Solar Rotation, Activity and the Interplanetary Magnetic Field: Forecasting the Strength of the Solar Cycle 24

摘要

This report results from a contract tasking Faculty of Geodesy as follows: Present status: A prediction of the strength of future solar cycles is not an easy task (e.g., Wilson, 1994, Solar and Stellar Activity Cycles, Cambridge Univ. Press; Hanslmeier, Denkmayr, and Weiss, 1999, Sol. Phys. 184, 213). There are currently two principal predictions of the strength of the next solar cycle (no. 24). The first one forecasts that the next solar cycle will be stronger than the last one. This prediction is based on a flux-transport dynamo model (e.g., Dikpati and Gilman, 2006, ApJ 649, 498; Dikpati, de Toma, and Gilman, 2006, GRL 33, L05102). The second prediction forecasts a smaller strength of the cycle no. 24 than was the no. 23. It is based on observations of polar magnetic fields on the Sun and the secular trend of the IMF (Svalgaard and Cliver, 2005; Svalgaard, Cliver, and Kamide, 2005, GRL 32, L01104). This prediction is consistent with the statistical analysis of long-term variability of solar activity (Solanki et al., 2004, Nature 431, 1084). Recently, Brajsa, Ruzdjak, and Woehl (2006, Sol. Phys. 237, 365) investigated temporal variations of the solar rotation determined by sunspot groups in the years 1874-1981. They have used the data set of sunspot groups' positions recorded at Greenwich (1874- 1976) extended by the measurements provided by the Solar Optical Observing Network (SOON) of the US Air Force and the National Oceanic and Atmospheric Administration (NOAA) for the years 1977-1981. The residual method of Gilman and Howard (1984, ApJ 283, 385) was used. This method yields a single number for each year describing the average deviation from the mean value of the solar rotation. A dependence of the rotation velocity residual on the phase of the solar cycle was found as well as a secular deceleration of the observed solar rotation contemporary with the well-known increase of the solar activity.