Browsing by Author "Denardini, C. M."
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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 Restricted Equatorial E region electric fields at the dip equator: 2. Seasonal variabilities and effects over Brazil due to the secular variation of the magnetic equator(American Geophysical Union, 2016-09-23) Moro, J.; Denardini, C. M.; Resende, L. C. A.; Chen, S. S.; Schuch, N. J.In this work, the seasonal dependency of the E region electric field (EEF) at the dip equator is examined. The eastward zonal (Ey) and the daytime vertical (Ez) electric fields are responsible for the overall phenomenology of the equatorial and low‐latitude ionosphere, including the equatorial electrojet (EEJ) and its plasma instability. The electric field components are studied based on long‐term backscatter radars soundings (348 days for both systems) collected during geomagnetic quiet days (Kp ≤ 3+), from 2001 to 2010, at the São Luís Space Observatory (SLZ), Brazil (2.33°S, 44.20°W), and at the Jicamarca Radio Observatory (JRO), Peru (11.95°S, 76.87°W). Among the results, we observe, for the first time, a seasonal difference between the EEF in these two sectors in South America based on coherent radar measurements. The EEF is more intense in summer at SLZ, in equinox at JRO, and has been highly variable with season in the Brazilian sector compared to the Peruvian sector. In addition, the secular variation on the geomagnetic field and its effect on the EEJ over Brazil resulted that as much farther away is the magnetic equator from SLZ, later more the EEJ is observed (10 h LT) and sooner it ends (16 h LT). Moreover, the time interval of type II occurrence decreased significantly after the year 2004, which is a clear indication that SLZ is no longer an equatorial station due to the secular variation of the geomagnetic field.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 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 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 Variabilities of the equatorial electrojet in Brazil and Perú(American Geophysical Union, 2010-06-16) Shume, E. B.; Denardini, C. M.; De Paula, E. R.; Trivedi, N. B.This report presents seasonal and longitudinal variabilities of the equatorial electrojet in the east (Brazil, São Luís: 2.3° S; 315.8° E; 0.5° S dip latitude) and west (Jicamarca, Perú: 11.95° S; 283.13° E; 0.6° N dip latitude) coasts of the continent of South America. Ground‐based magnetic field perturbation measurements ΔH for solar maximum (2001/2002) and solar minimum (2006/2007) conditions from the two equatorial stations (São Luís and Jicamarca) have been used for the study. The ΔH signal which is a measure of the strength of the equatorial electrojet is spectrally analyzed using wavelet analysis. The results of our analysis show that (1) the equatorial electrojet has maxima around equinoxes in Jicamarca, Perú but it has a prominent maximum during Southern Hemisphere summer (centered about December/January) in São Luís, Brazil. The observed seasonal behavior of the equatorial electrojet in São Luís is highly likely due to the large magnetic declination angle (about 20° west) there. (2) The equatorial electrojet is stronger in the west coast (Jicamarca) compared to the east coast (São Luís), irrespective of solar activity condition. (3) The magnitude of the equatorial electrojet is more variable with season and solar cycle over São Luís than over Jicamarca.