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

热带海洋上空的低层云层将阳光反射回太空，从而使地球气候降温。在全球气候模型(GCM)中，这些云层通常会放大温室气体导致的变暖，因为变暖会减少云层覆盖，让更多的阳光照射到地表，导致进一步变暖。但这种放大的强度在不同的模型之间有很大的不同，并在很大程度上导致了GCMS对全球变暖的大范围估计。此外，从明确表示低云的小尺度小域模式进行的云模拟显示，与通过参数化间接表示低云的GCM相比，云量减少得更少。另一方面，如果低层云组织成团，细尺度模式中的云量可以随着变暖而显著减少，这一行为在GCM中没有捕捉到。最近的研究表明，GCM之间以及GCM和细尺度模式之间的低云敏感度差异可以通过模式平衡热带海洋上的降水、表面蒸发、湍流混合和云的上升和下降的增湿和干燥效应的不同方式来理解。这项研究确定了导致云层对变暖敏感度较高或较低的特定平衡，从而可以进行对照观测的测试。进行这类测试需要新的观测。该奖项支持的工作收集了对水蒸气、雨滴和海水的同位素组成的观测，以检查决定低云特性和灵敏度的润湿和干燥过程。普通水(H2O)由两个氢原子和一个氧-16原子组成，但一些水分子含有较重的同位素氢、氧-17和氧-18的原子。与普通水相比，含有较重同位素的水分子更容易凝结，蒸发也更慢。因此，相同湿度的空气样本可能会有不同浓度的重同位素，这取决于湿度产生的过程。例如，如果湿度水平是由云层上方的干燥空气和海洋表面附近的潮湿空气混合设置的，重同位素的浓度通常会高于通过冷凝低湿空气中的水来建立相同湿度水平的情况。水同位素数据是作为一个缩写为EUREC4A的实地活动的一部分收集的，目的是阐明云-环流耦合在气候中的作用。EUREC4A是由德国马克斯·普朗克研究所和法国气象动力实验室领导的一项多国行动，部署在巴巴多斯，时间为2020年1月20日至2月20日。该奖项支持从两艘船、一架飞机和巴巴多斯云天文台进行同位素采样。数据收集和分析以各种方式与模型模拟相结合。许多工作涉及模拟重同位素的不同行为的模型，以便可以与同位素数据进行直接比较。这项研究具有更广泛的影响，因为它有可能减少基于GCM的未来气候变化严重程度估计的不确定性。EUREC4A活动还提供了一个加强国际科学合作的机会，该项目为两名研究生提供了实地经验。在活动期间，通过博客向公众进行宣传，PI与新墨西哥州自然历史和科学博物馆合作，通过包括青年探险家夏令营和青少年文献计划在内的项目进行宣传。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.