ORCID Profile
0000-0002-0250-4320
Current Organisation
University of Reading
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Publisher: Copernicus GmbH
Date: 28-11-2022
DOI: 10.5194/WCD-2022-59
Abstract: Abstract. Atmospheric blocking is a circulation pattern that describes the presence of large-scale, persistent anticyclones, which have the potential to bring severe impacts at the surface. However, the dynamical behaviour of blocks is still not fully understood. For ex le, the factors that determine the persistence of blocking events are not clear. In this study, the relationship between blocks and smaller-scale transient anticyclonic eddies is examined, with a particular focus on the impact of transients on the persistence of a block. Analysis is performed in two areas: the Euro-Atlantic and North Pacific, which are locations with both high blocking frequency and potential for severe impacts. Geopotential height anomalies at 500 hPa are used to identify blocking events and the anticyclonic transient eddies. This allows for a Eulerian definition of blocking, as well as a Lagrangian perspective on the eddies. It is found that anticyclonic eddies experience a northward acceleration prior to entering a block, which is indicative of ridge-building ahead of a block, but could also potentially provide evidence for the previously-proposed Selective Absorption Mechanism for block maintenance. A general pattern is found whereby longer blocks interact with more anticyclonic transients than less persistent blocks at all times of year. This effect is strongest in winter and weakest in summer, which agrees with the fact that blocks are most persistent in winter and least persistent in summer. However, the strength of the anticyclonic eddy, measured by its maximum 500 hPa geopotential height anomaly, that interacts with a block generally has very little bearing on the persistence of a block, aside from a few cases.
Publisher: Copernicus GmbH
Date: 28-06-2022
DOI: 10.5194/EMS2022-272
Abstract: & & Atmospheric blocking is often responsible for high-impact surface weather conditions such as heatwaves, cold spells, and droughts. Very long blocking events are particularly problematic due to the persistence of hazardous surface conditions. Despite their many impacts, understanding the dynamical behaviour of blocking events is still incomplete despite recent progress. Here, the relationship between block persistence and anticyclonic eddies contributing towards these blocks is investigated. Anticyclonic eddies that contribute to blocking are defined as large positive 500 hPa geopotential height (Z500) anomalies, obtained by filtering in both space and time, that pass through a blocked region. These features are then followed using an objective feature tracking algorithm. It emerges that stationary blocking conditions are often the result of more than one transient anticyclonic eddy entering the block itself, which is a reflection of the selective absorption mechanism (SAM) for block maintenance, proposed by Yamazaki and Itoh (2013). A relationship is found between the number of anticyclonic eddies contributing to a block and the persistence of the block itself, with longer-lasting blocks typically absorbing more eddies than less persistent events this behaviour is particularly noticeable in winter. The contribution of the smaller eddies to the blocks via the SAM is also observed as the anomalies speed up slightly just before entering the blocking region, before intensifying, becoming slow-moving, and sometimes reversing in direction inside the block itself. In addition to this climatological viewpoint, case studies have also been analysed to obtain a more detailed view of the process. From these, it is observed that some of the Z500 anomalies that contribute to blocking events originate from a long way upstream and travel along the wave guide until they are absorbed into a block, and this is again most evident in winter. The results from this work suggest there is an inherent link between repeated block maintenance and the persistence of block events, and also provides evidence that block maintenance processes may differ according to time of year.& &
Publisher: Copernicus GmbH
Date: 08-08-2023
Abstract: Abstract. Atmospheric blocking is a circulation pattern that describes the presence of large-scale, persistent anticyclones, which have the potential to bring severe impacts at the surface. However, the dynamical behaviour of blocks is still not fully understood. For ex le, the factors that determine the persistence of blocking events are not clear. In this study, the relationship between blocks and smaller-scale transient anticyclonic eddies is examined, with a particular focus on the impact of transients on the persistence of a block. Analysis is performed in two areas: the Euro-Atlantic and North Pacific, which are locations with both high blocking frequency and potential for severe impacts. Geopotential height anomalies at 500 hPa are used to identify blocking events and the anticyclonic transient eddies. This allows for a Eulerian definition of blocking, as well as a Lagrangian perspective on the eddies. It is found that anticyclonic eddies experience a northward acceleration prior to entering a block, which is indicative of ridge building ahead of the block but could also potentially provide evidence for the previously proposed selective absorption mechanism for block maintenance. A general pattern is found whereby longer blocks interact with more anticyclonic transients than less persistent blocks at all times of the year. This effect is strongest in winter and weakest in summer, which agrees with the fact that blocks are most persistent in winter and least persistent in summer. However, the strength of the anticyclonic eddy that interacts with a block, measured by its maximum 500 hPa geopotential height anomaly, has a more complicated relationship with block persistence. The strength of anticyclonic transient eddies is a more determining factor of block persistence in the North Pacific than in the Euro-Atlantic region. In the North Pacific the longest blocks interact with stronger eddies than the shortest blocks in all seasons except summer, when the reverse is true. By contrast, longer Euro-Atlantic blocks only result from stronger anticyclonic eddies in autumn and winter. We therefore conclude that the number of anticyclonic eddies that interact with a block is most important in determining its persistence, with the strength of the eddies having a more variable effect.
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Charlie Suitters.