the metamorphic internal zone of wopmay orogen early proterozoic canada 30 km of structural relief in a composite section based on plunge projection in wopmay orogen an early proterozoic volcano sedimentary marginal prism and its underlying archean structural basement deformed together during the 1885 ma calderian orogeny are exposed in oblique view as a result of regional cross folding a composite cross section displaying over 30 km of structural relief provides a framework in which to examine the geologic relationships in the metamorphic internal zone of the orogen a sole thrust separates archean basement and a thin mantle of autochthonous early proterozoic strata from the eastward transported calderian allochthon the allochthon is characterized by a transition from external thrust fold belt geometries in the east to polyphase isoclinal recumbent folds and thrusts in the west the center of the zone contains the hepburn batholith which has been been transported along with the deforming hot allochthon over the exposed basement both basement and allochthon are deformed by late large scale upright folds the metamorphic internal zone is interpreted to record the closing of a rift basin during which the basin fill was shortened thickened to over 30 km metamorphosed and thrust eastward while still hot over the relatively cool archean craton the basement presently exposed beneath the sole thrust remained relatively nondeformed during thrusting but underwent large scale folding due to continued compression during uplift of the internal zone

the nature and distribution of upper cenozoic ignimbrite centres in the central andes abstract a wide variety of upper cenozoic ignimbrite centres have been identified and studied on landsat imagery of the central andes some have been investigated in the field lower miocene ignimbrite centres are distributed along an arc which in north chile diverges markedly from the line of the present trench and parallels an arc of lower miocene plutons in the eastern cordillera of bolivia much of the ignimbrite erupted since the late miocene has been erupted around the faulted margins of the altiplano basin of western bolivia particularly where the western and eastern cordilleras converge typical examples of ignimbrite centres are described some centres take the form of ignimbrite shield volcanoes other ignimbrite sheets are more widely dispersed the degree of dispersal probably relates to the height of the eruption column partial or total caldera formation sometimes took place and a few of these calderas have resurgent centres late stage lava extrusions are common and some of these are located on caldera ring fractures

cycles and propagation of deep convection over equatorial africa abstractlong term statistics of organized convection are vital to improved understanding of the hydrologic cycle at various scales satellite observations are used to understand the timing duration and frequency of deep convection in equatorial africa a region with some of the most intense thunderstorms yet little has been published about the propagation characteristics of mesoscale convection in that region diurnal subseasonal and seasonal cycles of cold cloud proxy for convective precipitation are examined on a continental scale organized deep convection consists of coherent structures that are characteristic of systems propagating under a broad range of atmospheric conditions convection is triggered by heating of elevated terrain sea land breezes and lake breezes coherent episodes of convection result from regeneration of convection through multiple diurnal cycles while propagating westward they have an average 17 6 h duration and 673 km span most have zonal phase speeds of 8 16 m s 1 p

erosional control on the geometry and kinematics of thrust belt development in the central andes long term erosion rates in the central andes may have influenced not only mean elevation and relief but also the regional geometry and kinematic history of the orogenic belt a drastic along strike erosional gradient exists in the modern central andes from a high erosion region directly north of the 17 5 s bend in the andes to a low erosion region south of the bend this gradient has existed since 10 15 ma based on fission track analyses of middle miocene to holocene denudation and qualitative evaluations of the preservation potential of middle late tertiary volcanic edifices and synorogenic sediment global positioning system velocity data indicate conflicting patterns of active surface shortening north and south of the 17 5 s bend whereas present day shortening in the thrust belt north of the bend is distributed over much of the width of the belt south of the bend it is concentrated near the eastern frontal margin structural data suggest a similar kinematic situation during late miocene to holocene shortening an out of sequence chronology of thrusting in the narrow 200 km wide thrust belt to the north versus a forward breaking sequence of thrusting in the relatively wide 350 km wide thrust belt to the south the long term internal deformation and limited width of the thrust belt north of the bend are attributed to prolonged subcritical thrust wedge conditions induced by rapid erosion rates since 10 15 ma such conditions inhibit thrust front advance and favor distributed deformation within the thrust belt interior in the thrust belt south of the bend a progressive eastward migration of thrusting is interpreted to be the result of long term critical thrust wedge conditions promoted by extremely low rates of denudation since middle miocene time

the generation and propagation of a nocturnal squall line part ii numerical simulations abstract the mechanisms behind the convective regeneration that occurred at midnight on 26 may 1985 in the kansas pre storm network described in part i are examined with a numerical cloud model three mechanisms that could have caused the regeneration are identified 1 an increase in low level moisture 2 an increase in low level shear and 3 a mesoscale oscillation forced by previous convection the first numerical experiments begin with a horizontally uniform environment a primary squall line is generated in this environment and is then allowed to decay four hours after the decay a second convective system develops at the leading edge of the gust front from the primary squall line it is shown that this secondary generation is due to a mesoscale oscillation centered at 70 kpa that is forced by the previous convective system horizontal variations in the upstream environment are then considered an increase in low level moisture is examined first and it is shown that the consequent lowering of th

silurian graptolite biostratigraphy in the welsh basin silurian graptolite zones are of markedly shorter duration than those of the ordovician averaging 0 8 ma several can be sub divided and further refinement will undoubtedly follow a revision of many of the graptolite species and their stratigraphic range locally integration of palaeontological and sedimentological studies facilitates correlation a premilinary subdivision of the crispus and griestoniensis zones in central wales is made

kiruna type deposits their origin and relationship to intermediate subvolcanic plutons in the great bear magmatic zone northwest canada magnetite apatite actinolite rocks similar to those at kiruna sweden and the st francois mountains missouri are associated with seven epizonal plutons that intrude andesitic stratovolcanoes of a broadly folded early proterozoic continental magmatic arc located in the northwestern canadian shield the plutons mainly medium grained quartz monzonite monzodiorite diorite iugs sheets and laccoliths 5 to 25 km in diameter are spatially temporally and compositionally related to host andesitic stratovolcanoes they were emplaced at 2 to 3 km depth are compositionally heterogeneous metasomatically altered and had plagioclase as the liquidus phase in addition they have kilometer wide alteration halos comprising an inner zone of nearly complete wall rock albitization an intermediate zone of magnetite apatite actinolite veins pods breccias and wall rock replacement and an outer zone of disseminated sulfides one pluton balachey has a halo that is more or less completely outside the body but another rainy lake has a halo that is partly superimposed over it separation of iron phosphate and silicate melts by liquid immiscibility is not supported by 1 the gradual replacement of plagioclase by chessboard albite toward the roof of the rainy lake pluton 2 the chemical trends in the rainy lake intrusion 3 the mineralogical zoning low temperature mineralogy and replacement textures of the magnetite apatite actinolite and 4 the relationship of the magnetite apatite actinolite veins and bodies to the plutons however all available data are compatible with a deuteric origin it is concluded that high temperature low initial water content and shallow level emplacement by intermediate plutons are necessary for the development of kiruna type deposits

acid mine drainage at cerro rico de potosi i unabated high strength discharges reflect a five century legacy of mining intensive mining and processing of ag sn pb and zn ores have occurred in various locations within and around the city of potosi bolivia since 1545 surface and subsurface waters stream sediments and soils are contaminated with various ecotoxic metals in the headwaters of the economically vital yet highly impacted upper rio pilcomayo watershed previous studies have documented downstream trace metal contamination however not addressed specific sources the amd discharges identified in this study help link downstream pollution to primary origins the majority of amd would be considered high strength due to metal concentrations and acidity orders of magnitude greater than typical amd discharges from both operating and abandoned portals as well as tailings related deposits displayed a high degree of heterogeneity with total metal concentrations ranging from 0 11 to 7480 0 022 to 889 0 0006 to 65 3 0 001 to 310 0 12 to 72 100 0 3 to 402 0 012 to 34 8 and 0 24 to 19 600 mg l of al as cd cu fe mn pb and zn respectively net acidity and ph ranged from 10 to 246 000 mg l as caco3 equivalent and 0 90 6 94 standard units respectively data were gathered during two sampling events centered around the most extreme periods of the dry and wet seasons of one water year loadings to local streams were marginally greater for most metals in the wet season if observed loadings are historically representative cerro rico amd has contributed thousands of tonnes of ecotoxic metals to the upper rio pilcomayo over the last five centuries metal and hydrogen ion concentrations in the majority of amd sampled were several orders of magnitude above discharge limits set by the bolivian government yet no action has historically or contemporarily been taken

magmatism in the huarina belt bolivia and its geotectonic implications abstract the huarina belt is a tectono stratigraphic unit extending along the western side of the eastern cordillera and southern altiplano it includes the well known bolivian tin belt both geophysical and isotopic evidence suggest that the huarina belt is located between three cratonic blocks in a major lithospheric weakness zone that has probably been inherited from the proterozoic most of the phanerozoic backarc magmatism in the bolivian andes occurred along this belt local ordovician basalts and andesites and clasts of devonian granitoids occurring in late devonian early carboniferous sedimentary units are testimonies of a scarce palaeozoic igneous activity during the mesozoic rift related magmatism resulted in peraluminous to metaluminous high k calcalkaline triassic granitoids as well as discrete cretaceous centers of alkaline and carbonatitic rocks in the cenozoic huge high k generally peraluminous ignimbrite sheets along with numerous volcanic and intrusive centers were generated along the belt shoshonitic alkaline and ultrapotassic rocks have been locally described on the basis of both geochemical and geophysical evidence a general evolution model is proposed for the huarina belt during paleozoic and mesozoic times the predominant extensional regime of the continental crust led to lithospheric thinning basin generation and production of within plate magmas during the cenozoic prevailing compressional conditions led to a gradual thickening of the lithosphere inducing delamination of its denser and less viscous root the mantle generated magmas interplayed widely with crustal melts giving rise to the dominantly peraluminous magmas

a theory for strong long lived squall lines abstract we study herein the mechanics of long lived line oriented precipitating cumulus convection squall lines using two and three dimensional numerical models of moist convection these models used in juxtaposition enable us to address the important theoretical issue of whether a squall line is a system of special long lived cells or whether it is a long lived system of ordinary short lived cells our review of the observational literature indicates that the latter is the most consistent paradigm for the vast majority of cases but on occasion a squall line may be composed of essentially steady supercell thunderstorms the numerical experiments presented herein show that either type of squall line may develop from an initial line like disturbance depending on the magnitude and orientation of the environmental shear with respect to the line with shallow shear oriented perpendicular to the line a long lived line evolves containing individually short lived cells our analysis of this type o

a study of two propagating heavy rainfall episodes near taiwan during sowmex timrex iop 8 in june 2008 part i synoptic evolution episode propagation and model control simulation abstractthis paper is the first of a two part study to investigate two rain producing episodes in the longitude time hovmoller space upstream from taiwan during the eighth intensive observing period iop 8 12 17 june 2008 of the southwest monsoon experiment terrain influenced monsoon rainfall experiment sowmex timrex with a goal to better understand the mechanism and controlling factors for their organization and propagation both in a prefrontal environment the first episode moved eastward and the second was a rare westward moving event and each caused heavy rainfall in taiwan on 14 and 16 june respectively in part ii the roles played by synoptic conditions and terrain effects are further examined through sensitivity tests with the aid from a successful simulation with a grid spacing of 2 5 km the structure and organization of convection embedded in the two episodes are shown to be different with stronger low level vertical wind shear in its environment the first episode consisted of well

north pacific cold season surface cyclone activity 1975 1983 abstract an eight year sample of cold season 1 october through 31 march extratropical cyclones in the pacific ocean basin is used to study central pressure changes and life cycle characteristics we find that over 90 of the cyclones passing through the area of the kuroshio current intensify in this region corresponding percentages in excess of 60 extend from the kuroshio south of 45 n eastward to 130 w mean 24 h central pressure falls of all cyclones exceed 9 mb through the entire basin west of 140 w in the latitude band 30 to 50 n a statistical analysis of 24 h central pressure changes is performed on all cyclones within our domain a frequency distribution of 1996 cases of 24 h maximum deepening reveals statistically significant departures from a gaussian distribution with the coefficient of skewness substantially negative we also find similarly significant departures from normal in a frequency distribution of all 24 h central pressure changes in spite of the fact that this distribution wo

fault reconstructions using aeromagnetic data in the great bear magmatic zone northwest territories canada the great bear magmatic zone located in wopmay orogen is a 1 875 1 84 ga belt 450 km long by 100 km wide of volcanic and allied plutonic rocks interpreted as a paleoproterozoic magmatic arc the

numerical study of an observed orogenic mesoscale convective system part 2 analysis of governing dynamics abstract a detailed analysis of the dynamics and thermodynamics responsible for the structure growth and propagation of an orogenic mesoscale convective system simulated in two dimensions is made the process of scale interaction is addressed through fourier analysis and reynolds averaging analysis of representative predicted variables diabatic forcing and momentum acceleration terms additional dynamical analysis is accomplished through sensitivity experiments in which coriolis diabatic heating and ambient airflow are varied the general conclusion is that the simulated orogenic development is a geostrophic adjustment process to convective heating which is itself modulated and maintained by orographically induced flow systems the heating scales range over a nearly continuous spectrum ranging from 10 250 km the heating occurs in response to primary advective gravity modes the larger scale gravity wave disturbances modulate the smaller scales by organizing mean upward vertical motion patterns the la

the generation and propagation of a nocturnal squall line part i observations and implications for mesoscale predictability abstract the initiation and forcing of a squall line on 26 27 may 1985 near wichita kansas is examined the squall line is secondary convection in the sense that it is preceded in the diurnal cycle by other mesoscale convective systems the squall fine develops in synoptic conditions frequently associated with convective weather in the central united states this includes moderate shear moderate to high convective available potential energy a quasi stationary dryline a low level southerly jet and an 85 kpa moist tongue the initiation of free convection is specifically attributed to a gust front that propagates into a low level jet with attendant horizontal vorticity convergence and moisture the gust front initially propagates as a gravity current and subsequently as an internal undular bore observations of gravity currents gravity waves and the collision of radar echo boundaries provide valuable clues for short period forecasting they establish the presence of potential triggering mechanism

detection and prediction of warm season midtropospheric vortices by the rapid update cycle the authors perform a statistical and dynamical analysis of midtropospheric mesoscale vortices captured by analyses from the rapid update cycle version 2 ruc 2 during the period 1 may to 31 august 1999 a total of 203 vortices meeting conditions of an automated algorithm were found of these 86 were observed to form within organized convection and were termed mesoscale convective vortices mcvs mcvs were favored over a broad area from eastern colorado and western nebraska to the mississippi river valley essentially collocated with the loci of organized convection the remaining 117 vortices termed dry vortices clustered in the immediate lee of the rocky mountains and over the southeastern united states vortices arising from convection had considerably greater intensity and longevity than dry vortices they were roughly five times more likely to be involved with the triggering of new convection a relationship was found between intensity and longevity such that there appears to be a maximum vortex lifetime that can be estimated from its maximum intensity vortices arising from convection had markedly greater humidity and water vapor mixing ratio underneath their centers compared to dry vortices consistent with many dry vortices having a topographic origin and mcvs arising from organized convection parameters such as horizontal scale background vertical wind shear and horizontal deformation were not systematically related to intensity or longevity prediction of mesoscale vortices by the ruc 2 was examined for a subsample of all cases in general the ruc 2 was able to predict the evolution of vortices once analyzed but had virtually no skill at predicting 12 h in advance the formation of the vortices however forecasts of organized convection should still benefit from accurate predictions of long lived vortex tracks

diurnal variation of summer convection over west africa and the tropical eastern atlantic during 1974 and 1978 abstract four times daily infrared images from the geostationary satellite meteosat i are used to compare thediurnal variations of deep convection over west africa and the eastern atlantic during the summer of 1978with the variations observed by the sms l satellite during phases ii and iii of gate 28 july 19 september 1974 a subjective method similar to that employed by mcgarry and reed 1978 in analyzing the 1974 data is used in estimating the degree of convective activity a close agreement is found between the behavior of the convection in the two years in particular 1 maximum convective activity in the area of the gate ship hexagon occurred again in the lateafternoon and the amplitude of the convective cycle was again larger at the eastern edge of the outerhexagon than at the western edge 2 closer to shore the peak activity occurred near noon as in 1974 and in the immediate vicinity of theshore the amplitude of the cycle was again very small 3 over the highlands of west africa explosive grow

basinal and shelf sedimentation in relation to the archaean proterozoic boundary abstract in most countries the archaean proterozoic boundary has been designated as an unconformity between the oldest shelf type quartz arenites and a basement consisting of greenstone belts intruded by granitic rocks or high grade gneisses the quartz arenites have been characterized as shallow water shelf deposits and sediments in the greenstone belts as resedimented basinal wackes of volcanogenic origin radiometric ages for rocks of the canadian shield led to initial designation of the archaean proterozoic boundary as thus defined at about 2 5 ga subsequent age determinations have clearly established that a number of quartz arenites originally assigned to the proterozoic are 2 7 2 94 ga old e g witwatersrand and pongola supergroups of south africa to accommodate these old quartz arenites some have suggested that the arch aean proterozoic boundary should be regarded as diachronous embracing a span of time about equivalent to that of the phanerozoic however quartz arenites also are abundant in 3 2 3 5 ga old greenstone belts and high grade metamorphic terranes of south africa western australia and the u s a likewise large regions of basinal volcanogenic sediments occur in post 2 5 ga terranes this greatly expands the diachroneity of geological units that were initially regarded as either uniquely archaean or proterozoic we therefore recommend that chronometric and chronostratigraphic sense be retained for the archaean proterozoic boundary divested of the requirement for all quartz arenites to be proterozoic according to this analysis of the precambrian record shelf sediments have increased in abundance relative to basinal sediments through time but at different rates in different areas this change is attributable to progressive cratonization of shield areas a process that was strongly diachronous on a worldwide scale

synoptic conditions associated with propagating and nonpropagating cloud rainfall episodes during the warm season over the east asian continent abstractusing european centre for medium range weather forecasts ecmwf analyses this study identifies common synoptic flow patterns associated with propagating long lived and nonpropagating short lived precipitation cloud episodes in the warm season over east asia 25 40 n 95 125 e among 123 initial cases during may july 1997 2003 86 were classified into three categories propagating cases with strong and weak forcing and nonpropagating ones with strong inhibition consisting of 10 types based on their 500 hpa flow patterns for each type composites at various levels when episodes moved across 100 105 110 115 and 120 e were made and discussed to elucidate the influence of synoptic conditions for propagating episodes with strong 500 hpa forcing 46 cases four types were identified in their composites favorable positive vorticity advection forcing from an approaching trough short wave exists aloft and concurrent development of southwest vortex and front wind shift line at low lev

convectively forced diurnal gravity waves in the maritime continent abstractlong lived zonally propagating diurnal rainfall disturbances are a highly pronounced and common feature in the maritime continent mc a recent study argues that these disturbances can be

topographic effects on spatiotemporal variations of short duration rainfall events in warm season of central north china statistical analyses of the hourly station rainfall observation over the recent 8 years show that rainfalls in the warm season may october of the central north china are dominated by short duration rainfall events lasting less than or equal to 6 h and the southeastward delayed diurnal phases of total rainfall revealed by previous studies are mainly contributed by the propagating short duration rainfall rather than the long duration rainfall as that along the yangtze river valley the spatiotemporal features of rainfall events are highly correlated with elevation heights the largest frequency of short duration rainfall events locates in the southeastern inner periphery of taihangshan and yanshan mountains rainfall over the northwestern mountains often occurs in the afternoon some rainfall events propagate southeastward and influence the rainfall in the southeastern foothills and plain the rainfall with short duration time mainly begins around the late evening in the southeastern plain and even later in coastal regions the understanding of topographic effects to rainfall events is discussed based on reanalysis and station data results indicate that the topography influences the diurnal varied surface or low level temperature moisture and wind fields which benefit rainfall events occurring in the afternoon over the northwestern mountains first and the southeastward propagation afterward

the characteristics of weakly forced mountain to plain precipitation systems based on radar observations and high resolution reanalysis the metropolis of beijing in china is located on a plain adjacent to high mountains to its northwest and the gulf of the bohai sea to its southeast one of the most challenging forecast problems for beijing is to predict whether thunderstorms initiating over the mountains will propagate to the adjacent plains and intensify in this study 18 warm season convective cases between 2008 and 2013 initiating on the mountains and intensifing on the plains under weak synoptic forcing were analyzed to gain an understanding of their characteristics the statistical analysis was based on mosaic reflectivity data from six operational doppler radars and reanalysis data produced by the four dimensional variational doppler radar analysis system vdras the analysis of the radar reflectivity data shows that convective precipitation strengthened on the plains at certain preferred locations to investigate the environmental conditions favoring the strengthening of the mountain to plain convective systems statistical diagnoses of the rapid update 12 min 3 km reanalyses from vdras for the 18 cases were performed by computing the horizontal and temporal means of cape convective available potential energy cin convective inhibition vertical wind shear and low level wind for the plain and mountain regions separately the results were compared with those from a baseline representing the warm season average and from a set of null cases and found considerable differences in these fields between the three datasets the mean distributions of vdras reanalysis fields were also examined the results suggest that the convergence between the low level outflows associated with cold pools and the south southeasterly environmental flows correspond well with the preferred locations of convective intensification on the plains

understanding sibumasu in the context of ribbon continents abstract well described ribbon continent collision belts and modern examples with 2d seismic coverage particularly zealandia provide analogues for the permo triassic development of sibumasu two key parameters for the ribbon continents are their width and how rifting developed which in turn impact the structural metamorphic igneous and stratigraphic development of ribbon continents in ways that make them significantly different from the collisional development of major continents key characteristics of the tectonics of sibumasu are 1 a tendency towards basin inversion during the late triassic and possibly early jurassic and mixed thick skinned and thin skinned style deformation 2 extensional collapse around 215 ma is an important feature of sibumasu particularly in northern thailand and probably other areas too 3 slab delamination and extension related decompression melting were probably important mechanisms for generating granites in addition to crustal thickening 4 metamorphism is relatively high temperature lower pressure

offshore propagation of coastal precipitation abstractthis work focuses on the seaward propagation of coastal precipitation with and without mountainous terrain nearby offshore of india diurnal propagation of precipitation is observed over the bay of bengal on the eastern side of the bay a diurnal but nonpropagating signal is observed near the west coast of burma this asymmetry is consistent with the inertio gravity wave mechanism perturbations generated by diurnal heating over the coastal mountains of india propagate offshore amplify in the upwind direction and dissipate in the downwind direction relative to the steering wind owing to critical level considerations a linear model is applied to evaluate sensitivity to gravity waves as these affect deep moist convection and propagation analyses are performed for various heating depths mountain widths stability coriolis effect background mean wind and friction calculations reveal how these factors affect the amplitude dissipation initiation phase and propagation speed of the diurnal

convection initiation by density currents role of convergence shear and dynamical organization abstract steady state analytic models establish two key points concerning the impact of vertical shear on density currents and the implication for convection initiation first shear decreases the horizontal convergence and therefore the mean ascent associated with downshear propagating currents second shear has a basic effect on the dynamical organization if the downshear current travels at the speed of the ambient flow at a critical steering level an overturning circulation provides deep lifting although mean ascent is increased by shear in the case of upshear propagating currents the lifting is comparatively shallow because jumplike ascent occurs rather than deep overturning the convection initiation mechanism involving the downshear current is therefore very different from the upshear case these basic principles are borne out in two dimensional numerical simulations density currents generated by a stationary cold source imposed on an initially horizontally homogeneous sheared and neutra

the pallacos of cerro rico de potosi bolivia a new deposit type pallacos are a new kind of ore deposit and are described here in detail for the first time they are found on the flanks of the cerro rico de potosi bolivia the world s largest silver deposit fundamentally pallacos are gravels whose clasts contain sufficient disseminated silver so as to be bulk minable the silver bearing clasts originated from the summit of cerro rico and are composed of dacite porphyry or air fall tuffs or arkosic sands of the caracoles formation that have been altered to vuggy silica or jasperoid analysis of facies bedforms depositional textures and clast sizes and percentages suggests that there are two types of pallacos each with a different depositional mechanism one kind the huacajchi type formed from multiple water transported debris flows the other kind the potosina type is interpreted as catastrophic landslides metal zoning clast alteration style and silver grade vary between the two pallaco types

dynamics of a thunderstorm outflow abstract the kinematic and thermodynamic structures of a thunderstorm outflow are examined by means of dual doppler radar analysis mesonet lower and sounding data the data were collected in the denver colorado area during june 1984 the dual doppler analysis shows that the cold outflow is ducted beneath the pbl inversion along the gust front there is a narrow quasi two dimensional updraft kelvin helmholtz instability khi developed along the top of the gust front head near the surface front and propagated backwards dissipating in the wake of the head region an isothermal layer aloft appears to have limited billow amplification to the quasi neutral layer below the gust front s leading edge had numerous inflections which are believed to result from barotrophic instabilities small vortices develop at some of the inflection points detailed analysis of one such circulation shows evidence of the formation of two enhanced updrafts separated by an occlusion downdraft these observations are the firs

erosion and tectonics at the margins of continental plateaus the topography across the eastern margin of the central andean plateau north of 18 s beni region bears a strong resemblance to the topography of the southern margin of the tibetan plateau nepal himalaya with both regions featuring a steep frontal slope and high peaks at the plateau edge in contrast the topography of the eastern margin of the central andean plateau south of 18 s pilcomayo region tapers toward the foreland more gently and has no line of high peaks at the margin both the himalayan and the beni regions have been the sites for large amounts of denudation and in both regions geologic evidence suggests that erosion has been sufficiently vigorous for the physiographic plateau margin to have retreated toward the plateau interior during the neogene we hypothesize that the steep frontal slope and high peaks of the beni region and himalayan front largely reflect the high orographic precipitation and high erosion rates occurring in these regions and that the more gentle topography of the semiarid pilcomayo region reflects a tectonic landform only slightly modified by erosion we propose that orographic precipitation impinging on a plateau margin will generally tend to drop moisture low on the slope eroding back the plateau while enhancing or maintaining the steep long wavelength slope a numerical model coupling orographic precipitation erosion and tectonic uplift demonstrates the plausibility of this hypothesis the erosional efflux in both the beni and nepal himalaya have been considerable and simple mass balance calculations for the himalaya suggest that during the neogene the erosional mass efflux has generally outpaced the tectonic mass influx this contrasts with the apparent prior domination of tectonic influx and may reflect a decrease in the rate of tectonic addition during the same period and or increased late cenozoic erosion rates

downsag and extension at calderas new perspectives on collapse geometries from ice melt mining and volcanic subsidence structures at calderas may form as a result of precursory tumescence subsidence due withdrawal of magmatic support resurgence and regional tectonism structural reactivation and overprinting are common to explore which types of structures may derive directly from subsidence without other factors evidence is reviewed from pits caused by the melting of buried ice blocks mining subsidence scaled subsidence models and from over 50 calderas this review suggests that complex patterns of peripheral deformation with multiple ring and arcuate fractures both inside and outside caldera rims topographic embayments arcuate graben and concentric zones of extension and compression may form as a direct result of subsidence and do not require a complex subsidence and inflation history downsag is a feature of many calderas and it does not indicate subsidence on an inward dipping ring fault as has been inferred previously where magmatic inflation is absent or slight initial arcuate faults formed during collapse are likely to be multiple and dip outwards to vertical associated downsag causes the peripheries of calderas undergo radial centripetal extension and this accounts for some of the complex peripheral fractures arcuate crevasses graben and some topographic moats the structural boundary of a caldera defined here as the outermost limits of subsidence and related deformation including downsag commonly lies outside ring faults and outside the embayed topographic wall it is likely to be funnel shaped i e inward dipping even though ring and arcuate fractures within it may dip outward inward dipping arcuate normal faults at shallow levels and steep inward dipping contacts between a caldera s fill and walls may both occur at a caldera that has initially subsided on outward dipping ring faults they arise due to peripheral surficial extension gravitational spreading and scarp collapse topographic enlargement at some calderas and the formation of embayments may reflect general progressive downsag and localized downsag respectively these processes may occur in addition to surficial degradation of oversteep ring fault scarps

rainfall occurrence in the u s warm season the diurnal cycle the diurnal occurrence of warm season rainfall over the u s mainland is examined particularly in light of forcings at multiple scales the analysis is based on a radar dataset of 12 seasons duration covering the u s mainland from the continental divide eastward the dataset resolves 2 km features at 15 min intervals thus providing a detailed view of both large and regional scale diurnal patterns as well as the statistics of events underlying these patterns the results confirm recent findings with respect to the role of propagating rainfall systems and the high frequency at which these are excited by sensible heating over elevated terrain between the rockies and the appalachians 60 of midsummer rainfall occurs in this manner most rainfall in the central united states is nocturnal and may be attributed to the following three main forcings 1 the passage of eastward propagating rainfall systems with origins near the continental divide at 105 w 2 a nocturnal reversal of the mountain plains solenoid which is associated with widespread ascent over the plains and 3 the transport of energetic air and moisture convergence by the great plains low level jet other features of interest include effects of the appalachians semidiurnal signals of regional significance and the impact of breezes along the gulf of mexico a modest effort was put forth to discern signals associated with el nino and the southern oscillation while tendencies in precipitation patterns are observed the record is too short to draw conclusions of general significance

initiation of convective storms at radar observed boundary layer convergence lines abstract the origin of 653 convective storms occurring over a 5000 km2 area immediately east of the colorado rocky mountains from 18 may to 15 august 1984 was examined seventy nine percent of the 418 storms that initiated within the study area occurred in close proximity to radar observed boundary layer convergence lines this percentage increased to 95 when only the more intense storms 60 dbze were considered colliding convergence lines initiated new storms or intensified existing storms in 71 of the cases a new storm took a median time of 24 min to grow to 30 dbz following line collision the convergence lines ranged in length between ten and several hundred kilometers both radar and mesonet stations indicated that the primary convergence was concentrated in a zone 0 5 to 5 km in width these lines were characterized on doppler radar as thin lines of enhanced reflectivity between 0 and 20 dbze and as a line of strong radial or azimuthal gradient in doppler velocity these lines were observed ev

trace element discrimination of arc slab failure and a type granitic rocks abstract although widely used classification schemes for granitic rocks have until now failed to separate slab failure from arc magmatism in collisional orogens our previous work showed that cretaceous cordilleran type batholiths are composed of a pre collisional belt of mesozonal to epizonal arc plutons commonly emplaced into their own cover and a post accretion tract of what we interpret as slab failure plutons emplaced into the tectonically thickened collisional hinterland histograms based on new geochemical compilations of pre and post collisional igneous rocks were employed to derive trace element criterion to distinguish between these two plutonic types using rocks over the sio2 range of 55 70 wt and aluminum saturation index of 20 nb y 0 4 ta yb 0 3 la yb 10 gd yb 2 and sm yb 2 5 also we found that a type magmas can be distinguished from other post collisional igneous rocks based on ta yb 6 ppm and nb y 60 ppm these trace element differences between our pre collisional arc and post collisional slab failure plus a type groups allowed us to build composite discrimination diagrams for destructive margin igneous rocks although most s type granites are also post collisional they should not be plotted on our diagrams for some of their geochemical features overlap those of our slab failure group unlike our arc and slab failure groups a type granites are formed in diverse tectonic settings such that their classification is more related to geochemical signature and magma sources than to tectonic setting lastly we show how our discrimination diagrams delineate examples of slab failure magmatism through time and suggest links with porphyry cu au deposits

intracaldera structure and megabreccias at dorobu caldera northeastern honshu japan in the pliocene dorobu caldera 13 by 6 km in diameter on northeastern honshu japan a number of occurrences of a distinctive megabreccia block facies is found within voluminous ash flow tuffs the dorobu ash flow tuffs a and b dorobu tuff a is believed to be the deposit of the initial caldera forming eruption an isopach map of tuff b and orientation of narrow dikes indicate that an internal large depression occurred inside the present caldera margin this and locations of post caldera conduits and near vent facies of dorobu tuff c suggest that the caldera has a nested collapse structure and possible conduits of the tuff b are within the internal depression annular collapses that sequentially moved towards the caldera center occurred during eruption of tuffs a and b the overall structure of dorobu caldera is nested and it possibly has step like floor as described elsewhere from piecemeal calderas megabreccia block facies consists of polyhedral massive blocks composed of miocene to pliocene country rocks with large diameters up to several hundreds meters the block facies as a whole does not consist of sheets or piles of debris as described in the san juan mountains and stillwater range usa but as isolated blocks set in the matrix of dorobu tuffs a and b in previous studies of caldera development the mode of emplacement of caldera collapse breccias has been considered to be by rock fall or rock slide during the caldera forming eruption a paleo magnetic study of the block facies shows two significant characteristics predominant variations of the magnetic directions of blocks indicate that they were emplaced with rotations caused by rock slide rock fall or a toppling motion in contrast magnetized directions of one megabreccia block almost coincide with that of the caldera country rock suggesting that this block must have kept its original magnetic direction our findings suggest that it is not a rock slide deposit derived from caldera walls but rather a segment of subsided caldera floor the mode of emplacement of the megabreccia block facies at dorobu caldera is mostly similar to the other megabreccias however additionally it is necessary to distinguish segments of caldera floor from rolled or toppled megabreccia blocks

numerical simulation of episodes of organized convection in tropical northern africa abstracta large domain convection permitting numerical model is used to simulate episodes of deep convection which are generated during the day over the ethiopian highlands and then propagate westward over the eastern and central sahel region 5 20 n of northern africa the simulation comprises 12 5 days within the african monsoon multidisciplinary analysis amma field campaign in 2006 during this period long lived precipitation episodes that survived beyond a single diurnal cycle occurred in the lee of the ethiopian highlands only every 2 3 days in both the simulation and observations this contrasts with some other latitudinal corridors in the lee of major topography such as the central united states where long lived heavy precipitation episodes frequently occur on successive nights the intermittency of long lived events for the current case occurs despite regular daily triggering of convection along the upstream orography and is linked to strong lower tropospheric stabilization and reduction o

the propagation and diurnal cycles of deep convection in northern tropical africa the propagation and diurnal cycle of organized convection in northern tropical africa are examined using five years 1999 2003 of digital infrared imagery for may august reduced dimension techniques are used to document the properties of cold clouds proxies for deep convection and precipitation large scale environments are diagnosed from global analyses organized convection in africa consists of coherent sequences or episodes which span an average distance of about 1000 km and last about 25 h a substantial fraction of events exhibits systematic propagation at regional to continental scales while undergoing decay and regeneration episodes with 36 h duration and 1472 km span recur at a one per day interval most episodes have phase speed of 10 20 m s 1 which is faster than most african easterly waves convective episodes tend to initiate in the lee of high terrain consistent with thermal forcing from elevated heat sources average diurnal frequency maxima result from the superposition of local diurnal maximum with the delayed phase arrival of systems propagating from the east propagation occurs with moderate low to mid tropospheric shear which varies with the african easterly jet migration and west african monsoon phases frequent deep convection occurs with local shear maxima near high terrain for the peak monsoon period and for 10 w 10 e where easterly waves and convective systems are frequent 35 of cold cloud episodes occur east of the wave trough compared with about 24 to the west based on the coherent behaviour of organized propagating convection inferences may be made regarding the prediction of precipitation beyond one or two days copyright 2008 royal meteorological society

duration of magmatic hydrothermal and supergene activity at cerro rico de potosi bolivia new high precision 40ar 39ar dating of sanidine and biotite from two rhyolitic domes and an ignimbrite combined with existing fission track data and a hydrothermal sericite age suggests that the world class ag deposit at cerro rico was emplaced during a protracted period of magma related hydrothermal activity beginning at 13 77 0 03 ma and continuing for at least 0 2 m y this may have been sustained by a large single injection or repeated injections of fractionated ag enriched magma into a high level magma chamber k ar dating of alunite indicates that supergene oxidation had begun by about 13 5 ma soon after dome emplacement and progressed semicontinuously for at least 7 5 m y this oxidation while not leading to significant enrichment has significantly enhanced the economic viability of the disseminated part of the orebody

diurnal variations of summer precipitation over contiguous china 1 diurnal variations of summer precipitation over contiguous china are studied using hourly rain gauge data from 588 stations during 1991 2004 it is found that summer precipitation over contiguous china has large diurnal variations with considerable regional features over southern inland china and northeastern china summer precipitation peaks in the late afternoon while over most of the tibetan plateau and its east periphery it peaks around midnight the diurnal phase changes eastward along the yangtze river valley with a midnight maximum in the upper valley an early morning peak in the middle valley and a late afternoon maximum in the lower valley summer precipitation over the region between the yangtze and yellow rivers has two diurnal peaks one in the early morning and another in the late afternoon

absence of silicic volcanism on mars implications for crustal composition and volatile abundance on earth eruptions of silicic magmas with volumes of 1 100 km3 are generally associated with stratovolcanoes or composite cones whereas larger 100 1000 km3 ignimbrite deposits are erupted from resurgent calderas and related structures small volumes of silicic rocks are generated by differentiation within basic magma chambers associated with stratovolcanoes but large silicic deposits are largely confined to areas where the granitic crust is thicker than 25 km as mantle derived magmas rise through the thick granitic crust fractional crystallization and assimilation of hydrous crustal rocks concentrate volatiles and sio2 in the magma yielding explosive silicic eruptions on mars under similar chemical conditions ignimbrite eruptions could take place over a broader range of physical conditions than on earth but no large volume ignimbrite deposits can be identified positively explosive basic to ultrabasic eruptions may be responsible for small cinder conelike features on mars and perhaps for the ancient flank scoured paterae such eruptions may have been driven by near surface water ice magma interactions or volatile rich magmas the paterae represent a unique style of volcanism that stopped 2 b y ago we suggest that the volatiles associated with these features were derived from mantle sources and that the cessation of patera formation may coincide with the termination of the period of maximum planetary degassing volcanism since 2 b y ago has been dominantly effusive except for minor explosive ash events such as those which blanketed part of the summit of hecates tholus we propose that such eruptions were driven by volatiles generated by differentiation of a magma chamber similar to icelandic explosive eruptions the apparent lack of large scale silicic volcanism on mars is circumstantial evidence that mars is deficient in volatiles and lacks a granitic crust

precipitation and convective characteristics of summer deep convection over east asia observed by trmm abstractthis study examines precipitation and convective characteristics of summer deep convection for five distinct regions plateau foothill lowland south china and ocean in east asia using 13 yr of tropical rainfall measuring mission trmm based precipitation features every region has its own unique features in terms of elevation rainfall amount and dynamic thermodynamic environments results show that large deep convective systems contribute the majority of precipitation totals over all regions except the plateau mixed phase precipitation processes are more important in the south china and the lowland regions than in the foothill and ocean regions the plateau region also shows substantial dependence upon mixed phase processes though the mixed phase region has a smaller depth than the other regions most metrics indicate that the south china region has the most intense storms followed by the lowland plateau foothill and ocean regions however ice scattering signatures do show that the

graben structure in the las canadas edifice tenerife canary islands implications for active degassing and insights on the caldera formation abstract a graben structure has been identified at the western area of the las canadas caldera wall here referred as the los azulejos graben this graben is 1 km wide and is bounded by two major normal faults trending ne sw the los azulejos fault and the ucanca fault the graben was active for at least 0 5 ma from the end of the ucanca fm to the end of the guajara fm and before the collapse of the las canadas edifice that formed the western caldera a right lateral transtension regime operated in the graben as suggested by small fault orientations and kinematics the prolongation of the ne rift zone of tenerife to the canadas edifice is the most likely volcano tectonic scenario for the graben in this context inflation of phonolitic shallow magma chambers may have produced reverse faults and reactivation of normal faults an intense and widespread hydrothermal alteration here called azulejos type occurred mainly before the graben formation while a fault related hydrothermal alteration occurred during and after the graben diffuse carbon dioxide and hydrogen degassing in and around the las canadas caldera show relatively enriched values along a ne sw trend suggesting that faults in the los azulejos graben act as a pathway for deep seated gases to the surface diffuse degassing and hydrothermalism indicate that the graben area has been a zone of intense fluid circulation during the evolution of the las canadas edifice

diurnal evolution and distribution of warm season convective storms in different prevailing wind regimes over contiguous north china the diurnal evolution and distribution of warm season convective storms in different prevailing wind regimes at the 925 hpa and 500 hpa levels over contiguous north china have been studied using a climatology based on radar reflectivity mosaics soundings and reanalysis data from 15 may to 15 september in 2008 2011 in the wind regimes at the 925 hpa level the frequency of occurrence of convection is highest for south southwesterly flows followed by that for south southeasterly flows the low level southerly warm and moist flow over the foothills and plains favors initiation and intensification of convection resulting from topographic forcing among the wind regimes at the 500 hpa level the frequency of occurrence of convection shows a pronounced maximum for west southwesterly flows and most of these storms initiate and develop over the foothills and plains convection in the wind regime shows the morphology and slowly east southeastward moving characteristics of well organized longer lived systems with environmental conditions conducive to vertical wind shear and instability at the 500 hpa level the high frequency of occurrence of convection for west southwesterly flows is followed by that for west northwesterly flows under west northwesterly flows convective storms initiated over mountains located to the northwest in the early afternoon move rapidly to the plains in the southeast of the study region these storms show the primary formation characteristics of shorter lived convection and intensify noticeably as they move from the mountains to the foothills and plains

why nocturnal long duration rainfall presents an eastward delayed diurnal phase of rainfall down the yangtze river valley hourly observational records and 6 hourly reanalysis data were used to investigate the influences of large scale forcings on the diurnal variation of summer rainfall along the yangtze river yr the results show that longduration more than six hours rainfall events dominate the summer rainfall along the yr these events tend to start during the night and to peak after several hours of development the eastward delayed initiation of the nocturnal long duration rainfall events is thought to be due to the diurnal clockwise rotation of the lowtropospheric circulation especially the accelerated nocturnal southwesterlies in the early evening the anomalous easterly flow toward the tibetan plateau tp causes low level convergence over the plateau s eastern slope that induces the formation of rainfall in the upper yr valley the anomalous wind sequentially rotates clockwise to a southerly flow at midnight and accelerates the meridional wind in the middle valley resulting in the initiation of rainfall between 2300 and 0300 lst in the early morning the accelerated southwesterlies in southern china when combined with decelerated winds in the north of the yr causes a strong convergence along the yr and contributes to the early morning rainfall in the lower valley furthermore the development of the convection systems is suppressed in the afternoon by the mid and low level warm advection downstream from the tp this helps explain why long duration events do not typically start in the afternoon in the upper yr valley

behavior of deep convective clouds in the tropical pacific deduced from isccp radiances abstract we analyze the properties of deep convection over the equatorial pacific and its relationship to sea surface temperature sst and surface wind divergence using isccp radiance data for july 1983 and january 1984 deep convective clouds dcc are diagnosed with both a combined visible infrared threshold method and an infrared only threshold method the visible channel is important in diagnosing deep convection in different regions with different surface and atmospheric properties because of the existence of large scale variations of dcc top altitudes the itcz and spcz exhibit changes in these two months that are characteristic of both the el nino and seasonal cycles deep convection is latitudinally confined to a much smaller spatial scale than that suggested by maps of outgoing longwave radiation diurnal variations of dcc cover and associated mesoscale cirrus anvil cloud cac cover are out of phase with deep convection peaking in the early morning throughout the equatorial pacific the diurna

collapse mechanism of the paleogene sakurae cauldron sw japan the paleogene sakurae cauldron of sw japan is characterized by a nested structure with a polygonal outline 21 13 km2 including a circular collapsed part 5 km in diameter total thickness of the caldera infill amounts to 2 000 m the lower member of the infill consists mainly of felsic crystal tuff and lesser intercalated andesitic lava flows whereas the upper member is composed of high grade ignimbrite capped with a large rhyolitic lava dome these members represent the first and second stage eruptions respectively faults bounding the cauldron rim comprise intersecting radial and concentric faults producing the polygonal outline of this cauldron the primary collapse of this cauldron thus occurred as a polygonal caldera basin where products of the first stage eruption accumulated in contrast the inner collapse part is defined by a ring fracture system this sector subsided concurrently with accumulation of the high grade ignimbrite of the second stage eruption this inner circular collapse thus represents syn eruptional subsidence concurrent with the climactic eruption magma drainage during the first stage probably induced outward dipping ring fractures in the chamber roof opening of the ring fractures following subsidence of the central bell jar block caused rapid evacuation of magma as voluminous pumice flows even though magma pressure may have decreased to some degree

response of a stably stratified flow to cooling abstract the spreading of the low level cold pool produced by evaporation of precipitation is generally acknowledged to be an important mechanism for the regeneration of moist convection we show that cooling a stably stratified nocturnal boundary layer produces very different results from the corresponding daytime case in which the boundary layer is neutral in particular dynamic behavior is sometimes closer to that of a gravity wave than to a density current the gravity wave speed defines a minimum propagation speed for a self regenerating convective system

la pacana caldera and the atana ignimbrite a major ash flow and resurgent caldera complex in the andes of northern chile the recently discovered la pacana caldera 60 35 km is the largest caldera yet described in south america this resurgent caldera of pliocene age developed in a continental platemargin environment in a major province of ignimbrite volcanism in the central andes of northern chile at about 23 s latitude collapse of la pacana caldera was initiated by the eruption of about 900 km3 of the rhyodacitic atana ignimbrite the atana ignimbrite was erupted from a composite ring fracture system and formed at least four major ash flow tuff units that are separated locally by thin air fall and surge deposits all four sheets were emplaced in rapid succession about 4 1 0 4 ma ago caldera collapse was followed closely by resurgent doming of the caldera floor accompanied by early postcaldera eruptions of dacitic to rhyolitic lava domes along the ring fractures the resurgent dome is an elongated asymmetrical uplift 48 5 12 km which is broken by a complex system of normal faults locally forming a narrow discontinuous apical graben later postcaldera eruptions produced large andesitic and dacitic stratocones along the caldera margins and dacitic domes on the resurgent dome beginning about 3 5 ma ago and persisting into the quaternary hydrothermally altered rocks occur in the eroded cores of precaldera and postcaldera stratovolcanoes and along fractures in the resurgent dome but no ore deposits are known a few warm springs located in salars within the caldera moat appear to be vestiges of the caldera geothermal system

orographic effects on a squall line system over taiwan abstract a north south oriented multicellular squall line during the taiwan area mesoscale experiment s tamex intensive observation period 2 was studied using dual doppler radar data as it moved over the island of taiwan over the open ocean it moved eastward at a constant speed 15 5 m s 1 as the squall line encountered taiwan island s complex mountainous areas the leading edge moved slower in the mountain ridge areas than over the valleys as a result its orientation became approximately parallel to the terrain contours in the upper levels the eastward movement of the squall line aloft was less affected by the terrain compared to the low levels as a result the westward tilt of the rising motion at the front became less significant part of the system relative rear to front flow entered the rising branch of the storm s circulation as a result of orographic lifting as illustrated by the trajectory analysis and was enhanced by latent heat release the system relative rear to front flow did

experimental study of caldera formation scaled experiments have been carried out on caldera collapse mechanisms using silicone as analogue magma and dry sand as analogue rock experiments were carried out in two and three dimensions using a range of roof aspect ratios thickness width 0 2 to 4 5 appropriate for caldera collapse they reveal a general mechanism of collapse only weakly dependent on the shape of the reservoir for low roof aspect ratios 1 subsidence starts by flexure of the roof and the formation of outward dipping reverse ring faults which in turn trigger formation of peripheral inward dipping normal ring faults the subsidence always occurs asymmetrically in cross section the reverse faults delimit a coherent piston bounded on each side by an annular zone of inwardly tilted strata located between the reverse and normal ring fault sets the surface depression consists of a nondeformed area piston surrounded by an annular extensional zone tilted strata for high aspect ratios 1 multiple reverse faults break up the roof into large pieces and subsidence occurred as a series of nested wedges 2 d or cones 3 d the extensional zone dominates the surface depression in the case where preexisting regional faults do not play a major role the collapse mechanics of calderas probably depends strongly on the roof aspect ratio calderas with low roof aspect ratios are predicted to collapse as coherent pistons along reverse faults the annular extensional zone might be the source of the large landslides that generate intracaldera megabreccias collapse into magma reservoirs with high roof aspect ratios may be the origin of some funnel calderas where explosive reaming is not dominant

diurnal variations of warm season precipitation over northern china abstract this study examines the diurnal variations of the warm season precipitation over northern china using the high resolution precipitation products obtained from the climate prediction center s morphing technique cmorph during may august of 2003 09 the areas of focus are the yanshan taihangshan mountain ranges along the east peripheries of the loess and inner mongolian plateaus and the adjacent north china plains it is found that the averaged peak in local precipitation begins early in the afternoon near the top of the mountain ranges and propagates downslope and southeastward at a speed of 13 m s 1 the peak reaches the central north china plains around midnight and the early morning hours resulting in a broad area of nocturnal precipitation maxima over the plains the diurnal precipitation peak minimum is closely collocated with the upward downward branch of a mountain plains solenoid mps circulation both the mps and a low level southwesterly nocturnal jet are likely to be jointly resp

the global population of mesoscale convective complexes a global set of 714 mesoscale convective complexes is compiled and some of the common properties of the convective systems are identified and examined from a global perspective the data set includes date of occurrence time of first storms initiation maximum extent termination duration cold cloud shield areas and tracks from initiation to termination it is found that the typical convective complex is nocturnal generates a cold cloud shield area of approximately 350 000 km2 and persists for about 10 h the largest systems and most persistent systems tend to occur near the summer solstices for the globe about 400 systems occur each year primarily over land areas most systems develop in favoured zones although some activity occurs over every continent except antarctica and all major oceans the concentration of activity into favoured zones indicates that there must be special dynamic and or thermodynamic conditions necessary for convection to organize into convective complexes activity is strongly tied to the solar day and shifts from 35 s in early january to about 50 n during the boreal summer and back to 35 s by december within the northern hemisphere there is a pronounced poleward migration as the jet stream shifts northward relatively little migration occurs in the ocean dominated southern hemisphere where the subtropical jet remains quasi stationary over the convective complex regions the nocturnal life cycles copious rainfall large cloud shields and great frequency of mesoscale convective complexes suggest that they may be significant contributors to the global hydrologic cycle and earth system energy budget

excitation of rainfall over the tropical western pacific abstractthe authors have examined 4 years of satellite derived sst and rainfall data in anticipation of a relationship between sst structure and the excitation of convective rainfall the results exhibit a strong excitation signal consistent with the presence of mesoscale sst gradients in about 75 of approximately 10 000 rainfall onset events rainfall onset events occur at locations with enhanced horizontal convergence as inferred by the laplacian of sst on scales of order 100 km the daily sst field exhibits multiscale patchiness spanning a 2 c range the signal is disproportionately large at ssts that are 0 25 c above the mean near 29 5 c disproportionately weak for sst 28 8 c and proportionately neutral for sst 30 3 c the calculations suggest that a characteristic strength of this lower boundary forcing 3 10 5 s 1 is approximately one order of magnitude stronger than the mean regional background forcing 3 10 6 s 1 the periphery of warm oceanic patches exhibits both convergent an

midlevel cyclonic vortices generated by mesoseale convective systems abstract despite the large number of convective systems that occur over the central united states every year there are typically only a few well defined midlevel vortices apparent in satellite imagery after the overlying anvil debris from some convective complexes has dissipated or advected away a climatology of mesoscale convectively generated vortex mcv events for 1981 1988 is presented and the synoptic setting in which the circulation becomes apparent is discussed proximity sounding data from numerous cases are used to examine features of the kinematic and thermodynamic setting of mcvs at various lifelycle stages defined by satellite imagery features ofthe large scale environment that appear conducive to the formation and longevity of mcvs include weak flow weak vertical shear weak background relative vorticity and intense horizontal and vertical moisture gradients the rapid mesovortex generation observed can be explained by the stretching term of the vorticity equation most mcvs emerge fro

large scale meteorological conditions associated with midlatitude mesoscale convective complexes abstract objective analyses of composited meteorological conditions attending ten mesoscale couvective complexes mcc reveal a number of distinctive characteristics and important interactions with the large scale environment the systems appear to be linked to eastward progression of a weak middle tropospheric short wave trough initial thunderstorms develop within a region of mesoscale convergence and lifting that is apparently forced primarily by low level warm advection the mcc system acquires mesoscale organization while it moves eastward ahead of the short wave trough diabatic heating eventually produces a system that is warm core in the middle troposphere and cold core in upper levels the mature mcc exhibits many similarities to tropical convective systems although it occurs within a considerably different large scale setting inflow within the lower half of the troposphere feeds convection within a region characterized by significant net upward mass flux and widespread precipitation thickne

alteration facies linkages among iron oxide copper gold iron oxide apatite and affiliated deposits in the great bear magmatic zone northwest territories canada high temperature metasomatism driven by ascent of voluminous saline fluid columns in the upper crust plays a major role in the genesis of iron oxide alkali alteration ore systems but fundamental questions remain on genetic linkages among iron oxide copper gold iocg iron oxide apatite ioa albitite hosted uranium and skarn deposits that they produce excellent surface exposures of such systems in the great bear magmatic zone of northernwestern canada record the depth to paleosurface prograde evolution of iron oxide alkali alteration facies and mineralization across the belt albitite corridors that are tens of kilometers in length record the earliest reactions between highly saline fluids and host rocks along fault zones and subvolcanic intrusions pervasive albitization partitioned metals from the host rocks into the ascending fluid column leaving behind structurally weakened corridors of porous albitite these corridors were cut replaced and overprinted by amphibole and magnetite bearing calcic iron alteration assemblages in extreme cases the discharge of calcium iron and specialized metals formed iron oxide apatite deposits vanadium rare earth elements while recharging the outgoing fluids in sodium potassium and base and precious metals as temperatures declined and fluid chemistry evolved through fluid rock reactions the formation of potassic iron alteration assemblages breccias and sulfides resulted in magnetite and hematite group iocg mineralization within carbonate units skarns formed prior to are replaced by and evolved to calcic iron alteration facies skarns can locally host base metal mineralization tectonically uplifted albitite breccias replaced by potassic iron alteration assemblages became a preferential host for uranium mineralization the results of this study also illustrate that permutations and cyclical build up of alteration products can arise from a combination of faulting differential uplift and renewed magmatism framed within an alteration facies deposit model alteration zones and mineral occurrences play a pivotal role in predicting the mineral potential of iron oxide and alkali altered systems at district to deposit scales

mesoscale convective complexes in the western pacific region abstract a climatological study of mesoscale convective complexes mccs during 1983 1985 over the western pacific region wpr using full disc enhanced infrared satellite imagery from the japanese geostationary meteorological satellite is presented the results indicate that mccs are common in the wpr and display many of the same characteristics as those found in the americas the systems are nocturnal and tend to form over or in the immediate vicinity of land cold cloud shields in the americas last for about 10 h while wpr shields last about 11 h the cold cloud shield size distribution is similar to that of the americas with most systems exhibiting areas between 2 105 and 3 105 km2 seasonal distributions of wpr systems are also similar to that in the americas specifically the frequency of midlatitude systems peaks in late spring and early summer while low latitude mccs are distributed uniformly throughout the warm season as with western systems wpr mccs occur in preferred zones climatolog

secular variation in greenstone sequence development emphasizing superior province canada abstract evidence from the superior province of the canadian shield suggests the existence of several distinct lithostratigraphic associations in greenstone belts 1 quartz arenite and carbonate bearing sequences 2 mafic ultramafic volcanic sequences 3 mafic to felsic volcanic cycles and 4 timiskaming type sequences of fluviatile sediments and calc alkaline to alkaline volcanics recently recognized quartz arenite bearing sequences in the sachigo and wabigoon subprovinces are from base to top quartz arenite stromatolite bearing carbonate oxide facies iron formation and komatiite or tholeiite primary structures in the quartz arenites indicate shallow water deposition and represent mature sedimentation granitoid provenance of these sediments is postulated based upon petrography of coarse arenites and clasts of associated conglomerates the few dated superior province quartz arenite bearing sequences are 2 85 ga the shallow water origin of the primary structures and biota and the areal extent of the quartz arenite and carbonate sequences invite comparison with platform sediments at passive margins platform sequences unconformably overlie 3 ga granitoid rocks and older mafic volcanics where original lower contacts are preserved in two localities mafic volcanic sequences contain sheet flows iron formations and deep water argillites based on physical volcanology and sedimentology these sequences are compared to modern deep water mafic plain and hawaiian volcanism they generally underlie mafic to felsic volcanic cycles and overlie platform sequences mafic sequences are 2740 2700 ma in age mafic to felsic volcanic cycles consist of deep water tholeiitic flows overlain by shallow water to subaerial intermediate to felsic pyroclastics and flows the facies style of volcanism petrography and geochemistry of the mafic to felsic cycles most closely resemble the characteristics of crust in continental magmatic arc systems this type of lithostratigraphic association varies in age from 2775 to 2700 ma in the superior province with minor exceptions timiskaming type sequences consist of fluviatile conglomerate immature arenites and wackes with subaqueous to subaerial volcanics of variable chemistry longitudinal and lateral variation within fault bounded basins is extreme and the sequences have generally been affected by only late stages of deformation the combination of rock types facies distribution the fault bounded nature of the repositories and the locus of sedimentation along zones of transcurrent displacement suggest timiskaming sequences are best compared with modern pull apart basins superior province timiskaming sequences are within the superior province platform sequences are the earliest postorogenic lithostratigraphic unit in greenstone belts followed by mafic plain sequences arc volcanics and pull apart basins we suggest that platform sequences based upon limited evidence are preceded by an orogeny and that pull apart basins represent a subsequent orogeny the lithostratigraphic units above have distinct metallogenic associations 1 platform sequences based upon compilation of several shields may contain detrital au and u and oxide facies iron formations associated felsic volcanics contain no recognized volcanogenic cu zn deposits in the superior province the following metallogenic associations are noted 2 mafic plain sequences contain komatiite flow related ni deposits cu ni and platinum group deposits are associated with flows and coeval intrusions 3 arc volcanic sequences contain volcanogenic cu zn sulphide deposits and scarce deposits of porphyry type cu mo and 4 timiskaming sequences and related plutonism are related to lode au

impacts of mountain plains solenoid on diurnal variations of rainfalls along the mei yu front over the east china plains abstractconvection permitting numerical experiments using the weather research and forecasting wrf model are performed to examine the impact of a thermally driven mountain plains solenoid mps on the diurnal variations of precipitation and mesoscale convective vortices along the mei yu front over the east china plains during 1 10 july 2007 the focus of the analyses is a 10 day simulation that used the 10 day average of the global analysis at 0000 utc as the initial condition and the 10 day averages every 6 h as lateral boundary conditions with diurnal variations only despite differences in the rainfall intensity and location this idealized experiment successfully simulated the observed diurnal variation and eastward propagation of rainfall and mesoscale convective vortices along the mei yu front it was found that the upward branch of the mps along with the attendant nocturnal low level jet is primarily responsible for the midnight to early morning rainfall enhancement along the mei yu front th

convective instability associated with the eastward propagating rainfall episodes over eastern china during the warm season abstractanalysis of the latest satellite rainfall and reanalysis datasets from 1998 to 2012 demonstrates that eastward propagating rainfall episodes which typically occur in late night and morning are determinant factors for the rainfall diurnal cycle and climate anomalies over eastern china the episode growth and propagation are facilitated by an elevated layer of conditionally unstable air in a mesoscale zone at their eastern leading edge the convective available potential energy cape despite convection consumption and nocturnal cooling decreases only from a high value to a moderate one during episode duration an estimate of the cape generation budget suggests that low level horizontal advection and vertical lifting of the warm moist air can produce sufficient cape to balance other stabilization effects sustaining the mesoscale maximum of convective instability ahead of rainfall episodes these instability geneses are pronounced at the convection growth stage and linked closely to a mesoscale

folded cauldrons of the early proterozoic labine group northwestern canadian shield great bear magmatic zone 1 875 1 84 ga is a linear belt 100 km wide by 800 km long of little metamorphosed volcanic rocks and allied plutons of calc alkaline affinity the entire zone was folded shortly after magmatism and sections many kilometers thick through several cauldron complexes are exposed eruptions of rhyolite led to collapse of black bear cauldron in which 1 5 km of tuff ponded the cauldron then became the locus of fluvial and lacustrine sedimentation followed by augite plagioclase porphyritic andesite volcanism both of which also accumulated within the cauldron ash flow eruptions of dacite caused collapse of clut cauldron which was accompanied by landsliding and avalanching of the cauldron walls abundant andesitic and intrusive debris is intercalated with the propylitized intracauldron facies tuff adjacent to the walls and some blocks are as large as 1 km across clut cauldron also became the site for fluvio lacustrine sedimentation after collapse and was likely resurgent resurgence was probably related to the emplacement of a quartz monzonite pluton which occupies the core of the cauldron cornwall cauldron which is exposed entirely in cross section contains 1 2 km of intracauldron facies tuff overlain by a complex of dacite lava flows the cauldron was intruded by a granodiorite monzogranite pluton probably responsible for resurgence data from the area suggest the following 1 the similarity of early proterozoic cauldrons to cenozoic examples indicates that cauldron collapse is a process that has occurred since 1 9 ga 2 batholiths beneath ash flow tuff fields are probably composite bodies made up of many individual plutons 3 most of the plutons are sheetlike in cross section and 4 cauldron collapse begins as soon as ash flow eruptions and relief on the cauldron margin becomes large early in the subsidence history

structure of an internal bore and dissipating gravity current as revealed by raman lidar abstract detailed moisture observations from a ground based raman lidar and special radiosonde data of two disturbances associated with a dissipating gust front are presented a synthesis of the lidar data with conventional meteorological data in conjunction with theoretical calculations and comparison to laboratory studies leads to the conclusion that the disturbances seen in both the lidar and accompanying barograph data represent a weak gravity current and an associated undular bore the disturbances display excellent coherence over hundreds of kilometers upstream of the lidar site bore formation occurs at the leading edge of the gust front coincidentally with the rapid weakening of the gravity current analysis suggests that the bore was generated by the collapse of the gravity current into a stable nocturnal inversion layer and subsequently propagated along this wave guide at nearly twice the speed of the gravity current the raman lidar provided detailed measurements of the vertical structure o

thermally driven diurnally periodic wind signals off the east coast of china abstractthe characteristics of thermally driven diurnally periodic wind signals off the east coast of china are studied using hourly model data for the period june 2006 11 simulated with a mesoscale model analysis of these model data indicates low level diurnally periodic wind signals propagate eastward off the southeast coast whereas diurnal wind variations off the northeast coast are nearly in phase it is found that a simple 2d linear land sea breeze model with friction can capture this main difference in propagation character with respect to latitude idealized simulations using a simplified version of the mesoscale model that includes surface heating and terrain are found to explain certain features not captured by the present linear theory such as the absolute time phase and cross coast location of the maximum amplitude of the diurnally periodic winds

continental intra arc depressions a nonextensional model for their origin with a proterozoic example from wopmay orogen the 1 875 1 86 ga great bear magmatic zone is a linear belt 100 km wide by 800 km long of low tio 2 high al 2 o 3 volcanic rocks ranging continuously from basalt to rhyolite cut by allied hornblende biotite bearing plutonic rocks comprehensive study of the facies volcanic styles chemistry and petrography indicates that it is similar to cenozoic continental arcs preservation of high level volcanic rocks suggests that the zone never had an unusually thick crust and therefore is similar to some intra arc depressions such as the mesozoic paleogene depression of chile common in younger continental arcs these long linear depressions are the sites for voluminous pyroclastic volcanism contain sections tens of kilometres thick and are zones of subsidence whose surface remains close to sea level they originate when the mass of basaltic andesite arriving at the base of the crust equals the mass of vitric ash removed from the areas by high level atmospheric transport during ash flow eruptions

the geochemical characteristics of granitoids in contrasting arcs and comments on magma sources geochemical variations in modern subduction related igneous suites with respect to arc maturity in time and space are illustrated using data for both volcanic suites basalt andesite and dacite and intrusive granitoid suites diorite tonalite granodiorite and granite from circum pacific arcs using trace element data we suggest that two groups of processes control the natural variation in the parental magmas of both suites a subduction zone enrichment of lithospheric mantle locally coupled with crustal assimilation allied with fractional crystallization afc in zones of thickened crust all of which yield magmas with enhanced concentrations of the large ion lithophile lil elements k rb th u lrees etc b with increasing distance from the active trench contributions from within plate sub continental lithosphere producing mantle derived magmas with enhanced levels of high field strength hfs elements among which nb ta hf and y are particularly distinctive thus even for the evolved granitoids of intrusive arc series ratios of hfs lil elements not significantly affected by crystal fractionation such as ta nb k rb la may throw some light on the origin of mafic intermediate precursor magmas in terms of these elements we suggest the following groupings for interpreting the tectonic associations of granitoid suites 1 primitive calcic arc granitoids with low lil and hfs element abundances 2 normal calc alkaline continental arc granitoids with enhanced lil element abundances and low hfs lil ratios 3 mature alkali calcic arc granitoids with high levels of lil and hfs elements and higher hfs lil ratios 4 back arc anorogenic alkaline granitoids with the highest levels of hfs elements

variability of warm season cloud episodes over east asia based on gms infrared brightness temperature observations abstract the present study has used the geostationary meteorological satellite gms ir brightness temperature observations to investigate the regional and intraseasonal variability of east asian warm season cloud precipitation episodes in distance time space due to land sea contrast and latitudinal effects the data period was may august 1998 2001 and harmonic analysis was employed as the major tool for analysis the full domain of study 20 40 n 95 145 e was divided into northern and southern zones and into eastern and western sectors and statistics of episodes in each subregion were derived and compared for latitudinal effects episodes were found to be significantly larger in span and duration in northern 30 40 n than in southern 20 30 n zones in the northern zone the propagation characteristics were also stronger and remain evident even in midsummer while episodes south of 30 n reversed in direction and traveled westward in july and august for land sea contrast the may august tra

paleomagnetic evidence for the timing of collapse and resurgence of the lake city caldera san juan mountains colorado rocks of the 23 1 m y old lake city caldera consist of the compositionally zoned sunshine peak tuff postcollapse intracaldera lava flows and resurgent quartz syenite intrusions declinations of reversely magnetized i 45 to 75 sunshine peak tuff change from easterly d 93 130 throughout most of the tuff to southerly d 195 207 within the late eruptive phases the postcollapse lava flows are also reversely magnetized and their emplacement appears to have spanned resurgence of the caldera in contrast the uppermost levels of the resurgent intrusion record two distinct components of magnetization a reversed component isolated by thermal demagnetization typically at temperatures greater than 400 c and a normal component defined by thermal demagnetization at lower temperatures a baked contact test implies that emplacement and initial cooling of the intrusion occurred during a time of reversed polarity and that continued cooling at lower blocking temperatures took place during normal polarity assuming that the reversed directions of the extrusive and intrusive rocks record a single period of reversed polarity as suggested by the paleomagnetic and radiometric age data the time for caldera development from eruption of the ash flow tuffs to emplacement of the resurgent intrusion was less than about 300 000 years on the basis of best estimates of durations of reversed polarities in the early miocene the estimated 300 000 year time span for the development of the lake city caldera is very close in duration to the radiometrically determined time spans of much younger pleistocene calderas having similar dimensions and similar volumes of erupted material

a climatology of warm season cloud patterns over east asia based on gms infrared brightness temperature observations abstract in the present study hourly infrared ir brightness temperatures observed by the geostationary meteorological satellite gms over the region 20 40 n 95 145 e in may august 1998 2001 are used to compile a climatology of warm season cloud precipitation episodes over east asia with a goal to better understand the characteristics of warm season convection and the behavior of these episodes results are compared with those obtained in north america using radar derived data the convection in east asia similar to that in north america is shown to also exhibit coherent patterns and characteristics of propagating events in the longitude time hovmoller space with a preferred phase speed of 10 25 m s 1 considerably faster than warm season synoptic scale waves near the eastern edge of the tibetan plateau convection was most active with a strong diurnal signal peaking in late afternoon or early evening then propagating eastward the zonal span and duration of episodes could reach 3000 km and

diurnal variations of precipitation deep convection and lightning over and east of the eastern tibetan plateau abstract diurnal cycles of total rainfall precipitation features mesoscale convective systems mcss deep convection precipitation vertical structure and lightning over the eastern tibetan plateau tp and eastward through china are investigated using 11 yr of tropical rainfall measuring mission trmm measurements diurnal cycles of rainfall and precipitation features present apparent phase propagation eastward from the eastern tp for about 1000 km the phase propagation is most evident during the pre mei yu and mei yu seasons however it weakens with the northward progress of the east asian monsoon and ceases in midsummer during the pre mei yu season diurnal cycles of storm population total rainfall deep convection and lightning over the central and eastern tp foothills are in phase peaking during the early morning another striking feature of the pre mei yu season is that nocturnal rainfall and mcss prevail over the southeastern tp foothills following the deep convection and lightning maxim

the role of diurnal solenoidal circulation on propagating rainfall episodes near the eastern tibetan plateau abstract in this case study numerical simulations using the weather research and forecasting model wrf are performed for 3 4 may 2002 in which two propagating rain episodes occurred in successive days with close ties to the terrain of the tibetan plateau tp in east asia through sensitivity tests it is found that the eastern tp not only facilitated convective development in the afternoon but that the solenoidal circulation between this region and its leeside lowlands near the sichuan basin also contributed to the longevity and farther downstream propagation of the episodes under prevailing westerly winds reversed every 12 h the thermally driven circulation induced ascending motion near the eastern edge of the tp during daytime but over the leeside at night the episode propagation in this case as often observed was in phase with the ascent from eastern tp in the afternoon to the lee at night indicating both enhancing and modulating effects of the solenoidal circulation

mechanisms supporting long lived episodes of propagating nocturnal convection within a 7 day wrf model simulation abstract a large domain explicit convection simulation is used to investigate the life cycle of nocturnal convection for a one week period of successive zonally propagating heavy precipitation episodes occurring over the central united states similar to climatological studies of phase coherent warm season convection the longest lived precipitation episodes initiate during the late afternoon over the western great plains 105 100 w reach their greatest intensity at night over the central great plains 100 95 w and typically weaken around or slightly after sunrise over the midwest 95 85 w the longest lived episodes exhibit average zonal phase speeds of 20 m s 1 consistent with radar observations during the period composite analysis of the life cycle of five long lived nocturnal precipitation episodes indicates that convection both develops and then propagates eastward along an east west oriented lower tropospheric frontal zone an elevated 2 km deep layer of high e air helps sustain convect

the age and thermal history of cerro rico de potosi bolivia cerro rico de potosi bolivia is the world s largest silver deposit and has been mined since the sixteenth century for silver and for tin and zinc during the twentieth century together with by product copper and lead the deposit consists primarily of veins that cut an altered igneous body that we interpret to be a dacitic volcanic dome and its underlying tuff ring and explosion breccia the deposit is compositionally and thermally zoned having a core of cassiterite wolframite bismuthinite and arsenopyrite surrounded by a peripheral lower temperature mineral assemblage consisting principally of sphalerite galena lead sulfosalt and silver minerals the low temperature assemblage also was superimposed on the high temperature assemblage in response to cooling of the main hydrothermal system both the dacite dome and the ore fluids were derived from a larger magmatic hydrothermal source at depth the dome was repeatedly fractured by recurrent movement on the fault system that guided its initial emplacement the dome was extruded at 13 8 0 2 ma 2 based on u th pb dating of zircon mineralization and alteration occurred within about 0 3 my of dome emplacement as indicated by a 40ar 39ar date of 13 76 0 10ma 1 for sericite from the pervasive quartz sericite pyrite alteration associated with the main stage high temperature mineralization the last thermal event able to reset zircon fission tracks occurred no later than 12 5 1 1 ma 1 as indicated by fission tract dating minor sericite and magmatic steam alunite veins were episodically formed around 11 ma and between 8 3 and 5 7 ma the younger episodes occurring at the time of extensional fracturing at cerro rico and wide spread volcanism in the adjacent los frailes volcanic field none of these younger events appear to be significant thermal mineralizing events the exceptionally flat thermal release pattern of 39ar from sericite and the results of the fission tract dating of zircon show that none of the younger events was hot enough and lasted long enough to cause significant loss of ar or annealing of zircon fission tracks u th pb dating of zircon cores indicates a precambrian progenitor for some zircons and ree analyses of dated samples of hydrothermally altered dacite show the presence of a prominent positive eu anomaly which constrains interpretations of the origin and evolution of the magmatic hydrothermal system

nd isotopic evidence from wopmay orogen for 2 0 2 4 ga crust in western north america abstract nd isotopic data from the 1 9 ga wopmay orogen n w t canada strongly suggest the involvement of crust in the range of 2 0 2 4 ga remnants of three compositionally diverse magmatic arcs 1940 1902 ma 1890 1880 ma and 1875 1840 ma are preserved in wopmay orogen each of the three arcs originated west of the limit of exposed archean crust nineteen samples of plutonic and volcanic rocks from the three arcs yield a narrow range of initial e nd from 1 8 to 0 3 there is no apparent correlation between e nd and geographic distribution nor with whole rock chemistry sio 2 54 75 two basalt samples from west of the archean have initial e nd s between 2 and 3 two 1 87 ga granites which intrude through archean crust have much lower initial e nd s of 5 9 and 8 6 the data from the three magmatic arcs are best interpreted in terms of a source region which had a very limited range of e nd at 1 9 ga which we interpret as 2 0 2 4 ga crust presumably hottah terrane basement wopmay fault zone is therefore the surface manifestation of a suture between 2 0 2 4 ga hottah terrane and the archean slave craton there is a growing body of data which suggests that much of western north america may be underlain by 2 0 2 4 ga crust geochronologic and isotopic data from other precambrian cratons also suggest that 2 0 2 4 ga crust may be much more widespread than previously thought models of crustal growth which interpret 1 9 1 7 ga crust as mixtures of archean crust and proterozoic depleted mantle may be overestimating the amount of juvenile material added to the crust in this time period

rainy season precipitation over the sichuan basin and adjacent regions in southwestern china abstractthe spatial variability and diurnal propagation of mean precipitation in the summer rainy seasons from 2003 to 2010 over the sichuan basin scb and adjacent mountainous regions are examined using high spatiotemporal resolution satellite derived precipitation estimates the scb is located just east of the tibetan plateau tp and is prone to heavy precipitation that often peaks over nighttime and early morning the large scale environment over the scb during the rainy season is characterized by weak low to midtropospheric convergence in the lee of the tp and by the upper tropospheric jet stream to the north under this flow configuration the study links the unique diurnal variations in the precipitation pattern and propagation to the unique topography in this region it is found that during the rainy season the local diurnal precipitation maximum moves primarily downslope and southeastward from over the tp in the daytime to scb at night a secondary maximum moves northeastward downslope of t

characteristics of a subtropical squall line determined from tamex dual doppler data part i kinematic structure abstract in this study structural features of a subtropical squall line that occurred on 17 may 1987 over the taiwan straits were investigated using dual doppler data collected during the taiwan area mesoscale experiment tamex fields of the storm relative wind and reflectivity were derived in a horizontal domain of 45 km 25 km using an objective analysis scheme with 1 km grid spacing in all three directions there were ten analysis levels in the vertical ranging from 0 3 to 8 8 km vertical velocities were computed from the anelastic continuity equation by integrating downward with variational adjustment results show that many structural features of a subtropical squall line are similar to those for a fast moving tropical squall line a low level jet llj associated with the frontal system provides the necessary strong shear at lower levels on the front side of the squall line front to rear flow prevails at all levels and is accompanied by shallow rear to front flow on the back of the line ther

the genesis of severe long lived bow echoes abstract a series of idealized simulations using a nonhydrostatic cloud model is used to investigate the genesis of bow echoes a bow shaped system of convective cells that is especially noted for producing long swaths of damaging surface winds it is hypothesized that severe long lived bow echoes represent a dynamically unique form of mesoconvective organization being produced for a restricted range of environmental conditions including a convective available potential energy cape of at least 2000 m2 s2 and vertical wind shears of at least 20 m s 1 over the lowest 2 5 5 km agl the key structural features include a 40 100 km long bow shaped segment of convective cells with a strong rear inflow jet extending to the leading edge of the bow at 2 3 km agl and cyclonic and anticyclonic eddies referred to as bookend vortices on the northern and southern flanks of the bowed segment respectively this structure characteristically develops three to four hours into the lifetime of a convective system a

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

the kari kari caldera bolivia and the cerro rico stock abstract the rocks comprising the kari kari massif southeast of the city of potosi bolivia consist entirely of welded ignimbrites it is argued that the massif constitutes the resurgent centre of a 20 m y old resurgent caldera plutonic rocks are exposed in the south but volcanic rocks of the caldera rim are exposed in the north and indicate a shallower erosion level there the volcanic rocks consist of a coarse moat deposit consisting of angular fragments of basement material and juvenile clasts overlain by an extensive garnet bearing ignimbrite a plant fossil bearing lacustrine deposit was laid down in a lake within the caldera the cerro rico stock noted for its silver tin mineralisation may be a late intrusion along the caldera ring fractures