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

SGER：回归热带气旋在随后冬季气候调节中作用的显着性测试

• 批准号: 0627908
• 负责人: Robert Hart
• 金额: $ 2.38万
• 依托单位: Florida State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-06-01 至 2007-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0627908&HistoricalAwards=false
• 关键词: SGER; Significance; Testing; Role; Recurving

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.

PI最近的初步研究已经确定了半球总转向热带气旋（TC）的频率与随后的冬季气候之间的强烈和直观的关系。当北方半球TC在北纬40度以北转向的总数超过12个（比平均值9高出一个标准差）时，随后的冬季在斜压上的活跃程度显著降低（7 - 15%）。因此，中纬度地区比正常温度高（1月至3月的三个月平均值至少高出1摄氏度），降水量比正常水平高出至少10%。相反的情况也是如此，在几年中，折回TC的数量是5个或更少。这种冬季气候异常是由减少或增强，分别引起的冬季大气位能的早期TC诱导的热输送。这项初步研究认为，一个单一的反弯TC减弱了0.5 - 1.5%的极赤道温度梯度，这取决于所使用的历史再分析。平均每年有9个热带气旋折返，热带气旋承担了半球热量输送的5 - 15%，迄今为止，这一作用一直只是定性的。这些结果提出了许多关键问题，这是这项资助的基础：为什么TC影响的大气记忆如此之长（数月），而不是在几天内消除？世界上不同的盆地是如何对TC的热传输做出贡献的？秋季反弯TC驱动冬季气候异常的关键时间是什么？这些结果提出了一个独特的观点，其中TC是不可或缺的变率和全球气候的强迫，而不是偶然的，只响应于其他强迫，如厄尔尼诺-南方涛动（ENSO）。这项工作的智力价值是测试初步结果的鲁棒性。虽然已经作出努力，以确保反弯TC的强迫机制在这里工作，进一步的审查是必要的。是否有一个压倒一切的气候强迫，是驱动双方的转向TC频率和随后的冬季气候在一起？在反弯热带气旋被认为是主导强迫机制之前，需要消除其他潜在的压倒性强迫机制。该补助金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Madden Julian振荡（MJO），准两年振荡（QBO）和太阳周期活动。虽然PI已经建立了由反弯TC驱动的异常冬季平均500毫巴温度通量的统计意义，但其他已建立的异常的统计意义将被检查：冬季表面温度和降水异常，极地和副热带急流异常，以及平均纬向环流异常（Hadley，Ferrell，Polar cell异常）。 更广泛的影响：当在秋末或初冬知道TC的回归频率时，全球冬季季节性气候预报可能会有所改善。这种改进的预测将减少全球因预期能源使用效率低下而造成的财务损失。总体而言，初步研究的结果表明，TC在气候强迫中的作用比目前所承认的要大得多。如果要进行的工作建立了初步研究的鲁棒性，将为热带气旋气候强迫建立一个新的范式。