Abstract
The Global Energy and Water cycle Exchanges (GEWEX) Data and Assessments Panel (GDAP) initiated the GEWEX Water Vapor Assessment (G-VAP), which has the main objectives to quantify the current state of art in water vapour products being constructed for climate applications and to support the selection process of suitable water vapour products by GDAP for its production of globally consistent water and energy cycle products. During the construction of the G-VAP data archive, freely available and mature satellite and reanalysis data records with a minimum temporal coverage of 10 years were considered. The archive contains total column water vapour (TCWV) as well as specific humidity and temperature at four pressure levels (1000, 700, 500, 300 hPa) from 22 different data records. All data records were remapped to a regular longitude/latitude grid of 2°x2°. The archive consists of four different folders: 22 TCWV data records covering the period 2003-2008, 11 TCWV data records covering the period 1988-2008, as well as seven specific humidity and seven temperature data records covering the period 1988-2009. The G-VAP data archive is referenced under the following digital object identifier (doi): http://dx.doi.org/10.5676/EUM SAF CM/GVAP/V001. Within G-VAP, the characterisation of water vapour products is, among other ways, achieved through intercomparisons of the considered data records, as a whole and grouped into three classes of predominant retrieval condition: clear-sky, cloudy-sky and all-sky. Associated results are shown using the 22 TCWV data records. The standard deviations among the 22 TCWV data records have been analysed and exhibit distinct maxima over central Africa and the tropical warm pool (in absolute terms) as well as over the poles and mountain regions (in relative terms). The variability in TCWV within each class can be large and prohibits conclusions on systematic differences in TCWV between the classes.
Highlights
Water vapour is the most important natural greenhouse gas and the dominant source of infrared opacity in the clearsky atmosphere (Trenberth et al, 2007)
Reanalyses are performed with fixed model and data assimilation systems; data input to the reanalysis system changes over the years
It is planned to keep the overall format and technical specifications of the GEWEX Water Vapor Assessment (G-VAP) data archive, with one important change: In order to keep the gap between last year covered by elements of the archive and release date at minimum and in order to enhance applicability, the data records will not be provided on common period but on individual temporal coverage
Summary
Water vapour is the most important natural greenhouse gas and the dominant source of infrared opacity in the clearsky atmosphere (Trenberth et al, 2007). A large variety of satellite-based water vapour data records are available Information on such records is provided by the ECV (see Table A1 in the Appendix for a list of abbreviations) inventory Assessments in general provide an overview of available data records and enable users to judge the quality and fitness for purpose of CDRs by informing them about the strengths and weaknesses of existing and readily available records. With this in mind, GDAP initiated G-VAP whose major purpose is to quantify the current state of the art in water vapour products being constructed for climate applications and to support the selection process by GDAP.
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