黄海海雾目标观测的必要性和有效性的定量研究

Sea fog is a type of disastrous weather which forms under the certain atmospheric and marine meteorological conditions. With the development of economy over and around the Yellow Sea, sea fog has become high-impact weather over this area. However, due to the limitation of observation conditions, the current numerical prediction skill of sea fog is still limited, which is not able to meet the demand of the operational forecast. Targeted observation is an observation strategy which enhances observations by disposing the limited observation resources to the areas mostly needing to be observed, and assimilating the enhanced observations into the model to improve the forecasting of sea fog by improving the model initial conditions. Nowadays, the study of targeted observations has been carried on the atmospheric and oceanic fields, and certain positive results have been obtained. However, the systemic study of targeted observation on sea fog has not been started yet. Hence, the quantitative studies on the necessity and effectiveness of targeted observations for sea fog over the Yellow Sea are seriously needed. In this project, typical cases are planned to be selected based on different circulation types. Sensitivity experiments with assimilating simulated observations will be conducted to explore quantificationally the necessity of targeted observations for different types of sea fog over the Yellow Sea. Based on these results, the sensitive areas will be calculated based on the objective methods for determining the sensitive areas of targeted observations. Subsequently, the effectiveness of the targeted observations will be quantificationally validated by assimilating simulated observations and real observations. The results of this project could provide the scientific basis for planning the location of the observation stations for sea fog forecasting over the Yellow Sea. Moreover, the results of this project could provide a scientific basis for the operational targeted observation in the future.

海雾是在特定大气和海洋气象条件下形成的灾害天气。随着黄海及周边经济发展，海雾已成为该区域的高影响天气。但受观测条件限制，目前海雾数值预报水平仍有限，不能满足业务预报需求。目标观测是将有限观测资源配置在最需要观测区域来加强观测，通过同化加强观测信息改善初始场来提高数值预报水平的观测策略。现今目标观测已在大气和海洋领域相继开展，且取得了一定积极效果。然而，海雾目标观测的系统研究尚未起步，因此对于黄海海雾目标观测的必要性和有效性的定量研究急需开展。本项目计划基于黄海海雾不同环流型分别选取典型个例，进行模拟观测的同化试验，对不同类型海雾目标观测的必要性展开定量研究。在此基础上，采用客观敏感区识别方法对目标观测敏感区进行识别，并依次采用模拟观测和实际观测的同化试验对目标观测的有效性进行定量检验。本项目的研究结果可为黄海布设海雾预报观测站点提供科学指导，也为今后黄海目标观测业务化实施提供理论依据。

海雾是在特定大气与海洋气象条件下形成的灾害天气。但受观测条件限制，目前海雾数值预报水平仍十分有限。目标观测是在最需要观测区域加强有限观测，进而提高数值预报水平的观测策略。鉴于此，本项目针对黄海海雾生成对应的两种常见天气型-冷锋型和高压后部型，分别选取典型个例对目标观测的必要性和有效性进行了研究。.本项目主要内容是针对两种天气型，分别采用基于集合的合成分析方法，分析初始场中是否存在对海雾预报有潜在重要影响的大尺度信息，并以此探讨实施目标观测的必要性。采用基于集合的初始场替代方法，研究海雾预报对初始场中不同垂直层及物理量的敏感性。在此基础上，采用集合敏感性分析方法，客观识别海雾敏感区。并采用OSSE方法和EnKF资料同化技术，验证目标观测的有效性。.结果表明，对两种天气型个例而言，初始场中潜在的关键天气尺度信息均为高-低压相对强度。初始场中低层温度（冷锋型）/湿度（高压后部型）对雾预报影响最大。对冷锋型个例而言，以850hPa温度观测识别的高影响区集中在高低压过渡带上。在高影响区内增加观测能显著改善雾预报效果。海雾目标观测虽未达到预期有效性，但预报效果改善十分可观。对高压后部型个例而言，以低层湿度或多变量观测识别的高影响区主要集中在海上高压后部。在高影响区内增加观测，雾预报效果无改善，目标观测失效。这两种天气型个例目标观测效果有限的可能原因是集合敏感性分析方法本身局限性，而局限性大小与不同天气型海雾生成的关键机理有关。.除以上研究外，本项目还评估了已有的高频小尺度观测信息对海雾预报的影响。结果表明，当高频小尺度观测信息与大尺度分析信息一致结合时，可显著改善雾预报效果。.本项目加深了对不同天气型海雾形成机理及可预报性的理解，可为黄海布设海雾预报的观测站点提供科学指导，也为从天气型角度研究目标观测提供了新思路。