Mesoscale Vegetation-atmosphere Feedbacks

该奖项是根据2009年《美国复苏和再投资法案》(公法111-5)资助的。土地是气候系统的组成部分，土地覆盖的变化会对陆地天气和气候产生重大影响。该项目旨在调查亚马逊西南部巴西隆多尼亚的森林砍伐情况下，区域尺度上植被-大气反馈的季节性时间尺度。高速公路和次要道路上的森林砍伐形成了一种独特的“鱼骨”模式，迫使有组织的中尺度环流类似于海风，通常被称为“植被风”。这些植被风影响了当地的水文气象，增强了森林砍伐地区的积云和对流降水。这个项目将检验这样一种假设，即隆多尼亚的森林砍伐通过大气途径对自身产生负面反馈。鱼刺砍伐的水文气象影响在旱季和过渡季最为突出，此时过多的降雨可以促进砍伐地区的植物生长。这构成了一种负面反馈，因为森林砍伐斑块上的植被加速恢复部分补偿了森林砍伐的影响。该项目还将研究背景水文气象学在植被-大气反馈过程中的作用。特别是，它将调查系统是否表现出阈值行为，即，如果背景温度、降水和云量超过某些阈值，对砍伐森林的反应是否可以从负(自我修复)切换到正(失控)反馈。将使用植物生长模型进行敏感性研究，以估计这些阈值的大小(如果存在)。这将是对生物圈-大气耦合系统中的植被-大气中尺度反馈的首批研究之一，在中等尺度上--在空间上是区域性的，在时间上是季节性的，从而填补湍流尺度和气候尺度之间的光谱空白。该项目将支持和培训一名博士生和一名本科生实习生开发Java版的动态植被模型。该模型将作为一门课程的动手工具，供学生进行简单的数值实验，并探索推动生物圈-大气相互作用的关键过程。它将为2008年秋季在伊利诺伊大学开设的大气科学本科新专业的研究和教学课程做出贡献。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Land is an integral component of the climate system and changes in land cover can significantly influence terrestrial weather and climate. This project aims to investigate regional-scale vegetation-atmosphere feedbacks over seasonal timescales in the context of deforestation in Rondonia, a Brazilian state in southwestern Amazonia.Deforestation along highways and secondary roads has created a unique "fishbone" pattern that forces organized mesoscale circulations similar to sea-breezes, often referred to as "vegetation breezes." These vegetation breezes affect local hydrometeorology, enhancing cumulus clouds and convective precipitation over the deforested patches. This project will test the hypothesis that deforestation in Rondonia exerts a negative feedback on itself via the atmospheric pathway. The hydrometeorological effects of fishbone deforestation are most prominent during the dry and transition seasons when excess rainfall can enhance plant growth over deforested regions. This constitutes a negative feedback because accelerated vegetation recovery over deforested patches partially compensates for the effects of deforestation. This project will also study the role of background hydrometeorology in the vegetation-atmosphere feedback process. In particular, it will investigate if the system exhibits threshold behavior, i.e., whether the response to deforestation can switch from a negative (self-healing) to a positive (runaway) feedback if the background temperature, precipitation and cloud cover exceed certain threshold values. Sensitivity studies will be conducted with a plant growth model to estimate the magnitudes of these thresholds, if present. This will be among the first studies on vegetation-atmosphere mesoscale feedbacks in the coupled biosphere-atmosphere system over an intermediate scale - regional in space and seasonal in time, thereby filling the spectral gap between the turbulence and climate scales. The project will support and train a Ph.D student and also an undergraduate intern to develop the java-version of the dynamic vegetation model. This model will be used as a hands-on tool in a course for students to conduct simple numerical experiments and explore key processes driving biosphere-atmosphere interactions. It will contribute to the research and teaching curriculum of the new Undergraduate Major in Atmospheric Sciences starting in the fall of 2008 at the University of Illinois.