Model Runs: NAO type forcing

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Model Configuration

Model Cycle 25r5
Atmospheretime step: 1 hour. TL95, gaussian ~1.875deg, 29 levels
Oceantime step: 30 mins. Zonal 2.81 deg, merid. 0.25-1.2 (varied)
During initialisation, SST relaxed towards
Reynolds OI (-20W/m**2/K).
Reduced resolution wrt SysII

Synopsis

The ocean model is initialised by an ECMWF analysis at time 19891101. It is then run for a year in uncoupled mode, with surface forcing provided by ECMWF analysis plus any additional forcing that is required. At the end of this period, the ocean is coupled to an atmosphere, any perturbed forcing removed, and a six month forecast of 20-ensemble members executed (see figure).

NAO Experiment

For the NAO type forcing, taux, tauy and net-heatflux where regressed onto the first principle component of the NorthAtlantic MSLP (extended winter DJFM season). The PC is standardised, and all fields are detrended before the regression is performed. The regression coefficients will have the same units as the field of interest (as the PC is dimensionless).

Note: Plots will open in separate windows. When available, gzipped postscript versions are linked to in parenthesis

To obtain a feeling for the size of the regression coefficients wrt the temporal records, the ratio of reg_coeff/stdev(obs) is calculated for net heatflux, taux and tauy.

Positive Forcing (Magnitude*2)

Note: Calculation of the forcing fields did not include the detrending step.

Analysis experiment: b0b0
Forecast experiment: b0b1

The forcing is 2*stdev (ie twice the regression values).
Forcing applied for full 12 months.

Note: Plots will open in separate windows. Gzipped postscript versions available in parenthesis links.

The forcing fields can be viewed : heatflux, taux and tauy.

The signal (wrt control) seen in the forecast six months of ocean potential temperature at depths 10m (ps.gz), 100m (ps.gz), 206m (ps.gz) and 312m (ps.gz).

Heat is seen to be stored at depth (as per the previous idealized heatflux experiments), but no re-emergence is evident. This may be due to the relatively week forcing.

Negative Forcing (Magnitude*2)

Note: Calculation of the forcing fields did not include the detrending step.

Analysis experiment: b0b2
Forecast experiment: b0b3

Steve George | s.e.george@reading.ac.uk
Last Updated : Mon Aug 16 16:34:37 BST 2004