Using magnetic

observatory data to investigate the longitudinal and seasonal

variability of the counter electrojet

Soares, G. B. (1), Yamazaki, Y. (2), Matzka, J. (2) and

Pinheiro, K. (1)

(1) Geophysics

Department, Observatório Nacional, 20921-400 Rio de Janeiro, Brazil.

(2) GFZ German research Centre for Geosciences, 14473 Potsdam,



Data from magnetic observatories placed near

the magnetic equator can be used to study the equatorial electrojet

(EEJ) and its reversal, the so-called counter electrojet (CEJ). The

EEJ is an ionospheric current that flows eastwards at E-region heights

within a narrow band of about 4° from the magnetic equator. It causes

an enhancement of the normal daily Sq variations in the geomagnetic

horizontal component H. CEJ events result from the reversal of the

normal EEJ. The westward current during CEJ events can last for a few

hours and causes a depression in the H values. One method to isolate

the EEJ/CEJ signal from other external and internal sources of the

geomagnetic field is by taking the difference of H measured at an

equatorial station and at a low-latitude station with a similar

longitude, but outside the influence of the EEJ. In this work we aim

to provide the seasonal variability of CEJ events by using geomagnetic

data from the Peruvian sector (Huancayo observatory and Piura

station), the Brazilian sector (Tatuoca and Kourou observatories), the

African sector (Samogossoni station and Tamanrasset observatory), the

Indian sector (Tirunelveli and Alibag observatories) and the Asian

sector (Davao and Muntilupa stations). We investigate if the obtained

CEJ rates are in agreement with the longitudinal variation of the

ionospheric electric field, which is caused by atmospheric waves of

tropospheric origin. A better understanding of the mechanisms that

control the longitudinal difference of CEJ occurrences is important

for further studies of the whole EEJ/CEJ system.