Solar activity cycle and rotation of the corona

¹ Observatoire de Paris, LESIA, 92195 Meudon Cedex, France
² Observatoire de Bordeaux, Avenue Pierre Semirot, 33270 Floirac, France

Corresponding author: Z. Mouradian, zadig.mouradian@obspm.fr

Received: 5 June 2002
Accepted: 13 August 2002

Abstract

In this paper we consider the dependence of the coronal rotation period on solar activity. We analyzed the 10.7 cm radio emission flux covering cycles 19 to 22. We have established a new method for studying the rotation rate: by identifying the flux pulses with the recurrence of active longitudes. We first determined the frequency domain of the rotation and then analyzed each cycle separately. The entire domain of 51.7 years was divided into 480-day sections, which were analyzed independently and then grouped into frames for each cycle in order to study the time variation of prominent frequencies (Fig. [see full text]). Power spectra were obtained with the Maximum Entropy Method. The 10.7 cm emission rotation varies accordingly to the activity level, i.e. at the activity maxima the synodic period of rotation is about 25.4 days and at the minima it is around 30 days; it is 32 days for the quiet Sun (Table [see full text]). Empirical relations give the ratio of maximum and minimum sidereal rotation rate with respect to sunspot number (Fig. [see full text]). During the cycle increase phase, the average acceleration of the rotation period is per year, in decreasing phase that average is only -0.5.