Dear Lars and Dan I can't remember what I thought last time this was discussed, so I might be inconsistent! At present, it seems to me the most suitable solution is to have different standard names for strict inequalities and inequalities-allowing- equality, since as Lars says there that means only a dozen new standard names. Even if more are needed in future, it doesn't seem likely that there will be hundreds - but if so, we can adopt another solution when the need arises.
But one other consideration is whether, in a given dataset, or when comparing datasets, the distinction is critical. Would you have both kinds in a single dataset, and would you decide that a <= quantity in one dataset should *not* be regarded as comparable to a < quantity from another dataset? If Yes in either case, the distinction is needed; but if No then it may not have to be made in the standard name. It could be recorded in a non-standardised way instead. Best wishes Jonathan ----- Forwarded message from Bärring Lars <[email protected]> ----- > Date: Tue, 28 Mar 2017 15:02:02 +0000 > From: Bärring Lars <[email protected]> > To: "Hollis, Dan" <[email protected]>, "[email protected]" > <[email protected]> > Subject: Re: [CF-metadata] Request for new standard names for climatological > statistics based on thresholds > > Hi Dan, all > > Thanks for these pointers. Obviously I somehow managed to miss this thread > when searching the mail archive (which I actually did try despite all > evidence to the contrary). I am sorry for that. > > Anyway, in an attempt to restart this discussion let me my summarising the > previous thread: > > It started off from the need to distinguish between dry and wet days > according to a threshold of some small precipitation amount (say 0.2 > mm[/day]), that typically had been observed at limited precision (thus > discretized). For floating point data from models this not a problem and the > arguments were that it would be more appropriate to take actual limits > induced by the discretization into account. > > There was a suggestion to use the existing standard name but adding a (non > CF) logical flag attribute to handle non-strict inequality. But this met > opposition as it would split the description of the data into two places (the > standard name and the logical flag attribute). > > It was noted that a strict and a non-strict inequality are indeed two > different things and should not be mixed up in the context of standard names. > The last comment was to suggest that the way forward would be to rename > (redefine) all the relevant standard names to include non-strict > inequalities. But, as was noted, this seems cumbersome. > > I hope this is a reasonable summary of that thread. With this background, let > me add some real use-cases that may shed some new light on the need to make > the distinction. > > I have in previous posts referred to the two WMO/WCRP/etc. expert teams > ETCCDI and ET-SCI defining and producing core sets of climate indices (aka > climate indicators). I am member of neither and have no vested interests, > other than I do see the need to make this kind of data more easily available > in a unified way. > > ETCCDI defines Summer Days ("SU") as the number of days when the daily > maximum temperature is strictly above +25 degC. This perfectly handled by the > standard name number_of_days_with_air_temperature_above_threshold. > > ET-SCI defines Hot Days ("TXge30" previously known as "SU30") as the number > of days when the daily maximum temperature is equal to or above +30 degC. In > structure it similar to SU with the crucial exception of a non-strict > inequality. And, this small but crucial difference in definition cannot be > changed for any number reasons. > > Now, in various user-oriented tools and web services the requirement is to > allow the users to change the threshold value to enable them to explore the > data and carry out simple sensitivity studies on their own. Thus, there is a > concrete need to handle the situation of having the ETCCDI index SU modified > to use the threshold value +30 degC (in which case it might perhaps be be > called "SU30"). This was in fact the very reason for renaming the ET-SCI > index "SU30" to "TXge30" to avoid misunderstandings. Likewise, ET-SCI index > TXge30 can be modified to use the threshold value +25 degC (which then would > be called "TXge25"). > > To facilitate the dissemination of these kinds of datasets to a wider > community it would indeed be helpful to have standard names that reflect the > perhaps small but still crucial difference between strict and non-strict > inequalities. > > I therefore like to again raise the suggestion to introduce the two > constructs "._at_or_above_threshold" and "._at_or_below_threshold" for the > relevant standad names. > > As I have outlined, we have real use-cases that go beyond what was the driver > for the discussion in the previous thread. Moreover, with nine new standard > names requested in my initial post the additional burden on the standard name > space is modest. However, if this is a concern the use cases I have outlined > currently cover the following standard names > number_of_days_with_air_temperature_above_threshold > number_of_days_with_air_temperature_below_threshold > number_of_days_with_lwe_thickness_of_precipitation_amount_above_threshold > The remaining six I included without having an exhaustive overview of what > climate indices are used out there, and as they are identical in their > structure they could be changed at the same in one go without having to > revisit this issue again every time the need pops up. > > > Regards, > Lars > > > -- > Lars Bärring > > FDr, Forskare > PhD, Research Scientist > > SMHI / Swedish Meteorological and Hydrological Institute > Rossby Centre > SE - 601 76 NORRKÖPING > http://www.smhi.se > > E-post / Email: [email protected] > Tel / Phone: +46 (0)11 495 8604 > Fax: +46 (0)11 495 8001 > Besöksadress / Visiting address: Folkborgsvägen 17 > > > > > > -----Original Message----- > From: Hollis, Dan [mailto:[email protected]] > Sent: den 27 mars 2017 13:06 > To: Bärring Lars; [email protected] > Subject: RE: Request for new standard names for climatological statistics > based on thresholds > > Hi Lars, > > I raised a very similar question a couple of years ago: > http://mailman.cgd.ucar.edu/pipermail/cf-metadata/2014/057605.html > > The outcome was inconclusive. One suggestion was to add a Boolean attribute > that indicated whether the threshold value was included or not. Others > thought that adding more standard names was the way to go, while others > thought that a single name was sufficient. > > I encourage you to read through the rest of the thread and see if it helps > with your current request: > http://mailman.cgd.ucar.edu/pipermail/cf-metadata/2014/thread.html#57605 > > For info, we continue to use the existing standard names even though they do > not strictly match the definitions of our 'days of rain' statistics. > > Regards, > > Dan > > > Dan Hollis Climatologist > Met Office Hadley Centre FitzRoy Road Exeter Devon EX1 3PB United > Kingdom > Tel: +44 (0)1392 884535 Mob: +44 (0)7342058682 Fax: +44 (0)1392 885681 > E-mail: [email protected] Website: http://www.metoffice.gov.uk > For UK climate and past weather information, visit > http://www.metoffice.gov.uk/climate > > > -----Original Message----- > From: CF-metadata [mailto:[email protected]] On Behalf Of > Bärring Lars > Sent: 24 March 2017 08:10 > To: [email protected] > Subject: [CF-metadata] Request for new standard names for climatological > statistics based on thresholds > > Dear all, > > Several standard names oriented towards climate indices for various impacts > are based on thresholds, and the standard name includes the construct > "..._above_threshold" or "..._below_threshold". However, several > well-established climate indices use non-strict inequalities in their > definition. > > For model output using floating point precision the difference between using > a strict and a non-strict inequality is small or even negligible, but for > observational data discretized to some limited precision (typically one or no > decimal digit) this makes a difference. > > At a workshop last week people involved in WMO/CCl Expert Team on > Sector-specific Climate Indices (ET-SCI) and the joint CCl/WCRP/JCOMM Expert > Team on Climate Change Detection and Indices (ETCCDI), as well as the > European ECA&D programme and several research projects discussed this. > > The outcome of these discussions is to suggest new standard names similar to > the existing ones but using the contructs "..._at_or_above_threshold" and > "..._at_or_below_threshold". In all other respects these new standard names > should be patterned after the following existing ones: > > number_of_days_with_air_temperature_above_threshold > number_of_days_with_air_temperature_below_threshold > number_of_days_with_lwe_thickness_of_precipitation_amount_above_threshold > number_of_days_with_surface_temperature_below_threshold > number_of_days_with_wind_speed_above_threshold > spell_length_of_days_with_air_temperature_above_threshold > spell_length_of_days_with_air_temperature_below_threshold > spell_length_of_days_with_lwe_thickness_of_precipitation_amount_above_threshold > spell_length_of_days_with_lwe_thickness_of_precipitation_amount_below_threshold > > The specific use cases for these extension are several ET-SCI defined indices > that involves non-strict inequalities. > > The alternative of changing the ET-SCI definitions to use a strict inequality > is not an option because they have been painstakingly defined in > collaboration with user communities and/or are directly related to > well-established operational usage. > > Likewise, to just adjust the threshold in order to turn the non-strict > inequality to a strict equality (say from 30 C to 29.9 C or 29.99 C or ...) > is not attractive and prone to cause confusion. > > Kind regards, > Lars > > -- > Lars Bärring > > FDr, Forskare > PhD, Research Scientist > > SMHI / Swedish Meteorological and Hydrological Institute Rossby Centre SE - > 601 76 NORRKÖPING http://www.smhi.se > > E-post / Email: [email protected] > Tel / Phone: +46 (0)11 495 8604 > Fax: +46 (0)11 495 8001 > Besöksadress / Visiting address: Folkborgsvägen 17 > > > _______________________________________________ > 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 ----- End forwarded message ----- _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
