Page History

...

• 4-regime scheme is used to produce Regime Frequency Histograms in Extended Range Regime Charts.
• Mirrored 2-regime scheme is used to produce phase space diagrams in Medium Range Regime Charts and Extended Range Regime Charts. 

Regime assignment of forecast data is in each case computed in Empirical Orthogonal Function (EOF) space using "calibrated" anomalies of 500mb height/geopotential.  These anomalies are computed with respect to the re-forecast 20-year climate (ER-M-climate), and then those anomalies are compared with reference points for the regime definitions (that are themselves based on re-analysis data) in order to achieve regime assignment.   Fig8.1.15.1A and Fig8.1.15.1B show what these regime reference points look like in 500mb anomaly space for the two schemes.  These are for illustrative purposes only – the user should not expect a model forecast assigned to a particular regime to look exactly like these; ordinarily there will just be some vague resemblance.  

...

The use of regimes can be explored at medium range regime charts and extended range regime charts.

Read more about the use of "Weather regimes" at ECMWF (2020 article)

...