Impact of hindcast length on estimates of seasonal climate predictability.
Impact of hindcast length on estimates of seasonal climate predictability.
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DOI：
10.1002/2014gl062829
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发表时间：
2015-03-16
影响因子：
5.2
通讯作者：
Weisheimer, A.
中科院分区：
文献类型：
--
作者：
Shi, W.;Schaller, N.;MacLeod, D.;Palmer, T. N.;Weisheimer, A.
关键词：
最近有人认为，单一模式的季节预报集合过于分散，这意味着真实的世界比所谓的完美模式可预测性估计所表明的更可预测，特别是在北大西洋。然而，这种估计是基于相对较短的预测数据集，仅包括20年的季节性预测。在这里，我们研究了更长的40年的季节预报数据集，从多模式季节预报集成项目，并表明，由于后报期的长度抽样的不确定性是很大的。冬季北大西洋涛动的预报技巧在40年的数据集内各不相同，在某些子周期内发现了高水平的技巧。结果表明，虽然20年的季节性可靠性估计可以显示过度分散行为的证据，40年的估计是更稳定的，没有过度分散的证据。相反，这些较长时间尺度上的主要特征是分散不足，特别是在热带地区。由于后报长度的抽样误差，预测可能会出现过度分散。较长的后报更加稳健，分散性不足，特别是在热带地区。
It has recently been argued that single-model seasonal forecast ensembles are overdispersive, implying that the real world is more predictable than indicated by estimates of so-called perfect model predictability, particularly over the North Atlantic. However, such estimates are based on relatively short forecast data sets comprising just 20 years of seasonal predictions. Here we study longer 40 year seasonal forecast data sets from multimodel seasonal forecast ensemble projects and show that sampling uncertainty due to the length of the hindcast periods is large. The skill of forecasting the North Atlantic Oscillation during winter varies within the 40 year data sets with high levels of skill found for some subperiods. It is demonstrated that while 20 year estimates of seasonal reliability can show evidence of overdispersive behavior, the 40 year estimates are more stable and show no evidence of overdispersion. Instead, the predominant feature on these longer time scales is underdispersion, particularly in the tropics. Predictions can appear overdispersive due to hindcast length sampling error Longer hindcasts are more robust and underdispersive, especially in the tropics Twenty hindcasts are an inadequate sample size to assess seasonal forecast skill