G4.07     Error correlations for reference sonde (GRUAN) measurements.

Gap detailed description

Many applications of reference radiosonde measurements require an estimate of error correlations.  For example, as part of the comparison of reference sonde measurements and NWP fields, in terms of TOA brightness temperatures, it is necessary to have realistic estimates of the error correlation structure (i.e. between vertical levels) in the sonde measurements. Such estimates are a subject of current research, and as such, constitute a current gap. 

Activities within GAIA-CLIM related to this gap

Some estimate of the error correlations are required to carry out significance testing for the GRUAN processor as part of WP4. As a first approximation, error covariance matrices will be developed, in consultation with experts from the GRUAN community, to include an exponential dependence between vertical levels, based on physical constraints.  Longer term, and beyond the immediate scope of work within the GAIA-CLIM project, correlation estimates could be obtained from measurements. Such uncertainties are envisaged to be reported in the v3 GRUAN product (correlated, partially correlated and random terms) being developed by the GRUAN Lead Centre, which it is hoped will be released within the GAIA-CLIM project lifetime. A visit to the GRUAN Lead Centre is foreseen in autumn 2016 to discuss the issue and explore potential for collaboration on the matter.

Gap remedy

Remedy #1

Specific remedy proposed

Development of parametrised estimates of the vertical error correlation structure. Simple parametrised versions of the vertical error covariances will be developed and tested as part of the significance testing in the GRUAN processor.

Measurable outcome of success

·         Parametrised error covariances, developed and tested in consultation with experts from the GRUAN community

Achievable outcomes

Technological / organizational viability: High

Indicative cost estimate:  low (<1 million Euros)

Relevance

The solution proposed here is fully aligned with the requirement (to establish traceable uncertainties for NWP fields and radiances calculated from them).

Timebound

The remedy proposed here is a key focus, and deliverable, of GAIA-CLIM WP4, due for delivery (D4.4) in Month 24.

Gap risks to non-resolution