Periodicities in the coronal rotation and sunspot numbers

Abstract

The present study is an attempt to investigate the long term variations in coronal rotation by analyzing the time series of the solar radio emission data at 2.8 GHz frequency for the period 1947 - 2009. Here, daily adjusted radio flux (known as Penticton flux) data are used. The autocorrelation analysis shows that the rotation period varies between 19.0 to 29.5 sidereal days (mean sidereal rotation period is 24.3 days). This variation in the coronal rotation period shows evidence of two components in the variation; (1) 22-years component which may be related to the solar magnetic field reversal cycle or Hale's cycle, and (3) a component which is irregular in nature, but dominates over the other components. The crosscorrelation analysis between the annual average sunspots number and the coronal rotation period also shows evidence of its correlation with the 22-years Hale's cycle. The 22-years component is found to be almost in phase with the corresponding periodicities in the variation of the sunspots number.Comment: 9 pages, 5 figures, Accepted for publication in MNRA

A relationship between the solar rotation and activity in the period 1998–2006 analysed by tracing small bright coronal structures in SOHO-EIT images

“…Various frequencies correspond to various altitudes in the solar corona and different methods have been used (e.g., the Sun analysed as a star with no latitudinal dependence, autocorrelation analysis with a time lag, etc.). However, it seems that up to now either a very weak or no correlation between the coronal rotational period and the sunspot activity can be verified Chandra & Vats 2011). This result refers to the height of about 60 000 km and the observing frequency of 2.8 GHz.…”

Long-term variations of the coronal rotation and solar activity

“…Coronal differential rotation has been also investigated by white light, soft X‐ray, ultraviolet (UV) rays, radio, and so on (Chandra & Vats 2011). Studies of the white‐light corona show a radially rigid rotation in the corona.…”

“…Satellite observations allow us to study the coronal differential rotation using soft X‐ray and UV rays. Some authors have shown that there is an almost rigid corona in soft X‐ray and UV rays, or a shallower rotation profile of the corona that varies with latitudes unlike at the lower atmosphere (Timothy, Krieger & Vaiana 1975; Weber, Alexander & Acton 1997; Weber et al 1999; Chandra, Vats & Iyer 2010; Chandra & Vats 2011; Vats & Chandra 2011). However, others have obtained contrasting results (Brajs̆a et al 2002, 2004; Karachik et al 2006; Zaatri et al 2009; Wöhl et al 2010).…”

“…Chandra, Vats & Iyer (2009) and Chandra et al (2010) have calculated the yearly equatorial rotation rate using both radio images at 17 GHz during the period 1999–2001 and soft X‐ray telescope (SXT) data during 1992–2001. The equatorial rotation rate seems largely to be a function of the phases of the solar cycle (Chandra et al 2009, 2010; Chandra & Vats 2011). By utilizing solar radio flux data at various frequencies, some research groups have ascertained the rotation period of the solar corona (Vats et al 1998a,b; Kane, Vats & Sawant 2001; Mouradian et al 2002), its differentiality as a function of altitude (Vats et al 2001) and latitude (Chandra et al 2009), and its relationship with the sunspot cycle (Mehta 2005; Chandra & Vats 2011).…”

“…For example, we cannot clearly ascertain whether the coronal rotation is rigid or differential, as we can for the lower atmosphere, or whether the variation of the coronal rotation is independent of or dependent on a sunspot cycle. Chandra & Vats (2011) have obtained the yearly period length of the solar coronal rotation cycle by analysing the daily adjusted solar radio flux at the 10.7‐cm wavelength during the period 1947–2009. In this paper, we use the time series of the yearly period length to investigate the long‐term variations of the rotation of the solar radio emission corona and solar radio emission activity.…”