test ban treaty verification with regional data a review this paper summarizes the use of regional 30 seismic data in a test ban context for detecting locating identifying and determining the yield of underground nuclear explosions in many areas of the world eastern north america africa eastern ussr lg is the largest amplitude wave recorded on standard seismograph systems and thus is the most appropriate phase for monitoring small magnitude events excellent location capability for near regional events has been demonstrated at the norwegian small aperture array noress using lg and p waves lg and other regional phases may contain information on source depth but such information has not been exploited to date fifteen classes of regional discriminants have been identified including 1 1 first motion 2 2 ms mb 3 3 p2 p1 ratio 4 4 excitation of short period sh waves 5 5 lg rg amplitude ratios 6 6 pn lg pg lg and pmax lg amplitude ratios 7 7 lg group velocity and energy ratios in lg 8 8 excitation of sn 9 9 third moment of frequency 10 10 generation of higher mode surface waves 11 11 peak amplitudes of love and rayleigh waves and long period surface wave energy density 12 12 prevailing period of long period love waves 13 13 spectral ratio long period s waves to rayleigh waves 14 14 spectral ratio long period love waves to rayleigh waves 15 15 frequency of the peak spectral amplitudes and spectral ratios in pn pg s and lg each of these proposed discriminants has with differing degrees of success separated some explosions from some earthquakes however most have been tested only on limited data usually from one geographic region and only one or two recording stations no systematic analyses have been done to determine the best individual discriminant or combination of them preliminary evaluation of the use of lg for yield determination suggests that regional waves hold promise in this application theoretical studies have contributed significantly to the understanding of propagation characteristics of regional waves but further studies are required emphasizing modeling for realistic anisotropic sources the major conclusion of this study is that a systematic and comparative evaluation of all the proposed regional discriminants is now required utilizing a common data base derived from all present day test sites this evaluation would suggest the optimal discrimination procedure using regional waves and would also define areas of needed research without such an integrated evaluation it is still possible to speculate using existing results on the most promising regional discriminants

impact of tropical pacific precipitation anomaly on the east asian upper tropospheric westerly jet during the boreal winter abstractthe leading mode of boreal winter precipitation variability over the tropical pacific for the period 1980 2010 shows a west east dipole pattern with one center over the western north pacific wnp and maritime continent and the other center over the equatorial central pacific cp observational evidence shows that the variability of the east asian upper tropospheric subtropical westerly jet eaj has a significant correlation with precipitation anomalies over the wnp and cp and that tropical precipitation anomalies over wnp and cp have a distinct influence on the variation of the eaj a series of numerical experiments based on a linear baroclinic model are performed to confirm the influence of the heating anomalies associated with precipitation perturbations over the wnp and cp on the eaj the results of numerical experiments indicate that a heat source over the wnp can excite a northward propagating rossby wave train in the upper troposphere over east asia and facilitate a poleward eddy momentum

western pacific interannual variability associated with the el nino southern oscillation observations of sea surface temperature sst sea level pressure slp surface wind and outgoing longwave radiation olr show that the el nino southern oscillation enso displays western pacific anomaly patterns in addition to eastern pacific anomaly patterns during the warm phase of enso warm sst and low slp anomalies in the equatorial eastern pacific and low olr anomalies in the equatorial central pacific are accompanied by cold sst and high slp anomalies in the off equatorial western pacific and high olr anomalies in the off equatorial far western pacific also while the zonal wind anomalies over the equatorial central pacific are westerly those over the equatorial far western pacific are easterly the nearly out of phase behavior between the eastern and western tropical pacific is also observed during the cold phase of enso but with anomalies of opposite sign these western pacific interannual anomaly patterns are robust features of enso independent of data sets it is argued that equatorial easterly westerly wind anomalies over the far western pacific during the warm cold phase of enso are initiated by off equatorial western pacific cold warm sst anomalies and that these winds are important for the evolution of enso an atmosphere model is employed to demonstrate that small off equatorial western pacific cold warm sst anomalies compared to those in the east are sufficient to produce equatorial easterly westerly wind anomalies as observed over the far western pacific the coupled ocean atmosphere model of zebiak and cane is then modified to investigate the evolution of the western pacific interannual anomaly patterns in a coupled ocean atmosphere system by including a meridional structure to the subsurface temperature parameterization in the western pacific the modified model produces both western and eastern pacific interannual anomaly patterns

north pacific temperature and precipitation response to el nino like equatorial heating sensitivity to forcing location this study investigates the sensitivity of oceanic and atmospheric response in the extra tropics especially in the north pacific to the position of equatorial el nino like heating within a slab ocean climate model in a suite of numerical experiments we impose an idealized equatorial sea surface temperature sst anomaly in the pacific and systematically vary its longitudinal position along the equator to mimic different flavors of el nino we find that regardless of the forcing location the induced sst pattern closely resembles a positive phase of the pacific decadal oscillation with a characteristic warming along the north american coast as part of an arc shaped pattern accompanied by wind anomalies around the aleutian low however the extent and magnitude of the coastal warming vary nonmonotonically when the forcing shifts westward along the equator the strongest response is found when the equatorial forcing is located in the central pacific close to the dateline in contrast precipitation response over southern california is strongest for an eastern pacific warming centered at 150 w even though its magnitude is highly uncertain since the boundary between dry and wet precipitation anomalies passes through this region we repeat the experiments for cold i e la nina like anomalies and observe a significant asymmetry in the sst and atmospheric response between the warm and cold cases finally our experiments suggest that tropical heating or cooling over the western pacific warm pool generates the largest tropical rainfall response and hence the largest global mean sst anomaly

obtuse angle vs confluent sharp meander bends insights from the paraguay cuiaba confluence in the tropical pantanal wetlands brazil abstract river confluences are notable features in the drainage system with complex hydrodynamics bed morphology sediment transport and mixing processes junction planform plays a pivotal role in the confluence hydrodynamics however most investigations have concentrated on the junction of two straight channels and few studies have focused on confluent meander bends or obtuse angle confluences here we analyze a confluence with an obtuse angle planform the tributary enters the confluence at an angle higher than 180 that abruptly curves to join the main river in the pantanal wetlands the strong flood wave is responsible for significant variations of the discharge and momentum flux ratios within the confluence consequently the paraguay cuiaba confluence is able to shift from an obtuse angle working mode to a confluent meander bend working mode according to the hydrological conditions when the momentum ratio is greater than 1 mr 1 the confluence works as an obtuse angle junction whereas when the ratio is less than 1 mr

subtropical anticyclones and summer monsoons the summer subtropical circulation in the lower troposphere is characterized by continental monsoon rains and anticyclones over the oceans in winter the subtropical circulation is more strongly dominated by the zonally averaged flow and its interactions with orography here the mechanics of the summer and winter lowertropospheric subtropical circulation are explored through the use of a primitive equation model and comparison with observations by prescribing in the model the heatings associated with several of the world s monsoons it is confirmed that the equatorward portion of each subtropical anticyclone may be viewed as the kelvin wave response to the monsoon heating over the continent to the west a poleward flowing low level jet into a monsoon such as the great plains jet is required for sverdrup vorticity balance this jet effectively closes off the subtropical anticyclone to the east and also transports moisture into the monsoon region the low level jet into north america induced by its monsoon heating is augmented by a remote response to the asian monsoon heating the rossby wave response to the west of subtropical monsoon heating interacting with the midlatitude westerlies produces a region of adiabatic descent it is demonstrated here that a local diabatic enhancement can lead to a strengthening of the descent longitudinal mountain chains act to block the westerly flow and also tend to produce descent in this region below the descent sverdrup vorticity balance implies equatorward flow that closes off the subtropical anticyclone to the west and induces cool upwelling in the ocean through ekman transport feedbacks involving for example sea surface temperatures may further enhance the descent in these regions the conclusion is that the mediterranean type climates of regions such as california and chile may be induced remotely by the monsoon to the east hence it can be argued that the subtropical circulation in summer comprises a set of weakly interacting monsoon systems each involving monsoon rains a low level poleward jet a subtropical anticyclone to the east and descent and equatorward flow to the west in winter it is demonstrated how the nonlinear interaction between the strong zonal mean circulation associated with the winter hadley cell and the mountains can define many of the large scale features of the subtropical circulation the blocking effect of the longitudinal mountain chains is shown to be very important subsequent diabatic effects such as a local diabatic enhancement would appear to be essential for producing the observed amplitude of these features

interdecadal change in the principal mode of winter spring precipitation anomaly over tropical pacific around the late 1990s evidence show that the dominant mode of winter spring precipitation anomaly over the tropical pacific experienced a pronounced interdecadal change around 1998 based on the extended empirical orthogonal function eeof technique a zonal dipole pattern of precipitation anomaly is dominant during the pre 1998 period corresponding to a positive principle component pc1 positive precipitation anomaly over the equatorial eastern pacific ep decays eastward from winter to spring which is identified as an eastward decaying ep mode during the post 1999 period there is a zonal triple pattern with enhanced precipitation over the equatorial central pacific cp and reduced precipitation over the western north pacific and equatorial southeastern pacific with a positive pc1 this triple pattern of precipitation anomaly maintains with decreasing amplitude from winter to spring which is called the fixedly decaying cp mode for short such interdecadal shift is controlled by differing sea surface temperature sst anomaly pattern the interdecadal differences of winter spring wind stress and thermocline over tropical pacific might result in the interdecadal change in the sst anomaly and then precipitation mode via modulating physical oceanic feedback processes in addition the effect of two distinct precipitation modes on the north pacific teleconnection and north american surface temperature anomaly was strikingly different before 1998 the eastward decaying ep mode might induce a significant tropical northern hemisphere tnh like teleconnection only in winter leading to a north to south pattern of north american temperature anomaly which is greatly limited in spring after 1999 a northwest to southeast response of north american temperature sustains from winter to spring resulting from the maintenance of the pacific north america pna like pattern simulated by the fixedly decaying cp mode

the linkage between the eastern pacific teleconnection pattern and convective heating over the tropical western pacific abstractthe eastern pacific ep pattern is a recently detected atmospheric teleconnection pattern that frequently occurs during late winter through analysis of daily era interim data and outgoing longwave radiation data for the period of 1979 2011 it is shown here that the formation of the ep is preceded by an anomalous tropical convection dipole with one extremum located over the eastern indian ocean maritime continent and the other over the central pacific this is followed by the excitation of two quasi stationary rossby wave trains departing from the subtropics north of the region of anomalous convection one rossby wave train propagates eastward along the east asian jet from southern china toward the eastern pacific the second wave train propagates northward from east of japan toward eastern siberia and then turns southeastward to the gulf of alaska both wave trains are associated with wave activity flux convergence where the ep pattern develops the results from an examination of the e vecto

a further study of the tropical western hemisphere warm pool abstract variability of the tropical western hemisphere warm pool whwp of water warmer than 28 5 c which extends seasonally over parts of the eastern north pacific the gulf of mexico the caribbean and the western tropical north atlantic tna was previously studied by wang and enfield using the da silva data from 1945 93 using additional datasets of the ncep ncar reanalysis field and the ncep sst from 1950 99 and the levitus climatological subsurface temperature the present paper confirms and extends the previous study of wang and enfield the whwp alternates with northern south america as the seasonal heating source for the walker and hadley circulations in the western hemisphere during the boreal winter a strong hadley cell emanates northward from the amazon heat source with subsidence over the subtropical north atlantic north of 20 n sustaining a strong north atlantic anticyclone and associated northeast ne trade winds over its southern limb in the tna this circulation including the ne

linking observations of the asian monsoon to the indian ocean sst possible roles of indian ocean basin mode and dipole mode abstract the authors investigate the relationship between sea surface temperature sst in the tropical indian ocean tio and the seasonal atmosphere circulation in the asian monsoon region amr using the maximum covariance analyses mcas the results show that the asian monsoon circulation is significantly correlated with two dominant sst anomaly ssta modes the indian ocean basin mode iob and the indian ocean dipole mode iod the peak ssta of the iob appears in spring and has a much stronger relationship with the asian summer monsoon than the peak of the iod does whereas the peak ssta for the iod appears in fall and shows a stronger link to the asian winter monsoon than to the asian summer monsoon in addition the iob in spring has a relatively stronger link with the atmospheric circulation in summer than in other seasons the large scale atmospheric circulation and ssta patterns of the covariability of the first two dominant mca modes are described for the first mca mode a warm iob persis

effects of bed discordance on flow dynamics at open channel confluences although a discordance in bed elevation between mainstream and tributary channels is a common feature of most river confluences this height differential is largely ignored in many models of junction flow dynamics here we present new laboratory flume data that demonstrate the significant influence of bed discordance on flow at an acute angled confluence a difference in bed height between mainstream and tributary channels is shown to obliterate flow deflection at the bed and create a distortion of the mixing layer between the flows resulting in fluid upwelling at the downstream junction corner this upwelling is responsible for the absence of a flow separation zone near the bed at the downstream junction corner and the lack of a zone of marked flow acceleration in the postconfluence channel these experiments reveal complex flow fields generated by bed discordance and suggest the need for major revisions to current models of river channel confluence flow dynamics and their application to sediment routing at these sites

bed morphology and sedimentology at the confluence of unequal depth channels abstract spatial and temporal variations in the bed geometry and bed material size of a sand bed river confluence with unequal depth channels were monitored during a sequence of floods additionally two other sand bed confluences were surveyed to test the replicability of these observations the confluences studied here have only one avalanche face which corresponds to the front of a tributary mouth bar in the shallower channel and do not exhibit a marked scour zone three distinct morpho sedimentological zones are present 1 an area around the upstream corner of the junction where the sediments are generally finer than the mean 2 a maximum depth zone with coarser than average particles and 3 a bar at the downstream junction corner where grain size is finer than the mean and decreases slightly downstream changes in relative discharge between the two channels had little effect on the grain size of the downstream junction corner bar but exerted a strong influence on the position of the maximum depth zone and the front of the tributary mouth bar the downstream junction corner bar showed little evidence of the separation zone which is commonly observed at the confluences of laboratory channels the contrasting depths of the approach channels at the sites studied here may be partly responsible for the absence of the separation zone

mean and turbulent flow structure during the amalgamation process in fluvial bed forms 1 fluvial channels present bed forms such as dunes and ripples that alter instantaneous hydrodynamics parameters such as flow velocities water surface profiles bed shear stresses and reynolds stresses and create turbulent coherent structures that are significantly different from those presented in flat bed conditions it is known that les based models are more suitable than rans models to reproduce the complex hydrodynamics around bed forms herein a les model is applied to describe the mean and turbulent flow structure under superimposed bed forms three cases were simulated run i train of ripples run ii superimposed bed forms and run iii amalgamated bed forms the les modeling was performed using a free surface condition to allow the model to develop undulations and boils on the water surface caused by effect of the bed forms some important conclusions from this study are the division of high and low shear stresses on the stoss side of the dune the progression of the flow field topology from run i and run iii and the type of turbulent coherent structures found in each stage the region of high shear stresses was related to turbulence production in which the streamwise velocity fluctuations where strips structures are related to streaks were associated to the modification of the bed morphology the turbulence horseshoes vortices thv were more frequent in run i than in the other two cases where streamwise rolls were more frequent finally the frequency of the bursting events increased from run i to run ii and decreased from run ii to run iii implications of detailed hydrodynamics into bed forms processes are also presented and discussed

quasi stationary extratropical wave trains associated with distinct tropical pacific seasonal mean convection patterns observational and amip model results in this paper mechanisms for the formation of quasi stationary extratropical wave trains associated with four distinct winter patterns of seasonal mean tropical pacific convection anomalies including the western cp w cp pattern la nina ln pattern cp el nino cpen pattern and ep el nino epen pattern are investigated by utilizing observational and six atmospheric model intercomparison project phase 5 amip5 high skilled models access1 0 canam4 ccsm4 cmcc cm hadgem2 a mpi esm lr datasets the observational results show that tropical pacific forcing induces upper level anomalous rossby wave source that force vorticity over the central north pacific through modulating the local hadley circulation then excite eastward propagation of quasi stationary planetary waves penetrating into the north atlantic and finally establish the associated teleconnections in mid and high latitudes by local synoptic eddy mean flow interaction different structures of wave trains may be explained by evident differences in intensity and scale of the extratropical vorticity forcing originating from distinct convection anomalies over the tropical pacific the mme results further confirm the possible physical processes obtained from observations but there still exist some significant differences these cover the north pacific and north america and can possibly be attributed to the models simulation ability of extratropical vorticity forcing and local storm track intensity in addition the stratosphere troposphere interaction plays an important role for extratropical atmospheric circulation anomalies the stratospheric polar vortex not only modulates the underlying wave train especially for the north atlantic europe sector but is also affected by the upper tropospheric disturbance in high latitudes through the upward wave activity flux

nature of flow and turbulence structure around an in stream vertical plate in a shallow channel and the implications for sediment erosion 1 detailed knowledge of the dynamics of large scale turbulence structures is needed to understand the geomorphodynamic processes around in stream obstacles present in rivers detached eddy simulation is used to study the flow past a high aspect ratio rectangular cylinder plate mounted on a flat bed relatively shallow channel at a channel reynolds number of 2 4 105 similar to other flows past surface mounted bluff bodies the large amplification of the turbulence inside the horseshoe vortex system is because the core of the main necklace vortex is subject to large scale bimodal oscillations the presence of a sharp edge at the flanks of the obstruction fixes the position of the flow separation at all depths and induces the formation and shedding of very strong wake rollers over the whole channel depth compared with the case of a circular cylinder where the intensity of the rollers decays significantly in the near bed region because the incoming flow velocity is not sufficient to force the wake to transition from subcritical to supercritical regime in the case of a high aspect ratio rectangular cylinder the passage of the rollers was found to induce high bed shear stresses at large distances 6 8 d behind the obstruction also the nondimensional values of the pressure root mean square fluctuations at the bed were found to be about 1 order of magnitude higher than the ones predicted for circular cylinders overall this shows that the shape of the in stream obstruction can greatly modify the dynamics of the large scale coherent structures the nature of their interactions and ultimately their capability to entrain and transport sediment particles and the speed at which the scour process evolves during its initial stages

seismic and hydroacoustic observations from underwater explosions off the east coast of floridaseismic and hydroacoustic observations from underwater explosions off the east coast of florida

evolution of the hydromorphodynamics of mountain river confluences for varying discharge ratios and junction angles abstract mountain river confluences are characterized by narrow and steep tributaries that supply abundant sediment load to a main channel that in turn provides the dominant flow discharge in addition bed sediments consist of poorly sorted mixtures that promote bed armoring the knowledge of the hydrodynamics and morphodynamics of mountain river confluences is sparse because most of the existent studies on confluence dynamics focus on lowland confluences this study aims at examining the influence of the junction angle and discharge ratio q r q t q m on flow dynamics and bed morphology of mountain river confluences this study presents the results of six laboratory experiments in which three discharge ratios were tested q r q t q m 0 11 0 15 0 23 with two different junction angles 90 and 70 the experiments were conducted under movable bed conditions and with continuous sediment supply to both flumes measurements consisted of systematic bed topography and water surface surveys performed at different instants during the experiments and at equilibrium i e when the outgoing sediment rate coincided with the incoming and bed topography reached a steady state the results show that the discharge ratio and the junction angle parameters are major controls of the dynamics of mountain river confluences also the evolution of bed morphology and flow dynamics for varying junction angles and discharge ratios present some patterns that contrast with those reported for lowland confluences among these patterns are the different flow regimes adopted by the tributary for different junction angles and the decrease of the height of the bank attached bar for increasing discharge ratios moreover results show that the abundant sediment load of the tributary plays a major role on the dynamics of this type of confluence this load resulted in a marked bed discordance that in turn influenced flow dynamics and bed morphology of the confluence

on playfair s law of accordant junctions geomorphologists since playfair have apparently accepted that fluvial confluences will be morphologically accordant in distinction to the hanging junctions of glaciated troughs a view reinforced by gilbert s law of declivities the issue has been largely ignored despite field instances of discordant fluvial junctions and widespread engineering practice which favours discordant confluences in non erodible materials six categories of fluvial junctions are defined accordant hanging discordant barred impeded disrupted and disturbed the study focuses principally on the first two classes and defines discordance purely morphologically in terms of relative depth of incision of the confluent thalwegs likely controls of accordance discordance are identified as flow magnitudes synchroneity of flow regimes channel boundary materials and debris calibre field investigations in malawi france west malaysia and new zealand in small 100 km2 basins on a variety of rock types are described barred junctions are relatively rare but complex in character a high proportion of confluences are distinctly discordant and there is a general continuum from accordant cases tectonic control is improbable and the principal cause identified is the degree of difference in channel forming discharges estimated by stream magnitude and channel area some evidence for lithologic control is also apparent it appears that many confluences behave as if the tributary junction is non erodible and not in the fashion predicted by the law of declivities it is argued that the observed relation is a necessary result of the general down stream changes in hydraulic geometry limited comparison with glacial trough confluences reveals a difference in degree but not in nature although the relationship between discordance and channel size is affected by cross section geometry a 10 fold difference in the cross sectional areas of channels meeting at a junction produces on average a 2 4 fold difference in mean channel depths for fluvial cases and a 4 fold difference for glacial troughs the role of varying flow regimes seems to require attention nevertheless it is maintained that playfair s law is a misleading description of the morphology of fluvial junctions which behaves fundamentally in the same fashion as glacial troughs

interhemispheric influence of the atlantic warm pool on the southeastern pacific abstract the atlantic warm pool awp is a large body of warm water comprising the gulf of mexico caribbean sea and western tropical north atlantic the awp can vary on seasonal interannual and multidecadal time scales the maximum awp size is in the boreal late summer and early fall with the largest extent in the year being about 3 times the smallest one the awp alternates with the amazon basin in south america as the seasonal heating source for circulations of the hadley and walker type in the western hemisphere during the boreal summer fall a strong hadley type circulation is established with ascending motion over the awp and subsidence over the southeastern tropical pacific this is accompanied by equatorward flow in the lower troposphere over the southeastern tropical pacific as dynamically required by the sverdrup vorticity balance it is shown by analyses of observational data and ncar community atmospheric model simulations that an anomalously large small awp during the boreal summer f

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

hydromorphodynamic effects of the width ratio and local tributary widening on discordant confluences abstract river training works performed in the last couple of centuries constrained the natural dynamics of channel networks in locations that include the confluences between tributaries and main channels as a result the dynamics of these confluences are currently characterized by homogeneous flow depths flow velocities and morphologic conditions which are associated with impoverished ecosystems the widening of river reaches is seen as a useful measure for river restoration as it enhances the heterogeneity in flow depths flow velocities sediment transport and bed substrates the purpose of this study is to analyze the effects of local widening of the tributary mouth as well as the effects of the ratio between the width of the tributary and that of the main channel on the flow dynamics and bed morphology of river confluences for that purpose 12 experiments were conducted in a 70 laboratory confluence in these experiments three unit discharge ratios were tested q r 0 37 0 50 and 0 77 with two width ratios and two tributary configurations the unit discharge ratio is defined as the unit discharge in the tributary divided by that of the main channel measured upstream of the confluence the width ratio which is defined as the width of the tributary divided by that of the main channel was modified by changing the width of the main channel from 0 50 to 1 00 m corresponding to b r 0 30 and 0 15 respectively the tributary configurations consisted of i a straight reach with a constant width the so called reference configuration and ii a straight reach with a local widening at the downstream end the so called widened configuration during the experiments a uniform sediment mixture was continuously supplied to both channels this experimental setup is novel among existing experimental studies on confluence dynamics as it addresses new confluence configurations and includes a continuous sediment supply to both channels the experiments were run until the outgoing sediment rate was nearly the same as the incoming i e equilibrium had been achieved the bed topography and water surface were then recorded in both channels the results reveal that the width ratio and the locally widened tributary reach influence the dynamics of the confluence the different width ratios influenced the size of the bank attached bar at equilibrium which was wider and longer for b r 0 15 than for b r 0 30 other morphological differences were observed at equilibrium for the different width ratios such as deeper scour holes and increased penetration of the tributary into the main channel these differences were attributed to the different values of the ratio between the unit momentum flux of the tributary and that of the main channel that were noted at equilibrium for the different width ratios the local widening of the downstream reach of the tributary significantly enhanced the heterogeneity in flow depth flow velocity and bed morphology within the widened reach this heterogeneity contrasts with the homogeneity observed in the tributary without widening reference configuration additionally the effects of the local tributary widening were limited to the tributary with minor or negligible effects on the main channel

spectral characteristics of seismic events off the coast of the levant summary seismic events which occur off the coast of the levant may be grouped into two categories probable earthquakes and probable underwater explosions uwe spectral analysis of these events recorded by the israel seismic network isn helps to characterize these two types of events the observed spectral modulation of the seismic waves is compared with the expected spectra due to source mechanism of uwe and possible effects of the liquid layer i e bubbling reverberation and channelling a remarkably complete harmonic series of maxima up to the fifth order due to the bubbling phenomenon was found for all uwe recorded at stations far inland the same form of modulation and maxima at the same frequencies are present at different stations for both p and coda waves these effects were not observed in the case of earthquakes it is suggested that the uwe spectra are mainly induced by the source effect rather than by the path effects a distinct split of the fundamental mode was revealed in the observed spectra of the coda waves in some uwe from the tyre region this phenomenon may be the result of the asymmetry of the resonating water layer contributing to the energy of the first spectral maximum the results of the study demonstrate that spectral analysis of seismograms can be used to discriminate between off coast earthquakes and underwater explosions recorded in israel

regional model simulations of marine boundary layer clouds over the southeast pacific off south america part ii sensitivity experiments abstract the sensitivity of a regional climate model to physical parameterizations and model resolution is investigated in terms of its simulation of boundary layer stratocumulus scu clouds over the southeast pacific specifically the physical schemes being tested include shallow cumulus convection subgrid vertical mixing cloud droplet number concentration cdnc and drizzle as described in part i the model with standard settings captures the major features of the boundary layer in the region including a well mixed marine boundary layer a capping temperature inversion scu clouds and the boundary layer regime transition from the well mixed layer near the coast of south america to a decoupled cloud layer over warmer water to the west turning off the shallow cumulus parameterization results in a dramatic increase in the simulated scu clouds while the boundary layer structure becomes unrealistic losing the decoupled regime over warm water with reduced penetrative mixing at the top of shallow cu

a connection between the tropical pacific ocean and the winter climate in the asian pacific region the impact of the tropical pacific sea surface temperature sst anomaly on the winter mean surface air temperature sat in the asian pacific region is investigated during the period from 1948 to 2008 using both observations and a linear baroclinic model lbm a singular value decomposition svd analysis is conducted between the 500 hpa geopotential height z500 over the northern hemisphere and the sst over the tropical pacific ocean to obtain the large scale atmospheric patterns related to tropical pacific sst focus is given to the second pair of svd mode svd2 which bears some similarities in the z500 field to the arctic oscillation over the north atlantic sector and can impact the sat over a larger area of asian pacific in the winter of a positive svd2 the sat over the midlatitude to high latitude asian continent the arctic ocean the indian ocean and the western subtropical pacific ocean tends to be warmer than normal while the north pacific ocean around the bering strait is abnormally cold and vice versa examination of the associated surface general circulation shows that a positive svd2 tends to shift the siberian high southward and the aleutian low eastward resulting in anomalous weak pressure gradient between the asian continent the north pacific anomalous positive sea level pressure anomalies around japan and southerly wind along the east coast of the asian continent are observed at the same time the east asian trough at midtroposphere becomes weaker than normal and the east asian westerly jet stream is increased in magnitudes and shifted northward the analysis of the wave activity flux and result of idealized numerical experiments show a possible influence of the western tropical pacific sst forcing on the svd2

mixing layer distortion at the confluence of channels of different depth channel confluences have received considerable recent attention in the fields of geomorphology1 3 sedimentology4 9 and hydraulic engineering10 13 where channels join rapid changes in fluid velocity turbulence intensity channel hydraulic geometry and bed geometry may occur14 17 previous models of junction dynamics have tended to assume that the confluent channels are of equal depth10 18 a condition that may be found only rarely in natural junctions more often the depths of confluent channels are different19 this discordance is commonly the result of the forma tion at the mouth of each confluent channel of bars that possess steep avalanche faces which dip into a central junction scour1 2 5 20 here we suggest that when channels of different depth join the mixing layer that forms at their confluence is distorted by interacting with a separation zone which forms in the lee of the mouth of the shallower channel this mixing layer distortion imparts a complex three dimensional flow to the junction promoting vertical fluid upwelling and significantly enhancing rapid mixing within the flow of the shallow tributary while retarding the rate of mixing across the flow of the deeper channel suspended sediments or contaminants within the deeper channel may be transferred rapidly across the flow of the shallower tributary upwelling downstream of the junction

flow and sediment dynamics in channel confluences confluences with relatively low discharge and momentum flux ratios where a small steep tributary with a high supply of poorly sorted sediment joins a large low gradient main channel commonly occur in nature but they have not yet been investigated measurements of the three dimensional velocity field turbulence sediment transport bed material grain size and morphology are reported in a laboratory setting that is representative of confluences on the upper rhone river switzerland the difference between the low flow depth in the steep tributary and the higher flow depth in the main channel creates a marked bed discordance in the tributary zone due to this bed discordance the tributary flow penetrates into the main channel mainly in the upper part of the water column whereas the main channel flow is hardly hindered by the tributary in the lower part of the water column giving rise to a two layer flow structure in the confluence zone in confluences with high supply of coarse sediment from the tributary the development of a deposition bar downstream from the confluence reduces the flow area and causes flow acceleration that contributes to an increase in sediment transport capacity the sediment supplied by the tributary is mainly sorted and transported on the face of the bar by the near bed flow originating from the main channel the sediment transport capacity is further increased by the three dimensionality of the flow which is characterized by maximum velocities occurring near the bed and by a considerable increase in turbulent kinetic energy generated in the shear layer at the interface of the flows originating from the main channel and the tributary a conceptual model is proposed for the hydro morpho sedimentary processes and compared to existing conceptual models for confluences with different characteristics

changes in the relationship in the sst variability between the tropical pacific and the north pacific across the 1998 1999 regime shift this study shows that sea surface temperature sst variability in the central to eastern tropical pacific has a strong negative correlation with that of the central to eastern north pacific in the boreal winter after the 1998 1999 regime shift this phenomenon is in contrast to before the 1998 1999 regime shift the anomalous aleutian low pressure associated with the tropical sst forcing became stronger and its center shifted to the south and to the west after 1998 1999 such a modulation caused the change in the north pacific sst response this also resulted in a close relationship between the tropical pacific and north pacific sst variability the modulation of the aleutian low pressure is primarily due to the westward shift in the location of the tropical convective heating around the dateline which occurred during 1998 1999 the results of simple atmospheric model experiments support this hypothesis that the shift in the tropical convective heating to the west is responsible for the modulation of the aleutian low pressure and the associated change in the relationship of the sst variability between the tropical pacific and north pacific these results imply that the seasonal predictability of the north pacific sst has increased since 1998 1999 due to its increased correlation with the tropical pacific sst variability

numerical evaluation of the effects of planform geometry and inflow conditions on flow turbulence structure and bed shear velocity at a stream confluence with a concordant bed this study numerically investigates the effects of variations in inflow conditions and planform geometry on large scale coherent flow structures and bed friction velocities at a stream confluence with natural bathymetry and concordant bed morphology several numerical experiments are conducted in which either the kelvin helmholtz mode or the wake mode dominates within the mixing interface mi between the two confluent streams as the junction angle and alignments of the tributaries are altered in the kelvin helmholtz mode the mi contains mostly corotating vortices driven by the mean transverse shear across the mi while in the wake mode the mi contains counterrotating vortices forming by the interaction of the separated shear layers on the two sides of a zone of stagnant fluid near the junction corner a large angle between the two incoming streams is not necessary for the development of strongly coherent streamwise oriented vortical sov cells in the immediate vicinity of the mi results show that such sov cells can develop and produce high bed friction velocities even for cases with a low angle between the two tributaries and for cases where the downstream channel is approximately aligned with the axes of the two tributaries low curvature cases sov cells tend not to develop only when the incoming streams are parallel and aligned with the downstream channel junction angle of zero and the incoming flows produce a strong kelvin helmholtz mode under such conditions quasi 2 d mi vortices play the primary role in mixing and the production of high bed shear velocities simulations with and without natural bed morphology local bank line irregularities indicate that planform geometry and inflow conditions primarily govern the development of coherent flow structures but that bathymetric and bank line effects can locally modify details of these structures

spectra of quarry blasts and microearthquakes recorded at local distances in israel in northern israel quarry blasts and microearthquakes occur in a region with complicated tectonics therefore correct event identification preferably based on a simple method that can be applied on a routine basis is essential for accurate and detailed seismotectonic studies spectral analysis of quarry blasts and microearthquakes recorded at local distances 5 2000 km by stations of the israel seismograph network revealed spectral characteristics in the frequency range less than 12 5 hz that can be used routinely for event identification most quarry blasts in northern israel are ripple fired open pit blasts consequently we chose an event discrimination method based on the recognition of ripple firing patterns in the signal a simple model for ripple firing parameters based on interference theory of linear systems and including random effects predicts spectral minima at low frequencies identical for different seismic phases we compared the spectra of complete seismogram signals of 52 events recorded by the isn at different distances and azimuths including both microearthquakes and quarry blasts in a selected region of northern israel consistent spectral modulation was found in a band from about 2 to 8 hz for 18 of 21 reliably identified i e reported quarry blasts with time delays of 20 to 40 msec the spectral minima frequencies correspond to those predicted by the theory

dynamics of a river channel confluence with discordant beds flow turbulence bed load sediment transport and bed morphology 1 river channel confluences play a major role in the dynamics of all fluvial systems and yet our understanding of bed load routing at these sites is very sparse the dynamics of confluences are a function of the momentum ratio between the combining flows and the three dimensional geometry of the junction recent experiments have shown that discordance in bed height between the confluent rivers increases turbulence intensity and enhances upwelling of flow within the confluence however the significance of these flow characteristics on sediment transport is still unknown to examine the relations between flow and sediment transport we have measured near bed flow turbulence bed load transport rates and changes in bed morphology for eight different flow conditions at a sand bed discordant confluence detailed analysis of the near bed flow patterns reveals that within the shear layer low mean flow velocities are combined with the highest values of reynolds shear stresses and that turbulence generation is associated with intense upward movements of flow high sediment transport rates are found at the edges of the shear layer region where horizontal vertical cross stresses uw are high these patterns match changes in bed morphology where erosion occurs along the shear layer the relation between the shear layer and sediment transport confirms the role of bed discordance on the dynamics of the confluence migration of the shear layer into the confluence as a result of a change in momentum ratio modifies local near bed flow characteristics sediment transport rates and the spatial distribution of deposition and erosion zones

distinct winter patterns of tropical pacific convection anomaly and the associated extratropical wave trains in the northern hemisphere in this paper distinct patterns of boreal winter convection anomalies over the tropical pacific and associated wave trains in the extratropics are addressed the first leading mode eof1 of convection anomalies as measured by outgoing longwave radiation demonstrates an east west oscillation of deep convection with centers over the equatorial central pacific cp and over the tropical western north pacific and the maritime continent the second leading mode eof2 is also a dipole pattern with opposite centers straddling 170 w possibly modifying eof1 to some extent combining the first two leading modes five major categories of tropical convection anomalies can be identified for the period 1979 80 2012 13 the comparison between these five categories and the corresponding sst anomaly patterns indicates a nonlinear relationship between convection and sst the combination of eof1 and eof2 with in phase pcs exhibits an east west dipole pattern with opposite signs over west of the dateline and the maritime continent the negative phase of the two pcs named la nina pattern induces a negative pacific north american positive north atlantic oscillation teleconnection in the extratropics approximately opposite responses can be detected in its positive phase named cp el nino pattern the negative pc2 superposing positive pc1 named ep el nino pattern shows the strongest convection anomalies with enhanced depressed convection over the eastern western pacific and leads to a tropical northern hemisphere like teleconnection pattern and an anomalous anticyclone extending from the north pacific to the north atlantic the positive pc2 with neutral pc1 named western cp pattern shows weakly enhanced convection to the west of the dateline as a response to local sst warming around the dateline this convection anomaly pattern although weak is important and excites a northeastward wave train from the tropics to greenland resulting in surface air temperature cooling covering the northeastern north america and warmer and wetter conditions over western europe

study of local seismic events in lithuania and adjacent areas using data from the passeq experiment the territory of lithuania and adjacent areas of the east european craton have always been considered a region of low seismicity two recent earthquakes with magnitudes of more than 5 in the kaliningrad district russian federation on 21 september 2004 motivated re evaluation of the seismic hazard in lithuania and adjacent territories a new opportunity to study seismicity in the region is provided by the passeq pasive seismic experiment project that aimed to study the lithosphere asthenosphere structure around the trans european suture zone twenty six seismic stations of the passeq temporary seismic array were installed in the territory of lithuania the stations recorded a number of local and regional seismic events originating from lithuania and adjacent areas this data can be used to answer the question of whether there exist seismically active tectonic zones in lithuania that could be potentially hazardous for critical industrial facilities therefore the aim of this paper is to find any natural tectonic seismic events in lithuania and to obtain more general view of seismicity in the region in order to do this we make a manual review of the continuous data recorded by the passeq seismic stations in lithuania from the good quality data we select and relocate 45 local seismic events using the well known locsat and velest location algortithms in order to discriminate between possible natural events underwater explosions and on shore blasts we analyse spatial distribution of epicenters and temporal distribution of origin times and perform both visual analysis of waveforms and spectral analysis of recordings we show that the relocated seismic events can be grouped into five clusters groups according to their epicenter coordinates and origin and that several seismic events might be of tectonic origin we also show that several events from the off shore region in the baltic sea at the coasts of the kaliningrad district of the russian federation are non volcanic tremors although the origin of these tremor type events is not clear

impact of the atlantic warm pool on the summer climate of the western hemisphere abstract the atlantic warm pool awp is a large body of warm water that comprises the gulf of mexico the caribbean sea and the western tropical north atlantic located to its northeastern side is the north atlantic subtropical high nash which produces the tropical easterly trade winds the easterly trade winds carry moisture from the tropical north atlantic into the caribbean sea where the flow intensifies forming the caribbean low level jet cllj the cllj then splits into two branches one turning northward and connecting with the great plains low level jet gpllj and the other continuing westward across central america into the eastern north pacific the easterly cllj and its westward moisture transport are maximized in the summer and winter whereas they are minimized in the fall and spring this semiannual feature results from the semiannual variation of sea level pressure in the caribbean region owing to the westward extension and eastward retreat of the nash the ncar community atmospher

spectral evidence for source multiplicity in explosions application to regional discrimination of earthquakes and explosions abstract spectral and cepstral analysis were performed on regional array noress recordings of mining explosions in scandinavia and russia in order to detect the effects of delayed explosions or ripple firing commonly used in mine blasting practice noress array stacked spectra corrected for instrument and noise were computed in windows on pn pg sn and lg waves from the mine blasts by averaging individual channel spectra frequency by frequency across the array for comparison spectra were also computed for six western norway earthquakes located near the blasjo and titania norwegian mines also stack spectra of p coda sn and lg were computed using norsar seismograms for presumed peaceful nuclear explosions pnes located at near regional distances 10 in western russia the norsar spectra were determined in the same manner as the noress spectra except that an individual source correction was applied to the spectra comparison of western norway mine blast spectra and nearby earthquakes shows that the earthquake pn spectra are peaked in the 8 to 16 hz band with little energy below 6 hz whereas the explosion spectra have flatter spectra from 3 to 16 hz this difference in the pn spectra may be caused by the earthquakes occurring at greater depths than the explosions differences in the near source media or source mechanism effects in the earthquake spectra the main difference between earthquake and explosion spectra is that the explosion spectra exhibit marked scalloping or modulation patterns not observed in the earthquake spectra the modulation patterns are identical in spectra of all phases indicating that they are caused by multiple shot sequences or ripple firing simulated multiple source spectra determined using the noress seismograms for one of the western norway earthquakes resulted in spectra that resembled many of the explosion modulation patterns based on the simulation studies and cepstral analysis of the spectra the mine explosions appear to be composed of two to three separate explosions delayed by between 80 to 150 msec moreover the norsar spectra of pnes indicate that these signals are also produced by multiple explosions although they have larger delay times of between 0 9 to 1 5 sec these results show that spectral modulations in seismogram spectra of economic explosions including mine explosions and nuclear explosions fired for peaceful economic purposes can be used to distinguish them from earthquakes and nuclear explosion weapons tests

circulation regimes and low frequency oscillations in the south pacific sector abstract the characteristics of subseasonal circulation variability over the south pacific are examined using 10 day lowpass filtered 700 hpa geopotential height ncep ncar reanalysis data the extent to which the variability in each season is characterized by recurrent geographically fixed circulation regimes and or oscillatory behavior is determined two methods of analysis a k means cluster analysis and a cross validated gaussian mixture model both indicate three to four geographically fixed circulation regimes in austral fall winter and to some extent spring the spatial regime structures are found to be quite similar in each season they resemble the so called pacific south american psa patterns discussed in previous studies and often referred to as psa 1 and psa 2 oscillatory behavior is investigated using singular spectrum analysis this identifies a predominantly stationary wave with a period of about 40 days and a spatial structure similar to psa 1 it is most pronounced in winter and spr

the seasonal cycle over the tropical pacific in coupled ocean atmosphere general circulation models abstract the seasonal cycle over the tropical pacific simulated by 11 coupled ocean atmosphere general circulation models gcms is examined each model consists of a high resolution ocean gcm of either the tropical pacific or near global means coupled to a moderate or high resolution atmospheric gcm without the use of flux correction the seasonal behavior of sea surface temperature sst and eastern pacific rainfall is presented for each model the results show that current state of the art coupled gcms share important successes and troublesome systematic errors all 11 models are able to simulate the mean zonal gradient in sst at the equator over the central pacific the simulated equatorial cold tongue generally tends to be too strong too narrow and extend too far west ssts are generally too warm in a broad region west of peru and in a band near 10 s this is accompanied in some models by a double intertropical convergence zone itcz straddling the equator over the eastern pacific and in others

effects of variability associated with the antarctic circumpolar current on sound propagation in the ocean a series of small depth charges was detonated along a transect from new zealand to antarctica over a period of three days in late december of 2006 signals were recorded by hydrophones deployed near the source and at a sparse network of permanent hydrophone stations operated by the international monitoring system ims at distances up to 9 600 km our purpose was to determine how well signal characteristics could be predicted by the world ocean atlas 2005 woa05 climatological database for sources within the antarctic circumpolar current acc where recorded signal to noise ratios are high travel times and signal dispersion are predicted to within two seconds under the assumption that propagation is adiabatic and follows a geodesic path the deflection of the transmission path by abrupt spatial variations in sound speed at the northern acc boundary is predicted to decrease travel times to the ims stations by several seconds depending on the path the accuracy of source locations estimates based only on travel times depends on the monthly or seasonal database used to predict velocities and on whether we account for path deflection the configuration of the ims hydrophones limits source location accuracy within the acc comparison of signal spectra for recordings near the source and at distance show that transmission loss is nearly uniform as a function of frequency

the application of computational fluid dynamics to natural river channels eddy resolving versus mean flow approaches in the last decade as computing power has increased there has been an explosion in the use of eddy resolving numerical methods in the engineering earth and environmental sciences for complex geomorphic flows where accurate field investigations are difficult to perform and where experiments may be difficult to scale these numerical approaches are beginning to give key insights into the nature of these flows eddy resolving methods such as large and detached eddy simulation les des may be contrasted with the time averaged three dimensional simulations that only really began to be applied seriously in geomorphology fifteen years ago while the potential of les for geomorphology has been examined previously des is a relatively recent method that deserves further consideration in this paper we explain the method and then utilise examples from meander and confluence flows as well as flow near the bed of a gravel bed river to highlight the improvements to both the representation of the mean flow and to the representation of time varying processes that result from the use of les des some suggestions are provided for the future use of such techniques in geomorphology

hydrodynamics of mountain river confluences and its relationship to sediment transport mountain confluences are characterized by narrow and steep tributaries that provide important sediment load to the confluence whereas themain channel supplies the dominant flow discharge this results in a marked bed discordance between the tributary and main channel which induces key differences in the hydromorphodynamics of the confluence when compared to concordant bed and some common types of discordant bed confluences the processes of initiation and maintenance of the morphology of confluences are still unknown and research linking morphodynamics and hydrodynamics of river confluences is required to understand these phenomena in this paper eddy resolving simulations based on laboratory experiments made in a live bed model of a mountain river confluence are used to provide a detailed description of flow hydrodynamics and implications for morphodynamics the test case study corresponds to a confluence with an angle of 70 numerical simulations are performed for two extreme bathymetric conditions those at the start of the experiment and when equilibriummorphological conditions are reached results of the simulations and experimental observations are used tomake inferences on erosion mechanisms during the initial and final states of the erosion deposition process the relationship between the coherent structures present in the near bed region in the instantaneous and mean flow fields and sediment entrainment transport is described the present paper demonstrates the critical role played by large scale turbulence generated in the shear layers forming on the side of the tributary flow as it enters the main channel by the main vortex forming over the discordant bed region surrounding the downstream end of the tributary as well as by several near bed vortices induced by the deflection of the tributary flow by the incoming flow in the main channel the predicted patterns of bed shear stress are linked to pathways of sediment movement

separation zone at open channel junctions the configuration of open channel junctions controls local sedimentary processes channel scour and sidewall erosion through its influence on the flow patterns established as confluent streams compete for limited channel capacity entry of a tributary into a mainstream ensures detachment of flow from the channel sidewall immediately downstream from the junction and flume experiments show well defined relationships between the dimensions of the separation zone and discharge from the tributary other things equal both the width and length of the separation zone increase systematically with an increase in confluence angle though it is shown that values of width are much less than predicted by recent mathematical modelling the zone grows at the expense of the proportion of the channel occupied by the immediate post confluence flow with the consequence that near bottom velocity increases by a factor of 1 3 as confluence angle is increased from 15 90 the implications for sediment entrainment are reviewed briefly

a simple atmospheric model of the local and teleconnection responses to tropical heating anomalies abstract a minimal complexity model of both the local and remote stationary responses of the atmosphere to tropical heating anomalies is described and demonstrated two levels are recast as baroclinic and barotropic components with thermal advection in the tropics neglected the model is linearized about some idealized and realistic background wind fields and forced with a localized heating for illustration in the tropics the baroclinic responses are familiar from the matsuno gill model these excite barotropic responses by advective interactions with vertical background wind shear the barotropic signals are in turn transmitted to high latitudes only in the presence of barotropic background westerly winds for an el nino like equatorial heating the barotropic response has anticyclones to the north and south of the heating reinforcing opposing the anticyclonic cyclonic baroclinic gyres in the upper lower troposphere with realistic background flows the model reproduces the hemispheric asymmetry

some simple analytical solutions to the problem of forced equatorial long waves this paper describes some simple time dependent analytical solutions to the problem of a sudden switch on of heating localized about the equator the equations used are the shallow water equations on the plane under the long wave approximation it is shown that with a reasonable amount of dissipation it can take several days for a steady state response to be established in the early stages the circulation differs considerably from that of the steady state the long time scale for the adjustment process has implications in numerical weather prediction since it implies that if the initial data are not in balance with the model s forcing it may take several days for a balance to be established by which time the quasi stationary tropical flow may have been irrevocably changed

air sea interaction and the seasonal cycle of the subtropical anticyclones abstract the causes of the seasonal cycles of the subtropical anticyclones and the associated zonal asymmetries of sea surface temperature sst across the subtropical oceans are examined in all basins the cool waters in the east and warm waters in the west are sustained by a mix of atmosphere and ocean processes when the anticyclones are best developed during local summer subsidence and equatorward advection on the eastern flanks of the anticyclones cool ssts while poleward flow on the western flanks warms ssts during local winter the sst asymmetry across the subtropical north atlantic and north pacific is maintained by warm water advection in the western boundary currents that offsets the large extraction of heat by advection of cold dry air of the continents and by transient eddies in the southern hemisphere ocean processes are equally important in cooling the eastern oceans by upwelling and advection during local winter ocean dynamics are important in amplifying the sst asymmetry as experi

an intensity index for the east asian winter monsoon the thermal contrast betweenthe asian continentand the adjacent oceans is the primary aspect of the east asian winter monsoon eawm that can be well represented in the sea level pressure slp field based on this consideration a new slp based index measuring the intensity of the eawm is proposed by explicitly taking into account both the east west and the north south pressure gradients around east asia the new index can delineate the eawm related circulation anomalies well including the deepened shallow midtropospheric east asian trough sharpened and accelerated widened and decelerated upper tropospheric east asian jet stream and enhanced weakened lower tropospheric northerly winds in strong weak eawm winters compared with previous indices the new index has a very good performance describing the winter mean surface air temperature variations over east asia especially for the extreme warm or cold winters the index is strongly correlated with several atmospheric teleconnections including the arctic oscillation theeurasianpattern andthenorthpacificoscillation westernpacificpattern implyingthepossible internal dynamics of the eawm variability meanwhile the indexis significantly linked to el ni oscillation enso and the sea surface temperature sst over the tropical indian ocean moreover the sst anomalies over the tropical indian ocean are more closely related to the index than enso as an independent predictor this adds further knowledge to the prediction potentials of the eawm apart from enso the predictability of the index is high in the hindcasts of the centre national de recherches m cnrm model from development of a european multimodel ensemble system for seasonal to interannual prediction demeter hence it would be a good choice to use this index for the monitoring prediction and research of the eawm

three dimensional structure of flow at a confluence of river channels with discordant beds this paper presents three dimensional data of the mean and turbulent structure of flow collected at a natural confluence of rivers with discordant beds to 1 describe the three dimensional flow field of a natural junction of channels 2 assess the role of changes in bed morphology occurring during transport effective events on the structure of flow at a confluence and 3 examine how the three dimensional structure of flow varies with changes in the ratio of momentum flux between the two confluent streams three dimensional measurements of velocity were reconstructed from the measurements obtained with an array of four two component electromagnetic current meters six detailed velocity profiles were taken at five cross sections in a wide range of flow conditions the mean field of flow is characterised by 1 the acceleration of flow in the downstream portion of the post confluence channel but by lower velocities upstream in the mixing layer area 2 a stagnation zone at the apex of the junction 3 a zone of flow deviation and strong fluid upwelling close to the avalanche face and at the margin of the tributary mouth bar and 4 reduced velocities over the depositional bar at the downstream junction corner the position and extent of these zones vary with changes in the ratio of momentum flux very high intensity of turbulence peaks up to 50 and turbulent kinetic energy were observed in the mixing layer region distortion of the mixing layer characteristic of flow where bed discordance is present between the two tributary channels was evident from mean and turbulent flow data this field study suggests that the effects of bed discordance on flow sediment transport and the resultant bed morphology must be incorporated into conceptual and numeric models of these sites of complex flow

atlantic warm pool acting as a link between atlantic multidecadal oscillation and atlantic tropical cyclone activity 1 multidecadal variability of atlantic tropical cyclone activity is observed to relate to the atlantic multidecadal oscillation amo a mode manifesting primarily in sea surface temperature sst in the high latitudes of the north atlantic in the low latitudes of the north atlantic a large body of warm water called the atlantic warm pool awp comprises the gulf of mexico the caribbean sea and the western tropical north atlantic awp variability occurs on both interannual and multidecadal timescales as well as with a secular variation the awp multidecadal variability coincides with the signal of the amo that is the warm cool phases of the amo are characterized by repeated large small awps since the climate response to the north atlantic sst anomalies is primarily forced at the low latitudes and the awp is in the path of or a birthplace for atlantic tropical cyclones the influence of the amo on atlantic tropical cyclone activity may operate through the mechanism of the awp induced atmospheric changes the awp induced changes related to tropical cyclones that we emphasize here include a dynamical parameter of tropospheric vertical wind shear and a thermodynamical parameter of convective instability more specifically an anomalously large small awp reduces enhances the vertical wind shear in the hurricane main development region and increases decreases the moist static instability of the troposphere both of which favor disfavor atlantic tropical cyclone activity this is the most plausible way in which the amo relationship with atlantic tropical cyclones can be understood

spectral analysis of underwater explosions in the dead sea the present study utilizes the israel seismic network isn as a spatially distributed multichannel system for the discrimination of low magnitude events ml 2 5 namely earthquakes and underwater explosions in the dead sea in order to achieve this we began with the application of conventional single station methods such as spectral short period ratios we then applied a newly developed network oriented algorithm based on different spectral features of the seismic radiation from underwater explosions and earthquakes i e spectral semblance statistics twenty eight single shot underwater explosions uwes and 16 earthquakes in the magnitude range ml 1 6 2 8 within distances of 10 150 km recorded by the isn were selected for the analysis the analysis is based on a smoothed 0 5 hz window fourier spectrum of the whole signal defined by the signal to noise criterion without picking separate wave phases it was found that the classical discriminant of the seismic energy ratio between the relatively low frequency 1 6 hz and high frequency 6 11 hz bands averaged over an isn subnetwork showed an overlap between uwes and earthquakes and cannot itself provide reliable identification we developed and tested a new multistation discriminant based on the low frequency spectral modulation lfsm method in our case the lfsm is associated with the bubbling effect in underwater explosions the method demonstrates a distinct azimuth invariant coherency of spectral shapes in the low frequency range 1 12 hz of short period seismometer systems the coherency of the modulated spectra for different isn stations was measured by semblance statistics commonly used in seismic prospecting for phase correlation in the time domain the modified statistics provided an almost complete separation between earthquakes and underwater explosions

hydro morphodynamic evolution in a 90 movable bed discordant confluence with low discharge ratio confluences with low discharge and momentum ratios where narrow steep tributaries with high sediment load join a wide low gradient main channel that provides the main discharge are often observed in high mountain regions such as in the upper rhone river catchment in switzerland few existing studies have examined the hydro morphodynamics of this type of river confluence while considering sediment discharge in both confluent channels this paper presents the evolution of the bed morphology and hydrodynamics as observed in an experimental facility with a movable bed for that purpose one experiment was carried out in a laboratory confluence with low discharge and momentum ratios where constant sediment rates were supplied to both flumes during the experiment bed topography and water surface elevations were systematically recorded when the bed topography reached a steady state so called equilibrium and the outgoing sediment rate approximated the incoming rate flow velocity was measured at 12 different points distributed throughout the confluence and the grain size distribution of the bed surface was analyzed typical morphodynamic features of discordant confluences such as a bank attached bar and a flow deflection zone are identified in this study nevertheless the presence of a marked scour hole in the discordant confluence and distinct flow regimes for the tributary and main channel differ from results obtained in previous studies strong acceleration of the flow along the outer bank of the main channel is responsible for the scour hole this erosion is facilitated by the sediment discharge into the confluence from the main channel which inhibits bed armoring in this region the supercritical flow regime observed in the tributary is the hydrodynamic response to the imposed sediment rate in the tributary copyright 2015 john wiley sons ltd

spectral characteristics of regional phases recorded at noress abstract the spectral characteristics of pn and lg are studied for regional events recorded at the noress array in norway the emphasis is on the potential value of spectral ratios for identifying events as earthquake chemical explosions and nuclear explosions the events studied include a suite of explosions from the titania mine in southwest norway a suite of events of unknown source type from a site offshore about 90 km from this mine suites of explosions from several mines in the soviet union about 1000 km from noress events from several locations along the 90 azimuth from noress an apparent earthquake in the north atlantic and a nuclear explosion pne at a range of 1560 km the event identification issues addressed are as follows 1 can earthquakes and explosions be identified based on the ratio of high and low frequency energy in their signal spectra 2 do spectral ratios separate mine blasts from earthquakes for all source areas 3 will spectral ratio discriminants be effective for identifying decoupled underground nuclear explosions we conclude that spectral ratios can sometimes separate events an example is separation of the titania mine blasts from the events at the nearby offshore locations although we cannot be sure how much this is due to path differences however in general spectral ratios vary as much within classes of events as they do among different classes the pne in our data set allows the simulation of spectra from a decoupled nuclear explosion by simply applying the frequency dependent decoupling factor to the observed pn spectrum for this event after applying a distance correction the spectrum for this simulated decoupled nuclear explosion is similar to those for the soviet union mine blasts in our data set

decadal shift in el nino influences on indo western pacific and east asian climate in the 1970s abstract el nino s influence on the subtropical northwest nw pacific climate increased after the climate regime shift of the 1970s this is manifested in well organized atmospheric anomalies of suppressed convection and a surface anticyclone during the summer june august of the el nino decay year jja 1 a season when equatorial pacific sea surface temperature sst anomalies have dissipated in situ observations and ocean atmospheric reanalyses are used to investigate mechanisms for the interdecadal change during jja 1 the influence of the el nino southern oscillation enso on the nw pacific is indirect being mediated by sst conditions over the tropical indian ocean tio the results here show that interdecadal change in this influence is due to changes in the tio response to enso during the postregime shift epoch the el nino teleconnection excites downwelling rossby waves in the south tio by anticyclonic wind curls these rossby waves propagate slowly westward causing persistent sst warmi

impact of heating anomalies associated with rainfall variations over the indo western pacific on asian atmospheric circulation in winter observational data show that the dominant mode of the boreal winter rainfall anomalies in the tropical indo western pacific iwp is a west east dipolar pattern which is called the indo western pacific dipole iwpd mode and is related to el nino southern oscillation it is found that corresponded to the iwpd mode is a new atmospheric teleconnection pattern a wave train pattern emitted from the iwp toward asia and the northwest pacific in winter during the positive negative phase of the iwpd the teleconnection pattern features the negative positive anomalies of 200 hpa geopotential height h200 centered at 30 n 110 e and the positive negative anomalies of h200 centered at 45 n 140 e the teleconnection pattern represents the dominant mode of the boreal winter h200 anomaly over asia a series of simple atmospheric model experiments are performed to confirm that this winter teleconnection pattern is induced by the heating anomalies associated with the iwpd and the heating anomalies over the equatorial central pacific are not important to this teleconnection pattern from the iwp toward asia and the northeast pacific the iwpd is strengthened after the climate regime shift of the 1970s which leads to a stronger teleconnection pattern

3d calculations of equilibrium conditions in loose bed open channels with significant suspended sediment load the flow sediment transport and bathymetry at equilibrium conditions in loose bed open channels are predicted using a fully three dimensional 3d reynolds averaged navier stokes model that was validated for cases in which the bed load transport is dominant the paper focuses on two test cases corresponding to laboratory experiments performed in an s shaped channel in which the suspended sediment load is comparable to the bed load a modified version of the original model that accounts for gravitational force effects due to the total sediment load is proposed it is shown that the way bed slope effects are accounted for plays a major role in improving the predictive capabilities of the model for a case in which the equilibrium bathymetry is characterized by relatively large values and sharp variations of the transverse slope the model is then used to qualitatively and quantitatively analyze the distributions of several flow variables that are difficult to measure in the laboratory they include the dis

effect of boreal spring precipitation anomaly pattern change in the late 1990s over tropical pacific on the atmospheric teleconnection observational evidence showed that the leading mode of precipitation variability over the tropical pacific during boreal spring experienced a pronounced interdecadal change around the late 1990s characterized by a precipitation pattern shift from an eastern pacific ep type to a central pacific cp type the distinct impacts of such a precipitation pattern shift on the extratropical atmospheric teleconnection were examined an apparent poleward teleconnection extending from the tropics to the north atlantic region was observed after 1998 while there was no significant teleconnection before 1998 to understand why only the cp type precipitation mode is associated with a striking atmospheric teleconnection after 1998 diagnostic analyses with the eliassen palm flux and rossby wave source rws based on the barotropic vorticity equation were performed the results show that for the ep type precipitation mode no significant rws anomalies appeared over the subtropical pacific due to the opposite effect of the vortex stretching and absolute vorticity advection processes for the cp type precipitation mode however there are both significant vorticity forcing source over the subtropical cp and clear poleward propagation of rossby wave the spatial distribution of the cp type precipitation pattern tends to excite a conspicuous anomalous southerly and a well organized negative vorticity center over the subtropical cp where both the mean absolute vorticity gradient and mean divergence flow are large hence the interaction between the heating induced anomalous circulation and the basic state made the generation of rossby waves conceivable and effective such corresponding teleconnection responses to the prescribed heating were also examined by using a linear baroclinic model lbm it turned out that significant poleward teleconnection pattern is only caused by the cp type precipitation mode rather than by the ep type precipitation mode further sensitive experiments demonstrated that the change in spring basic state before and after 1998 played a relatively minor role in exciting such a teleconnection pattern when compared with the tropical precipitation anomaly pattern change

meridional displacement of the east asian trough and its response to the enso forcing this paper examined the underlying dynamic mechanisms associated with the meridional displacement of the east asian trough eat which is closely related to the temperature variability in the southern part of east asian winter monsoon eawm during the southward displacement of the eat the siberian high is stronger and the aleutian low is displaced southward this is due mainly to the anomalous cyclonic flow associated with seasonal eddies over the midlatitude central pacific which enhances the horizontal advection of cold warm air to the southern northern part of the eat in the lower troposphere the cold warm advection narrows thickens the height thickness and results in negative positive temperature anomalies in the southern northern part of the eat these anomalous circulation features can be reasonably explained by the phase of the el nino southern oscillation enso the results are also verified by the numerical experiments with prescribing enso like heat source anomalies over the tropical eastern and western pacific in an anomaly atmospheric general circulation model all of these results advance our understanding for the linkage between the enso and the eawm via its modulation of the eat

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

patterns of tropical pacific convection anomalies and associated extratropical wave trains in amip5 in this paper the performance of 18 coupled model intercomparison project phase 5 cmip5 models forced by observational ssts in simulating the tropical pacific convective variation and the atmospheric responses in the extratropics are assessed the multi model ensemble mean results of 18 cmip5 models show that five major patterns of tropical pacific convection anomaly in winter can indeed be well reproduced however the simulation of the corresponding extratropical responses for each pattern exists some deficiency except for the la nina pattern compared with observations we defined an optimized subset of well performing models access1 0 canam4 ccsm4 cmcc cm hadgem2 a mpi esm mr in tropical pacific deep convection according to the ranking of model skill score these models exhibit approximately identical convection anomaly patterns in both amplitude and spatial structure to the observation which potentially might improve the representation of extratropical teleconnections with the tropical pacific especially for the cp el nino cpen ep el nino epen and western cp w cp patterns both evident atmospheric anomalies of cpen and epen patterns over the na e sector and the northeastward propagating wave trains of w cp pattern can be quite well simulated in the high skilled models

interhemispheric influence of indo pacific convection oscillation on southern hemisphere rainfall through southward propagation of rossby waves tropical indo western pacific convection anomalies influence atmospheric circulation impacting climate far beyond the tropics here we present observational and modelling evidence for an interhemispheric effect of the boreal summer june august indo pacific convection oscillation ipco which is characterized by a zonal seesaw pattern between the north indian ocean nio and the western north pacific wnp it is found that the ipco is significantly correlated with simultaneous rainfall over many parts of the southern hemisphere sh including western australia and western brazil these interhemispheric connections in rainfall remain significant when then el nino southern oscillation the indian ocean dipole and the sh annular mode related signals are excluded simultaneously which may help to improve the sh seasonal predictions the physical mechanism that underlies this interhemispheric connection is investigated using observations rossby wave diagnostics and a series of atmospheric model experiments results suggest that convective heating anomalies associated with the ipco excite two distinct southward propagating equivalent barotropic wave trains that propagate into the extratropics in the sh the south africa mid latitudes wave train excited by the heat sink over the nio and the maritime continent subtropical australia wave train excited by the heat source over the wnp we further demonstrate that upper tropospheric northerlies over tropical africa and the indian ocean are responsible for the southward propagation of stationary rossby waves across the easterlies these equivalent barotropic waves then modulate the moisture transport baroclinicity and mid latitude storminess and thus affect rainfall anomalies in the sh the new wave train patterns provide novel insight into the teleconnection pathways of convective heating over the tropical indian ocean and western pacific

mechanisms of meridional teleconnection observed between a summer monsoon system and a subtropical anticyclone part i the pacific japan pattern abstract summertime atmospheric circulation over the midlatitude western north pacific wnp is influenced by anomalous convective activity near the philippines this meridional teleconnection observed in monthly anomalies and known as the pacific japan pj pattern is characterized by zonally elongated cyclonic and anticyclonic anomalies around the enhanced convection center and to its northeast respectively in the lower troposphere with an apparent poleward phase tilt with height the authors idealized two layer linear model whose basic state consists of a zonal subtropical jet and a pair of a monsoon system and a subtropical anticyclone can simulate a pj like response against diabatic heating located between the pair each of the observed and simulated patterns can gain energy through barotropic and baroclinic conversions from the zonally varying baroclinic mean flow in an efficiency comparable with that of energy generation due to the anomalous diabatic heating indicating a characteristic of

impact of the indian ocean sst basin mode on the asian summer monsoon 1 following an el nino event a basin wide warming takes place over the tropical indian ocean peaks in late boreal winter and early spring and persists through boreal summer our observational analysis suggests that this indian ocean warming induces robust climatic anomalies in the summer indo west pacific region prolonging the el nino s influence after tropical east pacific sea surface temperature has returned to normal in response to the indian ocean warming precipitation increases over most of the basin forcing a matsuno gill pattern in the upper troposphere with a strengthened south asian high near the ground the southwest monsoon intensifies over the arabian sea and weakens over the south china and philippine seas an anomalous anticyclonic circulation forms over the subtropical northwest pacific collocated with negative precipitation anomalies all these anomaly patterns are reproduced in a coupled model simulation initialized with a warming in the tropical indian ocean mixed layer indicating that the indian ocean warming is not just a passive response to el nino but important for summer climate variability in the indo west pacific region the implications for seasonal prediction are discussed

turbulent mixing in the amazon river the isotopic memory of confluences rivers continuously discharge dissolved material to the oceans dissolved compounds partially result from water rock interactions which produce a large range of water chemical and isotopic compositions these waters are collected by rivers that are commonly assumed to be well mixed with regard to their different tributaries as a result of turbulent dispersion in this paper we test this hypothesis on the solimoes river at manacapuru the largest tributary of the amazon river by analyzing the sodium concentration and strontium isotopic composition of river water on a transverse section at different depths high precision measurements reveal lateral heterogeneities this reflects poor mixing between two main river masses that have distinct chemical and isotopic signatures a hundred kilometers downstream from their confluence the solimoes mainstream and the purus river using sodium concentration data the transverse dispersion coefficient is estimated for the studied solimoes reach the earth s largest river on which such an estimate now exists and is found to be 1 8 0 2 m2 s comparison with previously reported data highlights the potential role of bed morphology and islands in the efficiency of lateral mixing in large rivers we finally demonstrate that the characteristic length of lateral mixing downstream from confluences in large rivers is at least of several tens of kilometers

what determines the position and intensity of the south atlantic anticyclone in austral winter an agcm study abstract the south atlantic anticyclone is a major feature of the austral winter climatology an atmospheric general circulation model agcm is used to study the dynamics of the south atlantic anticyclone by means of control simulations and experiments to investigate sensitivity to prescribed orography sea surface temperatures and soil wetness the south atlantic anticyclone in the first control simulation is unrealistically zonally elongated and centered too far west errors typical of coupled ocean atmosphere gcms results of the sensitivity experiments suggest that these deficiencies are associated with another family of systematic model errors the overprediction of convection over the tropical land surfaces particularly over eastern tropical africa and india and the concurrent large scale westward shift in the divergence center at upper levels and the convergence center at lower levels the results also confirm the important role of south american and african orography in localizing the south atl

the time frequency characteristics of quarry blasts and calibration explosions recorded in kazakhstan ussr summary in this paper we consider two fundamentally different processes that can be responsible for the organization of energy in seismic coda into discrete time independent frequency bands one process involves the resonance of energy in low velocity horizons and the other requires the interaction of time offset wavefields produced by subevents within multiple event mine explosions ripple fired quarry blasts we examined data collected by high frequency seismometers in kazakhstan ussr and observed regular time independent spectral modulations in coda resulting from events strongly suspected to be soviet quarry blasts but not in the coda from single event calibration explosions detonated at similar ranges we conclude these modulations are a source effect and due to ripple firing this modulation is independent of the source receiver azimuth and we infer that the spatial array of subshots in each event must be small we demonstrate that simple linear superposition theory can be used to reproduce effectively the spectral modulation observed in real quarry blasts on the basis of these observations we attempt to discriminate between the two types of events using a spectral pattern based algorithm that seeks time independent features we consider the detrimental effect that resonant energy in low velocity horizons can have on the successful application of our algorithm

sediment transport and bed morphology at river channel confluences river channel confluences form important morphological elements of every river system being points at which rapid changes in flow sediment discharge and hydraulic geometry must be accommodated this article presents results of a quantitative investigation of sediment transport at channel confluences accomplished through both scaled laboratory flume simulation and complementary monitoring of a natural channel confluence bed morphology at channel confluences is characterized by three distinct elements avalanche faces at the mouth of each confluent channel a deep central scour and a bar within the separation zone formed at the downstream junction corner these elements are controlled predominantly by the confluence angle and the ratio of discharges between the tributary and mainstream channels as confluence angle and discharge ratio increase the sediment contributions from the confluent channels are progressively segregated in their paths through the junction with sediment being transported around rather than through the centre of the confluence this segregation of sediment loads is accompanied by the retreat of the main channel avalanche face from the confluence an increase in the scour depth a change in the orientation of the scour and an increase in the size of the separation zone bar field measurements closely replicate the flume simulation a model of sediment transport and bed morphology links these features to the fluid dynamics of these sites an understanding of confluence dynamics is important not only in considerations of channel morphology and design criteria but must form the basis for the interpretation of confluence sediments in the ancient record

flow and turbulence structure around a spur dike in a channel with a large scour hole 1 the flow and turbulence structure around a vertical wall spur dike that extends over the whole depth of a straight channel are investigated using detached eddy simulation des the channel reynolds number in des and the corresponding experiment is red 2 4 105 which is typical of applications in small rivers and outside the range where well resolved large eddy simulation les can be conducted the bathymetry at equilibrium scour conditions is obtained from a loose bed experiment this paper discusses the main mechanisms which drive the growth of the scour hole upstream and downstream from the spur dike during the later stages of the scour process and how these mechanisms change between the initial flat bed conditions and later stages of the scour process scale effects are investigated by comparing simulation results at red 2 4 105 with those from simulations performed at a much lower reynolds number red 18 000 results show that while the structure of the horseshoe vortex hv system changes with respect to the case in which the bed is flat the main necklace vortex of the hv system is still subject to large scale aperiodic oscillations similar to the ones observed in flows past in stream bluff body obstacles mounted on a flat surface present results show that the amplification of the horizontal vorticity within the lower part of the separated shear layer ssl and the associated formation of streaks of high bed shear stress below the region where the ssl eddies are convected in the near bed region is a general feature of high reynolds number flow past a vertical wall spur dike placed in a loose bed channel at all stages of the scour process

atmospheric circulation cells associated with the el nino southern oscillation abstract atmospheric circulation cells associated with the el nino southern oscillation enso are described and examined using the ncep ncar reanalysis field and the ncep sea surface temperature sst from january 1950 to december 1999 the divergent wind and pressure vertical velocity are employed for the identification of atmospheric circulation cells the warm phase of enso shows positive sst anomalies in the equatorial eastern pacific and along the east coast of asia and the west coast of north america and negative sst anomalies in the off equatorial western pacific and in the central north pacific associated with this sst anomaly distribution are variations of atmospheric zonal and meridional circulation cells over the pacific the equatorial zonal walker circulation cell is weakened consistent with previous schematic diagrams the anomalous meridional hadley circulation cell in the eastern pacific shows the air rising in the tropics flowing poleward in the upper troposphere sinking in the subt