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Uncertainties within the IFS ensemble system are currently represented by a stochastic perturbation technique (SPPT).  This represents uncertainties due to the model integration, and is used:

• during the execution of the forecast
• during creation of the Ensemble of Data Assimilations (EDA) as part of the representation of uncertainties in the forecast initial conditions.

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Since the physics schemes operate through an entire grid box column, the perturbations act to preserve the shape of the unperturbed vertical profile of tendencies by multiplying a column of tendencies with a single random number.

SPPT perturbs tendencies but not fluxes and this may cause certain inconsistencies and different behaviour between perturbed and unperturbed forecasts.

Some Limitations of SPPT

The current SPPT scheme:

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