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Astron. Astrophys. 327, 795-799 (1997)

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Estimation of the depths of initial anchoring and the rising-rates of sunspot magnetic structures from rotation frequencies of sunspot groups

J. Javaraiah and M.H. Gokhale

Indian Institute of Astrophysics, Bangalore - 560 034, India

Received 11 April 1997 / Accepted 1 July 1997

Abstract

The mean variation of the 'initial' rotation frequency of sunspot groups, with the life span of spot groups in the range 12 to 2 days, has its trend similar to the radial variation of plasma rotation frequency, [FORMULA], across the convective envelope at [FORMULA] latitude as given by helioseismology.

The mean variation, with age, of the rotation frequency of sunspot groups which live for 10-12 days in latitudes [FORMULA] also has its trend similar to [FORMULA].

These results suggest: (i) In all latitudes, the magnetic structures (e.g, bunch of flux tubes) of spot groups which live for 2 days are initially anchored near the surface (radial distance [FORMULA] Mm), and those of spot groups which live successively longer are initially anchored in successively deeper layers, by [FORMULA] 21000 km per day, (ii) the structures which yield spot groups living 10-12 days are initially anchored near the base of the convective envelope.

For a spot group which lives 10-12 days in latitudes [FORMULA], the 'anchoring layer' of its magnetic structure rises at a rate [FORMULA] km day-1, as the spot group ages.

Key words: Sun: sunspots – Sun: rotation

Send offprint requests to: J. Javaraiah

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© European Southern Observatory (ESO) 1997

Online publication: April 6, 1998
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