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GEWEX/ESA DUE GlobVapour workshop on long term water vapour data sets and their quality assessment

The GEWEX/ESA DUE GlobVapour workshop will take place on the 8-10 March 2011, in ESA/ESRIN, Via Galieo Galilei, Frascati, Italy

 

Water vapour is a key climate variable. In the lower troposphere, condensation of water vapour into precipitation provides latent heating which dominates the structure of tropospheric diabatic heating. Water vapour is also the most important gaseous source of infrared opacity in the atmosphere, accounting for about 60% of the natural greenhouse effect for clear skies, and provides the largest positive feedback in model projections of climate change.

 

The network of radiosonde measurements provides the longest record of water vapour measurements in the atmosphere, dating back to the mid- 1940s. However, early radiosonde sensors suffered from significant measurement biases, particularly for the upper troposphere, and changes in instrumentation with time often lead to artificial discontinuities in the data record (e.g., see Elliott et al., 2002). Consequently, most of the analysis of radiosonde humidity has focused on trends for altitudes below 500 hPa and is restricted to those stations and periods for which stable instrumentation and reliable moisture soundings are available.

Satellite observations relevant for water vapour climatology were mostly build for weather forecasting purposes and their utilisation for building climate data records is rather complex and involves the creation of high quality radiance records, so called Fundamental Climate Data Records (FCDR) and subsequently so called ECV products that are water vapour parameters. Currently, water vapour climatology is obtained from satellite observations either using retrieval schemes or through assimilation into a Numerical Weather Prediction Model forming model-based reanalysis products.

GEWEX and in particular its Radiation Panel (www.gewex.org/projects-GRP.htm) is generating climate data records concerning the Earth Energy and Water Cycle by means of dedicated reprocessing activities. Currently, a missing element is a water vapour product that can be used in a consistent way with the other products. This workshop shall help to answer questions on how such a water vapour climatology should be designed to be most useful in the context of GEWEX.

Global organisations as CEOS, CGMS and WMO help to organise the creation of FCDRs and ECV products leading to the fulfilment of GCOS requirements. As a consequence space agencies have started several programs and projects to create both types of data records.

Motivation

There is a clear need of a global time series of temperature and humidity profiles for studies of the 3D T, q distribution, e.g., for water vapour transport, and the use within the derivation of cloud property data sets and components of the radiation budget climatology. Such a data set should cover a period of approximately 30 years starting in the late 1970ties. Taking the ISCCP data set as an example the use of T-, q-profile data from satellite data real time processing systems can easily corrupt the quality of a data set for long term climate variability analysis. Currently, no single retrieved data set or NWP model-based reanalysis is capable of completely fulfilling the needs in terms of temporal coverage, homogeneity and accuracy. There are manifold reasons for this:

 

Click here to see the workshop presentations

Working Group Summary Report