Within the Copernicus Marine Service, a new operational MEDiterranean diurnal optimally interpolated sea surface temperature (MED DOISST) product has been developed. This product provides hourly mean maps (level 4) of subskin SST at $\mathrm{1}/\mathrm{16}{}^{\circ }$ horizontal resolution over the Mediterranean Sea from January 2019 to the present. Subskin is the temperature at ∼1 mm depth of the ocean surface and then potentially subjected to a large diurnal cycle. The product is built by combining hourly SST data from the Spinning Enhanced Visible and InfraRed Imager (SEVIRI) on board the Meteosat Second Generation and model analyses from the Mediterranean Forecasting System (MedFS) through optimal interpolation. SEVIRI and MedFS (first layer) SST data are respectively used as the observation source and first guess. The choice of using a model output as first guess represents an innovative alternative to the commonly adopted climatologies or previous day analyses, providing physically consistent estimates of hourly SSTs. The accuracy of the MED DOISST product is assessed here by comparison against surface drifting buoy measurements covering the years 2019 and 2020. The diurnal cycle reconstructed from DOISST is in good agreement with the one observed by independent drifter data, with a mean bias of 0.041±0.001 K and root mean square difference (RMSD) of 0.412±0.001 K. The new SST product is more accurate than the input MedFS SST during the central warming hours, when the model, on average, underestimates drifter SST by $\mathrm{1}/\mathrm{10}$ of a degree. The capability of DOISST to reconstruct diurnal warming events, which may reach intense amplitudes larger than 5 K in the Mediterranean Sea, is also analyzed. Specifically, a comparison with the Operational Sea Surface Temperature and Sea Ice Analysis (OSTIA) diurnal skin SST product, SEVIRI, MedFS, and drifter data shows that the DOISST product is able to reproduce more accurately diurnal warming events larger than 1 K. This product can contribute to improving the prediction capability of numerical models that assimilate or correct the heat fluxes starting from level 4 SST data and the monitoring of surface heat budget estimates and temperature extremes which can have significant impacts on the marine ecosystem.The full MED DOISST product (released on 4 May 2021) is available upon free registration at https://doi.org/10.48670/moi-00170 (CNR, 2021). The reduced subset used here for validation and review purposes is openly available at https://doi.org/10.5281/zenodo.5807729 (Pisano, 2021).

中文翻译：

---

哥白尼海洋服务内新的可操作地中海昼夜最佳插值海表温度产品

在 Copernicus Marine Service 中，开发了一种新的可操作的地中海昼夜最佳插值海表温度 (MED DOISST) 产品。本产品提供皮下 SST 的每小时平均图（4 级），位于$\mathrm{1}/\mathrm{16}{}^{\circ }$2019 年 1 月至今的地中海水平分辨率。皮下是∼1的温度 毫米海洋表面的深度，然后可能会受到一个大的日循环。该产品是通过结合来自第二代气象卫星的旋转增强可见光和红外成像仪 (SEVIRI) 的每小时 SST 数据和来自地中海预报系统 (MedFS) 的模型分析通过优化插值构建的。SEVIRI和MedFS（第一层）SST数据分别作为观察源和第一猜测。选择使用模型输出作为第一个猜测代表了常用气候学或前一天分析的创新替代方案，提供了每小时 SST 的物理一致估计。MED DOISST 产品的准确性在此通过与 2019 年和 2020 年的表面漂移浮标测量值进行比较来评估。0.041±0.001  K 和均方根差 (RMSD) 为0.412±0.001  K。新 SST 产品在中央变暖时段比输入 MedFS SST 更准确，此时模型平均低估漂移 SST$\mathrm{1}/\mathrm{10}$一个学位。还分析了 DOISST 重建昼夜变暖事件的能力，这些事件在地中海可能达到大于 5 K 的强烈振幅。具体来说，与操作海表温度和海冰分析 (OSTIA) 日间皮肤 SST 产品、SEVIRI、MedFS 和漂流者数据的比较表明，DOISST 产品能够更准确地再现大于 1 K 的日间变暖事件。本产品可以有助于提高数值模型的预测能力，这些模型从第 4 级 SST 数据开始吸收或校正热通量，以及监测可能对海洋生态系统产生重大影响的表面热预算估计和极端温度。完整的 MED DOISST 产品 ( 2021 年 5 月 4 日发布）可在 https://doi.org/10 免费注册后获得。48670/moi-00170（CNR，2021）。此处用于验证和审查目的的缩减子集可在 https://doi.org/10.5281/zenodo.5807729（Pisano，2021 年）公开获得。