Exploring What Determines the Duration of Atmospheric Blocks
Abstract
In the midlatitudes, persistent weather patterns such as heatwaves and cold spells are often associated with organized high pressure systems known as blocks. Though the societal impacts of such structures are important, the dynamics of blocks are still not completely understood. In this work, the duration of block life cycles is analyzed in the context of the internal structure of the block, forcing from nearby extratropical cyclones, and wave breaking. Using reanalysis products and data from an aqua planet GCM, blocks are identified by a commonly used methodology that searches for anomalies in the 500 hPa geopotential height field (z500) that coincides with a reversal in its meridional gradient. To characterize the internal structure of the block, various block strength metrics are examined including the magnitude of meridional gradient reversal and area-averaged anomaly magnitude of z500, the zonal 500 hPa wind (u500), the potential vorticity at 500 hPa (PV500), and the vertically averaged potential vorticity (VAPV) within blocks. Some of the block strength metrics are found to have a strong, positive relationship with block area across models, but only a weak positive relationship with block duration. A conditional sorting analysis is used to show that the blocks that interact with extratropical cyclones have longer durations than those that do not. However, cause and effect is not clear for this result, and therefore, we explore local wave breaking characteristics to test for potential forcing mechanisms associated with the nearby cyclone. Separately, a test is performed with the aquaplanet in which various physics and boundary conditions are changed, and block duration characteristics are analyzed.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.A31N3133N
- Keywords:
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- 3305 Climate change and variability;
- ATMOSPHERIC PROCESSESDE: 3319 General circulation;
- ATMOSPHERIC PROCESSESDE: 3337 Global climate models;
- ATMOSPHERIC PROCESSESDE: 4313 Extreme events;
- NATURAL HAZARDS