Use of AMVs in the ECMWF model
Physical characteristics
Global Model
- Spectral model
- Horizontal resolution: TCo1279 (~9 km cubic octahedral
grid), analysis: TL399 (~50 km Gaussian grid) - Vertical resolution: 137 vertical levels
- Analysis times: 00,12 Z
Data assimilation method
Global Model
Since 29th June 2004, ECMWF have been running an early delivery stream (DA) and a delayed cut-off stream (DCDA). The DCDA is the equivalent of the Met Office update run and is used to generate the background for the next cycle. The early delivery stream is the equivalent of the Met Office main forecast run and is used to generate the operational forecasts. From 11th June 2019, the introduction of continuous data assimilation allowed the DA time window (previously T ± 3 hr with a cut off time of T+4) to be extended. Observations taken and received at any time before the cut off can now be included.
Assimilation window:
- DA: 4-D VAR, 8-h time window.
- DCDA: 4-D VAR, 12-h time window.
Observation time window:
- DA: T-3 hr – T+4 hr 25 mins
- DCDA: T-3 hr – T+9 hr
Time constraints (model runtime):
- DA: Model runs after data assimilation window finishes at T+5
- DCDA: 5 hr after time window ends
For further information see Lean et al. (2019, ECMWF Newsletter 158, pp. 21–26).
AMV types assimilated
Global Model
- Meteosat-9/-10 BUFR IR, VIS0.8, cloudy WV6.2 and cloudy WV7.3
- GOES-16/-18 BUFR IR, VIS, cloudy WV6.15
- HIMAWARI-9 BUFR IR, VIS, cloudy WV6.95
- Metop-B/C BUFR IR single product
- Metop-B/C BUFR IR dual product (B-C and C-B pairs only)
- NESDIS MODIS Aqua IR, cloudy WV, clear sky WV
- CIMSS AVHRR NOAA-15/18/19
- S-NPP/NOAA-20 VIIRS IR
Global quality control
Blacklisting in space
- All VIS winds at 700 hPa and above
- All geostationary WV winds below 400 hPa except for Meteosat-8/11 WV7.3 where all below 600 hPa.
- All goestationary winds over land below 500 hPa and additionally all winds over land (any height) in the following areas:
- North of 20 N in any region that is west of 20W or east of 100 E.
- North of 35 N for any longitude that is between 20W and 30E.
- Over the Himalayas.
- All MODIS/AVHRR/VIIRS winds equatorwards of ± 60° latitude
- All Metop-/B/C single product winds equatorwards of ± 60° latitude
- All Metop-B/C and Metop-C/B dual product winds equatorwards of ± 40° latitude and polewards of ± 60° latitude
- All MODIS/AVHRR/VIIRS and Metop winds over land below 400 hPa.
- All MODIS/AVHRR/VIIRS and Metop IR winds over sea below 700 hPa.
- All MODIS cloudy and clear sky WV winds over sea below 550 hPa.
- All Meteosat-9/-10 IR and WV winds below 250 hPa in the tropics (25N-25S)
- All HIMAWARI-9 IR winds below 300 hPa in the tropics (25N-25S)
- All GOES-16/-18 IR winds below 300 hPa and above 200hPa in the tropics (25N-25S)
- All GOES-16/-18 WV winds below 300 hPa in the tropics (25N-25S)
- All GOES-16/-18 WV winds above 200 hPa in the extratropics (> 25N, > 25S)
- All HIMAWARI-9, Meteosat-9 and GOES-16/-18 winds above 150 hPa
- Zenith angle > 64° for all geostationary winds
- All winds below 1000 hPa or above 100 hPa
Low-level height reassignment
All AMVs, between 700 hPa and the surface, which are above the model cloud level, have their pressure reassigned to the average pressure of the model cloud. Full details available in this paper
QI thresholds
The table below is intended only as a guide to the QI thresholds used.
Please see the section on blacklisting in space for specific details on which geographical areas are used.
| extratropics | tropics | |||||||
| HL | ML | LL | HL | ML | LL | |||
| GOES-16/18 | QI2 | IR | 90 | 90 | 90 | 90 | 90 | 90 |
| VIS | – | – | 90 | – | – | 90 | ||
| WV6.15 | 90 | – | – | 90 | – | – | ||
| Meteosat-9/-10 | QI2 | IR | 85 | 85 | 85 | 85 | – | – |
| VIS0.8 | – | – | 85 | – | – | 85 | ||
| WV7.3 | 85 | 85 | – | 85 | – | – | ||
| WV6.2 | 85 | – | – | 85 | – | – | ||
| Himawari-9 | QI2 | IR | 70 | 70 | 70 | 70 | 70 | 70 |
| VIS | – | – | 70 | – | – | 70 | ||
| WV6.95 | 70 | – | – | 70 | – | – | ||
| Metop/S-NPP/NOAA-20 | QI2 | IR | 60 | 60 | 60 | – | – | – |
tropics: 20S-20N
extratropics: polewards of 20S/N
hl: 100-400 hPa
ml: 400-700 hPa
ll: 700-1000 hPa
QI1 – EUMETSAT QI with first guess check
QI2 – EUMETSAT QI without first guess check
RFF – Recursive Filter Function (CIMSS/NESDIS)
For information on how the quality indicators are formulated see Holmlund (1998, Weather Forecasting 13 1093-1104) and Hayden and Purser (1995, Journal of Applied Meteorology 34 3-15).
Thinning
- All winds thinned in 200 km by 200 km by 50-175 hPa boxes. Vertical extent varying according to nearest standard pressure level. There are 16 vertical boxes.
- Wind selected by highest QI.
- Winds are assimilated in 30 min time-slots.
Background check
AMV observations undergo:
- Background check: comparison with short-term forecast from previous model run
- Variational quality control
Observation errors
Similar to Met Office – observation errors calculated individually for each wind using estimates of the error in vector, error in height and variation in the background wind column.