The stable isotope amount effect: New insights from NEXRAD echo tops, Luquillo Mountains, Puerto Rico
Article first published online: 11 DEC 2009
Copyright 2009 by the American Geophysical Union.
Water Resources Research
Volume 45, Issue 12, December 2009
How to Cite
2009), The stable isotope amount effect: New insights from NEXRAD echo tops, Luquillo Mountains, Puerto Rico, Water Resour. Res., 45, W12407, doi:10.1029/2008WR007515., , , and (
- Issue published online: 11 DEC 2009
- Article first published online: 11 DEC 2009
- Manuscript Accepted: 31 AUG 2009
- Manuscript Revised: 1 AUG 2009
- Manuscript Received: 9 OCT 2008
- water stable isotopes;
- tropical climate;
- cloud water
 The stable isotope amount effect has often been invoked to explain patterns of isotopic composition of rainfall in the tropics. This paper describes a new approach, correlating the isotopic composition of precipitation with cloud height and atmospheric temperature using NEXRAD radar echo tops, which are a measure of the maximum altitude of rainfall within the clouds. The seasonal differences in echo top altitudes and their corresponding temperatures are correlated with the isotopic composition of rainfall. These results offer another factor to consider in interpretation of the seasonal variation in isotopic composition of tropical rainfall, which has previously been linked to amount or rainout effects and not to temperature effects. Rain and cloud water isotope collectors in the Luquillo Mountains in northeastern Puerto Rico were sampled monthly for three years and precipitation was analyzed for δ18O and δ2H. Precipitation enriched in 18O and 2H occurred during the winter dry season (approximately December–May) and was associated with a weather pattern of trade wind showers and frontal systems. During the summer rainy season (approximately June–November), precipitation was depleted in 18O and 2H and originated in low pressure systems and convection associated with waves embedded in the prevailing easterly airflow. Rain substantially depleted in 18O and 2H compared to the aforementioned weather patterns occurred during large low pressure systems. Weather analysis showed that 29% of rain input to the Luquillo Mountains was trade wind orographic rainfall, and 30% of rainfall could be attributed to easterly waves and low pressure systems. Isotopic signatures associated with these major climate patterns can be used to determine their influence on streamflow and groundwater recharge and to monitor possible effects of climate change on regional water resources.