OCE-RIG: Role of Air-Sea Coupling on the Madden-Julian Oscillation under Suppressed External Forcing

概述：使用数值模型精确模拟麦登-朱利安振荡（MJO）仍然是非常困难的。对于MJO的启动机制，目前还没有公认的理论，这一事实使问题进一步恶化。然而，已经提出了几种假设，其中广泛包括局部强迫（即，再充放电机制）和外部影响（即，由环航波和温带因素引起的综合影响）。这些强迫对MJO及其启动的相对影响正在利用缺乏海气耦合的大气中尺度模式或大气环流模式（AGCMs）进行研究。然而，在MJO发生的印度洋，MJO受到海气相互作用的极大调制。本研究的主要目的是探讨在有无外界影响的情况下，不同季节海气耦合对MJO及其启动的影响程度。这里的关键是要区分模式中的本地强迫和外部强迫，而这些强迫是不能通过观测得到的。为了实现这一目标，构建了一个独特的基于总循环模型（GCM）的框架。将耦合模拟与非耦合模拟的GCM进行比较，探讨在所有强迫存在的情况下海气耦合的作用。在耦合和非耦合模拟中抑制了温带和环航波的影响，进一步进行了模拟，以探讨在没有外部影响的情况下，海气耦合对MJO的作用。智力优势：在本研究中，研究者将尝试在存在和不存在外部影响的情况下解决海气相互作用的作用。还将重点记录MJO在不同季节开始时的结构、组织和大规模背景。这种努力主要局限于北方冬季。这一研究将提高人们对MJO物理过程的认识，特别是对海气相互作用和对流与环境湿度相互作用的认识。这项工作还针对与MJO起始有关的观测不足的过程，即大尺度的水汽平流和辐合。该研究将进一步有助于发现MJO发生的必要条件，并可能对MJO的操作预测有很大帮助。更广泛的影响：本研究涉及的地理区域（热带印度洋和西太平洋）人口众多，对美国来说是一个日益增长的战略利益区域。了解MJO的启动及其预测对世界这一地区非常重要，MJO的全球影响力使其更加相关。值得注意的是，MJO与北美西海岸降水之间也发现了统计上显著的联系。该项目的外联活动将扩大代表性不足的群体对海洋科学的参与。佛罗里达理工学院（FIT）海洋与环境系统系（DMES）提供的两个已建立的暑期项目（实地项目和夏令营）将作为一个平台，通过强化培训和与海洋和大气科学相关的实地实践活动，吸引、激励和教育高中生和本科生。

Overview: An accurate simulation of the Madden-Julian Oscillation (MJO) using numerical models remains extremely difficult. The problem is further exacerbated by the fact that there is no accepted theory for the initiation mechanism of the MJO. However, several hypotheses have been proposed that broadly include local forcing (i.e., recharge-discharge mechanism) and external influences (i.e., combined influences due to circumnavigating waves and extratropics). Relative influences of these forcings on the MJO and its initiation are being studied using atmosphere only mesoscale models or atmospheric general circulation models (AGCMs), which lack air-sea coupling. However, MJO is greatly modulated by the air-sea interactions in the Indian Ocean where MJO initiation occurs. The primary objective of this study is to explore the extent to which MJO and its initiation are affected by the air-sea coupling in the presence and absence of external influences in different seasons. The key here is to separate the local and external forcing in a model that cannot be achieved using observations. A unique general circulation model (GCM)-based framework is constructed to fulfill the objective. A coupled simulation is compared to an uncoupled simulation of the GCM to explore the role of air-sea coupling in the presence of all forcings. Further simulations are conducted where the influences from extratropics and circumnavigating waves are suppressed in the coupled and uncoupled simulations to explore the roles of air-sea coupling on the MJO in the absence of external influences. Intellectual Merit: In this study, the investigator will attempt to address the role of air-sea interactions in the presence and absence of external influences. Emphasis will also be given to document the structure, organization, and large-scale context of the MJO at its initiation in different seasons. Such an effort has primarily been confined for boreal winter season. This research will improve the understanding of the aspects of physical processes associated with the MJO, especially the role of air-sea interaction and interaction between convection and environmental moisture. This work also targets poorly observed processes relevant to MJO initiation, namely, large-scale moisture advection and convergence. This study would further contribute towards detecting the necessary conditions for MJO initiation and might be greatly useful for operational prediction of the MJO. Broader Impacts: The geographical area (tropical Indian and West Pacific Ocean) that this research is concerned with has a large human population and it is a region of growing strategic interest for the United States. Understanding the MJO initiation and its forecasting is highly important for this part of the world and the MJO's global influence makes it even more relevant. Note that statistically significant connection between the MJO and precipitation along the North American west coast has also been found. Outreach activities for this project will broaden participation of under-represented groups in the ocean sciences. Two established summer programs (field project and summer camp) offered by the Department of Marine and Environmental Systems (DMES) at the Florida Institute of Technology (FIT) will be used as a platform for engaging, motivating, and educating high-school and undergraduate students through intensive training and hands-on field activities related to ocean and atmospheric sciences.