Collaborative Research: EUREC4A-iso--Constraining the Interplay between Clouds, Convection, and Circulation with Stable Isotopologues of Water Vapor

点击翻译按钮获取中文摘要

Low-level clouds over tropical oceans cool the earth's climate by reflecting sunlight back to space. In global climate models (GCMs) these clouds generally amplify greenhouse gas-induced warming, as warming reduces cloud cover and allows more sunlight to reach the surface, causing further warming. But the strength of this amplification varies considerably from model to model and contributes substantially to the large range of warming estimates from GCMs. Moreover, cloud simulations from fine-scale, small-domain models which explicitly represent low clouds show less reduction in cloudiness than GCMs, which represent low clouds indirectly through parameterizations. On the other hand, cloud cover in the fine-scale models can reduce significantly with warming if the low clouds organize into clusters, a behavior not captured in GCMs.Recent research suggests that low cloud sensitivity differences among GCMs, and between GCMs and fine-scale models, can be understood in terms of the various ways in which models balance the moistening and drying effects of precipitation, surface evaporation, turbulent mixing, and cloud updrafts and downdrafts over tropical oceans. This research has identified specific balances which lead to higher or lower cloud sensitivity to warming, allowing tests against observations to be made. New observations are required to conduct such tests.Work supported under this award collects observations of the isotopic composition of water vapor, raindrops, and sea water to examine the moistening and drying processes that determine low cloud properties and sensitivities. Ordinary water (H2O) consists of two hydrogen atoms and one oxygen-16 atom, but some water molecules contain atoms of the heavier isotopes deuterium, oxygen-17, and oxygen-18. Water molecules containing heavier isotopes condense more readily and evaporate more sluggishly than ordinary H2O. Thus air samples with the same humidity can have different concentrations of heavy isotopes depending on the processes through which that humidity came about. For instance, if the humidity level is set by the mixing of dry air above the cloud layer and moist air near the ocean surface, concentrations of heavy isotopes will generally be higher than if the same humidity level is established by condensing water out of moist low-level air. Water isotope data is collected as part of a field campaign with the acronym EUREC4A, for Elucidating the Role of Clouds-Circulation Coupling in Climate. EUREC4A is a multinational campaign led by the Max Planck Institute in Germany and the Laboratoire de Meteorologie Dynamique in France, with a deployment based in Barbados from January 20th to February 20th 2020. This award supports isotope sampling from two ships, an aircraft, and the Barbados Cloud Observatory. Data collection and analysis is combined with model simulations in a variety of ways. Much of the work involves models which simulate the distinct behaviors of heavy isotopes so that direct comparisons with isotopic data can be made.The research has broader impacts due to its potential for reducing uncertainty in GCM-based estimates of the severity of future climate change. The EUREC4A campaign also provides an opportunity to enhance international scientific collaboration, and the project provides field experience for two graduate students. Outreach to the public is conducted during the campaign through a blog, and the PIs have partnered with the New Mexico Museum of Natural History and Science to perform outreach through programs including the Young Explorers Summer Science Camp and the Junior Docent Program.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.