SGER: Understanding Tropical-Subtropical Forcing and Predictability of Long-Term North American Drought in Coupled Models

这是气候变化和可预测性（CLIVAR）计划试点项目DRICOMP下的一笔赠款，用于耦合模型项目中的干旱，主要对全球气候模式输出的干旱机制进行了初步探讨，并试图评估这些模式模拟干旱的可靠性。厄尔尼诺/南方涛动现象）是全球干旱变化的一个根本驱动因素，而类似拉尼娜现象的条件在导致北美干旱的环流异常中起着关键作用。 一个对理解和预测北美长期干旱具有重大意义的重要但知之甚少的过程是，耦合的海洋-大气系统如何在赤道太平洋维持持续的凉爽条件。（1）赤道太平洋的持续凉爽事件如何在最先进的耦合气候模式中表现出来，（2）通过什么物理机制这样的条件导致持续的北美干旱，（3）如何理解这些问题有助于延长预测的提前期北美长期干旱，（4）如何机制和前景的可预测性取决于气候的本质在转型？将采取双管齐下的办法：第一，根据海洋组成部分的详细情况选定一些耦合模式，用于描述和解释赤道太平洋持续凉爽状况的表现;第二，北美干旱的长期变化（根据帕尔默干旱严重程度指数- PDSI）及其与赤道太平洋的关系，包括这看起来如何依赖于人为强迫，将在全套气候模式比较项目3（CMIP 3）气候模式中进行分析。 通过确定远程强迫场本身（即，更广泛的影响在于它可能有助于改进对北美干旱的长期预测，并支持作为研究生的首席研究员。

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.A growing body of literature indicates that El Nino - Southern Oscillation (ENSO) is a fundamental driver of global drought variability and that La Nina-like conditions play a key role in the circulation anomalies leading to North American drought. An important yet poorly understood process with strong implications for understanding and predicting long-term North American drought is how the coupled ocean-atmosphere system maintains persistent cool conditions in the equatorial Pacific Ocean.This project will make an initial attempt to answer four questions: (1) how are persistent cool episodes in the equatorial Pacific Ocean represented in state-of-the-art coupled climate models, (2) through what physical mechanisms do such conditions lead to persistent North American drought, (3) how can an understanding of such questions serve to extend the predictive lead time for long-term North American drought, and (4) how do the mechanisms and prospects for predictability depend on the essence of a climate in transition?A two-pronged approach will be taken: first, a selection of coupled models as determined from the details of their ocean component will be used to characterize and explain the representation of persistent cool equatorial Pacific conditions; secondly, long-term North American drought variability (in terms of the Palmer drought severity index - PDSI) and its relationships with the equatorial Pacific, including how that appears to depend on anthropogenic forcing, will be analyzed in the full suite of Climate Model Intercomparison Project 3 (CMIP3) climate models. The problem of predictability at extended lead times will be explored by ascertaining how the remote forcing field itself (i.e., low-frequency evolution of equatorial Pacific SST) is modulated, and the coherence between that signal and the PDSI.Broader impacts of these are in its potential contribution to improved prediction of North American drought at extended leads and in supporting the principal investigator, who is a graduate student.