a paleohydrologic model for early proterozoic dolomitization and silicification abstract primary depositional features observed in the intertidal and supratidal facies of the 2 25 ga malmani dolomite including tepees and finely laminated domal stromatolites have equivalents in holocene salinas on the southern coast of australia the hydrological regime so important in the formation of these recent primary features is still active and so it has been possible to interpret the palaeohydrological significance of analogous features in the malmani dolomite the palaeoclimate of the malmani dolomite shoreline was probably humid to semi arid and the supratidal zone is interpreted as a zone of groundwater resurgence tepees indurated fenestral limestone sheets algal mats small domal stromatolites and intraclast breccias were forming on the supratidal flats in areas of periodically outcropping groundwaters in the shallow subsurface the mixing zone between these resurging continental groundwaters and the marine derived phreatic waters was probably a zone of secondary coarse grained dolomite precipitation and or chert nodule formation this groundwater controlled mixing zone model explains why such fabrics are restricted to porous and immediately adjacent units which at the time of diagenesis were below the regional water table in the upper supratidal zones above the regional water table no secondary dolomites or chert nodules could form nor could diagenetic fabrics form in the subtidal zone for there the stromatolitic mounds contained no palaeoaquifer

southeast asian sediments not from asia provenance and geochronology of north borneo sandstones eocene lower miocene sandstones of the crocker turbidite fan of north borneo were derived from nearby borneo and southeastern asian sources rather than distant asian sources eroded after india eurasia collision they are compositionally mature due to tropical weathering but are mostly first cycle sandstones derived from granitic rocks and subordinate metamorphic sedimentary and ophiolitic rocks detrital zircon ages range from archean to eocene and the majority are mesozoic the most important source areas were cretaceous granites of the schwaner mountains in southwest borneo during the eocene and permian triassic granites and proterozoic basement of the malay thai tin belt during the oligocene

sensitivity of typhoon track to asymmetric latent heating rainfall induced by taiwan topography a numerical study of typhoon fanapi 2010 1 typhoon fanapi 2010 traveled westward across the central mountain range of taiwan on 19 september and its rainfall shifted from a symmetric to an asymmetric pattern with convection mostly to the south and southeast meanwhile the storm slowed down from 22 to 14 km h 1 for 12 h upon leaving taiwan and led to heavy rainfall 800 mm and serious flooding over the low lying southwestern plains through simulation and sensitivity tests using the cloud resolving storm simulator at 3 km grid size this study shows that the sudden and temporary speed reduction was caused by the asymmetric latent heating lh not the environmental flow specifically over a 9 h period the model storm moved westward at 16 km h 1 in the control run but increasingly faster and more toward the northwest when the moisture and thus the lh effect and its asymmetry is gradually reduced steering flow analysis and estimation using model results suggest an eastward motion vector of about 8 km h 1 consistent with the observation is produced by the asymmetric lh effect when the effects from the vertical wind shear and beta drift are both taken into account this result is further supported by the diagnosis on storm motion based on potential vorticity tendency although important such feedback to typhoon track from rainfall asymmetry that is induced by the blocking effect of topography have not been reported or studied

effects of asymmetric sst distribution on straight moving typhoon ewiniar 2006 and recurving typhoon maemi 2003 abstractthe effects of asymmetric sea surface temperature sst distribution on the tropical cyclone tc motion around east asia have been examined using the weather research and forecasting model for the straight moving typhoon ewiniar 2006 and recurving typhoon maemi 2003 the sst tc motion relationships associated with the two different tcs and the physical mechanism of recurvature are investigated in the context of the potential vorticity tendency framework a zonally asymmetric sst distribution alters the tc translating direction and speed which is ascribable to the interaction between a tc and the environmental current associated with asymmetric sst forcing a north south sst gradient has an insignificant role in the tc motion it is noted that the straight moving i e northward moving tc deflects toward the region of warmer sst when sst is zonally asymmetric a contribution of the horizontal advection including asymmetric flow induced by asymmetric forcing is dominant for the deflection t

tropical cyclone recurvature an intrinsic property the typical track of a tropical cyclone tc in the northern hemisphere is an initial northwestward movement followed by an eventual turning toward the east such turning is referred to as recurvature and often explained by the change of the environmental flow that steers the tc here we show that even in the absence of background flow a tc initiated at a high enough latitude can recurve itself differential horizontal advection of the planetary vorticity by the tc circulation at different vertical levels leads to the development of vertical wind shear upper tropospheric anticyclone and asymmetric distribution of convection the flow associated with the upper tropospheric anticyclone on the equatorward side of the tc and the diabatic heating associated with the asymmetric convection combine to cause the tc to recurve such knowledge an intrinsic recurvature property of the tc is important in forecasting the tc track when the environmental flow is weak

the composition of the precambrian ocean waters abstract the composition of the precambrian oceans was different from the present composition this is a direct consequence of a co2 atmosphere depleted in oxygen at the beginning the mineralization was lower the oceans waters were chloro dicarbonated with a lower tenor of chlorine richer in phosphates and they were depleted in sulphates sulphur was in the reduced state of sulphides the abundance of phosphates supported the expansion of life the cations na and mg2 coexisted with ca2 fe2 and ba2 whose levels were higher than they are today the main trends of the evolution are schematized in the figure

why do model tropical cyclones intensify more rapidly at low latitudes abstractthe authors examine the problem of why model tropical cyclones intensify more rapidly at low latitudes the answer to this question touches on practically all facets of the dynamics and thermodynamics of tropical cyclones the answer invokes the conventional spin up mechanism as articulated in classical and recent work together with a boundary layer feedback mechanism linking the strength of the boundary layer inflow to that of the diabatic forcing of the meridional overturning circulation the specific role of the frictional boundary layer in regulating the dependence of the intensification rate on latitude is discussed it is shown that even if the tangential wind profile at the top of the boundary layer is held fixed a simple steady boundary layer model produces stronger low level inflow and stronger more confined ascent out of the boundary layer as the latitude is decreased similar to the behavior found in a time dependent three dimensional numerical model in an azimuthally averaged vi

chemistry and stromatolites of the sea linked satonda crater lake indonesia a recent model for the precambrian sea abstract the abundance of in situ calcified stromatolites in the precambrian paleontological record and their absence from modern seas is still an enigma we report on the discovery of the first recent in situ calcified stromatolites growing in a sea linked environment the stromatolites are produced by coccoid cyanobacteria and started to grow 4000 yr ago in the crater lake of satonda island indonesia compared to seawater the lake has gained alkalinity and lost ca its ph 8 45 as well as its saturation with respect to calcite is significantly higher than in seawater the additional alkalinity is provided by biogenic co2 and subsequent weathering of volcanic silicates satonda crater lake may provide an analogue to the stromatolite sustaining precambrian marine environments which therefore may have been more alkaline than present day seawater this conclusion is congruent with the recently advanced hypothesis of an early soda ocean

an early soda ocean in analogy to modern soda lakes commonly associated with volcanic regions it is postulated that the ancient sea had a high alkalinity a high ph and low ca and mg concentrations the change towards nacl dominance as observed in the present day ocean can best be explained by a series of mineral equilibria crustal differentiation and life processes in principle hydrothermal leaching of chlorine from the oceanic crust caused this ion to accumulate in the sea while at the same time dissolved carbonates became gradually removed by organisms and carbonates the switch from a soda to a halite ocean was accomplished 1 ga ago critical biochemical events marking the chemical evolution of the precambrian sea and their implications for the pco2 in air will be discussed

tropical cyclone motion and evolution in vertical shear abstract the motion and the evolution of tropical cyclone like vortices in an environmental flow with vertical shear are investigated using a baroclinic primitive equation model the study focuses on the fundamental dynamics of a baroclinic vortex in vertical shear the influence of vortex structure and the role of diabatic heating the results show that the initial response of the vortex to the vertical shear is to tilt downshear as soon as the tilt develops the upper level anticyclonic and lower level cyclonic circulations begin to interact with each other as a result of these interactions the tilted axis of the vortex reaches a stable state after an initial adjustment which varies with the structure of the vortex its environmental flow shear and the cumulus convective heating the motion of an adiabatic vortex in vertical shear is controlled by both the steering of the environmental flow and vertical coupling mechanisms most of the vortices move with the environmental flow at about 650 hpa or

baroclinic dynamics of simulated tropical cyclone recurvature abstract the mechanisms associated with tropical cyclone recurvature are investigated using a five level primitive equation model and an idealized environment with characteristics observed in cyclone recurvature conditions all cyclones moved generally with the flow in the lower and middle troposphere but the precise motion occurs by a combination of divergence and of advection in both the horizontal and the vertical the horizontal advection arises from a combination of the initial environmental flow and local changes from rearrangement of the potential vorticity field by cyclone environment interaction the so called effect the balance between these mechanisms changes as the vortex recurves since the gradients of potential vorticity increase sharply poleward of the subtropical ridge this is the preferred region for development of an anticyclonic gyre this gyre is advected eastward and becomes the dominant anticyclonic system recurvature is aided by horizontal deformation of the cyclone in the v

interactions between simulated tropical cyclones and an environment with a variable coriolis parameter abstract numerical simulations of tropical cyclones are performed to examine the effects of a variable coriolis parameter on the structure and intensity of hurricanes the simulations are performed using the nonhydrostatic fifth generation pennsylvania state university national center for atmospheric research mesoscale model using a 5 km fine mesh and fully explicit representation of moist processes when a variable conolis parameter f environment is applied to a mature tropical cyclone a persistent north northwesterly shear develops over the storm center as a result of an interaction between the primary circulation of the storm and the gradient in absolute vorticity as a result the variable f storm quickly develops a persistent wavenumber 1 asymmetry in its inner core structure with upward motion and rainfall concentrated on the left side of the shear looking downshear in agreement with earlier studies in comparison the constant f storm develops weak transient asymmetries in structure that are

the geochemistry of lewisian marbles summary to rectify the dearth of published petrographical and analytical data for lewisian marbles 307 samples from nearly all outcrops known have been examined in thin section and 114 samples analysed for 35 elements lewisian marbles can be divided texturally into 1 macrocrystalline generally white pure to silicate rich eg from glenelg 2 microcrystalline often coloured ornamental pure to silicate rich eg from iona 3 microbrecciated grey crushed fine grained silicate opaque rich eg from the loch maree group lmg lewisian marbles are geochemically typical of ancient carbonates tending to have lower contents of trace elements notably sr than younger eg scottish dalradian marbles whereas all analyzed marbles from the south harris and coll foreland outcrops and from the glenelg and kintail inliers are dolostones mgo 15 20 sio 2 5 15 those of the eastern inliers glen strathfarrar shinness are pure limestones mgo 2 eg scardroy inlier microbrecciated lmg marbles flowerdale belt of gairloch furnace belt of loch maree have notably higher chalcophile and siderophile element contents than macrocrystalline marbles in adjacent belts cloiche of gairloch gleann tulacha of loch maree aside from such local differences however limestones and dolostones of the inliers lmg and remaining foreland reveal few non trivial differences in composition moreover lewisian marbles collectively show strong pearson and spearman correlations between elements concentrated in accessory phases eg y la ce k rb al fe co v given established secular variations in the chemistry of global carbonate rocks these relationships between both marble groups and chemical variables are difficult to explain if some lewisian marbles eg s harris represent late scourian and others eg lmg early proterozoic sediments they may provide a tentative hint that most lewisian marbles were deposited contemporaneously

interactions between a barotropic vortex and an idealized subtropical ridge part i vortex motion abstract a series of barotropic modeling experiments are used to examine the motion of a vortex in the vicinity of an idealized subtropical ridge the vortex propagation is highly correlated with the absolute vorticity gradient in the initial imposed environment the signal is degraded when radial band averages are used to calculate the environmental advection and absolute vorticity gradient components it is shown here that this is due partially to the difficulties in separating the cyclone from its environment application of the modeling results to climatological mean fields indicates that considerable variations in vortex propagation can occur

anomalously low al2o3 tio2 values for archean cherts from the pilbara block western australia possible evidence for extensive chemical weathering on the early earth geochemical sedimentological and mineralogical features of 3 0 ga archean cherts and intercalated bifs from the pilbara block western australia were studied chert layers that are well exposed at point samson 20 km north northeast of roebourne consist of various types of chert white light gray chert brownish yellow chert gray chert dark gray chert massive black chert and light gray chert the cherts other than brownish yellow chert consist mostly of microcrystalline quartz with a minor amount of fine silicate minerals and carbonates the brownish yellow chert is characterized by a high concentration of goethite most cherts contain thin layers characterized by high concentrations of ti bearing minerals such as rutile anatase fe ti aggregates and fine tio2 grains accordingly al2o3 tio2 values in some samples are very low 1 0 indicating that these samples contain more tio2 than al2o3 this geochemical feature is attributed mainly to the supply of detrital materials with high ti bearing minerals to the site of deposition because the ti bearing minerals are generally associated with detrital quartz and zircon ti enriched detrital materials are possibly formed by al ti fractionation during 1 extensive chemical weathering or 2 hydrothermal alteration of the source rocks in the first hypothesis which we prefer it is suggested that low ph values 4 of meteoric waters accelerated the decomposition of rock forming minerals and prevented precipitation of dissolved al3 such low ph values of meteoric waters could have been attributed to more violent volcanic activities issuing acid materials e g h2s and hcl and or a higher concentration of atmospheric co2 in the archean than today

some aspects of vortex structure related to tropical cyclone motion abstract some effect of tropical cyclone structure on the vortex motion are examined in a nondivergent barotropic numerical model with no basic current as suggested earlier by demaria the initial maximum wind speed has little effect on the track vortex translation associated with the beta effect depends sensitively on the strength of the flow between 300 and 1000 km from the center if the flow in this annulus is made more cyclonic the track will turn cyclonically and move more toward the west in the northern hemisphere the dynamics of this beta drift is studied via a decomposition into symmetric and asymmetric circulations the symmetric flow experiences a slight weakening of the maximum wind speed and an anticyclonic circulation is induced beyond 600 km the asymmetric circulation is dominated by an azimuthal wavenumber one circulation with an anticyclonic gyre east of the center a cyclonic gyre to the west and a nearly uniform broad scale ventilation flow between the gyres the vortex translati

concurrent changes to hadley circulation and the meridional distribution of tropical cyclones abstractpoleward trends in seasonal mean latitudes of tropical cyclones tcs have been identified in direct observations from 1980 to the present paleoclimate reconstructions also indicate poleward equatorward migrations over centennial millennial time scales hadley circulation hc is often both implicitly and explicitly invoked to provide dynamical linkages to these shifts although no direct analysis of concurrent changes in the recent period has been presented here the observational tc record 1981 2016 and era interim jra 55 and merra 2 are studied to examine potential relationships between the two a zonally asymmetric hc is defined by employing helmholtz theory for vector decomposition and this permits the derivation of novel hc diagnostics local to tc basins coherent variations in both long term linear trends and detrended interannual variability are found tc genesis and lifetime maximum intensity latitudes share trend sign and magnitude with shifts in local hc extent with rates being a

a comprehensive mass flux scheme for cumulus parameterization in large scale models abstract observational studies indicate that a mass flux approach may provide a realistic framework for cumulus parameterization in large scale models but this approach through the introduction of a spectral cloud ensemble leads normally to rather complex schemes in this paper the question is addressed whether much simpler schemes can already provide realistic values of the thermal forcing by convection under various synoptic conditions this is done through verifying such a scheme first on data from field experiments for periods of tropical penetrative convection gate marshall islands tradewind cumuli atex bomex and extratropical organized convection sesame 79 and then in a nwp model the scheme considers a population of clouds where the cloud ensemble is described by a one dimensional bulk model as earlier applied by yanai et al in a diagnostic study of tropical convection cumulus scale downdrafts are included various types of convection are represented i e penetrative convection in c

geochemistry of precambrian carbonate intercalated in pillows and its host basalt implications for the ree composition of circa 3 4 ga seawater abstract the ree composition of early archean seawater has been estimated through analyses of dolomite intercalated in pillow basalts from the pilbara block western australia we have critically evaluated the possible disturbances that have affected the chemical composition of the carbonate through geologic time dolomite samples from the pilbara show a chondrite normalized lree enriched pattern with profound downward convex tetrad effects suggesting that these ree signatures are related to ancient seawater from which the dolomite precipitated contribution of a hydrothermal component to the seawater signature appears negligible based on the small eu anomalies observed in dolomite therefore dolomite samples from the pilbara block appear to preserve rees intrinsic to ancient seawater suggesting that the ree composition of seawater could be estimated given that carbonate seawater partition coefficients of rees are known we used ree partition coefficients based on the analyses of a dolomite reference sample jdo 1 from the geological survey of japan and show that ree concentrations of 3 4 ga seawater could have been one or two orders of magnitude higher than at present moreover it appears that 3 4 ga seawater was significantly enriched in hree and had less pronounced w type tetrad effects relative to that of present seawater these may reflect paleo environmental conditions particular to seawater in the archean such as high salinity and co32

an air sea interaction theory for tropical cyclones part ii evolutionary study using a nonhydrostatic axisymmetric numerical model abstract in part i of this study an analytical model for a steady state tropical cyclone is constructed on the assumption that boundary layer air parcels are conditionally neutral to displacements along the angular momentum surfaces of the hurricane vortex the reversible thermodynamics implied by this assumption allows the mature storm to be thought of as a simple carnot engine acquiring heat at the high temperature ocean surface and losing heat near the low temperature tropopause although the oceanic heat source is universally recognized as the sine qua non for the mature hurricane there is also wide acceptance of conditional instability of the second kind cisk which makes no specific reference to surface heat fluxes as the formative mechanism this ambivalence is seen in that all numerical simulation studies find it essential to have transfer from the ocean surface yet all start from a conditionally unstable atmosphere the hypothesis put forward in part i based on the steady state theory is t