Proceedings - C-SRNWP Project

Physics improvements in the NAE model, dust forecasting,
firefighting and chemistry
Met Office Fitzroy Road Exeter
+44 1392 886098 mike.bush@metoffice.gov.uk
1) NAE model physics upgrade 26 th September 2006
The physics package comprises changes to the Boundary Layer (BL) and convection schemes.
These changes were initially tested and then implemented in the Global model in March 2006.
Also included in the package is a solution to the ‘valley cooling problem’ (a numerical
instability caused by the theta advection scheme). This problem has previously lead to both
Global and NAE model failures in places such as Tibet and Greenland where ‘bowl’ shaped
orography has lead to runaway cooling of cold, stable pools of air. The previous solution has
been to locally smooth the orography to stop these cold pools from forming in the first place.
Convection changes
The changes to the convection scheme are:
1) mid-level changes - a selection of small modifications primarily aimed at improving
the behaviour of mid-level convection
2) adaptive detrainment - the triggering of forced detrainment (Figure 1) is set to be a
function of the parcel's buoyancy gradient resulting in a much smoother detrainment
profile (Figure 2).
Figure 1: Convection scheme: Updraught
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