distribution of helicity cape and shear in tropical cyclones abstract the previous study of helicity cape and shear in hurricane bonnie 1998 was extended to all eight tropical cyclones sampled by nasa during the convection and moisture experiments camex storms were categorized as having large or small ambient vertical wind shear with 10 m s 1 as the dividing line in strongly sheared storms the downshear mean helicity exceeded the upshear mean by a factor of 4 as in the previous study the helicity differences resulted directly from the tropical cyclone response to ambient shear with enhanced in up out flow and veering of the wind with height present downshear cape in strongly sheared storms was 60 larger downshear mean inflow near the surface and the depth of the inflow layer each were 4 times larger downshear at more than 30 of observation points outside the 100 km radius in the downshear right quadrant midlatitude empirical parameters indicated a strong likelihood of supercells no such points existed upshear in highly sheared storms much small

cloud to ground lightning in hurricane andrew the spatial and temporal distribution of cloud to ground lightning was examined in hurricane andrew of 1992 lightning locations available from the national lightning detection network were superimposed on infrared satellite images to relate lightning activity to hurricane cloud structure a distinct radial variation occurred in time averaged flash density with a weak maximum in the eye wall a region of near zero flash density 40 to 100 km from the center and a steady increase to a large maximum in the outer rainbands 190 km from the center this radial distribution is consistent with the convective structure of mature hurricanes eye wall lightning tended to be episodic occurring almost exclusively prior to and during periods of intensification of the storm during these periods negative flashes occurred several kilometers inward from the highest eye wall cloud tops in the region of the largest radar reflectivity positive eye wall flashes while small in number tended to occur directly under the highest cloud tops the results are suggestive of a normal dipole in sign but outwardly tilted along the sloping eye wall in general hurricane flash characteristics resembled those for a background data set of nonhurricane flashes from the same area the exception occurred for negative flashes in the eye wall which had a much smaller mean peak current than the background 25 3 ka versus 44 9 ka

exploration of remote triggering a survey of multiple fault structures in haiti triggering studies provide an important tool for understanding the fundamental physics of how faults slip and interact and they also provide clues about the stress states of faults in this study we explore how seismic waves from the 27 february 2010 mw8 8 maule chile mainshock interact with the left lateral strike slip enriquillo plantain garden fault epgf and surrounding reverse faults in the southern haiti peninsula the chile mainshock occurred 6 000 km away and just 46 days after the 12 january 2010 mw7 0 haiti earthquake a tragic event which activated multiple faults in the southern haiti peninsula during the surface waves of the chile mainshock several tectonic tremor signals were observed originating from south of the epgf trace cross correlation of the triggered tremor and transient stresses resolved onto to the epgf indicates that the love wave of the chile mainshock was the primary driving mechanism of the triggered deep shear slip and tremor signals as opposed to dilatational stress changes generated by the rayleigh wave we also searched for any influence of transient stresses on haiti aftershock activity by applying the matched filter technique to multiple days of seismic data around the time of the chile mainshock while we identified a slight increase in haiti aftershock activity rate the rate changes were significant only when small magnitude events were included in the significance tests these observations are generally consistent with recent inferences that deep tectonic tremor is more sensitive than shallow earthquakes to external stress perturbations

revisiting azimuthally asymmetric moist instability in the outer core of sheared tropical cyclones abstractthis study revisits the characteristics and physical processes of the azimuthally asymmetric distribution of moist instability in the outer core of vertically sheared tropical cyclones tcs

microscale evidence of liquefaction and its potential triggers during soft bed deformation within subglacial traction tills published conceptual models argue that much of the forward motion of modern and ancient glaciers is accommodated by deformation of soft sediments within the underlying bed at a microscale this deformation results in the development of a range of ductile and brittle structures in water saturated sediments as they accommodate the stresses being applied by the overriding glacier detailed micromorphological studies of subglacial traction tills reveal that these polydeformed sediments may also contain evidence of having undergone repeated phases of liquefaction followed by solid state shear deformation this spatially and temporally restricted liquefaction of subglacial traction tills lowers the shear strength of the sediment and promotes the formation of transient mobile zones within the bed which accommodate the shear imposed by the overriding ice this process of soft bed sliding alternating with bed deformation facilitates glacier movement by way of stick slip events the various controls on the slip events have previously been identified as i the introduction of pressurised meltwater into the bed a process limited by the porosity and permeability of the till and ii pressurisation of porewater as a result of subglacial deformation to which we include iii episodic liquefaction of water saturated subglacial traction tills in response to glacier seismic activity icequakes which are increasingly being recognized as significant processes in modern glaciers and ice sheets as liquefaction operates only in materials already at very low values of effective stress its process form signatures are likely indicative of glacier sub marginal tills

rapid filamentation zones in intense tropical cyclones intense tropical cyclones often possess relatively little convection around their cores in radar composites this surrounding region is usually echo free or contains light stratiform precipitation while subsidence is typically quite pronounced in this region it is not the only mechanism suppressing convection another possible mechanism leading to weak echo moats is presented in this paper the basic idea is that the strain dominated flow surrounding an intense vortex core creates an unfavorable environment for sustained deep moist convection strain dominated regions of a tropical cyclone can be distinguished from rotationdominated regions by the sign of s 2 s 2 2 where s1 ux y and s2 x uy are the rates of strain and x uy is the relative vorticity within the radius of maximum tangential wind the flow tends to be rotation dominated 2 s 2 s 2 so that coherent structures such as mesovortices can survive for long periods of time outside the radius of maximum tangential wind the flow tends to be strain dominated s 2 s 2 2 resulting in filaments of anomalous vorticity in the regions of strain dominated flow the filamentation time is defined as fil 2 s 2 s 2 2 1 2 in a tropical cyclone an approximately 30 kmwide annular region can exist just outside the radius of maximum tangential wind where fil is less than 30 min and even as small as 5 min this region is defined as the rapid filamentation zone since the time scale for deep moist convective overturning is approximately 30 min deep convection can be significantly distorted and even suppressed in the rapid filamentation zone a nondivergent barotropic model illustrates the effects of rapid filamentation zones in category 1 5 hurricanes and demonstrates the evolution of such zones during binary vortex interaction and mesovortex formation from a thin annular ring of enhanced vorticity

the use of vertical wind shear versus helicity in interpreting supercell dynamics a series of idealized simulations of supercell storms are presented for environments representing straight through circular hodographs to clarify the character of the storm dynamics over the large spectrum of hodograph shapes commonly observed the primary emphasis is on comparing and contrasting recent theories of supercell dynamics based on updraft shear interactions storm relative environmental helicity sreh and beltrami flow solutions to help clarify the degree to which each theory can represent the essential storm dynamics one of the particular questions being addressed is whether storm dynamics are significantly different for straight versus curved hodographs which has become a point of some controversy over recent years in agreement with previous studies the authors find that the physical processes that promote storm maintenance rotation and propagation are similar for all hodograph shapes employed and are due primarily to nonlinear interactions between the updraft and the ambient shear associated with the localized development of rotation on the storm s flank significant correlations between the updraft and vertical vorticity are also observed across the shear spectrum and in agreement with predictions of linear theories associated with sreh this correlation increases for increasing hodograph curvature however storm steadiness and propagation must already be known or inferred for such concepts to be applied thus limiting the applicability of this theory as a true predictor of storm properties tests of the applicability of beltrami solutions also confirm reasonable agreement for purely circular hodographs for which the analytical solutions are specifically designed however analysis of the model results indicates that the terms ignored for such solutions representing the nonlinear effects associated with storm rotation are more significant than those retained over most of the hodograph spectrum which severely limits the general applicability of such analyses

isolated regions of remote triggering in south southeast asia following the 2012 mw 8 6 indian ocean earthquake large earthquakes are capable of triggering either shallow earthquakes or deep tectonic tremors at long range distances so far most of remotely triggered tremors were found along major plate boundary faults around the pacific rim here we conduct a systematic search for remotely triggered earthquakes and tremors in south southeast asia following the april 11 2012 mw 8 6 indian ocean earthquake we find additional evidence of triggered tectonic tremors beneath the java island and the molucca island in eastern indonesia and triggered earthquakes in vietnam tremors mostly occurred during the large amplitude rayleigh waves of the indian ocean mainshock and were also triggered by several other large distant earthquakes although we are unable to locate them they were recorded at stations close to major tectonic faults suggesting that they are likely of tectonic origin however we find no evidence of triggered tremor earthquakes along the sumatra subduction zone and eastern portion of himalaya frontal thrusts indicating that remote triggering was not as widespread as previously thought

the kinematic structure of hurricane gloria 1985 determined from nested analyses of dropwindsonde and doppler radar data abstract a set of three dimensional filtered multiply nested objective analyses has been completed for the wind field of hurricane gloria for 0000 utc 25 september 1985 at this time gloria was one of the most intense hurricanes ever observed in the atlantic basin with a minimum sea level pressure of 919 mb the nested analyses based on observations from airborne doppler radar and omega dropwindsondes simultaneously describe eyewall and synoptic scale features and are the most comprehensive analyses of a single hurricane constructed to date the analyses have been used to document the multiscale kinematic structure of gloria and to investigate the relationship between the kinematic fields and the motion of the vortex the analyses indicate that the vortex was unusually barotropic the radius of maximum wind rmw was nearly vertical below 500 mb with a slight inward slope with height between 750 and 550 mb the strongest azimuthal mean tangential winds were found well above the boundary layer near

the evolution of vortex tilt and vertical motion of tropical cyclones in directional shear flows abstractrecent studies have demonstrated the importance of moist dynamics on the intensification variability of tropical cyclones tcs in directional shear flows here we propose that dry dynamic

buoyancy and shear characteristics of hurricane tornado environments abstract detailed composite profiles of temperature moisture and wind are constructed for tornado environments in tropical cyclones that affected the united states during the period 1948 86 winds are composited in components radial and tangential to the tropical cyclone center at observation time guided by observed patterns of tornado occurrence composites are constructed for a variety of different stratifications of the data including proximity to tornadoes position relative to the cyclone center time of day time after cyclone landfall cyclone translation speed and location of landfall the composites are also compared to composite soundings from great plains tornado environments a variety of sounding parameters am examined to see which are most closely related to the patterns of tornado distribution lower tropospheric vertical shears are generally stronger in the tropical cyclone tornado environments than on the great plains vertical shear and helicity parameters along with 700 hpa wind s

a previously unreported type of seismic source in the firn layer of the east antarctic ice sheet we identify a unique type of seismic source in the uppermost part of the east antarctic ice sheet recorded by temporary broadband seismic arrays in east antarctica these sources termed firnquakes are characterized by dispersed surface wave trains with frequencies of 1 10 hz detectable at distances up to 1000 km events show strong dispersed rayleigh wave trains and an absence of observable body wave arrivals most events also show weaker love waves initial events were discovered by standard detection schemes additional events were then detected with a correlation scanner using the initial arrivals as templates we locate sources by determining the l2 misfit for a grid of potential source locations using rayleigh wave arrival times and polarization directions we then perform a multiple filter analysis to calculate the rayleigh wave group velocity dispersion and invert the group velocity for shear velocity structure the resulting velocity structure is used as an input model to calculate synthetic seismograms inverting the dispersion curves yields ice velocity structures consistent with a low velocity firn layer 100 m thick and show that velocity structure is laterally variable the absence of observable body wave phases and the relative amplitudes of rayleigh waves and noise constrain the source depth to be less than 20 m the presence of love waves for most events suggests the source is not isotropic we propose the events are linked to the formation of small crevasses in the firn and several events correlate with shallow crevasse fields mapped in satellite imagery

transoceanic wave propagation links iceberg calving margins of antarctica with storms in tropics and northern hemisphere 1 we deployed seismometers on the ross ice shelf and on various icebergs adrift in the ross sea including b15a a large 100 km by 30 km fragment of b15 which calved from the ross ice shelf in march 2000 the data reveal that the dominant energy of these floating ice masses is in the 0 01 to 0 1 hz band and is associated with sea swell generated in the tropical and extra tropical pacific ocean in one example a strong storm in the gulf of alaska on 21 october 2005 approximately 13 500 km from the ross sea generated swell that arrived at b15a immediately prior to and during its break up off cape adare on 27 october 2005 if sea swell influences iceberg calving and break up a teleconnection exists between the antarctic ice sheet mass balance and weather systems worldwide

nucleation and seismic tremor associated with the glacial earthquakes of whillans ice stream antarctica 1 the ability to monitor transient motion along faults is critical to improving our ability to understand many natural phenomena such as landslides and earthquakes here we usedata from a gps and seismometer network that were deployed to monitor the regularly repeating glacial earthquakes of whillans ice stream west antarctica to show that a unique pattern of precursory slip precedes complete rupture along the bed of the ice stream additionally we show that rupture can be independently tracked by increased levels of microseismic activity including harmonic tremor that are coincident with the onset of slip at any location thus providing a remote means of monitoring stress and rupture propagation during the glacial earthquakes

kinematic and seismic analysis of giant tabular iceberg breakup at cape adare antarctica 1 satellite imagery reveals that a series of large icebergs b15b in april 2001 c19 in june 2003 and b15a in october 2005 broke up or fractured while exiting the ross sea in a narrowly defined area off cape adare antarctica examination of recent swath mapped bathymetric observations revealed that the principle agent of these breakups is a previously unknown 9 km long ridge with minimum depths of 215 m that we call davey shoal satellite imagery shows that the icebergs are driven into the shoal by coastal currents that converge over the narrow continental shelf one of the icebergs the 120 km by 30 km b15a was instrumented with a seismograph gps and fluxgate compass this instrumentation provided a unique opportunity to establish the details of the iceberg kinematics that were not revealed by satellite imagery alone and to correlate seismic events observed both on the iceberg and in the far field during breakup b15a fractured from multiple strikes against davey shoal and the adjacent possession islands these strikes were driven by the combination of tidal currents and the coastal mean flow the periods of iceberg sourced seismic radiation were correlated with the strikes the iceberg and land based seismic signals showed that the iceberg fracture its sliding across the shoals and the ice on ice stick slip contacts among the postbreakup iceberg fragments generated the strong chaotic and harmonic tremor episodes that were observed at distances as far as the south pole where these signals propagated as seismically coupled hydroacoustic t phases

testing for the predictability of dynamically triggered earthquakes in the geysers geothermal field abstract the geysers geothermal field is well known for being susceptible to dynamic triggering of earthquakes by large distant earthquakes owing to the introduction of fluids for energy production yet it is unknown if dynamic triggering of earthquakes is predictable or whether dynamic triggering could lead to a potential hazard for energy production in this paper our goal is to investigate the characteristics of triggering and the physical conditions that promote triggering to determine whether or not triggering is in anyway foreseeable we find that at present triggering in the geysers is not easily predictable in terms of when and where based on observable physical conditions however triggered earthquake magnitude positively correlates with peak imparted dynamic stress and larger dynamic stresses tend to trigger sequences similar to mainshock aftershock sequences thus we may be able to predict what size earthquakes to expect at the geysers following a large distant earthquake

objective convective updraft identification and tracking part 1 structure and thermodynamics of convection in the rainband regions of two hurricane simulations to better understand the life cycles of convective elements in numerical model simulations a convective updraft tracking algorithm dubbed the statistical and programmable objective updraft tracker spout is developed spout identifies updraft cores in horizontal slices through a given model data set links these cores in three dimensions to form vertically coherent updrafts and then tracks updrafts in time via estimates of the mean local advection spout is evaluated in idealized hurricane simulations from both the regional atmospheric modeling system rams and weather research and forecasting wrf in both simulations spout indicates most updrafts live less than 60 min but some can persist for over 2 h updrafts are typically manifested as shallow cumulus cumulus congestus and deep cumulonimbus overall there is reasonable agreement between the vigor of convection and the amount of localized conditional convective instability also the majority of updrafts attain a tilted structure that is in accordance with the localized vertical wind shear nonetheless there are striking differences between models with the higher resolution wrf simulation producing around twice as many updrafts as rams moreover the wrf updrafts are significantly weaker this paper highlights the utility of spout for studying convective life cycles in high resolution numerical simulations and provides some basic features of convection in two hurricane simulations

potential source rocks organic geochemistry and thermal maturation in the southern depocenter kipourio grevena of the mesohellenic basin central greece abstract the study area is the southern depocenter depth 4200 m of the mesohellenic basin which extends between kipourio and grevena central greece the mesohellenic basin is a middle tertiary intramontane basin developed within the hellenide orogen previous studies have focused on the depositional environments configuration and hydrocarbon potential of the basin in this paper we present additional geochemical and petrographic data from outcrop samples of the basin s southern depocenter which is considered the most promising area in terms of hydrocarbon prospectivity a total number of thirty six samples were analysed rock eval pyrolysis maceral analysis vitrinite reflectance and thermal alteration index bitumens extraction liquid chromatography and gc ms the samples were collected from deltaic deposits and submarine fan sediments of late eocene to late oligocene age the toc values of the analysed samples range between rich and very rich and the organic matter consists mainly of type iii kerogen and the organic matter consider to be predominately gas prone the thermal maturity assessed from tmax and vitrinite reflectance shows an immature stage of the organic matter along with the presence of layers having reached the very early mature stage vitrinite reflectance measurements and maturity calculations applying the lopatin modeling reveal that the lower part of the depocenter sediments falls within the oil window the extractable organic matter eom mg bitumens g toc indicate the existence of samples from deltaic deposits with high ratio of transformation eom 100 mg bitumen g toc the gc and gc ms analyses of the biomarkers indicate mainly the occurrence of terrestrial organic matter reflecting oxidizing conditions and both immature and very early mature stages the results of the rock eval pyrolysis and the distribution of the isoprenoids support the assumption of the input of an organic matter mixture

eastern pacific hurricanes jimena of 1991 and olivia of 1994 the effect of vertical shear on structure and intensity abstract shear is a key inhibitor of tropical cyclone intensification although its signature is readily recognized in satellite imagery and theoretical or modeling studies provide some insight detailed observations have been limited airborne radar and in situ observations in hurricanes jimena of 1991 and olivia of 1994 are a step toward better understanding each storm was observed on two consecutive days initially both had small eyes 16 18 km radius and maximum winds of 57 m s 1 over sea surface temperatures sst 28 c in easterly environmental shear jimena maintained constant intensity or weakened gradually for 2 days in 13 20 m s 1 easterly shear olivia intensified in 8 m s 1 shear on the first day overnight the shear diminished to reverse and became westerly on the second day olivia weakened as the shear increased to 15 m s 1 from the west the storm moved over cooler sst and became surrounded by dryer air as convection weakened and the outer rainbands ceased to be effective barriers

characterization of seasonal glacial seismicity from a single station on ice record at holtedahlfonna svalbard glacial seismicity provides important insights into glacier dynamic processes we study the temporal distribution of cryogenic seismic signals icequakes at holtedahlfonna svalbard between april

effects of vertical wind shear on the intensity and structure of numerically simulated hurricanes a series of numerical simulations of tropical cyclones in idealized large scale environments is performed to examine the effects of vertical wind shear on the structure and intensity of hurricanes the simulations are performed using the nonhydrostatic pennsylvania state university national center for atmospheric research fifth generation mesoscale model using a 5 km fine mesh and fully explicit representation of moist processes when large scale vertical shears are applied to mature tropical cyclones the storms quickly develop wavenumber one asymmetries with upward motion and rainfall concentrated on the left side of the shear vector looking downshear in agreement with earlier studies the asymmetries develop due to the storm s response to imbalances caused by the shear the storms in shear weaken with time and eventually reach an approximate steady state intensity that is well below their theoretical maximum potential intensity as expected the magnitude of the weakening increases with increasing shear all of the storms experience time lags between the imposition of the large scale shear and the resulting rise in the minimum central pressure while the lag is at most a few hours when the storm is placed in very strong 15 m s21 shear storms in weaker shears experience much longer lag times with th e5ms 21 shear case showing no signs of weakening until more than 36 h after the shear is applied these lags suggest that the storm intensity is to some degree predictable from observations of largescale shear changes in all cases both the development of the asymmetries in core structure and the subsequent weakening of the storm occur before any resolvable tilt of the storm s vertical axis occurs it is hypothesized that the weakening of the storm occurs via the following sequence of events first the shear causes the structure of the eyewall region to become highly asymmetric throughout the depth of the storm second the asymmetries in the upper troposphere where the storm circulation is weaker become sufficiently strong that air with high values of potential vorticity and equivalent potential temperature are mixed outward rather than into the eye this allows the shear to ventilate the eye resulting in a loss of the warm core at upper levels which causes the central pressure to rise weakening the entire storm the maximum potential vorticity becomes concentrated in saturated portions of the eyewall cloud aloft rather than in the eye third the asymmetric features at upper levels are advected by the shear causing the upper portions of the vortex to tilt approximately downshear the storm weakens from the top down reaching an approximate steady state intensity when the ventilated layer can descend no farther due to the increasing strength and stability of the vortex at lower levels

detecting remotely triggered microseismicity around changbaishan volcano following nuclear explosions in north korea and large distant earthquakes around the world we conduct a systematic survey on locally triggered earthquakes by large distant earthquakes in changbaishan volcano an active intraplate volcano on the border between china and north korea we examine waveforms of distant earthquakes recorded at broadband station changbaishan cbs near the volcano with estimated dynamic stresses over 5 kpa between 2000 and 2016 out of 26 selected distant earthquakes three of them show positive evidence of triggering during large amplitude surface waves the earthquakes that had positive or possible evidences of triggering generated larger long period surface waves indicating that they are more efficient in triggering microseismicity in addition since 2006 north korea has conducted five underground nuclear explosion une tests only 140 km away from changbaishan volcano by systematically examining waveforms of these unes recorded at station cbs we find that none of them have triggered microearthquakes in changbaishan volcano

the structure and classification of numerically simulated convective storms in directionally varying wind shears abstract using a three dimensional numerical cloud model we investigate the effects of directionally varying wind shear on convective storm structure and evolution over a wide range of shear magnitudes as with a previous series of experiments using unidirectional wind shear profiles weisman and klemp the current results evince a spectrum of storm types ranging from short lived single cells at low shears multicells at intermediate shears to supercells at high shears with a clockwise curved hodograph the supercellular growth is confined to the right flank of the storm system while multicellular growth is favored on the left flank an analysis of the dynamic structure of the various cells reveals that the quasi steady supercell updrafts are strongly enhanced by dynamically induced pressure gradients on the right flank of the storm system we use this feature along with other related storm characteristics such as updraft rotation to propose a dynamically based storm classification scheme following

the influence of helicity on numerically simulated convective storms abstract a three dimensional numerical cloud model is used to investigate the influence of storm relative environmental helicity sreh on convective storm structure and evolution with a particular emphasis on the identification of ambient shear profiles that are conducive to the development of long lived strongly rotating storms eleven numerical simulations are made in which the depth and turning angle of the ambient vertical shear vector are varied systematically while maintaining a constant magnitude of the shear in the shear layer in this manner an attempt is made to isolate the effects of different environmental felicities on storm morphology and show that the sreh and bulk richardson number rather than the mean shear in the low levels determine the rotational characteristics and morphology of deep convection the results demonstrate that storms forming in environments characterized by large sreh are longer lived than those in less helical surroundings further it appears that the storm relat

detailed mapping of shallow landslides in eastern oklahoma and western arkansas and potential triggering by oklahoma earthquakes abstract landslides have long been considered one of the main erosive drivers that sculpt hillslopes over time tectonic forces raise slopes that can be sculpted by climate and the degree to which they can be sculpted depends upon the underlying lithology and hillslope geomorphology landslides destroy life and property and contribute to the evolution of mountain landscapes by generating and transporting hillslope sediments in this study we investigate the dynamics of soil mantled hillslopes in eastern oklahoma and western arkansas usa by mapping shallow landslides evaluating the frequency and magnitude of the landslides and quantifying the surface geometries we mapped 185 shallow landslides in a 150 km2 area the approximate ages of landslides and the frequencies and magnitudes area volume and runout were estimated using historical aerial photographs the landslide database was then used to compute rate of landslide occurrence and sediment yield in addition landslide surface geometries including slope curvature and surface roughness were determined from 10 m ned and 2 m lidar elevation data the hillslope susceptibility studies derived from elevation data were augmented by our review of common historical accounts that link landslides in the study region to the 1952 m 5 4 el reno oklahoma earthquake 300 km away in light of that case study we determined the frequency of historical earthquakes that impart 2 kpa dynamic stresses for the study area since 1900 and find an increased potential for dynamic stress perturbation of landslide activity since 2010 all these characteristics were then evaluated to understand the dynamics of hillslopes and hillslope susceptibility to shallow landslides frequency assessment of mapped landslides suggested that frequency of landslides increased significantly during 2005 2016 compared to 1995 2005 on average 10 shallow landslides occurred every year during 2005 2016 these landslides alone contributed 1 5 105 m3 yr sediment yield rate 0 10 cm yr of sediments surface roughness values were relatively higher in landslide areas compared to that of surrounding non landslide areas the surface roughness index mapped 84 of observed landslides and suggests that the index could be used to map hillslope susceptibility to landslides for future planned studies

formation of mesoscale lines of pirecipitation severe squall lines in oklahoma during the spring abstract four distinct kinds of severe mesoscale convective line development are identified in oklahoma during the spring based on the analysis of an 11 year period of reflectivity data from the national severe storms laboratory s 10 cm radar in norman oklahoma the primary classes of fine formation are broken line back building broken areal and embedded areal each is described in detail along with illustrative examples comparisons are made with other observations and with numerical model simulations the former two classes of line formation have been previously documented while the latter two have not only the broken areal squall line has been realistically simulated numerically the environment for each of the types of line development was determined from data from the standard national weather service surface and upper air networks and from special rawinsonde launches it was found that broken line formation tends to occur along cold fronts in a multicell environment while back building occur

global ubiquity of dynamic earthquake triggering surface waves that were generated by 12 out of 15 earthquakes with magnitudes greater than 7 since 1990 led to a global increase in the number of small earthquakes this suggests that dynamic triggering of earthquakes is common and is independent of the tectonic environment earthquakes can be triggered by local changes in the stress field static triggering1 2 3 4 5 6 7 due to nearby earthquakes or by stresses caused by the passage of surface rayleigh and love waves from a remote large earthquake dynamic triggering8 9 10 11 12 13 14 15 16 17 18 however the mechanism frequency controlling factors and the global extent of dynamic triggering are yet to be fully understood because rayleigh waves involve compressional and dilatational particle motion volumetric changes as well as shearing whereas love waves only involve shearing triggering by either wave type implies fundamentally different physical mechanisms here we analyse broadband seismograms from over 500 globally distributed stations and use an automated approach to systematically identify small triggered earthquakes the low amplitude signals of such earthquakes would normally be masked by high amplitude surface waves our analysis reveals that out of 15 earthquakes studied of magnitude m greater than 7 0 that occurred after 1990 12 are associated with significant increases in the detection of smaller earthquakes during the passage of both the love and rayleigh waves we conclude that dynamic triggering is a ubiquitous phenomenon that is independent of the tectonic environment of the main earthquake or the triggered event

the relationship between storm motion vertical wind shear and convective asymmetries in tropical cyclones abstract the influence of the direction of storm motion on the azimuthal distribution of electrified convection in 35 atlantic basin tropical cyclones from 1985 to 1999 was examined using data from the national lightning detection network in the inner 100 km flashes most often occurred in the front half of storms with a preference for the right front quadrant in the outer rainbands r 100 300 km flashes occurred predominantly to the right of motion although the maximum remained in the right front quadrant the results are shown to be consistent with previous studies of asymmetries in rainfall radar reflectivity and vertical motion with respect to tropical cyclone motion the motion effect has been attributed to the influence of asymmetric friction in the tropical cyclone boundary layer the authors previously found a strong signature in the azimuthal distribution of lightning with respect to vertical wind shear because both effects show clearly vertical wind shear and storm motion must themse

the landsat image mosaic of antarctica abstract the landsat image mosaic of antarctica lima is the first true color high spatial resolution image of the seventh continent it is constructed from nearly 1100 individually selected landsat 7 etm scenes each image was orthorectified and adjusted for geometric sensor and illumination variations to a standardized almost seamless surface reflectance product mosaicing to avoid clouds produced a high quality nearly cloud free benchmark data set of antarctica for the international polar year from images collected primarily during 1999 2003 multiple color composites and enhancements were generated to illustrate additional characteristics of the multispectral data including the true appearance of the surface discrimination between snow and bare ice reflectance variations within bright snow recovered reflectance values in regions of sensor saturation and subtle topographic variations associated with ice flow lima is viewable and individual scenes or user defined portions of the mosaic are downloadable at http lima usgs gov educational materials associated with lima are available at http lima nasa gov

the dependence of numerically simulated convective storms on vertical wind shear and buoyancy abstract the effects of vertical wind shear and buoyancy on convective storm structure and evolution are investigated with the use of a three dimensional numerical cloud model by varying the magnitude of buoyant energy and one directional vertical shear over a wide range of environmental conditions associated with severe storms the model is able to produce a spectrum of storm types qualitatively similar to those observed in nature these include short lived single cells certain types of multicells and rotating supercells the relationship between wind shear and buoyancy is expressed in terms of a nondimensional convective parameter which delineates various regimes of storm structure and in particular suggests optimal conditions for the development of supercell type storms applications of this parameter to well documented severe storm cases agree favorably with the model results suggesting both the value of the model in studying these modes of convection as well as the value of this representation i

seismic wave triggering of nonvolcanic tremor episodic tremor and slip and earthquakes on vancouver island 1 we explore the physical conditions that enable triggering of nonvolcanic tremor and earthquakes by considering local seismic activity on vancouver island british columbia during and immediately after the arrival of large amplitude seismic waves from 30 teleseismic and 17 regional or local earthquakes we identify tremor triggered by four of the teleseismic earthquakes the close temporal and spatial proximity of triggered tremor to ambient tremor and aseismic slip indicates that when a fault is close to or undergoing failure it is particularly susceptible to triggering of further events the amplitude of the triggering waves also influences the likelihood of triggering both tremor and earthquakes such that large amplitude waves triggered tremor in the absence of detectable aseismic slip or ambient tremor tremor and energy radiated from regional local earthquakes share the same frequency passband so that tremor cannot be identified during these smaller more frequent events we confidently identify triggered local earthquakes following only one teleseism that with the largest amplitude and four regional or local events that generated vigorous aftershock sequences in their immediate vicinity earthquakes tend to be triggered in regions different from tremor and with high ambient seismicity rates we also note an interesting possible correlation between large teleseismic events and episodic tremor and slip ets episodes whereby ets events that are late and have built up more stress than normal are susceptible to triggering by the slight nudge of the shaking from a large distant event while ets events that are early or on time are not

a composite study of the interactions between tropical cyclones and upper tropospheric troughs abstract the objective of this study is to understand how interactions with upper tropospheric troughs affect the intensity of tropical cyclones the study includes all named atlantic tropical cyclones between 1985 and 1996 to minimize other factors affecting intensity change times when storms are over subcritical sea surface temperatures 26 c or near landfall are removed from the sample a trough interaction is defined to occur when the eddy momentum flux convergence calculated over a 300 600 km radial range is greater than 10 m s 1 day 1 the trough interaction cases are separated into four composites i favorable superposition tropical cyclone intensifies with an upper tropospheric potential vorticity pv maximum within 400 km of the tropical cyclone center ii unfavorable superposition iii favorable distant interaction upper pv maximum between 400 and 1000 km from the tropical cyclone center and iv unfavorable distant interaction for comparison two additional composites are cre

remotely triggered microearthquakes and tremor in central california following the 2010 mw 8 8 chile earthquake 1 we examine remotely triggered microearthquakes and tectonic tremor in central california following the 2010 mw 8 8 chile earthquake several microearthquakes near the coso geothermal field were apparently triggered with the largest earthquake ml 3 5 occurring during the large amplitude love surface waves the chile mainshock also triggered numerous tremor bursts near the parkfield cholame section of the san andreas fault saf the locally triggered tremor bursts are partially masked at lower frequencies by the regionally triggered earthquake signals from coso but can be identified by applying high pass or matched filters both triggered tremor along the saf and the ml 3 5 earthquake in coso are consistent with frictional failure at different depths on critically stressed faults under the coulomb failure criteria the triggered tremor however appears to be more phase correlated with the surface waves than the triggered earthquakes likely reflecting differences in constitutive properties between the brittle seismogenic crust and the underlying lower crust

motion of an antarctic glacier by repeated tidally modulated earthquakes subglacial seismicity reveals information about glacier behaviour analysis of repeated seismic events beneath an antarctic outlet glacier is consistent with sliding of debris laden ice over a bedrock asperity with an event frequency that is modulated by the ocean tides

numerical simulation of hurricane bonnie 1998 part i eyewall evolution and intensity changes abstract in this study a 5 day explicit simulation of hurricane bonnie 1998 is performed using the fifth generation pennsylvania state university national center for atmospheric research mesoscale model mm5 with the finest grid length of 4 km the initial mass wind and moisture fields of the hurricane vortex are retrieved from the advanced microwave sounding unit a amsu a satellite measurements and the sea surface temperature sst is updated daily it is shown that the simulated track is within 3 latitude longitude of the best track at the end of the 5 day integration but with the landfalling point close to the observed the model also reproduces reasonably well the hurricane intensity and intensity changes asymmetries in cloud and precipitation as well as the vertical structures of dynamic and thermodynamic fields in the eye and eyewall it is shown that the storm deepens markedly in the first 2 days during which period its environmental vertical shear increases substantially it is found

a thermodynamic kinematic and microphysical analysis of a jet and gigantic jet producing florida thunderstorm this paper presents a meteorological analysis of a storm that produced two jets four gigantic jets gj and a starter which were observed by two radars as well as the kennedy space center 4 dimensional lightning surveillance system on 3 august 2013 in central florida the work is the first application of dual polarization data to a jet producing storm and is the fifth case related to a tropical disturbance the storm environment is consistent with the moist tropical paradigm that characterizes about three quarters of the surface and aircraft observed jet and gj events the most unstable mu convective available potential energy is not unusual for florida summer convection and is below the climatological mean for these events an unusual speed shear layer is located near the storm equilibrium level el and the storm exhibits a tilted structure with cgs displaced upshear the turbulence as measured by the eddy dissipation rate is extreme near the storm top during the event window consistent with the gj mixing hypothesis the individual events are collocated with and track along the center axis of the divergent outflow at the el and occur within the region of the coldest goes ir temperatures placing the events within the overshoot the dual polarization data indicate a deep graupel column extending above the mixed phase layer to a 13 km altitude

rapid intensification of a sheared tropical storm abstract a weak tropical storm gabrielle in 2001 experienced a 22 hpa pressure fall in less than 3 h in the presence of 13 m s 1 ambient vertical wind shear a convective cell developed downshear left of the center and moved cyclonically and inward to the 17 km radius during the period of rapid intensification this cell had one of the most intense 85 ghz scattering signatures ever observed by the tropical rainfall measuring mission trmm the cell developed at the downwind end of a band in the storm core maximum vorticity in the cell exceeded 2 5 10 2 s 1 the cell structure broadly resembled that of a vortical hot tower rather than a supercell at the time of minimum central pressure the storm consisted of a strong vortex adjacent to the cell with a radius of maximum winds of about 10 km that exhibited almost no tilt in the vertical this was surrounded by a broader vortex that tilted approximately left of the ambient shear vector in a similar direction as the broad precipitation shield this st

surface wave potential for triggering tectonic nonvolcanic tremor corrected abstract source processes commonly posed to explain instances of remote dynamic triggering of tectonic nonvolcanic tremor by surface waves include frictional failure and various modes of fluid activation the relative potential for love and rayleigh wave dynamic stresses to trigger tectonic tremor through failure on critically stressed thrust and vertical strike slip faults under the coulomb griffith failure criteria as a function of incidence angle are anticorrelated over the 15 to 30 km depth range that hosts tectonic tremor love wave potential is high for strike parallel incidence on low angle reverse faults and null for strike normal incidence the opposite holds for rayleigh waves love wave potential is high for both strike parallel and strike normal incidence on vertical strike slip faults and minimal for 45 incidence angles the opposite holds for rayleigh waves this pattern is consistent with documented instances of tremor triggered by love waves incident on the cascadia megathrust and the san andreas fault saf in central california resulting from shear failure on weak faults apparent friction is 0 2 documented instances of tremor triggered by surface waves with strike parallel incidence along the nankai megathrust beneath shikoku japan however are associated primarily with rayleigh waves this is consistent with the tremor bursts resulting from mixed mode failure crack opening and shear failure facilitated by near lithostatic ambient pore pressure low differential stress with a moderate friction coefficient 0 6 on the nankai subduction interface rayleigh wave dilatational stress is relatively weak at tectonic tremor source depths and seems unlikely to contribute significantly to the triggering process except perhaps for an indirect role on the saf in sustaining tremor into the rayleigh wave coda that was initially triggered by love waves

ice flow of the antarctic ice sheet we present a reference comprehensive high resolution digital mosaic of ice motion in antarctica assembled from multiple satellite interferometric synthetic aperture radar data acquired during the international polar year 2007 to 2009 the data reveal widespread patterned enhanced flow with tributary glaciers reaching hundreds to thousands of kilometers inland over the entire continent this view of ice sheet motion emphasizes the importance of basal slip dominated tributary flow over deformation dominated ice sheet flow redefines our understanding of ice sheet dynamics and has far reaching implications for the reconstruction and prediction of ice sheet evolution

seismic detection of an active subglacial magmatic complex in marie byrd land antarctica numerous volcanoes exist in marie byrd land a highland region of west antarctica high heat flow through the crust in this region may influence the stability of the west antarctic ice sheet 1 4 volcanic activity progressed from north to south in the executive committee mountain range between the miocene and holocene epochs but there has been no evidence for recent magmatic activity 5 7 here we use a recently deployed seismic network to show that in 2010 and 2011 two swarms of seismic activity occurred at 25 40 km depth beneath subglacial topographic and magnetic highs located 55 km south of the youngest subaerial volcano in the executive committee range we interpret the swarm events as deep long period earthquakes based on their unusual frequency content such earthquakes occur beneath active volcanoes are caused by deep magmatic activity and in some cases precede eruptions 8 11 we also use radar profiles to identify a prominent ash layer in the ice overlying the seismic swarm located at 1 400 m depth the ash layer is about 8 000 years old and was probably sourced from the nearby mount waesche volcano together these observations provide strong evidence for ongoing magmatic activity and demonstrate that volcanism continues to migrate southwards along the executive committee range eruptions at this site are unlikely to penetrate the 1 2 to 2 km thick overlying ice but would generate large volumes of melt water that could significantly affect ice stream flow

effects of vertical wind shear and storm motion on tropical cyclone rainfall asymmetries deduced from trmm abstract vertical wind shear and storm motion are two of the most important factors contributing to rainfall asymmetries in tropical cyclones tcs global tc rainfall structure in terms of azimuthal distribution and asymmetries relative to storm motion has been previously described using the tropical rainfall measuring mission microwave imager rainfall estimates the mean tc rainfall distribution and the wavenumber 1 asymmetry vary with storm intensity and geographical location among the six oceanic basins this study uses a similar approach to investigate the relationship between the structure of tc rainfall and the environmental flow by computing the rainfall asymmetry relative to the vertical wind shear the environmental vertical wind shear is defined as the difference between the mean wind vectors of the 200 and 850 hpa levels over an outer region extending from the radius of 200 800 km around the storm center the wavenumber 1 maximum rainfall asymmetry is downshear left right in the northern

a numerical study of the 6 may 2012 tsukuba city supercell tornado part i vorticity sources of low level and midlevel mesocyclones abstracton 6 may 2012 an f3 supercell tornado one of the most destructive tornadoes ever recorded in japan hit tsukuba city in eastern japan and caused severe damage to clarify the generation mechanisms of the tornadic storm and tornado high resolution numerical simulations were conducted under realistic environmental conditions using triply nested grids the innermost simulation with a 50 m mesh successfully reproduced the tsukuba city tornadic supercell storm in this study the first of a two part study the vorticity sources responsible for mesocyclogenesis prior to tornadogenesis were investigated by analyzing vortex lines and the evolution of circulation of the mesocyclones vortex lines that passed through the midlevel mesocyclone 4 km height originated from the environmental streamwise vorticity whereas the low level mesocyclone and low level mesoanticyclone were connected by several arching vortex lines over the rear flank downdraft associated with the hook shaped distribution of hydromet

an integrated perspective of the continuum between earthquakes and slow slip phenomena slow slip a mechanism by which faults can relieve stress was thought to be distinct from earthquakes however a global review of slow slip phenomena suggests that instead there is a continuum between the two types of event

antarctic icequakes triggered by the 2010 maule earthquake in chile large earthquakes can trigger seismicity in remote regions analysis of seismic data from antarctica reveals ice quakes coincident with passing seismic waves from the 2010 chile earthquake suggesting that the ice sheet is sensitive to such triggers

a vortical hot tower route to tropical cyclogenesis abstract a nonhydrostatic cloud model is used to examine the thermomechanics of tropical cyclogenesis under realistic meteorological conditions observations motivate the focus on the problem of how a midtropospheric cyclonic vortex a frequent by product of mesoscale convective systems during summertime conditions over tropical oceans may be transformed into a surface concentrated warm core tropical depression as a first step the vortex transformation is studied in the absence of vertical wind shear or zonal flow within the cyclonic vorticity rich environment of the mesoscale convective vortex mcv embryo the simulations demonstrate that small scale cumulonimbus towers possessing intense cyclonic vorticity in their cores vortical hot towers vhts emerge as the preferred coherent structures the vhts acquire their vertical vorticity through a combination of tilting of mcv horizontal vorticity and stretching of mcv and vht generated vertical vorticity horizontally localized and exhibiting conve

temporal variation of tectonic tremor activity in southern taiwan around the 2010 ml6 4 jiashian earthquake deep tectonic tremor which is extremely sensitive to small stress variations could be used to monitor fault zone processes during large earthquake cycles and aseismic processes before large earthquakes in this study we develop an algorithm for the automatic detection and location of tectonic tremor beneath the southern central range of taiwan and examine the spatio temporal relationship between tremor and the 4 march 2010 ml6 4 jiashian earthquake located about 20 km from active tremor sources we find that tremor in this region has a relatively short duration short recurrence time and no consistent correlation with surface gps data we find a short term increase in the tremor rate 19 days before the jiashian mainshock and around the time when the tremor rate began to rise one gps station recorded a flip in its direction of motion we hypothesize that tremor is driven by a slow slip event that preceded the occurrence of the shallower jiashian mainshock even though the inferred slip is too small to be observed by all gps stations our study shows that tectonic tremor may reflect stress variation during the pre nucleation process of a nearby earthquake

miniature supercells in an offshore outer rainband of hurricane ivan 2004 abstract airborne doppler radar observations are used to document the structure of three miniature supercells embedded in an outer rainband of hurricane ivan on 15 september 2004 the cells were located more than 100 km offshore beyond the doppler range of coastal radars the combination of large cape large vertical wind shear and moderate cell relative helicity with an apparent midlevel dry air intrusion provided an offshore environment supporting rotating storms each shallow cell contained a 5 7 km diameter mesocyclonic updraft with midlevel updraft and vorticity maxima that exceeded 6 m s 1 and 0 008 s 1 respectively such offshore structures are consistent with miniature supercells observed onshore in association with tropical cyclone tornado outbreaks the strong updrafts resulted from a combination of kinematic convergence thermal instability and shear induced vertical perturbation pressure gradients mesocyclone production largely resulted from the tilting and subsequent stretching of low l

antarctic ice shelf calving triggered by the honshu japan earthquake and tsunami march 2011 we use european space agency envisat data to present the first observational evidence that a northern hemisphere tsunami triggered antarctic ice shelf calving more than 13 000 km away the honshu tsunami of 11 march 2011 traversed the pacific ocean in 46 years this event further illustrates the growing evidence of ocean wave impact on antarctic calving and emphasizes the teleconnection between the antarctic ice sheet and events as far away as the northern hemisphere

structural and environmental controls on antarctic ice shelf rift propagation inferred from satellite monitoring 1 iceberg calving from ice shelves accounts for nearly half of the mass loss from the antarctic ice sheet yet our understanding of this process is limited the precursor to iceberg calving is large through cutting fractures called rifts that can propagate for decades after they have initiated until they become iceberg detachment boundaries to improve our knowledge of rift propagation we monitored the lengths of 78 rifts in 13 antarctic ice shelves using satellite imagery from the moderate resolution imaging spectroradiometer and multiangle imaging spectroradiometer between 2002 and 2012 this data set allowed us to monitor trends in rift propagation over the past decade and test if variation in trends is controlled by variable environmental forcings we found that 43 of the 78 rifts were dormant i e propagated less than 500 m over the observational interval we found only seven rifts propagated continuously throughout the decade an additional eight rifts propagated for at least 2 years prior to arresting and remaining dormant for the rest of the decade and 13 rifts exhibited isolated sudden bursts of propagation after 2 or more years of dormancy twelve of the fifteen active rifts were initiated at the ice shelf fronts suggesting that front initiated rifts are more active than across flow rifts although we did not find a link between the observed variability in rift propagation rate and changes in atmospheric temperature or sea ice concentration correlated with we did find a statistically significant correlation between the arrival of tsunamis and propagation of front initiated rifts in eight ice shelves this suggests a connection between ice shelf rift propagation and mechanical ocean interaction that needs to be better understood

a lagrangian trajectory view on transport and mixing processes between the eye eyewall and environment using a high resolution simulation of hurricane bonnie 1998 the transport and mixing characteristics of a large sample of air parcels within a mature and vertically sheared hurricane vortex are examined data from a high resolution 2 km horizontal grid spacing numerical simulation of real case hurricane bonnie 1998 are used to calculate lagrangian trajectories of air parcels in various subdomains of the hurricane namely the eye eyewall and near environment to study the degree of interaction transport and mixing between these subdomains it is found that 1 there is transport and mixing from the low level eye to the eyewall that carries air possessing relatively high values of equivalent potential temperature e which can enhance the efficiency of the hurricane heat engine 2 a portion of the low level inflow of the hurricane bypasses the eyewall to enter the eye and this air both replaces the mass of the low level eye and lingers for a sufficient time order 1 h to acquire enhanced entropy characteristics through interaction with the ocean beneath the eye 3 air in the mid to upper level eye is exchanged with the eyewall such that more than half the air of the eye is exchanged i n5hi nthis case of a sheared hurricane and 4 that one fifth of the mass in the eyewall at a height of 5 km has an origin in the mid to upper level environment where e is much less than in the eyewall which ventilates the ensemble average eyewall e by about 1 k implications of these findings for the problem of hurricane intensity forecasting are briefly discussed

the effects of vertical wind shear on the distribution of convection in tropical cyclones abstract the influence of vertical wind shear on the azimuthal distribution of cloud to ground lightning in tropical cyclones was examined using flash locations from the national lightning detection network the study covers 35 atlantic basin tropical cyclones from 1985 99 while they were over land and within 400 km of the coast over water a strong correlation was found between the azimuthal distribution of flashes and the direction of the vertical wind shear in the environment when the magnitude of the vertical shear exceeded 5 m s 1 more than 90 of flashes occurred downshear in both the storm core defined as the inner 100 km and the outer band region r 100 300 km a slight preference for downshear left occurred in the storm core and a strong preference for downshear right in the outer rainbands the results were valid both over land and water and for depression storm and hurricane stages it is argued that in convectively active tropical cyclones deep divergent circulations oppose the ver

simulations of shallow supercell storms in landfalling hurricane environments abstract numerical simulations of the convective storms that form in tornado producing landfalling hurricanes show that shallow supercells are possible even though buoyancy is limited because ambient lapse rates are close to moist adiabatic updrafts generally reach peak intensity at low levels often around 2 km above the surface by comparison a simulated midlatitude supercell typical of the great plains of the united states exhibits a pronounced increase in storm size both horizontally and vertically at low levels however the hurricane spawned storms may contain updrafts that rival or exceed in intensity those of great plains supercells at similar levels simulations made using a tornado proximity sounding from the remnants of hurricane danny in 1985 produce a small but intense supercell a finding consistent with the available observational evidence although the amplitude of parcel buoyancy is often small in hurricane environments its concentration in the strongly sheared lower troposphere pro

triggered seismic events along the eastern denali fault in northwest canada following the 2012 mw 7 8 haida gwaii 2013 mw 7 5 craig and two mw 8 5 teleseismic earthquakes we conduct a systematic search for remotely triggered seismic activity along the eastern denali fault edf in northwest canada an intraplate strike slip region we examine 19 distant earthquakes recorded by nine broadband stations in the canadian national seismograph network and find that the 2012 m w 7 8 haida gwaii and 2013 m w 7 5 craig alaska earthquakes triggered long duration 10 s emergent tremor like signals near the southeastern portion of the edf in both cases tremor coincides with the peak transverse velocities consistent with love wave triggering on right lateral strike slip faults the 2011 m w 9 0 tohoku oki and 2012 m w 8 6 indian ocean earthquakes possibly triggered tremor signals although we were unable to locate those sources in addition we also identify many short duration 5 s bursts that were repeatedly triggered by the rayleigh waves of the 2012 m w 7 8 haida gwaii earthquake although we were unable to precisely locate the short duration 5 s events they appear to be radiating from the direction of the klutlan glacier and from a belt of shallow historical seismicity at the eastern flank of the wrangell st elias mountain range the fact that these events were triggered solely by the rayleigh waves suggests a different source mechanism as compared with triggered tremor observed along the edf and other plate boundary regions online material description of rayleigh wave polarization detection figures of spectograms s wave amplitudes polarization analysis and static stress changes tables of earthquake catalogs and velocity model and animations of tremors and bursts

extreme helicity and intense convective towers in hurricane bonnie abstract helicity was calculated in hurricane bonnie 1998 using tropospheric deep dropsonde soundings from the nasa convection and moisture experiment large helicity existed downshear of the storm center with respect to the ambient vertical wind shear it was associated with veering semicircular hodographs created by strong vortex scale radial vertical flow induced by the shear the most extreme values of helicity among the largest ever reported in the literature occurred in the vicinity of deep convective cells in the downshear left quadrant these cells reached as high as 17 5 km and displayed the temporal and spatial scales of supercells convective available potential energy cape averaged 861 j kg 1 downshear but only about one third as large upshear the soundings nearest the deep cells were evaluated using two empirical supercell parameters that make use of cape helicity and or shear these parameters supported the possible existence of supercells as a consequence of the exceptional hel

numerical simulation of tornadogenesis in an outer rainband minisupercell of typhoon shanshan on 17 september 2006 abstract on 17 september 2006 three tornadoes occurred along the east coast of kyusyu island in western japan during the passage of an outer rainband in the right front quadrant of typhoon shanshan to clarify the structure of the tornado producing storms and the mechanism of tornadogenesis quadruply nested numerical simulations were performed using a nonhydrostatic model with an innermost horizontal grid spacing of 50 m several simulated convective storms in the outermost rainband exhibited characteristics of a minisupercell one storm had a strong rotating updraft of more than 30 m s 1 and a large vertical vorticity exceeding 0 06 s 1 this storm spawned a tornado when the low level mesocyclone intensified the tornado was generated on the rear flank gust front near the mesocyclone center when a secondary rear flank downdraft rfd surge advanced cyclonically around the low level mesocyclone and overtook the rear flank gust front at its left front edge backward trajectories and vorticity budget anal

deep tremor in new zealand triggered by the 2010 mw8 8 chile earthquake 1 deep non volcanic tremor nvt is usually associated with episodic slow slip events new zealand is one notable exception where numerous slow slip events have been identified yet nvt has remained undetected here we present the first known case of triggered nvt at new zealand s hikurangi subduction margin following the mw8 8 chilean earthquake of february 27 2010 we identify coherent high frequency tremor signals that are in phase with and modulated by the passing rayleigh waves this is consistent with the surface wave triggering potential for strike normal incidence on a low angle thrust fault after constraining the tremor depth on the plate interface we locate the tremor source within 20 km of the source area of episodic slow slip the tremor location is also near the edge of a region with high seismic attenuation that marks the boundary between dehydrated subducted slab and inferred hydrated underplated sediment we speculate that reduced interface friction and high fluid pressures provided by fluid rich underplated sediment facilitates the tremor generation

microearthquakes and subglacial conditions 1 ten passive seismic recording stations were deployed in a 9 km by 6 km array on rutford ice stream west antarctica to detect microearthquakes from the ice stream bed the array covered an area where a varying distribution of basal sedimentary conditions had been identified from seismic reflection surveys and interpreted as areas of both basal sliding and subglacial sediment deformation the passive seismic experiment was designed to give an independent confirmation of this interpretation as basal sliding is believed to be associated with the release of more acoustic energy than a deforming bed the results show that this is the case basal sliding producing six times more events this confirms that the spatial pattern of basal conditions does indeed reflect the distribution of different ice flow mechanisms it also shows that microearthquake monitoring can be a valuable new technique for mapping ice stream basal conditions over wide areas

vertical motion characteristics of tropical cyclones determined with airborne doppler radial velocities abstract vertical motions in seven atlantic hurricanes are determined from data recorded by doppler radars on research aircraft the database consists of doppler velocities and reflectivities from vertically pointing radar rays collected along radial flight legs through the hurricane centers the vertical motions are estimated throughout the depth of the troposphere from the doppler velocities and bulk estimates of particle fallspeeds portions of the flight tracks are subjectively divided into eyewall rainband stratiform and other regions characteristics of the vertical velocity and radar structure are described as a function of altitude for the entire dataset and each of the four regions in all of the regions more than 70 of the vertical velocities range from 2 to 2 m s 1 the broadest distribution of vertical motion is in the eyewall region where 5 of the vertical motions are 5 m s 1 averaged over the entire dataset the mean vertical velocity is upward at all altitudes mean downward mot

evidence suggesting fluid flow beneath japan due to periodic seismic triggering from the 2004 sumatra andaman earthquake 1 we show that very large surface waves from the 2004 sumatra andaman earthquake m9 2 triggered deep low frequency dlf seismic tremors beneath japan over a 500 km wide region the triggered seismicity was periodically excited synchronized with the amplitudes and phases of the oscillatory surface waves incident on the region periodic excitation implies that the specific phase of the surface waves plays an important role for the triggering estimation of stress changes in the source regions showed that the volumetric dilatation larger than 10 8 was the predominant factor for triggering thereby strongly supporting the hypothesis that dlf events are caused by processes related to fluid flow

tectonic tremor beneath cuba triggered by the mw 8 8 maule and mw 9 0 tohoku oki earthquakes we provide additional evidence of tectonic tremor in cuba triggered by the 2010 m w 8 8 maule chile and the 2011 m w 9 0 tohoku oki japan earthquakes the high frequency tremor signals are modulated by long period surface waves similar to triggered tremors observed in other tectonically active regions we are able to locate two tremor sources triggered by the tohoku oki earthquake near the east west trending oriente fault around guantanamo bay the tremor around guantanamo bay was triggered primarily by a love wave of the maule mainshock and by both love and rayleigh waves of the tohoku oki mainshock this is consistent with frictional failures at a vertical strike slip fault under a coulomb failure criterion online material figure of envelope functions of tremor records and movies of spectogram and tremor correlation

mesoscale and convective scale characteristics of mature hurricanes part ii inner core structure of hurricane allen 1980 abstract the eyewall structure of hurricane alien is examined from analyses of multiple aircraft data on two days 5 and 8 august 1980 these data sets are unique in that for the first time three instrumented aircraft executed coordinated radial penetrations of the eyewall at multiple levels the data collected on 5 august illustrate the persistence of various features on horizontal scales 10 km over several hours composite cross sections constructed from the 8 august data show similar structure although the eye diameter had decreased to less than half that of 5 august the convergence of air in the eyewall was highly two dimensional this convergence supported organized ascent that was along the inner edge of the high reflectivity region and displaced inward several kilometers from the radius of maximum wind rmw a mean eyewall updraft of 5 6 m s 1 is computed from integration of the two dimensional continuity equation embedded within the two dimensional eyewall were cores of high reflectivity t

hodograph curvature and updraft intensity in numerically modeled supercells abstract a set of numerical simulations of supercell thunderstorms has been carried out with a range of low level curvatures in the environmental hodograph and midlevel shears they cover a range of hodograph shape as measured by the integrated helicity of the lowest 3 km of the hodograph the peak updraft occurs in the first hour of the storms and tends to be greater for larger values of environmental helicity there is also a slight tendency for greater updraft intensity with lesser values of midlevel shear significantly air in the core of the updrafts at midlevels 5 km is not the most unstable air at the level the most buoyant air rises in a region with a downward directed pressure gradient force which slows its ascent conversely pressure gradient forces at lower levels 2 3 km accelerate less buoyant air upward into the core of the midlevel updrafts the pressure gradient force is larger in the cases with more curvature in the environmental wind than the low curvature environments this i

migration of early aftershocks following the 2004 parkfield earthquake a significant number of the early aftershocks following large shallow earthquakes are missing in existing earthquake catalogues an analysis of the waveforms of 3 647 relocated earthquakes along the parkfield section of the san andreas fault reveals 11 times more aftershocks within three days of the 2004 parkfield earthquake than listed in a standard catalogue large shallow earthquakes are immediately followed by numerous aftershocks a significant portion of these events is missing in existing earthquake catalogues mainly because seismicity after the mainshock can be masked by overlapping arrivals of waves from the mainshock and aftershocks1 2 3 4 however recovery of the missing early aftershocks is important for understanding the physical mechanisms of earthquake triggering2 3 4 and for tracking postseismic deformation around the rupture zone associated with the mainshock5 6 7 here we use the waveforms of 3 647 relocated earthquakes8 along the parkfield section of the san andreas fault as templates9 10 to detect missing aftershocks within three days of the 2004 magnitude 6 0 parkfield earthquake we identify 11 times more aftershocks than listed in the standard catalogue of the northern california seismic network we find that the newly detected aftershocks migrate in both along strike and down dip directions with logarithmic time since the mainshock consistent with numerical simulations of the expansion of aftershocks caused by propagating afterslip11 12 the cumulative number of early aftershocks increases linearly with postseismic deformation in the first two days supporting the view that aftershocks are driven primarily by afterslip13 14

vertical motions in intense hurricanes abstract hurricane vertical motion properties are studied using aircraft measured 1 hz time series of vertical velocity obtained during radial penetrations of four mature hurricanes a total of 115 penetrations from nine flight sorties at altitudes from 0 5 to 6 1 km are included in the data set convective vertical motion events are classified as updrafts or downdrafts if the vertical velocity was continuously positive or negative for at least 500 m and exceed an absolute value of 0 5 m s 1 over 3000 updrafts and nearly 2000 downdrafts are included in the data set a second criteria was used to define stronger events called cores this criteria required that upward or downward vertical velocity be continuously greater than an absolute value of 1 m s 1 for at least 500 m the draft and core properties are summarized as distributions of average and maximum vertical velocity diameter and vertical mass transport in two regions eyewall and rainband in both regions updrafts dominated over downdraft

glacial earthquakes in greenland and antarctica glacial earthquakes are a new class of seismic events first discovered as signals in long period seismograms recorded on the global seismographic network most of these events occur along the coasts of greenland where they are spatially related to large outlet glaciers glacial earthquakes show a strong seasonality with most events occurring during the late summer the rateofglacial earthquakeoccurrenceincreasedbetween2000and2005 with a stabilization of earthquake frequency at 2003 2004 levels in 2006 2008 recent observations establish a strong temporal correlation between the distinct seismic signals of glacial earthquakes and large ice loss events in which icebergs of cubic kilometer scale collapse against the calving face linking the seismogenic process to the force exerted by these icebergs on the glacier andtheunderlyingsolidearth asuddenchangeinglacierspeedresultsfrom these glacial earthquake calving events seasonal and interannual variations in glacier terminus position account for general characteristics of the temporal variation in earthquake occurrence glacial earthquakes in antarctica are less well studied but they exhibit several characteristics similar to glacial earthquakes in greenland