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

Abstract

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 À2 ) 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.

Spatiotemporal variability of modern precipitation δ18O in the central Andes and implications for paleoclimate and paleoaltimetry estimates

“…First, we confirm anomalous precipitation amounts in upwind air source regions control both Altiplano and eastern flank δ 18 O p . The most likely explanation is changes in the fraction of water vapor removed from an air parcel upwind, which influences Altiplano δ 18 O p via convective processes and Rayleigh fractionation associated with parcel rainout [ Vimeux et al ., ; Vuille and Werner , ; Samuels‐Crow et al ., ]. Second, we show that the Bolivian High modulates the influence of the Amazon and Gran Chaco air source regions and thus their potential effect on central Andes δ 18 O p .…”

Tropical West Pacific moisture dynamics and climate controls on rainfall isotopic ratios in southern Papua, Indonesia

“…Although the correlation between daily rainfall δ 18 O and precipitation is improved when precipitation amounts are cumulated along the back trajectories from the upwind region, it is still weaker than the spatially integrated effect of convective activity on rainfall δ 18 O, indicating that convective activity is more important than precipitation amount on controlling rainfall δ 18 O. This is consistent with previous studies [ Gao et al ., ; Samuels‐Crow et al ., ; Lekshmy et al ., ] which indicate that the upwind regional convective activity is a good controlling factor on rainfall δ 18 O variation in the tropics.…”

“…[] in southern India during the monsoon season. Recently, upwind regional convective activity during the monsoon season has been identified as the main control of isotopic variation in the southern Tibetan Plateau [ Gao et al ., ] and over the tropical Andes [ Samuels‐Crow et al ., ].…”

Detecting shifts in tropical moisture imbalances with satellite‐derived isotope ratios in water vapor

“…Although δ D q bears resemblance to the metric Δδ D used by Samuels‐Crow et al . []—where Δδ D defines the difference between the isotope ratio estimated from satellite and the isotope ratio predicted from a Rayleigh distillation (equation )—δ D q does not require one to make assumptions about the environment near cloud base. Similarities between these metrics are discussed in the supporting information.…”