decadal evolution of a very small heavily debris covered glacier in an alpine permafrost environment glacier response to climate forcing can be heterogeneous and complex depending on glacier system characteristics this article presents the decadal evolution of the tsarmine glacier swiss alps a very small and heavily debris covered cirque glacier located in the alpine periglacial belt archival aerial photogrammetry and autocorrelation of orthophotos were used to compute surface elevation volume and geodetic mass changes as well as horizontal displacement rates for several periods between 1967 and 2012 a gpr survey allowed us to investigate glacier thickness 15 m mean and volume 4 10 6 m 3 in 2015 and to anticipate its future evolution different dynamics occurred in recent decades because of the heterogeneous surface characteristics the climate sensitive upper debris free zone contrasts with the progressively stagnant heavily debris covered glacier tongue between 1967 and 2012 the glacier lost 1 3 of its initial volume 2 10 6 m 3 the average mass balance stabilised at 0 3 m w e a 1 since 1999 compared with other local glaciers the tsarmine glacier shows a particular decadal behaviour both in time divergence of mass balance since the 2000s and space inverted ablation pattern this might be explained by the combined influence of debris cover shadow snow redistribution and permafrost conditions on this very small glacier

diurnal variations in vertical strain observed in a temperate valley glacier 1 during a period of diurnal fluctuations in glacial flow speed vertical strain was measured with sub daily temporal resolution on unteraargletscher switzerland mean vertical strain in boreholes up to 300 m deep in 400 m thick ice was found to fluctuate diurnally vertical strain rates were tensile in the daytime and compressive at night with a magnitude of up to 10 3 day 1 horizontal surface strain was observed to fluctuate in a manner consistent with the vertical deformation diurnal surface flow speed variations correlated well with basal water pressure suggesting a basal control on temporal flow variations nevertheless the strain rate measurements indicated that changes in surface flow speed are affected by internal ice deformation and not a direct measure of local basal motion basal conditions in the surrounding neighborhood and their temporal variations take an important role in short term glacial flow fluctuations

diurnal variability of subglacial drainage conditions as revealed by tracer experiments 1 the morphology of the drainage system of unteraargletscher switzerland and the diurnal variability of drainage conditions were investigated by conducting a series of tracer tests over a number of discharge cycles during the ablation season 2000 dye injections into a moulin were repeated at intervals of a few hours and were accompanied by simultaneous measurements of discharge of supraglacial meltwater draining into the moulin and bulk runoff in the proglacial stream fast transit velocities in conjunction with low dispersion values suggest that the tracer was routed through a hydraulically efficient channelized drainage system however detailed analyses reveal a large diurnal variability in terms of transit velocity and dispersion coefficient this finding underlines the difficulty of detecting a possible drainage system evolution based on single tracer tests conducted at coarse temporal intervals furthermore the obtained velocity discharge relationships display pronounced hysteresis we suggest that the evolution of the cross sectional area of an ice walled conduit and the modulation of inflow at the junction of a tributary moulin to a main subglacial channel are responsible for the observed behavior

the effect of the subglacial water pressure on the sliding velocity of a glacier in an idealized numerical model in order to interpret observed short term variations of the sliding velocity of a glacier the effect of a variable subglacial water pressure on the sliding velocity has been studied using an idealized numerical model in particular the transient stages of growing or shrinking water filled cavities at the ice bedrock interface were analysed it was found that the sliding velocity was larger when cavities were growing than when they had reached the steady state size for a given water pressure the smallest sliding velocities occurred while cavities were shrinking when cavitation is substantial a small drop of water pressure below the steady state value e g by 0 5 bar can temporarily cause backward sliding a limiting water pressure at which sliding becomes unstable is derived the consequences of more realistic assumptions than those of the model are discussed

water pressure and basal sliding on storglaciaren northern sweden the subglacial hydrology of the ablation area of storglaciaren a small valley glacier in northern sweden is dramatically affected by a subglacial ridge or riegel water pressures above this riegel are relatively constant while down glacier from it they vary significantly the lower part of the glacier accelerates in response to peaks in basal water pressure the upper part may be weakly coupled to the lower part during these peaks a power law fit of observed basal water pressures and measured surface velocities yields where u s is the surface velocity and p e is the effective water pressure ice overburden pressure minus subglacial water pressure data from findelengletscher reported by iken and bindschadler 1986 yield an identical exponent and a coefficient one order of magnitude larger the similar exponent implies that the process producing the velocity variations on both glaciers is similar the variations in velocity are inferred to be due to hydraulic jacking on both glaciers

the basic ingredients of the north atlantic storm track part ii sea surface temperatures abstractthe impact of north atlantic sst patterns on the storm track is investigated using a hierarchy of gcm simulations using idealized aquaplanet and semirealistic boundary conditions in the atmospheric component hadam3 of the third climate configuration of the met office unified model hadcm3 this framework enables the mechanisms determining the tropospheric response to north atlantic sst patterns to be examined both in isolation and in combination with continental scale landmasses and orography in isolation a gulf stream sst pattern acts to strengthen the downstream storm track while a north atlantic drift sst pattern weakens it these changes are consistent with changes in the extratropical sst gradient and near surface baroclinicity and each storm track response is associated with a consistent change in the tropospheric jet structure locally enhanced near surface horizontal wind convergence is found over the warm side of strengthened sst gradients associated with ascending air and i

atmospheric responses to north atlantic sst anomalies in idealized experiments part ii north american precipitation abstractthis is the second part of a two part paper that addresses deterministic roles of the sea surface temperature sst anomalies associated with the atlantic multidecadal oscillation amo in variations of atmospheric circulation and precipitation in the northern hemisphere using a sequence of idealized model runs at the spring equinox conditions this part focuses on the effect of the sst anomalies on north american precipitation major results show that in the model setting closest to the real world situation a warm sst anomaly in the north atlantic ocean causes suppressed precipitation in central western and northern north america but more precipitation in the southeast a nearly reversed pattern of precipitation anomalies develops in response to the cold sst anomaly further examinations of these solutions reveal that the response to the cold sst anomaly is less stable than that to the warm sst anomaly the former is dynamically charged in the sense that positive eddy kinetic energy eke

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

strong feedbacks between hydrology and sliding of a small alpine glacier 1 we report the spatial and temporal pattern of sliding on the 7 km long bench glacier alaska using five continuously recording gps antennas following motion of the surface ice distributed at 1 km spacing along the glacier center line we documented surface ice motion over 50 days during summer 2002 surface speeds in two previous winters constrain the motion component associated with ice deformation allowing isolation of the sliding speed history we observed two speedup events bracketing 2 weeks of steady slow sliding the first event was not associated with a meteorological trigger was more subtle than the second and propagated up glacier at a rate of several hundred meters per day the second event coincided with a warm up valley wind which triggered considerable melt of the glacier surface sliding speeds in this event reached 0 3 m d 1 and began almost simultaneously at all sites in the ablation area both the horizontal and vertical displacement time series can be explained by growth and collapse of cavities in the lee of bumps in the bedrock bed cavities grow during rapid sliding and decay by viscous creep we posit that effective pressure averaged over some large area of the bed is inversely proportional to the sliding speed this effective pressure then controls the collapse rate of cavities whose dimensions are estimated from a plausible stepped bed geometry this model explains well the horizontal and vertical surface displacement history through the first event and beginning of the second event the vertical record demands a substantial and abrupt drop in water pressure that departs from the posited sliding effective pressure relationship we argue that this pressure drop reflects establishment of efficient subglacial drainage also manifested in a nearly simultaneous step increase in water discharge in the exit stream the establishment of an efficient conduit system terminates sliding its maintenance inhibits further sliding over the remainder of the summer

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

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

changes in geometry and subglacial drainage derived from digital elevation models unteraargletscher switzerland 1927 97 digital elevation models of the bed and surface of unteraargletscher switzerland are used to reconstruct the theoretical pattern of basal water drainage for the years 1927 1947 1961 and 1997 during which period the glacier was thinning and receding the theoretical drainage pattern for 1997 compares well in a broad sense with the locations of active moulins and the hydraulic connection status of boreholes drilled to the glacier bed changes in the basal water flow pattern over the period 1927 97 that are revealed by the theoretical reconstructions of the subglacial drainage system structure are likely to have resulted from changes in glacier geometry concurrent with the retreat and thinning of the glacier the height of medial moraines increased probably due to the insulating effect of the debris cover reducing the melt of the underlying ice this increase of moraine heights has led to the formation of hydraulic barriers at the glacier bed such that water flow has become channelized beneath the ice along drainage axes that parallel the course of the medial moraines on the glacier surface

the basic ingredients of the north atlantic storm track part i land sea contrast and orography understanding and predicting changes in storm tracks over longer time scales is a challenging problem particularly in the north atlantic this is due in part to the complex range of forcings land sea contrast orography sea surface temperatures etc that combine to produce the structure of the storm track the impact of land sea contrast and midlatitude orography on the north atlantic storm track is investigated through a hierarchy of gcm simulations using idealized and semirealistic boundary conditions in a highresolution version of the hadley centre atmosphere model hadam3 this framework captures the largescale essence of features such as the north and south american continents eurasia and the rocky mountains enabling the results to be applied more directly to realistic modeling situations than was possible with previous idealized studies the physical processes by which the forcing mechanisms impact the large scale flow and the midlatitude storm tracks are discussed the characteristics of the north american continent are found to be very important in generating the structure of the north atlantic storm track in particular the southwest northeast tilt in the upper tropospheric jet produced by southward deflection of the westerly flow incident on the rocky mountains leads to enhanced storm development along an axis close to that of the continent s eastern coastline the approximately triangular shape of north america also enables a cold pool of air to develop in the northeast intensifying the surface temperature contrast across the eastern coastline consistent with further enhancements of baroclinicity and storm growth along the same axis

short term surface ice motion variations measured with a ground based portable real aperture radar interferometer we report measurements using a portable real aperture radar gamma portable radar interferometer gpri for interferometric imaging of the surface ice motion on gornergletscher switzerland during the drainage of the adjacent ice marginal lake gornersee the gpri tracked the surface ice motion in line of sight over an area of 3k m 2 down glacier of gornersee almost continuously during the drainage event the displacement maps derived from the acquired interferograms capture the spatial distribution of the surface ice motion due to fast acquisition times of the microwave images the gpri was able to record sub daily variations of the ice displacements most likely caused by the impact of the gornersee drainage on the ice motion of gornergletscher in situ point measurements of the ice displacement agree reasonably well with the results obtained by the gpri and highlight the use of the gpri for high resolution measurements of glacier surface ice motion motion of gornergletscher these variations in surface ice motion were triggered by the subglacial drainage of the adjacent marginal ice dammed lake gornersee we present ice displacement maps derived from the gpri interfero grams and analyze the performance of the radar device for remote sensing of surface ice motions of a glacier on spatial and temporal scales lower than in conventional d insar applications we compare the radar displacements against local in situ ice displacement measurements to complete the study a brief discussion of the observed displacements in relation to the drainage phenomena is given

short term variations in glacier flow controlled by subglacial water pressure at lauteraargletscher bernese alps switzerland short term variations in horizontal and vertical surface motion were studied with high temporal resolution during the ablation season in lauteraargletscher bernese alps switzerland horizontal surface flow speed oscillated diurnally showing a correlation with the water level in a borehole flow speed increased as a function of the water level with an asymptote at the ice overburden level this observation implied that the flow variations were principally controlled by the local water pressure which enhanced basal motions detailed examination of the diurnal variations however showed that the speed was larger when the pressure was increasing than when it was decreasing greater speed with increasing pressure was interpreted by subglacial watercavity opening and or longitudinal stress coupling with the upper reaches of the glacier upward surface movements were observed when the glacier flow speed increased simultaneous measurement of internal vertical strain in a borehole showed that the uplift had two different sources vertical straining of ice and volume increase of subglacial water cavities the vertical surface movement was largely affected by the vertical strain and the uplift events could not be simply attributed to cavity opening

evidence for excess pore water pressure generated in subglacial sediment implications for clast ploughing 1 pore water pressure in front of an object pulled through subglacial sediment and water pressure at the base of a borehole were simultaneously recorded at unteraargletscher switzerland to investigate the generation of excess pore pressures downglacier from ploughing clasts analysis of the strongly correlated pressure records revealed that the amplitude of the pore pressure fluctuations was larger than that of the corresponding borehole pressure fluctuations guided by high temporal resolution measurements of glacier surface motion from a different year this finding suggests that temporal changes in glacier speed lead to changes in the degree of excess pore pressure in front of the ploughing object the generation of excess pore water pressure has the potential to weaken the sediment downglacier from ploughing clasts instead of these clasts providing the roughness at the ice bed interface to resist glacier motion the ploughing process may in fact help to decouple the ice from the bed reducing basal resistance

waves of accelerated motion in a glacier approaching surge the mini surges of variegated glacier alaska u s a periods of dramatically accelerated motion in which the flow velocity increases suddenly from about 55 cm d to a peak of 100 300 cm d and then decreases gradually over the course of a day occurred repeatedly during june and july 1978 81 in variegated glacier alaska a surging type glacier that surged in 1982 83 these mini surges appear to be related mechanistically to the main surge the flow velocity peak propagates down glacier as a wave at a speed of about 0 3 km h over a reach of about 6 km in length it is accompanied by a propagating pressure wave in the basal water system of the glacier in which after a preliminary drop the pressure rises rapidly to a level greater than the ice overburden pressure at the glacier bed and then drops gradually over a period of 1 2 d usually reaching a new low for the summer the peak velocity is accompanied by a peak of high seismic activity due to widespread fresh crevassing it is also accompanied by a rapid uplift of the glacier surface amounting to 6 11 cm which then relaxes over a period of 1 2 d maximum uplift rate coincides with the peak in flow velocity the peak in accumulated uplift lags behind the velocity peak by 2 h the uplift is mainly due to basal cavitation driven by the high basal water pressure although the strain wave associated with the mini surge motion can also contribute basal cavitation is probably responsible for the pulse of high turbidity that appears in the terminal outflow stream in association with each mini surge in the down glacier reach where the mini surge waves are attenuating the observed strain wave corresponds to what is expected for the propagating pulse in flow velocity but in the reach of maximum mini surge motion the strain wave has a form quite different possibly related to special features in the mini surge initiation process from that point up stream the flow acceleration in the mini surges is due to enhanced basal sliding caused by the high basal water pressure and the consequent reduction of bed friction a preliminary velocity increase shortly before the pressure wave arrives is caused by the forward shove that the main accelerated mass exerts on the ice ahead of it and the resulting preliminary basal cavitation causes the drop in water pressure shortly before the pressure wave arrives the mini surge wave propagation is controlled by the propagation of the water pressure wave in the basal water conduit system the propagation characteristics result from a longitudinal gradient up glacier increase in hydraulic conductivity of the basal water system in response to the up glacier increase of the basal water pressure in the mini surge wave the mini surge waves are initiated in a succession of areas situated generally progressively up glacier during the course of the summer season in these areas presumably melt water that has accumulated in subglacial reservoirs is released suddenly into the basal water system immediately below generating a pressure rise that propagates down stream from there relationships of the mini surges to the main surge are seen in the role of high basal water pressure in causing the rapid glacier motion in both phenomena in the pulse propagation features of both and in the high outflow turbidity associated with both the mini surges of variegated glacier have a strong resemblance to movement and uplift events observed in unteraargletscher and findelengletscher switzerland this bears on the question whether the mini surges are a particular characteristic of surge type glaciers prior to surge

propagating strain anomalies during mini surges of variegated glacier alaska u s a analyse des deplacements acceleres observes a l aide de jauges de deformation et de geophones 1979 1980 1981 evolution des mini surges deformations glissement basal

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

downstream self destruction of storm tracks the northern hemisphere storm tracks have maximum intensity over the pacific and atlantic basins their intensity is reduced over the continents downstream here simulations with an idealized aquaplanet general circulation model are used to demonstrate that even without continents storm tracks have a self determined longitudinal length scale their length is controlled primarily by the planetary rotation rate and is similar to thatofearth sstormtracksforearth srotationrate downstream stormtracksself destruct thedownstream eddy kinetic energy is lower than it would be without the zonal asymmetries that cause localized storm tracks likely involved in the downstreamself destruction ofstormtracks arethe energyfluxesassociatedwiththem the zonalasymmetries that causelocalized stormtracksenhancetheenergytransport throughthe generation of stationary eddies and this leads to a reduced baroclinicity that persists far downstream of the eddy kinetic energy maxima

the central role of ocean dynamics in connecting the north atlantic oscillation to the extratropical component of the atlantic multidecadal oscillation abstractthe relationship between the north atlantic oscillation nao and atlantic sea surface temperature sst variability is investigated using models and observations coupled climate models are used in which the ocean component is either a fully dynamic ocean or a slab ocean with no resolved ocean heat transport on time scales less than 10 yr nao variations drive a tripole pattern of sst anomalies in both observations and models this sst pattern is a direct response of the ocean mixed layer to turbulent surface heat flux anomalies associated with the nao on time scales longer than 10 yr a similar relationship exists between the nao and the tripole pattern of sst anomalies in models with a slab ocean a different relationship exists both for the observations and for models with a dynamic ocean in these models a positive negative nao anomaly leads after a decadal scale lag to a monopole pattern of warming cooling that resembles the atlantic multidecadal oscillation amo although with sma

surface strain anomaly induced by the storage and drainage of englacial water in koryto glacier kamchatka russia to investigate short term flow pattern variations of a temperate glacier longitudinal surface strain was measured with a wire strainmeter in the ablation area of koryto glacier kamchatka russia strain rate anomalies were observed in late summer 2000 that were triggered by a water overflow from a moulin near the measurement site followed by the drainage of accumulated water the strain event started with compressive strain rates of 10 3 d 1 lasting for 6 hours which then became tensile similar strain rate variations were observed again on the next day during the event basal sliding speed measured at the margin in the lower reach of the glacier fluctuated by about 50 of the daily mean smaller and larger sliding speeds corresponded to the compressive and tensile surface strains respectively these measurements suggest that the storage and sudden drainage of water caused spatially non uniform water pressure fluctuations along the glacier changing the sliding regime over short time periods

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

surface melt induced acceleration of greenland ice sheet flow ice flow at a location in the equilibrium zone of the west central greenland ice sheet accelerates above the midwinter average rate during periods of summer melting the near coincidence of the ice acceleration with the duration of surface melting followed by deceleration after the melting ceases indicates that glacial sliding is enhanced by rapid migration of surface meltwater to the ice bedrock interface interannual variations in the ice acceleration are correlated with variations in the intensity of the surface melting with larger increases accompanying higher amounts of summer melting the indicated coupling between surface melting and ice sheet flow provides a mechanism for rapid large scale dynamic responses of ice sheets to climate warming

short term variations in flow velocity of glaciar soler patagonia chile short term variations in ice flow velocity were obtained at intervals of a few hours and a few days in the ablation area of glaciar soler patagonia chile in november 1985 a maximum flow rate was measured at about four times the minimum value a good correlation with a time lag of 7 5 h was found between the ice flow velocity in the lower reaches and the amount of water discharge from the glacier terminus it was concluded therefore that the velocity variations should have resulted from the variations in basal sliding velocity which is strongly controlled by the subglacial water pressure

observations of a reversal in vertical and horizontal strain rate regime during a motion event on unteraargletscher bernese alps switzerland during a motion event on unteraargletscher bernese alps switzerland in spring 1996 surface velocities were measured up to eight times a day at four different locations along the central flowline using global positioning system equipment in addition accumulated vertical strains over the uppermost 50 and 100 m were measured at a location where the total ice thickness is 260 m the motion event was accompanied by high horizontal and vertical strain rates as compared to annual mean values a reversal in strain regime was observed with horizontal strain rates changing to extension while vertical strain rates became compressive this strain rate reversal coincided within the temporal resolution of the data with a maximum in vertical ice displacement at the surface within a day variations in vertical strain from 0 04 a 1 to 0 06 a 1 were observed over the uppermost 100 m vertical stretching is estimated to have contributed to at least 20 of the anomalous vertical ice movement at the surface there were significant differences between measured longitudinal strain averaged over a distance corresponding to a few ice thicknesses and measured vertical strain in spring 1997 a similar but more detailed set of measurements was collected at the same measuring site and vertical strain rates were found to vary non uniformly with depth with the largest values closest to the surface

character of the englacial and subglacial drainage system in the lower part of the ablation area of storglaciaren sweden as revealed by dye trace studies

quiescent phase dynamics and surge history of a polythermal glacier hessbreen svalbard hessbreen is a 5 km 2 polythermal glacier in southern spitsbergen it is believed to have surged at the end of the 19th century and another surge started in 1969 not in 1972 as earlier studies suggested the surge was probably triggered in the middle section of the glacier and affected the upper part approximately 4 years before including the whole glacier present velocities are low increasing from 0 3 m a 1 at the snout to 4 8 m a 1 above the equilibrium line a distinct velocity reduction occurs where the glacier narrows this suggests the velocities here are affected by the cold marginal and frontal ice large seasonal variations with summer velocities of more than twice the winter velocities in the middle part of the glacier indicate a seasonal change in the drainage system in this area in the lower part there is no apparent sliding the balance flux estimate indicates that the actual ice flux is only about 50 of that required for steady state so hessbreen appears to be building up in the accumulation area the surge duration is now estimated to be 8 years

variations in north american summer precipitation driven by the atlantic multidecadal oscillation understanding the development and variation of the atmospheric circulation regimes driven by the atlantic multidecadaloscillation amo isessentialbecausethesecirculationsinteractwithotherforcingsondecadaland interannual time scales collectively they determine the summer june july and august precipitation variations for north america in this study a general circulation model gcm is used to obtain such understanding with a focus on physical processes connecting the amo and the summertime precipitation regime change in northamerica twoexperimentalrunsareconductedwithseasurfacetemperature sst anomaliesimposedin the north atlantic ocean that represent the warm and cold phases of the amo climatological ssts are used elsewhere in the oceans model results yield summertime precipitation anomalies in north america closely matching the observed anomaly patterns in north america suggesting that the amo provides a fundamental control on summertime precipitation in north america at decadal time scales the impacts of the amo are achieved by a chain of events arising from different circulation anomalies during warm and cold phases of the amo during the warm phase the north atlantic subtropical high pressure system nash weakens and the north american continent is much less influenced by it a massive body of warm air develops over the heated land in north america from june august associated with high temperature and low pressure anomalies in the lowertroposphereandhighpressureanomaliesintheuppertroposphere incontrast duringthecoldphaseofthe amo the north american continent particularly to the west is much more influenced by an enhanced nash cooler temperatures and high pressure anomalies prevail in the lower troposphere and a frontal zone forms in the upper troposphere these different circulation anomalies further induce a three cell circulation anomaly pattern over north america in the warm and cold phases of the amo in particular during the cold phase the three cell circulation anomaly pattern features a broad region of anomalous low level southerly flow from the gulf of mexico into the u s great plains superimposed with an upper troposphere front more frequent summertime storms develop and excess precipitation occurs over most of north america a nearly reversed condition occurs during the warm phase of the amo yielding drier conditions in north america this new understandingprovides a foundation for further studyand better prediction of the variations of north american summer precipitation especially when modulated by other multidecadal variations for example the pacific decadal oscillation and interannual variations associated with the enso and the arctic oscillation

reversal of ice motion during the outburst of a glacier dammed lake on gornergletscher switzerland during the outburst flood of a glacier dammed lake on gornergletscher switzerland in july 2004 the drained lake water triggered anomalous glacier motion at the onset of the outburst the ice flow direction in the vicinity of the lake became closer to the central flowline when the lake discharge magnitude decreased the flow direction altered such that the ice moved back to the azimuth of the initial motion at one of the survey points where the ice flows parallel to the central flowline the ice accelerated along the pre event flow direction followed by a 1808 backward motion that lasted over 2 days these observations indicate the impact of the lake outburst on the subglacial and englacial stress conditions however the reversal in the flow direction is difficult to explain by drawing on our current understanding of glacier mechanics the timing and the timescale of the flow direction changes suggest that the elastic glacier motion and its rebound played a role under the rapidly changing stress conditions but the young s modulus of ice is too large to cause the observed ice motion other processes including basal separation and subglacial sediment deformation are discussed as possible mechanisms for the reversal of the ice motion

winter cold of eastern continental boundaries induced by warm ocean waters in winter northeastern north america and northeastern asia are both colder than other regions at similar latitudes this has been attributed to the effects of stationary weather systems set by elevated terrain orography and to a lack of maritime influences from the prevailing westerly winds however the differences in extent and orography between the two continents suggest that further mechanisms are involved here we show that this anomalous winter cold can result in part from westward radiation of large scale atmospheric waves nearly stationary rossby waves generated by heating of the atmosphere over warm ocean waters we demonstrate this mechanism using simulations with an idealized general circulation model with which we show that the extent of the cold region is controlled by properties of rossby waves such as their group velocity and its dependence on the planetary rotation rate our results show that warm ocean waters contribute to the contrast in mid latitude winter temperatures between eastern and western continental boundaries not only by warming western boundaries but also by cooling eastern boundaries

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

atmospheric responses to north atlantic sst anomalies in idealized experiments part i northern hemispheric circulation abstractidealized model experiments using the ncar cesm1 0 5 under equinox conditions are designed and performed to address two fundamental questions about the effects of the sea surface temperature sst variation associated with the atlantic multidecadal oscillation amo on circulation and precipitation in north america and europe 1 is the observed relationship between the amo sst and the warm season precipitation in north america a statistical coincidence and 2 why is the response of negative precipitation anomaly to warm sst in the amo fairly uniform across most of north america whereas the positive precipitation anomaly in the cold sst rather spotty model experiments are done with either a warm or cold sst anomaly in an aquaplanet a planet with idealized continents and a planet with both idealized continents and orography major results show that the atmospheric response to warm sst anomaly in the north atlantic is fairly similar among the three sets of experiments in the lower troposphere

short term velocity variations on hansbreen a tidewater glacier in spitsbergen spatial and temporal variations of the flow of hansbreen a tidewater glacier in southern spitsbergen svalbard are investigated during summer 1999 surface flow velocities were measured in the ablation zone of hansbreen with a temporal reso lution of 3 4 hours short events with strongly increased surface velocities and a typical duration of 1 2 days were observed these speed up events are related to periods of strongly increased water input to the glacier due to rainfall or enhanced surface melt a close relation is found between the surface velocities and water pressure recorded in a moulin however there are indications from a short time lag between velocity and water pressure peak as well as from observed vertical surface uplifts that basal motion is related to basal water storage rather than directly to basal water pressure the observed short term velocity variations and associated processes on hansbreen are very similar to those observed on land based valley glaciers and suggest that the relevant mechanisms and physical processes that control the flow and its temporal variations are similar in contrast to the flow of land based glaciers sliding velocities on hansbreen are observed to be high all year round and velocities increase towards the calving front

high resolution measurements of spatial and temporal variations in surface velocities of unteraargletscher bernese alps switzerland data from automated in situ measurements of surface displacements on unteraargletscher bernese alps switzerland made a few times a day from late june until late october 1998 are presented two short term speed up events were observed and partial evidence for a third motion event was seen short term motion events are thus not limited to the start of the melting season strong correlation between the timing of the motion events and periods of heavy rainfall in conjunction with the large size of the area of the glacier which becomes activated during the events both point towards an external triggering mechanism in the time periods between two motion events surface velocities do not vary significantly with time after a motion event surface velocities do not return to previous values suggesting that the events have a lasting effect on the structure of the subglacial drainage system

surface ice motion deviating toward the margins during speed up events at gornergletscher switzerland 1 high frequency ice flow measurements during speed up events in gornergletscher switzerland revealed intriguing ice motion which has never been reported in detail before during the summer 2005 more than a 100 flow speed increase was observed three times at four gps stations installed across gornergletscher the speed ups were accompanied by a decimeter scale surface uplift two of the events were triggered by intensive surface melt and rainfall while the third one was due to the outburst of gornersee a glacier dammed lake located 2 km upglacier an interesting observation was ice motion deviating toward the side margins during the events as the glacier accelerated a transverse cross glacier velocity component was generated turning the flow direction away from the central flow line toward the margins when the glacier decelerated the transverse velocity component reversed so that the ice flowed back to the azimuth of the initial flow direction in the most significant case the trajectory of the survey stake deviated from the original track by 0 2 m in the transverse direction we hypothesize that the observed lateral ice motion was caused by locally elevated subglacial water pressure when the ice sole decoupled from the bed at a part of the glacier a point source of vertical displacement was transmitted to the surface through viscous ice this caused the transverse as well as vertical surface motion as observed in ground motion during magma intrusion the hypothesis was tested with a two dimensional ice flow model applied to the transverse glacier cross section the model confirmed that the surface ice would move toward the margins as observed in gornergletscher if subglacial water pressure exceeded the ice overburden pressure over a limited part of the bed

short term velocity and water pressure variations down glacier from a riegel storglaciaren sweden during the 1991 94 summer field seasons time correlated measurements of water pressure and surface speed were made over and down glacier from a major riegel on storglaciaren sweden measurements were made at sub hourly time scales in order to discern details in the diurnal cycle large water input events typically associated with rain storms produced coherent lagged surface velocity responses that could be understood in terms of till deformation or decoupling and these have been discussed elsewhere the consequences of smaller diurnal water pressure events were more enigmatic in that acceleration of ice flow generally preceded the onset of the local water pressure rise from consideration of these data and other work done on the hydrology of storglaciaren we infer that the ice in this area is generally pushed from behind via a relaxation in extensional strain across the riegel hence accelerations occur in response to increases in water pressure that occur up glacier and that precede local water pressure rises in addition following a period of large storm events surface speeds became more spatially coherent and were in phase with the diurnal ater pressure cycle this suggests that the large water pressure events lead to a spatially more homogeneous subglacial drainage system sliding laws need to take into accoun such temporal changes in spatial coherence of the subglacial drainage system

amplified melt and flow of the greenland ice sheet driven by late summer cyclonic rainfall intense rainfall events significantly affect alpine and alaskan glaciers through enhanced melting ice flow acceleration and subglacial sediment erosion yet their impact on the greenland ice sheet has not been assessed here we present measurements of ice velocity subglacial water pressure and meteorological variables from the western margin of the greenland ice sheet during a week of warm wet cyclonic weather in late august and early september 2011 we find that extreme surface runoff from melt and rainfall led to a widespread acceleration in ice flow that extended 140 km into the ice sheet interior we suggest that the late season timing was critical in promoting rapid runoff across an extensive bare ice surface that overwhelmed a subglacial hydrological system in transition to a less efficient winter mode reanalysis data reveal that similar cyclonic weather conditions prevailed across southern and western greenland during this time and we observe a corresponding ice flow response at all land and marine terminating glaciers in these regions for which data are available given that the advection of warm moist air masses and rainfall over greenland is expected to become more frequent in the coming decades our findings portend a previously unforeseen vulnerability of the greenland ice sheet to climate change

glacier surface velocities in alpine terrain from optical satellite imagery accuracy improvement and quality assessment the worldwide retreat of mountain glaciers has important consequences for the water food and power supply of large and densely populated areas in south and central asia successful mitigation of the hydrological impacts on societies as well as assessing glacier related hazards require large scale monitoring of glacier dynamics however detailed glaciological data from the asian highlands are lacking due to its size and difficult accessibility we have applied a novel technique for precise orthorectification co registration and sub pixel correlation of advanced spaceborne thermal emission and reflection radiometer aster satellite imagery to derive surface velocities of himalayan glaciers our approach allows for the correction of offsets due to attitude effects and sensor distortions as well as elevation errors if a digital elevation model dem from the shuttle radar topography mission srtm was used for orthorectification after post processing the error on the displacements is on the order of 2 4 m per correlation translated into annual velocities this error is reduced increased when the correlated images are more less than a year apart through application of a filtering procedure and several quality tests the consistency of the results is validated to provide confidence in the remotely sensed velocity measurements despite the lack of ground control this novel approach allows fast easy and economically viable acquisition of detailed glaciological data in areas of difficult access and provides a means for large scale monitoring of glaciers in high mountainous terrain

variations in the surface velocity of an alpine cirque glacier following pioneering work in norway cirque glaciers have widely been viewed as rigidly rotating bodies this model is incorrect for basin filling cirque glaciers as we have demonstrated at west washmawapta glacier a small glacier in the canadian rocky mountains here we report observations at the same glacier that assess whether complex temporal variations of flow also occur for parts of three summers we measured daily displacements of the glacier surface in one year four short duration speed up events were recorded three of the events occurred during the intervals of warmest weather when melt was most rapid the fourth event occurred immediately following heavy rain we interpret the speed up events as manifestations of enhanced water inputs to the glacier bed and associated slip lubrication by increased water volumes and pressures no further speed ups occurred in the final month of the melt season despite warm temperatures and several rainstorms the dominant subglacial water system likely transformed from one of poorly connected cavities to one with an efficient channel network the seasonal evolution of hydrology and flow resembles behaviors documented at other larger temperate glaciers and indicates that analyses of cirque erosion cannot rely on simple assumptions about ice dynamics

on the existence of storm tracks abstract given that middle latitude weather systems transport heat in a manner such as to weaken the baroclinicity that is thought to be crucial to their growth it is perhaps surprising that concentrated regions of such eddy activity i e storm tracks are found in the northern hemisphere winter the existence and possible self maintenance of storm tracks is investigated using a linear stationary wave model with storm track region forcings taken from data averaged over a number of winters it is found that the direct thermal effect of the eddies does indeed act against the existence of the storm track their vorticity fluxes lead to some reduction of this effect it is argued that the mean diabatic heating in the storm track region is an indirect eddy effect this heating is found to maintain the mean maximum in baroclinicity in the region further the mean low level flow induced by the eddy effects is such as to enhance the warm western oceanic boundary currents that are crucial to the existence of t

hydraulic and mechanical properties of glacial sediments beneath unteraargletscher switzerland implications for glacier basal motion the force on a ploughmeter and subglacial water pressure have been measured in the same borehole at unteraargletscher switzerland in order to investigate ice sediment coupling and the motion at the base of a soft bedded glacier a strong inverse correlation of the recorded pressure and force fluctuations in conjunction with a significant time lag between the two signals suggests that pore water pressures directly affect the strength of the subglacial sediment the lag is interpreted to reflect the time required for the water pressure wave to propagate through the pores of the sediment to the depth of the ploughmeter analysis of the propagation velocity of this pressure wave yielded an estimate of the hydraulic diffusivity a key parameter necessary to characterize transient pore water flow furthermore the inferred inverse relationship between pore water pressure and sediment strength implies that coulomb plastic deformation is an appropriate rheological model for the sediment underlying unteraargletscher however the sediment strength as derived from the ploughmeter data was found to be one order of magnitude smaller than that calculated for a coulomb frictional material using the water pressure measurements this significant discrepancy might result from pore water pressures in excess of hydrostatic down glacier from the ploughmeter as the ploughmeter is dragged through the sediment sediment is compressed if the rate of this compression is large relative to the rate at which pore water can drain away excess pore water pressures will develop that have the potential to weaken the sediment the same process could lead to highly fluid sediment down glacier from clasts that protrude into the glacier sole and thus would otherwise provide the roughness to couple the glacier to its bed iverson 1999 rapidly sliding glaciers overlying sediments might therefore move predominantly by ploughing which tends to focus basal motion near the glacier sole rather than at depth in the bed

short term velocity variations and basal coupling near a bergschrund storglaciaren sweden distance measurements using an automated electronic distance measurement system in the north cirque of storglaciaren sweden during the summer of 1989 revealed a diurnal variation in glacier speed amplitude and timing of the diurnal cycle correlate well with the timing and intensity of the diurnal temperature cycle indicating that speed responds to variations in daily melt with a lag of approximately 4 h one 2 d period of non diurnal velocity variations corresponded with a large rainfall event finite element modeling suggests that these velocity variations must be closely related to water inputs in the cirque rather than to longitudinal coupling with lower parts of the glacier

glacier dammed lake outburst events of gornersee switzerland gornersee switzerland is an ice marginal lake which drains almost every year subglacially within a few days we present an analysis of the lake outburst events between 1950 and 2005 as well as results of detailed field investigations related to the lake drainage in 2004 and 2005 the latter include measurements of lake geometry water pressure in nearby boreholes and glacier surface motion a distributed temperature index melt model coupled to a linear reservoir runoff model is used to calculate hourly discharge from the catchment of gornergletscher in order to distinguish between the melt precipitation component and the outburst component of the discharge hydrograph in this way drainage volume and timing are determined from 1950 there is a clear trend for the outburst flood to occur earlier in the melt season but there is no trend in lake discharge volumes peak discharges from the lake lie significantly below the values obtained using the empirical relation proposed by clague and mathews 1973 the shapes of the 2004 and 2005 lake outflow hydrographs differ substantially suggesting different drainage mechanisms from water balance considerations we infer a leakage of the glacier dammed lake in 2005 starting 1 week prior to the lake outburst during the drainage events up to half of the lake water is temporarily stored in the glacial system causing substantial uplift of the glacier surface

the influence of atlantic variability on asian summer climate is sensitive to the pattern of the sea surface temperature anomaly we simulate the response of asian summer climate to atlantic multidecadal oscillation amo like sea surface temperature sst anomalies using an intermediate complexity general circulation model igcm4 experiments are performed with seven individualamosst anomalies obtained from cmip5 pmip3 global climate models as well as their multimodel mean globally and over the north atlantic ocean only for both the positive and negative phases of the amo during the positive warm amo phase a rossby wave train propagates eastward causing a high pressure and warm and dry surface anomalies over eastern china and japan during the negative cool phase of the amo the midlatitude rossby wave train is less robust but the model does simulate a warm and dry south asian monsoon associated with the movement of the intertropical convergence zone in the tropical atlantic the circulation response and associated temperature and precipitation anomalies are sensitive to the choice of amo sst anomaly pattern a comparison between global sst and north atlantic sst perturbation experiments indicates that east asian climate anomalies are forced from the north atlantic region whereas south asian climate anomalies are more strongly affected by the amo related sst anomalies outside the north atlantic region experiments conducted with different amplitudes of negative and positiveamoanomalies show that the temperature response is linear with respect to sst anomaly but the precipitation response is nonlinear

intra seasonal changes in deformation profiles revealed by borehole studies storglaciaren sweden in 1985 1987 and 1988 we measured deformation of bore holes in the ablation zone of storglaciaren a different hole was used each year deformation profiles were determined for four consecutive time periods between mid july and early september all three holes were in an area where the glacier lies in an overdeepened part of the bed up glacier from a riegel the first hole was approximately on the glacier center line while the others were midway between the center line and one or the other margin despite large standard errors variations in the deformation profiles during the melt season are broadly consistent with other data we thus believe that they are real and that they reflect changes in the stress field resulting from changes in drag at the bed a decrease in drag early in the melt season coupled with convergence of the bed contours towards the riegel is believed to be responsible for a previously documented increase in vertical velocity just up glacier from the riegal at this time of year also noteworthy but perhaps problematical was an abrupt transverse shear of m at a depth of 25 m near the center of the glacier injuly 1985 the shear took place in the zone in which cold ice near the surface gives way to temperate ice deeper in the glacier