australian east coast cyclones part i synoptic overview and case study abstract the meteorological conditions for the development of australian east coast cyclones are described the main synoptic precursor is a trough or dip in the easterly wind regime over eastern australia the cyclones are a mesoscale development which occurs on the coast in this synoptic environment they form preferentially at night in the vicinity of a marked low level baroclinic zone and just equatorward of a region of enhanced convection resulting from flow over the coastal ranges three different types of east coast cyclone have been identified types 1 and 3 are very small systems which can have lifetimes as short as 16 hours during which hurricane force winds have been observed to develop the other type 2 system is a meso synoptic scale cyclone that can bring sustained strong winds and flood rainfall over several days because of their intensity rapid development and occasional tiny size these systems are a major forecast problem

the properties and genesis environments of south atlantic cyclones a new climatology of south atlantic cyclones is produced to provide new insights into the conditions leading to genesis in different regions of the domain cyclones are identified and tracked based on the relative vorticity at 850 hpa computed from the ncep cfsr winds the characteristics of the cyclones are obtained by diagnostic variables sampled within a radial distance from the cyclone centers to produce the spatial distribution of cyclone properties at the time of genesis also cyclone centered composites are used to analyze the cyclone structure and evolution during their genesis there are four main cyclogenesis regions in the south atlantic ocean the southern brazilian coast se br 30 circ text s over the continent near the la plata river discharge region la plata 35 circ text s the southeastern coast of argentina arg 40 circ text s 55 circ text s and the southeastern atlantic se sao centered at 45 circ text s and 10 circ text w we found that cyclogenesis northward of 35 circ text s occurs mainly due to low level forcing associated with moisture transport in the summer and is associated with upper level forcing in the winter due to a strong baroclinic environment southward of 35 circ text s cyclones develop in a high baroclinic environment throughout the year with only a small influence from moist processes the cyclone composites reveal that se br and se sao cyclones are associated with secondary development the la plata cyclones development is influenced by an orographic low in their early stages and arg cyclones are influenced by thermal advection as an essential mechanism in the reduction of static stability

conodont color and textural alteration an index to regional metamorphism contact metamorphism and hydrothermal alteration experimental and field data are used to extend the utility of conodonts as semi quantitative thermal indices into the regimes of regional and contact metamorphism as well as hydrothermal alteration an arrhenius plot of data from induced conodont color alteration by pyrolysis in air at 1 atm was used to generate the geologic temperatures for conodont color alteration indices cai above 300 c that is for cai values of 5 through 8 such cai values occur in very low to medium grade regionally metamorphosed contact metamorphosed and hydrothermally altered rocks the uniformity or variability of cai values within a sample together with conodont texture can help to distinguish grades and environments of metamorphism particularly in metacarbonate sequences induced cai by pyrolysis in a water methane mixture at kbar results in retardation of cai and in a disparate mixture of both low and high cai values within each experimental sample in this system color alteration processes above a cai of 2 to 3 seem to change from predominantly carbonization to predominantly loss of organic matter presumably by oxidation and volatilization of oxides these experiments approximate the type of cai mixture characteristically found in conodonts recovered from hydrothermally altered rocks these data indicate that cai values of 6 to 8 cannot be used to assess precise temperatures of hydrothermally altered rocks but may serve as useful indicators of potential mineralization

geothermal palaeogradients and metamorphic zonation from the conodont colour alteration index cai the conodont colour alteration index cal is potentially does not exist there are areas where cal and ki values are valuable in thermal history investigations but there are notably consistent for the anchizone boundaries however problems in its use an approach is proposed herein to anomalous correlations between cal and ki values have also overcome the problem of establishing reliable geothermal been found in some areas a cal anchizone or ancaizone is palaeogradients in areas with burial metamorphism based on defined in order to enable cal values to be used independently knowledge of the stratigraphic succession thickness the to establish a metamorphic zonation boundaries of chronostratigraphic units and the age and duration of deformation episodes although also problematical terra nova 13 79 83 2001 that a correlation between cal and kubler index ki values

geophysical and petrological evidence for the presence of an anomalous upper mantle beneath the sahara basins algeria abstract north of 20 n the northwest part of the stable african shield is characterized by an anomalous high heat flow zone 80 110 mw m 2 this east west elongated zone is oblique to major proterozoic structural units and cannot be related to differences in crustal heat production maximum heat flow occurs in the southern part of the sahara basins 100 120 mw m 2 only a mantle heat flow contribution of 60 70 mw m 2 can account for this very high surface heat flow the estimated geotherms suggest that the temperature of upper mantle is anomalously high and partial melting may be present at shallow depths this hypothesis is supported by the existence of a long wavelength negative component of the gravity field that corresponds with the high heat flow axis and with the very low lithospheric s wave velocities 4 2 4 4 km s down to 160 km obtained from surface wave studies in addition the chemistry of the scarce cenozoic melilitite lavas illizi volcanic district geographically associated with the thermal anomaly as well as the mineralogy of their inclusions phlogopitized garnet spinel peridotite and alkali clinopyroxenite show that the upper mantle beneath this region is locally highly metasomatised and partially melted from these preliminary results it appears that the northwest african upper mantle has been modified by recent thermal rejuvenation processes including gas transfer that are likely to be more extensive in the southern part of the sahara basins

classification and composite diagnosis of extratropical cyclogenesis events in the southwest pacific abstract characteristic patterns of cyclogenesis in the southwest pacific region are identified from a sample of 40 developing cyclones during 1990 94 cases were chosen objectively to ensure a realistic sampling of typical rather than ideal events a subjective classification based on synoptic scale upper tropospheric flow signatures prior to cyclone intensification suggested four classes into which all but three cases fell three categories each containing about a quarter of the population involved direct coupling with the upper jet they represent cyclone formation beneath i the poleward exit region of a 300 hpa jet upstream from a diffluent trough class u ii the confluent equatorward entrance region of the upper wind maximum e and iii the upper jet exit region where the jet is downstream from the upper trough class d these are analogous to previously identified categories for the western north atlantic region a fourth class involved cyclones forming beneath a preexisting intense up

thermal maturity of carbonaceous material in conodonts and the color alteration index independently identifying maximum temperature with raman spectroscopy abstract the color alteration index cai of conodont specimens is commonly used for identifying the maximum temperature to which units of sedimentary rock particularly carbonates have been heated observable color variations in these fossils are thought to be a result of the thermally induced structural evolution of organic carbonaceous matter cm such temperature history information is extremely valuable for applications in hydrocarbon exploration as well as for constraining other temperature related geological processes in sedimentary systems however the identification of cai depends on the qualitative visual assessment of color which along with a host of other potential complications may yield inaccurate determinations of maximum temperature raman spectroscopy allows thermally induced structural changes in cm to be quantified and it has been used to estimate the thermal maturity in metasedimentary rocks for almost two decades here we use raman spectroscopy of carbonaceous material rscm in conodont specimens and their mississippian to upper triassic host rocks from british columbia canada to estimate maximum temperatures based on the transformation structural reorganization of disordered carbon to graphite this study demonstrates that the maximum temperatures experienced by conodont specimens as calculated from rscm using the iterative fitting of raman spectra ifors technique correlate well with cai but lie outside the suggested ranges in some instances this may be due to complex thermal histories of these conodont specimens or the influence of diagenetic alteration not thermal histories on conodont color we recommend the application of raman spectroscopic analyses of cm in conodonts and their host rocks to obtain more confident accurate and precise estimations of maximum temperature that are independent of cai

chronology of the central atlantic magmatic province implications for the central atlantic rifting processes and the triassic jurassic biotic crisis abstract the central atlantic magmatic province camp is among the largest igneous provinces on earth emplaced synchronously with or just prior to the triassic jurassic t j boundary ca 200 ma in great part due to the controversial connection between the occurrence of camp and the events of the t j boundary the demand for better constraints on the duration and eruptive chronology of this province has increased more than 100 new 40 ar 39 ar ages have been published in the last 15 years with more than half of these in the last 3 years a careful review and selection of available ages as well as the publication of 16 new ages from the carolinas newark basin usa french guyana and morocco are presented judicious selection yields a total of 58 accepted age determinations for camp magmatism ranging from 202 to 190 ma covering every part of the camp a more complete picture develops with intrusive camp magmatism commencing as early as 202 ma extrusive activity initiated abruptly 200 ma reaching peak volume and intensity around 199 ma on the african margin the main period of camp magmatism is confirmed as brief but is suggested to consist of at least two phases over 1 5 ma with magmatism commencing along the africa north american margins and slightly later along the south american margin two volumetrically minor but distinctive magmatic peaks centered at 195 and 192 ma are mirrored in data from all three continents and highlighted by our statistical approach models describing rifting and thermal input and magma production on these timescales are explored despite significant advances in our understanding of the chronology of camp more data of better quality and broader geographical coverage are needed to completely characterize the evolution of the camp and infer its geodynamic origin in addition lack of a well defined t j boundary age as well as the absence of a relevant basis for comparison between u pb and 40 ar 39 ar data for this time period remain limiting factors to unambiguously linking camp in time with the events of the t j boundary

long term changes in the acid and salt concentrations of the greenland ice core project ice core from electrical stratigraphy continuous electrical records covering a climatic cycle are presented for the greenland ice core project deep ice core from greenland electrical conductivity measurement ecm measures the acid content of the ice and the dielectric profile dep responds to acid ammonium and chloride all features seen can be explained by chemical changes in the ice and there is no evidence so far for any major change in electrical response with depth or age of the ice both records are dominated by the acidity of the ice which varies strongly from acidic in warm periods to alkaline in cold periods controlled by neutralization by alkaline dust calcareous and other mineral dust when ca is low the acidity mainly nitric acid has a fairly constant background level throughout the cycle with slightly lower values in ice believed to be from the last interglacial ca has to rise only slightly to neutralize the available acidity so that acidity is a highly nonlinear reflection of climate changes if neutralization occurred in the aerosol rather than in the ice then the number of cloud condensation nuclei over parts of the northern hemisphere could have been reduced leading to reduced cloud albedo this nonlinear feedback may have some importance for modeling of climate change when both acid and ammonium levels are low the dep signal can be used to give a rapid indication of chloride trends

conodont thermal alteration patterns in palaeozoic rocks from belgium northern france and western germany in this paper thermal patterns based on conodont colour alteration indices cai have been studied in the devonian and carboniferous rocks from belgium northern france and western germany four maps with the exception of the southeastern rheinisches schiefergebirge have been compiled for the investigated area one for the eifelian and givetian a second for the frasnian another for the famennian and one for the tournaisian and visean conodonts have not been found in cambrian rocks from belgium and northern france and as they are scarce in the ordovician to lower devonian formations of this area it was impossible to integrate these cai data into an isograd map in germany in the eastern rheinisches schiefergebirge only a few cai values for the lower devonian strata are available in contrast to the ardennes where in general conodonts show cai values of 3 0 5 0 indices in areas adjacent to the anglo brabant massif e g in the western namur synclinorium and in the eifel hills range between 1 5 and 2 0 slightly higher values occur in the campine basin north of the anglo brabant massif by comparison with cai data from belgium conodont colour alteration indices from the same stratigraphic horizons in some areas of the northern and eastern rheinisches schiefergebirge are up to one index higher in most areas of the rheinisches schiefergebirge the level of metamorphism corresponds to the anchizone regional variations in cai data appear to be related to buried intrusions and associated hydrothermal activity in the southeastern rheinisches schiefergebirge cai data are not completely consistent but it is possible to discern an increase in coalification from the north to the south high index values in the southern rheinisches schiefergebirge are believed to result from regional metamorphism and heating related to numerous intrusive bodies

sedimentary evolution of a palaeozoic basin and ridge system the middle and upper devonian of the ahnet and mouydir algerian sahara the ahnet and mouydir regions of southern algeria are part of one of the world s largest almost undeformed exposures of palaeozoic rocks which exemplify a hitherto poorly known early variscan development of a devonian basin and ridge system this area includes a series of intracratonic basins along the northern margin of the west african craton which consists from w to e of the reggane basin azel matti ridge ahnet basin foum belrem ridge and mouydir basin the depositional and palaeogeographic interpretation is based on 71 sections in this region which for the first time were biostratigraphically calibrated by means of conodonts goniatites and brachiopods the structural evolution during devonian times was probably controlled by reactivation of ancient n s to nw se running faults in the precambrian basement which caused differential subsidence and uplift of a previously largely unstructured siliciclastic shelf a hiatus during emsian times indicates widespread emergence during this interval the entire area was flooded during the earliest eifelian when the first vestiges of the azel matti ridge become evident by stratigraphic condensation the palaeogeographic differentiation is most apparent during the givetian when a shoal with reduced carbonate sedimentation was established on the azel matti ridge passing towards the west and east into basinal environments of the reggane and ahnet basins respectively the foum belrem ridge is distinguished by increased subsidence during the early givetian and by revived uplift during the late givetian in the mouydir basin further east up to 1000 m of shales were deposited during the givetian the early frasnian is marked by the ubiquitous sedimentation of black shales and bituminous styliolinites these lithologies occur repeatedly already during the middle devonian and document intermittent anoxic conditions the basin and ridge topography is levelled by the shallowing up sequence of up to 1400 m thick upper frasnian and famennian shales which grade into a deltaic sequence of uppermost famennian tournaisian sandstones the up to now only vaguely discriminated lithostratigraphic formations of the devonian have been biostratigraphically defined in suitable type sections

temporal spatial reconstruction of the early frasnian late devonian anoxia in nw africa new field data from the ahnet basin algeria anoxic conditions were widespread in nw africa during the early frasnian late devonian that resulted in deposition of organic rich shales and limestones with total organic carbon toc values of up to 14 organic richness and thickness of these sediments vary laterally and organic rich vs organic poor facies boundaries are likely to have been diachronous a precise temporal spatial reconstruction of this anoxic phase in nw africa is complicated because the organic matter in outcrops is largely oxidised and biostratigraphic resolution in boreholes is generally low due to the lack of recoverable conodonts this contribution is based on eight outcrop sections at the margin of the central algerian ahnet basin where detailed spectral gammaray measurements were carried out using a handheld instrument the pre weathering organic richness in frasnian outcrop sections is approximated using the characteristic uranium enrichment in the anoxic facies that based on well studies is positively correlated with the total organic carbon content conodont biostratigraphic results from these sections suggest that the uraniumenriched interval the anoxic interval at the basin margin is most common in the basal frasnian conodont biozones 1 2 confirming previous results from the anti atlas in morocco in three of the eight localities studied the basal frasnian has not been deposited and the frasnian here commences with distinctly younger uranium enriched intervals including zones 4 11 well data from the eastern algerian berkine basin is interpreted to indicate a significantly longer anoxic phase there million yearscale diachroneities of the frasnian anoxia therefore clearly exist across the north africa shelf it is assumed that the palaeorelief might have been a major factor in controlling the onset duration and intensity of anoxia in the region d 2003 elsevier b v all rights reserved

pan african displaced terranes in the tuareg shield central sahara concepts developed in the recently published model of the air region eastern tuareg shield niger africa as a college of three displaced terranes integrated in a single geodynamic model lead us to propose a terrane map of the tuareg shield 500000 km 2 the 23 terranes recognized have their own lithological metamorphic magmatic and tectonic characteristics and are separated by subvertical strike slip megashear zones that can be traced for hundreds of kilometres or by major thrust fronts some of these boundaries have ophiolitic assemblages or molassic deposits the tuareg shield was shaped and partly accreted during the pan african orogeny 750 550 ma but not as a homogeneous body

high resolution dielectric profiling of ice cores a new method for high resolution 3 mm dielectric profiling of ice cores is described the method measures the capacitance and conductance of the ice at a single frequency chosen to be 50 khz in this case the technique requires only a few minutes per metre of core and no sophisticated data analysis the system is designed to operate on ice cores that have been cut longitudinally providing one flat and one curved surface the 50 khz conductance is dependent on the acid and neutral salt concentrations in the ice the new method was tested successfully on the grip core from summit greenland in 1991 it is useful for detecting seasonal variations in impurities in both acidic holocene ice and in normally alkaline wisconsin ice

new architectures of deep water carbonate buildups evolution of mud mounds into mud ridges middle devonian algerian sahara spectacular totally exhumed carbonate mud buildups of givetian age can be found in the southern ahnet basin of the central sahara their geometries range from isolated mud mounds to mud ridges up to 8 km long the latter are the result of lateral coalescence of closely spaced individual mounds mounds up to 40 m high and ridges up to 85 m high show original slopes of 25 to 65 frame builders in the massive core of the buildups are restricted to scattered small tabulate and solitary rugose corals the total absence of stromatoporoids colonial rugose corals and algae as well as the lack of debris at the toes of the buildups shows that they were constructed in deep water below the photic zone and storm wave base the arrangement of the buildups in north to northwest trending clusters and ridges suggests that their distribution was controlled by early variscan extensional movements inherited from precambrian patterns

downstream development and kona low genesis 1 a composite analysis of 43 kona lows in conjunction with a case study of a particularly damaging kona low indicate that downstream development is dynamically important to the subtropical cyclogenesis it takes the form of eastward propagating statistically significant upstream potential vorticity pv anomalies with accompanying meridional wind anomalies at the tropopause level prior to the formation of a kona low the downstream development culminates in the formation of a pv streamer a meridionally elongated stratospheric intrusion of high pv air into the troposphere associated with a breaking wave on the dynamical tropopause subsequently the streamer cuts off from the stratospheric reservoir of high pv and translates equatorward thereby providing a necessary dynamical forcing for the subtropical surface cyclogenesis

thermal and burial history of the cracow silesia region southern poland assessed by conodont cai analysis abstract conodont colour alteration cai data have been applied in the reconstruction of palaeothermal conditions in the cracow silesia region southern poland the analysis of conodont cai values supplemented by electron spin resonance esr data provided a complex maturity pattern which coincides well with the tectonostratigraphical divisions of this region during the variscan and alpine diastrophic cycles the palaeozoic rocks in the upper silesian coal basin attained the observed thermal maturity during late carboniferous or permian time just after the tectonic inversion of the basin vertical maturity trends suggest that palaeo geothermal gradients were significantly higher than the present values the irregular maturity pattern recognized in the cracow myszkow zone is related to the thermal overprint of intrusive igneous rocks on the maturity field resulting from the relatively shallow burial this pattern has not been modified by mesozoic hydrothermal events the low maturity level of devonian and early carboniferous rocks in the substrate of the carpathian foredeep is a product of the subsidence during miocene time the implications for hydrocarbon generation and further exploration are discussed the cai data are consistent with other indicators of organic metamorphism previously used in this region the study highlights also features about the conodont colour alteration such as the influence of silica mobilization on conodont colour which limit the application of the cai method

conodont thermal alteration patterns in devonian and carboniferous rocks of the ahnet and mouydir basins southern algeria abstract conodont colour alteration indices cai have been used to recognize the thermal maturation of the middle devonian to late carboniferous sedimentary infill of the ahnet and mouydir basins in southern algeria the study is based on a large set of conodont samples obtained from 69 sections and outcrops in the ahnet basin the middle and upper devonian rocks at the surface show a uniform thermal maturity level characterized by the cai values of 2 which suggests maximum burial temperatures about 50 c in contrast the carboniferous exposures yield a wide range of cai values from 1 to 3 5 besides the general tendency in maturity decreases upward in the sequence there are anomalies related to heating by small local magmatic bodies in the mouydir basin the cai values in the middle and upper devonian outcrops range from 2 to 3 5 the pattern indicates that the majority of middle devonian rocks have experienced burial temperatures of about 120 c while thermal maturation of the upper devonian strata is clearly lower with maximum heating temperatures about 50 c at the edges of the basin the observed thermal maturity has been mostly achieved during late carboniferous time prior to the variscan inversion and only locally during the mesozoic it is a product of loading by carboniferous overburden succession of which part is now removed approx 200 1300 m in the ahnet basin and up to 1200 m in the mouydir basin the analysis of palaeotemperatures suggests an average geothermal gradient of 30 c km during carboniferous time in the ahnet mouydir area in terms of hydrocarbon exploration the studied devonian succession is predominantly mature for oil and gas in contrary the carboniferous rocks are immature higher maturities are likely to occur in the subsurface

crustal and upper mantle velocity structure of the hoggar swell central sahara algeria abstract the hoggar region is known as one of the most important swells in the african continent its altitude culminates at 2908 m in the tahat hill atakor the hoggar and other massifs of central africa air eghei tibesti darfur cameroon mount form a system of domal uplifts with similar scale morphology and volcanic activity the knowledge of the structure beneath the hoggar swell will help us to understand the origin of continental swells in order to get an image of the lithosphere in this region we have performed a teleseismic field experiment the 33 short period seismic stations have been maintained for 2 1 2 month along a 700 km long nnw ssw profile this experiment crossed the central hoggar and extended northward into the in salah sahara basin which is characterized by high heat flow values of deep origin the high quality of the data recorded during this experiment allows us to perform a velocity inversion the hoggar appears to be characterized by lower mantle velocities the anomalous zone extends from the upper lithosphere to the mantle the weak velocity contrast is interpreted in agreement with gravity geothermal and petrological data as due to extensive mantle modifications inherited from cenozoic volcanic activity it confirms that the hoggar swell is not due to a large scale uplift of hot asthenospheric materials but corresponds to a now cooled off modified mantle on the contrary local low velocity zones associated with the atakor and tahalra volcanic districts show that hot materials still exist at depths in relation with recent basaltic volcanism

mise en evidence d importantes variations regionales du flux de chaleur en algerie evaluation of heat flow in 230 oil wells using temperature measurements bottom hole temperature and temperature of fluids in drill stem test and various rock porosity data reveals a high heat flow average 82 19 mw m 2 associated with the algerian sahara basins the isopleth map exhibits significant regional variations overprinted by short wavelength anomalies that in general are related to the local geological structure on a regional scale we observe an essentially north south zonation that is not directly related to the major structural units except for the northern alpine domain the southern area at the border of the hoggar precambrian basement is characterized by very high heat flow values 90 130 mw m 2 the anomalies define a major axis generally east west which seems to affect the northern part of the african plate from the canaries to libya locally some relationships with extensional miocene pliocene quaternary volcanism suggest an association with recent mantle thermal events

burial history and thermal evolution of the southern and western saharan basins synthesis and comparison with the eastern and northern saharan basins a quasi two dimensional analysis of burial history and thermal evolution was carried out along eight profiles for sedimentary sections in 24 wells in the southern and western saharan basins with the aid of one dimensional nonsteady numerical reconstructions the modeling shows that thermal activation during the permian triassic jurassic was most intense in the timimoun basin and the northern part of the ahnet and mouydir basins with a heat flow of about 70 80 mw m2 and a lithosphere thickness of 40 50 km activation was more moderate in the sbaa subbasin and reggane basin with a heat flow of approximately 63 67 mw m2 and a crustal thickness of 55 60 km these values are comparable to those for the eastern saharan basins where the intensity of the triassic activation decreased considerably from north to south the present day thermal regime of the ahnet and reggane basins and the central part of the timimoun basin is comparable to that of the illizi basin where the present day lithosphere is as thin as 25 km and recent volcanism has occurred moderate extension of the lithosphere with a maximum total amplitude of about 1 16 during the cenozoic is assumed in our modeling in the reggane basin and the southern half of the timimoun basin as well as in the central and eastern part of the illizi basin thermal analysis of the saharan basins has shown that the hercynian erosion can account for only a minor part of the jumps observed in the vitrinite profiles ro intrusive activity and the associated hydrothermal heat transfer during the triassic and early jurassic accurately explain the steplike character of maturation profiles in the saharan basins in particular the lower level of catagenesis and conservation of oil deposits in the relatively hot sbaa subbasin are the result of less intensive hydrothermal intrusive heating of the basin during the jurassic as compared to that in neighboring basins this could also be ascribed to a deeper location of the lithosphere and probably deeper intrusions in the sbaa subbasin this relatively moderate thermal regime of the sbaa subbasin might be connected to its structural position of as it was a shoulder to neighboring deeper depressions

exploration history of the palaeozoic petroleum systems of north africa subsurface exploration of the palaeozoic petroleum systems of libya algeria tunisia and morocco began in the early 1950s after the discovery of a large prospective palaeozoic basin in the sahara desert province of north africa the first exploration well to test this concept was drilled in algeria in 1952 a non commercial find in 1953 was followed by major discoveries in 1956 since that time approximately 1100 new field wildcats have been drilled to test palaeozoic and basal triassic reservoir targets in a variety of discrete petroleum systems this resulted in the discovery of approximately 330 palaeozoic sourced accumulations in the algerian libyan and tunisian portions of the sahara desert by the end of 1996 ultimate recoverable reserves in oil equivalent for these discoveries were estimated to be just over 46 billion barrels using measures of activity and reserves discovered it is seen that the history of exploration of this province has followed a normal cycle familiar to the petroleum industry which can be divided into five major periods they are pre discovery discovery post discovery boom post boom and revival it is anticipated that future advances in technology will result in new ideas and more effective exploration and ultimately in the future discovery of significant oil and gas reserves

atlantic subtropical storms part i diagnostic criteria and composite analysis abstract subtropical cyclones st have only recently gained attention as damaging weather systems a set of criteria for identifying and classifying these systems is introduced here and employed to identify 18 st cases forming in the 1999 2004 hurricane seasons to be classified as an st these systems must have near surface gale force winds and show hybrid structure for more than one diurnal cycle the 18 st cases are partitioned into four classes based upon their genesis environments genesis over waters with sst in excess of 25 c is observed in almost 80 of warm season cases in contrast with only 55 in an st climatology presented in a companion study the low shear magnitude constraint recognized for tropical cyclogenesis is less apparent for st formation with over 50 forming in the two partitions characterized by shear in excess of 10 m s 1 this relatively high shear environment corresponds to equatorward intrusion of upper troughs over the relatively warm sst present in the mid late hurricane s

a synoptic climatology of the subtropical kona storm ten years of surface and upper air analyses from the ecmwf tropical ocean global atmosphere toga dataset were used to construct a synoptic climatology of kona storms in the subtropical central and eastern pacific ocean within a sample of 115 cyclones that predominantly occurred during the northern hemisphere cool season three distinct types of kona storms were identified cold frontal cyclogenesis cfc cyclones coldfrontal cyclogenesis trade wind easterlies ct cyclones and trade wind easterlies twe cyclones of the three types cfc cyclones were found to be the most common type of kona storm while ct and twe cyclones occur much less frequently the geographical distribution propagation characteristics and the monthly and interannual variability in the number of kona storms are presented kona storms initially develop across a large portion of the subtropical pacific with the greatest concentration of kona storms found within a southwest to northeast oriented band from west of hawaii to 408n 1408w a distinct latitudinal stratification was evident for each type of kona storm with cfc ct and twe cyclones each more likely to initially develop at successively lower latitudes the analysis reveals that kona storms can propagate in any direction but exhibit a clear preference to propagate toward the northeast use of the multivariate enso index indicates that the number of kona storms that develop during each cool season is not correlated to the phase of enso an analysis of the composite structure and evolution of each type of kona storm revealed some common and some unique characteristics development of the surface cyclone in all types results from the intrusion of an upper level disturbance of extratropical origin into the subtropics although differences in the initial structure and subsequent evolution of the 300 hpa trough were noted for each type of kona storm the analysis also revealed that relatively weak 300 hpa winds are present throughout the evolution of each type of kona storm and that the composite kona storm tends to be nestled along the southern boundary of a region of higher surface pressure during the mature stage of its evolution the development of robust ridges in the 300 hpa geopotential and 1000 500 hpa thickness fields downstream of the composite surface cyclone were noteworthy features that characterized the evolution of all kona storms the latter feature strongly suggesting that these disturbances are fundamentally baroclinic in nature

synoptic scale influence of the saharan air layer on tropical cyclogenesis over the eastern atlantic abstract the formations of hurricane andrew tropical storm ernesto and hurricane luis which occurred respectively during the 1992 1994 and 1995 hurricane seasons over the eastern atlantic have been investigated by utilizing the european centre for medium range weather forecasts ecmwf gridded data analyses these cases were selected to illustrate the contrasting influences of the saharan air layer sal on tropical cyclogenesis analyses results show that tropical storm ernesto 1994 and hurricane luis 1995 formed from the merger of the low level 925 hpa and midlevel 700 hpa vortices over the eastern atlantic within the monsoon trough enhanced by surges in the trades midlevel vortices associated with each case appear to evolve from african wave troughs enhanced by cyclonic shear vorticity of the midtropospheric jet which existed to the south of an sal anticyclonic eddy as an elongated wind maximum vorticity budget calculations suggest that vortex stretching dominated the enhancement of

asiras airborne radar resolves internal annual layers in the dry snow zone of greenland 1 we present data from the european space agency s airborne sar interferometric radar altimeter system asiras flown during the cryovex 2004 field calibration validation campaign and new high resolution depth profiles of snow density measured in the field by neutron scattering we combine these data to calculate the depth of internal reflecting horizons in the asiras data the high resolution density data allow us to identify annual layers in the snow density profile and correlate their peaks with the reflecting horizons we use the thickness of the annual layers combined with the density profile to determine the spatial and temporal pattern of snow accumulation along the radar track for a period of 6 years from 1995 2002 our mean annual accumulation rate is 0 47 0 09 ma 1 water equivalent in agreement with the value determined from a core taken in this location in 1992 similarly our inter annual variability shows the same trends as recent model estimates over the entire ice sheet because asiras was designed to mimic as closely as possible the characteristics of the sar interferometric radar altimeter siral the principal payload of cryosat the detection of internal layering with asiras illuminates the possibility of detecting internal layers with a space borne radar and thus the possible application of this technique to the dry snow zones of antarctica greenland and smaller ice bodies

lower silurian hot shales in north africa and arabia regional distribution and depositional model abstract lowermost silurian organic rich hot shales are the origin of 80 90 of palaeozoic sourced hydrocarbons in north africa and also played a major role in petroleum generation on the arabian peninsula in most cases the shales were deposited directly above upper ordovician peri glacial sandstones during the initial early silurian transgression that was a result of the melting of the late ordovician icecap deposition of the main organic rich shale unit in the north african arabian region was restricted to the earliest silurian rhuddanian stage acuminatus atavus and probably early cyphus graptolite biozones during this short period 1 2 m y a favourable combination of factors existed which led to the development of exceptionally strong oxygen deficiency in the area in most countries of the study area the post rhuddanian silurian shales are organically lean and have not contributed to petroleum generation the distribution and thickness of the basal silurian hot shales have been mapped in detail for the whole north african region using logs from some 300 exploration wells in libya tunisia algeria and morocco in addition all relevant accessible published and unpublished surface and subsurface data of the lower silurian shales in north africa and arabia have been reviewed including sedimentological biostratigraphic and organic geochemical data the lowermost silurian hot shales of northern gondwana are laterally discontinuous and their distribution and thickness were controlled by the early silurian palaeorelief which was shaped mainly by glacial processes of the late ordovician ice age and by pan african and infracambrian compressional and extensional tectonism the thickest and areally most extensive basal silurian organic rich shales in north africa occur in algeria tunisia and western libya while on the arabian peninsula they are most prolific in saudi arabia oman jordan and iraq the hot shales were not deposited in egypt which was a large palaeohigh at that time the depositional model presented may help in better understanding the source potential of the basal silurian shales in less explored regions of north africa and arabia including morocco northern niger and the kufra basin in southeast libya

thermodynamic aspects of tropical cyclone formation abstractthe thermodynamic aspects of tropical cyclone tc formation near the center of the wave pouch a region of approximately closed lagrangian circulation within the wave critical layer are examined through diagnoses of a high resolution numerical simulation and dropsonde data from a recent field campaign it is found that the meso area near the pouch center is characterized by high saturation fraction small difference in equivalent potential temperature e between the surface and the middle troposphere and a short incubation time scale updrafts tend to be more vigorous in this region presumably because of reduced dry air entrainment while downdrafts are not suppressed the thermodynamic conditions near the pouch center are thus critically important for tc formation the balanced responses to convective and stratiform heating at the pregenesis stage are examined using the sawyer eliassen equation deep convection is concentrated near the pouch center the strong radial and vertical gradients o

conodont based thermal maturation of paleozoic rocks in arizona color changes in conodonts are established thermal indices that have been related to the thermal window for hydrocarbon generation and preservation and that also have value for targeting mineralization potential conodont color alteration values from 141 localities in arizona appear to characterize the thermal maturation of the major paleozoic outcrop areas in the state paleozoic rocks in the colorado plateau in part of the belt of faulted plateau like rocks bordering the plateau and in a small area from 31 20 prime to 31 44 primen and from 110 00 prime to 110 40 primew in southeast arizona have thermal potential for oil paleozoic rocks in the same areas as well as in the pedregosa basin southeasternmost arizona have thermal potential for gas f these areas southeast arizona appears to have the best hydrocarbon potential because of the association of possible source beds and favorable thermal maturation levels

subtropical cyclones over the southwestern south atlantic climatological aspects and case study abstracthurricane catarina 2004 and subtropical storm anita 2010 called attention to the development of subtropical cyclones scs over the south atlantic basin besides strong and organized storms a large number of weaker shallower cyclones with both extratropical and tropical characteristics form in the region impacting the south american coast the main focus of this study is to simulate a climatology of subtropical cyclones and their synoptic pattern over the south atlantic proposing a broader definition of these systems in addition a case study is presented to discuss the main characteristics of one weak sc the interim ecmwf re analysis era interim and ncep ncar reanalysis are used to construct the 33 yr 1979 2011 climatology and a comparison between them is established both reanalyses show good agreement in the scs intensity geographical distribution and seasonal variability but the interannual variability is poorly correlated anomaly composites for austral summer show that sub

large scale influences on the evolution of winter subtropical maritime cyclones affecting australia s east coast abstractsubtropical maritime low pressure systems frequently impact australia s eastern seaboard closed circulation lows in the tasman sea region are termed east coast cyclones ecc they can evolve in a range of climatic environments and have proven most destructive during the late autumn winter period using criteria based on pressure gradients inferred wind field and duration an objectively determined database of ecc occurrences is established to explore large scale influences on ecc evolution subclassification based on evolutionary trajectory reveals two dominant storm types during late autumn winter easterly trough lows etl and southern secondary lows ssl synoptic composites are used to investigate the climatological evolution of each storm type etl cyclogenesis occurs along the eastern seaboard at the confluence of warm moist subtropical easterlies and cool air over the continent that is advected from higher latitudes ssl develop when a cold extratropical cyclone moves equatorward and

synoptic scale diagnosis of the extratropical transition of a southwest pacific tropical cyclone abstract this is the first of two case studies on the transformation of tropical storms in the southwest pacific this study uses ecmwf analyses and observations to examine the behavior of tropical cyclone patsy in december 1986 prior to and during its transit to midlatitudes these analyses adequately depicted synoptic scale features during the extratropical phase but underestimated the inner core of strong wind during the hurricane phase interactions with troughs in the subtropical westerlies provided the impetus for the major motion and structure changes during patsy s life during the hurricane phase patsy was steered by the flow above 400 hpa the passage of a first trough to poleward led to disintegration of the characteristic tropical cyclone structure decay was due to shearing effects loss of upper level outflow and the transient incorporation of cooler air into the low level circulation a few days later patsy commenced moving rapidly south as a single center as ascent redeveloped in the p

hercynian compressional deformations of the ahnet mouydir basin algerian saharan platform far field stress effects of the late palaeozoic orogeny n s to nw se trending faults and reverse faults occur within the palaeozoic ahnet mouydir basin of the algerian saharan platform located to the east of the west african pan african suture zone deformation and stratigraphic analysis show that this basin underwent a nne ssw to ene wsw shortening at about the carboniferous permian transition or more probably during the early permian a brief review of the more or less synchronous deformations registered in the neighbouring regions and more specifically around the west african craton illustrates the mechanical coupling between intraplate tectonics and the hercynian plate margins orogenies

air sea interaction processes influencing the development of a shapiro keyser type cyclone over the subtropical south atlantic ocean this study analyzes the impacts of latent and sensible heat exchanges between the atmosphere and the ocean in a non explosive shapiro keyser type cyclogenesis event that occurred over the southwestern south atlantic ocean the synoptic evolution shows a relatively strong warm front and a cold frontal fracture during the system s development and a warm seclusion in its mature stage characterizing a shapiro keyser type cyclone numerical experiments with the arw wrf model version 3 3 were used to investigate the influences of sensible and latent fluxes on the track of the surface low intensity of the fronts and coupling of the lower and upper troposphere the simulations indicate that in the presence of these fluxes the cyclone underwent greater intensification had a longer life time and longer trajectory and presented a typical southeastward movement in the absence of these fluxes the cyclone developed a weaker warm front with consequent reduction of diabatic heating due to grid scale precipitation along it this reduced the negative pressure tendency southeast of the cyclone center and the surface cyclone moved northeastward showing a decoupling of the lower and upper level waves a consequence of this anomalous tracking is the location of the surface cyclone beneath the upper level trough axis where there is no upper level divergence associated with cyclonic vorticity advection contributing to the further system intensification numerical experiments suggest that for this shapiro keyser type cyclone the air sea interaction processes are crucial to obtain a cyclone with features similar to the observations

spatial variability at shallow snow layer depths in central dronning maud land east antarctica spatial variability at swallow snow layer depths in central dronning maud land east antarctic

deep structure of the hoggar domal uplift central sahara south algeria from gravity thermal and petrological data abstract initial heat flow determinations show that no significant regional thermal disturbance is associated with the volcanic hoggar swell however the large scale negative gravity anomaly associated with this swell strongly suggests the occurrence of a low density upper mantle beneath the hoggar this is inferred from the occurrence of the depleted metasomatized and intensely recrystallized and veined peridotitic upper mantle revealed by the study of xenoliths from the cenozoic basaltic eruptions we suggest that the low density of the upper mantle is due to magmatic events of asthenospheric origin from various observations including petrographie gravimetric and thermal constraints the age of these events is estimated to be late mesozoic to early cenozoic the alkali cenozoic volcanism cannot be regarded as the cause of the swelling the occurrence of an altered lithosphere now cooled and presently marked by low density magmatic materials is consequently proposed as a possible model for the hoggar

the hydrocarbon systems of north africa abstract north africa s hydrocarbon reserves are spread over a wide range of reservoirs and play types but derive from only a few key source rock intervals particularly those in the silurian late cretacous and eocene source rock maturity together with the timing of the generation relative to trap forming and destructive events seem to be the key controlling factors on success or failure at a basin level in most cases generation clearly post dates trap formation although a more complex relationship is evident in various parts of algeria where some traps did not form until gas was being generated source rock deposition and maturation can be tied to two main extensional tectonic cycles which ended in the compressional and destructive events of the hercynian and alpine orogenies remaining exploration potential in mature provinces may be tied largely to subtle and stratigraphic traps in addition significant frontier potential can be identified in two main fairways corresponding to regions where silurian devonian and cretaceous eocene sources respectively are likely to have generated petroleum critical factors in these areas are timing of generation and preservation the gas discoveries in the ahnet basin provide analogues for palaeozoic generation preservation models in the interior silurian devonian source fairway similarly the key to success for the mesozoic basins of the atlas region lies in demonstrating a favourable relationship between trap formation destruction and generation from late cretaceous and eocene source rocks

relative importance of the hercynian and post jurassic tectonic phases in the saharan platform a palaeomagnetic study of jurassic sills in the reggane basin algeria summary in the intracontinental domain of the northwestern saharan platform the deformation of the palaeozoic sedimentary cover is mainly attributed to a far field effect of the hercynian orogeny having occurred at the african laurusian plate boundary in the late carboniferous to early permian times however geological observations from different parts of africa and arabia provide evidence that several minor but widespread tectonic events occurred later particularly during the cretaceous contrary to elsewhere in the northwestern part of africa in the reggane basin outcropping doleritic sills of early jurassic age are intruded in folded palaeozoic sediments of devonian to carboniferous ages deposited before the hercynian orogeny in this favourable situation a palaeomagnetic study of the liassic dolerite is able to provide information on the tectonic history of the surrounding area independently from geological observations the present study aims to quantify the relative proportion of tilting related to respectively the hercynian and a post intrusion phase using a fold test based on the small circle analysis this method proved to be very efficient to unravel these tectonic events it shows that in the studied area the folds were initiated during the hercynian phase but mainly amplified during the post intrusion phase which turned out to be the dominant one in the reggane basin the age of this second event is not geologically well constrained between probably late jurassic and early cretaceous it could be the far field effect of either the cimmerian phase 140 ma or more likely the austrian tectonic phase late barremian 125 ma the late barremian tectonic episode corresponds to a major event the break up of western gondwana which led to the separation of africa from south america and to the incipient fragmentation of the african plate into three major blocks the conclusion drawn from the palaeomagnetic study in the reggane basin is consistent with the geological observations and representative of the intraplate cretaceous deformations recorded in many other places in africa it emphasizes once again that stresses can be transferred far from the plate boundaries into the continental plate interiors

the world s most spectacular carbonate mud mounds middle devonian algerian sahara abstract in the southern ahnet basin of algeria a unique middle devonian underwater scenery is revealed which consists of 191 mud mounds 15 mud ridges and 2 mud atolls distributed over nine discrete areas of a shallow pelagic carbonate shelf all the buildups are totally exhumed thus perfectly exhibiting their original morphologies slope angles elevations and the pattern of the onlapping strata as well as their relationship to the surrounding off buildup sequences types of buildups include 1 small mud mounds 1 5 m high 10 20 m diameter 2 large mud mounds up to 40 m high up to 200 m diameter 3 lens shaped mounds 1 30 m thick 10 15 slopes 4 mud ridges up to 100 m high 150 8500 m long and 5 semicircular mud atolls 2500 2800 m long 20 30 m high the buil ups were constructed during a short time span in the early givetian part of the lower varcus zone probably not exceeding a few hundred thousand years sedimentation rates in coeval off buildup areas were at least 3 10 times lower the lithology of the buildups is a massive boundstone with a high proportion of irregular spar filled cavities stromatactis but only very scattered potential frame builders the carbonate mud is considered to be an in situ cyanobacterial precipitate although evidence of such is poor organic components of the buildups are not significantly different from those of the off buildup lithologies and include numerous crinoid ossicles some tabulate and solitary rugose corals brachiopods mollusc debris trilobites and very rare sponge spicule and bryozoans the total absence of stromatoporoids large tabulate and colonial rugose corals green algae and micritic envelopes around grains suggests growth of the buildups in the lower part of the photic zone 100 200 m they are onlapped by a discontinuous sequence a few meters thick of skeletal packstones and grainstones and locally orthoceratid floatstones that were deposited later in the givetian a widespread rise of sea level in the early frasnian buried both buildups and adjacent areas under shales and siltstones postdepositional alteration of the mud buildups includes 1 formation of stromatactis cavities probably by dewatering and internal erosion 2 cementation of stromatactis cavities and interparticle pore spaces by early high mg calcite and late blocky low mg calcite 3 neomorphic transformation of mg calcitic mud and aragonitic skeletal debris 4 occasional formation of neptunian dikes 5 slight erosion of buildup surfaces 6 compaction and slumping of onlapping capping beds and 7 local dolomitization the formation and growth of the mud build ups is envisaged as a sequence of stages starting with patchy coral thickets evolving into small mud mounds that coalesced into larger mounds by continuous vertical and lateral growth closely spaced mounds amalgamated into mud ridges and mud atolls regular nw se and n s patterns of some mound rows and ridges show a relationship of buildup formation to rejuvenated late precambrian tectonic lineaments which reappear in the hercynian orogeny the isotopic signature of matrix and early ements of mound rocks however does not support the idea of fluid migration and hydrothermal co2 supply during buildup growth

tropopause undulations and the development of extratropical cyclones part ii diagnostic analysis and conceptual model abstract a case study of a developing cyclone is used to show that the three dimensional distribution of height change during development can be strongly sensitive to temperature changes which occur in the lower stratosphere in association with an evolving tropopause undulation quantitative analysis of the storm with a geopotential height tendency equation indicates that a synergistic process developed between the stratosphere and troposphere whereby the vertical motion pattern maintained and intensified the upper level temperature anomalies while the subsequent upper level temperature advection led to an enhanced vertical circulation using the results of this diagnostic study a conceptual model is constructed the conceptual model is based on the hydrostatic and wind field adjustments that occur as tropopause undulations propagate over favored regions of tropospheric warm advection and less stable air

atlantic subtropical storms part ii climatology abstract a 45 yr climatology of subtropical cyclones st for the north atlantic is presented and analyzed the sts pose a warm season forecasting problem for subtropical locations such as bermuda and the southern united states because of the potentially rapid onset of gale force winds close to land criteria for identification of st have been developed based on an accompanying case study analysis these criteria are applied here to the 40 yr european centre for medium range weather forecasts re analysis era 40 to construct a consistent historical database of 197 north atlantic st in 45 yr because st may eventually evolve into tropical cyclones sea surface temperatures sst and vertical wind shear conditions for tropical cyclogenesis are contrasted with the conditions for st genesis identified here around 60 of the 197 st formed over sst in excess of 25 c in a region of weak static stability further the mean environmental vertical wind shear at formation for these storms is 10 7 m s 1 a magnitud

airborne radar stratigraphy and electrical structure of temperate firn bagley ice field alaska u s a helicopter borne 135 mhz short pulse radar profiles of the bagley ice field southern alaska u s a have been analyzed to determine the nature of radio wave propagation through crevassed stratified wet and draining firn diffractions characterize the firn horizons along the trunk and reflections characterize those of overlying snow fields dynamic stacking was used to form and determine firn depths and unstacked diffraction analysis to determine firn layer properties refractive indices range from 4 1 to 4 5 for the near surface from 1 7 to 2 1 at about 13 17 m depth along the main trunk and to 2 6 to 58 m depth within a snowfield average trunk values correspond with volumetric water contents of about 0 09 which agree with values measured for other glaciers the analysis of the airborne recorded diffractions is confirmed by deriving the approximate refractive index of water from a supraglacial lake bottom diffraction the lack of snowfield diffractions suggests that crevassing and not firn structure caused the trunk diffractions the reasonable values of the indices imply that the diffractions originated from single points or edges orthogonal to the profile transect and they predict low interlayer transmission losses the snowfield penetration suggests that several hundred meters might be penetrated in uncrevassed accumulation zones with improved system design

a cyclone phase space derived from thermal wind and thermal asymmetry abstract an objectively defined three dimensional cyclone phase space is proposed and explored cyclone phase is described using the parameters of storm motion relative thickness asymmetry symmetric nonfrontal versus asymmetric frontal and vertical derivative of horizontal height gradient cold versus warm core structure via the thermal wind relationship a cyclone s life cycle can be analyzed within this phase space providing substantial insight into the cyclone structural evolution an objective classification of cyclone phase is possible unifying the basic structural description of tropical extratropical and hybrid cyclones into a continuum stereotypical symmetric warm core tropical cyclone and asymmetric cold core extratropical cyclone life cycles are illustrated using 1 navy operational global atmospheric prediction system nogaps operational analyses and 2 5 ncep ncar reanalyses the transitions between cyclone phases are clearly illustrated within the phase space including extratro

thermal effects of igneous intrusions on maturity of organic matter a possible mechanism of intrusion abstract this paper assesses thermal maturation of organic matter near a well dated intrusion in the dsdp 41 368 hole near cape verde rise eastern atlantic and near some other intrusions from the u k u s a and east greenland the traditional numerical model with instantaneous intrusion satisfactorily describes the thermal evolution and thermal maturity aureoles of igneous bodies only if the initial temperature of intrusion is close to or even lower than the solidus temperature calculations in this model with more real values of the intrusion temperature and with consideration of latent heat effects lead to considerable over estimation of thermal influence of the intrusion models which consider formation of the intrusive body over time as distinct from instantaneous intrusion and especially models of emplacement of an intrusive body in the shell of relatively cool magmatic rocks show better agreement between the computed and observed vitrinite reflectance profiles consideration of convective heat flow due to hydrothermal activity arising in the vicinity of the intrusion during its formation and cooling helps to explain the difference between maturation profiles above and below some sills

techniques for measuring high resolution firn density profiles case study from kongsvegen svalbard on an 11 m firn ice core from kongsvegen svalbard we have used dielectric profiling dep to measure electrical properties and digital photography to measure a core optical stratigraphy cos profile we also used a neutron scattering probe np to measure a density profile in the borehole from which the core was extracted the np and dep derived density profiles were similar showing large scale 30 cm variation in the gravimetric densities of each core section fine scale features 10 cm are well characterized by the cos record and are seen at a slightly lower resolution in both the dep and np records which show increasing smoothing a combination of the density accuracy of np and the spatial resolution of cos provides a useful method of evaluating the shallow density profile of a glacier improving paleoclimate interpretation mass balance measurement and interpretation of radar returns

structure and evolution of subtropical cyclone anita as evaluated by heat and vorticity budgets this paper explores the evolution of subtropical cyclone anita which occurred near the east coast of brazil 19 s 37 w in march 2010 thermodynamic and dynamic processes during anita s lifecycle are investigated using the heat and vorticity budget equations the cyclone developed with hybrid characteristics and moved anomalously to the southwest where it coupled with an upper level cut off low during the mature phase this coupling was the main dynamical mechanism for further cyclone deepening anita then remained quasi stationary about 30 s 47 w for two days due to an upper level dipole pattern which prevented earlier displacement of the upper level low counterpart when the dipole pattern dissipated the cyclone moved southeast and underwent extratropical transition whilst merging with a mid latitude frontal cyclone diabatic heating and horizontal temperature advection are found to be essential for the subtropical development during extratropical transition it is instead diabatic cooling together with adiabatic cooling and warm air advection that act as the main mechanisms to influence the local temperature tendencies at low levels low level cyclonic tendencies were mostly due to convergent flow and the residual vorticity partially destroyed the vorticity tendencies produced by the divergence term moreover in regions and levels where convection could explain some of the vorticity tendencies it is found that apparent sinks of cyclonic vorticity were related to negative vorticity due to divergence i e convergent flow whilst apparent sources were related to positive vorticity due to divergence i e divergent flow

classification and synoptic analysis of subtropical cyclones within the northeastern atlantic ocean abstractsince more research is needed on subtropical cyclones stcs formed within the north atlantic eastern basin this survey analyzes them from a synoptic point of view on a climatological basis with the main aims of studying their common features complementing other studies of these storms in the north atlantic and aiding the forecasting community fifteen cases of stcs were identified during the period 1979 2011 by applying a set of criteria from two databases composite analysis reveals that an extratropical depression acts as a precursor when it is isolated from the westerlies and then suffers a deepening when becoming subtropical instead of decaying through occlusion this process is accompanied by an atmospheric circulation within the north atlantic whose main feature is characterized by notable departures from the climatological pattern with a statistically significant anomalous high pressure to the north of the stcs three conceptual models of synoptic pattern of subtropical cyclogenesis