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Although they are valid at the specified time, rather than and NOT an average over the model time step, such parameters cannot represent variability on short time scales. This arises because the model values are a grid box average, without variability on spatial scales smaller than the grid. In contrast, high frequency observations at a fixed point will show temporal variability due to advection of small scale spatial variability. Therefore, when comparing with high frequency observations, the latter should be temporally averaged so as to remove the variability that is not represented in the model.
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