Errors of the day
They are instabilities of the background flow
They dominate the analysis and forecast errors
They are not taken into account in data assimilation
except for 4D-Var and Kalman Filtering (very
expensive methods)
Their shape can be estimated with breeding
Their shape is frequently simple (low dimensionality,
Patil et al, 2001)
A coupled ENSO system contains errors of the month