mean flow and variability in the kuroshio extension from geosat altimetry data using altimeter data from the geosat exact repeat mission erm we investigated the mean flow and temporal and spatial variations of the kuroshio extension in the region of 140 180 e and 30 40 n mean surface height profiles were estimated along individual tracks by assuming the velocity profile of the kuroshio extension to be gaussian shaped and by successively fitting this synthetic current s height profile to the residual height data using the mean profiles from ascending and descending tracks we derived the mean surface height field by an inverse method and obtained the absolute surface height fields for the first 2 5 years of the geosat erm both the mean and the instantaneous height fields thus derived compared well with the available hydrographic data and the sst patterns from the noaa satellites the mean surface height difference across the kuroshio extension attains its maximum around 146 e between the two quasi stationary meanders and its decrease thereafter is mainly due to large scale recirculations on the southern side of the kuroshio extension the ratio of the eddy kinetic energy over the mean kinetic energy has a nearly constant value of 1 5 2 0 along the kuroshio extension path propagation of mesoscale fluctuations in the height fields is generally westward except for the upstream region of the kuroshio extension effects of deep mean flow and baroclinic shear are found to be important in explaining the observed propagation speeds in the upstream region of 141 e and 154 e annual variations in the surface height difference across the kuroshio extension h have a september maximum with an average amplitude of 0 2m for large scale interannual fluctuations anomalies in h are found to be significantly correlated with those of the current axis positions a larger surface height difference corresponds to a more northerly position of the kuroshio extension the interannual changes in h are possibly related to the 86 87 enso event in the low latitude pacific ocean

sting jets in simulations of a real cyclone by two mesoscale models the existence of sting jets as a potential source of damaging surface winds during the passage of extratropical cyclones has recently been recognized however there are still very few published studies on the subject furthermore although it is known that other models are capable of reproducing sting jets in the published literature only one numerical model the met office unified model metum has been used to numerically analyze these phenomena this article aims to improve our understanding of the processes that contribute to the development of sting jets and show that model differences affect the evolution of modeled sting jets a sting jet event during the passage of a cyclone over the united kingdom on 26 february 2002 has been simulated using two mesoscale models namely the metum and the consortium for small scale modeling cosmo model to compare their performance given the known critical importance of vertical resolution in the simulation of sting jets the vertical resolution of both models has been enhanced with respect to their operational versions both simulations have been verified against surface measurements of maximum gusts satellite imagery and met office operational synoptic analyses as well as operational analyses from the ecmwf it is shown that both models are capable of reproducing sting jets with similar though not identical features through the comparison of the results from these two models the relevance of physical mechanisms such as evaporative cooling and the release of conditional symmetric instability in the generation and evolution of sting jets is also discussed

the turbulent kinetic energy budget for shallow cumulus convection turbulence kinetic energy tke budgets derived from large eddy simulations of the cumulus capped boundary layer are analysed using recently developed similarity ideas the budgets for the main part of the cumulus layer and the overlying inversion and the cloud base transition zone are considered separately the terms in the budget can be scaled using the similarity theory developed by grant and brown 1999 below the inversion tke is produced by buoyancy with the transport of tke representing a loss of tke in the inversion layer the transport of tke from the underlying cloud layer is the dominant production term although negatively buoyant downdraughts are present in the upper part of the inversion and contribute to the production of tke the terms in the tke budget in the transition zone between the subcloud and cloud layers scale with mixed layer scales but for the buoyancy production term there is a region in which both mixed layer and cloud layer scalings are valid using the mass flux approximation in conjunction with the scaling results it is shown that it is possible to obtain a parametrization of the cumulus mass flux profile

elastic finite difference modeling of the 1971 san fernando california earthquake finite difference seismograms calculated for the 1971 san fernando earthquake show strong effects due to lateral variation in sediment thickness in the san fernando valley and the los angeles basin using basin structure derived mostly from well logs and teleseismically determined source parameters two dimensional sh and p sv finite difference calculations reproduce the amplitude and duration of the strong motion velocities recorded across the los angeles and san fernando basins for the period range of 2 to 10 sec the edges of basins nearest the seismic source show ground motion amplification up to a factor of 3 over the case without the basin and tend to convert direct shear waves into love and rayleigh waves that travel within the basins

simulation of long period ground motion in the osaka sedimentary basin performance estimation and the basin structure effects summary we assessed the applicability of the 3 d subsurface velocity structure model of the osaka sedimentary basin in western japan for simulations of long period ground motion 3 20 s based on two types of long period ground motion characteristics 1 strong ground motion from a specific earthquake and 2 site specific event independent horizontal to vertical spectral ratio hv characteristics obtained from earthquakes with various azimuths for the first type we compared the observed and synthetic ground motions in terms of velocity waveforms and pseudo velocity response spectra we then proposed an objective index to evaluate the goodness of fit from one site to the next the simulation satisfactorily reproduced the observed ground motion at many stations however the model needs improvement for reproducing the ground motion at some stations for the second type we first demonstrated that site specific hv characteristics can be obtained from the coda portion of strong motion observation records for earthquakes with various azimuths we then demonstrated that the hvs obtained from 3 d ground motion simulations for earthquakes with various azimuths 3dhv also have sitespecific stable values the synthetic 3dhv was compared with the observed hv and the 3 d basin velocity structure model was demonstrated as able to reproduce the hv peak periods within 1 s at many stations however at some stations the peak periods of the 3dhv were systematically longer than those of the observed hv by more than 1 5 s which corresponded to the stations of poor goodness of fit scores in the ground motion simulation 3dhv was also compared with the theoretical ellipticity of the fundamental rayleigh wave 1dhv the peak periods of 3dhv and 1dhv were inconsistent with each other at some sites which implies that 3dhv is affected by the lateral heterogeneity of the structure around the site we found the systematically biased characteristics of the discrepancy in 3dhv and 1dhv peaks in specific regions the spatial extent of the area that affects 3dhv is related to the complexity in the bedrock structure and the dominant period of 3dhv

a convection permitting model for the lake victoria basin evaluation and insight into the mesoscale versus synoptic atmospheric dynamics aiming for an improved understanding of the different factors that determine the regional climate of the lake victoria basin the cosmo clm regional climate model is set up in a tropical convection permitting configuration and is directly nested in a recent reanalysis product era5 the convection permitting simulation outperforms state of the art climate integrations that rely on convection parametrisations yet the domain averaged model precipitation is larger than in the multi observational ensemble but the latter shows large spread overestimations of outgoing toa shortwave and longwave radiation are much reduced compared to the cosmo clm cordex africa integration but still suggest a general underestimation of the cloud fraction or frequency comparing the control with a no lake simulation the presence of lake victoria implies strong intensification of over lake rainfall but it only slightly increases the total domain averaged precipitation in addition the easterly trade winds are shown to largely affect the mesoscale circulation and precipitation patterns during daytime fast trades and anabatic slope winds trigger convection at the lee wind slopes and subsidence over the basin slow trades allow the stationary air to produce spontaneous convective cells and to develop anabatic winds that result in orographic precipitation during night time trade winds curl around the eastern branch of the east african rift generating a southerly and northerly evening convergence front entering the lake victoria basin thus our results highlight the key importance of the easterly trade winds and the complex orography in determining the total accumulation and location of precipitation in the lake victoria region

three dimensional simulations of ground motions in the san bernardino valley california for hypothetical earthquakes on the san andreas fault three dimensional finite difference simulations of elastic waves in the san bernardino valley were performed for two hypothetical earthquakes on the san andreas fault a point source with moment magnitude m5 and an extended rupture with m6 5 a method is presented for incorporating a source with arbitrary focal mechanism in the grid synthetics from the 3 d simulations are compared with those derived from 2 d vertical cross section and 1 d flat layered models the synthetic seismograms from the 3 d and 2 d simulations exhibit large surface waves produced by conversion of incident s waves at the edge of the basin seismograms from the flat layered model do not contain these converted surface waves and underestimate the duration of shaking the seismograms from the 3 d simulations have larger amplitude coda than do the seismograms from the 2 d case because of the presence of off azimuth surface wave arrivals in the 3 d simulations that are not included in the 2 d simulations snapshots of the wavefield of the 3 d simulation show that these off azimuth arrivals represent surface waves reflected from the edges of the basin the anelastic attenuation of the sediments is a key parameter controlling the overall duration of motion some of the coda energy at rock sites near the basin edges represents leakage of surface wave energy out of the basin for the m6 5 earthquake simulation the largest ground velocities occur where surface waves reflected from the edge of the basin interfere constructively with the trapped waves that follow the direct s wave maps of maximum ground velocity are produced for two directions of rupture propagation the largest velocities occur in localized portions of the basin the location of the largest velocities changes with the rupture propagation direction contours of maximum shaking are also dependent on asperity positions and radiation pattern

site amplification in the los angeles basin from three dimensional modeling of ground motion it is well established that sedimentary basins can significantly amplify earthquake ground motion however the amplification at any given site can vary with earthquake location to account for basin response in probabilistic seismic hazard analysis therefore we need to know the average amplification and intrinsic variability standard deviation at each site given all earthquakes of concern in the region due to a dearth of empirical ground motion observations theoretical simu lations constitute our best hope of addressing this issue here 0 0 5 hz finite difference finite fault simulations are used to estimate the three dimensional 3d response of the los angeles basin to nine different earthquake scenarios amplifi cation is quantified as the peak velocity obtained from the 3d simulation divided by that predicted using a regional one dimensional 1d crustal model average ampli fication factors are up to a factor of 4 with the values from individual scenarios typically differing by as much as a factor of 2 5 the average amplification correlates with basin depth with values near unity at sites above sediments with thickness less than 2 km and up to factors near 6 above the deepest 9 km and steepest dipping parts of the basin there is also some indication that amplification factors are greater for events located farther from the basin edge if the 3d amplification factors are divided by the 1d vertical sh wave amplification below each site they are lowered by up to a factor of 1 7 the duration of shaking in the 3d model is found to be longer by up to more than 60 seconds relative to the 1d basin response the simu lation of the 1994 northridge earthquake reproduces recorded 0 0 5 hz particle velocities relatively well in particular at near source stations the synthetic and observed peak velocities agree within a factor of two and the log standard deviation of the residuals is 0 36 this is a reduction of 54 and 51 compared to the values obtained for the regional 1d model and a 1d model defined by the velocity and density profile below a site in the middle of the basin dow respectively this result suggests that long period ground motion estimation can be improved consid erably by including the 3d basin structure however there are uncertainties con cerning accuracy of the basin model model resolution the omission of material with shear velocities lower than 1 km s and the fact that only nine scenarios have been considered therefore the amplification factors reported here should be used with caution until they can be further tested against observations however the results do serve as a guide to what should be expected particularly with respect to increased amplification factors at sites located above the deeper parts of the basin

mesoscale air motions associated with a tropical squall line abstract composites of radar and wind observations in a coordinate system attached to a moving tropical squall line confirm that such a squall system is composed of two separate circulation features a convective squall line region and a stratiform anvil region the squall line region is characterized by mesoscale boundary layer convergence which feeds deep convective updrafts and mid to upper level divergence associated with outflow from the cells the anvil region is characterized by mid level convergence which feeds both a mesoscale downdraft below the anvil and a mesoscale updraft within the anvil cloud before this study the mesoscale updraft in the anvil cloud of the tropical squall system had been somewhat speculative and both the anvil updraft and downdraft had been inferred only qualitatively the occurrence of the anvil updraft is now proven and quantitative profiles of the mesoscale anvil updraft and downdraft have been obtained

source complexity of the october 1 1987 whittier narrows earthquake long and short period body waveform data recorded at regional and teleseismic distances are modeled to obtain the source parameters of the whittier narrows earthquake of october 1 1987 although the long period data can be satisfied by a simple thrust earthquake on a plane striking 280 at a depth of 14 km we require a double source solution to satisfy both the long and short period teleseismic data the first subevent has a focal mechanism of strike 250 dip 30 n and a slip vector 90 the second is 280 40 n and 98 the second event occurred 1 0 s after the first was 5 times larger 1 2 1025 dyn cm for the second 0 23 1025 for the first in terms of seismic moment and was also shallower 12 km whereas the first subevent was at 15 km the two subevents probably occurred on a north dipping listric fault but may have occurred on two subparallel faults these features were determined by studying a variety of phases including teleseismic p and sh and regional pnl the whittier narrows earthquake was a high stress drop event but a single value for stress drop cannot be obtained because of the complex nature of the source if we define the fault area as the aftershock area we obtain a stress drop of about 750 bars

large scale atmospheric forcing by southeast pacific boundary layer clouds a regional model study abstract a regional model is used to study the radiative effect of boundary layer clouds over the southeast pacific on large scale atmosphere circulation during august october 1999 with the standard settings the model simulates reasonably well the large scale circulation over the eastern pacific precipitation in the intertropical convergence zone itcz north of the equator and marine boundary layer stratocumulus clouds to the south in a sensitivity experiment with the radiative effect of liquid clouds south of the equator over the eastern pacific artificially removed boundary layer clouds south of the equator almost disappear and precipitation in the itcz is reduced by 15 20 indicating that the stratocumulus clouds over the southeast pacific have both local and cross equatorial effects examination of the differences between the control and sensitivity experiments indicates that clouds exert a net diabatic cooling in the inversion layer in response to this cloud induced cooling an in situ anom

why the western pacific subtropical high has extended westward since the late 1970s the western pacific subtropical high wpsh is closely related to asian climate previous examination of changes in the wpsh found a westward extension since the late 1970s which has contributed to the inter decadal transition of east asian climate the reason for the westward extension is unknown however the present study suggests that this significant change of wpsh is partly due to the atmosphere s response to the observed indian ocean western pacific iwp warming coordinated by a european union s sixth framework programme understanding the dynamics of the coupled climate system dynamite five agcms were forced by identical idealized sea surface temperature patterns representative of the iwp warming and cooling the results of these numerical experiments suggest that the negative heating in the central and eastern tropical pacific and increased convective heating in the equatorial indian ocean maritime continent associated with iwp warming are in favor of the westward extension of wpsh the sst changes in iwp influences the walker circulation with a subsequent reduction of convections in the tropical central and eastern pacific which then forces an enso gill type response that modulates the wpsh the monsoon diabatic heating mechanism proposed by rodwell and hoskins plays a secondary reinforcing role in the westward extension of wpsh the low level equatorial flank of wpsh is interpreted as a kelvin response to monsoon condensational heating while the intensified poleward flow along the western flank of wpsh is in accord with sverdrup vorticity balance the iwp warming has led to an expansion of the south asian high in the upper troposphere as seen in the reanalysis

a shallow convection parameterization for mesoscale models part ii verification and sensitivity studies abstract formulations describing a new shallow convection parameterization intended for mesoscale models have been described in a companion paper part i in the present paper the convection scheme is tested and evaluated against observed datasets in both marine and continental environments additional experiments explore the sensitivity of the scheme to changes in model vertical resolution key parameters of the closure and the cloud dissipation mechanisms the new shallow convection scheme uses a hybrid mass flux closure that adjusts linearly between two closure options based on i boundary layer turbulent kinetic energy tke for very shallow clouds and ii convective available potential energy cape for deep clouds meanwhile cloud mass detrained from convective updrafts acts as the source for a second class of subgrid clouds having nearly neutral buoyancy which can persist for hours performance of the convection submodel is found to be quite reasonable in four cases covering a range of conditi

statistics of cold cumulonimbus anvils based on enhanced infrared photographs infrared photographs from the atlantic geosynchronous satellite enhanced to resolve cold anvil temperatures of tropical clouds are analyzed statistically to determine their spatial temporal variability during the nasa u2 flight experiment of 1980 diurnal dependence varies regionally indicating topographic control via low level convergence and release of convective instability anvil growth rates area covered and duration are discussed for individual and merging anvil systems gradients of anvil temperatures implied by infrared photographs are shown to be caused in part by radial decrease in anvil depth i e to emissivities less than 1 an error in cloud top temperature of 10c is caused by 10 reduction in emissivity errors are near zero in dense actively growing portions of the anvil

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

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

the relationship of surface pressure features to the precipitation and airflow structure of an intense midlatitude squall line abstract observations from the oklahoma kansas preliminary regional experiment for storm central ok pre storm have been used to document the surface pressure features accompanying an intense midlatitude squall line with trailing stratiform precipitation three well known features are observed a pre squall mesolow a squall mesohigh and a wake low particular attention is given to the wake low its life cycle and association with the trailing stratiform portion of the squall line during the formative stage the pressure field to the rear of the squall line mesohigh is relatively flat with only weak stratiform precipitation present as the squall line enters the developing to mature stages a pronounced wake low appears at the back edge of the surface stratiform precipitation area the squall line at this time is characterized by a strong rear inflow jet descending from the upper troposphere as far as 500 km behind the leading convective line to the lower troposphere just behind the line the trailin

transport in the low latitude tropopause zone diagnosed using particle trajectories abstract recent literature has described a transition zone between the average top of deep convection in the tropics and the stratosphere here transport across this zone is investigated using an offline trajectory model particles were advected by the resolved winds from the european centre for medium range weather forecasts reanalyses for each boreal winter clusters of particles were released in the upper troposphere over the four main regions of tropical deep convection indonesia central pacific south america and africa most particles remain in the troposphere descending on average for every cluster the horizontal components of 5 day trajectories are strongly influenced by the el nino southern oscillation enso but the lagrangian average descent does not have a clear enso signature tropopause crossing locations are first identified by recording events when trajectories from the same release regions cross the world meteorological organization lapse rate tropopause most crossing events occ

simulations of strong ground motion and 3d amplification effect in the taipei basin by using a composite grid finite difference method we perform full elastic wave field simulations within the taipei basin by using a three dimensional 3d discontinuous finite difference method the 3d taipei basin model is determined from a seismic reflection study two major subsurfaces the songshan formation surface soil layer and the basin basement are constituted in the model a parallel based composite grid technique a containing scalene grid and a discontinuous grid is developed in this study to deal with the possible numerical prob lem of thin depth and low velocity of the songshan formation taking advantage of the composite grid the resolution of the subsurface structure can be reached to 20 m and a higher frequency up to 3 hz of the synthetic waveform can be achieved in our strong ground motion simulations we assume a constant velocity in each subsurface three different types of models are considered in the study the songshan formation with a basement structure model a basin basement model and a layered half space model results indicate that only the model with both the songshan formation and the basement structure can produce the apparent basin amplification effects first the surface wave generated after the primary s wave is trapped at the shallow part of the basin then when the wave propagates through the deepest part of the basin most of the energy is reflected from the boundary and focused back into the basin in addi tion part of the seismic wavefront turns and follows the shallow basin edge resulting in further amplification our study indicates that the complex taipei basin geometry and fairly low velocity of the songshan formation dominate the amplification and wave propagation behavior that result in extraordinary strong shaking patterns in the taipei metropolitan region

three dimensional finite difference simulations of long period strong motions in the tokyo metropolitan area during the 1990 odawara earthquake mj 5 1 and the great 1923 kanto earthquake ms 8 2 in japan utilizing a crustal velocity model that includes the complexity of the irregular subsurface structure of the kanto basin we have performed three dimensional 3d finite difference fd simulations of near source long period strong ground motions in the tokyo metropolitan area for the 1990 odawara mj 5 1 and the 1923 kanto ms 8 2 earthquakes constraints on the development of the 3d velocity model come from available geological and geophysical data as well as our previous 1d waveform modeling results sato et al 1998a the simulation of the moderate sized odawara earthquake demonstrates that the 3d velocity model works quite well at reproducing the recorded long period t 3 33 sec strong motions including basin generated surface waves for a number of sites located throughout the kanto basin region using this validated 3d model along with the variable slip rupture model of wald and somerville 1995 we then simulate the long period t 4 sec ground motions in this region for the 1923 kanto earthquake the simulation results for the 1923 event show that the largest ground motions occur east of the epicenter along the central and southern part of the boso peninsula these large motions arise from strong rupture directivity effects and are comprised of relatively simple source controlled pulses with a dominant period of about 10 sec north of the epicentral region in the tokyo area 3d basin generated phases are quite significant and these phases produce large amplitude late arriving pulses in the ground motions at station hongo hng which is the only site having digitized and restored near fault strong motion records for this event our 3d simulations compare quite well with the ground motions of the restored imamura seismogram for the restored ewing record our 3d simulations reproduce the phase and amplitude of the initial pulses of motion however the dominant period of the large amplitude later phases is noticeably shorter in the simulations about 5 to 6 sec than in the observation 13 sec these results suggest that the restored imamura seismogram may be a better representation of the gross features of the actual motion than the restored ewing seismogram although the first clipped and restored part of the imamura seismogram may still underestimate the strength of the actual motion

reproduction of microseism h v spectral features using a three dimensional complex topographical model of the sediment bedrock interface in the osaka sedimentary basin summary estimating the velocity structure of microseisms based on the horizontal to vertical spectral ratio hvsr is an extremely practical means of modelling the subsurface structure necessary for strong ground motion predictions thus beyond the traditional framework of the 1 d velocity structure the hvsr derived from observation records of microseisms microtremors with a frequency of about 1 hz or lower originating from ocean waves in areas where the sediment bedrock interface has irregular topographies was reproduced by finite differential method fdm based simulation this study was conducted for the osaka sedimentary basin the sediment bedrock interface of which is three dimensionally complicated and contains grabens steps and ramps because high precision models for this basin have been constructed based on a wide range of existing exploration information the hvsrs of two components the east west direction and the north south direction to the vertical direction derived from the fdm simulations were both well reproduced in terms of not only the peak frequency hvfp but also the spectral curves for a number of observation sites above the sediment bedrock interface with complex geological features these results suggest that with a sufficient number of observation sites for microtremors and highly accurate a priori information on geophysical constants in the sedimentary layer that spatially serves as the reference the irregular shaped sediment bedrock interface may be estimated based on how well the hvsr curves and the hvfp agree between the observations and simulations furthermore the fdm simulations confirmed observed phenomena such as the polarization of the amplitude of horizontal motions and broad or plateau like hvsr peaks of microseisms in grabens and step structures it was determined that the hvfps in areas with these strong irregularities are higher than the peak frequency of rayleigh wave ellipticity for the fundamental mode rhvfp based on the 1 d velocity structure in addition there was a difference of about 20 per cent at most between the hvfp derived from fdm simulations and the rhvfp in areas where the depth of the sediment bedrock interface varies only slightly

excitation of secondary love and rayleigh waves in a three dimensional sedimentary basin evaluated by the direct boundary element method with normal modes summary this paper aims to present a new method to calculate surface waves in 3 d sedimentary basin models based on the direct boundary element method bem with vertical boundaries and normal modes and to evaluate the excitation of secondary surface waves observed remarkably in basins many authors have so far developed numerical techniques to calculate the total 3 d wavefield however the calculation of the total wavefield does not match our purpose because the secondary surface waves excited on the basin boundaries will be contaminated by other undesirable waves in this paper we prove that in principle it is possible to extract surface waves excited on part of the basin boundaries from the total 3 d wavefield with a formulation that uses the reflection and transmission operators defined in the space domain in realizing this extraction in the bem algorithm we encounter the problem arising from the lateral and vertical truncations of boundary surfaces extending infinitely in the half space to compensate the truncations we first introduce an approximate algorithm using 2 5 d and 1 d wavefields for reference media where a 2 5 d wavefield means a 3 d wavefield with a 2 d subsurface structure and we then demonstrate the extraction finally we calculate the secondary surface waves excited on the arc shape horizontal section of a vertical basin boundary subject to incident sh and sv plane waves propagating perpendicularly to the chord of the arc as a result we find that in the sh incident case the love waves are predominantly excited rather than the rayleigh waves and that in the sv wave incident case the love waves as well as the rayleigh waves are excited this suggests that the love waves are more detectable than the rayleigh waves in the horizontal components of observed recordings

structure of the annual mean equatorial planetary waves in the era 40 reanalyses abstract the three dimensional structure of the annual mean equatorial planetary waves in the 40 yr ecmwf re analysis era 40 is documented the features in the free atmosphere are predominantly equatorially symmetric driven by east west heating gradients the geopotential height and wind perturbations are strongest at or just below the 150 hpa level below the level of maximum amplitude the circulations in the waves are thermally direct with latent heat release in deep convective clouds and radiative cooling in the intervening cloud free regions within the overlying capping layer the wave related circulations are thermally indirect with rising of the coldest air and sinking of air that is less cold at the cold point just above the 100 hpa 17 km level the era 40 annual mean vertical velocity in the equatorial belt ranges up to 3 mm s 1 over the equatorial western pacific during the boreal winter implying diabatic heating rates of up to 3 c day 1 an order of magnitude larger than typical clear

variability of the wind stress curl over the north pacific implications for the oceanic response the subinertial frequency wavenumber structure and spatial coherence of wind stress curl and their spatial and temporal variability are described with the emphasis on characteristics which affect the ocean s response to the wind stress curl forcing function wind stress curl over the north pacific between 25 o and 60on was computed for 3 years 1985 1988 from the fleet numerical oceanography center wind product the range from winter peak to summer trough for the mean and variance are typically a factor of 3 4 and 10 respectively with superimposed interannual changes of up to a factor of 2 power spectra vary seasonally and interannually in an essentially frequency independent manner that is consistent with the curl variance however the spectrum over the period band 5 100 days often fails a statistical test for whiteness at the 95 level zonal and meridional wavenumber spectra were estimated for 13 sites distributed around the central eastern north pacific using the maximum likelihood method directional trends with frequency are comparable to those from earlier studies if 3 year long data segments are analyzed with approximate wavenumber symmetry except for the zonal term at mid latitudes for periods shorter than 10 days where eastward propagation is dominant however spectra for shorter data sections sometimes display eastward and westward excursions which are only weakly similar over distances of 1000 km and essentially dissimilar over longer separations the spatial correlation structure of wind stress curl is shown typically to have a main lobe of 1000 km and multiple intercorrelation lobes separated by 2000 km the strength and location of the intercorrelation peaks vary slowly with time these results suggest that curl behavior is more complex than was previously believed that the use of long term averages of or simple parameterizations for the frequency wavenumber spectrum of wind stress curl in model studies may be unrealistic and that more attention to actual curl characteristics at the time oceanic measurements are collected will be required to reconcile models with observations

elastic finite difference modeling of strong motion in ashigara valley for the 1990 odawara japan earthquake abstract finite difference seismograms are calculated for the 1990 odawara earthquake to model transverse and radial components of strong motion data using a basin structure derived from a geotechnical survey and double couple solution determined from p first motion data and sh sv amplitude ratio two dimensional sh and p sv finite difference calculation along with correction for soft surface layers reproduces the observed spatial variation in amplitude and waveform of the transverse and radial records at the ashigara valley blind prediction sites for frequencies up to 2 hz comparison of the synthetic and the observed seismograms suggests that the observed spatial variation in the sh amplitude is attributed to the source radiation and amplification due to the soft surface layers while the sv amplitude variation is controlled by the amplification due to the sedimentary basin as well as the source and surface layer effects

variations of zonal currents in the central tropical pacific during 1970 to 1987 sea level and dynamic height measurements the annual and interannual variations of the major zonal currents of the central tropical pacific for the period 1970 1987 are described by analyzing two data sets sea level data from a few selected island stations and ship of opportunity expendable bathythermograph xbt observations the annual cycles of geostrophic surface current indices dynamic height or sea level difference between the ridge and the trough defining the current in the north equatorial current nec and north equatorial countercurrent necc are found to be in phase maxima in november to be strong and to explain about 50 of the total variance the annual cycle of volume transport relative to 400 dbar in the necc is also strong but nec volume transport has a weak annual cycle the discrepancy between the nec surface current and the transport is due to the variation of the surface current being larger than that of the deep currents the annual cycle of the transport of the south equatorial current sec is 6 months out of phase with that of the nec and necc phases of the annual cycles of the sea level and dynamic height indices of flow agree well in general but there are significant differences between the annual amplitudes of the two types of measurements these differences arise from a variety of sources dynamic height reference level assumptions longitudinal spacing of sea level gauges meridional resolution of sea level array and different signal to noise ratios for the two sets of indices the necc shows marked flow maxima during the peaks of the strong ninos of 1972 and 1982 which were followed by near disappearance of the current the following year these fluctuations are clearly present in both the surface current indices and the volume transport in 1976 and 1986 1987 moderate ninos the same pattern is not marked the el nino signal in nec transport is weak there was a strong rise of equatorial sea level during the early phases of the 1972 and 1982 ninos followed by a fall the next year this resulted in a decrease of the transport of the sec in the first year followed by an increase to a maximum during the second year the maximum coincides with a minimum in necc transport

variability in the central equatorial pacific 1985 1989 we describe variability in the equatorial pacific ocean near 160 w during the 5 year period 1985 1989 encompassing normal el nino and la nina conditions this description is based on conductivity temperature depth and acoustic doppler current profiler data acquired during five cruises between 21 n and 4 s and on dynamic height time series from an array based mainly on the line islands at jarvis island near the equator the time series of dynamic height and near surface temperature go back to 1981 and show the 1986 1987 el nino anomalies starting later in the year and having longer duration than those of the 1982 1983 el nino dynamic height anomaly was less strong for the 1986 1987 event but the near surface temperature anomaly was of similar magnitude for the two el ninos the jarvis near surface temperature drop from 1986 1987 el nino maximum to 1988 1989 la nina minimum was 8 c empirical orthogonal function analysis of the time series shows that interannual and interseasonal variability in dynamic height was dominated by a mode with meridional form similar to a first vertical mode kelvin wave while intraseasonal variability had a primary mode with a single peak at 6 n and a secondary mode with peak at 6 n and trough at 2 n while the equatorial thermocline deepened to the east and shoaled to the west during the 1986 1987 el nino at 160 w it did not change depth during either this el nino or the subsequent la nina nevertheless just before el nino and just after la nina the thermocline was observed to be about 50 m deeper than at other times the south equatorial current and north equatorial countercurrent had markedly reduced increased transports during this el nino la nina however the northern tsuchiya jet strengthened during el nino and weakened during la nina

three dimensional simulation of a magnitude 7 75 earthquake on the san andreas fault simulation of 2 minutes of long period ground motion in the los angeles area with the use of a three dimensional finite difference method on a parallel supercomputer provides an estimate of the seismic hazard from a magnitude 7 75 earthquake along the 170 kilometer section of the san andreas fault between tejon pass and san bernardino maximum ground velocities are predicted to occur near the fault 2 5 meters per second and in the los angeles basin 1 4 meters per second where large amplitude surface waves prolong shaking for more than 60 seconds simulated spectral amplitudes for some regions within the los angeles basin are up to 10 times larger than those at sites outside the basin at similar distances from the san andreas fault

three dimensional modeling of near fault ground motions with nonplanar rupture models and topography case of the 2004 parkfield earthquake 1 we study the applicability of deterministic strong ground motion simulations at very near fault distances for a subvertical strike slip fault model corresponding to the 2004 m6 parkfield california earthquake in the frequency range up to 1 hz theoretical modeling under the assumptions of a planar rupture and 1 d medium shows that as a consequence of the s wave radiation pattern the particle motion for such close stations should be almost linear in the fault normal fn direction having fault parallel fp and vertical v components of almost zero however as shown on the parkfield earthquake recordings observed particle motions are rather circular with peak velocities at fp and v components comparable to those at fn components we investigate several realistic features that could explain this controversy namely nonplanar fault realistic three dimensional 3 d medium and the topography of the area we test and quantify these hypotheses using discrete wave number and discontinuous galerkin modeling methods applying 1 d and 3 d velocity structures respectively and two nonplanar rupture models we compare the synthetic and observed particle motions and peak velocity ratios and conclude that deviations from a planar rupture geometry in reasonable bounds for the parkfield fault and the influence of topography only partially explain the behavior of the observed seismograms on the contrary the heterogeneous 3 d velocity structure significantly reduces the synthetic peak ratios to values closer to 1 and provides rather circular particle motions therefore the 3 d velocity model is crucial to obtain realistic estimates of ground motions at near fault distances and is more important than the detailed fault geometry or topography in the parkfield area

further analysis of the composite wind and thermodynamic structure of the 12 september gate squall line abstract an objective analysis technique is applied to the time composite wind and thermodynamic fields of the 12 september gate tropical squall line previous subjective analyses described by gamache and houze are confirmed and several new results are obtained in the previous analyses mesoscale upward motion was found in the upper troposphere of the stratiform precipitation region immediately trailing the squall line mesoscale downward motion was found in the lower troposphere of the stratiform region the convective clouds were found to be the source of condensate for more than half of the stratiform precipitation but mesoscale updraft condensation was also found to be substantial in these previous studies thermodynamic structure was not analyzed the wind analyses were limited by the number of levels included and vorticity was not analyzed by employing an objective analysis method in the present study we have refined and extended the previous work by including more levels computing vorticity a

broadband ground motion simulation within the city of duzce turkey and building response simulation in areas with significant seismic activity and insufficient seismic networks simulated ground motions are required for both seismic hazard and engineering analyses one important task is evaluating the efficiency of the simulated records in building response estimation in this study a hybrid ground motion simulation framework is presented to obtain broadband ground motion time histories of a past major earthquake in duzce turkey the hybrid ground motion simulation framework presented herein is a combination of a discrete wavenumber finite element method for simulating low frequencies and a stochastic finite fault method for the higher frequencies the proposed technique is first validated by the simulation of the 12 november 1999 duzce earthquake m text w 7 1 which occurred in the north anatolian fault zone turkey peak simulated ground motions at selected nodes are then compared against ground motion prediction equations derived with global and local data sets next the spatial distribution of simulated peak ground motion intensities are obtained in the region and compared with the observed damage distribution results demonstrate that the earthquake is simulated effectively despite the limitations in number of stations and velocity models finally to evaluate the simulated records in building response estimation nonlinear time history analyses of three reinforced concrete multi degree of freedom structures are performed with real and simulated records of the 1999 duzce earthquake in the opensees platform the results reveal that reasonable predictions can be made regarding the dynamic response of structures using the records simulated with the approach presented herein

secondary cyclogenesis along an occluded front leading to damaging wind gusts windstorm kyrill january 2007 abstractwindstorm kyrill affected large parts of europe in january 2007 and caused widespread havoc and loss of life in this study the formation of a secondary cyclone kyrill ii along the occluded front of the mature cyclone kyrill and the occurrence of severe wind gusts as kyrill ii passed over germany are investigated with the help of high resolution regional climate model simulations kyrill underwent an explosive cyclogenesis south of greenland as the storm crossed poleward of an intense upper level jet stream later in its life cycle secondary cyclogenesis occurred just west of the british isles the formation of kyrill ii along the occluded front was associated i with frontolytic strain and ii with strong diabatic heating in combination with a developing upper level shortwave trough sensitivity studies with reduced latent heat release feature a similar development but a weaker secondary cyclone revealing the importance of diabatic processes during the formation of kyrill ii kyrill ii moved

experimental study of site effects in the fort de france area martinique island abstract we used weak motion recordings of regional events to quantify the site effects in the fort de france martinique area in the frequency band 1 to 25 hz the studied area extends over three distinct geological units the morne pitault volcanic massif 15 to 11 m a the carbet volcanic massif 4 to 2 m a and the lamentin alluvial plain quaternary age the topography being complex 31 sites were selected in order to get a representative sampling of the various topographical and geological configurations the large number of studied sites also allowed us to define a reference site whose selection was not obvious large broadband amplifications are observed in the lamentin plain instead of the expected peak resonances more surprising such resonance is observed around 2 to 3 hz on several sites of the volcanic vauclain pitault chain though no sedimentary layer is present on the other hand in the inner fort de france where significant effects were expected because of the very complex topography no large amplication is observed except for at one site clear three dimensional 3d effects are also observed at some stations though not very well documented the low frequency behavior deduced from teleseismic observations seems rather different illustrating the difficulty in finding a convenient reference site in such a volcanic area

seasonality and interannual variability of particle fluxes to the deep bay of bengal influence of riverine input and oceanographic processes abstract results from sediment trap experiments conducted from october 1987 until november 1997 in the deep northern central and southern bay of bengal northern indian ocean revealed significant monsoon induced seasonal and interannual variations in total and component fluxes distinct regional differences occurred related to the variable effect of terrestrial input and the development of relatively small scaled oceanographic processes the enormous fluvial input to the bay during swm is reflected in the high average content of lithogenic matter between 39 at the northernmost and 12 6 at the most distal sampling site in the southern bay of bengal generally the riverine input supports a relative increase in the fluxes of biogenic opal at the stations nearest to the continent nbbt n cbbt terrestrial inputs determine seasonal and interannual variabilities lateral supply of lithogenic matter from the shelf regions lead to distinct increase of fluxes with depth high flux events of 300 mg m 2 d 1 consisting of 50 lithogenics occur in the central bay of bengal during nem and in the northern bay of bengal during swm in response to resuspension of shelf sediments and severe floods when riverine input by ganges brahmaputra and the offshore propagation of the river plume during swm is reduced the advection from an upwelling area along the east coast of india during ne sw intermonsoon becomes the most prominent control mechanism for both biogenic and lithogenic fluxes at nbbt n in the central bay of bengal cbbt fluxes are characterized by a bimodal pattern high carbonate dominated fluxes during swm and nem occur mainly due to wind induced nutrient supply whereas high opal rich fluxes during sw ne intermonsoon are controlled by both upwelling as well as supply of riverine and shelf derived matter wind forcing is the dominant factor controlling particle fluxes at the most distal stations nbbt s sbbt leading to distinct maxima during swm with high abundance of biogenic components here interannual variations of particle fluxes are associated with changes in marine productivity induced by oceanographic processes this is most obvious for sbbt where the advection of upwelled water from the west coast of india in some years results in highest swm fluxes and a distinct shift towards biogenic opal

modelling of seismic waves in heterogeneous media using a wavelet based method application to fault and subduction zones summary the wavelet approach to numerical simulation of elastic wave propagation is applied to models with localized heterogeneity with significant contrasts with their surroundings we consider zones with both lowered wave speed such as a fault gouge zone and elevated wave speeds such as in a subduction zone in each of these situations the source lies within the heterogeneity the representation of the source region has therefore been adapted to work directly in a heterogeneous environment rather than using a locally homogeneous zone around the source this extension also allows the wavelet method to be used with a wider variety of sources e g propagating sources for the fault zone we consider both point and propagating sources through a moment tensor representation and reveal significant trapped waves along the gouge zone as well as permanent displacements for subduction zones a variety of effects are produced depending on the depth and position of the source relative to the subducting slab a variety of secondary waves such as reflected and interface waves can be produced on wave trains at regional distances and tend to be more important for greater source depths

boundary layer sources for the asian anticyclone regional contributions to a vertical conduit 1 the transport of air from the planetary boundary layer pbl into the asian summer monsoon anticyclone is investigated using backward trajectories initiated within the anti cyclone at 100 mb and 200 mb during august 2011 transport occurs through a well defined conduit centered over the southern tibetan plateau where convection lofts air parcels into the anticyclone the conduit as a dynamical feature is distinct from the anticyclone thus while the anticyclone influences transport through the upper troposphere and lower stratosphere it does not by itself define a transport pipeline through that region to quantify model sensitivities parcel trajectories are calculated using wind fields from multiple analysis data sets european centre for medium range weather forecasts national center for environmental prediction s global forecasting system and nasa s modern era retrospective analysis for research and applications merra and from synthetically modified data sets that explore the roles of vertical motion and horizontal resolution for discrepancies among these calculations all calculations agree on the relative contributions to pbl sources for the anticyclone from large scale regions with tibetan plateau and india se asia being the most important however they disagree on the total fraction of air within the anticyclone that was recently in the pbl at 200 mbar calculations using merra are clear outliers due to problematic vertical motion in those data large differences among the different data sets at 100 mbar are more closely related to horizontal resolution it is speculated that this reflects the importance of deep small scale convective updrafts for transport to 100 mbar

tropical intraseasonal variability in version 3 of the gfdl atmosphere model abstracttropical intraseasonal variability is examined in version 3 of the geophysical fluid dynamics laboratory atmosphere model am3 in contrast to its predecessor am2 am3 uses a new treatment of deep and shallow cumulus convection and mesoscale clouds the am3 cumulus parameterization is a mass flux based scheme but also unlike that in am2 incorporates subgrid scale vertical velocities these play a key role in cumulus microphysical processes the am3 convection scheme allows multiphase water substance produced in deep cumuli to be transported directly into mesoscale clouds which strongly influence large scale moisture and radiation fields the authors examine four am3 simulations using a control model and three versions with different modifications to the deep convection scheme in the control am3 using a convective closure based on cape relaxation both mjo and kelvin waves are weak relative to those in observations by modifying the convective closure and trigger assumptions to inhibit deep c

temperature moisture dependence of the deep convective transition as a constraint on entrainment in climate models abstractproperties of the transition to strong deep convection as previously observed in satellite precipitation statistics are analyzed using parcel stability computations and a convective plume velocity equation a set of alternative entrainment assumptions yields very different characteristics of the deep convection onset boundary here measured by conditional instability and plume vertical velocity in a bulk temperature water vapor thermodynamic plane in observations the threshold value of column water vapor above which there is a rapid increase in precipitation referred to as the critical value increases with temperature but not as quickly as column saturation and this can be matched only for cases with sufficiently strong entrainment this corroborates the earlier hypothesis that entraining plumes can explain this feature seen in observations and it places bounds on the lower tropospheric entrainment examination of a simple interactive entrainment scheme in which a minimum turbulent entrai

new evidence for the stratospheric dehydration mechanism in the equatorial pacific water vapor profile measurements obtained in the western and central pacific during the central equatorial pacific experiment cepex show a strong connection between the water vapor content near the tropopause and areas of deep convection we show that air ascending within deep convective towers can be dried to mixing ratios below 1 part per million by volume ppmv which is much lower than the average mixing ratio observed in the stratosphere a sharp increase of water vapor mixing ratio above the tropopause is an indication of the evaporation of ice particles at the top of deep convective cells a mixed layer of up to around 1 km thickness above the tropopause in the regions of deep convection is indicated by the vertical profiles of ozone water vapor and potential temperature furthermore a local maximum was observed at 20 km which is an indication for the seasonal cycle of the tropopause temperature

3d viscoelastic wave propagation in the upper borrego valley california constrained by borehole and surface data we have simulated 2 hz wave propagation in a three dimensional model of the upper borrego valley southern california for a m 4 9 earthquake with epicenter 5 km north of the valley a 4th order staggered grid finite difference method was used to calculate viscoelastic ground motion in a basin model 9 km by 5 km by 0 4 km consisting of heterogeneous sediments surrounded by bedrock we simulated the earthquake as a double couple point source and computed the ground motions in the valley separately for the parts of the source incident from below and from the north the earthquake was recorded by a surface array as well as a deep downhole array 0 238 m depth in the center of the valley all equipped with digital three component seismic instruments the simulation reproduces the overall pattern of ground motions at basin and borehole sites and shows a good correlation of observed to synthetic waveforms in particular the 3d simulation reproduces the recorded peak motions cumulative kinetic energies and fourier spectral amplitudes within a factor of 2 for most components at the individual sites the correlation between data and simulation allows us to identify the secondary arrivals in the records as love and rayleigh waves generated at the edges of the valley and the troughs of the basin the peak velocities for the waves incident into the valley from below are generally more than an order of magnitude larger than those for the waves incident from the north the success of the prediction requires the inclusion of anelastic attenuation in the simulation with q values for p and s waves in the alluvium of about 30 we also used a profile of the 3d model and the soil parameters at the deep borehole to examine the ability of 2 5d and 1d model approximations to predict the data the maximum peak velocities and total cumulative kinetic energies are reproduced at the recording sites within a factor of 2 for both 2 5d and 1d model approximations but are underpredicted by up to an order of magnitude at some depths for individual components in particular the 2 5d and 1d simulations tend to underpredict the duration

3d ground motion estimation in rome italy paleoseismic evidence and seismic hazard analysis suggest that the city of rome italy has experienced considerable earthquake ground motion since its establishment more than 2000 years ago seismic hazards in rome are mainly associated with two active seismogenic areas the alban hills and the central apennines regions located about 20 km southeast and 80 100 km east of central rome within the twentieth century m 6 8 and m 5 3 earthquakes in the apennines and the alban hills respectively have generated intensities up to mercalli cancani sieberg scale mcs vii in the city with a lack of strong motion records we have generated a 3d velocity model for rome embedded in a 1d regional model and estimated long period 1 hz ground motions for such scenarios from finite difference simulations of viscoelastic wave propagation we find 1 hz peak ground velocities pgvs and peak ground accelerations pgas of up to 14 cm sec and 44 cm sec2 respectively for a m 5 3 alban hills scenario largest near the northwestern edge of the tiber river our six simulations of a m 7 0 central apennine scenario generate 0 5 hz pgvs in rome of up to 9 cm sec as well as extended duration up to 60 sec the peak motions are similar to but the durations much longer than those from previous studies that omitted important wave guide effects between the source and the city the results from the two scenarios show that the strongest ground motion amplification in rome occurs in the holocene alluvial areas with strong basin edge effects in the tiber river valley our results are in agreement with earlier 2d sh wave results showing amplification of peak velocities by up to a factor of 2 in the alluvial sediments largest near the contact to the surrounding plio pleistocene formations our results suggest that both earthquakes from the alban hills and the central apennines regions contribute to the seismic hazards in rome although earthquakes from the former area may generate the larger peak motions seismic waves from the latter region may generate ground motions with extended durations capable of causing significant damage on the built environment

the 1987 whittier narrows earthquake in the los angeles metropolitan area california the whittier narrows earthquake sequence local magnitude m l 5 9 which caused over 358 million damage indicates that assessments of earthquake hazards in the los angeles metropolitan area may be underestimated the sequence ruptured a previously unidentified thrust fault that may be part of a large system of thrust faults that extends across the entire east west length of the northern margin of the los angeles basin peak horizontal accelerations from the main shock which were measured at ground level and in structures were as high as 0 6g where g is the acceleration of gravity at sea level within 50 kilometers of the epicenter the distribution of the modified mercalli intensity vii reflects a broad north south elongated zone of damage that is approximately centered on the main shock epicenter

doppler radar study of the trailing anvil region associated with a squall line abstract the kinematic structure and reflectivity distribution within a region of widespread precipitation associated with a summertime midlatitude illinois squall line as revealed by an analysis of doppler radar data are presented and discussed the squall line moved in a southeasterly direction while active convection forming on its leading edge moved in a northeasterly direction decaying thunderstorms and their anvils merged to form the extensive region of stratiform precipitation which trailed the squall line an extension of the vad velocity azimuth display method or the evad extended vad method has been developed for the analysis of single doppler radar data in contrast to the vad method which requires knowledge of the particle fall velocities or assumptions regarding it to calculate the divergence of the horizontal wind the evad method yields the vertical distributions of both the particle fall speed and the divergence also presented are results from a multiple doppler mdop analy

tide current eddy interaction a seasonal study using high frequency radar observations along the western bay of bengal near 16 n abstract the seasonally reversing boundary currents along the western bay of bengal bob provide a background for studying the rich and complex relationship between tidally driven currents mean current structure and mesoscale eddies a year long high resolution surface current data set from high frequency radars hfr during 2015 along the andhra pradesh coast near 82 e 16 n has been utilized to investigate the interaction of tidal currents with bathymetry and eddies during three seasons january march april and november december the seasonal variability shows the reversibility of boundary currents with speeds of 1 58 1 24 m s 1 during poleward equatorward flow associated with an offshore anticyclonic inshore cyclonic eddy in this region the amplitudes of the tidal constituents from the hfr currents are highly correlated r 0 80 with those from the sea level observations from a nearby tide gauge among the semi diurnal and diurnal tidal constituents m2 5 25 6 51 cm s 1 and k1 2 36 4 32 cm s 1 are the dominant two respectively in all three seasons the tidal variance of 40 70 is observed throughout the domain with highest contribution from the m2 tidal currents the m2 tidal ellipse patterns match well with the mean circulation pattern i e cyclonic anticyclonic during november december march april in the nearshore regions the tidal currents amplify mainly through shallow water tidal constituents m4 and ms4 interacting with bathymetry whereas in the offshore regions they are dominated by m2 which co vary with the mean seasonal circulation pattern the highest amplitude of m2 tidal currents during november december is predominantly due to high stratification along the western bob in the presence of stratification the loss of tidal kinetic energy into turbulent processes is reduced resulting in the amplification of m2 tidal currents the shallow water constituents are also observed with significant amplitudes of 0 50 3 50 cm s 1 in the nearshore region the amplitudes of overtides m3 m4 and s4 associated with an offshore anti cyclonic eddy are higher during march april whereas those for the compound tides mk3 sk3 ms4 2sk5 2mn6 and 2sm6 are associated with an inshore cyclonic eddy dominate during november december

causes of low frequency ground motion amplification in the salt lake basin the case of the vertically incident p wave summary we use simulations of 1 d 2 d and 3 d wave propagation to identify the major causes of low frequency 0 2 1 2 hz seismic amplification in the salt lake basin for a simple two layer basin model and a vertically incident p wave we examine how amplification is influenced by mode conversion surface wave generation impedance effects at the sediment bedrock boundary resonance and 2 d and 3 d focusing and scattering results show the following 1 approximately 30 per cent of the total cumulative kinetic energy at the salt lake valley floor consists of shear wave energy generated by p to s converted waves and surface waves the surface waves appear to be generated primarily along the edges of the basin and the instantaneous sip energy ratio in the sedimentary layer is as large as 3 2 the largest peak particle velocity at the free surface is due to the direct p wave the value is roughly predicted by the transmission coefficient of 1 46 at the sediment bedrock interface i e a normally incident p wave in the stiff bedrock will be magnified in amplitude by 1 46 times as it enters the softer sediments 3 the low frequency elastic response of the two layer salt lake basin model is characterized by surface wave propagation and resonance from vertically interfering waves 4 the peak particle velocities cumulative kinetic energies and mean spectral magnitudes computed from the 2 d 1 d synthetics underestimate the values computed from the 3 d synthetics by up to 40 per cent 48 per cent along a profile above the deepest part of the basin model the 2 d and 1 d signal duration times underestimate the 3 d values by up to 59 and 94 per cent respectively our results suggest that 2 d basin modelling may yield good approximations to the 3 d ground motion amplification above the deepest part of the salt lake basin our results show that several mechanisms contribute significantly to lowfrequency seismic amplification in the semi consolidated sediments of the salt lake basin p to s wave conversion surface wave generation impedance effects at the sediment bedrock boundary and resonance future attempts to estimate ground motion amplification in the salt lake basin should therefore account for the amplification effects of all these mechanisms

the radiative budgets of a tropical mesoscale convective system during the emex step amex experiment 1 observations this paper is the first of a series of two that aim to describe the spatial and temporal variation of the radiative heating associated with tropical mesoscale convective systems mcss this paper describes the analysis of data collected in and around a tropical cloud cluster system studied as part of the equatorial mesoscale experiment emex the data analysis indicates that the cluster originated off the northern coast of australia along the midlevel monsoon trough and lasted approximately 12 hours the system moved with a velocity of about 12 m s toward the northeast and the low level surface northwesterly flow at the vicinity of the premonsoon trough area seems continuously to feed the emex 9 cloud cluster with energetic warm moist equatorial air data obtained from aircraft penetrations show features similar to tropical mcss reported elsewhere such as an area of strong to moderate convection surrounded by a broad region of stratiform precipitation radar echo bright band in the stratiform region onion type sounding behind the convective region the vertical structures of the emex 9 cloud cluster also contain two types of imbedded convection an upright vertical structure and a pronounced rearward slope approximately 17 having a vertical extent of 14 5 km and above and a horizontal scale of about 40 km the cloud base and cloud top altitude in the stratiform region are estimated to be of the order of 4 8 km and 15 to 16 km respectively the composite aircraft shortwave radiation data from the stratiform region show a significant attenuation of shortwave flux through the cloud the estimated transmission is 14 at cloud base the upward and downward solar flux profiles are almost parallel to each other in the atmosphere inside and below the cloud base suggesting very little solar heating in these regions the upward and downward infrared radiation fluxes measured in the tropical mcs also show little infrared heating above and below the cloud cluster

the implications of tropical rossby waves for tropical tropopause cirrus formation and for the equatorial upwelling of the brewer dobson circulation this study puts forward a mechanism for the observed upwelling in the tropical upper troposphere and lower stratosphere in this hypothesis the tropical upwelling is driven by momentum transport by rossby waves that are generated by tropical convection to test this hypothesis model runs are conducted using an axisymmetric global primitive equation model in these runs the effect of rossby waves is included by driving the model with observed fields of large scale eddy momentum flux convergence the resulting overturning circulation includes both meridional flow from the intertropical convergence zone itcz to the equator and rising motion in the tropical tropopause transition layer ttl this circulation therefore helps to explain the transport of moisture from the lower portion of the ttl in the itcz to the equatorial cold point tropopause where tropopause cirrus layers frequently occur

structures and mechanisms of the northward propagating boreal summer intraseasonal oscillation abstract the spatial and temporal structures of the northward propagating boreal summer intraseasonal oscillation bsiso are revealed based on the analysis of both the echam4 model simulation and the ncep ncar reanalysis the bsiso structure and evolution characteristics simulated by the model bear many similarities to those derived from the ncep ncar reanalysis the most notable features are the remarkable meridional asymmetries relative to the bsiso convection in the vorticity and specific humidity fields a positive vorticity perturbation with an equivalent barotropic structure appears a few latitude degrees north of the convection center the maximum specific humidity also shows a clear northward shift in the lower troposphere two internal atmospheric dynamics mechanisms are proposed to understand the cause of the northward propagation of the bsiso the first is the vertical shear mechanism the key process associated with this mechanism is the generation of barotropic vorticity due to the couplin

a diagnostic modeling study of the stratiform region associated with a tropical squall line abstract wind and thermodynamic data analyzed in the startiform region of a tropical squall line have been combined with a kinematic three dimensional cloud model to study the precipitation processes in this region the flux of condensate into the stratiform region from the convective region has been parameterized by specifying vertical profiles of cloud water cloud ice snow and graupel at the boundary between these two regions through the use of a one dimensional time dependent cumulus model a standard case in which all four forms of condensate stream into the stratiform anvil is studied in detail the graupel entering this region rapidly removes snow advected into the anvil from the cells as well as snow produced by the mesoscale updraft the snow produced by the mesoscale updraft actively contributes to this precipitation by providing mass for the graupel particles to feed upon a series of sensitivity studies are discussed which reveal two distinct regions a precipitation region due to fallou

air motions and precipitation structure of an early summer squall line over the eastern tropical atlantic abstract the 28 june 1974 squall line over the ship army of the global atmospheric research programme s atlantic tropical experiment gate has been examined aircraft radar satellite sounding and surface data have been employed in the analysis this squall line is the third gate oceanic squall line to have been subjected to intensive case study analysis the vertical air motions and the relative amounts of convective and stratiform rain in this case were similar to those of the other two lines however this squall line moved more slowly without discrete jumps and the horizontal airflow relative to the system was quite different from that associated with the other two lines except at the surface the strong front to rear relative flow normal to the line observed at most levels in the other cases was absent with the relative flow tending instead to be parallel to the line in the low to middle troposphere relative flow parallel to the line from the north fed a post squall mesoscale downdraft in t

the march 1993 superstorm cyclogenesis incipient phase synoptic and convective scale flow interaction and model performance abstract the incipient stages of the 12 14 march 1993 superstorm ss93 cyclogenesis over the gulf of mexico are examined noteworthy aspects of ss93 include 1 it is the deepest extratropical cyclone ever observed over the gulf of mexico during the 1957 96 period and 2 existing operational prediction models performed poorly in simulating the incipient cyclogenesis over the northwestern gulf of mexico a dynamic tropopause dt analysis shows that ss93 is triggered by a potent potential vorticity pv anomaly as it crosses extreme northern mexico and approaches the gulf of mexico the low level environment over the western gulf of mexico is warmed moistened and destabilized by a persistent southerly flow ahead of the approaching pv anomaly ascent and a lowering of the dt associated with a lowering of the potential temperature ahead of the pv anomaly contributes to further destabilization that is realized in the form of a massive convective outbreak an examination of the national centers for envi

a multiple mass flux parameterization for the surface generated convection part i dry plumes abstract the present study introduces a parameterization for the mixing in the surface generated free convection regime including dry and moist convection cases the parameterization explicitly represents the plumes that drive the convective turbulence ascending parcels that have similar properties in the surface layer are grouped into updrafts with a determined fractional area the updrafts ascend according to an entraining plume model and may eventually overturn the plume model can either use a time or a length scale for the lateral entrainment closure the plumes environment is assumed to be horizontally uniform a one dimensional framework is used to evaluate the parameterization in the case of a dry convective boundary layer cbl the predicted variances are underestimated presumably due to the uniform environment assumption the contrast between the strong upward motions and the compensating subsidence is simulated and the skewness of w increases realistically with height the plumes dyn

three dimensional simulation of earthquakes on the los angeles fault system we have used a 3d finite difference method to simulate ground motion from elastodynamic propagating ruptures with constant slip on faults in the metropolitan area of los angeles california simulations are carried out for hypothetical m 6 75 earthquakes on the palos verdes and elysian park faults and for comparison an approximation to the 17 january 1994 m 6 7 northridge earthquake the dominant subsurface features of this area are the deep sedimentary los angeles basin and the smaller and shallower san fernando basin simulated ground motions are restricted to the frequency range 0 0 to 0 4 hz ground motion time histories show that in general sites associated with the largest particle velocities and cumulative kinetic energies are located 1 in the epicentral area 2 above the deepest parts of the basins and 3 near the steepest edges of the los angeles basin we find maximum particle velocities for the palos verdes elysian park and northridge simulations of 0 44 0 67 and 0 58 m sec respectively in each case both the directivity of the rupture and the lower impedance of the basins significantly amplify the ground motion although the gross radiation pattern from these ruptures is observable the 3d basin structure distorts the wave field and becomes a source for edge generated waves signal durations at some basin sites last beyond 90 sec due to love waves and refracted s waves that propagate into the sediments from the basin edges compared with the palos verdes event the durations are generally smaller for the elysian park earthquake due to a smaller amount of love waves generated at the basin edges a simple approximation to the northridge earthquake reproduces the overall spatial pattern of the long period particle velocities successfully predicts the timing of late arriving waves and matches the peak velocities with discrepancies generally less than a factor of 2 however for localized areas immediately north and south of the santa monica mountains the computed ground motion underpredicts the observed horizontal peak velocities but matches the vertical ones the pattern of simulated total cumulative kinetic energies is similar to that for the damage intensities observed near the epicenter of the northridge event while the northridge earthquake caused damage in the los angeles area the 3d simulations show that earthquakes with the same magnitude on the palos verdes or elysian park faults produce more severe ground shaking in the los angeles basin

observed structure of mesoscale convective systems and implications for large scale heating mesoscale convective cloud systems that produce large amounts of rain in mid latitudes and most of the rain in the tropics consist of a combination of convective and stratiform cloud the convective regions contain numerous deep cells that are often but not always arranged in lines the stratiform region is an outgrowth of the convective ensemble it lies adjacent to the convective region and is seeded by ice particles detrained from convective towers sometimes it lies to the rear of a propagating convective line while on other occasions it surrounds the convection the heating of the large scale environment by a mesoscale convective system is affected by both the convective and stratiform regions although processes such as melting and radiation are important the net heating by a system is dominated by condensation and evaporation associated with vertical air motions this paper reviews recent observational evidence regarding the mean vertical motion profiles in the convective and stratiform regions of mesoscale convective systems and the implications of these mean motions for the vertical distribution of heating of the large scale environment in both the convective and the stratiform regions vertical motions have been determined by various techniques including composites of rawinsonde and aircraft wind data single and dual doppler precipitation radar analyses and wind profiler observations in stratiform regions these data consistently show mean vertical velocity that is upward in the upper troposphere and downward in the lower troposphere the level separating upward from downward motion is located from 0 to 2 km above the 0 c level depending on location within the stratiform region diagnostic calculations show that these vertical motion profiles imply heating of the upper troposphere and cooling of lower levels by stratiform region processes data on vertical motions in the convective regions are less consistent from case to case these data sometimes indicate that the mean vertical velocity in convective regions is maximum in the lower troposphere in other cases the data indicate a maximum in the high troposphere diagnostic calculations show that heating profiles diagnosed from these two types of profile are quite different the first having a maximum of heating in the lower troposphere while the second has a maximum in the middle troposphere although it is difficult to determine whether or not the differences in estimates arise from different types of observations analysis methods or sampling strategies it seems likely that they stem from differences in the large scale environment of the different mesoscale systems the ubiquitous occurrence of stratiform regions in mesoscale convective systems and hurricanes together with their consistent heating profiles which systematically concentrate heating in upper levels while cooling lower levels are a major consideration in evaluating the interaction of mesoscale systems with the large scale environment however the consistency of the stratiform profiles from case to case indicates that the variability of net convective plus stratiform heating profiles from case to case lies primarily in the variation of the convective region profiles from one case to another it is suggested that future work should focus on the convective region vertical profiles of vertical motion and heating and on the large scale environmental factors that may control the variation of these profiles from case to case

variability in the eastern equatorial pacific ocean during 1986 1988 we examine variability in the eastern equatorial pacific during 1986 1988 using conductivity temperature depth data velocity and temperature data from equatorial moorings between 110 w and 140 w and wind data from a basin scale zonal array of islands and moorings between 110 w and 165 e the period studied coincides with the el nino southern oscillation enso event of 1986 1987 and a subsequent cold event in 1988 weak warm sea surface temperature anomalies first appeared in the eastern equatorial pacific in mid 1986 and increased to 1 c in september november 1986 in association with a 30 cm s 1 weakening of the south equatorial current and a 20 to 40 m depression of the thermocline these warm anomalies lasted until early 1988 after which a large scale shoaling of the thermocline led to sea surface temperatures more than 3 c colder than climatology year to year fluctuations in the eastern pacific were related primarily to zonal wind variations in the central and western pacific westerly wind stress anomalies of 0 02 0 05 n m 2 were observed between 140 w and 165 e from the latter half of 1986 until the end of 1987 these were replaced by easterly wind anomalies of similar magnitude between 157 w and 165 e in 1988 energetic intraseasonal fluctuations with periods of 2 3 months were also prominent in zonal current temperature and dynamic height time series these fluctuations propagate eastward at approximately first baroclinic mode kelvin wave phase speeds and are forced west of the date line by episodes of westerly winds extrema in several oceanic variables occurred in association with these waves though their precise dynamical link to the enso cycle is unclear from our data sea surface temperature and thermocline depth anomalies at 0 110 w were less pronounced during the 1986 87 enso than during the 1982 1983 enso the equatorial undercurrent though weaker than normal in early 1987 did not disappear as it did in early 1983

a multiple mass flux parameterization for the surface generated convection part ii cloudy cores abstract the multiple mass flux approach introduced in a companion paper aims at parameterizing the surface generated convection in the atmosphere the original aspects of this model are as follows a number of convective updrafts are released in the surface layer they initially have distinct fractional area and thermodynamic properties determined through surface layer similarity that is by assuming that the thermodynamic fluxes are constant throughout the surface layer each updraft ascent is diagnosed using an entraining plume model in the case of cumulus convection this comprehensive formulation provides consistent representations of the subcloud mixing the cloud mixing and the associated cloudiness in the present paper this model is evaluated in two shallow moist convection cases using the one dimensional modeling framework in the continental convection case the diurnal cloud growth and the related subcloud layer ventilation agree with large eddy simulations in the oceanic convection cas

impact of vertical mixing induced by small vertical scale structures above and within the equatorial thermocline on the tropical pacific in a cgcm oceanic vertical mixing is known to influence the state of the equatorial ocean which affects the climate system including the amplitude of el nino southern oscillation enso recent measurements of ocean currents at high vertical resolution capture numerous small vertical scale structures svss within and above the equatorial thermocline that contribute significantly to vertical mixing but which are not sufficiently resolved by coarse resolution ocean models we investigate the impact of the vertical mixing induced by the svss on the mean state and interannual variability in the tropical pacific by using a coupled general circulation model the vertical mixing induced by the svss is represented as an elevated vertical diffusivity from the surface down to the 20 c isotherm depth a proxy for the depth of the thermocline we investigate different forms for the elevated mixing it is found that the svs induced mixing strongly affect the mean state of the ocean leading to a warming of sea surface temperature sst and associated deepening and sharpening of the thermocline in the eastern equatorial pacific we find that the sst warming induced by the elevated mixing is further strengthened through the bjerknes feedback and sst shortwave flux feedback we also find a reduction in the number of large amplitude enso events and in certain cases an increase in the skewness of enso

the effect of freshwater discharge from the godavari river on the occurrence of local upwelling off the east coast of india abstract a numerical model is described and applied to investigate the combination of the wind and estuarially driven circulation of water off the east coast of india a previous numerical modelling study has shown that the estuarial discharge from the hugli and mahanadi rivers may consistently with an interpretation of observational data inhibit the occurrence of coastal upwelling as far south as visakhapatnam further south of this location there is a substantial discharge of freshwater during the monsoon season into the bay of bengal from the godavari river that might possibly have a similar suppressive effect on the coastal upwelling dynamics in a process orientated evaluation it is shown that a representative rate of discharge from the godavari river leads to a marked cross shelf spread of a plume of relatively low salinity water and that the associated dynamical structure is then correspondingly modified so as to weaken the local coastal upwelling tendencies in the surface layers of the ocean that would exist in the sole presence of south westerly wind stress forcing and the northern estuarial outflow

the madden julian oscillation in echam6 and the introduction of an objective mjo metric this study presents a quantitative evaluation of the simulated madden julian oscillation mjo in an ensemble of 42 experiments performed with echam6 and previous echam versions the echam6 experiments differ in their parameter settings resolution and whether the atmosphere is coupled to an ocean or not the analysis concentrates on a few basic features of the mjo namely the signatures of convection precipitation coupled with the circulation system and the eastward propagation strength of outgoing longwave radiation olr and 850 and 200 hpa zonal winds within the mjo related frequency wavenumber range it also examines whether precipitation and olr show similar signatures in the mjo as simulated by echam the experiments reveal an mjo however to different degrees and in different aspects so that a sound assessment requires a multivariate approach in particular the convective rainfall signatures are decoupled from the dynamic signature of the mjo in the simulations herein which eventually leads to the introduction of a new mjo diagram and metric that incorporate olr and the zonal winds in 850 and 200 hpa the analysis here confirms the importance of the convection scheme only with the nordeng modifications to the tiedtke scheme can realistic mjo features be simulated high resolution coupled experiments better represent the mjo as compared to low resolution amip experiments this is shown to follow from two more general findings namely that 1 air sea interaction mainly increases the convective signature and 2 increased resolution enhances eastward propagation

summertime precipitation variability over south america role of the large scale circulation abstract the observed large scale circulation mechanisms associated with summertime precipitation variability over south america are investigated particular attention is paid to the altiplano where a close relationship has been observed between rainfall and the position and intensity of the bolivian high empirical orthogonal function eof correlation and composite analyses suggest that on intraseasonal timescales typically 5 20 days rainy periods on the altiplano are associated with at least three types of circulation anomalies involving either extratropical cyclones cold core lows or the westward enhancement of the south atlantic high in each instance the primary support for high rainfall rates is a moist poleward flow at low levels along the eastern flank of the central andes in association with the south atlantic convergence zone sacz the warm low level flow along the sacz also inflates the overlying atmospheric column resulting in an intensification and southward shift of the bolivi

simulation of 3d elastic wave propagation in the salt lake basin abstract we have used a 3d finite difference method to model 0 2 to 1 2 hz elastodynamic site amplification in the salt lake valley utah the valley is underlain by a sedimentary basin which in our model has dimensions of 48 by 25 by 1 3 km simulations are carried out for a p wave propagating vertically from below and for p waves propagating horizontally to the north south east and west in a two layer model consisting of semi consolidated sediments surrounded by bedrock results show that in general sites with the largest particle velocities cumulative kinetic energies duration times of motion and spectral magnitudes overlie the deepest parts of the basin the maximum values of these parameters are generally found above steeply dipping parts of the basin walls the largest vector particle velocities are associated with p or sv waves that come from within 10 of the source azimuth low energy s and surface waves follow the strongest arrivals the largest peak particle velocities cumulative kinetic energies signal durations and spectral magnitudes in the simulations are respectively 2 9 15 9 40 0 and 3 5 times greater than the values at a rock site measured on the component parallel to the propagation direction of the incident p wave scattering and or mode conversions at the basin boundaries contribute significantly to the signal duration times as a check on the validity of our simulations we compared our 3d synthetic seismograms for the vertically incident plane p wave to seismograms of nearly vertically incident teleseismic p waves recorded at an alluvium site in the valley and at a nearby rock site the 3d synthetics for the alluvium site overestimate the relatively small amplification of the initial p wave and underestimate the large amplification of the coda using 2d simulations we find that most of the discrepancies between the 3d synthetic and observed records can be explained by an apparently incorrect total sediment thickness omission from the model of the near surface low velocity unconsolidated sediments and of attenuation and the inexact modeling of the incidence angle of the teleseism the records from a 2d simulation in which these deficiencies are remedied with q 65 and which also includes topography and a near surface velocity gradient in the bedrock provide a better match to the teleseismic data than the records from the simple two layer 3d simulation our results suggest that for steeply incident p waves the impedance decrease and resonance effects associated with the deeper basin structure control the amplification of the initial p wave arrival whereas reverberations in the near surface unconsolidated sediments generate the large amplitude coda these reverberations are caused mainly by p to s converted waves and their strength is therefore highly sensitive to the incidence angle of the source

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

3 d wave propagation in the los angeles basin for the whittier narrows earthquake abstract elastic wave propagation within and around the los angeles basin during the whittier narrows earthquake in 1988 is simulated with a 3 d finite difference method the model consists mainly of a sedimentary layer over the basement but lateral variations inside the sedimentary basin is also included to approximate observed variations in surface shear velocity the minimum shear velocity is 1 km sec on the surface and fairly reliable results are obtained up to 0 75 hz the total simulation lasts 26 sec our simulation can reproduce the general amplification pattern small east of the epicenter and large in the l a basin and the san fernando valley due to thick sediments of low velocity in these areas surface waves are generated by the primary s wave and trapped inside the basins in the southern part of the l a basin a distinct later phase delayed by 5 to 6 sec relative to the primary s wave is produced in our simulation which matches some strong motion records

analyzing the grell freitas convection scheme from hydrostatic to nonhydrostatic scales within a global model abstractthe authors implemented the grell freitas gf parameterization of convection in which the cloud base mass flux varies quadratically as a function of the convective updraft fraction in the global nonhydrostatic model for prediction across scales mpas they evaluated the performance of gf using quasi uniform meshes and a variable resolution mesh centered over south america the resolution of which varied between hydrostatic 50 km and nonhydrostatic 3 km scales four day forecasts using a 50 km and a 15 km quasi uniform mesh initialized with gfs data for 0000 utc 10 january 2014 reveal that mpas overestimates precipitation in the tropics relative to the tropical rainfall measuring mission multisatellite precipitation analysis data results of 4 day forecasts using the variable resolution mesh reveal that over the refined region of the mesh gf performs as a precipitating shallow convective scheme whereas over the coarse region of the mesh gf acts as a conventional deep convective scheme a

el nino southern oscillation and madden julian 30 60 day oscillations during 1981 1982 an important issue in understanding the low frequency oscillations of the atmosphere and the ocean atmosphere system concerns the role of transients during individual events this question is examined from an observational point of view for the period from september 1981 to april 1982 which includes the transitional phase of the 1982 1983 el nino southern oscillation enso cycle as well as six madden julian 30 60 day oscillations mjo for the developing enso it is shown that interannual transitions in the anomalous atmospheric circulation and in the sea surface temperatures in the western central pacific coincide with the passage of strong mjos from the indian to pacific oceans for a mjo during december 1981 evidence is provided that the shift of convection from the eastern indian ocean to the western pacific ocean involves transients having periods around 10 days the role of transients is discussed from the perspective of these interannual and intraseasonal modes

the excitation of lg waves by explosions a finite difference investigation several mechanisms have been proposed to explain the excitation of the regional lg phase by explosions we examine some of these mechanisms with finite difference simulations an energy flux technique is used to analyze the synthetic signals the method is adapted from conventional array analysis techniques and gives a clear characterization of wave field intensity wave slow ness and propagation direction the vector energy flux in the model is studied instead of the scalar distribution of energy in the space time domain the cal culations show that for an explosive source in a high p wave velocity crust p wave energy cannot be effectively trapped in the crust and the nongeomet rical phase s may be the primary contributor to thelg phase for an explosive source buried in a low velocity upper crust i e where the p wave velocity is lower than the upper mantle s wave velocity part of the ps wave can be trapped in the crustal wave guide to form the lg phase the relative lg excitation de pends on the ratio between the p wave velocity in the source region and the s wave velocity in the uppermost mantle scattering effects can transfer p wave or surface wave energy into lg but the efficiency strongly depends on both the wave frequency and the characteristic size of the scatterers any source process that directly excites s waves is more efficient for generating lg than the afore mentioned mechanisms spall directly generates s wave energy and conse quently is an efficient source for lg for actual explosions all of these factors may simultaneously contribute to lg excitation determining their relative im portance and interactions requires additional observations

transport of water through the tropical tropopause total water was measured in the high troposphere and low stratosphere over panama during ten aircraft flights the results show that convective storms provide the means of transporting water into the stratosphere from a consideration of the anvil heights over different areas of the tropical zone it follows that a negative gradient of water vapor mixing ratio with altitude must exist over most of the lower stratosphere

basin related effects on ground motion for earthquake scenarios in the lower rhine embayment summary the deterministic calculation of earthquake scenarios using complete waveform modelling plays an increasingly important role in estimating shaking hazard in seismically active regions here we apply 3 d numerical modelling of seismic wave propagation to m 6 earthquake scenarios in the area of the lower rhine embayment one of the seismically most active regions in central europe using a 3 d basin model derived from geology borehole information and seismic experiments we aim at demonstrating the strong dependence of ground shaking on hypocentre location and basin structure the simulations are carried out up to frequencies of ca 1 hz as expected the basin structure leads to strong lateral variations in peak ground motion amplification and shaking duration depending on source basin receiver geometry the effects correlate with basin depth and the slope of the basin flanks yet the basin also affects peak ground motion and estimated shaking hazard thereof outside the basin comparison with measured seismograms for one of the earthquakes shows that some of the main characteristics of the wave motion are reproduced cumulating the derived seismic intensities from the three modelled earthquake scenarios leads to a predominantly basin correlated intensity distribution for our study area

a comprehensive mass flux scheme for cumulus parameterization in large scale models abstract observational studies indicate that a mass flux approach may provide a realistic framework for cumulus parameterization in large scale models but this approach through the introduction of a spectral cloud ensemble leads normally to rather complex schemes in this paper the question is addressed whether much simpler schemes can already provide realistic values of the thermal forcing by convection under various synoptic conditions this is done through verifying such a scheme first on data from field experiments for periods of tropical penetrative convection gate marshall islands tradewind cumuli atex bomex and extratropical organized convection sesame 79 and then in a nwp model the scheme considers a population of clouds where the cloud ensemble is described by a one dimensional bulk model as earlier applied by yanai et al in a diagnostic study of tropical convection cumulus scale downdrafts are included various types of convection are represented i e penetrative convection in c

the 1986 87 pacific warm episode evolution of oceanic and atmospheric anomaly fields abstract the evolution of oceanic and atmospheric anomaly fields for the period prior to and during the 1986 87 el nino southem oscillation enso is presented a comparison is made between the 1986 87 enso and other warm episodes that occurred during the last 20 yr in addition for the first time an ocean general circulation model was run in a real time diagnostic mode the model output provided detailed information about the evolution of subsurface features throughout the pacific basin a slow trend towards warm episode enso conditions in the pacific was evident throughout the period 1985 86 in certain atmospheric and oceanic variables atmospheric and oceanic fields changed much more rapidly during late 1986 as enhanced atmospheric convection developed in the equatorial pacific near the date line thermocline depths rapidly increased decreased in the eastern western equatorial pacific as low level westerlies developed in the western portion of the basin a remote response to those westerlies wa

an analysis of simulated and observed blast records in the salt lake basin we have simulated 0 2 to 1 2 hz 3d elastic wave propagation in the salt lake basin from a blast at a nearby open pit mine a fourth order staggered grid finite difference method was used to simulate the blast in a two layer basin model 58 43 9 km consisting of semiconsolidated sediments up to 1 3 km thick surrounded by bedrock data from four blasts in the mine pit recorded by a network of 10 digital three component instruments were compared to the results of the simulation the simulation reproduces the overall pattern of ground motion amplification at basin sites relative to a rock site as measured by ratios of peak particle velocities cumulative kinetic energies and spectral magnitudes considering the simple two layer basin model used in the 3d simulation this finding suggests that the deep 3d basin structure significantly contributes to low frequency ground motion amplification in the salt lake basin 1 1 effects of a near surface layer of low velocity unconsolidated sediments p and s wave velocities of 1 65 and 0 41 km sec respectively that at soil sites along the profile increase the peak particle velocities by up to a factor of 3 and significantly increase the ground motion durations 2 2 attenuation in the sediments which greatly diminishes the ground motion durations on the synthetic seismograms when parameterized by realistic values of the quality factor q 20 for soil sites and 35 for bedrock sites 3 3 2d topographic scattering which increases the peak particle velocities by up to a factor of 2 and increases the signal durations for sites along the profile compared to the records from the simple two layer 3d simulation the records from a 2d p sv wave simulation that includes processes 1 through 3 provide a better match to the blast data especially the observed durations of shaking at five of the six stations along the profile the 2d simulation reproduces the normalized radial and vertical peak particle velocities to within a factor of 2 and the normalized cumulative kinetic energies and spectral amplitudes on these components to within generally a factor of 3 our results suggest that deep basin resonance reverberations in the near surface low velocity layer attenuation and topographic scattering significantly influence site amplification in the salt lake basin future studies of site amplification in the salt lake basin should include the effects of all of these mechanisms

radiosonde observations of equatorial atmosphere dynamics over indonesia 1 equatorial waves and diurnal tides this paper describes the characteristics of the mean winds equatorial waves with periods ranging from 4 to 20 days and diurnal tides determined by analyzing the profiles of wind velocity temperature and humidity obtained every 5 7 hours in the height range up to about 35 km with a height resolution of 150 m during an observation campaign conducted february 27 to march 22 1990 in east java indonesia the structures of the mean winds in the troposphere and lower stratosphere seemed to be affected by the australian monsoon and the quasi biennial oscillation respectively frequency spectra indicated that the equatorial waves as well as the diurnal tides were dominant below about 25 km while gravity waves with periods shorter than 4 days became more significant above 25 km a 7 day oscillation showing an antiphase relation between the eastward and northward components and exhibiting large amplitudes was observed in the lower troposphere the time height variations of the activity of this 7 day oscillation were clearly correlated with a region of high relative humidity perturbations in the zonal wind and temperature with wave periods varying from 15 to 17 days were also enhanced in the troposphere while kelvin waves with periods of about 7 and 20 days were detected in the lower stratosphere and activity near the tropopause was conspicuously enhanced we found that the 20 day kelvin wave greatly modified the structure of the tropopause such as the minimum temperature the tropopause height and the values of the brunt vaisala frequency squared n2 which further suggests the effects of kelvin waves on the transportation of tropospheric water vapor into the stratosphere and on the downward mixing of stratospheric minor constituents into the troposphere the observed profiles of the diurnal oscillation were compared with those of a numerical model assuming only migrating tides which reasonably agreed above about 25 km below 25 km however the observed amplitudes were 1 1 5 m s exceeding those of the model about 10 times moreover the phase profiles involved fluctuations with small vertical scales suggesting interference by many nonmigrating tides with short vertical wavelengths

a unified eddy diffusivity mass flux approach for modeling atmospheric convection abstracta fully unified parameterization of boundary layer and moist convection shallow and deep is presented the new parameterization is based on the stochastic multiplume eddy diffusivity mass

momentum transport by a line of cumulonimbus abstract the vertical transport of horizontal momentum normal to a line of cumulonimbus observed during gate on 14 september 1974 is against the vertical momentum gradient contrary to the predictions of mixing length theory data from repeated aircraft passes normal to the line s axis at heights from 0 15 to 5 5 km are used to document the flux and determine its source the flux is concentrated in roughly a 25 km wide active zone just behind the leading edge of the line in kilometer scale convective updrafts accelerated upward by buoyancy and toward the rear of the line by mesoscale pressure forces the fall in mesoscale pressure from the leading edge to the rear of the active zone is mainly hydrostatic resulting from relatively high virtual temperatures and the 60 degree tilt of the leading edge from the vertical with the clouds at the surface well ahead of those aloft evaluation of the terms in the momentum flux generation equation confirms that the above process reflected by the velocity buoyan

hadley cell dynamics in a virtually dry snowball earth atmosphere the hadley cell of a virtually dry snowball earth atmosphere under equinox insolation is studied in a comprehensive atmospheric general circulation model in contrast to the hadley cell of modern earth momentum transport by dry convection which is modeled as vertical diffusion of momentum is important in the upper branch of the snowball earth hadley cell in the zonal momentum balance mean meridional advection of mean absolute vorticity is not only balanced by eddies but also by vertical diffusion of zonal momentum vertical diffusion also contributes to the meridional momentum balance by decelerating the hadley cell through downgradient mixing of meridional momentum between its upper and lower branches when vertical diffusion of momentum is suppressed in the upper branch the hadley cell strengthens by a factor of about 2 this is in line with the effect of vertical diffusion in the meridional momentum balance but incontrastwithitseffectinthezonalmomentumbalance neitheraxisymmetrichadleycelltheoriesbasedon angular momentum conservation nor eddy permitting hadley cell theories that neglect vertical diffusion of momentum are applicable to the snowball earth hadley cell because the snowball earth hadley cell is a particular realization of a dry hadley cell these results show that an appropriate description of dry hadley cells should take into account vertical transport of momentum by dry convection