Future changes in southern hemisphere jet streams and atmospheric blocking during austral winter
Abstract
A robust projection of climate models, under scenarios of enhanced greenhouse gas forcing, is a poleward shift and strengthening of the southern hemisphere jet stream, particularly during austral summer. However, circulation changes during winter and spring are more complex. In both of these seasons the multi-model mean response exhibits distinct zonal asymmetries, with the largest tropospheric zonal wind increase located over New Zealand, where the subtropical and polar jets split. This is also a key region for the occurrence of atmospheric blocking which is often associated with extreme weather including persistent cold events and heavy precipitation in southern and south-eastern Australia.
We investigate wintertime circulation and blocking changes in an ensemble of CMIP5 models using data from the historical and RCP8.5 experiments. In this study, we find that most models show the maximum wind change in the Australia - New Zealand region and that the frequency of blocking events in this sector is reduced in all models, with a mean reduction of approximately one third of the historical mean by the end of the 21st century. It is also apparent that the magnitude of the wind response is linked to the bias in the historical simulation. We then go on to explore the mechanisms behind the zonally asymmetric response using an idealised model.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.A21T2789P
- Keywords:
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- 3305 Climate change and variability;
- ATMOSPHERIC PROCESSES;
- 3319 General circulation;
- ATMOSPHERIC PROCESSES;
- 3337 Global climate models;
- ATMOSPHERIC PROCESSES;
- 3373 Tropical dynamics;
- ATMOSPHERIC PROCESSES