comparison of berkeley and calnet magnitude estimates as a means of evaluating temporal consistency of magnitudes in california abstract magnitude estimates have been calculated independently by berkeley and the u s geological survey for a large number of events in central california the berkeley magnitudes have been determined using a stable set of wood anderson seismometers for many decades this relative stability allowed us to compare calnet magnitudes with the berkeley magnitudes in an attempt to evaluate the temporal stability of the calnet magnitudes the comparisons were carried out in six different regions of central california for events with 2 5 m berkeley

magnetospheric substorms and nighttime height changes of the f2 region at middle and low latitudes using the published plots of 15 min interval values of h f2 the minimum virtual height of the ionospheric f2 region at five japanese stations spread over 26 45 n 15 35 n geomagnetic and 128 142 e it is shown that there are frequent rapid increases and less frequent decreases of h f2 by 100 200 km in about 2 hours with near simultaneous start and end at all five stations in the postmidnight hours and at three to five stations in the premidnight hours in the months of september and december 1988 and march 1989 about 80 h f2 perturbations of the above type are identified the near simultaneity of the h f2 disturbances at the five stations suggests that an plasma drift due to an east west electric field is the cause of the h f2 disturbances this interpretation is validated by showing that there is a simultaneous presence of bay disturbances in auroral latitude magnetograms over a wide longitude range during almost all the h f2 increases it is shown that neutral wave disturbances propagating equatorward even with a speed of 750 m s cannot account for the h f2 disturbances the study reveals two categories of h f2 perturbations 1 h f2 increases starting near the beginning of the geomagnetic negative bays at auroral latitudes and 2 rapid h f2 increases starting near the maximum intensity phase of the auroral bays and preceded by h f2 decreases starting at the onset time of the bay disturbance or a little earlier using the vast amount of h f2 data collected all over the globe it is possible to quantify and characterize the substorm related electric fields and their variabilities such characterization is very useful in understanding the magnetospheric and the magnetosphere ionosphere interaction processes involved in the generation of magnetospheric substorms it is also pointed out that the understanding of f2 region changes during magnetic storms may improve greatly if the large f2 region changes caused by electric fields on the substorm time scale are taken into account the h f2 disturbances reported in this study are similar in time scale and appearance to the h f2 disturbances caused by long period atmospheric waves and this suggests the possibility of a mixup of the two effects and the consequent wrong identification on some occasions

storm time electric fields in the equatorial ionosphere observed near the dusk meridian 1 we compare the dynamics of plasma drifts vp and ionospheric electric fields ei measured near the dusk meridian at the magnetic equator by the defense meteorological satellite program dmsp f13 satellite with those of the dawn to dusk component of the interplanetary electric field ief ey during four large magnetic storms presented data indicate that during the main phase of the magnetic storms when the interplanetary magnetic field imf had a southward component vp had upward and westward components that ranged up to 120 and 210 m s 1 the corresponding eastward and upward components of ei were approximately 5 and 10 of ey the persistence of eastward ei for many hours indicates that electric field shielding of the inner magnetosphere is ineffective during prolonged periods of southward imf during periods of northward imf ey 0 ionospheric responses depended on prior history no ionospheric response is apparent after strong northward imf turnings preceded by geomagnetic quiet if they occurred after a long southward interval ei often had westward and downward components the polarity of the zonal component of ei remained well correlated with that of ey for up to 21 h during periods of slowly varying imf phenomena associated with southward imf periods are consistent with models that allow for prolonged penetration electric field from high latitudes superposed on those of the sq current system however it is not understood why the remarkable correspondence between the polarities of the zonal component of ei and the ief ey occurs during northward imf in some ey 0 periods the vertical component of ei remained upward dmsp detections of upward ei westward vp during periods of ey 0 are not predicted by existing models

low latitude zonal and vertical ion drifts seen by de 2 horizontal and vertical ion drift data from the de 2 spacecraft have been used to determine average zonal and vertical plasma flow electric field characteristics in the plus minus 26 degree dip latitude region during a time of high solar activity the data base consists of over 800 equatorial passes horizontal ion drift data were projected along magnetic field lines to the magnetic equator using a dipole model to yield their apex height dependence the average data local time profile for an apex height bin centered at 400 km indicates westward plasma flow from 0600 to 1900 solar local time slt with a maximum westward velocity of 80 m s in the early afternoon there is a sharp change to eastward flow at approximately 1900 hours with an early evening peak of 170 m s a secondary nighttime maximum exists a 0430 slt preceeding the reversal to westward flow this profile is in good agreement with jicamarca radar measurements made under similar solar maximum conditions harmonic analysis indicates a net superrotation which is strongest at lower apex altitudes the diurnal term is dominant but higher order terms through th quatradiurnal are significant vertical ion data taken at low plus minus 5 degree dip latitudes while possessing greatermore scatter generally agree wtih jicamarca values copyright american geophysical union 1989 less

advection of the equatorial anomaly over arecibo by small storm related disturbance dynamo electric fields during highly disturbed geomagnetic periods both the arecibo radar and the ramey ionosonde have recorded impressive nighttime ionospheric enhancements in which the peak electron density exceeded 1 1012 m 3 and the f2 peak height went above 400 km in the past it has been suggested that these events could be caused by either a downward plasmaspheric flux that increases the density in the f region or by an eastward electric field that pushes the equatorial anomaly poleward to the caribbean sector on february 17 18 1999 the arecibo radar made observations during an event in which the electron density again rose to daytime values near midnight for this event the peaks in density were observed predominantly southeast of arecibo while the ions sustained a northward eastward motion due to an eastward southward storm dynamo electric field tec maps from gps for this night confirmed that the density enhancements were due to a poleward expansion of the equatorial anomaly

westward plasma drift in the midlatitude ionospheric f region in the midnight dawn sector in this paper we report the observations of a sharp ionospheric plasma velocity reversal boundary at subauroral latitudes during magnetic storms in the midnight dawn sector the zonal plasma drift was eastward poleward of the velocity boundary and became westward equatorward of the boundary the latitudinal extent of the westward drifts was 20 a local maximum of the drift occurred only 2 5 below the boundary the magnitude of the maximum velocity was 200 400 m s 1 between 2100 and 0300 local time lt and as high as 780 m s 1 near midnight the large westward plasma drift immediately equatorward of the velocity boundary first occurred at 2100 lt and continuously extended across midnight to the dawn sector the location of the maximum velocity coincided with the minimum density within the midlatitude ionospheric trough the latitude of the velocity boundary decreased from geographic latitude 53 to 43 corresponding to geomagnetic latitude 65 to 55 between 2100 and 0800 lt we propose that the large westward drift at subauroral latitudes is driven by the polarization jet electric fields in the ring current and that the lower latitude westward drift with moderate magnitude is caused by the disturbance wind dynamo

long duration penetration of the interplanetary electric field to the low latitude ionosphere during the main phase of magnetic storms 1 it is well known that the interplanetary electric field can penetrate to the low latitude ionosphere it is generally believed that the penetration of electric fields can last only for 30 min because of the shielding effect in the ring current in this paper we present the observations of the dayside ionospheric electric field enhancements at middle and low latitudes in association with reorientations of the interplanetary magnetic field imf in six cases the eastward electric field in the dayside equatorial ionosphere measured by the jicamarca incoherent scatter radar was enhanced for 2 3 hours after the imf turned southward and remained continuously southward in one case the eastward electric field in the dayside midlatitude ionosphere measured by the millstone hill incoherent scatter radar was continuously enhanced for 10 hours during southward imf since millstone hill is close to the equatorward boundary of the auroral zone during magnetic storms the penetration electric field there may be different from that at the equatorial ionosphere the most striking feature of the measurements is that the enhancements of the ionospheric electric field can last for many hours without significant decay the electric field enhancements in the middle and low latitude ionosphere are closely related to magnetic activity and occur during the main phase of magnetic storms the observations show that the interplanetary electric field can continuously penetrate to the low latitude ionosphere without shielding for many hours as long as the strengthening of the magnetic activity is going on under storm conditions

observations from millstone hill during the geomagnetic disturbances of march and april 1990 the incoherent scatter radars at millstone hill operated continuously during the periods march 16 23 and april 6 12 1990 providing observations of large scale ionospheric structure and dynamics over a large portion of eastern north america major geomagnetic storms occurred during each of these periods with deep nighttime ionospheric troughs and large magnetospheric convection electric fields observed equatorward of millstone the millstone observations provide a comprehensive data set detailing storm induced ionospheric effects over a 35 span of latitude during both of these intervals at the latitude of millstone the ionospheric peak height hmf2 rose above 600 km in the trough on march 22 and 23 and reached 500 km at night on april 11 and 12 increased recombination apparently due to the strong electric fields the temperature dependent recombination rate coefficient and neutral composition changes greatly depleted the f2 region over a wide latitude range during the day on april 10 1990 this resulted in an ionosphere dominated by molecular ions with ionospheric peak heights below 200 km on this day a number of frictional heating events during the disturbed periods are seen from comparison of ion temperature and velocity measurements the most intense event took place near 1200 ut 0715 lmt on april 10 1990 when kp reached 8 at 0110 ut on march 21 line of sight ion velocities in excess of 500 m s 1 were observed at the extreme southern limit of the millstone steerable radar s field of view 40 apex magnetic latitude at an altitude of 700 km these could be due to penetration of magnetospheric electric fields or electric fields associated with ring current shielding in the storm time outer plasmasphere about an hour later ion outflow was observed just equatorward of millstone this is most likely due to heating from a latitudinally confined region of intense westward convection neutral meridional winds above millstone were obtained by three different techniques employing radar and fabry perot measurements the latitude variation of the winds was also estimated from radar measurements of hmf2 and electric fields using the servo model method strong equatorward nighttime neutral wind surges were found during both the march and april disturbances which reached the equatorward limit of the observations at f peak heights

east west ion drifts at mid latitudes observed by dynamics explorer 2 zonal ion drifts measured from the polar orbiting de 2 spacecraft are examined to determine the effects of dynamo electric fields and penetration of high latitude electric fields at middle latitudes construction of a local time distribution from satellite data results in a mixture of local time and season as well as a range of magnetic activity encompassing kp le 2 and kp ge 3 thus some combination of magnetospheric effects expected to dominate during disturbed times are seen during both quiet and disturbed times and solar tidal influences are most easily observed during quiet times during quiet times at invariant latitudes near 25 degrees the solar diurnal tide dominates the local time distribution of the ion drift at latitudes above 50 degrees a diurnal component of comparable magnitude is also present but its magnetospheric origin produces a shift in phase of almost 180 degrees from the lower latitude diurnal tide in the intervening region between 20 degrees and 50 degrees invariant latitude semidurnal and terdiurnal components in the local time distribution of the drift velocity are also seen these components are generally larger than those seen by ground based radars during quiet times and may be attributable in part to a difference in solarmore activity and in part to a combination of the solar tides and magnetospheric penetration fields less

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

equatorial ionospheric plasma bubble irregularity occurrence and zonal velocities under quiet and disturbed conditions from polarimeter observations amplitude scintillation and faraday rotation angle fluctuations of satellite vhf beacons registered by electronic polarimeters operated at two stations spaced 110 km apart in the magnetic east west direction namely cachoeira paulista 22 41 s 45 w dip angle of 26 and sao jose dos campos 23 12 s 45 51 w dip angle of 26 in brazil are analyzed for equinoctial and summer months of 1982 1983 to determine the irregularity patch occurrence characteristics and their zonal velocities under varying levels of magnetic disturbances the scintillation patch occurrences and total electron content fluctuations representing plasma depletion structures decrease during premidnight hours and are enhanced in the postmidnight period the occurrences often extend to morning hours with increasing magnetic activity index while the night events are associated with eastward irregularity patch motion the morning events have westward velocities the reversal occurring around 0400 lt reflecting the morning velocity reversal in the f region bulk plasma motion reported earlier from jicamarca radar measurements the westward plasma bubble motions reported here represent the first observation of this kind another important finding from the present investigation is a clear tendency for the zonal plasma motion namely the equatorial meridional electric field to become enhanced mainly in the premidnight hours immediately following strong magnetic activity

highly structured tropical airglow and tec signatures during strong geomagnetic activity a remarkable set of all sky images using the 630 nm airglow emission has been taken over the arecibo observatory in puerto rico wave like structures at a height of about 250 km are commonly found to travel in the southwest direction at speeds ranging from 20 120 m s most surprising is that geomagnetic activity seems to greatly amplify them forming very intricate patterns of light and dark simultaneous observations using gps satellite transmissions on one night reveal that dark regions are severely plasma depleted while bright regions have nighttime content as large as the full noontime ionosphere this unexpected geomagnetic effect at mid latitudes has implications for trans ionospheric radiowave propagation and space weather

statistical analysis of dayside equatorial ionospheric electric fields and electrojet currents produced by magnetospheric substorms during sawtooth events 1 substorms cause significant disturbances in the ionosphere however it has not been well understood how the electric field and electrojet in the dayside equatorial ionosphere respond to substorm onset previous studies found that the equatorial electric field after substorm onset could be eastward or westward because the onset of isolated substorms is often related to a northward turning of the interplanetary magnetic field imf the measured total electric field is determined by contributions from both imf northward turning and substorm onset and is not necessarily the signature of the onset in order to exclude the effect of imf northward turning we analyze the variations of ionospheric electric field and electrojet during storm time substorms when the imf remains stable thus the ionospheric variations can be identified to be caused solely by substorms the electric field data are measured by the jicamarca radar and the electrojet is derived from magnetometers at jicamarca and piura it is found that substorm onset induces an eastward electric field and electrojet in the dayside equatorial ionosphere when the imf remains continuously southward across the onset the equatorial electrojet starts to increase at the onset reaches a maximum value 30 min after the onset and then decreases to the pre onset value 60 min after the onset westward electric field and counter electrojet occur only if the substorm onset is associated with a northward turning of the imf it is concluded that the effect of substorm onset on the dayside equatorial ionosphere without involvement of imf reorientations is an enhanced eastward electric field

petrochemistry of the late archaean granites of the chinamora batholith zimbabwe abstract at least the lowermost successions of the main greenstone belts which surround the chinamora batholith were intruded by several discrete granite plutons prior to the intrusion of the great dyke into the rhodesian craton ca 2500 ma ago but after ca 2800 ma ago the intruded granites constitute the chinamora igneous granite suite c i g s the c i g s was emplaced over a time period spanning two tectonic events and the granites display considerable variation in both field and petrochemical characteristics the oldest plutons contain rather higher contents of mafic minerals than the younger ones and have on the whole undergone more intense deformation hence the recognition of two groups of plutons the older gneissic granites mainly trondhjemites and the younger late granites mainly granites samples from each of 22 plutons were analysed for both major and trace elements consideration of the major element data indicates that the c i g s plutons show characteristics of a calc alkaline suite the trace element data suggest that the c i g s has evolved by fractional crystallization in order to explain the origin of the oldest of the gneissic granite plutons a model deriving these plutons from a magma formed by a major addition of basaltic magma to the lower crust and its mixing with a partial melt derived from sialic crust is postulated the ultimate source material for the late granites is not known but simple modelling does show that their origin can be explained by fractionation along a liquid line of descent

seasonal and magnetic activity variations of ionospheric electric fields over millstone hill incoherent scatter observations of e and f region drifts over millstone hill 42 6 n were made routinely from may 1976 to november 1977 at monthly intervals some 667 hours of data gathered over this 19 month period have been analyzed to yield the ionospheric polarization electric field in the magnetic south and magnetic east directions for three seasons during quiet magnetic conditions as well as the annual average during magnetically disturbed conditions kp 3o the results for the quiet days are compared with earlier results obtained at millstone hill kirchhoff and carpenter 1976 and with those reported from st santin 44 6 n by blanc and amayenc 1979 we find that there is best agreement between millstone and st santin for the east west component of the field which exhibits a roughly 12 hour period variation during the daytime in all seasons the north south field exhibits a predominantly diurnal variation that in winter and equinox is almost identically opposite at the two stations this component shows substantial changes in summer at both stations and at millstone appears to exhibit a significant 1mv m average northward component not seen at st santin we attribute the differences in the quiet time behavior observed at millstone and st santin to the very large difference in the latitude of their conjugate points where presumably the tides and hence the dynamo effects are dissimilar there are marked differences in the electric field patterns between disturbed and quiet times which mainly are evident in the nighttime period commencing after noon there is a gradual enhancement of both the northward and eastward fields on disturbed days the eastward field reverses near midnight and becomes westward until dawn while the other component remains northward for most of the night these changes are thought to result from the penetration of auroral electric fields inside the plasmasphere

electrodynamic coupling of high and low latitudes observations on may 27 1993 the penetration of disturbance electric fields from the polar region to the magnetic equator on the dayside of the earth is examined with geomagnetic data on may 27 1993 first we examine a dayside equatorial disturbance that followed the rapid recovery of magnetic activity from a storm and that has the characteristics of overshielding caused by persistent region 2 field aligned currents it lasted 0 3 hours second we analyze a series of fluctuations with periods of 25 75 min to determine the variations of amplitude and phase with magnetic latitude and magnetic local time the fluctuations were highly coherent at all latitudes between the magnetic equator and the auroral zone but the coherency decreasedin the polar cap a northward fluctuation at the equator during midday hours accompanied auroral zone fluctuations that were southward before noon eastward around noon and northward after noon the amplitudes decreased away from the auroral zone toward midlatitudes but were amplified under the equatorial electrojet no detectablep hased ifferencesa re found indicating that any temporal lags which might be inducedb y persistencein the region 2f ield alignedc urrentsa re less than i min for fluctuations having periods like those examined here a synoptic inversion analysis of the high latitude magnetic data to estimate the time varying high latitude electric potential patterns shows that fluctuations of the high latitude east west potential gradient tended to be concentrated around midday where they were in phase with fluctuations in the midday east west potential gradient at the magnetic equator

auroral currents during the magnetic storm of november 8 and 9 1991 observations from the upper atmosphere research satellite particle environment monitor the magnetic storm of november 8 and 9 1991 lead to expansion of the auroral oval below 45 magnetic latitude mlat and auroral phenomena were sampled by the upper atmosphere research satellite uars the attitude precision and stability of uars allow monitoring of birkeland and ionospheric currents via magnetic field measurements from the particle environment monitor pem magnetometer this paper reports the development of the intensity and location of birkeland currents associated with this storm two principle results are obtained 1 total birkeland currents exceed 30 ma more than 6 times nominal values indicating joule heating of about 3 1012 w 2 birkeland currents below 50 polar cap currents indicative of anti sunward convection and cusp particle signatures of southward imf all persist at least eight hours into recovery phase of the storm

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

on the latitudinal variations of the ionospheric electric field during magnetospheric disturbances a joint alert campaign was organized during the month of october 1980 by the incoherent scatter radars in the american sector namely jicamarca arecibo millstone hill and chatanika the campaign which met with success was designed to study the behavior of the ionospheric electric field as a function of latitude during magnetically active conditions the arecibo data in this campaign support present and previous observations at jicamarca that suggest that when the convection e field suddenly decreases the alfven layer shielding field becomes unbalanced and penetrates the plasmasphere while this type of observation is reasonably convincing others are more difficult to categorize we suggest that beside the high latitude electric fields time varying auroral conductivity models will have to be considered in order to understand the morphology of the low latitude e field disturbances we present the first correlation analysis and determination of the amplitude ratio of the disturbed zonal electric field at 30 geometric latitude arecibo to the field at 0 jicamarca other highlights of the paper are a discussion of dp2 which may help clarify the controversy surrounding it and a discussion of the sensitivity of low and mid latitude radars to disturbances of magnetospheric origin we show that this sensitivity maximizes at the magnetic equator

f region east west drifts at jicamarca f region east west drifts have been measured at jicamarca for almost 10 years using incoherent scatter the drifts are westward during the day and eastward at night the daytime drift velocities are about 50 m s and change very little with season or solar cycle the evening reversal occurs at about 1600 local time throughout the solar cycle the maximum nighttime eastward drifts are about 105 and 130 m s during solar minimum and maximum respectively the daytime and nighttime drifts show very litle variation with magnetic activity these jicamarca incoherent scatter results especially the reversal times differ appreciably from results obtained using other techniques but there appear to be fairly simple explanations for the apparent disagreements

transient composite electric field disturbances near dip equator associated with auroral substorms ionosonde data of kodaikanal geog long 77 29 e dip 3 0 n and huancayo geog long 75 18 w dip 2 0 n are used to show the simultaneous occurrence of a transient disturbance in f region height of composite polarity in day and night sectors near the dip equator during the auroral substorm activity on 20 august 1979 at kodaikanal which is on the nightside at the time of the substorm activity h f first underwent an abrupt and rapid decrease 80km in 1 hr followed by a much larger increase 120km in 1 hr perturbation in hpf2 of exactly opposite polarity was simultaneously seen at huancayo which is on the dayside the decrease in h f at kodaikanal increase in hpf2 at huancayo occurred in association with an increase in polar cap potential drop o estimated from imf parameters and the subsequent increase decrease at huancayo with a decrease in polar cap potential the f region height disturbance is interpreted as the manifestation of a global transient composite disturbance in equatorial zonal electric field caused by the prompt penetration of substorm related high latitude electric fields into the equatorial ionosphere the polarity pattern of the electric field disturbance is consistent with the global convection models which predict westward eastward electric fields at night by day near the geomagnetic equator in response to an increase in polar cap potential drop and fields of opposite signs for a decrease in polar cap potential

on the vertical drift of ionospheric f layer during disturbance time results from ionosondes the morphology of low latitude ionosphere is greatly affected by the zonal electric field especially at disturbance time in this study historical data from two low latitude ionosondes located at haikou and chongqing china are used to study the disturbance vertical drift properties of ionospheric f layer during the initial and main phases of 50 intense storms the disturbance drift from an empirical model is used as an indicator to denote the e x b disturbance magnitude it is found that the drifts both at the base and at the peak height are increased in magnitude when the disturbance becomes stronger for the same disturbance ionospheric vertical drifts at the base height are comparable with those at the peak height over haikou but they are larger than the latter over chongqing both drifts being smaller than those at the magnetic equator the drifts are larger in daytime than in nighttime but no rule is found on their seasonal dependence this indicates that low latitude storm time ionospheric vertical drift of the ionospheric layer exhibits both consistent and individual properties at different locations

on the latitudinal changes in ionospheric electrodynamics and composition based on observations over the 76 77 e meridian from both hemispheres during a geomagnetic storm the relative contributions of the composition disturbances and the disturbance electric fields in the redistribution of ionospheric plasma is investigated in detail by taking the case of a long duration positive ionospheric storm that occurred during 18 21 february 2014 gps total electron content tec data from the indian antarctic station bharti 69 4 s 76 2 e geographic the northern midlatitude station hanle 32 8 n 78 9 e geographic northern low latitude station lying in the vicinity of the anomaly crest ahmedabad 23 04 n 72 54 e geographic dip latitude 17 n and the geomagnetic equatorial station trivandrum 8 5 n 77 e geographic dip latitude 0 01 s are used in the study these are the first simultaneous observations of tec from bharti and hanle during a geomagnetic storm the impact of the intense geomagnetic storm dst 130 nt on the southern hemisphere high latitude station was a drastic reduction in the tec negative ionospheric storm starting from around 0330 indian standard time ist on 19 february which continued till 21 february the maximum reduction in tec at bharti being 35 tec units on 19 february in the northern hemisphere midlatitude and equatorial stations a positive ionospheric storm started on 19 february at around 0900 ist and lasted for 3 days the maximum enhancement in tec at hanle was about 25 tecu on 19 february while over trivandrum it was 10 tecu this long duration positive ionospheric storm provided an opportunity to assess the relative contributions of disturbance electric fields and composition changes latitudinally the results indicate that the negative ionospheric storm over bharti and the positive ionospheric storm over hanle are the effect of the changes in the global wind system and the storm induced composition changes at the equatorial latitudes the positive ionospheric storm was due to the interplay of prompt penetration electric field and disturbance dynamo electric field

impact of oscillating imf bz during 17 march 2013 storm on the distribution of plasma over indian low latitude and mid latitude ionospheric regions we show evidence of a positive ionospheric storm occurring simultaneously at the equatorial low and mid latitude ionospheric regions in the indian sector in response to an intense geomagnetic storm on 17 march 2013 the storm had its onset time coinciding with the local noon an on site digisonde at trivandrum dip equator recorded a sharp decrease in the height of f region peak in the afternoon which is a signature of westward electric field associated with a cej coupled with it was a simultaneous increase in tec in the entire indian region the magnitude of increase in tec decreased slowly northward of the dip equator and had almost no change near the anomaly crest further northward of the anomaly crest the tec started increasing again and at shimla a mid latitude station it had a value close to 2 times its monthly mean we surmise that the westward electric field resulting from the cej pushed the f layer at the dip equator down to the altitude regions where recombination and diffusion played minimal roles no loss of plasma due to diffusion while photo production of ions was still taking place led to an enhancement in the electron density near the equatorial low latitude region the joule heating of the thermosphere on the other hand gave rise to the tads which pushed the plasma up in altitude at the equatorial anomaly region it supplemented the loss of plasma at the anomaly crest region resulting in no change in the tec and a marked increase in the tec in the mid latitude ionosphere