sims u pb dating of uranium mineralization in the katanga copperbelt constraints for the geodynamic context abstract the katanga copperbelt in the southeastern part of the democratic republic of the congo drc occurs within the pan african lufilian fold and thrust belt and hosts numerous uraniferous mineral occurrences in addition to the world class sediment hosted copper and cobalt ore deposits in the 1950s and 1960s cahen et al gave a relatively wide range of u mineralization ages using u pb dating on whole rock samples although these ages nowadays appear as inaccurate because of large error ranges they were frequently used to discuss the regional geodynamic events this paper offers a reappraisal of the age range previously published using in situ sims u pb analyses based on these analyses two ages are regarded as analytically reliable and significant 652 3 7 3 ma and 530 1 5 9 ma and hence as having implications for the understanding of geological and geodynamic context in the study area in the katanga copperbelt the siliciclastic rocks of the lower roan group are slightly enriched in uranium a major u mineralization re mobilization episode took place at 652 ma during proto oceanic rift basin development this phase took place in an extensional tectonic regime and led to the re mobilization of u within fractures and voids such deposits are observed along the 250 km long kalongwe luishia tectonic lineament this metal concentration was reworked at 530 ma at the occasion of the climax of lufilian deformation and metamorphism this event gave rise to the u deposits in the southern border of the katanga copperbelt and in northern zambia the kolwezi deposit is a deposit located further to the north notwithstanding its initial position further to the south the deposit is heavily faulted and the thrusts and faults could have focused the fluids associated with the deformation at 530 ma

polarimetric and dual doppler radar observations of the lipscomb county texas supercell thunderstorm on 23 may 2002 abstract polarimetric and dual doppler observations of a supercell observed by the national center for atmospheric research ncar s band polarimetric spol radar two doppler on wheels dow radars and the greek xpol radar on 23 may 2002 during the international h2o project ihop are presented the polarimetric radar observations began as the storm organized into a supercell and continued for over an hour while the storm was in its mature phase the hydrometeor distribution within the mature storm was retrieved using a fuzzy logic hydrometeor classification algorithm the dual doppler radar observations began around the time that the polarimetric radar observations concluded and they covered the end of the mature phase and much of the dissipation phase of the storm the dual doppler wind syntheses are used to evaluate the importance of the forward flank outflow in augmenting the horizontal vorticity field near the storm above 400 m in this case having a relatively weak low level mesocyclone the pa

a succession of quartz veins in archean metaturbidites yellowknife bay slave province the style of extensional quartz veins changed during deformation and metamorphism of greywacke mudstones near yellowknife with successive types of veins accompanying a progression from steeply plunging predominantly macroscopic f1 and f2 folds to mesoscopic f3 folds and subvertical s3 axial planar cleavages a early stage multiple bedding parallel veins are confined to pelitic units some form saddle reefs around hinges of f1 and a few later folds whereas others are unrelated to fold hinges emplacement of most bedding veins during or before f1 folding is suggested b echelon veins pre dominantly lie stratabound within pelites folding about s3 cleavage indicates a pre f3 or early f3 origin c foliation veins more commonly cross sandstones than pelites and follow s3 or f3 axial surfaces boudinage of the veins indicates emplacement before s3 was fully developed d sporadic veins discordant to bedding and cleavage vary from undeformed to folded about s3 evidently these veins were emplaced to

the sediment hosted stratiform copper ore system sediment hosted stratiform copper deposits comprise disseminated to veinlet cu and cu fe sulfides in siliciclastic or dolomitic sedimentary rocks sediment hosted stratiform copper deposits are extremely common though economically significant deposits are rare they account for approximately 23 percent of the world s cu production and known reserves in addition to being significant sources of co and ag three sedimentary basins the paleoproterozoic kodaro udokan in siberia the neoproterozoic katangan in central africa and the permian basin of central europe contain supergiant 24 million metric tons mt contained cu deposits sediment hosted stratiform copper deposits are the products of evolving basin scale fluid flow systems that include source s of metal and s source s of metal and s transporting fluids the transport paths of these fluids a thermal and or hydraulic pump to collect and drive the fluids and the chemical and physical processes which result in precipitation of the sulfides metal sources are undoubtedly red bed sedimentary rocks containing fe oxyhydroxides capable of weakly binding metals sulfur may be derived from marine or lacustrine evaporites reduced seawater or hydrogen sulfide bearing petroleum metals appear to have been transported at low to moderate temperatures in moderately to highly saline aqueous fluids with the temperature of the fluid largely dependent on the time of fluid migration in the basin s burial history these basinal fluids were focused to potential metal precipitation sites by thinning of the red bed sequence at basin margins by faults by differentially permeable sedimentary units by paleotopography within the basin or along the margins of salt diapirs fluid movement produced widespread basin scale alteration that has commonly been overlooked but can form an important exploration guide sulfide precipitation occurred due to reduction typically caused by reaction with carbonaceous rocks or petroleum the amount of sulfides present at any deposit may be either metals or sulfide limited or could have been controlled by the amount of available reductant e g petroleum while understanding of sediment hosted stratiform copper ore genesis at the deposit scale is relatively robust there are still significant questions in regards its position in terms of basin evolution a wide variety of basin architectures and processes can lead to the formation of sediment hosted stratiform copper deposits despite general agreement that sulfides postdate sedimentation the absolute age of mineralization in many deposits has been difficult to document and the available evidence suggests that deposits can form throughout a basin s evolution from early diagenesis of ore host sediments to basin inversion and metamorphism supergiant and giant deposits formed in basins which underwent prolonged periods of fluid flow and in which unique conditions allowed for the accumulation of large amounts of metal bearing fluid sufficient reduced s and large amounts of reductants

changes in occurrence of cold surges over east asia in association with arctic oscillation 1 it has been newly found that the occurrence of cold surges in east asia is significantly influenced by the arctic oscillation ao in the present study the events of cold surge are objectively determined based on several synoptic criteria and the phase dependency of its occurrences in association with the ao has been revealed during the negative ao phase the frequency of cold surge occurrence is relatively increased than that of neutral and positive ao phases the variation of upper level trough and jet stream over east asia and the siberian high in association of ao are suggested to explain the change of cold surge occurrences

eddies and the annular modes of climate variability the dominant modes of month to month varia tion in the troposphere are realistically simulated in a gen eral circulation model whose lower boundary is prescribed with realistic topography and seasonally varying climato logical sea surface temperatures in both hemispheres these internal modes describe a nearly zonally symmetric north south shifting of the zonal jets as anomalous westerlies vac illate between high 50 60 a nd low 30 40 latitudes the eddy structures evolve with the jets and the corre sponding eddy momentum forcings support the shifts in jet position stationary synoptic wave variations mainly ac count for the total eddy forcings in the northern south ern hemisphere pronounced eddy variations occur over the north atlantic sector

vorticity evolution leading to tornadogenesis and tornadogenesis failure in simulated supercells abstracta three dimensional idealized cloud model was used to study the storm scale differences between simulated supercells that produce tornado like vortices and those that do not each simulation was initialized with a different rapid update cycle version 2 ruc 2 sounding that was associated with tornadic and nontornadic supercells in nature the focus is an analysis of vorticity along backward integrated trajectories leading up to tornadogenesis 19 simulations and tornadogenesis failure 14 simulations in so doing the differences between the nontornadic and tornadic cases can be explored in relation to their associated environmental sounding backward integrated trajectories seeded in the near surface circulation indicate that the largest differences in vertical vorticity production between the tornadic and nontornadic simulations occur in parcels that descend to the surface from aloft i e descending thus the results from this study support the hypothesis that descending air in the rear

geochronology of unconformity related uranium deposits in the athabasca basin saskatchewan canada and their integration in the evolution of the basin the importance of geochronology in the study of mineral deposits in general and of unconformity type uranium deposits in particular resides in the possibility to situate the critical ore related processes in the context of the evolution of the physical and chemical conditions in the studied area the present paper gives the results of laser step heating 40ar 39ar dating of metamorphic host rock minerals pre ore and syn ore alteration clay minerals and laser ablation inductively coupled plasma mass spectrometer la icp ms u pb dating of uraninite from a number of basement and sediment hosted unconformity related deposits in the athabasca basin canada post peak metamorphic cooling during the trans hudson orogen of rocks from the basement occurred at ca 1 750 ma and gives a maximum age for the formation of the overlying athabasca basin pre ore alteration occurred simultaneously in both basement and sandstone hosted mineralizations at ca 1 675 ma as indicated by the 40ar 39ar dating of pre ore alteration illite and chlorite the uranium mineralization age is ca 1 590 ma given by la icp ms u pb dating of uraninite and 40ar 39ar dating of syn ore illite and is the same throughout the basin and in both basement and sandstone hosted deposits the mineralization event older than previously proposed as well as several fluid circulation events that subsequently affected all minerals studied probably correspond to far field continent wide tectonic events such as the metamorphic events in wyoming and the mazatzal orogeny ca 1 6 to 1 5 ga the berthoud orogeny ca 1 4 ga the emplacement of the mckenzie mafic dyke swarms ca 1 27 ga the grenville orogeny ca 1 15 to 1 ga and the assemblage and break up of rodinia ca 1 to 0 85 ga the results of the present work underline the importance of basin evolution between ca 1 75 ga basin formation and ca 1 59 ga ore deposition for understanding the conditions necessary for the formation of unconformity type uranium deposits

using high resolution simulations to quantify errors in radar estimates of tornado intensity abstractobservation experiments are performed on a set of high resolution large eddy simulations of translating tornado like vortices near surface doppler wind measurements are taken by emulating

the summer circulation over the eastern mediterranean and the middle east influence of the south asian monsoon the summer circulation over the eastern mediterranean and the middle east emme is dominated by persistent northerly winds etesians whose ventilating effect counteracts the adiabatic warming induced by large scale subsidence the era40 dataset is used to study the vertical distribution of these circulation features which both appear to be reconciled manifestations of the south asian monsoon influence as predicted by past idealized modeling studies in late spring a westward expanding upper level warm structure and subsidence areas are associated with rossby waves excited by the monsoon convection steep sloping isentropes that develop over the emme facilitate further subsidence on the western and northern periphery of the warm structure which is exposed to the midlatitude westerlies the northerly flow and descent over the eastern mediterranean have maxima in july that are strikingly synchronous to the monsoon convection over northern india where the weaker easterly jet favors a stronger rossby wave response and consequent impact on the emme circulation the pronounced emme topography modifies the monsoon induced structure firstly by inducing orographically locked summer anticyclones these enhance the mid and low level northwesterly flow at their eastern flanks leading to distinct subsidence maxima over the eastern mediterranean and iran secondly topography amplifies the subsidence and the northerly flow over the aegean red sea the iraq gulf region and to the east of the caspian sea

metal sources for the nkana and konkola stratiform cu co deposits zambian copperbelt insights from sr and nd isotope ratios abstract the central african copperbelt lies within the lufilian orogenic belt in the border region between the democratic republic of congo drc and zambia a sr and nd isotope study was performed on gangue carbonates associated with multiphase mineralisation at the zambian konkola and nkana deposits comparison with isotopic signatures of basement rocks provides new insights into the likely metal source s for the cu co mineralisation at least three mineralisation phases can be identified with respect to the lufilian orogeny gangue carbonates of the first pre to syn kinematic mineralisation phase in both deposits have sr and nd isotopic compositions that correspond to felsic rocks of the domes region a tectonic zone in the zambian part of the lufilian belt where basement rocks crop out however the isotopic signatures from both deposits differ this can be attributed to local variation in isotopic composition of the basement below the deposits radiogenic isotope ratios suggest that subsequent syn kinematic mineralisation at both sites occurred due to the remobilisation of precursor ore petrographic evidence indicates that the third late kinematic mineralisation phase at nkana resulted from a renewed input of metals with a mafic affinity e g co ni however sr and nd isotope ratios resemble those of the earlier mineralisation phases and do not reflect a change in source composition nonetheless comparison with the isotopic signatures of the co poor konkola deposit and co rich stratiform deposits in the drc might indicate a mafic component in the nkana metal source calculated mixed isotopic compositions support such a mafic component

quantification of the impact of moisture source regions on the oxygen isotope composition of precipitation over eagle cave central spain abstract the 5 day reconstruction of air mass history for the days with precipitation at eagle cave central spain together with the determination of moisture uptake locations along back trajectories is used to identify the moisture sources of precipitation for this site from 2009 to 2011 during this 3 year period around 30 of precipitation at eagle cave originated from the moisture recycled within the iberian peninsula ip with the proximal atlantic being also a main source region of moisture whereas the mediterranean sea and the distal atlantic have large variability during the studied period and other source regions are minor precipitation contributors the comparison of monthly oxygen isotope composition of precipitation at eagle cave with the monthly percentage of precipitation originated in source regions shows a significant negative correlation for the ip region thus the moisture recycling process in the ip region explains 12 of the variability of the monthly oxygen isotope composition of precipitation p value

observations related to the rotational dynamics of the 20 may 1977 tornadic storms abstract observations of the 20 may 1977 tornadic storms are used to evaluate recent theories on the initiation of rotation at mid and low levels and to verify recent thermodynamic retrieval results using the lengthy data record from a variety of sensors available for this day it appears that the mechanism that initiates low level rotation is different from that at midlevels attempts to identify the source of the low level rotation as vertical tilting baroclinically generated horizontal vorticity were inconclusive the recent thermodynamic retrieval results of hane and ray and of brandes for these storms are in good agreement with independent measurements where available however verification is hindered by the sparseness of these measurements noticeable differences in the region of the rear flank downdraft suggest that there is room for improvement in the retrieval methods investigation of the cyclic generation of rotation along gust fronts indicates that the source of low level rotation is not der

finestructure of the del city edmond tornadic mesocirculation abstract interrelationships among severe thunderstorm wind flow tornado parent circulation and tornado are examined with dense single and dual doppler radar observations from the del city edmond oklahoma storm of 20 may 1977 beginning with tornadogenesis rising inflow air from right hand quadrants and subsiding air from a developing downdraft on the storm s rear are wrapped in a large spiral pattern about the tornado the updraft appears to drive the tornado while the downdraft appears to form as entrained environmental air concentrated by the intensifying parent circulation is cooled evaporatively

a numerical simulation of cyclic mesocyclogenesis abstract a three dimensional nonhydrostatic numerical model the advanced regional prediction system is used to study the process of cyclic mesocyclogenesis in a classic supercell thunderstorm during the 4 h simulation the storm s mesocyclone undergoes two distinct occlusions with the beginning of a third indicated at the end of the simulation the occlusion process exhibits a period of approximately 60 min and is qualitatively similar in each case initial midlevel 3 7 km mesocyclogenesis proceeds according to the classic picture that is via tilting of streamwise environmental vorticity the development of an evaporatively driven rear flank downdraft rfd signals the beginning of the occlusion process the developing rfd wraps cyclonically around the mesocyclone causing the gust front to surge outward simultaneously the occluding mesocyclone rapidly intensifies near the surface trajectory analyses demonstrate that this intensification follows from the tilting and stretching of near ground

comparison between vertical ozone soundings and reconstructed potential vorticity maps by contour advection with surgery sudden jumps and deep laminations observed on vertical stratospheric ozone profiles during the european arctic stratospheric ozone experiment easoe winter 1991 1992 are explained as resulting from transport on isentropic layers this is obtained by comparing the ozone profiles with high resolution reconstruction of the potential vorticity multilayer isentropic contour advection with surgery cas is performed using european center for medium range weather forecasts ecmwf analyzed winds the results presented in this work are based on analyzing the location of the edge of the polar vortex the horizontal and vertical extents of filamentary structures and intrusions within the polar vortex the results are consistent with the assumption of high ozone content within the polar vortex which is valid during normal winter conditions of the northern hemisphere the resolution required to carry out this study is much higher than that of current operational analysis by weather centers while it is achievable by cas reconstructions which provide a dynamical understanding of the ozone variations

airborne pseudo dual doppler analysis of a rear inflow jet and deep convergence zone within a supercell abstract on 22 may 1995 numerous thunderstorms several of which produced large hail and small tornadoes formed along a dryline in the central and northern texas panhandle the only long lasting daytime severe storms developed later south of the earlier storms by late afternoon new cells merged and evolved into two large supercells the northern supercell produced three weak tornadoes and hail the southern supercell did not produce a tornado but did produce very large hail for an extended period of time verification of the origins of rotation in tornadoes experiment crews collected data in the southern supercell from its early stage through much of its mature stage the national center for atmospheric research electra doppler radar collected pseudo dual doppler radar data on this storm continuously for well over an hour detailed analyses of this high resolution dataset revealed several unusual features most notably an intense elevated rear inflow jet at midlevels having maximum wind speeds app

a three dimensional trajectory model with advection correction for tropical cyclones algorithm description and tests for accuracy abstractwhen computing trajectories from model output gridded winds are often temporally interpolated to a time step shorter than model output intervals to satisfy computational stability constrai

uncertainties in trajectory calculations within near surface mesocyclones of simulated supercells abstractthis study addresses the sensitivity of backward trajectories within simulated near surface mesocyclones to the spatiotemporal resolution of the velocity field these backward trajectories are compared to forward trajectories computed during run time within the numerical model it is found that the population of backward trajectories becomes increasingly contaminated with inflow trajectories that owe their existence to spatiotemporal interpolation errors in time varying and strongly curved confluent flow these erroneous inflow parcels may mistakenly be interpreted as a possible source of air for the near surface vortex it is hypothesized that unlike forward trajectories backward trajectories are especially susceptible to errors near the strongly confluent intensifying vortex although the results are based on model output dual doppler analysis fields may be equally affected by such errors

tropopause folds in era interim global climatology and relation to extreme weather events tropopause folds are intimately linked to upper level frontogenesis and jet stream dynamics they play an important role for stratosphere troposphere exchange the dynamical coupling of upper and lower tropospheric levels and for generating severe weather events this study presents a global climatology of tropopause folds using era interim reanalysis data from 1979 to 2012 and a refined version of a previously developed 3 d labeling and fold identification algorithm this algorithm objectively separates stratospheric and tropospheric air in complex situations e g in regions with strong low level inversions and in extratropical cyclones where diabatically generated potential vorticity anomalies typically occur three classes of tropopause folds are defined shallow medium and deep and their geographical distribution vertical extent and seasonal cycle are investigated most shallow folds occur along the subtropical jet stream in agreement with previous studies hot spots of medium and deep tropopause folds are found west of australia and along the coast of antarctica in the southern hemisphere and around the east coast of north america in the northern hemisphere seasonal cycles show maxima in winter for all fold classes medium and deep folds are frequently associated with surface wind gust and precipitation extremes as quantified for folds over the southern indian ocean wind gust extremes occur mainly in an elongated band upstream and equatorward of folds whereas precipitation extremes occur mainly east and poleward of folds overall in the considered region about 20 of medium folds and 33 of deep folds are associated with surface wind or precipitation extremes in the vicinity of the fold

cross tropopause transport over the eastern mediterranean 1 the transport of air from the troposphere to the stratosphere over the eastern mediterranean sea and the neighboring countries up to the black sea is investigated using a trajectory model and analyzed winds from the european centre for medium range weather forecasts it is found that in summer the upper troposphere in this region is influenced by both westerly winds in the polar front jet pfj and southerly winds at the western flank of the upper level anticyclones over the arabian and asian heat lows the convergence of these airflows accelerates the horizontal wind and increases the horizontal and vertical wind shear creating a jet streak within the subtropical jet stream stj and deep tropopause folds clear air turbulence caused by horizontal deformation and the vertical wind shear along the stj and consequently turbulent mixing of tropospheric and stratospheric air near the tropopause region appears to contribute strongly to the cross tropopause transport over the eastern mediterranean in summer

a northern hemispheric climatology of cross tropopause exchange for the era15 time period 1979 1993 1 a 15 year climatology of cross tropopause exchange in the extratropical northern hemisphere is presented based upon a previously developed lagrangian methodology and reanalysis data from the european centre for medium range weather forecasts ecmwf for the years 1979 1993 for this time period no apparent trends exist for upward troposphere to stratosphere tst and downward stratosphere to troposphere stt cross tropopause transport the seasonal cycles of hemispherically integrated tst and stt and the zonally integrated meridional exchange distributions show relatively little interannual variability the 15 year averaged geographical distribution of stt reveals significant deviations from zonal symmetry and pronounced seasonal variability stt occurs predominantly over the atlantic and pacific storm track regions during winter spring and autumn and also over the mediterranean in winter and spring in contrast during summer stt maxima are located over the continents particularly over southeastern europe and central asia tst is less variable and is strongest near the southern tip of greenland and the aleutian islands during all seasons aspects of the interannual variability of the geographical exchange distributions are investigated over the atlantic stt varies significantly in line with the changing storm tracks during different phases of the north atlantic oscillation nao whereas tst does less so special consideration is given to vertically deep exchange where the exchange air parcels transfer rapidly from the lowermost stratosphere to the boundary layer or vice versa these processes occur mainly during winter and exhibit pronounced maxima over the north american west deep stt and east deep tst coasts

three dimensional structure of involutions formed in a late pleistocene tephra layer northeastern japan abstract the involutions in the middle kitakami river basin in northeastern japan are formed between the murasakino pumice mp layer which fell on the area during the last glacial age and overlying brown volcanic ash soil these involutions are the festoon and or injection type in which the mp moved upward and brown volcanic ash soil sunk down this paper attempts to reconstruct the three dimensional structure of the involutions by examination of several horizontal and vertical forms at the lower middle and upper parts of the involutions in the horizontal sections at the lower part numerous circular and elliptic forms filled with a brown volcanic ash soil in the mp are observed at the middle part the circular forms are generally larger than those of the lower part in addition the mp exhibits circular or elliptic forms in the brown volcanic ash soil it is also observed that the mp decreases upward in the vertical sections the reconstruction shows that the mp shows an upturned structure vertically more than 30 cm in height and an irregular horizontal network circumscribing circular and elliptical forms each of which is 0 5 3 m in the long axis diameter this structure is interpreted as load structures that result from density inversion during thawing of seasonally frozen ground periglacial loading

single and dual doppler analysis of a tornadic vortex and surrounding storm scale flow in the crowell texas supercell of 30 april 2000 abstract fine resolution single and dual doppler data were collected in the tornadic region of a supercell storm intercepted by two doppler on wheels radars on 30 april 2000 near crowell texas eleven dual doppler analyses characterize the 2d and 3d near surface wind fields associated with a tornado during a 13 min period an interesting evolution of the low level rotation is observed initially concentric tornado 500 m wide and tornado cyclone 2 km wide radar velocity couplets make a transition into a solitary intermediate sized 750 m wide circulation that widens and makes a further transition into a two celled multiple vortex structure with an asymmetric distribution of vertical vorticity the asymmetry and eventual disruption of the multiple vortex structure may have been partially controlled by locally strong outflow winds that affect the convergence fields in its vicinity a smaller 500 m wide tornado embedded in a broad area of rotation is subsequently observed the dual doppler wi

variability of the observed midlatitude storm tracks in relation to low frequency changes in the circulation pattern abstract the principal modes of month to month variability of the wintertime storm tracks over the north pacific and north atlantic are identified by empirical orthogonal function analysis of the root mean square statistics of bandpass 2 5 6 day filtered geopotential height data for 19 yr one of the two leading modes depicts fluctuations in the level of synoptic scale activity without any noticeable spatial displacement of the storm track axes whereas the other mode is associated with meridional shifts of the storm tracks from their time averaged positions higher order modes are indicative of diversion or truncation of cyclone tracks in particular geographical regions it is demonstrated that the leading storm track modes are linked to some of the best known monthly averaged teleconnection patterns the dipolar western pacific and western atlantic patterns for the monthly mean flow are seen to be accompanied by marked changes in the intensity of the storm tracks over the western oceans whereas the m

spatial and temporal variability of the three dimensional flow around african easterly waves abstractthis study presents a large scale trajectory analysis of african easterly waves aews across west africa and the eastern atlantic back trajectories were initialized at multiple pressure levels from in and around the vortex center of the aew troughs to reveal the source regions of environmental inflow the trajectory analysis highlights a changing influence of environmental air on aew troughs over west africa monsoonal flow dominates with source regions of air from the southwest and east to northeast influencing the trough as the aew troughs leave west africa flow from the northwest becomes increasingly important cluster analysis highlighted that the contribution of trajectories from the northwest increased as the aew troughs move westward and that this cluster also had high variability in environmental characteristics correlation analysis of outgoing longwave radiation around the troughs with environmental characteristics 72 h earlier was conducted on 443 aews this analysis reveals that th

high resolution rainfall measurements by radar for very small basins the sampling problem reexamined abstract the dependence of the accuracy of short period radar rainfall accumulations on periodic sampling of the rainfield is investigated it is shown that errors due to sampling can be greater than all the other errors combined if accumulations are improperly computed however if the movement and the development of the storms are taken into account these errors can be reduced dramatically using an accumulation method taking storm movement and evolution into account the space and time resolution of radar maps resulting in the most accurate 5 min accumulations over areas smaller than 1 km 2 was determined it is shown that the best accumulations are obtained with very high time resolution data furthermore for a given time resolution there is an optimum spatial resolution that minimizes rainfall accumulation errors

radar observations of the kinematic microphysical and precipitation characteristics of two mcss in trmm lba 1 dual doppler and polarimetric radar observations are used to analyze two mesoscale convective systems mcss that occurred during the tropical rainfall measuring mission large scale biosphere atmosphere field campaign the mcss formed in different meteorological regimes based on profiles of atmospheric wind and thermodynamic data the first mcs event 26 january 1999 was a squall line that formed in low level easterly flow and had an intense leading line of convection in contrast the 25 february 1999 mcs formed in low level westerly flow and was best characterized by stratiform precipitation with embedded convective elements the radar analyses suggest that the mcss were distinct in terms of overall vertical structure characteristics in particular polarimetric radar cross sections indicated the presence of an active mixed phase zone in the easterly mcs that was largely absent in the westerly case the easterly mcs had considerably more precipitation ice in the middle to upper troposphere compared to the westerly mcs composite analyses showed that the easterly mcs had higher peak reflectivities and a smaller reflectivity gradient above the 08c level in convective regions of the storm compared to the westerly mcs event moreover mean profiles of both vertical air motion and vertical mass transport in the convective portion of the easterly mcs were larger over a factor of 2 at some heights below the 08 c level than those in the westerly event these observations suggest that the easterly and westerly wind regimes in the southwest amazon region produce convection with different vertical structure characteristics similar to regimes elsewhere in the global tropics e g maritime continent index terms 3314 meteorology and atmospheric dynamics convective processes 3329 meteorology and atmospheric dynamics mesoscale meteorology 3354 meteorology and atmospheric dynamics precipitation 1854 3374 meteorology and atmospheric dynamics tropical meteorology keywords microphysics tropical precipitation polarimetric radar mesoscale convective system

the 8 june 1995 mclean texas storm part ii cyclic tornado formation maintenance and dissipation abstract on 8 june 1995 scientists participating in the verification of the origins of rotation in tornadoes experiment vortex collected a unique dataset with the electra doppler radar eldora the eldora observations document the sequential life cycles of storm scale circulations associated with three large tornadoes in a supercell thunderstorm near mclean texas a qualitative description of the evolution of the storm was provided in part i of this paper during the first stage of development of each storm scale circulation interaction of the updraft with the environmental low level horizontal vorticity produced a vorticity column that increased in intensity with height as the vortex matured vorticity increased greatly at low levels i e below 2 km agl and exceeded that aloft each tornadic vortex was located near the rear side of the updraft where the surrounding low level horizontal vorticity was modified locally most likely by weak baroclinity within the storm tilting of low level horizo

relationship between the arctic oscillation and cold surges over east asia abstract the present study reveals the changes in the characteristics of cold surges over east asia associated with the arctic oscillation ao based on circulation features cold surges are grouped into two general types wave train and blocking types the blocking type of cold surge tends to occur during negative ao periods that is the ao related polarity of the blocking type however the wave train type is observed during both positive and negative ao periods although the wave train features associated with negative ao are relatively weaker the cold surges during negative ao are stronger than those during positive ao in terms of both amplitude and duration the cold surges during positive ao in which the extent of effect is confined to inland china passes through east asia quickly because of weaker siberian high and aleutian low leading to short duration of these cold surges in contrast the cold surge during negative ao characterized by a well organized anticyclone cyclone couplet with high p

diagenetic origin of the stratiform cu co deposit at kamoto in the central african copperbelt sediment hosted stratiform ore deposits that underwent metamorphism and orogenesis are interpreted either to have a multiphase origin that might in part predate these events or to be exclusively related to fluid migration during the orogeny this controversy concerns the formation of many world class sediment hosted ore deposits such as in the central african copperbelt here we present re os dating results for disseminated and stratiform cu co sulfide pseudomorphs after anhydrite in nodules and layers from the copperbelt results demonstrate that at least some of the ores formed at around 800 ma during rifting and basin development and thus predate the pan african lufilian orogeny younger re os ages i e between 682 28 and 230 36 ma may be due to the replacement of the early cu co sulfides by younger sulfide phases alternatively these younger ages may result from the disturbance or resetting of the re os system during recrystallization metamorphism or the transition of chalcocite from its high to its low temperature polymorph

the role of the siberian high in northern hemisphere climate variability the dominant mode of sea level pressure slp variability during the winter months in the northern hemisphere nh is characterized by a dipole with one anomaly center covering the arctic with the opposite sign anomaly stretched across the mid latitudes associated with the slp anomaly is a surface temperature anomaly induced by the anomalous circulation we will show that this anomaly pattern originates in the early fall on a much more regional scale in siberia as the season progresses this anomaly pattern propagates and amplifies to dominate much of the extratropical nh making the siberian high a dominant force in nh climate variability in winter also since the slp and surface temperature anomalies originate in a region of maximum fall snow cover variability we argue that snow cover partially forces the phase of winter variability and can potentially be used for the skillful prediction of winter climate

re os systematics and geochemistry of cobaltite coass in the idaho cobalt belt belt purcell basin usa evidence for middle mesoproterozoic sediment hosted co cu sulfide mineralization with grenvillian and cretaceous remobilization we report the first study of the re os systematics of cobaltite coass using disseminated grains and massive sulfides from samples of two breccia type and two stratabound deposits in the co cu au idaho cobalt belt icb lemhi subbasin to the belt purcell basin idaho usa using a 185re 190os spike solution magnetic and non magnetic fractions of cobaltite mineral separates give reproducible re os analytical data for aliquot sizes of 150 to 200 mg cobaltite from the icb has highly radiogenic 187os 188os ratios 17 45 and high 187re 188os ratios 600 1800 but low re and total os contents ca 0 4 4 ppb and 14 64 ppt respectively containing 30 to 74 radiogenic 187os cobaltite from the icb is amenable to re os age determination using the isochron regression approach re os data for disseminated cobaltite mineralization in a quartz tourmaline breccia from the haynes stellite deposit yield a model 1 isochron age of 1349 76 ma 2 n 4 mean squared weighted deviation mswd 2 1 initial 187os 188os ratio 4 7 2 2 this middle mesoproterozoic age is preserved despite a possible metamorphic overprint or a pulse of metamorphic hydrothermal remobilization of pre existing cobaltite that formed along fold cleavages during the ca 1190 1006 ma grenvillian orogeny this phase of remobilization is tentatively identified by a model 3 isochron age of 1132 240 ma 2 n 7 mswd 9 3 initial 187os 188os ratio of 9 0 2 9 for cobaltite in the quartz tourmaline breccia from the idaho zone in the blackbird mine all mesoproterozoic cobaltite mineralization in the district was affected by greenschist to lower amphibolite facies garnet zone metamorphism during the late jurassic to late cretaceous cordilleran orogeny however the fine to coarse grained massive cobaltite mineralization from the shear zone hosted chicago zone blackbird mine is the only studied deposit that has severely disturbed re os systematics with evidence for a linear trend of mixing with metamorphic fluids the new re os ages and extremely high initial 187os 188os ratios of cobaltite reported here favor a magmatic hydrothermal genetic model for a multi stage ree y co cu au mineralization occurring at ca 1370 to 1349 ma and related to the emplacement of the big deer creek granite pluton at ca 1377 ma in our model deposition of paragenetically early xenotime and gadolinite was followed by an influx of mesoproterozoic evaporitic brines and magmatic hydrothermal fluids containing metals and reduced sulfur derived from mafic and oceanic island arc archean to paleoproterozoic rocks in the laurentian basement cobaltite mineralization occurred upon cooling of these fluids at an inferred temperature of 300 c or below

boundary layer isentropic and kinematic trajectories during the august 1993 north atlantic regional experiment intensive four per day backward trajectories were computed from chebogue point nova scotia for the month of august 1993 using two different three dimensional approaches diagnostic vertical velocity fields kinematic and an isentropic assumption essentially 90 of all the kinematic isentropic trajectory pairs were displaced within 75 hpa of each other and differed in the horizontal by about 10 of the travel distance the greatest vertical displacement differences occurred with flow from the northwest and only three time periods were associated with the greatest displacements a cyclonic system was to the north of the trajectory starting location in each case precipitation was associated with two of these events a moist isentropic departure was computed for both kinematic and isentropic cases and departures were typically about 5 k comparison of co measurements and upwind trajectories suggested by temporal groupings of trajectories were consistent with transport from major urban areas however the peak measured co values seemed to occur more frequently with flow transition periods when trajectory uncertainty is the greatest

tornadogenesis in a simulated mesovortex within a mesoscale convective system abstractthe advanced regional prediction system arps is used to simulate a tornadic mesovortex with the aim of understanding the associated tornadogenesis processes the mesovortex was one of two tornadic mesovortices spawned by a mesoscale convective system mcs that traversed southwestern and central oklahoma on 8 9 may 2007 the simulation used 100 m horizontal grid spacing and is nested within two outer grids with 400 m and 2 km grid spacing respectively both outer grids assimilate radar upper air and surface observations via 5 min three dimensional variational data assimilation 3dvar cycles the 100 m grid is initialized from a 40 min forecast on the 400 m grid results from the 100 m simulation provide a detailed picture of the development of a mesovortex that produces a submesovortex scale tornado like vortex tlv closer examination of the genesis of the tlv suggests that a strong low level updraft is critical in converging and amplifying vertical vorticity associated with the mesovortex

genesis of the goshen county wyoming tornado on 5 june 2009 during vortex2 abstractthe genesis of a strong and long lived tornado observed during the second verification of the origins of rotation in tornadoes experiment vortex2 in goshen county wyoming on 5 june 2009 is studied mobile radar mobile mesonet rawinsonde and photographic data are used to produce an integrated analysis of the evolution of the wind precipitation and thermodynamic fields in the parent supercell to deduce the processes that resulted in tornadogenesis several minutes prior to tornadogenesis the rear flank downdraft intensifies and a secondary rear flank downdraft forms and cyclonically wraps around the developing tornado kinematic and thermodynamic analyses suggest that horizontal vorticity created in the forward flank and hook echo is tilted and then stretched near the developing tornado tilting and stretching are enhanced in the developing low level circulation as the secondary rear flank downdraft develops intensifies and wraps around the circulation center shortly thereafter the to

accuracy of trajectories as determined from the conservation of meteorological tracers dynamical structures as well as transport processes are often investigated using trajectories several alternative techniques are currently in use to calculate trajectories which may produce significantly different results in this study three dimensional isentropic isobaric and isoeta terrain following coordinate surfaces trajectories are calculated in the case of the isentropic trajectories both the kinematic and the dynamic calculation method are applied using a tracer that is conserved along the real three dimensional trajectories it is possible to determine which of these trajectories are the most accurate here conservative meteorological quantities namely potential vorticity specific humidity and potential temperature are used as these tracers are conserved only in the absence of diabatic processes regions of the atmosphere where these processes are important i e the boundary layer and moist regions are excluded tracer conservation along the different trajectories is studied to find the most accurate trajectory type it is found that three dimensional trajectories are the most accurate ones and kinematic isentropic trajectories affected more by dynamical inconsistencies between meteorological fields are the second best in the troposphere in the stratosphere three dimensional and isentropic trajectories may be of similar accuracy isobaric and isoeta trajectories are much less accurate both in the troposphere and in the stratosphere dynamic trajectories tend to perform unrealistic inertial oscillations and thus give clearly worse results than any of the kinematic trajectories since there exists no direct relationship between the average errors in tracer conservation and average spatial position errors of the trajectories a transformation of the tracer conservation errors into spatial position errors is difficult

tornadogenesis in a high resolution simulation of the 8 may 2003 oklahoma city supercell abstracta 50 m grid spacing advanced regional prediction system arps simulation of the 8 may 2003 oklahoma city tornadic supercell is examined a 40 min forecast run on the 50 m grid produces two f3 intensity tornadoes that track within 10 km of the location of the observed long track f4 intensity tornado the development of both simulated tornadoes is analyzed to determine the processes responsible for tornadogenesis trajectory based analyses of vorticity components and their time evolution reveal that tilting of low level frictionally generated horizontal vorticity plays a dominant role in the development of vertical vorticity near the ground this result represents the first time that such a mechanism has been shown to be important for generating near surface vertical vorticity leading to tornadogenesis a sensitivity simulation run with surface drag turned off was found to be considerably different from the simulation with drag included a tornado still developed in the no drag simulation but it was

age of the zambian copperbelt the sediment hosted stratiform cu co deposits and prospects of the central african copperbelt are characterized by two intimately associated mineralization styles disseminated sulfides and sulfide bearing quartz carbonate veins and veinlets it has been widely accepted that the disseminated mineralization was introduced during sediment diagenesis in a rift setting and possibly in multiple events spanning several hundred million years in contrast the veinlet hosted mineralization is commonly thought to have been derived either by remobilization of the disseminated sulfides during the lufilian collisional orogeny or introduced at broadly the same time s as the disseminated sulfides during diagenesis and subsequent orogeny the results of 15 re os molybdenite age determinations from cu co deposits and prospects across the zambian part of the central african copperbelt suggest that both the disseminated and veinlet mineralization styles were indeed generated together but in a 50 myr cambrian window 540 490 ma during the later stages of the lufilian collisional orogeny the molybdenite ages for the disseminated stratiform mineralization at two localities do not support the notion of syndiagenetic cu introduction the molybdenite ages also show that individual deposits formed over minimum time intervals of 10 24 myr

air mass trajectories to summit greenland a 44 year climatology and some episodic events the seasonal variation in atmospheric transport patterns to summit greenland is examined using a 44 year record of daily 10 day isobaric back trajectories at the 500 hpa level over 24 000 modeled trajectories are aggregated into distinct patterns using cluster analysis ten day trajectories reaching summit are longest during winter with 67 extending upwind westward as far back as asia or europe trajectories are shortest during summer with 46 having 10 day origins over north america during all seasons a small percentage 3 7 of trajectories originate in west asia europe and follow a meridional path over the arctic ocean before approaching summit from the northwest trajectories at the 700 hpa level tend to be shorter than at 500 hpa with many of the 700 hpa trajectories from north america tracking over the north atlantic and approaching summit from the south the long range transport climatology for summit is similar to a year round climatology prepared for dye 3 located 900 km to the south davidson et al 1993b an analysis of several aerosol species measured at summit during summer 1994 reveals examples of the usefulness and also the limitations of using long range air trajectories to interpret chemical data

climatic reconstruction of the weichselian pleniglacial in northwestern and central europe a multiproxy approach is applied to reconstructing accurately the weichselian pleniglacial climate 72 13 ka in northwestern and central europe standardised translations are used to transform proxy data into climate parameter values for six characteristic time windows quantitative reconstructions of the temperature regime are derived from periglacial coleoptera and botanical evidence while aeolian and fluvial evidence provide qualitative information on wind activity and precipitation respectively the early pleniglacial 74 59 ka the cold period between 41 38 ka and the late pleniglacial 27 13 ka are characterised by a strong north to south climatic gradient over northwestern europe during the last glacial maximum discontinuous permafrost was established in northern france whereas the continuous permafrost zone extended from the uk belgium the netherlands germany and poland to the nordic ice sheets prominent wind activity and a relatively low precipitation typify these periods in contrast an indistinct west to east climate gradient was present in the relatively more temperate intervals e g 50 41 ka seasonally frozen ground conditions prevailed in northwestern europe whereas discontinuous permafrost may be suggested for central germany it appears that the climate conditions in northwest and central europe were controlled by three major factors the scandinavian ice sheet the north atlantic surface water circulation and the russian continent 1998 john wiley sons ltd

an entropy based measure of mixing at the tropopause qualitative analysis of tracer correlations is now a well established technique for investigating mixing in the tropopause transition layer generally these studies rely on in situ data retrieved over short distances and time scales using satellite data from haloe we introduce a simple quantitative analysis technique based on entropy to provide a climatology of mixing from h2o o3 tracer correlations results compare well with previous studies using lagrangian based estimates of effective diffusivity and equivalent lengths and also climatologies of tropopause folding further analysis techniques reveal characteristics of the transition layer including its depth and position leading to the distinction of three primary forms of mixing within our analysis domain we estimate that half of total entropy can be attributed to subtropical rossby driven tropopause folding events the majority of the remaining entropy is associated with tropical convective mixing and a third form possibly linked to shear induced mixing at subtropical jet streaks copyright 2006 royal meteorological society

the evolution of low level rotation in the 29 may 1994 newcastle graham texas storm complex during vortex abstract this paper reports the results of an analysis of airflow evolution in the tornadic newcastle graham texas storm complex of 29 may 1994 a series of seven pseudo dual doppler analyses from 2242 to 2315 are performed from tail radar observations by the national oceanic and atmospheric administration p 3 aircraft subjective analyses of quasi horizontal single doppler radar observations provide a detailed look at structure and evolution of the hook echo and the low level newcastle mesocyclone special emphasis is placed on the evolution of low level i e below 1 km above ground level agl rotation of the parent mesoscale circulation of the newcastle tornado and the origins of mesoscale rotation preceding tornadogenesis the structure and evolution of the newcastle and graham mesocyclones are compared and contrasted the airborne doppler analyses reveal that the tornadic newcastle cell had supercell characteristics and that the newcastle storm circulation could be classified as a mesocyclone ba

on the linkage between the asian summer monsoon and tropopause fold activity over the eastern mediterranean and the middle east a climatology of tropopause folds occurring over the eastern mediterranean and the middle east emme has been established using the era interim reanalyses for the years 1979 2012 the methodology employs an algorithm that detects folds at grid points where the vertical profile features multiple crossings of the dynamical tropopause and allows their classification according to their vertical extent our results confirm the findings of an earlier 1 year climatology that recognized a global hot spot of summertime fold activity between the eastern mediterranean and central asia in the vicinity of the subtropical jet two distinct maxima of activity are identified over turkey and iran afghanistan where fold frequency exceeds 25 occasionally medium and deep folds form over the two regions at surprisingly low latitudes this summertime peak in fold activity diverges from the zonal mean seasonal cycle over the subtropics and is driven by the south asian monsoon starting in late spring the emme is gradually brought under the influence of the zonally asymmetric background state induced by the monsoon as areas of sharply sloping isentropes develop especially over the eastern mediterranean and iran afghanistan subsidence and fold formation are favored further investigation of the reanalysis data provided empirical evidence that the monsoon also drives the interannual variability of emme fold activity an upward trend in fold activity is identified especially in may attributed to the recent advanced monsoon onset and the deepening convective activity throughout summer which promotes upper level baroclinicity over the emme and favors folding

tropopause folds and cross tropopause exchange a global investigation based upon ecmwf analyses for the time period march 2000 to february 2001 1 a new methodology is proposed to identify folds of the dynamical tropopause taken as the 2 potential vorticity pv units pvu isosurface from global analysis data sets from the european centre for medium range weather forecasts ecmwf it consists of a three dimensional subdivision of the atmosphere into stratospheric and tropospheric parts and a subsequent examination of multiple tropopause crossings in vertical profiles of the analyses the method is applied to a 1 year period starting in march 2000 seasonal mean fold frequency distributions show that folds occur preferentially in the subtropics with maximum frequencies of about 30 pronounced maxima are located in the subtropical bands that extend from 20 e to 120 e on both hemispheres during summer generally subtropical folds are comparatively shallow deep folds occur most frequently in midlatitudes during winter over eastern north america and the western north atlantic with maximum frequencies of about 1 detailed investigation of the relationship between individual folds and cross tropopause exchange events reveals that on the average individual folds in the extratropics are associated with larger exchange mass fluxes compared to the subtropics however due to the much higher frequency of subtropical folds the percentage of exchange events that are associated with tropopause folds is larger near 20 40 latitude 50 70 than further poleward 20 30 during winter and 10 20 during summer this indicates that tropopause folds are the key feature for cross tropopause exchange in the subtropics whereas in the extratropics other tropopause structures are at least of equal importance

dual doppler analysis of winds and vorticity budget terms near a tornado abstract three dimensional dual doppler observations with unprecedented finescale spatial and temporal resolution are used to characterize the vector wind field and vorticity generation terms in and near a weak short lived tornado the beam widths of the two doppler on wheels dow mobile radars at the range of the tornado are 250 m with gate lengths of 75 m resulting in a resolution of less than 107 m3 one of the dows collected data during the 240 s prior to the formation of the tornado enabling examination of the genesis process a single set of volumetric scans suitable for dual doppler analyses were completed by both dows permitting the calculation of vertical and horizontal vorticity divergence and stretching and tilting terms in the vorticity budget of the large but weak tornado and its surroundings but no local tendency terms analyses of the dual doppler vector wind fields document for the first time in a supercellular tornado revealed several structures expected to be associated with

finescale dual doppler analysis of hurricane boundary layer structures in hurricane frances 2004 at landfall abstracttwo doppler on wheels dow mobile radars collected fine spatial scale dual doppler data in the right front quadrant and eye of hurricane frances 2004 as it made landfall near stuart florida a 5 7 km dual doppler baseline established a dual doppler domain south and east of fort pierce florida encompassing a 5 5 km 5 5 km horizontal area with a grid spacing of 20 m allowing for the resolution of subkilometer scale horizontal structures and associated kinematics three dimensional vector wind analyses of the boundary layer revealed the presence of linear coherent structures with a characteristic wavelength of 400 500 m near the surface that increased in size and became more cellular in shape with increasing height average horizontal perturbation winds were proportional to average total horizontal winds within the eye of the hurricane the features lost linear coherency despite a high mean wind speed possibly due to changes in stability a slight decrease in the characteristic wavelength

sensitivity of trajectory calculations to the temporal frequency of wind data abstract a mesoscale primitive equation model is used to create a 36 h simulation of the three dimensional wind field of an intense maritime extratropical cyclone the control experiment uses the simulated wind field every 15 min in a trajectory model to calculate back trajectories from various horizontal and vertical positions of interest relative to synoptic features of the storm the latter trajectories are compared to trajectories that were calculated with the simulated wind data degraded in time to 30 min 1 h 3 h 6 h and 12 h various error statistics reveal significant deterioration in trajectory accuracy between trajectories calculated with 1 and 3 h data frequencies trajectories calculated with 15 min 30 min and 1 h data frequencies yielded similar results while trajectories calculated with data time frequencies 3 h and greater yielded results with unacceptably large errors

the reconstruction of past climates using multi proxy evidence an example of the weichselian pleniglacial in northwest and central europe abstract different lines of terrestrial biotic and abiotic evidence are used for large scale climate reconstructions to transform proxy data into climate parameter values standardisation procedures are defined and described as each type of biotic and abiotic proxy provides its own climate parameter a detailed climate reconstruction may be obtained the multi proxy database for palaeoclimate reconstruction is a specially designed computer database that facilitates data processing and management of weichselian climate proxies this paper describes the application of multi proxy evidence to reconstruct the climate across lowland northwest and central europe during the interval 41 38 bp for this period the mean temperature of the warmest month is estimated at 10 to 11 c and the mean temperature of the coldest month ranges from 27 to 20 c the annual range suggests a cold continental setting with an estimated mean annual temperature between 9 and 4 c a north to south transition from dis continuous permafrost to seasonally frozen ground is suggested by periglacial evidence

reconstructing balloon trajectories in the tropical stratosphere with a hybrid model using analysed fields a hybrid lagrangian eulerian model of particle motion is employed to reproduce the observed trajectories of three constant level balloon flights along the 0 0987 kg m 3 and 0 110 kg m 3 isopycnic surfaces during the equateur experiment conducted by centre nationale d etudes spatiales in the summer of 1998 the hybrid model employs velocity temperature and geopotential fields as provided by the european centre for medium range weather forecasts analysed data for several three week periods of the flights the balloon in the model is advected primarily by the ambient air velocity to which a correctional velocity calculated on the basis of a lagrangian dynamical model is added the latter is driven by the montgomery stream function gradient interpolated to the relevant isopycnic surface from the geopotential and temperature standard fields and coriolis and drag forces this correctional velocity is free from the continuity constraint satisfied by the air flow altogether the model employs two physical parameters the rayleigh friction coefficient and the fraction weight of correctional velocity in the advection to quantify the difference between the calculated and observed trajectories we compute the temporal mean of the separation between the two trajectories on time scales on the order of three weeks the best calculated trajectories are obtained when the correctional velocity fraction in the advection is between 5 and 25 and these best fitting trajectories have a mean separation that is down to 20 of that of the advection by the ambient air velocity only the implication of our results is that although a balloon is advected primarily 75 to 95 by the ambient air velocity the small deviations from this velocity result in a significantly more accurate calculated trajectory over periods of three weeks when a trajectory remains in one hemisphere for the entire three week period the best fitting fraction of the correctional velocity is smaller and the rayleigh friction coefficient is larger than in the case when the trajectory straddles the equator but the improvement factor does not differ significantly

anhydrite pseudomorphs and the origin of stratiform cu co ores in the katangan copperbelt democratic republic of congo the stratiform cu co ore mineralisation in the katangan copperbelt consists of dispersed sulphides and sulphides in nodules and lenses which are often pseudomorphs after evaporites two types of pseudomorphs can be distinguished in the nodules and lenses in type 1 examples dolomite precipitated first and was subsequently replaced by cu co sulphides and authigenic quartz whereas in type 2 examples authigenic quartz and cu co sulphides precipitated prior to dolomite and are coarse grained the sulphur isotopic composition of the copper cobalt sulphides in the type 1 pseudomorphs is between 10 3 and 3 1 relative to the vienna canyon diablo troilite indicating that the sulphide component was derived from bacterial sulphate reduction bsr the generation of text hco 3 during this process caused the precipitation and replacement of anhydrite by dolomite a second product of bsr is the generation of h2s resulting in the precipitation of cu co sulphides from the mineralising fluids initial sulphide precipitation occurred along the rim of the pseudomorphs and continued towards the core precipitation of authigenic quartz was most likely induced by a ph decrease during sulphide precipitation fluid inclusion data from quartz indicate the presence of a high salinity 8 18 eq wt nacl fluid possibly derived from evaporated seawater which migrated through the deep subsurface 87sr 86sr ratios of dolomite in type 1 nodules range between 0 71012 and 0 73576 significantly more radiogenic than the strontium isotopic composition of neoproterozoic marine carbonates 87sr 86sr 0 7056 0 7087 this suggests intense interaction with siliciclastic sedimentary rocks and or the granitic basement the low carbon isotopic composition of the dolomite in the pseudomorphs 7 02 and 9 93 relative to the vienna pee dee belemnite v pdb compared to the host rock dolomite 4 90 and 1 31 v pdb resulted from the oxidation of organic matter during bsr

an investigation of the goshen county wyoming tornadic supercell of 5 june 2009 using enkf assimilation of mobile mesonet and radar observations collected during vortex2 part i experiment design and verification of the enkf analyses abstracthigh resolution doppler radar velocities and in situ surface observations collected in a tornadic supercell on 5 june 2009 during the second verification of the origins of rotation in tornadoes experiment vortex2 are assimilated into a simulated convective storm using an ensemble kalman filter enkf a series of enkf experiments using a 1 km horizontal model grid spacing demonstrates the sensitivity of the cold pool and kinematic structure of the storm to the assimilation of these observations and to different model microphysics parameterizations an experiment is performed using a finer grid spacing 500 m and the most optimal data assimilation and model configurations from the sensitivity tests to produce a realistically evolving storm analyses from this experiment are verified against dual doppler and in situ observations and are evaluated for their potential to confidently evaluate mesocyclone scale processes in the storm using trajectory analysis and calculations of lagrangian vorticity

the relation of moist symmetric instability and upper level potential vorticity anomalies to the observed evolution of cloud heads the cloud head phenomenon has been known for some time as a precursor of rapid cyclogenesis based upon satellite imagery two stages of cloud head development are identified in this study that can be related to early and late stages of the associated cyclone weakly convex cloud heads emerge from the baroclinic zone at an early stage in cyclogenesis and strongly convex cloud heads develop in association with the rapid deepening of the cyclone trajectories are used to highlight the role of an upper level potential vorticity pv anomaly in the growth of the strongly convex cloud head and the main flow associated with the growth of the strongly convex cloud head is viewed using isentropic analysis the possible role of moist symmetric instability in the development of both weakly and strongly convex cloud heads is discussed and a new diagnostic for measuring the vertically integrated extent of realizable symmetric vrs instability based on the moist geostrophic pv is introduced royal meteorological society 2002 g j shutt s contribution is crown copyright

accuracy of the isentropic trajectories calculated for the easoe campaign during easoe 10 day backward trajectories ending on most measurement sites were calculated on 6 isentropic levels every day the temporal and spatial coarseness of the ecmwf analyses used cause significant errors in the trajectories these interpolation errors are largest in the direction along the trajectories the difference between two trajectories of the polar vortex balloon experiment and calculated trajectories is 8 and 12 of the trajectory length after 1 83 and 2 14 days this discrepancy is not explainable by interpolation errors alone

age and tectonic setting of the udokan sediment hosted copper silver deposit transbaikalia russia abstract the udokan cu ag deposit in transbaikalian russia is one of the largest individual examples of the sediment hosted stratiform type mineralization is hosted by the udokan complex a 12 000 m thick metasedimentary sequence deposited between 2 2 and 2 06 ga in a large intra to peri cratonic basin constructed over archean basement of the siberian craton the basin was inverted and metamorphosed to dominantly greenschist facies at 1 9 ga as a consequence of the collision between the aldan and stanovoi domains titanite is a common constituent of the greenschist metamorphic assemblages of the udokan complex as well as being an integral part of the stratiform disseminated and associated veinlet cu sulfide mineralization at udokan titanite crystals were separated from a sample collected in the medny area of the deposit where typical high grade disseminated and veinlet chalcocite bornite mineralization is well exposed titanite crystals from the disseminated and veinlet fractions were separately dated by the id tims u pb method with the disseminated fraction returning a concordia age of 1895 3 9 7 ma and the veinlet fraction a concordia age of 1896 7 7 8 ma combination of both titanite fractions produced a concordia age of 1896 2 6 2 ma the titanite age effectively dates the associated cu sulfide mineralization since there is no evidence that titanite growth is appreciably younger than either the mineralization in the medny area or the udokan deposit as a whole a 1 9 ga age for the stratiform cu mineralization is considered likely this age is undistinguishable from that of regional metamorphism during the collisional orogeny that led to final amalgamation of the siberian craton and its incorporation into columbia the age also confirms udokan as the world s oldest sediment hosted cu deposit and that its formation coincided with a continental scale orogeny rather than with diagenesis and extensional basin development 150 m y earlier

reexamining the cold conveyor belt abstract despite the popularity of the conveyor belt model for portraying the airflow through midlatitude cyclones questions arise as to the path of the cold conveyor belt the lower tropospheric airflow poleward of and underneath the warm front some studies beginning with carlson s analysis of the eastern u s cyclone of 5 december 1977 depict the cold conveyor belt moving westward reaching the northwest quadrant of the storm turning abruptly anticyclonically rising to jet level and departing the cyclone downstream hereafter the anticyclonic path other studies depict the cold conveyor belt reaching the northwest quadrant turning cyclonically around the low center and remaining in the lower troposphere the cyclonic path to clarify the path of the cold conveyor belt the present study reexamines carlson s analysis of the cold conveyor belt using an observational and mesoscale numerical modeling study of the 5 december 1977 cyclone this reexamination raises several previously unappreciated

sulfide bearing veinlets throughout the stratiform mineralization of the central african copperbelt temporal and genetic implications the central african copperbelt of zambia and democratic republic of congo along with its broad time equivalents in botswana and namibia the kalahari copperbelt is the world s largest sediment hosted stratiform copper province the economically dominant stratiform copper cobalt or silver mineralization accepted by many as at least partly early diagenetic in origin is ubiquitously accompanied by sulfide bearing quartz carbonate veins and veinlets traditionally this veining is considered to be the product of either metamorphic lateral secretion or discrete late diagenetic to synorogenic mineralization events this view is challenged because identical sulfide assemblages and textures characterize both the disseminated and accompanying veinlet mineralization throughout the zoned sulfide assemblages that constitute many of the stratiform orebodies a situation that is taken to imply contemporaneity of the two styles consequently during the mineralization the siltstone sandstone or dolomite host rocks must have been sufficiently competent to undergo widespread brittle fracturing implying that the disseminated mineralization cannot have been introduced by passive fluid infiltration during early diagenesis this conclusion is further supported by the local occurrence of minor disseminated and veinlet mineralization hosted by mafic sills and dikes both the disseminated and veinlet mineralization styles lack ductile deformation features in many congolese deposits but are variably metamorphosed and deformed in some deposits in zambia botswana and namibia in conjunction these observations suggest that the stratiform copper orebodies were the results of massive saline fluid expulsion by hydraulic fracturing after the mafic magmatism 765 715 ma most probably spanning peak damara lufilian metamorphism and ductile deformation 530 ma and continuing in places until at least 500 ma thus basin inversion contractional tectonism and associated uplift and exhumation and not the earlier extension and rifting seem more likely to have been the ultimate drivers for the fluid mobilization and expulsion

a re os study of sulfide minerals from the bagdad porphyry cu mo deposit northern arizona usa rhenium and osmium isotopes in sulfide minerals from the bagdad porphyry cu mo deposit have been used to determine timing of mineralization and the source of osmium and by inference ore metals molybdenite chalcopyrite and pyrite were analyzed mainly from the quartz monzonite and porphyritic quartz monzonite units which are characterized by moderate to strong potassic alteration secondary biotite and k feldspar rhenium concentrations in molybdenite are between 330 and 642 ppm four re os analyses of two molybdenite samples from the quartz monzonite and porphyritic quartz monzonite yield a weighted average age of 71 8 0 2 ma 2 analyses of a third sample from a molybdenite vein in precambrian rocks outside of the main ore zone yield a weighted average age of 75 9 0 2 ma 2 and provide evidence of two separate mineralization episodes chalcopyrite samples contain 6 to 12 ppt os and 1 7 to 4 1 ppb re 187os 188os initial ratios are between 0 1 and 0 8 pyrite samples have osmium and rhenium concentrations varying in the range 8 17 ppt and 3 9 6 8 ppb respectively analyses from these pyrite samples yield an eight point isochron with an age of 77 15 ma 2 and an initial 187os 188os ratio of 2 1 0 8 mswd 0 90 the results presented here add to the growing body of work indicating that porphyry type mineralization is produced by long term multiple episodes of magmatism and associated mineralization the data also support the hypothesis that a significant part of the metals and magmas may have a crustal source as has been suggested for other copper deposits and districts in arizona

kinematics of the pacific equatorial undercurrent an eulerian and lagrangian approach from gcm results abstract three dimensional monthly velocity fields from an ocean general circulation model are used to study the annual mean mass balance of the pacific equatorial undercurrent euc eulerian diagnostics are used to evaluate the various meridional vertical and zonal mass fluxes related to the euc there are several distinct regimes along the equator showing clear asymmetries between the western and eastern parts of the basin and between the northern and southern edges of the euc meridional fluxes are decomposed into pure ekman divergence and geostrophic convergence and it is shown that the asymmetries are mainly related to the spatial structure of the ekman divergence and thus to that of the trade winds lagrangian calculations are used to evaluate accurately the mass transfers between various sections of the euc and between the euc domain and the tropics the authors show that geostrophic convergence only ventilates the upper layers of the euc and that the euc really is a tongue of water flowing

the arcadia oklahoma storm of 17 may 1981 analysis of a supercell during tornadogenesis abstract on 17 may 1981 an extensive dataset was collected for a supercell thunderstorm that produced an f2 tornado near arcadia in central oklahoma coordinated dual doppler scans of the storm by 10 cm research radars were collected at approximately 5 min intervals from 30 min before the tornado touched down until 15 min after the tornado had dissipated the arcadia storm was also well sampled by a 444 m tall instrumented tower the low level inflow updraft mesocyclone and rear precipitation core of the supercell all passed across the tower a comparison of the instrumented tower measurements with a dual doppler synthesis reveals that the latter qualitatively resolved the low level flow however the magnitudes of the low level horizontal winds and updraft speed were underestimated in addition the vertical shear of the horizontal wind in the lowest kilometer was unresolved in the doppler winds in the storm environment horizontal vorticity was strong 1 5 10 2 s 1 and approximately streamwise

comparison of the synoptic conditions in midlatitudes accompanying cold surges over eastern asia for the months of december 1974 and 1978 part i monthly mean fields and individual events abstract east asian cold surges during two periods of contrasting intensity december 1974 strong and december 1978 weak are studied it is shown that the midlatitude mechanisms initiating cold surges during both months are quite similar in nature synoptic scale short waves passing through the long wave trough position near the east asian coast act to release the cold air southward from the main reservoir over eastern siberia dynamic descent is initiated by these synoptic scale waves entering the northwesterly flow on the western side of the long wave trough anchored on the coast this is the descent center in the local direct circulation in the entrance region of the east asian jet maximum at 200 mb the frequency and intensity of the cold air surges for a given month depend on the large scale circulation pattern the average flow over asia for december 1974 and 1978 presents a contrast with respect to ridging over the midcontinent in december 1978 the flow was characterized by a low zonal inde

formation of an ozone lamina due to differential advection revealed by intensive observations 1 an intensive observation with ozonesondes radiosondes and the middle and upper atmosphere mu radar was conducted at shigaraki 34 9 n 136 1 e japan from 16 through 24 april 1998 to investigate the formation mechanism of ozone laminae in the midlatitude lower stratosphere in these observations the temporal variation of an ozone lamina at shigaraki was continuously observed through a short time interval of 8 hours during the observation period an ozone lamina with a thickness of 2 3 km appeared and ascended with a speed of 1 km day 1 in the height region of 18 21 km it is deduced that inertia gravity waves existing in this height region did not contribute to formation of the ozone lamina because their amplitudes were too small and their vertical phase propagation was in the opposite direction the reverse domain filling method was used to reconstruct the high resolution modified potential vorticity field using backward trajectory calculations the results indicate that this ozone lamina was caused by differential advection due to the vertical shear associated with the subtropical westerly jet and embedded stationary rossby wave therein this means that large scale motions concurrent with vertical wind shear can produce much smaller scale structures in material fields than those of the large scale motions themselves

tornado maintenance investigated with high resolution dual doppler and enkf analysis abstractdual doppler wind synthesis and ensemble kalman filter analyses produced by assimilating doppler on wheels velocity data collected in four tornadic supercells are examined in order to further understand the maintenance of tornadoes although tornado scale features are not resolved in these analyses larger scale processes involved with tornado maintenance are well represented the longest lived tornado is maintained underneath the midlevel updraft within a zone of low level horizontal convergence along a rear flank gust front for a considerable time and dissipates when horizontally displaced from the midlevel updraft the shortest lived tornado resides in a similar zone of low level convergence briefly but dissipates underneath the location of the midlevel updraft when the updraft becomes tilted and low level convergence is displaced several kilometers from the tornado this suggests that a location beneath the midlevel updraft is not always a sufficient condition for tornado maintenance particu

the garden city kansas storm during vortex 95 part i overview of the storm s life cycle and mesocyclogenesis abstract analysis of a supercell storm that produced an f1 tornado near garden city kansas is presented this event provided one of the first opportunities to synthesize data collected by a new airborne radar platform called eldora electra doppler radar developed by the national center for atmospheric research the early stages of development of the midlevel mesocyclone and the entire evolution of the low level mesocyclone are captured over a 70 min period the low level mesocyclone began as an incipient shallow circulation along a synoptic scale trough the circulation intensified and grew in depth via vortex stretching under the influence of a strong updraft as this rotation built up from the boundary layer it initially remained separate and distinct from the midlevel mesocyclone subsequently the two mesocyclones merge to produce a single column of rotation 4 5 km in diameter an occlusion downdraft develops within the mesocyclone circulation during the last passes by the storm signaling the beg

trace a trajectory intercomparison 2 isentropic and kinematic methods kinematic and isentropic trajectories are compared quantitatively during a single 5 day period october 13 18 1992 when several flights for the transport and atmospheric chemistry near the equator atlantic trace a experiment were conducted off the west coast of africa european centre for medium range weather forecasts ecmwf data are used to compute the 5 day backward trajectories arriving at locations over the south atlantic ocean and nearby parts of south america and southern africa two versions of kinematic trajectories are examined one version employs vertical motions supplied with the ecmwf data these trajectories often differ greatly from those based on the isentropic assumption the kinematic trajectories usually undergo considerably greater vertical displacements than their isentropic counterparts however most diabatic rates are consistent with those of synoptic scale systems ratios of acetylene to carbon monoxide are related to backward trajectories at various locations along a trace a flight a second version of kinematic trajectories employs vertical motions diagnosed from ecmwf horizontal wind components using the continuity equation these vertical motions are stronger than those supplied with the ecmwf data causing many of the trajectories to have larger vertical displacements and considerably different paths than the original kinematic versions many of these kinematic trajectories undergo diabatic rates that exceed generally accepted values on the synoptic scale this occurs in part because the diagnosed vertical motions are inconsistent with the ecmwf data the research indicates that the kinematic procedure yields realistic 5 day backward trajectories when the three dimensional wind data are available from a numerical model or other dynamically consistent data set such as provided by ecmwf

the genesis of three nonsupercell tornadoes observed with dual doppler radar abstract dual doppler radar analyses of three tornadoes associated with a multicellular line of storms are presented the f2 f3 intensity tornadoes occurred on 15 june 1988 near denver colorado during the terminal doppler weather radar tdwr project these tornadoes developed from misocyclones of no larger than 2 km in diameter that formed along the collision of two surface outflows the misocyclones were observed to build in height and intensify with time coincident with rapid storm growth overhead all three misocyclones were clearly associated with the maximum storm updrafts downdrafts and associated outflows did not play a role in the formation of one of the tornadoes but may have contributed to the genesis of the other two tornadoes it is clear that a downdraft is not a necessary condition for the formation of a nonsupercell tornado but when present likely plays a role in determining the timing and intensity of the tornado this is achieved by the downdraft and outflow causing an increase in

on the use of advection correction in trajectory calculations abstractan advection correction procedure is used to mitigate temporal interpolation errors in trajectory analyses constructed from gridded in space and time velocity data the procedure is based on a technique introduced by gal chen to reduce radar data analysis errors arising for the nonsimultaneity of the data collection experiments are conducted using data from a high resolution cloud model 1 cm1 numerical model simulation of a supercell storm initialized within an environment representative of the 24 may 2011 el reno oklahoma tornadic supercell storm trajectory analyses using advection correction are compared to traditional trajectory analyses using linear time interpolation backward trajectories are integrated over a 5 min period for a range of data input time intervals and for velocity pattern translation estimates obtained from different analysis subdomain sizes box widths and first guess options the use of advection correction reduces trajectory end point position errors for a large m

strain fringes and strain shadows at kamoa drc implications for copper mineralisation abstract the formation of strain shadows and strain fringes is described from diamictite and siltstone of the grand conglomerat unit nguba group at the kamoa copper deposit located within the drc at the western end of the central african copperbelt cacb fringes reveal a straight orientation of fibres during a coaxial deformation this supports the interpretation of a single phase of deformation during fringe growth within the deposit area the non deformed distal part of fringes and the straight orientation of fibres demonstrate the simple geometry of strain fringes quartz grains within strain fringes and strain shadows have generally straight or smoothly curved boundaries and lack undulose extinction in strain fringes muscovite and chlorite are generally observed on quartz grains where they define a foliation these characteristics suggest a static recrystallisation that developed under relatively high temperature and wet conditions a nw crustal shortening during the kolwezian deformation event of the lufilian orogeny is believed to be responsible for the coeval development of foliation strain shadows and strain fringes a syn orogenic origin of the copper sulphides during the lufilian orogeny is proposed

trajectories in the antarctic lower troposphere the statistics of air mass transport to the neumayer antarctic station 8 22 w 70 7 s are derived from three dimensional 5 day backward trajectories on the basis of a numerical weather prediction model the global model of the german weather service for the period april 1993 to march 1996 trajectory errors are discussed in detail and errors of individual trajectories may sum up to from a few hundred to more than a thousand kilometers during 5 days traveling time despite the high quality of the global model and trajectory module described the most frequent easterly flow at neumayer consists of advection from oceanic and continental regions during southeasterly flow mean trajectories document oceanic air passing coastal continental regions during the 3 days preceding arrival air arriving from above the antarctic continent south of 75 s usually descends over the marginal plateau and especially over the slope region advection from the central plateau regions poleward of 80 s is rare marine trajectories from latitudes north of 60 s mostly start in 0 3 km height the modeled transport for the arrival levels at 950 hpa and 850 hpa at neumayer station document that the frequency of oceanic source regions increases with height trajectories for 15 other coastal destinations show that near surface easterly winds with a downslope component dominate along the eastern shore of the weddell sea the prevailing transport from the south at the filchner ronne ice shelf arises from deflected barrier winds along the transantarctic mountains at the northern tip of the peninsula westerly winds prevail and the air usually originates from the bellingshausen sea the probability of contact with air masses from ice free continents is small for all coastal sites