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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 of 2m temperature 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.
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List of snow DA changes
| current system | candidate for 49r1 | |
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| 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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