longitudinal development of low latitude ionospheric irregularities during the geomagnetic storms of july 2004 1 during the period 22 28 july 2004 three geomagnetic storms occurred due to a sequence of coronal mass ejections in this paper we present and discuss the ionospheric observations from a set of in situ satellites and ground based gps total electron content and scintillation receivers a vhf radar and two chains of ionosondes 300 e and 120 e respectively that provide the evolutionary characteristics of equatorial and low latitude ionospheric irregularities versus longitude during these storm periods it is found that the irregularities occurred over a wide longitudinal range extending from around 300 e to 120 e on storm days 25 and 27 july 2004 on 25 july plasma bubbles pbs began premidnight in america and postmidnight in southeast asia on 27 july the occurrence of irregularities followed the sunset terminator and was observed sequentially after sunset from american to southeast asian longitudes past studies have reported that storm time low latitude ionospheric irregularities are mostly confined to a narrower longitude range 90 after sunset hours and are associated with the prompt penetration of eastward electric fields ppefs into low latitudes in june solstice months the occurrence of range type spread f or pbs is very low in southeast asian and south american sectors in contrast the present results indicate that geomagnetic storms triggered the wide longitudinal development of pbs in the american sector this was probably due to the effects of ppefs on both storm days however in the southeast asian sector the pbs on the 2 days probably arose from disturbance dynamo electric field ddef ppef and gravity wave seeding effects this study further shows that under complex storm conditions besides the long duration or multiple penetrations the combined effects of ppefs and ddefs could result in a wide longitude extent of ionospheric irregularities at times

penetration electric fields at the nightside dip equator associated with the main impulse of the storm sudden commencement of 8 july 1991 1 the geomagnetic storm sudden commencement ssc of 8 july 1991 was reported wilson et al 2001 to be characterized by a reduction enhancement of x component at midlatitudes in the noon midnight sector in the 1 hour period after its start at 1636 ut this distinctive feature is seen even after accounting for the effects of the chapman ferraro current by subtracting the step like increase of x h component at low latitude stations on the same magnetic meridian from the midlatitude data we present evidence to show that over the same 1 hour period after the start of the ssc on 8 july 1991 an eastward electric field disturbance peak value 1 2 mv m grew up and decayed at the premidnight dip equator the eastward electric field evidenced at the nightside dip equator is interpreted as the signature of the penetration of the dawn to dusk electric field associated with an enhancement of region 1 field aligned currents facs driven by the solar wind the negative disturbance in the h x component at midlatitudes in the noon sector is explained as the magnetic effect of facs that carry the large scale electric fields from the magnetosphere to the polar ionosphere as well as the disturbance of polar origin type 2 ionospheric currents excited by the large scale electric field

genesis of the carbonatite hosted fluorite deposit at amba dongar india evidence from fluid inclusions stability isotopes and whole rock mineral geochemistry the amba dongar carbonatite complex is located approximately 400 km northeast of bombay india and consists of a carbonatite ring dike and a number of syenitic intrusions which were emplaced into late cretaceous bagh sandstones and early to late eocene deccan volcanic rocks hydrothermal activity associated with intrusion of the carbonatite was responsible for fenitization of the surrounding sandstones and deposition of economic quantities of fluorite 11 6 mt of 30 caf 2 fluorite mineralization occurs as veins and vug fillings localized along fractures within the calcite carbonatite near its contact with the sandstone fluid inclusions in fluorite indicate a low temperature low salinity 42 and 3 5 respectively the presence of al and s in the fluid the molar equivalence of na and cl and the positive deviation of 18 o and d from the meteoric water line point to a small contribution from orthomagmatic fluids a model is proposed in which the intrusion of a carbonatite magma at high crustal levels caused faulting and fracturing of the surrounding country rocks and was accompanied by the release of orthomagmatic fluids expressed as extensive k and na metasomatism of the surrounding sandstones with the decline of orthomagmatic activity a meteoric water dominated hydrothermal system was initiated by the heat of the intrusion the interaction of ca bearing meteoric fluids with the last vestiges of f bearing orthomagmatic nacl brines caused deposition of large quantities of fluorite at the site of mixing

empirical models of storm time equatorial zonal electric fields ionospheric plasma drifts often show highly complex and variable signatures during geomagnetically active periods due to the effects of different disturbance processes we describe initially a methodology for the study of storm time dependent ionospheric electric fields we present empirical models of equatorial disturbance zonal electric fields obtained using extensive f region vertical plasma drift measurements from the jicamarca observatory and auroral electrojet indices these models determine the plasma drift perturbations due to the combined effects of short lived prompt penetration and longer lasting disturbance dynamo electric fields we show that the prompt penetration drifts obtained from a high time resolution empirical model are in excellent agreement with results from the rice convection model for comparable changes in the polar cap potential drop we also present several case studies comparing observations with results obtained by adding model disturbance drifts and season and solar cycle dependent average quiet time drift patterns when the disturbance drifts are largely due to changes in magnetospheric convection and to disturbance dynamo effects the measured and modeled drift velocities are generally in good agreement however our results indicate that the equatorial disturbance electric field pattern can be strongly affected by variations in the shielding efficiency and in the high latitude potential and energy deposition patterns which are not accounted for in the model these case studies and earlier results also suggest the possible importance of additional sources of plasmaspheric disturbance electric fields

birth of a volcanic margin off argentina south atlantic 1 based on a dense grid of multichannel reflection seismic lines we study the evolution of a volcanic rifted margin segment off argentina the segment under study is located between 44 s and 41 s we describe in detail the facies of the extrusive basaltic complexes across the margin these include single and multiple inner seaward dipping reflectors sdrs with varying architecture along the margin outer highs and outer sdr wedges a detailed interpretation of a transitional zone between the inner and outer sdr wedges is presented multiple inner sdrs are concentrated at the southern part of the margin segment while in the north only one steeply dipping wedge is present the dip of the inner sdr wedges changes along the margin and we propose subsidence by loading as main cause the transitional zone between the inner and outer sdr wedges becomes narrower toward the north by correlating with magnetic data we conclude that the emplacement of the 30 100 km wide multiple inner sdrs occurred episodically we propose an injection center which migrated in a seaward direction with proceeding extension as the origin for the multiple inner sdrs a scissor like opening of the margin segment resulted in different amounts of stretching along strike of the margin segment and is likely the cause for the varying distribution of the extrusive basaltic complexes the varying extension rates within the margin segment contribute to decreasing volumes of melts generated in a northward direction within this rift segment

holocene provenance shift of suspended particulate matter in the amazon river basin abstract the strontium sr neodymium nd and lead pb isotope signatures of suspended particulate matter spm in rivers reflect the radiogenic isotope signatures of the rivers drainage basin these signatures are not significantly affected by weathering transport or depositional cycles but document the sedimentary contributions of the respective sources we report new sr nd and pb isotope ratios and element concentrations of modern spm from the brazilian amazon river basin and document the past evolution of the basin by analyzing radiogenic isotopes of a marine sediment core from the slope off french guiana archiving the last 40 kyr of amazon river spm and the holocene section of sediment cores raised between the amazon river mouth and the slope off french guiana the composition of modern spm confirms two main source areas the andes and the cratonic shield in the marine sediment core notable changes occurred during the second phase of heinrich stadial 1 i e increased proportion of shield rivers spm and during the last deglaciation i e increased proportion of madeira river spm together with elsewhere constant source contributions furthermore we report a prominent offset in sr and nd isotopic composition between the average core value end 11 7 0 9 2sd 87sr 86sr 0 7229 0 0016 2sd and the average modern amazon river spm signal end 10 5 0 5 2sd 87sr 86sr 0 7213 0 0036 2sd we suggest that a permanent change in the amazon river basin sediment supply during the late holocene to a more andean dominated spm was responsible for the offset

response of the equatorial ionosphere at dusk to penetration electric fields during intense magnetic storms 1 we investigate the response of the equatorial ionosphere at dusk to the intense magnetic storms of 30 october 2003 and 20 november 2003 different aspects of which have been widely studied by the community we present here a very complete set of space and ground based diagnostics that provide the vertical and latitudinal structures of the ionosphere within the south atlantic magnetic anomaly sama region and the contiguous parts of south america and africa we show that for both storms the dusk sector corresponding to the universal time ut interval between the fast decrease of the sym h index and minimum sym h value determines uniquely the longitude interval populated by equatorial plasma bubbles and depletions further we find that the ut of these storms is such that the ionospheric density perturbations occur in the sama region which are most extended in latitude and altitude compared with other regions of the globe in the dusk sector the eastward penetration electric field associated with rapid sym h decrease adds to the postsunset eastward e field because of the f region dynamo which may be specially enhanced in this longitude interval because of the increased zonal conductivity gradient caused by energetic particle precipitation this enhanced e field at dusk causes a rapid uplift of the ionosphere and sets off plasma instabilities to form bubbles or bite outs the decreased ion density seen in the defense meteorological satellite program dmsp in situ data at 840 km indicates that the ionospheric plasma has been lifted above the dmsp altitude and transported away from the region by diffusion along magnetic field lines plasma bubbles and bite outs impact satellite communication and navigation systems by introducing scintillations and steep density gradients this paper corroborates that intense magnetic storms follow the framework developed by su basu et al 2001 for moderate storms that specifies the longitude interval in which such disturbances are most likely to occur

disturbance dynamo effects over low latitude f region a study by network of vhf spaced receivers generation of equatorial spread f esf irregularities resulting from magnetic disturbance is known for past few decades however better prediction models for this phenomenon are still lacking magnetic storms also affects the f region plasma drifts in this work we examined variability in i occurrence of such freshly generated esf and ii low latitude f region zonal plasma drifts over indian longitude for this purpose simultaneous observations of amplitude scintillations on 251 mhz signal recorded by a network of spaced receivers located at low latitude stations are utilized observational stations are situated such that it longitudinally latitudinally covers an area of 5 6 13 here effect of disturbance dynamo dd electric field at low latitude f region and its variability are studied for three magnetic storms occurring in 2011 these magnetic storms are having nearly similar type characteristics except their start time we find that as time difference i e t between local sunset and start of magnetic activity decreases the dd effects seen at low latitude f region zonal irregularity drift around midnight becomes stronger for a given magnetic storm the dd effect on f region zonal irregularity drifts is found to be only marginally stronger at dip equator in comparison to off equatorial stations although effect of dd on f region zonal irregularity drifts are felt simultaneously generation of fresh esf is variable within a smaller longitudinal belt of 5 6 it is attributed to the presence of lsws at the bottomside of f region as initiation of esf is highly likely unlikely in the vicinity of crest trough of such lsws

measurement of the latitudinal distributions of total electron content during equatorial spread f events we have constructed latitudinal profiles of the total electron content tec using measurements from six gps receivers conducted during 1998 the tec profiles have been divided into two groups one corresponds to days when plumes or equatorial spread f esf develops and the second group portrays days of no esf condition the presence absence of esf is based on the signature of the coherent echoes measured by the jicamarca unattended long term investigation julia radar and records of scintillations from two sites spaced in latitude one scintillation station is located near the magnetic equator ancon and the other 12 southward antofagasta the tec profiles display the typical day to day and seasonal variability seen at low latitudes during the equinoxes we observed quite often the crests of the anomaly located between 12 and 20 away from the magnetic equator and a trough in between the monthly distribution of the appearance of the anomaly and the local time of their appearance are in very good agreement with the reported variability of the upward vertical drifts and the current theory of the equatorial fountain effect during the equinoxes and the december solstice the tec anomaly is observed almost every day sometimes when there is no esf activity nevertheless fine inspection of the tec latitudinal profiles suggests the existence of a close relationship between the temporal evolution of the tec profiles near sunset and the onset of esf we have examined the tec latitudinal distributions in two different ways first we calculated time difference profiles using the distributions corresponding to 1800 and 2000 lt second we used a parameterization of the tec distributions obtained at 2000 lt the first method indicates quite drastic increases of the crest values and sharp decreases near the trough during esf days in contrast during days of no esf there exist almost uniform tec decreases at all latitudes the second method displays a preferred high crest trough ratio 2 small tec values at the trough and large latitudinal integrated values during esf events

duskside enhancement of equatorial zonal electric field response to convection electric fields during the st patrick s day storm on 17 march 2015 the equatorial zonal electric field responses to prompt penetration of eastward convection electric fields ppef were compared at closely spaced longitudinal intervals at dusk to premidnight sectors during the intense geomagnetic storm of 17 march 2015 at dusk sector indian longitudes a rapid uplift of equatorial f layer to 550 km and development of intense equatorial plasma bubbles epbs were observed these epbs were found to extend up to 27 13 n and 25 98 s magnetic dip latitudes indicating their altitude development to 1670 km at apex in contrast at few degrees east in the premidnight sector thailand indonesian longitudes no significant height rise and or epb activity has been observed the eastward electric field perturbations due to ppef are greatly dominated at dusk sector despite the existence of background westward ionospheric disturbance dynamo idd fields whereas they were mostly counter balanced by the idd fields in the premidnight sector in situ observations from swarm a and swarm c and communication navigation outage forecasting system satellites detected a large plasma density depletion near indian equatorial region due to large electrodynamic uplift of f layer to higher than satellite altitudes further this large uplift is found to confine to a narrow longitudinal sector centered on sunset terminator this study brings out the significantly enhanced equatorial zonal electric field in response to ppef that is uniquely confined to dusk sector the responsible mechanisms are discussed in terms of unique electrodynamic conditions prevailing at dusk sector in the presence of convection electric fields associated with the onset of a substorm under southward interplanetary magnetic field bz

characterizing the 10 november 2004 storm time middle latitude plasma bubble event in southeast asia using multi instrument observations 1 the development and dynamics of ionospheric plasma bubble pb irregularity during the super storm of 7 11 november 2004 are investigated using the data from a multi instrument network operated in southeast asia analysis of fluctuations in global positioning system total electron content gps tec ionosonde gps scintillation and in situ satellite density data indicates a series of intense pb associated irregularities at equatorial low and middle latitudes in the japanese longitude on 10 november however in the chinese sector the scintillations and pb irregularities are confined within the range of 20 50 n in geographic latitude and 110 125 e in geographic longitude the absence of equatorial pb irregularities in this sector shows a major difference from that in the close by longitude japanese sector in the southern hemisphere australian sector the irregularities occurrence is present as a symmetrical distribution at conjugate latitudes combined analysis of the data from osan and wuhan ionosondes illustrates that the middle latitude spread f irregularities initially develop at the lower part of the f region and then distribute in the whole f region this initiation of spread f at lower altitudes indicates that the middle latitude pb associated irregularities are locally generated these results together with the irregularities occurrence sequence from higher to lower latitudes and the onset time delay of several hours implies that the presence of pb associated irregularities within a latitude range of 20 50 n in the chinese sector cannot be attributed to the effects of prompt penetration electric fields ppefs although the equatorial pbs in the close by longitude are seen to be associated with ppefs the possible mechanism is the f region plasma instabilities triggered by wave structures which act as an external driving force and seed active plasma dynamics and instability growth at middle latitude

effects of interplanetary electric field on the development of an equatorial spread f event 1 on a geomagnetically disturbed night 7 january 2005 an equatorial spread f esf event was captured during premidnight hours by the indian mst radar operated in ionospheric mode at gadanki 13 5 n 79 2 e dip angle 12 5 n the base height of the ionospheric f region over dip equator and a low latitude station showed similar variation during most of the esf interval except mainly during 2145 2200 ist indian standard time ist universal time ut 5 5 hours the zonal electric field variation over dip equator responded to a prompt penetration event at 2000 ist by gradually changing its polarity from westward to eastward after 2015 ist leading to the initiation of esf at 2035 ist the linear growth rate analysis supports the generation of irregularities only when the eastward electric field owing to the prompt penetration effect is taken into account the zonal electric field became westward again after 2100 ist however it ephemerally turned eastward shortly after 2145 ist 1615 ut that is believed to be associated with an overshielding condition a plasma plume got resurrected after 30 min indicating the association of the development of this plume structure with the overshielding electric field the oi 630 0 nm airglow intensity variations observed by a collocated airglow photometer simultaneously operated in a bidirectional zenith and east mode corroborated well with the esf structure and dynamics during the disturbed period these observations evince the active role of interplanetary electric field ief in the development of esf in the premidnight hours

seeding of equatorial plasma depletions by polarization electric fields from middle latitudes experimental evidence 1 it is well known that large wedges of depleted plasma often form in the equatorial ionosphere after sunset irregularities in and around these depletions cause scintillation on trans ionospheric radio paths as well as strong vhf backscatter the ultimate stage of depletion growth is controlled by a collisional interchange instability however the initiation stages remain the subject of debate depletions formed in the first 1 3 hours after sunset are probably seeded by instability processes operating in the valley region from 150 250 km however depletions that form later in the evening do not benefit from the rapid pre reversal enhancement of the zonal electric field nor the sheared flow of the evening vortex we investigate evidence from airglow images and vhf coherent backscatter that a polarization electric field associated with an ionospheric instability process at middle latitudes may induce the formation of post midnight depletions at the geomagnetic equator during geomagnetically quiet periods

hemispheric asymmetries in the ionospheric response observed in the american sector during an intense geomagnetic storm 1 the main purpose of this investigation is to study the ionospheric f region response induced by the intense geomagnetic storm that occurred on 7 8 september 2002 the geomagnetic index dst reached a minimum of 181 nt at 0100 ut on 8 september in this study we used observations from a chain of 12 gps stations and another chain of 6 digital ionosonde stations it should be mentioned that soon after the sudden commencement sc at 1637 ut on 7 september the tec variations at midlatitude stations in both hemispheres showed an f region positive storm phase however during the recovery phase a strong hemispheric asymmetry was observed in the ionospheric response while a tid type soliton was observed to propagate in the southern american sector no tid activity was seen in the northern american sector also in the southern hemisphere the tec variations were less affected by the geomagnetic storm the northern hemisphere observations showed a strong and long lasting negative f region storm phase starting at about 1000 ut on 8 september lasting for about 24 h a perusal of tec phase fluctuations and equatorial spread f esf ionospheric sounding data indicates that on the disturbed night of 7 8 september some stations showed the occurrence of esf starting at about 0000 ut 2000 lt on 8 september whereas other stations showed that the esf occurrence started much later at about 0800 ut 0500 lt this hemispheric asymmetric response of the ionospheric f region possibly indicates the presence of different mechanisms for the generation of esf along the various latitudinal regions during the disturbed period

provenance of quaternary and modern alluvial deposits of the amazonian floodplain brazil inferred from major and trace elements and pb nd sr isotopes abstract chemical and pb nd and sr isotope data from floodplain sedimentary deposits in the solimoes river northwest brazil constrain the variability of the deposits through the quaternary and help reconstruct the paleogeography of amazonia since the uplift of the andes compared to the modern alluvial deposits in the active channel the quaternary terrace deposits in the solimoes river have a higher chemical index of alteration cia higher sio2 al2o3 ratios higher concentrations of immobile elements higher radiogenic sr isotopic compositions more negative end t 0 values and older nd tdm ages these geochemical characteristics indicate that the quaternary sediment sources were composed by more felsic and or recycled old continental crust derived rock materials than the younger source areas which contributed major arc volcanic materials to the flood plain deposits this shift in the composition of the sediment source areas indicates that a significant reorganization of the architecture of the solimoes river has occurred since the uplift of the andes

nature of the crust in the laxmi basin 14 20 n western continental margin of india 1 the nature of the crust in the laxmi basin western margin of india is an uncertain issue more importantly this has implications on paleogeographic reconstructions of the western indian ocean we have analyzed three geophysical data sets and modeled gravity and magnetic anomalies for determining nature of the crust basement of the laxmi basin includes numerous highs which make the basement uneven and shallower compared to the western basin the laxmi basin is characterized by a broad gravity high and a narrower prominent gravity low within it while within the basin the broad anomaly gradually increases toward north the panikkar ridge is associated with the gravity low which is comparable at least in sign to known negative gravity anomaly of the laxmi ridge intrusive structures mapped in the laxmi basin coincide with significant magnetic anomalies which were earlier interpreted as seafloor spreading anomalies model studies reveal that the laxmi basin consists of 14 km thick stretched continental crust in which magmatic bodies have been emplaced whereas the panikkar ridge remains less altered stretched continental crust the crust of the laxmi basin is mostly thinner than crust under the laxmi ridge and continental margin in addition to the rift drift related stretching of the continental margin the laxmi basin possibly has undergone extra stretching in e w direction during the pre tertiary period at 68 ma deccan volcanism on western india may have disrupted the initial conditions that were leading to onset of spreading in the basin subsequently the reunion hot spot had emplaced the volcanic material within the stretched thinned continental crust we interpret the laxmi basin as a failed rift undergone stretching following intraplate kinematics prior to deccan volcanism

ionogram recorded equatorial spread f and height changes at huancayo during sunspot maximum years the analyses presented here consider equatorial nighttime disturbance conditions as indicated by spread f traces on ionograms which record the presence of medium scale structures msss created by the passage of atmospheric gravity waves relationships between these msss and geomagnetic activity ga have been examined statistically particularly considering the ionospheric height h f changes increases and decreases associated with the presence or absence of these msss it is shown that for the postsunset height increases with spread f present the ga a few hours earlier has well defined low levels in contrast if these height increases are not accompanied by spread f the ga a few hours earlier is high when there are no height rises similar inverse associations with ga are recorded for both 1 spread f present and 2 spread f absent for the postsunset height decreases when no spread f occurs high ga levels are well defined at times about 7 h earlier thus all these results indicate an inverse relationship between the msss and ga the experimental evidence suggests that the presunrise height rises are produced by large scale traveling ionospheric disturbances generated in auroral zone regions by substorm onsets

local time dependent response of postsunset esf during geomagnetic storms 1 development or inhibition of esf during magnetically active periods has been an important space weather topic of interest during the recent past in view of its applications in the satellite based navigational systems particularly the postsunset period exhibits significant variability for storm time development of esf versus longitude in this paper we report the results of a multi instrumental ground based and space borne and multistation study on the development inhibition of postsunset esf during five moderate to intense geomagnetic storms occurred during the low and descending phase of the solar activity period 2004 2006 it has been observed that the prompt penetration of eastward electric fields into low latitudes and subsequent development of esf occurred in all longitudinal sectors where the local time corresponds to postsunset hours during the entire main phase of the storm in this paper we show the development of plasma bubble irregularities over a wide longitudinal extent of 92 owing to the dusk time penetration of eastward electric fields into low latitudes either the sudden increase in ae index and or a marked decrease in sym h index may be used as proxies to determine the occurrence as well as the time of penetration of electric fields into equatorial and low latitudes however in such cases where the ae index does not represent any sudden increase the dsymh dt seems to be the better index to determine the time of penetration in this paper is also presented an interesting case where the prompt penetration eastward electric fields dominated the existing strong westward electric fields and subsequently caused the onset of spread f and scintillations at both vhf 244 mhz as well as l band 1 5 ghz frequencies

source area and seasonal 87sr 86sr variations in rivers of the amazon basin we report the results of a detailed study of dissolved sr isotopes in the solimoes and beni madeira rivers of the amazon basin this study developed data collected over 8 years indicating large spatial and temporal variations in dissolved sr isotopes among the rivers of the amazon basin the large 87sr 86sr variations were found to be correlated with the geology of the source areas of the suspended sediments the beni madeira river displays a high average 87sr 86sr ratio and large 87sr 86sr fluctuations during the hydrological cycle this large average value and fluctuations were related to the presence of precambrian rocks and ordovician sediments in the source area of the suspended sediment of the river in contrast the solimoes river displays a narrow range of sr isotope ratio variations and an average value close to 0 709 this river drains mostly phanerozoic rocks of northern peru and ecuador that are characterized by low sr isotope ratios the isotopic fluctuations in the beni madeira river were observed to propagate downstream at least as far as obidos this signal is characterized by an inverse relationship between the concentration of elemental sr and its isotopic ratios we further demonstrate that the sr isotopic composition and content in the beni madeira river is controlled by suspended sediments derived from the andes despite draining areas underlain by precambrian rocks and having high 87sr 86sr ratios such rivers as the negro and tapajos play a minor role in the total sr budget of the amazon basin copyright 2013 john wiley sons ltd

toward a synthesis of equatorial spread f onset and suppression during geomagnetic storms 1 we present initial steps toward unifying our understanding of storm time equatorial spread f esf by searching for the common elements in past case studies and statistical occurrence patterns we show that the development or inhibition of equatorial irregularities during magnetically active periods can be understood using the ae parameterized fejer scherliess model for disturbance vertical drifts versus storm time and local time this model takes into account the different sources of perturbation electric fields magnetospheric and ionospheric dynamos that ultimately drive the equatorial vertical drifts showing prompt and delayed effects in the premidnight sector where both generation and suppression can occur as well as in the postmidnight period where generation dominates the postsunset period exhibits the greatest variability for storm time esf versus longitude and thus we demonstrate the fejer scherliess model s applicability in a test case 6 april 2000 that had an ae pattern compatible with their parameterization scheme the model successfully accounts for the pronounced longitude confinement in the observed postsunset esf patterns finally we move beyond the empirically derived relationships between geomagnetic indices and the occurrence of esf aarons 1991 into a framework of true solar terrestrial parameters that drive such effects additional case studies taken from the published literature are then used to show a consistent linkage between postsunset esf onset and the interplanetary electric field ief esw while ae dst kp and dst dt indices were used in earlier studies to determine the dusk longitude sector of disturbance electric fields here we attribute to the ief the main role in the determination of this longitude sector

controls over the strontium isotope composition of river water abstract strontium concentrations and isotope ratios have been measured in river and ground waters from the ganges orinoco and amazon river basins when compared with major element concentrations the data set has allowed a detailed examination of the controls over the strontium isotope systematics of riverine input to the oceans in the following environments 1 1 typical drainage basins containing limestones evaporites shales and alumino silicate metamorphic and igneous rocks 2 2 shield terrains containing no chemical or biogenic sediments and 3 3 the floodplains that constitute the largest areas of many large rivers the strontium concentration and isotope composition of river waters are largely defined by mixing of strontium derived from limestones and evaporites with strontium derived from silicate rocks the strontium isotope composition of the limestone endmember generally lies within the phanerozoic seawater range which buffers the 87 sr 86 sr ratios of major rivers a major exception is provided by the rivers draining the himalayas where widescale regional metamorphism appears to have led to an enrichment in limestones of radiogenic strontium derived from coexisting silicate rocks the strontium isotope systematics of rivers draining shield areas are controlled by the intense transportlimited nature of the weathering reactions and thereby limits variations in the strontium flux from these terrains floodplains are only a minor source of dissolved strontium to river waters and precipitation of soil salts in some floodplains can reduce the riverine flux of dissolved strontium to the oceans the most effective mechanisms for altering the isotope ratio and flux of riverine strontium to the oceans are increased glaciation and large scale regional metamorphism of the type produced during continental collision both mechanisms provide a means for increasing the 87 sr 86 sr ratio of the global riverine flux

storm time dependence of equatorial disturbance dynamo zonal electric fields we use jicamarca radar observations of f region vertical plasma drifts and auroral electrojet indices during 1968 1988 to study the characteristics and temporal evolution of equatorial disturbance dynamo zonal electric fields these electric fields result from the dynamo action of storm time winds and or thermospheric composition changes driven by enhanced energy deposition into the high latitude ionosphere during geomagnetically active conditions the equatorial vertical drift perturbations last for periods of up to 30 hours after large increases in the high latitude currents on the average this process can be described by two basic components with time delays of about 1 12 hours and 22 28 hours between the high latitude current enhancements and the equatorial velocity perturbations our data indicate strong coupling between dynamo processes with different timescales the short term disturbance dynamo drives upward equatorial drifts eastward electric fields at night with largest amplitudes near sunrise and small downward drifts during the day these perturbation drifts are in good agreement with results from the blanc richmond disturbance dynamo theory the dynamo process with time delays of about a day drives upward drift velocities at night with largest values near midnight and downward drifts in the sunrise noon sector in this case the amplitudes of the disturbance drifts maximize during geomagnetically quiet times preceded by strongly disturbed conditions we also present results of a new equatorial storm time dependent empirical model which illustrate the characteristics of the vertical disturbance dynamo drifts

response of the equatorial ionosphere in the south atlantic region to the great magnetic storm of july 15 2000 the effects of the great magnetic storm of july 15 2000 on the equatorial ionosphere have been studied by ground based and satellite in situ measurements a large westward plasma drift in the evening equatorial ionosphere was observed as a result of the ionospheric disturbance dynamo in that environment the imf bz turned southward and presumably caused penetration of e fields to low latitudes this e field initiated the onset of 250 mhz and l band scintillations at ascension island 15 w and precipitous tec decrease at fortaleza brazil 38 w bounding the narrow longitude region in the south atlantic these impulsive ionospheric effects were extremely well correlated with abrupt decreases of sym h 1 min resolution dst the dmsp in situ measurements showed the presence of severe ion density bite outs extending over 30 latitude in the south atlantic magnetic anomaly region the rocsat 1 satellite measured upward and large southward ion drifts in the same sector

neutral temperature anomaly in the equatorial thermosphere a source of vertical winds data obtained from the wats wind and temperature spectrometer instrument on de 2 dynamics explorer during high solar activity show new evidence for the presence of vertical winds of a significant magnitude in the equatorial thermosphere they reveal a latitudinal structure that can be related to the recently discovered phenomena of the equatorial temperature and wind anomaly etwa in the local evening hours the vertical winds usually are downward around the dip equator and collocated with the temperature minimum of etwa in general they are upward at about 24 dip latitude away from the dip equator and are collocated with the etwa temperature crests the magnitude of the vertical winds is in the 10 40 m s range it is proposed that the temperature and pressure ridges formed by the excess ion drag on the zonal winds around the two crests and ordered by the relatively lower ion drag at the trough of the well known equatorial ionization anomaly eia drive a new wind system in the meridional plane and that the measured vertical winds form part of this wind system

global electrodynamics observed during the initial and main phases of the july 1991 magnetic storm data acquired by seven fortuitously positioned satellites in the interplanetary medium the magnetosphere and the topside ionosphere as well as from numerous ground magnetometers have allowed us to follow the evolution of global currents and electric fields during the geomagnetic storm on july 8 9 1991 an interplanetary disturbance collided with the magnetosphere at 1636 ut on july 8th compressing the magnetopause inside of geostationary orbit for about 3 hours as observed by magnetometers on two goes satellites the resulting storm developed in four segments with a 7 hour lull separating the initial and main phases the initial phase was characterized by 1 an extensive dp 2 current system that produced an ae perturbation of 3500 nt with reporting stations on the dayside 2 a twenty fold increase in auroral electron fluxes and 3 the immediate appearance of electric fields in the inner magnetosphere the main phase intensification and earthward movement of the ring current are associated with southward turnings of the interplanetary magnetic field imf and a polar cap potential increase above 200 kv a significant fraction of the ring current growth was observed prior to the first of several substorms that occurred during the main and recovery phases the beginning of recovery was characterized by a diminution of the southward imf component the cross polar cap potential and magnetospheric electric fields it was also marked by a substorm onset considering the timing of dst modulations relative to substorm occurrence we conclude that during this magnetic storm the electric fields responsible for ring current transport energization were mostly associated with the dp 2 current system finally in the evening sector penetration electric fields of the initial and main phases led to the formation of upward moving equatorial plasma bubbles that were detected by two dmsp satellites in the topside ionosphere

the nature of the crust beneath the afar triple junction evidence from receiver functions the afar depression is an ideal locale to study the role of extension and magmatism as rifting progresses to seafloor spreading here we present receiver function results from new and legacy experiments crustal thickness ranges from 45 km beneath the highlands to 16 km beneath an incipient oceanic spreading center in northern afar the crust beneath afar has a thickness of 20 26 km outside the currently active rift segments and thins northward it is bounded by thick crust beneath the highlands of the western plateau 40 km and southeastern plateau 35 km the western plateau shows vp vs ranging between 1 7 1 9 suggesting a mafic altered crust likely associated with cenozoic flood basalts or current magmatism the southeastern plateau shows vp vs more typical of silicic continental crust 1 78 for crustal thicknesses 2 0 can only be explained by significant amounts of magmatic intrusions in the lower crust this suggests that melt emplacement plays an important role in late stage rifting and melt in the lower crust likely feeds magmatic activity the crust between the location of the miocene red sea rift axis and the current rift axis is thinner 2 0 than beneath the eastern part of afar 26 km vp vs 1 9 this suggests that the eastern region contains less partial melt has undergone less stretching extension and has preserved a more continental crustal signature than west of the current rift axis the red sea rift axis appears to have migrated eastward through time to accommodate the migration of the afar triple junction

the prereversal enhancement of the zonal electric field in the equatorial ionosphere the electric fields in the ionospheric e and f regions near the magnetic equator often show a strong eastward enhancement shortly after sunset and before the eastward normally daytime field reverses to westward several theoretical models of the low latitude fields suggest that this enhancement is caused mainly or entirely by f region winds the f region dynamo but some authors have suggested that it could be produced solely by e region tidal winds we give here additional calculations and arguments in support of the f region source the enhancement of the eastward field for an eastward f region wind turns out to be a simple direct consequence of the fact that after sunset the ionospheric conductivity decreases far more rapidly in the e region than in the f region

riverine li isotope fractionation in the amazon river basin controlled by the weathering regimes we report li isotope composition 7li 7li of river borne dissolved and solid material in the largest river system on earth the amazon river basin to characterize li isotope fractionation arl a continental scale the 7li 7li in the dissolved load 1 2 to 32 is fractionated toward heavy values compared to the inferred bedrock 1 to 5 and the suspended sediments 6 8 to 0 5 as a result of the preferential incorporation of 66li into secondary minerals during weathering despite having very contrasted weathering and erosion regimes both andean headwaters and lowland rivers share similar ranges of dissolved 7li 7li 1 2 to 18 correlations between dissolved 7li 7li and li na and li mg ratios suggest that the proportion of li incorporated in secondary minerals during weathering act as the main control on the 7lidiss 7lidiss across the entire amazon basin a batch steady state fractionation model for andean and lowland rivers satisfactorily reproduces these variations with a fractionation factor between weathering products and dissolved load sec dis sec dis of 0 983 two types of supply limited weathering regimes can be identified for the lowlands clearwaters with dominant incorporation of li in secondary minerals and black waters e g rio negro where dissolution of secondary minerals enhanced by organic matter produces low 7li 7li apart from the black waters the 7li 7li of andean and lowland rivers is negatively correlated to the denudation rates with the lowest 7li 7li corresponding to the rivers having the highest denudation rates in contrast the main tributaries draining both the andes and the lowlands have higher 7li 7li compared to other rivers we propose that part of the dissolved li derived from weathering in the andes is re incorporated in sediments during transfer of water and sediments in floodplains and that this results in an increase of the dissolved 7li 7li along the course of these rivers unlike other rivers the dissolved 7li 7li in the main tributaries is best described by a rayleigh fractionation model with a fractionation factor sec dis sec dis of 0 991 altogether the control imposed by residence time in the weathering zone and floodplain processes results in i a non linear correlation between dissolved 7li 7li and the weathering intensity defined as w d and ii a positive relationship between the dissolved li flux and the denudation rate these results have important implications for the understanding of past ocean 7li 7li and its use as a paleo weathering proxy

seasonal and provenance controls on nd sr isotopic compositions of amazon rivers suspended sediments and implications for nd and sr fluxes exported to the atlantic ocean abstract this study reports daily water discharge and suspended sediment load concentrations and sm nd and rb sr isotopic systematics and major and trace elements concentrations of twelve monthly sampled suspended load sediments of the solimoes and madeira rivers the two major andean tributaries of the amazon during the year 2004 as observed in other long term monitoring studies of amazon rivers the maximum of suspended sediment load occurs before or during the rising water period i e during the rainy season in 2004 the solimoes river exported 289 10 6 tonnes of suspended sediments and the madeira river 294 10 6 tonnes which correspond to erosion rates of 129 and 214 t km 2 yr for the solimoes and madeira rivers basins respectively both the solimoes and madeira suspended sediments are enriched in lree over hree and exhibit similar mree enrichment the difference being that the madeira sediments are more fractionated than the solimoes ones when plotted in al 2 o 3 cao na 2 o k 2 o diagram the suspended sediments of the solimoes and madeira rivers exhibit two different weathering trends which suggests that these sediments evolved along two different trends starting from felsic rocks with different chemical compositions the nd isotopic compositions end of the solimoes sediments 8 9 to 9 9 are slightly more radiogenic than the corresponding values of the madeira sediments 10 8 to 12 1 the 87 sr 86 sr isotopic compositions of the madeira sediments 0 728 to 0 740 are significantly more radiogenic than those of the solimoes 0 713 to 0 717 together with other major elements and ree evidences these isotopic compositions suggest that the solimoes sediments are more influenced by andean volcanic arc detritus than the madeira sediments that might be due to input of young basaltic products owing to strong volcanic activity in ecuador mineralogical compositions as well as nd isotopic compositions do not vary seasonally based on our data set and on previous published studies we have calculated that the nd suspended sediment flux dominates the nd total flux i e dissolved suspended sediment exported to the atlantic ocean by the amazon river representing 98 of the nd total flux and having a global end isotopic composition of 10 3 contrary to nd isotopic compositions sr isotopic compositions vary seasonally in both rivers the explanation for this variation remains unclear we suspect increasing physical weathering during the rainy season to be the main cause of this seasonal control in favouring landslides and river bank erosion that might induce input of more radiogenic sediments not easily mobilized during low water level we calculated that the sr isotopic composition of the dissolved load exported by the amazon river to the atlantic ocean is not seasonally dependent and remain fairly constant 0 715 0 716 by contrast the sr isotopic composition of the suspended load is strongly affected by the seasonal variation varying from 0 714 in the dry season to 0 730 in the rainy season consequently the total sr isotopic composition dissolved suspended sediment is also seasonally controlled varying from 0 716 to 0 722 we finally suggest that large seasonally controlled sr isotopic variations of great river is a phenomenon that has been underestimated in previous paleo climatic and paleo oceanic studies and should be taken into account in further studies

longitudinal variability of annual changes in activity of equatorial spread f and plasma bubbles global distribution maps of equatorial spread f esf activity for various annual periods were derived from the topside soundings by the ionosphere sounding satellite b iss b in 1978 1980 the esf activity during the northern winter period reveals maximum enhancement at the atlantic longitudes of large westward geomagnetic declination and during the northern summer at the pacific longitudes of large eastward declination on several orbits passing over the region of the esf activity enhancement abrupt depletions of the electron density or equatorial plasma bubbles were observed at the satellite altitude of about 1100 km it has also been found that the background electron density distributions tend to be symmetric with respect to the magnetic equator in the region of the enhanced esf activity and asymmetric in the region of the suppressed esf activity these observations are taken account of by the influence of a transequatorial thermospheric wind upon the suppression of the rayleigh taylor type plasma instability

effects of the vertical plasma drift velocity on the generation and evolution of equatorial spread f we use radar observations from the jicamarca observatory from 1968 to 1992 to study the effects of the f region vertical plasma drift velocity on the generation and evolution of equatorial spread f the dependence of these irregularities on season solar cycle and magnetic activity can be explained as resulting from the corresponding effects on the evening and nighttime vertical drifts in the early night sector the bottomside of the f layer is almost always unstable the evolution of the unstable layer is controlled by the history of the vertical drift velocity when the drift velocities are large enough the necessary seeding mechanisms for the generation of strong spread f always appear to be present the threshold drift velocity for the generation of strong early night irregularities increases linearly with solar flux the geomagnetic control on the generation of spread f is season solar cycle and longitude dependent these effects can be explained by the response of the equatorial vertical drift velocities to magnetospheric and ionospheric disturbance dynamo electric fields the occurrence of early night spread f decreases significantly during equinox solar maximum magnetically disturbed conditions due to disturbance dynamo electric fields which decrease the upward drift velocities near sunset the generation of late night spread f requires the reversal of the vertical velocity from downward to upward for periods longer than about half an hour these irregularities occur most often at 0400 local time when the prompt penetration and disturbance dynamo vertical drifts have largest amplitudes the occurrence of late night spread f is highest near solar minimum and decreases with increasing solar activity probably due to the large increase of the nighttime downward drifts with increasing solar flux

effects observed in the latin american sector ionospheric f region during the intense geomagnetic disturbances in the early part of november 2004 1 the sun was very active in the early part of november 2004 during the period of 8 10 november 2004 intense geomagnetic disturbances with two superstorms were observed in this paper we have investigated the generation and suppression of equatorial ionospheric irregularities and the daytime changes in the f region electron density in the latin american sector during the period of intense geomagnetic disturbances we present the ionospheric sounding observations carried out at manaus and sao jose dos campos brazil during this geomagnetically disturbed period also gps observations obtained from several stations in brazil argentina and st croix u s virgin islands during the disturbed period are presented during the main phase of the first superstorm around the prereversal enhancement time night of 7 8 november prompt penetration of electric field was observed and the presence of equatorial ionospheric irregularities was detected from st croix u s virgin islands in the northern hemisphere to bahia blanca argentina in the southern hemisphere the ionospheric sounding observations at manaus indicate inhibition of prereversal enhancement on the nights of 9 10 and 10 11 november possibly due to the disturbed thermospheric winds or disturbance electric fields virtually no phase fluctuations on the nights of 9 10 and 10 11 november were observed in the latin american sector during the daytime on 8 november the vertical total electron content vtec observations show a negative storm phase at porto alegre brazil and bahia blanca argentina again during the daytime on 10 november the vtec observations show a negative storm phase from brasilia brazil to bahia blanca these negative storm phases are associated with a decrease in the o n2 ratio during the daytime on 9 november the vtec observations show a positive storm phase extending from st croix to porto alegre and again on 10 november vtec observations show a positive storm phase these positive storm phases observed are possibly due to changes in large scale wind circulation and an increase in the o n2 ratio

onset conditions of equatorial range spread f at fortaleza brazil during the june solstice case studies are made of the ionospheric thermospheric and geomagnetic conditions associated with the occasional onset of range spread f at fortaleza 4 s 38 w dip latitude 1 8 and magnetic declination 21 w brazil in the june solstice a season in which frequency spread f is typically seen in the postsunset hours after 2000 lt it is found that the f layer experiences quite consistently a large vertical drift early in the evening hours 1815 1915 lt on days of range spread f in comparison to days of only frequency spread f the anomalously large dusk time vertical plasma drift occurs under both geomagnetically disturbed and quiet conditions there is no significant change in the pattern of meridional neutral winds at and prior to the time of onset of range spread f estimated from the data of f layer peak height hmax at the low latitude station cachoeira paulista 23 s 45 w and dip 26 5 s using a modified form of the servo model the results strongly suggest that though the meridional poleward wind is very effective in inhibiting the growth of rayleigh taylor r t instability and hence range spread f at fortaleza during the june solstice as shown by maruyama 1996 its variability does not play an important role in creating favorable conditions for r t instability on a day to day basis the prerequisite for the occasional occurrence of range spread f at fortaleza in the june solstice seems to be the presence of an impulsive and large f layer vertical plasma drift a condition favorable for destabilizing the bottomside f region through r t instability mechanism because of the high altitude of the layer

turbulent mixing in the amazon river the isotopic memory of confluences rivers continuously discharge dissolved material to the oceans dissolved compounds partially result from water rock interactions which produce a large range of water chemical and isotopic compositions these waters are collected by rivers that are commonly assumed to be well mixed with regard to their different tributaries as a result of turbulent dispersion in this paper we test this hypothesis on the solimoes river at manacapuru the largest tributary of the amazon river by analyzing the sodium concentration and strontium isotopic composition of river water on a transverse section at different depths high precision measurements reveal lateral heterogeneities this reflects poor mixing between two main river masses that have distinct chemical and isotopic signatures a hundred kilometers downstream from their confluence the solimoes mainstream and the purus river using sodium concentration data the transverse dispersion coefficient is estimated for the studied solimoes reach the earth s largest river on which such an estimate now exists and is found to be 1 8 0 2 m2 s comparison with previously reported data highlights the potential role of bed morphology and islands in the efficiency of lateral mixing in large rivers we finally demonstrate that the characteristic length of lateral mixing downstream from confluences in large rivers is at least of several tens of kilometers

structuring of intermediate scale equatorial spread f irregularities during intense geomagnetic storm of solar cycle 24 here we examine the structuring of equatorial plasma bubble epb during intense geomagnetic storm of solar cycle sc 24 that occurred on 17 march 2015 using spaced receiver scintillation observations on a 251 mhz radio signal recorded by a network of stations in indian region as yet this is the strongest geomagnetic storm dstmin 223nt that occurred in present sc present study reveals that the structuring of equatorial spread f esf irregularities was significantly different on 17 march as compared to quiet days of corresponding month esf irregularities of intermediate scale 100 m to few kilometers are observed at unusually higher altitudes 800 km covering wider longitudinal latitudinal belt over indian region a presence of large scale irregularity structures with stronger n at raised f peak with small scale irregularities at even higher altitudes is observed it caused strong focusing effect s4 1 that prevails throughout premidnight hours at dip equatorial station tirunelveli other observational aspect is that zonal irregularity drifts over low latitude station kolhapur exhibited a large deviation of 230 m s from their average quiet time pattern during this geomagnetic storm two southward turnings of significant strength bz 15 nt occurred at 11 4 ist indian standard time and 17 9 ist the later southward turning of interplanetary magnetic field imf bz resulted in a large eastward prompt penetration electric field ppef close to sunset hours in indian longitude estimates of ppef obtained from real time ionospheric model are too low to explain the observed large upliftment of f region in the post sunset hours possible reason for observed enhanced ppef linked effects is discussed

response of the equatorial and low latitude ionosphere in the indian sector to the geomagnetic storms of january 2005 1 the equatorial and low latitude ionospheric response to three moderate geomagnetic storms 17 18 and 22 january during the period from 16 to 23 january 2005 is investigated in the context of development inhibition of the equatorial ionization anomaly eia and the subsequent occurrence nonoccurrence of equatorial spread f esf irregularities on these days the study is carried out using the total electron content tec measured with the gps receivers along the 80 e longitude sector and the f layer bottom height obtained from the ionosonde located over the dip equatorial location of trivandrum 8 5 n 77 e dip latitude 0 5 n in india it is observed that for the storms on days 17 and 22 the development of the anomaly was inhibited probably due to the westward disturbance dynamo electric fields subsequently the post sunset enhancement in the vertical drift of the equatorial f region was also inhibited significantly compared to the quiet day pattern and as anticipated no esf was observed on these days a large vertical drift of the equatorial f region followed by nearly simultaneous onset of weak esf was observed on day 18 the late development of the eia on this day could be due to the eastward prompt penetration electric field associated with the southward turning of the interplanetary magnetic field also strong and distinct f3 layer appeared for a short time in the morning reappeared later in the noon time and then quickly ascended to the topside ionosphere during the main phase of the storm on day 18

seismicity during lateral dike propagation insights from new data in the recent manda hararo dabbahu rifting episode afar ethiopia seismicity released during lateral dike intrusions in the manda hararo dabbahu rift afar ethiopia provides indirect insight into the distribution and evolution of tensile stress along this magma assisted divergent plate boundary in this paper 5 dike intrusions among the 14 that form the 2005 present rifting episode are analyzed with local and regional seismic data during dike intrusions seismicity migrates over distances of 10 15 km at velocities of 0 5 3 0 km h away from a single reservoir in the center of the rift segment confirming the analogy with a slow spreading mid ocean ridge segment comparison with geodetic data shows that the reservoir is located 7 km down rift from the topographic summit of the axial depression dikes emplaced toward the north are observed to migrate faster and to be more voluminous than those migrating southward suggesting an asymmetry of tension in the brittle elastic lithosphere seismicity during dike injections is concentrated near the propagating crack front in contrast faults and fissures in the subsurface appear to slip or open aseismically coeval with the intrusions the seismic energy released during dike intrusions in the manda hararo rift appears to be primarily modulated by the local magnitude of differential tensile stress and marginally by the rate of stress change induced by the intrusion the low level of seismic energy accompanying dike intrusions despite their significant volumes is likely an indicator of an overall low level of tension in the lithosphere of this nascent plate boundary

effect of geomagnetic activity on equatorial radio vhf scintillations and spread f the paper discusses the occurrence of scintillations of ats 3 137 mhz beacons recorded at huancayo on geomagnetically quiet and disturbed days during the years 1969 1976 and compares the results with the corresponding occurrence of range and frequency spread f at huancayo during the equinoctial months and the december solsticial months the geomagnetic activity reduces the equatorial scintillations during premidnight hours but increases their occurrence during the postmidnight hours these features are very similar to the effect of geomagnetic activity on the occurrence of the range type of equatorial spread f rather than on the occurrence of frequency spread which decreases for any hour of the night during geomagnetic active periods during the june solsticial months the occurrence of both scintillations and spread f is very much reduced however both the phenomena are more frequent on disturbed than on quiet days for any of the hours of the night these effects are consistently the same for any of the years within the solar cycle it is suggested that the equatorial radio scintillations at 137 mhz during the nighttime are produced primarily by the occurrence of the range type of spread f the geomagnetic effects are due to the modifications of the equatorial electric field by the geomagnetic disturbance and thereby affect the development of f region irregularities causing scintillations