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

这是气候变异性和可预测性(CLIVAR)计划试点项目DRICOMP下的一项拨款，用于耦合模式干旱项目，重点是对干旱的机制进行初步探索，因为它们代表了全球气候模式的输出，并试图评估这些模式在模拟干旱方面的可靠性。越来越多的文献表明，厄尔尼诺-南方涛动(ENSO)是全球干旱可变性的根本驱动因素，而类拉尼娜条件在导致北美干旱的环流异常中起着关键作用。对于理解和预测北美长期干旱，一个重要但知之甚少的过程是海洋-大气耦合系统如何在赤道太平洋维持持续的凉爽条件。这个项目将初步尝试回答四个问题：(1)赤道太平洋的持续凉爽事件是如何用最先进的耦合气候模式表示的；(2)这种情况是通过什么物理机制导致北美持续干旱的；(3)对这样的问题的理解如何有助于延长北美长期干旱的预测提前时间，以及(4)可预报性的机制和前景如何取决于转型气候的本质？将采取双管齐下的方法：首先，根据海洋成分的细节选择一组耦合模式来表征和解释持续凉爽的赤道太平洋条件；其次，将在气候模式比较项目3(CMIP3)的全套气候模型中分析北美干旱的长期可变性(根据Palmer干旱严重程度指数--PDSI)及其与赤道太平洋的关系，包括这似乎如何取决于人为强迫。将通过确定远距离强迫场本身(即赤道太平洋海温的低频演变)是如何调制的，以及该信号与PDSI之间的一致性，来探讨延长提前期的可预测性问题。这些信号的广泛影响可能有助于改进对北美延长提前期干旱的预测，并支持首席研究员，他是一名研究生。

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.