deep oceanic zonal jets constrained by fine scale wind stress curls in the south pacific ocean a high resolution coupled gcm study 1 oceanic alternating zonal jets at depth have been detected ubiquitously in observations and ocean general circulation models gcms such oceanic jets are generally considered as being generated by purely oceanic processes here we explore a possible air sea interaction induced by surface signatures of the deep zonal jets using an eddy permitting coupled atmosphere ocean gcm cgcm the 23 year cgcm integration reproduces bands of latitudinally narrow alternating jets in the southeast pacific they extend from the sea surface to well below the main thermocline and are embedded in the large scale westward flowing south equatorial current the latter mostly confined above the thermocline these jets generate fine scale sea surface temperature sst anomalies through the advection of zonal temperature gradients the atmospheric boundary layer appears to respond thermally to this fine scale sst field which induces fine scale wind stress anomaly through atmospheric pressure adjustment as indicated by a good spatial correlation between the sst laplacian field and the fine scale wind stress curl a sverdrup calculation on the wind stress field of the cgcm predicts fine scale zonal currents driven by the meridional gradient of the fine scale wind stress curl the positions of these sverdrup currents are generally coincident with those of the original zonal jets and the sverdrup prediction explains roughly half of the amplitudes of the jets while the original cause of the deep zonal jets simulated in our cgcm is unidentified this analysis suggests that there is likely a positive air sea feedback the jets generate fine scale wind stress curl that reinforces themselves through the sverdrup dynamics

eddies in the red sea a statistical and dynamical study sea level anomaly sla data spanning 1992 2012 were analyzed to study the statistical properties of eddies in the red sea an algorithm that identifies winding angles was employed to detect 4998 eddies propagating along 938 unique eddy tracks statistics suggest that eddies are generated across the entire red sea but that they are prevalent in certain regions a high number of eddies is found in the central basin between 18 n and 24 n more than 87 of the detected eddies have a radius ranging from 50 to 135 km both the intensity and relative vorticity scale of these eddies decrease as the eddy radii increase the averaged eddy lifespan is approximately 6 weeks aes and cyclonic eddies ces have different deformation features and those with stronger intensities are less deformed and more circular analysis of long lived eddies suggests that they are likely to appear in the central basin with aes tending to move northward in addition their eddy kinetic energy eke increases gradually throughout their lifespans the annual cycles of ces and aes differ although both exhibit significant seasonal cycles of intensity with the winter and summer peaks appearing in february and august respectively the seasonal cycle of eke is negatively correlated with stratification but positively correlated with vertical shear of horizontal velocity and eddy growth rate suggesting that the generation of baroclinic instability is responsible for the activities of eddies in the red sea

leachate analyses of volcanic ashes from stromboli volcano a proxy for the volcanic gas plume composition 1 many volcanoes show a change in chemical composition of the gas phase prior to periods of eruptive activity fine grained tephra erupted from active vents and transported through volcanic plumes can adsorb and therefore rapidly scavenge volatile elements such as sulfur halogens and metal species in the form of soluble salts adhering to ash surfaces analysis of such water soluble surface materials is a suitable supplement for remote monitoring of volcanic gases at inaccessible volcanoes in this work ash samples of the 2004 to 2009 eruptive activity of stromboli volcano were sampled leached and analyzed for major and trace elements data analysis and interpretation was focused on determining the relationship between chemical composition of water soluble components adhering to volcanic ash and the volcano s activity state first results show significant temporal variations in ash leachate compositions reflecting changes in the eruptive style of the volcano in particular we reveal that ash leachates s f and mg na ratios showed marked increases prior to a large scale explosion on 15 march 2007

gas aerosol ash interaction in volcanic plumes new insights from surface analyses of fine ash particles the reactions occurring between gases aerosols and silicate ash particles in volcanic eruption plumes remain poorly understood despite the fact that they are at the origin of a range of volcanic environmental atmospheric and health effects in this study we apply x ray photoelectron spectroscopy xps a surface sensitive technique to determine the chemical composition of the nearsurface region 2 10 nm of nine ash samples collected from eight volcanoes in addition atomic force microscopy afm is used to image the nanometer scale surface structure of individual ash particles isolated from three samples we demonstrate that rapid acid dissolution of ash occurs within eruption plumes this process is favoured by the presence of fluoride and is believed to supply the cations involved in the deposition of sulphate and halide salts onto ash afm imaging also has permitted the detection of extremely thin 10 nm coatings on the surface of ash this material is probably composed of soluble sulphate and halide salts mixed with sparingly soluble fluoride compounds the surface approach developed here offers promising aspects for better appraising the role of gas aerosol ash interaction in dictating the ability of ash to act as sinks for various volcanic and atmospheric chemical species as well as sources for others c 2007 elsevier b v all rights reserved

atmospheric chemistry of a 33 34 hour old volcanic cloud from hekla volcano iceland insights from direct sampling and the application of chemical box modeling 1 on 28 february 2000 a volcanic cloud from hekla volcano iceland was serendipitously sampled by a dc 8 research aircraft during the sage iii ozone loss and validation experiment solve i it was encountered at night at 10 4 km above sea level in the lower stratosphere and 33 34 hours after emission the cloud is readily identified by abundant so2 1 ppmv hcl 70 ppbv hf 60 ppbv and particles which may have included fine silicate ash we compare observed and modeled cloud compositions to understand its chemical evolution abundances of sulfur and halogen species indicate some oxidation of sulfur gases but limited scavenging and removal of halides chemical modeling suggests that cloud concentrations of water vapor and nitric acid promoted polar stratospheric cloud psc formation at 201 203 k yielding ice nitric acid trihydrate nat sulfuric acid tetrahydrate sat and liquid ternary solution h2so4 h2o hno3 sts particles we show that these volcanically induced pscs especially the ice and nat particles activated volcanogenic halogens in the cloud producing 2 ppbv clox this would have destroyed ozone during an earlier period of daylight consistent with the very low levels of ozone observed this combination of volcanogenic pscs and chlorine destroyed ozone at much faster rates than other pscs that arctic winter elevated levels of hno3 and noy in the cloud can be explained by atmospheric nitrogen fixation in the eruption column due to high temperatures and or volcanic lightning however observed elevated levels of hox remain unexplained given that the cloud was sampled at night

rainwater and ash leachate analysis as proxies for plume chemistry at soufriere hills volcano montserrat chloride and sulphate concentrations in rainwater and water soluble leachates from volcanic ash samples track the compositions of gas emissions at the soufriere hills volcano montserrat from 1996 to 2001 there are both systematic spatial and temporal variations in the chloride sulphate ratio expressed as the equivalent hcl so2 mass ratio in rainwater and ash leachates temporal variations reflect changes in eruption rate and eruptive style mass ratios of hcl so2 in ash leachates correspond closely with those obtained by open path fourier transform infrared op ftir spectroscopy and reflect changes in volatile emissions throughout the eruption both leachate and op ftir spectroscopic analyses show mass ratios of hcl so2 1 during dome growth and hcl so2 1 during non eruptive periods the hcl so2 mass ratios in rainwater samples from 1996 and 1997 show temporal variations that correlate with changes in extrusion rate the hcl so2 ratios in plume affected rainwater and ash leachates from june and july 2001 correlate positively with increasing rockfall energy and with increasing eruption rate prior to a dome collapse event the hcl so2 mass ratios in water soluble ash leachates and rainwater samples collected at the same time and from the same sites are linearly correlated with rainwater hcl so2 ratios systematically two to three times higher than ash leachate ratios spatial patterns of rainwater ph and hcl so2 in rainwater and ash leachates are principally influenced by the proximity of the sampling sites to the active dome and to the typical pattern of dispersion of the plume by tropospheric winds these results demonstrate that rainwater chemistry and ash leachate analysis provides a useful indicator of volcanic activity and represents a valuable supplement to volcano surveillance efforts

injection of gases into the stratosphere by explosive volcanic eruptions 1 explosive eruptions can inject large amounts of volcanic gases into the stratosphere these gases may be scavenged by hydrometeors within the eruption column and high uncertainties remain regarding the proportion of volcanic gases which eventually reach the stratosphere these are caused by the difficulties of directly sampling explosive volcanic eruption columns and by the lack of laboratory studies in the extreme parameter regime characterizing them using the nonhydrostatic nonsteady state plume model active tracer high resolution atmospheric model atham we simulated an explosive volcanic eruption we examined the scavenging efficiency for the climatically relevant gases within the eruption column the low concentration of water in the plume results in the formation of relatively dry aggregates more than 99 of these are frozen because of their fast ascent to low temperature regions consideration of the salinity effect increases the amount of liquid water by one order of magnitude but the ice phase is still highly dominant consequently the scavenging efficiency for hcl is very low and only 1 is dissolved in liquid water however scavenging by ice particles via direct gas incorporation during diffusional growth is a significant process the salinity effect increases the total scavenging efficiency for hcl from about 50 to about 90 the sulfur containing gases so2 and h2s are only slightly soluble in liquid water however these gases are incorporated into ice particles with an efficiency of 10 to 30 despite scavenging more than 25 of the hcl and 80 of the sulfur gases reach the stratosphere because most of the particles containing these species are lifted there sedimentation of the particles would remove the volcanic gases from the stratosphere hence the final quantity of volcanic gases injected in a particular eruption depends on the fate of the particles containing them which is in turn dependent on the volcanic and environmental conditions

surface area porosity and water adsorption properties of fine volcanic ash particles our understanding on how ash particles in volcanic plumes react with coexisting gases and aerosols is still rudimentary despite the importance of these reactions in influencing the chemistry and dynamics of a plume in this study six samples of fine ash 500 a all the specimens had similar pore size distributions with a small peak centered around 50 a these findings suggest that fine ash particles have relatively undifferentiated surface textures irrespective of the chemical composition and eruption type adsorption isotherms for water vapour revealed that the capacity of the ash samples for water adsorption is systematically larger than predicted from the nitrogen adsorption a s values enhanced reactivity of the ash surface towards water may result from i hydration of bulk ash constituents ii hydration of surface compounds and or iii hydroxylation of the surface of the ash the later mechanism may lead to irreversible retention of water based on these experiments we predict that volcanic ash is covered by a complete monolayer of water under ambient atmospheric conditions in addition capillary condensation within ash pores should allow for deposition of condensed water on to ash particles before water reaches saturation in the plume the total mass of water vapour retained by 1 g of fine ash at 0 95 relative water vapour pressure is calculated to be 10 2 g some volcanic implications of this study are discussed

estimating suppression of eddy mixing by mean flows particle and tracer based estimates of lateral diffusivities are used to estimate the suppression of eddy mixingacrossstrongcurrents particlesandtracersare advectedusingavelocityfieldderivedfromseasurface height measurements from the south pacific in a region west of drake passage this velocity field has been used in a companion paper to show that both particle and tracer based estimates of eddy diffusivities are equivalent despite recent claims to the contrary these estimates of eddy diffusivities are here analyzed to show 1 that the degree of suppression of mixing across the strong antarctic circumpolar current is correctly predicted by mixing length theory modified to include eddy propagation along the mean flow and 2 that the suppressioncan beinferredfromparticletrajectoriesby studyingthestructureofthe autocorrelationfunction of the particle velocities beyond the first zero crossing these results are then used to discuss how to compute lateral and vertical variations in eddy diffusivities using floats and drifters in the real ocean

subtropical mode water variation in the northwestern part of the north pacific subtropical gyre temporal variations of the north pacific subtropical mode water npstmw are studied with the proper temporal resolution for describing seasonal variation using monthly hydrographic data taken near the ogasawara islands npstmw is formed south of the kuroshio and the kuroshio extension in late winter and advected to the ogasawara site by the southwestward westward return flow of the kuroshio recirculation while npstmw is seen at the ogasawara site in almost all seasons npstmw with a higher core temperature is advected to this site in april and one with a colder core follows in and after june until january or february furthermore the npstmw core temperature shows considerable interannual variation this variation is very similar to that found in other regions away from the ogasawara site suggesting that it reflects the larger scale variation of npstmw and that this site would be suitable for monitoring the npstmw core temperature a significant correlation between the npstmw core temperature and the monsoon index which is defined as the difference in the sea level pressure between nemuro japan and irkutsk russia as an indicator of wintertime cooling indicates that npstmw contains a memory of wintertime cooling in the preceding winter

the temporal autocorrelation structure of sea surface winds abstractthe temporal autocorrelation structures of sea surface vector winds and wind speeds are considered analyses of scatterometer and reanalysis wind data demonstrate that the autocorrelation functions acf of surface zonal wind meridional wind and wind speed generally drop off more rapidly in the midlatitudes than in the low latitudes furthermore the meridional wind component and wind speed generally decorrelate more rapidly than the zonal wind component the anisotropy in vector wind decorrelation scales is demonstrated to be most pronounced in the storm tracks and near the equator and to be a feature of winds throughout the depth of the troposphere the extratropical anisotropy is interpreted in terms of an idealized kinematic eddy model as resulting from differences in the structure of wind anomalies in the directions along and across eddy paths the tropical anisotropy is interpreted in terms of the kinematics of large scale equatorial waves and small scale convection modeling the vector w

influence of topography on the propagation of isolated eddies abstract an analytical and numerical study of isolated coherent vortices and topography is presented the motivation for this work comes from many observations of vortices influenced in trajectory propagation and decay by encounters with midocean ridges seamounts and bottom slopes in particular analytical predictions relevant to vortex propagation and evolution are compared with numerical results for lenses on bottom slopes and mixed barotropic baroclinic eddies over a variety of topographies the latter case includes examination of short term and long term behavior analytical theories are found to work well for the bottom lenses and short term behavior is captured well by a simple theory that emphasizes barotropic dynamics for mixed vortices the exception for the latter case occurs for counterrotating eddies i e eddies with opposing upper and lower layer swirl for which the evolution is dominated by vortex instability long term evolution has no comparable theory and the various possibili

quasi zonal jets in 3 d argo data of the northeast atlantic 1 time mean zonal velocities estimated from argo float trajectories and density profiles are systematically examined for quasi zonal jets or striations with the use of a simple search algorithm a comparison to altimeter data combined with an independent estimate of the mean dynamic topography shows that the jets in the 2004 2006 period examined are persistent and stationary the jets have a typical meridional width of 100 to 200 km and a median transport of 4 sverdrups the jets tilt at approximately 6 from southwest to northeast in the horizontal plane but show no significant tilt in the vertical plane velocities and the cross stream width are similar for the westward and eastward jets

eruption of the nevado del ruiz volcano colombia on 13 november 1985 gas flux and fluid geochemistry the 13 november 1985 eruption of nevado del ruiz volcano in colombia released a small volume of pyroclastic material and a disproportionately large volume of volcanic gas before the eruption summit fumarole gases became less water rich and the sulfur chlorine ratio increased remote measurements of sulfur dioxide flux after the eruption indicated active degassing at levels associated with eruptive or inter eruptive stages of other volcanoes thermal water analyses revealed increases in magnesium calcium and potassium and an increase in the magnesium chlorine ratio suggesting that these elements may have been leached from new magma ash leachate data showed sulfate and chloride concentrations and ratios that would be expected for the late stages ofa major plinian eruption water from the lahar contained high concentrations of sulfate and had a sulfur chlorine ratio of 4 67 suggesting that water ejected from the crater lake and turbulent mixing of pyroclasts and glacial ice triggered the lahar microprobe analyses of pumice from this eruption and the most recent previous event showed similar mixed andesites the uniform composition of the pumices and the unusually high ratio of gas to magma suggest that although a new batch of magma triggered this eruption the pumice that erupted may actually be old large volumes of new magma and glacial ice make the volcano dangerous and should stimulate development of an integrated long term monitoring program to include tolima volcano 25 kilometers to the south

oxygen and sulfur isotopic composition of volcanic sulfate aerosol at the point of emission volcanic sulfate aerosol is emitted from the vents of many active volcanoes but its origin has not yet been explained we report the first measurements of the isotopic compositions of near vent volcanic aerosol sulfate and use the combined sulfur and oxygen isotope systematics of the aerosol and magma at masaya volcano nicaragua to draw preliminary conclusions about the production mechanism of near source volcanic sulfate the sulfate aerosol does not display a significant mass independent oxygen or sulfur isotopic signature which suggests that primary volcanic aerosol does not contribute to the larger mass independent anomalies found in some ambient atmospheric aerosols and as preserved in ice cores the oxygen isotope composition of the sulfate appeared to become heavier on the particle filters with increasing amount of sample collected and suggests that the 18o value of the sulfate aerosol is 8 the sulfur isotopic composition of the sulfate did not vary with sample loading on the filters and had a mean 34s value of 7 7 0 8 similar to that of the magma 6 6 0 2 the low 17o value the 18o value of the magma 6 6 0 3 and the high 18o value of atmospheric oxygen 23 5 suggest that known atmospheric oxidation pathways at ambient temperatures are not the major routes of production for this sulfate instead the isotopic systematics of aerosol and magma are consistent with sulfate production either by high temperature equilibration of the magmatic gas mixture with small amounts of atmospheric oxygen or by direct emission of so4 2 from the magma

mount mazama eruption calendrical age verified and atmospheric impact assessed geochemical identification of mount mazama ash in the greenland ice sheet project 2 gisp2 ice core gives a calendrical age of 7627 150 cal yr b p 5677 150 b c for the eruption thus providing a more accurate early holocene stratigraphic time line than previously available the gisp2 record of volcanically derived sulfate suggests a total stratospheric aerosol loading between 88 and 224 mt spread over an 6 yr period following the eruption of mount mazama taking into account the likelihood of some tropospheric aerosol transport to greenland realistic estimates of the resulting atmospheric optical depth range from 0 6 to 1 5 these values may have produced a temperature depression of 0 6 to 0 7 c at mid to high northern latitudes for 1 3 yr after the eruption these results indicate that the 5677 b c eruption of mount mazama was one of the most climatically significant volcanic events of the holocene in the northern hemisphere we also calculate a maximum stratospheric cl release of 8 1 mt by the eruption which may have led to substantial stratospheric ozone depletion

assessment of leachable elements in volcanic ashfall a review and evaluation of a standardized protocol for ash hazard characterization abstract volcanic ash presents a widespread and common hazard during and after eruptions complex interactions between solid ash surfaces and volcanic gases lead to the formation of soluble salts that may be mobilized in aqueous environments a variety of stakeholders may be concerned about the effects of ash on human and animal health drinking water supplies crops soils and surface runoff as part of the immediate emergency response rapid dissemination of information regarding potentially hazardous concentrations of soluble species is critical however substantial variability in the methods used to characterize leachable elements makes it challenging to compare datasets and eruption impacts to address these challenges the international volcanic health hazard network www ivhhn org organized a two day workshop to define appropriate methods for hazard assessment the outcome of this workshop was a consensus protocol for analysis of volcanic ash samples for rapid assessment of hazards from leachable elements which was subsequently ratified by leading volcanological organizations the purpose of this protocol is to recommend clear standard and reliable methods applicable to a range of purposes during eruption response such as assessing impacts on drinking water supplies and ingestion hazards to livestock and also applicable to research purposes where possible it is intended that the methods make use of commonly available equipment and require little training to evaluate method transferability an interlaboratory comparison exercise was organized among six laboratories worldwide each laboratory received a split of pristine ash and independently analyzed it according to the protocol for a wide range of elements collated results indicate good repeatability and reproducibility for most elements thus indicating that the development of this protocol is a useful step towards providing standardized and reliable methods for ash hazard characterization in this article we review recent ash leachate studies report the outcomes of the comparison exercise and present a revised and updated protocol based on the experiences and recommendations of the exercise participants the adoption of standardized methods will improve and facilitate the comparability of results among studies and enable the ongoing development of a global database of leachate information relevant for informing volcanic health hazards assessment

the contribution of eddies to striations in absolute dynamic topography 1 distinct 4 year averages of absolute dynamic topography reveal striations in all ocean basins during 1993 2008 striations are alternating mesoscale jet like structures observed in time averaged zonal geostrophic velocity u they are characterized by speeds o 1 cm s 1 and are nominally separated by 200 km in the meridional direction similar patterns have been observed in sea level anomaly mean dynamic topography and argo float measurements use of a tracked eddy database in concert with a contour identification and eddy removal algorithm demonstrates that eddies are a dominant source of striations in u in the south pacific 20 s 50 s 200 e 280 e eddies with lifetimes 4 weeks account for 46 57 of the variance in u and correlation coefficients between total and eddy only u are 0 90 0 93 attention is given to the ability of the algorithm to correctly identify eddies and suggests that a more appropriate bound on the variance due to eddies is 30 70 this permits the existence of latent zonal jets and or plumes additional findings of the study include 1 a large number of eddies having a broad range of amplitudes and scales contribute most to the eddy induced patterns and 2 the standard deviation of u does not decay inversely with averaging period as proposed by a model of random eddies

the adsorption of hcl on volcanic ash understanding the interaction between volcanic gases and ash is important to derive gas compositions from ash leachates and to constrain the environmental impact of eruptions volcanic hcl could potentially damage the ozone layer but it is unclear what fraction of hcl actually reaches the stratosphere the adsorption of hcl on volcanic ash was therefore studied from 76 to 150 c to simulate the behavior of hcl in the dilute parts of a volcanic plume finely ground synthetic glasses of andesitic dacitic and rhyolitic composition as well as a natural obsidian from vulcano italy served as proxies for fresh natural ash hcl adsorption is an irreversible process and appears to increase with the total alkali content of the glass adsorption kinetics follow a first order law with rate constants of 2 13 10 6 s 1 to 1 80 10 4 s 1 in the temperature range investigated for dacitic composition the temperature and pressure dependence of adsorption can be described by the equation ln c 1 26 0 27ln p 715 3 t where c is the surface concentration of adsorbed hcl in mg m2 t is temperature in kelvin and p is the partial pressure of hcl in mbar a comparison of this model with a large data set for the composition of volcanic ash suggests that adsorption of hcl from the gas phase at relatively low temperatures can quantitatively account for the majority of the observed cl concentrations the model implies that adsorption of hcl on ash increases with temperature probably because of the increasing number of accessible adsorption sites this temperature dependence is opposite to that observed for so2 so that hcl and so2 are fractionated by the adsorption process and the fractionation factor changes by four orders of magnitude over a temperature range of 250 k the assumption of equal adsorption of different species is therefore not appropriate for deriving volcanic gas compositions from analyses of adsorbates on ash however with the experimental data provided here the gas compositions in equilibrium with the ash surfaces can be calculated in particular for dacitic composition the molar ratio of s cl adsorbed to the ash surface is related to the molar s cl ratio in the gas phase according to the equation ln s cl adsorbed 2855t 1 0 28ln s cl gas 11 14 our data also show that adsorption on ash will significantly reduce the fraction of hcl reaching the stratosphere only if the initial hcl content in the volcanic gas is low 1 mol for higher initial hcl concentrations adsorption on ash has only a minor effect while hcl scavenging by hydrometeors may remove a considerable fraction of hcl from the eruption column recent models suggest that this process is much less efficient than previously thought our experimental data therefore support the idea that the hcl loading from major explosive eruptions may indeed cause severe depletions of stratospheric ozone

particle fallout thermal disequilibrium and volcanic plumes we develop a model of a volcanic eruption column that includes the effects of fallout of pyroclasts and thermal disequilibrium we show that clast fallout with no thermal disequilibrium has only a small effect upon the column however disequilibrium changes column behaviour significantly and can even induce collapse our results may explain the lower plume heights and less widely dispersed fallout of cone forming eruptions contrasted with sheet forming eruptions the model also predicts that the transition from the gas thrust to the convective region in a column results in an inflection in dispersal curves that some features of the stratigraphy common to many fall deposits may result from column velocity structure and that there may exist a region near the volcanic vent in which maximum pyroclast size does not decrease significantly with distance

volcanic particle aggregation in explosive eruption columns part ii numerical experiments abstract the goal of this paper is to determine the parameters that control the aggregation efficiency and the growth rate of volcanic particles within the eruption column numerical experiments are performed with the plume model atham active tracer high resolution atmospheric model in this study we employ the parameterizations described in a companion paper this issue the presence of hydrometeors promotes the aggregation of ash particles which strongly increases their fall velocities and thus their environmental impact the tephra mass is about two orders of magnitude greater than that of hydrometeors during typical plinian eruptions without interaction of external water ice is highly dominant in comparison to liquid water 99 by mass this is caused by the fast column rise 100 m s 1 on average to very cold altitudes most particles occur in the form of frozen aggregates with low ice content the collection efficiency is governed by the availability of hydrometeors acting as adhesives at the particles surface in our study and wet ash particles have a higher sticking capacity than icy ones therefore aggregation is fastest during the eruption within the column when limited regions of liquid water exist and when particle concentrations are very high of the order of 10 5 cm 3 increased humidity in the background atmosphere generally leads to enhanced ice formation but shows only a weak influence on the aggregation process first sensitivity studies showed however a significant increase of the liquid water fraction when considering salinity effects the availability of water or ice at the particles surfaces is also governed by the surface properties the porosity and permeability of ash which are not well established to date particle growth is significantly enhanced for greater differences in the sizes and fall velocities among particles as gravitational capture becomes more efficient our experiments indicate a major influence of the erupted particle size distribution first sensitivity studies show that electrostatic forces result in a significant enhancement of aggregated particles the present exploratory study provides new insights into the sensitivity of the ash aggregation process to a number of key parameters our results indicate the need of further constraining particle composition size porosity permeability and surface properties at low temperatures by in situ observations in the laboratory and in the field in addition further research on electrostatic aggregation would be desirable

the formation of nonzonal jets over sloped topography coherentjetsareubiquitousfeaturesoftheocean scirculation andtheircharacteristics suchasorientation and energetics may be influenced by topography in this study the authors introduce a large scale topographic slope with an arbitrary orientation into quasigeostrophic doubly periodic barotropic and baroclinic systems in both systems the flow organizes itself into coherent tilted nonzonal jets that are aligned perpendicular to the barotropic potential vorticity pv gradient in the two layer system the upper layer the lower layer and the barotropic pv gradients all have different orientations and therefore the jets cross the layer wise pv gradients the fact that the jets cross layer wise pv gradients and the requirement of conservation of pv for fluid parcels together results in the drift of the tilted jets across the domain like their zonalcounterparts thetiltedjetsexhibitstrongtransportanisotropy thedynamicalresponsetojetdeflection is very strong in the two layer baroclinic case with eddy energy production increasing by orders of magnitude as the topographic slope becomes more zonal this increase in eddy energy is also reflected in an increase in jet spacing and a reduction in strength of the across jet transport barriers shown using an effective diffusivity diagnostic the dynamics identified here while formally valid within the constraints of quasigeostrophic scalings provide important insight into the sensitive relationship between flow orientation and flow stability in regions with broad topographic slopes

anisotropic material transport by eddies and eddy driven currents in a model of the north atlantic this study analyzes anisotropic properties of the material transport by eddies and eddy driven zonal jets in a general circulation model of the north atlantic through the analysis of lagrangian particle trajectories spreading rates defined here as half the rate of change in the particle dispersion in the zonal direction systematically exceed the meridional rates by an order of magnitude area averaged values for the upperocean zonal and meridional spreading rates are approximately 8100 and 1400 m 2 s 21 respectively and in the deep ocean they are 2400 and 200 m 2 s 21 the results demonstrate that this anisotropy is mainly due to the actionofthetransienteddiesandnotto thesheardispersionassociated withthetime meanjets thisproperty is consistent with the fact that eddies in this study have zonally elongated shapes with the exception of the upper ocean subpolar gyre eddies also cause the superdiffusive zonal spreading significant variations in the spreading rate in the vertical and meridional directions and the difference between the westward and eastward spreading

chemistry of ash leachates to monitor volcanic activity an application to popocatepetl volcano central mexico abstract monitoring volcanic activity and assessing volcanic risk in an on going eruption is a problem that requires the maximum possible independent data to reduce uncertainty a quick relatively simple and inexpensive method to follow the development of an eruption and to complement other monitoring parameters is the chemical analysis of ash leachates particularly in the case of eruptions related to dome emplacement here the systematic analysis of so 4 2 cl and f concentrations in ash leachates is proposed as a valuable tool for volcanic activity monitoring however some results must be carefully assessed as is the case for s cl ratios since eruption of hydrothermally altered material may be confused with degassing of incoming magma sulfur isotopes help to identify so4 produced by hydrothermal processes from magmatic so2 lower s isotopic values correlated with higher f percentages represent a better indicator of fresh magmatic influence that may lead to stronger eruptions and emplacement of new lava domes additionally multivariate statistical analysis helps to identify different eruption characteristics provided that the analyses are made over a long enough time to sample different stages of an eruption

observational evidence of alternating zonal jets in the world ocean 1 multiple zonal jets with the east west velocity direction alternating with latitude are discovered in satellite altimetry data the time varying jets are shown to populate every part of the world ocean and its marginal seas and are best seen in the anomaly of geostrophic vorticity at midlatitudes the jets have a meridional wavelength of about 300 kms with r m s sea level velocity and vorticity values of 2 4 cm 6 9 cm s and 1 5 10 6 s 1 correspondingly realistic data from the high resolution ogcm run on the earth simulator are used to justify high vertical coherence of the jets structure and relevance of the jets to an evolving mesoscale eddy field strong coupling between the jets and mesoscale eddies is hypothesized

wind driven zonal jets in the south pacific ocean 1 zonal jets west of the large islands of the south pacific ocean are predicted by theory commonly seen in ocean models with sufficiently high resolution and are beginning to be observed these jets are often taken to reflect the blocking effect of the islands in the south equatorial current through island rule dynamics here it is shown that quasi permanent structures of the basin wide wind field imply the existence of jets formed independently of the islands evidence for the existence of the wind driven jets is found in climatological geostrophic currents the hydrographic structures that produce the jets occur well below the thermocline

zonal jets in the pacific ocean 1 the spatial and temporal properties of zonally coherent jet like structures found in high resolution ocean models is examined we focus on the pacific ocean we find the properties of the jets are not very sensitive to the model configuration distinct differences are found in the persistence and vertical structure of the jets poleward of 30 n and s compared with those in the tropics we make a quantitative comparison between the meridional scale of the jets and the rhines scale we find a local scaling applies in that the horizontal variation of the meridional scale of the jets is consistent with horizontal variations in the rhines scale

stationary mesoscale jet like features in the ocean 1 xbt and float data of the world ocean database 2005 are used to validate new stationary jet like features striations recently found in the high resolution mean dynamic ocean topography mdot two study areas were selected in the eastern parts of the north and south pacific subtropical gyres free of any strong currents appropriate horizontal high pass filtering applied to the ensemble mean temperature at 100 m depth revealed the striation signal coherent with mdot the features are also distinct in the data of depth of 12 c isotherm lying close to the thermocline the striations are oriented nearly zonally and coherent vertically at least through 700 m depth their wavelength is approximately 400 km and the azimuth of wavevector is 13 9 in the northern southern domains correspondence between the striations in observations and ofes ogcm for the earth simulator model as well as the nature of the striations are discussed

spatial structure of anticyclonic eddies in the algerian basin mediterranean sea analyzed using the okubo weiss parameter abstract three algerian eddies open sea big anticyclonic eddies in the algerian basin western mediterranean sea are studied in detail using altimetric and in situ data to characterize their spatial structure we make use of the okubo weiss parameter which allows to separate the flow into vorticity dominated and deformation dominated regions the application of this parameter to geostrophic velocity fields obtained from sea level anomaly maps show that the observed eddies have a spatial structure in close resemblance to that found in coherent vortices of two dimensional turbulence these eddies appear to have a rather coherent vorticity dominated core region surrounded by an outer region dominated by deformation with a very complicated and variable in time structure this analysis is also applied to ctd data collected across three eddies sampled between 1997 and 1998 from these data eddy cores are equivalently defined as the interior region enclosed by the maximum of azimuthal velocity and are consistent with the horizontal structures seen in sla maps the distinction between the core and the outer region circulation cell is particularly important to understand the role of transport and stirring of properties associated to eddies as illustrated by the observed salinity structure some selected sst images and drifter trajectories the core is characterized by very small isopycnal salinity gradients while the surrounding cell is characterized by a strong slope of isohalines with respect to isopycnals persistent stagnation points are observed around the eddy and correspond to regions of high values of deformation with respect to vorticity these regions allow analyzing characteristic patterns seen in the corresponding sst images in addition drifters trajectories exhibit very different behavior when crossing such regions

interpretation of the propagation of surface altimetric observations in terms of planetary waves and geostrophic turbulence 1 the interpretation of surface altimetric signals in terms of rossby waves is revisited rather than make the long wave approximation the horizontal scale of the waves is adjusted to optimally fit the phase speed predicted by linear theory to that observed by altimetry assuming a first baroclinic mode vertical structure it is found that in the tropical band the observations can be fit if the wavelength of the waves is assumed to be large of order 600 km or so however poleward of 30 it is more difficult to fit linear theory to the observations and the fit is less good than at lower latitudes the required scale of the waves must be reduced to about 100 km somewhat larger than the local deformation wavelength it is argued that these results can be interpreted in terms of rossby wave baroclinic instability and turbulence theory at low latitudes there is an overlap between geostrophic turbulence and rossby wave timescales and so an upscale energy transfer from baroclinic instability at the deformation scale produces waves at high latitudes there is no such overlap and waves are not produced by upscale energy transfer these ideas are tested by using surface drifter data to infer turbulent velocities and timescales that are compared to those of linear rossby waves a transition from a field dominated by waves to one dominated by turbulence occurs at about 30 broadly consistent with the transition that is required to fit linear theory to altimetric observations

the impact of the atmosphere on the eyjafjallajokull 2010 eruption plume 1 the eruption of eyjafjallajokull volcano in 2010 lasted 39 days 14 april 23 may the eruption had two explosive phases separated by a phase with lava formation and reduced explosive activity during the explosive phases there were episodes of strong winds that advected ash to the south and southeast leading to widespread disruptions in air traffic the height of the eruption plume was monitored with a weather radar and with web cameras mounted with a view of the volcano three different types of the impact of the ambient atmosphere on the eruption plume are described first the weather situation throughout the eruption has been analyzed the frequency of northerly wind component is found to be unusually high or 71 in comparison to 49 on average in spring secondly during the effusive phase of the eruption diurnal variation was observed in the plume altitude and there is evidence that suggest that nocturnal inversions may have played a role limiting the rise of the weak plume thirdly images from a web camera were analyzed and the rise of individual cloud heads associated with explosions at the volcano vent mapped the velocity profiles obtained largely agree with conceptual models of volcanic plumes

the influence of mesoscale eddies on the detection of quasi zonal jets in the ocean 1 westward propagating gaussian eddies with statistical characteristics estimated from altimeter observations but with purely random starting locations and times produce striated features in time averaged maps of zonal velocity the striations in these simulations have magnitudes and meridional scales comparable to those reported from time averaged altimeter observations and model output in the central north pacific and the california current system time averages over the data records presently available are therefore not suitable for unambiguous detection of quasi zonal jets the presence of mapping error and background isotropic eddy kinetic energy also bias the regionally averaged anisotropy of time averaged velocity fields thus compromising the interpretation of anisotropy statistics

global observations of large oceanic eddies 1 ten years of sea surface height ssh fields constructed from the merged topex poseidon t p and ers 1 2 altimeter datasets are analyzed to investigate mesoscale variability in the global ocean the higher resolution of the merged dataset reveals that more than 50 of the variability over much of the world ocean is accounted for by eddies with amplitudes of 5 25 cm and diameters of 100 200 km these eddies propagate nearly due west at approximately the phase speed of nondispersive baroclinic rossby waves with preferences for slight poleward and equatorward deflection of cyclonic and anticyclonic eddies respectively the vast majority of the eddies are found to be nonlinear

the evolution and propagation of quasigeostrophic ocean eddies abstractthe long term evolution of initially gaussian eddies is studied in a reduced gravity shallow water model using both linear and nonlinear quasigeostrophic theory in an attempt to understand westward propagating mesoscale eddies observed and tracked by satellite altimetry by examining both isolated eddies and a large basin seeded with eddies with statistical characteristics consistent with those of observed eddies it is shown that long term eddy coherence and the zonal wavenumber frequency power spectral density are best matched by the nonlinear model individual characteristics of the eddies including amplitude decay horizontal length scale decay and zonal and meridional propagation speed of a previously unrecognized quasi stable state are examined the results show that the meridional deflections from purely westward flow poleward for cyclones and equatorward for anticyclones are consistent with satellite observations examination of the fluid transport properties of the eddies shows that an

mesoscale eddies off peru in altimeter records identification algorithms and eddy spatio temporal patterns relatively little is known about coherent vortices in the eastern south pacific along the peruvian coast even with regard to basic facts about their frequency of occurrence longevity and structure this study addresses these issues with nearly 15 years of relatively high resolution satellite altimetry measurements we first compare two distinct automated methods for eddy identification the objective validation protocol shows that the rarely used geometrical or winding angle method based on the curvature of the streamline functions is more accurate than the commonly used okubo weiss algorithm which defines a vortex as a simple connected region with values of okubo weiss parameter weaker than a given threshold we then investigate vortices off peru using more than 20 000 mesoscale eddies identified by the winding angle method coherent eddies characterized by a high ratio of vorticity to deformation rate are typically formed along the coast and propagate westward at 3 6 cm s 1 the vortices have a mean radius of 80 km increasing northward and are most frequently observed off of chimbote 9s and south of san juan 15s the mean eddy lifetime is about 1 month but if eddies survive at least 2 months the probability for surviving an additional week or month is constant at 90 or 67 anticyclonic eddies tend to propagate northwestward whereas cyclonic vortices migrate southwestward in general cyclones and anticyclones are similar except for eddies surviving at least 6 months in this case after a similar 3 4 months of radius and amplitude growth amplitudes or sizes decay particularly rapidly for anticyclonic or cyclonic eddies in terms of intensity cyclonic eddies show a rapid decay during the first 3 months before arriving at a quasi constant value whereas anticyclones exhibit steady decline finally eddy temporal variations were examined at seasonal and interannual scales in the coastal region favorable to the formation of energetic mesoscale structures on seasonal scales eddy activity is maximal in fall and minimum in spring at interannual scales the eddy activity index was maximal during the strong el nino of 1997 1998 but another strong maximum of eddy activity also occurred late in 2004 these temporal variations are probably associated with the intensification of the upwelling thermal front and with the passage of coastal trapped waves which generate baroclinic instabilities further investigation of the mechanisms involved on the eddy genesis is needed

pattern and velocity of propagation of the global ocean eddy variability 1 satellite altimeter data are used to study the characteristics of the horizontal propagation of eddy variability of the global oceans decade long time series of sea surface height is analyzed for finding the maximum cross correlation with neighboring time series within a window of space and time lags the space and time lags corresponding to the maximum correlation allow an estimate of the propagation velocity of the eddy variability that dominates the variance of sea surface height anomalies the method cannot distinguish the various forms of eddy variability isolated eddies and fronts the meandering of ocean currents or planetary waves however the results provide at a given location of the global oceans a uniquely determined propagation velocity that represents a time averaged description of the tendency of the movement of the local eddy variability the propagation velocity is highly inhomogeneous in space outside the equatorial zone the zonal propagation is intrinsically westward modified by ocean currents which could reverse the zonal propagation to eastward in regions like the gulf stream and the antarctic circumpolar current at midlatitudes and high latitudes the propagation pattern is highly affected by the path of ocean currents and the shape of bottom topography at tropical latitudes the meridional propagation is convergent toward the equator in the western basins and divergent away from the equator in the eastern basins comparison with the simulations of an eddy permitting ocean general circulation model shows overall agreement especially in the latitudinal variation of the zonal propagation velocity the result suggests that the model has captured the essence of the dynamics governing the propagation of ocean eddy variability

radiating instability of a meridional boundary current a linear stability analysis of a meridional boundary current on the beta plane is presented the boundary current is idealized as a constant speed meridional jet adjacent to a semi infinite motionless far field the far field region can be situated either on the eastern or the western side of the jet representing a western or an eastern boundary current respectively it is found that when unstable the meridional boundary current generates temporally growing propagating waves that transport energy away from the locally unstable region toward the neutral far field this is the so called radiating instability and is found in both barotropic and two layer baroclinic configurations a second but important conclusion concerns the differences in the stability properties of eastern and western boundary currents an eastern boundary current supports a greater number of radiating modes over a wider range of meridional wavenumbers it generates waves with amplitude envelopes that decay slowly with distance from the current the radiating waves tend to have an asymmetrical horizontal structure they are much longer in the zonal direction than in the meridional a consequence of which is that unstable eastern boundary currents unlike western boundary currents have the potential to act as a source of zonal jets for the interior of the ocean

an eddy resolving numerical model of the ventilated thermocline time dependence abstract a primitive equation eddy resolving numerical model is used to study the inherent time scales of variability in the subtropical ocean assuming temporally constant surface forcing three primary scales arise mesoscale variability of roughly 50 day period zonally elongated barotropic bands of 1 1 year period and basin scale undulations of approximately 4 year period the latter are identified as first baroclinic mode rossby waves associated with bursts of ventilation at isopycnal outcrops as a result the equatorward transport required by sverdrup theory in the subtropics occurs not as a broad sluggish drift throughout the interior but as a succession of more intense flows that slowly propagate westward the zonally elongated bands agree in characteristics to those predicted from theory of homogeneous turbulence eddy energy that is generated by baroclinic instability leaks from baroclinic to barotropic mode and thereafter due to rotational constraints seeks low zonal wavenumbers the gr

combined bromine and chlorine release from large explosive volcanic eruptions a threat to stratospheric ozone large explosive volcanic eruptions inject gases aerosols and fine ashes into the stratosphere potentially influencing climate emissions of chlorine cl and bromine br from such large eruptions play an important role for catalytic destruction of ozone in the stratosphere but hitherto the global effects of simultaneous catastrophic release of volcanic br and cl into the stratosphere have not been investigated the br release from 14 large explosive eruptions throughout nicaragua covering an entire subduction zone segment in the past 70 ka was determined with petrologic methods melt inclusions in volcanic phenocrysts were analyzed using a new optimized synchrotron x ray fluorescence microprobe set up single eruptions produced br outputs of 4 600 kt giving an average br emission of 27 kt per eruption using the assumption that 10 of the emitted halogens reach the stratosphere the average br and cl loading to the stratosphere would be 3 ppt and 1500 ppt respectively which together would account for 185 of the preindustrial equivalent effective stratospheric cl loading we thus conclude that many large tropical volcanic eruptions had and have the potential to substantially deplete ozone on a global scale eventually forming future ozone holes

linear wind forced beta plumes with application to the hawaiian lee countercurrent abstracttwo numerical ocean models are used to study the baroclinic response to forcing by localized wind stress curl i e a wind forced plume which is a circulation cell developing to the west of the source region and composed of a set of zonal jets with implications for the hawaiian lee countercurrent hlcc an idealized primitive equation model regional ocean modeling system roms and a global eddy resolving general circulation model ocean general circulation model for the earth simulator ofes in addition theoretical ideas inferred from a linear continuously stratified model are used to interpret results in roms vertical mixing preferentially damps higher order vertical modes the damping thickens the plume to the west of the forcing region weakening the near surface zonal jets and generating deeper zonal currents the zonal damping scale increases monotonically with the meridional forcing scale indicating a dominant role of vertical viscosity over diffusion a consequence of the

quantifying and interpreting striations in a subtropical gyre a spectral perspective abstractthe amplitude origin and direction of striations in the subtropical gyre are investigated using simulated and analytical multidimensional spectra striations defined as banded structures in the low frequency motions account for a noticeable percentage of zonal velocity variability in the east north pacific enp 25 42 n 150 130 w and central north pacific cnp 10 22 n 132 e 162 w regions in an eddying global ocean model thus they likely are nonnegligible in mixing and transport processes striations in the enp region are nonzonal and are embedded in the nonzonal gyre flow whereas striations in the cnp region are more zonal as are the mean gyre flows an idealized 1 5 layer model shows the gyre flow partially determines their directions which qualitatively resemble those in the global eddying model in the linear limit structures are quasi stationary frequency 0 linear rossby waves and the gyre flow influences the direction by influencing the nature of the zero rossby wave f

a multidimensional spectral description of ocean variability abstractan updated empirical analytical model for the frequency and wavenumber distribution of balanced motion in the ocean is presented the spectrum model spans periods longer than the inertial but shorter than a decade and wavelengths between 100 and 10 000 km assuming geostrophic dynamics a spectrum model for the streamfunction is constructed to be consistent with a range of observations including sea surface height from satellite altimetry velocity from moored and shipboard instruments and temperature from moorings first order characteristics of the observed spectra including amplitude and spectral moments vary slowly geographically the spectrum model is horizontally anisotropic accommodating observations that zonal wavenumber frequency spectra are dominated by a nondispersive line qualitative and quantitative agreement is found with one dimensional frequency and wavenumber spectra and observed vertical profiles of variance illustrative application is made of the model spectrum to obse

acid rain and ozone depletion from pulsed siberian traps magmatism the siberian traps flood basalts have been invoked as a trigger for the catastrophic end permian mass extinction widespread aberrant plant remains across the permian triassic boundary provide evidence that atmospheric stress contributed to the collapse in terrestrial diversity we used detailed estimates of magmatic degassing from the siberian traps to complete the first three dimensional global climate modeling of atmospheric chemistry during eruption of a large igneous province our results show that both strongly acidic rain and global ozone collapse are possible transient consequences of episodic pyroclastic volcanism and heating of volatile rich siberian country rocks we suggest that in conjunction with abrupt warming from greenhouse gas emissions these repeated rapidly applied atmospheric stresses directly linked siberian magmatism to end permian ecological failure on land our comprehensive modeling supplies the first picture of the global distribution and severity of acid rain and ozone depletion providing testable predictions for the geography of end permian environmental proxies