combining local and remote infrasound recordings from the 2009 redoubt volcano eruption abstract the explosive phase of the 2009 redoubt volcano eruption produced predominantly short duration high amplitude infrasound signals recorded up to 4500 km away all 19 numbered explosive events were recorded at a local microphone dfr 12 km as well as at an infrasound array in fairbanks alaska i53us 547 km most with high signal to noise ratios the local microphone provides an estimate of the source parameters and comparison between the two datasets allows the unique opportunity to evaluate acoustic source term estimation at a remote array high waveform similarity between dfr and i53us occurs during much of the explosive phase due to strong stratospheric ducting permitting accurate source constraints inferred from i53us data cross correlation analysis after applying a hilbert transform to the i53us data shows how the acoustic energy has passed through a single caustic as predicted by ray theory similar to previous studies significant low frequency infrasound from redoubt recorded at i53us is coincident with high altitude ash emissions the largest events also produced considerable energy at greater than 50 s periods likely related to the initial oscillations of the volcanic plume or jet many of the explosive events have emergent onsets somewhat unusual for explosive short duration eruptions comparison of the satellite derived so2 emissions with the relative amount of acoustic energy at i53us shows a very high statistically significant correlation this study reiterates the utility of using remote infrasound arrays for detection of hazardous emissions and characterization of large volcanic eruptions and demonstrates how under typical meteorological conditions remote infrasound arrays can provide an accurate representation of the acoustic source

the 1982 el chichon volcano eruptions a satellite perspective abstract the march 28 april 3 and april 4 1982 eruptions of el chichon volcano were detected and monitored using the goes and noaa 6 environmental satellites the satellite data provided information about the height and dispersal of the eruption plume and subsequent ash cloud on each of these dates based on the satellite data it was concluded that the march 28 eruption the second of two eruptions on april 3 and the april 4 eruption injected material into the stratosphere at heights between 17 and 31 km

on vertical advection truncation errors in terrain following numerical models comparison to a laboratory model for upwelling over submarine canyons 1 submarine canyons which indent the continental shelf are frequently regions of steep up to 45 three dimensional topography recent observations have delineated the flow over several submarine canyons during 2 4 day long upwelling episodes thus upwelling episodes over submarine canyons provide an excellent flow regime for evaluating numerical and physical models here we compare a physical and numerical model simulation of an upwelling event over a simplified submarine canyon the numerical model being evaluated is a version of the s coordinate rutgers university model scrum careful matching between the models is necessary for a stringent comparison results show a poor comparison for the homogeneous case due to nonhydrostatic effects in the laboratory model results for the stratified case are better but show a systematic difference between the numerical results and laboratory results this difference is shown not to be due to nonhydrostatic effects rather the difference is due to truncation errors in the calculation of the vertical advection of density in the numerical model the calculation is inaccurate due to the terrain following coordinates combined with a strong vertical gradient in density vertical shear in the horizontal velocity and topography with strong curvature

soil water flux in the southern great basin united states temporal and spatial variations over the last 120 000 years the disposal of hazardous and radioactive waste in arid regions requires a thorough understanding of the occurrence of soil water flux and recharge soil water chemistry and isotopic data are presented from three deep vadose zone boreholes 230 m at the nevada test site located in the great basin geographic province of the southwestern united states to quantify soil water flux and its relation to climate the low water contents found in the soils significantly reduce the mixing of tracers in the subsurface and provide a unique opportunity to examine the role of climate variation on recharge in arid climates tracing techniques and core data are examined in this work to reconstruct the paleohydrologic conditions existing in the vadose zone well beyond the timescales typically investigated stable chloride and chlorine 36 profiles indicate that the soil waters deep in the vadose zone range in age from approximately 20 000 to 120 000 years secondary chloride bulges that are present in two of the three profiles support the concept of recharge occurring at or near the last two glacial maxima when the climate of the area was considerably wetter and cooler the stable isotopic composition of the soil water in the profiles is significantly more depleted in heavy isotopes than is modern precipitation suggesting that recharge under the current climate is not occurring at this arid site past and present recharge appears to have been strongly controlled by surface topography with increased incidence of recharge where runoff from the surrounding mountains may have been concentrated the data obtained from this detailed drilling and sampling program shed new light on the behavior of water in thick vadose zones and in particular show the sensitivity of arid regions to the extreme variations in climate experienced by the region over the last two glacial maxima

eruption chronologies plume heights and eruption styles at tungurahua volcano integrating remote sensing techniques and infrasound article i nfo satellite remote sensing allows volcanic ash plumes to be detected and tracked and routinely aids in hazard mitigation especially to the aviation community although satellite imagery provides valuable information about volcanic plume processes i e plume heights plume composition and plume transport it has its limitations in addition to the observational gaps produced by meteorological clouds as well as temporal and spatial resolution restrictions large volcanic clouds often obscure the vent during an eruption therefore some key information about eruption dynamics and processes are impossible to obtain from satellite images in this paper we investigate four eruptions at tungurahua volcano ecuador during the 2006 2008 time period we integrate satellite derived eruption chronologies plume heights and plume aspect ratios with infrasound data primarily acoustic power and hand held thermal imagery when available integrating these datasets allows us to identify accurate eruption onsets durations and cessations as well as define different types of eruption styles ranging from plinian to weak vulcanian transitions between the different eruption styles were also documented results show that there is a positive correlation between plume height and acoustic power we conclude that combining the two datasets allows better constraints on eruption processes and source parameters using these methods in real time monitoring will allow more accurate eruption monitoring and ash hazard mitigation

tungurahua volcano ecuador structure eruptive history and hazards abstract tungurahua one of ecuador s most active volcanoes is made up of three volcanic edifices tungurahua i was a 14 km wide andesitic stratocone which experienced at least one sector collapse followed by the extrusion of a dacite lava series tungurahua ii mainly composed of acid andesite lava flows younger than 14 000 years bp was partly destroyed by the last collapse event 2955 90 years ago which left a large amphitheater and produced a 8 km3 debris deposit the avalanche collided with the high ridge immediately to the west of the cone and was diverted to the northwest and southwest for 15 km a large lahar formed during this event which was followed in turn by dacite extrusion southwestward the damming of the chambo valley by the avalanche deposit resulted in a 10 km long lake which was subsequently breached generating another catastrophic debris flow the eruptive activity of the present volcano tungurahua iii has rebuilt the cone to about 50 of its pre collapse size by the emission of 3 km3 of volcanic products two periods of construction are recognized in tungurahua s iii history from 2300 to 1400 years bp high rates of lava extrusion and pyroclastic flows occurred during this period the magma composition did not evolve significantly remaining essentially basic andesite during the last 1300 years eruptive episodes take place roughly once per century and generally begin with lapilli fall and pyroclastic flow activity of varied composition andesite dacite and end with more basic andesite lava flows or crater plugs this pattern is observed in the three historic eruptions of 1773 1886 and 1916 1918 given good age control and volumetric considerations tungurahua iii growth s rate is estimated at 1 5 106 m3 year over the last 2300 years although an infrequent event a sector collapse and associated lahars constitute a strong hazard of this volcano given the 3000 m relief and steep slopes of the present cone a future collapse even of small volume could cover an area similar to that affected by the 3000 year old avalanche the more frequent eruptive episodes of each century characterized by pyroclastic flows lavas lahars as well as tephra falls directly threaten 25 000 people and the agoyan hydroelectric dam located at the foot of the volcano

characteristics of two counter rotating eddies in the leeuwin current system off the western australian coast abstract a multi disciplinary r v southern surveyor cruise was conducted in october 2003 to quantify upper ocean productivity within two adjacent counter rotating mesoscale eddies an eddy pair off the coast of western australia wa in the southeast indian ocean in this study a combination of satellite data altimeter sea surface temperature and chlorophyll a and shipboard measurements acoustic doppler current profiler adcp and conductivity temperature depth ctd were used to characterize the temporal evolution and spatial structures of the eddy pair satellite data show that the eddy pair evolved from meander structures of the poleward flowing leeuwin current lc in may 2003 and fully detached from the current in late august early september gaussian fits to the adcp velocities show that the anticyclonic eddy had a maximum azimuthal velocity of 65 cm s 1 at 63 km from the eddy centre the apparent radius and the cyclonic eddy had a maximum azimuthal velocity of 60 cm s 1 at the apparent radius of 49 km the mixed layer temperature and salinity properties in the cores of the eddy pair were quite stable over the period of the cruise temperature salinity diagrams indicate that the mixed layer water in the core of the anticyclonic eddy was composed mainly of lc water while in the core of the cyclonic eddy the mixed layer water was similar to surrounding open ocean water the total volume of the lc water retained in the anticyclonic eddy was 5 6 1012 m3 equivalent to 19 days annual mean transport of the lc the chlorophyll a concentration in the surface layer of the anticyclonic eddy lc water was higher than in the cyclonic eddy open ocean water which was likely a result of the entrainment of the productive water from the continental shelf during the eddy formation stage the offshore transport of the chlorophyll a biomass may be important for the pelagic ecosystem off the coast of wa

on the pressure gradient force over steep topography in sigma coordinate ocean models abstract the error in computing the pressure gradient force near steep topography using terms following coordinates is investigated in an ocean model using the family of vertical differencing schemes proposed by arakawa and suarez the truncation error is estimated by substituting known buoyancy profiles into the finite difference hydrostatic and pressure gradient terms the error due to hydrostatic inconsistency which is not simply a space truncation error is also documented the results show that the pressure gradient error is spread throughout the water column and it is sensitive to the vertical resolution and to the placement of the grid points relative to the vertical structure of the buoyancy field being modeled removing a reference state as suggested for the atmosphere by gary reduces the truncation error associated with the two lowest vertical modes by a factor of 2 to 3 as an example the error in computing the pressure gradient using a standard 10 level primitive equation model appl

physical and chemical signatures of a developing anticyclonic eddy in the leeuwin current eastern indian ocean a multidisciplinary cruise aboard the r v southern surveyor was conducted in may 2006 to sample a developing anticyclonic eddy of the leeuwin current off western australia the eddy formed from a meander of the leeuwin current in mid april 2006 and remained attached to the current until mid august in this study a combination of satellite data altimeter sea surface temperature and chlorophyll a and shipboard measurements acoustic doppler current profiler and conductivity temperature depth were used to characterize the physical and chemical signatures of the eddy the temperature salinity properties of the mixed layer waters within the anticyclonic eddy and on the shelf were both connected to that of the leeuwin current indicating the water mass in the eddy is mainly derived from the leeuwin current and the modified leeuwin current water on the shelf above the salinity maximum near the eddy center there was a regionally significant concentration of nitrate 0 9 mol l 1 and the maximum 2 mol l 1 was at 150 in depth below the photic zone nitrification within the eddy and or local upwelling due to the forming eddy could be responsible for this high concentration of nitrate near the eddy center which potentially makes the eddy a relatively productive feature in the leeuwin current

contribution of storms to groundwater recharge in the semi arid region of karnataka india this paper describes the application of environmental isotopes and injected tracer techniques in estimating the contribution of storms as well as annual precipitation to groundwater recharge and its circulation in the semi arid region of bagepalli kolar district karnataka environmental isotopes 2h 18o and 3h were used to study the effect of storms on the hydrological system and an isotope balance was used to compute the contribution of a storm component to the groundwater some of the groundwater samples collected during the post storm periods were highly depleted in stable isotope content with higher deuterium excess relative to groundwater from the pre storm periods significant variation in deuterium excess in groundwater from the same area collected in two different periods indicates the different origin of air masses the estimated recharge component of a storm event of 600 mm to the groundwater was found to be in the range of 117 165 mm there was no significant variation in environmental tritium content of post storm and pre storm groundwater indicating the fast circulation of groundwater in the system after completion of the environmental isotope work an injected radiotracer 3h technique was applied to estimate the direct recharge of total precipitation to the groundwater the estimated recharge to the groundwater is 33 mm of the 550 mm annual precipitation during 1992 copyright 2003 john wiley sons ltd

integrated satellite observations of the 2001 eruption of mt cleveland alaska abstract satellite data were the primary source of information for the eruption of mt cleveland alaska on 19 february and 11 and 19 march 2001 multiple data sets were used pre syn and post eruption to mitigate the hazard and determine an eruption chronology the 19 february eruption was the largest of the three resulting in a volcanic cloud that formed an arc over 1000 km long moved to the ne across alaska and was tracked using satellite data over more than a 50 h period the volcanic cloud was concurrently detected on the goes avhrr and modis data at various times and their respective signals compared all three sensors detected a cloud that had a very similar shape and position but there were differences in their areal extent and internal structural detail goes data showed the largest volcanic cloud in terms of area probably due to its oblique geometry modis bands 31 and 32 which are comparable to goes and avhrr thermal infrared wavelengths were the least effective single channels at detecting the volcanic cloud of those investigated modis bands 28 29 31 and 32 modis bands 28 and 29 detected the largest volcanic clouds that could easily be distinguished from weather clouds of the split window data modis bands 29 minus band 32 detected the largest cloud but the band 31 minus band 32 data showed the volcanic cloud with the most internal structural detail the puff tracking model accurately tracked the movement and predicted the extent and shape of this complex cloud even into areas beyond satellite detection numerous thermal anomalies were also observed during the eruption on the twice daily avhrr data and the high spatial resolution landsat data the high resolution radarsat data showed that the avhrr thermal anomalies were due to lava and debris flow features and a newly formed fan along the west coast of the island field observations and images from a hand held forward looking infrared radiometer flir showed that the flow features were a a lava debris flows and a warm debris fan along the west coast real time satellite data were the primary tool used to monitor the eruption track changes and to mitigate hazards high resolution data even though coverage is infrequent were critical in helping to identify volcanic processes and to compile an eruption chronology

the 1997 eruption of okmok volcano alaska a synthesis of remotely sensed imagery abstract okmok volcano in the eastern aleutian islands erupted in february and march of 1997 producing a 6 km long lava flow and low level ash plumes this caldera is one of the most active in the aleutian arc and is now the focus of international multidisciplinary studies a synthesis of remotely sensed data airsar derived dems landsat mss and etm data avhrr ers jers radarsat has given a sequence of events for the virtually unobserved 1997 eruption elevation data from the airsar sensor acquired in october 2000 over okmok were used to create a 5 m resolution dem mosaic of okmok volcano avhrr nighttime imagery has been analyzed between february 13 and april 11 1997 landsat imagery and sar data recorded prior to and after the eruption allowed us to accurately determine the extent of the new flow the flow was first observed on february 13 without precursory thermal anomalies at this time the flow was a large single lobe flowing north according to avhrr band 3 and 4 radiance data and ground observations the first lobe continued growing until mid to late march while a second smaller lobe began to form sometime between march 11 and 12 this is based on a jump in the thermal and volumetric flux determined from the imagery and the physical size of the thermal anomalies total radiance values waned after march 26 indicating lava effusion had ended and a cooling crust was growing the total area 8 9 km 2 thickness up to 50 m and volume 1 54 10 8 m 3 of the new lava flow were determined by combining observations from sar landsat etm and airsar dem data while the first lobe of the flow ponded in a pre eruption depression our data suggest the second lobe was volume limited remote sensing has become an integral part of the alaska volcano observatory s monitoring and hazard mitigation efforts studies like this allow access to remote volcanoes and provide methods to monitor potentially dangerous ones

vadose zone tritium tracer test to estimate aquifer recharge from irrigated areas environmental tracers such as tritium have generally been used to estimate aquifer recharge under natural conditions a tritium tracer test is presented for estimating recharge under semi arid and irrigated conditions the test was performed along 429 days june 2007 august 2008 on an experimental plot located in se spain with drip irrigation and annual row crops rotation of lettuce and melon in which common agricultural practices were followed in open air tritiated water was sprinkled simulated rainfall over the plot soil cores were taken at different depths and a liquid scintillation analyzer was used to measure tritium concentration in soil water samples tritium transport as liquid or vapor phase was simulated with the one dimensional numerical code solveg simulations show that the crop water use was below potential levels despite regular irrigation continuous high water content in soil promoted a great impact of rainfall events on the aquifer recharge the results obtained from tritium tracer test have been compared with other independent recharge assessment soil water balance method to evaluate the reliability of the first one total recharge from tracer test was 476 mm for the october 2007 september 2008 period versus 561 mm from soil water balance method for the same period which represents 37 1 and 43 7 of the applied water 1284 mm irrigation precipitation respectively copyright 2012 john wiley sons ltd

generation and unstable evolution of a density driven eastern poleward current the iberian poleward current 1 the generation and evolution of a density driven eastern poleward current is investigated using a high resolution primitive equation numerical model the simulations focus on the iberian poleward current ipc as a case study the flow is generated by a meridional upper ocean density gradient balanced by an eastward surface intensified flow that adjusts at the coastal margin the resulting current system has a baroclinic character with poleward flow at the surface layer and equatorward flow underneath a few weeks after initialization the sheared along slope flow generates several vorticity structures downstream of the main topographic features in the lee of the topography persistent anticyclones are observed and deep cyclogenesis is induced in relation to the meandering of the upper layer jet these structures evolve preferentially as cyclone anticyclone eddy pairs and after interaction some dipoles are ejected offslope within a period of a few months the initial meridional gradient evolves into a complex system of fronts eddies and slope flows the dynamics of flow topography interaction is analyzed a comparison with satellite imagery of the ipc is conducted and similarity in scales and patterns is noted

the 5500 km long boundary flow off western and southern australia 1 the path of the shelf edge flow off southwestern australia is documented using results from satellite altimetry and sea surface temperature sst and a climatogical in situ analysis during austral winter a continuous current is shown to extend from its origin at north west cape to the southern tip of tasmania a distance of 5500 km satellite sst observations and surface buoy tracks confirm the location and continuity of the current trajectory while the leeuwin current is forced by the strong alongshore pressure gradient associated with the meridional portion of the western australian coastal boundary our results suggest that the essentially zonal shelf edge flow along the southern australian coast arises from the setup of coastal sea level by onshore ekman flow driven by the winter westerly wind and possibly a further alongshore pressure gradient the timing of these two different forcing mechanisms means that the west coast pressure gradient delivers the leeuwin current to the south coast just as the winds reverse and are thus able to maintain the eastward passage of the current the shelf edge flow consists of two main water masses a low salinity warm water type of tropical origin associated with the leeuwin current and a high salinity warm water inflow formed on the western end of the great australian bight continental shelf a naming convention is proposed the leeuwin current representing flow from north west cape to the great australian bight gab the south australian current between the eastern gab and western bass strait and the zeehan current off western tasmania

goes weather satellite observations and measurements of the may 18 1980 mount st helens eruption we demonstrate the use of geostationary operational environmental satellite goes images of the may 18 1980 mount st helens volcanic plume in providing details of the dynamics and changing character of this major explosive eruption visible and thermal infrared ir data from a sequence of images at 30 min intervals from 0850 to 1720 local time lt give information on dispersal and plume top temperature initial visible and ir images at 0850 show the top of a spreading co ignimbrite like umbrella plume and an overshooting column emerging from it both rising off the ground hugging pyroclastic gravity flow generated by the opening directed blast the overshooting column had a minimum temperature significantly colder than local ambient atmosphere indicating substantial undercooling and a maximum altitude of 31 2 km at 0920 this large plume system then formed a high velocity radially spreading gravitationally driven current before becoming advected in the wind field at an average downwind velocity of 29 m s within 30 to 60 min the undercooled plume adjusted to ambient temperatures after this initial event the eruption column fluctuated over the next 8 hours between stable plinian column rise and unstable conditions favoring column collapse leading to pyroclastic flows and further development of co ignimbrite ash columns over this period of observation profiles of plume top temperatures derived from ir data versus distance along the downwind axis have distinctive patterns with steep slopes associated with co ignimbrite plumes and shallower slopes associated with plinian plumes moreover reflectance values from visible goes data change from lower to higher during periods of transition from darker toned plinian to lighter toned coignimbrite plumes indicating that in this case satellite data resolved changes in eruptive style from plumes with a coarser to a finer dominant particle size

numerical simulation of flow around a tall isolated seamount part i problem formulation and model accuracy abstract a sigma coordinate ocean circulation model is employed to study flow trapped to a tall seamount in a periodic f plane channel in part i errors arising from the pressure gradient formulation in the steep topography strong stratification limit are examined to illustrate the error properties a linearized adiabatic version of the model is considered both with and without forcing and starting from a resting state with level isopycnals the systematic discretization errors from the horizontal pressure gradient terms are shown analytically to increase with steeper topography relative to a fixed horizontal grid and for stronger stratification as measured by the burger number for an initially quiescent unforced ocean the pressure gradient errors produce a spurious oscillating current that at the end of 10 days is approximately 1 cm s 1 in amplitude the period of the spurious oscillation about 0 5 days is shown to be a consequence of the particular form of the pressure gradient terms in th

ocean circulation in the great australian bight in an eddy resolving ocean reanalysis the eddy field seasonal and interannual variability abstract the ocean circulation in the great australian bight gab is dominated by the surface intensified leeuwin current lc over the outer continental shelf and the flinders current farther offshore in the gab the lc flows eastwards and varies seasonally with strongest currents of up to 0 8 m s at 130 5 e bringing warm and salty waters as far east as western tasmania the flinders current flows westwards as an undercurrent at depths of around 500 m over the continental slope and at the surface offshore of the lc off the shelf the gab is rich in mesoscale eddies with surface intensified currents of up to 0 4 m s that are coherent over the full water depth getting weaker with depth within deep water eddies isotherms are displaced vertically by up to 200 m eddies in the eastern gab are most energetic in austral winter and spring coincident with the seasonal weakening of the lc the eastern most penetration of gab eddies occurs in austral winter when the lc starts to weaken we hypothesise that the horizontal shear associated with the lc generates eddies in the eastern gab the volume transport of the lc at the head of the gab is typically between 1 and 7 sv with a clear seasonal cycle and the interannual variability of lc transport is up to 2 sv

estimating paleorecharge and paleoclimate from unsaturated zone profiles unsaturated zone solute and isotope profiles may be interpreted in terms of past changes in recharge rate in cases where water movement can be approximated by piston flow a model is presented which describes water movement in terms of piston flow below a surface mixing layer below the mixing layer diffusion and dispersion occur in the liquid phase in the case of solutes and in both the liquid and gas phases in the case of isotopically labeled water climatic events of 4 5 years duration may be preserved in the unsaturated zone for more than 50 years if the recharge rate is greater than approximately 20 mm yr 1 longer term fluctuations in climatic conditions century scale might be preserved for over 1000 years provided the recharge rate is greater than approximately 2 mm yr 1 and the unsaturated zone is sufficiently deep profiles from cyprus and northern senegal appear to record changes in recharge rate over periods up to 400 years the profiles are well correlated with known variations in rainfall and fluctuations in lake levels the model provides limiting conditions to be applied to the interpretation of profiles

the initial giant umbrella cloud of the may 18th 1980 explosive eruption of mount st helens abstract the initial eruption column of may 18th 1980 reached nearly 30 km altitude and released 10 17 joules of thermal energy into the atmosphere in only a few minutes ascent of the cloud resulted in forced intrusion of a giant umbrella shaped cloud between altitudes of 10 and 20 km at radial horizontal velocities initially in excess of 50 m s the mushroom cloud expanded 15 km upwind forming a stagnation point where the radial expansion velocity and wind velocity were equal the cloud was initiated when the pyroclastic blast flow became buoyant the flow reduced its density as it moved away from the volcano by decompression by sedimentation and by mixing with and heating the surrounding air observations indicate that much of the flow covering an area of 600 km 2 became buoyant within 1 5 minutes and abruptly ascended to form the giant cloud calculations are presented for the amount of air that must have been entrained into the flow to make it buoyant assuming an initial temperature of 450 c and a magmatic origin for the explosion these calculations indicate that the flow became buoyant when its temperature was approximately 150 c and the flow consisted of a mixture of 3 25 10 11 kg of pyroclasts and 5 0 10 11 kg of air if sedimentation is considered these figures reduce to 1 1 10 11 kg of pyroclasts and 1 0 10 11 kg of air

an automatic seismic event processing for detection and location the p m c c method we present a new method for automatic detection and location of seismic events recorded on a network it is based on a progressive study of the interstation correlation functions which leads to a consistent set of time delays when a seismic phase is present three different examples are processed on networks of different sizes

global morphology of infrasound propagation i atmospheric sound waves in the 0 02 10 hz region also known as infrasound exhibit long range global propagation characteristics measurable infrasound is produced around the globe on a daily basis by a variety of natural and man made sources as a result of weak classical attenuation 0 01 db km 1 at 0 1 hz these acoustic signals can propagate thousands of kilometers in tropospheric stratospheric and lower thermospheric ducts to model this propagation accurately detailed knowledge of the background atmospheric state variables the global winds and temperature fields from the ground to 170 km is required for infrasound propagation calculations we have developed a unique atmospheric specification system g2s that is capable of providing this information using acoustic ray tracing methods and detailed g2s atmospheric specifications we investigate the major aspects of the spatiotemporal variability of infrasound propagation characteristics

estimating groundwater recharge in hebei plain china under varying land use practices using tritium and bromide tracers summary tritium and bromide were used as applied tracers to determine groundwater recharge in hebei plain north china to evaluate the impacts of different soil types land use irrigation and crop cultivation practice on recharge additional objectives were to evaluate temporal variability of recharge and the effect on results of the particular tracer used thirty nine profiles at representative locations were chosen for investigation average recharge rates and recharge coefficient determined by tritium and bromide tracing for different sites were 0 00 1 05 mm d and 0 0 42 5 respectively the results showed relative recharge rates for the following paired influences items within each pair are listed with the influence producing greater recharge first flood irrigated cropland and non irrigated non cultivation land flood irrigation 0 42 0 58 mm d and sprinkling irrigation 0 17 0 23 mm d no stalk mulch 0 56 0 80 mm d and stalk mulch 0 44 0 60 mm d vegetable e g chinese cabbage and garlic 0 70 mm d and wheat maize 0 38 mm d peanut 0 51 mm d and peach 0 43 mm d the results also showed greater recharge for the first year of tracer travel than for the second because total precipitation and irrigation were greater in the first year than in the second this may reflect temporal variability of recharge the method may not be applicable where the water table is shallow less than 3 m a comparison of the near ideal tritium tracer with the more common but less ideal bromide showed that bromide moved approximately 23 faster than tritiated water perhaps because of anion exclusion

on the behavior of boundary undercurrents near canyons a simple finite froude number quasi geostrophic frictionless model is developed to study the response of a boundary undercurrent such as the california undercurrent to variations in the underlying topography despite its baroclinic nature the flow tends to follow contours of total depth although this pattern of response is not fully achieved over deep narrow canyons the flow separates from the bottom another simple model containing stratification and frictional effects predicts upwelling to occur in the underlying water within the canyon

interannual modulation of eddy kinetic energy in the southeast indian ocean by southern annular mode 1 interannual variability in the mesoscale eddy field over the southeast indian ocean of 15 s 35 s and 60 e 110 e is investigated on the basis of 16 year satellite altimetry observations eddy kinetic energy eke in this region appears stronger in 2000 2004 and weaker in 1993 1996 1998 2000 and 2007 it is found that this interannual modulation of eke is mediated by the southern annular mode sam with a positive negative sam corresponding to weak strong eddy activity in this region the interannual modulation of the eke by the sam is through modulating the baroclinic instability associated with the surface intensified south indian countercurrent sicc and the underlying south equator current sec system in the positive phase of the sam the southeastern subtropical indian ocean is dominated by an anomalous ekman upwelling which slackens the southward tilt of the isotherms and thus reduces the sicc this shall reduce the vertical velocity shear of the sicc sec current system leading to a weak instability and thus a weak eddy activity

subinertial response of a density driven eastern boundary poleward current to wind forcing a high resolution primitive equation numerical model is used to generate a poleward flow along a meridionally oriented eastern boundary slope shelf system by imposing an along coast density gradient as the forcing mechanism wind forcing is applied to the resulting quasi steady current system and the subinertial response is analyzed parallel experiments with no slope poleward flow are conducted for comparison moderately strong upwelling and downwelling favorable week to month scale wind events modify the poleward flow but do not significantly change the density driven current structure at the slope the alongshore transport within the slope region is reduced by 0 2 0 3 sv from 1 2 sv where sv 106 m3 s 21 under the influence of either downwelling or upwelling winds independent of the wind direction the density driven poleward flow always remains surface intensified wind driven shelf currents develop with a considerable degree of independence from the slopepoleward circulation on the shelf the density field is modified by cross shelf buoyancy advection within the boundary layers and by strong vertical mixing the presence of the poleward flow over the slope constitutes an important factor in the behavior of the bottom boundary layer at the shelf break and for the patterns of crossslope circulation

degassing patterns of tungurahua volcano ecuador during the 1999 2006 eruptive period inferred from remote spectroscopic measurements of so2 emissions this paper presents the results of 7 years aug 1999 oct 2006 of so2 gas measurements during the ongoing eruption of tungurahua volcano ecuador from 2004 onwards the operation of scanning spectrometers has furnished high temporal resolution measurements of so2 flux enabling this dataset to be correlated with other datasets including seismicity the emission rate of so2 during this period ranges from less than 100 to 35000 tonnes day t d with a mean daily emission rate of 1458 t d and a standard deviation of 2026 t d average daily emissions during inferred explosive phases are about 1 75 times greater than during passive degassing intervals the total amount of sulfur emitted since 1999 is estimated as at least 1 91 mt mostly injected into the troposphere and carried westwards from the volcano our observations suggest that the rate of passive degassing at tungurahua requires so2 exsolution of an andesitic magma volume that is two orders of magnitude larger than expected for the amount of erupted magma two possible and not mutually exclusive mechanisms are considered here to explain this excess degassing gas flow through a permeable stagnant magma filled conduit and gas escape from convective magma overturning in the conduit we have found that real time gas monitoring contributes significantly to better eruption forecasting at tungurahua because it has provided improved understanding of underlying physical mechanisms of magma ascent and eruption

a process oriented numerical study of currents eddies and meanders in the leeuwin current system abstract while observations provide insight for the basic nature of features in the leeuwin current system lcs process oriented studies are useful for systematically investigating the characteristics and dynamical forcing mechanisms for the currents and eddies in the lcs this process oriented numerical study investigates the roles of wind forcing thermohaline gradients and bottom topography on currents and eddy generation in the lcs with a terrain following primitive equation model in this case the princeton ocean model pom on a beta plane off the western and southwestern coast of australia results show that the lcs is an anomalous eastern boundary current that generates a surface poleward current predominantly over the shelf break an equatorward surface current with upwelling next to the coast in localized regions an equatorward undercurrent and highly energetic mesoscale features such as meanders and eddies thermohaline gradient effects are shown to be the primary mechanism in the generation of a poleward equatorward current undercurrent eddies and meanders in the lcs inshore of the poleward surface flow next to the coast wind forcing plays an important role in generating an equatorward coastal current and upwelling the major role of the wind is to slow the poleward surface flow enhance eddy spin up and create localized upwelling regions such as in the north near shark bay and just north of cape leeuwin bottom topography is shown to be an important mechanism for intensifying and trapping currents near the coast weakening subsurface currents and intensifying eddies off capes the surface poleward current is predominantly steered by the shelf break frequently leaving the coast as it follows the 200 m depth contour southward to cape leeuwin and eastward into the great australian bight overall the results of this process oriented study compare well with available observations in the lcs

the 16 september 1986 eruption of lascar volcano north chile satellite investigations landsat thematic mapper tm images acquired in 1984 and 1985 revealed a pronounced thermal anomaly on lascar volcano north chile subsequent images showed that the anomaly was persistent but variable and that after a significant eruption on 16 september 1986 it was weaker and divided into several sources tm studies and other observations of lascar indicate that the persistent thermal anomaly may be due to high temperature fumaroles within the summit crater goes weather satellite images and field investigations confirm that the 16 september event was a short lived vulcanian type eruption which produced an ash column that reached 15 km altitude the ash cloud can be tracked on geos images to about 400 km downwind and covered an area 112 000 km2 transport occurred in the upper troposphere at speeds up to 180 km h ash fall from the plume was well sorted and moderately fine grained md 200 m formation and fallout of ash as aggregates was unimportant in the deposition of the ash layer although small the lascar 16 september eruption is significant because few historic eruptions have been recorded in the central andes little would have been known of the eruption in the absence of remote sensed data

on the factors influencing the development of sporadic upwelling in the leeuwin current system cumulates the highest number of upwelling 140 days per year and is characterized by longer events the intensity of intermittent upwelling is influenced by the upwellingfavorable winds the characteristics of the leeuwin current e g onshore geostrophic flow mesoscale eddies and meanders stratification and nitracline and the local topography this suggests that short living nutrient enrichment of variable magnitude may occur at any time of the year at many locations along the wa coast

on the leeuwin current system and its linkage to zonal flows in the south indian ocean as inferred from a gridded hydrography abstractthe leeuwin current system lcs along the coast of western australia consists of the poleward flowing leeuwin current lc the equatorward flowing leeuwin undercurrent luc and neighboring flows in the south indian ocean sio using geostrophic currents obtained from a highly resolved hydrographic climatology csiro atlas of regional seas cars this study describes the spatial structure and annual variability of the lc luc and sio zonal currents estimates their transports and identifies linkages among them in cars the lc is supplied partly by water from the tropics an annual mean of 0 3 sv 1 sv 106 m3 s 1 but mostly by shallow 200 m eastward flows in the sio 4 7 sv and it loses water by downwelling across the bottom of this layer 3 4 sv the downwelling is so strong that despite the large sio inflow the horizontal transport of the lc does not much increase to the south from 0 3 sv at 22 s to 1 5 sv at 34 s this lc transport is significantly smaller than previous

evolution movement and decay of warm core leeuwin current eddies abstract characteristics of eddies originating in the leeuwin current lc have been investigated using 10 day sea level anomaly maps of combined topex poseidon and ers altimeter data for the period 1995 2000 during these 6 years 37 long lived anticyclonic eddies were tracked from the west coast of australian to 90 e between three and nine eddies were spawned each year and their trajectories are described in detail most long lived eddies are generated in may june when the lc is most intense and at three preferred locations 20 21 5 s 24 25 s and 28 31 s the temporal evolution and latitudinal variations of the sea level anomalies and their radius and drift speed are discussed topography plays an important role in the evolution and structure of the eddies interactions with topography can induce splitting or merging of eddies which further affects the eddy decay

mesoscale eddy characteristics in the interior subtropical southeast indian ocean tracked from the leeuwin current system abstract two oppositely rotating mesoscale eddies originating from the leeuwin current were captured during a research cruise in the interior southeast indian ocean in august 2012 a few hundred kilometers off the west coast of australia the two eddies had different vertical structures the anticyclonic eddy had stronger vertical shear above 200 m and a less stratified thermocline below the mixed layer while the cyclonic eddy had a more barotropic structure in the upper 500 m compared with the same types of eddies sampled in 2003 close to the australian coast the 2012 anticyclonic eddy had a larger radius deeper isothermal depths and higher peak velocity whereas the 2012 cyclonic eddy had a similar structure with the 2003 survey we use an argo float and three surface drifters deployed and trapped in the anticyclonic eddy to track its evolution over a 4 month period the eddy was observed to propagate 1000 km further to the west indicating that the leeuwin current properties of the eddy may be preserved for over 2000 km off the west coast of australia the eddy appeared to have experienced radial excursions relative to the eddy center with periodicity of 4 6 days and 15 days during their anticlockwise motions the radial movements of the drifters appeared to be constrained by the radial momentum balance within the eddy the importance of eddy distortions to ocean primary production in anticyclonic eddies in the southeast indian ocean warrants further studies

experiments on gas ash separation processes in volcanic umbrella plumes abstract we present a series of analogue laboratory experiments which simulate the separation of ash and gas and the formation of secondary intrusions from finite volcanic umbrella plumes we examined the lateral spreading of mixtures of freshwater and particles released into a laboratory tank containing a uniformly stratified aqueous solution for times smaller than the sedimentation time of particles through the intrusion the current remains coherent and intrudes laterally as some of the particles settle into the underlying ambient fluid a layer of particle depleted fluid develops below the upper surface of the current and the density of the residual fluid is reduced over longer times the intrusion ceases to be coherent with small fingers of relatively buoyant particle depleted fluid rising from the upper part of the intrusion into the overlying fluid meanwhile the lateral motion of the injected solution induces a return flow in the ambient fluid which sweeps some of the particles sedimenting from the lower surface of the intrusion inwards as a result relatively dense particle laden fluid collects below the intrusion and then sinks into the underlying fluid eventually this fluid reaches a new neutral buoyancy height where it intrudes to form a second laterally spreading current below the original intrusion the process then repeats to form further weaker intrusions below these results of the separation of the ash and volcanic gas in an umbrella plume are consistent with field observations at sakurajima volcano where positively charged plumes thought to consist of volcanic gas have been observed above negatively charged plumes of ash this work also suggests that volcanic aerosols may form up to a kilometer above the original injection height of the ash in a strong wind shear this could result in very different trajectories of the ash and gas and so be important for evaluating the impact of ash plumes on both aviation safety and volcanic aerosol formation the separation of the ash from the umbrella plume after a time of order 10 3 10 4 s corroborates recent models of the may 18 1980 eruption at mount st helens that after a few hours the motion of the ash was simply controlled by wind dispersal and gravitational settling the complex motion of the sedimenting ash may also explain some of the observations of multiple intrusions in short lived umbrella plumes such as observed at redoubt alaska in april 1990

early evolution of a stratospheric volcanic eruption cloud as observed with toms and avhrr this paper is a detailed study of remote sensing data from the total ozone mapping spectrometer toms and the advanced very high resolution radiometer avhrr satellite detectors of the 1982 eruption of el chichon mexico the volcanic cloud atmosphere interactions in the first four days of this eruption were investigated by combining ultraviolet retrievals to estimate the mass of sulfur dioxide in the volcanic cloud krueger et al 1995 with thermal infrared retrievals of the size optical depth and mass of fine grained 1 10 m radius volcanic ash wen and rose 1994 our study provides the first direct evidence of gravitational separation of ash from a stratospheric gas rich plinian eruption column and documents the marked differences in residence times of volcanic ash and sulfur dioxide in volcanic clouds the eruption column reached as high as 32 km carey and sigurdsson 1986 and was injected into an atmosphere with a strong wind shear which allowed for an observation of the separation of sulfur dioxide and volcanic ash the upper more sulfur dioxide rich part of the cloud was transported to the west in the stratosphere while the fine grained ash traveled to the south in the troposphere the mass of sulfur dioxide released was estimated at 7 1 109 kg with the mass decreasing by approximately 4 1 day after the peak the mass of fine grained volcanic ash detected was estimated at 6 5 109 kg amounting to about 0 7 of the estimated mass of the ash which fell out in the mapped ash blanket close to the volcano over the following days 98 of this remaining fine ash was removed from the volcanic cloud and the effective radius of ash in the volcanic cloud decreased from about 8 m to about 4 m

satellite observations and interpretation of the 1991 mount pinatubo eruption plumes we demonstrate the use of hourly geostationary meteorological satellite gms and noaa polar orbiting advanced very high resolution radiometer avhrr satellite images of the june 1991 mount pinatubo volcanic eruption plumes in providing details of the timing changing eruptive style and umbrella plume movement and dynamics a chronology of explosive events which culminated in a 9 hour long climactic phase on june 15 has been determined from satellite data and favorably compared to ground based and other ancillary information maximum eruption column altitudes of 40 km and column top undercooling in excess of 55 c below the ambient atmosphere occurred during the climactic phase phases dominated by plinian versus coignimbrite eruptive plumes can be distinguished on the images analysis of the spreading umbrella plume during the climactic phase suggests that over the first 4 5 hours the plume spread laterally as a gravitational intrusion before becoming advected in the ambient winds we compare the rate of plume growth to a model of a radially symmetric continuously fed intrusion to describe the motion the rate of plume growth shows good agreement with this simple model for the first 4 5 hours from column top heights we determine eruption rates and obtain an independent estimate of the total volume of magma erupted from june 12 16 of 5 5 km3 dense rock equivalent dre in good agreement with an independent estimate of the total eruptive volume made from deposits on land and submarine ash fall of up to 5 3 km3 dre we also show that secondary explosions in the pinatubo ignimbrite deposits produced ash plumes reaching altitudes as high as 19 km in september 1991 this study indicates that realistic interpretation and monitoring of major eruption plumes can be accomplished by analysis of high temporal resolution satellite data

thermal infrared remote sensing of volcanic emissions using the moderate resolution imaging spectroradiometer the volcanological community has a powerful new tool in the spaceborne moderate resolution imaging spectroradiometer modis which from its synoptic perspective provides satellite imagery of every volcano on earth every 2 days modis has the spectral characteristics to be able to utilise previously developed retrievals that quantify volcanic ash ice sulfates and sulfur dioxide using their thermal infrared 8 12 am transmission signature in this paper we present a detailed description of the methodologies based within the thermal infrared region that are being applied to modis data modis data for two eruptions hekla iceland and cleveland alaska are presented to show results from the ice ash and so2 retrieval schemes we look at current problems with the retrievals used to quantify volcanic emissions detail recent developments within the field that can be applied to modis data and suggest areas where improvements need to be made in the future published by elsevier b v

unsaturated zone tritium and chlorine 36 profiles from southern australia their use as tracers of soil water movement in this paper we present seven unsaturated zone profiles of 36cl and three 3h profiles from southern australia all profiles show single peaks corresponding to high radionuclide fallout from nuclear testing in the 1950s and 1960s the profiles are used to estimate rates of water movement leading to recharge of the groundwater among these profiles is the first profile on which high concentrations of 36cl have been found below a 2 m depth in this profile 3h and 36cl peaks coincide in six of the seven profiles total 36cl fallout was found to be between 1 2 and 2 4 1012 atoms m 2 and is of similar magnitude to that found at similar latitudes in the northern hemisphere comparisons of soil water fluxes estimated with 3h 36cl and chloride are briefly discussed

thermal imaging and analysis of short lived vulcanian explosions at volcan de colima mexico abstract vulcanian explosions present a major hazard at many active volcanoes but they also provide useful insights into the underlying behaviour of the volcanic system and therefore require close monitoring thermal infrared cameras are an effective tool for imaging vulcanian explosion plumes since they capture detailed temperature information and can reveal the internal dynamics of the plume forming explosions high spatial resolution thermal images of 200 small to moderate sized vulcanian explosions from the summit crater of volcan de colima mexico recorded between 2006 and 2011 were analysed to distinguish different event types and develop an explosion classification scheme explosions display a broad spectrum of sizes and characteristics ranging between two typical end members large impulsive events producing rapidly ascending explosion plumes up to heights of 600 1600 m above the crater rim and small diffusive events with plumes restricted to heights 1 to 29 m s 1 a time series of thermal imagery throughout the period 2006 2011 reveals a weak relationship between apparent plume temperatures and lava dome extrusion with the highest explosion temperatures coinciding with the onset of dome growth in early 2007 temporal variations in the source locations of explosions across the summit crater are also identified and appear to show a close relationship to the patterns of lava dome growth and thermal evolution with explosion source locations associated with the highest temperature thermal features

infrasonic jet noise from volcanic eruptions 1 the lowermost section of a vulcanian or plinian volcanic eruption column may be thought of as a momentum driven turbulent free shear jet flow we propose that large amplitude and long duration infrasonic 20 hz signals recorded at ranges of tens of kilometers during powerful eruptions at mount st helens usa and tungurahua ecuador represent a low frequency form of jet noise a preliminary test of this hypothesis is made by comparing the observed infrasonic spectra to the empirically derived similarity spectra for pure air jets although the spectral shapes are in approximate agreement the observed volcanic signals have additional complexities not present in the pure air laboratory data these features may result from multiphase flow containing solid particles and liquid droplets very high temperatures and perhaps complex crater morphology however the overall similarity between the volcanic signals and jet noise indicates that broadband infrasound measurements at volcanoes may provide a quantitative link to eruption jet dynamics and would aid substantially in the remote assessment of volcanic hazard

geostationary satellite observations of the april 1979 soufriere eruptions infrared images from the geostationary satellite sms 1 were used to study the growth of the eight major eruptions of soufriere st vincent during april 1979 these eruptions differed considerably in growth and intensity the most intense being that of 17 april which formed an ash cloud of 96 000 square kilometers in 4 hours the weakest eruption formed a cloud of only 16 000 square kilometers

infrasound from tungurahua volcano 2006 2008 strombolian to plinian eruptive activity abstract strombolian to plinian activity from tungurahua volcano ecuador has been recorded by the autonomous infrasound arrays of the acoustic surveillance for hazardous eruptions ashe project since early 2006 our studies suggest that acoustic energy release during large eruptions does appear to broadly scale with eruption intensity this manuscript provides a detailed chronology and characterization of tungurahua s eruptive activity between 2006 and 2008 and demonstrates the ability to constrain source parameters of significant eruptions such as onset duration and escalation at regional distances by combining infrasound and remote sensing techniques the ashe system in ecuador automatically detected over 20 000 volcanic explosions at an array 37 km from tungurahua and was successful at notifying the onset escalation and cessation of a hazardous february 2008 eruption with a latency of 5 min elevated infrasonic energy from sustained and intense tungurahua eruptions correlates well with ash column heights and their lateral extent during the study period the spectra of these sustained explosive eruptions appear to be recurrent readily recognizable and indicative of volcanic jetting and significant atmospheric ash injection the paroxysmal plinian phase of the august 2006 eruption produced an ash cloud that extended well into the stratosphere 24 km coinciding with a shift of the dominant jetting frequency from 0 25 hz to below 0 1 hz and radiation of over 5 107 w of acoustic power transient explosions were often marked by minor or no ash release and are presumed to be more gas rich a change in the acoustic spectrum of volcanic jetting was also detected in the transition from a sustained to collapsed eruption column at the end of the july 14 2006 eruption the jetting spectrum at tungurahua during a period of sustained pyroclastic density current production changes from a typical double peaked to a single peaked spectrum suggesting remote acoustic monitoring can help ascertain the stability and dynamics of an eruptive column

satellite and radar analysis of the volcanic cumulonimbi at mount pinatubo philippines 1991 1 several observers reported interesting convective phenomena in the months and years following the 15 june 1991 climactic eruption of mount pinatubo philippines the observed phenomena included deep convection resulting from 1 lower level eruptions 2 secondary phreatic explosions and 3 enhanced surface heating we have compared radar records and satellite imagery to obtain a more coherent understanding of these volcanic cumulonimbi from 17 june to 30 september 1991 and to identify observational challenges for future events geostationary satellite imagery analysis for the period shows that the dominant localized effect on convection following the eruption was to bring the afternoon evening peak in the diurnal convective cycle over the mountain forward by 2 3 hours we examined four cases in detail and identified a number of possible interactions between the volcano and the meteorological environment for three of these cases the volcanic emissions apparently mixed with cumulonimbi developing around the volcano on 21 june 1991 microphysical analyses clearly show a strong reduction in cloud top effective particle radius caused by the additional aerosols in the cloud while on the two other occasions there was a slight or barely detectible reduction in the fourth case for a cumulonimbus developing above a major secondary phreatic explosion no unusually small cloud top effective radii were found perhaps because the ash injected into the cloud was dominated by giant cloud condensation nuclei these cases verify that volcanic emissions can be released through the depth of the troposphere and lower stratosphere from relatively small eruptions future major tropical eruptions and their aftermaths should be studied using intensive ground and satellite based observations to explore these phenomena further

linking synoptic forcing and local mesoscale processes with biological dynamics off ningaloo reef 1 a hydrographic survey offshore ningaloo reef north west australia in austral autumn 2010 revealed relatively stable subsurface water masses in the region despite the influence of interannual variability of the leeuwin current lc the surface water mass seems slightly more variable at seasonal time scale probably due to various contributions of the geographically distinct source waters of the lc a subsurface nitrate maximum 110 230 m a prominent feature of the ningaloo area during autumn was consistently observed within different water masses tightly coupled variations of subsurface nitrate and oxygen at small vertical scale suggest it is due to local in situ remineralization of organic matter likely to accumulate along sharp physical interfaces and possibly favored by injections of oxygenated subsurface waters offshore enhanced levels of surface chlorophyll a within the downwelling favorable lc are associated with deeper mixed layer depth eroding the shallow source of nutrients close to the continental shelf these nutrients are observed to be efficiently uplifted within the core of quasi persistent topographically trapped submesoscale cyclonic eddies dominated by nonlinear effects a wind driven coastal upwelling event occurred in autumn and was characterized by a relatively deep source 100 150 m coinciding with the subsurface maximum of nutrients thus promoting coastal productivity locally and farther north by alongshore advection within the ningaloo current

flow near submarine canyons driven by constant winds circulation over coastal submarine canyons driven by constant upwelling or downwelling wind stress is simulated and analyzed with a primitive equation ocean model astoria canyon on the west coast of north america is the focus of this study and model results are consistent with most major features of mean canyon circulation observed in astoria canyon near surface flow crosses over the canyon while a closed cyclone occurs within the canyon upwelling prevails within the canyon and is larger than wind driven upwelling along the adjacent shelf break water rises from depths reaching 300 m to the canyon rim and subsequently onto the adjacent shelf onshore flow within the canyon is driven by the onshore pressure gradient force due to the free surface slope created by the upwelling wind and is enhanced by the limitation to alongshore flow by the canyon topography density gradients largely compensate the surface slope with realistic stratification but continual upwelling persists near the edges of the canyon within the upper canyon 50 150 m below the canyon rim a cyclone is created by flow turning into the canyon mouth separating from the upstream edge and advecting toward the downstream rim below this layer the cyclone is created by vortex stretching due to the upwelling downwelling winds create nearly the opposite flow in which compression and momentum advection create a strong anticyclone within the canyon momentum advection is found to be important both in creating strong circulation within the canyon and in allowing the surface flow to cross the canyon undisturbed model results indicate that astoria like submarine canyons produce across shore transport of sufficient volume to flush a continental shelf in a few 2 5 years

generation and propagation of infrasonic airwaves from volcanic explosions abstract analysis of infrasonic pressure waves generated by active volcanoes is essential to the understanding of volcanic explosion dynamics unlike seismic waves propagating in the earth infrasonic airwaves offer a relatively unfiltered representation of source motions at the vent during an eruption time varying acoustic propagation filters caused by changeable atmospheric conditions are minimal for microphones deployed at intermediate distances johnson et al j volcanol geotherm res in press

eddy formation through the interaction between the leeuwin current leeuwin undercurrent and topography abstract the surface and subsurface circulation off south west australia was simulated using the regional ocean modelling system roms a primitive equation ocean model with terrain following s coordinates the major currents in this region the leeuwin current and leeuwin undercurrent were reproduced by specifying only temperature and salinity distributions from climatology the application of wind stress subsequent to the model reaching a quasi steady state resulted in the generation of the seasonal capes current a northward flowing current on the continental shelf associated with coastal upwelling the simulated currents compared well with the observed current patterns including the location and maximum current speeds shelf topography variations and bottom shear which generated vorticity influenced eddy formation eddies separated from the leeuwin current and the leeuwin undercurrent migrated westward and exited the model domain through merging dissipating or through an open boundary in the model simulations the undercurrent produced mostly cyclonic eddies due to strong negative vorticity where the current flowed against the continental slope the leeuwin current produced anticyclonic warm core eddies initiated from the formation of meanders which were strongest at the surface the eddy field was dominated by anticyclonic eddies at the surface and cyclonic eddies at 500 m the interaction between the leeuwin current and leeuwin undercurrent led to the formation of eddy pairs

a separating coastal upwelling jet at cape blanco oregon and its connection to the california current system the coastal upwelling region near cape blanco oregon 433n o the west coast of the united states was studied using a towed ctd on seasoar a shipboard acoustic doppler current pro ler adcp satellite sea surface temperature maps and surface drifters during august 1995 the equatorward upwelling jet was inshore of the shelfbreak north of cape blanco meandered gently o shore around the cape and then veered sharply o shore just to the south of the cape analysis of vertical sections of density velocity and spicinessa con rmed the separation of an upwelling jet and front the jet was followed from over the shelfbreak north of the cape to 100 km o shore downstream of the cape the separating jet originates from the coastal upwelling jet leaving the shelf but is augmented by an o shore branching of the poleward undercurrent by combining information from adcp streamfunction maps with analysis of hydrographic data including distributions of the tracer like quantity spicinessa a conceptual model of the three dimensional circulation near the cape emerges a mid shelf upwelling jet encounters a coastal promontory then turns o shore stretching and deepening as it crosses the continental margin the jet then turns back shoreward cyclonically where the deepened equatorward ow encounters the top of the poleward undercurrent owing along the continental slope this causes a portion of the undercurrent to turn o shore to join and strengthen the equatorward transport in the separated jet throughout the separation process the coastal upwelling front and jet are continuous robust features separation of a coastal upwelling jet is an important mechanism for cross shelf transport from the coast to the deep ocean cape blanco appears to be the northernmost point where an equatorward jet regularly separates from the coast to become an oceanic jet and thus serves as the northern boundary of the region where an intense meandering current characteristic of the california current system