The stable isotope amount effect: New insights from NEXRAD echo tops, Luquillo Mountains, Puerto Rico

作者：M. A. Scholl, James B. Shanley, Jan P. Zegarra, Tyler B. Coplen · 发表于：Water Resources Research · 年份：2009 · DOI：10.1029/2008wr007515 · 研究领域：Groundwater and Isotope Geochemistry、Climate variability and models、Geology and Paleoclimatology Research

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 δ 18 O and δ 2 H. Precipitation enriched in 18 O and 2 H 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 18 O and 2 H and originated in low pressure systems and convection associated with waves embedded in the prevailing easterly airflow. Rain substantially depleted in 18 O and 2 H compared to the aforementioned weather patterns occurred during large low pressure systems. Weather analysis sho...