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

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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.