A Method for Adjoint Variational Data Assimilation with Physical “On–Off” Processes
Mu Mu,Jiafeng Wang +1 more
TLDR
In this paper, two kinds of typical on-off switches represented in idealized simple models are investigated: the zero-order discontinuous switch (Type I) and the first-order switching (Type II) in both time-continuous and discrete circumstances.Abstract:
Since the accuracy of the tangent linear approximation of moist physics in a mesoscale model is case dependent, the problem related to the variational data assimilation with physical “on–off” processes is studied further in both time-continuous and discrete circumstances. Two kinds of typical on–off switches represented in idealized simple models are investigated: the zero-order discontinuous switch (Type I) and the first-order discontinuous switch (Type II). The main results are as follows. For Type I: 1) For the case in which the model is time continuous, the gradient of the cost function with respect to the initial condition exists except for the threshold. 2) In the time-discrete case, there are zigzag discontinuities in the cost function, and the method that keeps the switches in the tangent linear model the same as in the forward model (called Zou's method) is able to compute the correct gradient where it exists. An optimization with this gradient might yield a local minimum rather than the...read more
Citations
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