1-02 Units

[joergklausen]

Branch

https://github.com/wmo-im/wmds/blob/issue159/tables_en/1-02.csv https://github.com/wmo-im/wmds/blob/issue159/tables_en/superseded.txt

Summary and Purpose

Improve the unit table by removing redundant or incorrect entries, adding or correcting names and descriptions, Changing the notations to a more consistent syntax and adding missing units.

Stakeholder(s)

@gaochen-larc

Proposal

1. Replace "_" in the notations by "." to symbolise multiplication. All entries in the table that use the underscore will be superseded by new entries using a period. Example: deg_s-1 is superseded by deg.s-1.

2. Add unique description to every unit to provide an unambiguous definition and correct names when necessary.

3. Add the following new variables:

   notation	name	description
   km-1	per kilometre	Unit of quantity with dimension of reciprocal length, e.g., optical attenuation coefficients, equal to 0.001 m-1
   Mm-1	per megametre	Unit of quantity with dimension of reciprocal length, e.g., optical attenuation coefficients, equal to 1E-6 m-1
   missing	(missing)	The correct value is not readily available to the sender of this data. Furthermore, a correct value may not exist.
   inapplicable	(inapplicable)	There is no value (categorical data).
   ug.m-3	micrograms per cubic metre	SI derived unit of mass concentration, equal to 1E-9 kg/m3
   mg.l-1	milligrams per litre	SI derived unit of mass concentration, equal to 0.001 kg/m3
   mg.cm-3	milligrams per cubic centimetre	SI derivd unit of mass concentration, equal to 1 kg/m3
   ng.kg-1	nanograms per kilogram	SI derived unit for mass mixing ratio, equivalent to pptm or ppt
   ug.kg-1	micrograms per kilogram	SI derived unit for mass mixing ratio, equivalent to ppbm or ppb
   mg.kg-1	milligrams per kilogram	SI derived unit for mass mixing ratio, equivalent to ppmm or ppm
   um3.cm-3	cubic micrometres per cubic centimetre	SI derived unit for volumetric mixing ratio, equivalent to pptv
   mm3.m-3	cubic millimetres per cubic metre	SI derived unit for volumetric mixing ratio, equivalent to ppbv
   cm3.m-3	cubic centimetres per cubic metre	SI derived unit for volumetric mixing ratio, equivalent to ppmv
   cm-3	per cubic centimetre	SI derived unit of specific volume, equal to 1E-6 m-3
   m-3	per cubic metre	SI derived unit of specific volume
   um	micrometre	Unit of length, equal to one millionth of a metre (1E-6 m)
   ug.l-1	micrograms per litre	SI derived unit of mass concentration, equivalent to milligrams per cubic metre, equal to 1E-3 g.m-3
   cm2	square centimetre	SI derived unit of area, equal to 1E-4 m2
   HU	Hazen units	Unit of color according to the Platinum/Cobalt or Apha/Hazen scale
   uS.cm-1	microsiemens per centimetre	SI derived unit of spatial gradient of electrical conductance, equal to 1E-4 S.m-1
   g.cm-3	grams per cubic centimetre	SI derived unit of density, equivalent to kilograms per litre, equal to one thousand kilograms per cubic metre (1E+3 kg.m-3)
   mV	millivolt	SI derived unit of voltage, electrical potential difference, electromotive force, equal one thousandth of a volt (1E-3 V)
   mbar	millibar	SI derived unit of pressure, equal to one thousandth of a bar (1E-3 bar)
   mmHg	millimetre of mercury	Unit of pressure, equal to 133.322387415 pascals
   kcal.cm-2	kilocalories per square centimetre	Unit of radiant exposure, equal to 4.184e+7 J.m-2
   NTU	nephelometric turbidity units	Units of turbidity from a calibrated nephelometer
   MPN.ml-1	most probable number index number in 1 millilitre	Unit of expected number concentration of bacteria in the original sample based upon the statistical probability of the coincidence of microorganisms in each sample replicate
   CFU.ml-1	colony-forming units per millilitre	Unit of number concentration of viable bacteria or fungal cells in a sample as a result of a plate count test
   km-1.sr-1	per kilometre per steradian	Unit of the scattering coefficient at a given direction, equal to 1E-3 m-1.sr-1
   m-1.sr-1	per metre per steradian	Unit of the scattering coefficient at a given direction
   Mm-1.sr-1	per megametre per steradian	Unit of the scattering coefficient at a given direction, equal to 1E-6 m-1.sr-1

4. Remove the following units from the code table

   notation	name	description	status
   log_(m-1)	logarithm per metre	invalid
   log_(m-2)	logarithm per square metre	invalid
   Cel	degree Celsius	supersede by degC
   degrees_true	deg true	supersede by deg
   s-1	per second (same as hertz)	supersede by Hz
   m2_Hz-1	square metres per hertz	supersede by m2.s
   ug_m-3_20C	micrograms per cubic metre at 20 degrees	supersede by ug.m-3
   ug_m-3_25C	micrograms per cubic metre at 25 degrees	supersede by ug.m-3
   mg_m-3_25C	milligrams per cubic metre at 25 degrees	supersede by mg.m-3
   ug_N_m-3	microgram N per cubic metre	supersede by ug.m-3
   ug_C_m-3	microgram C per cubic metre	supersede by ug.m-3
   ug_S_m-3	microgram S per cubic metre	supersede by ug.m-3
   ug_Cl_m-3	microgram CI per cubic metre	supersede by ug.m-3
   mg_N_l-1	milligram N per litre	supersede by mg.l-1
   mg_S_l-1	milligram S per litre	supersede by mg.l-1

Reason

1. The use of the underscore is inconsistent in table 1-02 (e.g. notation N_units”). It is useful to select one symbol to indicate a multiplication and only that. For compatibility reasons we choose “.”.
2. Changes to the unit name improve the consistency of the table. Description were added to enhance usability and clarity.
3. The added units make the code list more complete to represent common measurements or cases and promote the use of SI units. Missing units were reported from experts in aerosol remote sensing and hydrology.
4. Mathematically incorect entries are deprecated (status: invalid). Duplicate entries are superseded by the entries of the same concept. Units containing chemical species or temperature values are superseded by a more general concept.

---

original comment:

Consider how to link with CF / unidata, who maintain an excellent table of units at https://www.unidata.ucar.edu/downloads/udunits/ to augment/change how we manage units at https://codes.wmo.int/wmdr/_unit

old link: https://www.unidata.ucar.edu/software/udunits/udunits-current/doc/udunits/udunits2.html#Database

[steingod]

This is a similar issue as CF is experiencing with UGRID and NUG (potentially other activities as well). I haven't seen a conclusion on the CF work flow in this context, but assumes that could be used as a model?

[amilan17]

@gaochen-larc review notation for consistency and suggest descriptions

[gaochen-larc]

https://physics.nist.gov/cuu/Units/index.html. This site has a lot useful information. A good reference for what we need to do.

[gaochen-larc]

More information from NIST perspective: https://physics.nist.gov/cuu/Units/checklist.html in terms of governance...

[gaochen-larc]

Discussion Topics:

1. Geopotential metre, gpm: It appears this unit is for geopotential height. However, the geopotential height is always reported in the length unit, e.g., m. No precise definition of this unit is found through google search and limited textbook search. Comments are solicited in terms of the definition and the need of unit to justify if this unit should remain in the current code list.

2. Consolidate "ug_C_m-3", "ug_Cl_m-3", "ug_N_m-3", "ug_S_m-3", "ug_m-3_20C", "ug_m-3_25C" to "ug m-3": These units are on the current code list to represent the measurements of specific species of C, Cl, and N or measurements reported at specific temperature. However, the all these measurements are reported in "ug m-3". The additional information are used to define the variables or how the variable is reported. This practice mixes the physical quantities and units of physical quantities and is incompatible with the SI governance. The specific variable information and/or variable reporting information can be incorporated into variable name and variable definition/description. Comments are solicited to confirm if it is feasible to consolidate these non-SI units to SI unit: ug m-3.

3. Consolidate "mg_N_l-1" and "mg_S_l-1" to "mg l-1": For the reason stated in 2. Comments are solicited to move forward.

4. Change mg_m-3_25C to mg m-3: Similar to 2). "25 C" can be stated in variable description/definition or part of variable name. Please provide comments.

5. Label correction for "pptv", "ppbv", and "ppmv": the term "dry air" should be removed as these units are commonly used to represent volume fractions for dry air and ambient air. In addition, the SI equivalent units should be provided in description column. Comments?

6. Request addition of "ppt", "ppb", and "ppm": these are the units commonly used to report mass fractions or mole fractions for atmospheric composition measurements. SI equivalent units should be provided in description column. Comments, objections?

7. Request addition of "km-1" and "Mm-1": these are the units used to report particle scattering, absorption, and extinction coefficients. These are SI units. Comments, objections?

8. Question about "m2_Hz-1": should this unit be "m2 s"? need feedback here...

[gaochen-larc]

Unit Notation issue: all units in the current code list use "_" which is not compatible with SI notation. However, the SI notation may not be practical when data are reported in the ASCII files, like .ict files... Comments?

[semmerson]

Re: https://github.com/wmo-im/wmds/issues/159#issuecomment-776770571:

1. See https://glossary.ametsoc.org/wiki/Geopotential_height. Based on that URL, the SI unit for geopotential height is the meter.
2. Couldn't agree more
3. Couldn't agree more
4. Couldn't agree more
5. The SI units are 1e-12, 1e-9, and 1e-6, respectively, and I agree that the "v" should be removed, at least.
6. I suppose if you must use those units.
7. No objection
8. I don't know what "m2_Hz-1" is supposed to represent. What's a relevant physical quantity?

[gaochen-larc]

Practical data management issues with SI unit symbols in ASCII files:

1. Greek letter "µ" in one text editor was changed to "m" in a different text editor. I have experienced this kind of problems, i.e., "µm" and "µg" become to "mm" and "mg".
2. Superscript is allowed but may not be displayed.
3. Space between terms would be an issue for space delimited files.

Should we deal with these potential problems while resolving the compatibility with SI unit issue?

[semmerson]

@gaochen-larc, I'm afraid I don't understand what you mean by this:

3. Space between terms would be an issue for space delimited files.

Please elucidate.

[gaochen-larc]

@gaochen-larc, I'm afraid I don't understand what you mean by this:

1. Space between terms would be an issue for space delimited files.

Please elucidate.

"m s-1" => "m" and "s-1" when parsing the file

[joergklausen]

Greek and other 'strange' character are not per se a problem, nor are spaces in terms ... but it is prudent to avoid both. We should use UTF-8 character encoding for everything we do, and we should double quote all strings we use in CSV files. Unfortunately some very common tools like Excel (arrgh) doesn't support this out of the box. I think we are okay for definitions and descriptions etc, but I would recommend we stick to ASCII alphabet 5 and no spaces for any identifiers (called 'notations' on codes.wmo.int/wmdr).

[semmerson]

The US NIST (and I believe the BIPM) recommends a middle dot "·" (or a period if a middle dot can't be used) to separate the individual units of a compound unit specification.

[gaochen-larc]

The US NIST (and I believe the BIPM) recommends a middle dot "·" (or a period if a middle dot can't be used) to separate the individual units of a compound unit specification.

good idea! We can use this: ASCII CODE 250. any objections?

[gaochen-larc]

Greek and other 'strange' character are not per se a problem, nor are spaces in terms ... but it is prudent to avoid both. We should use UTF-8 character encoding for everything we do, and we should double quote all strings we use in CSV files. Unfortunately some very common tools like Excel (arrgh) doesn't support this out of the box. I think we are okay for definitions and descriptions etc, but I would recommend we stick to ASCII alphabet 5 and no spaces for any identifiers (called 'notations' on codes.wmo.int/wmdr).

Agree with you. Need clarification for "ASCII alphabet 5". I do not know what "ASCII alphabet 5" is and could not find it in google search...

[david-i-berry]

I'm not sure this is the correct place for this, apologies if not.

We’re in the process of mapping current metocean metadata (from Voluntary Observing Ships and Ships of Opportunity) to the WMDS and have some questions on the units field / table. We’ll also be mapping historic metadata in the future, going back pre 1900s and have a few questions over the intent and how to use the field appropriately.

1. Is the intent behind units to report the unit the data were originally measured in or is it the intent to report the units the data are distributed and available in. For example, we may have a temperature reading made in Fahrenheit but then converted to Kelvin and distributed in BUFR on the GTS. In this case what would the appropriate unit be for the WMDS record?
2. As part of the process we’re going through what we measure and the units required to report the observations, do we request new units in this issue or raise a new issue for each unit we wish to propose?
3. For the historic data we have pressure observations made in units such as Paris Inches, in the longer term is this something we want added to the WMDS?

Thanks,

Dave Berry.

[fstuerzl]

@gaochen-larc, I would like to add another adjustment to your list:

9. The notations log(m-1) and log(m-2) are confusing, because an underscore normally stands for a multiplication, which in this case makes no sense. With logarithmic scaling the units should be log(m-1) and log(m-2).

[gaochen-larc]

10. "Unknown": What is this intended for? unrecognized unit? more specific word should be used.
11. "N_Units": Is this newton? need to understand the original intent.
12. "g", notation for acceleration due to gravity: "g" has been used for gram. Propose to use "Gal" for acceleration due to gravity, following BIPM.

[fstuerzl]

11. I'm not sure either, what "N_units" means, but it can't stand for newton, because there is already an entry for this (notation "N", see https://codes.wmo.int/wmdr/unit/N). "N_units" also appears in the BUFR table C-6 (see https://codes.wmo.int/common/unit/N_units), on which the WIGOS measurement unit table was based.

[amilan17]

@gaochen-larc "Unknown": What is this intended for? unrecognized unit? more specific word should be used."

ISO CodeList for nilReason values 

inapplicable

missing

template

unknown

withheld

[david-i-berry]

1. I'm not sure either, what "N_units" means, but it can't stand for newton, because there is already an entry for this (notation "N", see https://codes.wmo.int/wmdr/unit/N).  "N_units" also appears in the BUFR table C-6 (see https://codes.wmo.int/common/unit/N_units), on which the WIGOS measurement unit table was based.

N Units comes from Common Code Table C-6 and is used to report the atmospheric refractivity (http://codes.wmo.int/bufr4/b/15/_036). The comment below appears in the manual on codes, Volume I.2

(5) The refractivity, N, is related to the refractive index, n, by the formula N = 106 (n – 1). N is therefore dimensionless but values computed by the formula are by convention described as being in "N units".

[amilan17]

https://codes.wmo.int/common/nil#:~:text=Nil%2Dreason%20terms%20are%20used,value%20within%20a%20data%20product

[gaochen-larc]

The US NIST (and I believe the BIPM) recommends a middle dot "·" (or a period if a middle dot can't be used) to separate the individual units of a compound unit specification.

good idea! We can use this: ASCII CODE 250. any objections?

More thoughts on middle dot: 1) Middle dot as well as the Greek letter "µ" are part of the extended ASCII codes (Character code 128-155), ISO 8859-1 2) Should we keep everything under ASCII printable characters (character code 32-127)? There were issues encountered when legacy text editor was used. @joergklausen @semmerson @amilan17 and Franziska comments or suggestions?

https://www.ascii-code.com/

[joergklausen]

https://codes.wmo.int/common/nil#:~:text=Nil%2Dreason%20terms%20are%20used,value%20within%20a%20data%20product

To me, 'unknown' is an adequate nilReason in this context, as it expresses that no value has been reported.

[joergklausen]

1. I'm not sure either, what "N_units" means, but it can't stand for newton, because there is already an entry for this (notation "N", see https://codes.wmo.int/wmdr/unit/N).  "N_units" also appears in the BUFR table C-6 (see https://codes.wmo.int/common/unit/N_units), on which the WIGOS measurement unit table was based.

N Units comes from Common Code Table C-6 and is used to report the atmospheric refractivity (http://codes.wmo.int/bufr4/b/15/_036). The comment below appears in the manual on codes, Volume I.2

(5) The refractivity, N, is related to the refractive index, n, by the formula N = 106 (n – 1). N is therefore dimensionless but values computed by the formula are by convention described as being in "N units".

Thanks @DavidBerryNOC very useful. @fstuerzl Please include a definition along these lines.

[joergklausen]

The US NIST (and I believe the BIPM) recommends a middle dot "·" (or a period if a middle dot can't be used) to separate the individual units of a compound unit specification.

good idea! We can use this: ASCII CODE 250. any objections?

More thoughts on middle dot:

1. Middle dot as well as the Greek letter "µ" are part of the extended ASCII codes (Character code 128-155), ISO 8859-1
2. Should we keep everything under ASCII printable characters (character code 32-127)? There were issues encountered when legacy text editor was used. @joergklausen @semmerson @amilan17 and Franziska comments or suggestions?

https://www.ascii-code.com/

I would not recommend the use of any character for notation (WMO306_CD) that I cannot easily find on my keyboard without resolving to +250 (·). This is what computers need to use in machine-to-machine communication and it is just too error-prone to go beyond ASCII 127 IMHO. As I said earlier, I am fully okay and in support of using the UTF-8 character set for definitions/descriptions, labels that are meant for humans.

[joergklausen]

@gaochen-larc, I would like to add another adjustment to your list:

1. The notations log(m-1) and log(m-2) are confusing, because an underscore normally stands for a multiplication, which in this case makes no sense. With logarithmic scaling the units should be log(m-1) and log(m-2).

I agree, this should be fixed, also the name is incorrect, there is no "log per m". If anything, it would be "logarithm of inverse meter", but there is a more fundamental problem here: logarithm is only defined for dimensionless numbers! So, the logarithm of a number of inverse meters divided by inverse meters exists, but not the logarithm of a number of inverse meters. Also, the base (presumably, base 10) needs to be specified. There are 2 entries that suffer from this as far as I can see. This notation is also used in the C-6 code list.

[semmerson]

@DavidBerryNOC I'm not sure the UDUNITS package can handle a unit that's a Galilean transformation of a dimensionless unit.

I'll have to check.

[semmerson]

At https://github.com/wmo-im/wmds/issues/159#issuecomment-781416666@gaochen-larc wrote

2. Should we keep everything under ASCII printable characters (character code 32-127)? There were issues encountered when legacy text editor was used. @joergklausen @semmerson @amilan17 and Franziska comments or suggestions?

I suppose it depends on whether the unit is produced by a human or by a computer:

• Human produced: Use US-ASCII (e.g., "kg.m/s2", "kg.m/s^2", "ug") (Tip of the hat to @joergklausen)
• Computer produced: Use UTF-8-encoded Unicode (e.g., "kg·m/s²", "µg")

[semmerson]

At https://github.com/wmo-im/wmds/issues/159#issuecomment-781475053, @joergklausen wrote

... Also, the base (presumably, base 10) needs to be specified. There are 2 entries that suffer from this as far as I can see. This notation is also used in the C-6 code list.

One could use "lg" for base 10, "ln" for base e, and "lb" for base 2. I believe these symbols are relatively common.

[fstuerzl]

Regarding the "log" issue: Similar to what Jörg wrote, I would interpret the given "units" as "inverse (square) meter displayed on a logarithmic scale", which means the actual units are m^(-1) and m^(-2) . Therefore I would propose to remove these two items from the table and - if neccessary - include m^(-1) and m^(-2). I checked the OSCAR database and found no instance, where they are used.

[gaochen-larc]

At #159 (comment)@gaochen-larc wrote

1. Should we keep everything under ASCII printable characters (character code 32-127)? There were issues encountered when legacy text editor was used. @joergklausen @semmerson @amilan17 and Franziska comments or suggestions?

I suppose it depends on whether the unit is produced by a human or by a computer:

• Human produced: Use US-ASCII (e.g., "kg.m/s2", "kg.m/s^2", "ug") (Tip of the hat to @joergklausen)
• Computer produced: Use UTF-8-encoded Unicode (e.g., "kg·m/s²", "µg")

So based on the discussion, middle dot is out. Could we use "." (period) to represent multiplication?

[gaochen-larc]

I came across this paper: UNITS FOR USE IN ATMOSPHERIC CHEMISTRY by Schwartz and Warneck (http://www.iupac.org/publications/pac/1995/pdf/6708x1377.pdf).

This paper highlighted the needs and issues to apply SI units in the field of atmospheric chemistry. It has some useful recommendations. I believe this paper is highly relevant to our discussion here.

[semmerson]

At https://github.com/wmo-im/wmds/issues/159#issuecomment-786306054, @gaochen-larc wrote

So based on the discussion, middle dot is out.

I didn't get that from the discussion. Computers can easily interpret and generate a middle dot, so I'd keep it for them.

Because 1) it can be difficult for humans to generate a middle dot; 2) humans can generate a period easily; and 3) computers can be told to interpret a period as a middle dot; I'd keep both.

Could we use "." (period) to represent multiplication?

Easily. I believe the NIST document recommends a period as a substitute for a middle dot.

[gaochen-larc]

I didn't get that from the discussion. Computers can easily interpret and generate a middle dot, so I'd keep it for them.

Sorry, I meant we use "." period for notation, i.e., kg.m/s2

[semmerson]

Sorry, I meant we use "." period for notation, i.e., kg.m/s2

I understand. My point is that there's really no reason to rule out use of the middle dot.

[gaochen-larc]

Sorry, I meant we use "." period for notation, i.e., kg.m/s2 I understand. My point is that there's really no reason to rule out use of the middle dot. …

My concern is very much on data reported in ASCII files. Space or middle dot is not a problem for HDF and netCDF files. However, the chemical measurements I deal with are mostly reported in ICARTT files... The csv or other ascii files are still popular in reporting air quality monitoring data.

[gaochen-larc]

The attached xlsx file is a version of the updated unit table. This spreadsheet contains the original labels and notations, as well as the updated ones, descriptions, and comments highlighting the changes. 15 original units were removed or replaced. 11 new units were added.

There are still two minor issues:

1) Acceleration due to gravity, g. Obviously “g” is often used for grams. However, this will not cause confusion if one reads both the label and notation. To avoid this potential conflict, we may choose to use “g0” for standard acceleration due to gravity.

2) Centibars per 12 hours. The original notation does not make sense to me. Hope this is not the unit the data providers have used for a long time. I wonder if we should remove this unit and add one for centibars per day, provided this will upset the data providers too much.

Looking for comment, suggestions, and/or corrections.

unit_table_revised_03092021.xlsx

[fstuerzl]

Branch: https://github.com/wmo-im/wmds/tree/issue159

Summary and Purpose: Improve the unit table: remove redundant or incorrect entries, add descriptions, correct labels and notations and add missing units

Stakeholder(s): @gaochen-larc

1. Notation, general

   Proposal: Change "_" to ".", where it symbolizes multiplication Reason: The use of the underscore is inconsistent in table 1-02 (e.g. notation N_units”). It is useful to select one symbol to indicate a multiplication and only that. For compatibility reasons we choose “.”.

2. Removal of units

   1. Proposal: Remove entry label	notation
      degree Celsius	Cel

      Reason: Entry is not needed, because the table also contains the unit “degC”. Semantically “degC” makes more sense.

   2. Proposal: Remove invalid entries label	notation
      logarithm per metre	log_(m-1)
      logarithm per square metre	log_(m-2)

      Reason: ill-defined, mathematically incorrect.

   3. Proposal: Remove the following entries and supersede them by existing concepts label	notation	superseded by
      milligram N per litre	mg_N_l-1	mg.l-1
      milligram S per litre	mg_S_l-1	mg.l-1
      microgram C per cubic metre	ug_C_m-3	ug.m-3
      microgram CI per cubic metre	ug_Cl_m-3	ug.m-3
      microgram N per cubic metre	ug_N_m-3	ug.m-3
      microgram S per cubic metre	ug_S_m-3	ug.m-3
      milligrams per cubic metre at 25 degrees	mg_m-3_25C	ug.m-3
      micrograms per cubic metre at 20 degrees	ug_m-3_20C	ug.m-3
      micrograms per cubic metre at 25 degrees	ug_m-3_25C	ug.m-3
      degrees true	deg_true	deg

      Reason: Concept too narrow, misleading

3. Change labels, notations and/or descriptions

   1. Proposal: Replace notations label	notation (old)	notation
      degrees Celsius per metre	C_m-1	degC.m-1
      degrees Celsius per 100 metres	C_(100m)-1	degC.hm-1

      Reason: Consistency, degree Celsius should always be represented as “degC” in the notations.

   2. Proposal: Change label label (old)	label	notation
      degrees Celsius	degrees Celsius (°C)	degC

      Reason: label contains symbol °C

   3. Proposal: Replace notation and add descriptions label	notation (old)	notation	description
      centibars per 12 hours	cb_-1	cb.(12h)-1	1 centibar is equivalent to SI unit 1 kPa
      centibars per second	cb_s-1	cb.s-1	1 centibar is equivalent to SI unit 1 kPa

      Reason: ill-defined

   4. Proposal: Replace notation label	notation (old)	notation
      nautical mile	nautical_mile	nmi

      Reason:

   5. Proposal: Replace notation, add description label	notation (old)	notation	description
      degree (angle)	degree_(angle)	deg	plane or phase angle

      Reason: unnecessary parts from notation removed, missing description added

   6. Proposal: Change Label and add descriptions label (old)	label	notation	description
      parts per billion by volume dry air	parts per billion by volume	ppbv	Ratio of the volume of a certain substance to the volume of medium/matrix in which it is contained.
      parts per million by volume dry air	parts per million by volume	ppmv	Ratio of the volume of a certain substance to the volume of medium/matrix in which it is contained.
      parts per trillion by volume dry air	parts per trillion by volume	pptv	Ratio of the volume of a certain substance to the volume of medium/matrix in which it is contained.

      Reason: old label incorrect, missing descriptions provided

   7. Proposal: Add description to existing units label	notation	description
      geopotential metre	gpm	The height of a given point in the atmosphere in units proportional to the potential energy of unit mass (geopotential) at this height relative to sea level. (AMS Glossary of Meteorology)
      Dobson Unit	DU	Equivalent to 2.687×1020 molecules m-2 at standard temperature and pressure (273 K, 1 atm pressure), https://glossary.ametsoc.org/wiki/Dobson_unit
      N units	N_units	Unit of atmospheric refractivity, the refractivity, N, is related to the refractive index, n, by the formula N = 106 (n – 1). N is therefore dimensionless but values computed by the formula are by convention described as being in "N units". (WMO Manual on Codes I.2)
      dekapascal	daPa	dekapascal or decapascal
      square degrees	deg2	square of phase or plane angle
      degrees per second	deg.s-1	plane or phase angle per second
      nanomoles per mole	nmol.mol-1	Equivalent to expressing mole fraction in ppb
      picomoles per mole	pmol.mol-1	Equivalent to expressing mole fraction in ppt
      (unknown)	unknown	The correct value is not known to, and not computable by, the sender of this data. However, a correct value probably exists.

      Reason: description added to enhance usability and clarity

4. Addition of new units

   1. Proposal: Add new units label	notation	description
      Per kilometre	km-1
      Per megametre	Mm-1
      (missing)	missing	The correct value is not readily available to the sender of this data. Furthermore, a correct value may not exist.
      (inapplicable)	inapplicable	There is no value (categorical data).

      Reason: make code list more complete to represent common measurements or cases

   2. Proposal: Add new units

      label	notation	description
      micrograms per cubic metre	ug.m-3
      milligrams per litre	mg.l-1
      milligrams per cubic centimetre	mg.cm-3
      nanograms per kilogram	ng.kg-1	SI unit for mass mixing ratio, equivalent to pptm or ppt
      micrograms per kilogram	ug.kg-1	SI unit for mass mixing ratio, equivalent to ppbm or ppb
      milligrams per kilogram	mg.kg-1	SI unit for mass mixing ratio, equivalent to ppmm or ppm
      cubic micrometres per cubic centimetre	um3.cm-3	SI unit for volumetric mixing ratio, equivalent to pptv
      cubic millimetres per cubic metre	mm3.m-3	SI unit for volumetric mixing ratio, equivalent to ppbv
      cubic centimetres per cubic metre	cm3.m-3	SI unit for volumetric mixing ratio, equivalent to ppmv
      per cubic centimetre	cm-3
      per cubic metre	m-3

      Reason: add new SI units to promote use of SI units

[gaochen-larc]

Propose to add two more units:

per cubic centimetre, cm-3 and per cubic metre, m-3.

These units are commonly used to report aerosol particle concentrations and cloud particle concentrations.

Sorry for not putting these with the other additions!

[gaochen-larc]

"Ratio of the amount (as mass, volume or number) of pure substance to the amount of medium/matrix in which it is contained." This description is more suitable for ppb, ppt, or ppm. "pptv", "ppbv", and "ppmv" are specific for volume mixing ratio.

[fstuerzl]

Branch created https://github.com/wmo-im/wmds/blob/issue159/tables_en/1-02.csv, superseded terms included here: https://github.com/wmo-im/wmds/blob/issue159/tables_en/superseded.txt. @amilan17, do you have any updates on the use of "." in a URL?

Discussion required for:

• Replacement of g by g0, correct approach?
• notation of "metres to the two thirds power per second" m(2.3-1).s-1 understandable? (in case the use of "." is allowed)

[fstuerzl]

Additional variables requested by @ejwelton in #269:

Proposal: Add new units

label	notation	description
micrometre	um
nanometre	nm

Reason: New entries are needed for the specification of wavelengths.

Branch: https://github.com/wmo-im/wmds/commit/95843c4d398faa403839834e210191d7ff086c80#diff-839fbcd828fed2d5a8724b523d5cc7faa3240cec8a18fb42badfe198e5388d39

[amilan17]

@gaochen-larc - I cannot find any external conversations about units. Please assume that you can move forward with current decisions.

[joergklausen]

@gaochen-larc Please confirm this can be considered 'validated'.

[gaochen-larc]

I confirm this version can be considered as "validated".

[joergklausen]

@gaochen-larc I am afraid, this issue is not ready still. I found 2 entries for nm (155, 175), one with british, the other with US spelling. Entry 175 should be dropped, entry 155 be renamed to british spelling (nanometre). After that, all entries are with britsh spelling. Also, many descriptions are still empty. @fstuerzl: Please provide descriptions where missing. If the name itself is sufficient as a description, please copy over.

[joergklausen]

@ferrighi Can you please assist in completing descriptions?

[fstuerzl]

@gaochen-larc I am afraid, this issue is not ready still. I found 2 entries for nm (155, 175), one with british, the other with US spelling. Entry 175 should be dropped, entry 155 be renamed to british spelling (nanometre). After that, all entries are with britsh spelling. Also, many descriptions are still empty. @fstuerzl: Please provide descriptions where missing. If the name itself is sufficient as a description, please copy over.

Second entry for nanometre is removed.

[fstuerzl]

@ferrighi , @gaochen-larc, here my proposal for some missing descriptions: 1-02_descriptions.xlsx

Updated branch: https://github.com/wmo-im/wmds/blob/issue159/tables_en/1-02.csv

[fstuerzl]

Table updated with @gaochen-larc and @joergklausen's additions: 1-02_descriptions_gc_v01_stf.xlsx [edit: corrections]

Descriptions for the following units are still missing: notation	name
mm6.m-3	millimetres to the sixth power per cubic metre
m2.s	square metres second
m2.s-2	square metres per square second
m2.rad-1.s	square metres per radian second
m2.Hz-1	square metres per hertz
m3.m-3	cubic metres per cubic metre
m(2.3-1).s-1	metres to the two thirds power per second
kg.m-2.s-1	kilograms per square metre per second
kg-2.s-1	per square kilogram per second
s.m-1	seconds per metre
K.m2.kg-1.s-1	kelvin square metres per kilogram per second
W.m-2.sr-1.cm	watts per square metre per steradian centimetre
W.m-2.sr-1.m	watts per square metre per steradian metre

Updated branch: Unit table https://github.com/wmo-im/wmds/blob/issue159/tables_en/1-02.csv Superseded file https://github.com/wmo-im/wmds/blob/issue159/tables_en/superseded.txt