This study aims to evaluate the impact of the in-situ ocean observations on seasonal forecasts. A series of seasonal reforecasts have been conducted for the period 1993-2015, in which different sets of ocean observations were withdrawn in the production of the ocean initial conditions, while maintaining a strong constrain in sea surface temperature (SST). By comparing the different reforecast sets, it is possible to assess the impact on the forecast of ocean and atmospheric variables. Results show that the in-situ observations have profound and significant impacts on the mean state of forecast ocean and atmospheric variables, which can be classified into different categories: i) impact due to local air-sea interaction, as direct consequence of changes in the mixed layer in the ocean initial conditions, and visible in the early stages of the forecasts; ii) changes due to different ocean dynamical balances, most visible in the Equatorial Pacific in forecasts initialized in May, which amplify and evolve with forecast lead time; iii) changes to the atmospheric circulation resulting from changes in large scale SST gradients; these are non-local, mediated by the atmospheric bridge, and they are obvious from the visible impact of the removing in-situ observations on the Atlantic basin only in the global atmospheric circulation; iv) changes in the atmospheric tropical deep convection associated with the structure of the warm pools. The ocean observations have also a significant impact on the representation of the trends of the ocean initial conditions, which affect the trends in the seasonal forecasts of ocean and atmospheric variables. The impact of the ocean observing system in the Atlantic and extratropics appears dominated by Argo, but this is not the case in the Tropical Pacific, where the other ocean observing systems play a role in constraining the ocean state.

中文翻译：

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海洋实地观测对ECMWF季节预报系统的影响


本研究旨在评估现场海洋观测对季节性预报的影响。 1993年至2015年期间进行了一系列季节性重新预报，其中在产生海洋初始条件时撤回了不同组的海洋观测，同时保持对海面温度（SST）的强烈限制。通过比较不同的重新预报集，可以评估对海洋和大气变量预报的影响。结果表明，现场观测对预测海洋和大气变量的平均状态具有深远而重大的影响，这些影响可分为不同的类别： i) 局地海气相互作用造成的影响，作为海洋和大气变化的直接后果。海洋初始条件中的混合层，在预测的早期阶段可见； ii) 由于不同的海洋动力平衡而产生的变化，在 5 月份初始化的预报中赤道太平洋最为明显，这些变化随着预报提前时间的推移而放大和演变； iii) 大规模海温梯度变化导致大气环流发生变化；这些都是非局域的，由大气桥介导，并且从仅在全球大气环流中删除对大西洋盆地的现场观测的明显影响中可以明显看出； iv) 与暖池结构相关的热带大气深对流变化。海洋观测还对海洋初始条件趋势的表示产生重大影响，从而影响海洋和大气变量的季节性预测趋势。 大西洋和温带海洋观测系统的影响似乎以Argo为主，但热带太平洋的情况并非如此，其他海洋观测系统对海洋状态发挥着约束作用。