A different interpretation of the annual and semiannual anomalies on the magnetic activity over the Earth

Azpilicueta, F.; Brunini, C.

doi:10.1029/2012ja017893

Cited by 10 publications

(7 citation statements)

References 24 publications

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“…Alternatively, there could be other ways in which solar wind-magnetosphere coupling affects geomagnetic activity, not necessarily involving the magnetic reconnection process. For instance, Azpilicueta and Brunini [2012] recently argued, following an earlier suggestion by Malin and Isikara [1976], that variations in m result in deformations of the shape of the magnetospheric cavity in which the ring current flows and that these could contribute to (semi)annual variations in magnetic perturbations on the ground. We were not able to test this hypothesis here, however, since CMIT does not yet give an accurate representation of the ring current.…”

Section: Discussionmentioning

confidence: 99%

The effects of seasonal and diurnal variations in the Earth's magnetic dipole orientation on solar wind–magnetosphere‐ionosphere coupling

2012

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.[1] The angle m between the geomagnetic dipole axis and the geocentric solar magnetospheric (GSM) z axis, sometimes called the "dipole tilt," varies as a function of UT and season. Observations have shown that the cross-polar cap potential tends to maximize near the equinoxes, when on average m = 0, with smaller values observed near the solstices. This is similar to the well-known semiannual variation in geomagnetic activity. We use numerical model simulations to investigate the role of two possible mechanisms that may be responsible for the influence of m on the magnetosphere-ionosphere system: variations in the coupling efficiency between the solar wind and the magnetosphere and variations in the ionospheric conductance over the polar caps. Under southward interplanetary magnetic field (IMF) conditions, variations in ionospheric conductance at high magnetic latitudes are responsible for 10-30% of the variations in the cross-polar cap potential associated with m, but variations in solar wind-magnetosphere coupling are more important and responsible for 70-90%. Variations in viscous processes contribute slightly to this, but variations in the reconnection rate with m are the dominant cause. The variation in the reconnection rate is primarily the result of a variation in the length of the section of the separator line along which relatively strong reconnection occurs. Changes in solar wind-magnetosphere coupling also affect the field-aligned currents, but these are influenced as well by variations in the conductance associated with variations in m, more so than the cross-polar cap potential. This may be the case for geomagnetic activity too.Citation: Cnossen, I., M. Wiltberger, and J. E. Ouellette (2012), The effects of seasonal and diurnal variations in the Earth's magnetic dipole orientation on solar wind-magnetosphere-ionosphere coupling,

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Section: Discussionmentioning

confidence: 99%

The effects of seasonal and diurnal variations in the Earth's magnetic dipole orientation on solar wind–magnetosphere‐ionosphere coupling

2012

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“…We hope that our results will also inspire researchers to explore these topics and possible terrestrial feedback mechanisms by means of which geometrically induced changes in the incoming solar output originated in planetary/lunar cycles could be interacting with internal periodicities of the climatic system and the whole Earth system in general. For example, our results could be relevant for specific problems where the Sun-Earth geometry is fundamental, such as seasonal changes in geomagnetic activity (e.g., Azpilicueta & Brunini, 2012), and in processes where oscillations of the lunar orbit have an impact through tidal forcing effects on the oceans (Mawad, 2017;Lin & Qian, 2019).…”

Section: Accepted Articlementioning

confidence: 99%

Possible Origin of Some Periodicities Detected in Solar‐Terrestrial Studies: Earth's Orbital Movements

Cionco

Kudryavtsev

Soon

2021

Earth and Space Science

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Planetary cycles have been argued to be detected in key geophysical time series 11 and attributed to planetary influence on solar activity 12 • These quasi-periods can be identified in the oscillations of the Earth's orbital 13 movement, which directly modulate incoming solar fluxes 14 • A hypothesis that some of these quasi-periods could be fully or partially origi-15 nated in changes of the Sun-Earth geometry is put forth

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“…When the solar wind compressed the Earth's magnetic field with a non‐zero tilt angle (the angle between the geomagnetic dipole axis and the Z ‐axis of the GSM coordinate frame) in summer or winter, the geomagnetic dipolar field lines within the nightside magnetospheric cavities were distorted. The ring current was displaced in the winter hemisphere (see Figure 6 in Malin & Mete Işikara, 1976; and Figure 7 in Azpilicueta & Brunini, 2012).…”

Section: Introductionmentioning

confidence: 99%

“…The annual latitudinal variation of the magnetic disturbances was believed possibly contributed by the warping effect of the cross‐tail current in the Malin–Mete Işikara model (Azpilicueta & Brunini, 2012). This process was considered also caused by the annual variations of the dipole tilt angle, making the neutral current sheet move seasonally between the hemispheres away from the GSM equatorial plane (e.g., Dandouras, 1988; Dayeh et al., 2015; Fairfield, 1980; Fairfield, 1987; Gosling et al., 1986; Lopez, 1990; Nakai et al., 1997; Russell & Brody, 1967; Speiser & Ness, 1967; Tsyganenko, 1989; Tsyganenko et al., 1998; Tsyganenko and Fairfield, 2004).…”

Section: Introductionmentioning

confidence: 99%

Statistical Study on the North‐South Asymmetric Distribution of the Mid‐Low‐Latitude Nightside Disturbed Magnetic Fields

et al. 2022

JGR Space Physics

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The nightside magnetic field at the middle and low latitude observatory is usually disturbed, decreasing in its north component (noted as Bx) during the periods of enhanced space weather activity. As indicated by the SYM‐H index, the decreasing field mainly originated from the magnetospheric westward ring current and the cross‐tail currents. In the meridian direction, the maximum of the disturbed field has been observed not always located at the geomagnetic dipole equator. One possible explanation is that the latitudinal position of the magnetotail current systems is affected by the orientation of solar wind to the Earth's geomagnetic dipole axis (noted as tilt angle). For a non‐zero tilt angle, the current deviates from the equatorial position (e.g., Malin & Mete Işikara, 1976; https://academic.oup.com/gji/article/47/3/445/614725). In this study, the mid‐low latitudinal distribution of the nightside disturbed field is systematically investigated every ∼1.5 hr, based on the magnetic surveys of the Swarm satellite constellation at polar orbits of ∼450 km altitude. The meridian distribution of Bx regularly appears like an upward‐opening parabolic shape with its vertex representing the magnetic minimum. In summer, the minimum is found generally located in the southern hemisphere, while in winter the pattern is reversed. The overall distribution demonstrates north‐south asymmetry. When the disturbed level is low, the deviation of the magnetic minimum from the dipole equator usually gets larger. The north‐south asymmetric distribution during storm times is further analyzed. In the initial phase, the magnetic minimum was shifted prominently (about 10°–30°) from the equator, then moved back (with the offset less than 10°) in the main phase and recovery phase in most cases. Moreover, the latitudinal deviation undergoes a diurnal variation, which is conspicuous in spring and autumn. It seems the asymmetric distribution is anti‐correlated to the contribution of the ring current, indicated by the SYM‐H index. The warping structure of the cross‐tail current sheet probably plays a predominant role in generating the north‐south asymmetry of the magnetic field disturbances for non‐zero dipole tilt angles. Monitoring the external magnetic configuration via the low‐Earth‐orbit satellites will provide fundamental evidence to identify the relative position of the ring current and the cross‐tail current, as well as the dynamic processes in the near magnetotail.

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A different interpretation of the annual and semiannual anomalies on the magnetic activity over the Earth

Cited by 10 publications

References 24 publications

The effects of seasonal and diurnal variations in the Earth's magnetic dipole orientation on solar wind–magnetosphere‐ionosphere coupling

The effects of seasonal and diurnal variations in the Earth's magnetic dipole orientation on solar wind–magnetosphere‐ionosphere coupling

Possible Origin of Some Periodicities Detected in Solar‐Terrestrial Studies: Earth's Orbital Movements

Statistical Study on the North‐South Asymmetric Distribution of the Mid‐Low‐Latitude Nightside Disturbed Magnetic Fields

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