ERA5 Reanalysis Monthly Means

Please note: Please use ds633.1 to access RDA maintained ERA-5 Monthly Mean data, see ERA5 Reanalysis (Monthly Mean 0.25 Degree Latitude-Longitude Grid), RDA dataset ds633.1. This dataset is no longer being updated, and web access has been removed.

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, though the first segment of data to be released will span the period 2010-2016.

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 (18 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. Together, the hourly analysis and twice daily forecast parameters form the basis of the monthly means (and monthly diurnal means) found in this dataset.

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.

NCAR's Data Support Section (DSS) is performing and supplying a grid transformed version of ERA5, in which variables originally represented as spectral coefficients or archived on a reduced Gaussian grid are transformed to a regular 1280 longitude by 640 latitude N320 Gaussian grid. In addition, DSS is also computing horizontal winds (u-component, v-component) from spectral vorticity and divergence where these are available. Finally, the data is reprocessed into single parameter time series.

Please note: As of November 2017, DSS is also producing a CF 1.6 compliant netCDF-4/HDF5 version of ERA5 for CISL RDA at NCAR. The netCDF-4/HDF5 version is the de facto RDA ERA5 online data format. The GRIB1 data format is only available via NCAR's High Performance Storage System (HPSS). We encourage users to evaluate the netCDF-4/HDF5 version for their work, and to use the currently existing GRIB1 files as a reference and basis of comparison. To ease this transition, 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.

请注意：为访问由RDA维护的ERA-5月平均数据，请使用ds633.1，详见ERA5再分析（月平均0.25度经纬度网格），RDA数据集ds633.1。此数据集现已停止更新，网络访问已移除。

在多年的研究和技术准备之后，旨在取代ERA-Interim的新一代ECMWF气候再分析工作正在进行中。ERA5是ECMWF全球气候大气再分析的第五代产品，其起源可追溯至20世纪80年代产生的FGGE再分析，随后是ERA-15、ERA-40，以及最近的ERA-Interim。ERA5将覆盖1950年1月至近实时的时间段，尽管首次发布的数据将涵盖2010-2016年期间。

ERA5采用高分辨率预报（HRES）的31公里分辨率（为运行模型的四分之一空间分辨率）和ECMWF集成预报系统（IFS）的CY41r2版本中62公里分辨率的十成员4D-Var数据同化（EDA）集合预报，IFS在垂直方向上具有137个混合sigma压力（模型）层，最高至0.01 hPa。在这些层次上的大气数据被插值到37个压力层级（与ERA-Interim相同），同时提供表面或单层数据，包含如降水、2米温度、大气顶辐射和整个大气垂直积分等二维参数。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（18小时）预报，每天两次从06 UTC和18 UTC的分析中初始化。大多数分析参数也来自预报。存在一些预报参数，例如平均速率和累积量，这些参数在分析中不可用。这些每小时分析和每日两次预报参数共同构成了本数据集中发现的月平均值（以及月日平均值）的基础。

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）和实施RTTOV11辐射传输。变分偏差校正不仅应用于卫星辐射，还应用于臭氧检索、飞机观测、表面压力和无线电探空资料。

美国国家大气研究中心（NCAR）的数据支持部门（DSS）正在提供ERA5的网格转换版本，其中原本以谱系数表示或存档在减少的高斯网格上的变量被转换到1280经度×640纬度的N320高斯网格上。此外，DSS还在计算水平风速（u分量、v分量），这些数据在谱涡度和散度可用时提供。最后，数据被重新处理成单一参数的时间序列。

请注意：截至2017年11月，DSS还为NCAR的CISL RDA生产了符合CF 1.6规范的netCDF-4/HDF5版本的ERA5。netCDF-4/HDF5版本是RDA ERA5在线数据格式的既定标准。GRIB1数据格式仅可通过NCAR的高性能存储系统（HPSS）获取。我们鼓励用户评估netCDF-4/HDF5版本用于他们的工作，并将现有GRIB1文件作为参考和比较的基础。为简化这一过渡，netCDF-4/HDF5和GRIB1文件之间存在一对一的对应关系，尽可能将GRIB1元数据纳入netCDF-4/HDF5的属性中。