This special issue is dedicated to the international project the Year of Tropics–Midlatitude Interactions and Teleconnections (YTMIT) fostered by the World Meteorological Organization through the Subseasonal to Seasonal (S2S) Prediction Project (Vitart, Robertson, & Anderson, 2012). The S2S time scales fill the gap between weather and climate (i.e., two weeks to two months), and significant progress has been made by climate modelling centres in improving the accuracy of climate simulations at these time scales and by operational centres in building S2S forecast systems. At the same time, teleconnections between the tropics and mid-latitudes have emerged as a potential source of predictability for the S2S time scales (Stan et al., 2017). The project was motivated by community interest in using a virtual field campaign for advancing our understanding of subseasonal tropical-extratropical interaction pathways with the ultimate goal of improving subseasonal prediction skill at regional and global scales. On S2S time scales, teleconnections manifest as a response of mid-latitude weather to the dominant modes of variability in the tropics (the Madden–Julian Oscillation (MJO) and the Boreal Summer Intraseasonal Oscillation) and as perturbations in the tropical weather induced by anomalous mid-latitude circulation patterns (e.g., mid-latitude blocking anticyclones), such as cold surges or monsoon breaks. This special issue is a collection of five papers documenting observational and modelling studies in the areas of atmospheric teleconnections on S2S time scales and the topics covered include (i) physical mechanisms underlying the interactions between the tropics and mid-latitudes on S2S time scales, (ii) prediction studies using the S2S database, (iii) the role of intraseasonal teleconnections in the occurrence and frequency of high-impact weather events, and (iv) the role of physical parameterizations and model biases in simulating and forecasting atmospheric teleconnections. Yadav, Straus, and Swenson (2019) show that EuroAtlantic circulation patterns are sensitive to the location of tropical diabatic heating and its speed of movement. The frequency of the North Atlantic Oscillation (NAO) regime is strongly influenced by diabatic heating in the western Pacific, whereas the frequency of the positive phase of the NAO can be related to diabatic heating in the Indian Ocean. Slow-propagating MJO events have a greater impact on mid-latitude circulation patterns, especially the Scandinavian blocking, than faster propagating events. In the same vein, Stan and Straus show that errors in the phase speed of the MJO result in erroneous mid-latitude teleconnection patterns. The model with faster-than-observed MJO simulation of the Scandinavian blocking has the largest errors among the mid-latitude circulation patterns. Luo, Wu, Zhang, and Dou (2019) show that interannual variability in the tropics associated with La Niña has an impact on the annual sea-ice concentration in the Barents– Kara Seas. The linkage between the tropics and high latitudes is through the atmospheric bridge created by the anticyclonic circulation over the North Atlantic and anomalous low geopotential height over the Barents–Kara Seas. This bridge allows surface winds to push warm waters and atmospheric moisture into the high latitudes and thus enhance the sea-ice reduction initiated by local processes. Lin, Mo, Vitart, and Stan (2018) show that the mid-latitude large-scale circulation pattern that led to a flooding event across eastern Canada in May 2017 can be interpreted as the extratropical response induced by a tropical MJO event, which preceded the high-impact weather event. The wave train provided a favourable environment for strong water vapour transport from the Gulf of Mexico and the western Atlantic to eastern Canada. The prediction analysis of 11 models of the S2S database show that most models made useful predictions of this event. They predicted a high probability of extreme precipitation two weeks in advance; however, the rainfall amount was underestimated. Mo and Lin (2019) show that a continental atmospheric river (AR) moving across the Rocky Mountains from the California coast was able to reach the northeastern United States

中文翻译：

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热带年特刊介绍 - 中纬度相互作用和遥相关 (YTMIT)

本期特刊专门介绍世界气象组织通过次季节到季节性 (S2S) 预测项目 (Vitart, Robertson, & Anderson, 2012) 推动的国际热带-中纬度相互作用和遥相关年 (YTMIT) 项目。S2S时间尺度填补了天气和气候之间的空白（即两周到两个月），气候建模中心在提高这些时间尺度气候模拟的准确性和业务中心在建立S2S预报方面取得了重大进展系统。与此同时，热带和中纬度地区之间的遥相关已成为 S2S 时间尺度可预测性的潜在来源（Stan 等，2017）。该项目的动机是社区对使用虚拟实地活动的兴趣，以促进我们对亚季节热带 - 温带相互作用路径的理解，最终目标是提高区域和全球范围内的亚季节预测技能。在 S2S 时间尺度上，遥相关表现为中纬度天气对热带地区主要变率模式（马登-朱利安涛动 (MJO) 和北方夏季季内涛动）的响应，以及异常引起的热带天气扰动。中纬度环流模式（例如，中纬度阻塞反气旋），例如寒潮或季风中断。本期特刊收录了五篇论文，记录了 S2S 时间尺度上大气遥相关领域的观测和建模研究，涵盖的主题包括 (i) S2S 时间尺度上热带和中纬度之间相互作用的基础物理机制，（ ii) 使用 S2S 数据库的预测研究，(iii) 季节内遥相关在高影响天气事件的发生和频率中的作用，以及 (iv) 物理参数化和模型偏差在模拟和预测大气遥相关中的作用。Yadav、Straus 和 Swenson（2019 年）表明，欧洲大西洋环流模式对热带非绝热加热的位置及其运动速度很敏感。北大西洋涛动 (NAO) 的频率受西太平洋非绝热加热的强烈影响，而 NAO 正相位的频率可能与印度洋的非绝热加热有关。慢速传播的 MJO 事件比传播速度快的事件对中纬度环流模式的影响更大，尤其是斯堪的纳维亚阻塞。同样，Stan 和 Straus 表明 MJO 相位速度的误差会导致错误的中纬度遥相关模式。斯堪的纳维亚阻塞的 MJO 模拟比观测快的模型在中纬度环流模式中误差最大。罗、吴、张、和 Dou (2019) 表明，与拉尼娜现象相关的热带地区的年际变化对巴伦支海-喀拉海的年度海冰浓度有影响。热带和高纬度地区之间的联系是通过北大西洋反气旋环流和巴伦支海 - 卡拉海异常低位势高度形成的大气桥。这座桥允许地表风将温暖的海水和大气中的水分推向高纬度地区，从而增强了由当地过程引发的海冰减少。Lin、Mo、Vitart 和 Stan（2018 年）表明，导致 2017 年 5 月加拿大东部发生洪水事件的中纬度大尺度环流模式可以解释为由热带 MJO 事件引起的温带响应。高影响天气事件。波列为从墨西哥湾和西大西洋到加拿大东部的强水汽输送提供了有利的环境。S2S数据库11个模型的预测分析表明，大多数模型对该事件做出了有用的预测。他们提前两周预测极有可能出现极端降水；然而，降雨量被低估了。Mo 和 Lin (2019) 表明，一条大陆大气河流 (AR) 从加利福尼亚海岸穿过落基山脉能够到达美国东北部 他们提前两周预测极有可能出现极端降水；然而，降雨量被低估了。Mo 和 Lin (2019) 表明，一条大陆大气河流 (AR) 从加利福尼亚海岸穿过落基山脉能够到达美国东北部 他们提前两周预测极有可能出现极端降水；然而，降雨量被低估了。Mo 和 Lin (2019) 表明，一条大陆大气河流 (AR) 从加利福尼亚海岸穿过落基山脉能够到达美国东北部