loading page

Confronting the convective gray zone in the global configuration of the Met Office Unified Model
  • +11
  • Lorenzo Tomassini,
  • Martin Willett,
  • Alistair Sellar,
  • Adrian Lock,
  • David Walters,
  • Michael Whitall,
  • Claudio Sanchez,
  • Julian Heming,
  • Paul Earnshaw,
  • José Rodríguez,
  • Duncan Ackerley,
  • Prince Kattanchery xavier,
  • Charmaine Franklin,
  • Catherine Senior
Lorenzo Tomassini
UK Met Office

Corresponding Author:[email protected]

Author Profile
Martin Willett
Met Office
Author Profile
Alistair Sellar
Hadley Centre, Met Office
Author Profile
Adrian Lock
Met Office
Author Profile
David Walters
Met Office
Author Profile
Michael Whitall
Met Office
Author Profile
Claudio Sanchez
Met Office
Author Profile
Julian Heming
Met Office, U.K.
Author Profile
Paul Earnshaw
Met Office
Author Profile
José Rodríguez
Met Office, FitzRoy Road, Exeter EX1 3PB, UK
Author Profile
Duncan Ackerley
Met Office
Author Profile
Prince Kattanchery xavier
Met Office
Author Profile
Charmaine Franklin
Australian Bureau of Meteorology
Author Profile
Catherine Senior
Met Office
Author Profile

Abstract

In atmospheric models with kilometer-scale grids the resolution approaches the scale of convection. As a consequence the most energetic eddies in the atmosphere are partially resolved and partially unresolved. The modeling challenge to represent convection partially explicitly and partially as a subgrid process is called the convective gray zone problem. The gray zone issue has previously been discussed in the context of regional models, but the evolution in regional models is constrained by the lateral boundary conditions. Here we explore the convective gray zone starting from a defined global configuration of the Met Office Unified Model using initialized forecasts and comparing different model formulations to observations. The focus is on convection and turbulence, but some aspects of the model dynamics are also considered. The global model is run at nominal 5km resolution and thus contributions from both resolved and subgrid turbulent and convective fluxes are non-negligible. The main conclusion is that in the present assessment, the configurations which include scale-aware turbulence and a carefully reduced and simplified mass-flux convection scheme outperform both the configuration with fully parameterized convection as well as a configuration in which the subgrid convection parameterization is switched off completely. The results are more conclusive with regard to convective organization and tropical variability than extratropical predictability. The present study thus endorses the strategy to further develop scale-aware physics schemes and to pursue an operational implementation of the global 5km-resolution model to be used alongside other ensemble forecasts to allow researchers and forecasters to further assess these simulations.