SGER: Studying the Causes of Recent Drought and Monsoon Changes over East Asia Using NCAR and GFDL Models

这是气候变率和可预报性（CLIVAR）计划试点项目DRICOMP下的一笔赠款，用于耦合模式项目中的干旱，该项目侧重于探索全球气候模式输出中所代表的干旱机制，并评估这些模式在模拟干旱方面的可靠性。在20世纪70年代后期，中国东部出现了一种通常被称为南涝北方旱的模式。与这种降水变化相关的是，近几十年来，中国东部中部的地面气温变冷，这与北方半球和地球仪的总体变暖趋势相反。了解这些十年降雨量变化背后的原因和物理过程是气候科学家面临的一个重大挑战。近年来的研究表明，大气污染气溶胶、太平洋年代际振荡（PDO）和热带海表温度（SST）等多种因素可能对东亚地区近期气候变化起到了一定的作用。然而，很少有详细的物理机制，可以解释该地区观测到的气候变化的研究。PI评估了所有政府间气候变化专门委员会第四次评估报告（IPCC AR 4）模式模拟东亚夏季风的能力。他们现在将研究东亚十年降雨量的变化，特别是近几十年来中国北方大范围的干旱。他们将专注于分析现有的和新的历史模拟使用国家大气研究中心（NCAR）和地球物理流体动力学实验室（GFDL）大气全球气候模型（GCM）所观察到的热带，北太平洋，或全球SST只强迫;东亚气溶胶只;和温室气体只在20世纪后半叶的世纪。我们的目标是量化的相对作用，这些单独的强迫，导致观测到的东亚地区的降雨量变化，并诊断潜在的物理过程。除了检查降水和大气环流场外，还将计算和分析帕尔默干旱严重程度指数等其他场，以更好地描述华北干旱。还将使用再分析数据，并与一些模式模拟进行比较，以帮助了解所涉及的大气过程。模型分析将扩展到气专委第四次评估报告的世纪模拟，以评估东亚季风降雨和干旱严重程度和范围的未来潜在变化。 该项目的结果将有助于评估NCAR和GFDL气候模式，并提高我们对东亚降水和干旱年代际变化的认识。该项目产生的更广泛影响将是提高我们对世界上一个支持10亿多人生计的地区的气候趋势和预测的理解。该项目将使研究生能够对NCAR进行长期访问。

This is a grant under a Climate Variability and Predictability (CLIVAR) Program pilot project called DRICOMP, for the Drought in Coupled Models Project, which focuses on exploring the mechanisms of drought as represented in the output of global climate models and on assessing the reliability of these models in simulating drought.Historical records of precipitation show distinct multi-decadal variations over East Asia, with a shift around the late 1970s to a pattern often referred to as Southern Flooding and Northern Drought over East China. Associated with this rainfall change, surface air temperatures have cooled during recent decades over central East China, in contrast to the general warming trend in the Northern Hemisphere and the globe. Understanding the causes and physical processes underlying these decadal rainfall changes represents a significant challenge for climate scientists. Recent studies suggest that several factors, including aerosols from air pollution, the Pacific Decadal Oscillation (PDO), and tropical sea surface temperature (SST), may have played a role in causing the recent climate changes over East Asia. There are, however, few detailed studies on the physical mechanisms that can explain the observed climate changes over this region. The PI has evaluated all the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4) models in terms of their ability to simulate the East Asian Summer Monsoon. They will now study the decadal rainfall changes in East Asia and, in particular, the widespread drought in North China during recent decades. They will focus on analyzing existing and new historical simulations using the National Center for Atmospheric Research (NCAR) and Geophysical Fluid Dynamics Laboratory (GFDL) atmospheric global climate models (GCMs) forced by observed tropical, North Pacific, or global SST only; by East Asian aerosols only; and by greenhouse gases only during the later half of the 20th century. The goal is to quantify the relative role of these individual forcings in causing the observed rainfall changes over East Asia and to diagnose underlying physical processes. Besides examining precipitation and atmospheric circulation fields, other fields such as the Palmer Drought Severity Index will also be computed and analyzed to better characterize the drought in North China. Reanalysis data will also be used and compared with some of the model simulations to help understand atmospheric processes involved. The model analyses will be extended to the IPCC AR4 21st century simulations in order to assess potential future changes in monsoon rainfall and drought severity and extent in East Asia. The results from this project will help evaluate the NCAR and GFDL climate models and improve our knowledge about decadal changes in precipitation and drought over East Asia. Broader impacts resulting from this project will be to improve our understanding of climate trends and projections in a region of the world that supports the livelihoods of more than a billion people. The project will enable an extended visit to NCAR by a graduate student.