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，潮湿空气的供应建立了对流系统，这些对流系统表现为降雨的干湿模式，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，对海洋对大气对流的反馈过程的理解仍然不完整，并阻碍了其在气候和预测模型中的代表性。MJO对上层海洋的稳定性很敏感，因为稳定的表层海洋不会很容易或很深地混合，这使得它更容易通过太阳能加热或蒸发冷却在浅表层内产生更大的温度异常。这种效应在温暖的表层中得到了更多的研究，但降雨形成的相对新鲜的薄层也可以增强表层的稳定性。由于这些层往往很小，而且时间很短，因此没有对它们进行太多的研究。该项目将使用一个区域大气模型和一个简化的上层海洋模型，以探讨降雨层对大气对流的影响。除了更好地理解MJO机制外，该项目还将引入一个新的模型来研究海气相互作用，以及对海洋反馈到大气对流的新分析。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周日暖层（DWL）对于MJO爆发的重要性、MJO对流和风异常如何与上层海洋热含量相互作用、并记录了由MJO降雨形成的大尺度海面盐度（SSS）模式的演变。然而，不太清楚的是，如何形成瞬态海洋表面淡水透镜体，或雨层（RL），可能会回火海洋混合，海洋表面通量，和MJO对流。RL通常比暖池表面沃茨更有浮力和更冷，在海洋表面产生冷斑。由于放射线较浅（0.5 - 5米），寿命较短（1天），现场观测系统可能对它们采样不足。在温暖的池中的RL的直接观测是稀疏的，并努力记录其观察到的空间和时间特性处于起步阶段。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。广泛对流产生的一系列雨层会通过SST冷却减少地表潜热和感热通量，但也会产生一个精细的SST梯度网络，这与对流的开始有关。本研究将使用区域大气模拟系统（RAMS）与一维KPP海洋混合层模式的多个列耦合：1）研究由表面加热和增鲜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）研究在MJO从抑制到活跃的过渡期内，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先前公布的海洋观测数据进行比较，这些数据是在海洋观测卫星实地活动期间收集的。海洋对对流的反馈将通过一系列诊断来评估，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知识价值和更广泛的影响审查标准进行评估来支持。