PowerPoint Presentation - Methods for dealing with spurious covariances arising from small samples in ensemble data assimilation

Flow Dependent Localization

Today’s fixed moderation functions limit adaptivity

Current ensemble DA techniques

reduce noise by multiplying ensemble

correlation function by fixed

moderation function (green line).

Resulting correlations (blue line) are too thin when true correlation is broad and too noisy when true correlation is

thin.

Stable flow error correlations

Unstable flow error correlations

Fixed moderation


	If the same localization is used for both cases, we may unduly sharpen the correlations in the stable case, while not removing enough of the noise in the unstable case. What is needed is ‘adaptivity’