present day south american climate abstract this paper documents the main features of the climate and climate variability over south america on the basis of instrumental observations gathered during the 20th century it should provide a modern reference framework for paleoclimate research in south america targeting high resolution proxies over the past few centuries several datasets suitable for present day climate research are first described highlighting their advantages as well as their limitations we then provide a basic physical understanding of the mean annual cycle of the precipitation and atmospheric circulation over the continent and the adjacent oceans in particular the diversity of precipitation temperature and wind patterns is interpreted in terms of the long meridional extent of the continent and the disruption of the large scale circulation caused by the andes cordillera the contrasting oceanic boundary conditions and the landmass distribution similarly the intensity and timing of the interannual and interdecadal climatic fluctuations exhibit considerable geographical dependence as some regions are more influenced by large scale phenomena rooted in the tropical oceans while others are more influenced by high latitude phenomena the impact of these large scale phenomena over south america is documented by a regression analysis between selected atmospheric indices and the precipitation and temperature fields we have included a discussion on the seasonality and long term stability of such impacts and complemented our general description by an updated review of the literature on climate variability over specific regions

first results from a pre operational system for automatic detection and recognition of seismic signals associated with avalanches a system for automatic reliable semi instantaneous estimation of avalanche activity is presented in an attempt to check deterministic models and improve the surveillance of risk zones the principle is the seismic detection of avalanches two experimental sites equipped with standard seismological equipment are described avalanche seismic signals are recorded as well as many extraneous signals of natural or human origin after several years of a posteriori identification of the signals we are now able to set up criteria for the automatic recognition of non avalanche signals we have therefore developed an automatic analysis decision system to discriminate betweenn avalanche signals and others this system worked satisfactorily in pre operational conditions during the winter of 1995 96 the results are presented and compared with other data related to avalanche activity although there is still room for improvement our system seems to be able to estimate avalanche activity better than human visual observations

the sea level response of a stratified ocean to barometric pressure forcing abstract the nature of the sea surface adjustment to atmospheric loading in a stratified ocean is examined for both midlatitude and equatorial regions using simple analytical solutions to the quasigeostrophic and equatorial plane equations while the interior response can have vertical structures ranging from oscillatory to surface trapped depending on the temporal and spatial scales of the forcing the sea surface reacts as an inverted barometer at most scales the inverted barometer or isostatic approximation breaks down only for narrow ranges of frequency and horizontal wavenumber values where the vertical dependence of solutions approaches that of the oceanic normal modes in these regions the sea surface adjustment can be both smaller and larger than the isostatic limit and is sensitive to frequency and wavenumber the vertical stratification introduces a number of nonisostatic regimes particularly in the equatorial regions not possible in a constant density ocean but the importance of these

observations of atmosphere ocean coupling in midlatitude western boundary currents oceanographic fields derived from the geosat altimeter and atmospheric fields from the european centre for medium range weather forecasts ecmwf were examined for both the western north pacific ocean and the western north atlantic ocean to determine the nature of the coupling despite the short data records approximately 2 5 years correlation analyses of nonseasonal fluctuations showed similar relationships for both oceans correlations between the height difference across the jets surface transport and the path of the western boundary currents suggested that there is a structural change of the recirculation gyres associated with a path change with timescales of 5 9 months both wind stress and wind stress curl were clearly correlated with the surface transport and path in each ocean although net surface heat flux and wind stress were correlated there was no clear correlation between net surface heat flux from ecmwf and surface transport over the entire study region additional regional analyses of the north atlantic showed a consistent relationship between cooling sea surface temperature sst and surface transport west of 62 w anomalous cooling accompanied by cyclonic wind anomalies corresponds to a weaker sst gradient across the gulf stream and decreasing surface transport because the surface transport fluctuations to the west and east of 62 w in the western north atlantic are not correlated structural changes in the recirculation gyres which have their maximum variations east of 62 w may not be related to surface heat flux variations

sea level pressure variability around antarctica since a d 1750 inferred from subantarctic tree ring records a tree ring chronology network recently developed from the subantarctic forests provides an opportunity to study long term climatic variability at higher latitudes in the southern hemisphere fifty long 1911 1985 homogeneous records of monthly mean sea level pressure mslp from the southern latitudes 15 65 s were intercorrelated on a seasonal basis to establish the most consistent long term trans polar teleconnections during this century variations in summer mslp between the south america antarctic peninsula and the new zealand sectors of the southern ocean are significantly correlated in a negative sense r 0 53 p 0 001 climatically sensitive chronologies from tierra del fuego 54 55 and new zealand 39 47 were used to develop verifiable reconstructions of summer november to february mslp for both sectors of the southern ocean these reconstructions which explain between 37 and 43 of the instrumentally recorded pressure variance indicate that inverse trends in mslp from diametrically opposite sides of antarctica have prevailed during the past two centuries however the strength of this relationship varies over time differences in normalized mslp between the new zealand and the south america antarctic peninsula sectors were used to develop a summer trans polar index stpi which represents an index of sea level pressure wavenumber one in the southern hemisphere higher latitudes tree ring based reconstructions of stpi show significant differences in large scale atmospheric circulation between the nineteenth and the twentieth centuries predominantly negative stpi values during the nineteenth century are consistent with more cyclonic activity and lower summer temperatures in the new zealand sector during the 1800s in contrast cyclonic activity appears to have been stronger in the mid twentieth than previously for the south american sector of the southern ocean recent variations in mslp in both regions are seen as part of the long term dynamics of the atmosphere connecting opposite sides of antarctica a detailed analysis of the mslp and stpi reconstructions in the time and frequency domains indicates that much of the interannual variability is principally confined to frequency bands with a period around 3 3 3 6 y cross spectral analysis between the stpi reconstruction and the southern oscillation index suggests that teleconnections between the tropical ocean and extra tropical mslp variations may be influencing climate fluctuations at southern latitudes

investigations of fennoscandian glacial isostatic adjustment using modern sea level records we present a new method for determining the rates from a network of regional tide gauge data the method involves using a model for the sea level observations annual averages of relative sea level that explicitly includes a term for the interannual sealevel variations which are assumed to be constant for all sites in the network the resulting simultaneous analysis of all the sea level observations yields sea level rates which are biased by the unknown temporal slope of the interannual variations by differencing sea level rate estimates with respect to one site site referenced sea level rates are calculated which are free from this bias the differencing procedure also removes any signal due to a common sea level rate such as might be associated with eustatic sea level rise the resulting site referenced sea level rates therefore in principle reflect only the relative vertical crustal motions of the tide gauge sites with respect to the geoid these site referenced sea level rates represent a potentially more accurate data set than have previously been used for sea level studies we have used these rates to investigate glacial isostatic adjustment gia in fennoscandia specifically we have used the site referenced sea level rates within the baltic sea to estimate adjustments to the ice history and earth model which are used to calculate vertical rates of adjustment due to gia a method never before used for fennoscandia the parameters selected were lithospheric thickness the viscosities of assumed isoviscous upper and lower mantles and a fennoscandian ice thickness scaling parameter we present the results of this estimation procedure for a specific test ice model we also find evidence that the sea level record for the site nearest the center of uplift furuogrund may be contaminated by systematic errors of unknown origin data from this site have previously been used to determine a rate for the maximum uplift that we find is perhaps 1 mm yr 1 or 10 too large

large scale response of the ocean to atmospheric forcing at low frequencies estimates of the time dependent sea surface topography on large space 500 2500 km and time 30 days to 2 years scales from altimetry and tide gauge data are compared with estimates of the surface meteorological fields winds and pressure on the same scales the comparisons are made in the north pacific and north atlantic despite the obvious remaining high noise level in the sea surface topography there is a significant correlation between the atmosphere and the time varying ocean circulation these relations are quantified using simple multichannel regression models with no time lags typically 50 of the sea level variance can be described by the wind curl and divergence and the pressure field some areas produce classical static inverted barometer effects but others suggest an amplified response the motions are believed to characterize most of the water column

the duration of the active phase on surge type glaciers contrasts between svalbard and other regions many glaciers in svalbard and in other glacierized areas of the world are known to surge however the time series of observations required to assess the duration of fast motion is very restricted data on active phase duration in svalbard come from aerial photographs satellite imagery field surveys and airborne reconnaissance evidence on surge duration is available for eight svalbard ice masses varying from 3 to 1250 km 2 worldwide active phase duration is recorded for less than 50 glaciers few observations are available on high polar ice masses the duration of the active phase is significantly longer for svalbard glaciers than for surge type glaciers in other areas from which data are available in svalbard the active phase may last from 3 to 10 years by contrast a surge duration of 1 2 years is more typical of ice masses in northwest north america iceland and the pamirs ice velocities during the protracted active phase on svalbard glaciers are considerably lower than those for many surge type glaciers in these other regions mass is transferred down glacier more slowly but over a considerably longer period svalbard surge type glaciers do not exhibit the very abrupt termination of the active phase over periods of a few days observed for several alaskan glaciers the duration of the active phase in svalbard is not dependent on parameters related to glacier size the quiescent phase is also relatively long 50 500 years for svalbard ice masses detailed field monitoring of changing basal conditions through the surge cycle is required from surge type glaciers in svalbard in order to explain the significantly longer length of the active phase for glaciers in the archipelago which may also typify other high polar ice masses the finding that surge behaviour in the form of active phase duration shows systematic differences between different regions and their environments has important implications for understanding the processes responsible for glacier surges

analysis of rock fall and rock fall avalanche seismograms in the french alps this study reviews seismograms from 10 rock fall events recorded between 1992 and 2001 by the permanent seismological network sismalp in the french alps a new seismic magnitude scale was defined which allowed us to compare and classify g round motion vibrations generated by these alpine rock falls each rock fall has also been cha racterized by its ground motion duration t30 at an epicentral distance of 30 km no relation was found between rock fall parameters fall height runout distance volume potential energy and rock fall s eismic magnitudes derived from seismogram amplitudes on the other hand the signal duration t30 shows a rough correlation with the potential energy and the runout distance highlighting the co ntrol of the propagation phase on the signal length the signal analysis suggests the existence of at le ast two distinct seismic sources one corresponding to the initial rupture associated with an elastic r ebound during the detachment and the other one generated by the rock impact on the slope although the fall phenomenon includes other complex processes fragmentation of the block interaction with topography plastic deformation during and after impact 2d finite element simulations of thes e two seismic sources are able to retrieve the main seismogram characteristics

seismic precursory patterns before a cliff collapse and critical point phenomena 1 we analyse the statistical pattern of seismicity before a 1 2 103 m3 chalk cliff collapse on the normandie ocean shore western france we show that a power law acceleration of seismicity rate and energy in both 40 hz 1 5 khz and 2 hz 10khz frequency range is defined on 3 orders of magnitude within 2 hours from the collapse time simultaneously the average size of the seismic events increases toward the time to failure these in situ results are derived from the only station located within one rupture length distance from the rock fall rupture plane they mimic the critical point like behavior recovered from physical and numerical experiments before brittle failures and tertiary creep failures our analysis of this first seismic monitoring data of a cliff collapse suggests that the thermodynamic phase transition models for failure may apply for cliff collapse

water level response in back barrier bays unchanged following hurricane sandy on 28 30 october 2012 hurricane sandy caused severe flooding along portions of the northeast coast of the united states and cut new inlets across barrier islands in new jersey and new york about 30 of the 20 highest daily maximum water levels observed between 2007 and 2013 in barnegat and great south bay occurred in 5 months following hurricane sandy hurricane sandy provided a rare opportunity to determine whether extreme events alter systems protected by barrier islands leaving the mainland more vulnerable to flooding comparisons between water levels before and after hurricane sandy at bay stations and an offshore station show no significant differences in the transfer of sea level fluctuations from offshore to either bay following sandy the post hurricane sandy bay high water levels reflected offshore sea levels caused by winter storms not by barrier island breaching or geomorphic changes within the bays

measurement of the deformation field associated with fracture propagation in weak snowpack layers 1 dry snow slab avalanches release as a result of the failure of a weakly bonded layer located below a slab like layer of cohesive snow traditionally the failure of the weak layer was attributed to the formation and propagation of volume conserving simple shear cracks over the past decade however evidence for slope normal subsidence associated with fracture propagation in snow has accumulated pointing toward a new understanding of fracture propagation in snow the typically very high porosity of weak layers implies a loss of volume during fracture as the aggregate of ice grains composing the weak layer collapses and rearranges in a tighter packing order therefore in the new models failure is attributed to the formation and propagation of mixed mode anticracks in order to experimentally investigate the nature of the deformation field associated with fracture propagation through weak snowpack layers we monitored propagating fractures in field tests on natural snowpacks with a high level of detail using high speed photography and analyzed the data with particle tracking velocimetry the collapse of the weak layer was always observed and ranged between 0 3 cm and 4 cm in all experiments the collapse was found to coincide with the fracture front a shear crack preceding the collapse front was not detected at any stage of the process it is concluded that the volumetric collapse of the weak layer which is characteristic of anticracking is the rule rather than the exception for the fracture process in stratified snow and therefore for slab avalanche release

contribution of the patagonia icefields of south america to sea level rise digital elevation models of the northern and southern patagonia icefields of south america generated from the 2000 shuttle radar topography mission were compared with earlier cartography to estimate the volume change of the largest 63 glaciers during the period 1968 1975 2000 these glaciers lost ice at a rate equivalent to a sea level rise of 0 042 0 002 millimeters per year in the more recent years 1995 2000 average ice thinning rates have more than doubled to an equivalent sea level rise of 0 105 0 011 millimeters per year the glaciers are thinning more quickly than can be explained by warmer air temperatures and decreased precipitation and their contribution to sea level per unit area is larger than that of alaska glaciers

southern hemisphere origins of the 1976 climate shift 1 observations from the tropical pacific ocean identify an abrupt climate shift in 1976 with surface temperatures changing from cooler than normal to warmer than normal in the span of about 1 year model results show that this climate shift originates with subsurface temperature anomalies in the south tropical pacific ocean which propagate first to the western boundary then northward to the equator and finally eastward along the equator to 140 w where they rise to the surface the results suggest that changes in the north pacific respond to changes in the tropical pacific

monitoring of snow avalanches using a seismic array location speed estimation and relationships to meteorological variables 1 monitoring snow avalanches is necessary in order to better understand their triggering mechanisms and ultimately improve forecast performance seismic monitoring has been developed by several groups over the last 20 years and holds great potential to detect locate and characterize snow avalanches during the 2009 2010 winter a seismic antenna was installed in the french alps close to the village of saint christophe en oisans 1700 m above sea level the array of seven sensors operated during 50 days in october and november 2009 under snow free conditions and during 40 days in january and february 2010 in presence of snow it recorded different types of seismic events including snow avalanches rockfalls shots and regional and local microearthquakes eighty avalanche signals were visually identified using a beam forming method we were able to locate snow avalanches on slopes of various orientations in a radius of about 3 km and track their propagation the location technique allowed for the estimation of avalanches front speed which ranged between 12 and 32 m s 1 the method can also distinguish dry and wet snow avalanches durations of avalanches can be as long as 380 s because of the length of the slopes in the area seismic monitoring provides a catalog of avalanches with precise times which can be used to analyze the impact of meteorological forcings on the avalanche triggering snowfall is found to be the dominant forcing of avalanche activity during this period as revealed by the strongest correlation for the period of study our results suggest that the impact of precipitation on the snowpack instability lasts for about 6 days

seismic sensor array for monitoring an avalanche start zone design deployment and preliminary results in snow acoustic emissions originate from the breaking of bonds between snow crystals and the formation of cracks previous research has shown that acoustic signals emanate from a natural snowpack the relation between these signals and the stability of the snowpack has thus far remained elusive studies on other hazardous gravitational processes suggest that damage accumulation precedes major failure if increased cracking activity could be detected in snow this might be used for avalanche prediction we report on the development of a seismic sensor array to continuously monitor acoustic emissions in an avalanche start zone during three winters over 1400 sensor days of continuous acoustic data were collected with the aid of automatic cameras and a microphone the main types of background noise were identified seismic signals generated by avalanches were also identified spectrograms from seismic signals generated by avalanches exhibit a unique triangular shape unlike any source of background noise suggesting that automatic detection and classification of events is possible furthermore discriminating between loose snow and snow slab avalanches is possible thus far we have not identified precursor events for natural dry snow slab avalanche release detailed investigation of one dry snow slab avalanche showed that signals observed prior to the release originated from background noise or small loose snow avalanches

global atmospheric loading and gravity abstract the purpose of this paper is to model atmospheric pressure effects on surface gravity pressure corrections are usually done with the help of an empirical trans fer function called barometric admittance between pressure and gravity both measured locally we show the validity of this local approach with the help of spectral coherency between air pressure and gravity residuals after subtraction from the superconducting gravimeter observations in strasbourg france of luni solar tides polar motion and instrumental drift contributions we compute the atmospheric surface loading effects using a green s function formalism and global surface pressure data provided by the european centre for medium range weather forecasts ecmwf we model a specific oceanic response to atmospheric loading which incorporates interactions between ocean atmosphere and solid earth and differs from the classical inverted or non inverted barometer hypotheses we investigate the contribution of this global pressure correction in a 3000 day 1987 1996 tidal analysis of the french superconducting gravimeter

a note on the barotropic response of sea level to time dependent wind forcing this study examines the extent to which sea level variations at periods between 30 days and 1 year and spatial scales greater than 1000 km can be described by the wind driven linear barotropic vorticity dynamics the topex poseidon altimetric observations of sea level and the wind products of the national meteorological center are used as the database for the study each term of the linear barotropic vorticity equation was evaluated by averaging over regions of 10 10 in most of the open ocean the result of the analysis suggests that the sea level variabilities at the scales considered cannot be fully described by the equation the apparent net vorticity change is more than what can be explained by the local wind stress curl in the few regions where the wind stress curl is strong enough to balance the vorticity budget predominantly in the northeast pacific and the southeast pacific the balance is basically achieved in terms of the time dependent topographic sverdrup relation namely the balance between the advection of the planetary vorticity plus the topography induced vorticity and the forcing by the wind stress curl

microseismic investigation of an unstable mountain slope in the swiss alps 1 risks associated with unstable rocky slopes are growing as a result of climate change and rapid expansions of human habitats and critical infrastructure in mountainous regions to improve our understanding of mountain slope instability we developed a microseismic monitoring system that operates autonomously in remote areas afflicted by harsh weather our microseismic system comprising 12 three component geophones was deployed across 60 000 m 2 of rugged crystalline terrain above a huge 30 million m 3 recent rockfall in the swiss alps during its 31 month lifetime signals from 223 microearthquakes with approximate moment magnitudes ranging from 2 to 0 were recorded determining the hypocenters was challenging for several reasons 1 p wave velocities were highly heterogeneous varying abruptly from 3 8 km s 2 first break picks were either inaccurate or lacking for some microearthquakes 3 there were no reliable s wave picks 4 numerous microearthquakes occurred just outside the network boundaries these issues were addressed by using a three dimensional 3 d p wave velocity model of the mountain slope determined from refraction tomography in a nonlinear inversion for hypocenter parameters and their probability density functions recordings from geophones at different altitudes and in boreholes constrained microearthquake depth estimates most microearthquakes were concentrated within 50 100 m of the surface in two zones one that followed the recent rockslide scarp and one that spanned the volume of highest fracture zone fault density these two active zones delineated a mass of rock that according to geodetic measurements has moved toward the scarp at 1 2 cm yr

analysis and representation of regional sea level variability from altimetry and atmospheric oceanic data summary a simple representation of the sea level variability in time at low and medium frequencies and at large and medium spatial scales is investigated that accounts for the correlation between sea level heights and other atmospheric and oceanic parameters the selected fields are sea level height sea surface temperature wind speed and sea surface atmospheric pressure they are considered in the interval between 1992 and 1997 the sea level height data correspond to a single space altimetry mission topex poseidon and provide a homogeneous data set the dominant characteristics of the variability of each field and the coupled variability between two fields are analysed in the european seas using the spectral analysis method and the statistical methods of principal component analysis and canonical correlation analysis in the single field study both the spectral and the principal component analyses show different characteristics of the sea level height variability in the three seas the strongest annual and semi annual signals are in the mediterranean sea whereas in the other two seas especially in the baltic sea the dominant spectral components have comparable power the trends are interpreted as interannual variability due to the shortness of the investigated time interval the highest positive trends are observed in the eastern mediterranean sea in the coupled fields study both the linear regression analysis and the canonical correlation analysis show a high correlation between the sea level height and the sea surface temperature in the mediterranean sea and between the sea level height and the wind speed in the north sea and the baltic sea the mediterranean sea is particularly suitable for building sea level height models from the statistical methods because the first four modes of both the single and the coupled fields models account for about 90 per cent of the variance of the sea level height field it is therefore chosen as a test area to check the accuracy of the models and the ability of the canonical correlation method to predict the sea level variability the accuracy of the statistical models is assessed by computing dual crossover height differences between the topex poseidon and ers 1 and ers 2 sea surface heights corrected using the variability models both the single and the coupled fields models are found to be a good representation of the sea level variability in the mediterranean sea whereas the extrapolated canonical correlation model derived using the sea surface temperature as a predictor is less accurate but still acceptable relative bias and drift between the topex poseidon and ers data result from the analysis and reflect a non homogeneous pre processing of the altimetry data the single mission sea level variability models are a first step towards the construction of a multimission sea level model from unified multimission altimetry data

fennoscandian summers from ad 500 temperature changes on short and long timescales quantitative estimates of 1480 years of summer temperatures in northern fennoscandia have previously been derived from continuous treering records from northern sweden here we show the results of spectral analyses of these data only a few peaks in the spectra are consistently significant when the data are analyzed over a number of sub periods relatively timestable peaks are apparent at periods of 2 1 2 5 3 1 3 6 4 8 32 33 and for a range between 55 100 years these results offer no strong evidence for solar related forcing of summer temperatures in these regions our previously published reconstruction was limited in its ability to represent long timescale temperature change because of the method used to standardize the original tree ring data here we employ an alternative standardization technique which enables us to capture temperature change on longer timescales considerable variance is now reconstructed on timescales of several centuries in comparison with modern normals 1951 70 generally extended periods when cool conditions prevailed prior to the start of the instrumental record include 500 700 790 870 1110 1150 1190 1360 1570 1750 a d with the most significant cold troughs centred on about 660 800 1140 1580 1620 and 1640 predominantly warm conditions occurred in 720 790 870 1110 and 1360 1570 with peaks of warmth around 750 930 990 1060 1090 1160 1410 1430 1760 and 1820

automatic detection of avalanches and debris flows by seismic methods the road along the oshli hillside in the west fjords region of iceland is one of the most hazardous roads in iceland due to avalanches rockfalls and debris flows the road has little traffic but nevertheless traffic accidents caused by the severe conditions at the site are common a number of avalanche tracks are found on the hillside in some of these tracks avalanches occur more frequently than in others when there is an avalanche threat avalanches generally flow over many tracks in a short time monitoring vibrations in the tracks with the highest avalanche frequency can indicate when avalanches start flowing down the hillside in a snowstorm and avalanche hazard can then be declared with the specific site indicated the same methodology can be used for rockfalls and debris flows which are strongly affected by weather conditions and typically occur in clusters based on this knowledge a research project was initiated in february 1996 with the objective of developing an automatic system based on seismic measurements to detect and analyze avalanches on the oshli hillside and to instantly

evidence of log periodic oscillations and increasing icequake activity during the breaking off of large ice masses in 1973 surface velocities were measured for the first time on an unstable hanging glacier to predict its collapse the observed velocities have been shown to increase as a power law function of time up to infinity at the theoretical time of failure known as finite time singularity this is the characteristic signature of critical phenomena and has been observed in the case of various other naturally occurring ruptures such as earthquakes landslides and snow avalanches recent velocity measurements performed on weisshorn and monch hanging glaciers switzerland confirmed this behaviour while log periodic oscillations superimposed on this general acceleration were also detected despite different rupture mechanisms in both cases the log frequency of the oscillations is shown to be the same the seismic activity was recorded near the unstable weisshorn hanging glacier simultaneously with the velocity measurements results show dramatically increasing icequake activity 3 days before the final collapse combined motion seismic monitoring seems to be a promising way to accurately predict the breaking off of hanging glaciers such a combined analysis is also useful for capturing the physical mechanisms of rupture in natural heterogeneous materials

assessing risks from glacier hazards in high mountain regions some experiences in the swiss alps assessing risks from potential glacier hazards in relation to safety considerations for settlements and other fixed installations in high mountain areas requires the application of experience gained from previous events combined with simple rules derived from basic glaciological theory the general characteristics of steep and usually un measured glaciers can be estimated on the basis of a rough parameterization scheme variations in glacier length ice avalanches and glacier floods then have to be considered for time periods ranging from a few years up to a few decades as a result of such systematic assessments maps of potentially dangerous zones can be prepared although the inhabitants of many alpine villages have always lived with the risk of glacier hazards it now appears that modern construction work especially that connected with the development of tourism has started to infiltrate previously avoided high risk zones more and more in order to plan reasonable safety measures risks from glacier hazards have to be compared with those from other natural hazards in mountain areas such as snow avalanches landslides rock falls or storm induced floods decisions about the acceptable level of risk are difficult and subjective they are also often influenced by political and economical considerations rather than by scientific reasoning

large scale sea level variations and associated atmospheric forcing in the subtropical north east atlantic ocean abstract the large scale sea level variations in the subtropical north eastern atlantic ocean are characterised by a predominant seasonal fluctuation analysis of 6 years 1993 98 of combined topex poseidon and ers 1 2 altimetric data together with data of concurrent oceanic surface geophysical fields ecmwf net heat fluxes ecmwf winds and reynolds sea surface temperature reveals that the dominant physical forcing of sea level variations on an annual timescale is the air sea net heat fluxes this local forcing generates a seasonal ocean steric response whose amplitude of the order of 4 5 cm varies spatially within the studied area and temporally over the 6 year period the residual variability is mainly characterised by a non seasonal signal which is observed northwards of the azores current 34 n and its time variation resembles that of the north atlantic oscillation nao a combination of steric effects wind induced heat fluxes and wind effects barotropic sverdrup response appear to explain this signal some evidence of a local ekman pumping response is also found regionally both in the seasonal and non seasonal variations of the observed sea level at the interannual timescale an overall sea level trend with a mean rate of 0 5 cm year is detected however the magnitude of the trend varies locally so that the entire sea surface appears to undergo a general tilt which extends beyond the studied area superimposed on this long term trend a sharp temporal sea level rise occurs in 1995 mainly between the azores and madeira islands all together these low frequency sea level variations seem to co vary with the large scale sea surface temperature sst variations this implies a comparable evolution of the sea level with the upper ocean thermal content which suggests a contribution from steric effects a weaker situation is observed in the northern area indicating a possible low frequency wind forcing enhanced contribution

snow avalanche formation 1 snow avalanches are a major natural hazard endangering human life and infrastructure in mountainous areas throughout the world in many countries with seasonally snow covered mountains avalanche forecasting services reliably warn the public by issuing occurrence probabilities for a certain region however at present a single avalanche event cannot be predicted in time and space much about the release process remains unknown mainly because of the highly variable layered character of the snowpack a highly porous material that exists close to its melting point the complex interaction between terrain snowpack and meteorological conditions leading to avalanche release is commonly described as avalanche formation it is relevant to hazard mapping and essential to short term forecasting which involves weighting many contributory factors alternatively the release process can be studied and modeled this approach relies heavily on snow mechanics and snow properties including texture while the effect of meteorological conditions or changes on the deformational behavior of snow is known in qualitative or semiquantitative manner the knowledge of the quantitative relation between snow texture and mechanical properties is limited but promising developments are under way fracture mechanical models have been applied to explain the fracture propagation and micromechanical models including the two competing processes damage and sintering have been applied to explain snow failure there are knowledge gaps between the sequence of processes that lead to the release of the snow slab snow deformation and failure damage accumulation fracture initiation and fracture propagation simultaneously the spatial variability that affects damage fracture initiation and fracture propagation has to be considered this review focuses on dry snow slab avalanches and shows that dealing with a highly porous media close to its melting point and processes covering several orders of scale from the size of a bond between snow grains to the size of a mountain slope will continue to be very challenging

bedmap a new ice thickness and subglacial topographic model of antarctica measurements of ice thickness on the antarctic ice sheet collected during surveys undertaken over the past 50 years have been brought together into a single database from these data a seamless suite of digital topographic models have been compiled for antarctica and its surrounding ocean this includes grids of ice sheet thickness over the grounded ice sheet and ice shelves water column thickness beneath the floating ice shelves bed elevation beneath the grounded ice sheet and bathymetry to 60 s including the sub ice shelf cavities these grids are consistent with a recent high resolution surface elevation model of antarctica while the digital models have a nominal spatial resolution of 5 km such high resolution is justified by the original data density only over a few parts of the ice sheet the suite does however provide an unparalleled vision of the geosphere beneath the ice sheet and a more reliable basis for ice sheet modeling than earlier maps the total volume of the antarctic ice sheet calculated from the bedmap grid is 25 4 million km3 and the total sea level equivalent derived from the amount of ice contained within the grounded ice sheet is 57 m comprising 52 m from the east antarctic ice sheet and 5 m from the west antarctic ice sheet slightly less than earlier estimates the gridded data sets can be obtained from the authors

global scale sea surface variability from combined altimetric and tide gauge measurements by correcting geosat altimetric data for a set of line frequencies and then doing a heavy average in space and time a set of global maps of sea surface variability is produced over time intervals ranging from three months to two years these maps are demonstrated to be consistent with the global network of tide gauges and sets of maps incorporating those data into the altimetric estimates are also produced tide gauge records too fragmentary for computation of a two year mean are employed by time differencing them an estimate of the global difference of sea level change over one year on very large space scales shows the effects of the 1987 el nino the spherical harmonic coefficients employed in the computations are then used to estimate the full three dimensional frequency wavenumber spectrum of surface circulation variability

how much do we really know about glacier surging some of the ideas about glacier surging are considered mainly but not entirely in the light of observations of temperate glaciers in alaska u s a made within the last 15 years climate has an influence on surge recurrence interval climate and weather also affect surge initiation termination and magnitude regional studies lead to the speculation that subglacial till plays a key role in surging and it has been found under all surge type glaciers studied so far including black rapids and variegated glaciers alaska in most of the glaciers studied till deformation processes dominate the motion in quiescence the linked cavity model of surge triggering and rapid motion is not consistent with these observations but the limited coverage of the observations does not rule it out under parts of the glaciers studied the till observations in alaska raise old questions about the interaction between till and the hydraulic systems of temperate glaciers the role of stored water which observations show to be active even in winter on black rapids glacier is noted

long term glacier variations in the central andes of argentina and chile inferred from historical records and tree ring reconstructed precipitation abstract snow and ice in the central andes of chile and argentina 33 36 s are the major source of water for the highly populated regions near the cities of santiago and mendoza however our knowledge of the forces driving the general glacier retreat in the region is limited in order to obtain a long term perspective of glacier fluctuations and their relationships with climate in the central andes historical glacier variations were documented and compared with a tree ring precipitation reconstruction based upon austrocedrus chilensis trees a multi proxy approach historical documents old aerial photographs and satellite imagery was used to map the fluctuations of eight glaciers including the cipreses glacier which provides the oldest record of glacier variations in the region starting in ad 1842 all the studied glaciers exhibited a negative trend during the 20th century with mean frontal retreats between 50 and 9 m y 1 thinning rates between 0 76 and 0 56 m y 1 and a mean ice area reduction of 3 since 1955 more than 350 tree ring cores were combined into three tree ring chronologies which strongly correlate with the instrumental precipitation in santiago de chile 33 26 s 70 41 w 520 m asl based on these records a 712 year precipitation reconstruction was developed this reconstruction is characterised by a centennial oscillation indicating marked dry conditions around the years 1440 and 1600 ad wet conditions were prevalent in the years 1500 1650 and particularly around 1850 ad since this precipitation maximum the reconstruction shows a clear secular decreasing trend the reduction in precipitation indicated by this reconstruction for the last 150 yr in combination with a significant warming recorded in central chile are the main causes of the observed current glacier retreats

quaternary glaciations in the rio mendoza valley argentine andes in the rio mendoza valley five pleistocene drifts and one holocene drift are distinguished by multiple relative age criteria including surface rock weathering development of rock varnish moraine morphology soil profile development and stratigraphic relationships several absolute ages suggest a preliminary chronology during the oldest uspallata glaciation a system of valley glaciers flowed 110 km from the andean drainage divide and 80 km from cerro aconcagua to terminate at 1850 m drift of this ice advance is older than a widespread tephra dated by fission track at 360 000 36 000 yr during the punta de vacas advance ice terminated at 2350 m while during the subsequent penitentes advance the glacier system ended at 2500 m a travertine layer overlying penitentes drift has u series age of 24 200 2000 yr b p the distribution of horcones drift which is inferred to represent the last glacial maximum delimits an independent ice stream that flowed 22 km down horcones valley to 2750 m a later readvance almacenes reached 3250 m confluencia drift is considered to be neoglacial in age and extends downvalley to 3300 m the moraine sequence is compared with those studied by caviedes 1972 along rio aconcagua on the chilean flank of the andes

sea level response to pressure forcing in a barotropic numerical model abstract a barotropic shallow water model is used to study the large scale sea level response to realistic barometric forcing at periods ranging from 1 day to 1 year results are presented from coarse resolution open ocean experiments i e no shallow continental shelf regions or marginal seas with coastal geometries and bottom topography representative of the north atlantic and pacific basins the validity of the inverted barometer ib approximation is examined in detail including nonlocal effects which result from taking into account the constant volume of the ocean these effects are found to be important at low latitudes where a considerable part of the sea level variability is related to pressure forcing over higher latitudes root mean square deviations from an ib response in the range of 1 3 cm are typical with most of the variance occurring at high frequencies basin averaged estimates yield ib deviations of only a few percent at time scales longer than 1 week increasing to 5 20 over the

observations of wind forced deep ocean currents in the north pacific this study examines the atmospheric response of the deep ocean using 200 instrument years of moored current measurements from across the breadth of the mid latitude north pacific we have found evidence of a seasonal modulation in the ocean eddy kinetic energy beneath the thermocline at several locations north of 35 n this modulation is often in phase with the local atmospheric forcing function at frequencies between 0 1 and 0 01 cpd correlations between the local wind stress curl and the deep currents have been found for a few locations the local forced response is parallel to the potential vorticity gradient f h and consistent in amplitude with a local topographic sverdrup balance nonlocal forcing in the form of flow along isolines of potential vorticity has been estimated and it is comparable to the observed flow at some locations but the modeled flow is not correlated with the observations throughout the mid latitude north pacific the bottom slope tends to enhance the effect this suggests that topography narrows the available bandwidth for forced barotropic rossby waves facilitating a quasi steady topographic sverdrup response over most of the basin however the enhanced effect reduces the magnitude of the ocean s response to wind forcing nonlocally forced sverdrup currents flow along isolines of f h are the dominant component but are only of the order of 1 cm s 1 locally forced sverdrup currents flow across isolines of f h are typically of the order of 0 1 cm s 1 rms and are not commonly measured hence these wind forced variations are a background level signal in the mid latitude eddy kinetic energy in a few isolated areas the bottom slope reduces the effect in these regions the local sverdrup response is amplified and has been observed

identification and characteristics of surge type glaciers on novaya zemlya russian arctic we present a comprehensive new inventory of surge type glaciers on the novaya zemlya archipelago using high resolution up to 4 m satellite imagery from 1976 77 hexagon 1989 landsat tm 2001 landsat etm and 2006 aster a total of 692 glaciers and their forelands were observed for glaciological and geomorphological criteria indicative of glacier surging e g looped moraines heavy surface crevassing surface potholes thrust block moraines concertina eskers this enabled the identification of 32 potential surge type glaciers compared with four previously identified representing 4 6 of the total but 18 by glacier area we assess the characteristics of surge type glaciers surge type glaciers are statistically different from non surge type glaciers in terms of their area length surface slope minimum elevation mid range elevation and terminus type they are typically long median length 18 5 km large median area 106 8 km 2 outlet glaciers with relatively low overall surface slopes median slope 1 7 and tend to terminate in water marine or lacustrine they are predominantly directed towards and located in the more maritime western region of the russian arctic and we suggest that surge occurrence might be related to large and complex catchment areas that receive increased delivery of precipitation from the barents sea

outburst floods from glacier dammed lakes the effect of mode of lake drainage on flood magnitude published accounts of outburst floods from glacier dammed lakes show that a significant number of such floods are associated not with drainage through a tunnel incised into the basal ice the process generally assumed but rather with ice marginal drainage mechanical failure of part of the ice dam or both non tunnel floods are strongly correlated with formation of an ice dam by a glacier advancing from a tributary drainage into either a main river valley or a pre existing body of water lake or fiord for a given lake volume non tunnel floods tend to have significantly higher peak discharges than tunnel drainage floods statistical analysis of data for floods associated with subglacial tunnels yields the following empirical relation between lake volume v and peak discharge qp qp 46v0 66 r2 0 70 when qp is expressed in metres per second and v in millions of cubic metres this updates the so called clague mathews relation for non tunnel floods the analogous relation is qp 1100v0 44 r2 0 58 the latter relation is close to one found by costa 1988 for failure of constructed earthen dams this closeness is probably not coincidental but rather reflects similarities in modes of dam failure and lake drainage we develop a simple physical model of the breach widening process for non tunnel floods assuming that 1 the rate of breach widening is controlled by melting of the ice 2 outflow from the lake is regulated by the hydraulic condition of critical flow where water enters the breach and 3 the effect of lake temperature may be dealt with as done by clarke 1982 calculations based on the model simulate quite well outbursts from lake george alaska dimensional analysis leads to two approximations of the form qp vqf hi 0 where q 0 5 to 0 6 hi is initial lake depth 0 is lake temperature and the form of f hi 0 depends on the relative importance of viscous dissipation and the lake s thermal energy in determining the rate of breach opening these expressions along with the regression relations should prove useful for assessing the probable magnitude of breach type outburst floods

departures from the local inverse barometer model at periods of 5 days in the central south atlantic tide gauge data from ascension and st helena in the central south atlantic supplemented by altimeter data from the topex poseidon mission suggest that the local inverse barometer lib model for the forcing of sea level variability by means of air pressure changes is not applicable within a narrow band of the variability spectrum with periods of approximately 5 days this is in contrast to other sections of the wider frequency band spanning approximately 0 05 to 0 5 cycles d wherein the data are either consistent with approximate lib response or at least suggest no departures from the lib model of similar magnitude these results have similarities to findings from pacific gauges obtained over a decade ago but so far no comparisons have been to data from other ocean areas they are also qualitatively similar to predictions for the region from a recent global barotropic numerical model the anomalous part of the spectrum coincides in frequency with the madden and julian 1972 1973 5 day pressure wave in the atmosphere if that global scale forcing is responsible for both the atlantic and pacific departures from the lib model around 5 days then similar features should be observable in tide gauge data from other tropical areas

use of remotely sensed and field data to estimate the contribution of chilean glaciers to eustatic sea level rise a synthesis of glaciological studies carried out in chile during recent decades is presented including inventories and records of glacier variations fluctuations of whicharerelatedtoregionalclimate changeandtheircontributionto eustatic sea level rise basedupon satelliteimagery aerialphotographsandhistorical records newdata for 20 glaciersarepresented these newdata arecombinedwithpreviousrecordsto coverthe historicalvariations of95 chileanglaciers oftheseglaciers only 6 showa netadvance during the study period 6 show no significant change while 88 have retreated the contributionof chileanglaciersto eustatic sea levelrisehasbeenestimatedtobeapproxi mately 8 2 of the worldwide contribution of small glaciers on earth during the last 51years most of the glacier variations are thought to have been driven by a temperature increase which has been documented by several stations in chile anomalies in rainfall and the decreasing trend in annual precipitation shown at a few stations have probably also contributedtoglacier recession basedonobservedclimatictrends itisexpectedthat the glacier retreat will continue that the mass balance will continue to show a negative trend and that thinning rates will increase all of these changes will ultimately affect the availability of water resources in chile that depend on glacierizedbasins

biases of srtm in high mountain areas implications for the monitoring of glacier volume changes because of its nearly global coverage the shuttle radar topographic mission srtm topography is a promising data set for estimating mountain glacier volume changes but first its absolute accuracy must be thoroughly investigated in a glacial environment we use topographic data available in the french alps to assess the usefulness of srtm for the monitoring of glacier volume variations we observe clear biases with altitude both on ice free and glacier covered areas at high altitudes srtm elevations are underestimated by up to 10 m these biases can have a significant impact on any estimate of glacier volume changes if srtm is the most recent of the two compared topographies the volume loss is overestimated and vice versa we cannot conclude definitively on the origin of these biases and whether they affect all high mountain areas but our findings invite reconsideration of previous estimates of glacier wastage based on srtm

acoustic and microseismic characterization in steep bedrock permafrost on matterhorn ch understanding of processes and factors in uencing slope stability is essential for assessingthe stability of potentially hazardous slopes passive monitoring of acoustic emissions and microseismologyprovides subsurface information on fracturing timing and identi cation of the mechanism and thereforecomplement surface displacement data this study investigates for the rst time acoustic and microseismicsignals generated in steep frac tured bedrock permafrost covering the broad frequency range of 1 105hz the analysis of arti cial forcing experiments using a rebound hammer in a controlled setting led to twomajor ndings first statistically insigni cant cross correlation between signals indicates that waveformschange strongly with propagation distance second a sign cant ampli cation is found in the frequencyband 33 67 hz this nding is strongly supported by evidence from arti cial rockfall events and moreimportantly by naturally occurring fracture events identi ed in fracture displacement data thus lteringthis frequency band enables enhanced detection of microseismic events relevant for slope stabilityassessment the analysis of 2 year time series in this frequency band further suggests that the detectedenergy rate baseline of all automatically triggered events using the sta lta algorithm is not sensitive totemperature forcing an observation of primary importance for long term data collection analysis andinterpretation the event detection in the established frequency band is not only improved but also nota ected by the short and long term temperature changes in such a rapidly changing environment

tree ring based reconstructions of northern patagonia precipitation since ad 1600 long term reconstructions 400 years of seasonal and annual precipitation variations were developed for northern patagonia east of the andes using a new set of 16 tree ring width chronologies from austrocedrus chilensis d don endl reconstructions which capture between 41 and 50 of the precipitation variance show that the twentieth century contains the most extreme long periods of wetness and dryness in the past 400 years since about ad 1910 the reconstructions are also characterized by an increase in interannual variability and one of the highest rates of extreme events within the last 400 years a prominent oscillation on the order of 2 2 1 years in length has been identified in the reconstructions using spectral analysis quasi biennial oscillations have been shown to be very marked in some circulation indices of the southern hemisphere although significant oscillations within the preferred frequency domain of el nino southern oscillation enso are present in the reconstructions no clear trod consistent responses to enso have been observed correlations of reconstructions with mean sea level pressure around south america for the interval ad 1912 1984 reveal the influence of subtropical and high latitude features of the atmospheric circulation on precipitation variations in northern patagonia droughts result from an intensification of the subtropical pacific anticyclone off the chilean coast and the deepness of the circum antarctic trough over the south orkney antarctic peninsula sector mean sea level pressure reconstructions for the south atlantic sector of the southern oceans were used to evaluate the temporal stability of the relationships between northern patagonia precipitation and high latitude climatic variations since ad 1750 the influence of high latitude circulation on precipitation appears to be more significant during the twentieth century which in turn may respond to an intensification of wavenumbers 3 on the mean planetary wave structure over the southern hemisphere recent increase of precipitation variability in northern patagonia may reflect stronger interactions between middle and high latitude atmospheric circulation in the southern hemisphere during the twentieth century

seasonality of the enso related rainfall variability in central chile and associated circulation anomalies the seasonality of the enso rainfall relationship in central chile 308 418s and associated circulation anomalies are studied using correlation and compositing techniques during el nino episodes there is a tendency for the occurrence of above average precipitation between 308 and 358s in winter june july august jja and from 358 to 388s in late spring october november on while rainfall deficit is typically observed from around 388 to 418s during the following summer january february march jfm when el nino reaches its maximum development opposite rainfall anomalies are characteristic during la nina events this study confirms results from previous investigations indicating that enhanced blocking activity over the amundsen bellings hausen seas area in the southeastern se pacific during el nino is a key feature explaining the wet conditions in winter it is also shown that the same circulation anomaly explains the relatively wet conditions in late spring in the 358 388s region during el nino episodes furthermore the southward displacement from winter to late spring of the area with significant enso related rainfall anomalies seems associated with the seasonal migration of the boundary separating the region under the influence of the subtropical domain from the extratropical domain where the westerly regime and associated disturbances prevail blocking episodes in the se pacific during el nino seem to be part of a wave structure particularly intense during spring characterized by a sequence of positive and negative quasi barotropic height anomalies stretching southeastward from the equator toward the se pacific and back to the southwestern atlantic on the other hand anomalously dry conditions in winter and late spring during la nina are favored by long lasting and intense ridges at subtropical latitudes over the se pacific and south america resulting in a southward migration of the midlatitude storm tracks in summer a higher frequency of ridges in the southern tip of the south america during el nino episodes presumably contributes to reinforcement of the southern edge of the subtropical anticyclone in the se pacific which at this time of the year reaches its southernmost position resulting in the annual rainfall minimum on the other hand an increased frequency of cyclonic circulation anomalies crossing the southern tip of the continent is associated with relatively wet conditions in southern central chile particularly during la nina events

measurement of crack face friction in collapsed weak snow layers 1 in this letter we analyze the frictional contact forces during and immediately after the collapse of a weak snowpack layer when the sliding plane consists of the freshly collapsed and crushed but not yet eroded granular debris of the weak layer the results from thirty four field experiments show that frictional contact forces per unit area are on the order of 0 6 times the normal stress equivalent to a friction angle close to 30 degrees the measurements show that there is a transient sharp drop in the coefficient of friction during the collapse of the weak layer and relatively constant values afterwards one implication of our findings is that the minimum angle for avalanche release does not depend on shear strength as commonly thought but results from crack face friction which comes into play only as the fracture through the weak layer is already propagating