On Predicting the Solar Cycle Using Mean-Field Models
On Predicting the Solar Cycle Using Mean-Field Models
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DOI：
10.1086/516628
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发表时间：
2007-04
期刊：
影响因子：
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通讯作者：
P. Bushby;S. Tobias
中科院分区：
文献类型：
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作者：
P. Bushby;S. Tobias
我们讨论了使用平均场模型预测太阳周期的困难。在这里，我们认为，这些困难是由于太阳活动周期的显著调制而产生的，这种调制是由于随机或确定性过程而产生的。我们通过考虑两个独立的太阳能发电机模型来分析这两种情况对可预测性的影响。第一个模型表示随机扰动通量输运发电机。在这里，即使是非常弱的随机扰动也能在活动周期中引起显著的调制。这种调制导致了可预测性的丧失。在第二个模型中，我们忽略了随机效应，并假设太阳磁场的产生可以用一个完全确定的非线性平均场模型来描述——这是预测的最佳情况。我们将这个确定性模型的输出（参数选择为产生混沌调制周期）指定为需要后续确定性平均场模型预测的目标时间序列。即使在预测中使用一个在所有细节上都正确的模型，也不可能进行长期预测。此外，我们还表明，如果基准模型的输入参数存在很小的差异，即使是短期预测也是不可能的。即使预测模型经过调整以重现之前周期的输出，情况也是如此。考虑到在确定平均场模式的输运系数和非线性响应时固有的不确定性，我们认为这使得利用这些模式的输出来预测太阳周期是不可能的。
We discuss the difficulties of predicting the solar cycle using mean-field models. Here we argue that these difficulties arise owing to the significant modulation of the solar activity cycle, and that this modulation arises owing to either stochastic or deterministic processes. We analyze the implications for predictability in both of these situations by considering two separate solar dynamo models. The first model represents a stochastically perturbed flux transport dynamo. Here even very weak stochastic perturbations can give rise to significant modulation in the activity cycle. This modulation leads to a loss of predictability. In the second model, we neglect stochastic effects and assume that generation of magnetic field in the Sun can be described by a fully deterministic nonlinear mean-field model—this is a best case scenario for prediction. We designate the output from this deterministic model (with parameters chosen to produce chaotically modulated cycles) as a target time series that subsequent deterministic mean-field models are required to predict. Long-term prediction is impossible even if a model that is correct in all details is utilized in the prediction. Furthermore, we show that even short-term prediction is impossible if there is a small discrepancy in the input parameters from the fiducial model. This is the case even if the predicting model has been tuned to reproduce the output of previous cycles. Given the inherent uncertainties in determining the transport coefficients and nonlinear responses for mean-field models, we argue that this makes it impossible to predict the solar cycle using the output from such models.