Non-monotonic growth and motion of the South Atlantic Anomaly

AbstractThe South Atlantic Anomaly (SAA) is a region at Earth’s surface where the intensity of the magnetic field is particularly low. Accurate characterization of the SAA is important for both fundamental understanding of core dynamics and the geodynamo as well as societal issues such as the erosion of instruments at surface observatories and onboard spacecrafts. Here, we propose new measures to better characterize the SAA area and center, accounting for surface intensity changes outside the SAA region and shape anisotropy. Applying our characterization to a geomagnetic field model covering the historical era, we find that the SAA area and center are more time dependent, including episodes of steady area, eastward drift and rapid southward drift. We interpret these special events in terms of the secular variation of relevant large-scale geomagnetic flux patches on the core–mantle boundary. Our characterization may be used as a constraint on Earth-like numerical dynamo models.

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Non-monotonous growth and motion of the South Atlantic Anomaly

10.21203/rs.3.rs-24657/v1 ◽

2020 ◽

Author(s):

Hagay Amit ◽

Filipe Terra-Nova ◽

Maxime Lézin ◽

Ricardo Trindade

Keyword(s):

Large Scale ◽

South Atlantic ◽

The South ◽

South Atlantic Anomaly ◽

Societal Issues ◽

Special Events ◽

Core Dynamics ◽

The Mean ◽

The Magnetic Field

Abstract The South Atlantic Anomaly (SAA) is a region at Earth’s surface where the intensity of the magnetic field is particularly low. Accurate characterization of the SAA is important for both fundamental understanding of core dynamics and the geodynamo as well as societal issues such as the erosion of instruments at surface observatories and onboard spacecrafts. Previous studies applied crude measures of the SAA. Here we propose new measures to better characterize the SAA area and center, accounting for global dipole changes and shape anisotropy. Applying our characterization to a geomagnetic field model covering the historical era, we find that the mean SAA area increase and westward drift rates are twice slower than previously reported. Our results reveal that the SAA area and center are much more time-dependent, including episodes of area decrease, eastward drift and rapid southward drift. We interpret these special events in terms of the secular variation of relevant large-scale geomagnetic flux patches on the core-mantle boundary. Our characterization may be used as a constraint on Earth-like numerical dynamo models.

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Characterization of the South Atlantic Anomaly

10.5194/npg-2018-51-rc1 ◽

2018 ◽

Author(s):

Anonymous

Keyword(s):

South Atlantic ◽

The South ◽

South Atlantic Anomaly

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MODELING THE SOUTH ATLANTIC OCEAN FROM MEDIUM TO HIGH RESOLUTION

Brazilian Journal of Geophysics ◽

10.22564/rbgf.v31i2.27 ◽

2014 ◽

Vol 31 (2) ◽

Author(s):

Mariela Gabioux ◽

Vladimir Santos da Costa ◽

Joao Marcos Azevedo Correia de Souza ◽

Bruna Faria de Oliveira ◽

Afonso De Moraes Paiva

Keyword(s):

High Resolution ◽

Atlantic Ocean ◽

Large Scale ◽

South Atlantic ◽

Surface Relaxation ◽

The South ◽

Small Surface ◽

Basic Model ◽

Basic Set ◽

Set Up

Results of the basic model configuration of the REMO project, a Brazilian approach towards operational oceanography, are discussed. This configuration consists basically of a high-resolution eddy-resolving, 1/12 degree model for the Metarea V, nested in a medium-resolution eddy-permitting, 1/4 degree model of the Atlantic Ocean. These simulations performed with HYCOM model, aim for: a) creating a basic set-up for implementation of assimilation techniques leading to ocean prediction; b) the development of hydrodynamics bases for environmental studies; c) providing boundary conditions for regional domains with increased resolution. The 1/4 degree simulation was able to simulate realistic equatorial and south Atlantic large scale circulation, both the wind-driven and the thermohaline components. The high resolution simulation was able to generate mesoscale and represent well the variability pattern within the Metarea V domain. The BC mean transport values were well represented in the southwestern region (between Vitória-Trinidade sea mount and 29S), in contrast to higher latitudes (higher than 30S) where it was slightly underestimated. Important issues for the simulation of the South Atlantic with high resolution are discussed, like the ideal place for boundaries, improvements in the bathymetric representation and the control of bias SST, by the introducing of a small surface relaxation. In order to make a preliminary assessment of the model behavior when submitted to data assimilation, the Cooper & Haines (1996) method was used to extrapolate SSH anomalies fields to deeper layers every 7 days, with encouraging results.

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