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Core Group on Theoretical Studies of the Convection Parameterization Problem


A research network is funded by the European COST program.

Current numerical models of the atmosphere, both for numerical weather prediction (NWP) and for climate projection, have difficulties in accounting for unresolved variability, most notably, the variability associated with convection. Convection is a crucial driver of the atmospheric general circulation and is a key process for the vertical distribution of energy. It is responsible for the bulk of global precipitation. Among other known deficiencies of climate projections, global forecast models produce too early an onset of afternoon convection and fail to represent the 20-60 day planetary-scale tropical oscillation (Madden-Julian oscillations: Link to Bechtold et al., 2008, QJ: available by request to: Peter.Bechtold@we dont want The most recent IPCC report singles out convection and cloud parameterizations as the key issues to be resolved in order to reduce uncertainties in future climate projections.

Massive efforts aimed at improving atmospheric models are underway at NWP centres. Collaborations are organized by various NWP consortia. International activities, such as the Global Energy and Water Cycle Experiment (GEWEX) Global Atmospheric System Studies (GASS) Panel, focus on cloud processes. Extensive  efforts are also undertaken through numerical calculations based either on "super-parameterization" or on global cloud-system resolving modelling, as currently performed in the USA and Japan, respectively.

This group extends the existing efforts at an European level by focusing on a critically missing element: fundamental theoretical studies of the   deep-convection parameterization problem.

Current operational parameterizations use various ad hoc assumptions that  often lack robust physical basis. The most notorious example is a closure that is required in order to define the total strength of convection produced by a parameterization. One more example is the rate of entrainment and detrainment characterizing the lateral exchange of air between a convective plume (convective tower) and environment. In spite of their critical importance in defining the vertical extent of deep convection, these parameters are currently simply tuned often in physically unreasonable way. More fundamentally, current parameterizations are designed to represent particular elements of the model physics (e.g., deep convection, boundary layer turbulence, radiation), whereas coupling between different physical processes (modules), that is crucial in view of the overall model performance, is to a large extend missing.

An increasing resolution poses new problems and requires a new generation  of physical parameterizations. This is a challenge that urgently needs a strong action.

Core Group on Theoretical Studies of the Convection Parameterization Problem is implemented as COST Activity ES0905.

You can look at COST ES0905 Memorandum of understanding.

Our activity is currently supported by COST Action ES0905.

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