SGER: Significance Testing of the Role of Recurving Tropical Cyclones in Subsequent Winter Climate Modulation

最近的初步研究已经确定了半球总环流热带气旋（TCs）的频率与随后的冬季气候之间强烈而直观的关系。当北半球环流向北纬40度的总数超过12个（高于平均值9个标准差）时，随后的冬季气压临床活动明显减少（7-15%）。因此，中纬度地区比正常温度高（从1月到3月的三个月平均值至少高出1摄氏度），降水也比正常温度至少高出10%。相反的情况也适用于那些循环tc少于5个的年份。这一冬季气候异常是由早期tc热输送引起的大气冬季位能减少或增强引起的。这一初步研究认为，根据所使用的历史再分析，单个递归的TC使两极到赤道的温度梯度减弱了0.5-1.5%。由于每年平均有9个回转热球，热球在半球热传输中发挥了5-15%的作用，从而量化了迄今为止仅定性的作用。这些结果提出了许多关键问题，这也是这项资助的基础：为什么大气层对TC撞击的记忆如此之长（数月），而不是在几天内被消除？世界上不同的盆地对这种TC热传输有何贡献？秋季的什么时候是纬向环流驱动冬季异常气候的关键时期？这些结果提出了一种独特的观点，即tc是全球气候变率和强迫的组成部分，而不是偶然的和仅仅响应其他强迫，如厄尔尼诺-南方涛动（ENSO）。这项工作的智力价值在于测试了初步结果的稳健性。虽然已作出努力，以确保在这里起作用的强迫机制是递归的技术转让，但仍有必要进一步审查。是否存在一种压倒一切的气候强迫，将TC频率和随后的冬季气候一起驱动？其他潜在的压倒性强迫机制需要被消除，然后才可以声称递归的tc是主要的强迫机制。该基金的目标是在可能的情况下消除那些可替代的慢流道强迫机制，如麦登朱利安振荡（MJO）、准两年振荡（QBO）和太阳周期活动。虽然PI已经建立了由反转tc驱动的冬季平均500mb温度通量异常的统计显著性，但将研究其他已建立的异常的统计显著性：冬季地表温度和降水异常、极地和副热带急流异常以及平均经向环流异常（Hadley, Ferrell， polar cell异常）。更广泛的影响：如果在深秋或初冬已知温带气旋的复发频率，就有可能改善全球冬季季节气候预报。这种改进的预测将减少由于预期能源使用效率低下而造成的全球经济损失。总的来说，初步研究的结果表明，tc在气候强迫中的作用比目前公认的要大得多。如果将要进行的工作建立了初步研究的稳健性，将为热带气旋强迫气候建立一个新的范例。

Recent preliminary research by the PI has identified a strong and intuitive relationship between the frequency of hemispheric-total recurving tropical cyclones (TCs) and the subsequent winter climate. When the total number of northern hemisphere TCs recurving north of 40 degrees latitude exceeds 12 (one standard deviation above the mean of 9), the subsequent winter is considerably less active (7-15%) baroclinically. Consequently, the midlatitudes are warmer than normal (by at least one degree Celsius for a three-month mean over January through March), and precipitation is at least 10% above normal for that three-month mean. The converse is also true for years in which the number of recurving TCs is five or less. This winter climate anomaly is caused by a reduction or enhancement, respectively, of the winter potential energy of the atmosphere induced by the earlier TC-induced heat transport. This preliminary research argues that a single recurving TC weakens the pole to equator temperature gradient by 0.5-1.5%, depending on the historical reanalysis used. With an average of nine recurving TCs per year, TCs perform 5-15% of the hemispheric heat transport, quantifying a role that has remained solely qualitative thus far. Many critical questions are raised by these results and that is the basis for this grant: Why is the atmospheric memory of the TC impact so long (months), rather than removed within days? How do the various basins of the world contribute toward this TC heat transport? What is the critical time of autumn for recurving TCs to drive anomalous winter climate? These results suggest a unique view wherein TCs are integral to the variability and forcing of global climate, rather than incidental and solely responsive to other forcings, such as the El Nino - Southern Oscillation (ENSO). The intellectual merit of this work is to test the robustness of the preliminary results. Although an effort has been made to ensure that the recurving TCs are the forcing mechanism at work here, further examination is necessary. Is there an overriding climate forcing that is driving BOTH the recurving TC frequency and the subsequent winter climate together? Other potential overriding forcing mechanisms need to be eliminated before the recurving TCs can be claimed as the dominant forcing mechanism. The grant's goal is to eliminate, when possible, those alternative slow-manifold forcing mechanisms, such as the Madden Julian Oscillation (MJO), Quasi-biennial Oscillation (QBO), and solar cycle activity. Although the PI has established the statistical significance for the anomalous winter mean 500mb temperature flux driven by recurving TCs, statistical significance of other established anomalies will be examined: winter surface temperature and precipitation anomalies, polar and subtropical jet stream anomalies, and mean meridional circulation anomalies (Hadley, Ferrell, Polar cell anomalies). Broader Impacts: When TC recurving frequency is known in late autumn or early winter, improved winter seasonal climate forecasts may be possible globally. Such improved forecasts would decrease the financial losses globally resulting from inefficient anticipated energy usage. Overall, the results of the preliminary research argue for a much larger role of TCs in climate forcing than is currently acknowledged. If the work to be conducted establishes the robustness of the preliminary research, a new paradigm will be set for tropical cyclone forcing of climate.