Atmospheric blocking dynamics: Persistence, re-intensification and interaction with other weather systems

当持续的高压系统（反气旋）在中纬度或高纬度的特定区域保持准静止状态时，就会发生大气阻塞。这些障碍物的作用是破坏低压系统在这些地区的正常通道。阻塞事件对人类活动有很大的影响，其影响取决于一年中发生的时间。在夏季，阻塞的地区可能会经历热浪，异常干燥的时期和停滞的空气条件。在冬天，它们可能与长期的寒冷有关。在阻塞区域之外，可能发生相反的影响，导致例如异常高的降水。所有这些影响都可能对特定人口的健康、农业、供水和能源生产和需求产生重大影响。尽管有这些重要的后果，在天气和气候模式中预测大气阻塞仍然是一项具有挑战性的任务。一个主要的影响因素是缺乏一个完整的理论来解释大气阻塞事件的生命周期（Woollings et al. 2018）。有几种与大气阻塞相关的大规模环流模式，例如夏季脊或气旋和反气旋波破碎（Woollings等人，2018）。然而，这些模式对诸如块体持续性和表面效应（降水和表面温度）等特征的影响尚未完全了解。此外，极长寿命事件的几个方面仍有待调查。该项目旨在回答以下科学问题：-某些模式会导致更持久的阻塞事件吗？- 极端持续的事件是否是经历持续再强化的单一模式的结果？- 或者，它们是由遵循各自生命周期的几种模式的共存和相互作用产生的？一种跟踪反气旋的新方法（Estareja 2018）将有助于研究瞬态天气系统在块维持中的作用（例如Luo等人，2014）和持久性和可预测性（Maddison et al.，2019年）。这种方法将应用于三种类型的数据集：长期观测约束再分析，高分辨率自由运行的气候模拟和高分辨率数值预报模拟。拟议的工作计划是-通过将已识别的反气旋与周围的气旋联系起来，对导致阻塞事件的大规模模式进行分类。调查大规模阻塞模式和事件持续性之间的关系。使用基于过程的评估工具，如位温和位涡示踪剂，研究极端持续事件发展和维持期间气旋/反气旋系统之间的相互作用（例如Martinez-Alvarado等人，2016）。根据前两点中确定的关系和相互作用，对比再分析和气候模式模拟的行为。在数值预报模拟中验证阻塞的发展、维持、面积范围和衰减，以确定阻塞事件期间造成误差发展的过程（类似于应用于气旋的方法，例如Froude等人，Estareja，B. J. N.（2018年）“跟踪阻塞高压系统”，硕士论文，UoR，46页弗劳德等人。（2010年）：Wea。Forecasting，25，819-836. Luo et al.（2014）：Q. J. R.陨石索科，140：1785- 1808. Maddison et al.（2019）：Mon.天气预报，147：1277-1296.Martinez-Alvarado等人（2016）：Mon.天气预报，144：3251-3276。Woollings，T.（2018）：Current Climate Change Reports 4：287-300.

Atmospheric blocking occurs when persistent high-pressure systems (anticyclones) remain quasi-stationary over a given region at mid- or high latitudes. These blocks act to disrupt the normal passage of low-pressure systems over such regions. Blocking events have high impact on human activities with a variety of effects depending on the time of the year in which they occur. In summer, blocked regions can experience heat waves, abnormally dry periods, and stagnant-air conditions. In winter, they may be associated with prolonged cold spells. Outside the blocked regions, the opposite effects can take place leading to, for example, abnormally high precipitation. All these effects can have important repercussions for a given population's health, agriculture, water supply and energy production and demand. Despite these important consequences, forecasting atmospheric blocking in weather and climate models remains a challenging task. One major contributing factor is the lack of a complete theory to explain the life cycle of atmospheric blocking events (Woollings et al. 2018). There are several large-scale circulation patterns associated with atmospheric blocking, such as summer ridges or cyclonic and anticyclonic wave breaking (Woollings et al. 2018). However, the influence of these patterns on features such as block persistence and surface effects (precipitation and surface temperature) are not fully understood. Moreover, several aspects of extremely long-lived events remain to be investigated. This project aims to answer the following science questions: - Do some patterns lead to more persistent blocking events? - Are extremely persistent events the result of a single pattern that undergoes a continuous re-intensification? - Or alternatively, do they result from the co-existence and interaction of several patterns that follow their own life cycles? A new methodology to track anticyclones (Estareja 2018) will be instrumental to investigate the role of transient synoptic systems in block maintenance (e.g. Luo et al., 2014) and persistence and predictability (Maddison et al., 2019). This methodology will be applied to three types of datasets: long-term observationally constrained reanalyses, high-resolution free-running climate simulations, and high-resolution NWP simulations. The proposed work plan is- Classify large-scale patterns contributing to blocking events by relating the identified anticyclones to surrounding cyclones.- Investigate relationships between large-scale blocking patterns and event persistence.- Investigate interactions between cyclonic/anticyclonic systems during the development and maintenance of extremely persistent events using process-based evaluation tools, such as tracers of potential temperature and potential vorticity (e.g. Martinez-Alvarado et al. 2016).- Contrast the behaviour of reanalyses and climate model simulations in terms of the relationships and interactions identified in the two previous points.- Verify block development, maintenance, areal extent and decay in NWP simulations to identify the processes that are responsible for error development during blocking events (analogous to the methods applied to cyclones e.g. Froude et al., 2010).ReferencesEstareja, B. J. N. (2018) "Tracking Blocking High Pressure Systems", MSc Thesis, UoR, 46pp Froude et al. (2010): Wea. Forecasting, 25, 819-836. Luo et al. (2014): Q. J. R. Meteorol. Soc., 140: 1785-1808.Maddison et al. (2019): Mon. Weather Rev., 147: 1277-1296.Martinez-Alvarado et al. (2016): Mon. Weather Rev., 144: 3251-3276. Woollings, T. et al. (2018): Current Climate Change Reports 4: 287-300.