SGER: Droughts in the Central Plains of the United States

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，用于耦合模式中的干旱项目，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。美国中原地区暖季干旱的地理偏好和远程强迫的可能原因如下：中原旱情的大范围流型以美国西部为脊状，东部为低谷为特征。这种模式类似于整个北美从春季到夏季的气流状况变化，并伴随着中原地区6-7月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秋年型和3-6月半年型构成的，它们比冬夏年型弱得多。。在没有任何特殊的年际强迫的情况下，大气环流应该只经历一个有规律的季节变化，以响应太阳加热的季节周期。因此，为了确定可能的年际强迫和大气对这种强迫的响应，应该去掉有规律的季节循环。应用这种方法，从西副热带太平洋上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型相耦合。利用这些结果，将探索两条研究途径：1)尝试评估全球和区域气候模式是否能很好地模拟形成有利于中原干旱环境的季节循环模式；2)初步检验模拟的中原干旱是否受到西副热带强迫的刺激。这项研究的目标是提出导致中原干旱的新机制。这项工作的广泛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.