FriOWL is a site selection tool for large or extremely large telescope projects. It consists of a graphical user interface
and a large global climatic and geophysical database, and is directly accessible on the world wide web. A new version
(version 3.1) of the software has recently been developed by scientists at the University of Bern (Switzerland) and
European Southern Observatory (Germany).
The main feature of the new FriOWL database is the inclusion of ERA40 re-analysis data, giving access to over 40 years
of long-term climate data. New software tools, programmed in the style of a Geographical Information System, include
the capability of resampling layers and time series extraction. A new global seismic hazard layer has been introduced, as
well as very high resolution (1km) topographic tiles. Reclassification and overlaying of layers is also possible.
Although FriOWL is primarily designed for site selection projects, it can equally be used in other climate studies. It is
especially important in the determination of the climatic stability of a potential site, and in the analysis of climatic
anomalies and trends. The long-term astroclimatological seeing and photometric statistics for the Paranal and La Silla
observatories can be used to validate FriOWL. A case study of ESO Paranal using FriOWL reveals that the deterioration
in seeing conditions since 1998 is co-incident with a strong increase in 1000 hPa geopotential height to the south-east of
the observatory; there may be a link with the Interdecadal Pacific Oscillation.
Selection of an ideal site for the new generation of Overwhelmingly Large (OWL) telescopes is dependent on many climatological and meteorological parameters. Among these are cloud cover, atmospheric humidity, aerosol content, air temperature, airflow direction, strength and turbulence. Even relatively minor changes in weather patterns can have a significant effect on seeing conditions.
A composite climatological database has been designed and built for the site selection task at the Department of Geosciences, University of Fribourg, Switzerland. The database is mainly composed of ECMWF and NCEP-NCAR reanalysis data at a global resolution of between 1° and 2.5° latitude / longitude. Using a Java based interface, codenamed "FriOWL", and programmed in the style of a Geographical Information System, all of this relevant information can be interrogated in order to find the best possible sites for the new telescope. Perhaps the most important variable in site selection is the interaction between air-flow and topography, as atmospheric turbulence greatly affects the image quality produced by the telescope.
Global climate is changing and it will continue to do throughout the 21st century. Therefore, it is important to ascertain the effect of global warming on potential sites. An ideal site in today’s climate may not prove ideal within 20 to 50 years. It is therefore planned to update the database with future climate data, using output from global climate models. High resolution modeling of the critical parameters at preferred sites under future climates is also planned.
The sitting of future giant telescopes poses a challenge to the astronomical community. Some of the top level existing observatories are already too crowded; others do not meet the specifications on particular environmental parameters such as wind or seismicity.
On the other hand it has been proven that continental sites can be as good as islands, opening the way for many candidates not yet properly studied. To operate a pre-selection, it is proposed to implement a dedicated geographical information system (GIS) handling the wealth of available remote sensing data worldwide. When focusing onto particular summits, the GIS should then be complemented by mesoscale modeling of the local flow.
Some examples are given to support this strategy.