First Global Observations of HDO/H2O ratio - A Tracer of Global Hydrological Processes


The hydrological cycle acts differently in different location. This slide shows first ever measurements of HDO and water from TES. Over Africa, HDO is high as is water suggesting rapid recycling of both HDO and water. Over the Indian ocean, HDO is depleted even though water is high suggesting the removal of water by precipitation but not much re-evaporation. At high latitudes, water is low as is HDO suggesting that air parcels have repeatedly lost HDO through precipitation events.

Water isotopes trace the history of an air parcel. Lighter isotopes preferentially evaporate and heavier isotopes preferentially condense thus more condensation leads to more isotope depletion. The TES measurements show that in the tropics, re-evaporation of precipitation is an important process controlling cloud formation. Up to 70% of precipitation is re-evaporated into the cloud.

H2O (103ppmv)
TES measurements

High H2O and HDO/H2O ratio over land indicates strong evapo-transpiration as the water vapor source

Relatively Low HDO/H2O ratio with high H2O indicates re-evaporation of precipitation in tropical cloud systems

Lower HDO/H2O ratio with latitude due to condensation along with poleward transport

HDO/H2O (delta-D)
TES measurements

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