Water Vapor ECV

Facilitating Access to Global Observing Systems Data and Information

GCOS Atmospheric Surface ECV*
Water Vapor

*over land, sea and ice

Definition: Water Vapor - (Also called aqueous vapor, moisture.) Water substance in vapor form; one of the most important of all constituents of the atmosphere. Its amount varies widely in space and time due to the great variety of both “sources” of evaporation and “sinks” of condensation that provide active motivation to the hydrologic cycle. Approximately half of all of the atmospheric water vapor is found below 2-km altitude, and only a minute fraction of the total occurs above the tropopause. Water vapor is important not only as the raw material for cloud and rain and snow, but also as a vehicle for the transport of energy (latent heat) and as a regulator of planetary temperatures through absorption and emission of radiation, most significantly in the thermal infrared (the greenhouse effect). The amount of water vapor present in a given air sample may be measured in a number of different ways, involving such concepts as absolute humidity, mixing ratio, dewpoint, relative humidity, specific humidity, and vapor pressure. (from the AMS Glossary of Meteorology)

Introduction: Water Vapor & Radiative Processes (article) (diagram) (from NOAA News)

Specific Issues with Water vapor ECV: Water vapour (humidity) measurements are obtained from the WWW/GOS surface synoptic observing networks over land. Over the oceans, the observations from VOS, including the higher-quality VOSClim, the Tropical Mooring Network, and the Reference Buoy Network provide a sparse but vital data resource. Homogeneous data are essential for assessment of the impact of changes of surface water vapour on natural and human systems. Surface water vapour data has begun to be studied in a global climate context and initial results are encouraging. Continued efforts to provide historical data to the GCOS analysis and archive centres are needed. (Source: WMO/IOC Implementation Plan for the Global Observing System for Climate in Support of the UNFCCC (2010 Update) GCOS-138/GOOS-184/GTOS-76/WMO-TD/No. 1523)

Data, Product, Metadata and Information Access
[ECV Matrix Main Page] [About the ECV Matrix] [Reference Documents] [Contact] [Updated June 6, 2010]

Non-satellite or in-situ

Satellite

IPCC High Resolution Observational Climatologies (IPCC) Climate Research Unit (CRU) high resolution climate data, version 2.1. Further details about this data can be found in a Tyndall Centre Technical report
A description of the methods used is given in: Mitchell TD and Jones PD (2005) An improved method of constructing a database of monthly climate observations and associated high-resolution grids. International Journal of Climatology 25, 693-712 (doi:10.1002/joc.1181). (data access) (metadata) (data documentation) (contact)

Real Time Integrated Atmospheric Water Vapor and TEC from GPS (UCAR) (Global Sites with Delay or PWV Estimates) (data access) (global sites map) (metadata) (contact)

Voluntary Observing Ships (VOS) Observations (NOAA/NDBC) Volunteer crew members on nearly 1,000 ships around the world observe the weather at their location, encode each observation in a standard format, and send the data over satellite or radio to the many national meteorological services that have responsibility for marine weather forecasts. The US VOS Project services about one quarter of the world's VOS fleet, providing ships' crews with weather observer training, handbooks and forms, observation encoding software, barometer calibration, the Mariners Weather Log, and weather observing tools. Located in the major ports around the country, Port Meteorological Officers are the VOS Project's field representatives and primary points of contact for ships. (variables) (data access) (metadata) (data documentation) (Program Information) (contact)

AIRS Weather and Climate from Space Products (NASA/JPL/AIRS) (global water vapor, total column - total precipitable water vapor (last 3 days combined) & today's near real-time satellite feed (AIRS is the Atmospheric Infrared Sounder instrument on the Earth Orbiting NASA Satellite Aqua) (data access) (data documentation) (contact)