Role of the Africa Magnetic Anomaly in Controlling the Magnetic Configuration and its Secular Variation

Xu, Weihua; Chen, Bai

doi:10.1002/cjg2.1402

Cited by 3 publications

(6 citation statements)

References 18 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Ion PERs with large negative amplitudes, for example, A < −100%, were successfully detected predominantly in winter during the night in most mentioned magnetic anomalies of the world, like the Africa anomaly and SAMA (Figure 7). Xu and Bai [57] concluded that these planetary-scale non-dipole fields could heavily control the secular variation in geomagnetic fields, and the combined effect from the Africa anomaly and SAMA have tremendously modified the shape and position of the magnetic equator. Unexpectedly, we also found a large negative ion density anomaly from Southeast China to the Japanese Ocean (Figure 7), but its formation mechanism remains unknown.…”

Section: Discussionmentioning

confidence: 99%

“…The key point is that these PERs are of similar space size at ~100 s, 700 km, if a velocity of the DEMETER satellite of 7 km/s is considered, possibly illustrating the outcome of the satellite flying over the same region at different times. Xu et al [57] reported that there are mainly five planetary-scale geomagnetic anomalies worldwide: Australia, Africa, the Southern Atlantic Ocean, the Eurasian continent, and Northern America. However, in these areas, a strong We examined all night PERs and found that there are 196 with an amplitude less than −100% in total, and they occurred mostly in equinox and winter, with a few occurring in summer.…”

Section: Seasonal Variation In Ionospheric Persmentioning

confidence: 99%

See 1 more Smart Citation

Topside Ionospheric Structures Determined via Automatically Detected DEMETER Ion Perturbations during a Geomagnetically Quiet Period

Li,

Yan,

Zhang

2024

Geosciences

View full text Add to dashboard Cite

In this study, 117,718 ionospheric perturbations, with a space size (t) of 20–300 s but no amplitude (A) limit, were automatically globally searched via software utilizing ion density data measured by the DEMETER satellite for over 6 years. The influence of geomagnetic storms on the ionosphere was first examined. The results demonstrated that storms can globally enhance positive ionospheric irregularities but rarely induce plasma variations of more than 100%. The probability of PERs with a space size falling in 200–300 s (1400–2100 km if a satellite velocity of 7 km/s is considered) occurring in a geomagnetically perturbed period shows more significance than that in a quiet period. Second, statistical work was performed on ion PERs to check their dependence on local time, and it was shown that 24.8% of the perturbations appeared during the daytime (10:30 LT) and 75.2% appeared during the nighttime (22:30 LT). Ionospheric fluctuations with an absolute amplitude of A < 10% tend to be background variations, and the percentages of positive perturbations with a small A < 20% occur at an amount of 64% during the daytime and 26.8% during the nighttime, but this number is reversed for mid–large-amplitude PERs. Large positive PERs with A > 100% mostly occurred at night and negative ones with A < −100% occurred entirely at night. There was a demarcation point in the space size of t = 120 s, and the occurrence probabilities of day PERs were always higher than that of nighttime ones before this point, while this trend was contrary after this point. Finally, distributions of PERs according to different ranges of amplitude and space scale were characterized by typical seasonal variations either in the daytime or nighttime. EIA only exists in the dayside equinox and winter, occupying two low-latitude crests with a lower Np in both hemispheres. Large WSAs appear within all periods, except for dayside summer, and are full of PERs with an enhanced amplitude, especially on winter nights. The WN-like structure is obvious during all seasons, showing large-scale space. On the other hand, several magnetically anomalous zones of planetary-scale non-dipole fields, such as the SAMA, Northern Africa anomaly, and so on, were also successfully detected by extreme negative ion perturbations during this time.

show abstract

Section: Discussionmentioning

confidence: 99%

Section: Seasonal Variation In Ionospheric Persmentioning

confidence: 99%

Topside Ionospheric Structures Determined via Automatically Detected DEMETER Ion Perturbations during a Geomagnetically Quiet Period

Li,

Yan,

Zhang

2024

Geosciences

View full text Add to dashboard Cite

show abstract

“…It is well known that the geomagnetic non-dipole field zones are five large-scale anomalies (Xu & Bai, 2009), which are listed according to their maximum intensities as follows: the South Atlantic Ocean anomaly (SAA), Africa anomaly (AFR), Eurasia anomaly (ERA), Australia anomaly (AST), and North America anomaly (NAM).…”

Section: Discussionmentioning

confidence: 99%

“…It is well known that the geomagnetic non‐dipole ﬁeld zones are five large‐scale anomalies (Xu & Bai, 2009), which are listed according to their maximum intensities as follows: the South Atlantic Ocean anomaly (SAA), Africa anomaly (AFR), Eurasia anomaly (ERA), Australia anomaly (AST), and North America anomaly (NAM). In particular, the two strongest negative anomalies (defined in total intensity) SAA and AFR dramatically distort the morphology of the geomagnetic field in the African sector, as shown in Figure 1.…”

Section: Discussionmentioning

confidence: 99%

Effect of the Non‐Dipole Field on the Seasonal Variation of the Geomagnetic Sq(Y)

Tian

Huang

et al. 2022

JGR Space Physics

View full text Add to dashboard Cite

It is well known that the solar quiet daily geomagnetic variation (Sq) at mid-low latitudes primarily originates from the dayside ionospheric E-region dynamo (Matsushita, 1967;Forbes & Lindzen, 1976;Richmond, 1979;Yamazaki & Maute, 2017). According to the classical dynamo theory, the distribution of the geomagnetic field, the tidal wind, and the ionospheric conductivity control the behavior of the Sq type variation (Campbell, 1982). In particular, the geomagnetic field not only modulates the conductivity through its dependence on the electron and ion gyrofrequencies but also controls the dynamo electric field (Le Sager & Huang, 2002;Stening, 1971;Takeda, 1996). The modulation on the conductivity is mainly through the change in the gyrofrequencies of the electrons and ions in the ionospheric dynamo region. At the regions with weaker geomagnetic field strength, such as the South Atlantic Ocean anomaly region (SAA), both the electron and ion gyrofrequencies are lower than those at other regions. The lower boundary of the dynamo region, which is defined by the altitude where the electron gyrofrequency is equal to the electron-neutral collision frequency, is higher at the SAA region. This is also the case at the upper boundary, which is defined by the altitude where the ion gyrofrequency is equal to the ion-neutral collision frequency. The dynamo region will upward shift at the SAA region, and thus they are located at altitudes where the electron density is larger. This upward shift causes the enhancement of both the height integrated Pedersen (Σ P ) and Hall conductivities (Σ H ). Using a numerical calculation, Takeda (1996) estimated the height of integrated Pedersen and Hall conductivities for different geomagnetic field strengths. He found that the Σ P and Σ H are 42 and 26 times stronger at the regions with 10% of the normal geomagnetic field strength, respectively. As a consequence of these factors, the Sq electric current systems show a remarkable dependence on season, solar activity,

show abstract

“…The key point is that these PERs are of the similar space size of ~100 s, 700 km if velocity of the DEMETER satellite 7 km/s is considered, maybe rightly illustrating the outcome of the satellite flying over the same region at different time. Xu et al [56] have reported that there are mainly five planetary scale geomagnetic anomalies worldwide: Australia, Africa, Southern Atlantic Ocean, Eurasia continent and Northern America. However, in these areas, strong negative ionospheric anomaly has not been detected in Northern America but in eastern Asia including southeast China and Japan in this time.…”

Section: Seasonal Variation Of Ionospheric Persmentioning

confidence: 99%

Topside Ionospheric Structures Determined by Automatically Detected DEMETER Ion Perturbations

Li,

Yan,

Zhang

2023

Preprint

View full text Add to dashboard Cite

In this research, 117,718 ionospheric perturbations, with a space size (t) of 20–300 s but no limit on amplitude (A) have been automatically searched globally by a software from ion density data measured by the DEMETER satellite for more than 6 years. The influence of the solar activity on the ionosphere has been firstly examined and the results have presented that the solar activities can globally enhance ionospheric irregularities but rarely induce plasma variations more than 100%. A statistical work has been performed on ion PERs to check their dependence on local time and it is shown that there are 24.8% perturbations appeared in daytime (10:30 LT) and 75.2% ones in nighttime (22:30 LT). Ionospheric fluctuations with an absolute amplitude A < 10% tend to be background variations and the percentages of positive perturbations with small A < 20% are 64% in daytime and 26.8% in nighttime, respectively, but this number is revers for mid-large amplitude PERs. There is a demarcation point in space size t = 120 s and occurrence probabilities of day PERs are always higher than that of nighttime ones before this point while this trend is contrary after this point. Distributions of PER according to various amplitudes or space scales have been characterized by typical seasonal variations either in daytime or in nighttime. The EIA only exists in dayside equinox and winter occupying two lowlatitude crests with lower Np. The huge WSA appears in all periods except for dayside summer full of PERs with enhanced amplitude, especially in winter night. The WN-like structure can be obviously figured out in all seasons showing absolutely space large-scales. In the meanwhile, several magnetic anomalous zones of planetary scale non-dipole fields, such as the SAMA, Northern Africa anomaly, and so on, have been also successfully detected by extreme negative ion perturbations in this time.

show abstract

Role of the Africa Magnetic Anomaly in Controlling the Magnetic Configuration and its Secular Variation

Cited by 3 publications

References 18 publications

Topside Ionospheric Structures Determined via Automatically Detected DEMETER Ion Perturbations during a Geomagnetically Quiet Period

Topside Ionospheric Structures Determined via Automatically Detected DEMETER Ion Perturbations during a Geomagnetically Quiet Period

Effect of the Non‐Dipole Field on the Seasonal Variation of the Geomagnetic Sq(Y)

Topside Ionospheric Structures Determined by Automatically Detected DEMETER Ion Perturbations

Contact Info

Product

Resources

About