Analysis of coherence areas between conjugate stations affected by the South Atlantic Magnetic Anomaly

Transionospheric radio communications and radio signals reflected from the Earth's ionosphere can be degraded when irregularities in the electron density of the ionosphere cause rapid variations in the amplitude and phase of such signals. Signals from GPS satellites which undergo scintillations can be used to characterise the location and extent of ionospheric scintillations and improve models for the prediction of ionospheric scintillations. The region in the South Atlantic Ocean where the Earth's magnetic field is weakest, known as South Atlantic Magnetic Anomaly (SAMA), is potentially a region where ionospheric scintillation may be more severe due to the precipitation of high energy particles from the Earth's radiation belts. This paper presents some of the first ionospheric scintillations observed by means of GPS signals received by dedicated scintillation monitors deployed in the mid-and auroral latitudes of the Southern Hemisphere since 2007.

A first regional model of the past Earth's magnetic field from Africa for the last 4000 years

The South Atlantic Anomaly (SAA) is an area of geomagnetic weakness that represents the most significant anomaly in the present‐day field. Notwithstanding anomalies such as these, a long‐lived hypothesis is that, if averaged over sufficient time (104–106 years), the Earth's magnetic field approximates a geocentric axial dipole (GAD). The question of how significant the non‐GAD features are in the time‐averaged field is an important and unresolved one. The SAA has not always been visible in the historic and paleo‐field models; yet an unstable field was reported in the South Atlantic region on a multimillion‐year timescale. This study presents the first paleointensity study from Saint Helena, a volcanic island in the South Atlantic consisting primarily of lavas emplaced between 10 and 8 Ma. While paleointensity success rates were low, we were able to recover results from five independent lavas that together suggest a low field intensity of 10.5 ± 3.0 μT corresponding to a virtual axial dipole moment (VADM) of 2.4 ± 0.7 × 1022 A m2. These low paleointensity estimates suggest a field in the South Atlantic that was not only unstable in directions, but also substantially weaker than expected. We consider this to constitute further evidence that the SAA is not a single occurrence but rather, the latest in a series of recurring weaknesses in the field in this region, probably caused by Reversed Flux Patches on the Core Mantle Boundary.

The South Atlantic Anomaly (SAA) represents the minimum magnetic field intensity on Earth, influencing the energetic particle motion within the radiation belts, drawing them closer to our planet. The anomaly region serves as a key location for understanding the dynamics of the radiation belts affected by the magnetospheric response to solar activity.Our investigation relied mainly on our recent numerical simulation results of the inner radiation belt during two magnetic storm events: May 15, 2005, and February 3-4, 2022. We developed a test particle simulation code to compute the 70-180 MeV proton trajectories in the inner magnetosphere. The IGRF and Tsyganenko models provided the background time-dependent electromagnetic field in response to the input solar conditions. The AP8 model and SAC-C satellite observation confirmed the numerical results. We summarize that protons tend to concentrate more in the SAA’s southern region, while further research found that electrons exhibit a higher tendency to populate the SAA’s northern region due to wave-particle interaction. In light of this conclusion, we identified prolonged Pc5 waves in the ground magnetic field data acquired from stations near the SAA’s northern region provided by MAGDAS/CPMN network.Examining the particle dynamics inside the SAA is crucial for predicting the radiation environment of LEO missions, forecasting the thermosphere’s response to intense space weather, and anticipating the possible long-term climate changes.

We analyzed the strongest geomagnetic storm of the past two decades, which occurred on May 10, 2024, focusing on plasma data from spacecraft, Earth's magnetic field variations recorded at the Villa Remedios Magnetic Observatory, and neutron data from the 12-NM64 monitor, both located in La Paz, Bolivia. Situated within the South Atlantic Magnetic Anomaly (SAA), this region offers a unique perspective on geomagnetic disturbances, emphasizing the relevance of localized studies. The Villa Remedios Magnetic Observatory recorded a Dst drop of -560 nT, significantly larger than the -412 nT reported by the Kyoto station, underscoring pronounced regional variations likely amplified by SAA's influence. Concurrently, the neutron monitor at Chacaltaya registered a Forbush decrease on May 10, linked to coronal mass ejections (CMEs) and solar flares that occurred on May 8. This decrease was followed by a prolonged 13-day recovery, mirroring patterns observed in the Dst index. The combined data highlight the intricate interplay between solar activity and its terrestrial impacts, revealing significant correlations among CMEs, solar wind velocity, proton and electron fluxes, and geomagnetic disturbances. What did we learn from this geomagnetic storm? The importance of considering the geographical location and magnetic environment when analyzing such phenomena.

The South Atlantic Anomaly (SAA) is the most prominent feature of Earth's magnetic field. Understanding past geomagnetic field variations in the SAA region is crucial for improving our knowledge of the geodynamo. Site Ocean Drilling Program (ODP) 1233, located within the modern SAA and characterized by a high sedimentation rate (∼190 cm/kyr), provides a valuable archive for reconstructing the anomaly's history. Although paleomagnetic data from shipboard and u‐channel measurements spanning the past 70 ka (Lund et al., 2006, 2024) have been reported, they have not been validated by rock magnetic analyses. Notably, during the 65–40 ka interval, which includes the Norwegian‐Greenland Sea and Laschamps excursions, relative paleointensity (RPI) and inclination from site ODP 1233 differ markedly from nearby and global records. SEM–EDS and rock magnetic results show alternating intervals dominated by silicate‐hosted magnetite inclusions, likely associated with reduced supply and partial dissolution of detrital titanomagnetite during Patagonian Ice Sheet retreat, and intervals dominated by detrital titanomagnetite. We therefore applied a log‐transformed RPI normalization that accounts for the magnetic properties of these carriers and rescales amplitudes to a common reference. The resulting RPI curve aligns well with regional and global paleointensity records. When the axial dipole moment was comparable to the present value at ∼57.5 and ∼47 ka, paleointensity minima appear confined to the South Atlantic region, analogous to the present‐day SAA behavior.

Deepening of radiation belt particles in South Atlantic Anomaly Region: A scenario over past 120 years

This work investigates how continuous magnetic pulsations (Pc4 and Pc5) are influenced by the South Atlantic Magnetic Anomaly (SAMA). Using data from geomagnetically conjugate stations in the America-SAMA region, the research compares pulsation characteristics at stations under the influence of the SAMA. The methodology included wavelet transform and wavelet coherence to assess the spectral properties and pulsation dynamics. The study found that pulsation amplitudes are higher in the SAMA region compared to the Northern Hemisphere. Coherence values between conjugate stations range from weak to moderate for Pc5 pulsations and are high for Pc4 pulsations. These differences are attributed to the influence of the SAMA, which enhances ionospheric conductivity in the South American region.

The South Atlantic Anomaly (SAA) represents the region of Earth’s weakest magnetic field intensity, where the inner radiation belt approaches closer to the planet’s surface. This anomaly is a critical region for understanding radiation belt dynamics and their responses to solar activity-induced magnetospheric changes.This study is based on our recent numerical simulations of the inner proton radiation belt [Girgis et al., JSWSC (2021), SW (2024)], extending the model to include electron dynamics in the inner magnetosphere. The simulations adopted the IGRF and Tsyganenko models to provide a time-dependent magnetic field driven by solar input conditions detected by ACE mission, including the associated inductive electric field. A key feature of this research is the incorporation of wave-particle interactions, identified through Pc4-Pc5 wave detections using the MAGDAS ground magnetometer network. The primary objective is to simulate the enhancement of electron flux in the northern SAA region due to wave-particle interactions.Understanding particle dynamics within the SAA is essential for predicting the radiation environment in low Earth orbit (LEO) missions, forecasting ionospheric responses to severe space weather, and assessing potential long-term impacts on Earth's climate system.

We studied the space weather effects on the South Atlantic Anomaly (SAA) magnetic response using Tsyganenko models. For the physical parameters characterizing the SAA, the study considered the minimum magnetic field, the location (longitude and latitude) of the SAA center, and the area of the SAA. Regarding the space weather parameters, we considered the solar wind dynamic pressure, the interplanetary magnetic field components, B_{yIMF} and B_{zIMF}, the Dst index, and the geodipole tilting angle. To study the magnetic field response of the SAA, several different versions of the Tsyganenko models, namely, T96, T01, and TS05, were used to describe the external magnetic field contributions. The main internal magnetic field was calculated by the International Geomagnetic Reference Field (IGRF-12). The magnetic field study of the SAA was realized in long- and short-term (seasonal and diurnal) variations. We found that the Dst index and the geodipole tilting angle were the strongest influencing parameters on the SAA magnetic field response at all altitudes. Moreover, it was revealed that both magnetic poles might be a possible cause of the SAA magnetic field response, resulting from the space weather conditions. Furthermore, the magnetic field behavior of the SAA was affected by hourly variations, where the largest changes occurred at dayside.

Abstract. This research intends to characterize the South Atlantic Anomaly (SAA) by applying the power spectrum analysis approach. The motivation to study the SAA region is due to its nature. A comparison was made between the stations in the SAA region and outside the SAA region during the geomagnetic storm occurrence (active period) and the normal period where no geomagnetic storm occurred. The horizontal component of the data of the Earth's magnetic field for the occurrence of the active period was taken on 11 March 2011 while for the normal period it was taken on 3 February 2011. The data sample rate used is 1 min. The outcome of the research revealed that the SAA region had a tendency to be persistent during both periods. It can be said that the region experiences these characteristics because of the Earth's magnetic field strength. Through the research, it is found that as the Earth's magnetic field increases, it is likely to show an antipersistent value. This is found in the high-latitude region. The lower the Earth's magnetic field, the more it shows the persistent value as in the middle latitude region. In the region where the Earth's magnetic field is very low like the SAA region it shows a tendency to be persistent.

The effect of mid-latitude electron precipitation on the geoelectric field

Temporal variations of strength and location of the South Atlantic Anomaly as measured by RXTE

In this paper, I present a low-cost interactive experiment for measuring the strength of Earth's local magnetic field. This activity can be done in most high schools or two-year physics laboratories with limited resources, yet will have a tremendous learning impact. This experiment solidifies the three-dimensional nature of Earth's magnetic field vector and helps reinforce the aspect of the vertical component of Earth's magnetic field. Students should realize that Earth's magnetic field is not fully horizontal (except at the magnetic equator) and that a compass simply indicates the direction of the horizontal component of Earth's magnetic field. A magnetic dip needle compass can be used to determine the angle (known as the “dip angle” or “inclination angle”) measured from the direction in which Earth's magnetic field vector points to the horizontal. In this activity, students will be able to determine the horizontal component of the field using a Helmholtz coil and, knowing the dip angle, the Earth's magnetic field strength can be determined.

We study energetic particles in the inner magnetosphere during the great storm of March 31, 2001, using low‐altitude NOAA‐15 and 16 satellites. The NOAA/SEM‐2 instruments can monitor energetic particles above 30 keV from the equator to nearly polar latitudes. The South Atlantic anomaly (SAA) is seen by NOAA/SEM‐2 as a region of an increased flux of precipitating energetic protons in a limited MLT sector at low latitudes. At 0945 UT the NOAA‐16 satellite observed a strong increase of trapped 100–300 keV electrons at a very low invariant latitude of L = 1.14 in the 02 MLT sector, i.e., a few MLT hours behind SAA. The injected electrons drifted eastwards and joined SAA, as first observed by the NOAA‐15 satellite at 1030 UT in the 07 MLT sector. Thereafter the electrons were permanently trapped within the SAA and drifted around the Earth together with SAA. The lower‐energy (30–100 keV) part of the injected electrons was first detected by NOAA‐16 at 1125 UT in the same MLT, and L region. These electrons drifted longer behind the SAA region at a drift speed which agrees well with the theoretical estimate. Later, they also joined SAA and were thereafter trapped in it. Inside the SAA region the electron fluxes decreased exponentially with an e‐folding decay time of about 8.6 h. The results show that a great storm can effectively fill the SAA region by trapped energetic electrons. We present the observations and discuss the generation of energetic electrons at very low latitudes, as well as the mechanism of trapping them inside the SAA.