recent mass changes of glaciers in the russian high arctic 1 glaciers and ice caps are known to contribute significantly to present day sea level rise but there are still glaciated regions where little is known about modern changes in glacier mass one of these regions is the russian high arctic archipelagos which has a total glaciated area of 51 500 km2 we have assessed the glacier mass budget of this region for a 6 year period between october 2003 and october 2009 using independent icesat laser altimetry and grace gravimetry over this period we found that the archipelagos have lost ice at a rate of 9 1 2 0 gt a 1 which corresponds to a sea level contribution of 0 025 mm a 1 approximately 80 of the ice loss came from novaya zemlya with the remaining 20 coming from franz josef land and severnaya zemlya meteorological records of temperature and precipitation for the period 1980 2009 suggest that the recent climatic mass budget is not substantially different from the longer term trend

assemblages of submarine landforms produced by tidewater glaciers in svalbard 1 high resolution swath bathymetry from the marine margins of several svalbard tidewater glaciers shows an assemblage of submarine landforms that is probably linked to glacier surging these landforms are essentially unmodified since their initial deposition over the past hundred years or so because they have not been subjected to subaerial erosion or periglacial activity swath images comprise an assemblage of superimposed landforms allowing reconstruction of relative age of deposition 1 large transverse ridges interpreted as recessional moraines overridden by a subsequent ice advance 2 a series of curvilinear streamlined bedforms orientated parallel to former ice flow interpreted as lineations formed subglacially during rapid advance 3 large terminal ridges marking the farthest extent of ice at the last advance with flow lobes immediately beyond interpreted as submarine debris flows 4 a series of interconnected rhombohedral ridges interpreted as a product of soft sediment squeezing into crevasses formed at the glacier bed probably formed during immediate post surge stagnation and 5 a series of fairly evenly spaced small transverse ridges interpreted as push moraines produced annually at tidewater glacier termini during retreat a simple descriptive landsystem model for tidewater glaciers of probable surge type is derived from these observations we also show that megascale glacial lineations can form not only beneath large ice streams but are also produced beneath surging tidewater glaciers lying on deforming sedimentary beds

responses of tropical deep convection to the qbo cloud resolving simulations abstractobservational studies suggest that the stratospheric quasi biennial oscillation qbo can modulate tropical deep convection the authors use a cloud resolving model with a limited domain representing a convective column in the tropics to study the mechanisms of this modulation the large scale circulation is parameterized using the weak temperature gradient wtg approximation under which the parameterized large scale vertical motion acts to relax the horizontal mean temperature toward a specified reference profile temperature variations typically seen in easterly and westerly phases are imposed in the upper troposphere and lower stratosphere of this reference profile the responses of convection are studied over different sea surface temperatures holding the reference temperature profile fixed this can be thought of as studying the response of convection to the qbo over different relative ssts and also corresponds to different equilibrium precipitation rates in the control simulation the

distinct patterns of seasonal greenland glacier velocity predicting greenland ice sheet mass loss due to ice dynamics requires a complete understanding of spatiotemporal velocity fluctuations and related control mechanisms we present a 5 year record of seasonal velocity measurements for 55 marine terminating glaciers distributed around the ice sheet margin along with ice front position and runoff data sets for each glacier among glaciers with substantial speed variations we find three distinct seasonal velocity patterns one pattern indicates relatively high glacier sensitivity to ice front position the other two patterns are more prevalent and appear to be meltwater controlled these patterns reveal differences in which some subglacial systems likely transition seasonally from inefficient distributed hydrologic networks to efficient channelized drainage while others do not the difference may be determined by meltwater availability which in some regions may be influenced by perennial firn aquifers our results highlight the need to understand subglacial meltwater availability on an ice sheet wide scale to predict future dynamic changes

ionospheric signatures of dayside magnetopause transients a case study using satellite and ground measurements a case study is presented of coordinated ground and space measurements featuring a set of transient auroral fragments located on the poleward side of a stable cusp cleft arc optical ground data from ny alesund svalbard and heiss island franz josef land were combined with dmsp f9 satellite measurements to examine the characteristics of these auroral features a stable red arc stretched across most of the dayside auroral zone in a region dominated by westward convection in accordance with the orientation of the imf poleward of the red arc were several westward moving auroral jets having characteristics similar to midday auroral breakup events such events may be ground signatures of transitory magnetic merging at the dayside magnetopause if so the driven convective motion of these structures should contribute to the polar cap potential within this limited data set we find that although the transitory structures have an inherent potential associated with the motion of the optical signatures the structures on the whole contribute a small fraction of the total polar cap potential

observed connection between stratospheric sudden warmings and the madden julian oscillation 1 the effect of the madden julian oscillation mjo on the northern hemisphere wintertime stratospheric polar vortex and major mid winter stratospheric sudden warmings ssws is evaluated using a meteorological reanalysis dataset the mjo influences the region in the tropospheric north pacific sector that is most strongly associated with a ssw consistent with this ssws in the reanalysis record have tended to follow certain mjo phases the magnitude of the influence of the mjo on the vortex is comparable to that associated with the quasi biennial oscillation and el nino the mjo could be used to improve intra seasonal projections of the northern hemisphere high latitude circulation and in particular of the tropospheric northern annular mode at lags exceeding one month

stratospheric influences on the mjo induced rossby wave train effects on intraseasonal climate abstractthe tropical madden julian oscillation mjo excites a northward propagating rossby wave train that largely determines the extratropical surface weather consequences of the mjo previous wo

ring shear studies of till deformation coulomb plastic behavior and distributed strain in glacier beds a ring shear device was used to study the factors that control the ultimate steady strength of till at high shear strains tests at a steady strain rate and at different stresses normal to the shearing direction yielded ultimate friction angles of 26 3 and 18 6 for tills containing 4 and 30 clay sized particles respectively other tests at steady normal stresses and variable shear strain rates indicated a tendency for both tills to weaken slightly with increasing strain rate this weakening may be due to small increases in till porosity these results provide no evidence of viscous behavior and suggest that a coulomb plastic idealization is reasonable for till deformation however viscous behavior has often been suggested on the basis of distributed shear strain observed in subglacial till we hypothesize that deformation may become distributed in till that is deformed cyclically in response to fluctuations in basal water pressure during a deformation event transient dilation ofdiscrete shear zones should cause a reduction in internal pore water pressure that should strengthen these zones relative to the surrounding till a process called dilatant hardening consequent changes in shear zone position when integrated over time may yield the observed distributed strain

climatic and geometric controls on the global distribution of surge type glaciers implications for a unifying model of surging financial support was provided by the conocophillips lundin northern area program project crios

force budget i theory and numerical methods a practical method is developed for calculating stresses and velocities at depth using field measurements of the geometry and surface velocity of glaciers to do this it is convenient to partition full stresses into lithostatic and resistive components the horizontal gradient in vertically integrated lithostatic stress is the driving stress and it describes the horizontal action of gravity the horizontal resistive stress gradients describe the reactions resistive stresses are simply related to deviatoric stresses and hence to strain rates through a constitutive relation a numerical scheme can be used to calculate stresses and velocities from surface velocities and slope and from ice thickness there is no mathematical requirement that the variations in these quantities be small

seasonal to multiyear variability of glacier surface velocity terminus position and sea ice ice melange in northwest greenland glacier ice discharge which depends on ice velocity and terminus fluctuations is a primary component of greenland ice sheet mass loss some research suggests that ice melange influences terminus calving in turn affecting glacier velocity the details and broad spatiotemporal consistency of these relationships however is undetermined focusing on 16 northwestern greenland glaciers during 2009 through summer 2014 we examined seasonal surface velocity changes glacier terminus position and sea ice and ice melange conditions for a longer term analysis we also produced extended records of four glaciers from 1999 to 2014 there is a strong correspondence between seasonal near terminus sea ice melange conditions and terminus change with rigid ice melange conditions associated with advance and open water associated with retreat extended sea ice free periods and reduced rigid melange are also linked with anomalously large terminus retreat in all but one case sustained multiyear retreat of greater than 1 km during both the 15 year and 6 year records was accompanied by interannual velocity increases seasonal velocity patterns however correspond more strongly with runoff changes than terminus behavior projections of continued warming and longer sea ice free periods around greenland indicate that notable retreat over wide areas may continue this sustained retreat likely will contribute to multiyear speedup longer melt seasons and earlier breakup of melange may also alter the timing of seasonal ice flow variability

seasonal evolution of subglacial drainage and acceleration in a greenland outlet glacier an acceleration of ice mass loss has been observed near the margin of the greenland ice sheet partly as a result of faster ice motion observations by gps receivers reveal high seasonal variability in ice motion with summer motion up to 220 higher than winter background levels the greenland ice sheet contains enough water to raise sea levels by 7 m however its present mass balance and future contribution to sea level rise is poorly understood1 accelerated mass loss has been observed near the ice sheet margin partly as a result of faster ice motion2 3 4 surface melt waters can reach the base of the ice sheet and enhance basal ice motion5 6 however the response of ice motion to seasonal variations in meltwater supply is poorly constrained both in space and time here we present ice motion data obtained with global positioning system receivers located along a 35 km transect at the western margin of the greenland ice sheet throughout a summer melt season our measurements reveal substantial increases in ice velocity during summer up to 220 above winter background values these speed up events migrate up the glacier over the course of the summer the relationship between melt and ice motion varies both at each site throughout the melt season and between sites we suggest that these patterns can be explained by the seasonal evolution of the subglacial drainage system similar to hydraulic forcing mechanisms for ice dynamics that have been observed at smaller glaciers

four large scale field aligned current systems in the dayside high latitude region a system of four current sheets of large scale field aligned currents facs was discovered in the data set of simultaneous viking and dmsp f7 crossings of the dayside high latitude region this paper reports four examples of this system that were observed in the prenoon sector the flow polarities of facs are upward downward upward and downward from equatorward to poleward the lowest latitude upward current is flowing mostly in the cps precipitation region often overlapping with the bps at its poleward edge and is interpreted as a region 2 current the pair of downward and upward facs in the middle of the structure are collocated with structured electron precipitation the precipitation of high energy 1 kev electrons is more intense in the lower latitude downward current sheet the highest latitude downward flowing current sheet is located in a weak low energy particle precipitation region suggesting that this current is flowing on open field lines simultaneous observations in the postnoon local time sector reveal the standard three sheet structure of facs sometimes described as region 2 region 1 and mantle referred to the midday region 0 currents a high correlation was found between the occurrence of the four fac sheet structure and negative interplanetary magnetic field imf by we discuss the fac structure in terms of three types of convection cells the merging viscous and lobe cells during strongly negative imf by two convection reversals exist in the prenoon sector one is inside the viscous cell and the other is between the viscous cell and the lobe cell this structure of convection flow is supported by the viking electric field and auroral uv image data based on the convection pattern the four fac sheet structure is interpreted as the latitudinal overlap of midday and morning fac systems we suggest that the four current sheet structure is common in a certain prenoon local time sector during strongly negative imf by

teleconnections in the geopotential height field during the northern hemisphere winter abstract contemporaneous correlations between geopotential heights on a given pressure surface at widely separated points on earth referred to as teleconnections in this paper are studied in an attempt to identify and document recurrent spatial patterns which might be indicative of standing oscillations in the planetary waves during the northern hemisphere winter with time scales on the order of a month or longer a review of existing literature on the subject reveals the existence of at least four such patterns the north atlantic and north pacific oscillations identified by walker and bliss 1932 a zonally symmetric seesaw between sea level pressures in polar and temperature latitudes first noted by lorenz 1951 and what we will refer to as the pacific north american pattern which has been known to operational long range forecasters in this country since the 1950 s a data set consisting of nmc monthly mean sea level pressure and 500 mb height analyses for a 15 year period is used as a basis fo

on the relationship between the qbo and tropical deep convection abstract the height and amount of tropical deep convection are examined for a correlation with the stratospheric quasi biennial oscillation qbo a new 23 yr record of outgoing longwave radiation olr and a corrected 17 yr record of the highly reflective cloud hrc index are used as measures of convection when binned by phase of the qbo zonal means and maps of olr and hrc carry a qbo signal the spatial patterns of the maps highlight the qbo signal of olr and hrc in typically convective regions spectral analysis of zonal mean olr and hrc near the equator reveals significant peaks at qbo frequencies rotated empirical orthogonal function reof analysis is used to determine if enso variations of convection are aliased into the observed qbo signals some analyses are repeated using the olr record after enso reof modes have been removed yielding very similar results compared to the original analyses it appears that the qbo signal is distinct from the enso signal although the relative brevity of the

the geomorphic imprint of glacier surges into open marine waters examples from eastern svalbard abstract seafloor morphology beyond nine tidewater glaciers terminating in open marine settings in eastern svalbard has been investigated using multibeam swath bathymetry historical information on tidewater glacier fluctuations over the past century or so shows that the seafloor offshore has been exposed only recently most glaciers have been observed to surge or have looped surface moraines indicating past surges during these ice advances and subsequent retreat a well preserved submarine landform assemblage has been produced a subglacial landforms include overridden moraine ridges mega scale glacial lineations msgls other streamlined lineations elongate drumlins and medial moraines small ridges forming a complex boxwork or rhombohedral pattern and meltwater related eskers and channels b ice marginal landforms include large terminal moraines with debris flow lobes on their outer flanks and indentations on their inner sides small transverse retreat moraines and crater like kettle holes c glacimarine features include iceberg ploughmarks and an otherwise relatively smooth sedimentary seafloor produced by fine grained debris rain out a schematic plan view landform assemblage model for tidewater glaciers advancing into open marine settings is developed arcuate terminal moraines marking the ice advance limit provide a distinctive component submarine basin s exposed inside these moraine ridges when ice retreats contain suites of individual landforms produced subglacially and ice marginally with a consistent order of timing of deposition and stratigraphic superposition the new schematic model is compared with earlier models based on submarine landforms associated with surges in the more topographically constrained setting of spitsbergen fjords differences include i the overall arcuate shape of the open marine assemblage ii the indented ice proximal sides of terminal moraine ridges iii the fan shaped pattern of streamlined lineations iv crater like kettle holes at the inner lateral margins of many submarine basins v prominent systems of eskers and channels modern glaciological analogues from ongoing surges of ice caps in eastern svalbard and severnaya zemlya provide contemporary observations of ice advance into open marine settings including heavily crevassed ice lobes with finger like termini

surge type glaciers in the russian high arctic identified from digital satellite imagery landsat digital imagery was used to search the island archipelagos of franz josef land severnaya zemlya and novaya zemlya russian high arctic for the presence of looped moraines characteristic of past glacier surges the imagery provides almost complete summer time coverage of the 60000 km 2 of ice in these islands very few surge type glaciers are identified none in franz josef land three in novaya zemlya and two on severnaya zemlya this contrasts greatly with svalbard ice covered area 36 600 km 2 to the west where 36 of glaciers and ice cap drainage basins are inferred to surge the strong climatic gradient across the eurasian high arctic with decreasing temperature and moisture eastward may provide a gross control on this pattern through colder glacier thermal structure limiting basal drainage on the thinner ice masses in particular

deformation induced melting in the margins of the west antarctic ice streams flow of glacial ice in the west antarctic ice sheet localizes in narrow bands of fast flowing ice streams bordered by ridges of nearly stagnant ice but our understanding of the physical processes that generate this morphology is incomplete here we study the thermal and mechanical properties of ice stream margins where flow transitions from rapid to stagnant over a few kilometers our goal is to explore under which conditions the intense shear deformation in the margin may lead to deformation induced melting we propose a 2 d model that represents a cross section through the ice stream margin perpendicular to the downstream flow direction we limit temperature to the melting point to estimate melt rates based on latent heat using rheology parameters as constrained by laboratory data and observations we conclude that a zone of temperate ice is likely to form in active shear margins

the distribution and flow characteristics of surge type glaciers in the canadian high arctic a systematic review of 1959 60 aerial photography and 1999 2000 landsat 7 imagery has identified 51 surge type polythermal glaciers in the canadian high arctic these were identified from the presence of features such as looped medial moraines intense folding visible at the surface rapid terminus advance heavy surface crevassing and high surface velocities these observations suggest that surging glaciers are much more common than previously believed in the canadian high arctic where only six surge type glaciers have previously been described of the 51 surge type glaciers identified in this study 15 were observed in the active phase in the 1959 60 and or 1999 2000 imagery the most dramatic advances have occurred on western axel heiberg island where iceberg good friday bay and airdrop glaciers have all advanced by 4 7 km between1959 and 1999 for glaciers with repeat landsat 7 coverage from 1999 and 2000 image correlation software was used to determine the magnitude and spatial distribution of surge velocities for example mittie glacier on manson icefield was moving at a rate of up to 1 kma over a distance of at least 25 km back from its terminus the terminus of this glacier has advanced by at least 4 km since 1959 and the glacier was observed to be heavily crevassed during overflights in april 2000 with clear signs of surface lowering of 10 25 m indicated by a strandline

the influence of the quasi biennial oscillation on the troposphere in winter in a hierarchy of models part i simplified dry gcms abstracta dry primitive equation model is used to explain how the quasi biennial oscillation qbo of the tropical stratosphere can influence the troposphere even in the absence of tropical convection anomalies and a variable stratospheric polar vortex qbo momentum anomalies induce a meridional circulation to maintain thermal wind balance this circulation includes zonal wind anomalies that extend from the equatorial stratosphere into the subtropical troposphere in the presence of extratropical eddies the zonal wind anomalies are intensified and extend downward to the surface the tropospheric response differs qualitatively between integrations in which the subtropical jet is strong and integrations in which the subtropical jet is weak while fluctuation dissipation theory provides a guide to predicting the response in some cases significant nonlinearity in others particularly those designed to model the midwinter subtropical jet of the north pacific prevents its universal application when the ext

the influence of the madden julian oscillation on northern hemisphere winter blocking abstractthe persistent and quasi stationary nature of atmospheric blocking is associated with long lasting extreme weather conditions that influence much of the northern hemisphere during boreal winter the madden julian oscillation mjo has been previously shown to influence important factors for blocking including rossby wave breaking and the north atlantic oscillation nao however the extent to which the mjo influences blocking across the northern hemisphere is not yet fully understood utilizing a two dimensional blocking index composites of north pacific north atlantic and european blocking are generated relative to mjo phase in the west and central pacific all mjo phases demonstrate significant changes in blocking particularly at high latitudes a significant decrease in east pacific and atlantic blocking occurs following phase 3 of the mjo characterized by enhanced convection over the tropical east indian ocean and suppressed convection in the west pacific the opposite signed mjo heatin

temporal and spatial aspects of the cusp inferred from local and global ground and space based observations in a case study 1 global and local observations from both ground and space facilities are brought to bear to understand the origin of a stepped cusp ion dispersion observed 3 hours prenoon under an interplanetary magnetic field characterized by strongly positive by conditions under which the cusp is believed to be shifted postnoon our main aim is to distinguish the temporal from the spatial cusp features the local observations from svalbard are from approximately the 0900 1200 mlt sector while the in situ observations are from polar at 0900 mlt the global auroral observations were acquired by the earth camera on polar the aurora from the ground perspective appeared as a periodic sequence of brightening events located on either side of a midday gap aurora centered at about 1030 mlt at noon the aurora appeared as a semiperiodic sequence of brightening events these were concurrent with enhancements of the overhead ionospheric hall current polar observed two steps of a staircase ion energy latitude dispersion these two steps were in turn concurrent with two consecutive auroral brightening events we argue from this complement of observations that the stepped cusp was temporal in nature and resulted from a time varying reconnection process global uv imagery was employed to complement the ground observations for the purpose of separating the temporal from the spatial aspects the imager captured namely two bands of strong uv emission in the prenoon and postnoon sectors between which there appeared a persistent weak uv aurora we interpret this to be an underlying spatial substratum patchy and bursty uv enhancements coincided with the transients seen in the local ground and space measurements corroborating further our distinction between space and time in the cusp comparing these inferences with recent work on the response of the dayside aurora to reconnection at the magnetopause we find a close correspondence in addition we document the field aligned currents associated with the stepped cusp which in turn compare favorably with recent theoretical ideas this work is a contribution to the current debate on the nature of the stepped cusp and suggests that multiple data sets are essential to study this problem

pleistocene ice at the bottom of the vavilov ice cap severnaya zemlya russian arctic the vavilov ice cap was perforated in 1988 by a drilling which reached the underlying frozen sediments in contrast to the overlying glacier ice the basal ice is composed of different ice layers with a variable debris load the stable isotope composition of these layers shows values much lower than everywhere else in the core or in the vavilov ice cap this is most probably the signature of a remnant of pleistocene ice which for the first time is shown to occur in the russian arctic

northern hemisphere mid winter vortex displacement and vortex split stratospheric sudden warmings influence of the madden julian oscillation and quasi biennial oscillation we investigate the connection between the equatorial madden julian oscillation mjo and different types of the northern hemisphere mid winter major stratospheric sudden warmings ssws i e vortex displacement and vortex split ssws the mjo ssw relationship for vortex split ssws is stronger than that for vortex displacement ssws as a result of the stronger and more coherent eastward propagating mjos before vortex split ssws than those before vortex displacement ssws composite analysis indicates that both the intensity and propagation features of mjo may influence the mjo related circulation pattern at high latitudes and the type of ssws a pronounced quasi biennial oscillation qbo dependence is found for vortex displacement and vortex split ssws with vortex displacement split ssws occurring preferentially in easterly westerly qbo phases the lagged composites suggest that the mjo related anomalies in the arctic are very likely initiated when the mjo related convection is active over the equatorial indian ocean around the mjo phase 3 further analysis suggests that the qbo may modulate the mjo related wave disturbances via its influence on the upper tropospheric subtropical jet as a result the mjo related circulation pattern in the arctic tends to be wave number one wave number two 25 30 days following phase 3 i e approximately phases 7 8 when the mjo related convection is active over the western pacific during easterly westerly qbo phases which resembles the circulation pattern associated with vortex displacement vortex split ssws

massive destabilization of an arctic ice cap abstract ice caps that are mostly frozen at the bedrock ice interface are thought to be stable and respond slowly to changes in climate we use remote sensing to measure velocity and thickness changes that occur when the margin of the largely cold based vavilov ice cap in the russian high arctic advances over weak marine sediments we show that cold based to polythermal glacier systems with no previous history of surging may evolve with unexpected and unprecedented speed when their basal boundary conditions change resulting in very large dynamic ice mass losses an increase in annual mass loss by a factor of 100 over a few years we question the future long term stability of cold and polythermal polar ice caps many of which terminate in marine waters as the climate becomes warmer and wetter in the polar regions

mapping the dayside ionosphere to the magnetosphere according to particle precipitation characteristics a long standing and vexing problem in magnetospheric physics is mapping the ionosphere to the magnetosphere to date almost all information on the topic has come from magnetic field mappings herein a complementary approach is tried regions are identified based on the plasma characteristics as observed by low altitude satellites using an automated identification scheme applied to approximately 60 000 individual satellite passes through the dayside oval probability maps are computed for observing various types of plasma precipitating into the ionosphere the synthesis of the various individual maps allows the construction of an ionospheric map into the magnetosphere based on plasma characteristics the results suggest a cusp which is about 2 5 hours in total local time extent an llbl which typically extends to about 0900 mlt and a mantle which reaches to about 0800 1600 consistent with earlier results the extension of the nightside region of discrete aurora into the dayside is far more substantial at dusk than at dawn

is there a single surge mechanism contrasts in dynamics between glacier surges in svalbard and other regions 1 during the 1990s monacobreen a 40 km long tidewater glacier in svalbard underwent a major surge we mapped the surge dynamics using ers synthetic aperture radar images differential dual azimuth interferometry and intensity correlation tracking a series of 11 three dimensional 3 d velocity maps covering the period 1991 1997 show a months long initiation and years long termination to the surge with no indication of a surge front travelling downglacier during the surge the front of the glacier advanced 2 km the velocity and derived strain rate increased by more than an order of magnitude and maximum ice flow rates measured during 1994 were 5 m d 1 the spatial pattern of both velocity and strain rate was remarkably consistent and must therefore be controlled by spatially fixed processes operating at the glacier bed we combine these results with those published in the literature to construct a typical svalbard glacier surge cycle and compare this to surge dynamics of glaciers from other cluster regions especially those of variegated glacier in alaska the strong contrast in dynamics suggests that there exist at least two distinct surge mechanisms

how do glaciers surge a review the quasi periodic oscillations between normal and fast motion exhibited by surge type glaciers provide the best observational opportunity to determine limiting conditions that allow fast motion the measurements from variegated glacier prove that its surge motion is caused by rapid sliding induced by high water pressure this arises from a major restructuring of the basal hydraulic system which impedes water discharge prior to and during surge although the evolving glacier geometry and stress distribution play a principal enabling role the seasonal timing of two distinct surge pulses each initiated in winter and terminated in summer indicates a major influence from variable external water inputs this influence is not considered in existing surge models and should promote caution in the use of data from temperate and subpolar surge type glaciers to deduce surge potential in polar ice masses the spatial spreading of surge motion from a zone of local initiation occurs by stress redistribution which may spread the surging zone rapidly upglacier or downglacier inside a region of active ice and by mass redistribution with compressional thickening at the surge front which enables down glacier propagation into less active ice the data from other surge type glaciers including the extensive data from medvezhiy glacier are not inconsistent with the above processes but are inadequate to establish whether completely different mechanisms operate in some surges the way by which water accumulates and produces fast sliding is not established in detail for any surge type glacier and may be different on different glaciers depending for example on the presence or absence of unconsolidated debris between the ice and rock

a reconciled estimate of glacier contributions to sea level rise 2003 to 2009 glaciers distinct from the greenland and antarctic ice sheets are losing large amounts of water to the world s oceans however estimates of their contribution to sea level rise disagree we provide a consensus estimate by standardizing existing and creating new mass budget estimates from satellite gravimetry and altimetry and from local glaciological records in many regions local measurements are more negative than satellite based estimates all regions lost mass during 2003 2009 with the largest losses from arctic canada alaska coastal greenland the southern andes and high mountain asia but there was little loss from glaciers in antarctica over this period the global mass budget was 259 28 gigatons per year equivalent to the combined loss from both ice sheets and accounting for 29 13 of the observed sea level rise

does the aurora provide evidence for the occurrence of antiparallel magnetopause reconnection 1 antiparallel merging at the magnetopause predicts a longitudinal bifurcation of the cusp during intervals of southeast or southwest interplanetary magnetic field imf orientation in the aurora this should manifest itself as a longitudinal gap in the midday sector bracketed by bright auroral forms on either side with the purpose of testing this prediction we searched for an auroral signature in our database from the arctic islands of svalbard focusing on strong isolated auroral brightenings belonging to the category of events which has been previously established as a signature of transient magnetopause reconnection flux transfer events ftes we found some very interesting events showing clear brightenings in the eastern and western parts of the field of view fov with a gap in between in this paper we present a 1 hour long interval of auroral observations in the 1100 1400 mlt sector showing two strong isolated auroral events which were separated by 20 min the imf was steady and directed southeast by 3 nt bz 3 nt clock angle 135 in a solar wind of low speed 370 km s 1 and low dynamic pressure 0 2 npa each auroral event is characterized by an initial strong brightening of the cusp equatorward boundary previously referred to as equatorward boundary intensification ebi which is followed by a westward and poleward moving auroral form pmaf the main point here is that the initial brightening is longitudinally bifurcated with near simultaneous auroral brightenings in the eastern 1300 1400 mlt and western 1100 1130 mlt parts of the all sky camera fov being separated by a 500 km wide gap the brightening event is discussed as a possible signature of transient antiparallel reconnection taking place at high magnetopause latitudes while the gap aurora is attributed to quasi steady component reconnection in the subsolar region

the linear and nonlinear extratropical response of the atmosphere to tropical intraseasonal heating abstract this study examines the dynamical nature of the linear and nonlinear extratropical response of the atmosphere to tropical intraseasonal heating with various temporal and spatial structures a global two level model is used it is found that the midlatitude response is very sensitive to the phase speed of the forcing and to a lesser extent to its spatial scale for a narrow monopolar heating source traveling eastward uniformly with an around the world period of 40 days as in gcm simulations of the madden julian oscillation mjo the response is weak and explains very little of the extratropical variance for dipolar beating with zonal scale around 15 000 km k 2 3 and wave period of 40 days propagating slowly eastward within a confined longitudinal domain a good approximation of the outgoing longwave radiation fields associated with the real mjo the extratropical response is wavelike and well defined and stands significantly above the background variability the nonlinear wavetrains evolv

unraveling the teleconnection mechanisms that induce wintertime temperature anomalies over the northern hemisphere continents in response to the mjo abstractsignificant extratropical surface air temperature variations arise as a result of teleconnections induced by the madden julian oscillation mjo the authors elucidate the detailed physical processes responsible for the development of temperature anomalies over northern hemisphere continents in response to mjo induced heating using an intraseasonal perturbation thermodynamic equation and a wave activity tracing technique a quantitative assessment demonstrates that surface air temperature variations are due to dynamical processes associated with a meridionally propagating rossby wave train over east asia a local hadley circulation causes adiabatic subsidence following mjo phase 3 to be a main driver for the warming meanwhile for north america and eastern europe horizontal temperature advection by northerlies or southerlies is the key process for warming or cooling a ray tracing analysis illustrates that rossby waves with zonal wavenumbers 2 and 3 influence the surface warming over north amer

holocene glacial history of svalbard status perspectives and challenges abstract we synthesize the current understanding of glacier activity on svalbard from the end of the late pleistocene 12 000 yrs before present to the end of the little ice age c 1920 ad our glacier history is derived from the svalhola database the first compilation of holocene geochronology for svalbard and the surrounding waters including over 1 800 radiocarbon terrestrial cosmogenic nuclide and optically stimulated luminescence ages data have been categorized by geological setting uniformly re calibrated quality assessed and ultimately used to constrain glacier fluctuations deglaciation ice free conditions glacier re advances and ice marginal positions we advance existing knowledge by mapping the extent and distribution of ice cover during the holocene glacial maximum and the glacial minimum as well as present retreat rates and percentages within early holocene fjord systems throughout the holocene svalbard glaciers have responded to a varying combination of climatic environmental and dynamic driving factors which influence both the extent and behavior of ice margins we discuss the complexities of glacier systems and their dynamics in response to changes in climate this review provides a holistic state of the art of holocene glaciers on svalbard suitable for orienting future works which address gaps in our current knowledge

recharge of a subglacial lake by surface meltwater in northeast greenland observations of rapid persistent elevation gains that occur on the ice surface above a subglacial lake as the lake is refilled with surface meltwater during the summer melt period in greenland show that surface meltwater may be trapped and stored at the bed of an ice sheet affecting ice dynamics downstream the discovery of a 70 metre deep collapse basin near the summit of the largest and most northerly peripheral ice cap of greenland and the use of high resolution stereo satellite imagery to monitor its evolution suggests that surface meltwater can be trapped and stored beneath the greenland ice sheet previously meltwater from the surface of the ice sheet had been assumed to drain efficiently through the basal hydrologic system during the summer melt period rapid persistent elevation gains occur on the ice surface above a subglacial lake as the lake is refilled with surface meltwater and stored at least on annual time scales these findings have potential implications for our understanding of ice sheet temperature and velocity in a warming climate surface meltwater production on large ice sheets is expected to increase if this water is delivered to the ice sheet base it may have important consequences for ice dynamics for example basal water distributed in a diffuse network can decrease basal friction1 2 and accelerate ice flow3 4 5 6 7 8 whereas channelized basal water can move quickly to the ice margin where it can alter fjord circulation and submarine melt rates9 10 less certain is whether surface meltwater can be trapped and stored in subglacial lakes beneath large ice sheets here we show that a subglacial lake in greenland drained quickly as seen in the collapse of the ice surface and then refilled from surface meltwater input we use digital elevation models from stereo satellite imagery and airborne measurements to resolve elevation changes during the evolution of the surface and basal hydrologic systems at the flade isblink ice cap in northeast greenland during the autumn of 2011 a collapse basin about 70 metres deep and about 0 4 cubic kilometres in volume formed near the southern summit of the ice cap as a subglacial lake drained into a nearby fjord over the next two years rapid uplift of the floor of the basin which is approximately 8 4 square kilometres in area occurred as surface meltwater flowed into crevasses around the basin margin and refilled the subglacial lake our observations show that surface meltwater can be trapped and stored at the bed of an ice sheet sensible and latent heat released by this trapped meltwater could soften nearby colder basal ice11 and alter downstream ice dynamics12 13 heat transport associated with meltwater trapped in subglacial lakes should be considered when predicting how ice sheet behaviour will change in a warming climate

svalbard surge dynamics derived from geometric changes geometric changes on a sample of svalbard glaciers were studied using subtraction of repeat digital terrain models to determine early surge stage dynamics changes in surface features were also analyzed a number of new surges were found for glaciers not known to have surged previously the surge development could be followed through three stages of which the first two had not been previously described in svalbard the first two stages are mainly identified from glacier thickness changes and showed little visual evidence in stage 1 initial surface lowering was found in the upper part of the glacier followed by a thickening further down glacier in stage 2 stage 3 represents the period of well developed surge dynamics that is usually reported some surges ceased at stage 2 as a partial surge and never developed into a fully active surge these partial surges could be misinterpreted as rapid response to climate change the results of this study further support previous findings that the majority of svalbard glaciers are of surge type data archives have greatly facilitated the search for signs of surges and the recapturing of the course of events in this paper we present a number of new observations of svalbard surge type behaviour based on evidence from geometric changes and complemented by observations of newly developed crevasse fields two criteria are used to identify a surge either individually or in combination 1 mass displacement from the upper to the lower glacier part and 2 presence of new crevasse fields which indicate rapid or strong changes in stresses the aims of our study are to contribute to a more complementary picture and better understanding of the transition from build up stage via initial surge dynamics to the previously described mature stage where the changes are more pronounced we also investi gate whether all surges develop fully the implications of partial surges for interpretation of surface lowering related to varying climate conditions and finally the large spread in estimates for the number of surge type glaciers in svalbard

controls on the distribution of surge type glaciers in svalbard we analyzed the possible controls on the distribution of surge type glaciers in svalbard using multivariate logit models including 504 glaciers and a large number of glacial and geological attributes specifically we examined the potential effect of geological boundaries mass balance conditions and thermal regime on surging it was found that long glaciers with relatively steep slopes overlying young fine grained sedimentary lithologies with orientations in a broad arc clockwise from northwest to southeast are most likely to be of surge type no relation between lithological boundaries and surge potential could be established possible explanations for length being conducive to surging are transport distance related substrate properties distance related attenuation of longitudinal stresses and the possible relation between thermal regime and glacier size analysis of glaciers with recorded radioecho sounding reveals that a polythermal regime accumulation area ratios close to balance and a large elevation span increase the surge potential the logit models also enabled us to detect 19 new surge type glaciers to reclassify six glaciers as normal and to identify unusual surge type glaciers our model results suggest that a polythermal regime and fine grained potentially deformable beds are conducive to the surge potential of svalbard glaciers

rapid dynamic activation of a marine based arctic ice cap we use satellite observations to document rapid acceleration and ice loss from a formerly slow flowing marine based sector of austfonna the largest ice cap in the eurasian arctic during the past two decades the sector ice discharge has increased 45 fold the velocity regime has switched from predominantly slow 101 m yr to fast 103 m yr flow and rates of ice thinning have exceeded 25 m yr at the time of widespread dynamic activation parts of the terminus may have been near floatation subsequently the imbalance has propagated 50 km inland to within 8 km of the ice cap summit our observations demonstrate the ability of slow flowing ice to mobilize and quickly transmit the dynamic imbalance inland a process that we show has initiated rapid ice loss to the ocean and redistribution of ice mass to locations more susceptible to melt yet which remains poorly understood

seasonal dependence of the mjo enso relationship abstract observations of the development of recent el nino events suggest a pivotal role for the madden julian oscillation mjo previous attempts to uncover a systematic relationship between mjo activity and the el nino southern oscillation enso however have yielded conflicting results in this study the mjo enso relationship is stratified by season and the focus is on mjo activity in the equatorial western pacific the results demonstrate that mjo activity in late boreal spring leads el nino in the subsequent autumn winter for the period 1979 2005 spring is the season when mjo activity is least asymmetric with respect to the equator and displays the most sensitivity to sst variations at the eastern edge of the warm pool enhanced mjo activity in the western pacific in spring is associated with an eastward expanded warm pool and low frequency westerly surface zonal wind anomalies these sustained westerly anomalies in the western pacific are hypothesized to project favorably onto a developing el n

relationship between birkeland current regions particle precipitation and electric fields data from eight dmsp f7 satellite passes coincident with sondrestrom radar observations have been examined to determine how the large scale dayside birkeland currents are related to the particle precipitation regions and to the convection pattern the classification schemes recently developed from dmsp particle data were adopted the observations were limited to the prenoon local time hours and led to the following conclusions 1 the local time of the mantle currents which were traditionally called cusp currents is not limited to the longitude of the cusp proper but covers a larger local time extent 2 the mantle currents flow entirely on open field lines where open field lines is defined as a region where the ion precipitation and electron precipitation have the characteristics of plasma mantle cusp or polar rain this confirms and extends to all local times similar results obtained from other observations 3 about half of region 1 currents flow on open field lines this is consistent with the assumption that the region 1 currents are generated by the solar wind dynamo and flow within the surface that separates open and closed field lines 4 more than 80 of the birkeland current boundaries do not correspond to particle precipitation boundaries region 2 currents extend beyond the plasma sheet poleward boundary region 1 currents flow in part on open field lines mantle currents and mantle particles are not coincident 5 on most passes when a triple current sheet is observed region 2 region 1 and mantle currents the convection reversal is located on closed field lines when only two current sheets are observed either region 2 region 1 or region 1 mantle currents the convection reversal is on open field lines 6 the data appear to be more consistent with a topology such that mantle currents are an extension of region 1 currents rather than a separate system located poleward of the region 1 current system

outlet glacier response to the 2012 collapse of the matusevich ice shelf severnaya zemlya russian arctic the matusevich ice shelf mis located within the severnaya zemlya archipelago in the russian arctic rapidly broke apart between 10 august and 7 september 2012 we examine the response of the outlet glaciers that fed the mis from local ice caps to the removal of the ice shelf we use spaceborne laser altimetry and multiple optically derived digital elevation models to track ice surface elevation change rates dh dt between 1984 and 2014 glacier speeds are measured by pixel tracking from optical and radar imagery between 2010 and 2014 and interferometric synthetic aperture radar in 1995 to compare precollapse and postcollapse velocities we find that the three main outlet glaciers that fed the mis are thinning an order of magnitude more rapidly than most of the rest of severnaya zemyla based upon icesat data from 2003 to 2009 recent 2012 to 2014 thinning rates are three to four times faster than the 30 year average thinning rate calculated between 1984 and 2014 the springtime speeds of the largest outlet glacier issledovateley have increased more than 200 at the terminus between april 2010 and april 2014 to date changes in surface elevation dh dt and velocity at the outlet glaciers near mis are smaller than glacier responses to ice shelf collapse in antarctica it is possible that the mis was already very weak prior to the 2012 collapse and unable to support back stress further observations are required to assess whether the thinning and nonmelt season glacier speeds are continuing to accelerate

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

role of poleward moving auroral forms in the dawn dusk auroral precipitation asymmetries induced by imf by 1 in a case study we document the detailed spatial temporal structure of the aurora in the 0900 1500 magnetic local time mlt sector during an interval of steady southeast imf orientation emphasis is placed on ground based observations of structure that is often averaged out in large statistical studies a central feature is the phenomenon of poleward moving auroral forms pmafs an ionospheric manifestation of pulsed magnetopause reconnection in the form of flux transfer events ftes whose evolution in both prenoon and postnoon mlts can be monitored under similar interplanetary conditions differences in auroral precipitation associated with pmafs about the noon meridian related to imf by are documented while the prenoon pmafs develop in three stages spanning a latitude range of 500 km the highest latitude stage is absent in postnoon pmafs for by 0 which after the initial intensification progressively fade we suggest that this auroral precipitation asymmetry is closely related to the different field aligned current configuration in pmafs prenoon and pmafs postnoon and the underlying plasma convection pattern we detail the association between the high latitude component of pmafs in the prenoon sector by 0 and a channel of plasma convection located in the dawnside convection cell the latter convection channel located in the regime of old open flux represents an aspect of the svalgaard mansurov effect which is not included in the traditional description the auroral and plasma convection data are placed in the context of recent work on solar wind magnetosphere interconnection topology for a southward pointing imf with a strong by component

on the mechanics of ice stream shear margins we investigate the mechanics of ice stream shear margins based on the assumption that the underlying bed behaves plastically sliding is assumed to occur if a prescribed locally defined yield stress is attained while no sliding is assumed possible if basal shear stress is lower than the yield stress mathematically the ice flow problem takes the form of a contact problem in which the zones of sliding are part of the solution and cannot be prescribed arbitrarily simplistic assumptions about the location of till failure or about mechanical conditions at the bed predict stress singularities at the margins which lead to corresponding singularities in the basal melt rate the ice flow problem is solved using a complex variable method and an associated quasi static thermal problem is also solved using a green s function high stress concentrations which coincide with high rates of strain heating are found on the ice stream side of the margins where basal melting is also greatest our results further indicate that a temperate zone may form over time above the bed in the margins these findings differ from earlier studies based on dif ferent sliding laws suggesting a high sensitivity of margin behaviour to basal conditions

the global response to tropical heating in the madden julian oscillation during the northern winter a life cycle of the madden julian oscillation mjo was constructed based on 21 years of outgoing long wave radiation data regression maps of ncep ncar reanalysis data for the northern winter show statistically significant upper tropospheric equatorial wave patterns linked to the tropical convection anomalies and extratropical wave patterns over the north pacific north america the atlantic the southern ocean and south america to assess the cause of the circulation anomalies a global primitive equation model was initialized with the observed three dimensional 3d winter climatological mean flow and forced with a time dependent heat source derived from the observed mjo anomalies a model mjo cycle was constructed from the global response to the heating and both the tropical and extratropical circulation anomalies generally matched the observations well the equatorial wave patterns are established in a few days while it takes approximately two weeks for the extratropical patterns to appear the model response is robust and insensitive to realistic changes in damping and basic state the model tropical anomalies are consistent with a forced equatorial rossby kelvin wave response to the tropical mjo heating although it is shifted westward by approximately 20 longitude relative to observations this may be due to a lack of damping processes cumulus friction in the regions of convective heating once this shift is accounted for the extratropical response is consistent with theories of rossby wave forcing and dispersion on the climatological flow and the pattern correlation between the observed and modelled extratropical flow is up to 0 85 the observed tropical and extratropical wave patterns account for a significant fraction of the intraseasonal circulation variance and this reproducibility as a response to tropical mjo convection has implications for global medium range weather prediction copyright 2004 royal meteorological society

an observed connection between the north atlantic oscillation and the madden julian oscillation abstract based on the bivariate madden julian oscillation mjo index defined by wheeler and hendon and 25 yr 1979 2004 of pentad data the association between the north atlantic oscillation nao and the mjo on the intraseasonal time scale during the northern hemisphere winter season is analyzed time lagged composites and probability analysis of the nao index for different phases of the mjo reveal a statistically significant two way connection between the nao and the tropical convection of the mjo a significant increase of the nao amplitude happens about 5 15 days after the mjo related convection anomaly reaches the tropical indian ocean and western pacific region the development of the nao is associated with a rossby wave train in the upstream pacific and north american region in the atlantic and african sector there is an extratropical influence on the tropical intraseasonal variability certain phases of the mjo are preceded by the occurrence of strong naos a significant change of upper zonal

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

sensitivity of barnes ice cap baffin island canada to climate state and internal dynamics barnes ice cap is a remnant of the laurentide ice sheet which covered much of northern north america during the last glacial maximum barnes reached a quasi equilibrium state 2000 years ago and has remained similar in size since then with a small increase during the little ice age in this study we combine historical observations 1960 1980 with more recent satellite and airborne data 1995 2010 to drive a mass balance model coupled to a transient thermomechanical model with an adaptive mesh geometry the model is used to characterize the current state of the ice cap and to investigate its stability as a function of climate and its own internal dynamics on millennial time scales we show that ice flow is influenced by adjustment of an unsteady shape by gently sloping bedrock and by contrasting viscosities between the pleistocene and holocene ice on shorter time scales barnes is affected by surge activity sensitivity tests reveal that barnes experienced climate conditions which enabled its stability 2000 to 3000 years ago but will disappear under current climate conditions in the next millennium

the randolph glacier inventory a globally complete inventory of glaciers the randolph glacier inventory rgi is a globally complete collection of digital outlines of glaciers excluding the ice sheets developed to meet the needs of the fifth assessment of the intergovernmental panel on climate change for estimates of past and future mass balance the rgi was created with limited resources in a short period priority was given to completeness of coverage but a limited uniform set of attributes is attached to each of the 198 000 glaciers in its latest version 3 2 satellite imagery from 1999 2010 provided most of the outlines their total extent is estimated as 726 800 34 000 km 2 the uncertainty about 5 is derived from careful single glacier and basin scale uncertainty estimates and comparisons with inventories that were not sources for the rgi the main contributors to uncertainty are probably misinterpretation of seasonal snow cover and debris cover these errors appear not to be normally distributed and quantifying them reliably is an unsolved problem combined with digital elevation models the rgi glacier outlines yield hypsometries that can be com bined with atmospheric data or model outputs for analysis of the impacts of climatic change on glaciers the rgi has already proved its value in the generation of significantly improved aggregate estimates of glacier mass changes and total volume and thus actual and potential contributions to sea level rise

form and flow of the academy of sciences ice cap severnaya zemlya russian high arctic 1 the 5 575 km2 academy of sciences ice cap is the largest in the russian arctic a 100 mhz airborne radar digital landsat imagery and satellite synthetic aperture radar sar interferometry are used to investigate its form and flow including the proportion of mass lost through iceberg calving the ice cap was covered by a 10 km spaced grid of radar flight paths and the central portion was covered by a grid at 5 km intervals a total of 1 657 km of radar data digital elevation models dems of ice surface elevation ice thickness and bed elevation data sets were produced cell size 500 m the dems were used in the selection of a deep ice core drill site total ice cap volume is 2 184 km3 5 5 mm sea level equivalent the ice cap has a single dome reaching 749 m maximum ice thickness is 819 m about 200 km or 42 of the ice margin is marine about 50 of the ice cap bed is below sea level the central divide of the ice cap and several major drainage basins in the south and east of the ice cap and of up to 975 km2 are delimited from satellite imagery there is no evidence of past surge activity on the ice cap sar interferometric fringes and phase unwrapped velocities for the whole ice cap indicate slow flow in the interior and much of the margin punctuated by four fast flowing features with lateral shear zones and maximum velocity of 140 m yr 1 these ice streams extend back into the slower moving ice to within 5 10 km of the ice cap crest they have lengths of 17 37 km and widths of 4 8 km mass flux from these ice streams is 0 54 km3 yr 1 tabular icebergs up to 1 7 km long are produced total iceberg flux from the ice cap is 0 65 km3 yr 1 and probably represents 40 of the overall mass loss with the remainder coming from surface melting driving stresses are generally lowest 40 kpa close to the ice cap divides and in several of the ice streams ice stream motion is likely to include a significant basal component and may involve deformable marine sediments

the generation of global rotational flow by steady idealized tropical divergence abstract tropical convective heating is balanced on the large scale by the adiabatic cooling of ascent the horizontal divergence of the wind above this heating may be viewed as driving the upper tropospheric rotational wind field a vorticity equation model is used to diagnose this relationship it is shown that because of the advection of vorticity by the divergent component of the flow the rossby wave source can be very different from the simple fd source often used in particular an equatorial region of divergence situated in easterly winds can lead to a rossby wave source in the subtropical westerlies where it is extremely effective this part of the source can be relatively insensitive to the longitudinal position of the equatorial divergence a divergence field which is asymmetric about the equator can lead to a quite symmetric rossby wave source for a steady frictionless flow the rossby wave source averaged over regions within closed streamfunction or absolute vorticity contours is under cert

glacier surge mechanism 1982 1983 surge of variegated glacier alaska the hundredfold speedup in glacier motion in a surge of the kind the kind that took place in variegated glacier in 1982 1983 is caused by the buildup of high water pressure in the basal passageway system which is made possible by a fundamental and pervasive change in the geometry and water transport characteristics of this system the behavior of the glacier in surge has many remarkable features which can provide clues to a detailed theory of the surging process the surge mechanism is akin to a proposed mechanism of overthrust faulting

storm track activity over the north pacific associated with the madden julian oscillation under enso conditions during boreal winter the present study investigates modulation by the madden julian oscillation mjo of storm track activity sta over the north pacific np during boreal winter for el nino and la nina periods sta defined by vertically averaged synoptic eddy kinetic energy eke greatly intensifies over the western north pacific wnp and central eastern north pacific during la nina and el nino years respectively when the mjo convection is located over the central indian ocean io maritime continent when the mjo moves into the western central pacific the sta in la nina years is suppressed enhanced at higher lower latitudes than in el nino years diagnoses of eke and eddy available potential energy budgets indicate that the difference in sta over the wnp for the mjo phases between el nino southern oscillation enso years is mainly contributed by baroclinic energy conversion and potential energy conversion between background and eddy bcpe we reveal that bcpe is mainly attributed to intraseasonal baroclinicity and eddy heat flux ehf anomalies and their interactions with strong winter mean baroclinic fields in the wnp through the ehf synoptic eddies act to counterbalance an intraseasonal temperature that is primarily caused by the anomalous horizontal advection of mean temperature by mjo related flow the intraseasonal circulation and associated temperature and ehf anomalies dominate in northwest southeast portion of the np during la nina el nino leading to bcpe difference changes in the spatial pattern and strength of the np circulation and sta are caused by dominance of strong mjo amplification over the io central pacific during la nina el nino

ice loss rates at the northern patagonian icefield derived using a decade of satellite remote sensing abstract we use a satellite based survey of glacier surface elevation changes speeds and surface melt conditions between 2000 and 2011 to quantify mass loss from the northern patagonian icefield npi chile a history of ice elevation change is found by differencing aster digital elevation models dems relative to a void filled version of the dem collected by the shuttle radar topography mission srtm in february 2000 thinning rates have accelerated at lower elevations while above the equilibrium line altitude ela recent thinning rates are not significantly different from those observed in previous studies a volumetric change of 4 06 0 11 km 3 yr is found by summing surface elevation changes over all glaciers in the npi this is regarded as a lower bound because volume loss due to frontal retreat and sub aqueous melting is not included this volume change is converted to a mass loss of 3 40 0 07 gt yr taking into account density differences above and below the equilibrium line we find that the npi is providing at least 0 009 0 0002 mm yr to ongoing sea level change in agreement with previous estimates sub pixel offset tracking of aster image pairs is used to produce glacier displacements over intervals typically ranging from 6 days to 18 months the first whole icefield composite velocity map is presented the terminus of the san rafael glacier on the western side of the npi sustained a peak calving front speed of 19 7 1 2 m day for 7 days in the austral fall of 2007 passive microwave observations indicate that the surface of the accumulation basin of the glacier was wet during this period of rapid motion suggesting that the fast speed may be a consequence of a rise in sub glacial water pressure sourced from melt or rainwater making its way to the glacier bed and reducing basal friction several other outlet glaciers including the benito and hpn1 glaciers on the isolated western side of the icefield accelerated while thinning between 2007 and 2011 marked acceleration also occurred after 2007 at the front of the san quintin glacier the largest outlet glacier of the npi the paucity of thickness measurements at the outlet glaciers means it is impossible to accurately gauge the mass flux of the icefield and thus give a full estimate of the mass balance

recent elevation changes of svalbard glaciers derived from icesat laser altimetry abstract we have tested three methods for estimating 2003 2008 elevation changes of svalbard glaciers from multi temporal icesat laser altimetry a linear interpolation of crossover points between ascending and descending tracks b projection of near repeat tracks onto common locations using digital elevation models dems and c least squares fitting of rigid planes to segments of repeat track data assuming a constant elevation change rate the two repeat track methods yield similar results and compare well to the more accurate but sparsely sampled crossover points most glacier regions in svalbard have experienced low elevation thinning combined with high elevation balance or thickening during 2003 2008 the geodetic mass balance excluding calving front retreat or advance of svalbard s 34 600 km2 glaciers is estimated to be 4 3 1 4 gt y 1 corresponding to an area averaged water equivalent w e balance of 0 12 0 04 m w e y 1 the largest ice losses have occurred in the west and south while northeastern spitsbergen and the austfonna ice cap have gained mass winter and summer elevation changes derived from the same methods indicate that the spatial gradient in mass balance is mainly due to a larger summer season thinning in the west and the south than in the northeast our findings are consistent with in situ mass balance measurements from the same period confirming that repeat track satellite altimetry can be a valuable tool for monitoring short term elevation changes of arctic glaciers

friction at the bed does not control fast glacier flow the largest uncertainty in the ice sheet models used to predict future sea level rise originates from our limited understanding of processes at the ice bed interface near glacier termini where basal sliding controls ice flow most predictive ice sheet models use a parameterization of sliding that has been theoretically derived for glacier flow over a hard bed we find that this sliding relation does not apply to the 140 greenland glaciers that we analyzed there is no relationship between basal sliding and frictional stress at the glacier bed contrary to theoretical predictions there is a strong relationship between sliding speed and net pressure at the glacier bed this latter finding is in agreement with earlier observations of mountain glaciers that have been largely overlooked by the glaciological community

observation of a correspondence between poleward moving auroral forms and stepped cusp ion precipitation in a case study we document for the first time a one to one association between three auroral forms which are separated in latitude and moving poleward and three intervals of almost constant but different low energy cutoffs in the ion precipitation in the cusp region stepped cusp precipitation the ground observations are from ny alesund at 75 magnetic latitude mlat and the precipitation pattern is observed by the dmsp f13 satellite as it crosses the noon meridian into the morning sector the energy cutoffs increase with decreasing latitude the auroral forms brighten up at different times but at practically the same mlat 73 and start fading 5 min later at 76 mlat interplanetary conditions monitored by wind show a stable slow and cold solar wind with an interplanetary magnetic field which points south and west by 0 staircase ion precipitation signatures such as observed in this example have been successfully interpreted in terms of a sequence of reconnection bursts at the low latitude dayside magnetopause the time history of the auroral activity observed from the ground confirms this interpretation we exclude the possibility that the auroral forms are triggered by changes in the interplanetary medium because the latter is very steady in particular the low dynamic pressure varies little about a mean value of 1 6 npa

enso regulation of mjo teleconnection the extratropical teleconnections associated with madden julian oscillation mjo are shown to have an action center in the north pacific where the pressure anomalies have opposite polarities between the phase 3 convective indian ocean and phase 7 convective western pacific of the mjo the teleconnection in the same phase of mjo may induce opposite anomalies over east asia and north america between el nino and la nina years during mjo phase 3 a gigantic north pacific anticyclonic anomaly occurs during la nina making coastal northeast asia warmer wetter than normal but the west us colder drier whereas during el nino the anticyclonic anomaly is confined to the central north pacific hence the northwest us experiences warmer than normal weather under influence of a downstream cyclonic anomaly during phase 7 an extratropical cyclonic anomaly forms over the northwest pacific during la nina due to convective enhancement over the philippine sea causing bitter winter monsoon over japan whereas during el nino the corresponding cyclonic anomaly shifts to the northeast pacific due to enhanced convection over the equatorial central pacific which causes warm and wet conditions along the west coast of us and canada further the presence of enso induced seasonal anomalies can significantly modify mjo teleconnection but the aforementioned mjo teleconnection can still be well identified during phase 3 the mjo teleconnection pattern over north pacific will be counterbalanced enhanced by el nino la nina induced seasonal mean anomalies during phase 7 on the other hand the mjo teleconnection anomalies in the northeastern pacific will be enhanced during el nino but reduced during la nina thereby the impacts of mjo teleconnection on the north america is expected to be stronger during el nino than during la nina

the possible transition from glacial surge to ice stream on vavilov ice cap an edited version of this paper was published by agu copyright 2019 american geophysical union

on spatial and temporal structures in the cusp we identify a series of magnetic conjunctions and close encounters of polar orbiting satellites to investigate cusp features including flux variations and sudden energy changes of cusp precipitating ions the variations and changes are generally interpreted as signatures of variations in the reconnection rate and or changes in the de hoffman teller velocity at the magnetopause they are expected to be temporal features which move poleward with convecting field lines however our analysis shows that a series of cusp features observed on one satellite are remarkably similar to cusp features observed up to 1 5 hours later by a second satellite this similarity suggests that these features are spatial structures and not temporal variations in reconnection parameters

observed changes in the lifetime and amplitude of the madden julian oscillation associated with interannual enso sea surface temperature anomalies the madden julian oscillation mjo is analyzed using the reanalysis zonal wind and satellite outgoing longwave radiation based indices of wheeler and hendon for the 1974 2005 period the average lifetime of the mjo events varies with season 36 days for events whose central date occurs in december and 48 days for events in september the lifetime of the mjo in the equinoctial seasons march may and october december is also dependent on the state of el nino southern oscillation enso during october december it is only 32 days under el nino conditions increasing to 48 days under la nina conditions with similar values in northern spring this difference is due to faster eastward propagation of the mjo convective anomalies through the maritime continent and western pacific during el nino consistent with theoretical arguments concerning equatorial wave speeds the analysis is extended back to 1950 by using an alternative definition of the mjo based on just the zonal wind component of the wheeler and hendon indices a rupture in the amplitude of the mjo is found in 1975 which is at the same time as the well known rupture in the enso time series that has been associated with the pacific decadal oscillation the mean amplitude of the mjo is 16 larger in the postrupture 1976 2005 compared to the prerupture 1950 75 period before the 1975 rupture the amplitude of the mjo is maximum minimum under el nino la nina conditions during northern winter and minimum maximum under el nino la nina conditions during northern summer after the rupture this relationship disappears when the mjo enso relationship is analyzed using all year round data or a shorter dataset as in some previous studies no relationship is found

contribution of antarctica to past and future sea level rise polar temperatures over the last several million years have at times been slightly warmer than today yet global mean sea level has been 6 9 metres higher as recently as the last interglacial 130 000 to 115 000 years ago and possibly higher during the pliocene epoch about three million years ago in both cases the antarctic ice sheet has been implicated as the primary contributor hinting at its future vulnerability here we use a model coupling ice sheet and climate dynamics including previously underappreciated processes linking atmospheric warming with hydrofracturing of buttressing ice shelves and structural collapse of marine terminating ice cliffs that is calibrated against pliocene and last interglacial sea level estimates and applied to future greenhouse gas emission scenarios antarctica has the potential to contribute more than a metre of sea level rise by 2100 and more than 15 metres by 2500 if emissions continue unabated in this case atmospheric warming will soon become the dominant driver of ice loss but prolonged ocean warming will delay its recovery for thousands of years