The radial gradient of the near-surface shear layer of the Sun

A. Barekat, J. Schou, Laurent Gizon

Research output: Contribution to journalArticle

Abstract

Context. Helioseismology has provided unprecedented information about the internal rotation of the Sun. One of the important achievements was the discovery of two radial shear layers: one near the bottom of the convection zone (the tachocline) and one near the surface. These shear layers may be important ingredients for explaining the magnetic cycle of the Sun. Aims. We measure the logarithmic radial gradient of the rotation rate (dlnΩ/dlnr) near the surface of the Sun using 15 years of f mode rotational frequency splittings from the Michelson Doppler Imager (MDI) and four years of data from the Helioseismic and Magnetic Imager (HMI). Methods. We model the angular velocity of the Sun in the upper ~10 Mm as changing linearly with depth and use a multiplicative optimally localized averaging inversion to infer the gradient of the rotation rate as a function of latitude. Results. Both the MDI and HMI data show that dlnΩ/dlnr is close to-1 from the equator to 60° latitude and stays negative up to 75°latitude. However, the value of the gradient is different for MDI and HMI for latitudes above 60°. Additionally, there is a significant difference between the value of dlnΩ/dlnr using an older and recently reprocessed MDI data for latitudes above 30°. Conclusions. We could reliably infer the value of dlnΩ/dlnr up to 60°, but not above this latitude, which will hopefully constrain theories of the near-surface shear layer and dynamo. Furthermore, the recently reprocessed MDI splitting data are more reliable than the older versions which contained clear systematic errors in the high degree f modes.

Original languageEnglish (US)
Article number24839
JournalAstronomy and Astrophysics
Volume570
DOIs
StatePublished - Oct 1 2014

Fingerprint

shear layers
sun
gradients
helioseismology
equators
angular velocity
guy wires
ingredients
systematic errors
convection
inversions
cycles
rate

Keywords

  • Sun: helioseismology
  • Sun: interior
  • Sun: rotation

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

The radial gradient of the near-surface shear layer of the Sun. / Barekat, A.; Schou, J.; Gizon, Laurent.

In: Astronomy and Astrophysics, Vol. 570, 24839, 01.10.2014.

Research output: Contribution to journalArticle

@article{9373f516f5824b5c8c2d8cf42de1f1c2,
title = "The radial gradient of the near-surface shear layer of the Sun",
abstract = "Context. Helioseismology has provided unprecedented information about the internal rotation of the Sun. One of the important achievements was the discovery of two radial shear layers: one near the bottom of the convection zone (the tachocline) and one near the surface. These shear layers may be important ingredients for explaining the magnetic cycle of the Sun. Aims. We measure the logarithmic radial gradient of the rotation rate (dlnΩ/dlnr) near the surface of the Sun using 15 years of f mode rotational frequency splittings from the Michelson Doppler Imager (MDI) and four years of data from the Helioseismic and Magnetic Imager (HMI). Methods. We model the angular velocity of the Sun in the upper ~10 Mm as changing linearly with depth and use a multiplicative optimally localized averaging inversion to infer the gradient of the rotation rate as a function of latitude. Results. Both the MDI and HMI data show that dlnΩ/dlnr is close to-1 from the equator to 60° latitude and stays negative up to 75°latitude. However, the value of the gradient is different for MDI and HMI for latitudes above 60°. Additionally, there is a significant difference between the value of dlnΩ/dlnr using an older and recently reprocessed MDI data for latitudes above 30°. Conclusions. We could reliably infer the value of dlnΩ/dlnr up to 60°, but not above this latitude, which will hopefully constrain theories of the near-surface shear layer and dynamo. Furthermore, the recently reprocessed MDI splitting data are more reliable than the older versions which contained clear systematic errors in the high degree f modes.",
keywords = "Sun: helioseismology, Sun: interior, Sun: rotation",
author = "A. Barekat and J. Schou and Laurent Gizon",
year = "2014",
month = "10",
day = "1",
doi = "10.1051/0004-6361/201424839",
language = "English (US)",
volume = "570",
journal = "Astronomy and Astrophysics",
issn = "0004-6361",
publisher = "EDP Sciences",

}

TY - JOUR

T1 - The radial gradient of the near-surface shear layer of the Sun

AU - Barekat, A.

AU - Schou, J.

AU - Gizon, Laurent

PY - 2014/10/1

Y1 - 2014/10/1

N2 - Context. Helioseismology has provided unprecedented information about the internal rotation of the Sun. One of the important achievements was the discovery of two radial shear layers: one near the bottom of the convection zone (the tachocline) and one near the surface. These shear layers may be important ingredients for explaining the magnetic cycle of the Sun. Aims. We measure the logarithmic radial gradient of the rotation rate (dlnΩ/dlnr) near the surface of the Sun using 15 years of f mode rotational frequency splittings from the Michelson Doppler Imager (MDI) and four years of data from the Helioseismic and Magnetic Imager (HMI). Methods. We model the angular velocity of the Sun in the upper ~10 Mm as changing linearly with depth and use a multiplicative optimally localized averaging inversion to infer the gradient of the rotation rate as a function of latitude. Results. Both the MDI and HMI data show that dlnΩ/dlnr is close to-1 from the equator to 60° latitude and stays negative up to 75°latitude. However, the value of the gradient is different for MDI and HMI for latitudes above 60°. Additionally, there is a significant difference between the value of dlnΩ/dlnr using an older and recently reprocessed MDI data for latitudes above 30°. Conclusions. We could reliably infer the value of dlnΩ/dlnr up to 60°, but not above this latitude, which will hopefully constrain theories of the near-surface shear layer and dynamo. Furthermore, the recently reprocessed MDI splitting data are more reliable than the older versions which contained clear systematic errors in the high degree f modes.

AB - Context. Helioseismology has provided unprecedented information about the internal rotation of the Sun. One of the important achievements was the discovery of two radial shear layers: one near the bottom of the convection zone (the tachocline) and one near the surface. These shear layers may be important ingredients for explaining the magnetic cycle of the Sun. Aims. We measure the logarithmic radial gradient of the rotation rate (dlnΩ/dlnr) near the surface of the Sun using 15 years of f mode rotational frequency splittings from the Michelson Doppler Imager (MDI) and four years of data from the Helioseismic and Magnetic Imager (HMI). Methods. We model the angular velocity of the Sun in the upper ~10 Mm as changing linearly with depth and use a multiplicative optimally localized averaging inversion to infer the gradient of the rotation rate as a function of latitude. Results. Both the MDI and HMI data show that dlnΩ/dlnr is close to-1 from the equator to 60° latitude and stays negative up to 75°latitude. However, the value of the gradient is different for MDI and HMI for latitudes above 60°. Additionally, there is a significant difference between the value of dlnΩ/dlnr using an older and recently reprocessed MDI data for latitudes above 30°. Conclusions. We could reliably infer the value of dlnΩ/dlnr up to 60°, but not above this latitude, which will hopefully constrain theories of the near-surface shear layer and dynamo. Furthermore, the recently reprocessed MDI splitting data are more reliable than the older versions which contained clear systematic errors in the high degree f modes.

KW - Sun: helioseismology

KW - Sun: interior

KW - Sun: rotation

UR - http://www.scopus.com/inward/record.url?scp=84908316345&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84908316345&partnerID=8YFLogxK

U2 - 10.1051/0004-6361/201424839

DO - 10.1051/0004-6361/201424839

M3 - Article

AN - SCOPUS:84908316345

VL - 570

JO - Astronomy and Astrophysics

JF - Astronomy and Astrophysics

SN - 0004-6361

M1 - 24839

ER -