I like the change, but please spell out NWP (and if a proper noun, make sure it is an unambiguous reference for anyone in the world).
john On Jun 19, 2014, at 03:55, Hedley, Mark <[email protected]> wrote: > Hi Heiko, Alison, CF > > that all sounds good to me, many thanks for your input and advice Heiko > > I would like to formally propose that the description text for standard names: > low_type_cloud_area_fraction > medium_type_cloud_area_fraction > high_type_cloud_area_fraction > > be altered such that > > 'X_type_cloud_area_fraction is determined on the basis of cloud type and not > on the vertical location of the cloud.' > > instead reads > > 'X_type_cloud_area_fraction is generally determined on the basis of cloud > type, though NWP models often calculate them based on the vertical location > of the cloud.' > > thank you > mark > ________________________________________ > From: Heiko Klein [[email protected]] > Sent: 18 June 2014 08:20 > To: Hedley, Mark; [email protected] > Subject: Re: [CF-metadata] cloud amounts > > Hi Mark, > > the first proposal for the *_cloud_area_fraction was in fact > high/medium/low, and not high_type etc. But then, we found out that we > do not manage to give a concise description where a 'high' cloud starts > and where it ends. The altitude of the clouds changes by latitude and > other factors. > > The 'high/medium/low_type' words are rather concepts than precise model > descriptions, and when doing inter-comparison from model to model or > from model to observations it will be possible to do so on that basis. > > > I just reread the description in the standard_name list, and I see that > only half of the proposal made it the the final list. The sentence: > > The cloud types can be used for models, too, e.g. by the definitions > like (taken from ECMWF): > Let sigma = pressure / surface pressure. > Low type cloud is for 1.0 > sigma > 0.8 > Medium cloud is for 0.8 >= sigma > 0.45 > High cloud is for 0.45 >= sigma > The definition depends usually on model and/or latitude. > > didn't make it. > > > > So, I agree, that the current description needs a slight modification > because it currently rules out a common usage. I suggest to change from > > X_type_cloud_area_fraction is determined on the basis of cloud type and > not on the vertical location of the cloud. > > to > > X_type_cloud_area_fraction is generally determined on the basis of cloud > type, though NWP models often calculate them based on the vertical > location of the cloud. > > > Otherwise, we might end up with two standard-names describing the same > concept, just because the description sounds to strict. > > > Best regards, > > Heiko > > On 2014-06-17 14:57, Hedley, Mark wrote: >> Hello Heiko, CF >> >> Many thanks for your feedback, that is really useful. I think I appreciate >> the utility of these standard names, the feedback I have had is that >> diagnostics like this are widely used by forecasters and model analysts. >> >> The concerns raised with me relate to the descriptions of these diagnostics, >> and the focus on 'cloud type identification' for classification. >> >> There are similarly named diagnostics in our models, which explicitly do not >> categorise clouds; they take defined vertical ranges and return data based >> on the amount of any cloud in a grid box for that range of model levels. >> >> The concern is that whilst the standard name is likely to be recognised by >> model developers and forecasters alike, the description which is bound to >> this standard name does not describe how these diagnostics are calculated >> within our model. >> >> This has lead to the concern that whilst these seem very useful standard >> names, they should not be used for our models, as the textual description of >> the standard names do not reflect the modelled quantity in our case. The >> |low/medium/high| cloud amount is always determined on the basis of the >> vertical location of the cloud, not on the cloud type, which is not modelled. >> >> Do you think that the description text statement: >> ''X_type_cloud_area_fraction is determined on the basis of cloud type and >> not on the vertical location of the cloud.'' >> properly represents the standard name and its usage across the community? >> >> Might we be better served by using a different name for these model outputs, >> even if this hides the generally accepted interpretation of high/medium/low >> cloud? (if so, what?) >> >> many thanks >> mark >> >> ________________________________________ >> From: Heiko Klein [[email protected]] >> Sent: 11 June 2014 18:53 >> To: Hedley, Mark; [email protected] >> Subject: Re: [CF-metadata] cloud amounts >> >> Hi Mark, >> >> I've been the original requestor for the >> low/middle/high_type_cloud_area_fraction. >> >> WMO has introduced the low/middle/high clouds already before models >> became as famous as they are today, and they still seem to be a >> excellent simplification and forecasters still use these 3 types (+fog). >> >> Model output can come in many levels, currently in Europe between 60 and >> 200. This is definitely too much to transfer and to handle for a >> forecaster and a reduction to 3 (4) cloud-types is done at all known >> centres (Norway/ECMWF/SMHI). You are right that this reduction is often >> just a summation of certain levels, but it doesn't need to - I've seen >> at least one model which calculates fog different than just taking >> clouds in ground-level. >> >> Examples: >> >> >> # using correct standard_name >> http://thredds.met.no/thredds/dodsC/arome25/arome_norway_default2_5km_latest.nc.html >> >> >> # layer named e.g. High cloud cover >> http://wrep.ecmwf.int/wms/?token=MetOceanIE&request=GetCapabilities&version=1.1.1&service=WMS >> >> >> Concerning your questions: >> >> 1. Forecasts are never accurate, but the definitions are at least well >> established by WMO, and it is the models task to translate them as best >> as possible >> >> 2. No, the cloud types predate models and model levels and eventually >> accurate height measurements. If a model-level - cloud type assumption >> is used, this is just a guess. >> >> 3. Really good question, I'll ask our modellers how they calculate the >> different types. >> >> Heiko >> >> On 2014-06-11 15:41, Hedley, Mark wrote: >>> 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 >>> >>> >>> _______________________________________________ >>> CF-metadata mailing list >>> [email protected] >>> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata >>> >> >> -- >> Dr. Heiko Klein Tel. + 47 22 96 32 58 >> Development Section / IT Department Fax. + 47 22 69 63 55 >> Norwegian Meteorological Institute http://www.met.no >> P.O. Box 43 Blindern 0313 Oslo NORWAY >> > > -- > Dr. Heiko Klein Tel. + 47 22 96 32 58 > Development Section / IT Department Fax. + 47 22 69 63 55 > Norwegian Meteorological Institute http://www.met.no > P.O. Box 43 Blindern 0313 Oslo NORWAY > _______________________________________________ > CF-metadata mailing list > [email protected] > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
