COLLABORATIVE RESEARCH: Nonlinear Dynamics of Soil Moisture Climate at Continental Scales: Climate Origins of Droughts

这个合作研究项目的目标是确定和分析陆地和大气之间的相互作用和反馈，这些相互作用和反馈导致观测到的复杂性和水文气候学缺乏可预测性。特别是，它旨在研究土壤水分的动态及其在干（旱）和湿（洪）状态下的漂移。第一个假设是，在大陆尺度上，水分的局部再循环和按季节到年的时间周期导致土壤水分动态，可以用带有乘法噪声的随机微分方程来描述。该非线性系统的解为至少具有两种模态的土壤水分概率分布；也就是说，有两种首选状态，一种是干的，一种是湿的。这与土壤水分分布的传统单峰观点形成对比。研究这种分布可以得到答案，比如干旱开始的概率，反之亦然，干旱期结束的概率。另一个令人感兴趣的问题是干旱的持续时间。多模态分布也可以作为气候区新分类的基础。第二个假设是，在个别事件发生的时间尺度上（即，周），土壤湿度对大气动力学具有延迟效应。这一现象不仅是由于土壤水分对地表温度和大气压力的动态影响，而且是由于土壤水分对地表温度和大气压力的动态影响。这一假设的含义是描述土壤湿度的高度非线性延迟微分方程。这个方程的解会导致一个固定的平衡，一个带分岔的极限环或混沌。这将用于研究亚马逊河流域等大陆地区季节性效应的放大，以及土壤湿度和一般水文气候学的可预测性。来自亚利桑那大学和麻省理工学院的主要研究人员和工作人员将在这个项目上合作。

The goal of this collaborative research project will identify and analyze the interactions and feedbacks between the land and atmosphere that result in observed complexities and lack of predictability of hydroclimatology. In particular, it is intended to study the dynamics of soil moisture and its excursions into dry (drought) and wet (flood) states. The first hypothesis is that local recycling of moisture at continental scales, and time periods on the order of seasons to years leads to soil moisture dynamics that can be described by a stochastic differential equation with multiplicative noise. The solution to such nonlinear system is a probability distribution of soil moisture with at least two modes; that is, two preferred states, one dry and one wet. This contrasts with the traditional unimodal view of the soil moisture distribution. This distribution can be studied to obtain answers like the probability of the onset of drought or vice versa the end of a drought period. Another question of interest is the duration of droughts. The multimodal distribution can also be the basis of a new classification of climatic regions. The second hypothesis is that at time scales on the order of the occurrence of individual events (i.e., weeks) the soil moisture has a delayed effect on atmospheric dynamics. This phenomena is due to the moisture supply as well as to dynamic influences resulting from soil moisture effect on surface temperature and atmospheric pressure. The implication of this hypothesis is a highly nonlinear delayed differential equation for the description of soil moisture. The solution of this equation leads to a fixed equilibrium, a limit cycle with bifurcations or to chaos. This will be used to study amplification of seasonal effects over continental regions like the Amazonia as well as the predictability of soil moisture and hydroclimatology in general. Principal Investigators and staff from the University of Arizona and the Massachusetts Institute of Technology will collaborate on this project.