"Studie-materiaal" ECMWF.

Sinds een aantal weken verdiep ik mij wat meer in ECMWF.

Zij geven onder andere veel informatie vrij over de achtergronden hoe ze verwachtingen maken, etc. 

Vanochtend kwam ik dit tegen. Het gaat erover hoe de verwachting tot 15 dagen wordt gemaakt en de verwachting tot 46 dagen. Een belangrijke rol is weggelegd voor de temperatuur van de Oceanen en de MJO wanneer de extended range in beschouwing wordt genomen.

Dit alles is te vinden in "The forecast user guide".

Remarks on the Extended Range

Extended Range Structure

The Extended Range (monthly) products covering the period up to Day46 are derived from an extension of the normal 15-day ENS twice per week on Mondays and Thursdays.  This is a time scale lying between:

• medium-range weather forecasting (ENS, Day0 to Day15) which is primarily governed by atmospheric initial values (background plus new observed data) but rather less on ocean temperature information, and
• seasonal forecasting, which although initial atmospheric data is carried over from the ENS, is more reliant on predictability of the oceans and on the impact that tropical sea-surface temperatures have on the atmospheric circulation.

This is a particularly difficult time range as it is:

• generally too long for the atmosphere to keep a memory of its initial conditions,
• too short for the ocean variability to have an impact on the atmospheric circulation.

The Extended Range forecasting system has ocean-atmosphere coupling throughout the forecast period at hourly intervals.  Sea-surface temperatures have an influence upon the atmospheric evolution and the oceanic ensemble has been introduced to enable the uncertainty of the sea-surface temperature and associated heat and moisture to be represented.  Also, the ocean-atmosphere coupling appears to help the IFS correctly capture the propagation of  Madden-Julian Oscillation (MJO) events, notably in the equatorial Indian and western Pacific oceans.  This high-frequency coupling can also influence the development of some synoptic-scale systems, such as tropical cyclones, and indeed also meteorological evolution and predictability in the extratropics.

The initial conditions of the oceanic ensemble are perturbed using five ocean assimilations (1 control and 4 perturbed) produced by addition and subtraction of two randomly selected wind stress perturbations. The same perturbations cannot be chosen for 2 consecutive months.

The LIM2 subprogram within NEMO forecasts changes in the sea-surface temperature and sea ice evolution, and these are used by the Extended ENS.  

Re-forecasts provide an Extended Range climate (ER-M-climate) and associated probability distribution functions (pdfs) for several variables.  The latest Extended Range ENS forecasts and the associated pdfs can be compared with the ER-M-Climate; this effectively removes, or nullifies, any model drift if the differences between the two are used as the basis of model products. 

https://confluence.ecmwf.int/display/FUG/5.2+Remarks+on+the+Extended+Range

https://confluence.ecmwf.int/display/FUG/Forecast+User+Guide