kinematic characteristics of a mei yu front detected by the quikscat oceanic winds abstract based on conventional surface observations and nasa quick scatterometer quikscat data a heavy rainfall event that occurred in the taiwan mei yu season was chosen to further study the kinematic characteristics of the accompanying surface front with the help of the quikscat oceanic surface winds it was found that the location and propagation of a mei yu front over the ocean to the east of taiwan during 10 12 june 2000 are better represented by the frontal wind shift line which was located approximately on the leading edge of the baroclinic zone the mesoscale system with cyclonic circulation embedded within the frontal zone was clearly shown in the wind field and kinematic parameters horizontal divergence and vorticity as well as satellite clouds and rainfall estimations the conditional instability of the second kind cisk process was suggested to be responsible for the intensification of the mei yu front and the frontal disturbance over the ocean under the influence of island topography

a method to estimate the phase velocities of microtremors using a time frequency analysis and its applications the phase velocities of rayleigh waves provide basic information for estimating the shear wave velocity structure of the ground many methods have been proposed for this purpose however it is difficult to estimate phase velocities directly from the data found in microtremor records on the differences in phase angles between two sites the reason for this difficulty is that the sources of microtremors are not stable in either time or space in order to counteract this problem therefore we consider the nonstationary characteristic of microtremors in short time range and propose a method that can find the instantaneously corresponding portions of microtremor records at two different sites and that can estimate the apparent phase velocities between the two sites we use the technique of a time frequency analysis for which the hilbert huang transform is adopted after we confirm the applicability of the proposed method based on some numerical calculations the method is applied to some actual data on microtremors and reasonable results are obtained

shallow velocity structure of stromboli volcano italy derived from small aperture array measurements of strombolian tremor abstract the properties of the tremor wave field at stromboli are analyzed using data from small aperture arrays of short period seismometers deployed on the north flank of the volcano the seismometers are configured in two semi circular arrays with radii of 60 and 150 m and a linear array with length of 600 m the data are analyzed using a spatiotemporal correlation technique specifically designed for the study of the stationary stochastic wave field of rayleigh and love waves generated by volcanic activity and by scattering sources distributed within the island the correlation coefficients derived as a function of frequency for the three components of motion clearly define the dispersion characteristics for both rayleigh and love waves love and rayleigh waves contribute 70 and 30 respectively of the surface wave power the phase velocities of rayleigh waves range from 1000 m sec at 2 hz to 350 m sec at 9 hz and those for love waves range from 800 to 400 m sec over the same frequency band these velocities are similar to those measured near puu oo on the east rift of kilauea volcano hawaii although the dispersion characteristics of rayleigh waves at stromboli show a stronger dependence on frequency such low velocities are consistent with values expected for densely cracked solidified basalt the dispersion curves are inverted for a velocity model beneath the arrays assuming those dispersions represent the fundamental modes of rayleigh and love waves

seismic interferometry reconstructing the earth s reflection response in1968 jonclaerboutshowedthatthereflectionresponseofa 1dacousticmediumcanbereconstructedbyautocorrelatingthe transmission response since then several authors have derived relationships for reconstructing green s functions at the surface using crosscorrelations of noise recordings that were taken at thesurfaceandthatderivedfromsubsurfacesources foracousticmedia wereviewrelationsbetweenthereflection response and the transmission response in 3d inhomogeneous lossless media these relations are derived from a one way wavefield reciprocity theorem we use modeling results to show howtoreconstructthereflectionresponseinthepresenceoftransientsubsurfacesourceswithdistinctexcitationtimes aswellas inthepresenceofsimultaneouslyactingnoisesourcesinthesubsurface weshowthatthequalityofreconstructedreflectionsdepends on the distribution of the subsurface sources for a situation with enough subsurface sources that is for a distribution that illuminates the subsurface area of interest from nearly all directions the reconstructed reflection responses and the migrated depth image exhibit all the reflection events and the subsurface structures of interest respectively with only a few subsurface sources that is with insufficient illumination the reconstructed reflection responses are noisy and can even become kinematically incorrect at the same time however the depth image which was obtained from their migration still shows clearly all the illuminated subsurface structures at their correct positions for the elastic case we review a relationship between the reflection green s functions and the transmission green s functionsderivedfromatwo waywavefieldreciprocitytheorem usingmodelingexamples weshowhowtoreconstructthedifferent components of the particle velocity observed at the surface and resulting from a surface traction source this reconstruciton is achievedusingcrosscorrelationsofparticlevelocitycomponents measured at the surface and resulting from separate p and s wavesourcesinthesubsurface

beyond the spac method exploiting the wealth of circular array methods for microtremor exploration we explore the wealth of alternative methods for inferring phase velocities of rayleigh waves using vertical component seismograms of microtremors from a circular array of seismic sensors which are formulable along the extension of the popularly used spatial autocorrelation spac method four such methods are illustrated here the centerless circular array cca method the henstridge methods of the zeroth and first orders the h0 and h1 methods respectively and what we tentatively call the fifth v method different methods of phase velocity estimation have different wavelength ranges of good resolution implementation to field data from two sites reveals that the traditional spac method and the h0 method are both capable of producing reasonable estimates of rayleigh wave phase velocities within a relatively narrow range on the short wavelength side whereas the h1 method is valid in a relatively narrow range on the long wavelength side the cca and v methods both remain valid over a very broad range of wavelengths the upper limit extending as far up as several 10s of times the array radius use of a noise compensation technique can further prolong the maximum resolvable wavelength of the cca method we also illustrate the field performance of circle phase methods which give without recourse to the conventional frequency wavenumber analysis estimates for the principal arrival directions of rayleigh waves on the basis of circular array seismograms of microtremors

constraining depth to basement for mineral exploration using microtremor a demonstration study from remote inland australia abstractwe constrain the depth and seismic structure of stiff sediment cover overlying a prospective basement terrane using a passive seismic technique which uses surface wave energy from microtremor also known as ambient seismic energy or seismic noise this may be applied to mineral exploration under cover to decrease the inherent ambiguity in modeling potential field data for exploration targeting we use data from arrays of portable broadband seismometers processed using both the multimode spatially averaged coherency mmspac method and the horizontal to vertical spectral ratio hvsr method to produce profiles of seismic velocity structure along a 12 km transect we have developed field protocols to ensure consistent acquisition of high quality data in near mine and remote locations and a variety of ground conditions a wavefield approaching the theoretical ideal for mmspac processing is created by combining the energy content of an off road vehicle driven around the seismometer array and ambi

mesoscale dynamics of a deepening secondary cyclone in fastex iop16 three dimensional structure retrieved from dropsonde data the mesoscale dynamics of a secondary cyclone sampled during the field phase of the fronts and atlantic storm track experiment fastex intensive observation period iop 16 are documented using airborne dropsonde data the method proposed to recover the mesoscale analytical three dimensional 3 d dynamic fields from the dropsonde measurements is evaluated using simulated fields airborne in situ measurements and airborne doppler radar measurements these simulations and comparisons indicate that the method is able to resolve the mesoscale structures within the studied secondary cyclone both in the regions of clear air and precipitation it appears however that the most accurate description of the 3 d dynamic fields in both these regions would be obtained by combining doppler and dropsonde measurements the studied secondary cyclone is a fast moving frontal wave that developed on the trailing cold front of a parent low situated over greenland using the dropsonde derived 3 d fields the mesoscale flows involved in the organization of the secondary cyclone are described the potential vorticity and equivalent potential vorticity fields deduced from the basic analytical fields indicate that the atmosphere is roughly neutral to moist slantwise instability this configuration is known to significantly promote frontogenesis the vertical configuration of the jets and circulations within this secondary cyclone are compared with the coupling uncoupling scheme of shapiro a slight coupling is found between the thermally indirect circulation and the ageostrophic circulation the obtained coupling is however not as developed as in the ideal case described by shapiro which may explain the small upward velocities in our case airborne doppler radar and dropsonde measurements are combined so as to infer the multi scale processes involved in the mesoscale and convective scale organization of the atlantic secondary cyclones and to evaluate the new emerging theoretical interpretations of secondary cyclogenesis

diagnosis of frontal instabilities over the southern ocean the development of three fronts over the southern ocean is described using seawinds on quikscat scatterometer surface winds and an attribution technique to partition the wind field in three components nondivergent and irrotational components at the scale of the front and the remaining harmonic component or environmental flow induced by the synoptic scale flow the front and the environment in which the front is embedded are analyzed separately a frontal wave is shown to develop out of the first front when the large scale alongfront stretching decreases the environmental flow becomes frontolytic and a connection with the upper levels is established in the second case the stretching remains relatively strong and no frontal wave develops the third front exhibits a developing wave but is not in a favorable configuration with the upper levels the frontal wave does not deepen significantly

carbon isotopic compositions of prokaryotic lipids as tracers of carbon cycling in diverse settings recent work has highlighted the ubiquity of bacteria and archaea and continues to affirm their significance in diverse biogeochemical processes the 13c values and distributions of diagnostic lipids derived from such microorganisms can provide insights into prokaryotic processes in modern settings and are one of the few means by which past prokaryotic processes in depositional settings can be elucidated here we present a brief review of prokaryotic lipids commonly observed in sediments and the controls on their carbon isotopic compositions we then present two case studies one of mediterranean cold seeps at which anaerobic oxidation of methane occurs and one of a holocene peat deposit in which a variety of aerobic and anaerobic microorganisms govern the degradation of organic matter these two studies illustrate the potential utility of compound specific carbon isotope analyses to deconvolute pathways of carbon flow in microbial communities

unsteady sediment discharge in earth flows a case study from the mount pizzuto earth flow southern italy abstract surface mapping gps surveys t lidar surveys boreholes seismic profiles and hvsr measurements were used to study the mechanisms of sediment transport along the mount pizzuto earth flow in southern italy the earth flow has several kinematic zones with transitional areas marked by changing structural styles from compressional structures thrusts upslope to extensional structures normal faults downslope we relate sediment discharge at these transitional zones to internal strain the results suggest that during surge events flow acceleration starts within the head and propagates downslope inducing a cascade effect between kinematic zones during surge events the average sediment discharge is nearly constant and a change from sliding to flowing allows propagation of movement towards the toe during slow movement kinematic zones are independent and sediment discharge varies along the flow in general the velocity profile and the structural style are controlled by the basal slip surface the implications are i sediment discharge is not constant but is a function of the earth flow activity ii during surge earth flow material behaves similar to an incompressible fluid and iii the distribution of surface structures can provide information about the geometry of the slip surface and the velocity profile additionally earth flows with a well defined neck seem to be more likely to surge with respect to those without

surface dynamics of observed maritime fronts abstract the problem of establishing the important mechanisms and processes in surface fronts is examined it is shown that boundary layer processes may modify the details of frontal dynamics near the surface and that at the same time fronts may alter boundary layer solutions a similarity model that assumes a horizontally homogeneous steady state planetary boundary layer is used to test the effects of baroclinity and stratification on the ageostrophic vorticity model response to baroclinity and stratification is tested a boundary layer positive feedback mechanism that stems from the variation in stratification and thermal advection across a front and favors the creation of stronger temperature gradients in cold fronts is proposed a compatible model that includes the effects of horizontal inhomogeneity is derived and used in conjunction with scatterometer data to observe the behavior of five surface fronts observations are compared to results of numerical models by several authors and it is concluded

characteristics of seismic noise fundamental and higher mode energy observed in the northeast of the netherlands we study seismic noise recorded in the northeast of the netherlands by beamforming and by using empirical green s functions obtained by seismic interfero metry from beamforming we found differences in noise directions in different fre quency bands the main source region for primary microseisms 0 05 0 08 hz is in the west northwest direction while the secondary microseisms 0 1 0 14 hz have a west southwest back azimuth furthermore we observed a fast 4 km s arrival corresponding to the rayleigh wave overtone this arrival is also in the secondary microseism band between 0 15 and 0 2 hz but has a west northwest back azimuth both arrivals in the secondary microseism band gain in strength during winter as does the average wave height in the north atlantic we measured phase velocity dispersion curves from both beamforming and noise cross correlations as well as group velocity from the latter these are then jointly inverted for an average 1d s wave model the results show how the combination of different methods leads to a more complete char acterization of the propagation modes and an improved knowledge of the subsurface especially as the group velocity measurements increase the upper frequency limit of analysis providing valuable information of the shallowest subsurface

atmospheric connections with the north atlantic enhanced the deglacial warming in northeast china variations in atmospheric circulation across the last deglaciation in the northernmost monsoon influenced regions of asia are not well constrained highlighting a fundamental gap in our understanding of asian climate here we reconstruct continental air temperatures for northeast china across the last deglaciation past 16 k y based on the distribution of bacterial branched glycerol dialkyl glycerol tetraethers in a sequence of the hani peat jilin province northeast china our results indicate large as much as 10 degrees c oscillations in temperature in northeast china across the deglaciation oscillations significantly larger than observed in other temperature records from low latitude or same latitude east asia but consistent with climate model simulations this enhanced magnitude as well as the timing of temperature variations provides evidence for atmospheric teleconnections with high latitudes in particular we suggest that highlatitude cooling associated with arctic ice expansion and changes in atlantic meridional overturning circulation enhanced the intensity and lowered the temperature of eurasian mid latitude westerlies and northwesterly winds over east asia during the last glacial delivering cold air masses to northeast china during the deglaciation the westerlies and therefore delivery of cold air masses weakened amplifying the deglacial warming in this region we conclude that changes in north atlantic climate had a particularly strong impact on the northernmost parts of the east asian monsoon influenced area

scattering and attenuation abstract an extensive existence of strong small scale heterogeneity in the earth is suggested by the great variability of direct waves and remarkable stability of scattered waves both in the case of teleseismic p coda and in the case of local earthquake s coda quantitative studies of small scoale heterogeneities have been made by the following three methods a lower bound of heterogeneity in the lithosphere has been estimated by the deterministic or stochastic modeling of travel time and amplitude fluctuation of teleseismic p waves across a large aperture seismic array an upper bound of heterogeneity has been estimated by modeling the attenuation of s waves as a scattering loss due to heterogeneity these two approaches suggest the existence of heterogeneity with rms velocity fluctuations from 3 to 10 per cent the third method is based on the estimation of heterogeneity from the amplitude of coda waves we found a significant discrepancy between the result obtained by the third method and those from the first two and attribute the discrepancy to the assumption of a single scattering model adopted in the coda generation theory the need for including multiple scattering as well as for considering vector elastic waves rather than scalar waves is emphasized

on bias and noise in passive seismic data from finite circular array data processed using spac methods the finite nature of typical small seismic arrays used in conjunction with spatial autocorrelation spac processing for observing the microtremor wavefield causes predictable perturbationsofthespacspectrumwhensourcesofseismic noiseareconfinedtoarestrictedrangeofazimuths suchperturbations are especially evident at higher frequencies where wavelengths are on the order of the array radius the effects arereadilymodeledandshowthatthetriangulararraygeometries commonly used for microtremor studies require azimuthal distributions of wave energy on the order of 60 or greatertohaveahighprobabilityofbeingfreeofsuchperturbations the imaginary component of the spac spectrum which is ideally zero for a sufficiently dense circular array and or a sufficiently isotropic wavefield is in practice often nonzero and provides three quality control indicators 1 an indication of insufficient spatial averaging 2 an empirical measure of the level of statistical uncertainty in spac spectralestimates and3anindicationofdeparturesfromplanewavestationarityoftheseismicnoisewavefield

shallow structure of mt vesuvius volcano italy from seismic array analysis data from a portable dense seismic array deployed on mt vesuvius in may 1994 during a 2d seismic tomography experiment are analyzed in the present paper the array consisted of two groups of short period geophones 4 5 hz natural frequency formed by 16 and 25 vertical components plus two horizontal components distributed along an arc like shape along the summit crater stacks of later arrivals interpreted as reflected phases provide a significant constraint to a boundary layer located in the depth range 1 5 2 2 km beneath the summit crater with average velocity v 1 8 2 2 km s interpreted as the top of the limestone basement the correlation methods applied on microtremor records allowed to infer the shallow velocity structure up to 400 m beneath the crater rim

potential misidentification of love wave phase velocity based on three component ambient seismic noise people have calculated rayleigh wave phase velocities from vertical component of ambient seismic noise for several years recently researchers started to extract love waves from transverse component recordings of ambient noise where transverse is defined as the direction perpendicular to a great circle path or a line in small scale through observation sensors most researches assumed rayleigh waves could be negligible but rayleigh waves can exist in the transverse component when rayleigh waves propagate in other directions besides radial direction in study of data acquired in western junggar basin near karamay city china after processing the transverse component recordings of ambient noise we obtain two energy trends which are distinguished with rayleigh wave and love wave phase velocities in the frequency velocity domain using multichannel analysis of surface waves masw rayleigh waves could be also extracted from the transverse component data because rayleigh wave and love wave phase velocities are close in high frequencies 0 1 hz two kinds of surface waves might be merged in the frequency velocity domain rayleigh wave phase velocities may be misidentified as love wave phase velocities to get accurate surface wave phase velocities from the transverse component data using seismic interferometry in investigating the shallow geology our results suggest using masw to calculate real love wave phase velocities

glacial interglacial wetland biomass burning and geologic methane emissions constrained by dual stable isotopic ch4 ice core records atmospheric methane ch4 records reconstructed from polar ice cores represent an integrated view on processes predominantly taking place in the terrestrial biogeosphere here we present dual stable isotopic methane records 13ch4 and d ch4 from four antarctic ice cores which provide improved constraints on past changes in natural methane sources our isotope data show that tropical wetlands and seasonally inundated floodplains are most likely the controlling sources of atmospheric methane variations for the current and two older interglacials and their preceding glacial maxima the changes in these sources are steered by variations in temperature precipitation and the water table as modulated by insolation local sea level and monsoon intensity based on our d ch4 constraint it seems that geologic emissions of methane may play a steady but only minor role in atmospheric ch4 changes and that the glacial budget is not dominated by these sources superimposed on the glacial interglacial variations is a marked difference in both isotope records with systematically higher values during the last 25 000 y compared with older time periods this shift cannot be explained by climatic changes rather our isotopic methane budget points to a marked increase in fire activity possibly caused by biome changes and accumulation of fuel related to the late pleistocene megafauna extinction which took place in the course of the last glacial

quasi stationary wave variability in nscat winds planetary and interseasonal properties of the nasa scatterometer nscat winds are explored in the context of the quasi stationary waves qsws of the southern hemisphere the qsws are examined by means of zonal asymmetries of 3 month running averages of the meridional velocity derived from nscat the study period spans the entire nscat record from september 15 1996 through june 29 1997 meridional winds from the european space agency ers 2 scatterometer are used to augment 3 month averages centered on august 1996 through may 1997 the time period corresponds to the transition from year 1 to 0 of the 1997 warm event in the southern oscillation comparisons are made with qsw signals in geopotential height anomalies from the national centers for environmental prediction national center for atmospheric research climate data assimilation system the zonal anomalies of meridional wind from nscat are shown to be in approximate geostrophic balance with zonal gradients in the zonal anomalies of geopotential height at 500 and 1000 hpa

ocean surface pressure fields from satellite sensed winds abstract the university of washington s planetary boundary layer model is inverted to use remotely sensed satellite scatterometer derived surface winds as input to calculate maritime surface pressure fields the analysis of three different synoptic storm situations is performed using the model and is then compared to conventional national weather service analyses agreement is good isolation of the pbl secondary flow stratification and thermal wind effects in the model revealed that each may be significant under certain conditions however the model shows sensitivity to the thermodynamic features only in a general sense and even a neutral stratification solution gives a good approximation the high density of the scatterometer data produces mesoscale hundreds of kilometers dynamic details which cannot be confirmed by conventional data at this stage

the role of the environmental flow in the development of secondary frontal cyclones the impact of the environmental flow on the development of secondary frontal cyclones is investigated several case studies are examined as examples of secondary frontal cyclone events observed in the north atlantic western europe sector a simple measure of growth is defined to chart their development the vorticity attribution technique of bishop is utilized to calculate the action of the large scale environmental flow on the fronts in particular the environmental along front stretching shown to be important in theoretical models of frontal instabilities is calculated the role of the environmental deformation appears to be crucial as part of a baroclinic life cycle stretching deformation acts to build up a front but suppress along front waves if the stretching rate diminishes barotropic instabilities may then break out diagnostics are examined to try to ascertain the growth mechanisms at work in each frontal cyclone case a range of values for the commonly prescribed deformation frontogenesis and shearing frontogenesis parameters are calculated

characteristics of seismic waves composing hawaiian volcanic tremor and gas piston events observed by a near source array a correlation method specifically designed for describing the characteristics of a complex wave field is applied to volcanic tremor and gas piston events recorded by a semicircular array of geos instruments set at the foot of the puu oo crater on the east rift of kilauea volcano hawaii the spatial patterns of correlation coefficients obtained as functions of frequency for the three components of motion over the entire array are similar for gas piston events and tremor and clearly depict dispersive waves propagating across the array from the direction of puu oo the wave fields are composed of comparable amounts of rayleigh and love waves propagating with similar and extremely slow phase velocities ranging from 700 m s at 2 hz to 300 m s at 8 hz the highly cracked solidified lava flow on which the array was deployed and subjacent structure of alternating lava and ash layers formed during repeated eruptions of puu oo since 1983 appear to be responsible for the low velocities observed the results from puu oo stand in sharp contrast to those obtained in an experiment conducted in 1976 on the partially solidified lava lake of kilauea iki rayleigh waves were not observed in kilauea iki but well developed trains of love waves were seen to propagate there with velocities twice as high as those observed near puu oo these differences in the propagation characteristics of surface waves at the two sites may be attributed to the presence of a soft horizontal layer of molten rock in kilauea iki which may have lowered the phase velocity of rayleigh waves more drastically than that of love waves resulting in severe scattering of the rayleigh wave mode on the other hand the thin superficial pahoehoe flow under our array at puu oo may have favored the development of vertical columnar joints more extensively at this location than at kilauea iki which may have reduced the shear moduli controlling the love wave mode the average phase velocities in the frequency band from 2 to 5 hz found at puu oo are roughly similar to those determined for tremor at klyuchevskoy volcano kamchatka but the frequency dependence appears much stronger at puu oo

seismic velocity and q model for the shallow structure of the arabian shield from short period rayleigh waves the shear velocity and q sub beta structure for the upper 1 km in different tectonic regions of the arabian shield have been investigated using high frequency vertical component records of rayleigh waves 1 20 hz which were recorded at source to receiver separations 55 80 km during a deep seismic refraction survey group and phase velocities of the fundamental and first higher modes were inverted for the shear wave velocity structure rayleigh wave attenuation coefficients were determined from the decay of the amplitude spectrum of the fundamental mode and used to invert for the q sub beta structure models derived from the data were tested by calculating synthetic seismograms for the fundamental and the first higher modes from surface wave theory with a center of compression used to represent the source both band pass filtered step and dirac delta source time functions were tested modeling indicates that the shear wave velocity of the shield increases from 2 6 km s to 3 4 km s in the upper 400 m of the crust q sub beta increases from 30 in the upper 50 m to 150 at 500 m depth the underlying material has a q sub beta of 400 500 for the outcropping igneous rocks such as granite and may reach values higher than 700 for the metamorphic green schist rock a band pass filtered dirac delta source time function produces the synthetic that is the best fit with observations

lateral propagation effects observed at parkway new zealand a case history to compare 1d versus 2d site effects abstract the importance of 2d or 3d site effects has been shown by theoretical studies however there is a lack of observational evidence of site effects due to lateral heterogeneities we have evaluated 1d and 2d site effects in the data obtained by a dense seismograph array that operated for more than 2 months in the alluvial basin of parkway new zealand 1d site effects were evaluated using three independent techniques spectral ratios relative to a reference station spectral ratios of horizontal relative to vertical ground motion and a generalized inversion scheme site effects due to lateral heterogeneity were investigated in detail for two events using frequency wavenumber analysis our results show that it is not possible to separate 1d from 2d site effects using frequency domain techniques this explains the scatter obtained from standard 1d data analysis the 1d resonance peaks will be more or less contaminated with laterally propagating waves for different events

hvsr deep mapping tested down to 1 8 km in po plane valley italy abstract the horizontal to vertical spectral ratio hvsr of seismic noise is extensively used in seismic microzonation for its capability to provide a good approximation to the subsoil main resonance frequencies of geotechnical and seismic engineering interest this implies in turn that it has also an approximate passive subsoil mapping capability independent of the level of noise illumination albeit limited to relatively shallow depths since tilt sensitivity makes hvsr unreliable below 0 1 hz however we have experimentally verified that hvsr subsoil mapping capability extends to depths in the kilometer range by applying it to the largest sedimentary basin of italy the po plain valley there we were able to resolve the major stratigraphic discontinuities down to the sediment bedrock interface for which we estimated a depth of 1 6 km with a 25 uncertainty while the surface mapped from oil exploration indicates a depth of 1 8 km quarter of an hour recordings gave always stable signals that fitted to synthetic curves using as a constraint the parameters of the shallow subsoil provided a stratigraphic map consistent with the independent survey this candidates hvsr as a fast and inexpensive first order subsoil mapping tool down to depths of geological and exploration interest

site characterization for urban seismic hazards in lower manhattan new york city from microtremor array analysis 1 we characterize the shear wave velocity vs of soil deposits in lower manhattan at six sites using the spac and hvsr microtremor methods the soil vs ranges from 140 m s to 300 m s over bedrock we believe that bedrock depth is constrained to 15 with these microtremor data but an accurate quantification of bedrock vs is unattainable because of low spectral coherency at frequencies below 3 hz hvsr data corroborate the spac microtremor results at sites based on good alignment of theoretical rayleigh ellipticity peaks 1d sh amplifications and peak hvsr resonant frequencies vary between 1 4 and 5 5 hz between the sites from both observed hvsr and predicted 1d sh amplification shear wave velocities to 30 m classify the sites as c d or e this study demonstrates that given relatively shallow bedrock depth the spac method can work in extremely urbanized areas

a new method to determine phase velocities of rayleigh waves from microseisms we have developed a new method to determine phase velocities from the vertical component of microseisms recorded with an array of seismic sensors spaced around the circumference of a circle we calculate two different time histories by taking the average of the seismograms with differing sets of weights for the sensor stations the spectral ratio of these two time histories contains no information on the arrival directions or on the amplitudes of the incoming waves but depends solely on the phase velocities of the arriving modes theoretical considerations indicate that the effects of directional aliasing caused by the use of a finite number of sensors in the field implementation of our method are small in most situations except for short wavelengths the presence of incoherent noise limits the efficacy of our method for long wavelengths in field tests using arrays of three seismic sensors we obtained appropriate estimates of phase velocities in the wavelength range from 5r to 30r where r the array radi

faster better shear wave velocity to 100 meters depth from refraction microtremor arrays current techniques of estimating shallow shear velocities for assessment of earthquake site response are too costly for use at most construction sites they require large sources to be effective in noisy urban settings or specialized independent recorders laid out in an extensive array this work shows that microtremor noise recordings made on 200 m long lines of seismic refraction equipment can estimate shear velocity with 20 accuracy often to 100 m depths the combination of commonly available equipment simple recording with no source a wavefield transformation data processing technique and an interactive rayleigh wave dispersion modeling tool exploits the most effective aspects of the microtremor spectral analysis of surface wave sasw and multichannel analysis of surface wave masw techniques the slowness frequency wavefield transformation is particularly effective in allowing accurate picking of rayleigh wave phase velocity dispersion curves despite the presence of waves propagating across the linear array at high apparent velocities higher mode rayleigh waves body waves air waves and incoherent noise two locations illustrate the application of this technique in detail coincident with a large accelerometer microtremor array in reno nevada and atop a borehole logged for shear velocity in newhall california refraction equipment could duplicate microtremor results above 3 hz but could not estimate velocities deeper than 100 m refraction microtremor cannot duplicate the detail in the velocity profile yielded by a suspension logger but can match the average velocity of 10 to 20 m depth intervals and suggest structure below the 100 m logged depth of the hole eight additional examples from southern california and new zealand demonstrate that the refraction microtremor technique quickly produces good results from a wide range of hard and soft sites

spatially averaged coherencies krspac and rayleigh effective mode modeling of microtremor data from asymmetric arrays abstractthe spatial autocorrelation and spatially averaged coherency spac methods of processing rayleigh wave microtremor noise observations for estimation of s wave velocity profiles traditional

subsoil structure using spac measurements along a line the spac spatial autocorrelation method was proposed almost 50 years ago by aki 1957 this method allows a phase velocity dispersion curve to be obtained from microtremor measurements using an array of stations arranged in a circle the subsoil structure is subsequently derived from the inversion of that dispersion curve in this article we show that it is possible to get similar results using microtremors recorded along a line we use microtremor records obtained by using four broadband seismographs disposed along a line with different interstation spacings 5 10 20 and 40 m our data are precessed by using the standard spac procedure with the exception of the azimuthal average the final subsoil structure as determined from the inversion of the phase velocity dispersion curve shows excellent agreement with previous results at the site of our measurements our results suggest that the use of the spac method is not restricted to a particular geometry of the array provided that the basic requirement of stationarity is fulfilled

the impact of deformation strain on the formation of banded clouds in idealized modelling experiments experiments are performed using an idealized version of an operational forecast model to determine the impact on banded frontal clouds of the strength of deformational forcing low level baroclinicity and model representation of convection line convection is initiated along the front and slantwise bands extend from the top of the line convection elements into the cold air this banding is attributed primarily to m adjustment the cross frontal spreading of the cold pool generated by the line convection leads to further triggering of upright convection in the cold air that feeds into these slantwise bands secondary low level bands form later in the simulations these are attributed to the release of conditional symmetric instability enhanced deformation strain leads to earlier onset of convection and more coherent line convection a stronger cold pool is generated but its speed is reduced relative to that seen in experiments with weaker deformational strain because of inhibition by the strain field enhanced low level baroclinicity leads to the generation of more inertial instability by line convection for a given capping height of convection and consequently greater strength of the slantwise circulations formed by m adjustment these conclusions are based on experiments without a convective parametrization scheme experiments using the standard or a modified scheme for this model demonstrate known problems with the use of this scheme at the awkward 4 km grid length used in these simulations copyright 2008 royal meteorological society

secondary frontal waves in the north atlantic region a dynamical perspective of current ideas the current understanding of the dynamics of secondary cyclogenesis on frontal systems in the north atlantic region is reviewed these secondary cyclones are often poorly forecast and in extreme cases can have damaging consequences but because of their small scales and potential for rapid growth detailed observations and analyses are limited in this paper recent work is described and compared it is argued that on the synoptic scale the development of primary baroclinic waves is well understood but on the subscales of these systems where the secondaries develop there is a wider variety of mechanisms which may cause or modify cyclone growth this variety may be reflected in a wider range of resulting systems various dynamical models have been postulated secondary frontal waves are seen as the instability of a low level potential vorticity strip or warm band at a front with possible finite amplitude triggering by upper level features latent heating is thought to provide a suitable unstable potential vorticity strip but the degree to which the latent heating contributes to the instability itself is a matter of dissent secondary systems are often shallow so boundary layer processes are important but the influence of these is not well understood laboratory experiments have suggested that the boundary layer will act to suppress instability in general frontogenetic strain flow while acting to intensify the basic state front suppresses wave development in contrast recent work suggests that a frontolytic strain flow may be important in enhancing the development of one class of waves the fastex experiment an international field study of north atlantic secondary cyclogensis has recently attempted to observe these systems in detail it is hoped that the data which have been obtained will help to resolve some of the outstanding issues in this field

secondary cyclogenesis the initiation phase of a frontal wave observed over the eastern atlantic the initiation phase of a secondary frontal wave in the wake of a primary cyclogenesis event over the atlantic is documented north of the trailing surface cold front and south west of the primary cyclone an intense upper level jet generates a direct and transverse ageostrophic circulation in its entrance region evidence is shown for two conflicting roles of this circulation first stabilization of the front through frontogenetic cross frontal low level convergence and second an increase of the potential for instability of the front through diabatic e g latent heat release potential vorticity pv redistribution in the upward branch of the circulation following saturation of the primary cyclogenesis and the associated along front north eastwards shift of the upper level jet the low level branch of the ageostrophic circulation behaves like a zipper closing on the front while in the upward branch an anomalous strip of pv builds along the cold front isentropic pv maps show that parcles of stratospheric origin embedded in the downward branch of the ageostrophic circulation a tropopause fold may have ended in the vicinity of the strip of anomalous low level pv perhaps contributing to an increase in the potential for instability of the surface front using the domain independent attribution method of bishop it is shown that the frontal wave forms on a part of the cold front where first the along front stretching rate due to the environmental flow decays below the critical threshold value 0 6 10 5 s 1 prescribed by theoretical studies and second the across front frontogenetic component due to the ageostrophic circulation decays this is consistent with semi geostrophic theory where the cross frontal convergence and the stretching deformation are linked through the sawyer eliassen equation results add to other recent observational findings that the potential for instability the evolving environmental flow and the induced ageostrophic convergence each have a crucial role in differentiating between frontal waves that will grow and those that will be suppressed

cyclone surface pressure fields and frontogenesis from nasa scatterometer nscat winds two extratropical marine cyclones and their associated frontal features are examined by computing surface pressure fields from nasa scatterometer nscat winds a variational method solves for a new surface pressure field by blending high resolution 25 km relative vorticity computed along the satellite track with an initial geostrophic vorticity field employing this method with each successive pass of the satellite over the study area allows this surface pressure field to evolve as dictated by the relative vorticity patterns computed from nscat winds the result is a high resolution surface pressure field that captures features such as fronts and low pressure centers in more detail than national centers for environmental prediction ncep reanalyses while using the actual relative vorticity to adjust the geostrophic vorticity ignores the ageostrophy of surface winds which can be significant in the vicinity of fronts and jet streaks it is a necessary approximation given that the technique uses only surface data the nscat surface pressure fields prove to be nearly as accurate as ncep reanalyses when compared to ship and buoy observations which is an encouraging result given that ncep reanalyses incorporate a myriad of data sources and the nscat fields rely primarily on one source in addition the high resolution relative vorticity fields computed from nscat winds reveal the location of surface fronts in great detail these fronts are verified using ncep analyses in situ data and satellite imagery

a seismic passive imaging step beyond spac and remi abstractthe basic property of passive imaging is that given any two points one of them can be taken as the source of the waves and the other as the recording station this property can be derived from the statistical self alignment of the rays along the vector joining the two points and applies also to nondiffuse wavefields like seismic tremor it provides a statistical basis for the use of the stationary phase integral allowing passive interferometry under the mild constraint of mechanical homogeneity at a local scale combined with the tremor s large spectral bandwidth it allows one to recover the local green s function from spatial correlation furthermore combining this property also with the azimuthal isotropy of either the wavefield or the array and using the statistical mode as the estimator provides a new technique to measure the local velocity dispersion in the subsoil this technique exploits the potential of spatial autocorrelation spac and refraction microtremor remi allowing one

upper and lower troposphere coupling processes involved in the fastex iop16 frontal cyclone this paper investigates processes involved in the development of the secondary low sampled on 17 february 1997 during the field phase of the fronts and atlantic storm track experiment fastex this low is a fast moving frontal wave that emerged from the trailing cold front of a parent low situated over greenland the dynamics of this cyclone and its environment are described using the european centre for medium range weather forecasts analysis corresponding to intensive observing period 16 of fastex the ageostrophic circulation is retrieved and analysed in the upper and in the lower levels in the upper levels it is found that the curvature of the upper level jet plays a crucial role in suppressing or amplifying the vertical motions in the lower levels in the region where the cloud head emerges the vertical motion is scrutinized in the light of forcings which are acting it is found that the vertical motions are the response to a geostrophic forcing reinforced by diabatic processes the conjunction of vertical motions in the lower levels associated with vertical motions in the upper levels leads in the developing period to a coupling process that seems to be following theoretical calculations at the origin of the subsequent development of the cyclone the instability processes involved in the development of the studied secondary cyclone are also investigated the atmosphere appears neutral for upright convection while the region of the coupling corresponds to a region which is potentially unstable with respect to slantwise convection the tendency of the atmosphere is to relax this instability the vertical motions of the coupling processes are then reinforced by the relaxation of slantwise instability copyright 2002 royal meteorological society

identification and climatology of southern hemisphere mobile fronts in a modern reanalysis abstractpresented here is an objective approach to identify characterize and track southern hemisphere mobile fronts in hemispheric analyses of relatively modest resolution such as reanalyses among the principles in its design were that it should be based on broadscale synoptic considerations and be as simple and easily understood as possible the resulting eulerian scheme has been applied to the european centre for medium range weather forecasts ecmwf re analysis era interim and a climatology of frontal characteristics at both the 10 m and 850 hpa levels derived for the period 1 january 1989 28 february 2009 the knowledge of the character of these features is central to understanding weather and climate over the hemisphere in both summer and winter the latitude belt 40 60 s hosts the highest frequency of frontal points but there are significant zonal asymmetries within this band the climatology reveals that the longest fronts are in the indian ocean where mean lengths exceed 2000 km the me

lateral heterogeneities and microtremors limitations of hvsr and spac based studies for site response abstract we report a site effect study carried out in a small alluvial valley nari basin in ulleung island republic of korea in that small valley a permanent broad band array of five stations records ground motion continuously in addition we performed microtremor measurements using two arrays of stations a small aperture array 60 m and a medium aperture one 500 m ambient vibration was also recorded at 38 points inside the basin the records were analyzed using horizontal to vertical spectral ratios hvsr to estimate dominant frequency and maximum amplification and the spatial autocorrelation spac method to estimate the subsoil structure via phase velocity dispersion curves nari basin is clearly a 3d structure but it was expected that a laterally irregular model might be built from the interpolation of several 1d models dominant frequency maps based on results from hvsr suggest a simple sedimentary structure with mostly smooth lateral variations in contrast maximum amplification distribution is very irregular and shows no correlation with dominant frequency in the case of nari it seems that the complexity of the basin structure cancels the usefulness of hvsr we could estimate a phase velocity dispersion curve for 81 of the station pairs recording simultaneously ambient vibration in our arrays in all the cases the resulting dispersion curve had a simple shape suggesting that the subsoil structure consists of a single layer over a half space however the dispersion curves are incompatible among them even for different station pairs covering the same path something impossible if the subsoil structure were 1d it seems that the passive methods we have used in nari basin are not adapted to its structure this makes a tomography unfeasible and we are unable to propose a subsoil structure for nari basin our results show that surface wave dispersion may be estimated using the spac method even when the medium is far from 1d we believe that this problem is enhanced by the small size of this basin which amplifies the effect of lateral heterogeneities

delineating shallow s wave velocity structure using multiple ambient noise surface wave methods an example from western junggar china abstract aiming for a geophysical survey to around 1 5 km depth we conduct a passive source surface wave survey along a 70 km long line on the western side of the junggar basin in northwest china we use frequency time analysis and spatial autocorrelation methods to extract surface wave dispersion curves from ambient noise data of station pairs as well as ambient noise multichannel analysis of surface waves from multistations dispersion curves corresponding to the same positions obtained by these three methods independently are comparable which shows the validity of using these methods after inverting more than 400 dispersion curves and aligning their results together we construct a 2d shear s wave velocity image around 1 5 km deep and 60 km long a less than 6 difference between the inverted s wave velocity profile and the borehole data in situ shows the relatively high accuracy of our method the 2d s wave velocity image clearly delineates the main geologic structures including transition of landform intrusion of rock mass and shape of bedrock beneath the survey line

widespread global peatland establishment and persistence over the last 130 000 y glacial interglacial variations in co2 and methane in polar ice cores have been attributed in part to changes in global wetland extent but the wetland distribution before the last glacial maximum lgm 21 ka to 18 ka remains virtually unknown we present a study of global peatland extent and carbon c stocks through the last glacial cycle 130 ka to present using a newly compiled database of 1 063 detailed stratigraphic records of peat deposits buried by mineral sediments as well as a global peatland model quantitative agreement between modeling and observations shows extensive peat accumulation before the lgm in northern latitudes 40 n particularly during warmer periods including the last interglacial 130 ka to 116 ka mis 5e and the interstadial 57 ka to 29 ka mis 3 during cooling periods of glacial advance and permafrost formation the burial of northern peatlands by glaciers and mineral sediments decreased active peatland extent thickness and modeled c stocks by 70 to 90 from warmer times tropical peatland extent and c stocks show little temporal variation throughout the study period while the increased burial of northern peats was correlated with cooling periods the burial of tropical peat was predominately driven by changes in sea level and regional hydrology peat burial by mineral sediments represents a mechanism for long term terrestrial c storage in the earth system these results show that northern peatlands accumulate significant c stocks during warmer times indicating their potential for c sequestration during the warming anthropocene

site effect evaluation using spectral ratios with only one station the spectral ratio technique is a common useful way to estimate empirical transfer function to evaluate site effects in regions of moderate to high seismicity the purpose of this paper is to show that it is possible to estimate empirical transfer function using spectral ratios between horizontal and vertical components of motion without a reference station the technique originally proposed by nakamura to analyze rayleigh waves in the microtremor records is presented briefly and it is discussed why it may be applicable to study the intense s wave part in earthquake records results are presented for three different cities in mexico oaxaca oax acapulco gro and mexico city these cities are very different by their geological and tectonic contexts and also by the very different epicentral distances to the main seismogenic zones affecting each city each time we compare the results of nakamura s technique with standard spectral ratios in all three cases the results are very encouraging we conclude that if site effects are caused by simple geology a first estimate of dominant period and local amplification level can be obtained using records of only one station

effect of air sea ice interaction on winter 1996 southern ocean subpolar storm distribution air sea ice interaction processes in the southern ocean are investigated utilizing space observed surface winds sea ice concentration and sea surface temperature sst from september through december 1996 the sea ice edge sie shows three ice extent maxima around the antarctic during september and october when sea ice coverage is maximum they are located in the central indian ocean east of the ross sea and in the eastern weddell gyre during september and october most of the strong and long lasting storms initiate northeast of the three sea ice maxima such spatial distributions of storms and sea ice reflect coupling processes of the air sea ice interaction a relatively stable wave number 3 atmospheric circulation pattern that is believed to be fixed by the land ocean distribution prevails during the ice maximum season the ice extent maxima coincide with strong southerlies and divergent wind fields associated with this pattern which suggests that the mean atmospheric circulation determines the ice distribution the ice extent maxima can enhance the regional meridional surface pressure gradient and therefore strengthen the westerly winds north of the ice edge the decreasing ice extent east of the ice maxima creates a local zonal thermal gradient which enhances local southerlies this positive feedback between the wave pattern in the mean atmospheric circulation and ice distribution partially causes the eastward propagation of the ice maxima and also provides a favorable condition for cyclogenesis northeast of the ice extent maxima the mechanism of the cyclogenesis is the baroclinic instability caused by the cold air blown from the ice pack to the warm open ocean waters where the sst is warmest off the sie and the southerlies are the strongest the potential for cyclogenesis is most likely this is consistent with the observations

velocity structure under the trans mexican volcanic belt preliminary results using correlation of noise summary prediction of ground motion in central mexico is of great consequence not only for mexico city but also for several other cities in the region however the geometry and velocity distribution of the geological structures in central mexico is unknown in this paper the velocity structure in central mexico is investigated using seismic noise records from three different arrays one permanent and two temporary distances between stations span 3 300 km seismic noise is analysed using time domain cross correlation to estimate the green s function between stations only the fundamental mode of rayleigh waves is recovered in the cross correlation of vertical component records between 5 and 10 s period at smaller periods we obtain no correlation even between closely spaced stations this suggests that the heterogeneity of the trans mexican volcanic belt tmvb hampers the propagation of rayleigh waves smaller than 9 km we observe a large velocity contrast between the guerrero terrain and the tmvb this velocity contrast measured here for the first time at this scale explains the appearance of regional amplification in central mexico and the origin of the diffracted waves behind the long duration of ground motion observed in mexico city in the large scale average rayleigh wave group velocity at 5 s period is about 2 5 km s 1 in the tmvb and larger than 3 6 km s 1 outside it significant lateral heterogeneity is evident in the stations of the dense meso american subduction experiment array we analysed we observe in addition a significant increase in velocity from north to south in the central portion of the tmvb our results are part of ongoing studies with the final objective of building a model of tmvb that may be used to simulate ground motion in central mexico from subduction zone earthquakes

3d bedrock structure of bornova plain and its surroundings izmir western turkey an earthquake record is needed on engineering bedrock to perform soil deformation analysis this record could be obtained in different ways seismographs on engineering bedrock by the help of the soil transfer function scenario earthquakes s wave velocity v s profile must be known at least till engineering bedrock for calculating soil transfer functions true and completely in addition 2d or 3d soil engineering seismic bedrock models are needed for soil response analyses to be carried out these models are used to determine changes in the amplitude and frequency content of earthquake waves depending on the seismic impedance from seismic bedrock to the ground surface and the basin effects in this context it is important to use multiple in situ geophysical techniques to create the soil bedrock models in this study 2d and 3d soil bedrock models of bornova plain and its surroundings western turkey which are very risky in terms of seismicity were obtained by combined survey of surface wave and microgravity methods results of the study show that the engineering bedrock depths in the middle part of bornova plain range from 200 to 400 m and the southern and northern parts which are covered limestone and andesite show the engineering bedrock v s 760 m s feature in addition seismic bedrock v s 3000 m s depth changes from 550 to 1350 m the predominant period values obtained from single station microtremor method change from 0 45 to 1 6 s while they are higher than 1 s in the middle part of bornova plain where the basin is deeper bornova plain has a very thick sediment units which have very low v s values above engineering bedrock in addition it is observed sudden changes at the interfaces of the layer in horizontal and vertical directions

frontal instability generated by tropospheric potential vorticity anomalies the development of secondary disturbances on a two dimensional front is described using a linear stability analysis a two stage process is envisaged in which first strong frontogenesis produces condensation at the front this leads to the generation of a lower tropospheric zone of high potential vorticity pv lying along the front as frontogenesis weakens the second stage is entered in which an essentially steady front is susceptible to the growth of linear normal modes along the front owing to the existence of the pv anomaly or equivalently the frontal rainband thus for a typical band of width 160 km a frontal wave of some 800 km is produced with a growth rate of about 1 day 1 the dynamics of these modes is examined by considering both the realistic frontal flow as well as idealized strips of pv anomalies the idealized case is potentially applicable to a variety of meteorological situations such as upper jet streaks useful insight is gained from an analysis of the energetics of the modes this shows that for narrow frontal pv anomalies the waves main energy source is the basic kinetic energy and further they have a negative vertical heat flux recent observations suggest that frontal waves are indeed characterized by such a heat flux as most frontal zones involve significant condensation and therefore are likely to exhibit a lower tropospheric pv maximum it is stressed that studies of frontal waves need to include this aspect of the frontal structure

are microtremors useful in site response evaluation we have reviewed the applicability of microtremor measurements to evaluate site response of soft soils to this end we evaluated three different techniques commonly used to estimate site effects from microtremor measurements interpretation of fourier amplitude spectra computation of spectral ratios relative to a firm reference station and finally computation of spectral ratios of horizontal components relative to the vertical component of ground motion nakamura s technique these techniques are applied to microtremor records obtained in three cities in mexico mexico city oaxaca and acapulco these cities differ in their local geological conditions and in their seismotectonic environment in order to evaluate the results obtained from microtremor measurements we compare them with standard spectral ratios of the intense s wave part of weak or strong motion records obtained at the same sites our results showed that microtremor measurements can be used to estimate the dominant period of a site with very acceptable reliability in the range 0 3 to 5 hz the best results were obtained with nakamura s technique which also gives a rough estimate of amplification of seismic waves when the local geology is relatively simple simple numerical simulations indicate that the underlying assumptions of nakamura s technique are consistent with the propagation of rayleigh waves these simple numerical simulations also explain why different researchers have been able to successfully characterize 1d site effects using microtremor records regardless of whether they consider microtremors to consist of surface or body waves our results strongly suggest that the technique by nakamura effectively compensates for source effects in microtremor measurements which eliminates a major limitation to their application in earthquake engineering

the seismic noise wavefield is not diffuse passive seismology is burgeoning under the apparent theoretical support of diffuse acoustics however basic physical arguments suggest that this theory may not be applicable to seismic noise a procedure is developed to establish the applicability of the diffuse field paradigm to a wavefield based on testing the latter for azimuthal isotropy and spatial homogeneity this procedure is then applied to the seismic noise recorded at 65 sites covering a wide variety of environmental and subsoil conditions considering the instantaneous oscillation vector measured at single triaxial stations the hypothesis of azimuthal isotropy is rejected in all cases with high confidence which makes the spatial homogeneity test unnecessary and leads directly to conclude that the seismic noise wavefield is not diffuse however such a conclusion has no practical effect on passive imaging which is also possible in non diffuse wavefields

a satellite derived classification scheme for rapid maritime cyclogenesis abstract guided by the conjecture that there exist characteristic synoptic scale flow patterns conducive to extratropical cyclogenesis a satellite based classification scheme is proposed to differentiate between various types of rapid maritime cyclogenesis in the western north atlantic region the scheme is derived from signatures in visible and infrared satellite imagery observed prior to and during rapid deepening consideration of the western north atlantic region is motivated by the presence of a relatively dense upstream observational network and by the absence of the direct influence of orography in a maritime environment the focus on rapid development is predicated upon the assumption that the cloud signatures will be more clearly defined than in cases of slower ordinary development examination of satellite imagery for an ensemble of 50 cyclogenesis events that occurred during the 1970s and 1980s 46 of which satisfied the experiment on rapidly intensifying cyclones over the atlantic criterio

satellite based midlatitude cyclone statistics over the southern ocean 1 scatterometer derived pressure fields and storm tracking 1 a wavelet based method is described for incorporating swaths of surface pressure derived from scatterometer measurements into surface pressure analyses obtained from the european centre for medium range weather forecasts ecmwf the resulting modified pressure fields are used to identify low pressure centers over the southern ocean and to build statistics of midlatitude cyclones during 7 years of the seawinds on quikscat operational period july 1999 to june 2006 the impact of the scatterometer derived pressure swaths is assessed with a statistical analysis of cyclone characteristics central pressure radius depth performed in parallel on the ecmwf and on the modified pressure fields more low pressure centers 5 10 depending on the season are identified with the modified pressure fields in particular incipient lows captured earlier than ecmwf and more short lived mesoscale cyclones with a life span less than 4 days the cyclones identified with the modified pressure fields are characterized by lower central pressure and tighter isobars on average a parallel spectral analysis reveals 1 additional energy at scales less than 2000 km in the modified pressure fields

transition from a warm and dry to a cold and wet climate in ne china across the holocene abstract northeast ne china lies in the northernmost part of the east asian summer monsoon easm region although a series of holocene climatic records have been obtained from lakes and peats in this region the holocene hydrological history and its controls remain unclear more specifically it is currently debated whether ne china experienced a dry or wet climate during the early holocene here we reconstruct changes in mean annual air temperature and peat soil moisture across the last 13 000 year bp using samples from the gushantun and hani peat located in ne china our approach is based on the distribution of bacterial branched glycerol dialkyl glycerol tetraethers brgdgts and the abundance of the archaeal isoprenoidal iso gdgt crenarchaeol using the recently developed peat specific maatpeat temperature calibration we find that ne china experienced a relatively warm early holocene 5 7 c warmer than today followed by a cooling trend towards modern day values during the mid and late holocene moreover crenarchaeol concentrations brgdgt based ph values and the distribution of 6 methyl brgdgts all indicate an increase in soil moisture content from the early to late holocene in both peats which is largely consistent with other data from ne china this trend towards increasing soil moisture wetter conditions across the holocene in ne china records contrasts with the trends observed in other parts of the easm region which exhibit an early and or mid holocene moisture precipitation maximum however the holocene soil moisture variations and temperature moisture relationships warm dry and cold wet observed in ne china are similar to those observed in the core area of arid central asia which is dominated by the westerlies we therefore propose that an increase in the intensity of the westerlies across the holocene driven by increasing winter insolation expanding arctic sea ice extent and the enhanced okhotsk high caused an increase in moisture during the late holocene in ne china

nondiffuse elastic and anelastic passive imaging the property at the basis of passive acoustic imaging is that taken any two points one of them can be seen as the source of the waves and the other as the recording station this property which was shown to hold also in nondiffuse fields is here exploited 1 to allow an undistorted passive imaging through the simple use of the statistical mode to estimate wave velocity 2 to determine the azimuth of the instantaneous huygens sources of the noise wavefield and 3 to measure provided that the noise bandwidth is wide with respect to that of the local system the material dissipation constant as a function of frequency the authors applied this theory to study the seismic noise field in the ravenna north central italy shore area and found it capable to provide velocity dispersion curves matching those of independent surveys to track the sources of seismic noise to a few major firms in ravenna port with the prevailing source switching at the time scale of seconds and to measure the dissipation

the three dimensional shear wave structure in the mantle by overtone waveform inversion i radial seismogram inversion summary the three dimensional 3 d shear wave structure of the mantle down to the depth of about 900 km is obtained by inverting waveforms of radial component seismograms radial component seismograms contain large amplitude overtone signals which circle the earth as wave packets and are sometimes called x1 x2 x3 we use data which contain r1 x1 and x2 and filtered between 2 and 10mhz it is shown that unless each seismogram is weighted all seismograms are not fitted uniformly only data from large earthquakes are fitted and the final velocity anomalies are biased by the small number of large earthquake data resolution is good at shallow depths becomes worse in the intermediate depth range between about 400 and 500 km and then becomes better at greater depth ranges 600 900km even though we use only spheroidal mode data velocity anomalies in the shallow structure show excellent correlation with the age of the surface rocks of the earth in the deeper regions between about 600 and 900km south america shows a fast velocity anomaly which may indicate the slab penetration beyond 700 km there another region which shows a fast velocity anomaly is the mariana trench but other subduction regions do not show such features

effects of a low level precursor and frontal stability on cyclogenesis during fastex iop17 the fronts and atlantic storm track experiment fastex has provided comprehensive data to document the life cycle of secondary frontal cyclones over the north atlantic and to improve the understanding of cyclogenesis mechanisms this study analyses the processes leading to the triggering of a particularly well sampled frontal cyclone that developed on the trailing cold front of a mature primary cyclone during fastex intensive observation period 17 iop17 between 16 and 20 february 1997 the case features both a classical low level vorticity strip along the primary front where the frontal cyclone develops and more unexpectedly a pre existing continental surface low further west the importance of which is revealed in the pilot study of arbogast and joly in order to study possible cyclogenetic contributions along the primary front the domain independent vorticity divergence attribution technique of bishop is used to partition the flow into contributions from the continental low and from the large scale environment results indicate that the frontal cyclone is triggered where and when along front stretching decreases below the theoretical critical threshold of bishop and thorpe it is shown that the cyclone is developing under normalized strain less than 1 in agreement with other case studies finally the role of the continental low is investigated using a series of numerical forecasts made from different initial conditions manipulated with a potential vorticity inversion tool the wind attributable to the continental low accounts for roughly 30 of the along front stretching decrease the continental low also has a frontolytic effect on the western part of the primary front where its thermal advection pattern favours cyclogenesis in general terms the frontal cyclone triggering seems to support the bishop and thorpe theoretical framework of frontal instability in low strain areas however a more complex picture arises when considering the role of the continental surface low which also acts as a low level precursor

site effects in a volcanic environment a comparison between hvsr and array techniques at colima mexico colima city is the capital of the mexican federal state of the same name it is located close to the pacific coast and is subjected to a large seismic risk we present a microzonation study in this city based on microtremors using single station and array measurements we applied horizontal to vertical spectral ratios hvsr analysis to single station measurements at 310 sites within the city concentrating measurements in zones that were damaged by the january 2003 m 7 4 earthquake the results show that a seismic zonation based exclusively on single station microtremor measurements is not a reliable alternative when the local geology is complex and site effects are not the result of a single impedance contrast for this reason we applied two independent analysis techniques to array measurements of microtremors the spatial autocorrelation spac method and the refraction microtremor remi method we used linear arrays to record 25 sec microtremor windows at eight sites within the city which were analyzed with those two techniques the result of both techniques of analysis is a phase velocity dispersion curve which can be inverted to obtain a shallow s wave velocity profile two of the sites were the location of shallow 50 m boreholes where p and s wave velocity profiles were measured using a p s suspension log the phase velocity dispersion curves obtained from the remi and spac analyses of the microtremor records showed very good agreement the velocity profiles inverted from the phase velocity dispersion curves showed good agreement with the suspension logging measurements at one of the two sites where they were available and poor agreement at the other site the transfer functions computed from the inverted soil profiles are in good agreement with previous estimates of local amplification from spectral ratios analysis of earthquake records our results are compatible with previous indications of site effects and explain the failure of single station microtremor measurements when the concept of dominant frequency loses its meaning finally we propose an estimate of local site amplification at the city of colima which will be useful for future predictions of ground motion at this city