Secular variation at Tatuoca magnetic observatory (Brazil)

Martins, C. M. (1), Baldez, R. M. (1), Pinheiro, K. J.

(2), Matzka, J. (3), Soares, G. B. (2) and Morschhauser, A.


(1) Geoscience

Institute, Universidade Federal do Pará (UFPA), 66075-110, Belém,

Brazil. (2) Geophysics Department, Observatório Nacional, 20921-400

Rio de Janeiro, Brazil. (3) GFZ German Research Centre for

Geosciences, 14473 Potsdam, Germany.


The secular

variation (SV) represents the geomagnetic field time variations due to

core dynamics. The SV occurs in long timescales, from months to

centuries, and it is well observed in magnetic observatories. Tatuoca

Magnetic Observatory (TTB) is located at an island 30km from Belém,

Brazil and 132km south from the geographic equator. This location is

important for three reasons: it lies at the magnetic equator; it is

useful to study the Equatorial Electrojet (EEJ) and the Counter

Electrojet (CEJ) behaviors; and to observe the South Atlantic Magnetic

Anomaly (SAMA) growth and effect.


TTB produces high quality data since 1957 but not all dataset is

available to be used in global field models. In this work, we analyse

two distinct periods: the first is from 1981 to 1999 and the second

from 2009 to 2015. We use hourly mean values from the total field (F)

and the three magnetic field components (X, Y, Z). We calculated

monthly and annual means based on two datasets: all available days and

only non-disturbed days. We compared these mean observed data and SV

at TTB with IGRF12 and CHAOS6 global models. Both models are in

reasonable agreement to the SV of TTB, though they do not reproduce

all high frequency variations. We search for geomagnetic jerks in the

SV of TTB and in both global models, by using two straight-line and

polynomial fits.