Home » Latest News » A new look at the atmospheric water cycle: Isotope measurements from space using SCIAMACHY

A new look at the atmospheric water cycle: Isotope measurements from space using SCIAMACHY

Researchers from SRON Netherlands Institute for Space Research, Utrecht University and various international partners have obtained the first global observations of water isotopes in the lowest part of our atmosphere. They analysed measurements from the satellite instrument SCIAMACHY, providing new insights into the hydrological cycle that are expected to further improve climate models. The researchers published their results this week in Science.

Global distribution of the water isotope HDO shown as relative abundance of water vapour. High fractions of HDO are found in the tropics and subtropics where water evaporates from the oceans and is then transported towards the poles. The relative quantity of heavy water in the remaining water vapour will be reduced as the heavy isotope rains out preferentially resulting in lower abundances at higher latitudes. The same occurs when moist air from the oceans travels over the continents. North America is a good example of this. A zoom shows enhanced HDO fractions due to strong evaporation over the Red Sea.

Water is vital to the Earth’s climate system. As a vapour, it is the strongest greenhouse gas and as precipitation it makes our planet habitable. When water evaporates from the Earth’s oceans and surface, moves through the atmosphere and falls back as rain, evaporation and condensation processes change the relative amount of heavy water, HDO. Therefore, the isotopic composition contains information about the history of water. SRON scientists used the SCIAMACHY instrument onboard the European Space Agency’s (ESA) research satellite ENVISAT to provide a global view on the isotopic composition of water in the atmospheric vapour. These are the first global isotope measurements with high sensitivity towards the lowest layers of the atmosphere, where most of the water vapour resides.

Together with their fellow researchers SRON-scientists prof. dr. Ilse Aben and dr. Christian Frankenberg focussed on a comparison with atmospheric General Circulation Models in two regions, the Sahel zone and the high arctic around Spitsbergen. In both cases current models cannot fully reproduce the measurements. This points to misrepresentations of both the tropical-subtropical hydrological cycle and the water transport to Arctic latitudes.

Satellite data bear the potential to rigorously test and subsequently improve the hydrological cycle in climate models. Eventually this will improve predictions of potential changes to the hydrological cycle (e.g. drought, precipitation events) in a future warming climate and reconstructions of climates in the past.

The SCIAMACHY measurements are a proof of concept and open up new research opportunities. The future instrument TROPOMI, scheduled to be launched in 2014 on board ESA’s Precursor Sentinel 5 mission, will further improve the accuracy of the measurements and, most importantly, their coverage in space and time promising more detailed insights into the global hydrological cycle.

SCIAMACHY animation (Quick Time – 3.9Mb)