On initialization and non-synoptic data assimilation

The responses of physical and simulated fluid systems to the introduction of new field values are compared to provide a basis for understanding the dynamic aspects of data assimilation by general circulation models. It is shown that the concept of an optimal set of initial values is only meaningful with reference to one particular forecasting model as this initial state must be adjusted to the special dynamic reponse of the model. From this standpoint, non-synoptic data or simultaneous field measurements are equivalent. This is demonstrated by numerical tests of one possible iterative adjustment procedure based on forward and backward integration of the dynamic equations between successive map times. DOI: 10.1111/j.2153-3490.1971.tb00563.x