Australia: The Land Where Time Began

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Convective and Stratiform Precipitation – Proportions Revealed in Water Isotope Ratio

There are fundamentally 2 types of tropical and midlatitude precipitation, which are limited spatially and high-intensity convective or widespread and of lower-intensity stratiform, as a result of differences in vertical air motions and microphysical processes governing the formation of rain. Partition of precipitation into rain types is critical for understanding how the water cycle responds to climatic changes, as these processes are difficult to observe or model. In this study Aggarwal et al. combined 2 independent data sets – convective and stratiform precipitation fractions, which had been derived from the Tropical Rainfall Measuring Mission satellite or synoptic observations of clouds, and stable isotope and tritium composition of surface precipitation, which had been derived from a global network, to show that rain type proportions are reflected in the isotope ratios and are negatively correlated with stratiform fractions. Higher isotope ratios in convective rain, as well as higher tritium when riming in deep convection occurs with entrained air at higher altitudes, are produced by condensation and riming associated with boundary layer moisture. On the basis of the data obtained by Aggarwal et al., it is possible to use stable isotope ratios to monitor changes in the character of precipitation in response to periodic variability or climate changes. Observational constraints for an improved simulation of convection in climate models and a better understanding of isotope variations in proxy archives, such as speleothems and tropical ice, are also provided by the results of this study.

Sources & Further reading

1. Aggarwal, P. K., U. Romatschke, L. Araguas-Araguas, D. Belachew, F. J. Longstaffe, P. Berg, C. Schumacher and A. Funk (2016). "Proportions of convective and stratiform precipitation revealed in water isotope ratios." Nature Geosci 9(8): 624-629.