ERA5 monthly mean back extension 1950-1978 (Preliminary version)

ECMWF has announced that the Copernicus Climate Change Service (C3S) has begun the release of the ERA5 back extension data covering the period 1950-1978 on the Climate Data Store (CDS).

Although in many other respects the quality of this dataset is quite satisfactory, the current back extension appears to suffer from tropical cyclones that are sometimes unrealistically intense. This is in contrast with the ERA5 product from 1979 onwards (also available from the CDS and RDA ds633.0). For more details see the article, ERA5 back extension 1950-1978 (Preliminary version): tropical cyclones are too intense [https://confluence.ecmwf.int/display/CKB/ERA5+back+extension+1950-1978+(Preliminary+version):+tropical+cyclones+are+too+intense].

For this reason the current release of the back extension is preliminary.

It is therefore available from separate CDS catalogue entries (hourly, monthly, single level and pressure levels), and this RDA dataset. Around the end of 2021 an updated version of the back extension is to be made available which will be added to the ERA5 catalogue entries that currently reach back to 1979. After an overlap period (the duration of which is not yet decided), the preliminary back extension will be deprecated.

The full back extension preliminary dataset is expected to be made available near the end of 2020/early 2021.

After many years of research and technical preparation, the production of a new ECMWF climate reanalysis to replace ERA-Interim is in progress. ERA5 is the fifth generation of ECMWF atmospheric reanalyses of the global climate, which started with the FGGE reanalyses produced in the 1980s, followed by ERA-15, ERA-40 and most recently ERA-Interim. ERA5 will cover the period January 1950 to near real time.

ERA5 is produced using high-resolution forecasts (HRES) at 31 kilometer resolution (one fourth the spatial resolution of the operational model) and a 62 kilometer resolution ten member 4D-Var ensemble of data assimilation (EDA) in CY41r2 of ECMWF's Integrated Forecast System (IFS) with 137 hybrid sigma-pressure (model) levels in the vertical, up to a top level of 0.01 hPa. Atmospheric data on these levels are interpolated to 37 pressure levels (the same levels as in ERA-Interim). Surface or single level data are also available, containing 2D parameters such as precipitation, 2 meter temperature, top of atmosphere radiation and vertical integrals over the entire atmosphere. The IFS is coupled to a soil model, the parameters of which are also designated as surface parameters, and an ocean wave model. Generally, the data is available at an hourly frequency and consists of analyses and short (12 hour) forecasts, initialized twice daily from analyses at 06 and 18 UTC. Most analyses parameters are also available from the forecasts. There are a number of forecast parameters, e.g. mean rates and accumulations, that are not available from the analyses.

Improvements to ERA5, compared to ERA-Interim, include use of HadISST.2, reprocessed ECMWF climate data records (CDR), and implementation of RTTOV11 radiative transfer. Variational bias corrections have not only been applied to satellite radiances, but also ozone retrievals, aircraft observations, surface pressure, and radiosonde profiles.

Please note: DECS produces a CF 1.6 compliant netCDF-4/HDF5 version of ERA5 for the CISL RDA at NCAR. The netCDF-4/HDF5 version is the de facto RDA ERA5 online data format. The GRIB1 data format is also available online. There is a one-to-one correspondence between the netCDF-4/HDF5 and GRIB1 files, with as much GRIB1 metadata as possible incorporated into the attributes of the netCDF-4/HDF5 counterpart.

欧洲中期天气预报中心（ECMWF）宣布，哥白尼气候变化服务（C3S）已开始在气候数据存储（CDS）上发布覆盖1950-1978年期间的ERA5后延伸数据。尽管在许多其他方面，该数据集的质量相当令人满意，但当前的后延伸似乎受到了有时过于强烈的台风的影响。这与1979年及以后发布的ERA5产品形成对比（这些产品也可在CDS和RDA ds633.0上获取）。更多详情请参阅文章《ERA5后延伸1950-1978年（初步版）：台风强度过高》[https://confluence.ecmwf.int/display/CKB/ERA5+back+extension+1950-1978+(Preliminary+version):+tropical+cyclones+are+too+intense]。因此，当前发布的后延伸数据为初步版。因此，它可通过单独的CDS目录条目（每小时、每月、单层和压强层）以及本RDA数据集获取。预计到2021年底，将提供后延伸更新的版本，该版本将被添加到目前追溯到1979年的ERA5目录条目中。在重叠期（其持续时间尚未确定）之后，初步后延伸将被弃用。预计将在2020年底/2021年初提供完整的后延伸初步数据集。经过多年的研究和技术准备，用于取代ERA-Interim的新的ECMWF气候再分析的生产工作正在进行中。ERA5是ECMWF第五代全球气候大气再分析，始于20世纪80年代生产的FGGE再分析，随后是ERA-15、ERA-40，以及最近的ERA-Interim。ERA5将覆盖从1950年1月到接近实时的时间段。ERA5采用高分辨率预报（HRES）在31公里分辨率（是业务模型的四分之一空间分辨率）下生成，并在ECMWF综合预报系统（IFS）的CY41r2中实施了一个62公里分辨率、十成员的4D-Var数据同化（EDA）集合，垂直方向上有137个混合sigma压强（模型）层，最高可达0.01 hPa。在这些层上的大气数据被插值到37个压强层（与ERA-Interim相同的层），同时提供表面或单层数据，包含二维参数，如降水量、2米温度、大气顶辐射以及整个大气垂直积分。IFS与土壤模型耦合，其参数也被指定为表面参数，以及海洋波浪模型。通常，数据以每小时频率提供，包括分析和短期（12小时）预报，每天从06和18 UTC的分析中初始化两次。大多数分析参数也可从预报中获得。存在一些预报参数，例如平均速率和累积量，这些参数不能从分析中获得。与ERA-Interim相比，ERA5的改进包括使用HadISST.2、重新处理的ECMWF气候数据记录（CDR）以及实施RTTOV11辐射传输。变分偏差校正不仅应用于卫星辐射，还应用于臭氧反演、飞机观测、地表压力和探空仪廓线。请注意：DECS为NCAR的CISL RDA生成符合CF 1.6规范的netCDF-4/HDF5版本的ERA5，这是RDA ERA5在线数据格式的既定格式。GRIB1数据格式也在线提供。netCDF-4/HDF5文件与GRIB1文件之间存在一对一的对应关系，尽可能多的GRIB1元数据被纳入netCDF-4/HDF5对应文件的属性中。