precise ages of the reunion event and huckleberry ridge excursion episodic clustering of geomagnetic instabilities and the dynamics of flow within the outer core the reunion event is one of the earliest recognized periods of normal polarity within the reversed matuyama chron named for the site at which it was first discovered on reunion island it has since purportedly been found globally in both volcanic rocks and sediments and thus has become a key chronostratigraphic marker however geochronologic results from several locations thought to have recorded this event have caused considerable confusion regarding not only its age and duration but also the number of reunion events new 40ar 39ar ages from eight reunion island lavas in three distinct sections are indistinguishable from one another thereby placing the event at 2 200 0 007 0 010 ma2 200 0 007 0 010 ma 2 2 analytical total uncertainty note this format is used throughout the paper the paleomagnetic behavior recorded at two of the island sites shows that the opposite normal polarity was reached and sustained for a period during which several lava flows were erupted whether this can be classified as a very short subchron bounded by a rapid set of back to back reversals or as a special case of a geomagnetic excursion is unclear hence we choose to continue labeling the dynamo activity recorded by these reunion island lavas as an event this event preceded a 38 kyr 38 kyr period of normal polarity that we name the feni subchron after its locality of discovery at odp site 981 the feni subchron was succeeded by the huckleberry ridge excursion for which 40ar 39ar sanidine and u pb zircon ages of 2 077 0 001 0 003 ma2 077 0 001 0 003 ma and 2 084 0 012 0 013 ma2 084 0 012 0 013 ma respectively from member b of the huckleberry ridge tuff in idaho are in agreement these findings suggest that the full normal polarity recorded on reunion island is a singular brief period of unstable field behavior at the onset of a 125 kyr 125 kyr bundling of dynamo instabilities from 2 20 to 2 07 ma disturbances to the axial dipole component of earth s magnetic field during this period and by analogy similar periods of temporally clustered excursions during the early and late portions of the brunhes chron may reflect disruptions to convective flow arising from parcels of material introduced into the outer core from either the inner core or core mantle boundaries a proposition that might be tested by future numerical dynamo simulations

kinematic and precipitation characteristics of convective systems observed by airborne doppler radar during the life cycle of a madden julian oscillation in the indian ocean abstractthis study presents characteristics of convective systems observed during the dynamics of the madden julian oscillation dynamo experiment by the instrumented noaa wp 3d aircraft nine separate missions with a focus on observing mesoscale convective systems mcss were executed to obtain data in the active and inactive phase of a madden julian oscillation mjo in the indian ocean doppler radar and in situ thermodynamic data are used to contrast the convective system characteristics during the evolution of the mjo isolated convection was prominent during the inactive phases of the mjo with deepening convection during the onset of the mjo during the mjo peak convection and stratiform precipitation became more widespread a larger population of deep convective elements led to a larger area of stratiform precipitation as the mjo decayed convective system top heights increased though the number of convective systems decreased eventually transitioning back to isolated convection a distinct

zonal and vertical structure of the madden julian oscillation abstract a statistical study of the three dimensional structure of the madden julian oscillation mjo is carried out by projecting dynamical fields from reanalysis and radiosonde data onto space time filtered outgoing longwave radiation olr data mjo convection is generally preceded by low level convergence and upward motion in the lower troposphere while subsidence cooling and drying prevail aloft this leads to moistening of the boundary layer and the development of shallow convection followed by a gradual and then more rapid lofting of moisture into the middle troposphere at the onset of deep convection after the passage of the heaviest rainfall a westerly wind burst region is accompanied by stratiform precipitation where lower tropospheric subsidence and drying coincide with continuing upper tropospheric upward motion the evolution of the heating field leads to a temperature structure that favors the growth of the mjo the analysis also reveals distinct differences in the vertical structure

mechanisms and timescales of generating eruptible rhyolitic magmas at yellowstone caldera from zircon and sanidine geochronology and geochemistry we constrain the physical nature of the magma reservoir and the mechanisms of rhyolite generation at yellowstone caldera via detailed characterization of zircon and sanidine crystals hosted in three rhyolites erupted during the c 170 70 ka central plateau member eruptive episode the most recent post caldera magmatism at yellowstone we present 238 u 230 th crystallization ages and trace element compositions of the interiors and surfaces i e unpolished rims of single zircon crystals from each rhyolite we compare these zircon data with 238 u 230 th crystallization ages of bulk sanidine separates coupled with chemical and isotopic data from single sanidine crystals zircon age and trace element data demonstrate that the magma reservoir that sourced the central plateau member rhyolites was long lived 150 250 kyr and genetically related to the preceding episode of magmatism which occurred c 256 ka the interiors of most zircons in each rhyolite were inherited from unerupted material related to older stages of central plateau member magmatism or the preceding late upper basin member magmatism i e are antecrysts conversely most zircon surfaces crystallized near the time of eruption from their host liquids i e are autocrystic the repeated recycling of zircon interiors from older stages of magmatism demonstrates that sequentially erupted central plateau member rhyolites are genetically related sanidine separates from each rhyolite yield 238 u 230 th crystallization ages at or near the eruption age of their host magmas coeval with the coexisting zircon surfaces but are younger than the coexisting zircon interiors chemical and isotopic data from single sanidine crystals demonstrate that the sanidines in each rhyolite are in equilibrium with their host melts which considered along with their near eruption crystallization ages suggests that nearly all central plateau member sanidines are autocrystic the paucity of antecrystic sanidine crystals relative to antecrystic zircons requires a model in which eruptible rhyolites are generated by extracting melt and zircons from a long lived mush of immobile crystal rich magma in this process the larger sanidine crystals remain trapped in the locked crystal network the extracted melts plus antecrystic zircon amalgamate into a liquid dominated i e eruptible magma body that is maintained as a physically distinct entity relative to the bulk of the long lived crystal mush zircon surfaces and sanidines in each rhyolite crystallize after melt extraction and amalgamation and their ages constrain the residence time of eruptible magmas at yellowstone residence times of the large volume rhyolites 40 70 km 3 are 1 kyr conservatively 6 kyr which suggests that large volumes of rhyolite can be generated rapidly by extracting melt from a crystal mush because the lifespan of the crystal mush that sourced the central plateau member rhyolites is two orders of magnitude longer than the residence time of eruptible magma

an ensemble of convective systems on 11 february 1993 during toga coare morphology rainfall characteristics and anvil cloud interactions abstract an active day during the coupled ocean atmosphere response experiment coare intensive observation period iop is examined in which nine convective systems evolved and moved eastward across the region of shipboard radar coverage in the intensive flux array ifa within westerly wind burst conditions the detailed genesis morphology and interactions between these cloud systems are documented from a radar and satellite perspective one of these systems was a large and complex elliptical cluster among the largest observed during the tropical ocean global atmosphere coare multiple parallel deep convective lines spaced 20 30 km apart and embedded within this system were initially oriented from north northwest to south southeast oblique to the storm motion furthermore the lines underwent counterclockwise realignment as the system moved eastward the influence of strong lower tropospheric directional and speed shear on these convective system properties is examined in the context of a dynamic

radar observed characteristics of precipitating systems during name 2004 abstract a multiradar network operated in the southern gulf of california goc region during the 2004 north american monsoon experiment is used to analyze the spatial and temporal variabilities of local precipitation based on the initial findings of this analysis it is found that terrain played a key role in this variability as the diurnal cycle was dominated by convective triggering during the afternoon over the peaks and foothills of the sierra madre occidental smo precipitating systems grew upscale and moved wnw toward the gulf distinct precipitation regimes within the monsoon are identified the first regime a corresponded to enhanced precipitation over the southern portions of the coast and goc typically during the overnight and early morning hours this was due to precipitating systems surviving the westward trip 7 m s 1 3 4 m s 1 in excess of steering winds from the smo after sunset likely because of enhanced environmental wind shear as diagnosed from local soundings the second

flake failure a new mass movement mechanism affecting peat beds eroded intertidally severn estuary southwest britain abstract flake failures as observed on the welsh bank of the severn estuary sw britain are large 10 m but thin 1 m flake shaped masses that became detached along subhorizontal concave up fractures from holocene peat beds exposed intertidally on cliff bound ledges the failure surfaces are marked by patterns of radially divergent hackles and concentric hesitation lines that indicate brittle fracture of the peat in response to concentrated and probably impulsive forces applied to the edge of a bed exposed on the cliff mechanical theory indicates that the impulse was applied roughly horizontally but in some cases with a significant upward bending moment the failures are linked to storm events suggesting that large waves breaking close to or against the upper part of the cliff provided the destructive force the spatio temporal frequency of flake failure is unknown but the effect of the particular events studied was to release of the order of 90 m 3 km 1 of peat from the edge of the ledge

the precipitating cloud population of the madden julian oscillation over the indian and west pacific oceans 1 the variability of the precipitating cloud population of the madden julian oscillation mjo is represented by statistics of echo features seen by the tropical rainfall measuring mission s precipitation radar over the central indian and west pacific oceans echo features include isolated shallow echoes deep convective cores wide convective cores and broad stratiform regions isolated shallow echoes are ever present but most numerous during suppressed mjo phases broad stratiform regions dominate variability in areal coverage and maximize during active phases deep convective and wide convective cores are more common and variable in number than broad stratiform regions the magnitude of variability is similar in both regions in the central indian ocean active mjo phases have synchronous maximization of deep convective entities in the west pacific broad stratiform regions maximize prior to wide convective cores reanalysis indicates that isolated shallow echoes are most numerous in dry mid tropospheric conditions and strong low level 1000 750 hpa shear mid tropospheric moisture increases before deeper convective features increase in number maximizes as deep convective features maximize and decreases as wide convective cores and broad stratiform regions decline in population active stage deep and wide convective cores occur preferentially with moist mid tropospheric conditions and strong low level shear acute shear may favor downdraft momentum transport and consequently more robust gust front convective triggering broad stratiform regions maximize with a moist mid troposphere strong low level shear and moderate upper level 750 500 hpa shear that is not so strong that the stratiform region disconnects from its convective moisture source

interactions between the mjo aerosols and convection over the central indian ocean abstractthis study examines covariability of boundary layer cloud condensation nuclei ccn concentrations estimated using the geos 3d chemical transport model geos chem convective clouds precipitation and lightning observed over the central equatorial indian ocean cio three distinct madden julian oscillation mjo episodes were observed during the recent dynamics of the mjo dynamo 2011 12 field campaign coherent relationships between ccn rainfall and lightning are apparent in time series from dynamo and more lightning located north of the equator is noted compared to south of the equator more polluted environments north of the equator contained deep convective clouds that had stronger radar reflectivities 2 3 db in the mixed phase region 5 10 km altitude compared to south of the equator following discussion of the mjo episodes that occurred during dynamo 22 cycles of the mjo observed during boreal cold seasons in the years 2004 11 are examined with the aid of trmm satellite obser

erosion of a cyclic saltmarsh in morecambe bay north west england this paper presents results of investigations 1983 1992 into rates of change morphology and processes occurring during the current erosional phase in a morecambe bay cyclic saltmarsh in which it has narrowed from c 1000 m 1975 to c 150 m 1992 monthly monitoring of marsh edge erosion and creek knickpoint retreat has revealed temporal and spatial variations highest frequency changes of low magnitude coincided with non storm conditions and overmarsh tides above 5 80 m od which submerged the whole marsh less frequent changes of greater magnitude were associated with both overmarsh tides and strong onshore winds over 15 ms 1 which generated high energy waves the lowest frequency change of greatest magnitude occurred during an extreme onshore storm event and surge morphologically during the erosional phase a low angled landward slope was generated as erosion of the c 0 5 m high active seaward cliff coincided with vertical accretion of 0 07 ma 1 of relatively coarse sediment on the marsh surface immediately landward tidal hydrodynamics strongly influence the saltmarsh which is confined to the upper 2 5 m of the macrotidal range maximum c 10 5 m during overmarsh spring tides maximum creek flood flow rate 0 13 ms 1 up to bankfull level flooding begins over lower landward creek banks before submerging the higher marsh edge during ebb tides water trapped by this higher edge can escape seaward only via the creeks maximum ebb velocities 2 07 ms 1 below bankfull level wave erosion also is limited to spring tides monthly mapping of the kent estuary channel pattern seaward of the saltmarsh showed that medium term higher erosion rates were related to the presence of a large channel which lowered the adjacent creek base level and allowed larger waves to attack the marsh edge than when a sandbank flanked the marsh major river kent channel shifts appear to initiate accretional or erosional phases of cyclic saltmarsh development

equatorial dry air intrusion and related synoptic variability in mjo initiation during dynamo abstractdynamics of the madden julian oscillation dynamo was conducted over the equatorial indian ocean io from october 2011 to march 2012 during mid to late november a strong madden julian oscillation mjo event denoted mjo 2 initiated in the western io and passed through the dynamo observation array dry air intrusions associated with synoptic variability in the equatorial region played a key role in the evolution of mjo 2 first a sharp dry air intrusion surging from the subtropics into the equatorial region suppresses convection in the itcz south of the equator this diminishes subsidence on the equator associated with the itcz convection which leads to an equatorward shift of convection it is viewed as a contributing factor for the onset of equatorial convection in mjo 2 once the mjo convection is established a second type of dry air intrusion is related to synoptic gyres within the mjo convective envelope the westward propagating gyres draw drier air from the subtropics into the equa

investigation of microphysical processes occurring in isolated convection during name abstracta major objective of the north american monsoon experiment name was to quantify microphysical processes within convection occurring near the steep topography of northwestern mexico a previous study compared examples of isolated convection using polarimetric radar data and noted a dependence on mixed phase processes via drop freezing and subsequent riming growth along the coastal plain and western slopes with an even greater role of melting ice in rainfall production over the highest terrain despite the higher frequency of these isolated cells compared to organized convective systems the latter were responsible for 75 of rainfall therefore this study seeks to evaluate the role of mesoscale organization on microphysical processes and describes the evolution of these systems as a function of topography similar to isolated convection both warm rain and ice based processes played important roles in producing intense rainfall in organized convection although similarities existed between cell

measurement of recent intertidal sediment transport in morecambe bay using the waterline method abstract an illustration of how sediment transport may be measured over a large dynamic intertidal area at reasonable cost and spatiotemporal resolution using the waterline method employing remote sensing and hydrodynamic modelling is presented areas and volumes of accretion and erosion were measured in the study area of morecambe bay in north west england over the period 1992 97 tidal asymmetry is considered to be the dominant agent of sediment movement in the bay with waves being of secondary importance waterlines i e land sea boundaries were extracted from 31 synthetic aperture radar images of the bay covering a substantial fraction of the tidal range heights were attached to the waterlines using water elevations from nested hydrodynamic tide surge models interpolation in space and time was carried out to produce a continuous spatiotemporal height map of the intertidal zone height maps with a spatial resolution of about 50 m and height accuracy of about 40 cm were constructed over an area of about 350 km 2 strong temporal decorrelation in the bay limited the height accuracy achievable differences between height maps for 1992 94 and 1995 97 allowed sediment volume changes to be extracted the intertidal region showed a loss of 16 1 4 5 10 6 m 3 over the period almost all the change being due to a significant decrease between mean sea level and the low water mark changes were also measured in three of the main river estuaries within the bay the leven kent and lune these included movement of the leven north east by about 2 km cutting into cartmel wharf accretion seaward of grange over sands and changes in the low water channels at the mouth of the lune these changes could be used to validate sediment transport models of the bay

vertical diabatic heating structure of the mjo intercomparison between recent reanalyses and trmm estimates abstractcapitalizing on recently released reanalysis datasets and diabatic heating estimates based on tropical rainfall measuring mission trmm the authors have conducted a composite analysis of vertical anomalous heating structures associated with the madden julian oscillation mjo because diabatic heating lies at the heart of prevailing mjo theories the intention of this effort is to provide new insights into the fundamental physics of the mjo however some discrepancies in the composite vertical mjo heating profiles are noted among the datasets particularly between three reanalyses and three trmm estimates a westward tilting with altitude in the vertical heating structure of the mjo is clearly evident during its eastward propagation based on three reanalysis datasets which is particularly pronounced when the mjo migrates from the equatorial eastern indian ocean eeio to the western pacific wp in contrast this vertical tilt in heating structure is not readily seen in the three trmm product

volcanism at 1 45 ma within the yellowstone volcanic field united states abstract rhyolitic volcanism in the yellowstone volcanic field has spanned over two million years and consisted of both explosive caldera forming eruptions and smaller effusive flows and domes effusive eruptions have been documented preceding and following caldera forming eruptions however the temporal and petrogenetic relationships of these magmas to the caldera forming eruptions are relatively unknown here we present new 40ar 39ar dates for four small volume eruptions located on the western rim of the second cycle caldera the source of the 1 300 0 001 ma mesa falls tuff we supplement our new eruption ages with whole rock major and trace element chemistry pb isotopic ratios of feldspar and paleomagnetic and rock magnetic analyses eruption ages for the effusive green canyon flow 1 299 0 002 ma and moonshine mountain dome 1 302 0 003 ma are in close temporal proximity to the eruption age of the mesa falls tuff in contrast our results indicate a period of volcanism at ca 1 45 ma within the yellowstone volcanic field including the eruption of the bishop mountain flow 1 458 0 002 ma and tuff of lyle spring 1 450 0 003 ma these high silica rhyolites are chemically and isotopically distinct from the mesa falls tuff and related 1 3 ma effusive eruptions the 40ar 39ar data from the tuff of lyle spring demonstrate significant antecrystic inheritance prevalent within the upper welded ash flow tuff matrix and minimal within individual pumice antecrysts are up to 20 kyr older than the eruption with subpopulations of grains occurring every few thousand years we interpret these results as an indicator for the timing of magmatic pulses into a growing magmatic system that would ultimately erupt the tuff of lyle spring and which we more broadly interpret as the tempo of crustal accumulation associated with bimodal magmatism we propose a system whereby chemically isotopically and temporally distinct isolated small volume magma batches are periodically generated and erupted in a low magmatic flux state which is punctuated by larger volume caldera forming eruptions

granulometric characterization and evaluation of annually banded mid holocene estuarine silts welsh severn estuary uk coastal change sea level and climate abstract holocene silts salt marshes and highest intertidal supratidal peats are superbly exposed on a 15 km coastal transect which reveals two laterally extensive units of annually banded silts beds 3 7 associated with three transgressive regressive silt peat cycles early sixth early fourth millennium bc bed 3 in places is concordantly and gradationally related to peats above and below but in others transgresses older strata bed 7 also grades up into peat but everywhere overlies a discordance the banding in bed 3 at three main and two minor sites was resolved and characterized texturally at high resolution 2 5 5 mm contiguous slices using laser granulometry ls230 with pids and a comprehensive scheme of data assessment most of bed 3 formed very rapidly at peak values of several tens of millimetres annually in accordance with modelled effects of sea level fluctuations on mature marshes bed concordant and gradational and on marshes growing up after coastal erosion and retreat bed with discordant base using data from the modern severn estuary the textural contrast within bands and its variation between bands points to a variable but overall milder mid holocene climate than today the inter annual variability affected marsh dynamics as shown by the behaviour of the finely divided plant tissues present given local calibration the methodology is applicable to other tidal systems with banded silts in britain and mainland northwest europe

strong indian ocean sea surface temperature signals associated with the madden julian oscillation in late 2007 and early 2008 a moored buoy was recently deployed at 8 degrees s 67 degrees e in the shallow thermocline region of the indian ocean known as seychelles chagos thermocline ridge sctr where the madden julian oscillation mjo is associated with strong sea surface temperature sst variability we use observations from this mooring to describe the oceanic signature of two mjos between november 2007 and february 2008 the four month average upper ocean heat balance was largely between heating by atmospheric forcing 2 0 0 3 degrees c month and a significant cooling by subsurface processes 2 2 0 8 degrees c month consistent with climatological ekman pumping in the region the two mjo events resulted in strong intraseasonal sst variations 1 5 to 2 degrees c in similar to 20 days in the sctr at the mooring site atmospheric fluxes dominated the upper ocean heat balance at the mjo timescale with the net surface heat flux into the ocean decreasing from an average 105 w m 2 during suppressed phases to 15 w m 2 during active phases of the mjo it is difficult to establish if mjo induced variations of subsurface processes also contributed to the cooling because of large uncertainty in this term lateral advection had no systematic fluctuations on mjo timescales but cannot be neglected at the mooring site

re evaluation of the ages of 40ar 39ar sanidine standards and supereruptions in the western u s using a noblesse multi collector mass spectrometer abstract the rewards from resolving the tempo of magmatic paleobiologic paleoclimatic and tectonic processes at better than the per mil level of precision have spurred a quest within the geochronology community to improve the precision accuracy and calibration of several chronometers including the 40 ar 39 ar variant of the k ar clock a new generation of multi collector mass spectrometers for 40 ar 39 ar geochronology provides the means to address these issues as well as to evaluate the ages of 40 ar 39 ar standards and key marker horizons deposited by large volume caldera forming supereruptions in the western u s at unprecedented temporal resolution we highlight the utility of a 5 collector noblesse mass spectrometer that has a sufficiently high mass resolving power to distinguish 36 ar h 35 cl from a 36 ar h 35 cl 12 c 3 sum peak at m e 36 maintains a remarkably low and stable background and thus yields 40 ar 39 ar dates of exceptionally high precision we have calibrated a reference gas and developed a simple analytical routine involving one peak hop both of which are used to evaluate detector bias correction factors because the 40 ar 39 ar chronometer is a relative dating technique that relies on calibration against mineral standards of known age precise and accurate determination of the ages of these standards and verification of isotopic composition and homogeneity is essential we present results from both total fusion and incremental heating experiments on single crystals of the widely used alder creek acs and fish canyon fcs sanidine standards several recent independent measurements of acs using multi collector mass spectrometers including those presented herein favor an age of 1 1864 0 0003 0 0012 ma 95 confidence analytical full external uncertainty that is 1 younger than the widely used value obtained by nomade et al 2005 using a single collector mass spectrometer incremental heating experiments on single crystals of fcs most commonly do not yield plateau ages instead many crystals appear to be affected by ar loss or excess ar our findings obtained using ion counters independently confirm those recently obtained using a multiple faraday detectors or a combination of faraday and ion counting detectors thus careful consideration must be given to using fcs in future high precision 40 ar 39 ar calibrations of the geologic timescale notwithstanding 40 ar 39 ar dating of sanidine using the 5 collector noblesse can now provide leverage critical to interpreting the large range of u pb zircon dates commonly found in rhyolitic lavas and tuffs

rapid magma evolution constrained by zircon petrochronology and 40ar 39ar sanidine ages for the huckleberry ridge tuff yellowstone usa understanding the time scales of magmatic differentiation storage and eruption of large volume silicic magmas is a primary goal of igneous petrology within the huckleberry ridge tuff hrt idaho usa representing the earliest and largest caldera forming eruption associated with yellowstone volcanic activity zircon morphological zoning patterns coupled to strongly correlated changes in ti in zircon thermometry and trace element indicators of progressive differentiation provide a proxy record for the evolution of the hrt member b magma body tandem in situ and isotope dilution u pb dating of single zircon crystals demonstrates an absence of pre pleistocene xenocrysts but reveals the presence of antecrysts recycled from pre caldera rhyolites in the hrt magma the petrochronologic interpretation of autocrystic zircon thermal chemical and temporal characteristics suggests that hrt member b differentiated over 10 k y prior to eruption at 2 0794 0 0046 ma as defined by new astronomically calibrated single crystal total fusion 40 ar 39 ar sanidine analyses this refined eruption age demonstrates that the transitional polarity preserved by hrt member b does not record the reunion subchron but rather a separate younger geomagnetic event our novel approach places the thermal and chemical regime of silicic magmas within a temporal context and demonstrates the rapid evolution of a large volume of silicic magma

prolonged ascent and episodic venting of discrete magma batches at the onset of the huckleberry ridge supereruption yellowstone abstract how exceedingly large volcanic supereruptions begin provides crucial information on the storage ascent and release of silica rich magma in catastrophic events initial fall deposits of the 2 08 ma 2500 km 3 huckleberry ridge eruption are multiply bedded and in several places contain reworked intervals indicating time breaks in the opening phases of the eruption a 2 5 m section of these fall deposits was sampled at nine levels below the earliest ignimbrite member a at mount everts mammoth wyoming we analyzed major and trace elements and volatiles in quartz hosted melt inclusions mis reentrants res unsealed melt inclusions and associated obsidian pyroclasts thick walled shards to establish quartz crystallization and storage depths and melt compositional groupings systematic relationships between rb and other incompatible elements u cl b indicate 55 fractional crystallization between the least and most evolved glass compositions in contrast h 2 o concentrations in mis show scattered relationships with trace elements and are interpreted to reflect variable loss of h 2 o by diffusion through the quartz host during magma ascent the wide h 2 o variations 1 0 4 7 wt in mis from individual fall horizons imply as much as 14 days of diffusive loss reflecting highly variable and surprisingly slow decompression conditions water and co 2 gradients in reentrants however are consistent with final ascent times of 0 3 1 5 m s similar to those represented by mis that we infer to have experienced little to no diffusive h 2 o loss the wide range of ascent rates for co erupted crystals mirrors that of intermittent explosive activity at mount st helens in summer 1980 and implies that the huckleberry ridge magma body was not strongly overpressured at eruption onset restored entrapment pressures and geochemical data for mis provide evidence for six distinct populations of quartz that originally crystallized in geochemically distinct magma domains the compositions of res and obsidian pyroclasts by comparison show that by the onset of eruption the quartz had been brought together into three discrete magma bodies which we interpret to have been cupolas on the roof of the main magma body these cupolas were erupted sequentially and episodically from separate vents to generate the fall deposits before escalating activity led to generation of voluminous pyroclastic flows and this pattern of activity suggests that tectonic triggering may have destabilized multiple magma bodies supereruptions as large as the huckleberry ridge event may start hesitatingly if the parental magma bodies are not strongly overpressured with small scale episodic activity that is modulated by external controls that may leave no other geological evidence for their presence

the hydrodynamics of surface tidal flow exchange in saltmarshes abstract modeling studies of estuary circulation show great sensitivity to the water exchange into and out of adjacent marshes yet there is significant uncertainty in resolving the processes governing marsh surface flow the objective of this study is to measure the estuary channel to saltmarsh pressure gradient and to guide parameterization for how it affects the surface flow in the high marsh current meters and high resolution pressure transducers were deployed along a transect perpendicular to the nearby little ogeechee river in a saltmarsh adjacent to rose dhu island near savannah georgia usa the vertical elevations of the transducers were surveyed with static gps to yield high accuracy water surface elevation data it is found that water level differences between the little ogeechee river and neighboring saltmarsh are up to 15 cm and pressure gradients are up to 0 0017 m of water surface elevation change per m of linear distance during rising and falling tides the resulting little ogeechee river to saltmarsh pressure gradient substantially affects tidal velocities at all current meter locations at the velocity measurement station located closest to the little ogeechee river bank the tidal velocity is nearly perpendicular to the bank at this location surface flow is effectively modeled as a balance between the pressure gradient force and the drag force due to marsh vegetation and bottom stress using the darcy weisbach lindner s equations developed for flow through vegetation analysis in open channel flow the study thus provides a direct connection between the pressure gradient and surface flow velocity in the high marsh thereby overcoming a long standing barrier in directly relating flow through saltmarsh studies to flow through vegetation studies in the open channel flow literature

structural evolution in heating profiles of the mjo in global reanalyses and trmm retrievals abstract diabatic and latent heating profiles from four global reanalyses and three tropical rainfall measuring mission trmm algorithms were compared first generally for the tropics and then in the context of the madden julian oscillation mjo most of them exhibit three heating maxima corresponding to known convection centers over south america africa and the indian western pacific warm pool but they still differ substantially in many ways most noticeably a double peak vertical structure with one peak in the upper and the other in the lower troposphere and relative weak heating over the maritime continent in comparison to heating over the indian and western pacific oceans are clearly seen in some heating data but absent in others heating profiles associated with the mjo were diagnosed through composites and case studies the composites were constructed as functions of mjo phases at three longitudes representing the indian ocean maritime continent and western pacific respectively four mjo ev

low δ18o rhyolites from yellowstone magmatic evolution based on analyses of zircons and individual phenocrysts the yellowstone plateau volcanic field is one of the largest centers exchange time to form zoned zircons is between a few hundred and a few thousand years which reflects the residence time of lowo of rhyolitic magmatism on earth major caldera forming eruptions are followed by unusual lowo rhyolites new oxygen isotope magmas after formation and before eruption petrologic and geochemical data from rhyolites belonging to the 2 0 my eruptive history of yellowstone are presented with emphasis on the genesis of lowo magmas erupted after the huckleberry ridge tuff 2 0 ma 2500 km and lava creek tuff 0 6 ma

cloud to ground lightning observations from toga coare selected results and lightning location algorithms abstract recently observations of electrified oceanic convection and associated cloud to ground cg lightning were obtained over the tropical western pacific ocean during toga coare tropical ocean global atmosphere coupled ocean atmosphere response experiment during coare observations of convection were made using a variety of instrument platforms including ship and airborne doppler radars an advanced lightning direction finder aldf network and a shipborne inverted electric field mill this study focuses on data collected by the coare aldf network fusion of those data with observations and the methods used to calculate accurate cg return stroke locations analysis of cg lightning data and doppler radar data indicates that lightning producing oceanic convection is characterized by deep vertically developed convective cells with radar reflectivities exceeding 30 dbz above the height of the 10 c level in several cases a peak in cg frequency occurred coincident with the descent of precipitation

convective characteristics of the madden julian oscillation over the central indian ocean observed by shipborne radar during dynamo abstractthis study investigates the convective population and environmental conditions during three mjo events over the central indian ocean in late 2011 using measurements collected from the research vessel r v roger revelle deployed in dynamics of the mjo dynamo radar based rainfall estimates from the revelle c band radar are first placed in the context of larger scale tropical rainfall measuring mission trmm rainfall data to demonstrate that the reduced revelle radar range captured the mjo convective evolution time series analysis and mjo phase based composites of revelle measurements both support the recharge discharge mjo theory time series of echo top heights indicate that convective deepening during the mjo onset occurs over a 12 16 day period composite statistics show evident recharging discharging features in convection and the environment population of shallow isolated convective cells sst cape and the lower tropospheric moisture increase recharge substantially approximately tw

split grain 40ar 39ar dating integrating temporal and geochemical data from crystal cargoes nerc is acknowledged for continued funding of aif at suerc east kilbride this work was supported by an eth research grant eth 05 13 2 and funds from swiss national science foundation research grants snsf 200021 146268 and snsf 200021 155923 1 and us national science grant 1425491

seasonal and annual variations in the volumetric sediment balance of a macro tidal salt marsh abstract this paper examines the spatial and temporal variability in the volumetric sediment balance of allen creek marsh a macro tidal salt marsh in the bay of fundy the volumetric balance was determined as the balance of inputs of sediments and organic matter via accretion on the marsh surface and outputs of sedimentary material primarily due to erosion of the marsh margin changes in marsh surface elevation were measured at 20 buried plates and 3 modified sediment elevation tables from 1996 2002 and detailed margin surveys were conducted in 1997 1999 and 2001 using a differential global positioning system changes in surface area were calculated using gis overlay analysis and used in conjunction with accretion and erosion data to derive volumetric estimates of gains and losses of sedimentary material in the marsh system currently the volumetric sediment balance at allen creek marsh is positive however the processes of erosion and accretion demonstrate seasonal annual and spatial variability inputs to the system include deposition on the marsh surface from sediment laden waters and from ice rafting of sediments sediment is deposited onto the marsh surface year round even during the winter when vegetation cover is sparse and the amount of deposition in general is not significantly correlated with the frequency of tidal inundations based on the data from 1996 to 2002 the mid and high marsh zones experience mean accretion rates of approximately 1 4 cm year 1 whereas accretion rates in the low marsh region are statistically significantly lower 0 8 cm year 1 the absolute amount of accretion varies between seasons and from year to year the main loss to the marsh is through erosion of the marsh margin cliffs which can remove a comparatively large volume of sedimentary material in one mass wasting event and which also decreases the vegetated surface area available for deposition from sediment laden waters the volume of material removed from the marsh margin almost tripled between 1997 169 m3 and 2001 502 m3 following breaching of the side of a tidal creek channel altering the patterns of margin erosion and deposition in the marsh system during this time however other sheltered areas of the marsh system such as along the tidal creek banks showed evidence of new vegetation growth increasing the amount of vegetated surface area available for deposition the processes of erosion and deposition on the marsh surface exhibit considerable spatial variability with different regions of the marsh being more or less sensitive to seasonal variability in the dominant controls influencing sediment deposition and erosion in this system namely wave activity vegetation ice and water depths a key factor in predicting how a marsh will evolve and respond to a number of different controls e g sea level rise or reduced sediment supply is to quantify both accretion of the marsh surface and erosion of the marsh margin evaluating the marsh system as a volumetric whole this study demonstrates that a marsh system should be assessed in three dimensions rather than simply as a surface of accumulation this is particularly important for open coastal marshes exposed to the erosive action of waves

a satellite derived climatology of the itcz abstract this paper presents fundamental climatological characteristics of the intertropical convergence zone itcz in a simple concise manner using the highly reflective cloud hrc dataset this satellite derived dataset uses both visible and infrared observations to measure the frequency of occurrence of large scale convective systems over the global tropics at a 1 spatial resolution these dataset characteristics make the hrc particularly well suited for climatological analysis of the itcz because the dataset is based on estimates of organized deep convective cloud systems rather than observations of clouds as a whole and it provides the spatial resolution needed to identify thew large wale convective structures furthermore the dataset covers a time period extending nearly two decades which provides for a fairly robust climatology and the opportunity to examine seasonal and interannual variability of both the convection and the latitude of the itcz

three dimensional kinematic and microphysical evolution of florida cumulonimbus part ii frequency distributions of vertical velocity reflectivity and differential reflectivity abstract high resolution radar data collected in florida during the convection and precipitation electrification experiment are used to elucidate the microphysical and kinematic processes occurring during the transition of a multicellular storm from convective to stratiform stages a statistical technique is employed to examine the evolving properties of the ensemble small scale variability of radar reflectivity vertical velocity and differential reflectivity over the entire storm differential radar reflectivity data indicate that the precipitation at upper levels was nearly glaciated early in the storm s lifetime dual doppler radar data show that throughout the storm s lifetime both updrafts and down drafts were present at all altitudes and that most of the volume of the radar echo contained vertical velocities incapable of supporting precipitation size particles thus the ensemble microphysical properties of the storm were increasingly dominated by particles falling in an environment of weak vertic

40ar39ar geochronology of rhyolites erupted following collapse of the yellowstone caldera yellowstone plateau volcanic field implications for crustal contamination abstract single crystal laser probe 40 ar 39 ar dating of 133 grains of sanidine and plagioclase has enabled us to resolve the eruption ages of the upper basin member rhyolites the lava flows and related tuffs that erupted within the yellowstone caldera shortly after its collapse 630 ky ago on eruption of the lava creek tuff two lavas and a tuff that erupted from the eastern ring fracture zone yield an eruptive age of 481 8 ka whereas two flows from the western ring fracture zone yield eruptive ages of 516 7 and 198 8 ka most of the units contain old xenocrysts explaining why previous attempts at dating these earliest post caldera units by the conventional k ar method yielded poorly resolved and in some cases anomalous ages the tuff shows the most severe contamination grains from a single pumice lapilli in the tuff show as large an age range as those from bulk vitrophyre indicating that the xenocrysts were incorporated in the magma prior to its near surface explosive fragmentation diffusion calculations indicate that the xenocrysts could not have remained in the magma for more than a few years without degassing and giving ages indistinguishable from the phenocrysts thus the contamination represented by the xenocrysts probably occurred during fracturing and conduit propagation rather than during caldera collapse which took place more than 100 ky earlier the apparent ages of xenocrysts and their compositions as determined by electron microprobe suggest that the eocene absaroka volcanics are the main contaminant with a single xenocryst probably coming from precambrian basement rocks most of the xenocrysts are difficult to distinguish optically or chemically from feldspar phenocrysts illustrating the necessity of single crystal to date many young volcanic rocks accurately

evolution properties and spatial variability of mjo convection near and off the equator during dynamo abstractthis study investigates the evolution structure and spatial variability of madden julian oscillation mjo convection observed during the 2011 12 dynamics of the mjo dynamo field campaign generally the c band radars located in the near equatorial indian ocean shared mobile atmospheric research and teaching radar smart r on addu atoll gan and nasa toga on the r v roger revelle revelle observed similar trends in echo top heights stratiform rain fraction and precipitation feature size across the mjo life cycle these trends are closely related to changes in mid to upper tropospheric moisture sea surface temperature sst zonal wind and diagnosed vertical air motions however the evolution of convection moisture and vertical air motion at the r v mirai mirai located in the intertropical convergence zone itcz at 8 s exhibited a pattern nearly opposite to gan and revelle when the mjo was active over the equator convection was suppressed around mirai owing to induced subsiden

the onset of convection in the madden julian oscillation abstract an observational study of the onset of convection in the madden julian oscillation mjo was performed composites of radiosonde data from the comprehensive aerological reference data set were constructed for an ensemble of tropical stations located in the indian ocean maritime continent and western pacific ocean the composites suggest that for the off equatorial stations used in this study the mjo period may be set by the buildup and discharge of the low level moist static energy this result supports the discharge recharge hypothesis of blade and hartmann mjo events appear to begin when the off equatorial atmosphere has been destabilized through a combination of low level moist static energy buildup and concurrent drying of the middle troposphere by subsidence in the wake of the previous cycle of mjo convection the low level moist static energy buildup is controlled by a corresponding increase in low level moisture the increase in low level moisture is not caused by the 1000 mb convergen

gas driven filter pressing in magmas most silicic and some mafic magmas expand via second boiling if they crystallize at depths of about 10 km or less the buildup of gas pressure due to second boiling can be relieved by expulsion of melt out of the region of crystallization and this process of gas driven filter pressing assists the crystallization differentiation of magmas for gas driven filter pressing to be effective the region of crystallization must inflate slowly relative to buildup of pressure and expulsion of melt these conditions are satisfied in undercooled magmatic inclusions and in thin sheets of primitive magma underplating cooler magma reservoirs gas driven filter pressing thereby adds fractionated melt to magma bodies gas driven filter pressing is probably the dominant process by which highly evolved melts segregate from crystal mush to form aplitic dikes in granitic plutons this process could also account for the production of voluminous crystal poor rhyolites

the role of mantle derived magmas in the isotopic evolution of yellowstone s magmatic system injection of mantle derived magmas into the earth s crust provides the heat necessary to develop and maintain large silicic magmatic systems however the role of mantle derived magmas in controlling the compositional evolution of large silicic systems remains poorly understood here we examine the role of mantle derived magmas in the post caldera magmatic system at yellowstone plateau the youngest magmatism associated with the yellowstone hotspot using microbeam techniques we characterize the age and hf isotope composition of single zircon crystals hosted in rhyolites from the most recent eruptive episode at yellowstone plateau which produced the central plateau member rhyolites we place these zircon data into context by comparing them to new solution hf isotope data for the central plateau member glasses yellowstone basalts and potential local crustal sources zircons in the central plateau member rhyolites record a wide range of hf isotope compositions relative to their host melts and extend from values similar to previously erupted yellowstone rhyolites to values similar to yellowstone basalts most zircons 90 are in isotopic equilibrium with their host melt but a significant proportion show ehf values higher than their host melt thus providing the direct evidence that silicic derivatives of mantle derived basalts have recharged yellowstone s magmatic system mixing models confirm that the isotopic characteristics of the youngest yellowstone rhyolites can be explained by recharge of yellowstone s magma reservoir with silicic derivatives of underplating mantle derived basalts 5 to 10 material added by mass this process helps drive the long term isotopic evolution of yellowstone s magmatic system this article is protected by copyright all rights reserved

the process of sedimentation on the surface of a salt marsh abstract an unditched salt marsh creek drainage basin holland glade marsh lewes delaware has a sedimentation rate of 0 5 cm year 1 during normal storm free conditions the creek carries negligible amounts of sand and coarse silt of the material in the waters flooding the marsh surface over 80 disappears from the floodwaters within 12 m of the creek about one half of the lost material is theoretically too fine to settle even if flow were not turbulent however sediment found on spartina stems can account for the loss the quantity of suspended sediment that does reach the back marsh during these normal tides is inadequate to maintain the marsh surface against local sea level rise this suspended sediment is also much finer than the deposited sediments additionally remote sections of low marsh sections flooded by only the highest spring tides have 15 30 cm of highly inorganic marsh muds this evidence indicates that normal tidal flooding does not produce sedimentation in holland glade study of the effects of two severe storms of a frequency of once per year suggests that such storms can deposit sufficient sediment to maintain the marsh the actual deposition of fine grained sediments fine silt and clay appears to result primarily from biological trapping rather than from settling in addition this study proposes that the total sedimentation on mature marshes results from a balance between tidal and storm sedimentation storms will control sediment supply and movement on micro and meso tidal marshes and will have less influence on macro tidal marshes

drop size distributions and radar observations of convective and stratiform rain over the equatorial indian and west pacific oceans abstracttwo dimensional video disdrometer 2dvd data were analyzed from two equatorial indian gan and west pacific ocean manus islands where precipitation is primarily organized by the intertropical convergence zone and the madden julian oscillation mjo the 18 3 5 months of 2dvd data from manus gan island show that 1 the two sites have similar drop size distribution dsd spectra of liquid water content median diameter rain rate r radar reflectivity z normalized gamma number concentration nw and other integral rain parameters 2 there is a robust nw based separation between convective c and stratiform s dsds at both sites that produces consistent separation in other parameter spaces the 2dvd data indicate an equatorial maritime average c s rainfall accumulation fraction frequency of 81 19 41 59 at these locations it is hypothesized that convective fraction and frequency estimates are slightly higher than previous radar based studies because the ubiquitous weak shallow convec

the relationship between precipitation and lightning in tropical island convection a c band polarimetric radar study one of the primary scientific objectives of the maritime continent thunderstorm experiment was to study cloud electrification processes in tropical island convection in particular the coupling between ice phase precipitation and lightning production to accomplish this goal a c band polarimetric radar was deployed in the tropics 11 68s 130 88e for the first time accompanied by a suite of lightning measurements using observations of the propagation corrected horizontal reflectivity and differential reflectivity along with specific differential phase rain and ice masses were estimated during the entire life cycle of an electrically active tropical convective complex known locally as hector over the tiwi islands on 28 november 1995 hector s precipitation structure as inferred from these raw and derived radar fields was then compared in time and space to the measured surface electric field cloud to ground cg and total lightning flash rates and ground strike locations during hector s developing stage precipitating convective cells along island sea breezes were dominated by warm rain processes no significant electric fields or lightning were associated with this stage of hector despite substantial rainfall rates aided by gust front forcing a cumulus merger process resulted in larger taller and more intense convective complexes that were dominated by mixed phase precipitation processes during the mature phase of hector lightning and the surface electric field were strongly correlated to the mixed phase ice mass and rainfall merged convective complexes produced 97 of the rainfall and mixed phase ice mass and 100 of the cg lightning as hector dissipated lightning activity rapidly ceased as evidenced from the multiparameter radar observations the multicell nature of hector resulted in the continuous lofting of supercooled drops to temperatures between 2108 and 2208c in discrete updraft cores during both the early and mature phases the freezing of these drops provided instantaneous precipitation sized ice particles that may have subsequently rimed and participated in thunderstorm electrification via the noninductive charging mechanism

evolution of the population of precipitating convective systems over the equatorial indian ocean in active phases of the madden julian oscillation three dimensional radar reflectivity fields from a dual wavelength doppler polarimetric radar s polka deployed in the equatorialindian ocean are used to evaluate the composition of the populationof convective cloud elements during active phases of the mjo rainfall in active periods was intermittent occurring in 11 episodesofabout 2 4days separated byseveralnonrainydays dataforthese 2 dayperiodswerecomposited relative to the time of maximum rainfall analysis of the s polka data shows the makeup of the convective population during the rainfall episodes four types of echo structures were analyzed statistically for the 11 rainfallepisodes shallowconvectiveechoes sce deepconvectivecores dcc wideconvectiveechocores wcc and broad stratiform bsr echo regions sce and dcc events were most frequent before the maximum rainfall with the peak frequency of sce leading that of dccs wccs were most frequent during therainfallmaximum and bsr regionswere most frequentinthe later part oftherainfallepisode composited ecmwf interim re analysis era interim data and 3 hourly atmospheric soundings indicate that the 2 4 day episodes were related to the passage of equatorial waves in the early part of a rainfall episode the wave passageconditionswereunstable favoringdeeppenetratingconvectiveelements whileinthelaterperiod the wave divergence profile was commensurate with convective systems in late anvil producing stages these results support the stretched building block notion of the life cycle of tropical convection and confirm satellitebased interpretations of sce dcc wcc and bsr statistics in the composition of the convective population

months between rejuvenation and volcanic eruption at yellowstone caldera wyoming rejuvenation of previously intruded silicic magma is an important process leading to effusive rhyolite which is the most common product of volcanism at calderas with protracted histories of eruption and unrest such as yellowstone caldera wyoming long valley caldera california and valles caldera new mexico in the united states although orders of magnitude smaller in volume than rare caldera forming supereruptions these relatively frequent effusions of rhyolite are comparable to the largest eruptions of the 20th century and pose a considerable volcanic hazard however the physical pathway from rejuvenation to eruption of silicic magma is unclear particularly because the time between reheating of a subvolcanic intrusion and eruption is poorly quantified this study uses nanometer scale trace element diffusion in sanidine crystals to reveal that rejuvenation of a near solidus or subsolidus silicic intrusion occurred in 10 mo or less following a protracted period 220 k y of volcanic repose and resulted in effusion of 3 km3 of high silica rhyolite lava at the onset of yellowstone s last volcanic interval the future renewal of effusive silicic volcanism at yellowstone will likely require a comparable energetic intrusion of magma that remelts the shallow subvolcanic reservoir and generates eruptible rhyolite on month to annual time scales

characteristics of precipitation cloud and latent heating associated with the madden julian oscillation abstract this study investigates the evolution of cloud and rainfall structures associated with madden julian oscillation mjo using tropical rainfall measuring mission trmm data two complementary indices are used to define mjo phases joint probability distribution functions pdfs of cloud top temperature and radar echo top height are constructed for each of the eight mjo phases the genesis stage of mjo convection over the western pacific phases 1 and 2 features a bottom heavy pdf characterized by abundant warm rain low clouds suppressed deep convection and higher sea surface temperature sst as mjo convection develops phases 3 and 4 a transition from the bottom heavy to top heavy pdf occurs the latter is associated with the development of mixed phase rain and middle to high clouds coupled with rapid sst cooling at the mjo convection peak phase 5 a top heavy pdf contributed by deep convection with mixed phase and ice phase rain and high echo top heights 5 km dominates the decay

diurnal cycle of the itcz in dynamo abstractduring the 2011 special observing period of the dynamics of the madden julian oscillation dynamo field experiment two sounding arrays were established over the central indian ocean one

argon geochronology of kilauea s early submarine history submarine alkalic and transitional basalts collected by submersible along kilauea volcano s south flank represent early eruptive products from earth s most active volcano strongly alkalic basalt fragments sampled from volcaniclastic deposits below the mid slope hilina bench yield 40 ar 39 ar ages from 212 38 to 280 20 ka these ages are similar to high precision 234 9 and 239 10 ka phlogopite ages from nephelinite clasts in the same deposits above the mid slope bench two intact alkalic to transitional pillow lava sequences protrude through the younger sediment apron samples collected from a weakly alkalic basalt section yield 138 30 to 166 26 ka ages and others from a transitional basalt section yield 138 115 and 228 114 ka ages the ages are incompatible with previous unspiked k ar studies from samples in deep drill holes along the east rift of kilauea the submarine birth of kilauea volcano is estimated at 300 ka if the weakly alkalic sequence we dated is representative of the volcano as a whole the transition from alkalic to tholeiitic basalt compositions is dated at 150 ka

incremental heating of bishop tuff sanidine reveals preeruptive radiogenic ar and rapid remobilization from cold storage abstract accurate and precise ages of large silicic eruptions are critical to calibrating the geologic timescale and gauging the tempo of changes in climate biologic evolution and magmatic processes throughout earth history the conventional approach to dating these eruptive products using the 40ar 39ar method is to fuse dozens of individual feldspar crystals however dispersion of fusion dates is common and interpretation is complicated by increasingly precise data obtained via multicollector mass spectrometry incremental heating of 49 individual bishop tuff bt sanidine crystals produces 40ar 39ar dates with reduced dispersion yet we find a 16 ky range of plateau dates that is not attributable to excess ar we interpret this dispersion to reflect cooling of the magma reservoir margins below 475 c accumulation of radiogenic ar and rapid preeruption remobilization accordingly these data elucidate the recycling of subsolidus material into voluminous rhyolite magma reservoirs and the effect of preeruptive magmatic processes on the 40ar 39ar system the youngest sanidine dates likely the most representative of the bt eruption age yield a weighted mean of 764 8 0 3 0 6 ka 2 analytical full uncertainty indicating eruption only 7 ky following the matuyama brunhes magnetic polarity reversal single crystal incremental heating provides leverage with which to interpret complex populations of 40ar 39ar sanidine and u pb zircon dates and a substantially improved capability to resolve the timing and causal relationship of events in the geologic record

magma storage and evolution of the most recent effusive and explosive eruptions from yellowstone caldera between 70 and 175 ka over 350 km3 of high silica rhyolite magma erupted both effusively and explosively from within the yellowstone caldera phenocrysts in all studied lavas and tuffs are remarkably homogenous at the crystal eruption and caldera scale and yield quilf temperatures of 750 25 c phase equilibrium experiments replicate the observed phenocryst assemblage at those temperatures and suggest that the magmas were all stored in the upper crust quartz hosted glass inclusions contain 1 0 2 5 h2o and 50 600 ppm co2 but some units are relatively rich in co2 300 600 ppm and some are co2 poor 50 200 ppm the co2 rich magmas were stored at 90 150 mpa and contained a fluid that was 60 75 mol co2 co2 poor magmas were stored at 50 70 mpa with a more h2o rich fluid x text co 2 40 60 storage pressures and volatiles do not correlate with eruption age volume or style trace element contents in glass inclusions and host matrix glass preserve a systematic evolution produced by crystal fractionation estimated to range from 36 12 to 52 12 wt because the erupted products contain 10 wt crystals crystal poor melts likely separated from evolving crystal rich mushes prior to eruption in the tuffs of bluff point and cold mountain creek matrix glass is less evolved than most inclusions which may indicate that more primitive rhyolite was injected into the reservoir just before those eruptions the presence and dissolution of granophyre in one flow may record evidence for heating prior to eruption and also demonstrate that the yellowstone magmatic system may undergo rapid changes the variations in depth suggest the magmas were sourced from multiple chambers that follow similar evolutionary paths in the upper crust

a dynamical ocean feedback mechanism for the madden julian oscillation composite analysis is applied to study the dynamical ocean response to madden julian mj events measured by anomalies in sea surface height from the merged topex poseidon european remote sensing satellite altimetry dataset in each of the tropical ocean basins significant equatorial waves are forced which are shown to modulate the sea surface temperature sst by 0 2 0 3 degc in the absence of strong surface heat fluxes in the indian ocean there is a clear dynamical response which may play a significant role in generating later mj events surface westerly winds associated with the active phase of the madden julian oscillation mjo force an eastward propagating oceanic downwelling equatorial kelvin wave which on reaching the eastern boundary at sumatra forces reflected downwelling equatorial rossby waves and coastal kelvin waves the coastal kelvin waves propagate southwards towards northern australia and northwards into the bay of bengal and will be important for local physical chemical and biological processes the equatorial rossby waves propagate westward across the indian ocean arriving in the western indian ocean approximately 80 100 days after the initial kelvin wave was generated the arrival of these waves generates positive sst anomalies which leads to convection and may trigger the next but one mj event or amplify the low frequency tail of the mjo this constitutes a coupled feedback mechanism from the ocean dynamics onto the mjo somewhat similar to the delayed oscillator mechanism for the el nino southern oscillation

evolution of salt marsh cliffs in muddy and sandy systems a qualitative comparison of british west coast estuaries salt marsh cliffs in the muddy severn estuary are mostly strong and tall they are retreating in response to the erosive attack of wave and tidal currents chiefly through toppling failures and rotational slips in the sandy solway firth and morecambe bay systems marsh cliffs are strong only in their upper parts where a dense root mat of marsh grasses binds the sediments here cantilever and toppling failures are the main response of the cliffs to tidal and wave erosion the differences between the three estuarine systems in the mechanisms of marsh cliff erosion are partly reflected in the mode of preservation of the cliffs on the restoration of the conditions leading to renewal of marsh growth

large scale textural patterns and sedimentary processes on tidal salt marshes in the severn estuary southwest britain abstract approximately 840 km2 of largely reclaimed estuarine alluvium border the severn estuary and inner bristol channel today using a direct measure of grain size and the proxy evidence of sediment controlled early land use medieval early modern it is shown that the grain size of the tidal mud deposited on the marshes prior to reclamation declined outward from the main and larger tidal channels toward the bedrock limit of the alluvium variations in the altitude of the marsh surfaces as they survive after reclamation suggest that the deposition rate of this sediment also decreased outward from these sources at elmore a representative narrow ca 1 km marsh grain size change is steep and well defined in contrast at hill in a representative sector from a large and broad ca 5 km marsh the measured change is gradual and disorderly and disturbed by an extensive arcuate belt of relatively coarse sediments based on a review of processes and sedimentation and appealing to a broad geomorphological and hydraulic analogy between tidal wetlands and river floodplains it is suggested that marshes of the elmore type may be supplied with sediment largely by transverse diffusion from the tidal channel whereas hill type marshes may receive considerable mud by convection as well as diffusion

tropospheric turbulence over the tropical open ocean role of gravity waves a large set of soundings obtained in the indian ocean during 3 field campaigns is used to provide statistical characteristics of tropospheric turbulence and its link with gravity wave gw activity the thorpe method is used to diagnose turbulent regions of a few hundred meters depth above the mixed layer turbulence frequency varies from 10 in the lower troposphere up to 30 around 12km heights gw are captured by their signature in horizontal wind normalized temperature and balloon vertical ascent rate these parameters emphasize different parts of the wave spectrum from longer to shorter vertical wavelengths respectively composites are constructed in order to reveal the vertical structure of the waves and their link with turbulence the relatively longer wavelength gw described by their signature in temperature gwt are more active in the lower troposphere where they are associated with clear variations in moisture turbulence is then associated with minimum static stability and vertical shear stressing the importance of the former and the possibility of convective instability conversely the short waves described by their signature in balloon ascent rate gww are detected primarily in the upper troposphere and their turbulence is associated with a vertical shear maximum suggesting the importance of dynamic instability furthermore gww appear to be linked with local convection whereas gwt are more active in suppressed and dry phases in particular of the madden julian oscillation these waves maybe associated with remote sources such as organized convection or local fronts such as those associated with dry air intrusions

the timing and origin of pre and post caldera volcanism associated with the mesa falls tuff yellowstone plateau volcanic field abstract we present new sanidine 40ar 39ar ages and paleomagnetic data for pre and post caldera rhyolites from the second volcanic cycle of the yellowstone plateau volcanic field which culminated in the caldera forming eruption of the mesa falls tuff at ca 1 3 ma these data allow for a detailed reconstruction of the eruptive history of the second volcanic cycle and provide new insights into the petrogenesis of rhyolite domes and flows erupted during this time period 40ar 39ar age data for the biotite bearing bishop mountain flow demonstrate that it erupted approximately 150 kyr prior to the mesa falls tuff integrating 40ar 39ar ages and paleomagnetic data for the post caldera island park rhyolite domes suggests that these five crystal rich rhyolites erupted over a centuries long time interval at 1 2905 0 0020 ma 2 the biotite bearing moonshine mountain rhyolite dome was originally thought to be the downfaulted vent dome for the pre caldera bishop mountain flow due to their similar petrographic and oxygen isotope characteristics but new 40ar 39ar dating suggest that it erupted near contemporaneously with the island park rhyolite domes at 1 2931 0 0018 ma 2 and is a post caldera eruption despite their similar eruption ages the island park rhyolite domes and the moonshine mountain dome are chemically and petrographically distinct and are not derived from the same source integrating these new data with field relations and existing geochemical data we present a petrogenetic model for the formation of the post mesa falls tuff rhyolites renewed influx of basaltic and or silicic recharge magma into the crust at 1 2905 0 0020 ma led to 1 the formation of the island park rhyolite domes from the source region that earlier produced the mesa falls tuff and 2 the formation of moonshine mountain dome from the source region that earlier produced the biotite bearing bishop mountain flow these magmas were stored in the crust for less than a few thousand years before being erupted contemporaneously along a 30 km long structurally controlled vent zone related to extracaldera basin and range faults these data highlight the rapidity with which magma can be generated and erupted over large distances at yellowstone

microphysical characteristics of mjo convection over the indian ocean during dynamo the microphysical characteristics of precipitating convection occurring in various stages of the madden julian oscillation mjo over the indian ocean are determined from data obtained from the national center for atmospheric research dual polarimetric doppler s band radar s polka deployed as part of the dynamics of the mjo dynamo field experiment active mjo events with increased rainfall occurred in october november and december 2011 during each of these active mjo phases in addition to enhanced rainfall convection became deeper and ice phase microphysics played a greater role s polka consistently showed nonoriented small ice particles dominating the radar echoes at altitudes of 9 10 km dry aggregates concentrated between 7 and 9 km and wet aggregates and graupel near the melting level 5 km graupel occurred mainly in actively convective towers while the wet aggregates occurred almost exclusively in the stratiform regions of mesoscale convective systems mcss during each of the three multiweek mjo active phases the maximum rainfall occurred in short bursts lasting a few days each multiday rainy period began with deepening convective elements and a concurrent increase in occurrence of dry aggregates which maximized just prior to organization into mcss the peak rainfall occurrence coincided with the maximum coverage of the radar domain by mcss reflecting large stratiform regions that exhibited the most frequent occurrence of wet aggregates during the december active mjo phase however the mcss were shallower and had a slightly lower tendency for wet aggregates in the stratiform regions and therefore generally weaker brightbands

physical volcanology of the pavagadh rhyolites northern deccan traps stratigraphic structural and textural record of explosive and effusive eruptions abstract mount pavagadh 840 m in the northern deccan traps india is mainly composed of mafic lava flows picrites ankaramites mugearites basalts and capped by rhyolites rhyolites also found at lower elevations on and around the mountain are thought to represent blocks of the eroded upper rhyolites or local eruptions in situ although the pavagadh sequence has been studied for 150 years the stratigraphy structures textures and physical volcanology of the pavagadh rhyolites have been poorly documented and are discussed here at length the upper rhyolite sequence contains tens of non welded crystal bearing glass and pumice rich ash beds of 47 m total thickness these represent a primary fallout ash succession derived from distant plinian eruptions possibly corresponding with massive ignimbrite deposits recently recognised in saurashtra several hundred kilometers to the southwest the fallout ash succession is overlain by a 50 m thick lava flow showing well developed flow banding and folding basal and upper breccias and a local basal vitrophyre the lava flow is overlain by an ignimbrite with a basal vitrophyre both these units showing excellent vitroclastic textures the upper rhyolites thus represent alternating explosive effusive explosive eruptions the lower level rhyolites in the area showing intense rheomorphic deformation in outcrop but lacking vitroclastic textures are probably also lavas however they are not blocks of the eroded upper rhyolite lava flow but from separate eruptions the pavagadh rhyolites were probably far more laterally extensive than their present outcrops with a minimum original volume of 9 km3 their source areas remain unknown geochemical and geochronological work on the pavagadh rhyolites is needed in the stratigraphic and volcanological context provided here to understand their petrogenesis and potential relationship with the cretaceous palaeogene k pg boundary mass extinction

zircon petrochronology and 40ar 39ar sanidine dates for the mesa falls tuff crystal scale records of magmatic evolution and the short lifespan of a large yellowstone magma chamber

vertical velocity in oceanic convection off tropical australia abstract time series of 1 hz vertical velocity data collected during aircraft penetrations of oceanic cumulonimbus clouds over the western pacific warm pool as part of the equatorial mesoscale experiment emex are analyzed for updraft and downdraft events called cores an updraft core is defined as occurring whenever the vertical velocity exceeds 1 m s 1 for at least 500 m a downdraft core is defined analogously over 19 000 km of straight and level flight legs are used in the analysis five hundred eleven updraft cores and 253 downdraft cores are included in the dataset core properties are summarized as distributions of average and maximum vertical velocity diameter and mass flux in four altitude intervals between 0 2 and 5 8 km distributions are approximately lognormal at all levels examination of the variation of the statistics with height suggests a maximum in vertical velocity between 2 and 3 km slightly lower or equal vertical velocity is indicated at 5 km near the freezing level virtual t

origin and evolution of silicic magmatism at yellowstone based on ion microprobe analysis of isotopically zoned zircons the origin of large volume yellowstone ignimbrites and smallervolume intra caldera lavas requires shallow remelting of enormous volumes of variably o depleted volcanic and sub volcanic rocks altered by hydrothermal activity zircons provide probes of these processes as they preserve older ages and inherited do values this study presents a high resolution oxygen isotope examination of volcanism at yellowstone using ion microprobe analysis with an average precision of 0 2o and a 10 mm spot size we report 357 analyses of cores and rims of zircons and isotope profiles of 142 single zircons in 11 units that represent majoryellowstone ignimbrites and post caldera lavas many zircons from these samples were previously dated in the same spots by sensitive high resolution ion microprobe shrimp and all zircons were analyzed for oxygen isotope ratios in bulk as a function of grain size by laser fluorination we additionally report oxygen isotope analyses of quartz crystals in three units the results of this work provide the following new observations 1 most zircons from post caldera low do lavas are zoned with higher do values and highly variable u pb ages in the cores that suggest inheritance from pre caldera rocks exposed on the surface 2 many of the higher do zircon cores in these lavas have u pb zircon crystallization ages that postdate caldera formation but pre date the eruption age by 10 20 kyr and represent inheritance of unexposed post caldera sub volcanic units that have do similar to the lava creek tuff 3 young and voluminous 0 25 0 1ma intra caldera lavas which represent the latest volcanic activity atyellowstone contain zircons with both high do and lowdo cores surrounded by an intermediate do rim this implies inheritance of a variety of rocks from high do pre caldera and low do post caldera units followed by residence in a common intermediate do melt prior to eruption 4 major ignimbrites of huckleberry ridge and to a lesser extent the lava creek and mesa falls tuffs contain zoned zircons with lower do zircon cores suggesting that melting and zircon inheritance from the lowdo hydrothermally altered carapace was an important process during formation of these large magma bodies prior to caldera collapse 5 the do zoning in the majority of zircon core rim interfaces is step like rather than smoothly inflected suggesting that processes of solution reprecipitation were more important than intracrystalline oxygen diffusion concave downward zircon crystal size distributions support dissolution of the smaller crystals and growth of rims on larger crystals this study suggests that silicic magmatism atyellowstone proceeded via rapid shallow level remelting of earlier erupted and hydrothermally alteredyellowstone source rocks and that pulses of basaltic magma provided the heat for melting each postcaldera yellowstone lava represents an independent homogenized magma batch that was generated rapidly by remelting of source rocks of various ages and do values the commonly held model of a single large volume super solidus mushy state magma chamber that is periodically reactivated and produces rhyolitic offspring is not supported by our data rather the source rocks for theyellowstone volcanism were cooled below the solidus hydrothermally altered by heated meteoric waters that caused low do values and then remelted in distinct pockets by intrusion of basic magmas each packet of new melt inherited zircons that retained older age and do values this interpretation may have significance for interpreting seismic data for crustal low velocity zones in which magma mush and solidified areas experiencing hydrothermal circulation occur side by side new basalt intrusions into this solidifying batholith are required to form the youngest volcanic rocks that erupted as independent rhyolitic magmas we also suggest that the lava creek tuff

paleomagnetic correlation of columbia river basalt flows using secular variation a statistical method is developed to evaluate stratigraphic correlations that are based on the similarity of paleomagnetic directions it involves comparison of the probabilities that such directions could have arisen by either simultaneous or random samplings of the ancient magnetic field to calculate these probabilities one must estimate the effects of paleomagnetic errors and paleosecular variation respectively the method is tested successfully on sections of 8 10 grande ronde basalt columbia river basalt group flows at sentinel gap and umtanum ridge which are separated by only 25 km and contain two flows thought to be the same on geological grounds more significantly for widely separated sections at sentinel gap and butler canyon the analysis again shows that simultaneous magnetization is a much more likely explanation of the general similarity of paleomagnetic directions than chance agreement of ancient field directions the simplest interpretation of this result is that many of the flows at the two sites are the same implying that series of grande ronde flows extended over distances of several hundred kilometers

roles of deep and shallow convection and microphysics in the mjo simulated by the model for prediction across scales the november event of the madden julian oscillation mjo during the dynamo field campaign was simulated using the global compressible nonhydrostatic model for prediction across scales mpas with global coarse 60 and 15 km and regional the indian ocean cloud permitting 3 km meshes the purpose of this study is to compare roles of parameterized deep and shallow cumulus and microphysics in mjo simulations two cumulus schemes were used tiedtke and grell freitas the deep and shallow components of tiedtke scheme can be turned on and off individually the results reveal that microphysics alone without cumulus parameterization is able to produce strong signals of the mjo in precipitation with 3 km mesh and weak mjo signals with 15 km mesh a shallow scheme tiedtke along with microphysics strengthens the mjo signals but makes them less well organized on large scales a deep cumulus scheme can either improve the large scale organization of mjo precipitation produced by microphysics and shallow convection tiedtke or impair them grell freitas the deep scheme of tiedtke cannot reproduce the mjo well without its shallow counterpart the main role of shallow convection in the model is to transport moisture upward to the lower mid troposphere by doing so it removes dry biases in the lower mid troposphere a distinct feature in simulations with weak or no mjo signals and enhances total precipitation and diabatic heating produced by microphysics and deep cumulus schemes changing model grid spacing from 60 to 15 km makes a little difference in the model fidelity of reproducing the mjo all roles of shallow convection in 15 km simulations with parameterized deep convection cannot be reproduced in 3 km simulations without parameterized deep convection results from this study suggest that we should pay more attention to the treatment of shallow convection and its connection to other parameterized processes for improving mjo simulations in other words a holistic approach should be taken that consider parameterization of shallow cumulus microphysics boundary layer as well as deep cumulus as a whole for model improvement

crystal scale anatomy of a dying supervolcano an isotope and geochronology study of individual phenocrysts from voluminous rhyolites of the yellowstone caldera a voluminous 600 km3 and long lived 520 75 ka phase of rhyolitic eruptions followed collapse of the yellowstone caldera 640 ka whether these eruptions represent a dying cycle or the growth of a new magma chamber remains an important question we use new u th zircon ages and 18o values determined by ion microprobe and sanidine pb isotope ratios determined by laser ablation to investigate the genesis of voluminous post caldera rhyolites the oldest post caldera rhyolites erupted between 520 and 470 ka exhibit extreme age and oxygen isotopic heterogeneity requiring derivation from individual parcels of low 18o melts we find a progressive increase in zircon homogeneity for rhyolite eruptions from 260 to 75 ka with homogeneous low 18o zircon values of 2 7 2 8 that are in equilibrium with low 18o host melts for the majority of the youngest eruptions new sanidine pb isotope data define separate arrays for post caldera rhyolites and the caldera forming tuffs that preceded them indicating that they were not sourced from a mushy lava creek tuff batholith that remained after caldera collapse rather our new age and isotopic data indicate that the post caldera rhyolites were generated by remelting of a variety of intracaldera source rocks consisting of pre lava creek tuff volcanic and plutonic rocks and earlier erupted post lava creek tuff rhyolites batch assembly of low 18o melts starting at 260 ka resulted in progressive homogenization followed by differentiation and cooling up until the last rhyolite eruption 75 ka a trend that we interpret to be characteristic of a dying magma reservoir beneath the yellowstone caldera

magma mixing and the generation of isotopically juvenile silicic magma at yellowstone caldera inferred from coupling 238 u 230 th ages with trace elements and hf and o isotopes in zircon and pb isotopes in sanidine the nature of compositional heterogeneity within large silicic magma bodies has important implications for how silicic reservoirs are assembled and evolve through time we examine compositional heterogeneity in the youngest 170 to 70 ka post caldera volcanism at yellowstone caldera the central plateau member cpm rhyolites as a case study we compare 238u 230th age trace element and hf isotopic data from zircons and major element ba and pb isotopic data from sanidines hosted in two cpm rhyolites hayden valley and solfatara plateau flows and one extracaldera rhyolite gibbon river flow all of which erupted near the caldera margin ca 100 ka the hayden valley flow hosts two zircon populations and one sanidine population that are consistent with residence in the cpm reservoir the gibbon river flow hosts one zircon population that is compositionally distinct from hayden valley flow zircons the solfatara plateau flow contains multiple sanidine populations and all three zircon populations found in the hayden valley and gibbon river flows demonstrating that the solfatara plateau flow formed by mixing extracaldera magma with the margin of the cpm reservoir this process highlights the dynamic nature of magmatic interactions at the margins of large silicic reservoirs more generally hf isotopic data from the cpm zircons provide the first direct evidence for isotopically juvenile magmas contributing mass to the youngest post caldera magmatic system and demonstrate that the sources contributing magma to the cpm reservoir were heterogeneous in 176hf 177hf at ca 100 ka thus the limited compositional variability of cpm glasses reflects homogenization occurring within the cpm reservoir not a homogeneous source

multiscale variability of deep convection in relation to large scale circulation in toga coare deep convection over the indo pacific oceanic warm pool in the tropical ocean global atmosphere coupled ocean atmosphere response experiment toga coare occurred in cloud clusters which grouped together in regions favoring their occurrence these large groups of cloud clusters produced large scale regions of satellite observed cold cloud top temperature this paper investigates the manner in which the cloud clusters were organized on time and space scales ranging from the seasonal mean pattern over the whole warm pool region to the scale of individual cloud clusters and their relationship to the large scale circulation and sea surface temperature sst the dominant convective variability was associated with the intraseasonal oscillation iso a large eastward propagating ensemble of cloud clusters marked the iso s progress the meridional structure of the iso was strongly affected by the seasonal cycle with a southward shift from the northern hemisphere in october november to the southern hemisphere in january february the sst had an intraseasonal signal in lagged quadrature with the cold cloudiness and rainfall in coare the sst increased decreased during the convectively suppressed active phases of the iso enhanced low level westerly winds occurred toward the later stages of the enhanced convection periods of the iso though not always centered at the equator the strongest westerlies tended to be located between two synoptic scale cyclonic gyres which were often not symmetric about the equator in the low level wind field this asymmetry in the anomalous equatorial low level westerlies may have different implications for the oceanic response in the coupled atmosphere ocean system than those centered on the equator the cyclonic gyres contained highly concentrated deep convection and in four cases the gyres developed into tropical cyclones within the envelope marking the convectively active phase of the iso cloud clusters were frequently concentrated into westward propagating disturbances with a local periodicity of similar to 2 days these 2 day disturbances have been identified in earlier spectral studies and appear to be related to westward propagating inertio gravity waves in coare they typically contained numerous cloud clusters which underwent a distinct diurnal cycle most of the cloud clusters embedded in the 2 day disturbances moved westward though some were stationary and a few moved eastward a cloud duster tracking program identified groups of clusters lime dusters that exhibited continuity in time and space in the most convectively active period of the iso the tracking program identified almost the entire iso cloud ensemble as a long lasting trackable superconvective system this observation indicates the lack of a distinct scale separation between convection and large scale disturbances during the most intense convective periods in coare

clouds associated with the madden julian oscillation a new perspective from cloudsat abstractthe evolution of total cloud cover and cloud types is composited across the madden julian oscillation mjo using cloudsat data for june 2006 may 2010 two approaches are used to define mjo phases 1 the local phase is determined at each longitude and time from filtered outgoing longwave radiation and 2 the global phase is defined using a popular real time multivariate mjo rmm index which assigns the tropics to an mjo phase each day in terms of local phase cloudsat results show a familiar evolution of cloud type predominance in the growing stages shallow clouds coexist with deep intense but narrow convective systems widespread cloud coverage and rainfall appear during the active phases becoming more anvil dominated with time and finally suppressed conditions return results are compared to the convectively coupled kelvin wave which has a similar life cycle to the mjo convection in the mjo tends to be modulated more by moisture variations compared to the kelvin wave in terms of globa

climatology of banded precipitation over the contiguous united states abstracta climatology of banded precipitation features over the contiguous united states from 2003 to 2014 is constructed a band is defined as a precipitation feature with a major axis of 100 km or greater and a ratio of major axis length to minor axis length hereafter aspect ratio of 3 1 or greater by applying an automated feature based detection algorithm to composite radar imagery a database of 48 916 844 precipitation features is created of which 7 213 505 14 8 are bands this algorithm produces the first climatology of precipitation bands over the contiguous united states banded precipitation occurrence is broadly similar to total precipitation occurrence with a maximum of 175 h of banded precipitation annually over the ohio river valley in the warm season there is a strong diurnal signature associated with convective storm development for both the precipitation feature area and total area covered by precipitation but little diurnal signature in aspect ratio strong west east gradients

long range lightning geolocation using a vlf radio atmospheric waveform bank 1 lightning discharges generate broadband electromagnetic pulses with a peak component in the very low frequency vlf 3 30 khz range vlf waves propagate through the earth ionosphere waveguide with relatively low attenuation enabling the detection of these radio atmospherics at great distances from the lightning discharge a new technique of long range 6000 km global lightning geolocation via sferic detection is presented this new technique catalogs the dominant variation in expected received waveforms in a set of waveform banks which are then used to estimate the propagation distance and accurately determine the arrival time using three sensors in a trial network this new technique is used to demonstrate a median accuracy of 1 4 km depending on the time of day an overall cloud to ground cg stroke detection efficiency between 40 and 60 is estimated by correlating individual lightning stroke events to data from the national lightning detection network nldn additional events reported by the trial network are shown to have a tight spatial clustering to storm clusters identified by nldn suggesting that many of the unmatched events correspond to weak cloud to ground strokes m components or cloud pulses exploiting an empirical correlation between peak vlf field strength and peak current values reported by nldn we also provide unvalidated estimates of the peak current and lightning channel polarity the trial network does not distinguish between cloud and ground discharges so these peak current estimates only relate to an earth referenced channel current for the subset of reported events that are return strokes

the vertical profile of radar reflectivity of convective cells a strong indicator of storm intensity and lightning probability abstract reflectivity data from doppler radars are used to construct vertical profiles of radar reflectivity vprr of convective cells in mesoscale convective systems mcss in three different environmental regimes the national center for atmospheric research cp 3 and cp 4 radars are used to calculate median vprr for mcss in the oklahoma kansas preliminary regional experiment for storm central in 1985 the national oceanic and atmospheric administration tropical ocean global atmosphere radar in darwin australia is used to calculate vprr for mcss observed both in oceanic monsoon regimes and in continental break period regimes during the wet seasons of 1987 88 and 1988 89 the midlatitude and tropical continental vprrs both exhibit maximum reflectivity somewhat above the surface and have a gradual decrease in reflectivity with height above the freezing level in sharp contrast the tropical oceanic profile has a maximum reflectivity at the lowest level and a very rapid decrease in reflectivity with he

the oxygen isotope composition of karoo and etendeka picrites high δ18o mantle or crustal contamination oxygen isotope compositions of karoo and etendeka large igneous province lip picrites and picrite basalts are presented to constrain the effects of crustal contamination versus mantle source variation olivine and orthopyroxene phenocrysts from lavas and dykes mg 64 80 from the tuli and mwenezi nuanetsi regions of the ca 180 ma karoo lip have 18o values that range from 6 0 to 6 7 they appear to have crystallized from magmas having 18o values about 1 1 5 higher than expected in an entirely mantle derived magma olivines from picrite and picrite basalt dykes from the ca 135 ma etendeka lip of namibia and karoo age picrite dykes from dronning maud land antarctica do not have such elevated 18o values a range of 18o values from 4 9 to 6 0 and good correlations between 18o value and sr nd and pb isotope ratios for the etendeka picrites are consistent with previously proposed models of crustal contamination explanations for the high 18o values in tuli mwenezi picrites are limited to 1 alteration 2 crustal contamination and 3 derivation from mantle with an abnormally high 18o previously a variety of models that range from crustal contamination to derivation from the enriched mantle lithosphere have been suggested to explain high concentrations of incompatible elements such as k and average end and esr values of 8 and 16 in mwenezi nuanetsi picrites however the primitive character of the magmas mg 73 combined with the lack of correlation between 18o values and radiogenic isotopic compositions mgo content or mg is inconsistent with crustal contamination thus an 18o enriched mantle source having high incompatible trace element concentration and enriched radiogenic isotope composition is indicated high 18o values are accompanied by negative nb and ta anomalies consistent with the involvement of the mantle lithosphere whereas the high 18o themselves are consistent with an eclogitic source magma 18o values about 1 higher than expected for mantle derived magma are also a feature of the bushveld mafic and ultramafic magmas and the possibility exists that a long lived 18o enriched mantle source has existed beneath southern africa a mixed eclogite peridotite source could have developed by emplacement of oceanic lithosphere into the cratonic keel during archaean subduction

the relationship between the itcz and mjo initiation over the indian ocean abstractunderstanding convective initiation of the madden julian oscillation mjo remains an unmet challenge mjo initiation has been perceived as a process starting from a convectively suppressed

revised ages for tuffs of the yellowstone plateau volcanic field assignment of the huckleberry ridge tuff to a new geomagnetic polarity event 40 ar 39 ar ages were determined on the three major ash flow tuffs of the yellowstone plateau volcanic field in the region of yellowstone national park in order to improve the precision of previously determined ages total fusion and incremental heating ages of sanidine yielded the following mean ages huckleberry ridge tuff 2 059 0 004 ma mesa falls tuff 1 285 0 004 ma and lava creek tuff 0 639 0 002 ma the huckleberry ridge tuff has a transitional magnetic direction and has previously been related to the reunion normal polarity subchron dating of the reunion event has been reviewed and its ages have been normalized to a common value for mineral standards the age of the huckleberry ridge tuff is significantly younger than lava flows of the reunion event on re union island supporting other evidence for a normal polarity event younger than the reunion event