GRUAN Processor

The characterisation of uncertainties in NWP models is a major challenge that has been addressed as part of GAIA-CLIM WP4. In this regard, radiosonde observations from the GCOS Reference Upper-Air Network (GRUAN) have been used at the Met Office and ECMWF to assess uncertainties associated with model data.

A software tool has been developed based on a core radiative transfer modelling capability built around two existing open-source software packages (EUMETSAT’s NWP-SAF RTTOV fast radiative transfer model and Radiance Simulator). This software, referred to as the ‘GRUAN Processor’, enables the comparison of co-located geophysical fields and simulated brightness temperatures between radiosondes and model fields. A key innovation of the GRUAN Processor is the conversion of geophysical profiles into Top of the Atmosphere (TOA) radiance equivalents via RTTOV that enables comparisons in level-1 space that include an expression of the uncertainty in the reference in-situ profile data.

The GRUAN Processor has been developed as a stand-alone module, decoupled from the NWP systems at the Met Office and ECMWF, which will enable the capability to be developed and maintained on longer term as part of the core capability of the Virtual Observatory.

Post-processed outputs of the GRUAN Processor (monthly averaged profiles per GRUAN station) are publicly available on a demonstrator web-page.