Hydrological processes as seen with high resolution distributions of δD derived from IASI/MetOp

Abstract:

The interest for observations of the water isotopic ratio in the vapor has rapidly increased this last decade. Some of the remote sounders in orbit can be used to derive information on the deuterium isotopic ratio, δD, with the great advantage to be able to provide global data. The Infrared Atmospheric Sounding Interferometer (IASI) operational since 2007 for a 15 to 20 years period can provide δD estimates in the free troposphere at high spatio-temporal resolution, allowing for unprecedented daily analyses of the isotopic variations in the troposphere. After a summary of IASI capabilities to retrieve vertical profile of δD - which is mainly sensitive in the free troposphere - we present newly available δD distributions derived from IASI and explore how they can contribute to improve our understanding of several aspects of the hydrological cycle.

Among the different hydrological processes seen with IASI we emphasis on the role of the convection. In the tropics, we noticed that the isotopic composition in the free troposphere is sensitive to the height of convection: regions where the convection is the highest show depleted δD values while regions associated to shallow convection are more enriched. This finding could help to evaluate the representation of deep and shallow convection in GCMs (General Circulation Model) which has been suggested to be in a great part associated with the climate sensitivity uncertainty.

The interest of IASI measurements is further illustrated with examples of enriched water vapour above and around the tropical continents that indicate an important contribution of the evapotranspiration on the water budget. We also investigate the differences between the Northern and Southern hemispheres during the water vapour transport poleward.