partitioning of pyroclasts between ballistic transport and a convective plume kīlauea volcano 19 march 2008 we describe the discrete ballistic and wind advected products of a small but exceptionally well characterized explosive eruption of wall rock derived pyroclasts from k lauea volcano on 19 march 2008 and for the first time integrate the size distribution of the two subpopulations to reconstruct the true size distribution of a population of pyroclasts as it exited from the vent based on thinning and fining relationships the wind advected fraction had a mass of 6 1 105 kg and a thickness half distance of 110 m placing it at the bottom end of the magnitude and intensity spectra of pyroclastic falls the ballistic population was mapped in the field and using structure from motion techniques to a diameter 10 20 cm over an area of 0 1 km2 with an estimated mass of 1 105 kg initial ejection velocities of 50 80 m s were estimated from inversion of isopleths the total grainsize distribution was estimated using a mass partitioning of 98 of wind advected material and 2 of ballistics resulting in median and sorting values of 1 7 and 3 1 it is markedly broader than those calculated for the products of magmatic explosive eruptions because the grainsize of 19 march 2008 clast population is unrelated to a volcanic fragmentation event and instead was inherited from a population of talus clasts that temporary blocked the vent prior to the eruption despite a conspicuous near field presence the ballistic subpopulation has only a minor influence on the grainsize distribution because of its rapid thinning and fining away from source

inertia gravity waves observed in the lower stratosphere over macquarie island abstract this study examines the properties of inertia gravity waves observed in the lower stratosphere over macquarie island how these properties vary with season and the likely source of the waves the waves are observed in high resolution upper air ozonesonde soundings of wind and temperature released from macquarie island during the 1994 ashoe maesa program the properties of the inertia gravity waves observed in the soundings are quantified using hodograph and rotary spectral analyses the analyzed waves have horizontal wavelengths between 100 and 1000 km vertical wavelengths between about 1 and 7 km intrinsic frequencies between f and 2f and horizontal trace speeds between 50 and 30 m s 1 there appears to be a seasonal cycle in the inertia gravity wave activity in the lower stratosphere the minimum being in the austral winter when the background zonal flow is strong and westerly and its vertical shear is positive in contrast the variance of the horizontal perturbation winds does not show a

a multidisciplinary effort to assign realistic source parameters to models of volcanic ash cloud transport and dispersion during eruptions during volcanic eruptions volcanic ash transport and dispersion models vatds are used to forecast the location and movement of ash clouds over hours to days in order to define hazards to aircraft and to communities downwind those models use input parameters called eruption source parameters such as plume height h mass eruption rate duration d and the mass fraction m63 of erupted debris finer than about 4 or 63 m which can remain in the cloud for many hours or days observational constraints on the value of such parameters are frequently unavailable in the first minutes or hours after an eruption is detected moreover observed plume height may change during an eruption requiring rapid assignment of new parameters this paper reports on a group effort to improve the accuracy of source parameters used by vatds in the early hours of an eruption we do so by first compiling a list of eruptions for which these parameters are well constrained and then using these data to review and update previously studied parameter relationships we find that the existing scatter in plots of h versus yields an uncertainty within the 50 confidence interval of plus or minus a factor of four in eruption rate for a given plume height this scatter is not clearly attributable to biases in measurement techniques or to well recognized processes such as elutriation from pyroclastic flows sparse data on total grain size distribution suggest that the mass fraction of fine debris m63 could vary by nearly two orders of magnitude between small basaltic eruptions 0 01 and large silicic ones 0 5 we classify eleven eruption types four types each for different sizes of silicic and mafic eruptions submarine eruptions brief or vulcanian eruptions and eruptions that generate co ignimbrite or co pyroclastic flow plumes for each eruption type we assign source parameters we then assign a characteristic eruption type to each of the world s 1500 holocene volcanoes these eruption types and associated parameters can be used for ash cloud modeling in the event of an eruption when no observational constraints on these parameters are available

gsett 3 evaluation of the detection and location capabilities of an experimental global seismic monitoring system this article presents the results of the seismological evaluation of the first 18 months january 1995 to june 1996 of the group of scientific experts third technical test gsett 3 performance measures such as completeness estimates of detection thresholds and equivalent circle areas as an estimate of location accuracies are obtained by comparing the reb reviewed event bulletin of gsett 3 to global and regional reference bulletins and also by intrinsic methods incremental detection thresholds are stated on the pde preliminary determination of epicenter m b scale magnitude conversion formulae are derived to convert reb m b and other reference bulletin magnitudes to this scale at the 90 confidence level an incremental detection threshold of about m b pde 3 5 or better is attained in northwest europe and parts of north america central asia and australia apart from these areas the threshold is generally around 4 0 in the northern hemisphere in the southern hemisphere it is 4 2 or better in most of south america and northern and equatorial africa and between 4 2 and 4 6 in other regions with the highest values being attained in some remote parts of the southern oceans still at the 90 confidence level equivalent circle areas for the m b pde 4 4 5 magnitude range come close to 1 000 km 2 in northern europe the global average is about 8 000 km 2 at the 50 level the median of all detected events most northern hemisphere regions have equivalent circle areas at or below 1 000 km 2 and even in the southern hemisphere 5 000 km 2 are not exceeded observed performance is used to calibrate network simulation codes which allow to interpolate system capabilities over aseismic regions and to extrapolate for the capabilities of the future international monitoring system ims seismic network it is concluded that at the 90 confidence level except in remote ocean areas a global incremental detection threshold of m b pde 4 and a location accuracy of the order of 1 000 km 2 are attainable with the ims seismic network however this will require a full calibration of the network and an optimized usage of the auxiliary station network new computational methods as well as calibration will help to improve the depth determination

a statistical study of gravity waves in the polar regions based on operational radiosonde data gravity waves in the lower polar stratosphere are examined using operational radiosonde observations gathered from 33 stations over a period of 10 years both the potential and kinetic energies of the gravity waves vary annually and reach maxima in winter in the arctic and in spring in the antarctic in the antarctic spring a region of large gravity wave energy propagates downward following the movement of a zone of high static stability associated with southern hemispheric warming moreover the enhanced energy region and the high stability zone coincide in the horizontal plane and move gradually from 135 e 50 s to 45 w 70 s over the south pole the vertical and horizontal directions of wave propagation are examined using hodograph analysis in the vertical most gravity waves transfer energy upward in the arctic while the percentage of downward energy propagation is relatively high in winter and spring in the antarctic horizontally gravity waves propagate westward relative to the mean wind in the arctic while in the antarctic the dominant direction varies from station to station the correlation between gravity wave energy in the lower stratosphere and the mean wind is also examined in the arctic gravity wave energy is highly correlated with the surface wind though in the antarctic it correlates with the stratospheric wind these results suggest that gravity waves observed in the arctic are forced by topography whereas in antarctica some sources may exist in the stratosphere one such source candidate is likely to be the polar night jet

dispersal of key subplinian plinian tephras from hekla volcano iceland implications for eruption source parameters hekla is the most active silicic volcano in iceland with 18 subplinian plinian eruptions since ad 1104 in the period 1970 to 2000 the frequency of such eruptions increased to once every decade hekla is currently inflated to above the levels observed prior to the most recent eruptions in 1991 and 2000 the next eruption could pose a hazard to air traffic between north america and europe because explosive eruptions of hekla independent of size typically start with a subplinian or plinian phase that produces a sustained ash plume we present an overview of five of the largest historical hekla eruptions taking place in 1104 1158 1300 1693 and 1766 these eruptions cover a compositional range of rhyolite to andesite previously estimated volcanic explosivity index vei values of 4 5 and are characterised by contrasting wind dispersal dispersal axes nw ne new isopach maps show both greater deposit thicknesses in the proximal region and wider dispersal than previously inferred resulting in different volume estimates minimal values ranging between 0 18 and 0 91 km3 new isopleth maps were also compiled and resulted in inferred plume heights of about 13 25 km these changes in the estimated values of volume and mass eruption rates have large implications on the forecasting and impacts of future hekla eruptions

gravity wave generation around the polar vortex in the stratosphere revealed by 3 hourly radiosonde observations at syowa station intensive radiosonde observations were performed at syowa station 69 0 s 39 6 e over about 10 days in each of march june october and december 2002 to examine inertia gravity wave characteristics in the antarctic lower stratosphere based on the 3 hourly observation data two dimensional i e vertical wavenumber versus frequency spectra of wind fluctuations were examined utilizing a double fourier transform method clear signals of gravity waves whose phases propagate upward suggesting downward energy propagation are detected in june and october when the polar night jet pnj was present on the other hand downward phase propagation i e upward energy propagation components are dominant in all months there is a spectral peak around the inertial frequency in a wide range of vertical wavenumbers in december when the background wind was weak whereas large spectral densities are distributed over lower frequency regions in june and october these spectral characteristics are consistent with the results obtained using a gravity wave resolving global circulation model gcm by sato et al dynamical characteristics are examined separately for upward and downward propagating gravity waves in june using a hodograph analysis method as a result it is found that upward and downward propagating wave packets observed simultaneously in the same height regions have similar horizontal wavelengths and phase velocities this fact suggests that these gravity waves are generated from the same source with a similar mechanism when the wave packets were observed both the local rossby number and the residual in the nonlinear balance equation estimated using ncep ncar reanalysis data are large around the pnj situated slightly to the lower latitudes of syowa station therefore it is likely that the observed inertia gravity waves are generated by a spontaneous adjustment around the geostrophically unbalanced pnj and propagate toward syowa station the possibility of spontaneous gravity wave generation around the pnj is confirmed by comparison with the gcm simulation by sato et al

a gravity wave climatology for antarctica compiled from challenging minisatellite payload global positioning system champ gps radio occultations 1 the seasonal geographical and altitudinal dependence of gravity wave activity in the lower stratosphere over antarctica is presented gravity wave activity is estimated by calculating potential energy ep from radio occultation profiles obtained by the challenging minisatellite payload global positioning system champ gps experiment significant seasonal variation of wave activity is observed smaller wave activity in summer is attributed to waves with small phase velocities experiencing critical level filtering at other times of the year when wave activity is large less filtering occurs and the strong background wind is likely to cause doppler shifting of waves to longer vertical wavelengths which can reach larger amplitudes before saturating relationships between gravity wave activity and geographic location indicate that topography is a strong source for wave activity especially over the antarctic peninsula however wind rotation in this area was found to reduce the wave energy in summer at certain altitudes a strong enhancement of wave energy is observed at the edge of the polar vortex again reduced critical level filtering and doppler shifting in the area of the jet are likely to be major causes for this finding possible limitations to this study due to observational filtering are discussed

the horizontal kinetic energy spectrum and spectral budget simulated by a high resolution troposphere stratosphere mesosphere gcm abstract horizontal kinetic energy spectra simulated by high resolution versions of the geophysical fluid dynamics laboratory skyhi middle atmosphere general circulation model are examined the model versions considered resolve heights between the ground and 80 km and the horizontal grid spacing of the highest resolution version is about 35 km tropospheric kinetic energy spectra show the familiar 3 power law dependence on horizontal wavenumber for wavelengths between about 5000 and 500 km and have a slope of 5 3 at smaller wavelengths qualitatively similar behavior is seen in the stratosphere and mesosphere but the wavelength marking the transition to the shallow regime increases with height taking a value of 2000 km in the stratosphere and 4000 km in the mesosphere the global spectral kinetic energy budget for various height ranges is computed as a function of total horizontal wavenumber contributions to the kinetic energy tendency from nonlinear advective processes from conversion of avai

a three dimensional eulerian model for transport and deposition of volcanic ashes abstract volcanic ash fallout represents a serious threat to people living near active volcanoes because it can produce several undesirable effects such as collapse of roofs by ash loading respiratory sickness air traffic disruption or damage to agriculture the assessment of such volcanic risk is therefore an issue of vital importance for public safety and its mitigation often requires to evaluate the temporal evolution of the phenomenon through reliable computational models we develop an eulerian model named fall3d for the transport and deposition of volcanic ashes the model is based on the advection diffusion sedimentation equation with a turbulent diffusion given by the gradient transport theory a wind field obtained from a meteorological limited area model lam and the source term derived from by buoyant plume theory it can be used to forecast either ash concentration in the atmosphere or ash loading on the ground model inputs are topography meteorological data given by a lam mass eruption rate and a particle settling velocity distribution a test application to the july 2001 etna eruption is presented

general aspects of a t213l256 middle atmosphere general circulation model 1 a high resolution middle atmosphere general circulation model gcm developed for studying small scale atmospheric processes is presented and the general features of the model are discussed the gcm has t213 spectral horizontal resolution and 256 vertical levels extending from the surface to a height of 85 km with a uniform vertical spacing of 300 m gravity waves gws are spontaneously generated by convection topography instability and adjustment processes in the model and the gcm reproduces realistic general circulation in the extratropical stratosphere and mesosphere the oscillations similar to the stratopause semiannual oscillation and the quasi biennial oscillation qbo in the equatorial lower stratosphere are also spontaneously generated in the gcm although the period of the qbo like oscillation is short 15 months the relative roles of planetary waves large scale gws and small scale gws in maintenance of the meridional structures of the zonal wind jets in the middle atmosphere are evaluated by calculating eliassen palm diagnostics separately for each of these three groups of waves small scale gws are found to cause deceleration of the wintertime polar night jet and the summertime easterly jet in the mesosphere while extratropical planetary waves primarily cause deceleration of the polar night jet below a height of approximately 60 km the meridional distribution and propagation of small scale gws are shown to affect the shape of the upper part of mesospheric jets the phase structures of orographic gws over the south andes and gws emitted from the tropospheric jet stream are discussed as examples of realistic gws reproduced by the t213l256 gcm

procedures for computing focal mechanisms from local sv p z data abstract a procedure for calculating the focal mechanism of an earthquake from the distribution of the ratio of the amplitudes of sv to p waves has been developed and tested the input consists of information taken from the hypocenter solution for the earthquake a factor for each station that corrects for the effect of the free surface on the observed wave amplitudes and the observed values of the ratio of the vertical component of p to the vertical component of sv the procedure starts with the selection of a slip direction the program then finds the best fault strike and dip corresponding to that slip direction with best measured by the smallest scatter of the dip for any strike all three fault parameters are then adjusted by an iterative least squares adjustment sv p z is a strongly nonlinear function of the fault parameters so the solution found by the procedure is inherently nonunique the acceptable solutions can be quite well constrained if the slip direction can be estimated initially on the basis of independent information a variety of tests of the procedure have been carried out on real and synthetic data given a set of amplitude data for an earthquake in bear valley california and told only that the mode of slip was predominantly strike slip the program found the san andreas fault i e converged to a fault with strike and dip close to the known values further work on a german earthquake served to bring out some of the ambiguities of the solutions analysis of data from a brief swarm of earthquakes in southwest germany showed that the method yields useful mechanisms for small events and revealed a rotation of the focal mechanisms during the swarm processing of amplitudes from synthetic seismograms gave a fault plane close to the known input but marked disagreement between the sv amplitudes on the synthetic seismograms and the amplitudes predicted by simple dislocation theory is unresolved

gravity waves in the tropical lower stratosphere a model study of seasonal and interannual variability a model study is presented to clarify the relationship between gravity wave properties observed in the stratosphere and the sources for the waves presumed to be in the troposphere the observations are balloon borne radiosondes launched from cocos island in the tropical indian ocean 12 s 97 e and the analysis of these data is described in a companion paper vincent and alexander this issue the dominant time variations in the observed gravity wave activity are annual and quasi biennial patterns in the zonal momentum flux and kinetic energy density the background zonal winds at this site vary with the same periods and these are known to be capable of causing dramatic variations in the observable properties of the waves even if the sources for the waves are constant in time the results presented here clarify 1 the nature of the sources for the gravity waves observed in the stratosphere 2 the limitations of the observations for observing the full range of gravity wave perturbations potentially present in the atmosphere and 3 the role the observed waves can play in forcing the quasibiennial oscillation qbo in the zonal winds at this latitude the stratospheric waves appear to originate near the height of the tropopause so the source is apparently related to deep convection no seasonal or interannual variations in the convection need be assumed to understand the observations the waves at the tropopause appear to have a phase speed distribution that is narrowly confined near zero phase speed relative to the ground the source is likely related to slowly propagating tropospheric convection and the wind near the tropopause variations observed in the stratospheric data are caused by both the wind shear in the stratosphere and the ability of waves with these characteristics to propagate vertically without severe dissipation higher phase speed waves may be present and could carry significant momentum flux vertically into the stratosphere and mesosphere but would be extremely difficult to see in these radiosonde data the observed waves can contribute substantially to the descent of the eastward shear zones characteristic of the westerly phase of the qbo in the lower stratosphere zonal winds

inversion for source parameters from sparse data sets test of the method and application to the 1951 m 6 9 kona hawaii earthquake we have tested a method originally developed by beisser et al 1990 to retrieve the source parameters strike dip rake and depth of sparsely recorded earthquakes from the inversion of teleseismic waveform data the complete wave train of all body waves is modeled using the reflectivity method the parameter space of strike dip and rake is searched to find the source orientation which leads to the minimum misfit between the observed and the synthetic seismogram the 1983 kaoiki hawaii earthquake ms 6 6 was chosen as a test case the inversion of the full data set 16 stations gave a fault plane solution similar to the best double couple moment tensor solution of harvard university and national earthquake information centre these three solutions were averaged to create a standard solution sparse data sets were simulated by decimating the full data set and the resulting fault plane solutions were compared with the standard we found that as few as one to three stations were sufficient to retrieve the focal mechanism of the 1983 kaoiki event we applied this technique to the 1951 kona hawaii earthquake ms 6 9 a total of four stations and nine components were used to model the source parameters of this earthquake the depth was estimated at 13 3 km the fault plane solution was a decollement type with a near horizontal plane dipping at about 15 to the southwest and a near vertical plane striking nw se this observation supports a tectonic model for the kona coast similar to that of kilauea s south flank the upper crust is pushed away from the center of hawaii slipping westward along a near horizontal plane of weakness

gravity waves in the tropical lower stratosphere an observational study of seasonal and interannual variability radiosonde observations made at cocos islands 12 s 97 e in the indian ocean between september 1992 and june 1998 are used to study seasonal and interannual variations in gravity wave activity in the lower stratosphere 18 25 km the islands are located in a region of generally strong convection that occurs at all times of the year with the period of strongest convective activity between december and july wet season the prevailing zonal winds during the observational period and height range are westward with a quasi biennial oscillation qbo superimposed time series of wave energy show that largest wave amplitudes occur during the wet season when convection is strongest but a qbo like variation is also apparent maximum energy densities of about 25 j kg 1 occur early 1993 1995 and 1997 at the times when the westward shears are largest wave energy is found to be propagating upward and in the horizontal there is considerable azimuthal anisotropy with predominate eastward propagation against the prevailing wind upward fluxes of zonal momentum flux u w are estimated by combining the temperature and wind information fluxes show a similar temporal behavior to the energy the motion and temperature fields are dominated by waves with vertical wavelengths 2 km using a stokes parameter analysis it is found that the intrinsic frequencies are on average 2 3 times the inertial frequency corresponding to intrinsic periods of 20 25 hours horizontal wavelengths between 200 and 2000 km are inferred with a mean value of about 1000 km the mean intrinsic phase speeds are about 10 ms 1 but ground based phase speeds are centered on 0 ms 1

depth determination of north italian earthquakes using grafenberg data surface reflections such as pp and sp have long been used to determine the source depth of teleseismic events due to difficulties in identifying these phases at single narrow band stations they have rarely been used for regional events correlation over an array of stations and the possibility of applying different filters to broadband data allows such phases to be identified we describe a method to determine the source depth which uses such depth phases at regional distances complete theoretical seismograms are an important aid for the interpretation of these depth phases the method is demonstrated using small events from the lombardia region and large events from friuli northern italy good agreement is achieved with depth determinations by other authors for the friuli events relative source depths are determined very accurately since only time differences need to be compared

energy enhancements of gravity waves in the antarctic lower stratosphere associated with variations in the polar vortex and tropospheric disturbances 1 gravity waves in the antarctic lower stratosphere are examined using original operational radiosonde data obtained at syowa station 69 0 s 39 6 e with fine vertical resolution in the lower stratosphere the temporal variation in gravity wave energy depends on height in the height region of 13 15 km just above the tropopause the seasonal variation in gravity wave energy is not evident the wave energy is rather enhanced when the absolute value of potential vorticity in the upper troposphere becomes small over syowa station this fact implies that tropospheric disturbances affect the dynamical processes of gravity waves there however the gravity wave energy in the height region of 15 25 km shows clear seasonal variation having a maximum in spring the time variation in gravity wave energy is examined in detail in terms of the polar vortex by using the equivalent latitude coordinate energy enhancements occur when the edge of the polar vortex approaches syowa station and the enhancements are especially large when the polar vortex breaks down in spring these results suggest that height variation in the background atmosphere leads to the difference of wave characteristics between the two height regions the enhancements of wave energy are partly explained as modification of the wave structure by the background wind speed and the static stability but it is also likely that enhancements of wave activity contribute to the energy enhancement at the edge of the polar vortex in spring

constraining explosive volcanism subjective choices during estimates of eruption magnitude when estimating the magnitude of explosive eruptions from their deposits individuals make three sets of critical choices with respect to input data the spacing of sampling sites the selection of contour intervals to constrain the field measurements and the hand contouring of thickness isomass data respectively volcanologists make subjective calls as there are no accepted published protocols and few accounts of how these choices will impact estimates of eruption magnitude here for the first time we took a set of unpublished thickness measurements from the 1959 k lauea iki pyroclastic fall deposit and asked 101 volcanologists worldwide to hand contour the data first there were surprisingly consistent volume estimates across maps with three different sampling densities second the variability in volume calculations imparted by individuals choices of contours is also surprisingly low and lies between s 5 and 8 third volume estimation is insensitive to the extent to which different individuals smooth the raw data in constructing contour lines finally large uncertainty is associated with the construction of the thinnest isopachs which is likely to underestimate the actual trend of deposit thinning the net result is that researchers can have considerable confidence in using volume or dispersal data from multiple authors and different deposits for comparative studies these insights should help volcanologists around the world to optimize design and execution of field based studies to characterize accurately the volume of pyroclastic deposits

sources of gravity waves in the lower stratosphere above south pole 1 five year 2001 2005 high resolution radiosonde data were processed to obtain the gravity wave gw variabilities in the lower stratosphere over south pole sp our results show that gw activities in the lowermost section 10 15 km are strongest in may and september and weakest in the austral summer whereas in the altitude range of 15 25 km strongest weakest gw kinetic energy is observed around september january we also explored the relationships of gws to the synoptic scale variations in the troposphere and the ageostrophic motions in the upper troposphere over the antarctic which are expected to be significant mechanisms for gw generation a ray tracing model grograt was used to explore the relationship between gw propagation and the background field in the altitude of 15 25 km the annual cycle of gw activity resembles that of adjustment process below 15 km the annual cycle of gw activity has two peaks in may and september our analysis suggests that these two peaks are due to the variation of topographic gw generation and filtering of background atmosphere due to critical level filtering in the lowermost section topographic gws cannot propagate upward which makes the shape of gw annual cycle at higher altitudes closer to the annual cycle of adjustment processes the analysis suggests that the minimum of gw activity at sp during the austral summer may be due to the combination of weaker wave generation from adjustment processes associated with synoptic scale systems flow over topography and unfavorable background field for gw propagation

inversion of source parameters for subcrustal earthquakes in the hellenic arc summary a one station method was developed to invert simultaneously for seismic moment focal depth and the orientations of the nodal planes this method was tested on seismograms recorded at the broadband grefenberg array grf for earthquakes in the central to eastern hellenic arc and southern turkey the complete p and s body wave responses including all near source surface reflections were synthesized using the reflectivity method the minimum misfit between the observed and theoretical seismograms in the wwssn lp band was determined by cross correlation searching the whole parameter space of strike dip and rake of a pair of orthogonal nodal planes and adjusting the source depth and seismic moment the initial searching step of 20 was reduced to 5 in the vicinity of the minimum misfit position for a final search the best fitting solution was then compared to the harvard hrvd moment tensor solution best double couple which was derived using long period data and to the p wave first motion polarities reported by the isc most solutions based on grf data agree well with those found by hrvd but in some cases some features of the observed grf signals cannot be matched by the hrvd solution or solutions similar to it the nine earthquakes we analysed in detail had magnitudes between 5 2 and 5 8 our depth determinations ranged from 35 to 155 km the deepest events 80 155 km were located near rhodes and to the east of it one earthquake located in southern turkey was confirmed to have a focus at about 125 km depth the focal mechanisms of the intermediate depth earthquakes in the eastern hellenic arc show p axes approximately parallel to the strike of the deep slab

characteristics of atmospheric gravity wave activity in the polar regions revealed by gps radio occultation data with champ 1 using gps radio occultation data during 2001 2005 we studied the climatological behavior of atmospheric gravity waves in the polar stratosphere we calculated temperature fluctuations with vertical wavelengths shorter than 7 km and then determined the wave potential energy ep every month in a longitude latitude cell of 20 10 between 12 km and 33 km in the arctic region 50 90 n ep shows an annual variation with maximum in winter consistent with the zonal mean horizontal wind v and the eliassen palm e p flux fz the large fz values indicate higher planetary wave activity resulting in distortion of the polar vortex the unbalanced flow can then excite gravity waves through geostrophic adjustment in the antarctic region 50 90 s ep gradually increases during winter and reaches its maximum in spring before decreasing rapidly the time derivative of v coincides with the ep peak and the horizontal distribution of ep has a similar structure to v suggesting that the ep enhancement is closely related to the decay of the polar vortex during major warming events over the arctic the divergence of e p flux f was enhanced coinciding with large ep in the antarctic f strongly correlates with ep in spring gravity waves seem to be effectively generated through planetary wave transience and or breaking orographic generation of gravity waves seems to be important in limited areas only such as scandinavia and the antarctic peninsula showing that it is less important than the polar night jet in determining the climatological behavior of gravity waves

earthquake locations in the western hellenic arc relative to the plate boundary four vertical component seismograph stations were operated in western crete southeastern peloponnesus the island of milos and south of corinth on mount didimon from 1981 to 1984 combining arrival times from this network the greek national network and volnet we relocated hypocenters within greece and the surrounding area the difference between the relocations and the locations published in the national observatory of athens bulletin in most instances were minor except for earthquakes located in the vicinity of the western hellenic arc in this area we found that epicenters thought to lie south of the plate boundary within the african plate relocated an average of approximately 60 km to the n30 e which places them at or north of the plate boundary we suggest that this difference is a minimum estimate of the location error and the true locations may lie still further to the nne we propose that anomalously slow seismic velocities in the aegean back arc upper mantle cause travel time delays to the seismograph stations located to the ne of the source volumes resulting in location errors in a direction away from these stations extrapolating from our observations to other segments of the hellenic plate boundary and to periods not covered by our operation we hypothesize that most or all earthquakes thought to have originated on the african plate within about 100 km of the hellenic arc were actually located at the plate boundary or on the aegean plate

alleviation of a systematic westerly bias in general circulation and numerical weather prediction models through an orographic gravity wave drag parametrization systematic westerly biases in the northern hemisphere wintertime flow of the meteorological office 15 layer operational model and 11 layer general circulation model are described evidence that the failure to parametrize subgrid scale orographic gravity wave drag may account for such biases is presented this evidence is taken from aircraft studies surface pressure drag measurements and studies of the zonally averaged momentum budget a parametrization scheme is described in which the surface stress is proportional to the near surface wind speed and static stability and to the variance of subgrid scale orography the stress is absorbed in the vertical by considering the influence of such gravity wave activity on static stability and vertical wind shear a richardson number dependent wave breaking formulation is devised and the vertical stress profile determined by a saturation hypothesis whereby the breaking waves are maintained at marginal stability it is shown that wave breaking preferentially occurs in the boundary layer and in the lower stratosphere results from a simple zonally symmetric model show how the adjustment to thermal wind balance with a wave drag in the stratosphere warms polar regions by adiabatic descent and decelerates the mean westerlies in the troposphere the influence of the parametrization scheme on integrations of the 11 layer model is described and found to be generally beneficial in a discussion of the reasons why this problem has only recently emerged it is suggested that the satisfactory northern hemisphere winter circulations of previous coarser general circulation models were due to a compensation implied by underestimating both the surface drag and the horizontal flux of momentum by explicitly resolved large scale eddies

source parameters of the june 29 1992 little skull mountain earthquake from complete regional waveforms at a single station the june 29 1992 m sub b 5 5 little skull mountain earthquake occurred 20 km southeast of yucca mountain within the boundaries of the nevada test site this event was recorded at a very broadband station located about 310 km to the east at kanab utah both body and surface waves from this single station were used in a grid search technique for the best fitting double couple moment tensor the technique minimizes the misfit between reflectivity generated complete synthetic seismograms and the three component displacement data via a search over the strike dip and rake of the source in the passband of 50 15 s period the grid search results in a well defined nearly pure normal mechanism with a strike of 35 degrees a dip of 54 degrees a rake of minus 87 degrees and a seismic moment of 4 1 x 10 sup 17 n m applying the same technique to the large aftershock on july 5 1992 the authors obtain a somewhat less well defined minimum with a strike of 358 degrees a dip of 36 degrees a rake of minus 177 degrees and a moment of 4 3 x 10 sup 15 n m the minimum compression axes of these mechanisms are consistent with northwest southeast extension in the basin and range 14more refs 7 figs less

determination of the largest clast sizes of tephra deposits for the characterization of explosive eruptions a study of the iavcei commission on tephra hazard modelling the distribution of clasts deposited around a volcano during an explosive eruption typically contoured by isopleth maps provides important insights into the associated plume height wind speed and eruptive style nonetheless a wide range of strategies exists to determine the largest clasts which can lead to very different results with obvious implications for the characterization of eruptive behaviour of active volcanoes the iavcei commission on tephra hazard modelling has carried out a dedicated exercise to assess the influence of various strategies on the determination of the largest clasts suggestions on the selection of sampling area collection strategy choice of clast typologies and clast characterization i e axis measurement and averaging technique are given mostly based on a thorough investigation of two outcrops of a plinian tephra deposit from cotopaxi volcano ecuador located at different distances from the vent these include 1 sampling on a flat paleotopography far from significant slopes to minimize remobilization effects 2 sampling on specified horizontal area sections with the statistically representative sampling area depending on the outcrop grain size and lithic content 3 clast characterization based on the geometric mean of its three orthogonal axes with the approximation of the minimum ellipsoid lithic fragments are better than pumice clasts when present and 4 use of the method of the 50th percentile of a sample of 20 clasts as the best way to assess the largest clasts it is also suggested that all data collected for the construction of isopleth maps be made available to the community through the use of a standardized data collection template to assess the applicability of the new proposed strategy on a large number of deposits and to build a large dataset for the future development and refinement of dispersal models

source inversion of seismic waveforms the koyna india earthquakes of 13 september 1967 abstract the treatment of the seismic source inverse problem when diverse forms of waveform data are available is simple and elegant using a moment tensor formalism if earth structure is known and its effects predictable in terms of vertically inhomogeneous elastic layered models then all types of wave phenomena e g surface waves body waves leaky modes etc for a purely deviatoric moment tensor point source may be represented by at most a sum of three green9s functions for an arbitrary symmetric moment tensor point source one additional green9s function is needed for the p sv system however elegant this formalism may be for posing the linear inverse problem the major difficulties lie in earth structure unknowns and resultant nonlinearities in the green9s functions which can cause significant trade offs with source parameters a hybrid inversion procedure is set up to gain insight into the probable unknowns in particular problems by incorporating both a linearized least squares gradient method for the moment tensor or double couple and smoothed time function parameters and a nonlinear systematic trial and error search for moment tensor or double couple parameters for several assumptions of green9s function the inversion technique is applied to near regional waveform data from a small earthquake associated with the koyna reservoir which occurred 13 september 1967 as the second in a group of three events with very similar waveshapes but differing amplitudes the magnitudes of the second and third events are smaller by 0 2 and 0 8 units respectively compared to the first the absolute magnitude for the first event is poorly constrained but is estimated to be 4 0 to 4 5 rather than the previously published value of 5 5 to 6 0 from the similarity of waveshapes all three events are inferred to have the same mechanism and occurred within about 2 km of the same hypocenter the results from moment tensor and double couple inversions for event 2 data indicate that source depth was 5 km and that left lateral faulting occurred on a plane with a strike of n20 e 5 dip of 90 15 and a rake of 0 35 the inferred far field time function is approximately 3 sec in duration unusually long for the seismic moment of 9 10 22 dyne cm yielding a possible stress drop of about 0 05 bars a fault map was constructed from landsat image interpretation and shows a predominance of nnw to nne striking faults in the koyna area which is used to infer the appropriate nodal plane in the inversion results these faults tend to define a broad en echelon zone which parallels the western ghats in this area

quasi lagrangian superpressure balloon measurements of gravity wave momentum fluxes in the polar stratosphere of both hemispheres 1 superpressure balloons were flown in 2002 and 2005 in the winter polar vortices of both hemispheres the balloons can drift for months in the stratosphere acting as quasi lagrangian tracers of air parcel motions the meteorological datasets acquired are used to retrieve small scale internal atmospheric gravity wave parameters using wavelet techniques for the first time gravity wave momentum fluxes are estimated over wide geographical areas and the results will help constrain gravity wave parameterization schemes used in general circulation climate models the importance of mountain waves is confirmed with largest fluxes observed in the lee of greenland and the antarctic peninsula however significant momentum fluxes are also observed over the oceans showing the importance of other wave generation mechanisms

three dimensional model of hellenic arc deformation and origin of the cretan uplift 1 the hellenic arc of greece is the most seismically active part of europe but little is know about its mechanics we modeled deformation along the arc using a finite element model the model was intended to capture large scale 3 d structure of nubian plate subduction beneath the aegean block and its deformational consequences the shape of the interface was developed using mapped traces at the surface and earthquake hypocenters at depth model block motions were constrained by recent compilations of gps velocity vectors we simulated a 10 ka period of convergence between nubia and the aegean and calculated the strain field in the overriding plate as well as the spatial distribution and orientation of differential stress 1 3 from these calculations we derived testable quantities such as the expected seismic moment rate on the interplate contact uplift pattern and distribution of strain modes our relatively simple model broadly reproduced observed uplift patterns earthquake activity and loci of extension and contraction the model showed a localization of uplift near the island of crete where the fastest aegean uplift rates are well documented comparison of calculated expected seismic moment and observed earthquake catalogs implies a nearly fully coupled interplate contact on the basis of our modeling results we suggest that south aegean deformation is driven primarily by the fast moving 33 mm a 1 aegean upper plate overriding a nearly stalled 5 mm a 1 nubian lower plate this tectonic setting thus more closely resembles a continental thrust than it does a typical oceanic subduction zone

nonorographic generation of arctic polar stratospheric clouds during december 1999 1 during december 1999 polar stratospheric clouds pscs were observed in the absence of conditions conducive to generation by topographic gravity waves the possibility is explored that pscs can be generated by inertia gravity waves igw radiating from breaking synoptic scale rossby waves on the polar front jet the aerosol features on 7 and 12 december are selected for comparison with theory and with simulations using the university of wisconsin nonhydrostatic modeling system uwnms consistent with rossby adjustment theory a common feature in the uwnms simulations is radiation of igw from the tropopause polar front jet especially from sectors which are evolving rapidly in the rossby wave breaking process packets of gravity wave energy radiate upward and poleward into the cold pool while individual wave crests propagate poleward and downward causing mesoscale variations in vertical motion and temperature on 12 december the eastbound dc 8 lidar observations exhibited a fairly uniform field of six waves in aerosol enhancement in the 14 20 km layer consistent with vertical displacement by a field of igw propagating antiparallel to the flow with characteristic horizontal and vertical wavelengths of 300 and 10 km uwnms simulations show emanation of a field of igw upward and southwestward from a northward incursion of the polar front jet the orientation and evolution of the aerosol features on 7 december are consistent with a single psc induced by an igw packet propagating from a breaking rossby wave over western russia toward the northeast into the coldest part of the base of the polar vortex with characteristic period 9 hours vertical wavelength 12 km and horizontal wavelength 1000 km linear theory shows that for both of these cases igw energy propagates upward at 1 km hour and horizontally at 100 km hour with characteristic trace speed 30 m s the spatial orientation of the psc along igw phase lines is contrasted with the nearly horizontal filamentary structures in the psc which are indicative of flow streamlines it is suggested that vertical displacement is a crucial factor in determining whether a psc will form and that most pscs are relatable to specific synoptic and mesoscale motions

gravity waves appearing in a high resolution gcm simulation global characteristics of gravity waves in the lower stratosphere are examined using a gcm with high resolution in both the horizontal t106 corresponding to about 120 km and the vertical 600 m the bottom boundary condition of the model is that of an aquaplanet with perpetual february sea surface temperature the simulated gravity waves are in good agreement with mesosphere stratosphere troposphere mst radar observations at a middle latitude on the gravity wave structure and on the frequency spectra as a function of height the frequency spectra of simulated wind and temperature fluctuations are also examined as a function of latitude large values of spectral density are observed at frequencies higher than the inertial frequency f in a weak wind region around 20 km which is consistent with the characteristics of internal gravity waves an isolated peak is observed near f for horizontal wind spectra at latitudes higher than 108 while the energy is distributed in a wide range of frequency at lower latitudes where f approaches zero further analysis is performed of those fluctuations having periods shorter than 24 h and those having vertical wavelengths smaller than 5 km these are frequently analyzed as gravity waves using observation data the distribution of energy and momentum fluxes in the latitude height section is examined the result indicates that short period waves mostly propagate upward and poleward from the equatorial region the wave energy reaches about 508 lat at the 27 km altitude a negative positive maximum of vertical flux of meridional momentum y9w9 is seen above the subtropical jet in the northern southern hemisphere for small vertical scale gravity waves this is consistent with the preferred equatorward propagation of the wave indicated by a statistical analysis based on mst radar observations the ratio of potential to kinetic energy maximizes over the equator and decreases poleward the eliassen palm flux divergence associated with gravity waves is decelerative above the subtropical jet albeit small

a meridional scan of the stratospheric gravity wave field over the ocean in 2001 messo2001 1 in order to examine gravity wave characteristics over the ocean we conducted a radiosonde observation campaign to scan the stratosphere meridionally over the middle pacific with hakuho maru research vessel operated by the ocean research institute university of tokyo seventy vertical profiles of temperature winds and humidity were successfully obtained over a wide latitude range of 28 n to 48 s with an interval of 1 degree gravity wave energy and vertical wavenumber spectra were examined as a function of latitude gravity wave energy is maximized in the tropical region where the convection is active and in the middle latitude region where the subtropical westerly jet is situated the wave energy in the tropical region is greater than the climatology based on operational radiosonde observation over land regions the gravity wave amplitude does not necessarily increase with altitude in contradiction to simple vertical propagation the latitudinal distribution of wave energy rather suggests that gravity waves propagate meridionally toward higher latitudes an interesting feature is that a wave packet having large horizontal wind and temperature amplitudes is observed continuously over 7 days in the latitudinal region extending 26 degrees results of hodograph analysis indicate that the wave packet is due to an inertia gravity wave with horizontal and vertical wavelengths of about 1800 km and 4 5km respectively this inertia gravity wave is likely generated in association with vigorous convection in the intertropical convergence zone itcz in the northern hemisphere and propagated southward interhemispherically the results in this study show that there are strong nonstationary gravity wave sources over the ocean the importance of meridionally propagating gravity waves is discussed

moment and duration of shallow earthquakes from love wave modelling for regional distances abstract love waves from five earthquakes in southwest germany italy yugoslavia greece and algeria as recorded at the broadband grafenberg array in eastern bavaria are modelled in detail using an extended reflectivity method the focal mechanisms are taken from the literature or determined from long period wwnss data the theoretical double couple moment function used for modelling increases smoothly during the risetime t from zero to the seismic moment m0 t and m0 are determined by matching the observed and theoretical love wave seismograms in the long period wwnss frequency band t is approximately equal to the rupture duration values from 1 4 to 20 s are found seismic moments generally agree within a factor of about two with those found by other authors from larger data sets the earthquakes in southwest germany and greece were simple events and can be modelled very well by one double couple in the case of the other earthquakes the theoretical love wave seismograms are too short for these earthquakes there is some independent evidence for a multiple event nature this evidence is condensed into source models consisting of two or three double couples representing separate and complete sub earthquakes which then explain the observations quite well in the case of the algerian earthquake the long love wave duration may also be due to complications in structure along the wavepath across the mediterranean and the alps the present results show that accurate love wave modelling for a single station at regional distance from an epicentre is a reliable method for estimation of seismic moment and rupture duration use of a digitally recording station with large dynamic range allows events over a large magnitude interval to be studied the grafenberg array is well suited for such an investigation of european and north african earthquakes

detection and location of earthquakes in the central aleutian subduction zone using island and ocean bottom seismograph stations a network of eight university of texas ocean bottom seismographs obs operated for 6 weeks in 1978 about 50 km offshore of adak island alaska and nearby islands in 1979 a similar network of nine instruments was deployed for 7 weeks farther offshore within and up to 100 km seaward of the aleutian trench for shallow earthquakes on the outer trench slope for shallow earthquakes in the thrust zone and for intermediate depth events we have analyzed the obs and island based network data and evaluated the island network s capabilities for earthquake detection and location and for focal mechanism determination our three major conclusions are presented the first concerns shallow earthquakes on the outer trench slope in 1979 about 30 earthquakes occurred within the aleutian trench and up to 60 km seaward of the trench axis the island network located none of these events and detected p phases for only three of them ray tracing shows that the islands lie in a geometric shadow zone for events on the outer trench slope the best located events are shallower than 20 km and exhibit first motions consistent with normal faulting several authors have suggested that these events are caused by bending of the oceanic lithosphere at the outer rise prior to subduction if so then the event locations reported here show that the bending stresses exceed the strength of lithosphere only in a narrow zone extending about 10 km landward and 60 km seaward of the trench axis the second conclusion concerns shallow earthquakes in the thrust zone epicenters determined by island stations alone are virtually identical to epicenters determined using data from both island and obs stations the locations are similar whether they are determined using flat layered velocity models or a more realistic model and a ray tracing scheme nearly all the earthquakes detected by the obs network are also recorded by island stations three composite focal mechanism solutions that use data from both island and obs stations have p axes parallel to the direction of plate convergence the thrust zone events are separated from events on the outer trench slope by a gap in seismicity about 50 km wide situated on the inner trench slope the third conclusion concerns earthquakes deeper than 70 km epicenters determined using island network stations alone lie 10 to 80 km south of those determined using obs and island stations with the differences between epicenters depending both on event depth and on the velocity model used ray tracing with a realistic velocity model shows that for events at 200 km depth locations are about 80 km north of locations determined from island data alone these results do not support the observed increase in the dip of the benioff zone beneath 100 km depth that is suggested by locations determined from island network data alone using a flat layered velocity model

single station cmt application to the michoacan mexico earthquake of september 19 1985 observations of three dimensional ground motion at a single point on the surface of the earth following an earthquake can be sufficient to determine the zeroth order moment tensor of the event we adapt the centroid moment tensor cmt method dziewonski et al 1981 of analysis to single station data and apply it to the september 19 1985 michoacan earthquake the obtained mechanism indicates faulting on a shallow plane consistent with the ongoing subduction of the cocos plate the scalar moment is 1 3 1028 dyne cm a direct deconvolution of the observed p wave train indicates that the moment release occurred in two subevents each of 20 seconds duration with a peak to peak separation in time of 25 seconds

middle atmosphere simulated with high vertical and horizontal resolution versions of a gcm improvements in the cold pole bias and generation of a qbo like oscillation in the tropics abstract the large scale circulation in the geophysical fluid dynamics laboratory skyhi troposphere stratosphere mesosphere finite difference general circulation model is examined as a function of vertical and horizontal resolution the experiments examined include one with horizontal grid spacing of 35 km and another with 100 km horizontal grid spacing but very high vertical resolution 160 levels between the ground and about 85 km the simulation of the middle atmospheric zonal mean winds and temperatures in the extratropics is found to be very sensitive to horizontal resolution for example in the early southern hemisphere winter the south pole near 1 mb in the model is colder than observed but the bias is reduced with improved horizontal resolution from 70 c in a version with 300 km grid spacing to less than 10 c in the 35 km version the extratropical simulation is found to be only slightly affected by enhancements of the vertical resolution by contrast the tropical middle atmospheric s

single station fault plane solutions abstract fault plane solutions are derived from systematic trial and error grid testing of three component body waveform data from a single station modeling p and sh waveform data from five shallow events recorded teleseismically demonstrates that radiation pattern information contained within the interference of the direct wave and surface reflections and the overall relative amplitude between p and sh waveforms is sufficient to discriminate between fault type e g strike slip versus dip slip and often agrees with well constrained first motion studies events studied are the 9 april 1968 borrego mountain california 20 june 1978 thessaloniki greece 13 august 1978 santa barbara california 20 may 1979 alaska and 6 august 1979 coyote lake california earthquakes it is also shown using data from the 27 july 1980 sharpsburg kentucky earthquake that inclusion of pp p and sp p polarity and amplitude information to an otherwise unconstrained first motion study can significantly improve the quality of the fault plane solution although there are many potential problems source multiplicity directivity etc which can prohibit finding a good model with these techniques and inclusion of data from many stations is clearly desirable the results of this study suggest that sparse high quality waveform data sets may be as or more useful for obtaining source mechanisms than standard first motion studies at a minimum they should be performed together as a consistency check this procedure would be most useful in the common situation where only a few receivers are available for a particular event

a general circulation model study of the orographic gravity waves over antarctica excited by katabatic winds 1 in this study we simulated orographic gravity waves ogws over antarctica using a t213l250 general circulation model gcm the gcm has a fine vertical resolution of 300 m throughout the middle atmosphere the simulation was run for a 1 year period results from 21 28 june were primarily considered ogws are excited by katabatic winds that travel down the surface slopes of the antarctic ice sheet a strong eastward katabatic wind blows over the west coast of the ross sea at the approach of the synoptic scale upper tropospheric westerly jets a quasi stationary ogw is then excited above the coast and propagates upward into the mesosphere an ogw appears sporadically during the antarctic winter and spring its amplitude is determined by the strength of the eastward katabatic wind dissipation of ogws within the middle atmosphere results in a localized deceleration of westerly winds greater than 30 m s 1 d 1 this in turn modifies the horizontal circulation in the polar vortex strong vertical mixing occurs within the mesosphere and is associated with wave breaking large temperature fluctuations associated with the ogws affect the formation or suppression of polar stratospheric clouds in the lower stratosphere katabatic wind excitation is the most powerful source of gravity waves over antarctica around the time of the winter solstice

pigeonholing pyroclasts insights from the 19 march 2008 explosive eruption of kīlauea volcano we think conventionally of volcanic explosive eruptions as being triggered in one of two ways by release and expansion of volatiles dissolved in the ejected magma magmatic explosions or by transfer of heat from magma into an external source of water phreatic or phreatomagmatic explosions we document here an event where neither magma nor an external water source was involved in explosive activity at k lauea instead the eruption was powered by the expansion of decoupled magmatic volatiles released from deeper magma which was not ejected by the eruption and the trigger was a collapse of near surface wall rocks that then momentarily blocked that volatile flux mapping of the advected fall deposit a day after this eruption has highlighted the difficulty of constraining deposit edges from unobserved or prehistoric eruptions of all magnitudes our results suggest that the dispersal area of advected fall deposits could be miscalculated by up to 30 of the total raising issues for accurate hazard zoning and assessment eruptions of this type challenge existing classification schemes for pyroclastic deposits and explosive eruptions and in the past have probably been interpreted as phreatic explosions where the eruptive mechanism has been assumed to involve flashing of groundwater to steam

generation of mesoscale gravity waves in upper tropospheric jet front systems abstract multiply nested mesoscale numerical simulations with horizontal resolution up to 3 3 km are performed to study the generation of mesoscale gravity waves during the life cycle of idealized baroclinic jet front systems long lived vertically propagating mesoscale gravity waves with horizontal wavelengths 100 200 km are simulated originating from the exit region of the upper tropospheric jet streak in a manner consistent with past observational studies the residual of the nonlinear balance equation is found to be a useful index in diagnosing flow imbalance and predicting wave generation the imbalance diagnosis and model simulations suggest that balance adjustment as a generalization of geostrophic adjustment is likely responsible for generating these mesoscale gravity waves it is hypothesized that through balance adjustment the continuous generation of flow imbalance from the developing baroclinic wave will lead to the continuous radiation of gravity waves

sensitivity of mesoscale gravity waves to the baroclinicity of jet front systems abstract this study investigates the sensitivity of mesoscale gravity waves to the baroclinicity of the background jet front systems by simulating different life cycles of baroclinic waves with a high resolution mesoscale model four simulations are made starting from two dimensional baroclinic jets having different static stability and wind shear in order to obtain baroclinic waves with significantly different growth rates in all experiments vertically propagating mesoscale gravity waves are simulated in the exit region of upper tropospheric jet streaks a two dimensional spectral analysis demonstrates that these gravity waves have multiple components with different wave characteristics the short scale wave components that are preserved by a high pass filter with a cutoff wavelength of 200 km have horizontal wavelengths of 85 161 km and intrinsic frequencies of 3 11 times the coriolis parameter the medium scale waves that are preserved by a bandpass filter with 200 and 600 km cutoff wavelengths ha

pushing the volcanic explosivity index to its limit and beyond constraints from exceptionally weak explosive eruptions at kīlauea in 2008 estimating the mass volume and dispersal of the deposits of very small and or extremely weak explosive eruptions is difficult unless they can be sampled on eruption during explosive eruptions of halema uma u crater kilauea hawaii in 2008 we constrained for the first time deposits of bulk volumes as small as 9 300 m 3 1 10 4 to 8 10 5 kg and can demonstrate that they show simple exponential thinning with distance from the vent there is no simple fit for such products within classifications such as the volcanic explosivity index vei the vei is being increasingly used as the measure of magnitude of explosive eruptions and as an input for both hazard modeling and forecasting of atmospheric dispersal of tephra the 2008 deposits demonstrate a problem for the use of the vei as originally defined which classifies small yet ballistic producing explosive eruptions at kilauea and other basaltic volcanoes as nonexplosive we suggest a simple change to extend the scale in a fashion inclusive of such very small deposits and to make the vei more consistent with other magnitude scales such as the richter scale for earthquakes eruptions of this magnitude constitute a significant risk at kilauea and elsewhere because of their high frequency and the growing number of volcano tourists visiting basaltic volcanoes

characteristics of gravity waves with short vertical wavelengths observed with radiosonde and gps occultation during dawex darwin area wave experiment 1 we conducted radiosonde soundings during three intensive observation periods iop of the darwin area wave experiment dawex campaign in october to december 2001 and measured humidity temperature and wind velocity up to 30 35 km every 3 hours for 40 times at three sites in each iop we analyzed height profiles of kinetic ek and potential ep energy per unit mass caused by gravity waves with vertical wavelengths less than 3 km the wave energy was clearly enhanced between 15 20 km and 25 30 km and it was considerably depressed at 20 25 km between the two height regions this feature was seen at all the sites during the three iops different types of wave activity seem to contribute to the enhancement of ek and ep below 20 km and at 25 30 km height distribution of the wave energy at 20 30 km seems to correlate with the structure of the mean zonal wind shear we also analyzed a latitude height section of ep in october to december 2001 using gps occultation data with the champ satellite collected around the dawex sites 80 180 e and 30 n to 30 s compared with the latitude distribution of ep with gps the dawex results were slightly smaller and larger at 20 25 km and 25 30 km respectively the longitude variation of ep is also analyzed from the gps data at 10 15 s which generally agreed well with the dawex results at both 20 25 km and 25 30 km

timed saber observations of global gravity wave climatology and their interannual variability from stratosphere to mesosphere lower thermosphere the present study for the first time reports the global gravity wave activity in terms of their potential energy derived from timed saber observations right from the stratosphere to the mesosphere lower thermosphere mlt region the potential energy profiles obtained from saber temperature are validated by comparing them with ground based lidar observations over a low latitude site gadanki 13 5 n 79 2 e the stratospheric and mesospheric global maps of gravity wave energy showed pronounced maxima over high and polar latitudes of the winter hemisphere the interannual variability of the stratospheric gravity wave activity exhibited prominent annual oscillation over mid latitudes the equatorial gravity wave activity exhibited quasi biennial oscillation in the lower stratosphere and semi annual oscillation in the upper stratosphere the mlt region maps revealed summer hemispheric maxima over polar latitudes and secondary maxima over the equatorial region the results are discussed in the light of present understanding of global gravity wave observations the significance of the present study lies in emphasizing the importance of satellite measurements in elucidating gravity waves which is envisaged to have profound impact on parameterizing these waves

physical parameterization of strombolian eruptions via experimentally validated modeling of high speed observations pressurized gas drives explosive volcanic eruptions existing models can predict the amount and pressure of gas in erupting magma but application and testing of such models is currently limited by the accuracy of input parameters from natural systems here we present a new methodology based on a novel integration of 1 high speed imaging and 2 shock tube modeling of volcanic activity in order to derive estimates of sub second variations in the pressure mass and volume of gas that drive the dynamics of unsteady eruptions first we validate the method against laboratoryscale shock tube experiments having validated the method we then apply it to observations of eruptions at stromboli volcano italy finally we use those results for a parametric study of the weight of input parameters on final outputs we conclude that strombolian explosions with durations of seconds result from discrete releases of gas with mass and pressure in the 4 714 kg and 0 10 0 56 mpa range respectively and which occupy the volcano conduit to a depth of 4 190 m these variations are present both among and within individual explosions

a determination of source properties of large intraplate earthquakes in alaska historically large and potentially hazardous earthquakes have occurred within the interior of alaska however most have not been adequately studied using modern methods of waveform modeling the 22 july 1937 16 october 1947 and 7 april 1958 earthquakes are three of the largest events known to have occurred within central alaska ms 7 3 ms 7 2 andms 7 3 respectively we analyzed teleseismic body waves to gain information about the focal parameters of these events in order to deconvolve the source time functions from teleseismic records we first attempted to improve upon the published focal mechanisms for each event synthetic seismograms were computed for different source parameters using the reflectivity method a search was completed which compared the hand digitized data with a suite of synthetic traces covering the complete parameter space of strike dip and slip direction in this way the focal mechanism showing the maximum correlation between the observed and calculated traces was found source time functions i e the moment release as a function of time were then deconvolved from teleseismic records for the three historical earthquakes using the focal mechanisms which best fit the data from these deconvolutions we also recovered the depth of the events and their seismic moments the earthquakes were all found to have a shallow foci with depths of less than 10 km

tephrostratigraphy and provenance from iodp expedition 352 izu bonin arc tracing tephra sources and volumes from the oligocene to recent provenance studies of widely distributed tephras integrated within a well defined temporal framework are important to deduce systematic changes in the source scale distribution and changes in regional explosive volcanism here we establish a robust tephro chronostratigraphy for a total of 157 marine tephra layers collected during iodp expedition 352 we infer at least three major phases of highly explosive volcanism during oligocene to pleistocene time provenance analysis based on glass composition assigns 56 of the tephras to a japan source including correlations with 12 major and widespread tephra layers resulting from individual eruptions in kyushu central japan and north japan between 115 ka and 3 5 ma the remaining 101 tephras are assigned to four source regions along the izu bonin arc one of exclusively oligocene age is proximal to the bonin ridge islands two reflect eruptions within the volcanic front and back arc of the central izu bonin arc and a fourth region corresponds to the northern izu bonin arc source first order volume estimates imply eruptive magnitudes ranging from 6 3 to 7 6 for japan related eruptions and between 5 5 and 6 5 for ibm eruptions our results suggest tephras between 30 and 22 ma that show a subtly different izu bonin chemical signature compared to the recent arc after a 11 m y gap in eruption tephra supply from the izu bonin arc predominates from 15 to 5 ma and finally a subequal mixture of tephra sources from the palaeo honshu and izu bonin arcs occurs within the last 5 ma

timber framed building damage from tephra fall and lahar 2015 calbuco eruption chile abstract assessing the damage to buildings from volcanic eruptions is an important aspect of volcanic risk assessment and management however there is a limited empirical evidence base to draw upon when describing the relation between volcanic hazard intensity and resulting physical damage the 2015 subplinian eruption of calbuco volcano chile caused damage to buildings near the volcano because of tephra fall and lahars chilean authorities conducted a damage assessment of 961 properties 990 buildings to inform an assistance programme for property owners affected by the eruption property assessments typically contained observations and classification of damage to a house and in some instances accessory buildings such as sheds garages and exterior storage rooms in this study we used this unique damage data set to adapt damage state frameworks for tephra fall and lahar for classifying and analysing damage observations we developed data quality indicators to provide transparency for how we accounted for data quality issues we assigned a tephra and or lahar damage state to 571 buildings 530 houses and 41 accessory buildings the 419 buildings for which we did not assign a damage state either had too little information or fell outside of tephra and or lahar hazard zones the minimum tephra thickness isopach band that caused complete collapse was 10 to 15 cm dry deposit loading 1 to 1 6 kn m 2 saturated deposit loading 1 6 to 2 4 kn m 2 but most commonly 55 of tephra exposed ds5 houses n 11 this occurred at 15 to 30 cm dry deposit loading 1 5 to 3 3 kn m 2 saturated deposit loading 2 4 to 4 8 kn m 2 lahar damage was typically described as complete ds5 with 26 houses being swept away or destroyed around the blanco south river our results add to the limited evidence base of post eruption tephra and lahar impacts to buildings and contribute to volcanic risk and impact assessment

inertia gravity wave generation by the tropospheric midlatitude jet as given by the fronts and atlantic storm track experiment radio soundings 1 generation of inertia gravity waves by the midlatitude tropospheric jet is studied on the basis of the data obtained from the radio soundings over the north atlantic during the fronts and atlantic storm track experiment campaign a sample of 224 radio soundings is used to analyze the wave activity as a function of the distance to the jet it is shown that radio soundings displaying the most intense gravity wave activity both in the stratosphere and in the troposphere are the ones closest to the jet axis thus the jet region is the dominant source of gravity waves in this region far from orography further examination allows for identification of two specific regions of the flow that are associated with intense gravity wave activity the vicinity of the maximum of the jet velocity and the regions of strong curvature of the jet the detailed case studies we provide suggest that geostrophic adjustment is the dynamical mechanism responsible for the generation of large amplitude inertia gravity waves in the regions of the strong curvature of the wind the generation of waves in the vicinity of the regions where the wind veers in the deep troughs of the geopotential appears to be systematic

greek tectonics and seismicity abstract the validity of existing tectonic models for the area of greece is examined in the light of the new recalculated parameters for earthquakes of the region makropoulos and burton 1981 relocated hypocentral positions are extracted from the catalogue to form radial and vertical distance depth cross sections centred on a reference point near the mid point of the aegean volcanic arc and these are used to form a three dimensional topography of the base of earthquake occurrence below 60 km isodepth maps are extracted from this topography as both three and two dimensional map presentations these maps reveal several significant features of deep seated tectonic processes in the region isodepths exceeding 150 km are seen in the northwest aegean and these are more closely linked to the sporadhes and gulf of thermaicos rather than the north aegean trough the 150 km isodepths are also seen in the northeast aegean straddling the dardanelles in the northeastern part of the peloponnesus gulf of saronikos and eastern gulf of corinth in the southern peloponnesus towards crete and extending from north of kos to south of rodos the largest extent of deepest activity is seen south of rodos and this continues towards southwest of turkey the subduction zone of the hellenic arc is clear but smooth benioff zones are not the norm and these data show that structural complexity is more readily observed it is concluded that none of the proposed tectonic models completely explain the observed activity over the whole area and rather than propose yet another model places where further work is still particularly necessary are identified

quasi monochromatic inertia gravity waves in the lower stratosphere from mst radar observations 1 the frequency of occurrence of quasi monochromatic oscillations with periods near the inertial period is examined using hourly mean wind observations from the mst radars at white sands missile range new mexico and vandenberg air force base california spanning 6 years and 4 years respectively power spectral analyses show that the energy levels near the inertial frequency during summer are nearly constant with altitude from about 12 km up to the highest altitude available about 20 km while energy levels at lower frequencies decrease with altitude this decrease leads to a relative enhancement of energy near the inertial frequency during winter the relative enhancement near the inertial frequency is much smaller results from least squares curve fitting used to find the percent of wind variance explained pev by a single wave over data blocks 72 hours long and 2 km deep indicate that a quasi monochromatic oscillation is present when pev 25 during summer in the stratosphere over 50 of the cases have pev 25 the best fit waveform has mean period near 21 hours and vertical wavelength near 3 km the wind vectors exhibit anticyclonic rotation in time and with height consistent with upward propagating gravity waves the mean ratio of the intrinsic to the inertial frequency is about 1 3 in this data set and the associated mean horizontal wavelength of these waves is slightly over 1000 km

highly explosive eruption of the monogenetic 8 6 ka bp la vache et lassolas scoria cone complex chaine des puys france abstract the eruption of the trachy basaltic la vache and lassolas cone complex was the youngest eruption ca 8 6 ka bp and one of the most violent in the chaine des puys france here we present field data and results of grain size componentry and clast density measurements of different layers of the widespread tephra deposit that is associated with this cone forming eruption our data indicates five main eruption phases comprising a vent opening phase a second sustained highly explosive phase a third and fourth violent strombolian phase and a fifth dominantly effusive phase the layer formed by the opening phase is rich in lithic material which was previously considered to be the result of phreatomagmatic activity the data presented here on the componentry and textures of the pyroclastic material contradict this hypothesis we propose instead that the material of the basal layer results from fragmentation caused by the explosion of a first arriving gas dominated phase the variations in eruption intensity during the main eruption phases are interpreted here to be the result of gas segregation within the plumbing system and fluxes in the magma ascent rate during the eruption significant amount of gas segregation is indicated by the deposition of both gas poor and gas rich material and by the presence of plate tephra this is also supported by the simultaneous ejection of tephra and lava from both cones during most of the explosive activity we suggest that gas segregation occurred within shallow intrusions and that fresh ascending material in the main conduit mixed with degassed material that flow back into the conduit from the intrusion before fragmentation the interaction of the ascending magma and the opening of intrusions may have controlled the evolution and explosivity of the eruption the high explosivity at the beginning of the eruption and the wide dispersal area demonstrate that scoria cone eruptions in monogenetic fields can impose a major threat to the population and infrastructures nearby as these events may occur with little warning and therefore research on this kind of eruptions is of a major importance to better understand the processes driving these events

the synoptic setting and possible energy sources for mesoscale wave disturbances abstract thirteen case studies of mesoscale wave disturbances characterized by either a singular wave of depression or wave packets with periods of 1 4 h horizontal wavelengths of 50 500 km and surface pressure perturbation amplitudes of 0 2 7 0 mb are reviewed to isolate common synoptic features for these cases and to shed light on possible energy sources for the waves a strong thermal inversion in the lower troposphere north of a frontal boundary and a jet streak propagating toward a ridge axis in the upper troposphere are commonly observed in all the cases in general the area of wave activity is bounded by the jet axis to the west or northwest a surface front to the southeast an inflection axis between the trough and ridge axes to the southwest and the ridge axis to the northeast the conditions specified by lindzen and tung as being necessary to form a wave duct which include the existence of the lower tropospheric inversion seem to be met in many of these cases this suggests that a du

a 400 ka tephrochronological framework for central america from lake peten itza guatemala sediments highlights dating 400 ka paleoclimate record of neotropics revision and new eruptive volumes for large central american eruptions age models for peten itza sediments linking lacustrine ash inventory to eruptions from central america and mexico abstract lake peten itza northern guatemala lies within a hydrologically closed basin in the south central area of the yucatan peninsula and was drilled under the auspices of the international continental scientific drilling program icdp in 2006 at 16 55 n latitude the lake is ideally located for study of past climate and environmental conditions in the neotropical lowlands because of its great depth 160 m lake peten itza has a record of continuous sediment accumulation that extends well into the late pleistocene a key obstacle to obtaining long climate records from the region is the difficulty of establishing a robust chronology beyond 40 ka the limit of 14c dating tephra layers within the lake peten itza sediments however enable development of age depth relations beyond 40 ka ash beds from large magnitude pleistocene to holocene silicic eruptions of caldera volcanoes along the central american volcanic arc cava were found throughout drill cores collected from lake peten itza these ash beds were used to establish a robust chronology extending back 400 ka we used major and trace element glass composition to establish 12 well constrained correlations between the lacustrine tephra layers in lake peten itza sediments and dated deposits at the cava source volcanoes and with their marine equivalents in eastern pacific ocean sediments the data also enabled revision of eight previous determinations of erupted volumes and masses and initial estimates for another four eruptions as well as the designation of source areas for 14 previously unknown eruptions the new and revised sedimentation rates for the older sediment successions identify the interglacial of mis5a between 84 and 72 ka followed by a stadial between 72 and 59 ka that corresponds to mis4 we modified the age models for the lake peten itza sediment sequences extended the paleoclimate and paleoecological record for this neotropical region to 400 ka and determined the magnitude and timing of cava eruptions

gravity wave characteristics in the lower atmosphere at south pole a 4 year 1993 1996 temperature and wind data set obtained from over 2000 high resolution balloon soundings at south pole is used to study gravity wave characteristics in the troposphere and lower stratosphere extensive analyses of energy density spectra and static stability are performed to present a comprehensive view of the gravity wave characteristics in the lower atmosphere at south pole our results show that the gravity waves are ubiquitous and often fairly strong at south pole even though the generation mechanisms are not clear gravity wave characteristics are in general similar to those obtained at other high latitude southern hemisphere stations potential energies vary between about 0 5 j kg and 5 j kg with season and altitude variations in kinetic energies are not well correlated with potential energy variations and range from 1 j kg to 11 j kg we observe significant seasonal variations of the slope and magnitude of the vertical wavenumber spectrum of temperature fluctuations especially in the stratosphere in general the gravity waves in the stratosphere are stronger weaker in austral spring fall wave activity in the troposphere has little seasonal dependence stability analysis shows that instabilities are more likely to occur in the troposphere than in the stratosphere the probability of wave instability is 13 7 in the troposphere and 5 4 in the stratosphere this is due to the less stable stratification in the troposphere where the buoyancy period averages 8 3 min compared to 4 9 min in the stratosphere dynamic shear instability is more likely to occur than convective instability 11 versus 2 6 in the troposphere and 4 7 versus 0 7 in the stratosphere due to the prevailing strong wind shear the instability probabilities vary seasonally with the austral winter exhibiting the highest probability of instabilities dynamic and convective instabilities combined in both the troposphere and stratosphere