Upwind convective influences on the isotopic composition of atmospheric water vapor over the tropical Andes

We take advantage of the spatial coverage provided by the Tropospheric Emission Spectrometer on‐board the Aura satellite to evaluate processes that control seasonal variations in atmospheric water vapor HDO/H 2 O values ( δD vapor ) over the tropical Andes. δD vapor is lower in austral summer (December, January, and February, DJF) than austral winter (June, July, and August, JJA), which is broadly consistent with precipitation studies and with δ 18 O snow preserved in tropical Andean glaciers. In DJF, 64% of δD vapor measurements over the tropical Andes are lower than predicted by Rayleigh distillation while 40% of JJA δD vapor measurements are lower than predicted by Rayleigh distillation. Air that has lower δD vapor than predicted by Rayleigh distillation at a given water vapor concentration ( q ) encounters low minimum outgoing longwave radiation (<240 W m −2 ) en route to the tropical Andes, suggesting convective intensity controls the isotopic ratios of these measurements. The broad regional coverage of the satellite data allows us to map the spatial extent of the region where isotopic ratios reflect convective processes in different seasons. In DJF, convection strongly influences δD vapor in the central tropical Andes. In JJA, convection influences δD vapor north of the tropical Andes. This pattern suggests that monsoon convection controls δD vapor in austral summer while large‐scale advective mixing controls Andean δD vapor in austral winter.