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Solar Physics

, Volume 189, Issue 1, pp 69–83 | Cite as

Measurement of Kodaikanal white-light images – IV. Axial Tilt Angles of Sunspot Groups

  • K.R. Sivaraman
  • S.S. Gupta
  • Robert F. Howard
Article

Abstract

The Kodaikanal sunspot data set, covering the interval 1906–1987, is used in conjunction with the similar Mount Wilson sunspot data set, covering the interval 1917–1985, to examine characteristics of sunspot group axial tilt angles. Good agreement is demonstrated between various results derived from the two independent data sets. In particular, the tendency for sunspot groups near the average tilt angle to be larger than those far from the average tilt angle is confirmed. Similarly the faster residual rotation rate for groups near the average tilt angle is also confirmed. Other confirmations are made for the relationships between latitude drift of sunspot groups and tilt angle, polarity separations, and axial expansion. Evidence is presented that tilt angles averaged over these long time intervals differ between the north and south hemispheres by about 1.4 deg. It is suggested that residual tilt angles show a slight systematic variation with phase in the activity cycle.

Keywords

Tilt Angle Rotation Rate Systematic Variation Independent Data Activity Cycle 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Kluwer Academic Publishers 1999

Authors and Affiliations

  • K.R. Sivaraman
    • 1
  • S.S. Gupta
    • 1
  • Robert F. Howard
    • 2
  1. 1.Indian Institute of AstrophysicsBangaloreIndia
  2. 2.National Solar Observatory, National Optical Astronomy ObservatoriesTucsonU.S.A

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