Longitudinal variability of the equatorial counter electrojet during the solar cycle 24

Soares, Gabriel Brando; Yamazaki, Yosuke; Matzka, Jürgen; Pinheiro, Katia; Stolle, Claudia; Alken, Patrick; Yoshikawa, Akimasa; Уозуми, Т.; Fujimoto, Akiko; Kulkarni, Atul

doi:10.1007/s11200-018-0286-0

Cited by 11 publications

(23 citation statements)

References 44 publications

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“…The corresponding QD latitude of TTB is shown on the upper abscissa. The results from SC 24 (2009–2019) indicate a predominance of MCEJ and an anticorrelation of ACEJ with the SC, which is consistent with previous results for the years 2008 to 2018 (Soares et al, 2018, 2019). For SC 23 (1996–2008), we find very low MCEJ rates of around 15% from 1996 until 2001.…”

Section: Resultssupporting

confidence: 91%

“…Instead, magnetic disturbance effects were mitigated by limiting the analysis to quiet days as selected by a Kp index criterion (Kp ≤ 3). This allows for comparison with previous studies (e.g., Marriott et al, 1979; Rastogi, 1974; Soares et al, 2019, 2018). The sunspot number (http://www.sidc.be/silso/) was also used for the CEJ analysis in order to account for CEJ solar cycle (SC) modulation.…”

Section: Data and Modelmentioning

confidence: 81%

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Evolution of the Geomagnetic Daily Variation at Tatuoca, Brazil, From 1957 to 2019: A Transition From Sq to EEJ

et al. 2020

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The magnetic equator in the Brazilian region has moved over 1,100 km northward since 1957, passing the geomagnetic observatory Tatuoca (TTB), in northern Brazil, around 2013. We recovered and processed TTB hourly mean values of the geomagnetic field horizontal (H) component from 1957 until 2019, allowing the investigation of long-term changes in the daily variation due to the influence of secular variation, solar activity, season, and lunar phase. The H day-today variability and the occurrence of the counter electrojet at TTB were also investigated. Until the 1990s, ionospheric solar quiet currents dominated the quiet-time daily variation at TTB. After 2000, the magnitude of the daily variation became appreciably greater due to the equatorial electrojet (EEJ) contribution. The H seasonal and day-today variability increased as the magnetic equator approached, but their amplitudes normalized to the average daily variation remained at similar levels. Meanwhile, the amplitude of the lunar variation, normalized in the same way, increased from 5% to 12%. Within the EEJ region, the occurrence rate of the morning counter electrojet (MCEJ) increased with proximity to the magnetic equator, while the afternoon counter electrojet (ACEJ) did not. EEJ currents derived from CHAMP and Swarm satellite data revealed that the MCEJ rate varies with magnetic latitude within the EEJ region while the ACEJ rate is largely constant. Simulations with the Thermosphere-Ionosphere-Electrodynamics General Circulation Model based on different geomagnetic main field configurations suggest that long-term changes in the geomagnetic daily variation at TTB can be attributed to the main field secular variation.

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Section: Resultssupporting

confidence: 91%

Section: Data and Modelmentioning

confidence: 81%

Evolution of the Geomagnetic Daily Variation at Tatuoca, Brazil, From 1957 to 2019: A Transition From Sq to EEJ

et al. 2020

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“…The occurrence peak patters are same for all longitudinal sector. For our result, the trough of semidiurnal variations is agreed with the lunar phase modulation of CEJ in Soares et al (2019). That is, the semidiurnal lunar tidal variation mainly causes the CEJ variability and dominantly modulates the quiet EEJ structure.…”

Section: Seasonal/longitudinal Dependencesupporting

confidence: 84%

“…In addition, their semidiurnal structure is completely different ours. It seems to be reasonable to expect that we could demonstrate more appropriate semidiurnal variation due to the enough analyzed data than Yizengaw et al [35] examines that the longitudinal variability of the equatorial counter electrojet (CEJ) during the solar cycle 24. They show the lunar phase modulation of CEJ and results in the morning CEJ occurrence peak rates around the half of moon and the afternoon CEJ around the new and full moons.…”

Section: Seasonal/longitudinal Dependencementioning

confidence: 94%

Seasonal dependence of semidiurnal equatorial magnetic variation during quiet and disturbed periods

et al. 2019

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The analysis of 20-year long-term semidiurnal lunar tidal variations gave the evidence that the semidiurnal variations are completely different between the magnetic quiet and disturbed periods. This is the first time that the seasonal dependence of disturbance-time semidiurnal variation has been provided from the analysis of the EE-index. We found the Kp dependence of semidiurnal variation: For full and new moon phase, counter troughs are amplified during disturbance time, possibly related to disturbance dynamo. For all moon phase, there are positive enhancements in dawn and strong depressions after sunset, resulting from the penetration of polar electric filed. For Seasonal dependence, semidiurnal variations are divided to three seasonal groups, and characterized as deep trough, enhanced crest and weak structure for D-solstice, Equinoxes and J-solstice, respectively. There is no significant longitudinal difference between Ancon and Davao, except for the amplitude of semidiurnal variations. The deep troughs occur during D-solstice and the enhanced crests during Equinoxes, at both Ancon and Davao.

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“…1. The morning and evening CEJs during winter season at ETT can be inferred to the superposition of the lunar semidiurnal (M2) wave over the solar daily wave of the horizontal component (Rastogi, 1974;Soares et al, 2019;Zhou et al, 2018). 2.…”

Section: Journal Of Geophysical Research: Space Physicsmentioning

confidence: 99%

Imprints of Sunspot Cycles on Normal and Abnormal Geomagnetic Fields: Case Study From Equatorial and Low‐Latitude Sites of India

Chandrasekhar

Roy

2020

JGR Space Physics

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The quiet time characteristics of equatorial electrojet (EEJ), counter electrojet (CEJ), and solar quiet (Sq) day geomagnetic field over two decades (1980-2002) are established using Principal component analysis (PCA) from equatorial (Ettaiyapuram) and off-equatorial (Hyderabad) Magnetic Observatories, India, over sunspot cycles 21-23. The patterns of normal field shows that the diurnal amplitudes were strong during equinox compared to other seasons. Varying contributions of abnormal field in different Lloyd's seasons were evident in different phases of sunspot cycle. The diurnal amplitudes have reduced from the 21st to the 23rd sunspot maxima following the trend of weakening of sunspot cycle. Analysis of seasonal means shows evening CEJs were more pronounced when compared to morning and afternoon in different phases of sunspot cycle. The abnormal field variations have a strong correlation with the occurrence of afternoon CEJs during solar minima; a correlation of seasonal occurrences of CEJs with phases of sunspot cycles is revealed.

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Longitudinal variability of the equatorial counter electrojet during the solar cycle 24

Cited by 11 publications

References 44 publications

Evolution of the Geomagnetic Daily Variation at Tatuoca, Brazil, From 1957 to 2019: A Transition From Sq to EEJ

Evolution of the Geomagnetic Daily Variation at Tatuoca, Brazil, From 1957 to 2019: A Transition From Sq to EEJ

Seasonal dependence of semidiurnal equatorial magnetic variation during quiet and disturbed periods

Imprints of Sunspot Cycles on Normal and Abnormal Geomagnetic Fields: Case Study From Equatorial and Low‐Latitude Sites of India

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