The Solar Terrestrial Centre of Excellence (STCE) re-groups the existing expertise, collaboration and activities concerning the physics all the way from the Sun to Earth in three federal scientific institutes: the Royal Observatory of Belgium (ROB), the Royal Belgium Institute for Space Aeronomy (BIRA), and the Royal Meteorological Institute of Belgium (RMI).

The Solar-Terrestrial Centre of Excellence is a scientific project which aims at the creation of an international expert centre and the valorization of Solar and Solar-Terrestrial research and services.

The concept of the STCE can be summarized as:

• an integration of the existing Belgian research groups in one overarching structure: the STCE, not a new institute.
• stabilization and consolidation of the existing knowhow scattered over different existing institutes
• explicit support for visiting fellows & communication
• long term funding.

The solid base of the STCE is our existing experience in fundamental solar and earth atmospheric physics research, our involvement in earth-based and space missions and a fully operational eligible space weather application centre. Our skills are based on know-how, man power, infrastructure and a reliable network in the field of 'Sun-Space-Earth'.

Our team is involved in the following two work packages.

This work package (WP) combines the BIRA and RMI activities on monitoring the solar UV radiation from the ground, as well as the monitoring of the ozone and aerosol concentrations in the terrestrial atmosphere, which have a direct impact on the amount of solar UV radiation reaching the surface of the Earth. All those measurements are done with ground-based techniques, and a lot of attention is paid to the retrieval, calibration, validation, and intercomparison of the instruments and the datasets. When long time series are available, the data are homogenized and exploited for trend studies.

The work package consists of four sub-WPs:

1. UV-radiation: The RMI operates Brewer spectrophotometers at Uccle and Princess Elisabeth station (Antarctica) that measure the UV index under all sky conditions. Clear-sky UV-forecasts for Uccle are produced operationally. The BIRA measures the global (direct + diffuse) solar irradiance (GSI) from surface sites distributed over the Belgian territory. Spectral UV-VIS GSI measurements are provided by a double monochromator spectrophotometer at Uccle.
2. Ozone: Total ozone data is available at Uccle from Dobson/Brewer instruments since 1971 and at Princess Elisabeth station Antarctica since 2011, while the ozonesondes measure the vertical profiles of ozone at Uccle since 1969. A Pandora instrument at Uccle also provided the total ozone amount and might give information about the tropospheric ozone distribution. Ozone partial columns are obtained from FTIR instruments operated by BIRA at La Réunion and Porto Velho, in the framework of NDACC.
3. Aerosols: A network of 4 ceilometers providing the aerosol backscatter profiles is available at the RMI. At Uccle, continuous measurements of aerosol optical properties with an aethalometer and nephelometer are performed. Within the framework of the European research infrastructure (RI) ACTRIS, additional instruments will be acquired and exploited to become a national facility for the aerosol in situ component within ACTRIS RI (instruments for aerosol total number and size distribution from 10 nm to 20 µm). At the Princess Elisabeth station in Antarctica, a whole range of instruments are available, measuring aerosol properties like total number, number size distribution, presence of particle formation events, spectral dependency of scattering, absorption and single scattering albedo.
4. VIS-NIR radiation: BIRA performs measurements of solar irradiance in the VIS (visual) and NIR (near infra-red) spectral range. These global (direct + diffuse) ground-based acquisitions are obtained from total solar pyranometers (TSP), and photosynthetically active radiation (PAR) from filter radiometer. BIRA performs also direct Sun and spectral measurement in the VIS and the NIR using solar tracker and double monochromators, namely for the top of atmosphere retrieval of solar spectral irradiance or aerosols optical depth measurements. At its automatic weather stations, RMI operates global NIR observation (downwelling and upwelling). In the VIS range direct, global and reflected radiation is measured at a number of stations. Additionnaly global, diffuse and direct VIS radiation is measured at Uccle.

Ground-based Global Navigation Satellite Systems (GNSS) are widely used for precise positioning. During the GNSS analysis, the delay induced by the neutral atmosphere on the GNSS signal propagation can be estimated. Using additional meteorological observations (e.g. surface pressure and temperature) and/or model data, this delay, named tropospheric delay, can then be converted into the amount of atmospheric water vapour (Integrated Water Vapour, IWV) above the observing GNSS site. This work package combines the activities of ROB, BIRA, and RMI activities related the monitoring, studying, and monitoring the Earth's neutral atmosphere and its water vapour.

It consists of two sub-WPs:

1. Observing the neutral atmosphere with GNSS: monitoring and modelling the tropospheric delay and the associated atmospheric water vapour content using observations from continuously operating GNSS stations.
2. Comparison and exploitation of multi-technique atmospheric water vapour observations: Inter-comparison, validation, and exploitation of tropospheric delay and water vapour observation techniques and models (e.g. for meteorological and climate studies).

The project has been approved by a decision of the Federal Government in April 2006 and its funding is recurrent.

Roeland Van Malderen, Quentin Laffineur, Natacha Pezzetti, Alexander Mangold
Royal Meteorological Institute
Ringlaan 3,
B-1180 Brussels, Belgium

Contact: Roeland Van Malderen (ozone, water vapour), Natacha Pezzetti (UV, aerosols), Alexander Mangold (aerosols), or Quentin Laffineur (LIDAR-ceilometer)