ECMWF是什么？

欧洲中期天气预报中心（European Centre for Medium-Range Weather Forecasts 简称 ECMWF）是一个包括34个国家支持的国际性组织，是当今全球独树一帜的国际性天气预报研究和业务机构。其前身为欧洲的一个科学与技术合作项目。1975年ECMWF正式成立，总部设在英国的Bracknell。

参考1：https://zhuanlan.zhihu.com/p/365505749（批量下载ECMWF欧洲中心数据）

ERA5

ERA5 provides hourly estimates of a large number of atmospheric, land and oceanic climate variables. The data cover the Earth on a 30km grid and resolve the atmosphere using 137 levels from the surface up to a height of 80km. ERA5 includes information about uncertainties for all variables at reduced spatial and temporal resolutions.

Quality-assured monthly updates of ERA5 (1959 to present) are published within 3 months of real time. Preliminary daily updates of the dataset are available to users within 5 days of real time.

A preliminary ERA5 dataset from 1950 to 1978 is also available on the Climate data store (CDS) (1959-1978 is superseded by the quality assured dataset).

ERA5 combines vast amounts of historical observations into global estimates using advanced modelling and data assimilation systems.

ERA5 replaces the ERA-Interim reanalysis which stopped being produced on 31 August 2019. You can read about the key characteristics of ERA5 and important changes relative to ERA-Interim.

Download ERA5 from the Copernicus Climate Change Service (C3S) Climate Date Store >

ERA5 documentation

• Instructions to download ERA5
• ERA5 Documentation

参考：https://www.ecmwf.int/en/forecasts/datasets/reanalysis-datasets/era5

>>ECMWF降雨性能检测：

How to download ERA5

1 - Introduction
This article describes how users can access the family of ERA5 datasets via the Climate Data Store (CDS) infrastructure.

本文描述了用户如何通过气候数据存储（CDS）基础设施访问ERA5数据集系列。

ERA5 data can be downloaded through the CDS either via the CDS web interface or programmatically using the CDS API service.

ERA5数据可以通过CDS通过CDS web界面或使用CDS API服务以编程方式下载。

Any data in the CDS catalogue can be accessed in these two ways. And since such data is kept online, access is usually fast. Some parts of the ERA5 dataset are not listed in the CDS catalogue. These are only accessible through the CDS API service. An example is ERA5 model level data that resides in the ECMWF's MARS tape archive. The extraction of such data from tape can lead to significantly longer retrieval times than data that is available online.

CDS目录中的任何数据都可以通过这两种方式访问。而且由于这些数据保持在线，访问通常很快。ERA5数据集的某些部分未列入CDS目录。这些只能通过CDS API服务访问。一个例子是驻留在ECMWF的MARS磁带归档中的ERA5模型级数据。从磁带中提取此类数据可能会导致比在线可用数据更长的检索时间。

Users are now able to check the status of the CDS queue. You will be able to view status of requests submitted by yourself (you need to log into the CDS) and other users: https://cds.climate.copernicus.eu/live/queue

用户现在可以检查CDS队列的状态。您将能够查看自己（您需要登录CDS）和其他用户提交的请求的状态：https://cds.climate.copernicus.eu/live/queue

2 - Prerequisites前提

• Learn more about the family of ERA5 datasets, and browse through the ERA5 data documentation and ERA5-Land data documentation.了解有关ERA5数据集系列的更多信息，并浏览ERA5的数据文档和ERA5土地数据文档。
• CDS account - If you do not yet have a CDS account, please create one HERE.CDS帐户-如果您还没有CDS帐户，请在此处创建一个。
• Accept the Copernicus licence by creating a test download using the CDS Download web form interface (see below).通过使用CDS下载web表单界面创建测试下载，接受哥白尼许可证（见下文）。

目前，ERA5数据集系列由ERA5、ERA5.1和ERA5-Land组成。

1. ERA5 是一套全面的再分析资料，从1979年(不久将追溯到1950年)到接近实时，它吸收了尽可能多的高空和近地面的观测数据。ERA5大气模型与一个陆地表面模型、一个波浪模型结合在一起。
2. 目前，从1950年到1978年的ERA5回溯扩展(初步版本)与ERA5(1979年以后)分开提供。虽然在许多其他方面，这个数据集的质量相当令人满意，但它似乎受到热带气旋的影响，有时热带气旋的强度不切实际。由于这个原因，目前发布的回溯扩展是初步的，直到新的更新版本的 ERA5（1950年） 到接近实时的版本发布。
3. ERA5.1 是对ERA5的再运行，只适用于2000年至2006年，它的制作是为了改善这一时期ERA5中明显的低平流层寒冷偏差。ERA5在对流层大部分地区的作用与ERA5.1类似。
4. ERA5-Land 是一个陆地表面数据集，从1981年(很快将追溯到1950年)到现在(2个月的时间)，以较高的分辨率(9公里)制作，并由ERA5大气参数和流逝率校正来强制执行，但没有额外的数据同化。

通常情况下，通过C3S气候数据存储库(CDS)获取ERA5数据集系列。完整的数据集保存在ECMWF的MARS中，但数据集的一个子集（ERA5-Land的所有数据集）已经被插值到常规的经纬度网格中，并放在CDS磁盘上。从CDS磁盘上获取数据的速度比从MARS上获取数据的速度要快，所以如果可能的话，最好从CDS磁盘上检索数据。详情请见气候数据存储（CDS）文件。

参考：https://confluence.ecmwf.int/display/CKB/The+family+of+ERA5+datasets

其中ERA5 DAILY提供每天7个ERA5气候再分析参数的汇总值：2m空气温度、2m露点温度、总降水量、平均海平面气压、表面气压、10m的u风分量和10m的v风分量。此外，根据每小时的2米空气温度数据，计算出2m处的每日最低和最高空气温度。每日总降水值以每日总和给出。所有其他参数都以日平均数提供。

参考：https://zhuanlan.zhihu.com/p/581829748

3 - Downloading online ERA5 family data through the CDS web interface

1. Go to the C3S climate data store (CDS).
2. Type  'ERA5' in the search box.
3. Follow the ERA5 dataset title link of interest (there will be many more hits).

4. Currently there are eight online ERA5 and two ERA5-Land catalogue entries  

    Show ERA5 catalogue entries in the CDS
5. Each of these dataset catalogue entries includes the following tabs:
   • Overview . This gives a description of the selected dataset and metadata information (e.g. spatial details, file format, variables, etc).
   • Documentation . This provides links to detailed documentation about the dataset.
     
   • Download data . This is a download web form.
6. Go to the Download data tab to make your selection for ERA5 data retrieval. Using this web interface, you can:
   • make selections as per your requirements. For your convenience only valid combinations will show; invalid combinations are greyed out interactively.

   • accept the data licence in the Terms of use section (in case you had not yet accepted it). You will only see this section after you have logged in.

     You will need to do this regardless whether you are accessing data through the web interface or through the CDS API (see below).

7. Click on the button Submit Form at the bottom right to submit your data request (you must be logged in and have accepted the terms and conditions before submitting your request).

8. You will now be redirected to the Your requests page.

Once your request has been processed you can download the data by clicking the green Download button. You can check the Live status of your request .

4 - Download ERA5 family data through the CDS API

First: Install CDS API on your machine

1. This is Python based.
   • This may require some basic knowledge of Python. However, in most cases common-sense adaptions of example requests obtained from the web interface should be sufficient.
2. Install the CDS API:
   • this may require some basic knowledge of pip, in particular know how to install packages on your local machine using pip.
   • On linux or on cygwin, please follow the instructions HERE.
   • Windows users may follow the instructions HERE instead.
   • Mac users may follow the instructions HERE.
3. You are recommended to use the latest release of package CDS API.
4. Run CDS API requests, either interactively or in batch mode.

In a small number of cases, users may experience some issues when requesting data from the CDS API. The most common issues are documented here.

Option A: Download ERA5 family data stored on CDS disks - FAST ACCESS

1. Build a basic CDS API request.

   • You can use the CDS web interface to help you build your CDS API download script.

   • In the Download data  tab, make some selections, then click the button Show API request at the bottom left and you will be presented with the script.

   • Copy and paste this to your preferred text editor.

      Basic CDS API script example (for ERA5 1979-present) to download temperature at a given pressure level, 1000 hPa is shown HERE.
2. Refine your CDS API script for ERA5 data listed in CDS for optional post-processing.
   
   • For a different grid resolution, use the key 'grid'.
   • Please note that the ERA5 native grid of online CDS is 0.25°x0.25° (atmosphere), 0.5°x0.5° (ocean waves), mean, spread and members: 0.5°x0.5° (atmosphere), 1°x1° (ocean waves). ERA5-Land: 0.1°x0.1°. So this will be returned by default.
   •  Click here for a sample script (for ERA5 1959-present) that downloads temperature at a given pressure level at 1000 hPa for a geographical subset of the data and specified grid

To retrieve data efficiently using the CDS API please have a look at the efficiency tips section on CDS documentation.

Requests for ERA5 data in NetCDF

When requesting ERA5 data from the CDS in NetCDF (web or CDS API), users should not request ERA5 reanalysis atmospheric data, wave data, and ensemble data in one request. This is because the data has different spatial grids, which can cause issues for the current grib to NetCDF converter and produce incorrect results.

Option B: Download ERA5 family data that is NOT listed in the CDS online catalogue - SLOW ACCESS

Although some flavours of the ERA5 family data is not online in the CDS (i.e. not available through the interactive web download form), it is accessible through CDS API. This embraces ERA5-complete, ERA5.1-complete and ERA5-complete-preliminary, which provide data in the 'raw' format as they were produced:

• native grid rather than regridded into regular lat-lon,
• model and potential temperature/vorticity levels, in addition to  pressure levels and  surface fields,
• full two-dimensional ocean-wave spectra in addition to integrated wave parameters,
• explicit distinction between analysis, short-forecast and other, more technical, products.

The ERA5-Land dataset at the native 9km octahedral grid is an exception and is not available via the CDS API protocol. However, all information is available online at the slightly reduced 0.1°x0.1° regular lat-lon grid (access via Option A, above).

Due to the vast volume of these datasets (currently about 10petabyte) these are not stored on spinning disk, but reside in the ECMWF's MARS tape archive, instead. Access to this data is in general much slower, except for the latest couple of months of ERA5-complete, which are also kept online.

 

Please be aware that there is an additional queueing system for downloading data from the ECMWF's MARS archive - expect several hours to several days for submitted requests to complete at this time. You can check the Live status of your request

You can discover the ERA5-complete structure (1959-present) and learn how to build a CDS API request by following these steps:

1. Open the MARS ERA5 catalogue

2. browse for discovery, and browse your way to the parameter level to build a request.

   • More information on the available streams, product types and levels is available in the ERA5 data documentation.
   • On the parameter level, use the left-mouse button and the shift key to select more than one field in one retrieval.
   • The MARS catalogue only shows data for the final quality controlled data that is made available 2-3 months in arrear. However, data is also available from preliminary timely updates up to 5 days behind real time, using the same retrieval structure.

   To retrieve MARS data efficiently (and get your data quicker!) you should retrieve all the data you need from one tape, then from the next tape, and so on.

   As a rule of thumb everything shown on one page at parameter level in the MARS ERA5 catalogue is grouped together on one tape

   • For analysis fields this is one month of data with respect to one particular level type (e.g. surface).
   • For forecast fields on model levels this is limited to one single day.

3. Use the " View MARS request " feature - this will help you build your own CDS API Python script to retrieve the data through the CDS API.

    Example: Download ERA5 model level analysis data (temperature) in the native spherical harmonics representation in GRIB format.
4. Tailor your request to
   1. re-grid to the desired regular lat-lon resolution
   2. convert to NetCDF (works for regular grids only, i.e., so you need to use the 'grid' keyword as well)

   3. select sub areas

       Example to download model level ERA5 analysis data (temperature) for a given area at a regular lat/lon grid in NetCDF format.

For ERA5.1-complete follow the same procedure as for era5-complete explained above, however:

Please read: Technical issue fixed on ERA5.1 CDS API

1. edit the script to change: