Breakthrough in forecasting equilibrium and non-equilibrium convection
Bechtold, Peter ; Semane, Noureddine ; Lopez, Philippe ; Chaboureau, Jean-Pierre ; Beljaars, Anton ; Bormann, Niels
A new diagnostic convective closure has been developed. Important improvements in global NWP forecasts have been obtained with the new convective closure. In particular, there is not only a better representation of the diurnal cycle of convection, but also a better depiction of its spatial distribution. A comparison of low-resolution seasonal integrations and high-resolution short-range forecasts against satellite and radar data shows that with the new convective closure it is possible to realistically represent non-equilibrium convection. Other investigations, which involve comparisons with a cloud resolving model (CRM) for the Sahel region and with satellite data, confirm the good performance of the new scheme. The new convective closure is dependent on an extended convective available potential energy (CAPE). It has been derived under a quasi-equilibrium assumption for the free troposphere subject to boundary-layer forcing. The simple closure involves adjustment timescales for the free troposphere and the land and ocean boundary-layers.
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