印度洋海温初始误差对拉尼娜可预报性的影响

ENSO forecast is one of the most important tasks for both National Meteorological and Oceanic Administrations and also for all the prediction centers worldwide. For ENSO forecasts, except the influences from the air-sea coupled systems from the tropical Pacific, the influences from tropical Indian Ocean should also be considered. Thus, it is of great importance to explore the effect of initial errors of sea temperature in the Indian Ocean on the predictability of ENSO from the perspective of initial error growth. Former studies mainly focused on the effect of initial errors in the tropical Indian Ocean on the predictability of El Niño events. However, since the negative phase of ENSO, i.e., La Niña events can also lead to severe weather and climate disasters in China, therefore, it is urgent to study the effect of initial errors in the tropical Indian Ocean on the predictability of La Niña events.. In this study, a lot of sensitivity experiments on the initial field are carried out with earth system model CESM1.0.3. The work mainly includes: to study the most quickly growing initial errors, i.e., Conditional Nonlinear Optimal Perturbation (CNOP) in the tropical Indian Ocean that has large influence on the predictability of La Niña; to analyze the mechanisms of the error growth, and discuss the roles of both atmospheric bridge and the oceanic channel on the influence of initial errors in the tropical Indian Ocean on the ENSO-related SSTs; to identify the sensitivity area in the tropical Indian ocean for La Niña predictions, and evaluate the contribution of applying targeted observations in this sensitivity area to the improvement of La Niña prediction skills.

ENSO预报是我国乃至世界各国气象和海洋业务部门预测的主要内容之一，对于ENSO预报，除了热带太平洋地区海气耦合系统的影响之外，也需要考虑热带印度洋地区的影响。因此，从初始误差增长的角度出发，考察热带印度洋初始海温不确定性对ENSO可预报性影响的研究就具有非常重要的实际意义。以往的研究只关注了热带印度洋海温对厄尔尼诺可预报性的影响，而鉴于拉尼娜事件对我国天气气候的重要影响，印度洋海温初始误差对拉尼娜可预报性的影响就成为了亟待解决的科学问题。. 本项目拟使用地球系统模式CESM1.0.3，通过大量初值敏感性试验来研究对拉尼娜可预报性影响最大的印度洋地区的最快增长初始误差（即非线性最优扰动CNOP）；分析误差发展的机制，探讨印度洋海温初始误差影响太平洋海温过程中热带大气桥和海洋通道的作用；研究确立拉尼娜预报的印度洋海温目标观测敏感区，考察该敏感区在提高拉尼娜预报技巧中的作用。

本项目展开的拉尼娜可预报性研究，是气象海洋业务部门预测的主要内容之一。本项目主要考虑了热带印度洋地区海温初始误差对拉尼娜可预报性的影响。本项目使用地球系统模式CESM，通过大量初值敏感性试验，找到了对拉尼娜预报影响最大的两类最快增长初始误差（即非线性最优扰动CNOP）；分析了两类误差的空间结构特征，探讨了两类误差的发展特征及可能的物理机制，即两类印度洋海温误差分别通过大气桥和海洋通道印尼贯穿流影响热带太平洋海温，进而影响拉尼娜海温预测。印度洋海温初始误差的大值区同时也是目标观测的敏感区。敏感性试验结果表明，在热带印度洋海温目标观测敏感区内优先增加观测，减少其初始误差，也能有效提高拉尼娜的预报水平。以上科研结果可以为拉尼娜的预测及目标观测敏感区的选择提供建议。