Background
The ROM SAF has produced two climate reanalyses as part of its CDOP2 activities. These reanalyses were recommended by the IROWG climate subgroup (see recommendation 6 to CGMS, in section 4.2), where is was stated that:
"Encourage NWP centers to engage in reanalysis activities based only on data types that are not bias-corrected, especially RO. ECMWF, e.g., carries out such an activity as part of the ROM SAF CDOP-2 plans."
Two reanalyses that meet this recommendation have been completed, for the period 20070101 to 20151231. The first reanalysis assimilates just reprocessed GPS-RO data provided the ROM SAF and AMSUA channel 14 to constrain the upper stratosphere. The second reanalysis also includes conventional measurements (e.g., sondes, synop, ...) that are not bias corrected as part of the variational bias correction (VAR-BC) scheme. Notably, this excludes aircraft temperature measurements that are bias corrected in VAR BC.
The reanalyses provide gridded analysis files at for the hours (00,03,06,09,12,15,18,21) for each day, and monthly mean files. The data are provided on a fixed set of pressure levels, model levels and for the surface. We also provide the departure statistics for the data assimilated to compute the analyses.
Access via web-api
The ROM SAF datasets are available from the ECMWF public datasets service via the web-api. This is a "programmatic approach" for data download with python scripts. The basic web-api documentation for accessing the data is given here., but we will note some key steps required to download the data and provide the main links.
Firstly, you will need to download the appropriate python modules in order to run the python download scripts. For example, the python scripts will contain "from ecmwfapi import" commands, like in this simple example, retrieving a monthly mean zonal wind at 1000 hPa, in netcdf format (More complex retrieval scripts are provided here):
#!/usr/bin/env python
#
from ecmwfapi import ECMWFDataServer
# To run this example, you need an API key
# available from https://api.ecmwf.int/v1/key/
server = ECMWFDataServer(verbose=1)
server.retrieve({
'dataset' : "rom_saf_3198",
'stream' : "moda",
'levtype' : "pl",
'levelist': "1000",
'date' : "20150301",
'type' : "an",
'param' : "131.128",
'grid' : "0.5/0.5",
'format' : "netcdf",
'target' : "rom_saf_3198.nc"
})
General information related to downloading the data via web-api, is described here:
https://confluence.ecmwf.int/display/WEBAPI/Web-API+Downloads
Specifically, follow the steps here to install the latest code version:
https://pypi.org/project/ecmwf-api-client/