in which the planetary gradient of q may be dominant the homogenized regions occur where direct forcing by external stress or heating within the closed isoline is negligible upon the potential density surface under consideration in the stably stratified ocean such regions are found at depths greater than those of direct wind induced stress or penetrative cooling in channel models of the atmosphere we again find constant q when mesoscale eddies cause the dominant potential vorticity flux in the real atmosphere the results here can apply only where internal heating is negligible the derivations given here build upon the prandtl batchelor theorem which applies to non rotating steady two dimensional flow supporting evidence is found in numerical circulation models and oceanic observations

ensemble forecast of the kuroshio meandering 1 focusing on predictability of the kuroshio meandering we have done an ensemble forecast experiment the application of the method to the problem addressed seems to be the first comprehensive attempt in the community of physical oceanography by assimilating sea surface height anomaly into an ocean general circulation model in the preceding 40 day period the observed kuroshio meandering manifested south of japan in november 1999 was successfully predicted 2 months before the event the experiment yields a forecasting skill of the kuroshio meander position for 60 days in the sense that the rms error does not exceed the magnitude of the model climatic variation and those obtained from the non assimilated simulation and persistence in addition to a single trajectory forecast experiment ensemble forecasts were conducted using 10 perturbed initial states generated by the breeding method the predicted states realized as the ensemble members of the 80 day forecast are classified into two categories large and non large meander it is found that the intensity of an anticyclonic eddy in the initial state seems to play a key role in selecting one of the two states

two paradigms of baroclinic wave life cycle behaviour two idealized baroclinic wave 6 life cycles examined here suggest a framework of opposite extremes a in which to view the behaviour of real synoptic scale disturbances in middle latitudes and b in which to interrelate the synoptic and wave theoretic viewpoints using the saturation propagation saturation sps picture of wave 6 life cycle behaviour the two life cycles dented by lc1 and lc2 are higher resolution versions of the simmons hoskins basic and anomalous cases showing strong and weak late decay of eddy kinetic energy eke they illustrate in varying degrees two extreme types of behaviour here disignated anticyclonic and cyclonic and epitomized by strongly contrasting upper air trough behaviour anticyclonic behaviour dominates the late stages of lc1 and is characterized by backward tilted thinning troughs being advected anticyclonically and equatorward as in the commoner cases of planetary scale mid stratospheric rossby wave breaking cyclonic behaviour dominates lc2 and is characterized by forward tilted broadening troughs wrapping themselves up cyclonically and poleward producing major cut off cyclones in high latitudes these morphologies are visualized by upper air maps of potential temperature on the nominal tropopause defined as a constant potential vorticity surface some atmospheric mid latitude disturbances examined here using the same visualization applied to operational analyses show the same two extreme types of trough behaviour together with intermediate cases the sps picture is re examined using eliassen palm and refractive index cross sections it is shown in particular by reference to a wave activity theorem of haynes that the late stages of lc2 can be looked upon as a remarkably clear and morphologically novel large amplitude counterpart of the nonlinear reflection scenario of rossby wave critical layer theory the late stages of lc1 by constrast look more akin to an nonlinear critical layer absorption scenario lc2 exhibits region of largely undular pv contours adjacent to a nonlinear of irreversiby deformen pv contous in the latter region pv rearrangement and hence absorption of rossby wave activity has largely ceased this accounts for the more persistent ekee in the lc2 case

anticyclonic eddies and kuroshio meander formation a meander formation mechanism of the kuroshio that involves anticyclonic eddies propagating from the kuroshio extension is presented using the analysis of observations of the topex poseidon t p altimeter data and in situ data support of the mechanism comes also from a numerical simulation in october 1997 a current meter mooring over the izu ridge at 500 m depth captured large velocity fluctuations of about 50 cm s 1 that were associated with a strong anticyclonic eddy the observations from t p show that the anticyclonic eddy propagated westward and collided with the kuroshio off kyushu at collision the anticyclonic eddy coupled with a cyclonic circulation accompanied by a small meander and formed a vortex pair they were then advected downstream and finally formed a large meander like path off the south coast of honshu the meander lasted for a few months subsequently the anticyclonic eddy was detached and the meander grew smaller in amplitude numerical experiments successfully simulate this interaction between the kuroshio and anticyclonic eddies

late pleistocene stratigraphy and implications for deglaciation and subglacial processes of the flathead lobe of the cordilleran ice sheet flathead valley montana usa abstract the flathead lobe of the cordilleran ice sheet advanced and retreated across the flathead valley a 90 km long by 15 25 km wide basin the glacier terminated at the southern end of the flathead valley during its last glacial maximum i used geologic mapping sedimentologic study and mapping from 3300 descriptive water well logs to define the stratigraphy of glacial and post glacial deposits in the flathead valley and to infer subglacial processes and retreat rates units in the 30 200 m thick stratigraphic sequence include deep sand and gravel proglacial alluvium diamicton till locally gravelly silt and clay coarse grained subaqueous deposits at recessional moraines and glaciolacustrine deposits and surficial sand and gravel outwash and holocene stream deposits a nearly continuous till overlies alluvium and is in turn directly overlain by glaciolacustrine deposits glaciolacustrine shoreline indicators at altitudes of 940 958 m show that the flathead lobe receded as a proglacial lake expanded in that range of altitudes this lake the ancestral flathead lake was impounded behind bedrock that was downcut 60 78 m since the late pleistocene glaciolacustrine deposits are as much as 180 m thick in discontinuous troughs that locally cut through till to alluvium and bedrock the troughs are mostly 1 5 km in width 6 25 km in length sinuous in plan view and undulatory in longitudinal profile the troughs extend below the elevation of flathead lake and have been below local base level since glaciation these characteristics point to incision by meltwater hydrostatically pressurized beneath the flathead lobe in subglacial tunnel channels sand and gravel at the trough bases and part of the glaciolacustrine fill in the troughs are subglacial deposits tunnel channels that terminate at recessional moraines suggest excavation occurred sporadically during deglaciation the distribution of glaciolacustrine silts indicates that the flathead lobe retreated and the ancestral flathead lake expanded by 87 km before the lake outlet stream could downcut its dam by 500 m year 1

lake core record of grinnell glacier dynamics during the latest pleistocene deglaciation and the younger dryas glacier national park montana usa abstract few records in the alpine landscape of western north america document the geomorphic and glaciologic response to climate change during the pleistocene holocene transition while moraines can provide snapshots of glacier extent high resolution records of environmental response to the end of the last glacial maximum younger dryas cooling and subsequent warming into the stable holocene are rare we describe the transition from the late pleistocene to the holocene using a 17 000 yr sediment record from swiftcurrent lake in eastern glacier national park mt with a focus on the period from 17 to 11 ka total organic and inorganic carbon grain size and carbon nitrogen data provide evidence for glacial retreat from the late pleistocene into the holocene with the exception of a well constrained advance during the younger dryas from 12 75 to 11 5 ka increased detrital carbonate concentration in swiftcurrent lake sediment reflects enhanced glacial erosion and sediment transport likely a result of a more proximal ice terminus position and a reduction in the number of alpine lakes acting as sediment sinks in the valley

sensitivity of the eddy momentum flux to meridional resolution in atmospheric gcms abstract gcm experiments with zonally symmetric climates are used to demonstrate that the increase in the meridional eddy momentum fluxes and zonal surface winds that occurs when resolution is increased is primarily due to the increase in meridional rather than zonal resolution it is argued that the sensitivity to meridional resolution reflects the need to resolve the small scales generated in the rossby wave field as waves radiate from the midlatitude baroclinic eddy source region into regions with small mean winds some additional experiments highlight the sensitivity of surface winds and eddy momentum fluxes to the subgrid scale horizontal mixing formulation in low revolution models

new perspectives on the generation and maintenance of the kuroshio large meander abstractthe internal dynamical processes underlying the kuroshio large meander are investigated using a recently developed analysis tool multiscale window transform mwt and the mwt based canoni

data assimilation in the low noise regime with application to the kuroshio abstractonline data assimilation techniques such as ensemble kalman filters and particle filters lose accuracy dramatically when presented with an unlikely observation such an observation may be caused by an unusually large measurement error or reflect a rare fluctuation in the dynamics of the system over a long enough span of time it becomes likely that one or several of these events will occur often they are signatures of the most interesting features of the underlying system and their prediction becomes the primary focus of the data assimilation procedure the kuroshio or black current that runs along the eastern coast of japan is an example of such a system it undergoes infrequent but dramatic changes of state between a small meander during which the current remains close to the coast of japan and a large meander during which it bulges away from the coast because of the important role that the kuroshio plays in distributing heat and salinity in the surrounding region prediction of these transit

the impact of changing the horizontal diffusion scheme on the northern winter climatology of a general circulation model a general circulation model was used in perpetual january mode to study the wintertime climatological sensitivity to changes in the horizontal hyper laplacian diffusion scheme at both spectral t21 and t42 horizontal resolutions analysis of the global energy cycle revealed a large impact especially on the conversion of eddy to zonal kinetic energy less diffusion resulted in less zonal available potential energy weaker baroclinic conversions and caused the barotropic conversion of eddy to zonal kinetic energy to become significantly weaker it was found that by weakening the diffusion in the t21 model the eddy kinetic energy increased and became more realistic yet at the same time the conversion of eddy to zonal kinetic energy decreased and became less realistic weakening the horizontal diffusion caused a northern hemisphere tropospheric response similar to that obtained by increasing the upper level orographic gravity wave drag in the model the zonal mean zonal winds weakened poleward of the subtropical jets the ferrel cells weakened and the troposphere warmed up at high latitudes the weakening of the zonal wind and the ferrel cells was associated with a weakening of the upper level convergence of the poleward eddy momentum flux and the wave mean flow interaction was demonstrated using eliassen palm diagnostics a substantial part of the change in the poleward eddy momentum flux was due to large changes in the poleward momentum flux of the transient eddies in the mid latitude stormtracks and changes in their horizontal phase tilt a large northern hemisphere stationary wave change appeared in these regions and had a similar structure in the atlantic sector to that seen when strengthening upper level gravity wave drag

bimodality of the kuroshio abstract a barotropic ocean model is used to study the bimodal behavior of the kuroshio to the south of japan by considering the combined effects of the beta plane the kyushu coastal perturbation the izu ridge and the sw ne tilted coastline the two frequently observed meander patterns have been numerically verified as the two quasi steady solutions contained n the model the small meander state is identified as an upstream disturbance largely forced by the izu ridge its width decreases as the strength of the current increases the large meander state is forced by the presence of both the kyushu wedge and the izu ridge topography for small volume transports the large meander state behaves like the small meander state in that the meander width decreases as the current speed increases for large volume transports it behaves like a lee rossby wave in that the width of the meander increases as the current speed increases the birth of the large meander state occurs as a consequence of the ocean spin do

kuroshio path variation south of japan 1 barotropic inflow outflow model we examined the dynamics of the variation in the path of the kuroshio current along the south coast of japan by use of a barotropic inflow outflow ocean model the model basin has an inclined coastline and includes a part of the east china sea so that we could investigate the effect of kyushu on the kuroshio we obtained three regimes of the kuroshio s path variation according to the magnitude of its inlet velocity vmax similar to the previous study the kuroshio takes a straight path along the south coast of japan in regime i with a low vmax a meandering path in regime ii with a high vmax and both of these paths multiple equilibrium state in regime iii with an intermediate vmax the transition from the straight state to the meandering state occurs with an increase in vmax from regime i iii to ii preceded by an eastward progression of a small meander which is produced as a separated vortex by the nonlinear effect of the flow and the effect of kyushu it takes 120 days consistent with observations the nonlinearity of the flow has two effects in the transition one causes a downstream shift of the small meander and the other enlarges it by pulling out positive vorticity from the no slip coast with an increase in the meander scale due to the latter effect the former effect becomes small to be balanced with the beta effect causing an upstream shift of the meander thus a large meander path is formed a small meander does not progress eastward to develop into a large meander until vmax exceeds a critical value this behavior causes a multiple equilibrium state in regime iii and only the meandering path in regime ii

the age of glacier peak tephra in west central montana at sheep mountain bog near missoula montana a late glacial tephra that probably fell in late summer is preserved as an 8 mm thick graded bed overlain by another 8 mm of redeposited ash mixed with lake deposits sediment surrounding the ash was 14c dated to about 11 200 yr b p electron microprobe analyses of the volcanic glass and hornblende phenocrysts from this ash layer indicate that they are similar in major element chemistry to those of glacier peak layer g previously considered to be about 12 000 yr old or older

dynamics of the kuroshio large meander two layer model abstract a simple two layered in outflow model is studied to explain the peculiarity of the kuroshio path the geometry south of japan with a length scale l and the characteristic velocity u of the kuroshio give an important parameter 2 u l the kuroshio can take two kinds of paths for a given value of multiple equilibria one is straight path and the other a meandering path the selection of a path the selection of a path in a multiple equilibrium state depends upon the history of the parameter the hysteresis phenomenon the combined effect of horizontal viscosity along the coast and the inclination of the coastline are essential factors which control the kuroshio path as well as an increase in the coastline inclination increases the effect of horizontal viscosity along the coast where a western boundary layer is formed due to the effect of an increase in the viscous effect along the coast makes a straight path possible when the inlet velocity is small the effect of stratification i

sensitivity of simulated climate to model resolution abstract dynamical measures of the climate e g winds eddy fluxes simulated by a general circulation model are compared at different horizontal and vertical resolutions for the december january and february period the simulations of the troposphere are found to improve significantly as the horizontal resolution increases in the range of spectral truncations from t21 to t63 little sensitivity is found to changes in vertical resolution between about 2 8 km and 0 7 km vertical grid spacing the improvements in the southern hemisphere troposphere are greater than in the northern hemisphere as the horizontal resolution increases the eddy momentum fluxes and kinetic energies in both hemispheres increase monotonically with horizontal resolution at t63 the southern hemisphere winds eddy fluxes and eddy kinetic energies agree favorably with observations while serious discrepancies are present at lower resolutions in the northern hemisphere the eddy momentum flux at t63 is slightly larger than obser

structure and variability of the kuroshio current in tokara strait four years of mooring array measurements in tokara strait south of kyushu japan from 1992 to 1996 are used to analyze the structure and temporal variability of the kuroshio current the mean kuroshio current in tokara strait shows a nearly permanent subsurface double core structure possibly due to topographic blockage effects the dominant variations of the kuroshio in tokara strait are separated into long term variability typically 100 day period and short term variability 10 days to 1 month according to spectrum and wavelet analysis the long term variability has a large horizontal scale across the strait with a striking twofold banded structure in spatial correlations this is due to the north south kuroshio axis shift that advects the double core structure of the mean current the axis shift can be indexed with the northeastward current velocity at the northernmost station a composite analysis using this index shows well defined northward and southward axis shift structures of the kuroshio current from the composite of the topex poseidon sea level anomaly in terms of this index the kuroshio axis shift and the current structure change are associated with a dipole shape sea level anomaly east of tokara strait on the other hand the short term variability of high kinetic energy only has a small horizontal scale within the northern part of the current which is related to frontal variability there exists a deep southwestward undercurrent below 600 m in the northern part of tokara strait flowing along the isobaths the undercurrent becomes stronger during the northward shift of the kuroshio axis while it almost disappears during the southward shift

columbia mountain landslide late glacial emplacement and indications of future failure northwestern montana usa abstract the well preserved and undissected columbia mountain landslide which is undergoing suburban development was studied to estimate the timing and processes of emplacement the landslide moved westward from a bedrock interfluve of the northern swan range in montana usa onto the deglaciated floor of the flathead valley the landslide covers an area of about 2 km2 has a toe to crown height of 1100 m a total length of 3430 m a thickness of between 3 and 75 m and an approximate volume of 40 million m3 deposits and landforms define three portions of the landslide from the toe to the head they are i clast rich diamictons made up of gravel sized angular rock fragments with arcuate transverse ridges at the surface ii silty and sandy deposits resting on diamictons in an internally drained depression behind the ridges and iii diamictons containing angular and subangular pebble to block sized clasts some of which are glacially striated in an area of lumpy topography between the depression and the head of the landslide drilling data suggest the diamictons cover block to slab sized bedrock clasts that resulted from an initial stage of the failure the landslide moved along a surface that developed at a high angle to the ne dipping thinly bedded metasediments of the proterozoic belt supergroup the exposed slope of the main scarp dips 30 37 w a hypothetical initial rotational failure of the lower part of a bedrock interfluve may have transported bedrock clasts into the valley the morphology and deposits at the surface of the landslide indicate deposition by a rock avalanche sturzstrom derived from a second stage of failure along the upper part of the scarp the toe of the columbia mountain landslide is convex west in planview except where it was deflected around areas now occupied by glacial kettles on the north and south margins landsliding therefore occurred during deglaciation of the valley while ice still filled the present day kettles available chronostratigraphy suggests that the 1 km thick glacier in the region melted before 12 000 14c years bp within 3000 years of the last glacial maximum deglaciation and hillslope failure are likely causally linked failure of the faceted interfluve was likely due tensile fracturing of bedrock along a bedding normal joint set shortly after glacial retreat from the hillslope open surficial tension fractures and grabens in the swan range are limited to an area above the crown of the landslide movement across these features suggests that extensional flow of bedrock sackung is occurring in what remains of the ridge that failed in the columbia mountain landslide the fractures and grabens likely were initiated during failure but their morphologies suggest active extension across some grabens continued movement of bedrock above the crown may result in future mass movements from above the previous landslide scarp landslides sourced from bedrock above the scarp of the late glacial columbia mountain landslide which could potentially be triggered by earthquakes are geologic hazards in the region

a 12 000 year radiocarbon date of deglaciation from the continental divide of northwestern montana during the pinedale late wisconsinan glaciation an outlet glacier from a mountain ice field flowed eastward across the continental divide through marias pass in northwestern montana this outlet glacier was the major source of the two medicine glacier a large piedmont glacier that extended from the mountain front east about 55 km onto the plains an accelerator mass spectrometry radiocarbon age of 12 194 145 bp aa 9530 was obtained from a wood fragment underlying a glacier peak tephra and a mount saint helens set j tephra in a section of lake sediments near marias pass this radiocarbon age provides a minimum date of deglaciation for the marias pass area that is about 800 years older than a previous estimate furthermore the radiocarbon age indicates that the two medicine glacier was no longer being supplied by its major source and if it still existed was only as a dying stagnant ice mass

effects of koshu seamount on the development of baroclinic instability leading to the kuroshio large meander abstractthe kuroshio south of japan shows bimodal path fluctuations between the large meander lm path and the nonlarge meander nlm path the transition from the nlm path to the lm path is triggered by a small meander generated off southwestern japan the small meander first propagates eastward downstream along the kuroshio and then rapidly amplifies over koshu seamount located about 200 km south of japan leading to the formation of the lm path of the kuroshio although koshu seamount is essential for the rapid amplification of the small meander the underlying physical mechanism is not fully understood in this study the role of koshu seamount is revisited using a two layer quasi geostrophic model that takes into account the effects of bottom topography numerical experiments show that the transition from the nlm path to the lm path can be successfully reproduced only when bottom topography mimicking koshu seamount is incorporated in this case the upper layer meander trough is rapidly amplified

west coast volcanic ashes provide a new continental scale lateglacial isochron abstract the lateglacial period 14 7 11 7 cal ka bp eruptions of mount st helens and glacier peak in the cascade range deposited ash layers tephras within a short time span across much of western north america where they form event stratigraphic marker layers or isochrons they were deposited at a time which has long been of interest because it represents the transition between two fundamental states of the climate system the late pleistocene glacial world when ice sheets were widespread and the modern interglacial holocene world this transition was marked by rapid changes in the distribution of plants animals and humans on the landscape and is characterised by short rapid climate reversals in the warming trend yet despite the importance of understanding this period for many areas of palaeoclimatology palaeobotany and archaeology it remains one of the most difficult for which to develop accurate chronologies because of fluctuations in atmospheric radiocarbon concentration hence the occurrences of distinctive tephra isochrons are valuable for chronological control here we report the first detection of the mount st helens set j and glacier peak tephras as closely spaced cryptotephra layers not visible in stratigraphy to the naked eye in three eastern seaboard lakes and dated to 13 74 13 45 cal ka bp the presence of these tephras 4000 km from their sources affords an opportunity for continent wide correlations by providing a high precision chronological benchmark that is otherwise often lacking in north american studies of palaeoenvironmental change and deglaciation megafaunal extinction and palaeoindian colonisation

numerical study on the kuroshio path states in the northern okinawa trough of the east china sea 1 previous observations have indicated that the kuroshio in the northern okinawa trough is quasibimodal in character with distinct northern and southern path states the kuroshio path states are examined here through simulations using a primitive inflow outflow model for 16 inflow structures parameterized by the location of maximum surface velocity and the rate of velocity decrease with depth the simulations reveal three distinct path states in the northern okinawa trough a weakly stable northern path state associated with blocking of an anticyclonic kuroshio meander a highly stable southern path state maintained by blocking of a cyclonic kuroshio meander and an intermediate unstable path state the variations in the unstable state occurring as either periodic transitions between the northern and southern path states or periodic fluctuations of an otherwise stable path are driven by self sustained internal oscillation in the northern okinawa trough cyclogenesis in the continental slope area due to baroclinic instability appears to play an important role in kuroshio path variations in the unstable state and this instability is effectively controlled by the location of the kuroshio mean path on the slope rather than its velocity as conventionally thought

a numerical study of the kuroshio south of japan abstract a numerical model is used to study the interaction of the kuroshio with boundary constraints south of japan the model consists of two layers with the lower layer inert and is both nonlinear and quasi geostrophic the boundary constraints are highly idealized the kyushu peninsula and its adjacent continental shelf have the form of a v shaped wedge on an otherwise rectilinear coastline the izu ridge is represented as a square island solutions almost always form a meander downstream from kyushu the dynamics of meander formation involve the interaction of a rossby lee wave generated by the kyushu peninsula and a westward disturbance forced by the izu ridge three different quasi steady paths have been identified the first path has a meander between kyushu and the izu ridge passes to the north of the ridge and is associated with a current of low volume transport the second path has a large meander between kyushu and the izu ridge passes to the south of the izu ridge and always occurs when

wind driven variability of the subtropical north pacific ocean abstractthe argo array provides a unique dataset to explore variability of the subsurface ocean interior this study considers the subtropical north pacific ocean during the period from 2004 to 2011 when argo coverage has been relatively complete in time and space two distinct patterns of argo dynamic height transport function are observed in 2004 05 the gyre is stronger and in 2008 09 it is weaker the orientation of the subtropical gyre also shifts over time the predominantly zonal major axis shifts to a more northwest southeast orientation in 2004 05 and to a more southwest northeast orientation in 2008 09 the limited temporal range of the argo observations does not allow analysis of the correlation of ocean transport and wind forcing in the basin for the multiyear time scale 6 8 yr period typical of the dominant gyre patterns the meridional geostrophic transport anomaly between 180 and 150 e is computed both from argo data 0 2000 db and from the sverdrup relation using reanalysis winds

long term enso like events represented in the middle pleistocene shelf successions boso peninsula japan abstract millennial century and decadal scale stratigraphic cyclicities are described from transgressive shelf successions of the middle pleistocene ichijiku and kakinokidai formations ca 0 7 ma in the boso peninsula japan the ichijiku formation ca 400 m thick represents a shelf sandridge complex developed under the influence of the large meanders of the paleo kuroshio current and intertongues with outer shelf muddy deposits of the kakinokidai formation ca 170 m thick to the northeast most of the two formations are classified as a transgressive systems tract formed during the rise in glacioeustasy from oxygen isotope stages 18 to 17 three different types of cyclicities are identified in the transgressive shelf deposits the first cyclicity ca 3000 years duration is represented by coarsening upward units of the kakinokidai formation associated with the northeastward extension of the sandridge complex lower parts of each coarsening upward unit are characterized by intercalations of tempestites more than the upper parts the second cyclicity ca 250 years duration is defined by master bedding surfaces within sandridge deposits interpreted as formed in response to lateral migration of foresets of the sandridge complex the third cyclicity ca a few decades or shorter duration is defined as the units bounded by reactivation surfaces within large scale trough cross bedded sandstone units the three different types of cyclicities are interpreted to document fluctuations in the paths and speeds of the paleo kuroshio current in response to the large meanders oscillations of the large meanders of the modern kuroshio current every few to 10 years are interpreted to be in response to enso el nino southern oscillation events and are also associated with the decrease in frequency of typhoons in the western pacific if our stratigraphic interpretation is true the paleo kuroshio current controlled shelf successions document high frequency oscillations in paleoclimates responding to the long term enso like events in the western pacific during the middle pleistocene

distinguishing meanders of the kuroshio using machine learning the kuroshio south of japan is often described as being bimodal with abrupt transitions between a straight path state that stays near the coast small meander and a meandering state that deviates from the coast large meander despite evidence of the existence of two or more states of the kuroshio previous data driven studies have shown only high variability of the current they have not however demonstrated bimodality in the sense of two states of relatively high probability separated by a region of relatively low probability we use singular value decomposition svd a standard time series analysis method for characterizing variability and diffusion maps and spectral clustering dmsc a machine learning algorithm that seeks multimodality to investigate kuroshio reanalysis output by applying these methods to a time series of velocity fields we find that 1 the kuroshio is bimodal with high inflow and low path variability in the small meander and low inflow and high path variability in the large meander 2 the state of the system correlates highly with the location of the recirculation gyre south of japan and 3 the meanders are better characterized by path variability than by mean path because these results are consistent with satellite sea surface height data they are not an artifact of the model used for reanalysis further our results provide evidence for a previously proposed transition mechanism based on the strengthening migration and weakening of the recirculation gyre south of japan and can therefore help direct future modeling studies

the eddy driven jet and storm track responses to boundary layer drag insights from an idealized dry gcm study abstractsimulations using a dry idealized general circulation model gcm are conducted to systematically investigate the eddy driven jet s sensitivity to the location of boundary layer drag pert

ice streams of the late wisconsin cordilleran ice sheet in western north america abstract the late wisconsin cordilleran ice sheet cis of western north america is thought to have reached its maximum extent 2 5 106 km2 as late at c 14 5 ka most 80 of the ice sheet s bed consists of high mountains but its core zone sited on plateaux of the intermontane belt of british columbia and coterminous parts of the usa shows broad swaths of subglacially streamlined rock and sediment broad scale mapping from new digital imagery data identifies three subglacial bed types 1 hard beds of variably streamlined bedrock 2 drumlinized soft beds of deformation till reworked from antecedent sediment and 3 mixed beds of variably streamlined bedrock protruding through drumlinized sediment drumlins on soft beds appear to be erosional features cut into till and antecedent sediments and identify the catchment areas of paleo ice streams expressed downglacier as flow sets of megascale glacial lineations msgls grooved and cloned drumlins appear to record the transition from drumlins to msgls the location of paleo ice streams reflects topographic funneling of ice from plateau surfaces through outlet valleys and a soft bed that sustained fast flow rock cut msgls are also present locally on the floors of outlet valleys cis disintegrated in

a numerical study on the coastal topographic effect of a peninsula on the western boundary current abstract coastal topographic effects of a peninsula on the western boundary current are studied numerically with reference to the difference in northern boundary inclination nbi from a zonal direction it is shown from the numerical experiments that the two dominant path patterns of the western boundary current exist one flow pattern is a large meander path with spinup and spindown of the cyclonic eddy and the other is a nonlarge straight path along the northern boundary if a peninsula is located upstream west of the separation point of the mean flow flowing out from the northernmost area of the western boundary region a large meander path with spinup and spindown of the cyclonic eddy is changed to an irregular oscillation by the topographic effect of the peninsula in the case of no nbi a nonlarge meander path with a small cyclonic eddy just downstream of the peninsula is formed in the cases with nbi larger than 10 formation of the large meander path and the nonlarge meander path agrees with m

effects of stratification and bottom topography on the kuroshio path variation south of japan part ii path transitions in a multiple equilibrium regime abstract the effects of stratification and bottom topography on the kuroshio path transitions in a multiple equilibrium regime due to a short term velocity increase are examined using a two layer inflow outflow model with simplified coastal geometry and bottom topography for an imposed velocity increase on a straight path state the typical transition from a straight to a meandering path occurs with or without bottom topography through the same process as in a barotropic case with flat bottom thus the geometrical effect of kyushu is essential to this transition or to the formation of a small meander triggering the transition stratification and bottom topography are somewhat secondary nevertheless under the influence of stratification a small meander significantly develops south of kyushu during a decreasing phase of velocity through shoaling of the interface depth and triggers the transition with the amplification rate of velocity amp of 1 5 the continental slope south of japan prevents a small me

covariations of sea surface temperature and wind over the kuroshio and its extension evidence for ocean to atmosphere feedback abstract satellite microwave measurements are analyzed revealing robust covariability in sea surface temperature sst and wind speed over the kuroshio extension ke east of japan ocean hydrodynamic instabilities cause the ke to meander and result in large sst variations increased reduced wind speeds are found to be associated with warm cold sst anomalies this positive sst wind correlation in ke is confirmed by in situ buoy measurements and is consistent with a vertical shear adjustment mechanism namely an increase in sst reduces the static stability of the near surface atmosphere intensifying the vertical turbulence mixing and bringing fast moving air from aloft to the sea surface south of japan the kuroshio is known to vary between nearshore and offshore paths these paths are very persistent and can last for months to years as the kuroshio shifts its path coherent wind changes are detected from satellite data in particular winds are high south of tokyo when the kuroshio takes the near

stochastic dynamics of sea surface height variability sea surface height anomalies measured by the ocean topography experiment topex poseidon satellite altimeter indicate high values of skewness and kurtosis except in a few regions including the gulf stream the kuroshio extension and the agulhas retroflection that display bimodal patterns of sea surface height variability kurtosis is uniformly greater than 1 5 times the squared skewness minus an adjustment constant this relationship differs substantially from what standard gaussian or double exponential noise would produce however it can be explained by a simple theory in which the noise is assumed to be multiplicative meaning that a larger background state implies larger random noise elements the existence of multiplicative noise can be anticipated from the equations of motion if ocean dynamics are split into a slowly decorrelating deterministic component and a rapidly decorrelating contribution that is approximated as noise such a model raises the possibility of predicting the probabilities of extreme sea surface height anomalies from first physical principles and may provide a useful null hypothesis for non gaussian sea surface height variability

the impact of ocean surface currents on sverdrup transport in the midlatitude north pacific via the wind stress formulation abstracta more complete wind stress n formulation takes into account the ocean surface currents vo while the conventional wind stress c popularly used in ocean circulation models is only a function of 10 m winds v10 an analytical solution is derived for the difference of sverdrup transport induced by using n instead of c a scaling analysis of the analytical solution indicates a 6 reduction of the sverdrup transport in the north pacific i e the kuroshio transport in the east china sea when ekman velocity dominates the ocean surface currents because of the quadratic nature of wind stress four nonlinear terms contribute equally to this difference two vorticity torque terms and two speed gradient torque terms a pair of 12 5 yr july 2002 14 hybrid coordinate ocean model simulations that only differ in the wind stress formulation are used to test the analytical solution the model results 2004 14 confirm that using n instead of c reduces the sverdrup transport in the north pacific by 8 17

effects of stratification and bottom topography on the kuroshio path variation south of japan part i dependence of the path selection on velocity abstract numerical experiments are executed using a two layer inflow outflow ocean model with simplified geometry to investigate the effects of stratification and bottom topography on the path variation of the kuroshio south of japan in a flat bottom ocean the dependence of the kuroshio path selection on its inflow velocity vmax is basically the same as in a barotropic ocean that is the kuroshio takes a straight path at low vmax regime i a meandering path at high vmax regime ii and both paths at intermediate vmax regime iii multiple equilibrium state however the range of regime iii shifts to higher vmax by 0 10 0 30 m s 1 stratification causes and maintains the offshore shift of the current path south of kyushu through the conservation of potential vorticity as a result a small meander stagnates southeast of kyushu not developing into a large meander even for higher vmax since the vorticity supply from the coast is reduced for the same reason higher vmax is needed to maintain a meande