Formation of rain layers in the Warm Pool and their feedbacks to atmospheric convection in an idealized modeling framework

理想化建模框架中暖池雨层的形成及其对大气对流的反馈

• 批准号: 1924659
• 负责人: Charlotte Demott
• 金额: $ 61.25万
• 依托单位: Colorado State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-10-15 至 2024-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1924659&HistoricalAwards=false
• 关键词: Formation; rain; layers; Warm; Pool

Over the warm tropical ocean, the supply of moist air sets up convective systems which manifest themselves in rainfall as a pattern of wet and dry spells, each lasting 30 to 60 days and propagating slowly Eastward. Within this so-called Madden-Julian Oscillation (MJO), the understanding of ocean feedback processes to atmospheric convection remains incomplete, and hinders its representation in climate and forecast models. The MJO is sensitive to upper ocean stability, because a stable surface ocean does not mix as readily or deeply, which makes it easier to generate larger temperature anomalies within a shallow surface layer through solar heating or evaporative cooling. This effect has been studied more with warm surface layers, but thin layers of relatively fresh water often formed by rainfall can also enhance stability of the surface layer. Because these layers tend to be small and ephemeral, they have not been studied as much. This project will use a regional atmospheric model coupled with a simplified model of the upper ocean to explore the impacts of rain layers on atmospheric convection. In addition to better understanding MJO mechanisms, the project will introduce a new model for investigating air-sea interactions, and novel analyses of ocean feedbacks to atmospheric convection. The project will also enable collaboration between atmospheric and oceanographic scientists, support for female scientists, and graduate education.Studies during the past decade have advanced our understanding of the importance of diurnal warm layers (DWLs) for the onset of the MJO, how MJO convection and wind anomalies interact with the upper ocean heat content, and have documented the evolution of large- scale sea surface salinity (SSS) patterns shaped by MJO rainfall. Less clear, however, is how the formation of transient ocean surface freshwater lenses, or rain layers (RLs), may temper ocean mixing, marine surface fluxes, and MJO convection. RLs are typically more buoyant and colder than Warm Pool surface waters, producing a cold patch on the ocean surface. Because RLs are shallow (0.5 - 5 m) and short-lived ( 1 day), they are likely undersampled by in situ observing systems. Direct observations of RLs in the Warm Pool are sparse, and efforts to document their observed spatial and temporal characteristics are in their infancy. The frequency, intensity, and duration of RLs, and their effects on atmospheric convection throughout the MJO lifecycle are largely unknown. A collection of rain layers generated by widespread convection would reduce surface latent and sensible heat fluxes via SST cooling, but would also generate a fine-scale network of sharp SST gradients, which have been linked to convective initiation. This study will use the Regional Atmospheric Modeling System (RAMS) coupled to many columns of a 1-dimensional KPP ocean mixed layer model 1) to study the formation of upper ocean stable layers by surface heating and freshening, including their frequency, spatial variability, and duration, and their regulation of upper ocean stability and mixing, and 2) to study how rain layers may interact with convection during the MJO suppressed-to-active transition period. Model-generated stable layer statistics will be compared to previously published ocean observations collected during the DYNAMO field campaign. Ocean feedbacks to convection will be assessed through a progression of diagnostics designed to link variations in upper ocean stability to surface fluxes and the organization of tropical convection.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.

在温暖的热带海洋上空，潮湿的空气供应建立了对流系统，这些对流系统在降雨中表现为潮湿和干燥的模式，每次持续 30 至 60 天，并缓慢向东传播。在这种所谓的马登-朱利安振荡（MJO）中，对海洋对大气对流反馈过程的理解仍然不完整，并阻碍了其在气候和预报模型中的表现。 MJO 对上层海洋的稳定性很敏感，因为稳定的表层海洋不容易或深度混合，这使得更容易通过太阳加热或蒸发冷却在浅表层内产生更大的温度异常。人们对温暖表层的这种效应进行了更多研究，但通常由降雨形成的相对淡水的薄层也可以增强表层的稳定性。由于这些层往往较小且短暂，因此尚未得到足够的研究。该项目将使用区域大气模型和上层海洋的简化模型来探索雨层对大气对流的影响。除了更好地了解 MJO 机制之外，该项目还将引入一种用于研究海气相互作用的新模型，以及海洋对大气对流反馈的新颖分析。该项目还将促进大气和海洋科学家之间的合作、对女性科学家的支持以及研究生教育。过去十年的研究加深了我们对日暖层 (DWL) 对于 MJO 爆发的重要性、MJO 对流如何产生的理解。和风异常与上层海洋热含量相互作用，并记录了 MJO 降雨形成的大规模海面盐度（SSS）模式的演变。然而，不太清楚的是，短暂的海洋表面淡水透镜体或雨层 (RL) 的形成如何可能缓和海洋混合、海洋表面通量和 MJO 对流。 RL 通常比暖池表层水更有浮力且温度更低，从而在海洋表面产生冷斑。由于 RL 很浅（0.5 - 5 m）且寿命短（1 天），因此现场观测系统可能对它们进行采样不足。对暖池中 RL 的直接观察很少，记录其观察到的空间和时间特征的努力还处于起步阶段。 RL 的频率、强度和持续时间，以及它们在整个 MJO 生命周期中对大气对流的影响在很大程度上是未知的。广泛的对流产生的雨层集合将通过海温冷却减少地表潜热和感热通量，但也会产生尖锐的海温梯度的细尺度网络，这与对流的启动有关。本研究将使用区域大气模拟系统 (RAMS) 与一维 KPP 海洋混合层模型 1) 的许多列相结合，研究通过表面加热和清新形成的上层海洋稳定层，包括其频率、空间变化、和持续时间，以及它们对上层海洋稳定性和混合的调节，2) 研究 MJO 抑制到活跃过渡期间雨层如何与对流相互作用。模型生成的稳定层统计数据将与之前发布的 DYNAMO 现场活动期间收集的海洋观测数据进行比较。海洋对对流的反馈将通过一系列诊断进行评估，这些诊断旨在将上层海洋稳定性的变化与表面通量和热带对流的组织联系起来。该奖项反映了 NSF 的法定使命，并被认为值得通过使用基金会的智力价值进行评估来支持以及更广泛的影响审查标准。

项目成果

Rain‐Induced Stratification of the Equatorial Indian Ocean and Its Potential Feedback to the Atmosphere

降雨引起的赤道印度洋分层及其对大气的潜在反馈

• DOI: 10.1029/2021jc018025
• 发表时间: 2022-03
• 期刊: Journal of Geophysical Research: Oceans
• 作者: Shackelford, Kyle;DeMott, Charlotte A.;van Leeuwen, Peter Jan;Thompson, Elizabeth;Hagos, Samson
• 通讯作者: Hagos, Samson