Showing papers by "Inez S. Batista published in 2011"

Equatorial Ionization Anomaly: The Role of Thermospheric Winds and the Effects of the Geomagnetic Field Secular Variation

Abstract: The vertical plasma drift is the well known driver of the equatorial ionization anomaly (EIA). The latitudinal distribution of ionization in the EIA is determined also by thermospheric meridional wind whose precise role can only be evaluated through the use of theoretical models because it depends not only upon the local configuration of the wind, but is a complex function of its distribution along the entire magnetic field line. Besides, in the Brazilian region, the magnetic field secular variations are fast enough for their effects on the ionosphere to be observed in the time span of the order of a solar cycle. In this work we use the Sheffield University Plasmasphere-Ionosphere Model (SUPIM) to investigate the role of the vertical plasma drift, thermospheric meridional wind and of the magnetic field secular variations in the changing trend of the EIA over the Brazilian region.

Tomographic imaging of the equatorial and low-latitude ionosphere over central-eastern Brazil

Abstract: A four-dimensional time-dependent tomographic algorithm, named Multi Instrument Data Analysis System (MIDAS), is used to image the equatorial and low-latitude ionosphere over the central-eastern sides of the Brazilian territory. From differential phase data obtained by a chain of ground-based GPS receiver the total electron content (TEC) is estimated and then, together with a modeled ionosphere from International Reference Ionosphere (IRI) model, the electron density distribution is reconstructed and the parameters of the F2-peak layer are accessed from the images. This paper presents the first study of ionospheric tomography using real dual-frequency data from the Brazilian Network for Continuous GPS Monitoring (RBMC). Ionospheric F2-peak electron density (NmF2) accessed from the images are compared to concurrent measurements from three ionosondes installed across Brazil. One year of data during the solar maximum period from March/2001 to February/2002 is used to analyze the seasonal and hourly variation of the F2-layer peak density. The accuracy with which MIDAS images the electron density during geomagnetic quiet periods is investigated through its correlation and deviation with the ionosonde and IRI model data, respectively. The main aspects of the reconstruction results at the equatorial ionization anomaly (EIA) region over Brazil are highlighted and discussed.

Spaced transmitter measurements of medium scale traveling ionospheric disturbances near the equator

Abstract: [1] The motion of Medium Scale Traveling Ionospheric Disturbances (MSTIDs) was measured for 1 year from the eastern tip of Brazil, about 10° degrees south of the magnetic and geographic equators using spaced fixed frequency radio transmitters. The motion was very similar during all of the year. The daytime average direction was towards 150° azimuth (clockwise from north) and speed was typically in the range 150–300 m/s. The azimuth varied only slightly during the day being slightly more easterly during evening-morning hours. During winter months there were also some TIDs whose motion was northward. None of the known sources for MSTIDs fits well with MSTIDs having these velocity patterns. A possible unconfirmed source is the Inter-Tropical Convergence Zone (ITCZ).

Mesosphere–Ionosphere Coupling Processes Observed in the F Layer Bottom-Side Oscillation

Abstract: During the Spread FEx campaign, under the NASA Living with a star (ILWS) program which was carried out in the South American Magnetic Equatorial region from September to November 2005, we observed formation of the bottom-type spread F and simultaneous occurrence of mesospheric gravity wave events. The events were monitored by the ionosonde, coherent radar and airglow OI 630.0 nm and OH imager. It is found that the bottom-type scattering layer has a wave form generated most probably by local gravity waves. Reverse ray-tracing of the observed gravity waves indicate their possible sources in the troposphere or thermosphere. Forward ray-tracing indicates their penetration into the ionosphere. The present work summarizes the observational evidence and results of the data analysis and discusses the mesosphere–ionosphere coupling processes.