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Heavy Water HDO

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Heavy Water – HDO

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 content of heavy water (HDO). Therefore, the isotopic composition contains information about the history of water. SCIAMACHY’s measurements permit obtaining a global view on the water vapour isotopic composition in the atmosphere (Frankenberg et al. 2009). These are the first global isotope measurements with high sensitivity towards the lowest layers of the atmosphere down to the surface, where most of the water vapour resides. By exploiting the capability of SCIAMACHY to retrieve H2O and its heavier isotopologue HDO, new insights into the hydrological cycle are provided.

Fig. 3-4 presents the global distribution of the water isotope HDO shown as relative abundance of water vapour. High fractions of HDO are found in the tropics and sub-tropics where water evaporates from the oceans and is then transported towards the poles. The relative amount 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 as e.g. clearly seen in North America. The satellite data bear the potential to rigorously test and subsequently improve the description of such cycles in climate models. This will eventually even result in better predictions of the changes in the hydrological processes, e.g. drought and precipitation in a future climate.


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fig. 3-4

Global distribution of the water isotope HDO shown as relative abundance of water vapour averaged between 2003 and 2005. The inset displays enhanced HDO fractions due to strong evaporation over the Red Sea (Graphics: C. Frankenberg, SRON - now JPL)

Absorbing Aerosol Index and Precipitation

Water in the form of precipitation plays a dominant role in local climate and weather. This is particularly the case in Africa where the monsoon is the driving mechanism for the climate and therefore, also for the social and economic development. The northern part of Africa hosts large dry areas such as the Sahara and the Sahel. Dust storms arise frequently from the dry areas and have a profound impact on the weather conditions and lives of the local people. A linkage between the African monsoon systems and aerosol loading in Africa is suggested by the analysis of GOME and SCIAMACHY measurements. De Graaf et al. (2010) investigated multi-year satellite observations of UV-absorbing aerosols and compared these with precipitation data.


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fig. 3-5

Zonally averaged AAI from SCIAMACHY for each day between August 2002 and April 2008 as a function of latitude in Western and Eastern Africa (upper panels). The bottom panels display the monthly and zonally averaged precipitation for the same areas and the same period. (Graphics: M. de Graaf, KNMI)


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