Nonlinear aspects of the systematic error of the ECMWF coupled model

Principal Investigator

Dr Franco Molteni
International Centre for Theoretical Physics
Strada Costiera, 11
I-34014 Trieste
Italy

molteni@ictp.trieste.it

Project description

ECMWF has recently developed a system for seasonal prediction based on ensemble integration of a coupled ocean-atmosphere general circulation model (GCM). Currently, the model systematic error is corrected 'a posteriori'; this procedure is implicitly based on the assumption of a quasi-linear behaviour of atmospheric and ocean anomalies. However, the importance of non-linear effect for the dynamics of extratropical large-scale anomalies is well established. The aim of the above mentioned project is to assess the ability of the ECMWF model to represent non-linear dynamical processes affecting large-scale atmospheric systems (particularly in the Euro-Atlantic sector), and to study their interactions with the systematic errors of both the uncoupled and the coupled GCM.  

In the previous years, the following issues have been investigated within the NASEC project:

• Non linear response of the ECMWF atmospheric model to ENSO-like SST anomalies of different sign and amplitude.
• Impact of the SST drift generated by the ECMWF coupled system1 on the mean state and low-frequency variability simulated by the atmospheric GCM
• Sensitivity of the model climate to land-surface properties over tropical continents (specifically over the Amazon basin).

For 2004 research will be focused on the effect of ocean-atmosphere coupling on the simulated atmospheric variability. Coupled model experiments will be compared with uncoupled simulations forced by the same time-varying SST.

Results from the ECMWF system will be compared with those obtained with a coupled model based on the ICTP intermediate complexity AGCM (SPEEDY) and the University of Miami ocean model (MICOM), jointly developed by the ICTP Physics of Weather and Climate Section and KNMI Climate Research Section.

For more details, please refer to the latest progress report.

Additional information

Project started in 1999.