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The convection processes are similarly calculated using a complex suite of programs dealing with the interactions between the phases of water.  The convection process "detrains" cloud and precipitation into the large-scale cloud scheme.  This allows representation of convective anvils and also the precipitation associated with the more stratiform part of the convective cell.  However, the main part of the precipitation from the core of the updraught is treated diagnostically in the convection scheme, and assumes all the precipitation falls out within the grid column in a timescale less than the model timestep.  Convective precipitation in the model falls vertically and immediately; it is not advected with winds underlying the model cloud.  Thus Thus, model showers are not advected with the wind during their life-cycle.  In particular, any showers that the model develops over the sea do not penetrate beyond the coast .  In while in reality, showers normally advect with the wind during their life-cycle.  Users should allow for:

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Cloud Fraction

Cloud fraction is a prognostic model variable for each grid box.  This means at each timestep cloud fraction is advected into the grid box by the model wind and then acted upon by sources and sinks of moisture.   

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Convective cloud top height

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This can be derived from modelled vertical profiles of temperature throughout the troposphere.  At any given grid point the convection scheme inspects the temperature structure of the model atmosphere

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progressively from the surface to 300hPa.  If there exists a level of free convection (LFC) the scheme searches upward to the level where the model parcel temperature becomes the same as the model environment temperature.  This is considered as the altitude where free convection ceases and is taken as the convective cloud top height.    

 Image Added

Fig2.1.5.-5: Assessment of cloud top height from a schematic vertical profile.

(FUG Associated with Cy49r1)

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