Statistical and Dynamical Exploration of Land-Ocean-Atmosphere Interactions in Two Contrasting Monsoon Regions: China and Northern Australia

季风系统覆盖了热带和亚热带的大部分地区，季风雨为世界上大部分人口提供了农业和家庭水资源。因此，季风的变化可能会对人类造成戏剧性的影响，因此更好地理解导致季风变化的过程是可取的。迄今为止的研究表明，季风变化的一部分可能与遥远的海表面温度异常有关，例如与厄尔尼诺事件有关的异常，这会引起大气环流的大范围变化，从而调节季风区的降雨。季风变化的第二个潜在原因是当地陆地表面的状况，它受到降雨的影响，并可能通过各种陆地-大气反馈过程对降雨量产生进一步的影响。本项目试图确定遥远的海温和当地陆地-大气相互作用在调节季风区的降雨和大气条件方面的单独影响。研究集中在两个代表副热带季风系统和热带季风系统的地区，分别是中国和澳大利亚北部。首席调查员(PI)以前的工作表明，通过减少植被覆盖来改变陆地表面会在这两个地区产生相反的结果，中国的夏季风爆发得更早(与更大的海陆热对比有关)，春季降水增加，而澳大利亚北部的季风延迟和更弱(与植物蒸腾导致降水的水汽来源减少有关)。通过一系列区域气候模式实验和统计分析，研究了遥远的海温和当地陆地-大气相互作用的相对作用。模型模拟将通过实验来检验陆地-大气反馈的作用，其中陆地表面的各个方面保持固定(例如，固定叶面积，以便植被在干燥条件下不会枯萎)。统计分析使用了PI首创的一种技术，称为广义均衡反馈分析(GEFA)。该方法使用多变量滞后相关来确定来自偏远海温的季风降水和强迫与当地地表条件(包括以叶面积指数表示的植被)之间的因果关系。如上所述，季风变化具有强烈的人类影响，包括对农作物、牲畜和澳大利亚火季持续时间的影响。如果成功，这里进行的研究可能会改进用于预测季风降水的模型。此外，PI计划领导一个为期两天的关于陆地-大气相互作用、区域气候建模和陆地表面建模的研讨会，这将有助于向学生和职业生涯早期的科学家介绍用于研究区域气候和陆地-大气相互作用的方法。

Monsoon systems cover much of the tropics and subtropics, and monsoon rains provide the agricultural and domestic water resource for much of the world's population. Thus, variations of the monsoons can have dramatic human consequences, and a better understanding of the processes which cause monsoon variability is desirable. Research to date has shown that some portion of monsoon variability can be linked to anomalies in remote sea surface temperatures (SSTs) such as those associated with El Nino events, which cause large-scale changes in atmospheric circulation that modulate rainfall in the monsoon regions. A second potential cause of monsoon variability is the condition of the local land surface, which is affected by rainfall and can potentially have a further influence on rainfall through a variety of land-atmosphere feedback processes.This project seeks to identify the separate effects of remote SSTs and local land-atmosphere interactions in modulating rainfall and atmospheric conditions over monsoon regions. The research is focused on two regions chosen to represent subtropical and tropical monsoon systems, China and Northern Australia respectively. Previous work by the Principal Investigator (PI) suggests that modification of the land surface by a reduction in vegetation cover produces opposing results in the two regions, with an earlier summer monsoon onset in China (linked to greater ocean-land thermal contrast) and enhanced springtime rainfall, and a delayed and weaker monsoon in Northern Australia (linked to reduction in the source of moisture for precipitation due to transpiration from plants).The research addresses the relative roles of remote SSTs and local land-atmosphere interactions through a suite of regional climate model experiments and statistical analysis. The model simulations will examine the role of land-atmosphere feedbacks through experiments in which aspects of the land surface are held fixed (e.g. fixing the leaf area so that vegetation does not wilt under dry conditions). The statistical analysis uses a technique pioneered by the PI known as Generalized Equilibrium Feedback Analysis (GEFA). The method uses multivariate lagged correlation to identify causal relationships between monsoon precipitation and forcing from remote SSTs and local land surface conditions (including vegetation as represented by the Leaf Area Index).As noted above, monsoon variations have strong human impacts, including impacts on crops, livestock, and the duration of the Australian fire season. If successful, the research performed here may lead to improvements in models used to forecast monsoon precipitation. In addition, the PI plans to lead a 2-day workshop on land-atmosphere interactions, regional climate modeling and land surface modeling, which will serve to introduce students and early-career scientists to methods used for research on regional climate and land-atmosphere interactions.