The main goals of the symposium is to understand the origin and to seek the predictability of solar cycle, by an interdisciplinary and systematic investigation of the available solar, stellar, heliospheric, geomagnetic, and cosmogenic longterm datasets relevant to the solar magnetic activities.

There are two necessities to hold the symposium. One is the potential problems and divergences in the datasets, which seriously hinder and even mislead the understanding of the solar dynamo. The contradictory results among different datasets are even a usual problem. Indices of solar activities, like the sunspot number, exist in different versions with conflicting results. Different indices having similar origin sometimes show unexpected behaviors. The differences are attributed to :

  1. Limitations or biases affects the observations. The well-known examples are magnetic saturation, scattered light, polarization crosstalk and so on in the magnetic field measurement.
  2. The difficulties in cross-calibrations among different time periods and different instruments. These are the major causes of the different versions of the solar total and spectral irradiance datasets.
  3. The difficulties to invert the physical parameters based on the observations.

The conflicting results about the meridional flow, which are deduced from different inversion techniques using the same SDO/HMI data, in the convective zone is an example. All these issues show the necessity for a symposium to assemble available indices of the solar activities and the available datasets versions of different indices, to outline the statues and the divergences, to do the cross-comparisons of the datasets, to build up the homogeneous datasets and to learn something about the solar magnetic cycle.

The other necessity is that, up to now there were no dedicated meetings focused specifically to look at these long-term data in their totality. There were some workshops and symposia focused on the different aspects of various datasets. Here we plan for the first dedicated meeting to investigate these long-term data in depth by an interdisciplinary, system-wide view on the datasets and to discuss what the reliable data tell us about our real Sun, especially the natural cycle. This is the most unique feature of the meeting.