SGER: El Nino-Southern Oscillation (ENSO) and Droughts over North America--The Interdecadal Variability of the Sea Surface Temperature (SST) Forced Signal

这是气候变率和可预报性（CLIVAR）计划试点项目DRICOMP的资助，用于耦合模式项目中的干旱，该项目的重点是对全球气候模式输出中所代表的干旱机制进行初步探索，并试图评估这些模式在模拟干旱方面的可靠性。理论，大气环流模式（AGCMs）的结果，观测和代用数据支持热带年际变化的频率和幅度的变化可以调节北美干旱的发生和持续时间的假设。 热带太平洋和北美之间大气遥相关的各种机制已经被假设来解释在冷海表面温度（SST）异常存在下发生干旱的趋势，即，在拉尼娜的条件下。 然而，从最近几十年的仪器记录的分析表明，我们对这些相互作用的理解是不完整的，这个项目是一个探索性的调查，使用新提供的模式输出，热带太平洋在20世纪下半叶和未来温暖的气候中可能发挥的作用，在调制的发生和持续时间的干旱在北美。 研究者将尝试回答以下问题：造成北美干旱的环流异常的哪一部分是热带SST强迫（特别是ENSO，厄尔尼诺-南方涛动）的结果，哪一部分是大气内部模态的结果？厄尔尼诺/南方涛动特征的变化-特别是方差和平均状态-是否会影响美国发生干旱的概率和/或干旱的持续时间和范围？第一个问题将通过对作为20世纪世纪气候（C20 C）国际项目的一部分收集的大量模拟进行探索性分析来解决。 将通过系统地比较1950-1999年期间以及分别在1950 -1976年和1977-1999年期间不同大气环流模型的输出，评估北美观测到的降雨量的潜在可预测性。 这可能使与北美降水量在1976年太平洋气候转变前后的大气模式变化的重要性得到评估。 为了研究第二点，首席研究员将分析一套IPCC AR 4（政府间气候变化专门委员会第四次评估报告）进行了耦合试验，以检验ENSO变化的作用、SST异常的传播方向、以及热带地区普遍变暖在调节北美干旱的发生和持续时间方面的作用。这项工作的潜力在于评估北美干旱的风险在本世纪将如何演变。

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 making initial explorations into the mechanisms of drought as they are represented in the output of global climate models and on attempting to assess the reliability of these models in simulating drought.Theory, results from atmospheric general circulation models (AGCMs), and observational and proxy data support the hypothesis that changes in the frequency and amplitude of interannual variability in the tropics can modulate the occurrence and duration of droughts over North America. Various mechanisms for the atmospheric teleconnection between the tropical Pacific and North America have been hypothesized to explain the tendency for droughts to occur in the presence of cool sea surface temperature (SST) anomalies, i.e., in La Nina-like conditions. Analyses of instrumental records from the most recent decades, however, reveal that our understanding of these interactions is incomplete.This project is an exploratory investigation, using newly available model output, of the possible role played by the tropical Pacific during the second half of the 20th century and in future warmer climates in modulating the occurrence and duration of droughts in North America. The investigators will attempt to answer the following questions:. Which part of the circulation anomalies that create droughts over North America results from tropical SST forcing (ENSO, El Nino-Southern Oscillation, in particular) and which part results from internal modes of the atmosphere?. Would changes in the ENSO characteristics - variance and mean state in particular - affect the probability of drought occurrence and/or drought duration and extent in the United States?The first question will be addressed by means of exploratory analyses of a large number of simulations collected as part of the Climate of the 20th Century (C20C) international project. The potential predictability of North American observed rainfall will be assessed by systematically comparing the output of different AGCMs during the period 1950-1999 and separately during the 1950-1976 and 1977-1999 intervals. This may allow the significance of changes in the atmospheric patterns associated with North American precipitation before and after the 1976 climate shift in the Pacific to be assessed. To investigate the second point the principal investigator will analyze a suite of IPCC AR4 (Intergovernmental Panel on Climate Change Fourth Assessment Report) coupled runs to test the role of ENSO variance, direction of propagation of SST anomalies, and persistence of SST and wind anomalies as well as the role of the general warming in the tropics in modulating the occurrence and duration of droughts over North America.Broader impacts of the work lie in its potential for assessing how the risk of North American drought will evolve over this century.