SAMPEX observations of the South Atlantic anomaly secular drift during solar cycles 22–24

Abstract

It is observed that charged particle intensities are very high near the South Atlantic anomaly (SAA) and are a potential hazard to spacecraft passing through the region. In this study, we examine the secular drift of the SAA location at ∼400–600 km altitude over nearly two solar cycles, using particle count rates to trace the geomagnetic field lines in the region near the SAA. We use data from the Low‐Energy Ion Composition Analyzer sensor on board the SAMPEX (Solar, Anomalous, and Magnetospheric Particle Explorer) spacecraft to measure both the longitudinal and latitudinal drifts of the SAA. We find that the longitudinal drift rate is 0.20 ± 0.04° west per year and that the latitudinal drift rate is 0.11 ± 0.01° south per year. These measurements are compared with the IGRF12 (International Geomagnetic Reference Field) model calculations based on an analysis of magnetic field minima in the region of the SAA. Our results, which are in good agreement with model results and prior measurements when declining spacecraft altitude is taken into account, have important space weather implications.

The Secular Variation of the Center of Geomagnetic South Atlantic Anomaly and Its Effect on the Distribution of Inner Radiation Belt Particles

“…Comparing the location of PSAA center shown in Figures and and MFSAA center shown in Figure , we can see the following: All PSAA centers are to the southeast of MFSAA centers, the PSAA centers corresponding to higher energy protons locate closer to MFSAA centers. This is consistent with AP8MAX model result (Heynderickx, ) and SAMPEX observation in 2000 by Jones et al (). Figure shows the proton fluxes and the magnetic field intensity at the same time, and it could clearly illustrate this point. As the orbit altitude drops, the PSAA centers (mainly for the lower two energy channels) show a southwest move (except for the disturbance from 2002 to 2006), which is in agreement with the MFSAA variations: at a higher altitude, the MFSAA center moves closer to the northeast.…”

“…All PSAA centers are to the southeast of MFSAA centers, the PSAA centers corresponding to higher energy protons locate closer to MFSAA centers. This is consistent with AP8MAX model result (Heynderickx, 1996) and SAMPEX observation in 2000 by Jones et al (2017). Figure 9 shows the proton fluxes and the magnetic field intensity at the same time, and it could clearly illustrate this point.…”

“…The Weibull distribution fits the particle flux curve much better than the Gaussian distribution. Moreover, the latitudinal fits are better than the longitudinal fits, which is possibly caused by orbit feature of SAMPEX(Jones et al, ). The inclination of SAMPEX orbit is 82 ∘ .…”

“…Most of former studies did not pay much attention to the different energies of particles (Badhwar, ; Casadio & Arino, ; Fürst et al, ; Jones et al, ; Konradi et al, ; Pu et al, ; Schaefer et al, ; Xie et al, ). Several former studies (Bühler et al, ; Heynderickx, ; Jones et al, ) mentioned the difference but detailed discussion was not given. With AP8 proton model, Heynderickx () found the PSAA center corresponding to higher energy protons located closer to the MFSAA at 500 km altitude, that is, closer to the northwest.…”

Analysis of the Impact of Long‐Term Changes in the Geomagnetic Field on the Spatial Pattern of the Weddell Sea Anomaly

“…Significant evidence of the westward migration of the Earth's magnetic field is documented by secular variation of the SAA. Numerous studies (Jones et al, 2017; Pavón‐Carrasco & Santis, 2016, and references therein) confirm that the total intensity of the magnetic field is changing. Strong expansion of the South Atlantic Anomaly towards continental regions of South America is recorded, with the minimum of the magnetic field intensity located in Brazil.…”