基于资料同化的南海北部陆坡流季节内变化的可预报性研究

At present, most researches on the South China Sea circulation are focused on revealing the evolution law and controlling mechanism on the multi spatial and temporal scales, but there are few researches on the predictability. The slope current in the Northern South China Sea (NSCS) is the northern branch of the western boundary current in the South China Sea. Modulated by the wind field, Kuroshio, and the flow-eddy interaction, the intra-seasonal variation of the slope current in the NSCS is very active. Accurate prediction of the intra-seasonal variation of the slope current in the NSCS is of great significance for improving the prediction level of the thermal and dynamic state in the South China Sea. The predictability of the intra-seasonal variation of the slope current in the NSCS is an important scientific problem to be studied and solved. However, the influence of the uncertainties of the controlling factors on the predictable time of the intra-seasonal variation of the slope current in the NSCS is still unclear,that limits the further study in this area. Therefore, based on the multi-source observations in the South China Sea, the predictable time of the intra-seasonal slope current in the NSCS influenced by the uncertainties of the wind filed, Kuroshio, and the background currents in the NSCS will be analyzed by reducing the uncertainties of the different controlling factors using the technique of data assimilation in the hindcast. The dynamic mechanism about how the uncertainties of controlling factors influence the predictable time will be further explored using the vorticity and energy diagnostic methods.

目前围绕南海环流的研究大多关注于揭示其多时空尺度的演化规律及控制机理，很少涉及可预报性。南海北部陆坡流是南海西边界流的北部分支，受风场、黑潮、涡流相互作用等因素的影响，其季节内变化十分活跃。准确的预报南海北部陆坡流的季节内变化对提高南海热、动力状态的预测水平具有重要意义，因此其可预报性已是目前有待尝试和解决的一个重要科学问题。但当前在预报中主要控制因子的不确定性对于南海北部陆坡流季节内变化预报时效的影响仍不明确，这一定程度地限制了对其可预报性研究的进一步深化。鉴于此，本项目将借助南海多源观测系统，采用资料同化技术在后报试验中减小各主要控制因子的不确定性，进而给出风、黑潮和南海北部背景流场的不确定性影响南海北部陆坡流季节内变化预报时效的规律性认识。在此基础上，利用涡度和能量学的诊断方法，阐明控制因子的不确定性影响预报时效的动力机制。

准确的预报南海北部陆坡流的季节内变化对提高南海热、动力状态的预测水平具有重要意义。.本项目首先基于长期的定点潜标观测，结合卫星观测，揭示了南海北部陆坡流季节内存在10-65天和65-110天两个主要周期，并受到黑潮背景流和西太西传中尺度涡的调制。这其中，黑潮流套在吕宋海峡脱落入南海的过程会显著影响南海北部陆坡流季节内变化。.项目进一步针对2016-2017年冬季一次极强的黑潮流套脱落南海事件开展了预报试验。结果表明，该次事件预报时效主要与亚热带逆流区（STCC）区域初始场不确定性有关，但也受到北赤道流（NEC）初始场不确定性影响。其中STCC区域的一个向西传播的气旋涡在吕宋海峡与黑潮相撞，进而切断了黑潮向北流动，并导致黑潮流套涡旋脱落。而NEC区域偏北的流轴导致了异常弱的黑潮上游背景流，这进一步有助于在吕宋海峡形成强的黑潮流套，有易于涡脱落的发生。此外，南海内部背景流的不确定性将进一步影响涡脱落后在南海内部西传过程的预报。.最后，项目开展了多源观测同化的研究。重点发展了选尺度的潜标海流同化方案，减小了西太环流模拟的不确定性。