Background
The EUMETSAT ROM SAF has produced two atmospheric reanalyses as part of its CDOP-2 activities. These reanalyses were recommended by the IROWG climate subgroup (see recommendation 6 to CGMS, in section 4.2), where it 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."
The two atmopsheric reanalyses cover the the period 20070101 to 20151231. They have been run using the ERA5 reanalysis system, but at low resolution (T159 ~ 125 km grid), and using a static B matrix rather than ERA5's flow-dependent version which uses the Ensemble of Data Assimilations approach. The first ROM SAF 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 two atmospheric reanalyses provide:
- gridded daily analysis fields at the hours (00,03,06,09,12,15,18,21) (class=ea, stream=oper, type=an)
- monthly mean fields from 20070201 to 20151201 (class=ea, stream=moda, type=an)
- the observation departure statistics for the data assimilated in the reanalyses (class=ea, stream=oper, type=mfb)
The reanalyses can be summarised as follow:
| Experiment id | Name of reanalysis dataset | Description | Class | Dates |
|---|---|---|---|---|
| 21 | rom_saf_21 | Assimilating reprocessed ROM SAF GPS-RO, AMSU-A channel 14 and conventional data not used in VAR-BC | ea | 200701-20151231 |
| 22 | rom_saf_22 | Assimilating reprocessed ROM SAF GPS-RO, AMSU-A channel 14 | ea | 200701-20151231 |
This atmospheric reanalysis data is available for the surface, on 37 fixed pressure levels and on 137 model levels.
A selection of science results presented at the Joint 6th ROM SAF User Workshop and 7th IROWG Workshop are given here. This data has also been used to demonstrate how QBO zonal wind information can be retrieved from GNSS-RO measurements.
Access to the ROM SAF data using Web API
The ROM SAF datasets can be retrieved using the ECMWF Web API service. The Web API is a "programmatic approach" for data download using python scripts.
Frequently asked web api questions (FAQs) can be found here: Web API FAQ
General information on downloading with web api is given here: Web API Downloads
Specifically, follow the steps here to install the latest code version:
https://pypi.org/project/ecmwf-api-client/
Retrieval efficiency when using Web API
The importance retrieval efficiency when using Web API is discussed here. This page includes Web API retrieval examples for other reanalyses, such as ERA5.
Specific examples of efficient, working scripts for the ROM SAF reanalyses are given here.
These are based on examples used for other reanalyses and they can be adapted easily to the users needs.