Precipitable Water Vapor (PWV) Statistic (1948-2002)
As with many outdoor activities the conditions for astronomical observing are highly dependent on weather, and QuasarChile CANNOT GUARANTEE PERFECT conditions for all of its expeditions. Nevertheless, the Atacama desert area surrounding San Pedro is world-renowned for its outstanding clear, dry skies for major fractions of the year. An illustration of the quantity of precipitable water vapor (PWV) (correlated with cloud cover) in the Chajnantor high mountain region (~16,500 ft.) of Chile near San Pedro is shown in the accompanying diagram, which covers the period from 1948 to 2002.
|Credit: Bustos, R., ALMA Memo Series No. 433. NCEP/NCAR Reanalysis data is provided by the NOAA-CIRES Climate Diagnostics Center, Boulder, CO, USA.|
Optimal observing conditions in Chajnantor occur throughout the April “ November (inclusive) time period, although some small fluctuations (<3mm) are also seen during July-August corresponding to the chilean winter. The conditions are even slightly better at the lower elevations ( ~ 7500 ft.) closer to San Pedro where most of the QuasarChile observing sessions take place (QC-01 /QC-02).
Statistically, the chances of having one or more observing sessions prevented by clouds are very low during the April – May – June and Sept – October – November months and quite low during July – August. See the Satellite infrared image here (link).