add water vapour mixing ratio to atmospheric variables (1-01-01) #550
Description
Initial request
OSCAR/Requirements updated Water Vapour mixing ratio in summer of 2024. This issue is an attempt to align with WIGOS metadata codes.
Add water vapour mixing ratio to atmospheric variables (1-01-01)
The term 'water vapour mixing ratio' refers to a mole fraction in OSCAR/Requirements.
| Name | Description |
|---|---|
| Water Vapour Mixing Ratio | "3D field of water vapour mixing ratios in the UTLS. Mixing ratio is the mole fraction of a substance in dry air (UTLS, MUS)" |
The following are relevant in the context of this issue (superseded codes are not mentioned here). Definitions were added in italic where none exists as part of proposed improvements. Further, to align with consistent metrological nomenclature, 'mixing ratio' will be changed to 'fraction'. To help users more familiar with older terminology, additional notes will be added to the descriptions. The existing definition in OSCAR/Requirements is discouraged for the following reasons:
- Reference is made to the vertical layer, UTLS. This is not useful, as the term can be applied to all vertical layers in principle.
- The term 'mole fraction' is strongly discouraged by SI, because there is no concept of the fraction of a unit. Instead, 'amount fraction' should be used.
| Notation | Name | Description | Status |
|---|---|---|---|
| 252 | Integrated water vapour | Total amount of water vapour in a vertical column of air per unit area. Integrated water vapour (IWV) is also known as Precipitable Water Vapour (PWV). | stable |
| 255 | Water vapour pressure | Partial pressure of water in the atmosphere | stable |
| 12249 | Relative humidity (with respect to water) | The ratio of the amount fraction of the water vapour in the air to the corresponding amount fraction if the air were saturated with respect to water at a particular pressure and temperature. Relative humidity is typically reported in percent (%). [Based on definition of R1490 in International Vocabulary of Meteorology (WMO-No. 182). 1992.] | stable |
| 12250 | Specific humidity | The ratio of the mass of water vapour in the air to the mass of a moist air parcel, where the mass of the moist air parcel is the sum of the mass of water vapour and the dry air. Synonym: Moisture content. [Based on definition of M1750 in International Vocabulary of Meteorology (WMO-No. 182). 1992.] | stable |
| 253 | Mass mixing ratio | stable |
The term 253 (Mass mixing ratio) is not defined, but it appears in OSCAR/Surface under >Atmosphere>Humidity. It has been used by (only) 3 stations so far. It is the closest to 'water vapour mixing ratio' of the available terms, however, the latter refers to an amount fraction. The term 253 is a misnomer for 'mixing ratio' used in BUFR and GRIB. In GRIB, it is described as 'mass fraction in air'. Considering its current path, and the ambiguity of the label, and the lack of a description, the term 253 should be better defined.
Amendment details
In response to the original request, the following will be added as a new term:
| Notation | Label | Description |
|---|---|---|
| 12330 | Water vapour amount fraction | The ratio of the amount of water vapour and the amount of a dry air. Older literature may have used the term 'water vapour mixing ratio'. |
Update descriptions:
| Notation | Name | Description | Status |
|---|---|---|---|
| 252 | Integrated water vapour | Total amount of water vapour in a vertical column of air per unit area. Integrated water vapour (IWV) is also known as Precipitable Water Vapour (PWV). | stable |
| 255 | Water vapour pressure | Partial pressure of water in the atmosphere | stable |
Correct label and add description:
| Notation | Name | Description | Status |
|---|---|---|---|
| 253 | Mixing ratio | In meteorology, the ratio between the mass of water vapour and the mass of dry air | stable |
Summary
- Add descriptions to notations 252, 255
- Add new term 'water vapour amount fraction'
- Correct label for notation 253 and add a (slightly) amended definition
Requestor(s)
GCOS, OSCAR/Requirements, @kpremec
Stakeholder(s)
Enter list of stakeholder(s).
Applications or Systems
- OSCAR/Surface
- OSCAR/requirements
- Radar/DB
- OceanOPS
- WHOS
- WDQMS
- GBON Compliance Monitor
- Other
Expected impact of change
None
Collaborators
No response
References
https://space.oscar.wmo.int/variables/view/water_vapour_mixing_ratio
Comments
This may be related to
Water vapour (no definition) which doesn't have a definition.
Publication(s)
Example: Manual on Codes (WMO-No. 306), Volume I.3, WMO Codes Registry, Code table 1-01-01
Validation
No response