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Astroclimatology of Paranal

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  • Paranal Atmospheric Transmission
  • The data files for Paranal atmospheric absorption and extinction of the E-ELT Background Model

  • Precipitable Water Vapour at Paranal LaSilla and APEX during the E-ELT site survey: radiosoundings
  • Campaign Report by University Valparaiso

  • Precipitable Water Vapour at Paranal during the VLT site survey: ground based measurements
  • A median value of 2.3 mm H2O was measured at Paranal during the VLT Site Survey, 1983-1989 (VLT Report 62, 1990), using the KPNO Infrared Sky Radiance Monitor (Morse, D and Gillett,F. 1982: AURA Eng. Report 73)
    Overall and Seasonal distribution at Paranal
    (VLT Site Survey, Jul92-Dec94)


  • PWV at Paranal during VLT operation: Statistics from Satellite Imagery

  • Clear time [Aug 1999-Nov 2005] PWV at Paranal and La Silla from 3-hourly satellite images
    (data file, format: YYYY MM DD HH PWV)

    Clear time [Aug 1999-Nov 2005] PWV at Paranal and La Silla from 3-hourly satellite images
    (data file, format: MM PWVPAR PWVSIL)


    Monthly Average Precipitable Water Vapour at Paranal (mm H2O, clear time only)
    3-hourly GOES8 Satellite Images 199920002001 2002200320042005
    January 8.1 3.2 3.5 3.1 2.7 4.0
    February 4.3 4.6 6.2 5.5 3.2 3.1
    March 4.8 7.3 6.6 3.9 3.1 3.1
    April 4.5 4.9 4.6 2.2 3.0 2.4
    May 3.1 3.3 4.2 2.5 1.8 2.2
    June 2.8 2.5 2.4 2.0 1.7 2.4
    July 1.7 2.4 3.0 2.0 2.3 1.8
    August 2.0 1.6 2.2 2.6 1.4 1.4 2.1
    September2.2 1.6 2.7 2.2 1.8 2.0 1.8
    October 2.5 1.8 2.6 2.7 1.9 1.8 1.3
    November 2.5 1.6 2.9 2.9 2.3 2.4 1.9
    December 2.6 2.4 3.5 3.1 2.3 3.2
    Year (ave/median) 3.2/2.4 3.5/3.0 3.5/3.0 2.7/2.3 2.4/1.9

  • Calculated Refractivity of Water Vapor and Moist Air in the Atmospheric Window at 10 micron
  • R. J. Mathar; Appl. Opt. 43, 4, 928-932, Feb. 2004 (
    other publications):

    Absolute Humidity at Paranal


    The densities are calculated by taking the relative humidity and the temperature at the same time from the weather pole, then using standard water saturation pressure curves.

  • Comparison to Satellite PWV
  • PRIMA Atmospheric Dispersion Correction, ESO Technical Archive Doc:UL-TRE-AOS-15753-0010_V1

  • Nighttime Satellite PWV
  • From GOES image processing by A. Erasmus (
    Text archive).

  • IR Atmospheric Transmission ISAAC User Manual (pdf).

    Spectra of the atmospheric transmission above Mauna Kea (Lord, 1992) in the near-IR (0.9-5.5 mu) are available on the Gemini Observatory Observing Conditions page. They show that an increase of 1 to 3 mm H2O is similar to increasing the observation airmass from 1 to 2:

    - AM=1.0 and 2.0 at 1.0mm precipitable water vapour: 0.9 - 1.4, 1.4 - 1.9, 1.9 - 2.3, 2.3 - 2.7, 2.7 - 3.3, 3.3 - 4.3, 4.3 - 5.0 and 5.0 - 5.6Ám
    -1.0 and 3.0mm H2O at AM=1.0: 0.9 - 1.4, 1.4 -1.9, 1.9 - 2.3, 2.3 - 2.7, 2.7 - 3.3, 3.3 - 4.3, 4.3 - 5.0 and 5.0 - 5.6Ám


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