The Influence of Convective Aggregation on the Stable Isotopic Composition of Water Vapor

Remote sensing datasets of water vapor isotopic composition are used along with objective measures of convective aggregation to better understand the impact of convective aggregation on the atmospheric hydrologic cycle in the global tropics (30°N to 30°S) for the period 2015–2020. When convection is unaggregated, vertical velocity profiles are top‐heavy, mixing ratios increase and water vapor δD decreases as the mean precipitation rate increases, consistent with partial hydrometeor evaporation below anvils into a relatively humid atmospheric column. Aggregated convection is associated with bottom‐heavy vertical velocity profiles and a positive correlation between mixing ratio and δD , a result that is consistent with isotopic enrichment from detrainment of shallow convection near the observation level. Intermediate degrees of aggregation do not display significant variation in δD with mixing ratio or precipitation rate. Convective aggregation provides a useful paradigm for understanding the relationships between mixing ratio and isotopic composition across a range of convective settings. The results presented here may have utility for a variety of applications including the interpretation of paleoclimate archives and the evaluation of numerical simulations of convection. Convective clouds in the atmosphere can aggregate in a variety of ways, from individual cells to larger systems like tropical cyclones and squall lines. Some recent studies have examined how the aggregation of clouds affects water vapor, which can have an impact on the Earth's climate. In this study, we use remote sensing measurements of water vapor isotopic composition along with objective measurements of cloud organization to understand how the convective aggregation affects the water cycle in the tropics from 2015 to 2020. When clouds are not aggregated, there is more moisture in the atmosphere and water vapor becomes more isotopically depleted with increasing rain rates, while aggregated clouds are associated with less moisture and isotopic enrichment of water vapor with increasing rain rates. These findings could be useful for understanding past climates and for evaluating computer simulations of clouds and climate. Remote sensing datasets are used to study the impact of convective aggregation on the atmospheric hydrologic cycle in the global tropics Unaggregated convection is associated with top‐heavy ascent profiles, increased mixing ratios, and decreased water vapor isotopic ratios