Current shipping, tourism, and resource development requirements call for more accurate predictions of the Arctic sea-ice concentration (SIC). However, due to the complex physical processes involved, predicting the spatiotemporal distribution of Arctic SIC is more challenging than predicting its total extent. In this study, spatiotemporal prediction models for monthly Arctic SIC at 1- to 3-month leads are developed based on U-Net—an effective convolutional deep-learning approach. Based on explicit Arctic sea-ice–atmosphere interactions, 11 variables associated with Arctic sea-ice variations are selected as predictors, including observed Arctic SIC, atmospheric, oceanic, and heat flux variables at 1- to 3-month leads. The prediction skills for the monthly Arctic SIC of the test set (from January 2018 to December 2022) are evaluated by examining the mean absolute error (MAE) and binary accuracy (BA). Results showed that the U-Net model had lower MAE and higher BA for Arctic SIC compared to two dynamic climate prediction systems (CFSv2 and NorCPM). By analyzing the relative importance of each predictor, the prediction accuracy relies more on the SIC at the 1-month lead, but on the surface net solar radiation flux at 2- to 3-month leads. However, dynamic models show limited prediction skills for surface net solar radiation flux and other physical processes, especially in autumn. Therefore, the U-Net model can be used to capture the connections among these key physical processes associated with Arctic sea ice and thus offers a significant advantage in predicting Arctic SIC.
摘要
准确地预测北极海冰密集度 (SIC) 对北极航运, 旅游和资源开发等十分重要. 由于北极海冰的复杂多变, 预测北极SIC的时空分布比预测海冰范围更具有挑战性. 基于一个有效的卷积类机器学习模型—U-Net, 本文研制了可用于预测未来1至3个月北极SIC的模型. 基于北极海–冰–气物理过程, 本文选取了前期11个与北极海冰变化密切相联的变量作为预测因子, 包括北极SIC, 大气, 海洋和热通量等变量. 较CFSv2和NorCPM而言, 本文研制的U-Net模型具有更高的预测技巧. 此外, 诊断各预测因子的相对重要性显示, 提前1个月的预测模型更依赖于前期的SIC, 但提前2和3个月的预测模型则更依赖于前期的地表净短波辐射通量. 然而, 动力模式对地表净短波辐射和其相关物理过程的预测技能有限, 这可能是U-Net模型预测技巧较动力模式更高的原因之一. 本研究既有利于提升对北极SIC空间分布的预测能力, 也有助于进一步认识动力模式对海冰预测效能有限的原因.
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