A Comparison of Solar Cycle Variations in the Equatorial Rotation Rates of the Sun’s Subsurface, Surface, Corona, and Sunspot Groups
- 240 Downloads
Using the Solar Optical Observing Network (SOON) sunspot-group data for the period 1985 – 2010, the variations in the annual mean equatorial-rotation rates of the sunspot groups are determined and compared with the known variations in the solar equatorial-rotation rates determined from the following data: i) the plasma rotation rates at 0.94R⊙,0.95R⊙,…,1.0R⊙ measured by the Global Oscillation Network Group (GONG) during the period 1995 – 2010, ii) the data on the soft-X-ray corona determined from Yohkoh/SXT full-disk images for the years 1992 – 2001, iii) the data on small bright coronal structures (SBCS) that were traced in Solar and Heliospheric Observatory (SOHO)/EIT images during the period 1998 – 2006, and iv) the Mount Wilson Doppler-velocity measurements during the period 1986 – 2007. A large portion (up to ≈ 30∘ latitude) of the mean differential-rotation profile of the sunspot groups lies between those of the internal differential-rotation rates at 0.94R⊙ and 0.98R⊙. The variation in the yearly mean equatorial-rotation rate of the sunspot groups seems to be lagging behind that of the equatorial-rotation rate determined from the GONG measurements by one to two years. The amplitude of the GONG measurements is very small. The solar-cycle variation in the equatorial-rotation rate of the solar corona closely matches that determined from the sunspot-group data. The variation in the equatorial-rotation rate determined from the Mount Wilson Doppler-velocity data closely resembles the corresponding variation in the equatorial-rotation rate determined from the sunspot-group data that included the values of the abnormal angular motions (> |3∘| day−1) of the sunspot groups. Implications of these results are pointed out.
KeywordsSolar Cycle Rotation Rate Sunspot Group Global Oscillation Network Group Solar Convection Zone
The author thanks the anonymous referee for the detailed comments and useful suggestions, and H.M. Antia for providing the values of the internal-rotation rates that he has determined from GONG data. The author also thanks Luca Bertello for helpful comments and suggestions, B.A. Varghese for his help in making the figures, and the organizers of the LWS/SDO-3/SOHO26/GONG-2011 workshop for kindly providing a partial financial support to attend the workshop. This work used data obtained by the Global Oscillation Network Group (GONG) Program, managed by the National Solar Observatory (NSO), which is operated by AURA, Inc. under a cooperative agreement with the National Science Foundation. The data were acquired by instruments operated by the Big Bear Solar Observatory, High Altitude Observatory, Learmonth Solar Observatory, Udaipur Solar Observatory, Instituto de Astrofísico de Canarias, and Cerro Tololo Interamerican Observatory.
- Carrington, R.C.: 1863 Observations of the Spots on the Sun, Williams and Norgate, London. Google Scholar
- Javaraiah, J.: 2003b, In: Pevtsov, A.A., Uitenbroek, H. (eds.) Current Theoretical Models and Future High Resolution Solar Observations: Preparing for ATST CS-286, Astron. Soc. Pac., San Francisco, 325. Google Scholar
- Javaraiah, J., Gokhale, M.H.: 2002, The Sun’s Rotation, Nova Science, New York. Google Scholar
- Kosovichev, A.G.: 2002, Astron. Nachr. 323, 186. doi: 10.1002/1521-3994(200208)323:3/4<186::AID-ASNA186>3.0.CO;2-I. ADSCrossRefGoogle Scholar
- Rosner, R., Weiss, N.O.: 1992, In: Harvey, K.L. (ed.) The Solar Cycle CS-27, Astron. Soc. Pac., San Francisco, 511. Google Scholar