ESO Ambient Conditions Database

The ESO Ambient Conditions Database includes measurements of the environmental parameter at both ESO observatories, La Silla and Paranal. While the La Silla data is being updated in real-time, the data from Paranal is, for the time being, being transferred only at the end of the local Paranal night (typically at 13:00 hrs MET).

Please see the ESO Astroclimatology Overview web pages for more information.

Environmental Conditions on La Silla

Location: Cerro La Silla 2400m; 70 42' W; 29 16' S

Distance from coast: 40km

Description: The Vaisala meteorological station was installed at La Silla in February 1985, it includes, on a 30m high mast, a number of sensors. The on-line database started storing data on January 1st, 1994. The following, selected measurements are displayed:

30m level:   Wind speed ([m/s]) and direction ([deg]), 
2.5m level:  Temperature ([C]), Humidity([%]), Barometric pressure ([hPa])

The ESO seeing monitor (DIMM2) was installed in March 1991, on a 5m high tower, close to the Schmidt telescope as part of the permanent Astronomical Weather Station (AWS). Routine operation started in September 1991 and full automation was reached in December 1993. Seeing measurements were initially conducted from Cerro Vizcachas, 7km to the East of La Silla, and once candidate site for the VLT, from Oct. 1988 to Feb. 1991. As part of the same ridge, Vizcachas and La Silla present similar seeing conditions.

The meteorological stations compute and store average, root mean square and extrema of each parameter during a preset averaging period (20 mn). The sampling intervals are 2 seconds for digital sensors (wind speed and direction) and one minute for analog sensors (T, Rh, P). One minute averages are ingested into the database.

The seeing is defined as the Full Width Half Maximum of a stellar image observed with a perfect large telescope, at 500nm wavelength and at zenith. It is measured over periods of a few minutes all night long. Maximum wind speed for operation is about 18m/s and sky must be clear in the zenith area. The resolution of the various sensors is the following:

Wind direction: 5.63 deg (threshold: 0.3m/s)
Wind speed: accuracy ~2% over 10m/s (threshold: 0.4m/s)
Temperature: accuracy ~0.1 deg
Humidity: linearity about 1%
Seeing: better than 10% above 0.25 arcsec

Environmental Conditions on Paranal

Location: Cerro Paranal, 2635m (after levelling) 70 24' 5" W; 24 37' 24" S

Distance from coast: 12km

Description: The Vaisala meteorological station was installed in Paranal in October 1984 and upgraded in June 1998. It includes, on a 30m high mast, a number of sensors. The following, selected measurements are displayed:

30m level:   Wind speed ([m/s]) and direction ([deg])
             Temperature ([C]) and Humidity ([%])
2m level:    Barometric pressure ([hPa])

The ESO seeing monitor (DIMM1) was installed in April 1987, at the northern edge of the summit, and replaced by a more modern copy (DIMM3) in September 1990. Measurements were suspended in July 1991 for the 14 months duration of the levelling work. Seeing has been then monitored during the construction period of the VLT observatory with few interruptions. Finally, DIMM3, upgraded to VLT standards and fully automatized was re-commissioned in August 98 as part of the VLT Astronomical Site Monitor (ASM). The database includes only data starting with August 17th, 1998. All seeing values above 2.5 arcsec have been truncated.

The meteorological stations compute and store average, root mean square and extrema of each parameter during a preset averaging period (20 minutes). The sampling intervals are 2 seconds for digital sensors (wind speed and direction) and one minute for analog sensors (T, Rh, P). One minute averages are ingested into the database.

The seeing is defined as the Full Width Half Maximum of a stellar image observed with a perfect large telescope, at 500nm wavelength and at zenith. It is measured over periods of about a minute all night long. Maximum wind speed for operation is about 18m/s and sky must be clear in the zenith area.

The resolution of the various sensors is the following:

Wind direction: 5.63 deg (threshold: 0.3m/s)
Wind speed: accuracy ~2% over 10m/s (threshold: 0.4m/s)
Temperature: accuracy ~0.1 deg
Humidity: linearity about 1%
Seeing: better than 10% above 0.25 arcsec

Acknowledgements

The graphical display was inspired by a layout made by Olivier Hainaut for the La Silla real-time MeteoMonitor tool.

The circumstances are calculated by the Skycalc program developed by John Thorstensen.

Many colleagues made comments and suggestions to earlier versions of this tool -- thanks.

Send comments to the ESO Operations Helpdesk
Last modified: June 25, 2021