Sun rotation

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Understanding Sun Rotation: Key Insights from Recent Research

Methods of Measuring Solar Rotation

Surface Tracers and Doppler Effect

The rotation of the Sun has been extensively studied using two primary methods: tracking the positions of surface tracers and measuring line-of-sight velocities through the Doppler effect. These methods have provided a comprehensive understanding of solar rotation, despite the experimental and interpretational challenges they present .

Differential Rotation of the Sun

Present and Pre-Main-Sequence Sun

The Sun exhibits differential rotation, where the equator rotates faster than the poles. This phenomenon is not only observed in the present Sun but also modeled for its pre-main-sequence evolution. The differential rotation is influenced by convective heat transport and is consistent with observations, showing that the normalized horizontal shear decreases with increasing rotation rate .

Latitudinal Variation

The Sun's rotation is not uniform; gas near the poles rotates slower than at the equator. This latitudinal variation extends to the base of the convection zone, below which the angular velocity becomes more uniform. Observations of solar oscillation modes have revealed that the Sun's interior rotates more slowly than its surface, suggesting a complex rotational structure 34.

Internal Rotation and Helioseismology

Core and Radiative Interior

Helioseismology has significantly advanced our understanding of the Sun's internal rotation. The core and radiative interior exhibit different rotational characteristics compared to the convection zone. The "tachocline" shear layer at the base of the convection zone plays a crucial role in this differential rotation .

Rotational Splitting and Solar Oscillations

The rotational splitting of solar oscillation modes provides insights into the Sun's internal dynamics. These observations indicate that the Sun's core rotates much faster than its surface, with the core's rotation rate being 2-9 times that of the surface .

Theoretical Models and Simulations

Hydrodynamic Instabilities

The Sun's low surface rotation rate is attributed to angular momentum loss due to stellar wind, leading to differential rotation. Hydrodynamic instabilities, such as the axisymmetric baroclinic diffusive (ABCD) instability, limit the increase in rotation speed with depth, ensuring the Sun's rotation remains close to marginal stability .

High-Resolution Simulations

Recent high-resolution simulations have successfully reproduced the Sun's differential rotation, showing that strong magnetic fields generated by small-scale dynamos significantly impact thermal convection. These simulations are crucial for understanding the underlying mechanisms driving solar activity, including the 11-year sunspot cycle .

Conclusion

The rotation of the Sun is a complex and multi-faceted phenomenon, influenced by various factors including differential rotation, internal dynamics, and magnetic fields. Advances in observational techniques and theoretical models have provided a deeper understanding of these processes, revealing the intricate nature of solar rotation and its implications for solar activity.

Sources and full results

Most relevant research papers on this topic

The rotation of the Sun

The rotation of the Sun can be determined using two methods: measuring daily or monthly positions of tracers on the surface or in the corona, and measuring line-of-sight velocities in spectrum lines.

1978·

27citations

·Robert Howard

Differential rotation of the present and the pre-main-sequence Sun

The present Sun's differential rotation model is in good agreement with observations, while the pre-main-sequence Sun's model is weakly dependent on the mixing-length parameter.

2001·

55citations

·M. Küker et al.

Slow rotation of the Sun's interior

There is a substantial region inside the Sun rotating more slowly than the surface, likely a transient situation, and this dynamical problem remains unsolved.

Highly Cited

1995·

77citations

·Y. Elsworth et al.

Solar Interior Rotation and its Variation

The solar interior rotation has been determined through continuous helioseismic observations, revealing core and radiative interior rotation, tachocline shear layer, differential rotation, near-surface shear, and torsional oscillation.

Highly Cited

2009·

278citations

·R. Howe

Internal rotation of the Sun

The internal rotation rate of the Sun is limited by hydrodynamic instabilities, with the lowest threshold being the axisymmetric baroclinic diffusive (ABCD) instability, which is close to marginal stability.

1983·

20citations

·H. Spruit et al.

Rotation of the Sun

The Sun's fast rotation is unstable, and mixing below its convective zone leads to lithium depletion in the photosphere.

1967·

35citations

·P. Goldreich et al.

Asteroseismic detection of latitudinal differential rotation in 13 Sun-like stars

Some Sun-like stars have equators that spin faster than poles, potentially driving magnetic activity.

Highly Cited

2018·

75citations

·O. Benomar et al.

Solar differential rotation reproduced with high-resolution simulation

High-resolution simulations successfully reproduce the solar-like differential rotation, convection, and magnetic field, advancing our understanding of solar activity and the 11-year cycle of sunspots.

2021·

33citations

·H. Hotta et al.

Rapid rotation of the solar interior

The Sun's core rotates 2-9 times as rapidly as its surface, demonstrating a nonuniform rotation and rapid internal rotation.

Highly Cited

1981·

102citations

·A. Claverie et al.

THE ROTATION OF THE SUN [BY PROFESSOR N. C. DUNÉR]

The Rotation of the Sun, [by Professor N. C. Dunér, Director of the Observatory of Upsala]. From a note in the Astronomische Nachrichten, No. 2968, the following very brief summary is made : During the years 1887-8-9 Professor Dunér studied the laws of the rotation of the surface of the sun at different latitudes, by means of a spectroscope and a Rowland grating. The method employed was to compare the spectra of the two borders of the sun. One of these borders is moving towards the earth, the other is moving away from it. Hence the spectral lines of the former are shifted towards the violet end of the spectrum, while the lines of the latter are shifted towards the red end. Measures of the amount of the displacement give a means of calculating the velocity of the motion towards or from the earth, expressed in miles, and this velocity is, of course, a measure of the angu• lar rotation of the surface of the sun at the particular latitude in question. The measures of Professor Dunér were extremely precise, and the following results must be very near the truth. I have added the third column, where his results are expressed in a familiar unit :

1890·

1citation

·E. Holden

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