imaging and modeling the ionospheric airglow response over hawaii to the tsunami generated by the tohoku earthquake of 11 march 2011 1 although only centimeters in amplitude over the open ocean tsunamis can generate appreciable wave amplitudes in the upper atmosphere including the naturally occurring chemiluminescent airglow layers due to the exponential decrease in density with altitude here we present the first observation of the airglow tsunami signature resulting from the 11 march 2011 tohoku earthquake off the eastern coast of japan these images are taken using a wide angle camera system located at the top of the haleakala volcano on maui hawaii they are correlated with gps measurements of the total electron content from hawaii gps stations and the jason 1 satellite we find waves propagating in the airglow layer from the direction of the earthquake epicenter with a velocity that matches that of the ocean tsunami the first ionospheric signature precedes the modeled ocean tsunami generated by the main shock by approximately one hour these results demonstrate the utility of monitoring the earth s airglow layers for tsunami detection and early warning

thickness and extent of the subglacial till layer beneath an antarctic paleo ice stream fast flowing ice streams and outlet glaciers currently account for as much as 90 of the discharge from the antarctic and greenland ice sheets although the deformation of subglacial material has been proposed as the mechanism for this rapid motion such sediment is usually hidden under several kilometers of ice marine geophysical records have allowed reconstruction of the three dimensional thickness of the sedimentary bed beneath a large antarctic paleo ice stream for the first time fast flow is indicated by streamlined seafloor lineations that form the surface of a layer of low shear strength unsorted sediment averaging 4 6 m thick rapid motion of the paleo ice stream was a result of subglacial deformation within this layer

glacial geological implications of overconsolidated sediments on the lomonosov ridge and yermak plateau with the coupled use of multibeam swath bathymetry high resolution subbottom profiling and sediment coring from icebreakers in the arctic ocean there is a growing awareness of the prevalence of quaternary ice grounding events on many of the topographic highs found in present water depths of 1000 m in some regions such as the lomonosov ridge and yermak plateau overconsolidated sediments sampled through either drilling or coring are found beneath seismically imaged unconformities of glacigenic origin however there exists no comprehensive analysis of the geotechnical properties of these sediments or how their inferred stress state may be related to different glacigenic processes or types of ice loading here we combine geophysical stratigraphic and geotechnical measurements from the lomonosov ridge and yermak plateau and discuss the glacial geological implications of overconsolidated sediments the degree of overconsolidation determined from measurements of porosity and shear strength is shown to result from consolidation and or deformation below grounded ice and with the exception of a single region on the lomonosov ridge cannot be explained by erosion of overlying sediments we demonstrate that the amount and depth of porosity loss associated with a middle quaternary w790e950 thousand years ago e ka grounding on the yermak plateau is compatible with sediment consolidation under an ice sheet or ice rise conversely geotechnical properties of sediments from beneath late quaternary ice groundings in both regions independently dated to marine isotope stage mis 6 indicate a more transient event commensurate with a passing tabular iceberg calved from an ice shelf

development and tropical transition of an alpine lee cyclone part i case analysis and evaluation of numerical guidance abstract the development and tropical transition tt of a subsynoptic scale cyclone in the gulf of genoa during the mesoscale alpine project map demonstration of probabilistic hydrological and atmospheric simulation of flood events in the alpine region d phase project is investigated using analyses and model simulations cyclogenesis occurs in association with the passage of a synoptic scale trough and attendant surface cold front across the alps on 15 november 2007 an embedded coherent tropopause disturbance ctd plays an important role in promoting the initial development of the lower level vortex by simultaneously providing quasigeostrophic forcing for ascent and reducing the bulk column stability over warm mediterranean waters persistent convection thereafter erodes the ctd as the storm transitions into a hurricane like vortex in addition to this upper level forcing a pair of diabatically generated lower level cyclonic potential vorticity pv features associated with distinct flow regimes i

multi scale topographic control of southwest vortex formation in tibetan plateau region in an idealized simulation the southwest vortex swv is a lee vortex occurring on the leeside of the tibetan plateau in southwestern china which is strongly affected by the different scale topography of the tibetan plateau hengduan cordillera and sichuan basin the roles of these topographic features in swv formation were investigated by conducting simulations with dry dynamics in an idealized background flow two shallow topographically induced vorticity streams are found to be the main contributors to swv formation the first vorticity stream extends out from the southeastern hengduan cordillera and the second from the east side of the tibetan plateau conjoint with the hengduan cordillera and sichuan basin the stretching tilting and friction play different roles in vertical vorticity generation along the two vorticity streams in which the stretching of the planetary vorticity dominates other vertical vorticity sources at the upper level of the first vorticity stream the swv forms due to the combined effects of the topographic features the hengduan cordillera turns the southwesterly airflow around the tibetan plateau to induce the first vorticity stream and the sichuan basin enhances the second one which is associated with the stretching and tilting of airflow from the top of the tibetan plateau moreover the sichuan basin provides a natural site favorable for the merging of the two vorticity streams and then promoting swv formation the sensitivity experiments show that the location and scale of the swv are controlled mainly by the tibetan plateau and hengduan cordillera and the sichuan basin plays a secondary role

physical conditions at the base of a fast moving antarctic ice stream boreholes drilled to the bottom of ice stream b in the west antarctic ice sheet reveal that the base of the ice stream is at the melting point and the basal water pressure is within about 1 6 bars of the ice overburden pressure these conditions allow the rapid ice streaming motion to occur by basal sliding or by shear deformation of unconsolidated sediments that underlie the ice in a layer at least 2 meters thick the mechanics of ice streaming plays a role in the response of the ice sheet to climatic change

far field simulation of tsunami propagation in the pacific ocean impact on the marquesas islands french polynesia the islands in the marquesas archipelago are most exposed to far field tsunamis in french polynesia four recent earthquakes located at the pacific rim kurile 1994 chile 1995 mexico 1995 and peru 1996 earthquakes generated trans pacific tsunamis and caused contrasting inundations in several inhabited marquesian bays the aim of this study is to better understand the amplification phenomena observed in the marquesas islands and to improve the risk assessment we present here numerical simulations of these four tsunamis by means of a finite difference model solving the equations of tsunami propagation at different scales the water heights computed in the bays are in excellent agreement with the available observations and thus validate our numerical method these numerical results allow us to determine 1 which propagation azimuths are dangerous for the whole marquesas archipelago and 2 the behavior of each studied bay amplitude frequency in response to tsunami waves we observe that the seismogenic subduction zone along south america is likely to define one of the most dangerous tsunami generation areas for the marquesas archipelago owing to the source geometries and to the trapping of the tsunami energy by bathymetric features in the southern pacific ocean fracture zones seamount chains

a modified approach to initialize an idealized extratropical cyclone within a mesoscale model abstract a technique for initializing realistic idealized extratropical cyclones for short term 0 72 h numerical simulations is described the approach modifies select methods from two previous studies to provide more control over the initial cyclone structure additional features added to the technique include 1 deformation functions to initialize more realistic low level fronts tropopause structure and enhanced jet maximum at upper levels 2 a barotropic shear function to help develop different cyclone and frontal geometries and 3 damping functions to create an isolated baroclinic wave in the horizontal therefore the initialized cyclone is not influenced by the domain boundaries for relatively short simulations since this procedure allows for control of the initialized cyclone structures it may be useful for studies of frontal and cyclone interaction with topography and mesoscale predictability the initialization system produces a variety of basic states and synoptic disturbances ranging f

the plio pleistocene glaciation of the barents sea svalbard region a new model based on revised chronostratigraphy based on a revised chronostratigraphy and compilation of borehole data from the barents sea continental margin a coherent glaciation model is proposed for the barents sea ice sheet over the past 3 5 million years ma three phases of ice growth are suggested 1 the initial build up phase covering mountainous regions and reaching the coastline shelf edge in the northern barents sea during short term glacial intensification is concomitant with the onset of the northern hemisphere glaciation 3 6 2 4 ma 2 a transitional growth phase 2 4 1 0 ma during which the ice sheet expanded towards the southern barents sea and reached the northwestern kara sea this is inferred from step wise decrease of siberian river supplied smectite rich sediments likely caused by ice sheet blockade and possibly reduced sea ice formation in the kara sea as well as glacigenic wedge growth along the northwestern barents sea margin hampering entrainment and transport of sea ice sediments to the arctic atlantic gateway 3 finally large scale glaciation in the barents sea occurred after 1 ma with repeated advances to the shelf edge the timing is inferred from ice grounding on the yermak plateau at about 0 95 ma and higher frequencies of gravity driven mass movements along the western barents sea margin associated with expansive glacial growth

goce the first seismometer in orbit around the earth the first in situ sounding of a post seismic infrasound wavefront is presented using data from the goce mission the atmospheric infrasounds following the great tohoku earthquake on 11 march 2011 induce variations of air density and vertical acceleration of the goce platform these signals are detected at two positions along the goce orbit corresponding to a crossing and a doubling of the infrasonic wavefront created by seismic surface waves perturbations up to 11 of air density and 1 35 10 7 m s2 of vertical acceleration are observed and modeled with two different solid atmosphere coupling codes these perturbations are a due to acoustic waves creating vertical velocities up to 130 m s amplitudes and arrival times of these perturbations are reproduced respectively within a factor 2 and within a 60 s time window waveforms present a good agreement with observed data the vertical acceleration to air density perturbation ratio is higher for these acoustic waves than for gravity waves combining these two pieces of information offers a new way to distinguish between these two wave types this new type of data is a benchmark for the models of solid atmosphere coupling amplitude and frequency content constrain the infrasound attenuation related to atmosphere viscosity and thermal conductivity observed time shifts between data and synthetics are ascribed to lateral variations of the seismic and atmospheric sound velocities and to the influence of atmospheric winds these effects should be included in future modeling this validation of our modeling tools allows to specify more precisely future observation projects

from sumatra 2004 to tohoku oki 2011 the systematic gps detection of the ionospheric signature induced by tsunamigenic earthquakes the recent tsunamigenic earthquake in tohoku 11 march 2011 strongly affirms one more time after the sumatra event 26 december 2004 the necessity to open new paradigms in oceanic monitoring detection of ionospheric anomalies following the sumatra tsunami demonstrated that ionosphere is sensitive to the tsunami propagation observations supported by modeling proved that tsunamigenic ionospheric anomalies are deterministic and reproducible by numerical modeling via the ocean neutral atmosphere ionosphere coupling mechanism in essence tsunami induces internal gravity waves propagating within the neutral atmosphere and detectable in the ionosphere most of the ionospheric anomalies produced by tsunamis were observed in the far field where the tsunami signature in the ionosphere is clearly identifiable in this work we highlight the early signature in the ionosphere produced by tsunamigenic earthquakes and observed by gps measuring the total electron content close to the epicenter we focus on the first hour after the seismic rupture we demonstrate that acoustic gravity waves generated at the epicenter by the direct vertical displacement of the source rupture and the gravity wave coupled with the tsunami can be discriminated with theoretical support we illustrate the systematic nature of those perturbations showing several observations nominally the ionospheric perturbation following the tsunamigenic earthquakes in sumatra on 26 december 2004 and 12 september 2007 in chile on 14 november 2007 in samoa on 29 september 2009 and the recent catastrophic tohoku oki event on 11 march 2011 based on the analytical description we provide tracks for further modeling efforts and clues for the interpretation of complex and thus often misleading observations the routine detection of the early ionospheric anomalies following the rupture highlights the role of ionospheric sounding in the future ocean monitoring and tsunami detection

the 2009 samoa and 2010 chile tsunamis as observed in the ionosphere using gps total electron content 1 ground based global positioning system gps measurements of ionospheric total electron content tec show variations consistent with atmospheric internal gravity waves caused by ocean tsunamis following two recent seismic events the samoa earthquake of 29 september 2009 and the chile earthquake of 27 february 2010 both earthquakes produced ocean tsunamis that were destructive to coastal communities near the epicenters and both were observed in tidal gauge and buoy measurements throughout the pacific ocean we observe fluctuations in tec correlated in time space and wave properties with these tsunamis using the jet propulsion laboratory s global ionospheric mapping software these tec measurements were band pass filtered to remove ionospheric tec variations with wavelengths and periods outside the typical range for tsunamis observable variations in tec appear correlated with the tsunamis in some locations hawaii and japan but not in others southern california or near the epicenters where variations are observed the typical amplitude tends to be 0 1 0 2 tec units for these events on the order of 1 of the background tec value these observations are compared to estimates of expected tsunami driven tec variations produced by embry riddle aeronautical university s spectral full wave model an atmosphere ionosphere coupled model and are found to be in good agreement significant tec variations are not always seen when a tsunami is present but in these two events the regions where a strong ocean tsunami was observed coincided with clear tec observations while a lack of clear tec observations coincided with smaller sea surface height amplitudes there exists the potential to apply these detection techniques to real time gps tec data providing estimates of tsunami speed and amplitude that may be useful for early warning systems

a groove ploughing theory for the production of mega scale glacial lineations and implications for ice stream mechanics mega scale glacial lineations msgls are longitudinally aligned corrugations ridge groove structures 6 100 km long in sediment produced subglacially they are indicators of fast flow and a common signature of ice stream beds we develop a qualitative theory that accounts for their formation and use numerical modelling and observations of ice stream beds to provide supporting evidence ice in contact with a rough scale of 10 10 3 m bedrock surface will mimic the form of the bed because of flow acceleration and convergence in ice stream onset zones the ice base roughness elements experience transverse strain transforming them from irregular bumps into longitudinally aligned keels of ice protruding downwards where such keels slide across a soft sedimentary bed they plough through the sediments carving elongate grooves and deforming material up into intervening ridges this explains msgls and has important implications for ice stream mechanics groove ploughing provides the means to acquire new lubricating sediment and to transport large volumes of it downstream keels may provide basal drag in the force budget of ice streams thereby playing a role in flow regulation and stability we speculate that groove ploughing permits significant ice stream widening thus facilitating high magnitude ice discharge

an arctic ocean ice shelf during mis 6 constrained by new geophysical and geological data the hypothesis of floating ice shelves covering the arctic ocean during glacial periods was developed in the 1970s in its most extreme form this theory involved a 1000 m thick continuous ice shelf covering the arctic ocean during quaternary glacial maxima including the last glacial maximum lgm while recent observations clearly demonstrate deep ice grounding events in the central arctic ocean the ice shelf hypothesis has been difficult to evaluate due to a lack of information from key areas with severe sea ice conditions here we present new data from previously inaccessible unmapped areas that constrain the spatial extent and timing of marine ice sheets during past glacials these data include multibeam swath bathymetry and subbottom profiles portraying glaciogenic features on the chukchi borderland southern lomonosov ridge north of greenland morris jesup rise and yermak plateau sediment cores from the mapped areas provide age constraints on the glaciogenic features combining these new geophysical and geological data with earlier results suggests that an especially extensive marine ice sheet complex including an ice shelf existed in the amerasian arctic ocean during marine isotope stage mis 6 from a conceptual oceanographic model we speculate that the cold halocline of the polar surface water may have extended to deeper water depths during mis 6 inhibiting the warm atlantic water from reaching the amerasian arctic ocean and thus creating favorable conditions for ice shelf development the hypothesis of a continuous 1000 m thick ice shelf is rejected because our mapping results show that several areas in the central arctic ocean substantially shallower than 1000 m water depth are free from glacial influence on the seafloor

atmospheric airglow fluctuations due to a tsunami driven gravity wave disturbance 1 a spectral full wave model is used to study the upward propagation of a gravity wave disturbance and its effect on atmospheric nightglow emissions gravity waves are generated by a surface displacement that mimics a tsunami having a maximum amplitude of 0 5 m a characteristic horizontal wavelength of 400 km and a horizontal phase speed of 200 m s the gravity wave disturbance can reach f region altitudes before significant viscous dissipation occurs the response of the oh meinel nightglow in the mesopause region 87 km altitude produces relative brightness fluctuations which are 1 of the mean for overhead viewing the wave amplitudes grow as the wave disturbance propagates upward which causes the thermospheric nightglow emission responses to be large for overhead viewing the brightness fluctuations are 50 and 43 of the mean for the oi 6300 a and o 1356 a emissions respectively the total electron content fluctuation is 33 of the mean for overhead viewing for oblique viewing the relative brightness fluctuations are slightly smaller than those obtained for overhead viewing in spite of this the thermospheric nightglow brightness fluctuations are large enough that oblique viewing could provide early warning of an approaching tsunami thus the monitoring of thermospheric nightglow emissions may be a useful augmentation to other observational techniques of tsunami effects in the thermosphere ionosphere system

preconsolidation of tills and intertill clays by glacial loading in southern saskatchewan canada preconsolidation of pre battleford tills and intertill clays resulted in a narrow range of effective pressures 1800 200 kpa at 10 sites along a 1300 km transect across southern saskatchewan these data suggest an almost invariant loading system that is independent of total ice thickness which ranged from 1150 to 2000 m the preconsolidation process apparently took place in a temperate glacier environment the loading system is characterized as a variable thickness of ice related to distance from the glacier terminus a steady hydraulic grade line sustained a potentiometric surface within the subglacial sediments at an elevation consistently 69 76 of the total ice thickness this mechanism maintains small fluctuations in effective stress

a method for quantifying the impacts and interactions of potential vorticity anomalies in extratropical cyclones the theory of potential vorticity pv allows us to describe the life cycle of mid latitude baroclinic systems in terms of the individual impacts and interactions of distinct pv anomalies embedded in the background flow pv anomalies associated with the undulating tropopause the low level thermal field and key diabatic processes such as the latent heat release within the cloudy systems of the cyclone are often considered as evolving features regulated by their lateral and vertical mutual interactions and their interaction with the stratospheric high latitude pv reservoir under some balance flow assumptions pv inversion can be used to quantify the contribution of the pv anomalies to the cyclone depth or other attributes at various stages of its life cycle a static approach but it is less clear how to diagnose with similar quantitative detail the various types of time dependent interactions among the anomalies and mean flow that govern the processes of cyclogenesis and cyclolysis a dynamic approach this paper presents a method that implements the concepts of pv thinking quantitatively the method first applies a piecewise pv inversion scheme formulated according to the charney nonlinear mass wind balance approximation then it combines a prognostic system of balance equations that are consistent with the applied inversion scheme with a factor separation technique by switching on and off the pv anomalies of interest various flow configurations are generated and the corresponding solutions to the prognostic equations can be algebraically combined to isolate the magnitude of both the individual and the synergistic effects of the pv anomalies on the spatial pattern of geopotential height tendency and vertical motion around the cyclone with low computational cost the potential of the method to elucidate the relative importance of physically meaningful pv anomalies for the growth or decay of baroclinic systems is illustrated for the intense mediterranean cyclone of 10 12 november 2001 using the ncep meteorological grid analyses at 12 h intervals the upper level pv anomalies contributed very significantly during the whole life cycle of this mediterranean cyclone surface thermal anomalies were fundamental during the development period and induced the general northeastward movement of the system during the later stages during the mature stage of the cyclone the interaction between the two types of anomalies became the dominant effect all other contributions including the individual and synergistic effects of diabatically generated pv were generally most relevant during this mature stage copyright 2008 royal meteorological society

equatorial mountain torques and cold surge preconditioning the evolution of the two components of the equatorial mountain torque emt applied by mountains on the atmosphere is analyzed in the ncep reanalysis a strong lagged relationship between the emt component along the greenwich axis tm1 and the emt component along the 90 e axis tm2 is found with a pronounced signal on tm1 followed by a signal of opposite sign on tm2 it is shown that this result holds for themajor massifs antarctica the tibetan plateau the rockies and the andes if a suitable axis systemis used for each of them for the midlatitude mountains this relationship is in part associated with the development of cold surges following these results two hypotheses are made i the mountain forcing on the atmosphere is well measured by the regional emts and ii this forcing partly drives the cold surges to support these a purely dynamical linear model is proposed it is written on the sphere uses an f plane quasigeostrophic approximation and includes the mountain forcings in this model a positive negative peak in tm1 produced by a mountain massif in the northern southern hemisphere is due to a large scale high surface pressure anomaly poleward of the massif at a later stage high pressure and low temperature anomalies develop in the lower troposphere east of the mountain explaining the signal on tm2 and providing the favorable conditions for the cold surge development it is concluded that the emt is a good measure of the dynamical forcing of the atmospheric flow by the mountains and that the poleward forces exerted by mountains on the atmosphere are substantial drivers of the cold surges at least in their early stage therefore the emt time series can be an important diagnostic to assess the representation of mountains in general circulation models 2010 american meteorological society

formation of mega scale glacial lineations observed beneath a west antarctic ice stream most discharge from large ice sheets takes place through fast flowing ice streams and their speed is strongly modulated by interactions between the ice and the underlying sediments seismic surveys and investigations through boreholes have revealed a spatial association between fast ice flow and saturated deformable sediments nevertheless our knowledge of the morphology of the interface between ice and sediments is still limited resulting in only rudimentary understanding of the basal boundary conditions beneath ice streams and the generation of subglacial bedforms here we present radar data from the bed of a west antarctic ice stream that reveal the presence of mega scale glacial lineations we combine these data with previously published seismic data and show that these lineations develop in areas of dilatant deforming till and are part of a dynamic sedimentary system that undergoes significant change by erosion and deposition on decadal timescales we find that the mega scale glacial lineations are indistinguishable from those found on beds of palaeo ice streams providing conclusive evidence for the hypothesis that highly elongate bedforms are a characteristic of fast flow regions in ice sheets

ionospheric disturbances triggered by the 11 march 2011 m9 0 tohoku earthquake 1 an earthquake of magnitude 9 0 occurred near the east coast of honshu tohoku area japan producing overwhelming earth surface motions and inducing devastating tsunamis which then traveled into the ionosphere and significantly disturbed the electron density within it hereafter referred to as seismotraveling ionospheric disturbances stids the total electron content tec derived from nationwide gps receiving networks in japan and taiwan is employed to monitor stids triggered by seismic and tsunami waves of the tohoku earthquake the stids first appear as a disk shaped tec increase about 7 min after the earthquake occurrence centered at about 200 km east of the epicenter near the west edge of the japan trench fast propagating disturbances related to rayleigh waves quickly travel away from the epicenter along the main island of japan with a speed of 2 3 3 3 km s accompanied by sequences of concentric circular tec wavefronts and followed by circular ripples close to a tsunami speed of about 720 800 km h that travel away from the stid center these are the most remarkable stids ever observed where signatures of rayleigh waves tsunami waves etc simultaneously appear in the ionosphere

response of subglacial sediments to basal freeze on 1 theory and comparison to observations from beneath the west antarctic ice sheet 1 we have constructed a high resolution numerical model of heat water and solute flows in sub ice stream till subjected to basal freeze on the model builds on quantitative treatments of frost heave in permafrost soils the full version of the clapeyron equation is used hence ice water phase transition depends on water pressure osmotic pressure and surface tension the two latter effects can lead to supercooling of the ice base this supercooling in turn induces hydraulic gradients that drive upward flow of pore water which feeds the growth of segregation ice onto the freezing interface this interface may progress into the till and form ice lenses if supercooling is sufficiently strong hence the ice segregation process develops a stratified basal ice layer in our model a high basal temperature gradient 0 054 c m 1 triggers ice stream stoppage and the loss of basal shear heating leads to relatively high basal freeze on rates 3 5 mm a 1 in response the subglacial till experiences comparatively rapid consolidation till porosity can decrease from 40 to 120 kpa approximately within one century basal supercooling arising from redistribution of solutes and ice water interfacial effects amounts to ca 0 35 c below the pressure melting point fine grained till is in our model associated with widely spaced thick ice lenses coarse grained till yields thinner ice lenses that are more closely spaced our model results compare favorably although not in all details with available observational evidence from borehole studies of west antarctic ice streams

seabed erosion on the lomonosov ridge central arctic ocean a tale of deep draft icebergs in the eurasia basin and the influence of atlantic water inflow on iceberg motion 1 the submarine lomonosov ridge which bisects the arctic ocean is covered by 450 m of hemipelagic sediments high resolution chirp sonar and side scan data have documented erosion of a section of the ridge here we present multichannel seismic and chirp sonar data which show removal of unconsolidated sediments along the eurasia basin side of the lomonosov ridge where the central ridge is shallower than 1000 m the incomplete erosion of the hemipelagic drape and probable topographic control of ice motion suggest that the deepest draft glacier ice which reached the central arctic ocean from the eurasia basin was in the form of armadas of large icebergs embedded in sea ice rather than a single continuous floating ice shelf massive rapid discharge of glacier ice was probably required to produce the deepest draft 800 m icebergs eastward and northward drift trajectories from a likely iceberg source area on the kara barents sea margin would reflect the relative strength of atlantic inflow through the fram strait however only icebergs with drafts exceeding bathymetric thresholds on the lomonosov ridge would leave an erosive imprint on the seabed advection of atlantic water may have been relatively strong at times of discharge from the saalian ice sheet icebergs exiting the arctic ocean caused massive erosion and redeposition of the hemipelagic sediments on top of yermak plateau

a theory of deep cyclogenesis in the lee of the alps part i modifications of baroclinic instability by localized topography abstract observational and numerical studies on alpine cyclogenesis have shown that a developing baroclinic wave approaching the mountain region gives rise to a disturbance of dipolar structure extending throughout the troposphere with horizontal scales comparable to the rossby deformation radius it is possible to interpret such disturbances as modifications of baroclinically unstable modes induced by localized topography in the present approach the effect of the mountain is introduced in a perturbative sense in the framework of quasi geostrophic theory even in this simple approach the spatial structure of the unstable modes is modified by a localized topography in the direction required in order to explain the observed features in the case of a continuously stratified fluid the basic characteristics of the observed vertical structure are also reproduced

traveling ionospheric disturbances propagating ahead of the tohoku oki tsunami a case study we document two kinds of traveling ionospheric disturbances namely ctids co tsunami traveling ionospheric disturbances and atids ahead of tsunami traveling ionospheric disturbances related to the tohoku oki tsunami of 2011 march 11 they are referred to the disturbances that remain behind and ahead of the principal tsunami wave front respectively we first note their presence in a numerical experiment performed using a simulation code coupling the tsunami atmosphere and ionosphere this code uses the tsunami wavefield as an input and simulates acoustic gravity waves agws in the atmosphere and tids in the form of total electron content tec disturbance in the ionosphere the simulated tec reveals the excitation of ctids at about 2 tecu and atids at about 1 tecu representing up to 5 per cent disturbance over the ambient electron density and they arise from the dissipation of agws in the thermosphere a novel outcome is that during the tsunami passage between 6 and 12 of epicentral distance strong atids arrive 20 60 min ahead of the tsunami wave front covering 3 10 of distance from the tsunami location simulation results are compared with the far field observations using gnss satellites and confirm that atids are the first detected tec maximum occurring 20 60 min ahead of the tsunami arrival our simulation also confirms the presence of largest tec maximum representing ctids 10 20 min after the first tsunami wave atids reported in this study have characteristics that can be potentially used for the early warning of the tsunami

a new physics based modeling approach for tsunami ionosphere coupling tsunamis can generate gravity waves propagating upward through the atmosphere inducing total electron content tec disturbances in the ionosphere to capture this process we have implemented tsunami generated gravity waves into the global ionosphere thermosphere model gitm to construct a three dimensional physics based model wp wave perturbation gitm wp gitm takes tsunami wave properties including the wave height wave period wavelength and propagation direction as inputs and time dependently characterizes the responses of the upper atmosphere between 100 km and 600 km altitudes we apply wp gitm to simulate the ionosphere above the west coast of the united states around the time when the tsunami associated with the march 2011 tohuku oki earthquke arrived the simulated tec perturbations agree with global positioning system observations reasonably well for the first time a fully self consistent and physics based model has reproduced the gps observed traveling ionospheric signatures of an actual tsunami event

stratosphere perturbed by the 2011 mw9 0 tohoku earthquake this study examined the formosat 3 cosmic radio occultation soundings of total electron content in the ionosphere from 150 to 550 km and refractivity index in the lower atmosphere from 0 to 60 km after during the 2011 mw9 0 tohoku earthquake tsunami the refractivity index observations show the first evidence of the tohoku earthquake tsunami induced vertical oscillations in the lower atmosphere the atmospheric oscillations with vertical wavelength ranging from 0 5 to 8 km and from 10 to 40 km respectively appear in the stratosphere and ionosphere after the earthquake onset the short vertical wavelengths suggest that the oscillations are the atmospheric oscillatory tail due to the wavefront of the earthquake tsunami the radio occultation technique is a tool for detecting the atmospheric waves induced by earthquake or some other sources plain language summary it has been well known that the sudden uplift of the earth s surface due to earthquake tsunami significantly disturbs the upper atmosphere and ionosphere however the evidence of earthquake tsunami induced waves in the lower atmosphere is insufficient due to the lack of observation supporting here the formosat 3 cosmic f3 c radio occultation refractivity index is for the first time to capture the tohoku earthquake induced vertical oscillations at the stratosphere altitudes from 30 to 40 km the results in this study not only shed lights on understanding of earthquake tsunami waves perturbing the whole atmosphere but also suggest that the radio occultation technique can benefit to the earthquake tsunami warning system

overconsolidated section on the yermak plateau arctic ocean ice sheet grounding prior to ca 660 ka the sediment sequence at ocean drilling program odp site 910 556 m water depth on the yermak plateau in the arctic ocean features a remarkable overconsolidated section from 19 to 70 95 m below sea floor m bsf marked by large increases in bulk density and sediment strength the odp leg 151 shipboard scientific party interpreted the overconsolidated section to be caused by 1 grounding of a marine based ice sheet derived from svalbard and perhaps the barents sea ice sheet and or 2 coarser grained glacial sedimentation which allowed increased compaction here i present planktonic foraminiferal 18 o data based on neogloboquadrina pachyderma sinistrally coiling that date the termination of overconsolidation near the boundary between isotope stages 16 and 17 ca 660 ka no evidence is found for coarser grained sedimentation because lithic fragments 150 m exhibit similar mean concentrations throughout the upper 24 5 m bsf the overconsolidated section may reflect more extensive ice sheet grounding prior to ca 660 ka suggesting a major change in state of the svalbard ice sheets during the mid quaternary furthermore continuous sedimentation since that time argues against a pervasive arctic ice shelf impinged on the yermak plateau during the past 660 k y these findings suggest that svalbard ice sheet history was largely independent of circum arctic ice sheet history during the middle to late quaternary

giant ionospheric disturbances excited by the m9 3 sumatra earthquake of 26 december 2004 1 an mw 9 3 earthquake originated in the indian ocean off the western coast of northern sumatra at 00 58 53 universal time ut on 26 december 2004 two giant ionospheric disturbances at 01 19 and 04 10 ut are observed by a network of digital doppler sounders in taiwan the first disturbance excited mainly by rayleigh waves which consists of a packet of short period doppler shift variations results in vertical ionospheric fluctuations with a maximum velocity of about 70 m s and displacement of about 200 m the second disturbance in a w shaped pulse propagating at a horizontal speed of 360 70 m s is attributable to coupling of the atmospheric gravity waves agw excited by broad crustal uplift together with the following big tsunami waves around the earthquake source zone the accompanying ionosonde data suggest that the agw in the atmosphere may have caused the ionosphere to move up and down by about 40 km

interpretation of the effect of mountains on synoptic scale baroclinic waves abstract linear and nonlinear simulations of idealized baroclinic waves interacting with topography are examined in the context of quasigeostrophy the purpose is to provide a simple conceptual interpretation of the transients resulting from this interaction a perturbation expansion is employed with the small parameter being proportional to topographic slope to isolate fundamentally different topographic effects and show how they enter systematically at each order first and second order corrections appear to capture the essence of the topographic effect for all cases considered even for values of the small parameter as large as 0 5 and are qualitatively useful for a parameter value of unity results indicate the importance of surface rossby wave dynamics at first order near the mountain and downshear from the mountain a distance inversely proportional to the growth rate of the most unstable mode of the system the second order correction projects onto the initial baroclinic wave being primarily

statistical properties of low frequency variability in the northern hemisphere abstract we discuss some statistical properties of the observed tropospheric circulation in northern hemisphere mid latitudes the data used consist of the twice daily 500 mb height nmc analyses for the period 1966 77 our analysis is performed in the context of the quasi unidimensional theory estimates of the probability distribution of wave amplitude in the low frequency range 10 40 days seem to reveal a bimodal character while similar estimates for the zonal wind fail to show stable multiple peaks in the occupation frequency although the process involved seems to be more complex than gaussian possible dynamical interpretations of such statistical properties are discussed in the light of other properties resulting from different types of analysis the emerging physical picture reveals an intermittent process operating on planetary scales through a predominantly baroclinic conversion in agreement with the theoretical considerations of benzi et al

ice sheet extent of the antarctic peninsula region during the last glacial maximum lgm insights from glacial geomorphology we present marine geological and geophysical data for the antarctic peninsula that call for a larger ice sheet reconstruction during the last glacial maximum lgm than suggested by previous studies such glacial reconstructions are important for quantifying post lgm sea level rise and providing boundary conditions for general circulation models megascale glacial lineations on the continental shelf surrounding antarctica provide documentation for grounded ice that was streaming swath bathymetry data nbp02 01 reveal lineations in each of the major glacial troughs except for smith trough which features grooves and bedrock drumlins 0 5 3 km spacing 1 20 elongation ratios on crystalline bedrock we place the maximum extent of ice at the seaward limit of the lineations at or near megascale glacial lineations imaged in this study and other areas surrounding antarctica including the ross sea pine island bay have a consistent morphology with elongation ratios of 80 1 and spacings of 200 600 m mode of 300 m in contrast lineations bundles canals et al 2000 in the gerlache boyd trough exhibit larger spacing 1 5 km and the upstream portions 7 km are carved directly into bedrock rather than till as suggested by previously unpublished air gun 120 hz seismic data these features have yet to be dated however they are believed to have been active during the lgm radiocarbon dates in glaciomarine sediments foraminifera and organic matter from seven glacial troughs indicate that megascale glacial lineations were formed during the lgm other geomorphic features such as the grounding zone wedge in the northwestern weddell sea formed when the ice sheet was retreating the initial retreat of the grounded ice from the outer shelf occurred by 18 500 cal yr b p the inner shelf was mostly ice free by 13 000 cal yr b p this is significantly earlier than numerical models which suggest antarctic deglaciation began at 12 000 cal yr b p this also suggests the peninsula area contributed to global sea level rise associated with meltwater pulse mwp 1a

mid cenozoic tectonic and paleoenvironmental setting of the central arctic ocean drilling results from the integrated ocean drilling program s arctic coring expedition acex to the lomonosov ridge lr document a 26 million year hiatus that separates freshwater influenced biosilica rich deposits of the middle eocene from fossil poor glaciomarine silty clays of the early miocene detailed micropaleontological and sedimentological data from sediments surrounding this mid cenozoic hiatus describe a shallow water setting for the lr a finding that conflicts with predrilling seismic predictions and an initial postcruise assessment of its subsidence history that assumed smooth thermally controlled subsidence following rifting a review of cenozoic tectonic processes affecting the geodynamic evolution of the central arctic ocean highlights a prolonged phase of basin wide compression that ended in the early miocene the coincidence in timing between the end of compression and the start of rapid early miocene subsidence provides a compelling link between these observations and similarly accounts for the shallow water setting that persisted more than 30 million years after rifting ended however for much of the late paleogene and early neogene tectonic reconstructions of the arctic ocean describe a landlocked basin adding additional uncertainty to reconstructions of paleodepth estimates as the magnitude of regional sea level variations remains unknown

high resolution geophysical observations of the yermak plateau and northern svalbard margin implications for ice sheet grounding and deep keeled icebergs high resolution geophysical evidence on the seafloor morphology and acoustic stratigraphy of the yermak plateau and northern svalbard margin between 79 20 and 81 30 n and 5 and 22 e is presented

atmospheric gravity waves due to the tohoku oki tsunami observed in the thermosphere by goce oceanic tsunami waves couple with atmospheric gravity waves as previously observed through ionospheric and airglow perturbations aerodynamic velocities and density variations are computed from gravity field and steady state ocean circulation explorer goce accelerometer and thruster data during tohoku oki tsunami propagation high frequency perturbations of these parameters are observed during three expected crossings of the tsunami generated gravity waves by the goce satellite from theoretical relations between air density and vertical and horizontal velocities inside the gravity wave we demonstrate that the measured perturbations are consistent with a gravity wave generated by the tsunami and provide a way to estimate the propagation azimuth of the gravity wave moreover because goce measurements can constrain the wave polarization a marker noted c3 of any gravity wave crossing by the goce satellite is constructed from correlation coefficients between the observed atmospheric state parameters these observations validate a new observation tool of thermospheric gravity waves generated by tsunamis above the open ocean

traveling ionospheric disturbances over the united states induced by gravity waves from the 2011 tohoku tsunami and comparison with gravity wave dissipative theory

analysis of observed and predicted tsunami travel times for the pacific and indian oceans i have examined over 1500 historical tsunami travel time records for 127 tsunamigenic earthquakes that occurred in the pacific and indian oceans after subjecting the observations to simple tests to rule out gross errors i compare the remaining reports to simple travel time predictions using huygens method and the long wave approximation thus simulating the calculations that typically take place in a tsunami warning situation in general i find a high correspondence between predicted and reported travel times however significant departures exist some outliers imply significantly slower propagation speeds than predicted many of these are clearly the consequences of observers not being able to detect the possibly weak first arrivals other outliers imply excessively long predicted travel times these outliers reflect peculiar geometric and bathymetric conditions that are poorly represented in global bathymetric grids leading to longer propagation paths and consequently increased travel times analysis of t the difference between observed and predicted travel time yields a mean t of 19 minutes with a standard deviation of 131 minutes robust statistics being less sensitive to outliers yield a median t of just 18 seconds and a median absolute deviation of 33 minutes care is needed to process bathymetry to avoid excessive travel time delays in shallow areas i also show that a 2 2 arc minute grid yields better results that a 5 5 arc minute grid the latter in general yielding slightly slower propagation predictions the largest remaining source of error appears to be the inadequacy of the point source approximation to the finite tsunami generating area

resonance vibrations of the ross ice shelf and observations of persistent atmospheric waves recently reported lidar observations have revealed a persistent wave activity in the antarctic middle and upper atmosphere that has no counterpart in observations at mid and low latitude locations the unusual wave activity suggests a geographically specific source of atmospheric waves with periods of 3 10 hours here we investigate theoretically the hypothesis that the unusual atmospheric wave activity in antarctica is generated by the fundamental and low order modes of vibrations of the ross ice shelf ris simple models are developed to describe basic physical properties of resonant vibrations of large ice shelves and their coupling to the atmosphere dispersion relation of the long surface waves which propagate in the floating ice sheet and are responsible for its low order resonances is found to be similar to the dispersion relation of infragravity waves in the ice free ocean the phase speed of the surface waves and the resonant frequencies determine the periods and wave vectors of atmospheric waves that are generated by the ris resonant oscillations the altitude dependent vertical wavelengths and the periods of the acoustic gravity waves in the atmosphere are shown to be sensitive to the physical parameters of the ris which can be difficult to measure by other means predicted properties of the atmospheric waves prove to be in a remarkable agreement with the key features of the observed persistent wave activity

comments on cyclogenesis in the lee of the alps a case study by a buzzi and s tibaldi 104 271 287

ionospheric gravity waves detected offshore hawaii after tsunamis 1 on board satellites techniques provide global coverage and could play an important role in the continuous oceanic survey to prevent the damage produced by powerful tsunamis we report here new ionospheric observations related to three significant transpacific tsunami events triggered by the 2006 kuril earthquake the 2009 samoa earthquake and the 2010 chile earthquake total electron content tec variations extracted from data recorded by a dense global positioning system gps network based in hawaii show ionospheric disturbances within the hours following the tsunami wave passage at sea level for each event we observe ionospheric gravity waves propagating with velocity direction and arrival time coherent with the tsunami the tsunamigenic signature in the ionosphere is also compared to in situ sea level measurements these observations provide new examples of the sensitivity of the ionosphere to tsunamigenic gravity waves and confirm that ionospheric monitoring by gps can provide complementary information on tsunami propagation

three dimensional waveform modeling of ionospheric signature induced by the 2004 sumatra tsunami 1 the sumatra december 26th 2004 tsunami produced internal gravity waves in the neutral atmosphere and large disturbances in the overlying ionospheric plasma to corroborate the tsunamigenic hypothesis of these perturbations we reproduce with a 3d numerical modeling of the ocean atmosphere ionosphere coupling the tsunami signature in the total electron content tec data measured by the jason 1 and topex poseidon satellite altimeters the agreement between the observed and synthetic tec shows that ionospheric remote sensing can provide new tools for offshore tsunami detection and monitoring

vertical structure of the ionospheric response following the m w 7 9 wenchuan earthquake on 12 may 2008 the response of the vertical ionospheric electron density structure to the mw 7 9 wenchuan earthquake on 12 may 2008 was recorded by the formosat 3 cosmic f3 c radio occultation ro precise orbit determination pod total electron content tec the horizontal propagation characteristics of the seismo traveling ionospheric disturbances were identified by combining ground based global navigation satellite system gnss tec data and ro tec data the postseismic ionospheric infrasound wavefront with wavelength of around 80 km at altitude of 150 350 km was scanned vertically by an individual ro tec profile a large amount of tec profiles around the epicenter from 0000 to 1200 ut provide evidence of continental earthquake induced vertical oscillations that lasted in the ionosphere for several hours ro observed vertical perturbations appear on both the southward and northward sides of the epicenter the vertical structure of the ionospheric oscillations with wavelength ranging from 10 to 80 km increased with altitude between 230 and 650 km

synoptic responses to mountain gravity waves encountering directional critical levels abstract a heuristic model is used to study the synoptic response to mountain gravity waves gws absorbed at directional critical levels the model is a semigeostrophic version of the eady model for baroclinic instability adapted by smith to study lee cyclogenesis the gws exert a force on the large scale flow where they encounter directional critical levels this force is taken into account in the model herein and produces potential vorticity pv anomalies in the midtroposphere first the authors consider the case of an idealized mountain range such that the orographic variance is well separated between small and large scale contributions in the absence of tropopause the pv produced by the gw force has a surface impact that is significant compared to the surface response due to the large scales for a cold front the gw force produces a trough over the mountain and a larger amplitude ridge immediately downstream it opposes somehow to the response due to the large scales of the mountain range whic

sediment deformation beneath glaciers and its coupling to the subglacial hydraulic system abstract the extent and style of shear deformation in sediments beneath modern glaciers and the geological evidence for such deformation in deposited sediments are reviewed new evidence is presented from beneath a modern glacier of the spatial and temporal patterns of water pressure fluctuation and of time dependent patterns of deformation in sediments it is concluded that in most experimental sites beneath soft bedded modern glaciers deformation is a significant or major contributor to glacier movement and the resultant discharge of till is large enough to make sediment deformation a major till forming process particular modes of deformation facilitate incorporation of underlying material into the till whilst the capacity of a deforming till to absorb strain can protect the underlying strata from deformation leading to the commonly found relationship where till overlies other strata with a sharp planar interface it is argued that the almost ubiquitous occurrence of drumlins on the beds of former ice sheets is a reflection of the widespread occurrence of sediment deformation beneath them with important implications for the coupling of ice sheet flow and bed properties it is argued that the mechanical behaviour of the subglacial system is not simply determined by till properties but largely controlled by the subglacial water pressure regime determined by the nature of subglacial drainage results of field experiments show how the nature of the basal hydraulic system can play a vital role in controlling the coupling between the glacier and till deformation processes they show that rapid glacier advances can produce undrained loading of sediments that effective pressure may increase either upwards or downwards in a till according to the direction of drainage and that interstitial water pressures in subglacial sediments can show large and rapid variations producing strong variations in the rate and distribution of strain and in the partitioning of basal movement between sliding and deformation

first high resolution chirp sonar profiles from the central arctic ocean reveal erosion of lomonosov ridge sediments the swedish arctic ocean 96 expedition to the central arctic ocean with the icebreaker oden carried out a geological geophysical program focused mainly on lomonosov ridge sediments approximately 195 km of high resolution seismic data from the ridge crest and slope were collected with a chirp sonar system providing new insights into the sediment stratigraphy and the accompanying depositional history these data reveal evidence of substantial erosion that acted in laterally limited areas on shallow parts of the investigated ridge segment more than 50 m of sediment stratigraphy is missing in the most eroded parts moreover the chirp sonar records indicate that below the erosional surface the ridge crest and slope is characterized by a low energy sedimentary environment the termination of the erosional phase is indicated by a prominent reflector the subsequent depositional phase resulted in an approximately 3 m thick stratigraphic unit the cause of the erosion is attributed to either ice grounding or current erosion furthermore oden echo sounding data has been used together with data from the us navy scicex program in order to update existing bathymetric charts in the arctic ocean 96 working area the update shows a narrower ridge crest with a different outline than in previously published charts with a minimum depth of 607 m which is the shallowest depth of the lomonosov ridge recorded in the public domain in the central arctic ocean 1999 elsevier science b v all rights reserved

mountain torques and synoptic systems in the mediterranean the mountains surrounding the mediterranean exert torques t during the passage of north atlantic systems which affect the angular momentum of the airflow passing over and around the massifs the alps the atlas range and the orographic block of asia minor are selected to investigate the typical flow conditions during torque events these mountain ranges are small enough to justify a local angular momentum analysis both the zonal and the meridional components of a mountain s torque t and t are used as stratification parameters in a statistical investigation of the interaction of large scale perturbations with this mountain how are these flows affected by the obstacle a simple scheme is tested which attempts to interpret results the torque analysis singles out eastward moving large scale systems their isobars are oriented from southwest northwest to northeast southeast near the mountain in zonal torque t t cases the massifs tend to generate a low level distortion of the pressure field such that the angular momentum of the flow over the mountain is reduced these results can be explained within the framework of the scheme the influence of the mountains on the pressure field is seen only at heights 4000 m the low level distortions of the pressure field contribute positively to the total torque for lags 0 in the alps and for all lags 2 2 days in asia minor where only t is evaluated the impact of the atlas mountains is seen only at 0

mega scale glacial lineations and cross cutting ice flow landforms landsat images reveal a previously unsuspected large scale pattern of streamlining within drift that is assumed to reflect former phases of ice flow such a glacial grain can be regarded as a landform assemblage comprised of a number of components drumlins and megaflutes form part of the pattern but in addition there are two previously undocumented ice moulded landform elements streamlined lineations of much greater proportions referred to as mega scale glacial lineations and a distinctive cross cutting topology within the grain the ice moulded landform assemblage is described and illustrated with reference to examples from canada possible modes of genesis of such landforms are discussed and their glaciological implications outlined the discovery of this pattern indicates the pervasive nature of subglacial deformation of sediment and demands a radical re interpretation of ice sheet dynamics

a coupled consolidation shear model for the process of formation of glaciated soils it has been generally observed that the measured preconsolidation pressure values for glaciated soils are not compatible with the measured effective pressure values at the bed of the glacier if one dimensional consolidation alone is considered as the formation process for these soils in this paper a new model for the process of formation of glaciated soil termed the coupled consolidation shear ccs model is developed using the frameworks of critical state soil mechanics and small strain consolidation theory the ccs model includes simultaneous shearing and consolidation of subglacial sediments and is able to simulate profiles of preconsolidation pressure versus depth that closely resemble those observed in glaciated soils the ccs model is validated by successfully simulating the profile of preconsolidation pressure versus depth for an 80 m deep battleford till layer in birsay saskatchewan canada the ccs model suggests the existence of anisotropic yield strength and stiffness in glaciated soils as