Solar Cycle 24 Predictions

(News & views on the paper by Wang et al.(2009), RAA, 2009, vol.9, 133-136)

Huaning Wang

( National Astronomical Observatories, Chinese Academy of Sciences

It is well-known that solar cycle prediction is a long lasting hot point in the field of solar physics. Experts provide their predictions for a new solar cycle as early as possible because planning for satellite orbits and space missions often requires knowledge of solar activity levels years in advance. However, none of the experts always give reliable predictions. Hathaway et al.  (1994) believe that predicting the behavior of a sunspot cycle is fairly reliable once the cycle is well underway (about 3 years after the minimum in sunspot number occurs), and prior to that time, the predictions are less reliable.

As usual, many predictions for Solar Cycle 24 have been provided before its beginning. Some of them were given during the ascending phase and the maximum period of Solar Cycle 23 (Kane  1999Badalyan et al.  2001). The third panel charged with determining the official prediction for Solar Cycle 24 for NOAA, NASA and the International Space Environment Service (ISES) summarized most of predictions for Solar Cycle 24 (Biesecker  2008). The prediction techniques are divided into four types: climatology and recent climatology, spectral and neural networks, precursor, and physical-based models. Pesnell  (2007) made a summary of 51 predictions from different predicting techniques, which indicates that the predicted maxima smoothed monthly mean spot number (SMSN) spans the range 40-185. It is interesting that the panel provides two quite different predictions for the Solar Cycle 24 maximum SMSN: 90 (August 2012) or 140 (October 2011). The panel is split! However, all of the panelists predicted that the minimum between Cycles 23 an 24 will appear in March 2008, which has been verified to be an acceptable prediction within 6 months error bars even if there are several months without sunspots on the solar disk after March 2008.

Based on a similar cycle method, Wang et al.  (2009) provide their predictions for Solar Cycle 24. The prediction for the minimum time (March or April 2008) is in agreement with that of the panel, while the prediction for the maximum SMSN is close to 90 (March-October, 2012). Actually, the predicted maxima SMSN of Solar Cycle 24 by the experts in China span the range 78-190 (Wang et al.  2002Le & Wang  2003Li et al.  2005Jiang et al.  2007Du et al.  2008Xu et al.  2008). In order to verify which of the predicted maxima is close to the observed one, we should keep observing the evolution of the new solar cycle. In general, the prediction techniques of climatology and recent climatology, spectral and neural networks, and precursor can be regarded as empirical methods based on statistics. It should be noted that the prediction technique based on the solar dynamo model represents important progress, although some predictions provided with this technique are quite different due to different understandings of solar internal velocity fields (Dikpati et al.  2006Choudhuri et al.  2007). When the solar internal velocity fields are clarified, the solar dynamo models will be well applied for predictions of the long-term behavior of solar activity.


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