## Stochastic Parametrization

**Using the Plant-Craig stochastic convective parameterization in an
ensemble forecast system**

We have implemented the Plant-Craig (PC) stochastic convection scheme
into the limited-area COSMO (Consortium
for Small-scale Modeling) model. We have run the model with initial
and boundary conditions provided
by selected members of the ECMWF Ensemble Prediction System (EPS).
This allows us to compare how much
ensemble spread is introduced to the ensemble by the stochastic scheme
relative to that already present.
A stochastic parameterization, like the PC-scheme, takes into account
the fact that the intensity of unresolved
convection is not merely determined by resolved-scale parameters, but
also by unresolved physics. To this
aim, the PC-scheme, being based on statistical physics, uses
convective plumes that are randomly drawn from a
probability density function that describe the chance of launching a
plume with a certain mass flux each time the
scheme is called.