Climate scientists from the University of Colorado and the University of New Mexico have deployed a Picarro water isotope analyser at a monitoring station near the top of Mauna Loa, Hawaii.
Sampling water vapour at this altitude (11,000 feet above sea level) is difficult because the water concentration can drop to a few hundred parts per million.
The Picarro G1102-i, which utilises wavelength scanned cavity ring down spectroscopy, samples the outside air at this location every ten seconds.
The calibration was checked with liquid water standards every few hours.
This confirmed the instrument had little drift over a six day period.
Dr David Noone of the University of Colorado said: 'While much attention has been focused on the role of CO2 in driving global warming, changes in the water cycle and the amount of water vapour in the air also have a significant impact.
'We need more water field data, both concentration and isotope ratios.
'Before the advent of portable isotope analysers, obtaining water isotope data from a remote site required capturing samples and chemically processing these before separately analysing them for deuterium and oxygen-18 in two separate mass spectrometers.
'Until now, this has precluded continuous real-time isotope monitoring.' The high frequency variability seen with the G1102-i reveals a richness of isotope data.
Dr Joe Galewsky, from the Department of Earth and Planetary Sciences at the University of New Mexico, said: 'Real time isotope tracking could be a new way of detecting fundamental changes in Earth's atmospheric circulation.' Mauna Loa was the obvious place to conduct the experiment because of its height and location in the subtropics, which is influenced by tropical and northerly atmospheric currents.
