multipoint observations of a small substorm in this paper the authors present multipoint observations of a small substorm which occurred just after 0110 ut on april 25 1985 the observations were made by spacecraft ampte cce ampte irm dmsp f6 and dmsp f7 ground auroral stations eiscat magnetometer cross syowa narssarssuaq great whale river and fort churchill and mid latitude stations furstenfeldbruck toledo and argentine island these data provide them with a broad range of observations including the latitudinal extent of the polar cap visual identification of substorm aurorae and the magnetic perturbations produced directly beneath them in situ magnetic field and energetic particle observations of the disruption of the cross tail current sheet and observations concerning the spatial expansion of the current disruption region from two radially aligned spacecraft the dmsp data indicate that the event took place during a period when the polar cap was relatively contracted yet the disruption of the current sheet was observed by cce at 8 56 r sub e they have been able to infer a considerable amount of detail concerning the structure and westward expansion of the auroral features associated with the event and they show that those auroral surges were located more than 10 degree equatorward of the boundary between open andmore closed field lines moreover they present evidence that the current sheet disruption observed by cce in the neutral sheet was located on field lines which mapped to the westward traveling surge observed directly overhead of the ground station at syowa furthermore the observations strongly imply that disruption of the cross tail current began in the near earth region and that it had a component of expansion which was radially antisunward less

development and validation of inversion technique for substorm current wedge using ground magnetic field data the classic substorm current wedge model represents ground and space magnetic perturbations measured during substorms we have developed an inversion technique to calculate parameters determining the intensity and geometry of the current system using magnetic field data at midlatitudes the current wedge consists of four segments a sheet like field aligned current downward to the ionosphere postmidnight a westward current across the auroral bulge an upward sheet like current from the westward surge premidnight and an eastward current in the equatorial plane the model has five parameters including the current strength the locations and breadths of the two field aligned current sheets simultaneous changes in the ring current are represented by the superposition of a symmetric ring current and a partial ring current characterized by three additional parameters parameters of the model are determined as a function of time based on midlatitude ground magnetometers using realistic field lines and accounting for earth s induction the model is validated by a variety of techniques first the model predicts more than 80 of the variance in the observations second the intensity of the current wedge and the ring current follows the same trends of the westward electrojet and the ring current indices third the intensity of the westward electrojet agrees extremely well with the intensity of the current wedge finally spacecraft observations of the aurora correspond with the evolution deduced from the model this model of the substorm current wedge provides a valuable tool for the study of substorm development and its relation to phenomena in space

a note on the impact factor of gondwana research with a view towards understanding the evolutionary history of the complex south indian shield several geological and geophysical studies have been carried out recent geophysical studies include magnetotelluric mt deep seismic sounding dss gravity magnetic and deep resistivity soundings drs in the present study mt results along 140 km andiyur turaiyur east west profile is presented the data are subjected to groom bailey decomposition and static shift correction before deriving a 2 d model the 2 d modeling results have shown that the upper crust up to about 15 km towards western part of the profile have exhibited high resistive character of about 40 000 ohm m as compared to the eastern part less than 5 000 ohm m the mid lower crust has shown a decrease in resistivity in western part of the profile the order of resistivity being 2 000 ohm m an anomalous steep conductive feature less than 100 ohm m is observed near sankari at mid lower crustal depths 20 km towards middle part of the profile this feature is spatially correlatable with the well known moyar bhavani shear zone mbsz the features obtained in the present study are consistent with earlier mt studies in this region and correlatable with other geophysical studies dss studies near the study region gave an evidence for differing crustal structure on either side of mbsz variation in geoelectric character along the profile both in the upper crust and mid lower crust indicate a block structure in the sgt with shear zones acting as boundaries the new evidence in the form of distinct geoelectric structure and also variation in seismic structure indicate a continent continent collision zone in this region and plays an important role for the gondwana reconstruction models of south indian shield

a proposed production model of rapid subauroral ion drifts and their relationship to substorm evolution multisatellite data are used to examine the temporal relationship between subauroral ion drifts said and the phases of an auroral substorm utilizing images of auroral luminosities taken by the dynamics explorer 1 de 1 spacecraft and observations of particle injection at geosynchronous orbit we identify the time of expansive phase onset and estimate the time at which recovery begins noting the times at which said are observed simultaneously by the de 2 spacecraft we find that said typically occur well after substorm onset more than 30 min during the substorm recovery phase substantial westward ion drifts and field aligned currents are observed well equatorward of the auroral oval during the expansion phase of a substorm but the drifts lack the narrow spike signature associated with said prior to substorm onset and after substorm recovery field aligned currents are absent equatorward of the auroral oval and the ionosphere is very nearly corotating a phenomenological model of said production is proposed that qualitatively agrees with the observed ionospheric signatures and substorm temporal relationship in this model substorm generated subauroral field aligned currents close via pedersen currents with the outward flowing region 1 currents at higher latitudes these pedersen currents flow in the region of low conductivity equatorward of the auroral oval and are associated with relatively large poleward directed electric fields the frictional heating of the ions caused by collisions with the corotating neutral atmosphere substantially increases the rate of ion atom interchange between o and n2 subsequent fast recombination of no with electrons further reduces the subauroral f region conductivities with a corresponding increase in the electric field and the frictional heating this heating leads to thermal expansion substantial field aligned plasma flow and very large depletions in the f peak concentration thus additionally reducing the height integrated pedersen conductivity

on the coupling between the harang reversal evolution and substorm dynamics a synthesis of superdarn dmsp and image observations 1 the harang reversal is a prominent feature frequently observed in the electric and magnetic field patterns in the high latitude auroral zone and plays an important role in substorm dynamics a comprehensive set of instruments including super dual auroral radar network superdarn defense meteorological satellite program dmsp and imager for magnetopause to aurora global exploration image is used to investigate the relationship between the harang reversal and substorms on the basis of nine events that have been analyzed we find that the harang reversal forms and becomes well defined during the growth phase azimuthal flows equatorward of the harang reversal a majority of which are in the subauroral region enhance during the growth phase the observations indicate that subauroral polarization streams saps and the harang reversal evolve together as part of the growth phase development of the region 2 current system furthermore the substorm auroral onset is seen to occur quite near the center of the harang flow shear which suggests that the substorm upward field aligned current develops there after onset the evolution of convection flows in the vicinity of the harang region depends strongly on their location relative to that of the onset saps flows equatorward of the harang reversal suddenly increase at the substorm onset flow shear east of the auroral onset relaxes after the onset and poleward flows part of a clockwise vortex are observed west of the auroral onset after the onset these observations demonstrate the strong coupling between the harang reversal evolution and substorm dynamics and suggest that the nightside region 2 physics is closely related to substorm dynamics

response of large scale ionospheric convection to substorm expansion onsets a case study 1 we have studied the response of large scale ionospheric convection to substorm expansion onsets on the basis of two weak substorms of 1 may 2001 during which a large part of the dawn cell of the two cell ionospheric convection pattern was monitored by the superdarn radars ionospheric convection began to enhance first in a localized region of the equatorward part of the dawn cell 2 minutes before the expansion onsets of both substorms and then enhanced in the entire dawn cell successively the enhanced convection persisted throughout their expansion phase possibly even near the footprint of a plasma sheet region without fast flows observed by geotail these observations suggest that ionospheric convection begins to enhance just before substorm expansion onset and then enhances in the entire cell possibly regardless of the presence of fast earthward flows in the corresponding plasma sheet region of the magnetotail the global enhancement of ionospheric convection is consistent with that of magnetotail convection which also begins just before onset

dendritic calcite crystals formed by calcification of algal filaments in a vadose environment abstract uncalcified and calcified algae grow on and color walls of cavities that occur in karst breccia which fills pockets in the tertiary bluff formation of grand cayman island the calcified algae are important because the calcification has been achieved through the formation of dendritic calcite crystals although common in metals such branching crystals have not been widely recognized in naturally occurring calcite the dendritic calcite crystals are exactly like most dendritic crystals in that they have a primary needle or stem with secondary and tertiary branches most dendritic calcite crystals have an open treelike form and are easy to recognize as calcification proceeds the dendritic crystals become progressively filled in and are increasingly difficult to recognize as dendritic crystals filling of the dendritic crystals can result in two dimensional sheets or three dimensional columns assuming the three dimensional columnar dendritic crystals developed planar and or curving smooth surfaces then lacking other evidence they would be indistinguishable from normal columnar calcite crystals and their dendritic origin would be hidden variables thought to control dendrite crystal formation include a creation of localized highly supersaturated solutions leading to rapid rates of nucleation and crystal growth and b impurities in the form of organic molecules and other substances algae are excellent candidates for controlling a via their metabolism and contributing to b via their decay combining these ideas with the results of this study and with the known common occurrence of algae in many speleothemic environments provides an impetus for a reexamination of the origin of subaerially formed calcite crystals

application and validation of the spherical elementary currents systems technique for deriving ionospheric equivalent currents with the north american and greenland ground magnetometer arrays 1 with data from the canadian magnetic observatory system canadian array for real time investigations of magnetic activity geophysical institute magnetometer array greenland time history of events and macroscale interactions during substorms themis and magnetometer array for cusp and cleft studies ground magnetometer arrays we applied the state of art technique on the basis of spherical elementary currents systems secs developed by amm and viljanen 1999 in order to calculate maps of ionospheric equivalent currents over the whole north american auroral region this study is the first to apply the secs technique to a large nonrectangular area with widely separated ground magnetometers 350 km for this study we will first demonstrate the validity of the technique using synthetic data and then examine equivalent ionospheric currents associated with a harang discontinuity for a case study on 10 december 2007 the results show in detail the dynamic evolution of the currents over the entire north american ground magnetometer network equivalent ionospheric current eic maps inferred at the minimum resolution of the database in this case 10 s can thus be analyzed further in conjunction with near simultaneous images of the themis all sky imager mosaics and super dual auroral radar network radar data the eic maps represent a value added product from the raw magnetometer database and can be used for contextual interpretation as well as help with our understanding of magnetosphere ionosphere coupling mechanisms using the ground arrays and the themis spacecraft data

relation of substorm onset to harang discontinuity 1 in this study we investigate the relation of auroral substorm onset to the harang discontinuity hd various studies have reported that the substorm onset occurs poleward equatorward or within the hd the motivation for the present study is to further investigate this relation with a much larger database using a database of over 3700 onsets determined from auroral images taken on the image spacecraft we statistically examine the magnetic latitude location of the onset with respect to the location of the hd the location of the discontinuity is determined with data from the image ground magnetometer network we define the location of the hd as the transition from relatively strong eastward to relatively strong westward equivalent ionospheric currents at the latitude of the main nightside auroral electrojet flow our results show that the location of 75 onsets that occurred above the image ground array about 31 occurred within 6 of latitude of the hd observed during the growth phase of the substorm and 37 occur within 5 of latitude of the hd observed during the expansion phase we also find that 23 of the onsets occur in association with vortices of ionospheric currents observed during the growth phase the remaining 31 of the onsets do not appear to be associated with a hd or a vortex during the growth phase ten of the initial 75 onsets were identified as likely pseudo breakups and not fully developed substorms seven of the initial 75 onsets were probably poleward boundary intensifications pbi this study demonstrates that approximately 2 3 of the auroral substorm onsets do not occur within or near the hd identified in the growth phase these results do not support the prediction made by lyons et al 2003 that substorm auroral onset should occur within the upward field aligned current in the harang discontinuity

late quaternary coastal evolution and aeolian sedimentation in the tectonically active southern atacama desert chile abstract analyses of aeolianites and associated dune surficial carbonate and marine terrace sediments from north central chile 27 54 s yield a record of environmental change for the coastal southern atacama desert spanning at least the last glacial interglacial cycle optically stimulated luminescence dating indicates phases of aeolian dune construction at around 130 111 98 77 69 and 41 28 ka thin section and stable carbon and oxygen isotope analyses suggest a predominantly marine sediment source for the three oldest dune phases aeolianites appear to have accumulated mainly from tectonically uplifted interglacial marine sediments that were deflated during windier and or stormier intervals bedding orientations indicate that sand transporting winds varied in direction from s ese during mis 5e and wnw ese during mis 5c 5a winds from the southeast quadrant are unusual today in this region of the atacama suggesting either major shifts in atmospheric circulation or topographic airflow modification thin section evidence indicates that the aeolianites were cemented by two phases of vadose carbonate tentatively linked to wetter periods around 70 and 45 ka tectonic uplift in the area has proceeded at an average rate of 305 542 mm kyr 1 the study illustrates the complexity of understanding onshore offshore sediment fluxes in the context of late quaternary sea level fluctuations for an area undergoing rapid tectonic uplift

aragonite to calcite transformation during fresh water diagenesis of carbonates insights from pore water chemistry dissolved strontium and calcium concentrations in fresh water lenses fwl and associated mixing zones mz on two small holocene ooid sand islands in the schooner cays bahamas were monitored during a 1 yr period to quantitatively analyze the transformation of aragonite to calcite the observed characteristics of this mass transfer are functions of climate and hydrology aragonite to calcite transformation in all hydrologic zones is primarily associated with meteoric recharge the transformation occurs throughout the fwl and in the mz to relative salinities of 19 and 36 sea water on the two islands rates of transformation are rapid in all zones and are greatest in the fwl a limestone composed of 100 calcite should form from an aragonite precursor within 4 700 to 15 600 yr in the fwl and within 8 700 to 60 000 yr in the upper mz efficiencies of transformation can vary between hydrologic zones due to pco2 effects yet the efficiency of the entire system fwl mz is high 87 this indicates that most caco3 derived from aragonite dissolution is reprecipitated as calcite somewhere in the fresh water system or upper mixing zone co2 effects fresh water sea water mixing and the differing solubilities between aragonite and calcite all drive the mass transfer the latter is the most significant accounting for up to nine times more mass transfer than co2 effects and at least ten times more mass transfer than fresh water sea water mixing differing solubilities should also cause mass transfer to occur throughout the hydrologic cycle but it apparently becomes ineffective after the rainy season possibly due to the inhibition of calcite precipitation

identification of substorm onset location and preonset sequence using reimei themis gbo pfisr and geotail 1 we present state of the art multiple instrument observations of an isolated substorm on october 12 2007 the auroral breakup was observed simultaneously by reimei themis asi and pfisr the footprint of geotail was also near the breakup these observations allow for detailed study of the breakup location in terms of large and small scale auroral morphology particle precipitation and ionospheric convection which has not previously been achieved it also allows for detailed identification of the sequence leading to the breakup we report the first spaceborne high spatial and temporal resolution images of part of a breakup arc and a wave like auroral enhancement captured by reimei observations suggest a sudden plasma sheet thinning initiated 10 min before the onset wave like auroral enhancements were observed twice at the most equatorward arc 3 min and 1 min before the breakup these enhancements are likely due to some near earth instability such as ballooning instability unlike the usual substorm sequence this most equatorward arc did not develop into the breakup arc but remained almost stable until being engulfed by the auroral equatorward expansion from higher latitude after onset the wave like auroral enhancement was associated with three fine inverted v arcs and embedded within energetic ion precipitation following this enhancement an arc likely a poleward boundary intensification formed at higher latitude just adjacent to the plasma sheet boundary layer psbl this arc then extended southwestward and led to the breakup arc which was located poleward of the wavy structures assuming longitudinal homogeneity of ion precipitation over 1 this breakup arc was located in a region without ion precipitation just poleward of the energetic ion precipitation these observations suggest the possible existence of a low entropy flow channel associated with the arc adjacent to the psbl which might be associated with instability in the near earth plasma sheet responsible for the auroral breakup

two component auroral electrojet importance for substorm studies this paper attempts to synthesize the diverse number of observations of electric fields and currents in the high latitude ionosphere during substorms by demonstrating that there are often spatial shifts among regions of high ionospheric conductivity large electric fields and intense currents in the auroral electrojet it is shown that substorm time variations of the current patterns over the entire polar region consist of two basic components the first is related to the two cell convection pattern and the second to the westward electrojet in the dark sector which is in turn related to the three dimensional wedge current system these two components result from the relative strength of electric fields and conductivities in the intensification of the auroral electrojet and are identified as the signatures for directly driven and the unloading components in solar wind magnetosphere interactions we contend that disturbed intervals do not necessitate the presence of substorm expansion phase activity and that the vast number of earlier complex results concerning the auroral electrojet can be ascertained from the high degree of variability of the two components depending on substorm events substorm phases and their own spatial temporal scale sizes it is demonstrated that several major issues that have remained controversial are now accounted for reasonably well in terms of this two component electrojet model we also predict specific features of the substorm auroral electrojet that have not yet been observed

substorms fundamental observational features distinction from other disturbances and external triggering fundamental observational signatures of substorms and other auroral zone disturbances are summarized in this review it is shown that at least three distinct types of major geomagnetic disturbance have been identified in the auroral zones and it is suggested that care should be taken in distinguishing substorms from the other types of disturbance when reaching observational conclusions concerning substorms substorms can be uniquely identified by the formation of the current wedge and by the associated westward electrojet and region of active aurora that move poleward within the ionosphere during the expansion phase periods of enhanced convection have been observed to continue without substorms for as long as the interplanetary magnetic field imf remains stably southward they can have al signatures that look very much like intense substorms but these signatures result from strong dp 2 ionospheric currents driven by enhanced convection rather than from a nightside westward electrojet a third type of disturbance is characterized by short intervals of enhanced equatorward flow within the ionosphere and enhanced auroral emissions these enhancements move equatorward from near the polar cap boundary and they may be associated with several minute long enhancements of earthward flow within the plasma sheet studies that have examined the triggering of substorm expansions by imf changes are also reviewed when considered together and substorms are distinguished from the other disturbances these studies imply that most and perhaps all expansions are triggered by imf changes these changes include both northward turnings and reductions in the magnitude of the y component if most substorms are indeed externally triggered as suggested here then substorms must generally not be the result of an internal magnetospheric instability

evaluation of low latitude pi2 pulsations as indicators of substorm onset using polar ultraviolet imagery impulsive pi2 pulsations have long been recognized as one of the key signatures of magnetic activity during substorm periods due to their wide observable range both in latitudes and longitudes it is well documented that there is usually more than one pi2 wave burst associated with a substorm and only one of them corresponds to the onset of the substorm this observational fact poses obstacles to determining substorm onsets with pi2 signals although the pi2 have become one of the most popular indicators for substorm onsets the reliability of using the pi2 in this fashion has not been seriously investigated in this paper we address this question with a statistical approach by using 650 auroral substorm onsets identified with polar ultraviolet images for a time interval from april 1996 to may 1997 a comparison of the low latitude pi2 pulsation onsets from kakioka l 1 07 with the auroral breakups indicates that identifying substorm onset with the pi2 alone is often ambiguous of a total of 119 isolated defined as 10 min of quiet time preceding the onset pi2 bursts seen within 10 min from a magnetic positive bay there were 65 events 55 taking place within 3 min from breakups and 34 events 29 indicating no sign of an auroral breakup within 10 min of the pi2 burst this result suggests that pi2 may not be as a good indicator of the substorm onset as it was thought to be interestingly it is always possible to associate pi2 pulsations with some forms of auroral intensification when compared to auroral breakups pi2 onsets are subject to a small delay of 1 3 min with a peak around l min delays of pi2 onsets are revealed to be a function of location relative to auroral breakup this dependence is found to be consistent with the time of flight for a fast mode wave in a plasmapause cavity mode model propagating in the magnetosphere

themis observations of substorms on 26 february 2008 initiated by magnetotail reconnection 1 on 26 february 2008 the themis satellites observed two substorms that occurred at about 0405 and 0455 ut angelopoulos et al 2008 made a comprehensive study of the second event in this paper we display detailed features of the two substorms with emphasis on the first in both substorms a distinct auroral intensification occurred during the earliest stage of onset about 1 to 2 min after midtail reconnection began this initial intensification was weak and localized and thus had the signatures of a pseudobreakup in both substorms a second major intensification occurred next in the substorm onset sequence followed by rapid and extensive poleward expansion this second intensification had the features of the major expansion onset and was nearly coincident with observations of earthward flows and magnetic dipolarization in the near earth tail during the growth phase of the two substorms open magnetic flux accumulated in the polar cap in the expansion recovery phase the polar cap open flux was quickly reduced these observations are in agreement with the assertion that tail reconnection initiates the initial pseudobreakup and the ensuing major expansion and releases and transports energy to eventually cause near earth dipolarization and the expansion phase onset of these two substorms

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

multi instrument observations of sed during 24 25 october 2011 storm implications for sed formation processes 1 we present multiple instrument observations of a storm enhanced density sed during the 24 25 october 2011 intense geomagnetic storm formation and the subsequent evolution of the sed and the midlatitude trough are revealed by global gps vertical total electron content maps in addition we present high time resolution poker flat incoherent scatter radar pfisr observations of ionospheric profiles within the sed we divided the sed observed by pfisr into two parts both parts are characterized by elevated ionospheric peak height hmf2 and total electron content compared to quiet time values however the two parts of the sed have different characteristics in the electron temperature te the f region peak density nmf2 and convection flows the first part of the sed is associated with enhanced te in the lower f region and reduced te in the upper f region and is collocated with northward convection flows the nmf2 was lower than quiet time values the second part of the sed is associated with significantly increased nmf2 elevated te at all altitudes and is located near the equatorward boundary of large northwestward flows based on these observations we suggest that the mechanisms responsible for the formation of the two parts of the sed may be different the first part is due to equatorward expansion of the convection pattern and the projection of northward convection flows in the vertical direction which lifts the ionospheric plasma to higher altitudes and thus reduces the loss rate of plasma recombination the second part is more complicated besides equatorward expansion of the convection pattern and large upward flows evidences of other mechanisms including horizontal advection due to fast flows energetic particle precipitation and enhanced thermospheric wind in the topside ionosphere are also present estimates show that contribution from precipitating energetic protons is at most 10 of the total f region density the thermospheric wind also plays a minor role in this case

the role of skeletal porosity in aragonite neomorphism strombus and montastrea from the pleistocene key largo limestone florida abstract the neomorphism of aragonite to calcite involves complex textural and chemical alterations that are in part controlled by the degree of communication between diagenetic and ambient formation fluids two taxa montastrea annularis and strombus gigas from the vadose zone of the pleistocene key largo formation in southern florida were examined in order to evaluate the effect of initial skeletal porosity on system closure during neomorphism fabrics of replacement calcite in both taxa are similar consisting of blocky crystals largely restricted to areas of former skeletal aragonite oriented aragonite and organic inclusions result in the preservation of relic fabrics in both taxa the chemical signatures of coralline and molluscan aragonite and calcite are strongly dependent on initial skeletal porosity compared to original aragonite montastrea calcite is enriched in magnesium 1 151 64 ppm versus 2 114 619 ppm and depleted in strontium 7 397 376 ppm versus 2 510 43 ppm these data in conjunction with large calcite oxygen depletions 3 8 0 2 versus 5 7 0 3 and variable calcite carbon depletions 0 6 0 6 versus 1 3 to 7 3 demonstrate significant exchange between neomorphic front and formational fluids in contrast strombus calcite composition is largely inherited from original aragonite and is only slightly enriched in strontium and magnesium 2 299 316 ppm versus 2 519 759 ppm and 96 23 ppm versus 173 79 ppm while carbon exhibits a small depletion 5 3 0 5 versus 4 4 0 8 similarity of str mbus aragonite and calcite compositions reflects high rock water ratios in relatively closed diagenetic systems calcite oxygen depletion 0 5 0 5 versus 3 6 0 4 observed in strombus however requires some exchange between formation and neomorphic front fluids differences in the thickness of replacement calcite rims between taxa reflect variable skeletal porosities and rates of migration of neomorphic fronts neomorphism was six times faster by volume in porous montastrea than in dense strombus skeletal structures thus skeletal porosity influences degrees of system openness during aragonite neomorphism

structure and dynamics of the nightside poleward boundary sounding rocket and ground based observations of auroral electron precipitation in a rayed curtain 1 the cascades2 auroral sounding rocket provides a case study for comparing multipoint in situ ionospheric observations of a nightside auroral poleward boundary intensification with ground based optical observations of the same event cascades2 was launched northward from poker flat alaska on 20 march 2009 at 11 04 ut the 13 min flight reached an apogee of 564 km over the northern coast of alaska the experiment included a five payload array of in situ instrumentation ground cameras at three different points under the trajectory multiple ground magnetometers the poker flat incoherent scatter radar pfisr radar and the time history of events and macroscale interactions during substorms themis spacecraft in the magnetotail the rays of the poleward boundary intensification pbi curtain have along arc motions of 8 5 km s and along arc spacings of 16 km modulated maximum energy envelopes and energy fluxes of the associated electron precipitation correspond to this spatial structure of the visible rays the electron precipitation is additionally modulated at a higher frequency and velocity dispersion analysis of these 8 hz signatures implies alfvenic wave particle acceleration of an ambient ionospheric electron source occurring a few hundred km above the observation point these observations parameterize the curtain of alfvenic activity above the pbi event both in the dispersive ionosphere and in the magnetotail reconnection region the along arc variations in brightness correspond to variations in precipitating electron energy flux interpreted as an along arc modulation of the maximum energy of the alfvenic wave particle acceleration process this is a new interpretation of the formation of rayed structures in auroral curtains we consider the various possible magnetospheric and ionospheric drivers for the control of the observed along arc structuring and motions

geodynamics of rifting and implications for hydrocarbon habitat abstract rifting activity is probably mainly governed by frictional forces exerted on the base of the lithosphere by the convecting sub lithospheric upper mantle combined with deviatoric tensional stresses developing over upwelling branches of the asthenospheric convection system and by far filed stresses controlling the interaction of lithospheric plates moving relative to each other mantle plumes rising from the deep mantle do not appear to be a major driving force of rifting therefore it is questioned whether a distinction between active and passive rifts is still justified lithospheric extension triggers by decompression partial melting of the lower lithosphere and upper asthenosphere magmatic processes contribute materially to thinning of the subcrustal lithosphere and probably also of the lower crust this could explain the frequently observed discrepancy between upper crustal extension by faulting and lower crustal attenuation as defined by refraction and deep reflection seismic data the duration of the rifting stage of palaeorifts and passive margins is highly variable depending on plate interaction crustal separation can be achieved after as little as 7 ma and as much as 280 ma of rifting activity the availability of crustal discontinuities does not appear to play a significant role in the time required for crustal separation to be achieved the structural style of rifts is controlled by the physical state of the lithosphere the mode and amount of its extension and the lithological composition of pre and syn rift sediments subsidence of rift basins is controlled by the balance between isostatic adjustment of the crust to lithospheric stretching and uplift induced by mechanical and thermal attenuation of the subcrustal lithosphere post rift basin subsidence is mainly governed by the decay of rift induced thermal anomalies densification of the lower crust and intra plate stresses provide overprinting effects in view of this it is unlikely that quantitative analyses of post rift basin subsidence give a direct measure of lithospheric extension tectonically active rifts palaeorifts and passive margin basins contain major hydrocarbon provinces their hydrocarbon charge can rely exclusively on pre rift syn rift or post rift sedimentary sequences or a combination thereof maturation of source rocks can be achieved during the syn and or post rift stage of basin evolution during rifting conductive and convective heat transfer accounts for elevated geothermal gradients these play an important role in the maturation of pre and syn rift source rocks thermal gradients decrease asymptotically during the post rift stage

westward traveling surges sliding along boundary arcs and distinction from onset arc brightening 1 after onset auroral brightening rapidly spreads azimuthally along the onset arc typically but not always extending substantially farther westward than eastward expansion phase auroras also expand poleward and can contact an arc along the auroral poleward boundary for such events we find that poleward expansion of the region of active aurora accelerates after contact forming a bulge region that protrudes into the preexisting polar cap and expands westward as the westward traveling surge this westward motion is slower than and initiates later than the azimuthal spreading of the onset arc brightening the poleward boundary arc remains connected to the surge as the surge slides along the equatorward moving edge of the boundary arc and this connection appears to set off the westward traveling poleward protruding activity of the surge via localized polar cap flow adjacent to the boundary arc ground magnetic signatures show a relatively weak h component depression moving westward with the onset arc brightening and a delayed substantially larger depression moving with the westward propagating surge that must be associated with a substantially larger westward ionospheric current the clear distinction between onset arc brightening and the westward traveling surge seen in auroral and magnetometer current signatures implies that their underlying processes are very different evidence suggests that flow channels adjacent to the boundary arc possibly feed surge development these results are consistent with current wedge formation being more associated with post onset activity than with onset and with flow channels from the polar cap being important for surge bulge development

substorm triggering by new plasma intrusion incoherent scatter radar observations received 4 december 2009 revised 16 march 2010 accepted 30 march 2010 published 27 july 2010 1 in the companion paper we identified a repeatable sequence of events leading to substorm onset in themis all sky imager observations enhanced flows bring new plasma into the plasma sheet the new plasma then moves earthward as a flow channel bringing it to the near earth plasma sheet and where it produces onset instability new plasma entering the dusk dawn convection cell drifts equatorward and eastward and then around the harang reversal leading to pre midnight near and post midnight onset here we present evidence supporting this sequence using incoherent scatter radar isr ionospheric observations using the sondrestrom isr we find that enhanced flows of new plasma commonly enter the plasma sheet from the polar cap 8 min prior to onset these flows are related to poleward boundary intensification signatures consistent with the inferences from the imagers using the poker flat isr pfisr we find that shortly before onset enhanced westward flows reach the subauroral polarization streams saps region equatorward of the harang reversal dusk cell onsets or enhanced eastward flows enter the onset region from the poleward direction dawn cell onset pfisr proton precipitation signatures are consistent with the possibility that the enhanced flows consist of reduced entropy plasma sheet plasma and that onset occurs poleward of much of the enhanced saps flow dusk cell onsets or equatorward of the enhanced eastward flows dawn cell onsets consistency with reduced entropy plasma is seen only within the enhanced flows leading us to suggest that intrusion of low entropy plasma may alter the radial gradient of entropy toward onset instability

distribution of region 1 and 2 currents in the quiet and substorm time plasma sheet from themis observations although earth s region 1 and 2 currents are related to activities such as substorm initiation their magnetospheric origin remains unclear utilizing the triangular configuration of themis probes at 8 12 re downtail we seek the origin of nightside region 1 and 2 currents our statistical study reveals that both kinds of currents exist in the plasma sheet during quiet and active times region 2 currents are deep inside the plasma sheet region 1 currents which are farther away from the neutral sheet extend to the plasma sheet boundary layer at geomagnetic quiet times the separation between the two currents is located 2 5 re from the neutral sheet during substorms the separation migrates towards away from the neutral sheet as the plasma sheet thins thickens these findings suggest that the plasma sheet is a source of region 1 and 2 currents and its deformation is associated with redistribution of fac sources in the magnetotail

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

a statistical study of the subauroral polarization stream over north american sector using the millstone hill incoherent scatter radar 1979 2019 measurements this work conducts a statistical study of the subauroral polarization stream saps feature in the north american sector using millstone hill incoherent scatter radar measurements from 1979 to 2019

substorm triggering by new plasma intrusion themis all sky imager observations 1 a critical long standing problem in substorm research is identification of the sequence of events leading to substorm auroral onset based on event and statistical analysis of themis all sky imager data we show that there is a distinct and repeatable sequence of events leading to onset the sequence having similarities to and important differences from previous ideas the sequence is initiated by a poleward boundary intensification pbi and followed by a north south n s arc moving equatorward toward the onset latitude because of the linkage of fast magnetotail flows to pbis and to n s auroras the results indicate that onset is preceded by enhanced earthward plasma flows associated with enhanced reconnection near the pre existing open closed field line boundary the flows carry new plasma from the open field line region to the plasma sheet the auroral observations indicate that earthward transport of the new plasma leads to a near earth instability and auroral breakup 5 5 min after pbi formation our observations also indicate the importance of region 2 magnetosphere ionosphere electrodynamic coupling which may play an important role in the motion of pre onset auroral forms and determining the local times of onsets furthermore we find motion of the pre onset auroral forms around the harang reversal and along the growth phase arc reflecting a well developed region 2 current system within the duskside convection cell and also a high probability of diffuse appearing aurora occurrence near the onset latitude indicating high plasma pressure along these inner plasma sheet field lines which would drive large region 2 currents

equatorward and poleward expansion of the auroras during auroral substorms using all sky tv auroral data with high spatial and temporal resolution the formation of the auroral bulge is investigated we show how the discrete auroral structures within the poleward expanding bulge develop systematically toward the west the east and also equatorward from a localized breakup region auroral structure at the western end of the bulge a surge develops with clockwise rotation as viewed along the magnetic field direction at the eastern part of the bulge thin auroral features propagate eastward from the breakup region around the central meridian of the bulge auroral features expand equatorward and become north south aligned the n s aurora the n s aurora and the eastward propagating aurora develop into diffuse and pulsating aurora after the expansion we suggest that these discrete auroral structures in the bulge develop along the plasma streamlines in a localized distorted two cell equipotential distribution the negative potential peak is concentrated at the western part of the bulge and the positive potential region is spread poleward of the eastward propagating aurora equatorward expansion of auroral structures would be attributed in this scenario to the subsequent earthward transport of plasma from the onset region energetic particles would also be injected at the n s auroral region as well as to the east of the region and would trigger the pulsating auroral activity poleward expansion on the other hand would be produced by the tailward motion of the onset region in accordance with the tailward moving current disruption region

aurora and electrojet configuration in the early morning sector nearly simultaneous data from the chatanika radar the triad satellite and the ims alaska meridian chain of magnetic and auroral observatories are utilized to examine the spatial relationship among auroras field aligned currents ionospheric electric fields and conductivities in the westward electrojet in early morning hours the westward electrojet is found to be dominated by one of two different quantities depending on latitudinal locations in this local time sector the poleward half of the electrojet is governed by a relatively intense southward electric field on the other hand the hall conductivity is the dominant factor in controlling the electrojet current in the equatorward half the electrojet center appears to be located within the region of the upward field aligned current major auroral activity is present only in the equatorward half of the electrojet in which the upward field aligned current prevails although it appears that the latitudinal variations of the conductivity and current intensity are not well related within that region

dc variations in late jurassic carbonates jaisalmer formation western india abstract the carbon isotope measurements carried out on subsurface carbonate samples from oxfordian jaisalmer formation western india yield positive d 13 c values up to 3 17 the most positive oxfordian c isotope value corresponds to the carbon isotope excursion measured in samples from from other late jurassic basins of world the latest oxfordian c isotope values of jaisalmer basin fluctuate around 2 while the c isotope values of 1 50 mark the base of kimmeridgian the oxfordian c isotope excursion appears to correspond to a time of overall increased organic carbon burial triggered by increased nutrient transfer from continents to oceans during a time of rising global sea level

contributions to geotechnique 1948 2008 engineering geology rock mechanics and rock engineering throughout its history geotechnique has regularly published papers on the fundamentals of engineering geology the core concepts of rock mechanics and the practice of rock engineering in totality these papers provide a concise history of the development of these areas of geotechnics here a review of many of these papers is presented in terms of the specific themes of engineering geology rock slope instability behaviour of intact rock and discontinuities in rock field measurements in rock mechanics discontinuous rock masses numerical modelling and rock engineering papers covering a wide range of issues within these themes are outlined together with an indication of how they have influenced later developments the review clearly demonstrates how geotechnique has been at the forefront of rock mechanics rock engineering and engineering geology for the whole of its 60 year existence

rates of vadose diagenesis in quaternary dune and shallow marine calcarenites warrnambool victoria australia abstract progressively younger cycles of quaternary dune limestones and shallow marine calcarenites infill a coastal embayment near warrnambool in southeastern australia the formations have been dated using u th and c 14 methods or have had their ages estimated by comparison with adjacent deposits they provide a well dated framework for the quantification of diagenetic rates in the fresh water vadose zone the sequence as a whole shows progressive increase in diagenetic alteration with age related to increasing duration of subaerial exposure diagenesis includes alteration of high mg calcite to low mg calcite dissolution of aragonite and precipitation of increasing amounts of void filling low mg calcite spar these changes are reflected in the progression of bulk rock isotope values from the youngest to the oldest strata the rocks at warrnambool pass through 3 main stages of diagenetic evolution the end of stage 1 is marked by the disappearance of high mg calcite this occurs in just less than 90 000 years the end of stage 2 occurs between 400 000 and 700 000 years and is marked by the disappearance of aragonite the end of stage 3 and the beginning of stage 4 is marked by the complete infilling of all pore space by low mg calcite spar this is not generally seen in this sequence but is restricted to specific diagenetic sites such as immediately below paleosol horizons

wavelet based ulf wave diagnosis of substorm expansion phase onset 1 using a discrete wavelet transform with a meyer wavelet basis we present a new quantitative algorithm for determining the onset time of pi1 and pi2 ulf waves in the nightside ionosphere with 20 to 40 s resolution at substorm expansion phase onset we validate the algorithm by comparing both the ulf wave onset time and location to the optical onset determined by the imager for magnetopause to aurora global exploration image far ultraviolet imager fuv instrument in each of the six events analyzed five substorm onsets and one pseudobreakup the ulf onset is observed prior to the global optical onset observed by image at a station closely conjugate to the optical onset the observed ulf onset times expand both latitudinally and longitudinally away from an epicenter of ulf wave power in the ionosphere we further discuss the utility of the algorithm for diagnosing pseudobreakups and the relationship of the ulf onset epicenter to the meridians of elements of the substorm current wedge the importance of the technique for establishing the causal sequence of events at substorm onset especially in support of the multisatellite time history of events and macroscale interactions during substorms themis mission is also described

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

magnetic dipolarization with substorm expansion onset 1 we compare the timing and spatial extent of dipolarization with auroral breakup by using magnetic field data 1 min time resolution from goes 8 and goes 9 and global auroral images 37 s frame rate from the polar ultraviolet imager we survey the entire year of 1997 data and obtain 32 unambiguous dipolarization events that had ionospheric footprints within 2 hours in magnetic local time mlt from their associated auroral breakups it is found that the auroral breakup preceded the arrival of dipolarization at goes by an average of 1 7 2 7 min 1 0 2 1 min for events 1 hour from the auroral breakup the delay of geosynchronous dipolarization represents a propagation time as the substorms rarely initiated at the goes location propagation velocities derived from the propagation time are 60 km s 1 eastward 75 km s 1 westward and 270 km s 1 earthward at geosynchronous orbit we also show for the first time that auroral bulge and dipolarization region closely map the bulge is the region of currents out of the ionosphere the eastern edge of the dipolarization region where field aligned currents are flowing into the ionosphere is based on the t89 magnetic field model located at 0 5 hour in mlt eastward of the eastern edge of the auroral bulge within the initiation site meridian the dipolarization onset was observed 1 min prior to the auroral breakup at the goes altitude this time is associated with alfven transit time and therefore depends on the radial location of the onset the azimuthal scale of the initiation site is found to be 0 5 hour in mlt in the ionosphere or less than 1 earth s radius at 6 6 re these results support current diversion into the ionosphere as a critical part of substorms finally a simple timing analysis of specific substorm onset time features suggests that near earth reconnection cannot occur before current disruption and therefore cannot be the cause of substorm

why joints are more abundant than faults a conceptual model to estimate their ratio in layered carbonate rocks it is a commonplace field observation that extension fractures are more abundant than shear fractures the questions of how much more abundant and why are posed in this paper and qualitative estimates of their ratio within a rock volume are made on the basis of field observations and mechanical considerations a conceptual model is also proposed to explain the common range of ratios between extension and shear fractures here called the j f ratio the model considers three major genetic stress components originated from overburden pore fluid pressure and tectonics and assumes that some of the remote genetic stress components vary with time i e stress rates are included other important assumptions of the numerical model are that i the strength of the sub volumes is randomly attributed following a weibull probabilistic distribution ii all fractures heal after a given time thus simulating the cementation process and therefore iii both extensional jointing and shear fracturing could be recurrent events within the same sub volume as a direct consequence of these assumptions the stress tensor at any point varies continuously in time and these variations are caused by both remote stresses and local stress drops associated with in situ and neighbouring fracturing events the conceptual model is implemented in a computer program to simulate layered carbonate rock bodies undergoing brittle deformation the numerical results are obtained by varying the principal parameters like depth viz confining pressure tensile strength pore fluid pressure and shape of the weibull distribution function in a wide range of values therefore simulating a broad spectrum of possible mechanical and lithological conditions the quantitative estimates of the j f ratio confirm the general predominance of extensional failure events during brittle deformation in shallow crustal rocks and provide useful insights for better understanding the role played by the different parameters for example as a general trend it is observed that the j f ratio is inversely proportional to depth viz confining pressure and directly proportional to pore fluid pressure while the stronger is the rock the wider is the range of depths showing a finite value of the j f ratio and in general the deeper are the conditions where extension fractures can form moreover the wider is the strength variability of rocks i e the lower is the m parameter of the weibull probabilistic distribution function the wider is the depth range where both fractures can form providing a finite value of the j f ratio natural case studies from different geological and tectonic settings are also used to test the conceptual model and the numerical results showing a good agreement between measured and predicted j f ratios

electric currents of a substorm current wedge on 24 february 2010 the three dimensional substorm current wedge scw was postulated by mcpherron et al 1973 to explain substorm magnetic perturbations the origin and coherence as a physical system of this important paradigm of modern space physics remained unclear however with progress hindered by gross undersampling and uniqueness problems in data inversion complementing ampere active magnetosphere and planetary electrodynamics response experiment space derived radial electric currents with ground magnetic data allowing us to determine currents from the ionosphere up we overcome problems of uniqueness identified by fukushima 1969 1994 for a substorm on 24 february 2010 we quantify scw development consistently from ground and space data its westward electrojet carries 0 5 ma in the more poleward part of the auroral oval in region 1 r1 sense spanning midnight the evening sector electrojet also feeds into its upward current we thus validate the scw concept and obtain parameters needed for quantitative study of substorms

mechanism of substorm current wedge formation themis observations 1 this paper presents themis measurements of two substorm events to show how the substorm current wedge scw is generated in the late growth phase when an earthward flow burst in the near earth magnetotail brakes and is diverted azimuthally pressure gradients in the x and y directions are observed to increase in the pileup and diverting regions of the flow the enhanced pressure gradient in the y direction is dawnward duskward on the dawnside duskside where a clockwise counter clockwise vortex forms this dawn dusk pressure gradient drives downward upward field aligned current fac on the dawnside duskside of the flow which when combined with the facs generated by the clockwise counter clockwise vortex forms the scw substorm auroral onset occurs when the vortices appear near earth dipolarization onset is observed by the themis spacecraft probes when a rapid jump in the y component of pressure gradient is detected the total facs from the vortex and the azimuthal pressure gradient are found to be comparable to the dp 1 current in a typical substorm

sounding rocket study of two sequential auroral poleward boundary intensifications 1 the cascades 2 sounding rocket was launched on 20 march 2009 at 11 04 00 ut from the poker flat research range in alaska and flew across a series of poleward boundary intensifications pbis the rocket initially crosses a diffuse arc then crosses the equatorward extent of one pbi a streamer and finally crosses the initiation of a separate pbi before entering the polar cap each of the crossings have fundamentally different in situ electron energy and pitch angle structure and different ground optics images of visible aurora it is found that the diffuse arc has a quasi static acceleration mechanism and the intensification at the poleward boundary has an alfvenic acceleration mechanism the streamer shows characteristics of both types of acceleration pfisr data provide ionospheric context for the rocket observations three themis satellites in close conjunction with the rocket foot point show earthward flows and slight dipolarizations in the magnetotail associated with the in situ observations of pbi activity an important goal of the cascades 2 study is to bring together the different observational communities rocket ground cameras ground radar satellite with the same case study the cascades 2 experiment is the first sounding rocket observation of a pbi sequence enabling a detailed investigation of the electron signatures and optical aurora associated with various stages of a pbi sequence as it evolves from an alfvenic to a more quasi static structure

substorm onset observations by image fuv 1 over the first 2 5 years of operation the fuv instrument on the image spacecraft observed more than 2400 substorm onsets in the northern hemisphere the observations confirm earlier results of statistical studies in terms of a median substorm onset location at 2300 hours mlt and 66 4 degrees magnetic latitude the purpose of this report is to publish the list to allow for further investigation the list can easily be searched for onsets close to certain ground stations or at specific magnetic latitudes or local times as one example of such use we demonstrate how the probability of onset observation was determined for the ground based automatic observatories of the themis time history of events and macroscale interactions during substorms project

variability of the harang discontinuity as observed by the chatanika radar and the ims alaska magnetometer chain the relative location of ionospheric parameters and ground magnetic perturbations in the vicinity of the harang discontinuity is examined for this purpose we use combined observations of the chatanika incoherent scatter radar and of the ims alaska meridian chain of magnetometers which were continuously measuring the crucial ionospheric parameters near the harang discontinuity when a sizeable substorm took place the harang discontinuity as defined by the reversal of the north south electric field is found to be located at 1 2 poleward of the discontinuity identified by the conventional method of using ground magnetic perturbations it is also found that the relative location of auroral conductivity enhancements is quite variable depending perhaps upon substorm time during relatively quiet times and the early stage of a substorm a conductivity enhancement occurs only on the poleward side of the harang discontinuity defined by the electric field reversal whereas the enhancement surges equatorward extending beyond the discontinuity during the maximum to recovery phase of a substorm

near earth plasma sheet azimuthal pressure gradient and associated auroral development soon before substorm onset 1 the azimuthal plasma pressure gradient in the near earth plasma sheet makes crucial contributions to field aligned current fac formation numerical simulations and statistical observations have shown that a plasma pressure peak tends to build up in the premidnight region of the near earth plasma sheet during the substorm growth phase owing to enhanced magnetic drift this leads to azimuthal pressure gradients in this region the temporal variation of the azimuthal pressure gradient may provide an indication for the fac variations associated with the substorm growth phase and may set up a plasma sheet precondition for the substorm onset being triggered near this region we take advantage of two of the time history of events and macroscale interactions during substorms themis spacecraft separated azimuthally near the orbit apogee and investigate the azimuthal plasma pressure gradient before substorm onset in the r 10 12 re region equatorial plasma pressure is estimated by removing the curvature force effect five events with the spacecraft footprints mapped very close to the aurora onset region were selected these events show substantial duskward pressure gradient enhancement 1 5 min before onset the onset arc which results from enhanced energetic electron precipitation was found to intensify simultaneously with the pressure gradient enhancement before onset breakup occurs since the energy and energy flux of precipitating electrons reflect the upward fac strength these results indicate that the duskward azimuthal pressure gradient enhancement is associated with enhanced upward fac during the late growth phase and leads to the intensification of the onset auroral arc soon before it breaks up it is possible that this pressure gradient enhancement may lead to ballooning mode instability and thus substorm onset along the intensifying arc

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

multipoint observations of substorm pre onset flows and time sequence in the ionosphere and magnetosphere 1 in this paper we use a rare and close longitudinal conjunction of the themis spacecraft with the sondrestrom radar to present multipoint observations of important features of the time sequence of substorm pre onset plasma flows in the ionosphere and magnetotail on march 5 2008 we found that the onset was preceded sequentially by enhanced polar cap flows heading equatorward near the polar cap boundary and then by tail fast flows from the mid tail to the near earth region we also observed in situ fluctuations in short period pi2 band 30 50 s in both the magnetic field and plasma pressure during the initial couple of min of the fast flows occurring nearly simultaneously with the dipolarization and the fast flows and propagating earthward our results suggest that these fluctuations may be triggered by the fast flows and may play an important role in the substorm onset process our event suggests that localized tail reconnection may be triggered by the enhanced polar cap flows though the reconnection location cannot be unambiguously determined earthward fast flows are generated as a result of the tail reconnection and reach the inner magnetosphere to initiate the substorm onset the presented case is consistent with that predicted by the nishimura et al 2010a scenario

polar equatorial ionospheric currents driven by the region 2 field aligned currents at the onset of substorms 1 the dawn to dusk convection electric field increases during the growth phase of substorms driving dp2 currents composed of two cell current vortices in high latitude and leading to an increase in the eastward electrojet at the dayside dip equator eej during the expansion phase of substorms electric field and currents are often reversed in direction to the normal dp2 currents at subauroral to equatorial latitudes when the convection electric field reduces abruptly the reversed current at the dayside dip equator appears as a counterelectrojet cej and causes an equatorial enhancement of the negative bay in the afternoon sector conversely the convection electric field increases during substorms as deduced from sawtooth events causing an increase in the eej in this study by analyzing isolated substorms with magnetometer array data and superdarn super dual auroral radar network convection maps we deduce that the reversed electric field and currents develop at the subauroral to equatorial latitudes at the onset of substorms while the convection electric field increases at auroral latitudes these observations imply that both the region 1 and region 2 field aligned currents r1 and r2 facs develop on the dayside concurrently with the current wedge responsible for the midlatitude positive bay at midnight the substorm associated r2 facs are strong enough to cause the reversed current at the subauroral latitude and the cej at the equator we also deduce that the dayside equatorial cej begins simultaneously with or even earlier than the midlatitude positive bay at midnight while the midlatitude positive bay onset is delayed by several minutes as the station departs from the midnight meridian these observations suggest that the substorm begins with the intensification of the r2 facs responsible for the equatorial cej

a superposed epoch study of superdarn convection observations during substorms 1 case studies of flow patterns during substorms have revealed characteristic patterns in the period leading to expansion onset velocities in the premidnight region have been observed to become strongly sheared and the premidnight convection reversal has been observed to extend across the midnight meridian at expansion onset the shear decreases and flow at midnight becomes meridional out of the polar cap the study presented here superposes flow patterns from 10 substorm intervals to determine the average flow patterns the study confirms the findings of the case studies and extends them to additional local time sectors in addition changes to the flow pattern after expansion onset are examined

fabric selective diagenesis in the late pleistocene miami limestone abstract the miami limestone is a late pleistocene ooid sand body which has undergone 130 000 years of meteoric diagenesis the resultant limestone has a generally high but variable 15 60 porosity which is indirectly related to the amount of primary aragonite remaining in the limestone 0 45 the predominant textural theme in porosity development is the role of the primary sediment fabric which controls early cementation and porosity development on the scale of individual grains and sedimentary structures and is still influential during late development of channel and cavernous porosity the porosity development within the miami limestone reflects a change from an early system wherein fabric selective diagenesis occurred primarily as a function of the ability of the sediment to retain pore water to a system wherein the cemented sediments channelize water flow and effectively isolate portions of metastable aragonitic limestone from meteoric waters

comparison of uv optical signatures with the substorm current wedge as predicted by an inversion algorithm optical images of the auroral bulge as seen by the viking uv imager were compared in several cases with the substorm current wedge scw upward and downward field aligned currents fac whose positions were determined using the inversion algorithm based on the substorm related magnetic variations observed at midlatitudes with reasonable accuracy better than 0 5 hours mlt the estimated longitudes of the upward fac generally pointed to the surge or to the brightest luminousity region in the western half of the bulge the latter feature may imply a more complicated structure of the net facs than can be described by the simple substorm current wedge scheme similarly the estimated positions of the downward fac pointed close to the eastern termination of the bulge the associated optical signatures of this current system ranged from the well defined emission depletion regions to new auroral intensifications the downward current appears to correspond in some cases at least with the division between the morning sector portion of the double oval and the nightside portion connected more directly to the substorm bulge the results in general confirm the expected association between the auroral bulge and the scw as well as showing a reasonably good results from the inversion algorithm based on midlatitude magnetic observations our results however also indicate that one must be careful in interpreting the apparent motion of scw related field aligned currents inferred from midlatitude observations in terms of a true westward or eastward expansion of the scw or of the auroral bulge the observed changes may instead sometimes be related to the redistribution of the net facs within than a shift or expansion of the simple current system

large scale current systems and ground magnetic disturbance during deep substorm injections 1 we present a detailed analysis of the large scale current systems and their effects on the ground magnetic field disturbance for an idealized substorm event simulated with the equilibrium version of the rice convection model the objective of this study is to evaluate how well the bubble injection picture can account for some classic features of the substorm expansion phase the entropy depletion inside the bubble is intentionally designed to be so severe that it can penetrate deep into geosynchronous orbit the results are summarized as follows 1 both the region 1 sense and region 2 sense field aligned currents facs intensify substantially the former resembles the substorm current wedge and flows along the eastern and western edges of the bubble the latter is connected to the enhanced partial ring current in the magnetosphere associated with a dipolarization front earthward of the bubble in the ionosphere these two pairs of facs are mostly interconnected via pedersen currents 2 the horizontal ionospheric currents show a significant westward electrojet peaked at the equatorward edge of the footprint of the bubble the estimated ground magnetic disturbance is consistent with the typical features at various locations relative to the center of the westward electrojet 3 a prominent harang reversal like boundary is seen in both ground h disturbance and plasma flow pattern appearing in the westward portion of the equatorward edge of the bubble footprint with a latitudinal extent of 5 and a longitudinal extent of the half width of the bubble 4 the dramatic dipolarization inside the bubble causes the ionospheric map of the inner plasma sheet to exhibit a bulge like structure which may be related to auroral poleward expansion 5 the remarkable appearance of the westward electrojet harang reversal like boundary and poleward expansion starts when the bubble reaches the magnetic transition region from tail like to dipole like configuration we also estimate the horizontal and vertical currents using magnetograms at tens of ground stations for a deep injection substorm event occurred on april 9 2008 resulting in a picture that is qualitatively consistent with the simulation based on the simulations and the observations an overall picture of the ionospheric dynamics and its magnetospheric drivers during deep bubble injections is obtained

dynamic subauroral ionospheric electric fields observed by the falkland islands radar during the course of a geomagnetic storm ion drift said located between 53 and 58 magnetic south and lasting 6 5 hours was observed by the falkland islands radar in the pre midnight sector coincident flow data from the dmsp satellites and the magnetically near conjugate northern hemisphere blackstone hf radar reveal that the said was embedded within the broader subauroral polarization streams saps dmsp particle data indicate that the said location closely followed the equatorward edge of the auroral electron precipitation boundary while remaining generally poleward of the equatorward boundary of the ion precipitation the latitude of the said varied throughout the interval on similar timescales to variations in the interplanetary magnetic field and auroral activity while variations in its velocity were more closely related to ring current dynamics these results are consistent with said electric fields being generated by localized charge separation in the partial ring current but suggest that their location is more strongly governed by solar wind driving and associated large scale magnetospheric dynamics

substorm convection patterns observed by the super dual auroral radar network a study of convection patterns during substorms observed by the super dual auroral radar network superdarn radar network is presented specific attention is given to the growth phase and the time immediately following expansion onset it is found that the growth phase is characterized by the enhancement of the velocity shear near midnight and its extension to low latitudes and to local times across the midnight meridian the velocity shear was observed to diminish at expansion onset in addition the ionospheric flow velocity magnitude was observed to be enhanced for some period of time prior to expansion onset and to decrease at expansion onset possible explanations for the establishment of the midnight velocity shear during growth phase and its subsequent disappearance at expansion onset are presented also arguments are presented regarding the decrease of ionospheric flow velocity at expansion onset

gps tec observations of dynamics of the mid latitude trough during substorms 1 in this study we combine gps vertical total electron content vtec and other complementary instruments such as the poker flat incoherent scatter radar and all sky imagers to investigate the dynamics of the mid latitude trough during non storm time substorms for solar minimum condition and focus on alaska region we find that the poleward wall of the mid latitude trough shifts equatorward rapidly after substorm onset with a maximum speed reaching 4 5 of geomagnetic latitude per hour this equatorward motion results in narrowing and even disappearance of the mid latitude trough and is due to enhanced energetic electron precipitation the mid latitude trough can reappear during the substorm recovery phase as auroral activity retreats poleward this phenomenon has not been reported before probably because of limited field of view of previous instruments used in trough studies comparisons of the trough minimum location predicted by models that are based on global kp and ae indices show good agreement before substorm activity reaches the peak and relatively poor agreement during the recovery phase the observations suggest that a local index such as the local al index may be a better index to use to parameterize the trough location at a given meridian than a global index

chatanika radar and s3 2 measurements of auroral zone electrodynamics in the midnight sector measurements made by the incoherent scatter radar at chatanika alaska have been combined with s3 2 satellite data to study the relationships between conductivities electric fields and currents near the harang discontinuity three s3 2 passes were chosen for the study based on the quality of the radar and satellite data and the availability of supplementary ground and space based observations the radar measured electric fields and conductivities as a function of latitude and local time the satellite measured the latitudinal distribution of electric field and field aligned current during the three polar passes the dominant field aligned current in the midnight sector is upward equatorward of this current a downward sheet is observed which is the eastern end of the evening sector region 2 sheet poleward of the upward current are several sheets of varying directions and magnitudes these sheets are associated with active aurora during substorms the most intense electric fields were located at the poleward and equatorward boundaries of the upward current sheet a model is presented which demonstrates the self consistency of the observed relationships between conductivities electric fields and currents

electrodynamics of the high latitude trough its relationship with convection flows and field aligned currents 1 we present a detailed case study of the electrodynamics of a high latitude trough observed at 12 ut 1 mlt on 8 march 2008 using multiple instruments including incoherent scattering radar isr gps total electron content tec magnetometers and auroral imager the electron density within the trough dropped as much as 80 within 6 minutes this trough was collocated with a counterclockwise convection flow vortex indicating divergent horizontal electric fields and currents together with a collocated dark area shown in auroral images the observations provide strong evidence for an existence of downward field aligned currents facs collocated with the high latitude trough this is further supported by assimilative mapping of ionospheric electrodynamics results in addition the downward facs formed at about the same time as a substorm onset and east of the harang reversal suggesting it is part of the substorm current wedge it has long been a puzzle why this type of high latitude trough predominantly occurs just east of the harang reversal in the postmidnight sector we suggest that the high latitude trough is associated with the formation of downward facs of the substorm current system which usually occur just east of the harang reversal in addition we find that the ionospheric electron temperature within the high latitude trough decreases in the f region while increasing in the e region we discuss possible mechanisms responsible for the complex change in electron temperature such as ion composition change and or presence of downward facs

late jurassic climate and its impact on carbon cycling abstract the climate of the late jurassic has been characterized by high atmospheric co2 levels and by a monsoonal rainfall pattern in this study we traced the evolution of the global carbon cycle through the late jurassic with the help of carbonate carbon isotope stratigraphy the oxfordian tithonian 13c curve is marked by one major positive carbon isotope excursion with an amplitude 13 c 1 0 middle to late oxfordian and a second minor positive excursion with an amplitude 13 c late kimmeridgian the early kimmeridgian and early tithonian 13c values fluctuate around 13 c 2 0 3 and contrast with the less positive 13c values of early oxfordian and late tithonian age 13 c 1 0 5 a comparison of the late jurassic carbonate carbon isotope curve with the occurrence of organic rich sediments suggests that not only fluctuations in organic carbon burial but also in carbonate carbon burial had an impact on the c isotope record the oxfordian c isotope excursion appears to correspond to a time of overall increased organic carbon burial triggered by increased nutrient transfer from continents to oceans during a time of rising global sea level however episodes of enhanced organic carbon burial during the kimmeridgian and early tithonian are not reflected by prominent spikes in the c isotope record favourable conditions for carbonate platform growth at a time of high global sealevel may have resulted in the stabilisation of the c org c carb burial ratio and hence maintained the 13c record at steady but relatively positive values the middle and late tithonian c isotope values drop below 13 c 1 5 a similar shift to less positive c isotope values was recognized in other c isotope records from the tethys and atlantic oceans and reflects a decrease in the c org c carb burial ratio possibly related to a reorganisation of the global climate system globally widespread marine black shale mature quartzose sandstone assemblages suggest that the relative efficiency of the late jurassic carbon pumps was controlled by weathering erosion and runoff causing widespread marine eutrophication eutrophication favoured the organic carbon pump but it diminished the carbonate platform growth potential the monsoonal rainfall distribution pattern may explain why late jurassic carbonate platforms experienced less severe growth crises than early cretaceous carbonate platforms

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

observations of the electric field fine structure associated with the westward traveling surge and large scale auroral spirals the characteristics of the fine scale electric field associated with the westward traveling surge and large scale auroral spirals and surges are investigated using high resolution electric field magnetic field particle and uv imager observations from four eveningside auroral oval crossings by the freja satellite three of the crossings were associated with signatures of auroral substorms and one crossing went directly through the head of a surge close in time and space to substorm onset three passes were adjacent to auroral spiral formations one poleward of and one equatorward of such forms and one through the multiple arc region near the front of an extended region of auroral activity the ambient electric field was found to intensify in the direction toward the spiral head or the center of the auroral activity region over a region comparable to the size of the visible auroral forms these results confirm previous findings that the spiral or surge head is associated with negative space charge and an intense upward field aligned current the fourth pass directly through the surge head reveals a very complicated structure of the surge region narrowly structured intense up to 700 mv m and mostly converging electric fields associated with intense electron precipitation of both high and medium energies and balanced field aligned currents up to 30 a m2 are seen near the edge of the surge head and adjacent to auroral structures in the wake these narrow regions are embedded within more extended regions of intense high energy electron precipitation but very weak electric fields and field aligned currents according to some existing models of the surge a pronounced westward electric field component and a southward polarisation electric field is expected within the entire high conductivity region but evidence in support of this was not found in the data rather these suggest that a significant part of the upward surge current is closed by distributed downward field aligned currents from the near surroundings the freja electric field is typically seen to intensify at the edges of or in between bright auroral structures and to decrease within the arcs similar to what is observed in the ionosphere the surge electric field is however much more intense than previously observed or anticipated at these altitudes with characteristics rather similar to those observed in the auroral acceleration region since the particle data indicate that most of the acceleration takes place above freja altitudes it seems as if freja traversed the lower part of the auroral acceleration region associated with the surge

coupling of dipolarization front flow bursts to substorm expansion phase phenomena within the magnetosphere and ionosphere 1 recent themis spacecraft observations have shown longitudinally narrow earthward moving plasma sheet flow channels with large abrupt magnetic field dipolarizations that have been referred to as dipolarization fronts we undertake a detailed study of the subset of these events that had good quality auroral imaging we find that many occurred during the substorm expansion phase after onset determined by auroral intensification and were related to auroral streamers both the fronts relation to streamers and their plasma sheet changes are similar to what has been previously shown for other plasma sheet flow channels and to other flow channels seen during the expansion phases of the events considered here surprisingly the dipolarization fronts examined made major contributions to substorm onset ground and space magnetic signatures these include substorm near earth dipolarization which indicates that the current wedge may develop via a series of well defined narrow post onset wedge like structures these also include the auroral zone ground magnetic field which showed only modest responses to the onsets but abrupt large responses to post onset dipolarization front related streamers and midlatitude positive bays which started near the time of streamer formation our observations suggest that traditional magnetic signatures of substorm onset such as near earth dipolarization auroral zone negative bays and midlatitude positive bays may misidentify the expansion phase onset determined by auroral intensification by up to 10s of minutes for some events it should be interesting in the future to determine the generality of the above relations between dipolarization front signatures and onset signatures

nightside ionospheric electrodynamics associated with substorms pfisr and themis asi observations 1 observations from the newly available poker flat incoherent scatter radar have been used to study the ionospheric electrodynamics during the substorm expansion phase substorm events selected have been divided into three categories based on onset location relative to the radar and repeatable features have been identified west of onset westward flows increased in response to the passage of the westward traveling surge wts poleward of them the enhanced flows occurred within the sub auroral polarization streams region of downward region 2 currents which extend equatorward from near the equatorward boundary of electron precipitation strong e region ionization increase associated with the wts occurred poleward of the enhanced westward flows suggesting that poleward pedersen currents fed by the downward region 2 field aligned current fac further equatorward contribute at least partially to closure of the upward fac of the wts an enhanced eastward flow channel developed east of onset e region ionization decreased poleward of this flow peak implying formation of downward fac and further increased equatorward of the flow peak suggesting strengthening of preexisting region 2 upward fac these observations indicate that the downward fac formed at onset at least partially closes via the upward region 2 currents the enhanced eastward flows decreased after passage of the auroral bulge and the reduced e region ionization increased again when onset occurred within the radar fov the thin breakup arc of onset occurred at the center of the harang reversal while if the optical onset was poleward of the radar fov the harang reversal was observed after the onset a 2 d picture of the evolution of ionospheric electrodynamics was generated by synthesizing observations from the three categories which provides a schematic description of the relationship between region 2 and substorm expansion electrodynamics

currents in auroral substorms 1 we present a model of the three dimensional current system in the nighttime sector during the expansion phase through early recovery phase for bulge type aurora substorms the height integrated horizontal ionospheric currents are calculated from models of the height integrated conductivity and convection electric field previously published gjerloev and hoffman 2000a 2000b 2001 that were based on a set of data from the dynamics explorer 2 satellite while the field aligned currents are deduced from the divergence of the horizontal currents these model derived field aligned currents are then compared with the field aligned currents determined from magnetometer data from the same data set used to develop the conductance and electric field models the comparison shows good agreement thereby serving as an independent verification of the entire self consistent substorm model we find that the feeding as well as the drainage of the substorm current wedge component of the westward electrojet is principally due to an imbalance of the downward region 0 and upward region 1 current sheets under which the electrojet is flowing we do not find evidence of a simple downward current postmidnight and upward current premidnight the eastward electrojet which almost entirely originates on the dayside is partly drained by a poleward current flowing across the harang region into the westward electrojet at 19 21 magnetic local time mlt and partly by net upward field aligned currents located just prior to midnight

magnetic mapping effects of substorm currents leading to auroral poleward expansion and equatorward retreat magnetotail fast flows magnetic field dipolarization and its relaxation are linked to auroral brightening poleward expansion and equatorward motion during substorm onset expansion and recovery respectively while auroral brightening is often attributed to the field aligned currents produced by flow vorticity and pressure redistribution the physical causes of auroral poleward expansion and equatorward retreat are not fully understood simplistically such latitudinal changes can be directly associated to the tailward motion of the flux pileup region and the earthward flux transport toward the dayside that depletes the near earth plasma sheet however because the equatorial magnetic field profile and the magnetospheric field aligned current system change significantly mapping is severely distorted to investigate this distortion we superimpose a substorm current wedge model dynamically driven by ground based observations on the global tsyganenko model t96 during an isolated substorm on 13 february 2008 observed by the time history of events and macroscale interactions during substorms and goes 10 spacecraft and by ground all sky imagers we validate our model by showing that the timing and ionospheric projection of the flux pileup region and flow bursts observed at the spacecraft match auroral activations we then use the improved mapping enabled by the model to demonstrate that in this event auroral poleward expansion and equatorward retreat are mainly caused by substorm current wedge induced mapping changes