The solar magnetic field and the solar wind: Existence of preferred longitudes

Neugebauer, M.; Smith, E. J.; Ruzmaikin, A.; Feynman, J.; Vaughan, A. H.

doi:10.1029/1999ja000298

Cited by 72 publications

(59 citation statements)

References 26 publications

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“…Takalo and Mursula (2002) showed that such a node-antinode structure of the ACF can be reproduced if the 27.6-day rotation periodicity is phase/frequency modulated by the solar magnetic cycle. Figure 4b depicts the same ACF together with multiples of a slightly shorter period of 27.03 days which was claimed (Neugebauer et al, 2000) to be the most persistent rotation period in HMF sector structure. The 27.03-day multiples match with the ACF maxima during all antinodes.…”

Section: Longitudinal Asymmetry In Hmf: Need For a Non-axisymmetric Mmentioning

confidence: 99%

Systematically Asymmetric Heliospheric Magnetic Field: Evidence for a Quadrupole Mode and Non-Axisymmetry with Polarity Flip-Flops

Мурсула

Hiltula

2004

Sol Phys

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Abstract.Recent studies of the heliospheric magnetic field (HMF) have detected interesting, systematic hemispherical and longitudinal asymmetries which have a profound significance for the understanding of solar magnetic fields. The in situ HMF measurements since 1960s show that the heliospheric current sheet (HCS) is systematically shifted (coned) southward during solar minimum times, leading to the concept of a bashful ballerina. While temporary shifts can be considerably larger, the average HCS shift (coning) angle is a few degrees, less than the 7.2• tilt of the solar rotation axis. Recent solar observations during the last two solar cycles verify these results and show that the magnetic areas in the northern solar hemisphere are larger and their intensity weaker than in the south during long intervals in the late declining to minimum phase. The multipole expansion reveals a strong quadrupole term which is oppositely directed to the dipole term. These results imply that the Sun has a symmetric quadrupole S0 dynamo mode that oscillates in phase with the dominant dipole A0 mode. Moreover, the heliospheric magnetic field has a strong tendency to produce solar tilts that are roughly opposite in longitudinal phase. This implies is a systematic longitudinal asymmetry and leads to a "flip-flop" type behaviour in the dominant HMF sector whose period is about 3.2 years. This agrees very well with the similar flip-flop period found recently in sunspots, as well as with the observed ratio of three between the activity cycle period and the flip-flop period of sun-like stars. Accordingly, these results require that the solar dynamo includes three modes, A0, S0 and a non-axisymmetric mode. Obviously, these results have a great impact on solar modelling.

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Section: Longitudinal Asymmetry In Hmf: Need For a Non-axisymmetric Mmentioning

confidence: 99%

Systematically Asymmetric Heliospheric Magnetic Field: Evidence for a Quadrupole Mode and Non-Axisymmetry with Polarity Flip-Flops

Мурсула

Hiltula

2004

Sol Phys

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“…A strong correlation exists between the SMMF and the interplanetary magnetic field measured from Earth (Severny et al, 1970;Scherrer et al, 1977;Bremer, 1996) as well as between the SMMF and the solar wind speed (Neugebauer et al, 2000). In a number of papers Sheeley et al (Sheeley, DeVore, and Boris, 1985;Sheeley and DeVore, 1986a,b) investigated the evolution of photospheric magnetic fields and the connection between the SMMF and magnetic transport parameters, including differential rotation and the diffusion coefficient.…”

Section: Introductionmentioning

confidence: 99%

Using SDO/HMI Magnetograms as a Source of the Solar Mean Magnetic Field Data

Kutsenko

Abramenko

2016

Sol Phys

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The solar mean magnetic field (SMMF) provided by the Wilcox Solar Observatory (WSO) is compared with the SMMF acquired by the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamic Observatory (SDO). We found that despite the different spectral lines and measurement techniques used in both instruments the Pearson correlation coefficient between these two datasets equals 0.86 while the conversion factor is very close to unity: B(HMI) = 0.99(2)B(WSO). We also discuss artifacts of the SDO/HMI magnetic field measurements, namely the 12 and 24-hour oscillations in SMMF and in sunspots magnetic fields that might be caused by orbital motions of the spacecraft. The artificial harmonics of SMMF reveal significant changes in amplitude and the nearly stable phase. The connection between the 24-hour harmonic amplitude of SMMF and the presence of sunspots is examined. We also found that opposite phase artificial 12 and/or 24-hour oscillations exist in sunspots of opposite polarities.

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“…But the duration of the periods of one-longitude dominance found in this paper (1.5-2.5 years) remains within the limits of 1.5-3 years observed for sunspots in individual solar cycles (Berdyugina and Usoskin, 2003). However, an incomplete solar cycle of SOHO LASCO data does not allow one to draw a general conclusion about a typical "flip-flop" period for CMEs, especially as the longitudinal dependence of solar activity varies significantly from cycle to cycle (see, for example, Bogart, 1982;Neugebauer et al, 2000;Berdyugina and Usoskin, 2003;Bai, 2003).…”

Section: Discussionmentioning

confidence: 70%

“…The authors were not able to explain this phenomenon. Furthermore, parameters of solar wind exhibit annual cyclicity (see, for example, Neugebauer et al, 2000). It is supposed that it may result from latitudinal dependence of solar wind parameters introduced by the annual variation of the heliographic latitude of the Earth.…”

Section: Discussionmentioning

confidence: 99%

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The east-west asymmetry in Coronal Mass Ejections: evidence for active longitudes

Skirgiello

2005

Ann. Geophys.

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Abstract. Various manifestations of solar activity are not uniformly distributed with heliographic longitude. By using east-west asymmetry in the occurrence rate of CMEs (coronal mass ejections), the longitudinal dependence in SOHO LASCO 1996 data has been studied in this work. The solar rotation periodicity has been found, indicating the presence of active longitudes, whose phase is reversed twice during the studied period. It is more prominent in the Southern Hemisphere. The east-west asymmetry is also present when calculated for longer time periods. Sometimes (particularly during low solar activity), there is an alternation of the eastern and western domination every six months. Taking into account the orbital revolution of the Earth about the Sun, this indicates the existence of enhanced activity, fixed in space (not undergoing Carrington rotation). Moreover, there is about a 3.7% overall excess of western events, lasting for the entire reported time, suggesting some bias in the observations. A hypothesis to explain this phenomenon is proposed.

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The solar magnetic field and the solar wind: Existence of preferred longitudes

Cited by 72 publications

References 26 publications

Systematically Asymmetric Heliospheric Magnetic Field: Evidence for a Quadrupole Mode and Non-Axisymmetry with Polarity Flip-Flops

Systematically Asymmetric Heliospheric Magnetic Field: Evidence for a Quadrupole Mode and Non-Axisymmetry with Polarity Flip-Flops

Using SDO/HMI Magnetograms as a Source of the Solar Mean Magnetic Field Data

The east-west asymmetry in Coronal Mass Ejections: evidence for active longitudes

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