Solar Cycle Observations

Norton, Aimee; Howe, Rachel; Upton, Lisa; Usoskin, Ilya

doi:10.1007/s11214-023-01008-3

Cited by 8 publications

(4 citation statements)

References 147 publications

(177 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The differential rotation varies only weakly across these low latitudes, varying in total by about 13% (see Methods) across latitudes ±15 • of the equator (20; 31; 32). Since the meridional flow is 1-2 orders of magnitude weaker (32), this supports the overall picture that extreme eruptions initiated at mid latitudes are ultimately powered by shearing of magnetic field driven by the latitudinal gradient in differential rotation, corresponding to more frequent and higher energy CMEs, so that CME rates roughly track the SSN (29) and are less energetic around solar minimum (33). Conditions around solar maximum then result in the most intense, CME driven geomagnetic activity.…”

Section: Mainsupporting

confidence: 68%

A solar cycle clock for extreme space weather

Chapman,

de Wit

2024

Preprint

View full text Add to dashboard Cite

The variable solar cycle of activity is a long-standing problem in physics. It modulates the overall level of space weather activity at earth, which in turn can have significant societal impact. The Hilbert transform of the sunspot number is used to map the variable length, approximately 11 year Schwabe cycle onto a uniform clock. The clock is used to correlate extreme space weather seen in the aa index, the longest continuous geomagnetic record at earth, with the record of solar active region areas and latitudes since 1874. This shows that a clear switch-off of the mostextreme space weather events occurs when the solar active regions move to within 15 degrees of the solar equator, from regions of high gradient in solar differential rotation which can power coronal mass ejections, to a region where solar differential rotation is almost constant with latitude. This overlaps with the onset of more moderate space weather events which coincide with 27 day solar rotation recurrences in the aa index, consistent with stable, persistent source regions.This offers a physical explanation for the longstanding identification of a two component cycle of activity in the aa index.

show abstract

Section: Mainsupporting

confidence: 68%

A solar cycle clock for extreme space weather

Chapman,

de Wit

2024

Preprint

View full text Add to dashboard Cite

show abstract

“…. We choose τ ξ = 2 months, which is roughly equal to the lifetime of big active regions (Norton et al 2023). The ξ α varies independently in the northern and southern hemispheres.…”

Section: Discussionmentioning

confidence: 99%

Toroidal Magnetic Flux Budget in Mean-field Dynamo Model of Solar Cycles 23 and 24

Pipin,

Kosovichev

2024

ApJ

View full text Add to dashboard Cite

We study the toroidal magnetic flux budget of the axisymmetric part of a data-driven 3D mean-field dynamo model of Solar Cycles 23 and 24. The model simulates the global solar dynamo that includes the effects of the formation and evolution of bipolar magnetic regions (BMRs) emerging on the solar surface. By applying Stokes’s theorem to the dynamo induction equation, we show that the hemispheric magnitude of the net axisymmetric toroidal magnetic field generation rate in the bulk of the convection zone can only partially be estimated from the surface parameters of the differential rotation and the axisymmetric radial magnetic field. The contribution of the radial integral along the equator, which is mostly due to the rotational radial shear at the bottom of the convection zone, has the same magnitude and is nearly in phase with the effect of the surface latitudinal differential rotation. Also, the toroidal field generation rate estimate strongly depends on the latitudinal profile of the surface radial magnetic field near the poles. This profile in our dynamo models significantly deviates from the polar magnetic field distribution observed during the minima of Solar Cycles 22, 23, and 24. The cause of this discrepancy requires further observational and theoretical studies. Comparing the 2D axisymmetric and the 3D nonaxisymmetric dynamo models, we find an increase in the toroidal field generation rate in the 3D model due to the surface effects of BMRs, resulting in an increase in the axisymmetric poloidal magnetic field magnitude.

show abstract

“…The axisymmetric differential rotation increases with decreasing latitude, maximising at the solar equator. The differential rotation varies only weakly across these low latitudes, varying in total by about 13% (see Methods) across latitudes of the equator 30 – 32 . Since the meridional flow is 1–2 orders of magnitude weaker 32 , this supports the overall picture that extreme eruptions initiated at mid latitudes are ultimately powered by shearing of magnetic field driven by the latitudinal gradient in differential rotation, corresponding to more frequent and higher energy CMEs, so that CME rates roughly track the SSN 28 and are less energetic around solar minimum 33 .…”

Section: Introductionmentioning

confidence: 99%

A solar cycle clock for extreme space weather

Chapman,

Dudok de Wit

2024

Sci Rep

View full text Add to dashboard Cite

The variable solar cycle of activity is a long-standing problem in physics. It modulates the overall level of space weather activity at earth, which in turn can have significant societal impact. The Hilbert transform of the sunspot number is used to map the variable length, approximately 11 year Schwabe cycle onto a uniform clock. The clock is used to correlate extreme space weather seen in the aa index, the longest continuous geomagnetic record at earth, with the record of solar active region areas and latitudes since 1874. This shows that a clear switch-off of the most extreme space weather events occurs when $$>90$$ > 90 % of solar active region areas have moved to within about 15° of the solar equator, from regions of high gradient in solar differential rotation which can power coronal mass ejections, to a region where solar differential rotation is almost constant with latitude. More moderate space weather events which coincide with 27 day solar rotation recurrences in the aa index, consistent with stable, persistent source regions of high speed streams, commence when the centroid of solar active region areas moves to within 15° of the solar equator. This offers a physical explanation for the longstanding identification of a two component cycle of activity in the aa index.

show abstract

Solar Cycle Observations

Cited by 8 publications

References 147 publications

A solar cycle clock for extreme space weather

A solar cycle clock for extreme space weather

Toroidal Magnetic Flux Budget in Mean-field Dynamo Model of Solar Cycles 23 and 24

A solar cycle clock for extreme space weather

Contact Info

Product

Resources

About