the dominant intraseasonal mode of intraseasonal south asian summer monsoon from june through september the intraseasonal variability of the asian summer monsoon is dominated by the so called monsoon intraseasonal oscillation miso this paper provides a comprehensive description of the miso based on outgoing longwave radiation olr data the miso is characterized by alternating active periods in which the primary rain area of the asian summer monsoon that stretches from the northern arabian sea east southeastward almost all the way to the northwest pacific intertropical convergence zone is relatively intense and break periods in which the heaviest rainfall shifts from south asia to the central and eastern equatorial indian ocean the miso is attended by well defined but weak sea surface temperature sst perturbations whose phase is indicative of a negative feedback upon the atmospheric perturbations meridional profile of variables on the various regression maps shown in this paper averaged along a set of tilted axes parallel to the west northwest to east southeast wnw ese sloping lines in empirical orthogonal function 1 of olr have been made and it is found that the strongest westerly 850 hpa wind anomalies are located two grid points 5 of latitude to the south of the reference latitude at the 150 hpa level the meridional profile of divergence is closely aligned with the olr profile sst profile is lowest at approximately 2 5 of latitude to the south of the minimum olr and 2 5 to the north of the strongest westerly 850 hpa wind anomalies the sea level pressure profiles and the midlower tropospheric geopotential height profiles are almost in phase it is observed that in most years there are two three bands of intensified and suppressed rainfall that cross the reference line from south to north northward propagating at the interval of 30 60 days over south asia the degree of correspondence between the miso and active and break spells of the indian summer monsoon rainfall is also documented

application of extended empirical orthogonal function analysis to interrelationships and sequential evolution of monsoon fields abstract extended empirical orthogonal function eeof analysis has been employed to study linear relationships among the mean sea level pressure 700 mb height and rainfall over india and their low frequency sequential evolution during the peak summer monsoon months the interrelationships between these fields are strongest over central india and while the rainfall activity is colocated with the corresponding changes in the 700 mb heights it is displaced southward with respect to the pressure changes the first two eeof s of all the three fields averaged over 5 or 7 days show that the dominant low frequency sequential evolution is associated with north and northeastward movement of the anomaly centers with a recurrence period of about 40 days in addition the presence of a westward moving wave in sea level pressure anomalies located roughly near 15 n latitude is revealed by the third eeof

on the anomalous precipitation enhancement over the himalayan foothills during monsoon breaks an intriguing feature associated with breaks in the indian summer monsoon is the occurrence of intense flood producing precipitation confined to central eastern parts of the himalayan ceh foothills and north eastern parts of india past studies have documented various large scale circulation aspects associated with monsoon breaks however the dynamical mechanisms responsible for anomalous precipitation enhancement over ceh foothills remain unclear this problem is investigated using diagnostic analyses of observed and reanalysis products and high resolution model simulations the present findings show that the anomalous precipitation enhancement over the ceh foothills during monsoon breaks emerges as a consequence of interactions between southward intruding mid latitude westerly troughs and the south asian monsoon circulation in its weak phase these interactions facilitate intensification of mid tropospheric cyclonic vorticity and strong ascending motion over the ceh foothills so as to promote deep convection and concentrated rainfall activity over the region during monsoon breaks mesoscale orographic effects additionally tend to amplify the vertical motions and precipitation over the ceh foothills as evidenced from the high resolution model simulations it is further noted from the model simulations that the coupling between precipitation and circulation during monsoon breaks can produce nearly a threefold increase of total precipitation over the ceh foothills and neighborhood as opposed to active monsoon conditions

synsedimentary formation of ooidal ironstone an example from the jurassic deposits of se central iran abstract the study of the upper lower to middle jurassic badamu formation in se of central iran represents the first report of jurassic ooidal ironstone in iran and exhibits a record of ferruginous radial ooid dominated ironstone the studies showed that this chamosite or ferric oxide chamosite type ooidal ironstone is similar to minette type ironstones a shoreface zone in an epeiric or epicontinental sea is proposed for formation and accumulation of the ferruginous ooids and the ooidal ironstone fe derived from lateritic weathering has been transported into the shoreface zone via a fluvial current during the synsedimentary formation of the ooidal ironstone during the periods with moderate to lower energy or weakly agitated and quiet environmental conditions suspended ferruginous small radial ooids and fe were increased in the lower shoreface subzone higher environmental energy resulted in the development of large concentric ooids and limited distribution of fe in the upper shoreface subzone higher environmental energy also prevented the development of radial ooids and restricted fe precipitation on carbonate ooids variations in environmental energy in the middle shoreface subzone were unfavorable for increasing ferruginous ooids and fe in the environment although short term periods with weakly agitated and quiet or moderate to lower energy conditions could had been existed in the middle shoreface subzone but precipitation of fe on a few small radial ooids was allowed environmental energy in the shoreface zone was the major factor controlling precipitation of fe especially suspended river fe loads on the ooids however precipitation of dissolved fe could have been related to oxidizing conditions in the environment also the probable presence of fe oxidizing bacteria in the cortexes of the ferruginous small radial ooids indicates that bacteria could have possibly contributed to precipitation of fe on the ooids in a calm environment

stromatolites the challenge of a term in space and time abstract several definitions of stromatolites are discussed and kalkowsky s most important statements about stromatolites are translated from german to english a new definition for stromatolites is proposed namely stromatolites are laminated rocks the origin of which can clearly be related to the activity of microbial communities which by their morphology physiology and arrangement in space and time interact with the physical and chemical environment to produce a laminated pattern which is retained in the final rock structure unconsolidated laminated systems clearly related to the activity of microbial communities and often called recent stromatolites or living stromatolites are defined as potential stromatolites the main microbial activities which are important in the formation of potential stromatolites and stromatolites are described and examples of stromatolites of various types including iron stromatolites are also described

vertical structures of anvil clouds of tropical mesoscale convective systems observed by cloudsat abstracta global study of the vertical structures of the clouds of tropical mesoscale convective systems mcss has been carried out with data from the cloudsat cloud profiling radar tropical mcss are found to be dominated by cloud top heights greater than 10 km secondary cloud layers sometimes occur in mcss but outside their primary raining cores the secondary layers have tops at 6 8 and 1 3 km high topped clouds extend outward from raining cores of mcss to form anvil clouds closest to the raining cores the anvils tend to have broader distributions of reflectivity at all levels with the modal values at higher reflectivity in their lower levels portions of anvil clouds far away from the raining core are thin and have narrow frequency distributions of reflectivity at all levels with overall weaker values this difference likely reflects ice particle fallout and therefore cloud age reflectivity histograms of mcs anvil clouds vary little across the tropics except that i in continental mcs anvils

interaction of low level flow with the western ghat mountains and offshore convection in the summer monsoon abstract seven year averaged values of percent frequency of occurrence of highly reflective cloud for the months june july and august indicate that offshore convection is a major component of the cloudiness of the southwest monsoon principal areas of convection occur off of the western coats of india burma thailand and the philippines this study concentrates on the area upstream of the western ghats mountains of india analysis of a special boundary layer mission flown during the wmo icsu summer monsoon experiment leads us to believe that partial deceleration of the monsoon flow by upstream blocking effects of the mountains initiates and maintains a vertical and horizontal motion field that could support the observed convection data obtained on this mission allow a large scale momentum budget computation for the subcloud layer which shows pressure deceleration to be significant the budget dominated by advection predicts an increase of average wind speed which is observed the pressure decelera

facies analysis and palaeoclimatic significance of ironstones formed during the eocene greenhouse lower and middle eocene ironstone sequences of the naqb and qazzun formations from the north east bahariya depression western desert egypt represent a proxy for early palaeogene climate and sea level changes these sequences represent the only palaeogene economic ooidal ironstone record of the southern tethys these ironstone sequences rest unconformably on three structurally controlled cenomanian palaeohighs for example the gedida harra and ghorabi mines and formed on the inner ramp of a carbonate platform these palaeohighs were exposed and subjected to subaerial lateritic weathering from the cenomanian to early eocene the lower and middle eocene ironstone sequences consist of quiet water ironstone facies overlain by higher energy ironstone facies the distribution of low energy ironstone facies is controlled by depositional relief these deposits consist of lagoonal burrow mottled mud ironstone and laterally equivalent tidal flat stromatolitic ironstones the agitated water ironstone facies consist of shallow subtidal intertidal nummulitic ooidal oncoidal and back barrier storm generated fossiliferous ironstones the formation of these marginal marine sequences was associated with major marine transgressive regressive megacycles that separated by subaerial exposure and lateritic weathering the formation of lateritic palaeosols with their characteristic dissolution and reprecipitation features such as colloform texture and alveolar voids implies periods of humid and warm climate followed major marine regressions the formation of the lower to middle eocene ironstone succession and the associated lateritic palaeosols can be linked to the early palaeogene global warming and eustatic sea level changes the reworking of the middle eocene palaeosol and the deposition of the upper eocene phosphate rich glauconitic sandstones of the overlying hamra formation may record the initial stages of the palaeoclimatic transition from greenhouse to icehouse conditions

origin of ooidal ironstones in relation to warming events cretaceous eocene bakchar deposit south east western siberia abstract an integrated study involving petrographical mineralogical and geochemical investigations proposes the origin of the bakchar ironstone deposit by upward migration of a mixture of fe rich brine and hydrothermal fluid through marine sediments trace element concentrations of the ironstone deposits rule out continental derivation of fe while high ree concentrations indicate mixed hydrogeneous and hydrothermal source three main types of ironstone within the bakchar deposit are characterized by distinct mineralogical assemblage of authigenic minerals corresponding to oxic methanic and weakly sulfidic dysoxic conditions changing redox conditions of the depositional environment methane seepage in warm seawater and availability of iron influx possibly determined the final mineralogy of three varieties of ironstones the association of siderite with ferrimagnetic sulfides like greigite and pyrrhotite in type 1 ore indicate anaerobic oxidation of methane with limited bacterial sulfate reduction the ironstone deposits of narym kolpashevo and bakchar are contemporaneous with geological events like ocean anoxic event 3 oae 3 cretaceous paleogene k pg boundary and palaeocene eocene thermal maximum petm respectively all corresponding to warm seawater conditions

the dynamic and thermodynamic structure of the monsoon over southern india new observations from the incompass iop some of the highest summer monsoon rainfall in south asia falls on the windward slopes of the western ghats mountains on india s west coast and offshore over the eastern arabian sea understanding of the processes determining the spatial distribution and temporal variability of this region remains incomplete in this paper new interaction of convective organization and monsoon precipitation atmosphere surface and sea incompass aircraft and ground based measurements of the summer monsoon over the western ghats and upstream of them are presented and placed within the context of remote sensing observations and reanalysis the transition from widespread rainfall over the eastern arabian sea to rainfall over the western ghats is documented in high spatial and temporal resolution heavy rainfall offshore during the campaign was associated primarily with mid tropospheric humidity secondarily with sea surface temperature and only weakly with orographic blocking a mid tropospheric dry intrusion suppressed deep convection offshore in the latter half of the campaign allowing the build up of low level humidity in the onshore flow and enhancing rainfall over the mountains rainfall on the lee side of the western ghats occurred during the latter half of the campaign in association with enhanced mesoscale easterly upslope flow diurnal cycles in rainfall offshore maximum in the morning and on the mountains maximum in the afternoon were observed considerable zonal and temporal variability was seen in the offshore boundary layer suggesting the presence of convective downdrafts and cold pools persistent drying of the subcloud mixed layer several hundred kilometres off the coast was observed suggesting strong mixing between the boundary layer and the free troposphere these observations provide quantitative targets to test models and suggest hypotheses on the physical mechanisms determining the distribution and variability in rainfall in the western ghats region

monsoon convection in the himalayan region as seen by the trmm precipitation radar three dimensional structure of summer monsoon convection in the himalayan region and its overall variability are examined by analyzing data from the tropical rainfall measuring mission trmm precipitation radar over the june september seasons of 2002 and 2003 statistics are compiled for both convective and stratiform components of the observed radar echoes deep intense convective echoes 40 dbz echo reaching heights 10 km occur primarily just upstream south of and over the lower elevations of the himalayan barrier especially in the northwestern concave indentation of the barrier the deep intense convective echoes are vertically erect consistent with the relatively weak environmental shear they sometimes extend above 17 km indicating that exceptionally strong updraughts loft graupel to high altitudes occasionally scattered isolated deep intense convective echoes occur over the tibetan plateau wide intense convective echoes 40 dbz echo 1000 km2 in horizontal dimension also occur preferentially just upstream of and over the lower elevations of the himalayas most frequently in the northwestern indentation of the barrier the wide intense echoes have an additional tendency to occur along the central portion of the himalayas and they seldom if ever occur over the tibetan plateau the wide intense echoes exhibit three mesoscale structures amorphous areas lines parallel to the mountain barrier and arc shaped squall lines perpendicular to and propagating parallel to the steep himalayan barrier the latter are rare generally weaker than those seen in other parts of the world and occur when a midlevel jet is aligned with the himalayan escarpment deep and wide intense convective echoes over the northwestern subcontinent tend to occur where the low level moist layer of monsoon air from the arabian sea meets dry downslope flow in a manner reminiscent of severe convection leeward of the rocky mountains in the central usa as the low level layer of moist air from the sea moves over the hot arid northwestern subcontinent it is capped by an elevated layer of dry air advected off the afghan or tibetan plateau the capped low level monsoonal airflow accumulates instability via surface heating until this instability is released by orographically induced lifting immediately adjacent to or directly over the foothills of the himalayas broad 50 000 km2 in area stratiform echoes occur in the eastern and central portions of the himalayan region in connection with bay of bengal depressions their centroids are most frequent just upstream of the himalayas in the region of the concave indentation of the barrier at the eastern end of the range the steep topography apparently enhances the formation and longevity of the broad stratiform echoes monsoonal depressions provide a moist maritime environment for the convection evidently allowing mesoscale systems to develop larger stratiform echoes than in the western himalayan region copyright 2007 royal meteorological society

interplay between depositional facies diagenesis and early fractures in the early cretaceous habshan formation jebel madar oman abstract diagenesis and fracturing can significantly alter petrophysical properties of subsurface carbonate reservoirs but the impacts of these processes at the inter well scale are hard to predict however the initial distribution of sedimentary facies is easier to predict and could template future diagenetic transformation and potentially influence fracturing as well this paper provides a case study investigating the mutual influence of depositional facies on diagenesis and interpreted early fractures in the berriasian valanginian habshan formation in jebel madar oman the habshan formation mostly comprises ooidal limestones but dolomitized beds a few metres in thickness and laterally correlatable over at least 5 km are present discordant vertical dolomite streaks are present in the limestone but are rare the various sedimentary and diagenetic processes were investigated using fieldwork xrd analysis petrography and geochemistry major and trace elements stable carbon and oxygen isotopes and strontium isotopes the lithologies consist of mud lean ooidal grainstones mud rich ooidal packstones and bioturbated limestones the changes in the amount of fine grained sediment suggest changing energy conditions at a backshoal position of a carbonate platform the mud lean versus mud rich depositional textures impacted on early diagenesis by promoting abundant calcite cementation in the mud lean ooidal grainstones and dolomitization in the mud rich packstones the discordant bodies interpreted as sediment filled early fractures are dolomitized in the same way as the mud rich ooidal packstones dolomitization occurred probably during the valanginian hauterivian in a shallow burial setting and was most likely caused by seepage reflux salt doming post dated dolomitization of the habshan formation the results of this study document the inter relationship between sedimentary facies early diagenesis and early fractures

acigol rhyolite field central anatolia part 1 high resolution dating of eruption episodes and zircon growth rates protracted pre eruptive zircon residence is frequently detected in continental rhyolites and can conflict with thermal models indicating briefer magma cooling durations if scaled to erupted volumes here we present combined u th and u th he zircon ages from the acigol rhyolite field central anatolia turkey which is part of a quaternary bimodal volcanic complex unlike other geochronometers this approach dates crystallization and eruption on the same crystals allowing for internal consistency testing despite the overall longevity of acigol rhyolite volcanism and systematic trends of progressive depletion in compatible trace elements and decreasing zircon saturation temperatures we find that zircon crystallized in two brief pulses corresponding to eruptions in the eastern and western part of the field during middle and late pleistocene times respectively for late pleistocene zircon resolvable differences exist between interior average 30 7 0 9 ka 1 error and rim 21 9 1 3 ka crystallization ages these translate into radial crystal growth rates of 10 13 to 10 14 cm s broadly consistent with those constrained by diffusion experiments rim crystallization and u th he eruption ages 24 2 0 4 ka overlap within uncertainty evidence for brief zircon residence at acigol contrasts with many other rhyolite fields suggesting that protracted zircon crystallization in or recycling from long lived crystal mushes is not ubiquitous in continental silicic magma systems instead the span of pre eruptive zircon ages is consistent with autochthonous crystallization in individual small volume magma batches that originated from basaltic precursors

geophysiology of mineral deposits a model for a biological driving force of global changes through earth history the upper mantle crust hydrosphere and atmosphere of earth are kept in a geophysical geochemical and thermodynamical state far from astrophysical and planetary equilibrium the system oscillates around a quasi stable centre following laws governing dissipative or dynamic systems the energy and materials necessary for such global pseudo equilibria are fed in stored and released on a geological time scale by a the energy and electron channelling processes of photosynthesis respiration and fermentation b biologically controlled accumulation of energy and matter into crustal reservoirs and much later c release of the latter from crust and upper mantle into surface related geotectonical and geochemical cycles phototrophic and chemorganotrophic bacterial microorganisms of microbial mats potential stromatolites or microbialites are capable of anoxygenic and oxygenic photosynthesis of aerobic and anaerobic respiration and of organic and inorganic fermentation i e disproportioning of energy rich molecules in this way large amounts of photosynthate are transformed on a global scale into hydrocarbons and sulphides sulphate serving as electron acceptor for anaerobic respiration or fermentation inorganic reduced compounds produced by the same processes of photosynthesis followed by respiration and fermentation are stored as sulphides of iron lead zinc silver gold etc all the aforementioned microbial processes can transfer energies and matter at a global scale thus disparities of the earth s crust and mantle from the geochemical equilibrium may not be caused solely by internal temperature radioactivity and gravity gradients but increasingly by life processes the biogenic formation of energy rich compounds on a global scale delivers huge amounts of energy and electrons to the crust which are recycled through geological time the quantities of energy involved appear in themselves to be sufficient to provide the driving force for geotectonic processes thus a model of geophysiological equilibration of geochemical cycles and geotectonics is proposed in which the biota play the role of energy and matter transmitters for geodynamic processes living matter controls and transfers more than 10 of the earth s mass in this system with turnover times of up to 500 million years the transfer speed of each individual atom according to the model must have gradually decreased since the precambrian while the amounts of energy and matter stored and cycled have in turn increased as also witnessed by the increase in the thickness of the crust earth as a bioplanet has come of age

structural diversity of biogenic carbonate particles in microbial mats non skeletal carbonate particles in microbial mats were studied using thin sections and scanning electron microscopy the microbial mats form biolaminated units so called potential stromatolites in salterns this study emphasizes the coexistence of different particle forms and makes a genetic connection between the heterogeneity of the organic substrate built by bacteria and diatoms and their extracellular polymeric substances eps whereas allochthonous particles are scarce lanzarote microbial mats provide various autochthonous surfaces for the attachment of cells and eps including sheaths and capsules of cyanobacteria frustules of diatoms metabolic products such as gas bubbles liquid globules and faecal pellets as well as the carbonate precipitates themselves morphologically different carbonate precipitates are i calcified organic clumps peloids ii particles composed of concentric aragonite and biofilm laminae ooids and oncoids hi isolated particles floating in gel supported mats and coated by rims of fibrous cement cortoids iv particles bound by cryptocrystalline matrices or cement resulting in aggregate grains and v lobate cement which fills out spaces and pores and fixes the particles peloids are suggested to represent faecal pellets although microbial systems also generate cell clumps by non faecal processes ooid and oncoid constructions clearly record alternating processes of biofilm accumulation and aragonite encrustation further characteristic features of carbonate particles generated within a microbial mat are i an irregular distribution ranging from isolated particles floating within the gel like matrix to closely packed particles ii the amalgamation of different particle types e g peloids and ooids in aggregate grains iii the heterogeneous nature of nuclei comprising bacterial clumps intraclasts individual cells cell colonies and bubbles iv the enrichment of remains casts and imprints of cells within precipitates and v deformation e g truncated cortices of particles

real time multivariate indices for the boreal summer intraseasonal oscillation over the asian summer monsoon region the boreal summer intraseasonal oscillation bsiso of the asian summer monsoon asm is one of the most prominent sources of short term climate variability in the global monsoon system compared with the related madden julian oscillation mjo it is more complex in nature with prominent northward propagation and variability extending much further from the equator in order to facilitate detection monitoring and prediction of the bsiso we suggest two real time indices bsiso1 and bsiso2 based on multivariate empirical orthogonal function mv eof analysis of daily anomalies of outgoing longwave radiation olr and zonal wind at 850 hpa u850 in the region 10 s 40 n 40 160 e for the extended boreal summer may october season over the 30 year period 1981 2010 bsiso1 is defined by the first two principal components pcs of the mv eof analysis which together represent the canonical northward propagating variability that often occurs in conjunction with the eastward mjo with quasi oscillating periods of 30 60 days bsiso2 is defined by the third and fourth pcs which together mainly capture the northward northwestward propagating variability with periods of 10 30 days during primarily the pre monsoon and monsoon onset season the bsiso1 circulation cells are more rossby wave like with a northwest to southeast slope whereas the circulation associated with bsiso2 is more elongated and front like with a southwest to northeast slope bsiso2 is shown to modulate the timing of the onset of indian and south china sea monsoons together the two bsiso indices are capable of describing a large fraction of the total intraseasonal variability in the asm region and better represent the northward and northwestward propagation than the real time multivariate mjo rmm index of wheeler and hendon

primary bedded phosphorites in the campanian mishash formation negev southern israel abstract thin lentiform beds up to 1 cm thick of primary non pelletal phosphate have been found sporadically in the highly condensed anticlinal sections of the late campanian mishash formation of the central negev southern israel these primary phosphate beds are typically associated with iron rich montmorillonites of probable authigenic origin and occur at the top of upward fining phosphate dominated sequences the clay rich and primary phosphate levels are commonly truncated by amalgamated beds of high energy coarse grained phosphorites which form the basal part of these sequences with ripped up clasts of the primary phosphate commonly re incorporated in these rocks sem eds study of both the primary phosphate levels and the reworked phosphate clasts shows that they are built by a crudely stratified network of closely packed and gently compressed capsule like phosphate cells 2 5 m in external diameter and with walls of 0 5 m thick these structures are interpreted as being the synsedimentarily phosphatized remnants of former mat forming coccoid prokaryotes now represented as extracellular envelopes which intermittently colonized the mishash sea bottoms at the end of the high energy episodes differential degradation of the periphytic mat community possibly coupled with fe p redox cycling across the surficial mat iron was trapped as iron rich montmorillonites in the anoxic zone below the living mat probably resulted in an excess of dissolved phosphate immobilized as solid phases on decay resistant microbial remains which escaped total degradation development of the mat forming microbes on the mishash bottoms and their mineralization to form primary phosphorite beds occurred during periods of halted deposition which resulted in a high residence time of the mat on the seafloor and hence in intensified interface linked biogeochemical reactions ending in phosphate precipitation the restriction of primary phosphate occurrences to the condensed mishash sections of marginal palaeohigh positions strengthens previous assumptions that these zones were probably the main locus of mishash phosphate production it also points to a phosphate grain supply from marginal to basinal sites leading to the accumulation of pelletal phosphorites in the latter areas

geology of the early devonian oolitic iron ore of the gara djebilet field saharan platform algeria abstract the oolitic iron ore of the gara djebilet field occurs within the early devonian sediments of the tindouf basin algerian sahara particularly in the upper djebilet formation of pragian age three large lenses form three individual deposits extending e w for about 60 km namely gara west gara center and gara east the mineralization is interbedded with argillaceous to sandy sediments and it can be related to a barrier island palaeoenvironment bordered by an inner lagoon or shallow embayment and an epicontinental sea trapped by palaeozoic shoals the oolitic sediments show a mineralogy marked mainly by magnetite hematite goethite maghemite chamosite bavalite siderite apatite and quartz three paragenetic associations present a vertical distribution with a lower non magnetitic ore a magnetitic ore and an upper non magnetitic ore three petrographical facies types have been defined a cemented facies foc a detrital facies fod and a non detrital facies fond chemical data for the whole field show a difference between the lower non magnetitic ore fe 54 6 the magnetitic ore fe 57 8 and the upper non magnetitic ore fe 53 the magnetitic ore which corresponds mainly to the workable ore cutoff grade at 57 has the following composition sio2 4 9 al2o3 4 2 fe2o3 61 43 feo 19 2 and p2o5 1 8 the corresponding calculated economical ore reserves are 985 106t with 57 8 fe regarding the genesis of the oolitic iron ore a southern source is suggested for the iron with deposition taking place in a quiet environment there the ooids developed by an intrasedimentary accretion mechanism around detrital grain within an iron rich mud the gara djebilet field is an important occurrence of the north african palaeozoic ironstone belt extending from the zemmour to libya which also includes ironstones of ordovician silurian and devonian age

short eruption window revealed by absolute crystal growth rates in a granitic magma giant volcanic eruptions occur when large volumes of magma accumulate in crustal reservoirs and do not cool and crystallize to form a solid pluton of rock within the crust geochronological dating of a pluton from elba italy shows that the magma solidified in the crust within just 10 40 thousand years of being injected into the crust implying that the time window for an eruption was short

a mechanism for the southward propagation of mesoscale convective systems over the bay of bengal equatorward propagating precipitation episodes over the bay of bengal have been documented in many previous observational studies proposed propagation mechanisms include mean surface to midtropospheric wind shear driving the convection orthogonal to the lower tropospheric winds and the gravity currents generated by outflow from convection initiated by the diurnally varying land ocean circulations dispersing south in this study we perform high resolution simulations using the weather research and forecast model capable of resolving mesoscale convective systems during the south asian summer monsoon season this mesoscale system is shown to have squall line like structure with leading line trailing stratiform the rear inflow due to saturated downdraft and jump updraft indicates a gravity current like structure the rear inflow jet produces horizontal momentum tendencies in the direction of propagation the center of convection is shown to move faster than the midtropospheric winds and at the same speed as that of the rear inflow jet near the surface these systems are also shown to be tightly coupled to the diurnal land surface heating cycle we perform additional model simulations with varying horizontal resolution and with the inclusion of cumulus parameterization a model with cumulus parameterization is unable to simulate the updraft downdraft pair and the gravity current structure of this southward propagating mesoscale system we find that high model resolution is needed to resolve the updraft downdraft pair and cumulus parameterization assumptions break down at such high resolutions using cloud microphysics exclusively becomes essential in simulating these mesoscale systems

global variability of mesoscale convective system anvil structure from a train satellite data abstract mesoscale convective systems mcss in the tropics produce extensive anvil clouds which significantly affect the transfer of radiation this study develops an objective method to identify mcss and their anvils by combining data from three a train satellite instruments moderate resolution imaging spectroradiometer modis for cloud top size and coldness advanced microwave scanning radiometer for earth observing system amsr e for rain area size and intensity and cloudsat for horizontal and vertical dimensions of anvils the authors distinguish three types of mcss small and large separated mcss and connected mcss the latter are mcss sharing a contiguous rain area mapping of the objectively identified mcss shows patterns of mcss that are consistent with previous studies of tropical convection with separated mcss dominant over africa and the amazon regions and connected mcss favored over the warm pool of the indian and west pacific oceans by separating the anvil from the raining regions of

multiscale interaction with topography and extreme rainfall events in the northeast indian region flash floods associated with extreme rain events are a major hydrological disaster in the northeast indian nei region because of the unique topographic features of the region as well as increased frequency of occurrence of such events knowledge of the spatiotemporal distribution of these events in the region and an understanding of the factors responsible for them therefore would be immensely useful for appropriate disaster preparedness using daily rainfall data from 15 stations over the region for 32 years 1975 2006 it is shown that the frequency of occurrence of these events is largest not during the premonsoon thunderstorm season but during the peak monsoon months june july august this fact together with the fact that most of these events occur during long rainy spells indicate that the extreme events in the nei region largely occur in association with the monsoon synoptic events rather than isolated thunderstorms we also find that the aggregate of extreme rain events over the region has a significant decreasing trend in contrast to a recent finding of an increasing trend of such events in central india goswami et al 2006 this decreasing trend of extreme events is consistent with observed decreasing trend in convective available potential energy and increasing convective inhibition energy over the region for the mentioned period examination of the structure of convection associated with the extreme rain events in the region indicates that they occur through a multiscale interaction of circulation with the local topography it is found that at all the stations the events are associated with a mesoscale structure of convection that is embedded in a much larger scale convective organization we identify that this large scale organization is a manifestation of certain phases of the tropical convergence zone associated with the northward propagating active break phases of the summer monsoon intraseasonal oscillation further it is shown that the mesoscale circulation interacting with the local topography generates southward propagating gravity waves with diurnal period the strong updrafts associated with the gravity waves within the mesoscale organization leads to very deep convective events and the extreme rainfall the insights provided by our study would be useful when designing models to improve the prediction of extreme events

a phenomenological paradigm for midtropospheric cyclogenesis in the indian summer monsoon abstractmidtropospheric cyclones mtcs are a distinct class of synoptic disturbances characterized by quasi stationary cyclonic circulation in midtropospheric levels which often produce heavy ra

intraseasonal periodicities in indian rainfall abstract spectral analysis of a 70 year 1901 70 record of daily precipitation from 3700 stations in the country of india is carried out to search for periodicities on subseasonal time scales during the summer monsoon two statistically significant spectral peaks are found a 40 50 day spectral peak corresponding to the madden julian oscillation is found over most of the portion of india south of 23 n the phase of the oscillation is such that the precipitation maximum appears first over the relatively dry southeastern portion of the peninsula ten to 12 days later the precipitation peaks simultaneously all along the coast west of the western ghats and along a line running across india between 20 and 25 n the precipitation maximum then spreads slowly northward and loses significance cross spectral analysis shows strong coherence between the precipitation patterns and wind oscillations the zonal wind oscillations at 850 and 200 mb am about 180 degrees out of phase equatorward of about 20 n but in pha

rapid remobilization of magmatic crystals kept in cold storage we lack thermal histories for magma reservoirs but here the magma under mount hood oregon usa is shown to have been too cold to mobilize for most of the time it has been stored which implies that magma mobilizes at which point it can be imaged geophysically very quickly prior to eruption this paper presents a novel approach to constraining the thermal history of the subsurface magma bodies that feed eruptions by combining temporal information from a variety of sources kari cooper and adam kent combine timescales derived from uranium series disequilibria textural information and trace element zoning in crystals they show that at mount hood oregon only a small fraction of the total storage duration has been spent at temperatures above the critical crystallinity the point at which magma is easily mobilized they conclude that largely liquid bodies that could be imaged geophysically will be ephemeral features and therefore their detection could indicate imminent eruption the processes involved in the formation and storage of magma within the earth s upper crust are of fundamental importance to volcanology many volcanic eruptions including some of the largest result from the eruption of components stored for tens to hundreds of thousands of years before eruption1 2 3 although the physical conditions of magma storage and remobilization are of paramount importance for understanding volcanic processes they remain relatively poorly known4 5 eruptions of crystal rich magma are often suggested to require the mobilization of magma stored at near solidus conditions6 7 8 however accumulation of significant eruptible magma volumes has also been argued to require extended storage of magma at higher temperatures7 8 9 what has been lacking in this debate is clear observational evidence linking the thermal and therefore physical conditions within a magma reservoir to timescales of storage that is thermal histories here we present a method of constraining such thermal histories by combining timescales derived from uranium series disequilibria crystal sizes and trace element zoning in crystals at mount hood oregon usa only a small fraction of the total magma storage duration at most 12 per cent and probably much less than 1 per cent has been spent at temperatures above the critical crystallinity 40 50 per cent at which magma is easily mobilized partial data sets for other volcanoes also suggest that similar conditions of magma storage are widespread and therefore that rapid mobilization of magmas stored at near solidus temperatures is common magma storage at low temperatures indicates that although thermobarometry calculations based on mineral compositions may record the conditions of crystallization they are unlikely to reflect the conditions of most of the time that the magma is stored our results also suggest that largely liquid magma bodies that can be imaged geophysically will be ephemeral features and therefore their detection could indicate imminent eruption

active break cycles diagnosis of the intraseasonal variability of the asian summer monsoon in this study various diagnostics have been applied to daily observed outgoing longwave radiation olr and ecmwf reanalysis era products to provide a comprehensive description of the active break cycles associated with the asian summer monsoon and to address the differing behaviour of the two dominant time scales of intraseasonal variability 10 20 days and 30 60 days composite analysis of olr based on filtered daily all india rainfall air for the 40 day 30 60 days intraseasonal mode indicates that during active phases convection is significantly enhanced over the indian continent extending over the bay of bengal maritime continent and equatorial west pacific while convection is suppressed over the equatorial indian ocean and northwest tropical pacific resulting in a quadrapole structure over the asian monsoon domain in response to this heating pattern the large scale hadley lateral and the two east west transverse tropical circulations are enhanced there is also a significant impact on the extra tropical circulation through excitation and propagation of rossby waves in contrast the 15 day mode is more regional to the monsoon domain and has a prominent east west orientation in convection only the local hadley circulation over the monsoon region is modulated by this mode the evolution of these two modes as revealed by pop principal oscillation pattern analysis shows that the 40 day mode originates over the equatorial indian ocean once formed it has poleward propagation on either side of the equator and eastward propagation into the equatorial west pacific from the equatorial west pacific northward propagation over the west pacific and westward propagation into the indian longitudes are prominent the propagative features are complex and interactive and are responsible for the quadrapole structure in convection seen from the composites the interannual variability assessed from the pop coefficient time series indicates that the 40 day mode is strong during the onset phase of the monsoon in all the years but systematic propagation over the entire season depends crucially on the activity of the oceanic tcz tropical convergence zone the pop analysis of the 15 day mode indicates that this event originates over the equatorial west pacific associated with westward propagating rossby waves amplifies over the northwest tropical pacific and modulates both the continental and oceanic tczs over indian longitudes simultaneously this mode is pronounced during the established phase of the monsoon due to the complexity in the propagational features of both the intraseasonal modes it is concluded that understanding the subseasonal variability of one regional component of the asian summer monsoon asm requires understanding the entire asm system

organic remains in late palaeoproterozoic granular iron formations and implications for the origin of granules toward the end of the palaeoproterozoic era over 109 billion tonnes of banded bif and granular gif iron formations were deposited on continental platforms granules in iron formations are typically sub spherical structures 0 2 to 10 mm in size whereas concretions are 10 mm both types of spheroids are preserved throughout the sedimentological record their formation has typically been interpreted to originate from reworked fe rich sediments in high energy wave agitated shallow marine environments new evidence from six different late palaeoproterozoic granular iron formations gif however suggests that some granules are the result of diagenetic reactions in addition to other features driven by microbial processes and mechanical movements characteristic coarse grain interiors and septarian type cracks inside granules akin to those features in decimetre to meter size concretions are interpreted as desiccation features from hydrated diagenetic environments where sulphate and or ferric iron were reduced while organic matter om was oxidised inside granules those granules derived from sulphate reduction preserve diagenetic pyrite rims whereas those formed via ferric iron reduction preserve diagenetic magnetite along their rims other diagenetic minerals including apatite mixed with om and various carbonate phases are commonly preserved within granules combined with systematically 13c depleted carbonate these diagenetic mineral assemblages point to the oxidative decay of om as a major process involved in the formation of granules spheroidal equidistant haematite laminations surround some granules and contain apatite associated with carbonate om and ferric ferrous silicates and oxides that further suggest these structures were not shaped by wave action along sediment water interfaces but rather by chemical wave fronts and biomineralisation our results demonstrate that the formation mechanisms of gif also involve microbial activity and chemically oscillating reactions as such granules have excellent potential to be considered as promising biosignatures for studying precambrian biogeochemistry as well as astrobiology

petrography mineralogy and geochemistry of the late eocene oolitic ironstones of the jebel ank southern tunisian atlas abstract the oolitic ironstones ore deposit of jebel ank central tunisia is a simply folded stratiform ore body of about 2 5 8 m thickness located in the upper part of the epicontinental souar formation late eocene and is covered by the continental segui formation mio pliocene the deposit contains about 20 mt of ore with an average grade of 50 fe generally oolitic iron deposition occurs in shallow water lagoonal environments the jebel ank deposit lies between two regional disconformities late eocene and miocene and is evidence of a transitional stage at the end of regional regression before renewed transgression the footwall of the oolitic iron ore bearing bed consists of a fine grained sandstone bed 10 20 cm thick pinching out laterally westward into green clays the hanging wall is composed of thin bedded limestone and clay alternations 2 3 5 m thick iron occurs in the form of cryptocrystalline goethite with limited al fe substitution the goethite contains around 48 fe 5 al and up to 1 5 p jarosite alunite and manganese minerals cryptomelane psilomelane and manjiorite are supergene secondary minerals probably related to descending surface fluids these manganese minerals occur as accessory minerals with the goethite and are most abundant at the lowermost part of the succession showing varied morphologies local cement space filling and free centimeter sized nodules fe oolites in the deposit are similar to those documented in many other oolitic ironstone deposits the dominant fe oolite type 90 has a concentrically laminated cortex with no nucleus the nuclei of the oolites that do have a nucleus are most commonly detrital quartz grains major elements in high grade samples fe 2 o 3 65 vary within a limited range and show higher concentrations of sio 2 average 7 85 and al 2 o 3 average 5 1 with minor tio 2 mno mgo na 2 o k 2 o and so 3 less than 1 paas normalized trace elements of bulk samples and fe oolite generally show similar behavior both are enriched in v co ni mo as zn and y and are depleted in cu rb zr nb ba and hf anomalous v cr ni zn and ree y are correlated with goethite paas normalized ree y patterns of both bulk samples and fe oolite show slight hree enrichment positive ce with negative y anomalies the mineralogy goethite and cryptomelane along with the geochemistry si vs al as cu mo pb v zn vs ni co binary plots zn ni co triangular diagram ree y content and patterns and ce ce vs nd and ce ce vs y n ho n binary plots of the studied oolitic ironstone are congruent with a hydrogenetic type while two possible sources of iron for jebel ank ironstone can be proposed i submarine weathering of glauconite rich sandstone and ii detrital iron from adjacent continental hinterland the later is the more plausible source of iron based on paleogeographic setting the occurrence of fine sandstone underlying the iron level occurrence of mn ores in the lower part of the fe ores succession high phosphorous zinc ree y concentrations and y ho ratios and low la ce ratios

iron bacterial and fungal mats bajocian stratotype mid jurassic northern normandy france abstract the oolithe ferrugineuse de bayeux formation is located at the historical bajocian stratotype of sainte honorine des pertes north of bayeux normandy the condensed formation ranges from the base of the humphriesianum zone to the parkinsoni zone and is divided into four beds of decimetric scale three main microfacies are present 1 oncoid rudstones 2 ooid bioclastic packstones and 3 silty burrowed wackestones packstones sedimentation took place in a very quiet environment below the photic zone and below or near the storm wave base the general setting is a distal carbonate ramp its lower part characterized by hemipelagic sedimentation indicated by the presence of planktonic foraminifers the inferred depth is around 100 m free oxygen concentration was low dysaerobic conditions are indicated by a scarcity of benthic macrofauna ferruginous structures are numerous in the first two microfacies and absent in the last hematite staining is not uniform and follows many sedimentary patterns among the more widespread fe structures are perforation infillings with endolithic micro organisms microstromatolites oncoids ooids blisters coatings and hardgrounds these structures can be associated and none are mutually exclusive hematite coated filaments of different sizes and shapes are observed in the micrite matrix the walls of various organisms the calcite crystals associated with the fe cortical laminations the perforations and burrow the hardgrounds and microstromatolites petrographical and sem examinations suggest that the laminated crusts oncoids and hardgrounds are formed by microbial iron mats dominated by filamentous bacteria and fungi seven types of microbes are recognized filaments five morphotypes spheroidal bodies and stalked bodies filamentous microfossils of type 1 to 4 resemble the present day filamentous bacteria beggiatoales and cytophagaceae because of their large diameter and their branching nature filaments of type 5 are possibly filamentous fungi another argument in favor of fungi is the presence of stalked and spheroidal bodies that resemble zoosporangia and oogonia of some oomycota in deep calm and dysaerobic waters many interfaces e g between aerobic and dysaerobic waters are present in the sediments the stability of the soluble reduced state of iron fe 2 is higher at such interfaces and many ferric iron encrusted microbial fossils are observed iron could thus serve as an electron donor for microbial iron oxidation processes other microbial iron deposition pathways are also possible it appears that regardless of geological age paleozoic mesozoic and geographical location the same microbiological mechanisms are probably responsible for the red color in calcareous stratified or unstratified bodies the presence of fossilized iron encrusted bacteria and fungi at interfaces may therefore serve as an indicator of anoxic to dysaerobic conditions in various paleo micro environments

the role of intraseasonal variability in the nature of asian monsoon precipitation abstract the structure of the mean precipitation of the south asian monsoon is spatially complex embedded in a broad precipitation maximum extending eastward from 70 e to the northwest tropical pacific ocean are strong local maxima to the west of the western ghats mountain range of india in cambodia extending into the eastern china sea and over the eastern tropical indian ocean and the bay of bengal bob where the strongest large scale global maximum in precipitation is located in general the maximum precipitation occurs over the oceans and not over the land regions distinct temporal variability also exists with time scales ranging from days to decades neither the spatial nor temporal variability of the monsoon can be explained simply as the response to the cross equatorial pressure gradient force between the continental regions of asia and the oceans of the southern hemisphere as suggested in classical descriptions of the monsoon monthly 1979 2005 and daily 1997 present rainfall estimates

terminal proterozoic cyanobacterial blooms and phosphogenesis documented by the doushantuo granular phosphorites i in situ micro analysis of textures and composition abstract in order to ascertain the origin of granular phosphorites and the roles of microorganisms in phosphogenesis we conducted comprehensive petrographic surveys and correlated in situ micro analyses of granular phosphorites from the doushantuo formation near yichang south china phosphatic granules display organically zoned internal structures often associated with abundant cyanobacteria like microfossils the internal ultrastructure of the granules as documented by raman microspectroscopy scanning electron microscopy sem and transmission electron microscopy tem is characterized by randomly oriented apatite nano crystals embedded with ubiquitous carbonaceous particles in the apatite groundmass these represent primary textures formed by the rapid growth of apatite provided with abundant nucleation sites within microbial biofabrics nanosims elemental mapping revealed close correspondence of carbon and nitrogen with microfossil structures at the cellular and sub cellular level we propose that the doushantuo granules themselves were formed by microbially mediated accretionary growth followed by rapid phosphatization occurring at the sediment water interface extracellular polymeric substances eps produced by cyanobacteria would have played crucial roles in these processes by promoting aggregated granule growth in addition to providing nucleation sites for apatite crystallization while previous studies have suggested a dominant role of sulfur metabolizing microorganisms in the precipitation of phosphate in phosphorites new observations indicate that the emplacement of most sulfur bearing minerals in the doushantuo phosphorites postdate phosphatization itself our new model of phosphorite formation thus places cyanobacterial eps as an earlier key component of the mineralization of the doushantuo granular phosphorites

a study of vertical cloud structure of the indian summer monsoon using cloudsat data precise specification of the vertical distribution of cloud optical properties is important to reduce the uncertainty in quantifying the radiative impacts of clouds the new global observations of vertical profiles of clouds from the cloudsat mission provide opportunities to describe cloud structures and to improve parameterization of clouds in the weather and climate prediction models in this study four years 2007 2010 of observations of vertical structure of clouds from the cloudsat cloud profiling radar have been used to document the mean vertical structure of clouds associated with the indian summer monsoon ism and its intra seasonal variability active and break monsoon spells associated with the intra seasonal variability of ism have been identified by an objective criterion for the present analysis we considered cloudsat derived column integrated cloud liquid and ice water and vertically profiles of cloud liquid and ice water content over the south asian monsoon region deep convective clouds with large vertical extent up to 14 km and large values of cloud water and ice content are observed over the north bay of bengal deep clouds with large ice water content are also observed over north arabian sea and adjoining northwest india along the west coast of india and the south equatorial indian ocean the active monsoon spells are characterized by enhanced deep convection over the bay of bengal west coast of india and northeast arabian sea and suppressed convection over the equatorial indian ocean over the bay of bengal cloud liquid water content and ice water content is enhanced by 90 and 200 respectively during the active spells an interesting feature associated with the active spell is the vertical tilting structure of positive clwc and ciwc anomalies over the arabian sea and the bay of bengal which suggests a pre conditioning process for the northward propagation of the boreal summer intra seasonal variability it is also observed that during the break spells clouds are not completely suppressed over central india instead clouds with smaller vertical extent 3 5 km are observed due to the presence of a heat low type of circulation the present results will be useful for validating the vertical structure of clouds in weather and climate prediction models

regional seasonal and diurnal variations of extreme convection in the south asian region abstract temporal and spatial variations of convection in south asia are analyzed using eight years of tropical rainfall measuring mission trmm precipitation radar pr data and ncep reanalysis fields to identify the most extreme convective features three types of radar echo structures are defined deep convective cores contiguous 3d convective echo 40 dbz extending 10 km in height represent the most vertically penetrative convection wide convective cores contiguous convective 40 dbz echo over a horizontal area 1000 km2 indicate wide regions of intense multicellular convection and broad stratiform regions stratiform echo contiguous over an area 50 000 km2 mark the mesoscale convective systems that have developed the most robust stratiform regions the preferred locations of deep convective cores change markedly from india s east coast in the premonsoon to the western himalayan foothills in the monsoon they form preferentially in the evening and over land as near surface moist flow is cap

d h of late miocene meteoric waters in western australia paleoenvironmental conditions inferred from the δd of u th he dated cid goethite abstract nineteen u th he ages were determined for eight samples from a core drilled in an ore grade channel iron deposit cid of the robe pisolite robe formation of mesa j in western australia with one exception uncorrected ages of the analyzed aliquots range from 6 7 0 4 ma to 30 2 3 1 ma while molar ratios of th u range from 0 42 to 5 06 the exception is an aliquot with an apparent age of 2 7 ma and th u of 5 70 a three component mixing model involving one generation of goethite and two generations of hematite suggests that the age of crystallization of the oolitic goethites is 7 1 ma if so the goethites have effectively been closed systems for 7 million years and should preserve a stable hydrogen isotope record of late miocene rainfall in the vicinity of mesa j cenozoic movement of the australian continent had placed mesa j and environs in the subtropics at a paleolatitude of about 29 s during the late miocene al adjusted d values of oolitic goethite in the eight cid samples range from 153 to 146 and imply that the d of the late miocene meteoric waters ranged from 61 to 53 with an average of 56 these relatively negative d values might indicate that near coastal late miocene rain was derived primarily from summer season tropical cyclones with storm tracks that extended into the subtropics of western australia the postulated late miocene tropical cyclones would have occurred more often and or exhibited greater intensity at a paleolatitude of 29 s than is the case for modern sites at approximately 30 s on the west coast of australia e g perth higher fluxes of meteoric water in the miocene summers would have facilitated dissolution and removal of bif sourced silica with concomitant enrichment in oxidized fe moreover wetter late miocene summers could have promoted multiple cycles of microbially mediated dissolution and recrystallization of fe iii oxides in the aerobic systems the oolitic textures may be indicative of such recycling however the oolitic goethites of mesa j were closed systems after 7 ma therefore the climate in the vicinity of mesa j seems to have changed in the late miocene to conditions that did not favor widespread recycling of fe iii oxides perhaps changing from seasonally wet to the modern dry climate

seasonal and intraseasonal variability of mesoscale convective systems over the south asian monsoon region abstractseasonal and intraseasonal differences in mesoscale convective systems mcss over south asia are examined using a train satellites a ground based lightning network and reanalysis fields premonsoon april may mcss occur primarily over bangladesh and the eastern bay of bengal during the monsoon june september small mcss occur over the meghalaya plateau and northeast himalayan notch while large and connected mcss are most widespread over the bay of bengal monsoon mcss produce less lightning and exhibit more extensive stratiform and anvil reflectivity structures in cloudsat observations than do premonsoon mcss during the monsoon bay of bengal and meghalaya plateau mcss vary with the 30 60 day northward propagating intraseasonal oscillation while northeast himalayan notch mcss are associated with weak large scale anomalies but locally enhanced cape during intraseasonal active periods a zone of enhanced large and connected mcss precipitation and lightning extends from the northeastern a

possible microbial pathways in the formation of precambrian ore deposits extant micro organisms and their products interact with heavy metals in a variety of ways consideration of these activities provides a background against which possible influences of microbes on the mobilization accumulation and deposition of heavy metals in modern and ancient environments may be examined several different interactions between micro organisms and their products and heavy metals are described experiments on the uptake and metabolism of gold uranium iron and other heavy metals are reported several examples from recent studies and younger fossil deposits are reported and discussed concerning their applicability to precambrian conditions

summer monsoon convection in the himalayan region terrain and land cover effects during the asian summer monsoon convection occurs frequently near the himalayan foothills however the nature of the convective systems varies dramatically from the western to eastern foothills the analysis of high resolution numerical simulations and available observations from two case studies and of the monsoon climatology indicates that this variation is a result of region specific orographically modified flows and land surface flux feedbacks convective systems containing intense convective echo occur in the western region as moist arabian sea low level air traverses desert land where surface flux of sensible heat enhances buoyancy as the flow approaches the himalayan foothills the soil may provide an additional source of moisture if it was moistened by a previous precipitation event low level and elevated layers of dry warm continental flow apparently cap the low level moist flow inhibiting the release of instability upstream of the foothills the convection is released over the small foothills as the potentially unstable flow is orographically lifted to saturation convectivesystemscontainingbroadstratiformecho occur in the eastern himalayas in association with bay of bengal depressions as strong low level flow transports maritime moisture into the region as the flow progresses over the bangladesh wetlands additional moisture is extracted from the diurnally heated surface convection is triggered as conditionally unstable flow is lifted upstream of and over the foothills the convective cells evolve into mesoscale convective systems mcss with convective and stratiform areas the mcss are advected farther into the himalayan eastern indentation where orographic lifting enhances the stratiform precipitation copyright c 2010 royal meteorological society

anvil clouds of tropical mesoscale convective systems in monsoon regions the anvil clouds of tropical mesoscale convective systems mcss in west africa the maritime continent and the bay of bengal have been examined with trmm and cloudsat satellite data and arm ground based radar observations the anvils spreading out from the precipitating cores of mcss are subdivided into thick medium and thin portions the thick portions of anvils show distinct differences from one climatological regime to another in their upper portions the thick anvils of west africa mcss have a broad flat histogram of reflectivity and a maximum of reflectivity in their lower portions the reflectivity histogram of the bay of bengal thick anvils has a sharply peaked distribution of reflectivity at all altitudes with modal values that increase monotonically downward the reflectivity histogram of the maritime continent thick anvils is intermediate between that of the west africa and bay of bengal anvils consistent with the fact this region comprises a mix of land and ocean influences it is suggested that the difference between the statistics of the continental and oceanic anvils is related to some combination of two factors 1 the west african anvils tend to be closely tied to the convective regions of mcss while the oceanic anvils are more likely to be extending outward from large stratiform precipitation areas of mcss and 2 the west african mcss result from greater buoyancy so that the convective cells are more likely to produce graupel particles and detrain them into anvils copyright 2009 royal meteorological society

mesoscale organization and cloud microphysics in a bay of bengal depression abstract airborne radar and cloud microphysical data were obtained throughout a monsoon depression observed over the bay of bengal on 3 8 july 1979 during the summer monsoon experiment of the global atmospheric research programme the precipitation in the disturbance occurred in mesoscale rain areas 100 300 km in horizontal dimension with the largest areas tending to be elongated in the east west or northwest southeast direction these mesoscale precipitation features resembled the rain areas of equatorial cloud clusters each mesoscale precipitation feature contained intense convective cells but the area covered by rain was predominantly stratiform the convective cells in the mesoscale features were sometimes arranged in rapidly moving rather narrow arc shaped east west lines with the stratiform precipitation trailing the line in other cases the convective cells were more randomly embedded in the stratiform rain ice particle images obtained at flight level temperatures of 5 to 25 c indicated the

role of stratiform rainfall in modifying the northward propagation of monsoon intraseasonal oscillation 1 the stratiform and convective rain rate measurement from the tropical rainfall measuring mission trmm satellite data can give a realistic idea of the latent heating distribution in the tropics the vertical profile of diabatic heating related to the convective and the stratiform rain is known to modulate the dynamical response of atmosphere and also the vertical structure of madden julian oscillation in this study the contribution of the stratiform and convective rain rate to the total rain rate during different phases of the northward propagating boreal summer monsoon intraseasonal oscillation iso is examined using the trmm data two new insights have emerged from this analysis first unlike conventional wisdom the convective component shows weak northward propagation and grows and decays in situ during the evolution of active and break phases while the northward propagation of the monsoon iso is largely achieved by organized movement of the stratiform component second the trademark meridional dipole pattern of total rainfall between the monsoon trough zone and the southern equatorial indian ocean also arises largely from the contribution of stratiform anomalies as the northward propagation of the monsoon iso is known to be due to the anomalous response of the atmosphere to heating in the presence of mean easterly vertical shear modification of the vertical profile of heating due to a contribution from stratiform rain could influence the northward propagation of the monsoon iso this hypothesis is tested using a simple global atmospheric circulation model to study the response of the convective and stratiform heating profiles on the modification of the mean condition modification in the large scale response of the atmosphere as a result of proper specification of convective and stratiform heating anomalies indicates that the presence of stratiform heating favors the northward propagation of the heat source thereby facilitating the positive feedback leading to northward propagation of the monsoon iso these results underline the importance of simulating the partitioning of convective and stratiform rain by cumulus parameterization in climate models if they have to get the space time structure of the summer isos correct

impact des ecosystemes microbiens sur la sedimentation impact of microbial ecosystems on sedimentation abstract the microbial communities which often give rise to the fine lamination in sediments are very diverse both in species composition e g phototrophic and chemotrophic bacteria fungi algae and metabolism e g oxygenic and anoxygenic photosynthesis organic and inorganic chemosynthesis anaerobic and aerobic respiration organic and inorganic fermentation these microbial ecosystems have separated for more than 3 5 ga 3500 m y they intervene in the biostructuration of sediments by active mineral deposition particle trapping and sediment stabilisation they build bioconstructions stromatolites oncolites oolites and microbial bioherms further they are active in a number of biogeochemical biomineralisation processes including phosphatogenesis carbonate genesis and the formation of iron ore and sulfur deposits and petroleum and kerogen they are also active agents in the biocorrosion and bioerosion of sedimentary rocks under marine and terrestrial conditions since they have an enormous capacity for proliferation microbial laminated communities invade new habitats practically instantaneously where suitable energy sources and gradients for electron flow are available in addition such microbial systems are excellent and sensitive paleoecological indicators in order to study their impact on sedimentation and fossilisation a close collaboration between geologists and microbiologists is needed only in this way can the nature of fossil microbial ecosystems and the metabolisms that were at work be recognized and reconstructed

the role of microbial activity in the generation of lower cretaceous mixed fe oxide phosphate ooids from the provencal domain french maritime alps abstract early hauterivian mixed fe oxide phosphate ooids from the lower cretaceous condensed succession of the alpine provencal domain are ellipsoidal 200 2000 m in diameter and the main component of a sedimentary body 0 100 cm thick that can be traced laterally for tens of kilometers cathodoluminescence eds microprobe backscattered electron imaging epifluorescence xrd and micro raman spectroscopy reveal that ooid cortices consist of variable proportions of fe oxide rich and ca phosphate rich layers sem observations show that phosphate rich layers are composed of a dense matrix of micrometer size rod shaped commonly curved phosphate grains whose size and shape strongly suggest a microbial origin conversely fe oxide rich ooid cortical layers consist of aggregates of micrometer size plate like crystals of hematite that point to an inorganic precipitation we suggest that the ooidal condensed interval records a long sedimentary history in an open shelf environment subject to a background accumulation of organic rich fine grained sediments it was periodically interrupted by high energy storm related events that resulted in winnowing reworking and oxygenation that favored precipitation of fe oxides around nuclei of biogenic origin such precipitation was not uniform on the outer surface of ooids and influenced their ellipsoidal shape after the return to background conditions fe ooids were buried and driven from an oxic to a post oxic subbottom geochemical environment where rod shaped fe reducing bacteria colonized fe ooid outer surfaces decomposition of organic matter and release of p bound on fe oxides increased pore water concentration of phosphate which precipitated at the outer surfaces of the ooids thus preserving the microbial community the bimineralic composition of these ooids discloses a complex and prolonged history of cyclic alternations of oxic and post oxic geochemical conditions which are in turn related to alternating sediment accumulation and winnowing phases with exposure at the seafloor

the depositional record of sandy versicolored tidal flats mellum island southern north sea abstract cyanobacteria fix and bind sediments and generate versicolored laminated patterns in quartz sand flats they are developed in the lower supratidal zone between mean high water and mean high water springs the cyanobacteria mats protect the sediments from erosion and desiccation and provide food for marine and terrestrial invertebrates burrowing and grazing polychaetes amphipods and gastropods are present as well as a diverse meiofauna the bioturbation structures are described at some places the population density of the macrofauna averages 20 000 individuals per m2 typical are smooth surfaces and erosional pockets with rippled sand the deposits consist of laminated sand in which organic rich mat generations are intercalated the sediment is medium to fine grained sand the development of versicolored systems by interaction of migrating cyanobacteria and episodic low rate sedimentation was studied in the laboratory the depositional record reveals characteristics from both the terrestrial and the marine surrounding there are bioturbation structures from marine and terrestrial burrowing animals hard skeletal parts from shelled marine organisms and plant roots of halophytes fenestrae produced by burrowing beetles are observed the described mats characterize the type of quartz sandy potential stromatolites

the boreal summer intraseasonal oscillation relationship between northward and eastward movement of convection the summertime intraseasonal oscillation iso is an important component of the south asian monsoon lagged regressions of intraseasonally filtered 25 80 days outgoing longwave radiation olr reveal that centers of convection move both northward and eastward from the central equatorial indian ocean subsequent to the initiation of an iso eastward movement of convection is also seen at indian subcontinent latitudes 10 8 208n based on the regression results the summertime iso convection signal appears as a band tilting northwestward with latitude and stretching from the equator to about 208n viewed along any meridian convection appears to propagate northward while equatorial convection propagates to the east to examine the robustness of the connection between eastward and northward movement individual isos are categorized and composited relative to the strength of the large scale eastward component of convection in the central equatorial indian ocean it is found that the majority of isos that exhibit northward movement onto the indian subcontinent 42 out of 54 isos or 78 also exhibit eastward movement into the western pacific ocean it is also found that when convection in the central indian ocean is not followed within 10 20 days by convection in the western pacific ocean 12 out of 54 isos or 22 the independent northward movement of convection in the indian ocean region is somewhat stunted the link between the eastward and northward movement of convection is consistent with an interpretation of the summertime iso in terms of propagating equatorial modes the northward moving portion of convection is forced by surface frictional convergence into the low pressure center of the rossby cell that is excited by equatorial iso convection a similar convergence pattern is seen for the northern winter iso but it does not generate poleward movement due to relatively cool ssts underlying the surface convergence

paleolandscape and paleoenvironmental interpretation of spring deposited sediments in dakhleh oasis western desert of egypt abstract iron rich sediments in dakhleh oasis western desert of egypt have been recognized as spring mounds and as archaeological sites where paleolithic materials have been recovered detailed sedimentologic investigation and mapping of these features reveal that spring mound sediments were deposited in a shallow vegetated wetland formed by the discharge of iron rich nubian aquifer waters along the southern margin of the oasis controlled largely by localized faulting and the variable paleotopography of the basin floor the spring sediments represent peri lacustrine or lake independent features and can be differentiated from fully lacustrine deposits on the basis of their sedimentary characteristics as well as the presence of goethite and jarosite in a region where authigenic deposition during pleistocene pluvial activity principally resulted in tufas and lacustrine marls spring mound formation incorporated sediment through the ponding of surface water aeolian entrapment by local vegetation and the formation of iron precipitates in a low energy oxidative and acidic environment that was not dependent upon surface water inputs into the dakhleh basin the potentially interpluvial nature of this water resource makes it an important sedimentary archive for archaeological investigations in the basin the dakhleh spring mounds record a unique groundwater controlled paleoenvironment providing the first evidence of a bog iron in egypt and one of the few occurrences of iron rich wetland remnants in the modern sahara

comprehensive pattern of deep convective systems over the tibetan plateau south asian monsoon region based on trmm data abstractdiurnal and seasonal variation intensity and structure of deep convective systems dcss with 20 dbz echo tops exceeding 14 km over the tibetan plateau south asian monsoon region from the tibetan plateau tp to the ocean are investigated using 14 yr of tropical rainfall measuring mission trmm data four unique regions characterized by different orography are selected for comparison including the tp the southern himalayan front shf the south asian subcontinent sas and the ocean dcss and intense dcss idcss with 40 dbz echo tops exceeding 10 km occur more frequently over the continent than over the ocean about 23 of total dcss develop into idcss in the shf followed by the tp 21 and the sas 15 with the least over the ocean 2 the average 20 dbz echo top height of idcss exceeds 16 km and 9 of them even exceed 18 km dcss and idcss are the most frequent over the shf especially in the westernmost shf where the intensity in terms of strong radar echo top viz 40 dbz he

microbial signatures in peritidal siliciclastic sediments a catalogue a catalogue of microbial structural signatures is presented based upon the coupling of fundamental biogeochemical microbial processes and local morphogenetic determinants it summarizes a collection of sedimentary structures obtained from two modern siliciclastic peritidal environments in different climatic zones temperate humid mellum island southern north sea subtropical arid coast of southern tunisia textural geometries reveal a high structural diversity but their determinants are primarily based upon six major parameters 1 intrinsic biofactors structural diversification of sedimentary microbial films and mats inherent in the organisms i e their construction morphology growth taxis and behaviour and local abundance of specific morphotypes most prominent are the ensheathed filamentous cyanobacteria microcoleus chthonoplastes and lyngbya aestuarii and the sheathless filamentous cyanobacterium oscillatoria limosa 2 biological response to physical disturbances sediment supply erosion and fracturing of surface layers resulting from desiccation cause growth responses of biofilms and microbial mats 3 trapping binding effects physicobiological processes give rise to grain orientations and wavy to lenticular lamina lamina specific grain arrangements and sucrose calcium carbonate accumulations 4 secondary physical deformation of biogenic build ups mechanical stresses acting upon sediments overgrown and biostabilized by biofilms and mats produce erosional and overthrust structures 5 post burial processes textural fabrics that evolve from mechanical effects of gas formation from decaying mats and features related to the formation of authigenic minerals calcium carbonates calcium sulphates pyrite 6 bioturbation and grazing post depositional structures such as skolithos type dwellings traces of burrowing insects gastropod grazing traces and faecal pellets in synopsis the catalogue firstly comprises a sound set of ubiquitous signatures this uniformity in architectural characteristics is attributed to the presence and local dominance of certain microbes throughout the different settings the catalogue secondly documents signatures that are extremely sensitive to tidal position hydrodynamic regime and overall climatic conditions these kinds of signature indicate narrow facies zones which often coincide with the activity or dominance zones of certain organisms an overview of structures of microbial origin from the fossil record underlines the potential of many of the signatures included in this catalogue to become fossilized and provide strong indicators of former siliciclastic tidal settings

phanerozoic ironstones an introduction and review s u m m a r y ironstones particularly ooidal ironstones have long fascinated sedimentary geologists and have generated an enormous variety of interpretations but have remained poorly understood a recent upsurge in interest in this group of rocks has generated much new information derived from many different disciplines within the earth sciences the first part of this introduction examines recent advances and attempts to produce a synthesis of them with particular reference to the genesis of marine ooidal ironstones current models for the formation of marine oolitic ironstone formations are discussed and a working model based on various lines of recent research is proposed this model invokes the intrasedimentary formation of berthierine ooids in marine environments during postoxic diagenesis the ooids may be mechanically modified and mineralogically transformed by reworking as well as by later diagenesis goethite ooids may be oxidized berthierine ooids reworked lateritic ooids or primary grains the formation of oolitic ironstoneformations is favoured by a break in clastic sediment supply continued supply of iron and physical reworking many sedimentary environments may supply these parameters but changes in sea level leading to the flooding of land masses and the reworking of suitable terrestrial soils may be both an important source for the iron and provide a break in clastic sediment supply in the second part of this introduction the terminology and classification are discussed and conventions proposed the term berthieroid is introduced as a non specific term for material of undetermined berthierine or chamosite composition the term ironstone is proposed as a petrological term and as an informal lithostratigraphic term a deposit composed of ironstones may be termed an ironstone formation it is recommended that a dunham style of classification is employed petrographically with ironstone replacing the stone of the original carbonate classification the nomenclature of allochems in ironstones is also discussed a glossary of ironstone terminology is provided

sequence stratigraphy and paleogene tectonic evolution of the transylvanian basin romania eastern europe abstract the transylvanian basin of romania belongs to the 800 400 km wide pannonian domain of the european alpine megasuture bordered to the east and the north by the carpathians it represents a digitation of the epicontinental tethyan seaways locally connected during the palaeogene to the peripheral foredeep troughs during that time it was filled up by a 500 m thick sediment pile organized into three shallow marine and non marine facies alternations each evolved from alluvial fans to restricted marine and outer marine environments they are dated from lutetian to chattian times the study is focused on the lowermost alternation onlapping the basal post maastrichtian unconformity this alternation consists of the superimpossition of a thick retrogradational and a thin progradational depositional system the retrogradational depositional system grades upwards from stacked fault controlled deposits of alluvial fan ephemeral stream salina and sabkha and restricted marine bioclastic shales the progradational depositional system is composed of outer marine to estuarine sandstones and shales the two depositional systems are bounded at their tops by two baselevel change unconformities underlain by highly mobile low relief sandstone bodies that were deposited in shoal belts these two unconformities mark significant changes in the regime of the subsidence these are respectively a baselevel rise or drowning unconformity where the shoal deposits were associated with oolitic ironstones and glauconitic shales that typify basin starvation during a period of maximum basin drowning and a baselevel fall or uplifting unconformity where the bioclastic shoal deposits were buried by alluvial flood plain deposits that characterize periods of relief rejuvenation tentatively attributed to compressive events this bimodal succession is interpreted in terms of underfilled overfilled stages related to intraplate tectonic deformation the underfilled stage corresponds to the fault controlled drowning of the basin and the overfilled stage to the increasing flexural rigidity of the substrate culminating in differential uplift in the area three of these successions comprise the palaeogene sedimentary record of the transylvanian basin they attest to a large scale pulsating evolution of this continental microplate during its northward migration towards the european plate

the formation of fluvio lacustrine ferruginous pisoliths in the extensive palaeochannels of the yilgarn craton western australia abstract iron pisoliths and nodules are common within the fluvio lacustrine kaolinitic clays of tertiary paleochannels developed in the yilgarn craton of southern western australia deposition within these channels began in the late eocene with sediments comprised a fining upward sequence from sands at the base to lacustrine clay deposits above iron pisoliths are found randomly distributed in the clays in deposits more than 300 km apart the pisoliths are composed of goethite and hematite and minor quartz and clays they are 2 to 30 mm in diameter and formed of an inner nucleus surrounded by up to 200 iron oxide laminations there is no evidence for transportation of pisoliths into the channels but the internal fragmented nature of some of the pisoliths suggests some movement has occurred and multiple generations of pisoliths have developed the interface between river water and sediment was a redox boundary between reduced slightly acidic sediments and oxidised river water pisoliths formed on or just beneath the surface of the sediment by redox reactions likely mediated by microorganisms pisoliths have undergone cycles of exposure growth and movement linked to the height and course of the palaeoriver system

microbial structures in oolitic iron formations ferriferous ooids and microoncoids occur in many sedimentary iron formations these ferriferous coated grains are found in fine grained carbonate rich groundmasses iron mineral encrusted microbiota are observed in both the coated grains and the groundmass the branching nature and other morphological features of the microorganisms suggest fungal origins for the oolitic iron ores particularly of the lower jurassic lorraine minette the similarity of the microbial structures in coated grains and their groundmasses suggests that both had developed within microbial mats growing under calm environmental conditions the contribution of stromatolitic marine fungal mats to the fast extraction and immobilization of iron and thus to the genesis of iron ores is demonstrated observations on well preserved freshwater derived fungal stromatolites of the tertiary and laboratory experiments with organotrophic fungal mats confirm the findings on the jurassic and imply a general role of microorganisms in the formation of such deposits

formation and stratigraphic facies distribution of early jurassic iron oolite deposits from west central nevada usa abstract the stratigraphic context and geochemical proxy potential are described for a newly reported early jurassic marine iron ooid deposit in west central nevada u s a sedimentary analysis of the ferguson hill member in the sinemurian aged sunrise formation was conducted in the gabbs valley range of nevada u s a iron ooids were examined by transmitted light microscopy and electron scanning microscopy and found to consist of chamosite berthierine and amorphous silica in cortical layers of the sunrise formation sedimentological characteristics of the uppermost beds of the ferguson hill member show iron ooids are associated with transgressive deposits on the earliest known first post extinction metazoan carbonate factory identified in eastern panthalassa the ferguson hill member iron ooids are unique among most iron ooid deposits for being distributed grains within the carbonate the formation of such a deposit required concentrations of iron and silica and fluctuating oxidation reduction conditions sufficient to produce chamosite berthierine and silica while not completely shutting down the shallow marine carbonate factory for this reason iron ooids observed in shallow carbonate sections serve as a useful indicator of shallow water geochemical conditions in the sedimentary record

the 30 50 day mode at 850 mb during monex abstract the analyzed wind field at 850 mb during the summer monsoon experiment monex is subjected to a time series analysis to confirm the existence of a peak in the time range of 30 50 days having established that this study presents a mapping of the motion field for this time scale in this short paper we illustrate the steady meridional propagation of a train of troughs and ridges that seem to form near the equator and dissipate near the himalayas the meridional scale of this mode is around 300 km and its meridional speed of propagation is 0 75 latitude per day the amplitude of the wind for this mode is around 3 6 m s 1 the salient contributions here are the mapping and the demonstration of a very regular behavior of this mode its existence is here noted from a period well before the onset of monsoon i e from early may to late july three major storms during monex were noted to form within the trough line of this system and the period of major cessation of rains over the indian subconti

neogene and quaternary rollback evolution of the tyrrhenian sea the apennines and the sicilian maghrebides reconstruction of the evolution of the tyrrhenian sea shows that the major stage of rifting associated with the opening of this basin began at similar to10 ma it involved two episodes of back arc extension which were induced by the rollback of a west dipping subducting slab the first period of extension 10 6 ma was prominent in the northern tyrrhenian sea and in the western part of the southern tyrrhenian sea the second period of extension mainly affected the southern tyrrhenian sea began in the latest messinian 6 5 ma and has been accompanied by subduction rollback at rates of 60 100 km myr 1 slab reconstruction combined with paleomagnetic and paleogeographic constraints indicates that in the central apennines the latest messinian 6 5 ma arrival of a carbonate platform at the subduction zone impeded subduction and initiated a slab tear and major strike slip faults these processes resulted in the formation of a narrow subducting slab beneath the ionian sea that has undergone faster subduction rollback and induced extreme rates of back arc extension

frutexites from microbial metazoan bioconstructions of recent and pleistocene marine caves sicily italy abstract frutexites like structures were recorded in small bioconstructions from recent and pleistocene marine caves the skeletal microbialite frameworks hosting frutexites form in cryptic environments characterized by poor light availability and reduced water circulation leading to confinement oligotrophic conditions and the development of typical cave communities biostalactites and biotic crusts develop in the more confined parts of the both recent and pleistocene caves they are composed of skeletal organisms engulfed in fine micrite sediments deposited in situ via microbial metabolic activity the frutexites composed of iron and manganese oxides are confined to microcavities or microfractures of the bioconstructions they grow from an original discontinuity surface into the surrounding consolidated micritic sediments a model based on the increase of the microporosity of micritic sediments due to the dissolution of the original material and precipitation of ferromanganesiferous compounds was proposed this process occurs during the syndepositional diagenetic stage due to the intrusion in the bioconstruction framework of acidic continental water rich in iron and manganese mesophilic fe mn autotrophic and chemoheterotrophic bacteria flourish on the microcavities and induce the precipitation of fe and mn oxides

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

dynamical response of the south asian monsoon trough to latent heating from stratiform and convective precipitation simulation experiments using a simplified atmospheric gcm and supplementary diagnostic analyses of observations are performed to understand how the south asian monsoon trough mt responds dynamically to latent heating from mesoscale convective systems mcss observations reveal that the mt during active monsoons is characterized by a deep cyclonic vorticity extending from the surface to 350 hpa and organized mcss covering over 3500 4000 km along the indo gangetic plains the mcss during active monsoons are composed of a relatively higher abundance of stratiform type precipitation mostly nimbostratus as compared to the convective type the results suggest that a stratiform type heating profile is very effective in promotingupward development of continental scale cyclonic circulation well above the midtroposphere over the mt region the vertical development involves a dynamical uplift of the layer of cyclonic circulation and is induced by midlevel 600 500 hpa convergence and vorticity stretching above 500 hpa by varying the population of stratiform and convective rain types in the simulation the horizontal scale of midlevel vorticity response is shown to increase significantly with stratiform population in contrast the midlevel response is more localized when the mcs is dominated by deep convective clouds for large stratiform populations the midlevel responseis found to extend far westward up to the northernflanks of the africanitcz indicativeof rossby wave dispersion of pv anomalies that are generated near the level of maximum heating gradient from the present findings one can conclude that the vertical deepening of mt during active monsoons is not merely a localized phenomenon instead it represents a large scale dynamical response to organized mcss that exert pivotal influence on the upward development of cyclonic circulation well above the midtroposphere

diffusion coupling between trace and major elements and a model for calculation of magma residence times using plagioclase residence times of plagioclase crystals in magma reservoirs can be determined by modeling the compositional zoning of trace elements in these crystals we present a formulation to model diffusion of trace elements in plagioclase paying special attention to certain thermodynamic and kinetic aspects in particular we account for the compositional dependence on anorthite content of the chemical potential and diffusion coefficients of trace elements e g mg the choice of suitable boundary conditions and potential effects of diffusion in more than one dimension we show that contrary to intuition diffusive fluxes of trace elements may be coupled to major element concentration gradients and ignoring such coupling can lead to incorrect estimates of timescales we illustrate application of the model using plagioclase crystals from a suite of gabbroic xenoliths from a holocene dacitic lava flow of volcan san pedro chilean andes 36 s the inferred timescale for metasomatism of the xenoliths by evolved liquids is on the order of 100 30 to 148 yr and serves to illustrate how trace element zoning in plagioclase provides a window into timescales of magmatic processes inaccessible by isotopic or other methods

a note on propagating rainfall episodes over the bay of bengal an observational analysis of precipitation episodes over the bay of bengal and the adjacent coastal region is conducted using the trmm real time multi satellite precipitation analysis mpa rt products for three warm seasons i e may to september for 2002 2004 time distance diagrams hovmuller diagrams of rainfall episodes reveal frequent travelling precipitation episodes having lifetimes greatly exceeding those of individual convective systems the majority of the episodes translate southward and many do not appear to have a steering level i e they propagate in a hydraulic like manner unlike those previously documented over midlatitude and tropical continents which usually have a steering level on average the coherent systems have a latitudinal span of 5 degrees and a 1 day duration and a meridional propagation speed of 8 m s 1 approximately the episodes mostly initiate over the coastal land around midday and offshore around midnight copyright 2008 royal meteorological society