Summary
The impact of snow DA changes has been investigated for 49r1. Snow depth on the Tibetan Plateau and the Rocky Mountains is reduced by assimilating IMS except on complex orography. RMSE is reduced for 2m temperature by 0.5% for winter and 1% for spring in the Northern Hemisphere. In addition, computational time for the 'snow' task is reduced about 30 seconds at 0 UTC by reducing radius for observation scanning and number of IMS input in 2D-OI.
List of snow DA changes
| current system | candidate for 49r1 | |
|---|---|---|
| IMS mask | based on altitude (>1500m) | based on SDFOR (>200) |
| IMS thinning | select 1 for every 36 | select nearest IMS on a gaussian grid of 31km (TL639) |
| IMS rejection on IMS mask | No | Yes |
| Cap value for snow depth | 1.4m | 3.0m |
| RSCALE_Z | 800m | 500m |
| SCAN_RAD | 3000km | 300km |
IMS mask
| IMS mask based on altitude (>1500m) | IMS mask based on SDFOR (>200) |
|---|---|
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IMS thinning
| Simple thinning (select 1 from every 36 observation) | Updated thinning (select nearest IMS on a gaussian grid of 31km) |
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Cap value for snow depth analysis
Suspicious increments accumulated on IMS mask
| control | before modifications | after modifications |
|---|---|---|
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Scanned radius for 2D-OI
Experiment list
Results
Results for winter 2020/21 and summer 2020 (against Andrew's control)
| control (hut8) | test (hybs) | hybs - hut8 |
|---|---|---|
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| RMSE for 2m temperature against analysis in the NH | RMSE for 2m temperature against observations in the NH |
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| Scorecard for winter | Scorecard for summer |
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