seismic image quality beneath strongly scattering structures and implications for lower crustal imaging numerical simulations summary the aim of this paper is to analyse how the scattered wavefield in a highly heterogeneous structure influences the image quality of structures below it and how the velocity control during processing of data from highly heterogeneous areas is important in the imaging problem statistical 2 d two layer models are built based on deep borehole data the layers are characterized by a fractal dimension hurst exponent and by the standard deviation of the velocity fluctuations over a constant background velocity value shot gathers are generated in these models with a 2 d elastic and viscoelastic finite difference simulator the synthetic data are first stacked and migrated using an average background velocity function as would be done in a realistic situation during which only a smooth version of the velocity field can be resolved second the full heterogeneous velocity models are applied to the migration scheme the final sections are compared using a semblance based technique to quantify the amount of contamination from an upper heterogeneous structure of a lower heterogeneous structure in data that are not properly migrated multiple scattering in the upper layer seems to dominate the lower part of the section this contamination is controlled by the standard deviation of the velocity fluctuations and it is reduced when viscoelasticity is introduced in the simulations counterintuitively a low q value may improve deep imaging when the seismograms are migrated with the real complex velocity field this contamination is reduced to acceptable levels residual contamination cannot be corrected completely because of the single scattering assumption inherent to all migration techniques

an interannual link between arctic sea ice cover and the north atlantic oscillation this work investigates links between arctic surface variability and the phases of the winter djf north atlantic oscillation nao on interannual time scales the analysis is based on era reanalysis and model data from the ec earth global climate model our study emphasizes a mode of sea ice cover variability that leads the nao index by 1 year the mechanism of this leading is based on persistent surface forcing by quasi stationary meridional thermal gradients associated thermal winds lead a slow adjustment of the pressure in the following winter which in turn feeds back on the propagation of sea ice anomalies the pattern of the sea ice mode leading nao has positive anomalies over key areas of south davis strait labrador sea the barents sea and the laptev ohkostsk seas associated to a high pressure anomaly over the canadian archipelago baffin bay and the laptev east siberian seas these anomalies create a quasi annular quasi steady positive gradient of sea ice anomalies about coastal line when leading the positive nao phase and force a cyclonic vorticity anomaly over the arctic in the following winter during recent decades in spite of slight shifts in the modes spectral properties the same leading mechanism remains valid encouraging actual models appear to reproduce the same mechanism leading model s nao relative to model areas of persistent surface forcing this indicates that the link between sea ice and nao could be exploited as a potential skill source for multi year prediction by addressing the key problem of initializing the phase of the nao ao arctic oscillation

imaging and interpreting the shallow crystalline crust abstract in the past many tests of high resolution seismic imaging methods utilizing off the shelf technology from hydrocarbon exploration have had only limited success some problems associated with the application of seismic profiling in the shallow crystalline crust differ from those encountered in sedimentary basins perhaps the most fundamental distinction stems from differences in statistical properties of the reflection coefficient time series analysis of power spectra derived from borehole data indicates that the reflection coefficients in the crystalline crust are depleted in the seismic bandwidth relative to sedimentary basins this fundamental difference must be considered in the design of shallow crustal seismic surveys in order to achieve success to a first approximation acoustic impedance variations in sedimentary basins are controlled by velocity changes whereas velocity and density can vary independently in the crystalline crust and changes in density may be relatively more important in controlling reflectivity in certain instances density fluctuations outweigh velocity fluctuations for example physical rock property data from mining districts in the canadian shield suggest that massive fe oxide or sulphide bodies will generate strong seismic reflections

arctic sea ice variability in the context of recent atmospheric circulation trends abstract forty years 1958 97 of reanalysis products and corresponding sea ice concentration data are used to document arctic sea ice variability and its association with surface air temperature sat and sea level pressure slp throughout the northern hemisphere extratropics the dominant mode of winter january march sea ice variability exhibits out of phase fluctuations between the western and eastern north atlantic together with a weaker dipole in the north pacific the time series of this mode has a high winter to winter autocorrelation 0 69 and is dominated by decadal scale variations and a longer term trend of diminishing ice cover east of greenland and increasing ice cover west of greenland associated with the dominant pattern of winter sea ice variability are large scale changes in sat and slp that closely resemble the north atlantic oscillation the associated sat and surface sensible and latent heat flux anomalies are largest over the portions of the marginal sea ice zone in which the tr

effects of near surface waveguides on shallow high resolution seismic refraction and reflection data waveguides formed between the earth s free surface and sharp subsurface velocity discontinuities such as the watertable may have a significant impact on high resolution seismic refraction and reflection data energy trapped in such waveguides may propagate over long distances with little loss due to geometrical spreading the dispersive nature of the guided waves results in pronounced shingling of the first arrivals this narrows the optimum reflection window between the first arrivals and the ground roll and may lead to mispicking of first breaks and difficulties in identifying and processing shallow reflections

arctic sea ice variability on a timescale of weeks and its relation to atmospheric forcing abstract northern hemisphere sea ice concentration 500 hpa height sea level pressure and 1000 500 hpa thickness at 7 day intervals are examined for the period 1972 1989 with emphasis on the winter season the temporal variability of sea ice concentration is largest along the climatological mean ice edge where its frequency distribution is strongly bimodal with ice free and ice covered conditions being observed much more frequently than partial ice cover these results confirm impressions based on visual inspection of satellite imagery that most of the variability in these regions is associated with the advance and retreat of the ice edge relationships between large scale patterns of atmospheric variability and sea ice variability are investigated making use of singular value decomposition of the temporal covariance matrix the analysis is conducted separately for the atlantic and pacific sectors in agreement with earlier studies based upon monthly mean data on sea ice concentration the strongest

mapping brittle fracture zones in three dimensions high resolution traveltime seismic tomography in a granitic pluton summary fractured and altered zones within a granitic pluton are mapped in three dimensions by means of high resolution seismic traveltime tomography the input traveltimes were picked from offset and azimuth variable vertical seismic profiles ovsp acquired in three boreholes and from seismic shot gathers of four cdp high resolution seismic reflection profiles recorded on the surface for the ovsp data a hydrophone streamer placed in the boreholes recorded the acoustic energy generated a signal with a frequency content between 15 to 150 hz by a vibroseis truck at source points distributed every 30 m in a rectangular grid of 620 m by 150 m the combination of borehole and surface seismic data resulted in an increase in the ray density of the shallow subsurface the tomographic algorithm uses a variable model grid with a finer grid spacing close to the surface were ray density is highest and the velocity variations are strongest therefore the resulting velocity models feature more detail at shallow levels a simple and smooth starting velocity model was derived from p wave velocity logs careful surface geological mapping and borehole geophysical data p and s wave velocity logs and poisson s ratio depth functions provided key constraints for a physically reasonable 3 d interpretation of the tomograms the low velocity anomalies constrained by the tomographic images were interpreted as unconsolidated rock fractures and altered zones which correlate with structures mapped at the surface or velocity anomalies identified in the logs subsequent resolution analysis revealed that the derived velocity model is well constrained to depths of 60 m

seismic scattering near the earth s surface the seismic coda is usually thought to be composed of waves scattered from the heterogeneities in the earth three classes of scattering mechanisms have been recognized repeated specular reflection of primary waves in a uniformly layered structure volume scattering of primary waves from localized volume heterogeneities and scattering of primary waves from irregularities in an otherwise generally layered structure the presence of the earth s surface complicates the description of all these scattering phenomena whenever the scattering obstacles are near or at the surface in this paper i review work which demonstrates the effects of scattering near the earth s surface emphasizing three general areas of investigation scattering of body waves from an irregular free surface scattering of body waves in irregular layers and propagation of surface waves across irregular topography or in irregular wave guides most of the effects of importance have been recognized in model studies of idealized geometries observational evidence in support of the model studies exists but is often inferred few controlled experiments to measure scattering have been performed

modeling of seismic wave propagation near the earth s surface abstract realistic modeling of seismic wave propagation in the vicinity of the earth s surface is complicated by large velocity contrasts strong heterogeneity severe attenuation and topographic relief to account for these complications we employ a finite difference solution of the 2d viscoelastic equations a grid refinement technique in the shallow parts of the model and a generalized imaging condition to model free surface topography the grid refinement approach allows us to vary the discretization of the model and the wavefiedl with respect to the velocity structure compared to a standard uniform finite difference grid approach this saves considerable amount of memory and computations thus enables modeling of wave propagation through large portions of the earth s crust moreover the decreasing accuracy of the finite difference method near the irregular free surface is compensated by using a finer grid spacing in this region numerical tests show that the method is reliable and accurate by applying this modeling technique to several canonical models of the near surface region and upper crust we find that scattering and mode conversions from topographic relief waveguide effects and attenuation in the immediate subsurface tend to dominate the seismic coda at near lapse times

atmospheric impact of arctic sea ice loss in a coupled ocean atmosphere simulation the atmospheric response to an idealized decline in arctic sea ice is investigated in a novel fully coupled climatemodel experiment in this experimenttwo ensembles of single year model integrations are performed starting on 1 april the approximate start of the ice melt season by perturbing the initial conditions of sea ice thickness sit declines in both sea ice concentration and sit which result in sea ice distributions that are similar to the recent sea ice minima of 2007 and 2012 are induced in the ice loss regions there are strong 3k local increasesin sea surface temperature sst additionally there are remoteincreases in sst in the central north pacific and subpolar gyre in the north atlantic over the central arctic there are increases in surface air temperature sat of 8k due to increases in ocean atmosphere heatfluxes there are increases in sat over continental north america that are in good agreement with recent changes as seen by reanalysis data it is estimated that up to two thirds of the observed increase in sat in this region could be related to arctic sea ice loss in early summer there is a significant but weak atmospheric circulation response that projects onto the summer north atlantic oscillation nao in early summer and early autumn there is an equatorward shift of the eddy driven jet over the north atlantic as a result of a reduction in the meridional temperature gradients in winter there is no projection onto a particular phase of the nao

dynamic and thermodynamic characteristics of atmospheric response to anomalous sea ice extent in the sea of okhotsk abstract influence of sea ice extent anomalies within the sea of okhotsk on the large scale atmospheric circulation is investigated through an analysis of the dynamic and thermodynamic characteristics of the response in an atmospheric general circulation model to specified anomalous sea ice cover significant response appears not only around the sea of okhotsk but also downstream over the bering sea alaska and north america in the form of a stationary wave train in the troposphere this remote response associated with wave activity flux emanating from the okhotsk area to the downstream is regarded as a stationary rossby wave generated thermally by the anomalous turbulent heat fluxes from the ocean surface as a result of the anomalous sea ice cover the pacific storm track in the model that extends zonally at 35 n is located too far south of the sea of okhotsk to exert substantial feedback forcing on the local and remote response since a similar stationary wave train is identified in the composite di

a mechanism of decadal variability of the sea ice volume in the northern hemisphere a long term simulation performed with a coarse resolution global atmosphere ocean sea ice model displays strong decadal variability of the sea ice volume in the northern hemisphere with a significant peak at about 15 18 years this model results from the coupling of ecbilt a spectral t21 3 level quasi geostrophic atmospheric model and clio a sea ice ocean general circulation model first the mechanism underlying the variability of ice volume in the model was studied by performing correlation analyses between the simulated variables in a second step a series of additional sensitivity experiments was performed in order to illustrate the role of specific physical processes this as allowed us to identify a feedback loop in the ice ocean system which proceeds as follows an increase in at tic sea ice volume induces an increase in the salinity there this salinity anomaly is transported to the greenland sea where it promotes convective activity this warms up the surface oceanic layer and the atmosphere in winter and induces a decrease of the ice volume completing half a cycle the changes in ice volume are driven by a geopotential height pattern characterised by centres of action of opposite signs over greenland and the barents kara central arctic area thermodynamic feedback between the ice and the atmosphere appear also to be very important for the persistence of the oscillation the dynamical response of the atmosphere to sea ice and temperature anomalies at surface plays a smaller role

local wintertime tropospheric response to oceanic heat anomalies in the nordic seas area abstracta regression analysis between observed summertime atlantic water temperature anomalies at the entrance to the barents sea and atmospheric fields in the following winter from the ncep ncar reanalysis in the period 1982 2006 is carried out it shows that the ocean plays a key role in shaping wintertime tropospheric variability in the nordic seas greenland iceland norwegian and barents seas region the oceanically driven atmospheric circulation anomaly around the nordic seas marginal ice zone is intensified at the surface as a result of a thermally direct baroclinic adjustment frictional convergence in the cyclonic disturbance corresponding to warm ocean temperature anomalies forces ascending motion at the top of the planetary boundary layer and a compensating divergence aloft which over the barents sea is extreme at the tropopause a quasi meridional overturning circulation anomaly is closed by descending motion south of the cyclonic disturbance in addition an equivalent barotropic flow anomal

the effects of north atlantic sst and sea ice anomalies on the winter circulation in ccm3 part i main features and storm track characteristics of the response observed multidecadal trends in extratropical atmospheric flow such as the positive trend in the north atlantic oscillation nao index may be attributable to a number of causes this study addresses the question of whether the atmospheric trends may be caused by observed trends in oceanic boundary forcing experiments were carried out using the ncar atmospheric general circulation model with specified sea surface temperature sst and sea ice anomalies confined to the north atlantic sector the spatial pattern of the anomalous forcing was chosen to be realistic in that it corresponds to the recent 40 yr trend in sst and sea ice but the anomaly amplitude was exaggerated in order to make the response statistically more robust the wintertime response to both types of forcing resembles the nao to first order even for an exaggerated amplitude the atmospheric response to the sst anomaly is quite weak compared to the observed positive trend in the nao but has the same sign indicative of a weak positive feedback the anomalies in sea ice extent are more efficient than sst anomalies at exciting an atmospheric response comparable in amplitude to the observed nao trend however this atmospheric response has the opposite sign to the observed trend indicative of a significant negative feedback associated with the sea ice forcing additional experiments using sst anomalies with opposite sign to the observed trend indicate that there are significant nonlinearities associated with the atmospheric response the transient eddy response to the observed sst trend is consistent with the positive nao response with the north atlantic storm track amplifying downstream and developing a more pronounced meridional tilt in contrast the storm track response to the observed sea ice trend corresponds to a weaker southward shifted more zonal storm track which is consistent with the negative nao response

two circulation regimes of the wind driven arctic ocean the major goal of this paper is to demonstrate the existence in the arctic ocean of two regimes of wind forced circulation we simulated the vertically averaged currents sea level heights and ice drift in the arctic ocean from 1946 to 1993 using a two dimensional wind forced barotropic model that includes frictional coupling between the ocean and ice the model has a spatial resolution of 55 5 km and is driven by winds river runoff and an imposed but realistic sea level slope between the pacific and the atlantic oceans there is a good agreement between velocities from observed buoy motions and velocities of modeled ice drift even though the model lacks ocean baroclinicity and ice thermodynamics the results indicate that wind driven motion in the central arctic alternates between anticyclonic and cyclonic circulation with each regime persisting for 5 7 years based upon our analysis of the modeled sea level and ice motion anticyclonic wind driven motion in the central arctic appeared during 1946 1952 1958 1963 1972 1979 and 1984 1988 and cyclonic motion appeared during 1953 1957 1964 1971 1980 1983 and 1989 1993 shifts from one regime to another are forced by changes in the location and intensity of the icelandic low and the siberian high the two regimes may help explain the significant basin scale changes in the arctic s temperature and salinity structure observed recently the great salinity anomaly and the variability of ice conditions in the arctic ocean

relationships between atmospheric internal variability and the responses to an extratropical sst anomaly abstract the january and february responses of a gcm to an imposed extratropical pacific sst anomaly are compared with the patterns of the model s internal variability relevant patterns of internal variability are diagnosed from ensembles of model control runs by regressing monthly mean geopotentials and temperatures against low level temperatures in the vicinity of the sst anomaly and by eof analysis these patterns are found to play a significant role in determining the local and the remote responses to the sst anomaly different responses to the sst anomaly in the gcm s january and february climates are largely explained by the differences in the regression patterns and in the leading eof the gcm response may be considered as comprising a direct linear response to low level heating that is local to the forcing and baroclinic and an eddy forced component that closely resembles patterns of the model s internal variability it is equivalent barotropic and extends over the entire hemisphere the results

autumn atmospheric response to the 2007 low arctic sea ice extent in coupled ocean atmosphere hindcasts the autumn and early winter atmospheric response to the record low arctic sea ice extent at the end of summer 2007 is examined in ensemble hindcasts with prescribed sea ice extent made with the european centre for medium range weather forecasts state of the art coupled ocean atmosphere seasonal forecast model robust warm anomalies over the pacific and siberian sectors of the arctic as high as 10 c at the surface are found in october and november a regime change occurs by december characterized by weaker temperatures anomalies extending through the troposphere geopotential anomalies extend from the surface up to the stratosphere associated to deeper aleutian and icelandic lows while the upper level jet is weakened and shifted southward over the continents it is intensified over both oceanic sectors especially over the pacific ocean on the american and eurasian continents intensified surface highs are associated with anomalous advection of cold warm polar air on their eastern western sides bringing cooler temperatures along the pacific coast of asia and northeastern north america transient eddy activity is reduced over eurasia intensified over the entrance and exit regions of the pacific and atlantic storm tracks in broad qualitative agreement with the upper level wind anomalies potential predictability calculations indicate a strong influence of sea ice upon surface temperatures over the arctic in autumn but also along the pacific coast of asia in december when the observed sea ice extent from 2007 is prescribed throughout the autumn a higher correlation of surface temperatures with meteorological re analyses is found at high latitudes from october until mid november this further emphasises the relevance of sea ice for seasonal forecasting in the arctic region in the autumn

coherent noise in marine seismic data three mechanisms that might produce noise patterns on stacked sections are examined direct and trapped waves that propagate outward from the seismic source cable motion caused by the tugging action of the boat and tail buoy and scattered energy from irregularities in the water bottom and sub bottom different noise patterns can be observed on shot profiles and common midpoint cmp gathers these patterns can be diagnostic of the dominant mechanism in a set of data field data suggest that the dominant noise is from waves scattered within the shallow sub bottom this type of noise is enhanced by cmp stacking moreover it can be as strong as surface wave noise on stacked land seismic data as well moveout filtering is best for suppressing the noise while preserving signal since the scattered noise does not exhibit a linear moveout pattern on cmp sorted gathers moveout filtering must be applied either to traces within shot records and common receiver gathers or to stacked traces our data example demonstrates that although it is more costly moveout filtering of the unstacked data is particularly effective because it conditions the data for the critical data dependent processing steps of predictive deconvolution and velocity analysis modified journal abstract

on the relationship between winter sea ice and summer atmospheric circulation over eurasia abstractusing ncep ncar reanalysis and japanese 25 yr reanalysis jra 25 data this paper investigates the association between winter sea ice concentration sic in baffin bay southward to the eastern coast of newfoundland and the ensuing summer atmospheric circulation over the mid to high latitudes of eurasia it is found that winter sic anomalies are significantly correlated with the ensuing summer 500 hpa height anomalies that dynamically correspond to the eurasian pattern of 850 hpa wind variability and significantly influence summer rainfall variability over northern eurasia spring atmospheric circulation anomalies south of newfoundland associated with persistent winter spring sic and a horseshoe like pattern of sea surface temperature sst anomalies in the north atlantic act as a bridge linking winter sic and the ensuing summer atmospheric circulation anomalies over northern eurasia indeed this study only reveals the association based on observations and simple simulation experiments with s

decadal climate oscillations in the arctic a new feedback loop for atmosphere ice ocean interactions a combined complex empirical orthogonal function analysis of 40 years of annual sea ice concentration sic and winter sea level pressure slp data reveals the existence of an approximately 10 year climate cycle in the arctic and subarctic the cycle is characterized by a clockwise propagating signal in the sic anomalies and a standing oscillation in the slp anomalies the latter being linked to a fluctuation between the two phases of the north atlantic oscillation to describe the formation and evolution of the sic and slp anomalies associated with the cycle a simple feedback loop is proposed

variability of north pacific sea ice and east asia north pacific winter climate abstract sea ice variability in the north pacific and its associations with the east asia north pacific winter climate were investigated using observational data two dominant modes of sea ice variability in the north pacific were identified the first mode features a dipole pattern between the sea of okhotsk and the bering sea the second mode is characterized by more uniform ice changes throughout the north pacific using the principal components of the two dominant modes as the indices pc1 and pc2 analyses show that the positive phases of pc1 feature a local warming cooling in the sea of okhotsk the bering sea which is associated with the formation of the anomalous anticyclone extending from the northern pacific to siberia accompanied by a weakening of the east asian jet stream and trough the associated anomalous southeasterlies easterlies reduce the climatological northwesterlies westerlies leading to warm and wet conditions in northeast china and central siberia the positive phases of pc2

observed interaction between pacific sea ice and the western pacific pattern on intraseasonal time scales the relationship between north pacific sea ice and the western pacific wp pattern is examined using wintertime observational data between 1978 and 2008 weekly averaged data are chosen to capture the characteristically short time scale of the wp a clear relationship is found between the wp and sea ice concentrations in the bering sea where the positive polarity of the wp is accompanied by increasing sea ice concentrations and the negative wp by decreasing sea ice concentrations sea ice concentrations in the sea of okhotsk however are shown to be largely insensitive to the strength of the wp feedback of bering sea sea ice concentrations onto the wp is tested by fitting weekly averaged observations to a vector autoregressive var model results from the var model indicate that feedback of bering sea sea ice onto the wp plays a significant role in the dynamics of the wp and that this feedback is positive that is wp induced changes in bering sea sea ice concentrations help sustain existing wp conditions thereby lengthening the time scale of variability of the wp

imaging low velocity anomalies with the aid of seismic tomography abstract theoretical considerations snell s law suggest that low velocity fanomalies are undersampled and therefore should be poorly resolved by inversion schemes based on ray tracing methods a synthetic study considering a 40 20 m low velocity anomaly 300 m s placed at the center of a 400 50 m block with gradient background velocity model from 3000 m s at the surface to 4000 m s at the base indicates that the low ray density in ray tracing coverage diagrams of tomographic inversion studies can be used as evidence for the existence of low velocity anomalies combined normal incidence seismic reflection images and the velocity models obtained by tomographic inversions of first arrival travel times form an efficient scheme to resolve low velocity anomalies such as fracture zones furthermore the velocity models derived from tomographic inversions are used in a wave equation datuming algorithm to account for statics caused by a strongly laterally variable shallow surface weathering layer and provide seismic reflection images of fracture zones low velocity anomaly within a granitic pluton

intra seasonal relationship between the northern hemisphere sea ice variability and the north atlantic oscillation 1 an intra seasonal relationship including a possible feedback is investigated between the north atlantic oscillation nao and a hemispheric scale seesaw like pattern dominant in sea ice variability over the wintertime northern hemisphere with one polarity in the bering and labrador seas and the other in the okhotsk and greenland barents seas statistical analysis using observational data suggests that a particular phase of nao and anomalous atmospheric circulation in the pacific during early winter contribute toward the development of the midwinter hemispheric sea ice seesaw in contrast the ice seesaw tends to damp the preexisting nao signal during late winter indicating a reversal of the phase relation between them this nao damping may be triggered by the pacific sea ice anomalies results from numerical experiments generally support this notion and further suggests a stationary rossby wave train emanated from the north pacific as a dynamical mechanism for damping the nao signal

the use of seismic shear waves and compressional waves for lithological problems of shallow sediments from a great variety of in situ shear wave experiments i e reflection refraction and borehole surveys in the shallow sediments of the north german plains several specific properties have been derived shear waves s differ from compressional waves p in that correlations have been established between v s and the confining pressure and between reduced v s values and several lithological parameters like the grain size of sandy material more lithological and hydrological information is obtained by using s and p wave surveys along the same profile the best information on a sedimentological structure is obtained by the simultaneous observation of v s v p q s and q p

on the relationship between atmospheric circulation and the fluctuations in the sea ice extents of the bering and okhotsk seas monthly and 3 day averaged nimbus 5 electrically scanning microwave radiometer sea ice data have been analyzed to document the fluctuations of the bering sea and sea of okhotsk ice covers for the four winters 1972 1973 through 1975 1976 on the short term seasonal and interannual time scales and to define those periods for which there is an out of phase relationship between the fluctuations of the two sea ice covers the sea ice fluctuations are shown to be related to changes in the position and intensity of quasi stationary high and low pressure systems associated with large scale standing wave patterns in the atmosphere through a comparison of the areal changes in ice cover with changes in the amplitude and phase of zonal harmonics 1 2 and 3 of the sea level pressure field on the seasonal time scale the sea level pressure for december the month of most rapid seasonal sea ice growth for both the bering and okhotsk seas is dominated by harmonic 2 which explains almost 60 of the total sea level pressure variance on average over the four winters the phase of harmonic 2 which is associated with the position of the aleutian low shifts from 156 e in 1972 1973 to 190 e in 1975 1976 thus providing a connection between the increasingly heavy bering sea ice cover over these four winters and the general circulation of the atmosphere on the short term episodes of midwinter bering sea ice retreat are generally preceded by or coincident with the breakdown of harmonic 1 and the intensification of harmonics 2 and 3 these episodes are also related to the coincidence of the phases of harmonics 2 and 3 with a mean position of 165 e this result is in excellent agreement with a study of the north pacific oscillation showing that the two modes of the oscillation are associated with the longitudinal position of the aleutian low it is suggested here that these two modes result from changes in the amplitudes and phases of atmospheric long waves 1 2 and 3 evidence is also presented indicating that the interaction of standing and transient components of wave 1 may play an important role in these fluctuations finally these results establish an observational connection relating climate dynamics to changes in ice covers in seasonal sea ice zones

arctic contribution to upper ocean variability in the north atlantic abstract because much of the deep water of the world s oceans forms in the high latitude north atlantic the potential climatic leverage of salinity and temperature anomalies in this region is large substantial variations of sea ice have accompanied north atlantic salinity and temperature anomalies especially the extreme and long lived great salinity anomaly of the late 1960s and early 1970s atmospheric pressure data are used hem to show that the local forcing of high latitude north atlantic ocean fluctuations is augmented by antecedent atmospheric circulation anomalies over the central arctic these circulation anomalies are consistent with enhanced wind forcing of thicker older ice into the transpolar drift stream and an enhanced export of sea ice fresh water from the arctic into the greenland sea prior to major episodes of ice severity in the greenland and iceland seas an index of the pressure difference between southern greenland and the arctic asian coast reached its highest value of the twe

analysis of the warmest arctic winter 2015 2016 december through february 2015 2016 defines the warmest winter season over the arctic in the observational record positive 2 m temperature anomalies were focused over regions of reduced sea ice cover in the kara and barents seas and southwestern alaska a third region is found over the ice covered central arctic ocean the period is marked by a strong synoptic pattern which produced melting temperatures in close proximity to the north pole in late december and anomalous high pressure near the taymyr peninsula atmospheric teleconnections from the atlantic contributed to warming over eurasian high latitude land surfaces and el nino related teleconnections explain warming over southwestern alaska and british columbia while warm anomalies over the central arctic are associated with physical processes including the presence of enhanced atmospheric water vapor and an increased downwelling longwave radiative flux preconditioning of sea ice conditions by warm temperatures affected the ensuing spring extent

empirical relationships between summertime oceanic heat anomalies in the nordic seas and large scale atmospheric circulation in the following winter a lagged regression analysis between an index of observed summertime atlantic water temperature awt variability at the entrance to the barents sea in the period 1982 2005 and year round atmospheric ncep ncar reanalysis data is used to show that subsurface oceanic heat anomalies in high latitudes are significant precursors of wintertime atmospheric variability in middle latitudes in particular positive awt anomalies precede predominantly westerly wind anomalies in high latitudes and easterly wind anomalies in middle latitudes the mid latitude wind anomalies while being generally equivalent barotropic in the upper troposphere have a strong low level baroclinic contribution over eurasia the near surface easterly wind anomalies in this area are locally deflected southward maintaining cold spots near orography the summertime oceanic anomalies explain about 40 of the variance in the surface air temperature averaged over eurasia from 35 to 45 n and about 50 of the variance in surface winds over the far east asia in the following winter we suggest that the remote connections arise from reorganization of the mid latitude storm tracks the awt anomalies explain about 60 of the variance in the upper tropospheric storm track activity averaged over the pacific and eurasia from 35 to 55 n and in the lower tropospheric poleward synoptic eddy heat flux over western eurasia finally we show that the awt associated wintertime atmospheric anomalies appear in quadrature with the concurrent anomalies associated with the north atlantic oscillation these findings suggest that oceanic heat anomalies in high latitudes may be a useful predictor of atmospheric variability

the effects of north atlantic sst and sea ice anomalies on the winter circulation in ccm3 part ii direct and indirect components of the response the wintertime atmospheric circulation responses to observed patterns of north atlantic sea surface temperature and sea ice cover trends in recent decades are studied by means of experiments with an atmospheric general circulation model here the relationship between the forced responses and the dominant pattern of internally generated atmospheric variability is focused on the total response is partioned into a portion that projects onto the leading mode of internal variability the indirect response and a portion that is the residual from that projection the direct response this empirical decomposition yields physically meaningful patterns whose distinctive horizontal and vertical structures imply different governing mechanisms the indirect response which dominates the total geopotential height response is hemispheric in scale with resemblance to the north atlantic oscillation or northern hemisphere annular mode and equivalent barotropic in the vertical from the surface to the tropopause in contrast the direct response is localized to the vicinity of the surface thermal anomaly sst or sea ice and exhibits a baroclinic structure in the vertical with a surface trough and upper level ridge in the case of a positive heating anomaly consistent with theoretical models of the linear baroclinic response to extratropical thermal forcing both components of the response scale linearly with respect to the amplitude of the forcing but nonlinearly with respect to the polarity of the forcing the deeper vertical penetration of anomalous heating compared to cooling is suggested to play a role in the nonlinearity of the response to sst forcing

sea ice anomalies observed in the greenland and labrador seas during 1901 1984 and their relation to an interdecadal arctic climate cycle two independent ice data sets from the greenland and labrador seas have been analyzed for the purpose of characterizing interannual and decadal time scale sea ice extent anomalies during this century sea ice concentration data for the 1953 1984 period revealed the presence of a large positive anomaly in the greenland sea during the 1960s which coincided with the great salinity anomaly an upper ocean low salinity water mass that was observed to travel cyclonically around the northern north atlantic during 1968 1982 this ice anomaly as well as several smaller ones propagated into the labrador sea and then across to the labrador and east newfoundland coast over a period of 3 to 5 years a complex empirical orthogonal function analysis of the same data also confirmed this propagation phenomenon an inverse relation between sea ice and salinity anomalies in the greenland labrador sea region was also generally found an analysis of spring and summer ice limit data obtained from danish meteorological institute charts for the period 1901 1956 indicated the presence of heavy ice conditions i e positive ice anomalies in the greenland sea during 1902 1920 and in the late 1940s and generally negative ice anomalies during the 1920s and 1930s only limited evidence of the propagation of greenland sea ice anomalies into the labrador sea was observed however probably because the data were from the ice melt seasons on the other hand several large ice anomalies in the greenland sea occurred 2 3 years after large runoffs in the early 1930s and the late 1940s from northern canada into the western arctic ocean similarly a large runoff into the arctic during 1964 1966 preceded the large greenland sea ice anomaly of the 1960s these facts together with recent evidence of climatic jumps in the northern hemisphere tropospheric circulation suggest the existence of an interdecadal self sustained climate cycle in the arctic in the greenland sea this cycle is characterized by a state of large sea ice extent overlying an upper layer of cool relatively fresh water that does not convectively overturn which alternates every 10 15 years with a state of small sea ice extent and relatively warm saline surface water that frequently overturns

variability of the observed midlatitude storm tracks in relation to low frequency changes in the circulation pattern abstract the principal modes of month to month variability of the wintertime storm tracks over the north pacific and north atlantic are identified by empirical orthogonal function analysis of the root mean square statistics of bandpass 2 5 6 day filtered geopotential height data for 19 yr one of the two leading modes depicts fluctuations in the level of synoptic scale activity without any noticeable spatial displacement of the storm track axes whereas the other mode is associated with meridional shifts of the storm tracks from their time averaged positions higher order modes are indicative of diversion or truncation of cyclone tracks in particular geographical regions it is demonstrated that the leading storm track modes are linked to some of the best known monthly averaged teleconnection patterns the dipolar western pacific and western atlantic patterns for the monthly mean flow are seen to be accompanied by marked changes in the intensity of the storm tracks over the western oceans whereas the m

introduction seismic wave scattering in three dimensionally heterogeneous earth the classical earth model of spherical symmetry or layered structure is undergoing a revolution the earth has been revealed to be laterally heterogeneous everywhere from the crust mantle to the core with scale from the grain size of rocks to the lowest orders of global spherical harmonics figure 1 shows the strength and scale length of heterogeneities in the crust and mantle of the earth in terms of v the perturbation index of seismic p or s wave speed defined as the r m s fractional variations of wave speed over the measured region the scale length of heterogeneities revealed by seismic waves not including the laboratory measurements of rock samples spans 8 orders of magnitude these heterogeneities with different scales have different effects to seismic waves the velocity and density heterogeneities can cause the change in waveform phase or travel time and amplitude fluctuation as well as apparent attenuation of the direct arrivals they can also generate coda waves such as the p coda s coda and lg coda caused by the lithospheric heterogeneities and precursory waves such as the scattered pkp waves as the precursors to pkikp caused by the heterogeneities near the core mantle boundary the near source or near receiver structures can modify the seismic waveforms by resonance and other effect rough topography or rough interface can cause the coupling between body wave and surface wave aligned cracks in the crust can produce the effective anisotrophy a great complexity arises when heterogeneities have interaction with anisotrophy and nonlinearity

mechanisms determining the atmospheric response to midlatitude sst anomalies abstract previous gcm experiments demonstrated that a model atmosphere produces two different responses to a midlatitude warm sst anomaly over the pacific under perpetual january and february conditions to elucidate the mechanisms responsible for the different gcm responses and their dependence on the background flow experiments with two idealized models are conducted experiments with a linear baroclinic model reveal that the gcm responses at equilibrium are primarily maintained by the anomalous eddy forcing the anomalous flow induced directly by an idealized initial heat source exhibits little sensitivity to the background flow eddy feedbacks on the heating induced anomalous flow are examined using a linear storm track model the anomalous eddy forcing produced by the storm track model is sensitive to the basic state the eddy forcing in january acts to shift the heating induced upper level ridge toward the northeast of the gulf of alaska while in february it acts to reinforce the ridge this sugge

interannual variations of the dominant modes of east asian winter monsoon and possible links to arctic sea ice two dominant modes of the winter temperature over east asia a northern mode and a southern mode and their links with arctic climate conditions are analyzed the relationships of the two modes with arctic sea ice are different the northern mode is closely linked to variations in sea ice of the arctic barents laptev sea in previous autumn and most of the arctic in concurrent winter the southern mode seems independent from the arctic sea ice variations but is associated with sea surface temperature sst anomalies in the equatorial central eastern pacific results suggest an effect of arctic sea ice variation on the northern mode and an influence of tropical sst anomalies on the southern mode reduced sea ice over the arctic increases 1000 500 hpa thickness over the high latitudes of eurasian continent which reduces the meridional thickness gradient between the middle and high latitudes and thus weakens the extratropical upper level zonal wind the weakened zonal wind provides a favorable dynamic condition for the development of a high latitude ridge around the ural mountain reduced arctic sea ice also tends to enhance the siberian high through both thermodynamic and dynamic processes the above atmospheric circulation patterns provide a favorable condition for the intrusion of cold air to northern east asia

sea ice response to wind forcing from amip models abstract the arctic surface circulation simulated by atmospheric general circulation models is assessed in the context of driving sea ice motion a sea ice model is forced by geostrophic winds from eight models participating in the first atmospheric model intercomparison project amip1 and the results are compared to simulations with the sea ice model forced by observed winds the mean sea level pressure in the amip models is generally too high over the arctic ocean except in the beaufort and chukchi seas where it is too low this pattern creates anomalous winds that tend to transport too much ice away from the coast of greenland and the canadian archipalego and into the east siberian sea producing a pattern of ice thickness in the arctic that is rotated by roughly 180 relative to what is expected based on observations amip winds also drive too little ice transport through fram strait and too much transport east of svalbard by way of the barents sea these errors in ice thickness and transport inf

cmip5 model simulations of warm arctic cold eurasia pattern in winter surface air temperature anomalies the second empirical orthogonal function mode eof2 of winter surface air temperature sat over 0 180 e 40 90 n during 1979 2005 is defined as warm arctic cold eurasia wace pattern the present study evaluates the performance of 25 coupled model inter comparison project phase 5 cmip5 models in simulating the wace pattern based on historical runs there exist large inter model spreads in the simulation of the wace pattern analyses show that the ability of a cmip5 model in capturing the wace pattern is connected with the model s performance in representing the observed atmospheric circulation anomalies related to the winter sea ice concentration sic variation over barents kara seas sea ice loss over barents kara seas can induce significant positive geopotential height anomalies over arctic region and negative geopotential height anomalies around the baikal lake resulting in warm anomalies over barents kara seas and cold anomalies over eurasia further analysis shows that cmip5 model s performance in representing the sat anomalies related to the wace pattern is partly due to simulation of the amplitude of winter sic variability over barents kara seas larger standard deviations of winter sic over barents kara seas can instigate stationary wave train more easily which further induces the sat anomalies

winter weather patterns over northern eurasia and arctic sea ice loss abstractusing ncep ncar reanalysis and japanese 25 yr reanalysis jra 25 winter daily 1 december 28 february data for the period 1979 2012 this paper reveals the leading pattern of winter daily 850 hpa wind variability over northern eurasia from a dynamic perspective the results show that the leading pattern accounts for 18 of the total anomalous kinetic energy and consists of two subpatterns the dipole and the tripole wind patterns the dipole wind pattern does not exhibit any apparent trend the tripole wind pattern however has displayed significant trends since the late 1980s the negative phase of the tripole wind pattern corresponds to an anomalous anticyclone over northern eurasia during winter as well as two anomalous cyclones occurring over southern europe and in the mid to high latitudes of east asia these anomalous cyclones in turn lead to enhanced winter precipitation in these two regions as well as negative surface temperature anomalies over the mid to high latitudes of asia the

interdecadal variability of the warm arctic and cold eurasia pattern and its north atlantic origin abstractthis study investigates the origin of the interdecadal variability in the warm arctic and cold eurasia wace pattern which is defined as the second empirical orthogonal function of surface air temperature sat variability over eurasian continent in northern winter by analyzing the twentieth century reanalysis dataset while previous studies highlight recent enhancement of the wace pattern ascribing it to anthropogenic warming we found that the wace pattern has experienced a seemingly periodic interdecadal variation over the twentieth century this long term variation in the eurasian sat is attributable to the altered coupling between the siberian high sh and intraseasonal rossby wave emanating from the north atlantic as the local wave branch interacts with the sh and consequentially enhances the continental temperature perturbation it is further identified that these atmospheric circulation changes in eurasia are largely controlled by the decadal amplitude modulation of the climatological

the melting arctic and midlatitude weather patterns are they connected abstractthe potential of recent arctic changes to influence hemispheric weather is a complex and controversial topic with considerable uncertainty as time series of potential linkages are short 10 yr and understanding involves the relative contribution of direct forcing by arctic changes on a chaotic climatic system a way forward is through further investigation of atmospheric dynamic mechanisms during several exceptionally warm arctic winters since 2007 sea ice loss in the barents and kara seas initiated eastward propagating wave trains of high and low pressure anomalous high pressure east of the ural mountains advected arctic air over central and eastern asia resulting in persistent cold spells blocking near greenland related to low level temperature anomalies led to northerly flow into eastern north america inducing persistent cold periods potential arctic connections in europe are less clear variability in the north pacific can reinforce downstream arctic changes and arctic amplification

unstable patterns in partly vegetated channels unstable patterns are identified in the results of numerical simulations of two cases of partly vegetated open channels at the free unobstructed flow side of the shear layer that separates the unobstructed channel from the vegetated zones a time dependent pattern was identified in a rectangular open channel compound with a vegetated bank and cellular structure was found in a wide ractangular open channel spanning over a vegetated thin layer at the channel bed distinction between three modes of algebraic stress models a prompt algebraic stress model a delayed algebraic stress model and an algebraic stress model with longitudinal vorticity sources relaxation and the modeling of time dependent turbulence is made and discussed in the present context

influence of okhotsk sea ice extent on atmospheric circulation an atmospheric general circulation model was used to investigate the influence of okhotsk sea ice on large scale atmospheric circulation significant differences in the model responses between heavy and light ice cover are evident not only around the sea of okhotsk but also downstream towards north america in the form of a stationary wavetrain in the troposphere because the wave activity flux associated with the wavetrain emanates downstream from the sea of okhotsk this remote response is regarded as a stationary rossby wave excited thermally through an anomalous surface heat flux over the sea of okhotsk the wavetrain is thermally reinforced downstream by the anomalous heat flux associated with wind anomalies over the ocean surface which are induced by the wavetrain itself

wavefield separation using a volume distribution of three component recordings by making multiple three component 3c measurements around a volume so that the rate of change of the wavefield in all directions can be estimated it is possible to calculate the divergence and the curl of the wavefield which in turns corresponds to p and s waves the volume may be of arbitrary shape but the equations for wavefield separation are simplified if the volume has a known shape such as that of a tetrahedron the dimensions of the volume should be smaller than approximately one fifth of the minimum wavelength of the recorded wavefield a field test was carried out in oman in april 1998 with a lack of distinct p and s waves in the data the technique was instead evaluated on the airwave induced ground motion the airwave arrival was found to consist mainly of vertical motion that decays with depth the wavefield separation technique was successfully tested on this arrival

decadal variations in labrador sea ice cover and north atlantic sea surface temperatures 1 the spatial and temporal evolution of winter sea ice anomalies in the labrador sea and associated sea surface temperature sst variations in the north atlantic are documented for three periods of above normal ice cover 1972 1974 1983 1985 and 1990 1992 these events are notable for their winter to winter persistence despite the fact that the ice margin retreats to northern baffin bay each summer and for their spatial evolution progressing from the northern labrador sea to the southern tip of newfoundland over a 3 year period above normal sea ice is consistently accompanied by below normal ssts in the subpolar atlantic the latter persist 1 3 years after the decay of the ice anomalies and in some cases exhibit a tendency for eastward movement across the gyre spring summer freshwater anomalies at 100 m depth in the west greenland current are found to precede by 8 months the initial occurrence of above normal ice cover in the northern labrador sea the role of atmospheric forcing in the joint evolution of anomalous sea ice and sst is assessed by means of an ice ocean mixed layer model forced with observed air temperature and wind fields the model results indicate that thermodynamic atmospheric forcing accounts for much of the winter to winter persistence and spatial evolution of the ice and concurrent sst anomaly patterns however the subsequent persistence of sst anomalies in the subpolar region is not well simulated suggesting that oceanic processes omitted from the simple slab mixed layer formulation play a contributing role

on the association between spring arctic sea ice concentration and chinese summer rainfall 1 a statistical relationship between spring arctic sea ice concentration sic and chinese summer rainfall is identified using singular value decomposition svd results show that decreased increased spring sic in the arctic ocean and the greenland sea corresponds to increased decreased summer rainfall in northeast china and central china between the yangtze river and the yellow river 28 36 n and decreased increased rainfall in south china corresponding summer 500 hpa height anomalies show a eurasian wave train structure which originates in northern europe and extends southeastwards to northeast china and a south north dipole structure over east asia south to lake baikal such a spatial distribution of 500 hpa height anomalies and corresponding summer rainfall anomalies cannot be entirely attributed to the impact of east asian summer monsoon easm variability the spring arctic sic provides a complementary precursor for chinese summer rainfall variability the combined impacts of both spring arctic sic and eurasian snow cover on the eurasian wave train may explain their statistical linkage

architecture of fault zones determined from outcrop cores 3 d seismic tomography and geostatistical modeling example from the albala granitic pluton sw iberian variscan massif abstract the 3 d seismic tomographic data are used together with field core and well log structural information to determine the detailed 3 d architecture of fault zones in a granitic massif of volume 500 575 168 m at mina ratones area in the albala granitic pluton to facilitate the integration of the different data geostatistical simulation algorithms are applied to interpolate the relatively sparse structural hard control data conditioned to abundant but indirect 3 d soft seismic tomographic data to effectively integrate geologic and tomographic data 3 d migration of the velocity model from the time domain into the depth domain was essential the resulting 3 d model constitutes an image of the fault zone architecture within the granitic massif that honours hard and soft data and provides an evaluation of the spatial variability of structural heterogeneities based on the computation of 3 d experimental variograms of fracture index fault intensity data this probabilistic quantitative 3 d model of spatially heterogeneous fault zones is suitable for subsequent fluid flow simulations the modeled image of the 3 d fault distribution is consistent with the fault architecture in the mina ratones area which basically consists of two families of subvertical structures with nne ssw and ene wsw trends that displaces the surfaces of low angle faults north fault and follows their seismically detected staircase geometry these brittle structures cut two subvertical dykes 27 and 27 dykes with a nne ssw to n s trend the faults present high fi fi 12 adjacent bands of irregular geometry in detail that intersect in space delimiting rhombohedral blocks of relatively less fractured granite fi

sea ice and polar climate in the ncar csm the climate system model csm consists of atmosphere ocean land and sea ice components linked by a flux coupler which computes fluxes of energy and momentum between components the sea ice component consists of a thermodynamic formulation for ice snow and leads within the ice pack and ice dynamics using the cavitating fluid ice rheology which allows for the compressive strength of ice but ignores shear viscosity the results of a 300 yr climate simulation are presented with the focus on sea ice and the atmospheric forcing over sea ice in the polar regions the atmospheric model results are compared to analyses from the european centre for medium range weather forecasts and other observational sources the sea ice concentrations and velocities are compared to satellite observational data the atmospheric sea level pressure slp in csm exhibits a high in the central arctic displaced poleward from the observed beaufort high the southern hemisphere slp over sea ice is generally 5 mb lower than observed air temperatures over sea ice in both hemispheres exhibit cold biases of 2 4 k the precipitationminus evaporation fields in both hemispheres are greatly improved over those from earlier versions of the atmospheric gcm the simulated ice covered area is close to observations in the southern hemisphere but too large in the northern hemisphere the ice concentration fields show that the ice cover is too extensive in the north pacific and subarctic north atlantic oceans the interannual variability of the ice area is similar to observations in both hemispheres the ice thickness pattern in the antarctic is realistic but generally too thin away from the continent the maximum thickness in the arctic occurs against the bering strait not against the canadian archipelago as observed the ice velocities are stronger than observed in both hemispheres with a consistently greater turning angle to the left in the southern hemisphere they produce a northward ice transport in the southern hemisphere that is 3 4 times the satellite derived value sensitivity tests with the sea ice component show that both the pattern of wind forcing in csm and the air ice drag parameter used contribute to the biases in thickness drift speeds and transport plans for further development of the ice model to incorporate a viscousplastic ice rheology are presented in spite of the biases of the sea ice simulation the 300 yr climate simulation exhibits only a small degree of drift in the surface climate without the use of flux adjustment this suggests a robust stability in the simulated climate in the presence of significant variability

effects of the shallow subsurface on upper crustal seismic reflection images abstract seismic imaging of the upper crust is strongly affected by the interactions of the seismic wavefield with the shallow subsurface in order to better understand these effects we have evaluated the seismic responses of a suite of canonical models of the upper crystalline crust and the near surface region our modelling is restricted to two dimensions but otherwise includes the full seismic wavefield notably the effects of attenuation and topographic variations along the free surface we find that s wave scattering is important in the upper crust and contributes significantly to the vertical component of the seismic reflection response the backscattered wavefield undergoes mode conversions when it interacts with the free surface even moderate topographic variations or velocity variations in the near surface region enhance these mode conversions and cause additional scattering much of the earth s surface is covered by thin layers of unconsolidated material or weathered bedrock with high attenuation and high velocity contrasts at the layer boundaries scattered and mode converted seismic energy gets trapped in these layers and thus interacts repeatedly with the free surface and its topography in analogy to large scale seismic resonance effects of sedimentary valley fills the level and duration of source generated noise depends heavily on the degree of attenuation in the shallow layers low attenuation causes high noise levels and vice versa in contrast the level of source generated noise is less sensitive to near surface layer thicknesses and velocity contrasts

wave equation datuming for improving deep crustal seismic images abstract reflection quality in deep crustal seismic sections is often poor due to surface waves irregularities in the surface layer and variations in topography in an effort to remove the effects of the variable near surface layer and topography we have used wave equation datuming to downward continue shot gathers to the base of the surface layer and then redatumed upward to a flat surface using the basement velocity as the replacement velocity we discuss briefly the theory behind the method present a simple synthetic example of a datumed shot gather and conclude with an example of a datumed shot gather from the risc crustal seismic experiment in southeastern california

arctic sea ice reemergence the role of large scale oceanic and atmospheric variability abstractarctic sea ice reemergence is a phenomenon in which spring sea ice anomalies are positively correlated with fall anomalies despite a loss of correlation over the intervening summer months this work employs a novel data analysis algorithm for high dimensional multivariate datasets coupled nonlinear laplacian spectral analysis nlsa to investigate the regional and temporal aspects of this reemergence phenomenon coupled nlsa modes of variability of sea ice concentration sic sea surface temperature sst and sea level pressure slp are studied in the arctic sector of a comprehensive climate model and in observations it is found that low dimensional families of nlsa modes are able to efficiently reproduce the prominent lagged correlation features of the raw sea ice data in both the model and observations these families provide an sst sea ice reemergence mechanism in which melt season spring sea ice anomalies are imprinted as sst anomalies and stored over the summer months allowing for

p and sv velocity structure of the south portuguese zone fold and thrust belt sw iberia from traveltime tomography imaging the architecture of the shallow crust of the south portuguese zone fold and thrust belt is essential to extend surface mapped geological information to depth and to help in developing model

towards an improved seismic imaging technique for crustal structures the lithoprobe sudbury experiment under the canadian lithoprobe program conventional low 10 55 hz and high frequency 30 140 hz vibroseis reflection surveys were conducted across the sudbury structure the main objective of the study was to evaluate the performance of seismic exploration techniques in a complex mainly crystalline geological setting the sudbury experiment demonstrated that high input frequencies can be preserved through appropriate acquisition and processing procedures consequently the high frequency seismic data proved capable of imaging complex shallow crustal structures not seen by the conventional low frequency seismic survey in crystalline environments improved high frequency seismic exploration technology will provide a better link between seismic images and surface geology

wind feedback mediated by sea ice in the nordic seas air sea interactions play a critical role in the climate system this study investigates wind induced changes in the ocean surface temperature and sea ice cover feeding back onto the atmospheric circulation this interaction was modeled in the nordic seas using a partial coupling method to constrain the ocean with prescribed wind forcing in an otherwise fully coupled earth system model this enabled the evaluation of not only the direct oceanic but also the indirect atmospheric response to idealized forcing scenarios of perturbed winds over the nordic seas the results show that an anticyclonic wind anomaly forcing leads to significant surface cooling in the greenland sea mostly due to anomalous drift of sea ice during winter the cooling reduces the net surface heat flux to the atmosphere and increases sea level pressure the pressure gradients result in anomalous geostrophic southerly winds which locally are comparable both in direction and in velocity to the prescribed forcing anomalies suggesting a positive feedback

geological geophysical and geochemical structure of a fault zone developed in granitic rocks implications for fault zone modeling in 3 d the structure of a fault zone developed in granitic rocks can be established on the basis of the spatial variability of geological geophysical and geochemical parameters in the north fault of the mina ratones area sw iberian massif spain fault rocks along two studied traverses sr 2 and sr 3 boreholes exhibit systematic changes in mineralogy geochemistry fabrics and microstructures that are related to brittle deformation and alteration of granite to form cataclasite and subsequent gouge the spatial distribution and intensity of these changes suggest a north fault morphology that is consistent with the fault core damage zone model proposed by chester et al 1993 to describe a fault zone architecture north fault damage zone thickness can be defined by the development of mechanically related mesoscopic faults and joints that produce a fracture index fi 10 high fi values are spatially correlated with relative low seismic velocity zones vp 5 km s and vs 2 5 km s in the well logs more probably related to a high concentration of fractures and geochemical alteration produced by meteoric water granite interaction along fault surfaces this correlation is the base of a geostatistical model proposed in the final part of this study to image the fault zone architecture of a granitic massif

the great salinity anomaly in the northern north atlantic 1968 1982 the widespread freshening of the upper 500 800m layer of the northern north atlantic which this paper describes represents one of the most persistent and extreme variations in global ocean climate yet observed in this century though a range of explanations have been advanced to explain this event including in situ changes in the surface moisture flux this paper describes the great salinity anomaly as largely though not entirely an advective event traceable around the atlantic subpolar gyre for over 14 years from its origins north of iceland in the mid to late 1960s until its return to the greenland sea in 1981 1982 the overall propagation speed around this subpolar gyre is estimated at about 3cm s 1 of the total salt deficit associated with the anomaly as it passed south along the labrador coast in 1971 1973 about 72 109 tonnes a deficit equivalent to about two thirds of this figure 47 109 tonnes ultimately passed through the faroe shetland channel to the barents sea arctic ocean and greenland sea during the mid 1970s possible effects on deep water formation and on the representativeness of historical section data are discussed

upper crustal seismic velocity heterogeneity as derived from a variety of p wave sonic logs sonic log measurements provide detailed 1 d information on the distribution of elastic properties within the upper crystalline crust at scales from about one metre to several kilometres 10 p wave sonic logs from six upper crustal drill sites in europe and north america have been analysed for their second order statistics the penetrated lithological sequences comprise archean volcanic sequences proterozoic mafic layered intrusions and precambrian to phanerozoic gneisses and granites despite this variability in geological setting tectonic history and petrological composition there are notable similarities between the various data sets after removing a large scale deterministic component from the observed velocity depth function the residual velocity fluctuations of all data sets can be described by autocovariance functions corresponding to band limited self affine stochastic processes with quasi gaussian probability density functions depending on the maximum spatial wavelength present in the stochastic part of the data the deterministic trend can be approximated either by a low order polynomial best fit or by a moving average of the original sonic log data the choice of the trend has a significant impact on the correlation length and on the standard deviation of the residual stochastic component but does not affect the hurst number for trends defined by low order polynomial best fits correlation lengths were found to range from 60 to 160 m whereas for trends defined by a moving average the correlation lengths are dominated by the upper cut off wavenumber of the corresponding filter regardless of the trend removed the autocovariance functions of all data sets are characterised by low hurst numbers of around 0 1 0 2 or equivalently by power spectra decaying as 1 k a possible explanation of this statistical uniformity is that sonic log fluctuations are more sensitive to the physical state in particular to the distribution of cracks than to the petrological composition of the probed rocks

cyclone climatology of the bering sea and its relation to sea ice extent abstract a monthly storm track climatology is derived from monthly maps of cyclone tracks for the winter season october through march averaged over 23 years 1957 58 1979 80 for a 2 latitude 4 longitude grid bounded by 51 n 65 n 157 w and 171 e there is a decrease in the number of cyclones with latitude in all months and division into two storm tracks one propagating north northeast along the siberian peninsula and one entering the southern bering sea on a northeasterly course and either curving northward into the central bering sea or continuing parallel to the aleutian island chain monthly average ice extents are established for february and march 1958 80 along a line from norton sound southwest toward the ice edge perpendicular to the average maximum extent comparison of composite cyclone charts summed over the winter season and over the five heaviest and five lightest ice years shows a shift in cyclone centers toward the west in light ice years the correlation between maximum seasonal ice

seismic reflection imaging over the south portuguese zone fold and thrust belt sw iberia 1 we reprocessed an 35 km long part of the ibesreis seismic reflection profile which runs over the iberian pyrite belt section of the south portuguese zone sw iberia with the goal to image the upper crust 15 km depth the applied processing sequence enhanced numerous prominent reflections and diffraction patterns within the uppermost 5 s travel time relative to high amplitude source generated noise a complex subsurface characterized by conflicting dips and a survey following winding roads require a crooked line prestack migration scheme for coherent imaging to interpret sources of diffracted energy we additionally employed a diffraction imaging scheme which enhances diffractions at the expense of reflections the final seismic images show south vergent imbricate fold and thrust tectonics documenting the contractive deformation that the south portuguese zone experienced during the variscan orogeny based on surface geological information we correlate a low reflective unit with the shallow upper carboniferous flysch group a highly reflective unit ranging in depth from 2 to 4 km with the middle carboniferous volcano sedimentary complex group which hosts massive sulfide deposits and a moderately reflective unit with the upper devonian phyllite quartzite group below these units another low reflective facies is present which may represent older paleozoic metasediments in addition the seismic and diffraction images reveal bands of high reflectivity and distinct diffraction patterns that were interpreted as extensive layered mafic intrusions these proposed mafic bodies may be related to the same event that triggered a huge hydrothermal activity assumed in early carbonifereous times

seismic scattering in the upper crystalline crust based on evidence from sonic logs summary evidence from sonic logs indicates that velocity fluctuations in the upper crystalline crust are remarkably uniform this motivates a generic approach to classifying uppercrustal seismic heterogeneity and to studying implications for seismic wave propagation the resulting canonical model of upper crustal seismic structure is characterized by a spatially isotropic von karman autocovariance function with a z 100 m 0 15 and cj 300 m s small angle scattering theory is used to predict the transition from weak to strong scattering as well as phase fluctuations and scattering attenuation compared with exponential random media v 0 50 the high fractal dimension i e small values of v of upper crustal heterogeneity causes smaller phase fluctuations and transition from weak to strong scattering at lower frequencies and shorter path lengths acoustic finite difference modelling shows that seismic reflections from deterministic features surrounded by heterogeneities are severely degraded when they fall into the strong scattering regime conversely traveltime fluctuations of transmitted waves are found to be relatively insensitive to the transition from weak to strong scattering upper crustal scattering q is predicted to lie between 600 and 1500 which is one to two orders of magnitude higher than q values inferred from seismic data this suggests that seismic attenuation in the upper crystalline crust is dominated by anelastic effects rather than by scattering

patterns of low frequency monthly sea level pressure variability 1899 1986 and associated wave cyclone frequencies abstract spatial patterns of low frequency sea level pressure slp variability are identified by performing rotated principal component analysis rpca on a long term 1899 1986 northern hemisphere gridded dataset the analysis is limited to the region 160 e eastward to 40 e due to missing data early in the century the objective is to identify a comprehensive set of highly recurrent slp teleconnection patterns to examine some aspects of their seasonality and to identify the associated mean winter pressure fields and cyclone frequencies occurring at times of opposite eigenvector polarity the results are further described in the context of the southern oscillation and known midtropospheric teleconnection patterns four low frequency variability patterns are identified over the atlantic european sector including i the north atlantic 0scillation nao and spatial patterns with slp variability centers over ii the eastern atlantic eatl iii southern europe and the northern mediterranean basin s

the atmospheric response to realistic arctic sea ice anomalies in an agcm during winter abstract the influence of realistic arctic sea ice anomalies on the atmosphere during winter is investigated with version 3 6 of the community climate model ccm3 6 model experiments are performed for the winters with the most 1982 83 and least 1995 96 arctic ice coverage during 1979 99 when ice concentration estimates were available from satellites the experiments consist of 50 member ensembles using large ensembles proved critical to distinguish the signal from noise the local response to ice anomalies over the subpolar seas of both the atlantic and pacific is robust and generally shallow with large upward surface heat fluxes 100 w m 2 near surface warming enhanced precipitation and below normal sea level pressure where sea ice receded and the reverse where the ice expanded the large scale response to reduced enhanced ice extent to the east west of greenland during 1982 83 resembles the negative phase of the arctic oscillation north atlantic oscillation ao nao with a ridge over t

shallow 3d seismic reflection imaging of fracture zones in crystalline rock a limited 3d seismic reflection data set was used to map fracture zones in crystalline rock for a nuclear waste disposal site study seismic reflection data simultaneously recorded along two roughly perpendicular profiles 1850 and 1060 m long and with a 400 x 400 m receiver array centered at the intersection of the lines sampled a 680 x 960 m 2 area in three dimensions high levels of source generated noise required a processing sequence involving surface consistent deconvolution which effectively increased the strength of reflected signals and a linear tau p filtering scheme to suppress any remaining direct sv wave energy a flexible binning scheme significantly balanced and increased the cmp fold but the offset and azimuth distributions remain irregular a wide azimuth range and offsets 800 m are only found at the edges of the site three dimensional dip moveout and 3d poststack migration were necessary to image events with conflicting dips up to about 40 degrees despite the irregular acquisition geometry and the high level of source generated noise we obtained images rich in structural detail seven continuous to semicontinuous reflection events were traced through the final data volume to a maximum depth of around 750 m previous 2d seismic reflection studies and borehole data indicate that fracture zones are the most likely cause of the reflections

climatic effects of reduced arctic sea ice limits in the giss ii general circulation model in this paper we present results of an atmospheric general circulation model gcm experiment in which arctic sea ice limits were substantially reduced in all months march sea ice limits were set equivalent to modern september limits and all sea ice was removed in september sea ice coverage for other months varied between these two extremes this climate sensitivity experiment makes predictions about mean northern hemisphere atmospheric conditions including temperature pressure wind patterns and precipitation consistent with these boundary constraints the major effects of reduced sea ice limits are observed in winter they include large regional warming of the circum arctic region northward migration of the icelandic low pressure system and strengthening of the azores high changes in net heating over the north atlantic ocean suggest that increases in sea surface temperatures and salinities in this region would also accompany reductions in arctic sea ice limits in the wind field a weakening of the polar easterlies and an intensification of cyclonic circulation over the norwegian greenland sea suggest that surface water exchange between the atlantic and arctic would increase when sea ice limits are reduced however zonally averaged changes in strength of the westerlies or upper level jet stream are minimal the late pliocene cooling of the north atlantic ocean and north american arctic margin may have been linked in part to the development of perennial sea ice cover

on the feedback of the winter nao driven sea ice anomalies satellite derived sea ice concentration sic and re analysed atmospheric data are used to analyse the potential feedback of the north atlantic oscillation nao driven sea ice anomalies in winter onto the atmosphere during 1979 2013 a maximum covariance analysis shows that this feedback can be detected with monthly data when sic leads the covariability between atlantic sic and the euro atlantic atmospheric circulation in february is statistically significant but shows intra seasonal differences the december sic influence is dominated by anomalies east of greenland with maximum amplitude in the greenland sea gs while the january sic influence is dominated by anomalies west of greenland in the davis strait labrador sea dl region the lagged atmospheric anomalies are likewise different a reduction of sic over gs in december is followed in february by a negative nao like pattern near the surface and a hemispheric signature in the upper troposphere thus acting as a negative feedback on the other hand a reduction of sic over dl in january is followed by an atmospheric anomaly over the north atlantic that projects on the positive phase of the east atlantic pattern the dynamics associated with these atmospheric anomalies is described indicating that transient eddy activity is likely at work in settling the large scale patterns the role of concomitant north atlantic sea surface temperature anomalies is discussed

evaluation of topographic effects on p and s waves of explosions at the northern novaya zemlya test site using 3 d numerical simulations using a 3 d finite difference simulation we calculated the effects of surface topography on the amplitudes and waveforms of seismic waves generated by a hypothetical nuclear explosion at the northern novaya zemlya test site matochkin shar the simulation shows substantial azimuthal variations in the amplitude of the downgoing p waveform at shallow depths beneath the source caused by variations in the amplitude of pp however these azimuthal amplitude variations diminish as the wavefront propagates deeper in the crust based on these results we estimate that the topographic scarp considered here produces a maximum azimuthal variation of 0 05 magnitude units for mb determined from teleseismic p waves the sloping topography causes substantial sh motion for azimuths along the strike of the scarp

effects of el nino southern oscillation and north pacific weather patterns on interannual variability in the subarctic bering sea extraordinary interannual variability in ice cover air and sea surface temperatures sst and surface winds in the eastern bering sea have been observed over recent years to investigate the causes of this interannual variability long term 20 30 years time series of air ocean and ice parameters from the bering sea were cross correlated with the southern oscillation index soi an index of el nino southern oscillation enso events in the tropical southern hemisphere as well as with an index of pacific north american pna events in the north pacific five to thirty percent of the interannual variability linear regression with various smoothing in the bering sea data sets with the exception of surface winds is explained by the soi when the bering sea data lags the soi for comparison 29 52 of the variability in the sst off south america can be explained by the soi the signs of the correlations all suggest that warming in the bering sea follows negative anomalies in the soi that is enso events positive anomalies in the soi which tend to precede el nino events were found to precede cooling in the bering sea significant correlation persists for 18 20 months higher order polynomial regressions between the soi and bering sea data can explain up to 40 of the bering sea variability the mechanism for the connection between enso events and bering sea interannual variability appears to be of atmospheric nature and is associated with the winter position and intensity of the aleutian low the aleutian low is intensified and eastward of normal in association with el nino i e warm events but is weaker and westward of normal during cool events it is the regional winds associated with the variable position of the aleutian low that cause the regional warming and cooling events this seesaw in the aleutian low is also used to explain the out of phase ice conditions between the bering sea and the sea of okhotsk pna events are also associated with an intensified aleutian low as well as 700 mbar ridging over northwestern north america causing southerly flow over alaska however while correlation between enso events and pna was significant the correlation between the bering sea and pna was marginal except for surface winds here surface winds from the north were significantly correlated with the pna this apparent inconsistency as well as the lack of correlation of surface winds with the soi is explained by the lack of preferred site of the aleutian low during enso events this lack of preferred site helps explain why the major el nino event of 1982 1983 had little apparent effect on the bering sea

modelling and imaging the moho transition the case of the southern urals summary synthetic seismic modelling is used to test different possible structures and forming processes of the lower crust and moho one and two dimensional synthetic seismic modelling of the moho reflection is carried out to constrain the internal structure of a crust mantle transition a reflectivity algorithm was used to calculate the synthetic seismograms for models of the crust mantle transition consisting of gradient zones and layered sequences the synthetic seismograms for models consisting of laterally variable velocity structure were calculated by an explicit finite difference wave equation algorithm the laterally heterogeneous transition models can be achieved by assuming a moho with different degrees of variable topography or laterally discontinuous layering the effects of a low velocity surface cover on the seismic signature of deep signals is also analysed the seismic modelling coupled with stacked images of wide angle seismic reflection data constrain the case history of the moho transition beneath the southern urals a smooth gradational crust mantle transition gradient velocity depth function does not predict the seismic features observed in the shot records the coda of the pmp and the amplitude behaviour of this phase with offset are modelled with a 6 km thick transition zone which consists of approximately 600 m thick laterally variable layers with a bimodal velocity distribution the horizontal component stacks of the wide angle data feature arcuate events suggesting boudin like structures or a boundary with topographic relief high amplitude sub moho reflections support that the structural complexity of the crust mantle transition can be followed to the upper mantle suggesting eastward dipping structures indicating either remnants of an old subduction zone trapped crustal material within the mantle or active crust mantle interactions

moho topography and lower crustal wide angle reflectivity around the tesz in southern scandinavia and northeastern europe abstract the moho topography is strongly undulating in southern scandinavia and northeastern europe a map of the depth to moho shows similarities between the areas of the teisseyre tornquist zone ttz in poland and the fennoscandian border zone fbz which is partly coinciding with the sorgenfrei tornquist zone stz in denmark the moho is steeply dipping at these zones from a crustal thickness of approximately 32 km in the young palaeozoic platform and basin areas to approximately 45 km in the old precambrian platform and baltic shield the moho reflectivity pmp waveform in the polonaise 97 refraction wide angle seismic data from poland and lithuania is variable ranging from sharp to strongly reverberating signals of up to 2 s duration there is little or no lower crustal wide angle reflectivity in the thick precambrian platform whereas lower crustal reflectivity in the thin palaeozoic platform is strongly reverberating suggesting that the reflective lower crust and upper mantle is a young phenomena from stochastic reflectivity modelling we conclude that alternating high and low velocity layers with average thicknesses of 50 300 m and p wave velocity variations of 3 4 of the background velocity can explain the lower crustal reflectivity sedimentary layering affects the reflectivity of deeper layers significantly and must be considered in reflectivity studies although the reverberations from the deeper crust cannot be explained by the sedimentary layering only the reflective lower crust and upper mantle may correspond to a zone that has been intruded by mafic melts from the mantle during crustal extension and volcanism

patterns of asian winter climate variability and links to arctic sea ice abstractthis paper describes two dominant patterns of asian winter climate variability the siberian high sh pattern and the asia arctic aa pattern the former depicts atmospheric variability closely associated with the intensity of the siberian high and the latter characterizes the teleconnection pattern of atmospheric variability between asia and the arctic which is distinct from the arctic oscillation ao the aa pattern plays more important roles in regulating winter precipitation and the 850 hpa meridional wind component over east asia than the sh pattern which controls surface air temperature variability over east asia in the arctic ocean and its marginal seas sea ice loss in both autumn and winter could bring the positive phase of the sh pattern or cause the negative phase of the aa pattern the latter corresponds to a weakened east asian winter monsoon eawm and enhanced winter precipitation in the midlatitudes of the asian continent and east asia for the sh pattern sea ice loss in the