Atmospheric Physics

The physical processes associated with radiative transfer, convection, clouds, turbulent mixing, sub grid-scale orographic drag and non-orographic gravity wave drag have a strong impact on the large-scale flow of the atmosphere.  However, these mechanisms are often active at scales smaller than the resolved scales of the model grid.  The effect of sub-scale physical processes on weather systems is expressed in the model in terms of resolved model variables using parameterisation.  This involves both statistical methods and simplified mathematical-physical models, (e.g. the air closest to the earth’s surface exchanges heat with the surface through turbulent diffusion or convection, which adjusts stability in the lowest layers).

Moist Physics

An upgrade of the moist physics package (the so-called "New Moist Physics") was introduced within Cycle 47R3 (implemented 12 October 2021).  This aims to improve the representation of complicated interactions between turbulence in the lowest part of the atmosphere, convective motions and the cloud physics.  It is important that these processes interact with each other in a physically consistent way to represent real-world processes effectively.  The upgrade adjusts the following:

In most cases, but not all, the changes listed above manifest themselves as improvements in model output fields, but for more forecaster-oriented detail on product impacts see here.

Aspects of the moist physics package are given below:


Fig2.1.5-1: Outline of revisions to the physics within Cycle 47R3 upgrade.  Schematic of the representation of the cloudy convective boundary layer in the IFS, consisting of moist convective mass flux in the moist convection scheme and dry mass flux and turbulent diffusion in the turbulence scheme.  Turbulent diffusion is confined within the dry boundary layer.  However, it is extended to the cloud top of Sc where there is also an additional contribution from radiative cooling and cloud top entrainment. 

The Convective Boundary Layer

The turbulent and convective mixing in the convective boundary layer is formulated in a simple and consistent way but there are several important differences which have been introduced:

Saturation adjustment and the cloud scheme

The moist physics upgrade has brought:

Microphysical  processes and interaction with radiation

The moist physics upgrade improves the parameterisation of microphysical processes by:

Even small changes in the processes can have significant impacts on the cloud and precipitation field and can affect shortwave and longwave radiation.

Deep convection and mesoscale convective systems

The moist physics upgrade improves the parameterisation of deep convection, especially addressing: 

These include the coupling between the convection and the dynamics, which is particularly delicate in the case of mesoscale convective systems that propagate and regenerate by producing their own horizontal convergence.

New and revised products.

Cycle 47r3 included:

Additional Sources of Information

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