TY  - JOUR
A1  - Soares, Gabriel Brando
A1  - Yamazaki, Yosuke
A1  - Cnossen, Ingrid
A1  - Matzka, Jürgen
A1  - Pinheiro, Katia J.
A1  - Morschhauser, Achim
A1  - Alken, Patrick
A1  - Stolle, Claudia
T1  - Evolution of the geomagnetic daily variation at Tatuoca, Brazil, From 1957 to 2019
BT  - a transition from Sq to EEJ
JF  - Journal of geophysical research : Space physics
N2  - 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.
Y1  - 2020
U6  - https://doi.org/10.1029/2020JA028109
SN  - 2169-9380
SN  - 2169-9402
VL  - 125
IS  - 9
PB  - American Geophysical Union
CY  - Washington
ER  -