| Physical characteristics |
- Spectral model
- Horizontal resolution: TL1279 (~16 km Gaussian grid),
analysis: TL255 (~78 km Gaussian grid)
- Vertical resolution: 137 vertical levels
- Analysis times: 00,12 Z
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| Data assimilation method |
- Since 29th June 2004, ECMWF have been running an
early delivery stream (DA) and a delayed cut-off
stream (DCDA). The DCDA is the equivelent of the
Met Office update run and is used to generate the
background for the next cycle. The early delivery
stream is the equivelent of the Met Office main forecast
run and is used to generate the operational forecasts.
- DA: 4-D VAR, 6-h time window.
- DCDA: 4-D VAR, 12-h time window.
- Time window:
- DA: T ± 3 hr
- DCDA: T-3 hr - T+9 hr
- Time constraints (model runtime):
- DA: 1 hr after time window ends
- DCDA: 5 hr after time window ends
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| Scatterometers assimilated |
WindSat (if assimilated) should also be included here
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| Scat name |
Product |
Models assimilated |
| ASCAT-A |
Wind retrieval from the ASCAT L1 BUFR 25km products using the CMOD5.N GMF |
Global Deterministic Model , Global Ensemble Prediction System, Seasonal Forecast |
| ASCAT-B |
Wind retrieval from the ASCAT L1 BUFR 25km products using the CMOD5.N GMF |
Global Deterministic Model , Global Ensemble Prediction System, Seasonal Forecast |
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| Monitoring |
| External monitoring web pages
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| Generic Quality Control |
Blacklisting
- All observations where model sea ice is greater than 0.01%
- All observations with SST less than 273.15 K according to OSTIA products.
- ASCAT-A/B: All wind speeds greater than 35 m/s
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Ambiguity removal
ASCAT-A/B:
Normally two ambiguous pairs of U and V wind components are found at each location.
In 4D-Var both ambiguous winds are used and the most appropriate solution is
dinamically determined by comparison with ECMWF background fields.
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Bias correction
ASCAT-A/B:
A sigma nought bias correction is applied to ASCAT backscattering measurements before
the wind inversion. The bias correction is computed by the use of the ocean
calibration method, by comparison to ECMWF first-guess winds. The sigma nought bias
correction is dependent of the beam and the incidence angle.
A wind speed bias correction is applied to ASCAT wind after the wind inversion.
It is wind speed and incidence angle dependent.
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Thinning
ASCAT-A/B:
- Prior to assimilation observations are thinned. In the across track direction only
predefined wind-vector cells are selected. For ASCAT, from 42 cells (two swaths of
21 cells each) only cells 1, 5, 9, 13, 17, 21, 22, 26, 30, 34, 38, 42 are selected
resulting in about 100 km of resolution.
- Winds are assimilated in 30 min time-slots.
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Background check
- Background check: very relaxed first-guess check
- Variational quality control is applied in the second and third
outer loops. The weight of the scatterometer observations in the
analysis is based on the probability of gross error.
Data with high probability of gross error are
considered `rejected' and flagged accordingly.
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| Specific Quality Control |
| Global model
|
| Scat name |
ASCAT-A/B |
| Operational since |
June 2007 (ASCAT-A) and July 2013 (ASCAT-B) |
| Observation error U/V |
1.5 m/s |
| Wind speed range |
Observed and background winds < 35m/s |
| Bias corrected? |
Sigma nought and wind speed bias correction applied |
| Crosstrack cells used |
Nodes 1,5,9,13,17,21,22,26,30,34,38,42 |
| QC thresholds |
Rank-1 distance to the cone < 1.5 |
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| Observation Operator |
| Observations are assimilated as equivalent-neutral 10m winds.
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| Lowest model level
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- Height of the lowest model level: ~10m
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| Interpolation
|
- Model wind fields are horizontally interpolated to the observation location using
a 4-point bi-linear interpolation.
- The vertical interpolation between the lowest model level and the surface is
performed using the formulation of Geleyn that is based on Monin-Obukhov
similarity theory.
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| History of Changes |
The list includes the main scatterometer or model changes implemented operationally
in the ECMWF model.
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| References |
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