Hello CF I have been having an interesting conversation with some modelling colleagues regarding the standard names and descriptions for cloud amount:
cloud_area_fraction: 'X_area_fraction' means the fraction of horizontal area occupied by X. 'X_area' means the horizontal area occupied by X within the grid cell. Cloud area fraction is also called 'cloud amount' and 'cloud cover'. The cloud area fraction is for the whole atmosphere column, as seen from the surface or the top of the atmosphere. The cloud area fraction in a layer of the atmosphere has the standard name cloud_area_fraction_in_atmosphere_layer. low_type_cloud_area_fraction: Low type clouds are: Stratus, Stratocumulus, Cumulus, Cumulonimbus. "X_area_fraction" means the fraction of horizontal area occupied by X. Cloud area fraction is also called "cloud amount" and "cloud cover". X_type_cloud_area_fraction is determined on the basis of cloud type and not on the vertical location of the cloud. middle_type_cloud_area_fraction: Middle type clouds are: Altostratus, Altocumulus, Nimbostratus. "X_area_fraction" means the fraction of horizontal area occupied by X. Cloud area fraction is also called "cloud amount" and "cloud cover". X_type_cloud_area_fraction is determined on the basis of cloud type and not on the vertical location of the cloud. high_type_cloud_area_fraction: High type clouds are: Cirrus, Cirrostratus, Cirrocumulus. "X_area_fraction" means the fraction of horizontal area occupied by X. Cloud area fraction is also called "cloud amount" and "cloud cover". X_type_cloud_area_fraction is determined on the basis of cloud type and not on the vertical location of the cloud. In our local models, we have diagnostics labelled: TOTAL CLOUD AMOUNT - RANDOM OVERLAP LOW CLOUD AMOUNT MEDIUM CLOUD AMOUNT HIGH CLOUD AMOUNT The model calculates LOW CLOUD AMOUNT by finding the maximum amount of cloud cover in a model level which exists within a range defined as low. The model has no inclination about cloud types and makes no evaluation of overlap for these diagnostics. The model calculates TOTAL CLOUD AMOUNT - RANDOM OVERLAP by evaluating the cloud over all vertical levels and its spatial displacement. Base on this, it seems reasonable to use the CF standard name cloud_area_fraction for output fields but based on the descriptive text then I do not see how we could ever be able to use low_type_cloud_area_fraction for data output from our model. I would be really interested to hear from people who use these standard names regularly on the applicability to our case; specifically: 1. Are these definitions explicit, complete and accurate? 2. Should all uses of these standard names be sure that they are based on typing the cloud correctly, not on the level of the cloud within the model? 3. Do these high/medium/low cloud type standard names also assume that spatially displaced levels are summed, or are they aiming to report the maximum in any one level within the range? many thanks mark
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