A non-hydrostatic semi-implicit, semi-Lagrangian dynamics formulation for the Met Office Unified Model (UM) is undergoing pre-operational trials. The UM has been coupled to the Met Office 3DVAR data assimilation system. Increments of pressure, potential temperature, horizontal winds and specific humidity are added to the model over a 6 hour time window centred at the analysis time. Two one-month (December 1999, July 2000) trial periods are being used to test against the current operational system.

Several problems have been uncovered and rectified during the trials. This included control of humidity increments near the tropopause. The New Dynamics performance does not yet quite match the current UM overall but significant improvements have been noted in the forecasting of winter storms during December 1999.