Upper-air Water Vapour
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Water vapour is the predominant gaseous source of infrared opacity in the atmosphere, accounting for about 60% of the natural greenhouse effect for clear skies. Water vapour condenses to produce clouds, changing radiative properties and releasing latent heat that drives or modifies atmospheric circulation systems. Water vapour in the lower stratosphere, though present only in small amounts, is radiatively significant. Consequently, there is potential for additional climate change feedbacks through perturbations of the processes that control the amount of water vapour in the stratosphere, such as the Brewer-Dobson circulation that strongly influences tropical tropopause temperatures and the amount of CH4 oxidized in the stratosphere. |
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| Domain: | Atmosphere | |
| Subdomain: | Upper Atmosphere | |
| Scientific Area: | Hydrosphere | |
| ECV Steward: | ||
| Products: | Water Vapour Mixing Ratio in the Upper Troposphere and Lower Stratosphere, Water Vapour Mixing Ratio in the Middle and Upper Stratosphere, Water Vapour Mixing Ratio in the Mesosphere, Relative Humidity in the Boundary Layer, Relative Humidity in the Free Troposphere, Relative Humidity in the Upper Troposphere and Lower Stratosphere, Specific Humidity in the Boundary Layer, Specific Humidity in the Free Troposphere, Integrated Water Vapour | |
ECV Products and Requirements
These products and requirements reflect the Implementation Plan 2022 (GCOS-244).
The requirements are found in the complete 2022 ECVs Requirements document as well: ECV Upper-air Water Vapour.
| Products | Water Vapour Mixing Ratio in the | ||||
| Upper Troposphere and Lower Stratosphere | Middle and Upper Stratosphere | Mesosphere | |||
| (*) | Unit | Values | Values | Values | |
| Horizontal Resolution | G | km | 15 | 50 | 50 |
| B | 100 | 500 | 500 | ||
| T | 500 | 1500 | 1500 | ||
| Vertical Resolution | G | km | 0.01 | 0.5 | 0.5 |
| B | 0.1 | 1 | 1 | ||
| T | 0.25 | 3 | 3 | ||
| Temporal Resolution | G | h | 3 | 3 | 3 |
| B | 6 | 6 | 6 | ||
| T | 24 | 72 | 72 | ||
| Timeliness | G | h | 1 | 1 | 1 |
| B | 120 | 168 | 168 | ||
| T | 720 | 720 | 720 | ||
| Required Measurement Uncertainty (2-sigma) | G | ppmv | 0.1 | 0.1 | 0.1 |
| B | 0.25 | 0.25 | 0.25 | ||
| T | 0.5 | 0.5 | 0.5 | ||
| Stability | G | ppmv/decade | <0.1 | <0.2 | <0.2 |
| B | 0.1 | 0.2 | 0.2 | ||
| T | 0.25 | 0.5 | 0.5 | ||
| Products | Relative Humiditiy in the | ||||||
| Boundary Layer | Free Troposphere | Upper Troposphere and Lower Stratosphere | |||||
| (*) | Unit | Values | Unit | Values | Values | ||
| Horizontal Resolution | G | km | 15 | km | 15 | 15 | |
| B | 100 | 100 | 100 | ||||
| T | 500 | 1000 | 500 | ||||
| Vertical Resolution | G | m | 1 | km | 0.01 | 0.01 | |
| B | 10 | 0.1 | 0.1 | ||||
| T | 100 | 1 | 0.25 | ||||
| Temporal Resolution | G | h | <1 | h | <1 | 3 | |
| B | 6 | 6 | 6 | ||||
| T | 12 | 12 | 24 | ||||
| Timeliness | G | h | 1 | h | 1 | 1 | |
| B | 120 | 120 | 120 | ||||
| T | 720 | 720 | 720 | ||||
| Required Measurement Uncertainty (2-sigma) | G | %RH | 0.1 | %RH | 0.1 | 0.5 | |
| B | 0.5 | 0.5 | 1 | ||||
| T | 1 | 1 | 2 | ||||
| Stability | G | %RH/ decade | 0.1 | %RH/ decade | 0.1 | <0.5 | |
| B | 0.5 | 0.5 | 0.5 | ||||
| T | 1 | 1 | 2 | ||||
| Products | Specific Humidity in the | Integrated Water Vapour | |||||||
| Boundary Layer | Free Troposphere | ||||||||
| (*) | Unit | Values | Unit | Values | Unit | Values | |||
| Horizontal Resolution | G | km | 15 | km | 15 | km | 25 | ||
| B | 100 | 100 | 250 | ||||||
| T | 500 | 1000 | 1000 | ||||||
| Vertical Resolution | G | m | 1 | km | 0.01 | - | |||
| B | 10 | 0.1 | - | ||||||
| T | 100 | 1 | - | ||||||
| Temporal Resolution | G | h | <1 | h | <1 | h | 0.2 | ||
| B | 1 | 1 | 1 | ||||||
| T | 3 | 3 | 24 | ||||||
| Timeliness | G | h | 1 | h | 1 | h | 24 | ||
| B | 120 | 120 | 120 | ||||||
| T | 720 | 720 | 720 | ||||||
| Required Measurement Uncertainty (2-sigma) | G | g Kg-1 | 0.1 | g Kg-1 | 0.1 | Kg m-3 | 0.1 | ||
| B | 0.5 | 0.5 | 0.5 | ||||||
| T | 1 | 1 | 1 | ||||||
| Stability | G | g Kg-1/ decade | 0.01 | g Kg-1/ decade | 0.01 | Kg m-3/ decade | 0.1 | ||
| B | 0.05 | 0.05 | 0.2 | ||||||
| T | 0.1 | 0.1 | 0.5 | ||||||
(*) Goal (G): an ideal requirement above which further improvements are not necessary. Breakthrough (B): an intermediate level between threshold and goal which, if achieved, would result in a significant improvement for the targeted application. The breakthrough value may also indicate the level at which specified uses within climate monitoring become possible. It may be appropriate to have different breakthrough values for different uses. Threshold (T): the minimum requirement to be met to ensure that data are useful
Data Sources
This list provides sources for openly accessible data sets with worldwide coverage for which metadata is available. It is curated by the respective GCOS ECV Steward(s). The list does not claim to be complete. Anyone with a suitable dataset who wishes it to be added to this list should contact the GCOS Secretariat.
In Situ:
- Network for the Detection of Atmospheric Composition Change (NDACC)
- Integrated Global Radiosonde Archive (IGRA)
- GCOS Reference Upper-Air Network (GRUAN)
Reanalysis:
- REANALYSES.ORG (Inventory for Reanalysis)
Satellite:
- Satellite ECV Inventory by the CEOS/CGMS Working Group on Climate (WGClimate)
- Aura Microwave Limb Sounder (MLS)
