Preprints
https://doi.org/10.5194/wcd-2022-59
https://doi.org/10.5194/wcd-2022-59
 
28 Nov 2022
28 Nov 2022
Status: this preprint is currently under review for the journal WCD.

Transient Anticyclonic Eddies and Their Relationship to Atmospheric Block Persistence

Charlie C. Suitters1, Oscar Martínez-Alvarado1,2, Kevin I. Hodges1,2, Reinhard K. H. Schiemann1,2, and Duncan Ackerley3 Charlie C. Suitters et al.
  • 1Department of Meteorology, University of Reading, Reading, United Kingdom
  • 2National Centre for Atmospheric Science (NCAS), University of Reading, Reading, United Kingdom
  • 3Met Office, Exeter, United Kingdom

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 example, 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.

Charlie C. Suitters et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on wcd-2022-59', Dehai Luo, 03 Dec 2022
  • RC1: 'Comment on wcd-2022-59', Anonymous Referee #1, 02 Jan 2023
  • RC2: 'Comment on wcd-2022-59', Anonymous Referee #2, 20 Jan 2023

Charlie C. Suitters et al.

Charlie C. Suitters et al.

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Short summary
Atmospheric blocking describes large and persistent high surface pressure. In this study, the relationship between block persistence and smaller-scale systems is examined. Persistent blocks result from more interactions with small systems, but a block’s persistence does not depend on the strength of these smaller features. This work is important because it provides more knowledge as to how blocks can be allowed to persist, which is something we still do not yet fully understand.