gravity field determination and characteristics retrospective and prospective gravimetry has had a long history using pendulums torsion balances and static spring gravimeters relative accuracy adequate for many geophysical problems was already attained by 1900 but it took another half century to build readily portable gravimeters calibration and datum definition remained problems until the 1970s when free fall absolute gravimeters were developed that now have a precision of 10 3 mgal the problems of geographic inaccessibility and field party costs notably in areas of greatest tectonic interest are now being overcome by airborne gravimetry that has already achieved accuracies of 1 3 mgal with resolutions of 10 to 20 km satellite techniques are the best way to determine the long wavelength variations of the gravity field the resolution of the models has steadily improved with the number of satellites and the precision of the observations the best current model includes tracking data from more than 30 satellites satellite altimetry and surface gravimetry and has a resolution of about 290 km harmonic degree 70 with the most recent improvements coming from doppler orbitography and radiopositioning integrated by satellite doris tracking of the spot 2 satellite and satellite laser ranging slr doris and global positioning system gps tracking of the topex poseidon satellite meanwhile radar altimetry has become the dominant technique to infer the marine geoid with a resolution of tens of kilometers or shorter similarly the gravity fields of the moon venus and mars have been determined to harmonic degrees 70 75 and 50 respectively although tracking limitations result in variations of spatial resolution modeling earth s gravity field from the abundance of precise data has become an increasingly complex task with which the development of computer capacity has kept pace contemporary solutions now entail about 10 000 parameters half of them for effects other than the fixed gravity field of earth temporal variations arising from tides have long been well modeled and nontidal changes are now being identified the improvement in gravitational models engendered corresponding advances in geophysical interpretation isostatic models were refined and expanded to account for regional thermal and tectonic histories interpretation of the long wavelength gravity field determined by satellite techniques has been mainly in terms of plate tectonics as a manifestation of mantle convection gravity has been significant in inferring that there must be a large increase in viscosity with depth most strongly from the apparent slow sinking of subducted slabs the prospects for increasing accuracy and resolution in the determination of earth s gravity field rest primarily with the development of new measurement systems airborne gravimetry is taking promising new steps using gps but significant global model improvement awaits a dedicated satellite gravimetry system and future satellite altimeter missions will do more for ocean dynamics studies than geoid improvement advances in interpretation will occur through the development of other data such as seismic tomography and larger scale computer modeling of tectonics and convection

alternative workflow for three dimensional basin modeling in areas of structural complexity case study from the middle magdalena valley colombia basin modeling in structurally complex areas involves several difficulties associated with its geometric and thermal history approaches there have been multiple developments concerning the structural geometry in doing three dimensional 3 d basin modeling in these settings however their applicability is limited because most of these improvements require 3 d structural restorations which is an input that is not always available at basin scale although a traditional basin model using backstripping could give a faster overview of the petroleum system elements it is an alternative method that may distort the structural evolution and consequently the petroleum potential evaluation equally important are the thermal history uncertainties in these environments where several factors disturb the thermal regime despite these difficulties traditional 3 d basin modeling could be a reliable tool when we are able to understand the geometric and thermal histories and implement the proper adjustments we propose alternative methods to tackle common problems when building 3 d basin models and we demonstrate their validity with an example in the middle magdalena valley colombia this hydrocarbon province located in the northern andes corresponds to an intermountain basin that has undergone a complex evolution its structural configuration represents a modeling challenge by means of the backstripping method additionally a high variability exists in the present day basal heat flow related to its structural evolution the result of our model not only fits the calibration data but also reflects the geological processes better the proposed methodology intends to aid basin modelers in providing additional options when modeling in structurally deformed basins

methane leakage from evolving petroleum systems masses rates and inferences for climate feedback abstract the immense mass of organic carbon contained in sedimentary systems currently estimated at 1 56 10 10 tg des marais et al 1992 bears the potential of affecting global climate through the release of thermally or biologically generated methane to the atmosphere here we investigate the potential of naturally occurring gas leakage controlled by petroleum generation and degradation as a forcing mechanism for climate at geologic time scales we addressed the potential methane contributions to the atmosphere during the evolution of petroleum systems in two different petroliferous geological settings the western canada sedimentary basin wcsb and the central graben area of the north sea besides 3d numerical simulation different types of mass balance and theoretical approaches were applied depending on the data available and the processes taking place in each basin in the case of the wcsb we estimate maximum thermogenic methane leakage rates in the order of 10 2 10 3 tg yr and maximum biogenic methane generation rates of 10 2 tg yr in the case of the central graben maximum estimates for thermogenic methane leakage are in the order in 10 3 tg yr extrapolation of our results to a global scale suggests that at least as a single process thermal gas generation in hydrocarbon kitchen areas would not be able to influence climate although it may contribute to a positive feedback conversely only the sudden release of subsurface methane accumulations formed over geologic timescales can possibly allow for petroleum systems to exert an effect on climate

modelling generation and dissipation of overpressure in sedimentary basins an example from the halten terrace offshore norway a pressure simulator modelling the dynamic overpressure history in sedimentary basins is developed using a pressure compartment methodology simple models for porosity reduction are used for controlling pressure generation and different empirical models are used to estimate the lateral and vertical sealing dissipation mechanisms the equations describing the flow of formation water between the pressure compartments are used to calculate the resulting pressure dissipation on a geological time scale the methodology is tested and applied to the jurassic fangst group in the halten terrace area offshore norway dynamic allocation and an explicit numerical solution technique ensure a fast and accurate solution of the flow equations the results suggest a the probable mechanisms and processes that have generated the overpressure b the timing and location of hydraulic fracturing and c the nature and behaviour of the overpressure in addition to the overpressure history

basin modelling how well have we done model developers have been highly successful in building usable useful and reliable one dimensional models and in convincing explorationists to use them development of convenient universal software played an instrumental role in the acceptance of 1 d modelling the remaining weaknesses in technology and training while serious can be resolved through a few years of intensive work in certain specific areas 2 d and 3 d fluid flow modelling in contrast finds itself today largely in the position occupied by 1 d modelling more than a decade ago the concept of fluid flow modelling has not yet been adequately sold to explorationists mainly because existing software is often inadequate to meet the real needs of exploration personnel development of appropriate software will probably have to precede widespread popularization of fluid flow modelling to improve existing software two major areas must be addressed 1 making models more comprehensive by including all relevant geologic phenomena and 2 making software easier to use

challenges associated with near earth nightside current every magnetic field of solar and planetary space environments is associated with a current of differentially flowing charged particles electric potential patterns in geospace and near other planets are also closely linked with currents close to the earth particularly in the near earth nightside magnetosphere several current systems wax and wane during periods of space weather activity the velocity dependent drift energization and loss processes in this region complicate current system evolution there is a discrepancy about the magnitude timing and location of these currents however and this commentary pitches the case for a concerted community effort to resolve this issue

electrodynamic parameters in the nighttime sector during auroral substorms the characteristics of the large scale electrodynamic parameters field aligned currents facs electric fields and electron precipitation which are associated with auroral substorm events in the nighttime sector have been obtained through a unique analysis which places the ionospheric measurements of these parameters into the context of a generic substorm determined from global auroral images a generic bulge type auroral emission region has been deduced from auroral images taken by the dynamics explorer 1 de 1 satellite during a number of isolated substorms and the form has been divided into six sectors based on the peculiar emission characteristics in each sector west of bulge surge horn surge middle surge eastern bulge and east of bulge by comparing the location of passes of the dynamics explorer 2 de 2 satellite to the simultaneously obtained auroral images each pass is placed onto the generic aurora the organization of de 2 data in this way has systematically clarified peculiar characteristics in the electrodynamic parameters an upward net current mainly appears in the surge with little net current in the surge horn and the west of bulge the downward net current is distributed over wide longitudinal regions from the eastern bulge to the east of bulge near the poleward boundary of the expanding auroral bulge a pair of oppositely directed fac sheets is observed with the downward fac on the poleward side this downward fac and most of the upward fac in the surge and the middle surge are associated with narrow intense antisunward convection corresponding to an equatorward directed spikelike electric field this pair of currents decreases in amplitude and latitudinal width toward dusk in the surge and the west of bulge and the region 1 and 2 facs become embedded in the sunward convection region the upward fac region associated with the spikelike field on the poleward edge of the bulge coincides well with intense electron precipitation and aurora appearing in this western and poleward portion of the bulge the convection reversal is sharp in the west of bulge and surge horn sectors and near the high latitude boundary of the upward region 1 fac in the surge the convection reversal is near the low latitude boundary of the upward region 1 with a near stagnation region often extending over a large interval of latitude in the eastern bulge and east of bulge sectors the region 1 and 2 facs are located in the sunward convection region while a spikelike electric field occasionally appears poleward of the aurora but usually not associated with a pair of fac sheets in the eastern bulge magnetic field data show complicated fac distributions which correspond to current segments and filamentary currents

seasonal variations of high latitude field aligned currents inferred from orsted and magsat observations 1 in this paper we report on field aligned currents inferred from high precision three component geomagnetic field observations made on board the danish satellite orsted over polar regions because of a slow drift in local time of the satellite orbit through the noon midnight sector we were able to study the seasonal dependence of the dynamic properties of the dayside and nightside field aligned current systems over the northern and southern hemispheres we find an average over the pole distance between dayside and nightside currents of 32 during summer but 37 during winter and 36 during equinox the decrease in the size of the summer polar cap is caused by a shift of both daytime and nighttime current systems to higher magnetic latitudes for comparison the dawn dusk cross polar distance of the region 1 region 2 field aligned currents has been determined from high precision data observed by magsat a satellite flown in 1979 1980 in a dawn dusk orbit the latter results show that the dawn dusk distance between r1 r2 currents exhibits little seasonal dependence and amounts to 34 for all seasons in both polar caps the seasonal dependence is confirmed for the high latitude field aligned intensities they are larger by a factor of 1 5 1 8 in the sunlit summer polar cap in comparison with the winter hemisphere our results suggest that the r1 r2 and dayside field aligned currents are well balanced between the pairs of downward upward currents for all seasons as well as between hemispheres during equinox we were not able to confirm results reported in earlier studies that the net currents tend to increase with an enhancement of ionospheric conductivity caused by the solar illumination or substorm activity

thermal history model for the south central graben north sea derived using both tectonics and maturation abstract the thermal history modelling of basins is essential for petroleum systems analysis the methodology involves the derivation of the heat flow history by calibration using a kinetic model to match the predicted and observed vitrinite reflectance values in wells although this method is almost universally used by basin modellers a simple check using two independent methods with tectonic subsidence history being the second method shows that the thermal histories derived from the subsidence history do not match those predicted by the vitrinite reflectance method for any point in a basin there can only be one thermal history and the derivation of two different thermal histories indicates that there is a problem that has been ignored by geochemists and basin modellers the thermal history must predict the tectonic subsidence history and this heat flow history must also account for the maturation data e g vitrinite reflectance sediments subside under the action of forces and energy e g heat is a function of force during subsidence the downward force exceeds the upward force and the heat flow supplied to the basin must be reduced as the upward force is reduced while force and heat flow must be increased during uplift applying this relationship to the central graben north sea a heat flow history is derived that accounts for the rifting and subsequent subsidence tectonic history of two wells the british 23 26 2z and the danish lulu 1 the vitrinite reflectance predicted by this thermal history and the easy ro kinetic vitrinite reflectance model are higher than the measured values in both wells both wells are overpressured and the problem with the vitrinite reflectance calibration method is that the kinetic parameters used do not correctly account for the retardation produced by pressure le chatelier s principle without the pressure retardation effect incorporated into the kinetic parameters the modeller has to use lower temperatures to simulate retardation using the presro vitrinite reflectance model which incorporates pressure retardation as required by thermodynamics the thermal history derived from the rifting subsidence history can also be used to model the vitrinite reflectance data in the british 23 26 2z and danish lulu 1 wells this method of deriving an unknown e g thermal history using two independent models is widely used in physical sciences as an essential check on any prediction and this scientific rigor has to be followed by geoscientists modelling the thermal history of basins

pore fluid evolution in the kimmeridge clay formation of the uk outer moray firth implications for sandstone diagenesis abstract carbonate concretions in upper jurassic kimmeridge clay formation from three overpressured wells provide a detailed record of pore fluid evolution in the outer moray firth northern central graben the concretions contain multiple generations of septarian cements with morphologies ranging from simple cracks to complex fractures discrepancy exists between diagenetic studies which indicate these concretions formed during the initial 1 1 5 km of burial and palaeotemperature predictions based on a thermal history calibrated from the vitrinite reflectance kinetic model which indicate formation at much greater depths of between 1 5 and 2 5 km modelling undertaken for this study indicate that the concretions formed during the initial stages of burial under high heat flows fitting the early diagenetic model for their formation these conclusions have important implications for understanding the cementation of adjacent sandstone reservoirs where cement sequences have similar mineralogy and isotopic compositions with precipitation in the same temperature range from mudrock derived pore fluids early cementation of these sandstones is implied by analogy with the mudrock concretions

empirical modeling of a cir driven magnetic storm 1 the empirical analysis of structure and evolution of the geomagnetic field and underlying electric currents during the 8 11 march 2008 magnetospheric storm driven by a corotating interaction region is presented it is based on the high resolution geomagnetic field model ts07d http geomag field jhuapl edu model and the low altitude mapping of field aligned currents obtained using iridium satellites compared to storms driven by coronal mass ejections the equatorial currents are found to be overall more dawn dusk symmetric only in the early main phase a moderate hook like westward current flowing from the region 2 inflow area on the dawn side to the dusk afternoon magnetopause is detected along with an eastward current near the pre noon magnetopause new tail type currents are found to dominate the storm time magnetosphere in early main and recovery phases at the moments of strong peaks of the solar wind dynamic pressure similar effects found in cme driven storms coincide in time with the plasma sheet density bursts a clear distinction between the periods dominated by the partial ring current and the tail type currents seen in the model agrees with the iridium data that indicate a significant reduction and contraction of the field aligned current pattern in the latter case overall small magnitudes of the total field aligned currents with rather transient enhancements appear to be the most distinctive feature of cir driven storms comparison between the model and observations made by five themis probes shows good agreement on storm timescales moreover every deviation arising during a substorm reveals characteristic signatures of the tail current sheet thinning and dipolarization

fluorescence alteration and the suppression of vitrinite reflectance abstract vitrinite reflectance is a highly important thermal maturity indicator in petroleum exploration but there are a number of problems in its successful application which are basically the consequence of it being a single parameter technique fluorescence alteration of macerals which can be conveniently measured with the laser raman microprobe is a multi parameter technique which can be used to overcome some of these limitations on a fluorescence alteration diagram most vitrinite plots on or close to a line which may be called the normal vitrinite line fluorescence alteration data for a suite of randomly selected macerals from coal or dispersed organic matter plot along a curve which cuts the normal vitrinite line at the equivalent vitrinite reflectance of the sample as determined by calibration againsta suite of reference coals the technique posseses a high degree of objectivity and can be employed to determine the equivalent vitrinite reflectance of samples in which the vitrinite is difficult to identify or even absent perhydrous vitrinites with suppressed vitrinite reflectance are readily recognized as they plot in a field laterally displaced with respect to the normal vitrinite line the method is exemplified by a study of coals from the greta and pelton seams sydney basin which provides a classic example of vitrinite reflectance suppression and is further illustrated by a study of the dampier 1 well from the north west shelf of australia which contains both perhydrous macerals and dispersed organic matter in which vitrinite is difficult to identify

the joint gravity model 3 an improved earth geopotential model complete to spherical harmonic degree and order 70 has been determined by combining the joint gravity model 1 jgm 1 geopotential coefficients and their associated error covariance with new information from slr doris and gps tracking of topex poseidon laser tracking of lageos 1 lageos 2 and stella and additional doris tracking of spot 2 the resulting field jgm 3 which has been adopted for the topex poseidon altimeter data rerelease yields improved orbit accuracies as demonstrated by better fits to withheld tracking data and substantially reduced geographically correlated orbit error methods for analyzing the performance of the gravity field using high precision tracking station positioning were applied geodetic results including station coordinates and earth orientation parameters are significantly improved with the jgm 3 model sea surface topography solutions from topex poseidon altimetry indicate that the ocean geoid has been improved subset solutions performed by withholding either the gps data or the slr doris data were computed to demonstrate the effect of these particular data sets on the gravity model used for topex poseidon orbit determination

mirror symmetry of the crust in the oil gas region of shengli china abstract the concept of mirror image symmetry describes the correlation between the bottom of a sedimentary basin and the top of the underlying mantle the degree of mirror symmetry is analyzed here using thickness data from mesozoic cenozoic sedimentary basins and the moho depth with the purpose of investigating the implications for tectonics and exploratory practices in oil gas bearing basins our attention is focused on different tectonic elements of a multi scale tectonic partition in the oil gas region of shengli southeast of bohai bay china by applying standard least squares analysis methods to both datasets we obtained the average thickness h of the consolidated crust and the mirror symmetry factor a for every tectonic unit thereby allowing us to explore the correlation between the bottom depth of a sedimentary basin and the top of the underlying mantle a detailed analysis of data uncertainties and their potential effects led to small fluctuations of h and a within a narrow band around the mean values of 33 26 km and 1 43 respectively thus the results can be considered valid if they are constrained by these error bounds the issues of crust mantle interaction and the deviation of the crust from isostatic equilibrium are also addressed for their tectonic implications other structural parameters related to the deep rooted crust beneath the tectonic elements that make up the study region such as the ratio r of the thickness of the consolidated crust to the absolute value of the symmetry factor the ratio k of the maximum sediment thickness to the maximum uplift of the mantle and the product kh are also evaluated for their implications in geophysical prospecting the symmetry signature of the crust is compared to the symmetry of other sedimentary basins in china and in the world suggesting symmetry as a feasible prognostic tool in exploration for oil gas reservoirs the key result is that those locations where oil gas reservoirs have been found to date are basins in which the crust mantle interaction is active and the crust is isostatically compensated both of those parameters can be quantitatively constrained conversely oil and gas reserves are poor or nonexistent in regions where the crust mantle interaction is inactive and the crust is far from isostatic equilibrium however an intermediate case between these two extreme scenarios wherein the crust mantle interaction is rather moderate but the crust is in a state close to isostasy cannot be entirely ruled out

time and temperature in petroleum formation application of lopatin s method to petroleum exploration n v lopatin in the soviet union has developed a method for taking both time and temperature into account as factors in thermal maturation of kerogen lopatin s time temperature index of maturity tti values correlate with the thermal regimes corresponding to generation and preservation of hydrocarbons because such information is potentially of great interest for oil exploration a calibration and evaluation have been made of lopatin s method within the limitations of the data presently available the following statements can be made 1 the rate of the chemical reactions involved in thermal maturation of organic material appears to double with every 10 c 18 f rise in temperature 2 threshold values of lopatin s time temperature index of maturity tti are 15 onset of oil generation 75 peak oil generation 160 end oil generation 500 40 oil preservation deadline 1 000 50 oil preservation deadline 1 500 wet gas preservation deadline 65 000 dry gas preservation deadline 3 tti values calculated from lopatin reconstructions consistently agree with other maturation parameters commonly used by petroleum geochemists potential applications of lopatin s method for oil exploration include timing of oil generation calculation of volume of hydrocarbons generated within a basin and determination of economic deadlines

dpy currents in the cusp cleft region a crucial role of southward interplanetary magnetic field geomagnetic variations observed at the meridional chain of stations in greenland during 1982 1992 are utilized for the study of relationships between occurrence of azimuthal currents in the dayside cusp cleft region and changes in the interplanetary magnetic field imf by and bz components events were selected for analysis if 1 the greenland west coast stations were located near magnetic noon 1400 ut and 2 the absolute values of the imf bz were less than by sixteen events were selected under these conditions the analysis shows that intensive azimuthal currents develop in the cusp cleft region in association with the southward imf despite the fact that the imf by component had the same orientation during the few previous hours the direction of these currents westward or eastward is specified by the sign of the by component negative or positive respectively if the imf by is not zero but bz is mainly northward no significant currents are observed in the cusp cleft region at all as a result because magnetic substorms usually follow extended periods of southward bz the dayside cusp cleft magnetic perturbations often precede substorm activity in the midnight sector of the auroral zone this can simply be a connection between the dayside cusp cleft and nighttime auroral electrojets and therefore could be used as the dayside substorm precursors

thermal history of sedimentary basins maturation indices and kinetics of oil and gas generation temperature is the most sensitive parameter in hydrocarbon generation thus reconstruction of temperature history is essential when evaluating petroleum prospects no measurable parameter can be directly converted to paleotemperature maturation indices such as vitrinite reflectance tmax from rock eval pyrolysis spore coloration thermal alteration index tai or concentration of biological markers offer an indirect approach all these indices are a function of the thermal history through rather complex kinetics frequently influenced by the type of organic matter their significance and validity are reviewed besides the problems of identification e g vitrinite and interlaboratory calibration it is important to simultaneously interpret kerogen type and maturation and to avoid difficult conversions from one index to another geodynamic models where structural and thermal histories are connected are another approach to temper ture reconstruction which could be calibrated against the present distribution of temperature and the present value of maturation indices kinetics of kerogen decomposition controls the amount and composition of hydrocarbons generated an empirical time temperature index tti originally introduced by lopatin does not allow such a quantitative evaluation due to several limitations no provision for different types of kerogen and different rates of reactions poor calibration on vitrinite reflectance it is of limited interest unless one has no access to a desk top computer kinetic models based on a specific calibration made on actual source rock samples can simulate the evolution of all types of organic matter and can provide a quantitative evaluation of oil and gas generated examples from the jurassic source rocks of the paris basin monterey formation of california green river shales of utah paleozoic source eds of the algerian sahara and miocene rocks of the mahakam delta indonesia illustrate various aspects of the discussion geological geochemical models are the most efficient way to integrate geological seismic and geochemical data and they should greatly help to reduce the risk in exploration

elastic anisotropy of source rocks implications for hydrocarbon generation and primary migration we combined acoustic velocities and anisotropy measurements with x ray diffraction mineralogy rock eval organic geochemical analyses vitrinite reflectance and scanning electron microscope observations on 69 cores of hydrocarbon source rocks collected from eight sedimentary basins the velocity data indicate the lamellar distribution of solid organic matter kerogen in compacted black shales and show a strong correlation between their elastic anisotropy and organic richness the experimental results are consistent with the two component anisotropic model of black shales with a continuous kerogen network in both bedding parallel and bedding normal directions beginning from relatively low toc values the strong elastic anisotropy of tight thermally mature source rocks i further enhanced by overpressure induced bedding subparallel microcrack development during the main stage of hydrocarbon hc generation and primary migration at r0 greater than 0 75 in agreement with published petrographic observations these microcracks significantly aid primary hc migration particularly horizontally elastic anisotropy of medium to high porosity illite smectite shales is weaker than in lower porosity predominantly illite shales however the overall positive trend of elastic anisotropy with kerogen content remains unchanged

estimates of virgin rock temperature derived from bht measurements bias and error virgin rock temperatures are important to hydrocarbon exploration as these temperatures are necessary for the computation of source rock temperatures and for hydrocarbon generation computations several methods have been developed for determination of virgin rock temperatures from maximum temperatures recorded during logging in the past decades this paper describes an investigation where the calculated virgin rock temperatures from several different methods were examined for bias and accuracy using 18 different measurement series at the oseberg field the temperatures were corrected for different depths of burial and then compared with each other and with drill stem test dst measurements to investigate the inaccuracy of the methods the most advanced methods gave values close to the dst temperatures on average but with standard deviations as high as 9 degrees c the less advanced models like the horner plot method have systematically too low virgin rock temperatures by about 8 degrees c for the oseberg field with standard deviations of 8 degrees c the errors in calculated virgin rock temperatures are large enough to completely alter predictions of hydrocarbon generation in an area the large errors are attributed to poor quality data and to physical effects that are not properly taken into account in the temperature calculations improved sampling of temperature data can probably reduce the errors to some extent

should fluorescence alteration replace vitrinite reflectance as a major tool for thermal maturity determination in oil exploration abstract the fluorescence alteration multiple macerals famm technique is closely related to vitrinite reflectance until recently fluorescence alteration study of dispersed organic matter dom in sedimentary rocks has been regarded as technically difficult with the introduction of optical microprobes equipped with small continuous wave gas lasers having a very stable output of blue radiation readily focused to 1 2 m on the sample this work has now become routine famm has important advantages over vitrinite reflectance stemming from the possibility of resolving the data into two parameters one related to the level of maturation and the other related to the hydrogen richness of a maceral this enables the resolution of what are often difficult problems for the single parameter vitrinite reflectance technique namely the identification of indigenous vitrinite in dom the recognition of caved and reworked organic matter and the suppression of vitrinite reflectance for these reasons famm is a powerful tool for investigating vitrinite reflectance anomalies especially those associated with unconformities it is also well suited to investigate the tacit assumption in the vitrinite reflectance technique that all telocollinite matures along a single compositional pathway the famm technique is not without problems the range is restricted to equivalent mean random vitrinite reflectance rm o 0 4 1 2 the results are more sensitive to ambient temperature oxidation than vitrinite reflectance and the technique demands a high level of technical expertise the famm technique is calibrated on coals and it is therefore more likely to give high quality results on types ii and iii kerogens rather than type i kerogens which have not yet been intensively investigated although famm is unlikely to replace vitrinite reflectance considerable confidence may be had in a maturation assessment when consistent results are obtained from these two closely related but independent techniques

field aligned current signatures during the march 13 14 1989 great magnetic storm characteristics of field aligned currents facs in the evening and morning regions during the march 13 14 1989 great magnetic storm have been determined using magnetic and electric field data obtained from the exos d spacecraft this storm began with an ssc at 0128 ut on march 13 and the second ssc occurred at 0747 ut on the same day the storm continued until march 14 the equatorward boundary of the fac region began to move equatorward right after the first ssc in both the evening and morning sectors but the poleward boundary did not immediately respond to the ssc the equatorward boundary of the fac system reached as low as below 48 invariant latitude which corresponds to l 2 2 and the latitudinal width of the fac region increased greatly particularly in the morning sector 33 in invariant latitude in the evening sector the conventional current system characterized by a pair of upward region 1 and downward region 2 facs changed into complicated patterns consisting of many pairs of upward and downward facs with the development of the storm particularly around 22 ut on march 13 when an intense eastward electrojet was observed as low as 50 invariant latitude on the ground in the morning sector an additional large scale upward fac was observed poleward of the conventional downward region 1 and upward region 2 fac system throughout the storm in addition a pair of facs with a narrow latitudinal width 1 5 was observed at the poleward boundary of the extra upward fac

absolute positioning using doris tracking of the spot 2 satellite the french doris doppler satellite tracking positioning system has been operational on the spot 2 satellite since 1990 we have analyzed 80 days of data from 42 ground beacons and determined three dimensional site coordinates which agree with a set of slr vlbi positions at the 20 30 millimeter level in each coordinate after removal of common rotations translations and a scale difference the accuracy of the vertical component is comparable to that of the horizontal components indicating that residual troposphere error is not a limiting factor the translation parameters indicate that the doris network realizes a geocentric frame to about 50 mm in each component the considerable amount of data provided by the nearly global all weather doris network allowed this complex parameterization required to reduce the unmodelled forces acting on the low earth satellite the positioning results obtained from tracking using essentially the same ground network and the higher altitude topex poseidon spacecraft should be superior to those obtained for spot 2

burial and exhumation history of the galilee basin australia implications for unconventional hydrocarbon prospectivity this multidisciplinary study describes the burial and exhumation history of the frontier galilee basin in central queensland australia with implications for understanding its geohistory and unconventional gas prospectivity seismic interpretation stratigraphic mapping and an analysis of exhumation through quantifying overcompaction show total subsidence of approximately 2 km 6600 ft from the carboniferous to the late cretaceous punctuated by two major exhumation events triassic exhumation was less than 600 m 1970 ft whereas late cretaceous exhumation was in the order of 1000 m 3300 ft increasing eastward to greater than 1600 m 5250 ft geohistory reconstructions show that permian coal measures generated up to 45 m3 t 1590 ft3 t of gas when modeled temperatures exceeded 100 c 210 f during maximum burial of 1 5 2 km 4920 6560 ft in the late cretaceous in the carboniferous to the mid cretaceous the basin was situated to the west of the eastern australian subduction zone where proto pacific oceanic lithosphere was subducted until circa 100 ma when subduction ceased our study shows that the geohistory of the basin is characterized by rapid subsidence of 50 m m y 165 ft m y followed by rebound at circa 95 ma resulting in an uplift and erosion phase the undersaturation of the coals at present day is explained by this uplift event carbon isotopes indicate that the remaining gas 8 m3 t 280 ft3 t is of mixed biogenic and thermogenic origin therefore dynamic surface topography driven by subduction dynamics and slab breakoff had a profound effect on the subsidence uplift and resource potential of the galilee basin

the near earth magnetic field at 1980 determined from magsat data data from the magsat spacecraft for november 1979 through april 1980 and from 91 magnetic observatories for 1978 through 1982 are used to derive a spherical harmonic model of the earth s main magnetic field and its secular variation at epoch 1980 0 the model is called gsfc 12 83 constant coefficients are determined through degree and order 13 and secular variation coefficients through degree and order 10 the first degree external terms and corresponding induced internal terms are given as a function of dst preliminary modeling using separate data sets at dawn and dusk local time showed that the dusk data contain a substantial field contribution from the equatorial electrojet current the final data set was therefore selected first from dawn data and then augmented by dusk data to achieve a good geographic data distribution for each of three time periods 1 november december 1979 2 january february 1980 and 3 march april 1980 a correction for the effects of the equatorial electrojet was applied to the dusk data utilized the solution included calculation of fixed biases or anomalies for the observatory data although similar in many respects gsfc 12 83 differs from international geomagnetic reference field 1980 by 3 6 nt in the g10 term and shows a slightly negative b in the northern polar region as well as other differences in secular variation pattern

storm time duskside equatorial current and its closure path 1 we study the closure path of the equatorial current which flows on the duskside in the inner magnetosphere during the moderate two dip storm on 22 july 2009 this work was motivated by the result obtained in tsyganenko and sitnov 2007 that the prominent part of the duskside equatorial current might close through the dayside magnetopause during magnetic storms assuming the electric current conservation we compared the value of the total downward region 2 current with the intensity of the equatorial current on the duskside to infer what part of the latter closes through the ionosphere the estimates of the intensity of the equatorial current were based on the themis and goes magnetic field measurements in the vicinity of geosynchronous orbit it was found that the duskside equatorial current intensifies simultaneously with sym h decrease however unlike the conventional partial ring current it occupies the region of the highly stretched magnetic configuration magnetic field inclination 24 at r 5 4re at the same time the magnetic field measurements onboard three dmsp satellites showed that the local time distribution of the storm time region 2 currents preserves the pattern typical for more quiet periods with upward downward current in the prenoon afternoon sector the peak intensities of the downward region 2 current were recorded within 1 h from the sym h minima in the vicinity of the dusk meridian the peak values of the total downward region 2 current were found to be within 5 5 8 ma while the intensity of the equatorial current at r 5 4 6 6re was found to be 0 8 1 7 ma per 1re keeping a current continuity the radial extent of the partial ring current is estimated as 3 4 6re this indicates that most of the duskside current was diverted to the ionosphere during the main phase of this storm

geology and geothermal origin of grant canyon and bacon flat oil fields railroad valley nevada eastern nevada s grant canyon and bacon flat oil fields show strong evidence of formation in a still active moderate temperature geothermal system modern manifestations of this system include unusually elevated oil reservoir temperature at shallow depth 116 122 c at 1 1 1 6 km and dilute na hco3 cl thermal waters directly associated with hot oil hydrogen and oxygen isotopic compositions indicate that these thermal waters are meteoric in origin but were probably recharged prior to the holocene before 10 ka the waters apparently ascended to oil reservoir elevations after deep heating in response to the normal regional thermal gradient there is no evidence for a modern magmatic heat source the beginning of oil reservoir evolution at both fields is recorded by late stage fracture filling quartz in the vuggy brecciated paleozoic dolostone reservoir rocks oil and aqueous solutions were trapped as fluid inclusions in the quartz at temperatures comparable to those now prevailing in the reservoirs apparent salinities of the aqueous inclusions closely match the actual concentrations of current oil field waters and the quartz has the oxygen isotopic composition predicted for its crystallization from these waters at contemporary temperatures present day and fluid inclusion temperatures define essentially coincident isothermal profiles through and beneath the oil reservoir interval a phenomenon consistent with near constant convective heat transfer since inception of the eothermal system textural and mineralogic clues indicate that hot waters circulating in this system also increased porosity by dissolving carbonate minerals and helped seal reservoir margins by precipitating silica and kaolin more importantly the rising thermal waters may have aided oil transport and accelerated source rock maturation through an increase in the shallow 3 km local thermal budget along with the aforementioned fluid inclusion and isotopic evidence radiometrically dated life spans for numerous extinct geothermal systems epithermal ore deposits in the basin and range make it likely that the grant canyon bacon flat system and associated oil reservoirs are no older than 2 5 ma

local time distribution of net field aligned currents derived from high altitude satellite data 1 in order to explain features of geomagnetic disturbances observed at low and middle latitudes such as the dawn dusk asymmetry in the north south component an antisunward current system has been proposed the antisunward current system consists of net downward field aligned currents on the dayside antisunward auroral electrojet currents and net upward field aligned currents on the nightside however the net field aligned currents consisting in this current system have not been established by spacecraft observations yet in order to discuss whether this antisunward current system actually exists or not and whether this current system actually causes the features of geomagnetic disturbances at low and middle latitudes or not we statistically investigated the global structure of the geomagnetic disturbances generated by the field aligned currents in the inner magnetosphere by using the magnetic field data obtained by the de 1 satellite on the basis of the results local time distribution of the net field aligned currents was estimated net downward currents are found in the prenoon sector and net upward currents are found in the premidnight sector in the postnoon and the postmidnight sector net field aligned currents are rather small on an average the net downward field aligned currents in the prenoon would feed some portions of the auroral electrojets and the portions would flow from the prenoon to the premidnight to connect with the net upward field aligned currents in the premidnight these results are consistent with ground geomagnetic observations in the auroral region in addition we proposed a possible current system which consistently explains our results and many other observations it was also confirmed that the current system can actually cause the features of geomagnetic disturbances on the ground

large scale tectonic plate motions measured with the doris space geodesy system we have analysed approximately 3 years of doppler tracking measurements of the doris system on the spot2 and topex poseidon satellites absolute velocities of 19 stations of the doris network have been computed through a dynamic orbit computation method these stations are located on 9 major tectonic plates for 14 stations relative velocities across 28 plate boundaries involving 8 different plates agree quite well with the nuvel 1 geological estimates with a correlation coefficient of 0 982 and a slope of 1 00 0 02 this study provides the first space geodesy derived motion of the african plate which is based on data taken at 4 stations computed rotation vectors for the relative motions between the eurasian pacific and african plates show a good agreement with nuvel 1 vectors for the remaining sites which are typically located close to plate boundaries measured motions depart significantly from the ones predicted by nuvel 1 the site of fairbanks alaska appears to move anomalously compared to earlier vlbi results

balancing sub and supra salt strain in salt influenced rifts implications for extension estimates the structural style of salt influenced rifts may differ from those formed in predominantly brittle crust salt can decouple sub and supra salt strain causing sub salt faults to be geometrically decoupled from but kinematically coupled to and responsible for supra salt forced folding salt influenced rifts thus contain more folds than their brittle counterparts an observation often ignored in extension estimates fundamental to determining whether sub and supra salt structures are kinematically coherent and the relative contributions of thin i e gravity driven and thick skinned i e whole plate stretching deformation to accommodating rift related strain is our ability to measure extension at both structural levels we here use published physical models of salt influenced extension to show that line length estimates yield more accurate values of sub and supra salt extension compared to fault heave before applying these methods to seismic data from the halten terrace offshore norway we show that given the abundance of ductile deformation in salt influenced rifts significant amounts of extension may be ignored leading to the erroneous interpretations of thin skinned gravity gliding if a system is kinematically coherent supra salt structures can help predict the occurrence and kinematics of sub salt faults that may be poorly imaged and otherwise poorly constrained

present day tectonic plate motions and crustal deformations from the doris space system doppler orbitography and radiopositioning integrated by satellite doris data acquired between january 1993 and december 1996 from the spot 2 spot 3 and topex poseidon satellites have been analyzed to determine velocities for 45 sites on eight major tectonic plates for 28 sites far from deformation zones the velocity estimates agree with plate model predictions least squares computation of poles of rotation which model the plate motions shows that for eurasia africa pacific and south america plates the agreement is better with nuvel 1 while for australia antarctica nazca and north america plates the doris euler vectors are closer to ntjvel 1a in general doris results do not differ significantly from other space geodetic techniques determinations but provide better estimates for plates poorly or inhomogeneously covered by global positioning system gps very long baseline interferometry vlbi and satellite laser ranging slr networks such as africa the doris coverage of this plate allows discussion of intraplate deformations due to the motion of the eastern africa part which constitues the somalia plate sites located in deformation zones such as western eurasia boundaries central asia southwestern america coast south east asia show motion with respect to their own plates comparisons with other geodetic measurements for colocated stations or with regional geodynamical models show the interest of doris in active zones where global plate models are not valid

correction criteria for the suppression of vitrinite reflectance in hydrogen rich kerogens preliminary guidelines abstract thermal maturity is an important factor when assessing the petroleum potential of a basin or particular source rocks although the vitrinite reflectance vr technique provides excellent results from coal samples it has limitations when source rocks are used one problem is the anomalously low vrs the suppression of vr vr suppression in hydrogen rich kerogens the anomalously low suppressed vrs discussed in this article are mainly caused by the problems that organic petrographers encounter in finding and measuring appropriate vitrinite particles in hydrogen rich kerogens vr suppression is recognized when lower than normal vrs are measured on exinite rich or amorphous rich intervals in a vr well profile vr vs depth it can also be recognized when anomalously low vrs relative to the regional coalification maturation pattern or to regional oil gas occurrences are encountered in an interval although vr suppression in organic rich rocks coals and oil shales is well documented guidelines for its correction are lacking a preliminary model fig 1 is presented to help correct the vr suppression in hydrogen rich kerogens measured suppressed vr in r o along with original when immature hydrogen index hio estimated via rock eval pyrolysis and or organic petrography data of a sample can be used to estimate the maximum true unsuppressed vr although the vr and hio data for an individual sample is sufficient to estimate the maximum true vr we recommend the use of data from several closely spaced samples the model was tested with examples from published data and found to reasonably correct vr suppression in hydrogen rich kerogens we plan to refine the model using data from rock samples suppressed unsuppressed pairs and pyrolysis data

terrestrial and planetary gravity fields the determination of the gravity field together with knowledge of the surface topography provides one of the primary means of inferring the density structure and dynamics of planetary interiors phillips and lambeck 1980 hager 1985 after removing the topographic gravity signal the distribution of internal density anomalies caused by thermal or compositional differences can be studied gravity field models can also be used to study the compensation of surface topography which can provide information on the mechanical properties and state of stress of the lithosphere the determination of these models has been accomplished using a wide variety of different measurement types and solution techniques the near earth measurement types can be divided into satellite tracking measurements surface gravity measurements and satellite altimeter measurements in both near earth and interplanetary contexts tracking data are used to measure gravitational perturbations affecting satellites with the accuracy and spatial temporal distribution of the data being the most important factors in the resulting field accuracy and resolution surface gravity data provide a more direct measurement of the gravity field but acquiring data uniformly over the earth has always been difficult satellite altimetry provides precise measurements of the marine gravity field provided that satellite orbit errors and non geoidal sea surface height variations can be adequately modeled comprehensive gravity field solutions must incorporate these disparate data types in order to estimate mathematical parameters describing the gravity field such as spherical harmonic coefficients the proper combination of these data along with the desire to acquire an accurate representation of the model errors require that complex procedures be developed for computing these solutions

simple kinetic models of petroleum formation part iii modelling an open system abstract the movement of petroleum from organic rich source beds to potential carrier beds is the net result of two processes expulsion the release of generated petroleum from kerogen within the source bed and primary migration flow of a petroleum phase through the inorganic void networks of the source bed and all other intervening fine grained rocks expulsion is by far the more important process within the source bed orgas a simple zero dimensional model of the source rock as an open system explicitly models expulsion concurrent with oil and gas generation and oi lgas cracking as a storage threshold problem oil and gas are retained adsorbed absorbed within kerogen until their concentrations exceed the respective sorptive capacity of the residual organic carbon 0 1 and 0 02 g g ck 1 the initial hydrogen index hl 0 controls the important balance between potential sorbate petroleum and sorbant residual carbon using simple geochemical measurements the initial organic carbon is divided into initial oil inert kerogen and oil and gas generative reactive kerogen components reactive kerogens are assigned to one of five global kinetic organofacies with pre determined kinetic parameter sets governing separately rates of oil and gas generation kinetic parameters governing the rates of oil cracking within the source rock are predicted from hl 0 the two most important determinants of source rock behaviour are organofacies and hl 0 at a reference constant heating rate of 2 c ma 1 the projected oil expulsion threshold for typical organofacies members increases in the order a de 100 110 120 135 c f typically expels no oil an order of magnitude increase decrease in heating rate increases decreases these thresholds by ca 15 c typical cumulative gas mass fractions in their ultimate expulsion products are a f 0 25 0 3 0 25 0 65 and 1 0 g g 1 a value of 200 mg hc g c 1 is an approximate minimum hl 0 prerequisite for oil expulsion irrespective of absolute petroleum potential p 0 as a family coals vary dramatically in their expulsion behaviour as their hl 0 ranges both above and velow this value primary migration is efficient for expulsive source rocks movement within the source bed is limited only at low p 0 a source rocks total genetic potential p 0 thickness becomes important during migration outside the source bed it potentially restricts the primary migration distance and the excess of petroleum available for secondary migration and entrapment we evaluate primary migration approximately using a small migration loss factor no more than about 10 saturation of porosity or 1 mg g 1 coupled with an understanding of fluid potential gradients which determine migration direction within the stratigraphic architecture ultimately kerogen degradation and oil to gas cracking in the source rock are the rate limiting processes in petroleum accumulation

electric potential patterns in the northern and southern polar regions parameterized by the interplanetary magnetic field electric potential patterns have been obtained from the izmiran electrodynamic model izmem for the northern and southern polar regions during summer winter and equinox the model is derived from a large quantity of high latitude ground based geomagnetic data above 4 57 o corrected geomagnetic latitude at all magnetic local time hours a linear regression analysis technique has been used to obtain the quantitative response of each magnetic observatory to changes of interplanetary magnetic field imf components since no ionospheric conductivity model exists specifically for the southern polar region the statistical model of wallis and budzinski 1981 has been applied in both hemispheres a cross polar background potential of 35 kv derived by reiff et al 1981 is used to calibrate izmem s potential patterns the model s responses to changes in the imf by and bcomponents are analyzed to obtain a set of elementary convection patterns in both polar regions for each season of the year asymmetry in the potential pattern geometry in both hemispheres can be attributed either to the influence of the northern ionospheric conductivity model which was applied to the southern polar region or to some natural phenomena the modeled background cross polar potential for the condition when b by 0 is found to be 37 kv average values of the modeled potential drop caused by each nanotesla of the imf are the following 14 kv for southward b 4 kv for northward b and 4 4 5 kv for by components the latter is not applicable to the dawn dusk potential drop it may be applied across the cusp region only nevertheless a combination of the background and elementary potential patterns in the case studies gives a certain estimation of the cross polar potential drop which may be strongly distorted during time of large by it is concluded that izmem provides realistic convection patterns parameterized by the imf component directions and magnitudes and may be used to provide routine estimates of convection patterns and electric potentials if imf data are available

storm time field aligned currents on the nightside inferred from ground based magnetic data at midlatitudes relationships with the interplanetary magnetic field and substorms 1 on the basis of analysis of east west geomagnetic disturbance fields at midlatitudes we investigated the characteristics of temporal variations of field aligned currents on the nightside during geomagnetic storms the results indicate that upward field aligned currents develop on the nightside especially in the postmidnight when the interplanetary magnetic field imf is directed southward this suggests that the upward field aligned currents are principally associated with the convection electric field it is also found that the upward field aligned currents in the postmidnight can be intensified at substorm expansion while they principally depend on the southward component of the imf the intensification of the upward currents is regarded as a different physical process from the formation of a substorm current wedge at a substorm expansion we discuss some possible effects of the imf and substorms on the generation of the upward currents on the nightside especially in the postmidnight

positioning results with doris on spot2 after first year of mission a new space system named doris has been developed by the centre national d etudes spatiales in france with the collaboration of the institut geographique national for precise orbit determination and positioning it is a doppler based system with a worldwide ground network of transmitting beacons and an onboard receiver the spot2 satellite launched in january 1990 carries doris as an experimental instrument in this study we present positioning results obtained from the analysis of the first 10 months of doris data through a semi dynamical approach i e the satellite orbit is improved simultaneously with the beacon positions external calibration with satellite laser ranging slr and very long baseline interferometry vlbi positions indicates that doris accuracy from a few months of data is presently 15 20 cm rms in absolute and relative baseline length 1000 km positioning for very short baselines 1000 km positioning results is in the range 10 20 cm rms for the shortest baselines 100 km the month to month repeatability is better than 5 cm in cartesian coordinates this repeatability is only 2 cm in the north and east components whereas it is 12 cm in the vertical component suggesting that tropospheric errors are important it should be possible to improve these results in the future by reducing the residual orbit error especially the atmospheric drag perturbation which was particularly troublesome in 1990 a year having very large solar activity and by improving modeling of the tropospheric correction

characteristics of the field aligned current system in the nighttime sector during auroral substorms fujii et al 1994 obtained characteristics of the electrodynamic parameters that is field aligned currents electric fields and electron precipitation which are associated with auroral substorm events in the nighttime sector through a unique analysis that places the ionospheric measurements of these parameters into the context of a generic substorm determined from global auroral images in this paper we investigate in considerably more detail the characteristics of the field aligned currents using data from the same set of passes as the previous study we show for the first time that the net upward field aligned currents throughout the surge and surge horn are sufficient to account for most if not all of the converging currents of the auroral electrojets current densities are largest in the surge and surge horn current region continuity does not appear to exist across the substorm bulge region much of the auroral substorm field aligned current is composed of filamentary currents and finite current segments at large angles to each other the westward electrojet may contain large gradients in intensity both in local time and latitude due to sets of localized field aligned currents the net downward current for several hours to the west of the surge is insufficient to account for the eastward electrojet consistent with the concept that this electrojet originates primarily on the dayside our pattern of field aligned currents associated with the surge has common features and also differs significantly from the patterns previously derived from data from radars and ground based magnetometer arrays our pattern is considerably more complex probably due to the much higher resolution in latitude of the satellite data it is also larger in area since our average substorm is much larger than those pertaining to the previous patterns giving a substorm wedge considerably wider than that obtained from the radar and array data

ionospheric and birkeland current distributions inferred from the magsat magnetometer data the magsat vector magnetometer data with the aid of an accurate magnetic field model have been used to infer ionospheric and field aligned sheet current density distributions the magsat spacecraft is uniquely suited for this study because it provides for the first time from a satellite simultaneous observations of effects due to both ionospheric and birkeland current systems the method emphasized here consists of a fourier transform technique developed for use on surface magnetometer data and recently used by baumjohann et al 1979 data acquired by magsat on two days in 1979 were analyzed in detail the first was december 21 1979 a reasonably quiet 5 kp 8 time when data acquired in the sunlit hemisphere with presumably uniform conductivity were analyzed the second example deals with a rather active time november 13 1979 5 kp 35 in the northern hemisphere with more complicated conductivity and current distributions by comparing hall current densities inferred from the magsat data and those inferred from simultaneously recorded ground based data acquired by the scandinavian magnetometer array it is found during two other events that the former are underestimated due to the considerably high damping of magnetic variations with high spatial wave numbers between the ionosphere and the magsat orbit important results of this study include the fact that the birkeland and electrojet current systems are colocated in addition more realistic ionospheric current distributions have been developed the analyses have shown a tendency for triangular rather than constant electrojet current distributions as a function of latitude which is also consistent with the statistical uniform region 1 and region 2 birkeland current patterns

seasonal dependence of large scale birkeland currents the seasonal dependence of large scale birkeland currents has been determined from the analysis of vector magnetic field data acquired by the triad satellite in the northern hemisphere statistical characteristics of single sheet i e net currents and double sheet birkeland currents were determined from 555 triad passes during the summer and 408 passes during the winter more complicated multiple sheet current systems were not included in this study the average kp value for the summer events is 1 9 and for the winter events is 2 0 the principal results include the following 1 the single sheet birkeland currents are statistically observed more often than the double sheet currents in the dayside of the auroral zone during any season the single sheet currents are also observed more often in the summer than in the winter as much as 2 to 3 times as often depending upon the mlt sector 2 the intensities of the single and double sheet birkeland currents on the dayside from approximately 1000 mlt to 1800 mlt are larger during the summer in comparison to winter by a factor of about 2 3 the intensities of the double sheet birkeland currents in the nightside the dominant system in this local time do not show a significant difference from summer to winter 4 the single and double sheet currents in the dayside between 0600 and 1800 mlt appear at higher latitudes by about 1 to 3 during the summer in comparison to the winter these characteristics suggest that the birkeland current intensities are controlled by the ionospheric conductivity in the polar region the greater occurrence of single sheet birkeland currents during the summertime supports the suggestion that these currents close via the polar cap when the conductivity there is sufficiently high to permit it since the intensities of birkeland currents are larger during periods of greater ionospheric conductivity an important source but perhaps not the only source of these currents must be a voltage generator in the magnetosphere possibly related to the convective electric field

global geodesy using doris data on spot 2 the doris system developed for precise orbitography and precise positioning has been operational since the launch of the spot 2 satellite in january 1990 doppler doris data have been currently analysed since the beginning of the mission for geodetic objectives absolute positioning results based on a semi dynamical orbital analysis approach have been derived with the 2 years of doris data available cartesian coordinates of the global doris network 43 beacons derived on a monthly basis show a month to month repeatability of 5 7 cm rms comparison between doris station coordinates and those determined by vlbi or slr collocated with doris beacons indicates an accuracy of 5 7 cm rms in the 3 coordinates earth pole positions are determined at 5 day intervals with a standard deviation of 1 2 mas the comparison of the pole positions estimated from the doris data with a homogeneous series provided by the international earth rotation service shows differences with an amplitude of a few mas

field aligned currents during imf 0 we report on field aligned currents fac ob tained from precise magnetic field measurements made on board the orsted and magsat satellites when the interplan etary magnetic field imf was near zero we found that region 1 region 2 currents persist through southward imf imf 0 and northward imf also the central area of both the northern and southern polar caps is always filled with facs even during slightly southward imf a statis tical distribution of the latter currents resembles the day side nbz system with the downward upward currents at post noon pre noon hours discovered earlier from magsat observations we hypothesize that the quasi viscous inter action of the solar wind with the magnetospheric lobes may cause a sunward convection of the lobes field lines through the bunch s core effectively mapping the facs of nbz type down to the near pole area