latitudinal structure and extension of the polar atmospheric disturbance the dissipation of solar wind energy in the upper atmosphere generates a disturbance whose morphology depends on local time season and magnetic activity a statistical analysis of esro 4 data reveals that 1 in the afternoon evening sector the disturbance boundary coincides with the region of electric current dissipation along the auroral oval 2 in the midnight early morning sector dynamical effects extend the disturbance zone to lower latitudes and this expansion is strongly dependent on season and magnetic activity and 3 in the late morning sector direct heating effects along the auroral oval are superimposed on the residuals of the early morning disturbance these results are consistent with previous observations and provide new boundary conditions for upper atmospheric models

rock composition dolomite stoichiometry and rock water reactions in dolomitic carbonate rocks dolomitic carbonate rock units from a variety of phanerozoic localities and depositional environments throughout north america were evaluated with respect to their dolomite content and dolomite composition by x ray diffraction analysis dolomite compositions range from 48 to 57 mole caco 3 with well defined modes at 51 nearly stoichiometric dolomite and 55 distinctly calcian dolomite caco 3 values of percentage of dolomite also exhibit a pronounced albeit less well defined bimodal distribution with modes at 97 dolostones and 20 dolomitic limestones dolomite similar distributions characterize most other published data on phanerozoic dolomitic carbonates these data suggest that two separate processes may lead to two distinct populations of sedimentary dolomite 1 dolomitic limestones originate in diagenetically closed systems during magnesian calcite dissolution calcite and dolomite precipitation reactions and 2 dolostones originate in diagenetically open systems during th

comments and reply on precambrian dolomites petrographic and isotopic evidence that they differ from phanerozoic dolomites comment

global observation of traveling atmospheric disturbances tads in the thermosphere 1 densities derived from accelerometer measurements on the champ satellite near 400 km are used to elucidate global scale characteristics of traveling atmospheric disturbances tads in connection with 3 sudden injections of energy at high latitudes on 29 may 2003 dayside tads with typical amplitudes 20 30 propagate towards the equator from the northern hemisphere southern hemisphere auroral region with phase speeds of order 730 ms 1 460 ms 1 some evidence is found for tad penetration from the northern to the southern hemisphere and for the first time for trans polar propagation nighttime tad signatures are less well defined but have phase speeds similar to the dayside tads the above day night and hemisphere differences possibly reflect dependencies on direction and intensity of the prevailing solar driven circulation and on generation efficiency and ion drag dissipation with respect to solar zenith angle

synsedimentary dolospar cementation a possible devonian example in the camsell formation northwest territories canada1 a unique association of beds containing fenestral pore filling medium crystalline dolomite with beds of dolospar and quartz sandstone occurs in the lower devonian camsell formation many of these sandstones consist almost entirely of dolospar sand sedimentological petrographic cathodoluminescent and chemical data indicate that the dolospar sands consist of grains that have been eroded and reworked during camsell deposition from fenestral dolostone beds that directly underlie these sandstones erosional truncation of individual dolomite crystals and of intracrystalline cathodoluminescent zonations along the edges of sand grains indicates that either dolomitization or dolomite cementation of the pore filling carbonate cements within fenestrae of the fenestral fabrics occurred before erosion and deposition of dolospar sand the fine details of the cathodoluminescent zonations suggest that the pore filling fenestral dolomite originated as primary cements that underwent some annealing recrystallization under the influence of high subsurface temperatures this unique occurrence may document synsedimentary devonian cementation by medium to coarsely crystalline dolomite

ionospheric response to the initial phase of geomagnetic storms common features 1 ionospheric responses to the initial phases of three geomagnetic storms 2 5 april 2004 7 9 november 2004 and 13 16 december 2006 were compared using both ground based gps total electron content tec data and coupled magnetosphere ionosphere thermosphere cmit model simulations the onset times for these storms all occurred at local daytime in the north american sector this similarity of onset times and other factors resulted in some common features in their ionospheric response these common features include 1 enhanced tec positive response at low and middle latitudes in the daytime 2 depleted tec negative response around the geomagnetic equator in the daytime 3 a north south asymmetry in the positive response as the northern hemispheric response appeared to be more pronounced and 4 negative response at high latitudes as the storms progressed the cmit model captured most of these features analysis of model results showed that storm time enhancements in the daytime eastward electric field were the primary cause of the observed positive storm effects at low and middle latitudes as well as the negative response around the geomagnetic equator in the daytime these eastward electric field enhancements were caused by the penetration of high latitude electric fields to low latitudes during southward interplanetary magnetic field imf periods when imf bz oscillated between southward and northward direction in the initial shock phase of the storms consequently the ionosphere was lifted up at low and middle latitudes to heights where recombination was weak allowing the plasma to exist for a long period resulting in higher densities in addition the cmit model showed that high latitude negative storm responses were related to the enhancements of molecular nitrogen seen in timed global ultraviolet imager observations whereas the negative storm effects around the geomagnetic equator were not associated with thermospheric composition changes they were the result of plasma transport processes

dolomitization a critical view of some current views the principal models in vogue today for dolomitization are the mixing zone and the sabkha models despite the wide acceptance of these models there has been little critical assessment of their validity such an assessment is the objective of the present paper a close look at the dorag mixing zone model badiozamani 1973 reveals several serious weaknesses 1 the range of freshwater seawater mixtures that meet the dorag requirement for dolomitization shrinks to a small window if the geologically more realistic disordered dolomite is used in the calculations instead of the ordered dolomite on which the model is based 2 in none of the known modern coastal mixing zones in limestone or lime sediments has replacement by dolomite been observed 3 in a number of dolomites interpreted to be of mixing zone origin dolomite has precipitated without dissolution of the calcite substrate evidence that negates the fundamental premise of the dorag model in addition to these weaknesses isotope and trace element data used to identify mixed water dolomite are inadmissible because 1 isotopic fractionation factors for dolomites remain unresolved 2 isotope values uncorrected for temperature for a host of dolomites interpreted to be of different origins overlap 3 nonisomorphous trace elements such as na in dolomite cannot on theoretical grounds be relied on to identify dolomitizing fluids similar overall objections can be brought against folk and land9s 1975 schizohaline version of mixing zone dolomitization in summary mixing zone models have such weak underpinnings that they should be questioned as viable explanations for massive dolomitization contemporaneous dolomite formation in modern sabkhas is well documented but the important question of whether the mechanism of dolomite formation is replacement or direct precipitation remains to be resolved in the well studied sabkha at abu dhabi brine chemistry changes have been used as evidence of a replacement origin for the dolomite but it is shown here that this evidence is far from unequivocal an alternative origin of direct precipitation of dolomite is offered an origin in keeping with dolomite precipitation known from other modern sabkhas and saline lakes and in line with our laboratory experience with dolomite synthesis moreover it is suggested here that in general contemporaneous dolomite will form at low temperatures only by direct precipitation a mechanism that requires special conditions of highly super saturated waters of high mg ca ratio and elevated co 3 hco 3 concentrations this may explain why modern dolomite is mainly restricted to evaporitic environments a bias not shared by ancient dolomites in contrast replacement dolomite appears to require at low temperatures long reaction times or 10 4 yr a requirement that is mainly to be met in large regional groundwater flow systems both marine and nonmarine a third dolomitization model considered here is that of baker and kastner 1981 based on the experimental finding that sulfate ions inhibit or retard dolomitization a number of modern sedimentary dolomites are not in accord with this model in that they are forming from brines with large sulfate concentrations 2 to 70 times that of seawater thus the baker kastner model should be held in abeyance until these serious contradictions are resolved the current emphasis on mixing zone and sabkha dolomitization has diverted attention from other promising avenues of approach to the dolomite problem four of these avenues each of which deemphasizes the special water approach are briefly addressed and are as follows 1 influence of temperature and time 2 mass transfer processes 3 burial diagenesis of epigenetic dolomites 4 fluid inclusion studies at elevated temperatures the dolomite problem essentially disappears ordered dolomite can be made in the laboratory in days at 100 degrees c what is more at temperatures above 60 degrees c ca rich waters become dolomitizing fluids which makes most natural subsurface waters capable of dolomitization at low temperatures time may be the key element so that seawater will become a major dolomitizing fluid only where stable circulation systems such as kohout convention can drive seawater through carbonate platforms for many thousands to millions of years this paper has tried to show that currently favored models of dolomitization carry serious uncertainties enough to warn us to look more critically at the validity of these models and also it is hoped enough to spur new efforts to find new solutions to the problems of dolomitization

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

micromorphology of atlantic rankers on the coast of northern portugal summary the micromorphological examination of atlantic rankers on the coast of northern portugal shows the importance of alternating phases of landscape stability and instability during the genesis of the profiles archaeological artifacts and marine deposits allow the dating of these events recent pedogenesis is characterized by the formation of a microgranular structure and the illuviation of amorphous organic matter remnants of an older leached phase in the gelfa section reflect an initial weakly base desaturation stage during historical times the soil was buried under eolian sands

zonal meridional wind and disturbance dynamo electric field control of the low latitude ionosphere based on the sundial atlas 1 campaign we present an evaluation of global scale equatorial and low latitude ionospheric disturbances in response to the weak to moderate disturbed conditions that marked the sundial atlas1 twelve day campaign of march 22 to april 2 1992 ionosonde data from south american and indian asian longitudes are analyzed to examine first the climatological the average pattern of the critical f region parameters the layer peak density and height in comparison with the empirical international reference ionospheric model and then to characterize the day to day variabilities aiming at identifying potential causal contributions from either disturbance zonal and meridional winds or magnetospheric and disturbance dynamo electric fields included in this analysis are data from south american midlatitude locations which are used to determine meridional winds using an adaptation of the servo analysis technique in the field line integrated plasma flip model we have made an assessment of the causal mechanism of the day to day variabilities as arising from latitude dependent disturbance meridional winds and from electric fields produced by disturbance zonal winds and disturbance dynamo while the contribution from disturbance meridional winds decreases from middle to equatorial latitudes that of the electric fields maximizes around the equator in particular first time evidence based on ionosonde data is provided for a disturbance dynamo electric field in the equatorial ionosphere it is found that there are two time intervals of maximum ionospheric variability resulting from the weak to moderate magnetospheric disturbance conditions that prevailed during the campaign one near the evening postsunset hours and the other in the postmidnight sunrise hours over low latitudes at midlatitudes a broad maximum of the response occurs from premidnight to morning hours we provide a comparison of results for the south american and indian asian longitudes and a discussion of the competing roles of the disturbance zonal and meridional winds and magnetospheric and disturbance dynamo electric fields as a function of latitude

middle and low latitude ionosphere response to 2015 st patrick s day geomagnetic storm this paper presents a study of the st patrick s day storm of 2015 with its ionospheric response at middle and low latitudes the effects of the storm in each longitudinal sector asian african american and pacific are characterized using global and regional electron content at the beginning of the storm one or two ionospheric positive storm effects are observed depending on the longitudinal zones after the main phase of the storm a strong decrease in ionization is observed at all longitudes lasting several days the american region exhibits the most remarkable increase in vertical total electron content vtec while in the asian sector the largest decrease in vtec is observed at low latitudes using spectral analysis we were able to separate the effects of the prompt penetration of the magnetospheric convection electric field ppef and of the disturbance dynamo electric field ddef on the basis of ground magnetic data concerning the ppef earth s magnetic field oscillations occur simultaneously in the asian african and american sectors during southward magnetization of the b z component of the interplanetary magnetic field concerning the ddef diurnal magnetic oscillations in the horizontal component h of the earth s magnetic field exhibit a behavior that is opposed to the regular one these diurnal oscillations are recognized to last several days in all longitudinal sectors the observational data obtained by all sensors used in the present paper can be interpreted on the basis of existing theoretical models

essai d interpretation des transferts sous forme figuree dans les podzols du quebec meridional a partir de l etude micromorphologique des profils abstract in the podzolic soils of southern quebec the migration of clay silt and even fine sand particles results in the formation of various kinds of accumulations and organizations which develop during the podzolization process the internal morphology of the accumulations is characterized by a coarse layered structure often irregular and presenting evidence of microerosion and also by their weak orientation and birefringence these accumulations do not integrate within the matrix and they are present in a large volume of soil with no clear lower boundary the horizons which form below the podzolic b horizons in the profiles developed in well sorted coarse sands contain accumulations of clay particles mixed with organic matter and or sesquioxides as coatings on the grains or agglomerates between the grains in the loamy sandy tills there is an horizon with silty caps which grades into a lamellar horizon at depth in the loamy tills the voids of the fragic horizon are partly blocked with accumulations of unsorted material

textural and geochemical alternations in late cenozoic bahamian dolomites dolomitized intervals of a core from san salvador island bahamas exhibit variations of two texturally and geochemically distinct end members in the pliocene section of the dolomitized interval the two end members alternate in a pattern that may reflect originally and or diagenetically modified depositional facies formerly mud free intervals locally capped by exposure surfaces are massive crystalline mimetic dolomites cm muddier sediments are replaced by friable microsucrosic dolomites ms cm and ms dolomites also differ in porosity 30 permeability 100 md mol mgco3 44 9 vs 47 7 mol oxygen isotopic composition 1 7 vs 2 7 and strontium content 241 vs 106 ppm these data indicate that depositional and diagenetic fabric are the principal controls governing the distribution of dolomite types differences in texture and geochemistry are suggested as arising through differential rates of crystallization produced as a result of variations in permeability and reactivity of the precursor sediments and rocks

response of low latitude ionospheric total electron content to the geomagnetic storm of 24 august 2005 1 response of low latitude ionosphere to the geomagnetic storm of 24 august 2005 has been studied using total electron content tec data obtained from the global positioning system gps receivers these studies were carried out using the receivers that were located 1 near the northern crest 15 n mag lat of the equatorial ionization anomaly around 56 e 74 e and 102 e longitude and 2 from the northern crest of the ionization anomaly down to the magnetic equator in the longitude belt 75 e 3 e these studies have been substantiated with the ground based magnetometer data at tirunelveli and alibag an equatorial and off equatorial station respectively the ground based ionosonde data at new delhi a low latitude station have also been used to substantiate the tec observations the storm day tec shows two well defined humps at all stations wherein enhancements of the order of 80 100 have been observed while the first of the enhancements has been attributed to the prompt penetration electric field associated with an interplanetary electric field ief ey of about 35 mv m the other one has been attributed to the second episode of the prompt penetration electric field ief ey 20 mv m and abnormal equatorial plasma fountain in late evening hours respectively during the unsteady ring current conditions when the imf bz was still southward penetration of a westward electric field has been inferred two peaks in fof2 have been observed whose time of occurrence coincides with those of the humps in the low latitude tec results from stations having nearly the same magnetic latitude show that the ionospheric response in terms of gps tec to the prompt penetration electric fields is longitudinally independent formation of the first hump in tec is progressively delayed in time from low to near equatorial latitudes for stations in different magnetic latitudes along nearly the same longitude however its time of appearance at diego garcia a station magnetically conjugate to udaipur is the same as that at udaipur the results also reveal the poleward expansion of the ionization anomaly due to the storm disturbance dynamoelectric fields have been inferred to be responsible for the suppressed plasma fountain resulting in suppressed tec values and equatorward contraction of the ionization anomaly on 25 august compared to a reference quiet day

ionospheric and magnetic signatures of a space weather event on 25 29 august 2018 cme and hssws we present a study concerning a space weather event on 25 29 august 2018 accounting for its ionospheric and magnetic signatures at low latitudes and midlatitudes the effects of a storm in several longitudinal sectors asia africa america and the pacific have been analyzed using various parameters such as total electron content tec geomagnetic field and column o n2 ratio positive ionospheric storms are found in all the longitudinal sectors having its maximum effects in the asian sector whereas the negative ionospheric storms have been observed in the summer hemisphere northern hemisphere a large decrease in o n2 ratio in the northern hemisphere is a possible cause of the observed negative storm effects ionospheric f2 region maximum electron density nmf2 and tec have shown a positive correlation during this storm the study suggests that storm time generated wind does not have a uniform planetary extension and mainly affects dayside america and pacific and duskside africa sectors during the space weather event we observe an asymmetric variation of the magnetic field as a function of the longitude on the other hand the magnetic variations at midlatitudes are found to be symmetric in both hemispheres a signature of the disturbance dynamo anti sq circulation has been observed mainly at low latitudes we emphasize that the partial ring current prc estimated by the asym h magnetic index must also be taken into account along with the sym h index for a better approximation of ionospheric currents the study further suggests existence of several electric current cells in the ionosphere which is consistent with the blanc richmond model

simulation of low latitude ionospheric response to 2015 st patrick s day super geomagnetic storm using ionosonde derived pre vertical drifts over indian region

equatorial f region vertical plasma drifts seasonal and longitudinal asymmetries in the american sector longitudinal and seasonal asymmetries in the evening ionospheric f region plasma vertical drift v sub z enhancements between two longitudinally separated stations situated along the magnetic equator in the american sector are investigated under solar maximum conditions based on results obtained from the analysis of ionosonde data for these stations the two stations are huancayo peru and fortaleza brazil which have markedly different magnetic declination angles the observed asymmetries are interpreted using a detailed numerical simulation of the e and f region electrodynamic coupling process that takes into account also its asymmetry about the magnetic equator arising from the finite magnetic declination angle the results of the simulation show in agreement with observations that the occurrence time of the evening f region vertical drift prereversal peak and its seasonal variation at a station are controlled by the magnetic declination angle at that station which determines the seasonal variation of the sunset times and hence the integrated pedersen conductivity longitudinal gradient at its magnetic conjugate e layers the amplitude of the prereversal peak on the other hand undergoes the influence of the magnetic declination angle as well as of the thermospheric zonal wind component

ionospheric electron content within the equatorial f 2 layer anomaly belt this paper describes some new results on the day to day behavior of the location of the equatorial anomaly in the columnar electron content the measurements were made from a unique network of stations covering dip latitudes from 0 n to 25 n during the period in 1975 1976 near sunspot minimum when the ats 6 satellite was visible from india the latitudinal distribution of the total electron content on a particular day was found to depend only on the strength of the electrojet current as determined by the difference of the horizontal magnetic field at stations on the magnetic equator and another outside the equatorial electrojet rather than on the horizontal magnetic field measured only at the equatorial station during magnetically disturbed periods the presence or absence of the anomaly was also found to depend only upon the strength of the electrojet current the varying electrojet current that is the equatorial electric field is very effective in moving the ionization to the anomaly latitudes of 15 20 but the columnar electron content over the magnetic equator remains relatively constant

response of the equatorial ionosphere in the indian midnight sector to the severe magnetic storm of july 15 2000 1 during the severe magnetic storm of july 15 2000 an impulsive and remarkably large downward movement of f region occurred simultaneously at locations throughout the equatorial region dip 0 3 20 n in the indian sector in close association with episodes of rapid ring current intensification the abnormal midnight descent of equatorial f region maximum amplitude close to the magnetic equator 215 km hr indicative of a short lived westward electric field disturbance peak amplitude 4 6 mv m is interpreted as the signature of prompt penetration electric fields associated primarily with impulsive ring current injections the westward electric field disturbance in the indian midnight sector occurred near simultaneous with the eastward electric field disturbances in the dusk sector reported by basu et al 2001a moreover the prompt electric field penetration to the magnetic equator both in the dusk and midnight sectors occurred in an environment already under the influence of ionospheric disturbance dynamo idd electric fields illustrating the profound manner in which the equatorial f region plasma dynamics can get modified globally during the main phase of severe magnetic storms

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

equatorial ionospheric electric fields during the november 2004 magnetic storm 1 we use radar measurements from the jicamarca radio observatory magnetometer observations from the pacific sector and ionosonde data from brazil to study equatorial ionospheric electric fields during the november 2004 geomagnetic storm our data show very large eastward and westward daytime electrojet current perturbations with lifetimes of about an hour indicative of undershielding and overshielding prompt penetration electric fields in the pacific equatorial region during the november 7 main phase of the storm when the southward imf the solar wind and reconnection electric fields and the polar cap potential drops had very large and nearly steady values this result is inconsistent with the recent suggestion that solar wind electric fields penetrate without attenuation into the equatorial ionosphere for several hours during storm main phase the largest daytime prompt penetration electric fields about 3 mv m ever observed over jicamarca occurred during the november 9 storm main phase when large equatorial electrojet current and drift perturbations were also present in the pacific and brazilian equatorial regions the rise and decay times of these equatorial electric fields were about 20 min longer than of the corresponding solar wind electric fields the ratios of prompt penetration electric fields and corresponding solar wind electric field changes were highly variable even during the day and had largest values near dawn also the prompt penetration electric fields did not show polar cap potential drop saturation effects our results clearly highlight that the relationships of prompt penetration and solar wind electric fields and polar cap potentials are far more complex than implied by simple proportionality factors

midlatitude tec enhancements during the october 2003 superstorm 1 we use observations from the array of north american gps receivers to examine the formation and severity of midlatitude enhancements and steep gradients in total electron content tec during the october 30 31 2003 superstorm a large 10x enhancement in dayside tec was observed over the us mainland during these events as dst decreased sharply and strong saps electric fields eroded the outer reaches of the post noon plasmasphere boundary layer pbl forming poleward streaming plumes of storm enhanced density tec increased to 250 tecu equatorward of the pbl tec gradients across the pbl over the central us exceeded 60 tecu per deg latitude while intense these features are qualitatively similar to those seen in lesser storms

deposition and pedogenesis of periglacial sediments and buried soils at the serpentine hot springs archaeological site seward peninsula ak abstract soil micromorphology is an excellent tool for relating quantitative laboratory data to soil development in complex pedogenic settings this study utilizes micromorphology scanning electron microscopy bulk soil geochemistry clay mineralogy and particle size analysis to reconstruct the depositional and pedogenic history of the serpentine hot springs fluted point site on the seward peninsula alaska sediment deposition occurred via colluviation which dominated during the late glacial period and early to middle holocene and aeolian processes which dominated during the younger dryas yd and late holocene two buried soils are present one dating to the holocene thermal maximum htm and the other dating just before the neoglacial period pedofeatures fall into four categories 1 cryogenic features 2 clay illuviation features 3 podzolization redox features and 4 anthropogenic features the spatial relationships among these features provides insight into the pedogenic history of the soil the htm soil is characterized by clay illuviation suggesting warm mildly acidic well drained soil conditions the pre neoglacial soil is characterized by incipient placic horizon development and podzolization indicative of moist acidic variably drained conditions cryogenic features associated with late holocene neoglaciation dominate the modern soil despite cryogenic activity and the presence of permafrost the cultural stratigraphy of the site remains intact

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

simulation of electric field and current during the 11 june 1993 disturbance dynamo event comparison with the observations 1 the ionospheric disturbance dynamo signature in geomagnetic variations is investigated using the national center for atmospheric research thermosphere ionosphere electrodynamics general circulation model the model results are tested against reference magnetically quiet time observations on 21 june 1993 and disturbance effects were observed on 11 june 1993 the model qualitatively reproduces the observed diurnal and latitude variations of the geomagnetic horizontal intensity and declination for the reference quiet day in midlatitude and low latitude regions but underestimates their amplitudes the patterns of the disturbance dynamo signature and its source anti sq current system are well reproduced in the northern hemisphere however the model significantly underestimates the amplitude of disturbance dynamo effects when compared with observations furthermore the largest simulated disturbances occur at different local times than the observations the discrepancies suggest that the assumed high latitude storm time energy inputs in the model were not quantitatively accurate for this storm

signature of the coronal hole near the north crest equatorial anomaly over egypt during the strong geomagnetic storm 5 april 2010 in this paper we study the ionospheric magnetic disturbance during a strong magnetic storm on 5 april 2010 associated to a coronal hole the earth was under the influence of a high speed solar wind stream during four days and imf was southward during a very long period the variation of the disturbed magnetic observations and gps tec are compared with the variation of quiet days during the same month in order to obtain the characteristics of gps tec and magnetic disturbances due to the coronal hole effect we use multi instruments as scinda gps station at helwan egypt 29 86 n 31 32 e and asw magdas station at aswan egypt 23 59 n 32 51 e in the equatorial region at the beginning of the storm our data highlights the effect of the prompt penetration of the magnetosphere electric field which strongly increases the tec during the recovery phase of the storm we observe on tec and magnetic data the signature of the ionospheric disturbance dynamo due to wind produced by joule heating in the auroral zone it is the first time that we observe an anti sq circulation on magnetic data during four consecutive days associated to the high speed solar wind streams

ionospheric response to 22 23 june 2015 storm as investigated using ground based ionosondes and gps receivers over india in this paper we present response of equatorial and low latitude ionosphere to 22 23 june 2015 geomagnetic storm using a chain of ground based ionosondes located at tirunelveli 8 73 n 77 70 e geomagnetic latitude 0 32 n hyderabad 17 36 n 78 47 e geomagnetic latitude 8 76 n and allahabad 25 45 n 81 85 e geomagnetic latitude 16 5 n along with a chain of gps receivers uniqueness of this storm is that in contrast to the equatorial plasma bubbles that were detected in the european sector we see suppression of plasma bubbles in the indian sector the observations suggest that westward penetration electric field during local midnight caused abrupt decrease of virtual height h f km to 200 km and suppressed plasma bubbles due to undershielding later the layer increased to 500 km simultaneously due to overshielding effect on 23 june we observed negative storm in the northern hemisphere while positive storm in the southern hemisphere in addition absence of equatorial es layers at tirunelveli and presence of f3 layer at tirunelveli hyderabad seem to be associated with equatorial electrojet eej counter electrojet cej variations however on 24 june we observed strong negative storm effects at allahabad hyderabad while positive storm effect at tirunelveli simultaneous enhancement of h f km at all three ionosonde stations at 20 30 ut on 23 june during recovery phase suggest eastward disturbance dynamo dd electric field that caused presunrise spread f at hyderabad allahabad but void of spread f at tirunelveli suggesting its midlatitude origin periodogram analysis of fof2 and h f km in the present analysis suggest the presence of shorter periods 2 h associated with dd electric field winds

formation of saddle dolomites in upper cambrian carbonates western tarim basin northwest china implications for fault related fluid flow abstract the saddle dolomites occur more intensely in cores closely to fault than that in cores far away from the fault in upper cambrian carbonate of western tarim basin suggesting that formation of the saddle dolomites is likely related to fault controlled fluid flow they partially fill in fractures and vugs of replacement dolomite the saddle dolomites exhibit complex internal textures commonly consisting of core and cortex in comparison with the matrix dolomites the saddle dolomites show lower sr content and 87 sr 86 sr ratios higher fe and mn content and more negative 18 o values combined with high th 100 130 c of primary fluid inclusions it is suggested that the saddle dolomites precipitated from hydrothermal fluid derived from the deep evaporite bearing middle cambrian strata and the magnesium source may be due to dissolution of host dolomite during hydrothermal fluid migration fault activity resulted in petrographic and geochemical difference of the core and cortex of the saddle dolomites the cores precipitated from the formation water mixed by deep brines at the early stage of fault activity and the cortexes precipitated from the deep fluid with higher temperatures through the middle cambrian later in summary the formation of the saddle dolomites implies a hydrothermal fluid event related to fault activity which also resulted in high porosity in upper cambrian carbonate in western tarim basin

a mu radar based study of mid latitude f region response to a geomagnetic disturbance during the night of january 20 21 1989 ionospheric incoherent scatter power measurements were made with the mu middle and upper atmosphere radar at shigaraki geographic latitude 34 85 n longitude 136 10 e geomagnetic latitude 24 9 longitude 204 3 japan and the electron density profiles in the 180 to 1000 km height range were derived at 8 min intervals the observations showed the presence of three f region disturbances during the night during the very large first disturbance which lasted from 2300 to 0240 lt approximately the height of maximum electron density nm increased by 220 km in 2 hours to reach an altitude of 600 km the other two smaller disturbances occurred during 0300 0500 lt and 0530 0700 lt approximately a detailed interpretation of the above f region disturbances is given examination of some high and middle latitude magnetograms showed the beginning of an intense geomagnetic substorm at auroral latitudes at the start of the first f region disturbance and a less intense substorm around the starting time of the second f region disturbance on the basis of this evidence the first two f region disturbances are interpreted as the result of large vertical drifts of f region ionization due to the substorm generated east west electric fields appearing at mid latitudes the patterns of h f variations during this night at five ionospheric stations in japan support the above interpretation additionally during the second disturbance the possible presence of a wind perturbation due to the equatorward propagation of a wave disturbance generated probably by the first major substorm is indicated by the mu radar data and the ionosonde data the third f region disturbance is attributed to a neutral wind perturbation associated with a gravity wave traveling equatorward the wave being generated most plausibly by the joule heating during the first major substorm the brief unusual distortions of the f layer shape as revealed by mu radar observations are also interpreted as the consequence of an unusually large convergence of ionization in the bottomside of the f layer due to the unusually large electric field and wind perturbations theoretical calculations are made using the mu radar data and f region continuity equation and the east west electric field values during the disturbances are quantified during the first major rise of the f layer during 2300 0115 lt the inferred eastward electric field in the ionosphere at shigaraki is found to be as large as 6 1 mv m and after this disturbance a westward electric field and or a poleward meridional wind is found to occur for some time an eastward electric field of about 3 0 mv m is found to occur during the second f region disturbance along with a possible meridional wind perturbation the large eastward electric field around local midnight is most unusual in both magnitude and direction because the theoretical models of disturbance electric fields predict a strong westward electric field in this lt sector this result has important implications for understanding the physics of disturbance electric fields at middle and low latitudes during substorms

equatorial density depletions observed at 840 km during the great magnetic storm of march 1989 early on march 14 1989 a thermal plasma probe on the defense meteorological satellite program dmsp f9 spacecraft detected extensive and dramatic decreases in the ion density at 840 km near 2130 lt during two consecutive transequatorial passes over south america the order of magnitude decreases in the ion density extended more than 4000 km along the satellite track the depletions were accompanied by upward and westward plasma drifts both in excess of 100 m s their onsets and terminations were marked by extremely sharp density gradients dmsp f9 observed no similar depletions over the atlantic during preceding orbits a partial depletion was detected over the eastern pacific during the following orbit the dmsp f9 ground track passed slightly west of a brazilian total electron content tec station and two brazilian ionosondes during the first depletion encounter the tec fell far below normal during the night of march 13 14 the ionosonde measurements indicate that in the hour after sunset before dmsp passed through the depletions the f2 layer rose rapidly and disappeared but at the time of the first depletion encounter hmf2 was decreasing over one of the stations the dmsp f8 satellite which orbits in the dawn dusk meridian made related measurements on march 13 and 14 crossing the equator at dust on march 13 at the same longitude where dmsp f9 encountered the first depletion dmsp f8 detected upward and westward drifts but it measured extremely large rather then depleted ion densities during two dawn passes over the eastern pacific on march 14 dmsp f8 observed depletions somewhat similar to those detected by dmsp f9 large westward drifts accompanied the depletions detected by dmsp f8 it is quite probable that the morningside depletions detected on march 14 are remnants of those detected earlier by dmsp f9 in the evening sector we develop a phenomenological model reconciling dmsp f8 f9 and ground based measurements our calculations show that rapid upward drifts sustained for several hours can produce depletions in the equatorial ion density with sharp gradients at their high latitude boundaries consistent with the data we discuss possible contributing mechanisms for generating these upward drifts these include direct penetration of the magnetospheric electric field to low latitudes the electric fields generated by the disturbance dynamo and the effects of conductivity gradients near the dusk terminator and the south atlantic anomaly

ionospheric response to the geomagnetic storm of 15 may 2005 over midlatitudes in the day and night sectors simultaneously the ionospheric response to the geomagnetic storm of 15 may 2005 has been studied over midlatitude stations in the dayside and nightside simultaneously in the day side the ionospheric response has been studied using the ground based gps and ionosonde measurements from the stations pol2 and alma ata respectively the dayside total electron content tec and fof2 variations are characterized by two well separated enhancements of which the first enhancement in both the parameters is attributed to the episode of prompt penetration electric field caused by the sudden southward turning of interplanetary magnetic field imf bz around 0600 ut the second enhancement which was also superposed by wave like modulations has been attributed to the storm induced winds the maximum peak to peak amplitude of modulation in tec is found to be 5 tecu total electron content unit 1 tecu 1016 el m 2 the enhanced plasma density observed during the daytime at midlatitudes is found to be locally produced and not transported from the equatorial ionization anomaly region because the time of enhanced plasma density at midlatitude is earlier than that observed at low latitudes during the storm main phase the nightside gps observations from the midlatitude station algo algonquin park canada show moderate to large tec fluctuations and short duration depletions that occur in a narrow latitude zone these fluctuations and depletions in tec have been attributed to the combined effect of storm induced equatorward movement of the midlatitude ionospheric trough due to the expansion of auroral oval and the storm time enhanced density the maximum amplitude of the tec depletions is found to be of the order of 20 tecu rate of tec index is also found to be high with a maximum value of 2

diagenetic evolution of the upper cretaceous limestone and sandstone exhumed reservoirs in the western basque cantabrian basin north spain abstract the basque cantabrian basin ne spain has been considered one of the most interesting areas for hydrocarbon exploration in the iberian peninsula since the 60th to 70th of last century this basin is characterized by the presence of numerous outcrops of tar sands closely associated with fractures and triassic diapirs the aims of this work is to establish the diagenetic evolution of the upper cretaceous reservoir rocks with special emphasis in the emplacement of oil and their impact on reservoir quality the studied rocks are constituted of carbonates and sandstones that contain massive quantities of bitumen filling vugs and fractures petrographic results indicate that the carbonate rocks from maestu outcrops are bioclastic grainstones and wackestones whereas the tar sandstones from atauri and loza outcrops are dominated by quartzarenites and subordinated subarkoses the paragenetic sequence of the main diagenetic phases and processes include pyrite bladed and drusy calcite cement calcite overgrowths silicification of bioclasts and microcrystalline rhombic dolomite cement and first stage of oil emplacement blocky calcite cement coarse crystalline calcite cement calcitized dolomite calcite veins saddle dolomite and stylolites filled by the second phase of oil entrance together with the above mentioned diagenetic alterations the arenites are affected by early kaolinitization of feldspars and the scarce formation of clay rim and epimatrix of illite all sandstones and dolomitized carbonate rocks show high intercrystalline and intergranular porosity which is full by biodegraded hydrocarbons solid bitumen the biodegradation affects alkanes isoprenoids and partially hopanes and steranes saturated hydrocarbons aromatics hydrocarbons like naphthalenes phenanthrenes dibenzothiophenes and triaromatics are also affected by biodegradation results indicate that the first hc emplacement corresponds to early stage of calcite and dolomite cementation and the second and more important emplacement is related to fracturation processes resulting in the formation of excellent reservoirs

ionospheric storm of early november 1993 in the indian equatorial region an investigation is made of the response of equatorial ionosphere in the indian 75 e sector to the major magnetic storm of november 3 1993 using data from the ionosonde and magnetometer networks spanning the region 0 3 34 5 n dip some outstanding and new aspects of the storm time ionospheric behaviour are revealed an anomalous and striking positive gradient in 0f2 from the magnetic equator to 34 5 dip developed under counter electrojet cej condition in the morning on november 4 corresponding to the early stage of the storm main phase this storm effect is attributed to plasma transport by a poleward surge in transequatorial winds due to large scale atmospheric gravity waves agws launched by auroral heating remarkable wave like variations in hpf2 and 0f2 immediately followed at locations away from dip equator till local sunset with concomitant disruptions in the development of the equatorial ionization anomaly eia rapid variations in meridional neutral winds due to large scale agws are assessed as the cause of the oscillations in hpf2 and the associated cyclic sequence of development and inhibition of eia as the outcome of the combined effects of plasma transport due to meridional winds and the plasma fountain driven by e b drift just after the onset of the storm recovery phase at 1800 lt a sudden and anomalous drop 54 57 in 0f2 prevailed throughout the anomaly region over the interval 1915 2330 lt with an apparent time delay in occurrence toward the magnetic equator this premidnight collapse of equatorial f region is interpreted in terms of horizontal transport of plasma across the equator toward the opposite hemisphere by an equatorward surge in meridional winds the case study showed that besides disturbances in the zonal electric field due to prompt penetration and ionospheric disturbance dynamo effects perturbations in neutral meridional winds played a prominent role in the ionospheric storm of november 4 1993 in the indian equatorial region

equatorial disturbance dynamo electric fields f region vertical drift data from jicamarca peru show that equatorial east west electric fields are sometimes perturbed 16 24 hours after the onset of geomagnetic storms these disturbance dynamo electric fields which must be caused primarily by the action of neutral winds at low and middle latitudes decrease and sometimes even reverse the quiet time electric field pattern during both daytime and nighttime the long delay excludes the possibility that gravity waves are responsible and suggests that the thermospheric circulation is disturbed the data also show that after some storms there are no such delayed disturbances a fact which may be due to the longitudinal structure of the disturbances at high latitudes and or that only very strong storms can produce major thermospheric perturbations that extend to middle and low latitudes

precambrian dolomites petrographic and isotopic evidence that they differ from phanerozoic dolomites dolomites are more common in precambrian than in phanerozoic rocks and from a petrographic isotopic study of the middle to upper proterozoic beck spring dolomite of eastern california it is suggested that precambrian dolomites are different from those of the phanerozoic petrographically all fabric details of precambrian dolomites studied are preserved just as if they were limestones and isotopically they show the same trend as limestones increasingly negative i8 o and to a lesser extent increasingly light i8 c from depositional components through early fibrous dolomite cements to later dolomite spar cements the data suggest that in precambrian time dolomite was the principal carbonate mineral precipitated from seawater and during diagenesis and this implies that precambrian seawater was different from that of the phanerozoic

low latitude ionospheric disturbance electric field effects during the recovery phase of the 19 21 october 1998 magnetic storm 1 low latitude ionospheric electric fields and currents are often strongly disturbed during periods of enhanced geomagnetic activity these perturbations can last for several hours after geomagnetic quieting we use incoherent scatter radar measurements from jicamarca and arecibo during 19 21 october 1998 to study for the first time the low latitude disturbance electric fields during the recovery phase of a large magnetic storm on 19 october the jicamarca data showed initially large and short lived time scale of about 10 20 min upward and westward drift perturbations in the early afternoon sector due to the penetration of strong magnetospheric electric fields probably driven by an increase in the solar wind dynamic pressure following the decrease of auroral activity very strong afternoon and nighttime zonal and vertical disturbance dynamo drifts were observed over jicamarca but surprisingly only small and sporadic perturbation drifts were present over arecibo the latitudinal variation of the daytime zonal disturbance dynamo drifts during this day is in good agreement with that previously observed for thermospheric disturbance winds the disturbance dynamo drifts also indicate significantly different local storm time and possibly latitudinal dependences for their vertical perpendicular and zonal drift components suggesting large variations in both the amplitude and direction of the disturbance dynamo electric field vector in the next day during moderately disturbed conditions the daytime perturbation drifts were small but following transient increases in geomagnetic activity large upward perpendicular drifts were observed near dusk over jicamarca and arecibo where simultaneous westward perturbation drifts were also seen these perturbations are consistent with the occurrence of strong prompt penetration electric fields reaching the magnetic equator the measured prompt penetration drift patterns are generally in good agreement with predictions from global convection models later at night under moderately disturbed conditions relatively large zonal and meridional disturbance dynamo electric fields were observed by the two radars our results illustrate the large variability of the low latitude perturbation electric fields relative to their climatological values after large storms probably due to the importance of additional disturbance processes they also indicate that a much deeper understanding of solar wind magnetospheric ionospheric processes is required for accurate predictions of these electric fields

large density depletions in the nighttime upper ionosphere during the magnetic storm of july 15 2000 1 we measured electron density and temperature of the nighttime upper ionosphere for the several key intervals during the progress of the magnetic storm on 15 july 2000 with the langmuir probe on korea multipurpose satellite 1 kompsat 1 during the main phase of the storm kompsat 1 detected near 0 e a very deep and extensive trough of electron density centered around the geomagnetic equator the electron density dropped sharply from 4 105cm 3 to less than 2 104cm 3 with the trough region extended over 1400 km along the satellite track later in the recovery phase kompsat 1 observed severe distortion still persisted near 230 e with enhanced density in the southern hemisphere together with dmsp observations we estimate the size of the observed trough to be at least 5500 km in the longitudinal direction dmsp data indicates that the trough was caused by the enhanced eastward electric field which lifted the equatorial f region ionosphere upward

low latitude ionosphere response to super geomagnetic storm of 17 18 march 2015 results from a chain of ground based observations over indian sector in this paper we present unique results of equatorial and low latitude ionosphere response to one of the major geomagnetic storms of the current solar cycle that occurred during 17 18 march 2015 where dst reached its minimum of 228 nt here we utilized data from magnetometers chain of ionosondes located at tirunelveli 8 73 n 77 70 e geometry 0 32 n hyderabad 17 36 n 78 47 e geometry 8 76 n and allahabad 25 45 n 81 85 e geometry 16 5 n along with multistation gps receivers over indian sector the observations showed a remarkable increase of h f to as high as 560 km over tirunelveli magnetic equator with vertical drift of 70 m s at 13 30 ut due to direct penetration of storm time eastward electric fields which exactly coincided with the local time of pre reversal enhancement pre and caused intense equatorial spread f irregularities in ionosondes and scintillations in gps receivers at wide latitudes plasma irregularities are so intense that their signatures are seen in allahabad lucknow storm time thermospheric meridional winds as estimated using two ionosondes suggest the equatorward surge of gravity waves with period of 2 h suppression of anomaly crest on the subsequent day of the storm suggests the complex role of disturbance dynamo electric fields and disturbance wind effects our results also show an interesting feature of traveling ionospheric disturbances possibly associated with disturbance meridional wind surge during recovery phase in addition noteworthy observations are nighttime westward zonal drifts and pre related total electron content enhancements at anomaly crests during main phase and counter electrojet signatures during recovery phase

first observation of interhemispheric asymmetry in the epbs during the st patrick s day geomagnetic storm of 2015 in this work we have studied the characteristics of epbs such as their zonal drift and tilt from the low latitude and dip equatorial region in the indian longitude sector during the main phase of the 17 march 2015 storm all sky airglow imaging observations from tirunelveli 8 7on 77 8oe geographic 1 7on dip latitude and kolhapur 16 7on 74 3oe geographic 11 5on dip latitude are utilized here on 17 march 2015 epbs were observed to drift eastward during 14 30 16 30 ut between 3os and 15on dip latitudes a westward drift presumably under the influence of the disturbance dynamo electric field ddef initially appeared at higher dip latitudes almost 10 hours after the storm onset and subsequently the same was observed at lower dip latitudes the epbs attained a peak westward drift at 17 00 ut followed by a gradual decrease in their speed till 18 30 ut after regaining their westward speed the epbs continued to drift westward till 22 00 ut moreover a latitudinal gradient in the drift motion of the epbs was also observed on this night another interesting observation made from the images obtained from tirunelveli was the presence of a large westward tilt of the epbs the most intriguing finding of this study however was the asymmetry in the tilt of the epbs at conjugate points during the pre midnight hours on 17 march 2015 in this study the possible mechanisms that can explain these observations are discussed in the light of the current understanding of the equatorial electrodynamics and epbs