identification of substorm expansive phase onsets 1 over the years many different particle and electromagnetic signatures have been invoked to identify the onset of what is called a substorm in this paper i shall first clarify what is generally meant by the term substorm onset and i shall show that some disturbances identified as substorm onsets should be treated with care i shall review the substorm in terms of its two recognized characteristic components directly driven and storage release i shall then discuss the importance of pseudobreakups in deciding what constitutes a legitimate substorm onset and in doing so will illustrate the subjective nature of present substorm onset identification techniques i shall stress that substorm like disturbances can take place both near the equatorward edge of the midnight sector oval mapping to the near earth magnetotail inside 12 re and near the poleward edge of the evening sector oval mapping to regions much farther downtail i shall present case studies that illustrate that some poleward edge disturbances have magnetic and auroral signatures that may be incorrectly interpreted as legitimate expansive phase onsets on the basis of this study i suggest that what may appear to be a lengthy series of closely spaced expansive phases may in fact be a single expansive phase followed by an arbitrarily long period of poleward border activity

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

sondrestrom radar initial results operation of an incoherent scatter radar at sondre stromfjord greenland began in early february 1983 marking the beginning of a new effort in ground based ionospheric research in the vicinity of the polar cusp and polar cap the sondrestrom radar is located north of the arctic circle on the west coast of greenland near the sondrestrom air base at an invariant latitude of 75 the effects of the polar cusp may frequently be observed at local noon the radar measured signature in the f region is an increase of more than a factor of two in electron density additionally the daytime variations in the f1 region electron density are dramatic in contrast to auroral zone measurements enhanced electron density at 150 km altitude has been observed and a marked absence of detectable e region ionization at night has also been noticed

quantitative biostratigraphy of the taranaki basin new zealand a deterministic and probabilistic approach a quantitative biostratigraphic analysis of the paleocene to lower miocene of the taranaki basin has enabled high precision in correlation zonation and assessment of depositional history biostratigraphic range end events based on 493 taxa in cuttings samples from eight wells representing foraminifera nannofossils dinoflagellates and miospores were culled to 87 range top events that were then analyzed by deterministic constrained optimization conop and probabilistic ranking and scaling rasc techniques all except 16 of the events are found to have relatively good biostratigraphic reliability the rasc probable sequence and probabilistic zonation give the best estimate of the sequence of events and zones to be encountered in any new well in the basin and a precise biostratigraphic scale for future exploration the conop composite section which matches well with that derived by conventional graphic correlation graphcor is readily related to previous zonations based on maximum ranges of taxa but gives an order of magnitude greater precision conop provides a precise correlation framework and reveals marked variation in thickness of stages across the basin when the composite section is calibrated against the time scale basinwide changes in depositional rate are revealed the upper eocene and oligocene mark an interval of slow deposition whereas the miocene marks a sharp increase in deposition the time calibrated composite section enables unconformities and changes in depositional rate found in individual wells to be precisely estimated many new unconformities are indicated particularly in the paleocene and eocene

analysis of substorm expansion and surge development we have used simultaneous magnetogram radar and viking imager data from evening local time to study several substorm expansion phase onsets and an expansion phase auroral surge that formed near the radar field of view at the onsets auroral brightenings developed within the region of the electric field gradient of the harang discontinuity and if not already present a westward electrojet began poleward of the eastward electrojet immediately following onsets the poleward boundary of the westward electrojet moved poleward along with the poleward boundary of the aurora however no consistent motion of the harang discontinuity was found in the ionosphere the auroral surge formed along the poleward boundary of the westward electrojet and of the aurora we argue that the distortion of the poleward boundary of the aurora associated with the surge was a manifestation of a distortion of the separatrix between open and closed magnetic field lines the distortion being caused by the field aligned currents within the head of the surge we suggest that rapid surge development may result from a tapping of the westward electrojet current at the surge head we also suggest that the separatrix distortion could lead to the escape of trapped plasma sheet particles along open field lines in the tail

electrodynamics of the westward traveling surge it is shown that the global convection pattern the ionospheric current and the field aligned current associated with the westward traveling surge in the asymptotic state can be modeled quantitatively as consequences of a blockage of the hall current from closure in the magnetosphere via field aligned currents the conductivity is allowed to increase self consistently with increasing upward field aligned current in the model this inclusion of the self consistent enhanced ionospheric conductivity due to discrete auroral precipitations is found to generate a localized intense westward electrojet on the poleward side of the harang discontinuity the westward electrojet is also found to rotate counterclockwise merging into the eastward electrojet around the leading edge of the surge thus the major features of the westward traveling surge can be reproduced reasonably well in our model

insights on why graphic correlation shaw s method works in 1964 a b shaw presented a method of correlating fossiliferous sedimentary rocks based on interpretation of graphic plots of first and last occurrences of taxa because there is no way to determine the true total ranges of fossil taxa it is instructive to test the accuracy of the method using hypothetical datasets the dataset used here consists of 16 taxa in six sections with differing known rates of rock accumulation in all graphs a single straight line correlation was a reasonable interpretation the resulting ranges after the first and third rounds of compositing reproduce the true ranges but with small errors slight errors in the positioning of individual correlation lines are more likely to lengthen ranges artificially than to shorten them shaw s method works well because whereas actually sampled ranges will be shorter than true ranges errors in correlation will be likely to extend some ranges this or any exercise using simulated data is useful only if the hypothetical situation resem

a precise worldwide correlation of early ordovician graptolite sequences fourteen early ordovician tremadoc llandeilo graptolite sequences from around the world are precisely infrazonally correlated based on the stratigraphic ranges of 130 species and species groups the composite standard sequence css of graptolites has been determined from the six best regional sequences by a nonparametric graphic correlation two data sets were selected one comprised first appearance events of 103 taxa the other first and last appearance events of 45 taxa the results of the two runs accord well and reveal respectively 66 and 73 successive bioevents in early ordovician time event spacing averages 0 7 0 8 ma and enables fine subdivision correlation and homotaxial testing for diachroneity the strong correlation between each of the six regional sequences and the css indicates the high level of accordance among graptolite successions around the world

a comparison of magnetic signatures and dmsp auroral images at substorm onset three case studies the authors explore the relationship between mid latitude and synchronous orbit magnetic signatures and the location of the auroral surge at the onset of three isolated magnetospheric substorms mid latitude data come from the air force geophysics laboratory magnetometer network synchronous orbit data form the satellites goes 2 and 3 and auroral data from defense meteorological satellite program auroral images and auroral magnetograms they find that the surge forms with its western edge approximately 1 hour west of the longitude where the major axis of the mid latitude pi 2 polarization ellipse is along magnetic north and where the d component perturbation of the magnetic bay is near zero these observations are in qualitative agreement with a current wedge consisting of a localized upward current in the west and a longitudinally distributed current in the east at synchronous orbit the longitude of the surge head appears to separate a region to the west where the magnetic field becomes more taillike from one to the east where the magnetic field becomes more dipolar

high resolution early paleozoic ordovician silurian time scales for much of the geologic time scale resolving power appears to be limited by the duration of biostratigraphic zones and subzones yet these zones exploit the appearance and disappearance events of only a small fraction of the species they span computer algorithms can sequence an order of magnitude more events and make explicit the uncertainties that arise when calibrating the resulting time line an illustrative case history builds an ordovician and silurian time scale from the geologic record of the entire graptolite clade over 1900 species from more than 400 localities and sections worldwide the same approach can be applied to any stratigraphic interval with detailed biostratigraphic observations it provides the foundation for time scales and paleobiologic time lines using logic similar to graphic correlation optimizing algorithms search for a composite sequence of species first and last appearance events that minimizes the implied shortcomings of all the field observations the algorithms minimize the number of species coexistences that are implied but never observed and the net adjustments needed to bring local range charts into agreement with a single composite sequence of events after total section thicknesses have been rescaled to help normalize for variation in depositional rate mean stratigraphic thicknesses are used to scale the intervals between adjacent events in the composite sequence the resulting scaled composite sequence is converted to a relative geologic time scale by identifying stage and zone boundaries within the sequence of graptolite events this relative scale is in turn calibrated by dated volcanic ash beds that were incorporated in the search for the optimal sequence these dated events are also used to test for linearity of the scaled composite the final time scale has a potential resolving power of 0 02 0 1 m y more than ten times better than can be achieved by traditional zones graptolite zones vary widely in duration from as short as 0 1 m y to nearly 5 0 m y the mean duration of zones or zonal groupings calibrated here is 1 44 m y in the ordovician and 0 91 m y in the silurian the average uncertainty in locating zone boundaries in a single composite sequence is about one fourth of the mean zone duration the variance resulting from differences in time scales developed from differing numbers of field observations and in response to changes in the optimization criteria gives a very conservative measure of the overall robustness of the method these differences indicate an average uncertainty in the age of graptolite zone boundaries that is more nearly equal to the mean zone duration for zone duration the mean uncertainty amounts to about one half of the length of an average zone

planktic foraminiferal events in early miocene zones n 6 and n 7 at southwest pacific dsdp site 593 relation with climatic changes in oxygen isotope zone milb abstract oxygen isotope data are compared with relative abundances of selected planktic foraminifera through a ca 15 m interval at dsdp site 593 tasman sea southwest pacific 40 s in which there are prominent changes in population sizes as well as several evolutionary events we focus on the relation between faunal and climatic histories the base of early miocene oxygen isotope zone milb uppermost planktic foraminiferal zone n 6 is identified from close sampled 14 kyr isotope records of globigerina woodi and cibicides kullenbergi chronostratigraphic interpolations using the first occurrences of globorotalia praescitula g miozea and praeorbulina curva give an age estimate of ca 18 4 ma cf 18 1 18 3 ma for the base of the zone at dsdp site 608 type level north atlantic 43 n another significant benthic 18o enrichment event informally designated as the base of zone milc is identified 10 m higher in the sequence at ca 17 8 ma populations of globoquadrina dehiscens and globigerinoides trilobus inferred to be near the southern margin of their distributions either reduced considerably or withdrew particularly in the vicinity of zone milc a bioseries linking globorotalia incognita with g zealandica developed following the benthic 18o enrichment spike at the base of zone milb the latter species became extinct at least regionally just above the base of zone milc in contrast the apparently opportunistic globorotalia praescitula increased dramatically in abundance at this time there were also transformations in its architecture leading to the evolutionary appearance of g miozea while planktic foraminifera abundances often do not closely covary with the detailed isotope records and tend to be more stable through time the near coincidence of evolutionary and biogeographic events with isotopic events suggests at least indirect adaptive responses to climatic changes early miocene middle latitude planktic foraminiferal evolution biogeography and biostratigraphy may be intimately connected with climatic history

stratigraphy of the southern norfolk ridge and the reinga basin a record of initiation of tonga kermadec northland subduction in the southwest pacific abstract seismic stratigraphic interpretations of a large new 2d seismic reflection dataset from the reinga basin region northwest of new zealand constrain the history of cretaceous fragmentation of gondwana and cenozoic initiation of tonga kermadec northland subduction the southern norfolk ridge system lay in a proximal location to plate boundaries that were active during both cretaceous and cenozoic events and persistent marine conditions led to a relatively complete record of sedimentation cretaceous extension was followed by regional subsidence and transgression two cenozoic contractional events are separated by substantial 1 km subsidence late eocene contraction led to reverse faulting and folding between new caledonia and the southern norfolk ridge system and topographic highs created in the north western sector were locally eroded by wave abrasion reinga basin was located at the southern tip of this event which had only limited impact in adjacent northern new zealand regional oligocene and miocene subsidence was contemporaneous with late oligocene and early miocene emplacement of nappes in northern new zealand and the onset of arc volcanism early miocene contraction in the reinga basin led to formation of the wanganella ridge these events can be related to calculated plate motions and are shown to be consistent with models of induced subduction nucleation that require c 150 km of convergence the first contraction is associated with regional inception of tonga kermadec subduction whereas oligocene to miocene events and the onset of hikurangi northland subduction were in response to a local change in plate boundary displacement rate and consequent linkage between subduction north of new zealand with alpine fault formation farther south

the convection electric field in auroral substorms dynamics explorer 2 de 2 electric field and ion drift data are used in a statistical study of the ionospheric convection electric field in bulge type auroral substorms thirty one individual de 2 substorm crossings were carefully selected and organized by the use of global auroral images obtained by de 1 the selected passes which occurred during substorm expansion phase maximum or early recovery phase cover the entire nighttime substorm the organization of the data used the method developed by fujii et al 1994 which divided the data into six local time sectors covering the nighttime substorm region following the procedures employed in the paper by gjerloev and hoffman 2000b the latitudinal width and location of each auroral oval crossing was then adjusted to fit the sector average in addition to the detailed study of the characteristics of the field within each sector this database enabled us to compile a model of the ionospheric convection electric field the characteristics of the premidnight convection reversal show a pronounced local time dependency far west of the surge it is a fairly well defined point reversal or convection shear approaching the surge and within the surge it is a region of weak electric fields increasing in width toward midnight that separates regions of equatorward and poleward electric fields therefore we adopt the term harang region rather than the harang discontinuity for the premidnight convection reversal a relatively narrow convection channel is coincident with the highest conductances located just poleward of the harang region this channel drives the substorm current wedge component of the westward electrojet in the surge and middle surge sectors it is present in all premidnight passes and consequently is an integral part of the three dimensional substorm current wedge system

joint two dimensional observations of ground magnetic and ionospheric electric fields associated with auroral zone currents 32 auroral zone currents during the passage of a westward travelling surge

climatic influences on the paleogene evolution of alkenones application of the alkenone paleotemperature proxy uk 37 for marine sediments is typically constrained by three factors i an absence of alkatrienones in sediments deposited where ocean temperatures exceed 28 c ii loss of alkenones in thermally altered sediments and iii poor preservation of alkenone signals due to oxidative degradation in addition there appears to be a temporal limit on the occurrence of alkatrienones which are conspicuously absent in all alkenone containing sediments from the early aptian to the immediate aftermath of the early eocene climatic optimum eeco when they first appeared in arctic ocean sediments compilation of reported and previously unpublished alkenone distributions for the paleogene coupled with assessment of co occurring calcareous nannoplankton genera within the noelaerhabdaceae provide evidence that evolutionary developments in alkenone occurrences include biosynthetic responses likely triggered by climate change the timing of emergence of alkatrienones post eeco and their subsequent appearance at all latitudes during the middle eocene accompanies expansion of the calcareous nannoplankton genus reticulofenestra coincident with significant climate driven changes in oceanic conditions including i modification of trophic structure associated with weakened thermal stratification ii higher productivity facilitated by enhanced nutrient influx and iii changes in seasonality initially at high latitudes related to greater latitudinal temperature gradients collectively these changes would serve to favor eurythermal eurytrophic algae like reticulofenestra with a biomechanism to store energy through production of lipid bodies rich in alkenones during episodes of higher nutrient availability this ability likely enhanced the viability of this marine haptophyte when nutrients were limiting ultimately ensuring its evolutionary success

scientific results from the viking ultraviolet imager an introduction the ultraviolet imager on the viking spacecraft provides global images of aurora in both night and day hemispheres at rates of up to three per minute first results summarized in this and a set of eight companion papers reveal new aspects of the patterns and dynamics of the aurora including eastward as well as westward expanding substorm intensifications but very little evidence of bulk westward motion of auroral surges rapid poleward and equatorward expansions during some substorms resulting in the formation of an intense eye shaped bulge containing diffuse aurora and north south aligned arc segments substorm like intensifications at the point where transpolar arcs join the nightside oval rapid small scale auroral brightenings or hot spots over a wide range of local times and very rapid changes in auroral forms in the noon sector

toward an observational synthesis of substorm models precipitation regions and high latitude convection reversals observed in the nightside auroral oval by dmsp satellites and hf radars a combination of simultaneous measurements from high low and ground altitude instruments has been used to infer the rapid evolution of the coupled nightside magnetosphere ionosphere during substorms reversals from an eastward zonal convection to westward zonal convection become apparent inside the volume of the substorm bulge a few minutes after the intensification of the westward electrojet these reversals persist for periods of 10 20 min and appear to have a one to one correspondence with the occurrence of dipolarizations the changes in convection are accompanied by changes in precipitation flux depletion regions fdr are measured by the dmsp satellites inside the surge near the equatorward portion of the westward electrojet intensification the poleward boundary of every fdr is collocated with a convection reversal and an arc intensification that marks a poleward transition into a region initially dominated by intense discrete electron precipitation and velocity dispersed ion structures vdis convection in the fdr constitutes an eastward electrojet channel that may produce a transient recovery signature as observed by ground magnetometers the observations of fdr s and the fast westward flows that accompany them are consistent with the scenario of a rarefaction and or a neutral line in the near earth tail that produces fast earthward flows after the breakup the arc intensification at the poleward boundary of the depletion region and the collocated transient convection reversal favor an enhancement of the magnetosphere ionosphere coupling and thus the continuation of the substorm expansion in a multiple cell convection system arguments are presented to explain how a series of pseudobreakups modify the near earth magnetic field into an increasingly dipolar geometry until a breakup is possible

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

detection of late cretaceous eustatic signatures using quantitative biostratigraphy this study tested the potential for high resolution quantitative biostratigraphic methods to distinguish tectonic from supposedly eustatic sequences the study employed automated multidimensional graphic correlation using constrained optimization program conop our analysis was based on 15 onshore sections in eastern new zealand spanning the coniacian to maastrichtian stages upper cretaceous and 398 well constrained lowest or highest occurrence records derived from 245 dinoflagellate species the age of the resulting composite section was calibrated using six dated bioevents two of these events were tied to geochemical or paleomagnetic datums following calibration the composite section had an average relative temporal resolution of less than 130 k y through the study interval although the succession of events was not dated to this level of precision in an absolute sense although the conop composite will not resolve unconformities or condensed intervals that occur across all studied sections such global unconformities can be identified using clusters of events that are placed at a single composite level fifteen major event clusters were identified 10 of which coincided closely with sequence boundaries identified in the northern hemisphere the probability of this coincidence arising by chance alone is 8 although these results must be regarded as provisional they suggest that high resolution quantitative stratigraphy can provide a potent tool for the identification and correlation of stratigraphic sequences furthermore our findings add significant support for recent studies that have argued for the presence of late cretaceous eustasy

the mid oligocene marshall paraconformity new zealand coincidence with global eustatic sea level fall or rise the marshall paraconformity is a regional mid oligocene unconformity that occurs widely in shelf sequences from the eastern new zealand passive continental margin the paraconformity represents a break in sedimentation of at least 3 m y and coincided with a regional sea level highstand in contrast to the prediction of global lowstand at 29 m y b p similar paraconformities are widespread on other southern continents deep sea hiatuses of similar age occurred in the adjacent southwest pacific ocean basins they may or may not have a common origin with the hiatus associated with the marshall paraconformity possible causes for the paraconformity and its associated glauconitic and bioclastic sediments are sea level fluctuations including those related to local geoidal effects or erosive bottom waters stemming from the development of antarctic glaciation or from splitting of the southern continents

thinking outside the zone high resolution quantitative diatom biochronology for the antarctic neogene abstract developing a coherent neogene history of the antarctic ice sheet and southern ocean requires a high resolution biostratigraphic age model one that is applicable to the array of existing onshore and offshore paleoenvironmental records this study integrates comprehensive diatom biostratigraphy magnetostratigraphy and tephrostratigraphy from 32 neogene sections around the southern ocean and antarctic continental margin framing their correlation as a constrained optimization conop permits the use of computer implemented approaches that resemble multidimensional versions of graphic correlation the method establishes the most parsimonious sequence of events subject to an expert s selection of suitable input data determination of geological feasibility constraints and the most appropriate measure of fit to the data optimization quantitative output includes assessments of record quality and confidence intervals on all age assignments thorough review and testing of conop model settings and input datasets established the solution s sensitivity to these factors and guided the selective removal of unreliable data to produce a robust precise and reproducible biochronology two complementary models based on different assumptions about reworking yield independent estimates of average local ranges and total regional ranges of fossil taxa in the southern high latitudes the resulting composite sequences include range data of 116 diatom taxa as well as 52 paleomagnetic reversals and two radiometrically dated ashes which enable age calibration to within an average of 0 08 m y for first and last appearances as old as 18 ma deviations of new model ages from previously published estimates are generally small and reflect the different sample sizes available for traditional versus new quantitative biostratigraphic calibrations our results confirm the reliability and regional isochroneity of most commonly utilized diatom zonal marker events identify many new potentially useful events and provide up to an order of magnitude greater temporal resolution than traditional zonations the anticipated expansion of this new southern ocean chronostratigraphic framework to new localities and other microfossil groups will pave the way to further age refinement and broader application of this approach in the future

isrm suggested methods for land geophysics in rock engineering this paper presents seven suggested methods each suggested method is composed of seven section 1 general 2 applicability 3 planning 4 field operation 5 data processing 6 interpretation 7 output and report