SGER: Droughts in the Central Plains of the United States

这是气候变率和可预测性计划（CLIVAR）试点项目DRICOMP下的一笔拨款，该项目是干旱耦合模式项目的一部分，重点是对干旱机制进行初步探索，因为它们在全球气候模型的输出中有所体现，并试图评估这些模型在模拟干旱方面的可靠性。美国中部平原暖季干旱的地理偏好和远程强迫的可能原因有：。中部平原干旱的大尺度流型表现为美国西部为脊，东部为槽。这种模式类似于北美春夏流态的变化，伴随着6 - 7月中原地区最大降雨量的急剧减少。这种有利的大陆尺度干旱环境是由全球春季-秋季年模态和3 - 6月半年模态建立的，它们远弱于冬季-夏季年模态。在没有任何特殊的年际强迫的情况下，大气环流只应响应太阳加热的季节周期而经历有规律的季节变化。因此，为了确定可能的年际强迫和大气对这种强迫的响应，应该去掉常规的季节周期。应用这种方法，从副热带太平洋西部的年际降水异常中心发出的跨太平洋短波序列似乎与横跨美国大陆的中原干旱流模式耦合。在此基础上，本文将探索两个研究方向：1)尝试评估全球和区域气候模式是否能够很好地模拟形成中原干旱有利环境的季节周期模式；2)初步验证模拟的中原干旱是否受到西部副热带强迫的刺激。这项研究的目的是提出导致中原干旱的新机制。这项工作更广泛的影响在于它有可能提高大平原干旱的可预测性。

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.Possible causes for the geographic preference and remote forcing of warm-season droughts in the U.S. Central Plains have been suggested: . The large-scale flow pattern of Central Plains drought is characterized by a ridge in the western United States and a trough in the eastern United States. This pattern resembles the spring-to-summer flow regime change across North America, which is accompanied by a drastic June-July decrease in the Central Plains rainfall maximum. This favorable continental-scale environment for drought is established by the global spring-fall annual and the March-June semiannual modes which are much weaker than the winter-summer annual mode. . Without any special interannual forcing, the atmospheric circulation should only undergo a regular seasonal variation in response to the seasonal cycle of solar heating. Thus, to identify possible interannual forcing and the atmospheric response to this forcing, the regular seasonal cycle should be removed. Applying this approach, a cross-Pacific short-wave train emanating from an interannual rainfall anomaly center over the western subtropical Pacific appears to couple with the Central Plains drought flow pattern across the U.S. continent. Using these findings, two avenues of research will be explored: 1) to attempt an evaluation of whether the seasonal-cycle modes forming environments favorable for Central Plains droughts are well simulated by global and regional climate models, and 2) to make an initial test of whether simulated Central Plains droughts are stimulated by the western subtropical forcing. The goal of the study is to propose new mechanisms leading to Central Plains droughts.Broader impacts of this work lie in its potential for providing enhanced predictability of drought in the Great Plains.