Browsing by Author "Abdu, M. A."
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Item Open Access Abnormal evening vertical plasma drift and effects on ESF and EIA over Brazil-South Atlantic sector during the 30 October 2003 superstorm(American Geophysical Union, 2008-11) Abdu, M. A.; De Paula, E. R.; Batista, I. S.; Reinisch, B. W.; Matsuoka, M. T.; Camargo, P. O.; Veliz, Oscar; Denardini, C. M.; Sobral, J. H. A.; Kherani, E. A.; De Siqueira, P. M.Equatorial F region vertical plasma drifts, spread F and anomaly responses, in the south American longitude sector during the superstorm of 30 October 2003, are analyzed using data from an array of instruments consisting of Digisondes, a VHF radar, GPS TEC and scintillation receivers in Brazil, and a Digisonde and a magnetometer in Jicamarca, Peru. Prompt penetrating eastward electric field of abnormally large intensity drove the F layer plasma up at a velocity 1200 ms−1 during post dusk hours in the eastern sector over Brazil. The equatorial anomaly was intensified and expanded poleward while the development of spread F/plasma bubble irregularities and GPS signal scintillations were weaker than their quiet time intensity. Significantly weaker F region response over Jicamarca presented a striking difference in the intensity of prompt penetration electric field between Peru and eastern longitudes of Brazil. The enhanced post dusk sector vertical drift over Brazil is attributed to electro-dynamics effects arising energetic particle precipitation in the South Atlantic Magnetic Anomaly (SAMA). These extraordinary results and their longitudinal differences are presented and discussed in this paper.Item Open Access Abnormally large magnetospheric electric field on 9 November 2004 and its effect on equatorial ionosphere around the world(Springer Verlag, 2012-10) Rastogi, R. G.; Chandra, H.; Condori, Louis; Abdu, M. A.; Reinisch, B.; Tsunoda, R. T.; Prasad, D. S. V. V. D.; Pant, T. K.; Maruyama, T.There was a solar event around 1850 UT on 9th November 2004, associated with an abnormally large solar wind flow pressure and large southward interplanetary magnetic field, causing an abnormally large prompt penetration electric field between 1850 and 2100 UT. Abnormally large vertical F-region drifts by Jicamarca backscatter radar were reported associated with the event. The F-region over Jicamarca, Peru (14–16 LT) and Sao Luis, Brazil (16–18 LT) was lifted upward, broken into two portions and the upper one was blown out of the range of the ionosonde. At Fortaleza, an off-equatorial station in Brazil, the F-region was also lifted up but later the foF2 increased due to the flow of ionization from upper layer blown up over the equatorial region. The F-region at Ascension Island (19–21 LT), an off-equatorial station, was lifted up without any deformations till 1915 LT but descended at 1930 LT due to reversal of electric field polarity. At Indian stations, Trivandrum and Waltair (00–02 LT), the F-region was pushed down and later disappeared as a consequence of enhanced westward ionospheric electric field in the night sector. The ionosonde did not receive any echo for a couple of hours till the next sunrise. The F-region at Kototaban (03–05 LT), Indonesia also disappeared after a rapid descend. At Kwajelien (06–08 LT) there was no equatorial type of sporadic-E at 07 to 09 LT due to the westward electric field.Item Restricted Disturbance zonal and vertical plasma drifts in the Peruvian sector during solar minimum phases(American Geophysical Union, 2016-02-11) Santos, A. M.; Abdu, M. A.; Souza, J. R.; Sobral, J. H. A.; Batista, I. S.In the present work, we investigate the behavior of the equatorial F region zonal plasma drifts over the Peruvian region under magnetically disturbed conditions during two solar minimum epochs, one of them being the recent prolonged solar activity minimum. The study utilizes the vertical and zonal components of the plasma drifts measured by the Jicamarca (11.95°S; 76.87°W) incoherent scatter radar during two events that occurred on 10 April 1997 and 24 June 2008 and model calculation of the zonal drift in a realistic ionosphere simulated by the Sheffield University Plasmasphere‐Ionosphere Model‐INPE. Two main points are focused: (1) the connection between electric fields and plasma drifts under prompt penetration electric field during a disturbed periods and (2) anomalous behavior of daytime zonal drift in the absence of any magnetic storm. A perfect anticorrelation between vertical and zonal drifts was observed during the night and in the initial and growth phases of the magnetic storm. For the first time, based on a realistic low‐latitude ionosphere, we will show, on a detailed quantitative basis, that this anticorrelation is driven mainly by a vertical Hall electric field induced by the primary zonal electric field in the presence of an enhanced nighttime E region ionization. It is shown that an increase in the field line‐integrated Hall‐to‐Pedersen conductivity ratio urn:x-wiley:21699380:media:jgra52445:jgra52445-math-0001, which can arise from precipitation of energetic particles in the region of the South American Magnetic Anomaly, is capable of explaining the observed anticorrelation between the vertical and zonal plasma drifts. Evidence for the particle ionization is provided from the occurrence of anomalous sporadic E layers over the low‐latitude station, Cachoeira Paulista (22.67°S; 44.9°W)—Brazil. It will also be shown that the zonal plasma drift reversal to eastward in the afternoon two hours earlier than its reference quiet time pattern is possibly caused by weakening of the zonal wind system during the prolonged solar minimum period.Item Restricted Equatorial electrojet 3-M irregularity dynamics during magnetic disturbances over Brazil: results from the new VHF radar at São Luı́s(Elsevier, 2003-10) Abdu, M. A.; Dinardini, C. M.; Sobral, J. H. A.; Batista, I. S.; Muralikrishna, P.; Iyer, K. N.; Veliz, O.; De Paula, E. R.Data collected during the first two observational campaigns, conducted in August 1998 and December 1999, using the new coherent back-scatter radar, developed at INPE, that became operational at the magnetic equatorial site at São Luı́s, (2.33S,44.2W), Brazil, are analyzed in this paper. The spatial and temporal distribution of 3-m irregularity power in the form of range–time–intensity maps and spectral distribution in the form of spectrograms are analyzed for ‘quiet’ conditions and during geomagnetic storm disturbances. The analysis has brought out some new findings, besides confirming some of the already known storm response features of the EEJ and its plasma instabilities. Among the highlights of the results are: the electrical coupling between the equatorial and auroral electrojets is important even on a ‘quiet’ day, and gets very strong during magnetic storm disturbances; disturbance prompt penetration electric field, and the delayed electric field from disturbance dynamo, control the 3-m plasma wave development and inhibition in different degrees during the storm main phase and recovery phase; the amplitudes of the disturbance are larger during the morning hours than in the afternoon, in agreement with theoretical models; the height dependence of the relative dominance of the type-1 and type-2 waves generated by disturbance electric field is different from that of quiet conditions, the relative power of the type-2 getting enhanced at higher levels in the former case. A few other results are also discussed in this paper.Item Restricted Equatorial electrojet responses to intense solar flares under geomagnetic disturbance time electric fields(American Geophysical Union, 2017-01-12) Abdu, M. A.; Nogueira, P. A. B.; Souza, J. R.; Batista, I. S.; Dutra, S. L. G.; Sobral, J. H. A.Large enhancement in the equatorial electrojet (EEJ) current can occur due to sudden increase in the E layer density arising from solar flare associated ionizing radiations, as also from background electric fields modified by magnetospheric disturbances when present before or during a solar flare. We investigate the EEJ responses at widely separated longitudes during two X‐class flares that occurred at different activity phases surrounding the magnetic super storm sequences of 28–29 October 2003. During the 28 October flare we observed intense reverse electrojet under strong westward electric field in the sunrise sector over Jicamarca. Sources of westward disturbance electric fields driving large EEJ current are identified for the first time. Model calculations on the E layer density, with and without flare, and comparison of the results between Jicamarca and Sao Luis suggested enhanced westward electric field due to the flare occurring close to sunrise (over Jicamarca). During the flare on 29 October, which occurred during a rapid AE recovery, a strong overshielding electric field of westward polarity over Jicamarca delayed an expected EEJ eastward growth due to flare‐induced ionization enhancement in the afternoon. This EEJ response yielded a measure of the overshielding decay time determined by the storm time Region 2 field‐aligned current. This paper will present a detailed analysis of the EEJ responses during the two flares, including a quantitative evaluation of the flare‐induced electron density enhancements and identification of electric field sources that played dominant roles in the large westward EEJ at the sunrise sector over Jicamarca.Item Restricted Equatorial F region evening vertical drift, and peak height, during southern winter months: A comparison of observational data with the IRI descriptions(Elsevier, 2006-05-03) Abdu, M. A.; Batista, I. S.; Reinisch, B. W.; Sobral, J. H. A.; Carrasco, A. J.The equatorial F region evening vertical drift, due to pre-reversal electric field enhancement, is an important condition for the spread F/plasma bubble irregularity generation, that is more frequent during summer-equinoctial months over South America. A comparative study of these vertical drifts with their IRI representations was presented at the Grahamstown IRI 2003 workshop. During southern winter months the post-sunset ESF development is relatively infrequent over South America due to the generally weaker intensity of the sunset zonal electric field, which, however, is critical in determining the equatorial spread F (ESF) development under magnetospherically disturbed conditions. Therefore a detailed understanding of the characteristics of the evening F layer vertical drift, hmF2 and foF2 during southern winter months is important for developing/improving their representations in the IRI scheme. In this paper we have undertaken a study of these parameters over the Brazilian equatorial sites, Sao Luis (2.33S, 44.2W, dip angle: −0.5°, declination angle: 21W°) and the low latitude site, Cachoeira Paulista (22.6°S, 315°E; dip angle: −32°) in comparison with their existing representations in the IRI. The study is made as a function of the solar flux varying from the solar activity minimum to maximum conditions. Some of the results in the Brazilian longitude sector are compared with results from Jicamarca (12°S, 76.9°W; dip latitude: 1°N, declination angle: ∼3°E) in Peru, separated by a large difference in magnetic declination angle. The magnetic equatorial and the low latitude stations analyzed here are all located in the southern geographic hemisphere. Systematic patterns of difference between the observed characteristics of these parameters and their IRI representations are identified for eventual corrections to their existing representations in the IRI model. The study has yielded further important clues towards a better understanding of the possible mechanism for the infrequent ESF occurrence in winter over South America, and especially over Brazil.Item Restricted Equatorial F-layer heights, evening prereversal electric field, and night E-layer density in the American sector: IRI validation with observations(Elsevier, 2004) Abdu, M. A.; Batista, I. S.; Reinisch, B. W.; Carrasco, A. J.The equatorial F-layer height variations resulting from the variabilities in the zonal electric fields and winds and associated variability in ionospheric dynamo strength are important factors in determining the distribution and structuring of the electron density of the equatorial ionization anomaly (EIA) region. Especially, the evening enhancement in the F-layer heights and the associated prereversal enhancement in the zonal electric field due to the F-layer dynamo are believed to provide the most basic precondition for the equatorial spread F plasma bubble irregularity (ESF) generation. A realistic description by the International Reference Ionosphere (IRI) of the quiet time equatorial F-layer heights is therefore of fundamental importance for applications related to the studies of the ESF and EIA variabilities. The existing IRI description scheme (that uses the CCIR coefficients) appears to represent the equatorial F-layer peak density (N m F 2 ƒ o F2) better than the peak height (h m F2) and the heights of specific densities, the largest disagreement with observations being verified during the evening hours. Digisonde data from the three permanent stations in Brazil: Sao Luis (2.33S, 44.2W, dip angle: − . 5); Fortaleza (3.9S, 38.45W, dip angle: − 9); and Cachoeira Paulista (22.6S, 315E; dip angle: − 28) and from Jicamarca (12S, 76.9W; dip latitude: 1N) in Peru have been analysed, to determine the quiet time mean behavior of the key F-layer parameters as a function of local time, season, and solar activity. These are complemented by data from the three conjugate point stations: Boa Vista (02.8N; 60.66W, dip angle: 22.5) in the north and Campo Grande (20.45S; 54.65W, dip angle: − 22.5) in the south, and an equatorial station, Cachimbo (9.47S; 54.83W, dip angle: − 3.9) that were operated during the 2002 COPEX (Conjugate Point Experiment) campaign conducted in Brazil. The data for São Luis and Jicamarca are used to evaluate the longitudinal differences in the prereversal F-layer vertical drift, arising from the large magnetic declination angle difference that characterize these Brazilian and Peruvian longitude sectors. An attempt is made to characterize and quantify any systematic difference that exists between the mean behavioral patterns of the critical parameters as described by the IRI and those observed, with an objective to improve the IRI prediction capability.Item Open Access Equatorial ionospheric electric fields during the November 2004 magnetic storm(American Geophysical Union, 2007-10) Fejer, B. G.; Jensen, J. W.; Kikuchi, T.; Abdu, M. A.; Chau Chong Shing, Jorge LuisWe 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.Item Restricted F3 layer during penetration electric field(American Geophysical Union, 2008-09-04) Balan, N.; Thampi, S. V.; Lynn, K.; Otsuka, Y.; Alleyne, H.; Watanabe, S.; Abdu, M. A.; Fejer, B. G.The occurrence of an additional layer, called F3 layer, in the equatorial ionosphere at American, Indian, and Australian longitudes during the super double geomagnetic storm of 7–11 November 2004 is presented using observations and modeling. The observations show the occurrence, reoccurrence, and quick ascent to the topside ionosphere of unusually strong F3 layer in Australian longitude during the first super storm (8 November) and in Indian longitude during the second super storm (10 November), all with large reductions in peak electron density (Nmax) and total electron content (GPS‐TEC). The unusual F3 layers can arise mainly from unusually strong fluctuations in the daytime vertical E × B drift as indicated by the observations and modeling in American longitude. The strongest upward E × B drift (or eastward prompt penetration electric field, PPEF) ever recorded (at Jicamarca) produces unusually strong F3 layer in the afternoon hours (≈1400–1600 LT) of PPEF, with large reductions in Nmax and TEC; the layer also reappears in the following evening (≈1700–1800 LT) owing to an unusually large downward drift. At night, when the drift is unusually upward and strong, the F region splits into two layers.Item Restricted Longitudinal variation in Global Navigation Satellite Systems TEC and topside ion density over South American sector associated with the four‐peaked wave structures(American Geophysical Union, 2013-12-10) Nogueira, P. A. B.; Abdu, M. A.; Souza, J. R.; Bailey, G. J.; Batista, I. S.; Shume, E. B.; Denardini, C. M.Recent observations of the low‐latitude ionospheric electron density revealed a four‐peaked longitudinal structure in the equatorial ionization anomaly when plotted at a constant‐local‐time frame. It was proposed that neutral wind‐driven E region dynamo electric fields due to nonmigrating tidal modes are responsible for this pattern. We examine the four‐peaked structure in the observed topside ion density and its manifestation as longitudinal structures in total electron content (TEC) over South America. The strong longitudinal variation in TEC characterized by larger value over Brazilian eastern longitude sector as compared to that over the Peruvian western longitude is modeled using the Sheffield University plasmasphere‐ionosphere model (SUPIM) aiming to identify the control factors responsible for the longitude variation. We found that the SUPIM runs using as input the existing standard models of vertical drift, and thermospheric winds do not explain the TEC longitudinal structure. Realistic values of these control parameters were generated based on the strong vertical drift longitudinal variation as determined from magnetometer and Digisonde data and appropriately adjusted winds (horizontal wind model). These realistic vertical drifts together with the modified thermospheric wind, when used as input to the SUPIM, are found to satisfactorily explain the longitudinal differences in the TEC and topside ion density (Ni) over South America. The study shows that the TEC in the whole latitude distribution is larger over the east coast than over the west coast of South America and that the vertical drift and thermospheirc winds control the longitudinal four wave structure in the TEC and Ni.Item Restricted Low‐ and mid‐latitude ionospheric electric fields during the January 1984 GISMOS Campaign(American Geophysical Union, 1990-03) Fejer, B. G.; Kelley, M. C.; Senior, C.; De la Beaujardiere, O.; Holt, J. A.; Tepley, C. A.; Burnside, R.; Abdu, M. A.; Sobral, J. H. A.; Woodman Pollitt, Ronald Francisco; Kamide, Y.; Lepping, R.An alternative approach for estimating E region density profiles using radio occultation total electron content (ROTEC) measurements is presented. In this approach, the F region contribution to the measured ROTEC is removed using the estimated F region from an assimilative model of ionospheric density. E region density profiles are then obtained from a numerical inversion of the residual ROTEC, which is assumed to be the E region contribution to the ROTEC. The proposed technique has been applied to radio occultation measurements made by the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC), while the F region specification is obtained from the Ionospheric Data Assimilation Four-Dimensional (IDA4D) algorithm. Examples of E region profiles obtained with this approach are presented and compared with nearby radar measurements at the magnetic equator. The results indicate that accurate estimates of the E region peak height and density can be obtained with this approach. This technique may be applicable to the estimation of E region conductivities with the global coverage provided by the radio occultation measurements.Item Restricted Modeling the equatorial and low‐latitude ionospheric response to an intense X‐class solar flare(American Geophysical Union, 2015-03-11) Nogueira, P. A. B.; Souza, J. R.; Abdu, M. A.; Paes, R. R.; Sousasantos, J.; Marques, M. S.; Bailey, G. J.; Denardini, C. M.; Batista, I. S.; Takahashi, H.; Cueva, R. Y. C.; Chen, S. S.We have investigated the ionospheric response close to the subsolar point in South America due to the strong solar flare (X2.8) that occurred on 13 May 2013. The present work discusses the sudden disturbances in the D region in the form of high‐frequency radio wave blackout recorded in ionograms, the E region disturbances in the form of the Sq current and equatorial electrojet intensifications, and the enhancement and decay in the ionospheric total electron content (TEC) as observed by a network of Global Navigation Satellite Systems receivers, the last of these manifestations constituting the main focuses of this study. The dayside ionosphere showed an abrupt increase of the TEC, with the region of the TEC increase being displaced away from the subsolar point toward the equatorial ionization anomaly (EIA) crest region. The decay in the ΔTEC following the decrease of the flare EUV flux varied at a slower ratio near the EIA crest than at the subsolar point. We used the Sheffield University Plasmasphere‐Ionosphere Model to simulate the TEC enhancement and the related variations as arising from the flare‐enhanced solar EUV flux and soft X‐rays. The simulations are compared with the observational data to validate our results, and it is found that a good part of the observed TEC variation features can be accounted for by the model simulation. The combined results from model and observational data can contribute significantly to advance our knowledge about ionospheric photochemistry and dynamics needed to improve our predictive capability on the low‐latitude ionospheric response to solar flares.Item Restricted Processes in the quiet and disturbed equatorial-low latitude ionosphere: Sundial campaign, 1984(European Geosciences Union, 1987-04) Abdu, M. A.; Reddy, B.M.; Walker, G. O.; Hanbaba, R.; Fejer, B.G.; Woodman Pollitt, Ronald Francisco; Schunk, R.W.; Szuszczewicz, E.P.A network of ionospheric diagnostic instruments was operated on a world wide basis during the October 5-13. 1984 SUNDIAL campaign. The network provided a unique opportunity for a truly multiple technique global analysis of the equatorial-low latitude ionospheric behavior during the campaign period. The SUNDIAL equatorial-low latitude data set included electric field and spread F data from Jicamarca radar, ionosonde data from 15 stations and magnetograms from 5 stations operated in the American, African, Asian and Indian sectors. Also included are data from electronic polarimeters at 8razilian low-latitude sites. The data analysis has focused attention on the global scale steady state ionospheric behavior and its predictability by global theoretical model of Sojka and Schunk (1985) and by the lnternational Reference lonospheric (IRI). The results are suggestive of the need to modify existing quiet time electric field and neutral wind models in varying degrees for different longitude sectors. The analysis also concerns global scale ionospheric transient behavior in response to exo-ionospheric variabilities under disturbed conditions, in an approach towards a hotter understanding of the factors that effect short-term prediction schemes. Among the important outcomes of this study is the possibility of using longitude chains of equatorial region ionosondes (and magnetometers) for investigation of equatorial ionospheric response to magnetospheric electric field penetration events and disturbance dynamo effects.Item Restricted Sporadic E layer development and disruption at low latitudes by prompt penetration electric fields during magnetic storms(American Geophysical Union, 2013-04-11) Abdu, M. A.; Souza, J. R.; Batista, I. S.; Fejer, B. G.; Sobral, J. H. A.An investigation of low‐latitude sporadic E layers during magnetic storms shows that the formation and disruption of these layers are strongly controlled by the magnetospheric electric fields that penetrate to equatorial ionosphere. It is observed that a prompt penetration electric field (PPEF) of westward polarity that dominates the nightside ionosphere can cause formation of sporadic E layers near 100 km, while a PPEF of eastward polarity that dominates the dayside and eveningside can lead to disruption of an Es layer in progress. It is shown that a vertical Hall electric field, induced by the primary zonal PPEF, in the presence of the storm‐associated enhanced conductivity of the night E layer, can be responsible for vertical ion velocity convergence sufficient to influence the Es layer formation. A downward polarity of the Hall electric field leads to Es layer formation, while an upward polarity causes the Es layer disruption. An interplay of magnetic storm associated prompt penetration electric field and energetic particle precipitation is evident in the observed Es layer response features in the region of the South Atlantic/American magnetic anomaly reported here.Item Restricted Storm time equatorial plasma bubble zonal drift reversal due to disturbance Hall electric field over the Brazilian region(American Geophysical Union, 2016-05-18) Santos, A. M.; Abdu, M. A.; Souza, J. R.; Sobral, J. H. A.; Batista, I. S.; Denardini, C. M.The dynamics of equatorial ionospheric plasma bubbles over Brazilian sector during two magnetic storm events are investigated in this work. The observations were made at varying phases of magnetic disturbances when the bubble zonal drift velocity was found to reverse westward from its normally eastward velocity. Calculation of the zonal drift based on a realistic low‐latitude ionosphere modeled by the Sheffield University Plasmasphere‐Ionosphere Model showed on a quantitative basis a clear competition between vertical Hall electric field and disturbance zonal winds on the variations observed in the zonal velocity of the plasma bubble. The Hall electric field arising from enhanced ratio of field line‐integrated conductivities, ΣH/ΣP, is most often generated by an increase in the integrated Hall conductivity, arising from enhanced energetic particle precipitation in the South American Magnetic Anomaly region for which evidence is provided from observation of anomalous sporadic E layers over Cachoeira Paulista and Fortaleza. Such sporadic E layers are also by themselves evidence for the development of the Hall electric field that modifies the zonal drift.Item Restricted Strong longitudinal difference in ionospheric responses over Fortaleza (Brazil) and Jicamarca (Peru) during the January 2005 magnetic storm, dominated by northward IMF(American Geophysical Union, 2012-08-29) Santos, A. M.; Abdu, M. A.; Sobral, J. H. A.; Koga, D.; Nogueira, P. A. B.; Candido, C. M. N.In this study we investigate the response of the equatorial F layer to disturbance zonal electric field associated with IMF (interplanetary magnetic field) variations dominated by a strong northward Bz episode during the magnetic storm that occurred on 21 January, 2005. We compared the results obtained from Digisondes operated at Fortaleza, Brazil (Geogr. 3.9 S, 38.45 W; dip angle: 11.7 ) and Jicamarca, Peru (Geogr. 12.0 S, 76.8 W; dip angle: 0.64 ). A large auroral activity (AE) intensification that occurred at 1715 UT produced a large F-layer peak height increase (from 300 km to 600 km) over Jicamarca with no noticeable simultaneous effect over Fortaleza. Then the Bz turning northward at 1940 UT with a rapid change in AE that was accompanied by a large decrease of F layer height and total suppression of the PRE over Fortaleza with no simultaneous effect over Jicamarca. Strong increase in the AE index (from 400 to 1000 nT) with superimposed oscillations, under Bz North, that soon followed was associated with increases in both the F layer height and the vertical drift velocity over Fortaleza (at 2130 UT), with no corresponding signatures over Jicamarca. These remarkable contrasting responses to prompt penetration electric field (PPEF) as well as to disturbance wind dynamo electric field (DDEF) and other effects observed at the two locations separated only by 2 h in LT in the South American sector are presented and discussed in this paper. Effects on spread-F development and foF2 behavior during this storm event are also addressed in this work.Item Open Access Sundial: A world-wide study of interactive ionospheric processes and their roles in the transfer of energy and mass in the sunearth system(European Geosciences Union, 1988-01-01) Szuszczewicz, E. P.; Fejer, B. Q.; Roelof, E. C.; Schunk, R. W.; Leitinger, R.; Abdu, M. A.; Reddy, B. M.; Joselyn, J. C.; Wilkinson, P.; Woodman Pollitt, Ronald Francisco; Wolf, R. A.During the period 5-13 October 1984 a coordinated solar-terrestrial data base was acquired to develop a comprehensive understanding and an associated predictive capability for the cause-effect relationships which control the global-scale ionosphere. The effort, the first in a series of continuing investigations in a program called SUNDIAL, combined modelling of the ionospheric, magnetospheric, and thermospheric domains with a measurements activity that included a network of ionospheric monitoring stations at high-, middle-, and low latitudes in the American, European/African, and Asian/Australian sectors. Solar, solar wind, interplanetary, and geomagnetic data were also obtained through the NOAA Space Environment Services Center. The period began with nearly two full days of typically quiescent solar mínimum conditions, with the night of the 6th marking a transition to a substantial increase in solar wind velocities, and enhanced dynamics in the interplanetary magnetic field with associated geomagnetic disturbances. The increased solar wind velocities resulted from a corotating high-speed stream coupled to a transequatorial solar coronal hole. Evidence points to a step-wise coupling of processes from the coronal hole through the interplanetary and magnetospheric domains down to the equatorial ionosphere, where penetrating electric fields participated in triggering the most disturbed condition of equatorial spread-F ever recorded by the Jicamarca Observatory. The correlation of events also included : (1) enhanced particle precipitation power at high latitudes, (2) an associated cross polar cap potential of 75 k Y, and (3) simultaneous global observations of F-region dynamics. In addition, detailed model comparisons with observations of the quiet and disturbed ionosphere point to requirements for improved global specification of thermospheric winds and electric fields. The content of this paper presents an overview of the program, its initial findings, recommendations, and future perspectives.Item Restricted Superposed epoch analysis of the dayside ionospheric response to four intense geomagnetic storms(American Geophysical Union, 2008-07-09) Mannucci, A. J.; Tsurutani, B. T.; Abdu, M. A.; Gonzalez, W. D.; Komjathy, A.; Echer, E.; Iijima, B. A.; Crowley, G.; Anderson, D.Prompt daytime ionospheric responses are presented for the following four intense geomagnetic storms: 29 October 2003, 30 October 2003, 20 November 2003, and 7 November 2004. We perform a superposed epoch analysis of the storms by defining the start time of the epoch when the Kan‐Lee interplanetary electric field (proportional to the reconnection electric field) first reaches 10 mV/m during a period of continuously southward Bz. Measurements from the GPS receiver onboard the CHAMP satellite at 400 km altitude indicate significant low‐ to middle‐latitude daytime total electron content (TEC) increases above the satellite within 1–2 h of the defined start time for three of the storms (∼1400 local solar time). The 20 November 2003 data follow a different pattern: the largest TEC increases appear several hours (∼5–7) following the interplanetary magnetic field Bz event onset. TEC data obtained from ground‐based GPS receivers for the November 2003 storm tend to confirm a “late” TEC increase for this storm at ∼1400 LT. Estimates of vertical plasma uplift near the equator at Jicamarca longitudes (∼281 E) using the dual‐magnetometer technique suggest that variability of the timing of the TEC response is associated with variability in the prompt penetration of electric fields to low latitudes. It is also found that for the November 2003 magnetic storm the cross‐correlation function between the SYM‐H index and the interplanetary electric field reached maximum correlation with a lag time of 4 h. Such a large lag time has never been noted before. The long delays of both the ionosphere and magnetosphere responses need to be better understood.