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- systematic errors reflect the limitations of the NWP model’s ability to simulate the physical and dynamic properties of the system.
- non-systematic errors reflect synoptic phase and intensity errors (as indicated by the left hand green arrow in Fig3.2-1).
- systematic and non-systematic errors occur when the NWP output is verified against point observations. The NWP output may not be representative of the location, height, aspect of the observation or capture sub-grid scale variability.
Fig3.2-1: Comparison between NWP model output and observations ought ideally to follow a two-step procedure:
- first step: compare grid point average to observation area average. The systematic errors are then due to model shortcomings; the non-systematic errors stem from synoptic phase and intensity errors.
- second step: compare the systematic errors between observation average and point observation. The systematic errors come from station representativeness (i.e. the location, height and aspect of the observation). The non-systematic errors come from sub-grid scale variability.
Fig3.2-2: In reality, the comparison between NWP and observations must for simplicity bypass the area average stage. This results in the systematic and non-systematic errors arising from distinctly different sources. The effects related to the two green arrows in Fig3.2-1 are here combined into one.
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