Height of convective cloud top (HCCT) is a new output parameter introduced with cycle 43r1. HCCT gives the height in metres (m) of the tops of clouds produced by all three forms of parametrized convection:
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Since HCCT includes all forms of convection mentioned above, sometimes high convective cloud tops can be related to mid-level convection that produces relatively thin high-level clouds. To check whether this is the case one can use the difference between HCCT and the cloud base height (CBH) in order to obtain cloud depth as it is shown in Fig.1 a). On that plot these clouds will appear to be quite thin. Both HCCT and CBH are computed relative to the model orography.
Looking globally we can notice quite widespread coverage of convective clouds. This is due to the fact that the convective detrainment of cloudy air into the environment is the main source of clouds in the model, and detrained air of this type counts as convective cloud.
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Fig.1 a) HCCT; b) Cloud depth (HCCT-CBH); c) Cloud cover. On all three plots areas of different types of convection are labelled as follows: 1 → Shallow convection, 2 → DMC, 3 → Mid-level convection.
HCCT represents instantaneous values and as such the field itself could be quite noisy. It can happen that seemingly cloudless grid boxes where DMC has not been triggered (yet) are surrounded by very high and thick convective clouds produced by DMC (Fig.2). In such instances there will often be heavy precipitation underneath, but the model would be diagnosing this as large scale not convective. It is as if the convection is being completely resolved.
Fig. 2. HCCT in a widespread area of DMC over Western Africa. Marked blank areas represent areas where DMC is not active surrounded by thick clouds where DMC is taking place.
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