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.<br>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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