Superlong-period oscillations of sunspots according to SOHO MDI data

The work is devoted to the study of the oscillation properties of the magnetic and velocity fields of sunspots with typical periods of up to about 10⁴ min. These oscillations were revealed at the beginning of the 1980s (Gopasyuk, 1981) but remain understudied. Using SOHO MDI data and a technique that allows for measurements of magnetic field H and the heliographic coordinates of sunspots φ and λ with higher accuracy than direct measurements of individual pixels, we have studied 72 sunspots observed on the Sun’s visible hemisphere during no less than 9–11 days (±60–70° from the central meridian) with a time resolution of 1 min. Estimates of random errors of a measurement give σ _H ≈ 60 Gs, σ_φ ≈ 0.055°, and σ_λ ≈ 0.050°. It is found that the main periods of the maximum superlong-period oscillations of sunspots are equal to eight days, according to earlier ground-based measurements. Space observations allow the effect of the Earth’s atmosphere to be totally eliminated; therefore, on the basis of recent data, one can conclude that long-period oscillations of sunspot parameters are a real Sun phenomenon.