| 3D-Var used in operational forecasting centers |
| Distance to forecast |
| Distance to observations |
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| It
is the same as the scalar formula for T, but now x
is a |
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| model
state vector, with 106-8d.o.f., and yo is the
set of |
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| observations,
with 105-9 d.o.f. |
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| R is the observational error covariance, |
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| B the forecast error covariance. |
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| In
3D-Var B is constant: it does not include
“errors of the |
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| day” |
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