Evolution of the geomagnetic daily variation at Tatuoca, Brazil, from 1957 to 2019: a transition from Sq to EEJ

The magnetic equator in the Brazilian region has moved over 1,100 km northward since 1957, passing the geomagnetic observatory Tatuoca (TTB), in northern Brazil, around 2013. We recovered and processed TTB hourly mean values of the geomagnetic field horizontal (H) component from 1957 until 2019, allowing the investigation of long‐term changes in the daily variation due to the influence of secular variation, solar activity, season, and lunar phase. The H day‐to‐day variability and the occurrence of the counter electrojet at TTB were also investigated. Until the 1990s, ionospheric solar quiet currents dominated the quiet‐time daily variation at TTB. After 2000, the magnitude of the daily variation became appreciably greater due to the equatorial electrojet (EEJ) contribution. The H seasonal and day‐to‐day variability increased as the magnetic equator approached, but their amplitudes normalized to the average daily variation remained at similar levels. Meanwhile, the amplitude of the lunar variation, normalized in the same way, increased from 5% to 12%. Within the EEJ region, the occurrence rate of the morning counter electrojet (MCEJ) increased with proximity to the magnetic equator, while the afternoon counter electrojet (ACEJ) did not. EEJ currents derived from CHAMP and Swarm satellite data revealed that the MCEJ rate varies with magnetic latitude within the EEJ region while the ACEJ rate is largely constant. Simulations with the Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model based on different geomagnetic main field configurations suggest that long‐term changes in the geomagnetic daily variation at TTB can be attributed to the main field secular variation

International equatorial electrojet year : the African sector

International audienceThis paper presents the IEEY project in the African sector. The amount of our interpreted data is presently too short to allow proper scientific conclusions. Nevertheless, fist typical results illustrate our network possibilities. Some preliminary observations are briefly pre- , sented for their interest towards immediate research goals

Comparison of two views on the structure of ionospheric currents

There are two views on the structure of ionospheric currents, here symbolized as VIEW 1 and VIEW 2. The essential difference between them is that VIEW I supports the existence of two ionospheric current layers in the dip equatorial zone as measured by many rockets (Onwumechili,1992b,c). Contrary to the rocket measurements, VIEW 2 believes that ionospheric currents in the dip equatorial zone flow in only one current layer. This paper presents 11 relevant experimental results for explanations by VIEW 1 and VIEW 2 side by side. After reviewing many papers on related topics and judging the performances of the two views, it emerges that VIEW 2 is conjectural and has feasibility problems. On the other hand, VIEW 1 is based on observational results, and it simply and naturally explains the experimental results. Key words: ionospheric currents, current layers, magnetic dip equator, abnormal phase quiet days, counter equatorial eletrojet. (Global Journal of Pure and Applied Sciences: 2003 9(2): 273-302