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
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