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

国际热带气旋协会最近的初步研究发现，半球-全下弯热带气旋(TCS)的频率与随后的冬季气候之间存在着强烈而直观的关系。当北半球TC在北纬40度以北下弯的总数超过12个(比平均值9高一个标准差)时，次年冬季的斜压活动明显减少(7-15%)。因此，中纬度地区比正常温度高(从1月到3月，三个月平均气温至少高出1摄氏度)，三个月平均降水量至少比正常高10%。相反的情况也适用于技术转换公司数量在5个或更少的年份。这种冬季气候异常分别是由于前期热带气旋引起的热量输送引起的大气冬季势能的减弱或增强所致。这项初步研究认为，一个下弯的热带气旋会使极地到赤道的温度梯度减弱0.5-1.5%，这取决于使用的历史再分析。由于平均每年有9个下弯的TC，TC完成了半球热量传输的5%-15%，量化了到目前为止仅停留在定性上的作用。这些结果提出了许多关键问题，这也是这笔赠款的基础：为什么对TC影响的大气记忆如此之久(几个月)，而不是在几天内消除？世界各地的盆地对这种热带气旋热量输送有何贡献？下降型热带气旋驱动异常冬季气候的关键秋季是什么时候？这些结果提出了一种独特的观点，即TCS是全球气候变异性和强迫的组成部分，而不是附带的和仅对其他强迫的响应，例如厄尔尼诺-南方涛动(ENSO)。这项工作的学术价值在于检验初步结果的稳健性。尽管已作出努力确保下弯的技术转换是在这里发挥作用的强迫机制，但仍有必要进行进一步的检查。是否有一个压倒一切的气候强迫将TC频率的下降和随后的冬季气候一起驱动？需要消除其他潜在的压倒强迫机制，然后才能声称下弯的TCS是主要的强迫机制。赠款的目标是在可能的情况下消除那些替代的慢流形强迫机制，如马登-朱利安振荡(MJO)、准两年一次的振荡(QBO)和太阳周期活动。虽然PI已经建立了由TCS循环驱动的冬季平均500毫巴温度通量异常的统计意义，但还将检查其他已建立的异常的统计意义：冬季地面温度和降水异常，极地和副热带急流异常，以及平均经向环流异常(Hadley，Ferrell，极圈异常)。更广泛的影响：当已知热带气旋在秋末或初冬的下沉频率时，全球冬季季节性气候预报的改善是可能的。这种改进的预测将减少因预期能源使用效率低下而造成的全球财务损失。总体而言，初步研究的结果表明，TCS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确立了初步研究的稳健性，将为热带气旋对气候的强迫设定一个新的范例。

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.