temporal static stress drop variations due to injection activity at the geysers geothermal field california we use a high quality data set from the nw part of the geysers geothermal field to determine statistical significance of temporal static stress drop variations and their relation to injection rate changes we use a group of 322 seismic events which occurred in the proximity of prati 9 and prati 29 injection wells to examine the influence of parameters such as moment magnitude focal mechanism hypocentral depth and normalized hypocentral distances from open hole sections of injection wells on static stress drop changes our results indicate that 1 static stress drop variations in time are statistically significant 2 statistically significant static stress drop changes are inversely related to injection rate fluctuations therefore it is highly expected that static stress drop of seismic events is influenced by pore pressure in underground fluid injection conditions and depends on the effective normal stress and strength of the medium

high injection rates counteract formation of far reaching fluid migration pathways at the geysers geothermal field deep underground water injections induce seismicity when the seismic fractures coalesce into far reaching pathways for fluid migration the migrating fluid may reach pre existing faults and by de

strong and highly variable push of ocean waves on southern ocean sea ice sea ice in the southern ocean has expanded over most of the past 20 y but the decline in sea ice since 2016 has taken experts by surprise this recent evolution highlights the poor performance of numerical models for predicting extent and thickness which is due to our poor understanding of ice dynamics ocean waves are known to play an important role in ice break up and formation in addition as ocean waves decay they cause a stress that pushes the ice in the direction of wave propagation this wave stress could not previously be quantified due to insufficient observations at large scales sentinel 1 synthetic aperture radars sars provide high resolution imagery from which wave height is measured year round encompassing antarctica since 2014 our estimates give an average wave stress that is comparable to the average wind stress acting over 50 km of sea ice we further reveal highly variable half decay distances ranging from 400 m to 700 km and wave stresses from 0 01 to 1 pa we expect that this variability is related to ice properties and possibly different floe sizes and ice thicknesses a strong feedback of waves on sea ice via break up and rafting may be the cause of highly variable sea ice properties

seismic observations of sea swell on the floating ross ice shelf antarctica 1 a seismometer operating on the floating ross ice shelf near its seaward ice front nascent iceberg for 340 days out of 730 days during the 2004 2005 and 2006 antarctic field seasons recorded the arrival of 93 distantly sourced ocean swell events displaying frequency dispersion characteristic of surface gravity waves propagating on deep water comparison of swell event dispersion with the noaa wave watch iii nww3 ocean wave model analysis reveals that 83 of these events were linked to specific storms located in the pacific southern and indian oceans nearly all major storms in the nww3 analysis of the pacific ocean were linked to signals observed at the nascent site during the period of seismometer operation swell induced motion of the ross ice shelf is found to increase by several orders of magnitude over the time period that sea ice surrounding antarctica decreases from its maximum extent october to its minimum extent february the amplitude of vertical vibration of the ice shelf in the frequency band between 0 025 and 0 14 hz varies between tens of micrometers to millimeters as sea ice decays to its minimum seasonal extent this suggests that climate influence on sea ice extent may indirectly modulate swell energy incident on the calving margins of the antarctic ice sheet the largest swell signals observed on the ross ice shelf come from storms in the tropical pacific and gulf of alaska these remote events emphasize how the iceberg calving margin of antarctica is connected to environmental conditions well beyond antarctica

boundary layer mechanisms in extratropical cyclones this paper revisits the mechanism for the interaction of the boundary layer with extratropical cyclones two diagnostic approaches are compared ekman pumping and potential vorticity ekman pumping derives from the boundary layer stress which induces convergence and ascent boundary layer potential vorticity contains in a single quantity both the vorticity and stratification these quantities are compared for an idealized extratropical cyclone life cycle simulated with the met office unified model a significant component of the boundary layer stress and thus ekman pumping at occlusion is forced by the cold conveyor belt jet in the unstable boundary layer in contrast much of the boundary layer depth averaged potential vorticity is contained within the stable warm sector region inversion of the warm sector pv indicates a small local deepening of about 2 5 hpa moreover switching off the boundary layer mixing in the unstable cold sector has much more impact than in the stable warm sector the sensitivity of the cyclone and its boundary layer to basic state jet strength is then investigated the maximum friction velocity scales closely with the initial maximum jet strength this demonstrates the important role of the large scale flow in organizing the boundary layer structure changes in the minimum pressure produced by altering the boundary layer parametrization correspond closely to changes in the surface stress averaged over the cyclone different operational changes to the boundary layer scheme produce small and compensating changes to the cyclone minimum pressure over three days crown copyright 2007 reproduced with the permission of the controller of hmso published by john wiley sons ltd

a new perspective on southern hemisphere storm tracks abstract a detailed view of southern hemisphere storm tracks is obtained based on the application of filtered variance and modern feature tracking techniques to a wide range of 45 yr european centre for medium range weather forecasts ecmwf re analysis era 40 data it has been checked that the conclusions drawn in this study are valid even if data from only the satellite era are used the emphasis of the paper is on the winter season but results for the four seasons are also discussed both upper and lower tropospheric fields are used the tracking analysis focuses on systems that last longer than 2 days and are mobile move more than 1000 km many of the results support previous ideas about the storm tracks but some new insights are also obtained in the summer there is a rather circular strong deep high latitude storm track in winter the high latitude storm track is more asymmetric with a spiral from the atlantic and indian oceans in toward antarctica and a subtropical jet related lower latitu

storm tracks in the southern hemisphere abstract from 1979 to 1989 global european centre for medium range weather forecasts ecmwf analyses of many meteorological variables important in baroclinic storms have been bandpass filtered to highlight fluctuations on 2 to 8 day time scales in order to illuminate the relationships among the variables in baroclinic storm track regions because of the greater zonal symmetry in the southern hemisphere sh versus the northern hemisphere nh it is possible to examine these relationships over a zonal sector without being dominated by local effects associated with jet stream entrance and exit regions of the storm tracks the bandpassed variance of geopotential height is used to define the storm track and its meridional profile has a pronounced midlatitude maximum in the sh the locations of the jet stream and the variance maxima of meridional and zonal velocity components vorticity vertical motion specific humidity and temperature all bear a distinctive relationship to the storm track but the lat

monitoring and analysis of ocean swell fields from space new methods for routine observations 1 satellite synthetic aperture radar sar observations can provide a global view of ocean swell fields when using a specific wave mode sampling a methodology is presented to routinely derive integral properties of the longer wavelength swell portion of the wave spectrum from sar level 2 products and both monitor and predict their evolution across ocean basins sar derived estimates of swell height and energy weighted peak period and direction are validated against buoy observations and the peak directions are used to project the peak periods in one dimension along the corresponding great circle route both forward and back in time using the peak period group velocity the resulting real time data set of great circle projected peak periods produces two dimensional maps that can be used to monitor and predict the spatial extent and temporal evolution of individual ocean swell fields as they propagate from their source region to distant coastlines the result is found to be consistent with the dispersive arrival of peak swell periods at a midocean buoy the simple great circle propagation method cannot project the swell heights in space like the peak periods because energy evolution along a great circle is a function of the source storm characteristics and the unknown swell dissipation rate a more general geometric optics model is thus proposed for the far field of the storms this model is applied here to determine the attenuation over long distances for one of the largest recorded storms observations of 15 s period swells are consistent with a constant dissipation rate that corresponds to a 3300 km e folding scale for the energy in this case swell dissipation is a significant term in the wave energy balance at global scales

ross sea ice motion area flux and deformation abstract the sea ice motion area export and deformation of the ross sea ice cover are examined with satellite passive microwave and radarsat observations the record of high resolution synthetic aperture radar sar data from 1998 and 2000 allows the estimation of the variability of ice deformation at the small scale 10 km and to assess the quality of the longer record of passive microwave ice motion daily and subdaily deformation fields and radarsat imagery highlight the variability of motion and deformation in the ross sea with the passive microwave ice motion the area export at a flux gate positioned between cape adare and land bay is estimated between 1992 and 2003 a positive trend can be seen in the winter march november ice area flux that has a mean of 990 103 km2 and ranges from a low of 600 103 km2 in 1992 to a peak of 1600 103 km2 in 2001 in the mean the southern ross sea produces almost twice its own area of sea ice during the winter cross gate sea level pressure slp gra

effects of long term fluid injection on induced seismicity parameters and maximum magnitude in northwestern part of the geysers geothermal field the long term temporal and spatial changes in statistical source and stress characteristics of one cluster of induced seismicity recorded at the geysers geothermal field u s are analyzed in relation to the field operations fluid migration and constraints on the maximum likely magnitude two injection wells prati 9 and prati 29 located in the northwestern part of the field and their associated seismicity composed of 1776 events recorded throughout a 7 year period were analyzed the seismicity catalog was relocated and the source characteristics including focal mechanisms and static source parameters were refined using first motion polarity spectral fitting and mesh spectral ratio analysis techniques the source characteristics together with statistical parameters b value and cluster dynamics were used to investigate and understand the details of fluid migration scheme in the vicinity of injection wells the observed temporal spatial and source characteristics were clearly attributed to fluid injection and fluid migration toward greater depths involving increasing pore pressure in the reservoir the seasonal changes of injection rates were found to directly impact the shape and spatial extent of the seismic cloud a tendency of larger seismic events to occur closer to injection wells and a correlation between the spatial extent of the seismic cloud and source sizes of the largest events was observed suggesting geometrical constraints on the maximum likely magnitude and its correlation to the average injection rate and volume of fluids present in the reservoir

synoptic activity in the seas around antarctica abstract the recent ncep department of energy doe reanalysis 2 update of the original ncep ncar dataset provides what is arguably the highest quality analyses spanning two decades available for the high southern latitudes it therefore offers an excellent starting point from which to assemble a modern comprehensive and reliable picture of synoptic activity in the subantarctic region this set covering the modern satellite era from january 1979 to february 2000 is used herein in addition the exploration in this study has been conducted with sophisticated feature tracking and trajectory analysis software it is shown that the high southern latitude cyclone system density is greatest in the indian ocean and to the south of australia near or to the south of 60 s the numbers in winter exceed those in summer except over a few but important regions such as the bellingshausen sea the antarctic coastal region is confirmed as one of high cyclonicity as is that in the northern part of the antarctic

depth migration of seasonally induced seismicity at the geysers geothermal field seismicity from injected fluids provides insight into the hydraulically conductive fracture network at the geysers tg california geothermal reservoir induced earthquakes at tg result from both thermoelastic and poroelastic stresses as injected fluids cool the rocks and increase pore pressure the spatiotemporal evolution of m 1 5 seismicity is characterized as a function of depth in the northwest and southeast regions of tg to develop time dependent earthquake rates using an epidemic type aftershock sequence model the seismicity and injection follow an annual cycle that peaks in the winter months and is correlated by depth the results indicate a time lag of 6 months for fluids to migrate 3 km below the injection depth water injection is the main cause of seismicity as fluids penetrate into the reservoir our results suggest that a steeply dipping fracture network of hydraulically conductive faults allows fluid migration to a few kilometers below the point of injection

boundary layer friction in midlatitude cyclones results from an idealized three dimensional baroclinic life cycle model are interpreted in a potential vorticity pv framework to identify the physical mechanisms by which frictional processes acting in the atmospheric boundary layer modify and reduce the baroclinic development of a midlatitude storm considering a life cycle where the only non conservative process acting is boundary layer friction the rate of change of depth averaged pv within the boundary layer is governed by frictional generation of pv and the flux of pv into the free troposphere frictional generation of pv has two contributions ekman generation which is directly analogous to the well known ekman pumping mechanism for barotropic vortices and baroclinic generation which depends on the turning of the wind in the boundary layer and low level horizontal temperature gradients it is usually assumed at least implicitly that an ekman process of negative pv generation is the mechanism whereby friction reduces the strength and growth rates of baroclinic systems although there is evidence for this mechanism it is shown that baroclinic generation of pv dominates producing positive pv anomalies downstream of the low centre close to developing warm and cold fronts these pv anomalies are advected by the large scale warm conveyor belt flow upwards and polewards fluxed into the troposphere near the warm front and then advected westwards relative to the system the result is a thin band of positive pv in the lower troposphere above the surface low centre this pv is shown to be associated with a positive static stability anomaly which rossby edge wave theory suggests reduces the strength of the coupling between the upper and lower level pv anomalies thereby reducing the rate of baroclinic development this mechanism which is a result of the baroclinic dynamics in the frontal regions is in marked contrast with simple barotropic spin down ideas finally we note the implications of these frictionally generated pv anomalies for cyclone forecasting

scaling of seismicity induced by nonlinear fluid rock interaction 1 fluid injections into geothermal systems sometimes can produce significant seismic events with magnitudes of up to 4 however in the case of hydraulic fracturing of hydrocarbon reservoirs such events occur extremely seldom in the last case in contrast to the former one the structure of rocks is being actively destroyed e g opening of tensile fractures and the fluid rock interaction is strongly nonlinear e g a strong increase of permeability what is the role of this nonlinearity we consider nonlinear pore pressure diffusion to explain features of seismicity we formulate seismicity triggering front its propagation is sensitive to a grade of nonlinearity to spatial dimension of diffusion and to the injection rate we show that a probability of an event with a magnitude larger than a given one increases proportionally to the injected mass an increase of this probability with time is insensitive to the nonlinearity we compare different borehole experiments in some cases the injection produces clearly nonlinear impact on rocks in others this impact is approximately linear we find a well agreement with our theory we observe an insensitivity of temporal increments of magnitude probability to the grade of nonlinearity these increments are controlled by injection rate increments in contrast nonlinear fluid rock interactions are characterized by a strong dominance of small earthquakes defects activated by a nonlinear diffusion possibly obey gutenberg richter statistics with anomalous high b values in the case of a linear diffusion magnitude distributions of events are probably inherited from pre existing fracture systems

a reconciled estimate of ice sheet mass balance we combined an ensemble of satellite altimetry interferometry and gravimetry data sets using common geographical regions time intervals and models of surface mass balance and glacial isostatic adjustment to estimate the mass balance of earth s polar ice sheets we find that there is good agreement between different satellite methods especially in greenland and west antarctica and that combining satellite data sets leads to greater certainty between 1992 and 2011 the ice sheets of greenland east antarctica west antarctica and the antarctic peninsula changed in mass by 142 49 14 43 65 26 and 20 14 gigatonnes year 1 respectively since 1992 the polar ice sheets have contributed on average 0 59 0 20 millimeter year 1 to the rate of global sea level rise

on the stress dependence of the earthquake b value laboratory experiments have shown that the b value in the size distribution of acoustic emission events decreases linearly with differential stress there have been a number of observations that indicate that this relation may also hold for earthquakes here using a simple frictional strength model for stresses in the continental lithosphere combined with earthquake b values measured as a function of depth in a wide variety of tectonic regions we verify and calibrate that relation finding b 1 23 0 06 0 0012 0 0003 1 3 where the stress difference 1 3 is in megapascal for subduction zones we find that b value correlates linearly with the slab pull force and with the net reduction of plate interface normal force both of which also indicate a negative linear relation between b value and differential stress

surface cyclones in the era 40 dataset 1958 2001 part i novel identification method and global climatology abstract a novel method is introduced to generate climatological frequency distributions of meteorological features from gridded datasets the method is used here to derive a climatology of extratropical cyclones from sea level pressure slp fields a simple and classical conception of cyclones is adopted where a cyclone is identified as the finite area that surrounds a local slp minimum and is enclosed by the outermost closed slp contour this cyclone identification procedure can be applied to individual time instants and climatologies of cyclone frequency fc are obtained by simple time averaging therefore unlike most other climatologies the method is not based on the application of a tracking algorithm and considers the size of cyclones in combination with a conventional cyclone center tracking algorithm that allows the determination of cyclone life times and the location of cyclogenesis and cyclolysis additional frequency fields can be obtained for special categories of cyclones that are gener

induced seismicity associated with fluid injection into a deep well in youngstown ohio 1 over 109 small earthquakes mw 0 4 3 9 were detected during january 2011 to february 2012 in the youngstown ohio area where there were no known earthquakes in the past these shocks were close to a deep fluid injection well the 14 month seismicity included six felt earthquakes and culminated with a mw 3 9 shock on 31 december 2011 among the 109 shocks 12 events greater than mw 1 8 were detected by regional network and accurately relocated whereas 97 small earthquakes 0 4 mw 1 8 were detected by the waveform correlation detector accurately located earthquakes were along a subsurface fault trending ene wsw consistent with the focal mechanism of the main shock and occurred at depths 3 5 4 0 km in the precambrian basement we conclude that the recent earthquakes in youngstown ohio were induced by the fluid injection at a deep injection well due to increased pore pressure along the preexisting subsurface faults located close to the wellbore we found that the seismicity initiated at the eastern end of the subsurface fault close to the injection point and migrated toward the west away from the wellbore indicating that the expanding high fluid pressure front increased the pore pressure along its path and progressively triggered the earthquakes we observe that several periods of quiescence of seismicity follow the minima in injection volumes and pressure which may indicate that the earthquakes were directly caused by the pressure buildup and stopped when pressure dropped

water mass transformation by sea ice in the upper branch of the southern ocean overturning sea ice formation is a key factor in the lower branch of the southern ocean overturning circulation observation based data in conjunction with a water mass transformation framework reveal that sea ice plays a central role in the upper branch too

anthropogenic seismicity rates and operational parameters at the salton sea geothermal field geothermal power is a growing energy source however efforts to increase production are tempered by concern over induced earthquakes although increased seismicity commonly accompanies geothermal production induced earthquake rate cannot currently be forecast on the basis of fluid injection volumes or any other operational parameters we show that at the salton sea geothermal field the total volume of fluid extracted or injected tracks the long term evolution of seismicity after correcting for the aftershock rate the net fluid volume extracted injected provides the best correlation with seismicity in recent years we model the background earthquake rate with a linear combination of injection and net production rates that allows us to track the secular development of the field as the number of earthquakes per fluid volume injected decreases over time

an advective mechanism for deep chlorophyll maxima formation in southern drake passage we observe surface and subsurface fluorescence derived chlorophyll maxima in southern drake passage during austral summer backscatter measurements indicate that the deep chlorophyll maxima dcms are also deep biomass maxima and euphotic depth estimates show that they lie below the euphotic layer subsurface offshore and near surface onshore features lie along the same isopycnal suggesting advective generation of dcms temperature measurements indicate a warming of surface waters throughout austral summer capping the winter water ww layer and increasing off shelf stratification in this isopycnal layer the outcrop position of the ww isopycnal layer shifts onshore into a surface phytoplankton bloom a lateral potential vorticity pv gradient develops such that a down gradient pv flux is consistent with offshore along isopycnal tracer transport model results are consistent with this mechanism subduction of chlorophyll and biomass along isopycnals represents a biological term not observed by surface satellite measurements which may contribute significantly to the strength of the biological pump in this region

spatiotemporal variations in the b value of earthquake magnitude frequency distributions classification and causes abstract interpretation of the b value of earthquake frequency magnitude distributions has received considerable attention in recent decades this paper provides a comprehensive review of previous investigations of spatial and temporal variations in b value including their classification and possible causes based on least squares regression of seismicity data compiled from the neic iris and isc catalogs we find an average value of 1 02 0 03 for the whole earth and its two hemispheres consistent with the general view that in seismically active regions the long term average value is close to unity nevertheless wide ranging b variations 0 3 b 2 5 have been reported in the literature this variability has been interpreted to arise from one or more of the following factors prevailing stress state crustal heterogeneity focal depth pore pressure geothermal gradient tectonic setting petrological environmental geophysical characteristics clustering of events incomplete catalog data and or method of calculation excluding the latter all of these factors appear to be linked directly or indirectly with the effective state of stress although time dependent changes in b value are well documented conflicting observations reveal either a precursory increase or decrease in b value before major earthquakes our compilation of published analyses suggests that statistically significant b variations occur globally on various timescales including annual monthly and perhaps diurnal taken together our review suggests that b variations are most plausibly linked with changes in effective stress

ross ice shelf vibrations broadband seismic stations were deployed across the ross ice shelf ris in november 2014 to study ocean gravity wave induced vibrations initial data from three stations 100 km from the ris front and within 10 km of each other show both dispersed infragravity ig wave and ocean swell generated signals resulting from waves that originate in the north pacific spectral levels from 0 001 to 10 hz have the highest accelerations in the ig band 0 0025 0 03 hz polarization analyses indicate complex frequency dependent particle motions with energy in several frequency bands having distinctly different propagation characteristics the dominant ig band signals exhibit predominantly horizontal propagation from the north particle motion analyses indicate retrograde elliptical particle motions in the ig band consistent with these signals propagating as rayleigh lamb flexural waves in the ice shelf water cavity system that are excited by ocean wave interactions nearer the shelf front

antarctic ice shelf disintegration triggered by sea ice loss and ocean swell understanding the causes of recent catastrophic ice shelf disintegrations is a crucial step towards improving coupled models of the antarctic ice sheet and predicting its future state and contribution to sea level rise an overlooked climate related causal factor is regional sea ice loss here we show that for the disintegration events observed the collapse of the larsen a and b and wilkins ice shelves the increased seasonal absence of a protective sea ice buffer enabled increased flexure of vulnerable outer ice shelf margins by ocean swells that probably weakened them to the point of calving this outer margin calving triggered wider scale disintegration of ice shelves compromised by multiple factors in preceding years with key prerequisites being extensive flooding and outer margin fracturing wave induced flexure is particularly effective in outermost ice shelf regions thinned by bottom crevassing our analysis of satellite and ocean wave data and modelling of combined ice shelf sea ice and wave properties highlights the need for ice sheet models to account for sea ice and ocean waves

violations of gutenberg richter relation in anthropogenic seismicity anthropogenic seismicity as is the undesired dynamic rockmass response to technological processes as environments are shallow hence their heterogeneities have important impact on as moreover as is controlled by complex and changeable technological factors this complicated origin of as explains why models used in tectonic seismicity may be not suitable for as we study here four cases of as testing statistically whether the magnitudes follow the gutenberg richter relation or not the considered cases include the data from mponeng gold mine in south africa the data observed during stimulation of geothermal well basel 1 in switzerland the data from acu water reservoir region in brazil and the data from song tranh 2 hydropower plant region in vietnam the cases differ in inducing technologies in the duration of periods in which they were recorded and in the ranges of magnitudes in all four cases the observed frequency magnitude distributions statistically significantly differ from the gutenberg richter relation although in all cases the gutenberg richter b value changed in time this factor turns out to be not responsible for the discovered deviations from the gutenberg richter born exponential distribution model though the deviations from gutenberg richter law are not big they substantially diminish the accuracy of assessment of seismic hazard parameters it is demonstrated that the use of non parametric kernel estimators of magnitude distribution functions improves significantly the accuracy of hazard estimates and therefore these estimators are recommended to be used in probabilistic analyses of seismic hazard caused by as

hydrogeochemistry of high temperature geothermal systems in china a review as an important part of the mediterranean himalayas geothermal belt southern tibet and western yunnan are the regions of china where high temperature hydrothermal systems are intensively distributed of which rehai yangbajing and yangyi have been investigated systematically during the past several decades although much work has been undertaken at rehai yangbajing and yangyi to study the regional geology hydrogeology geothermal geology and geophysics the emphasis of this review is on hydrogeochemical studies carried out in these geothermal fields understanding the geochemistry of geothermal fluids and their environmental impact is critical for sustainable exploitation of high temperature hydrothermal resources in china for comparison the hydrogeochemistry of several similar high temperature hydrothermal systems in other parts of the world are also included in this review it has been confirmed by studies on cl and stable isotope geochemistry that magma degassing makes an important contribution to the geothermal fluids from rehai yangbajing and yangyi though meteoric water is still the major source of recharge for these hydrothermal systems however the mechanisms of magma heat sources appear to be quite different in the three systems as recorded by the 3he 4he ratios of escaping geothermal gases a mantle derived magma intrusion to shallow crust is present below rehai although the intruding magma has been heavily hybridized by crustal material by contrast the heat sources below yangbajing and yangyi are inferred to be remelted continental crust besides original sources the geochemistry of characteristic constituents in the geothermal fluids have also been affected by temperature dependent fluid rock interactions boiling and redox condition changes occurring in the upper part of hydrothermal systems and mixing with cold near surface waters the geothermal fluids from rehai yangbajing and yangyi contain very high concentrations of some toxic elements since local drinking water sources may be mixed with geothermal water and irrigation with water containing geothermally derived harmful elements possibly leading to accumulation in crops consumed by human beings the natural geothermal spring discharge or anthropogenic geothermal wastewater drainage of these fields poses a threat to the environment and human health future research work should focus on estimation of stable o and h isotope compositions of magmatic water related to high temperature hydrothermal systems in china which is of significance for the quantitative source study of geothermal fluid recharged by degassed magmatic waters attention should also be paid to some constituent species in geothermal fluid of strong environmental significance such as thioarsenate that is crucial for the fate of as discharged from geothermal springs especially sulfidic hot springs

ocean waves across the arctic attenuation due to dissipation dominates over scattering for periods longer than 19 s the poorly understood attenuation of surface waves in sea ice is generally attributed to the combination of scattering and dissipation scattering and dissipation have very different effects on the directional and temporal distribution of wave energy making it possible to better understand their relative importance by analysis of swell directional spreading and arrival times here we compare results of a spectral wave model using adjustable scattering and dissipation attenuation formulations with wave measurements far inside the ice pack in this case scattering plays a negligible role in the attenuation of long swells specifically scattering dominated attenuation would produce directional wave spectra much broader than the ones recorded and swell events arriving later and lasting much longer than observed details of the dissipation process remain uncertain average dissipation rates are consistent with creep effects but are 12 times those expected for a laminar boundary layer under a smooth solid ice plate

sea ice transport driving southern ocean salinity and its recent trends the southern ocean has freshened over the past few decades but the underlying mechanisms involved have remained unclear alex haumann and colleagues bring together multiple lines of evidence and despite large uncertainties in the underlying datasets they find that northward transport of sea ice formed around the antarctic coast can explain the bulk of the observed freshening

evolution of seismicity in relation to fluid injection in the north western part of the geysers geothermal field the geysers geothermal field located in california usa is the largest geothermal site in the world operating since the 1960s we here investigate and quantify the correlation between temporal seismicity evolution and variation of the injection data by examination of time series through specified statistical tools binomial test to investigate significant rate changes cross correlation between seismic and injection data b value variation analysis to do so we utilize seismicity and operational data associated with two injection wells prati 9 and prati 29 which cover a time period of approximately 7 yr from november 2007 to august 2014 the seismicity is found to be significantly positively correlated with the injection rate the maximum correlation occurs with a seismic response delay of 2 weeks following injection operations those results are very stable even after considering hypocentral uncertainties by applying a vertical shift of the events foci up to 300 m our analysis indicates also time variations of b value which exhibits significant positive correlation with injection rates

the life cycle of an extratropical marine cyclone part ii mesoscale structure and diagnostics abstract this is the second of two articles describing the evolving structure and selected physical processes within an intense extratropical marine cyclone observed during the experiment on rapidly intensifying cyclones over the atlantic erica field program part i describes the 24 h frontal cyclone evolution through 6 h horizontal analyses of observations taken by specially deployed observing systems from air land and sea part ii presents frontal scale and precipitation structures and physical processes from analyses based primarily on research aircraft observations taken during three phases of the cyclone s life cycle horizontal analyses at 350 m above ground level describe the cyclone s mesoscale frontal baroclinic structure and associated flow patterns the vertical structure and evolution of the cyclone s cold front warm front and bent back front are illustrated in cross sectional analyses of potential temperature wind velocity potential vorticity pv front relative transverse flow vecto

seismic observations of glaciogenic ocean waves micro tsunamis on icebergs and ice shelves seismometers deployed over a 3 year period on icebergs in the ross sea and on the ross ice shelf antarctica reveal that impulsive sources of ocean surface waves are frequent e g 200 events per year in the ross sea in the ice shelf and iceberg covered environment of coastal antarctica the 368 events recorded by our field deployment suggest that these impulsive events are generated by glaciological mechanisms such as 1 small scale calving and edge wasting of icebergs and ice shelf fronts 2 edge on edge closing and opening associated with iceberg collisions and 3 possibly the impulsive opening of void space associated with ice shelf rifting and basal crevasse formation the observations described here provide a background of glaciogenic ocean wave phenomena relevant to the ross sea and suggest that these phenomena may be exploited in the future using more purposefully designed observation schemes to understand iceberg calving and ice shelf disintegration processes

estimating southern ocean storm positions with seismic observations author s hell momme c gille sarah t cornuelle bruce d miller arthur j bromirski peter d crawford alex d

small scale open ocean currents have large effects on wind wave heights tidal currents and large scale oceanic currents are known to modify ocean wave properties causing extreme sea states that are a hazard to navigation recent advances in the understanding and modeling capability of open ocean currents have revealed the ubiquitous presence of eddies fronts and filaments at scales 10 100 km based on realistic numerical models we show that these structures can be the main source of variability in significant wave heights at scales less than 200 km including important variations down to 10 km model results are consistent with wave height variations along satellite altimeter tracks resolved at scales larger than 50 km the spectrum of significant wave heights is found to be of the order of 70 hs 2 g2 tm0 1 2 times the current spectrum where hs is the spatially averaged significant wave height tm0 1 is the energy averaged period and g is the gravity acceleration this variability induced by currents has been largely overlooked in spite of its relevance for extreme wave heights and remote sensing

spatiotemporal changes faulting regimes and source parameters of induced seismicity a case study from the geysers geothermal field the spatiotemporal kinematic and source characteristics of induced seismicity occurring at different fluid injection rates are investigated to determine the predominant physical mechanisms responsible for induced seismicity at the northwestern part of the geysers geothermal field california we analyze a relocated hypocenter catalog from a seismicity cluster where significant variations of the stress tensor orientation were previously observed to correlate with injection rates we find that these stress tensor orientation changes may be related to increased pore pressure and the corresponding changes in poroelastic stresses at reservoir depth seismic events during peak injections tend to occur at greater distances from the injection well preferentially trending parallel to themaximum horizontal stress direction in contrast at lower injection rates the seismicity tends to align in a different direction which suggests the presence of a local fault during peak injection intervals the relative contribution of strike slip faulting mechanisms increases furthermore increases in fluid injection rates also coincide with a decrease in b values our observations suggest that regardless of the injection stage most of the induced seismicity results from thermal fracturing of the reservoir rock however during peak injection intervals the increase in pore pressure may likewise be responsible for the induced seismicity by estimating the thermal and hydraulic diffusivities of the reservoir we confirm that the characteristic diffusion length for pore pressure is much greater than the corresponding length scale for temperature and also more consistent with the spatial extent of seismicity observed during different injection rates

coefficients for sea surface wind stress heat flux and wind profiles as a function of wind speed and temperature surface layer coefficients for wind profiles wind stress and heat flux in typical open sea conditions are briefly reviewed businger dyer flux gradient relationships and a charnock wind stress formula fit the empirical data and are dimensionally consistent these have been solved by an iterative method and the results are presented in a tabular form suitable for climatological calculations from marine wind and temperature data

on the oblique reflexion and transmission of ocean waves at shore fast sea ice a mathematical model is reported describing the oblique reflexion and penetration of ocean waves into shore fast sea ice the arbitrary depth model allows all velocity potentials occurring in the open water region to be matched precisely to their counterparts in the ice covered region matching is done using a preconditioned conjugate gradient technique which allows the complete solution to be found to a predefined precision the model enables the reflexion and transmission coefficients at the ice edge to be found and examples are reported for ice plates of different thicknesses a critical angle is predicted beyond which no travelling wave penetrates the ice sheet in this case the deflexion of the ice is due only to evanescent modes critical angle curves are provided for various ice thicknesses on deep intermediate and shallow water the strain field which is set up within the ice sheet due to the incoming waves is also discussed principal strains are provided as are the strains normal to the ice edge finally the spreading function within the ice cover and some consequences of this function to unimodal seas with realistic open water spreading functions are reported with the aim of generalizing the work to model the effect of shore fast ice on an incoming directional wave spectrum of specified structure

characterization of the deep water surface wave variability in the california current region surface waves are crucial for the dynamics of the upper ocean not only because they mediate exchanges of momentum heat energy and gases between the ocean and the atmosphere but also because they determine the sea state the surface wave field in a given region is set by the combination of local and remote forcing the present work characterizes the seasonal variability of the deep water surface wave field in the california current region as retrieved from over two decades of satellite altimetry data combined with wave buoys and wave model hindcast wavewatch iii in particular the extent to which the local wind modulates the variability of the significant wave height peak period and peak direction is assessed during spring summer regional scale wind events of up to 10 m s are the dominant forcing for waves off the california coast leading to relatively short period waves 8 10 s that come predominantly from the north northwest the wave climatology throughout the california current region shows average significant wave heights exceeding 2 m during most of the year which may have implications for the planning and retrieval methods of the surface water and ocean topography swot satellite mission

thick and deformed antarctic sea ice mapped with autonomous underwater vehicles satellites have documented trends in antarctic sea ice extent and its variability for decades but estimating sea ice thickness in the antarctic from remote sensing data remains challenging in situ observations needed for validation of remote sensing data and sea ice models are limited most have been restricted to a few point measurements on selected ice floes or to visual shipboard estimates here we present three dimensional 3d floe scale maps of sea ice draft for ten floes compiled from two springtime expeditions by an autonomous underwater vehicle to the near coastal regions of the weddell bellingshausen and wilkes land sectors of antarctica mean drafts range from 1 4 to 5 5 m with maxima up to 16 m we also find that on average 76 of the ice volume is deformed ice our surveys indicate that the floes are much thicker and more deformed than reported by most drilling and ship based measurements of antarctic sea ice we suggest that thick ice in the near coastal and interior pack may be under represented in existing in situ assessments of antarctic sea ice and hence on average antarctic sea ice may be thicker than previously thought

variability and trends in sea ice extent and ice production in the ross sea the trend in ice production the increase in brine rejection in the ross shelf polynya associated with the estimated increase with the ice production however is not consistent with the reported ross sea salinity decrease the locally generated sea ice enhancement of ross sea salinity may be offset by an increase of relatively low salinity of the water advected into the region from the amundsen sea a consequence of increased precipitation and regional glacial ice melt

does the summer arctic frontal zone influence arctic ocean cyclone activity abstractextratropical cyclone activity over the central arctic ocean reaches its peak in summer previous research has argued for the existence of two external source regions for cyclones contributing to this summer maximum the eurasian continent interior and a narrow band of strong horizontal temperature gradients along the arctic coastline known as the arctic frontal zone afz this study incorporates data from an atmospheric reanalysis and an advanced cyclone detection and tracking algorithm to critically evaluate the relationship between the summer afz and cyclone activity in the central arctic ocean analysis of both individual cyclone tracks and seasonal fields of cyclone characteristics shows that the arctic coast and therefore the afz is not a region of cyclogenesis rather the afz acts as an intensification area for systems forming over eurasia as these systems migrate toward the arctic ocean they experience greater deepening in situations when the afz is strong at midtropospheric levels