Measurements of water vapor isotopic composition on the Chajnantor Plateau, Chilean Andes: Implications for regional water vapor transport

The 5 km high Chajnantor Plateau is one of the driest sites on Earth and is situated in the Chilean Andes next to the hyper-arid Atacama Desert. Owing to its extreme aridity, the Chajnantor Plateau is a prime site for submillimeter astronomy. Since 2012, we have made continuous measurements of surface atmospheric water vapor isotopic composition using cavity ringdown spectroscopy and ozone concentration at the Atacama Large Millimeter Array (ALMA) Observatory. During southern hemisphere (SH) winter nighttime, the specific humidity and isotopic composition are consistent with aircraft measurements made in the upper tropical troposphere and are consistent with models of large scale mixing as a control on subtropical humidity. During the daytime hours, heating of the Andes drives anomalous convergence that drives boundary layer water vapor from coastal regions into the high Andes and is associated with increasing specific humidity and increasing water vapor delta-values that can be used to constrain the source of the boundary layer water vapor. During SH summer, the anomalous circulation associated with the South American monsoon transports moist but isotopically depleted air over the Andean range crest to the site and is likely associated with convection in the monsoon region. Ozone measurements allow us to document the intrusion of stratospheric air to the site and the use of water vapor isotopic composition data provide new constraints on upper tropospheric mixing processes during intrusion events.