ERA5 monthly averaged data on single levels from 1940 to present

ERA5 is the fifth generation ECMWF reanalysis for the global climate and weather for the past 8 decades. Data is available from 1940 onwards. ERA5 replaces the ERA-Interim reanalysis.
Reanalysis combines model data with observations from across the world into a globally complete and consistent dataset using the laws of physics. This principle, called data assimilation, is based on the method used by numerical weather prediction centres, where every so many hours (12 hours at ECMWF) a previous forecast is combined with newly available observations in an optimal way to produce a new best estimate of the state of the atmosphere, called analysis, from which an updated, improved forecast is issued. Reanalysis works in the same way, but at reduced resolution to allow for the provision of a dataset spanning back several decades. Reanalysis does not have the constraint of issuing timely forecasts, so there is more time to collect observations, and when going further back in time, to allow for the ingestion of improved versions of the original observations, which all benefit the quality of the reanalysis product.
Hersbach, H., Bell, B., Berrisford, P., Biavati, G., Horányi, A., Muñoz Sabater, J., Nicolas, J., Peubey, C., Radu, R., Rozum, I., Schepers, D., Simmons, A., Soci, C., Dee, D., Thépaut, J-N. (2023): ERA5 monthly averaged data on single levels from 1940 to present. Copernicus Climate Change Service (C3S) Climate Data Store (CDS), DOI: 10.24381/cds.f17050d7 (Accessed on DD-MMM-YYYY)

ERA5是欧洲中期天气预报中心（ECMWF）第五代全球气候与天气再分析（Reanalysis）数据集，覆盖过去80年时段，数据可追溯至1940年，其替代了ERA-Interim再分析数据集。
再分析（Reanalysis）依托物理定律，将全球模式数据与观测数据整合为一套完整一致的全球数据集。这一核心原理被称为数据同化（data assimilation），其方法源自数值天气预报中心的业务流程：每隔固定时长（欧洲中期天气预报中心为12小时），将前期预报结果与最新获取的观测数据以最优方式融合，得到大气状态的最优估计值（即分析场，analysis），并据此发布更新优化后的预报。
再分析的运行逻辑与此一致，但为了生成覆盖数十年的长时序数据集，会降低空间分辨率。由于再分析无需受限于及时发布预报的约束，因此可预留充足时间收集观测数据；在回溯更早的历史时段时，还可引入原始观测数据的优化版本，全面提升再分析产品的质量。
Hersbach, H., Bell, B., Berrisford, P., Biavati, G., Horányi, A., Muñoz Sabater, J., Nicolas, J., Peubey, C., Radu, R., Rozum, I., Schepers, D., Simmons, A., Soci, C., Dee, D., Thépaut, J-N. (2023): 1940年至今单层逐月平均ERA5数据集. 哥白尼气候变化服务局（C3S）气候数据存储库（CDS）, DOI: 10.24381/cds.f17050d7（访问日期：DD-MMM-YYYY）