Stochastic Tendency Perturbations

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:

Stochastically Perturbed Parameterisation Tendencies (SPPT)

SPPT randomly perturbs the tendencies from the physical parameterisation schemes.  This is done to represent uncertainties in the effects of under-resolved processes.  These uncertainties arise from either or both:

The physics schemes operate through an entire grid box column.  The shape of the unperturbed column of tendencies is preserved by multiplying by 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:


It should be stressed that overall stochastic perturbations undoubtedly do deliver clear improvements in the ensemble performance.

Additional Sources of Information

(Note: In older material there may be references to issues that have subsequently been addressed)