La Nina-like mean state drives winter extremes in North America
Abstract
In the past decade, North America has frequently experienced opposing temperature extremes during winter, and it is of great interest whether such wide temperature swings are associated with human-induced climate change. By analyzing observational and pre-industrial control experiment data, this study substantiates that the long-term variability in the tropical Pacific mean state can indirectly affect winter regional temperature extremes in North America, particularly via alterations in the atmospheric background flow over the North Pacific and consequent changes in the North Pacific Oscillation (NPO). While the tropical Pacific exhibits La Nina-like decadal cooling, a wave response to steady tropical forcing acts to deepen the climatological stationary wave over the extratropical North Pacific, thus leading to enhanced zonal gradient between the Eurasian continent and the North Pacific. This changes in the background flow affects the available potential energy conversion process which is crucial for the growth of the NPO and causes eastward shift of the NPO at an interdecadal time scale. As the NPO shift eastward, it becomes more influential in causing abnormal warming and cooling in North America. These results suggest that the current state of North America is attributable in part to natural climate variability and uncertainty of climate change may be larger than we have estimated.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.A53N2711S
- Keywords:
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- 3305 Climate change and variability;
- ATMOSPHERIC PROCESSESDE: 3319 General circulation;
- ATMOSPHERIC PROCESSESDE: 1620 Climate dynamics;
- GLOBAL CHANGEDE: 1630 Impacts of global change;
- GLOBAL CHANGE