Solar activity and the solar cycle

Solar activity prediction methods have been wide-ranging, mostly numerical, and essentially curve fitting. Thus for many years the search for physically based methods has remained elusive. Surprisingly, a new class of methods does seem to be making Progress, and it relates to the structure of the field within the Sun and heliosphere. This class is. now based on solar dynamo physics, but began with some surprising observations that the Sun's activity can be predicted by monitoring geomagnetic precursors, namely geomagnetic fluctuations near solar minimum. It was puzzling how the Sun could broadcast its future activity levels to the Earth! We have developed some understanding for how these methods work based on the Sun's dynamo and the structure of the magnetic field in the heliosphere. Additionally, we have expanded the prediction methods using a SODA index (SOlar Dynamo Amplitude), which monitors the Sun's buried dynamo fields. Thus the prediction methods have changed from numerical schemes to an understanding of the Sun's dynamo processes- to explain a connection between how the Sun's fields are generated and how the Sun broadcasts its future activity levels to Earth. This has led to better monitoring of the Sun's dynamo fields buried deep within the Sun, leading to more accurate prediction techniques, based on the Sun's polar and toroidal magnetic fields. We explain how these methods work and discuss solar activity predictions for solar cycles #23 and #24. At the present time the SODA index suggests a reduced amount of buried magnetic flux, hence unless dynamo processes increase dramatically, solar cycle #24 will likely be significantly smaller than cycle #23! At present, the mean smoothed F10.7 value is forecasted as 155 +/- 30, corresponding to Rz of 100+/-30. (C) 2003 COSPAR. Published by Elsevier Ltd. All rights reserved.