stabilizing feedbacks in glacier bed erosion glaciers often erode transport and deposit sediment much more rapidly than nonglacial environments1 with implications for the evolution of glaciated mountain belts and their associated sedimentary basins but modelling such glacial processes is difficult partly because stabilizing feedbacks similar to those operating in rivers2 3 have not been identified for glacial landscapes here we combine new and existing data of glacier morphology and the processes governing glacier evolution from diverse settings to reveal such stabilizing feedbacks we find that the long profiles of beds of highly erosive glaciers tend towards steady state angles opposed to and slightly more than 50 per cent steeper than the overlying ice air surface slopes and that additional subglacial deepening must be enabled by non glacial processes climatic or glaciological perturbations of the ice air surface slope can have large transient effects on glaciofluvial sediment flux and apparent glacial erosion rate

motion induced stresses in pack ice we consider motion induced stresses in pack ice through the analyses of a variety of observations collected during the sea ice mechanics initiative study conducted in the beaufort sea during 1993 motion induced components of in situ stress from stress gauge data are compared to stresses calculated as residuals based on a force balance argument using observed wind current and ice motion data there is reasonable qualitative and quantitative agreement between the observed and calculated motion induced stresses in the north south direction if the residual stress is assumed to be distributed over a horizontal distance of 10 m to obtain a general agreement with the magnitudes of the observed and calculated stresses in the east west direction the residual stress must be considered to be distributed over a horizontal distance of 50 m there are three significant stress events determined by the force balance calculations but only the one event in the north south direction has a strong corresponding signal in the stress gauge data there is very little indication of the two events in the east west direction in the gauge data numerical simulations of the distribution of motion induced stresses within a floe show that significant variations in the character of the stresses can occur over short horizontal distances throughout the floe hence a seeming lack of a clear correspondence between the observed and calculated stress may be due to our inability to properly recognize the modified signature of the event at the specific locations of the stress gauges the results suggest that to effectively develop an understanding of the role that point stress measurements can play in developing our understanding of the process of ice deformation it may be necessary to couple the stress measurements with models of the patterns of motion induced stresses within a floe finally we consider the relationship between the residual stress and the differential motion of the ice pack as seen by a cluster of drifters on various floes the three main stress events seen in the residual stresses all occurred during periods of convergence of the floes however we have tested various relationships between stress and strain and they indicate that there should have been additional stress events as a result of other periods of substantial convergences of the ice pack this suggests the possibility that the residual stresses were not locally generated

response of winter moisture circulation to the india burma trough and its modulation by the south asian waveguide abstractthe response of moisture circulation to the daily evolution of the india burma trough ibt and the modulation of disturbances along the south asian waveguide are analyzed to seek a potential precursor of winter precipitation over south china daily observational precipitation and reanalysis data from era interim during 1979 2012 are employed it is found that moisture circulation in response to the ibt is part of the zonally oriented wave trains along the south asian waveguide but it persists longer and migrates farther eastward than other lobes cyclonic moisture transport enhances the moisture supply to south china as a strong ibt develops and shifts eastward abruptly after the peak of ibt with enhanced precipitation shifting from southwest to southeast china this response is a joint effect of synoptic intraseasonal and interannual components that show similar wave train structures whereas slight differences still occur the synoptic component shows a shorter wavelength more southerly pa

geometry bed topography and drainage system structure of the haut glacier d arolla switzerland as part of an integrated study of the hydrology meltwater quality and dynamics of the haut glacier d arolla switzerland the glacier s drainage network structure was determined from patterns of dye recovery in 342 injection experiments conducted from 47 moulins distributed widely across the glacier this structure was compared with theoretical predictions based upon reconstructed patterns of water flow governed by a the subglacial hydraulic potential surface and b the subglacial bedrock surface these reconstructions were based on measurements of ice surface and bedrock topography obtained by a combination of ground survey and radio echo sounding techniques the two reconstructions simulate the drainage system structures expected for a closed channels in which water is pressurized by the overlying ice and b gravity driven open channel flow the closed channel model provides the best fit to the observed structure even though theoretical calculations suggest that under summer discharge conditions open channel flow may be widespread beneath the glacier possible reasons for this apparent discrepancy are discussed

an integrated approach to modelling hydrology and water quality in glacierized catchments the results are summarized of an integrated investigation of glacier geometry ablation patterns water balance meltwater routing hydrochemistry and suspended sediment yield the ultimate objective is to evaluate the assumptions of lumped two component mixing models as descriptors of glacier hydrology and to develop a semi distributed physically based model as an alternative the results of the study demonstrate that a reconstruction of probable subglacial drainage alignments can be achieved through a combination of terrain modelling based on estimated potential surface and dye tracing experiments recession curve analysis evidence of the seasonal instability of the englacial and subglacial electrical conductivities assumed in a mixing model evidence of the non conservative behaviour of water chemistry in the presence of suspended sediment and evidence of the seasonal evolution of the subglacial drainage system based on dye tracing all indicate that an alternative to a lumped static model of the hydrology is necessary the alternative presented in this paper is based on the combination of an energy balance model for surface melt which operates on an hourly time step and accounts for the changing spatial distribution of melt through the day as shading patterns change and routing procedures that transfer surface melt to moulins on the basis of glacier surface gradients then route water through reconstructed conduit systems using a hydraulic sewer flow routing procedure

modulation of south asian jet wave train on the extreme winter precipitation over southeast china comparison between 2015 16 and 2018 19 abstracttwo extremely wet winters in 2015 16 and 2018 19 over southeast china are compared in this study south to north discrepancies appear in the spatial distribution of precipitation with anom

discharges of turbid water during mini surges of variegated glacier alaska u s a discharges of water sediment and dissolved impurities from variegated glacier ala ska were monitored in the early summers of 1980 and 1981 during the occurrence of mini surg es sea sonal trends weat her related eve nts and diurnal variat ions similar to behavior of other temperat e gl acier streams were found the prin cipal effect in the stream associated with mini surge occurrence was a brief discharge of extremely turbi d water the turbidity is assumed to be introduced into the basal hydraulic system by initiation of the fast motion of a mini surge at a time and locat ion on the upper glacier known from oth er meas ure ments the mean water velocity in the hydraulic system over the int erven ing distance is thereby determined 0 3 m s i the mean water velocity together with the water discharge 16 m3 s 1 at the terminus places con straints on the distribution of water velocity u and total cros s sectional area at of the flow paths along the gl acier base this leads to the con clusion that within the zone of mini surge occurrence in its unpe rturbed state u is about 0 1 m s 1 or possibly less at is about 10 2 m2 or possibly more and it must be divided into a very large number of small passag eways be blocked by constrict ions or both the total water cro ss se ction corresponds to a layer 0 1 2 m thick when spr ead unifo rmly over the glacier width the water velocity is clos e to or less than the propa gation velo city of the mini s urges bet ween the zone affected by mini surges and the stream a dyna mically less active lower section of the glacier is proba bly underlain by a small number of conduits in which the water velocity may be very high 2 m s i water di scharge follo wing the mini surges puts an upper limit on water storage changes ass ociated with the anomalous ice motion

circumglobal teleconnections the jet stream waveguide and the north atlantic oscillation abstract monthly and seasonally averaged upper tropospheric northern hemisphere winter fields are examined to determine whether the waveguiding effect of the time averaged tropospheric jets on low frequency disturbances that is predicted by theory does affect the behavior of these disturbances it is found that indeed disturbances in the vicinity of the mean jets particularly the jet that stretches across south asia are fundamentally different from those that reside in regions where the mean winds have weaker meridional gradients like the mid pacific patterns of variability in the jets tend to be smaller scale and to consist of zonally oriented chains of anomalies while variability in the mid pacific is composed of patterns with distinct meridional orientation because they are meridionally trapped and zonally elongated patterns associated with the jet stream waveguide connect activity at points that are much farther apart than do patterns in other regions of the globe within the south asian waveg

sediment deformation beneath glaciers rheology and geological consequences experiments beneath breidamerkurjokull in iceland have led to development of flow laws for the subglacial till relating strain rate to shear stress and effective pressure and assuming either bingham fluid or nonlinearly viscous fluid behavior water pressures in the till are less than ice pressures and it is suggested that this may lead to infiltration of ice into the sediment which inhibits sliding at the ice sediment interface where water pressures are equal or near to ice pressures infiltration does not occur and sliding may result a one dimensional theory of subglacial deformation is developed in which the empirical flow law is coupled with a model of subglacial hydrology and consolidation this predicts stable states in which subglacial sediment either does not deform or a dilatant deforming horizon forms with positive effective pressures at the ice bed interface or unstable states where zero or negative effective pressures are predicted time dependent analyses show that response times following perturbations of the system may be of the order of 103 years and thus that unsteady behavior may be normal on glaciers flowing over unlithified sediment beds it is suggested that the natural variability of material properties in subglacial sediment beds leads to the development of drumlins on the glacier bed it is suggested that unstable deformation at zero or negative effective stress leads to piping in subglacial sediments at the glacier terminus and the growth of sediment floored subglacial tunnels their frequency is that which is sufficient to draw down subglacial water pressures so as to prevent unstable deformation where they discharge large water volumes subglacial sediments flow laterally toward them producing tunnel valleys this sediment is then removed by water flowing along the axial tunnel tunnel valleys can be regarded as the equivalent in soft sediment areas of eskers in bedrock areas

influence of subglacial drainage conditions on the velocity distribution within a glacier cross section substrate properties and hydrological conditions at the base of haut glacier d arolla switzerland are nonuniform the thickness and grain size of subglacial sediment vary on length scales less than one ice thickness whereas hydrological conditions vary seasonally and on length scales of about one ice thickness transverse to ice motion there is a close relationship between the annually averaged velocity field and this nonuniformity of bed conditions basal motion dominates in an area with large water level variations in boreholes whereas ice deformation contributes significantly to total movement elsewhere localized enhanced basal motion occurs primarily in summer especially during a july spring event but this motion is barely discernible in annually averaged surface velocity measurements because transverse coupling suppresses surface expression of the basal motion discontinuity these results highlight the need to include representations of bed nonuniformity in models of glacier flow and to consider ice deformation and basal motion as interdependent processes

interdecadal changes of 30 yr sst normals during 1871 2000 abstract sst predictions are usually issued in terms of anomalies and standardized anomalies relative to a 30 yr normal climatological mean cm and standard deviation sd the world meteorological organization wmo suggests updating the 30 yr normal every 10 yr in complying with the wmo s suggestion a new 30 yr normal for the 1971 2000 base period is constructed to put the new 30 yr normal in historical perspective all the 30 yr normals since 1871 are investigated starting from the beginning of each decade 1871 1900 1881 1910 1971 2000 using the extended reconstructed sea surface temperature ersst on a 2 grid for 1854 2000 and the hadley centre sea ice and sst dataset hadisst on a 1 grid for 1870 1999 eleven 30 yr normals are calculated and the interdecadal changes of seasonal cm seasonal sd and seasonal persistence p are discussed the interdecadal changes of seasonal cm are prominent 0 3 0 6 in the tropical indian ocean the midlatitude north pacific the midlatitude no

energetics and dynamics associated with two typical mobile trough pathways over east asia in boreal winter two dominant types of east asian mobile trough eamt are identified by a novel mobile trough detection algorithm the two major eamts likely pass through to the north and the south of lake baikal in this study both of synoptic and planetary time scales influences on east asia are studied for synoptic scale southern path of mobile trough shows a higher rate of intensification that of northern path southern path has stronger impact on southeast asia temperature fluctuation because of more southern pathway and stronger magnitude of wave train but duration of fluctuation is shorter in southern due to the downstream development for planetary scale the northern path shows a large warm anomaly over southeast asia and a cold anomaly over northeast asia which is associated with the northward shift of the jet stream the southern path shows a cold anomaly over east asia due to a northwesterly anomaly the forcing of high frequency eddy on low frequency eddy is estimated in terms of momentum and energy the reinforcement of high frequency eddy flux on low frequency variation can be observed in northern path but not in southern path the energy difference for two paths is also caused by the variations of barotropic and baroclinic conversion the energy tendency of interaction between two frequency eddies is only responsible for sustention of energy anomaly over southwestern japan

relationship between stationary planetary wave activity and the east asian winter monsoon 1 the variability of both the stationary planetary wave activity and the east asian winter monsoon is strongly associated with the thermal contrast between oceans and landmasses in this study we explore the interannual relationship between the monsoon and the wave activity defined by an index of the difference in the divergence of eliassenpalm flux between 50 n at 500 hpa and 40 n at 300 hpa it is found that compared to the winters of low wave activity the equatorward propagation of planetary waves in the middle and upper troposphere is stronger in the high wave activity winters during these high activity winters the upward wave propagation from the troposphere into the stratosphere becomes weaker this is accompanied by a smaller perturbation in the polar vortex which tends to be colder and stronger in the meantime the east asian westerly jet stream the east asian trough the siberian high and the aleutian low all become weaker apparently in particular the weakening of the siberian high and the aleutian low decreases the northeasterly wind over east asia leading to a warming condition in the region especially in northeastern asia a further analysis reveals that the zonal wavenumber 2 pattern of planetary waves contributes dominantly to the variability of the east asian winter monsoon

seasonal reorganization of subglacial drainage inferred from measurements in boreholes the effect of the formation of a major subglacial drainage channel on the behaviour of the subglacial drainage system of haut glacier d arolla switzerland was investigated using measurements of borehole water level and the electrical conductivity and turbidity of basal meltwaters electrical conductivity profiles were also measured within borehole water columns to identify the water sources driving water level changes and to determine patterns of water circulation in boreholes prior to channel formation boreholes showed idiosyncratic and poorly coordinated behaviour diurnal water level fluctuations were small and driven by supraglacial englacial water inputs even when boreholes were connected to a subglacial drainage system this system appeared to consist of hydraulically impermeable patches interspersed with storage spaces and transmitted a very low water flux drainage reorganization which occurred around 31 july 1993 in response to rapidly rising meltwater and rainfall inputs seems to have involved the creation of a connection between an incipient channel and a well established channelized system located further down glacier once a major channel existed within the area of the borehole array borehole water level fluctuations were forced by discharge related changes in channel water pressure although a diversity of responses was observed these included i synchronous ii damped and lagged iii inverse and iv alternating inverse lagged responses synchronous responses occurred in boreholes connected directly to the channel while damped and lagged responses occurred in boreholes connected to it by a more resistive drainage system pressure variations within the channel resulted in diurnal transfer of mechanical support for the ice overburden between connected and unconnected areas of the bed producing inverse and alternating patterns of water level response 1998 john wiley sons ltd

alpine subglacial hydrology abstract the size and shape of subglacial flow pathways exert a strong influence over the pressure and speed at which meltwaters are routed through glaciers these characteristics in turn influence glacier sliding velocity and the quantity and quality of bulk meltwaters discharging from glaciers in this paper we summarise four empirical research approaches that have been developed to improve our understanding of the subglacial hydrology of predominantly temperate based alpine glaciers investigations of bulk meltwater discharge and chemistry tracer studies proglacial bedrock investigations and borehole investigations as a result of linking these studies to conceptual or numerical models three arborescent and four non arborescent or distributed subglacial drainage configurations are described these drainage networks may be neither spatially nor temporally persistent but may compete with and replace each other on a seasonal basis a qualitative model of the temporal and spatial evolution of a typical alpine subglacial drainage system is advanced on the basis of research conducted at haut glacier d arolla switzerland

asian jet waveguide and a downstream extension of the north atlantic oscillation abstract anomalous atmospheric fields associated with the north atlantic oscillation nao are analyzed on interannual and intraseasonal time scales in order to examine the extent to which the nao is a regional phenomenon analyses on the interannual time scale reveal that the nao signal is relatively confined to the euro atlantic sector in december while it extends toward east asia and the north pacific in february the difference is most clearly seen in the meridional wind anomaly which shows a wave train along the asian jet collocated with an anomalous vorticity source near the jet entrance diagnoses using a linear barotropic model indicate that this wave train is interpreted as quasi stationary rossby waves trapped on the asian jet waveguide and effectively excited by the anomalous upper level convergence over the mediterranean sea it is found that when the nao accompanies the mediterranean convergence mc anomaly most frequently seen in february the nao indeed has a much wider horizontal str

how glaciers entrain and transport basal sediment physical constraints abstract simple insights from the physics of ice water and sediment place constraints on the possible sediment transport behavior of glaciers and ice sheets because glaciers concentrate runoff streams generated by glaciers transport much sediment and may erode bedrock rapidly deforming glacier beds also can transport much sediment particularly in marginal regions rapid sediment entrainment producing thick debris rich basal zones may occur by regelation into subglacial materials and by freeze on from rising supercooled waters numerous other mechanisms may be important but primarily near ice margins especially those of advancing or fluctuating glaciers several sediment entrainment mechanisms may be active beneath a single glacier but one process is likely to be dominant at any place and time

precipitation stable isotope records from the northern hengduan mountains in china capture signals of the winter india burma trough and the indian summer monsoon abstract this project reports results of the first precipitation stable isotope 18 o and d time series produced for qamdo in the northern hengduan mountains in the southeastern tibetan plateau the data showed that the fluctuations of precipitation stable isotopes at qamdo during the different seasons revealed various moisture sources the westerlies and local recycling moisture dominated at the study area before the pre monsoon and after the post monsoon seasons which resulted in similar trends of both precipitation stable isotopes and temperature the marine moisture was transported to the northern hengduan mountains by the winter india burma trough combined with convection consequently stable isotopes in subsequent precipitation were occasionally observed to decrease suddenly however 18 o and d values of precipitation at qamdo were lower during the monsoon period and the duration of those low values was longer because of the effects of the indian summer monsoon and the strengthening convection our findings indicate that the effects of seasonal precipitation differences caused by various climate systems including the winter india burma trough and indian summer monsoon need to be considered when attempting to interpret tree ring and ice core records for the hengduan mountains

hydraulics of subglacial cavities modele theorique du comportement a l etat stationnaire des cavites remplies d eau et interconnectees sur le lit du glacier

observed interannual oscillations of planetary wave forcing in the northern hemisphere winter 1 using ncep ncar reanalysis data from 1958 to 1998 two interannual oscillations in the eddy forcing due to planetary waves wavenumbers 1 3 are found in the northern hemisphere winter called as the stratospheric interannual oscillation sio and the tropospheric interannual oscillation tio the temporal evolutions are different between the sio and the tio suggesting different dynamic mechanisms the planetary waves tend to be bent equatorward in the troposphere during a positive tio phase and in the mid and upper stratosphere during a positive sio phase the result also suggests that upward propagation of planetary waves into the polar waveguide across the tropopause is closely associated with the tio further regression and correlation analyses suggest that the tio is closely linked to the northern annular mode nam whereas the sio is closely associated with the el nino southern oscillation enso

structure and dynamics of a wave train along the wintertime asian jet and its impact on east asian climate based on observational and reanalysis datasets this study investigates the structure and dynamics of a wave like atmospheric teleconnection pattern along the wintertime asian jet and its influence on east asian climate along the jet the leading empirical orthogonal function eof mode of monthly meridional winds at 250 hpa in winter december january and february is organized as a wave train with maximum anomalies at upper troposphere the wave train propagates northeastward from the north atlantic to europe turns southeastward to the middle east with amplifying amplitude propagates along the jet to south china and reaches japan which is partly induced by sea surface temperature sst anomalies in the equatorial eastern pacific and the north atlantic oscillation over the sector from europe to the middle east the anomalous vortices in the wave train tilt northwestward with height and tilt northeast southwest in horizontal at 250 hpa favoring for extracting available potential energy and kinetic energy from mean flows effectively in addition there exists a positive feedback between transient eddies and the wave train related anomalous circulation over the north atlantic and europe these processes help to maintain and amplify the wave train moreover the wave train can exert significant influences on the wintertime climate in east asia when it is in the phase with a cyclone anticyclone over south china japan rainfall tends to be above normal in south and east china and surface air temperature tends to be above normal around japan and the korea peninsula

on the role of mechanical energy in maintaining subglacial water conduits at atmospheric pressure recent theo retical studies of glacier hydrology have assumed that subglacial conduits are completely filled with water under steady state conditions this however is not necessarily the case where discharges are larger than a few tens of liters per second and the down glacier slope of the bed is more than a few degrees the potential energy released by water descending this slope may be capable of melting the walls of a subglacial conduit many times faster than the conduit can close by plastic flow of the ice as a result the pressure in such tunnels may normally be atmospheric or possibly even at the triple point pressure if there is no open connection to the glacier surface simple calcu lations suggest that such pressures in subglacial conduits may be more common than herclofore anticipated the positions of such open conduits may be unstable to small per turbations in discharge or ice veloci ty this is because the mechanical energy available in excess of that needed to balance closure can instead offset the gene ral flow of the ice cond ui ts can thus trend diago nally across the direction of ice aow if an increase in the angle which such a conduit makes with the ice flow direction also results in an increase in slope of he conduit more mechanical energy will become available resulting in a positive feedback process subglacial channels at atmospheric pressure may inauence the origin and morphology of certain glacial landforms such as eskers and plastically molded features resume sur le role de l inergie newtonnienne dam le maintien du riseau aquiflrl sous glaciaire cl la pression almosph irique de recentes etudes theoriques d hydrologie glaciaire ont suppose que le reseau sous glaci aire clait corn pletement rempli d eau en condition d cquil ibre stable ceci neanmoins n est pas necess airement le cas lorsque les debits sonl superieurs a quelques dizaines de litres par seconde et que la pente du lit du glacier est superieure a quelques degres i energie potentielle mise en oeuvre par i eau descendant celle pente peut ire capable de fondre les parois d un chenal sous glaciaire beaucoup plus vite que le chenal ne peut se refermer par le auage plastique de la glace il en resuhe que la pression dans de tels chenaux peut nor rnalement etre atrnospherique

hydrological discharges and motion of fels and black rapids glaciers alaska u s a implications for the structure of their drainage systems characteristics of the hydrology and motion of black rapids and fels glaciers alaska were observed from 1986 to 1989 hydrological measurements included stage electrical conductivity and suspended sediment concentration in the discharge stream of each glacier and were made at 0 5 1 h intervals continuously through most of the melt seasons variations in the glacier speed were monitored through the full year at a number of locations along the length of each glacier using time lapse photography 1 d time resolution strain meters 0 5 1 h resolution and seismometers set up to count acoustic emissions both glaciers show similar seasonal diurnal and short term event changes in hydrological discharges and ice speed the hydrological behavior is analyzed in terms of a fast sub system composed of surface streams moulins and large tunnels with discharge that responds rapidly and a slow sub system composed of heterogeneous small passageways through the ice and distributed over the bed that maintain approximately uniform discharge over a day the timing and amplitude of water discharge in the diurnal cycle indicate that roughly 10 40 of the water is routed directly into the fast system the remaining 90 60 of the water enters the slow system dilution of the solute discharged from the slow system by the variable discharge in the fast system results in changes in water discharge and solute concentration that are approximately equal in relative amplitude and inversely related a small time lag from discharge maximum minimum to solute minimum maximum suggests that the fast system is confined to roughly the lowermost 30 40 of the full glacier length the residence time of water in the fast system is short compared to 1 d the slow system contains both short and long residence time passages characteristics of the diurnal cycles are somewhat variable through the melt season but no systematic evolutionary patterns were discerned even though large changes in the mean discharges of water and solutes occur which suggests parallel evolution of the variables that control the response of the fast system events were characterized by contemporaneous increases in suspended sediment concentration in the discharge water and distinct changes in straining on the glaciers events caused by increases in melt or precipitation related to weather and events related to release from reservoirs internal to the glaciers could be distinguished based on the changes in electrical conductivity of the discharge water the correlated changes in sediment discharge and motion of the glaciers indicate that the events were associated with temporary modifications of the slow passages distributed over the bed that allowed enhanced sliding and access of basal water flow to erosion products hydrological differences between black rapids and fels glaciers can be explained by differences in the size of the glaciers if there is a difference in bed structure that explains the difference in dynamics surge black rapids glacier versus non surge fels glacier it does not affect the hydrological parameters that were observed

modulation of the interannual variation of the india burma trough on the winter moisture supply over southwest china anomalous moisture circulation associated with the interannual variation of the india burma trough was investigated to examine how the trough affects the moisture supply to southwest china in winter when the india burma trough is strong abnormal moisture is transported to southwest china mainly via the southern boundary in the 750 650 hpa layer instead of via the western boundary in contrast to the climatological situation the abnormal moisture convergence is constrained in a thin layer along the windward side of the tibetan plateau the moisture circulation response to the variation of the india burma trough shows great baroclinicity over the bay of bengal bob northwesterly transport behind and southwesterly transport ahead of the trough appear only between 850 and 650 hpa with anticyclonic moisture circulation underneath and cyclonic moisture circulation on top beyond the bob the moisture circulation response can be traced upstream with abnormal anticyclonic cyclonic moisture circulations over the mediterranean sea and arabian sea red sea above 850 hpa and downstream with anticyclonic moisture circulation over the philippine sea near the surface the activity of the india burma trough is not a local phenomenon but a part of the south asian jet wave trains and is modulated by the enso via the philippine sea anticyclone further investigation of the separate role of wind and moisture disturbances shows that the abnormal moisture flux is dominated by the wind disturbance as is the abnormal moisture divergence in the lower level while that in the upper level is dominated by both the wind and moisture disturbances

pacific east asian teleconnection how does enso affect east asian climate observational evidence is presented to show a teleconnection between the central pacific and east asia during the extreme phases of enso cycles this pacific east asian teleconnection is confined to the lower troposphere the key system that bridges the warm cold events in the eastern pacific and the weak strong east asian winter monsoons is an anomalous lower tropospheric anticyclone cyclone located in the western north pacific the western north pacific wind anomalies develop rapidly in late fall of the year when a strong warm or cold event matures the anomalies persist until the following spring or early summer causing anomalously wet dry conditions along the east asian polar front stretching from southern china northeastward to the east of japan kuroshio extension using atmospheric general circulation and intermediate models the authors show that the anomalous philippine sea anticyclone results from a rossby wave response to suppressed convective heating which is induced by both the in situ ocean surface cooling and the subsidence forced remotely by the central pacific warming the development of the anticyclone is nearly concurrent with the enhancement of the local sea surface cooling both the anticyclone and the cooling region propagate slowly eastward the development and persistence of the teleconnection is primarily attributed to a positive thermodynamic feedback between the anticyclone and the sea surface cooling in the presence of mean northeasterly trades the rapid establishment of the philippine sea wind and sst anomalies implies the occurrence of extratropical tropical interactions through cold surge induced exchanges of surface buoyancy flux the central pacific warming plays an essential role in the development of the western pacific cooling and the wind anomalies by setting up a favorable environment for the anticyclone sst interaction and midlatitude tropical interaction in the western north pacific

seasonal changes in the morphology of the subglacial drainage system haut glacier d arolla switzerland dye tracing techniques were used to investigate the glacier wide pattern of change in the englacial subglacial drainage system of haut glacier d arolla during the ablation seasons of 1990 and 1991 analysis of breakthrough curve characteristics indicate that over the course of a melt season a system of major channels developed by headward growth at the expense of a hydraulically inefficient distributed system by the end of the melt season this channel system extended at least 3 3 km from the snout of the 4 km long glacier and drained the bulk of supraglacially derived meltwater passing through the glacier the upper limit of the channel system closely followed the retreating snowline up glacier rates of headward channel growth reached c 65 m d 1 although these rates decreased in the upper 1 km of the glacier where snowline retreat exposed a patchy firn aquifer it appears that the removal of snow with its high albedo and significant water storage capacity from the glacier surface resulted in a dramatic increase in the volume of runoff into moulins and in the peakedness of daily runoff cycles this induced transient high water pressures within the distributed drainage system which caused it to evolve rapidly into a channelised system it is therefore likely that at a local scale channel growth occurred down glacier from moulins and that the overall up glacier directed pattern of channel formation was caused by the retreating snowline exposing new moulins and crevasses to inputs of ice derived meltwater damping of diurnal melt inputs by storage in the firm aquifer accounts for the slowing of channel growth in the upper glacier 1998 john wiley sons ltd

in situ measurements of basal water quality and pressure as an indicator of the character of subglacial drainage systems continuous subglacial measurements of turbidity and electrical conductivity two indicators of basal water quality can be used to help characterize subglacial drainage systems these indicators of water quality yield information that complements that provided by water pressure measurements quantitative attributes of subglacial drainage systems such as water velocity and subglacial residence time as well as qualitative behaviour for example spatial and temporal variations in system morphology can be deduced using water quality measurements interpretation is complicated by the many potential influences on turbidity and electrical conductivity but when these complications are appreciated a richer interpretation results to demonstrate the utility of basal water quality measurements observations from trapridge glacier yukon territory canada were examined the data reveal complex behaviour of the drainage system but constraints imposed by basal water quality measurements help to clarify the nature of the subglacial flow system the measurement and interpretation methods described and demonstrated are applicable to other glaciers as such they should prove useful for characterizing different subglacial drainage configurations and behaviours thereby improving our general understanding of the hydrology and dynamics of wet based glaciers

relationship between ural siberian blocking and the east asian winter monsoon in relation to the arctic oscillation and the el nino southern oscillation this study attempts to assess the possible linkage between ural siberian blocking and the east asian winter monsoon eawm during the boreal winter the dominance of blocking thermally enhances cold advection downstream the frequent occurrence of ural siberian blocking potentially promotes a cold eawm and vice versa the seasonal blocking activity can be regarded as the combined effect of the arctic oscillation ao and the el nino southern oscillation enso weakened strengthened meridional flow in the positive negative phase of the ao is unfavorable favorable for the formation of blocking highs because the ao shows a close relationship with the north atlantic oscillation nao its teleconnection with ural siberian blocking may exist in the form of an eastward propagating wave train be that as it may the wave train signal across east asia may be disturbed by the external effect of a strong enso event which probably enhances weakens the westerlies near siberia in its warm cold phase consequently the blocking eawm relationship is stronger weaker when the ao and enso are in phase out of phase if both ao and enso attain the positive negative phase the siberian high tends to be weaker stronger and the temperature tends to be higher lower in east asia with less more ural siberian blocking on the other hand if they are out of phase they are not strongly linked to the intensity of the siberian high and the blocking activity over ural siberia is unclear

pacific east asian teleconnection part ii how the philippine sea anomalous anticyclone is established during el nino development the anomalous philippine sea anticyclone psac conveys impacts of el nino to east asian climate during the mature and decay of an el nino from the winter to ensuing summer it is shown that the anomalous psac forms in fall about one season prior to the peak el nino its strength increases with the el nino intensity and its sign reverses during a la nina the psac formation concurs with abnormal deepening of the east asian trough and with increasing number of northward recurvature of tropical storms in the western pacific the psac establishment is abrupt coupling with a swing from a wet to dry phase of an intraseasonal oscillation iso and often concurrent with early retreat of the east asian summer monsoon the iso becomes inactive after psac establishment the development of the psac is attributed to combined effects of the remote el nino forcing tropical extratropical interaction and monsoon ocean interaction the developing el nino induces off equatorial as cending rossby wave responses and land surface cooling in northeast asia both deepen the east asian trough in fall and induces vigorous tropical extratropical exchange of air mass and heat which enhances the cold air outbreak and initiation of the psac through exciting descending rossby waves the el nino induced indonesian subsidence generates low level anticyclonic vorticity over south asia which is advected by mean monsoon westerly instigating the anomalous psac the iso interacting with the underlying ocean plays a critical role in the abrupt establishment of psac the wind evaporation entrainment feedback tends to amplify suppress iso before after winter northeasterly monsoon commences suggesting the roles of atmosphere ocean inter action and the seasonal march of background winds in changing the philippine sea iso intensity and maintaining psac

interannual variations of stationary planetary wave activity in the northern winter troposphere and stratosphere and their relations to nam and sst 1 with the national centers for environmental prediction national center for atmospheric research ncep ncar reanalysis data from 1958 to 1998 two teleconnection patterns in the eliassen palm ep flux divergence field due to stationary planetary waves with wavenumbers wns 1 to 3 are studied in the northern hemisphere winter both patterns appear as dipole structures with divergence of ep flux in the north and convergence in the south or vice versa one dipole evolves mainly in the stratosphere and is referred to as the stratospheric interannual oscillation sio the other evolves mostly in the troposphere and is referred to as the tropospheric interannual oscillation tio the tio and the sio are shown to be associated with anomalous meridional planetary wave propagation in the troposphere and stratosphere respectively the upward and poleward refraction of planetary waves into the polar waveguide across the tropopause is closely linked to the tio examination of individual waves indicates that the tropospheric dipole ofep flux divergence comes basically from wn 3 whereas the stratospheric one comes totally from wns 1 and 2 the reduced refraction of planetary waves into the polar waveguide across the tropopause associated with positive tio index is dominantly contributed from both wns 1 and 2 regression and correlation analyses suggest that the tio is closely related to the northern annular mode nam its relation to the sea surface temperature sst is consistent with previous studies on the relation of nam to sst on the other hand the sio is shown to be closely associated with anomalous zonal mean winds in the subtropics of the midstratosphere and has a moderate correlation with an augmented pacific north american pna pattern in 500 hpa geopotential height for the leading eof of stratospheric u variability the sio accounts for a smaller fraction than the tio however with the teleconnectivity in stratospheric ep flux divergence one can distinguish a stratospheric variation of anomalous north south planetary wave propagation from the total amount of wave activity entering the stratosphere which may help us to understand the variability of transport circulation in the stratosphere significant correlation of sio with tropical sst reveals that tropical sst is leading the sio by up to around 9 months which suggests a strong impact of el nino southern oscillation enso on the sio planetary waves tend to be bent poleward in the midstratosphere when there is a warm event the situation tends to be reverse during a cold event

vertical structure physical properties and energy exchange of the east asian trough in boreal winter the relation between the intensity of the east asian trough and the strength of the east asian winter monsoon is documented a prominent dipole of the available potential energy of the zonal mean flow can be observed over the midlatitudes and polar regions and is related to temperature anomalies variation in the intensity of the east asian trough is caused by variation in the energy conversion from the available potential energy of the zonal mean flow to the east asian trough the in phase relation between the intensities of the east asian jet and east asian trough is illustrated by the relation between the potential energy and kinetic energy of stationary eddies the dipole of height anomalies over the midlatitude and polar regions develops in late autumn and decays in early spring we investigate the effect of both stationary and transient eddy forcing on the evolution of the dipole the combined forcing of the two types of eddy makes an important contribution to the development maintenance and decay of the dipole

structure and dynamics of a springtime atmospheric wave train over the north atlantic and eurasia the leading pattern of boreal spring 250 hpa meridional wind anomalies over the north atlantic and mid high latitude eurasia displays an obvious wave train the present study documents the structure energy source relation to the north atlantic sea surface temperature sst and impacts on eurasian climate of this wave train during 1948 2018 this atmospheric wave train has a barotropic vertical structure with five major centers of action lying over subtropics and mid latitudes of the north atlantic northern europe central eurasia and east asia respectively this spring wave train can efficiently extract available potential energy from the basic mean flow the baroclinic energy conversion process and positive interaction between synoptic scale eddies and the mean flow both play important roles in generating and maintaining this wave train the north atlantic horseshoe like nah sst anomaly contributes to the persistence of the wave train via a positive air sea interaction specifically the nah sst anomaly induces a rossby wave type atmospheric response which in turn maintains the nah sst anomaly pattern via modulating surface heat fluxes this spring atmospheric wave train has significant impacts on eurasian surface air temperature sat and rainfall during the positive phase of the wave train pronounced sat warming appears over central eurasia and cooling occurs over west europe and eastern eurasia in addition above normal rainfall appears over most parts of europe and around the lake baikal accompanied by below normal rainfall to east of the caspian sea and over central asia

predecessor rain events over china s low latitude highlands associated with bay of bengal tropical cyclones a predecessor rain event pre is defined as organized heavy rainfall that occurs far ahead of tropical cyclone tc yet directly associated with the deep tropical moisture originating from the tc vicinity the pres occurring over china s low latitude highlands cllh in association with bay of bengal tcs were investigated from 1981 to 2012 results indicate that about 19 of bay of bengal tcs produces pre the pres frequently occur when tcs are active in the northern bay of bengal with northeastward paths the pres are more likely to appear in the pre monsoon and post monsoon seasons with peaks in may and october respectively the median lifetime of the pres was approximately two days the distances between pres and parent tcs are ranged from 745 to 1849 km with a median distance of 1118 km composite results of pres suggested that deep moisture is advected from the tc vicinity to the remote cllh region which is situated beneath the equatorward entrance of the upper level east asia subtropical jet easj the lower level southwesterly flow which is associated with a strong pressure gradient between the western pacific subtropical high and a trough in bay of bengal steers tcs conveying abundant moisture from the bay of bengal to the cllh region the enhancement of the ascent and frontogenesis within the equatorward entrance region of the easj is favorable for occurrence of pres in cllh tcs may also have a dynamical role in occurrence of pres by intensifying the upper level easj

observational climatology and characteristics of wintertime atmospheric blocking over ural siberia this study investigates the climatological aspects and temporal characteristics of wintertime ural siberian blocking usb centered over 30 100 e for the period 1980 1981 2009 2010 sixty eight events are identified and their physical structure is diagnosed using thermodynamic and geostrophic vorticity tendency equations in climatology horizontal advections play a fundamental role in constructing a usb event in which the anticyclonic center is a warm core in the troposphere and a cold core in the lower stratosphere the decay of the thermal structure is related to diabatic cooling along the vertical structure and warm advection in the lower stratosphere meanwhile the collapse of the height structure is caused primarily by cyclonic vorticity advection a strong interrelationship exists between the intensity and extension of usb events the temporal characteristics of usb events are analyzed by examining strong and weak events which are of high and low intensity the strong events are probably preceded by an open ridge over europe and a cyclogenesis over the mediterranean sea and their formation is followed by the stronger amplification of a rossby wave packet across eurasia on the other hand the weak events are likely to be triggered by surface cold anomalies over siberia overall the evolution of a usb event forms a dynamic linkage with the siberian high in which the decay stage of the usb event is accompanied by a southeastward migration of the siberian high and a subsequent cold air outbreak in east asia these results advance our understanding of usb and its relationship with east asian winter monsoon activities

analysis and interpretation of patterns within and between hydroclimatological time series in an alpine glacier basin this paper explores patterns within and between climatological and hydrological time series from an alpine glacier basin time series recorded in the basin of the haut glacier d arolla over the 1989 ablation season are subdivided into five subperiods box jenkins arima autoregressive integrated moving average and tfn transfer function noise models are estimated for each of the five subperiods and differences between the models are interpreted in the context of changing glacier hydrology particularly the changing nature and extent of the glacier drainage network

the role of mjo and mid latitude fronts in the south china sea summer monsoon onset previous studies have suggested that the south china sea scs summer monsoon onset is concurrent with the arrival of a 30 60 day northward propagating trough on the other hand from a synoptic viewpoint some studies pointed out that the arrival of a mid latitude front may be the triggering mechanism of the scssm onset this study attempts to link these two viewpoints and to investigate their relative role in inducing the scssm onset composites of low level zonal winds geopotential heights and temperatures during the 1991 1999 scssm onsets based on the european centre for medium range weather forecast era 40 data indicate that both the madden and julian oscillation mjo kelvin waves and mid latitude trough are apparently involved in the onset the mjo kelvin waves play a major role in inducing the large scale easterly westerly shift over the central scs while the effect of the acceleration of westerlies ahead of the mid latitude trough is limited to the northern scs only numerical experiments using a regional climate model further demonstrate that the mjo kelvin waves control the timing of the onset by changing the background meridional geopotential height gradient over the scs when the mjo is at its peak phase over the maritime continent it imposes a positive meridional geopotential height gradient over the scs such that easterly winds are induced which significantly reduces the strength of a mid latitude trough after the equatorial convection has dissipated a rossby wave response is induced leading to the formation of a northward moving trough when this trough moves northward the meridional geopotential height gradient is reversed and westerly winds are induced at the same time if a mid latitude trough arrives in south china the westerlies associated with the mid latitude trough will strengthen because of the background meridional geopotential height gradient which gives the impression that both the northward moving trough and mid latitude trough are in phase and work together to induce the onset

geomorphic implications of subglacial drainage configuration rates of basal sediment evacuation controlled by seasonal drainage system evolution abstract although basal sediment evacuation by subglacial meltwater is widely assumed to dominate the sediment budget of most temperate glaciers and ice caps its potential influence for glacial geomorphic processes and landforms has largely been overlooked in the glacial literature data collected at haut glacier d arolla switzerland during the 1998 ablation season are used to test theoretical predictions that subglacial drainage configuration should exert a primary control on rates of basal sediment evacuation by subglacial meltwater seasonal evolution of the subglacial drainage system enables observation of sediment evacuation from both distributed and channelised drainage systems daily suspended sediment load exhibits an extreme nonlinear increase with respect to discharge between winter and summer periods which correspond to periods of predominantly distributed and channelised subglacial drainage respectively these results suggest that subglacial drainage configuration should significantly impact upon a rates of subglacial erosion and debris production b the nature of debris transport and the proportion of sediment in glacial versus fluvioglacial transport pathways and c rates and styles of ice marginal sedimentation in contrast to their distributed counterparts channelised drainage configurations are predicted to encourage subglacial erosion through the removal of basal sediment from the ice bedrock interface and with the exception of supraglacial transport will discourage sediment transport by alternative glacial mechanisms direct sedimentation at the glacier margin may therefore be reduced resulting in smaller moraines despite an overall increase in sediment production an appreciation of the coupling between glacier hydrology and geomorphic processes suggests new frameworks for the understanding of rates and styles of glacial erosion sediment transfer and deposition and the complex geomorphology of ice marginal environments

basal sediment evacuation by subglacial meltwater suspended sediment transport from haut glacier d arolla switzerland proglacial suspended sediment transport was monitored at haut glacier d arolla switzerland during the 1998 melt season to investigate the mechanisms of basal sediment evacuation by subglacial meltwater sub seasonal changes in relationships between suspended sediment transport and discharge demonstrate that the structure and hydraulics of the subglacial drainage system critically influenced how basal sediment was accessed and entrained under hydraulically inefficient subglacial drainage at the start of the melt season sediment availability was generally high but sediment transport increased relatively slowly with discharge later in the melt season sediment transport increased more rapidly with discharge as subglacial meltwater became confined to a spatially limited network of channels following removal of the seasonal snowpack from the ablation area flow capacity is inferred to have increased more rapidly with discharge within subglacial channels because rapid changes in discharge during highly peaked diurnal runoff cycles are likely to have been accommodated largely by changes in flow velocity basal sediment availability declined during channelization but increased throughout the remainder of the monitored period resulting in very efficient basal sediment evacuation over the peak of the melt season increased basal sediment availability during the summer appears to have been linked to high diurnal water pressure variation within subglacial channels inferred from the strong increase in flow velocity with discharge basal sediment availability therefore appears likely to have been increased by 1 enhanced local ice bed separation leading to extra channel flow excursions and sol or 2 the deformation of basal sediment towards low pressure channels due to a strong diurnally reversing hydraulic gradient between channels and areas of hydraulically less efficient drainage copyright 2005 john wiley sons ltd

glacial sediment production and development of hydro electric power in glacierized areas by jim bogen glaciology section norwegian water resources and energy administration p o box 5091 majorstua n 0301 oslo 3 norway abstract this paper discusses the results of a sediment monitoring programme carried out in connection with hydro electric power development plans in the river basins surrounding the jostedalsbreen ice cap in norway whereas the highest suspended sediment transport rates occur during years with several flash flood events the bed load is more dependent upon the duration of large magnitude flood events bed load transport has been obtained from annual measurements of deltaic growth in small lakes at the front of glaciers during the years 1968 86 the mean ratio of bed load to total load amounted to 0 30 0 50 of the total load but in years with large magnitude floods this ratio decreased the mean annual suspended sediment yield of norwegian glaciers ranges from 100 tonnes km2 a i to 1300 tonnes km2 a i valley glaciers cause the highest erosion rates with the exception of the small cirque glacier trollbergdalsbreen which is thought to be a soft bed glacier the investigation programme undertaken involved monitoring the volume of suspended sediments together with the size distribution mineralogy and shape of grains in general the valley glaciers supply more sand than the smaller cirque glaciers whereas particles in the fine sand and silt size ranges in almost all of the glaciers are angular in shape methods of comparing the abrasive capacity of the sediment load at various intakes in a power plant are discussed long term sediment supply from the glaciers was investigated by studies of varves and rythmites in sediment cores from glacier fed lakes introduction during the last few years several glacier areas in norway have been developed for hydro electric power in this paper the results of a sediment monitoring programme carried out in connection with hydro electric power plans in the river basins surrounding the jostedalsbreen ice cap are discussed the hydro electric power plans on the western side the breheimen stryn project involve diversions of water at 32 intakes fig

hydrological controls on patterns of surface internal and basal motion during three spring events haut glacier d arolla switzerland three early melt season high velocity events or spring events occurred on haut glacier d arolla switzerland during the melt seasons of 1998 and 1999 the events involve enhanced glacier velocity during periods of rapidly increasing bulk discharge in the proglacial stream and high subglacial water pressures however differences in spatial patterns of surface velocity internal ice deformation rates the spatial extent of high subglacial water pressures and in rates of subglacial sediment deformation suggest different hydrological and mechanical controls the data from two of the events suggest widespread ice bed decoupling particularly along a subglacial drainage axis creating the highest rates of basal motion and plug flow in the overlying ice the other event showed evidence of less extensive ice bed decoupling and sliding along the drainage axis with more mechanical support for ice overburden transferred to areas adjacent to decoupled areas we suggest that 1 plug flow may be a common feature on glaciers experiencing locally induced reductions in basal drag 2 under certain circumstances enhanced surface motion may be due in part to non locally forced enhanced bed deformation and 3 subglacial sediment deformation is confined to a depth of the order of centimetres to decimetres

meridional displacement of the east asian trough and its response to the enso forcing this paper examined the underlying dynamic mechanisms associated with the meridional displacement of the east asian trough eat which is closely related to the temperature variability in the southern part of east asian winter monsoon eawm during the southward displacement of the eat the siberian high is stronger and the aleutian low is displaced southward this is due mainly to the anomalous cyclonic flow associated with seasonal eddies over the midlatitude central pacific which enhances the horizontal advection of cold warm air to the southern northern part of the eat in the lower troposphere the cold warm advection narrows thickens the height thickness and results in negative positive temperature anomalies in the southern northern part of the eat these anomalous circulation features can be reasonably explained by the phase of the el nino southern oscillation enso the results are also verified by the numerical experiments with prescribing enso like heat source anomalies over the tropical eastern and western pacific in an anomaly atmospheric general circulation model all of these results advance our understanding for the linkage between the enso and the eawm via its modulation of the eat

physical and chemical characterization of a spring flood event bench glacier alaska u s a evidence for water storage previous studies of alpine glaciers have demonstrated that as water discharge increases through the summer the predominant mode of subglacial drainage shifts from a distributed system to a more efficient conduit drainage system we observed an early melt season speed up and flood event lasting roughly 2 days in a small uncomplicated alaskan glacier that appears to have resulted from a sudden shift of the subglacial system in response to a significant accumulation of meltwater within the glacier calculated melt water inputs exceeded discharge before the event the implied change in storage over this 10 day period was equivalent to roughly 0 13 m averaged over the entire glacier bed the pattern of discharge and suspended sediment variations and the appearance of large ice chunks in the stream suggest that the speed up occurred during a period of establishment of new subglacial conduits a culminating flood and associated suspended sediment pulse appear to have marked the final establishment of the new section of subglacial conduit the flood ended the episode of high sliding velocity but released water with high solute concentrations that reflect relatively long contact time with sediments discharge of stored water inferred from high solute concentrations and lack of diurnal variation in discharge continued for at least 3 days while events such as this must recur through the melt season as the conduit system extends up glacier and the locus of meltwater inputs shifts their manifestations in the outlet stream will likely be more subdued later in the season

borehole water level variations and the structure of the subglacial hydrological system of haut glacier d arolla valais switzerland late summer subglacial water pressures have been measured in a dense array of boreholes in the ablation area of haut glacier d arolla switzerland interpolated surfaces of minimum diurnal water pressure and diurnal water pressure variation suggest the presence of a subglacial channel within a more widespread distributed drainage system the channel flows along the centre of a variable pressure axis vpa some tens of metres wide that is characterized by low minimum diurnal water pressures frequently atmospheric and high diurnal water pressure variations these characteristics are transitional over a lateral distance of c 70 m to higher and more stable subglacial water pressures in the adjacent distributed system water pressure variations recorded in boreholes located close to the centre of the vpa reflect the delivery of surface derived meltwater to the glacier bed and result in a diurnally reversing transverse hydraulic gradient that drives water out from the channel into the distributed system during the afternoon and back to the channel overnight subglacial observations suggest that such flow occurs through a vertically confined sediment layer borehole turbidity records indicate that the resulting diurnal water flows are responsible for the mobilization and transport of fine debris in suspension analysis of the propagation velocity and amplitude attenuation of the diurnal pressure waves suggests that the hydraulic conductivity of the sediment layer decreases exponentially with distance from the channel falling from c 10 4 m s 1 at the channel boundary to c 10 7 ms 1 70m away these apparent hydraulic conductivities are consistent with darcian flow through clean sand and typical glacial till respectively we suggest that fine material is systematically flushed from basal sediments located adjacent to large melt season drainage channels beneath warm based glaciers this process may have important implications for patterns of glacier erosion hydrochemistry and dynamics

links between proglacial stream suspended sediment dynamics glacier hydrology and glacier motion at midtdalsbreen norway two hourly suspended sediment concentration variations observed during the summer of 1987 in the proglacial stream draining midtdalsbreen norway are modelled using multiple regression and time series techniques suspended sediment fluctuations are influenced by stream discharge variations diurnal hysteresis effects medium term sediment supply and transport variations and the recent suspended sediment concentration history of the stream they do not appear to be influenced by seasonal exhaustion or rainfall variations possible reasons for this are discussed large positive residuals from the fitted models are major pulses of suspended sediment unrelated to discharge variations these sediment flushes correlate with periods of enhanced glacier motion they cannot be explained by enhanced sediment production by subglacial erosion but are probably due to the tapping of subglacially stored sediment during sudden changes in the hydraulics and or configuration of the subglacial hydrological system seasonal changes in the lag between glacier motion peaks and suspended sediment flushes suggest that the subglacial hydrological system evolves over the summer from a distributed to a more channelized configuration

chemical weathering in glacial environments do glaciers enhance or inhibit chemical weathering rates relative to other environments the importance of glaciers in the global carbon cycle and climate change hinges on the answer we show that catchments occupied by active alpine glaciers yield cation denudation rates greater than the global mean rate but do not exceed rates in nonglacial catchments with similar water discharge silica denudation rates are distinctly lower in glacier covered catchments than in their nonglacial counterparts because sediment yields are high from glaciers this suggests that water flux rather than physical erosion exerts the primary control on chemical erosion by glaciers potassium and calcium concentrations are high relative to other cations in glacial water probably due to dissolution of soluble trace phases such as carbonates exposed by comminution and cation leaching from biotite preferential weathering of biotite may result in higher 87 sr 86 sr in glacial runoff than expected from whole rock compositions thus although glaciers do not influence total chemical denudation rates at a given runoff they may yield compositionally distinctive chemical fluxes to the oceans disruption of mineral lattices by grinding increases dissolution rates this and high surface area should make glacial sediments exceptionally weatherable weathering of glacial erosion products in environments beyond the glacier margin deserves attention because it may figure prominently in global chemical cycles

high and low latitude types of the downstream influences of the north atlantic oscillation using reanalysis data we find that the downstream propagating quasi stationary rossby wave train associated with the north atlantic oscillation nao generally propagates along a high low latitude pathway during warm cold el nino southern oscillation enso boreal winters consistent with the different propagation directions of the nao related downstream wave train during the warm cold enso winters the nao is associated with significant 300 hpa geopotential height anomalies over eastern siberia the arabian sea the east coast of asia at around 40 n and the north pacific and the near surface air temperature perturbations associated with the nao over the high latitudes of asia are relatively strong weak based on these differences we argue that the nao has two distinct types of downstream influence a high latitude type and a low latitude type furthermore we argue that the two types of nao s downstream influence are modulated by the intensity of the subtropical potential vorticity pv meridional gradient over africa when this gradient is weak strong as in the warm cold enso winters the nao s downstream influence tends to be of the high low latitude type these results are further supported by analysis of intraseasonal nao events we separate nao events into two categories in terms of the intensity of the subtropical pv gradient over africa composites of the nao events accompanied by a weak strong subtropical pv gradient show that the nao related downstream wave train tends to propagate along a high low latitude pathway

fluvial suspended sediment transport from cold and warm based glaciers in svalbard an analysis of temporal variability in proglacial suspended sediment concentration is undertaken using time series data collected from three svalbard basins which include one largely cold based glacier austre broggerbreen one largely warm based glacier finsterwalderbreen and one intermediate polythermal glacier erdmannbreen the temporal variability in proglacial suspended sediment concentration is analysed using multiple regression techniques in which discharge is supplemented by other predictors acting as surrogates for variability in sediment supply at diurnal medium term and seasonal timescales these multiple regression models improve upon the statistical explanation of suspended sediment concentration produced by simple sediment rating curves but need to account for additional stochastic elements within the time series before they may be considered successful an interpretation of the physical processes which are responsible for the regression model characteristics is offered as a basis for comparing the different arctic glaciofluvial suspended sediment transport systems with that of their better known temperate glaciofluvial counterparts it is inferred that the largely warm based glacier is dominated by sediment supply from subglacial reservoirs which evolve in a similar manner to temperate glaciers and which cause a pronounced seasonal exhaustion of suspended sediment supply the largely cold based glacier however is dominated by sediment supply from marginal sources which generate a responsive system at short time scales but no significant seasonal pattern the intermediate polythermal glacier basin which was anticipated to be similar to the warm based glacier instead shows a highly significant seasonal increase in suspended sediment supply from an unusual subglacial reservoir emerging under pressure in the glacier foreland the temperate model of glaciofluvial suspended sediment transport is therefore found to be of limited use in an arctic context copyright 1999 john wiley sons ltd