[Stoch] Paper on stochastic physics in convection-permitting ensemble

[BOUTTIER Francois]

Dear all,

  the following paper has been published as an 'early online release' in Monthly Weather
Review:

François Bouttier, Benoît Vié, Olivier Nuissier, Laure Raynaud, 2012:
Impact of stochastic physics in a convection-permitting ensemble.
Mon. Wea. Rev., in press.
doi: http://dx.doi.org/10.1175/MWR-D-12-00031.1 

Abstract
A stochastic physics scheme is tested in the AROME short range convection-permitting 
ensemble prediction system. It is an adaptation of ECMWF's stochastic perturbation of 
physics tendencies (SPPT) scheme. The probabilistic performance of the AROME ensemble 
is found to be significantly improved, when verified against observations over two 
two-week periods. The main improvement lies in the ensemble reliability and the 
spread/skill consistency. Probabilistic scores for several weather parameters are 
improved. The tendency perturbations have zero mean, but the stochastic perturbations 
have systematic effects on the model output, which explains much of the score improvement. 
Ensemble spread is an increasing function of the SPPT space and time correlations. A 
case study reveals that stochastic physics do not simply increase ensemble spread, they 
also tend to smooth out high spread areas over wider geographical areas. Although the 
ensemble design lacks surface perturbations, there is a significant end impact of SPPT 
on low-level fields through physical interactions in the atmospheric model.

-- 
François Bouttier CNRM-GAME/GMME/MICADO Météo-France 42 Av Coriolis 31057 Toulouse France
  tél +33 5 6107 9825    fax +33 5 6107 9626     francois.bouttier at meteo.fr