The role of anticyclonic transient eddies in atmospheric blocking dynamics

Suitters, C. (2024) The role of anticyclonic transient eddies in atmospheric blocking dynamics. PhD thesis, University of Reading. doi: 10.48683/1926.00119752

Abstract/Summary

Atmospheric blocks are large, quasi-stationary anticyclones with a lifetime from several days to multiple weeks. While blocks are relatively common in mid-latitudes, their dynamics are not completely understood, contributing to their un-predictability in medium-range numerical weather prediction (NWP). This study quantifies the role of anticyclonic (AC) synoptic-scale eddies towards blocking through a combined Eulerian and Lagrangian technique for block and AC eddy identification, respectively. It is shown for the first time that there is a statistically significant relationship between the mean number of block-AC eddy interactions and block persistence. Longer blocks absorb more AC eddies than shorter blocks, due to the associated increase in area and/or strength of the block after an AC eddy-block interaction, preventing dissipation or downstream advection of the block. However, for blocks with a particular persistence, there is large variability around the mean in the number of AC eddies it absorbs. In analysis of three blocks with similar persistence but different numbers of AC eddy interactions, AC eddies are only important towards the PV budget of a block when they first enter. Furthermore, the relative importance of diabatic processes varies spatially and temporally in each block, but there is no robust relationship between the relative importance of diabatic processes and AC eddies towards blocking dynamics. Accurate forecasts of block-AC eddy interactions are shown to be important for accurate blocking forecasts in medium-range NWP. Forecast errors in AC eddy speed, size, or strength can result in errors in block size, position, strength, or persistence. Conversely, forecasts that better represent AC eddies are more accurate in their forecasts of blocking. These results help to further the understanding of the role of AC eddies towards blocking dynamics, and show that poor AC eddy representation is one of the key reasons medium-range NWP performs so poorly for blocking.

Item Type	Thesis (PhD)
URI	https://reading-clone.eprints-hosting.org/id/eprint/119752
Identification Number/DOI	10.48683/1926.00119752
Divisions	Science > School of Mathematical, Physical and Computational Sciences > Department of Meteorology
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