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 ...

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 enhan...

Directional ionogram and F-region drift observations were conducted at seven digisonde stations in South America during the COPEX campaign from October to December 2002. Five stations in Brazil, one in Argentina, and one in Peru, monitored the ionosphere across the continent to study the onset and development of F-region density depletions that cause equatorial spread F (ESF). New ionosonde techniques quantitatively describe the prereversal uplifting of the F layer at the magnetic equator and the eastward motion of the depletions over the stations. Three of the Brazilian stations were located along a field line with a 350-km apex over the equator to investigate the relation of the occurrence of ESF and the presence of sporadic E-layers at the two E-region intersections of the field line. No simple correlation was found.

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 e...

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 flu...

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 ...