The Impact of Canonical and Non-canonical El Nino and the Atlantic Meridional Mode on Atlantic Tropical Cyclones

本项目研究热带大西洋和太平洋海面温度变化对大西洋热带气旋(包括飓风)的作用。所考虑的海温变化与两种类型的厄尔尼诺事件有关，传统的东太平洋(EP)事件和非传统的中太平洋(CP)厄尔尼诺事件，其中最大的SST增暖发生在赤道EP中，而非传统的中太平洋(CP)厄尔尼诺事件中的最大增暖发生在赤道附近。此外，这项工作还将考虑与大西洋子午线模式(AMM)有关的海温异常的影响，AMM是一种赤道以北变暖、赤道以南变冷的经向偶极模式，反之亦然。以前的研究将拉尼娜事件与大西洋TC活动增强联系在一起，而厄尔尼诺事件与大西洋TC活动的抑制有关，特别是PI估计，一个或多个主要飓风在厄尔尼诺期间登陆美国海岸的可能性为23%，而在拉尼娜期间为63%。然而，这些关系在多大程度上适用于CP和EP厄尔尼诺事件还没有确定，已经进行的少数几项研究显示出相互矛盾的结果。AMM也被认为对大西洋TCS有影响，但这种影响的机制尚不清楚，部分原因是AMM调节了几个环境因素，这些环境因素共同影响大西洋TCS。本研究检验了三个具体的假设，第一个假设认为，AMM对大西洋TCS的主要影响是通过与SST异常相关的越赤道SST梯度来调制上覆大气的环流和热力学。第二个假设是，CP和EP厄尔尼诺事件之间的地理差异不如海温异常的强度重要，因此CP厄尔尼诺事件的影响可能比EP事件小，因为CP事件的影响往往较弱。第三种假设认为，拉尼娜事件与正AMM漂移之间存在相长干扰，因此两者的结合对大西洋热带气旋具有极强的支持作用，而厄尔尼诺事件与负AMM之间的类似破坏性干扰导致了接近平均的大西洋TC活动。该项目的大部分工作包括使用天气研究和预报(WRF)模式的数值实验，该模式被配置为热带通道模式(Tcm)，意味着在纬向维度上具有30度和50度经向边界的折返域。由于更好地了解与厄尔尼诺和AMM有关的大西洋TCS和SST变率之间的关系具有潜在的价值，可以用来预测特定年份大西洋飓风季节的活跃程度。此外，这项工作还支持一位来自传统上代表性不足的群体的早期职业科学家。

This project examines the roles of sea surface temperature (SST) variations in the tropical Atlantic and Pacific on Atlantic Tropical Cyclones (TCs, including hurricanes). The SST variations considered are those associated with two types of El Nino events, the traditional East Pacific (EP) events in which the largest SST warming occurs in the equatorial EP, and the non-traditional Central Pacific (CP) El Nino events in which the maximum warming occurs along the equator near the dateline. In addition, the work will consider the impact of SST anomalies associated with the Atlantic Meridional Mode (AMM), a meridional dipole pattern with warming north of the equator accompanied by cooling south of the equator and vice versa. Previous research associates La Nina events with enhanced Atlantic TC activity while El Nino events are associated with suppression of TCs in the Atlantic, and in particular the PIs estimate that the probability of one or more major hurricanes making landfall on the U.S. coast is 23% during El Nino compared to 63% during La Nina. However, the extent to which these relationships hold for both CP and EP El Nino events has not been determined, and the few studies that have been performed show conflicting results. The AMM is also believed to have an impact on Atlantic TCs, but the mechanism of this influence is not well understood, in part because the AMM modulates several environmental factors that cooperate in their influence on Atlantic TCs. The research tests three specific hypotheses, the first of which posits that the primary influence of the AMM on Atlantic TCs is through the cross-equatorial SST gradient associated with the SST anomalies, which modulates the circulation and thermodynamics of the overlying atmosphere. The second hypothesis is that the geographic difference between CP and EP El Nino events is of less importance than the strength of the SST anomalies, thus CP El Ninos are expected to have a smaller influence than EP events simply because the CP events tend to be weaker. the third hypothesis is that there is constructive interference between La Nina events and positive AMM excursions, so that the combination of two is extremely supportive of Atlantic TCs, while a similar destructive interference between El Nino and negative AMM results in near-average Atlantic TC activity. The bulk of the work for the project consists of numerical experiments using the Weather Research and Forecasting (WRF) model, configured as a Tropical Channel Model (TCM), meaning a re-entrant domain in the zonal dimension with meridional boundaries at 30S and 50N.The work has broader societal impacts due to the potential value of better understanding of relationships between Atlantic TCs and SST variability associated with El Nino and the AMM, which could be used to anticipate how active the Atlantic hurricane season will be in a given year. In addition, the work supports an early-career scientist from a traditionally underrepresented group.